JP6943047B2 - A method for producing a paper strength enhancer and a method for producing paper - Google Patents

Description

The present invention relates to a method for producing a paper strength enhancer, paper, and a method for producing paper.

Conventionally, anionic, cationic or amphoteric acrylamide-based polymers have been widely used as paper strength agents for imparting strength to paper.
In recent years, due to the increase in the usage ratio of used paper, paper mills are using raw pulp containing short fibers derived from used paper and having low paper strength. In addition, due to the use of recycled paper, the metal ions contained in the white water of the papermaking increase the electrical conductivity in the papermaking system, making it difficult for the paper strength enhancer added to the raw material pulp to supplement the paper strength. doing. In the production of paperboard, which is required to have a higher paper strength effect in such an environment, it is necessary to add a large amount of a paper strength enhancer, but the water quality is more likely to deteriorate, which is not preferable in terms of the environment.

In order to maintain the paper strength effect of paper in these papermaking environments, a method of increasing the molecular weight of the paper strength enhancer is known (Patent Document 1). However, if the paper strength enhancer is simply increased in molecular weight, the product viscosity may increase, the handleability may deteriorate, or the viscosity may increase during long-term storage, making the product unusable. Furthermore, if a large amount of high molecular weight paper strength enhancer is added to the raw material pulp, even if the paper strength enhancer is fixed to the pulp, overcoagulation occurs and the texture of the paper is deteriorated, and the paper strength effect is reduced. There is also the problem of doing. As a technique for suppressing an increase in the viscosity of the paper strength enhancer, for example, at least one monomer selected from N, N-dimethylacrylamide and N, N-dimethacrylamide, a single amount of cationic vinyl A body, an anionic vinyl monomer, and a mixture of at least one monomer selected from acrylamide and methacrylicamide are polymerized in an aqueous medium in the presence of a radical polymerization initiator to obtain a weight average molecular weight. A method for producing a papermaking additive, which comprises forming 500,000 to 1.5 million prepolymers, and then adding a persulfate to carry out polymerization until the weight average molecular weight becomes at least 1.1 times. Is also known (Patent Document 2). However, in the above-mentioned production method, a step of cross-linking the polymers with each other is required, and in that step, there is a concern that the degree of branching varies and a paper strength enhancer having a wide molecular weight distribution is produced.

In addition, as a technique for controlling the molecular weight distribution, a water-soluble cationic monomer and / or salts thereof, α, β-unsaturated carboxylic acid and / or salts thereof, acrylamide and / or methacrylamide are essential constituent monomer components. An amphoteric paper strength enhancer characterized by being polymerized, having a specific cation equivalent value and anion equivalent value, having a weight average molecular weight of 1 million to 6 million, and having a multi-branching degree representing the width of the molecular weight distribution of 10 or less. Is known (Patent Document 3). However, the molecular weight distribution of the paper strength enhancer is also wide, and an excellent paper strength effect has been an issue.

Japanese Unexamined Patent Publication No. 2-61197 Japanese Unexamined Patent Publication No. 5-287693 Japanese Unexamined Patent Publication No. 7-189177

An object of the present invention is to have excellent storage stability in spite of having a high molecular weight, reduce unreacted (meth) acrylamide, and further, when added to the raw material pulp, by hyperaggregation while fixing to the pulp. without disturbance paper formation is to provide a superior method for producing a paper strength agent also exhibits paper strength effect, paper and paper manufacturing methods.

As a result of diligent studies, the present inventor has found that a paper strength enhancer containing a copolymer in which the weight average molecular weight and the molecular weight distribution are controlled in a specific range solves the above-mentioned problems. In particular, it has also been found that the effect of the present invention becomes remarkable by applying a method for producing a paper strength enhancer including three steps of adding a polymerization initiator separately. That is, the present invention relates to the following paper strength enhancer, a method for producing a paper strength enhancer, and a paper and a method for producing paper.

1. 1. The polymerization component (A) contains (meth) acrylamide (a1), a cationic vinyl monomer (a2), an anionic vinyl monomer (a3) and a crosslinkable vinyl monomer (a4), and has a weight average molecular weight (Mw). A paper strength enhancer containing a copolymer (B) having a molecular weight distribution (Mw / Mn) of 1.5 to 3.0 and 1 million to 8 million.

2. Item 2. The paper strength enhancer according to Item 1, wherein the unreacted component (a1) contained in the copolymer (B) is 50 ppm or less.

3. 3. Among the polymerization components (A), the component (a1) is 55 to 97.95 mol%, the component (a2) is 1 to 20 mol%, the component (a3) is 1 to 20 mol%, and the component (a4) is 0.05. Item 3. The paper strength enhancer according to Item 1 or 2, which contains ~ 5 mol%.

4. The paper strength enhancer according to any one of Items 1 to 3 above, wherein the gelation rate of the paper strength enhancer is 0.05% by weight or less in terms of solid content.

