Shock absorber-forming composition and shock absorber

Abstract

To provide a shock absorber exhibiting superior compressive recoverability under humid heat conditions, and a shock absorber-forming composition for forming the shock absorber.SOLUTION: A shock absorber-forming composition comprises an acrylic resin (A), a curing agent (B), a surfactant (C), and an aqueous liquid medium (D). The acrylic resin (A) has a gel fraction of 60% or more. In a water dispersion containing the acrylic resin (A) at a concentration of 55 mass%, the Ti value represented by the following formula (1) is from 10 to 20. The surface tension is 35 mN / m or less. Formula (1): Ti value=(viscosity at a shear rate of 0.1 [1 / s]) / (viscosity at a shear rate of 10 [1 / s]).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composition for forming a shock absorber and a shock absorber.

Background Art

[0002] Shock absorbers are used in various applications such as electronic materials, automotive components, and building materials. In recent years, particularly in the fields of electronic materials and automotive components, the requirements for long-term durability and reliability have become more stringent. As an index indicating the long-term durability and reliability of shock absorbers, compression recovery under humid and hot conditions can be mentioned. However, conventional acrylic foams (for example, Patent Document 1) have had a problem that the compression recovery under humid and hot conditions is insufficient.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem to be solved by the present invention is to provide a shock absorber excellent in compression recovery under humid and hot conditions and a composition for forming a shock absorber for forming the same.

Means for Solving the Problems

[0005] As a result of intensive studies to solve the above problems, the present inventors have found that a composition for forming a shock absorber using a specific acrylic resin and having a specific surface tension exhibits excellent foaming properties and foam stability, and a shock absorber made of the composition for forming a shock absorber is excellent in compression recovery under humid and hot conditions, and thus completed the present invention.

[0006] That is, the present invention relates to a composition for forming a shock-absorbing material containing an acrylic resin (A), a curing agent (B), a surfactant (C), and an aqueous liquid medium (D), wherein the gel fraction of the acrylic resin (A) is 60% or more, and in an aqueous dispersion having a concentration of the acrylic resin (A) of 55% by mass, the Ti value represented by the following formula (1) is 10 to 20, and the surface tension is 35 mN / m or less. Ti value = (viscosity at a shear rate of 0.1 [1 / s]) / (viscosity at a shear rate of 10 [1 / s]) ··· Formula (1) Further, the present invention relates to the composition for forming a shock-absorbing material, wherein in a total of 100% by mass of the ethylenically unsaturated monomers constituting the acrylic resin (A), 0.1 to 5% by mass of a carboxy group-containing ethylenically unsaturated monomer (ma), 0.1 to 5% by mass of a cyano group-containing ethylenically unsaturated monomer (mb), and 0.1 to 3% by mass of a monomer (mc) having two or more ethylenically unsaturated bonds are included, and the glass transition temperature of the acrylic resin (A) is -50 to 20°C.

[0007] Further, the present invention relates to the composition for forming a shock-absorbing material, wherein the curing agent (B) is an epoxy-based curing agent.

[0008] Further, the present invention relates to the composition for forming a shock-absorbing material, wherein the surfactant (C) contains a fatty acid salt having 12 to 28 carbon atoms and / or a sulfosuccinate.

[0009] Further, the present invention relates to a shock-absorbing material formed from the composition for forming a shock-absorbing material.

Effects of the Invention

[0010] According to the present invention, a shock-absorbing material excellent in compression recovery under wet heat conditions can be obtained.

Modes for Carrying Out the Invention

[0011] Hereinafter, abbreviations of terms, symbols, etc. used in this specification will be explained. In this specification, a numerical range specified using "~" shall include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. Also, "(meth)acrylamide", "(meth)acrylate", "(meth)acrylic acid" and "acid (anhydride)" shall represent "acrylamide or methacrylamide", "acrylate or methacrylate", "acrylic acid or methacrylic acid" and "acid or acid anhydride", respectively. "Carboxy group-containing ethylenically unsaturated monomer (ma)", "cyano group-containing ethylenically unsaturated monomer (mb)" and "monomer (mc) having two or more ethylenically unsaturated bonds" may be abbreviated as "monomer (ma)", "monomer (mb)" and "monomer (mc)", respectively.

