Heat-expandable microcapsules, masterbatch, and molded object

Abstract

The present invention provides heat-expandable microcapsules which do not require any special molding machine even when an engineering plastic, etc. is used, and which have excellent heat resistance and gas-barrier properties in a high-temperature range and hence have high expandability even in the high-temperature range. Also provided are a masterbatch including the heat-expandable microcapsules and a molded object obtained using the heat-expandable microcapsules.

Description

Thermally expandable microcapsules, masterbatches and molded products

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

[0002] In recent years, in the automotive field, there has been a trend toward replacing metal parts of automobiles with lightweight foam molded articles in line with the trend toward weight reduction and electrification. For this reason, the practical application of foam molded articles has been actively investigated.

[0003] For example, a method for producing a foamed molded article involves foaming a resin material using a foaming agent, and the foaming agent is generally a thermally expandable microcapsule or a chemical foaming agent. A widely known example of such a thermally expandable microcapsule is one in which a volatile expanding agent that becomes gaseous at a temperature below the softening point of the thermoplastic polymer is encapsulated in a shell containing a thermoplastic polymer.

[0004] Patent Document 1 discloses heat-expandable microspheres comprising a thermoplastic resin shell and a blowing agent encapsulated therein that vaporizes upon heating, the thermoplastic resin containing a nitrile monomer (A) essentially containing methacrylonitrile, a carboxyl group-containing monomer (B), and a monomer (C) having a group reactive with a carboxyl group. Patent Document 2 discloses heat-expandable microspheres comprising a thermoplastic resin shell and a blowing agent encapsulated therein that vaporizes upon heating, the thermoplastic resin containing a nitrile monomer (A) essentially containing acrylonitrile and methacrylonitrile, a carboxyl group-containing monomer (B), and a monomer (C) having one polymerizable double bond.

[0005] Furthermore, as a method for foaming highly heat-resistant engineering plastics and super engineering plastics (hereinafter referred to as engineering plastics, etc.), a method is adopted in which a molten resin such as an engineering plastic is melted by shear mixing with a high-pressure supercritical fluid, and then foam injection molding is performed.

[0006] International Publication No. WO 2016 / 190178 International Publication No. WO 2016 / 084612

[0007] However, foam injection molding using a supercritical fluid requires a special molding machine, and it is difficult to introduce the manufacturing equipment. On the other hand, when the thermally expandable microcapsules of Patent Documents 1 and 2 are used for foam molding of engineering plastics, etc., there is a problem in maintaining the encapsulated volatile expansion agent (gas barrier property) due to thermal expansion in a high temperature range.

[0008] The present invention aims to provide thermally expandable microcapsules that have excellent heat resistance and gas barrier properties at high temperatures and therefore have high foaming performance even at high temperatures, without requiring a special molding machine even when using engineering plastics, etc. Also, the present invention aims to provide a masterbatch containing the thermally expandable microcapsules and a molded article made using the thermally expandable microcapsules.

