CA2073610C

CA2073610C - Papermaking process and paper thus obtained

Info

Publication number: CA2073610C
Application number: CA002073610A
Authority: CA
Inventors: Lucien Bourson
Original assignee: Elf Atochem SA
Current assignee: Arkema France SA
Priority date: 1991-07-12
Filing date: 1992-07-10
Publication date: 1996-09-17
Anticipated expiration: 2012-07-10
Also published as: GR3021763T3; DE69213850D1; ATE143075T1; CA2073610A1; NO922672L; DK0522940T3; FI923194A; US5501771A; IE922269A1; NO922672D0; ES2092074T3; EP0522940B1; JPH05195486A; DE69213850T2; FR2678961A1; FI923194A0; NO179255B; EP0522940A1; FR2678961B1

Abstract

A method for manufacturing paper is disclosed which includes adding to the fibrous composition entering the head box:
a) a mineral filler, b) a sizing agent, and c) a retention system comprised of :
c) 1) cationic starch, c) 2) polyaluminum chloride, and c) 3) silica of anionic nature.
The percentages by weight of products c)1), c)2), and c)3), based on the weight of composition entering the head box, are as follows: 0.2 to 1.7%, 0.01 to 0.3% expressed as percentage of Al203, and 0.01 to 0.3% expresses as percentage of SiO2, the cationic starch having a molecular weight of 3.104 to 12.104 and a degree of substitution of 0.01 to 0.1.

