JP6441653B2 - Thermally expandable microcapsule and stampable sheet molded body - Google Patents

Description

The present invention uses a thermally expandable microcapsule having excellent gas barrier properties, excellent durability over a long period of time at high temperature, and hardly causing coloration when used in foam molding, and the thermally expandable microcapsule. The present invention relates to a stampable sheet molded body.

Thermally expandable microcapsules are used in a wide range of applications as a design-imparting agent and a lightening agent, and are also used in paints for the purpose of weight reduction such as foamed ink and wallpaper.
As such a heat-expandable microcapsule, one in which a volatile expansion agent that becomes gaseous at a temperature below the softening point of the shell polymer is included in a thermoplastic shell polymer is widely known. In Patent Document 1, an oily mixed liquid obtained by mixing a volatile expansion agent such as a low-boiling point aliphatic hydrocarbon with a monomer is added to an aqueous dispersion medium containing a dispersant together with an oil-soluble polymerization catalyst while stirring. A method for producing thermally expandable microcapsules encapsulating a volatile swelling agent by performing suspension polymerization is disclosed.

However, although the heat-expandable microcapsules obtained by this method can be thermally expanded by gasification of a volatile expansion agent at a relatively low temperature of about 80 to 130 ° C., they expand when heated at a high temperature or for a long time. There has been a problem that the expansion ratio is reduced by the escape of gas from the microcapsules. In addition, due to problems with heat resistance and strength of the thermally expandable microcapsules, a phenomenon called “sag” has occurred and sometimes collapsed at high temperatures.

On the other hand, Patent Document 2 discloses a thermally expansible microscopic material having a 5% thermal weight loss temperature of 280 to 350 ° C. with a vinyl monomer having an epoxy group or an isocyanate group and a vinyl monomer having a hydroxyl group or an amino group as constituent units. A capsule is disclosed.
Such thermally expandable microcapsules are said to have excellent mechanical strength even under high temperature and high humidity.
However, since the gas barrier property is still low, there is a problem that it cannot withstand high-temperature and long-time heating, and there is a problem that gas escapes during heating and foaming does not occur in the foaming process.

Patent Document 3 discloses that the foaming start temperature Ts and the maximum foaming temperature Tmax satisfy the relationship of 120 <Ts ≦ 250 and 0 ≦ Tmax−Ts <30. A method for obtaining a compact is disclosed.
However, since the particles obtained by the method of Patent Document 3 have low gas barrier properties, there is a problem that foaming displacement is small and does not swell so much. There is also a problem that it cannot withstand high temperature and long time heating.

JP-T42-26524 JP 2005-272633 A Japanese Patent No. 5512404

In particular, since car ceiling materials are manufactured through a foam molding process at a high temperature for a long time, the heat-expandable microcapsules used as a foaming agent have higher durability and heat resistance for a longer time than before. Is required.
Therefore, in order to improve the durability, a method is used in which a monomer having an amide group and a compound having a glycidyl group are used to crosslink the amide group and the glycidyl group.

However, when such a method is used, although heat resistance and durability can be improved by using methacrylamide, there is a problem that the resulting particles are colored yellowish brown. Also, when using acrylamide, compared to using methacrylamide, it is possible to prevent yellowish brown coloration, but the effect of improving the heat resistance and durability of the resulting particles is insufficient. was there.

In order to solve the above-mentioned problems, the present invention provides a thermally expandable microcapsule having excellent gas barrier properties, excellent durability over a long period of time at high temperature, and hardly causing coloring when used in foam molding, An object of the present invention is to provide a stampable sheet molding using a thermally expandable microcapsule.

The present invention relates to a thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell, and the shell includes a nitrile monomer, a monomer having an amide group, and a molecule. A monomer composition containing a compound having a glycidyl group is polymerized, and the monomer having an amide group includes at least one of acrylamide and methacrylamide, and the monomer having a glycidyl group in the molecule is It contains at least one of glycidyl methacrylate and 2 to 5 functional epoxy compounds, and the monomer composition contains 0.1 to 7% by weight of the monomer having the amide group and 0.1 to 0.1% of the compound having the glycidyl group. It is a thermally expandable microcapsule containing 5% by weight.
The present invention is described in detail below.

The present inventors set the content of the monomer having a specific amide group and the compound having a glycidyl group in the molecule as a raw material for the shell constituting the thermally expandable microcapsule within a predetermined range. By doing so, it has been found that high foaming ratio can be realized in a wide range of temperature from low temperature to high temperature, and coloring at the time of foam molding can be suppressed while having high durability for a long time at high temperature. .

The thermally expandable microcapsule of the present invention has a structure in which a volatile expansion agent is included as a core agent in a shell made of a polymer. By having such a structure, for example, by molding the thermally expandable microcapsule of the present invention in a matrix resin, the core agent becomes gaseous by heating during molding, and the shell softens. The foamed article can be produced.

The monomer composition for forming the polymer contains a nitrile monomer. When the monomer composition contains the nitrile monomer, the resulting heat-expandable microcapsules have high heat resistance and gas barrier properties.
The nitrile monomer is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, or a mixture thereof. Of these, acrylonitrile and methacrylonitrile are particularly preferred. These may be used independently and 2 or more types may be used together.

The preferable lower limit of the content of the nitrile monomer in the monomer composition is 80% by weight, and the preferable upper limit is 99% by weight. When the content of the nitrile monomer is 80% by weight or more, the gas barrier property is not lowered, and a high expansion ratio can be obtained. When the content is 99% by weight or less, the content of other components can be made sufficient, and the effect obtained by bonding of the amide group and the glycidyl group at the time of heat foaming can be sufficiently obtained.
A more preferred lower limit is 85% by weight, and a more preferred upper limit is 98% by weight.

The monomer composition for forming the polymer contains a monomer having an amide group.
The monomer having an amide group includes at least one of acrylamide and methacrylamide. When the monomer composition contains the monomer having the amide group, the resulting heat-expandable microcapsule bonds the amide group and the compound having a glycidyl group in the molecule due to heat generated when heating and foaming. Further, heat resistance and durability can be further improved.

