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

Abstract

The present invention addresses the problem of providing expandable particles of a methyl-methacrylate-based resin which are able to efficiently provide molded foam having excellent internal fusion bonding. The expandable particles of a methyl-methacrylate-based resin comprise a base resin comprising methyl methacrylate units and acrylic acid ester units and a blowing agent, and not only have excellent expansibility but also can provide expanded particles which show low expansibility and, after heating, are highly inhibited from shrinking.

Description

Technical Field

[0001] The present invention relates to expandable methyl methacrylate resin particles, methyl methacrylate resin foam particles, a methyl methacrylate resin foam molded body, and a lost mold.

Background Art

[0002] When performing metal casting, a lost mold casting method (full mold method) for casting a casting is known, in which a mold made of a foam molded body is buried in casting sand, and molten metal is poured into the foam molded body to replace the foam molded body with metal. In the full mold method, a foam molded body of a methyl methacrylate polymer is used from the viewpoint of reducing residues during casting. In addition, many foam molded bodies for castings are those obtained by cutting from large block molded bodies.

[0003]

[0004] As expandable methyl methacrylate resin particles for producing a foam molded body of a methyl methacrylate polymer, for example, Patent Document 1 discloses expandable methyl methacrylate resin particles obtained by polymerizing methyl methacrylate, an acrylic ester, and a polyfunctional monomer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] ​ However, the conventional technologies described above have room for improvement in terms of internal fusion properties and production efficiency of methyl methacrylate-based resin foam molded articles.

[0007] In view of the above circumstances, an object of one embodiment of the present invention is to provide foamable methyl methacrylate resin particles that can efficiently provide a foamed molded article of methyl methacrylate resin with excellent internal fusion properties. [Means for solving the problem]

[0008] The inventors diligently studied and investigated the aforementioned problems, and as a result, completed the present invention.

[0009] In other words, the foamed methyl methacrylate resin particles according to one embodiment of the present invention include a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, and satisfy the following (a) to (c): (a) When the foamed methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamed methyl methacrylate resin particles to reach foamed methyl methacrylate resin particles with a bulk ratio of 60 times is less than 810 seconds; (b) 100 cm³ of foamed methyl methacrylate resin particles obtained by foaming the foamed methyl methacrylate resin particles 3 The volume (B) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 30 seconds and then letting it stand at 25°C for 1 minute is 140 cm³. 3 (c) less than; and (c) foamed methyl methacrylate resin particles obtained by foaming the foamed methyl methacrylate resin particles 100 cm 3 The volume (C) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 180 seconds and then letting it stand at 25°C for 1 minute is 160 cm³. 3 It's incredible.

[0010] Furthermore, another embodiment of the present invention provides foamed methyl methacrylate resin particles, wherein the foamed methyl methacrylate resin particles comprise a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, the foamed methyl methacrylate resin particles either contain no solvent or contain a solvent in an amount greater than 0.0 part by weight and less than or equal to 2.0 parts by weight per 100 parts by weight of the base resin, wherein, per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, (a) the content of methyl methacrylate units is 95.0 parts by weight to 98.0 parts by weight, and (b) the content of acrylic acid ester units is 2.0 parts by weight to 5.0 parts by weight, and the total amount of acrylic acid ester units and the solvent per 100 parts by weight of the base resin is 3.0 parts by weight to 5.0 parts by weight.

[0011] Furthermore, a method for producing foaming methyl methacrylate resin particles according to one embodiment of the present invention includes a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, wherein the copolymerization step includes (a) an initiation step of starting copolymerization of the monomer mixture in the presence of 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, and (b) an addition step of adding 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture to the reaction mixture after the initiation step when the polymerization conversion rate is 35% to 70%, The copolymer comprises the above, and in the copolymerization step, the amount of methyl methacrylate monomer used is 95.0 to 98.0 parts by weight and the amount of acrylic acid ester monomer used is 2.0 to 5.0 parts by weight per 100 parts by weight of the total amount of methyl methacrylate monomer and acrylic acid ester monomer used, and in the copolymerization step and / or the foaming agent impregnation step, (i) no solvent is used, or more than 0.0 part by weight and no more than 2.0 parts by weight of solvent are used per 100 parts by weight of the copolymer, and (ii) the total amount of acrylic acid ester monomer and solvent used per 100 parts by weight of the copolymer is 3.0 to 5.0 parts by weight. [Effects of the Invention]

[0012] According to one embodiment of the present invention, it is possible to provide foamable methyl methacrylate resin particles that can efficiently provide a foamed molded article with excellent internal fusion properties. [Modes for carrying out the invention]

[0013] 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. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)."

[0014] In this specification, "foaming methyl methacrylate resin particles" may also be referred to as "foaming resin particles," "foaming methyl methacrylate resin particles" may also be referred to as "foaming particles," and "foaming molded articles of methyl methacrylate resin" may also be referred to as "foaming molded articles."

[0015] [1. Technical Concept of One Embodiment of an Embodiment] Methyl methacrylate-based resin foam molded articles with poor internal fusion properties have poor processability, such as the detachment of methyl methacrylate-based resin foam particles from the cut surface when the molded article is cut.

[0016] The present inventors have found that the foamed molded articles obtained using the foamed resin particles disclosed in Patent Documents 1 and 2 have room for improvement in terms of internal fusion properties.

[0017] In view of the above circumstances, the inventors diligently conducted research with the aim of providing foamable methyl methacrylate resin particles that can efficiently provide foamed molded articles of methyl methacrylate resin with excellent internal fusion properties.

[0018] The inventors, through diligent research, have found the following points and have completed the present invention: (a) Foamable methyl methacrylate resin particles with excellent foaming speed (foaming properties) can efficiently provide methyl methacrylate resin foam particles, and (b) Foamable methyl methacrylate resin particles with a slow foaming speed and small shrinkage after heating can provide a methyl methacrylate resin foam molded article with excellent internal fusion properties.

[0019] [2. 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 that include a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, and satisfy the following conditions (a) to (c): (a) When the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to become foamed methyl methacrylate resin particles with a bulk ratio of 60 is less than 810 seconds; (b) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles, 100 cm 3 The volume (B) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 30 seconds and then letting it stand at 25°C for 1 minute is 140 cm³. 3 Less than; and (c) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles, 100 cm² 3 The volume (C) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 180 seconds and then letting it stand at 25°C for 1 minute is 160 cm³. 3 It's incredible.

[0020] "Foamable methyl methacrylate resin particles according to one embodiment of the present invention" may also be referred to as "the foamable resin particles" below.

[0021] By foaming the expandable resin particles by a known method, expandable particles can be provided. By performing in-mold molding on the expandable particles obtained by foaming the expandable resin particles by a known method, an expanded molded article can be provided.

[0022] Since the expandable resin particles have the above-described configuration, they have the advantage of being able to efficiently provide an expanded molded article excellent in internal fusion properties.

[0023] The time (A) of the expandable resin particles is less than 810 seconds. The time (A) can be said to be the time (heating time) required for the expandable resin particles to provide expanded particles with a bulk expansion ratio of 60 times. The shorter the time (A), the faster the foaming speed of the expandable resin particles is intended, and the more excellent the expandability of the expandable resin particles is intended. Expandable resin particles excellent in expandability can reduce the production time and production cost when producing expandable particles using the expandable resin particles. Therefore, the expandable resin particles have the advantage of being able to efficiently provide expandable particles, and as a result, being able to efficiently provide an expanded molded article.

[0024] The volume (B) of the expandable particles obtained by foaming the expandable resin particles is less than 140 cm 3 The volume (B) indicates the degree of foaming of the expandable particles within a certain period of time and can reflect the foaming speed of the expandable particles. The smaller the volume (B), the slower the foaming speed of the expandable particles is intended, and the lower the expandability of the expandable particles is intended. Expandable particles with low expandability can provide an expanded molded article excellent in internal fusion properties by allowing steam to sufficiently reach the expandable particles at the center inside the mold in in-mold molding using the expandable particles. Therefore, the expandable resin particles have the advantage of being able to provide an expanded molded article excellent in internal fusion properties.

[0025] The volume (C) of the expandable particles obtained by foaming the expandable resin particles is 160 cm 3This is superior. Volume (C) indicates the degree of shrinkage of the foam particles after heating. A larger volume (C) indicates that the foam particles are less likely to shrink after heating, and thus the foam particles exhibit superior shrinkage suppression. Foam particles with superior shrinkage suppression make it easier to maintain adhesion (fusion) between foam particles within the foam molded body during or after in-mold molding using these foam particles, resulting in a foam molded body with superior internal fusion. Therefore, these foamable resin particles have the advantage of providing a foam molded body with superior internal fusion.

[0026] The foaming of foamed resin particles can be called "primary foaming." Therefore, the foaming rate and foaming properties of foamed resin particles can be said to be the foaming rate and foaming properties of primary foaming, respectively. On the other hand, the foaming of foamed particles can be called "secondary foaming." Therefore, the foaming rate and foaming properties of foamed particles can be said to be the foaming rate and foaming properties of secondary foaming, respectively.

[0027] (Base resin) The base resin contained in these foamed resin particles contains methyl methacrylate units and acrylic acid ester units as constituent units. In this specification, "methyl methacrylate unit" refers to a constituent unit derived from methyl methacrylate monomer, and "acrylic acid ester unit" refers to a constituent unit derived from acrylic acid ester monomer. In this specification, the term "monomer" may be omitted. Therefore, in this specification, for example, when simply "methyl methacrylate" and "acrylic acid ester" are used, they refer to "methyl methacrylate monomer" and "acrylic acid ester monomer," respectively.

[0028] In the base resin contained in these foamed resin particles, it is preferable that (a) the content of methyl methacrylate units is 95.0 to 98.0 parts by weight and the content of acrylic acid ester units is 2.0 to 5.0 parts by weight per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, (b) the content of methyl methacrylate units is 95.5 to 97.5 parts by weight and the content of acrylic acid ester units is 2.5 to 4.5 parts by weight, and (c) the content of methyl methacrylate units is 96.0 to 97.0 parts by weight and the content of acrylic acid ester units is 3.0 to 4.0 parts by weight. In the base resin, when the content of methyl methacrylate units is 98.0 parts by weight or less per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, the foaming properties of the foamed resin particles tend to be excellent. In a base resin, if the content of acrylic acid ester units is 5.0 parts by weight or less per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, the foamed particles obtained by foaming the foamed resin particles tend to exhibit superior shrinkage suppression.

