JP2002097204A - Copolymer latex, its production method and paper coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copolymer latex for a paper coating which has excellent blocking resistance and excellent balance between the dry-pick strength, the wet-pick strength and anti-blister property of a coated paper, and to provide a producing method therefor and a paper coating composition using the latex. SOLUTION: The producing method for the latex is characterized in that a monomer of 100 pts.wt. comprising (a) a conjugated diene monomer of 29-71 wt.%, (b) an ethylenic unsaturated nitrile monomer of 20-50 wt.% and (c) other copolymerizable ethylenic unsaturated monomer of 9-51 wt.% is subjected to emulsion polymerization in two steps. In the first step, the monomer of 30-70 pts.wt. comprising (a) the conjugated diene monomer, (b) the ethylenic unsaturated nitrile monomer and (c) other copolymerizable ethylenic unsaturated monomer is subjected to emulsion polymerization until the polymerization conversion rate reaches to 70% or more and, in the second step, it is subjected to emulsion polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copolymer latex suitable for paper coating, a method for producing the same, and a paper coating composition. More specifically, the present invention is excellent in blocking resistance, improved dry pick strength in coated paper, wet pick strength, and improved the balance of blister resistance,
The present invention relates to a copolymer latex for paper coating, a method for producing the same, and a paper coating composition using the same.

[0002]

2. Description of the Related Art In recent years, with the rapid development of printing technology such as high-speed printing, the quality required for coated paper has become increasingly severe. In particular, for the purpose of cost reduction, there is a trend to reduce the number of parts of the latex with respect to the pigment,
Improvement in surface strength (dry pick strength), which is a basic performance as a binder, is strongly required for copolymer latex. Even with surface strength, in the case of offset printing,
Since the dampening water is involved, water resistance is a problem, and a high surface strength (wet pick strength) when the coating layer is wet is also required. Also, in the production of coated paper, the demand for coating operability (stickiness of latex film) typified by roll dirt suitability has become strict with high-speed coating. Further, in offset printing, high-speed printing is followed by drying at a high temperature, so that blisters are easily generated. Conventionally, in order to improve the blister resistance, a solvent-insoluble component (gel amount) such as toluene or tetrahydrofuran of the latex film has been reduced, but the surface strength has been reduced accordingly.

Hitherto, as a means for balancing surface strength and operability, a two-stage polymerization has been proposed in which the inside is increased with a soft monomer such as butadiene and the outside is increased with a hard monomer such as styrene and acrylonitrile. Kaihei 7-
247327, JP-A-7-258308, JP-A-7-324112). However, although these methods are very effective for improving the surface strength and improving the balance with operability,
The balance with the wet pick strength was lacking, and the blister resistance had to be reduced as much as the surface strength was improved.

[0004]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is based on the background described above, which is excellent in blocking resistance and balances dry pick strength, wet pick strength and blister resistance in coated paper. An object of the present invention is to provide an excellent copolymer latex for paper coating, a method for producing the same, and a paper coating composition using the same.

The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, have obtained a copolymer latex for paper coating which has better surface strength than the known two-stage polymerization of inner soft outer rigid type. This led to the completion of the present invention based on this finding.

[0006]

According to the present invention, the following solutions are provided. (1) (a) 29 to 71% by weight of a conjugated diene monomer, (b) 20 to 50% by weight of an ethylenically unsaturated nitrile monomer, (c) other copolymerizable ethylenically unsaturated monomer 9 To 51% by weight of a monomer latex (where (a) + (b) + (c) = 100% by weight) in a two-stage emulsion polymerization method. (A-1) 50 to 80% by weight of a conjugated diene monomer (b-1) 20 to 50% of an ethylenically unsaturated nitrile monomer
% By weight (c-1) Other copolymerizable ethylenically unsaturated monomers 0 to 30% by weight (where (a-1) + (b-1) + (c-1) = 10
0% by weight. ) Is emulsion-polymerized until the polymerization conversion reaches 70% or more, and as a second step, (a-2) a conjugated diene monomer 20 to 50% by weight (b- 2) ethylenically unsaturated nitrile monomer 20-50
% By weight (c-2) 30-60% by weight of other copolymerizable ethylenically unsaturated monomers (where (a-2) + (b-2) + (c-2) = 10
0% by weight. (30) to 70 parts by weight of a monomer composed of the following (1) (where the first-stage monomer mixture + the second-stage monomer mixture = 100 parts by weight). (2) A method for producing a copolymer latex according to (1), wherein the polymerization temperature T (° C.) in the first-stage emulsion polymerization satisfies the following formula (1): 0 ≦ T ≦ 150 -{(A-1) + (b-1)} (1) (where (a-1) and (b-1) are
This corresponds to the ratio (% by weight) of the conjugated diene monomer and the ethylenically unsaturated nitrile monomer in the first-stage emulsion polymerization. ), (3) a copolymer latex obtained by the method for producing a copolymer latex according to (1) or (2),
(4) Copolymer latex tetrahydrofuran (TH
F) From the main peak areas derived from the conjugated diene unit and the ethylenically unsaturated nitrile monomer unit in the pyrolysis chromatography of the insoluble matter and the soluble matter, the γ value defined by the following formula (2) is 0. 60 or more and 0.85 or less, the copolymer latex according to (3),

