Expandable methyl methacrylate-based resin particles and use thereof

Abstract

To provide expandable methyl methacrylate-based resin particles that can yield expandable methyl methacrylate-based foam particles having superior blocking resistance during pre-foaming and superior filling capability into molds during molding.SOLUTION: Expandable methyl methacrylate-based resin particles are used, wherein the resin particles contain a base resin including, as structural units, a methyl methacrylate unit and an acrylate ester unit, and a foaming agent; and a specific amount of N,N-bis(2-hydroxyethyl)alkylamine is present on a surface thereof.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to expandable methyl methacrylate resin particles and their use.

Background Art

[0002] When performing metal casting, a lost foam casting method (full mold method) 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, thereby casting a casting.

[0003] Conventionally, a foam molded body obtained by using expandable methyl methacrylate resin particles has been widely used as a lost mold for casting because a casting with a beautiful surface can be obtained.

[0004] For example, Patent Document 1 discloses acrylic resin particles and expandable acrylic resin particles containing an acrylic resin and a foaming agent.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the conventionally known expandable acrylic resin particles as described above have room for improvement from the viewpoints of blocking resistance during pre-foaming and filling property of the acrylic foam particles formed by foaming the expandable acrylic resin particles into a mold during molding.

[0007] In such a situation, an aspect of the present invention is to provide expandable methyl methacrylate resin particles that are excellent in blocking resistance during pre-foaming and excellent in mold filling properties during molding.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the inventors have completed the present invention. That is, one embodiment of the present invention includes the following configurations.

[0009] 〔1〕Expandable methyl methacrylate resin particles containing a base resin containing a methyl methacrylate unit and an acrylate unit as structural units, and a foaming agent, wherein on the surface of the expandable methyl methacrylate resin particles, 0.06 parts by weight to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine is contained with respect to 100 parts by weight of the expandable methyl methacrylate resin particle body.

[0010] 〔2〕The expandable methyl methacrylate resin particles according to 〔1〕, wherein the acrylate unit is a butyl acrylate unit.

[0011] 〔3〕The expandable methyl methacrylate resin particles according to 〔1〕 or 〔2〕, wherein the base resin contains 2.0 parts by weight to 6.0 parts by weight of butyl acrylate unit with respect to 100 parts by weight of the resin.

[0012] 〔4〕The expandable methyl methacrylate resin particles according to any one of 〔1〕 to 〔3〕, wherein the expandable methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.60 mm.

[0013] 〔5〕Methyl methacrylate resin foam particles obtained by foaming the expandable methyl methacrylate resin particles according to any one of 〔1〕 to 〔4〕.

[0014] A methyl methacrylate resin foam molded body formed by in-mold molding of the methyl methacrylate resin foam particles described in [6] [5].

[0015] A lost mold including the methyl methacrylate resin foam molded body described in [7] [6].

Advantages of the Invention

[0016] According to one aspect of the present invention, it is possible to provide foaming methyl methacrylate-based resin particles that are excellent in blocking resistance during preliminary foaming and excellent in filling property into a mold during molding.

Modes for Carrying Out the Invention

[0017] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope shown in the claims. Also, 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. Furthermore, by combining the technical means disclosed in each embodiment, new technical features can be formed. All academic documents and patent documents described in this specification are incorporated herein by reference. Also, unless otherwise specified in this specification, "A to B" representing a numerical range is intended to mean "A or more (including A and greater than A) and B or less (including B and less than B)".

[0018] In this specification, the structural unit derived from the X monomer contained in the polymer or copolymer may be referred to as "X unit".

[0019] In this specification, "foaming methyl methacrylate-based resin particles" may also be referred to as "foaming resin particles", "methyl methacrylate-based resin foam particles" may also be referred to as "foam particles", and "methyl methacrylate-based resin foam molded body" may also be referred to as "foam molded body".

[0020] [1. Technical idea of an embodiment of the present invention] Conventional foaming acrylic resin particles as disclosed in Patent Document 1 had room for improvement from the viewpoints of blocking resistance during pre-foaming and mold filling property during molding of acrylic foam particles formed by foaming the foaming acrylic resin particles.

[0021] Under the above circumstances, the present inventors conducted intensive studies to provide foaming acrylic resin particles having excellent blocking resistance during pre-foaming and mold filling property during molding of acrylic foam particles formed by foaming the foaming acrylic resin particles. As a result, in the case of methyl methacrylate-based resin particles which are one type of foaming acrylic resin particles, by containing a predetermined amount of N,N-bis(2-hydroxyethyl)alkylamine on the surface of the resin particles, the blocking resistance during pre-foaming of the resin particles can be improved (in other words, the sticking together of acrylic foam particles obtained by pre-foaming can be suppressed), and at the same time, a new finding that the mold filling property during molding of acrylic foam particles formed by foaming the resin particles can also be improved was found, leading to the completion of the present invention.

[0022] The finding that N,N-bis(2-hydroxyethyl)alkylamine can improve the blocking resistance during pre-foaming of methyl methacrylate-based resin particles and the mold filling property during molding of methyl methacrylate-based resin foam particles formed by foaming the methyl methacrylate-based resin particles is a very surprising and novel finding that could not be predicted from the prior art.

[0023] [2. Methyl methacrylate-based resin particles for foaming] The expandable methyl methacrylate resin particles according to one embodiment of the present invention are expandable methyl methacrylate resin particles containing a base resin containing a methyl methacrylate unit and an acrylate unit as constituent units, and a foaming agent, and on the surface of the expandable methyl methacrylate resin particles, 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine is contained with respect to 100 parts by weight of the expandable methyl methacrylate resin particle main body.

[0024] The "expandable methyl methacrylate resin particles according to one embodiment of the present invention" may sometimes be referred to as the "present expandable resin particles" hereinafter.

[0025] In the present specification, expandable resin particles that do not contain N,N-bis(2-hydroxyethyl)alkylamine on the surface are referred to as "expandable resin particle main bodies", and expandable resin particles that contain N,N-bis(2-hydroxyethyl)alkylamine or other externally added agents on the surface are referred to as "expandable resin particles".

[0026] By foaming the present expandable resin particles by a known method, expandable particles can be provided. By molding the expandable particles obtained by foaming the present expandable resin particles in a mold by a known method, an expanded molded article can be provided.

[0027] Since the present expandable resin particles have the above configuration, they have the advantage of being able to provide expandable resin particles that are excellent in blocking resistance during pre-foaming and in mold filling property (sometimes simply referred to as filling property) during molding of the expandable particles obtained by foaming the expandable methyl methacrylate resin particles. The evaluation methods for the blocking resistance during pre-foaming of the expandable resin particles and the filling property of the expandable particles will be described in detail in the following examples.

[0028] (2-1. Base resin) The base resin contained in the present expandable resin particles contains a methyl methacrylate unit and an acrylate unit as constituent units.

[0029] In this specification, the notation "monomer" may be omitted. Therefore, in this specification, for example, when simply denoted as "methyl methacrylate" and "acrylate", they respectively intend "methyl methacrylate monomer" and "acrylate monomer".

