Thermally expandable microcapsules

Abstract

The present invention provides: thermally expandable microcapsules which have excellent foamability, and which enable the achievement of a foam molded body having excellent flame retardancy; and a foamable masterbatch, a foamable resin composition, and a foam molded body, each of which uses the thermally expandable microcapsules. The present invention pertains to thermally expandable microcapsules each comprising a shell, and a volatile expanding agent enclosed as a core agent in the shell, wherein the shell contains a flame retardant.

Description

Thermally Expandable Microcapsules

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

[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 an oil-soluble polymerization catalyst and a dispersant, followed by suspension polymerization. Patent Document 2 also discloses thermally expandable microspheres containing a polymer composed of a crosslinkable monomer having a molecular weight of 500 or more and a (meth)acryloyl group and a reactive carbon-carbon double bond.

[0004] Japanese Patent Publication No. 42-26524 International Publication No. 2019 / 150951

[0005] The thermally expandable microcapsules (thermally expandable microspheres) described in Patent Documents 1 and 2 can be added to a resin such as a thermoplastic resin and then subjected to a foaming process to produce a foamed molded article. However, while it is desired to impart flame retardancy to the resulting foamed molded article, there is a problem in that when a foamed molded article is produced by mixing a general flame retardant with conventional thermally expandable microcapsules, the foaming ability is insufficient.

[0006] The present invention aims to provide a thermally expandable microcapsule that has high expandability and can give a foamed molded article having excellent flame retardancy, a foamable masterbatch that uses the thermally expandable microcapsule, a foamable resin composition, and a foamed molded article.

[0007] Disclosure (1) is a thermally expandable microcapsule having a shell encapsulating a volatile expanding agent as a core agent, the shell containing a flame retardant. Disclosure (2) is a thermally expandable microcapsule according to Disclosure (1), in which the flame retardant includes at least one selected from the group consisting of phosphorus-based flame retardants and halogen-based flame retardants. Disclosure (3) is a thermally expandable microcapsule according to Disclosure (1) or (2), in which the average particle size of the flame retardant is 10 nm or more and 5,000 nm or less. Disclosure (4) is a thermally expandable microcapsule according to any one of Disclosures (1) to (3), in which the ratio (A / B) of the average particle size (A) of the flame retardant to the shell thickness (B) is 0.002 to 0.8. Disclosure (5) is a thermally expandable microcapsule according to any one of Disclosures (1) to (4), in which the content of the flame retardant is 0.01% by weight or more and 10% by weight or less, based on the entire thermally expandable microcapsule. Disclosure (6) is a thermally expandable microcapsule according to any one of Disclosures (1) to (5), in which the flame retardant is contained inside the shell. Disclosure (7) is a thermally expandable microcapsule according to any one of Disclosures (1) to (6), in which the content of the flame retardant element is 0.001% by weight or more and 10% by weight or less, based on the entire thermally expandable microcapsule. Disclosure (8) is a thermally expandable microcapsule according to any one of Disclosures (1) to (7), further containing at least one inorganic compound selected from the group consisting of Si-based compounds and Mg-based compounds. Disclosure (9) is a thermally expandable microcapsule according to Disclosure (8), in which the content of the inorganic compound is 0.01 to 10% by weight, based on the entire thermally expandable microcapsule. The present disclosure (10) is a thermally expandable microcapsule according to the present disclosure (8) or (9), in which the weight ratio of the inorganic compound to the flame retardant (inorganic compound / flame retardant) is 0.01 to 10,000. The present disclosure (11) is a foamable masterbatch containing the thermally expandable microcapsule according to any one of the present disclosures (1) to (10) and a thermoplastic resin. The present disclosure (12) is a foamable resin composition containing the thermally expandable microcapsule according to any one of the present disclosures (1) to (10), a flame-retardant compound, and a thermoplastic resin.The present disclosure (13) is the foamable resin composition according to the present disclosure (12), in which the ratio (A / C) of the average particle size (A) of the flame retardant contained in the thermally expandable microcapsules to the average particle size (C) of the flame retardant compound is 0.0003 to 1.0. The present disclosure (14) is a foamed molded article obtained using the thermally expandable microcapsules according to any one of the present disclosures (1) to (10), the foamable masterbatch according to the present disclosure (11), or the foamable resin composition according to the present disclosure (12) or (13). The present invention will be described in detail below.

[0008] The shell constituting the thermally expandable microcapsule according to one embodiment of the present invention contains a flame retardant. By including the flame retardant in the shell constituting the thermally expandable microcapsule, when added to a foamable resin composition, a decrease in the flame retardant content of the entire resin composition can be suppressed, thereby improving the flame retardancy. As a result, it is possible to achieve both high foamability and excellent flame retardancy. Furthermore, the flame retardant is localized in a finely divided state in the shell, thereby improving the flame retardancy. Furthermore, there is no need to increase the amount of flame retardant in the entire foamable resin composition, thereby preventing a decrease in foamability. Furthermore, the inclusion of the flame retardant improves the affinity with the resin and improves dispersibility. As a result, a molded article having uniform cells can be produced. In the present invention, the shell may contain a component corresponding to the flame retardant. The shell may contain the flame retardant and the polymer compound separately, or the flame retardant and the polymer compound may be integrated. The flame retardant is a substance that, when added to a flammable material such as plastic, wood, or fiber, can impart flame retardancy to the resulting material.

[0009] Examples of the flame retardant include phosphorus-based flame retardants, halogen-based flame retardants, nitrogen-containing flame retardants, inorganic flame retardants, etc. Among these, it is preferable to include at least one selected from the group consisting of phosphorus-based flame retardants and halogen-based flame retardants because of their high flame retardancy, and phosphorus-based flame retardants are particularly preferable because of their small impact on the environment and human body.

[0010] Examples of the phosphorus-based flame retardant include aromatic phosphate esters, aliphatic phosphate esters, halogen-containing phosphate esters, polymerizable phosphorus compounds, phosphates, polyphosphates, and phosphorus-based spiro compounds. Examples of the aromatic phosphate esters include triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, and aromatic pentaerythritol diphosphonate. Examples of the fatty acid phosphate esters include trioctyl phosphate. Examples of the halogen-containing phosphate esters include tris(halopropyl)phosphate and tris(haloethyl)phosphate. Examples of the polymerizable phosphorus compounds include vinyl phosphonate and allyl phosphonate.