[0029] Examples of acrylic acid esters according to one embodiment of the present invention include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. Among the acrylic acid esters, butyl acrylate is particularly preferred.

[0030] In other words, it is particularly preferable that the acrylic acid ester units are butyl acrylate units derived from butyl acrylate monomers. Butyl acrylate has a significant effect in lowering the glass transition temperature of the base resin. Therefore, this configuration makes it possible to provide foamed resin particles with excellent foaming properties and moldability (e.g., shrinkage suppression).

[0031] The base resin of these foamed resin particles may contain constituent units derived from a crosslinking agent (hereinafter also referred to as crosslinking agent units). When the base resin of these foamed resin particles contains constituent units derived from a crosslinking agent, the following advantages are obtained: (a) the foamed resin particles have excellent foaming properties; (b) the foamed particles obtained by foaming the foamed resin particles have low foaming properties and excellent shrinkage suppression; and (c) the foamed molded body obtained by in-mold molding the foamed particles has excellent internal fusion properties and produces less residue during combustion. Furthermore, foamed resin particles containing a base resin that includes constituent units derived from a crosslinking agent as constituent units also have the advantage that the molecular weight can be easily adjusted during the manufacturing process.

[0032] Examples of crosslinking agents include compounds having two or more functional groups that exhibit radical reactivity. Among compounds having two or more functional groups that exhibit radical reactivity, it is preferable to use a difunctional monomer having two functional groups as the crosslinking agent. In other words, it is preferable that the base resin of the foamed resin particles contains a difunctional monomer unit, which is a constituent unit derived from a difunctional monomer, as a constituent unit derived from the crosslinking agent. With this configuration, (a) the foamed resin particles have superior foaming properties, (b) the foamed particles obtained by foaming the foamed resin particles have lower foaming properties and superior shrinkage suppression properties, and (c) the foamed molded body obtained by in-mold molding the foamed particles has superior internal fusion properties and less residue during combustion.

[0033] Examples of bifunctional monomers include (a) compounds obtained by esterifying both terminal hydroxyl groups of ethylene glycol or oligomers of ethylene glycol, such as (a-1) ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate, with acrylic acid or methacrylic acid; (b) compounds obtained by esterifying the hydroxyl group of a divalent alcohol, such as neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate (e.g., 1,6-hexanediol diacrylate), and butanediol di(meth)acrylate, with acrylic acid or methacrylic acid; and (c) aryl compounds having two alkenyl groups, such as divinylbenzene. Hexanediol di(meth)acrylate is preferred as a bifunctional monomer due to the ease of adjusting its molecular weight. In this specification, "(meth)acrylate" means "acrylate and / or methacrylate". For example, hexanediol di(meth)acrylate is intended to be hexanediol diacrylate and / or hexanediol dimethacrylate.

[0034] When the base resin contains constituent units derived from a crosslinking agent, the content of the crosslinking agent units (e.g., bifunctional monomer units) in the foamed resin particles is preferably 0.05 parts by weight or more and 0.15 parts by weight or less, and more preferably 0.08 parts by weight or more and 0.13 parts by weight or less, based on 100 parts by weight of the total content of methyl methacrylate units and acrylic acid ester units. According to the above configuration, (a) the foamed resin particles have superior foaming properties, (b) the foamed particles obtained by foaming the foamed resin particles have lower foaming properties and superior shrinkage suppression properties, and (c) the foamed molded article obtained by in-mold molding the foamed particles has superior strength and internal fusion properties and less residue during combustion.

[0035] The base resin of these foamed resin particles may or may not 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 of these foamed resin particles contains aromatic units, a foamed molded article with excellent strength can be obtained.

[0036] (Foaming agent) The foaming agent contained in these foamed resin particles is not particularly limited. Examples of foaming agents include (a) aliphatic hydrocarbons having 3 to 5 carbon atoms, such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentane, and (b) hydrofluorocarbons with zero ozone depletion potential, such as difluoroethane and tetrafluoroethane. These foaming agents may be used individually or in combination of two or more.

[0037] In these foamed resin particles, the foaming agent content is preferably 5 to 12 parts by weight, and more preferably 7 to 10 parts by weight, 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.

[0038] (solvent) These foamed resin particles may or may not contain a solvent. Preferably, these foamed resin particles contain a solvent. When these foamed resin particles contain a solvent, (a) the foamed resin particles have excellent foaming properties, and (b) the foamed particles obtained by foaming these foamed resin particles have low foaming properties and excellent shrinkage suppression properties. In other words, when these foamed resin particles contain a solvent, they have the advantage of being able to efficiently provide foamed molded articles with excellent internal fusion properties.

[0039] The solvent is not particularly limited, but examples include (a) aliphatic hydrocarbons having 6 or more carbon atoms (C6 or more) such as hexane and heptane, (b) alicyclic hydrocarbons having 6 or more carbon atoms such as cyclohexane and cyclooctane, and (c) aromatic compounds such as xylene and toluene. As the solvent, one compound selected from the group consisting of the above compounds may be used alone, or two or more may be used in combination. Since foamed resin particles with excellent foaming properties can be obtained, these foamed resin particles preferably contain a solvent with a boiling point of 50°C to 108°C, and more preferably contain cyclohexane as the solvent.

[0040] The foamed resin particles preferably contain no solvent or contain more than 0.0 part by weight and up to 2.0 parts by weight of solvent per 100 parts by weight of the base resin. In the foamed resin particles, the solvent content per 100 parts by weight of the base resin is preferably 2.0 parts by weight or less, more preferably 1.9 parts by weight or less, more preferably 1.8 parts by weight or less, more preferably 1.7 parts by weight or less, more preferably 1.6 parts by weight or less, more preferably 1.5 parts by weight or less, more preferably 1.4 parts by weight or less, more preferably 1.3 parts by weight or less, more preferably 1.2 parts by weight or less, more preferably 1.1 parts by weight or less, more preferably 1.0 part by weight or less, more preferably 0.9 parts by weight or less, more preferably 0.8 parts by weight or less, more preferably 0.7 parts by weight or less, even more preferably 0.6 parts by weight or less, and particularly preferably 0.5 parts by weight or less. In these foamed resin particles, the solvent content per 100 parts by weight of the base resin is preferably more than 0.0 part by weight, more preferably 0.1 part by weight or more, more preferably 0.2 parts by weight or more, more preferably 0.3 parts by weight or more, even more preferably 0.4 parts by weight or more, and particularly preferably 0.5 parts by weight or more. This configuration has the advantages that (a) the foamed resin particles have superior foaming properties, and (b) the foamed particles obtained by foaming the foamed resin particles have lower foaming properties and superior shrinkage suppression properties.

[0041] In these foamed resin particles, the total amount of acrylic acid ester units and solvent per 100 parts by weight of base resin is preferably 3.0 to 5.0 parts by weight, more preferably 3.1 to 4.9 parts by weight, more preferably 3.2 to 4.8 parts by weight, more preferably 3.3 to 4.7 parts by weight, more preferably 3.4 to 4.6 parts by weight, more preferably 3.5 to 4.5 parts by weight, even more preferably 3.6 to 4.4 parts by weight, even more preferably 3.7 to 4.3 parts by weight, and particularly preferably 3.8 to 4.2 parts by weight. With this configuration, (a) the foamed resin particles have superior foaming properties, and (b) the foamed particles obtained by foaming the foamed resin particles have lower foaming properties and superior shrinkage suppression properties.

[0042] (Other additives) These foamed resin particles may contain, in addition to a base resin, a foaming agent, and an optionally included solvent, other additives. Examples of these other additives include crosslinking agents, foam regulators, plasticizers, flame retardants, flame retardant enhancers, heat radiation inhibitors, pigments, dyes, and antistatic agents.

[0043] (Bubble regulator) Examples of foam regulators include (a) aliphatic bisamides such as methylenebisstearate and ethylenebisstearate, and (b) polyethylene wax. The content of the foam regulator per 100 parts by weight of the base resin is preferably 0.01 to 0.50 parts by weight.

[0044] (Aromatic monomers and aromatic compounds) From the viewpoint of obtaining a foamed molded article with minimal residue during combustion, it is preferable that the amount of aromatic monomers and aromatic compounds, or structures derived from aromatic monomers and aromatic compounds (e.g., aromatic rings), contained in the foamed resin particles be as small as possible. Specifically, it is preferable that (a) the amount of constituent units derived from aromatic monomers contained in the base resin be as small as possible, and (b) the amount of aromatic compounds (e.g., toluene and xylene) contained as a solvent be as small as possible.

[0045] (i) The base resin preferably does not contain constituent units derived from aromatic monomers, or contains more than 0.0 parts by weight and no more than 2.5 parts by weight of constituent units derived from aromatic monomers per 100 parts by weight of the base resin. In the base resin, the content of constituent units derived from aromatic monomers per 100 parts by weight of the base resin is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight. In other words, it is most preferable that the base resin of the foamed resin particles does not contain constituent units derived from aromatic monomers.

[0046] The foamed methyl methacrylate resin particles preferably contain no aromatic compounds, or contain more than 0.0 parts by weight and up to 2.5 parts by weight of aromatic compounds per 100 parts by weight of the base resin. In these foamed resin particles, the content of aromatic compounds per 100 parts by weight of the base resin is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight. In other words, it is most preferable that these foamed resin particles do not contain aromatic compounds. More specifically, in these foamed resin particles, the total content of toluene and xylene per 100 parts by weight of the base resin is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight. In other words, it is most preferable that these foamed resin particles do not contain toluene and xylene.

