Foaming methyl methacrylate resin particles, methyl methacrylate foamed particles, methyl methacrylate foamed molded articles, and lost-wax models.

Abstract

To provide a novel foamable methyl methacrylate resin particle that offers excellent surface aesthetics, fusion properties, and castability, as well as excellent anti-blocking, antistatic, and mold-filling properties. [Solution] Foaming methyl methacrylate resin particles comprising a base resin having methyl methacrylate units as constituent units and a foaming agent, further comprising, on the surface, 0.01 parts by weight or more and 0.10 parts by weight or less of silicone oil, more than 0.40 parts by weight and 0.80 parts by weight or less of fatty acid metal salt, and 0.05 parts by weight or more and 0.55 parts by weight or less of nonionic surfactant per 100 parts by weight of the resin particle body.

Description

Technical Field

[0001] The present invention relates to expandable methyl methacrylate resin particles, methyl methacrylate expanded particles, a methyl methacrylate expanded molded article, and a lost pattern.

Background Art

[0002] A lost pattern casting method (full mold method) is known in which, when performing metal casting, a pattern made of an expanded molded article is embedded in casting sand, and molten metal is poured into the sand to replace the pattern, thereby casting a casting.

[0003] As an expanded molded article used in the full mold method, an expanded molded article obtained by in-mold expansion molding of expandable acrylic resin particles is known. Examples of the expandable acrylic resin particles include expandable acrylic resin particles described in Patent Document 1, which include a particle body containing an acrylic resin and a physical blowing agent, and a coating material that covers the surface of the particle body.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] However, the conventional technology as described above is not sufficient from the viewpoints of (i) anti-blocking property, antistatic property and mold filling property of expandable methyl methacrylate resin particles, and (ii) surface smoothness, fusion property and castability of a methyl methacrylate expanded molded article obtained using the expandable methyl methacrylate resin particles, and there remains room for further improvement.

[0006] One embodiment of the present invention has been made in view of the above-mentioned problems, and its objective is to provide a methyl methacrylate-based foamed molded article that is excellent in surface beauty, fusion properties and castability, and to provide novel foamable methyl methacrylate-based resin particles that are excellent in blocking prevention, antistatic properties and mold filling properties. [Means for solving the problem]

[0007] The inventors diligently studied and investigated the aforementioned problems, and as a result, completed the present invention. In other words, the foamed methyl methacrylate resin particles according to one embodiment of the present invention are foamed methyl methacrylate resin particles comprising a base resin and a foaming agent, wherein the base resin has methyl methacrylate units as constituent units, and the foamed methyl methacrylate resin particles further contain silicone oil, a fatty acid metal salt and a nonionic surfactant on their surface, wherein the content of the silicone oil is 0.01 parts by weight or more and 0.10 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body, the content of the fatty acid metal salt is more than 0.40 parts by weight and 0.80 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body, and the content of the nonionic surfactant is 0.05 parts by weight or more and 0.55 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a methyl methacrylate-based foamed molded article that is excellent in surface beauty, fusion properties and castability, and to provide foamed methyl methacrylate-based resin particles that are excellent in blocking prevention, antistatic properties and mold filling properties. [Modes for carrying out the invention]

[0009] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference.

[0010] In this specification, "X unit" in a polymer, copolymer, or resin means "a constituent unit derived from an X monomer." For example, "methyl methacrylate unit" means "a constituent unit derived from a methyl methacrylate monomer." In this specification, the term "monomer" may be omitted; for example, "X monomer" may be simply written as "X."

[0011] [Technical concept of one embodiment of the present invention] In their investigation of conventional foamed acrylic resin particles as described in Patent Document 1, the present inventors have newly discovered that the frictional resistance of the surface of the foamed acrylic resin particles is high, which can lead to deterioration of antistatic properties and mold filling properties. Furthermore, the present inventors have newly discovered that with conventional foamed acrylic resin particles as described in Patent Document 1, there may be a lot of adhesion between the foamed resin particles and / or among the foamed particles (hereinafter sometimes referred to as "blocking") during the pre-foaming of the foamed resin particles, in other words, the blocking prevention performance may be insufficient. In addition, it is known that the surface beauty, fusion properties, and castability of the molded article are also important for foamed molded articles used in the full-mold casting method.

[0012] Therefore, the present inventors diligently conducted research with the aim of providing foamed methyl methacrylate resin particles that can provide a methyl methacrylate-based foamed molded article with excellent surface beauty, fusion properties, and castability, and that also have excellent blocking prevention, antistatic properties, and mold filling properties. Here, it is known that it is difficult to achieve a good balance between the mold filling properties of foamed acrylic resin particles and the surface beauty and fusion properties of the foamed molded article. On the other hand, it is known that improving these properties in a good balance is important, for example, when manufacturing molded articles with complex shapes.

[0013] However, as a result of diligent research, the present inventors have made it possible to provide a methyl methacrylate-based foamed molded article with excellent surface aesthetics, fusion properties, and castability, as well as foamed methyl methacrylate-based resin particles with excellent anti-blocking properties, antistatic properties, and mold-filling properties, thus completing the present invention.

[0014] [1. Foaming methyl methacrylate resin particles] The foamed methyl methacrylate resin particles according to one embodiment of the present invention are foamed methyl methacrylate resin particles comprising a base resin and a foaming agent, wherein the base resin has methyl methacrylate units as constituent units, and the foamed methyl methacrylate resin particles further contain silicone oil, a fatty acid metal salt, and a nonionic surfactant on their surface, wherein the content of the silicone oil is 0.01 parts by weight or more and 0.10 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body, the content of the fatty acid metal salt is more than 0.40 parts by weight and 0.80 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body, and the content of the nonionic surfactant is 0.05 parts by weight or more and 0.55 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body.

[0015] In this specification, foamed methyl methacrylate resin particles themselves (themselves) that do not contain silicone oil, fatty acid metal salts, nonionic surfactants, and other coating materials described later on their surface are referred to as "foamed methyl methacrylate resin particle bodies" or "resin particle bodies." Also in this specification, foamed methyl methacrylate resin particles that optionally contain silicone oil, fatty acid metal salts, nonionic surfactants, and other coating materials described later on their surface are referred to as "foamed methyl methacrylate resin particles" or "foamed resin particles." Furthermore, in this specification, particles obtained by foaming foamed methyl methacrylate resin particles are referred to as "methyl methacrylate foamed particles" or "foamed particles." In addition, in this specification, "methyl methacrylate foamed molded articles" may also be referred to as "foamed molded articles." Foamed particles can also be said to be manufactured by foaming foamed resin particles to obtain foamed molded articles. Therefore, the foaming of foamed resin particles may be referred to as "pre-foaming," and foamed particles may also be referred to as "pre-foamed particles."

[0016] In this specification, "foaming methyl methacrylate resin particles according to one embodiment of the present invention" may also be referred to as "the foaming resin particles."

[0017] Foamed resin particles can be provided by foaming these foamable resin particles using a known method. Foamed molded articles can be provided by molding these foamed resin particles using a known method (e.g., in-mold molding).

[0018] In this specification, "further comprising silicone oil, fatty acid metal salt, and nonionic surfactant on the surface" means any of the following: (i) the total amount of silicone oil, fatty acid metal salt, and nonionic surfactant contained in the foaming resin particles forms a layer on at least a portion of the surface of the foaming resin particle body; (ii) the total amount of silicone oil, fatty acid metal salt, and nonionic surfactant contained in the foaming resin particles is impregnated into at least a portion of the surface layer of the foaming resin particle body; or (iii) a portion of the total amount of silicone oil, fatty acid metal salt, and nonionic surfactant contained in the foaming resin particles forms a layer on at least a portion of the surface of the foaming resin particle body, and the remaining portion of the total amount of silicone oil, fatty acid metal salt, and nonionic surfactant is impregnated into at least a portion of the surface layer of the foaming resin particle body.

[0019] These foamed resin particles contain a base resin having methyl methacrylate units as constituent units. As a result, foamed molded articles produced from these foamed resin particles have good flammability, are less likely to generate combustion residues such as soot, and can prevent or reduce defects during casting that may occur due to such combustion residues, thus exhibiting excellent castability.

[0020] These foamed resin particles contain a predetermined amount of silicone oil on their surface. The silicone oil coats the surface of the base resin without causing adverse effects such as dissolving the base resin, thereby reducing frictional resistance during filling. This provides functions to improve the blocking prevention and filling properties of the base resin, as well as the surface beauty of the molded product. Therefore, these foamed resin particles offer improved blocking prevention and filling properties, and the foamed molded product obtained using these foamed resin particles exhibits improved surface beauty.

[0021] The expandable resin particles contain a predetermined amount of fatty acid metal salt on the surface. Here, since the fatty acid metal salt covers the surface of the base resin, it functions as an antiblocking agent. Therefore, in the expandable resin particles, by containing a predetermined amount of fatty acid metal salt on the surface, the antiblocking property is further improved. In addition, in the expandable resin particles, the fatty acid metal salt covering the surface of the base resin reduces frictional resistance during filling like silicone oil, and thus has a function of improving filling properties into a mold and the surface appearance of the produced molded article. Therefore, the expandable resin particles have improved filling properties into a mold, and the foam molded article obtained by using the expandable resin particles has improved surface appearance.

[0022] The expandable resin particles contain a predetermined amount of nonionic surfactant on the surface. Here, the nonionic surfactant functions as an antistatic agent because applying the surfactant to the surface of the base resin collects moisture on the surface and prevents the generation of static electricity. Therefore, in the expandable resin particles, by containing a predetermined amount of nonionic surfactant on the surface, the antistatic property is further improved.

[0023] In addition, the nonionic surfactant has lower hydrophilicity compared to other surfactants that can function as an antistatic agent. For this reason, compared with expandable resin particles containing said other surfactants, the expandable resin particles of the present invention make it difficult for moisture to collect on the surface, thereby preventing or reducing stickiness during filling into a mold. Therefore, in the expandable resin particles of the present invention, since said stickiness is prevented or reduced, the filling property into a mold is further improved.

[0024] In the expandable resin particles, the contents of the fatty acid metal salt and the nonionic surfactant are respectively more than 0.40 parts by weight and 0.05 parts by weight or more based on 100 parts by weight of the resin particle body. Through intensive studies, the present inventors have independently found a novel finding that, when the expandable acrylic resin particles contain more of the fatty acid metal salt and the nonionic surfactant compared with the contents of the fatty acid metal salt and the nonionic surfactant in conventional expandable acrylic resin particles that contain the fatty acid metal salt and the nonionic surfactant as coating materials on the surface, the large frictional resistance on the surface of the expandable acrylic resin particles is surprisingly reduced. Therefore, the expandable resin particles of the present invention contain more of the fatty acid metal salt and the nonionic surfactant compared with the contents of the fatty acid metal salt and the nonionic surfactant in conventional expandable acrylic resin particles that contain the fatty acid metal salt and the nonionic surfactant as coating materials on the surface. Accordingly, the expandable resin particles of the present invention prevent or reduce the aforementioned deterioration of antistatic properties and fillability into a mold, thereby further improving the antistatic properties and fillability into a mold.

[0025] Further, in the expandable resin particles, the contents of the fatty acid metal salt and the nonionic surfactant are respectively 0.80 parts by weight or less and 0.55 parts by weight or less based on 100 parts by weight of the resin particle body. Accordingly, in the expandable resin particles of the present invention, the deterioration of the fusion bonding property of a molded article produced due to inhibition of fusion bonding between expanded particles constituting the molded article during molding, which is caused by excessive content of a substance functioning as an antiblocking agent, is prevented or reduced. Therefore, the expandable resin particles of the present invention have improved fusion bonding property of the produced molded article.

[0026] Furthermore, the silicone oil also functions as an adhesive to bond the fatty acid metal salt and the nonionic surfactant to the resin particle body. Therefore, in these foamed resin particles, the decrease in anti-blocking properties and antistatic properties due to the peeling of the fatty acid metal salt and the nonionic surfactant from the resin particle body is prevented or reduced. As a result, the anti-blocking properties and antistatic properties are further improved in these foamed resin particles. In addition, in these foamed resin particles, because the silicone oil also functions as the adhesive, the amount of the fatty acid metal salt and the nonionic surfactant contained on the surface as a coating material is increased, and the surface friction resistance is further reduced. This also further improves the antistatic properties and mold filling properties of these foamed resin particles.

