JP5993366B2 - Method for producing copolymer latex - Google Patents

Description

  The present invention relates to a copolymer latex.

  Diene copolymer latex is known as a binder widely used in the field of paper processing and carpet backsizing. The diene copolymer latex can relatively easily control the change of the monomer composition, the molecular weight of the copolymer, and the like, and can satisfy the required performance of the binder depending on the application.

  For example, in the paper processing field, it is known to use, as a diene copolymer latex, a styrene-butadiene copolymer latex containing an ethylenically unsaturated carboxylic acid as a polymerization unit for coated paper. .

  Coated paper is used for a large number of printed materials because of its high printing effect. The coated paper is produced by applying a paper coating composition to the surface of a coated base paper and drying it. The composition for paper coating is composed of a pigment dispersion in which white pigments such as clay and calcium carbonate are dispersed in water, a binder for adhering and fixing the pigments to each other and the base paper for coating, and other additives. It is a water-based paint. In addition to the styrene-butadiene copolymer latex described above, natural binders such as starch and casein are used as the binder.

  In the paper processing field, high-speed coating and high-speed printing have been promoted in recent years. Therefore, in order to cope with high-speed coating, the paper coating composition has high fluidity and mechanical stability under high shear, as well as high reusability that can be removed immediately even if it adheres to the backing roll. Dispersibility (roll cleanability) is required. Further, the coated paper is required to have surface strength and the like in order to cope with high-speed printing.

  For example, increasing the proportion of ethylenically unsaturated carboxylic acid in the styrene-butadiene copolymer latex is known to improve the mechanical stability of the paper coating composition and the strength of the coated paper. ing.

  However, there is a problem that the viscosity of the styrene-butadiene copolymer latex and the viscosity of the paper coating composition are remarkably increased, and it is a problem to achieve both low viscosity and quality of the styrene-butadiene copolymer latex. It has become.

  For example, in Patent Document 1 below, as a method for lowering the latex viscosity, a part of the latex is extracted from the polymerization tank in the middle of the polymerization, and continuously introduced into the polymerization tank again in the final stage of the polymerization. A method has been proposed in which the reaction is completed, the particle size distribution of the polymer is widened, and the latex viscosity is lowered.

  Patent Document 2 below proposes a method in which a seed latex using a surfactant or the like is obtained, a basic compound is added, and then a specific monomer mixture containing no surfactant is added to perform polymerization. ing.

  Patent Document 3 below discloses a method of polymerizing a monomer in the presence of a seed latex having a specific composition and a specific surface carboxylic acid amount.

U.S. Pat. No. 4,130,523 JP-A 61-252203 JP-A-6-248004

  However, in the method described in Patent Document 1 described above, a part of the latex is extracted in the middle of the polymerization, so that the resulting latex contains a large amount of unreacted monomer, lacks stability, and has a final product quality. There is a problem that the properties are easily changed.

  Further, even the methods described in Patent Document 2 and Patent Document 3 described above do not satisfy the required low viscosity and high level of quality, and further improvement is required.

  Accordingly, an object of the present invention is a copolymer latex having a low viscosity and good dispersion stability, and when used as a binder for a paper coating composition, the paper coating composition under high shear is used. An object of the present invention is to provide a copolymer latex excellent in fluidity and redispersibility and excellent in dry pick strength of the coated paper obtained.

  In order to solve the above problems, the copolymer latex of the present invention comprises an aliphatic conjugated diene monomer 20 to 69.5% by weight, an ethylenically unsaturated carboxylic acid monomer 0.5 to 20% by weight, And a copolymer latex obtained by emulsion polymerization of a monomer containing 10.5 to 79.5% by weight of an ethylenically unsaturated monomer copolymerizable therewith, which is bonded to latex particles. The peak top molecular weight (Mp) obtained by gel permeation chromatography of a non-carboxyl group component is 15,000 or less.

