JPH0770988A - Composition for paper coating - Google Patents

Abstract

PURPOSE:To obtain a composition for paper coating, containing a copolymer latex obtained by subjecting an aliphatic diene monomer, etc., to emulsion copolymerization and excellent in balance of mechanical stability and fluidity under high shearing rate in production of coated paper. CONSTITUTION:This composition for paper coating contains a copolymer latex having 0.06-0.18mum average particle diameter of latex. This copolymer latex is produced from 100 pts.wt. of a mixture of (A) 25-55 pts.wt. of an aliphatic conjugated diolefin-based monomer (preferred example: 1,3-butadiene), (B) 1-5 pts.wt. of an ethylene-based unsaturated acid (e.g. mono- or dicarboxylic acid), (C) a hydrophilic functional group-containing ethylene-based unsaturated monomer [e.g. (meth)acrylamide], (D) 35-73 pts.wt. of other vinyl monomer (preferred example: styrene) copolymerizable with the component A, B or C. In production of the copolymer latex, >=80wt.% of these component B and C is used in the first state of the production and parts of these components A and D are added thereto and these components are copolymerized when total amount of these monomers used becomes 20-70 pts.wt. and then, in the second stage, 80-20 pts.wt. of these components excepting each monomer mixture used in the first stage are copolymerized.

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 which is excellent in fluidity and mechanical stability particularly in high-concentration high-speed coating when producing printing coated paper.

[0002]

2. Description of the Related Art In recent years, as a trend of coating technology, a composition for paper coating (hereinafter referred to as "paint") accompanying the practical use of neutral papermaking.
As a pigment of, the high concentration of the coating is aimed at in order to use a large amount of inexpensive calcium carbonate, while the speed of the coater is being promoted for the purpose of improving the quality of coated paper and productivity.
It aims to improve the quality of coated paper and reduce the coating cost and the drying energy during coating. With these high-speed coating and high-concentration coating, various properties have come to be required for paints. In any case, the fluidity of the coating material and the stability with respect to mechanical operations such as blades are required in high-speed coating. In high-speed coating of high-concentration paint, generally, when the paint is made high in concentration, the fluidity deteriorates, and under high-speed coating (at high shear rate), the fluidity is further adversely affected, and problems such as bleeding are likely to occur. For coatings with poor mechanical stability, backing roll stains may occur, and residue on the coating blade blades and flow clean doctor blade blades may adhere to the coating blades, which not only greatly affects the workability during coating, but also the coating workability. It causes a big problem that the quality of the paper is deteriorated.

As a method for improving the fluidity of such a coating material under a high shear rate, a method of increasing the use ratio of heavy calcium carbonate having a small particle diameter in the pigment surface and a method of increasing the binder surface in the conventional coating material have been proposed. A method for reducing the amount of natural water-soluble binders such as casein and starch, which have a large viscous action, and carboxy-modified latex, which is a synthetic binder, have been proposed for making latex particles smaller and for the type and polymerization method of ethylenically unsaturated acids. There is. However, these methods, namely increasing the proportion of heavy calcium carbonate used and reducing the amount of natural water-soluble binder used,
It causes a decrease in the rigidity of the coated paper and also a water resistance as a paint, which causes a decrease in the adhesive strength. Furthermore, if the particle size of the carboxy-modified latex, which is a synthetic binder, is made smaller, the fluidity of the paint at high shear rates will improve, but the mechanical stability of the latex particles will decrease, causing problems in operability on high-speed coating surfaces. Occurs. In order to increase the mechanical stability of the latex particles, it is possible to increase the ratio of ethylenically unsaturated acid in the latex to stabilize it, but unexpectedly, the viscosity of the paint increases and the shear rate increases. Poor fluidity below. As described above, there is no conventional technology that can achieve high-speed coating with high-concentration paint, that is, viscosity reduction and mechanical stability of paint at high shear rates at the same time. It was rare.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the fluidity of a high-concentration paint at a high shear rate and to coat a paper with excellent mechanical stability. To provide a composition to be used.

[0005]

SUMMARY OF THE INVENTION The present inventors
As a result of diligent study to achieve the goal, the present invention is completed.
It has come. That is, the present invention provides (a) aliphatic conjugation
Diolefin monomer a₁25-55 parts by weight, (b) d
Tylene-based unsaturated acid monomer b₁1 to 5 parts by weight, (c) hydrophilic
Functional group-containing ethylenically unsaturated monomer c₁1-5 weight
Part, (d) a₁, B₁And c₁Other copolymerizable with
Vinyl monomer d₁35-73 parts by weight of monomer
Copolymer latex produced from 100 parts by weight of the mixture
At the first stage of manufacturing at ₁And c₁80% by weight of
Using the above,₁And d₁Add some of the first
The total amount of monomers used in the step is in the range of 20 to 70 parts by weight.
After polymerizing
From 100 parts by weight of the body mixture each single amount used in the first stage
Using 80 to 20 parts by weight excluding the body,
So that the average particle size is in the range of 0.06 to 0.18 μm
Paper containing as a main component the copolymer latex produced by
It is a composition for coating.