[0012] The composition for forming a shock-absorbing material of the present invention is a composition for forming a shock-absorbing material containing an acrylic resin (A), a curing agent (B), a surfactant (C) and an aqueous liquid medium (D), wherein the gel fraction of the acrylic resin (A) is 60% or more, and the Ti value represented by the following formula (1) in an aqueous dispersion having a concentration of the acrylic resin (A) of 55% by mass is 10 to 20, and the surface tension is 35 mN / m or less.

[0013] The gel fraction of the acrylic resin (A) is 60% or more, and since the compression recovery under wet heat conditions is improved, it is preferably in the range of 70 to 90%. The gel fraction in this specification is determined by the following formula (2). Gel fraction [%] = {(weight after immersion in tetrahydrofuran) / (weight before immersion in tetrahydrofuran)} × 100 ··· Formula (2) It is important that the acrylic resin (A) has a Ti value in the range of 10 to 20 when it is made into an aqueous dispersion with a concentration of 55% by mass. When the Ti value is less than 10, the foam stability during the formation of the shock-absorbing material deteriorates, and the compression recovery property under humid and heat conditions deteriorates. On the other hand, when the Ti value is greater than 20, the foaming property of the composition for forming the shock-absorbing material deteriorates, and the compression recovery property under humid and heat conditions deteriorates. Since the balance between foam stability and foaming property is improved, the Ti value is preferably in the range of 12 to 18.

[0014] The Ti value in this specification is calculated based on formula (1). Ti value = (viscosity at a shear rate of 0.1 [1 / s]) / (viscosity at a shear rate of 10 [1 / s]) ··· formula (1) The "viscosity" in formula (1) represents the viscosity at 25°C measured by a method compliant with JIS K7117-2 using a rheometer "AR-2000ex" (manufactured by TA Instrument).

[0015] The Ti value may be in the range of 10 to 20, but since the balance between foam stability and foaming property is improved, it is preferably in the range of 5 to 30 [mPa·s] for the viscosity at a shear rate of 0.1 [1 / s]. Also, it is preferably in the range of 0.25 to 2 [mPa·s] for the viscosity at a shear rate of 10 [1 / s].

[0016] The surface tension of the composition for forming the shock-absorbing material is 35 mN / m or less, but is preferably in the range of 27 to 32 mN / m from the viewpoints of coatability and foam stability. The method for determining the surface tension in this specification is described in the examples below. <Acrylic resin (A)> The acrylic resin (A) is preferably a copolymer of a monomer mixture containing a carboxy group-containing ethylenically unsaturated monomer (ma), a cyano group-containing ethylenically unsaturated monomer (mb), and a monomer (mc) having two or more ethylenically unsaturated bonds.

[0017] The content rate of monomer (ma) in the above monomer mixture is preferably in the range of 0.1 to 5% by mass, more preferably in the range of 0.5 to 5% by mass, and even more preferably in the range of 1 to 3% by mass.

[0018] Examples of the monomer (ma) include unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; unsaturated dicarboxylic acids (anhydrides) such as itaconic acid (anhydride), maleic acid (anhydride), and fumaric acid. The carboxy group-containing ethylenically unsaturated monomer (ma) can be used alone or in combination of two or more.

[0019] The content rate of monomer (mb) in the above monomer mixture is preferably in the range of 0.1 to 5% by mass, more preferably in the range of 0.5 to 5% by mass, and even more preferably in the range of 2 to 4% by mass. Examples of the monomer (mb) include cyano(meth)acrylates such as acrylonitrile, methacrylonitrile, methyl-2-cyano(meth)acrylate, ethyl-2-cyano(meth)acrylate, n-butyl cyano(meth)acrylate, and 2-octyl cyano(meth)acrylate. The cyano group-containing ethylenically unsaturated monomer (mb) can be used alone or in combination of two or more. Incidentally, the ethylenically unsaturated monomer having both a carboxy group and a cyano group shall belong to the monomer (ma).

