JP3242972B2 - Method for producing copolymer latex, copolymer latex, and paper coating composition using the same - Google Patents

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, which is characterized by carrying out emulsion polymerization by devising a method for adding a specific polymerization chain transfer agent, and more particularly, to an adhesive strength in coated paper. A method for producing a copolymer latex that is useful as a binder for a paper coating composition with excellent balance in physical properties such as water resistance, ink adhesion, and glossiness of white paper, and can also be used as a backing agent or adhesive for carpets. About.

[0002]

2. Description of the Related Art In recent years, as the demand for coated paper has increased rapidly, the production speed of paper coating has increased, and the printing speed has been increased in order to increase the production of printed matter.
Particularly in offset printing, this tendency is increasing. For this reason, the following properties are required for the copolymer latex which is a component of the paper coating composition and is used as a binder. One of them is to have excellent adhesive strength. If the adhesive strength is low, the pigment will fall off and the coated layer will peel off from the base paper due to the mechanical force on the pigment coated paper surface during printing. Such destruction of the paper surface becomes more severe as the printing speed increases and the number of times of overprinting 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, in offset printing, since "fountain solution" is used, it is required that the pigment-coated paper surface has strength against mechanical force by printing in a wet state, that is, water resistance.
Yet another property is that with the speeding up of printing,
Further superior ink inking property is required as compared with the related art. In addition to the above properties, coated paper is required to have optical properties such as glossiness of white paper.

[0003] As described above, the coated paper has an adhesive strength, water resistance,
Various properties such as ink deposition and blank gloss are required,
Heretofore, there has been no coated paper which balances these properties at a high level. The reason for this is that the adhesive strength, the water resistance, the ink inking property, and the glossiness of the white paper are mutually contradictory to each other. That is, as a method for improving the water resistance, a method in which the gel content of a polymer latex used as a binder is relatively low is conventionally known. However, when the gel content is reduced, the adhesive strength and ink inking property are reduced. If the gel content is further reduced, the water resistance also decreases. As a method for improving the ink inking property and the glossiness of white paper, a method of increasing the particle diameter of the polymer latex or increasing the glass transition temperature is known, but if this method is performed, the adhesive strength and water resistance are improved. There is a technically difficult problem that the performance is reduced.

[0004]

SUMMARY OF THE INVENTION The present inventors have conducted intensive studies in view of the above-mentioned problems of the prior art, and as a result, have found that a conjugated diene monomer, an ethylenically unsaturated monomer and In the emulsion polymerization of a monomer mixture containing an ethylenically unsaturated carboxylic acid monomer, two
A polymerization chain transfer agent having a solubility in water at 0 ° C. of 0.006 mol / L or more is used, and the solubility in water at 20 ° C. is 0.0
By using a polymerization chain transfer agent of less than 06 mol / liter, a copolymer which can be used in a paper coating composition having a well-balanced adhesive strength, water resistance, ink inking property, white paper gloss and the like in coated paper. The inventor has found that latex can be obtained, and as a result of further research, the present invention has been completed.

[0005]

[Means for Solving the Problems] That is, the present invention provides:
In emulsion-polymerizing a monomer mixture containing (1) a conjugated diene monomer, (2) an ethylenically unsaturated monomer, and (3) an ethylenically unsaturated carboxylic acid monomer, (a) first, 0.5 to 60 parts by weight of 100 parts by weight of the monomer mixture is 0.006 parts by weight in water at 20 ° C.
Emulsion polymerization is carried out in the presence of a polymerization chain transfer agent of not less than mol / l to obtain a copolymer latex (a), (b) Then, the remaining monomer mixture is converted into a copolymer latex (a)
0.006m in water at 20 ° C
The present invention relates to a method for producing a copolymer latex, wherein emulsion polymerization is carried out in the presence of a polymerization chain transfer agent of less than ol / liter. Hereinafter, the present invention will be described in detail.

The conjugated diene monomer (1) used in the present invention includes, for example, 1,3-butadiene, isoprene, 2-chloro-1,3-butadiene, 2-methyl-
What is usually used at the time of latex manufacture, such as 1,3-butadiene, is mentioned. These monomers (1) are used alone or in combination of two or more. Of these, 1,3-butadiene is particularly preferred. The monomer (1) is used for imparting appropriate elasticity and film hardness to the obtained copolymer. The amount of the monomer (1) used is about 10 to 80% by weight, preferably about 20 to 60% by weight, based on the total monomer mixture. 10% by weight
If the amount is less than the above, sufficient adhesive strength of the obtained coated paper may not be obtained, while if it is more than 80% by weight, the water resistance and the adhesive strength may decrease.

