JP2019173257A - Surface paper strength enhancer, coating liquid, paper manufacturing method - Google Patents

Abstract

To provide a surface paper strength enhancer having an excellent paper strength enhancing effect on paper containing an aluminum compound such as aluminum sulfate.SOLUTION: A surface paper strength enhancer comprises a polymer (A) of monomer components including (meth) acrylamide (a1), N-substituted (meth) acrylamide (a2), unsaturated monomer (a3) having a sulfonic acid group, and α, β-unsaturated dicarboxylic acid (a4) and has turbidity at pH 6.5 of a solution containing 1 wt.% of component (A) and 0.5 wt.% of aluminum sulfate in terms of solid content concentration of 70 to 1500 NTU.SELECTED DRAWING: None

Description

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

  In recent years, due to an increase in environmental awareness and demands for cost reduction, an increase in the distribution of waste paper pulp or weight reduction of the base paper itself has been progressing. Therefore, it is difficult to maintain the paper strength due to the influence of impurities such as fine fibers and calcium ions contained in the paper only by internally adding a paper strength enhancer to the raw material pulp. In addition, a surface paper strength enhancer such as polyacrylamide is coated on the surface of the base paper. Also, in surface coating, the speed of paper machines has been increasing due to the improvement of productivity, and the size transfer of the film transfer method such as gate roll and rod metalling has been applied from the conventional method of 2 roll size press. There is a need for a coating liquid permeability and high paper strength enhancement effect.

  In order to achieve a high paper strength enhancing effect, for example, it is necessary to increase the molecular weight of polyacrylamide, which is a paper strength enhancing agent. Since the enhancement effect is also insufficient, as an alternative, the composition of the surface paper strength enhancer is also considered, and the pseudo polyion complex is obtained by interacting with the aluminum compound contained in the base paper without impairing the permeability. (Hereinafter referred to as PIC) may be formed to impart a high paper strength enhancing effect to the paper.

  As a technique for the surface paper strength enhancer, for example, a solubility parameter obtained by polymerizing a monomer group containing the carboxyl group-containing monomer and (meth) acrylamide in the presence of a sulfur chain transfer agent by the present applicant is used. A specified paper strength enhancer for paperboard is disclosed (Patent Document 1). This technique pays attention to the permeability of the paper strength enhancer and uses acrylic acid as the carboxyl group-containing monomer, but the paper strength enhancing effect is insufficient.

JP 2014-205938 A

  An object of the present invention is to provide a surface paper strength enhancing agent having an excellent paper strength enhancing effect particularly on paper containing an aluminum compound such as aluminum sulfate.

  In addition to appropriately combining the types of monomers, the present inventors have also intensively studied the interaction between the obtained paper strength enhancer and the aluminum compound, and those that exhibit specific turbidity solve the above problems. As a result, the present invention has been completed. That is, the present invention relates to the following surface paper strength enhancer, coating liquid, and paper manufacturing method.

1. Polymer of monomer component containing (meth) acrylamide (a1), N-substituted (meth) acrylamides (a2), unsaturated monomer (a3) having sulfonic acid group, and α, β-unsaturated dicarboxylic acid (a4) A surface paper strength enhancer having a turbidity at pH 6.5 of an aqueous solution containing (A) and containing 1% by weight of component (A) and 0.5% by weight of aluminum sulfate in a solid content concentration of 70 to 1500 NTU.

2. The amount of the monomer component used is (a1) component 72 to 97 mol%, (a2) component 0.05 to 10 mol%, (a3) component 0.8 to 10 mol%, and (a4) component 0.1 to 15 2. The surface paper strength enhancer according to item 1, which is mol%.

3. (A2) The surface paper strength enhancer according to item 1 or 2, wherein the component contains N, N-dialkyl (meth) acrylamide.

4). 4. The surface paper strength enhancer according to any one of items 1 to 3, wherein the monomer component further contains an α, β-unsaturated monocarboxylic acid (a5).