[0027] In addition, when the anti-blocking properties of foamed resin particles are improved, the average particle size of the pre-foamed particles filled into the mold becomes smaller, improving fluidity, and thus improving mold filling performance.

[0028] Based on the above, the foamed resin particles, by further comprising a predetermined amount of silicone oil, a predetermined amount of fatty acid metal salt, and a predetermined amount of nonionic surfactant on their surface, can provide a methyl methacrylate-based foamed molded article with excellent surface beauty, fusion properties, and castability, and also have the advantages of excellent anti-blocking properties, antistatic properties, and mold-filling properties. The configuration of the foamed resin particles, further comprising a predetermined amount of silicone oil, a predetermined amount of fatty acid metal salt, and a predetermined amount of nonionic surfactant on their surface, will hereinafter also be referred to as "Configuration A".

[0029] In this specification, "foamed methyl methacrylate resin particles exhibit excellent blocking prevention properties" means that, when measured using the method described in the (evaluation of blocking prevention properties) section of the examples of this application, the blocking ratio of the foamed methyl methacrylate resin particles is small (for example, 1.0% by weight or less). The smaller the blocking ratio, the better the foamed resin particles exhibit blocking prevention properties. Foamed resin particles with excellent blocking prevention properties prevent or reduce the occurrence of blocking, which is the adhesion between foamed resin particles and / or foamed particles themselves, when manufacturing foamed particles using the foamed resin particles. Therefore, foamed resin particles with excellent blocking prevention properties prevent or reduce the decrease in productivity and / or the decrease in the surface beauty of the manufactured foamed molded articles, which are caused by the aforementioned blocking. Consequently, foamed resin particles with excellent blocking prevention properties have the advantage of efficiently providing foamed molded articles with excellent surface beauty.

[0030] In this specification, "foamed methyl methacrylate resin particles exhibit excellent antistatic properties" means that, when measured by the method described in the (evaluation of antistatic properties) section of the examples of this application, the amount of charge is low (for example, 1.0 kV or less). The lower the amount of charge, the better the antistatic properties of the foamed resin particles. Foamed particles obtained by foaming foamed resin particles with excellent antistatic properties are less likely to become charged when filled into a mold, and can therefore be easily filled into every corner of the mold. As a result, foamed particles obtained by foaming foamed resin particles with excellent antistatic properties have fewer gaps, a smooth surface, and have the advantage of easily providing a foamed molded article with excellent surface beauty.

[0031] In this specification, "the foamed methyl methacrylate resin particles have excellent fillability into the mold" means that when a methyl methacrylate foamed molded article is produced using foamed methyl methacrylate resin particles by the method described in the present embodiment, the resulting methyl methacrylate foamed molded article satisfies the following conditions. A methyl methacrylate-based foamed molded article that has no filling defects as measured by the method described in the section (evaluation of filling properties into the mold) of the embodiment of this application. Foamed resin particles with excellent mold-filling properties mean that the foamed particles obtained through foaming have excellent mold-filling properties. When foamed resin particles with excellent mold-filling properties are used in in-mold molding to manufacture foamed molded articles, the foamed resin particles can be filled into the mold in a short time. Therefore, foamed resin particles with excellent mold-filling properties have the advantage of reducing the manufacturing time when producing foamed particles, improving productivity, and efficiently providing foamed molded articles. Furthermore, foamed resin particles with excellent mold-filling properties can be filled into the mold more uniformly in the in-mold molding process. As a result, foamed resin particles with excellent mold-filling properties can improve the accuracy of the film thickness of the manufactured foamed molded article, eliminate or reduce surface irregularities, and improve surface aesthetics. Therefore, foamed resin particles with excellent mold-filling properties also have the advantage of providing foamed molded articles with superior surface aesthetics.

[0032] In this specification, "a methyl methacrylate-based foamed molded article with excellent surface aesthetics can be provided" means that when a methyl methacrylate-based foamed molded article is produced using foamable methyl methacrylate-based resin particles by the method described in the examples of this application, the resulting methyl methacrylate-based foamed molded article satisfies the following conditions. A methyl methacrylate-based foamed molded article having a high score (for example, 4.00 points or higher) representing the degree of gaps between foam particles constituting the molded article, as measured by the method described in the section (evaluation of surface aesthetics) of the embodiments of this application, and exhibiting very good filling properties. The larger the score representing the degree of gaps between the foam particles, the better the surface aesthetics of the foamed molded article produced from the foamed resin particles. A molded article with excellent surface aesthetics means a molded article with few gaps and a smooth surface. When casting is performed using a molded article with excellent surface aesthetics, the occurrence of irregularities on the casting surface caused by the gaps in the molded article is prevented or reduced, and as a result, a casting with no or few irregularities on the surface, i.e., a casting with excellent surface aesthetics, can be cast. Therefore, foamed methyl methacrylate resin particles that can provide a molded article with excellent surface aesthetics have the advantage of being usable as a raw material for producing castings with excellent surface aesthetics by metal casting methods such as the full-mold method.

[0033] In this specification, "a methyl methacrylate-based foamed molded article with excellent fusion properties can be provided" means that when a methyl methacrylate-based foamed molded article is produced using foamable methyl methacrylate-based resin particles by the method described in the examples of this application, the resulting methyl methacrylate-based foamed molded article satisfies the following conditions. A methyl methacrylate-based foamed molded article having a high fusion rate (unit: %), which is the ratio of foamed particles that fracture outside the particle interface to all particles constituting the fracture surface formed by fracturing the molded article, as measured by the method described in the section (evaluation of fusion properties) of the embodiments of this application (for example, greater than 50%). The greater the aforementioned fusion rate, the better the fusion rate of the foamed molded article from which the foamed resin particles are produced. A molded article with excellent fusion properties means a molded article in which the gaps between the foamed particles constituting the molded article are small and the article has a smooth surface. When casting is performed using a molded article with excellent fusion properties, the occurrence of irregularities on the casting surface caused by these gaps is prevented or reduced, and as a result, it is possible to cast a casting with no or minimal irregularities on the surface, i.e., a casting with excellent surface aesthetics. Therefore, foamed methyl methacrylate resin particles that can provide a molded article with excellent fusion properties have the advantage of being usable as a raw material for the production of castings with excellent surface aesthetics by metal casting methods such as the full-mold method.

[0034] In this specification, "providing a methyl methacrylate-based foamed molded article with excellent castability" refers to foamed methyl methacrylate-based resin particles that do not leave soot when thermally decomposed by the method described in the (evaluation of castability) section of the examples of this application. When metal casting such as the full-mold method is carried out using the foamed methyl methacrylate-based resin particles that can provide a molded article with excellent castability, the molded article is thermally decomposed without leaving soot and replaced with molten metal. Therefore, no soot remains in the manufactured casting, and deterioration of quality such as poor appearance of the casting caused by the presence of soot is prevented. Thus, foamed methyl methacrylate-based resin particles that can provide a molded article with excellent castability have the advantage of being usable as a raw material for manufacturing castings with excellent quality, such as appearance, by metal casting such as the full-mold method.

[0035] In summary, these foamed resin particles have the advantage of providing molded articles with excellent anti-blocking properties, antistatic properties, and mold-filling properties, as well as excellent surface aesthetics, fusion properties, and castability. Furthermore, these foamed resin particles have the advantage of being usable as a raw material for manufacturing castings with superior surface aesthetics and appearance quality through metal casting methods such as the full-mold method.

[0036] (1-1. Base resin) The base resin contained in these foamed resin particles has methyl methacrylate units as constituent units.

[0037] In one embodiment of the present invention, the content of methyl methacrylate units in the base resin is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 97% by weight or more, of 100% by weight of the base resin, from the viewpoint of providing a molded article with superior castability. Alternatively, the content of methyl methacrylate units in the base resin may be 100% by weight, i.e., the base resin may consist only of methyl methacrylate units. Furthermore, from the viewpoint of the foaming properties of foamed resin particles during foam particle production and the moldability of foamed particles during molded article production, the content of methyl methacrylate units in the base resin is preferably 99% by weight or less, and more preferably 98% by weight or less, of 100% by weight of the base resin.

[0038] In one embodiment of the present invention, the base resin may further contain constituent units other than methyl methacrylate units. In this specification, "constituent units other than methyl methacrylate units" may be referred to as "other constituent units." The content of the other constituent units in the base resin is not particularly limited as long as it does not impair the effects of the present invention, and may be, for example, more than 0% by weight or 2% by weight or more, and 5% by weight or less or 10% by weight or less, per 100% by weight of the base resin.

[0039] Other constituent units include, but are not limited to, (i) constituent units derived from styrene monomers (i.e., styrene units), and (ii) constituent units derived from (meth)acrylic acid monomers other than methyl methacrylate. Examples of styrene monomers include styrene, α-methylstyrene, p-methylstyrene, t-butylstyrene, and chlorostyrene. In this specification, "(meth)acrylic acid" means methacrylic acid and / or acrylic acid. Examples of (meth)acrylic acid monomers other than methyl methacrylate include methacrylic acid, acrylic acid, methacrylic acid esters other than methyl methacrylate, and acrylic acid esters.

[0040] In one embodiment of the present invention, the other constituent units are not particularly limited, and for example, it is preferable to include one or more selected from the group consisting of styrene units, methacrylate ester units other than methyl methacrylate units, and acrylic acid ester units; it is more preferable to include one or more selected from the group consisting of butyl acrylate units, ethyl acrylate units, propyl acrylate units, 2-ethylhexyl acrylate units, isobornyl acrylate units, and dicyclopentanyl acrylate units; it is more preferable to include one or more selected from the group consisting of butyl acrylate units, ethyl acrylate units, propyl acrylate units, and 2-ethylhexyl acrylate units; it is even more preferable to include one or more selected from the group consisting of butyl acrylate units, ethyl acrylate units, and propyl acrylate units; and it is particularly preferable to include butyl acrylate units. When the base resin further contains butyl acrylate units as the other constituent units, the foamed resin particles have the advantages of being easy to manufacture, having excellent foaming properties, and having excellent moldability.

[0041] In one embodiment of the present invention, if the base resin further contains butyl acrylate units as other constituent units, the content thereof is preferably 2% by weight or more, more preferably 2.5% by weight or more, of 100% by weight of the base resin, from the viewpoint of lowering the softening point of the resin. Furthermore, the content of butyl acrylate units in the base resin is preferably 4% by weight or less, more preferably 3% by weight or less, of 100% by weight of the base resin, from the viewpoint of preventing shrinkage during foaming and molding.

[0042] In one embodiment of the present invention, the total content of methyl methacrylate units and butyl acrylate units in the base resin is preferably 80% by weight or more, more preferably 90% by weight or more, and even more preferably 95% by weight or more, of 100% by weight of the base resin, from the viewpoint of providing a molded article with superior castability. The total content of methyl methacrylate units and butyl acrylate units in the base resin may be 100% by weight of 100% of the base resin. That is, the base resin may consist only of methyl methacrylate units and butyl acrylate units.

[0043] In one embodiment of the present invention, the base resin may be, for example, a base resin composed of methyl methacrylate units and butyl acrylate units. For example, the base resin may be a base resin in which the content of methyl methacrylate units is 97% by weight or more and 99% by weight or less, and the content of butyl acrylate units is 1% by weight or more and 3% by weight or less, per 100% by weight of the base resin. More specifically, the base resin may be a base resin in which the content of methyl methacrylate units is 97% by weight and the content of butyl acrylate units is 3% by weight, per 100% by weight of the base resin. Alternatively, the base resin may be a base resin in which the content of methyl methacrylate units is 99% by weight and the content of butyl acrylate units is 1% by weight, per 100% by weight of the base resin.

[0044] In one embodiment of the present invention, the base resin may contain constituent units derived from aromatic monomers (hereinafter also referred to as aromatic units) as constituent units. Examples of aromatic monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. When the base resin contains aromatic units, a foamed molded article with excellent strength can be obtained.

