CA1285356C - Multilayer composite hollow fibers and method of making same - Google Patents
Multilayer composite hollow fibers and method of making sameInfo
- Publication number
- CA1285356C CA1285356C CA000512301A CA512301A CA1285356C CA 1285356 C CA1285356 C CA 1285356C CA 000512301 A CA000512301 A CA 000512301A CA 512301 A CA512301 A CA 512301A CA 1285356 C CA1285356 C CA 1285356C
- Authority
- CA
- Canada
- Prior art keywords
- hollow fiber
- polymer
- layers
- layer
- separating
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/24—Formation of filaments, threads, or the like with a hollow structure; Spinnerette packs therefor
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0023—Organic membrane manufacture by inducing porosity into non porous precursor membranes
- B01D67/0025—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching
- B01D67/0027—Organic membrane manufacture by inducing porosity into non porous precursor membranes by mechanical treatment, e.g. pore-stretching by stretching
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/08—Hollow fibre membranes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/1213—Laminated layers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/1216—Three or more layers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/08—Specific temperatures applied
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/08—Specific temperatures applied
- B01D2323/081—Heating
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
- Y10T428/2929—Bicomponent, conjugate, composite or collateral fibers or filaments [i.e., coextruded sheath-core or side-by-side type]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
- Y10T428/2933—Coated or with bond, impregnation or core
- Y10T428/2935—Discontinuous or tubular or cellular core
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
- Y10T428/2973—Particular cross section
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2913—Rod, strand, filament or fiber
- Y10T428/2973—Particular cross section
- Y10T428/2975—Tubular or cellular
Abstract
Abstract of the Disclosure Disclosed are a multilayer composite hollow fiber comprising at least one nonporous separating membrane layer (A) performing a separating function and two or more porous layers (B) performing a reinforc-ing function, the layer (A) and the layers (B) being alternately laminated so as to give a structure having internal and external surfaces formed by the porous layers (B), as well as a method of making such a hollow fiber.
In this multilayer composite hollow fiber, the separating membrane can be formed as an ultrathin, homogeneous membrane. Moreover, the separating mem-brane is not liable to get damaged owing to the unique structure of the hollow fiber. Furthermore, such hollow fibers can be readily and stably produced on an industrial scale.
In this multilayer composite hollow fiber, the separating membrane can be formed as an ultrathin, homogeneous membrane. Moreover, the separating mem-brane is not liable to get damaged owing to the unique structure of the hollow fiber. Furthermore, such hollow fibers can be readily and stably produced on an industrial scale.
Description
SPECIFICATION
Title of the Invention Multilayer Composite Hollow Fibers and Method of Making Same Background of the Invention 1. Field of the }nvention This invenkion relates to high-performance multilayer composite hollow fibers including at least one nonporous membrane layer and suitable fox the separation of gases and for o~her purposes, as well as a method of making the same.
Title of the Invention Multilayer Composite Hollow Fibers and Method of Making Same Background of the Invention 1. Field of the }nvention This invenkion relates to high-performance multilayer composite hollow fibers including at least one nonporous membrane layer and suitable fox the separation of gases and for o~her purposes, as well as a method of making the same.
2. Description of the Prior Art : A large number of methods for the separation and purification of substances have been developed and improved from long ago.
The membrane separation technique is one of these methods. On a broad survey of the progress of its improvement, the general trend of technological advancement involves the development of excellent membrane materials, the development of techniques for forming thin membranes serving to enhance separating efficiency and the development of hollow fibers capable of enhancing equipment efficiency.
~2~
Among various separating membranes are non-porous membranes useful for the separation of gases and for other purposes. In such a nonporous membrane, the permeation rate for a gas is determined by its diffusion throuyh the membrane, and the diffusion rate of the gas is greatly influenced by the thickness of the membrane.
Accordingly, it is common practice to make the nonporous membrane as thin as possible. Moreovex, since such a thin nonporous membrane has inadequate strength~ attempts have been made to ~orm a composite structur~ by combin-ing the membrane with a porous layer. As one o such techniques for the formation of a thin membrane, a method is being extensively~employed in which a thin membrane is ~ormed on a porous substrate according to the coating or vapor depsition process. However, when a coating material is applied to a porous substrate, it penetrates into the pores of the substra~e and fails to form a substantially thin mem~rane. More specifically, the membrane is sufficiently thin in the regions not corresponding to the pores of th~ porous substrate, but is undesirably thic~ in the regions corresponding to the pores. If an attempt is made to overcome this disadvantage by reducing the thickness of the membrane in ths reyions corresponding to the pores, pinholes will appear. For this re~son, it is practically impos-sible to form a thin membrane of uniform thickness 1~535~
according to this method.
In order to overcome the above-described disadvanta~e, another method has been proposed in which the pores of a porous substrate are filled with a soluble material in advance, a thin membrane layer is formed on the surface of the substrate, and the soluble material is then laached out of the substrate. How-ever, this method can hardly yield a thin membrane layer of uniform thic~ness. Moreover, th1s method is disadvantageous in that the thin membrane layer is liable to be damaged during the leaching process and in that ~he thin membrane layer tends to peel away from the finished composite membrane. Furthermore, it is difficult to apply this method to ths manufaature of hollow fibers.
Still another;me~hod for forming a thin separating membrane is the formation of an asymmetric membrane from a polymer solutlon. For example, reverse osmosis membranes formed of aromatic polyamide and ultrafiltration membranes formed of polyacrylonitrile are being commercially produced by this method.
However, all of these membranes are formed according to such a technique that, in forming a membrane from a polymer solution, the superficial part of the me~brane is solidified densely and the internal part thereof is made porous by~selection of proper solidifying 353S~
conditions or by use of the leaching process. Thus~
these separating mem~ranes consist of a single material.
Accordingly, ~he structure of the membrane~
formed by this method changes continuously from the superficial dense part toward the internal porous part and includes an intermediate structural part performing no important function. This is not so de irable from the viewpoint of filtering efficiency.
Moreo~er, the thin, nonporous membrane layer per~orming a separating function is exposed on one side of these composite membranes. This i9 disadvantayeous in ~hat any mechanical force exer~ed during manufacture or use tends ~o result in pinholes or ~ause damage to the nonporous membrane layer.
Summary of the Invention It is an object of an aspect of the present invention to provide a novel membrane ~tructure including a ~ry thin, nonporous separating membrane having excellent durability.
It is an object of an aspect of the present invention to provide hollow fibers including a nonporous separat-ing membrane having excellent separa~ion characteristics.
It is an object of an aspect of the present invention to provide a method of making hollow fibers i35S
including a very thin, nonporous separating membrane which method permits such hollow fibers to be stably produced on an industrial scale.
According to the present invention, there is provided a multilayer composite hollow fiber comprising at least one nonporous separating membrane layer (A~
performing a separating function and two or more porous layers (B) performing a reinforcing function, the layer (A) and the layers (B) being alternately laminated so as to gi~e a structure having inner and outer surfaces formed by the porous layers (B).
According to the present invention, there i5 also provided a method of making a multilayer composite hollow fiber as described above which comprises the steps of co-spinning a polymer (At) for forming the separating membrane layer and a polymer (B') for forming the porous layers through a spinning nozzle of multiple tubular construction so as to sandwich the polymer (A') between two layers of the polymer (B'), the spinning of said polymers taking place at a temperature between the melting point of said polymer (B'~ and about 80C above said melting point and at a spin draw ratio above about 30, and stretching the resulting hollow fiber so as to make the layers (B) porous while leaving the layer ~A) nonporous.