[0009] The present disclosure (1) provides a thermally expandable microcapsule in which a volatile expanding agent is encapsulated as a core agent in a shell containing a polymer, the polymer containing a constituent unit derived from a nitrile-based monomer (I) and a constituent unit derived from a carboxyl group-containing monomer (II), the content of the constituent unit derived from the carboxyl group-containing monomer (II) in the polymer is 35% by weight or more and 55% by weight or less, the nitrile-based monomer (I) contains methacrylonitrile and acrylonitrile, and the ratio of the constituent unit derived from the acrylonitrile to the constituent unit derived from the methacrylonitrile in the polymer is 100% by weight or more, and the content of the constituent unit derived from the acrylonitrile in the polymer is 100% by weight or more. The thermally expandable microcapsules are characterized in that the weight ratio (acrylonitrile / methacrylonitrile) of the structural units derived from the methacrylonitrile to the structural units derived from the carboxyl group-containing monomer (II) in the polymer (methacrylonitrile / carboxyl group-containing monomer (II)) is 1.05 or more, the weight ratio of the structural units derived from the methacrylonitrile to the structural units derived from the carboxyl group-containing monomer (II) in the polymer (methacrylonitrile / carboxyl group-containing monomer (II)) is 0.8 or less, the polymer does not contain structural units derived from a monomer (III) that does not have a functional group reactive with a carboxyl group, or the content of structural units derived from the monomer (III) is 1.5 wt% or less, and the core agent does not contain a fluorine atom-containing compound. Disclosure (2) is the thermally expandable microcapsules of Disclosure (1) having a maximum foaming temperature Tmax of 240°C or higher. Disclosure (3) is the thermally expandable microcapsules of Disclosure (1) or (2) having a degree of gelation of 30 wt% or less as measured in N,N-dimethylformamide (DMF) solvent. The present disclosure (4) is a thermally expandable microcapsule according to the present disclosure (1), (2), or (3), wherein the polymer does not contain a structural unit derived from a polymerizable monomer having two or more double bonds in the molecule. The present disclosure (5) is a thermally expandable microcapsule according to the present disclosure (1), (2), (3), or (4), wherein the content of the metal cation salt in the shell is 0.5% by weight or more and 10% by weight or less. The present disclosure (6) is a masterbatch containing the thermally expandable microcapsule according to any one of the present disclosures (1) to (5). The present disclosure (7) is a molded article made using the thermally expandable microcapsule according to any one of the present disclosures (1) to (5). The present invention will be described in detail below.

[0010] The shell of the thermally expandable microcapsule according to one embodiment of the present invention contains a polymer. The polymer is obtained by polymerizing a monomer composition containing a nitrile monomer (I) and a carboxyl group-containing monomer (II). That is, the polymer contains a structural unit derived from the nitrile monomer (I) and a structural unit derived from the carboxyl group-containing monomer (II).

[0011] The nitrile monomer (I) includes methacrylonitrile and acrylonitrile. The weight ratio of the acrylonitrile-derived structural units to the methacrylonitrile-derived structural units in the polymer (acrylonitrile / methacrylonitrile) is 1.05 or more. By satisfying the above configuration, thermally expandable microcapsules with excellent heat resistance and gas barrier properties can be obtained. The weight ratio is preferably 1.10 or more, preferably 2.00 or less, and more preferably 1.50 or less.

[0012] The content of the acrylonitrile-derived structural units in the polymer is preferably 23% by weight or more, more preferably 26% by weight or more, and preferably 43% by weight or less, more preferably 37% by weight or less. The content of the methacrylonitrile-derived structural units in the polymer is preferably 15% by weight or more, more preferably 20% by weight or more, and preferably 31% by weight or less, more preferably 28% by weight or less.

[0013] The nitrile monomer (I) may contain other nitrile monomers in addition to acrylonitrile and methacrylonitrile. The other nitrile monomers are not particularly limited, and examples thereof include α-chloroacrylonitrile, α-ethoxyacrylonitrile, fumaronitrile, and mixtures thereof.

[0014] The content of the structural unit derived from the nitrile monomer (I) in the polymer is preferably 45% by weight or more and 65% by weight or less. By making it 45% by weight or more, the gas barrier property of the shell can be improved and the expansion ratio can be increased. By making it 65% by weight or less, the heat resistance can be improved. The content is more preferably 48% by weight or more and more preferably 60% by weight or less.

[0015] The carboxyl group-containing monomer (II) can be, for example, a radically polymerizable unsaturated carboxylic acid monomer having a carboxyl group and 3 to 8 carbon atoms. Specific examples include unsaturated carboxylic acids such as unsaturated monocarboxylic acids and unsaturated dicarboxylic acids, their anhydrides, and monoesters of unsaturated dicarboxylic acids. These can 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, and unsaturated dicarboxylic acids such 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 preferred, with methacrylic acid being more preferred.

