US3785921A

US3785921A - Paper reinforcing composition containing starch and a starch-acrylamide graft polymer

Info

Publication number: US3785921A
Application number: US00210595A
Authority: US
Inventors: F Ide; T Kodama; Y Kotake
Original assignee: Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Rayon Co Ltd
Priority date: 1970-12-26
Filing date: 1971-12-21
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15
Also published as: CA949691A; FR2124662A5; JPS5247044B1

Abstract

PAPER REINFORCING AGENT COMPOSED MAINLY OF A POLYMER COMPOSITION WHICH INCLUDES A GRAFT POLYMER, A WATERSOLUBLE POLYSACCHARIDE, AND, IF NECESSARY, AN ACRYLAMIDE TYPE RANDOM COPOLYMER. THE GRAFT POLYMER IS THAT HAVING THE WATER-SOLUBLE POLYSACCHARIDE AS ITS BACKBONE POLYMER AND A COPOLYMER DERIVED FROM A MONOMER MIXTURE OF ACRYLAMIDE AND AN UNSATURATED CARBOXYKIC ACID, AS ITS BRANCH POLYMER; SAID RANDOM COPLYMER IS THAT WHICH IS DERIVED FROM THE AFORESAID MONOMER MIXTURE. THE WATER-SOLUBLE POLYSACCHARIDE CONTENT IS 5-22% BY WEIGHT BASED ON THE COMPOSITION. THE PAPER REINFORCING AGENT IS OBTAINED BY POLYMERIZING THE AFORESAID MONOMER MIXTURE IN THE PRESENCE OF THE WATER-SOLUBLE POLYSACCHRIDE, OR BY FURTHER ADDING THERETO A SUITABLE AMOUNT OF THE WATER-SOLUBLE POLYSACCHARIDE AMD/OR THE ACRYLAMIDE TYPE RANDOM COPOLYMER. THE REINFORCING AGENT EXHIBITS HIGH PAPER-REINFORCING PROPERTY EVEN IN A SMALL QUANTITY AND IS MARKEDLY CHEAPER THAN ANY OF THE KNOW ACRYLAMIDE TYPE PAPER REINFORCING AGENTS.

Description

"United States Patent PAPER REINFORCING COMPOSITION CONTAIN- ING STARCH AND A STARCH-ACRYLAMIDE GRAFT POLYMER Fumio lde, Tsuneo Kodama, and Yahide Kotake, Hiroshima, Japan, assiguors to Mitsubishi Rayon Co., Ltd., and Nitto Kagyo Co., Ltd., both of Tokyo, Japan N0 Drawing. Filed Dec. 21, 1971, Ser. No. 210,595 Int. Cl. C08d 9/06; D21h 3/08, 3/28 US. Cl. 162-168 17 Claims ABSTRACT OF THE DISCLOSURE Paper reinforcing agent composed mainly of a polymer composition which includes a graft polymer, a watersoluble polysaccharide, and, if necessary, an acrylamide typerandom copolymer. The graft polymer is that having the water-soluble polysaccharide as its backbone polymer and a copolymer derived from a monomer mixture of acrylamide and an unsaturated carboxylic acid, as its branch polymer; said random copolymer is that which is derived from the aforesaid monomer mixture. The Water-soluble 'polysaccharide content is -22% by Weight based on the composition.

The paper reinforcing agent is obtained by polymerizing the aforesaid monomer mixture in the presence of the water-soluble polysaccharide, or by further adding thereto a suitable amount of the Water-soluble polysaccharide and/or the acrylamide type random copolymer.

The reinforcing agent exhibits high paper-reinforcing property even in a small quantity and is markedly cheaper than any of the known acrylamide type paper reinforcing agents.

This invention relates to a paper reinforcing agent having a novel composition.

In recent years, the supply of needle-leaf trees is running short throughout the world. In the circumstances, the paper industry hasno alternative but to use shortfiber pulp of broad-leaf trees as the raw material for paper products. In order that the paper manufactured from the pulp such as of broad-leaf trees acquires the same strength as the paper from the pulp of needle-leaf trees, it is necessary to use a paper reinforcing agent. The paper reinforcing agent is also very effective in improving the yield of pulp, the yield of loading material, and the sheet forming rate.

As the paper reinforcing agent, there have predominantly been used starches and water-soluble polysaccharides obtained by subjecting starches to such treatment as oxidation or 'etherific'ation. These starches are inexpensive. Since they are natural products, however, they have a defect that they are susceptible to weather conditions and their prices are not stable. Further, their paper-reinforcing effects are insuflicient.

