JPH05186508A - Production of copolymer latex, copolymer latex, and paper-coating composition containing the same - Google Patents

Abstract

PURPOSE:To produce a copolymer latex which is useful for, e.g. a paper coating composition excellent in such properties of coated paper as adhesion strength, water resistance, ink adhesion, and whiteness and gloss and is also usable for a carpet backing material and an adhesive, and to provide a paper coating composition containing the latex. CONSTITUTION:A monomer mixture comprising a conjugated diene monomer, an ethylenic monomer, and an ethylenic carboxylic acid monomer is emulsion- polymerized in the presence of a water-soluble chain transfer agent having at least one hydrophilic group selected among a carboxyl group, a salt thereof, and an amino group and at least one mercapto group to thereby produce a copolymer latex. This latex can be used to produce a paper coating composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a copolymer latex characterized by emulsion polymerization in the presence of a specific polymerization chain transfer agent. More specifically, it relates to the adhesive strength and water resistance of coated paper. The present invention relates to a method for producing a copolymer latex which is useful for a composition for paper coating having excellent properties such as ink receptivity and gloss on a white paper, and can also be used as a backing agent or adhesive for carpet.

[0002]

2. Description of the Related Art In recent years, as the demand for coated paper has rapidly increased, the production speed of paper coating has increased, and the printing speed has been increased to increase the production amount of printed matter.
Particularly in offset printing, this tendency is becoming stronger. Therefore, the copolymer latex used as a binder, which is one component of the paper coating composition, is required to have the following properties. One of them is to have excellent adhesive strength. If the adhesive strength is low, the mechanical force applied to the surface of the pigment-coated paper during printing causes the pigment to come off and the coating layer to be peeled off from the base paper. Such destruction of the paper surface becomes more severe as the printing speed increases and the number of overprints increases. Therefore, a binder having excellent adhesion between the pigment particles and between the pigment coating layer and the base paper is required. Another is that it has excellent water resistance. In particular, since "fountain solution" is used in offset printing, it is required to have strength against mechanical force caused by printing, that is, water resistance, when the surface of the pigment coated paper is wet. As another property, as the printing speed increases, ink receptivity far superior to the conventional one is required. In addition to the above properties, coated paper is also required to have optical properties such as white paper gloss.

As described above, the coated paper has adhesive strength, water resistance,
Various properties such as ink receptivity and white paper gloss are required,
In the past, there has been no coated paper that balances these properties at a high level. The reason is that the adhesive strength and the water resistance are in a relationship of being incompatible with ink receptivity and white paper gloss. That is, as a conventional method for improving water resistance, a method of decreasing the gel content of the polymer latex used as a binder is known, but if the gel content is decreased, ink receptivity deteriorates. Further, as a method for improving ink receptivity and white paper gloss, it is known to increase the particle size of the polymer latex or increase the glass transition temperature. Then, there was a technically difficult problem that the water resistance was lowered. As a method for solving these problems, there has been proposed a method of using a thioglycolic acid alkyl ester as a chain transfer agent at the time of producing a copolymer latex (Japanese Patent Application Laid-Open No. HEI 3)
No. 37203), the coated paper obtained by using the latex as a binder was not sufficient in physical properties such as adhesive strength, water resistance, ink receptivity, and white paper gloss.

[0004]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies in view of the problems of the prior art as described above, and as a result, a conjugated diene monomer, an ethylenically unsaturated monomer and When emulsion-polymerizing a monomer mixture containing an ethylenically unsaturated carboxylic acid monomer, water-soluble having at least one hydrophilic group and at least one mercapto group selected from a carboxyl group or a salt thereof and an amino group. Adhesive strength in coated paper by using a polymerizable polymerization chain transfer agent,
It was found that a copolymer latex that can be used in a paper coating composition having excellent water resistance, ink receptivity, and white paper gloss, etc. was obtained, and as a result of further research, the present invention was completed. ..

