JP3120553B2 - Paper coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a paper coating composition,
More particularly, the present invention relates to a paper coating composition which provides a coated paper excellent in water resistance and ink receptivity required particularly in offset printing, and has excellent coating operability in the production of the coated paper.

[0002]

2. Description of the Related Art Coated paper is produced in large quantities because it improves the gloss, whiteness, smoothness and print image reproducibility of the paper itself.
Has been consumed. The coated paper is generally obtained by coating a base paper with a paper coating composition containing a pigment and a binder, and is mainly used as printing paper or printing paperboard.

[0003] As the pigment, for example, inorganic pigments such as clay, calcium carbonate, titanium dioxide, aluminum hydroxide, and satin white, and organic pigments formed from organic compounds such as polystyrene are used.

[0004] Carboxy-modified latex is mainly used as a binder, and starch, casein, soybean protein, polyvinyl alcohol and the like are used as secondary binders. The main role required for the latex used as a binder is to adhere the pigments to each other and to fix them on the base paper, that is, to develop the adhesive strength. For high-speed printing and multi-coat printing, it is essential to prevent the pigment from falling off the coated paper surface and the peeling of the coated layer to achieve beautiful printing. This adhesive strength is usually indicated as the surface strength of the coated paper.

[0005] In the production of coated paper, a base paper is coated with a paper coating composition. As a coating apparatus, a roll coater, an air knife coater, a bar coater, a blade coater, or the like is used. By the way, during the coating work,
The paper coating composition may adhere to various rolls and the like attached to these coaters. If this deposit is difficult to remove by washing with water, it takes a lot of labor and time to wash, lowers coating operability and productivity, and when the remaining deposit is transferred to coated paper. Is a major problem in quality control because defects occur in coated paper.

[0006] On the other hand, the manufactured coated paper is usually printed and finally turned into a commercial printed matter such as a publication, a poster, a flyer, or a catalog. In recent years, offset printing has become the mainstream printing method. Since most offset printing uses a fountain solution, the coated paper as a printing medium is required to have sufficient water resistance (water resistant surface strength). Further, in order to make print reproducibility sufficient, coated paper is required to have excellent ink receptivity.

[0007] As described above, with the adoption of the offset printing method and the sophistication of the demand for the quality of printed matter, the quality requirements for coated papers are becoming increasingly sophisticated, and the required properties for paper coating compositions are also becoming more sophisticated. . That is, the coating composition is
When it adheres to various rolls attached to the coater at the time of coating, it is required to be easily washed off with water and to have good washing properties. In other words, in a state where the film adheres to a roll or the like and is dried, it is required that the water resistance and the adhesiveness of the coating film formed by the paper coating composition are low. On the other hand, a coated paper obtained by coating a paper coating composition on a base paper with a coater and subsequently drying the coated paper composition is required to have excellent water resistance and ink acceptability.

The latex used as a binder has a significant effect on these properties required of the paper coating composition. Conventionally, in a paper coating composition, an aliphatic conjugated diene-based monomer as a binder, an ethylenically unsaturated carboxylic acid monomer, and a monomer mixture composed of other copolymerizable monomers by emulsion polymerization. A carboxy-modified copolymer latex obtained by copolymerization is widely used. In order to improve the water resistance of the coated paper, it is effective to reduce the particle size of the latex, but the problem is that the ink receptivity is reduced and the washability of the coating film adhered to a roll or the like is reduced. Occurs. If the proportion of the aliphatic conjugated diene-based monomer in the monomer composition is reduced, the washability of the coating film is improved, but the adhesive strength is reduced and the water resistance of the coated paper is reduced. I will. Therefore, it is extremely difficult to balance the required qualities such as water resistance, ink acceptability, and detergency in a paper coating composition using a carboxy-modified copolymer latex as a binder.

In recent years, since both the coating speed in producing coated paper and the printing speed of coated paper have been increasing,
There is an increasing demand for improving the coating operability such as the cleaning property of the deposits on the rolls and the like, and for improving the offset printing suitability of the coated paper, that is, the water resistance and ink acceptability of the coated paper.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a paper coating composition which is excellent in coating operability and can provide a coated paper excellent in water resistance and ink receptivity. It is in. The present inventors have conducted intensive studies to overcome the problems of the prior art and found that aliphatic conjugated diene monomers, ethylenically unsaturated carboxylic acid monomers, and other copolymerizable monomers In the emulsion polymerization of a monomer mixture consisting of a solid, after the polymerization conversion exceeds 90%,
When a latex obtained by adding a monomer having a solubility in water at 0 ° C. of 0.5 g / 100 g or more and further continuing polymerization is used as a binder in a paper coating composition, washing at the time of coating is performed. It has been found that the properties and the water resistance and ink acceptability of the obtained coated paper are improved, and the present invention has been completed based on the findings.