The content of the monomer having an amide group in the monomer composition is from 0.1% by weight to 7% by weight with respect to 100% by weight of the total monomer composition.
When the content of the monomer having an amide group is 0.1% by weight or more, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming can be made sufficient. When the content of the monomer having an amide group is 7% by weight or less, coloring of the stampable sheet molding can be suppressed.
The content of the compound having an amide group is preferably 1% by weight, more preferably 3% by weight, more preferably 6% by weight, and more preferably 5% by weight.

When the monomer composition contains acrylamide as a monomer having an amide group, the content of acrylamide in the monomer composition is preferably 1% by weight with a preferred lower limit and 7% by weight with a preferred upper limit.
When the content of the acrylamide is 1% by weight or more, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming can be made sufficient. When the acrylamide content is 7% by weight or less, coloring of the stampable sheet molding can be suppressed.
The content of the acrylamide is more preferably a lower limit of 2% by weight and a more preferable upper limit of 6% by weight.

When the monomer composition contains methacrylamide as a monomer having an amide group, the content of methacrylamide in the monomer composition is preferably 0.1% by weight and preferably 6% by weight.
When the content of the methacrylamide is 0.1% by weight or more, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming can be made sufficient. When the content of the methacrylamide is 6% by weight or less, when the obtained heat-expandable microcapsules are used for foam molding, it is possible to sufficiently suppress the occurrence of coloring in the molded body.
The more preferable lower limit of the methacrylamide content is 0.5% by weight, and the more preferable upper limit is 5% by weight.

When the monomer composition contains acrylamide and methacrylamide as monomers having an amide group, the content ratio of acrylamide to methacrylamide (acrylamide / methacrylamide) has a preferable lower limit of 0.01 and a preferable upper limit of 100.
When the thermally expandable microcapsule obtained when the content ratio of acrylamide to methacrylamide is 0.01 or more is used for foam molding, coloring of the molded product can be sufficiently suppressed. When the content ratio of acrylamide to methacrylamide is 100 or less, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming can be made sufficient.
The content ratio of acrylamide to methacrylamide is more preferably a lower limit of 0.1 and a more preferable upper limit of 10.

The monomer composition may contain a monomer having an amide group other than acrylamide and methacrylamide as the monomer having an amide group (hereinafter also referred to as “a monomer having another amide group”).
Examples of the other monomer having an amide group include N-substituted (meth) acrylamide, N, N-substituted (meth) acrylamide, and N-vinylamide.
Examples of the N-substituted (meth) acrylamide include N-methylolacrylamide, N-methylolmethacrylamide, N-methoxymethylacrylamide, N-isopropoxymethylacrylamide, N-butoxymethylacrylamide, N-isobutoxymethylacrylamide, N-octyloxymethylacrylamide, N-carboxymethyleneoxymethylacrylamide, isopropylacrylamide and the like can be mentioned.
Examples of the N, N-substituted (meth) acrylamide include dimethylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, and the like.
Examples of the N-vinylamide include N-vinylacetamide.
When N-substituted (meth) acrylamide or N, N-substituted (meth) acrylamide is used as the monomer having the other amide group, the number of carbon atoms of the substituent on nitrogen is preferably 1 to 4, more preferably. Has 1-2 carbon atoms of the substituent on the nitrogen.

When the monomer composition contains a monomer having the other amide group, the content of the monomer having the other amide group is preferably 0.1% by weight with respect to 100% by weight of the total monomer composition. The preferred upper limit is 5% by weight.
When the content of the other amide group-containing monomer is 0.1% by weight or more, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming can be made sufficient. . When the amount is 5% by weight or less, when the obtained heat-expandable microcapsules are used for foam molding, it is possible to sufficiently suppress the occurrence of coloring in the molded body.
The more preferable lower limit of the content of the monomer having another amide group is 0.5% by weight, and the more preferable upper limit is 3% by weight.

The monomer composition for forming the polymer contains at least one of glycidyl methacrylate and a 2-5 functional epoxy compound as a compound having a glycidyl group in the molecule.
While the glycidyl group and the amide group undergo a curing reaction at 140 to 300 ° C., the temperature at the time of polymerization is generally 100 ° C. or less, and therefore the glycidyl group and the amide group are cured at the time of polymerization of the polymer. There is no reaction.
On the other hand, since the temperature at the time of heat expansion of the thermally expandable microcapsule is generally 100 to 300 ° C., the glycidyl group reacts with the amide group at a high temperature at the time of heat expansion, thereby providing high heat resistance and gas barrier properties. Can be realized. Further, the shape can be maintained even after expansion, and the retainability is excellent.
The compound having a glycidyl group in the molecule cures not at the time of polymerization of the monomer composition but at the time of heat expansion of the thermally expandable microcapsule, so that the expansion at the time of expansion is not hindered and the expansion ratio is increased. Can do.

The compound having a glycidyl group in the molecule may be a monomer that forms a shell by being polymerized with a nitrile monomer or the like, and is not polymerized with a nitrile monomer or the like. It may be contained in a shell made of
For example, when the compound having a glycidyl group in the molecule is a compound having at least one polymerizable unsaturated bond in the molecule such as glycidyl methacrylate, the compound having a glycidyl group in the molecule is polymerized with a nitrile monomer or the like. By being incorporated into the main chain of the shell polymer, the curability of the thermally expandable microcapsule when heated and foamed can be further strengthened, and the heat resistance and durability can be greatly improved. .
When the compound having a glycidyl group in the molecule is a compound having two or more glycidyl groups in the molecule and having no polymerizable unsaturated bond, the compound having a glycidyl group in the molecule is a nitrile monomer. It is contained in a shell made of a polymer such as amide group and glycidyl group more strongly bonded by heat when heat-expanding microexpandable microcapsules is heated and foamed, and heat resistance and durability can be greatly improved. It becomes possible.