The ethylenically unsaturated monomer (2) used in the present invention includes, for example, aromatic vinyl compounds such as styrene, α-methylstyrene, vinyltoluene and p-methylstyrene, for example, methyl acrylate, acrylic acid Alkyl or methacrylic acid alkyl ester compounds such as ethyl, butyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, and glycidyl methacrylate, for example, acrylamide, methacrylamide, N, N-dimethyl Acrylamide or acrylamide or methacrylamide compound of ethylenically unsaturated carboxylic acid such as N-methylol acrylamide, for example, carboxylic acid vinyl esters such as vinyl acetate, for example, acrylonitrile, methacrylonitrile, α- Vinyl cyanide compounds such as chloroacrylonitrile, for example, 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, And ethylenically unsaturated monomers other than (a). These are used alone or in combination of two or more. Of these, styrene is particularly preferred as the aromatic vinyl compound, methyl methacrylate is preferred as the alkyl ester compound, and acrylonitrile is preferred as the vinyl cyanide compound. The amount of the monomer (2) used is about 20 to 90% by weight, preferably about 40 to 80% by weight, based on the total monomer mixture.
It is. If the amount is too small, the resulting coated paper may have poor water resistance, 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. Acids or their anhydrides, for example, half esters such as methyl maleate and methyl itaconate can be mentioned. These are used alone or in combination of two or more. The amount of the monomer (3) is about 0.2 to 12% by weight, preferably about 0.5 to 8% by weight, based on the total monomer mixture. When the amount 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.If the amount is too large, the viscosity of the copolymer latex is high. It may be too practical to be practical.

As the polymerization chain transfer agent having a solubility in water at 20 ° C. of not less than 0.006 mol / liter (hereinafter referred to as a highly soluble polymerization chain transfer agent) used in the present invention, any one having such a solubility can be used. Any one may be used, for example, alkyl mercaptans having 4 or less carbon atoms such as ethyl mercaptan and n-butyl mercaptan;
For example, a mercaptancarboxylic acid such as 2-mercaptopropionic acid, 3-mercaptopropionic acid, and mercaptoacetic acid or a salt thereof (for example, ammonium mercaptoacetate); for example, a mercaptandicarboxylic acid such as mercaptosuccinic acid or a salt thereof (for example, mercaptandicarboxylate) For example, mercaptans having a hydroxyl group in the molecule such as 2-mercaptoethanol and 3-mercapto-1,2-propanediol, such as mercaptans having an amino group in the molecule such as 2-mercaptoethylamine, such as thioglycolic acid; Monosulfides having a carboxyl group in the molecule such as 3,3'-thiodipropionic acid or salts thereof, for example, monosulfides having a hydroxyl group in the molecule such as β-thiodiglycol such as thiodiethylamido Monosulfide compound having an amino group in the molecule, such as, for example, dithiodiglycolic acid, 2,
Disulfides having a carboxyl group in the molecule such as 2'-dithiodipropionic acid, 3,3'-dithiodipropionic acid, and 4,4'-dithiodibutyric acid, or salts thereof, such as thiodiglycolic anhydride; As described above, acid anhydrides of monosulfides and disulfides such as D-, L
-Or monosulfides and disulfides having a carboxyl group and an amino group in the molecule such as DL-cystine and the like, for example, chloromethanol, 2-chloroethanol, 1-chloro-2-propanol, 2 or 3-
Halogenated hydrocarbons having a hydroxyl group in the molecule such as chloro-n-propanol, 2-, 3- or 4-chloro-n-butanol, chloropentanol, for example, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, chlorodifluoroacetic acid , 2-chloropropionic acid, 3-chloropropionic acid, 2-bromopropionic acid, 3-bromopropionic acid, 2-bromopentanoic acid, chlorosuccinic acid, chlorofumaric acid, chloromaleic acid, chloromalonic acid, etc. Examples thereof include halogenated hydrocarbons having a carboxyl group or salts thereof, for example, acid anhydrides of halogenated hydrocarbons such as chloromaleic anhydride.

Among the highly soluble polymerization chain transfer agents used in the present invention, those having at least one carboxyl group are preferably used in the present invention because they generate little coagulated product and have excellent polymerization stability. Can be The amount of the highly soluble chain transfer agent used in all the polymerization stages of (a) and (b) is about 0.005 to 8 parts by weight, preferably about 0. The range is from 01 to 5 parts by weight. If the amount used is less than 0.005 parts by weight, the adhesive strength and water resistance may be inferior, and if it exceeds 8 parts by weight, the adhesive strength may also decrease. These are used alone or in combination of two or more.