(Equation 2) (Where, AS _Di : a main peak area derived from a conjugated diene unit in a THF-soluble portion; AS _Ni : a main peak area derived from an ethylenically unsaturated nitrile monomer unit in a THF-soluble portion; AG _Di : a conjugated portion in a THF-insoluble portion. Main peak area derived from diene unit AG _Ni : Main peak area derived from ethylenically unsaturated nitrile monomer unit in THF-insoluble portion), (5) (3) or (4) A paper coating composition comprising a pigment.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a copolymer latex of the present invention, 29-71% by weight of the conjugated diene monomer ("29% by weight or more, 71%
% By weight or less ", and the same applies hereinafter. ),
(B) 20 to 50% by weight of an ethylenically unsaturated nitrile monomer, and (c) 9 to 51% by weight of another copolymerizable ethylenically unsaturated monomer copolymerizable with (a) and (b). %, And 100 parts by weight of the monomer consisting of the above components are emulsion-polymerized in two stages. (A) The conjugated diene monomer is used in an amount of 29 to 71% by weight, preferably 34 to 63% by weight. The conjugated diene monomer is
If it is less than 29% by weight, the dry pick strength decreases, and if it exceeds 71% by weight, the wet topic strength and the blocking resistance decrease. (B) The ethylenically unsaturated nitrile monomer is 20 to 50
%, Preferably 25-42% by weight. When the amount of the ethylenically unsaturated nitrile monomer is less than 20% by weight, dry pick strength, wet pick strength and blister resistance decrease, and when it exceeds 50% by weight, dry pick strength decreases. (C) Other copolymerizable ethylenically unsaturated monomers include:
It is used in an amount of 9 to 51% by weight, preferably 12 to 41% by weight. Other copolymerizable ethylenically unsaturated monomers are 9
If the amount is less than 5% by weight, the balance between the dry pick strength and the wet pick strength decreases. If the amount exceeds 51% by weight, the balance between the dry pick strength, the wet pick strength and the blister resistance decreases.

The copolymer latex of the present invention is produced by two-stage emulsion polymerization. In the first-stage emulsion polymerization, a monomer comprising at least (a) and (b) as essential components and (c) as an optional component 30 to 70 parts by weight of the mixture was charged, and when the polymerization conversion in the first stage reached 70% or more, the emulsion polymerization in the second stage was carried out using the monomers comprising (a), (b) and (c). 70 to 30 parts by weight of the mixture (the total of the monomer mixture charged in the first and second stages of emulsion polymerization is 100 parts by weight). The charged composition of the conjugated diene monomer (a-1) and the ethylenically unsaturated nitrile monomer (b-1) in the monomer mixture in the first-stage emulsion polymerization is 70 to 100.
% By weight, and the charged composition of the conjugated diene monomer (a-2) and the ethylenically unsaturated nitrile in the monomer mixture added in the second stage is 40 to 70% by weight. When the ratio of the monomer mixture of the first stage and the second stage is out of the range of the present invention, the balance of dry pick strength, wet pick strength and blister resistance in the coated paper is poor.

The conjugated diene monomer constituting the monomer (a) includes 1,3-butadiene, isoprene, 2,3-
Dimethyl-1,3-butadiene, 2-ethyl-1,3-
Butadiene, 1,3-pentadiene, chloroprene and the like can be mentioned. Of these conjugated diene monomers, 1,3-butadiene is preferred.

Examples of the ethylenically unsaturated nitrile monomer constituting the monomer (b) include acrylonitrile, methacrylonitrile, 2-ethylpropenenitrile, 2-propylpropenenitrile, 2-chloropropenenitrile, -Butenenitrile. Of these ethylenically unsaturated nitrile monomers, acrylonitrile is preferred.

Other ethylenically unsaturated monomers composing monomer (c) and copolymerizable with (a) and (b) include aromatic vinyl monomers; ethylenically unsaturated carboxylic acid esters Monomers; ethylenically unsaturated carboxylic acid amide monomers and derivatives thereof; carboxylic acid vinyl ester monomers; vinyl halide monomers; and unsaturated carboxylic acid monomers.