[0011]

Thus, according to the present invention, (a) 15 to 60% by weight of an aliphatic conjugated diene monomer, and (b) 0.5 to 50% by weight of an ethylenically unsaturated carboxylic acid monomer.
30% by weight, and (c) other copolymerizable monomers 10
Emulsion polymerization of a monomer mixture consisting of 84.5% by weight is carried out, and after the polymerization conversion exceeds 90%, (d) unsaturated carboxylic acid alkyl is added to 100 parts by weight of the total amount of the above monomers.
Esters and ethylenically unsaturated nitrile compounds.
The solubility in water at 20 ° C. is 0.
5 g / 100 g or more and less than 10 g / 100 g of monomer (d
1) or the monomer (d1) in water at 20 ° C
Combination with monomer (d2) having a resolution of 10 g / 100 g or more
The copolymerizable monomers consisting allowed added in a proportion of 0.5 to 10 parts by weight, and further a copolymer latex obtained by continuing the polymerization reaction, and characterized in that it contains a pigment Kaminuri A composition is provided. Hereinafter, the present invention will be described in detail.

(Monomer) (a) Aliphatic conjugated diene monomer Examples of the (a) aliphatic conjugated diene monomer used in the present invention include 1,3-butadiene and 2-methyl- Examples thereof include 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and halogen-substituted butadiene.
These can be used alone or in combination of two or more. Particularly preferred are 1,
3-butadiene.

The proportion of the aliphatic conjugated diene monomer used is as follows:
It is 15 to 60% by weight, preferably 20 to 55% by weight in the monomer mixture. If the use ratio is less than 15% by weight, the surface strength decreases, while if it exceeds 60% by weight, the water resistance decreases, and the characteristics required in offset printing cannot be satisfied.

(B) Ethylenically unsaturated carboxylic acid monomer The (b) ethylenically unsaturated carboxylic acid monomer used in the present invention includes, for example, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, Examples include itaconic acid, fumaric acid, maleic acid, butenetricarboxylic acid and the like. These ethylenically unsaturated carboxylic acid monomers can be used alone or in combination of two or more. Further, unsaturated polycarboxylic acid alkyl esters having at least one carboxyl group such as itaconic acid monoethyl ester, fumaric acid monobutyl ester, and maleic acid monobutyl ester can also be used.

The proportion of the ethylenically unsaturated carboxylic acid monomer used is 0.5 to 30% by weight in the monomer mixture.
Preferably it is 0.5 to 20% by weight. When the use ratio is less than 0.5% by weight, both the surface strength and the water resistance are reduced, and the stability of the copolymer latex becomes insufficient, so that the paper latex may be used at the time of preparing a paper coating composition or paper. Causes trouble during application of the coating composition. On the other hand, when the use ratio exceeds 30% by weight, the viscosity of the copolymer latex becomes too high and it becomes difficult to handle.

(C) Other copolymerizable monomers (c) Other copolymerizable monomers used in the present invention include, for example, styrene, α-methylstyrene, monochlorostyrene, vinyltoluene, etc. Aromatic vinyl compounds; alkyl esters of unsaturated carboxylic acids such as methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate; ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; β-hydroxy acrylate Hydroxyalkyl esters of unsaturated carboxylic acids such as ethyl, β-hydroxypropyl acrylate and β-hydroxyethyl methacrylate; amides of unsaturated carboxylic acids such as acrylamide, methacrylamide, N-methylolacrylamide, diacetoneacrylamide and derivatives thereof ; Le glycidyl, glycidyl esters of unsaturated carboxylic acids such as glycidyl methacrylate; methyl aminoethyl (meth) acrylate, t- butyl aminoethyl (meth) acrylate,
Examples include aminoalkyl esters of ethylenically unsaturated carboxylic acids such as N, N-dimethylaminoethyl (meth) acrylate; and other vinyl compounds such as acrolein, allyl alcohol, and vinyl acetate. These monomers can be used alone or in combination of two or more.

