JP5242116B2 - Copolymer latex for paper coating - Google Patents

Description

  The present invention relates to a copolymer latex for paper coating. Specifically, by using the obtained copolymer latex, the paint has excellent storage stability, the viscosity of the paint at high shear (denoted as high shear viscosity) is low, and the viscosity at medium shear (denoted as medium shear viscosity) The present invention relates to a copolymer latex for paper coating that has a coating viscosity suitable for blade coating and is excellent in water-absorbing property and white paper gloss.

In recent years, coated paper has been used in a large number of printed materials because of its high printing effect. Even in periodicals such as quarterly and monthly papers, the use of coated paper on all pages has increased considerably. In particular, most direct mails and product catalogs in the mail order business use coated paper for all pages.
Coated paper has many advantages such as whiteness, glossiness, smoothness, and printability compared to non-coated paper, but the paper coating composition is applied to the blade coater after the base paper is made. However, recently, coating with a blade coater has become the mainstream, and the suitability of blade coating for paper coating compositions has increased productivity and finality. Therefore, the viscosity control of the paper coating composition, which greatly affects the blade coating suitability, is an important factor.

  In general, a composition for paper coating is composed of a pigment dispersion in which a white pigment such as clay or calcium carbonate is dispersed in water, a binder for adhering and fixing the pigments to each other and a base paper, and other additives. It is a water-based paint. As the binder, a synthetic emulsion binder represented by styrene-butadiene copolymer latex and a natural binder represented 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 as the most suitable binder for paper coating compositions today. Greatly affects the performance of the paper coating composition or the final coated paper product.

  Therefore, with regard to the quality design and manufacturing method of styrene-butadiene copolymer latex for paper coating, it has excellent paint viscosity and coating properties, and in order to obtain further excellent coated paper quality, Technical improvements have been proposed. For example, Japanese Patent Application Laid-Open No. 2003-192726 (Patent Document 1) describes a method for improving polymerization stability by seed polymerization, reducing the particle size even when the amount of the emulsifier is small, and having good fluidity under high shear. There is an introduction of polymer latex. JP-A-7-70990 (Patent Document 2) discloses a paper coating composition having excellent paint viscosity and coating workability by using a latex obtained by emulsion polymerization using a polyphosphate in the latex composition. There is an introduction that things can be obtained. Furthermore, JP-A-2005-139777 (Patent Document 3) reduces the finished latex pH to reduce the alkali metal content, and is excellent in operability and wet strength. There is a description that a composition for use is obtained.

However, these various improved technologies have not yet reached a level that sufficiently satisfies the work operability required for making coated paper and the performance required for coated paper, and further improvements are strongly required. It was.
JP 2003-192726 A JP 7-70990 A JP 2005-139777 A

  The present invention provides a paint latex suitable for blade coating having a low high shear viscosity and a high medium shear viscosity, and having excellent water absorption property and white paper gloss. It is intended to provide.

That is, the present invention relates to an aliphatic conjugated diene monomer 30 to 70% by weight, an ethylenically unsaturated carboxylic acid monomer 0.5 to 10% by weight, and other copolymerizable monomers 20 to 69.%. A copolymer latex formed by emulsion polymerization of 5% by weight monomers (total 100 parts by weight), the content of alkali metal contained in the copolymer latex film is in the range of 17000-25000 ppm, And the amount of sodium which occupies in an alkali metal provides the copolymer latex for paper coating which exists in the range of following formula (1).
Sodium / (total of alkali metals) = 0.61 to 0.85 (1)

  By using the copolymer latex of the present invention, the coating stability is excellent, the high shear viscosity of the coating is low, and the coating viscosity of the medium shear viscosity is high, so the coating workability in blade coating is excellent, In addition, there is an effect that a coated paper excellent in water absorbability and white paper gloss can be obtained.

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

  Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. It can be used above.