The said 2-5 functional epoxy compound means the compound which has 2-5 glycidyl groups in a molecule | numerator.
Examples of the 2 to 5 functional epoxy compound include bisphenol A type epoxy resin (jER-828: manufactured by Mitsubishi Chemical Corporation, number of glycidyl groups: 2), hydrogenated bisphenol A type epoxy resin (YX-8000: manufactured by Mitsubishi Chemical Corporation). , Number of glycidyl groups: 2), bisphenol F type epoxy resin (jER-807: manufactured by Mitsubishi Chemical Corporation, number of glycidyl groups: 2), biphenyl type epoxy resin (YX-4000: manufactured by Mitsubishi Chemical Corporation, number of glycidyl groups) : 2), phenol novolac type epoxy resin (jER-152: manufactured by Mitsubishi Chemical Corporation, number of glycidyl groups: 2), cresol novolac type epoxy resin (N-660: manufactured by DIC Corporation, number of glycidyl groups: 2-4) , Dicyclopentadiene type epoxy resin (HP-7200L: manufactured by DIC, number of glycidyl groups: 2 to 4), glycidyl Emission type epoxy resin (jER-630: manufactured by Mitsubishi Chemical Corporation, the number of glycidyl groups: 2) and epoxy resins such as.

Examples of the 2-5 functional epoxy compound include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, and cyclohexanedimethanol diglycidyl ether. , Triethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, pentaerythritol polyglycidyl ether, trimethylolpropane polyglycidyl ether, etc. Alternatively, a compound having 2 to 5 glycidyl groups may be used.
In addition, the repeating number of the oxyethylene part of the polyethylene glycol diglycidyl ether is not particularly limited. For example, the repeating number of the oxyethylene part is 2, 4, 9, 13, or 23 (n = 2, 4, 9, 13, or 23). Polyethylene glycol diglycidyl ether can be used. In addition, the number of repetitions of the oxypropylene portion of the polypropylene glycol diglycidyl ether is not particularly limited. For example, the number of repetitions of the oxypropylene portion is 2, 3 or 11 (n = 2, 3 or 11). Can be used.
A compound having two or more glycidyl ether structures in the molecule may be used.
Examples of the compound having two or more glycidyl ether structures in the molecule include, for example, polyglycidyl ether of a compound in which 0 to 1 mol of epichlorohydrin is added to 1 mol of glycerin and a mixture thereof, or epichlorohydrin to 1 mol of ethylene glycol. Also included are polyglycidyl ethers of compounds to which 0 to 2 moles have been added, and mixtures thereof.

Content of the compound which has a glycidyl group in the said molecule | numerator in the said monomer composition is 0.1 to 5 weight% with respect to 100 weight% of all monomer compositions.
When the content of the compound having a glycidyl group is 0.1% by weight or more, the effect obtained by combining with a monomer having an amide group at the time of heat foaming can be made sufficient. When the content of the compound having a glycidyl group is 5% by weight or less, a sufficient expansion ratio can be obtained at the time of heat foaming.
As for content of the said compound which has a glycidyl group, a more preferable minimum is 1 weight% and a more preferable upper limit is 3 weight%.

When the monomer composition contains glycidyl methacrylate as the compound containing the glycidyl group, the content of glycidyl methacrylate with respect to 100% by weight of the total monomer composition is preferably 0.1% by weight, and preferably 5% by weight. It is.
When the content of the glycidyl methacrylate is 0.1% by weight or more, the effect obtained by combining with a monomer having an amide group at the time of heating and foaming can be made sufficient. When the content of the glycidyl methacrylate is 5% by weight or more, a sufficient expansion ratio can be obtained at the time of heat foaming.
The more preferable lower limit of the glycidyl methacrylate content is 0.5% by weight, and the more preferable upper limit is 2% by weight.

When the said monomer composition contains the said 2-5 functional epoxy compound, as for content of the said 2-5 functional epoxy compound with respect to 100 weight% of all monomer compositions, a preferable minimum is 0.1 weight% and a preferable upper limit Is 5% by weight.
When the content of the 2-5 functional epoxy compound is 0.1% by weight or more, the effect obtained by bonding with a monomer having an amide group at the time of heat foaming can be made sufficient. When the content of the 2 to 5 functional epoxy compound is 5% by weight or less, a sufficient expansion ratio can be obtained at the time of heat foaming.
As for content of the said 2-5 functional epoxy compound, a more preferable minimum is 0.3 weight% and a more preferable upper limit is 3 weight%.

When the monomer composition contains glycidyl methacrylate and the 2-5 functional epoxy compound, the content ratio of glycidyl methacrylate to the 2-5 functional epoxy compound (glycidyl methacrylate / 2-5 functional epoxy compound) is preferably the lower limit. Is 0.1, and a preferred upper limit is 10.
When the content ratio of glycidyl methacrylate to the 2-5 functional epoxy compound is 0.1 or more, the effect obtained by combining with a monomer having an amide group at the time of heat foaming can be made sufficient. When the content ratio of glycidyl methacrylate to the 2-5 functional epoxy compound is 10 or less, a sufficient expansion ratio can be obtained at the time of heat foaming.
As for the content ratio of the glycidyl methacrylate with respect to the said 2-5 functional epoxy compound, a more preferable minimum is 0.2 and a more preferable upper limit is 5.

The monomer composition contains a compound having a glycidyl group in a molecule other than glycidyl methacrylate and the 2-5 functional epoxy compound (hereinafter also referred to as “compound having a glycidyl group in another molecule”). May be.

Examples of the compound having a glycidyl group in the other molecule include a glycidyl group-containing monomer and an epoxy resin having 6 or more glycidyl groups in the molecule.
In addition, a glycidyl group containing monomer means the monomer which has a glycidyl group and a radically polymerizable double bond.

Examples of the glycidyl group-containing monomer include glycidyl acrylate, allyl glycidyl ether, 4-hydroxybutyl acrylate glycidyl ether, phenol type epoxy diacrylate, allyl alcohol type epoxy diacrylate, 1,6-hexanediol type epoxy diacrylate, and bisphenol type. Epoxy (meth) acrylates such as epoxy diacrylate, phthalic acid type epoxy diacrylate, polypropylene glycol type epoxy diacrylate (n = 1, 3, 11), polyethylene glycol type epoxy dimethacrylate (n = 1, 2, 9), etc. Can be mentioned.