[0047] (Volume-average particle size) The volume-average particle diameter of the foamed resin particles is preferably 0.5 mm to 1.4 mm, more preferably 0.6 mm to 1.2 mm, more preferably greater than 0.6 mm and 1.0 mm or less, and more preferably 0.7 mm to 0.9 mm. When the volume-average particle diameter is 0.5 mm or more, there is no risk of reduced foaming properties and / or increased blocking during foaming. When the volume-average particle diameter is 1.4 mm or less, there is no risk of the foamed particles formed by foaming the foamed resin particles becoming too foamy, and when molding using these foamed particles, the surface of the molded body is formed slowly, allowing steam to enter the interior of the foamed molded body. As a result, the fusion properties inside the foamed molded body are good. In this specification, the volume-average particle diameter of the foamed resin particles is defined as the particle size at which the volume cumulative distribution reaches 50%, obtained by measuring the particle size of the foamed resin particles on a volume basis using a particle size analyzer (e.g., an image processing type Millitrack JPA particle size analyzer), displaying the obtained results as a cumulative distribution, and determining the particle size at which the volume cumulative distribution reaches 50%.

[0048] In addition, the foamed methyl methacrylate resin particles may be sieved to separate them into particles with a diameter of 0.5 mm to 1.4 mm. In this case, the volume-average particle diameter of the separated foamed methyl methacrylate resin particles will be within the range of 0.5 mm to 1.4 mm.

[0049] (Weight average molecular weight) The foamed resin particles are preferably measured by gel permeation chromatography (GPC) and have a weight-average molecular weight converted to polystyrene of 100,000 to 400,000. With this configuration, the foamed resin particles can provide a foamed molded article with excellent internal fusion properties.

[0050] (Foaming properties of foaming methyl methacrylate resin particles) The foamable resin particles have a time (A) of less than 810 seconds and exhibit excellent foaming properties. Since the foamable resin particles exhibit superior foaming properties, the time (A) is preferably 805 seconds or less, more preferably less than 805 seconds, more preferably 800 seconds or less, more preferably less than 800 seconds, more preferably 780 seconds or less, more preferably 760 seconds or less, more preferably 740 seconds or less, more preferably 720 seconds or less, more preferably 710 seconds or less, more preferably 700 seconds or less, more preferably 680 seconds or less, more preferably 660 seconds or less, more preferably 640 seconds or less, more preferably 620 seconds or less, more preferably 600 seconds or less, more preferably 580 seconds or less, more preferably 560 seconds or less, more preferably 540 seconds or less, even more preferably 520 seconds or less, and particularly preferably 500 seconds or less. A shorter time (A) is preferable, and its lower limit is not particularly limited, but the time (A) is at least greater than 0 seconds.

[0051] Here, the method for measuring the time (A) (foaming rate) of foamed resin particles is not particularly limited, but for example, the following method can be used, in order: (1) Put the foamed resin particles into a pressurized foaming machine (for example, a BHP manufactured by Daikai Kogyo Co., Ltd.); (2) Next, steam (for example, water vapor) is blown into the foaming machine under conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) At regular intervals, the foamed particles formed from the foamed resin particles are removed from the foaming machine and the bulk ratio of the foamed particles is measured; (4) Measure the time (A) (also called heating time (A)) from when steam is blown into the foamed resin particles until foamed particles with a bulk ratio of 60 are obtained.

[0052] Compared to heating foamed resin particles at a steam injection pressure of 0.10 MPa, heating them at a steam injection pressure of 0.16 MPa slightly reduces the time required to obtain foamed resin particles with a bulk ratio of 60, but the time is substantially unchanged. In this specification, time (A) is defined as the time required to obtain foamed resin particles with a bulk ratio of 60 when heated under the conditions of a steam injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa. Furthermore, the foamed resin particles used to measure time (A) may be those with a particle diameter of 0.5 mm to 1.4 mm obtained by sieving.

[0053] In this specification, the bulk ratio of the foamed particles shall be the value obtained by performing the following steps (1) to (3) in order: (1) Weigh out 10 g of foamed particles and measure 1000 cm² 3 (1) Place the foam particles into a graduated cylinder; (2) Measure the volume of 10g of foam particles from the scale on the graduated cylinder; (3) Calculate the bulk ratio of the foam particles using the following formula; Bulk magnification (cm 3 ( / g) = Volume of foamed particles (cm³) 3 ) / 10g.

[0054] In this specification, the bulk ratio of foamed particles can also be called the foaming ratio. Furthermore, the unit of the bulk ratio is actually cm based on the above formula. 3 Although the unit is / g, for convenience, in this specification the unit of bulk ratio will be expressed as "times".

[0055] The foamed particles obtained by foaming these foamed resin particles have a volume (B) of 140 cm³. 3 It is less than 138 cm³ and has low foaming properties. Since it can provide a foamed molded product with superior internal fusion properties, the volume (B) is 138 cm³. 3 The following is preferable: 136cm 3 The following is more preferable: 135cm 3 The following is more preferable: 134cm 3 The following is more preferable: 132cm 3 The following is more preferable: 130cm 3 The following is more preferable: 128cm3 The following is more preferable: 126cm 3 The following is more preferable: 124cm 3 The following is even more preferable: 122 cm 3 The following is particularly preferable: A smaller volume (B) is preferable, and there is no particular lower limit, but a volume (B) of at least 100 cm³ is preferable. 3 It exceeds.

[0056] Here, the method for measuring the volume (B) of foamed particles obtained by foaming the foamed resin particles is not particularly limited, but for example, the following method can be used, in order: (1) Foam the foamed resin particles to a bulk ratio of 60 times to prepare foamed particles with a bulk ratio of 60 times; (2) Disperse 100 cm³ of the foamed particles 3 (3) Weigh out the amount and put it into a steamer (for example, a steamer with an air outlet); (4) Supply 100°C steam to the steamer and heat the foam particles for 30 seconds; (5) After heating, remove the foam particles from the steamer and leave them at 25°C for 1 minute; (6) Place the foam particles in a 1000cm³ container. 3 Place the mixture into the graduated cylinder; (6) Measure the volume (B) of the foamed particles from the scale on the graduated cylinder.

[0057] The foamed particles obtained by foaming these foamed resin particles have a volume (C) of 160 cm³. 3 It is superior in shrinkage suppression. Because it can provide a foamed molded body with superior internal fusion properties, the volume (C) is 162 cm³. 3 The above is preferable, 164cm 3 The above is more preferable, 165cm 3 Super is preferable, 166cm 3 The above is more preferable, 168cm 3 The above is more preferable, 170cm 3 The above is more preferable, 172cm 3 The above is more preferable, 174cm 3 The above is even more preferable, 176cm 3 The above are particularly preferable.

[0058] Here, the method for measuring the volume (C) of foamed particles obtained by foaming the foamed resin particles is not particularly limited, but for example, the following method can be used in order: (1) Foam the foamed resin particles to a bulk ratio of 60 times to prepare foamed particles with a bulk ratio of 60 times; (2) Disperse 100 cm³ of the foamed particles 3 (3) Weigh out the amount and put it into a steamer (for example, a steamer with an air outlet); (4) Supply 100°C steam to the steamer and heat the foam particles for 180 seconds; (5) After heating, remove the foam particles from the steamer and leave them at 25°C for 1 minute; (6) Place the foam particles in a 1000cm³ container. 3 Place the foam particles into the graduated cylinder; (6) Measure the volume (C) of the foam particles from the scale on the graduated cylinder.

[0059] The method for producing foamed particles with a bulk ratio of 60 times used for measuring volume (B) and volume (C) is not particularly limited, but for example, the following method can be used, in which (1) to (3) are performed in order: (1) Foamable resin particles are put into a pressurized foaming machine (for example, a BHP manufactured by Daikai Kogyo Co., Ltd.); (2) Steam (e.g., water vapor) is blown into the foaming machine at a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) The foamed resin particles are foamed according to (2) until a desired foaming ratio (e.g., a bulk ratio of 60 times) is reached to obtain foamed particles. The foamed resin particles used in the production of foamed particles with a bulk ratio of 60 times used for measuring volume (B) and volume (C) may be foamed resin particles with a particle diameter of 0.5 mm to 1.4 mm obtained by sieving.

[0060] (Variation 1) In the process of diligently studying to provide foamable methyl methacrylate resin particles that can efficiently provide foamed molded articles of methyl methacrylate resin with excellent internal fusion properties, the inventors have also independently discovered the following: (i) The higher the solvent content and / or the total amount of acrylic acid ester units and solvent in the foamable resin particles, the higher the foaming rate of the foamable resin particles, i.e., the superior foaming properties, and as a result, foamed particles and foamed molded articles can be efficiently provided; (ii) On the other hand, if the solvent content and / or the total amount of acrylic acid ester units and solvent in the foamable resin particles is too high (exceeding a certain value), the foaming rate of the foamed particles obtained by foaming the foamable resin particles becomes faster, and (iii) The shrinkage of the foamed particles after heating is large, and as a result, the foamed molded article provided by the foamed particles has poor internal fusion properties; (iii) The less solvent content and / or the total amount of acrylic acid ester units and solvent in the foamed resin particles, the slower the foaming rate of the foamed particles obtained by foaming the foamed resin particles becomes, and the smaller the shrinkage of the foamed particles after heating becomes, and as a result, a foamed molded article with excellent internal fusion properties can be provided; (iv) On the other hand, if the solvent content and / or the total amount of acrylic acid ester units and solvent in the foamed resin particles is too small (below a certain value), the foaming rate of the foamed resin particles becomes slow, i.e., the foaming properties are poor, and as a result, foamed particles and foamed molded articles cannot be efficiently provided.

[0061] Based on these new findings, and after further diligent study, the inventors have found the following and have completed another embodiment of the present invention: By setting the solvent content and / or the total amount of acrylic acid ester units and solvent in the foamed resin particles within a specific range, it is possible to provide foamed resin particles that can efficiently provide a foamed molded article with excellent internal bonding properties; specifically, by setting the solvent content and / or the total amount of acrylic acid ester units and solvent in the foamed resin particles within a specific range, it is possible to provide foamed resin particles that (a) have excellent foaming properties, (b) have a slow foaming rate when foamed, and (c) have small shrinkage after heating.

[0062] That is, a foamed methyl methacrylate resin particle according to another embodiment of the present invention has the following configuration: a foamed methyl methacrylate resin particle comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the foamed methyl methacrylate resin particle contains no solvent, or contains a solvent in an amount of more than 0.0 part by weight and less than or equal to 2.0 parts by weight per 100 parts by weight of the base resin, wherein, per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, (a) the content of methyl methacrylate units is 95.0 parts by weight to 98.0 parts by weight, and (b) the content of acrylic acid ester units is 2.0 parts by weight to 5.0 parts by weight, and the total amount of acrylic acid ester units and the solvent per 100 parts by weight of the base resin is 3.0 parts by weight to 5.0 parts by weight.