The other copolymerizable monomers are used in a proportion of 10 to 84.5% by weight in the monomer mixture. Among these monomers, preferably, aromatic vinyl monomer 1
0 to 75% by weight, 5 to 40% by weight of an unsaturated carboxylic acid alkyl ester monomer, 5 to 40% by weight of an ethylenically unsaturated nitrile monomer, and other copolymerizable monomers.

The use of the aromatic vinyl monomer has the effect of imparting appropriate hardness and water resistance to the copolymer. The aromatic vinyl monomer is preferably used in a range of 10 to 75% by weight. If this use ratio is less than 10% by weight,
If the effect cannot be obtained sufficiently and exceeds 75% by weight, the film-forming property is reduced and the adhesiveness is reduced.
Of the aromatic vinyl monomers, styrene is particularly preferred.

The alkyl ester monomer of unsaturated carboxylic acid is effective for imparting appropriate hardness to the copolymer and imparting appropriate hydrophilicity, and is preferably in the range of 5 to 40% by weight. used. If the use ratio is less than 5% by weight, sufficient effects cannot be obtained, and if it exceeds 40% by weight, water resistance and the like are adversely affected. As the alkyl ester monomer of the unsaturated carboxylic acid, methyl methacrylate, butyl acrylate, and the like are particularly preferable.

The ethylenically unsaturated nitrile monomer imparts oil resistance to the copolymer and is effective in increasing the printing gloss of coated paper, and is preferably used in the range of 5 to 40% by weight. . If the use ratio is less than 5% by weight, a sufficient effect cannot be obtained, and if it exceeds 40% by weight, the copolymer becomes too hard or the ink receptivity of the coated paper is unfavorably reduced. Acrylonitrile is particularly preferred as the ethylenically unsaturated nitrile monomer.

Monomers such as hydroxyalkyl ester monomers of unsaturated carboxylic acids and unsaturated carboxylic acid amides and derivatives thereof are effective for improving the stability of the copolymer latex, and are preferably 40% by weight or less. Used in range. These (c) other copolymerizable monomers are usually 2
It is preferable to use a combination of two or more kinds in view of the balance of various properties.

(D) The solubility in water is 0.5 g / 10
0 g or More of Monomer In the present invention, when a copolymer latex is produced by emulsion polymerization using the monomer mixture of (a), (b) and (c), the polymerization conversion rate is 90%. After that, (d) it is copolymerizable with each of these monomers and has a solubility in water at 20 ° C. of 0.5 g / 100 g.
g or more monomers, the (a), the total charge amount 100 parts by weight of the monomer mixture (b) and (c), 0.5
The polymerization is further performed by adding at a ratio of 10 to 10 parts by weight ,
At this time, as the monomer (d), an unsaturated carboxylic acid alkyl
Esters and ethylenically unsaturated nitrile compounds.
The solubility in water at 20 ° C. selected from the group
5 g / 100 g or more and less than 10 g / 100 g of monomer (d
1) or the monomer (d1) in water at 20 ° C
Combination with monomer (d2) having a resolution of 10 g / 100 g or more
It is characterized by the use of a set. The solubility of the monomer is represented by the amount (g) dissolved at 20 ° C. in 100 g of water.

The solubility in water at 20 ° C. is 0.5 g /
Is up to 100g or more copolymerizable monomers, for example,
Alkyl esters of unsaturated carboxylic acids such as methyl acrylate, methyl methacrylate, ethyl acrylate; ethylenically unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid , Ethylenically unsaturated carboxylic acids such as fumaric acid, maleic acid and butenetricarboxylic acid; hydroxyalkyl esters of unsaturated carboxylic acids such as β-hydroxyethyl acrylate, β-hydroxypropyl acrylate, β-hydroxyethyl methacrylate; Amides of unsaturated carboxylic acids such as acrylamide, methacrylamide, N-methylol acrylamide, diacetone acrylamide and derivatives thereof; glycidyl esters of unsaturated carboxylic acids such as glycidyl methacrylate; And the like. In the present invention,
(D) As monomers, unsaturated carboxylic acids
Acid alkyl esters and ethylenically unsaturated nitrile compounds
Dissolution in water at 20 ° C selected from the group consisting of
The degree is 0.5g / 100g or more and less than 10g / 100g.
Monomer (d1) or the monomer (d1) with water at 20 ° C.
With a monomer (d2) having a solubility of 10 g / 100 g or more
Use mating .