[0020] The monomer (mc) in the above monomer mixture is preferably in the range of 0.1 to 3% by mass, more preferably in the range of 0.2 to 2% by mass. Examples of the monomer (mc) include divinyl monomers such as divinyl adipate, divinyl ether of diethylene glycol, divinyl ether of triethylene glycol, and divinylbenzene; diallyl monomers such as diallyl 1,4-cyclohexanedicarboxylate, allyl ether, diallylamine, diallyl phthalate, diallyl terephthalate, diallyl maleate, and diallyl adipate; triallyl monomers such as triallylamine and triallyl cyanurate; di(meth)acrylates such as 1,3-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 4,4-biphenol di(meth)acrylate, bisphenol A di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, and tetramethylene glycol di(meth)acrylate; tri(meth)acrylates such as glycerin triacrylate, etc. The monomer (mc) can be used alone or in combination of two or more. In addition, monomers having two or more ethylenically unsaturated bonds and having either one or both of a carboxy group and a cyano group shall belong to the monomer (mc).

[0021] The above monomer mixture may contain an ethylenically unsaturated monomer (md) other than monomers (ma), (mb), and (mc) (hereinafter sometimes abbreviated as "monomer (md)"). The monomer (md) may be any monomer copolymerizable with monomers (ma), (mb), and (mc). For example, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate; (meth)acrylates having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate; (meth)acrylates having an amino group such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, N,N-diethylaminopropyl (meth)acrylate; (alkoxy)polyalkylene glycol (meth)acrylates such as polyethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, polybutylene glycol (meth)acrylate, methoxypolybutylene glycol (meth)acrylate; monomers having an amide group such as (meth)acrylamide, N-methylol (meth)acrylamide; vinyl monomers such as styrene, α-methylstyrene, paramethylstyrene, chloromethylstyrene, vinyl acetate;Monomers having an alkoxysilyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, vinylmethyldimethoxysilane, vinyltris(2-methoxyethoxy)silane, (meth)acryloyloxymethyltrimethoxysilane, (meth)acryloyloxymethyltriethoxysilane, 2-(meth)acryloyloxyethyltrimethoxysilane, 2-(meth)acryloyloxyethyltriethoxysilane, 3-(meth)acryloyloxypropyltrimethoxysilane, 3-(meth)acryloyloxypropyltriethoxysilane, 3-(meth)acryloyloxypropylmethyldimethoxysilane, etc.; Tetrahydrofurfuryl (meth)acrylate, benzyl (meth)acrylate, glycidyl (meth)acrylate, etc. can be mentioned. The monomer (md) can be used alone or in combination of two or more kinds.;

[0022] The glass transition temperature (Tg) of the acrylic resin (A) is preferably in the range of -50 to 20°C, more preferably in the range of -40 to 0°C. <Method for producing acrylic resin (A)> Examples of the method for producing the acrylic resin (A) include an emulsion polymerization method using water as an aqueous liquid medium (D) and a solution polymerization method using an organic solvent as a solvent. However, since the aqueous dispersion of the acrylic resin (A) can be obtained more simply, the emulsion polymerization method is preferred. Examples of the emulsion polymerization method include a method of radical polymerizing a monomer mixture in the presence of a polymerization initiator and a surfactant in an aqueous liquid medium (D).

[0023] Examples of the polymerization initiator include azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), and azobiscyanovaleric acid; organic peroxides such as tert-butyl peroxypivalate, tert-butyl peroxybenzoate, tert-butyl peroxy-2-ethylhexanoate, di-tert-butyl peroxide, cumene hydroperoxide, benzoyl peroxide, and tert-butyl hydroperoxide; and inorganic peroxides such as hydrogen peroxide, ammonium persulfate, potassium persulfate, and sodium persulfate. The polymerization initiator can be used alone or in combination of two or more. Further, the polymerization initiator is preferably used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the monomers.

