Thermally-expandable microcapsules

Abstract

The present invention provides: thermally-expandable microcapsules with which it is possible to obtain a foam molded body, said microcapsules having excellent foamability, being capable of suppressing the occurrence of white spots, and suppressing color difference defects in a molded body after foaming; and a foamable master batch and a foam molded body using the thermally-expandable microcapsules. The present invention involves thermally-expandable microcapsules, each being obtained by enclosing a volatile expanding agent as a core in a shell. The shell contains a polymer compound, a black pigment and a dye.

Description

Thermally Expandable Microcapsules

[0001] The present invention relates to a thermally expandable microcapsule, a foamable masterbatch using the thermally expandable microcapsule, and a foamed molded article.

[0002] Thermally expandable microcapsules are widely used as design-imparting agents and weight-reducing agents, and are also used in foaming inks, wallpapers, and other lightweight coating materials. Widely known thermally expandable microcapsules contain a thermoplastic shell polymer encapsulating a volatile expanding agent that becomes gaseous at temperatures below the softening point of the shell polymer.

[0003] For example, Patent Document 1 discloses thermally expandable microcapsules containing a volatile expanding agent, which are obtained by adding, with stirring, an oily mixture of a volatile expanding agent such as a low-boiling aliphatic hydrocarbon and a monomer to an aqueous dispersion medium containing a dispersant together with an oil-soluble polymerization catalyst, followed by suspension polymerization. Patent Document 2 also discloses thermally expandable microspheres containing a polymer of a crosslinkable monomer having a molecular weight of 500 or more and a (meth)acryloyl group and a reactive carbon-carbon double bond. Patent Document 3 also discloses hollow resin particles consisting of a thermoplastic resin shell and a hollow space surrounded by the shell, with fine particles attached to the outer surface of the shell.

[0004] However, when the thermally expandable microcapsules described in Patent Documents 1 to 3 are added to a molded product made of a base polymer such as rubber or elastomer, the whiteness of the thermally expandable microcapsules can cause color difference defects in the molded product, especially after foaming. Furthermore, white spots can appear on the surface of the resulting molded product. In contrast, Patent Document 4 describes thermally expandable microcapsules in which a volatile expanding agent is encapsulated as a core agent in a shell containing a black pigment or dye and a polymer compound.

[0005] Japanese Patent Publication No. 42-26524 International Publication No. 2019 / 150951 International Publication No. 2018 / 025575 International Publication No. 2021 / 221160

[0006] However, after extensive research, the inventors discovered that even when the thermally expandable microcapsules described in Patent Document 4 were added, the resulting molded body had insufficient foaming properties and white spots, and that there was still room for improvement.

[0007] The present invention aims to provide a thermally expandable microcapsule that has excellent foaming properties, can suppress the occurrence of white spots, and can produce a foamed molded article that is less likely to have color difference defects after foaming, as well as a foamable masterbatch and a foamed molded article that use the thermally expandable microcapsule.

[0008] Disclosure (1) is a thermally expandable microcapsule having a shell encapsulating a volatile expanding agent as a core agent, the shell containing a polymer compound, a black pigment, and a dye. Disclosure (2) is a thermally expandable microcapsule according to Disclosure (1), in which the dye is an oil-soluble dye. Disclosure (3) is a thermally expandable microcapsule according to Disclosure (1), in which the dye is a black dye. Disclosure (4) is a thermally expandable microcapsule according to any one of Disclosures (1) to (3), in which the dye content is 0.5% by weight or more and 10% by weight or less, based on the entire thermally expandable microcapsule. Disclosure (5) is a thermally expandable microcapsule according to any one of Disclosures (1) to (4), in which the dye content is 5 parts by weight or more and 1,000 parts by weight or less, based on 100 parts by weight of the black pigment. The present disclosure (6) is a foamable masterbatch containing the thermally expandable microcapsules and a thermoplastic resin according to any one of the present disclosures (1) to (5). The present disclosure (7) is a foamed molded article obtained using the foamable masterbatch according to the present disclosure (6). The present invention will be described in detail below.

[0009] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention contains a black pigment. By including the black pigment, the strength of the shell can be increased against melt-kneading during molding, and light-blocking properties and appearance performance can be further improved. The black pigment exhibits black color by absorbing all light rays, including those in the visible light range of sunlight. While typical black pigments exhibit black color by absorbing light in the visible light range (approximately 380 to 780 nm), they also absorb light in the near-infrared range, including the wavelength range of 800 to 1,400 nm, which contributes significantly to heat generation.

[0010] The optical density (OD value) of the black pigment preferably has a lower limit of 1.5 and an upper limit of 5.0. By setting the optical density within the above range, a black coating film and a black matrix that combine high light-blocking properties and jet blackness can be obtained. The optical density (OD value) of the black pigment refers to the optical density (OD value) when measuring an acrylic resin (coating film thickness 1 μm) containing 50% by weight of the black pigment. In this specification, the optical density (OD value) refers to the optical density (OD value) obtained by measuring the intensity of light incident on the optical density variable element. ０ , the transmitted light intensity is I Ｔ When X = -log(I Ｔ / I ０ The optical density (OD value) can be measured using a color difference meter, a Macbeth densitometer, or the like.

[0011] Examples of the black pigment include inorganic black pigments such as carbonaceous black pigments, oxide-based black pigments, and nitride-based black pigments, as well as organic black pigments. Among these, at least one selected from the group consisting of carbonaceous black pigments and oxide-based black pigments is preferred. Examples of the carbonaceous black pigment include carbon black, graphite, activated carbon, graphene, and carbon nanotubes. Examples of the oxide-based black pigment include titanium black, iron oxide, magnetite, and cuprous oxide (cuprous oxide), as well as composite oxide black pigments containing copper and chromium, copper and manganese, copper, iron and manganese, or cobalt, chromium, and iron as the main metal components. Examples of the nitride-based black pigment include zirconium nitride. Examples of the organic black pigment include aniline black (C.I. Pigment Black 1). Among these, carbon black is more preferred due to its excellent heat resistance, excellent dispersibility in resins, and ability to impart a uniform black color. Furthermore, black pigments having aromatic functional groups are preferred. By using the black pigment having the aromatic functional group, the aromatic functional group of the black pigment interacts with the aromatic group of the dye, improving the dispersibility of the black pigment and increasing the degree of blackness. Examples of the black pigment having the aromatic functional group include carbon black and carbon nanotubes (both of which have an aromatic functional group).

[0012] Among the black pigments, black pigments in the form of fine particles (black fine particles) are preferred. The black fine particles preferably have an average primary particle diameter of 1 μm or less, more preferably 10 to 500 nm. By setting the diameter within this range, the black fine particles are dispersed in the resin, resulting in a uniform hue (black). The average primary particle diameter is the average value of primary particle diameters measured using a transmission electron microscope or the like after preparing a thin film that passes through the vicinity of the center of the thermally expandable microcapsules dispersed in the embedding resin.

