JPH07173798A - Composition for coated paper - Google Patents

Abstract

PURPOSE:To obtain a paper-coating composition composed of a copolymer latex obtained by the emulsion polymerization of a specific monomer and having well-balanced adhesion and blister resistance by adjusting the get fraction of the latex, the molecular weight of a specific soluble component and the particle diameter within respective specific ranges. CONSTITUTION:This composition for coated paper contains a copolymer latex produced by carrying out the emulsion copolymerization of (A) 20-60 pts.wt. of an aliphatic conjugated diene monomer, (B) 0.5-10 pts.wt. of an ethylenic unsaturated acid monomer and (C) 30-79.5 pts.wt. of other copolymerizable monomer [e.g. styrene, methyl methacrylate and (meth)acrylamide] using a chain transfer agent composed of 0.1-3 pts.wt. of a methylstyrene dimer and 0.1-3 pts.wt. of a sulfur-containing compound under a condition to satisfy the formula XY/Z>=150X+10000 wherein X (wt.%) is get fraction of the emulsion polymerized latex, Y is weight-average molecular weight of tetrahydrofuran- soluble component and Z (nm) is particle diameter. A coated paper suitable for web offset printing can be produced by the use of the composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for coated paper which is excellent in adhesive strength and blister resistance.

[0002]

2. Description of the Related Art In recent years, an offset rotary printing press has become remarkably popular in the printing industry as printing speed increases. 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, various proposals have been made to satisfy this. For example, Japanese Examined Patent Publication (Kokoku) No. 57-10237 discloses a means for adjusting the gel fraction in the latex as a binder by the amount of the chain transfer agent. However, it has been recognized that the higher the gel fraction of the coated paper, the better the adhesive strength, whereas the lower the gel fraction, the better the blister resistance. As a means to improve both sexes to a high level at the same time, the above technique is not fully satisfactory.

[0004]

SUMMARY OF THE INVENTION Based on the above background, the present invention provides a composition for coated paper, which has excellent balance between adhesive strength and blister resistance.

[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. By adjusting the gel fraction, tetrahydrofuran (hereinafter abbreviated as THF) soluble component weight average molecular weight and particle diameter of the copolymer latex obtained by emulsion-polymerizing various monomers within a certain range, They have found that a latex having a good balance of blister resistance can be obtained, and have completed the present invention. That is, the present invention includes (A) 20-60 parts by weight of an aliphatic conjugated diene monomer, (B) an ethylenically unsaturated acid monomer of 0.5-10.
Parts by weight, (C) other copolymerizable monomer 30-7
A copolymer latex obtained by emulsion-polymerizing 9.5 parts by weight, wherein the gel fraction (X% by weight) of the latex is:
A coated paper composition, characterized in that it contains a copolymer latex having a weight-average molecular weight (Y) and a particle diameter (Znm) of a tetrahydrofuran-soluble component satisfying the following condition XY / Z> 150X + 10000.

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 particularly 1,3-butadiene is preferably used. The amount of the monomer (A) used is 20-60 parts by weight based on the total amount of the monomers. When the amount used is less than the above range, sufficient adhesive strength cannot be obtained, and when the amount is too large, water resistance and adhesive strength decrease, which is not preferable. (B) Examples of the 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 and half esters thereof. Examples thereof include sulfonic acid group-containing unsaturated monomers such as styrene sulfonic acid, 2-sulfoethyl acrylate and acrylamidopropanesulfonic acid, 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. (C) Examples of other copolymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, p-methylstyrene, methyl (meth) acrylate, and (meth) acrylic. (Meth) acrylic acid esters such as ethyl acrylate and butyl (meth) acrylate, (meth)
Vinyl cyanides such as acrylonitrile and the like,
In particular, styrene as the aromatic vinyl monomer, (meth)
Methyl methacrylate is preferably used as the acrylic ester, and acrylonitrile is preferably used as the vinyl cyanide. Furthermore, examples of other copolymerizable monomers include ethylenically unsaturated carboxylic acid amides such as (meth) acrylamide and N-methylol (meth) acrylamide, and N-substituted compounds thereof, (meth) acrylic acid-
Hydroxyl group-containing unsaturated monomers such as 2-hydroxyethyl,
Examples thereof include glycidyl group-containing unsaturated monomers such as glycidyl methacrylate and vinyl esters such as vinyl acetate and vinyl propionate.

