CA1239507A

CA1239507A - Production of paper, cardboard and board having high dry strength, wet strength and alkali resistance

Info

Publication number: CA1239507A
Application number: CA000468871A
Authority: CA
Inventors: Sigberg Pfohl; Heinrich Hartmann; Theo Proll; Erhard Klahr
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1983-11-29
Filing date: 1984-11-28
Publication date: 1988-07-26
Also published as: DE3343105A1; ATE28340T1; FI80279C; EP0146000A1; JPS60134098A; NO164852C; EP0146000B1; FI844506A0; FI80279B; NO164852B; FI844506L; DE3464772D1; NO844730L

Abstract

Abstract of the Disclosure: Paper, cardboard and board having high dry strength, wet strength and alkali resist-ance are produced by adding resin solutions, which are obtained by reacting homopolymers and copolymers of vinyl-imidazoles with epichlorohydrin in a ratio of from 0.02 to 2.9 moles of epichlorohydrin per equivalent of basic nitrogen in the polymer, to the paper stock and then draining the latter on a screen to form sheets.

Description

- ~2395~7 - 1 - OOZE. 0050t36829 Production of paper, cardboard and board having high dry strength, wet strength and alkali resistance Wet-strength paper is produced in practice by adding to the paper stock at neutral or slightly alkaline pi virtually exclusively resins which are prepared by reacting epichlorohydrin with basic long-chain polyamide-amine of U.S. Patent Z,926,116). Since the polyamide chain on which the resins are based undergoes as hydrolytic cleavage relatively easily, these resins have the disk advantage of a relatively short shelf life. The alkali resistance of the papers treated with these resins is us-satisfactory.
U.S. Patent 3,7û0,623 discloses resins which are prepared by reacting epichlorohydrin with polymers of dip allylaminesO Such products make it possible to prepare papers having high dry strength, wet strength and alkali resistance. However, the resins are very expensive and are therefore not used in industry. The disadvantages of these resins are that they first have to be activated with an alkali in the paper factory before they reach optimum activity, and that they cause pronounced dulling of the whiteness of the paper treated with them.
It is an object of the present invention to pro-vise resins which, when added to the paper stock at neutral or slightly alkaline phi increase the dry strength, wet strength and alkali resistance of the paper thus produced. The resins should be capable of being used directly without activation, and furthermore should not cause any dulling of the whiteness of the paper.
We have found that this object is achieved, in accordance with the invention, by a process for the pro-diction of paper, cardboard and board having high dry strength, wet strength and alkali resistance, by adding an aqueous polymer solution to the paper stock and draining the latter over a screen to form a sheet, if the aqueous polymer solution used is a product which is obtained by I
I`

Lowe

- 2 - OOZE. 0050~368Z9 reacting (1) a homcpolymer of a vinylimidazole of the formula I

CON
R N' t I ) Choctaw where R1, R2 and R3 are each H or SHEA, and R1 may 5 furthermore be C2Hs, C3H7 or C4Hg, or to) a water-soluble copolymer of a) not less than 10X by weight of a vinyl;midazole of the formula I, b) not more than 90X by weight of acrylamide and/or moth-10 acrylamide and, of requ;red,c) not more than 30X by eight of acrylonitrile, moth-acrylonitrile, vinyl acetate, vinylpyrrolidone, an ethylene-gaily unsaturated C3-C5-carboxylic acid or one of its esters, 15 with ep;chlorohydr;n in a ratio of from 0.02 to Z.9 moles of epichlorohydrin per equivalent of basic nitrogen in the homopolymer or copolymer.
Homopolymers and copolymers of vinylimidazole are known. They are obtained by, for example, polymerization 2 of vinylimidazoles of the formula I

CON
R 3 TIC - R 1 ( I ) SCHICK

where R1, R2 and R3 are each H or SHEA and R1 may furthermore be C2Hs~ C3H7 or C4H9~ in aqueous solution on the presence of a free-radical polymerization 25 initiator, at from 40 to 100C, preferably from 60 to 100C. Where R1 is colloquial, it can be n-propyl or isopropyl and where R1 is C4 alkyd, it can be n-butyl, isobutyl or tert.-butyl.