When the monomer composition contains a compound having a glycidyl group in the other molecule, the preferred lower limit of the content of the compound having a glycidyl group in the other molecule is 100% by weight based on 100% by weight of the total monomer composition. 1% by weight, and a preferred upper limit is 4% by weight.
When the content is 0.1% by weight or more, the effect obtained by combining with a monomer having an amide group at the time of heat foaming can be made sufficient. When the content is 4% by weight or less, a sufficient expansion ratio can be obtained during heat foaming.
The content is more preferably a lower limit of 0.3% by weight and a more preferable upper limit of 3% by weight.

The content ratio of the monomer having an amide group to the compound having a glycidyl group in the molecule (a monomer having an amide group / a compound having a glycidyl group in the molecule) has a preferable lower limit of 0.2 and a preferable upper limit of 70. .
When the content of the monomer having an amide group with respect to the compound having a glycidyl group in the molecule is within the above range, the effect obtained by bonding with the compound having a glycidyl group in the molecule at the time of heat foaming is further improved. Become.
The content ratio of the monomer having an amide group to the compound having a glycidyl group in the molecule has a more preferable lower limit of 1.0 and a more preferable upper limit of 30.

The content ratio of the monomer having an amide group to the nitrile monomer (monomer having an amide group / nitrile monomer) has a preferable lower limit of 0.01 and a preferable upper limit of 0.1.
When the content of the monomer having an amide group with respect to the nitrile monomer is within the above range, the effect obtained by bonding with a compound having a glycidyl group in the molecule at the time of heat foaming is further improved.
The content ratio of the amide group-containing monomer to the nitrile monomer is more preferably a lower limit of 0.03 and a more preferable upper limit of 0.07.

The monomer composition preferably further contains a crosslinkable monomer having two or more double bonds in the molecule. The crosslinkable monomer has a role as a crosslinking agent. By containing the crosslinkable monomer, the strength of the shell can be enhanced, and the cell wall is less likely to break during thermal expansion. The crosslinkable monomer having two or more double bonds in the molecule does not contain a compound having a glycidyl group in the molecule.

Examples of the crosslinkable monomer include monomers having two or more radical polymerizable double bonds. Specific examples include divinylbenzene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol. Di (meth) acrylate, propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, Polyethylene glycol di (meth) acrylate having a weight average molecular weight of 200 to 600, glycerin di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolpropane tri (meth) acrylate, ethylene oxide Modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, triallyl formal tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dimethylol-tricyclodecandi (Meth) acrylate etc. are mentioned. Among these, trifunctional ones such as trimethylolpropane tri (meth) acrylate and bifunctional (meth) acrylates such as polyethylene glycol are relatively uniformly crosslinked in the shell mainly composed of acrylonitrile. Since the microcapsules that have been applied and thermally expanded even in a high temperature region exceeding 200 ° C. are difficult to contract and easily maintain the expanded state, a so-called “sag” phenomenon can be suppressed and is preferably used.

The upper limit with preferable content of the said crosslinkable monomer in the said monomer composition is 1.0 weight%.
When the content of the crosslinkable monomer is 1.0% by weight or less, the expansion ratio of the thermally expandable microcapsule can be improved. The minimum with preferable content of the said crosslinkable monomer is 0.1 weight%, and a more preferable upper limit is 0.8 weight%.

In addition to the nitrile monomer, the monomer having an amide group, the compound having a glycidyl group in the molecule, and a crosslinkable monomer, the monomer composition may include other monomers that can be copolymerized with the nitrile monomer (hereinafter, (It may be simply referred to as another monomer).
The other monomers are not particularly limited and can be appropriately selected depending on the properties required for the thermally expandable microcapsules to be obtained. For example, methyl acrylate, ethyl acrylate, butyl acrylate, dicyclohexane Examples include acrylic acid esters such as pentenyl acrylate, methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and isobornyl methacrylate, vinyl monomers such as vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. .
These may be used independently and 2 or more types may be used together.

When the monomer composition contains the other monomer, the content of the other monomer in the monomer composition is not particularly limited, but a preferable upper limit with respect to 100% by weight of the total monomer composition is 40% by weight.
When the content of the other monomer is 40% by weight or less, the content of the nitrile monomer is sufficient, and the heat-expandable microcapsules obtained are not deteriorated in heat resistance and gas barrier properties. , The occurrence of rupture and shrinkage can be suppressed, and the resulting thermally expandable microcapsules can be foamed at a high expansion ratio.

In the monomer composition, the content of the monomer having a carboxyl group is preferably 0.001 part by weight or less with respect to 100 parts by weight of the total monomer components, and it is particularly preferable that the monomer composition does not contain a monomer having a carboxyl group.
By containing the monomer having the carboxyl group, the residual monomer of the monomer having the carboxyl group mainly promotes oxidative degradation of the base resin used for molding, so the molded product is colored yellowish brown. In some cases, the residual monomer volatilizes due to heating during molding, and an irritating odor peculiar to acid spreads, which may adversely affect the working environment.

Examples of the monomer having a carboxyl group include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid, and unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid, and citraconic acid. An acid etc. are mentioned. These salts and anhydrides are also included.

It is preferable to add a polymerization initiator to the monomer composition.
The polymerization initiator is not particularly limited, and examples thereof include dialkyl peroxide, diacyl peroxide, peroxyester, peroxydicarbonate, and azo compound.
The dialkyl peroxide is not particularly limited, and examples thereof include methyl ethyl peroxide, di-t-butyl peroxide, dicumyl peroxide, isobutyl peroxide and the like.

The diacyl peroxide is not particularly limited, and examples thereof include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide, and the like.

The peroxy ester is not particularly limited, and examples thereof include t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1- Cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumylperoxyneodecanoate, (α, α-bis-neodecanoylper And oxy) diisopropylbenzene.