5. The paper strength enhancer according to any one of Items 1 to 4, wherein the polymerization component (A) further contains a chain transfer agent (a5).

6. The paper strength enhancer according to any one of Items 1 to 5, wherein the component (a2) contains a tertiary amino group-containing vinyl monomer and / or a quaternized salt of the vinyl monomer.

7. The paper strength enhancer according to any one of Items 1 to 6, wherein the component (a3) contains a vinyl monomer having a carboxyl group.

8. The paper strength enhancer according to any one of Items 1 to 7, wherein the component (a4) contains a crosslinkable vinyl monomer having an N, N-substituted amide group.

9. The paper strength enhancer according to any one of Items 1 to 8, wherein the solid content concentration is 20% by weight and the viscosity at a temperature of 25 ° C. is 2,500 to 80,000 mPa · s.

10. Step (I): A step of obtaining a reaction product (1) by reacting the polymerization component (A) in the presence of a polymerization initiator.
Step (II): A step of obtaining a reaction product (2) by reacting the reaction product (1) with a persulfate as a polymerization initiator.
And step (III): The above-mentioned item including a step of obtaining a copolymer (B) by reacting the reaction product (2) with an azo-based polymerization initiator and / or a redox initiator as a polymerization initiator. A method for producing a paper strengthening agent according to any one of 1 to 9.

11. A paper containing the paper strength enhancer according to any one of Items 1 to 9.

12. A method for producing paper using the paper strength enhancer according to any one of claims 1 to 9.

Since the paper strength enhancer of the present invention has a high molecular weight while suppressing the formation of excessively branched high molecular weight bodies by controlling the weight average molecular weight and the molecular weight distribution, when it is added to the raw material pulp, it is increased. Although it was fixed on the pulp, the formation was not disturbed by over-aggregation, and the obtained grown paper also exhibited an excellent paper strength effect. In particular, in the paper strength enhancer obtained from the above-mentioned production method, their effects are remarkable, the residual amount of unreacted acrylamide is small, and the storage stability is also excellent.

In the paper strength enhancer of the present invention, as the polymerization component (A), (meth) acrylamide (a1) (hereinafter referred to as (a1) component), a cationic vinyl monomer (a2) (hereinafter referred to as (a2) component), A copolymer (B) containing an anionic vinyl monomer (a3) (hereinafter referred to as (a3) component) and a crosslinkable vinyl monomer (a4) (hereinafter referred to as (a4) component) and having the weight average molecular weight and molecular weight distribution. ) Is included.

The component (a1) means acrylamide and methacrylamide.

As the content ratio of the component (a1), the total content ratio of the polymerized component (A) is 100 mol%, and it is usually about 55 to 97.95 mol%, preferably about 60 to 95 mol%, more preferably 70 to 70 to It is about 90 mol%.

The component (a2) is not particularly limited, and various known ones can be used. However, since the paper strength enhancer is well fixed to the raw material pulp and exhibits an excellent paper strength effect, 3 It preferably contains a grade amino group-containing vinyl monomer and / or a quaternized salt of the vinyl monomer. Specific examples of the vinyl monomer include N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, N, N-. Examples thereof include a tertiary amino group-containing vinyl monomer such as diethylaminopropyl (meth) acrylamide; a quaternized salt of the vinyl monomer obtained by reacting these tertiary amino group-containing vinyl monomers with a quaternizing agent. The vinyl monomer salt may be an inorganic acid salt such as a hydrochloride or sulfate, or an organic acid salt such as an acetate. Examples of the quaternary agent to be reacted include methyl chloride, benzyl chloride, dimethyl sulfate, epichlorohydrin and the like. Among these, benzyl chloride quaternized salts of N, N-dimethylaminoethyl (meth) acrylate and / or N, N-dimethylaminoethyl (meth) acrylate are more preferable from the viewpoint of availability and the same points as described above. These can be used alone or in combination of two or more.

The content ratio of the component (a2) is usually 100 mol% with the total content ratio of the polymerized component (A) set to 100 mol% from the viewpoint that the paper strength enhancer firmly fixes to the raw material pulp and exerts an excellent paper strength effect. Is about 1 to 20 mol%, preferably about 2 to 17 mol%, and more preferably about 2 to 12 mol%.

The component (a3) is not particularly limited, and various known ones can be used, but carboxyl is obtained from the viewpoint that the paper strength enhancer is well fixed to the raw material pulp and exhibits an excellent paper strength effect. It preferably contains a vinyl monomer having a group. Specific examples of the vinyl monomer include α, β-unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; α, β such as maleic acid, fumaric acid, itaconic acid, muconic acid and citraconic acid. -Unsaturated dicarboxylic acid; organic sulfonic acid such as vinyl sulfonic acid and styrene sulfonic acid, or sodium salt, potassium salt and the like of the various organic acids can be mentioned. Among these, acrylic acid and / or itaconic acid are preferable from the viewpoint of availability and the same points as described above. These can be used alone or in combination of two or more.