In order to increase the ink receptivity and weather resistance of the coated paper, an ethylenically unsaturated carboxylic acid ester monomer is preferably used, and the dry pick strength and the wet pick strength of the coated paper are well balanced. In order to improve the mechanical and chemical stability of the latex and to facilitate the preparation of the paper coating composition, an ethylenically unsaturated carboxylic acid is preferably used. Acid amide monomers or ethylenically unsaturated carboxylic acid monomers are preferably used. The ethylenically unsaturated carboxylic acid monomer is particularly suitable for enhancing the polymerization stability, enhancing the dispersion stability of the latex polymer particles, and suppressing the generation of fine coagulated products.

Examples of the aromatic vinyl monomer include, in addition to styrene, α-methylstyrene, vinyltoluene, monochlorostyrene, p-methylstyrene, hydroxymethylstyrene and the like. Among them, styrene is preferred.

The ethylenically unsaturated carboxylic acid ester monomers include methyl methacrylate, methyl acrylate,
Ethylenically unsaturated carboxylic acid ester monomers such as ethyl methacrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, glycidyl methacrylate, glycidyl acrylate, etc. Is mentioned. Among them, methyl methacrylate is preferred.

Examples of the ethylenically unsaturated carboxylic acid amide monomer and its derivative include methacrylamide, acrylamide, N-methylol methacrylamide, N-methylol acrylamide and the like. Among them, acrylamide is preferred.

As the carboxylic acid vinyl ester monomer, vinyl acetate is typical, and as the vinyl halide monomer, vinyl chloride is typical.

Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid and crotonic acid; ethylenically unsaturated polycarboxylic acids such as maleic acid and itaconic acid; Ethylenically unsaturated polycarboxylic acid partial esters such as monomethyl acid; and the like.

In the latex of the present invention, the charged ratio of the conjugated diene monomer (a-1) used in the first stage emulsion polymerization is (a-1), (b-1) and (c-1). ) Is 50 to 80% by weight, preferably 5
5 to 75% by weight. If the charged amount of (a-1) is less than 50% by weight, the component for absorbing the impact force is lacking, and the dry pick strength of the coated paper decreases. If the amount exceeds 80% by weight, the blocking resistance of the latex film and the wet pick strength of the coated paper decrease.

The charged amount of the ethylenically unsaturated nitrile monomer (b-1) used in the first-stage emulsion polymerization is (a-
1), 20 to 50% by weight, preferably 25 to 45% by weight based on the total charged amount of (b-1) and (c-1)
It is. When the charged amount is less than 20% by weight or more than 50% by weight, the dry pick strength of the coated paper decreases.

The charged amounts of the other copolymerizable ethylenically unsaturated monomer (c-1) used in the first-stage emulsion polymerization are (a-1), (b-1) and (c-1). 0 to 30% by weight based on the total charged amount of 1), preferably 0 to 20% by weight.
% By weight. If the charged amount exceeds 30% by weight, the dry pick strength of the coated paper decreases.

The ethylenically unsaturated carboxylic acid monomer is subjected to (c-1) or (c) in the first and / or second emulsion polymerization.
-2) Preferably used as a component. The charge ratio of the ethylenically unsaturated carboxylic acid monomer is 1 to 10% by weight, preferably 1.5 to 8% by weight, more preferably 2 to 6% by weight in both the first and second stages. It is.

The second stage emulsion polymerization is carried out after the first stage polymerization conversion reaches 70% or more. When the polymerization conversion is 70
%, The blocking resistance decreases, and the wet pick strength of the coated paper decreases. It is preferable that the polymerization conversion rate is in the range of 70% or more and 85% or less in terms of excellent balance between dry pick strength and wet pick strength of the coated paper. The monomer preparation composition of the second stage emulsion polymerization is as follows. (A-2) 20 to 50% by weight of a conjugated diene monomer (b-2) 20 to 50 ethylenically unsaturated nitrile monomers
% By weight (c-2) Other copolymerizable ethylenically unsaturated monomers 30 to 60% by weight

In the latex of the present invention, the charged amounts of the conjugated diene monomer (a-2) used in the second stage emulsion polymerization are (a-2), (b-2) and (c-2). ) Is 20 to 50% by weight based on the total charged amount, and preferably 25% by weight.
~ 35% by weight. If the charged amount is less than 20% by weight, the film-forming property of the film is deteriorated, and the dry pick strength and wet pick strength of the coated paper are reduced. If the charged amount exceeds 50% by weight, the blocking resistance of the latex film and the wet pick strength of the coated paper decrease.

The charged amount of the ethylenically unsaturated nitrile monomer (b-2) used in the second stage emulsion polymerization is (a-
2), 20 to 50% by weight, preferably 25 to 35% by weight based on the total charged amount of (b-2) and (c-2).
It is. If the charged amount is less than 20% by weight, the wet pick strength and blister resistance of the coated paper decrease. If the charged amount exceeds 50% by weight, the balance between the dry pick strength and the wet pick strength of the coated paper decreases.

