JPH07173793A - Composition for paper coating and coated paper obtained by coating the composition - Google Patents

Abstract

PURPOSE:To obtain a paper-coating composition containing fine particles having specific physical properties and obtained by the emulsion polymerization of a specific monomer as a main component and capable of giving an ultrafine coated paper having excellent white paper gloss and whiteness by applying to a base paper. CONSTITUTION:This paper-coating composition is composed mainly of resin particles obtained by the emulsion copolymerization of an aromatic vinyl monomer (e.g. styrene) and a monomer copolymerizable with the monomer [e.g. 1,3-butadiene or (meth)acrylic acid ester] as main components and having a glass transition temperature of 40-80 deg.C, a toluene-insoluble content of >=90wt.% and a particle diameter of 0.1-1.0mum. A coated paper having excellent white paper gloss in spite of the use of ultrafine coating and exhibiting excellent white paper opacity can be produced by coating a base paper such as wood-free paper, medium-quality paper or paper board with the composition at an areal weight of <=5g/m<2> per one surface using an air knife coater, etc.

Description

Detailed Description of the Invention

[0001]

The present invention is particularly excellent in white paper gloss,
The present invention also relates to a paper coating composition capable of stably producing an ultrafine coated paper excellent in white paper opacity and whiteness, and a coated paper coated with the composition.

[0002]

2. Description of the Related Art In recent years, in the paper manufacturing industry, along with the weight reduction of printed matter, there is an increasing demand for weight reduction of coated paper. However, to reduce the weight of coated paper, simply reducing the amount of coating or keeping the basis weight of the base paper low will lead to a decrease in the white gloss of the coated paper, white paper opacity, etc. It will result in lowering. Furthermore, it is natural that conventional inorganic pigments have a limit in fine coating of coated paper due to their high density.

Further, as a means for improving the opacity and whiteness of white paper, there is JP-A-2-74698, and in the method mainly composed of hollow particles, considering the white paper gloss and coating workability. Not practically satisfactory. From the above, there is a strong need for a paper coating composition which is particularly excellent in white paper gloss and which can stably produce ultrafine coated paper excellent in white paper opacity and whiteness.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems associated with conventional fine coating, further promotes the performance of ultrafine coated paper, and enables stable production. Even though a coated paper having a particularly small coating amount was obtained, its white paper gloss was excellent, and the present invention was completed.

[0005]

The present invention is as follows. (A) In a paper coating composition, obtained by emulsion-polymerizing an aromatic vinyl-based monomer and a component mainly containing a monomer copolymerizable with the aromatic vinyl-based monomer. , A glass transition temperature (hereinafter abbreviated as Tg) of 40 to 80 ° C., a toluene insoluble content (hereinafter referred to as gel content) of 90% by weight or more, and particles having a particle diameter of 0.1 to 1.0 μm. A composition for paper coating, which comprises a main component. (B) A coated paper obtained by coating the composition described in (a) on one side at 5 g / m ² or less.

The present invention will be described in detail below. The emulsion polymer used in the present invention is, in a broad sense, referred to as a styrene emulsion, an acrylic emulsion, an SBR latex, an MBR latex, an SMBR latex produced by emulsion polymerization, and is generally used for paper coating. It has the same composition as the plastic pigment or latex used in the composition.

The aromatic vinyl monomer required for the polymerization of the emulsion polymer used in the present invention is, for example, styrene or α-
Methylstyrene, vinyltoluene, etc. are mentioned. These may be used alone or in combination of two or more. Monomers copolymerizable with the above aromatic vinyl monomers include 1,3-butadiene, 2-methyl-1,3-butadiene and 2-chloro-1,3-butadiene.
Aliphatic conjugated diene-based monomers such as butadiene, conjugated pentadienes, conjugated hexadienes, methyl acrylate,
Acrylic esters such as ethyl acrylate, monomers such as methacrylic acid esters such as methyl methacrylate, acrylonitrile, α-chloroacrylonitrile,
Vinyl cyanide monomers such as methacrylonitrile, and unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid and maleic acid, and further itaconic acid monoethyl ester, fumaric acid monobutyl Esters and monoalkyl esters of unsaturated dicarboxylic acids such as maleic acid monopropyl ester, and unsaturated sulfonic acids such as 2-sulfoethyl acrylate, styrene sulfonic acid, acrylamidopropane sulfonic acid and the like can be mentioned. Further, unsaturated carboxylic acid amides such as acrylamide, methacrylamide, and N-methylol acrylamide, and N-substituted compounds thereof, functional alkyl ester compounds such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and glycidyl methacrylate, and vinyl acetate. And the like, such as vinyl esters, and the like, and they can be used alone or in combination of two or more kinds.

