JPH0215679B2 - - Google Patents

Description

[Detailed description of the invention]

(A) Industrial Application Field The present invention relates to a paper strength enhancer made of cation-modified polyvinyl alcohol. (B) Conventional technology Polyvinyl alcohol (hereinafter abbreviated as PVA)
has been known as a typical synthetic water-soluble polymer and has been used in a wide range of industrial applications as a raw material for synthetic fiber vinylon or as a sizing agent. In particular, PVA's film-forming properties and strength are effectively used for paper surface sizing and fiber warp sizing. However, on the other hand, although PVA is expected to be effective as a sizing agent, that is, a paper strength enhancer, which is used internally during paper making to improve the strength of paper, it has not been applied to date. This is the actual situation. This is because PVA is essentially a so-called nonionic polymer that does not contain ionic groups, and even if a PVA aqueous solution is added to the papermaking system, it will not be substantially adsorbed by the pulp. It has been proposed to use PVA as a paper strength enhancer by modifying it by introducing anionic groups such as carboxyl groups and adsorbing it to the pulp using sulfuric acid (Japanese Patent Publication No. 46-401, No. 46-38601). issue)
However, it has not yet been used industrially. This is denatured under acidic conditions when combined with sulfuric acid.
This seems to be attributable to the fact that the anionic groups in PVA form intramolecular esters with hydroxyl groups and do not function as effective active sites, so that the fixation to the pulp cannot be improved as intended. It is known that instead of anionic groups, cationic groups also have the effect of fixing to pulp, and in this case, it is not necessary to use sulfuric acid together, and starch or polyacrylamide into which cationic groups have been introduced has been industrially produced. There is. Therefore, it is possible to consider introducing cationic groups into PVA to make it possible to fix it in pulp and to demonstrate the excellent strength properties of PVA. Each of these methods has its own difficult problems, and the reality is that no industrially viable solution has yet been found. (C) Problems to be solved by the invention Under these circumstances, the inventors have found a stable and effective solution.
By establishing an industrially inexpensive manufacturing method that introduces cationic groups into PVA, we have achieved cationic modification.
The present invention was completed as a result of intensive studies aimed at obtaining a paper strength enhancer containing PVA as a main component. That is, the purpose of the present invention is to obtain a paper strength enhancer whose main ingredient is cationically modified PVA containing vinyl alcohol units and cationic groups. The object of the present invention is to produce a novel and excellent paper strength enhancer by imparting a cationic charge and imparting excellent adsorption performance to pulp and the like. (D) Means for solving the problems The paper strength enhancer of the present invention has the general formula Contains 0.01 to 20 mol% of copolymerized units represented by
It is characterized by being composed of a cationic group-modified polyvinyl alcohol having a degree of saponification of vinyl ester units of 70 mol% or more and a Bruckfield viscosity of 4% aqueous solution at 20°C of 4 centipoise or more. R ¹ is a hydrogen atom or a methyl group, and A is

[Formula] (R ⁶ , R ⁷ , R ⁸ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is 0 to 2
indicates an integer. ), and B is

[expression] or

[Formula] (R ² , R ³ , and R ⁴ are lower alkyl groups that may contain substituents, and X ^- represents a negative group that forms a salt with ammonium nitrogen.)
It is. Among them, A in the general formula () is (-CH ₂ -CH ₂ -CH ₂ )-, and B is -N(CH ₃ ) ₂
It is preferable that A is (-CH ₂ -CH ₂ -CH ₂
)- and B is -N ⁺ (CH ₃ ) _3.Cl ^- . Furthermore, A is (-C( _CH3 ) ₂ - _CH2 - _CH2 )-,
It is even more preferable that B is -N( _CH3 ) ₂ or -N ^{+ (} _CH3 ) _3.Cl- . The cation-modified PVA, which is the main component of the paper strength agent of the present invention, is, for example, vinyl ester and the general formula [In the formula, R ¹ : hydrogen atom or methyl group A:

[Formula] (R ⁶ , R ⁷ , R ⁸ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is 0 to 2
indicates an integer. ) B:

[expression] or

[Formula] (R ² , R ³ , and R ⁴ are lower alkyl groups that may contain substituents, and X ^- represents a negative group that forms a salt with ammonium nitrogen.) ] is copolymerized with the polymerizable monomer represented by B in the presence of a radical polymerization initiator, and then B is copolymerized with

In the case of [Formula], vinyl ester units in the copolymer are partially converted by applying an alkali or acid catalyst to an alcohol solution of the copolymer, with or without quaternizing with a quaternizing agent. Alternatively, it can be highly saponified to form vinyl alcohol units, and B can be

[Formula] and if the above-mentioned quaternization is not carried out, a quaternizing agent is used after the saponification reaction.