[0030] In the base resin contained in the expandable resin particles, with respect to a total of 100 parts by weight of the methyl methacrylate unit and the acrylate unit, (a) the content of the methyl methacrylate unit is preferably 93.0 to 99.0 parts by weight, and the content of the acrylate unit is preferably 1.0 to 7.0 parts by weight; (b) the content of the methyl methacrylate unit is preferably 93.5 to 98.5 parts by weight, and the content of the acrylate unit is preferably 1.5 to 6.5 parts by weight; (c) the content of the methyl methacrylate unit is more preferably 94.0 to 98.0 parts by weight, and the content of the acrylate unit is more preferably 2.0 to 6.0 parts by weight; (d) the content of the methyl methacrylate unit is more preferably 94.5 to 97.5 parts by weight, and the content of the acrylate unit is more preferably 2.5 to 5.5 parts by weight; (e) the content of the methyl methacrylate unit is more preferably 95.0 to 97.0 parts by weight, and the content of the acrylate unit is more preferably 3.0 to 5.0 parts by weight; (f) the content of the methyl methacrylate unit is more preferably 95.5 to 97.0 parts by weight, and the content of the acrylate unit is more preferably 3.0 to 4.5 parts by weight; (g) the content of the methyl methacrylate unit is more preferably 97.0 to 96.0 parts by weight, and the content of the acrylate unit is more preferably 3.0 to 4.0 parts by weight. When the content of the methyl methacrylate unit and the content of the acrylate unit in the base resin of the expandable resin particles are within the above-mentioned ranges respectively, the expandable resin particles have the advantages of excellent blocking resistance during pre-expansion and excellent mold filling property during molding of the expanded particles formed by expanding the expandable resin particles.

[0031] In the base resin, when the content of the acrylate unit relative to 100 parts by weight of the total amount of the methyl methacrylate unit and the acrylate unit is within the above-described range, it has the advantage of being excellent in blocking resistance during pre-foaming and in mold filling property during molding of the foam particles formed by foaming the expandable resin particles. Further, the expandable resin particles (foam particles) have the advantage of being able to provide a foam molded body excellent in fusibility.

[0032] In one embodiment of the present invention, the total content of the methyl methacrylate unit and the acrylate unit in 100% by weight of the base resin is preferably 95.0% by weight or more, more preferably 96.0% by weight or more, more preferably 96.0% by weight or more, more preferably 97.0% by weight or more, more preferably 97.5% by weight or more, more preferably 98.0% by weight or more, more preferably 98.5% by weight or more, more preferably 99.0% by weight or more, still more preferably 99.5% by weight or more, and particularly preferably 100.0% by weight (in other words, the base resin consists of the methyl methacrylate unit and the acrylate unit). According to this configuration, the expandable resin particles have the advantage of being excellent in blocking resistance during pre-foaming and in mold filling property during molding of the foam particles formed by foaming the expandable resin particles.

[0033] Examples of the acrylate unit that the base resin may contain include a methyl acrylate unit, an ethyl acrylate unit, a propyl acrylate unit, a butyl acrylate unit, a pentyl acrylate unit, a hexyl acrylate unit, and a 2-ethylhexyl acrylate unit.

[0034] The acrylic ester unit is preferably at least one selected from the group consisting of (a) methyl acrylate unit, ethyl acrylate unit, propyl acrylate unit, butyl acrylate unit, pentyl acrylate unit, hexyl acrylate unit, and 2-ethylhexyl acrylate unit; more preferably at least one selected from the group consisting of (b) methyl acrylate unit, ethyl acrylate unit, propyl acrylate unit, butyl acrylate unit, pentyl acrylate unit, and hexyl acrylate unit; still more preferably at least one selected from the group consisting of (c) methyl acrylate unit, ethyl acrylate unit, propyl acrylate unit, and butyl acrylate unit; and particularly preferably (d) butyl acrylate unit. According to this configuration, the expandable resin particles have the advantage of being excellent in blocking resistance during pre-expansion and in mold filling property during molding of the expanded particles formed by expanding the expandable resin particles.

[0035] In one embodiment of the present invention, it is particularly preferable that the base resin contained in the expandable resin particles contains 94.0 to 98.0 parts by weight of methyl methacrylate units and 2.0 to 6.0 parts by weight of butyl acrylate units as acrylic ester units. When the base resin contained in the expandable resin particles contains 2.0 parts by weight or more of butyl acrylate units, the expandable resin particles are excellent in expandability during pre-expansion. Also, by setting the content of butyl acrylate units to 6.0 parts by weight or less, expanded particles excellent in heat resistance can be provided. As a result, it is also possible to provide an expanded molded article excellent in surface elongation.

[0036] The base resin of the expandable resin particles may contain a structural unit derived from a crosslinking agent (hereinafter also referred to as a crosslinking agent unit). When the base resin of the expandable resin particles contains a crosslinking agent unit, the expandable resin particles have the advantages of being able to provide expanded particles excellent in shrinkage suppression and excellent in expandability.

[0037] The base resin of the expandable resin particles may further contain, as a constituent unit, a constituent unit derived from an aromatic monomer (hereinafter also referred to as an aromatic unit). Examples of the aromatic monomer include aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. When the base resin of the expandable resin particles contains an aromatic unit, a foam-molded article excellent in strength can be obtained.

[0038] On the other hand, from the viewpoint of obtaining a foam-molded article with less residue during combustion, the amounts of the constituent unit derived from an aromatic monomer (for example, a monomer having an aromatic ring) and the constituent unit having a ring structure (for example, a constituent unit derived from an alicyclic compound, hereinafter also referred to as a ring structure unit) contained in the base resin of the expandable resin particles are preferably as small as possible. For example, the total amount of the aromatic unit and the ring structure unit contained in the base resin of the expandable resin particles is 2.5% by weight or less, preferably less than 2.5% by weight, more preferably 2.0% by weight or less, more preferably 1.5% by weight or less, further preferably 1.0% by weight or less, further preferably 0.5% by weight or less, and particularly preferably 0% by weight in 100% by weight of the base resin. That is, it is particularly preferable that the base resin of the expandable resin particles does not contain an aromatic unit and a ring structure unit. Here, the "total amount of the aromatic unit and the ring structure unit contained in the base resin" means (a) when the base resin contains an aromatic unit and does not contain a ring structure unit, the amount of the aromatic unit is intended; (b) when the base resin contains a ring structure unit and does not contain an aromatic unit, the amount of the ring structure unit is intended; and (c) when the base resin contains an aromatic unit and a ring structure unit, the total amount of the aromatic unit and the ring structure unit is intended.

[0039] (2-2. Blowing agent) The blowing agent contained in the expandable resin particles is not particularly limited.

[0040] Specific examples of the foaming agent include, for example, (a) aliphatic hydrocarbons having 3 to 5 carbon atoms such as propane, n-butane, isobutane, n-pentane, isopentane, and neopentane; and (b) fluorocarbons having a zero ozone depletion potential such as difluoroethane and tetrafluoroethane; and other volatile foaming agents.

[0041] These foaming agents may be used alone or in combination of two or more without any problem.

[0042] In the case of the foaming resin particles, the content of the foaming agent with respect to 100 parts by weight of the base resin is preferably 5 to 12 parts by weight, more preferably 7 to 10 parts by weight. According to this configuration, there is an advantage that foaming resin particles having sufficient foamability can be provided and heavy polymerization equipment is not required.

[0043] (2-3. Other Additives) The foaming resin particles may optionally contain other additives in addition to the base resin and the foaming agent. Examples of the other additives include solvents, plasticizers, cell regulators, flame retardants, flame retardant aids, heat ray radiation inhibitors, pigments, dyes, and antistatic agents.