As a method for producing an emulsion polymer of a paper coating composition according to the present invention, any known emulsion polymerization method can be adopted.
There is no particular limitation. The emulsion polymer of the present invention has a Tg of 40 ° C.
It is necessary to be above, and when the temperature is lower than 40 ° C., the whiteness and the opacity of the white paper decrease, the adhesiveness of the coated paper increases, and the coating workability significantly decreases. The emulsion polymer has a Tg of 80.
When the temperature exceeds ℃, the glossiness of the white paper is lowered and the adhesive strength of the coating layer is lowered, which is not preferable.

Examples of the emulsifier used in the present invention include anionic surfactants such as higher alcohol sulfates, alkylbenzene sulfonates, and aliphatic sulfonates, alkyl ester type polyethylene glycols,
Nonionic surfactants such as alkylphenyl ether type and alkyl ether type, amphoteric surfactants such as betaine type, and reactive surfactants having reactivity to these are used alone or in combination of two or more kinds. .

The particle size of the emulsion polymer of the present invention is adjusted by appropriately selecting the kind and amount of the emulsifier, the kind of the monomer and the like, but it is preferably in the range of 0.1 to 1 μm,
If it is less than 0.1 μm, the opacity and whiteness of the white paper are reduced and the coating workability is deteriorated. On the other hand, when it exceeds 1 μm, the glossiness of white paper is lowered. It is preferably 0.15 to 0.7, more preferably 0.2 to 0.5.

The polymerization initiator used in the present invention includes
For example, water-soluble initiators such as potassium persulfate, ammonium persulfate and sodium persulfate, oil-soluble initiators such as benzoyl peroxide and azobisisobutyronitrile, or redox initiators can be used. The molecular weight and gel content of the emulsion polymer is adjusted by using a chain transfer agent during the emulsion polymerization, but as the chain transfer agent, octyl mercaptan, n-dodecyl mercaptan, mercaptans such as t-dodecyl mercaptan, tetraethylthiuram sulfide. And the like, and α-methylstyrene dimer, etc., and these may be used alone or in combination of two or more kinds.

The gel content of the emulsion polymer of the present invention is 90.
It is necessary that the content is at least% by weight, and if it is less than 90% by weight, the adhesiveness of the coated paper increases, and the workability at the time of manufacturing and handling decreases, which is not preferable. The gel content was measured by accurately weighing about 1 g of the dried latex film, immersing it in a container containing 100 ml of toluene for 2 days, collecting 10 ml of the toluene solution, and evaporating the toluene solvent to determine the solid content. Weigh and carry out by the following method.

[0013]

Polymerization of the emulsion polymer used in the present invention is
Polymerization temperature 50 to 100 ° C, gauge pressure 0 to 10 kg / c
It is carried out in the range of m ² , and the monomer and other additives to be used can be added by batch addition, divided addition or continuous addition. Further, for the purpose of stabilizing the particles during polymerization, as a protective colloid agent, for example, hydroxyethyl cellulose, carboxymethyl cellulose,
Polyvinyl alcohol or the like may be added.

When the pH is adjusted with an alkali metal compound after the polymerization of the above-mentioned monomers, examples of the neutralizing agent used include sodium hydroxide, potassium hydroxide, lithium hydroxide, trisodium phosphate and phosphorus. Acid disodium, tripotassium phosphate, dipotassium phosphate and the like, and these can be used alone or in combination of two or more kinds.

As the pigment that can be used in the present invention, for example, all inorganic pigments such as clay, calcium carbonate, titanium oxide, aluminum hydroxide, satin white, barium sulfate, magnesium oxide, talc and colloidal silica are used. be able to. Further, as the adhesive, water-soluble polymers such as starch, casein and polyvinyl alcohol, and emulsions such as polyvinyl acetate and acrylic ester copolymer can be used in combination.

In addition to the pigment and the adhesive, the paper coating composition of the present invention contains various additives such as a dispersant, a water-proofing agent, a viscosity modifier, an antifoaming agent, an antiseptic, a coloring agent, a coagulant and a release agent. It is also effective to add additives as necessary.

The composition for paper coating thus obtained is, for example, an air knife coater, a blade coater,
By coating equipment such as roll coater, bar coater,
The coating is performed in the same manner as in the production of general coated paper, but the solid content of the composition for coated paper is 20 to 50% by weight. The coated paper may be high-quality paper, basis weight of 25 to 300 g / m ² , medium-quality paper, paperboard, or coated paper in which a paper coating composition is previously coated on one or both sides as a base paper. Used. However, it can be said that a basis weight of 25 to 50 g / m ² is preferable for an ultrafine coated paper. Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the following examples, parts and% used are based on weight unless otherwise specified.