It is produced by quaternizing or not quaternizing the formula. In addition, as another method for producing the copolymer of the present invention, vinyl ester and the general formula (In the formula, R ¹ and A have the same meanings as in the general formula (), and Y means a halogen atom.) The vinyl ester units in the copolymer are partially or highly saponified by acting on the polymer with an alkali or acid catalyst to form vinyl alcohol units, and before or after this saponification reaction, dialkylamine or A method in which a trialkylamine is used can be mentioned. However, compared to this method, the above-mentioned method, ie, the method using monomer (), is industrially superior, and this case will be explained below as an example. Vinyl esters that can be used in producing the copolymer of the present invention include vinyl acetate, vinyl propionate, vinyl formate, etc., but vinyl acetate is preferred from an economical standpoint. Further, the cationic polymerizable monomer containing an amino group used in the present invention is represented by the above-mentioned general formula (). R ¹ in the general formula () is a hydrogen atom or a methyl group, and is preferably a hydrogen atom since the polymerization rate in the copolymerization reaction is high. B is a tertiary amino group

[expression] or Quaternary ammonium salt

[Formula], R ² , R ³ and R ⁴ represent a lower alkyl group which may contain a substituent, and X represents a negative group that forms a salt with ammonium nitrogen. R ² , R ³ , and R ⁴ are all preferably methyl groups for normal purposes, but for special purposes, they may be lower alkyl groups such as ethyl or propyl groups, or methylol groups for the purpose of imparting reactivity.
Alternatively, lower alkyl groups containing substituents such as aminoalkyl groups are also used for the purpose of improving the density of cationic groups. X is a halogen atom such as chlorine, silium, iodine, or
CH ₃ OSO ₃ or CH ₃ C ₆ H ₄ SO ³ is preferred, but
In particular, a chlorine atom is preferred from the viewpoint of economy, safety, or physical properties of the copolymer. In many cases, it is preferable for the amino group to be in the form of a quaternary ammonium salt since it exhibits cationic performance regardless of the hydrogen ion concentration of the system, but it is preferred that the amino group be in the form of a tertiary amine, that is, B.

It may be necessary to use polymerizable monomers of the form. When using a tertiary amine monomer, alkyl halide,
Quaternization may be carried out using a quaternizing agent such as dimethyl sulfate or methyl P-toluenesulfonate, particularly by bubbling methyl chloride gas into the solution.
% quaternization is possible. The alcohol solution of the quaternized copolymer can be directly subjected to the saponification reaction described below, and can be made into a copolymer containing a quaternary ammonium salt. When a tertiary amine monomer is used, a saponification reaction is carried out without quaternization, the resulting copolymer is made into an aqueous solution, and the above-mentioned quaternizing agent, especially methyl chloride, is added to the solution. May be quaternized. In addition, when using a tertiary amine monomer, an appropriate acid salt such as hydrochloride, sulfate,
It may also be used as an acetate salt, in which case the hydrogen ion concentration is preferably adjusted to neutrality at a suitable point after carrying out the quaternization reaction. The present invention also includes a copolymer obtained by carrying out copolymerization and saponification reaction using a tertiary amine monomer without quaternization, but in this case, the cationic property is effectively exhibited. In many cases, an aqueous solution is used in an acidic state. A, which is a group that connects the nitrogen atom in the amino group B and the nitrogen atom in the amide group, is

