JPH05179599A - Latex for paper coating - Google Patents

Abstract

PURPOSE:To provide a paper-coating latex containing two specific kinds of polymer latex containing butadiene component and giving a printing paper having high surface strength and stiffness and free from print nonuniformity. CONSTITUTION:The objective latex is composed of (A) 65-95wt.% (in terms of solid) of a polymer latex composed of (i) 15-40wt.% of butadiene, (ii) 0.5-8wt.% of an ethylenically, unsaturated carboxylic acid and (iii) 52-84.5wt.% of copolymerizable other monomers, having an average particle diameter of 900-2,500Angstrom and giving a latex film having a glass transition temperature of -10 to +50 deg.C and a get content of 60-95wt.% and (B) 5-35wt.% (in terms of solid) of a polymer latex composed of 50-80wt.% of the component (i), 0.5-8wt.% of the component (ii) and 12-49.5wt.% of the component (iii), having an average particle diameter of 900-2,500Angstrom and giving a latex film having a glass transition temperature of -30 to -70 deg.C provided that the difference in the glass transition temperatures between the components A and B is >=30 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a latex for paper coating. More particularly, it relates to a latex for paper coating for obtaining a printing paper having good surface strength, paper stiffness and even printing in sheet-fed offset printing.

[0002]

2. Description of the Related Art In order to impart printability and optical suitability to paper, kaolin, calcium carbonate,
Inorganic pigments such as titanium oxide, satin white, and aluminum hydroxide, synthetic latex such as styrene-butadiene latex as a binder, and water-soluble polymers such as starch, polyvinyl alcohol, and casein as auxiliary binders or water retention agents Water-based paint is applied.

By the way, recently, as the weight of coated paper has been reduced and the printing speed has been increased, a decrease in printing workability due to a shortage of paper has become a serious problem particularly in sheet-fed offset printing. There is.

As a countermeasure, it is possible to consider the pulp composition of the coated base paper, the beating degree, and the aspect of the filler, but the fact is that the study is not progressing due to various restrictions. As another measure, it is possible to increase the rigidity of the coating layer. An easy method is to increase the amount of starch used as an auxiliary binder, but there is a certain limit in consideration of a decrease in workability due to an increase in paint viscosity and an adverse effect on paper quality. Further, increasing the rigidity of the latex polymer used as a binder is also effective for imparting paper stiffness, but a decrease in surface strength is unavoidable, and a large coating layer that tends to cause printing unevenness in the dark tone portion is produced. The current situation is that problems have arisen and no satisfactory countermeasures have been established.

[0005]

In view of such circumstances, the present inventors provide a latex for paper coating for obtaining a printing paper which has good surface strength and paper stiffness and has no printing unevenness. To do.

[0006]

[Means for Solving the Problems] That is, the present invention is
It consists of the following polymer latex (A) 65 to 95% by weight (solid content conversion) and polymer latex (B) 5 to 35% by weight (solid content conversion), and the glass transition temperature of (A) and (B). The present invention provides a latex for paper coating, which has a difference of 30 ° C or more. Polymer latex (A) Butadiene 15-40% by weight Ethylenically unsaturated carboxylic acid monomer 0.5-8% by weight Other copolymerizable monomer 52-84.5% by weight, 900-2500 It has an average particle diameter of angstrom, and the glass transition temperature of the obtained latex film is −10 to 50 ° C. and the gel content is 60 to
95% polymer latex (A). Polymer latex (B) Butadiene 50 to 80% by weight Ethylenically unsaturated carboxylic acid monomer 0.5 to 8% by weight Other copolymerizable monomer 12 to 49.5% by weight, 900 to 2500 A polymer latex (B) having an average particle diameter of angstrom and having a glass transition temperature of -30 to -70 ° C of the obtained latex film.

The present invention will be described in detail below. Butadiene used in the polymer latex (A) is 15 to 40% by weight.
Used in the range of. If it is less than 15% by weight, sufficient surface strength cannot be obtained, and if it exceeds 40% by weight, the expression of paper stiffness is insufficient, which is not preferable. It is preferably 20 to 35% by weight.

The butadiene used in the polymer latex (B) is used in the range of 50 to 80% by weight. 50% by weight
If it is less than 8, the effect of improving printing unevenness is insufficient, and 8
If it exceeds 0% by weight, the paper stiffness is lowered and the wet strength is also lowered, which is not preferable. It is preferably 52 to 70% by weight.

The ethylenically unsaturated carboxylic acid monomer used in the polymer latex (A) and (B) is
Acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid and the like can be mentioned, and one or more kinds can be used. The ethylenically unsaturated carboxylic acid monomers in the polymer latices (A) and (B) are each used in the range of 0.5 to 8% by weight. If it is less than 0.5% by weight, mechanical stability and surface strength will be lowered, and if it exceeds 8% by weight, the latex viscosity will be too high and handling will be difficult, such being undesirable. Preferably 1-6
% By weight.