Monomer (c) used in the second stage emulsion polymerization
The amount of the other copolymerizable ethylenically unsaturated monomer (c-2) constituting (a) is based on the total amount of (a-2), (b-2), and (c-2). It is 30 to 60% by weight, preferably 40 to 50% by weight. The charge amount is 30
If the amount is less than 60% by weight or less than 60% by weight, it is difficult to obtain the effects of the present invention.

The monomers (a), (b), (c) and (a-
1), (b-1), (c-1), (a-2), (b-
In each of 2) and (c-2), a single monomer may be used, or two or more different monomers may be used in combination.

In the present invention, when 100 parts by weight of the monomer consisting of the above (a), (b) and (c) are emulsion-polymerized in two stages, (a-1)
The total charged amount of the conjugated diene monomer and (b-1) the ethylenically unsaturated nitrile monomer is 70 to 100% by weight,
Preferably it is 80 to 100% by weight. If the total charge is less than 70% by weight, the dry pick strength of the coated paper decreases.

In the second stage emulsion polymerization, the total charged amount of (a-2) the conjugated diene monomer and (b-2) the ethylenically unsaturated nitrile monomer is 40 to 70% by weight,
Preferably it is 50 to 60% by weight. If the total charge is less than 40% by weight, the wet strength and blister resistance of the coated paper will be reduced. Conversely, if it exceeds 70% by weight, the balance between the dry pick strength and the wet pick strength of the coated paper will be reduced. .

In the method for producing a copolymer latex of the present invention, the temperature T of the first-stage emulsion polymerization is preferably in a specific range represented by the following formula (1). 0 ≦ T ≦ 150-{(a-1) + (b-1)} (1) If T is less than 0 ° C., the soluble matter in THF becomes too high in molecular weight, so that the wet strength and the resistance of the coated paper are reduced. Blister properties decrease.
On the other hand, when T exceeds 150-{(a-1) + (b-1)}, the soluble matter in THF becomes too low in molecular weight, and the balance between dry pick strength and wet strength of the coated paper decreases. More preferably, T is 5 ° C. or more, and 145-｛(a-1) +
(B-1)｝ The range is as follows. The temperature of the first stage emulsion polymerization can be set to two or more different temperatures within the range of the expression (1) in the first half and the second half thereof. The temperature of the second-stage emulsion polymerization is usually in the range of 0 to 100 ° C., and is preferably equal to or higher than the first-stage emulsion polymerization temperature.

The second-stage emulsion polymerization is carried out after the polymerization conversion in the first-stage emulsion polymerization reaches 70% or more. Specifically, the monomers (a-1), (b-1) and (c-1) are emulsion-polymerized, and subsequently the monomers (a-2),
The polymerization may be carried out by adding the monomer mixture of (b-2) and (c-2), or a latex produced by the first-stage emulsion polymerization is prepared, and the latex is added in a predetermined amount. The emulsion polymerization may be continued by transferring to a reactor and adding a monomer mixture used for the second-stage emulsion polymerization.

The method of adding the monomer mixture or the polymerization auxiliary material in the first or second stage emulsion polymerization includes a method such as an initial batch addition method, a division addition method, and a continuous addition method. It is preferable that the monomer mixture used for the second-stage emulsion polymerization be continuously added.

As the polymerization auxiliary material used in the emulsion polymerization in the first stage or the second stage, those usually used in emulsion polymerization can be used. For example, as the chain transfer agent, various chain transfer agents generally used for radical polymerization can be used. Examples thereof include sulfides, α-methylstyrene dimer, carbon tetrachloride and the like, and these can be used alone or in combination of two or more. If necessary, continuous and sequential addition of a chain transfer agent as disclosed in JP-A-4-41511 and JP-A-4-41512 can be used in combination with the present invention.

As the polymerization retarder, various polymerization retarders generally used for radical polymerization can be used.
Quinones such as-, m- or p-benzoquinone; nitro compounds such as nitrobenzene, o-, m- or p-dinitrobenzene; amines such as diphenylamine; catechol derivatives such as tert-butyl catechol;
Examples thereof include 1,1-disubstituted vinyl compounds such as 1,1-diphenylethylene and α-methylstyrene, and these can be used alone or in combination of two or more.

As the surfactant, a surfactant generally used in emulsion polymerization can be used. Examples thereof include fatty acid soap, rosin acid soap, sodium alkylbenzenesulfonate, sodium alkylsulfonate, sodium dialkylarylsulfonate, and alkyl. Examples thereof include anionic surfactants such as sodium sulfosuccinate and sodium polyoxyethylene alkyl sulfate, and nonionic surfactants such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, and polyoxyethylene sorbitan fatty acid ester. It is also possible to use a reactive emulsifier having a functional group reactive with a monomer such as sodium styrenesulfonate, and if necessary, an amphoteric surfactant such as a betaine type. Usually, an anionic surfactant is used alone or in a mixed system of two or more anionic, nonionic and amphoteric surfactants.

The polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition in the presence of heat or a reducing substance generally used in radical polymerization, and has both oil solubility and water solubility. Can be used. For example, peroxodisulfates such as potassium peroxodisulfate, sodium peroxodisulfate, and ammonium peroxodisulfate,
And peroxides such as benzoyl peroxide, cumene hydroxy peroxide, t-butyl peroxide, hydrogen peroxide, and 2,2-azobisisobutyronitrile, 4,4′-azobis (4-cyanokiloxide) An azobis compound such as herbic acid) is generally used. Among them, peroxodisulfate brings out the effect of the present invention particularly well. The initiator in the present invention may be sodium bisulfite, ascorbic acid and salts thereof, erythorbic acid and salts thereof, Rongalit,
It can be used as a so-called redox polymerization initiator in combination with a reducing agent such as Fe and Fe / chelating agent.

As the various polymerization regulators, polymerization regulators generally used for emulsion polymerization can be used. For example, sodium hydroxide, potassium hydroxide, sodium hydrogen carbonate,
There are pH adjusters such as sodium carbonate and sodium hydrogen phosphate, and chelating agents such as tetrasodium ethylenediamine. These are added to the reaction system as needed.

Further, the copolymer latex of the present invention has a main peak derived from a conjugated diene monomer unit when tetrahydrofuran (THF) insoluble and soluble components of the copolymer latex are analyzed by pyrolysis gas chromatography. The γ value defined by the formula (2), which is determined from the area and the total sum of the main peak areas derived from the ethylenically unsaturated nitrile monomer units, is preferably 0.60 or more and 0.85 or less. When the γ value is less than 0.60, in the case of coated paper, the dry pick strength of the coated paper decreases, and when it exceeds 0.85, the dry pick strength and wet topic strength of the coated paper and the blister resistance Balance is reduced. In addition, the detailed measurement conditions of the pyrolysis gas chromatography are based on the conditions described in Examples.

The average particle size of the copolymer particles constituting the copolymer latex of the present invention is usually from 60 to 200 nm,
Preferably 70 to 150 nm, particularly preferably 70 to 1
00 nm. When the average particle diameter is small, the viscosity of the latex becomes high, so that the preparation of the paper coating composition tends to be difficult. Conversely, when the average particle size increases, the dry pick strength and wet pick strength of the coated paper tend to decrease. The average particle diameter was determined by observing the latex with an electron microscope, and randomly selecting the latex particles in the photographed photograph.
This is a value represented by the number average value of 0 particles selected and the particle diameter measured.

The copolymer constituting the copolymer latex of the present invention generally has a glass transition temperature of -30 to + 30 ° C.
Preferably it is -15 to + 20 ° C. As the glass transition temperature decreases, the wet pick strength of the coated paper tends to decrease. Conversely, as the glass transition temperature increases, the dry pick strength of the coated paper tends to decrease. As for the glass transition temperature, the latex was cast on a glass plate with a frame and left in a constant temperature and humidity room at a temperature of 23 ° C. and a relative humidity of 50% for 48 hours to obtain a film.
This is a value obtained by measuring the film using a differential scanning calorimeter (DSC, manufactured by Seiko Instruments Inc .: SSC5200) under the conditions of a starting temperature of -100 ° C and a heating rate of 10 ° C / min.

The amount of the tetrahydrofuran-insoluble content of the copolymer constituting the copolymer latex of the present invention is usually 55 to 95% by weight, preferably 70 to 70% by weight in coated paper for offset sheet-fed printing or gravure printing. ~ 90% by weight. Further, in coated paper for web offset printing, the content is usually 20 to 80% by weight, preferably 30 to 60% by weight. The amount of the tetrahydrofuran insoluble matter is a value determined by the method described below. The copolymer latex of the present invention is suitable for a paper coating composition, and particularly suitable for a coated paper requiring dry pick strength, wet pick strength and blister property.

The paper coating composition of the present invention contains the above-mentioned copolymer latex and pigment as essential components.

Examples of the pigment used in the paper coating composition of the present invention include inorganic pigments such as clay, barium sulfate, calcium carbonate, talc, titanium oxide and satin white, and organic pigments such as plastic pigment. The ratio of the copolymer latex of the present invention to the pigment is
The solids content of the copolymer latex relative to parts by weight is usually
It is at least 1 part by weight, preferably 3 to 20 parts by weight.

The paper coating composition of the present invention may further contain, if necessary, a water-soluble polymer, a pH adjuster, a pigment dispersant, a water-proofing agent, a defoamer, a dye, a lubricant, an organic solvent, and the like. can do.