As for the content ratio of the component (a3), the total content ratio of the polymerized component (A) is usually 100 mol% from the viewpoint that the paper strength enhancer firmly adheres to the raw material pulp and exerts an excellent paper strength effect. Is about 1 to 20 mol%, preferably about 2 to 17 mol%, and more preferably about 2 to 12 mol%.

The component (a4) is not particularly limited, and various known components can be used. Specific examples of the component (a4) include a crosslinkable vinyl monomer having an allyl group such as allyl (meth) acrylate, N-allyl (meth) acrylamide, and N, N-diallyl (meth) acrylamide; diethylene glycol mono (meth). ) Acrylate, polyethylene glycol mono (meth) acrylate such as triethylene glycol mono (meth) acrylate, tetraethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, polytrimethylene Crosslinkable vinyl monomer having a polyalkylene glycol group such as glycol mono (meth) acrylate, polytetramethylene glycol mono (meth) acrylate, polyethylene glycol propylene glycol mono (meth) acrylate; diacetone acrylamide, N-isopropylacrylamide, 2- A crosslinkable vinyl monomer having an N-substituted amide group such as acrylamide-2-methylpropanesulfonic acid and a salt thereof; a crosslink having an N, N-substituted amide group such as N, N-dimethylacrylamide and N, N-diethylacrylamide. Sexual vinyl monomer; divinylbenzene, 1,3,5-triacrylloylhexahydro-1,3,5-triazine, triallyl isocyanurate, triallyl trimellitate, triallylamine, tetramethylolmethanetetraacrylate, tetraallylpyromery Examples thereof include aromatic polyvinyl-based crosslinkable monomers such as late. Among these, a crosslinkable vinyl monomer having an N, N-substituted amide group is preferable, and N, N-dimethylacrylamide is more preferable, from the viewpoint of improving the weight average molecular weight of the copolymer (B). These can be used alone or in combination of two or more.

The content ratio of the component (a4) is usually 0.05 to 5 when the total content ratio of the polymer component (A) is 100 mol% from the viewpoint of controlling the weight average molecular weight and the molecular weight distribution of the copolymer (B). It is about mol%, preferably about 0.07 to 2.5 mol%, and more preferably about 0.1 to 1 mol%.

Further, the polymerization component (A) may contain a chain transfer agent (a5) (hereinafter, referred to as the component (a5)), if necessary. When the component (a5) is used, the polymer chain before the cross-linking reaction becomes shorter, and a copolymer having a lower viscosity and a higher molecular weight can be obtained. Specific examples of the component (a5) include mercaptans such as 2-mercaptoethanol and n-dodecyl mercaptan, α-methylstyrene dimer, sodium methallyl sulfonate, potassium methallyl sulfonate, ammonium metharyl sulfonate and the like. Metalyl sulfonate, ethanol, alcohols without allyl group such as isopropyl alcohol and pentanol, carbon tetrachloride, ethylbenzene, isopropylbenzene, cumene, 2,4-diphenyl-4-methyl-1-pentene, etc. Can be mentioned. Among these, methallyl sulfonate is preferable, and sodium metharyl sulfonate is more preferable, from the viewpoint of adjusting the weight average molecular weight and viscosity of the paper strength enhancer. These can be used alone or in combination of two or more.

The content ratio of the component (a5) is usually 0.05, where the total content ratio of the polymerized component (A) is 100 mol% from the viewpoint of obtaining the copolymer (B) having a relatively low viscosity while increasing the molecular weight. It is about 5 mol%, preferably about 0.1 to 3 mol%, and more preferably about 0.2 to 2 mol%.

Further, the polymerization component (A) may contain a component (a6) (hereinafter referred to as (a6) component) other than the components (a1) to (a5) as long as the effect of the present invention is not impaired. Specific examples of the component (a6) include bis (meth) acrylamides such as methylol acrylamide, methylene bis (meth) acrylamide, and ethylene bis (meth) acrylamide; ethylene glycol di (meth) acrylate and diethylene glycol di (meth) acrylate. , Di (meth) acrylates such as polyethylene glycol di (meth) acrylate; Divinyl esters such as divinyl adipate and divinyl sebacate; Epoxy acrylates and urethane acrylates; Fragrances such as styrene, α-methylstyrene and vinyltoluene Group vinyl monomers; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, -2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. Alkyl (meth) acrylates; carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate; cumene, α-methylstyrene dimer, 2,4-diphenyl-4-methyl-1-pentene and the like can also be exemplified. These may be used alone or in combination of two or more.

The content ratio of the component (a6) is not particularly limited, but is usually 5 mol% or less, preferably 2.5 mol% or less, assuming that the total content ratio of the polymerized component (A) is 100 mol%.