[0045] On the other hand, from the viewpoint of obtaining a foamed molded article with less residue during combustion, it is preferable that the amount of constituent units derived from aromatic monomers (e.g., monomers having aromatic rings) and constituent units having a ring structure (e.g., constituent units derived from alicyclic compounds, hereinafter also referred to as ring structure units) contained in the base resin be as small as possible. For example, the total amount of aromatic units and ring structure units contained in the base resin may be 2.5% by weight or less per 100% by weight of the base resin, preferably less than 2.5% by weight, more preferably 2.0% by weight or less, more preferably 1.5% by weight or less, even more preferably 1.0% by weight or less, even more preferably 0.5% by weight or less, and particularly preferably 0% by weight. In other words, it is particularly preferable that the base resin does not contain aromatic units or ring structure units. Here, "total amount of aromatic units and cyclic structural units contained in the base resin" means: (a) if the base resin contains aromatic units but does not contain cyclic structural units, it means the amount of aromatic units; (b) if the base resin contains cyclic structural units but does not contain aromatic units, it means the amount of cyclic structural units; and (c) if the base resin contains both aromatic units and cyclic structural units, it means the total amount of aromatic units and cyclic structural units.

[0046] In one embodiment of the present invention, it is preferable that the base resin contains styrene units as other constituent units, from the viewpoint of reducing surface frictional resistance and improving antistatic properties and mold filling properties. On the other hand, even if the base resin does not contain styrene units, the foamable resin particles can still achieve the above effects. Therefore, one embodiment of the present invention is effective when used when a base resin that does not contain styrene units is used as the base resin. Examples of base resins that do not contain styrene units include a base resin consisting only of methyl methacrylate units, and a base resin consisting of methyl methacrylate units and other constituent units other than styrene units, such as butyl acrylate.

[0047] In one embodiment of the present invention, the weight-average molecular weight of the base resin is preferably greater than 300,000, more preferably 320,000 or more, even more preferably 340,000 or more, and particularly preferably 350,000 or more. Alternatively, the weight-average molecular weight of the base resin is preferably 450,000 or less, more preferably 400,000 or less, even more preferably 380,000 or less, and particularly preferably 360,000 or less. By having the weight-average molecular weight of the base resin within the above range, the foamable resin particles have the advantage of being able to suitably provide a foamed molded article that is excellent in foaming properties and has excellent surface beauty and fusion properties over a wide range of molding pressures. The method for measuring the weight-average molecular weight of the base resin is not particularly limited, and known methods can be used, for example, the method described in the section (weight-average molecular weight, number-average molecular weight, molecular weight distribution of base resin) of the examples of this application.

[0048] In one embodiment of the present invention, the molecular weight distribution of the base resin is preferably 4 or more, more preferably 4.3 or more, even more preferably 4.5 or more, and particularly preferably 5 or more. Furthermore, the molecular weight distribution of the base resin is preferably 6 or less, more preferably 5.8 or less, even more preferably 5.6 or less, and particularly preferably 5.5 or less. In this specification, "molecular weight distribution" is a value expressed as the ratio of weight-average molecular weight to number-average molecular weight. By having the molecular weight distribution of the base resin within the aforementioned range, the foamable resin particles have the advantage of providing a foamed molded article with excellent foaming properties and excellent surface beauty and fusion properties over a wide range of molding pressures. The molecular weight distribution of the base resin can be calculated by measuring the weight-average molecular weight and number-average molecular weight of the base resin and using the measured values ​​of the weight-average molecular weight and number-average molecular weight. The method for measuring the weight-average molecular weight and number-average molecular weight of the base resin is not particularly limited, and known methods can be employed; for example, the method described in the section (Weight-average molecular weight, number-average molecular weight, molecular weight distribution of base resin) of the examples of this application can be cited.

[0049] (1-2. Covering material) The foamed resin particles contain silicone oil, a fatty acid metal salt, and a nonionic surfactant on their surface. The content of the silicone oil is 0.01 parts by weight or more and 0.10 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body. Furthermore, the content of the fatty acid metal salt is more than 0.40 parts by weight and 0.80 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body. In addition, the content of the nonionic surfactant is 0.05 parts by weight or more and 0.55 parts by weight or less per 100 parts by weight of the foamed methyl methacrylate resin particle body.

[0050] The silicone oil, fatty acid metal salts, and nonionic surfactants contained on the surface of foamed resin particles can be said to "coat" the foamed resin particles, and are therefore sometimes referred to as "coating materials."

[0051] (1-2-1. Silicone oil) In this specification, "silicone oil" refers to a compound having organopolysiloxane units. The silicone oil is not particularly limited, and examples include methylphenyl silicone oil, dimethyl silicone oil, methylhydrogen silicone oil, cyclic silicone oil, branched silicone oil, etc. The silicone oil may be used as a single compound or as a combination of two or more compounds. The methylphenyl silicone oil is the same compound as the compound referred to as methylphenyl silicone. The dimethyl silicone oil is the same compound as the compound referred to as dimethyl silicone. The methylhydrogen silicone oil is the same compound as the compound referred to as methylhydrogen silicone.

[0052] From the viewpoint of uniformly coating the base resin and stably exhibiting a friction reduction effect during filling, the silicone oil preferably (i) contains a compound that is liquid at room temperature, and may consist only of compounds that are liquid at room temperature, and (ii) is more preferably one or more selected from the group consisting of methylphenyl silicone oil and dimethyl silicone oil, and may consist only of one or more selected from this group. Both methylphenyl silicone oil and dimethyl silicone oil are liquid at room temperature (for example, 25°C). Furthermore, from the viewpoint of further improving the antistatic properties of the foamed resin particles and the fusion properties of the molded article produced, the silicone oil preferably is a silicone oil with low polarity, and more preferably a nonpolar silicone oil. From this viewpoint, the silicone oil is more preferably methylphenyl silicone oil, and particularly preferably consists only of methylphenyl silicone oil.

[0053] The foamed resin particles contain at least 0.01 parts by weight of the silicone oil on their surface, per 100 parts by weight of the resin particle body. This configuration improves the fillability of the foamed resin particles in the mold, the ability to prevent blocking, and the surface beauty of the molded articles produced. From the viewpoint of further improving these properties, it is preferable that the foamed resin particles contain at least 0.03 parts by weight of the silicone oil on their surface, and more preferably 0.05 parts by weight or more, per 100 parts by weight of the resin particle body.

[0054] The foamed resin particles contain 0.10 parts by weight or less of the silicone oil on their surface, per 100 parts by weight of the resin particle body. This configuration prevents a decrease in filling performance due to the foamed particles, formed when the foamed resin particles are foamed, peeling off the mold during in-mold foaming, thereby improving the filling performance of the foamed resin particles into the mold. Furthermore, this configuration minimizes the effect of silicone oil application to the surface of the base resin on fusion inhibition during molding, thus preventing a decrease in the fusion properties and surface aesthetics of the manufactured molded article, and as a result, a molded article with improved fusion properties and surface aesthetics can be provided. From the viewpoint of further improving these properties, it is preferable that the foamed resin particles contain 0.08 parts by weight or less of the silicone oil on their surface, and more preferably 0.06 parts by weight or less, per 100 parts by weight of the resin particle body.

[0055] (1-2-2. Fatty Acid Metal Salts) The fatty acid metal salt is not particularly limited. Examples of the fatty acid metal salt include metal salts of fatty acids in which the number of carbon atoms in the alkyl group is preferably 12 or more and 20 or less, more preferably 16 or more and 18 or less. Specific examples of the fatty acid metal salt include, for example, the compounds listed in (a) to (c) below. (a) Metal stearate salts such as zinc stearate, calcium stearate, magnesium stearate, and aluminum stearate; (b) Metal oleate salts such as zinc oleate and magnesium oleate; and (c) Metal laurate salts such as zinc laurate and calcium laurate.

[0056] Among the specific examples of fatty acid metal salts listed above, it is preferable that the fatty acid metal salt includes stearate metal salt because it exhibits superior affinity with the resin particle body and the base resin, and has a melting point suitable for coating. It may also consist solely of stearate metal salt. Furthermore, from the viewpoint of improving the blocking prevention effect during foaming and the effect of preventing inhibition of foam particle (bead) fusion during molding, it is more preferable that the fatty acid metal salt includes one or more selected from the group consisting of zinc stearate and magnesium stearate. It may also consist solely of one or more selected from this group. Moreover, in terms of not inhibiting the fusion of foam particles during molding, it is even more preferable that the fatty acid metal salt includes zinc stearate. Furthermore, in terms of improving the moldability of the foamable resin particles, it is even more preferable that the fatty acid metal salt includes zinc stearate. It may also consist solely of zinc stearate. The fatty acid metal salt may be used individually or in combination of two or more types.

[0057] The foamed resin particles contain more than 0.40 parts by weight of the fatty acid metal salt on their surface, per 100 parts by weight of the resin particle body. This configuration further improves the anti-blocking properties and mold-fillability of the foamed resin particles. From the viewpoint of further improving these properties, it is preferable that the foamed resin particles contain 0.45 parts by weight or more, and more preferably 0.50 parts by weight or more, of the fatty acid metal salt on their surface, per 100 parts by weight of the resin particle body.

[0058] The foamed resin particles contain the fatty acid metal salt on their surface in an amount of 0.80 parts by weight or less per 100 parts by weight of the resin particle body. With this configuration, the foamed resin particles can provide a molded article with improved fusion properties. From the viewpoint of providing a molded article with even better fusion properties, it is preferable that the foamed resin particles contain the fatty acid metal salt on their surface in an amount of 0.70 parts by weight or less per 100 parts by weight of the resin particle body, and more preferably 0.60 parts by weight or less.

[0059] (1-2-3. Nonionic surfactants) The nonionic surfactant is not particularly limited, and examples include glycerin fatty acid esters; sorbitan fatty acid esters; sucrose fatty acid esters; polyoxyethylene fatty acid esters such as polyoxyethylene alkyl ethers and polyoxyethylene alkylphenyl ethers; and polyoxyethylene polyoxypropylene glycol. Examples of glycerin fatty acid esters include fatty acid monoglycerides, fatty acid diglycerides, and fatty acid triglycerides. Examples of fatty acid monoglycerides include lauric acid monoglyceride, stearate monoglyceride (glycerin monostearate), and linoleic acid monoglyceride. The nonionic surfactant may be used individually or in combination of two or more types.

[0060] From the viewpoint of melting point and balance between lipophilicity and hydrophilicity, the nonionic surfactant preferably (i) contains a glycerin fatty acid ester, and may consist only of a glycerin fatty acid ester; (ii) more preferably contains a fatty acid monoglyceride, and may consist only of a fatty acid monoglyceride; and (iii) more preferably contains stearate monoglyceride (glycerin monostearate), and may consist only of stearate monoglyceride (glycerin monostearate).

[0061] The foamed resin particles contain at least 0.05 parts by weight of the nonionic surfactant on their surface, per 100 parts by weight of the resin particle body. This configuration further improves the antistatic properties and mold-fillability of the foamed resin particles. From the viewpoint of further improving these properties, it is preferable that the foamed resin particles contain at least 0.10 parts by weight of the nonionic surfactant on their surface, more preferably 0.15 parts by weight or more, and even more preferably 0.20 parts by weight or more, per 100 parts by weight of the resin particle body.

[0062] The foamed resin particles contain the nonionic surfactant on their surface in an amount of 0.55 parts by weight or less per 100 parts by weight of the resin particle body. With this configuration, the foamed resin particles can provide a molded article with improved fusion properties. From the viewpoint of providing a molded article with even better fusion properties, it is preferable that the foamed resin particles contain the nonionic surfactant on their surface in an amount of 0.50 parts by weight or less, more preferably 0.40 parts by weight or less, and even more preferably 0.30 parts by weight or less, per 100 parts by weight of the resin particle body.

[0063] (1-2-4. Other covering materials) The foamed resin particles may further contain, in addition to the silicone oil, fatty acid metal salt, and nonionic surfactant, other coating materials on their surface, to the extent that they do not impair the effects of the present invention. The other coating materials may be known coating materials that can be contained on the surface of the foamed resin particles. Examples of the other coating materials include fusion accelerators, antistatic agents, and water repellents. Nonionic surfactants are generally known to function as fusion accelerators and / or antistatic agents. However, in this specification, "fusion accelerator" means a substance other than the nonionic surfactant that functions as a fusion accelerator, and "antistatic agent" means a substance other than the nonionic surfactant that functions as an antistatic agent.

[0064] When these foamed resin particles further contain a fusion accelerator on their surface, they have the advantage of ensuring fusion properties during molding when producing a foamed molded product from these foamed resin particles.

[0065] Examples of the aforementioned fusion accelerators include vegetable oil-derived components such as olive oil and hydrogenated castor oil. These fusion accelerators may be used individually or in combination of two or more types.

