JP3434055B2 - Internal additives for paper - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an internal additive for paper.
More specifically, the present invention relates to an internal additive for paper which has a paper strength enhancing effect and can improve the opacity of the paper.

[0002]

2. Description of the Related Art In recent years, in the case of newspapers, newspapers, magazines, dictionaries, telephone books, timetables, etc., the weight of the paper has been reduced. These lightweight papers can (1) pack the ever-increasing amount of information and advertising volume into papers with a small weight, (2) enable the miniaturization with the same amount of information, and reduce transportation costs. ) In particular, there are advantages such as easy folding of multi-page paper such as newspaper, and (4) resource saving and cost reduction. However, there are many problems associated with the weight reduction of paper, and insufficient strength of paper strength, in particular, insufficient tear strength, backing of printed characters and images, and lack of opacity have become problems. It is said that. Further, as the coating speed of the coating agent has been increased, uneven coating of the coating agent has occurred, and the weight reduction by coating a small amount on the paper surface has reached the limit. Under these circumstances, insufficient strength of paper strength, particularly insufficient tear strength, backing of printed characters and images, and insufficient opacity have become problems, and improvements are needed.

Conventionally, as internal additives for paper for strengthening paper strength, there are polyacrylamide, carboxymethylcellulose, modified starch, carboxymethylcellulose, melamine resin, polyethyleneimine, etc., but the breaking length, bursting strength, folding endurance, etc. Although the effect of improving the strength and IGT pick is recognized, it has a serious defect that the tear strength is lowered. In addition, in order to solve problems such as printed marks and backing of images and lack of opacity, inorganic fillers such as calcium carbonate, titanium oxide, talc, clay, colloidal hydrous silica (commonly called white carbon) and urea resin-based These organic fillers are used as internal additives. Addition of these fillers improves opacity, whiteness, smoothness, printability, etc., and the effect of improving opacity after printing is recognized. However, when the above-mentioned filler is used as a filler at the time of paper making, a decrease in paper strength becomes a problem,
There is an urgent need to reduce the use of fillers in order to reduce the weight of paper. In addition, as a solution to the above problem of insufficient opacity, it is disclosed in Japanese Patent Publication No. HEI 6-6 that a cationic polymer emulsion obtained by emulsion polymerization of vinyl acetate in the presence of cationic polyvinyl alcohol is used as an opacity improver for paper. No. 15756. However, in the polyvinyl acetate emulsion described in the above publication, the cationic polyvinyl alcohol is merely physically adsorbed on the emulsion surface as a dispersant, and the intended effect in the present invention is not sufficiently exhibited. As described above, those which have been proposed as internal additives for paper such as polyacrylamide, colloidal hydrous silica and cationic polymer emulsion have so far been described in terms of strength of paper strength, particularly tear strength and opacity. The current situation is that no one has a satisfactory improvement effect.

[0004]

The object of the present invention is to improve the opacity of the paper without lowering the tear strength of the paper, and to increase the breaking length, burst strength, folding endurance,
An object is to provide an internal additive for paper which provides rigidity and tear strength. In particular, it is to provide an internal additive for paper which is useful for lightweight paper.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that an ethylenically unsaturated monomer or diene containing a cationic polyvinyl alcohol having a mercapto group as a dispersant. The present invention has been completed by finding an internal additive for paper which is composed of polymer fine particles of a system monomer. That is, the internal additive for paper of the present invention exhibits excellent effects on the breaking length, burst strength, folding endurance, IGT pick and tear strength without lowering the tear strength of the paper, and the opacity of the paper. It has been found that the above requirements can be met and requirements for weight reduction of paper, speeding up of printing speed, color printing and minute amount coating can be satisfied.