The method for producing the paper strength enhancer of the present invention is not particularly limited, but if it is a method capable of producing a copolymer having the above-mentioned weight average molecular weight and molecular weight distribution in a specific range, it is a step-growth polymerization, a drop polymerization, or a multi-step polymerization. Various known polymerization methods such as the above can be adopted. For example, a manufacturing method including the steps (I) to (III) described later can be mentioned. Hereinafter, each step will be described.

<About process (I)>
The step (I) in the production method of the present invention is a step of obtaining a reaction product (1) by reacting the polymerization component (A) by polymerizing it in the presence of a polymerization initiator.

The polymerization component (A) can also be used as a solution. As the solvent, water is usually preferable from the viewpoint that the polymerization component (A) is sufficiently dissolved or dispersed and does not adversely affect the polymerization reaction, but a hydrophilic organic solvent such as ethanol or isopropanol may be used in combination as an auxiliary solvent. good. Further, when the polymerization component (A) contains a component that is easily hydrolyzed, sulfuric acid or the like may be added.

The polymerization conditions in the step (I) are not particularly limited, but for example, the polymerization temperature is about 35 to 100 ° C., and the polymerization time is about 1 to 10 hours.

The polymerization initiator used in the step (I) is not particularly limited, and various known ones can be used. Specific examples of the polymerization initiator include persulfates such as ammonium persulfate, potassium persulfate, and sodium persulfate, and azo-based polymerization initiators such as 2,2'-azobis (2-amidinopropane) hydrochloride. Can be mentioned. Among these, ammonium persulfate, potassium persulfate and / or 2,2'-azobis (2-amidinopropane) hydrochloride are preferably used from the viewpoint of sufficiently advancing the polymerization reaction of the polymerization component (A). These may be used alone or in combination of two or more. Further, although optional, a reducing agent may be used in combination in terms of facilitating the generation of radicals of the organic peroxide. Examples of the reducing agent include sulfites such as sodium sulfite, hydrogen sulfites such as sodium hydrogen sulfite, triethanolamine and cuprous sulfate.

The amount of the polymerization initiator used in the step (I) is not particularly limited, but is usually 0. It is about 05 to 2.0 parts by weight, preferably about 0.1 to 0.5 parts by weight.

The reaction product (1) when the step (I) is completed preferably has a polymerization rate of about 95 to 98%. By setting the polymerization rate, the amount of the polymerization component (A) remaining in the step (II) is small, so that, for example, the generation of gel due to sudden heat generation can be easily suppressed. Further, it becomes easy to obtain a product having a high molecular weight and a relatively low viscosity. The polymerization rate here is a ratio of the polymerization component (A) consumed in the polymerization reaction.

<About process (II)>
The step (II) in the production method of the present invention is a step of obtaining the reaction product (2) by reacting the reaction product (1) with a persulfate as a polymerization initiator.

The polymerization conditions in the step (II) are not particularly limited, but for example, the polymerization temperature is about 50 to 100 ° C., and the polymerization time is about 0.5 to 5 hours.

As the polymerization initiator used in the step (II), a persulfate is used from the viewpoint of cross-linking the reaction product (1) obtained in the step (I) while controlling the molecular weight distribution while increasing the molecular weight. Of these, ammonium persulfate is preferable. On the other hand, the use of an azo-based polymerization initiator is not preferable because the cross-linking reaction is difficult to proceed and the molecular weight of the reaction product (2) does not increase.

The amount of the polymerization initiator used in the step (II) is not particularly limited, but from the same point as described above, it is usually about 0.05 to 2 parts by weight, preferably 0, based on 100 parts by weight of the polymerization component (A). It is about 1 to 0.5 parts by weight.

As the reaction product (2) when the step (II) is completed, the polymerization rate is preferably 99.8% or more. By setting the polymerization rate, the amount of the polymerization component (A) remaining in the step (III) is small, so that, for example, the generation of gel due to sudden heat generation can be easily suppressed. In addition, the final paper strength enhancer also tends to exert a good texture and paper strength effect.

<About process (III)>
In the step (III) in the production method of the present invention, the copolymer (B) is produced by reacting the reaction product (2) with an azo-based polymerization initiator and / or a redox initiator as a polymerization initiator. This is the process of obtaining.

The polymerization conditions in the step (III) are not particularly limited, but for example, the polymerization temperature is about 50 to 100 ° C., and the polymerization time is about 0.5 to 5 hours.

As the polymerization initiator used in the step (III), an azo-based polymerization initiator and / or a redox initiator is used because a high-molecular-weight copolymer (B) having a controlled molecular weight distribution can be obtained. Here, the redox initiator means an initiator in which a persulfate is combined with a reducing agent.

