CA1179809A - Process for preparation of improved semipermeable composite membranes - Google Patents

Abstract

ABSTRACT
In a process for producing a semipermeable composite membrane which comprises forming on a microporous substrate a thin layer of a polymeric material comprising a polyamino polymer containing at least 1 milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, and thereafter interfacially cross-linking a surface portion of said thin layer with a crosslinking agent having at least two functional groups (a) capable of easily reacting with either the primary or secondary amino groups or both in said polymer; the improvement wherein (1) said polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in said polymer at a temperature at which the interfacial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in said polymer at a temperature at least 30°C higher than said crosslinking temperature, and (2) the interfacially crosslinked thin layer is heated to a temperature at which said polyfunctional compound reacts with the primary or secondary amino groups or both in said polymer.

Description

7~ 9 FROCESS ~OR PREPAR~ION 0~ IME~OVED
SEMIPERM~ABIE COMEOSITE MEMERA~ES
This invention relates to a process for produc-ing a permselecti~e composite membrane. Mor~ specifi-call~, it relates to a process ~eor producing a perm-selective composite membrane which has high salt rejection and water flux, durability, pressure compaction re~istance, chemical resistance, oxidation resistance, soiling resistance and heat resistance, can be stored in the dried state, and is suitable for ultrafiltration or reverse o~mosis, especia~ly the latter.
The permselective membrane is a membrane which has selective permeability to specified molecules. It is frequently used to remove very small amounts of contami-natea molecules dissolved or diffused in a liquid or gas.
In recent years, reverse osmosis has attracted a great deal of interest for utili~ation in fields involv-in~ purification of liquids. ~his is o~ especial import-ance when utilizing this system in the purification of water and brackish waterO Likewise~ the process is also used to remove impurities from li~uids such as water or, in the fields of dialysis, blood. When utilizing reverse osmosis in the purification of saline water, a pressure in excess o~ the osmotic pressure of the feed solution is applied to ~he solution from which puri~ied water is preparedO Pure water dif~uses through the membrane while the sodium Ghloride molecules or other impurities which may be present in the water are retained by the membrane.
~ he ef~iciency of the reverse osmosis method is greatly affected b~ the properties of the permselective membrane used. Much effort has therefore been made to develop membranes having high performance, and resulted in some specific proposals.
~ or example, U. S. Patents Nos0 3,133,132 and 3,133,137 disclose the early Loeb_type membranes made of cellulose diacetateO These membra~es are asymmetric ~l17~ 9 membranes which are characterized by a very -thin, dense surface layer or skin that is supported upon an integrated much thicker supporting layerO ~hese known membranes based on cellulose diacetate have the defect of poor pressure compaction resistance, low resistances to chemical and biological degrada-tion, a short service life, and insufficient flux and salt reJection characteristics.
In an attempt to overcome these defects of the ~oeb-type membranes, some membranes composed basically of synthetic polymers have recently been suggested. ~or example, U. S. Patent No. 3,567,632 proposed a reverse osmosis membrane having a wholly aromatic polyamide as a baseO Althou~h this membrane has achieved a great improvement in hydrolysis resistance and biodegradation resistance, it does not surpass the Loeb_type membrane in regard to the two basic properties, io eO water flux and salt rejectionO Moreover, it still has the defect that its pressure compaction resistance is low and it cannot be stored in the dry stateO
These membranes are called heterogeneous mem-branes prepared by a so-called "phase separation method", and the semipermeable homogeneous layer participating in separation and the porous support layer having to do with the reinforcing of the membrane are made o~ the same material.
Some methods were suggested in which a porous layer is prepared from a separate material, and a hydro-philic reactive polymer and a crosslinking agent are reacted on the porous layer to form a crosslinked ~ilm-like semipermeable layer thereon. It was suggested thatby these methods, there can be obtained a semipermeable composite membrane having greatly improved hydrolysis resistance, biodegradation resistance, pressure com~
paction resistance and storability in the dried state in addition to improved basic propertiesO ~or example, U. S. Pate~t ~oO 3,951,815 discloses a composite semi-permeable membrane comprising a microporous substrate ~'798~9 and an ultrathin film formed of a crosslinked, grafted polye-thylenimine disposed on one surface of said micro-porous substrate that has been crosslinked with a di- or tri-functional compound such as isophthaloyl chloride and grafted with a graft reactant such as acrylonitrile or epichlorohydrinO UO S~ Patent NoO 4,005,012 describes a composite semipermeable membrane comprising an ultrathin *ilm formed by contacting an amine-modified polyepihalo-hydrin with a poly~unctional agent on a microporous substrate to form this film on one surface of the microporous substrateO Also~ UO SO Patent NoO 4,039,440 discloses a reverse osmosis membrane prepared ln ~
on a porous support by initial formation of a layer of polyethyleneimine on the support, followed by interfacial reaction with a polyfunctional reagent to produce a thin surface coating which possesses salt barrier character-isticso The membrane composed basically of crosslinked polyethyleneimine disclosed in UOSO Patent ~oO 4~039,L~0 has a high salt rejection, but has the defect of pos-sessing insufficient water flux and low oxidation resistance (eOgO, low resi~tance to deterioration by the presence of chlorine in the feed saline or brackish water)O As one method of improving the oxidation resist-ance, U, SO Patent ~oO 3,951,815 suggests the grafting of acrylonitrile to the polyethyleneimineO. ~he acrylo-nitrile-grafted and cros 51 inked polyethyleneimine shows some improvement in oxidation resistance, but suffers from the serious defect that its water flux is markedly reducedO ~he membrane composed basically of the amine-modified polyepihalohydrin disclosed in UO S0 Patent ~oO 4,005,012 exhibits a high salt rejection but its water flux is not sufficientO It has been strongly desired therefore to develop.membranes having a higher water flux~
~ n the aforesaid semipermeable composite membrane composed o* the interfacial crosslinked product of polyethyleneimine or amine-modified polyepichlorohydrin, ~liLt7~ 9 may primary and/or secondary amino groups and/or second-ary amide groups (~C~ ) which are susceptible tooxidation or soil deposition remain in the cross-linked polymer. In order to reduce the amount of residual reactive sites which may possibl~ undergo oxidative at-tack or soil deposition in such a crosslinked product, there was suggested a method comprising blocking these sites by grafting a reagent which induces addition reaction at these reactive sites (see British Patent No. 1,536,227 and U. S. Patent ~oO 3,951,815)~ ~he ~ritish Patent discloses a grafting method which com-prises impregnating a crosslinked composite membrane ~ith a grafting reagent (to be referred to as the method l); a grafting method comprising grafting the reagent to the membrane before crosslinking, and then performing the cross-linking reaction of the membrane (to be referred to as the method 2)j and a grafting method which com-prises performing the crossli~king reaction and the grafting reaction simultaneously (to be referred to as the method 3)~ According to the method 1, since the surface layer of the membrane is rendered compact by the interfacial cl~ssli~king before the grafting reaction, the penetration of the grafting reagent is insufficient and the unreacted amino groups or secondary amide groups still remain in large amounts in the interior layer.
~ence9 it is difficult to improve the resistance o~ the membrane to oxidation or soiling~ Accordi~g to the method

2, if the grafting reaction before the interfacial cross-linking reaction is performed sufficiently. the amount ~0 of amino groups to be involved in the subsequent inter-facial crosslinking reaction decreases even at the surface layer, and therefore, the crosslinking density of the surface layer becomes insufficient, thus making it impossible to obtain a semipermeable composite membrane ha~ing excellent propertiesO Qn the contra~y, an attempt to increase the crosslinking densit~ of the l~t7~9 surface layer by inhibiting the grafting reaction results in an insufficient effect of grafting in the interior layer, making it difficult to obtain a composite membrane of excellent properties. According -to the method 3, unless there is a considerable difference in reactivity with the amino groups between the grafting agent and the crosslinking agent, the grafting agent and the cross-linking agent compe-titively react with the amino groups. For this reason, the crosslinking density is not sufficiently high even at the surface of the membrane which is to form an active layer, and i-t is difficult to obtain a membrane having suitable salt rejecting characteristics.
The present inventors have disclosed that crosslinked permselective composite membranes having improved oxidation resistance, etc. can be produced by using water-soluble polymers containing substantially only secondary amino groups (see Japanese Laid-Open Paten-t Publications Nos. 146800/78, 2980/79 and 3153/79, laid open to public inspection on December 20, 1978, January 10, 1979 and January 11, 1979, respectively, and all in the name of Teijin). Since in these membranes, too, the polymer in the interior layer is not crosslinked and is still water-soluble, it flows away little by little on long-term operation, and this may possibly lead to a degradation in the strength and performance of the membranes. Thus, the durability of these membranes is not satisfactory.
This phenomenon is observed not only in crosslinked composite membranes obtained from a polymer having secondary amino group, but also in crosslinked composite membranes obtained from other amine-containing polymers whose thermal self-gellability is not sufficient. The durability of these membranes can be increased by performing the thermal self-gellation of these polymers at a very high temperature. But this results in increased durability at the sacrifice of a drastic degradation in membrane performance, especially water flux.
It has been strongly desired therefore to develop a technique which can meet the inconsistent requirements of maintaining the water flux at a high level and of increasing the durability.

; ~ - 5 -According to this invention, there is provided a process for producing a semiper1neable composite membrane, which process comprises:
(I) forming on a microporous substrate a thin layer of a polymeric material comprising a polyamino polymer containing at least l milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, wherein the polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups ~b) substantially incapable of reacting with the primary or secondary amino groups in the polymer at a temperature at which a subsequent interfacial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in the polymer at a temperature at least 30C higher than the subsequent crosslinking temperature, ~II) interfacially crosslinking a surface portion of the thin layer with a crosslinking agent having at least two functional groups ~a) capable of easily reacting with either the primary or secondary amino groups or both in the polymer, and ~III) heating the interfacially crosslinked thin layer to a temperature at which the polyfunctional compound reacts with the primary or secondary amino groups or both in the polymer.
According to this invention, there is also provided a semipermeable composite membrane which comprises a microporous substrate and, formed on the substrate, a thin layer of a polymeric material comprising a polyamino polymer containing at least one milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, a surface portion of said thin layer having been interfacially ~ ~.
:~`
: .~

crosslinked with a crosslinking agent having at least two functional groups ~a) capable of easily reacting with either the primary or secondary amino groups or both in said polymer, wherein said polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in said polymer at a temperature at which the interfacial cross-linking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in said polymer at a temperature at least 30C higher than said crosslinking temperature, and wherein the interfacially crosslinked thin layer has been heated to a temperature at which said poly-functional compound reacts with the primary or secondary amino groups in said polymer.
The basic concept of this invention consists in the fact that a polyfunctional compound having substantially lower reactivity with active amino groups than the interfacial crosslinking agent is incorporated beforehand into the polyamino polymer used to form the semipermeable membrane layer of the semipermeable composite membrane, and after the interfacial crosslinking, a crosslinking reaction is induced between the polyamino polymer and the poly-functional compound to form an internal anchor layer rendered water-insoluble by the crosslinking and having markedly improved oxidation resistance, soiling resistance, pressure compaction resistance (or mechanical strength), etc.
between the ultrathin semipermeable layer on the surface and the microporous substrate.
The polyamino polymer used ~o form the semipermeable membrane layer in the process of this invention has film formability by itself contains at least 1 milliequivalent, preferably at least 2.0 milliequivalent, more pre-ferably at least 5.0 milliequivalents, per gram of the polymer in the dry ` ~ li798~9 state, of active amino groups selected from primary amino groups and secondary amino groups in the main chain and/or side chain of the polymer. Any of those polyamino polymers which contain the active amino groups in such an amount and which have heretofore been used for the production of semipermeable membranes can be used in this invention. Polyamino polymers containing 2.0 to 23.0 milliequivalents, particularly 5.0 to 23.0 milliequivalents, per gram of the dry polymer, or the active amino groups are especially - 7a -~:17~ ?9 suitable for use in this inventionO
~he polyamino polymer should have the property of forming a continuous ultrathin film on the micro-porous substra-te, and desirably has a number average molecular weight of generally 500 to 200,000, preferably 700 to 150,000, more preferably 1,000 to 10090000 Advantageously, the polyamino polymer has an intrinsic viscosity (~), determined at 20C for a 1/10~ NaCl aqueous solution, of generally 0~05 to 5O0 dl/g, preferably 0~07 to 3O0 dl/g, more preferably Ool to 200 dl/go The polyamino polymer is applied in solution in the form of a solution to the substrate as is done in the prior art~ Accordingly~ the polyamino polymer should be soluble in a solventO For the ease of operation, the solvent is desirably waterq a water-miscible organic solvent having a boiling point of not more than 140C, preferably not more than 120C, or a mixture of water and the organic solvent, or a mixture of the organic solvents with each otherO Advantageously, the polyamino-polymer used in this invention dissolves in at least one solvent selected from water and water-miscible organic solvQnts having a boiling point of not more than 140C, preferably not more than 120C, to an extent of at least generally at least 002 ~100 ml of the solvent, preferably at least 0~5 ~100 ml of the solvent, more preferably at least 1 ~100 ml of solvent a at 20Co The polyamino polymer contains structural units composed of a primary and/or a secondary amino group and a hydrocarbon group having 2 to 20 carbon atoms, preferably 2 to 15 carbon atoms, which may contain in addition to the amino group, a nitrogen atom (N), an oxygen atom (0), a halogen atom (eOgO, chlorine or bromine), or a s~fur atom (S) as a heteroatom~ When there is a hetero atom, it may exist in various formsO
For example, the nitrogen atom may exist in the form of a ter~iary or quaternary amino group; the ox~gen atom may :
.

exist in the form of an ether linkage, an ester linkage, a carbonyl linkage or a hydroxyl group; and the halogen atom may exist as a substituen~ for hydrogenO
Examples of preferred structural units are those of the following general formula (I), (II~, (III) and (IV) Rl CH2_C_~l_ (I) wherein Zl represents a direct bond, -O-, -N_, or -N_ ; Rl represents a hydrogen atom CH2~C~2-NHR3 H
or a methyl group; when Zl is _N_ or _N_ , R2 represents a hydrogen atom, and when Zl represents a direct bond or -O-, R2 represents the group _Y_R4; R~ represents an alkyl g~oup having 1 to 5 carbon atoms; Y
represents a direct bond, -O-, , or - ~ -;
R4 represents the group _~HR5, _R6_~HR7; R5 and R7 represent an alkyl group having 1 to 5 carbon atoms; and R~ represents a divalent aliphatic group (eOg., alkylene group) having 1 to 5 carbon atoms which ma~ contain an oxygen a-tom.
2-~H2-C~-CH2~H~
OH
wherein Z2 represents a direct bond or -O-.
/C~2-R8 - ~ O- (III) wherein R8 represents a halogen atom or the group -~HR10; Rg represents the group -~EIRlO;
and Rlo represents a hydrogen atom or an al~yl group having 1 to 5 carbon atoms~

~.