Alkyl esters of unsaturated carboxylic acids and
Selected from the group consisting of thylene unsaturated nitrile compounds
The solubility in water at 20 ° C. is 0.5 g / 100 g
Specific examples of the monomer (d1) having a solubility of less than 10 g / 100 g include, for example, methyl acrylate (5.
6g / 100g), methyl methacrylate (1.72g /
100 g), ethyl acrylate (1.51 g / 100
unsaturated carboxylic such as g) San'a alkyl ester acrylonitrile (8.5g / 100g), methacrylonitrile (2.57 g / 100 g) and an ethylene-unsaturated nitrile compound such. One or two of these
Use more than seeds .

In the present invention, the above monomer (d1) and 2
A simple substance having a solubility in water at 0 ° C. of 10 g / 100 g or more.
The combination with the monomer (d2) is used. As a monomer having a solubility in water at 20 ° C. of 10 g / 100 g or more,
For example, a water-soluble ethylenically unsaturated carboxylic acid such as acrylic acid and methacrylic acid; a hydroxyalkyl ester of a water-soluble unsaturated carboxylic acid such as β-hydroxyethyl acrylate; a water-soluble unsaturated ester such as acrylamide Amides of carboxylic acids and derivatives thereof; and the like.

However, the total amount of the ethylenically unsaturated carboxylic acid, the hydroxyalkyl ester of the unsaturated carboxylic acid, or the amide of the unsaturated carboxylic acid and its derivative is preferably less than 2 parts by weight. When these monomers are added in excess of 2 parts by weight, the viscosity of the latex or the viscosity of the paper coating composition may be too high to make it difficult to handle or cause problems during coating.

The monomer (d) is used in an amount of 0.5 to 0.5 parts by weight based on 100 parts by weight of the total charged amount of the monomers (a), (b) and (c).
Used in the range of 10 parts by weight. If the amount is less than 0.5 part by weight, the desired effect cannot be obtained. If the amount exceeds 10 parts by weight, the adhesive strength is reduced, the latex viscosity or the paper coating composition viscosity is increased. A preferable usage ratio is 1 to 5 parts by weight.

The solubility in water at 20 ° C. is 0.5 g /
By using a copolymerizable monomer of 100 g or more, it is possible to achieve the object of the present invention to improve the washability during coating and to improve the water resistance and ink acceptability of the obtained coated paper. it can. The solubility in water at 20 ° C. is 0.5 g / 10
Even if less than 0 g of a monomer, for example, styrene or butadiene is used, the desired effect cannot be obtained.

(Polymerization Auxiliary Material) The emulsifier, molecular weight modifier, initiator, chelating agent, inorganic salt and the like used in the emulsion polymerization of the copolymer latex of the present invention are not limited, and known ones may be used. it can. As the emulsifier, any of an anionic surfactant, a nonionic surfactant and an amphoteric surfactant can be used, and two or more kinds can be used in combination.

In general, the gel content of the copolymer in the copolymer latex for paper coating has a significant effect on the properties of the coated paper. The copolymer latex of the present invention does not particularly limit the gel content. For example, for an offset sheet-fed coated paper, a copolymer latex having a gel content of 50% or more is used for offset rotary printing. For coated paper, a copolymer latex having a gel content of 70% or less is preferred. The gel content is measured as a toluene-insoluble content of the copolymer, and is usually about 20 to 95% by weight. The gel content of the copolymer in the copolymer latex is affected by the monomer composition, polymerization temperature, final conversion, polymerization method, and the like, but is generally controlled by using a molecular weight modifier.

Examples of the molecular weight modifier include mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan and n-stearyl mercaptan; halogenated hydrocarbons such as bromoform, carbon tetrachloride, carbon tetrabromide; tetraethylthiuram sulfide; Sulfides such as pentamethylenethiuram sulfide and diisopropylxanthogen disulfide; terpinolene, α-pinene,
terpenes such as β-pinene, α-terpinene, β-terpinene, γ-terpinene, myrcene, dipentene; hydrocarbons such as pentaphenylethane; acrolein;
Examples include methacrolein, allyl alcohol, α-methylstyrene dimer, 2,5-dihydrofuran, and 1,4-cyclohexadiene. These can be used alone or in combination of two or more, and the type and amount can be appropriately selected according to the desired gel content and properties. Generally, the molecular weight modifier is used in an amount of 0.1 to 100 parts by weight of the monomer mixture.
Used in the range of ~ 5 parts by weight.