[0063] Another embodiment of the present invention provides foamed methyl methacrylate resin particles that, having the above-described structure, have the advantage of providing foamed particles that (a) exhibit excellent foaming properties and (b) have low foaming properties and excellent shrinkage suppression properties. In other words, foamed resin particles having the above-described structure have the advantage of efficiently providing foamed molded articles with excellent internal fusion properties.

[0064] Other embodiments of foamed methyl methacrylate resin particles according to another embodiment of the present invention are provided by relating to the above description as appropriate.

[0065] (Modification 2) These foamed resin particles can provide foamed molded articles with excellent internal fusion properties. The internal fusion properties of a foamed molded article can be evaluated by the proportion of foamed particles that are fractured at locations other than the interface of the foamed particles in the fracture surface obtained by fracturing the foamed molded article. For example, if the proportion of foamed particles (D) that are fractured at locations other than the interface of the foamed particles in the fracture surface obtained by fracturing a foamed molded article made by molding foamed particles of these foamed resin particles is 80% or more, then the foamed molded article can be said to have excellent internal fusion properties.

[0066] That is, foamed methyl methacrylate resin particles according to another embodiment of the present invention have the following configuration: foamed methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, satisfying the following (a) to (d): (a) When the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to become foamed methyl methacrylate resin particles with a bulk ratio of 60 is less than 810 seconds; (b) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles, 100 cm 3 The volume (B) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 30 seconds and then letting it stand at 25°C for 1 minute is 140 cm³. 3 Less than; (c) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles, 100 cm² 3The volume (C) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 180 seconds and then letting it stand at 25°C for 1 minute is 160 cm³. 3 It is greater than; and (d) In the fracture surface of the methyl methacrylate resin foam molded article obtained by molding methyl methacrylate resin foam particles, which are obtained by foaming the foamable methyl methacrylate resin particles, the proportion (D) of methyl methacrylate resin foam particles that are fractured at a location other than the interface of the methyl methacrylate resin foam particles is 80% or more.

[0067] Here, the method for measuring the proportion (D) of foamed particles obtained by foaming the foamed resin particles in the fracture surface of a foamed molded body is not particularly limited, but for example, the following method can be used, in order: (1) Foamed particles obtained by foaming the foamed resin particles are molded in a mold (for example, a mold having a molding space of length 2000 mm, width 1000 mm and thickness 525 mm) to prepare a foamed molded body; (2) The foamed molded body is cut perpendicular to the thickness direction using a hot wire slicer so that the foamed molded body is divided equally into 5 parts in the thickness direction; (3) For the middle of the 5 parts (the part of the foamed molded body in the thickness direction from 210 mm to 315 mm before cutting), the plane perpendicular to the thickness direction is bent along the width direction at the center in the length direction to break the foamed molded body; (4) The obtained fracture surface is visually observed, and the number of foamed particles that have broken outside of the particle interface is measured, and the proportion (D) is calculated based on the following formula; Percentage (D) (%) = Number of particles fractured outside the particle interface on the fracture surface / Number of particles constituting the fracture surface × 100.

[0068] The method for manufacturing the foamed molded article used to measure the ratio (D) is not particularly limited, but for example, the following method is performed in order: (1) Put foamable resin particles into a pressurized foaming machine (e.g., a BHP manufactured by Daikai Kogyo Co., Ltd.); (2) Blow steam (e.g., water vapor) into the foaming machine under conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamable resin particles; (3) Foam the foamable resin particles according to (2) above until a desired foaming ratio (e.g., bulk ratio of 60 times) is reached; (4) Leave the obtained foamed particles at room temperature (e.g., 25°C) for 3 days to obtain foamed particles with a bulk ratio of 60 times; (5) Use a mold (e.g., 2000 mm in length, 1000 mm in width) (6) A molding machine (e.g., PEONY-205DS made by Daisen) having a mold with a molding space of mm and a thickness of 525 mm is filled with foam particles with a bulk ratio of 60; (7) Steam (e.g., water vapor) is blown into the mold at a steam blowing pressure of 0.15 MPa to 0.25 MPa, and in-mold molding is performed by vacuum suction heating under conditions where the pressure inside the mold is 0.030 MPa to 0.060 MPa, until the foam pressure reaches 0.070 MPa to 0.080 MPa, causing the foam particles to fuse together; (8) After the foam pressure reaches 0.070 MPa to 0.080 MPa, the mold is left in the mold at 80°C to 110°C for 1000 seconds, and then the foam molded body is removed; (9) The removed foam molded body is left at 60°C for 3 days to obtain a foam molded body. Furthermore, the foamed resin particles used in the production of the foamed molded body used for measuring the proportion (D) may be foamed resin particles with a particle size of 0.5 mm to 1.4 mm obtained by sieving.

[0069] The ratio (D) can also be called the fusion rate. Since it is superior in terms of internal fusion properties, the ratio (D) is preferably 80% or more, more preferably 82% or more, more preferably 84% or more, more preferably 86% or more, even more preferably 88% or more, and particularly preferably 90% or more.

[0070] [3. Method for producing foaming methyl methacrylate resin particles] The method for producing these foamed resin particles is not particularly limited, and examples include suspension polymerization, in which a monomer mixture is polymerized in an aqueous suspension.

[0071] A preferred embodiment of the method for producing the foamed resin particles is, for example, the following method: a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, wherein the copolymerization step includes (a) an initiation step of starting copolymerization of the monomer mixture in the presence of 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, and (b) an addition step of adding 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture to the reaction mixture after the initiation step when the polymerization conversion rate is 35% to 70%, and the copolymerization step A method for producing foaming methyl methacrylate resin particles, wherein, in the process, the amount of methyl methacrylate monomer used is 95.0 to 98.0 parts by weight and the amount of acrylic acid ester monomer used is 2.0 to 5.0 parts by weight, and in the copolymerization step and / or the foaming agent impregnation step, (i) no solvent is used, or a solvent is used in an amount greater than 0.0 part by weight and less than or equal to 2.0 parts by weight per 100 parts by weight of the copolymer, and (ii) the total amount of acrylic acid ester monomer and the solvent used per 100 parts by weight of the copolymer is 3.0 to 5.0 parts by weight.

[0072] In this specification, "poorly water-soluble inorganic salt" refers to an inorganic salt whose solubility in water at 25°C is 0.1 mg / ml or less.

[0073] The preferred embodiment of the method for producing the foamed resin particles described above is also one embodiment of the present invention. The preferred embodiment of the method for producing the foamed resin particles described above, that is, the method for producing foamed methyl methacrylate resin particles according to one embodiment of the present invention, will be described below. Except for matters described in detail below, the description in section [2. Foamed Methyl Methacrylate Resin Particles] will be referred to as appropriate. In addition, the copolymer (which can also be called the base resin) obtained in the copolymerization step may be simply referred to as "resin particles" below. Also, in this specification, "the method for producing foamed methyl methacrylate resin particles according to one embodiment of the present invention" may be referred to as "this production method".

[0074] In one embodiment of the present invention, "aqueous suspension" refers to a liquid obtained by dispersing monomer droplets and / or resin particles in water or an aqueous solution using a stirrer or the like. The aqueous suspension may contain (a) water-soluble surfactants and monomers, or (b) water-insoluble dispersants, polymerization initiators, chain transfer agents, crosslinking agents, foam regulators, flame retardants, solvents, etc., dispersed together with the monomers.

[0075] In the aqueous suspension, the weight ratio of monomers and polymers (methyl methacrylate resins, also called copolymers) to water or aqueous solution is preferably 1.0 / 0.6 to 1.0 / 3.0 as the resulting methyl methacrylate resin / water or aqueous solution ratio. The term "aqueous solution" as used herein refers to a solution consisting of water and components other than the methyl methacrylate resin.

[0076] A copolymerization step according to one embodiment of the present invention includes an initiation step in which copolymerization of a monomer mixture is initiated in the presence of 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture. The initiation step is a step in which copolymerization of a monomer mixture is initiated using an aqueous suspension containing, for example, (a) water, (b) a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, (c) a solvent, (d) 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, and optionally (e) a crosslinking agent, polymerization initiator, surfactant, dispersant other than a poorly water-soluble inorganic salt, chain transfer agent, foam regulator, flame retardant, etc.

[0077] In this specification, the period "before the initiation step," that is, "before the start of the polymerization reaction," may also be referred to as the "initial polymerization stage." The first poorly water-soluble inorganic salt added to the aqueous suspension in the initiation step, and optionally added polymerization initiators, can be considered substances (raw materials) used in the initial polymerization stage.

[0078] In the initial step, the first poorly water-soluble inorganic salt can function as a dispersant. Examples of the first poorly water-soluble inorganic salt used in the initial step, i.e., the initial stage of polymerization, include tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin.

[0079] Furthermore, in the initial step according to one embodiment of the present invention, (a) a water-soluble polymer such as polyvinyl alcohol, methylcellulose, polyacrylamide, or polyvinylpyrrolidone, and / or (b) an anionic surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzenesulfonate may be used in combination with the first poorly water-soluble inorganic salt.

[0080] As the first poorly water-soluble inorganic salt used in the initiation step according to one embodiment of the present invention, tricalcium phosphate is preferred from the viewpoint of protecting resin particles and / or monomer droplets. The initiation step is preferably a step in which copolymerization of the monomer mixture is started in the presence of tricalcium phosphate, which is the first poorly water-soluble inorganic salt, and sodium α-olefin sulfonate, which is an anionic surfactant, from the viewpoint of droplet dispersion stability.