The peroxydicarbonate is not particularly limited. For example, bis (4-t-butylcyclohexyl) peroxydicarbonate, di-n-propyl-peroxydicarbonate, diisopropyl peroxydicarbonate, di (2-ethylethyl) Peroxy) dicarbonate, dimethoxybutyl peroxydicarbonate, di (3-methyl-3-methoxybutylperoxy) dicarbonate, and the like.

The azo compound is not particularly limited. For example, 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis ( 2,4-dimethylvaleronitrile), 1,1′-azobis (1-cyclohexanecarbonitrile) and the like.

If necessary, the monomer composition may further contain a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, a flame retardant, a silane coupling agent, a colorant, and the like.

The weight average molecular weight of the polymer obtained by polymerizing the monomer composition as described above is not particularly limited, but the preferable lower limit is 100,000 and the preferable upper limit is 2 million.
When the weight average molecular weight is less than 100,000, the resulting heat-expandable microcapsule has low shell strength, tends to rupture and shrink at high temperatures, and may not foam at a high expansion ratio. When the said weight average molecular weight exceeds 2 million, the intensity | strength of a shell becomes too high and the foaming performance may fall in the thermally expansible microcapsule obtained.

The thermally expandable microcapsule of the present invention includes a volatile expansion agent as a core agent.
In this specification, the volatile swelling agent refers to a substance that becomes gaseous at a temperature below the softening point of the shell.

Examples of the volatile swelling agent include ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isoparaffinic petroleum solvent. low molecular weight hydrocarbons _{like, CCl 3 F, CCl 2 F} 2, CClF 3, CClF 2 -CClF 2 such chlorofluorocarbons, tetramethylsilane, trimethylethyl silane, trimethyl isopropyl silane, tetra such trimethyl -n- propyl silane Examples include alkyl silane. Of these, isobutane, n-butane, n-pentane, isopentane, n-hexane, petroleum ether, isoparaffinic petroleum solvent, and mixtures thereof are preferable. These volatile swelling agents may be used alone or in combination of two or more.

In the heat-expandable microcapsule of the present invention, it is preferable to use a low-boiling hydrocarbon having 10 or less carbon atoms among the above-described volatile expansion agents. By using such a hydrocarbon, it is possible to obtain a thermally expandable microcapsule having a high expansion ratio and promptly starting foaming.
Moreover, it is good also as using the thermal decomposition type compound which thermally decomposes by heating and becomes a gaseous state as a volatile expansion | swelling agent.

In the thermally expandable microcapsule of the present invention, the preferred lower limit of the content of the volatile swelling agent used as the core agent is 10% by weight, and the preferred upper limit is 30% by weight.
The thickness of the shell varies depending on the content of the core agent, but if the core agent content is reduced and the shell becomes too thick, the foaming performance is reduced, and if the core agent content is increased, the shell strength is reduced. To do. When the content of the core agent is 10 to 30% by weight, it is possible to achieve both the prevention of the sag of the thermally expandable microcapsule and the improvement of the foaming performance.

The maximum foaming temperature (Tmax) of the thermally expandable microcapsule of the present invention is not particularly limited, but a preferable lower limit is 190 ° C. and a preferable upper limit is 220 ° C. When the maximum foaming temperature is less than 190 ° C., the heat-expandable microcapsules have low heat resistance, are liable to burst and shrink at high temperatures, and cannot be foamed at a high foaming ratio. If the maximum foaming temperature exceeds 220 ° C., sufficient foaming ratio may not be obtained during heat foaming.
In the present specification, the maximum foaming temperature means the temperature at which the thermally expandable microcapsule reaches the maximum displacement when the diameter is measured while heating the thermally expandable microcapsule from room temperature. .

In the thermally expandable microcapsule of the present invention, a preferable lower limit of the foaming start temperature (Ts) is 185 ° C., and a preferable upper limit is 210 ° C. When the foaming start temperature is lower than 185 ° C., particularly when used in a stampable sheet molded article, the thermally expandable microcapsule foams during the production of the raw material, and a sufficient foaming ratio cannot be obtained during heat foaming. There is a case. When the foaming start temperature exceeds 210 ° C., the foaming ratio may not increase during heat foaming. A more preferable lower limit of the foaming start temperature is 190 ° C, and a more preferable upper limit is 205 ° C.

The volume average particle diameter of the thermally expandable microcapsule of the present invention is not particularly limited, but a preferable lower limit is 10 μm and a preferable upper limit is 70 μm. When the volume average particle diameter is less than 10 μm, for example, when foaming a thermally expandable microcapsule into a matrix resin and molding, the resulting foamed molded article has too small bubbles, resulting in insufficient weight reduction. There is. When the volume average particle diameter is more than 70 μm, for example, when a thermally expandable microcapsule is blended with a matrix resin and molded, the resulting foamed molded article has excessively large bubbles, which is problematic in terms of strength and the like. Sometimes. The volume average particle diameter has a more preferable lower limit of 15 μm and a more preferable upper limit of 40 μm.

The method for producing the heat-expandable microcapsule of the present invention is not particularly limited. For example, a step of preparing an aqueous dispersion medium, a nitrile monomer, a monomer having an amide group, and a molecule in the aqueous dispersion medium The monomer composition is polymerized by performing a step of dispersing an oily mixture containing a compound having a glycidyl group and a volatile swelling agent and a step of polymerizing the monomer composition. Examples include a method of obtaining a thermally expandable microcapsule containing a volatile expansion agent as a core agent in a shell containing the polymer formed.

In the step of preparing the aqueous dispersion medium, for example, an aqueous dispersion medium containing the dispersion stabilizer is prepared by adding water, a dispersion stabilizer, and, if necessary, an auxiliary stabilizer to the polymerization reaction vessel. Moreover, you may add alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. to the said aqueous dispersion medium as needed.

The dispersion stabilizer is not particularly limited. For example, silica, calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, calcium carbonate, carbonate Examples include barium and magnesium carbonate.

