JP2018177852A - Water-swellable copolymer latex, water-swellable composition, and water-swellable sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water-swellable copolymer latex excellent in water swellability and at the same time excellent in mechanical strength of the dried film.SOLUTION: The water-swellable copolymer latex contains, based on the total amount (100 pts.mass) of monomer units, not less than 20 pts.mass to less than 50 pts.mass of an aliphatic conjugated diene-based monomer unit, 3 pts.mass to 30 pts.mass of an acidic functional group-containing unsaturated monomer unit, 25 pts.mass to 50 pts.mass of an alkyl unsaturated carboxylate monomer unit and 0.1 pt.mass to 30 pts.mass of a unit from a reactive emulsifier (b).SELECTED DRAWING: None

Description

  The present invention relates to a water-swellable copolymer latex, a water-swellable composition, and a water-swellable sealing material. More particularly, the present invention relates to a copolymer latex used as a raw material for coated paper binders, carpet backing binders, various adhesives and paints, and water-swellable sealants.

  Conventionally, it has been strongly demanded to impart water absorption performance and / or water swelling performance to a synthetic rubber or synthetic resin which is a hydrophobic material, and a water-swellable sealing material in which a water-absorbent polymer is mixed with a soft resin or rubber. Many are known (for example, refer patent document 1).

  In addition, Patent Document 2 discloses a hydrophilic copolymer which is internally crosslinked by emulsion polymerization using a reactive emulsifier containing an unsaturated double bond. Furthermore, as described in Patent Document 3, the use of a reactive emulsifier is a widely used technique in the field of styrene-butadiene copolymer latex.

Patent No. 2882633 Patent No. 4627871 Patent No. 3924450 Japanese Patent Application Laid-Open No. 56-33032 Japanese Patent Application Laid-Open No. 57-108143

  However, in the conventional water-swellable sealing material described in Patent Document 1, the strength is lowered to impart water-swelling property, and the balance between the mechanical strength and the swelling property is bad and is not satisfactory (for example, , Patent Documents 4 and 5). In addition, water-swellable polymers obtained by co-crosslinking an emulsion of a carboxyl-modified polymer and a water-soluble carboxyl-modified diene polymer by drying and heat treatment using a crosslinking agent require complicated processes such as heat treatment Therefore, sufficient performance can not be exhibited depending on the conditions.

  In addition, the hydrophilic copolymer disclosed in Patent Document 2 does not have sufficient levels of water-swelling property, film strength and elongation in this composition range. Furthermore, the purpose of using a reactive emulsifier for emulsion polymerization as disclosed in Patent Document 3 is for the purpose of improving the water resistance of the latex film, and does not consider the water swelling performance.

  Therefore, an object of the present invention is to provide a water-swellable copolymer latex which is excellent in water-swelling ability and at the same time, excellent in mechanical strength of a dry film.

  As a result of intensive investigations to solve the above problems, the present inventors have studied aliphatic conjugated diene monomer units, acid functional group-containing unsaturated monomer units, unsaturated carboxylic acid alkyl ester monomer units And water-swellable copolymer latex each containing a predetermined amount of a reactive emulsifier, it has been found that it has excellent water-swelling performance and mechanical strength of a dry film, and the present invention has been achieved. .

That is, the present invention provides the following copolymer latex.
[1]
With respect to the total amount (100 parts by mass) of monomer units,
Aliphatic conjugated diene monomer unit from 20 parts by mass to less than 50 parts by mass
3 to 30 parts by mass of an acidic functional group-containing unsaturated monomer unit,
25 parts by mass or more and 50 parts by mass or less of unsaturated carboxylic acid alkyl ester monomer units, and 0.1 parts by mass or more and 30 parts by mass or less of reactive emulsifier (b) units,
Water-swellable copolymer latex.
[2]
And 0.5 parts by mass or less of a non-reactive emulsifier based on the total amount (100 parts by mass) of the monomer units
The water-swellable copolymer latex as described in [1].
[3]
The toluene insoluble fraction is 80% or more and 99% or less,
The water-swellable copolymer latex as described in [1] or [2].
[4]
The toluene swelling degree is 3.0 or more and 15 or less,
The water-swellable copolymer latex according to any one of [1] to [3].
[5]
The water-swellable copolymer latex according to any one of [1] to [4],
Water-swellable composition.
[6]
The water-swellable copolymer latex according to any one of [1] to [4],
Water-swellable sealing material.

  By using the water-swellable copolymer latex according to the present invention, it is possible to obtain high water absorption (water swelling) and high mechanical strength of the dry film.

  Although the form (henceforth "this embodiment") for carrying out the present invention is explained in detail below, the present invention is not limited to this, and various modification in the range which does not deviate from the gist Is possible.