The amount of the polymerization initiator used in the step (III) is not particularly limited, but from the same point as described above, it is usually about 0.05 to 2 parts by weight, preferably 0, based on 100 parts by weight of the polymerization component (A). It is about 1 to 1 part by weight, more preferably about 0.2 to 0.5 part by weight. When a redox initiator is used, the ratio of the polymerization initiator and the reducing agent used is usually about 90/10 to 40/60, preferably 80/20, in terms of solid weight ratio. It is about 50/50.

The copolymer (B) obtained by the production method of the present invention has a small amount of unreacted component (a1) because it suppresses gel formation and is excellent in storage stability of the paper strength enhancer. preferable. The content of the unreacted component (a1) may be measured by liquid chromatography or the like. From the same point as above, the content of the unreacted component (a1) contained in the paper strength enhancer is usually 50 ppm or less, preferably 20 ppm or less in terms of solid content.

The weight average molecular weight of the copolymer (B) of the present invention is 1 million to 8 million, preferably 1.5 million to 8 million, more preferably 1.8 million to 7 million, and particularly preferably 2.5 million to 2.5 million. It is 6 million. When the weight average molecular weight is less than 1 million, the fixing rate of the paper strength enhancer to the raw material pulp is lowered, and the paper strength effect is lowered when the paper is made into paper. On the other hand, if it exceeds 8 million, it becomes difficult to control the molecular weight distribution, the paper strength enhancer causes over-aggregation, and the texture of the paper is easily disturbed.

The molecular weight distribution (Mw / Mn) of the copolymer (B) is 1.5 to 3.0, preferably 2.0 to 3.0, and more preferably 2.2 to 2.9. Is. When the molecular weight distribution (Mw / Mn) exceeds 3.0, the pulp slurry tends to be over-aggregated, the formation is disturbed, and the paper strength improving effect and storage stability of the paper strength enhancer tend to be inferior. If the molecular weight distribution (Mw / Mn) is less than 1.5, it is presumed that it is easily affected by fluctuations in the papermaking system and it becomes difficult to exert a stable paper force effect. Here, Mw is an abbreviation for weight average molecular weight and Mn is an abbreviation for number average molecular weight.

The paper strength enhancer of the present invention has a reduced amount of insoluble matter in order to exert excellent storage stability and paper strength effect, and its content ratio is represented by "gelling rate". The gelation rate is the ratio of the gel (solid content) contained in the total solid content of the paper strength enhancer, and the "gel" is a copolymer insolubilized in water during the production of the paper strength enhancer. It is an insoluble matter such as. The gelation rate in the present invention is 0.05% by weight or less, preferably 0.03% by weight or less in terms of solid content, more preferably 0.03% by weight or less, from the viewpoint that the paper strength enhancer exhibits excellent storage stability and paper strength effect. Is 0.02% by weight or less. The gelation rate of the present invention is calculated using (Equation 1).
(Formula 1) Gelation rate (%) = (Amount of gel (solid content) (g)) / (Amount of total solid content in paper strength enhancer (g)) × 100

The measurement of the gelation rate is not particularly limited, and examples thereof include a method of naturally filtering a liquid obtained by diluting the paper strength enhancer as it is or with deionized water using a mesh (wire mesh) or the like. When the paper strength enhancer is naturally filtered, the residue (gel) after filtration contains water, so it is preferable to dry it under heating. The drying conditions are, for example, a temperature of about 100 to 160 ° C. (preferably about 105 to 140 ° C.) and a time of about 0.5 to 5 hours (preferably about 1 to 4 hours).

Paper strength enhancers have problems such as agglomeration and gelation due to the influence of temperature and climate during long-term storage, making them unusable. In the present invention, the gelation rate is also adopted as an index of storage stability, and it is evaluated that the lower the value, the better.

From the viewpoint of storage stability in the present invention, for example, the gelation rate of the paper strength enhancer after storage at 40 ° C. for 2 weeks is 0.05% by weight or less, preferably 0.03% by weight or less. It is preferably 0.02% by weight or less.

Further, as another physical property of the paper strength enhancer of the present invention, the solid content concentration is 20% by weight and the viscosity at a temperature of 25 ° C. is usually 2, from the viewpoint that the texture of the paper is not disturbed and the paper strength effect is excellent. It is about 500 to 80,000 mPa · s, preferably about 5,000 to 60,000 mPa · s.

The paper strength enhancer of the present invention can be prepared by blending various additives, if necessary. Examples of the additive include antifoaming agents, preservatives, chelating agents, water-soluble aluminum compounds, bow glass, urea, polysaccharides and the like.

The method of using the paper strength enhancer is not particularly limited, and examples thereof include a method of internally adding to the raw material pulp slurry and a method of coating on the surface of the base paper.

