JPH06263925A - Paper coating composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition composed of a polymer latex synthesized by emulsion polymerization of a monomer mixture having a specified composition and a specified particle size, excellent in dry strength, wet strength, printing gloss, etc., exhibiting a low viscosity and capable of providing a mixture excellent in stability when blended with a pigment. CONSTITUTION:This coating composition is composed mainly of a polymer latex synthesized by emulsion polymerization of a monomer mixture composed of (A) 0.1 to 10wt.% ethylenic unsaturated amide monomer (e.g. methacrylamide) of the formula [R1 and R2 are each H or an alkyl; R3 is an alkyl; R4 is H or a (substituted)alkyl], (B) 0.5 to 10wt.% ethylenic unsaturated carboxylic acid monomer (acrylic acid), (C) 20 to 80wt.% conjugated diene monomer (e.g. 1,3-butadiene) and (D) 0 to 79.4wt.% monomer copolymerizable therewith and satisfying <=10 product of the used amount of the component (A) multiplied by that of the used amount of the component (B) of <=10 and having 0.03 to 0.1mum average diameter of the latex particle.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a paper coating composition.

[0002]

2. Description of the Related Art In recent years, with the rapid development of printing technology, the performance required for coated paper has become severe.
For example, a paper coating composition that satisfies characteristics such as dry strength, wet strength, and printing gloss, has low viscosity, and has good stability when a pigment is blended, and has a good balance of performances is desired. Has been. It is known that the composition for paper coating has the same composition and the same concentration, although it is known that the surface area is improved because the adhesion area is increased by reducing the average particle size of the polymer latex used for the composition. However, simply decreasing the particle size was not practical because the viscosity increased. For example, a paper coating composition containing a polymer latex having a particle size uniformity of 1.1 or less, an average particle size of 0.1 to 0.2 μm, and a toluene insoluble content of 75 to 90%. Material (Japanese Patent Laid-Open No. 63-12647)
Is proposed. This paper coating composition has a high viscosity and insufficient workability.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a paper coating composition which satisfies characteristics such as dry strength, wet strength and printing gloss, has a low viscosity, and is stable when a pigment is blended. The object is to provide an improved copolymer latex capable of forming a product.

[0004]

In order to solve the above technical problems, that is, in order to prevent the viscosity increase due to the decrease of the average particle size of the polymer latex for paper coating, the present inventors have made various studies. did. For example, the particle size distribution of the latex, the type and amount of the initiator, the emulsifier or the electrolyte were changed and examined. It was also found that the viscosity is lowered by widening the particle size distribution, reducing the amount of the initiator, increasing the amount of the electrolyte or the emulsifier, or the like. However, if the particle size distribution is widened, the adhesion area between the particles is reduced, so that the surface strength is reduced. Further, when the amount of the initiator is reduced, aggregation is likely to occur during polymerization, and mechanical stability and stability when a pigment is blended decrease. Further, it has been found that when the amount of the electrolyte or the emulsifier is increased, the surface strength such as wet strength is lowered.

However, unexpectedly (A) the following formula (I)
An ethylenically unsaturated amide monomer represented by 0.1 to 10
% By weight, (B) ethylenically unsaturated carboxylic acid monomer
5 to 10% by weight, (C) a conjugated diene monomer 20 to 80% by weight, and (D) a monomer copolymerizable therewith 0 to 79.
4% by weight, and the amount of (A) used (% by weight)
The average particle size of latex particles obtained by emulsion-polymerizing the above-mentioned respective monomer mixtures having a numerical value of the product of (1) and (B) used (% by weight) is 10 or less, 0.03 μm or more, 0.1 μm.
The present invention has been completed by finding that the above problems can be solved by using a paper coating composition containing a polymer latex of less than m as the main component.