[Water-swellable copolymer latex]
The water-swellable copolymer latex (hereinafter also referred to as “copolymer latex (A)”) of the present embodiment is 20 parts by mass or more and 50 parts by mass with respect to the total amount (100 parts by mass) of the monomer units. Aliphatic conjugated diene monomer unit less than 1 part, acidic functional group containing unsaturated monomer unit not less than 3 parts by mass and not more than 30 parts by mass, unsaturated carboxylic acid alkyl ester unit amount of not less than 25 parts by mass and not more than 50 parts by mass It contains a body unit and a reactive emulsifier (b) unit of 0.1 parts by mass or more and 30 parts by mass or less.

  Hereinafter, the content of the water-swellable copolymer latex (including the monomer unit and the reactive emulsifier unit) contained in the water-swellable copolymer latex used in the present embodiment, and the polymerization of the water-swellable copolymer latex The addition amount (use amount) of the raw materials (including the monomer and the reactive emulsifier) is the total amount (100 parts by mass) of the monomer units and the total amount (100 parts by mass) of the monomers unless otherwise specified. Expressed in parts by mass with respect to Here, the term "monomer" means not only aliphatic conjugated diene monomers, acid functional group-containing unsaturated monomers, and unsaturated carboxylic acid alkyl ester monomers, but also monomers other than these. The monomer which contains a unit is meant. However, reactive emulsifier (b) is excluded.

<Aliphatic conjugated diene monomer>
The aliphatic conjugated diene-based monomer of the present embodiment is not particularly limited, and, for example, 1,3-butadiene, isoprene, 2,3-dimethyl 1,3-butadiene, 2-ethyl-1,3-butadiene And 2-methyl-1,3-butadiene, 1,3-pentadiene, chloroprene, 2-chloro-1,3-butadiene, cyclopentadiene and the like.

  In the present embodiment, at least one kind of aliphatic conjugated diene-based monomer may be used, but plural kinds of aliphatic conjugated diene-based monomers may be used at the same time. Among the above-mentioned aliphatic conjugated diene monomers, butadiene is preferable in terms of availability.

  The content of the aliphatic conjugated diene monomer is 20 parts by mass or more and less than 50 parts by mass with respect to the total amount (100 parts by mass) of the monomer units contained in the copolymer latex (A), It is preferable that it is mass part or more and less than 50 mass parts, and it is more preferable that it is 35 mass parts or more and less than 50 mass parts. When the amount is less than 50 parts by mass, the water swellability is higher, and when the amount is 20 parts by mass or more, the strength of the dry film is excellent.

<Acidic functional group-containing unsaturated monomer>
The acidic functional group-containing unsaturated monomer of the present embodiment is not particularly limited, and examples thereof include monobasic acid monomers and dibasic acid monomers. The acidic functional group-containing unsaturated monomer used in the present embodiment is an unsaturated monomer containing an acidic functional group such as a carboxyl group, a sulfonic acid group, a phosphoric acid group or a boric acid group, and the reaction described later It does not contain any emulsifying emulsifiers.

  More specifically, as a monobasic acid monomer, for example, acrylic acid, methacrylic acid, crotonic acid, vinylbenzoic acid, cinnamic acid, styrenesulfonic acid, methallylsulfonic acid, allylsulfonic acid, vinylsulfonic acid and the like Examples thereof include sodium salts, potassium salts and ammonium salts of monobasic acid monomers.

  Examples of dibasic acid monomers include itaconic acid, fumaric acid, maleic acid, citraconic acid, muconic acid, and sodium salts, potassium salts and ammonium salts of these dibasic acid monomers.

  In the present embodiment, at least one kind of acidic functional group-containing unsaturated monomer may be used, but plural kinds of acidic functional group-containing unsaturated monomers may be used simultaneously. The acidic functional group-containing unsaturated monomer is preferably a monobasic acid monomer from the viewpoint of the stability at the time of polymerization, and among these, combined use of acrylic acid and methacrylic acid is more preferable.

  The content of the acidic functional group-containing unsaturated monomer is 3 parts by mass or more and 30 parts by mass or less with respect to the total amount (100 parts by mass) of the monomer units contained in the copolymer latex (A). And 5 parts by mass or more and 20 parts by mass or less, and more preferably 7 parts by mass or more and 15 parts by mass or less. By being 3 mass parts or more, water swellability is favorable (high), and the strength of a dry film is excellent by being 30 mass parts or less.