[0011] Examples of the phosphate salts include melamine orthophosphate, piperazine orthophosphate, melamine pyrophosphate, piperazine pyrophosphate, calcium phosphate, magnesium phosphate, etc. Examples of the polyphosphate salts include ammonium polyphosphate, melamine polyphosphate, melamine melam melem polyphosphate, piperazine polyphosphate, etc. Among these, ammonium polyphosphate is preferred.

[0012] "Melamine" or "piperazine" in the above examples of phosphates and polyphosphates includes N,N,N',N'-tetramethyldiaminomethane, ethylenediamine, N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-diethylethylenediamine, 1,2-propanediamine, 1 , 3-propanediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, trans-2,5-dimethylpiperazine, 1,4-bis(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine, acetoguanamine, benzoguanamine, acrylguanamine, 2,4-diamino-6-nonane 2,4-diamino-6-hydroxy-1,3,5-triazine, 2-amino-4,6-dihydroxy-1,3,5-triazine, 2,4-diamino-6-methoxy-1,3,5-triazine, 2,4-diamino-6-ethoxy-1,3,5-triazine, 2,4-diamino-6-propoxy-1,3,5-triazine, 2,4-diamino-6-isopropoxy-1,3,5-triazine, 2,4-diamino-6-methyl- Compounds with names substituted with melamine cyanurate, melamine pyrophosphate, butylenediguanamine, norbornenediguanamine, methylenediguanamine, ethylenedimelamine, trimethylenedimelamine, tetramethylenedimelamine, hexamethylenedimelamine, and 1,3-hexylenedimelamine can also be used.

[0013] In the present invention, one of the above phosphates and polyphosphates may be used alone, or two or more selected from the above phosphates and polyphosphates may be mixed and used as an intumescent flame retardant. Furthermore, one or more selected from the above phosphates and polyphosphates may be mixed with a metal oxide and used as an intumescent flame retardant. Examples of metal oxides to be used in combination with one or more selected from the above phosphates and polyphosphates include zinc oxide, magnesium oxide, calcium oxide, silicon dioxide, titanium oxide, manganese oxide (MnO, MnO ２ ), iron oxide (FeO, Fe ２ O ３ , Fe ３ O ４ ), copper oxide, nickel oxide, tin oxide, aluminum oxide, calcium aluminate, etc. Among these, zinc oxide, magnesium oxide, and calcium oxide are preferred. When one or more selected from the above phosphates and polyphosphates are used in combination with a metal oxide, the mass ratio thereof is preferably adjusted as follows. From the viewpoint of improving flame retardancy, the mass ratio of one or more selected from phosphates and polyphosphates to the metal oxide [total mass of phosphate and polyphosphate / mass of metal oxide] is preferably 4 or more and 100 or less, more preferably 6 or more and 50 or less, and even more preferably 10 or more and 35 or less. That is, the ratio of the total mass of the above phosphate and polyphosphate to the mass of the metal oxide is preferably 4 to 100, more preferably 6 to 50, and even more preferably 10 to 35.

[0014] The phosphazene compound is an organic compound having a -P=N- bond in the molecule. As the phosphazene compound, one represented by the following general formula (1) is preferred because it has a relatively high decomposition temperature:

[0015]

[0016] In the above formula (1), R １ ~R ６each independently represents an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, an amino group, or a halogen atom. Examples of such phosphazene compounds include "SPB-100" commercially available from Otsuka Chemical Co., Ltd.

[0017] The phosphorus-based spiro compound is not particularly limited as long as it is a spiro compound having a phosphorus atom. A spiro compound is a compound having a structure in which two cyclic compounds share one carbon, and a spiro compound having a phosphorus atom is a compound in which at least one of the elements constituting the two cyclic compounds is a phosphorus atom. As the phosphorus-based spiro compound, for example, a compound having a structure represented by the following formula (2) in the molecule is preferably used. In formula (2), * indicates a linking portion to other substituents.

[0018]

[0019] Examples of the nitrogen-containing flame retardant include triazine derivatives, tris(2-hydroxyethyl)isocyanurate, tris(2,3-epoxypropyl)isocyanurate, melamine cyanurate, benzoguanamine, melamine, etc., and those containing oxygen in the structure are preferred. Note that the nitrogen-containing flame retardant in this specification refers to a flame retardant that does not contain phosphorus.

[0020] The halogen-based flame retardant is preferably a chlorine-based flame retardant or a bromine-based flame retardant. Examples of the chlorine-based flame retardant include chlorinated paraffin and chlorinated polyethylene perchloropentacyclodecane. The bromine-based flame retardant is not particularly limited as long as it contains bromine in its molecular structure. Examples of the brominated flame retardant include decabromodiphenyl ether, octabromodiphenyl ether, tetrabromobisphenol A (TBBA), TBBA epoxy oligomer, TBBA carbonate oligomer, TBBA bis(dibromopropyl ether), TBBA bis(aryl ether), decabromodiphenylethane [bis(pentabromophenyl)ethane], 1,2-bis(2,4,6-tribromophenoxy)ethane, 2,4,6-tris(2,4,6-tribromophenoxy)-1,3,5-triazine, 2,6-or(2,4-)dibromophenol homopolymer, brominated polystyrene, polybrominated styrene, ethylene bistetrabromophthalimide, hexabromocyclododecane, hexabromobenzene, pentabromobenzyl acrylate monomer, and pentabromobenzyl acrylate polymer. Among these, decabromodiphenylethane is preferred from the viewpoints of flame retardancy and foaming property. These bromine-based flame retardants may be used alone or in combination of two or more. Note that the halogen-based flame retardants do not include halogen-based phosphorus-based flame retardants, nitrogen-containing flame retardants, and inorganic flame retardants.

[0021] Examples of the inorganic flame retardant include metal compounds such as metal oxides, metal hydroxides, and metal salts, etc. Examples of the metal compounds include zirconium oxide, aluminum hydroxide, dawsonite, calcium aluminate, gypsum dihydrate, calcium hydroxide, zinc borate, barium metaborate, borax, kaolin clay, calcium carbonate, molybdenum compounds, ammonium aluminum hydroxycarbonate, ferrocene, and tin compounds.