Description

NOVEII PAPERMAKING PROCESS AND PAPER THUS OBTAINED
BACKGROUND OF TEiE INVENTION
Field of the invention The present invention relates to a method of producing 5 paper and also to the paper thus obtained.
In papermaking, raw paper pulp essentially consisting of cellulosic fibers is formed into a diluted aqueous suspension which if fed to the head box of the papermaking machine from whence it is distributed over a filtering surface on which the 10 web of paper forms. The web is then drained and dried. The quality and properties of the paper obtained are notably de~rmi ne~ by the papermaking machine ' s operating conditions, the state of the raw pulp, the various additives that are added to the suspension before formation of the web as well as 15 products that are layed onto the paper web downstream of the filter surface.
Among those products that are added to the fiber suspen-sion entering the head box, we can mention mineral fillers, sizing agents, agents designed to improve the mechanical 20 characteristics of the paper, coloring agents, etc... The mineral ~illers, such as CaCO3, Tio2, etc render the sheet of paper opaque, thus facilitating writing and printing. Sizing agents, such as those of the alkylketene dimers are added to impart liquid resistance properties to the sheet, and to allow 5 the sized sheet of paper to be employed for writing and print-ing .
One of the qualities of paper, paperboard and other products is the regularity of its characteristics. One of these is the so called look-thru or "sheet formation", which 10 is extremely important and is representative of the general quality of the paper. The look-thru ef fectively represents a greater or lesser degree of homogeneity of fiber distribution over the surface and thickness of the sheet. The look-thru quality will hence have considerable influence on the general 15 quality of the print in the case, for example, of paper used for printing and writing, and on mechanical properties in the case, for example, of paper used for packaging. In order to improve the look-thru, more and more additives are being added to the suspension entering the head box. But, in order to 20 meet the increasing strictness of pollution standards require-ments, pap~ k i n~ plants are being led to decrease their water consumption, which leads to an increase in the pollutant loading associated with this type of industry (suspended matter, biological oxygen requirement, chemical oxygen re-25 quirement, salinity, etc.) along with other problems, such as the problem of pitches, rosins and the like, and, moregenerally, pollutants linked to the presence of so called anionic trash. As the characteristics of the paper must however remain ldentical and the problems associated with 5 cleaning up the environment need to be tackled, one of the methods proposed in the prior art consists in increasing re-tention of the elements within the web during formation there-of on the filtering surface. This result is attained to a certain point, by adding retaining agents to the fiber suspen-10 sion entering the head box. Unfortunately, this method issubject either to variations in its effectiveness, or leads to a significant deterioration in the look-thru of the paper, depending on the products used.
The present invention hence sets out to provide a novel 15 process for producing paper and the like, in which, in addi-tion to the mineral filler and the sizing agent, a novel ternary retention system is mixed with the fiber suspension or composition entering the head box.
Prior art The following documents essentially constitute the state of the art in this area.
EP-A-348 366 describes a ternary system comprising cationic starch, a polyaluminum compound, and a silicic acid polymer. There is no mention of anionic silica and, in 2a736 ~ ~
addition, the polysilicic acid must have a given specific surface area (>1,050 M2/g) .
WO 88/6 659 describes a ternary system comprising a cationic polymer, a polyaluminum compound, and silica. The s cationic polymer is preferably polyacrylamide and cationic starch is not cited.
EP-A-285486 describes a retention system based on cationic starch and polyaluminum chloride. The mineral filler can for example be silica. Nevertheless, this application 10 does not specially describe the ternary retention system according to the present invention.
US-A-4 643 801 describes a retention system based on cationic starch, a high molecular weight anionic polymer and silica in parts by weight of starch/silica of 100/1 to 1/1 and of anionic polymer/silica from 20/1 to 1/10. An aluminum com-pound can also be added. The present ternary retention system alone is however not described.
In "polyaluminium hydroxychloride application on neutral pH rosin sizing of paper", by B.H. Wortley and J.C.
20 StePlh -r, a retention system is mentioned comprising cationic starch, bentonite and an anionic polymer, but the use of polyaluminum chloride (PAC) is neither mentioned nor suggested in this particular retention system.
None of the above mentioned publications either alone or 25 in combination with other references describes or suggests the ~ 207361 ~
use of a retention system of the type according to this pre-sent invention nor are the surprising and unexpected results obtained thanks to this new retention system described or suggested .
SUMMARY OF THE INVENTION
The present invention hence sets out, among other things, to obtain high retention rates as well as to enable improved dewatering of paper to be obtained while maintaining the look-thru quality and other characteristics thereof. The present invention enables a greater amount of filler to be employed, notably in products that are sensitive to acids, leading to waste and ef f luent that is less polluting . The present invention hence provides a method for manufacturing paper which comprises adding to the fibrous composition enter-ing the head box:
a ) a minera 1 f i 1 ler, b) a sizing agent, and c) a retention system comprised of:
c) 1) cationic starch, c) 2) polyaluminum chloride, and c) 3) silica of anionic nature.
The suspension containing the cellulosic fibers can be crude or bleached pulp, bleached chemical pulp of resinous, foliaceous, or annual vegetable matter, natural unbleached 2s chemical pulps of resinous or foliaceous origin, bleached or ~ 20735 1 0 unbleached mechanical pulps (SGW, TMP; CT~P, . . . ), bleached or unbleached de-inked pulps, pulps that already contain addi-tives, and mixtures thereof.
The cationic .starch - mentioned as component c) 1) - used in the present invention is mixture of one or several products marketed under the generic name of cationic starch. The starch has an average molecular weight of 2.104 to 2.105, preferably from 3.104 to 12.104. The cationic starches have a degree of substitution (D . S . ) comprised between O . 01 and O .1.
The cationic starches are, for example, those described in Kirk Othmer, 3rd edition, volume 21, page 503. Preferably, they represent, by weight, from 0.2 to 1.7~ of the weight of the fibrous suspension entering the head box.
The polyaluminum chloride (PAC) - mentioned as component c) 2) - employed in the present invention designates products that are usually known as aluminum polychloride, basic polychloride of-aluminum, basic polychlorosulfate of aluminum and preferably consist of one o~r several of the following products:
1. The salt of =formula:
A1 (OH) C1 (I) n m 3n-m in which m and n are positive lntegers and 3n-m is positive; said salt being further able to contain a polyvalent anion Y selected from the anions of sulfuric, phosphoric, polyphosphoric, silicilic, chromic, carboxylic, and sulfonic acids, the molar ratio Y/Al being comprised in the range 0 . 015 and 0 . 4;