  Further, the copolymer latex of the present invention is preferably obtained by polymerizing a carboxyl group component not bonded to latex particles with a monomer containing an ethylenically unsaturated carboxylic acid monomer as a main component. It is.

  Moreover, it is suitable for the copolymer latex of this invention that the amount of detected carboxyl groups exists in the range of 0.15-1.90 (meq / g) with respect to solid content of copolymer latex.

  The copolymer latex of the present invention preferably has a number average particle size of 30 to 200 nm.

  The copolymer latex of the present invention is preferably used as a binder for paper coating.

  According to the copolymer latex of the present invention, since it has a low viscosity and good dispersion stability, a paper coating composition excellent in fluidity and redispersibility under high shear can be obtained.

  Moreover, according to the copolymer latex of the present invention, a coated paper having excellent dry pick strength can be obtained.

Embodiments of the Invention

  The copolymer latex of the present invention comprises an aliphatic conjugated diene monomer, an ethylenically unsaturated carboxylic acid monomer, and a monomer (single monomer containing an ethylenically unsaturated monomer copolymerizable therewith). Obtained by emulsion polymerization.

  Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro-1,3-butadiene. Substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. Of these aliphatic conjugated diene monomers, 1,3-butadiene is preferable.

  In addition, these aliphatic conjugated diene monomers can be used alone (one kind) or in combination of two or more kinds.

  Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid, methacrylic acid, and crotonic acid, for example, ethylenically unsaturated monomers such as maleic acid, fumaric acid, and itaconic acid. Saturated dicarboxylic acid monomer (or its anhydride) etc. are mentioned.

  Further, these ethylenically unsaturated carboxylic acid monomers can be used alone (one kind) or in combination of two or more kinds.

  Examples of the ethylenically unsaturated monomer copolymerizable with the above aliphatic conjugated diene monomer and ethylenically unsaturated carboxylic acid monomer include alkenyl aromatic monomers and vinyl cyanide monomers. , Unsaturated carboxylic acid alkyl ester monomers, hydroxyalkyl group-containing unsaturated monomers, unsaturated carboxylic acid amide monomers, and the like.

  Examples of the alkenyl aromatic monomer include styrene, α-methylstyrene, methyl α-methylstyrene, vinyl toluene, and divinylbenzene.

  Of these alkenyl aromatic monomers, styrene is preferable.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like.

  Of these vinyl cyanide monomers, acrylonitrile or methacrylonitrile 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, and dimethyl itaco. Nate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like.

  Of these unsaturated carboxylic acid alkyl ester monomers, methyl methacrylate is preferable.

  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. Examples include methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate.

  Of these unsaturated monomers containing a hydroxyalkyl group, β-hydroxyethyl acrylate is preferable.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N-methylol dimethyl acrylamide and the like.

  Of these unsaturated carboxylic acid amide monomers, acrylamide or methacrylamide is preferable.

  In addition to these ethylenically unsaturated monomers, any of the monomers used in normal emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride can be used. is there.

  Moreover, these ethylenically unsaturated monomers can be used alone (one type only) or in combination of two or more types.

  As for the monomer, the aliphatic conjugated diene monomer is, for example, 20 to 69.5% by weight, preferably 30 to 60% by weight, based on the total amount of the monomer, and an ethylenically unsaturated carboxylic acid monomer. The body is, for example, 0.5 to 20% by weight, preferably 1 to 15% by weight, and the ethylenically unsaturated monomer copolymerizable therewith, for example, 10.5 to 79. 5% by weight, preferably 25 to 69% by weight.

  When the aliphatic conjugated diene monomer is less than 20% by weight, the dry pick strength of the coated paper is inferior, and when it exceeds 69.5% by weight, the redispersibility of the paper coating composition may be inferior. Yes, the coating operability at the time of creating coated paper may be reduced.