[Formula] (R ⁶ , R ⁷ and R ⁸ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n represents an integer of 0 to 2.)
From copolymerizability, A is (-CH ₂ -CH ₂ -CH ₂
)- is preferred, and (-C( _CH3 ) ₂ - _CH2 - _CH2 )- is more preferred. The following are representative monomers that satisfy the above-mentioned structural characteristics and meet the purpose. N-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide Trimethyl-3-(1-acrylamide-1,
1-dimethyl-propyl)ammonium chloride The above two monomers are relatively inexpensive to produce industrially, have a fast copolymerization rate with vinyl esters, especially vinyl acetate, and can synthesize copolymers with a high degree of polymerization. It is particularly preferable because the stability of the amide bond is particularly high, which meets the purpose of the present invention. This monomer is disclosed in West German Patent No. 2254905 or US Patent No. 3666810, US Pat.
No. 3917594, No. 3943114, etc., and it has been shown that it can be copolymerized with many polymerizable monomers including vinyl esters such as vinyl acetate. There is no known copolymer produced by this method, and it is completely unknown that a copolymer having excellent industrially important performance as shown in the present invention can be obtained. Furthermore, other monomers that can be used for the purposes of the present invention include: N-(3-dimethylaminopropyl)acrylamide _CH2 =CHCONH-CH2CH2CH2N( _{CH3 ) 2trimethyl} -3-(1- _{acrylamidopropyl} ) _ammonium chloride _CH2 = _{CHCONH - CH2CH2CH2} N ⁺
(CH ₃ ) ₃ Cl ^- Copolymerization of the above-mentioned polymerizable monomer containing an oticane group and vinyl ester can be carried out using any polymerization method: bulk polymerization, solution polymerization, suspension polymerization, or emulsion polymerization. Although solution polymerization is usually preferred for many purposes of this invention. As the solvent used, lower alcohols, particularly methanol, are industrially preferred. Bulk polymerization and solution polymerization can be carried out either batchwise or continuously, while suspension polymerization and emulsion polymerization are usually carried out batchwise. In the case of a batch method, it is well known that the monomer composition changes with the polymerization rate according to the comonomer reactivity ratio (r ₁ , r ₂ ), but when the monomer composition is constant, In order to obtain a copolymer having a uniform copolymerization composition, it is desirable to adopt a so-called semi-batch method in which one or both monomers are added so that the following is achieved. One way to calculate the amount added in this case is to use RJHanna.
Ingustrial and Engineering Chemistry;
The formula presented in Vol. 49, No. 2, 208-209 (1957) is mentioned. In the case of continuous multi-column copolymerization, for the same reason, it is desirable to add monomers to the second and subsequent columns so that the monomer composition in each column is constant. As the polymerization initiator, known initiators for radical polymerization such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, and acetyl peroxide can be used. The polymerization reaction temperature is usually selected from the range of 50°C to the boiling point. The reaction rate of the monomers is appropriately determined depending on the purpose, such as economical efficiency and adjustment of the degree of polymerization. After the copolymerization is completed, if vinyl ester remains in the reaction solution, it is necessary to separate and remove it by distillation or the like. Cationic monomers may be removed,
Moreover, there are many cases where there is no problem even if it is left in place. The vinyl ester portion of the copolymer thus obtained is then saponified. It is usually advantageous to carry out the saponification reaction as a solution of the copolymer in alcohol, especially methanol. Not only anhydrous alcohols but also those containing a small amount of water can be used depending on the purpose, and organic solvents such as methyl acetate and ethyl acetate may be optionally contained. As saponification catalysts, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alcoholates such as sodium methylate and potassium methylate, alkaline catalysts such as ammonia, or hydrochloric acid,
Acid catalysts such as sulfuric acid may be used. Among these, sodium hydroxide is economically advantageous from an industrial standpoint.
The saponification temperature is usually selected from the range of 10 to 50°C.
It is undesirable to leave the product under strong alkaline or acidic conditions at high temperatures for a long time because the amide bond will gradually decompose, but it is usually not necessary to leave it under such conditions and the amide bond will decompose during saponification. It is kept stable without any problems. Through the saponification reaction, vinyl ester units are partially or highly saponified and converted into vinyl alcohol units, but this conversion rate, or degree of saponification, can be set to any value depending on the purpose of use of this cation-modified PVA. You can, but
The range of degree of saponification that can be produced industrially advantageously is usually
