JP5249396B2 - Copolymer latex for paper coating and composition for paper coating - Google Patents

Description

The present invention relates to a copolymer latex for paper coating and a composition for paper coating. Specifically, it is a copolymer latex that is used as a binder in a paper coating composition, has excellent coating operability in the coated paper manufacturing process, and has excellent strength during printing of coated paper. The present invention relates to a copolymer latex for use and a paper coating composition containing the copolymer latex.

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.
In general, a paper coating composition is a water dispersion 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 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, and the performance of styrene-butadiene copolymer latex. However, it is known that it affects the performance of the composition for paper coating, the operability at the time of preparing the coated paper, the quality of the final coated paper product, such as the surface strength and printing gloss.

  Regarding the improvement of operability when preparing coated paper, for example, in JP-A-11-50390 (Patent Document 1), a paper coating composition containing 30% by weight or more of heavy calcium carbonate in a specific particle size range. When using a paper coating composition that uses a copolymer latex with a specific particle size range, high-quality coated paper with excellent high-speed coating with a blade coater and almost no gloss unevenness can be obtained. Technology is introduced.

In order to improve the quality of the coated paper product such as the surface strength, for example, JP 2006-152484 A (Patent Document 2) uses a core-shell type copolymer latex obtained by multistage polymerization with an average particle size of 150 nm or less. Thus, a technique for providing a matte coated paper with good printing gloss, ink set and ink drying properties has been introduced. JP-A-9-31894 (Patent Document 3) is obtained by polymerizing a monomer mixture containing the total amount of unsaturated dicarboxylic acid and methacrylic acid in the first stage and then polymerizing the second and subsequent stages. Coated paper coated with a composition for paper coating using a copolymer latex is a coated paper for off-wheel printing with excellent surface strength during printing, water resistance, ink inking properties, and blister resistance. There is a technical disclosure that it can be obtained. Furthermore, in JP 2008-248446 A (Patent Document 4), by defining the contact angle of the copolymer latex film with soybean oil, the printability such as surface strength at the time of printing, printing gloss, ink set, etc. It is introduced that it is possible to provide a coated paper that is superior to the above, and multi-stage polymerization is preferred for obtaining the copolymer latex.
However, these various improved technologies have not yet reached a level that sufficiently satisfies the coating operability and physical properties required for a paper coating composition that can be applied to coating machines that are increasing in speed every day. In particular, there is a strong demand for further improvements from latex.

Japanese Patent Laid-Open No. 11-50390

JP 2006-152484 A

JP 9-31894 A

JP 2008-248446 A

  The present invention is excellent in the stickiness of the latex film (that is, it is difficult to stick) and the redispersibility of the paper coating composition is excellent, so that the coating operability is excellent and the printing strength is good. It is an object of the present invention to provide a copolymer latex and a paper coating composition from which coated paper can be obtained.

The copolymer latex of the present invention is a copolymer latex used as a binder in a paper coating composition, and includes an aliphatic conjugated diene monomer 20 to 70% by weight, an ethylenically unsaturated carboxylic acid monomer. In the emulsion polymerization of a monomer composed of 0.1 to 20% by weight of a monomer and 10 to 99.9% by weight of an ethylenically unsaturated monomer copolymerizable therewith, the following alkyl is used as a molecular weight regulator: The present invention provides a copolymer latex for paper coating characterized by using mercaptan with respect to 100 parts by weight of a monomer.
(1) 0.005 to 0.6 parts by weight of undecyl mercaptan,
(2) 0.025 to 1.8 parts by weight of dodecyl mercaptan,
(3) Tridecyl mercaptan 0.0005 to 0.6 parts by weight,
(4) Tetradecyl mercaptan 0-0.2 parts by weight (5) Other mercaptans 0-0.2 parts by weight

  The copolymer latex of the present invention is excellent in the stickiness of the latex film, which is a factor affecting the coating operability during the preparation of the coated paper, and the paper coating composition of the present invention is excellent in redispersibility. . Moreover, the coated paper obtained by applying the paper coating composition of the present invention is excellent in printing strength.

The copolymer latex of the present invention is obtained by emulsion polymerization of an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, and other monomers copolymerizable therewith.
Aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted Examples thereof include linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like, and these can be used alone or in combination. In particular, the use of 1,3-butadiene is preferred.
The aliphatic conjugated diene monomer needs to be used in the range of 20 to 70% by weight in all monomers. When the aliphatic conjugated diene monomer is less than 20% by weight, the printing strength of the resulting coated paper is lowered. On the other hand, if the aliphatic conjugated diene monomer exceeds 70% by weight, the stickiness of the latex film increases and the redispersibility of the paper coating composition decreases. Preferably it is 30 to 60% by weight.