[0016] The content of the structural unit derived from the carboxyl group-containing monomer (II) in the polymer is 35% by weight or more and 55% by weight or less. By making it 35% by weight or more, the heat resistance of the obtained thermally expandable microcapsules can be improved. Furthermore, by making it 55% by weight or less, the powder fluidity of the obtained thermally expandable microcapsules can be improved. The content is preferably 40% by weight or more and 53% by weight or less.

[0017] In the polymer, the weight ratio of the constituent units derived from methacrylonitrile to the constituent units derived from the carboxyl group-containing monomer (II) (methacrylonitrile / carboxyl group-containing monomer (II)) is 0.8 or less. By setting it to 0.8 or less, thermally expandable microcapsules with excellent heat resistance and gas barrier properties can be obtained. The weight ratio is preferably 0 or more, more preferably 0.35 or more, and preferably 0.75 or less.

[0018] The polymer may contain a structural unit derived from a polymerizable monomer having two or more double bonds in the molecule, but preferably does not contain such a structural unit. When the polymer does not contain such a structural unit, it can exhibit a high expansion ratio even when molded in a high temperature range.

[0019] Examples of the polymerizable 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.

[0020] The polymer does not contain a structural unit derived from the nitrile monomer (I) or a structural unit derived from the carboxyl group-containing monomer (II), or does not contain a structural unit derived from the monomer (III) that does not have a functional group reactive with a carboxyl group, or the content of the structural unit derived from the monomer (III) is 1.5 wt% or less. By having the above-mentioned structure, thermally expandable microcapsules with high gas barrier properties can be obtained. The monomer (III) is different from the nitrile monomer (I) and the carboxyl group-containing monomer (II).

[0021] Examples of the monomer (III) 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, and in particular, methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate, or alicyclic, aromatic, or heterocyclic ring-containing methacrylic acid esters such as cyclohexyl methacrylate, benzyl methacrylate, and isobornyl methacrylate are preferred.

[0022] The content of the structural unit derived from the monomer (III) in the polymer is 0% by weight or more and 1.5% by weight or less, preferably 0.1% by weight or more and 1.3% by weight or less, which makes it possible to improve the gas barrier properties of the cell walls and to improve the thermal expansion properties.

[0023] 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).

[0024] The shell may contain a metal cation salt. When the shell contains a metal cation salt, if the copolymer constituting the shell contains carboxyl groups, the metal cations derived from the metal cation salt react with the carboxyl groups 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.

[0025] 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.

[0026] The content of the metal cation salt in the shell is 0% by weight or more, preferably 0.5% by weight or more, and preferably 10% by weight or less. By setting the content within this range, heat resistance can be further improved. The content is more preferably 0.8% by weight or more, and more preferably 8% by weight or less.

[0027] 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 with each other in the resin during molding.

[0028] 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.

[0029] 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 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.

[0030] 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.

[0031] The content of the inorganic compound is 0.01% by weight, preferably 7% by weight, of the total thermally expandable microcapsules. By making it 0.01% by weight or more, it is possible to suppress fusion of the thermally expandable microcapsules in the resin during molding. By making it 7% by weight or less, it is possible to further improve the resin dispersibility during molding. A more preferred lower limit is 0.3% by weight, and a more preferred upper limit is 5% by weight. The content of the inorganic compound can be calculated from the weight of the monomer composition and volatile expanding agent that form the thermally expandable microcapsules.

[0032] 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.

[0033] 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 core agent does not contain a fluorine-containing compound. By not containing a fluorine-containing compound, excellent gas barrier properties can be achieved. The volatile expanding agent is a substance that becomes gaseous at a temperature below the softening point of the polymer constituting 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. Other examples include 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, a thermally decomposable compound that thermally decomposes into a gaseous form upon heating may also be used as the volatile expanding agent. In particular, the core agent preferably contains 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more of those having 8 or more carbon atoms.