The auxiliary stabilizer is not particularly limited, and examples thereof include a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, a water-soluble nitrogen-containing compound, polyethylene oxide, tetramethylammonium hydroxide, gelatin, Examples include methyl cellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, and various emulsifiers.
The water-soluble nitrogen-containing compound is not particularly limited, and examples thereof include polyvinyl pyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl (meth) acrylate represented by polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, Examples thereof include polydialkylaminoalkyl (meth) acrylamides represented by polydimethylaminopropylacrylamide and polydimethylaminopropylmethacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Of these, polyvinylpyrrolidone is preferred.

The combination of the dispersion stabilizer and the auxiliary stabilizer is not particularly limited. For example, a combination of colloidal silica and a condensation product, a combination of colloidal silica and a water-soluble nitrogen-containing compound, magnesium hydroxide or calcium phosphate and an emulsifier. And the like. Among these, a combination of colloidal silica and a condensation product is preferable, and the condensation product is preferably a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of diethanolamine and adipic acid, diethanolamine and A condensation product with itaconic acid is particularly preferred.

When colloidal silica is used as the dispersion stabilizer, the amount of colloidal silica added is not particularly limited and can be appropriately determined depending on the particle size of the target thermally expandable microcapsule, but is preferably based on 100 parts by weight of the total monomer components. The lower limit is 1 part by weight, the preferred upper limit is 20 parts by weight, the more preferred lower limit is 2 parts by weight, and the more preferred upper limit is 10 parts by weight.
In addition, when the condensation product or the water-soluble nitrogen-containing compound is used as the auxiliary stabilizer, the addition amount of the condensation product or the water-soluble nitrogen-containing compound is not particularly limited, and the target thermally expandable microcapsule Although it can be determined appropriately depending on the particle size, the preferred lower limit with respect to 100 parts by weight of all monomer components is 0.05 parts by weight, and the preferred upper limit is 2 parts by weight.

In addition to the dispersion stabilizer and the auxiliary stabilizer, an inorganic salt such as sodium chloride or sodium sulfate may be further added to the aqueous dispersion medium. By adding such an inorganic salt, a thermally expandable microcapsule having a more uniform particle shape can be obtained.
The amount of the inorganic salt added is not particularly limited, but the preferable upper limit with respect to 100 parts by weight of all monomer components is 100 parts by weight.

The aqueous dispersion medium is prepared by blending the dispersion stabilizer and the auxiliary stabilizer with deionized water, and the pH of the deionized water is appropriately determined according to the type of the dispersion stabilizer and auxiliary stabilizer used. Can do. For example, when silica such as colloidal silica is used as the dispersion stabilizer, an acid such as hydrochloric acid is added as necessary to adjust the pH of the system to 3 to 4, and polymerization can be performed under acidic conditions in the steps described later. Done. When magnesium hydroxide or calcium phosphate is used as the dispersion stabilizer, the system is adjusted to be alkaline, and polymerization is performed under alkaline conditions in the steps described later.

In producing the thermally expandable microcapsule of the present invention, a step of dispersing an oily mixed solution containing the monomer composition and the volatile swelling agent in the aqueous dispersion medium is then performed.
In this step, the monomer composition and the volatile swelling agent may be separately added to the aqueous dispersion medium to prepare the oily mixture in the aqueous dispersion medium. Are mixed into an oily mixture and then added to the aqueous dispersion medium. At this time, after preparing the oily mixed liquid and the aqueous dispersion medium in separate containers in advance and mixing them with stirring in another container, the oily mixed liquid is dispersed in the aqueous dispersion medium, You may add to a polymerization reaction container.
A polymerization initiator is used to polymerize the monomer in the monomer composition. The polymerization initiator may be added to the oily mixture in advance, and the aqueous dispersion medium, the oily mixture, May be added after stirring and mixing in the polymerization reaction vessel.

In the step of dispersing the oily mixture containing the monomer composition and the volatile swelling agent in the aqueous dispersion medium, the oily mixture is emulsified and dispersed in the aqueous dispersion medium with a predetermined particle size.
The method of emulsifying and dispersing is not particularly limited. For example, a method of stirring with a homomixer (for example, manufactured by Tokushu Kika Kogyo Co., Ltd.) or the like, a method of passing through a static dispersing device such as a line mixer or an element type static dispersing device. Etc. The aqueous dispersion medium and the oily mixed liquid may be separately supplied to the static dispersion apparatus, or a dispersion liquid that has been mixed and stirred in advance may be supplied.

In producing the thermally expandable microcapsule of the present invention, a step of polymerizing the monomer composition is then performed. The method for polymerizing is not particularly limited, and examples thereof include a method for polymerizing the monomer composition by heating.
Thus, a volatile swelling agent as a core agent is formed on a shell made of a polymer obtained by polymerizing a monomer composition containing a nitrile monomer, a monomer having an amide group, and a compound having a glycidyl group in the molecule. Is obtained. The obtained thermally expandable microcapsules may be subsequently subjected to a dehydration step, a drying step, and the like.

For example, the heat-expandable microcapsules of the present invention are blended into a matrix resin and molded using a molding method such as injection molding, extrusion molding, compression molding, etc. It is possible to produce a foamed molded article having vibration and weight reduction. The heat-expandable microcapsules of the present invention are suitable for foam molding having a step of heating at a high temperature, because they are difficult to burst and shrink even at high temperatures and can be foamed at a high expansion ratio. It is suitably applied to a stampable sheet molded body formed by compression molding.
A stampable sheet molded article using the thermally expandable microcapsule of the present invention is also one aspect of the present invention.

The stampable sheet molded article of the present invention is formed, for example, by producing a nonwoven fabric using the thermally expandable microcapsules of the present invention, inorganic fibers, and a thermoplastic resin, and compression molding using a press machine.
The stampable sheet molded body of the present invention may be formed by either a wet process or a dry process, but is preferably formed by a wet process.