[0005]

[Means for Solving the Problems] That is, the present invention is
A monomer mixture containing (1) a conjugated diene-based monomer, (2) an ethylenically unsaturated monomer, and (3) an ethylenically unsaturated carboxylic acid monomer is prepared from a carboxyl group or a salt thereof and an amino group. Process for producing copolymer latex, emulsion copolymerization in the presence of a water-soluble polymerization chain transfer agent having at least one hydrophilic group and at least one mercapto group selected, a copolymer latex and the same The present invention relates to a paper coating composition using.

The present invention will be described in detail below. Examples of the conjugated diene-based monomer (1) used in the present invention include 1,3-butadiene, isoprene, and 2-chloro-1,3.
-Butadiene, 2-methyl-1,3-butadiene and the like which are usually used in the production of latex can be mentioned.
These monomers (1) may be used alone or in combination of two or more. Of these, 1,3-butadiene is particularly preferable.

The monomer (1) is used to impart appropriate elasticity and film hardness to the resulting copolymer. The amount of the monomer (1) used is 10 to 80 with respect to the total monomer mixture.
%, Preferably 20-60% by weight. When the amount used is less than 10% by weight, sufficient adhesive strength of the coated paper obtained may not be obtained, while when it is more than 80% by weight, water resistance and adhesive strength may decrease, which is not preferable.

Examples of the ethylenically unsaturated monomer (2) used in the present invention include aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene and p-methylstyrene, such as methyl acrylate and acrylic acid. Alkyl ester compounds of acrylic acid or methacrylic acid such as ethyl, butyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, such as acrylamide, methacrylamide, N, N-dimethyl Acrylamide or methacrylamide compound of ethylenically unsaturated carboxylic acid such as acrylamide, N-methylol acrylamide, carboxylic acid vinyl ester such as vinyl acetate, such as acrylonitrile, methacrylonitrile, α- Vinyl cyanide compounds such as chloroacrylonitrile, eg methylaminoethyl (meth)
Acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate,
Monomers such as dibutylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, ethylenically unsaturated amine compounds such as 2-vinylpyridine and 4-vinylpyridine, which will be described later (3 Other than ethylenically unsaturated monomers can be mentioned. These may be used alone or in combination of two or more. Of these, styrene is particularly preferable as the aromatic vinyl compound, methyl methacrylate is preferable as the alkyl ester compound, and acrylonitrile is preferable as the vinyl cyanide compound.

The amount of the monomer (2) used is 20 to 90% by weight, preferably 40 to 80% by weight, based on the total monomer mixture.
Is. If the amount used is too small, the water resistance of the coated paper obtained may be poor, while if it is too large, the rigidity may be too high and the adhesive strength may be reduced.

Examples of the ethylenically unsaturated carboxylic acid monomer (3) used in the present invention include monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, and dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid. Examples thereof include acids or their anhydrides such as half-esters of methyl maleate and methyl itaconate. These may be used alone or in combination of two or more.

The amount of the monomer (3) used is 0.2 to 12% by weight, preferably 0.5 to 8% by weight, based on the total monomer mixture.
Is. If the amount used is too small, the mechanical stability of the obtained paper coating composition and the adhesive strength of the obtained coated paper may not be sufficiently obtained, and if it is too large, the viscosity of the copolymer latex is high. It may become too practical to be suitable for practical use.

