Thermally expandable microcapsules, foaming resin compositions and foams

Abstract

This invention provides a thermally expandable microcapsule capable of manufacturing molded articles with high expansion ratio, lightweight and excellent appearance, as well as a foaming resin composition and foam using the thermally expandable microcapsule. The invention relates to a thermally expandable microcapsule containing a volatile expanding agent as a core agent within a shell made of a polymer. The shell comprises a polymer formed by polymerizing a monomer composition containing a carbonyl monomer, and silicon dioxide. The volatile content of the thermally expandable microcapsule after standing at 70°C for 1 hour is 0.55% to 2% by weight.

Description

Thermally expandable microcapsules, foaming resin compositions and foams This invention relates to a thermally expandable microcapsule, and a foaming resin composition and foam using the thermally expandable microcapsule. To date, foaming agents have been used to foam resin materials for the purpose of reducing their weight or increasing their functionality. These foaming agents are usually thermally expandable microcapsules or chemical foaming agents. As for thermally expandable microcapsules, it is well known that some contain a liquid volatile expander that becomes gaseous at temperatures below the softening point of the shell polymer, encapsulated within a thermoplastic shell polymer. For example, Patent Document 1 discloses a method in which an oily mixture of a low-boiling-point aliphatic hydrocarbon or other volatile expander and a monomer is added, while stirring, to an aqueous dispersion medium containing a dispersant for suspension polymerization, thereby producing thermally expandable microcapsules encapsulating the volatile expander. (Prior Art Documents, Patent Documents) Patent Document 1: Japanese Patent Publication No. 42-26524 [The problem that the invention aims to solve] However, when using thermally expandable microcapsules obtained by this method as a foaming agent, defects such as dents occur in the resulting molded articles, resulting in poor appearance. Furthermore, when implementing countermeasures to address the aforementioned poor appearance, the following problems arise: foaming performance decreases, and the density of the resulting molded articles becomes insufficient. The object of this invention is to provide a thermally expandable microcapsule capable of manufacturing molded articles with high expansion ratio, lightweight, and excellent appearance, as well as a foaming resin composition and foam using the thermally expandable microcapsule. [Technical Means for Solving the Problem] The present invention (1) is a thermally expandable microcapsule, which contains a volatile expander as a core agent within a shell made of a polymer, wherein the shell comprises: a polymer formed by polymerizing a monomer composition containing a carbonyl monomer, and silicon dioxide, and the volatile matter content of the thermally expandable microcapsule after standing at 70°C for 1 hour is 0.55% to 2% by weight. The present invention (2) is a thermally expandable microcapsule as described in the present invention (1), wherein the volatile matter content after standing at 210°C for 20 minutes is 20% to 30% by weight. The present invention (3) is a thermally expandable microcapsule as described in the present invention (1) or (2), wherein the ratio of the volatile matter content after standing at 70°C for 1 hour to the volatile matter content after standing at 210°C for 20 minutes is 8% or less. The present invention (4) is a thermally expandable microcapsule as described in any one of the present invention (1) to (3), wherein the weight gain rate after standing for 12 hours at a temperature of 50°C and a humidity of 80% or higher is less than 60% by weight. The present invention (5) is a thermally expandable microcapsule as described in any one of the present invention (1) to (4), wherein the average particle size is 10 μm or more and 45 μm or less. The present invention (6) is a thermally expandable microcapsule as described in any one of the present invention (1) to (5), wherein the maximum foaming temperature (Tmax) is 180°C or more and 225°C or less. The present invention (7) is a foaming resin composition comprising the thermally expandable microcapsule as described in any one of the present invention (1) to (6) and a thermoplastic resin. The present invention (8) is a foam body obtained by using the foaming resin composition described in the present invention (7). The present invention will be described in detail below. Through intensive research, the inventors discovered that the volatile matter content of thermally expandable microcapsules has a significant impact on the properties of the resulting molded articles. Therefore, they found that by setting the volatile matter content within a defined range, thermally expandable microcapsules containing a polymer formed by polymerizing a monomer composition containing carbonyl monomers and silicon dioxide can be used to manufacture molded articles with high foaming ratios, lightweight properties, and excellent appearance, thus completing this invention. The thermally expandable microcapsules of the present invention have a volatile content of 0.55% to 2% by weight when left to stand at 70°C for 1 hour. By achieving a volatile content of 0.55% to 2% by weight, both the appearance and foaming properties of the molded article can be improved. Furthermore, by achieving a volatile content of 2% to 2% by weight, the appearance of the molded article is particularly improved. Moreover, these thermally expandable microcapsules are less prone to aggregation during foaming, which helps to improve foaming performance. Furthermore, these thermally expandable microcapsules exhibit excellent flowability when formed into multi-particle aggregates, allowing for stable feeding from a hopper or similar material during molding. The preferred lower limit for the volatile content when left to stand at 70°C for 1 hour is 0.57% by weight, a more preferred lower limit is 0.6% by weight, a more preferred upper limit is 1.8% by weight, and a more preferred upper limit is 1.5% by weight. Furthermore, in this specification, the volatile matter content after standing at 70°C for 1 hour can be determined based on the weight change after heating in an oven at 70°C and humidity below 20% for 1 hour. In the determination of this volatile matter content, when the humidity is below 20%, the difference in weight change caused by different humidity levels is negligible. In this invention, by adjusting the composition of the thermally expandable microcapsules, or by adjusting the reaction steps, washing steps, and drying steps during the manufacture of the thermally expandable microcapsules, it is possible to control the volatile matter content when standing at 70°C for 1 hour, the volatile matter content when standing at 210°C for 20 minutes, the ratio of volatile matter content, the weight gain rate, and the average