JP3339124B2 - Aqueous dispersion of copolymer particles and composition for paper coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper coating composition and an aqueous dispersion of copolymer particles, and more particularly to a paper for obtaining a coated paper having excellent white paper gloss, print gloss and blocking resistance. The present invention relates to a coating composition and an aqueous dispersion of copolymer particles used for the composition.

[0002]

2. Description of the Related Art Conventionally, paper coating compositions containing organic pigments have been applied to paper to improve the white gloss and print gloss of coated paper. As the organic pigment to be contained in the paper coating composition, for example, a conjugated diene monomer of 80 to
A copolymer obtained by polymerizing 100 parts by weight of an aromatic vinyl monomer or a monomer composed of (meth) acrylonitrile in the presence of 25 to 150 parts by weight of a polymer obtained by polymerizing a monomer containing 100% by weight. Organic pigments composed of polymers (JP-A-6
3-303195) has been proposed. Further, in the presence of 43 to 230 parts by weight of a polymer comprising an aromatic vinyl monomer and an ethylenically unsaturated carboxylic acid monomer, a monomer 100 containing 30 to 80% by weight of a conjugated diene monomer is used.
An organic pigment composed of a copolymer having a microdomain structure and polymerizing parts by weight (JP-A-3-167398) has been proposed. Coated paper obtained by coating the paper coating composition containing these organic pigments is excellent in blank gloss and printed gloss, but has a drawback of low blocking resistance.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a paper coating composition for obtaining a coated paper having excellent white paper gloss and print gloss and high blocking resistance, and a co-use composition used therefor. An object of the present invention is to provide an aqueous dispersion of polymer particles. The present inventors have conducted intensive studies to achieve this object, and as a result, in the presence of a copolymer latex composed of an aromatic vinyl monomer and a conjugated diene monomer, an aromatic vinyl monomer It has been found that this object can be achieved by emulsion-copolymerizing a monomer containing as an essential component, and the present invention has been completed based on this finding.

[0004]

Thus, according to the present invention, 20 to 80% by weight of an aromatic vinyl monomer, 20 to 80% by weight of a conjugated diene monomer and 0 to 80% of a monomer copolymerizable therewith. A copolymer (A) having a glass transition temperature of −60 to + 45 ° C. and a latex of 0.5 to 25 parts by weight (solid content) obtained by copolymerizing a monomer (a) consisting of 60% by weight. In the presence, from 60 to 99.5% by weight of an aromatic vinyl monomer,
0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer
And a monomer comprising 0 to 39.5% by weight of a monomer copolymerizable therewith, and the copolymer (B) obtained by polymerizing the monomer alone has a glass transition temperature of +60 to + 140 ° C. An aqueous dispersion of copolymer particles obtained by emulsion copolymerization of 100 parts by weight of the monomer (b) is provided. Further, according to the present invention, there is provided a paper coating composition containing an aqueous dispersion of the copolymer particles and a binder as essential components.

The aqueous dispersion of the copolymer particles of the present invention is obtained by copolymerizing a monomer (a) comprising an aromatic vinyl monomer, a conjugated diene monomer and a monomer copolymerizable therewith. Monomer (b) comprising an aromatic vinyl monomer, an ethylenically unsaturated carboxylic acid monomer and a monomer copolymerizable therewith in the presence of a latex of the copolymer (A) obtained It is obtained by emulsion copolymerization.

The latex of the copolymer (A) used in the present invention is obtained by copolymerizing a monomer (a) comprising an aromatic vinyl monomer, a conjugated diene monomer and a monomer copolymerizable therewith. It is obtained by doing.

[0007] As the aromatic vinyl monomer, styrene,
α-methylstyrene, p-methylstyrene, hydroxymethylstyrene and the like. Of these aromatic vinyl monomers, styrene is preferred. The amount of the aromatic vinyl monomer is 20 to 80% by weight, preferably 30 to 60% by weight of the monomer (a). When the amount is less than 20% by weight, the blocking resistance of the coated paper decreases, and when the amount is more than 80% by weight, the glossiness of the coated paper decreases.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene and chloroprene. Can be mentioned.
Of these conjugated diene monomers, 1,3-butadiene is preferred. The amount of the conjugated diene monomer is 20 to 80% by weight of the monomer (a), preferably 40 to 60% by weight. When the amount is less than 20% by weight, the glossiness of the coated paper decreases, and when the amount is more than 80% by weight, the blocking resistance of the coated paper decreases.

