JP2008037956A - Resin composition for foamed sheet and foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for a foamed sheet affording the foamed sheet having excellent compression recovery properties. <P>SOLUTION: The resin composition for the foamed sheet is characterized by comprising an aqueous emulsion (A), heat expandable hollow spheres (B) and an inorganic filler (C). The aqueous emulsion (A) comprises an ethylene-vinyl ester-based copolymer containing 5-35 pts.wt. of a structural unit (a1) derived from ethylene and 95-65 pts.wt. of a structural unit (a2) derived from a vinyl ester and has 90-160°C flow middle point and <30 wt.% content of a toluene-insoluble portion. The heat expandable hollow spheres (B) have 15-30 μm average particle diameter, ≤30% C<SB>v</SB>coefficient of variation of particle size distribution and 10-30% amount of an entrapped gas. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resin composition for a foam sheet and a foam sheet formed by foaming the composition.

  Conventionally, a resin for a foamed sheet comprising an ethylene / vinyl ester copolymer-containing aqueous emulsion having a flow midpoint of 110 to 170 ° C. and a toluene insoluble content of less than 30% by weight, a thermally expandable hollow sphere, and an inorganic filler A composition is known (Patent Document 1).

It is disclosed that a foamed sheet obtained by foaming this composition is excellent in properties such as flame retardancy, foamability, crack resistance, and mechanical strength, and further excellent in blocking resistance.
JP 2003-13396 A

  However, when the present inventors examined a foamed sheet having a high foaming ratio of 6.5 to 8.5 times produced by using the technique described in Patent Document 1, there was a problem that the compression recovery property was not sufficient. It was revealed. Here, the compression recoverability refers to the recoverability of the weight of the foam sheet itself during storage and the crushing of dents and embossed irregularities caused by roller pressing during construction.

  An object of the present invention is to provide a resin composition for a foam sheet that has all of the expansion ratio, compression recovery property, and embossability and gives an excellent foam sheet.

The resin composition for a foam sheet according to the present invention includes 5 to 35 parts by weight of a structural unit (a1) derived from ethylene and 95 to 65 parts by weight of a structural unit (a2) derived from a vinyl ester, and has a flow midpoint. An aqueous emulsion (A) containing an ethylene / vinyl ester copolymer having a toluene insoluble content of less than 30% by weight at 90 to 160 ° C., an average particle diameter of 15 to 30 μm, and represented by the following formula: The thermal expansion hollow sphere (B) whose particle size distribution variation coefficient C _V is 30% or less and the amount of encapsulated gas is 10 to 30%, and the inorganic filler (C) are contained.

In the above formula, n is the number of thermally expandable hollow spheres whose particle diameter is measured, and i is 1 to n. Variation coefficient C _v of the particle size distribution value is the particle size the smaller means that nearly uniform.

  In the resin composition for a foam sheet of the present invention, the component (A) includes a surfactant and a protective colloid as a dispersant, and the weight ratio of (surfactant / protective colloid) is 25/75 to 90/10. Preferably there is.

  In the resin composition for a foam sheet of the present invention, 2 to 30 parts by weight of the heat-expandable hollow sphere (B) and 20 to 350 inorganic fillers (C) with respect to 100 parts by weight of the solid content of the component (A). It is preferable to contain a weight part.

  The foam sheet according to the present invention is obtained by foaming the above composition.

  ADVANTAGE OF THE INVENTION According to this invention, the resin composition for foamed sheets which has all of foaming magnification, compression recovery property, and embossing property and can provide the outstanding foamed sheet can be provided.

  Hereinafter, the present invention will be described in more detail.