roundness. The thermally expandable microcapsules of the present invention preferably have a volatile content of 20% to 30% by weight when left to stand at 210°C for 20 minutes. By ensuring a volatile content of 20% or more, sufficient foaming properties are ensured. Furthermore, by ensuring a volatile content of 30% or less, a good appearance is ensured when the foamed molded article is formed. The preferred lower limit for the volatile content when left to stand at 210°C for 20 minutes is 23% by weight, further preferably 25% by weight, more preferably 28% by weight, and further preferably 27% by weight. Moreover, in this specification, the volatile content when left to stand at 210°C for 20 minutes can be determined by the weight change after heating in an oven at 210°C and with a humidity not exceeding 20% ​​for 20 minutes. The thermally expandable microcapsules of the present invention preferably have a volatile content of 8% or less ([volatile content at 70°C for 1 hour / volatile content at 210°C for 20 minutes] × 100) relative to the volatile content at 70°C for 1 hour. By keeping this ratio below 8%, aggregation after foaming can be suppressed, resulting in a foamed molded article with a good appearance (smooth) and a high foaming ratio. A more preferred upper limit is 7.5%, further preferably 5%, and even more preferably 3%. There is no particular limitation on the lower limit of the preferred values, which is 0%. The thermally expandable microcapsules of the present invention preferably exhibit a weight gain rate of 60% by weight or less when left to stand for 12 hours at a temperature of 50°C and humidity of 80% or higher. By achieving a weight gain rate of 60% by weight or less, the appearance of the foamed molded article can be improved. The preferred upper limit of the aforementioned weight gain rate is 50% by weight, further preferably 35% by weight, the preferred lower limit is 10% by weight, and the most preferred lower limit is 20% by weight. Furthermore, in this specification, the aforementioned weight gain rate can be measured based on the weight change when left to stand for 12 hours at a temperature of 50°C and humidity of 80% or higher using a constant temperature and humidity apparatus. In this measurement of the weight gain rate, when the humidity is 80% or higher, the difference in weight change caused by different humidity levels is negligible. The preferred lower limit of the maximum foaming temperature (Tmax) of the thermally expandable microcapsules of this invention is 180°C, and the preferred upper limit is 225°C. By setting it within the above range, the heat resistance is increased, and when the composition containing the thermally expandable microcapsules is molded in a high-temperature region, the rupture and shrinkage of the thermally expandable microcapsules can be prevented. Furthermore, the aggregation of the thermally expandable microcapsules during molding can be suppressed, resulting in a good appearance. A more preferred lower limit is 185°C, and a more preferred lower limit is 190°C, a more preferred upper limit is 222°C, and a more preferred upper limit is 220°C. Furthermore, 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 heating the thermally expandable microcapsules from room temperature. The temperature at which the displacement begins to increase is defined as the foaming initiation temperature. Furthermore, the preferred upper limit of the foaming initiation temperature (Ts) is 170°C. By setting it below 170°C, foaming becomes easier, and the desired expansion ratio can be achieved. The preferred upper limit is 165°C, the preferred lower limit is 145°C, and the preferred upper limit is 165°C. Furthermore, the preferred lower limit of the maximum displacement (Dmax) of the thermally expandable microcapsules of the present invention, measured in thermomechanical analysis, is 350 μm, the preferred upper limit is 1600 μm, the more preferred lower limit is 500 μm, and the more preferred upper limit is 1500 μm. By setting it within the above range, the foaming ratio can be increased, and the desired foaming performance can be obtained. Moreover, the aforementioned maximum displacement refers to the value when the diameter of the entire specified amount of thermally expandable microcapsules reaches its maximum when the specified amount is heated from room temperature while its diameter is measured. The preferred lower limit of the average particle size (volume average particle size) of the thermally expandable microcapsules of the present invention is 10 μm, and the preferred upper limit is 45 μm. By setting it within the above range, the bubble size of the obtained molded article becomes moderate, a sufficient foaming ratio can be obtained, and the appearance is also excellent. A more preferred lower limit is 15 μm, further a more preferred lower limit is 20 μm, a more preferred upper limit is 35 μm, further a more preferred upper limit is 32 μm, and a particularly preferred upper limit is 30 μm. Furthermore, the volume average particle size (CV) value of the thermally expandable microcapsules of the present invention is preferably 35% or less, typically 10% or more, and preferably 15% or more. Moreover, the above-mentioned average particle size (volume average particle size) and CV value can be measured using a particle size distribution diameter measuring instrument or the like. The preferred lower limit for the average roundness of the thermally expandable microcapsules of this invention is 0.910, and the preferred upper limit is 0.980. By setting it within the above range, the appearance during molding can be smooth and free of depressions. A more preferred lower limit is 0.920, and a more preferred upper limit is 0.970. The above-mentioned average roundness is, for example, measured based on images obtained from wet chromatography using a Mastersizer 3000 (manufactured by Malvern Panalytical). Furthermore, the above-mentioned roundness represents a value obtained by dividing the area calculated from the image of the thermally expandable microcapsule by the area of ​​the circumscribed circle of the image of the thermally expandable microcapsule (image area of ​​thermally expandable microcapsule / area of ​​the circumscribed circle of the image of the thermally expandable microcapsule). Alternatively, the roundness can also be measured based on images obtained from dry chromatography using CALPAS (Japan Laser Corporation) to calculate the average roundness. The shell of the thermally expandable microcapsule constituting the present invention comprises a polymer formed by polymerizing a monomer composition containing a carbonyl monomer, and silicon dioxide. The aforementioned shell contains silicon dioxide. The silicon dioxide may adhere to the surface of the shell or be mixed within the shell. Furthermore, the aforementioned silicon dioxide also contains silicon dioxide hydrates. Examples of the aforementioned silicon dioxide include silicon dioxide contained in silica microparticles and silicon dioxide contained in silica gel. The aforementioned