[0066] If the foamed resin particles further contain an antistatic agent on their surface, there is the advantage that static electricity can be prevented or reduced during the transport of the foamed resin particles and the foamed particles described later, and that the foamed particles described later can be prevented or reduced from adhering to silos.

[0067] The aforementioned antistatic agents include commonly used N-hydroxyethyl-N-(2-hydroxytetradecyl)amine, N-hydroxyethyl-N-(2-hydroxyhexadecyl)amine, and N-hydroxyethyl-N-(2-hydroxyoctadecyl)amine, N-hydroxyethyl-N-(2-hydroxyalkyl)amines, (ii) N,N-bis(hydroxyethyl)dodecylamine, N,N-bis(hydroxyethyl)tetradecylamine, N,N-bis(hydroxyethyl)hexadecylamine, N,N-bis(hydroxyethyl)octadecylamine, and N-hydroxypropyl-N-(2-hydroxytetradecyl Examples include (iii) hydroxyl compounds such as (ii)amine, N-hydroxybutyl-N-(2-hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxyhexadecyl)amine, N-hydroxypentyl-N-(2-hydroxyoctadecyl)amine, N,N-bis(2-hydroxyethyl)dodecylamine, N,N-bis(2-hydroxyethyl)tetradecylamine, N,N-bis(2-hydroxyethyl)hexadecylamine and N,N-bis(2-hydroxyethyl)octadecylamine, and (iii) glycerin. These antistatic agents may be used individually or in combination of two or more. N-hydroxyethyl-N-(2-hydroxyalkyl)amine is particularly preferred as an antistatic agent because it provides the best antistatic performance.

[0068] In the method for producing the foamed resin particles described later, the silicone oil, the fatty acid metal salt, the nonionic surfactant, and the other coating materials are used in the step of incorporating the silicone oil, etc., into the surface of the resin particle body. The total amount of the silicone oil, the fatty acid metal salt, the nonionic surfactant, and the other coating materials used in the step of incorporating the silicone oil, etc., into the surface of the resin particle body may be contained on the surface of the foamed resin particles produced. Therefore, the content of the silicone oil on the surface of the foamed resin particles can be said to be the amount of the silicone oil used in the step of incorporating the silicone oil, etc., into the surface of the resin particle body. Similarly, the content of the fatty acid metal salt on the surface of the foamed resin particles can be said to be the amount of the fatty acid metal salt used in the step of incorporating the silicone oil, etc., into the surface of the resin particle body. Similarly, the content of the nonionic surfactant on the surface of the foamed resin particles can be said to be the amount of the nonionic surfactant used in the step of incorporating the silicone oil, etc., into the surface of the resin particle body. Similarly, the amount of the other coating material on the surface of the foamed resin particles can be said to be the amount of the other coating material used in the process of incorporating the silicone oil, etc., onto the surface of the resin particle body.

[0069] (1-3. Foaming agent) The type of blowing agent contained in these foamed resin particles is not particularly limited. Examples of blowing agents include (a) aliphatic hydrocarbons having 3 to 5 carbon atoms, such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentane, and (b) volatile blowing agents such as hydrofluorocarbons with zero ozone depletion potential, such as difluoroethane and tetrafluoroethane. These blowing agents may be used individually or in combination of two or more.

[0070] From the viewpoint of enabling the manufacturing process of foamed resin particles to be carried out easily and at low cost, enabling the foaming temperature to be controlled within a suitable range, and reducing the environmental burden, the foaming agent preferably contains (i) one or more selected from the group consisting of aliphatic hydrocarbons and hydrofluorocarbons having an ozone depletion potential of zero, and may consist only of one or more selected from the said group; (ii) more preferably contains one or more selected from the group consisting of propane, isobutane, n-butane, difluoroethane and tetrafluoroethane, and may consist only of one or more selected from the said group; (iii) still more preferably contains one or more selected from the group consisting of propane, isobutane and n-butane, and may consist only of one or more selected from the said group; (iv) particularly preferably contains one or more selected from the group consisting of isobutane and n-butane, and may consist only of one or more selected from the said group; and (v) most preferably contains isobutane and n-butane, and may consist only of isobutane and n-butane.

[0071] In these foamed resin particles, the content of the foaming agent is not particularly limited, but is preferably 5 parts by weight or more and 12 parts by weight or less, and more preferably 7 parts by weight or more and 10 parts by weight or less, per 100 parts by weight of the base resin. This configuration has the advantage of providing foamed resin particles with sufficient foaming properties and eliminating the need for heavy polymerization equipment.

[0072] (1-4. Foaming agents) In addition to the components described above and other additives described later, these foaming resin particles may further contain foaming aids. The foaming aid is not particularly limited, and any foaming aid that can be contained in the foaming resin particles can be used. Examples of the foaming aid include solvents with a boiling point of 50°C or higher and less than 100°C, specifically (i) aliphatic hydrocarbons having 6 or more carbon atoms (C6 or higher) such as hexane and heptane, and (ii) alicyclic hydrocarbons with 6 or more carbon atoms such as cyclohexane and cyclooctane. These foaming aids may be used individually or in combination of two or more. Cyclohexane is preferred as a foaming aid because it has good foaming power.

[0073] In these foamed resin particles, the content of the foaming aid is not particularly limited, but is preferably 0.2 parts by weight or more and 5.0 parts by weight or less, more preferably 0.5 parts by weight or more and 4.0 parts by weight or less, even more preferably 1.0 part by weight or more and 3.0 parts by weight or less, and particularly preferably 1.5 parts by weight or more and 2.5 parts by weight or less, per 100 parts by weight of the base resin. This configuration has the advantage of providing sufficient foaming power while preventing or reducing the expansion of the surface of the foamed resin particles when foaming them.

[0074] (1-5. Other Additives) The resin particle body may contain other additives different from the coating material, in addition to the base resin and foaming agent. The content of the other additives is not particularly limited, as long as it does not impair the effects of the present invention. The other additives may be known additives that can be contained in foamed resin particles. Examples of the other additives include solvents, plasticizers, foam regulators, nucleating agents, flame retardants, and flame retardant aids. The other additives may be contained in parts other than the surface of the foamed resin particle, i.e., inside the resin particle body, such as inside the base resin. In this specification, the inside of the resin particle body means the area inside the position where the silicone oil, fatty acid metal salt, and nonionic surfactant are present (arranged) in the foamed resin particle, i.e., the side in the direction of the base resin.

[0075] The content of the other additives is not particularly limited as long as it does not impair the effects of the present invention. For example, it may be less than 4.0 parts by weight, preferably less than 3.0 parts by weight, and more preferably less than 2.0 parts by weight, per 100 parts by weight of the resin particles.

[0076] The solvent preferably has a boiling point of 50°C or higher. Specific examples of solvents include, for example, (a) aliphatic hydrocarbons having 6 or more carbon atoms, such as toluene, hexane, and heptane; and (b) alicyclic hydrocarbons having 6 or more carbon atoms, such as cyclohexane and cyclooctane. These solvents may be used individually or in combination of two or more.

[0077] The aforementioned plasticizer is added (used) when preparing the base resin in the method for producing the foamed resin particles (during polymerization). The plasticizer is preferably a compound commonly used as a plasticizer, having a boiling point of 200°C or higher. One type may be used, or two or more types may be used in combination.

[0078] Specific examples of the foam regulator include, for example, (a) aliphatic bisamides such as methylene bisstearate amide and ethylene bisstearate amide; and (b) polyethylene wax. These foam regulators may be used individually or in combination of two or more.

[0079] Specific examples of the nucleating agent include, for example, methyl methacrylate copolymers, polyethylene wax, talc, fatty acid bisamides, and ethylene-vinyl acetate copolymers. Specific examples of fatty acid bisamides include, for example, methylene bisstearyl amide, ethylene bisstearyl amide, hexamethylene bispalmitate amide, and ethylene bisoleate amide. These nucleating agents may be used individually or in combination of two or more.

[0080] Specific examples of the aforementioned flame retardants include, for example, (a) halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; (b) brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; (c) tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), and tetrabromobisphenol A-diglyceride. Examples include sidyl ethers, brominated phenol derivatives such as 2,2-bis[4'-(2",3”-dibromoalkoxy)-3',5'-dibromophenyl]-propane; and (d) brominated butadiene-vinyl aromatic hydrocarbon copolymers such as brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers (for example, EMERALD3000 manufactured by Chemtura, or copolymers described in Japanese Patent Publication No. 2009-516019). Other known flame retardants besides those mentioned above can also be used as the flame retardant. These flame retardants may be used individually or in combination of two or more.

[0081] Specific examples of the aforementioned flame retardant include, for example, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, and 2,3-dimethyl-2,3-diphenylbutane. Other known flame retardants not mentioned above can also be used as the aforementioned flame retardant. These flame retardants may be used individually or in combination of two or more.

[0082] In the method for producing the foamed resin particles described later, the other additives are used in the step of preparing the base resin and / or the step of preparing the resin particle body. The entire amount of the other additives used in the step of preparing the base resin and / or the step of preparing the resin particle body may be contained in the foamed resin particles produced. Therefore, the content of the other additives in the foamed resin particles can also be said to be the amount of the other additives used in the step of preparing the base resin and / or the step of preparing the resin particle body in the method for producing the foamed resin particles.

[0083] (1-6. Physical properties of this foamed resin particle) <Weight average molecular weight> The weight-average molecular weight of the foamed resin particles is preferably greater than 300,000, more preferably 320,000 or more, even more preferably 340,000 or more, and particularly preferably 350,000 or more. Alternatively, the weight-average molecular weight of the foamed resin particles is preferably 450,000 or less, more preferably 400,000 or less, even more preferably 380,000 or less, and particularly preferably 360,000 or less. By having a weight-average molecular weight within the aforementioned range, the foamed resin particles have the advantage of being able to suitably provide molded articles with excellent surface aesthetics and fusion properties. The method for measuring the weight-average molecular weight of the foamed resin particles is not particularly limited, and known methods can be employed.

[0084] <Molecular weight distribution> The molecular weight distribution of the foamed resin particles is preferably 4 or higher, more preferably 4.3 or higher, even more preferably 4.5 or higher, and particularly preferably 5 or higher. Furthermore, the molecular weight distribution of the foamed resin particles is preferably 6 or lower, more preferably 5.8 or lower, even more preferably 5.6 or lower, and particularly preferably 5.5 or lower. The foamed resin particles have the advantage of being able to suitably provide molded articles with excellent surface beauty and fusion properties due to their molecular weight distribution being within the aforementioned range. The molecular weight distribution of the foamed resin particles can be calculated by measuring the weight-average molecular weight and number-average molecular weight of the foamed resin particles and using the measured values ​​of the weight-average molecular weight and number-average molecular weight. The method for measuring the weight-average molecular weight and number-average molecular weight of the foamed resin particles is not particularly limited, and known methods can be employed.

[0085] <Particle size> The particle size of the foamed resin particles is not particularly limited. However, when foamed resin particles are filled into a mold of a complex shape, foamed, and molded to produce a molded article of a complex shape, it is preferable that the particle size of the foamed resin particles be small. On the other hand, it is known that when the particle size of foamed resin particles is small, the foamed resin particles do not expand easily even when foamed, and as a result, the surface beauty of the molded article produced tends to deteriorate. However, as mentioned above, the surface beauty of the molded article produced by these foamed resin particles is improved, so even when the particle size is small, it is possible to provide a molded article with excellent surface beauty. Therefore, one embodiment of the present invention is effective when foamed resin particles with a small particle size are foamed and molded in a mold of a complex shape to produce a molded article of a complex shape. The small particle size of these foamed resin particles means, for example, that the upper limit of the volume average particle size of these foamed resin particles is 0.65 mm or less, preferably 0.60 mm or less, and more preferably 0.55 mm or less. Furthermore, the lower limit of the volume-average particle diameter of the foamed resin particles is not particularly limited, and may be 0.35 mm or more, preferably 0.40 mm or more, and more preferably 0.45 mm or more. The method for measuring the volume-average particle diameter is not particularly limited, and known methods can be employed, for example, the methods shown below. This method involves using an image processing-type Millitrack JPA particle size analyzer to measure the particle size of foamed resin particles based on volume at 0.005 mm intervals, displaying the obtained results as a cumulative distribution, and defining the particle size at which the volume cumulative distribution reaches 50% as the volume-average particle size.