[0022] The flame retardant may be used in combination with a flame retardant synergist. This allows for a synergistic effect with the flame retardant, improving flame retardancy and reducing the amount of flame retardant used. In particular, when a halogen-based flame retardant is used as the flame retardant, the flame retardant synergist reacts with the halogen-based flame retardant during combustion to form a non-flammable halide. This produces an oxygen-shielding effect.

[0023] The flame retardant aid is preferably an antimony-based flame retardant aid, such as antimony trioxide or antimony pentoxide, and examples of commercially available products include "PATOX-M," "PATOX-MK," and "PATOX-K" manufactured by Nippon Seiko Co., Ltd.

[0024] From the viewpoint of a synergistic effect with the flame retardant, the content of the flame retardant aid is preferably 20 to 80 parts by weight, more preferably 30 to 70 parts by weight, and even more preferably 40 to 60 parts by weight, relative to 100 parts by weight of the flame retardant. The content of the flame retardant may be calculated from the charged amount, or may be measured using X-ray structural analysis of the thermally expandable microcapsules.

[0025] The melting point of the flame retardant is preferably 240 to 600° C., more preferably 250 to 550° C., and even more preferably 255 to 500° C. By setting the melting point within the above range, the flame retardant is easily melted by the heat during combustion, and combustion of the foamed molded article can be suppressed.

[0026] The flame retardant is preferably in the form of fine particles (flame-retardant fine particles). In this case, the average particle diameter of the flame retardant is preferably 10 nm or more and 5000 nm or less, more preferably 50 nm or more and 1000 nm or less. By setting the average particle diameter within the above range, the flame-retardant fine particles are dispersed in the resin. That is, the average particle diameter of the flame retardant is preferably 10 to 5000 nm, more preferably 50 to 1000 nm. The average particle diameter can be measured by observation using a particle size distribution measuring device (ELSZ-2000ZS, manufactured by Otsuka Electronics Co., Ltd.).

[0027] The flame retardant 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 flame retardant is dispersed in the resin. 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 flame retardant from the measurement results in accordance with the BET method.

[0028] The preferred lower limit of the flame retardant content is 0.01 wt % and the preferred upper limit is 10 wt % based on the total thermally expandable microcapsule content. By setting the content at 0.01 wt % or more, a decrease in the flame retardancy of the foamed molded product can be suppressed. By setting the content at 10 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 9 wt %, an even more preferred upper limit is 8 wt %, and an even more preferred upper limit is 7 wt %. That is, the flame retardant content is preferably 0.01 to 10 wt %, more preferably 0.3 to 9 wt %, even more preferably 0.3 to 8 wt %, and even more preferably 0.3 to 7 wt %. The flame retardant content can be determined from the weight loss in thermogravimetric analysis. The flame retardant content can also be calculated from the amounts of the flame retardant and other components added.

[0029] 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.

[0030] 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.

[0031] The preferred lower limit of the content of the nitrile monomer in the monomer composition is 40% by weight, and the preferred upper limit is 90% by weight. By making it 40% 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 50% by weight, and a more preferred upper limit is 80% by weight. That is, the content of the nitrile monomer is preferably 40 to 90% by weight, and more preferably 50 to 80% by weight.

[0032] 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 carboxylic 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 carboxylic 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.

[0033] 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 60% by weight. That is, the content of the nitrile-based monomer is preferably 5 to 70% by weight, and more preferably 10 to 60% by weight. The above content refers to the content relative to the total amount of monomers.

[0034] 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.

[0035] 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.

[0036] 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 %.

[0037] 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, and alicyclic, aromatic, and heterocyclic methacrylates such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate being particularly preferred.

[0038] 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 30 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 30 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 25 wt %. That is, the content of the other monomer is preferably 0.1 to 30 wt %, and more preferably 0.3 to 25 wt %.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 enhanced. 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.

[0044] When the flame retardant and the polymer compound are integrally contained, the polymer compound preferably contains a polymer of a monomer composition containing a flame-retardant monomer. Examples of the flame-retardant monomer include phosphorus atom-containing monomers and halogen-containing monomers. Examples of the phosphorus atom-containing monomer include phosphoric acid derivatives, phosphine derivatives, phosphinic acid derivatives, phosphonic acid derivatives, phosphorane derivatives, and phosphazene derivatives.

[0045] Examples of the phosphoric acid derivatives include 2-acryloyloxyethyl phosphate, 2-methacryloyloxyethyl phosphate, 2-acryloyloxypropyl phosphate, 2-methacryloyloxypropyl phosphate, di(2-acryloyloxyethyl)phosphate, di(2-methacryloyloxyethyl)phosphate, di(2-acryloyloxypropyl)phosphate, di(2-methacryloyloxypropyl)phosphate, methyl-2-acryloyloxyethyl phosphate, and methyl-2-methacryloyloxyethyl. Phosphate, methyl-2-acryloyloxypropyl phosphate, methyl-2-methacryloyloxypropyl phosphate, ethyl-2-acryloyloxyethyl phosphate, ethyl-2-methacryloyloxyethyl phosphate, ethyl-2-acryloyloxypropyl phosphate, ethyl-2-methacryloyloxypropyl phosphate, propyl-2-acryloyloxyethyl phosphate, propyl-2-methacryloyloxyethyl phosphate, propyl-2-acryloyloxypropyl phosphate, propyl-2 -methacryloyloxypropyl phosphate, butyl-2-acryloyloxyethyl phosphate, butyl-2-methacryloyloxyethyl phosphate, butyl-2-acryloyloxypropyl phosphate, butyl-2-methacryloyloxypropyl phosphate, phenyl-2-acryloyloxyethyl phosphate, phenyl-2-methacryloyloxyethyl phosphate, phenyl-2-acryloyloxypropyl phosphate, phenyl-2-methacryloyloxypropyl phosphate, tri(2-acryloyloxyethyl tri(2-methacryloyloxyethyl)phosphate, tri(2-acryloyloxypropyl)phosphate, tri(2-methacryloyloxypropyl)phosphate, dimethyl-2-acryloyloxyethyl phosphate, dimethyl-2-methacryloyloxypropyl phosphate, dimethyl-2-methacryloyloxypropyl phosphate, diethyl-2-acryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate,Examples of the acryloyloxypropyl phosphate include diethyl-2-acryloyloxypropyl phosphate, diethyl-2-methacryloyloxypropyl phosphate, dipropyl-2-acryloyloxyethyl phosphate, dipropyl-2-methacryloyloxyethyl phosphate, dipropyl-2-acryloyloxypropyl phosphate, dipropyl-2-methacryloyloxypropyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxypropyl phosphate, dibutyl-2-methacryloyloxypropyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, diphenyl-2-acryloyloxypropyl phosphate, and diphenyl-2-methacryloyloxypropyl phosphate.