In recent years, synthetic high molecular compounds are arresting keen attention as useful paper reinforcing agents. Particularly, acrylamide type paper reinforcing agents have entered the limelight as dry paper reinforcing agents. Namely, homopolymer and copolymers of acrylamide are used as such dry paper reinforcing agents. The homopolymer of acrylamide is nonionic and does not easily form anionic bond with pulp. Therefore, it is difficult for the horn opolymer to provide stable adhesion to the pulp and, as a consequence, it has insufficient paper ice reinforcing capacity. The copolymers of acrylamide are divided into two typesanionic type and cationic type. The anionic copolymers include the copolymers of acrylamide with unsaturated compounds having such acid radicals as carboxyl and sulfonyl groups in their molecular units. The anionic copolymer exhibits strong aflinity to the pulp in the presence of such polyvalent cation as aluminum ion, with the result that the greater part of the copolymer adheres fast to the pulp. Thus, it shows excellent paper reinforcing effect even if it is used in a small amount. The acrylamide type paper reinforcing agents are highly effective as mentioned above, but quite expensive. A method is suggested in which acrylamide is copolymerized with an inexpensive nonionic monomer such as, for example, acrylonitrile, styrene or methyl methacrylate, in order to reduce the price of the anionic acrylamide type paper reinforcing agent. Paper reinforcing capacity is inevitably degraded as an amount of the nonionic monomer is increased. Thus, this method has not fully attained the goal of greatly lowering the price of paper reinforcing agent so as to permit ample use of the agent for obtaining a fixed level of paper reinforcing effect.

Japanese patent publication No. 17,051/1963 teaches that a product obtained by polymerizing 10-300 parts of acrylamide and an unsaturated carboxylic acid in the presence of parts of a water-soluble polysaccharide is used as an additive to a heater of a paper mill. The product mentioned here contains as much as 25 to 91% by weight of polysaccharide, and its paper reinforcing capacity is a little more than that of a mixture of a polysaccharide and an acrylamide copolymer. Such an improvement obtained, however, is not large enough.

It is an object of this invention to provide an acrylamide type paper reinforcing agent containing a watersoluble polysaccharide in a specified amount.

It is another object of this invention to provide an inexpensive paper reinforcing agent having high paper reinforcing capacity.

According to the present invention, a paper reinforcing agent is provided, which has, as its main ingredient, a polymer composition comprising (A) a water-soluble polysaccharide and (B) a graft polymer. The graft polymer (B) has (A) as the backbone polymer and a copolymer (C) as the branch polymer, said copolymer (C) being derived from a monomer mixture (D) of acrylamide and an unsaturated carboxylic acid. Proportion of (A) including that contained in the backbone polymer ranges from 5 to 22% by Weight, based on the entire composition. The present paper reinforcing agent may further be incorporated with an acrylamide type random copolymer (C') derivable from the monomer mixture (D).

The Water-soluble polysaccharides (A) include various carbohydrates such as, for example, Indian corn starch, wheat starch, potato starch, and sweet potato starch, and derivatives thereof. The derivatives include oxidized starches, solubilized tarches, etherified starches, etc.

The monomer mixture (D) is composed of 55-98% by weight of acrylamide and 2-20% by Weight of at least one unsaturated carboxylic acid of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid and/or crotonic acid. Besides, up to 25% by weight of one or more vinyl monomers (E) of methacrylamide, acrylonitrile, methacrylonitrile, alkyl acrylates and/or alkyl methacrylate may be contained. The alkyl esters of acrylic acid or methacrylic acid include methyl, ethyl, npropyl, isopropyl, n-butyl, isobutyl, secondary butyl, tertiary butyl, hydroxyethyl and hydroxypropyl esters.

Polymer (C) is copolymer of the monomer mixture (D), i.e. carboxylic acid-acrylamide or carboxylic acidacrylamide-vinyl compound (E). The polymer (C) constitutes branch polymer of the graft polymer (B), and has molecular weight of 2000 or more.

Polymer (C) is polymer of the monomer mixture (D) in the absence of polysaccharide (A). It has molecular weight of 2000 or more. Polymer (C) is sometime the same as Polymer (C).