[0013] The preferred lower limit of the black pigment content is 0.01 wt % and the preferred upper limit is 30 wt % based on the total weight of the thermally expandable microcapsules. By setting the content at 0.01 wt % or more, fusion between the thermally expandable microcapsules in the resin during molding can be suppressed. By setting the content at 30 wt % or less, the shell strength against melt-kneading during molding can be increased, and light-blocking properties and appearance performance can be further improved. A more preferred lower limit is 0.3 wt %, a more preferred upper limit is 15 wt %, an even more preferred upper limit is 10 wt %, and an even more preferred upper limit is 7 wt %. That is, the content of the black pigment is preferably 0.01 to 30 wt %, more preferably 0.3 to 15 wt %, even more preferably 0.3 to 10 wt %, and even more preferably 0.3 to 7 wt %. The black pigment content can be determined, for example, by heating a thermally expandable microcapsule in a nitrogen atmosphere to 600°C at 10°C / min, maintaining this temperature for 10 minutes, then lowering the temperature to 400°C at 10°C / min and maintaining this temperature for 10 minutes, switching the atmosphere to air, and heating the microcapsule in air to 1000°C and maintaining this temperature for 10 minutes.The black pigment content can be determined from the weight loss from 400°C to 1000°C.

[0014] The black pigment has a specific surface area of ​​500 m ２ / g or less, and more preferably 5 to 300m ２ / g. By setting the specific surface area within the above range, the black pigment is dispersed in the resin, resulting in a uniform hue (black). The specific surface area can be measured by measuring a nitrogen adsorption isotherm using a surface area / pore size analyzer (NOVA4200e, manufactured by Quantachrome Instruments) and calculating the specific surface area of ​​the black pigment from the measurement results in accordance with the BET method.

[0015] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention contains a dye. In the present invention, the use of a black pigment and a dye in combination synergistically improves the blackness of the thermally expandable microcapsule, thereby further suppressing white spots.

[0016] Examples of the dye include oil-soluble dyes, water-soluble dyes, disperse dyes, direct dyes, acid dyes, basic dyes, mordant dyes, acid mordant dyes, vat dyes, azoic dyes, and reactive dyes. Oil-soluble dyes are preferred, particularly in terms of affinity with the polymer (monomer mixture) constituting the shell, the core agent, and the like. The oil-soluble dye may be any dye that is insoluble in water and soluble in an oily organic solvent and capable of producing color, and is appropriately selected depending on factors such as the color tone, the type of oily organic solvent in which the dye is dissolved, and the type of particles. Examples of the oil-soluble dye include azine (nigrosine) dyes, azo dyes, disazo dyes, triazo dyes, tetraazo dyes, xanthene dyes, triarylmethane dyes, metal-containing dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoimine dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, naphthalimide dyes, perinone dyes, and phthalocyanine dyes. The metal-containing dyes include metal complex dyes obtained by complexing metals such as chromium, cobalt, nickel, copper, and iron, and may be, for example, metal complex azo dyes.

[0017] Examples of the dyes that can be used include black dyes, red dyes, orange dyes, yellow dyes, green dyes, blue dyes, and purple dyes. Black dyes are particularly preferred from the viewpoint of improving the blackness of the thermally expandable microcapsules. The term "black" as used herein is not particularly limited as long as it does not impair the effects of the present invention, but includes black, bluish black, and yellowish black. It is not limited to a strictly pure black color, but includes colors that are roughly recognized as black. Examples of the black dyes include inorganic black dyes and organic black dyes. Organic black dyes are particularly preferred. Examples of the inorganic black dyes include metal complex azo black dyes. Examples of the organic black dyes include disazo black dyes, azine black dyes, phthalocyanine black dyes, anthraquinone black dyes, and indigoid black dyes.

[0018] Preferred examples of the oil-soluble black dye include disazo dyes, nigrosine dyes, azo dyes, azine dyes, metal-containing dyes, metal complex azo dyes, and xanthene dyes, with disazo dyes, nigrosine dyes, metal complex azo dyes, and xanthene dyes being more preferred. Examples of the oil-soluble black dye include Sudan Black X60 (manufactured by BASF), Nubian Black PC-8550 (a mixture of an oil-soluble azine dye and an oil-soluble anthraquinone dye, manufactured by Orient Chemical Industries Co., Ltd.), Solvent Black 3 (an oil-soluble disazo dye, manufactured by Orient Chemical Industries Co., Ltd.), Solvent Black 5 (an oil-soluble nigrosine dye, manufactured by Orient Chemical Industries Co., Ltd.), Solvent Black 7 (an oil-soluble nigrosine dye, manufactured by Orient Chemical Industries Co., Ltd.), Solvent Black 27 (an oil-soluble azo chromium alloy dye, manufactured by Orient Chemical Industries Co., Ltd.), and Solvent Black 29 (an azo compound Cr complex, manufactured by Orient Chemical Industries Co., Ltd.), and polymerizable dyes. K01 (oil-soluble xanthene dye, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the like, and it is preferable to use Solvent Black.

[0019] Other specific examples of the dyes include, for example, Solvent Yellow 2, 3, 5, 7, 8, 16, 17, 21, 24, 30, 31, 35, 44, 88, 89, 98, 102, 103, 104, 105, 111, 114, 162, and C.I. Yellow dyes such as Disperse Yellow 160; red dyes such as Solvent Red 3, 8, 14, 17, 18, 22, 23, 51, 53, 87, 127, 128, 131, 145, 146, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 176, and 179; orange dyes such as Solvent Orange 63, 68, 71, 72, and 78; and Solvent Blue. Examples of blue dyes that can be used include blue dyes such as Nos. 4, 5, 8, 19, 21, 22, 50, 55, 63, 78, 82, 83, 84, 85, 86, 90, 91, 92, 93, 94, 95, 97, and 104, and mixtures thereof can also be used. Among these, preferred are Solvent Red 8 (metal complex dye, manufactured by Orient Chemical Industries Co., Ltd.), Solvent Blue 5 (metal complex dye, manufactured by Orient Chemical Industries Co., Ltd.), and Solvent Yellow 21 (metal complex dye, manufactured by Orient Chemical Industries Co., Ltd.).

[0020] The dye may be a monomolecular compound or a polymer, but from the viewpoint of the blackness (uniformity of color tone) of the thermally expandable microcapsules, it is preferable that the dye be a monomolecular compound. Furthermore, the dye is preferably a compound having a nitrogen atom. The number of nitrogen atoms per molecule is preferably 1 to 20, more preferably 2 to 15. By setting the number within the above range, the interaction between the dye and the black pigment is strengthened, and the dispersibility of the black pigment is improved, thereby increasing the blackness of the thermally expandable microcapsules.

[0021] The molecular weight of the compound used as the dye is preferably 100 or more and 5,000 or less, and more preferably 200 or more and 1,000 or less. By setting the molecular weight within this range, the interaction between the dye and the black pigment can be strengthened, and the dispersibility of the black pigment can be improved. The molecular weight can be calculated from the atomic species constituting the compound used as the dye.

[0022] The compound used as the dye preferably has a melting point of 150° C. or higher and 400° C. or lower. The melting point can be measured using a melting point measuring device or the like.

[0023] The preferred lower limit of the dye content is 0.5 wt % and the preferred upper limit is 10 wt % based on the total weight of the thermally expandable microcapsules. By setting the content at 0.5 wt % or more, the degree of blackness can be synergistically improved. By setting the content at 10 wt % or less, the expansion ratio can be improved. A more preferred lower limit is 1.0 wt %, an even more preferred lower limit is 2.5 wt %, and an even more preferred upper limit is 7.0 wt %. That is, the content of the dye relative to the total weight of the thermally expandable microcapsules is preferably 0.5 to 10 wt %, more preferably 1.0 to 7.0 wt %, and even more preferably 2.5 to 7.0 wt %.