[0046] Examples of the halogen-containing monomer include 2,4,6-tribromophenyl methacrylate, 2,4,6-tribromophenyl acrylate, 2,4-dichlorostyrene, 2,4-dibromostyrene, 2,4,6-trichlorostyrene, 2,4,6-tribromostyrene, pentachlorostyrene, pentabromostyrene, pentabromobenzyl acrylate, and pentabromobenzyl methacrylate.

[0047] The preferred lower limit of the content of the flame-retardant monomer in the monomer composition is 0.1 wt %, and the preferred upper limit is 25 wt %. By setting the content of the flame-retardant monomer to 0.1 wt % or more, it is possible to improve the flame retardancy when using thermally expandable microcapsules, and by setting the content to 25 wt % or less, it is possible to improve the gas barrier properties of the cell walls and improve thermal expandability. A more preferred lower limit of the content of the flame-retardant monomer is 0.3 wt %, and a more preferred upper limit is 22 wt %. That is, the content of the flame-retardant monomer is preferably 0.1 to 25 wt %, and more preferably 0.3 to 22 wt %.

[0048] 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).

[0049] The weight-average molecular weight of the polymer compound constituting the shell preferably has a lower limit of 50,000 and an upper limit of 2,000,000. That is, the weight-average molecular weight of the resin constituting the shell is preferably 50,000 to 2,000,000. When the weight-average molecular weight is 50,000 or more, the strength of the shell can be improved, and when the weight-average molecular weight is 2,000,000 or less, the shell strength does not become too high and the expansion ratio can be maintained. The weight-average molecular weight is a value determined by measuring by gel permeation chromatography (GPC) using DMF as a solvent and calculated in terms of polymethyl methacrylate. Examples of columns used when measuring the weight-average molecular weight in terms of polymethyl methacrylate by GPC include HSPgel RT MB-H (manufactured by Waters), and examples of molecular weight standards include M-75 (manufactured by Shodex).

[0050] 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 including the inorganic compound, it is possible to suppress fusion of the thermally expandable microcapsules in the resin during molding. Furthermore, by including the inorganic compound, it is possible to improve flame retardancy. Note that the inorganic compound is different from the flame retardant.

[0051] 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.

[0052] 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.

[0053] Other examples of the inorganic compound that may be added include 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.

[0054] 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).

[0055] The content of the inorganic compound is 0.01 wt % relative to the total weight of the thermally expandable microcapsules, with a preferred upper limit of 10 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 10 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 is preferably 0.01 to 10 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, and flame retardant that form the thermally expandable microcapsules.

[0056] The weight ratio of the inorganic compound to the flame retardant (inorganic compound / flame retardant) is preferably 0.01 to 10,000. By setting the ratio to 0.01 or more, fusion between thermally expandable microcapsules in the resin during molding can be suppressed. By setting the ratio to 10,000 or less, resin dispersibility during molding can be further improved, and flame retardancy can be further improved. A more preferred lower limit is 0.3, an even more preferred lower limit is 0.5, a more preferred upper limit is 3,000, an even more preferred upper limit is 2,000, an even more preferred upper limit is 1,000, a particularly preferred upper limit is 900, and an especially preferred upper limit is 800. That is, the inorganic compound / flame retardant ratio is preferably 0.01 to 10,000, more preferably 0.3 to 3,000, even more preferably 0.5 to 2,000, even more preferably 0.5 to 1,000, particularly preferably 0.5 to 900, and especially preferably 0.5 to 800.

[0057] In the present invention, the flame retardant and inorganic compound may be present on the shell surface of the thermally expandable microcapsule, inside the shell, or at the interface between the shell and the core material. However, it is preferable that the flame retardant and inorganic compound are contained inside the shell of the thermally expandable microcapsule. In a preferred embodiment of the present invention, the flame retardant is preferably contained inside the shell. When the flame retardant is contained inside the shell, it is 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 flame retardant and inorganic compound. This configuration further enhances the flame retardancy of the resulting foamed molded product. The location of the flame retardant and inorganic compound can be confirmed using a transmission electron microscope or the like after preparing a thin film passing through the center of the thermally expandable microcapsules dispersed in the embedding resin.

[0058] In the present invention, the content of the flame-retardant element is preferably 0.001 wt% or more and 10 wt% or less based on the total weight of the thermally expandable microcapsules. By setting the content of the flame-retardant element to 0.001 wt% or more, the flame retardancy of the foamed molded article obtained using the thermally expandable microcapsules can be improved, while setting the content to 10 wt% or less can improve the gas barrier properties of the shell and improve thermal expandability. The lower limit of the content of the flame-retardant element is more preferably 0.01 wt%, even more preferably 0.1 wt%, and particularly preferably 0.3 wt%, and the upper limit is more preferably 7 wt%, even more preferably 5 wt%, and particularly preferably 4 wt%. That is, the content of the flame-retardant element is preferably 0.001 to 10 wt%, more preferably 0.01 to 7 wt%, even more preferably 0.1 to 5 wt%, and particularly preferably 0.3 to 4 wt%. The content of the flame-retardant element can be measured by solid-state NMR measurement. The flame-retardant element refers to elements such as phosphorus, halogen elements, antimony, aluminum, tin, etc. Among these, phosphorus and halogen elements are preferred, with phosphorus being particularly preferred.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] In one embodiment of the thermally expandable microcapsules of the present invention, the ratio (A / B) of the average particle size (A) of the flame retardant to the shell thickness (B) is preferably 0.002 to 0.8. By achieving this ratio within the above range, both high foaming properties and excellent flame retardancy can be achieved. A more preferred lower limit is 0.01, and a more preferred upper limit is 0.5. That is, the A / B ratio is more preferably 0.01 to 0.5. Furthermore, the shell thickness is preferably 0.5 μm or more and 8 μm or less. The shell thickness can be measured by measuring the thickness at any five points on the cross section of 10 thermally expandable microcapsules fixed on a silicon wafer using a FIB-SEM (Helios 650, FEI) so that the cross section passes through the center of the thermally expandable microcapsules, and then calculating the average value.