The paper coating composition of the present invention can improve the dry pick strength, wet pick strength, etc. of the coated paper by coating it on paper. Paper that can be coated may be either paperboard or paper. Moreover, the paper which can be coated is preferably a band-shaped paper since the coating operation can be continuously performed.

The coating method is not particularly limited, and the coating is performed using a coating apparatus such as a blade coater, a roll coater, an air knife coater, and a short dwell coater. The coating amount is usually in the range of ³ to 30 g / m ² , preferably 5 to 25 g / m ² , in terms of the solid content of the composition.

[0046]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the examples. The parts and percentages in the examples are on a weight basis.

The evaluation method used in this embodiment will be described below. (Amount of tetrahydrofuran [THF] insolubles) After adjusting the pH of the latex to 8, it was cast on a glass plate with a frame.
The film was dried by being left in a constant temperature and humidity room at a temperature of 23 ° C. and a relative humidity of 50% for 48 hours to obtain a film. 0.3 g of this film
Was placed in a basket of 80 mesh wire mesh and immersed in 100 ml of tetrahydrofuran at 20 ° C. for 48 hours.
The film remaining in the basket of the wire mesh was dried under reduced pressure at 100 ° C., and the residual ratio was calculated to determine the amount of the THF-insoluble component.

(Average Particle Diameter) A small amount of a copolymer latex prepared to a solid content of 0.01% was dropped onto a mesh for observation with a transmission electron microscope, and dyed and fixed in osmium tetroxide vapor. After evaporating the water, with a transmission electron microscope,
Latex particles on the mesh were observed at a magnification of 1 to 30,000 times. The diameter of 100 arbitrary particles was measured, and the number average particle diameter was determined.

(Measurement by pyrolysis gas chromatography)
Approximately 1 mg of a sample is weighed, wrapped in Pyrofoil 590 (manufactured by Nippon Kagaku Kogyo Co., Ltd.), and heated at 590 ° C. for 7 seconds to gasify it.
It measured using -14A (made by Shimadzu Corporation). At this time, the column was TC-1701 (size: 30 m × 0.2
5 mm, inner diameter 1.0 μm) at a temperature rising rate of 10 ° C. /
In a range of 50 ° C to 200 ° C in minutes. In addition, as a measurement sample, in measurement of a THF insoluble content, THF was used.
A component remaining as an insoluble component and a component obtained as a THF-soluble component obtained by distilling THF from a THF solution after the immersion treatment were used. Data collection and analysis is C
-R4A (manufactured by Shimadzu Corporation). (See FIG. 1.) From the conjugated diene monomer unit obtained from pyrolysis gas chromatography and the main peak area derived from the unsaturated nitrile monomer made of ethylene, the γ value defined by the formula (2) was determined. .

(Equation 3) (Where, AS _Di : a main peak area derived from a conjugated diene unit in a THF-soluble portion; AS _Ni : a main peak area derived from an ethylenically unsaturated nitrile monomer unit in a THF-soluble portion; AG _Di : a conjugated portion in a THF-insoluble portion. Main peak area derived from diene unit AG _Ni : Indicates the main peak area derived from the ethylenically unsaturated nitrile monomer unit of the THF-soluble component.)

(Dry pick strength) An RI tester (manufactured by Akashi Seisakusho) using 0.4 cm ³ of printing ink (tack value: 20)
After that, the coated paper was overprinted four times using this RI tester (manufactured by Akashi Seisakusho). The state of peeling (picking) of the paper surface was observed and evaluated by a five-point method.
The higher the score, the higher the dry pick strength.

(Wet pick strength) Water is applied to a coated paper with a Molton roll, and then the printing ink (tack value 1) is applied.
4) Solid printing was performed using an RI tester having 0.4 cm ³ attached to a rubber roll. Peeling of paper (picking)
The condition was evaluated by a 5-point method in the same manner as in the evaluation method of dry pick strength. The higher the score, the higher the wet pick strength.

(Blister resistance) Coated paper was treated at a temperature of 25
After leaving for 24 hours in an atmosphere of 65 ° C. and a relative humidity of 65%,
The test piece was placed in a silicon oil thermostat heated to a predetermined temperature of 5 ° C., and the minimum temperature at which blisters were generated was determined. The higher the temperature, the better the blister resistance.

(Blocking resistance) After applying and drying latex on a high-quality paper, lath paper was superimposed on the coated surface, and a temperature of 8
A calender treatment was performed under the conditions of 0 ° C. and a linear pressure of 30 kg / cm. Thereafter, the rasha paper was peeled off by hand, and the peeled state was
Evaluate by the point method. The higher the score, the higher the blocking resistance.