The monomers copolymerizable with the aromatic vinyl monomer and the conjugated diene monomer used in the monomer (a) include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-chloroacrylonitrile and α-chloroacrylonitrile. Cyano group-containing ethylenically unsaturated monomers such as cyanoethyl acrylonitrile; ethylenically unsaturated monomers such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-hydroxyethyl acrylate and glycidyl methacrylate Carboxylic acid esters; ethylenically unsaturated carboxylic acid amides such as (meth) acrylamide and N-methylol (meth) acrylamide; ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid; maleic acid, itaconic acid and the like Ethylenically unsaturated polycarboxylic acids; And ethylenically unsaturated carboxylic acid partial esters such as monomethyl oleate. These monomers are not more than 60% by weight, preferably not more than 30% by weight of the monomer (a). In particular, among these monomers, an ethylenically unsaturated carboxylic acid monomer is preferably used. The amount of the ethylenically unsaturated carboxylic acid monomer is usually 0.01 to 10% by weight, preferably 0.05 to 6% by weight of the monomer (a).

The glass transition temperature of the copolymer (A) is -6.
0 to + 45 ° C, preferably -40 to + 20 ° C. When the glass transition temperature is lower than −60 ° C., the blocking resistance decreases, and when the glass transition temperature is higher than + 45 ° C., the gloss of white paper decreases. The glass transition temperature was determined by casting a latex of a copolymer on a glass plate with a frame at 23 ° C. and 65% RH. H. The film was left for 48 hours in the atmosphere described above, and a film was obtained using a differential scanning calorimeter (DSC, manufactured by Seiko Denshi Kogyo KK: DSC2200) at a starting temperature of -100 ° C.
This is a value measured under the condition of a temperature rising rate of 10 ° C./min.

The average particle size of the copolymer (A) is usually 3
It is 0 to 300 nm, preferably 40 to 200 nm.
If it is too large or too small, the gloss of blank paper and the printing gloss may decrease.

In the present invention, the monomer (b) comprises an aromatic vinyl monomer, an ethylenically unsaturated carboxylic acid monomer and a monomer copolymerizable therewith.

Examples of the aromatic vinyl monomer include the same aromatic vinyl monomers as described above. The amount of the aromatic vinyl monomer is 60 to 99.5% by weight of the monomer (b),
Preferably it is 80 to 99.5% by weight. If the amount is less than 60% by weight, the glossiness of the coated paper and the blocking resistance are reduced.

Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid; ethylenically unsaturated polycarboxylic acids such as maleic acid and itaconic acid; And ethylenically unsaturated polycarboxylic acid partial esters such as monomethyl acid. The amount of the ethylenically unsaturated carboxylic acid monomer used for the monomer (b) is 0.5 to 100% of the monomer (b).
It is 10% by weight, preferably 0.5 to 5% by weight. 10
If the amount is more than 10% by weight, aggregates are generated when the monomer (b) is polymerized, or the glossiness of the coated paper is reduced. Conversely, 0.
If the amount is less than 5% by weight, the mechanical stability of the aqueous dispersion of the copolymer particles of the present invention becomes low.

The monomer copolymerizable with the aromatic vinyl monomer and the ethylenically unsaturated carboxylic acid monomer in the monomer (b) includes a cyano group-containing ethylenically unsaturated monomer and an ethylenically unsaturated monomer. Examples include unsaturated carboxylic acid esters, ethylenically unsaturated carboxylic acid amides, conjugated diene monomers and the like. These monomers are 39.5% by weight or less, preferably 19.5% by weight or less of the monomer (b). Of these monomers, the amount of the conjugated diene monomer is
Is usually 20% by weight or less, preferably 10% by weight or less. If the amount is too large, the blocking resistance of the coated paper may decrease.

In the present invention, the monomer (b) has a glass transition temperature of +60 to + 140 ° C., preferably +70 to + 12 ° C., of the copolymer (B) obtained by copolymerizing the monomer alone.
It will be 0 ° C. When the glass transition temperature is lower than + 60 ° C, the blocking resistance of the coated paper decreases, and
If it is higher, the blank gloss and print gloss of the coated paper decrease.

The ratio of the latex of the copolymer (A) to the monomer (b) is such that the solid content of the latex of the copolymer (A) is 0.1 to 100 parts by weight of the monomer (b). 5-2
It is 5 parts by weight, preferably 1 to 15 parts by weight. If it is more than 25 parts by weight, the blocking resistance of the coated paper decreases, and
If the amount is less than 5 parts by weight, the glossiness of the coated paper is reduced.

The latex of the copolymer (A) used in the present invention is usually obtained by an emulsion polymerization method, but can also be obtained by a phase inversion method. The polymerization of the monomer (b) is performed in the presence of a latex of the copolymer (A). In particular,
The monomer (a) may be polymerized and then the monomer (b) may be added for polymerization, or the monomer (a) may be polymerized to prepare a latex of the copolymer (A). The latex of the copolymer (A) may be appropriately transferred to a reactor to polymerize the monomer (b).