silica gel is a colloid of silicon dioxide or silicon dioxide hydrates. Preferably, the silica gel containing the aforementioned silicon dioxide has an average particle size of 10–300 nm. The preferred lower limit of the silica content in the thermally expandable microcapsules of the present invention is 1% by weight, and the preferred upper limit is 5% by weight. By setting the silica content to 1% by weight or more, the average particle size of the thermally expandable microcapsules can be stably maintained, and by setting the silica content to 5% by weight or less, thermally expandable microcapsules with excellent foaming properties can be obtained. The preferred lower limit of the silica content is 1.5% by weight, the preferred upper limit is 3% by weight, the preferred lower limit is 1.7% by weight, and the preferred upper limit is 2.8% by weight. The aforementioned shell comprises a polymer formed by polymerizing a monomer composition containing a carbonyl monomer, and silicon dioxide. Examples of carbonyl-containing monomers include free radical polymerizable unsaturated carboxylic acid monomers with 3 to 8 carbon atoms, free radical polymerizable unsaturated carboxylic acid ester monomers with 3 to 8 carbon atoms, and polyfunctional carboxylic acid ester monomers. As free radical polymerizable unsaturated carboxylic acid monomers with 3 to 8 carbon atoms, those having one free carboxyl group per molecule for ionic crosslinking can be used, for example. Specifically, examples include unsaturated carboxylic acids and their anhydrides, which can be used alone or in combination of two or more. Examples of unsaturated carboxylic acids include unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, ethylacrylic acid, butenoic acid, and cinnamic acid, as well as unsaturated dicarboxylic acids such as maleic acid, itconic acid, fumaric acid, citraconic acid, and chloromaleic acid. Among these, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, and itconic acid are particularly preferred. The preferred lower limit of the content of the free radical polymerizable unsaturated carboxylic acid monomer with 3 to 8 carbon atoms in the above monomer composition is 5% by weight, and the preferred upper limit is 50% by weight. By setting it to 5% by weight or more, the maximum foaming temperature can be increased, and by setting it to 50% by weight or less, the foaming ratio can be increased. The preferred lower limit is 10% by weight, and the preferred upper limit is 30% by weight. As the free radical polymerizable unsaturated carboxylic acid ester monomer with 3 to 8 carbon atoms, (meth)acrylates are preferred, and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate are particularly preferred. Also preferred are cyclohexyl methacrylate, benzyl methacrylate, and isomethacrylate. Esters, etc., are methacrylates containing alicyclic, aromatic, or heterocyclic rings. The preferred lower limit of the content of the free radical polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms in the above-mentioned monomer composition is 0.01% by weight, and the preferred upper limit is 35% by weight. By setting the content of the free radical polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms to 0.01% by weight or more, the dispersibility of the composition of the thermally expandable microcapsule can be improved, and by setting it to 35% by weight or less, the gas barrier properties of the capsule wall can be improved, thus improving thermal expansion properties. The preferred lower limit of the content of the free radical polymerizable unsaturated carboxylic acid ester monomer having 3 to 8 carbon atoms is 0.05% by weight, and the preferred upper limit is 30% by weight. The aforementioned polyfunctional carboxylic acid ester monomers refer to carboxylic acid ester monomers with two or more free radical polymerizable double bonds, which differs from the aforementioned free radical polymerizable unsaturated carboxylic acid ester monomers with 3 to 8 carbon atoms. These polyfunctional carboxylic acid ester monomers function as cross-linking agents. By containing these polyfunctional carboxylic acid ester monomers, the shell strength can be enhanced, and the shell wall is less prone to rupture during thermal expansion. Specifically, examples of the aforementioned multifunctional carboxylic acid ester monomers include di(meth)acrylates and (meth)acrylates with three or more functionalities. Examples of the aforementioned di(meth)acrylates 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. Examples also include 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, glycerol di(meth)acrylate, trimethylolpropane di(meth)acrylate, and dimethyloltricyclodecane di(meth)acrylate. Furthermore, polyethylene glycol di(meth)acrylates with a weight average molecular weight of 200 to 600 can also be used. Examples of trifunctional (meth)acrylates include trimethylolpropane trimethacrylate, ethylene oxide-modified trimethylolpropane trimethacrylate, neopentyl tetroxide trimethacrylate, and triallyl formaldehyde trimethacrylate. Examples of quadruple-functional or higher (meth)acrylates include neopentyl tetroxide tetramethacrylate and dinepentyl tetroxide hexamethacrylate. Among these, trifunctional (meth)acrylates such as trimethylolpropane trimethacrylate and difunctional (meth)acrylates such as polyethylene glycol can be crosslinked more uniformly within an acrylonitrile-based shell. The preferred lower limit of the content of the aforementioned polyfunctional carboxylic acid ester monomer in the above-mentioned monomer composition is 0.1% by weight, and the preferred upper limit is 1.0% by weight. By setting the content of the aforementioned polyfunctional carboxylic acid ester monomer to 0.1% by weight or more, its effect as a crosslinking agent can be fully exerted; by setting the content of the aforementioned polyfunctional carboxylic acid ester monomer to 1.0% by weight or less, the foaming ratio of the thermally expandable microcapsules can be improved. The preferred lower limit of the content of the aforementioned polyfunctional carboxylic acid ester monomer is 0.15% by weight, and the preferred upper limit is 0.9% by weight. The aforementioned monomer composition preferably contains, in addition to the carbonyl-containing monomers mentioned above, nitrile monomers such as acrylonitrile and methacrylonitrile. Adding these nitrile monomers can improve the gas barrier properties of the shell. Furthermore, in addition to the aforementioned carbonyl-containing monomers and nitrile monomers, it may also contain vinylidene chloride, divinylbenzene, vinyl acetate, styrene monomers, etc. The preferred lower limit for the content of nitrile monomers in the above-mentioned monomer composition is 40% by weight, and the preferred upper limit is 90% by weight. By setting it to 40% by weight or more, the gas barrier properties of the shell can be improved, thereby increasing the foaming ratio. By setting it to 90% by weight or less, the heat resistance can be improved and yellowing can be prevented. The