  If the amount of the ethylenically unsaturated carboxylic acid monomer is less than 0.5% by weight, the mechanical stability and the standing stability of the copolymer latex may be inferior. On the other hand, when the amount of the ethylenically unsaturated carboxylic acid monomer exceeds 20% by weight, the viscosity of the copolymer latex, and thus the viscosity of the paper coating composition, increases, and the copolymer latex is transported by a liquid feed pump. Transportability may be inferior.

  When the copolymerizable ethylenically unsaturated monomer is out of the range of 10.5 to 79.5% by weight, the dry pick strength of the coated paper is remarkably lowered.

  And in order to obtain copolymer latex, an emulsifier and a polymerization initiator are added to a monomer, and a monomer is emulsion-polymerized.

  Examples of the emulsifier include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, formalin condensates of naphthalene sulfonic acid, Anionic surfactants such as sulfate ester salts of ionic surfactants, for example, nonionic surfactants such as alkyl ester type, alkyl phenyl ether type, and alkyl ether type of polyethylene glycol.

  These emulsifiers can be used alone (one kind only) or in combination of two or more kinds.

  An emulsifier is mix | blended in the ratio of 0.05-8 weight part with respect to 100 weight part of monomers, Preferably, 0.1-3 weight part.

  Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate, such as cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, and acetyl peroxide. Examples thereof include oil-soluble polymerization initiators such as oxide, diisopropylbenzene hydroperoxide, and 1,1,3,3-tetramethylbutyl hydroperoxide.

  Of these polymerization initiators, potassium persulfate, sodium persulfate, cumene hydroperoxide, and t-butyl hydroperoxide are preferable.

  The blending ratio of the polymerization initiator is appropriately adjusted in consideration of the combination of the monomer composition, the pH of the polymerization reaction system, and other additives.

  The polymerization initiator is added at a ratio of, for example, 0 to 3 parts by weight, preferably 0.01 to 2 parts by weight, with respect to 100 parts by weight of the monomer.

  Moreover, in order to emulsion-polymerize a monomer, a reducing agent and a chain transfer agent (molecular weight regulator) can be added as needed.

  Examples of the reducing agent include sulfite, bisulfite, pyrosulfite, nitrite, nithionate, thiosulfate, formaldehyde sulfonate (eg, formaldehyde sodium sulfoxylate), benzaldehyde sulfonate, and the like. Examples thereof include carboxylic acids such as L-ascorbic acid, erythorbic acid, tartaric acid and citric acid and salts thereof, for example, reducing sugars such as dextrose and saccharose, and amines such as dimethylaniline and triethanolamine.

  Of these reducing agents, L-ascorbic acid and erythorbic acid are preferable.

  For example, 0 to 3 parts by weight, preferably 0.005 to 1 part by weight of the reducing agent is added to 100 parts by weight of the monomer.

  Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan, such as dimethylxanthogen disulfide, diisopropyl. Xanthogen compounds such as xanthogen disulfide, for example, thiuram compounds such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide, such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol Phenolic compounds such as allyl compounds such as allyl alcohol, eg halogenated such as dichloromethane, dibromomethane, carbon tetrabromide Hydrogenated compounds such as vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, such as triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2 -Ethylhexyl thioglycolate, terpinolene, α-methylstyrene dimer and the like.

  These chain transfer agents can be used alone (one kind only) or in combination of two or more kinds.

  The chain transfer agent is added in an amount of, for example, 0 to 3 parts by weight, preferably 0.01 to 2 parts by weight, with respect to 100 parts by weight of the monomer.

  In the emulsion polymerization, if necessary, a hydrocarbon solvent can be added.

  Examples of the hydrocarbon solvent include saturated hydrocarbons such as pentane, hexane, heptane, octane, cyclohexane, and cycloheptane, such as pentene, hexene, heptene, cyclopentene, cyclohexene, cycloheptene, 4-methylcyclohexene, and 1-methylcyclohexene. And unsaturated hydrocarbons such as aromatic hydrocarbons such as benzene, toluene and xylene.

