JPH10298208A - Production of copolymer latex and paper coating composition containing the copolymer latex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the resistance to backing roll staining, adhesive strength, and resistance to blistering by subjecting a mixture of a conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, a monomer comprising an alkyl ester of an ethylenically unsaturated carboxylic acid, methacrylonitrile, a hydroxyalkylated unsaturated monomer, and other copolymerizable monomer to emulsion polymerization in two steps. SOLUTION: A conjugated diene monomer in an amount of 20-60 wt.% is mixed with an ethylenically unsaturated carboxylic acid monomer in an amount of 1-10 wt.%, a monomer comprising an alkyl ester of an ethylenically unsaturated carboxylic acid, in an amount of 3-40 wt.%, methacrylonitrile in an amount of 3-30 wt.%, a hydroxyalkylated unsaturated monomer in an amount of 1-5 wt.%, and other copolymerizable monomer in an amount of 15-60 wt.% to give a monomer mixture. 45-99 wt.% of this mixture is charged into a polymerization tank for emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon having one unsaturated bond in the ring to give a copolymer latex. The remaining 1-45 wt.% of the mixture is subjected to emulsion polymerization in the presence of the obtained copolymer latex.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a copolymer latex. More specifically, the present invention relates to a method for producing a copolymer latex for paper coating having excellent adhesive strength, blister resistance, and backing roll stain resistance.

[0002]

2. Description of the Related Art In recent years, coated paper has been used for a very large number of printed materials because of its high printing effect.
In the periodicals such as quarterly and monthly newspapers, the number of cases in which coated paper is used for all pages has increased considerably. In particular, most of direct mail and product catalogs in the mail order business use coated paper for all pages.

[0003] Coated paper has many excellent points such as whiteness, glossiness, smoothness and printability as compared with uncoated paper. Is required using a blade coater or a roll coater, and the performance of the paper coating composition greatly affects the quality of the final coated paper product. For this reason, the paper coating composition is required to have a high level of washability, mechanical stability, fluidity, water retention and the like as high-speed coating suitability.

Generally, a paper coating composition is a pigment dispersion in which a white pigment such as clay or calcium carbonate is dispersed in water.
It is a water-based paint composed of pigments, a binder for bonding and fixing the pigments to the base paper, and other additives. As the binder, a synthetic emulsion binder typified by a styrene-butadiene copolymer latex or a natural binder typified by starch and casein are used. Among them, styrene-butadiene copolymer latex has a large degree of freedom in quality design, and is widely used today as the most suitable binder for paper coating compositions. Is the performance of the paper coating composition or the surface strength of the final coated paper product, blister resistance,
It is said that it greatly affects quality such as.

For example, Japanese Patent Application Laid-Open No. Hei 5-279406 discloses that a copolymer latex obtained by emulsion polymerization in the presence of a specific compound is used to obtain fluidity during paper coating and a coating liquid. Has excellent mechanical stability and improved printing strength, printing gloss and blister resistance during printing.

Japanese Patent Application Laid-Open No. 5-239113 discloses that in carrying out emulsion polymerization of a carboxy-modified styrene-butadiene latex, two-stage polymerization is carried out, and a monomer containing at least methacrylonitrile and methacrylamide is contained in a second stage. A production method for polymerization is shown. By using the copolymer latex as a paper coating composition, the problem of backing roll dirt and super calendar dirt during coating is improved, and the pick strength, blister resistance, and print gloss of coated paper are improved. It has been proposed.

[0007]

However, these various improved techniques have not yet reached a level which sufficiently satisfies the performance required for the copolymer latex for paper coating.
Further improvement was strongly sought. In particular, the backing roll stains due to the drying of the water-based paint during the production of coated paper are removed by the washing device attached to the coating machine, but it is difficult to completely clean the coated paper, and the coated paper produced due to accumulation of the stain is difficult. This leads to a decrease in the quality of the product and a decrease in the productivity itself.