preferred lower limit is 50% by weight, and the preferred upper limit is 80% by weight. In particular, from the viewpoints of heat resistance, foaming ratio, lightweight, hardness, and wear resistance, the above-mentioned monomer composition is preferably composed of 40 to 90% by weight of nitrile monomers and 10 to 60% by weight of carbonyl monomers. To polymerize the aforementioned monomers, the monomer composition contains a polymerization initiator. Suitable polymerization initiators include, for example, dialkyl peroxides, diacyl peroxides, peroxide esters, dicarbonates peroxide, and azo compounds. Specifically, examples include dialkyl peroxides such as methyl ethyl peroxide, di-tert-butyl peroxide, and diisopropylphenyl peroxide; and diacyl peroxides such as isobutyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, and 3,5,5-trimethylhexyl peroxide. Examples also include tert-butyl peroxypentanoate, tert-hexyl peroxypentanoate, tert-butyl peroxyneodecanate, tert-hexyl peroxyneodecanate, 1-cyclohexyl-1-methylethyl peroxyneodecanate, and 1,1,3,3-tetramethylbutyl peroxyneodecanate. Examples of peroxide esters include: cumyl peroxynedecanoate, (α,α-bis-neodecaylperoxy)diisopropylbenzene, etc.; bis(4-tert-butylcyclohexyl) peroxide dicarbonate, di-n-propyl peroxide dicarbonate, diisopropyl peroxide dicarbonate, etc. Furthermore, examples of dicarbonate peroxides include: di(2-ethylethyl) peroxide dicarbonate, dimethoxybutyl peroxide dicarbonate, di(3-methyl-3-methoxybutyl) peroxide dicarbonate, etc. Additionally, examples of azo compounds include: 2,2'-azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylpentanitrile), 2,2'-azobis(2,4-dimethylpentanitrile), 1,1'-azobis(1-cyclohexanenitrile), etc. The preferred lower limit of the weight average molecular weight of the polymer constituting the aforementioned shell is 100,000, and the preferred upper limit is 2 million. If it is above 100,000, the decrease in shell strength can be suppressed; if it is below 2 million, the excessive increase in shell strength can be suppressed, and the decrease in foaming ratio can be suppressed. The shell may also contain stabilizers, ultraviolet absorbers, antioxidants, antistatic agents, flame retardants, silane coupling agents, colorants, etc., as needed. The thermally expandable microcapsules of this invention contain a volatile expanding agent as a core agent within the aforementioned shell. This volatile expanding agent is a gaseous substance that becomes gaseous at temperatures below the softening point of the polymer constituting the shell, and is preferably a low-boiling-point organic solvent. Examples of such volatile expanding agents include: ethane, ethylene, propane, propylene, n-butane, isobutane, butene, isobutene, n-pentane, isopentane, neopentane, n-hexane, heptane, petroleum ether, isooctane, octane, decane, isododecane, dodecane, hexadecane, and other low molecular weight hydrocarbons. Also, examples include: CCl4. 3F, CCl 2F 2. CClF 3. CClF 2-CClF 2. Chlorofluorocarbons; tetramethylsilane, trimethylethylsilane, trimethylisopropylsilane, trimethyln-propylsilane, and other tetraalkylsilanes. Preferably, isobutane, n-butane, n-pentane, isopentane, n-hexane, isooctane, isododecane, and mixtures thereof. These volatile expanding agents can be used alone or in combination of two or more. Furthermore, thermally decomposable compounds that decompose into gaseous form upon heating can also be used as volatile expanding agents. In the thermally expandable microcapsules of the present invention, among the aforementioned volatile expanders, low-boiling-point hydrocarbons with 5 or fewer carbon atoms are preferably used. By using such hydrocarbons, thermally expandable microcapsules with high foaming ratio and rapid foaming initiation can be produced. Alternatively, thermally decomposable compounds that undergo thermal decomposition into gaseous form upon heating can also be used as volatile expanders. The method for manufacturing the thermally expandable microcapsules of the present invention is not particularly limited. For example, it can be manufactured by performing the following steps: preparing an aqueous medium, dispersing an oily mixture containing a monomer composition and a volatile expanding agent in the aqueous medium, and polymerizing the monomer. As the monomer composition, for example, a monomer composition containing 40 to 90% by weight of the nitrile monomer and 10 to 60% by weight of a carbonyl monomer can be used. In manufacturing the thermally expandable microcapsules of the present invention, the first step is to prepare an aqueous medium. Specifically, for example, a dispersion stabilizer containing water and silicon dioxide, and an auxiliary stabilizer as needed, are added to the polymerization reaction vessel to prepare an aqueous dispersion medium containing silicon dioxide. Alternatively, alkali metal salts of nitrite, stannous chloride, stannous chloride, potassium dichromate, etc., may be added as needed. As a dispersion stabilizer containing silica, silica gel can be cited as an example. As the silica gel, an alkaline silica gel with a pH greater than 7 in the colloidal solution (aqueous dispersion) can be used, or an acidic silica gel with a pH less than 7 can be used. Alkaline silica gel is more preferred. Furthermore, as the silica gel, it is preferable to contain 10-50% by weight of silica as a solid component and to be monodisperse. Examples of dispersants and stabilizers other than silicon dioxide include calcium phosphate, magnesium hydroxide, aluminum hydroxide, iron hydroxide, barium sulfate, calcium sulfate, sodium sulfate, calcium oxalate, calcium carbonate, barium carbonate, and magnesium carbonate. The amount of the silica-containing dispersant stabilizer added can be appropriately determined based on the particle size of the thermally expandable microcapsules. 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). Further, the preferred lower limit is 3 parts by weight, and the preferred upper limit is 5 parts by weight. Furthermore, the amount of the oil phase mentioned above refers to the combined amount of the monomer and the volatile expander. Examples of auxiliary stabilizers mentioned above include the condensation products of diethanolamine and aliphatic dicarboxylic acids, and the condensation products of urea and formaldehyde. Other examples include polyvinylpyrrolidone, polyethylene oxide, polyethyleneimine, tetramethylammonium hydroxide, gelatin, methylcellulose, polyvinyl alcohol, dioctyl sulfosuccinate, sorbitan ester, and various emulsifiers. Furthermore, the combination of the aforementioned dispersant and auxiliary stabilizer is not particularly limited; examples include combinations of silica gel and condensation products, and combinations of silica gel and water-soluble nitrogen-containing compounds. Among these, the combination of silica gel and condensation products is preferred. Moreover, the aforementioned condensation product is preferably a condensation product of diethanolamine and aliphatic dicarboxylic acids, particularly preferably