Examples of the water-soluble polymerization chain transfer agent used in the present invention include those having at least one hydrophilic group and at least one mercapto group selected from a carboxyl group or a salt thereof and an amino group in the molecule. Be done. Examples of the hydrophilic group include a carboxyl group or a salt thereof, an amino group and the like, and among these, a carboxyl group or a salt thereof is preferable. More specifically, the chain transfer agent is, for example, a compound represented by the following general formula (I). [Wherein R is a hydrocarbon residue which may be substituted with halogen, X ₁ is one group selected from a carboxyl group or a salt thereof and an amino group, and X ₂ is a hydrogen atom, a hydroxyl group or a carboxyl group. A group or a salt thereof, and one group selected from an amino group are shown. Here, the hydrocarbon residue which may be substituted with halogen is, for example, methyl, ethyl, propyl, butyl, octyl or the like having 1 to 1 carbon atoms.
8, preferably 1-8, alkyl groups such as cyclobutyl, cyclopentyl, cyclohexyl, dimethylcyclohexyl and the like having 3-12 carbon atoms, preferably 4-8 cycloalkyl groups, such as vinyl, allyl, 2-butynyl, etc. 2-8, preferably 2-4 alkenyl groups, such as ethynyl, propynyl, butynyl, etc., having 2-18 carbon atoms, preferably 2-4 alkynyl groups, such as phenyl, tolyl, naphthyl, etc., having 6-12 carbon atoms,
Preferably, an aryl group having 6 to 10 carbon atoms such as benzyl, phenylethyl, naphthylmethyl and the like, 6 to 12,
Preferably, 7 to 11 aralkyl groups and the like can be mentioned. Among the water-soluble polymerization chain transfer agents used in the present invention, those in which at least one of X ₁ or X ₂ in the general formula (I) is a carboxyl group have less generation of fine coagulation and are excellent in polymerization stability. Therefore, it is preferably used in the present invention. Further, examples of the halogen include fluorine, chlorine and bromine, and the number of substituents is 1 or 2.

Specific examples of the water-soluble polymerization chain transfer agent represented by the general formula (I) include mercaptancarboxylic acid such as 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoacetic acid and o-mercaptobenzoic acid. Or a salt thereof (for example, ammonium mercaptoacetate), a mercaptan dicarboxylic acid such as mercaptosuccinic acid or a salt thereof (for example, a mercaptan dicarboxylic acid salt), for example, a mercaptan having an amino group in the molecule such as 2-mercaptoethylamine. Be done.

The amount of the water-soluble polymerization chain transfer agent used is
The range is 0.005 to 8 parts by weight, preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the total monomer mixture. If the amount used is less than 0.005 parts by weight, the adhesive strength and water resistance may be poor, and if it exceeds 8 parts by weight, the adhesive strength may decrease again, which is not preferable. These may be used alone or in combination of two or more.

The water-soluble polymerization chain transfer agent in the present invention is
If necessary, they can be used in combination with other well-known chain transfer agents. The polymerization chain transfer agent that can be used in combination with the water-soluble polymerization chain transfer agent of the present invention may be any known polymerization chain transfer agent that is generally used in emulsion polymerization, specifically, For example, mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, and n-tetradecyl mercaptan, for example, xanthogen disulfides such as dimethylxanthogen disulfide, diethylxanthogen disulfide, and diisopropylxanthigen disulfide, for example tetra Thiuram disulfides such as methyl thiuram disulfide, tetraethyl thiuram disulfide and tetrabutyl thiuram disulfide, for example, halogenated hydrocarbons such as carbon tetrachloride, carbon tetrabromide and ethylene bromide. , And allyl alcohol, 2-ethylhexyl thioglycolate, alpha-methylstyrene dimer, terpinolene, alpha-terpinene, .gamma.-terpinene, mention may be made of dipentene, anisole and the like. These may be used alone or in combination of two or more. Among these, mercaptan, xanthogen disulfide, thiuram disulfide, carbon tetrachloride, α-methylstyrene dimer, terpinolene and the like are preferable.

The proportion of these known polymerization chain transfer agents used is less than 95% by weight, preferably less than 90% by weight, based on the total polymerization chain transfer agents used for emulsion polymerization. When the use ratio of the known polymerization chain transfer agent is 95% by weight or more,
The resulting coated paper is inferior in physical properties such as adhesive strength, water resistance, ink receptivity and white paper gloss, and is not preferable.