5). (A) The surface paper strength enhancer in any one of the preceding clauses 1-4 whose weight average molecular weights of a component are 100,000-2,000,000.

6). The surface paper strength enhancer according to any one of 1 to 5 above, wherein the viscosity (temperature 25 ° C.) in a B-type viscometer in an aqueous solution having a solid content concentration of 20% by weight of component (A) is 50 to 1000 mPa · s. .

7). Coating liquid containing the surface paper strength enhancer in any one of the preceding clauses 1-6.

8). A method for producing paper, comprising a step of coating the surface of the base paper with the coating liquid according to item 7 above.

9. 9. The method for producing paper according to 8 above, wherein the base paper contains an aluminum compound.

  According to the surface paper strength enhancer of the present invention, an aluminum compound such as aluminum sulfate is included by using a surface paper strength enhancer that exhibits a predetermined turbidity under specific conditions as an index of interaction with the aluminum compound. Excellent paper strength enhancement effect for paper.

The graph of the turbidity change of the aqueous solution which mixed the surface paper strength enhancer of Example 2 and Comparative Example 4 with the aluminum sulfate aqueous solution

  The paper strength enhancer of the present invention comprises (meth) acrylamide (a1) (hereinafter referred to as component (a1)), N-substituted (meth) acrylamides (a2) (hereinafter referred to as component (a2)), and a sulfonic acid group. And a monomer component polymer (A) containing an unsaturated monomer (a3) (hereinafter referred to as component (a3)) and an α, β-unsaturated dicarboxylic acid (a4) (hereinafter referred to as component (a4)). . “Unsaturated” means one having one or more double bonds or triple bonds in the molecule.

  Examples of the component (a1) include acrylamide and methacrylamide.

  The content of the component (a1) is not particularly limited, and is generally 72 to 97 mol%, preferably 74 to 97 mol, based on 100 mol% of all monomer components, from the viewpoint of exhibiting an excellent paper strength enhancing effect. %, More preferably 75 to 96 mol%.

  The component (a2) is a component used for introducing a crosslinked structure into the polymer, and is not particularly limited, and various known ones can be used. For example, N-alkyl such as N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-tert-butyl (meth) acrylamide, etc. (Meth) acrylamide; N, N-dialkyl (meth) acrylamide such as N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide; N, N ′ -N, N'-alkylene (meth) acrylamides such as methylenebis (meth) acrylamide and N, N'-ethylenebis (meth) acrylamide; and diacetone (meth) acrylamide. These may be used alone or in combination of two or more. Among these, N, N-dialkyl (meth) acrylamide is preferably included, and N, N-dimethylacrylamide is more preferable because it is easy to introduce a crosslinked structure into the polymer.

  The content of the component (a2) is not particularly limited, and is generally 0.05 to 10 mol% with 100 mol% of all monomer components. When the content is less than 0.05 mol%, a crosslinked structure is hardly introduced into the polymer, and when it exceeds 10 mol%, the crosslinked structure is excessively introduced and the polymer is easily gelled. Further, from the same viewpoint, it is preferably 0.1 to 8 mol%, more preferably 0.2 to 7 mol%.

  The component (a3) is a component for adjusting the weight average molecular weight of the component (A), and is not particularly limited, and various known ones can be used. For example, (meth) allyl sulfonic acid, vinyl sulfonic acid, styrene sulfonic acid and the like can be mentioned. It does not specifically limit as a salt, For example, sodium, potassium, calcium, ammonium etc. are mentioned. These may be used alone or in combination of two or more. Among these, methallyl sulfonic acid and / or a salt thereof is preferably included, and sodium methallyl sulfonate is more preferable from the viewpoint of easy adjustment of the weight average molecular weight of the polymer.

  The content of the component (a3) is not particularly limited, and is usually 0.8 to 10 mol% with 100 mol% of all monomer components. When the content is less than 0.8 mol%, the crosslinking reaction cannot be suppressed, and the high molecular weight is promoted to facilitate gelation. When the content exceeds 10 mol%, the polymer has a short chain length. It becomes difficult to produce a large amount of paper and it is difficult to obtain a sufficient paper strength enhancing effect. Moreover, from the same viewpoint, it is preferably 0.8 to 8 mol%, more preferably 0.9 to 7 mol%.