DescriPtion of the Preferred Embodiments The hollow fibers of the present invention have a structure in which one or each thin separating ,J~
1~853~
membrane layer ~A) is sandwiched between two highly permeable, porous layers (B).
Specifically, the hollow fibers are compa~.ed of at least thxee layers. The outermo~t and innermost layers consist of porous layers (B) serving as reinforcements, while the intermediate layer co~sists of a very thin membrane layer (A) performing a separat-ing function. Basically, a separating membrane layer (A) of single-layer construction will ~u~fice. However, the separating mambrane layer (A) may optionally be composed of two or more ~ub~ayar~ according to the intended purpose. By using such a separating mem~rane layer (A) of multilayar construction, the possibility of p~or performance due ~o pinholes and similar defec~s can be minimized. Although nothing can be ~etter than the absence of pinholes and simila defects, there is an unavoidable tendency ~or such defects to increase a the separating membrane i~ made thinner so as to enhance ~he separating performance to the utmost. Consequently, such hollow fibers must be produced on the basis of a trade-off among membrane thickness, performance and defect lavel. From the standpoint of a manufacturer, it is a great advantage that little care i9 required to preven~ the develop-ment of defects.
Generally, the layer performing a separating ~85356 function is the most important of all layers constitutinga separating membrane. If this layer is situated on the outermost side of the membrane, there is a risk of causing damage to its surface during handling or the likeO In contrast, the hollow fibers of the present invention are desirably free from such a risk because the separating membrane layer ~A) performing a separat-ing function constitutes an intermediate layer of a structure consisting three or more layers.
~n the practice of the present invention, a variety of polymers may be used as the~polymer (A') for forming the nonporous separating membrane layer (A).
Examples of such polymers include silicones, poly-urethanes, cellulosics, polyolefins, polysulfones, polyvinyl alcohol, polyestersj polyethers, polyamides and polyimides.
1~ may be practically impossible to form some of these polymers into a film. Howe~er, the present invention only requires that a separating membrane formed of the aforesaid polymer (A') is pre~ent in the finished hollow fibers. Accordingly, there may be used any polymer that can have the form of a viscous fluid at the time of spinning.
~hus, the polymer (A') need not be a straight-chain polymer having solubility or fusibility.
More specifically, if it is d.ifficult to melt ~2~35~
a polymer in itself, it may be used in the form of asolution or in the state of a prepolymer.
Alternatively, its fluidity may be controlled by the addition of a suitable plasticizer. The plasticizer can be any of various compounds that are c~mmonly used as plasticizers. Howe~er, it is preferable to use a plasticizer selected from phthalic acid esters, fatty acid esters, glycerol, polyethylene glycol and the like.
As the polymer (B') for forming the porous layers (B), there may be used any material that can form hollow fibers. However, judging from the ease of manufacture and the paucity of soluble matter, it is preferable to use a crystalline material which can be formed to the hollow fi~er by melt spinning and can h~ made porous by ~tretching it at low or ordinary temperatures to create microcrazes between crystals. It should be noted that when a crystalline polymer is stretched, the interfaces of crystalline phases separate and slip-like micropores are formed between the polymer substrates stretched in fibril formO Such micropores are referred to as microcrazes. Among the materials useful for this purpose are crystalline thermoplastic polymers.
Specific examples thereof include polyolefins, as typified by polyethylene and polypropylene, polycarbonates, polyesters and the l~ke.
Where the porous layers (B~ are formed by stretching, it is to be understood that, under the stretching conditions for forming the porous layers (B) which perform a reinforcing function, the separating membrane layer (A) performing a separating function must be suitably stretched so as to remain nonporous.
, .
~2~35~
To this end, a noncrystalline polymer may be used as the polymer (A') for forming the separating membrane layer (A). Alternatively, where a crystalline polymer is used as the polymer (A'), it should have a lower melting point or a greater melt :index than the polymer (B') for forming the porous layers (B) performing a reinorcing function It is a matter of course ~hat, as described above/ a solvent or a plasticizer may be added ~o the polymer IA') so as ~o enhance its fluidity.
rrhe hollow ibers o the present invention preferably ha~e an internal diameter of 0.1 to 5 mm and a wall thickness of 10 to 1000 ~m. From the viewpoint of separating efficiency, the thickness of the separat-ing mer~rane should preferably be not greater than S ~m and more preferably not greater than 2 ~m.
The hollow fibers of the present invention have a multilayer composite structure in which one or each nonporous separating membrane~layer performing a separating function is sandwiched between two porous layers performing a reinforcing function. Thus, no bond is needed between the layers and the materials of the layers may be chosen without consideration for their bonding properties. This is beyond imagination in the case of flat membranes and constitutes one of the distinctive features of hollow fibersO
Now, the present method of making a multilayer 35~
composite hollow fiber will be more specifically described hereinbelow in accordance with an embodiment in which the porous layers performing a reinforcing function are formed by mel~ spinning and subsequent stretching.
As described above, a crystalline thermoplastic polymer is used as the polymer (B') for forming the porous layerq performing a reinforcing function, whereas a noncrystalline polymer or a polymer ~a~ing a lower melting point or a greater melt index than the polymer (B') is used as the polymer (A') for forming the separat-ing membrane layer perfonming a separating function.
Using a spinning nozzle of ~he multiple tubular con~truc-tion, a composite hollow fi~0r is spun in such a way that the polymer (B') forms the outerm~st and innermost layers and the polymer (A') is sandwiched therebetween.
The spinning nozzle may have three or five concentrially arranged orifices.
For this purpose, it is preferable to employ an extrusion temperature ranging from the melting point of the polymer (B') to a temperature about 80C higher than the melting point, and it is also preferable to employ a spinning draw ratio of not less than 30. If the extrusion temperature is higher than the melting poi~t by more than about 80C, it is difficult to achieve stable spinning. If the spinning draw ratio is less ~3535~
than 30, the melt-spun polymer (B') has a low degree of orientation and cannot be satisfactorily drawn in a subsequent stretching step. ~s a result, it is difficult *o form micropores in the layers (B).
The hollow fiber so formed i~ preferably annealed at a temperature ranging from the glass transi-tion point to the melting point of the polymer (B ' ) .
Thereafter, the hollow fiber is stretched with a stretch of 5 ko 150% at a temperature ranging from 0C to a temperature SC lower than the melting point of the polymer ~B') 90 as to create microcrazes in the layers (B1 consi~ting of the polymer (B'). Then, the hollow fiber i stretched in one or more stages at a tempera-ture higher than the aforesaid st~etching temperature and lower than the melting poi~t of the polymer (B').
This serves ~o expand the pores formed by the microcrazes and stabilize the shape of the pores. Furthermore, in order to obtain improved thermal stability, the hollow fiber may be heat-treated under constant-length or relaxed conditions at a temperature ranging from the melting point of the polymer tB') to a temperature 5C lower than its melting point.