[0086] (1-7. Method for producing foamed resin particles) The method for producing these foamed resin particles is not particularly limited and can employ known methods for producing foamed methyl methacrylate resin particles. For example, the method for producing these foamed resin particles may include a step of preparing a base resin, a step of preparing the resin particle body, and a step of incorporating silicone oil or the like onto the surface of the resin particle body.

[0087] (1-7-1. Process for preparing the base resin) In the step of preparing the base resin in the method for manufacturing the foamed resin particles, the method of preparing the base resin is not particularly limited, as long as it can prepare the base resin that constitutes the foamed resin particles. Examples of methods for preparing the base resin include purchasing a commercially available resin corresponding to the base resin, and preparing the base resin. Therefore, in one example, the step of preparing the base resin may be the step of preparing the base resin.

[0088] The process for preparing the base resin can be carried out using known methods and is not particularly limited. For example, the process for preparing the base resin can be a step of polymerizing monomer components in the presence of a radical polymerization initiator, a chain transfer agent, and a crosslinking agent.

[0089] One example of the polymerization method used in the polymerization step of the monomer component is suspension polymerization, which is carried out in an aqueous suspension. Furthermore, since a radical polymerization initiator is used in the polymerization step of the monomer component, the polymerization in the polymerization step may be radical polymerization.

[0090] The term "aqueous suspension" refers to a state in which droplets containing monomer components and / or polymers are dispersed in water or an aqueous medium by stirring or other means. The droplets may further contain a radical polymerization initiator, a chain transfer agent, and a crosslinking agent. The aqueous suspension may also contain further dissolved water-soluble surfactants and / or monomers, and may also contain water-insoluble, poorly water-soluble inorganic salts, as well as other additives such as foam regulators, flame retardants, and plasticizers.

[0091] <Monomer components> The monomer component contains methyl methacrylate. The monomer component may also contain other monomers besides methyl methacrylate. The polymer obtained by polymerizing the monomer component is the base resin in the foamed resin particles obtained by the manufacturing method. Therefore, the composition of the monomers contained in the monomer component may be the same as the composition of the constituent units of the base resin described in section (1-1. Base Resin). Preferred embodiments for the constituent units of the base resin described in section (1-1. Base Resin) can also be considered preferred embodiments for the monomers contained in the monomer component. Specifically, the types of monomers contained in the monomer component may be the same as the types of monomers from which the constituent units of the base resin described in section (1-1. Base Resin) originate. The monomers from which the preferred constituent units of the base resin described in section (1-1. Base Resin) originate can also be considered preferred monomers for the monomers contained in the monomer component. The content of each monomer contained in the monomer component may be the same as the content of each constituent unit of the base resin described in section (Base Resin). The preferred content of each constituent unit in the base resin described in the above section (Base Resin) can also be said to be a preferred content for each monomer contained in the monomer component.

[0092] Specifically, the monomer component includes methyl methacrylate, and the other monomer may optionally include the same monomer as the monomer from which the other constituent units described in section (1-1. Base Resin) originate. Furthermore, it is preferable that the monomer component includes butyl acrylate as the other monomer in addition to methyl methacrylate.

[0093] <Chain movement agent> The chain transfer agent is not particularly limited, and for example, one or more chain transfer agents selected from chain transfer agents having a mercaptan structure and chain transfer agents not having a mercaptan structure can be used. Specific examples of chain transfer agents having a mercaptan structure include alkyl mercaptans and phenyl mercaptans. Examples of alkyl mercaptans include n-dodecyl mercaptan (also known as 1-dodecanethiol) and t-dodecyl mercaptan. Specific examples of chain transfer agents not having a mercaptan structure include methylstyrene dimer (also known as 2,4-diphenyl-4-methyl-1-pentene) and tetrachloromethane.

[0094] The amount of the chain transfer agent used may be 0.05 parts by weight or more and 0.5 parts by weight or less per 100 parts by weight of monomer component, preferably 0.1 parts by weight or more and 0.4 parts by weight or less, and more preferably 0.2 parts by weight or more and 0.3 parts by weight or less.

[0095] (Radical polymerization initiator) The radical polymerization initiator used in the polymerization process is not particularly limited, and any radical-generating polymerization initiator commonly used in the production of thermoplastic polymers can be used.

[0096] In this specification, a "radical polymerization initiator with a 1-hour half-life temperature of 85°C or higher and less than 100°C" may be referred to as "radical polymerization initiator (X)" or "initiator (X)," and a "radical polymerization initiator with a 1-hour half-life temperature of 100°C or higher" may be referred to as "radical polymerization initiator (Y)" or "initiator (Y)."

[0097] Examples of radical polymerization initiators (X) include benzoyl peroxide and t-butylperoxy-2-ethylhexanoate. These radical polymerization initiators (X) may be used individually or in combination of two or more.

[0098] Examples of radical polymerization initiators (Y) include t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-di(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, and t-butylperoxy-2-ethylhexyl monocarbonate. These radical polymerization initiators (Y) may be used individually or in combination of two or more.

[0099] Examples of radical polymerization initiators other than initiators (X) and (Y) include (i) organic peroxides with a half-life temperature of less than 85°C, such as dilauroyl peroxide (half-life temperature of 79.5°C), and (ii) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These radical polymerization initiators other than initiators (X) and (Y) may be used individually or in combination of two or more.

[0100] In the polymerization process, it is preferable to use initiator (X) as a radical polymerization initiator. This configuration has the advantage that the polymerization reaction can proceed at a polymerization temperature that makes it easy to adjust the polymerization rate and molecular weight. In the polymerization process, initiator (X) may be used in combination with radical polymerization initiators other than initiator (X) and initiator (Y).

[0101] In the polymerization process, initiator (X) and initiator (Y) may be used in combination as radical polymerization initiators. In the polymerization process, the polymerization reaction may be carried out by initiator (X) at the start of polymerization, and initiator (Y) may be added to the reaction system after the polymerization reaction has progressed to a certain extent. For example, after carrying out the main polymerization reaction (until the monomer residue is less than 10%) with initiator (X), initiator (Y) can be used to increase the polymerization temperature and reduce the monomer residue. Note that the step of increasing the polymerization temperature and reducing the monomer residue may be carried out simultaneously with the impregnation of the foaming agent. Initiators (X) and (Y) may both be present in the aqueous suspension at the start of polymerization or in the early stages of polymerization. For example, initiator (Y) may be added to the aqueous suspension together with initiator (X) at the start of polymerization or in the early stages of polymerization. By setting the polymerization temperature relatively low during the initial or first half of polymerization and relatively high during the final or second half of polymerization, even if both initiator (X) and initiator (Y) are present in the aqueous suspension at the initial stage of polymerization, the polymerization reaction will proceed mainly by initiator (X) at the start of polymerization, and initiator (Y) can be applied after the polymerization reaction has progressed to a certain extent. In the polymerization process, initiator (X), initiator (Y), and radical polymerization initiators other than initiator (X) and initiator (Y) may be used in combination.

[0102] The amount of initiator (X) used in the polymerization process, for example, initiator (X) that decomposes in the main polymerization reaction, will be described. The amount used is not particularly limited, but for example, it is preferably 0.02 parts by weight or more and 0.50 parts by weight or less, more preferably 0.02 parts by weight or more and 0.45 parts by weight or less, more preferably 0.03 parts by weight or more and 0.40 parts by weight or less, more preferably 0.03 parts by weight or more and 0.30 parts by weight or less, even more preferably 0.05 parts by weight or more and 0.20 parts by weight or less, and particularly preferably 0.05 parts by weight or more and 0.15 parts by weight or less, per 100 parts by weight of monomer component. This configuration has the advantage that a large amount of radicals are generated during the polymerization reaction, and as a result, it is easy to obtain a polymer (base resin) that contains a relatively large amount of low molecular weight polymers.

[0103] The amount of initiator (Y) used in the polymerization process, for example, an initiator (Y) that mainly decomposes after the main polymerization reaction is completed and the reaction system is heated to a high temperature for the reduction of residual monomers and impregnation with a blowing agent, will be described. The amount used is not particularly limited, but for example, it is preferably 0.03 parts by weight or more and 0.30 parts by weight or less, more preferably 0.04 parts by weight or more and 0.20 parts by weight or less, even more preferably 0.05 parts by weight or more and 0.15 parts by weight or less, and particularly preferably 0.07 parts by weight or more and 0.13 parts by weight or less, per 100 parts by weight of monomer components. This configuration has the advantage of making it easy to efficiently reduce residual monomers in the blowing agent impregnation process.

[0104] When initiator (X) is used as a radical polymerization initiator in the polymerization process, the amount of initiator (X) used is preferably more than 50% by weight, more preferably 60% by weight or more, even more preferably 65% ​​by weight or more, and particularly preferably 65% ​​by weight or more and less than 80% by weight, based on 100% by weight of the total amount of radical polymerization initiators used in the polymerization process. In the polymerization process, initiator (X) alone may be used as the radical polymerization initiator.

[0105] <Crosslinking agent> Examples of crosslinking agents include compounds having two or more radical-reactive functional groups. Examples of radical-reactive functional groups include vinyl groups. Examples of crosslinking agents include compounds having two or more vinyl groups. When a crosslinking agent is used in the polymerization process, it has the advantage of being able to obtain foamed resin particles that do not shrink easily due to heat during molding, i.e., foamed particles with excellent heat resistance. It is more preferable to use a bifunctional monomer having two vinyl groups as a crosslinking agent in order to further enjoy these advantages.

[0106] Examples of bifunctional monomers having two vinyl groups include (a) compounds obtained by esterifying both terminal hydroxyl groups of ethylene glycol or an oligomer of ethylene glycol with (meth)acrylic acid (e.g., ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, etc.), (b) compounds obtained by esterifying the hydroxyl group of a dihydric alcohol with (meth)acrylic acid (e.g., neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate (e.g., 1,6-hexanediol diacrylate, etc.), butanediol di(meth)acrylate, etc.), and (c) aryl compounds having two alkenyl groups (e.g., divinylbenzene, etc.). In this specification, "(meth)acrylate" means methacrylate and / or acrylate.

[0107] Hexanediol di(meth)acrylates make it easy to adjust the molecular weight of the base resin. Therefore, in the polymerization process, it is particularly preferable to use hexanediol di(meth)acrylates such as 1,6-hexanediol diacrylate as a crosslinking agent.

[0108] The amount of the crosslinking agent used may be 0 parts by weight or more and 0.2 parts by weight or less, preferably 0.05 parts by weight or more and 0.18 parts by weight or less, and more preferably 0.10 parts by weight or more and 0.15 parts by weight or less, per 100 parts by weight of monomer component.

[0109] <Poorly water-soluble inorganic salts> In the process of preparing the base resin, a poorly water-soluble inorganic salt may be used. The poorly water-soluble inorganic salt can function as a dispersant. In the process of preparing the base resin, for example, monomer components, a radical polymerization initiator, a chain transfer agent, and a crosslinking agent may be added to a mixture containing water and a poorly water-soluble inorganic salt to initiate the polymerization reaction of the monomer components.

[0110] Examples of poorly water-soluble inorganic salts include tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin.

[0111] In the process of preparing the base resin, the poorly water-soluble inorganic salt and a water-soluble polymer and / or an anionic surfactant may be used in combination. Examples of the water-soluble polymer include polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone. Examples of the anionic surfactant include sodium α-olefin sulfonate and sodium dodecylbenzenesulfonate.

[0112] The volume-average particle size of the resulting foamed resin particles can be adjusted by the type and amount of poorly water-soluble inorganic salt used at the start of polymerization, as well as the type and amount of poorly water-soluble inorganic salt added to the aqueous suspension during polymerization.

[0113] In the process of preparing the base resin, polymerization of the monomer component is started using an aqueous suspension containing a poorly water-soluble inorganic salt, and then the poorly water-soluble inorganic salt may be further added to the aqueous suspension during polymerization.

[0114] When using the aforementioned poorly water-soluble inorganic salt, the amount used may be 0.1 parts by weight or more and 1.0 part by weight or less, preferably 0.3 parts by weight or more and 0.9 parts by weight or less, and more preferably 0.5 parts by weight or more and 0.8 parts by weight or less, per 100 parts by weight of monomer component.

[0115] <Other additives> In the process of preparing the base resin, other additives described in section (1-5. Other Additives) may be used. The timing of using the other additives is not particularly limited; for example, the other additives may be added to the monomer components before or during polymerization, and / or to the base resin obtained after polymerization. The method of adding the other additives to the monomer components and / or base resin is not particularly limited, and known methods may be employed. The other additives added to the monomer components before or during polymerization may mainly be present inside the base resin.

