JPH11286891A - Paper reinforcing agent for filling in papermaking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a paper reinforcing agent for filling in a papermaking, excellent in paper strengths and stability in storage by preparing an aqueous solution containing a polyacrylamide containing carboxyl groups and a chelating agent. SOLUTION: This paper reinforcing agent is obtained by preparing an aqueous solution obtained by blending a polyacrylamide containing carboxyl groups, having 100,000-5,000,000 weight-average molecular weight and consisting of constituting monomers of a polyfunctional monomer such as 1,3,5- triacryloylhexahydro-S-triazine and/or an N-substituted (meth)acrylamide expressed by the formula: CH2 =C(R<1> )CONR<2> (R<3> ) (R<1> is H or methyl; R<2> is H so a 1-4C alkyl, R<3> is a 1-4C alkyl), e.g. N,N-dimethylacrylamide, with at least one kind of a chelating agent selected from a group of malic acid, tartaric acid and lactic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an internal paper strength agent for papermaking.

[0002]

2. Description of the Related Art In the papermaking industry, polyacrylamide has been conventionally used as an internal paper strength agent for paper. Since the internal paper strength agent containing such polyacrylamide is usually used as an aqueous solution, it is stored in an aqueous solution state.

[0003] Such polyacrylamide is copolymerized with various monomers or variously modified in order to improve the fixability to pulp and improve the paper strength. For example, copolymerization of polyacrylamide and a carboxyl group-containing monomer to introduce a carboxyl group into polyacrylamide is one of the common means. However, when the carboxyl group-containing polyacrylamide is stored in the state of an aqueous solution, it tends to gel due to poor stability. In particular, storage stability of amphoteric polyacrylamide having a cationic group together with a carboxyl group, and carboxyl group-containing polyacrylamide having a high molecular weight by copolymerizing a polyfunctional monomer or the like is generally not good.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a papermaking internal paper strength agent comprising an aqueous solution containing a carboxyl group-containing polyacrylamide and having excellent storage stability. .

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems. As a result, the tendency of poor storage stability of carboxyl group-containing polyacrylamide is proportional to the concentration of metal ions such as iron present in the aqueous solution. It was determined to be due to chelation. And, in order to prevent the chelation of the carboxyl group by the metal ion, by pre-containing the chelating agent in the aqueous solution containing the carboxyl group-containing polyacrylamide, if the metal ion in the aqueous solution is effectively chelated, The present inventors have found that a carboxyl group-containing polyacrylamide is stably present in an aqueous solution, and that an internal additive for papermaking having excellent storage stability can be obtained. The present invention has been completed based on such new knowledge.

That is, the present invention relates to an internal strength agent for papermaking comprising an aqueous solution containing a carboxyl group-containing polyacrylamide and a chelating agent.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The carboxyl group-containing polyacrylamide of the present invention is a polyacrylamide containing acrylamide as a main component and can be used without any particular limitation as long as it has a carboxyl group in the molecule. Examples of the carboxyl group-containing polyacrylamide of the present invention include acrylamide, a carboxyl group-containing vinyl monomer, and a copolymer obtained by copolymerizing a vinyl monomer other than the above as required.

The proportion of acrylamide to be used is usually preferably 50 to 99 mol% based on the total mol of vinyl monomers. The lower limit of the use ratio of acrylamide is more preferably 70 mol%, and the upper limit is more preferably 98 mol%. In addition,
If the use ratio of acrylamide is less than 50 mol%, the paper strength is not sufficient.

As the carboxyl group-containing vinyl monomer, (meth) acrylic acid ｛(meth) acrylic acid means acrylic acid and / or methacrylic acid. Hereinafter, (meta) has the same meaning.モ ノ, monocarboxylic acids such as crotonic acid and (meth) allyl carboxylic acid, dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid, and muconic acid; and alkali metal salts such as sodium salts and potassium salts of these various organic acids. , Ammonium salts and the like. Among these, (meth) acrylic acid and itaconic acid are preferred.

The proportion of the carboxyl group-containing vinyl monomer used is 1 to 50 relative to the total mole of the vinyl monomer.
Molar% is preferred. The lower limit of the use ratio of the carboxyl group-containing vinyl monomer is 2 mol%, and the upper limit is 10 mol%.
Molar% is more preferred. If the use ratio of the carboxyl group-containing vinyl monomer is less than 1 mol%, the paper strength is not sufficient.

As the vinyl monomer other than the above, various types can be mentioned. For example, anionic vinyl monomers include vinyl sulfonic acid, styrene sulfonic acid,
2-acrylamido-2-methylpropanesulfonic acid,
Organic sulfonic acids such as (meth) allylsulfonic acid; and alkali metal salts such as sodium salt and potassium salt of these various organic acids, and ammonium salts.