[0081] The starting step according to one embodiment of the present invention is preferably a step of starting copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt in an amount of preferably 0.08 to 1.20 parts by weight, more preferably 0.10 to 1.20 parts by weight, more preferably 0.10 to 0.70 parts by weight, and even more preferably 0.10 to 0.30 parts by weight, per 100 parts by weight of the monomer mixture. When copolymerization of the monomer mixture is started in the presence of a first poorly water-soluble inorganic salt in an amount of 0.08 parts by weight or more per 100 parts by weight of the monomer mixture, there is no risk that the volume average particle size of the resulting foamed resin particles will become too large. When copolymerization of the monomer mixture is started in the presence of a first poorly water-soluble inorganic salt in an amount of 1.20 parts by weight or less per 100 parts by weight of the monomer mixture, there is no risk that a large amount of fine particles of foamed resin will be generated. In other words, by initiating copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt in the amount described above, foamed resin particles having a desired volume-average particle size can be obtained in good yield.

[0082] In the initial step according to one embodiment of the present invention, a case in which a water-soluble polymer and / or anionic surfactant is used in combination with a first poorly water-soluble inorganic salt will be described. In this case, the concentration of the water-soluble polymer and / or anionic surfactant in the aqueous suspension is preferably 30 ppm to 100 ppm, with the concentration of the monomer mixture as the reference (1,000,000 ppm).

[0083] The copolymerization step preferably includes an addition step in which, after the initiation step, when the polymerization conversion rate is 35% to 70%, 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture is added to the reaction mixture.

[0084] In this specification, the period "after the initiation step," that is, "after the start of the polymerization reaction," may also be referred to as "in the process of polymerization." The second poorly water-soluble inorganic salt added to the reaction mixture in the addition step can be considered a substance (raw material) used in the process of polymerization.

[0085] In a copolymerization process according to one embodiment of the present invention, when the polymerization (copolymerization) of the monomer mixture is carried out by suspension polymerization, the reaction mixture in the addition step can also be called an aqueous suspension.

[0086] In the addition step according to one embodiment of the present invention, the second poorly water-soluble inorganic salt can function as a dispersant. The second poorly water-soluble inorganic salt used in the addition step, i.e., during polymerization, is the substance already exemplified as the first poorly water-soluble inorganic salt. The second poorly water-soluble inorganic salt is preferably one or more selected from the group consisting of tricalcium phosphate, hydroxyapatite, and kaolin, and more preferably tricalcium phosphate. This configuration has the advantage that coalescence of resin particles after the addition of the dispersant can be prevented, and foamed resin particles with the desired volume-average particle size can be easily obtained.

[0087] The addition step is preferably a step in which, after the initiation step, when the polymerization conversion rate is 35% to 70%, a second poorly water-soluble inorganic salt is added to the reaction mixture in an amount of preferably 0.08 to 0.50 parts by weight, more preferably 0.10 to 0.50 parts by weight, more preferably 0.10 to 0.40 parts by weight, even more preferably 0.10 to 0.30 parts by weight, and particularly preferably 0.10 to 0.20 parts by weight, per 100 parts by weight of the monomer mixture. When 0.08 parts by weight or more of the second poorly water-soluble inorganic salt is added to the reaction mixture per 100 parts by weight of the monomer mixture in the addition step, there is no risk that the volume average particle size of the resulting foamed resin particles will become too large. When 0.50 parts by weight or less of the second poorly water-soluble inorganic salt is added to the reaction mixture per 100 parts by weight of the monomer mixture in the addition step, the amount of poorly water-soluble inorganic salt used will not be excessive, and production costs can be reduced. In other words, by adding a second poorly water-soluble inorganic salt in the amount within the above range to the reaction mixture during the addition step, foamed resin particles having a desired volume-average particle size can be obtained at a low production cost.

[0088] In the addition step, it is preferable to add the second poorly water-soluble inorganic salt to the reaction mixture when the polymerization conversion rate is preferably 35% to 70%, more preferably when the polymerization conversion rate is 35% to 60%, and even more preferably when the polymerization conversion rate is 40% to 50%. When the second poorly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is 35% or higher in the addition step, there is no risk that the volume average particle size of the resulting foamed resin particles will become too small. When the second poorly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is 70% or lower in the addition step, there is no risk that the volume average particle size of the resulting foamed resin particles will become too large. In other words, when the second poorly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is within the above range in the addition step, foamed resin particles having the desired volume average particle size can be easily obtained. The method for measuring the polymerization conversion rate in this specification will be described in detail in the following examples.

[0089] The copolymerization process according to one embodiment of the present invention is preferably carried out in at least two stages by changing the polymerization temperature. For convenience, the two copolymerization processes with different polymerization temperatures will be referred to below as the first copolymerization process and the second copolymerization process. It is also preferable that the copolymerization process includes a consecutive first copolymerization process and a second copolymerization process with different polymerization temperatures.

[0090] A copolymerization step according to one embodiment of the present invention preferably includes, for example, (a) a first copolymerization step carried out at a polymerization temperature of 70°C to 90°C and using a low-temperature decomposition type polymerization initiator, and (b) a second copolymerization step carried out continuously with the first copolymerization step and at a higher polymerization temperature (e.g., 90°C to 110°C) than the first copolymerization step and using a high-temperature decomposition type polymerization initiator. In the copolymerization step, it is preferable that the main polymerization reaction is carried out in the first copolymerization step described above, and that the remaining monomers are reduced in the second copolymerization step described above. Note that (i) the temperature of the first copolymerization step may be 70°C or higher and less than 90°C, and the temperature of the second copolymerization step may be 90°C to 110°C, and (ii) the temperature of the first copolymerization step may be 70°C to 90°C, and the temperature of the second copolymerization step may be greater than 90°C and 110°C or less.

[0091] As polymerization initiators, radical-generating polymerization initiators commonly used in the production of thermoplastic polymers can be used. Typical radical-generating polymerization initiators include, for example, (a) organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl monocarbonate, and (b) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used individually or in combination of two or more.

[0092] Of the radical-generating polymerization initiators mentioned above, (a) benzoyl peroxide, lauroyl peroxide, t-butyl perpivalate, di-t-butyl peroxyhexahydroterephthalate, azobisisobutyronitrile, and azobisdimethylvaleronitrile are low-temperature decomposition polymerization initiators, and (b) t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyisopropyl carbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl monocarbonate are high-temperature decomposition polymerization initiators.

[0093] The amount of polymerization initiator used is preferably 0.1 to 0.5 parts by weight or less per 100 parts by weight of monomer mixture, when totaled in the first copolymerization step and the second copolymerization step. This configuration yields foamable resin particles with excellent foaming properties.

[0094] The initiation step according to one embodiment of the present invention may be (a) a step of initiating copolymerization of a monomer mixture in the presence of a first poorly water-soluble inorganic salt, a low-temperature decomposition type polymerization initiator, and a high-temperature decomposition type polymerization initiator, or (b) a step of initiating copolymerization of a monomer mixture in the presence of a first poorly water-soluble inorganic salt and a low-temperature decomposition type polymerization initiator. If the initiation step is a step of initiating copolymerization of a monomer mixture in the presence of a first poorly water-soluble inorganic salt and a low-temperature decomposition type polymerization initiator, the high-temperature decomposition type polymerization initiator may be added to the reaction mixture (aqueous suspension) after the initiation step, i.e., during polymerization.

[0095] The initiation step may be carried out (initiated) at a polymerization temperature of 70°C to 90°C or 70°C or higher but less than 90°C. If the initiation step is a step in which copolymerization of the monomer mixture is started at a polymerization temperature of 70°C to 90°C or 70°C or higher but less than 90°C, the polymerization temperature may be changed to a higher temperature than at the start of polymerization (for example, greater than 90°C and 110°C or 90°C to 110°C) after the initiation step, i.e., during polymerization.

[0096] In the copolymerization step according to one embodiment of the present invention, it is preferable to use a chain transfer agent. The chain transfer agent is not particularly limited, and well-known substances used in the polymerization of methyl methacrylate resins can be used. Examples of chain transfer agents include (a) monofunctional chain transfer agents such as alkyl mercaptans and thioglycolic acid esters, and (b) polyfunctional chain transfer agents obtained by esterifying the hydroxyl group of a polyhydric alcohol (e.g., ethylene glycol, neopentyl glycol, trimethylolpropane, sorbitol, etc.) with thioglycolic acid or 3-mercaptopropionic acid. Examples of alkyl mercaptans include n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan. As the chain transfer agent, n-dodecyl mercaptan is preferred. The amount of chain transfer agent used is preferably 0.1 parts by weight or more and less than 0.5 parts by weight per 100 parts by weight of the monomer mixture.

[0097] In the foaming agent impregnation step according to one embodiment of the present invention, foaming methyl methacrylate resin particles can be obtained by impregnating methyl methacrylate resin particles, which are copolymers obtained in the copolymerization step, with a foaming agent.

[0098] The foaming agent impregnation step according to one embodiment of the present invention can be performed at any time, for example, together with the second copolymerization step or after the second copolymerization step.

[0099] In the foaming agent impregnation step according to one embodiment of the present invention, it is preferable to impregnate the obtained copolymer with the foaming agent when the polymerization conversion rate from monomer to copolymer is 80% to 95%. When the foaming agent is impregnated into the copolymer when the polymerization conversion rate is 80% or higher, the foaming agent is adequately impregnated into the interior of the copolymer, so there is no risk of aggregation of copolymers due to softening of the copolymer, and the production yield is good. When the foaming agent is impregnated into the copolymer when the polymerization conversion rate is 95% or lower, the foaming agent is sufficiently impregnated into the interior of the copolymer, so there is no risk of a double-cell structure (hard core) being formed in the foamed particles obtained by foaming the resulting foamed resin particles. As a result, a foamed molded article with excellent surface quality can be obtained by in-mold molding the foamed particles.

[0100] In the foaming agent impregnation step according to one embodiment of the present invention, the amount of foaming agent to be impregnated into the methyl methacrylate resin particles, which are copolymers, includes preferred embodiments and is the same as the foaming agent content in foamed resin particles as described in the (Foaming Agent) section of [2. Foamed Methyl Methacrylate Resin Particles]. With this configuration, foamed resin particles with sufficient foaming properties can be obtained, and foamed resin particles can be safely manufactured without causing aggregation of the copolymer in the foaming agent impregnation step.

[0101] In the foaming agent impregnation process according to one embodiment of the present invention, the processing temperature (also referred to as impregnation temperature) and processing time (also referred to as impregnation time) when impregnating the copolymer with the foaming agent are not particularly limited.