[0063] 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.

[0064] 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.

[0065] The thermally expandable microcapsules according to one embodiment of the present invention preferably have a maximum expansion temperature (Tmax) of 150°C or higher. By setting the Tmax at 150°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 molded at high temperatures. Furthermore, aggregation of the thermally expandable microcapsules during molding can be suppressed, resulting in a good appearance. A more preferred lower limit is 160°C, and a more preferred upper limit is 240°C. That is, the Tmax is preferably 150 to 240°C, and more preferably 160 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 is measured while the thermally expandable microcapsules are heated from room temperature.

[0066] 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.

[0067] The upper limit of the foaming initiation temperature (Ts) is preferably 180°C. By setting the temperature to 180°C or less, foaming becomes easy and a desired foaming ratio can be achieved. The lower limit is preferably 125°C, and the upper limit is more preferably 175°C. That is, the Ts is preferably 125 to 180°C, and more preferably 125 to 175°C.

[0068] The preferred lower limit of the volume-average particle diameter of the thermally expandable microcapsules according to one embodiment of the present invention is 3 μm, and the preferred upper limit is 45 μm. A volume-average particle diameter of 3 μm or more ensures that the resulting molded article has an appropriate amount of bubbles, resulting in a sufficient expansion ratio. A volume-average particle diameter of 45 μm or less prevents the bubbles from becoming too large, resulting in an excellent appearance. A more preferred lower limit is 5 μm, and a more preferred upper limit is 35 μm. That is, the volume-average particle diameter of the thermally expandable microcapsules is preferably 3 to 45 μm, and more preferably 5 to 35 μm. The CV value (coefficient of variation) of the volume-average particle diameter of the thermally expandable microcapsules is preferably 40% or less, more preferably 30% or less, and even more preferably 20% or less. A volume-average particle diameter of 40% or less ensures that the resulting molded article has uniform bubbles and a uniform thickness. Furthermore, the bubbles present on the surface of the molded article are also uniform, resulting in an excellent appearance. While the preferred lower limit is not particularly limited, 0% is preferred. The volume average particle size of the thermally expandable microcapsules can be measured using a laser diffraction / scattering particle size distribution analyzer, etc. The CV value can also be calculated during the measurement.

[0069] The method for producing the thermally expandable microcapsules is not particularly limited, but for example, they can be produced by carrying out the steps of preparing an aqueous dispersion medium containing a flame retardant (and a flame retardant auxiliary) and an inorganic compound, dispersing an oily mixture containing a monomer composition and a volatile expanding agent in the aqueous dispersion medium, and polymerizing the monomer. The monomer composition can contain the nitrile monomer, a monomer having a carboxyl group, a crosslinkable monomer, or other monomers.

[0070] In the production of thermally expandable microcapsules according to one embodiment of the present invention, an aqueous dispersion medium is first prepared by adding water, a flame retardant, an inorganic compound, and, if necessary, a co-stabilizer to a polymerization reaction vessel to prepare an aqueous dispersion medium containing the flame retardant and the inorganic compound.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] An aqueous dispersion medium containing the flame retardant, inorganic compound, co-stabilizer, and optionally a dispersant is prepared by blending the flame retardant, inorganic compound, co-stabilizer, and optionally a dispersant with deionized water. The pH of the aqueous phase is determined appropriately depending on the types of flame retardant, 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. To acidify the aqueous dispersion medium, 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.

[0075] Next, in the method for producing thermally expandable microcapsules, a step of dispersing an oily mixture containing a monomer composition and a volatile expanding agent in an aqueous dispersion medium is carried out. Specifically, a step of dispersing an oily mixture containing a monomer composition and a volatile expanding agent in an aqueous dispersion medium is carried out. In this step, the monomer composition and the volatile expanding agent may be added separately to the aqueous dispersion medium to prepare the oily mixture in the aqueous dispersion medium, but 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 while stirring in the separate containers, and then added to the polymerization reaction vessel. In this step, 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 surface of the resulting thermally expandable microcapsules. 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 stirred and mixed in a polymerization reaction vessel. The flame retardant and, if necessary, a dispersant may be added to the monomer composition rather than the aqueous dispersion medium, and the process may be carried out. In this case, the flame retardant used can be present inside the thermally expandable microcapsules. Furthermore, when the flame retardant and the polymer compound are integrated, a monomer composition containing a flame-retardant monomer may be used without adding a flame retardant.

[0076] Examples of methods for emulsifying and dispersing the oily mixture in an aqueous dispersion medium to a predetermined particle size include stirring with a homomixer (e.g., manufactured by Tokushu Kika Kogyo Co., Ltd.) or a homogenizer, or 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. Furthermore, the flame retardant may be added after adjusting the average particle size by a pulverization / dispersion treatment or the like. Examples of methods for the pulverization / dispersion treatment include a crusher, a mill (e.g., a wet or dry bead mill, a ball mill, a jet mill, a planetary mill), a blender, and the like.

[0077] 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 molded at high temperatures.

[0078] The present invention also includes a foamable masterbatch containing the thermally expandable microcapsules and a thermoplastic resin (base resin).The present invention also includes a foamable resin composition containing the thermally expandable microcapsules, a flame-retardant compound, and a thermoplastic resin (base resin).

[0079] The flame-retardant compound refers to a flame-retardant component contained separately from the thermally expandable microcapsules. The same flame-retardant compounds as those described above can be used as the flame-retardant compounds. The content of the flame-retardant compound in the foamable resin composition 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.

[0080] In the foamable resin composition, the ratio (A / C) of the average particle size (A) of the flame retardant contained in the thermally expandable microcapsules to the average particle size (C) of the flame-retardant compound is preferably 0.0003 to 1.0. By being within this range, both high foamability and excellent flame retardancy can be achieved. The average particle size of the flame-retardant compound is preferably 1 μm or more and 50 μm or less, more preferably 5 μm or more and 30 μm or less. That is, the average particle size of the flame-retardant compound is preferably 1 to 50 μm, more preferably 5 to 30 μm. The average particle size can be measured by observation using a scanning electron microscope (Regulus 8220, manufactured by Hitachi High-Technologies Corporation).

