JPH09316131A - Copolymer latex and composition for coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolymer latex having an excellent balance between adhesiveness and blistering resistance and a composition for coated paper containing the same. SOLUTION: This latex is obtained by emulsion-copolymerizing an aliphatic conjugated diene monomer with an ethylenically unsaturated monomer and other comonomers and satisfies the following relationships: XY/Z>28,000-8(Z-70)<2> (wherein X (wt.%)) is the gel fraction of the latex, Y is the molecular weight of tetrahydrofuran insolubles, and Z (nm) is the mean particle diameter). A composition containing this latex can provide coated paper excellent in adhesiveness and blistering resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolymer latex having a specific physical property value, which is preferably blended in a composition for coated paper, and further contains the copolymer latex. The present invention relates to a composition for coated paper having excellent adhesive strength and blister resistance.

[0002]

2. Description of the Related Art In the printing industry, an offset rotary printing press has been remarkably spread with the increase in printing speed. Compared with sheet-fed offset printing, this printing method requires high-temperature, high-speed drying immediately after printing, so it is necessary to prevent blistering due to evaporation of water in the paper during drying. Blister resistance is one of the extremely important required properties of paper (hereinafter also referred to as coated paper). However, the blister resistance and the other important required quality characteristic, adhesive strength, have a negative correlation, and it is extremely difficult to obtain these well-balanced characteristics.

Conventionally, in order to satisfy this, Japanese Patent Publication Sho 5
Although a means for adjusting the gel fraction of latex as described in 7-10237 by the amount of a chain transfer agent is widely used, the adhesive strength and blister resistance of coated paper are contrary to the gel fraction. Therefore, in order to achieve a high level while balancing these physical properties, it is difficult to carry out only by adjusting the gel fraction. In order to improve the balance of these physical properties, JP-A-7-173798 discloses a method of adjusting the gel fraction of the copolymer latex, the weight average molecular weight of the tetrahydrofuran-soluble component, and the particle size of the latex so as to have a constant relationship. Has been done. In this method, the balance between the adhesive strength and the blister resistance is improved as compared with the method of only adjusting the gel fraction, but the required performance for the copolymer latex used as the binder in the composition for coated paper becomes more severe. Nowadays, there is no choice but to say that it is still inadequate, and there is a demand for achieving a more sophisticated physical property balance.

[0004]

On the basis of the above background, the present invention is directed to a copolymer latex having characteristics of excellent balance between adhesive strength and blister resistance, and a coating containing the copolymer latex. Provided is a composition for paper.

[0005]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that aliphatic conjugated diene-based monomers, ethylenically unsaturated acid monomers and other copolymerizable compounds can be copolymerized. Adhesive strength by adjusting the gel fraction, tetrahydrofuran (hereinafter abbreviated as THF) soluble content weight average molecular weight and average particle diameter of the copolymer latex obtained by emulsion polymerization of various monomers to a certain range. It was found that a latex having a good balance of blister resistance was obtained, and the present invention was completed.

That is, the present invention comprises (1) 15-55 parts by weight of (A) aliphatic conjugated diene monomer, (B) 0.5-10 parts by weight of ethylenically unsaturated acid monomer, and (C) ) Other copolymerizable monomers 35-84.5 parts by weight of a copolymer latex obtained by emulsion copolymerization, wherein the gel fraction (X% by weight) of the latex and the weight of the tetrahydrofuran-soluble component. Average molecular weight (Y) and average particle size (Zn
m) is a copolymer latex satisfying the following condition XY / Z> 28000-8 (X-70) ² , and (2) the chain transfer constant for styrene at 60 ° C. at the time of emulsion copolymerization is 1.6 or less. The copolymer latex according to (1), wherein the chain transfer agent is added in an amount of 0.2 to 8 parts by weight with respect to 100 parts by weight of the monomer mixture, and (3) the melting point at the time of emulsion copolymerization. The copolymer latex according to (1), wherein the phenol compound at 30 ° C. or lower is added in an amount of 0.2-8 parts by weight with respect to 100 parts by weight of the monomer mixture, (4) (1) (3) A composition for coated paper, characterized by comprising the copolymer latex according to any one of (3) to (3).