2. the salt of formula:
Aln(OH)mcl3n-m-2k(s 4) (II) in which k, m and n are positive integers and 3n >
m + 2k, the basicity m/3n is comprised between 0.3 and 0.7 and k/n = 0.01 to 0.03;
this product being able to be prepared according to the process described in United States patent 3,929,666;

3. the salt of formula:
[Aln (HO) 3n_m_2pClm (S4) p (III) in which (3n-m-2p) /3n = 0.4 to D.7; p = 0.04 to 0.25n;
m/p = 8 to 35, k, m, n, and p are integers and z is at least l;
this product being described in GB-A-2 ,128, 977;

4. the chlorosulfate of basic aluminum of formula:
AlnOHm(sO4)kcl3n-m-2k (IV) in which the basicity (m/3n) 100 is comprised between about 40% and about 65% and has an Al equivalent/C1 equivalent ratio comprised between 2. 8 and 5, an appar-ent molecular mass MA measured by conventional light dif fusion and apparent hydrodynamic diameters 0Z and 0W
measured by quasi-elastic light diffusion of the follow-ing values:
MA = 7000-35000 ~73~1 0 0Z (A) = 350-2500 0W(A) = 200-1200.
this product being described in FR-A-2 584 699.
Preferably, the PAC is present in the fibrous composi-5 tion entering the head box in an amount of 0.01 to 0.3% byweight, based on the weight of said fibrous composition, said percentage being expressed on the basis of Al2O3. Preferably, the PAC is WAC of formula IV.
The anionic nature silica - mentioned as component c) 3) lO - employed in the present invention is a mixture of one or several silicas selected from the group comprising: silica sol, silica gel, microparticulate silica, silico-aluminate, bentone and bentonite. Preferably, the silica is present in the fibrous composition in an amount of 0.01 to 0.3% by lS weight, based on the weight of said fibrous composition, the percentage being expressed as a percentage of active matter, in other words in SiO2. The silica of anionic nature employed preferably is in sol form, with advantageously 15% SiO2.
The mineral filler - component a) mentioned above - can 20 be one or several of the conventionally used fillers such as the following, provided by way of example: clay, CaCO3, hy-drated alumina, talc, TiO2, etc. The mineral filler repre-sents less than 40% by weight, preferably 10 to 25% by weight, based on the weight of said fibrous composition. The pre-25 ferred mineral filler is CaCO3.

The sizing agent - companent b) mentioned above - can be one or several of the following conventional fillers employed for a neutral medium: alkyl ketene dimers (AKD), fluorinated phosphates, carboxylic acid anhydrides, styrene/maleic 5 anhydride copolymers, and derivatives thereof. The amount of sizing agent employed is less than 10% by weight, preferably comprised between 0 . 01 and 2% by weight of the commercial product with 6% of active material, based on the weight of said composition. The preferred sizing agent is AKD.
Components a), b), c) 1) c) 2) and c) 3) mentioned above can be added separately or in the form of a mixture of two or more thereof.
The fibrous suspension can also contain conventional additives such as coloring agents, optical brighteners, me-chanical strengthening agents, anti-foaming agents, anti-slime agents as well as products selected from the group comprising:
the polyacrylamides, polyethylene imines, carboxymethyl cellu-lose, urea-formol resins, melamin-formol resins, aminopolyamide-epichlorhydrine resins, polyamide-epichlor-hydrine.
Preferably, the components added are:
a) from 5 to 30% of CaCO3, b) from 0.01 to 1% of ~KD, and c) 1 from 0 . 2 to 1. 7% of cationic starch of molecular weight 2.104 to 12.105 and a degree of substitution of from 0.01 to 0.1; c)2 from 0.1 to 3''6 o~ WAC as 10% A1203 commercial product; and c)3 from 0.01 to 0.3% of silica sol, expressed as 9~ of SiO2.
EXAMPLES
The following examples illustrate the present invention but should not be considered as limiting thereof. In these examples, WAC is a product marketed by Atochem and corresponds to a polyaluminum chloride of formula IV with 10% of A1203.
The silica is in the form of a silica sol and is available in the trade under the name CECASOL from Ceca. The cationic starch is manufactured by Roquette and marketed under the name HICAT 142. The AKD sizing agent is manufactured by Hercules and marketed under the name AQUAPEL.
Example 1 The paper being manufactured is paper for printing or writing suitable for carbonless copying paper.
. machine employed ........ flat bed fitted with a ;3el ~30nd former speed ..................... 5 9 0 m/min . width ................... 3 m . weight .,,,,,,..,,,....,,, 50 g/m Fiber composition:
. Resinous bleached kraft pulp ...................... 45%
. Foliaceous bleached kraft 20736 ~ ~
pulp .................. 559~
. Filler .............. CaCO3 . Amount of filler in finished paper......... 14%
. Sizing (AKD) ........ 0 .15%
cationic starch ....... 0 . 6%
The tests carried out on the product obtained, under the conditions listed in the Table below produced the results indicated in said Table:
RESIILTS
Total WAC Silica ll) retention look-thru(2) Test 1 . . . 0 0 . 5% 5~% 104 Test 2 ... 1.65% 0 57% 70 15 Test 3 . . . 1. 65% 0 .15% 67% 72 (1) In commercial product at 15% active material.
(2) The look-thru was continuously measures using an item of equipment ~rom the "Centre technique du papier" of Grenoble (France).
Comparing test 1 and test 2, the very significant im-provement in look-thru caused by the use of WAC instead of silica can be noted, this result being what would be expected by those skilled in the art.
Test 3 illustrates the synergy developed by the asso-ciation of small amounts of silica in the presence of WAC.