The present invention will be described in detail below. The raw material monomers used for producing the copolymer latex of the present invention include the following. (A) The aliphatic conjugated diolefin-based monomer a ₁ includes 1,
There are 3 butadiene, 2-chloro-1,3 butadiene, 2-methyl-1,3 butadiene and the like, and 1,3 butadiene is particularly preferable. The amount of a ₁ used is based on all monomers.
It is 25 to 55 parts by weight, and when the amount used is less than the above range, sufficient adhesive strength of the copolymer latex cannot be obtained, and when it is too large, the water resistance is lowered, which is not preferable.

(B) Ethylenically unsaturated acid monomers b ₁ include monocarboxylic acids such as acrylic acid, crotonic acid and methacrylic acid, dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. , Itaconic acid monoethyl ester, fumaric acid monobutyl ester and other unsaturated carboxylic acid esters, styrene sulfonic acid, acrylamido propane sulfonic acid and other sulfone group-containing aliphatic unsaturated carboxylic acids, etc., these are one or two The above can be mixed and used. The amount of b ₁ used is 1 to 5 parts by weight based on the total amount of the monomers. If the amount used is less than the above range, the mechanical stability and sufficient adhesive strength of the copolymer latex cannot be obtained. On the other hand, if it is too large, the viscosity may be too high and the workability may be poor.

(C) Hydrophilic functional group-containing ethylenically unsaturated monomer c ₁ includes ethylenically unsaturated carboxylic acid amides such as (meth) acrylamide and N-methylol (meth) acrylamide and N-substituted compounds thereof, There are hydroxyl group-containing unsaturated monomers such as 2-hydroxyethyl (meth) acrylate and the like, and these can be used alone or in combination of two or more. The amount of c ₁ used is 1 to 5 parts by weight with respect to the total amount of the monomers. If the amount of c ₁ is less than the above range, the mechanical stability and sufficient adhesive strength of the copolymer latex cannot be obtained. On the other hand, if it is too large, the viscosity may be too high and the workability may be poor.

[0009] (d) a _1, the b ₁ and c ₁ and other copolymerizable vinyl monomer d _1, a _1, b ₁ and c ₁
Any known vinyl-based monomer copolymerizable with can be used, but in particular, olefin-based aromatic monomers such as styrene, α-methylstyrene and p-methylstyrene, methyl (meth) acrylate, (meth) ) There are (meth) acrylic acid esters such as ethyl acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and vinyl cyanide-based monomers such as (meth) acrylonitrile. These are one type. Alternatively, two or more kinds can be mixed and used. The amount of d ₁ used is 35 to 65 parts by weight with respect to the total amount of the monomers. If this amount is less than the above range, the copolymer latex will have poor water resistance, and if it is too large, it will be too hard and will adhere. The strength is reduced, which is not preferable. It is produced by the following emulsion polymerization using the above-mentioned monomer composed of a ₁ , b ₁ , c ₁ and d ₁ .

The emulsion polymerization is carried out in two steps. First, 80% by weight or more of b ₁ and c ₁ is used in the first step of the production, and a ₁ and a part of d ₁ are added to this, and the total amount of the monomers used in the first step is 20 to 70% by weight. Polymerize in an amount in the range of parts. Then, in the second step, 80 to 20 parts by weight of each monomer used in the first step is removed from 100 parts by weight of the mixture of monomers, and the average particle diameter of the latex is 0.06 to 0.18 μm. A copolymer latex is obtained by producing the copolymer latex within the range. In this case, if the amount of the monomer used in the first step is out of the range of 20 to 70 parts by weight, the stability at the time of polymerization may be deteriorated if it is less than 20 parts by weight, and exceeds 70 parts by weight. And the fluidity and mechanical stability of the paint under high shear rate are insufficient. Further, when 80% by weight or more of b ₁ and c ₁ is not used in the first stage, the coating composition is insufficient in fluidity and mechanical stability under a high shear rate.