[0081] 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, PP, 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.

[0082] The content of the thermally expandable microcapsules in the foamable masterbatch and foamable resin composition is not particularly limited, but a preferred lower limit is 10 parts by weight and a preferred upper limit is 90 parts by weight per 100 parts by weight of the thermoplastic resin.

[0083] The method for producing the expandable masterbatch is not particularly limited, but may include pre-kneading raw materials such as a base resin (e.g., 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 (e.g., 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 produce a masterbatch. Alternatively, a pellet-shaped masterbatch may be produced by kneading raw materials such as a base resin (e.g., a thermoplastic resin) and thermally expandable microcapsules using a batch kneader and then granulating them using a granulator. Another method for producing the expandable masterbatch includes adding the flame-retardant compound to the thermally expandable microcapsules. The kneader is not particularly limited as long as it can knead the materials without destroying the thermally expandable microcapsules. Examples of the kneader include a pressure kneader and a Banbury mixer.

[0084] The present invention also provides a foam molded article obtained using the thermally expandable microcapsules, expandable masterbatch, or expandable resin composition. In particular, the thermally expandable microcapsules can be suitably used in applications requiring flame retardancy, and are therefore suitable for applications such as foam sheets with high appearance quality, such as uneven surfaces, and residential wallpaper. Specifically, a foam molded article can be obtained by kneading and molding the thermally expandable microcapsules, expandable masterbatch, or expandable resin composition with a matrix resin. Alternatively, a foam molded article can be obtained by molding the expandable resin composition alone. According to the present invention, gas barrier properties can be improved during thermal expansion, improving durability, and the expansion ratio and flame retardancy can be improved.

[0085] 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-short 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.

[0086] According to the present invention, it is possible to provide a thermally expandable microcapsule that has high expandability and is capable of producing a foamed molded article having excellent flame retardancy, and a foamable masterbatch, a foamable resin composition, and a foamed molded article that use the thermally expandable microcapsule.

[0087] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0088] Example 1 Preparation of Thermally Expandable Microcapsules 19 parts by weight of colloidal silica (manufactured by Asahi Denka, primary average particle size: 20 nm) as an inorganic compound (dispersant) and 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF) were added to 250 parts by weight of ion-exchanged water and mixed to prepare an aqueous dispersion medium. 20% by weight of acrylonitrile, 30% by weight of methacrylonitrile, 40% by weight of methacrylic acid, and 10% by weight of methyl methacrylate were mixed to prepare a homogeneous monomer composition. 0.2 parts by weight of an amine salt of polyether ester acid (Disparlon-234, manufactured by Kusumoto Chemicals) as an additive, and 2.7 parts by weight of ammonium polyphosphate (AP423, manufactured by Clariant Chemicals, pulverized) as a phosphorus-based flame retardant 1 were added to 97 parts by weight of this monomer composition, and the mixture was pulverized and dispersed using a bead mill (Easy Nano RMB, manufactured by AIMEX), followed by charging into an autoclave. Furthermore, 0.8 parts by weight of a polymerization initiator (2,2'-azobisisobutyronitrile), 0.6 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile), 5 parts by weight of isopentane, and 20 parts by weight of isooctane were added and mixed in an autoclave (oil-based mixture). The ammonium polyphosphate in the oil-based mixture had an average particle size of 150 nm. This was then added to an aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was stirred and mixed using a homogenizer, placed in a nitrogen-substituted pressure polymerization vessel, and reacted at 60°C for 20 hours under pressure (0.5 MPa) to obtain a reaction product. The resulting reaction product was repeatedly filtered and washed with water, then dried to obtain thermally expandable microcapsules. The resulting 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 thermally expandable microcapsule-embedded resin. A thin film was prepared using a microtome (EM UC7, manufactured by LEICA) so as to pass through the vicinity of the center of the thermally expandable microcapsules dispersed in the embedding resin, and the location of the flame retardant was confirmed using a transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.). It was confirmed that the flame retardant was present inside the shell.

[0089] [Preparation of Foamable Resin Composition and Foam Molded Article] 80 parts by weight of polypropylene resin and 20 parts by weight of polyethylene resin were mixed with 40 parts by weight of the obtained thermally expandable microcapsules, 0.5 parts by weight of 2,6-di-t-butyl-p-cresol as an antioxidant, 0.3 parts by weight of dilauryl thiodipropionate, 3.2 parts by weight of trimethylolpropane trimethacrylate as a crosslinking aid, and 15 parts by weight of ammonium polyphosphate (Exolit AP462, Clariant, average particle size: 20 μm) as a flame retardant compound to obtain a foamable resin composition. The obtained foamable resin composition was used to prepare a roll sheet at 130 ° C. using an 8-inch roll (191-TM, Yasuda Seiki Seisakusho Co., Ltd.). This roll sheet was cut and heated at 170 ° C. in a press (PA-40E / 40C, Kodaira Seisakusho Co., Ltd.) to obtain a foam molded article with a sheet thickness of 7 mm.

[0090] (Examples 2 to 9) [Preparation of Thermally Expandable Microcapsules] Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that the monomer composition, flame retardant, flame retardant aid, and inorganic compound were mixed in the compositions shown in Table 1. In Example 2, the flame retardant was a phosphorus-based flame retardant 2 (Fireguard FCX-210, a spirocyclic diphosphonate compound manufactured by Teijin Limited, pulverized, melting point: 250°C, specific surface area: 1.0 m). ２ In Example 3, a phosphorus-based flame retardant 3 (ADEKA STAB FP-2500S, halogen-free phosphate ester, manufactured by ADEKA Corporation, crushed, melting point: 270°C, specific surface area: 1.4 m) was used as the flame retardant. ２ In Example 4, decabromodiphenylethane (SAYTEX 8010, manufactured by Albemarle Japan, crushed, melting point: 350°C) was used as the flame retardant, and antimony trioxide (PATOX-M, manufactured by Nippon Seiko Co., Ltd., crushed, melting point: 656°C, specific surface area: 3.0 m) was used as the flame retardant aid. ２ The average particle size of the phosphorus-based flame retardants 2 and 3 and decabromodiphenylethane in the oil mixture was 150 nm.