## STR00002 ## Among the monomers used for producing the copolymer latex of the present invention, a compound represented by the above formula (I) is used. The ethylenically unsaturated amide monomer is represented by the following formula (I):
R ₁ and R ₂ are hydrogen or an alkyl group; R ₃ is an alkyl group; R ₄ is hydrogen, an alkyl group or a substituted alkyl group. Examples of the alkyl group include a methyl group, an ethyl group and an isobutyl group, and R ₃ is preferably a methyl group. The number of carbon atoms in the above formula (I) is preferably 8 or less. If it exceeds 8, the polymer may become hard and the ink acceptability may be deteriorated. Further, the substituted alkyl group is one in which a hydroxyl group, a halogen group and the like are substituted. Examples of the ethylenically unsaturated amide monomer represented by the above formula (I) include methacrylamide, N-methylolmethacrylamide, N-methylmethacrylamide, N-hydroxyethylmethacrylamide, and N-chloromethylmethacrylamide. Can be mentioned.

When the amount of the ethylenically unsaturated amide monomer represented by the formula (I) is less than 0.1% by weight, surface strength, gloss and chemical stability are low, and when it exceeds 10% by weight. Since the viscosity increases and the workability deteriorates, it is 0.1 to 10% by weight, more preferably 1.0 to 5.0% by weight. Examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, maleic acid, fumaric acid and itaconic acid. When the amount of these monomers is less than 0.5% by weight, the surface strength and chemical stability are low, and when the amount exceeds 10% by weight, the latex viscosity increases.
It is used in an amount of 10% by weight, preferably 1 to 7% by weight. In the present invention, the amount of the ethylenically unsaturated amide monomer and the ethylenically unsaturated carboxylic acid monomer used is
The object of the present invention is achieved not only by satisfying the above requirements for the amount used, but also by setting the numerical value of the product with the amount (% by weight) of each of these monomers to be 10 or less, preferably 7 or less. Is necessary for. That is, when the above numerical value exceeds 10, the viscosity of the polymer latex of the present invention increases, and the object of the present invention is not achieved. Examples of the conjugated diolefin monomer include 1,3-butadiene and 2-methyl-1,3-
Examples include butadiene and 2-chloro-1,3-butadiene. Usually, these monomers are used in a range of 20 to 80% by weight, preferably 30 to 60% by weight, as a monomer unit. If it is less than 20% by weight, the surface strength will be low, and if it exceeds 80% by weight, the viscosity of the latex will increase and the workability will decrease.

The polymer latex for paper coating of the present invention contains the above-mentioned ethylenically unsaturated amide monomer, ethylenically unsaturated carboxylic acid monomer and conjugated diene monomer as essential components. In order to further optimize strength and properties other than these, a monomer copolymerizable with each of the above-mentioned monomers can be appropriately used in combination as necessary. Examples of the copolymerizable monomer include vinyl aromatic monomers, ethylenically unsaturated carboxylic acid ester monomers, vinyl cyanide monomers, and ethylenic monomers other than those represented by the above formula (I). Examples include saturated amide monomers. These monomers may be used alone or in combination of two or more. Examples of the vinyl aromatic monomer include styrene, α-methylstyrene, vinyltoluene and dimethylstyrene. The vinyl aromatic monomer is used in an amount of usually 0 to 60% by weight, preferably 0 to 50% by weight in order to give the copolymer an appropriate hardness. Examples of ethylenically unsaturated carboxylic acid ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl methacrylate, dimethyl fumarate,
Examples thereof include diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate and monoethyl fumarate. The ethylenically unsaturated carboxylic acid ester monomer is used in the range of usually 0 to 40% by weight, preferably 0 to 30% by weight in order to improve the ink receptivity. Examples of the ethylenically unsaturated nitrile monomer include acrylonitrile and methacrylonitrile. The ethylenically unsaturated nitrile monomer is usually used in the range of 0 to 25 parts by weight in order to impart appropriate hardness and oil resistance to the copolymer. Examples of ethylenically unsaturated amide monomers other than formula (I) include acrylamide and N-substituted compounds of acrylamide. The ethylenically unsaturated amide monomer other than the formula (I) improves the mechanical stability of the latex and is usually used in the range of 0 to 5% by weight, preferably 0 to 3% by weight.