..

798~9 ~CH2\
-C-Rll R12-C-C~12-Z3- (IV) H2 C~ ~ CH2 N

wherein Rl~ and R12, independently from each other, represent a hydrogen atom or a methyl group, and Z3 represents a direct bond or -SO2-.
The proportion of the structural unit in the polyamino polymer is selected such that the proportion of the primary and secondary amino groups present in the structural unit is within the range speci~ied hereinabove.
The polyamino polymer used in this invention may include those which gel by itself upon heating or those which have no self-gelling ability.
I~hen the process of this invention is carried out using a polyamino polymer of the self-gelling type having too low a gelling temperature, its ~elf-gellation is likely to proceed substantially before the reaction of the active amino group in the polymer with the polyfunctional compound is sub-stantially completed. It is very desirable therefore that the polyamino polymer used in this invention, even if when it is of the self-gelling type, should not gel at a temperature below 50C, preferably below 60C.
Specific examples of the polyamino polymer are given below. It is to be understood that these examples are merely illustrative for facili-tating an understanding of the invention, and do not in any way limit the scope of this invention.
C~ ~olyam~nQ polymers which have anly primary amino groups in the polymer molecule as amino groups having an active hydrogen atom ~active amino groupS~ and do not gel by themselves at a ~emperature of 150C or below:

Typical examples of the polyamino polymers which belong to this group are as follows:

~17g~V9 (a) Polyvinyl amine type polymers which are homopolymers or copolymers having structural units of the formula ~CH2_CH~

(b) Polyaminostyrene~-type polymers which are homopolymers or copolymers having structural units of the formula ~CH2_C~
~H

(c) Polyallylamine-type polymers which are homopolymers or copolymers having structural units of the formula ~CH2_CH~
C,H2 ~H2 (d) Homopolymers or copolymers having structural units o~ the formula -~CH2_CH~ CH2~H2 CH21!1H2 CH2~H2 (see, for example, European Patent Publication ~oOl0,425~0 (II) Polyamino polymers which contain only pri.mary amino groups as the active amino groups in the polymer molecule and have sel~-gelling ability at an elevated temperature:-~ypical examples of the polyamino polymer of this group are as follows:
(a) Partially ammonia-modified polyepichloro-hydrin which :is a polymer consisting mainly of structural unit 8 of the form~la `' 117g8~9 -~CH2-CH-O} and -~CH2-cH-o-}

for example, the polymer described in U.S. Patent No. 4,005,012.
(b) Partially ammonia-modified poly(chloroethyl vinyl ether) which is a polymer consisting mainly of structural units of the formulas -~C}I2-CH~ and -~CH2-cH~

(for example, the polymer described in European Patent Plblication NO. 10,425).
(c) Partially hydrazine-modified poly~meth) acrylate which is a polymer consisting mainly of structural units of the formulae ~R13 ~R13 -~CH2-c~ and ~CH2-lc~
C=O C~O

wherein R13 represents a hydrogen atom or a methyl group, all R13 groups may not always be the same, and R14 represents an alkyl group having 1 to 4 carbon atoms, for example the polymer described in European Patent Publication NO. 8945 laid open to public inspection on March 3, 1980, in the name of Teijin.
(d) Ammonia-modified polyglycidyl (meth~acrylate acrylate which is a polymer consisting mainly of structural units of the formula CH2 - lC
C-O
Q~`CH2CHCH2NH2 OH
wherein R13 ls the same as defined hereinabove, for example the poly~er described in Eu~pean Patent Publication No. 10,425.

.
' ~, ` 11798~9 (III) Polyamino polymers which have both a primary amino group and a secondary amino group in the polymer molecules and do not have self-gelling property at an elevated temperature:-Typical polyamino polymers of this group are the polyadditionproducts between polyepoxy compounds and polyamino compounds having at least two active amino groups which are d:isclosed in German Published Patent Application No. 2822784, published November 30, 1978, in the name of Téijin.
More specific examples are polymers consisting mainly of the following structural units.

~a) ~NH-CH2-CH2-NH-CH2-CH-CH2-O-CH2-CH2-O-OH
CH2 -CH-CH2~
OH OH

~b~ CH2-CH-CH2-NH-CH2-cH2-Nlk ~ C~N\C ~
, -CH2-CH-C~12-N~ ~N-cH2-cH-cH2-NH-cH2-cl~l2-NH- _.
OH C OH .

(c) tNH-CH2-CH2-NH-CH2-~CH-CH2-o- ~ CH3 C~2- ,CH-CH2-~
OH

1'0 q ~d~ ~C~NII.(ÇH2 ~`CH2 '`N~L2 ~m ~

-. ~

: , , .: . , . .; , , 798~9 - 13a -(IV) Polyamino polymers containing both a primary amino group and a secondary amino group as the active amino groups ln the polymer molecule and having self-gelling ability at an elevated temperature:-Examples of the polyamino polymers of this .
s~ ~

~ , .

:, 0g group are as follows:
(a) Polyethyleneimine consisting mainly of structural units of the formula ~CH2-CH2-~H ~ and tCH2-CH2-~
CH2-CH2~ 2 Particularly the one described in U.S. Patent ~oO4,039~4~0 (b) Polyamine-modified polyepichlorohydrin, for example a polymer consisting mainly of structural units of the formula ~CH2_CH_O ~

wherein R15 represents an aliphatic hydrocarbon radical containing 2 to about 15 carbon atoms which may contain a nitrogen atom in the form o~
a primary~ secondary or tertiary amino group and an oxygen atom in the form of a hydroxyl group or ether bond, an alicyclic hydrocarbon contain-ing from about 4 to about 8 carbon atoms in the ring, or a heterocyclic radical, which is described in UO SO Patent No. 4,005,012.
(c) Polyamine-modified poly(2-chloroethylvinyl ether), for example a polymer consisting mainly of structural units of the formula tCH2-CH~
O_CH2-cH2-~H-~cH2-cH2-NE ~ H (m 2 1) especially the one described in European Patent Publi cation ~oO 10,4250 (V) Polyamino polymers which have only secondary amino groups as the active amino groups and do not have self-gelling ability at an elevated temperature:-The polyamino polymers of this group include polymers consisting of structural units of formu~.a (IV) given hereinabove particularly structural units of the formula ` ~ ~ and polymers consisting mainly of at H
least one structural units selected from the following group:
:.

.~, . . . .

l~g8~

(a) -CH2-CH2-NH_ (b) (c) -CH2-~CH-N~lR16 NHR16 (dl -CH2-CH- (e) -CH2-fH-C=O
O-CH2-CH-CH2-NHRl6 (f) ~cH2-cH2-NH~and ~CH2 CH2-N~
CH2 CH2 N~IR16 (g) -CH2-CH-o CH2-NH~-cH2-c~l2-NH~mRl6 (m ~

(for example, United States Patent NO. 4,005,012) wherein R16 represents an alkyl group having 1 to 5 carbon atoms.

(VI) Polymers which have only serondary amino groups as the active amino groups in the polymer molecules and have self-gelling ability 10at an elevated temperature.
The polyamino polymers of this group include polymers consisting mainly of str~ctural units selected from the following groups:

Ca) ~CH2-CH-O~ and ~CH2-CH-O~

CH2Cl CH2NHR16 CEor example, Japanese Laid-Open Patent Publication No. 67573/79 published Ma~ 31~ 1979~ applicant Toray Industries Inc.

C~) ~cH2-cH3 and ~CH2-CH~
O CH2~CH2Cl O-CH2-CH2-NHRl6 ~, .

9~

(for example, European Laid-Open Patent Application No.
EP 0010425A (laid open April 30, 1980.) (c) ~CH2- 1CH3 C=O
b-CH2- ICH-CH2-NHR16 OH

- 15a -. .

' , ' ~

~17g8~9 CH2Br ~d) ~ ~

(e, C3~ ~ CH

H CH2--CH~ CH2 In the above formulae, R16 is as defined hereinabove.
Among the above polyamino polymers, those which can be preferably used in this invention are the polymers (A) to (D) below.
(A) The addition polymer between a polyepoxy compound and a polyamine compound having at least two active amino groups which is described, for example, in DAS No. 2822784.
CB) Polyethylenimine, Polyamine-modified polyepichlorohydrin and polyamine-modified poly(2-chloroethylvinyl ether) (see U.S. Patents Nos.
4,039,440 and 4,005,012 and European Patent Publication No. 10,425).
(C) Polymers containing at least 30 mole% of structural units of the following formula /, CH2 - C_Rll R12 _C--cH2-Z3 H2 C. ''- C~12 N

wherein Rll? R12 and Z3 are as de$ined hereinabove (see U.K, Patent Application GB No. 2027614A published February 27, 1980 in the name of Teijin.

; .

: ' ' 1~7g~9 (D) Polymers consisting mainly of two s-truc-tural units of the formulae _CH2_CH_0_ and _CH2_CH_0_ CH2Cl CH2~HR16 or of two structural units of the formulae - 2-C and _CH2_CE_ O_CH2_CH2Cl O_CH2_CH2NHR16 wherein R16 is as defined above, (see Japanese Patent Publication ~oO 67573/79 and European Patent Publication ~o. 10~425)D
When those polyamino polymers which do not have self-gelling ability at an elevated temperature are used, it is possible to improve long-term durability and pressure compaction resistance of the resulting permselective composite membraneO Particularly~ when the polyamino polymer has only secondary amino groups as the active amino groups, a properly chosen poly-functional compound included in the polymer reacts under heat with the amino groups remaining in the membrane after the interfacial crosslinking reaction, and con-sequently, the membrane finally obtained is substantially free from secondar~ amino groups which are susceptible to oxidationO Hence~ the oxidation resistance as well as the durability ancl pressure compaction resistance of the membrane can be improvedO
The polyfunctional compound may be included in a polyamino polymer which has self-gelling ability at an elevated temperature. By so doing, the crosslinking of the polymer can be induced at a temperature lower than the ordinary self-gelling temperature (usually 100C or more higher) of the polymer. ~his can obviate severe heating required for self-gellation~ and therefore, the reduction of the molecular weight of the polymer and the heat decomposition of the amino groJ/uhps can be prevented and the resulting composite ~ilm ~ excellent performanceO
The inclusion of the polyfunctional compound C~n ~ c ~'ve.
is also e~ 4e to adjustment of the flexibility or ~L1.7~9 hydrophilicity of the membrane in ad.ition to the improve-ment of its durability, pressure compaction resistance and oxidation resistanceO
The polyfunctional compound included in the polyamino polymer in accordance with the aforesaid basic concept of this invention is a compound having per molecule at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in the polymer at a temperature at which the interfacial crosslinking is carried out but capable of easily reacting wi-th either the primar~ or secondary amino groups or both in the polymerO
~ he term "substantially incapable of reacting"
used herein in regard to the functional groups (b) means that the functional groups ~b) of the polyfunctional compound mixed in the polyamino polymer do not at all react with the polymer within 30 minutes at the temper-ature in question, eOgO the temperature at which the interfacial crosslinking is carried out, or even when the reaction does occur, the amount of the functional groups (b) reacted is at most 10 mole%, preferably at most 5 mole/0, of the entire functional groups (b)~
Likewise~ the term "capable of easily reacting"
used herein in regard to the functional groups (b) and the functional ~roups (a) to be described means that the func-tional groups can react with the polymer at the temperature in question to an extent of at least 30 mol~/o~
preferably at least 50 mole%.
~he functional groups (b) present in the poly-functional compound can be selected from a wide rangeof compounds which meet the aforesaid requirements.
~dvantageously, they are functional groups which do not substantially reac-t with any of the primary and secondary amino groups in the polymer at a temperature of not more than 20C, p:referably no-t more than 30C, but can easily react with either the primary or secondary amino groups or both in the polymer at a te~.perature of a-t least 50C, 8~9 ,9 preferably at least 70C but lower than the self-gelling temperature (TC~ of the polyamino polymer, preferably not more than (T - 20)Co ~he sel~-gelling temperature, as used herein, 5 denotes a temperature at which 7~/0 by weight of a poly-amino polymer becomes water-soluble when a solution of of the polyamino polymer alone in the same concentration as the pol~amino pol~mer in the thin layer to be subjected to interfacial crosslinking reaction is ~aintained for 30 minutes.
The type of the functional groups (b) meeting this requirement di~fers depending upon the types of the primary and/or seconda~y amino groups in the poly-amino polymer, the mode of bonding thereof in the polymer structure, etc~, but generally they can be selected from the following group~
_c~(oH~cH2xL
_COOA
_l~XCOOA2 ~
~O "C 0 , ,A~ ~C=0, _COCH=CH2 ~
_C0_~\ IN , and activel~alomethyl groupsO
In the above formulae, ~ represents a halogen atom~ Al and A2 each represent a hydrogen atom or an organic radical capable of being split off together with the oxygen atom to which it is bonded, and A3 represents a trivalent or tetravalent saturated aliphatic group having 2 to 5 carbon atomsO
The "halogen atom" represented by ~ denotes four elements, fluorine, chlorine, bromine and iodine, the chlorine atom being preferred~ Examples of the "organic radical capable of being split off together wi-th the oxygen atom to which it is bonded" represented by Al and A2 are -CH3~ -C2H5' _C3H7~ _C4Hg, CH2 2 9~9 _ 20 ---CH2_C6H5 and -C6H50 Specific examples of-the "trivalent or tetravalent saturated aliphatic group having 2 to 5 carbon atoms" are _CH?_CH_CH2C~I_, _CH_CH2_CH_, CH CH CH _CH-, _~H2_C_CH2_, _CH_C~2~H2 , , 2 The term "active halomethyl group" denotes the group _CH2X a benzyl group, an allyl group, etc~ in which is a halogen atom, preferably Cl and Br.
~ ypical examples of the functional groups (b) are given below.
_CHCH2Cl, -CHCH2~r, .COOH, _COOCH3, _COOC2H5, - OH OH
_COOC3H7, _COOC4H~, _COOCH2C~=CH2, _COOCH