  The component (a4) is a component that forms a pseudo PIC by interacting with the aluminum compound contained in the base paper, and is not particularly limited, and various known ones can be used. For example, maleic acid, fumaric acid, itaconic acid, muconic acid, citraconic acid, or sodium salt or potassium salt of the above acid can be used. These may be used alone or in combination of two or more. Among these, itaconic acid is preferable because it interacts particularly with the aluminum compound contained in the base paper and easily forms a pseudo polyion complex.

  The content of the component (a4) is not particularly limited, and is usually from 0.1 to 15 mol%, assuming that all monomer components are 100 mol%. When the content is less than 0.1 mol%, it becomes difficult to interact with the aluminum compound, and thus the paper strength enhancing effect is hardly exhibited. Moreover, when it exceeds 15 mol%, it becomes difficult to exhibit the paper strength enhancing effect due to the decrease in the content of the component (a1). Moreover, from the same viewpoint, it is preferably 0.2 to 12 mol%, more preferably 0.5 to 10 mol%.

  In addition to the component (a4), an α, β-unsaturated monocarboxylic acid (a5) (hereinafter referred to as the component (a5)) may be used as the monomer component. The component (a5) is not particularly limited, and examples thereof include (meth) acrylic acid, crotonic acid, isocrotonic acid, 3-butenoic acid, and 4-pentenoic acid.

  The content of the component (a5) is not particularly limited, and from the viewpoint of ensuring a sufficient paper strength enhancing effect, the total monomer component is 100 mol%, usually 12 mol% or less, preferably 10 mol% or less, More preferably, it is 5 mol% or less.

  The monomer component may be further used in combination with a cationic unsaturated monomer (a6) (hereinafter also referred to as the component (a6)). The component (a6) is not particularly limited. For example, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, N Tertiary amino group-containing vinyl monomers such as N, diethylaminopropyl (meth) acrylamide; quaternized salts of the vinyl monomers obtained by reacting these tertiary amino group-containing vinyl monomers with a quaternizing agent. It is done. The vinyl monomer salt may be an inorganic acid salt such as hydrochloride or sulfate, or an organic acid salt such as acetate. Examples of the quaternizing agent to be reacted include methyl chloride, benzyl chloride, dimethyl sulfate, epichlorohydrin and the like. These may be used alone or in combination of two or more.

  The content of the component (a6) is not particularly limited, but from the viewpoint of securing a sufficient paper strength enhancing effect, the total monomer component is 100 mol%, preferably about 0.1 to 10 mol%, more preferably It is about 0.5-5 mol%.

  An unsaturated monomer (a7) other than the components (a1) to (a6) (hereinafter also referred to as component (a7)) may be used in combination with the monomer component. The component (a7) is not particularly limited, and examples thereof include di (meth) acrylates such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and polyethylene glycol di (meth) acrylate; divinyl adipate, sebacin Divinyl esters such as divinyl acid; epoxy acrylates, urethane acrylates; aromatic unsaturated monomers such as styrene, α-methylstyrene, vinyltoluene; methyl (meth) acrylate, ethyl (meth) acrylate, (meth) Alkyl (meth) acrylates such as propyl acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl (meth) acrylate; vinyl carboxylates such as vinyl acetate and vinyl propionate Kind Cumene, alpha-methylstyrene dimer, 2,4-diphenyl-4-methyl-1-pentene.

  The content of the component (a7) is not particularly limited, but from the viewpoint of securing a sufficient paper strength enhancing effect, the total monomer component is set to 100 mol%, preferably about 0.1 to 10 mol%, more preferably. It is about 0.5-5 mol%.