Examples of the ethylenically unsaturated carboxylic acid monomer include monobasic acids or dibasic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Or 2 or more types can be used.
These ethylenically unsaturated carboxylic acid monomers need to be used in the range of 0.1 to 20% by weight. If the ethylenically unsaturated carboxylic acid monomer is less than 0.1% by weight, the chemical stability of the copolymer is poor. On the other hand, when the ethylenically unsaturated carboxylic acid monomer exceeds 20% by weight, the viscosity of the copolymer becomes high and handling becomes difficult. Preferably it is 0.5 to 10 weight%, More preferably, it is 1 to 6 weight%.

  Examples of other monomers copolymerizable with the above aliphatic conjugated diene monomers and ethylenically unsaturated carboxylic acid monomers include alkenyl aromatic monomers, unsaturated carboxylic acid alkyl ester monomers, cyanide. And vinyl chloride monomers, unsaturated monomers containing a hydroxyalkyl group, and unsaturated carboxylic acid amide monomers.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyltoluene, divinylbenzene, and the like, 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 maleate, dimethyl itaconate, Examples thereof include monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like can be used alone or in combination of two or more. In particular, the use of methyl methacrylate 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 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 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.

  Further, in addition to the above monomers, any of the monomers used in ordinary emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride can be used.

These other copolymerizable monomers need to be used in the range of 10 to 79.9% by weight in the total monomers. If these other copolymerizable monomers are less than 10% by weight, the stickiness of the latex film increases and the redispersibility of the paper coating composition decreases. On the other hand, when these other copolymerizable monomers exceed 79.9% by weight, the printing strength of the resulting coated paper decreases. Preferably it is 20 to 70% by weight.

When the copolymer latex of the present invention is emulsion-polymerized, the following alkyl mercaptan is used as a molecular weight modifier with respect to 100 parts by weight of the monomer.
(1) Undecyl mercaptan 0.0005 to 0.6 parts by weight, preferably 0.0005 to 0.5 parts by weight,
(2) Dodecyl mercaptan 0.025 to 1.8 parts by weight, preferably 0.025 to 1.5 parts by weight,
(3) Tridecyl mercaptan 0.0005 to 0.6 parts by weight, preferably 0.0005 to 0.5 parts by weight,
(4) tetradecyl mercaptan 0 to 0.2 parts by weight, preferably 0 to 0.16 parts by weight,
(5) Other mercaptans 0 to 0.2 parts by weight, preferably 0 to 0.16 parts by weight When one kind of alkyl mercaptan according to (1) to (5) is used, or two or more kinds are out of the above range. When the amount is used, the printing strength of the coated paper is lowered or the stickiness of the latex is inferior. Alkyl mercaptan alkyl groups include straight-chain and branched types, but when the amount is within the above range, both the straight-chain and branched types have excellent print strength. can get. However, a branched type having a tertiary butyl group is not preferable because the redispersibility of the paper coating composition is poor.

  In order to obtain the alkyl mercaptan which is the amount specified in (1) to (5) used in the present invention, the mercaptan is adjusted after adjusting the raw materials having different carbon numbers (for example, halogenated hydrocarbons) to the specified amount. Or a method of using a mixture of two or more kinds of alkyl mercaptans having already been obtained so as to be within a specified range.

  For the polymerization of the copolymer latex of the present invention, a molecular weight modifier other than the above-mentioned alkyl mercaptan can be used. For example, xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide and tetramethylthiuram monosulfide, 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-benzyloxyacrylonitrile, α-benzyloxy Vinyl ethers such as acrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl Ogurikoreto, Tapinoren, alpha-methyl styrene dimer and the like, can be used one or more of them.

  A known emulsifier (surfactant) can be used for the polymerization of the copolymer latex of the present invention. For example, sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalene sulfonic acid, nonionic surface activity Nonionic surfactants such as anionic surfactants such as sulfuric acid ester salts, polyethylene glycol alkyl ester type, alkylphenyl ether type, alkyl ether type, etc., and one or more of these should be used Can do.