Example 1 In a stainless steel autoclave, 100 parts of water, 1 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium hydrogencarbonate, and the monomer composition and chain transfer agent in the first stage shown in Table 1 (Equivalent to 50 parts of the first-stage monomer mixture), and the mixture was heated to 40 ° C. while stirring and mixing, and then 0.5 part of potassium peroxide was added to initiate polymerization. On the other hand, in another stainless steel autoclave, 30 parts of water, 0.2 parts of sodium dodecylbenzenesulfonate, and 0.2 parts of sodium bicarbonate were added.
2 parts, and a mixture of the monomer composition and the chain transfer agent in the second stage shown in Table 1 (second stage monomer mixture 50
Parts equivalent), and mixed and stirred to prepare a second-stage monomer emulsion. When the polymerization conversion in the first-stage polymerization reached 75%, the polymerization temperature was raised to 60 ° C., and the second-stage monomer emulsion was added for 2 hours (equivalent to 25 parts of the monomer mixture per hour). (The rate at which is added). Simultaneously with the start of addition of the second-stage monomer emulsion, 0.5 part of potassium persulfate was continuously added as a 3% aqueous solution for the same addition time as the second-stage monomer emulsion. In the table, tDM represents tert-dodecyl mercaptan, and MSD represents α-methylstyrene dimer. Further, when the polymerization conversion reached 85%, the polymerization temperature was raised to 85 ° C., and the reaction was continued until the polymerization conversion reached 98%.

The latex after the reaction was cooled to room temperature, and after depressurizing, the latex was taken out of the reaction vessel. afterwards,
After removing unreacted monomers under reduced pressure, the pH was adjusted to 8 with sodium hydroxide to obtain a copolymer latex of Example 1. The THF-insoluble content, average particle size and blocking resistance of the obtained latex were measured, and the results are shown in Table 2. Γ value of the copolymer latex of Example 1 The main peak area values obtained from the gas chromatography chart were as follows. In addition, the gas chromatography was measured on the above-mentioned conditions. The γ values are shown in Tables 1 and 2.

[Table 1] γ = 1.632 / 2.257 = 0.72 (composition for paper coating)

Next, 10 parts of the copolymer latex, kaolin clay (UW90, manufactured by Engelhard Co.) 60
Part, heavy calcium carbonate (Carbita, manufactured by ECC)
1-90) 40 parts, dispersant (Toa Gosei Co., Aron T-
40) 0.2 parts, 0.15 parts of sodium hydroxide and 3 parts of oxidized starch were mixed and stirred, and the solid content was 65%, p
The composition was adjusted to H10 to obtain a paper coating composition.

This paper coating composition was applied to a high-quality paper so that the coating amount was 15 g / m ² per side, and immediately after application, dried with hot air at 120 ° C. for 10 seconds. It was left overnight in a 65% constant temperature and humidity room. Thereafter, a super calender treatment was performed twice at a temperature of 50 ° C. and a linear pressure of 100 kg / cm to obtain a coated paper. Table 2 shows the evaluation results of the coated paper.

Examples 2 to 6 and Comparative Examples 1 to 6 Example 2 was repeated except that the monomer composition, the amount of the chain transfer agent, the polymerization temperature, and the ratio of the monomer mixture in the first and second stages were changed as shown in Table 2. In the same manner as in Example 1, copolymer latexes shown in Examples 2 to 6 and Comparative Examples 1 to 6 were obtained. Table 2 shows the results. The THF insoluble content, the average particle size, the γ value and the blocking resistance of each copolymer latex were measured, and the evaluation of the coated paper using each copolymer latex was performed in the same manner as in Example 1. Table 2 shows the results.

[0059]

[Table 2]

Table 2 shows the following. Coated paper using a copolymer latex in which the amount of acrylonitrile in the second-stage monomer composition is smaller than the range of the present invention is inferior in wet pick strength and blister resistance. (Comparative Example 1) Coated paper using a copolymer latex in which the amount of acrylonitrile in the first-stage monomer composition is smaller than the range of the present invention is inferior in dry pick strength and wet pick strength. (Comparative Example 2) A copolymer latex in which the butadiene content in the second-stage monomer composition is smaller than the range of the present invention is excellent in blocking resistance, but the coated paper using this copolymer latex is dry. Poor pick strength and wet pick strength. (Comparative Example 3) A copolymer latex in which the ratio of the first stage to the second stage is out of the range of the present invention is inferior in blocking resistance, and coated paper using this copolymer latex has dry pick strength and wetness. Poor balance between pick strength and blister resistance (Comparative Examples 4 and 5) The butadiene content in the first-stage monomer composition is less than the range of the present invention, and the butadiene content in the second-stage monomer composition is low. A copolymer latex having more than the range of the present invention has poor blocking resistance, and a coated paper using this copolymer latex has poor balance of dry pick strength, wet pick strength and blister resistance. (Comparative Example 6)