  In the monomer component, unless the effect of the present invention is impaired, mercaptans such as 2-mercaptoethanol and n-dodecyl mercaptan; alcohols such as ethanol, isopropyl alcohol and pentanol; α-methylstyrene dimer, ethylbenzene and isopropyl Aromatic compounds such as benzene and cumene; carbon tetrachloride and the like may be further used in combination. These may be used alone or in combination of two or more, and is preferably about 0.001 to 5 parts by weight with respect to 100 parts by weight of the total monomer components.

  The component (A) is not particularly limited, and can be obtained by a conventionally known monomer dropping polymerization method, a simultaneous polymerization method in which a monomer solution is charged all at once, or a method combining these. As a specific example, a solution of a polymerization initiator is added to a solution containing components (a1) to (a4) and, if necessary, components (a5) to (a7), in a solvent charged in the reactor in advance. After the addition, a method of polymerizing at about 50 to 100 ° C. for 1 to 8 hours may be mentioned. In addition, although it does not specifically limit as a solvent, Usually, it is preferable to use water from the point which fully dissolves and disperse | distributes (a1)-(a7) component.

  The polymerization initiator is not particularly limited, and examples thereof include inorganic peroxides such as ammonium persulfate and potassium persulfate; organic peroxides such as benzoyl peroxide, dicumyl peroxide, and lauryl peroxide; 2,2 ′ -Azo compounds such as azobisisobutyronitrile and dimethyl-2,2'-azobisisobutyrate. These may be used alone or in combination of two or more. If necessary, the reaction system may be a redox system by using a reducing agent such as sodium bisulfite or sodium thiosulfate together. Although it does not specifically limit as content of a polymerization initiator, About 0.05-2 weight part is preferable with respect to 100 weight part of all the monomer components.

  As the physical properties of the component (A) of the present invention, in particular, 1% by weight of the component (A) and aluminum sulfate in solid content concentration so as to exert a good paper strength enhancing effect on paper containing an aluminum compound such as aluminum sulfate. The turbidity of the aqueous solution containing 0.5% by weight is important. Hereinafter, the turbidity will be described.

  Turbidity is the degree of turbidity, and is a value obtained by measuring 180 degree scattered light using 900 nm infrared light using ANALITE NEPHELOMETER 152 (manufactured by McVan Instruments). The value refers to a relative evaluation value with respect to a standard substance (formazine standard solution 400 NTU, manufactured by Wako Pure Chemical Industries, Ltd.).

  The turbidity in the present invention is measured with an aqueous solution containing the component (A) and aluminum sulfate at respective predetermined concentrations. As the method for preparing the aqueous solution, the component (A) may be mixed with an aqueous aluminum sulfate solution diluted in advance with ion-exchanged water to a predetermined concentration. The component (A) and aluminum sulfate may be mixed with ion-exchanged water. It may be diluted to a concentration and mixed. The turbidity of component (A) correlates with the degree of PIC formation, and its value varies depending on pH. When the component (A) starts to form PIC, turbidity occurs in the diluted solution. When the pH is changed, the turbidity value increases and the distribution has a maximum value. Thereafter, when the pH is further changed, the turbidity value starts to decrease. In the present invention, turbidity at pH 6.5 is used as a value as a condition closer to the papermaking environment.

  The turbidity is usually 70 to 1500 NTU. When the turbidity is less than 70 NTU, the formation of a pseudo PIC of the aluminum compound in the base paper and the component (A) tends to be weakened, and when it exceeds 1500 NTU, it can interact with the aluminum compound in the base paper (a4) Since the content of the component is relatively increased, the content of the component (a1) is decreased, and the paper strength enhancing effect is hardly exhibited. From the same viewpoint, the turbidity at pH 6.5 is preferably 80 to 1400 NTU, more preferably 100 to 1200 NTU.

  In addition, the other physical properties of the component (A) are not particularly limited, and from the viewpoint of the paper strength enhancing effect, for example, the weight average molecular weight (obtained by polyethylene oxide conversion value by gel permeation chromatography (GPC) method). The value is the same; the same applies hereinafter) is usually 100,000 to 2,000,000. From the same viewpoint, it is preferably 200,000 to 1,900,000, more preferably 300,000 to 1,500,000.