[0102] In the foaming agent impregnation step according to one embodiment of the present invention, the impregnation temperature when impregnating the copolymer with the foaming agent is preferably 95°C to 120°C or lower, and more preferably 100°C to 117°C or lower. When the impregnation temperature is 95°C or higher, the foaming agent is sufficiently impregnated into the interior of the copolymer, so there is no risk of a double-cell structure (hard core) being formed in the methyl methacrylate-based resin foam particles obtained by foaming the resulting foaming resin particles. As a result, a foamed molded article with excellent surface quality can be obtained by in-mold molding the foam particles. When the impregnation temperature is 120°C or lower, the pressure inside the polymerization machine does not become too high, so foaming resin particles with a uniform cell structure can be obtained without requiring heavy-duty impregnation equipment that can withstand high pressure.

[0103] In a method for producing foamed methyl methacrylate resin particles according to one embodiment of the present invention, the amount of solvent used is the same as the solvent content in foamed resin particles described in section [2. Foamed Methyl Methacrylate Resin Particles], including in preferred embodiments. When using a solvent (for example, a solvent with a boiling point of 50°C or higher), it is preferable to add the solvent to the reaction mixture (aqueous suspension) immediately before or simultaneously with the foaming agent impregnation step.

[0104] In this manufacturing method, when a solvent is used, the solvent may be used in both the copolymerization step (e.g., immediately before the foaming agent impregnation step) and the foaming agent impregnation step, or the solvent may be added to the reaction mixture (aqueous suspension) in both steps. The case in which a solvent is used in both the copolymerization step (e.g., immediately before the foaming agent impregnation step) and the foaming agent impregnation step will be described below. In this case, the total amount of solvent used in both steps is preferably more than 0.0 weight and 2.0 weight or less per 100 weight parts of copolymer, more preferably more than 0.0 weight and 1.5 weight or less, even more preferably more than 0.0 weight and 1.0 weight or less, even more preferably more than 0.0 weight and less than 1.0 weight, and particularly preferably more than 0.0 weight and less than 0.5 weight. In this case, the total amount of solvent used in both steps and the total amount of acrylic acid ester monomer used is preferably 3.0 to 5.0 weight per 100 weight parts of copolymer.

[0105] In order to obtain foamable resin particles that can provide foamed molded articles with excellent strength, aromatic monomers (for example, aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene) may be used in the preparation of the copolymer in this manufacturing method. For example, the monomer mixture may contain aromatic monomers. Furthermore, the solvent used in this manufacturing method may contain aromatic compounds such as xylene and toluene. In other words, aromatic compounds may be used in this manufacturing method.

[0106] On the other hand, in order to obtain foamable resin particles that can provide a foamed molded article with less residue during combustion, it is preferable that the amount of aromatic monomers and aromatic compounds used in this manufacturing method be as small as possible. In this manufacturing method, the content of aromatic monomers per 100 parts by weight of monomer mixture is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight. In other words, it is most preferable that the monomer mixture in this manufacturing method does not contain aromatic monomers. Furthermore, in this manufacturing method, the content of aromatic compounds in 100 parts by weight of solvent is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight. In other words, it is most preferable that the solvent in this manufacturing method does not contain aromatic compounds. Furthermore, in this manufacturing method, the amount of aromatic compounds used is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably less than 1.0 part by weight, particularly preferably less than 0.5 parts by weight, and most preferably 0 parts by weight, per 100 parts by weight of copolymer. In other words, it is most preferable that aromatic compounds are not used in this manufacturing method.

[0107] [4. Methyl methacrylate-based resin foamed particles] The methyl methacrylate resin foam particles according to one embodiment of the present invention are foam particles obtained by foaming foam methyl methacrylate resin particles described in section [2. Foaming methyl methacrylate resin particles] or foaming methyl methacrylate resin particles produced by the manufacturing method described in section [3. Method for producing foaming methyl methacrylate resin particles].

[0108] "Methyl methacrylate-based resin foamed particles according to one embodiment of the present invention" may also be referred to as "the foamed particles" below.

[0109] These foamed resin particles can be produced by a general foaming method. Specifically, methyl methacrylate-based foamed resin particles can be obtained by performing the following steps (1) to (3) in order: (1) Put the foamed resin particles into a pressurized foaming machine (for example, a BHP manufactured by Daikai Kogyo Co., Ltd.); (2) Blow steam (e.g., water vapor) into the foaming machine at a steam injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) Foam the foamed resin particles according to (2) until a desired foaming ratio (e.g., a bulk ratio of 60 times) is reached to obtain foamed particles.

[0110] The foaming of foamable methyl methacrylate resin particles can be considered a preliminary foaming process performed in order to obtain a methyl methacrylate resin foam molded product, as described later, from these foamable methyl methacrylate resin particles. Therefore, the foaming of foamable methyl methacrylate resin particles is sometimes referred to as "pre-foaming," and the methyl methacrylate resin foam particles themselves are sometimes referred to as "methyl methacrylate pre-foamed particles." The foaming machine used for foaming foamable methyl methacrylate resin particles (for example, the foaming machine used to measure time (A)) is sometimes referred to as a "pre-foaming machine."

[0111] Because these foamed particles have the above-described structure, the volume (B) is 140 cm³. 3 It is less than [a certain value], and therefore the foaming rate is slow. Furthermore, because these foamed particles have the above-described structure, the volume (C) is 160 cm³. 3 It is ultra-high quality and therefore has excellent shrinkage suppression properties. In other words, these foamed particles have the advantage of being able to provide foamed molded articles with excellent internal fusion properties.

[0112] [5. Methyl methacrylate-based resin foam molded product] A foamed molded article of methyl methacrylate resin according to one embodiment of the present invention is a foamed molded article obtained by in-mold molding of methyl methacrylate resin foam particles as described in section [4. Foamed Particles of Methyl Methacrylate Resin].

[0113] The "methyl methacrylate-based resin foam molded article according to one embodiment of the present invention" may also be referred to as "this foam molded article" below.

[0114] These foamed particles can be molded into a foamed molded body by a general in-mold molding method. Specifically, a foamed molded body can be obtained by performing the following operations (1) to (3) in order: (1) Fill a molding machine with a mold (for example, a PEONY-205DS manufactured by Daisen) with foamed particles; (2) Blow steam (e.g., water vapor) into the mold at a steam blowing pressure of 0.15 MPa to 0.25 MPa, and perform in-mold molding by vacuum suction heating under conditions where the pressure inside the mold is 0.030 MPa to 0.060 MPa, until the foaming pressure reaches 0.070 MPa to 0.080 MPa, thereby fusing the foamed particles together; (3) After the foaming pressure reaches 0.070 MPa to 0.080 MPa, leave it in the mold at 80°C to 110°C for 1000 seconds, and then remove the foamed molded body to obtain the foamed molded body.

[0115] Because this foamed molded product has the above-described structure, it exhibits excellent internal fusion properties. Preferably, the foamed molded product has (D) at 80% or more. As a result, this foamed molded product can be suitably used as a lost-wax model.

[0116] [6. Vanishing model] A lost-wax model according to one embodiment of the present invention includes a methyl methacrylate-based resin foam molded article described in section [5. Methyl methacrylate-based resin foam molded article].

[0117] The lost-wax model according to one embodiment of the present invention has excellent internal fusion properties and can therefore be suitably used in various metal castings.

[0118] One embodiment of the present invention may have the following configuration: [1] Foamable methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, satisfying the following (a) to (c): (a) When the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to reach foamed methyl methacrylate resin particles with a bulk ratio of 60 times is less than 810 seconds; (b) 100 cm³ of foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles 3 The volume (B) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 30 seconds and then letting it stand at 25°C for 1 minute is 140 cm³. 3 (c) less than; and (c) foamed methyl methacrylate resin particles obtained by foaming the foamed methyl methacrylate resin particles 100 cm 3 The volume (C) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 180 seconds and then letting it stand at 25°C for 1 minute is 160 cm³. 3 It's incredible. [2] Furthermore, the foamed methyl methacrylate resin particles according to claim 1 satisfy the following (d): (d) In the fracture surface of the methyl methacrylate resin foam molded article obtained by molding methyl methacrylate resin foam particles obtained by foaming the foamed methyl methacrylate resin particles, the proportion (D) of methyl methacrylate resin foam particles that are fractured at a location other than the interface of the methyl methacrylate resin foam particles is 80% or more. [3] Foaming methyl methacrylate resin particles according to [1] or [2], further comprising a solvent. [4] The foaming methyl methacrylate resin particles according to [3], wherein the content of the solvent per 100 parts by weight of the base resin is more than 0.0 parts by weight and 2.0 parts by weight or less. [5] Foaming methyl methacrylate resin particles, wherein the foaming methyl methacrylate resin particles comprise a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the foaming methyl methacrylate resin particles contain no solvent, or contain more than 0.0 part by weight and no more than 2.0 parts by weight of solvent per 100 parts by weight of the base resin, wherein in the base resin, per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, (a) the content of methyl methacrylate units is 95.0 parts by weight to 98.0 parts by weight, and (b) the content of acrylic acid ester units is 2.0 parts by weight to 5.0 parts by weight, and the total amount of acrylic acid ester units and solvent per 100 parts by weight of the base resin is 3.0 parts by weight to 5.0 parts by weight. [6] Foaming methyl methacrylate resin particles according to [4] or [5], wherein the solvent comprises cyclohexane. [7] The foaming methyl methacrylate resin particle according to any one of [1] to [6], wherein the acrylic acid ester unit is a butyl acrylate unit. [8] The foaming methyl methacrylate resin particles according to any one of [1] to [7], wherein the volume average particle diameter of the foaming methyl methacrylate resin particles is 0.5 mm to 1.4 mm. [9] (i) The base resin does not contain any constituent units derived from aromatic monomers, or contains more than 0.0 part by weight and up to 2.5 parts by weight of constituent units derived from aromatic monomers per 100 parts by weight of the base resin, and (ii) The foaming methyl methacrylate resin particles do not contain any aromatic compounds, or contain more than 0.0 part by weight and up to 2.5 parts by weight of aromatic compounds per 100 parts by weight of the base resin, as described in any one of [1] to [8].