[0044] The solvent is not particularly limited, but a solvent having a boiling point of 50°C or higher is preferred. Examples of the solvent having a boiling point of 50°C or higher include (a) aliphatic hydrocarbons having 6 or more carbon atoms (C6 or more) such as toluene, hexane, and heptane, and (b) alicyclic hydrocarbons having 6 or more carbon atoms such as cyclohexane and cyclooctane.

[0045] Since expandable resin particles with excellent foamability can be obtained, as the solvent having a boiling point of 50°C or higher, toluene and / or cyclohexane is preferable. In these expandable resin particles, the content of the solvent with respect to 100 parts by weight of the base resin is preferably 1.5 to 3.0 parts by weight. When the content of the solvent with respect to 100 parts by weight of the base resin is (a) 1.5 parts by weight or more, expandable resin particles having sufficient foaming power can be obtained, and when it is (b) 3.0 parts by weight or less, an expansion-molded article with suppressed surface expansion, that is, excellent dimensional stability can be obtained.

[0046] The plasticizer is not particularly limited, but a high-boiling plasticizer having a boiling point of 200°C or higher is preferable.

[0047] Examples of the high-boiling plasticizer include (a) fatty acid glycerides such as triglyceride stearate, triglyceride palmitate, triglyceride laurate, diglyceride stearate, and monoglyceride stearate, (b) vegetable oils such as coconut oil, palm oil, and palm kernel oil, (c) aliphatic esters such as dioctyl adipate and dibutyl sebacate, and (d) organic hydrocarbons such as liquid paraffin and cyclohexane.

[0048] When the above-described substances are contained (coated) on the surface of the expandable resin particles, the above-described substances are not regarded as other additives (in this case, regarded as other external additives). In other words, these expandable resin particles may contain the various other additives described above as other external additives.

[0049] (2-4.N,N-bis(2-hydroxyethyl)alkylamine) These expandable resin particles contain 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine on the surface of the expandable resin particle body with respect to 100 parts by weight of the expandable resin particle body.

[0050] By containing N,N-bis(2-hydroxyethyl)alkylamine on the surface of the expandable resin particles, the expandable resin particles have the advantages of excellent blocking resistance during pre-expansion and excellent mold filling property during molding of the expanded particles formed by expanding the expandable resin particles.

[0051] In this specification, "containing (X component) on the surface of the expandable methacrylic resin particles" is intended to mean that "at least a part or the whole of the surface of the expandable methacrylic resin particle body is covered with (X component)". Also, in this specification, "containing (X component) on the surface of the expandable methacrylic resin particles" can also be said to mean that "(X component) is applied to at least a part or the whole of the surface of the expandable methacrylic resin particle body".

[0052] Also, in this specification, containing (X component) on the surface of the expandable resin particles means any one of (i) a state where the total amount of (X component) contained in the expandable resin particles forms a layer on the surface of the expandable resin particle body, (ii) a state where the total amount of (X component) contained in the expandable resin particles is impregnated in the surface layer portion of the expandable resin particle body, or (iii) a state where a part of (X component) contained in the expandable resin particles forms a layer on the surface of the expandable resin particle body and the remaining part of the (X component) is impregnated in the surface layer portion of the expandable resin particle body.

[0053] As an embodiment of containing (X component) on the surface of the expandable resin particles, among the above-mentioned states (i) to (iii), the state where the total amount of (X component) contained in the expandable resin particles forms a layer on the surface of the expandable resin particle body is more preferable. According to this configuration, the expandable resin particles have the advantages of excellent blocking resistance during pre-expansion and excellent mold filling property during molding of the expanded particles formed by expanding the expandable resin particles.

[0054] The content of N,N-bis(2-hydroxyethyl)alkylamine on the surface of the expandable resin particles is 0.06 to 0.28 parts by weight, preferably 0.06 to 0.28 parts by weight, more preferably 0.06 to 0.28 parts by weight, still more preferably 0.06 to 0.28 parts by weight or less, and particularly preferably 0.06 to 0.2 parts by weight, based on 100 parts by weight of the expandable resin particle body. According to this configuration, the expandable resin particles have the advantages of excellent blocking resistance during pre-expansion and excellent mold filling property during molding of the expanded particles formed by expanding the expandable resin particles, and can provide an expanded molded article with excellent surface elongation.

[0055] In addition, the above values are intended to be values obtained by rounding the third decimal place with respect to the content of N,N-bis(2-hydroxyethyl)alkylamine based on 100 parts by weight of the expandable resin particle body. That is, for example, "0.03 parts by weight or more and 0.14 parts by weight or less based on 100 parts by weight of the expandable resin particle body" is strictly intended to be "0.025 parts by weight or more and less than 0.145 parts by weight based on 100 parts by weight of the base resin".

[0056] (2-5. Other external additives) The expandable resin particles may contain external additives other than N,N-bis(2-hydroxyethyl)alkylamine (also referred to as "other external additives" in this specification) on the surface of the expandable resin particles.

[0057] The other external additives are not particularly limited. For example, fatty acid metal salts such as magnesium stearate, zinc stearate, and magnesium stearate, waxes such as carnauba wax, antistatic agents such as polyglycol, and fusion accelerators such as fatty acid triglycerides, fatty acid diglycerides, fatty acid monoglycerides, or vegetable oils can be mentioned. As the other external additives, one of these may be used alone, or two or more of them may be used in combination.

[0058] In addition, when the above-described substance is impregnated into the expandable resin particles, the above-described substance is not regarded as other external additives (in this case, it is regarded as other additives). In other words, the expandable resin particles may contain the above-described various other external additives as other additives.

[0059] The content of other external additives on the surface of the expandable resin particles (the total amount when two or more external additives are included) is not particularly limited, but is preferably 0.01 to 0.50 parts by weight, more preferably 0.02 to 0.40 parts by weight, still more preferably 0.05 to 0.30 parts by weight, and particularly preferably 0.07 to 0.20 parts by weight with respect to 100 parts by weight of the expandable resin particle body.

[0060] (2-6. Physical properties of expandable methyl methacrylate resin particles) (Volume average particle diameter) The volume average particle diameter of the expandable resin particles is preferably 0.30 to 0.60 mm, more preferably 0.35 to 0.55 mm, and still more preferably 0.40 to 0.50 mm. By setting the volume average particle diameter of the expandable resin particles to 0.30 mm or more, the expandability during foaming of the expandable resin particles can be improved and blocking can be suppressed. Further, by setting the volume average particle diameter of the expandable resin particles to 0.60 mm or less, the filling property of the foamed particles formed by foaming the expandable resin particles can be further improved. Foamed particles with excellent filling properties can fill the narrow space in the molding machine corresponding to the thin part (the part having a complex shape) in the obtained foamed molded body without gaps. Therefore, it can be suitably used for molding a molded body having a complex shape. The method for measuring the volume average particle diameter of the expandable resin particles will be described in detail in the examples below.

[0061] The volume average particle diameter of the expandable resin particles can be adjusted by changing (a) the amount of the initial dispersant (for example, calcium tertiary phosphate, sodium α-olefin sulfonate), (b) the amount of the dispersant added during polymerization (for example, calcium tertiary phosphate), and (c) the timing of adding the dispersant during polymerization (for example, the time from the start of polymerization to the addition of the dispersant).

[0062] [3. Method for producing expandable methyl methacrylate resin particles] The method for producing the expandable resin particles is not particularly limited, and examples thereof include suspension polymerization in which a monomer mixture is polymerized in an aqueous suspension.