The polymerization method of the polymer latex of the present invention is as follows:
Both a batch polymerization method and a continuous polymerization method are possible.
The addition method of various components in the emulsion polymerization is not particularly limited, and may be a batch addition method, a divided addition method, or a continuous addition method. In the polymerization, known emulsifiers, polymerization initiators, chain transfer agents and the like are used. As the emulsifier, anionic surfactant such as higher alcohol sulfate, alkylbenzene sulfonate, and aliphatic sulfonate, or nonionic surfactant such as polyethylene glycol alkyl ester type, alkyl phenyl ether type, and alkyl ether type Are used alone or in combination of two or more. Considering the water resistance of the obtained copolymer latex, it is preferably used in an amount of 2 parts by weight or less based on the total amount of the monomers. As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate or sodium persulfate, a redox initiator or an oil-soluble initiator such as benzoyl peroxide can be used. As the chain transfer agent, mercaptans, halogenated hydrocarbons, α-methylstyrene dimer and the like can be used. The average particle size of the polymer latex particles of the present invention is 0.03 μm or more and less than 0.1 μm, preferably 0.06 μm.
It is within the range of 0.095 μm. If it is less than 0.03 μm, the viscosity is high and the workability is poor. If it is 0.1 μm or more, the surface strength is low. The average particle size of the latex particles is
Observed with an electron microscope, 50 or more particle diameters of the polymer were measured and expressed by the number average value. Further, the latex is preferably one that does not cause aggregation even when added dropwise to a sodium chloride aqueous solution having a concentration of 20% or less. Particularly preferred is one that does not cause aggregation even when added dropwise to a 25% or less aqueous sodium chloride solution. In this agglutination test, an aqueous sodium chloride solution was adjusted to a prescribed concentration, then the solution was allowed to stand still, and a few drops of latex were gently dropped onto the solution to visually inspect whether the dropped latex agglomerated. Observe. The results of this test are an indication of the chemical stability of the latex.

The paper coating composition of the present invention is applied to mineral pigments generally used for paper coating such as clay, barium sulfate, titanium oxide, calcium carbonate and satin white.
The copolymer latex of the present invention and, if necessary, a natural or synthetic binder such as casein, starch and polyvinyl alcohol can be added. The preferred use ratio of the copolymer latex of the present invention and the pigment is 5 to 40 parts by weight based on 100 parts by weight of the pigment. Further, various compounding agents generally used in the coating field, for example, water resistance improvers, water resistance reaction accelerators, pigment dispersants, viscosity modifiers, color pigments, organic or inorganic color developers, pH modifiers, decolorizers. A foaming agent and other additives can be optionally mixed. Next, examples will be shown to make the present invention easier to understand, but the present invention is not limited thereto.

[0010]

【Example】

Example 1 (Preparation of latex) 70 parts of water (parts by weight, the same applies hereinafter) 0.3 part of sodium dodecylbenzenesulfonate, 100 parts of the monomer shown in Table 1, 0.4 part of t-dodecyl mercaptan in a tank with stirring. And 1.0 part of α-methylstyrene dimer were charged and stirred to prepare a monomer emulsion. In a reactor with stirring, 55 parts of water, sodium dodecylbenzene sulfonate 0.
1 part and 1.0 part of potassium persulfate were charged, then 10% of the above monomer emulsion was transferred to a reactor and the reaction was continued at 80 ° C. for 2 hours while continuing stirring. The remaining monomer emulsion was then added continuously at 80 ° C. over 4 hours. After the addition was completed, the reaction was continued for 6 hours. The conversion rate was 97% or more. For comparison, the monomer components shown in Table 2 were used instead of the monomers shown in Table 1, and the same emulsion polymerization as above was carried out. The conversion was also 97% or higher. The average particle size and chemistor value of the latex particles of the obtained polymer latex are shown in Tables 3 and 4.