[10] [1] to [9] Foamed methyl methacrylate resin particles obtained by foaming foamed methyl methacrylate resin particles. A methyl methacrylate resin foamed molded article obtained by in-mold molding the methyl methacrylate resin foamed particles described in

[11] and

[10] . Loss-wax model comprising a methyl methacrylate resin foam molded product as described in

[12] and

[11] .

[13] A copolymerization step comprising copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, and a foaming agent impregnation step comprising impregnating the obtained copolymer with a foaming agent, wherein the copolymerization step comprises (a) an initiation step of starting copolymerization of the monomer mixture in the presence of 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, and (b) an addition step of adding 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture to the reaction mixture after the initiation step when the polymerization conversion rate is 35% to 70%, and in the copolymerization step, the methyl methacrylate monomer A method for producing foaming methyl methacrylate resin particles, wherein the amount of methyl methacrylate monomer used is 95.0 to 98.0 parts by weight per 100 parts by weight of the total amount of the copolymer and the acrylic acid ester monomer used is 2.0 to 5.0 parts by weight, and in the copolymerization step and / or the foaming agent impregnation step, (i) no solvent is used, or a solvent is used in an amount greater than 0.0 part by weight and less than or equal to 2.0 parts by weight per 100 parts by weight of the copolymer, and (ii) the total amount of the acrylic acid ester monomer and the solvent used per 100 parts by weight of the copolymer is 3.0 to 5.0 parts by weight.

[14] The method for producing foaming methyl methacrylate resin particles according to

[13] , wherein (i) the monomer mixture does not contain an aromatic monomer, or contains more than 0.0 part by weight and no more than 2.5 parts by weight of the aromatic monomer per 100 parts by weight of the monomer mixture, and (ii) does not use an aromatic compound, or uses more than 0.0 part by weight and no more than 2.5 parts by weight of an aromatic compound per 100 parts by weight of the copolymer. [Examples]

[0119] One embodiment of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0120] (Polymerization and conversion rate of foamed methyl methacrylate resin particles) During polymerization, an aqueous suspension was sampled and filtered. The weight of the resin component remaining on the filter paper was measured and taken as the weight before heating. Next, a polymerization inhibitor was added to the resin component, and the resin component was heated at 150°C for 30 minutes to remove volatile components. After that, the weight of the resulting resin component was measured and taken as the weight after heating. The polymerization conversion rate was calculated using the following formula. Polymerization conversion rate (%) = Weight after heating / Weight before heating × 100.

[0121] (Foaming properties of foaming methyl methacrylate resin particles) The foamed resin particles were sieved to separate foamed resin particles with a particle size of 0.5 mm to 1.4 mm. Using the separated foamed resin particles, the following steps (1) to (4) were performed in order, and the time (A) (heating time) for the foamed resin particles to be heated until foamed particles with a bulk ratio of 60 times were obtained was measured: (1) The separated foamed resin particles were put into a BHP, a pressurized foaming machine manufactured by Daikai Kogyo Co., Ltd.; (2) Next, steam was blown into the foaming machine under conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, and the foamed resin particles were heated; (3) At regular intervals, the foamed particles formed from the foamed resin particles were removed from the foaming machine, and the bulk ratio of the foamed particles was measured; (4) The time (A) from when steam was blown into the foamed resin particles until foamed particles with a bulk ratio of 60 times were obtained was measured. Here, the bulk ratio of the foamed particles was determined by performing the following steps (1) to (3) in order: (1) Weigh out 10g of foamed particles and measure 1000cm² 3 (1) The foam particles were placed in a graduated cylinder; (2) The volume of 10g of foam particles was measured from the scale on the graduated cylinder; (3) The bulk ratio of the foam particles was calculated using the following formula; Bulk magnification (cm 3 ( / g) = Volume of foamed particles (cm³) 3 ) / 10g.

[0122] Based on the following criteria, the foaming properties of the foamed resin particles were evaluated from the obtained time (A). ◎ (Excellent): Time (A) is 710 seconds or less ○ (Good): Time (A) is between 710 seconds and less than 810 seconds. × (Bad): Time (A) is 810 seconds or more.

[0123] (Foaming properties of methyl methacrylate resin foam particles) The foamed resin particles were sieved to separate foamed resin particles with a particle size of 0.5 mm to 1.4 mm. Using the separated foamed resin particles, the following steps (1) to (3) were performed in order to obtain foamed resin particles with a bulk ratio of 60: (1) The foamed resin particles were put into a BHP, a pressurized foaming machine manufactured by Daikai Kogyo Co., Ltd.; (2) Steam was blown into the foaming machine at a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) The foamed resin particles were foamed according to (2) until a bulk ratio of 60 was obtained.

[0124] Using the obtained foamed particles, the following steps (1) to (5) were performed in order, and the volume (B) of the foamed particles was measured: (1) 100 cm³ of foamed particles with a bulk ratio of 60 times 3 (1) Weigh out the foam particles and put them into a steamer with an outlet; (2) Supply 100°C steam to the steamer and heat the foam particles for 30 seconds; (3) After heating, remove the foam particles from the steamer and leave them at 25°C for 1 minute; (4) Disperse the foam particles at 1000 cm 3 (5) The foamed particles were placed in a graduated cylinder; the volume (B) of the foamed particles was measured from the scale on the graduated cylinder. The foaming properties of the foamed particles were evaluated from the obtained volume (B) based on the following criteria. A smaller volume (B), i.e., a lower foaming property of the foamed particles, was given a higher evaluation. ◎ (Excellent): Volume (B) is 130 cm³ 3 below ○ (Good): Volume (B) is 130 cm³ 3 Super 140cm 3 less than × (Defective): Volume (B) is 140 cm³ 3 That's all.

[0125] (Shrinkage suppression of methyl methacrylate-based resin foam particles) Foaming particles with a bulk ratio of 60 times were obtained by the method described in the section above (Foaming properties of methyl methacrylate resin foaming particles). Using the obtained foaming particles, the following (1) to (5) were carried out in order and the volume (C) of the foaming particles was measured: (1) 100 cm³ of foaming particles with a bulk ratio of 60 times 3 (1) Weigh out the foam particles and put them into a steamer with an outlet; (2) Supply 100°C steam to the steamer and heat the foam particles for 180 seconds; (3) After heating, remove the foam particles from the steamer and leave them at 25°C for 1 minute; (4) Dissolve the foam particles in 1000cm³ 3 (5) The foam particles were placed in a graduated cylinder; the volume (C) of the foam particles was measured from the scale on the graduated cylinder. Based on the following criteria, the shrinkage suppression ability of the foam particles was evaluated from the obtained volume (C). ◎ (Excellent): Volume (C) is 165 cm³ 3 super ○ (Good): Volume (C) is 160 cm³ 3 Super 165cm 3 below × (Defective): Volume (C) is 160 cm³ 3 below.

[0126] (Internal fusion properties of methyl methacrylate-based resin foam molded articles) The foamed resin particles were sieved to separate them into particles with a diameter of 0.5 mm to 1.4 mm.

[0127] Using the separated foamed resin particles, the following steps (1) to (8) were carried out in order to obtain a foamed molded product: (1) The foamed resin particles were put into a BHP, a pressurized foaming machine manufactured by Daikai Kogyo Co., Ltd.; (2) Steam was blown into the foaming machine at a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) The foamed resin particles were foamed up as in (2) until the bulk ratio reached 60 times; (4) The obtained foamed particles were left at room temperature (25°C) for 3 days to obtain foamed particles with a bulk ratio of 60 times; (5) A mold with a length of 2000 mm, a width of 1000 mm and a thickness of 525 mm was used. (6) A molding machine (PEONY-205DS manufactured by Daisen) was filled with foam particles having a bulk ratio of 60; (7) Steam was blown into the mold at a steam blowing pressure of 0.15 MPa to 0.25 MPa, and under conditions where the pressure inside the mold was 0.030 MPa to 0.060 MPa, in-mold molding was performed by vacuum suction heating until the foam pressure reached 0.070 MPa to 0.080 MPa, fusing the foam particles together; (8) After the foam pressure reached 0.070 MPa to 0.080 MPa, the mold was left in the mold at 80°C to 110°C for 1000 seconds, and then the foam molded body was removed; (9) The removed foam molded body was left at 60°C for 3 days to obtain a foam molded body. The obtained foam molded body was 2000 mm in length, 1000 mm in width, and 525 mm in thickness.

[0128] Using the obtained foamed molded body, the following steps (1) to (3) were performed in order to measure the proportion (D) of the fracture surface of the foamed molded body: (1) The foamed molded body was cut perpendicular to the thickness direction using a hot wire slicer so that it was divided equally into 5 sections in the thickness direction; (2) For the middle of the 5 sections (the part of the foamed molded body from 210 mm to 315 mm in the thickness direction before cutting), the plane perpendicular to the thickness direction was bent along the width direction at the center in the length direction to fracture the foamed molded body; (3) The obtained fracture surface was visually observed, and the number of foamed particles that made up the fracture surface and the number of fractured foamed particles other than at the particle interface were measured, and the proportion (D) was calculated based on the following formula; Percentage (D) (%) = Number of particles fractured outside the particle interface on the fracture surface / Number of particles constituting the fracture surface × 100.

[0129] Based on the obtained proportion (D), the internal fusion properties of the foamed molded product were evaluated according to the following criteria. ◎ (Excellent): Percentage (D) is 90% or higher ○ (Good): Percentage (D) is between 80% and 90% × (Defective): Percentage (D) is less than 80%.

[0130] (Evaluation of residue during combustion of methyl methacrylate-based foamed molded products) Based on the description in the section (Internal fusion properties of methyl methacrylate-based resin foam molded articles), a foam molded article was obtained. Approximately 7 g (approximately 300 cm³) of the obtained foam molded article was obtained. 3 The foamed molded material was burned by igniting it with a gas burner. The amount of soot generated during the combustion of the foamed molded material was observed visually.