[0024] When polymerizing the monomer mixture, a polymerization initiator and a reducing agent can also be used in combination. Examples of the reducing agent include sodium bisulfite, sodium metabisulfite, formaldehyde sulfoxylate, ferrous chloride, ascorbic acid, erythorbic acid, and salts thereof. The reducing agent can be used alone or in combination of two or more.

[0025] Examples of surfactants include nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene - polyoxypropylene block copolymers, sorbitan fatty acid esters; anionic surfactants such as sulfates of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, polyoxyethylene alkyl phenyl ether sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene alkyl sulfonates, alkyl ether phosphates, alkenyl sulfosuccinates, dialkyl sulfosuccinates, monoalkyl sulfosuccinates; cationic surfactants such as carboxylates and quaternary ammonium salts of tertiary amines having long - chain alkyl groups such as N,N - dimethyllaurylamine, N,N - dimethyloctadecylamine; reactive surfactants such as compounds having both an anionic group such as a carboxylate group, sulfate group, phosphate group and a polymerizable double bond, compounds having both a nonionic group and a polymerizable double bond, compounds having both a cationic group such as a quaternary ammonium group and a polymerizable double bond, etc. The surfactant can be used alone or in combination of two or more. Also, the surfactant is preferably in the range of 0.01 to 15 parts by mass, more preferably in the range of 0.05 to 10 parts by mass, based on 100 parts by mass of the total amount of monomers. <Hardener (B)> Examples of the hardener (B) include epoxy - based hardeners, carbodiimide - based hardeners, oxazoline - based hardeners, etc. Among them, epoxy - based hardeners are preferred because the compression recovery under wet - heat conditions is further improved.

[0026] Examples of epoxy - based hardeners include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6 - hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, N,N,N’,N’ - Tetraglycidyl-m-xylenediamine (manufactured by Mitsubishi Gas Chemical Company, trade name "Tetrad X"), 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Company, trade name "Tetrad C"), 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, etc. may be mentioned. The epoxy curing agent can be used alone or in combination of two or more.

[0027] The curing agent (B) is preferably blended so that the functional group reacting with the carboxyl group is in the range of 0.1 to 5 moles per mole of the carboxyl group in the acrylic resin (A). <Surfactant (C)> As the surfactant (C), surfactants such as those mentioned as being used in the above emulsion polymerization method can be used. The surfactant (C) can be used alone, but it is preferably contained a higher fatty acid salt or sulfosuccinate having 12 to 28 carbon atoms, more preferably contains a higher fatty acid salt having 12 to 28 carbon atoms and a sulfosuccinate, and even more preferably contains ammonium stearate and sodium dialkylsulfosuccinate, since the foam stability and foaming property are improved. The surfactant (C) is preferably blended in an amount of 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass, based on 100 parts by mass of the acrylic resin (A). <Aqueous liquid medium (D)> Examples of the aqueous liquid medium (D) include water, an organic solvent miscible with water, and a mixture thereof. Examples of the organic solvent miscible with water include alcohols such as methanol, ethanol, propanol, and 2-propanol; ketones such as acetone and methyl ethyl ketone; polyalkylene glycols such as ethylene glycol, diethylene glycol, and propylene glycol; alkyl ethers of polyalkylene glycols; lactams such as N-methyl-2-pyrrolidone. In the present invention, only water may be used, or a mixture of water and an organic solvent miscible with water may be used, or only an organic solvent miscible with water may be used. However, it is preferable to use only water or a mixture of water and an organic solvent miscible with water, and it is more preferable to use only water.

