JPH0643677B2 - Paper coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Purpose of the Invention [Field of Industrial Application] The present invention relates to a paper coating composition. More specifically, white paper gloss, print gloss, wet pick strength,
The present invention relates to an improved paper coating composition which gives a coated paper having good printability such as dry pick strength, ink acceptability and blister resistance.

[Conventional technology]

As a binder component of a paper coating composition, a carboxy-modified styrene / butadiene copolymer latex has been widely used from the viewpoint of coating workability, coated paper quality and economical efficiency.

However, the fact is that it has not been able to sufficiently cope with the recent intensification of quality competition of coated paper and the remarkable development of printing technology, and a higher quality paper coating composition is desired.

[Problems to be Solved by the Present Invention]

In recent years, rotary offset (hereinafter referred to as "off wheel") printing has been adopted for speeding up printing, and the spread thereof is remarkable today. With the spread of off-ring printing, coated paper is required to have various properties such as wet pick strength, dry pick strength, ink acceptability, and blister resistance that can withstand high-speed off-ring printing.

Further, for the purpose of increasing the commercial value of the coated paper, it has been desired to improve the white gloss and the printing gloss of the coated paper. It is known that these properties are affected by the properties of the synthetic copolymer latex contained as the main binder component in the paper coating composition. However, it is also known that the performance of the above-mentioned coated paper is in a reciprocal relationship. That is, improving the dry pick strength and wet pick strength results in lowering blister resistance, and improving the white paper gloss and printing gloss results in blister resistance, ink acceptance and wet pick strength. There is a problem that the strength is lowered, and a paper coating composition that satisfies all of these various properties is desired.

[Means for solving problems]

The present inventors have conducted extensive studies to solve the above-mentioned problems, and a latex obtained by mixing a carboxy-modified synthetic copolymer latex (I) and an amide group-modified synthetic copolymer latex (II) in a specific ratio. By performing a paper coating treatment with a paper coating composition mainly containing a mixture and a mineral pigment, the resulting coated paper has white paper gloss, printing gloss, wet pick strength, dry pick strength, ink Acceptability,
It was found that the performance such as blister resistance was significantly improved, and the present invention was completed.

Therefore, it is an object of the present invention to provide a paper coating composition in which the above-mentioned various properties are comprehensively improved.

(B) Structure of the Invention [Constitution of the Invention] That is, according to the present invention, the synthetic copolymer latex is composed of the following (I) and (II), and the solid content weight ratio is (I) / (II) = 1/3 The present invention provides a composition for paper coating, characterized in that it mainly contains a latex mixture in the range of ˜3 / 1 and a mineral pigment.

Synthetic copolymer latex (I): 20 to 60% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid, and alkenyl aromatic monomer alone or alkenyl aromatic monomer A mixture of a monomer and an unsaturated carboxylic acid alkyl ester-based monomer, a hydroxyalkyl group-containing monomer, and one or more monomers selected from vinyl cyanide monomers 30 to
A synthetic copolymer latex having a monomer composition of 79.5% by weight.

Synthetic copolymer latex (II): 20 to 60% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of acrylamide and / or methacrylamide and alkenyl aromatic monomer alone or alkenyl aromatic monomer A mixture of a monomer and an unsaturated carboxylic acid alkyl ester-based monomer, a monomer containing a hydroxyalkyl group, and one or more monomers selected from vinyl cyanide monomers 30 to 79.5% by weight % Synthetic latex having a monomer composition of 100%.

The present invention will be described in more detail below.

Examples of the aliphatic conjugated diene-based monomer used in the present invention include 1,3-butadiene, 2-methyl-1,3-butadiene, 2-chloro-1,3-methylbutadiene, and the like. 1,3-butadiene is preferred.

The aliphatic conjugated diene-based monomer is used in the range of 20 to 60% by weight in each of (I) and (II), but if the amount used is less than 20% by weight, the dry pick strength decreases. On the other hand, if it exceeds 60% by weight, the wet pick strength decreases, which is not preferable.