When internally added to the raw material pulp slurry, the paper strength enhancer of the present invention is added to the pulp slurry to make paper. The amount of the paper strength enhancer used is not particularly limited, but is about 0.01 to 4.0% by weight with respect to the dry weight of the pulp. The type of pulp is not particularly limited, and examples thereof include chemical pulps such as LBKP and NBKP, mechanical pulps such as GP and TMP, and used paper pulps. When the paper strength enhancer is added internally, in addition, a sulfate band or aluminum hydroxide is used as a fixing agent, sulfuric acid or sodium hydroxide is used as a pH adjuster, a sizing agent or wet paper strength agent is used as a filler, and talc is used as a filler. Clay, kaolin, titanium dioxide, calcium carbonate and the like can be added.

When coating on the surface of the base paper, the paper strength enhancer of the present invention is used in a solution diluted with water or the like, and the surface of the base paper is coated by various known means. The viscosity of the diluted solution is usually 1 to 40 mPa · s at 50 ° C. at a solid content concentration of 5% by weight. As the type of base paper, uncoated paper made from wood cellulose fiber can be used, and the coating means is not particularly limited. For example, bar coater, knife coater, air knife coater, calender, gate. Examples include roll coaters, blade coaters, 2-roll size presses and rod metering. The coating amount (solid content) of the paper strength enhancer is also not particularly limited, but is usually ^{about 0.001 to 2} g / m 2, preferably about 0.005 to 1.0 g / m ² .

Since the paper of the present invention is less likely to cause over-aggregation of the paper strength enhancer, it does not disturb the formation and exhibits an excellent paper strength effect.

The paper of the present invention is used in various products, for example, coated base paper, newspaper paper, liner, core, paper tube, printing writing paper, foam paper, PPC paper, cup base paper, inkjet paper, thermal paper, etc. Can be mentioned.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. Both parts and% are based on weight. For convenience, monomers and the like are abbreviated as follows.

The following compounds are shown by abbreviations.
AM: Acrylamide DM: Dimethylaminoethyl methacrylate DML: benzyl chloride quaternary salt of dimethylaminoethyl methacrylate DMAEA-BQ: benzyl chloride quaternary salt of dimethylaminoethyl acrylate DMAEA-Q: Methyl chloride quaternary salt of dimethylaminoethyl acrylate Chemical Salt IA: Itaconic Acid AA: Acrylate DMAA: N, N-Dimethylacrylamide TAF: 1,3,5-Triacryl Hexahydro-1,3,5-Triazine SMAS: Sodium Metalyl Sulfonate APS: Ammonium Persulfate NPS: Sodium Persulfate KPS: Potassium Persulfate SPS: Sodium Disulfide V-50: 2,2'-azobis (2-amidinopropane) hydrochloride

(viscosity)
The viscosity of the sample adjusted to 25 ° C. was measured using a Brookfield type viscometer (manufactured by Toki Sangyo Co., Ltd.).

(Weight average molecular weight, molecular weight distribution)
The weight average molecular weight and the molecular weight distribution were measured by the gel permeation chromatography (GPC) method under the following measurement conditions.
GPC body: Tosoh Corporation column: Tosoh Corporation guard column 1 PWXL and 2 GMPWXL (temperature 40 ° C)
Eluent: 0.5 mol / l acetic acid buffer (0.5 mol / l acetic acid (manufactured by Wako Pure Chemical Industries, Ltd.) + 0.5 mol / l sodium acetate (manufactured by Kishida Chemical Industries, Ltd.) aqueous solution, pH about 4.2 )
Flow velocity: 0.8 ml / min Detector:
Viscotec TDA MODEL 301 (concentration detector and 90 ° light scattering detector and viscosity detector (temperature 40 ° C.)) RALLS method measurement sample: so that the solid content concentration of the copolymer (B) is 0.5%. After diluting with deionized water, add an aqueous sodium hydroxide solution until the pH reaches 10 to 12, soak in a hot water bath at 80 ° C. or higher for 1 hour, adjust the pH to 6 to 8 with sulfuric acid, and use an eluent to adjust the pH to 0. It was diluted to 025% and measured.

Example 1
<Step (I)>
276.2 parts of ion-exchanged water was placed in a reactor equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas introduction tube and three dropping funnels, and after removing oxygen in the reaction system through nitrogen gas, 90 Heated to ° C. In the dropping funnel (1), 106.7 parts (29.0 mol%) of AM, 32.5 parts (4.0 mol%) of DM, 0.3 parts (0.05 mol%) of DMAA, SMAS 2.0 parts (0.25 mol%), 15.9 parts of 62.5% sulfuric acid, and 319 parts of ion-exchanged water were charged, and the pH was adjusted to around 3.0 with sulfuric acid (mixture (a)). ). In the dropping funnel (2), 229.3 parts (62.4 mol%) of AM, 26.9 parts (4.0 mol%) of IA, 0.3 parts (0.05 mol%) of DMAA, 2.0 parts (0.25 mol%) of SMAS and 408.2 parts of ion-exchanged water were charged, and the pH was adjusted to around 3.0 with sulfuric acid (mixed solution (a)). 0.6 part of APS and 180 parts of ion-exchanged water were charged into the dropping funnel (3) (initiator solution (c)). Next, the initiator solution (c) was added dropwise from the dropping funnel (3) over 3 hours. In parallel, the mixed solution (a) in the dropping funnel (1) is added dropwise over about 1.5 hours, and immediately after the completion of the dropping, the mixed solution (a) in the dropping funnel (2) is added over about 1.5 hours. Dropped.
<Step (II)>
After completion of the dropping, 0.4 part of APS and 10 parts of ion-exchanged water were added and kept warm for 1 hour.
<Step (III)>
Further, 0.8 part of V-50 and 10 parts of ion-exchanged water were added and kept warm for 1 hour, and then 400 parts of ion-exchanged water was added, and the solid content concentration was 20.0% and the viscosity (25 ° C.) was 8,000 mPa. -A copolymer of s (B-1) was obtained. The physical characteristics of the copolymer (B-1) are shown in Table 1 (the same applies hereinafter).