[0024] The preferred lower limit of the dye content is 5 parts by weight per 100 parts by weight of black pigment, and the preferred upper limit is 1,000 parts by weight. By using an amount of 5 parts by weight or more, the degree of blackness can be synergistically improved. By using an amount of 1,000 parts by weight or less, the expansion ratio can be improved. A more preferred lower limit is 50 parts by weight, an even more preferred lower limit is 80 parts by weight, and a more preferred upper limit is 500 parts by weight, and an even more preferred upper limit is 200 parts by weight. That is, the content of the dye per 100 parts by weight of black pigment is preferably 5 to 1,000 parts by weight, more preferably 50 to 500 parts by weight, and even more preferably 80 to 200 parts by weight. Furthermore, the preferred lower limit of the dye content relative to the black pigment (dye / black pigment) is 0.05, and the preferred upper limit is 10, and more preferably 0.5, and more preferably 5. That is, the content ratio is preferably 0.05 to 10, and more preferably 0.5 to 5.

[0025] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention may contain a black conductive polymer in addition to the black pigment or dye. Examples of the black conductive polymer include polythiophene, polydopamine, polypyrrole, polyaniline, polyphenylene vinylene, polyphenylene, polyacetylene, polyquinoxaline, polyoxadiazole, polybenzothiadiazole, and the like, as well as polymers having multiple conductive skeletons thereof. Among these, polythiophene and its derivatives are preferred, with poly(3,4-ethylenedioxythiophene) [PEDOT], poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) [PEDOT / PSS], and polythienothiophene being particularly preferred.

[0026] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention contains a polymer compound. The polymer compound is preferably a polymer of a monomer composition containing a nitrile monomer and a monomer having a carboxyl group.

[0027] The nitrile monomer is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and mixtures thereof. Among these, acrylonitrile and methacrylonitrile are particularly preferred. These may be used alone or in combination of two or more.

[0028] The preferred lower limit of the content of the nitrile monomer in the monomer composition is 30% by weight, and the preferred upper limit is 90% by weight. By making it 30% by weight or more, the gas barrier properties of the shell can be improved, thereby improving the expansion ratio. By making it 90% by weight or less, it is possible to improve heat resistance and prevent yellowing. A more preferred lower limit is 40% by weight, and a more preferred upper limit is 80% by weight. That is, the content of the nitrile monomer is preferably 30 to 90% by weight, and more preferably 40 to 80% by weight.

[0029] Examples of the carboxyl group-containing monomer include a radically polymerizable unsaturated carboxylic acid monomer having a carboxyl group and 3 to 8 carbon atoms. Specific examples include unsaturated dicarboxylic acids and their anhydrides, and monoesters and derivatives of unsaturated dicarboxylic acids. These may be used alone or in combination of two or more. Examples of the unsaturated dicarboxylic acids include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, and cinnamic acid, as well as maleic acid, itaconic acid, fumaric acid, citraconic acid, and chloromaleic acid. Examples of the monoesters of unsaturated dicarboxylic acids include monomethyl maleate, monoethyl maleate, monobutyl maleate, monomethyl fumarate, monoethyl fumarate, monomethyl itaconate, monoethyl itaconate, and monobutyl itaconate. Among these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itaconic acid are particularly preferred.

[0030] The preferred lower limit of the content of the carboxyl group-containing monomer in the monomer composition is 5% by weight, and the preferred upper limit is 70% by weight. By setting the content to 5% by weight or more, the maximum foaming temperature can be increased, and by setting the content to 70% by weight or less, the foaming ratio can be improved. A more preferred lower limit is 10% by weight, and a more preferred upper limit is 50% by weight. That is, the content of the carboxyl group-containing monomer is preferably 5 to 70% by weight, and more preferably 10 to 50% by weight.

[0031] The monomer composition preferably contains a crosslinkable monomer having two or more double bonds in the molecule. The crosslinkable monomer functions as a crosslinking agent. By containing the crosslinkable monomer, the strength of the shell can be increased, making the cell walls less likely to break during thermal expansion.

[0032] Examples of the crosslinkable monomer include monomers having two or more radically polymerizable double bonds, and specific examples include divinylbenzene, di(meth)acrylate, and tri- or higher functional (meth)acrylates. Examples of the di(meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Other examples include 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, and dimethylol-tricyclodecane di(meth)acrylate. Furthermore, di(meth)acrylate of polyethylene glycol having a weight average molecular weight of 200 to 600 may also be used. Examples of the trifunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, triallyl formal tri(meth)acrylate, etc. Examples of the tetrafunctional or higher (meth)acrylate include pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, etc. Among these, trifunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate and bifunctional (meth)acrylates such as polyethylene glycol provide relatively uniform crosslinking to the acrylonitrile-based shell.

[0033] The preferred lower limit of the content of the crosslinkable monomer in the monomer composition is 0.1 wt %, and the preferred upper limit is 1.0 wt %. By setting the content of the crosslinkable monomer to 0.1 wt % or more, the effect as a crosslinking agent can be fully exerted, and by setting the content of the crosslinkable monomer to 1.0 wt % or less, the expansion ratio of the thermally expandable microcapsules can be improved. The more preferred lower limit of the content of the crosslinkable monomer is 0.15 wt %, and the more preferred upper limit is 0.9 wt %. That is, the content of the crosslinkable monomer is preferably 0.1 to 1.0 wt %, and more preferably 0.15 to 0.9 wt %.

[0034] The monomer composition preferably contains other monomers in addition to the nitrile monomer, the carboxyl group-containing monomer, and the crosslinkable monomer. The inclusion of the other monomers improves the miscibility of the thermally expandable microcapsules with matrix resins such as thermoplastic resins, resulting in foamed molded articles using the thermally expandable microcapsules with excellent appearance. Examples of the other monomers include (meth)acrylic acid esters as well as vinyl monomers such as vinyl chloride, vinylidene chloride, vinyl acetate, and styrene. These may be used alone or in combination of two or more. Among these, (meth)acrylic acid esters are preferred, with alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate being particularly preferred, as well as alkyl acrylates such as methyl acrylate, ethyl acrylate, and n-butyl acrylate, and alicyclic, aromatic, and heterocyclic methacrylic acid esters such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate being particularly preferred. Among these, alkyl methacrylates are preferred.

[0035] The preferred lower limit of the content of the other monomer in the monomer composition is 0.1 wt %, and the preferred upper limit is 35 wt %. By setting the content of the other monomer to 0.1 wt % or more, the dispersibility of the composition using thermally expandable microcapsules can be improved, and by setting the content to 35 wt % or less, the gas barrier properties of the cell walls can be improved, thereby improving thermal expandability. A more preferred lower limit of the content of the other monomer is 0.3 wt %, and a more preferred upper limit is 32 wt %. That is, the content of the other monomer is preferably 0.1 to 35 wt %, and more preferably 0.3 to 32 wt %.

[0036] The monomer composition may contain a thermosetting resin in addition to the nitrile monomer, the carboxyl group-containing monomer, the crosslinkable monomer, and other monomers. Examples of the thermosetting resin include epoxy resin, phenol resin, melamine resin, urea resin, polyimide resin, and bismaleimide resin. Among these, epoxy resin and phenol resin are preferred.