[0063] The method for producing expandable methyl methacrylate resin particles according to an embodiment of the present invention includes a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylate monomer, a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, and applying 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine to the surface of the obtained expandable methyl methacrylate resin particle body per 100 parts by weight of the expandable methyl methacrylate resin particle body. The copolymerization step may preferably further include (a) a start step of starting the copolymerization of the monomer mixture in the presence of 0.20 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 to the reaction mixture at a time when the polymerization conversion rate is 35% to 70% after the start step.

[0064] In the present specification, the "poorly water-soluble inorganic salt" is intended to mean an inorganic salt having a solubility in water at 25°C of 0.1 mg / ml or less.

[0065] The "method for producing expandable methyl methacrylate resin particles according to an embodiment of the present invention" may sometimes be referred to as the "present production method" hereinafter.

[0066] Since the present manufacturing method has the above configuration, the resulting expandable resin particles have the advantages of excellent blocking resistance during pre-foaming and excellent mold filling properties during the molding of foam particles formed by foaming the expandable resin particles. Since the present manufacturing method has the above configuration, for example, the expandable methyl methacrylate resin particles according to an embodiment of the present invention described in the section of [2. Expandable methyl methacrylate resin particles] can be provided. The present manufacturing method is preferably used for manufacturing the expandable resin particles described in the section of [2. Expandable methyl methacrylate resin particles]. Note that the "copolymer" in the present manufacturing method corresponds to the "base resin" contained in the expandable resin particles described in the section of [2. Expandable methyl methacrylate resin particles].

[0067] Hereinafter, each step related to the present manufacturing method will be described. Except for the matters described in detail below, the description in the section of [2. Expandable methyl methacrylate resin particles] will be incorporated as appropriate. In addition, the expandable resin particles described in the section of [2. Expandable methyl methacrylate resin particles] are preferably manufactured by the present manufacturing method, but may also be manufactured by a method other than the present manufacturing method. That is, the manufacturing method of the expandable resin particles is not limited to the embodiment of the present manufacturing method as described below.

[0068] (3-1. Copolymerization step) As the copolymerization step of the present manufacturing method, suspension polymerization in which a monomer mixture is polymerized in an aqueous suspension can be mentioned. Hereinafter, the copolymer (base resin) obtained in the copolymerization step may sometimes be simply referred to as "resin particles".

[0069] Basically, the amount of monomers used in the copolymerization step is the amount of structural units derived from each monomer in the resulting base resin. Therefore, the usage amounts of each monomer (methyl methacrylate and acrylic ester) in the copolymerization step are the same as the amounts of the methyl methacrylate unit and the acrylic ester unit, which are the structural units of the base resin, described in the section of (2-1. Base resin) of [2. Expandable methyl methacrylate resin particles], including preferred embodiments.

[0070] The "aqueous suspension" in the present invention refers to a liquid in a state where monomer droplets and / or resin particles are dispersed in water or an aqueous solution by using stirring or the like. In the aqueous suspension, (a) a water-soluble surfactant and monomer may be dissolved, and (b) a dispersant, polymerization initiator, chain transfer agent, crosslinking agent, bubble regulator, flame retardant, solvent, plasticizer, etc. that are insoluble in water may be dispersed together with the monomer.

[0071] The weight ratio of the monomer and polymer (resin) in the aqueous suspension to water or the aqueous solution is preferably 1.0 / 0.6 to 1.0 / 3.0 as the ratio of the obtained methyl methacrylate-based resin / water or aqueous solution. Here, the "aqueous solution" mentioned herein is intended to be a solution composed of water and components other than the methyl methacrylate-based resin.

[0072] The copolymerization step includes an initiation step of initiating the copolymerization of the monomer mixture in the presence of 0.20 to 1.20 parts by weight of a first hardly water-soluble inorganic salt with respect to 100 parts by weight of the monomer mixture. The initiation step is, for example, a step of initiating the copolymerization of the monomer mixture using an aqueous suspension containing (a) water, (b) a monomer mixture containing a methyl methacrylate monomer and an acrylate monomer, (c) 0.20 to 1.20 parts by weight of a first hardly water-soluble inorganic salt with respect to 100 parts by weight of the monomer mixture, (d) a crosslinking agent, and optionally (e) a polymerization initiator, surfactant, dispersant other than the hardly water-soluble inorganic salt, chain transfer agent, bubble regulator, flame retardant, solvent, plasticizer, etc.

[0073] In this specification, "before the start of the polymerization reaction" may also be referred to as "the initial stage of polymerization". The first hardly water-soluble inorganic salt and optionally the polymerization initiator, etc. compounded (added) to the aqueous suspension in the initiation step can be said to be substances (raw materials) used in the initial stage of polymerization.

[0074] In the initiation step, the first hardly water-soluble inorganic salt can function as a dispersant. Examples of the first hardly water-soluble inorganic salt used in the initiation step, that is, the initial stage of polymerization, include tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, kaolin, etc.

[0075] In the starting step, (a) a water-soluble polymer such as polyvinyl alcohol, methylcellulose, polyacrylamide, polyvinylpyrrolidone, and / or (b) an anionic surfactant such as sodium α-olefin sulfonate and sodium dodecylbenzenesulfonate may be used in combination with the first sparingly water-soluble inorganic salt.

[0076] As the first sparingly water-soluble inorganic salt used in the starting step, tricalcium phosphate is preferred from the viewpoint of the protective power of resin particles and / or monomer droplets. The starting step is preferably a step of initiating copolymerization of a monomer mixture in the presence of tricalcium phosphate, which is a sparingly water-soluble inorganic salt, and sodium α-olefin sulfonate, which is an anionic surfactant, from the viewpoint of the dispersion stability of the droplets.

[0077] The starting step is preferably a step of initiating copolymerization of a monomer mixture in the presence of 0.20 to 1.20 parts by weight, more preferably 0.20 to 1.10 parts by weight, still more preferably 0.40 to 1.10 parts by weight, of the first sparingly water-soluble inorganic salt per 100 parts by weight of the monomer mixture. When initiating copolymerization of the monomer mixture in the presence of 0.20 parts by weight or more of the first sparingly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, there is no risk that the volume average particle diameter of the resulting foamed resin particles will become too large. When initiating copolymerization of the monomer mixture in the presence of 1.10 parts by weight or less of the first sparingly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, there is no risk that many fine particles of the foamed resin particles will be generated. That is, by initiating copolymerization of the monomer mixture in the presence of an amount of the first sparingly water-soluble inorganic salt within the above range, foamed resin particles having a desired volume average particle diameter can be obtained with good yield.

[0078] When a water-soluble polymer and / or an anionic surfactant is used in combination with the first sparingly water-soluble inorganic salt in the starting step, the concentration in the aqueous suspension of the water-soluble polymer and / or anionic surfactant is preferably 30 to 100 ppm based on the concentration of the monomer mixture.

[0079] The copolymerization process includes an addition step of adding 0.08 to 0.50 parts by weight of a second sparingly water-soluble inorganic salt to 100 parts by weight of the monomer mixture in the reaction mixture when the polymerization conversion rate is 35% to 70% after the start step.

[0080] In this specification, "after the start of the polymerization reaction" may also be referred to as "during the polymerization". In the addition step, the second sparingly water-soluble inorganic salt added to the reaction mixture can be said to be a substance (raw material) used during the polymerization.

[0081] When the polymerization (copolymerization) of the monomer mixture in the copolymerization process is carried out by suspension polymerization, the reaction mixture in the addition step can also be said to be an aqueous suspension.