Further, the adhesive strength and the blister resistance of the coated paper are mutually contradictory properties. For example, the gel content of the copolymer strongly influences these properties;
That is, when a latex having a high gel content is used, the adhesive strength is excellent but the blister resistance is inferior. Conversely, when a latex having a low gel content is used, the blister resistance is excellent but the adhesive strength is inferior. It is known. It was difficult to simultaneously improve the adhesive strength and the blister resistance.

[0009]

DISCLOSURE OF THE INVENTION The present inventors have made intensive studies to solve the present problems in view of the above-mentioned circumstances, and as a result, have found that a cyclic unsaturated hydrocarbon having one unsaturated bond in the ring is obtained. A monomer of a specific composition consisting of a specific ratio in the presence of
By performing emulsion polymerization in at least two stages, a copolymer latex having excellent backing roll stain resistance, adhesive strength, and blister resistance can be obtained, and it has been found that the above problems can be solved. It was completed.

That is, the present invention relates to a conjugated diene monomer 2
0 to 60% by weight, ethylenically unsaturated carboxylic acid monomer 1
10 to 10% by weight, ethylenically unsaturated carboxylic acid alkyl ester monomer 3 to 40% by weight, methacrylonitrile 3 to
A monomer consisting of 30% by weight, 1 to 5% by weight of an unsaturated monomer containing a hydroxyalkyl group and 15 to 60% by weight of another monomer copolymerizable therewith is combined with an unsaturated bond in the ring. In producing a copolymer latex by emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon having one of the above, 45 to 99% by weight of all the monomers among the above monomers is charged into a polymerization reaction tank. A method for producing a copolymer latex, which comprises emulsion-polymerizing the remaining monomer equivalent to 1 to 55% by weight of all monomers in the presence of the obtained copolymer latex after emulsion polymerization; and An object of the present invention is to provide a paper coating composition containing the copolymer latex obtained by the production method.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

In the present invention, the aliphatic conjugated diene monomer is used in an amount of 20 to 60% by weight. When the amount of the aliphatic conjugated diene monomer is less than 20% by weight, the adhesive property such as dry pick strength required at the time of printing is obtained. When the amount exceeds 60% by weight, wet adhesive property such as wet pick strength required at the time of printing. Is inferior.

The aliphatic conjugated diene monomer in the present invention includes 1,3-butadiene and 2-methyl-1,3-
Butadiene, 2,3-dimethyl-1,3-butadiene,
Examples thereof include 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and one or more of these can be used. In particular, use of 1,3-butadiene is preferred.

In the present invention, the ethylenically unsaturated carboxylic acid monomer is used in an amount of 1 to 10% by weight. If the amount of the ethylenically unsaturated carboxylic acid monomer is less than 1% by weight, the mechanical stability of the copolymer latex itself and the paper coating composition is poor, and if it exceeds 10% by weight, the viscosity of the copolymer latex is high. This causes problems in handling the copolymer latex.

The ethylenically unsaturated carboxylic acid monomer in the present invention includes mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. 1
Species or two or more can be used.

In the present invention, the ethylenically unsaturated carboxylic acid alkyl ester monomer is used in an amount of 3 to 40% by weight. When the amount of the ethylenically unsaturated carboxylic acid alkyl ester monomer is less than 3% by weight, the blister resistance is poor, and
If it exceeds 0% by weight, wet adhesion such as wet pick strength required for printing is poor.

The ethylenically unsaturated carboxylic acid alkyl ester monomer in the present invention includes methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, Examples thereof include diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate, and one or more of these can be used. Particularly, use of methyl methacrylate is preferred.

In the present invention, methacrylonitrile is
It is used in an amount of 3 to 30% by weight. When the amount of methacrylonitrile is less than 3% by weight, the backing roll stain resistance is poor, and
If it exceeds 0% by weight, wet adhesion such as wet topic strength required at the time of printing is inferior.