[0037] The epoxy resin is not particularly limited, and examples thereof include bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, dicyclopentadiene epoxy resins, and glycidylamine epoxy resins. Examples of the phenol resins include novolac phenol resins, resol phenol resins, and benzylic ether phenol resins. Of these, novolac phenol resins are preferred.

[0038] The thermosetting resin preferably has two or more functional groups reactive with carboxyl groups per molecule. Having two or more functional groups reactive with carboxyl groups can further strengthen the curing properties of the thermosetting resin. In particular, when the monomer composition contains a monomer having a carboxyl group, the heat generated during heating and foaming causes the carboxyl group and the thermosetting resin to bond more strongly, significantly improving heat resistance and durability. The thermosetting resin preferably does not have a radically polymerizable double bond.

[0039] Examples of the functional group reactive with the carboxyl group include a glycidyl group, a phenol group, a methylol group, and an amino group. Of these, a glycidyl group is preferred. The functional groups reactive with the carboxyl group may be the same or two or more different groups.

[0040] The preferred lower limit of the content of the thermosetting resin in the monomer composition is 0.01% by weight, and the preferred upper limit is 30% by weight. By making the content of the thermosetting resin 0.01% by weight or more, it is possible to improve compression resistance during heat foaming. By making the content of the thermosetting resin 30% by weight or less, the gas barrier properties of the shell are improved, and foaming properties are improved. A more preferred lower limit is 0.1% by weight, and a more preferred upper limit is 15% by weight. That is, the content of the thermosetting resin is preferably 0.01 to 30% by weight, and more preferably 0.1 to 15% by weight.

[0041] A polymerization initiator is added to the monomer composition to polymerize the monomers. Suitable examples of the polymerization initiator include dialkyl peroxides, diacyl peroxides, peroxyesters, peroxydicarbonates, and azo compounds. Specific examples include dialkyl peroxides such as methyl ethyl peroxide, di-t-butyl peroxide, and dicumyl peroxide; and diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and 3,5,5-trimethylhexanoyl peroxide. Other examples include t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate, t-hexyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, and 1,1,3,3-tetramethylbutyl peroxyneodecanoate. Other examples include peroxyesters such as cumyl peroxy neodecanoate and (α,α-bis-neodecanoylperoxy)diisopropylbenzene; bis(4-t-butylcyclohexyl)peroxydicarbonate, di-n-propyl-oxydicarbonate, and diisopropyl peroxydicarbonate. Further examples include peroxydicarbonates such as di(2-ethylethylperoxy)dicarbonate, dimethoxybutyl peroxydicarbonate, and di(3-methyl-3-methoxybutylperoxy)dicarbonate. Additionally, other examples include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 1,1'-azobis(1-cyclohexanecarbonitrile).

[0042] The weight-average molecular weight of the polymer compound constituting the shell preferably has a lower limit of 100,000 and an upper limit of 2,000,000. The weight-average molecular weight of the polymer compound constituting the shell is preferably 100,000 to 2,000,000. If it is less than 100,000, the strength of the shell may decrease, and if it exceeds 2,000,000, the strength of the shell may become too high, resulting in a decrease in the expansion ratio.

[0043] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention preferably further contains at least one inorganic compound selected from the group consisting of Si-based compounds and Mg-based compounds. By containing the inorganic compound, it is possible to suppress fusion of the thermally expandable microcapsules in the resin during molding. Note that the inorganic compound is different from the black pigment.

[0044] The Si-based compound and Mg-based compound preferably contain an oxide, hydroxide, carbonate, or hydrogencarbonate of silicon or magnesium. These Si-based compounds and Mg-based compounds may be used alone or in combination of two or more.

[0045] Examples of the Si-based compounds include colloidal silica, silicate sol, No. 3 water glass, sodium orthosilicate, sodium metasilicate, etc. Among these, colloidal silica is preferred. Examples of the Mg-based compounds include magnesium oxide, magnesium hydroxide, magnesium oxide hydroxide, hydrotalcite, dihydrotalcite, magnesium carbonate, basic magnesium carbonate, magnesium calcium carbonate, magnesium phosphate, magnesium hydrogen phosphate, magnesium pyrophosphate, magnesium borate, etc. Among these, magnesium hydroxide is preferred.

[0046] Other examples of the inorganic compounds that may be added include calcium phosphate, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, etc. Furthermore, inorganic salts such as sodium chloride and sodium sulfate, alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. may also be added as needed.

[0047] The inorganic compound is preferably in the form of fine particles. When the inorganic compound is in the form of fine particles, the primary particle diameter is preferably 0.5 μm or less, more preferably 5 to 100 nm (0.1 μm). By keeping the diameter within this range, fusion between thermally expandable microcapsules in the resin during molding can be suppressed. The primary particle diameter can be measured by observation using a scanning electron microscope (Regulus 8220, manufactured by Hitachi High-Technologies Corporation).

[0048] The preferred lower limit of the content of the inorganic compound relative to the total amount of the thermally expandable microcapsules is 0.01 wt %, and the preferred upper limit is 7 wt %. By setting the content at 0.01 wt % or more, fusion between the thermally expandable microcapsules in the resin during molding can be suppressed. By setting the content at 7 wt % or less, resin dispersibility during molding can be further improved. A more preferred lower limit is 0.3 wt %, and a more preferred upper limit is 5 wt %. That is, the content of the inorganic compound relative to the total amount of the thermally expandable microcapsules is preferably 0.01 to 7 wt %, and more preferably 0.3 to 5 wt %. The content of the inorganic compound can be calculated from the weights of the monomer composition, volatile expanding agent, dye, and black pigment that form the thermally expandable microcapsules.

[0049] The weight ratio of the inorganic compound to the black pigment (inorganic compound / black pigment) is preferably 0.001 to 400. By setting the ratio to 0.001 or more, fusion between thermally expandable microcapsules in the resin during molding can be suppressed. By setting the ratio to 400 or less, resin dispersibility during molding can be further improved, and light-blocking properties and appearance performance can be further improved. A more preferred lower limit is 0.1, an even more preferred lower limit is 0.3, a more preferred upper limit is 300, an even more preferred upper limit is 200, an even more preferred upper limit is 150, a particularly preferred upper limit is 120, and an especially preferred upper limit is 100.

[0050] The weight ratio of the inorganic compound to the dye (inorganic compound / dye) is preferably 0.2 to 10. By making it 0.2 or more, the blackness can be synergistically improved. By making it 10 or less, the expansion ratio can be improved. A more preferred lower limit is 0.3, an even more preferred lower limit is 0.5, a more preferred upper limit is 8, and an even more preferred upper limit is 6.