[0034] 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.

[0035] The preferred lower limit of the true density of the thermally expandable microcapsules of the present invention is 1.08 g / cm ３ The preferred upper limit is 1.50 g / cm ３By setting the density within the above range, the uniformity of the thermally expandable microcapsules can be improved. A more preferable lower limit is 1.10 g / cm ３ , the preferred upper limit is 1.40 g / cm ３ The true density can be measured using a true density meter (Ultrapyc 5000, manufactured by Anton Parr, etc.) under conditions of a pressure of 12 psi, a temperature of 25° C., and a gas type of helium.

[0036] The thermally expandable microcapsules according to one embodiment of the present invention preferably have a maximum foaming temperature (Tmax) of 240°C or higher. A temperature of 240°C or higher increases heat resistance, 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. The Tmax is more preferably 245°C or higher, more preferably 290°C or lower, and even more preferably 270°C or lower. In this specification, the maximum foaming 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.

[0037] The foaming initiation temperature (Ts) is preferably 185° C. or higher. By setting the temperature at 185° C. or higher, it is possible to obtain thermally expandable microcapsules with excellent heat resistance. The Ts is more preferably 190° C. or higher, and is preferably 270° C. or lower, and more preferably 260° C. or lower.

[0038] The thermally expandable microcapsules according to one embodiment of the present invention preferably have a gelation degree of 30% by weight or less as measured in N,N-dimethylformamide (DMF) solvent. By achieving this range, a high expansion ratio can be achieved even at high temperatures. The gelation degree can be measured by a method conforming to ASTM D2765.

[0039] The preferred lower limit of the volume average particle diameter of the thermally expandable microcapsules according to one embodiment of the present invention is 1 μm, and the preferred upper limit is 100 μm. If the diameter is 1 μm or more, the cells in the resulting molded article can be made sufficiently large, thereby enabling a sufficiently high expansion ratio. If the diameter is 100 μm or less, the cells in the resulting molded article will not become too large, preventing poor appearance. A more preferred lower limit is 3 μm, and a more preferred upper limit is 50 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.

[0040] 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, dispersing an oily mixture containing a monomer composition, a volatile expanding agent, a metal cation salt, etc. in the aqueous dispersion medium, and polymerizing the monomer composition. The monomer composition may contain the nitrile monomer (I), the carboxyl group-containing monomer (II), and other monomers.

[0041] When producing thermally expandable microcapsules, which is one embodiment of the present invention, a step of preparing an aqueous dispersion medium is first carried out. Specifically, for example, an aqueous dispersion medium containing silicon dioxide is prepared by adding water and a dispersion stabilizer containing silicon dioxide, and optionally a co-stabilizer, to a polymerization reaction vessel. Furthermore, alkali metal nitrite, stannous chloride, stannic chloride, potassium dichromate, etc. may also be added as necessary.

[0042] Examples of the silicon dioxide-containing dispersion stabilizer include colloidal silica. As the colloidal silica, alkaline colloidal silica having a colloidal solution (aqueous dispersion) with a pH of more than 7 may be used, or acidic colloidal silica having a pH of less than 7 may be used. Of these, alkaline colloidal silica is more preferred. Furthermore, the colloidal silica preferably contains 10 to 50% by weight of silicon dioxide as a solid content and is monodispersed.

[0043] Examples of dispersion stabilizers other than silicon dioxide include calcium phosphate, magnesium hydroxide, aluminum hydroxide, ferric hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate.

[0044] The amount of the dispersion stabilizer containing silicon dioxide added is determined appropriately depending on the particle size of the thermally expandable microcapsules, but the preferred lower limit is 2.5 parts by weight and the preferred upper limit is 7 parts by weight relative to 100 parts by weight of the oily mixture (oil phase).The more preferred lower limit is 3 parts by weight and the more preferred upper limit is 5 parts by weight.The amount of the oil phase refers to the total amount of the monomer and the volatile expanding agent.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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 monomers. 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.