Examples of the method for forming the stampable sheet molded article of the present invention using a wet process include the following methods. Specifically, first, a heat-expandable microcapsule of the present invention, a thermoplastic resin, and inorganic fibers are mixed to prepare a mixed emulsion. The obtained mixed emulsion is subjected to dehydration filtration to produce a nonwoven fabric. Next, the obtained non-woven fabric is dried at a temperature lower than the expansion start temperature of the thermally expandable microcapsule of the present invention to remove the aqueous medium. Furthermore, the thermoplastic resin is melted and pressed while being heated at a temperature lower than the thermal expansion start temperature of the thermally expandable microcapsule of the present invention, and then cooled. In this way, the stampable sheet molded body of the present invention can be formed.

Examples of the inorganic fibers include amorphous fibers such as glass fibers, carbon fibers, and rock wool, polycrystalline fibers such as alumina fibers, and single crystal fibers such as wollastonite and potassium titanate fibers.

Although the fiber diameter of the said inorganic fiber is not specifically limited unless the objective of this invention is inhibited, It is preferable that it is 0.1-100 micrometers, and it is more preferable that it is 1-30 micrometers.
When the average diameter of the inorganic fibers is within the preferable range, the inorganic fibers are sufficiently entangled, and the stampable sheet molded body can be sufficiently reinforced.

Although the cut length of the said inorganic fiber is not specifically limited unless the objective of this invention is inhibited, It is preferable that it is 1-100 mm, and it is more preferable that it is 10-100 mm.
When the cut length of the inorganic fiber is within the preferable range, the inorganic fibers are sufficiently entangled, and the stampable sheet molded body can be sufficiently reinforced.

The content of the inorganic fiber in the mixed emulsion is not particularly limited, but is preferably 0.1 to 20% by weight, more preferably 0.3 to 10% by weight, and still more preferably 0.5 to 5% by weight. . When the content of the inorganic fiber is within the preferable range, the dispersibility of the inorganic fiber in the obtained stampable sheet molded body is improved, and the strength of the stampable sheet molded body can be made sufficient. .

The thermoplastic resin is not particularly limited as long as the object of the present invention is not impaired. For example, general thermoplastic resins such as polyvinyl chloride, polystyrene, polypropylene, polypropylene oxide, and polyethylene; polybutylene terephthalate, nylon, Engineering plastics such as polycarbonate and polyethylene terephthalate are listed. Further, thermoplastic elastomers such as ethylene, vinyl chloride, olefin, urethane, and ester may be used, or these resins may be used in combination.

The thermoplastic resin is preferably a resin powder.
The average particle size of the resin powder is not particularly limited, but is preferably 10 to 1000 μm, more preferably 20 to 400 μm.
When the average particle diameter of the resin powder is within the preferable range, the inorganic fibers can be sufficiently bound to each other, and the strength of the stampable sheet molded body can be made sufficient.
The average particle diameter of the resin powder can be measured, for example, by a method such as microscopic observation or a light transmission particle diameter measuring method.

The content of the thermoplastic resin in the mixed emulsion is not particularly limited, but is preferably 0.1 to 20% by weight, more preferably 0.3 to 10% by weight, still more preferably 0.5 to 5% by weight. is there.
When the content of the thermoplastic resin is within the preferable range, the inorganic fibers can be sufficiently bound to each other, and the strength of the stampable sheet molded body can be made sufficient.

The content of the thermally expandable microcapsule of the present invention in the mixed emulsion is not particularly limited, but is preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, and still more preferably 0.1 to 0.1%. 2% by weight. When the content of the thermally expandable microcapsule of the present invention is within the above preferred range, the stampable sheet molded body is sufficiently heated when heated at a temperature higher than the expansion start temperature of the thermally expandable microcapsule of the present invention. A high expansion ratio can be obtained.

The mixed emulsion may contain a flame retardant.
The flame retardant is not particularly limited, nitrogen-containing compounds such as urea and melamine cyanurate, phosphoric acid compounds such as polyphosphoric acid, organic halogen compounds such as chlorinated paraffin and decabromobiphenyl ether, aluminum hydroxide and magnesium hydroxide, etc. And hydrated metal oxides. These may be used independently and 2 or more types may be used together.

The mixed emulsion may contain a surfactant. The surfactant is not particularly limited, and examples thereof include a cationic surfactant, an anionic surfactant, and a nonionic surfactant.

According to the present invention, a thermally expandable microcapsule having excellent gas barrier properties, excellent durability over a long period of time at high temperature, and hardly causing coloration when used in foam molding, and the thermally expandable microcapsule are provided. The stampable sheet molding used can be provided.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

(Examples 1-10, Comparative Examples 1-6)
(Production of thermally expandable microcapsules)
In a polymerization reaction vessel, 250 parts by weight of water, 25 parts by weight of colloidal silica (20% by weight, manufactured by Asahi Denka Co., Ltd.) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) as a dispersion stabilizer, 1.8% by weight of 1N hydrochloric acid The aqueous dispersion medium was prepared.
Subsequently, the monomer composition, the volatile swelling agent and the polymerization initiator (0.8 parts by weight of 2,2′-azobisisobutyronitrile, 2,2′-) having the blending ratios shown in Table 1 and Table 2. An oily mixture composed of 0.6 parts by weight of azobis (2,4-dimethylvaleronitrile)) was added to an aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was stirred and mixed with a homogenizer, charged into a nitrogen-substituted pressure polymerization reactor, and reacted at 60 ° C. for 20 hours while applying pressure (0.5 MPa) to obtain a reaction product. The obtained reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules.
In addition, as a compound having a glycidyl group in the molecule, glycidyl methacrylate (manufactured by Kyoeisha Chemical Co., Ltd., number of glycidyl groups: 1, number of polymerizable unsaturated bonds: 1), bisphenol A type epoxy resin (jER-828: Mitsubishi) Chemicals, number of glycidyl groups: 2), trimethylolpropane polyglycidyl ether (EX-321: manufactured by Nagase ChemteX, number of glycidyl groups: 3), pentaerythritol polyglycidyl ether (EX-411: Nagase Chemtex) The number of glycidyl groups manufactured by the company, 4), polyglycerol polyglycidyl ether (EX-521: manufactured by Nagase ChemteX, the number of glycidyl groups: 5) was used.
In addition to isopentane and isooctane, isoparaffin-based petroleum solvent (Isopar H: manufactured by ExxonMobil) was used as the volatile swelling agent.