[0051] In the present invention, the black pigment, dye, and inorganic compound may be present on the surface or inside of the thermally expandable microcapsule. However, it is preferable that the black pigment, dye, and inorganic compound be contained inside the shell of the thermally expandable microcapsule. In a preferred embodiment of the present invention, the black pigment and dye are preferably contained inside the shell. When the black pigment and dye are contained inside the shell, they are less likely to fall off, improving the appearance of the foam and making it easier to maintain high foaming performance. Furthermore, it is preferable that the thermally expandable microcapsule has an outermost layer, and the outermost layer contains the black pigment, dye, and inorganic compound. This configuration further improves dispersibility in the resin during molding. In the present invention, "contained inside the shell of the thermally expandable microcapsule" means that the black pigment, dye, and inorganic compound are present in the shell of the thermally expandable microcapsule, which is composed of a shell and a core, and is not simply synonymous with "the black pigment, dye, and inorganic compound being contained in the thermally expandable microcapsule." The locations of the above black pigments, dyes, and inorganic compounds can be confirmed using a transmission electron microscope, a fluorescence microscope, or the like after preparing a thin film that passes through the vicinity of the center of the thermally expandable microcapsules dispersed in the embedding resin.

[0052] The shell may contain a metal cation. When the copolymer constituting the shell contains a carboxyl group, the metal cation reacts with the carboxyl group to ionically crosslink the copolymer, improving heat resistance and enabling the formation of thermally expandable microcapsules that do not burst or shrink for long periods of time at high temperatures. Furthermore, since the elastic modulus of the shell is less likely to decrease even at high temperatures, the thermally expandable microcapsules do not burst or shrink even when subjected to molding processes that apply strong shear forces, such as kneading, calendaring, extrusion, and injection molding. The aforementioned ionic crosslinking refers to the formation of crosslinks between free carboxyl groups present as side chains of the copolymer. The number of carboxyl groups arranged per monovalent metal cation varies depending on the metal type.

[0053] The metal cation is not particularly limited as long as it reacts with the carboxyl groups of the copolymer to ionically crosslink the copolymer, and examples thereof include ions of Li, Na, K, Zn, Mg, Ca, Ba, Sr, Mn, Al, Ti, Ru, Fe, Ni, Cu, Cs, Sn, Cr, and Pb. These may be used alone or in combination of two or more. Among these, Ca, Zn, and Al ions are preferred, with Zn ions being particularly preferred. When two or more of the metal cations are used, the combination is not particularly limited, but it is preferable to use an alkali metal ion in combination with a metal cation other than the alkali metal. The presence of the alkali metal ion activates functional groups such as carboxyl groups, thereby promoting the reaction between the metal cations other than the alkali metal and the carboxyl groups of the copolymer. Examples of the alkali metal include Na, K, and Li.

[0054] The shell may further contain, as necessary, a stabilizer, an ultraviolet absorber, an antioxidant, an antistatic agent, a flame retardant, a silane coupling agent, a coloring agent, and the like.

[0055] In one embodiment of the thermally expandable microcapsules of the present invention, a volatile expanding agent is encapsulated in the shell as a core agent. The volatile expanding agent is a substance that becomes gaseous at a temperature below the softening point of the polymer that constitutes the shell, and a low-boiling organic solvent is suitable. Examples of the volatile expanding agent include low-molecular-weight hydrocarbons such as ethane, ethylene, propane, propene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, and hexanedecane. Also, CCl ３ F, CCl ２ F ２ , CClF ３ , CClF ２ -CClF ２ and chlorofluorocarbons such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyl-n-propylsilane, and tetraalkylsilanes such as tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, and trimethyl-n-propylsilane. Among these, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, and mixtures thereof are preferred. These volatile expanding agents may be used alone or in combination of two or more. Furthermore, as the volatile expanding agent, a thermally decomposable compound that is thermally decomposed into a gaseous form by heating may be used.

[0056] In the thermally expandable microcapsules according to one embodiment of the present invention, among the above-mentioned volatile expanding agents, it is preferable to use low-boiling hydrocarbons having 5 or less carbon atoms. By using such hydrocarbons, it is possible to obtain thermally expandable microcapsules with a high expansion ratio and rapid expansion start. Furthermore, a thermally decomposable compound that decomposes into a gaseous form when heated may be used as the volatile expanding agent.

[0057] The thermally expandable microcapsules according to one embodiment of the present invention preferably have an optical density (OD value) of 0.5 or more. By setting the OD value to 0.5 or more, a black coating film or black matrix that combines high light-blocking properties and jet blackness can be obtained. A more preferred lower limit is 0.8, and a more preferred upper limit is 1.6. The optical density (OD value) can be measured using a Macbeth densitometer or the like.

[0058] The thermally expandable microcapsules of the present invention preferably have an ash content of 0.1% by weight (lower limit) and 7% by weight (upper limit) after heating at 750°C for 180 minutes. By achieving this range, the thermally expandable microcapsules can exhibit excellent appearance while maintaining their foaming properties and compression resistance. In this specification, the ash content is calculated from the weight of the thermally expandable microcapsules before heating and the weight of the ash after heating at 750°C for 180 minutes. The ash content serves as a guide for the content of black pigment and inorganic compounds contained in the thermally expandable microcapsules.

[0059] The thermally expandable microcapsules according to one embodiment of the present invention preferably have a maximum expansion temperature (Tmax) of 170°C or higher. By setting the Tmax at 170°C or higher, heat resistance is improved, preventing the thermally expandable microcapsules from bursting or shrinking when a composition containing the thermally expandable microcapsules is applied at high temperatures. Furthermore, aggregation of the thermally expandable microcapsules during application can be suppressed, resulting in a good appearance. A more preferred lower limit is 180°C, and a more preferred upper limit is 240°C. That is, the Tmax is preferably 170 to 240°C, and more preferably 180 to 240°C. In this specification, the maximum expansion temperature refers to the temperature at which the diameter of the thermally expandable microcapsules reaches its maximum (maximum displacement) when the diameter of the thermally expandable microcapsules is measured while being heated from room temperature.

[0060] In the thermally expandable microcapsules according to one embodiment of the present invention, the maximum displacement (Dmax) measured by thermomechanical analysis preferably has a lower limit of 10 μm. If the Dmax is less than 10 μm, the expansion ratio decreases, and the desired expansion performance may not be achieved. A more preferred lower limit is 20 μm, an even more preferred lower limit is 100 μm, and an even more preferred lower limit is 300 μm. The preferred upper limit of the maximum displacement is 2000 μm, an even more preferred upper limit is 1800 μm, and an even more preferred upper limit is 1500 μm. That is, the Dmax is preferably 10 to 2000 μm, more preferably 20 to 1800 μm, even more preferably 100 to 1500 μm, and even more preferably 300 to 1500 μm. The maximum displacement refers to the value at which the diameter of a predetermined amount of thermally expandable microcapsules as a whole is maximized when the diameter is measured while heating a predetermined amount of thermally expandable microcapsules from room temperature.

[0061] The upper limit of the foaming initiation temperature (Ts) is preferably 175°C. By setting the temperature to 175°C or less, foaming becomes easy and a desired foaming ratio can be achieved. The lower limit is preferably 130°C, and the upper limit is more preferably 170°C. That is, the Ts is preferably 130 to 175°C, and more preferably 130 to 170°C.

[0062] The preferred lower limit of the volume average particle diameter of the thermally expandable microcapsules according to one embodiment of the present invention is 5 μm, and the preferred upper limit is 45 μm. If the diameter is less than 5 μm, the cells in the resulting molded product will be too small, resulting in an insufficient expansion ratio. If the diameter exceeds 45 μm, the cells in the resulting coated product will be too large, resulting in problems with appearance. A more preferred lower limit is 10 μm, and a more preferred upper limit is 35 μm. That is, the volume average particle diameter is preferably 5 to 45 μm, and more preferably 10 to 35 μm. The volume average particle diameter of the thermally expandable microcapsules can be measured using a laser diffraction / scattering particle size distribution analyzer or the like.