[0116] The amount of the aforementioned other additives used can be the same as the amount of the aforementioned other additives described in section (1-5. Other Additives).

[0117] <Polymerization conditions: polymerization temperature and polymerization time> In the process of preparing the base resin, the temperature at which the monomer components are polymerized is sometimes referred to as the polymerization temperature. The polymerization temperature is not particularly limited, as long as it is a temperature at which the monomer components can be polymerized to prepare the base resin. From the viewpoint of adjusting the polymerization rate and molecular weight, the polymerization temperature may be, for example, 70°C or higher and 95°C or lower, preferably 75°C or higher and 90°C or lower, and more preferably 80°C or higher and 85°C or lower.

[0118] In the process of preparing the base resin, the "time during which polymerization of the monomer components is carried out" is sometimes referred to as the "polymerization time." The polymerization time is not particularly limited, as long as it is sufficient time to carry out the polymerization of the monomer components and prepare the base resin. From the viewpoint of polymerization stability and control of the particle size of the resulting foamed resin particles, the polymerization time may be, for example, 2.5 hours or more and 6.0 hours or less, preferably 3.0 hours or more and 5.0 hours or less, and more preferably 3.5 hours or more and 4.5 hours or less.

[0119] By adjusting at least one of the conditions listed above—the radical polymerization initiator, the polymerization temperature, and the chain transfer agent—to the aforementioned preferred range, a base resin can be prepared having a weight-average molecular weight greater than 300,000 and 450,000 or less, and / or a molecular weight distribution of 4 or more and 6 or less.

[0120] (1-7-2. Process for preparing the resin particle body) The process of preparing the resin particle body is not particularly limited, as long as it involves mixing the base resin and the foaming agent to prepare the resin particle body. Examples of methods for mixing the base resin and the foaming agent include the methods shown in (A) and (B) below. (A) A method of preparing the resin particle body by adding water, a base resin, and a foaming agent to a container to prepare an aqueous suspension, and impregnating the base resin with the foaming agent in the aqueous suspension. (B) A method for preparing the resin particle body by adding a foaming agent to an aqueous suspension containing the base resin obtained in the step of preparing the base resin using suspension polymerization, thereby impregnating the base resin with the foaming agent in the aqueous suspension.

[0121] The foaming agent can be the same as the foaming agent described in section (1-3. Foaming Agent). The amount of foaming agent used can be the same as the amount of foaming agent described in section (1-3. Foaming Agent).

[0122] In the method for producing foamed resin particles, a foaming aid may be used further. When a foaming aid is used, it is preferable to use it together with the foaming agent. Specifically, for example, when step (A) is adopted, it is preferable to add the foaming aid together with the foaming agent to the container, and when step (B) is adopted, it is preferable to add the foaming aid together with the foaming agent to the aqueous suspension.

[0123] The foaming agent can be the same as the foaming agent described in section (1-4. Foaming Agents). The amount of foaming agent used can be the same as the amount of foaming agent described in section (1-4. Foaming Agents).

[0124] In both of the above steps (A) and (B), the temperature at which the foaming agent is impregnated into the base resin in the aqueous suspension may be referred to as the "impregnation temperature." The impregnation temperature is not particularly limited and should be any temperature at which the foaming agent can impregnate the base resin. From the viewpoint of improving the impregnation rate of the foaming agent and achieving a suitable pressure rise in the polymerizer, the impregnation temperature may be, for example, 95°C or higher and 120°C or lower, preferably 100°C or higher and 115°C or lower, and more preferably 100°C or higher and 110°C or lower.

[0125] In both of the above steps (A) and (B), the "time during which the foaming agent is impregnated into the base resin in an aqueous suspension" may be referred to as the "impregnation time." The impregnation time is not particularly limited and should be any time that allows the foaming agent to be impregnated into the base resin. In order to impregnate the foaming agent into the interior of the polymer (resin particles) and to sufficiently reduce the monomers with the initiator (Y), the impregnation time may be, for example, 8 hours or more and 15 hours or less, preferably 9 hours or more and 13 hours or less, and more preferably 10 hours or more and 12 hours or less.

[0126] (1-7-3. Step of incorporating silicone oil, etc., into the surface of the resin particle body) In the step of incorporating the silicone oil, etc., into the surface of the resin particle body, the surface of the resin particle body is made to contain the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials. Known methods can be used as the method for incorporating the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials into the surface of the resin particle body, and are not particularly limited. For example, one such method is to put the resin particle body, the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials into a mixing device and mix them. This method allows the surface of the resin particle body to contain the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials. The types and amounts of the silicone oil, the fatty acid metal salt, the nonionic surfactant, and other coating materials used can be the same as the types and amounts of the silicone oil, fatty acid metal salt, and nonionic surfactant and other coating materials described in section (1-2. Coating Materials).

[0127] The method of introducing the resin particle body, the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials into the mixing device is not particularly limited. For example, the resin particle body, the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials may all be introduced into the mixing device at once. Alternatively, the resin particle body, the silicone oil, the fatty acid metal salt, the nonionic surfactant, and optionally other coating materials may be introduced into the mixing device first and mixed, and then the remainder may be introduced into the mixing device and mixed further.

[0128] Here, the silicone oil also functions as an adhesive to bond the fatty acid metal salt and the nonionic surfactant to the surface of the resin particle body. Therefore, from the viewpoint of suitably incorporating the silicone oil, the fatty acid metal salt, and the nonionic surfactant onto the surface of the resin particle body, it is preferable to adopt a method that includes the following steps (1) and (2). (1) A step of putting the resin particle body, the silicone oil and, if necessary, other coating material into a mixing device and mixing the resin particle body, the silicone oil and, if necessary, the other coating material. In this step, a resin particle body with at least the silicone oil coated on its surface is obtained. (2) After step (1), the step of adding the fatty acid metal salt and nonionic surfactant, and other coating materials as necessary, to the mixing apparatus and mixing the resin particle body on which at least the silicone oil is coated on its surface with the fatty acid metal salt and nonionic surfactant, and other coating materials as necessary. In this step, a resin particle body is obtained on which at least the fatty acid metal salt and nonionic surfactant are further coated on the surface of the resin particle body on which at least the silicone oil is coated, i.e., the foamable resin particle.

[0129] Furthermore, the appropriate timing for adding other coating materials to the mixing equipment, for example, whether to add them in step (1) or step (2), can be selected according to the type and function of the other coating materials. When using a coating material that is liquid at room temperature as the other coating material, it is preferable to add the coating material to the mixing equipment together with the silicone oil in step (1). In this case, in step (1), resin particle bodies coated with silicone oil and the coating material that is liquid at room temperature can be obtained. When using a coating material that is solid at room temperature as the other coating material, it is preferable to add the coating material to the mixing equipment together with the fatty acid metal salt and nonionic surfactant in step (2).

[0130] The mixing apparatus is not particularly limited, and any known mixing apparatus capable of uniformly mixing the base resin, the silicone oil, the fatty acid metal salt, and the nonionic surfactant, as well as optionally other coating materials, can be used. Examples of the mixing apparatus include mixers and blenders. Specific examples of mixers include Super Mixer, Nauta Mixer, Universal Mixer, ProSher Mixer, Apex Mixer, Henschel Mixer, and Redigee Mixer. Specific examples of blenders include ribbon blenders and tumbler-type blenders.

[0131] The conditions such as the mixing time in the mixing apparatus may be adjusted by considering (a) the mixing capacity; and (b) the ratio of the content of the silicone oil, the fatty acid metal salt, and the nonionic surfactant, and optionally other coating materials, to the content of the base resin; etc. The mixing time may be, for example, 30 seconds or more and 300 seconds or less. Furthermore, when carrying out steps (1) and (2), the mixing time for step (1) may be, for example, 30 seconds or more and 120 seconds or less, and the mixing time for step (2) may be, for example, 30 seconds or more and 180 seconds or less.

[0132] [2. Methyl methacrylate-based foaming particles] The methyl methacrylate-based foamed particles according to one embodiment of the present invention are obtained by foaming the foamable resin particles. Hereinafter, the methyl methacrylate-based foamed particles according to one embodiment of the present invention will also be referred to as "the foamed particles."

[0133] Since these foamed particles are formed by foaming these foamable resin particles, they have the advantage of efficiently providing molded articles with excellent surface aesthetics, fusion properties, and castability.

[0134] The method for producing these foamed particles, or in other words, the method for foaming these foamable resin particles, is not particularly limited and any known method can be used. For example, the foamed resin particles can be placed in a container equipped with a stirrer and heated with a heat source such as steam to foam them to a desired foaming ratio.

[0135] [3. Methyl methacrylate-based foamed molded product] A methyl methacrylate-based foamed molded article according to one embodiment of the present invention is formed by molding the foamed particles. Hereinafter, the methyl methacrylate-based foamed molded article according to one embodiment of the present invention will also be referred to as "the foamed molded article".

[0136] This foamed molded product has the advantage of being able to be efficiently supplied and having excellent surface beauty, fusion properties, and castability, as it is made by molding foamed particles which are formed by foaming foamed resin particles. Furthermore, this foamed molded product has the advantage of being able to provide castings with excellent surface beauty and appearance quality when cast using metal casting methods such as the full-mold method.

[0137] The method for manufacturing this foamed molded article, or in other words, the method for molding the foamed particles, is not particularly limited and any known method can be used. For example, the foamed particles can be filled into a mold that can be closed but not airtight, and the foamed particles can be heated and fused together with steam to form the foamed molded article.

[0138] By burying this foamed molded body in casting sand and pouring molten metal into it to replace it, a casting can be made. In other words, this foamed molded body can be suitably used as a lost-wax model when performing metal casting using the full-mold method.

[0139] [4. Vanishing model] A lost-wax model according to one embodiment of the present invention includes the foamed molded body. Hereinafter, the lost-wax model according to one embodiment of the present invention will also be referred to as "the lost-wax model."

[0140] This lost-wax model, because it includes this foamed molded body, has the advantage of being excellent in surface beauty, fusion properties, and castability, and can be provided efficiently. Furthermore, this lost-wax model also has the advantage of being able to produce castings with excellent surface beauty and appearance quality through metal casting using methods such as the full-mold method.

[0141] This lost-wax model may consist solely of this foam molded body. In other words, this lost-wax model may be this foam molded body used as a lost-wax model. This lost-wax model may include components other than this foam molded body. These components other than this foam molded body may be known components and are not particularly limited; for example, one or more components selected from the group consisting of adhesives and mold coatings can be cited.

[0142] The method for manufacturing the lost-wax model is not particularly limited and may include, for example, a step of preparing the foam molded body by the method for manufacturing the foam molded body described above, and optionally a step of adding a member other than the foam molded body to the foam molded body. In the step of adding a member other than the foam molded body to the foam molded body, the method of adding the member other than the foam molded body to the foam molded body is not particularly limited and a known method can be used.

[0143] Similar to this foamed molded body, this lost-wax model can be embedded in casting sand, and molten metal can be poured in to replace it and cast a product. In other words, this lost-wax model can be suitably used as a lost-wax model when performing metal casting using the full-mold method.

[0144] One embodiment of the present invention may have the following configuration. [1] Foaming methyl methacrylate resin particles containing a base resin and a foaming agent, The aforementioned base resin has methyl methacrylate units as constituent units, The foaming methyl methacrylate resin particles further contain a silicone oil, a fatty acid metal salt, and a nonionic surfactant on their surface. The content of the silicone oil is 0.01 parts by weight or more and 0.10 parts by weight or less per 100 parts by weight of the foaming methyl methacrylate resin particle body. The content of the fatty acid metal salt is greater than 0.40 parts by weight and less than or equal to 0.80 parts by weight per 100 parts by weight of the foaming methyl methacrylate resin particle body. The foaming methyl methacrylate resin particles have a nonionic surfactant content of 0.05 parts by weight or more and 0.55 parts by weight or less per 100 parts by weight of the foaming methyl methacrylate resin particle body. [2] The foaming methyl methacrylate resin particles according to [1], wherein the base resin further comprises butyl acrylate units as constituent units. [3] Foaming methyl methacrylate resin particles according to [1] or [2], wherein the weight-average molecular weight of the base resin is greater than 300,000 and 450,000 or less. [4] Foaming methyl methacrylate resin particles according to any one of [1] to [3], wherein the molecular weight distribution of the base resin is 4 or more and 6 or less. [5] Foaming methyl methacrylate resin particles according to any one of [1] to [4], wherein the silicone oil is one or more selected from the group consisting of methylphenyl silicone oil and dimethyl silicone oil. [6] The foaming methyl methacrylate resin particle according to any one of [1] to [5], wherein the fatty acid metal salt is one or more selected from the group consisting of zinc stearate and magnesium stearate. [7] The expandable methyl methacrylate resin particle according to any one of [1] to [6], wherein the nonionic surfactant comprises a fatty acid monoglyceride. [8] Expanded methyl methacrylate particles obtained by expanding the expandable methyl methacrylate resin particles according to any one of [1] to [7]. [9] An expanded molded article obtained by molding the expanded methyl methacrylate particles according to [8].