Other copolymerizable monomers used in the polymer latexes (A) and (B) are styrene,
Aromatic vinyl compounds such as α-methylstyrene, vinyltoluene and divinylbenzene, methyl acrylate,
Ethylenically unsaturated carboxylic acid alkyl ester compounds such as methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate Examples thereof include hydroxyalkyl group-containing compounds such as hydroxypropyl acrylate and hydroxypropyl methacrylate, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, and amide compounds such as acrylamide, methacrylamide, and N-methylol acrylamide. Of these, styrene, methyl methacrylate, acrylonitrile, β-hydroxyethyl acrylate, and acrylamide are particularly preferably used.

The other copolymerizable monomer in the polymer latex (A) is used in the range of 52 to 84.5% by weight. If it is less than 52% by weight, the development of paper stiffness becomes insufficient,
Further, if it exceeds 84.5% by weight, the surface strength is unfavorably reduced. It is preferably 59 to 79% by weight.

The other copolymerizable monomer in the polymer latex (B) is used in the range of 12 to 49.5% by weight. If it is less than 12% by weight, the paper stiffness and wet strength are lowered, and if it exceeds 49.5% by weight, the effect of improving printing unevenness is insufficient, which is not preferable. Preferably 24-4
It is 7% by weight.

The glass transition temperature of the polymer latex (A) must be in the range of -10 to 50 ° C. -1
If the temperature is lower than 0 ° C, the paper stiffness is lowered, and if it exceeds 50 ° C, the surface strength is lowered, which is not preferable. Also, polymer latex (A)
It is necessary for the gel content to be in the range of 60 to 95% by weight.

The glass transition temperature of the polymer latex (B) must be in the range of -30 to -70 ° C. −
If it is less than 70 ° C, the wet strength is lowered, and if it exceeds -30 ° C, it is not preferable because improvement of printing unevenness cannot be expected.

Both the polymer latexes (A) and (B) have an average particle diameter of 900 to 2500 angstroms. If it is less than 900 angstrom, the viscosity of the latex becomes too high, which makes it difficult to handle, and if it exceeds 2,500 angstrom, the surface strength is lowered, which is not preferable. Preferably 1
000-2000 Angstroms.

In the present invention, each of these polymer latexes (A) and (B) is (A) 65-65 in terms of solid content.
It is necessary to mix 95% by weight and (B) 5 to 35% by weight, and make the glass transition temperature difference between the polymer latexes (A) and (B) 30 ° C or more.
When the proportion of the polymer latex (A) is less than 65% by weight, the development of paper stiffness is insufficient, and when it exceeds 95% by weight, improvement in printing unevenness cannot be expected. Further, even if the glass transition temperature difference is less than 30 ° C., improvement in printing unevenness cannot be expected, and the object of the present invention cannot be achieved.

The above polymer latexes (A) and (B)
As a method for producing the above, known emulsion polymerization methods such as continuous emulsion polymerization, batch emulsion polymerization, two-step emulsion polymerization, and divided addition emulsion polymerization can be employed. In addition, at the time of emulsion polymerization, known additives such as emulsifiers, chain transfer agents, polymerization initiators, chelating agents, and additives and auxiliaries used in general emulsion polymerization can be used.

Examples of emulsifiers include sulfuric acid ester salts of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether sulfonates, aliphatic sulfonates,
1 is an anionic surfactant such as an aliphatic carboxylate or a nonionic surfactant such as a sulfate ester salt, or a nonionic surfactant such as an alkyl ester type of polyethylene glycol, an alkylphenyl ether type or an alkyl ether type.
It is used in one kind or two or more kinds.

Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, dimethylxanthogen disulfide, diethylxanthogen. Xanthogen compounds such as disulfide, diisopropylxanthogen disulfide, α-methylstyrene dimer, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide and other thiuram compounds, 2,6-di-t-butyl -4
-Phenolic compounds such as methylphenol and styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrachloride and carbon tetrabromide, triphenylethane, pentaphenylethane, acrolein , Methacrolein, thioglycolic acid, 2-ethylhexyl thioglycolate and the like, and one or more of them can be used.

As the initiator, water-soluble initiators such as potassium persulfate, ammonium persulfate and sodium persulfate, oil-soluble initiators such as benzoyl peroxide and redox type initiators can be used.

The latex for paper coating of the present invention is prepared as an aqueous dispersion together with a pigment and, if necessary, other auxiliary binder.

At this time, 8 to 25 parts by weight of the latex for paper coating of the present invention is added to 100 parts by weight of the pigment in terms of solid content,
Other auxiliary binders can be used in an amount of 0 to 30 parts by weight.
If the amount of the latex for paper coating of the present invention used is less than 8 parts by weight, the surface strength will be insufficient, and if it exceeds 25 parts by weight, the glossiness of the white paper will be low and the ink drying property will be poor, which is not preferable.

Here, as the pigment, kaolin clay,
Talc, barium sulfate, titanium oxide, calcium carbonate,
Inorganic pigments such as aluminum hydroxide, zinc oxide and satin white, and organic pigments such as polystyrene latex may be mentioned, and these may be used alone or in combination.