The polymerization chain transfer agent having a solubility in water at 20 ° C. of less than 0.006 mol / liter (hereinafter referred to as a low solubility polymerization chain transfer agent) used in the present invention is generally used in emulsion polymerization. The solubility in water at 20 ° C. is 0.006 mol
Any known polymerization chain transfer agent of less than 1 / liter may be used. Specifically, for example, hexyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-hexadecyl mercaptan, t-hexa Alkyl mercaptans having 5 or more carbon atoms, such as decyl mercaptan, n-tetradecyl mercaptan, and t-tetradecyl mercaptan, for example, xanthogen disulfides such as dimethyl xanthogen disulfide, diethyl xanthogen disulfide, and diisopropyl xanthogen disulfide, for example, tetramethylthiuram disulfide Disulfides such as thiamine, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, for example, carbon tetrachloride, carbon tetrabromide, ethylene bromide What halogenated hydrocarbons, and 2-ethylhexyl thioglycolate, alpha-methylstyrene dimer, terpinolene, alpha-terpinene, .gamma.
Terpinene, dipentene and the like can be mentioned. These are used alone or in combination of two or more. Of these, alkyl mercaptans, xanthogen disulfide, thiuram disulfide, carbon tetrachloride,
α-Methylstyrene dimer, terpinolene and the like are preferred, and more preferred are alkyl mercaptans having 14 to 16 carbon atoms such as, for example, n-hexadecyl mercaptan, t-hexadecyl mercaptan, n-tetradecyl mercaptan and t-tetradecyl mercaptan. No. The proportion of the low solubility polymerization chain transfer agent used in all the polymerization stages of (a) and (b) is less than about 99.5% by weight, preferably about 98%, of the total polymerization chain transfer agent used.
% By weight. When the use ratio is 99.5% by weight or more, the obtained coated paper may have poor physical properties such as adhesive strength, water resistance, ink adhesion, and white paper gloss.

The copolymer latex of the present invention can be emulsified by a conventionally known emulsion polymerization method, that is, by adding a monomer mixture, a polymerization initiator, an emulsifier, a polymerization chain transfer agent and the like to an aqueous medium (eg, water). Obtained by performing polymerization. The polymerization initiator used in the emulsion polymerization of the present invention is not particularly limited. For example, inorganic persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, such as cumene hydroperoxide and benzoyl peroxide Organic peroxides such as isopropylbenzene peroxide and azo-based 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 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 usually about 0.1 to 5 per 100 parts by weight of all monomers.
Parts by weight, preferably about 0.2 to 2 parts by weight.

The emulsifier used in the emulsion polymerization of the present invention is not particularly limited. For example, sodium dodecylbenzenesulfonate, sodium lauryl sulfate,
Sodium dodecyl diphenyl ether disulfonate,
Examples of anionic surfactants such as dialkyl succinate sodium sulfonate and the like, nonionic surfactants such as polyoxyethylene alkyl ester and polyoxyethylene alkyl allyl ether, and examples of the amphoteric surfactant include lauryl betaine and stearyl betaine. Examples thereof include alkyl betaine-type salts such as salts, and amino acid-type salts such as salts of lauryl-β-alanine, lauryl di (aminoethyl) glycine, and octyldi (aminoethyl) glycine. These can be used alone or in combination of two or more. Among these emulsifiers, in particular, sodium dodecylbenzenesulfonate,
Sodium dodecyl diphenyl ether disulfonate and the like are preferred. The amount of emulsifier used is 10
The amount is usually about 0.05 to 2.5 parts by weight, preferably about 0.1 to 1.5 parts by weight, per 0 parts by weight. When the use amount of the emulsifier exceeds 2.5 parts by weight, the water resistance of the coated paper obtained is poor, and the foaming of the paper coating composition may become severe.

If necessary, a chelating agent such as sodium ethylenediaminetetraacetate, a dispersant such as sodium formaldehyde sulfoxylate, and an inorganic salt can be added. The method for producing a copolymer latex of the present invention is a multi-stage polymerization method in which a monomer mixture is polymerized in two or more stages. That is, (a) First, 0.5 to 60 parts by weight of 100 parts by weight of the monomer mixture is
The solubility in water at 20 ° C. is 0.006 mol /
Emulsion copolymerization in the presence of a polymerization chain transfer agent of at least 1 liter to obtain a copolymer latex (a), and (b) the remaining monomer mixture is then mixed with the copolymer latex (a) and 2
Emulsion polymerization is carried out in the presence of a polymerization chain transfer agent having a solubility in water at 0 ° C. of less than 0.006 mol / l.