[10] A lost foam comprising the expanded methyl methacrylate molded article according to [9]. Examples

[0145] Hereinafter, one embodiment of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0146] [Measurement Method and Evaluation Method] >(Weight Average Molecular Weight, Number Average Molecular Weight, Molecular Weight Distribution of Base Resin) The weight average molecular weight, number average molecular weight, and molecular weight distribution obtained by measurement according to the following method were taken as the weight average molecular weight, number average molecular weight, and molecular weight distribution of the base resin contained in the expandable resin particles: (1) 0.02 g of the expandable resin particles was dissolved in 20 mL of tetrahydrofuran (hereinafter sometimes abbreviated as "THF"); (2) Thereafter, gel components in the obtained solution were filtered; (3) Next, using only the component soluble in THF (i.e., the filtrate) as a sample, GPC measurement was performed under the following conditions using gel permeation chromatography (GPC); (4) The weight average molecular weight (Mw), number average molecular weight (Mn), and molecular weight distribution (Mw / Mn) were calculated from the GPC measurement chart obtained by GPC measurement. Note that the weight average molecular weight (Mw) and number average molecular weight (Mn) are relative values in terms of polystyrene. <GPC Measurement Conditions> Measurement device: High-speed GPC device HLC-8220, manufactured by Tosoh Corporation Columns used: 2 columns of SuperHZM-H, 2 columns of SuperH-RC, manufactured by Tosoh Corporation Column temperature: 40°C, Mobile phase: THF (tetrahydrofuran) Flow rate: 0.35ml / min, injection volume: 10μl Detector: RI.

[0147] (Evaluation of blocking prevention) <Preparation of foaming particles> Using foamed methyl methacrylate resin particles, the following operations (1) to (3) were performed in order to obtain foamed methyl methacrylate resin particles with a bulk ratio of 50: (1) 940g of foamed methyl methacrylate resin particles were placed into a pressurized foaming machine, the BHP110, manufactured by Daikai Kogyo Co., Ltd.; (2) Steam was blown into the foaming machine under conditions of a steam blowing pressure of 0.30 MPa or more and 0.35 MPa or less, and a foaming machine internal pressure of 0.030 MPa or more and 0.040 MPa or less, thereby heating the foamed methyl methacrylate resin particles; (3) The foamed methyl methacrylate resin particles were foamed according to (2) until the bulk ratio reached 50, thereby obtaining foamed methyl methacrylate resin particles with a bulk ratio of 50.

[0148] <Evaluation of blocking prevention properties> The weight of the obtained methyl methacrylate foam particles was measured and defined as the "amount of resin added." Next, the methyl methacrylate foam particles were placed on a 3 mm mesh sieve, and the foam particles remaining on the sieve were defined as "blocked foam particles," and their weight was measured. Using the measured weights of the "amount of resin added" and the "blocked foam particles," the blocking ratio (weight %) was calculated based on the following formula. Blocking ratio (weight %) = (Weight of blocked foam particles (g) / Amount of resin added (g)) × 100 The blocking properties of the foamed methyl methacrylate resin particles were evaluated based on the obtained blocking ratio and the <Indicators of Blocking Prevention Properties> described below. <Indicators of Blocking Prevention> A (Excellent): Blocking ratio (by weight) is 0.1% by weight or less. B (Good): Blocking ratio (by weight) is greater than 0.1% by weight and less than or equal to 0.3% by weight. C (Fairly Good): Blocking ratio (by weight) is greater than 0.3% by weight and less than or equal to 1.0% by weight. D (Defective): Blocking ratio (by weight) exceeds 1.0% by weight Furthermore, foamed resin particles were considered to have excellent blocking properties if their blocking resistance was rated "A," "B," or "C" according to the aforementioned blocking resistance index.

[0149] (Evaluation of antistatic properties) Foaming methyl methacrylate resin particles were spread in a metal tray to a thickness of 2 cm to 3 cm, and the amount of charge of the foaming methyl methacrylate resin particles was measured using an electrostatic measuring instrument (Statilon DZ4 model, manufactured by Shishido Electrostatics).

[0150] The antistatic properties of the foamed methyl methacrylate resin particles were evaluated based on the obtained charge amount and the <antistatic properties index> described below. <Indicators of antistatic properties> A (Excellent): Charge level is 0.1kV or less B (Good): Charge level greater than 0.1kV and less than or equal to 0.3kV C (Fairly Good): Charge level greater than 0.3kV and less than or equal to 1.0kV D (Defective): Charge level exceeds 1.0kV Furthermore, foamed resin particles were considered to have excellent antistatic properties if their antistatic properties were rated "A," "B," or "C" according to the aforementioned antistatic properties index.

[0151] (Evaluation of filling properties within the mold) <Preparation of foaming particles> Methyl methacrylate-based foaming particles with a bulk ratio of 50 times were prepared by the same method as described in the section on "Preparation of foaming particles" in (Evaluation of blocking resistance).

[0152] <Preparation of foamed molded products> Using the prepared methyl methacrylate foam particles, the following operations (1) to (4) were performed in order to obtain a methyl methacrylate foam molded article: (1) Methyl methacrylate foam particles with a bulk ratio of 50 times were left at room temperature (25°C) for 3 days; (2) Methyl methacrylate foam particles with a bulk ratio of 50 times were filled into a flat mold measuring 450 mm in length, 300 mm in width, and 10 mm in thickness, mounted on a molding machine (DAISEN KR-57); (3) Steam injection pressure 0 (4) After the foaming pressure reached 0.10 MPa or higher and 0.180 MPa or lower, steam was blown into the mold, and under conditions where the pressure inside the mold was 0.030 MPa or higher and 0.100 MPa or lower, in-mold molding by steam heating was performed until the foaming pressure reached 0.100 MPa or higher and 0.180 MPa or lower, fusing the methyl methacrylate foam particles together.

[0153] <Evaluation of filling properties within the mold> The resulting methyl methacrylate-based foamed molded product was visually inspected for areas with poor filling, and the fillability of the foamed methyl methacrylate-based resin particles into the mold was evaluated based on the following <Indicators for Fillability into Molds>: <Indicators of mold filling ability> Good: No areas with filling defects. Defect: There are areas with poor filling.

[0154] Furthermore, "poorly filled areas" refer to areas where foam particles are not filled at the edges of the flat plate, or areas where the foam particles are not uniformly filled to the edges, resulting in excessive foaming and particles at the edges being significantly larger than those in the center of the molded body. In addition, foamed resin particles were considered to have excellent mold filling properties when the fillability into the mold was rated as "good" according to the <Indicator of Fillability into Mold> mentioned above.

[0155] (Evaluation of surface aesthetics) <Preparation of foaming particles> Methyl methacrylate-based foaming particles with a bulk ratio of 50 times were prepared by the same method as described in the section on "Preparation of foaming particles" in (Evaluation of blocking resistance).

[0156] <Preparation of foamed molded products> Using the prepared methyl methacrylate foam particles, the following operations (1) to (4) were performed in order to obtain a methyl methacrylate foam molded body: (1) Methyl methacrylate foam particles with a bulk ratio of 50 times were left at room temperature (25°C) for 3 days; (2) Methyl methacrylate foam particles with a bulk ratio of 50 times were filled into a box-shaped mold with a bottom thickness of 30 mm, a side thickness of 25 mm, a length of 550 mm, a width of 350 mm, and a height of 120 mm, mounted on a molding machine (DAISEN KR-57); (3) Steam blow (4) After the foaming pressure reached 0.100 MPa or higher and 0.180 MPa or lower, steam was blown into the mold at a filling pressure of 0.30 MPa or higher and 0.50 MPa or lower, and in-mold molding by steam heating was performed under conditions where the pressure inside the mold was 0.050 MPa or higher and 0.080 MPa or lower, until the foaming pressure reached 0.100 MPa or higher and 0.180 MPa or lower, thereby fusing the methyl methacrylate foam particles together.

[0157] <Evaluation of surface aesthetics> The surface of the methyl methacrylate foam molded body removed from the mold was visually observed, and its surface beauty was evaluated based on the following <Surface Beauty Index>. The "gaps between foam particles" in the <Surface Beauty Index> refers to the degree of gaps between the methyl methacrylate foam particles constituting the methyl methacrylate foam molded body. Specifically, the degree of gaps is expressed as a score ranging from 0 (gaps between particles are not filled at all) to 5 (gaps between particles are completely filled) in increments of 0.25 points. Furthermore, the "filling" in the <Surface Beauty Index> refers to the uniformity of the foam particles constituting the molded body. Uniform particle size indicates "very good filling," while insufficient filling to the edges, with excessive foaming and uneven particle size at the edges, indicates "poor filling." Note that the mold used for (evaluation of surface aesthetics) differs in size and shape from the mold used for (evaluation of mold filling), and is more easily filled with methyl methacrylate foam particles. Therefore, the evaluation results of filling in (evaluation of surface aesthetics) may differ from the evaluation results of filling in (evaluation of mold filling) above. <Indicators of surface aesthetics> A (Excellent): The gaps between foam particles are 4.50 points or higher, and the filling performance is excellent. B (Good): The gaps between foam particles are 4.25 or higher and less than 4.50, and the filling performance is very good. C (Fairly Good): The gaps between foam particles are 4.00 or higher and less than 4.25, and the filling performance is very good. D (Poor): The gaps between foam particles are less than 4.00 points, or the filling performance is poor.

[0158] Furthermore, if the surface beauty of the molded article is "A," "B," or "C" according to the surface beauty index, the molded article is considered to have excellent surface beauty, and the foamed resin particles are considered to be able to provide a molded article with excellent surface beauty.

[0159] (Evaluation of fusion properties) <Preparation of foamed molded products> A methyl methacrylate-based foamed molded article was obtained by the same method as described in the sections on <Preparation of foamed particles> and <Preparation of foamed molded article> of (Evaluation of surface aesthetics).

[0160] <Evaluation of fusion properties> The obtained methyl methacrylate foam molded material was left at room temperature (25°C) for 24 hours. Afterward, the fracture surface obtained by rupturing the methyl methacrylate foam molded material was visually observed, and all particles constituting the fracture surface, as well as foam particles that fractured outside of the particle interfaces, were measured. Based on the measurement results, the fusion rate (%) was calculated using the following formula. Fusion rate (%) = (Number of particles fractured outside the particle interface on the fracture surface / Total number of particles constituting the fracture surface) × 100 The fusion properties of the methyl methacrylate-based foamed molded article were evaluated based on the calculated fusion rate and the following <Fusion Properties Index>. <Indicators of fusion properties> A (Excellent): Fusion rate exceeds 90% B (Good): Fusion rate is between 70% and 90%. C (Fairly Good): Fusion rate is between 50% and 70%. D (Defective): Fusion rate is 50% or less Furthermore, when the fusion properties of the molded article are "A," "B," or "C" according to the fusion rate index, the molded article is considered to have excellent fusion properties, and the foamed resin particles are considered to be able to provide a molded article with excellent fusion properties.

[0161] (Evaluation of castability) Using foamed methyl methacrylate resin particles, the following operations (1) to (3) were performed in order to thermally decompose the foamed methyl methacrylate resin and evaluate its castability: (1) 5 g of foamed methyl methacrylate resin particles were heated in a 150°C oven for 30 minutes to remove the foaming agent contained inside the foamed methyl methacrylate resin particles; (2) The foamed methyl methacrylate resin particles from which the foaming agent had been removed in (1) were placed in a crucible and heated in an electric furnace at a rate of 15°C / min to 400°C, and held at 400°C for 60 minutes to decompose the resin; (3) After heating was complete, the crucible was allowed to cool.