a condensation product of diethanolamine and adipic acid, or a condensation product of diethanolamine and itaconic acid. Examples of the aforementioned water-soluble nitrogen-containing compounds include polyvinylpyrrolidone, polyethyleneimine, polyoxyethylene alkylamine, and poly(meth)acrylate dialkylaminoalkyl alkyl esters, represented by poly(dimethylaminoethyl methacrylate) and poly(dimethylaminoethyl methacrylate). Examples also include poly(dialkylaminoalkyl(meth)acrylates), polyacrylamide, polycationic acrylamide, polyamine, and polyallylamine, represented by poly(dimethylaminopropylacrylamide) or poly(dimethylaminopropylmethacrylamide). Among these, polyvinylpyrrolidone is suitable for use. The amount of the condensation product or water-soluble nitrogen-containing compound can be appropriately determined according to the particle size of the thermally expandable microcapsules. The preferred lower limit is 0.05 parts by weight and the preferred upper limit is 0.2 parts by weight relative to 100 parts by weight of the oily mixture. In addition to the aforementioned dispersants and auxiliary stabilizers, inorganic salts such as sodium chloride and sodium sulfate can also be added. By adding inorganic salts, thermally expandable microcapsules with more uniform particle shape can be obtained. Generally, the amount of the aforementioned inorganic salt added is preferably 0 to 100 parts by weight relative to 100 parts by weight of the monomer. The aqueous dispersion medium containing the above-mentioned dispersant stabilizer is prepared by incorporating the dispersant stabilizer or auxiliary stabilizer into deionized water. The pH of the aqueous phase can be appropriately determined according to the type of dispersant stabilizer or auxiliary stabilizer used. For example, when using silicon dioxide as a dispersant stabilizer, polymerization is carried out in an acidic medium. To make the aqueous medium acidic, an acid such as hydrochloric acid can be added as needed to adjust the pH of the system to 3-4. On the other hand, when using magnesium hydroxide or calcium phosphate, polymerization is carried out in an alkaline medium. Subsequently, in the method for manufacturing thermally expandable microcapsules, a step is performed to disperse an oily mixture containing a monomeric component and a volatile expanding agent in an aqueous medium. Specifically, for example, a step is performed to disperse an oily mixture containing a monomeric component and a volatile expanding agent in an aqueous medium, wherein the monomeric component contains 40-90% by weight of the aforementioned nitrile monomer and 10-60% by weight of a carbonyl monomer. In this step, the monomeric component and the volatile expanding agent can also be added separately to the aqueous dispersion medium to prepare an oily mixture in the aqueous dispersion medium, but usually, the two are mixed in advance to prepare an oily mixture before being added to the aqueous dispersion medium. In this case, the oily mixture and the aqueous dispersion medium can also be prepared in advance in different containers, and then mixed while stirring in another container to disperse the oily mixture in the aqueous dispersion medium (primary dispersion) before being added to the polymerization reaction vessel. Furthermore, in order to use a polymerization initiator for the polymerization of the above monomers, the polymerization initiator can be added to the above oily mixture in advance, or the aqueous dispersion medium and the oily mixture can be stirred and mixed in the polymerization reaction vessel before being added. As a step for dispersing an oily mixture containing the aforementioned monomeric components and volatile expanding agents in an aqueous medium, examples of methods include stirring using swept-wing blades or batch-type high-speed rotating high-shear dispersers (e.g., Japanese Patent Application Laid-Open No. 7-96167) and continuous high-speed rotating high-shear dispersers (e.g., Japanese Patent Application Laid-Open No. 2000-191817). Alternatively, methods can be employed such as passing the mixture through a pipeline mixer or a static in-pipe mixer (static mixer). In this invention, in the step of dispersing the oily mixture containing the aforementioned monomeric components and the volatile expanding agent in an aqueous medium, it is preferable to use a static in-tube mixer. By using the static in-tube mixer, mixing can be performed inside a tube rather than a tank, and static mixing without the use of stirring blades can be achieved, thus making it suitable for manufacturing the thermally expandable microcapsules of this invention. Furthermore, it is preferable to prepare a dispersion of the oily mixture and the aqueous dispersion medium in separate containers beforehand, and then introduce it into the static in-tube mixer under pressure. Moreover, the static in-tube mixer (static mixer) has a plurality of plate-like elements with multiple holes installed within a cylindrical body open at both ends. Furthermore, the plurality of plate-like elements are stacked in such a way that the centers of the holes of adjacent plate-like elements are not aligned with each other, but at least a portion of their openings face each other. By performing this step, it is suitable for manufacturing the thermally expandable microcapsules of this invention. Furthermore, the aforementioned pressurization is preferably performed at 1 to 6 MPa. Also, the number of orifices in the element is preferably set according to the flow rate. Furthermore, the aforementioned pressurization can be set by the orifice diameter and flow rate. The orifice diameter is preferably 1 to 3 mm. The flow rate is preferably 100 to 500 L / min. Specifically, a combination of an orifice diameter of 2 mm and a flow rate of 200 L / min is preferred. The thermally expandable microcapsules of this invention can be manufactured by performing the following steps: heating the dispersion obtained by the above steps to polymerize the monomers; and washing. The thermally expandable microcapsules manufactured by this method have a high maximum foaming temperature and excellent heat resistance, and will not rupture or shrink even when formed in high-temperature regions. In the method for manufacturing the thermally expandable microcapsules of the present invention, a washing step is performed. Examples of washing steps include immersion washing, running water washing, and spray washing, and further, washing methods combining these with ultrasound or oscillation can be applied. Furthermore, combining the washing step with a dewatering step can improve production efficiency. Specifically, the following method can be used: After the slurry supplied by the press dewatering machine is made into a wet filter cake, a predetermined amount of washing water (preferably ion-exchanged water) is supplied to the dewatering machine, and pressing is performed again. Washing water is supplied again and pressing is performed. This step is repeated several times. The amount of slurry supplied to the