  Of these hydrocarbon solvents, cyclohexene and toluene are preferable. Cyclohexene and toluene have a moderately low boiling point and are easy to recover and reuse after the polymerization by steam distillation or the like, and are preferable from the viewpoint of environmental problems.

  Further, as other additives, for example, known additives such as electrolytes such as sodium hydroxide and sodium carbonate, polymerization inhibitors such as hydroquinone, polymerization accelerators, chelating agents, oxygen scavengers, and dispersants may be used as necessary. Can be added.

  Moreover, it does not specifically limit as a polymerization method of the copolymer latex of this invention, Polymerization methods, such as one-stage polymerization, two-stage polymerization, or multistage polymerization, are employable.

  Among these polymerization methods, a two-stage or more other-stage polymerization method is preferable. When the polymerization is performed by two or more stages of other polymerization methods, the balance between the redispersibility of the paper coating composition and the dry pick strength of the coated paper can be further improved.

  Moreover, the addition method of various components is not particularly limited, and a batch addition method, a divided addition method, a continuous addition method, a power feed method, or the like can be used.

  Specifically, in the emulsion polymerization of the copolymer latex of the present invention, the monomer is divided into a first-stage monomer composition and a second-stage monomer composition. After the body composition is emulsion-polymerized to obtain a pre-copolymer, the second-stage monomer composition is emulsion-polymerized in the presence of the pre-copolymer.

  The first-stage monomer composition contains an aliphatic conjugated diene monomer, for example, 5 to 30% by weight, preferably 8 to 27% by weight, an ethylenically unsaturated carboxylic acid monomer, for example, 0.5 to 15% by weight, preferably 1 to 13% by weight, and an ethylenically unsaturated monomer copolymerizable therewith, for example, 10 to 45% by weight, preferably 15 to 42%. Contains by weight.

  The second-stage monomer composition is an aliphatic conjugated diene monomer, for example, 7 to 35% by weight, preferably 15 to 30% by weight, an ethylenically unsaturated carboxylic acid monomer, for example, 0 to 10% by weight, preferably 0 to 8% by weight, and an ethylenically unsaturated monomer copolymerizable therewith, for example, 10 to 25% by weight, preferably 12 to 23% by weight ,contains.

  Thereby, the copolymer latex of the present invention is prepared.

  Of the obtained copolymer latex, the peak top molecular weight (Mp) obtained by gel permeation chromatography of the carboxyl group component not bonded to the latex particles is 15,000 or less, preferably 1,000-13. , 000. If the peak top molecular weight (Mp) exceeds 15,000, the viscosity of the latex may increase significantly. In addition, the carboxyl group component not bonded to the latex particle is hydrophilicity generated by polymerization of a monomer containing an ethylenically unsaturated carboxylic acid monomer as a main component on the aqueous phase side in the emulsion polymerization described above. It is a polymer.

  In order to measure the peak top molecular weight (Mp) of the carboxyl group component not bonded to the latex particles, first, the solvent is swelled into the copolymer latex particles and centrifuged in a state where the specific gravity difference is given, and then the supernatant liquid is obtained. Take out. Subsequently, it measures using the gel permeation chromatograph (GPC) about the taken-out supernatant liquid. Then, based on a calibration curve prepared in advance with a polycarboxylic acid having a known molecular weight, the peak top molecular weight of the chromatogram obtained by GPC is calculated as the peak top molecular weight (Mp).

  The peak top molecular weight (Mp) of the carboxyl group component not bonded to the latex particles can be controlled by appropriately adjusting the polymerization temperature, the type and blending ratio of the chain transfer agent, and the blending ratio of the polymerization initiator. Specifically, the peak top molecular weight (Mp) of the carboxyl group component can be lowered by increasing the polymerization temperature or increasing the amount of radical generation by increasing the amount of the polymerization initiator. Moreover, the peak top molecular weight (Mp) of a carboxyl group component can be lowered | hung by using a highly hydrophilic chain transfer agent or increasing the amount of chain transfer agents.

