JP3046039B2 - Method for producing diene copolymer latex - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a copolymer latex.
More specifically, the present invention relates to a high-performance copolymer latex suitable for paper coating.

[Conventional technology]

Conventionally, synthetic copolymer latex is, for example, a binder for paper coating, a binder for carpet backsizing,
It is widely used as a binder for bonding fibers such as nonwoven fabric and artificial leather, or as an adhesive for various materials.
And when the copolymer latex is used for such an application, the copolymer latex has a high adhesive strength,
It is also required to be excellent in water resistance, blister resistance by drying and heating, and the like.

For example, coated paper, for the purpose of improving the printability of paper and the improvement of optical properties such as gloss, on the surface of the base paper made, kaolin clay, calcium carbonate, satin white, talc, pigments such as titanium oxide, Coated with a latex copolymer as their binder and starch as a water retention agent or auxiliary binder, casein, polyvinyl alcohol, a water-soluble polymer such as carboxymethyl cellulose as a main component, Conventionally, styrene and butadiene are used as main monomer components as a copolymer latex, and a styrene-butadiene copolymer latex obtained by emulsion polymerization of these is used.
So-called SB latex is widely used.

By the way, in recent years, the production of coated paper has increased remarkably with the increase in demand for magazines, pamphlets and advertisements printed in color. In particular, with the trend toward high-speed printing in offset printing, the required level for the quality of coated paper and pigment binders is becoming increasingly sophisticated, and therefore, among the quality of coated paper, especially ink pick resistance, so-called pick strength There is a strong demand for improvement. Moreover, this pick strength performance is different from other print properties, such as wet pick strength,
Blister resistance, halftone dot reproducibility, and the like are in a negative correlation, and therefore, further improvement is required to balance these various properties to a high level.

Since these properties of the coated paper greatly depend on the performance of the SB latex used as a pigment binder, various studies have been made on the performance of the SB latex.

For example, it has been confirmed that the proportion of the insoluble portion of a copolymer latex film in a solvent such as benzene, toluene, and tetrahydrofuran is a controlling factor for pick strength and blister resistance. Specifically, it has been proposed to exhibit excellent performance by adjusting the composition of the copolymer and the gel fraction in the latex to specific ranges (Japanese Patent Publication No. 59-3598). Gazette, Japanese Patent Publication No. Sho 60-17879,
No. 8-4894). This gel fraction is generally adjusted by the polymerization temperature and the amount of the chain transfer agent.

However, when the gel fraction is adjusted by the amount of the chain transfer agent, the pick strength of the coated paper generally becomes the highest in the SB latex when the gel fraction is in the range of 75 to 95% by weight. It has been recognized that the lower the gel fraction, the better the blister resistance is, and in order to simultaneously improve both the pick strength and the blister resistance to a high level, both of the above techniques are sufficiently satisfactory. It is not possible.

Further, when the gel fraction is adjusted by lowering the polymerization temperature, there is a disadvantage that the time required for the polymerization becomes extremely long.

[Problems to be solved by the invention]

As described above, the conventional technology cannot cope with a further increase in the speed of printing of coated paper, and the emergence of a copolymer latex as a binder capable of producing high quality coated paper is strongly demanded. It is the present situation.

[Means for solving the problem]

Under such circumstances, the present inventors have aimed to provide a high-performance copolymer latex for further improving the balance between pick strength and other properties in coated printing paper. As a result of intensive studies to develop the above-mentioned high-performance copolymer latex, as a monomer, at least three kinds of other monomers copolymerizable with a conjugated diene compound and an ethylenically unsaturated carboxylic acid were used. Using, in the aqueous medium, these monomers are emulsion-polymerized at a temperature of 70 ° C to 100 ° C to produce a copolymer latex, using a seed latex, and maintaining a constant polymerization conversion rate of the monomers. It has been found that the object can be achieved by adjusting the range, and the present invention has been completed.

That is, the present invention provides a paper coating copolymer by emulsion-polymerizing at least three kinds of other monomers copolymerizable with a conjugated diene compound and an ethylenically unsaturated carboxylic acid in an aqueous medium at 70 ° C to 100 ° C. In producing polymer latex,
Uses seed latex and has a monomer polymerization conversion of 85.
% Is a method for producing a copolymer latex for paper coating in which the polymerization is stopped at the time of from 95% to 95%.

 Hereinafter, the present invention will be described in detail.

A feature of the present invention is that the polymerization conversion of the monomer is stopped at 85% to 95% in the emulsion polymerization.
If the polymerization conversion is set outside the above range, it is not possible to obtain a good balance between pick strength and other performances, which is an effect of the present invention. As a method of stopping the polymerization when the desired polymerization conversion rate is reached, there are a method of adding a polymerization inhibitor at that time and a method of lowering the polymerization temperature at that time.