[0028] The composition for forming a shock absorber of the present invention may contain, as components other than the acrylic resin (A), the curing agent (B), the surfactant (C), and the aqueous liquid medium (D), additives such as a foaming agent, a filler, a thickener, a flame retardant, a dispersant other than the surfactant (C), a wetting agent, an antifoaming agent, an antioxidant, an ultraviolet absorber, and a preservative.

[0029] Examples of the filler include calcium carbonate, magnesium carbonate, aluminum hydroxide, magnesium hydroxide, barium hydroxide, basic zinc carbonate, basic lead carbonate, ferric hydroxide, silica sand, clay, and diatomaceous earth.

[0030] Examples of the thickener include alkali-neutralized acrylic thickeners such as sodium polyacrylate and acrylic emulsions; polyvinyl alcohol-based thickeners; associative urethane-based thickeners; thickening polysaccharides such as carboxymethyl cellulose and hydroxyethyl cellulose.

[0031] <Method for Producing Composition for Forming Shock Absorber> As a method for manufacturing the composition for forming an impact absorber of the present invention, for example, a method of mixing a curing agent (B) and a surfactant (C) into an aqueous dispersion of an acrylic resin (A) can be mentioned. When a surfactant is used in the production of the aqueous dispersion of the acrylic resin (A), the surfactant used in the production can be regarded as the surfactant (C).

[0032] <Impact absorber> The composition for forming an impact absorber of the present invention can be easily foamed, for example, by mechanical stirring using a hand mixer or the like. The foaming ratio can be selected according to the use of the product, but a foaming ratio of 1.5 to 5 times is preferable. The impact absorber of the present invention is obtained by heating the composition for forming an impact absorber after foaming as described above. For example, it can be obtained by heating and drying at 50 to 150°C for 3 to 60 minutes after coating on a substrate or the like.

[0033] Since the impact absorber of the present invention is excellent in compression recovery under wet heat conditions, it is suitably used for electronic materials, automobile parts, food packaging materials, building materials, clothing, etc.