<Unsaturated carboxylic acid alkyl ester monomer>
The unsaturated carboxylic acid alkyl ester monomer of the present embodiment is not particularly limited, and examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, and t -Butyl (meth) acrylate, isobutyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl hexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) Acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, 2-ethyl-hexyl (meth) acrylate, hydroxyethyl (meth) acrylate Hydroxypropyl (meth) acrylate, hydroxycyclohexyl (meth) acrylate, glycidyl (meth) acrylate, glycol di (meth) acrylate, glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4- Butylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,5-pentanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, di Glycol di (meth) acrylate, triglycol di (meth) acrylate, tetraglycol di (meth) acrylate, polyglycol di (meth) acrylate, polypropylene glycol di (meth) acrylate , Pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, allyl (meth) acrylate, bis (4-acryloxypolyethoxyphenyl) propane, methoxypolyethyling Recall (meth) acrylate, β- (meth) acryloyloxyethyl hydrogen phthalate, β- (meth) acryloyloxyethyl hydrogen succinate, 3-chloro-2-hydroxypropyl (meth) acrylate, stearyl (meth) acrylate, Phenoxyethyl (meth) acrylate, phenoxy polyglycol (meth) acrylate, 2-hydroxy-1,3-di (meth) acryloxypropane, 2,2-bis [4-((meth)) Chlorooxyethoxy) phenyl] propane, 2,2-bis [4-((meth) acryloxydiethoxy) phenyl] propane, 2,2-bis [4-((meth) acryloxypolyethoxy) phenyl] propane, isobornyl ( Meta) acrylate etc. are mentioned.

Also, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, n-amyl (meth) acrylate, Isoamyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, cyclohexyl (meth) acrylate, Phenyl (meth) acrylate, benzyl (meth) acrylate, hydroxyethyl (meth) acrylate,
2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 1-hydroxypropyl acrylate, 1-hydroxypropyl methacrylate, hydroxycyclohexyl (meth) acrylate,
Also, crotonic acid alkyl ester, itaconic acid alkyl ester, fumaric acid alkyl ester, maleic acid alkyl ester and the like can be mentioned.

  In the present embodiment, at least one or more types of unsaturated carboxylic acid alkyl ester monomers may be used, but plural types of unsaturated carboxylic acid alkyl ester monomers may be used simultaneously. The unsaturated carboxylic acid alkyl ester monomers are, among those mentioned above, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, isoamyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl More preferred are alkyl acrylates having a glass transition temperature of -30 ° C. or less, such as acrylates and decyl acrylates.

  The content of the unsaturated carboxylic acid alkyl ester monomer is 25 parts by mass or more and 50 parts by mass or less with respect to the total amount (100 parts by mass) of the monomer units contained in the copolymer latex (A). And 25 parts by mass or more and 45 parts by mass or less, and more preferably 25 parts by mass or more and 40 parts by mass or less. By being 25 parts by mass or more, the water swellability is good (high), the elongation of the dry film is large, and by being 50 parts by mass or less, the strength of the dry film is excellent.

<Other copolymerizable monomers>
Monomers other than the aliphatic conjugated diene-based monomer, the acid functional group-containing unsaturated monomer, and the unsaturated carboxylic acid alkyl ester monomer of the present embodiment, and monomers copolymerizable therewith (Hereinafter, it is also referred to as "other unsaturated monomers"), for example, aromatic vinyl compounds, maleic anhydride, vinyl cyanide compounds, acrylamides, methacrylamides, vinyl esters, vinyl ethers, for example. Examples thereof include vinyl halides, basic monomers having an amino group, vinyl pyridine, olefins, silicon-containing α, β-unsaturated monomers, and allyl compounds.

  The aromatic vinyl compound is not particularly limited. For example, styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, vinyltoluene, vinylxylene, bromostyrene, vinylbenzyl Chloride, p-t-butylstyrene, chlorostyrene, alkylstyrene, divinylbenzene, trivinylbenzene and the like can be mentioned.

  The vinyl cyanide compound is not particularly limited, and examples thereof include acrylonitrile and methacrylonitrile.

  Although it does not specifically limit as acrylamide and methacrylamide, For example, (meth) acrylamide, N- methylol (meth) acrylamide, N- alkoxy (meth) acrylamide etc. are mentioned.

  The vinyl ester is not particularly limited, and examples thereof include vinyl acetate, vinyl butyrate, vinyl stearate, vinyl laurate, vinyl myristate, vinyl propionate, and vinyl versatate.

  The vinyl ether is not particularly limited, and examples thereof include methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, amyl vinyl ether, hexyl vinyl ether and the like.

  The vinyl halide is not particularly limited, and examples thereof include vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride and the like.

  The basic monomer having an amino group is not particularly limited, and examples thereof include aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate and the like.

  The olefin is not particularly limited, and examples thereof include ethylene, propylene and the like.

  The silicon-containing α, β-unsaturated monomer is not particularly limited, and examples thereof include vinyltrichlorosilane and vinyltriethoxysilane.

  The allyl compound is not particularly limited, and examples thereof include allyl ester and diallyl phthalate.

  As another unsaturated monomer except having mentioned above, the monomer etc. which have 3 or more double bonds, such as triallyl isocyanurate, etc. are mentioned.