  In addition, by setting the pH at the initial stage of polymerization to the alkali side, even after the ethylenically unsaturated carboxylic acid monomer is polymerized into an oligomer, it can be easily present on the aqueous phase side without being taken into the latex particles. .

  Moreover, the amount of carboxyl groups detected with respect to the solid content of the obtained copolymer latex is, for example, 0.15 to 1.90 meq / g, preferably 0.20 to 1.80 meq / g, more preferably 0.8. 35 to 1.50 meq / g.

  If the detected carboxyl group amount is less than 0.15, the redispersibility of the paper coating composition and the dry pick strength of the coated paper may be inferior. When the detected carboxyl group amount exceeds 1.90, the latex viscosity may increase or the viscosity of the paper coating composition may increase.

  Moreover, the number average particle diameter of the obtained copolymer latex (measured by the measurement method described in Examples described later) is, for example, 30 to 200 nm, preferably 30 to 150 nm, and more preferably 50 to 110 nm. When the number average particle diameter is in this range, the dry pick strength of the coated paper is more excellent.

  In addition, well-known additives, such as an antifoamer, anti-aging agent, antiseptic | preservative, an antibacterial agent, a flame retardant, and an ultraviolet absorber, can also be suitably added to copolymer latex. Further, the copolymer latex can be appropriately blended with other latexes depending on the purpose of use.

  The copolymer latex of the present invention is preferably blended into a paper coating composition as a paper coating binder.

  The paper coating composition can be obtained by blending and mixing a copolymer latex and a pigment.

  Examples of the pigment include inorganic pigments such as kaolin clay, calcium carbonate, talc, barium sulfate, titanium oxide, aluminum hydroxide, zinc oxide, and satin white, and organic pigments such as polystyrene latex.

  These pigments can be used alone (only one kind) or in combination of two or more kinds.

  In order to prepare the composition for paper coating, the copolymer latex is, for example, 1 to 20 parts by weight, preferably 2 to 12 parts by weight in terms of solids with respect to 100 parts by weight (solid content) of the pigment. Part mix. If the ratio of the copolymer latex (solid content) is less than 1 part by weight, the pigment may not be sufficiently adhered. When the ratio of the copolymer latex (solid content) exceeds 20 parts by weight, the opacity and white paper gloss may be lowered.

  In addition, for the paper coating composition, if necessary, for example, modified starch such as starch, oxidized starch, esterified starch, natural binders such as soybean protein, casein, such as polyvinyl alcohol, carboxymethylcellulose, etc. Water-soluble synthetic binders such as synthetic latexes such as polyvinyl acetate latex and acrylic latex can also be blended.

  The paper coating composition may contain other auxiliary agents, for example, dispersants (sodium pyrophosphate, sodium polyacrylate, sodium hexametaphosphate, etc.) and antifoaming agents (polyglycols, fatty acid esters, Phosphate ester, silicone oil, etc.), leveling agents (funnel oil, dicyandiamide, urea, etc.), preservatives, mold release agents (calcium stearate, paraffin emulsion, etc.), fluorescent dyes, color water retention agents (sodium alginate, etc.) It can also be blended.

  The obtained paper coating composition is applied to coated paper by a known technique, for example, a coating machine such as an air knife coater, a blade coater, a roll coater, or a bar coater. In addition, the coated paper is prepared by drying the surface of the coated paper coated with the paper coating composition and finishing it by calendering 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. In the examples, “part” and “%” indicating the blending ratio are based on weight.
1. Synthesis of copolymer latex (1) Example 1
A pressure-resistant polymerization reactor was charged with 250 parts of polymerized water, 2.02 parts of sodium alkylbenzene sulfonate, and 0.35 part of sodium alkyldiphenyl ether disulfonate, and after sufficient stirring, the unit amount of the first stage shown in Table 1 The body (first-stage monomer composition) and other compounds were added, polymerization was started at 70 ° C., and the reaction was performed for 4 hours.