(Preparation of stampable sheet compact)
To 1 L of ion-exchanged water, add 4 g of the obtained thermally expandable microcapsules, 8 g of glass fiber (fiber diameter 13 μm, cut length 20 mm) and 10 g of polypropylene resin powder (melting point 165 ° C., average particle size 300 μm), and disperse and mix. An emulsion was obtained. The obtained mixed emulsion was filtered under reduced pressure using a stainless steel mesh (Φ100 μm) to obtain a nonwoven fabric. The obtained nonwoven fabric was dried in a heating oven at 110 ° C. for 20 minutes, and then pressed at 2 MPa for 10 minutes in a press machine heated to 170 ° C. Thereafter, a cooling press was performed to obtain a stampable sheet molded body.

(Evaluation)
The following evaluation was performed on the thermally expandable microcapsules and stampable sheet moldings obtained in Examples and Comparative Examples. The results are shown in Tables 1 and 2.

(1) Foam start temperature Ts, maximum foam temperature Tmax
Using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA instruments), the foaming start temperature Ts and the maximum foaming temperature Tmax were measured. Specifically, 25 μg of a sample is placed in an aluminum container having a diameter of 7 mm and a depth of 1 mm, and heated from 80 ° C. to 250 ° C. at a temperature rising rate of 5 ° C./min with a force of 0.1 N applied from above. Then, the displacement in the vertical direction of the measurement terminal was measured, and the temperature at which the displacement began to rise was defined as the foaming start temperature. Further, the expansion ratio was measured, and the temperature at which the expansion ratio was the maximum was defined as the maximum expansion temperature.

(2) Using a foaming ratio heating foaming microscope (manufactured by Japan High-Tech), a small amount of thermally expandable microcapsules was sprayed on the stage, and the expansion behavior was observed up to 280 ° C. while heating at 5 ° C./min. The diameter φT was measured with a caliper every 5 ° C. with respect to five arbitrary thermally expandable microcapsules in the observed image, and the average diameter φT (Ave) at each temperature was obtained. The expansion ratio DT at each temperature was DT = φT (Ave) / φ30, and the ET at the temperature at which the ET was maximum was defined as the maximum expansion ratio DTmax.
Here, φ30 is the diameter of the thermally expandable microcapsule at 30 ° C.
When the maximum foaming ratio is less than 3 times, it is evaluated as “X”, when it is 3 times or more and less than 5 times, “○”, and when it is 5 times or more, it is evaluated as “XX”. did.

(3) Using a heat-resistant heating foaming microscope (manufactured by Japan High-Tech), spray a small amount of thermally expandable microcapsules on the stage and observe the expansion behavior up to 280 ° C while heating at 5 ° C / min. The expansion ratio D220 at 220 ° C. when the diameter of the thermally expandable microcapsule was expanded by 1 was measured. The case where D220 is less than 2 times is “×”, the case where it is 2 times or more and less than 3 times is “◯”, the case where it is 3 times or more and less than 4 times is “○”, and 4 times. The case where it was above was evaluated as "XXX".

(4) Using a durable heating foaming microscope (manufactured by Japan Hightech), the expansion behavior was observed under the same conditions as heat resistance, and the temperature width (ΔT) at which the foaming ratio was 2 times or more was measured. The case where ΔT is less than 40 ° C. is “x”, the case where it is 40 ° C. or more and less than 50 ° C. is “◯”, the case where it is 50 ° C. or more and less than 60 ° C. is “○○”, 60 ° C. The case where it was above was evaluated as "XXX".

(5) Colored stampable sheet molded body was heated and foamed in a heating oven at 205 ° C. for 4 minutes, and then used as a C light source with a viewing angle of 2 using HANDY COLORIMTER NR-3000 (manufactured by Nippon Denshoku Industries Co., Ltd.). Tristimulus values X, Y, and Z were measured at 0 °. The YI value was calculated from the obtained X, Y, and Z values using Equation (1), and the color of the stampable sheet molded body was evaluated.
YI value = 100 (1.28X-1.06Z) / Y (1)
When the obtained YI value is less than 50, “◯◯”, when it is 50 or more and less than 65, “◯◯”, when it is 65 or more and less than 72, “◯”, 72 The case where it was above was evaluated as "x".

According to the present invention, a thermally expandable microcapsule having excellent gas barrier properties, excellent durability over a long period of time at high temperature, and hardly causing coloration when used in foam molding, and the thermally expandable microcapsule are provided. The stampable sheet molding used can be provided.

Claims (5)

A thermally expandable microcapsule in which a volatile expansion agent is encapsulated as a core agent in a polymer shell,
The shell is obtained by polymerizing a monomer composition containing a nitrile monomer, a monomer having an amide group, and a compound having a glycidyl group in the molecule,
The monomer having an amide group includes at least one of acrylamide and methacrylamide,
The monomer having a glycidyl group in the molecule includes at least one of glycidyl methacrylate and a 2-5 functional epoxy compound,
The monomer composition contains 0.1 to 7% by weight of the monomer having an amide group and 0.1 to 5% by weight of the compound having a glycidyl group. In the monomer composition, the weight ratio of the monomer having an amide group to the compound having a glycidyl group in the molecule (monomer having an amide group / compound having a glycidyl group in the molecule) is 0.2 to 70, The thermally expandable microcapsule according to claim 1. 3. The monomer composition according to claim 1, wherein the weight ratio of the monomer having an amide group to the nitrile monomer (monomer having an amide group / nitrile monomer) is 0.01 to 0.1. Thermally expandable microcapsule. Monomer composition, in the molecule a double bond of two or more with claim 1, 2 or 3 thermally expandable microcapsule according content of the crosslinking monomer is characterized in that 1.0 wt% or less . A stampable sheet molded article comprising the thermally expandable microcapsule according to claim 1, 2, 3 or 4.