~Z395~7

- 3 - I Ought For the preparation of copolymers of vinylimida-zone, not less than 5X by weight of a vinylimidazole of the formula I is used as component pa), while not more than 95% by weight of acrylamide and/or methacrylamide are 5 employed as component (b) of the copolymers. polymers of tax from 15 to 30% by weight of a v;nylimidazoLe of the formula I, where R1, R2 and R3 are each H, or R2 and R3 are each H and R1 is methyl, or a mixture of the monomers, and tub) from 85 to 70X by weight of acryl-10 aside are preferably used as the starting polymer for the preparation of the wet-strength resins.
The copolymers can be modified, for example, in that they contain, as component (c) in the form of Capella-merited units, not more than 30Z by weight of acrylo-15 nitrite, methacrylonitrile, vinyl acetate, vinylpyrroli-done, an ethylenically unsaturated C3-C5-carbo~ylic acid or one of its esters. The monomers of component (c) are employed in an amount such that the resulting copolymers are still water-soluble. Hence, for example, long-chain 20 esters of ethylenically unsaturated C3-C5-carboxylic acids are copolymerized in an amount of not more than about 5X by weight, whereas methyl acrylate or acrylo-neutral can be present on the copolymers in an amount as high as 30X by weight. The copolymers can also be mod;-25 fled by simultaneously using a number of the monomers stated under lo) in the polymerization, ego acrylonitrile and acrylic acid, acrylonitrile, vinyl acetate and vinyl-pyrrolidone, or acrylic acid and acrylates.
The homopolymers and copolymers of the vinyl-30 imidazole have K values of from 30 to 150, preferably from to 120 determined according to H. Fikentscher on 0.1Z
strength polymer solutions in SO strength aqueous sodium chloride solution at Z0C). They are reacted with opt-chlorohydrin in an aqueous medium to give resins, from 35 0.02 to 2.9, preferably from 1.0 to 2.5, mules of epichloro-hydrin being employed per equivalent of basic nitrogen in the polymer. The resins are preferably prepared by adding opt-~2395;~'7

- 4 - OOZE 0050/36829 chlorohydrin to an aqueous solution of the homapolymer or copolymer of a compound of the formula I and allowing the mixture to react until epoxide is no longer detectable.
In order to be able to monitor the reaction satisfactorily,

5 the ep;chlorohydrin is added continuously or bushes.
The reaction temperature is from 0 to 100C, preferably from 20 to 80C, and the reaction time is about 2 - 6 hours. The condensation takes place at pi 5 - 10. In order to obtain stable resin solutions, the pi of the aqueous solution is brought to 2 - 4 before or after con-sensation is complete, this preferably being done using sulfuric acid or formic acid. The readyrprepared aqueous resin solutions have a solids content of from 10 to 20X by weight and a viscosity of from 100 to S,000 maps (measured in a 10X strength solution according to rook-field, 20 rum, 20C).
The aqueous resin solutions can be used in paper-making either directly or, if required, after further dilution with water they can be diluted with water in Z0 any ratio). For paper making they are added to the paper stock before sheet formation, in an amount of from 0.1 to S, preferably from 0.25 to 1, % by weight, based in each case on the solids. If from 0.005 to I based in each case on dry fiber material and 100X strength resin, of the Z5 aqueous resin solution is added to the paper stock slightly upstream from the head box, these resins constitute excel-lent creeping assistants, for example for sanitary papers.
The resin solutions used according to the invent lion are added to the fiber suspension under the usual 30 conditions for paper making. The resins are effective for all conventional grades of paper, board and cardboard, for example in the manufacture of writing paper, printing paper and packaging paper. The papers or boards and card-boards may have been manufactured from a large variety of 35 fibrous materials, for example bleached or unbleached sulfite or sulfate pulp, grounded or waste paper, or a mixture of the stated types of fiber. The pi of the stock ~2395~7 - 5 - OOZE. 0050/36829 suspension us from 4 to 9, preferably from 6 to 8. It is also possible to apply the resin solution, for example in a size press, onto the surface of paper which has already been formed.
In the Examples which follow, parts and percent-ages are by weight.
The sheets were produced on a Rapid-Kothen labor-tory sheet former. The dry tear length was determined according to DIN 53,112, sheet I and the wet tear length according to DIN 53,112, sheet 2.
The alkali resistance was determined in the same manner as the wet strength, except that, instead of water, a 1X strength sodium hydroxide solution was used for impregnating the paper (5 minutes at 50C).
The whiteness of the paper sheets was determined with the aid of an Elrefo reflecting photometer, in accordance with DIN 53,145.
The K value of the polymers was determined accord-in to H. Fikentscher, Cellulosechemie 13 t1932), 58-64 20 and 71-i4, at 20C in SO strength aqueous sodium chloride solution; K = k . 103.
Preparation of the resin solutions Resin 1 a) Preparation of an aqueous solution of a homopolymer of N-vinylimidazole 500 parts of vinylimidazole and 450 parts of water were initially taken in a polymerization vessel, and 8 parts of tert.-butyl perethylhexanoate in 40 parts of methanol were added in the course of 1 hour at 100C, 30 while nitrogen was passed through. When the addition of the polymerization initiator was complete, the reaction mixture was polymerized for a further 7 hours at 91C, and the resulting mixture was then diluted to a solids content of 30.3% by adding water. A brown, slightly 35 cloudy, very viscous polymer solution was obtained, the K
value of the homopolymer being 86.