  Furthermore, the viscosity (temperature 25 ° C.) in a B-type viscometer in an aqueous solution having a solid content concentration of 20% by weight of the component (A) is usually 50 to 1000 mPa · s from the viewpoint of permeability. Moreover, from the same viewpoint, Preferably it is 60-900 mPa * s, More preferably, it is 80-800 mPa * s.

  The surface paper strength enhancer of the present invention includes additives such as antifoaming agents, preservatives, chelating agents, water-soluble aluminum compounds, urea; oxidized starch, phosphate esterified starch, APS-modified starch, enzyme-modified starch, You may mix | blend starches, such as cationized starch and amphoteric starch.

  The coating liquid of the present invention contains a surface paper strength enhancer, and the stock solution of the surface paper strength enhancer may be used as it is, but from the viewpoint of the permeability of the coating liquid and uniform coating, It is preferable to dilute to a concentration of 0.1 to 15% by weight with water or the like.

  The physical properties of the coating liquid of the present invention are not particularly limited. For example, the viscosity in a B-type viscometer at a temperature of 50 ° C. of an aqueous solution having a solid content concentration of 5% by weight is usually 50 mPa · s or less, preferably 40 mPa · s. s or less.

  Moreover, various well-known additives can also be mix | blended with the said coating liquid as needed. Examples of additives include surface sizing agents, oxidized starches, phosphate esterified starches, APS-modified starches, enzyme-modified starches, cationized starches, and amphoteric starches, celluloses such as carboxymethylcellulose, polyvinyl alcohols, Paper strength enhancers such as water-soluble polymers such as sodium alginate, anti-slip agents, antiseptics, rust preventives, pH adjusters, antifoaming agents, thickeners, fillers, antioxidants, water-proofing agents, Examples include film aids, pigments, and dyes.

  The coated paper of the present invention is obtained by coating the surface of a base paper with the coating liquid of the present invention.

  The base paper is not particularly limited, and examples thereof include PPC paper, ink jet recording paper, foam paper, paperboard, liner, core, newsprint paper, coated base paper, and thermal paper. Among these, it is preferable to apply to the paperboard because the surface paper strength enhancer penetrates well into the base paper and has an excellent paper strength enhancing effect. Further, in the base paper, various chemicals such as a filler, an internal sizing agent, and a paper strength enhancer may be added. In order to exert the paper strength enhancing effect in the present invention, sulfuric acid is contained in the base paper. It is preferable to include an aluminum compound such as aluminum or polyaluminum chloride. As the method, an aluminum compound may be added to the raw material pulp constituting the base paper, or an aluminum compound may be applied to the surface of the obtained base paper.

The addition rate when the aluminum compound is internally added is not particularly limited. However, when the coating liquid is applied, the solid content weight of the raw pulp is determined from the point of interaction with the aluminum compound contained in the base paper. On the other hand, about 0.3-7 weight% is preferable and 0.5-5 weight% is more preferable. Further, even if the coating amount in the case of coating on the surface is not particularly limited, from the same viewpoint, preferably about 0.05-5 g / ^{m 2,} about 0.1-4 g / ^{m 2} is more preferable.

  Moreover, it does not specifically limit as a coating machine for coating to a base paper, A conventionally well-known thing is applicable. For example, a 2 roll size press, a film press, a gate roll coater, a bar coater, an air knife coater, a blade coater, a calendar coater, a spray coater and the like can be mentioned.

The coating amount (solid content) of the coating liquid is not particularly limited, but is preferably about 0.001 to 3 g / m ² from the viewpoint of exerting an excellent paper strength enhancing effect, and preferably 0.005 to ² g / m. ^{About 2} is more preferable.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, the part and% in an Example and a comparative example are a basis of weight unless there is particular notice.