The present invention will be described in detail below. The polyvinyl alcohol used as a dispersant in the present invention (hereinafter, polyvinyl alcohol may be abbreviated as PVA) must have both a mercapto group and a cationic group. First, a method of introducing a mercapto group into PVA will be described. PVA having mercapto group
Has a sufficient effect even in a polymer having a mercapto group in the main chain of the PVA molecule, but in this case, it may be insolubilized by forming a disulfide bond due to the oxidation of PVA itself, so mercapto may be present only at one end of the molecule. PVA having a group is more preferable because it is easy to handle without fear of insolubilization. A PVA having a mercapto group only at one end of such a PVA molecule is a vinyl ester polymer obtained by polymerizing a vinyl monomer mainly containing a vinyl ester monomer in the presence of thiol acid. Is obtained by saponification by a conventional method. The thiol acid used above is −
It includes an organic thiol acid having a COSH group. Examples thereof include thiol acetic acid, thiol propionic acid, thiol butyric acid, and thiol valeric acid, with thiol acetic acid being most preferred. The vinyl ester-based monomer can be used as long as it can be radically polymerized. Examples thereof include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate, among which PVA is obtained. From the viewpoint, vinyl acetate is preferable.

The cationic PVA of the present invention is obtained by copolymerizing the above vinyl ester with the cationic monomer represented by the following general formula (1), and saponifying this by a conventional method.

CH ₂ = CXY (1)

(However, X; H or CH ₃ Y; CONR ¹ R ² or CH ₂ OCH ₂ ABR ¹ ; H, CH ₃ , C ₂ H ₅ , n-C ₃ H ₇ or i-
C ₃ H ₇ R ² ; H, CH ₃ , C ₂ H ₅ or CR ³ R ⁴ (C
^{_{H 2) n N + (CH}} 3) 3 · X - A; CH (OH) CH 2, C (CH 3) (OH) CH 2
Or _{CH (OH) CH 2 CH 2} B; N (R 5) 2 or ^{_{N + (R 5) 3 ·}} X - R 3, R 4; H or ^{_{CH 3 R 5; CH 3,}} C 2 H 5 n; 1-9 integer X ^-; represents an anion, respectively. ) Examples of the above-mentioned monomer include trimethyl- (3-acrylamido-3-dimethylpropyl) -ammonium chloride, 3-acrylamidopropyltrimethylammonium chloride, 3-methacrylamidopropyltrimethylammonium chloride and N- (3-allyloxy- 2-Hydroxypropyl) dimethylamine quaternary ammonium salt, N- (4-
Allyloxy-3-hydroxybutyl) diethylamine quaternary ammonium salt , further acrylamide, N-
Methyl acrylamide, N-ethyl acrylamide,
Examples thereof include quaternary ammonium salts such as N, N-dimethylacrylamide, diacetoneacrylamide, N-methylolacrylamide, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, and N-methylolmethacrylamide. The content of these cationic group-containing monomer units is preferably 0.01 to 20 mol%, more preferably 0.05 to 12 mol%, and 0.1 to 20 mol% is preferable.
8 mol% is particularly preferred. When the content of the cationic group-containing monomer is less than 0.01 mol%, there is no effect of introducing the cationic group, and when it exceeds 20 mol%, the characteristics of the cationic PVA of the present invention are impaired and tear strength is increased. In addition, the breaking length, burst strength, folding endurance, and IGT pick are reduced, and it is difficult to obtain the emulsion targeted by the present invention.

Further, it is possible to copolymerize the vinyl ester and the cationic group-containing monomer with the copolymerizable monomer in the coexistence thereof, within the range not impairing the gist of the present invention. For example, olefins such as ethylene, propylene, 1-butene and isobutene, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-acrylate
Acrylic esters such as butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate. , Methacrylic acid n-
Methacrylic acid esters such as butyl, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, methyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl. Vinyl ethers such as vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, nitriles such as acrylonitrile and methacrylonitrile, vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride. , Allyl compounds such as allyl acetate, allyl chloride, fumaric acid, maleic acid, itaconic acid,
Carboxyl group-containing compounds such as maleic anhydride, phthalic anhydride, trimellitic anhydride or itaconic anhydride and esters thereof, ethylenesulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-
Examples thereof include sulfonic acid group-containing compounds such as methylpropanesulfonic acid, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate. The amount of the above monomer is preferably 5 mol% or less.