  In the present embodiment, at least one other unsaturated monomer may be used, but plural other unsaturated monomers may be used simultaneously.

<Reactive emulsifier (b)>
The reactive emulsifier (b) (hereinafter, also simply referred to as "reactive emulsifier") of the present embodiment is not particularly limited as long as it is an emulsifier having reactivity with the above-described monomer or its polymer Among them, those having a radically polymerizable double bond, a hydrophilic functional group, and a hydrophobic group, respectively, and having an emulsifying, dispersing, and wetting function, as in a general emulsifying agent, can be mentioned.

  Examples of the structure of the radically polymerizable double bond in the molecular structure include, for example, a vinyl group, an acryloyl group, and a methacryloyl group.

  The hydrophilic functional group in the molecular structure includes, for example, anionic groups such as sulfuric acid group, nitric acid group, phosphoric acid group, boric acid group and carboxylic acid group, cationic groups such as amino group; polyoxyethylene, polyoxymethylene, Polyoxyalkylene chains such as polyoxypropylene; hydroxyl groups and the like.

  As a hydrophobic group in molecular structure, an alkyl group, a phenyl group, etc. are mentioned, for example.

  Reactive emulsifiers include anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers and the like depending on the kind of hydrophilic functional group contained in the structure. Moreover, the radically polymerizable double bond in the molecular structure, the hydrophilic functional group, and the hydrophobic group can also have a plurality of types of structures and functional groups.

  Among the above, the reactive emulsifier preferably has a polyoxyalkylene chain and a sulfate group as a hydrophilic functional group at least in the molecular structure.

  The content of the reactive emulsifier is 0.1 parts by mass or more and 30% by mass or less based on the total amount (100 parts by mass) of the monomer units contained in the copolymer latex (A). By being 0.1 mass part or more, the favorable copolymer latex (A) of stability is obtained, and when it is 30 mass parts or less, it is excellent in the intensity | strength of a dry film.

  The trade name generally marketed as such a reactive emulsifier is not particularly limited. For example, Adekaria Soap SE, SDX (Asahi Denka Kogyo Co., Ltd.), Aqualon HS, BC, KH (Daiichi Kogyo Seiyaku Co., Ltd.) Ltd., Latemul PD (Kao Co., Ltd.), Eleminol JS (Sanyo Chemical Industries, Ltd.), Antox MS (Nippon Emulsifier Co., Ltd.) and the like.

  Further, by using a reactive emulsifier having a polyoxyalkylene chain and a sulfuric acid group inside the molecular structure, a copolymer using only a reactive emulsifier having no polyoxyalkylene chain or a reactive emulsifier having no sulfuric acid group Compared to the case where the latex (A) is prepared, the decrease in the chemical stability of the copolymer latex (A) at the initial stage of polymerization and the final product can be suppressed, and the performance can be sufficiently exhibited.

(Water swelling degree)
The water swelling degree of the copolymer latex (A) is 1.4 times or more and 5.0 times or less, preferably 1.5 times or more and 5.0 times or less, and more preferably 2.0 times or more. .0 or less. When the degree of water swelling is 1.4 times or more, the water absorption performance is good, and when it is 5.0 times or less, the strength of the dry film is good.

Here, the degree of water swelling is measured by the following method. The aqueous dispersion of the copolymer latex (A) is dried at 23 ° C. and 60% humidity for 3 days to prepare a dry film having a thickness of 0.5 mm. After further heating at 90 ° C. for 30 minutes to completely dry, this film is cut into 5 × 5 cm, and its mass V (g) is measured. The dried film is immersed in water at 23 ° C., and after 2 hours, the weight W (g) is measured. The degree of water swelling is calculated by the following equation.
Water swelling degree = W (g) / V (g)

(Toluene insolubles)
The toluene insoluble content of the copolymer latex (A) is preferably 80% or more and 99% or less. By being 80% or more, the mechanical strength of the copolymer latex tends to be better, and by being 99% or less, the film forming property of the copolymer latex tends to be better.

(Toluene swelling degree)
The toluene swelling degree of the copolymer latex (A) is preferably 3.0 or more and 15 or less, more preferably 3.5 or more and 14 or less, and still more preferably 3.5 or more and 13 or less. By being 3.0 or more, better water swellability tends to be obtained, and by being 15 or less, mechanical strength tends to be better.