Examples of the conjugated diene compound used in the present invention include butadiene, isoprene, 2-chloro-1,3-butadiene and the like. These conjugated diene compounds are
One type may be used, or two or more types may be combined.
The amount used is selected from 5% by weight or more based on the weight of all monomers, preferably from 20 to 70% by weight in terms of cohesion.

As the ethylenically unsaturated carboxylic acid used in the present invention, for example, acrylic acid, methacrylic acid, itaconic acid,
Maleic acid, fumaric acid, crotonic acid and the like can be mentioned. One of these ethylenically unsaturated carboxylic acids may be used alone, or two or more thereof may be used in combination. The amount of the ethylenically unsaturated carboxylic acid to be used is 0.2% by weight or more, preferably 0.2 to 15% by weight based on the weight of all monomers. %.

Other copolymerizable monomers used in the present invention include aromatic monovinyl compounds and divinyl compounds, acrylates and methacrylates, vinyl cyanide compounds, ethylenic amides, and the like. Among them, aromatic monovinyl compounds and divinyl compounds are particularly preferable.

Examples of the aromatic monovinyl compound and divinyl compound include styrene, α-methylstyrene, chlorostyrene, alkylstyrene, and divinylbenzene. As the acrylate or methacrylate, for example, methyl of acrylic acid or methacrylic acid,
Examples include ethyl, propyl, butyl, 2-ethylhexyl, hydroxyethyl glycidyl ester, and ethylene glycol diacrylate or dimethacrylate. Examples of the vinyl cyanide compound include acrylonitrile and methacrylonitrile, and examples of the ethylenic amide include acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide.

Further, in addition to these monomers, vinyl esters such as vinyl acetate, vinyl chloride, vinyl halides such as vinylidene chloride, aminoethyl acrylate or methacrylate, dimethylaminoethyl acrylate or methacrylate, diethylaminoethyl acrylate or methacrylate and the like Ethylenic amines, sodium styrenesulfonate and the like can also be used.

One of these copolymerizable monomers may be used,
Two or more kinds may be used in combination.

Examples of the chain transfer agent used in the present invention include t-dodecyl mercaptan, n-dodecyl mercaptan, alkyl mercaptans such as mercaptoethanol, thioglycolic acid esters such as pentaeristol tetrathioglycolate, terpinolene, dipentene, t- Examples thereof include halogenated hydrocarbons such as terpinene and carbon tetrachloride, and sulfides.

The method of using these chain transfer agents is not particularly limited, and known methods, such as a batch addition method, a continuous addition method, an intermittent addition method, a concentration gradient addition method in which the addition rate is sequentially changed, and the like are used. be able to.

The method for producing a copolymer latex of the present invention is to emulsion-polymerize the conjugated diene compound and another monomer copolymerizable with the ethylenically unsaturated carboxylic acid in an aqueous medium. This emulsion polymerization method is not particularly limited except for terminating the polymerization described above, and conventionally known methods, for example, water and the monomers, a chain transfer agent, a surfactant, a radical polymerization initiator, and In a dispersion containing the other additive component used as a basic component, a method of producing an aqueous dispersion of copolymer particles, that is, a copolymer latex, by polymerizing the monomer is used. The concentration of the copolymer in the copolymer latex is
Usually, it is selected in the range of 40 to 60% by weight, and its average particle size is advantageously in the range of 0.05 to 1 μm, preferably 0.07 to 0.3 μm. The average particle size can be adjusted by the use ratio of a surfactant or seed latex, and generally, the higher the use ratio, the smaller the average particle size of the produced copolymer latex tends to be.

Examples of the surfactant include anionic surfactants such as fatty acid soap, rosin acid soap, alkyl sulfonate, dialkylaryl sulfonate, alkyl sulfosuccinate, polyoxyethylene alkyl sulfate, and polyoxyethylene alkylaryl sulfate. Examples of the surfactant include nonionic surfactants such as an activator, polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene sorbitan fatty acid ester, and oxyethylene oxypropylene block copolymer. This surfactant is usually used in an anionic surfactant alone or in an anionic / nonionic mixed system, and the amount of the surfactant is usually 0.05 to 0.05% based on the weight of all monomers.
It is selected in the range of 2% by weight.

The radical polymerization initiator has a function of radically decomposing by heat or a reducing substance to cause addition polymerization of a monomer. Examples of such a radical polymerization initiator include water-soluble or oil-soluble peroxodiacids. Sulfates, peroxides, azobis compounds and the like, specifically, potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate, hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2-azobisiso Examples thereof include butyronitrile and cumene hydroperoxide. Among them, peroxodisulfate is particularly preferable. The amount of the polymerization initiator used is usually selected in the range of 0.2 to 1.5% by weight based on the weight of all monomers.

The polymerization temperature in this emulsion polymerization is usually selected in the range of 70 to 100 ° C.