Polymerization of vinyl esters such as vinyl acetate in the presence of thiol acid and a vinyl-based monomer mainly containing a monomer having a cationic group is carried out in the presence of a radical polymerization initiator in a bulk polymerization method, Although any method such as a solution polymerization method, a suspension polymerization method and an emulsion polymerization method can be used, the solution polymerization method using methanol as a solvent is industrially most advantageous. The amount and method of addition of the thiol acid present during the polymerization to the polymerization system are not particularly limited, and are appropriately selected depending on the physical properties of the intended polyvinyl ester polymer. As a polymerization method, a known method such as a batch method, a semi-continuous method or a continuous method can be adopted. Examples of the radical polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,
Known radical polymerization initiators such as 4-dimethylvaleronitrile), benzoyl peroxide and carbonate carbonate can be used, but azo initiators such as 2,2′-azobisisobutyronitrile are easy to handle and preferred. Radiation, electron beam, etc. can also be used. Although the polymerization temperature is determined by the physical properties of the target modified PVA, it is usually 1
It is selected from the range of 0 to 90 ° C. The initiator used at that time is appropriately selected depending on the polymerization temperature. After the polymerization for a predetermined time, the unpolymerized vinyl esters are removed by a usual method to obtain a cationically modified polyvinyl ester polymer having a thiol ester group at the terminal.

The polyvinyl ester polymer thus obtained is saponified by a conventional method, but it is usually preferable to saponify it in an alcohol solution, especially a methanol solution. As the alcohol, not only an anhydride but also a small amount of water-containing alcohol may be used according to the purpose, and an organic solvent such as methyl acetate or ethyl acetate may be optionally contained. The saponification temperature is usually selected from the range of 10 to 90 ° C. As the saponification catalyst, for example, alkaline catalysts such as sodium hydroxide, potassium hydroxide, sodium methylate and potassium methylate are preferable, and the amount of the catalyst used is appropriately determined depending on the degree of saponification and the water content. The molar ratio to the ester unit is 0.001 or more, preferably 0.002 or more. If the amount of alkali is too large, it becomes difficult to remove the residual alkali from the polymer, and the polymer is not colored, which is not preferable, and the molar ratio is preferably 0.2 or less. When the polyvinyl ester-based polymer contains a component that reacts with an alkali catalyst such as a carboxyl group or its ester group to consume an alkali, the amount of the alkali catalyst added is used.

By the above saponification reaction, the thiol ester at the end of the cationic modified polyvinyl ester polymer having a thiol ester group at the end and the vinyl ester bond in the main chain are saponified, and the polymer end is mainly linked to the mercapto group. Although the chain is vinyl alcohol, the degree of saponification of the vinyl ester unit in the main chain is appropriately selected according to the purpose of use. The polymer precipitated after the saponification reaction can be usually obtained as a white powder by purifying by a known method such as washing with methanol or the like, removing residual alkali, impurities such as an alkali metal salt of acetic acid, and drying. it can. The method for producing a cationic modified PVA having a mercapto group at the terminal used in the present invention has been described above. The modified PVA has a viscosity average degree of polymerization (hereinafter abbreviated as polymerization degree) of 50 to 8,000. Is necessary
100-6000 are preferable and 100-5000 are more preferable. The degree of polymerization of the modified PVA is JIS-K6726.
Quasi-Ji, for the polymer, which was purified after re-saponification, underwater,
It is represented by the viscosity average degree of polymerization (P) obtained by the following formula from the intrinsic viscosity [η] measured at 30 ° C. P = ([η] × 10 ³ /8.29) ^{(1 / 0.62) When the} degree of polymerization is less than 50 or more than 8000,
Stable polymer particles cannot be obtained . The saponification degree of the modified PVA having a mercapto group and a cation structural unit of the present invention varies depending on the types of other modifying groups and cannot be generally stated, but from the viewpoint of water solubility and paper strength development, it is 40 to 99.
It is preferably 99 mol%, more preferably 50 to 99.9 mol%, still more preferably 60 to 99.5 mol%.