Reinforcing capacity is improved conspicuously when the proportion of the water-soluble polysaccharide (A) exceeds 5% by Weight and it is maximized when the proportion falls in the neighborhood of -15% by weight. The capacity begins to decline gradually when the proportion exceeds by weight. If the proportion increases over 22%, the capacity become substantially equal to the capacity attained by using the acrylamide copolymer alone. If the proportion further increases, the capacity abruptly approaches the level of capacity calculated on the assumption that the acrylamide copolymer and the water-soluble polysaccharide act independently. Thus, the advantages derived from the graft polymer is lost practically completely.

For use in the agent of this invention, the amount of the un aturated carboxylic acid present in the monomer mixture (D) is required to fall in the range of from 2 to This is an important requirement for the paper reinforcing agent to manifest its excellent effect as contemplated. When the amount deviates from the aforesaid range, the special elfects brought about by the agent hereof cannot be observed. In this case, the paper reinforcing agent has a lower degree of reinforcing capacity than when the acrylamide copolymer is used alone. Random terpolymer such as, for example, acrylamide, acrylonitrile and unsaturated carboxylic acid, is said to be inferior to random binary copolymer such as, for example, acrylamide and unsaturated carboxylic acid, so far as paper reinforcing capacity is concerned. However, there is seen little reduction in paper reinforcing capacity, as long as the aforesaid vinyl monomer (E) is used in an amount pecified above.

The paper reinforcing agent of this invention can be obtained by either of the following methods:

(i) the monomer mixture (D) is polymerized in the presence of such an amount of the water-soluble polysaccharide (A) as to give a proportion of 522% by weight in the total composition.

(ii) the monomer mixture (D) is polymerized in the presence of the water-soluble polysaccharide (A) and then the water-soluble polysaccharide (A) and/or the acrylamide type copolymer (C) is added to the resultant polymerization product in such an amount that (A) in the total composition may be in the range of 522% by weight.

The method of (ii) is preferable, because the ratio of graft polymer (B) in the composition, the average molecular weight and an amount of the acrylamide type copolymer (C), and the proportion of unaltered water soluble polysaccharide can freely be varied. According to the method of (ii), the proportion of the graft polymer (B) in the composition can be controlled at a suitable value by adding the acrylamide copolymer (C) to the graft polymer (B). It is no matter how much grafting degree of the graft polymer (B) may be.

In carrying out the graft polymerization, it is desirable to use a medium. The medium to be used for this purpose may be either a solvent or non-solvent for the polymer being produced. Preferably, water is used as the medium. In this case, the water-soluble polysaccharide may preferably be converted in advance to a homogeneous solution by being heated to a temperature exceeding the gelatinizing point and then put to use in the form of solution.

The polymerization of monomer mixture (D) i conducted in the presence of a radical polymerization initiator. Otherwise, there may be used a compound that forms a radical upon reaction with the water-soluble polysaccharide'. The catalysts which are suitable for the polymerization in the medium of water include ammonium persulfate, potassium persulfate, hydrogen peroxide, etc. Redox catalysts made of such peroxides and such reducing substances as amines may also be used. Besides, water-soluble ceric salts, such as ceric ammonium nitrate, are also usable. These ceric salts are capable of causing water-soluble polysaccharides to form radicals. If a ceric. salt is used as the catalyst for polymerization, the proportion of graft polymer (B) in the product will be quite high. If this proportion is too high, the reinforcing capacity rather tends to decline. In this case, therefore, it is desirable to control the contents of component (B) by adding thereto a suitable amount of the acrylamide type copolymer (C) obtained by polymerizing the monomer mixture (D) and/or the water-soluble polysaccharide capacity which is obtained by using the water-soluble polysaccharide, the acrylamide type graft polymer, or the acrylamide type random copolymer alone. This shows that a mixture of the graft polymer and a specific amount of water-soluble polysaccharides has synergistic effect. In fact, a remarkably large amount of the water-solublepolysaccharides is deposited on pulp in the present paper reinforcing agent, although the polysaccharides themselves do not deposit on pulp in a large amount. This is explained with reference to preferred embodiments of the invention cited hereinafter.

Each example describes a method for manufacturing the paper reinforcing agent of this invention. The properties of the agents prepared in these examples are collectively shown in the table given at the end of the text. Parts and percent all are referred to by weight.

EXAMPLE 1 The aqueous solution of a polymer containing soluble starch by 10% based on the polymer was obtained by following the procedure of Example 1, except there were used 10 parts of soluble starch and 90 parts of a monomer mixture incorporating acrylic acid in place .of the' methacrylic acid.