In the present invention, the unsaturated monomer having a hydroxyalkyl group is used in an amount of 1 to 5% by weight. 1% by weight of unsaturated monomer containing hydroxyalkyl group
If it is less than 5%, the adhesion such as dry pick strength required at the time of printing will be poor. If it exceeds 5% by weight, wet adhesion such as wet pick strength required at the time of printing will be poor.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
Hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate,
Di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl)
Maleate, 2-hydroxyethyl methyl fumarate and the like can be mentioned, and one or more of these can be used. Particularly, use of β-hydroxyethyl acrylate is preferred.

The above aliphatic conjugated diene monomer, ethylenically unsaturated carboxylic acid monomer, ethylenically unsaturated carboxylic acid alkyl ester monomer, methacrylonitrile and unsaturated monomer containing a hydroxyalkyl group Examples of other monomers copolymerizable with the above include aromatic vinyl monomers, unsaturated carboxylic acid amide monomers, and acrylonitrile.

The aromatic vinyl monomers include styrene, α-methylstyrene, methyl α-methylstyrene,
Vinyl toluene and divinyl benzene, and the like,
One or more of these can be used. Particularly, the use of styrene is preferred.

The unsaturated carboxylic acid amide monomers include:
Acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,
N-dimethylacrylamide and the like can be mentioned, and one or more of these can be used. Particularly, acrylamide is preferably used.

In the present invention, among these monomers,
Emulsion polymerization was carried out by charging 45 to 99% by weight into a polymerization reactor, and the remaining 1% was added in the presence of the obtained copolymer latex.
It is necessary to emulsion polymerize ~ 55% by weight of the monomers. If this polymerization method is not used, the backing roll stain resistance and wet adhesion such as wet pick strength required during printing are poor. In the polymerization method, 45 to 99% by weight of a monomer containing the entire amount of methacrylonitrile was charged into a polymerization reactor and emulsion polymerization was carried out. In the presence of the obtained copolymer latex, the remaining 1 to 55% by weight was used. % Of the monomer is preferably emulsion-polymerized in order to sufficiently obtain the effects of the present invention.

In the present invention, one unsaturated bond is contained in the ring.
It is necessary to carry out emulsion polymerization in the presence of a cyclic unsaturated hydrocarbon. A copolymer latex emulsion-polymerized in the absence of the hydrocarbon does not sufficiently provide the effects of the present invention on backing roll stain resistance, adhesive strength, and blister resistance. Most of the cyclic unsaturated hydrocarbon having one unsaturated bond in the ring used in the present invention remains unreacted after the polymerization, and it is necessary to recover the unreacted product. And those having a boiling point of 140 ° C. or less are desirable. Specifically, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, 1-
Methylcyclohexene and the like.

The hydrocarbon is usually used in an amount of 5 to 50 parts by weight based on 100 parts by weight of the monomer.

In the emulsion polymerization of the present invention, conventional chain transfer agents, emulsifiers, polymerization initiators, electrolytes, polymerization accelerators, chelating agents and the like can be used. The method for adding the various polymerization aids in the present invention is not particularly limited, and any of a batch addition method, a division addition method, and a continuous addition method can be employed.

The chain transfer agent used in the emulsion polymerization of the present invention includes alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan and n-stearyl mercaptan. Xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide; terpinolene; thiuram-based compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide; and 2,6-di-t.
-Butyl-4-methylphenol, phenolic compounds such as styrenated phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide, α-benzyloxystyrene, α-benzyl Oxyacrylonitrile, α-
Vinyl ether such as benzyloxyacrylamide, α
-Methylstyrene dimer, triphenylethane, pentaphenylethane, acrolein, methacrolein,
Thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate and the like.
More than one species can be used. These chain transfer agents are usually used in an amount of 0 to 10 parts by weight based on 100 parts by weight of the monomer.