[0162] The cooled crucible was visually inspected, and the castability of the molded article produced from foamed methyl methacrylate resin particles was evaluated based on the following <castability index>: <Indicators of castability> Good: No soot remains. Defective: Soot remains.

[0163] Furthermore, when the castability is rated as "good" according to the above-mentioned <castability index>, the foamed resin particles were considered to be capable of providing a molded article with excellent castability.

[0164] [Example 1] (Process of preparing the base resin) In a 6L autoclave equipped with a stirrer, 150 parts by weight of water, 0.46 parts by weight of tricalcium phosphate as the first poorly water-soluble inorganic salt, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide, 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as the first poorly water-soluble inorganic salt, 0.13 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, 0.300 parts by weight of n-dodecyl mercaptan, and 0.024 parts by weight of Sumisorb were charged to prepare a mixture containing the first poorly water-soluble inorganic salt. Subsequently, 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate were added to the mixture as a monomer mixture, and then 1.0 part by weight of toluene was added to prepare an aqueous suspension. Next, the temperature of the aqueous suspension was raised to 80°C to start polymerization. The point at which the temperature of the aqueous suspension reached 80°C was defined as the "start of polymerization". After 1 hour and 45 minutes from the start of polymerization, the polymerization conversion rate was measured to be between 40% and 50%. After 1 hour and 45 minutes from the start of polymerization, 0.12 parts by weight of tricalcium phosphate was added to the reaction mixture (aqueous suspension) as a second poorly water-soluble inorganic salt. Furthermore, the polymerization reaction was continued until 4 hours and 20 minutes had elapsed from the start of polymerization, that is, until 2 hours and 35 minutes had elapsed from the time the second poorly water-soluble inorganic salt was added. A polymer (base resin) was obtained by this procedure.

[0165] (Process for preparing the resin particle body) Subsequently, 2 hours and 35 minutes after the addition of the second poorly water-soluble inorganic salt, 1.5 parts by weight of cyclohexane as a foaming aid and 9 parts by weight of n-rich butane as a foaming agent were added to the aqueous suspension. The weight ratio of n-butane to isobutane (n-butane / isobutane) in the n-rich butane was 70 / 30. The temperature of the aqueous suspension was then raised to 101°C. Next, the temperature of the aqueous suspension was maintained at 101°C for 10 hours to impregnate the polymer (base resin) with the foaming agent.

[0166] Subsequently, the aqueous suspension was cooled. After cooling, the resulting product was washed, dehydrated, and dried to obtain resin particle bodies containing at least a base resin and a foaming agent.

[0167] The obtained resin particles were sieved using sieves with mesh sizes of 0.35 mm and 0.700 mm. Through this procedure, resin particles with particle sizes of 0.35 mm or more and 0.700 mm or less were obtained.

[0168] (A process of incorporating silicone oil, etc., into the surface of the resin particle body.) 100 parts by weight of the obtained resin particle body was placed into a mixing device (universal mixer). Next, 0.05 parts by weight of methylphenyl silicone oil was added to the mixing device with 100 parts by weight of the resin particle body and coated onto the surface of the resin particle body to be incorporated. Subsequently, 0.60 parts by weight of zinc stearate and 0.2 parts by weight of glycerin monostearate were simultaneously added to the mixing device with 100 parts by weight of the resin particle body to be further coated onto the surface of the resin particle body that had been coated with methylphenyl silicone oil. By this operation, foaming methyl methacrylate-based resin particles 1 were produced. Note that methylphenyl silicone oil corresponds to a silicone oil, zinc stearate corresponds to a fatty acid metal salt, and glycerin monostearate corresponds to a nonionic surfactant.

[0169] [Example 2] Except for changing the fatty acid metal salt used to 0.6 parts by weight of magnesium stearate, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 2.

[0170] [Example 3] Except for changing the fatty acid metal salt used to a mixture of 0.3 parts by weight of zinc stearate and 0.3 parts by weight of magnesium stearate, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 3.

[0171] [Example 4] Except for changing the amount of methylphenyl silicone oil used to 0.02 parts by weight, the same procedure as in Example 1 was followed to produce foaming methyl methacrylate resin particles 4.

[0172] [Example 5] Except for changing the amount of methylphenyl silicone oil used to 0.09 parts by weight, the same procedure as in Example 1 was followed to produce foaming methyl methacrylate resin particles 5.

[0173] [Example 6] Except for changing the amount of zinc stearate used to 0.45 parts by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 6.

[0174] [Example 7] Except for changing the fatty acid metal salt used to 0.45 parts by weight of magnesium stearate, the same procedure as in Example 1 was followed to produce foaming methyl methacrylate resin particles 7.

[0175] [Example 8] Except for changing the amount of glycerin monostearate used to 0.1 parts by weight, the same procedure as in Example 1 was followed to produce foaming methyl methacrylate resin particles 8.

[0176] [Example 9] Except for changing the amount of glycerin monostearate used to 0.5 parts by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 9.

[0177] [Example 10] Except for changing the amount of methyl methacrylate used in the monomer mixture to 99 parts by weight and changing the amount of butyl acrylate used to 1 part by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 10.

[0178] [Example 11] Except for changing the amount of methyl methacrylate used in the monomer mixture to 95 parts by weight and the amount of butyl acrylate used to 5 parts by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 11.

[0179] [Example 12] Except for changing the amount of lauroyl peroxide used to 0.12 parts by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 12.

[0180] [Example 13] Except for changing the amount of lauroyl peroxide used to 0.05 parts by weight, the same procedure as in Example 1 was followed to produce foamed methyl methacrylate resin particles 13.

[0181] [Example 14] Except for changing the silicone oil used to dimethyl silicone oil (0.05 parts by weight), the same procedure as in Example 1 was followed to produce foaming methyl methacrylate resin particles 14.

[0182] [Comparative Example 1] Comparative foamed resin particles 1 were produced by performing the same procedure as in Example 1, except that the monomer mixture used was changed to 100 parts by weight of styrene.

[0183] [Comparative Example 2] Comparative foamed resin particles 2 were manufactured using the same procedure as in Example 1, except that silicone oil was not used.

[0184] [Comparative Example 3] A comparative foamed resin particle 3 was produced by performing the same procedure as in Example 1, except that the amount of methylphenyl silicone oil used was changed to 0.12 parts by weight.

[0185] [Comparative Example 4] A comparative foamed resin particle 4 was produced by performing the same procedure as in Example 1, except that the amount of zinc stearate used was changed to 0.35 parts by weight.

[0186] [Comparative Example 5] A comparative foamed resin particle 5 was produced by performing the same procedure as in Example 1, except that the amount of zinc stearate used was changed to 0.9 parts by weight.

[0187] [Comparative Example 6] The same procedure as in Example 1 was followed to obtain comparative foaming resin particles 6, except that glycerin monostearate, a nonionic surfactant, was not used.

[0188] [Comparative Example 7] A comparative foamed resin particle 7 was produced by performing the same procedure as in Example 1, except that the amount of glycerin monostearate used was changed to 0.6 parts by weight.

[0189] [Comparative Example 8] A comparative foaming resin particle 8 was produced by performing the same procedure as in Example 1, except that the nonionic surfactant glycerin monostearate used was replaced with 0.2 parts by weight of hydroxyalkylamine, which is not a nonionic surfactant.

[0190] (result) The types and content of constituent substances, as well as the results evaluated by the method described above, for foamed methyl methacrylate resin particles 1 to 14 and comparative foamed resin particles 1 to 8 are shown in Tables 1 and 2 below. In Tables 1 and 2, "MePh" means methylphenyl silicone oil, and "MEME" means dimethyl silicone oil. In Tables 1 and 2, "GMSt" means glycerin monostearate, and "HAA" means hydroxyalkylamine. In Table 2, "-" means that the substance is not contained.

[0191] [Table 1]

[0192] [Table 2]

[0193] As shown in Table 1, the foamed methyl methacrylate resin particles 1 to 14 produced in Examples 1 to 14 satisfy the following requirements (a) to (d), and therefore qualify as foamed resin particles.

[0194] (a) Includes a base resin having methyl methacrylate units; (b) Contains 0.01 parts by weight or more and 0.10 parts by weight or less of silicone oil per 100 parts by weight of foaming methyl methacrylate resin particles; (c) Contains more than 0.40 parts by weight and 0.80 parts by weight or less of a fatty acid metal salt per 100 parts by weight of the foaming methyl methacrylate resin particle body; (d) Contains 0.05 parts by weight or more and 0.55 parts by weight or less of a nonionic surfactant per 100 parts by weight of foaming methyl methacrylate resin particles.

[0195] Furthermore, as shown in Table 1, foamed methyl methacrylate resin particles 1 to 14 exhibited excellent anti-blocking properties, antistatic properties, and mold filling properties, as well as superior surface aesthetics, fusion properties, and castability of the manufactured molded articles.

[0196] On the other hand, as shown in Table 2, comparative foamed resin particles 1 to 8, manufactured in comparative examples 1 to 8, do not meet one of the requirements (a) to (d) above, and therefore do not qualify as the foamed resin particles of this type. Furthermore, as shown in Table 2, comparative foamed resin particles 1 to 8 had poor blocking prevention, antistatic properties, and mold filling properties, as well as poor surface appearance, fusion properties, and castability of the molded articles produced.

[0197] In summary, it was found that by satisfying the requirements (a) to (d) above, the foamed resin particles suppress blocking and static charge during foaming, which are problems of the conventional technology, have excellent fillability in molds, and are superior in surface beauty, fusion, and castability of the resulting molded articles. On the other hand, it was found that foamed resin particles that do not satisfy at least one of the requirements (a) to (d) above suffer from problems in one or more of the conventional technology issues: blocking and static charge during foaming, fillability in molds, surface beauty, fusion, and castability of the resulting molded articles.

[0198] Therefore, it was found that these foamed resin particles have the effect of providing molded articles with excellent anti-blocking properties, antistatic properties, and mold filling properties, as well as excellent surface beauty, fusion properties, and castability. [Industrial applicability]

[0199] According to one embodiment of the present invention, foamed methyl methacrylate resin particles can be provided that offer a molded article with excellent anti-blocking properties, antistatic properties, and mold filling properties, as well as excellent surface aesthetics, fusion properties, and castability. Therefore, one embodiment of the present invention can efficiently provide a foamed molded article that can be suitably used as a lost-wax model when performing metal casting by the full-mold method.

Claims

1. Foaming methyl methacrylate resin particles containing a base resin and a foaming agent, The aforementioned base resin has methyl methacrylate units as constituent units, The foaming methyl methacrylate resin particles further contain a silicone oil, a fatty acid metal salt, and a nonionic surfactant on their surface. The content of the silicone oil is 0.01 parts by weight or more and 0.10 parts by weight or less per 100 parts by weight of the foaming methyl methacrylate resin particle body. The content of the fatty acid metal salt is greater than 0.40 parts by weight and less than or equal to 0.80 parts by weight per 100 parts by weight of the foaming methyl methacrylate resin particle body. The foaming methyl methacrylate resin particles have a nonionic surfactant content of 0.05 parts by weight or more and 0.55 parts by weight or less per 100 parts by weight of the foaming methyl methacrylate resin particle body.

2. The foaming methyl methacrylate resin particles according to claim 1, wherein the base resin further comprises butyl acrylate units as constituent units.

3. The foaming methyl methacrylate resin particles according to claim 1, wherein the weight-average molecular weight of the base resin is greater than 300,000 and less than or equal to 450,000.

4. The foaming methyl methacrylate resin particles according to claim 1, wherein the molecular weight distribution of the base resin is 4 or more and 6 or less.

5. The foaming methyl methacrylate resin particles according to claim 1, wherein the silicone oil is one or more selected from the group consisting of methylphenyl silicone oil and dimethyl silicone oil.

6. The foaming methyl methacrylate resin particles according to claim 1, wherein the fatty acid metal salt is one or more selected from the group consisting of zinc stearate and magnesium stearate.

7. The foaming methyl methacrylate resin particles according to claim 1, wherein the nonionic surfactant comprises a fatty acid monoglyceride.

8. Methyl methacrylate foamed particles obtained by foaming the foamable methyl methacrylate resin particles described in any one of claims 1 to 7.

9. A methyl methacrylate-based foamed molded article obtained by molding methyl methacrylate-based foamed particles as described in claim 8.

10. A lost-wax model comprising a methyl methacrylate-based foamed molded body as described in claim 9.

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