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The monomers used for producing the copolymer latex of the present invention will be described. Examples of the (A) aliphatic conjugated diene-based monomer include 1,3
-Butadiene, 2-methyl-1,3-butadiene, 2-
Examples thereof include chloro-1,3-butadiene, and these can be used alone or in combination of two or more. The amount of the monomer (A) used is 1 with respect to all the monomers.
5-55 parts by weight. When the amount used is less than the above range, it becomes difficult to obtain sufficient adhesive strength when used as a composition for coated paper, and when it is too large, water resistance and adhesive strength decrease, which is not preferable.

Examples of the (B) ethylenically unsaturated acid monomer include monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. , Half esters, styrene sulfonic acid, 2-sulfoethyl acrylate, acrylamide propane sulfonic acid, and other sulfonic acid group-containing unsaturated monomers and salts thereof. The amount of the monomer (B) used is 0.5-10 parts by weight with respect to all the monomers. If the amount used is outside the above range, the stability and adhesive strength of the copolymer latex may be insufficient, or the viscosity of the copolymer latex may become too high, resulting in poor workability.

Examples of (C) other copolymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene and p-methylstyrene, methyl (meth) acrylate, ( (Meth) ethyl acrylate,
Examples thereof include (meth) acrylic acid esters such as butyl (meth) acrylate, vinyl cyanides such as (meth) acrylonitrile, and the like. Particularly, styrene is used as the aromatic vinyl monomer, and (meth) acrylic acid esters are used. Methyl methacrylate is preferably used as the above, and acrylonitrile is preferably used as the vinyl cyanides. Furthermore, examples of other copolymerizable monomers include (meth) acrylamide, N,
Ethylenically unsaturated carboxylic acid amides such as N-dimethyl (meth) acrylamide and N-methylol (meth) acrylamide and N-substituted compounds thereof, ethylenically unsaturated carboxylic acid amides such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate. Saturated amine compounds,
Examples include hydroxyl group-containing unsaturated monomers such as (meth) acrylic acid-2-hydroxyethyl, glycidyl group-containing unsaturated monomers such as glycidyl methacrylate, vinyl acetates such as vinyl acetate and vinyl propionate. To be

The polymerization initiator used in the emulsion copolymerization of the present invention includes potassium persulfate, ammonium persulfate, sodium persulfate and other persulfates, hydrogen peroxide and other water-soluble initiators, or bisulfite and bisulfite. Redox initiators in combination with reducing agents such as sodium and amines are preferable, and water-soluble azo initiators, benzoyl peroxide, oil-soluble initiators such as azobisisobutyronitrile, etc. can also be used. In addition, as an example of an emulsifier used for imparting sufficient stability to the copolymer latex while controlling the particle size of the copolymer latex to be produced during emulsion copolymerization, sulfuric acid of a higher alcohol is used. Anionic surfactants such as esters, alkylbenzene sulfonates, aliphatic sulfonates, alkyl diphenyl ether (di) sulfonates, nonionic surfactants such as alkyl ester type of polyethylene glycol, alkyl phenyl ether type, alkyl ether type The agents and amphoteric surfactants such as betaine type are used alone or in combination of two or more kinds.

Examples of chain transfer agents or molecular weight regulators used in the production of the copolymer latex of the present invention include t
-Dodecyl mercaptan, n-dodecyl mercaptan,
Sulfur element-containing compounds such as n-octyl mercaptan, mercaptoethanol, mercaptopropionic acid and its esters, disulfides such as tetraethylthiuram disulfide, diethylxanthogen disulfide, halogenated alkyls such as carbon tetrachloride, terpenoids such as terpinolene, α -Methylstyrene dimer, 3-
In addition to phenyl-1-pentene, 1,4-cyclohexadiene, etc., hydroquinone, t-butylcatechol, 2,6
Known chain transfer agents or molecular weight regulators generally used for emulsion polymerization such as -di-t-butyl-4-methylphenol and 2,6-xylenol can be used alone or in combination of two or more kinds.