[0091] [Preparation of Foamable Resin Composition and Foam Molded Article] Foamable resin compositions and foam molded articles were obtained in the same manner as in Example 1, except that the thermoplastic resin, thermally expandable microcapsules, antioxidant, crosslinking aid, and flame-retardant compound were mixed in the compositions shown in Table 2. In Example 2, a phosphorus-based flame retardant (Fireguard FCX-210, manufactured by Teijin Limited) was used as the flame-retardant compound. In Example 3, an intumescent flame retardant (ADK STAB FP-2500S, manufactured by ADEKA Corporation) was used as the flame-retardant compound. In Example 4, decabromodiphenylethane (SAYTEX 8010, manufactured by Albemarle Japan) was used as the flame-retardant compound, and antimony trioxide (PATOX-M, manufactured by Nippon Seiko Co., Ltd.) was used as the flame-retardant aid.

[0092] Examples 10 to 14 Preparation of Thermally Expandable Microcapsules Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that the monomer composition, flame retardant, and inorganic compound were mixed in the composition shown in Table 1. In Example 10, ammonium polyphosphate (AP423, pulverized) was used as the flame retardant, and the average particle size after pulverization and dispersion using a bead mill was 10 nm. In Example 11, ammonium polyphosphate (AP423, pulverized) was used as the flame retardant, and the average particle size after pulverization and dispersion using a bead mill was 100 nm. In Example 12, ammonium polyphosphate (AP423, pulverized) was used as the flame retardant, and the average particle size after pulverization and dispersion using a bead mill was 250 nm. In Example 13, ammonium polyphosphate (AP423, pulverized) was used as the flame retardant, and the average particle size after pulverization and dispersion using a bead mill was 500 nm. In Example 14, ammonium polyphosphate (AP423, pulverized) was used as the flame retardant, and the average particle size after pulverization and dispersion treatment using a bead mill was 1000 nm.

[0093] [Preparation of Foamable Resin Composition and Foam Molded Article] A foamable resin composition and a foam molded article were obtained in the same manner as in Example 1, except that the thermoplastic resin, the thermally expandable microcapsules, the antioxidant, the crosslinking aid, and the flame retardant compound were mixed in the compositions shown in Table 2.

[0094] Example 15 Preparation of Thermally Expandable Microcapsules 2.7 parts by weight of ammonium polyphosphate (pulverized) as a flame retardant and 0.2 parts by weight of a copolymer (DISPERBYK-102, manufactured by BYK) having an acidic group as an additive were added to 100 parts by weight of ion-exchanged water, mixed, and then pulverized and dispersed using a bead mill to obtain a flame retardant dispersion. 19 parts by weight of colloidal silica (manufactured by Asahi Denka Co., Ltd., primary average particle size: 20 nm) as inorganic compounds, 0.8 parts by weight of polyvinylpyrrolidone (manufactured by BASF), and 1.8 parts by weight of 1N hydrochloric acid were added to 150 parts by weight of ion-exchanged water, mixed, and the pH was adjusted to 3.5 to prepare an aqueous dispersion medium. The ammonium polyphosphate in the flame retardant dispersion was in the form of particles with an average particle size of 150 nm. A homogeneous monomer composition was prepared by mixing 20% ​​by weight of acrylonitrile, 30% by weight of methacrylonitrile, 40% by weight of methacrylic acid, and 10% by weight of methyl methacrylate. 97 parts by weight of this monomer composition was mixed with 0.8 parts by weight of a polymerization initiator (2,2'-azobisisobutyronitrile), 0.6 parts by weight of 2,2'-azobis(2,4-dimethylvaleronitrile), and 30 parts by weight of isopentane, and the mixture was then charged into an autoclave and mixed. The mixture was then added to an aqueous dispersion medium and suspended to prepare a dispersion. The resulting dispersion was stirred and mixed using a homogenizer, charged into a nitrogen-substituted pressure polymerization vessel, and reacted at 60°C for 20 hours under pressure (0.5 MPa), yielding a reaction product. The resulting reaction product was repeatedly filtered and washed with water, and then dried to yield thermally expandable microcapsules. The resulting thermally expandable microcapsules were added to an embedding resin (Technovit 4000, manufactured by Kulzer) so that the particle content was 3 wt %, and dispersed to produce a resin embedding thermally expandable microcapsules. A thin film was prepared using a microtome (EM UC7, manufactured by LEICA) so that it passed through the center of the thermally expandable microcapsules dispersed in the embedding resin, and the location of the flame retardant was confirmed using a transmission electron microscope (JEM-2100, manufactured by JEOL Ltd.), confirming that the flame retardant was present on the surface of the particles.

[0095] [Preparation of Foamable Resin Composition and Foam Molded Article] Foamable resin compositions and foam molded articles were obtained in the same manner as in Example 1, except that the obtained thermally expandable microcapsules were mixed in the compositions shown in Table 2.

[0096] Example 16: Thermally expandable microcapsules were obtained in the same manner as in Example 1, except that 0.4 parts by weight of FLOWLEN DOPA-15BHFS (Kyoeisha Chemical Co., Ltd.) was added as an additive to the oily mixture in the [Preparation of Thermally Expandable Microcapsules]. The resulting thermally expandable microcapsules were added to an embedding resin (Technovit 4000, Kulzer) so that the particle content was 3% by weight, and dispersed to produce a resin embedding thermally expandable microcapsules. A thin film was prepared using a microtome (EM UC7, LEICA) so as to pass through the center of the thermally expandable microcapsules dispersed in the embedding resin. The location of the flame retardant was confirmed using a transmission electron microscope (JEM-2100, JEOL Ltd.). The presence of the flame retardant at the interface between the shell and core material was confirmed. Furthermore, a foamable resin composition and a foam molded article were obtained in the same manner as in Example 1, except that the resulting thermally expandable microcapsules were mixed in the composition shown in Table 3.

[0097] (Example 17) A thermally expandable microcapsule, a foamable resin composition, and a foamed molded article were obtained in the same manner as in Example 1, except that a monomer composition was used that was a homogeneous solution obtained by mixing 20% ​​by weight of acrylonitrile, 30% by weight of methacrylonitrile, 35% by weight of methacrylic acid, 5% by weight of 2-(methacryloyloxy)ethyl phosphate, and 10% by weight of methyl methacrylate.

[0098] Examples 18 and 19 Thermally expandable microcapsules, expandable resin compositions and foam molded articles were obtained in the same manner as in Example 1, except that the sheet thickness of the foam molded article was changed as shown in Table 3.

