JP2023049915A - Expandable methyl methacrylate resin particles - Google Patents

Abstract

To provide expandable methyl methacrylate resin particles capable of efficiently providing an expanded molding having excellent internal fusion properties and castability.SOLUTION: There are provided expandable methyl methacrylate resin particles which contain a base resin containing a methyl methacrylate unit and an acrylic ester unit and having a specific glass transition temperature and a foaming agent and can provide expanded particles having excellent foaming property, low foaming property and excellent shrinkage suppressing property after heating.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to expandable methyl methacrylate-based resin particles.

When performing metal casting, a model 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 the metal, thereby casting a casting. A casting method (full mold method) is known. In the full mold method, a foam molded product of a methyl methacrylate polymer is used from the viewpoint of reducing residue during casting. In addition, foamed moldings for casting are often cut from large block moldings.

Several techniques are known as expandable methyl methacrylate-based resin particles for producing foamed moldings of methyl methacrylate-based polymers.

Patent Document 1 discloses expandable acrylic resin particles containing specific amounts of a methacrylic acid ester component and a specific acrylic acid ester component and having a glass transition temperature of 112 to 125°C.

Patent Document 2 discloses an expandable methacrylic acid containing specific amounts of methyl methacrylate units and acrylic acid ester units, having an average particle size of 0.6 to 1.0 mm, and having a particle size variation coefficient of 20% or less. Methyl acid based resin particles are disclosed.

Patent Document 3 discloses a method for producing expandable methyl methacrylate-based resin particles obtained by suspension polymerization of acrylic monomers containing specific amounts of methyl methacrylate and acrylic ester.

Patent Document 4 discloses expandable methyl methacrylate-based resin particles obtained by polymerizing specific amounts of methyl methacrylate, an acrylic ester, and a polyfunctional monomer.

JP 2015-183111 WO2020/203537 JP 2018-135407 WO2016/047490

However, the conventional techniques described above have room for improvement from the viewpoint of internal fusion bondability, castability, and production efficiency of the methyl methacrylate-based resin foam molded product.

In view of the above circumstances, an object of one embodiment of the present invention is to provide an expandable methyl methacrylate resin that can efficiently provide a methyl methacrylate resin foam molded article having excellent internal fusion bondability and castability. It is to provide particles.

The inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, one embodiment of the present invention includes the following configurations.
[1] Expandable methyl methacrylate-based resin particles containing a base resin containing methyl methacrylate units and acrylic acid ester units as structural units and a foaming agent and satisfying the following (a) to (d):
(a) The bulk density (A) of the expanded methyl methacrylate resin particles obtained by heating the expandable methyl methacrylate resin particles with water vapor at 100° C. for 300 seconds is 0.0285 g/cm ³ or less;
(b) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 30 seconds, and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. The volume (B) of the expanded resin particles is 140 cm ³ or less;
(c) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 180 seconds and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. and (d) the base resin has a glass transition temperature of 114.5° C. ^or higher.
[2] The expandable methyl methacrylate resin particles according to [1], wherein the base resin has a weight average molecular weight of 220,000 to 310,000.
[3] including a base resin containing methyl methacrylate units and acrylic acid ester units as structural units, and a foaming agent,
The weight average molecular weight of the base resin is 220,000 to 310,000,
The expandable methyl methacrylate-based resin particles, wherein the base resin has a glass transition temperature of 114.5° C. or higher.
[4] The expandable methyl methacrylate-based resin particles according to any one of [1] to [3], wherein the acrylate unit is a butyl acrylate unit.
[5] In the base resin,
(a) the content of the methyl methacrylate unit is more than 97.0 parts by weight and not more than 99.0 parts by weight, and (b) The expandable methyl methacrylate-based resin particles according to any one of [1] to [4], wherein the content of the acrylate unit is 1.0 parts by weight or more and less than 3.0 parts by weight.

According to one embodiment of the present invention, it is possible to provide expandable methyl methacrylate-based resin particles that can efficiently provide a methyl methacrylate-based resin expansion molded article having excellent internal fusion bondability and castability. Effective.

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. Further, embodiments or examples obtained by combining technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. In addition, all the scientific literatures and patent documents described in this specification are used as references in this specification. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

In this specification, "expandable methyl methacrylate-based resin particles" may be referred to as "expandable resin particles", and "methyl methacrylate-based resin expanded particles" may be referred to as "expanded particles". A "methyl acid-based resin foam molded product" may also be referred to as a "foam molded product".

[1. Technical idea of one embodiment of the present invention]
In the methyl methacrylate resin foam molded product with poor internal fusion bondability, methyl methacrylate resin foam particles are released from the cut surface of the methyl methacrylate resin foam molded product as the methyl methacrylate resin foam mold is cut. It is inferior in workability, such as falling off.

In addition, the main use of the methyl methacrylate-based resin foam molded product is casting use during metal casting. When used as a casting, the methyl methacrylate-based resin foam molded article is particularly required to have castability.

As a result of studies by the present inventors, there is room for improvement in the foam molded articles obtained using the expandable resin particles disclosed in Patent Documents 1 to 5 from the viewpoint of internal fusion bondability, castability, and production efficiency. be.

In view of the above circumstances, the present invention aims to provide expandable methyl methacrylate-based resin particles capable of efficiently providing a methyl methacrylate-based resin expansion molded article having excellent internal fusion bondability and castability. The inventor has made extensive studies.