i23~5~i7

- 6 - OOZE. 0050/36829 b) Reaction of the homopolymer with epichlorohydrin 878 9 (corresponding to 2.7 equivalents of basic nitrogen) of a 30.3X strength aqueous solution of the poly-N-v;nyl;m;dazole obtained as described in a) were S dotted Thea 1,630 9 of water, 677 9 (7.3 moles) of en;-chlorohydr;n were added at room temperature, and the mix-lure was stirred. During thus procedure, the viscosity of the solution increased slowly. After 30 minutes, 193 9 (2 moles) of sulfuric acid were added, the pi being brought to 2 as a result. The reaction mixture was heated to 80C and stirred for 4 hours at this temperature, 2,100 9 of water being added a little at a tome. The resulting aqueous solution of resin 1 had a solids content of 17.2X, a pi of 1.7 and a viscosity of 380 maps Resin 2 a Preparation of an aqueous copolymer solution 250 parts of water were initially taken on a polyp Morristown vessel, and feeds I and II were added s;multane-ouzel from two separate feed vessels, on the course of 1 hour, at 90C, while nitrogen was passed through. Feed I consisted of 150 parts of acrylam;de, 150 parts of vinylim;dazole and 150 parts of water, whole feed II was a solution of 3 parts of Z,2'-azobis-(2-am;dinopropane) d;hydrochlor;de on 47 parts of water. The reaction mix-25 lure was then polymerized for a further 4 hours at 90C, and the resulting mixture was brought to a solids content of 30.3% by adding water. The K value of the copolymer was 68.
b) Reaction of the copolymer with ep;chlorohydr;n 233 9 (corresponding to 0.4 equivalent of basic nitrogen) of the 30.3% strength aqueous solution of the copolymer described in a) were diluted with Z86.5 9 of water, and 41.6 9 (0.45 mole) of ep;chlorohydrin were added at room temperature. The reaction mixture was then 35 heated slowly to 75C. After 60 minutes, the v;scos;tyof the reaction mixture had increased substantially. It was then brought to pi 2 with 44 9 (0.8 mole) of 85X