[0049] 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.

[0050] The thermally expandable microcapsules, which are one embodiment of the present invention, can be produced by subjecting the dispersion obtained through the above-mentioned steps to a process of polymerizing the monomer by heating, a process of washing, and a process of drying.

[0051] A masterbatch can be obtained by mixing the thermally expandable microcapsules of the present invention with a resin (base resin). A masterbatch containing the thermally expandable microcapsules of the present invention also constitutes one aspect of the present invention. Furthermore, a foamable resin composition can be obtained by adding a matrix resin, such as a thermoplastic resin, to the thermally expandable microcapsules of the present invention. An ink containing the thermally expandable microcapsules and resin can also be used as a foamable ink. Compositions containing the thermally expandable microcapsules and resin of the present invention are preferably used for adhesives, rubber chips, foam chips, flooring materials, rock consolidation materials, paints, coating materials, reinforcing fibers, composite materials, electronic components, molding materials, and the like. The molding materials are preferably used for molding by injection molding, extrusion molding, blow molding, rotational molding, vacuum molding, inflation molding, calendar molding, slush molding, dip molding, foam molding, fused deposition modeling, inkjet molding, stereolithography, laser sintering, and the like.

[0052] The resin used for the base resin is not particularly limited, and thermoplastic resins and curable resins commonly used in conventional foam molding can be used. Specific examples of the thermoplastic resin include polyolefins such as low-density polyethylene (LDPE) and polypropylene (PP), polyvinyl acetate, ethylene-vinyl acetate copolymer (EVA), vinyl chloride, polystyrene, thermoplastic elastomers, and ethylene-methyl methacrylate copolymer (EMMA). Among these, LDPE, EVA, EMMA, and thermoplastic elastomers are preferred due to their low melting points and ease of processability. These may be used alone or in combination of two or more. Examples of the curable resin include epoxy resins, (meth)acrylic resins, urethane resins, phenolic resins, cyanate resins, isocyanate resins, maleimide resins, benzoxazine resins, silicone resins, fluororesins, polyimide resins, and phenoxy resins. Of these, epoxy resins are preferred as the curable resin. These curable resins may be used alone or in combination of two or more.

[0053] The content of the thermally expandable microcapsules in the masterbatch pellets 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.

[0054] The method for producing the masterbatch pellets is not particularly limited, but examples include pre-kneading raw materials such as a base resin and various additives using a co-rotating twin-screw extruder or the like. Next, the mixture is 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 the masterbatch. Alternatively, a pellet-shaped masterbatch may be produced by kneading raw materials such as the base 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.

[0055] Furthermore, foamed molded articles can be obtained using the thermally expandable microcapsules and master batches. Molded articles using the thermally expandable microcapsules of the present invention also constitute one aspect of the present invention. In particular, the thermally expandable microcapsules can be suitably used in applications requiring post-processing at high temperatures, allowing foamed sheets with high appearance quality, such as uneven shapes, to be obtained. Specifically, foamed molded articles can be obtained by kneading the thermally expandable microcapsules or a masterbatch containing the thermally expandable microcapsules with a matrix resin and molding the mixture. 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.

[0056] 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.

[0057] According to the present invention, it is possible to provide thermally expandable microcapsules that have excellent heat resistance and gas barrier properties at high temperatures and therefore have high foaming performance even at high temperatures, without requiring a special molding machine even when using engineering plastics, etc. Furthermore, it is possible to provide a masterbatch containing the thermally expandable microcapsules and a molded article made using the thermally expandable microcapsules.

[0058] The following examples will further illustrate the present invention, but the present invention is not limited to these examples.