Particularly in the production of the copolymer latex of the present invention, the copolymer latex of the present invention can be obtained relatively easily by adding a chain transfer agent having a specific chain transfer constant. Here, the "chain transfer constant" used in the present invention means the chain transfer constant of the chain transfer agent when it is alone, and when a plurality of types of chain transfer agents are used in combination, It refers to the molar weighted average value calculated from the chain transfer constant of the chain transfer agent and its addition molar ratio.

That is, in (a) emulsion polymerization, 60 ° C.
In 100 parts by weight of the monomer mixture (b), a chain transfer agent having a chain transfer constant of 1.6 or less for styrene in
When 0.2-8 parts by weight is added, a copolymer latex satisfying the conditions of the present invention can be obtained relatively easily. At this time, when a plurality of kinds of chain transfer agents are used in combination, each chain transfer agent is as described above. The chain weighted average value of the chain transfer constants of
When it is within the range of 1 and satisfies (b), a copolymer latex satisfying the conditions of the present invention can be obtained relatively easily. If the chain transfer constant is outside this range, the molecular weight of the tetrahydrofuran-soluble component of the copolymer latex is too low, and it is difficult to obtain the copolymer latex of the present invention. When the amount is too small, the gel fraction of the copolymer latex is remarkably increased, and when used as a composition for coated paper, the adhesive strength and the blister resistance are deteriorated, which is not preferable. Further, if the amount added is more than this range, the decrease in the polymerization rate may be too large, which is not preferable because the productivity is decreased. For some of the above-mentioned chain transfer agents, the values of the chain transfer constants for styrene at 60 ° C. with reference to the literature and technical materials related to production / sales are, for example, t-dodecyl mercaptan 2.9,
n-dodecyl mercaptan 12.8, tetramethyl thiuram disulfide 1.11, terpinolene 0.03
4, α-methylstyrene dimer 0.21 and these values were used in the present invention.

In the production of the copolymer latex of the present invention, the melting point is 30 with respect to 100 parts by weight of the monomer mixture.
It is preferable to use 0.2-8 parts of a phenolic compound at a temperature of not higher than 0 ° C. because a copolymer latex satisfying the conditions of the present invention can be obtained relatively easily. Examples of the phenol compound having a melting point of 30 ° C. or lower include 2,4-xylenol (melting point of about 26 ° C.) and 2,4-dimethyl-6-t-butylphenol (melting point of about 14 ° C.). As the phenolic compound, 2,4-dimethyl-6-t-butylphenol is preferable. A compound having a melting point of higher than 30 ° C. is regarded as a substantially solid raw material under normal conditions. The use of a solid raw material makes it extremely difficult to add it to the polymerization system while accurately controlling the amount of addition during the production of the copolymer latex, and also to generate aggregates when added to the latex system. This is not preferable because it causes the problem. There is also a method of using these solid raw materials by dissolving them in other liquid raw materials, for example, monomers, water, etc., but in this case, there is a problem that the addition amount cannot be adjusted independently. However, this decreases the degree of freedom in preparing the copolymer latex, which is not preferable. When the amount added is less than this range, it is difficult to obtain the copolymer latex of the present invention, and when used as a composition for coated paper, the balance between adhesive strength and blister resistance is lowered, which is not preferable. . Further, if the addition amount is more than this range, the decrease in the polymerization rate may be too large,
This is not preferable because productivity is reduced.