[0082] In the addition step, the second sparingly water-soluble inorganic salt can function as a dispersant. Examples of the second sparingly water-soluble inorganic salt used during the addition step, that is, during the polymerization, include the substances already exemplified as the first sparingly water-soluble inorganic salt. The second sparingly water-soluble inorganic salt is preferably at least one selected from the group consisting of tricalcium phosphate, hydroxyapatite, and kaolin, and more preferably tricalcium phosphate. According to this configuration, it is possible to prevent the coalescence of resin particles after the addition (addition) of the dispersant, and there is an advantage that resin particles having a desired particle size can be obtained.

[0083] In the addition step, after the start step, when the polymerization conversion rate is 35% to 70%, preferably 0.08 parts by weight to 0.50 parts by weight, more preferably 0.10 parts by weight to 0.50 parts by weight, more preferably 0.10 parts by weight to 0.40 parts by weight, still more preferably 0.10 parts by weight to 0.30 parts by weight, particularly preferably 0.10 parts by weight to 0.20 parts by weight, of a second poorly water-soluble inorganic salt is added to the reaction mixture with respect to 100 parts by weight of the monomer mixture. In the addition step, when adding 0.08 parts by weight or more of the second poorly water-soluble inorganic salt to the reaction mixture with respect to 100 parts by weight of the monomer mixture, there is no risk that the volume average particle diameter of the resulting foamed resin particles becomes too large. In the addition step, when adding 0.50 parts by weight or less of the second poorly water-soluble inorganic salt to the reaction mixture with respect to 100 parts by weight of the monomer mixture, the production cost increases due to excessive use of the poorly water-soluble inorganic salt. That is, in the addition step, by adding the second poorly water-soluble inorganic salt in an amount within the above range to the reaction mixture, foamed resin particles having a desired volume average particle diameter can be obtained at a low production cost.

[0084] The addition step is preferably carried out at a time when the polymerization conversion rate is 35% to 70%, more preferably at a time when the polymerization conversion rate is 40% to 50%, to add the second poorly water-soluble inorganic salt to the reaction mixture. According to this configuration, foamed resin particles having a desired volume average particle diameter can be obtained. The method for measuring the polymerization conversion rate in this specification will be described in detail in the following examples.

[0085] In the copolymerization step, it is preferable to use a crosslinking agent. Examples of the crosslinking agent include compounds having two or more functional groups exhibiting radical reactivity. Among the compounds having two or more functional groups exhibiting radical reactivity, as the crosslinking agent, it is preferable to use a bifunctional monomer having two functional groups. In other words, the base resin of the expandable resin particles preferably contains a bifunctional monomer unit which is a structural unit derived from a bifunctional monomer as a crosslinking agent unit. According to this configuration, (a) the expandable resin particles are excellent in foamability, (b) the foamed particles obtained by foaming the expandable resin particles are excellent in shrinkage suppression property, and (c) the expandable resin particles have the advantages that (i) they can provide foamed particles with suppressed blocking and (ii) they can provide a foam molded article excellent in fusibility.

[0086] Examples of the bifunctional monomer include (a) compounds obtained by esterifying both terminal hydroxyl groups of ethylene glycol such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate with (meth)acrylic acid, and / or compounds obtained by esterifying both terminal hydroxyl groups of an oligomer of the ethylene glycol with (meth)acrylic acid, (b) compounds obtained by esterifying the hydroxyl groups of a divalent alcohol such as neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate (e.g., 1,6-hexanediol diacrylate, etc.), and butanediol di(meth)acrylate with acrylic acid or methacrylic acid, and (c) aryl compounds having two alkenyl groups such as divinylbenzene. Since hexanediol di(meth)acrylate is easy to adjust the molecular weight of the base resin, as the bifunctional monomer, hexanediol di(meth)acrylate such as 1,6-hexanediol diacrylate is preferable. In the present specification, “(meth)acrylate” is intended to mean methacrylate and / or acrylate, and “(meth)acrylic acid” is intended to mean methacrylic acid and / or acrylic acid.

[0087] In the copolymerization step, the amount of the crosslinking agent used is preferably 0 parts by weight or more and less than 0.20 parts by weight, more preferably 0 parts by weight to 0.19 parts by weight, still more preferably 0 parts by weight to 0.17 parts by weight or less, still more preferably 0 parts by weight to 0.15 parts by weight or less, and even more preferably 0 parts by weight to 0.13 parts by weight, based on 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic ester monomer. According to the above configuration, (a) the expandable resin particles are excellent in expandability, and (b) the expanded particles obtained by expanding the expandable resin particles are excellent in shrinkage suppression. The expandable resin particles have the advantages that (i) they can provide expanded particles with suppressed blocking and (ii) they can provide a foam-molded article excellent in fusibility. In the copolymerization step, the amount of the crosslinking agent used may be 0.01 parts by weight or more, may be 0.03 parts by weight or more, may be 0.05 parts by weight or more, or may be 0.08 parts by weight or more, based on 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic ester monomer.

[0088] In these expandable resin particles, the crosslinking agent is incorporated into the copolymer (base resin) obtained. Therefore, the base resin of the expandable resin particles may contain a structural unit derived from the crosslinking agent. On the other hand, since the amount of the crosslinking agent used is very small relative to the amount of the monomer mixture used, the amount of the crosslinking agent used (in other words, the content of the structural unit derived from the crosslinking agent) is not considered when calculating the amount (content) of the base resin. Therefore, in this specification, the amount of the bifunctional monomer used is not included in the amount of the monomer mixture used.

[0089] The copolymerization step is preferably carried out in at least two stages by changing the polymerization temperature. For the sake of convenience, the two polymerization steps with different polymerization temperatures are hereinafter referred to as the first polymerization step and the second polymerization step. It can also be said that the copolymerization step preferably includes consecutive first and second polymerization steps with different polymerization temperatures.

[0090] The copolymerization process preferably includes, for example: (a) a first polymerization step carried out at a polymerization temperature of 70°C to 90°C and using a low-temperature decomposable polymerization initiator; and (b) a second polymerization step continuously carried out after the first polymerization step, at a polymerization temperature higher than that of the first polymerization step (for example, 90°C to 110°C) and using a high-temperature decomposable polymerization initiator. In the copolymerization process, the main polymerization reaction is preferably carried out in the above-described first polymerization step, and the monomers remaining in the above-described second polymerization step are preferably reduced.

[0091] As the polymerization initiator, a radical-generating polymerization initiator generally used in the production of thermoplastic polymers can be used. Representative 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, t-butyl peroxy-2-ethylhexyl monocarbonate; and (b) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination of two or more.

[0092] Among the radical-generating polymerization initiators described above, (a) benzoyl peroxide, lauroyl peroxide, t-butyl perpivalate, di-t-butyl peroxyhexahydroterephthalate, azobisisobutyronitrile, and azobisdimethylvaleronitrile are low-temperature decomposition type 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 type polymerization initiators.

[0093] The total amount of the polymerization initiator used in the first polymerization step and the amount used in the second polymerization step is preferably, for example, 0.05 parts by weight to 0.5 parts by weight or less based on 100 parts by weight of the monomer mixture. According to this configuration, foaming resin particles excellent in foamability can be obtained.

[0094] The initiation step may be (a) a step of initiating copolymerization of the monomer mixture in the presence of a first sparingly 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 the monomer mixture in the presence of a first sparingly water-soluble inorganic salt and a low-temperature decomposition type polymerization initiator. When the initiation step is a step of initiating copolymerization of the monomer mixture in the presence of a first sparingly 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, that is, during the polymerization.