The following compounds are indicated by the following abbreviations.
AM: Acrylamide DMAA: N, N-dimethylacrylamide SMAS: Sodium methallyl sulfonate IA: Itaconic acid AA: Acrylic acid APS: Ammonium persulfate

<Weight average molecular weight>
The weight average molecular weight of the component (A) was measured by gel permeation chromatography (GPC) method under the following measurement conditions. In addition, when (A) component has a cationic functional group, the 1% density | concentration aqueous solution of (A) component is adjusted to pH = 10-11 using 48% sodium hydroxide, and it is 1 at 90 degreeC. After heating for a period of time, the sample is cooled and adjusted to pH = 6-7 using sulfuric acid, and then measured.
(Measurement condition)
・ Device: HLC8120GPC (manufactured by Tosoh Corporation)
-Column used: TSKgel ALPHA-M (manufactured by Tosoh Corporation)
-Detector: UV-visible detector UV-8020 (manufactured by Tosoh Corporation)
RI detector: differential refractometer (manufactured by Tosoh Corporation)
・ Developing solvent: 0.2M sodium nitrate aqueous solution ・ Measured value: The weight average molecular weight obtained in terms of polyethylene oxide was used as the measured value.

<Viscosity>
The component (A) was diluted with ion-exchanged water to a concentration of 10%, adjusted to a temperature of 25 ° C., and then the viscosity was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd.).

Example 1
Put 522 parts of ion-exchanged water into a reactor equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet tube and two dropping funnels, remove oxygen in the reaction system through nitrogen gas, and then heat to 85 ° C did. Separately, 767.8 parts of 50% AM aqueous solution, 5.6 parts of DMAA, 26.8 parts of SMAS, 3.7 parts of IA and 305 parts of ion-exchanged water were charged into the dropping funnel (1). In addition, 1.5 parts of APS and 150 parts of ion-exchanged water were charged into the dropping funnel (2). Next, it was dripped over 3 hours from the dropping funnel (1) and the dropping funnel (2) to the reactor (I). After the completion of dropping, 0.5 part of APS and 10 parts of ion-exchanged water are added, and when the estimated viscosity with a B-type viscometer reaches about 550 mPa · s (temperature 25 ° C., solid content concentration 20% conversion), polymerization is performed. It was made to complete | finish and it cooled and obtained the polymer (A-1). The weight average molecular weight and viscosity of the obtained polymer (A-1) (hereinafter referred to as component (A-1)) are shown in Table 1 (the same applies hereinafter).

Examples 2-9, Comparative Examples 1-5
In the same manner as in Example 1, the monomer components shown in Table 1 were synthesized, and the components (A-2) to (A-9) having a solid content concentration of 20%, (B-1) to (B-5) were synthesized. ) Each component was obtained. In addition, since (B-2) component gelatinized during manufacture, it did not use for subsequent evaluation.

[Preparation of aqueous solution for turbidity measurement]
In advance, 10 parts of aluminum sulfate · 14-18 hydrate (manufactured by Wako Pure Chemical Industries, Ltd.) and 990 parts of ion-exchanged water were mixed to prepare an aluminum sulfate aqueous solution having a solid content concentration of 1%. Next, after mixing 5 parts of (A-1) component (solid content: 1 part) and 45 parts of ion-exchanged water, 50 parts of the aqueous aluminum sulfate solution was added, and an aqueous solution for turbidity measurement (solid content concentration− (A) component: 1%, aluminum sulfate: 0.5%) was prepared. In addition, aqueous solutions were similarly prepared for the components (A-2) to (A-9), the component (B-1), and the components (B-3) to (B-5).

(Turbidity)
The aqueous solution was adjusted to a temperature of 25 ° C. and stirred with a stirrer at 500 rpm. Using a turbidimeter (device name: “ANALITE NEPHELOMETER 152”, manufactured by McVan Instruments), a 1% sodium hydroxide aqueous solution is used to increase the pH, a 1% sulfuric acid aqueous solution is used to lower the pH, and the pH is adjusted to 0.1. The solution was gradually added dropwise so as to change one by one, and the turbidity value at pH 6.5 was measured. If the turbidity value is not stable, wait until it stabilizes, and the value at the stable point is the turbidity value. The turbidity value is a relative value when a formazine standard solution (400 NTU, manufactured by Wako Pure Chemical Industries, Ltd.) is used as a standard substance, and a scattered light of 180 degrees using 900 nm infrared light. It is shown by measuring. Moreover, the graph of the turbidity using the paper strength enhancer of Example 2 and Comparative Example 4 is shown in FIG. The results are shown in Table 1.