When the monomer (a) is polymerized and then the monomer (b) is added for polymerization, the polymerization conversion of the monomer (a) is usually at least 70%, preferably at least 70%. After 90% or more, polymerization of the monomer (b) is started. If the content is less than 70% by weight, the glossiness of the coated paper, the glossiness of the printed paper, or the blocking resistance is reduced.

The polymerization of monomer (a) and monomer (b)
There is no particular limitation on the polymerization conditions, and examples of the method for adding the monomer or the polymerization auxiliary material include initial batch addition, split addition, and continuous addition.
Further, the polymerization temperature is usually from 0 to 100 ° C.

The polymerization auxiliary materials used in the polymerization of the monomer (a) and the monomer (b) are not particularly limited. Examples of the polymerization initiator include persulfates, organic peroxides and azo compounds. , As a molecular weight regulator, mercaptans, disulfides, terpenes, α-methylstyrene dimer,
Examples of emulsifiers include halogenated hydrocarbons, and the like include nonionic surfactants, anionic surfactants, and cationic surfactants.

In the aqueous dispersion of the copolymer particles of the present invention, the copolymer particles constituting the aqueous dispersion can be suitably used as an organic pigment. When the copolymer particles constituting the aqueous dispersion of the copolymer particles of the present invention are used as an organic pigment, the average particle size is usually 50 to 5000 nm, preferably 100 to 1000 nm. Outside of this range, the gloss of the coated paper and the gloss of the printed paper may be reduced.

The paper coating composition of the present invention comprises an aqueous dispersion of the copolymer particles of the present invention and a binder as essential components.

The binder is generally used in a paper coating composition, and examples thereof include carboxy-modified conjugated diene latex, starch, casein, protein, hydroxymethylcellulose, carboxymethylcellulose, sodium alginate and the like. The amount of the binder is usually 1 part by weight or more, preferably 3 to 3 parts by weight, based on 100 parts by weight (solid content) of the aqueous dispersion of the copolymer particles of the present invention or the inorganic pigment described below. 20 parts by dry weight.

The paper coating composition of the present invention may contain an inorganic pigment. Examples of the inorganic pigment include clay, barium sulfate, calcium carbonate, talc, titanium oxide, and satin white. The ratio of the aqueous dispersion of the copolymer particles of the present invention to the inorganic pigment is such that the aqueous dispersion of the copolymer particles is usually 5 to 30 parts by weight per 100 parts by weight of the inorganic pigment.
It will be dry parts by weight, preferably 5 to 15 parts by dry weight.

The paper coating composition of the present invention may optionally contain a pH adjuster, a pigment dispersant, a water-proofing agent, a defoamer, a dye, a lubricant, an organic solvent, and the like.

The paper coating composition of the present invention can improve white paper gloss, print gloss and blocking resistance of the coated paper by coating it on paper. The coating method is not particularly limited. For example, the coating is performed using a coating apparatus such as a blade coater, a roll coater, an air knife coater, and a short dwell coater. The coating amount is usually 3 to 30 g / m ² in terms of solid content of the composition,
Preferably, it is in the range of ⁵ to 25 g / m ² .

[0028]

As described above, according to the paper coating composition of the present invention, a coated paper excellent in white paper gloss, printed gloss and blocking resistance can be obtained.

[0029]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the examples. The parts and percentages in the examples are on a weight basis, and the latex and the aqueous dispersion are in terms of solid content. The aqueous dispersion of the copolymer particles and the coated paper obtained by coating the paper coating composition containing the same were evaluated according to the following methods.

(Evaluation Method of Aqueous Dispersion of Copolymer Particles) Average Particle Diameter The copolymer particles in the aqueous dispersion were stained with osmic acid, photographed with a transmission electron microscope, and from the photograph, 350 particles were determined. Is randomly selected and its particle size is measured. The average particle diameter is a value (n) obtained by dividing the sum of the measured values by the number of measured particles.
m).

Polymerization stability The judgment is made based on whether or not aggregates are present in the aqueous dispersion of the copolymer particles immediately after production. ○ ・ ・ No aggregate ×× ・ Aggregate

(Evaluation of Coated Paper) Blank Gloss For the coated paper, a gloss meter (manufactured by Murakami Color Co., Ltd., GM
-26D), the light reflectance of the coated paper is measured under the conditions of an incident angle of 75 degrees and a reflection angle of 75 degrees.

Printing Gloss After using a RI printing machine (manufactured by Meiji Seisakusho) to coat the coated paper with a blue ink, the gloss is measured by the same method as that for measuring white paper gloss.

Blocking resistance The coated paper is laid on lasha paper, and the temperature is 50 ° C. and the linear pressure is 20 kg.
The calendar treatment was performed under the condition of / cm. Thereafter, the rasha paper is peeled off by hand, and the peeled state is evaluated by a 5-point method. The higher the score, the higher the blocking resistance.