[0095] In these expandable resin particles, part of the polymerization initiator may be incorporated into the resulting copolymer. Therefore, the base resin of the expandable resin particles may contain a polymerization initiator. On the other hand, since the amount of the polymerization initiator used is very small relative to the amount of the monomer mixture used, the amount of the polymerization initiator used is not considered when calculating the amount (content) of the base resin.

[0096] In the copolymerization step, 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 the chain transfer agent include (a) monofunctional chain transfer agents such as alkyl mercaptans and thioglycolic acid esters, and (b) polyfunctional chain transfer agents obtained by esterifying polyhydric alcohol hydroxyl groups such as ethylene glycol, neopentyl glycol, trimethylolpropane, and sorbitol with thioglycolic acid or 3-mercaptopropionic acid. Examples of the alkyl mercaptans include n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan. The amount of the chain transfer agent used is preferably 0.100 parts by weight or more and less than 0.500 parts by weight, more preferably 0.200 parts by weight or more and less than 0.300 parts by weight, based on 100 parts by weight of the base resin.

[0097] In these expandable resin particles, part of the chain transfer agent may be incorporated into the resulting copolymer. Therefore, the base resin of the expandable resin particles may contain a chain transfer agent. On the other hand, since the amount of the chain transfer agent used is very small relative to the amount of the monomer mixture used, the amount of the chain transfer agent used is not considered when calculating the amount (content) of the base resin.

[0098] In the copolymer, it is preferable to use a light stabilizer. The light stabilizer is not particularly limited as long as it is generally known. Commercially available products such as Sumisorb 200 (registered trademark) (manufactured by Sumitomo Chemical Tex Co., Ltd.) can also be used as the light stabilizer. The amount of the light stabilizer used is preferably 0.01 parts by weight to 0.05 parts by weight based on 100 parts by weight of the monomer components contained in the monomer mixture.

[0099] (3-2. Foaming agent impregnation step) In the foaming agent impregnation step, the foaming agent is impregnated into the methyl methacrylate resin particles, which are the copolymer obtained in the copolymerization step, whereby the foaming methyl methacrylate resin particle body can be obtained.

[0100] The foaming agent impregnation step can be carried out at any time. For example, it can be carried out together with the second polymerization step or after the second polymerization step.

[0101] In the foaming agent impregnation step, it is preferable to impregnate the obtained copolymer with the foaming agent when the polymerization conversion rate from the monomer to the copolymer is 80% to 95%. When the copolymer is impregnated with the foaming agent at a polymerization conversion rate of 80% or more, the foaming agent is appropriately impregnated into the interior of the copolymer, so there is no risk of agglomeration of the copolymers due to softening of the copolymer, and the production yield is good. When the copolymer is impregnated with the foaming agent at a polymerization conversion rate of 95% or less, the foaming agent is sufficiently impregnated into the interior of the copolymer, so there is no risk of forming a double bubble structure (hard core) in the foamed particles obtained by foaming the obtained foaming resin particles. As a result, by molding the foamed particles in a mold, a foamed molded body excellent in surface beauty can be obtained.

[0102] In the foaming agent impregnation step, the amount of the foaming agent impregnated into the methyl methacrylate resin particles, which are the copolymer, includes a preferred embodiment and is the same as the content of the foaming agent in the foaming resin particles described in the section of (2-2. Foaming agent) of [2. Foaming methyl methacrylate resin particles]. According to this configuration, foaming resin particles having sufficient foamability can be obtained, and the foaming resin particles can be safely produced without causing agglomeration of the copolymer in the foaming agent impregnation step.

[0103] In the foaming agent impregnation step, the treatment temperature (also referred to as the impregnation temperature) and the treatment time (also referred to as the impregnation time) when impregnating the copolymer with the foaming agent are not particularly limited.

[0104] In the foaming agent impregnation step, when impregnating the copolymer with the foaming agent, the impregnation temperature is preferably 95°C to 120°C or lower, more preferably 100°C to 117°C or lower. When the impregnation temperature is 95°C or higher, since the foaming agent is sufficiently impregnated into the interior of the copolymer, there is no risk of forming a double bubble structure (hard core) in the foamed particles obtained by foaming the obtained expandable resin particles. As a result, by molding the foamed particles in a mold, a foamed molded article excellent in surface beauty can be obtained. When the impregnation temperature is 120°C or lower, since the pressure in the polymerization machine does not become too high, it is possible to obtain expandable resin particles that can provide expandable particles having a uniform bubble structure without requiring impregnation equipment with heavy equipment that can withstand a large pressure.

[0105] In this production method, when using a solvent (for example, a solvent having a boiling point of 50°C or higher), it is preferable to add the solvent to the reaction mixture (aqueous suspension) immediately before the foaming agent impregnation step or simultaneously with the foaming agent impregnation step.

[0106] (3-3. Coating step) In the coating step, 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine (and optionally other external additives) is applied to the surface of the expandable methyl methacrylate-based resin particle body obtained in the foaming agent impregnation step, based on 100 parts by weight of the expandable methyl methacrylate-based resin particle body. By passing through the coating step, expandable resin particles containing 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine on the surface can be obtained.

[0107] In the coating step, the amount of N,N-bis(2-hydroxyethyl)alkylamine (and optionally other external additives) applied to the expandable resin particles includes preferred embodiments and is the same as the content of N,N-bis(2-hydroxyethyl)alkylamine and other external additives in the expandable resin particles described in the section of (2-4. N,N-bis(2-hydroxyethyl)alkylamine) and the section of (2-5. Other external additives) of [2. Expandable methyl methacrylate-based resin particles].

[0108] 〔4. Methyl methacrylate resin foamed particles〕 The methyl methacrylate resin foamed particles according to one embodiment of the present invention are foamed particles obtained by foaming the foaming methyl methacrylate resin particles described in the section of 〔2. Foaming methyl methacrylate resin particles〕, or the foaming methyl methacrylate resin particles produced by the production method described in the section of 〔3. Production method of foaming methyl methacrylate resin particles〕.

[0109] According to this configuration, the methyl methacrylate resin foamed particles according to one embodiment of the present invention have the advantages that they can provide foamed particles with suppressed blocking and can also provide a foamed molded article with excellent fusibility.

[0110] The "methyl methacrylate resin foamed particles according to one embodiment of the present invention" may also be referred to as "the present foamed particles" hereinafter.

[0111] The present foaming resin particles can be made into foamed particles by a general foaming method. Specifically, for example, the following operations (1) to (3) can be performed in sequence to obtain foamed particles: (1) Put the foaming resin particles into a container equipped with a stirrer; (2) Heat the foaming resin particles with a heat source such as steam; (3) By the above (2), perform foaming to a desired foaming ratio to obtain foamed particles.

[0112] The foaming of the foaming resin particles can also be said to be a preliminary foaming in order to obtain a foamed molded article described later from the foaming resin particles. Therefore, the foaming of the foaming resin particles may be referred to as "preliminary foaming", and the foamed particles obtained by this "preliminary foaming" may also be referred to as "methyl methacrylate resin preliminary foamed particles".

[0113] The evaluation method of the bulk specific gravity of the foamed particles will be described in detail in the following examples.

[0114] 〔5. Methyl methacrylate resin foamed molded article〕 The methyl methacrylate resin foam molded body according to an embodiment of the present invention is a foam molded body obtained by molding the methyl methacrylate resin foam particles described in the section of [4. Methyl methacrylate resin foam particles] in a mold.