[0019]

【Example】

(Production of Emulsion Polymer A) Production Example 1 Deionized water 215 was placed in a reactor equipped with a stirrer and a thermometer.
Parts, 0.1 part of sodium lauryl sulfate were charged, and while maintaining the temperature at 70 ° C. while substituting with nitrogen while stirring, 1.0 part of potassium persulfate was added and completely dissolved.
Part, Latemur S-180 (manufactured by Kao Corporation) 0.4 part, styrene 55 parts, acrylonitrile 11 parts, acrylic acid 2-
20% of ethylhexyl and 4 parts of methacrylic acid were added under stirring, 5% of the emulsion prepared was charged into the reactor and polymerized for 30 minutes, and the remaining emulsion was added for about 2 hours for polymerization. After the total amount was added, aging was performed for 2 hours.

Next, the pH was adjusted with a 25% aqueous sodium hydroxide solution.
Adjust to 8.0 and do steam stripping,
After removing unreacted monomer, add deionized water,
The solid content concentration was adjusted to 50.0% to obtain an emulsion polymer A.

(Production of Emulsion Polymers B and C) Production Examples 2 and 3 Emulsion weights were changed except that the amounts of styrene and other monomers used were changed as shown in Table 1 in the production examples of the emulsion polymers. Emulsion polymers B and C were obtained by producing under the same conditions as the combination A.

(Production of Emulsion Polymers D, E, F, G, H) Production Comparative Examples 1 to 5 Production Comparative Examples are emulsion polymers to be compared in the present invention.
The manufacturing process was the same as in Manufacturing Example 1, but the amounts of styrene and other monomers used were changed as shown in Table 1. In addition, Coulter N4 is used for the measurement of the particle size in Table 1.
(Nikkaki Co., Ltd.) and the glass transition temperature (T
g) was measured using a differential scanning calorimeter (DSC, Shimadzu Corporation).

[0023]

[Table 1]

(Production of Coated Paper) Example 1 A composition for paper coating was prepared using the emulsion polymer produced above. The emulsion polymer was adjusted to a solid content of 40% to obtain a paper coating composition. The above-mentioned composition for paper coating is coated on a coated base paper with an applicator bar having an appropriate clearance so that the dry coating amount on one side is 3 g / m ^2, and the box type hot air dryer is immediately applied. Dry at 120 ° C for 10 seconds.
The obtained coated paper was further seasoned at 20 ° C. and 65% relative humidity for one day and then subjected to super calender treatment twice at 60 ° C. and a linear pressure of 100 kg / cm. The coated paper obtained was subjected to a printing surface strength test and the like.

Examples 2 and 3 Comparative Examples 1, 2, 3, 4, 5 In all the Examples and Comparative Examples, the formulations are shown in Table-2.
A paper coating composition was prepared under the same conditions as in Example 1 to obtain a coated paper. The obtained coated paper was evaluated according to the test methods shown below, and the results are shown in Table 2.

[0026]

[Table 2]

(1) Dry Strength Test Using a RI printing aptitude tester (manufactured by Akira Seisakusho Co., Ltd.), a tack ink (Toyo Ink SMX Tuck 15) was printed to visually judge the state of paper loss, and a 10-point method (10 The points were evaluated as excellent and 1 as inferior. (2) Gloss of white paper The gloss of the coated paper after the super calender treatment was measured with a Murakami gloss meter at a reflectance of 75 ° to 75 °. (3) Whiteness (JIS P-8123) The coated paper after the super calender treatment was measured with a Hunter whiteness meter. (4) White paper opacity (JIS P-8138) The coated paper after the super calender treatment was measured with a Hunter whiteness meter. (5) Blocking test Black Rasha paper is applied to the coated surface of the coated paper, and the paper is passed twice between metal rolls at a linear pressure of 10 kg / cm. After the coated paper and the Racha paper have been peeled off, the degree of discoloration of the Racha paper is visually judged. (There is no waste at all ◎, it is badly disused ---- ×)

[0028]

In the examples, the coated paper obtained by the composition for paper coating of the present invention has a good white paper gloss even though it is a super fine coating. It is clear that it has opacity and whiteness and suggests stable production of ultra-fine coated paper.

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Claims (2)

[Claims] 1. A composition for paper coating, which comprises subjecting an aromatic vinyl monomer and a component mainly comprising a monomer copolymerizable with the aromatic vinyl monomer to emulsion polymerization. A composition for paper coating, which comprises a glass transition temperature of 40 to 80 ° C., a toluene insoluble content of 90% by weight or more, and a particle size of 0.1 to 1.0 μm as a main component. . 2. The composition according to claim 1 on one side of 5 g / m ²
Coated paper obtained by coating below.