[0059] (Examples 1 to 17, Comparative Examples 1 to 12) (Preparation of Thermally Expandable Microcapsules) An aqueous dispersion medium was prepared by adding 8 L of water, 5 parts by weight of colloidal silica as a dispersant, and 0.3 parts by weight of polyvinylpyrrolidone to a polymerization reaction vessel. An oily mixture containing the monomers and metal cation salts in the amounts shown in Tables 1 and 2 was then added to the 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 (0.2 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.

[0060] (Preparation of Masterbatch Pellets) 100 parts by weight of a propylene-based elastomer and 10 parts by weight of a fatty acid ester lubricant were kneaded in a Banbury mixer. When the temperature reached approximately 100°C, 100 parts by weight of the obtained thermally expandable microcapsules were added to the propylene-based elastomer. The mixture was further kneaded for 30 seconds, extruded, and simultaneously pelletized to obtain masterbatch pellets. The propylene-based elastomer used had a melt index of 3.7 g / 10 min, a melting point of 75°C, a propylene content of 91% by weight, and an ethylene content of 9% by weight.

[0061] (Preparation of foamed molded article) Masterbatch pellets and 100 parts by weight of PA66 resin (Zytel 103HSL NC010 (Celanese)) were mixed to obtain mixed pellets containing 6 wt% masterbatch pellets. The obtained mixed pellets were fed into the hopper of a screw-type injection molding machine equipped with an accumulator, melt-kneaded, and injection-molded using a core-back method with a core-back amount of 2 mm to obtain a plate-shaped molded article. The molding conditions were a cylinder temperature of 260°C, an injection speed of 100 mm / s, a cooling time of 20 s, a back pressure of 5 MPa, a dwell pressure of 0 MPa, and a mold temperature of 80°C.

[0062] (Evaluation Method) The obtained thermally expandable microcapsules were evaluated by the following methods. The results are shown in Tables 1 and 2.

[0063] (1) Measurement of Volume Average Particle Diameter The volume average particle diameter of the obtained thermally expandable microcapsules was measured using a particle size distribution diameter measuring instrument (LA-910, manufactured by HORIBA Co., Ltd.).

[0064] (2) Measurement of Foaming Initiation Temperature and Maximum Foaming Temperature The foaming initiation temperature (Ts) 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 temperature increase rate of 5° C. / min under a force of 0.1 N applied from above. The vertical displacement 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.

[0065] (3) True Density The true density (g / cm) of the obtained thermally expandable microcapsules was measured using a true density meter (Ultrapyc 5000, manufactured by Anton Parr, etc.) under conditions of a pressure of 12 psi, a temperature of 25°C, and a gas type of helium. ３ ) was measured.

[0066] (4) Tg% Measurement The weight change rate (Tg%) of the thermally expandable microcapsules was measured using a thermogravimetric / differential thermal analyzer (TG / DTA) (TG / DTA6200 (manufactured by Hitachi, Ltd.)). Specifically, 20 μg of the sample was placed in an aluminum container with a diameter of 5 mm and a depth of 2 mm, heated from 40°C to 350°C at a heating rate of 5°C / min, and the weight change of the sample was measured. The difference between the Tg% at the foaming onset temperature Ts obtained from the TMA measurement results and the Tg% at the foaming onset temperature Ts + 20°C was calculated. A small difference in Tg% can be said to indicate excellent gas barrier properties.

[0067] (5) Durability (Recovery Rate) Using a thermomechanical analyzer (TMA) (TMA2940, manufactured by TA Instruments), the displacements D1 to D3 were measured under the following conditions, and the ratio (D3 / D1) of the displacements D3 to D1 was calculated. The larger the D3 / D1 value, the better the durability at high temperatures. 1) 25 μg of sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm, and heated at the maximum foaming temperature (Tmax) for 10 minutes with a force of 0.1 N applied from above. The displacement D1 in the vertical direction of the measuring probe was measured. 2) Next, the force from above was changed to 0.5 N, and the sample was heated at the maximum foaming temperature (Tmax) for an additional 5 minutes. The displacement D2 in the vertical direction of the measuring probe was measured. 3) Finally, the force from above was changed to 0.1 N, and the sample was heated at the maximum foaming temperature (Tmax) for an additional 5 minutes. The displacement D3 in the vertical direction of the measuring probe was measured.