dewatering machine, the amount and ratio of washing water, and the number of washing cycles are more important for removing inorganic salts such as sodium chloride and sodium sulfate. This step removes inorganic salts and prevents equipment corrosion in semiconductor applications or automotive component applications (molding applications). The washing water volume in the above washing steps is preferably 2.5 to 5 times the volume of the polymer slurry. In the method for manufacturing the thermally expandable microcapsules of the present invention, a drying step is then performed. In the drying step described above, in addition to evaporating the liquid components, the silicon dioxide content of the shell can also be adjusted. As part of the drying step described above, natural drying, hot air drying (fluidized bed drying), vacuum drying, or other methods can be used. The drying temperature is preferably 30°C or higher, more preferably 32°C or higher, further preferably 35°C or higher, and preferably 70°C or lower, more preferably 68°C or lower, and further preferably 65°C or lower. Furthermore, the drying time (total drying time) in the above drying step is preferably 12 hours or higher, more preferably 13 hours or higher, more preferably 14 hours or higher, and preferably 20 hours or lower, and more preferably 18 hours or lower. The above drying steps can be carried out at a constant temperature or by changing the drying temperature in stages. When changing the drying temperature in stages, the drying can be performed several times. Preferably, the number of drying steps is 2 to 4, more preferably 3 (drying steps 1 to 3). In this case, the average drying temperature for the first drying step is preferably set below 40°C, the average drying temperature for the second drying step is preferably set above 40°C but below 50°C, and the average drying temperature for the third drying step is preferably set above 50°C. Of the aforementioned drying methods, vacuum drying is particularly preferred. In this case, methods such as using a heated vacuum vibration dryer can be cited as examples. Furthermore, the range of vacuum values ​​in the aforementioned vacuum drying is preferably -0.065 to -0.100 MPa, more preferably -0.070 to -0.095 MPa, and even more preferably -0.075 to -0.090 MPa. Moreover, the aforementioned vacuum values ​​can be measured using a vacuum pressure gauge or a vacuum meter. By adding a matrix resin such as a thermoplastic resin to the thermally expandable microcapsules of the present invention to obtain a foaming resin composition, or by mixing the thermally expandable microcapsules with a base resin such as a thermoplastic resin, masterbatch particles can be obtained. Furthermore, by adding a foaming resin composition containing a matrix resin such as a thermoplastic resin to the aforementioned masterbatch particles, molding them using a molding method such as injection molding, and then using heating during molding to foam the aforementioned thermally expandable microcapsules, a foamed body can be manufactured. The foaming resin composition of the present invention preferably contains 0.1 to 10 parts by weight of thermally expandable microcapsules relative to 100 parts by weight of the matrix resin. Furthermore, the aforementioned foaming resin composition may contain a chemical foaming agent. As for the aforementioned chemical foaming agent, it is not particularly limited as long as it is in powder form at room temperature; commonly known and widely used chemical foaming agents can be used. The aforementioned chemical foaming agents can be classified into organic foaming agents and inorganic foaming agents, which can be further classified into thermally decomposable and reactive types. Commonly used organic thermally decomposable foaming agents include ADCA (azodimethylamine), DPT (N,N'-dinitropentamethylenetetramine), and OBSH (4,4'-oxobis(benzenesulfonylhydrazine)). Inorganic thermally decomposable foaming agents include bicarbonates, carbonates, and combinations of bicarbonates and organic acid salts. Thermally decomposable chemical foaming agents are preferred. Furthermore, the performance of thermally decomposable chemical foaming agents is determined by their decomposition temperature, gas production rate, and particle size. The decomposition temperature of the aforementioned chemical foaming agent is preferably 180–200°C. This decomposition temperature can be adjusted by combining it with urea-based or zinc-based foaming agents as needed. The gas production rate of the aforementioned chemical foaming agent is preferably 220–240 ml / g. Furthermore, the aforementioned gas production rate refers to the volume of gas produced during the decomposition of the chemical foaming agent. This gas becomes part of the bubbles and therefore affects the foaming ratio. Furthermore, by using the aforementioned chemical foaming agent in combination with citrate or zinc oxide, the bubble diameter can be reduced. The aforementioned chemical foaming agents are typically in powder form. The smaller the particle size, the greater the number of particles per unit weight. There is a tendency for a higher particle size to result in a greater number of bubbles. The preferred lower limit for the average particle size (median particle size) of the aforementioned chemical foaming agent is 4 μm, and the preferred upper limit is 20 μm. By setting it within the above range, the resulting molded article has a moderate amount of bubbles, achieving a sufficient foaming ratio and resulting in excellent appearance. A more preferred lower limit is 5 μm, and a more preferred upper limit is 10 μm. There are no particular limitations on the molding method for the aforementioned foamed articles; examples include compounding molding, calendering molding, extrusion molding, and injection molding. In the case of injection molding, the processing method is not particularly limited; examples include short-shot molding where a portion of resin material is added to the mold and foamed, and core-pulling molding where the mold is filled with resin material and then opened to the desired foaming position. [Effects of the Invention] According to the present invention, it is possible to manufacture thermally expandable microcapsules capable of producing molded articles with high foaming ratios, lightweight, and excellent appearance, as well as foaming resin compositions and foamed articles using the thermally expandable microcapsules. Furthermore, the thermally expandable microcapsules of the present invention are suitable for use in automotive components, coatings, adhesives, and inks. The following examples illustrate the present invention in further detail, but the present invention is not limited to these examples. (Example 1) (Preparation of Thermally Expandable Microcapsules) 330 parts by weight of silica gel (average particle size 20 nm), 12 parts by weight of polyvinylpyrrolidone, 1096 parts by weight of sodium chloride, and 0.85 parts by weight of sodium nitrite, comprising 20% ​​by weight of solids, were added to 3300 parts by weight of deionized water and mixed to prepare an aqueous dispersion medium. Furthermore, alkaline silica gel was used as the silica gel (aqueous dispersion). 