JPH06287503A - Latex for paper coating - Google Patents

Abstract

(57) [Summary] [Purpose] It has both high rigidity and high strength and gloss,
Provided is a latex for paper coating for obtaining a coated paper having excellent blister resistance. [Structure] Glass transition temperature of 35 ° C. composed of styrene, methyl methacrylate, itaconic acid, acrylamide and butadiene, tetrahydrofuran insoluble content 32% by weight,
A latex of a copolymer having an average particle diameter of the latex particles of 0.120 μm, a glass transition temperature of 10 ° C. composed of styrene, methyl methacrylate, itaconic acid, acrylamide, acrylonitrile, and butadiene, a tetrahydrofuran insoluble content of 70% by weight, and latex particles A latex for paper coating is obtained by mixing with a latex of a copolymer having an average particle diameter of 0.101 μm.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a latex for paper coating. More specifically, it relates to a latex for paper coating for obtaining a coated paper having both high rigidity and high adhesive strength and excellent in gloss and blister resistance.

[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.
There is a demand for a latex for paper coating which improves both the contradictory properties of the adhesive strength and the rigidity of the coated paper and has a good balance between them. Conventionally, as a latex for paper coating,
A latex of a carboxy-modified diene-based copolymer having a glycidyl group or a hydroxyl group is known (JP-A-61-34297, JP-A-57-51703). However, although these latexes for paper coating have a good balance of adhesive strength, blister resistance and gloss, they have low rigidity and do not satisfy the above requirements.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a paper coating latex for obtaining a coated paper which has both high rigidity and high adhesive strength and is excellent in gloss and blister resistance. is there. The present inventor conducted studies to improve both the rigidity and the adhesive strength characteristics of coated paper.
As a result, it was effective to apply polymer latex having a high glass transition temperature in order to improve the rigidity of the coated paper. However, this coated paper has a drawback of low adhesive strength. Further, in order to improve the adhesive strength of the coated paper, it is effective to coat a polymer latex having a low glass transition temperature, a polymer latex having a high gel content or a polymer latex having a small average particle size of latex particles. Met. However, in the case of a polymer latex having a low glass transition temperature, the stiffness of the coated paper may decrease, in a polymer latex having a high gel content, the blister resistance may decrease, and in a polymer latex having a small average particle size, It was found that the gloss was reduced.

However, a carboxy-modified diene copolymer latex having a high glass transition temperature, a low gel content and a large average particle diameter of latex particles, and a low glass transition temperature, a high gel content and an average particle of latex particles. It has been found that this object can be achieved by mixing with a carboxy-modified diene copolymer latex having a small diameter, and the present invention has been completed.

[0005]

Thus, according to the present invention, the glass transition temperature is 20 to 50 ° C., the tetrahydrofuran insoluble content is 20 to 50% by weight, and the average particle size is 0.
A carboxy-modified diene copolymer (A) having a thickness of 11 to 0.14 μm, a glass transition temperature of 0 to 30 ° C., a tetrahydrofuran insoluble content of 51 to 80% by weight, and an average particle diameter of 0.08 to 0. A latex for paper coating containing a carboxy-modified diene-based copolymer (B) having a thickness of 11 μm is provided.

The paper coating latex of the present invention contains a carboxy-modified diene-based copolymer (A) and a carboxy-modified diene-based copolymer (B).

In the latex for paper coating of the present invention, the carboxy-modified diene copolymer (A) has a glass transition temperature of 20 to 50 ° C, preferably 25 to 40 ° C. If the glass transition temperature is too low, the rigidity of the coated paper obtained by coating the latex for paper coating becomes low. On the contrary, if it is too high, the adhesive strength of the coated paper becomes low.

Carboxy-modified diene copolymer (A)
Has a tetrahydrofuran insoluble content (hereinafter, simply referred to as "gel content") of 20 to 50% by weight, preferably 2
It is 5 to 40% by weight. The lower the gel content, the lower the adhesive strength of the coated paper. On the contrary, when the gel content increases, the blister resistance of the coated paper decreases.

Carboxy-modified diene copolymer (A)
Have an average particle size of 0.11 to 0.
It is 14 μm, preferably 0.11 to 0.13 μm.
The smaller the particle size, the lower the gloss of the coated paper, and the larger the particle size, the lower the adhesive strength of the coated paper.

As the carboxy-modified diene copolymer (A), the latex particles are polymer particles having a core-shell structure consisting of a core and a shell, and the glass transition temperature of the core polymer is shell. From the glass transition temperature of some polymers,
Those having a temperature of 1 to 40 ° C., preferably 1 to 20 ° C. are preferably used because both the adhesive strength and the rigidity of the coated paper are increased. If the difference in glass transition temperature exceeds 40 ° C, the adhesive strength or blister resistance of the coated paper may decrease.
The weight ratio of the core part to the shell part is usually 5: 5 to 9: 1,
It is preferably 6: 4 to 9: 1.