[Table 1]

[Table 2]

[Table 3]

[Table 4] For the chemical stability, latex is added dropwise to an aqueous sodium chloride solution having the concentration shown below, and it is visually judged whether the added latex aggregates. The evaluation results are shown at the highest concentration that does not cause aggregation. NaCl concentration 2.5% 5.0% 10.0% 12.5% 15.0% 20.0% 25.0% Example 2 Each of the following formulation components were blended in the weight proportions shown there and coated. A working solution was produced. Primary clay 50 parts (solid weight part, (Engelhard Ultra White 90) same below) Secondary clay 20 parts (Engelhard Ultracoat) Fine particle heavy calcium carbonate 30 parts (ECC Carbital 90) Dispersant 0.2 parts (Toagosei Co., Ltd. Aron T-40) Starch 4 parts (Nippon Shokuhin Kogyo Co., Ltd. MS4600) Latex 11 parts Coating solutions having the viscosities shown in Tables 3 and 4 are applied using an applicator bar and basis weight. 70 g / m ^{2 It} was coated on ^high- quality paper so that the coating amount was 15 g / m ² , and then at 130 ° C. for 3
After drying for 0 seconds, leaving it overnight, linear pressure 135kg / c
m and a temperature of 40 ° C. were applied to a super calendar.
The absorbent paper, the dry strength and the wet strength of the obtained coated paper were measured. The results are shown in Tables 3 and 4, and as is clear from comparison between the results shown in both tables,
The coating liquid containing the polymer latex of the present invention as a main component is excellent in absorption swimwear meat, dry strength and wet strength, and is well balanced. Regarding each of the above performances,
It tested by the test method shown below. Using a swimsuit meat RI tester, water is drained with a slight gap between the metal roll and the rubber roll, and then a black ink for newspaper is solidly printed. Ink density is measured with an ink densitometer. The larger the number, the better. Surface strength (i) Dry strength: Using an RI tester, the picking test ink [TV (tack value) 22] is used to visually judge the state of paper peeling after several overprints. The larger the number, the better the 5-point evaluation. (Ii) Wet strength: Using a RI tester, water was added with a molton roll, and then the picking test ink (T
In V14), solid printing is performed, and the state of paper peeling is visually determined. The larger the number, the better the 5-point evaluation. As is clear from the results shown in Table 4 above, Examples 1 to 8 of the present invention were excellent in dry strength, wet strength and inking property, and had low viscosity. On the other hand, in Comparative Examples 1 to 4 shown in Table 3 above, the following problems occurred. That is, Comparative Example 1 is an example in which the amount of the monomer represented by the above formula (I) is 0%, whereas Comparative Example 2 is the amount of (A) and (B) used (% by weight). The product has an example of a numerical value of 10 or more. In this example, the viscosity is increased and the wet strength is low. Comparative Example 3 is an example in which the particle diameter is less than 0.03 μm, but in this example, the viscosity increases and the inking property decreases. Comparative Example 4 is an example in which the particle size is 0.1 μm or more, but this example has low dry strength and wet strength.

[0011]

According to the present invention, a polymer latex for a paper coating composition having low viscosity and excellent dry strength, wet strength, and inking property is provided.

Claims (1)

[Claims] 1. An ethylenically unsaturated amide monomer represented by formula (I) (0.1 to 10% by weight), and an ethylenically unsaturated carboxylic acid monomer (B) (0.5 to 10% by weight). %, (C)
20 to 80% by weight of a conjugated diene monomer and (D) 0 to 79.4% by weight of a monomer copolymerizable therewith, and the amount of (A) used (% by weight) and (B) A polymer in which the average particle size of latex particles obtained by emulsion-polymerizing each of the above-mentioned monomer mixtures whose product with the amount used (% by weight) is 10 or less is 0.03 μm or more and less than 0.1 μm. A composition for paper coating containing the latex as a main component. [Chemical 1] (However, R ₁ and R ₂ are hydrogen or an alkyl group; R ₃ is an alkyl group; R ₄ is hydrogen, an alkyl group or a substituted alkyl group.)