Examples of the emulsifier include anionic salts such as sulfates of higher alcohols, alkylbenzene sulfonates, alkyldiphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, and sulfate esters of nonionic surfactants. Surfactants or nonionic surfactants such as alkyl ester type, alkyl phenyl ether type and alkyl ether type of polyethylene glycol can be mentioned, and one or more of these can be used.

As the polymerization initiator, a water-soluble polymerization initiator such as potassium persulfate, sodium persulfate and ammonium persulfate, a redox-based polymerization initiator, and an oil-soluble polymerization initiator such as benzoyl peroxide can be appropriately used. In particular, use of a water-soluble polymerization initiator is preferred.

Examples of pigments for paper coating compositions in which the copolymer latex produced according to the present invention is used include kaolin clay, talc, barium sulfate, titanium oxide, calcium carbonate, and aluminum hydroxide. And inorganic pigments such as zinc oxide and satin white; and organic pigments such as polystyrene latex. These may be used alone or in combination.

If necessary, starch, oxidized starch, modified starch such as esterified starch, a natural binder such as soybean protein and casein, or a water-soluble synthetic binder such as polyvinyl alcohol may be used. Further, synthetic latex such as polyvinyl acetate latex and acrylic latex may be used in combination with the copolymer latex of the present invention. (Solid content) of the copolymer latex is preferably less than 50% by weight.

In preparing a paper coating composition using the copolymer latex of the present invention, other auxiliaries such as dispersants (eg, sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate), Antifoaming agents (polyglycol, fatty acid ester, phosphate ester,
Requires silicone oil), leveling agent (funnel oil, dicyandiamide, urea, etc.), preservative, release agent (calcium stearate, paraffin emulsion, etc.), fluorescent dye, color water retention improver (carboxymethyl cellulose, sodium alginate, etc.) May be added according to the requirements.

Further, the method for applying the paper coating composition to the coating paper may be performed by a known technique, for example, using any coating machine such as an air knife coater, a blade coater, a roll coater, and a bar coater. No problem. After coating, the surface is dried and finished with a calender ring or the like.

[0035]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples unless it exceeds the gist. In the examples, parts and% indicating percentages are based on weight unless otherwise specified. The evaluation of various physical properties in the examples was based on the following methods.

Evaluation of Dry Pick Strength of Coated Paper The degree of picking when simultaneously printing each coated paper sample with an RI printing machine was judged with the naked eye and relatively evaluated from 5 to 1 point. The higher the score, the better. The average value of 6 times is shown.

Evaluation of Wet Pick Strength of Coated Paper Using a RI printer, moistening water is simultaneously applied to each coated paper sample by a Molton roll, and immediately thereafter, each coated paper sample is simultaneously printed by an ink roll. The degree of picking at this time was judged with the naked eye and relatively evaluated from 5 points to 1 point. The higher the score, the better. The average value of 6 times is shown.

Evaluation of Blister Resistance A double-sided coated paper sample was conditioned for about 1 day and night in an atmosphere of 20 ° C. and a relative humidity of 65%, and was thrown into a temperature-controllable oil bath to generate blisters. The minimum temperature was determined. The higher the temperature, the better the blister resistance.

Evaluation of backing roll stain resistance The paper coating composition was applied on an NBR rubber sheet and dried,
After washing with water at 30 ° C., the remaining state of the paper coating composition on the NBR rubber sheet was visually judged and relatively evaluated from 5 points to 1 point. The higher the score, the better. The average value of 6 times is shown.

Measurement of Gel Content of Copolymer Latex Copolymer latex was treated with sodium hydroxide to adjust the pH
Adjust to 8.0. Next, the copolymer latex is applied on a glass plate and dried in a hot air drier at 80 ° C. for 4 hours to form a latex film having a thickness of about 0.5 mm.
Then, after accurately weighing about 1 g of the latex film,
It is immersed in 00 cc of toluene for 48 hours, filtered through a 300 mesh wire gauze, dried, and the toluene insoluble (gel) on the wire gauze is weighed to calculate the gel content.