The copolymer latex according to the present invention is obtained by ordinary emulsion polymerization, and is usually carried out in an aqueous medium using an emulsifier, a polymerization initiator and the like. Examples of the emulsifier include anionic activators such as alkyl sulfonate, alkyl allyl sulfonate, alkyl sulfate, alkyl naphthalene sulfonate, and alkyl succinate sulfonate, polyoxyethylene alkyl ether, polyoxyethylene alkyl allyl ether,
Nonionic activators such as polyoxyethylene aliphatic ester may be used alone or in combination. The amount of these emulsifiers to be used is usually 5% by weight or less with respect to the total latex constituent polymer component. As the polymerization initiator, an oxidizing agent such as potassium, sodium or ammonium salt of persulfate, hydrogen peroxide, diisobutylbenzoyl peroxide, cumene hydroperoxide or lauryl peroxide may be used alone or may be oxidized. The agent can be used in combination with a reducing agent such as sodium sulfite, sodium bisulfite, sodium thiosulfate, that is, a redox system. To control the gel content of the latex, which is an important physical property of the present invention, one or two alkyl mercaptans such as butyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan, and one or two chain transfer agents such as alcohols are used during emulsion polymerization. It can be done using more than one species. Further, as a protective colloid agent for the purpose of stabilizing the particles during polymerization, for example, hydroxyethyl cellulose,
Carboxymethyl cellulose, polyvinyl alcohol, etc. may be added.

Polymerization of the latex used in the present invention is
Normally 50-100 ° C, gauge pressure 0-10 Kg / cm ²
The above-mentioned monomers and other additives can be added all at once, dividedly, or continuously. The copolymer latex thus obtained is used in the present invention after adding a basic substance such as caustic soda and caustic potash so as to have a pH of about PH7 and removing and concentrating unreacted monomers. The copolymer latex constituting the paper coating composition of the present invention has an average particle diameter of polymer particles constituting the dispersed phase of 0.06 to 0.18 μm.
It is necessary to be in the range of m, and the average particle diameter is 0.0
If it is less than 6 μm, the viscosity of the copolymer latex increases and the mechanical stability of the paper coating composition upon heating deteriorates,
When it exceeds 0.18 μm, the fluidity of the paper coating composition at a high shear rate is lowered, which is not preferable.

In the present invention, as the adhesive that can be used in the composition for coating paper, the above-mentioned copolymer latex and, in addition to this, a water-soluble agent that imparts adhesiveness and water retention to the coating composition are used. Polymers such as casein, oxidized starch, phosphoric acid esterified starch, carboxymethyl cellulose and the like are preferably used alone or in combination of two or more kinds, and usually pigment 1
A total of 5 to 30 parts by weight is used with respect to 00 parts by weight. Examples of the pigment include clay used for ordinary coated paper, light calcium carbonate, heavy calcium carbonate, titanium oxide, aluminum hydroxide, satin white, inorganic pigments such as talc and colloidal silica, and plastic pigments and white urea resin pigments. The organic pigments may be used alone or in combination of two or more. Other additives include defoaming agents,
It is also effective to add an auxiliary agent such as a dispersant, a water-proofing agent, and a release agent as needed. The composition for paper coating thus obtained is a high-quality paper having a basis weight of 40 to 300 g / m ² for general printing coated paper by a coating device such as a blade coater, a roll coater, and a bar coater. It is applied to a base paper for coated paper such as medium-quality paper, and the solid content concentration of the coating composition for coated paper at this time is usually adjusted in the range of 40 to 67% by weight. The coating composition is particularly suitable for high-concentration coatings of 60% by weight or more.

[0014]

The present invention will be described in more detail below with reference to examples and comparative examples of the present invention, but the present invention is not limited thereto. In addition, the parts and% used in the following examples
Indicates weight basis unless otherwise specified. (1) Production Example of Copolymer Latex Example 1 An autoclave was charged with 76.1 parts of deionized water and 0.15 part of sodium dodecylbenzenesulfonate, the inside of the autoclave was replaced with nitrogen, and the internal temperature of the autoclave was adjusted to 7
After the temperature was raised to 0 ° C., 1.2 parts of potassium persulfate, an emulsion mixture of the monomers and the raw materials of the first step of the copolymer latex A shown in Table 1 and the amounts thereof were added to initiate polymerization. .
The addition of the emulsified mixture of the first stage was completed in about 2 hours, and subsequently the emulsified mixture of the monomers and the raw materials of the second stage of the copolymer latex A shown in Table 1 was added in about 6 hours to carry out polymerization. About 12 hours after the start, a latex having a polymerization rate of 98% was obtained, so the reaction was stopped by cooling, then the pH was adjusted to 8 with a 25% caustic soda aqueous solution, and steam stripping was performed, followed by deionized water. Was added to adjust the solid content concentration to 48% to obtain a copolymer latex A.