The modified PVA obtained by the above-mentioned method is used as a dispersion stabilizer for polymerization to (co) polymerize an ethylenically unsaturated monomer or a diene-based monomer to obtain an aqueous solution of polymer fine particles. As a method for obtaining the dispersion liquid, a known polymerization method such as an emulsion polymerization method, a dispersion polymerization method or a suspension polymerization method can be adopted. Further, a polymer obtained by dehydrating the above-mentioned aqueous polymer fine particles by coagulation filtration, drying or the like to obtain fine powder particles by the method of disassembling or pulverizing can also be used in the present invention. The average particle size of the polymer fine particles of the present invention has a great influence on the physical properties of paper, and is preferably 0.1 to 200 μm. From the viewpoint of light scattering effect and paper strength improvement, 0.10 to 100 μm is more preferable, and 0.1 to 50 μm.
μm is particularly preferred. From the viewpoint of the average particle size of the obtained polymer fine particles and the easiness of production, the polymer fine particles of the present invention are produced by using the modified PVA as a dispersion stabilizer for emulsion polymerization in an ethylenically unsaturated monomer or diene monomer unit amount. Emulsify body (co)
Aqueous emulsions of polymers obtained by polymerization are particularly preferred.

In carrying out emulsion (co) polymerization of an ethylenically unsaturated monomer or a diene monomer by using the modified PVA of the present invention as a dispersion stabilizer for emulsion polymerization, water,
The above-mentioned monomers may be added temporarily or continuously in the presence of a dispersion stabilizer for emulsion polymerization and a polymerization initiator, and any ordinary emulsion polymerization method such as heating or stirring may be carried out. A method of continuously adding the emulsion obtained by mixing and emulsifying the monomer with the modified PVA aqueous solution may also be carried out.

Examples of the ethylenically unsaturated monomer in the present invention include olefins such as ethylene, propylene and isobutene, vinyl chloride, vinylidene chloride, vinyl fluoride,
Halogenated olefins such as vinylidene fluoride, vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, vinyl pivalate, etc. vinyl esters, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, I-Propyl acrylate, n-butyl acrylate, i-butyl acrylate, t acrylate
-Butyl, 2-ethylhexyl acrylate, acrylic acid dodecyl, octadecyl acrylate, and other acrylic acid esters, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-methacrylate. Butyl, i-butyl methacrylate, t-butyl methacrylate, methacrylic acid 2
-Methacrylic acid esters such as ethylhexyl, dodecyl methacrylate, octadecyl methacrylate, acrylamide, methacrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, acrylamide-2-methylpropanesulfonic acid and its sodium salt, an acrylamide-based single Polymers, acrylonitrile,
Nitriles such as methacrylonitrile, allyl compounds such as allyl acetate and allyl chloride, styrene, α-methylstyrene, styrene monomers such as p -methylstyrenesulfonic acid and its sodium and potassium salts, and other N-vinyls Examples thereof include pyrrolidone, and examples of the diene-based monomer include butadiene, isoprene, chloroprene and the like. Among these, from the viewpoint of improving the opacity of paper, a monomer having a high refractive index is preferable, and specifically, a styrene-based monomer having an aromatic group is used. These monomers are used alone or in combination of two or more.

The amount of the dispersion stabilizer for emulsion polymerization comprising a cationic PVA having a mercapto group according to the present invention varies somewhat depending on the degree of polymerization of the modified PVA, the degree of saponification, and the required solid content of the emulsion. Usually, it is 0.2 to 20 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the monomer. When the amount of the modified PVA used is less than 0.2 parts by weight with respect to 100 parts by weight of the monomer, polymerization stability and chemical stability are deteriorated, and P
Mechanical stability, which is a feature of the VA protective colloid based aqueous emulsions are also impaired, undesirable from becoming poor fixing to pulp not only eliminates valuable as an emulsion. On the other hand, if the amount of the modified PVA is more than 20 parts by weight, and at the same time the emulsion viscosity is high enrichment it is difficult, difficult to fix to pulp.