Example 2
With the monomer composition shown in Table 1, in step (I) of Example 1, 0.6 parts of V-50 and 180 parts of ion-exchanged water were charged into the dropping funnel (3) to synthesize the copolymer (B). -2) was obtained.

Example 3
In step (I) of Example 1, 0.6 parts of APS and 90 parts of ion-exchanged water (initiator solution (c)) were added to the dropping funnel (3), and 0 SPS was added to the dropping funnel (4). .5 parts and 90 parts of ion-exchanged water were charged (initiator solution (d)), and each of them was dropped into the system over 3 hours for synthesis to obtain a copolymer (B-3).

Example 4
In the step (III) of Example 1, 0.8 parts of APS, 0.67 parts of SPS and 10 parts of ion-exchanged water were added and synthesized to obtain a copolymer (B-4).

Example 5
In the step (II) of Example 1, 0.4 part of NPS and 10 parts of ion-exchanged water were added and synthesized to obtain a copolymer (B-5).

Example 6
With the monomer composition shown in Table 1, in step I of Example 1, 0.6 part of KPS and 180 parts of ion-exchanged water were charged into the dropping funnel (3), and in step II of Example 1, KPS was 0. .4 parts and 10 parts of ion-exchanged water were added and synthesized to obtain a copolymer (B-6).

Example 7
The copolymer (B-) was synthesized by charging 0.6 parts of V-50 and 180 parts of ion-exchanged water into the dropping funnel (3) with the monomer composition shown in Table 1 and in step I of Example 4. 7) was obtained.

Examples 8 and 9
The monomer compositions shown in Table 1 were synthesized in the same manner as in Example 4 to obtain copolymers (B-8) and (B-9).

Examples 10-23
The monomer compositions shown in Table 1 were synthesized in the same manner as in Example 1 to obtain copolymers (B-10) to (B-23).

Comparative Examples 1 to 3 and Comparative Examples 5 to 7
With the monomer composition and polymerization initiator shown in Table 1, the copolymers (B-24) to (B-26) and (B-28) to (B-30) were synthesized in the same manner as in Example 1. Obtained.

Comparative Example 4
In the step (II) of Example 1, 0.4 part of APS, 0.33 part of SPS and 10 parts of ion-exchanged water were added and synthesized to obtain a copolymer (B-27).

(Content of unreacted component (a1))
The copolymers (B-1) to (B-30) were subjected to HPLC using the following eluent, and the content of the unreacted component (a1) was calculated.
(Measurement condition)
Column: Shiseido CAPCELL PAC C18 MG II S5; 1.5 mm I. D. × 250 mm
Eluent: Water / acetonitrile = 95/5 solution containing N / 100 sodium dodecyl sulfate (adjusted to pH 2.3 with phosphoric acid)
Detector: Shiseido NANOSPACE SI-2 UV-VIS detector 3002
Detection wavelength: 205 nm

The following physical properties and papermaking evaluations were performed on the copolymers (B-1) to (B-30). The evaluations using (B-1) to (B-30) are described as Evaluation Examples 1 to 23 and Comparative Evaluation Examples 1 to 7, respectively (composite same order).

(Gelification rate)
After diluting the copolymers (B-1) to (B-30) with deionized water so that the solid content concentration becomes 1.0%, 100 g of the diluted solution is weighed in advance with a 350 mesh wire mesh. Filtered. The amount of gel (solid) after drying in a circulation dryer at a temperature of 105 ° C. for 3 hours was measured and calculated by (Equation 1). The lower the gelation rate, the better. The results are shown in Table 2 (the same applies hereinafter).
(Formula 1) Gelation rate (%) = (Amount of gel (solid content) (g)) / (Amount of total solid content in paper strength enhancer (g)) × 100

(Storage stability)
The copolymers (B-1) to (B-30) were allowed to stand in a constant temperature bath at 40 ° C. for 2 weeks, and then the gelation rate was measured by the same method as described above. The lower the gelation rate, the better the storage stability.