The copolymer latex of the present invention is a conventionally known emulsion polymerization method, that is, a monomer mixture, a polymerization initiator, an emulsifier and a water-soluble polymerization chain transfer agent are added to an aqueous medium (for example, water). It is obtained by carrying out emulsion polymerization. The polymerization initiator used in the emulsion polymerization of the present invention is not particularly limited, and examples thereof include inorganic persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, cumene hydroperoxide, benzoyl peroxide, Organic peroxides such as isopropylbenzene peroxide, and azo initiators such as azoisobutyronitrile can be used. These can be used alone or in combination of two or more. Of these, persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate are preferably used from the viewpoint of polymerization stability.

The polymerization initiator can also be used as a so-called redox type polymerization initiator in combination with a reducing agent such as sodium bisulfite and ferrous sulfate. The amount of the polymerization initiator used in the present invention is 1
It is usually about 0.1 to 5 parts by weight, preferably about 0.2 to 2 parts by weight, per 00 parts by weight.

The emulsifier used in the emulsion polymerization of the present invention is not particularly limited, and examples thereof include sodium dodecylbenzenesulfonate and sodium lauryl sulfate.
Sodium dodecyl diphenyl ether disulfonate,
Anionic surfactants such as sodium succinate dialkyl ester sulfonate, nonionic surfactants such as polyoxyethylene alkyl ester, polyoxyethylene alkyl allyl ether, and amphoteric surfactants such as lauryl betaine and stearyl betaine. Examples thereof include alkyl betaine type salts such as salts, amino acid type salts such as lauryl-β-alanine, lauryl di (aminoethyl) glycine, and octyl di (aminoethyl) glycine salts. These may be used alone or in combination of two or more. Of these emulsifiers, sodium dodecylbenzene sulfonate and sodium dodecyl diphenyl ether disulfonate are particularly preferable.

The amount of emulsifier used is 100 parts of the total monomer mixture.
It is usually about 0.05 to 2.5 parts by weight, preferably about 0.1 to 1.5 parts by weight per part by weight. When the amount of the emulsifier used exceeds 2.5 parts by weight, the water resistance of the resulting coated paper is poor and the composition for paper coating may be prone to foaming, which is not preferable. If necessary, a chelating agent such as sodium ethylenediaminetetraacetate, a dispersant such as sodium formaldehyde sulfoxylate, and an inorganic salt may be added.

As the emulsion polymerization method in the present invention, either a seed polymerization method or a non-seed polymerization method can be used. The seed polymerization method, an internal system in which a part of the mixture of the monomers to be used is put in a polymerization vessel in advance and reacted, and then the remaining monomer mixture is added,
There is an external system in which an ultrafine particle size latex is prepared in advance, a predetermined amount is put in a polymerization vessel, and then a monomer mixture is added thereto. The non-seed polymerization method is a method in which a predetermined amount of emulsifier is put in a polymerization vessel in advance and the monomer mixture is added thereto. In any case, the addition method of the monomer mixture and the polymerization chain transfer agent may be a batch addition method, a divided addition method, a continuous addition method, or a combination thereof. In the case of the divided addition method, the composition and the amount of the monomer mixture and the polymerization chain transfer agent mixture may be changed at each stage. Also in the case of the continuous addition system, the composition and the amount of the monomer mixture and the polymerization chain transfer agent mixture may be continuously or intermittently changed with the addition time. The polymerization conversion rate in the production of the copolymer latex of the present invention is preferably about 90% by weight or more, more preferably about 95% by weight or more.

The copolymer latex of the present invention can be used as a binder for a paper coating composition and as various adhesives such as carpet backing agents, paints, and industrial and household adhesives. Among them, it is advantageously used as a binder for a paper coating composition.