  In the present invention, the component (A) contains 5 to 35 parts by weight of the structural unit (a1) derived from ethylene and 95 to 65 parts by weight of the structural unit (a2) derived from the vinyl ester, and has a flow midpoint of 90. It is an aqueous emulsion containing an ethylene / vinyl ester copolymer having a temperature of about -160 ° C, preferably about 110-150 ° C, and a toluene insoluble content of less than 30% by weight, preferably about 0.1-20%. . If the midpoint of flow is less than 90 ° C, the compression recovery tends to be poor, and if the midpoint of flow exceeds 160 ° C, the foamability tends to be poor.

  (A) The measuring method of the flow middle point of a component is demonstrated. First, the component (A) is dried according to the conditions of 4.9 of JIS K6828. Next, after heating a cylinder having an inner diameter of 1 mm × a length of 1 mm to an inner diameter of 10 mm to 80 ° C., about 1.7 g of the obtained dry resin is filled in the cylinder and preheated for 360 seconds. Subsequently, while heating at a rate of 6 ° C./min while applying a piston pressure of 2.9 MPa, the heating temperature of the cylinder when the piston is pushed down by 7.5 mm due to the resin flowing out of the die is defined as the flow middle point. To do. For example, a flow tester CFT-500 (manufactured by Shimadzu Corporation) is used as the measuring device for the midpoint of flow.

  (A) The measuring method of the toluene insoluble part of a component is demonstrated. The component (A) was dried at room temperature according to the conditions of 4.9 of JIS K6828, and then the resulting dried resin was cut into small pieces, and 0.5 g of the dried resin was used at 95 ° C. with 100 ml of toluene. After extraction for 3 hours, the mixture is filtered through a 300-mesh wire mesh, and the weight of the recovered insoluble matter is measured to obtain a toluene insoluble matter.

  The ethylene / vinyl ester copolymer constituting the component (A) contains a structural unit (a1) derived from ethylene and a structural unit (a2) derived from vinyl ester. Further, if necessary, it may contain a structural unit (a3) derived from a monomer that is copolymerizable with ethylene and vinylethylene and is different from ethylene and vinyl ester (hereinafter referred to as a copolymerizable monomer). .

  In the component (A), the content of the structural unit (a1) derived from ethylene is 5 to 35 parts by weight, preferably about 8 to 30 parts by weight with respect to 100 parts by weight of the solid content of the component (A). .

  Examples of the vinyl ester constituting the structural unit (a2) include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl laurate, and vinyl versatate. Among vinyl esters, vinyl acetate and a combination of vinyl acetate and other vinyl esters are preferable.

  The content of the structural unit (a2) derived from the vinyl ester in the component (A) is 95 to 65 parts by weight with respect to 100 parts by weight of the solid content of the component (A).

  Examples of the copolymerizable monomer constituting the structural unit (a3) include (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and (meth) acrylic acid. Butyl, amyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, (meth) (Meth) acrylic acids such as lauryl acrylate, stearyl (meth) acrylate, γ- (meth) acryloxypropylmethyldimethoxysilane; crotonic acid, itaconic acid (including half ester), maleic acid (including half ester) Carboxyl group-containing monomers such as and their anhydrides; N-methylolacrylamide, N- N-methylol derivative monomers such as toximethylacrylamide; hydroxy groups such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, mono (meth) acrylate of polyhydric alcohol and monoallyl ether of polyhydric alcohol Containing monomers; amino group-containing monomers such as dimethylaminoethyl methacrylate and dimethylaminopropyl acrylamide; epoxy group-containing monomers such as glycidyl (meth) acrylate; amide group-containing monomers such as acrylamide, methacrylamide and maleamide; sodium vinyl sulfonate; Sulfone group-containing monomers such as sodium methallyl sulfonate and sodium 2-acrylamido-2-methylpropane sulfonate; triallyl isocyanurate; vinyl tri Examples thereof include vinyl silanes such as chlorosilane and vinyl methoxysilane; vinyl halides such as vinyl chloride and vinyl bromide; styrene; olefins such as butadiene. Among the copolymerizable monomers, (meth) acrylic acids, N-methylol derivative monomers and triallyl isocyanurate are preferable, and acrylic acid, 2-ethylhexyl acrylate, N-methylol acrylamide and triallyl isocyanurate are particularly preferable. Is preferred. Two or more different copolymerizable monomers may be used.