Where the polymer (A') forming the layer (A) is a noncrystalline polymer or a polymer containing a solvent or a plasticizer, the above-described stretching process does not make the layer (A) porous, but allows ~ 28~356 it to be amenably stretched with a gradual reduction in thickness. If the polymer (A') forming the layer ~A) has a lower melting point than the polymer ~B'), the extrusion temperature should be within the aforesaid extrusion temperature range but above a temperature 60C higher than the melting point of the pol~mer (A'~, or the first-stage stretchi~g temperature should be within the afoxesaid stretching temperature range but above a temperature 70C lower than the melting point of the polymer (A'). If the polymer (A') forming the layer (A) is of the same type as the polymer (B') but has a melt index different from that of ~he polymer (B'), it is preferable to reduce its melt viscosity and thereby decrease the stress applied to the polymer melt for the purpose of suppressing the orientation and crystallization of the polymer (A'). More specifically, the layers (B~ alone can be made porous by employing an extrusion temperature above a temperature 30C
higher than the melting point of ~he polymer ~A').
In the prior art, it has ~een difficult to form a thin membrane having a uniform thickness of not greater than 5 ~m on a porous substrate. However, in the practice of the present invention and especially in its embodiment in which the layers (B) are made porous by stretching, the layers (B~ become porous without any reduction in thickness, and the layer (A) alone is ~53~5~
stretched at the intended stretch ratio and thereby reduced in thickness. Thus, the present invention make it possible to form a thin mem~rane having a smaller and more uni~orm thickness than has been attainable in the prior art.
The present invention is further illustrated by tha following examples.
Example l A hollow fiber was melt-spun from a combina-tion of two dif~erent materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, polyethylene ha~ing a density of 0.968 g/cm and a melt index o 5.5 was melt-extruded through the innermost and outermost oriices of the nozzle, while polyPthylene having a density of 0.920 g/cm and a melt index of 5.0 was melt-extruded through the intermediate orifice of the nozzle. This spinning was carried out at an extrusion temperature of 160C and an extrusion line speed of 5 cm/rnin., and the hollow fiber so formed was taken up at a take-up speed of 800 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 200 ~m and consisted of three concentrically arranged layers having thickness of 10, 2 and 10 ~ml respectively, from inside to outside.
~2~535~S
This unstretched hollow fiber was passed over a roller heated to 115C under constant-length conditions so as to bring the hollow *iber into contact with the roller for 100 seconds and thereby effect its annealing.
Thereafter, ~he annealed hollow ~iber was cold-stretched at a stretch of 80~ by rollers kept at 28C, hot-stretched by rollers in a box heated at 105~C until a total stretch of 400% was achieved, and t~en heat-set in a box heated at 115C while bing xelaxed by 28% of the total elongation to obtain a c~mposite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 190 ~m and consisted of three concentrically arranged layers having thicknesses of 8, 0.6 and 8 ~m, respectively, from inside to outside. Electron micro-scopic ob~ervation revealed that slit-like pores having a width of 0 r 3 to 0.5 ~m and a length of 0.8 to 1.1 ~m had been formed in the innermost and oUtermo3t layers.
On the other hand, measurement of gas permeation rate revealed that the intermediate layer was a homogeneous membrane having neither pores nor pinholes. This com-posite hollow fiber had an oxygen permeation rate of 4.5 x 10 6 cm3/cm2~sec~cmHg and a nitrogen permeation rate of 1.5 x 10 6 cm3/cm2~sec~cmHg, indicating that it was selectively permeable to oxygen and had an excel-lent permea~ion rate~
The membrane separation technique is one of these methods. On a broad survey of the progress of its improvement, the general trend of technological advancement involves the development of excellent membrane materials, the development of techniques for forming thin membranes serving to enhance separating efficiency and the development of hollow fibers capable of enhancing equipment efficiency.
~2~
Among various separating membranes are non-porous membranes useful for the separation of gases and for other purposes. In such a nonporous membrane, the permeation rate for a gas is determined by its diffusion throuyh the membrane, and the diffusion rate of the gas is greatly influenced by the thickness of the membrane.
Accordingly, it is common practice to make the nonporous membrane as thin as possible. Moreovex, since such a thin nonporous membrane has inadequate strength~ attempts have been made to ~orm a composite structur~ by combin-ing the membrane with a porous layer. As one o such techniques for the formation of a thin membrane, a method is being extensively~employed in which a thin membrane is ~ormed on a porous substrate according to the coating or vapor depsition process. However, when a coating material is applied to a porous substrate, it penetrates into the pores of the substra~e and fails to form a substantially thin mem~rane. More specifically, the membrane is sufficiently thin in the regions not corresponding to the pores of th~ porous substrate, but is undesirably thic~ in the regions corresponding to the pores. If an attempt is made to overcome this disadvantage by reducing the thickness of the membrane in ths reyions corresponding to the pores, pinholes will appear. For this re~son, it is practically impos-sible to form a thin membrane of uniform thickness 1~535~
according to this method.
In order to overcome the above-described disadvanta~e, another method has been proposed in which the pores of a porous substrate are filled with a soluble material in advance, a thin membrane layer is formed on the surface of the substrate, and the soluble material is then laached out of the substrate. How-ever, this method can hardly yield a thin membrane layer of uniform thic~ness. Moreover, th1s method is disadvantageous in that the thin membrane layer is liable to be damaged during the leaching process and in that ~he thin membrane layer tends to peel away from the finished composite membrane. Furthermore, it is difficult to apply this method to ths manufaature of hollow fibers.
Still another;me~hod for forming a thin separating membrane is the formation of an asymmetric membrane from a polymer solutlon. For example, reverse osmosis membranes formed of aromatic polyamide and ultrafiltration membranes formed of polyacrylonitrile are being commercially produced by this method.
However, all of these membranes are formed according to such a technique that, in forming a membrane from a polymer solution, the superficial part of the me~brane is solidified densely and the internal part thereof is made porous by~selection of proper solidifying 353S~
conditions or by use of the leaching process. Thus~
these separating mem~ranes consist of a single material.
Accordingly, ~he structure of the membrane~
formed by this method changes continuously from the superficial dense part toward the internal porous part and includes an intermediate structural part performing no important function. This is not so de irable from the viewpoint of filtering efficiency.
Moreo~er, the thin, nonporous membrane layer per~orming a separating function is exposed on one side of these composite membranes. This i9 disadvantayeous in ~hat any mechanical force exer~ed during manufacture or use tends ~o result in pinholes or ~ause damage to the nonporous membrane layer.
Summary of the Invention It is an object of an aspect of the present invention to provide a novel membrane ~tructure including a ~ry thin, nonporous separating membrane having excellent durability.
It is an object of an aspect of the present invention to provide hollow fibers including a nonporous separat-ing membrane having excellent separa~ion characteristics.
It is an object of an aspect of the present invention to provide a method of making hollow fibers i35S
including a very thin, nonporous separating membrane which method permits such hollow fibers to be stably produced on an industrial scale.
According to the present invention, there is provided a multilayer composite hollow fiber comprising at least one nonporous separating membrane layer (A~
performing a separating function and two or more porous layers (B) performing a reinforcing function, the layer (A) and the layers (B) being alternately laminated so as to gi~e a structure having inner and outer surfaces formed by the porous layers (B).
According to the present invention, there i5 also provided a method of making a multilayer composite hollow fiber as described above which comprises the steps of co-spinning a polymer (At) for forming the separating membrane layer and a polymer (B') for forming the porous layers through a spinning nozzle of multiple tubular construction so as to sandwich the polymer (A') between two layers of the polymer (B'), the spinning of said polymers taking place at a temperature between the melting point of said polymer (B'~ and about 80C above said melting point and at a spin draw ratio above about 30, and stretching the resulting hollow fiber so as to make the layers (B) porous while leaving the layer ~A) nonporous.
DescriPtion of the Preferred Embodiments The hollow fibers of the present invention have a structure in which one or each thin separating ,J~
1~853~
membrane layer ~A) is sandwiched between two highly permeable, porous layers (B).