[0115] In this specification, the "methyl methacrylate resin foam molded body according to an embodiment of the present invention" may sometimes be referred to as the "present foam molded body".

[0116] These foam particles can be made into a foam molded body by molding them by a general in-mold molding method. Specifically, for example, by performing the following operations (1) to (3) in order, a foam molded body can be obtained: (1) filling the foam particles into a mold that can be closed but not sealed; (2) heating the foam particles with steam; (3) obtaining a foam molded body by fusing the foam particles together by the above (2).

[0117] This foam molded body is a foam molded body obtained by molding these foam particles with excellent filling properties. Therefore, this foam molded body can be suitably used as a lost foam pattern, particularly a lost foam pattern having a complicated shape.

[0118] 〔6. Lost foam pattern〕 The lost foam pattern according to an embodiment of the present invention includes the foam molded body (this foam molded body) described in the section of [5. Methyl methacrylate resin foam molded body].

[0119] The lost foam pattern according to an embodiment of the present invention can be suitably used for various metal castings, particularly for casting metals having a complicated shape.

Examples

[0120] Examples and comparative examples will be given below to explain an embodiment of the present invention in more detail, but the present invention is not limited thereto.

[0121] <Evaluation method> (Volume average particle diameter of expandable methyl methacrylate resin particles) Using an image processing method, a millitrack JPA particle size analyzer was used to measure the particle size of the foaming methyl methacrylate resin particles at intervals of 0.005 mm in terms of volume basis. The obtained results were displayed in a cumulative distribution, and the particle size at 50% volume cumulative was defined as the volume average particle size.

[0122] (Foaming property of foaming resin particles) The method for evaluating the foaming property of the foaming resin particles was as follows. Using the foaming resin particles produced in the examples and comparative examples, the following steps (1) to (4) were carried out in sequence to obtain foamed particles with a bulk expansion ratio of 50 times: (1) The foaming resin particles were spread on a tray to a thickness of 2 - 3 cm and dried in a dryer at 60°C for 5 days; (2) The foaming resin particles (850 g) obtained in (1) above were put into the BHP110 manufactured by Daikai Kogyo Co., Ltd., a pressure-type foaming machine; (3) Steam was blown into the foaming machine under the conditions of a steam injection pressure of 0.20 MPa - 0.30 MPa and an internal pressure of the foaming machine of 0.030 MPa - 0.040 MPa to heat the foaming resin particles; (4) Under the conditions of (3) above, the heating of the foaming resin particles was continued until the bulk expansion ratio reached 50 times. By such an operation, foamed particles with a bulk expansion ratio of 50 times were obtained.

[0123] Based on the following criteria, the foaming property of the foaming resin particles was evaluated from the heating time (A) required to obtain foamed particles with a bulk expansion ratio of 50 times. The heating time (A) is the time required from the start of blowing steam into the foaming machine in the operation of (3) above until the bulk expansion ratio of the foaming resin particles reaches 50 times in the operation of (4) above. A (Very good): The heating time (A) is 150 seconds or less B (Good): The heating time (A) exceeds 150 seconds and is 250 seconds or less C (Poor): The heating time (A) exceeds 250 seconds.

[0124] (Evaluation of blocking resistance of foaming resin particles) The method for evaluating the blocking resistance of the foamed resin particles was as follows. (Foamability of the foamed resin particles) The foamed particles obtained were sieved through a screen with an opening of 5 mm, and the foamed particles remaining on the screen were defined as "blocked foamed particles". The weight of the blocked foamed particles was measured, and the blocking amount (weight %) was calculated according to the following formula. Blocking amount (weight %) = (weight of blocked foamed particles (g) / total amount of foamed particles sieved (g)) × 100.

[0125] Based on the obtained blocking amount, the blocking resistance of the foamed particles was evaluated according to the following criteria. A (very good): blocking amount (weight %) is 0.10 wt% or less B (good): blocking amount (weight %) is more than 0.10 wt% and 0.20 wt% or less C (poor): blocking amount (weight %) is more than 0.20 wt%.

[0126] (Packing property of the foamed particles) The method for evaluating the packing property of the foamed particles was as follows. Using the foamed particles obtained in (Foamability of the foamed resin particles), the following (1) to (4) were carried out in order to obtain a foamed molded body: (1) The foamed particles with a bulk expansion ratio of 50 times were left at room temperature (25 °C) for 3 days; (2) The foamed particles with a bulk expansion ratio of 50 times were filled with air from the moving side mold into a mold with a length of 450 mm, a width of 300 mm, and a thickness of 10 mm. Also, during air filling, the cracking of the mold was set to 0 mm, and the drain valve and the exhaust valve were closed; (3) Steam was blown into the mold at a steam blowing pressure of 0.30 MPa to 0.50 MPa, and in-mold forming by steam heating was carried out until the foaming pressure reached 0.100 MPa to 0.180 MPa under the condition that the pressure in the mold was 0.050 Mpa to 0.110 MPa, and the foamed particles were fused together; (4) After the foaming pressure reached 0.100 MPa to 0.180 MPa, the mold was left for 100 seconds, and then the foamed molded body was taken out.

[0127] The defective filling parts of the obtained foamed molded body were visually confirmed, and the packing property of the foamed particles was evaluated based on the following indicators. A (good): There are no defective filling parts C (Defect): There is a defective filling area.

[0128] (Surface elongation of the foam molded body) The evaluation method of the surface elongation of the foam molded body was as follows. For the foam molded body obtained in (Fillability of the foam molded body), each of the bottom surface and each side surface of the foam molded body was visually observed, and for the degree of the gap between the foam particles constituting the observed surface of the foam molded body, it was scored at intervals of 0.25 points between 0 (the gap between the particles is not filled at all) and 5 points (the gap between the particles is completely filled), and based on the scoring result, it was evaluated according to the following index.: A (Very good): In all the bottom and side surfaces of the molded body, the degree of the gap between the foam particles is 4.00 points or more A (Good): In all the bottom and side surfaces of the molded body, the degree of the gap between the foam particles is 3.50 points or more C (Defect): In either the bottom or side surface of the molded body, there is a portion where the degree of the gap between the foam particles is less than 3.50 points.

[0129] (Example 1) To a 6 L autoclave equipped with a stirrer, 150 parts by weight of water, 0.46 parts by weight of tricalcium phosphate as the first sparingly water-soluble inorganic salt and 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide and 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as polymerization initiators, 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, 0.240 parts by weight of n-dodecyl mercaptan as a chain transfer agent, and 0.03 parts by weight of "Sumisorb 200" (registered trademark, manufactured by Sumitomo Chemical Tex) as a light stabilizer were added to prepare a mixed solution containing the first sparingly water-soluble inorganic salt. Then, 96.5 parts by weight of methyl methacrylate (abbreviation MMA) and 3.5 parts by weight of butyl acrylate (abbreviation BA) as a monomer mixture and 1.0 part by weight of toluene as a solvent were added to the mixed solution to prepare an aqueous suspension. Next, the temperature of this aqueous suspension was raised to 80°C to initiate polymerization, that is, the initiation step was carried out. When the polymerization conversion rate was measured 1 hour and 45 minutes after the start of polymerization (after the initiation step), it was 40% to 50%. 1 hour and 45 minutes after the start of polymerization (after the initiation step), 0.12 parts by weight of tricalcium phosphate as the second sparingly water-soluble inorganic salt was added to the reaction mixture (aqueous suspension), and the addition step was carried out. 2 hours and 35 minutes after the addition step, 1.5 parts by weight of cyclohexane as a solvent and 9 parts by weight of normal rich butane (in normal rich butane, the weight ratio of normal butane to isobutane (normal butane / isobutane) is 70 / 30.) as a foaming agent were added to the aqueous suspension. Then, the temperature of the aqueous suspension was raised to 101°C. Next, by maintaining the temperature of the aqueous suspension at 101°C for 10 hours, copolymerization and impregnation of the foaming agent into the copolymer (copolymerization step and foaming agent impregnation step) were carried out. After the completion of the copolymerization step and the foaming agent impregnation step, the aqueous suspension was cooled. After cooling the aqueous suspension, the obtained product was washed, dehydrated and dried to obtain a foaming methyl methacrylate-based resin particle body containing a base resin containing methyl methacrylate units as structural units and butyl acrylate units which are acrylic esters.