  In the component (A), the content of the structural unit (a3) derived from the copolymerizable monomer is 30 parts by weight or less, preferably 10 parts by weight or less with respect to 100 parts by weight of the solid content of the component (A). is there.

  The glass transition temperature of the ethylene / vinyl ester copolymer constituting the component (A) is usually about −25 to 15 ° C., preferably about −10 to 5 ° C. If the glass transition temperature is lower than −25 ° C., the blocking resistance of the resulting foamed sheet tends to decrease, such being undesirable. On the other hand, if the glass transition temperature is higher than 15 ° C., the cold resistance of the resulting foamed sheet tends to decrease, which is not preferable.

  The component (A) is usually in the form of an aqueous emulsion, but may be in the form of a re-emulsifiable powder resin as described in JP-A-6-24820, for example.

  As a method for producing the component (A), for example, ethylene, vinyl ester and, if necessary, a copolymerizable monomer are emulsified using a surfactant and a protective colloid as a dispersant, and emulsion polymerization is performed under pressure. The method of obtaining as an aqueous emulsion containing a copolymer is mentioned.

  Examples of the surfactant used for the production of the component (A) include alkyl sulfate sulfonate, alkyl benzene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, polyoxyethylene alkali sulfate, and polyoxyethylene. Anionic surfactant such as alkyl phosphate ester; polyoxyethylene / polyoxypropylene block copolymer, polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan Nonionic surfactants such as fatty acid esters, polyoxyethylene alkylamines and glycerin fatty acid esters; cations such as alkylamine salts and quaternary ammonium salts Surfactants. Of these, alkyl sulfate ester salts, alkylbenzene sulfonates, alkylsulfosuccinates, and polyoxyethylene / polyoxypropylene block copolymers are preferred.

  Examples of the protective colloid used in the production of the component (A) include polyvinyl alcohols such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, and silanol group-modified polyvinyl alcohol. Cellulose derivatives such as hydroxyethylcellulose, methylcellulose, carboxymethylcellulose; Of these, partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol are preferable, and 80-100% saponified polyvinyl alcohol is particularly preferable. As the polyvinyl alcohol, those having a polymerization degree of about 300 to 3000 are usually used.

The weight ratio (solid content) of the surfactant and the protective colloid is usually (surfactant / protective colloid) = 25/75 to 90/10, preferably 25/75 to 85/15. If the weight ratio of the surfactant is 25 or more, the toluene insoluble matter tends to be less than 30% by weight, which is preferable.
In the present invention, two or more types of component (A) may be mixed and used.

  In the present invention, the thermally expansible hollow sphere as component (B) encapsulates a low boiling point liquid (volatile expansive agent) serving as an encapsulated gas in the hollow portion of a shell made of a polymer obtained by polymerizing a polymerizable monomer. It is a microcapsule. Such a heat-expandable hollow sphere is obtained by adding a polymerizable mixture containing a polymerizable monomer, a low-boiling-point liquid, a polymerization initiator, etc. to an aqueous phase dispersion medium containing a dispersion stabilizer, and stirring and mixing the fine particles. In a state where the droplets are dispersed, the temperature is raised to cause suspension polymerization of the droplet-like polymerizable mixture. The coefficient of variation of the average particle size and particle size distribution of the thermally expandable hollow sphere (B) can be adjusted, for example, by controlling the dispersion step by stirring and mixing, and the amount of inclusion gas is the low boiling point to be added. It can be adjusted by the amount of liquid.