Specifically, the hollow fibers are compa~.ed of at least thxee layers. The outermo~t and innermost layers consist of porous layers (B) serving as reinforcements, while the intermediate layer co~sists of a very thin membrane layer (A) performing a separat-ing function. Basically, a separating membrane layer (A) of single-layer construction will ~u~fice. However, the separating mambrane layer (A) may optionally be composed of two or more ~ub~ayar~ according to the intended purpose. By using such a separating mem~rane layer (A) of multilayar construction, the possibility of p~or performance due ~o pinholes and similar defec~s can be minimized. Although nothing can be ~etter than the absence of pinholes and simila defects, there is an unavoidable tendency ~or such defects to increase a the separating membrane i~ made thinner so as to enhance ~he separating performance to the utmost. Consequently, such hollow fibers must be produced on the basis of a trade-off among membrane thickness, performance and defect lavel. From the standpoint of a manufacturer, it is a great advantage that little care i9 required to preven~ the develop-ment of defects.
Generally, the layer performing a separating ~85356 function is the most important of all layers constitutinga separating membrane. If this layer is situated on the outermost side of the membrane, there is a risk of causing damage to its surface during handling or the likeO In contrast, the hollow fibers of the present invention are desirably free from such a risk because the separating membrane layer ~A) performing a separat-ing function constitutes an intermediate layer of a structure consisting three or more layers.
~n the practice of the present invention, a variety of polymers may be used as the~polymer (A') for forming the nonporous separating membrane layer (A).
Examples of such polymers include silicones, poly-urethanes, cellulosics, polyolefins, polysulfones, polyvinyl alcohol, polyestersj polyethers, polyamides and polyimides.
1~ may be practically impossible to form some of these polymers into a film. Howe~er, the present invention only requires that a separating membrane formed of the aforesaid polymer (A') is pre~ent in the finished hollow fibers. Accordingly, there may be used any polymer that can have the form of a viscous fluid at the time of spinning.
~hus, the polymer (A') need not be a straight-chain polymer having solubility or fusibility.
More specifically, if it is d.ifficult to melt ~2~35~
a polymer in itself, it may be used in the form of asolution or in the state of a prepolymer.
Alternatively, its fluidity may be controlled by the addition of a suitable plasticizer. The plasticizer can be any of various compounds that are c~mmonly used as plasticizers. Howe~er, it is preferable to use a plasticizer selected from phthalic acid esters, fatty acid esters, glycerol, polyethylene glycol and the like.
As the polymer (B') for forming the porous layers (B), there may be used any material that can form hollow fibers. However, judging from the ease of manufacture and the paucity of soluble matter, it is preferable to use a crystalline material which can be formed to the hollow fi~er by melt spinning and can h~ made porous by ~tretching it at low or ordinary temperatures to create microcrazes between crystals. It should be noted that when a crystalline polymer is stretched, the interfaces of crystalline phases separate and slip-like micropores are formed between the polymer substrates stretched in fibril formO Such micropores are referred to as microcrazes. Among the materials useful for this purpose are crystalline thermoplastic polymers.
Specific examples thereof include polyolefins, as typified by polyethylene and polypropylene, polycarbonates, polyesters and the l~ke.
Where the porous layers (B~ are formed by stretching, it is to be understood that, under the stretching conditions for forming the porous layers (B) which perform a reinforcing function, the separating membrane layer (A) performing a separating function must be suitably stretched so as to remain nonporous.
, .
~2~35~
To this end, a noncrystalline polymer may be used as the polymer (A') for forming the separating membrane layer (A). Alternatively, where a crystalline polymer is used as the polymer (A'), it should have a lower melting point or a greater melt :index than the polymer (B') for forming the porous layers (B) performing a reinorcing function It is a matter of course ~hat, as described above/ a solvent or a plasticizer may be added ~o the polymer IA') so as ~o enhance its fluidity.
rrhe hollow ibers o the present invention preferably ha~e an internal diameter of 0.1 to 5 mm and a wall thickness of 10 to 1000 ~m. From the viewpoint of separating efficiency, the thickness of the separat-ing mer~rane should preferably be not greater than S ~m and more preferably not greater than 2 ~m.
The hollow fibers of the present invention have a multilayer composite structure in which one or each nonporous separating membrane~layer performing a separating function is sandwiched between two porous layers performing a reinforcing function. Thus, no bond is needed between the layers and the materials of the layers may be chosen without consideration for their bonding properties. This is beyond imagination in the case of flat membranes and constitutes one of the distinctive features of hollow fibersO
Now, the present method of making a multilayer 35~
composite hollow fiber will be more specifically described hereinbelow in accordance with an embodiment in which the porous layers performing a reinforcing function are formed by mel~ spinning and subsequent stretching.
As described above, a crystalline thermoplastic polymer is used as the polymer (B') for forming the porous layerq performing a reinforcing function, whereas a noncrystalline polymer or a polymer ~a~ing a lower melting point or a greater melt index than the polymer (B') is used as the polymer (A') for forming the separat-ing membrane layer perfonming a separating function.
Using a spinning nozzle of ~he multiple tubular con~truc-tion, a composite hollow fi~0r is spun in such a way that the polymer (B') forms the outerm~st and innermost layers and the polymer (A') is sandwiched therebetween.
The spinning nozzle may have three or five concentrially arranged orifices.
For this purpose, it is preferable to employ an extrusion temperature ranging from the melting point of the polymer (B') to a temperature about 80C higher than the melting point, and it is also preferable to employ a spinning draw ratio of not less than 30. If the extrusion temperature is higher than the melting poi~t by more than about 80C, it is difficult to achieve stable spinning. If the spinning draw ratio is less ~3535~
than 30, the melt-spun polymer (B') has a low degree of orientation and cannot be satisfactorily drawn in a subsequent stretching step. ~s a result, it is difficult *o form micropores in the layers (B).
The hollow fiber so formed i~ preferably annealed at a temperature ranging from the glass transi-tion point to the melting point of the polymer (B ' ) .
Thereafter, the hollow fiber is stretched with a stretch of 5 ko 150% at a temperature ranging from 0C to a temperature SC lower than the melting point of the polymer ~B') 90 as to create microcrazes in the layers (B1 consi~ting of the polymer (B'). Then, the hollow fiber i stretched in one or more stages at a tempera-ture higher than the aforesaid st~etching temperature and lower than the melting poi~t of the polymer (B').
This serves ~o expand the pores formed by the microcrazes and stabilize the shape of the pores. Furthermore, in order to obtain improved thermal stability, the hollow fiber may be heat-treated under constant-length or relaxed conditions at a temperature ranging from the melting point of the polymer tB') to a temperature 5C lower than its melting point.
Where the polymer (A') forming the layer (A) is a noncrystalline polymer or a polymer containing a solvent or a plasticizer, the above-described stretching process does not make the layer (A) porous, but allows ~ 28~356 it to be amenably stretched with a gradual reduction in thickness. If the polymer (A') forming the layer ~A) has a lower melting point than the polymer ~B'), the extrusion temperature should be within the aforesaid extrusion temperature range but above a temperature 60C higher than the melting point of the pol~mer (A'~, or the first-stage stretchi~g temperature should be within the afoxesaid stretching temperature range but above a temperature 70C lower than the melting point of the polymer (A'). If the polymer (A') forming the layer (A) is of the same type as the polymer (B') but has a melt index different from that of ~he polymer (B'), it is preferable to reduce its melt viscosity and thereby decrease the stress applied to the polymer melt for the purpose of suppressing the orientation and crystallization of the polymer (A'). More specifically, the layers (B~ alone can be made porous by employing an extrusion temperature above a temperature 30C
higher than the melting point of ~he polymer ~A').