It is 70 mol% or more. If the content of cationic monomers in cation-modified PVA is 10 mol% or less, when the saponification reaction proceeds in alcohol, a white gel or precipitate will be formed as in the case of ordinary PVA. A white polymer powder can be obtained by crushing, washing and drying as necessary. The content of cationic monomer in the copolymer is
If the content is 10 mol% or more, or even if the content is 10 mol% or less, the product may not precipitate if the degree of saponification achieved is low, but in this case, an organic solvent such as methyl acetate is used as a precipitant. A method of precipitating it is adopted. The cation-modified PVA of the present invention can generally be stored and transported in powder form, similar to PVA, and when used, a uniform paste solution can be obtained by dispersing it in water and heating it while stirring. Regarding the composition ratio of each component of the cation-modified PVA of the present invention, firstly, the cationic monomer component is 0.01
It is preferably selected from the range of 0.05 to 5 mol%, particularly 0.05 to 5 mol%. If it is less than 0.01 mol%, the fixing effect on pulp will not be sufficient when used as a paper strength enhancer, while if it is more than 20 mol%, the fixing effect will be reduced. In addition, the degree of saponification is 70 mol% or more,
Particularly preferred is a content of 85 mol% or more in terms of physical properties. If it is less than 70 mol%, the strength decreases significantly and it is not suitable as a paper strength enhancer. In addition, the degree of polymerization of the cation-modified PVA of the present invention is 4.
% aqueous solution at 20° C. is usually selected to have a Bruckfield viscosity of 4 centipoise or more, especially 20 centipoise or more. (E) Action and Effects of the Invention The cationically modified PVA of the present invention, which has the above-mentioned components and is useful as a paper strength enhancer, looks similar to PVA at first glance, but its fixability to paper pulp is better than that of PVA. It is easily distinguished from other PVAs by its distinctive property of being extremely high. In other words, while conventional PVA basically does not show any fixation to pulp slurry, the paper strength agent based on the copolymer of the present invention shows no fixation in the range of approximately 1% addition to pulp. , usually shows a fixing rate of 80 to 100% of the total amount of copolymer, and shows a fixing rate of 50% or more even under bad conditions. Due to this outstanding performance, this copolymer can be used as an internal paper strength enhancer by the beater addition method, and its characteristics are as follows. 1) High efficiency in improving dry paper strength. 2) Excellent water resistance. 3) Pigment yield is improved. 4) Drainage sludge is reduced. 5) Neutral papermaking is possible. The paper strength enhancer of the present invention has high performance compared to conventionally known starch-based and polyacrylamide-based paper strength enhancers. This is thought to be due to the fact that its main skeleton structure is PVA, which provides a high paper strength improvement effect. The paper strength enhancer of the present invention can be carried out by a so-called beater addition method in which the paper strength enhancer is added to an aqueous pulp dispersion, adsorbed onto pulp fibers, and then subjected to conventional paper making and drying. In addition, it may be used by impregnating coating by spraying or size press. The amount added when using the beater addition method varies depending on the paper type and purpose, but it is added in the range of 0.05 to 5% of the paper strength enhancer solid content based on dry pulp weight, and generally 0.1 to 2%. A sufficient effect can be obtained within this range. (F) Examples The present invention will be specifically explained below using examples. Example 1 500 g of vinyl acetate, 75 g of methanol, and 3 g of N-(3-dimethylaminopropyl)acrylamide were placed in a flask equipped with a stirrer, a thermometer, a dropping funnel, and a reflux condenser, and the flask was placed in a constant temperature bath and stirred. After purging the system with nitrogen, the internal temperature was raised to 60°C. In this system, 2,2'-azobisisobutyronitrile
0.125g was added together with 50g of methanol to initiate polymerization. During the polymerization time of 2 hours and 10 minutes, 20 g of a 25% methanol solution of N-(3-dimethylaminopropyl)acrylamide was added dropwise at a constant rate. The solid content concentration in the system at the time of termination of polymerization was 9.9%. Attach the gas introduction pipe and vacuum distillation device to the flask,
After blowing methanol vapor into the polymerization reaction solution under reduced pressure to drive out unreacted vinyl acetate monomer,
A 31% methanol solution of the copolymer was obtained. This copolymer contains 5.0 mol% of N-(3-dimethylaminopropyl)acrylamide units and vinyl acetate units.
It was confirmed by nuclear magnetic resonance analysis that it contained 95.0 mol%. Methanol solution of this copolymer80
While stirring the mixture at 40° C., 5.8 ml of 1N caustic soda methanol solution was added thereto, mixed well, and left to stand. After 8 minutes and 30 seconds, the entire system gelled. Furthermore