_COO- ~ g _NHCOOCH3, _NHCOOC2~I5, _~HCOOC3H7, _~HCOOC~H9, -NHCOOCH2CH=CH2, -NHCOOCH2 ~ , ~CH2 ~CH2~
-~HCOO ~ , _CH /C=O, _C /C=O, O O O O
~ 11 /~ ,. ..................................... .
_C_CH=CH2, _C_N~==JN, _C_CH2Cl, _C_CH2Br, _CH=CH_CH2Cl, _CH=CHCH2Br~ ~ CH2Cl and ~ CH2:E3r.
The polyfunctional compound used in this in-vention has at least two such functional groups (b) per molecule, and the two or more functional groups (b) may be identical or different.
Since the polyfunctional compound is used as a uniform dispersion in the polyamino pol~mer, it is very desirable that it be soluble to some extent in a solvent for the polymer, iOeO at least one solvent select-ed from water and water-miscible organic solvents having a boiling point of not more than 1~0C/ Generally, it is advantageous that the polyfunctional compound be soluble ' ~7~ 9 at 20C in the solvent to an extent of at least 0.1 g/lOO ml of solvent, preferably at least 0.2 g/100 ml of solvent, more preferably at least 0.5 g/100 ml of solvent.
The type of the polyfunctional compound used in this invention is not particularly limited so long as it has at least two functional groups ~b) and shows the above-mentioned solubility. It may be of low to high molecular weight.
Suitable low-molecular-weight polyfunctional compounds are organic compounds, especially aliphatic organic compo~mds, generally containing 2 to 4, preferably 2 or 3, such functional groups (b) per molecule and having a molecular waight of 90 to 500, preferably 100 to 500. Suitable high-molecular-weight polyfunctional compounds are high molecular-weight poly-functional organic compounds, especially vinyl polymers, which contain the functional groups (b) in an amount of 2.0 to 15.0 milliequivalents, especially 5.0 to 15.0 milliequivalents, per gram of the compounds, and have a numher average molecular weight of 1,000 to 100,000, preferably 2,000 to 10,000.
Typical examples of the polyfunctional compound that can be used in this invention are as follows:
(A) Low-molecular-weight polyfunctional compounds -~CH-CH2-X2)q OH
~ herein X2 represents a halogen atom, preferably a chlorine atom, Q ~eR~esents an alkyl ~oup ha~ing 2 to 20 carbon atoms which may contain an oxygen ~r a hal~gen atom, a direct bon~ or an ether linkage, and q is an li~9~9 - 21a -integer of 2 to 6. Specific examples are as follows:
cH2cH-cH2cH2cHcH2cl~ C~2C~ICH20CH2CH20CH2CHCH2Cl~
Cl OH OH Cl OH OH
ClcH2cHcH2o(cH2)4ocH2cHcH2cl~
OH OH

::

:. ' ,: ,.

, ~:179~3U9 - 22 _ ClCH2CHCH20-CH2CHCH20CH2C~ICH2Cl, OH I OH
OCH2CHCH2Cl OH
OCH2CH~OH)CH2Cl ClCH2CHCH20CH2CH_CH_CE20CH2CHCH2Cl, OH OCH2CHCH2Cl OH
OH
Cl ClCH2CHCH2~CH2CH2~ CH2CHCH2' OH OH
2CHCH20 ~ CH2CH203~ CH2CHCE2Cl OH OH
OH
CH2-dH-CH2-X4 / N \
(ii) O=C C=O
5 2 , 2 \ / 2 , 2 6 OH C OH
o wherein X~ X5 and X6 each represent a halogen atom, preferably a chlorine atomv (iii) A ~ COOA6)a wherein A5 represents a hydroxyl group, ~
sulfonic acid salt group, a carboxylic acid salt group, an aliphatic group Gontaining 1 to 12 carbon atoms and having a valence o~ a which may con-tain an oxygen or halogen atOm, an ~ aromatic group containing 6~10 carbon atoms and : ~ ~ 15 having a valence of ~, or an alicyclic group con-taining 5 or 6 carbon atoms and havi~g a valence of a, A6 represents an alkyl group having 1 to 4 carbon a~tDms, an allyl groupt an aralkyl group having 7 to 10 carbon atoms, or a phenyl group~
a~d a is an integer of 2 to 4.
~he "aliphatic group" nay be o~ linear or branch-ed ChaiD~ and saturated or unsaturated (containing a double bond), and the "aromatic group" may consist of a benzene ringO

~ , .

:~79~

Specific examples of the compounds (iii) are as follows:
HOOC_CEI2_COOH, HOOC_CH2CH2_COOH, HOOC_CH2-CH2-CH2-COOH, H3COOC-CH2-COOCH3.
H3COOC_CH2_CH2_COOCH~, H3COOC_CH_CH_COOCH3, OH OH
~3CH2-ooC-CH2-~OOC-CH2CH2-COO-~) .
CH2=CH~CH2_00C_CH(OH)~CH(OH)_COO_CH2_CH=CH2 5 2 2_CH2_COOC2H5, H5C200C-CHCH2-OH
5 2 2 2 2 5' 3 3' O,H H COOC COOCH
H3_C_OOC_CHCHCH_COOCH3, 3 ~ 3 OH OH
H3COOC ~ COOCH3, H3COOC ~ COOCH3, COOCH3 Co3Na H3COOC ~ COOCH3~ COOCH3 COONa OOCH3 (iv) A7_00CNH_Ag_NHCOO_A8 wherein A7 and A8 each represent an alkyl grou~
having 1 to 4 carbon atoms, an allyl group. an aralkyl group having 7 to 10 carbon atoms, or a phenyl group, and Ag represents an alkylene group having 2 to 10 carbon atoms. or an arylene group which may be substituted by a halogen atom or an alkyl group having 1 to 6 carbon atomsO
Specific examples of the compounds (iv~ are given belowO
H3COOCMEI- ~ _NHCOOCH3, H5C200C~H- ~ NHCOOC2H5 H3COOC~I-~CH2 ~ NHCOOCH3, o ~-O_C_MH- ( CH2~ ~COO- ~, , ~.
:

~9~3~9 CH2=C~CH200CNH~-CH2~L~ ~HCOOCH2CH=CH2 ' ~)-CH200CNHt CH2-~ NHCOOCH2 (v) Al ~ OOC_CH=CH2)b wherein Alo represents a hydroxyl group, a sulfonic acid salt group, a carboxylic acid salt group~ an aliphatic group containing 1 to 12 carbon atoms and having a valence of b which may contain an oxygen or halogen atom.
an aromatic group containing 6 to 10 carbon atoms and h~ving a valence of b, or an alicyclic group containing 5 or 6 carbon atoms and having a valence of b, and b is an integer of 2 to 4~
Specific examples of the compounds (v) include the following.
2 CH_COO-~CH2 ~ 0_C_CH=CH2, CH2=CE_COO(CH2~ O_C_CH=CH2, o H2 CH_COO~CH2CH20 ~ C_CH=CH2, CH2=CH-COO ~CH2CH20 ~C_CH=CH2, CH2=CH_COO-~CH2CH20 ~ C_CH=CH2 7 ' O O
1~ 11 CH2_CH_CO ~,OCCH=CH2, O ~J O
CH2=CH_CO_CH2_CH_CH2_0_C_CH=CH
O_C_CH=CH2 O, o o_C-CH=CH2 OCCH=CH2 o ' `' ~ ` ' .

~, ' .

~:1798~)9 (vi) hl ~ CO_N ~ N)c wherein All represents a hydroxyl group, a sulfonic acid salt g:roup, a carboxylic acid salt group, an aliphatic group containing 1 to 12 carbon atoms and having a valence of c which may contain an oxygen or halogen atom7 an aromatic group conta:ining 6 to 10 carbon atoms and having a valence of c, or an alicyclic group containing 5 o:r 6 carbon atoms and havi~g a valence of c, and~c is an integer of 2 to 4.
Specific examples of the compounds (vi) are as follows:
~\ 11 tl /~
N _C_CH CH _C_N N
~==J 2 2 \~=) N N_C-(CH2 ~ C_N~ N , N~'`N_C-(CH2 ~ C_N "~N , N N-o-oH2ooH2o-N~ N~ ~N ~-C ~ ~==J

<N 3-C ~ C_N ~ N, N'~`\N_C ~ C_N ~JN, : SO ~ a C=O

CON N
' ~==) N

O=C
N
N

' ' :~1798(~9 (vii) X7_CH2_COO_A12 wherein X7 represents a halogen atom, and A12 represents an alkyl group having 1 to 4 carbon atoms. an allyl group. a phenyl group and an aralkyl group having 7 to 10 carbon atoms.
Examples o~ the compound6 (vii) include the followingO
ClCH2COOH, BrCH2COOH~ ClCH2COOCH3, ClCH2COOC2H5, ClCH2COOCH2CH=CH2, ClCH2C00 ~ 3, ClCH2COOCH
Among the above examples. especially preferred low-molecular-weight polyfunctional compounds (i~ to (vii) are shown belowO
( i ) ClCH2CHCH20tCH2CH20~9CH2CHCH2Cl OH OH
OH
CH2CHCH2Cl (ii) O C~,N \ C O
2, 2 \ C 2, 2 : OH " OH
o : OE OH
(iii) CX300CC~IdHCOOCH3, C2~500C_CHCHCOOC2H5, OX OH
o CX2 CHCE20C_CH2 H2 H2CH CH2 (iv) H2COOC~H-~CH2 ~ NHCOOCH3, ': O
~1 : CH2=CHCE200C~X(CH2~6NHC_CH2 , CH
O O dH2 ; 20 ~ --C-~H-(C~2)6-~H-C-~.