To obtain a paper coating composition using the copolymer latex of the present invention, for example, kaolin clay, talc,
Inorganic pigments such as titanium oxide, calcium carbonate, aluminum hydroxide, satin white, such as casein, starch,
A natural binder such as protein, for example, a synthetic latex such as polyvinyl alcohol or polyvinyl acetate emulsion is appropriately blended by a known method. Further, known additives such as a dispersant, a defoaming agent, a leveling agent, a preservative, a water-proofing agent, and a release agent can be added if necessary.
The paper coating composition containing the copolymer latex of the present invention can be applied using a conventionally known method, for example, an air knife coater, a blade coater, a roll coater, an applicator or the like.

[0024]

The present invention will be described in more detail below with reference to specific examples. In addition, all "%" and "part" of an Example are weight standards. Example 1 5 parts of 1,3-butadiene, 6 parts of styrene, 6 parts of methyl methacrylate, 2 parts of fumaric acid, 0.5 part of potassium persulfate, 100 parts of water, 100 parts of sodium alkylbenzene sulfonate were added to a nitrogen-substituted 5 l autoclave. 1 part and 0.05 part of 2-mercaptopropionic acid were charged and reacted at 70 ° C. with stirring. After 2 hours, the remaining monomers of butadiene 30 parts, styrene 45 parts, methyl methacrylate 8 parts, acrylic acid 1 part, methacrylic acid 1 part, 2-
0.2 part of mercaptopropionic acid was charged with 0.5 part of sodium alkylbenzene sulfonate. After 15 hours of reaction time, when the polymerization conversion rate reached 97% or more (per 100 parts of the monomer), it was cooled to 30 ° C. and adjusted to pH 7.5 ± 0.2 with sodium hydroxide. Next, steam was blown to remove unreacted monomers, and the solid content of the latex was concentrated to 50% to obtain the desired latex. Next, the obtained latex was used to prepare a paper coating composition having the following composition. Ultra White-90 (Engelhard, first grade kaolin) 70 parts Carbital-90 (Ecc, heavy calcium carbonate) 30 parts Aron T-40 (manufactured by Toagosei Chemical Industry Co., Ltd., sodium polyacrylate) 0 .1 part Copolymer latex 14 parts Modified starch MS-4600 (manufactured by Nippon Shokuhin Kako Co., Ltd.) 3 parts Water amount to make total solid content 60% by weight Coating amount of this paper coating composition is 15.0 ± 0 0.5 g / m ²
So that the basis weight was 64 g / m ² on both sides of the high-quality paper, and then dried with a hot air dryer at 120 ° C. for 30 seconds. The obtained coated paper was left to stand overnight at 23 ° C. and 60% RH, and then subjected to super calender treatment twice at a linear pressure of 100 kg / cm and a roll temperature of 70 ° C. The physical properties of the obtained coated paper were measured, and the results are shown in [Table 3].

Examples 2 to 15 Emulsion copolymerization was conducted in the same manner as in Example 1 except that the polymerization was carried out with the monomer composition and the polymerization chain transfer agent composition shown in [Table 1] and [Table 2]. Then, latex was produced, and after adjusting the composition for paper coating, a coated paper was obtained. The results of measuring the physical properties of the obtained coated paper are shown in [Table 3] and [Table 4].

Comparative Examples 1 to 5 Emulsion copolymerization was carried out in the same manner as in Example 1 except that the monomer composition and the polymerization chain transfer agent composition shown in Table 2 were used to produce a latex. Then, after adjusting the composition for paper coating, a coated paper was obtained. The results of measuring the physical properties of the obtained coated paper are shown in [Table 4].