Here, the toluene insoluble fraction and the degree of swelling in toluene are measured by the following method. 0.5 g of a film obtained by drying the dispersion liquid of the copolymer latex (A) at 130 ° C. for 30 minutes is immersed in 30 mL of toluene at 25 ° C., and shaken for 3 hours using a shaker. After filtration, the resultant is filtered through 320 SUS mesh, and the weight X (g) of non-passing portion is measured. Further, after drying the non-passed portion at 130 ° C. for 1 hour, the weight Y (g) is measured. The toluene insoluble fraction and the degree of swelling in toluene are calculated by the following equation.
Toluene insoluble fraction (%) = Y (g) / 0.5 (g) x 100
Toluene swelling degree = X (g) / Y (g)

(Tensile strength, elongation at cutting)
The copolymer latex (A) has a tensile strength of 2 MPa or more and an elongation at break of 200 for a latex dry film having a thickness of 0.3 mm or more and 0.5 mm or less manufactured using the copolymer latex. % Or more is preferable.

Here, the tensile strength and the elongation at break of the latex dried film are measured by the following method.
The copolymer latex is thinned with a film applicator and dried. Drying can be carried out by leaving for 40 to 48 hours under the conditions of 20 to 25 ° C. and 45 to 65% RH. In the case where a continuous dry film of latex can not be obtained under the above temperature conditions, the temperature and humidity 45 to 65% higher by 17 to 23 ° C. than the minimum film forming temperature of latex measured according to the method of JIS K6828-2. It may be left to dry for 40 to 48 hours under the conditions of RH. Next, the dried thin film is subjected to heat treatment at 90 ° C. for 30 minutes, whereby a latex dried film having a thickness of 0.3 mm to 0.5 mm can be obtained.

  About the obtained dried latex film, it punches out to the shape and dimension of the dumbbell-like No. 3 type | mold of JISK-6251 except thickness, and it is set as a test piece. After leaving this test piece in a desiccator equipped with silica gel for drying for 24 hours or more, the tensile stress and the elongation (displacement) are measured by testing at a tension rate of 500 mm / min using a tensile compression tester. Do. As a tensile compression tester, a tensile compression tester (for example, trade name: TECHNO GRAPH TG-20 kN manufactured by Minebea Co., Ltd.) can be used. Based on the obtained measurement results, tensile strength and elongation at break (elongation when the latex film is cut) can be determined. In addition, the test conditions etc. at the time of the measurement of tensile stress and elongation rate are as follows.

(Test conditions etc.)
Chuck distance: 50 mm
Test capacity: 100 N
Test temperature: 23 ° C, 60% RH
Elongation rate: Ratio to initial based on the distance between benchmarks of dumbbell shape No. 3 (%)
Stress: Stress according to the definition of term according to JIS K-6251, unit is MPa
Tensile strength: The maximum tensile force recorded when pulling the specimen until it is cut divided by the initial cross-sectional area of the specimen

  From the viewpoint of strength, the film properties of the copolymer latex determined by the above method are that the tensile strength of the dried latex film is 3.5 MPa or more and the elongation at break of the dried latex film exceeds 200%. More preferable.

(Average particle size)
The average particle diameter of the copolymer latex (A) is preferably in the range of 5 nm to 500 nm, and more preferably in the range of 40 nm to 200 nm. The average particle size can be adjusted by the use ratio of the seed latex and the surfactant, etc. Generally, the higher the use ratio, the smaller the average particle size of the formed latex tends to be.

(Glass-transition temperature)
The glass transition temperature Tg of the copolymer latex (A) is preferably −60 ° C. or more and 40 ° C. or less, and more preferably −50 ° C. or more and 10 ° C. or less. When the temperature is −60 ° C. or higher, the strength of the dried film tends to be better. When the temperature is 40 ° C. or lower, no problem occurs in the film formability of the copolymer latex.

(Solid content concentration)
It is preferable that solid content concentration in copolymer latex (A) is chosen in 10 mass% or more and 60 mass% or less.

  The method for polymerizing the monomer is not particularly limited. For example, a predetermined amount of water, a reactive emulsifier (reactive surfactant), and other additives are charged in advance in a reaction system adjusted to a polymerizable temperature. Emulsion polymerization is carried out by adding a polymerization initiator and an unsaturated monomer, a reactive emulsifying agent, a preparation agent and the like to this system by batch operation or continuous operation into the reaction system to synthesize.

  In addition, it is a commonly used method that, in advance, a predetermined amount of seed latex, an initiator, and other preparation agents are pre-charged and placed in the reaction system, if necessary.

  Furthermore, the layer structure of the water-swellable copolymer latex particles to be synthesized can be changed stepwise by adding unsaturated monomers, reactive emulsifiers, other additives, and preparation agents to the reaction system. It is. As physical properties representative of the structure of each layer, hydrophilicity, glass transition point, molecular weight, crosslinking density and the like can be mentioned. Further, in the present embodiment, the number of stages of the layer structure is not particularly limited.