~ 9 ( V) CH2=CHCOO --~CH2CH20 2~6CH=CH2 O O CON N
(vi) ~ N_C ~ C_N N , ~ '-~
/N -C=O CON N
o o ~`~3 ~
<~ C~C~2~8C-N~=~N

(Vii) ClCH2COOH, ClCH2COOCH3,, ClCH2COOC2H5, ClCH2COOCH2CH=CH2, ClCH2COO ~
(B) High_molecular-weight polyfunctional compounds containing at least 40 mol ~/O of at least one recurring unit selected from ~13 ( i ) -CH2_C, _ 2 , 2 8 OH

10 ( ii) _CH2_C_ C00~14 A,13 ( i ii ) _CH2_C
C=O
, O \ , and CH ~ C=O
2 ~ CH
A
(iV) CH2_C
C=O

wherein X8 represents a halogen atom, Al3 is a hydrogen atom or a methyl group. Al4 represents a hydro~en atom or an alkyl group having 1 to 4 carbon atoms, an allyl group, an aralkyl group ha~ing 7 to lO carbon atoms, or a phenyl group, . j :

~ '' . , ~7~ 9 and d is 1 or 2.
~ hese high-molecular-weight compounds may con-sist only of at least one of such recurring units, or may contain another recurring unitO Examples of the other recurring unit which may exist are as ~ollows:
_CH2-CH- , _CH2CH._ , _CH2CH_ C=O C=O C=O
~(CH3)2 ~H2 ~(CH2CH3)2 _CH2CH- , _CH2_CH~ CH2_, ~HcH2oH ~ CH \CH
CH2_S02-, _CH2CH-, _CH2CE_ C1~3 OCH3 C2H5

3 3 _CH2CIH_ , _CH2CH_ , -CH _ CH_ , _CH CH- , O,C,C~I3 OH COOH COOH 3 COOH
o ~hus, examples of the polyfunctional high-molecular-weight compounds include those which contain at least 30 mol~O~ ~ore preferably at least 50 mol%, of at least one of the following recurring units.
CH
( i ) _CH2CH~ , _CH2C_ COOCH2CHCH2Cl COOCH2CHCH2Cl OH OH
CH
( i i ) _CH2CH_ ~ _CH2C- . _CH2CH_ C,H3 COO~CE2CH20~H
( ii i ) _CH2CH_ , _CH2, CoocH-cH2 COOCH_C~H2 O\C/bH2 ~`C/~H2 O O

7~8{~9 CH
( i V) _CH2CH_ , _CH2C_ C=O C=O

Especially preferred high-molecular-weight polyfunctional compounds are those contai~ing the follow-ing recurring units~
_GH2CH-COOCH2CHCH2Cl OH
- (CH2CH) COO-~CH2CH20 ~ H
_CH2CH- , _CH2CH_ C=O C=O
C_CH_CH2 6~

Especially preferred polyfunctional compounds for use in this invention are those which react with the active amino groups in the polyamino polymer to form a so-called hydrophilic hydrogelO If the hydrophobicity of the~polyfunctional compound (more stric~ly5 the hydrophobicity of the crosslinked structure formed by : the reaction of the functional compound with the active amino groups) is too high, the anchor layer (located between the microporous substrate and the crosslinked active layer formed by interfacial crosslinking) acts as an internal barrier to water permeation, result-: ~ ing in a reduction in the water flux of the membraneO
In this sense, the polyfunctional compound prefera~lyhas high hydrophilicity, and aliphatic compounds and alicyclic compounds are preferred to aromatic compounds, the aliphatic compounds being especially preferredO
Examples of polyfunctional compounds which are :.

.
'~
. . , .

preferred from this standpoint include ethylene glycol dichlorohydrin, glycerol dichlorohydrin, glycero]
trichlorohydrin, sorbitol dichlorohydrin, sorbitol trichlorohydrin, sorbitol tetrachlorohydrin, dimethyl f ~ 7f c ~ ~ r a J~
~e and diethyl ~rtratcO
The polyamino polymer and the polyfunctional compound which have been described in detail hereinabove are pre-mixed and used in the form of a solutionO ~he solution does not denote a uniform clear solution alone, and may include an emulsion if a film can be prepared from the emulsion by means to be described~
A solvent system consisting of at least one solvent selected from water and water-miscible organic solvents having a boiling point of not more than 140C, preferably not more than 120C, is suitable as the solvent used to form such a solution. ~he solvent system should be selected such that it does not substantially swell or dissolve the microporous substrate to be described.
Examples of preferred solvents are (i) water, ~ii) a lower alcohol such as methanol, ethanol and propanol, ~iii) a ketone such as acetone, methyl ethyl ketone and diethyl ketone, and (iv) a lower carboxylic acid such as formic acid, acetic acid and propionic acid~
~hese solvents can be used either alone or as a mixture of two or moreO Water, the lower alcohols, and the mixtures thereof are preferredO Water is especial-ly preferredO
The mixing ratio between the polyamino polymer and the polyfunctional compound are not critical, and can generally be changed widely depending upon the types of the polymer and~or polyfunctional compound used.
Ge~erallyt it can be determined according to the equivalent weight of the active amino groups contained in the polyamino polymer~ The polyfunctional compound can be - :' 11798~9 mixed in such a ratio that -the ratio of the eguivalent weight of the functional groups in the poly~unctional compound to that of the active amino groups in the poly-amino polymer is generally 0005-l:l, preferably 001-007:1, more pre~erably 0.2~005:10 The conce.ntration of the polyamino polymer in the solution is not critical, and can be varied widely depending upon the type of the polymer used, and the properties required of the final membrane, etcO Advanta geously, it is generally at least 00~/o by weight, preferably 1.0 to 5.~/o by weight, especially preferably 1.5 to 3.~/o by weightO
The solution so prepared may, if re~uired, include a monofunctional compound containing only one functional group (b) of the type exemplified above per moleculeO This can lead to the improvement of the hydrophilicity, flexibility or oxidation resistance of the resultin~ semipermeable membraneO
~xamples of the monofunctional compound that can be used for this purpose include ethylene carbonate O ~ O
( ~C~ butyrolactone ( ,C ~ lactone (C-0), o ~x-methyl-~-butyrolactone(O~CH3), ~-methyl-~-lactone ( ~ 0), methyl acetate, ethyl acetate, propanesultone c~3 ( ~ ), ethyl or-tho-formate ~CH(OC2H5)3), ethyl methyl-carbamate, acetic acid and propionic acidO
~ he monofunctional compounds may be used singly or as a mixture of two or more~ ~he amount of the mono-functional. compound is used in such an amount that the concentration of the functional group is 0.1 to 0.7 `"' ' " ` ' :~79~3~9 equivalent, preferably 002 to 005 equivalent. per equiva-lent of the active amino groups in the polyamino polymerO
Usually~ it is used in a smaller amount than the poly-functional compound.
As required, an acid acceptor may be added to the solution. When the functional group (a) of the crosslinking agent used in the interfacial crosslinking reaction to be described is, for example, an acid chloride group, the acid acceptor accepts an acid released as a result of the crosslinking reaction, and promotes the reaction. Inorganic and organic basic compounds are used as the acid accep-tor. Typical examples are alkaline or alkaline earth me-tal hydroxides such as sodium hydroxide, potassium hydroxide and calcium hydroxide and alkali or alkaline earth metal carbonates such as sodium bicarbonate7 sodium carbonate and calcium carbonate, and amine com~
pounds such as pyridine and piperazineO ~he amount of the acid acceptor is generally 002 to 105 moles, prefer-ably 0.5 to 1~0 mole, per mole of the active amino groups in the polyamino polymer.
The solution of the polyamino polymer and the polyfunctional compound so prep~red is coated on, or impregnated in, a microporous substrate ~ be described in a manner known er se. to form thereon a thin layer containing the polymer and the polyfunctional compoundO
The resulting thin film needs not to have self-supporting property, and may contain the aforesaid additives and solvent Substrates that can be used may be any of the types conventionally used in a reverse osmosis processD
They include porous glass, sintered metals, ceramics, and organic polymeric materials such as cellulose estersl styrene resins, vinyl butyral resins, polysulfone, chlori-nated polyvinyl chloridel etc~ described in UD SO Patent ~o~ 3,676,2030 Polysulfone film has been found to be a particularly effective support material for the membranes of the invention7 and chlorinated polyvinyl chloride is ~'7~ 9 ano-ther very effective support material, Preparation of polysulfone microporous substrate is described in "Office of Saline Water Research and Development Progress Report ~o. 359, Oct~, 1958".
~hese substrates preferably have a surface pore size of generally 100 to 1000 ~9 but are not limited to these specific sizesO Depending upon the use of the final membrane product, surface pores ranging in size from about 50 A to about 5000 ~ may be acceptableO
The subs-trate may be of an isotropic structure or an anisotropic structure, desirably of the latter structureD When the membrane constant of the substrate is less than 10-4 ~cm2osecoatm, the water permeability of the substrate is too low, and when it is more than 1 ~ cm2~secOatm, the salt rejection tends to be extremely lowO Accordingly, preferred membrane constants are 1 to 10-4 ~ cm2Osec~atm, and the best results are obtained with a membrane constant of 1~-l to 10 3 ~cm20secOatm~
The term "membrane constant", as used herein, denotes the amount of pure water which permeates the membrane under a pressure of 2 k ~ cm2, and is expressed in g/cm2.
sec. atmO
Preferably, the substrate used is reinforced at its back with a woven or non-woven cloth, etcO Ex_ amples of the woven or non-woven cloth are those of polyethylene terephthalate, polystyrene, polypropylene, nylon or vinyl chloride resinsO
~ o form the thin layer containing the polyamdno polymer and the polyfunctional compound on the micro-porous substrate, the microporous substrate is treatedwith the aforesaicl solution containing the polyamino polymer and the poly~unctional compound.
The treatment can be performed by coating at least one surface of the subs-trate wi-th a solution of the base polymer by a suitable method such as solution casting, brush coating, spraying, wick coating or roll coating; or by immersing the substrate in a solution of the base polymer~

1..~7~ g The subs-trate so treated by coa-ting or immersion is then subjected to a drain treatmentO ~he drain treat-ment can be carried out generally at room temperature for 1 to 30 minutes, preferably 5 to 20 minutesO ~his results in the formation of a pseudo-thin film layer comprising the polyamino polymer and the polyfunctional compound and having a total thickness of about 500 to about 10,000 ~, preferably about 1,000 to about 4,000 ~, on the surface of the substrate. ~he pseudo.-thin film layer so formed can be air-dried, as re~uired. It is very desirable that ~he pseudo-thin film layer should contain at least l~/o by weight, preferably 20 to 7~/0 by weight of the poly-amino polymer and at least 2~/o by weight, preferably 30 to 8~/o Of the a~oresaid solvent remaining therein~
The substrate having the thin layer formed thereon is then subjected to interfacial crosslinking reaction using a crosslir~ing agent containing at least -two functional groups (a) capable of easily reacting with the primary or secondary amino groups or both in the polyamino polymerO As a result, a thinner crosslinked layer (located outwardly of the permselective layer) is formed on the surface of the pseudo~thin layerO
The functional groups (a) which are present in this highly reactive crosslinking agent are functional groups capable of easily reacting with the primary or secondary amino groups or both in the polyamino polymer, and specifically include carbonyl halide groups (_COHal), sulfonyl halide groups (-so2Hal)~ an isocyanate group (_NCO), acid anhydride group ( _CO = o) of these, the carbonyl halide groups and sulfonyl halide groups are preferredO In these groups, Hal represents a halogen atom, perferably chlorine and bromineO
~ he crosslinking agent used in this invention may contain at least two, preferably two or three, functional groups (a) per molecule~ Phosgene can also be used as the crosslinking agent containing at least two functional groups (a) since it is equivalent to a ~77~8~S~

compound having two acid halide groups. ~he two or more ~unctional groups present in one molecule may be the same or differentO Generally, -the crosslinking agent desirably has a cyclic structure, and may be of any of aromatic, heterocyclic and alicyclic structuresO It has been found that aromatic crosslinking agents are especially effective for the objects of this inventionO
Aromatic crosslinking agents tha-t can be used advantageously in this invention are mononuclear or polynuclear (binuclear, in particular) compounds which contain at least two~ preferably 2 or ~, functional groups bonded to the aromatic nucleus and 6 to 20 carbon atoms, preferably 6 to 15 carbon atomsO Preferably, substituents other -than the aforesaid functional groups should not be present on the aromatic ringO The aromatic ring, however, may have 1 or 2 groups which do not substantially affect the crosslinking reaction, such as a lower alkyl group, a lower alkoxy group, a halogen atom, etc.
An especially preferred group of such aromatic crosslinking agents includes compounds of the ~ollowing formula Yl~ /Y2 Ar wherein Ar represents a ben~ene ring, a naphthalene ring?
or the ring ~ -Y4_ ~ in which Y4 represents -CH2_, C~
~ 2 ~ 1~ Y2 and Y3, independently from each other, represent a carbonyl halide, sulfonyl halide or isocyanate group. or Y2 and Y3 together represent an acid anhydride group, and one of Yl, Y2 and Y~ may be a hydrogen atom~ It is especially desirable ~lt7~9 that Yl, Y2 and Y3 be selected from carbonyl halide and sulfonyl halide groupsO ~ypical examples of the aromatic polyfunctional compounds used as the crosslinking agent are show~ below.
COCl COCl COCl COCl. ~ ' COCl COCl Cl_C SO2Cl o S,02Cl "
~S02cl~ o~C~JCcl ~C~cC\O, ll ll ll O O O
CH2COCl o O
~3 , \C ~XC\
CH2COCl ~1 "
O O
O O O COCl O, C ~ C ~ C \ O , ~ _COCl, O O
NCO CH
NCO, ~ ~CO , NCO
C102S~-Y5~-S02Cl, ClOC ~ O )-Y5~ ~ COCl, (Y5 rep.resents a direct bond, _O-, _CH2_, C~
-S2 or -C-Especially advantageous aromatic polyfunctional compound used as the crosslinking agent are isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride and 3-chlorosulfonyl-isophthaloyl chloride~
Preferred heterocyc]ic polyfunctional compounds that can be used as the crosslinking agents in this in-vention are 5- or 6-~embered heteroaromatic or hetero-alicyclic compounds having two or three functional groups bonded to the heterocyclic ring and containing 1 to 2 nitrogen, oxygen or sulfur atoms as heteroatoms~ Examples are as follows:
COCl OC1 , ~ ~COCl , ClOC ~ ~OCl , ClOC ~ COC1 C10 ~ OCl , ~ C10 ~ COCl ClOC 6 COC1 , C10 ~ COCl , C10 ~ OCl , 15(Y6= O or S) H3C~
/ \ r~
ClOC-N N-COCl, ClOC-N N-GOCl, / ~<
~H3 ClOC-N ~ ~CH2 ~ ~ N-COCl Preferred cyclic polyfunctional compounds that can be used as the crosslinking agent are those having 8~g 2 or 3 functional groups bonded to the alicyclic ring and containing 5 to 20, preferably 6 to 15, carbon a-tomsO
Examples are as follows:
COCl COCl COCl COC1 COCl ~`COC1 , ~ , ~ W
COCl COCl ClOC ~ -CH2 ~ COCl, ClOC ~ C- ~ COCl, NCO NCO
ClOC ~ O ~ COC1, NCO