Preparation of Copolymer Latex 150 parts of polymerization water, 1.0 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium carbonate, and 1 part of potassium persulfate were charged into a pressure-resistant polymerization reaction tank, and then sufficiently charged. After stirring, each monomer of the first stage shown in Tables 1 and 2 was added and polymerization was carried out at 70 ° C., and the polymerization conversion of the first stage monomer reached 70% by weight. At this point, the second stage monomers were added to continue the polymerization. The polymerization was terminated when the conversion of all the monomers exceeded 95%. Next, these copolymer latexes are p-pulped with an aqueous sodium hydroxide solution.
H was adjusted to 7, and unreacted monomers and other low-boiling compounds were removed by steam distillation. The copolymer latexes 1 to 7 of Examples shown in Tables 1 and 2 and the copolymers of Comparative Examples Latexes 8 to 15 were obtained. In the table, the left side indicates the amount (parts by weight) of the first stage and the right side indicates the amount (parts by weight) of the first stage with "/" therebetween. The gel content of the obtained copolymer latex was measured, and the results are shown in Tables 1 and 2.

[0042]

[Table 1]

[0043]

[Table 2]

Preparation and Evaluation of Paper Coating Composition Copolymer latex 1 was prepared according to the following formulation.
Using No.-15, a paper coating composition was prepared. (Blending formulation of composition for paper coating) 70 parts kaolin clay 30 parts heavy calcium carbonate 4 parts starch oxide 4 parts copolymer latex 11 parts .... Solid content concentration 63%

Preparation and Evaluation of Coated Paper The obtained paper coating composition was coated on a base paper for coating (basis weight 55 g / m 2) using a commercially available hot air coating dryer MLC-100S. A coated paper was produced. In addition, each coated paper was produced under the same conditions shown below. Coating conditions: Coating was performed with a hot air coating dryer MLC-100S using a wire bar so that the coating amount of the above composition was 13 g / m2 on one side. Coating speed is 46m / mi
n. Set to. Drying conditions: About 0.5 seconds after the coating, drying was performed for 3 seconds with hot air at a temperature of 210 ° C and a wind speed of 33 m / second in a drying furnace at 150 ° C. The obtained coated paper was conditioned for 24 hours at a relative humidity of 65% and a temperature of 20 ° C., and then subjected to a linear pressure of 70 kg / cm and a temperature of 5 kg.
The paper was subjected to super calendering under the conditions of 5 ° C., a paper passing speed of 7 m / min, and a total of four passes, two times for each of the front and back sides, and the obtained coated paper was subjected to each test and evaluated. It was shown to.

[0046]

[Table 3]

[0047]

[Table 4]

[0048]

By using the copolymer latex obtained by the production method of the present invention as a binder for coated paper, coated paper excellent in adhesive strength, blister resistance and backing roll stain resistance can be obtained. Can be

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 220: 12 220: 42 220: 20) (72) Inventor: Tatsuo Misaki 2-10-2 Kikumotocho, Niihama-shi, Ehime AVS Latex Co., Ltd. Ehime Laboratory

Claims (2)

[Claims] 1. A conjugated diene monomer in an amount of 20 to 60% by weight,
1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer, 3 to 3% of an ethylenically unsaturated carboxylic acid alkyl ester monomer
40% by weight, 3 to 30% by weight of methacrylonitrile, 1 to 5% by weight of an unsaturated monomer containing a hydroxyalkyl group
And a monomer comprising 15 to 60% by weight of another monomer copolymerizable therewith is emulsion-polymerized in the presence of a cyclic unsaturated hydrocarbon having one unsaturated bond in the ring to form a copolymer. In producing the combined latex, 45 to 99% by weight of all the monomers among the above-mentioned monomers is charged into a polymerization reaction tank and emulsion-polymerized. A method for producing a copolymer latex, which comprises subjecting 1 to 55% by weight of the remaining monomer to emulsion polymerization. 2. A paper coating composition containing the copolymer latex obtained by the production method according to claim 1.