The method for producing the copolymer latex of the present invention is not particularly limited as long as the conditions of the present invention are satisfied, and any conventionally known emulsion polymerization method may be used. The above-mentioned chain transfer agent or molecular weight modifier may be used. In addition to the factors involved, it is also effective to appropriately adjust and combine the polymerization temperature, the monomer addition rate, the polymerization initiator addition amount, the addition method, and the like. For example, in emulsion polymerization of a copolymer latex, the polymerization conversion rate at the end of addition of all monomers to the reaction system is 85% or less, preferably 80%.
Hereinafter, more preferably, a method of adjusting to 75% or less, or a polymerization conversion rate in the range of 85% to 95% by weight is used in the reaction system such as NN-diethylhydroxyamine, potassium dimethylthiocarbamate, methylhydroquinone, etc. It is possible to add a compound generally used for terminating the emulsion polymerization and to forcibly terminate the polymerization reaction in combination.

Further, in the composition for coated paper of the present invention,
Pigments include kaolin, clay, calcium carbonate, satin white, titanium oxide, aluminum hydroxide, barium sulfate, zinc oxide, and other inorganic pigments, polystyrene, SBR
And organic pigments such as phenolic resins are used alone or in combination of two or more, and dispersants, water-proofing agents, viscosity modifiers, defoamers, water-retaining agents, dyes, fluorescent dyes, lubricants, p
H regulators, surfactants, preservatives, other auxiliaries, additives and the like can be used as required.

Further, as the binder, in addition to the copolymer latex of the present invention, a water-soluble polymer such as starch, casein or polyvinyl alcohol, if necessary,
Latexes such as polyvinyl acetate and acrylate copolymers can be used in combination. The copolymer latex of the present invention is usually used in the range of 5 to 30 parts by weight (solid content) with respect to the pigment (solid content).

[0018]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, all parts and% in the examples are parts by weight and% by weight. 1) Production Example of Copolymer Latex Examples 1 to 13 and Comparative Examples ag In an autoclave equipped with a stirrer, 100 parts by weight of water, 1.2 parts by weight of potassium persulfate, 1 part by weight of itaconic acid and necessary amount of lauryl sulfate were added. Soda was charged, and the mixture was sufficiently stirred and mixed, and the inside of the autoclave was replaced with nitrogen. After the internal temperature of the autoclave was raised to 65 ° C., the remaining 99 parts of the monomer shown in Table 1, a chain transfer agent or a molecular weight modifier, 40 parts of water and 0.2 part of sodium lauryl sulfate were autoclaved for 6 hours. Added in. After the completion of the addition of the monomer, the reaction was further continued at 65 ° C. for a predetermined time and then cooled, and 0.1 part of NN-diethylhydroxyamine was added to complete the polymerization. After the completion of the polymerization, the pH was adjusted to 8.0 with sodium hydroxide, and then unreacted monomers and volatile residual organic substances were removed by steam stripping, and the solid content concentration was 50%. Polymer latex production examples 1 to 13 and production comparative examples a to g were obtained.

2) Properties of copolymer latex a) Gel fraction of copolymer latex and weight-average molecular weight of tetrahydrofuran (THF) -soluble component: The copolymer latex is uniformly cast on a polypropylene plate and allowed to stand at room temperature. After static drying for 1 week, 1 in a hot air circulation dryer at 80 ° C
Dry for hours to form a film. After accurately weighing about 1 g with an analytical balance, immersing it in a container containing 100 CC of THF for 2 days, collecting 10 ml of the THF solution, weighing the solid content after drying, and calculating the gel fraction by the following method . In addition, a part of the above THF solution was sampled and the concentration was adjusted, then filtered through a 0.45 μm filter, and the weight average molecular weight was measured by a gel filtration chromatography device. The measurement results were converted by a calibration curve using polystyrene standard samples having a weight average molecular weight of 19,000, 50,000 and 100,000.