  Examples of the polymerizable monomer used for the shell of the thermally expandable hollow sphere (B) include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, acrylic acid, methacrylic acid, itaconic acid. , Maleic acid, fumaric acid, citraconic acid, vinylidene chloride, vinyl acetate, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, (Meth) acrylic esters such as isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, β-carboxy (meth) acrylate, styrene such as styrene, α-methylstyrene, chlorostyrene Monomers, acrylamide, substituted acrylamides, methacrylamides, substituted methacrylamides, such as butadiene and the like. These polymerizable monomers can be used alone or in combination of two or more. The combination of the polymerizable monomers can be selected in consideration of the softening temperature, heat resistance, chemical resistance, etc. of the polymer depending on the application. For example, a copolymer containing vinylidene chloride and a copolymer containing a nitrile monomer are excellent in gas barrier properties. Further, as shown in Japanese Patent No. 2131557, a copolymer containing 80% by weight or more of a nitrile monomer is excellent in heat resistance and chemical resistance.

  The shell of the thermally expandable hollow sphere as the component (B) may contain a crosslinking agent as necessary. Examples of the crosslinking agent include divinylbenzene, ethylene glycol dimethacrylate, triethylene glycol dimethacrylate, triacryl formal, trimethylolpropane trimethacrylate, allyl methacrylate, 1,3-butyl glycol dimethacrylate, triallyl. Although isocyanate etc. are mentioned, it is not limited to these.

  As the polymerization initiator used for preparing the shell of the thermally expandable hollow sphere as the component (B) by polymerization, known substances such as peroxides and azo compounds can be used. Examples of the polymerization initiator include azobisisobutyronitrile, benzoyl peroxide, lauryl peroxide, diisopropyl peroxydicarbonate, t-butyl peroxide, and 2,2′-azobis (2,4-dimethylvaleronitrile). However, it is not limited to these. Preferably, an oil-soluble polymerization initiator soluble in the polymerizable monomer is used.

  As the low boiling point liquid that becomes the inclusion gas contained in the thermally expandable hollow sphere as the component (B), a gas that becomes a gas below the softening point of the shell during thermal expansion is used. Examples of the inclusion gas include propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, cyclopentane, hexane, heptane, petroleum ether, octane, isooctane, and decane. Preferably, isobutane, normal butane, isopentane, neopentane, cyclopentane, petroleum ether and the like are used alone or in admixture of two or more.

The thermally expandable hollow sphere as component (B) has an average particle diameter of 15 to 30 μm, a particle size distribution variation coefficient C _V of 30% or less, and an inclusion gas amount of 10 to 30%. When the variation coefficient C _V of the particle size distribution exceeds 30%, the surface of the foamed sheet becomes rough due to the destruction of the thermally expandable hollow sphere. When the thermally expandable hollow sphere as described above is foamed, the shell thickness at the time of foaming becomes 0.07 to 0.18 μm, and the compression recovery property of the obtained foamed sheet can be improved.

  The average particle diameter of the thermally expandable hollow sphere can be measured with a Microtrac particle size analyzer (for example, manufactured by Nikkiso). The average particle diameter is obtained by volume average.

  The amount of gas included in the thermally expandable hollow sphere is calculated as follows. An organic solvent is added to the dried thermally expandable hollow sphere to swell the outer wall of the sphere, and then the sphere is broken at a high temperature and the volatile content is measured. On the other hand, the moisture of the thermally expandable hollow sphere dried by a moisture measuring device is measured. The amount obtained by subtracting moisture from the volatile matter is taken as the amount of gas contained (%).

  The shell thickness of the thermally expandable hollow sphere at the time of foaming is measured as follows. The shell thickness is measured in advance by observing the cross section of the thermally expandable hollow sphere before foaming with a laser microscope. As the ethylene / vinyl ester copolymer-containing aqueous emulsion as component (A), for example, ethylene acetate having a flow midpoint of 130 to 150 ° C., a toluene insoluble content of 15% by weight or less, and an ethylene content of 15 to 20% by weight. An aqueous emulsion (A ′) containing a vinyl copolymer is prepared, and the aqueous emulsion (A ′): calcium carbonate (inorganic filler) and the thermally expandable hollow sphere are dried in a dry ratio. : Heat-expandable hollow sphere = 100: 60: 10 is blended and foamed under the conditions of 180 ° C. × 30 seconds to obtain the expansion ratio. The condition at this time is the maximum foaming condition, and the foaming ratio obtained is the maximum foaming ratio. Then, based on the shell thickness of the thermally expandable hollow sphere before foaming and the maximum expansion ratio, the shell thickness of the thermally expandable hollow sphere at the time of foaming is calculated.