In the present invention, if desired, various polymerization regulators such as sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate, sodium carbonate, disodium hydrogen phosphate, etc.
Various chelating agents such as pH adjusters and sodium ethylenediaminetetraacetate can be added.

When the copolymer latex produced according to the present invention is used as a binder for a paper coating paint, a commonly used method, for example, in water in which a dispersant is dissolved, an inorganic pigment or an inorganic / organic pigment, A method in which the copolymer latex is added and mixed with a water-soluble polymer and various additives and used as a homogeneous dispersion can be adopted.
And this paper coating paint, various blade coater,
The base paper can be coated by a usual method using a roll coater or the like.

〔Example〕

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

 In addition, each characteristic was calculated | required as follows.

(1) Properties of copolymer latex (A) Average particle size Light scattering particle size analyzer (Model 600 manufactured by CN Wood Co., Ltd.)
The average particle diameter of the polymer latex was measured according to 0).

(B) Polymerization conversion rate About 1 gram of the extracted reaction solution is precisely weighed, dried at 130 ° C. for 1 hour, and the residue is weighed. The solid content is calculated by the following method.

The charged solid content is calculated by the following method.

From these, the polymerization conversion is calculated by the following equation.

(2) Evaluation of paper coating performance (a) Blister resistance Solid printing 0.3 cc of printing ink (Dainippon Ink Co., Ltd. Webb Zett Yellow) on both sides of coated paper using RI printing tester (manufactured by Meiji Seisakusho). . The printed coated paper is cut into an appropriate size, and the test piece is immersed in a silicone oil thermostat adjusted to a predetermined temperature to observe whether blisters are generated. This test is performed by changing the temperature of the thermostatic bath, and the lowest temperature at which blistering is observed is determined. The higher the temperature, the better the blister resistance.

(B) Dry pick strength Using a RI printing tester, the printing ink (SD super deluxe 50 red B; Tack value: 18) manufactured by Toka Dye Co., Ltd. was overprinted 0.4 cc five times, and the picking condition that appeared on the rubber roll was changed. Back up on mount and observe the situation. The evaluation was performed by a 10-point evaluation method, and the smaller the picking phenomenon, the higher the score.

Examples 1-2 and Comparative Examples 1-2 Four parts by weight of an aqueous dispersion of seed particles having a diameter of 0.04 μm (seed solid concentration 25% by weight) were placed in a pressure-resistant reaction vessel equipped with a stirrer and a temperature control jacket. And 70 more water
Parts by weight, 0.2 parts by weight of sodium laurate sulfate and 2.5 parts by weight of fumaric acid, the internal temperature was raised to 80 ° C., and then an oily mixture comprising the monomers and chain transfer agent shown in Table 1 and 15 parts by weight of water And an aqueous solution consisting of 1 part by weight of sodium peroxodisulfate, 0.2 part by weight of sodium hydroxide, and 0.1 part by weight of sodium laurin sulfate were added at a constant flow rate over 4 hours and 5 hours, respectively. Then, after maintaining the temperature of 80 ° C. as it is for the time shown in Table 1, it was cooled, and the resulting copolymer latex was then sodium hydroxide.
After adjusting the pH to 7, unreacted monomers were removed by a steam stripping method, and the mixture was filtered through a 200-mesh filter cloth. In addition, all the copolymer latexes were adjusted so that the solid content concentration was finally 50% by weight.

Table 1 shows the average particle size and polymerization conversion of these copolymer latexes.

Application Examples The performance of the copolymer latexes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 as a binder for paper coating was evaluated. Table 4 shows the results.

The coating composition was prepared by a high-speed stirrer with the composition shown in Table 2 and the amount of water at which the nonvolatile content was 63% by weight. Paint
The pH was adjusted to 9.0 with aqueous ammonia. Table 3 shows the preparation conditions of the coated paper using this paint.

From Table 4, it is understood that the coated paper using the copolymer latex of the present invention as a binder has a highly balanced pick strength and other physical properties.

[Effects of the Invention] According to the present invention, a high-performance copolymer latex capable of further improving the balance between pick strength and other properties in coated paper for printing, and improving the adhesive strength in carpet backsizing and adhesives Can be easily obtained.

────────────────────────────────────────────────── (5) References JP-A-52-121511 (JP, A) JP-A-63-243115 (JP, A) US Patent 3,332,455 (US, A) (58) Fields studied (Int .Cl. ⁷ , DB name) C08F 2/22 D21H 19/58

Claims (1)

(57) [Claims] 1. Copolymer for paper coating by subjecting at least three kinds of other monomers copolymerizable with a conjugated diene compound and an ethylenically unsaturated carboxylic acid to emulsion polymerization at 70 to 100 ° C. in an aqueous medium. A method for producing a copolymer latex for paper coating, comprising using a seed latex in producing a latex, and terminating the polymerization at a time when a polymerization conversion of a monomer is 85% to 95%.