Examples

[0034] Hereinafter, the present invention will be described more specifically with reference to examples. However, the following examples do not limit the scope of the rights of the present invention in any way. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass". The numerical values in the table are the solid content mass, and blanks indicate that they are not used. <Synthesis of acrylic resin (A)> (Synthesis Example 1) 0.3 parts of acrylic acid, 1.2 parts of methacrylic acid, 2.5 parts of acrylonitrile, 0.5 part of diallyl phthalate, 15 parts of ethyl acrylate, 79.5 parts of butyl acrylate, 1 part of 2-hydroxyethyl methacrylate, 1 part of sodium lauryl sulfate as a surfactant, and 35 parts of water were charged into a dropping tank and stirred to prepare a pre-emulsion liquid. 0.2 part of the above pre-emulsion liquid and 35 parts of water were charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas inlet tube, and a dropping tank, and the temperature was raised to 68°C. After confirming that the internal temperature of the reaction vessel was 68°C, 0.1 part of ammonium persulfate as a polymerization initiator and 0.05 part of sodium bisulfite as a reducing agent were added and an initial reaction was carried out for 5 minutes. After the initial reaction was completed, while maintaining the reaction vessel at 70°C, the remaining pre-emulsion liquid in the dropping tank, 0.3 part of ammonium persulfate, and 0.15 part of sodium bisulfite were dropped over 4 hours. After the dropping was completed, the reaction was continued for another 3 hours and then cooled to 40°C. Then, it was neutralized with 2.8 parts of an aqueous ammonia solution with a concentration of 25%, and water was added so that the solid content concentration became 58% to obtain an aqueous dispersion of acrylic resin (A-1). [Measurement of Ti value] The aqueous dispersion of acrylic resin (A-1) obtained above was diluted with water so that the concentration of acrylic resin (A-1) became 55%. Using a rheometer "AR-2000ex" (manufactured by TA Instrument), the viscosity was measured under the condition of 25°C while changing the shear rate from 0.001 [1 / s] to 1000 [1 / s]. The cone plate used had a diameter of 60 mm and an angle of 1°, and the shear rate was changed from 0.001 to 1000 [1 / s] in 2 minutes. The obtained viscosity was substituted into the following formula (1) to calculate the Ti value. Ti value = (viscosity at a shear rate of 0.1 [1 / s]) / (viscosity at a shear rate of 10 [1 / s]) ··· Formula (1) [Measurement of gel fraction] The aqueous dispersion of the acrylic resin (A-1) obtained above was allowed to stand in a constant temperature bath at 40 °C for 3 days to obtain a dried film. This dried film was wrapped with a 200-mesh stainless steel wire mesh and immersed in tetrahydrofuran at 50 °C. The weight change of the dried film after 72 hours was measured, and the gel fraction was calculated from the following formula (2). Gel fraction [%] = {(weight after immersion in tetrahydrofuran) / (weight before immersion in tetrahydrofuran)} × 100 ··· Formula (2) [Measurement of glass transition temperature (Tg)] Measurement was carried out using a differential scanning calorimeter "DSC Q-100" (manufactured by TA Instrument) in accordance with the method specified in JIS K7121. Specifically, the dried sample was measured for heat quantity change in the range of -80 to 200 °C at a heating rate of 3 °C / min, and the point where a straight line equidistant from the vertical axis direction from the extended straight line of each baseline in the DSC chart intersects the curve of the stepwise change part of the glass transition was defined as the glass transition temperature. (Synthesis Examples 2 to 9, 12, 14) Except for changing the raw materials and compounding amounts shown in Tables 1 and 2, aqueous dispersions of acrylic resins (A-2) to (A-9), (A-12), and (A-14) were obtained in the same manner as in Synthesis Example 1. (Synthesis Example 10) Into a dropping tank, 2 parts of methacrylic acid, 10 parts of acrylonitrile, 37 parts of ethyl acrylate, 48 parts of butyl acrylate, 3 parts of 3-methacryloxypropyltrimethoxysilane, 7 parts of polyoxyethylene alkyl ether sulfate (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Hytenol 08E") as a surfactant, and 27 parts of water were charged and stirred to prepare a pre-emulsion liquid. Into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas inlet tube, and a dropping tank, 0.3 part of the above surfactant, 35 parts of water, and 1 part of the above pre-emulsion liquid were charged and the temperature was raised to 68°C. After confirming that the internal temperature of the reaction vessel was 68°C, 0.1 part of ammonium persulfate as a polymerization initiator and 0.05 part of sodium bisulfite as a reducing agent were added and an initial reaction was carried out for 5 minutes. After the completion of the initial reaction, while maintaining the reaction vessel at 70°C, the pre-emulsion liquid in the dropping tank, 0.3 part of ammonium persulfate, and 0.15 part of sodium bisulfite were added dropwise over 4 hours. After the completion of the dropping, the reaction was further carried out for 3 hours and then cooled to 40°C. Then, it was neutralized with 2.8 parts of an aqueous ammonia solution having a concentration of 25%, and water was added so that the solid content concentration became 55% to obtain an aqueous dispersion of an acrylic resin (A-10). (Synthesis Examples 11, 13) An aqueous dispersion of acrylic resins (A-11) and (A-13) was obtained in the same manner as in Synthesis Example 10 except that the raw materials and compounding amounts shown in Table 2 were changed. (Synthesis Example 15) 2 parts of acrylonitrile, 0.5 part of divinylbenzene, 7.5 parts of methyl methacrylate, 24 parts of n-butyl methacrylate, 66 parts of 2-ethylhexyl acrylate, 1 part of sodium lauryl sulfate as a surfactant, and 35 parts of water were charged into a dropping tank and stirred to prepare a pre-emulsion liquid. 35 parts of water was charged into a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas inlet tube, and a dropping tank, and the temperature was raised to 70°C. While maintaining the reaction vessel at 70°C, the pre-emulsion liquid in the dropping tank, 0.3 part of ammonium persulfate, and 0.15 part of sodium bisulfite were dropped over 4 hours. After completion of the dropping, the mixture was further reacted for 3 hours and then cooled to 40°C. Then, it was neutralized with 2.8 parts of an aqueous ammonia solution having a concentration of 25%, and water was added so that the solid content concentration became 55% to obtain an aqueous dispersion of an acrylic resin (A-15). (Synthesis Example 16) An acrylic resin (A-16) was obtained in the same manner as in Synthesis Example 15 except that the raw materials and compounding amounts shown in Table 2 were changed.