As the initiator, any of an inorganic initiator and an organic initiator can be used. Examples of the inorganic initiator include sodium persulfate, potassium persulfate, ammonium persulfate, hydrogen peroxide, and mixtures thereof. Of these, persulfates are preferred. The amount of the inorganic initiator to be used is preferably 0.1 to 5 parts by weight based on 100 parts by weight of the monomer mixture.

Examples of the organic initiator include t-butyl peroxide, cumene hydroperoxide, diisopropylpropylbenzene hydroperoxide, p-menthane hydroperoxide, di-t-butyl peroxide, t-butyl Cumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, benzoyl peroxide, t
-Butyl peroxyisobutyrate, cumyl peroxy neodecanoate, t-butyl peroxy 2-ethylhexanoate, t-butyl peroxybenzoate, t
Organic peroxides such as -butyl peroxyallyl carbonate; azobisisobutyronitrile, azobis-2,4-
Azo compounds such as dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate; and the like.

These organic initiators can be used alone or in combination of two or more. Also, the organic initiator can be used in a redox system in combination with a reducing agent. The amount of the organic initiator to be used is preferably 0.01 to 5 parts by weight based on 100 parts by weight of the monomer mixture.

(Emulsion polymerization) The monomer (a) of the present invention,
In the emulsion polymerization of the mixture consisting of (b) and (c), a method in which the whole amount of the monomer mixture is charged at once into a reaction vessel (polymerization can), the monomer mixture is continuously or continuously added as the polymerization proceeds. Any method may be used, such as an intermittent charging method, a method in which a part of the monomer mixture is collectively charged and polymerization is performed, and a method in which the remaining monomer mixture is charged collectively or continuously or intermittently and polymerized. Even if the composition of the monomer mixture added continuously or intermittently is the same,
Or it may change. However, the polymerization conversion rate is 9
It is necessary that the entire amount of the monomer mixture has been charged to the reaction system by the time when it exceeds 0%.

The particle size of the copolymer latex of the present invention is as follows:
Although not particularly limited, usually, the average particle diameter is 30.
nm to 1000 nm, preferably 50 nm to 500 nm
Range. In order to control the particle size of the latex, a method of changing the type and amount of the emulsifier or a method of performing seed polymerization using a seed latex can be used. The polymerization of the seed latex can be carried out in the same polymerization vessel prior to the polymerization of the latex of the present invention, but seed latex obtained in a different polymerization vessel may be used.

In the present invention, the total sum of the monomers (a), (b) and (c) is charged into a polymerization vessel and the polymerization conversion rate exceeds 90%, regardless of which polymerization method is employed. After that, 0.5 to 10 parts by weight of a copolymerizable monomer (d) having a solubility in water at 20 ° C. of 0.5 g / 100 g or more is added to 100 parts by weight of the total charged amount of the above monomers. , And the polymerization reaction is continued to be completed.

The method of adding the monomer (d) may be any method such as batch addition, intermittent, continuous or partial addition followed by continuous addition of the remainder. An initiator can be added simultaneously with or after the addition of the monomer (d). In addition, alkalis can be added for the purpose of adjusting an emulsifier and pH.

The time of addition of the monomer (d) is after the polymerization conversion of the monomer mixture exceeds 90%, but is preferably at least 92%, more preferably at least 95%. It is time. Even if the monomer (d) is added when the polymerization conversion is 90% or less, the washing property is poor, and the water resistance and ink receptivity of the coated paper are not improved.

After the addition of the monomer (d), the polymerization reaction is further continued, and the polymerization conversion rate is 90% or more, preferably 97%.
Above.

After the completion of the polymerization, the obtained copolymer latex is subjected to removal of residual monomers and, if necessary, NaO.
The pH is adjusted to a desired pH with H, KOH aqueous solution, ammonia aqueous solution or the like. In addition, concentration can be adjusted to a desired solid content concentration. Further, a preservative, a stabilizer, a dispersant and the like can be added to the copolymer latex as needed.

(Paper Coating Composition) The obtained copolymer latex is combined with a pigment to form a paper coating composition. Pigments used in the paper coating composition include, for example, inorganic pigments such as clay, calcium carbonate, titanium dioxide, aluminum hydroxide, and satin white; organic pigments known as plastic pigments and binder pigments; and the like. Each can be used alone or in combination of two or more. The copolymer latex of the present invention is used usually in a proportion of 5 to 40 parts by weight on a solid basis with respect to 100 parts by weight of a pigment (solids).