Examples of the ethylenically unsaturated carboxylic acid used in the synthetic copolymer latex (I) of the present invention include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid and the like, and these are one kind or two or more kinds. It can be used in combination. The ethylenically unsaturated carboxylic acid is 0.5 to
It is used in the range of 10% by weight, but the amount used is 0.
If it is less than 5% by weight, the dry pick strength and the mechanical stability of the latex decrease, and if it exceeds 10% by weight, the viscosity of the latex becomes too high, which is not preferable.

The acrylamide and / or methacrylamide used in the synthetic copolymer latex (II) of the present invention is 0.
When used in an amount of less than 0.5% by weight, the dry pick strength and the mechanical stability of the latex decrease, and when it exceeds 10% by weight, the viscosity of the latex becomes low. It is not preferable because it becomes too high.

Examples of the alkenyl aromatic monomer used in the present invention include styrene, alphamethylstyrene, methylalphamethylstyrene and vinyltoluene.
Particularly preferred is styrene.

Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate. , Monomethyl fumarate, monoethyl fumarate, etc., but methyl methacrylate is particularly preferable.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl methacrylate and 3-chloro-
2-hydroxybutyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol)
Itaconate, 2-hydroxyethyl maleate, bis- (2-hydroxyethyl) maleate, 2-hydroxyethyl fumarate and the like can be mentioned.

Examples of vinyl cyanide monomers include aliphatic unsaturated nitriles such as acrylonitrile, alpha-chloroacrylonitrile, methacrylonitrile and alpha-ethylacrylonitrile.

These monomers include alkenyl aromatic monomer alone or alkenyl aromatic monomer and unsaturated carboxylic acid alkyl ester monomer, hydroxyalkyl group-containing monomer and vinyl cyanide monomer. Used as a mixture with one or more monomers selected from the body.

Further, these monomers are used in the range of 30 to 79.5% by weight in each of (I) and (II), but when the amount used is less than 30% by weight, the wet pick strength is If it exceeds 79.5% by weight, the dry pick strength will decrease, which is not preferable.

The latex mixture of the present invention has a solid content weight ratio of (I) / (I
I) = Must be in the range of 1/3 to 3/1. (I) becomes (I
If it exceeds 3 times as much as I), the white paper gloss, print gloss and blister resistance will decrease, and if (I) is less than 1/3 of (II), dry pick strength and It is not preferable because the wet pick strength is lowered.

The addition method of various components in the emulsion polymerization of the synthetic copolymer latexes (I) and (II) of the present invention is not particularly limited, and any of a batch addition method, a divided addition method and a continuous addition method may be used. A so-called two-step polymerization method or a power feed polymerization method in which the monomer composition is changed on the way may be used. As the emulsifier, a known anionic emulsifier is used. Further, in emulsion polymerization, a commonly used polymerization initiator, electrolyte, polymerization accelerator, chain transfer agent, chelating agent, etc. may be used.

Mineral pigments used in the present invention include titanium dioxide, satin white, kaolin, aluminum hydroxide,
Examples thereof include calcium carbonate, and these may be used alone or in combination of two or more.

Furthermore, in the paper coating composition of the present invention, commonly used binders such as starch, casein, and polyvinyl alcohol, as well as thickeners, crosslinking agents, water retention agents, alkali stabilizers, defoamers, and surface active agents. Various additives such as agents may be used if necessary.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to examples.
The present invention is not limited to the examples.
All percentages and parts used in the examples mean% by weight and parts by weight unless otherwise specified.

Example-1 (Polymerization of Carboxy-Modified Copolymer Latex) In a pressure-resistant container of 10, the number of parts of the monomer shown in Table-1, 6 parts of carbon tetrachloride, 0.8 parts of potassium persulfate, dodecylbenzenesulfonic acid were used. Charge 0.8 parts of sodium, 0.4 parts of sodium hydrogen carbonate and 90 parts of pure water, and stir 6
Emulsion polymerization was performed at 5 ° C. The polymerization conversion rates of the obtained copolymer latexes were all 97% or more. Then
After adjusting the pH of the copolymer latex to 7 with an aqueous sodium hydroxide solution, unreacted monomers were removed by steam distillation to obtain copolymer latexes A to E.