<Polymerization reaction inhibitor>
A polymerization reaction inhibitor can be further used in the emulsion polymerization used in the present embodiment, if necessary. The "polymerization reaction inhibitor" means a compound capable of reducing the radical polymerization rate by adding to the emulsion polymerization system. More specifically, a polymerization rate retarder, a polymerization inhibitor, a chain transfer agent having low radical reinitiation reactivity, and a monomer having low radical reinitiation reactivity.

  The polymerization reaction inhibitor is used to adjust the polymerization reaction rate and to adjust the physical properties of the latex. These polymerization reaction inhibitors are added to the reaction system in batch operation or continuous operation. When a polymerization reaction inhibitor is used, the strength of the latex film tends to be further improved. Although the details of the reaction mechanism are unknown, the polymerization reaction inhibitor seems to be closely involved in the steric structure of the polymer, and it is presumed that this is effective in adjusting the physical properties of the latex film.

  These polymerization reaction inhibitors are not particularly limited, and examples thereof include quinones such as o-, m- or p-benzoquinone, nitrobenzene, nitro compounds such as o-, m- or p-dinitrobenzene, diphenylamine Such as amines, catechol derivatives such as tert-butyl catechol, 1,1-disubstituted vinyl compounds such as 1,1-diphenyl or α-methylstyrene, 2,4-diphenyl-4-methyl-1-pentene And 1,2-disubstituted vinyl compounds such as 2,4-diphenyl-4-methyl-2-pentene and cyclohexene. In addition to this, "POLYMER HANDBOOK 3rd Ed. (J. Brandup, E. H. Immergut: John Wiley & Sons, 1989)", "Revision of Polymer Synthesis Chemistry (Otsu: Chemical Doujin, 1979.)" The compounds described as inhibitors or polymerization inhibitors may be mentioned.

  Among these, the polymerization reaction inhibitor is preferably 2,4-diphenyl-4-methyl-1-pentene (α-methylstyrene dimer) in terms of reactivity.

  One of these polymerization reaction inhibitors may be used alone, or two or more thereof may be mixed and used. The amount of the polymerization reaction inhibitor used is preferably 0.1 based on the polymerization rate with respect to the total amount (100 parts by mass) of the monomers used for the polymerization of the water-swellable copolymer latex (A). It is 10 parts by mass or less and 10 parts by mass or less.

<Chain transfer agent>
If necessary for the emulsion polymerization used in the present embodiment, a known chain transfer agent can be further used. The chain transfer agent is not particularly limited, but as a chain transfer agent containing sulfur element, alkanethiols such as t-dodecyl mercaptan and n-dodecyl mercaptan etc., thioalkyl alcohols such as mercaptoethanol and mercaptopropanol, thioglycolic acid, Thioalkyl carboxylic acids such as thiopropionic acid, thiocarboxylic acid alkyl esters such as thioglycolic acid octyl ester and thiopropionic acid octyl ester, and sulfides such as dimethyl sulfide and diethyl sulfide. In addition, halogenated hydrocarbons such as terpinorene, dipentene, t-terpinene, carbon tetrachloride and the like can be mentioned.

  Among these, alkanethiols are preferable because they have a high chain transfer rate and a well-balanced physical property of the obtained latex. One of these chain transfer agents may be used alone, or two or more thereof may be mixed and used. These chain transfer agents may be mixed with the monomers and supplied to the reaction system or may be independently added in predetermined amounts at predetermined times. The amount of these chain transfer agents used is preferably 0.1 parts by mass or more and 10 parts by mass with respect to the total amount (100 parts by mass) of the monomers used for the polymerization of the water-swellable copolymer latex (A) When the content is 0.1 mass part or more, the film forming property and the adhesion strength tend to be suppressed, and when the content is 10 mass parts or more, the molecular weight (toluene gel fraction) is significantly reduced. It tends to suppress the decrease in mechanical strength.

<Radical polymerization initiator>
The radical polymerization initiator of this embodiment is to cause radical decomposition in the presence of heat or a reducing substance to initiate addition polymerization of the monomer, and any of inorganic initiators and organic initiators can be used. Such materials are not particularly limited, but, for example, water-soluble or oil-soluble peroxodisulfates, peroxides, azobis compounds, etc., specifically, potassium peroxodisulfate, sodium peroxodisulfate, ammonium peroxodisulfate Hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, 2,2-azobisbutyronitrile, cumene hydroperoxide, etc., and POLYMER HANDBOOK (3rd edition), J. Am. Brandrup and E.I. H. Mention may also be made of the compounds described in Immergut, John Willy & Sons (1989).

  In the present embodiment, a so-called redox polymerization method may be employed in which a reducing agent such as sodium acid sulfite, ascorbic acid or a salt thereof, erythorbic acid or a salt thereof or Rongalite is used in combination with a polymerization initiator. Among these, peroxodisulfate is suitable as a polymerization initiator. The amount of the polymerization initiator used is the stability of the polymerization of the copolymer latex with respect to the total amount (100 parts by mass) of the monomers used for the polymerization of the water-swellable copolymer latex (A). From this, the content is preferably 0.1 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.2 parts by mass or more and 3.0 parts by mass or less. With such a range, the water resistance of the film tends to be more excellent.