At this time, a low solubility polymerization chain transfer agent may be used in combination in the polymerization step (a), and a high solubility polymerization chain transfer agent may be used in combination in the polymerization step (b).
In the polymerization step (a), about 20% by weight or more, preferably about 2% by weight of the total polymerization chain transfer agent used in this step.
5% by weight or more is a highly water-soluble polymerization chain transfer agent, and (b)
In the weight step, about 40% by weight or more, preferably about 50% by weight, of the total polymerization chain transfer agent used in the step
The above is the low solubility polymerization chain transfer agent. As a method of adding the monomer mixture and the polymerization chain transfer agent mixture at each stage, either a batch addition method or a continuous addition method, or a combination of both methods may be used. In the case of the continuous addition method, the composition and amount of the monomer mixture and the polymerization chain transfer agent mixture may be changed continuously or intermittently with the addition time within the above-mentioned range.

The polymerization conversion 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, as a carpet backing agent, a paint, and various adhesives such as industrial and household adhesives. It is advantageously used as a binder in a coating composition. In order to obtain a paper coating composition using the copolymer latex of the present invention, inorganic pigments such as kaolin clay, talc, titanium oxide, calcium carbonate, aluminum hydroxide, and satin white, for example, casein,
A natural binder such as starch or protein, for example, a synthetic latex such as polyvinyl alcohol or polyvinyl acetate emulsion is appropriately blended by a known method. Further, known components such as a dispersant, an antifoaming agent, a leveling agent, a preservative, a waterproofing agent, and a release agent can be added as required. The paper coating composition containing the copolymer latex of the present invention can be applied by a conventionally known method, for example, using an air knife coater, blade coater, roll coater, applicator, or the like.

[0017]

The present invention will be described below in more detail with reference to specific examples. In the examples, "%" and "part" are all based on weight. Example 1 In a 5-liter autoclave purged with nitrogen, 5 parts of 1,3-butadiene, 6 parts of styrene, 2 parts of methyl methacrylate,
Fumaric acid 2 parts, potassium persulfate 0.5 part, water 100 parts,
0.1 part of sodium alkylbenzenesulfonate and 0.05 part of 2-mercaptopropionic acid were charged and reacted at 70 ° C. with stirring. After 2 hours, 30 parts of 1,3-butadiene and 45 parts of styrene as the remaining monomers
Parts, methyl methacrylate 8 parts, acrylic acid 1 part, methacrylic acid 1 part, 2-mercaptopropionic acid 0.2 part, t
0.2 parts of dodecyl mercaptan were charged together with 0.5 parts of sodium alkylbenzenesulfonate. After a reaction time of 15 hours, when the polymerization conversion reached 97% or more (per 100 parts of monomer), the mixture was cooled to 30 ° C. and adjusted to pH 7.5 ± 0.2 using sodium hydroxide. Then, steam was blown to remove unreacted monomers, and the solid content of the latex was further concentrated to 50% to obtain the desired latex. Next, a paper coating composition having the following composition was prepared using the obtained latex. Ultra White-90 (first grade kaolin, manufactured by Engelhard) 70 parts Carbital-90 (heavy calcium carbonate, manufactured by Ecc) 30 parts Alon T-40 (sodium polyacrylate, manufactured by Toa Gosei Chemical Industry Co., Ltd.) 0 .1 part Copolymer latex 14 parts Modified starch MS-4600 (manufactured by Nippon Shokuhin Kako Co., Ltd.) 3 parts Water Amount that total solid content becomes 60% by weight. Coating amount of this paper coating composition is 15.0 ± 0. 0.5 g / m ²
The coated paper was coated on both sides of a high-quality paper having a basis weight of 64 g / m ² and dried with a hot-air dryer at 120 ° C. for 30 seconds. The resulting coated paper was allowed to stand at 23 ° C. and 60% RH for 24 hours, and then subjected to a 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 9].

Examples 2 to 21 The procedure was carried out except that the polymerization was carried out with the monomer composition and the polymerization chain transfer agent composition shown in Tables 1 to 3 and Tables 5 to 7. A latex was produced by emulsion copolymerization in the same manner as in Example 1, and a paper coating composition was prepared, to obtain a coated paper. The results of measuring the physical properties of the obtained coated paper are shown in [Table 9] to [Table 11].