OCN ~ -CH2 ~ -NCO, OCN- ~ C- ~ NCO, OCN ~ O ~ -NCO

Preferred aliphatic polyfunctional compounds that can be used as the crosslinking agent are those.
having 2 functional groups and containing 5 to 20, pre-ferably 6 to 15, carbon atomsO Fxamples are as follows:
ClCCH CH CC1, ClCCH CH CH CCl, ClCCH CH CH -" 2 2" " 2 2 2" " 2 2 2 O O O O O

CH2CCl, ClCCH2CH2C~2CH2CH2CCl, ClCCH2CH2CH2_ O O O O
CH2CH2CH2CCl, ClC-~CH2-~ CCl, OCN-~CE ~ NCO
O O O

-'~ .

~L~1'79~3~9 The aromatic heterocyclic or alicyclic poly-functional compounds can be used either alone or as a mixture of two or moreO
In addition to these compounds, cyanuric acid chloride of the following formula (Cl- ~ ~ C1 ) can also be used in this invention as the crosslinking agentO
It has been found that the salt rejecting and/or flux properties of the finely obtained membrane can be improved by using trifunctional compounds ra-ther than di~
functional ones when -they are used. singly, and by using a combination of a difunctional compound and a -trifun-ctional compound when they are used in combinationO Thus, especially preferred polyfunctional compounds to be used in the present invention are trifunctional aromatic com-pounds; and mixtures of difunctional aromatic compounds and trifunctional aromatic compoundsO When a mixture of a difunctional compound and a trifunctional compound is used, the mixing ratio between them is not criticalO
Generally, the weight ratio of the difunctional compound to the trifun~tional compound is from 10:1 to 1:3, prefer-ably from 5:1 to l lo ~he aforesaid crosslinking of the pseudo thin film can be performed usually by contacting the film with a solution of the crosslinking agent described herein-aboveO The solvent used to dissolve the crosslinking agent is a solvent which is not easily miscible with the solution containing the polyamino polymer and the poly-functional compound and does not subs-tantially dissolve the substrateO ~xamples of the solvent include hydro-carbons such as n-hexane, n-heptaneg n-octane, cyclo-hexane, n-nonane and n-dec~neO ~he optimal concentration 1:175at~-~9 of the polyfunctional compound in the solvent may ~ary considerably depending upon the specific compounds, sol-vent, substrate, etcO, and is best determined experimentallyO
However, concentrations o~ about 005 to 500, preferabLy about loO to 300% by weight9 are generally satisfactoryD
Conveniently, the crosslinking is accomplished on the interface between the thin film layer and the solution by immersing the -thin film layer in the solution of the crosslinking agentO In order to promote this crosslinking reaction, it is possible to include a cross-linking accelerator into the ~ilm layer or the solution of the crosslinking agentO ~his accalerator serves to help the crosslinking agent diffuse into the film layer, and/or to capture hydrogen halide released at the time of crosslinking reactionO Such an accelerator may include, for example, soluble basic compounds and surface-active agentsO
Advantageously, suitable soluble basic compounds have a solubility in water or a lower alcohol such as methanol, ethanol or propanol or a mixture thereof of at least Ool g, preferably at least 0~2 g, more preferably at least 005 g, per 100 g of water, the lower alcohol or a mixture thereof at 25Co As such compounds, inorganic basic compounds and organic basic Gompounds having the abo~e solubility can be mentio~ed~ Any inorganic basic compounds having the above-mentioned solubility can be usedO The organic basic compounds should desirably have a pKa value of generally 5 to 12, preferably 8 to 120 Examples of the soluble basic compounds are (1) inorganic bases such as sodiurn hydroxide, potassium hydro-xide, lithium hydroxide, sodium carbonate, lithium carbo-nate, potassium carbonate, sodium bicarbonate, potassiurn bicarbonate, lithium bicarbonate, sodium phosphate (Na3P04) and potassium phosphate (K3P04); and (2) organic bases such as triethylamine, trimethylamine, diazabicyclo-(2,2,2)octane, hexamethylenetetramine, ethylenediamine, triethylenetetramineg methylamine, e-thylamine, triethanol-' . ' "

11798(~9 amine, diethanolamine, pyridine, ~,N-dimeth~laniline, N-methylpiperidine, and N-methylpyrrolidineO
~ hese basic compounds capture hydrogen halide, which may be formed by the crosslinking reaction to promote the crosslinking reaction, positively participate in the crosslinking reaction itself, and also have the effect of improving the mechanical strength or oxidation resistance of the resulting semipermeable membraneO ~hey are especially suitable as crosslinking acceleratorsO
~he basic compound is used in an amount of`
generally 0O5 to 200 moles, preferably 0O7 to lo 2 moles, per equivalent of the active amino group in the polymerO
~ he interfacial crosslinking reaction between the surface of the thin film layer and the crosslinking agent can be carried out at a temperature lower than the temperature at which the aforesaid polyfunctional compound having the functional groups (b) reacts, generally at about -10C to about 100C, preferably about 5C to about 40C, more preferably 20C to 35C, for a period of 10 seconds to 10 minutes, preferably 30 seconds to 5 minutesO
This interfacial reaction can be carried out so that it takes place largely on the surface of the thin film layerO
It is not necessary to reduce the water content of the internal region of the thin film layerO ~ ~ d If desired, the thin film la~er ~ on the substrate is -then subjected to a drain treatmen-t to drain the excess of the crosslinking agent solution for 10.
seconds to 2 minutes, and then heat-treated at a tempera-ture of 50 to 150C, preferably 50 to 130C, for about 1 to about 30 minutesg preferably abou~ 5 to about 20 minutesO
As a result of this hea-t-trecatment9 crosslink-ing reaction proceeds between the polyfunctional com~ound remaining unreacted in the thin film layer and the re-sidual active amino groups in the polyamino polymer to promote gellation of the anchor 1cayer of the thin film layer and improve oxidation resistance by blocking the actlve amino groupsO

.

.: :

~1798~9 _ L~2 --~ hus, -there is obtained a composite membrane consisting of the microporous substra-te and formed on its surface, an ultrathin surface layer of a permselective crosslinked polyamino poiymer formed by the interfacial crosslinking reactionO Basically, this composite membrane consists of three layers, io eO the microporous substrate, the crosslinked interlayer (inwardly of the permselective ultrathin surface layer) usually bonded thereto ~nchoredly and the outer ultrathin semipermeable surface layer there-onO ~he internal anchor layer has a thickness of usu~llyOol to 10 microns9 preferably 0O3 to 5 microns, and the outside ultrathin semipermeable surface layer has a thickness of usually OoOl to 1 micron, preferably 0O03 to 005 micronO The ratio of the tl1ickness of the surface layer to that of the anchor layer ~Ry be generally at ~ost 1:5, preferably from 1:5 to 1:150 In the resulting asy~metrically crosslinked thin film layer, the semipermeable surface layer and the anchor layer are OEontinuously integrated and both are substantially insoluble in waterO Under standard conditions, the semipermeable surface layer may have a water flux of generally at least 20 liters/m2ohr, pre-ferably at least 30 liters/m2ohr, and an NaCl rejection of generally at least 80%, preferably at least 90%, and the anchor layer may have a water flux of generally at least 50 liters/m2ohr, preferably at least 100 liters/m2ohr, and an NaCl rejection of generally not more than 70~, preferably lower than 50%O
The term i'standard conditions"~ used herein with regard to the water flux and NaCl rejection~ denotes conditions in which the system operating pressure is 600 psi, the operating -temperature is 25C, and the feed solution is a 0O5% by weight aqueous solution of ~aClO
~he presumed structure of the interfacially cross-linked portion of the crosslinked thin film layer on themicroporous substrate which is formed by the process of this in~ention ma-g be represented by the following general ` : !

1~9~3~)9 formula IQl Ql4 -N-Q2-T-Q3-1~-wherein Ql and Q4 represent a hydrogen atom or an alkyl group having 1 to 5 carbon a-toms which may have an oxygen atom, or taken -together with the nitrogen atoms to which they are bonded, represent a methylene group (-CH2-) forming the polya.nino polymer chain; Q2 and Q3 represent ; O ` O O
-C-, -S- or -C-NH-, or taken to~ether with T to which they S ~l~r are bonded, represent ~' ~ ; and T represents a C2-C15 aliphatic, aromatic, heterocyclic-aromatic, or alicyclic hydrocarbon group which may contain an oxygen atom, a sulfur atom, a halogen atoin or a tertiary nitrogen atomO
Some specific examples of this crosslinked structure are shown belowO
(1) ~CH2C-~
o CH2CH2NHCH2C~I2-NH
O=C

O=C
0, ~CH2C:~2-NHCH2-CH2_NH
~CH-CH
(2) ~ ~ H

O=C
~ -COOH
O=C

H

(3) ~CH2CH2-N~
0=S=O

O=S=O
~CH2CH2-N~

(4) ~CH2CH0~
CH2NHCH2CH2~1H
C=O

~C1-12CH0~ \1~/
CEI2NHcH2cI~2N~-c-NH

In practising the process of this invention de-scribed in detail hereinabove, the following combinations of the polyamino polymer, the polyfunctional compound and the crosslinking agent are especially preferredO
(a) A combination of a water-soluble polyamino polymer containing only second~ry amino groups as the active amino groups in an amount of at least loO milli-equivalent/g and havi~g no self-gelling property at an elevated temperature ~for example the polymers described in (V) hereinabove, especially the polymers composed of structural units of the formula ~ , -CH2-CH2-NH or ~[
2 , ); a water-soluble aliphatic diester (eOgO, diethyl tartrate) and/or a water-soluble dihalohydrin (eOgO, nonaethylene glycol dichlorohydrin) as the polyfunctional co~pound; and an aro~atic polyacid halide or aro~atic polyisocyana-te ~eOgo 9 isophthaloyl chloride (IPC for short)~ terephthaloyl chloride (~PC for short), trimesoyl chloride (TMC for short), 3-chloro-.
, ~
: .

,~ '"

sulfonylisophthaloyl chl.oride (3-CSIPC for short) and tolylene diisocyanate (~DI for short)) as the crosslinking agentO
(b) A combination of a water-soluble polyamino polymer containing at least loO milliequivalent/g of both primary and secondary amino groups as the active amino groups, the proportion of the secondary amino groups being at least 50 mole%, and having no self-gelling property at an elevated temperature ~for example, the polyamine-modified polyepoxy resins described in (III) hereinabove);the polyfunctional compound exemplified in (a) above; and the crosslinking agent exemplified in (3) above.
(c) A combination of a water-soluble polyamino polymer containing at least lnO milliequivalent/g of secondary .~mino groups alone as the active amino group and having self-gelling property at an elevated tem-perature (for example, the polymers described in (VI) hereinabove, especially the polymers composed of the recurring units of the for~ulae ~CH2-CH-O~ and ~CH2-CH-O~
CH2Cl CH2N~R16 or ~ CH2~ and ~ H2~ );
H CH2-CH=Cil2 the polyfunctional compound exemplified in (a) above;
and the crosslinking agent exemplified in (a) aboveO
(d) A combination of a water-soluble polyamino polymer containing at least loO milliequivalent/g of both pri.mary and secondary amino groups as the active amino groups, the proportion of the secondary amino groups being at least 50 mole% of the active amino groups, and having self-gelling property at an elevated temperature;
the polyfunctional compound exemplified in (a) above; and the crosslinking agent exemplified in (a) aboveO

:.