The physical properties in [Table 3] and [Table 4] were measured and evaluated by the following methods. (1) Toluene-insoluble matter (gel content) The obtained copolymer latex is poured into a glass mold,
A film having a thickness of 0.3 mm is prepared. This film is cut into 2 to 3 mm squares and 0.4 g is finely ground. The sample is immersed in 100 ml of toluene and shaken in a shaking constant temperature bath at 30 ° C. for 6 hours. After that, the solid content of the filtrate is obtained by filtering with a 100 mesh wire mesh, and the gel content is calculated from this sol solid content. (2) Adhesive strength (dry pick) Using a RI tester (manufactured by Akira Seisakusho), tack No. 10
Overprint several times with the black ink. The picking of the printing surface is visually judged. The larger the number is, the better the five-level evaluation is. (3) Water resistance (wet pick) Using a RI tester, water was applied to the surface of the test piece with a molton roll, and immediately after that, tack No. Printing is performed with 12 red inks, and picking of the printed surface is visually judged. The larger the number is, the better the five-level evaluation is. (4) Ink inking property It is measured by the same method as water resistance, but ink with a lower tack value is used for printing to prevent picking, and the state of ink transfer is visually compared. It was judged. The larger the number is, the better the five-level evaluation is. (5) White Paper Gloss The gloss value of the coated paper at 75 ° -75 ° is measured using a Murakami gloss meter. (6) Suitability for blister Double-sided solid printing is performed with a web offset ink, and the temperature at the time of blister generation is measured by a blister tester (manufactured by Kumagai Riki).

[0028]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

From the examples and comparative examples, the coated paper obtained using the copolymer latex of the present invention is excellent in all physical properties such as adhesive strength, water resistance, ink receptivity and white paper gloss. That is clear.

[0030]

The copolymer latex produced by the method of the present invention is excellent in adhesive strength, water resistance, ink receptivity and white paper gloss, and therefore coated paper, especially coated paper for offset rotary printing. In addition to being advantageously used as a binder for the paper coating composition of
It can be used for various adhesive applications such as paints, industrial and household adhesives.

Claims (9)

[Claims] 1. A monomer mixture containing (1) a conjugated diene-based monomer, (2) an ethylenically unsaturated monomer, and (3) an ethylenically unsaturated carboxylic acid monomer is converted into a carboxyl group or its group. A method for producing a copolymer latex, which comprises emulsion-polymerizing in the presence of a water-soluble polymerization chain transfer agent having at least one hydrophilic group selected from salts and amino groups and at least one mercapto group. 2. The monomer mixture comprises 10 to 80% by weight, based on the total monomer mixture, of the (1) conjugated diene monomer, 20 to 20.
90% by weight of (2) ethylenically unsaturated monomer and
The method for producing a copolymer latex according to claim 1, which is a monomer mixture containing 2 to 12% by weight of (3) ethylenically unsaturated carboxylic acid monomer. 3. The method for producing a copolymer latex according to claim 1, wherein the water-soluble polymerization chain transfer agent is a compound represented by the following general formula. [In the formula, R represents a hydrocarbon residue which may be substituted with halogen, X ₁ represents one group selected from a carboxyl group or a salt thereof, and an amino group, X ₂ represents a hydrogen atom, a hydroxyl group, One group selected from a carboxyl group or a salt thereof and an amino group is shown. ] 4. The method for producing a copolymer latex according to claim 1, wherein the water-soluble polymerization chain transfer agent is a mercaptan carboxylic acid or a salt thereof. 5. The method for producing a copolymer latex according to claim 4, wherein the mercaptan carboxylic acid is 2-mercaptopropionic acid. 6. The method for producing a copolymer latex according to claim 4, wherein the mercaptan carboxylic acid is 3-mercaptopropionic acid. 7. The method for producing a copolymer latex according to claim 4, wherein the mercaptancarboxylic acid is mercaptoacetic acid. 8. A monomer mixture containing (1) a conjugated diene-based monomer, (2) an ethylenically unsaturated monomer, and (3) an ethylenically unsaturated carboxylic acid monomer is converted into a carboxyl group or its group. A copolymer latex obtained by emulsion polymerization in the presence of a water-soluble polymerization chain transfer agent having at least one hydrophilic group selected from salts and amino groups and at least one mercapto group. 9. A composition for paper coating, which comprises the copolymer latex according to claim 8.