[0035] Tables 1 and 2 are shown below. The abbreviations in Tables 1 and 2 are as follows. The acrylic resins obtained in Synthesis Examples 1 to 8 are acrylic resins (A), and the acrylic resins obtained in Synthesis Examples 9 to 15 are acrylic resins that are not acrylic resins (A). AA ··· Acrylic acid MAA ··· Methacrylic acid IA ··· Itaconic acid ECA ··· Ethyl-2-cyanoacrylate MAN ··· Methacrylonitrile AN ··· Acrylonitrile DAP ··· Diallyl phthalate DVB ··· Divinylbenzene St ··· Styrene MMA ··· Methyl methacrylate nBMA ··· n-Butyl methacrylate EA ··· Ethyl acrylate BA ··· Butyl acrylate 2EHA ··· 2-Ethylhexyl acrylate HEMA ··· 2-Hydroxyethyl methacrylate

[0036] [Table 1]

[0037] [Table 2]

[0038] (Example 1) In a 500 mL plastic container, 172 parts of the aqueous dispersion of the acrylic resin (A-1) obtained in Synthesis Example 1 (100 parts as the acrylic resin (A-1)), 3 parts of N,N,N’,N’-tetraglycidyl-m-xylenediamine (manufactured by Mitsubishi Gas Chemical Company, trade name "Tetrad X") as the curing agent (2.6 moles of epoxy groups per mole of carboxyl groups of the acrylic resin (A-1)), 1.5 parts of an ammonium stearate aqueous dispersion (active ingredient 33% of "Nopco DC-100-A" manufactured by San Nopco Co., Ltd.) as the surfactant (C) (0.5 part as the solid content), and 1.0 part of sodium dialkyl sulfosuccinate (active ingredient 70% of "Pelec OTP" manufactured by Kao Corporation) (0.7 part as the solid content) were added, and the mixture was stirred so that no bubbles were generated to obtain a composition (1) for forming a shock-absorbing material. [Measurement of surface tension] The composition (1) for forming a shock-absorbing material obtained above was measured by the Wilhelmy method under the condition of 23°C using an automatic surface tension meter "DY-300" (manufactured by Kyowa Interface Science Co., Ltd.). The measurement was performed 5 times for the same sample, and the average of the measured values excluding the maximum value and the minimum value was taken as the surface tension of the sample. [Production of shock-absorbing material] The composition (1) for forming a shock-absorbing material was foamed to a three-fold volume by high-speed stirring using a hand mixer and coated on a release paper to a thickness of 3 mm. It was dried in a dryer at 130°C for 30 minutes to obtain a shock-absorbing material (1). [Appearance of shock-absorbing material] The shock-absorbing material (1) obtained above was cut, and its cross-section was visually confirmed and evaluated based on the following evaluation criteria.