In the latex for paper coating of the present invention, the carboxy-modified diene copolymer (B) has a glass transition temperature of 0 to 30 ° C, preferably 0 to 15 ° C. If the glass transition temperature is too low, the stiffness of the coated paper will be low. On the contrary, if it is too high, the adhesive strength of the coated paper becomes low.

Carboxy-modified diene copolymer (B)
Has a gel content of 51-80% by weight, preferably 60
~ 75% by weight. The lower the gel content, the lower the adhesive strength of the coated paper. On the contrary, when the gel content increases, the blister resistance of the coated paper decreases.

Carboxy-modified diene copolymer (B)
Has an average particle diameter of the latex particles of 0.08 to 0.
It is 11 μm, preferably 0.09 to 0.11 μm.
The smaller the particle size, the lower the gloss of the coated paper, and the larger the particle size, the lower the adhesive strength of the coated paper.

As the carboxy-modified diene-based copolymer (B), the latex particles are polymer particles having a core-shell structure consisting of a core and a shell, and the polymer of the core has a glass transition temperature of the shell. From the glass transition temperature of the polymer of 1
A material having a temperature of -40 ° C, preferably 1-20 ° C is preferably used because both the adhesive strength and the rigidity of the coated paper are increased. If the difference in glass transition temperature exceeds 40 ° C, the adhesive strength or blister resistance of the coated paper may decrease. The weight ratio of the core part to the shell part is usually 5: 5 to 9: 1, preferably 6: 4 to 9: 1.

In the present invention, the glass transition temperature of the carboxy-modified diene copolymer (A) is higher than the glass transition temperature of the carboxy-modified diene copolymer (B) by 10 ° C. or more, and particularly 20 ° C. or more. preferable. When the difference in glass transition temperature is less than 10 ° C, the balance between the adhesive strength, the rigidity and the blister resistance of the coated paper may deteriorate.

The average particle size of the latex particles of the carboxy-modified diene copolymer (A) is 0.010 μm or more, particularly 0, compared with the average particle size of the latex particles of the carboxy-modified diene copolymer (B). It is preferably higher than 0.15 μm. Difference in average particle size is 0.010 μm
If it is less than the range, the balance between the adhesive strength, the rigidity and the blister resistance of the coated paper may be deteriorated.

In the present invention, the carboxy-modified diene copolymer (A) and the carboxy-modified diene copolymer (B) are both a conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer and a copolymer thereof. It is obtained by polymerizing a polymerizable monomer.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene and chloroprene. Can be mentioned.

Examples of the ethylenically unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, maleic acid and itaconic acid.

Examples of monomers copolymerizable with the aliphatic conjugated diene monomer and the ethylenically unsaturated carboxylic acid monomer include acrylonitrile, methacrylonitrile, fumaronitrile, α-chloroacrylonitrile, α-cyanoethylacrylonitrile and the like. Cyano group-containing ethylenically unsaturated monomers; styrene, α-methylstyrene, and other aromatic vinyl monomers; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and other ethylenic monomers Unsaturated carboxylic acid ester; (meth) acrylamide,
Examples thereof include ethylenically unsaturated amides such as N-methylol (meth) acrylamide. These monomers are used in appropriate combination for improving the physical properties of coated paper such as adhesive strength and inking property.

The amount of each monomer used to obtain the carboxy-modified diene-based copolymer (A) is 10 to 30 parts by weight of the conjugated diene monomer and 100 parts by weight of the total monomers, and the amount of the ethylenic monomer is 100% by weight. 1 to 5 parts by weight of unsaturated carboxylic acid monomer and 30 to 90 parts by weight of a monomer copolymerizable therewith, preferably 15 to 30 parts by weight of conjugated diene monomer, ethylenically unsaturated The carboxylic acid monomer is 2 to 4 parts by weight, and the copolymerizable monomer is 60 to 85 parts by weight. Outside of this range, physical properties of the coated paper such as adhesive strength and inking property may deteriorate.

The amount of each monomer used to obtain the carboxy-modified diene copolymer (B) is 1
The amount of the conjugated diene monomer is 20 to 50 parts by weight, the ethylenically unsaturated carboxylic acid monomer is 1 to 5 parts by weight, and the copolymerizable monomer is 50 to 80 parts by weight. Preferably, the conjugated diene monomer is 25 to 40 parts by weight, the ethylenically unsaturated carboxylic acid monomer is 2 to 4 parts by weight, and the monomer copolymerizable therewith is 50 to 75 parts by weight. Outside of this range, physical properties of the coated paper such as adhesive strength and inking property may deteriorate.