[Preparation of coating solution]
The components (A-1) to (A-9), the component (B-1), and the components (B-3) to (B-5) are diluted with ion-exchanged water so that the concentration becomes 5%. A liquid was prepared.

[Preparation of base paper]
Corrugated used paper is beaten with a Niagara-type beater and adjusted to 350 ml of Canadian Standard Freeness (C.S.F.), and aluminum sulfate 14-18 hydrate is added to the solid content weight of the raw pulp. A slurry with 1.0% added was obtained. The papermaking pH at that time was 6.5. Next, the slurry was dehydrated with a tapi sheet machine, pressed at 5 kg / cm ² for 2 minutes, then dried with a rotary dryer at 105 ° C. for 4 minutes, and kept at a temperature of 23 ° C. and a humidity of 50% for 24 hours. The base paper 1 was prepared by adjusting the humidity. Separately, base paper 2-4 under the condition that 0.5%, 2.0%, and 5.0% of aluminum sulfate 14-18 hydrate was added, and base paper under the condition that 1.0% of polyaluminum chloride was added. Each of 5 was also prepared.

Evaluation Examples 1-9, Comparative Evaluation Examples 1-4
Each coating liquid preheated to 50 ° C. was applied to both sides of the base paper using a bar coater on the base paper 1. The coated paper was obtained by drying with a rotary drum dryer at 105 ° C. for 1 minute. In this evaluation, coating was performed so that the solid adhesion amount of the coating liquid was 1.5 g / m ² .

Evaluation Examples 10-13
The base paper 1 was changed to the base papers 2 to 5 by the above method, and coated papers were obtained using the component (A-2).

<Compressive strength>
It measured based on JISP8126 using each coated paper, and showed with specific compressive strength (N * m < ² > / g). The results are shown in Table 2.

<Tensile strength>
Each coated paper was measured according to JIS P8113 and indicated by specific tensile strength (N · m / g). The results are shown in Table 2.

Claims (9)

  Polymer of monomer component containing (meth) acrylamide (a1), N-substituted (meth) acrylamides (a2), unsaturated monomer (a3) having sulfonic acid group, and α, β-unsaturated dicarboxylic acid (a4) A surface paper strength enhancer having a turbidity at pH 6.5 of an aqueous solution containing (A) and containing 1% by weight of component (A) and 0.5% by weight of aluminum sulfate in a solid content concentration of 70 to 1500 NTU.   The amount of the monomer component used is (a1) component 72 to 97 mol%, (a2) component 0.05 to 10 mol%, (a3) component 0.8 to 10 mol%, and (a4) component 0.1 to 15 The surface paper strength enhancer according to claim 1, which is mol%.   The surface paper strength enhancer according to claim 1 or 2, wherein the component (a2) contains N, N-dialkyl (meth) acrylamide.   The surface paper strength enhancer according to any one of claims 1 to 3, wherein the monomer component further contains an α, β-unsaturated monocarboxylic acid (a5).   (A) The weight average molecular weight of a component is 100,000-2,000,000, The surface paper strength enhancer in any one of Claims 1-4.   The surface paper strength enhancement according to any one of claims 1 to 5, wherein the viscosity (temperature 25 ° C) in a B-type viscometer in an aqueous solution having a solid content concentration of 20% by weight of component (A) is 50 to 1000 mPa · s. Agent.   The coating liquid containing the surface paper strength enhancer in any one of Claims 1-6.   A method for producing paper, wherein the coating liquid according to claim 7 is coated on the surface of a base paper.   The paper manufacturing method according to claim 8, wherein the base paper contains an aluminum compound.