~239S~7

7 OOZE. 005~/36~29 strength formic acid, and stirred at 75~C for a further 2 hours, after which the reaction was compute. the reaction mixture was brought to a solids content of 15% by adding 200 9 of water. The aqueous solution of resin 2 had a viscosity of 230 maps and a pi of 3Ø
Resin 3 a Preparation of an aqueous copolym~r solution 125 parts of water were initially taken in a polymerization vessel and heated to 80C Chile being stirred and while nitrogen was passed through. As soon as the temperature of 30C had been reached, two differ-en feeds were introduced continuously into the vessel on the course of one hour. Feed I consisted of a solution of 225 parts of acryLamite and 75 parts of N-viny~imida-zone in Z25 parts of water, while feed II was a solution of 3 parts of Z,2'-azobis-~Z-a~idinopropane) dodder-chloride in 47 parts of water. When the addition of the monomers and the initiator was complete, the reaction mix-lure was polymerized for a further 4 hours at awoke, and Z0 the resulting mixture was brought to a solids content of 10.1X by adding water. The K value of the copolymer was 84.
b) Reaction of coupler a) with epich~orohydrin 150 9 of water, 16.7 9 ~0.18 mole) of epichloro-25 hydrin and 9.7 9 Tao mole) of 85% strength formic acid were added to Z97.6 9 corresponding to 0.1 equivalent of basic nitrogen) of the 10.1X strength aqueous solution of copolymer a), and the mixture was heated to 75C. React lion for 4 hours at 75C gave an 8.4% strength aqueous 30 solution of resin 3, the solution having a viscosity of 3,8ûQ maps and a pi of 3.6.
Resin 4 .
a) Preparation of an aqueous copolymer solution 145 parts of water were initially taken in a 35 polymerization vessel and heated to ~0C while being stirred and while nitrogen was passed through. When the temperature of the water initially taken had reached 80C,

- 8 - OOZE. 0050/3~829 feeds I and II were introduced simultaneously in the course of one hour. Feed I consisted of a solution of 255 parts of acrylamide and 45 parts of N-vinylimidazole in 255 parts of water, while feed II was a solution of 1.5 9 of 2,2'-azobis-(2-amidinopropane) dihydrochloride in 48.5 parts of water. When the addition of the monomers and the initiator was complete, the reaction mixture was polyp merited for a further 4 hours at 80~, and the resulting mixture was diluted to a solids content of 5X by adding 1û water. The K value of the copolymer was 113.
b) Reaction of copolymer a) with epichlorohydrin 6 9 9 (0.13 mole) of 85% strength formic acid and 11.8 q (û.13 mole) of epichlorohydr;n were added to 894.6 9 (corresponding to 0.08 equivalent of basic nitrogen) of the 5% strength aqueous solution of copolymer a) described above. The reaction mixture was heated to 80C and stirred for 5 hours at this temperature. The resulting aqueous solution of resin 4 had a solids content of 6~0X, a pi of 3.6 and a viscosity of 600 maps 100X pine sulfite pulp was converted to a OX
strength stock suspension in water, the pi of the suspend soon being 7.5 and the degree of freeness 35SR. The stock suspension was divided into three equal parts, and each part was processed under the following conditions to give sheets having a weight per unit area of 80 g/m2:
a) Nothing was added to the stock suspension.
b) 1X, based on the solids, of an aqueous solution of a commercial neutral wet-strength resin based on a react lion product of epichlorohydrin with a polyamidoamineobtained from diethylenetriamine and adipic acid was added to the stock suspension. The neutral wet-strength resin was prepared as described in Example 1 of U.S.
Patent 2,926,116.
35 c) 1X, based on the solids, of resin 3 described above was added to the stock suspension.
The dry tear length, the wet tear length, the ~Z395~7

- 9 - OOZE. 0050/36829 alkali resistance and the whiteness of the three sheets obtained as described in a), b) and c) were tested. The results are summarized in Table 1.

S a) b) c3 Dry tear length (m) 4,450 5,340 5,990 Wet tear length to) 0 1,120 1,190 Paper unaged Wet tear length (m) 120 1,5Z0 1,450 Paper aged for 5 minutes at 1 1 û C
Alkali resistance 0 725 980 1X strength sodium hydroxide solution for 5 minutes at 50C
Paper unaged Alkali resistance 1,0Z0 1,090 1X strength sodium hydroxide solution for 5 minutes at 50C
Paper aged for 5 minutes at 50C
Whiteness 80 n 5 6 9 O 73 5 Diffuse reflectance (Xj 100% mixed waste paper was converted to a 0.5X
strength aqueous stock suspension, the pi of the suspend soon being 7.2 and the degree of freeness 50SR. Theistic suspension was then divided into five equal parts, and each part was processed under the following conditions to give sheets having a weight per unit area of 80 g/mZ:
a) no further substances were added to the stock suspension;
30 b) 0.5%, based on dry fiber, of the neutral wet-strength resin described in Example 1b) was added;
c) 1.0X, based on dry fiber, of the neutral wet-strength resin described in Example 1b) was added;
d) 0.5%, based on the solids, of resin 4 was added;
35 e) 1.0X, based on the solids, of resin 4 was added.
The dry tear length and the wet tear length of all paper sheets produced in this manner were measured. The ~23~ 7