EXAMPLE 3 The aqueous solution of a polymer containing soluble starch by 15 based on the polymer was obtained by following the procedure of Example 1, except there were used 15 parts of soluble starch and parts of monomer mixture. l

EXAMPLE 4 The aqueous solution of a polymer containing soluble starch by 22% based on the polymer was obtained by following the procedure of Example 1, except there were used 22 parts of soluble starch and 78 parts of monomer mixture.

The paper reinforcing agent of the present invention. has outstanding reinforcing capacity as comparedwith the EXAMPLE 5 In 900 parts of water were dissolved 15 parts of soluble starch and 85 parts of a monomer mixture consisting of 95% of acrylamide and 5% of methacrylic acid. The solution was adjusted to pH 2.5 with nitric acid and displaced thoroughly with N In the presence of 1.0 part of ceric ammonium nitrate added thereto, the solution was subjected to polymerization at 50 C. for six hours to afford the aqueous solution of a graft polymer.

EXAMPLE 6 In 450 parts of water were dissolved 45 parts of acrylamide and 5 parts of acrylic acid. The solution was adjusted to pH 7.0 and, in the presence of 1.0 part of potassium persulfate added thereto, subjected to polymerization at 60 C. for two hours to aiford the copolymer of acrylamide. The copolymer was mixed with the aqueous solution of graft polymer obtained by the procedure of Example 5, to afford a homogeneous solution.

EXAMPLE 7 Ten parts of oxidized starch was suspended in 40 parts of water and then dissolved by heating. The resultant aqueous solution was combined with the aqueous solution of graft polymer obtained by following the procedure of Example 1, to form a homogeneous solution.

EXAMPLE 8 Five (5) parts of oxidized starch was suspended in 45 parts of water and dissolved by heating to afford the aqueous solution of oxidized starch. Separately, 45 parts of acrylamide and 5 parts of acrylic acid were dissolved in 450 parts of water. The solution was adjusted to pH 7.0 and, in the presence of 0.5 part of ammonium persulfate added thereto, subjected to polymerization at 60 C. for four hours, to afford the aqueous solution of acrylamide copolymer. The two aqueous solutions thus prepared were mixed with the aqueous solution of graft polymer obtained by following the procedure of Example 2, to obtain a homogeneous solution. 7

EXAMPLE 9 Ten (10) parts of oxidized starch was dissolved by heating in 900 parts of water. In the resultant solution were further dissolved 2 parts of acrylamide, 10 parts of acrylonitrile, and 8 parts of acrylic acid. The final solution was adjusted to pH 2.5 with nitric acid. This was displaced thoroughly with nitrogen and, in the presence of 1.5 parts of ceric ammonium nitrate, subjected to polymerization at 50 C. for eight hours, to afford the aqueous solution of graft polymer (A). Separately, 5 parts of soluble starch was dissolved by heating in 45 parts of water. This solution was combined with the aqueous solution of graft polymer (A), to produce a homogeneous solution.

EXAMPLE 10 In 450 parts of water were dissolved 35 parts of acrylamide, 10 parts of methyl acrylate, and 5 parts of methacrylic acid. The solution was adjusted to pH 7.0 and, in the presence of 0.5 part of potassium persulfate added thereto, subjected to polymerization at 60 C. for four hours, to produce the aqueous solution of copolymer having acrylamide as the main component. The aqueous solution was combined with the aqueous solution of graft polymer synthesized by following the procedure of Example 5, to afford a homogeneous solution.

EXAMPLE 11 In 270 parts of water were dissolved 25 parts of acrylamide, 3 parts of methacrylic'acid, and 2 parts of acrylonitrile. The solution was adjusted to pH 7.0 and, in the presence of 0.5 part of ammonium persulfate added thereto, subjected to polymerization at 60 C. for four hours,

6 to produce the aqueous solution of acrylamide copolymer (B). The solution having 15 parts of oxidized starch dissolved by heating in 135 parts of water was combined the aqueous solution (B) mentioned above and the aqueous solution of graft polymer obtained by following the procedure of Example 1, to afford a homogeneous solution.

COMPARATIVE EXAMPLE 1 In 900 parts of water were dissolved 90 parts of acrylamide and 10 parts of acrylic acid. The solution was adjusted to pH 7.0 and, in the presence of 2 parts of potassium persulfate added thereto, subjected to polymerization at 60 C. for two hours, to produce the copolymer of acrylamide.

COMPARATIVE EXAMPLE 2 The solution obtained by dissolving 10 parts of oxidized starch under heating in 90 parts of water was combined with the aqueous solution of acrylamide copolymer obtained by following the procedure of Comparative Example 1, to afford a homogeneous solution.