[0131] (Example 1) A mixture containing the first poorly water-soluble inorganic salt was prepared by charging 150 parts by weight of water, 0.15 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, 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, and 0.24 parts by weight of n-dodecyl mercaptan into a 6 L autoclave equipped with a stirrer. Subsequently, 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate as a monomer mixture were charged into the mixture to prepare an aqueous suspension. Next, the temperature of the aqueous suspension was raised to 80°C to start polymerization, i.e., the initiation step was carried out. After 1 hour and 45 minutes from the start of polymerization (after the initiation step), the polymerization conversion rate was measured to be 40% to 50%. One hour and forty-five minutes after the start of polymerization (after the initiation step), 0.12 parts by weight of tricalcium phosphate was added to the reaction mixture (aqueous suspension) as the second poorly water-soluble inorganic salt, and the addition step was carried out. The initiation step and the addition step described above can also be called the first copolymerization step.

[0132] After another 2 hours and 35 minutes, 0.5 parts by weight of cyclohexane as a solvent and 9 parts by weight of n-rich butane (the weight ratio of n-butane to isobutane in the n-rich butane (n-butane / isobutane) is 70 / 30) were added to the aqueous suspension. 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 carry out copolymerization and impregnation of the copolymer with the blowing agent (copolymerization step (also called the second copolymerization step) and blowing agent impregnation step). The aqueous suspension was then cooled. After cooling the aqueous suspension, the obtained product was washed, dehydrated, and dried to obtain foaming methyl methacrylate resin particles.

[0133] The obtained foamed methyl methacrylate resin particles were sieved using sieves with mesh sizes of 0.500 mm and 1.400 mm. Through this procedure, foamed methyl methacrylate resin particles with particle sizes ranging from 0.500 mm to 1.400 mm were collected.

[0134] Following the method described above, the foaming properties of foamed methyl methacrylate resin particles, the foaming properties and shrinkage suppression properties of foamed methyl methacrylate resin particles, and the internal fusion properties of foamed molded articles of methyl methacrylate resin were evaluated. The evaluation results are shown in Table 1.

[0135] (Example 2) Except for changing the monomer mixture used to 96.5 parts by weight of methyl methacrylate and 3.5 parts by weight of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0136] (Example 3) Except for changing the monomer mixture used to 96.5 parts by weight of methyl methacrylate, 3.5 parts by weight of butyl acrylate, and 1.0 part by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0137] (Example 4) Except for changing the monomer mixture used to 97.0 parts by weight of methyl methacrylate, 3.0 parts by weight of butyl acrylate, and 1.5 parts by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0138] (Example 5) Except for changing the monomer mixture used to 95.0 parts by weight of methyl methacrylate and 5.0 parts by weight of butyl acrylate, and 0 parts by weight of cyclohexane (i.e., no cyclohexane was used), the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0139] (Example 6) Except for changing the monomer mixture used to 98.0 parts by weight of methyl methacrylate, 2.0 parts by weight of butyl acrylate, and 1.0 part by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0140] (Comparative Example 1) Except for changing the monomer mixture used to 95.0 parts by weight of methyl methacrylate and 5.0 parts by weight of butyl acrylate, and changing the solvent used to 1.5 parts by weight of cyclohexane and 1.0 part by weight of toluene, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0141] (Comparative Example 2) Except for changing the monomer mixture used to 96.0 parts by weight of methyl methacrylate, 4.0 parts by weight of butyl acrylate, and 1.5 parts by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0142] (Comparative Example 3) Except for changing the monomer mixture used to 94.5 parts by weight of methyl methacrylate and 5.5 parts by weight of butyl acrylate, and 0 parts by weight of cyclohexane (i.e., no cyclohexane was used), the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0143] (Comparative Example 4) Except for changing the amount of cyclohexane used to 0 parts by weight (i.e., no cyclohexane was used), the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0144] (Comparative Example 5) Except for changing the monomer mixture used to 98.5 parts by weight of methyl methacrylate, 1.5 parts by weight of butyl acrylate, and 1.5 parts by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0145] (Comparative Example 6) Except for changing the monomer mixture used to 96.5 parts by weight of methyl methacrylate, 3.5 parts by weight of butyl acrylate, and 2.0 parts by weight of cyclohexane, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0146] (Comparative Example 7) Except for changing the monomer mixture used to 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate, and changing the solvent used to 1.5 parts by weight of cyclohexane and 1.0 part by weight of toluene, the same procedure as in Example 1 was carried out to obtain foaming methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0147] Using the foamed methyl methacrylate resin particles with particle sizes of 0.500 mm to 1.400 mm obtained in Examples 1 to 6 and Comparative Examples 1 to 7, foamed methyl methacrylate resin molded articles were obtained according to the method described above, and the residue during combustion of these foamed methyl methacrylate resin molded articles was evaluated. As a result, no soot was visible to the naked eye in the foamed methyl methacrylate resin resin particles obtained in Examples 1 to 6 and Comparative Examples 2 to 6, confirming that almost no residue (soot) was generated during combustion. In contrast, soot was visible to the naked eye in the foamed methyl methacrylate resin particles obtained in Comparative Examples 1 and 7, confirming that residue (soot) was generated during combustion.

[0148] [Table 1] [Industrial applicability]

[0149] According to one embodiment of the present invention, foamable methyl methacrylate resin particles can be provided that can efficiently provide a foamed molded article with excellent internal fusion properties. Therefore, one embodiment of the present invention can be suitably used as a lost-wax model when performing metal casting by the full-molding method.

Claims

1. The material comprises a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, satisfying the following conditions (a) to (c): Free from solvents, or containing solvents, If the aforementioned solvent is included, the content of aromatic compounds in 100 parts by weight of the solvent is 2.5 parts by weight or less. The aforementioned acrylic acid ester units are butyl acrylate units, foaming methyl methacrylate resin particles: (a) When the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to become foamed methyl methacrylate resin particles with a bulk ratio of 60 is less than 810 seconds; (b) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles 100 cm ３ The volume (B) of the methyl methacrylate resin foam particles obtained by heating with 100°C steam for 30 seconds and then letting it stand at 25°C for 1 minute is 140 cm³. ３ Less than; and (c) Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles 100 cm ３ The volume (C) of the methyl methacrylate-based resin foam particles obtained by heating with 100°C steam for 180 seconds and then letting it stand at 25°C for 1 minute is 160 cm³. ３ It's incredible.

2. Furthermore, the foaming methyl methacrylate resin particles according to claim 1 satisfy the following (d): (d) In the fracture surface of the methyl methacrylate resin foam molded article obtained by molding methyl methacrylate resin foam particles, which are obtained by foaming the foamable methyl methacrylate resin particles, the proportion (D) of methyl methacrylate resin foam particles that are fractured at a location other than the interface of the methyl methacrylate resin foam particles is 80% or more.

3. The foaming methyl methacrylate resin particles according to claim 1, wherein the content of the solvent per 100 parts by weight of the base resin is more than 0.0 parts by weight and 2.0 parts by weight or less.

4. Foaming methyl methacrylate resin particles, The foamed methyl methacrylate resin particles comprise a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent. The foaming methyl methacrylate resin particles either contain no solvent or contain more than 0.0 parts by weight and no more than 2.0 parts by weight of solvent per 100 parts by weight of the base resin. In the aforementioned base resin, relative to 100 parts by weight of the total amount of the methyl methacrylate units and the acrylic acid ester units, (a) The content of the methyl methacrylate units is 95.0 parts by weight to 98.0 parts by weight, (b) The content of the acrylic acid ester units is 2.0 parts by weight to 5.0 parts by weight, The total amount of the acrylic acid ester units and the solvent per 100 parts by weight of the base resin is 3.0 to 5.0 parts by weight. If the aforementioned solvent is included, the content of aromatic compounds in 100 parts by weight of the solvent is 2.5 parts by weight or less. The aforementioned acrylic acid ester unit is a butyl acrylate unit, The foamed methyl methacrylate resin particles have a volume-average particle diameter of 0.5 mm to 1.4 mm.

5. The foaming methyl methacrylate resin particles according to claim 3 or 4, wherein the solvent comprises cyclohexane.

6. The foamed methyl methacrylate resin particles according to any one of claims 1 to 3, wherein the volume average particle diameter of the foamed methyl methacrylate resin particles is 0.5 mm to 1.4 mm.

7. (i) The base resin does not contain any constituent units derived from aromatic monomers, or contains more than 0.0 part by weight and no more than 2.5 parts by weight of constituent units derived from aromatic monomers per 100 parts by weight of the base resin, (ii) The foaming methyl methacrylate resin particles according to any one of claims 1 to 6, wherein the foaming methyl methacrylate resin particles do not contain an aromatic compound, or contain an aromatic compound in an amount of more than 0.0 part by weight and up to 2.5 parts by weight per 100 parts by weight of the base resin.

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

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

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

11. The process includes a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, and a foaming agent impregnation step of impregnating the resulting copolymer with a foaming agent. The copolymerization step is, (a) A starting step in which copolymerization of the monomer mixture is started in the presence of 0.08 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, (b) After the initial step, when the polymerization conversion rate is 35% to 70%, the process includes an addition step of adding 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt to the reaction mixture per 100 parts by weight of the monomer mixture, In the copolymerization step described above, the amount of methyl methacrylate monomer used is 95.0 to 98.0 parts by weight, and the amount of acrylic acid ester monomer used is 2.0 to 5.0 parts by weight, relative to a total of 100 parts by weight of the methyl methacrylate monomer and the acrylic acid ester monomer used. In the copolymerization step and / or the foaming agent impregnation step, (i) No solvent is used, or more than 0.0 part by weight and no more than 2.0 parts by weight of solvent are used per 100 parts by weight of the copolymer, (ii) The total amount of the acrylic acid ester monomer and the solvent used per 100 parts by weight of the copolymer is 3.0 to 5.0 parts by weight. (iii) When the solvent is used, the content of aromatic compounds in 100 parts by weight of the solvent is 2.5 parts by weight or less. A method for producing foaming methyl methacrylate resin particles, wherein the acrylic acid ester monomer is butyl acrylate.

12. In the method for producing the foamed methyl methacrylate resin particles, (i) The monomer mixture does not contain an aromatic monomer, or contains more than 0.0 part by weight and no more than 2.5 parts by weight of the aromatic monomer per 100 parts by weight of the monomer mixture, (ii) A method for producing foaming methyl methacrylate resin particles according to claim 11, wherein no aromatic compound is used, or an aromatic compound is used in an amount greater than 0.0 part by weight and less than or equal to 2.5 parts by weight per 100 parts by weight of the copolymer.

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