  Other monomers copolymerizable with the above aliphatic conjugated diene monomer and ethylenically unsaturated carboxylic acid monomer include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers, hydroxy Examples thereof include unsaturated monomers containing an alkyl group, vinyl cyanide monomers, and unsaturated carboxylic acid amide monomers.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene and divinylbenzene, and these can be used alone or in combination. In particular, use of styrene is preferable.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl malate, dimethyl itaconate, Examples thereof include monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like can be used alone or in combination. In particular, the use of methyl methacrylate is preferred.

  Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 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. Or 2 or more types can be used. In particular, the use of β-hydroxyethyl acrylate is preferred.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, and the like, and one or more of these can be used. In particular, the use of acrylonitrile or methacrylonitrile is preferred.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide, and the like, and one or more of these may be used. it can. Particularly preferred is the use of acrylamide or methacrylamide.

  The monomer composition is 30 to 70% by weight of aliphatic conjugated diene monomer, 0.5 to 10% by weight of ethylenically unsaturated carboxylic acid monomer, and 20 to 20% of other copolymerizable monomer. It is a monomer consisting of 69.5% by weight (total 100 parts by weight).

  If the aliphatic conjugated diene monomer is less than 30% by weight, the glossiness of white paper gloss is undesirably, and if it exceeds 70% by weight, the stickiness of the latex film is inferior. More preferably, it is 35 to 65% by weight.

  If the amount of the ethylenically unsaturated carboxylic acid monomer is less than 0.5% by weight, the mechanical stability of the copolymer latex is inferior. If it exceeds 10% by weight, the viscosity of the latex increases, and the copolymer latex itself is handled. Since the above problem may occur, it is not preferable. More preferably, it is 2 to 8% by weight.

  If the amount of other copolymerizable monomer is less than 20% by weight, the water absorption property of the ink is unfavorable, and if it exceeds 69.5% by weight, the glossiness of the white paper is inferior.

  In the present invention, any one of single-stage polymerization, two-stage polymerization, multi-stage polymerization, seed polymerization, power feed polymerization and the like may be employed.

  In the emulsion polymerization, conventional emulsifiers, chain transfer agents, polymerization initiators, hydrocarbon solvents, electrolytes, polymerization accelerators, chelating agents and the like can be used.

  As an emulsifier, anionic surfactants such as sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether sulfonates, aliphatic sulfonates, aliphatic carboxylates, sulfate salts of nonionic surfactants, etc. One or two or more nonionic surfactants such as an alkyl ester type, an alkyl phenyl ether type, and an alkyl ether type of polyethylene glycol can be used in combination.

  Examples of chain transfer agents include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, dimethylxanthogen disulfide, diisopropylxanthogen disulfide, etc. Xanthogen compounds, terpinolene, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, α-methylstyrene dimer, 2,6-di-t-butyl-4-methylphenol, styrenation Phenolic compounds such as phenol, allyl compounds such as allyl alcohol, halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide, α -Vinyl ethers such as benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate, etc. These can be used alone or in combination of two or more.

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

  In the polymerization, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane and cycloheptane, and unsaturated hydrocarbons such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene and 1-methylcyclohexene. Hydrocarbon compounds such as aromatic hydrocarbons such as benzene, toluene and xylene may be used.

  The particle diameter of the paper coating copolymer latex used in the present invention is not particularly limited, but the number average particle diameter is preferably 50 to 150 nm. If the number average particle size is less than 50 nm, the latex viscosity is high, and if it exceeds 150 nm, the high shear viscosity of the paint is inferior.

  The gel content of the paper coating copolymer latex used in the present invention is not particularly limited, but is 50 to 100% by weight. If it is less than 50%, the adhesiveness of the latex film is inferior.

  Although there is no restriction | limiting in particular about the pH adjuster of the copolymer latex for paper coatings used by this invention, Commonly used caustic soda, caustic potash, ammonia, etc. can use together 1 type, or 2 or more types. The finished latex preferably has a pH of 6 to 9. If the pH is less than 6, the stability of the latex is inferior. If the pH exceeds 9, the latex viscosity increases and handling becomes difficult.