  Next, the second stage monomer (second stage monomer composition) and other compounds shown in Table 1 and other compounds were continuously added over 3.5 hours to continue the polymerization. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (a).
(2) Example 2
A pressure-resistant polymerization reactor was charged with 158 parts of polymerized water, 1.5 parts of sodium alkylbenzene sulfonate, and 0.05 part of sodium hydrogen carbonate, and after sufficient stirring, the first stage monomer shown in Table 1 (1 The stage monomer composition) and other compounds were added and polymerization was started at 67 ° C. and reacted for 4.5 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 1 were continuously added over 4.0 hours, and then polymerization was continued at 72 ° C. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (b).
(3) Example 3
A pressure-resistant polymerization reactor was charged with 175 parts of polymerized water, 1.15 parts of sodium alkylbenzenesulfonate, 0.7 part of sodium alkyldiphenyl ether disulfonate, and 0.02 part of sodium bicarbonate, and after stirring sufficiently, Table 1 The first-stage monomer shown (first-stage monomer composition) and other compounds were added, polymerization was started at 75 ° C., and the reaction was allowed to proceed for 3 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 1 were continuously added over 4.5 hours, and the polymerization was continued thereafter. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (c).
(4) Example 4
A pressure-resistant polymerization reactor was charged with 195 parts of polymerized water, 1.15 parts of sodium alkylbenzene sulfonate, and 0.7 parts of sodium alkyldiphenyl ether disulfonate, and after sufficient stirring, the unit amount of the first stage shown in Table 1 The body (first-stage monomer composition) and other compounds were added and reacted at 43 ° C. for 6 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 1 were continuously added in 4 hours, and then polymerization was continued at 60 ° C. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (d).
(5) Example 5
A pressure-resistant polymerization reactor was charged with 115 parts of polymerized water, 0.85 part of sodium alkylbenzene sulfonate, and 0.10 part of sodium hydrogen carbonate, and after sufficient stirring, the first-stage monomer shown in Table 1 ( The first-stage monomer composition) and other compounds were added and reacted at 65 ° C. for 5 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 1 were continuously added over 4 hours, and then polymerization was continued at 70 ° C. The polymerization was terminated when the polymerization conversion rate exceeded 95%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (e).
(6) Example 6
A pressure-resistant polymerization reactor was charged with 99 parts of polymerized water, 0.25 part of sodium bicarbonate, and 0.65 part of sodium alkylbenzene sulfonate, and after sufficient stirring, the first-stage monomer shown in Table 1 ( The first-stage monomer composition) and other compounds were added and reacted at 65 ° C. for 4 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 1 were continuously added over 4 hours, and then polymerization was continued at 68 ° C. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (f).
(7) Comparative Example 1
A pressure-resistant polymerization reactor was charged with 150 parts of polymerized water, 0.01 part of sodium bicarbonate and 1.35 parts of sodium alkylbenzenesulfonate, and after sufficient stirring, the first stage monomer shown in Table 2 ( The first-stage monomer composition) and other compounds were added and reacted at 70 ° C. for 3.5 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 2 were continuously added over 3.5 hours, and the polymerization was continued thereafter. The polymerization was terminated when the polymerization conversion rate exceeded 98%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (g).
(8) Comparative Example 2
A pressure-resistant polymerization reactor was charged with 180 parts of polymerized water, 1.20 parts of sodium alkylbenzenesulfonate, 0.3 part of sodium alkyldiphenyl ether disulfonate, and 0.21 part of sodium hydrogen carbonate. The first-stage monomer shown (first-stage monomer composition) and other compounds were added and reacted at 70 ° C. for 4 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 2 were continuously added over 1.0 hour, and the polymerization was continued thereafter. The polymerization was terminated when the polymerization conversion rate exceeded 95%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (h).
(9) Comparative Example 3
A pressure-resistant polymerization reactor was charged with 225 parts of polymerized water and 2.20 parts of sodium alkylbenzenesulfonate, and after sufficient stirring, the first-stage monomer shown in Table 2 (first-stage monomer composition) ) And other compounds were added and reacted at 44 ° C. for 4 hours.