390 parts by weight (28% by weight) of acrylonitrile, 585 parts by weight (42% by weight) of methacrylonitrile, 420 parts by weight (29.9% by weight) of methacrylic acid, and 1.4 parts by weight (0.1% by weight) of methyl methacrylate were mixed to prepare a homogeneous solution of the monomer composition (the percentage in parentheses is relative to the total weight of the monomer composition). 11.1 parts by weight of 2,2'-azobis(isobutyronitrile), 8.3 parts by weight of 2,2'-azobis(4-methoxy-2,4-dimethylpentanonitrile), and 440 parts by weight of n-pentane were added to tank 1 for mixing. Then, an aqueous dispersion medium was added to tank 2, and the oily mixture from tank 1 was added to tank 2 for mixing to obtain a primary dispersion. At this point, the pH of the primary dispersion was 3.5–4.0. Using a static in-tube mixer (static mixer, manufactured by Fujikin Corporation, Dispersion King), the obtained primary dispersion was passed through at a flow rate of 200 L / min and a pressure of 1.5 MPa. The passed liquid entered an autoclave. Furthermore, the element-type static disperser used was as follows: plate elements with a thickness of 5 mm, an effective diameter of 15 mm, and a pore diameter of 2 mm were formed into a club shape, and at least some of the adjacent different types of plate elements had 78 holes facing each other. Furthermore, the number of units composed of the combination of element 1 and element 2 is 10, arranged so that fluid passes through the holes of each plate-shaped element. Subsequently, nitrogen purging is performed, and the reaction is carried out at a reaction temperature of 60°C for 15 hours. The reaction pressure is 0.5 MPa, and the stirring system operates at 200 rpm. Then, 8000 L of the obtained polymer slurry is fed in batches to a dewatering press (manufactured by Ishigaki Corporation, filter press). After dewatering, a specified amount of wash water is supplied to the dewatering machine for a washing step, thereby obtaining thermally expandable microcapsules before drying. Furthermore, the washing step involves washing 300 L of polymer slurry with 1000 L of wash water. The obtained thermally expandable microcapsules were vacuum dried using a heated vacuum vibration dryer (manufactured by Central Chemical Machinery Co., Ltd., VU type) (total drying time: 12.5 hours, vacuum value: -0.085 MPa) to obtain thermally expandable microcapsules. Specifically, the vacuum drying process involved drying at set temperatures of 45, 50, and 55°C for 5.5 hours (drying step 1) (heating at 10°C / hr), followed by drying at set temperatures of 60 and 65°C for 1.5 hours (drying step 2) (heating at 10°C / hr). Then, after heating at 5°C / hr, drying was carried out at a set temperature of 70°C, a drying temperature (initial) of 43°C, and a drying temperature (final) of 60°C for 5.5 hours (drying step 3). Furthermore, the set temperature refers to the jacket set temperature of the dryer, and the drying time refers to the actual drying time. The drying temperature and time at each set temperature are shown in Tables 2 and 3. (Preparation of Foam Precursor) The foaming resin composition was obtained by mixing the components shown in Table 1 using a Henschel mixer (dried at 120°C). 300 g of the obtained foaming resin composition was heated and kneaded for 3 minutes using an 8-inch laboratory roller press. The roller temperature was set to within ±30°C to 50°C below the foaming initiation temperature of the foam. Subsequently, using the kneaded roller-pressed sheet as material, it was shaped into a pressed sheet with a thickness of 1–2 mm and a length of 150 mm × width using a press with the same temperature setting as the roller, thereby obtaining a pressed sheet (foaming precursor). Furthermore, the pressing conditions were preheating for 3 minutes, pressurizing for 3 minutes, and cooling for 3 minutes. The surface pressure was set to 5–8 MPa during preheating and 20 MPa during pressurization and cooling. (Examples 2-6, Comparative Examples 1-6) Except for the drying and washing conditions (drying steps 1-3, total drying time, vacuum value) and washing conditions (washing water volume relative to 300 L of polymer slurry) shown in Tables 2 and 3, the thermally expandable microcapsules and foaming precursors were obtained in the same manner as in Example 1. (Comparative Example 7) (Preparation of Thermally Expandable Microcapsules) 330 parts by weight of silica gel (average particle size 20 nm), 12 parts by weight of polyvinylpyrrolidone, 1096 parts by weight of sodium chloride, and 0.85 parts by weight of sodium nitrite, comprising 20% ​​by weight of solids, were added to 3300 parts by weight of ion-exchanged water and mixed to prepare an aqueous dispersion medium. Furthermore, alkaline silica gel was used as the silica gel (aqueous dispersion). 978 parts by weight (70% by weight) of acrylonitrile and 418 parts by weight (30% by weight) of methacrylonitrile were mixed to prepare a homogeneous solution of the monomer composition (the percentage in parentheses is relative to the total weight of the monomer composition). 11.1 parts by weight of 2,2'-azobis(isobutyronitrile), 8.3 parts by weight of 2,2'-azobis(2,4-dimethylpentanonitrile), and 440 parts by weight of n-pentane were added to this mixture, and then added to tank 1 for mixing. Next, an aqueous dispersion medium was added to tank 2, and the oily mixture from tank 1 was added to tank 2 for mixing, thereby obtaining a primary dispersion. At this time, the pH of the primary dispersion was 3.5–4.0. Using a static in-tube mixer (static mixer, manufactured by Fujikin Corporation, Dispersion King), the obtained primary dispersion was passed through at a flow rate of 200 L / min and a pressure of 1.5 MPa. The passed liquid entered an autoclave. Furthermore, the element-type static disperser used was as follows: plate elements with a thickness of 5 mm, an effective diameter of 15 mm, and a pore diameter of 2 mm were formed into a club shape, and at least some of the adjacent different types of plate elements had 78 holes facing each other. In addition, the number of units composed of the combination of the first element and the second element was 10 sets, arranged so that the fluid passed through the holes of each plate element. Subsequently, nitrogen purging was performed, and the reaction was carried out at a reaction temperature of 60°C for 15 hours. The reaction pressure was 0.5 MPa, and the stirring system operated at 200 rpm. Subsequently, 8000 L of the resulting polymer slurry was fed in batches to a dewatering unit (Ishigaki Corporation, filter press). After dewatering, a specified amount of washing solution was fed to a dewatering machine for a washing step, thereby obtaining thermally expandable microcapsules before drying. Furthermore, the washing step involved washing 300 L of the polymer slurry with 1000 L of washing water. Except for the drying