[0130] The obtained foaming methyl methacrylate resin particle body was sieved with sieves having an aperture of 0.300 mm and 0.710 mm. By such an operation, foaming methyl methacrylate resin particle bodies having a particle size of 0.300 mm to 0.710 mm were collected. Then, with respect to 100 parts by weight of the foaming methyl methacrylate resin particle body, 0.15 part by weight of N,N-bis(2-hydroxyethyl)alkylamine (manufactured by Tanaka Chemical Laboratory, product name EC-5), and as an external additive, 0.05 part by weight of magnesium stearate (manufactured by NOF Corporation, product name Emagnesium Stearate, abbreviation StMg), which is a fatty acid metal salt, and 0.05 part by weight of Cast Wax (manufactured by NOF Corporation, product name Cast Wax A, abbreviation W) were applied to the surface of the foaming methyl methacrylate resin particle body, whereby foaming methyl methacrylate resin particles containing 0.15 part by weight of N,N-bis(2-hydroxyethyl)alkylamine on the surface were obtained.

[0131] Regarding the obtained foaming methyl methacrylate resin particles, according to the above-described method, each evaluation item (foaming property and blocking during pre-foaming of the foaming methyl methacrylate resin particles, filling property of the methyl methacrylate resin particles, and surface elongation of the methyl methacrylate resin foam molding) was evaluated. The results are shown in Table 1.

[0132] (Example 2) The same operations as in Example 1 were performed except that the amount of butyl acrylate used was changed to 2.5 parts by weight, to obtain foaming methyl methacrylate resin particles. Regarding the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0133] (Example 3) The same operations as in Example 1 were performed except that the amount of butyl acrylate used was changed to 5.0 parts by weight, to obtain foaming methyl methacrylate resin particles. Regarding the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0134] (Example 4) The same operations as in Example 1 were carried out except that the amount of N,N-bis(2-hydroxyethyl)alkylamine used was changed to 0.10 part by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0135] (Example 5) The same operations as in Example 1 were carried out except that the amount of N,N-bis(2-hydroxyethyl)alkylamine used was changed to 0.25 part by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0136] (Example 6) The same operations as in Example 1 were carried out except that the amount of butyl acrylate used was changed to 1.5 parts by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0137] (Example 7) The same operations as in Example 1 were carried out except that the amount of butyl acrylate used was changed to 6.5 parts by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0138] (Comparative Example 1) The same operations as in Example 1 were carried out except that the amount of N,N-bis(2-hydroxyethyl)alkylamine used was changed to 0.05 part by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0139] (Comparative Example 2) The same operations as in Example 1 were carried out except that the amount of N,N-bis(2-hydroxyethyl)alkylamine used was changed to 0.30 parts by weight, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0140] (Comparative Example 3) The same operations as in Example 1 were carried out except that 0.15 parts by weight of monoglyceryl stearate (manufactured by Riken Vitamin Co., Ltd., product name Rheodol S-100, abbreviation S-100) was used instead of N,N-bis(2-hydroxyethyl)alkylamine, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0141] (Comparative Example 4) The same operations as in Example 1 were carried out except that 0.30 parts by weight of monoglyceryl stearate (S-100) was used instead of N,N-bis(2-hydroxyethyl)alkylamine, and foaming methyl methacrylate resin particles were obtained. For the obtained foaming methyl methacrylate resin particles, each evaluation item was evaluated in the same manner as in Example 1.

[0142] When the volume average particle diameters of each Example and Comparative Example were measured by the above method, all were in the range of 0.30 mm to 0.60 mm.

[0143]

Table 1

[0144] (Summary) From Examples 1 to 7, by incorporating a specific amount (0.06 to 0.28 parts by weight based on 100 parts by weight of the expandable resin particle body) of N,N-bis(2-hydroxyethyl)alkylamine on the surface of the expandable resin particles, it was clearly shown that expandable resin particles excellent in antiblocking property during pre-expansion and filling property into a mold during molding of expanded particles formed by expanding the expandable resin particles can be provided.

[0145] Also, from the results of Comparative Examples 1 and 2, it can be seen that even if the surface of the expandable resin particles contains an amount of N,N-bis(2-hydroxyethyl)alkylamine that exceeds or is less than the specific amount, the filling property into a mold during molding of the expanded particles formed by expanding the expandable resin particles does not improve. Further, from the results of Comparative Examples 3 and 4, it can be seen that even if monoglyceryl stearate, which is generally used as an antistatic agent, is incorporated on the surface of the expandable resin particles instead of N,N-bis(2-hydroxyethyl)alkylamine, the antiblocking property during pre-expansion of the expandable resin particles does not improve. From the above results, it was clearly shown that when N,N-bis(2-hydroxyethyl)alkylamine is not incorporated, or when N,N-bis(2-hydroxyethyl)alkylamine is incorporated but the amount exceeds or is less than the predetermined range, it is impossible to achieve both the antiblocking property during pre-expansion of the expandable resin particles and the filling property into a mold during molding of the expanded particles formed by expanding the expandable resin particles.

Industrial Applicability

[0146] According to one embodiment of the present invention, expandable resin particles excellent in antiblocking property during pre-expansion and filling property into a mold during molding of expanded particles formed by expanding the expandable resin particles can be provided. Therefore, one embodiment of the present invention can be suitably used for applications such as lost molds when performing metal casting by the full mold method.

Claims

1. A foaming methyl methacrylate resin particle comprising a base resin containing methyl methacrylate units and acrylate units as constituent units, and a foaming agent, wherein on the surface of the foaming methyl methacrylate resin particle, it contains 0.06 to 0.28 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine with respect to 100 parts by weight of the foaming methyl methacrylate resin particle body, the foaming methyl methacrylate resin particle.

2. The foaming methyl methacrylate resin particle according to Claim 1, wherein the acrylate unit is a butyl acrylate unit.

3. The foaming methyl methacrylate resin particle according to Claim 1, wherein the base resin contains 2.0 to 6.0 parts by weight of butyl acrylate units with respect to 100 parts by weight of the resin.

4. The foaming methyl methacrylate resin particle according to Claim 1, wherein the foaming methyl methacrylate resin particle has a volume average particle diameter of 0.30 mm to 0.60 mm.

5. A methyl methacrylate resin foamed particle obtained by foaming the foaming methyl methacrylate resin particle according to any one of Claims 1 to 4.

6. A methyl methacrylate resin foamed molded article obtained by in-mold molding of the methyl methacrylate resin foamed particle according to Claim 5.

7. A lost mold comprising the methyl methacrylate resin foamed molded article according to Claim 6.

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