Example 1 In an autoclave equipped with a stirrer, 40 parts of styrene, 55 parts of butadiene, 5 parts of methacrylic acid, 0.15 part of t-dodecyl mercaptan, 4 parts of sodium dodecylbenzenesulfonate,
After charging 0.3 parts of potassium persulfate and 150 parts of soft water, the mixture was heated to 60 ° C. with stirring and maintained at 60 ° C. for polymerization. Next, when the polymerization conversion rate exceeds 70%, the temperature is raised to 70 ° C.
And the polymerization was continued while maintaining the temperature at 70 ° C. After a lapse of 12 hours from the time when the mixture was heated to 60 ° C., the mixture was cooled to room temperature to obtain a latex of the copolymer (A1). The polymerization conversion of the copolymer (A1) was 96% or more. Next, 50 parts of soft water, 2 parts of the latex of the copolymer (A1) and 0.1 part of sodium dodecylbenzenesulfonate were placed in another autoclave equipped with a stirrer.
And 0.51 part of potassium persulfate, and heated to 80 ° C. Next, a monomer (b) consisting of 85 parts of styrene, 8 parts of butadiene, 5 parts of methyl methacrylate and 2 parts of acrylic acid while maintaining the inside of the autoclave at 80 ° C.,
An emulsion comprising 0.16 parts of sodium dodecylbenzenesulfonate and 50 parts of soft water was continuously added to the autoclave over 4 hours. After the addition of the emulsion was completed, the mixture was further polymerized for 4 hours and cooled to room temperature to obtain an aqueous dispersion of the copolymer particles of the present invention. The polymerization conversion in the polymerization of the monomer (b) was 96% or more. Next, 10 parts of an aqueous dispersion of the copolymer particles was mixed with kaolin clay (Ulgelhard Co.,
W90) 90 parts, dispersant (Toa Gosei Co., Aron T-4)
0) 0.1 part, sodium hydroxide 0.05 part, oxidized starch 3 parts, and carboxy-modified conjugated diene-based latex (LX407F, manufactured by Nippon Zeon Co., Ltd.) 11 parts were mixed and stirred to obtain a solid content of 65%. % And pH 9.5 to obtain a paper coating composition. This paper coating composition is applied to a high quality paper so that the coating amount is 15 g / m ² per one side,
Immediately after coating, dry with hot air at 140 ° C for 30 seconds,
65% R. H. Was left overnight in a constant temperature and humidity room. Thereafter, a super calender treatment was performed twice at a temperature of 50 ° C. and a linear pressure of 100 kg / cm to obtain a coated paper. The evaluation results of the aqueous dispersion of the copolymer particles and the coated paper are shown in Table 1.

Examples 2-4, Comparative Examples 1-4 Copolymers were prepared in the same manner as in Example 1 except that the monomer composition in Example 1 was changed to the monomer compositions shown in Tables 1 and 2. An aqueous dispersion of the coalesced particles, a paper coating composition and a coated paper were obtained. The evaluation results of the aqueous dispersion of these copolymer particles and the coated paper are shown in Tables 1 and 2.

[0037]

[Table 1]

[0038]

[Table 2]

As can be seen from Tables 1 and 2, a coated paper having excellent white paper gloss, printed gloss and blocking resistance can be obtained by using the coating composition containing the aqueous dispersion of the copolymer particles of the present invention as a component. We can see that we can do it.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-199493 (JP, A) JP-A-63-99395 (JP, A) JP-A-62-117895 (JP, A) 64597 (JP, A) JP-A-63-303195 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08F 291/00 C08F 212/08 C08F 279/02 D21H 19/58

Claims (2)

(57) [Claims] 1 to 20% by weight of an aromatic vinyl monomer,
Having a glass transition temperature of -60 to + 45 ° C, obtained by copolymerizing a monomer (a) comprising 20 to 80% by weight of a conjugated diene monomer and 0 to 60% by weight of a monomer copolymerizable therewith;
In the presence of 0.5 to 25 parts by weight (solid content) of a latex of the copolymer (A), 60 to 99.5% by weight of an aromatic vinyl monomer and 0 of an ethylenically unsaturated carboxylic acid monomer And a copolymer (B) obtained by polymerizing the monomer alone, having a glass transition temperature of 0.5 to 10% by weight and 0 to 39.5% by weight of a monomer copolymerizable therewith. An aqueous dispersion of copolymer particles, which is obtained by emulsifying and copolymerizing 100 parts by weight of the monomer (b) at +60 to + 140 ° C. 2. A paper coating composition comprising an aqueous dispersion of the copolymer particles according to claim 1 and a binder as essential components.