  If the shell thickness during foaming is less than 0.07 μm, the compression recovery rate of the foam sheet tends to decrease, such being undesirable. When the shell thickness at the time of foaming exceeds 0.18 μm, the embossability of the foamed sheet is inferior, and it becomes difficult to form the embossing well when the roller is pressed. This is because the repulsion of the hollow sphere is enhanced when the hollow sphere having a thick shell of the foam sheet is present.

  If the average particle diameter of the thermally expandable hollow sphere before foaming is less than 15 μm, the shell thickness after foaming becomes thin and the compression recovery property of the foamed sheet tends to be inferior. When the average particle diameter of the thermally expandable hollow sphere before foaming exceeds 30 μm, it is difficult to form emboss on the foamed sheet and the surface property is inferior.

  When the encapsulated gas amount of the thermally expandable hollow sphere is less than 10%, the expansion ratio of the hollow sphere is reduced, and the emboss formed on the foamed sheet tends to be crushed, which is not preferable. If the amount of encapsulated gas in the thermally expandable hollow sphere exceeds 30%, the hollow sphere expands too much, the shell thickness after foaming becomes thin, and the compression recovery property of the foamed sheet tends to be inferior.

  In the present invention, two or more kinds of thermally expandable hollow spheres may be used as the component (B). In the composition of the present invention, the content of the thermally expandable hollow sphere as the component (B) is 2 to 30 parts by weight, preferably 5 to 15 parts by weight per 100 parts by weight of the solid content of the component (A). If the heat-expandable hollow sphere is less than 2 parts by weight, the foamability tends to be insufficient. If the thermally expandable hollow sphere exceeds 30 parts by weight, the mechanical strength of the foamed sheet tends to decrease, such being undesirable.

  In the present invention, as the inorganic filler as the component (C), for example, aluminum hydroxide, magnesium hydroxide, barium hydroxide, calcium carbonate, magnesium carbonate, calcium sulfate, barium sulfate, silica sand, clay, talc, silicas, Examples thereof include titanium dioxide and magnesium silicate. Of these, aluminum hydroxide, magnesium hydroxide, calcium carbonate, magnesium carbonate, and titanium dioxide are preferable.

  In the composition of the present invention, the content of the inorganic filler as the component (C) is 20 to 350 parts by weight, preferably 50 to 150 parts by weight per 100 parts by weight of the solid content of the component (A). If the inorganic filler is less than 20 parts by weight, the flame retardancy tends to decrease, such being undesirable. When the inorganic filler exceeds 350 parts by weight, the foamability, the mechanical strength of the foamed sheet, and the crack resistance tend to be inferior, which is not preferable.

  Examples of the resin composition for a foam sheet of the present invention include flame retardants other than inorganic fillers such as dyes, pigments, thickeners, dispersants, brominated epoxy resins, brighteners, thixotropic agents, adhesion promoters, You may contain additives, such as surface modifiers, such as surfactant, a ultraviolet absorber, anti-aging agent, antioxidant, and an antistatic agent. Moreover, you may mix | blend other emulsions other than this invention, such as EVA emulsion, water-based polyurethane, SBR, an acrylic emulsion, or water-soluble resin in the range which does not have a bad influence on the compression recovery property of a foam sheet.