As the cationic vinyl monomer, for example, vinyl having a tertiary amino group such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylamide, diethylaminopropyl (meth) acrylamide, etc. By reacting monomers or their salts of inorganic or organic acids such as hydrochloric acid, sulfuric acid and acetic acid, or the tertiary amino group-containing vinyl monomer with quaternizing agents such as methyl chloride, benzyl chloride, dimethyl sulfate and epichlorohydrin; Examples of the obtained quaternary ammonium salt-containing vinyl monomer include:

Examples of the nonionic vinyl monomer include a carboxyl group-containing vinyl monomer or an alkyl ester of the anionic vinyl monomer (alkyl group having 1 to 8 carbon atoms), acrylonitrile, styrenes, vinyl acetate, methyl vinyl ether, N-vinyl pyrrolidone. And so on.

The proportion of the vinyl monomer used as required is preferably 0 to 40 mol% based on the total mole of the vinyl monomer. In addition, an internal paper strength agent for papermaking containing amphoteric polyacrylamide containing the cationic vinyl monomer tends to have poor storage stability, and the present invention is particularly effective.

Further, the vinyl monomer optionally used may be a polyfunctional monomer and / or a compound of the general formula (1): CH ₂ ＣC (R ¹ ) -CONR ² (R ³ ) (R ¹ is a hydrogen atom or A methyl group, R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a linear or branched alkyl group having 1 to 4 carbon atoms), (Meth) acrylamides. These are intended to increase the molecular weight of polyacrylamide by crosslinking or branching.The paper-making internal additive for papermaking containing polyacrylamide containing these vinyl monomers as components has poor storage stability. It is valid.

The polyfunctional monomer is a compound having at least two functional groups in a molecule and capable of cross-linking ionic polyacrylamide. Specifically, di (meth) acrylates such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, methylenebis (meth) acrylamide, ethylenebis (meth) acrylamide, Bis (meth) acrylamides such as hexamethylenebis (meth) acrylamide, divinyl esters such as divinyl adipate and divinyl sebacate, allyl methacrylate, diallylamine, diallyldimethylammonium, diallyl phthalate, diallyl chlorendate, divinyl benzene,
Bifunctional vinyl monomers such as N, N-diallylacrylamide, 1,3,5-triacryloylhexahydro-
Trifunctional vinyl monomers such as S-triazine, triallyl isocyanurate, triallylamine, triallyl trimellitate, tetramethylolmethanetetraacrylate, tetraallyl pyromellitate, N, N, N ',
Examples include tetrafunctional vinyl monomers such as N'-tetraallyl-1,4-diaminobutane, tetraallylamine salt, tetraallyloxyethane, and N-methylolacrylamide. Among these polyfunctional monomers, 1,3,5-triacryloylhexahydro-S-triazine, triallyl isocyanurate and the like are preferable.
Usually, the amount of the polyfunctional monomer used is preferably about 0 to 2 mol% based on the total molar amount of the vinyl monomer.

General formula (1): CH ₂ ＣC (R ¹ ) -CON
R ² (R ³ ) (R ¹ is a hydrogen atom or a methyl group; R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms; R ³ is a linear or branched chain having 1 to 4 carbon atoms) N-substituted (meth) acrylamides represented by (alkyl group in the chain) have a methyl or methylene group in the N-alkyl group acting as a chain transfer point, and the ionic poly (meth) acrylamide has many branches. The structure is introduced into a branched polymer without gelation. R ² or R ^{3 in the} general formula (1)
Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an isopropyl group, a t-butyl group and the like. Specific examples of N-substituted (meth) acrylamides Is N, N-dimethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-methyl (meth) acrylamide, N
-Ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide and Nt-butyl (meth)
Acrylamide is mentioned. Among these, N, N-dimethylacrylamide is preferred in terms of copolymerizability and chain transfer. The amount of the N-substituted (meth) acrylamides is 0 to 10 mol% based on the total mol of the vinyl monomers.
The degree is preferred.

The method for producing a carboxyl group-containing polyacrylamide by copolymerizing acrylamide, a carboxyl group-containing vinyl monomer and, if necessary, a vinyl monomer other than the above-mentioned ones can employ ordinary means. For example, the desired carboxyl group-containing polyacrylamide can be obtained by charging the above various monomers and water into a predetermined reaction vessel, adding a radical polymerization initiator, and heating under stirring. The reaction temperature is usually 50 to 10
The reaction time is about 0 ° C. and the reaction time is about 1 to 5 hours. Others
The monomer can be charged by various conventionally known methods such as simultaneous polymerization and continuous drop polymerization. As the radical polymerization initiator, a normal radical polymerization initiator such as a persulfate such as potassium persulfate or ammonium persulfate, or a redox polymerization initiator in the form of a combination thereof with a reducing agent such as sodium bisulfite is used. it can. Further, an azo-based initiator may be used as the radical polymerization initiator. The amount of the radical polymerization initiator used is about 0.05 to 2% by weight of the total weight of the vinyl monomers.