In the prior art, it has ~een difficult to form a thin membrane having a uniform thickness of not greater than 5 ~m on a porous substrate. However, in the practice of the present invention and especially in its embodiment in which the layers (B) are made porous by stretching, the layers (B~ become porous without any reduction in thickness, and the layer (A) alone is ~53~5~
stretched at the intended stretch ratio and thereby reduced in thickness. Thus, the present invention make it possible to form a thin mem~rane having a smaller and more uni~orm thickness than has been attainable in the prior art.
The present invention is further illustrated by tha following examples.
Example l A hollow fiber was melt-spun from a combina-tion of two dif~erent materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, polyethylene ha~ing a density of 0.968 g/cm and a melt index o 5.5 was melt-extruded through the innermost and outermost oriices of the nozzle, while polyPthylene having a density of 0.920 g/cm and a melt index of 5.0 was melt-extruded through the intermediate orifice of the nozzle. This spinning was carried out at an extrusion temperature of 160C and an extrusion line speed of 5 cm/rnin., and the hollow fiber so formed was taken up at a take-up speed of 800 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 200 ~m and consisted of three concentrically arranged layers having thickness of 10, 2 and 10 ~ml respectively, from inside to outside.
~2~535~S
This unstretched hollow fiber was passed over a roller heated to 115C under constant-length conditions so as to bring the hollow *iber into contact with the roller for 100 seconds and thereby effect its annealing.
Thereafter, ~he annealed hollow ~iber was cold-stretched at a stretch of 80~ by rollers kept at 28C, hot-stretched by rollers in a box heated at 105~C until a total stretch of 400% was achieved, and t~en heat-set in a box heated at 115C while bing xelaxed by 28% of the total elongation to obtain a c~mposite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 190 ~m and consisted of three concentrically arranged layers having thicknesses of 8, 0.6 and 8 ~m, respectively, from inside to outside. Electron micro-scopic ob~ervation revealed that slit-like pores having a width of 0 r 3 to 0.5 ~m and a length of 0.8 to 1.1 ~m had been formed in the innermost and oUtermo3t layers.
On the other hand, measurement of gas permeation rate revealed that the intermediate layer was a homogeneous membrane having neither pores nor pinholes. This com-posite hollow fiber had an oxygen permeation rate of 4.5 x 10 6 cm3/cm2~sec~cmHg and a nitrogen permeation rate of 1.5 x 10 6 cm3/cm2~sec~cmHg, indicating that it was selectively permeable to oxygen and had an excel-lent permea~ion rate~
3~;
Example 2 A hollow fiber was melt-spun from a combination of two different materials by using a spinning nozzle having three concentrically arranged annular orifices.
Specifically, polypropylene having a density of 0.913 g/cm3 and a melt index of 15 was melt-extruded through the innermost and outermost orifices of the nozzle, while poly-4-methylpentene-l having a density of 0.835 g/cm3 and a melt index vf 26 was melt-extruded through the intermediate oriice of the nozzle. This spinning was carried out at an extrusion temperature of 250C and an extrusion line speed of 5 cm/min., and the hollow fiber so formed was taken up at a ~ake-up speed of 400 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 280 ~m and consisted of three concentrically arranged layers having thicknesses of 14, 1.5 and 17 ~m, xespecti~ely, from inside to outside.
This u~stretched hollow fiber was passed o~er a roller heated to 140C under constant-length conditions so as to bring the hollow fiber into contact with the xoller for lO0 seconds and thereby effect its annealing.
Thereafter, the annealed hollow fiber was cold-stretched at a stretch of 20% by rollers kept at 60C, hot-stretched by rollers in a box heated at 135C until a 28~;3~;6 total stretch of 200~ was achieved, and then heat set in a box heated at 140C while ~eing relaxed by 28% of the total elongation to obtain a compositP
hollow fiber.
The hollow fiber thus obtained had an internal diameter of 265 ~m and consisted of three concentrically arranged layers having thicknesses of 12, 0.7 and 14 ~m, respectively, from inside to outside. Electron microscopic observa~ion revealed that slit-like pores having a wid~h of 0.07 to 0O09 ~m and a length of 0.2 to O . 5 ~m had ~ee~ formed in the innermost and outermost layers. On the other hand, measurement of ga3 perme-ation rate revealad that the in ermediate layer consisting of poly-4-methylpentene-1 was a homogeneous -membrane having neither pores nor pinholes. This composite hollow ~iber had an oxygen permeation rate of 4.7 x 10 6 cm3/cm2~sec-cmHg and a nitrogen permeation rate of 1.5 x 10 6 cm3/cm2~sec.cmHg, indicating that it was selectively permeable to oxygen and had an excellent permeation rate.
Example 3 A hollow fiber was melt-spun from a combination of two different materials by using a spinning n~zzle having three concentrically arranged annular orifices.
Specifically, the same polypropylene as used in Example ~;~853~6 2 was melt-extruded through the innermost and outermost orifices of the nozzle, while ethyl cellulose having a degree of ethoxylation of 49~ was melt-extruded through the intermediate orifice of the nozzleO This spinning was carried out at an extrusion temperature of 205C
and an extrusion line speed of 4 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 2~0 ~m and consisted of three concentrically arranged layers having thicknesses of 16, 1.9 and 18 ~m, respectively, from inside to outside.
This ~nstretched hollow fiber wa~ passed over a roller heated to 130C under constant-length condi-tions so as to bring the hollow fiber into contact with the roller for 180 seconds and ~hereby effect its annealing. Thereafter, the annealed hollow fiber was cold-stretched at a stretch of 17~ by rollers kept at 6~C, hot-stretched by rollers i~ a box heated at 130C until a total stretch of 180~ was achie~ed, and then heat-set in a box heated at 130C while being relaxed by 25~ of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 273 ~m and consisted of three concentrically 35;~i arranged layers having thicknesses of 14, 0.9 and 16 ~m, respectively, from inside to outside. Electron microscopic observation revealed that slit-like pores having a width of 0.07 to 0.09 ~m and a length of 0.1 to 0.4 ~m had been formed in the innermost and outer-most layers. On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of ethyl cellulose was a homogeneous membrane having neither pores nor pinholes. This composite hollow fiber had an oxygen permeation rate of 2.3 x 10 5 cm3/cm2~sec~cmHg and a nitrogen permeation rate o O.7 x 10 5 cm3/cm2sec c~Xg, indicating hat it was selectively permeable to oxygen and had a very high permeation rateu Example 4 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, polyethylene having a density of 0.965 g/cm3 and a melt index of 5.2 was melt-extruded through the innermost and outermost orifices of the nozzle, while an ultraviolet-curable silicone resin (commercially available from Toshiba Silicone Co., Ltd., under the trade name of TUV6020) was melt-extruded through the intermediate orifice of the nozzle. This 353~i6 spinning was carried out at an extrusion temperature of 160C and an extrusion line speed of 10 cm/min., and the hollow fiber so formed was taken up at a taXe-up speed of 350 m/min The uns~retched hollow fiber thus obtained had an internal diameter of 290 ~m and consisted of three concentrically arranged layers having thicknesses of 27, 2.5 and 32 ~m, respectively, from inside to outside.
lQ This unstretched hollow fiber was passed over a roller heated to 110C under constant-length conditions so as to bring the hollow fiber into contact with the roller for 100 seconds and thereby effect its annealing. Thereafter, while being irradiated with an 80 W/cm high pressure mercury vapor lamp from a distance of about 10 cm, the annealed hollow flber was cold-stretched at a stretch~ratio of 50% by rollers kept a~ 30C, hot-stretched by rollers in a box heated at 100C until a total stretch ratio of 300~ was achieved, and then heat-set in a box heated at 115C
while being relaxed by 10% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diametex of 270 ~m and consisted of three concentrically arranged layers having thicknesses of 22, 0.8 and 25 ~m, respectively, from inside to outside. Electron ~2~;3~
microscopic observation revealed that the innermost and outermost layers had been made porous and that slit-like pores having a width of 0.1 to 0.3 ~m and a length of 0.5 to 0.9 ~m had been formed therein. On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of silicone rubber was a homogerleous membrane having neither pores nor pinholes.