(e) The same combination as (d) except that the polyamino polymer contains only primary amino groups as the active amino groupsO
The semipermeable composite membrane provided by this invention comprises a l~icroporous substrate and a permselective thin film layer supported thereon and comprising a polyamino polymer asymmetrically crosslinked in its entirety, the permselective thin film consisting of an ultrathin surface layer having permselectivity and an anchor layer continuous -thereto between the micro-porous substrate and the surface layer for supporting the surface layer and/or bonding it to the microporous sub-strate, said surface layer mainly containing a cros~linked structural unit of the formula , Q5 ~ ~ ~ Y5 ')p Ul U2 o wherein Q5 represents -C-, ~S02- or -NHCO-9 o preferably -C- or -~2' Ul represents a hydrogen atom or a methyl group, preferably the hydrogen atom, U2 represents a hydrogen atom, a carboxyl group, or a sulfo group, and p is an integer of 1 to ~, especially 1 or 2, and said anchor lc~yer having a structure containing mainly a crosslinked structure of the following formula , O O
, r,~ ", N-C-Tl~C-N ) q .
O~I OH
N-cH-T2~ cH-N )r ~ or 2-cH2-Q6-T3~- (Q6-CH2-CH2-..

~17~309 wherein ~1~ T2 and ~3 each represent ~n aliphatic group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, which may have a nitrogen, oxygen, sulfur or halogen atom ~s a hetero atom, o Q6 represents -C- or -S02-, and q, r and s each represent an integer of 1 or 2, particularly 1~
~he membrane ~s produced by the process of this invention may be used as such in applications to be de-scribed belowO If required, it mc~y be subjected to a post-treatment step to be describedO
~ or example, the membrane can be treated with a solution of a compound containing a metal atom having the ability to form a chelate with a primary amino groupt a secondary amino group, a hydroxyl group, a carboxyl group and/or a sulfo group -to form a membrane in which such a functional group that may be present in the crosslinked thin film is chelated with the metal atomO ~his membrane has enhanced flux properties as compared with the un-treated membraneO. Examples of the metal compound which can be used for this treatment include BaC12, MgC12, HgC12, CuC12, CaC12, FeG13, AlC13 and CoC13O Of these, ~eC13, BaC12, CaC12 and MgC12 are preferredO
~ his treatment can be easily performed by im-mersing the membrane in an aqueous solution of the metal compound (in a concentration of 1 to 30% b~ weight) for about 10 to 60 minutesO
The membrane thus obtained can be treated with a liquid polyepoxy compound, acrylonitrile, a lactone such as ~-butyrolactone or ~-lactone, or propanesultone to improve its oxidation resistance and salt rejection furtherO ~his treatment can be performed by immersing the membrane in a sclution (concentration about 005 to 3% by weight) of the treating agent at room temperature for 1 to 10 minutesO
Thus, according to this inven-tion9 there is provided a semipermeable composite membrane comprising a , ~ . .
.

~1798~9 microporous substrate and a semipermeable thin fil~ of the type described hereinabove formed on one surface of the microporous substrateO In the composite membrane, the thickness of the semipermeable thin film is not strictly set, and it may have a total thickness of at least 100 ~, usually 1,000 to 4 9 000 ~o Since the semipermeable composite membrane produced by the process of this invention contains the aforesaid anchor layer which is watex-insoluble and has improved mechanical strength, it has e~cellent hydrolysis resistance7 pressure compaction resistance and/or oxi-dation resistance in addition to high salt rejection and water fluxo Furthermore, because of having a crosslinked structure, the membrane of this invention has resistance to attack by organic solvents, and can be advantageously used in a wide range of application including not only the desalination of sea water and brine but also the separation of organic mixed liquids, the treatment of in-dustrial waste waters containing organic matter, and the recovery of valuable matter in the food industryO ~hus, the composite membrane provided by this invention has a water flux of generally at least 30 liters/m2ohr, prefer-ably at least 50 liters/m2ohr and an ~aCl rejection of a generally at least 80%7 preferably at least 90%, under standard conditions, and has such excellent durability that the ratio of the permeation velocity of ~aCl in the initial stage to that after use for 200 hours is generally : not more than 105, preferably not more than loO and -the pressure compaction coefficient (m) defined by the follow-ing equation is not more than 0O03O
,r m = 1 log ~ 200 wherein (I~)o is the water flux of the membrane 1 hour later, and ( )200 is the water lux the membrane 200 hours laterO
~he composite membrane ob-tained by this invention , ~

, , , .

~798~39 can be used in various modulus, and r~ost preferably, in a spiral moduleO When the composite membrane of this in-vention is fabricated into a spiral module, it is prefer-able to cover the surface of the composite membrane with a film of a w~ter-soluble polymer for protective purposes.
Thus, it is also within the scope of this invention to provide a protective coating on the surface of the composite membrane of the inventionO Deposition of the protective coating on the thin film is carried out by coating the barrier film with a water-soluble organic polymer such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyacrylic acid, polyvinyl methyl ether, and polyvinyl ethyl etherO Polyvinyl alcohol, polyvinyl pyrrolidone and polyvinyl methyl ether are preferredO
The polymer is used as a 1-20 wt%, preferably 6-10 wt~, aqueous solutionO In a specific embodiment, the dried semipermeable composite membrane is passed through a solution of -the water-soluble organic polymer or coating the poly~er solution on the surface of this barrier film by kno~m means such as dip coating, spraying, or brush coating to coat the film continuously ~ith the solution of the water-soluble organic polymer; then the water is removed; and to form a final product9 the coated semi-permeable composite membrane is dried at a temperature of about 50 to 150C, preferably about 90 to 130C, for about

5 to 10 minutesO
The membrane having semipermeability provided by this invention is very suitable as a semipermeable membrane for the applications described above because it has superior salt rejection and flux properties, especially flux properties, superior flexibility, high resistance to pressure compaction and high resistances to chemical and biological degradation, especially oxida-tion resistance and hydrolysis resistanceO
The membrane of this invention can be advantage-ously used as a semipermeable membrane to separa-te and remove tiny amounts of contaminated molecules dispersed or dissolved in a liquid or gas, and can find extensive application, for example in the desalting of sea water and brackish water, and the treatment of industrial effluents containing organic matter, liquids containing mixtures oE
organic substances, and waste waters from the food industry, as stated herein-above.
The membrane of this invention can be used especially advantageously as a reverse osmosis membrane in the desalination of saline or brackish water by reverse osmosis which comprises contacting the saline or brackish water under pressure with the reverse osmosis membrane. This method is known, and a specific procedure described, for example, in Ind. Eng. Chem. Found. 3, 206 (1964) can be used.
The following Examples illustrate the present invention more specific-ally. The reverse osmosis test carried out in these examples followed the procedure described below.
~lethod for testing reverse osmosis The composite membrane sample was mounted on a continuously circulat-ing pump-type reverse osmosis device equipped with a flow meter, a thermometer and flow-through cells. Using an aqueous solution of NaCl in a concentration of 5000 ppm as a feed solution, a reverse osmosis test on the membrane sample was performed at 25C and 600 psi. The "standard conditions", as used in this application, mean the aforesaid test conditions.
Salt rejection The salt rejection (%) is a value calculated from the following equa-tion.
NaCl concentration \
Salt rejection ~%) = 1- NnaCPlecmoncenntratione ~x 100 in the test solution/
The "initial stage performance" means the performance of the compo-site membrane which has been operated continuously for 1 hour under the stand-ard condition.

.

:
: . :

8~9 The "NaCl permeability" of the membrane is defined by the following equation.

NaCl permeability _ W (100 _ 1) wherein WF is the water flux of the membrane in liters/m2 hr, and R is the salt rejection ~%) of the membrane.
Referential Example l Production of a microporous polysulfone substrate:- A Dacron*
poly~ethyleneterephthalate) non-woven fabric (basis weight 180 g/m2) was fixed to a glass plate. Then, a solution containing 12.5% by weight of polysulfone, 12.5% by weight of methyl Cellosolve and the remainder being dimethyl formamide was cast onto the fabric in a layer having a thickness of about 200 microns. Immediately, the polysulfone layer was gelled in a water bath kept at room temperature to form a non-woven fabric-reinforced microporous polysulfone membrane.
The resulting microporous polysulfone layer had a thickness of about 40 to about 70 microns and had an anisotropic structure. By observa-tion with an electron microscope, the surface of the microporous layer was found to contain numerous micropores with a size of 50 to 600 A.
The microporous substrate had a pure water flux ~membrane constant) of about 3.0 to 3.7 x 10-2 g/cm2 sec atm.
Referential Example 2 Mea$urement of the concentration of a polyamino polymer in a thin layer:- A solution of a polyamino polymer in a suitable concentration was applied to the polysulfone membrane obtained in Referential Example 1, *Trade Mark ~51-9~9 51a ~

and as required, the solvent was evaporated to form a thin layer containing the polyamino polymer.
The porous polysulfone substrate having the thin layer deposited thereon was put into chloroform to dissolve the polysulfGne in chloroform.
Thus, an aqueous ~.
, . ~

` , :

1-17~9 layer having the poly.~mino polymer dissolved therein and a chloroform layer having the polysulfone dissolved therein were formedO ~he aqueous lc~yer was taken out, and after measuring its weight, was evaporated to dryness to obtain the polyamino polymerO ~he polyamino polymer was weighed, and the concentration of it in the aqueous layer WAS de-terminedO ~his is the concentration of -the polyamino polymer in the thin layerc A 0O5-~/o by weight aqueous solution of each of the polyamin~3 polymers used in ~xamples 1 to 40 given here-inbelow was prepared, and a predetermined proportion of the polyfunctional compound ~as added and dissolved~ The resulting solution was applied to the aforesaid polysulfone substrate and drainedO It was then air-dried at room temperature for 10 to 20 minutes to form a porous poly-sulfone substrate having a thin layer of the poly er de-posited thereonO Using this substrate9 the concentration of the polyamino polymer in the thin layer was measured in accordance with the above procedureO It was within the range of 20 to 60Cjo by weightO
Referential Example_~
Methods for r.qeasurin~ ~he degree of water in-solubility and self-gellation temperature of the polyamino polymer--~ predetermined amount of a polyamino polymer was added to 100 parts of water, and they were stirred at room temperature to form a solutionO When it is desired to determine the effect of adding the polyfunctional com-pound, a predetermined amount of it is further added to the solution, and the mixture is stirred at room temperature to form a solutionO
: : ~he resulting polyamino polymer solution in a predetermined concentration was charged into arl autoclave, and the temperature was raised rapidly to a predetermined point under pressureO ~he solution was maintained at this temperature for 30 minutes to gel the polyamino polymer and then quenched to room -tempera-tureO

`'^

The polymer solution containing the gelled polymer was filtered to separate the dissolved polyamino polymer. The concentrate obtained was washed with 100 parts of water or alcohol at 70C and dried. The weight of the gelled polymer was then measured.
The percentage of the weight of the gelled polymer based on the weight of the polyamino polymer used (when the polyfunctional compound is used, its weight is added) is defined as the degree of water insolubility at the above-mentioned temperature of the polyamino polymer.
The degree of water insolubility of the polyamino polymer was plotted as the function of the heat-treating temperature under the conditions described above, and the temperature at which the degree of water solubility reached 70% was defined as the self-gelling temperature of the polyamino polymer.
Example 1 A three-necked flask ~500 ml) was charged with 14.6 g of tri-ethylene tetramine and 100 g of distilled water, and with stirring at room temperature in an atmosphere of nitrogen, a mixture of 10 g of bisphenol A diglycidyl ether (Epikote 828, a registered trademark for a product of Shell Chemical Co.~ and 7.6 g of glycerol polyglycidyl ether ~DENAKOL 314, a registered trademark for a product of Nagase-Ciba Co., Ltd.) was added drop-wise from a dropping funnel. The addition was completed in 1 hour, and the system was heated to 50C and stirred for 5 hours to form a uniform clear solut~on.
The aqueous solution was put into a Cellophane* regenerated cellulose film tube and dialyzed for one day to remove the unreacted amine *Trade Mark .

11798(;~9 - 53a ~

and low-molecular-weight by-products. The amine equivalent (primary amino groups~ secondary amino groups) of the resulting addition polymer was 22 milliequivalents/g of dried addition polymer.
Diethyl tartrate (0.2 g~ was uniformly dissolved in 100 g of a 0.7% by weight aqueous solution of the addition polymer. The polysulfone membrane rein-:;~

.