[0063] The method for producing the thermally expandable microcapsules according to one embodiment of the present invention is not particularly limited, but they can be produced, for example, by carrying out the steps of preparing an aqueous dispersion medium containing an inorganic compound, dispersing a black pigment dispersion containing a black pigment, a dispersant, and a monomer composition, a volatile expanding agent, and a dye in the aqueous dispersion medium, and polymerizing the monomers. The monomer composition can contain the nitrile monomer, a monomer having a carboxyl group, a crosslinkable monomer, and other monomers.

[0064] When producing thermally expandable microcapsules according to one embodiment of the present invention, the first step is to prepare an aqueous dispersion medium. Specifically, for example, an aqueous dispersion medium containing an inorganic compound is prepared by adding water, an inorganic compound, and, if necessary, a co-stabilizer to a polymerization reaction vessel.

[0065] Examples of the auxiliary stabilizer include a condensation product of diethanolamine and an aliphatic dicarboxylic acid, a condensation product of urea and formaldehyde, etc. Further examples include polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, various emulsifiers, etc.

[0066] In addition to the co-stabilizer, a condensation product or a water-soluble nitrogen compound may be added. As the condensation product, a condensation product of diethanolamine and an aliphatic dicarboxylic acid is preferred, and a condensation product of diethanolamine and adipic acid or a condensation product of diethanolamine and itaconic acid is particularly preferred.

[0067] Examples of the water-soluble nitrogen compounds include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, polydialkylaminoalkyl(meth)acrylates such as polydimethylaminoethyl methacrylate and polydimethylaminoethyl acrylate, polydialkylaminoalkyl(meth)acrylamides such as polydimethylaminopropyl acrylamide and polydimethylaminopropyl methacrylamide, polyacrylamide, polycationic acrylamide, polyamine sulfone, and polyallylamine. Among these, polyvinylpyrrolidone is preferably used.

[0068] An aqueous dispersion medium containing the inorganic compound and co-stabilizer is prepared by blending them with deionized water, and the pH of the aqueous phase is determined appropriately depending on the types of inorganic compound and co-stabilizer used. For example, when a Si-based compound such as colloidal silica is used as the inorganic compound, polymerization is carried out using an acidic aqueous dispersion medium, and to make the aqueous dispersion medium acidic, an acid such as hydrochloric acid is added as necessary to adjust the pH of the system to 3 to 4. On the other hand, when a Mg-based compound such as magnesium hydroxide or calcium phosphate is used as the inorganic compound, polymerization is carried out using an alkaline aqueous dispersion medium adjusted to a pH of 8 to 11.

[0069] Next, in the method for producing thermally expandable microcapsules, a step of dispersing a black pigment dispersion containing a black pigment, a dispersant, and a monomer composition, a volatile expanding agent, and a dye in an aqueous dispersion medium is carried out. The black pigment dispersion may be prepared by adding the black pigment, dye, and dispersant to a monomer composition. The step of preparing the black pigment dispersion preferably involves adding the dye to a monomer composition and dissolving it, and then adding and dispersing the black pigment. This step is believed to enable uniform dissolution of the dye. Known methods, such as stirring using a bead mill or the like, ultrasonic waves, and rotation, can be used for the dispersion. The step of dispersing the black pigment dispersion and the volatile expanding agent in the aqueous dispersion medium allows the black pigment used to be present inside the thermally expandable microcapsules. In this step, the black pigment dispersion, the volatile expanding agent, and the dye may be added separately to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium. However, typically, the two are mixed together to form an oily mixture before adding it to the aqueous dispersion medium. In this case, the oily mixture and the aqueous dispersion medium may be prepared in separate containers, and the oily mixture may be dispersed in the aqueous dispersion medium by mixing them in separate containers while stirring, and then added to the polymerization reaction vessel. In this process, an inorganic compound is present at the interface between the oil droplets of the oily mixture and the aqueous dispersion medium, resulting in the inorganic compound being present on the shell surface of the resulting thermally expandable microcapsules, allowing a black pigment or dye to be present inside the shell. Alternatively, thermally expandable microcapsules having a dye present on the shell surface may be prepared by first preparing thermally expandable microcapsules without adding a dye, and then adding the dye. A polymerization initiator is used to polymerize the monomer. The polymerization initiator may be added to the oily mixture in advance, or may be added after the aqueous dispersion medium and the oily mixture are mixed and stirred in the polymerization reaction vessel.

[0070] The dispersant to be added to the black pigment dispersion is not particularly limited, and examples thereof include polyurethane-based, polyamide-based, polyimide-based, polycarboxylic acid-based (e.g., poly(meth)acrylic acid) and poly(maleic anhydride) dispersants, polyamine-based, and polyester-based dispersants having poly(meth)acrylate, polylactone, polyalkylene oxide, or the like as the main chain or side chain, as well as dispersants having a quaternary ammonium salt, etc., incorporated into a portion thereof. These dispersants can be used alone or in combination of two or more. Commercially available dispersants include polyurethane-based dispersants such as Disperbyk-161, 166, and 167 manufactured by BYK Japan, and Solsperse 55000 and 76500 manufactured by Lubrizol Japan; polycarboxylic acid-based dispersants such as Disperbyk-106, 110, and 111, Solsperse 36000 and 41000, and EFKA-5060 manufactured by BASF Japan; and polyamine-based dispersants such as Disperbyk-116 and 130, Solsperse 24000, 32000, 33000, 35000, 86000, J200, and EFKA-4046, and Ajinomoto Fine-Techno Co., Ltd.'s Ajisper PB821, PB822, PB824, and PB881. Among these, Solsperse J200 and Solsperse 35000 are more preferred from the viewpoint of dispersibility of the black pigment.

[0071] Examples of a method for emulsifying and dispersing the oily mixture in an aqueous dispersion medium to a predetermined particle size include a method of stirring with a homomixer (for example, manufactured by Tokushu Kika Kogyo Co., Ltd.) or a method of passing the mixture through a static dispersion device such as a line mixer or an element-type static disperser. The aqueous dispersion medium and the polymerizable mixture may be supplied separately to the static dispersion device, or a dispersion liquid that has been mixed and stirred in advance may be supplied.

[0072] The thermally expandable microcapsules according to one embodiment of the present invention can be produced by subjecting the dispersion obtained through the above-described steps to a step of polymerizing the monomers by heating, and a step of washing. The thermally expandable microcapsules produced by this method have a high maximum foaming temperature, excellent heat resistance, and do not burst or shrink even when coated at high temperatures.

[0073] The present invention also includes a foamable masterbatch containing the above-mentioned thermally expandable microcapsules and a thermoplastic resin (base resin).

[0074] The thermoplastic resin used for the base resin is not particularly limited, and any thermoplastic resin commonly used in foam molding can be used. Specific examples of the thermoplastic resin include polyolefins such as low-density polyethylene (LDPE) and polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), vinyl chloride, polystyrene, thermoplastic elastomers, and ethylene-methyl methacrylate copolymer (EMMA). Among these, LDPE, EVA, and EMMA are preferred because of their low melting points and ease of processing. These resins may be used alone or in combination of two or more.