  In order to produce a foam sheet from the resin composition for a foam sheet according to the present invention, the resin composition is applied to a sheet base material with a coating such as a die coater, a lip coater, a comma coater, a knife coater, and a reverse roll coater. , Drying, printing, foaming, embossing and the like.

  Examples of the sheet base material to which the composition is applied include plain paper, newspaper, recycled paper, flame retardant paper, release paper, coated paper, cloth, plastic sheet, metal thin film, foaming treatment, embossing, etc. The thing which can construct etc. is mentioned.

[Production of EVA emulsion]
In this example, the total amount of vinyl acetate used was 100 parts by weight, and the blending amounts of other components were adjusted based on this.

Example 1
As initial charge, 75 parts by weight of vinyl acetate, polyvinyl alcohol (“Poval 203” manufactured by Kuraray Co., Ltd., saponification degree 88 mol%, average polymerization degree 300) 0.60 part by weight (equivalent to 40% of the total amount of polyvinyl alcohol used) Polyoxyethylene alkyl ether nonionic surfactant ("Emulgen 1135S-70" manufactured by Kao Corporation), 1.50 parts by weight, polyoxyethylene propylene condensate nonionic surfactant ("Buluronic L64" manufactured by Asahi Denka Kogyo Co., Ltd.) 2.25 parts by weight and 36 parts by weight of water, Emulgen 1135S-70 has a non-volatile content of 70% and is used for emulsion polymerization.In this example, surfactant / protective colloid = 68.4 / 31 Therefore, the range of 25/75 to 90/10 of claim 2 is satisfied. The polymerization was started from 25 ° C., and the temperature was raised stepwise to 60 ° C. and then kept at 60 ° C. until the completion of the polymerization. pressure was maintained at 45 kg / cm ² in. 0.30 parts by weight of sodium Erisoribin acid relative to the total amount of vinyl acetate as. the reducing agent used was a redox system as polymerization catalyst, as the oxidizing agent hydrogen peroxide Using 0.12 parts by weight with respect to the total amount of vinyl acetate, 8% of the reducing agent was added all at the time of initial charging, and the remaining reducing agent and oxidizing agent were continuously added during the polymerization.

  After the initiation of polymerization, 25 parts by weight of vinyl acetate and 0.90 part by weight of polyvinyl alcohol (same as above) were continuously added as a post-addition. The post-addition started from 1 hour after the start of polymerization and was completed after 7 hours. The polymerization reaction was terminated when the residual amount of vinyl acetate in the reaction system became 1% or less. The obtained aqueous emulsion contains a copolymer having an ethylene / vinyl acetate weight ratio of 18/82, a glass transition temperature of 0 ° C., a solid content of 73.1%, a viscosity of 4000 mPa · s, and a pH. 5.1, toluene insoluble content was 10%, and the heat flow midpoint was 140 ° C. This is referred to as EVA emulsion A1.

[Production of thermally expandable hollow sphere]
In this example, a thermally expandable hollow sphere was produced according to the method described in JP-A-2004-959.

  To 600 g of ion-exchanged water, 150 g of sodium chloride, 1.5 g of adipic acid-diethanolamine condensate and 80 g of a colloidal silica 20% aqueous solution are added, and then the pH is adjusted to 4 with sulfuric acid. To do. Acrylonitrile (180 g), methacrylonitrile (105 g), methyl methacrylate (15 g), dimethacrylic acid trimethylolpropane (1 g), isopentane (100 g), and azobisisobutyronitrile (1 g) are mixed, stirred and dissolved to obtain an oil phase. A water phase and an oil phase are mixed, and it stirs at 10000 rpm and 2 minutes by CLEARMIX, and makes it a suspension. This was transferred to a 1.5 L pressure reactor, purged with nitrogen, and reacted at 70 ° C. for 15 hours with stirring. The obtained reaction product was filtered to obtain a thermally expandable hollow sphere (MC1) having an average particle size of 29 μm, a coefficient of variation Cv of 22%, and an inclusion gas amount of 23%.