Examples of the polymerization initiator used in the emulsion copolymerization of the present invention include potassium persulfate, ammonium persulfate, sodium persulfate and other persulfates, water-soluble initiators such as hydrogen peroxide, and bisulfite and these. 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 sulfonates, alkyl ester type of polyethylene glycol,
Nonionic surfactants such as alkylphenyl ether type and alkyl ether type, and amphoteric surfactants such as betaine type are used alone or in combination of two or more kinds.

Examples of the chain transfer agent used for producing the copolymer latex of the present invention include sulfur such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, mercaptoethanol, mercaptopropionic acid and its ester. Element-containing compounds, sulfides such as tetraethylthiuram sulfide, alkyl halides such as carbon tetrachloride, α-methylstyrene dimer and the like. Chain transfer agents generally used for controlling the molecular weight in emulsion copolymerization reaction, alone or in combination. It can be used as a mixture of the above. In particular, when producing the copolymer latex of the present invention, by using (a) 0.1-3 parts by weight of α-methylstyrene dimer and (b) 0.1-3 parts by weight of a sulfur element-containing compound, It is preferable because a copolymer latex satisfying the conditions of the present invention can be obtained relatively easily.

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 a conventionally known emulsion polymerization method may be used. When emulsion polymerization of the body mixture in the reactor,
There is a method in which the polymerization conversion rate during the addition of the monomer is 80% or less, and the reaction is forcibly stopped within the range of 85% to 95% by weight. The polymerization conversion rate in the emulsion polymerization monomer feed can be controlled by the monomer addition time and the polymerization temperature.

As the reaction terminator for forcibly stopping the emulsion polymerization, compounds commonly used for stopping the emulsion polymerization can be used. Examples of this reaction terminator include NN-diethylhydroxyamine, potassium dimethylthiocarbamate, and methylhydroquinone. Furthermore, in the composition for coated paper of the present invention, as pigments, inorganic pigments such as kaolin, clay, calcium carbonate, satin white, titanium oxide, aluminum hydroxide, barium sulfate and zinc oxide, polystyrene, SBR and phenol. Organic pigments such as resins are used alone or in combination of two or more, a dispersant,
A water resistance agent, a viscosity modifier, an antifoaming agent, a water retention agent, a dye, a fluorescent dye, a lubricant, a pH adjusting agent, a surfactant, a preservative, other auxiliaries, additives and the like can be used if necessary.

As the binder, in addition to the copolymer latex of the present invention, if necessary, a water-soluble polymer such as starch, casein, polyvinyl alcohol, etc.,
Latex such as polyvinyl acetate and acrylic acid ester copolymer can be used together. 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).

[0012]

The present invention will be described in detail below 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 Production Examples 1 to 8 and Comparative Production Examples 1 to 7 In an autoclave equipped with a stirrer, 100 parts by weight of water, 1.5 parts by weight of potassium persulfate, 1 part by weight of maleic acid and necessary amount of Sodium lauryl sulfate was charged, thoroughly mixed with stirring, and deoxygenated by nitrogen substitution. Then, the production was performed according to the conditions shown in Table 1. That is, the internal temperature of the autoclave was raised to a predetermined temperature, and then the remaining 99
A mixture of 1 part of the monomer, the chain transfer agent, 40 parts of water and 0.2 part of sodium lauryl sulfate was added to the autoclave over a predetermined time. After the addition of the monomer was completed, the reaction was further continued for a predetermined time, followed by cooling, and 0.1 part of N—N-diethylhydroxyamine was added to complete the polymerization. The internal temperature of the autoclave was kept at a predetermined temperature from the addition of the monomer to the end of the polymerization. The polymerization conversion rate at the end of monomer addition and at the end of polymerization was measured by the following method. This value is shown in Tables 1 and 2.