[0075] The content of the thermally expandable microcapsules in the foamable masterbatch is not particularly limited, but the preferred lower limit is 10 parts by weight and the preferred upper limit is 90 parts by weight per 100 parts by weight of the thermoplastic resin.

[0076] The method for producing the expandable masterbatch is not particularly limited, but examples include pre-kneading raw materials such as a base resin such as a thermoplastic resin and various additives using a co-rotating twin-screw extruder or the like. The mixture is then heated to a predetermined temperature, a blowing agent such as thermally expandable microcapsules is added, and the resulting mixture is further kneaded. The resulting mixture is then cut into pellets of the desired size using a pelletizer to form a masterbatch. Alternatively, a pellet-shaped masterbatch may be produced by kneading raw materials such as a base resin such as a thermoplastic resin and thermally expandable microcapsules using a batch kneader and then granulating them using a granulator. The kneader is not particularly limited as long as it can knead the materials without destroying the thermally expandable microcapsules, and examples include a pressure kneader and a Banbury mixer.

[0077] The present invention also encompasses foamed molded articles obtained using the thermally expandable microcapsules or expandable masterbatch. In particular, the thermally expandable microcapsules can be suitably used in applications requiring post-processing at high temperatures, resulting in foamed sheets with high appearance quality, such as uneven surfaces, suitable for applications such as residential wallpaper. Specifically, foamed molded articles can be obtained by kneading and molding the thermally expandable microcapsules or expandable masterbatch containing the thermally expandable microcapsules with a matrix resin. According to the present invention, gas barrier properties can be improved during thermal expansion, improving durability, and the expansion ratio and heat resistance can also be improved.

[0078] The molding method for the foamed molded article is not particularly limited, and examples thereof include kneading molding, calendar molding, extrusion molding, injection molding, etc. In the case of injection molding, the process is not particularly limited, and examples thereof include the short shot method in which a resin material is partially placed in a mold and foamed, and the core back method in which the mold is fully filled with the resin material and then opened to the desired foaming point.

[0079] According to the present invention, it is possible to provide a thermally expandable microcapsule that has excellent expandability, can suppress the occurrence of white spots, and can produce a foamed molded article that is less likely to have color difference defects after foaming, and to provide a foamable masterbatch and a foamed molded article using the thermally expandable microcapsule.Furthermore, the thermally expandable microcapsule can also be made to have a uniform color tone after foaming.

[0080] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0081] Example 1 (Preparation of Thermally Expandable Microcapsules) 1.4 parts by weight of Solvent Red 8 (number of nitrogen atoms per molecule: 10, metal complex dye [oil-soluble dye], molecular weight: 730.6 [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) as a dye and 100 parts by weight of a monomer composition having the blending ratio shown in Table 1 were placed in a container, and the dye-containing compound was dissolved in the monomer composition. Carbon black (MA14, manufactured by Mitsubishi Chemical Corporation, primary average particle size: 40 nm, specific surface area: 56 m) as a black pigment was added to the container.２ A carbon black dispersion was obtained by adding 4 parts by weight of carbon black (20% by weight, manufactured by Asahi Denka Co., Ltd.) and 1 part by weight of Solsperse J200 (manufactured by Lubrizol Japan Co., Ltd.) as a dispersant for carbon black, and dispersing the carbon black using a bead mill. An aqueous dispersion medium was prepared by adding 300 parts by weight of water, 10 parts by weight of colloidal silica (20% by weight, manufactured by Asahi Denka Co., Ltd.) as a dispersion stabilizer (inorganic compound), 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF Corporation), and 1.8 parts by weight of 1N hydrochloric acid to a polymerization reaction vessel. Next, an oily mixture consisting of a volatile expanding agent, 106.4 parts by weight of carbon black dispersion, and 0.8 parts by weight of 2,2'-azobisisobutyronitrile and 0.6 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile) as polymerization initiators in the blending ratios shown in Table 1 was added to the aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was stirred and mixed with a homogenizer and charged into a nitrogen-substituted pressure polymerization vessel. The reaction was carried out at 60°C for 21 hours under pressure (0.5 MPa) to obtain a reaction product. The resulting reaction product was repeatedly filtered and washed with water, and then dried to obtain thermally expandable microcapsules. The obtained thermally expandable microcapsules were added to an embedding resin (Technovit 4000, manufactured by Kulzer) so that the particle content was 3% by weight, and dispersed to prepare a resin for embedding thermally expandable microcapsules. A microtome (EM) was used to pass through the vicinity of the center of the thermally expandable microcapsules dispersed in the embedding resin. A thin film was prepared using a microscope (UC7, LEICA) and the location of the black pigment was confirmed using a transmission electron microscope (JEM-2100, JEOL Ltd.), which confirmed that the black pigment was present inside the shell. Furthermore, the location of the dye was confirmed using a fluorescence microscope (System Biological Microscope BX51 and Epi-Fluorescence System, Olympus Corporation), which confirmed that the dye was present inside the shell.

[0082] (Examples 2 to 17) Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that the types and contents of black pigments and dyes shown in Tables 1 and 2 were used. The dyes used were as follows: Solvent Blue 5 (number of nitrogen atoms per molecule: 3, metal complex dye [oil-soluble dye], molecular weight: 495.7 [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) Solvent Yellow 21 (number of nitrogen atoms per molecule: 4, metal complex dye [oil-soluble dye], molecular weight: 323.3 [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) PC-8550 (mixture of oil-soluble azine dye and oil-soluble anthraquinone dye, manufactured by Orient Chemical Industries Co., Ltd.) Solvent Black 3 (number of nitrogen atoms per molecule: 6, oil-soluble disazo dye, molecular weight: 456.54 [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) Solvent Black Solvent Black 5 (number of nitrogen atoms per molecule: 6, oil-soluble nigrosine dye, polymer type, melting point: 300°C or higher, manufactured by Orient Chemical Industries Co., Ltd.) Solvent Black 7 (number of nitrogen atoms per molecule: 8 or higher, oil-soluble nigrosine dye, polymer type, melting point: 275°C, manufactured by Orient Chemical Industries Co., Ltd.) Solvent Black 27 (number of nitrogen atoms per molecule: 3, oil-soluble azo chromium alloy dye, molecular weight: 668.53 [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) Solvent Black 29 (number of nitrogen atoms per molecule: 2, azo compound Cr complex [oil-soluble dye], molecular weight: 668.53 or higher [single molecule type], manufactured by Orient Chemical Industries Co., Ltd.) Polymerizable dyes K01 (number of nitrogen atoms per molecule: 2, oil-soluble xanthene dye, molecular weight: 1324.84 [single molecule type], manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0083] Example 18 Thermally expandable microcapsules were obtained in the same manner as in Example 10, except that the types and contents of the monomer compositions and volatile expanding agents shown in Table 2 were used.

[0084] Example 19 Thermally expandable microcapsules were obtained in the same manner as in Example 7, except that no dye was added. Thereafter, 10 parts by weight of the obtained thermally expandable microcapsules, 5 parts by weight of Solvent Black 7 (number of nitrogen atoms per molecule: 8 or more, oil-soluble nigrosine dye, polymer type, melting point: 275°C, manufactured by Orient Chemical Industries Co., Ltd.) as a dye, and 20 parts by weight of xylene (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) were added to a reaction vessel, stirred for 5 hours, filtered, and dried to obtain thermally expandable microcapsules whose surfaces were coated with the dye.