Furthermore, in the present invention, one or more common dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.) are used in combination as a viscosity modifier for the copolymer latex for paper coating. Can do.

  In the present invention, it is important that the content of the alkali metal contained in the copolymer latex film is in the range of 17000 to 25000 ppm. If the alkali metal content is less than 17000 ppm, the medium shear viscosity of the paint is low, which is not preferable, and if it exceeds 25000 ppm, the high shear viscosity of the paint is high, which is not preferable.

In the present invention, it is important that the proportion of sodium in the total alkali metal contained in the copolymer latex film is in the range of 0.61 to 0.85, and the proportion of sodium is 0.61. If it is less than 1, the storage stability is inferior. On the other hand, if it exceeds 0.85, the shear viscosity in the paint is lowered, and the water absorption property is inferior.
As for the content of alkali metal and the proportion of sodium contained in the copolymer latex film, the types and amounts of polymerization initiators, emulsifiers, electrolytes, etc. used during polymerization and the above pH adjusters and dispersants are used. It can be prepared depending on the type and amount used.

  Examples of the pigment constituting the paper coating composition together with the paper coating copolymer latex of the present invention include kaolin clay, talc, barium sulfate, titanium oxide, calcium carbonate, aluminum hydroxide, zinc oxide, and satin white. An inorganic pigment such as polystyrene latex or an organic pigment such as polystyrene latex is used, and these are used alone or in combination.

  If necessary, modified starch such as starch, oxidized starch and esterified starch, natural binder such as soybean protein and casein, or water-soluble synthetic binder such as polyvinyl alcohol may be used. In addition, synthetic latex such as polyvinyl acetate latex and acrylic latex may be used in combination with the copolymer latex of the present invention. It is desirable to keep it below 50% by weight (solid content) of the polymer latex

  When preparing a paper coating composition using the copolymer latex for paper coating of the present invention, further auxiliary agents such as a dispersant (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc. ), Antifoaming agents (polyglycol, fatty acid ester, phosphate ester, silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes A color water retention improver (carboxymethylcellulose, sodium alginate, etc.) may be added as necessary.

  Furthermore, as a method for applying the paper coating composition to the coated paper, there are known techniques, for example, various coating machines such as an air knife coater, a blade coater, a roll coater, a bar coater, and the use of a blade coater in particular. However, the effect of the present invention is remarkably obtained. Also, after coating, the surface is dried and finished by calendaring or the like.

[Example]
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, this invention is not limited to these Examples, unless the summary is exceeded. In the examples, parts and percentages indicating percentages are based on weight unless otherwise specified. In addition, various physical properties in the examples were evaluated by the following methods.

Evaluation of B-type viscosity of paint The paint viscosity at 60 rpm was measured using a B-type viscometer immediately after preparation of the paint.

Standing stability of paint The prepared paint was allowed to stand for 24 hours under the conditions of 20 ° C. and 60%, and the static viscosity of the paint was measured with the B-type viscometer described above. The ratio with the B-type viscosity immediately after preparation of the paint is calculated by the following formula. Inferior).
Standing stability = B-type viscosity at 24 hours after standing / B-type viscosity immediately after coating

Evaluation of high shear viscosity of paint (high shear viscosity) Apparent at 8000 rpm when measured under conditions of Bob F, 8800 rpm and sweep time 10 sec using Hercules high shear viscometer manufactured by Kumagai Riki Kogyo Co., Ltd. The viscosity was taken as the viscosity at high shear. (The shear rate under this condition corresponds to 1.7 × 10 ⁵ sec ⁻¹ )

Evaluation of the medium shear viscosity (medium shear viscosity) of paint The appearance at 500 rpm when measured under conditions of Bob E, 2200 rpm, and sweep time 10 sec using a Hercules high shear viscometer manufactured by Kumagai Riki Kogyo Co., Ltd. The viscosity was defined as a medium shear viscosity. (The shear rate under this condition corresponds to 5.2 × 10 ³ sec ⁻¹ )

Evaluation of water-absorbing property of coated paper Using an RI printer, the ink was evenly spread on the ink roll, then water was dripped into the ink and sufficiently emulsified, and each coated paper sample was printed simultaneously. The degree of ink deposition on the occasion was judged with the naked eye, and was relatively evaluated up to (excellent) ◎>○>Δ> × (poor).