and washing steps performed on the obtained thermally expandable microcapsules under the drying conditions (drying steps 1 to 3, total drying time, vacuum value) and washing conditions (washing water volume relative to 300 L of polymer slurry) shown in Tables 2 and 3, the thermally expandable microcapsules and foaming precursors were obtained in the same manner as in Example 1. [Table 1] (1) Evaluation of thermally expandable microcapsules (1-1) Foaming initiation temperature, maximum foaming temperature, and maximum displacement were determined using a thermomechanical analysis apparatus (TMA) (TMA2940, manufactured by TA Instruments). Specifically, 25 μg of the sample was placed in an aluminum container with a diameter of 7 mm and a depth of 1 mm. Under the condition of applying a force of 0.1 N from above, the temperature was increased from 80°C to 220°C at a heating rate of 5°C / min. The displacement in the vertical direction of the measuring terminals was measured. The temperature at which the displacement began to increase was set as the foaming initiation temperature, the maximum value of the displacement was set as the maximum displacement, and the temperature at which the maximum displacement was reached was set as the maximum foaming temperature. (1-2) The average particle size (volume average particle size) and average roundness were measured using a particle size distribution diameter measuring instrument (LA-950, manufactured by HORIBA). Furthermore, the average roundness was measured using the above method based on images obtained from wet measurement with a Mastersizer 3000 (manufactured by Malvern Panalytical). (1-3) Volatile Matter (70℃ for 1 hour, 210℃ for 20 minutes) Weigh approximately 10 g of the thermally expandable microcapsules and place them in an aluminum cup. Heat at 70℃ for 1 hour, then allow to cool naturally to below 40℃ in a desiccator and weigh the contents. Calculate the volatile matter using the following formula. The volatile matter after heating at 210℃ for 20 minutes is also determined in the same manner. Furthermore, calculate the ratio of the volatile matter after standing at 70℃ for 1 hour to the volatile matter after standing at 210℃ for 20 minutes ([volatile matter after standing at 70℃ for 1 hour / volatile matter after standing at 210℃ for 20 minutes] × 100). V = [(B - C) / (B - A)] × 100 V: Volatile matter (weight %) A: Weight of aluminum cup (g) B: Mass of aluminum cup after adding the sample (g) C: Weight of aluminum cup after heating and natural cooling after adding the sample (g) (1-4) The weight gain rate was determined using the same method as in (1-3) above (70°C, 1 hour) for the volatile matter before and after standing for 12 hours at a temperature of 50°C and humidity of 80% or higher. The weight gain rate was determined according to the following formula: D=(E-F) / E×100 D: Weight gain rate E: Volatile matter after standing for 12 hours at a temperature of 50°C and humidity of 80% or higher F: Volatile matter before standing for 12 hours at a temperature of 50°C and humidity of 80% or higher (1-5)SiO 2. A trace amount (approximately 0.01 g) of thermally expandable microcapsules was collected, and the SiO2 content was determined using an EDS energy dispersive X-ray analyzer (JSM-6510, manufactured by Nippon Electronics Corporation). 2. Content (silicon dioxide content in thermally expandable microcapsules). (1-6) Agglomeration of thermally expandable microcapsules during foaming: Weigh 0.05 g of thermally expandable microcapsules and place them in an aluminum cup. Use a microscope to confirm the agglomeration of the foamed thermally expandable microcapsules after standing at 200°C for 1.5 minutes. Furthermore, the case where no agglomeration is observed is recorded as "none", the case where agglomeration is slight is recorded as "present", and the case where most of the thermally expandable microcapsules agglomerate is recorded as "strong agglomeration". (1-7) Hopper flowability: Using the container for measuring apparent specific gravity as described in JIS K7370, the obtained thermally expandable microcapsules were placed into the upper part of the hopper, and then allowed to fall under their own weight. The number of seconds it took for the hopper to become empty (when all the thermally expandable microcapsules had fallen) was measured. (2) Evaluation of the foamed body (molded body) (2-1) Appearance (number of dents) The obtained compressed sheet (foaming precursor) was placed on a Teflon (registered trademark) sheet and heated in a 200°C GIL aging oven for 10 minutes to allow the thermally expandable microcapsules to foam. After 10 minutes, it was removed from the GIL aging oven and allowed to cool naturally for at least 30 minutes. The appearance of the foamed body sample after natural cooling was observed, and the number of dents was counted based on the surface irregularities. Furthermore, regarding the foaming precursor obtained in Comparative Example 7, since its density exceeds 1 g / cm³, 3 Therefore, its appearance was not observed. (2-2) Density determination The density of the obtained foam (density after foaming) was determined by means of JIS K-7112 A method (displacement method in water). [Table 2] [Table 3] [Industrial Applicability] According to the present invention, it is possible to provide a thermally expandable microcapsule that can manufacture molded articles with high foaming ratio, light weight and excellent appearance, as well as a foaming resin composition and foam using the thermally expandable microcapsule. none none

Claims

1. A thermally expandable microcapsule, comprising a volatile expanding agent as a core agent encapsulated within a shell made of a polymer, wherein, The aforementioned shell comprises: a polymer formed by polymerizing a monomer composition containing a carbonyl monomer, and silicon dioxide, and the aforementioned thermally expandable microcapsules are left to stand at a temperature of 70°C for 1 hour, during which time the volatile matter content is more than 0.55% by weight and less than 2% by weight.

2. The thermally expandable microcapsules of claim 1 have a volatile content of 20% to 30% by weight when left to stand at 210°C for 20 minutes.

3. For the thermally expandable microcapsules of claim 1 or 2, the ratio of volatile matter at 70°C for 1 hour to volatile matter at 210°C for 20 minutes is less than 8%.

4. The thermally expandable microcapsules of claim 1 or 2, when left to stand for 12 hours at a temperature of 50°C and a humidity of 80% or higher, have a weight gain of less than 60% by weight.

5. The thermally expandable microcapsules of claim 1 or 2 have an average particle size of 10 μm or more and 45 μm or less.

6. For thermally expandable microcapsules as requested in item 1 or 2, the maximum foaming temperature (Tmax) is above 180°C and below 225°C.

7. A foaming resin composition comprising thermally expandable microcapsules and a thermoplastic resin according to any one of claims 1 to 6.

8. A foam body obtained by using the foaming resin composition of claim 7.