Compared with these, the copolymer latex within the range of the monomer charged composition of the present invention has excellent blocking resistance, and the coated paper using these copolymer latexes has a dry pick strength, wet Excellent balance between pick strength and blister resistance. In particular, when Examples 3 and 4 are compared, coated paper using the copolymer latex of Example 3 in which the polymerization temperature T of the first stage satisfies the following formula (1) shows dry pick strength and wet pick strength. Better. 0 ≦ T ≦ 150-{(a-1) + (b-1)} (1) (where (a-1) and (b-1) are respectively
This corresponds to the ratio (% by weight) of the conjugated diene monomer and the ethylenically unsaturated nitrile monomer in the first-stage emulsion polymerization. Among them, the copolymer latex having a γ value of 0.60 or more and 0.85 or less of the obtained copolymer latex has excellent blocking resistance, and coated paper using these copolymer latex is Excellent in balance between dry pick strength, wet pick strength and blister resistance.
(Examples 1 to 3)

[0062]

EFFECT OF THE INVENTION The copolymer latex of the present invention has excellent blocking resistance, and the coated paper obtained from the coated paper composition containing the copolymer latex has dry pick strength, wet pick strength and blister resistance. Excellent balance.

[Brief description of the drawings]

FIG. 1 shows an example of a chart obtained by analyzing the THF insoluble content of a copolymer latex of the present invention by pyrolysis gas chromatography. The main peaks (GD and GN, respectively) based on the conjugated diene monomer and the ethylenically unsaturated nitrile monomer are shown in the chart.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroaki Muraki 2-1-1, Yoko, Kawasaki-ku, Kawasaki-shi, Kanagawa F-term in the General Development Center of Zeon Corporation (reference) 4J011 BB01 BB07 KA02 KA10 NA01 NA12 NA13 NA14 NA23 WA02 4J100 AB02R AB03R AB04R AB07R AB08R AC03R AG04R AJ01R AJ02R AJ08R AJ09R AL03R AL08R AL36R AM01Q AM02Q AM03Q AM15R AS02P AS03P AS04P AS07P BE03R BB01Q BC54R CA05 EA07 AG04 AG07 AG20 EA32 EA33 FA11 FA13 FA19 GA19

Claims (5)

[Claims] (1) 29 to 71% by weight of a conjugated diene monomer (b) 20 to 50% by weight of an ethylenically unsaturated nitrile monomer (c) Other copolymerizable ethylenically unsaturated monomers 9 ~
A method for producing a copolymer latex in which 100 parts by weight of a monomer consisting of 51% by weight is emulsion-polymerized in two steps, wherein (a-1) 50 to 80% by weight of a conjugated diene monomer (b- 1) Ethylenically unsaturated nitrile monomer 20-50
(C-1) 30 to 70 parts by weight of a monomer comprising 0 to 30% by weight of another copolymerizable ethylenically unsaturated monomer having a polymerization conversion of 70%
Emulsion polymerization is carried out until the above is reached, and as a second step, (a-2) a conjugated diene monomer 20 to 50% by weight (b-2) an ethylenically unsaturated nitrile monomer 20 to 50%
(C-2) A method for producing a copolymer latex, which comprises emulsion-polymerizing 30 to 70 parts by weight of a monomer comprising 30 to 60% by weight of another copolymerizable ethylenically unsaturated monomer. . 2. The polymerization temperature T in the first stage emulsion polymerization.
The method for producing a copolymer latex according to claim 1, wherein (C) is in a range satisfying the following formula (1). 0 ≦ T ≦ 150-{(a-1) + (b-1)} (1) (where (a-1) and (b-1) are respectively
This corresponds to the ratio (% by weight) of the conjugated diene monomer and the ethylenically unsaturated nitrile monomer in the first-stage emulsion polymerization. ) 3. A copolymer latex obtained by the method for producing a copolymer latex according to claim 1. 4. The following formula based on the main peak area derived from a conjugated diene unit and an ethylenically unsaturated nitrile monomer unit in tetrahydrofuran (THF) insoluble matter and soluble matter of a copolymer latex in pyrolysis chromatography. 2) The γ value defined by the equation is 0.60 or more and 0.8
The copolymer latex according to claim 3, wherein the number is 5 or less. (Equation 1) (Where, AS _Di : a main peak area derived from a conjugated diene unit in a THF-soluble portion; AS _Ni : a main peak area derived from an ethylenically unsaturated nitrile monomer unit in a THF-soluble portion; AG _Di : a conjugated portion in a THF-insoluble portion. Main peak area derived from diene unit AG _Ni : Indicates the main peak area derived from the ethylenically unsaturated nitrile monomer unit in the THF-insoluble portion.) 5. A paper coating composition comprising the copolymer latex according to claim 3 and a pigment.