After 20 minutes, this gel was pulverized using a pulverizer, washed with methanol, and dried to obtain a white polymer powder. This copolymer has excellent solubility in water, and its 4
% aqueous solution at 20°C was 38 centipoise. The proton nuclear magnetic resonance spectrum of a heavy aqueous solution of this copolymer is shown in FIG. The absorption at 2.79PPM is attributed to the protons of the two methyl groups bonded to the nitrogen atom of the amino group in the N-(3-dimethylaminopropyl)acrylamide unit, and from the absorption intensity, it is determined that N-(3-dimethylaminopropyl) Acrylamide unit is 5.0 mol%
It was analyzed that it was contained. Furthermore, the degree of saponification of vinyl acetate units was 99.9 mol%. That is, the obtained copolymer is substantially a copolymer of N-(3-dimethylaminopropyl)acrylamide-vinyl alcohol. Example 2 80 g of a methanol solution (31%) of the N-(3-dimethylaminopropyl)acrylamide-vinyl acetate copolymer copolymerized in Example 1 was placed in a flask equipped with a stirrer, a gas inlet tube, and a reflux condenser. was added, and methyl chloride gas was bubbled therein for 3 hours while stirring. While stirring at 40°C, 5.8 ml of 1N caustic soda methanol solution was added, mixed well, and left to stand. After 6 minutes, the entire system gelled. After standing for 20 minutes, the mixture was crushed, washed with methanol, and dried to obtain a white copolymer powder. This powder has excellent solubility in water, and a 4% aqueous solution thereof had a Fulskfield viscosity of 35 centipoise at 20°C.
The proton nuclear magnetic resonance spectrum of the obtained copolymer is shown in FIG. The absorption at 2.79PPM disappeared, and instead, an absorption at 3.13PPM which was attributed to the protons of three methyl groups bonded to the nitrogen atom of the quaternary ammonium salt was found. Therefore, all the amino groups in the N-(3-dimethylaminopropyl)acrylamide unit are quaternized to form trimethyl-3-(1
-acrylaminopropyl) ammonium chloride unit, and its content is 5.0 mol% based on the absorption intensity of 3.13 PPM. In addition, the degree of saponification of vinyl acetate units was determined to be 99.9 mol%. Example 3 2500 g of vinyl acetate in a 5 flask equipped with a stirrer, thermometer, addition funnel and reflux condenser,
697 g of methanol and 4.8 g of white powder of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl) ammonium chloride were placed in a constant temperature bath, and the system was replaced with nitrogen while stirring.
After raising the internal temperature to 60°C, 3.5 g of 2,2'-azobisisobutyronitrile was added together with 50 g of methanol to initiate polymerization. During a polymerization time of 3 hours, 362 g of a 50% methanol solution of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl) ammonium chloride was added dropwise at a constant rate. The solid content concentration in the system at the time of termination of polymerization was 49.8%. A gas inlet pipe and a vacuum distillation device were attached to the flask, and methanol vapor was blown into the polymerization reaction solution under reduced pressure to drive out unreacted vinyl acetate monomer.
A 44.3% methanol solution of the copolymer was obtained. It was confirmed by nuclear magnetic resonance analysis that this copolymer contained 4.0 mol% of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl)ammonium chloride units and 96.0 mol% of vinyl acetate units. . 812g of methanol solution of this copolymer
While stirring the mixture at 35°C, 42.1 ml of 2N caustic soda methanol solution was added thereto, mixed well, and left to stand. The entire system gelled after 7 minutes and 20 seconds. After another 20 minutes, the gel was pulverized using a pulverizer, washed with methanol, and dried by heating to obtain a white polymer powder.
The proton nuclear magnetic resonance spectrum of the obtained polymer in a heavy aqueous solution is shown in FIG. The absorption of 3.13PPM is trimethyl-3-(1-acrylamide-1,
3 bonded to the quaternary ammonium nitrogen atom in the 1-dimethyl-propyl) ammonium chloride unit
trimethyl-3-(1-acrylamide-
It was confirmed that the content of 1,1-dimethyl-propyl) ammonium chloride units was 4.0 mol%. On the other hand, the degree of saponification of the vinyl acetate unit is 99.3 mol%, and the nitrogen content according to the Kjeldahl method is 2.17% by weight, which is trimethyl-3-(1
-Acrylamide-1,1-dimethyl-propyl)ammonium chloride units correspond to 4.0 mol%, which agrees with the results of the above nuclear magnetic resonance analysis. The Bruckfield viscosity of a 4% aqueous solution at 20℃ is
It was 34.1 centipoise. Example 4 154g of methyl acetate was added to 700g of methanol solution from which residual vinyl acetate monomer was removed after copolymerization in Example 3.
After adding 150 g of methanol and mixing well to make the mixture homogeneous, 15.7 ml of 2N caustic soda methanol solution was added thereto while stirring at 40°C, and after mixing well, the mixture was left to stand. The entire system gelled after 14 minutes and 50 seconds. After standing for another 20 minutes, the gel was pulverized using a pulverizer, washed with methanol, and dried to obtain a white polymer powder.