Examples 2 to 9 and Comparative Examples 1 to 8 The same conditions as in Example 1 except that the copolymer latex B was prepared by using the copolymer latex composition and its amount shown in Table 1 under other conditions. I got ~ Q. However, the addition time of the emulsified mixture of each copolymer latex raw material in Examples and Comparative Examples was 8 hours in total of the first step and the second step, and the number of monomer parts in each step relative to the total number of monomer parts It was set by the ratio.
The average particle diameters of all the obtained copolymer latexes were measured by the method described above and shown in Table 1.

(2) Manufacture of paper coating composition Using each of the copolymer latexes shown in Table 1, a paper coating composition was prepared according to the following compounding ratios. Raw material for coating composition Product name Solid ratio 1st class clay (Ultra white 90) 30 2nd class clay (HT) 20 Heavy calcium carbonate (Carbital 90) 50 Dispersant (Aron T-40) 0.2 Defoamer (Nopco 122NS) 0.15 Lubricant (Nopcoat C-104) 0.5 Starch (MS # 4600) 4 Copolymer latex (Latex A to Q) 12 Solid content concentration (Paper coating composition) 66% Each paper coating obtained The coating composition was subjected to the following coating suitability test and characteristic test.

(3) Coating Appropriate Test CLC (CYLINDRICAL LABORATOR)
Y COATER made by Warehauser), basis weight 6
1500m / mi using 4g / m ² high quality coated base paper
n. The presence or absence of spits and the like was visually judged from the surface condition of the coated paper obtained after coating at a coating speed of, and the results were ◎: not generated ○: very slightly generated △:
Occurred slightly ×: Severely generated (not practically possible)
The results are shown in Table 1.

(4) Characteristic test Mechanical stability under heat The paper coating composition was diluted with water to a concentration of 50%, filtered with # 300 mesh wire mesh, and heated to 50 ° C., and 150 g thereof was put into a container ( The container jacket is preliminarily circulated with warm water at 50 ° C), and a load is applied to a Marlon tester (manufactured by Rigaku Kogyo Co., Ltd.)
After loading at 5 Kg for 25 minutes, the mixture was filtered through a # 300 mesh gauze, and the amount of filtration residue after drying was measured and expressed in% by weight based on the solid content of the sample. The results are shown in Table 1. High shear viscosity With a capillary viscometer (manufactured by ANTON PAAR), using a sample temperature of 25 ° C., a capillary diameter of 0.4 mm and a capillary length of 1 mm, a shear rate of 5 × 10 ⁶ S
The viscosity was measured under the condition of ec ⁻¹ , and these results are shown in Table 1. As the results in Table-1 show, Examples 1, 2, 3, 4, 5, 6, within the claims of the present invention
In Nos. 7, 8 and 9, the fluidity and mechanical stability of the coating material are clearly excellent, and the suitability for high speed coating is also good. On the other hand, in Comparative Examples 3 and 4 which are out of the range, when the average particle diameter of the copolymer latex is less than 0.06 μm, the viscosity at high shear is low but the mechanical stability is insufficient, and
On the other hand, if it exceeds 18 μm, the viscosity at the time of high shear becomes high, and spits may occur during high-speed coating. Also,
Comparative Examples 1, 56, 7, 8 in which the amount of all the monomers used in the first stage exceeded 70 parts by weight, and the amounts of the monomers b, c used in the first stage were less than 80% by weight of each. In Comparative Example 2, the coating fluidity and the mechanical stability are all unbalanced.

[0019]

[Table 1]

[0020]

As described above, the paper coating composition using the copolymer latex of the present invention has an excellent balance between mechanical stability and fluidity under high shear rate, and high concentration, It is clear that it is a very useful coating composition that enables excellent coatability in the production of coated paper by high-speed coating.

Claims (1)

[Claims] 1. (a) Aliphatic conjugated diolefin-based monomer
a₁25-55 parts by weight, (b) ethylenically unsaturated acid unit amount
Body b₁1 to 5 parts by weight, (c) hydrophilic functional group-containing ethylene
Unsaturated monomer c₁1 to 5 parts by weight, (d) a₁, B₁Over
And c₁Other vinylic monomers copolymerizable with₁35
~ 100 parts by weight of a mixture of monomers consisting of 73 parts by weight
In the copolymer latex produced, the first stage of production
B on the floor ₁And c₁80% by weight or more of
₁And d₁The total amount of monomers used in the first step
After polymerizing an amount such that the sum is in the range of 20 to 70 parts by weight,
Then in the second stage 100 parts by weight of the mixture of monomers
80 to 20 weight excluding each monomer used in the first step
The average particle size of the latex is 0.06 to
Copolymer produced in the range of 0.18 μm
A composition for paper coating containing a body latex as a main component.