  The polymerization temperature in this emulsion polymerization is usually selected in the range of 60 to 120 ° C. However, in the case of the above-mentioned redox polymerization method or the like, the polymerization may be carried out at a lower temperature. Furthermore, as the redox catalyst, a metal catalyst such as divalent iron ion, trivalent iron ion, copper ion and the like may be made to coexist.

  In the present embodiment, various polymerization regulators can be further added as needed. For example, as a pH adjuster, a pH adjuster such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, sodium hydrogencarbonate, sodium carbonate, disodium hydrogenphosphate and the like may be further added, among which potassium hydroxide is preferred. It is more preferable in terms of enhancing the water resistance and the stability balance during synthesis, and is suitable as a pH adjuster after synthesis. Further, various chelating agents such as sodium diamine tetraacetate and the like can be further added as a polymerization regulator.

  Moreover, as additives other than those mentioned above, non-reactive emulsifiers, alkali sensitive latexes, viscosity reducing agents such as hexametaphosphoric acid, water-soluble polymers such as polyvinyl alcohol and carboxymethyl cellulose, thickeners, various anti-aging agents, ultraviolet rays Absorbents, preservatives, disinfectants, antifoaming agents, dispersants such as sodium polyacrylate, water resistance agents, metal oxides such as zinc flower, crosslinkers such as isocyanate compounds, epoxy compounds, lubricants, water retention agents, etc. Even if it adds various additives, it does not matter. The addition method of these additives is not particularly limited, and can be added during or after the polymerization of the copolymer latex.

<Non-reactive emulsifier>
Non-reactive emulsifiers are not particularly limited, but anionic surfactants such as fatty acid soaps, rosin acid soaps, sulfonates, sulfates, phosphates, phosphates, polyphosphates, acyl salicylates, etc., nitrileated fats and oils, fats and oils Derivatives, fatty acid derivatives, cationic surfactants such as α-olefin derivatives, alcohol ethoxylates, alkylphenol ethoxylates, propoxylates, aliphatic alkanolamides, alkyl polyglycosides, polyoxyalkyl aryl ethers, polyoxysorbitan fatty acid esters, oxyoxy oxy fatty acid esters Nonionic surfactants such as propylene block copolymers may be mentioned.

  Among these, sulfonic acid salts are preferable, and the sulfonic acid salt is not particularly limited. For example, alkyl sulfonic acid salts, dialkyl aryl sulfonic acid salts, alkyl sulfuric acid salts, alkyl aryl sulfuric acid salts, alkyl sulfosuccinic acid salts, polyoxyalkyl sulfuric acid Salts, polyoxyalkyl aryl sulfates, sulfonated oils and fats, alkyl diphenyl ether disulfonates, α-olefin sulfonates, alkyl glyceryl ether sulfonates, N-acylmethyl taurate and the like. Moreover, what is described in "surfactant handbook (Takahashi, Namba, Koike, Kobayashi: Engineering book, 1972)" is also mentioned.

  It is preferable to use non-reactive emulsifier for emulsion polymerization in the range which does not deteriorate the water resistance of the dry film of copolymer latex (A) obtained. The content of the non-reactive emulsifier is more preferably 0.5 parts by mass or less with respect to the total amount (100 parts by mass) of the monomer units contained in the copolymer latex (A).

[Water-swellable composition]
The water-swellable composition of the present embodiment comprises the copolymer latex (A) described above.

[Water-swellable sealing material]
The water-swellable sealing material of the present embodiment includes the copolymer latex (A) described above.

  Hereinafter, the present invention will be more specifically described using examples and comparative examples. The present invention is not limited at all by the following examples.

  The polymerization of the copolymer latex (A) of Examples 1 to 14 and Comparative Examples 1 to 10 was carried out by the following method.

  In the pressure-resistant reaction vessel equipped with a stirring device and a temperature control jacket, the initial tensioning material such as water and an emulsifier as shown in Table 1 is charged, the internal temperature is raised to 85 ° C. The monomers, chain transfer agent and polymerization reaction inhibitor were added at a constant flow rate over 5 hours in the proportions shown in Table 2. At the same time, an aqueous solution obtained by mixing the aqueous solution materials such as water, an emulsifier and a polymerization initiator shown in Table 3 in the proportions shown in Table 3 was added at a constant flow rate over 6 hours. Then, the temperature of 85 ° C. was maintained as it is for 1 hour to complete the polymerization reaction.