The obtained shield polymer is a copolymer containing 4.0 mol% of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl)ammonium chloride units and a saponification degree of vinyl acetate units of 88.0 mol%. The Bruckfield viscosity of its 4% aqueous solution at 20°C was 30.4 centipoise. Example 5 In an apparatus similar to Example 3, 3000 g of vinyl acetate,
108 g of methanol and 1.1 g of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl) ammonium chloride were charged, and 0.15 g of 2,
Copolymerization was initiated by addition of 2'-azobisisobutyronitrile and 50 g of methanol. Polymerization time
20 g of a 50% methanol solution of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl) ammonium chloride was added dropwise at a constant rate during 1.0 hour. The solid content concentration in the system when polymerization is stopped is
It was 15.7%. After removing the remaining vinyl acetate monomer by the same operation as in Example 3, a copolymer methanol solution with a solid content concentration of 31.7% was obtained. To 960 g of this methanol solution was added 39.2 ml of 2N caustic soda methanol solution while stirring at 40°C, mixed well, and then left to stand. The entire system gelled after 5 minutes and 35 seconds. After another 20 minutes, the gel was pulverized using a pulverizer, washed with methanol, and then dried by heating to obtain a white copolymer powder. The nitrogen content of this copolymer is 0.492
In weight percent, this corresponds to a content of 0.8 mole percent trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl)ammonium chloride units. Saponification degree of vinyl acetate unit is 99.4
The Bruckfield viscosity of a 4% aqueous solution at 20° C. was 167 centipoise. Example 6 In an apparatus similar to Example 3, 3000 g of vinyl acetate,
By charging 283 g of methanol and 0.5 g of N--(1,1-dimethyl-3-dimethylaminopropyl)acrylamide hydrochloride, and adding 0.3 g of 2,2'-azobisisobutyronitrile and 50 g of methanol. Copolymerization was started. During the polymerization time of 2.5 hours, 41 g of a 25% methanol solution of N-(1,1-dimethyl-3-dimethylaminopropyl)acrylamide hydrochloride was added dropwise at a constant rate. The solid content concentration in the system at the time of termination of polymerization was 30.3%. After removing the remaining vinyl acetate monomer by the same operation as in Example 3, a copolymer methanol solution with a solid content concentration of 33.0% was obtained. 1061g of this methanol solution
While stirring at 40°C, 51 ml of 2N caustic soda methanol solution was added, mixed well, and left to stand. The entire system gelled after 2 minutes and 15 seconds. After standing for 20 minutes, the gel was pulverized using a pulverizer, washed with methanol, and then dried by heating to obtain a white copolymer powder. This copolymer is N
It was analyzed to contain 0.4 mol% of -(1,1-dimethyl-3-dimethylaminopropyl)acrylamide units. The saponification degree of vinyl acetate unit is
The Bruckfield viscosity of a 4% aqueous solution at 20° C. was 71.2 centipoise. Example 7 N-(1,1-dimethyl-
3-dimethylaminopropyl)acrylamide-
Methyl chloride gas was bubbled into two flasks while stirring 1000 g of a 5% aqueous solution of vinyl alcohol-vinyl acetate copolymer. After bubbling for 5 hours, the copolymer in the aqueous solution was analyzed by proton nuclear magnetic resonance, and it was found that all the amino groups were quaternized and trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl) ammonium chloride. It was confirmed that the copolymer contained 0.4 mol% of Testing as a paper strength enhancer Canadian Standard Freeness 565
A predetermined amount of the aqueous solution of the copolymer synthesized in each of the examples and the polymer of the comparative example was added and mixed into 1% aqueous slurry of pulp (NBKP). Then, after 3 minutes, paper was made using a Tatsupi Standard paper machine to a basis weight of 80±5g/ ^m2 , and 3.5Kg/m2.
After press dehydration at cm ² for 5 minutes, use a rotating drum dryer.
After drying at 110℃ for 1 minute to form paper, 20℃, 65%
Humidity was controlled at RH for 48 hours. On the other hand, the white water during paper making was collected and concentrated, and the concentration of the copolymer in the white water was determined by JHFinley, Journal of Analytical
Chemistry, Vol. 33, No. 13, 1925 (1961) was used to determine the fixation rate of each added copolymer to the pulp. After humidity conditioning, the paper sample was measured for tensile strength (breaking length) in accordance with JIS-8113 and specific bursting strength in accordance with JIS-8112. The measurement results are shown in Table 1. Table 1 shows, as comparative examples, systems without paper strength additives and ordinary PVA without cationic groups (Kuraray Poval PVA-177, saponification degree 98.5%, polymerization degree
1750), and acrylamide copolymer-modified PVA
(acrylamide modification degree 5 mol%, saponification degree 98.3
%, degree of polymerization 1500), and acrylamide copolymerization modification (degree of PVA acrylamide modification 50 mol%, degree of saponification 97.5%, degree of polymerization 1200) for a sample made in the same manner.