Example 2
The reaction was carried out in the same manner as in Example 1 except that 85 g of isopentane and the rotation speed of CLEARMIX were changed to 15000 rpm. The obtained reaction product was filtered to obtain a thermally expandable hollow sphere (MC2) having an average particle diameter of 23 μm, a coefficient of variation Cv of 30%, and an inclusion gas amount of 20%.

Comparative Example 1
After adding 2 g of adipic acid-diethanolamine condensate and 80 g of colloidal silica 20% aqueous solution to 700 g of ion-exchanged water, the pH is adjusted to 4 with sulfuric acid and mixed uniformly to obtain an aqueous phase. Acrylonitrile (180 g), methyl methacrylate (120 g), trimethacrylic acid trimethylolpropane (1 g), isopentane (150 g), and azobisdimethylvaleronitrile (1 g) are mixed, stirred and dissolved to obtain an oil phase. The aqueous phase and the oil phase are mixed and stirred with a TK homomixer at 7000 rpm for 3 minutes to obtain a suspension. This was transferred to a 1.5 L pressure reactor, purged with nitrogen, and then reacted at 60 ° C. for 12 hours with stirring. The obtained reaction product was filtered to obtain a thermally expandable hollow sphere (MC3) having an average particle diameter of 7 μm, a coefficient of variation Cv of 54%, and an inclusion gas amount of 32%.

Comparative Example 2
The reaction was performed in the same manner as in Example 1 except that 100 g of colloidal silica, 110 g of isopentane, and the rotation speed of CLEARMIX were set to 15000 rpm. The obtained reaction product was filtered to obtain a thermally expandable hollow sphere (MC4) having an average particle size of 9 μm, a coefficient of variation Cv of 24%, and an inclusion gas amount of 25%.

Comparative Example 3
The reaction was performed in the same manner as in Example 1 except that 70 g of colloidal silica and 60 g of isopentane were used. The obtained reaction product was filtered to obtain a thermally expandable hollow sphere (MC5) having an average particle diameter of 31 μm, a coefficient of variation Cv of 21%, and an inclusion gas amount of 15%.

[Measurement of Particle Size, Shell Thickness, Encapsulated Gas Amount, Foaming Ratio of Composition, and Shell Thickness at Foaming of Thermally Expanded Hollow Sphere]
The particle size of the thermally expanded hollow sphere was measured with a Nikkiso Microtrac particle size analyzer.

  The shell layer of the thermally expanded hollow sphere before foaming was measured by observing the cross section of the hollow sphere with an Olympus scanning confocal laser microscope (model OLS1100).

The amount of encapsulated gas was calculated as follows. 30 ml of an organic solvent (acetonitrile) is added to 1 g of the dried hollow spheres, left to stand for 30 minutes and sufficiently swollen, and then the hollow spheres are broken at a high temperature and the volatile content is measured. Separately from this, the moisture content of the hollow spheres dried by the moisture measuring device was determined, and the amount of encapsulated gas was calculated according to the following formula.
Inclusion gas amount (%) = volatile content (%) − water content (%).

  The foaming ratio of the composition was determined as follows. The above EVA emulsion A1 was used as the aqueous emulsion (A ′). EVA emulsion A1 / calcium carbonate / thermally expansible hollow sphere = 100/60/10 (dry ratio) was applied to a fine paper with an applicator, 0.2 mm, and a foaming agent was applied. Dry in a temperature range that does not foam and measure the film thickness of the paint film. Heat treatment (180 ° C. × 30 seconds) is performed, and the coating thickness after foaming is measured. The expansion ratio is determined according to the following formula.

Foaming ratio = Thickness of coating layer after foaming / Thickness of coating layer before foaming (Thickness of coating layer after foaming = Thickness of all layers after foaming−Thickness of fine paper,
The thickness of the coating layer before foaming = the thickness of all layers before foaming-the thickness of the fine paper).