  For the polymerization of the copolymer latex of the present invention, known polymerization initiators include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, Oil-soluble polymerization initiators such as t-butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, or redox polymerization initiators may be used as appropriate. it can. In particular, it is preferable to use potassium persulfate, sodium persulfate, cumene hydroperoxide, or t-butyl hydroperoxide. The amount of the polymerization initiator is not particularly limited, but is appropriately adjusted in consideration of a combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  For the polymerization of the copolymer latex of the present invention, saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, cycloheptane, pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, 1-methyl Hydrocarbon compounds such as unsaturated hydrocarbons such as cyclohexene and aromatic hydrocarbons such as benzene, toluene and xylene can be used. In particular, cyclohexene and toluene, which have a moderately low boiling point and can be easily recovered and reused by steam distillation after the completion of polymerization, are suitable from the viewpoint of environmental problems, although they are different from the object of the present invention.

  The particle size of the copolymer latex in the present invention is not particularly limited but is preferably 50 to 200 nm. If the average particle diameter by the photon correlation method is less than 50 nm, the glossiness of white paper tends to be inferior, and if it exceeds 200 nm, the strength of the coated paper during printing tends to decrease. The particle size of the copolymer latex can be adjusted by appropriately changing the various emulsifiers used in the polymerization of the copolymer latex, the type and amount of polymerization initiator used, the addition method, the proportion of polymerization water used, etc. is there.

  The gel content of the copolymer latex in the present invention is not particularly limited, but the gel content is preferably 70 to 100% by weight. If the gel content is less than 70% by weight, the strength of the coated paper during printing tends to decrease, such being undesirable. Particularly preferred is 75 to 98% by weight.

  For the polymerization of the copolymer latex of the present invention, known additives such as oxygen scavengers, chelating agents, and dispersing agents may be used as necessary, and these are not particularly limited in both type and amount used. An appropriate amount can be used as appropriate. Furthermore, known additives such as antifoaming agents, anti-aging agents, antiseptics, antibacterial agents, flame retardants, and UV absorbers may be used. I can do it. Further, the copolymer latex of the present invention can be appropriately blended with other latexes depending on the purpose of use.

  In the production of the copolymer latex of the present invention, the addition method of the monomer and other components is not particularly limited, and the addition method of the monomer may be any of the divided addition method and the continuous addition method. Can be adopted.

  The paper coating composition of the present invention contains a pigment and the copolymer latex of the present invention. Examples of the pigment include known pigments such as kaolin clay, calcium carbonate, talc, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, satin white, and other organic pigments such as polystyrene latex, respectively. Can be used as a mixture. The content of the copolymer latex in the paper coating composition is preferably 2 to 20 parts by weight (solid content) with respect to 100 parts by weight (solid content) of the pigment. More preferably, 3 to 15 parts by weight are used. If the content of the copolymer latex is less than 2 parts by weight, it is not preferable because the pigment cannot be sufficiently adhered, and if it exceeds 20 parts by weight, the opacity and white paper gloss are lowered, and the cost of the composition for paper coating increases This is not preferable.

  If necessary, modified starches such as starch, oxidized starch and esterified starch, natural binders such as soybean protein and casein, or water-soluble synthetic binders such as polyvinyl alcohol and carboxymethyl cellulose 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.

  In preparing the paper coating composition of the present invention, further auxiliary agents such as dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.), antifoaming agents (polyglycol, fatty acid esters) , Phosphate esters, silicone oils, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsions, etc.), fluorescent dyes, color water retention agents (carboxymethylcellulose, alginic acid) Sodium or the like) may be added as necessary.

  Further, as a method for applying the paper coating composition to the coated paper, any known technique such as an air knife coater, blade coater, roll coater, bar coater, curtain coater or the like can be used. There is no problem. Also, after coating, the surface is dried and finished by calendaring or the like.

  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.

Measurement of average particle size of copolymer latex by photon correlation method The average particle size of each copolymer latex was measured by the photon correlation method. In the measurement, FPAR-1000 (manufactured by Otsuka Electronics) was used.

Measurement of gel content of copolymer latex A latex film of each copolymer latex is prepared at 80 ° C. Thereafter, about 1 g of the latex film is weighed to obtain Xg. This is put into 400 ml of toluene and swelled and dissolved for 48 hours. Thereafter, this is filtered through a weighed 300-mesh wire mesh, and then toluene is evaporated and dried. The weight of the wire mesh is subtracted from the weight after drying, and the weight after drying of the sample is weighed to obtain Yg. The gel content was calculated from the following formula.
Gel content (%) = (Y / X) * 100