- 10 - OOZE. 0050/3682 results are shown in Table 2.
TABLE Z
Exper;mentDry Wet Wet tear length (m), tear length tear length aged for 5 minutes (m) (Al) at 110C
a) 2,420 0 0 b) 2~570 390 590 c) 2,890 5Z0 900 d) 2,750 475 580 e) 3,050 714 910 A paper consisting of 80% of bleached pine sulfite pulp and 20% of bleached beech sulfite pulp and having a weight per unit area of 80 9/m2 was produced, at a speed of 60 main on an experimental paper machine having a working width of 75 cm. The pi of the stock suspension was 7.5, and the degree of freeness was 35SR. Papers were produced from this stock suspension under the cord;-lions a) to g) stated below:
a) No substances were added.
b) 0.25% of the neutral wet-strength resin stated on Example lb) was added.
c) 0.5X of the resin described in b) was added.
do 1.0X of the resin described in b) was added.
e) 0.25X of resin 4 was added.
f) 0.5X of resin 4 was added.
g) 1.0X of resin 4 was added.
The percentages in each case are based on the solids, to. of the stock suspension and of the resin soul-lions. The resin solutions described in a) to g) worded to the high density pulp. The wet tear length and the alkali resistance of the papers produced in this manner were determined. The values stated are mean values of measurements along the longitudinal and transverse directions of the paper with respect to the paper machine.
The following values were obtained:

~23~5~
OOZE. 0050/36829 Wet tear length Alkali resistance, (m) 1X strength Noah, _ 5 mint 50C
a) O O
b) 340 Z40 c) 550 3~0 d) 840 470 e) 405 515 f) 580 735 9) 870 940

Claims

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

1. A process for the production of paper, cardboard and board having high dry strength, wet strength and alkali resistance, wherein an aqueous polymer solution, which is obtained by reacting (1) a homopolymer of a vinylimidazole of the formula (I) (I) wherein R1, R2 and R3 are each H or CH3, and R1 may furthermore be C2H5, C3H7 or C4H9, or (2) a water-soluble copolymer of a) not less than 5% by weight of a vinylimidazole of the formula (I), b) not more than 95% by weight of acrylamide or methacrylamide or both, with epichlorohydrin in a ratio of from 0.02 to 2.9 moles of epichlorohydrin per equivalent of basic nitrogen in the homopolymer or copolymer, is added to the paper stock, and the latter is drained on a screen to form sheets.

2. A process as claimed in claim 1, wherein said water-soluble copolymer further comprises, c) not more than 30% by weight of acrylonitrile, methacrylonitrile, vinyl acetate, vinylpyrrolidone, an ethylenically unsaturated C3-C5-carboxylic acid or one of its esters.

3. A process as claimed in claim 1 or claim 2, wherein the reaction product used is one which is obtained by reacting a water-soluble copolymer of a) from 15 to 30% by weight of N-vinylimidazole and b) from 85 to 70% by weight of acrylamide with epichlorohydrin.

4. A process as claimed in claim 1 or claim 2, wherein the homopolymer or copolymer of a vinylimidazole of the formula I is reacted with epichlorohydrin in a ratio of from 1.0 to 2.5 moles of epichlorohydrin per equivalent of basic nitrogen.

5. A process as claimed in claim 1 or claim 2, wherein the reaction product is used in an amount of from 0.1 to 5% by weight, based on dry paper stock.

6. A process as claimed in claim 1 or claim 2, wherein the reaction product is used in an amount of from 0.25 to 1% by weight, based on dry paper stock.