20736~0 For equivalent look-thru, retention is increased by 10 points, equivalent to an increase in 15 to 20%. This results in reduced water pollution from the circuits and greater ease of treating waste water at a reduced cost.
5 Example 2 The paper to be manufactured was a paper for printing and writing. The machine was identical to that for example l.
. Machine speed ............. 540 m/min . Paper weight .............. 60 g/m2 Fiber composition:
. Resinous bleached kraft pulp ........................ 40%
. Foliaceous bleached kraft pulp ........................ 60%
. Filler .................... CaCO3 . Amount of filler in f ini shed paper ............ 11%
. Sizing (AKD) .............. 0.15% (in commercial product) . cationic starch .. , .. 0 . 5%
The tests carried out on the product obtained, under the conditions listed in the Table below produced the results indicated in said Table:

RESUI,TS
Total WAC Silica retention look-thru HBC (1) Test 1 .. 1.6% 0 60% 76 8.4 g/l 5 Test 2 .. 1.5% 0.15% 73% 75 6.5 g/l ( 1 ) E~BC = head box concentration E~xample 3 The same machine was usea as in the example 2 . ~achine speed ............. 520 m/min . Paper weight ..... ,.. 70 g/m2 Fiber composition:
. Resinous bleached kraft pulp ........................ 35%
. Foliaceous bleached kraft pulp ........................ 65%
. Filler .................... CaCO3 . Amount of ~iller in f inished paper ............. 14 %
. Sizing (AKD) .............. 0.15% (in commereial product) . cationie stareh ........... 0 . 6%
The tests carried out on the product obtained, under the conditions listed in the Table below produced the results indicated in said Table:

~ 20736 1 0 RESUI.TS
Total WAC ~ Silica Retention look-thru HBC
Test 1 .. 1.596 0 67% 75 8.7 g/l 5 Test 2 .. 1.5% 0.2596 78% 76 7.2 g/l .

Claims

1.- A method for manufacturing paper which comprises adding to the fibrous composition entering the head box:
a) a mineral filler, b) a sizing agent, and c) a retention system comprised of:
e) 1) cationic starch, e) 2) polyaluminum chloride, and e) 3) silica of anionie nature.

2.- A process for producing paper according to claim 1, wherein the amounts by weight of products c)1), c)2), and c) 3), based on the weight of composition entering the head box, expressed as a percentage are as follows: 0.2 to 1.7%, 0.01 to 0.3% expressed as pereentage of Al203, and 0.01 to 0.3% expresses as pereentage of SiO2.