Evaluation of coated paper blank gloss The gloss of each coated paper sample was measured according to JIS P-8142. The larger the value, the better the glossiness of the white paper.

Measurement of number average particle diameter of copolymer latex The number average particle diameter of the copolymer latex was measured by a dynamic light scattering method. In the measurement, LPA-3000 / 3100 (manufactured by Otsuka Electronics) was used.

Measurement of gel content of copolymer latex A latex film is prepared at room temperature. Thereafter, about 1 g of the latex film is weighed and placed in 400 cc of toluene to be dissolved for 48 hours. Thereafter, this was filtered through a 300-mesh wire mesh, and the toluene-insoluble portion captured by the wire mesh was dried and weighed.

Measurement of Alkali Metal Content in Copolymer Latex Film A copolymer latex is dried in a room temperature atmosphere to prepare a film. After thermal decomposition with sulfuric acid and nitric acid, inductively coupled plasma emission spectroscopy (ICP-AES: The alkali metal element was quantified by SPS4000 type manufactured by Seiko Denshi Kogyo.

Preparation of copolymer latex In a pressure-resistant polymerization reactor, 150 parts of polymerization water was charged, with sufficient stirring, each monomer and other compounds shown in Table 1 were added and polymerization was started at 70 ° C. For the two-stage polymerization, when the polymerization conversion rate of the first-stage monomer reaches 90% or more, each second-stage monomer is added and polymerized. When the polymerization conversion rate of the first monomer reached 90% or more, each third stage monomer was added and polymerized.) The polymerization was terminated when the final polymerization conversion rate exceeded 95%. (For the first stage polymerization, the polymerization was terminated when the final polymerization addition rate exceeded 95%).
Subsequently, these copolymer latexes are adjusted to a pH of 7.5 using a pH adjuster, unreacted monomers and other low-boiling compounds are removed by steam distillation, and copolymer latexes A to C are obtained. , And DG were obtained.

Preparation and Evaluation of Paper Coating Composition (Paint) Using the copolymer latexes A to C and D to G according to the formulation shown below, the paper coating composition (paint) shown in Table 1 is prepared. did. The B-type viscosity, standing stability, high shear viscosity, and medium shear viscosity of the obtained paint were measured, and the results are shown in Table 1.
(Formulation formulation of paper coating composition)
Formulation Kaolin clay 60 parts Heavy calcium carbonate 40 parts Modified starch 3 parts Copolymer latex 9 parts ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・
Solid content concentration 66%

Preparation and Evaluation of Coated Paper Coated paper (basis weight 55 g / m ² ) is coated with the above-mentioned composition for paper coating using a wire bar so that the coating amount per side is 10 g / m ^2. After being worked and dried, a super calender treatment was performed under the conditions of a linear pressure of 60 kg / cm and a temperature of 50 ° C. to obtain a coated paper. The obtained coated paper was subjected to each test and evaluated, and the results are shown in Table 1.

  As described above, the use of the copolymer latex of the present invention provides excellent coating stability, low paint shear viscosity, low paint shear viscosity, and high paint viscosity. Coated paper excellent in water absorbency, water absorbability and white paper gloss can be obtained.

Claims (2)

A monomer comprising 30 to 70% by weight of an aliphatic conjugated diene monomer, 0.5 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer and 20 to 69.5% by weight of another copolymerizable monomer. A copolymer latex obtained by emulsion polymerization of a polymer (100 parts by weight in total), wherein the content of alkali metal contained in the copolymer latex film is in the range of 17000 to 25000 ppm, and in the alkali metal Copolymer latex for paper coating in which the amount of sodium is within the range of the following formula (1).
Sodium / (total of alkali metals) = 0.61 to 0.85 (1)   A copolymer latex for blade coater paper coating comprising the copolymer latex according to claim 1.