[0085] Comparative Example 1 Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that no dye was added.

[0086] Comparative Example 2 Thermally expandable microcapsules were obtained in the same manner as in Example 10, except that the black pigment was not added.

[0087] Comparative Example 3 Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that the black pigment, dye, and dispersant were not added.

[0088] (Evaluation Method) The performance of the obtained thermally expandable microcapsules was evaluated by the following method. The results are shown in Tables 1 and 2.

[0089] (1) Evaluation of Thermally Expandable Microcapsules (1-1) Measurement of Volume Average Particle Diameter (Before Foaming) The volume average particle diameter of the obtained thermally expandable microcapsules was measured using a laser diffraction / scattering particle size distribution analyzer (LS 13 320, manufactured by Beckman Coulter).

[0090] (1-2) Measurement of Foaming Initiation Temperature, Maximum Displacement, and Maximum Foaming Temperature The foaming initiation temperature (Ts), maximum displacement (Dmax), and maximum foaming temperature (Tmax) were measured using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA Instruments). Specifically, 25 μg of a sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm, and heated from 80°C to 250°C at a heating rate of 5°C / min with a force of 0.1 N applied from above. The displacement in the vertical direction of the measuring probe was measured, and the temperature at which the displacement started to increase was defined as the foaming initiation temperature, the maximum value of the displacement as the maximum displacement, and the temperature at the maximum displacement as the maximum foaming temperature.

[0091] (1-3) Black Pigment Content Measurement Using a differential thermal thermogravimetric simultaneous analyzer (TA7200, Hitachi High-Tech Science Corporation), 1.0 mg of the obtained thermally expandable microcapsules was heated to 600 ° C at 10 ° C / min under a nitrogen atmosphere, held for 10 minutes, and then cooled to 400 ° C at 10 ° C / min and held for 10 minutes. The atmosphere was then switched to air, and the microcapsules were heated to 1000 ° C under air and held at 1000 ° C for 10 minutes. The weight loss from 400 ° C to 1000 ° C was determined and recorded as the high-temperature combustion product content. In addition, the high-temperature combustion product content of thermally expandable microcapsules of the same components but without black pigment was measured separately, and the difference between the high-temperature combustion product content when the black pigment was contained and the high-temperature combustion product content when the black pigment was not contained was calculated as the black pigment content.

[0092] (1-4) Color Tone Uniformity The obtained thermally expandable microcapsules were heated at their Tmax temperature and foamed for 3 minutes, and then observed under a microscope (Keyence Corporation, VHX-7100) to evaluate the color tone uniformity according to the following criteria. Note that the color tone uniformity is related to the state of the black pigment in the shell, and a rating of A below indicates that the black pigment is evenly present in the shell.

[0093] A: The entire thermally expandable microcapsule appears black after foaming. B: Part of the thermally expandable microcapsule appears white after foaming.

[0094] (2) Evaluation of Foam Molded Articles (2-1) Color Difference Evaluation (ΔE*ab Value) 100 parts by weight of base resin (low-density polyethylene), 100 parts by weight of the obtained thermally expandable microcapsules, and 10 parts by weight of lubricant (stearic acid) were added, kneaded in a Banbury mixer at 100°C for 30 seconds, and extruded and simultaneously pelletized to obtain masterbatch pellets. 6 parts by weight of the obtained masterbatch pellets and 194 parts by weight of TPV resin (Milastomer W600B, manufactured by Mitsui Chemicals, Inc.) were weighed and mixed, and the resulting mixed pellets were made into a roll sheet at 130°C using an 8-inch roll (191-TM, manufactured by Yasuda Seiki Seisakusho Co., Ltd.). This roll sheet was cut to obtain a pre-foamed molded article. Meanwhile, 6 parts by weight of the obtained masterbatch pellets and 194 parts by weight of TPV resin (Milastomer W600B, manufactured by Mitsui Chemicals, Inc.) were weighed and mixed, and the resulting mixed pellets were fed into the hopper of an injection molding machine, melt-kneaded, and injection-molded to obtain a plate-shaped foamed molded body after a 1.25 mm core back. The molding temperature was 200 ° C. Using a color difference meter (Konica Minolta "CM-26dG"), the L*, a*, and b* values ​​of the pre-foamed molded body and the foamed molded body were measured at any five locations, and the average value was calculated. The L*, a*, and b* values ​​of the pre-foamed molded body were used as a reference, and the difference ΔE*ab from the foamed molded body was calculated, and the resulting ΔE*ab was evaluated according to the following criteria.

[0095] A: Less than 3.0 B: 3.0 or more and less than 3.5 C: 3.5 or more and less than 4.0 D: 4.0 or more and less than 5.0 E: 5.0 or more

[0096] (2-2) Appearance (White Spots) 6 parts by weight of masterbatch pellets obtained in the same manner as in "(2-1) Color Difference Evaluation (ΔE*ab Value)" above and 194 parts by weight of TPV resin (Milastomer W600B, manufactured by Mitsui Chemicals, Inc.) were weighed and mixed, and the resulting mixed pellets were fed into the hopper of an injection molding machine, melt-kneaded, and injection-molded, followed by a 1.25 mm core back to obtain a plate-shaped foamed molded article. The molding temperature was 200°C. The surface of the molded article was binarized using an optical microscope, and the number of white spots was counted and evaluated according to the following criteria.

[0097] Less than 15: A 15 to less than 30: B 30 to less than 50: C 50 to less than 70: D 70 or more: E

[0098] (2-3) Expansion Ratio The density of the molded article before expansion and the density of the expanded molded article were measured by a method in accordance with JIS K 7112 Method A (underwater displacement method), and the expansion ratio was calculated from the densities of the molded article before and after expansion.

[0099] 1.15 or more: A 1.10 or more and less than 1.15: B 1.05 or more and less than 1.10: C Less than 1.05: D

[0100]

[0101]

[0102] According to the present invention, it is possible to provide a thermally expandable microcapsule that has excellent foaming properties, can suppress the occurrence of white spots, and can produce a foamed molded product that is less likely to have color difference defects after foaming, as well as a foamable masterbatch and a foamed molded product that use the thermally expandable microcapsule.

Claims

1. A thermally expandable microcapsule having a shell encapsulating a volatile expanding agent as a core agent, the shell containing a polymer compound, a black pigment and a dye.

2. The thermally expandable microcapsule according to claim 1, wherein the dye is an oil-soluble dye.

3. The thermally expandable microcapsule according to claim 1, wherein the dye is a black dye.

4. The thermally expandable microcapsule according to any one of claims 1 to 3, wherein the dye content is 0.5% by weight or more and 10% by weight or less based on the total weight of the thermally expandable microcapsule.

5. A thermally expandable microcapsule according to any one of claims 1 to 4, wherein the dye content is 5 parts by weight or more and 1,000 parts by weight or less per 100 parts by weight of the black pigment.

6. A foamable masterbatch comprising the thermally expandable microcapsules according to any one of claims 1 to 5 and a thermoplastic resin.

7. A foamed molded article obtained by using the foamable masterbatch according to claim 6.

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