[0099] Comparative Example 1 Thermally expandable microcapsules, a foamable resin composition, and a foamed molded article were obtained in the same manner as in Example 1, except that no flame retardant was added in [Preparation of thermally expandable microcapsules].

[0100] (Comparative Examples 2 to 9) The thermally expandable microcapsules of Comparative Example 1 were used. Further, foamable resin compositions and foamed molded articles were obtained in the same manner as in Example 1, except that the thermoplastic resin, thermally expandable microcapsules, antioxidant, crosslinking aid, and flame-retardant compound were mixed in the compositions shown in Table 3.

[0101] (Evaluation Method) The performance of the obtained thermally expandable microcapsules and foamed molded articles was evaluated by the following methods. The results are shown in Tables 1 to 3.

[0102] (1) Evaluation of Thermally Expandable Microcapsules (1-1) Measurement of Volume Average Particle Diameter 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, Inc.) Specifically, 100 mg of the thermally expandable microcapsules were dispersed in 3 ml of water, and then the dispersion was placed in the laser diffraction / scattering particle size distribution analyzer to measure the volume average particle diameter.

[0103] (1-2) Shell Thickness The shell thickness was measured by measuring the thickness at any five points on the cross section of 10 thermally expandable microcapsules fixed on a silicon wafer using a FIB-SEM (Helios 650, FEI) passing near the center of the thermally expandable microcapsules, and calculating the average value.

[0104] (1-3) Measurement of Flame-Retardant Element (P Element and Br Element) Content Using an NMR (ECZ-400R, manufactured by JEOL), a solid sample containing polyphosphoric acid was measured. 31 The content of the flame-retardant element (P element) was calculated by P-NMR measurement. In addition, the content of the flame-retardant element (Br element) was calculated by X-ray fluorescence measurement using decabromodiphenylethane as a standard sample with an X-ray fluorescence analyzer (EDX-800HS, manufactured by Shimadzu Corporation).

[0105] (1-4) 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 began 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.

[0106] (2) Evaluation of Foam Molded Articles (2-1) Density (Apparent Density) The apparent density of the foam molded articles was measured in accordance with JIS K 7222:2005.

[0107] (2-2) 25% Compression Strength The 25% compression strength of the foamed molded article was measured at 23°C in accordance with JIS K 6767.

[0108] (2-3) Gel fraction (degree of cross-linking) A test piece of about 100 mg was taken from the foamed molded article, and the weight A (mg) of the test piece was precisely weighed. Next, this test piece was immersed in 30 cm of xylene at 120°C. ３ After immersion for 24 hours, the insoluble matter on the wire mesh was filtered through a 200-mesh mesh and collected. The insoluble matter was dried in a vacuum, and the weight B (mg) of the insoluble matter was precisely weighed. The degree of crosslinking (mass%) was calculated from the obtained value using the following formula: Degree of crosslinking (mass%) = (B / A) × 100

[0109] (2-4) Evaluation of foamability The surface, cross-sectional appearance, and cell structure of the obtained foamed molded article were observed visually or with an electron microscope and evaluated according to the following criteria: A: The surface is smooth and the cells are uniform. B1: The cells are uniform, but the surface is rough. B2: The surface is smooth, but coarse cells are visible. C: The surface is rough and coarse cells are visible.

[0110] (2-5) Flame Retardancy Evaluation The total burning time was measured and evaluated according to official standards (ISO 3582, JIS K6400-6, ASTM D4986). Specifically, a test piece (150±1×50±1×t [mm]) was held horizontally and exposed to a 38 mm flame for 60 seconds, and the total burning time was measured based on the burning rate and burning behavior at a 100 mm interval.

[0111]

[0112]

[0113]

[0114] According to the present invention, it is possible to provide a thermally expandable microcapsule that has high expandability and can produce a foamed molded article having excellent flame retardancy, a foamable masterbatch that uses the thermally expandable microcapsule, a foamable resin composition, and a foamed molded article.

Claims

1. A thermally expandable microcapsule comprising a shell containing a volatile expanding agent as a core, wherein the shell contains a flame retardant and the average particle size of the flame retardant is 10 nm or more and 5000 nm or less.

2. The thermally expandable microcapsule according to claim 1, wherein the flame retardant comprises at least one selected from the group consisting of phosphorus-based flame retardants and halogen-based flame retardants.

3. The thermally expandable microcapsule according to claim 1 or 2, wherein the average particle size of the flame retardant is 50 nm or more and 1000 nm or less.

4. The thermally expandable microcapsule according to claim 1 or 2, wherein the ratio (A / B) of the average particle size of the flame retardant (A) to the thickness of the shell (B) is 0.002 to 0.

8.

5. The thermally expandable microcapsule according to claim 1 or 2, wherein the flame retardant content is 0.01% by weight or more and 10% by weight or less of the total thermally expandable microcapsule.

6. A thermally expandable microcapsule according to claim 1 or 2, wherein the flame retardant is contained inside the shell.

7. The thermally expandable microcapsule according to claim 1 or 2, wherein the content of flame-retardant elements is 0.001% by weight or more and 10% by weight or less of the total thermally expandable microcapsule.

8. Furthermore, the thermally expandable microcapsule according to claim 1 or 2 contains at least one inorganic compound selected from the group consisting of Si-based compounds and Mg-based compounds.

9. The thermally expandable microcapsule according to claim 8, wherein the content of the inorganic compound is 0.01 to 10% by weight relative to the entire thermally expandable microcapsule.

10. The thermally expandable microcapsule according to claim 8, wherein the weight ratio of the inorganic compound to the flame retardant (inorganic compound / flame retardant) is 0.01 to 10000.

11. A foaming masterbatch containing the thermally expandable microcapsules and thermoplastic resin described in claim 1 or 2.

12. A foamed resin composition comprising a heat-expandable microcapsule according to claim 1 or 2, a flame-retardant compound, and a thermoplastic resin.

13. The foamed resin composition according to claim 12, wherein the ratio (A / C) of the average particle size (A) of the flame retardant contained in the thermally expandable microcapsules to the average particle size (C) of the flame retardant compound is 0.0003 to 1.

0.

14. A foamed molded article comprising the thermally expandable microcapsules described in claim 1 or 2.