Comparative Examples 1 to 8 Emulsion copolymerization was carried out in the same manner as in Example 1 except that the polymerization was carried out using the monomer composition and the polymerization chain transfer agent composition shown in Tables 4 and 8. Then, a latex was produced to prepare a paper coating composition, and a coated paper was obtained. The results of measuring the physical properties of the obtained coated paper are shown in [Table 12]. In addition,
Each physical property in [Table 9] to [Table 12] was measured and evaluated by the following methods. (1) Toluene-insoluble content (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 a 2-3 mm square, and 0.4 g of the film is refined. The sample is immersed in 100 ml of toluene and shaken in a shaking thermostat at 30 ° C. for 6 hours. Thereafter, the mixture is filtered through a 100-mesh wire gauze, the solid content of the filtrate is obtained, and the gel content is calculated from the solid content of the sol. (2) Adhesive strength (dry pick) Tack No. was measured using an RI tester (manufactured by Mei Seisakusho) 10
Overprint several times with black ink. The picking of the printing surface is visually determined. The higher the number in the five-level evaluation, the better. (3) Water resistance (wet pick) Using a RI tester, water was supplied to the test piece surface with a Molton roll. Printing is performed with twelve red inks, and the picking of the printed surface is visually determined. The higher the number in the five-level evaluation, the better. (4) Ink adhesion property Measure by the same method as for water resistance, but print using ink with a lower tack value than in the case of water resistance measurement so as not to cause picking, and compare the state of ink transfer with the naked eye. Judged. The higher the number in the five-level evaluation, the better. (5) Blank Gloss The gloss value of the coated paper at 75 ° to 75 ° is measured using a Murakami gloss meter. (6) Blister aptitude Perform double-sided solid printing with a web offset ink, and measure the temperature at the time of blister generation with a blister tester (manufactured by Kumagai Riki). From the examples and comparative examples, the coated paper obtained by using the copolymer latex of the present invention has excellent balance of physical properties in adhesive strength, water resistance, ink inking property and white paper gloss. It is clear that the coated paper is excellent in overall physical properties.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

[Table 4]

[0024]

[Table 5]

[0025]

[Table 6]

[0026]

[Table 7]

[0027]

[Table 8]

[0028]

[Table 9]

[0029]

[Table 10]

[0030]

[Table 11]

[0031]

[Table 12]

[0032]

EFFECT OF THE INVENTION The copolymer latex produced by the method of the present invention is excellent in physical properties such as adhesive strength, water resistance, ink inking property and glossiness of white paper. It is advantageously used as a binder in a paper coating composition for rotary printing coated paper, and can be used for various adhesive applications such as carpet backing agents, paints, industrial and household adhesives.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-55-12197 (JP, A) JP-A-5-320216 (JP, A) JP-A-5-117308 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C08F 2/38-2/42 C08F 2/22-2/30 D21H 19/56-19/58

Claims (3)

(57) [Claims] 1. An emulsion polymerization of a monomer mixture containing (1) a conjugated diene monomer, (2) an ethylenically unsaturated monomer, and (3) an ethylenically unsaturated carboxylic acid monomer. (A) First, 0.5 to 60 parts by weight of 100 parts by weight of the monomer mixture is emulsion-polymerized in the presence of a polymerization chain transfer agent having a solubility in water at 20 ° C. of 0.006 mol / L or more. To obtain a copolymer latex (a), and (b) a polymerization chain transfer agent having a solubility in the copolymer latex (a) and water at 20 ° C. of less than 0.006 mol / liter. A process for producing a copolymer latex, which is carried out by emulsion polymerization in the presence of a polymer. 2. Emulsion polymerization of a monomer mixture containing (1) a conjugated diene monomer, (2) an ethylenically unsaturated monomer and (3) an ethylenically unsaturated carboxylic acid monomer. (A) First, 0.5 to 60 parts by weight of 100 parts by weight of the monomer mixture is emulsion-polymerized in the presence of a polymerization chain transfer agent having a solubility in water at 20 ° C. of 0.006 mol / L or more. To obtain a copolymer latex (a), and (b) a polymerization chain transfer agent having a solubility in the copolymer latex (a) and water at 20 ° C. of less than 0.006 mol / liter. Copolymer latex obtained by emulsion polymerization in the presence of 3. A paper coating composition comprising the copolymer latex according to claim 2.