(Papermaking evaluation)
The used corrugated cardboard was beaten with a Niagara beater, and 1.5% of aluminum sulfate was added to the pulp prepared to 370 ml of Canadian Standard Freeness (CSF), and 5% sodium hydroxide was used to adjust the pH. An aqueous solution was added to adjust the pH to 6.7. Next, 1.0% of the paper strength enhancer (B-1) obtained in each of the above Examples and Comparative Examples was added to the pulp, and after stirring, the basis weight was 180 g / m using a tappi sheet machine. papermaking so as to be ² was 2 minutes press dewatering at 5 kg / cm ^2. Then, it was dried in a rotary dryer at 105 ° C. for 3 minutes, and the humidity was adjusted for 24 hours under the conditions of a temperature of 23 ° C. and a humidity of 50% to obtain a grown paper 1. Paper strength enhancers (B-2) to (B-30) were also made in the same manner. In addition, papermaking was performed in the same manner without adding a paper strength enhancer, and a finished paper 2 was also obtained.

(Retention rate)
After measuring the nitrogen content of paper 1 and paper 2 using a nitrogen analyzer (manufactured by Mitsubishi Chemical Corporation), it was calculated from the following formula.
Fixing rate (%) = (Nitrogen content of paper 1-Nitrogen content of paper 2) ÷ (Theoretical nitrogen content of paper strength enhancer used x Addition rate of paper strength enhancer used) x 100
The theoretical nitrogen content means the molar ratio of the components (a1) to (a6) of the paper strength enhancer and the weight ratio of nitrogen in the paper strength enhancer calculated from the composition formula of each of these components. do.
(Formation)
The passing light (brightness) from each paper obtained by the above method is taken into a commercially available measuring instrument (trade name "Personal image processing system Hyper-700", manufactured by OBS), and the brightness distribution is statistically analyzed. The value obtained was used as the coefficient of variation of the formation. The smaller the coefficient of variation of the formation, the better the formation. The results are shown in Table 2 (the same applies hereinafter).
(Specific burst strength)
Using each of the sheets obtained by the above method, the specific burst strength (kPa · m ² / g) was measured according to JIS P 8131.
(Specific tensile strength)
The specific tensile strength (Nm / g) was measured according to JIS P 8113 using each of the sheets obtained by the above method.
(Specific compressive strength)
^{The specific compressive strength (Nm 2} / g) was measured according to JIS P 8126 using each of the sheets obtained by the above method.

Claims (10)

The polymerization component (A) contains (meth) acrylamide (a1), a cationic vinyl monomer (a2), an anionic vinyl monomer (a3) and a crosslinkable vinyl monomer (a4), and has a weight average molecular weight (Mw). A method for producing a paper strength enhancer containing a copolymer (B) having a molecular weight distribution (Mw / Mn) of 1.5 to 3.0 and 1 million to 8 million.
The method is
Step (I): A step of obtaining a reaction product (1) by reacting the polymerization component (A) in the presence of a polymerization initiator.
Step (II): A step of obtaining a reaction product (2) by reacting the reaction product (1) with a persulfate as a polymerization initiator.
And step (III): Paper strength including a step of obtaining a copolymer (B) by reacting the reaction product (2) with an azo-based polymerization initiator and / or a redox initiator as a polymerization initiator. A method for producing an enhancer. The method for producing a paper strength enhancer according to claim 1, wherein the unreacted (meth) acrylamide (a1) contained in the copolymer (B) is 50 ppm or less. The polymerization component (A) is 55 to 97.95 mol% of the (a1) component, 1 to 20 mol% of the (a2) component, 1 to 20 mol% of the (a3) component, and 0.05 to 5 mol% of the (a4) component. The method for producing a paper strength enhancer according to claim 1 or 2. The method for producing a paper strength enhancer according to any one of claims 1 to 3, wherein the gelation rate of the paper strength enhancer is 0.05% by weight or less in terms of solid content. The method for producing a paper strength enhancer according to any one of claims 1 to 4, wherein the polymerization component (A) further contains a chain transfer agent (a5). The method for producing a paper strength enhancer according to any one of claims 1 to 5, wherein the component (a2) contains a tertiary amino group-containing vinyl monomer and / or a quaternized salt of the vinyl monomer. (A3) The method for producing a paper strength enhancer according to any one of claims 1 to 6, wherein the component contains a vinyl monomer having a carboxyl group. The method for producing a paper strength enhancer according to any one of claims 1 to 7, wherein the component (a4) contains a crosslinkable vinyl monomer having an N, N-substituted amide group. The method for producing a paper strength enhancer according to any one of claims 1 to 8, wherein the solid content concentration is 20% by weight and the viscosity at a temperature of 25 ° C. is 2,500 to 80,000 mPa · s. A method for producing paper using the paper strength enhancer obtained by the production method according to any one of claims 1 to 9.