COMPARATIVE EXAMPLE 3 The aqueous solution of graft polymer containing soluble starch by 25% based on the polymer was obtained by following the procedure of Example 1, except there were used 25 parts of soluble starch and 75 parts of monomer mixture.

COMPARATIVE EXAMPLE 4 In 9 00 parts of water were dissolved 15 parts of oxidized starch and parts of acrylamide. In the presence of 1.0 part of potassium persulfate added thereto, the solution was subjected to polymerization at 60 C. for three hours to afford the aqueous solution of graft polymer.

COMPARATIVE EXAMPLE 5 In 900 parts of water were dissolved 15 parts of oxidized starch and 85 parts of a monomer mixture consisting of 75% of acrylamide and 25% of methacrylic acid. The solution was adjusted to pH 7.0 and, in the presence of 1.0 part of ammonium persnlfate added thereto, subjected to polymerization at 60 C. for four hours, to afford the aqueous solution of graft polymer.

DETERMINATION OF PAPER REINFORCING CAPACITY Papers using the polymer solutions of Examples 1-11 and Comparative Examples 1-5 as paper reinforcing agents were fabricated by the Tappi standard sheet machine and then tested for strength. The papers were made of pulp LBKP (bleached kraft pulp of broad-leaf trees) having Canadian Standard freeness 390 ml. The basis weight was 60-62 g./m. As the sizing agent, rosin maleate was used in an amount corresponding to 1.5% based on the pulp. Aluminum sulfate was used in an amount corresponding to 2.0% based on the pulp. The amount of paper reinforcing agent used was 0.5% based on the pulp.

Burst factor was measured with Miillen burst strength tester and breaking length with Schopper tensile machine respectively at 20 C. and 65% RH.

The strengths thus measured of the papers using the various reinforcing compositions are shown in the following table in terms of indexes based on the strengths of paper using no reinforcing agent taken as 100.

It is clear from the table that. the paper reinforcing agents according to the present invention, indicated in the table as No. 1 through 11, exhibited reinforcing effect far exceeding the effect which could be predicted from the results of independent use of the acrylamide copoly- TABLE Starch Index of Index of content burst breaking No. Kind percent 1 factor 8 length 3 Remarks 5 135 130 Example 1. 10 142 139 Example 2. 15 145 140 Example 3. 22 135 129 Example 4. 15 140 136 Example 5. 10 140 137 Example 6. 13. 6 142 138 Example 7. 9. 9 141 137 Example 8. 14. 3 136 131 Example 9.

6. 7 135 131 Example 10. 13. 8 140 139 Example 11.

130 127 Comparative polymer. Example 1. 13.- B 9. 1 132 128 Comparative Example 2. 14- G 25 128 126 Comparative Example 3. 15 115 113 Comparative Example 4 without acid monomer. 16...-.. G 15 130 126 Comparative Example 5, acid monomer used by 25%. 17.-- Soluble 103 102 starch. 18- Oxidized 103 102 starch.

G=graft polymerization product, B =blended composition, GB= graft polymerized and blended product.

(Starch)/ (starch plus charged monomer) X100 (percent). Absolute value calculated based on the strength of paper incorporating no reinforcing agent taken as 100.

What we claim is:

1. A paper reinforcing agent having, as its main component, a composition consisting essentially of (A) a watersoluble polysaccharide selected from the group consisting of starch and modified starch and (B) a graft polymer, said graft polymer having (A) as a backbone polymer and a copolymer (C) as a branch polymer, said copolymer (C) being the reaction product of a monomer mixture (D) consisting of 80 to 98% by weight of acrylamide and 2 to 20% by weight of at least one unsaturated carboxylic acid and derivatives thereoof selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid and crotonic acid, and the proportion of (A) including that contained in the backbone polymer falling in the range of from to 22% by weight based on the entire composition.

2. A paper reinforcing agent according to claim 1, wherein the proportion of the water-soluble polysaccharide (A) falls in the range of from to 20% by Weight.

3. A paper reinforcing agent according to claim 1, wherein the water-soluble polysaccharide is a modified starch derivative selected from the group consisting of oxidized starches, and etherified starches.

4. A paper reinforcing agent having, as its main component, a composition consisting essentially of (A) a water-soluble polysaccharide selected from the group consisting of starch and modified starch, (B) a graft copolymer and (C') a copolymer derived from a monomer mixture (D), said monomer mixture (D) being made up of 80 to 98% by weight of acrylamide and 2 to 20% by weight of at least one unsaturated carboxylic acid and derivatives thereof selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, and crotonic acid, and said graft polymer (B) having (A) as a backbone polymer and the copolymer (C') as a branch polymer, the proportion of (A) in the composition falling in the range of from 5 to 22% by weight.