As a binder for the paper coating composition, a water-soluble binder such as starch, casein, soybean protein, and polyvinyl alcohol can be used together with the copolymer latex of the present invention. Further, an emulsion-based binder such as another carboxylated styrene-butadiene copolymer latex, a polyvinyl acetate latex, or a polyacrylate latex may be used in a range that does not impair the object of the present invention.

The paper coating composition of the present invention includes a dispersant, a thickener, a dye, a coloring pigment, a fluorescent dye, an antifoaming agent, a preservative, a waterproofing agent, a lubricant, a meat improver, and a water retention agent. Are added as needed.

The paper coated with the paper coating composition of the present invention comprises
The type is not limited, and of course, paperboard is also included. As a coating apparatus, known coating equipment such as a roll coater, an air knife coater, a bar coater, and a blade coater can be used.

The coated paper obtained by coating the paper coating composition of the present invention has excellent water resistance and ink receptivity, and is suitable for offset printing using a fountain solution. It can also be used in printing methods such as offset printing, gravure printing, letterpress printing, etc., which do not use water.

[0047]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. In addition, the number of parts and% in Examples and Comparative Examples are based on weight unless otherwise specified. The parts by weight of the latex is in terms of solid content.

[Production Example 1] (Copolymer latex A) In a reaction vessel having an internal volume of about 10 liters, water 150 parts sodium lauryl sulfate 2 parts sodium bicarbonate 0.5 parts tetrasodium ethylenediaminetetraacetic acid 0.1 part butadiene 43 parts Itaconic acid 2 parts Styrene 30 parts Methyl methacrylate 15 parts Acrylonitrile 10 parts t-dodecylmercaptan 0.8 parts Potassium persulfate 1 part (hereinafter referred to as “prepared composition a”), 7 at a reaction temperature of 75 ° C. The reaction was carried out for a period of time to make the polymerization conversion rate 95%.

Next, methyl methacrylate 2 was added to the reaction vessel.
Was added and the reaction was further carried out for 4 hours. As a result, the polymerization conversion rate became 99%. At this stage, the polymerization reaction was completed and cooled. After removing unreacted monomers, the pH of the latex was adjusted to 8 with an aqueous sodium hydroxide solution, and then concentrated to obtain a copolymer latex (A) with a solid content concentration of 50%.

[Production Examples 2 to 7] (Copolymer latex B
To G) In Production Example 1, after setting the polymerization conversion to 95%, instead of adding 2 parts by weight of methyl methacrylate to the reaction vessel, a monomer or a monomer mixture of the type shown in Table 1 was used. Copolymer latexes (B) to (G) were obtained in the same manner as in Production Example 1 except that the number of parts shown in Table 1 was added.

[0051]

[Table 1]

[Production Example 8] (Copolymer Latex H) The following composition was charged into a tank equipped with a stirrer to prepare a monomer emulsion. Water 48 parts Sodium lauryl sulfate 0.2 part Sodium bicarbonate 0.5 part Butadiene 44 parts Styrene 28 parts Methyl methacrylate 15 parts Acrylonitrile 10 parts Methacrylic acid 2 parts α-methylstyrene dimer 2 parts

Next, the following composition was charged into an autoclave equipped with a stirrer and mixed well. Water 32 parts Ethylenediaminetetraacetic acid tetrasodium salt 0.1 part Sodium lauryl sulfate 0.1 part Seed latex 4 parts Potassium persulfate 0.5 part Itaconic acid 1 part The seed latex used is 98% by weight of styrene and 2 parts of methacrylic acid. Average particle size of 40% by weight monomer composition
nm latex.

After heating the internal temperature of the autoclave to 80 ° C., the monomer emulsion was uniformly added continuously over 6 hours into the autoclave. At the same time, the following aqueous potassium persulfate solution was uniformly added to the autoclave continuously over 6 hours. Water 10 parts Potassium persulfate 1 part

After the monomer emulsion and the aqueous solution of potassium persulfate were all added, the reaction was further continued for 1 hour. As a result, the conversion was 95%. Next, 2 parts of acrylonitrile were added and the reaction was continued for another 4 hours. The polymerization conversion reached 99%, and the reaction was completed. After removing the unreacted monomers, the pH of the latex was adjusted to 8 with an aqueous sodium hydroxide solution, and the solid content was further adjusted to 50.
% To obtain a copolymer latex (H).