As the polymerization initiator, known ones for emulsion polymerization can be used, but a nonionic initiator is preferred from the viewpoint of the effect of the cationic group, which is one of the features of the present invention, and for example, hydrogen peroxide. Is. In addition, the modified PV of the present invention
A mercapto group and potassium bromate, potassium persulfate,
Redox systems using water-soluble oxidizers such as ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, etc. are also possible. Among them, potassium bromate does not generate radicals under ordinary polymerization conditions, and is a PVA-based polymer. Since it decomposes only by a redox reaction with the terminal mercapto group to generate a radical, the modified PVA and the block copolymer are effectively produced, and as a result, the stabilizing effect of the emulsion is increased, which is preferable. It is also possible to use potassium bromate at the start of the polymerization and then add another polymerization initiator or oxidizing agent, preferably hydrogen peroxide. When emulsion (co) polymerization is performed using the dispersant composed of a cationic PVA having a mercapto group in the present invention, the polymerization system is preferably acidic. This is because the mercapto group, which exhibits extremely active reactivity in radical polymerization, is ionically added to the double bond of the monomer and disappears at a high rate under basic conditions, resulting in a marked decrease in polymerization efficiency. Because
Depending on the type of unsaturated monomer, all operations are at pH 6
Hereinafter, it is preferable to carry out the treatment at a pH of 4 or less. In the present invention, the cationic PVA-containing dispersant having a mercapto group is preferably used alone, but conventionally known anionic, nonionic, cationic surfactants and water-soluble polymer compounds are used. It can also be appropriately used within a range that does not impair the effects of the present invention. The average particle size of the emulsion particles obtained by the above-mentioned emulsion (co) polymerization greatly affects the paper performance, and thus the above-mentioned particle size is preferable. Since the primary particle diameter of the emulsion particles obtained varies depending on the type of the monomer used, it is possible to adjust the particle diameter to an arbitrary particle diameter by a technique such as a seed polymerization method or aggregation. From this point, a chain transfer agent may be added to the polymerization system. The average particle size of the emulsion particles is preferably 0.2 to 50 μm from the viewpoints of the light scattering effect, the yield on pulp, and the improvement of paper strength.

Next, an example of actual papermaking using the cationic polymer fine particles of the present invention will be described in detail. The amount of cationic polymer particles added to the paper depends on the type of pulp,
The emulsion solid content is 0.1 to 100% by weight, preferably 0.1 to 50% by weight, more preferably 0.1 to 50% by weight based on the solid material of the dried pulp, although it depends on the properties of the cationic group-containing fine particles. It is 20% by weight. When the emulsion solid content is less than 0.1% by weight based on the absolutely dried raw material pulp solid content, the effect of the present invention is not exhibited, and when it exceeds 100% by weight, the opacity of the paper is improved. In some cases, the paper strength may decrease, and the original performance of the paper will decrease. Further, conventionally known fillers may be used in combination as needed, but in the present invention, they can be used in combination within a range that does not impair the effects of the present invention. Examples of the inorganic filler include titanium oxide, talc, colloidal hydrous silica (usually white carbon), clay, calcium carbonate and the like. The amount of the inorganic filler used is 100% by weight or less based on the emulsion solid content. One of the effects of the paper internal strength additive of the present invention is that it is for lightweight paper, and the smaller the amount of inorganic filler used, the better, and most preferably unused. Further, it is also possible to use an aqueous dispersion of fine particles such as a conventionally known emulsion or powder fine particles in combination as long as the effect of the present invention is not impaired. Further, it is possible to use a known paper-strengthening agent such as polyacrylamide, carboxymethylcellulose, modified starch, carboxymethylcellulose, melamine resin and polyethyleneimine in combination with the polymer fine particles of the present invention.

The pulp used in the present invention is not particularly limited. For example, it is mainly composed of wood pulp such as KP, GP, DIP, or vegetable fiber, and can be appropriately selected and used. These pulps can be used alone or in combination.