5. A paper reinforcing agent according to claim 4, wherein the proportion of the water-soluble polysaccharide (A) falls in the range of from 10 to 20% by weight.

6. A paper reinforcing agent according to claim 1, wherein the copolymer (C) has a molecular weight of at least 2000.

, 7. A paper reinforcing agent according to claim 1, wherein the proportion of the water-soluble polysaccharide (A) falls in the range of from 10 to 15% by weight.

8. A paper reinforcing agent according to claim 1, wherein the unsaturated acid is acrylic acid.

9. A paper reinforcing agent having as its main compo nent a composition consisting essentially of (A) a watersoluble polysaccharide selected from the group consisting of starch and modified starch and (B) a graft polymer, said graft polymer having the watersoluble polysaccharide (A) as a backbone polymer and a copolymer (C) as a branch polymer, said copolymer (C) being the reaction product of a monomer mixture consisting essentially of from 55 to 98% by weight of acrylamide, 2 to 20% by weight of an unsaturated carboxylic acid and derivatives thereof selected from the group consisting of acrylic acid, methacrylic acid, maleic anhydride, itaconic acid and crotonic acid, and up to 25% by weight of at least one vinyl monomer selected from the group consisting of methacrylamide, acrylonitrile, methacrylonitrile, alkyl acrylates and alkyl methacrylates, and the proportion of the water-soluble polysaccharide (A), including that contained in the backbone polymer, falling within the range of from 5 to 22% by weight based on the entire weight of the composition.

10. A paper reinforcing agent having as its main component a composition consisting essentially of (A) a watersoluble polysaccharide selected from the group consisting of starch and modified starch, (B) a graft copolymer and (C') a coplymer derived from a monomer mixture (D), said monomer mixture (D) consisting essentially of from 55 to 98% by weight of acrylamide, 2 to 20% by weight of an unsaturated carboxylic acid and derivatives thereof selected from the group consisting of acrylic acid, methacrylic acid, malcic anhydride, itaconic acid and crotonic aid, and up to 25% by weight of at least one vinyl monomer selected from the group consisting of methacrylamide, acrylonitrile, methacrylonitrile, alkyl acrylates, and alkyl methacrylates, and said graft polymer (B) having the watersoluble polysaccharide (A) as a backbone polymer and (C') as a branch polymer, the proportion of (A) in the composition falling in the range of from 5 to 22% by weight.

11. A paper reinforcing agent according to claim 9, wherein the unsaturated acid is acrylic acid and the vinyl monomer is acrylonitrile.

12. A paper reinforcing agent according to claim 9, wherein the copolymer (C) has a molecular weight of at least 2000.

13. A paper reinforcing agent according to claim 10, wherein the copolymer (C') has a molecular weight of at least 2000.

14. A paper reinforcing agent according to claim 10, wherein the unsaturated acid is acrylic acid and the vinyl monomer is acrylonitrile.

15. A paper containing reinforcing amount of the reinforcing agent of claim 1.

16. A paper containing a reinforcing amount of the reinforcing agent of claim 4.

17. A paper according to claim 15, wherein the amount of reinforcing agent contained therein is 0.5% based on the weight of the pulp.

References Cited UNITED STATES PATENTS 3,095,391 6/1963 Brockway et al. 260-17.4 3,138,564 6/1964 Borunsky 260-17 3,635,857 1/1972 Restaino et al. 260--17.4 3,640,925 2/ 1972 Tovzinsky et a1. 26017.4 GC 3,687,884 8/1972 Haung 26029.6

WILLIAM H. SHORT, Primary Examiner E. WOODBERRY, Assistant Examiner US. Cl. XIR.

162175; 26017.4 GC, 17.4 ST

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 785,921 Dated January 15. I974 Inventor(s) Fumio Ide, Tsuneo Kodama, and Yahide Kotake It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 6, change Nitto Kagyo Co. Ltd." to Nitto Kagaku Kogyo C0., Ltd. 7 between lines 8 and 9, insert Claim priority, application Japan, December 26, 1970, 129611/70 Signed and sealed this 9th day of July 1974.

(SEAL) Attesc:

MCCOY M. GIBSON, JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents po'wso I p USCOMM-DC 6O376-P69 Ui5. GOVERNMENT PRINHNG OFFICE I969 0-366-334