The carboxy-modified diene copolymer (A) and the carboxy-modified diene copolymer (B) can be obtained by a known polymerization method. Monomer addition method, polymerization temperature,
Polymerization auxiliary materials (polymerization initiator, emulsifier, molecular weight modifier, etc.)
Is not particularly limited.

The latex for paper coating of the present invention is obtained by mixing the latex of the carboxy-modified diene copolymer (A) and the latex of the carboxy-modified diene copolymer (B).

The weight ratio of the carboxy-modified diene copolymer (A) and the carboxy-modified diene copolymer (B) is 99: 1 to 50:50, preferably 95: 5-6.
It is 0:40. If the amount of the carboxy-modified diene-based copolymer as the first component is too large, the adhesive strength of the coated paper may be low, and if it is too small, the rigidity of the coated paper may be low.

Before mixing the latex of the carboxy-modified diene-based copolymer (A) and the latex of the carboxy-modified diene-based copolymer (B), the latex of the carboxy-modified diene-based copolymer (A) and It is preferable to adjust both the pH of the latex of the carboxy-modified diene copolymer (B) to 7 to 10, preferably 8 to 9. Low pH may result in agglomerates when mixed.

The latex for paper coating of the present invention is mixed with a pigment, a dispersant, an auxiliary binder, a water resistance agent, an antifoaming agent, a dye, a lubricant and the like which are generally used for paper coating, and the mixture is stirred. , Applied to paper. Examples of the pigment include inorganic pigments such as clay, calcium carbonate, talc, titanium oxide and satin white; and organic pigments such as plastic pigments. The use ratio of the pigment and the latex for paper coating is usually 3 to 4 for latex for paper coating (solid content) per 100 parts by weight of the pigment.
It is 0 part by weight, preferably 5 to 30 parts by weight.

[0028]

Industrial Applicability According to the present invention, a paper coating latex for obtaining a coated paper having both high rigidity and high adhesive strength and excellent in gloss and blister resistance can be obtained.

[0029]

EXAMPLES The present invention will now be described in more detail by way of examples. The parts and% in the examples are based on weight unless otherwise specified.

The evaluation was performed by the following method. (Latex physical properties) Glass transition temperature Differential scanning calorimeter (DSC [manufactured by Seiko Denshi Kogyo KK:
SSC5200]) was used under the conditions of a temperature rising rate of 10 ° C / min and a starting temperature of -100 ° C. Gel content After adjusting the pH of latex to 8.0, it was cast on a glass plate with a frame and dried under reduced pressure at 100 ° C. to obtain a film. 0.5g of this film is put in a wire mesh basket of 80 mesh, and it is placed in tetrahydrofuran 100m at 20 ° C.
After being immersed in 1 for 24 hours, the film remaining in the cage of the wire net was dried under reduced pressure at 100 ° C., and the residual rate was calculated to determine the gel content. Average particle diameter Observed with an electron microscope, 500 particle diameters of the polymer were measured and expressed as the number average value.

Reference Example 1 35 parts of water, 0.14 part of sodium lauryl sulfate, 0.35 part of sodium bicarbonate, 0.5 part of t-dodecyl mercaptan, 30.7 parts of styrene and 22.9 of methyl methacrylate were placed in a tank equipped with a stirrer. Parts, itaconic acid 2 parts, acrylamide 0.6 parts and butadiene 13.9 parts were charged to obtain a monomer emulsion for the first stage. In another tank with a stirrer, 15 parts of water, 0.06 part of sodium lauryl sulfate, 0.15 part of sodium bicarbonate and 0.2 parts of t-dodecyl mercaptan.
Parts, styrene 12.4 parts, methyl methacrylate 9.8
Parts, itaconic acid 0.8 parts, acrylamide 0.2 parts and butadiene 6.7 parts were charged to obtain a second stage monomer emulsion. On the other hand, water 34
Parts, ethylenediaminetetraacetic acid tetrasodium salt 0.1
Parts, 0.1 part of sodium lauryl sulfate and 0.2 part of potassium persulfate were charged and heated to 80 ° C., 14% of the monomer emulsion for the first step was added to the autoclave and reacted for 1 hour. Then potassium persulfate 0.8
Parts and 20 parts of water were added, then the remaining first stage monomer emulsion was added continuously over 3 hours. After the addition of the first stage monomer emulsion was completed, the second stage monomer emulsion was continuously added over 2 hours. During this period, the autoclave was maintained at 80 ° C. After the addition of the second stage monomer emulsion, for another 4 hours, 8
After maintaining the temperature at 0 ° C., steam was blown in to remove unreacted monomers, and a 5% sodium hydroxide aqueous solution was added to add p.
By adjusting H to 8.5, a latex A1 having a core-shell structure was obtained as a latex of the carboxy-modified diene copolymer (A).