The shell thickness of the hollow sphere at the time of foaming was calculated on the assumption that the thermally expandable hollow sphere before foaming expanded from the original shell thickness to the expansion ratio obtained above as a true sphere.
These measured values are shown in Table 1 below.

[Production example of wallpaper coating composition and foamed wallpaper]
As shown in Table 1 below, the solid content of EVA emulsion is 100 parts by weight, the thermally expandable hollow sphere is 10 parts by weight, the dispersant is 1.5 parts by weight, the inorganic filler (calcium carbonate) is 80 parts by weight, and the antifoaming agent is 0.9 parts by weight. A coating composition for foamed wallpaper was prepared by blending parts by weight, 0.5 parts by weight of an antiblocking agent, 1.1 parts by weight of a wetting agent, and 15 parts by weight of an inorganic pigment, and a foamed wallpaper was prepared as follows.
Base material: wallpaper base paper, coating amount: 140 g / m ² (dry)
Drying conditions: hot air dryer 90 ° C. × 3 minutes, foaming conditions: 180 ° C. × 30 seconds.

The foaming ratio, compression recovery rate, and embossability of the foamed wallpaper were examined as follows.
(1) Foaming ratio Foaming ratio = (foamed layer thickness of wallpaper after foaming) / (thickness of wallpaper composition dry coating film before foaming)
(2) Compression recovery rate After pressurizing under the condition of a surface pressure of 250 g / cm ² × 24 hours, the pressure was released and the thickness after 24 hours was measured.
Compression recovery rate = (thickness of foamed wallpaper after 24 hours of decompression) × 100 / (thickness of wallpaper before pressurization)
(3) Embossing property Mechanical embossing was performed. FIG. 1 shows a cross-sectional view of the embossed wallpaper. As shown in FIG. 1, a foam wallpaper 2 is formed on a substrate 1. The foamed wallpaper 2 has a structure in which an inorganic filler (not shown) and a foamed hollow sphere 22 are dispersed in an ethylene / vinyl ester copolymer 21. The surface of the foam wallpaper 2 is a printing surface 3, and an emboss 4 is processed on this surface. Here, the case where the reproducibility of the pattern of the embossed plate was good was evaluated as ◯, and the case where the reproducibility of the embossed plate was poor was evaluated as x.
These results are also shown in Table 1. As can be seen from Table 1, the foamed wallpaper of Examples 1 and 2 has a high foaming ratio and can achieve both a high compression recovery rate of 95% or more and good embossability.

Cross section of embossed wallpaper.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Base material, 2 ... Foam wallpaper, 21 ... Ethylene vinyl ester copolymer, 22 ... Hollow sphere, 3 ... Printing surface, 4 ... Embossing.

Claims (4)

5 to 35 parts by weight of the structural unit (a1) derived from ethylene and 95 to 65 parts by weight of the structural unit (a2) derived from the vinyl ester, the flow midpoint is 90 to 160 ° C., and the toluene insoluble content is 30 An aqueous emulsion (A) containing an ethylene-vinyl ester copolymer that is less than% by weight;
A thermally expandable hollow sphere (B) having an average particle diameter of 15 to 30 μm, a coefficient of variation C _V of a particle size distribution represented by the following formula of 30% or less, and an inclusion gas amount of 10 to 30%;

A resin composition for a foam sheet, comprising an inorganic filler (C).   The component (A) contains a surfactant and a protective colloid as a dispersant, and the weight ratio of (surfactant / protective colloid) is 25/75 to 90/10. Resin composition for foam sheet.   The heat-expandable hollow sphere (B) is contained in an amount of 2 to 30 parts by weight and the inorganic filler (C) is contained in an amount of 20 to 350 parts by weight based on 100 parts by weight of the solid content of the component (A). Item 3. The resin composition for a foam sheet according to Item 1 or 2.   A foam sheet obtained by foaming the composition according to any one of claims 1 to 3.

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