:
, .

forced with the non-woven fabric obtained in ~eferential Examp].e 1 was dipped for 5 minutes in the resulting solution and drained for 5 minutes -to put it erect verticall-y to remove the excess of the solution adhering to the membraneO
~he drained membrane was -then dipped for 2 rninutes in a 005% by weight n-hexane solution of terephthaloyl chloride to perform crosslinking reactionO Subsequently, the mem-brane was heat-treated for 10 minutes in a hot air dryer at 100C to render the i~terlayer of the composite membrane l.rater-insolubleO
~he resulting composite membrane was subjected to a reverse osmosis test by the method described here-inabove (at 25C and 42~5 kg/m2 using a 005% aqueous solution of NaCl as a feed solution)0 ~he membrane showed a water flux of 340 5 liters/m20hr and a salt rejec-tion of 990 34%o ~hen this membrane was operated continuously, it showed stable performance after a lapse of 1000 hours represented by PA water flux of 3306 li-ters/m2hr and a salt iejection of 99043%0 (~he reverse osmosis c~evice was washed with a 005Yo aqueous solu-tion of citric acid for 3 hours after a lapse of 300 hours ancl 700 hours respectively in the c~ove operationO) Comparative Example 1 ~xample 1 was repeated except that diethyl tartrate was not used in -the production of the composite membraneO
~he resulting composite membrane showed initial performances represented by a water flux of 3204 liters/m2 hr and a salt rejection of 99031%o But after a lapse of 300 hours, the salt rejection decreased to 99002% and the water flux was 3406 liters/m20hrO
Example 2 Example 1 was repeated except that ethylene 35 glycol dichlorohydrin was used in an amount of 00 3 g in-stead of the diethyl tartrate in ~xample lo ~he c.omposite membrane showed ini-tial per~ormances represen-ted by a water flux of 2905 liters/m20hr and a salt rejection of 990~3%0 When this membrane was continuously operated for 300 hours~ it had a water flux of 2703 liters/m2ohr and a salt rejection of 9903~/o, showing very stable perform~ncesO
Examples 3 to 8 One gram of the addition polymer synthesized in Example 1 was rnixed with 003 mole, per equivalent weight of the primary and secondary arnino groups combined in the addition polymer, of each of the compounds shown in ~able 1 below, and the mixture was heat-treated at 120C for 30 minutes by the method shown in Referen-tial Example 3~
The arnount of water-insoluble gel formed was determinedO
The r~ixture before heat-treatr~ent was water-soluble at 25 CO When only the polymer alone w.~s heat treated at 120C for 30 minutes, the gel content was 307%O

~li79 ~able I

__ . _. _ _ ____ _ Degree of water 'SGlUbili~y ( ~) .
~xample Compound (%) . -- .~
3 Diethyl tartrate 4301 . ....
4 Ethylene glycol dichlorohydrin 375 . ,...... _ .__ . ... .
bisphenol A dichlorohydrin (clc~2cHcH~o-~ ~ 5603 . . . .

6 CH300C ~ OOCH3 3104 S03~a . .

CH21~1HCOOCH3

7 ~ 2503 CH2~1HCOOCH3 , _ . .

~orbitol tetrachlorohydrln 55 he weight percent o~ the water-insoluble gel contained in the mixture o~ the addition polymer of Example l and the above compound ~ after it was heated at 120C for 30 minutesO

Example ~
In a 100 ml flask, 1600 g of diallylamine nitrate was dissolved in 50 ml of dimethyl sulfoxide, and 005 g of ammonium persulfate was addedO With stirring, the mixture was gradually heated to 50Co ~he polymerization was performed ~or 3 hours, an~d the reaction mixture was le~t to stand overnight at room temperatureO ~he reaction

8~9 mixture was then put into a ccllophanc dialyzing tube and dialyzed to remove the unreacted monomer, the dimethyl sulfoxide .solvent, the catalyst, e-tcO to form poly-(diallylamine nitra-te) of the following structure ~1) in pure formO lhis polymer had an inherent viscosity, measured at 30C in a l/lON NaCl solution, of 00810 --CH

H H
~ wo grams of the polymer was put into 50 ml of a 005% by weight aqueous solution of sodium hydroxide, and with stirring at room temperature for 3 hours, the mixture was dialyzed in the same way as above to afford an aqueous solution of a polymer of the following structure ~2)o ~C~2~ ~ 2) When a 50% by weight aqueous solution of this polymer was heat-treated at 120C for 30 minutes by -the method of Referential Example 3, it did not at all gel by itselfO
A 1% by weight aqueous solution of -the polymer was prepared, and 004 g of pipera~ine and a solution of Ool g of ethyl monochloroacetate in 10 ml of ethanol were mixed to form a film-forming dopeO When this dope was concentrated to 50% by weight and tested for self-gel-lability in the same way as above, it showed a gel ratio of 6~o 2%O
The microporous polysulfone membrane obtained in Referen-tial ~xample 1 was dipped for 5 minutes in the resulting dope, and subsequently drained for 7 minutesD
The drained membrane was dipped for 2 minutes in a 003,~
by weight n-hexane solution of isoph-thaloyl chloride, and then heated a-t lOO~C for 10 minutesO The resulting ~ T~ Jcmc~rk ', :~ .

~:i798~g -- 5~3 --composite membrane was subjected to a reverse osmosis test at a pH of 600 to 60 5 and 4205 kg/cm2 in the presence of to 5 ppm of active chlorine using a 0.,5% aqueous solution of NaCl as a feed solutionu ~he compvsite membrane showed 5 initial performances represented by a water flux of 4507 liters/m20hr and a salt rejection of 9401%o ~he membrane was further opera-ted for 200 hours while maintaining the concentration of chlorine at 4 to 5 ppm and the pH a,, 6 to 6050 The merlbrane was found to have a water flux of 3906 10 liters/m2ohr ancl a salt rejection of 9604%, showing stable performancesO
Comparative Example 2 A composite membrane was produced in the same way as in Example 9 excep-t that ethyl monochloroace-tate was 15 not usedO ~he resulting composite membrane was subjected to the same reverse osmosis test as in :Example 90 It showed initial performances represen-ted by a water flux of 3500 liters/m20hr and a salt rejection of 9501/~o When this test was continuously performed for 200 hours, the 20 membrane showed a water flux of 7903 liters/m2ohr and a salt rejec-ti~ o:f 8403%o xamples 10 and 11 In the same way as in Lxample 9, the polymer shown in ~able II was synthesized~ and by using the polymer 25 and diethyl tartrate, a composi-te membrane was produced~
The composite membrane was subjected to a reverse osmosis test in the same way as in Example 9 in the presence of chlorine for 300 hours~ The results are shown in ~able IIo

9~3~9 C) _ . _ .~ ..
~:~ ~ ~ ~, ~ ~ o ~!o ~ ~ (~
hh ~ ~
h~ ~ h ~ h ~ ~ u U~ ~ L~ C~
,~ _ o ~ a~ ~ ~ O
O ~ CQ '~ Ci~
,1 a) ~
4 ~D u~`, l a5 h ~ h ~ Ci~ ~
H ~.q ~ ~ ~ o ~t o ~> t~ N
~; ~ !
_ ~ ~, ~ O=v ~ C~
~ ~ V{~v~
o ~ O =V \0~
H V r~, V
H__ . .. _ - ...... _ r5 h C~ ~ ~ ~ h E~ ~ o . ... __ ~ P~ ~ 1 ~ r~: ~! _ ~ ~ ..
~ V V
V V
~ ~ ~N\
q~ , ~
O O'- =O
~' Pl~

__ cn ~ ~o ~ = . ~

~ 17~39 Example 12 ~ en grams of polyepichlorohydrin havin~ a molecular weight of about 3,000 was dissolved in 100 ml of N-methyl-pyrrolidone, and 20 g of aniline was a(l~leclO ~he mixture was heated at 120 to 130C for 3 hours in an atmosphere of nitrOgen C' ~ he reaction mixture was put into a ee~h~3~
tube and dialyzed to remove N-methylpyrrolidone and the unreacted aniline to afford an aqueous suspension of partially aniline-modified polyepichlorohydrin having the following structural forrnula ~CH2CH0 ~ CH2,CH0~5038 CH2Cl CH2 H

One gram of -the polymer, 0O3 g of sebasic di-imidazolide ~ N N-G-~CH2 ~ C~ N ), Ool g of sodium dodecylsulfate and 10 ml of ethanol were ~dded to 100 g of distilled water, and they were vigorously stirred by a homogenizer to afford a white emulsionO
Using the emulsion, a composite membrane was produced in the same way as in ~xample lo ~he membrane was subjected to the same chlorine-resistan-t reverse osmosis test as in ~xample 9O ~he composite membrane was found to have initial performances represented by a water flux of 2707 liters/m2Ohr and a salt rejection of 9801%n When this test was continued for 200 hours, the composite membrane s-till showed a water flux of 2509 liters/m2ohr, and a salt rejection of 98~ 3%~ indicating stable perfor-mancesO
Comparative _xamPle 3 A composite membrane was produced in the same 30 way as in Example 12 except that diimidosebacamide was not usedO ~he resulting membrane was subjected to the rnork ' 11~79~3~9 same chlorine-resistant revsrse osmosis testO It was found that the composite membrane had initial performances re-presented by a water flux of 260 2 liters/m2ohr and a salt rejection of 9609%o Bu-t 50 hours later~ the membrane had a water flux of 4301 liters/m2hr and a salt rejection of 9004%~ showing degraded performancesO
Example 1~
A polymer of the following structure was produced in the s~me way as in Example 12 except that poly(2-chloroethylvinyl ether) having a molecular weight of about5,000 was used instead of the polyepichlorohydrin, and monoethanolamine was used instead of the anilineO
4~2 1 ~I) 1 ( CH2 I H~o 17 OCH2CH2Cl OCH2CH2NHCH2C~20H
One gram of the polymer, 003 g of diethyl tartrate, Ool g of sodi~n dodecylsulfate ancl 004 g of sodium bicarbonate were added to 100 g of distilled water, and they were vigorously stirred by a homogenizer to afford a white emulsion~
A composite membrane was produced in the same way as in Example 1 using the resulting emulsionO When the composite membrane was subjected to the same chlorine-resistant reverse osmosis test as in Exa~ple 9, the com-posite showed initial performances represente~ by a water flux of 2508 liters/m2ohr and a salt rejection of 9409%~
O~e hundred hours later, the membrane still had a water flux of 2201 li-ters/m2ohr and a salt rejection of 95~3%, showing stable performancesO
Comparative Example 4 A composite membrane was produced in the same way as in Example 13 except that diethyl tartrate was not usedO ~he composite membrane was subjected to the same reverse osmosis test as in Example 130 ~he membrane showed initial per~ormances represented by a water flux of 27~1 liter/m2ohr and a salt reaection of 9304%0 After 11t7~809 operating for 30 hours, the membrane showed a degrading tendency and had a water flux of 3807 liters/m2hr and a salt rejection of 8704%o Example 14 Chloromethylstyrene (10 g) was dissolved in 50 ml of benzene, and 00~ g of azobisisobutyronitrile was addedO ~he polymerization was performed for 8 hours in a nitrogen atmosphere a-t 70C to afford poly(p-chloromethyl--styrene) having a molecular weight of about 67500o Ethylamine (10 g) was added to a solution of 2 g of this polymer in 50 ml of N-methylpyrrolidone, and the mixture was stirred at 50C for 5 hours in an atmosphere of nitrogenO ~he reaction mixture was dialyzed to form a polymer of the following structureO
4 H ~H ~ CH2 ~ 88 CH2Cl CH2NHC~,H5 A composite membrane was produced in the same way as in Example 13 using the resulting polymerO The com-posite membrane was subjected to the same chlorine-resistant reverse osmosis test as in Example 90 It was found that the membrane showed initial performances represented by a water flux of 2203 liters/m2hr and a salt rejection of 9504%0 One hundred hours later, the composite membrane still had a water flux of 2007 liters/m2hr and a salt rejection of 9602%, showing stable performancesO
Comparative Exampl~e $
A composite membrane was produced in the same was as in Example 14 except that diethyl tartrate was not used, and the resulting membrane was subjected tG the sal~e reverse osmosis testO It was found that the membrane had a water flux of 2507 liters/m2hr and a salt rejection of 9401% in the initial stage and after a lapse of 70 hours, it had a water flux of 5103 liters/m2ohr and a salt ~ 9B~9 reaection of 8509~/o, showing degradell performancesO
Example 15 ~ ive grams of poly~.nethyl acrylate (molecular weight about 100,000) was dissolved in 95 g of N-methyl-pyrrolidone, and 60 g of diethylenetri&mine was addedO
The mixture was heated at 120C for 10 hoursO
~ he mixture wass put into 1 liter of tetrahydro-furan to precipitate the reaction product which was washed several times with tetrahydrofuran to form a polyamino polymer of the following structureO

~C 2l ~ H2lH ~
C=O COOCH3 -~C 2 2 )3 ~ he polymer had an intrinsic viscosity9 measured in 1/10~ aq~eous NaCl, of 00 950 When a 50% solution of this pol~mer was heat~treated at 120C for 30 minutes in the same way as in ~xample 3~ its self-~elling ratio was 43%O
A solution of 1 g of the resulting polymer in 50 ml of clistilled water was mixed with a solution of 002 g of isophthaloyl diimidazolide ( N ~ ~-C- ~ -C-N ~ ) in

10 ml of ethanol to form a film-forming dopeO When this dope was concentrated to 50% by weight? and subjected to the same self-gellation test as above, the self-gellation ratio of the polymer was 7803%o A composite membrane was produced in the s&me way as in Example 1 using the resulting film-forming dope, In the reverse osmosis test, this composite membrane showed a water flux of 7201 liters/m20hr and a salt rejection of 9103% in the initial stage, and after continuously operat-ing it for 200 hours, it still had a water flux of 6703 liters/m2ohr and a salt rejection of 950 8//o~ showing stable performancesO

.