After the completion of polymerization, the pH was adjusted to 8 with sodium hydroxide.
After adjusting to 0, unreacted monomer and volatile residual organic matter are removed by steam stripping, and the solid content is concentrated to 50% to obtain a copolymer latex (Production Example). 1 to 8) and a copolymer latex used for comparison (Comparative Production Examples 1 to 7) were obtained. Polymerization conversion rate and properties of copolymer latex a) Polymerization conversion rate: About 1 g of the extracted reaction solution was precisely weighed, and
After drying at 0 ° C. for 15 minutes, the residue is weighed, the solid content is calculated by the formula (1), and then the polymerization conversion rate is calculated by the formula (2). b) Gel fraction of copolymer latex and weight average molecular weight of tetrahydrofuran (THF) -soluble component: The copolymer latex was uniformly cast on a polypropylene plate,
After static drying at ℃ for 1 week, 1 at 80 ℃ in hot air circulation dryer
Dry for hours to form a film. After precisely 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 formula (3). To do.

[0014] 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. c) Particle size measurement 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)
The calculated values of XY / Z-150X are shown in Tables 1 and 2, together with the particle diameter (Znm).

[0015]

[Table 1]

[0016]

[Table 2] Table 1 continued

Examples 1 to 8 and Comparative Examples 1 to 7 The copolymer latexes of Production Examples 1 to 8 and Comparative Production Examples 1 to 7 were used to prepare Examples 1 to 1 according to the following formulation.
8 and the coated paper compositions of Comparative Examples I-7 were prepared,
Coated paper was manufactured by the following method and evaluated.
The results are shown in Table 2. Formulation of composition for coated paper NO-1 Kaolin clay 70 parts by weight Heavy calcium carbonate 30 parts by weight Dispersant 0.3 parts by weight NaOH 0.1 parts by weight Oxidized starch 4 parts by weight Copolymer latex 11 parts by weight Color Concentration 62% For each coated paper composition, test coated paper was further prepared under the following conditions.

Preparation of Test Coated Paper Each coated paper composition was coated on a high-quality paper at a dry weight of 15
g / m ² , and on the back surface of commercially available single-sided cast paper for blister resistance test, a coating amount of 15 g / m ² was applied using an applicator bar and immediately applied to a box-type hot air dryer. Then, it is dried at 120 ° C. for 20 seconds.
The coated paper obtained is further seasoned under conditions of 20 ° C. and 65% relative humidity. 60 ℃ linear pressure 100
2 super calender treatment under the condition of kg / cm
The coating paper thus obtained was subjected to a strength test and a blister resistance test.

The coated papers obtained were evaluated according to the test methods shown below, and the results are shown in Table 2. a) Dry pick strength test Using a RI printing aptitude tester (manufactured by Akira Seisakusho Co., Ltd.), a tacking ink (Toyo Ink SMX Tack 10) is visually checked for a paper peeling state, and a 10-point method (10 points are excellent) is used. 1 point was inferior). b) 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.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

The coated paper obtained by the coated paper composition of the present invention is excellent in adhesive strength and blister resistance, and the present invention is useful as a coated paper composition which has never been obtained. .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI technical display location // C08F 236/04 MPF 8416-4J (72) Inventor Kenichi Nakane 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa Address Mitsui Toatsu Chemicals, Inc.

Claims (2)

[Claims] 1. An aliphatic conjugated diene-based monomer (A) 20-
60 parts by weight, (B) ethylenically unsaturated acid monomer 0.5
-10 parts by weight, (C) other copolymerizable monomer 30
A copolymer latex obtained by emulsion-copolymerizing -79.5 parts by weight, wherein the latex has a gel fraction (X wt%), a tetrahydrofuran-soluble component weight average molecular weight (Y) and a particle diameter (Z nm). ) Contains a copolymer latex satisfying the following condition XY / Z> 150X + 10000: 2. A copolymer latex as a chain transfer agent at the time of emulsion copolymerization (a) α-methylstyrene dimer
0.1-3 parts by weight and (b) elemental sulfur-containing compound
The coated paper composition according to claim 1, which is produced by using 1 to 3 parts by weight.