Example-2 (Polymerization of Amide Group-Modified Copolymer Latex) In a pressure resistant container of 10, a monomer in the number of parts shown in Table-2, carbon tetrachloride 3 parts, potassium persulfate 1.0 part, dodecylbenzenesulfone were used. Charge 1.0 part of sodium acidate, 0.3 part of sodium hydrogen carbonate and 90 parts of pure water, and stir 6
Emulsion polymerization was performed at 5 ° C. The polymerization conversion rates of the obtained copolymer latexes were all 97% or more. Then, the same operation as in Example-1 is carried out to carry out copolymer latexes a to d.
Got

Comparative Example-1 All Examples except that the number of parts of the monomer shown in Table-1 was used.
The same operation as in 1 was performed to obtain copolymer latexes FI. Incidentally, FI are not the copolymer latex (I) of the present invention.

Comparative Example-2 All Examples other than using the number of parts of the monomer shown in Table-2.
The same operation as in 2 was performed to obtain copolymer latexes e to h. Incidentally, e to h are not the copolymer latex (II) of the present invention.

Example-3 (Preparation and Performance Evaluation of Paper Coating Composition) Copolymer Latex A Obtained in Examples-1 and-2
-E and a-d were used in the numbers of copies shown in Table 3, respectively, to prepare a paper coating composition based on the following formulation to obtain coated papers ~.

About the obtained coated paper ~, white gloss, printing gloss,
RI wet pick strength, RI dry pick strength,
Ink acceptability and blister resistance were tested. The results are shown in Table-3.

(Direction) Kaolin clay 80 parts Calcium carbonate 20 parts Modified starch 8 parts Latex mixture 12 parts (solid content) (Measurement method) White paper gloss JIS P-8142 "75 degree specular gloss test method for paper and board" Printing Gloss Printing was performed with an RI printing machine using an offset printing ink, and the gloss of the printing surface was measured by the same method as the above-mentioned white paper gloss.

・ RI wet pick strength The degree of picking when printed with dampening water on an RI printing machine is judged with the naked eye, and a five-step method from grade 1 (best) to grade 5 (worst) is used. evaluated. The average value of 6 times is shown.

-RI dry pick strength Evaluation was performed by the same method as the RI wet pick strength measurement method described above except that no fountain solution was used.

-Ink acceptability Using an RI printer, water was supplied by a rubber roll and a molton roll, and the acceptability of the ink at the time of printing was visually judged.

-Blistering resistance After controlling the humidity of the coated paper for double-sided printing to about 6%, it was put into a heated oil bath to show the minimum temperature when blisters occurred.

Comparative Example-3 Using the copolymer latexes shown in Table-4, the same operations as in Example-3 were carried out to obtain coated papers ~. Next, Example-
Performance evaluation was performed in the same manner as in 3. The results are shown in Table-4.

C. Effect of the invention [Effect of the present invention] As shown in the above examples, by using the paper coating composition of the present invention, white paper gloss, print gloss, wet pick strength, dry pick strength, ink It is possible to obtain an excellent coated paper in which various properties such as receptivity and blister resistance are comprehensively improved.

Claims (2)

[Claims] 1. A synthetic copolymer latex comprising the following (I) and (II) and having a solid content weight ratio of (I) / (II).
A composition for paper coating, which mainly contains a latex mixture in the range of 1/3 to 3/1 and a mineral pigment. Synthetic copolymer latex (I): 20 to 60% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid, and alkenyl aromatic monomer alone or alkenyl aromatic monomer A mixture of a monomer and an unsaturated carboxylic acid alkyl ester-based monomer, a hydroxyalkyl group-containing monomer, and one or more monomers selected from vinyl cyanide monomers 30 to
A synthetic copolymer latex having a monomer composition of 79.5% by weight. Synthetic copolymer latex (II): 20 to 60% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of acrylamide and / or methacrylamide and alkenyl aromatic monomer alone or alkenyl aromatic monomer A mixture of a monomer and an unsaturated carboxylic acid alkyl ester-based monomer, a monomer containing a hydroxyalkyl group, and one or more monomers selected from vinyl cyanide monomers 30 to 79.5% by weight % Synthetic latex having a monomer composition of 100%. 2. The paper coating composition according to claim 1, wherein the aliphatic conjugated diene monomer is butadiene.