[Production Example 9] [Copolymer Latex of Comparative Example (A)] Into a reaction vessel having an internal volume of about 10 liters, a raw material having the same composition a as in Production Example 1 was charged, and the reaction temperature was 75 ° C for 10 hours. The reaction was performed. The polymerization conversion was 99%. After removing unreacted monomers without adding additional monomers,
The pH of the latex was adjusted to 8 with an aqueous sodium hydroxide solution, and then the mixture was concentrated to a solid content concentration of 50% to obtain a copolymer latex (A).

[Production Example 10] [Copolymer latex of comparative example (a)] Into a reaction vessel having an internal volume of about 10 liters, a raw material having the same composition a as that of Production Example 1 was charged, and the reaction temperature was 75 ° C for 5 hours. The reaction was carried out, and the polymerization conversion was set to 80%. Next, 2 parts of methyl methacrylate was added to the reaction vessel, and the reaction was further performed for 6 hours. As a result, the polymerization conversion rate was 99%. At this stage, the polymerization reaction was completed and cooled. After removing the unreacted monomer, the pH of the latex was adjusted to 8 with an aqueous sodium hydroxide solution, and then the mixture was concentrated to a solid content concentration of 50% to obtain a copolymer latex (a).

[Production Example 11] [Copolymer Latex (C) of Comparative Example] A reaction vessel having an internal volume of about 10 liters was charged with a raw material having the same composition a as that of Production Example 1, and was reacted at a reaction temperature of 75 ° C for 7 hours. The reaction was carried out to make the polymerization conversion rate 95%. Next, 12 parts of methyl methacrylate was added to the reaction vessel, and the reaction was further performed for 6 hours. As a result, the polymerization conversion rate was 99%. At this stage, the polymerization reaction was completed and cooled. After removing unreacted monomers, the pH of the latex is adjusted with an aqueous sodium hydroxide solution.
Was adjusted to 8, and then concentrated to obtain a copolymer latex (C) with a solid content concentration of 50%.

Examples 1 to 8 and Comparative Examples 1 to 3 The copolymer latexes (A) obtained in Production Examples 1 to 11
Using (H) and the copolymer latexes (a) to (c) as the copolymer latex for paper coating, a coating composition was prepared according to the following formulation of solid parts. The amount of water was such that the total solids of the coating composition was 60%.

(Preparation of Paper Coating Composition) Kaolin Clay (UW90, manufactured by Engelhard Company) 70 parts Heavy calcium carbonate (Carpital 90, manufactured by ECC Japan) 30 parts Dispersant (Aron T40, Toa Gosei Chemical Co., Ltd.) 0.5 parts Copolymer latex 11 parts Oxidized starch (Oji Ace, manufactured by Oji Cornstarch Co., Ltd.) 4 parts

(Preparation of coated paper)
0 / m ² high quality paper was applied using a laboratory blade coater so that the coating amount on one side was 15 g / m ^{2 in} solid content. The coated paper was immediately dried in a dryer and then glossed with a laboratory super calender.

(Evaluation method) As an index of the coating operability of the paper coating composition, latex film adhesiveness, latex film cleaning property, and coating composition cleaning property were measured.
In addition, water resistance and ink acceptability were measured as characteristics of the coated paper. Each measuring method and evaluation criteria are as follows.

Latex Film Adhesive Latex is treated with a wire bar (Kumaya Riki Kogyo Co., Ltd.)
And dried at room temperature for 1 hour. Black lacia paper was superimposed on the latex-coated surface, passed through an experimental super calender, and the black rasha paper was peeled off to observe the state of adhesion to the latex-coated surface. Observation results were determined based on the following criteria. The lower the adhesion, the lower the adhesiveness of the latex film (the higher the score), and the better the operability during coating. Rating: Adhesion state of black lash paper on latex coated surface 5: No adhesion, 4: Slight adhesion, 3: Adhesion on about half surface, 2: Adhesion on almost entire surface, 1: Material destruction of black rash paper without peeling .

Latex film washability Latex is treated with a wire bar (manufactured by Kumagaya Riki Kogyo Co., Ltd.).
And dried at room temperature for 5 minutes. The sample paper piece was immersed in ice floe and the state of dissolution of the latex was observed. Observation results were determined according to the following criteria. The easier it is to dissolve (the higher the score), the better the latex washability and the better the coating operability. Rating: Dissolution state of latex applied to black brush paper 5: Completely dissolved, 4: Mostly dissolved and undissolved portion also became cloudy, 3: Partially dissolved and remaining cloudy, 2: Not dissolved and cloudy, 1: Does not dissolve and does not become cloudy.