  Next, the second-stage monomer (second-stage monomer composition) and other compounds shown in Table 2 were continuously added over 4 hours, and then polymerization was continued at 58 ° C. The polymerization was terminated when the polymerization conversion rate exceeded 97%.

Thereafter, the pH was adjusted to 7 using sodium hydroxide, and unreacted monomers and other low-boiling compounds were removed by heating under reduced pressure to obtain a copolymer latex (i).
2. Measurement of physical properties of copolymer latex (1) Method for measuring peak top molecular weight (Mp) of carboxyl group component not bonded to latex particles The copolymer latex of each Example and each Comparative Example was made 5% by weight with distilled water. After diluting, 50 g of 0.1N sodium hydroxide aqueous solution and 3 g of carbon tetrachloride were added to 100 g of the diluted solution of copolymer latex, followed by stirring for 1 hour.

Thereafter, the latex particles were centrifugally settled by a centrifugal separator to separate into a supernatant layer and a latex particle layer, and the obtained supernatant layer (including a carboxyl group component not bound to the latex particles) was vacuum freeze-dried. The vacuum freeze dried samples 0.05 g, diluted with _50mM-Na 2 HPO ₄ in 10 ml, were measured by GPC under the following conditions.

In the obtained chromatogram, the peak top molecular weight of the highest peak was determined based on five types of polycarboxylic acids with known molecular weights in advance (Calibration Kits for GPC / SEC PAA-10 (polyacrylic acid: peak top molecular weight (Mp) = 1, 250, 2,925, 7,500, 16,000, 62,900), manufactured by Polymer Laboratories). The results are shown in Table 1 and Table 2 below.
<GPC measurement conditions>
Detector: RID-10A (manufactured by Shimadzu Corporation)
Column: SB-802.5HQ and SB-803HQ (both manufactured by Showa Denko KK) connected in series Guard column: SB-G (manufactured by Showa Denko KK)
Column temperature: 40 ° C
Mobile phase: 50 mM Na ₂ HPO ₄ aqueous solution Flow rate: 0.4 mL / min Sample volume: 100 μL
(2) Measurement of the amount of detected carboxyl groups The copolymer latex of each Example and each Comparative Example was diluted to 1% by weight with distilled water, and 0.1 N hydrochloric acid was excessively added to the diluted solution of the copolymer latex. After the amount was added, the solution was back titrated with a 0.1N aqueous sodium hydroxide solution. From the obtained electrical conductivity curve, the detected carboxyl group amount (meq / g) relative to the solid content of the copolymer latex was calculated. The results are shown in Table 1 and Table 2 below.
(3) Measurement of number average particle diameter of copolymer latex The number average particle diameter of the copolymer latex obtained in each Example and each Comparative Example was measured by a dynamic light scattering method. In the measurement, LPA-3000 / 3100 (manufactured by Otsuka Electronics) was used. The results are shown in Table 1 and Table 2 below.
3. Preparation and Evaluation of Composition for Paper Coating (1) Preparation of Composition for Paper Coating According to the formulation shown below, the copolymer latex of each example and each comparative example is blended, and an aqueous sodium hydroxide solution is used. The composition for paper coating was adjusted to pH 9.5.
(Formulation formulation of paper coating composition)
Formulation Kaolin clay 60 parts Heavy calcium carbonate 40 parts Modified starch 4 parts Copolymer latex 10 parts ...
Solid content concentration 64%
(2) Evaluation of redispersibility of the paper coating composition Each of the obtained paper coating compositions was applied onto a NBR black rubber plate with a # 6 wire bar and dried in a 60 ° C hot air circulating oven for 3 minutes. Then, it was washed with running water at 30 ° C. for 1 minute.