B) Measurement of Average Particle Size of Copolymer Latex The copolymer latex was diluted with pure water to a predetermined concentration and then measured with a submicron particle size measuring instrument manufactured by Coulter Electronics. The gel fraction (X
%), Tetrahydrofuran-soluble matter weight average molecular weight (Y)
And average particle size (Znm), XY / Z + 8 (X
The calculated values of -70) ² are shown in Table 1.

3) Production of Coated Paper Using the copolymer latices of Production Examples 1 to 13 and Production Comparative Examples a to g, the following formulation was used to prepare Examples 1-13 and Comparative Examples a to g. After preparing the composition for coated paper of, the coated paper was manufactured by the following method, and the evaluation test was conducted. Table 1 shows the results.

(Formulation) NO-1 Kaolin clay 50 parts by weight Heavy calcium carbonate 50 parts by weight Dispersant 0.3 parts by weight NaOH 0.1 parts by weight Oxidized starch 3 parts by weight Copolymer latex 10 parts by weight Color density 69 %

[0023] The above coating composition was coated on a high-quality paper at a dry weight of 15 g / m ² , and on the back surface of a commercially available single-sided cast paper for a blister resistance test, a coating amount of 15 g / m 2.
Apply using an applicator bar so that it becomes ² .
Immediately, it is dried at 130 ° C. for 20 seconds in a box type hot air dryer. The coated paper obtained is further subjected to seasoning under conditions of 20 ° C. and 65% relative humidity. Then 6
The super calender treatment was performed twice under the condition of 0 ° C. linear pressure of 100 kg / cm, and the coated paper thus obtained was subjected to a strength test and a blister resistance test. The coated paper obtained was evaluated according to the test methods shown below, and the results are shown in Table 1.

A) Dry pick strength test Using a RI printing aptitude tester (manufactured by Akira Seisakusho Co., Ltd.), the peeling state is visually judged by printing the tack ink (Toyo Ink SMX tack 15), and the 10 point method (10) is used. The points were evaluated as excellent and 1 as inferior. b) Wet pick strength test Using a RI printability tester (manufactured by Akira Seisakusho Co., Ltd.), after applying dampening water to the coated paper surface, tack ink (Toyo Ink SM
X-tack 15) was used to visually determine the paper peeling state, and the evaluation was made by a 10-point method (10 points being excellent and 1 point being poor). c) Blister resistance test Dip the coated paper in an oil bath at 150 ° C to 200 ° C, and score the number of generated blisters (no blisters = 5).
Points) An average of 20 test pieces was evaluated.

[0025]

[Table 1]

[0026]

The coated paper obtained from the composition for coated paper containing the copolymer latex of the present invention is excellent in adhesive strength and blister resistance. It is clear from Table 1 that the composition for paper is a useful composition which has never been obtained.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kenichi Nakane 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Mitsui Toatsu Chemicals Co., Ltd.

Claims (4)

[Claims] 1. An aliphatic conjugated diene-based monomer (A) 15
-55 parts by weight, (B) ethylenically unsaturated acid monomer
5-10 parts by weight, (C) other copolymerizable monomer 3
A copolymer latex obtained by emulsion copolymerization of 5-84.5 parts by weight, wherein the gel fraction (X% by weight) of the latex, the weight average molecular weight (Y) and the average particle diameter of the tetrahydrofuran-soluble component. A copolymer latex in which (Znm) satisfies the following condition XY / Z> 28000-8 (X-70) ² . 2. During emulsion copolymerization, 0.2-8 parts by weight of a chain transfer agent having a chain transfer constant of 1.6 or less for styrene at 60 ° C. is added to 100 parts by weight of the monomer mixture. The copolymer latex according to claim 1. 3. The emulsion according to claim 1, wherein 0.2-8 parts by weight of a phenolic compound having a melting point of 30 ° C. or lower is added to 100 parts by weight of the monomer mixture during the emulsion copolymerization. Polymer latex. 4. A coated paper composition comprising the copolymer latex according to claim 1.