The weight-average molecular weight of the carboxyl group-containing polyacrylamide is usually about 100,000 to 5,000,000, and the viscosity is usually 2000 to 2000 at a solid content of 10 to 35% by weight.
It has a property of about 0 cps or less (25 ° C.).

The papermaking internal paper strength agent of the present invention is obtained by adding a chelating agent to the aqueous solution of the carboxyl group-containing polyacrylamide. As the chelating agent, various ones that coordinate with the metal ion can be used. In the present invention, it is preferable to use at least one selected from citric acid, malic acid, tartaric acid, and lactic acid.
Among these chelating agents, citric acid is particularly preferred. The amount of the chelating agent used is 50 ppm to 500 ppm based on the weight of the paper-making internal paper strength agent (polymer aqueous solution).
About 0 ppm is preferable.

The papermaking internal strength agent thus obtained is added to a pulp slurry by a usual method of use, and paper is produced by papermaking. The amount of papermaking internal strength agent used is
It may be the same as usual, in terms of solid content weight ratio, with respect to pulp,
It is good to be about 0.005 to 3% by weight, preferably about 0.01 to 1% by weight. A sulfuric acid band may be added to the papermaking.

[0022]

The internal strength agent for papermaking of the present invention contains a carboxyl group-containing polyacrylamide and is excellent in paper strength and storage stability.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Parts and% in each example are based on weight unless otherwise specified.

Synthesis Example 1 In a four-necked flask equipped with a thermometer, a reflux condenser, and a nitrogen inlet tube, 100 parts of acrylamide (95 mol% based on the total moles of monomers), 5.3 parts of acrylic acid (5 mol%) ,
5.3 parts of isopropyl alcohol and ion-exchanged water 4
Then, 00 parts were charged, and oxygen in the reaction system was removed through nitrogen gas. The temperature in the system was adjusted to 40 ° C., and 0.3 parts of ammonium persulfate and 0.2 parts of sodium bisulfite were charged as a polymerization initiator with stirring. The start of polymerization is confirmed by heat generation,
After the temperature of the reaction solution reached 90 ° C., the temperature was kept for 2 hours. After completion of the polymerization, 5.5 parts of a 48% aqueous sodium hydroxide solution and 11 parts of ion-exchanged water were added to obtain a carboxyl group-containing polyacrylamide aqueous solution having a pH of 7.5, a polymer concentration of 20%, and a viscosity of 4,300 cps.

Synthesis Example 2 280 parts of acrylamide (9 parts) were placed in the same reactor as in Synthesis Example 1.
1.1 mol%), acrylic acid 31.2 parts (8 mol%),
Synthetic Example 1 was prepared by charging 2.1 parts (0.5 mol%) of N, N-dimethylacrylamide, 2.7 parts (0.4 mol%) of sodium methallyl sulfonate and 1680 parts of ion-exchanged water.
Polymerization was carried out in the same manner as described above. After the completion of the polymerization, 65 parts of ion-exchanged water were charged, and the polymer concentration was 15% and the pH was 3.
8. A carboxyl group-containing polyacrylamide aqueous solution having a viscosity of 4400 cps was obtained.

Synthesis Example 3 80 parts of acrylamide (60 parts) was placed in the same reactor as in Synthesis Example 1.
Mol%), 29.9 parts (30 mol%) of acrylonitrile, 16.9 parts (10 mol%) of acrylic acid, 0.62 part of isopropyl alcohol and 489 parts of ion-exchanged water, and polymerization was carried out in the same manner as in Synthesis Example 1. Done. After completion of the polymerization, 12.5 parts of a 48% aqueous sodium hydroxide solution and 246 parts of ion-exchanged water were added to obtain a carboxyl group-containing polyacrylamide aqueous solution having a pH of 6.1, a polymer concentration of 15%, and a viscosity of 10,000 cps.

Synthesis Example 4 In a reactor similar to Synthesis Example 1, 88.9 parts (92.5 mol%) of acrylamide, 2.6 parts of 62.5% sulfuric acid, and 5.3 parts of dimethylaminoethyl methacrylate (2.5 parts) Mol%), 80% aqueous solution of acrylic acid 6.1 parts (5 mol%)
And 550 parts of ion-exchanged water were charged, and polymerization was carried out in the same manner as in Synthesis Example 1. After the completion of the polymerization, 330 parts of ion-exchanged water were added, and the polymer concentration was 10%, pH was 3.2, and the viscosity was 80.
A carboxyl group-containing amphoteric polyacrylamide aqueous solution of 00 cps was obtained.