  Next, the resulting copolymer aqueous dispersion is adjusted to pH 7 with sodium hydroxide, and then unreacted monomers are removed by a steam stripping method, and it is filtered through a 200 mesh wire net, and finally, It adjusted so that solid content concentration might be 40 mass%, and the dispersion liquid of copolymer latex (A) was obtained.

Here, as an emulsifier shown in Table 1 and Table 3, the reactive emulsifier provided by the following emulsifier manufacturer was used.
Adekaria Soap SE-1025N: manufactured by Asahi Denka Kogyo Co., Ltd. Aqualon HS-1025: manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

  The particle size, toluene insoluble fraction, and toluene swelling degree of the copolymer latex (A) of Examples 1 to 14 and Comparative Examples 1 to 9 obtained above were evaluated by the methods described below. The evaluation results are shown in Table 4.

(Particle diameter of copolymer latex (A))
The number average particle diameter was measured using Nikkiso Co., Ltd., MICROTRAC particle size distribution analyzer model: 9230 UPA).

(Toluene insoluble fraction and toluene swelling degree)
The copolymer latex (A) was dried at 130 ° C. for 30 minutes, and 0.5 g of the film was taken, immersed in 30 mL of toluene at 25 ° C., shaken for 3 hours using a shaker, and filtered through 320 SUS mesh And the weight X (g) of the non-passing portion was measured. Further, after drying the non-passed portion at 130 ° C. for 1 hour, the weight Y (g) was measured. The toluene insoluble fraction and the degree of swelling in toluene were calculated by the following equation.
Toluene insoluble fraction (%) = Y (g) / 0.5 (g) x 100
Toluene swelling degree = X (g) / Y (g)

  Further, the degree of water swelling, tensile strength and elongation at break of the dried film were evaluated by the methods described below. The evaluation results are shown in Table 5.

(Water swelling degree)
The copolymer latex (A) was dried at 23 ° C. and humidity 60% RH for 3 days to prepare a dry film having a thickness of 0.5 mm. After further heating at 90 ° C. for 30 minutes to completely dry, the film was cut into 5 × 5 cm, and its mass V (g) was measured. The film was immersed in water at 23 ° C., and after 2 hours, the mass W (g) was measured. The degree of water swelling was calculated by the following equation.
Water swelling degree = W (g) / V (g)

(Tensile strength and elongation at break)
The copolymer latex (A) was thinned with a film applicator and dried. Drying was left at 23 ° C. and humidity 60% RH for 48 hours. Next, the dried thin film was subjected to heat treatment at 90 ° C. for 30 minutes to obtain a latex dried film having a thickness of 0.3 mm or more and 0.5 mm or less.

  The dried latex film obtained was punched into the shape and size of a dumbbell-like No. 3 type described in JIS K-6251 except for the thickness to obtain a test piece. This test piece is left to stand for 24 hours or more in a desiccator equipped with silica gel for drying, and after measuring the exact thickness of the test piece with a micrometer, it is tested at a drawing speed of 500 mm / min using a tensile compression tester. Tensile stress and elongation (displacement) were measured. Tensile compression tester: TECHNO GRAPH TG-20 kN (manufactured by Minebea Co., Ltd.) was used. Based on the obtained measurement results, tensile strength and elongation at break (elongation when the latex film was cut) was determined. In addition, the test conditions at the time of measurement of tensile stress and elongation at break were as follows.

(Test conditions etc.)
Chuck distance: 50 mm
Test capacity: 100 N
Test temperature: 23 ° C, 60% RH
Elongation rate: Ratio to initial based on the distance between benchmarks of dumbbell shape No. 3 (%)
Stress: Stress according to the definition of term according to JIS K-6251, unit is MPa
Tensile strength: The maximum tensile force recorded when pulling the specimen until it is cut divided by the initial cross-sectional area of the specimen

Claims (6)

With respect to the total amount (100 parts by mass) of monomer units,
Aliphatic conjugated diene monomer unit from 20 parts by mass to less than 50 parts by mass
3 to 30 parts by mass of an acidic functional group-containing unsaturated monomer unit,
25 parts by mass or more and 50 parts by mass or less of unsaturated carboxylic acid alkyl ester monomer units, and 0.1 parts by mass or more and 30 parts by mass or less of reactive emulsifier (b) units,
Water-swellable copolymer latex. And 0.5 parts by mass or less of a non-reactive emulsifier based on the total amount (100 parts by mass) of the monomer units
The water-swellable copolymer latex according to claim 1. The toluene insoluble fraction is 80% or more and 99% or less,
The water-swellable copolymer latex according to claim 1 or 2. The toluene swelling degree is 3.0 or more and 15 or less,
The water-swellable copolymer latex according to any one of claims 1 to 3. A water-swellable copolymer latex according to any one of claims 1 to 4 comprising
Water-swellable composition. A water-swellable copolymer latex according to any one of claims 1 to 4 comprising
Water-swellable sealing material.