Coating Composition Detergency The coating composition was applied to a polyester film with an applicator bar and dried at room temperature for 30 minutes. The film was immersed in water, and the state after 10 minutes was observed. Observation results were determined according to the following criteria. The larger the area of the dissolving portion (the larger the score), the better the washability and the better the coating operability. Rating: dissolution state of coating composition 5: dissolution part area 100%, 4: dissolution part area 75% or more and less than 100% 3: dissolution part area 50% or more and less than 75% 2: dissolution part area 0% excess 50 %: Dissolution area 0%.

Using a RI printing tester (manufactured by Akira Seisakusho Co., Ltd.), water was applied to the coated paper by a Molton roll, and then a picking test ink (tack 18) was printed to generate picking on the printing surface. The condition was observed. Observation results were determined according to the following criteria. The higher the rating, the lower the occurrence of picks in the wet state and the better the water resistance. Rating: Percentage of area where picking occurred 5: 0%, 4: 0% or more, 25% or less, 3: 25% or less, 50% or less, 2: 50% or more, 75% or less, 1: 75% or more, 100% or less.

Ink Acceptability After applying water to the coated paper with a rubber roll coated with water using an RI printing tester (manufactured by Meiji Seisakusho Co., Ltd.), the ink for offset printing was printed, and the ink density was adjusted. Densitometer (DS-DM-400, manufactured by Dainippon Screen Mfg. Co., Ltd.)
Was measured. The larger the ink density value, the better the ink acceptability. Table 2 shows the evaluation results.

[0068]

[Table 2]

As is clear from Table 2, the paper coating compositions (Examples 1 to 8) using the copolymer latexes (A) to (H) of the present invention as binders were all adhesives for latex films. It has excellent properties, latex film washability, and coating composition washability. In the coated paper manufacturing process, there is little adhesion and accumulation of various rolls, and even when it adheres, it can be easily washed, so that coating operability In addition, the water resistance and the ink receptivity of the coated paper were good, and it was found that the coated paper was excellent in offset printing suitability.

On the other hand, the polymerization reaction was continued and completed without adding an additional copolymerizable monomer (d) having a solubility in water at 20 ° C. of 0.5 g / 100 g or more. The paper coating composition using the copolymer latex (a) obtained as a binder (Comparative Example 1) is inferior in all of latex film adhesiveness, latex film washability, and washability of the coating composition. The water resistance and ink receptivity of the paper were also unsatisfactory.

When the polymerization conversion of the monomer mixture is as low as 80%, a paper coating composition using latex (a) as a binder obtained by adding monomer (d) and continuing polymerization to complete the polymerization. (Comparative Example 2) is inferior in all of latex film adhesiveness, latex film cleaning property, and coating composition cleaning property, and further, water resistance and ink receptivity of coated paper are inferior. No improvement effect was obtained.

The paper coating composition (Comparative Example 3) containing latex (C) as a binder in which the proportion of the monomer (d) added was as large as 12 parts by weight was evaluated for its latex film adhesiveness, latex film washability, and Although excellent in cleaning properties of the composition, it is not suitable for offset printing because of poor water resistance of the coated paper.

[0073]

According to the present invention, there is provided a paper coating composition which is excellent in coating operability and can provide a coated paper having excellent water resistance and ink acceptability. The paper coating composition of the present invention hardly adheres to various rolls attached to a coater at the time of coating, and is easily washed when it adheres. Therefore, the paper coating composition of the present invention can be suitably used as a paper coating composition particularly used for coated paper for offset printing.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) D21H 19/00-27/42

Claims (1)

(57) [Claims] 1. An aliphatic conjugated diene monomer (a)
0% by weight, (b) 0.5-30% by weight of an ethylenically unsaturated carboxylic acid monomer, and (c) 10-84.5% by weight of another copolymerizable monomer. Is subjected to emulsion polymerization, and after the polymerization conversion exceeds 90%, the unsaturated carboxylic acid (d) is added to 100 parts by weight of the total amount of the above monomers.
Acid alkyl esters and ethylenically unsaturated nitrile compounds
Having a solubility in water at 20 ° C. of 0.5 g / 100 g or more and less than 10 g / 100 g selected from the group consisting of
Monomer (d1) or the monomer (d1) with water at 20 ° C.
With a monomer (d2) having a solubility of 10 g / 100 g or more
A paper containing a copolymer latex obtained by adding a copolymerizable monomer consisting of a combination at a ratio of 0.5 to 10 parts by weight, and further continuing a polymerization reaction, and a pigment. Coating composition.