Copolymer Latex Film Stickiness Test The stickiness (adhesiveness) of the copolymer latex film was tested as a measure of the ease with which the latex adheres to a backing roll or the like. Each copolymer latex is applied to a polyester film so as to have a coating amount of 12 g / m 2 as a solid content, dried in an oven at 120 ° C. for 1 minute, and cut into a 1 cm wide strip. Adhere the strips of all copolymer latex films synthesized on the black mount.
On top of that, filter paper is overlaid and crimped using an RI printer. Thereafter, the adhesion state of the fibers of the filter paper on the surface of each latex film after the filter paper was peeled off was visually determined, and the stickiness of each latex film was compared. Evaluation was made relatively as follows, where も の indicates that the fibers with less adhesion are excellent in stickiness, and × indicates that the fibers have much adhesion as inferior in stickiness.
(Excellent) ◎>○>△> × (poor)

Evaluation of Redispersibility of Composition for Paper Coating Each composition sample was placed on an NBR black rubber plate, applied with a # 6 wire bar, dried in a 60 ° C. hot air circulating oven for 3 minutes, and then heated at 30 ° C. The film of the composition which was washed with running water for 1 minute and remained on the NBR black rubber plate was visually observed. A film having a small amount of remaining film was evaluated as “Excellent” for redispersibility, and a film having a large amount of remaining film was evaluated as “poor” for poor redispersibility.
(Excellent) ◎>○>△>×> ×× (poor)

Evaluation of dry pick strength of coated paper The degree of picking when each coated paper sample is printed at the same time with an RI printing machine is judged with the naked eye, and relatively visually evaluated from grade 5 (excellent) to grade 1 (inferior). did.

Evaluation of wet pick strength of coated paper Picking when each coated paper sample is simultaneously printed with an ink roll immediately after applying dampening water to each coated paper sample with a molton roll using an RI printer. The degree of the above was determined with the naked eye, and was relatively visually evaluated from grade 5 (excellent) to grade 1 (poor).

Synthesis of copolymer latex Into a polymerization reactor made of pressure-resistant polymer, 150 parts of polymerization water and 1 part of potassium persulfate were charged and sufficiently stirred, and then each monomer shown in Addition 1 of Tables 1 and 2 as the first stage. And other compounds were added and the temperature was raised to 70 ° C. to initiate polymerization. When the polymerization conversion rate of the first-stage monomer exceeded 50%, each monomer and other compounds shown in Addition 2 in Tables 1 and 2 were continuously added over 7 hours. Further polymerization was carried out, and the polymerization was terminated when the polymerization conversion rate exceeded 98%.
Next, the obtained copolymer latex was adjusted to pH 7 using an aqueous potassium hydroxide solution, and unreacted monomers and other low-boiling compounds were removed by steam distillation. 10 was obtained.

Preparation and Evaluation of Composition for Paper Coating According to the formulation shown below, the copolymer latex 1 to 10 obtained by the above synthesis was used, adjusted to pH 9.5 with an aqueous sodium hydroxide solution, and coated with paper. A composition for use was prepared.
(Formulation formulation of paper coating composition)
Formulated kaolin 40 parts Heavy calcium carbonate 60 parts Modified starch 2 parts Copolymer latex 7 parts ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・
Solid content 67%

Preparation and Evaluation of Coated Paper Apply the above paper coating composition to a base paper (basis weight 55g / m2) using a wire bar so that the coating amount per side is 10g / m2. After drying, calendering was performed under 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. The results are shown in Tables 3 and 4.

  As shown in Tables 3 and 4, all of the copolymer latexes 1 to 4 according to the present invention have good latex film stickiness, and the paper coating compositions using these copolymer latexes are all re-used. The dispersibility is excellent, and the resulting coated paper has good dry pick strength and wet pick strength.

  As described above, the copolymer latex of the present invention is excellent in the stickiness of the latex film, and the paper coating composition of the present invention using the copolymer latex has good redispersibility. It is excellent in coating operability at the time of making paper and can respond to high-speed coating machines. Moreover, since the coated paper obtained by applying the paper coating composition of the present invention is excellent in printing strength, it is useful as a paper coating binder and composition.

Claims (2)

Aliphatic conjugated diene monomer 20 to 70% by weight, ethylenically unsaturated carboxylic acid monomer 0.1 to 20% by weight, and ethylenically unsaturated monomer 10 to 79.9 copolymerizable therewith A copolymer latex for paper coating, wherein the following alkyl mercaptan is used as a molecular weight modifier for 100 parts by weight of a monomer when emulsion polymerization of a monomer composed of% by weight is carried out.
(1) 0.005 to 0.6 parts by weight of undecyl mercaptan,
(2) 0.025 to 1.8 parts by weight of dodecyl mercaptan,
(3) Tridecyl mercaptan 0.0005 to 0.6 parts by weight,
(4) Tetradecyl mercaptan 0-0.2 parts by weight (5) Other mercaptans 0-0.2 parts by weight A composition for paper coating containing the copolymer latex according to claim 1.