Synthesis Example 5 159.1 parts (89.7 mol%) of acrylamide, 70% of benzyl dimethylaminoethyl methacrylate were placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube. 57.6 parts (5.7 mol%) of chloride quaternary substance, 2.3 parts (1 mol%) of an aqueous 80% acrylic acid solution, 6.9 parts (2.1 mol%) of itaconic acid,
2.5 parts (1 mol%) of N, N-dimethylacrylamide, 1,3,5-triacryloylhexahydro-S
0.06 parts (0.01 mol%) of triazine, 1.8 parts (0.45 mol) of sodium methallylsulfonate and 758 parts of ion-exchanged water (monomer concentration: 21%) were charged, and the reaction system was passed through nitrogen gas. Oxygen was removed. The temperature of the system was adjusted to 61 ° C., and 0.43 part of ammonium persulfate and 0.2 part of sodium hydrogen sulfite were added as a polymerization initiator with stirring. After the temperature was raised to 90 ° C., the temperature was kept for 2 hours. After completion of the polymerization, 58 parts of ion-exchanged water was added to obtain a carboxyl group-containing amphoteric polyacrylamide aqueous solution having a pH of 3.8, a polymer concentration of 20%, and a viscosity of 7,400 cps.

Synthesis Example 6 In a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 289 parts (89.1 mol%) of powdered acrylamide and 15.8 parts of 78.0% sulfuric acid were added. , Dimethylaminopropylacrylamide 42.7. Parts (6 mol%), 16.4 parts (4 mol%) of an 80% aqueous solution of acrylic acid, 2.3 parts of N, N-dimethylacrylamide (0.
5 mol%), 2.9 parts (0.4 mol%) of sodium methallylsulfonate, and 1293 parts of ion-exchanged water (monomer concentration: 21%), and oxygen in the reaction system was removed through nitrogen gas. The temperature of the system was adjusted to 61 ° C., and 0.35 part of ammonium persulfate was added as a polymerization initiator with stirring. 9
After the temperature was raised to 0 ° C., the temperature was kept for 2 hours. After completion of the polymerization, 150 parts of ion-exchanged water was added, and the pH was 4.2 and the solid content was 20.
%, A carboxyl group-containing amphoteric polyacrylamide aqueous solution having a viscosity of 6200 cps.

Examples 1 to 6 An aqueous solution was prepared by mixing 1 part of citric acid with 1000 parts of the aqueous solution of carboxyl group-containing polyacrylamide obtained in Synthesis Examples 1 to 6.

The aqueous solutions obtained in the Synthesis Examples and Examples were evaluated for storage stability and paper strength by the following methods. Table 1 shows the evaluation results.

(Storage stability) A commercially available nail that had not been subjected to rust-proofing was immersed in deionized water for 2 weeks to form rust on the nail surface. Then, one end of the nail was immersed in the gas phase about 1 cm from the interface of the aqueous solution prepared in the synthesis example or the example, and allowed to stand for 24 hours. The change in viscosity was visually observed, and the presence or absence of gelation was observed. Was judged.

[0033]

[Table 1]

(Paper Strength) A pulp slurry adjusted to 400 ml of Canadian Standard Freeness (CSF) was beaten from a cardboard waste paper with a Niagara beater, and a sulfuric acid band (Alum) was added to a pulp solid content ratio. Add 1.5% to pH 5.5, then aqueous solution obtained in Synthesis Examples or Examples (solid content ratio to pulp 0.4%)
added. The pulp slurry thus obtained was paper-made using a tappy sheet machine so as to have a basis weight of 150 g / m ^2, and was press-dewatered at 4 kg / cm ² for 4 minutes. Then, it is dried at 105 ° C. for 3 minutes in a rotary drier,
0 ° C., 65% R.C. H. After conditioning for 24 hours under the conditions described above, drainage and burst strength were measured according to JIS P8121 and JIS P8131. From the measurement results,
There was no difference in the performance between the aqueous solution of the synthesis example and the aqueous solution of the example depending on whether or not citric acid was added.

Claims (4)

[Claims] 1. An internal strength agent for papermaking comprising an aqueous solution containing a carboxyl group-containing polyacrylamide and a chelating agent. 2. The paper additive according to claim 1, wherein the carboxyl group-containing polyacrylamide is an amphoteric polyacrylamide. 3. The polyacrylamide having a carboxyl group is a polyfunctional monomer and / or a compound represented by the general formula (1):
H ₂ ＣC (R ¹ ) —CONR ² (R ³ ) (R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, and R ³ is a carbon atom. The paper additive according to claim 1 or 2, comprising an N-substituted (meth) acrylamide represented by a linear or branched alkyl group of formulas 1 to 4 as a constituent monomer. 4. The paper additive according to claim 1, wherein the chelating agent is at least one selected from malic acid, tartaric acid and lactic acid.