3.- A process for making paper according to claim 1, wherein the cationic starch has a molecular weight of 3.104 to 12.104 and a degree of substitution of 0.01 to 0.1.

4.- A progress for making paper according to claim 1, wherein the polyaluminum chloride is selected from the group comprising the salts of formulae I, II, III, and IV below and mixtures thereof:

Aln(OH)mCl3n-m (I) in whieh m and n are positive integers and 3n-m is positive; said salt being further able to contain a polyvalent anion Y selected from the anions of sulfuric, phosphoric, polyphosphoric, silicilic, chromic, carboxylic, and sulfonic acids, the molar ratio Y/A1 being comprised in the range 0.015 and 0.4;
Aln(OH)mCl3n-m-2k(SO4)k (II) in which k, m and n are positive integers and 3n >
m + 2k, the basicity m/3n is comprised between 0.3 and 0.7 and k/n = 0.01 to 0.03;
[Aln(HO)3n-m-2pClm(SO4)P]z (III) in which (3n-m-2p)/3n = 0.4 to 0.7; p = 0.04 to 0.25n;
m/p = 8 to 35, k, m, n, and p are integers and z is at least 1;
AlnOHm(SO4)kCl3n-m-2k (IV) in which the basicity (m/3n) 100 is comprised between about 40% and about 65% and has an Al equivalent/Cl equivalent ratio comprised between 2.8 and 5, an appar-ent molecular mass MA measured by conventional light diffusion and apparent hydrodynamic diameters ?Z and ?W
measured by quasi-elastic light diffusion of the follow-ing values:
MA = 7000-35000 ?Z(.ANG.) = 350-2500 ?W(.ANG.) = 200-1200.

5.- A papermaking process according to claim 1, wherein the anionic type silica is selected from the group comprising, silica sol, silica gel, microparticulate silica, silico-aluminate, bentone and bentonite and mixtures thereof.

6.- A process according to claim 1, wherein said poly-aluminum chloride is WAC.

7.- A process according to claim 5, wherein the anionic type silica is a silica sol.

8.- A process according to claim 1, wherein the amount of mineral filler a) is less than 40% by weight based on the weight of said fibrous composition.

9.- A process according to claim 8, wherein the amount of mineral filler a) is comprised between 5 and 30% by weight based on said fibrous composition.

10.- A process according to claim 1, wherein the mineral filler is selected from clay, calcium carbonate, titanium dioxide, talc, hydrated alumina, and mixtures thereof.

11.- A process according to claim 1, wherein the amount of sizing agent b) is less than 10% by weight based on the weight of said composition.

12.- A process according to claim 11, wherein the amount of sizing agent b) is comprised between 0.01 and 2% by weight based on the weight of said composition.

13.- A process according to claim 1, wherein the sizing agent is selected from the group comprising: alkyl ketene dimers (AKD), fluorinated phosphates, carboxylic acid anhydrides, styrene/maleic anhydride copolymers, and deriva-tives and mixtures thereof.

14.- A process according to claim 1, wherein the mineral filler is CaCO3.

15.- A process according to claim 13, wherein the sizing agent is AKD.

16.- A process according to claim 1, wherein there is added to said fibrous composition a component selected from polyethylene imines, carboxymethyl cellulose, urea-formol resins, melamin-formol resins, aminopolyamide-epichlorhydrine resins, polyamide-epichlorhydrine resins and mixtures thereof.

17.- A process according to claim 1, wherein the compo-nents added are:
a) from 5 to 30% of CaCO3, b) from 0.01 to 1% of AKD, and c) 1 from 0.2 to 1.7% of cationic starch of molecular weight 2.104 to 12.105 and a degree of substitution of from 0.01 to 0.1; c)2 from 0.1 to 3% of WAC as 10% Al203 commercial product; and c)3 from 0.01 to 0.3% of silica sol, expressed as % of SiO2.

18.- A paper obtained by the process according to any one of claims 1 to 17.

19