[0021]

EXAMPLES The present invention will be described in more detail by way of examples. In the following, "parts" and "%" mean "parts by weight" and "% by weight", respectively, unless otherwise specified.
In addition, the measuring method of each physical property value in an Example is based on the method shown below. Viscosity: Measured with a B-type viscometer manufactured by Tokyo Keiki at 20 ° C. and a rotor rotation speed of 12 rpm. Breaking length: determined by the following formula according to JIS P8113-1976. Breaking length (km) = tensile strength / (width of test piece x basis weight of test piece)
× 1000 Specific tear strength: determined by the following formula according to JIS P8116. Specific tear strength = (reading of scale / number of tears) × 16 / basis weight of test piece × 100 Folding endurance: determined according to JIS P-8115. Clark stiffness: determined according to JIS P-8143. White paper opacity: Value corrected to absolute dry basis weight of 42.5 g / m ^2.

[0022] Examples 1-9 and Comparative Example 5 (b) regulating manufactured reflux condenser cationic emulsion, dropping funnel, a thermometer, a nitrogen-introducing port, two liters mercapto group in a glass container at the end equipped with a stirrer 25 g of a cationic PVA having PVA (polymerization degree 510, saponification degree 98.7 mol%, 3-methacrylamidopropyltrimethylammonium chloride 1 mol% copolymer), ion-exchanged water 500 g, and dissolved by heating. The pH was adjusted to 4.0 with dilute sulfuric acid. Then 1
350 g and t of styrene while stirring at 50 rpm
-0.3 g of dodecyl mercaptan was charged, the temperature was raised to 70 ° C, and 10 g of a 4% potassium persulfate aqueous solution was added to initiate polymerization. 80 minutes after emulsion polymerization for 8 hours
The liquid temperature was raised to ℃ and aged for 30 minutes. Then, it was cooled to room temperature to obtain a cationic styrene resin emulsion. Solid content is 42.3%, viscosity at 20 ° C is 14600
cps, average particle size was 0.46 μm. This emulsion is referred to as emulsion A.

[0023]

[Table 1]

(Note) MAPTAC; 3-methacrylamidopropyltrimethylammonium chloride APTAC; 3-acrylamidopropyltrimethylammonium chloride

The modified PVs shown in Table 1 were prepared in the same manner as described below.
With A (PVA-1~5), conditions shown in Table 2, the cationic emulsion B~H was made tone. Table 2 shows the concentration, viscosity, average particle size and stability of the obtained cationic emulsion.

[0026]

[Table 2] (Note) MMA; methyl methacrylate VAc; vinyl acetate

As is clear from Table 2, the emulsion polymerization of styrene using a cationic colloid containing no mercapto group as a protective colloid blocked the emulsion during the polymerization, whereas the emulsion polymerization of styrene contained a cationic mercapto group-containing cationic polymer. It can be seen that emulsion polymerization of styrene and methyl methacrylate using PVA as a protective colloid gives an emulsion with excellent stability.

[0028] (b) by an emulsion A regulating manufactured Table 2 wherein the cationic powdery particles to spray drying to obtain a powdery cationic fine particles having a particle size of 25 [mu] m (spray dried particles). The addition using the same reactor and at the cationic emulsion tone made, Table 1 PVA-
3g 12g, deionized water 500g, methanol 500
After g was charged and dissolved by heating and replaced with nitrogen, the internal temperature was set to 70 ° C. A mixed solution of 150 g of methyl methacrylate and 0.5 g of azobisisobutyronitrile as a polymerization initiator was added, and the polymerization was continued at 70 ° C. for 6 hours. The average particle size is 2.
It was 4 μm. The dispersed polymer fine particles were cast on a PET film and dried at 50 ° C. under reduced pressure to obtain a film. The film was cooled and pulverized to obtain powdery cationic fine particles having an average particle diameter of 22 μm (dispersion polymerization fine particles).