As other auxiliary binders,
Modified starch such as starch, oxidized starch and esterified starch, natural binder such as soybean protein and casein, and synthetic latex such as polyvinyl alcohol, polyvinyl acetate latex and acrylic latex are used.

When preparing a water-based paint using the latex for paper coating of the present invention, other auxiliary agents such as a dispersant (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), defoaming agent, etc. Agents (polyglycol, fatty acid ester, phosphoric acid ester, silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, water resistance agents (formalin, hexamine, melamine resin, urea resin, glyoxal, etc.), A release agent (calcium stearate, paraffin emulsion, etc.), a fluorescent dye, and a color water retention agent (carboxymethyl cellulose, sodium alginate, etc.) are added as necessary.

When preparing the water-based paint, the polymer latexes (A) and (B) may be mixed in advance and then mixed with a pigment or the like, and the polymer latex (A) may be added at the time of dispersing the pigment. And (B) may be added separately.

The water-based coating composition prepared in this manner is used in a general coated paper production, such as a blade coater, an air knife coater, a roll coater, a brush coater, a curtain coater, a bar coater, a gravure coater, and a size press coater. The on-machine or off-machine coater provided with the coating device is used to coat the base paper in one or more layers. The solid content concentration of the coating composition at that time is generally 40 to 70% by weight, but it is preferably 45 to 67% by weight from the viewpoint of operability.

[Examples] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The used part and%
Means parts by weight and% by weight unless otherwise noted.

-Production of Polymer Latex- A 10-liter pressure vessel was charged with a predetermined amount of each compound, an emulsifier, and a chain transfer agent shown in Table 1, and 0.8 parts of potassium persulfate and sodium hydrogencarbonate of 0.2. Emulsion polymerization was carried out at 69 ° C. while charging 4 parts and 90 parts of pure water. The polymerization conversion rates of the obtained polymer latexes were all 98% or more. Then, after adjusting the pH of the polymer latex to 6.5 with an aqueous sodium hydroxide solution, unreacted monomers were removed by steam distillation to obtain each polymer latex shown in Table 1.

[0030] measured by the number-average particle diameter electron microscope. (Number average of 500 particles)

A latex film is prepared by drying the gel content at room temperature. After weighing approximately 1.0 gram of latex film,
The mixture is placed in 0 cc of toluene and left standing for 48 hours for dissolution, filtered through a 300-mesh wire net, dried, and the toluene insoluble content (gel) on the wire net is measured to calculate the gel content.

A latex film was prepared by drying at a glass transition temperature at room temperature and measured using a differential scanning calorimeter.

[0033]

[Table 1]

-Preparation of paint composition and performance evaluation-The performance of each polymer latex obtained was evaluated as a binder for paper coating. The coating formulation is as shown in Table-2, and the coating conditions and surface finishing conditions are as shown in Table-3.

[0035]

[Table 2]

[0036]

[Table 3]

The surface strength, paper stiffness, and print unevenness of the obtained coated paper were evaluated by the following methods. The evaluation results are shown in Table-4 and Table-5.

The degree of picking when printed with a fountain solution in a wet strength RI printer was visually judged, and evaluated in 5 grades from 1st grade (best) to 5th grade (worst). The average value of 4 times is shown.

Dry strength Evaluation was performed by the same method as the wet strength measuring method except that no fountain solution was used.

Paper Two kinds of strip-shaped coated test pieces (width: 15 mm) were prepared so as to be in the waist papermaking direction and the direction perpendicular thereto. The critical length was obtained by a Clark Stiffener tester by a conventional method, and the average value in each of the two directions was calculated. The average value of 4 times is shown.

Uneven printing By the method of trapping test using RI printing machine, 1
Two-color overprinting of 0.4 cc of the color yellow ink and 0.3 cc of the color red ink was performed, and the transfer uniformity of the color red ink of the second color was visually evaluated. From the one with less printing unevenness ◎ 〜 ××
It was judged in this order.

[0042]

[Table 4]

[Table 5]

Claims (1)

[Claims] 1. The following polymer latex (A) 65-95
Weight% (as solid content) and polymer latex (B) 5-3
A latex for paper coating, comprising 5% by weight (in terms of solid content) and having a glass transition temperature difference between (A) and (B) of 30 ° C. or more. Polymer latex (A) Butadiene 15-40% by weight Ethylenically unsaturated carboxylic acid monomer 0.5-8% by weight Other copolymerizable monomer 52-84.5% by weight, 900-2500 It has an average particle diameter of angstrom, and the glass transition temperature of the obtained latex film is −10 to 50 ° C. and the gel content is 60 to
95% polymer latex (A). Polymer latex (B) Butadiene 50 to 80% by weight Ethylenically unsaturated carboxylic acid monomer 0.5 to 8% by weight Other copolymerizable monomer 12 to 49.5% by weight, 900 to 2500 A polymer latex (B) having an average particle diameter of angstrom and having a glass transition temperature of -30 to -70 ° C of the obtained latex film.