This composite hollow fiber had an oxygen permeation rate of 6.2 x 10 4 cm3/cm2 sec~cmHg and a nitrogen permeation rate of 3.1 x 10 4 cm3~cm2-sec~cmHg, indicating its excellent selective permeability to oxygen.
Exmaple 5 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, the same polyethylene as used in Example 1 was melt-extruded through the innermost and outermost orifices of the nozzle, while a mixture of acetylcellulose having a degree of acetylation of 40% and polyethylene glycol used as a plasticizer (in an amount of 50% by weight based on the acetyl-cellulose) was melt-extruded through the intermediate orifice of the nozæle. This spinning was carried out at an extrusion temperature of 170C and an extrusion line speed of 7~5 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 285 ~m and consisted of three concentrically arranged layers having thicknesses of 25, 0.7 and 25 ~m, respectively, from inside to outside.
This unstretched hollow fiber was passed over a roller heated to 110C under constant-length conditions so as to bring the hollow fiber into contact with the roller or 180 seconds and thereby effect its aImealing. Thereafter, the annealed hollow fiber wa~
cold-stretched at a stretch ratio of 60~ by rollers lS kept at 30C, hot-stretched by rollers in a box heated at 110C until a total stretch ratio of 3Q0% was achieved, and then heat-set in a box heated at 110C
while being relaxed by 25% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 260 ym and consisted of three concentrically arranged layers having thicknesses of 18, 0.2 and l9 ~m, respectively, from inside to outside. Electron micro-scopic observation revealed that slit-like pores having 25 a width of 0.1 to 0.2 ~m and a length of 0.4 to 0.8 ym had been formed in the innermost and outermost layers.
~3S~56 On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of acetylcellulose was a homogeneous membrane having neither pores nor pinholes. This composite hollow fiber had an oxygen permeation rate of 1.2 x 10 5 cm3/cm2-sec-cN~g and a nitrogen permeation rate of 0.4 x 10 5 cm3/cm2~sec-cmHg, indicating that it was selectively permeable to oxygen and had a very high permeation rate.
Example 6 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular oriices. Specifically, the same polypropylene as used in Example 2 was melt-extruded through the innermost and outermost orifices of the nozzle, while a mixture of polyvinyl alcohol having a degree of saponification of 99 mole % and a degree of polymer-ization of 1700 and glycerol used as a plasticizer (inan amount of 50% by weight based on the polyvinyl alcohol) was melt-extruded through the intermediate orifice of the nozzle. This spinning was carried out at an extrusion temperature of 200C and an extrusion line speed of 7 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
~8~;;35~
The unstretched hollow fiber thus obtained had an internal diameter of 320 ~m and consisted of three concentrically arranged layers having thicknesses of 25, 1.2 and 27 ~m, respectively, from inside to outside.
This unstretched hollow fiber was passed over a roller heated ~o 130C under constant-leng~h condi-tions so as to bring the hollow fiber into contact with the roller for 180 seconds and thereby effect its annealing. Thereafter, the annealed hollow fiber was cold-stretched at a stretch ratio o 17~ by roller5 kept at 60C, hot-stretched by rollers in a box heated at 130C until a total stretch ratio of 150% was achieved, and then heat-set in a box heated at 130C
while being relaxed by 25% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 300 ~m and conslsted of three concentrically arranged layers having thicknesses of 21, 0.5`and 23 ~m, respectively, from inside to outside. Electron micro-scopic observation revealed that slit-like pores having a width o~ 0.07 to 0.09 ~m and a length of 0.1 to 0.3 ~m had been formed in the innermost and outermost layers.
On the other hand, measurement of gas permeation rate 2~ revealed that the intermediate layer consisting of poly-vinyl alcohol was a homogeneous membrane having neither ~85i3~6 pores nor pinholes.
Using composite hollow fibers made in the above-described manner, an aqueous ethanol solution having an ethanol concentration of 90% by weight was separated according to the pervaporation technique.
Thus, it was found that the flux was as high as 29 kg/m2-hr and the separation factor (aH20/C2H50H) was 80, indicating that these hollow fibers were selectively permeable to water. These hollow fibers made it pos-sibl0 to concentrate the aqueous ethanol solution to aconcentration higher than 99% by weight.
Example 2 A hollow fiber was melt-spun from a combination of two different materials by using a spinning nozzle having three concentrically arranged annular orifices.
Specifically, polypropylene having a density of 0.913 g/cm3 and a melt index of 15 was melt-extruded through the innermost and outermost orifices of the nozzle, while poly-4-methylpentene-l having a density of 0.835 g/cm3 and a melt index vf 26 was melt-extruded through the intermediate oriice of the nozzle. This spinning was carried out at an extrusion temperature of 250C and an extrusion line speed of 5 cm/min., and the hollow fiber so formed was taken up at a ~ake-up speed of 400 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 280 ~m and consisted of three concentrically arranged layers having thicknesses of 14, 1.5 and 17 ~m, xespecti~ely, from inside to outside.
This u~stretched hollow fiber was passed o~er a roller heated to 140C under constant-length conditions so as to bring the hollow fiber into contact with the xoller for lO0 seconds and thereby effect its annealing.
Thereafter, the annealed hollow fiber was cold-stretched at a stretch of 20% by rollers kept at 60C, hot-stretched by rollers in a box heated at 135C until a 28~;3~;6 total stretch of 200~ was achieved, and then heat set in a box heated at 140C while ~eing relaxed by 28% of the total elongation to obtain a compositP
hollow fiber.
The hollow fiber thus obtained had an internal diameter of 265 ~m and consisted of three concentrically arranged layers having thicknesses of 12, 0.7 and 14 ~m, respectively, from inside to outside. Electron microscopic observa~ion revealed that slit-like pores having a wid~h of 0.07 to 0O09 ~m and a length of 0.2 to O . 5 ~m had ~ee~ formed in the innermost and outermost layers. On the other hand, measurement of ga3 perme-ation rate revealad that the in ermediate layer consisting of poly-4-methylpentene-1 was a homogeneous -membrane having neither pores nor pinholes. This composite hollow ~iber had an oxygen permeation rate of 4.7 x 10 6 cm3/cm2~sec-cmHg and a nitrogen permeation rate of 1.5 x 10 6 cm3/cm2~sec.cmHg, indicating that it was selectively permeable to oxygen and had an excellent permeation rate.
Example 3 A hollow fiber was melt-spun from a combination of two different materials by using a spinning n~zzle having three concentrically arranged annular orifices.