(C) Papermaking test pulp (blended pulp, 130 ml CSF) 0.8% aqueous dispersion was thoroughly stirred, and the above cationic emulsions A to H were added to the pulp at a solid content ratio of 2.0%. After that, the mixture was stirred for 2 minutes, and the pH of the dispersion was adjusted to 4.0 with a sulfuric acid band. After that, the mixture is stirred for 2 minutes, and the solid content of the aqueous dispersion is diluted to 0.3% with water and stirred.
A square paper machine (made by Kumagai Riki) is used and the basis weight is 37 ± 2 g.
Paper was made so that it would be / m ² . Next, wet paper is 3.5 Kg / c
After decompressing with m ² for 5 minutes, exchanging blotter paper and decompressing with the same pressure for 2 minutes, rotary drier (surface temperature 1
Contact dried at 10 ° C for 7 minutes. The resulting paper is 20
The humidity was adjusted for 48 hours under conditions of ℃ and 65% RH, and the measurement was carried out for various physical properties of paper strength. The results are shown in Examples 1 to 9 and Comparative Example 5 in Table 3.

As controls, cation-modified PVA containing no internal additive and mercapto group-free cation-modified PVA (PVA-
5: polymerization degree 530, saponification degree 98.5 mol%, 3-methacrylamidopropyltrimethylammonium chloride 1 mol% copolymer), commercially available polyacrylamide alone (“Polystron 117”, manufactured by Arakawa Chemical Co., Ltd.) and white carbon. The results of the same tests as above are shown in Comparative Examples 1 to 4 in Table 3.

[0031]

[Table 3]

1) spray-dried fine particles, 2) dispersion-polymerized fine particles, 3) unit; cm3 / 100

As is clear from Comparative Examples 2, 3, and 5, polyacrylamide, cation-modified PVA, and cation-modified PVA, which are typical conventional internal additives, are used.
Cationic emulsion composed of a polymer is
Tear strength, in the folding endurance, the white paper opacity and Clark stiffness is substantially the same performance as an internal additive additive-free i.e. pulp itself, there is no effect as an internal additive. This seems to be due to the poor yield of the internal additive to the pulp. In addition, the white carbon of Comparative Example 4 has a higher yield on pulp than that of the other Comparative Examples, and has an effect of improving the opacity of white paper, but exhibits an effect of improving the breaking length, folding endurance and tear strength. Not done. In comparison with these, the internal additive for a paper of a cationic emulsion comprising a cationic PVA having a mercapto group of the present invention has excellent tear length, tear strength, folding endurance and Clark stiffness, Further, it can be seen that it has an improving effect on all physical properties of the paper such as improving the opacity of white paper, and shows a balanced improving effect.

[0034]

By using the cationic emulsion of the cationic PVA having a mercapto group of the present invention as an internal additive for paper, the breaking length, tear strength, folding endurance, Clark stiffness and It provides a well-balanced paper with all of the white paper opacity. Further, by using the cationic emulsion of the present invention as an internal additive for paper, a paper satisfying both the above-mentioned excellent tear strength and opacity improvement of the paper can be obtained at the same time. Manufacturing is achieved. In particular, the production of lightweight paper with excellent performance is achieved.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI // C08F 36/04 C08F 36/04 (56) Reference JP-A-7-70989 (JP, A) JP-A-6-128443 (JP, A) JP 5-112605 (JP, A) JP 60-197229 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) D21H 11/00-27 / 42 C08F 2/00-246/00 C08L 1/00-101/14

Claims (3)

(57) [Claims] 1. An internal additive for paper, which comprises fine polymer particles of an ethylenically unsaturated monomer or a diene monomer with a cationic polyvinyl alcohol having a mercapto group as a dispersant. 2. The polymer fine particles are an aqueous dispersion obtained by emulsion polymerization, dispersion polymerization or suspension polymerization.
Internal additive for paper described. 3. The internal additive for paper according to claim 1, wherein the cationic polyvinyl alcohol having a mercapto group is a cationic polyvinyl alcohol having a mercapto group at the terminal.