【table】

[Table] PVA-117 that does not contain cationic groups and acrylamide copolymer-modified PVA (5 mol% modified and 50 mol%
In contrast, paper strength enhancers based on the novel cationic water-soluble copolymer of the present invention all show a high fixation rate, whereas the paper strength enhancers based on the novel cationic water-soluble copolymer of the present invention show virtually no fixation and do not exhibit paper strength. , and has an excellent paper strength enhancement effect.

[Brief explanation of drawings]

Figures 1 to 3 are proton nuclear magnetic resonance spectra with a main frequency of 90MHz (VARIAN, FM-
390), both of which are 5% of the copolymer of the present invention.
This is a measurement of a heavy aqueous solution. Figure 1 shows N-
(3-dimethylaminopropyl)acrylamide-vinyl alcohol copolymer; Figure 2 shows trimethyl-3-(1-acrylamidopropyl)ammonium chloride, which is a quaternized product of the former copolymer.
Vinyl Alcohol Copolymer, FIG. 3 is a spectral diagram of trimethyl-3-(1-acrylamido-1,1-dimethyl-propyl)ammonium chloride-vinyl alcohol vinyl acetate copolymer. In each figure, the horizontal axis indicates the chemical shift in PPM from a reference substance (trimethylsilylpropionic acid- _d4 -sodium salt) coexisting in the sample solution.

Claims (1)

[Claims] 1. General formula [In the formula, R ¹ : Hydrogen atom or methyl group A: [Formula] (R ⁶ , R ⁷ , R ⁸ represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and n is 0 to 2
indicates an integer. ) B: [Formula] or [Formula] (R ² , R ³ , and R ⁴ are lower alkyl groups that may contain substituents, and X ^- represents a negative group that forms a salt with ammonium nitrogen.) , respectively. ] Contains 0.01 to 20 mol% of copolymerized units represented by
A paper strength enhancer comprising a cationically modified polyvinyl alcohol having a degree of saponification of vinyl ester units of 70 mol% or more and a Bruckfield viscosity of 4% aqueous solution at 20°C of 4 centipoise or more. 2 A is (-C(CH ₃ ) ₂ -CH ₂ -CH ₂ )-, and B
The paper strength enhancer according to claim 1 _{, wherein is -N(CH3)2 .} 3 A is (-C(CH ₃ ) ₂ -CH ₂ -CH ₂ )-, and B
The paper strength enhancer according to claim 1, wherein is -N ⁺ (CH ₃ ) _3.Cl ^- . 4 A is (-CH ₂ -CH ₂ -CH ₂ )- and B is -N
The paper strength enhancer according to claim 1, which is ( _CH3 ) ₂ . 5 A is (-CH ₂ -CH ₂ -CH ₂ )- and B is -
The paper strength enhancer according to claim 1, which is N ⁺ (CH ₃ ) ₃ ·Cl ⁻ .