Specifically, the same polypropylene as used in Example ~;~853~6 2 was melt-extruded through the innermost and outermost orifices of the nozzle, while ethyl cellulose having a degree of ethoxylation of 49~ was melt-extruded through the intermediate orifice of the nozzleO This spinning was carried out at an extrusion temperature of 205C
and an extrusion line speed of 4 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 2~0 ~m and consisted of three concentrically arranged layers having thicknesses of 16, 1.9 and 18 ~m, respectively, from inside to outside.
This ~nstretched hollow fiber wa~ passed over a roller heated to 130C under constant-length condi-tions so as to bring the hollow fiber into contact with the roller for 180 seconds and ~hereby effect its annealing. Thereafter, the annealed hollow fiber was cold-stretched at a stretch of 17~ by rollers kept at 6~C, hot-stretched by rollers i~ a box heated at 130C until a total stretch of 180~ was achie~ed, and then heat-set in a box heated at 130C while being relaxed by 25~ of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 273 ~m and consisted of three concentrically 35;~i arranged layers having thicknesses of 14, 0.9 and 16 ~m, respectively, from inside to outside. Electron microscopic observation revealed that slit-like pores having a width of 0.07 to 0.09 ~m and a length of 0.1 to 0.4 ~m had been formed in the innermost and outer-most layers. On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of ethyl cellulose was a homogeneous membrane having neither pores nor pinholes. This composite hollow fiber had an oxygen permeation rate of 2.3 x 10 5 cm3/cm2~sec~cmHg and a nitrogen permeation rate o O.7 x 10 5 cm3/cm2sec c~Xg, indicating hat it was selectively permeable to oxygen and had a very high permeation rateu Example 4 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, polyethylene having a density of 0.965 g/cm3 and a melt index of 5.2 was melt-extruded through the innermost and outermost orifices of the nozzle, while an ultraviolet-curable silicone resin (commercially available from Toshiba Silicone Co., Ltd., under the trade name of TUV6020) was melt-extruded through the intermediate orifice of the nozzle. This 353~i6 spinning was carried out at an extrusion temperature of 160C and an extrusion line speed of 10 cm/min., and the hollow fiber so formed was taken up at a taXe-up speed of 350 m/min The uns~retched hollow fiber thus obtained had an internal diameter of 290 ~m and consisted of three concentrically arranged layers having thicknesses of 27, 2.5 and 32 ~m, respectively, from inside to outside.
lQ This unstretched hollow fiber was passed over a roller heated to 110C under constant-length conditions so as to bring the hollow fiber into contact with the roller for 100 seconds and thereby effect its annealing. Thereafter, while being irradiated with an 80 W/cm high pressure mercury vapor lamp from a distance of about 10 cm, the annealed hollow flber was cold-stretched at a stretch~ratio of 50% by rollers kept a~ 30C, hot-stretched by rollers in a box heated at 100C until a total stretch ratio of 300~ was achieved, and then heat-set in a box heated at 115C
while being relaxed by 10% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diametex of 270 ~m and consisted of three concentrically arranged layers having thicknesses of 22, 0.8 and 25 ~m, respectively, from inside to outside. Electron ~2~;3~
microscopic observation revealed that the innermost and outermost layers had been made porous and that slit-like pores having a width of 0.1 to 0.3 ~m and a length of 0.5 to 0.9 ~m had been formed therein. On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of silicone rubber was a homogerleous membrane having neither pores nor pinholes.
This composite hollow fiber had an oxygen permeation rate of 6.2 x 10 4 cm3/cm2 sec~cmHg and a nitrogen permeation rate of 3.1 x 10 4 cm3~cm2-sec~cmHg, indicating its excellent selective permeability to oxygen.
Exmaple 5 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular orifices. Specifically, the same polyethylene as used in Example 1 was melt-extruded through the innermost and outermost orifices of the nozzle, while a mixture of acetylcellulose having a degree of acetylation of 40% and polyethylene glycol used as a plasticizer (in an amount of 50% by weight based on the acetyl-cellulose) was melt-extruded through the intermediate orifice of the nozæle. This spinning was carried out at an extrusion temperature of 170C and an extrusion line speed of 7~5 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
The unstretched hollow fiber thus obtained had an internal diameter of 285 ~m and consisted of three concentrically arranged layers having thicknesses of 25, 0.7 and 25 ~m, respectively, from inside to outside.
This unstretched hollow fiber was passed over a roller heated to 110C under constant-length conditions so as to bring the hollow fiber into contact with the roller or 180 seconds and thereby effect its aImealing. Thereafter, the annealed hollow fiber wa~
cold-stretched at a stretch ratio of 60~ by rollers lS kept at 30C, hot-stretched by rollers in a box heated at 110C until a total stretch ratio of 3Q0% was achieved, and then heat-set in a box heated at 110C
while being relaxed by 25% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 260 ym and consisted of three concentrically arranged layers having thicknesses of 18, 0.2 and l9 ~m, respectively, from inside to outside. Electron micro-scopic observation revealed that slit-like pores having 25 a width of 0.1 to 0.2 ~m and a length of 0.4 to 0.8 ym had been formed in the innermost and outermost layers.
~3S~56 On the other hand, measurement of gas permeation rate revealed that the intermediate layer consisting of acetylcellulose was a homogeneous membrane having neither pores nor pinholes. This composite hollow fiber had an oxygen permeation rate of 1.2 x 10 5 cm3/cm2-sec-cN~g and a nitrogen permeation rate of 0.4 x 10 5 cm3/cm2~sec-cmHg, indicating that it was selectively permeable to oxygen and had a very high permeation rate.
Example 6 A hollow fiber was melt-spun from a combina-tion of two different materials by using a spinning nozzle having three concentrically arranged annular oriices. Specifically, the same polypropylene as used in Example 2 was melt-extruded through the innermost and outermost orifices of the nozzle, while a mixture of polyvinyl alcohol having a degree of saponification of 99 mole % and a degree of polymer-ization of 1700 and glycerol used as a plasticizer (inan amount of 50% by weight based on the polyvinyl alcohol) was melt-extruded through the intermediate orifice of the nozzle. This spinning was carried out at an extrusion temperature of 200C and an extrusion line speed of 7 cm/min., and the hollow fiber so formed was taken up at a take-up speed of 300 m/min.
~8~;;35~
The unstretched hollow fiber thus obtained had an internal diameter of 320 ~m and consisted of three concentrically arranged layers having thicknesses of 25, 1.2 and 27 ~m, respectively, from inside to outside.
This unstretched hollow fiber was passed over a roller heated ~o 130C under constant-leng~h condi-tions so as to bring the hollow fiber into contact with the roller for 180 seconds and thereby effect its annealing. Thereafter, the annealed hollow fiber was cold-stretched at a stretch ratio o 17~ by roller5 kept at 60C, hot-stretched by rollers in a box heated at 130C until a total stretch ratio of 150% was achieved, and then heat-set in a box heated at 130C
while being relaxed by 25% of the total elongation to obtain a composite hollow fiber.
The hollow fiber thus obtained had an internal diameter of 300 ~m and conslsted of three concentrically arranged layers having thicknesses of 21, 0.5`and 23 ~m, respectively, from inside to outside. Electron micro-scopic observation revealed that slit-like pores having a width o~ 0.07 to 0.09 ~m and a length of 0.1 to 0.3 ~m had been formed in the innermost and outermost layers.