[0039] 〇: Only bubbles with a diameter of less than 1 mm (excellent quality for use) △: There are also bubbles with a diameter of 1 mm or more, but no bubbles with a diameter of 2 mm or more (usable quality) ×: There are bubbles with a diameter of 2 mm or more (unusable quality) [Evaluation of compression recovery under humid heat conditions] A sheet obtained by cutting the shock-absorbing material (1) into a size of 20 mm in length, 20 mm in width, and 2 mm in thickness was laminated in 10 layers in the thickness direction to prepare a test piece with a thickness of 20 mm. In an atmosphere of 80°C and 80% humidity, it was compressed in the thickness direction until it reached 50% of the initial thickness, and the compressed state was maintained for 3 days. The thickness of the test piece 1 minute after releasing the compression was measured, and the compression recovery rate was determined from the following formula (3). The higher the compression recovery rate, the better it can be said, but the usability was evaluated based on the following evaluation criteria. Compression recovery rate [%] = (thickness 1 minute after releasing compression) / (initial thickness) ··· Formula (3) Compression recovery rate is 80% or more (usable quality) Compression recovery rate is less than 80% (unusable quality) (Examples 2 to 13, Comparative Examples 1 to 9) Except for changing the raw materials and compounding ratios shown in Tables 3 and 4, shock-absorbing material-forming compositions (2) to (21) were obtained in the same manner as in Example 1. In Tables 3 and 4, the numerical values in parentheses for the curing agent (B) represent the number of moles of epoxy groups in the curing agent (B) per mole of carboxyl groups in the acrylic resins (A-1) to (A-16).

[0040]

Table 3

[0041]

Table 4

[0042] From the compositions for forming the shock-absorbing material of the present invention in Examples 1 to 13, it was confirmed that shock-absorbing materials excellent in compression recovery under wet and heat conditions can be obtained. In particular, Examples 1, 6, 7, and 8 had very excellent quality.

[0043] In Comparative Examples 1, 2, and 4, since the Ti value of the aqueous dispersion of the acrylic resin (A) was larger than the appropriate range, it was confirmed that they were inferior in compression recovery under wet and heat conditions.

[0044] In Comparative Examples 6 and 7, since the Ti value of the aqueous dispersion of the acrylic resin (A) was smaller than the appropriate range, it is presumed that the compression recovery under wet and heat conditions is inferior because the bubbles of the shock-absorbing material become large.

[0045] In Comparative Examples 3 and 5, since the gel fraction of the acrylic resin (A) was low, it is presumed that the shock-absorbing material fused during the compression test under wet and heat conditions and was inferior in compression recovery.

[0046] In Comparative Examples 8 and 9, since the surface tension of the composition for forming the shock-absorbing material was large, the foam stability decreased, and it is presumed that the compression recovery under wet and heat conditions was inferior because the bubbles became large.

Claims

1. A composition for forming a shock-absorbing material, comprising an acrylic resin (A), a curing agent (B), a surfactant (C), and an aqueous liquid medium (D), wherein the gel fraction of the acrylic resin (A) is 60% or more, the Ti value represented by the following formula (1) in an aqueous dispersion having a concentration of the acrylic resin (A) of 55% by mass is 10 to 20, and the surface tension is 35 mN / m or less. A composition for forming a shock-absorbing material, characterized by the above. Ti value = (viscosity at a shear rate of 0.1 [1 / s]) / (viscosity at a shear rate of 10 [1 / s])... Formula (1)

2. In a total of 100% by mass of the ethylenically unsaturated monomers constituting the acrylic resin (A), 0.1 to 5% by mass of a carboxy group-containing ethylenically unsaturated monomer (ma), 0.1 to 5% by mass of a cyano group-containing ethylenically unsaturated monomer (mb), and 0.1 to 3% by mass of a monomer (mc) having two or more ethylenically unsaturated bonds are included, and the glass transition temperature of the acrylic resin (A) is -50 to 20°C. The composition for forming a shock-absorbing material according to Claim 1.

3. The composition for forming a shock-absorbing material according to Claim 1 or 2, wherein the curing agent (B) is an epoxy-based curing agent.

4. The composition for forming a shock-absorbing material according to Claim 1 or 2, wherein the surfactant (C) contains a fatty acid salt having 12 to 28 carbon atoms and / or a sulfosuccinate.

5. A shock-absorbing material formed from the composition for forming a shock-absorbing material according to Claim 1 or 2.

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