Reference Examples 2 to 12 Reference Example 1 except that the monomer composition used in the monomer emulsion was changed to the formulation shown in Tables 1 and 2.
Carboxy-modified diene-based copolymer (A)
Latex A2 to A7 was obtained as the latex of the above, and Latex B1 to B6 were obtained as the latex of the carboxy-modified diene copolymer (B). Latex A1 to A7
The evaluation results of latexes B1 to B6 are shown in Tables 1 and 2.

[0033]

[Table 1]

[0034]

[Table 2]

Example 1 70 parts (solid content) of latex A1 and 30 parts (solid content) of latex B1 were mixed and stirred to obtain a latex for paper coating of the present invention.

Examples 2 to 7 A latex for paper coating of the present invention was obtained in the same manner as in Example 1 except that the formulation shown in Table 3 was changed.

Comparative Examples 1 to 7 Latex for paper coating was obtained by the same method as in Example 1 except that the formulation shown in Table 4 was changed.

Reference Example 13 A coated paper was obtained according to the following method using the latex for paper coating obtained in Examples 1 to 7 and Comparative Examples 1 to 7. (Preparation of coated paper) Kaolin clay (manufactured by Engelhard,
UW90) 70 parts, calcium carbonate (Sankyo Flour Milling Co., Escalon # 2000) 30 parts, dispersant (Toa Gosei Co., Ltd.,
Aron T-40) 0.15 parts, sodium hydroxide 0.1
5 parts, 3 parts of oxidized starch and 10 parts of latex for paper coating (solid content) are mixed and stirred to obtain a solid content concentration of 65% and pH.
A 9.5 paper coating composition was obtained. This composition was coated on a high-quality paper so that the coating amount was 15 g / m ^{2 on each} side, and immediately after coating, it was dried with hot air at 140 ° C. for 4 seconds, then at 20 ° C., 65
% R. H. It was left overnight in a constant temperature and humidity room. Then, super calendering was performed twice under the conditions of a temperature of 40 ° C. and a linear pressure of 40 kg / cm.

These coated papers were evaluated by the following method,
The results are shown in Tables 3 and 4. (Evaluation of Coated Paper) Dry Pick (Adhesive Strength) Using an RI tester (manufactured by Akashi Seisakusho Co., Ltd.) on the coated paper, after overprinting the printing ink (tack value 16) four times, the coated paper was peeled off. It was observed and evaluated by the 5-point method. The higher the score, the higher the dry pick. Stiffness It was measured using a Clark stiffness tester (manufactured by Kumagai Co., Ltd.). The printing ink (tack value 16) was printed once on the gloss-coated paper, and then measured using a gloss meter under the condition of an incident angle of 60 degrees. Blister resistance After controlling the humidity of the coated paper to about 6%, it was thrown into a heated oil bath and indicated by the minimum oil bath temperature at which blisters occur.

[0040]

[Table 3]

[0041]

[Table 4]

From Tables 3 and 4, it can be seen that the blister resistance is low in the case of blending latex A4 having a high gel content (Comparative Example 1). It can be seen that the one with the latex A5 having a low glass transition temperature (Comparative Example 2) or the one with the latex B4 (Comparative Example 5) has low rigidity. It can be seen that the dry pick becomes low in the case where the latex A6 having a high glass transition temperature is blended (Comparative Example 3) or the case where the latex B5 is blended. It can be seen that the one in which the latex A7 having a small average particle diameter is blended (Comparative Example 4) has low gloss. It can be seen that the dry pick becomes low in the case where the latex B6 having a large average particle diameter is blended (Comparative Example 7). On the other hand, according to the present invention, it is found that both high rigidity and high adhesive strength are combined, the gloss and the blister resistance are excellent, and each property is well balanced.

Claims (1)

[Claims] 1. A carboxy-modified diene-based copolymer (having a glass transition temperature of 20 to 50 ° C., a tetrahydrofuran insoluble content of 20 to 50% by weight, and an average particle diameter of latex particles of 0.11 to 0.14 μm ( A), a glass transition temperature of 0 to 30 ° C, and a tetrahydrofuran insoluble content of 51
˜80% by weight, and the average particle size of the latex particles is 0.
A latex for paper coating containing a carboxy-modified diene-based copolymer (B) having a particle size of 08 to 0.11 μm.