[0068] (6) Degree of gelation The thermally expandable microcapsules were immersed in DMF for 24 hours, and the degree of gelation in DMF was measured. Specifically, the solution was adjusted so that the sample was 3% by weight, and after leaving it to stand for 24 hours, centrifuged at 3000 rpm for 3 minutes to separate the solvent and the sample. After removing the supernatant solvent, the sample was dried in a vacuum dryer, and the degree of gelation was calculated using the following formula based on the dry weight of the gel and the weight of the sample. Degree of gelation = (dry weight of gel / weight of polymer contained in the sample) x 100

[0069] (7) Specific Gravity The density of the obtained foamed molded article was measured by a method conforming to JIS K 7112 Method A (underwater displacement method). The specific gravity is an index representing the heat resistance and gas barrier property, which are the objectives of the present invention. When the heat resistance is poor, the specific gravity becomes high because the microcapsule shrinks after expansion in a high temperature range. When the gas barrier property is poor, gas escape occurs, making it difficult to expand, and the specific gravity becomes high. Therefore, when a foamed molded article with a low specific gravity is obtained, it can be said that the thermally expandable microcapsule has excellent heat resistance and gas barrier properties.

[0070]

[0071]

[0072] According to the present invention, it is possible to provide thermally expandable microcapsules that have excellent heat resistance and gas barrier properties at high temperatures and therefore have high foaming performance even at high temperatures, without requiring a special molding machine even when using engineering plastics, etc. Furthermore, it is possible to provide a masterbatch containing the thermally expandable microcapsules and a molded article made using the thermally expandable microcapsules.

Claims

1. A thermally expandable microcapsule having a shell containing a polymer and a volatile expanding agent encapsulated as a core agent, wherein the polymer contains structural units derived from a nitrile monomer (I) and structural units derived from a carboxyl group-containing monomer (II), the content of the structural units derived from the carboxyl group-containing monomer (II) in the polymer is 35% by weight or more and 55% by weight or less, the nitrile monomer (I) contains methacrylonitrile and acrylonitrile, the weight ratio of the structural units derived from the acrylonitrile to the structural units derived from the methacrylonitrile in the polymer (acrylonitrile / methacrylonitrile) is 1.05 or more, and the weight ratio of the structural units derived from the methacrylonitrile to the structural units derived from the carboxyl group-containing monomer (II) in the polymer (methacrylonitrile / carboxyl group-containing monomer (II)) is 0.8 or less, a thermally expandable microcapsule, wherein the polymer does not contain a structural unit derived from a monomer (III) that does not have a functional group that reacts with a carboxyl group, or the content of the structural unit derived from the monomer (III) is 1.5% by weight or less; and the core agent does not contain a fluorine atom-containing compound.

2. The thermally expandable microcapsule according to claim 1, wherein the maximum foaming temperature Tmax is 240°C or higher.

3. The thermally expandable microcapsules according to claim 1 or 2, which have a gelation degree of 30% by weight or less as measured in N,N-dimethylformamide (DMF) solvent.

4. A thermally expandable microcapsule according to claim 1, 2 or 3, wherein the polymer does not contain any structural unit derived from a polymerizable monomer having two or more double bonds in the molecule.

5. A thermally expandable microcapsule according to claim 1, 2, 3 or 4, wherein the content of the metal cation salt in the shell is 0.5% by weight or more and 10% by weight or less.

6. A masterbatch comprising the thermally expandable microcapsules according to claim 1, 2, 3, 4 or 5.

7. A molded article made using the thermally expandable microcapsules according to claim 1, 2, 3, 4, 5 or 6.

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