  The film of the composition remaining on the NBR black rubber plate was visually observed, and ◎ indicates that the film is excellent in redispersibility with little film adhesion, and x indicates that the film is inferior in redispersibility with much film adhesion. Relative evaluation was made visually. The results are shown in Table 1 and Table 2 below.

(Excellent) ◎>○>△> × (poor)
(3) Evaluation of fluidity of composition for paper coating A double-cylinder Hercules high shear viscometer (manufactured by Kumagai Riki Kogyo Co., Ltd.) was used. Using the inner cylinder Bob F, the apparent viscosity (mPa · s) of each paper coating composition at 4000 rpm giving a high shear rate was measured. The results are shown in Table 1 and Table 2 below. The lower the value, the lower the apparent viscosity and the better the fluidity.
4). Preparation and Evaluation of Coated Paper (1) Preparation of Coated Paper A coating paper (basis weight 67 g / m ² ) is coated with the above paper coating composition so that the coating amount per side is 13 g / m ^2. Then, after coating using a wire bar and 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.
(2) Evaluation of dry pick strength of coated paper Relatively grade 5 (excellent) to grade 1 (inferior) is judged by naked eyes when picking up each coated paper sample at the same time with an RI printer. Was visually evaluated. The results are shown in Table 1 and Table 2 below.

  As shown in Table 1, the paper coating composition using the copolymer latex of each example has good fluidity and redispersibility, and these paper coating compositions were applied. The coated paper obtained in this way has good dry pick strength.

  As shown in Table 2, in Comparative Example 1, the amount of butadiene is less than the lower limit and the amount of unsaturated carboxylic acid exceeds the upper limit, so the dry pick strength of the coated paper is greatly inferior, and the flow of the composition for paper coating Also inferior.

  In Comparative Example 2, the peak top average molecular weight (Mp) of the carboxyl group component not bonded to the particles exceeds the upper limit of the present invention, and the fluidity of the paper coating composition and the dry pick strength of the coated paper are Inferior.

In Comparative Example 3, the amount of butadiene exceeds the upper limit, and the redispersibility of the paper coating composition is poor.
In addition, although the said invention was provided as embodiment of illustration of this invention, this is only a mere illustration and must not be interpreted limitedly. Modifications of the present invention apparent to those skilled in the art are intended to be included within the scope of the following claims.

  The copolymer latex of the present invention is used as a binder such as a paper coating binder.

Claims (5)

Including emulsion polymerization of the monomer,
The monomer includes an aliphatic conjugated diene monomer of 20 to 69.5% by weight, an ethylenically unsaturated carboxylic acid monomer of 0.5 to 20% by weight, and an ethylene-based unsaturated copolymerizable therewith. only contains the unsaturated monomer from 10.5 to 79.5% by weight,
The emulsion polymerization is a multi-stage polymerization,
The first-stage monomer composition in the multi-stage polymerization includes at least one selected from the group consisting of sodium hydroxide and sodium carbonate,
A method for producing a copolymer latex , wherein a peak top molecular weight (Mp) obtained by gel permeation chromatography of a carboxyl group component not bound to latex particles is 15,000 or less. The carboxyl group component that is not bonded to the latex particles is obtained by polymerization of a monomer containing the ethylenically unsaturated carboxylic acid monomer as a main component. A method for producing a copolymer latex. The copolymer latex according to claim 1 or 2, wherein the detected carboxyl group amount is in the range of 0.15 to 1.90 (meq / g) with respect to the solid content of the copolymer latex. Manufacturing method . The method for producing a copolymer latex according to any one of claims 1 to 3, wherein the number average particle diameter is 30 to 200 nm. The method for producing a copolymer latex according to any one of claims 1 to 4, which is used as a binder for paper coating.