Comparative ~xample _ A composi-te membrane WaS produced in the same way as in Ex~nple 15 except tha-t isophthaloyl cliimidazolide was not usedO ~he resulting membrane showed a water flux of 8003 liters/m2hr and a salt :rejection of 9002~/oO After a lapse of 200 hours, the membrane hacl water flux of 9804 liters/m2ohr and a salt rejection of 8704%, showing a de-grading tendency in performanceO
Example 16 A solution of 5 g of polyepichlorohydrin having a number average molecular weight of 20,000 in 100 ml of N-methylpyrrolidone was added to 70 g of ethylene~iamine and reacted at 100C for 20 hoursO ~he reaction mixture was then poured into 1 liter of tetrahydrofuran9 and washed several times with tetrahydrofuran to ,~`ford a polyamino polymer having the following structure and an intrinsic viscosity~ determined in a l/lON aqueous NaC1, of 00540 ~cH21cH~)g 5 (CH21CH
., CH2 C~2C

When a 50% by weight aqueous solu-tion of this polymer was heat-treated by the method of Referential Example 3, it showed a self-gelling ratio of 4501%o A solution of 2 g of the resulting polymer in 100 g of dis-tilled water was mixed with a solution of 002 g of poly(3-chloro-2-hydroxypropyl acrylate) having an intrinsic viscosity, determined in N-me-thylpyrrolidone, of 0038 and the follow-ing structural formula (C~I21CH)n COOCH2CHCH2Cl OH
in 10 ml of dioxane to form a film-forming dopeO
When this dope was concentrated to 50% by weight and heat-treated at 120~ for 30 minutes, the polymer showed a self -gelling ratio of 7908%o A composite membrane was obtained in the same way as i~ Example 1 using the film-forming dopeO ~llhe 5 com ?osite membrane showed a water flux of 6409 liters/
m ohr and a salt reaection of 9804% in the initial stageO
When this reverse osmosis test was continued for 200 hours, the composite membrane still had a water flux of 6001 liters/m~Ohr and a salt rejection of 9809%, showing very 10 stable performancesO
Comparative Example 7 -A composite membrane w~s produced in the same way as in :Example 16 exceot that poly(3-chloro-2-hydroxy-propyl acryla-te) was not usedO This composite membrane 15 had a water flux of 5802 liters/m2Dhr and a salt rejection of 98 7% in the initial state, anù after a lapse of 200 hours, it hacl a water flux of 5307 liters/m20hr and a salt rejection of 9706% showing a degrading tendency in performanceO
20 Compara-tive :E;xample 8 A composite membrane was produced in the sa~e way as in Comparative Example 7 except that the heat-treatment temperature for the production of the composite membrane was changed to 140Co This composite membrane 25 showed a water flux of 1307 liters/m2hr and a salt re-jection of 9707%, showi lg low performances in reverse osmosis.
~;xamples 17 to 27 Polyethyleneimine having a number average mole-30 cular weight of 10,000 (a product of ~ippon ShokubaiKagaku Kogyo CoO, Ltdo) was dissolved in distilled water to form a 005% aqueous solution of the polymerO.
Each of the polyflmctional compounds shown in Table III was added to the resulting solution~ and a 35 composite membrane was produced in the same way as in Example lo q~he performances of the resulting composite membranes in the reversè osmosis test in the initial stage and after a lapse of 200 hours are shown in ~able IIIo .

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~79~

E~amples_28 to 40 The self-gelling temperatures (for its defini-tion and the method for its measurement, see Referential Example 3) of the polyamino polymers used in ~xamples 1 to 27 and mixtures of these polyamino polymers with the polyfunctional compounds shown in Table IV were measuredO
A mixed solution of each of the polyamino polymers and each of the polyfunctional compounds was applied to the microporous polysulfone substrate obtained in Referential Example 1 and drained to form a thin layer containing about 50% by weight of the mixture of the polyamino polymer and the polyfunctional compound, and then without performing interfacial crosslinking, heat-treated for 30 minutes at the self-gelling temperatureO
lhis test gave information about the barrier property and durabili-ty of the anchor layer of this in-ventionO
The results are shown in Table IVo ~he heat-treatment of the composite membrane not containing the polyfunctional compound was performed at a self-gelling temperature range corresponding to that for the composite membrane containing the polyfu~ctional compoundO

~;179B~

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Claims (37)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a semipermeable composite membrane, which process comprises:
(I) forming on a microporous substrate a thin layer of a polymeric material comprising a polyamino polymer containing at least 1 milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, wherein the polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in the polymer at a temperature at which a subsequent interfacial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in the polymer at a temperature at least 30°C higher than the subsequent crosslinking temperature, (II) interfacially crosslinking a surface portion of the thin layer with a crosslinking agent having at least two functional groups (a) capable of easily reacting with either the primary or secondary amino groups or both in the polymer, and (III) heating the interfacially crosslinked thin layer to a temperature at which the polyfunctional compound reacts with the primary or secondary amino groups or both in the polymer.

2. The process of claim 1 wherein the functional groups (b) do not substantially react with either the primary or secondary amino groups in the polymer at a temperature of not more than 20°C, but react easily with either the primary or secondary amino groups or both in the polymer at a temperature of at least 50°C but below the self-gelling temperature of the polymer.

3. The process of claim 1 wherein the functional groups (b) do not substantially react with either the primary or secondary amino groups of said polymer at a temperature of not more than 30°C, but react easily with either the primary or secondary amino groups or both in said polymer at a temperature of at least 70°C but below the self-gelling temperature of said polymer.

4. The process of claim 1 wherein said functional groups (b) are selected from the group consisting of and active halomethyl groups, in which Xl represent a halogen atom, Al and A2 each represents a hydrogen atom or an organic radical capable of being split off together with the oxygen atom to which it is bonded, and A3 represents a trivalent or tetravalent saturated aliphatic group having 2 to 5 carbon atoms.

5, The process of claim 1 wherein the polyfunctional compound is a low-molecular-weight or high-molecular-weight polyfunctional compound which dissolves in a solvent selected from water and water-miscible organic solvents having a boiling point of not more than 140°C to an extent of at least 0.1 g/100 ml of the solvent at 20°C.

6. The process of claim 1 wherein the poly functional compound is an organic compound containing 2 to 4 functional groups (b) per molecule and having a molecular weight of 90 to 500.

7. The process of claim 6 wherein said organic compound is an aliphatic compound.

8. The process of claim 1 wherein the polyfunctional compound is a high-molecular-weight organic compound containing said functional groups (b) in an amount of 2.0 to 15.0 milliequivalents per gram of the compound and having a number average molecular weight of l,000 to 100,000.

9. The process of claim 8 wherein the high-molecular-weight organic compound is a vinyl polymer.

10. The process of claim l wherein the polyfunctional compound is a compound selected from compounds of the following formulae (i) (iii) A5 ? (COO-A6)a ;

(iv) A7-OOCNH-A9-NHCOO-A8 ;

(v) A10 ? (OOC-CH=CH2)b ;

(vi) and (vii) X7-CH2-COO-A12 in which formulae Q represents a direct bond, an ether linkage, or an alkyl group having 2 to 20 carbon atoms which may contain an oxygen or halogen atom, q is an integer of from 2 to 6, each of X2, X4, X5, X6 and X7 re-presents a halogen atom, each of A5, A10 and A11 represents a hydroxyl group, an aliphatic groups containing 1 to 12 carbon atoms and having a valence of a, b or c which may contain an oxygen or halogen atom, an aromatic group containing 6 to 10 carbon atoms and having a valence of a, b or c, or an alicyclic group containing 5 or 6 carbon atoms and having a valence of a, b or c, each of A6, A7, A8 and A12 represents an alkyl group having 1 to 4 carbon atoms, an allyl group, a phenyl group or an aralkyl group having 7 to 10 carbon atoms, A9 represents an alkylene group having 2 to 10 carbon atoms, or an arylene group which may be substituted by a halogen atom or an alkyl group having 1 to 6 carbon atoms, and a, b and c each represent an integer of 2 to 4.

11. The process of claim 1 wherein the polyfunctional compound is a high-molecular-weight compound containing at least 40 mole% of at least one recurring unit selected from the group consisting of (i) ;

(ii) ;

(iii) (iv) in which formulae X8 represents a halogen atom, A13 represents a hydrogen atom or a methyl group, A14 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, an allyl group, an aralkyl group having 7 to 10 carbon atoms, or a phenyl group, and d is 1 or 2.

12. The process of claim 1 wherein the polyfunctional compound is ethylene glycol dichlorohydrin, glycerol dichlorohydrin, glycerol tri-chlorohydrin, sorbitol dichlorohydrin, sorbitol trichlorohydrin, sorbitol tetrachlorohydrin, dimethyl tartarate or diethyl tartarate.

13. The process of claim 1 wherein said thin layer contains 0.05 to 1 equivalent, per equivalent of the active amino groups in said polyamino polymer, of said polyfunctional compound.

14. The process of claim 1 wherein said thin layer contains 0.1 to 0.7 equivalent, per equivalent of the active amino groups in the poly amino polymer, of said polyfunctional compound.

15. The process of claim 1 wherein said functional groups (a) react easily with the primary or secondary amino groups or both in said polymer at a temperature of not more than 30°C.

16. The process of claim 1 wherein said functional groups (a) react easily with the primary or secondary amino groups or both in said polymer at a temperature of not more than 20°C.

17. The process of claim 1 wherein said functional groups (a) are selected from the group consisting of carbonyl halide, sulfonyl halide, isocyanate, and acid anhydride groups.

18. The process of claim 1 wherein said functional groups (a) are carbonyl halide or sulfonyl halide groups.

19. The process of claim 1 wherein said crosslinking agent is a cyclic compound containing 2 or 3 functional groups (a).

20. The process of claim 18 wherein said cyclic compound is an aro-matic compound.

21. The process of claim 1 wherein said crosslinking agent is selected from the group consisting of isophthaloyl chloride, terephthaloyl chloride, trimesoyl trichloride and 3-chlorosulfonylisophthaloyl chloride.

22. The process of claim 1 wherein said polyamino polymer contains 5.0 to 23.0 milliequivalents, per gram of the polymer in the dry state, of said active amino groups.

23. The process of claim 1 wherein said polyamino compound has a number average molecular weight of 1,000 to 100,000.

24. The process of claim 1 wherein said polyamino polymer has an intrinsic viscosity, determined at 30°C
for a 1/10N aqueous solution of sodium chloride, of 0.1 to 200 dl/g.

25. The process of claim 1 wherein said polyamino polymer dissolves in at least one solvent selected from the group consisting of water and water-miscible organic solvents having a boiling point of not more than 140°C to an extent of at least 0.2 g/100 mg of the solvent at 20°C.

26. The process of claim 1 wherein said polyamino polymer is a polyaddition product between a polyepoxy compound and a polyamino compound having at least two active amino groups.

27. The process of claim 1 wherein the polyamino polymer is polyethyleneimine, a polyamine-modified poly-epichlorohydrin, or a polyamine-modified poly(2-chloro-ethyl vinyl ether).

28. The process of claim 1 wherein said polyamino polymer is a polymer containing at least 30 mole% of a recurring unit of the following formula wherein R11 and R12 each represent a hydrogen atom or a methyl group and Z3 represents a direct bond or -SO2-.

29. The process of claim 1 wherein the polyamino polymer is a polymer consisting mainly of two recurring units of the formulae and wherein R16 representsan alkyl group having 1 to 4 carbon atoms, or of two recurring units of the formulae and wherein R16 is as defined above.

30. The process of claim 1 wherein the polyamino polymer is a polymer which does not gel by itself at a temperature of not more than 60°C.

31. The process of claim 1 wherein said thin layer contains at least 10%
by weight of the polyamino polymer.

32. The process of claim 1 wherein said thin layer is formed by applying a solution containing the polyamino polymer and the polyfunctional compound to the microporous substrate.

33. The process of claim 32 which includes the step of partially evaporat-ing the solvent.

34. The process of claim 1 wherein the interfacial crosslinking is carried out at a temperature of about 5°C to about 40°C.

35. The process of claim 1 wherein the interfacially crosslinked layer is heated to about 50°C to about 130°C.

36. A semipermeable composite membrane which comprises a microporous substrate and, formed on the substrate, a thin layer of a polymeric material comprising a polyamino polymer containing at least one milliequivalent, per gram of the polymer in the dry state, of active amino groups selected from primary amino groups and secondary amino groups, a surface portion of said thin layer having been interfacially crosslinked with a crosslinking agent having at least two functional groups (a) capable of easily reacting with either the primary or secondary amino groups or both in said polymer, wherein said polymeric material contains dispersed therein a polyfunctional compound having at least two functional groups (b) substantially incapable of reacting with the primary or secondary amino groups in said polymer at a temperature at which the inter-facial crosslinking is carried out, but capable of reacting easily with either the primary or secondary amino groups or both in said polymer at a temperature at least 30°C higher than said crosslinking temperature, and wherein the inter-facially crosslinked thin layer has been heated to a temperature at which said polyfunctional compound reacts with the primary or secondary amino groups in said polymer.

37. The membrane of claim 36 which has a water flux of at least 30 liters/
m2.hr and a NaCl rejection of at least 90% under standard conditions, the ratio of the permeation velocity of NaCl in the initial stage to that after continuous use for 200 hours being not more than 1.50, and which also has a pressure com-paction coefficient expressed by the following equation of not more than 0.03:

log wherein (WF)0 is the water flux of the membrane in the initial stage (after 1 hour), and (WF)200 is the water flux of the membrane after 200 hours.