On the other hand, measurement of gas permeation rate 2~ revealed that the intermediate layer consisting of poly-vinyl alcohol was a homogeneous membrane having neither ~85i3~6 pores nor pinholes.
Using composite hollow fibers made in the above-described manner, an aqueous ethanol solution having an ethanol concentration of 90% by weight was separated according to the pervaporation technique.
Thus, it was found that the flux was as high as 29 kg/m2-hr and the separation factor (aH20/C2H50H) was 80, indicating that these hollow fibers were selectively permeable to water. These hollow fibers made it pos-sibl0 to concentrate the aqueous ethanol solution to aconcentration higher than 99% by weight.
Claims (5)
1. A multilayer composite hollow fiber comprising at least one nonporous separating membrane layer (A) performing a separating function and two or more porous layers (B) performing a reinforcing function, said layer (A) and said layers (B) being alternately laminated so as to give a structure having inner and outer surfaces formed by said porous layers (B).
2. A multilayer composite hollow fiber as claimed in claim 1 wherein said hollow fiber has an internal diameter of 0.1 to 5.0 mm and a wall thickness of 10 to 1000 µm and said separating membrane layer (A) has a thickness of not greater than 5 µm.
3. A multilayer composite hollow fiber as claimed in claim 1 where said porous layers (B) consist of a crystalline thermoplastic polymer.
4. A multilayer composite hollow fiber as claimed in claim 2 wherein said separating membrane layer (A) has a thickness of not greater than 2 µm.
5. A method of making a multilayer composite hollow fiber comprising (A) at least one nonporous separating membrane layer performing a separating function and (B) two or more porous layers performing a reinforcing function, said layer (A) and said layer (B) being alternately laminated so as to give a structure having inner and outer surfaces formed by said porous layers (B), said method comprising the steps of co-spinning a polymer (A') for forming said separating membrane layer and a polymer (B') for forming said porous layers through a spinning nozzle of multiple tubular construction so as to sandwich said polymer (A') between two layers of said polymer (B'), the spinning of said polymers taking place at a temperature between the melting point of said polymer (B') and about 80°C above said melting point and at a spin draw ratio above about 30, and stretching the resulting hollow fiber so as to make said layers (B) porous while leaving said layer (A) nonporous.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP141385/1985 | 1985-06-27 | ||
| JP60141385A JPS621404A (en) | 1985-06-27 | 1985-06-27 | Poly-composite hollow fiber membrane and its manufacturing process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1285356C true CA1285356C (en) | 1991-07-02 |
Family
ID=15290764
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000512301A Expired - Lifetime CA1285356C (en) | 1985-06-27 | 1986-06-24 | Multilayer composite hollow fibers and method of making same |
Country Status (5)
| Country | Link |
|---|---|
| US (2) | US4713292A (en) |
| EP (1) | EP0206354B1 (en) |
| JP (1) | JPS621404A (en) |
| CA (1) | CA1285356C (en) |
| DE (1) | DE3683196D1 (en) |
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| CN1318127C (en) * | 2004-02-16 | 2007-05-30 | 中国科学院大连化学物理研究所 | Composite hollow fiber membrane and its preparation and application |
| KR100966718B1 (en) * | 2005-10-13 | 2010-06-29 | 아사히 가세이 케미칼즈 가부시키가이샤 | Porous multilayered hollow-fiber membrane and process for producing the same |
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| US8187422B2 (en) * | 2006-03-21 | 2012-05-29 | Georgia-Pacific Consumer Products Lp | Disposable cellulosic wiper |
| US8187421B2 (en) * | 2006-03-21 | 2012-05-29 | Georgia-Pacific Consumer Products Lp | Absorbent sheet incorporating regenerated cellulose microfiber |
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| JP5500765B2 (en) * | 2007-05-02 | 2014-05-21 | 三菱レイヨン株式会社 | Composite hollow fiber membrane for deaeration and method for producing the same |
| WO2009125217A1 (en) * | 2008-04-08 | 2009-10-15 | Fujifilm Manufacturing Europe Bv | Process for preparing membranes |
| US8361278B2 (en) * | 2008-09-16 | 2013-01-29 | Dixie Consumer Products Llc | Food wrap base sheet with regenerated cellulose microfiber |
| US8758542B2 (en) | 2009-03-25 | 2014-06-24 | Nanyang Technological University | Filter |
| JP5745510B2 (en) | 2009-06-26 | 2015-07-08 | ビーエル・テクノロジーズ・インコーポレイテッド | Hollow fiber membrane reinforced with non-braided fabric |
| US9221020B2 (en) | 2010-09-15 | 2015-12-29 | Bl Technologies, Inc. | Method to make yarn-reinforced hollow fiber membranes around a soluble core |
| US9643129B2 (en) | 2011-12-22 | 2017-05-09 | Bl Technologies, Inc. | Non-braided, textile-reinforced hollow fiber membrane |
| US10478782B2 (en) | 2015-04-28 | 2019-11-19 | Toray Industries, Inc. | Composite hollow fiber membrane and method for producing same |
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| RU2636719C2 (en) * | 2016-12-15 | 2017-11-27 | Геннадий Леонидович Багич | Method of manufacture of membrane filter, and also method of coating with subsequent sealing of surface layer of parts and device for their implementation |
| EP3651877A4 (en) * | 2017-07-14 | 2021-01-13 | Khalifa University of Science and Technologie | Membrane gas separation under magnetic field |
| CN113226525A (en) | 2018-12-27 | 2021-08-06 | 3M创新有限公司 | Asymmetric hollow fiber membranes and methods of making and using the same |
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| DE2705734C3 (en) * | 1977-02-11 | 1982-04-22 | Akzo Gmbh, 5600 Wuppertal | Dialysis membrane for hemodialysis |
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| JPS5766114A (en) * | 1980-10-14 | 1982-04-22 | Mitsubishi Rayon Co Ltd | Porous polyethylene hollow fiber and its production |
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| US4421529A (en) * | 1982-07-02 | 1983-12-20 | The Dow Chemical Company | Membrane system for intermittent gas separation |
| JPS5962305A (en) * | 1982-09-30 | 1984-04-09 | Teijin Ltd | Composite membrane for gas separation and its production |
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| JPS59196706A (en) * | 1983-04-22 | 1984-11-08 | Dainippon Ink & Chem Inc | Heterogenous membrane and preparation thereof |
| US4666469A (en) * | 1985-05-29 | 1987-05-19 | The Dow Chemical Company | Hollow fiber membrane device with inner wrap |
-
1985
- 1985-06-27 JP JP60141385A patent/JPS621404A/en active Granted
-
1986
- 1986-06-24 CA CA000512301A patent/CA1285356C/en not_active Expired - Lifetime
- 1986-06-26 US US06/878,678 patent/US4713292A/en not_active Expired - Lifetime
- 1986-06-27 DE DE8686108786T patent/DE3683196D1/en not_active Expired - Lifetime
- 1986-06-27 EP EP86108786A patent/EP0206354B1/en not_active Expired - Lifetime
-
1987
- 1987-09-01 US US07/091,894 patent/US4802942A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE3683196D1 (en) | 1992-02-13 |
| JPS621404A (en) | 1987-01-07 |
| JPH0344811B2 (en) | 1991-07-09 |
| US4713292A (en) | 1987-12-15 |
| EP0206354B1 (en) | 1992-01-02 |
| EP0206354A2 (en) | 1986-12-30 |
| EP0206354A3 (en) | 1988-06-08 |
| US4802942A (en) | 1989-02-07 |
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