The inventors of the present invention found the following points as a result of intensive studies and completed the present invention: (a) The expandable methyl methacrylate-based resin particles having an excellent foaming rate (expandability) is a methyl methacrylate-based resin. (b) Methyl methacrylate-based resin foamed particles having a slow foaming speed and little shrinkage after heating are provided. It is possible to provide a methyl methacrylate-based resin foam molded article having excellent internal fusion bondability, and (c) the expandable methyl methacrylate-based resin particles having a high glass transition temperature of the base resin are formed by To be able to provide a system resin foam molded product.

[2. Expandable methyl methacrylate-based resin particles]
An expandable methyl methacrylate-based resin particle according to one embodiment of the present invention includes a base resin containing methyl methacrylate units and acrylic acid ester units as structural units, and a foaming agent. ) is an expandable methyl methacrylate-based resin particle that satisfies:
(a) The bulk density (A) of the expanded methyl methacrylate resin particles obtained by heating the expandable methyl methacrylate resin particles with water vapor at 100° C. for 300 seconds is 0.0285 g/cm ³ or less;
(b) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 30 seconds, and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. The volume (B) of the expanded resin particles is 140 cm ³ or less;
(c) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 180 seconds and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. and (d) the base resin has a glass transition temperature of 114.5° C. ^or higher.

The "expandable methyl methacrylate-based resin particles according to one embodiment of the present invention" may be hereinafter referred to as "present expandable resin particles".

Expanded beads can be provided by expanding the present expandable resin beads by a known method. A foam-molded product can be provided by subjecting the foamed particles obtained by foaming the present expandable resin particles to in-mold molding by a known method.

Since the present expandable resin particles have the above-described structure, they have the advantage of being able to efficiently provide a foamed molded article having excellent internal fusion bondability and castability.

The present expandable resin particles are such that the bulk density (A) of expanded particles obtained by expanding the expandable resin particles under specific conditions is 0.0285 g/cm ³ or less. It is intended that the smaller the bulk density (A), the higher the bulk ratio of the expanded beads, that is, the better the expandability of the expandable resin beads. Expandable resin particles with excellent expandability can reduce production time and production costs when producing expanded particles using the expandable resin particles. Therefore, the present expandable resin particles have the advantage of being able to efficiently provide expanded particles and, as a result, efficiently provide foam molded articles.

The volume (B) of the expandable resin particles obtained by expanding the expandable resin particles is 140 cm ³ or less. The volume (B) indicates the extent to which the expanded beads are expanded within a certain period of time, and can reflect the expansion speed of the expanded beads. The smaller the volume (B), the slower the expansion rate of the expanded beads, and the lower the expandability of the expanded beads. Expanded beads with low expandability can provide a foamed molded product with excellent internal fusion bondability by allowing steam to sufficiently reach the expanded beads in the center of the mold during in-mold molding using the expanded beads. Therefore, the present expandable resin particles have the advantage of being able to provide a foam molded article having excellent internal fusion bondability.

The volume (C) of the expandable resin particles obtained by expanding the expandable resin particles is more than 160 cm ³ . Volume (C) indicates the degree of contraction of the expanded beads after heating. The larger the volume (C), the more difficult it is for the expanded beads to shrink after heating, and the better the shrinkage-suppressing property of the expanded beads. The foamed beads having excellent shrinkage-suppressing properties easily maintain adhesion (fusion) between the foamed particles inside the foamed molded product during in-mold molding using the expanded beads or in the foamed molded product obtained by the in-mold molding. As a result, it is possible to provide a foam molded article having excellent internal fusion bondability. Therefore, the present expandable resin particles have the advantage of being able to provide a foam molded article having excellent internal fusion bondability.

The base resin of the expandable resin particles has a glass transition temperature of 114.5° C. or higher. In the course of intensive studies, the present inventors surprisingly discovered that when the base resin of the expandable resin particles has a glass transition temperature of 114.5°C or higher, expansion molding using the expandable resin particles We have independently discovered that the body has excellent castability. That is, the present expandable resin particles have the advantage of being able to provide a foam molded article with excellent castability.

Foaming of the expandable resin particles can also be called “primary foaming”. Therefore, the foaming speed and foamability of the expandable resin particles can also be said to be the foaming speed and foamability of primary foaming, respectively. On the other hand, foaming of foamed particles can also be called "secondary foaming". Therefore, the foaming speed and foamability of the expanded beads can also be said to be the foaming speed and foamability of secondary foaming, respectively.

(Base resin)
The base resin can be said to be a portion of the expandable resin bead other than the foaming agent and the external additive described later, and can also be said to be a portion that substantially constitutes the expandable resin bead. The base resin contained in the present expandable resin particles contains methyl methacrylate units and acrylate units as structural units. As used herein, the term "methyl methacrylate unit" refers to a structural unit derived from a methyl methacrylate monomer, and the term "acrylic acid ester unit" refers to a structural unit derived from an acrylic acid ester monomer. . In this specification, the notation of "monomer" may be omitted. Therefore, in this specification, for example, when simply described as "methyl methacrylate" and "acrylic acid ester", they are intended to mean "methyl methacrylate monomer" and "acrylic acid ester monomer", respectively.

In the base resin contained in the present expandable resin particles, the content of (a) methyl methacrylate units is more than 97.0 parts by weight and 99.0 parts by weight with respect to 100 parts by weight of the total amount of methyl methacrylate units and acrylate units. It is not more than parts by weight, and the content of acrylic acid ester units is preferably 1.0 parts by weight or more and less than 3.0 parts by weight, and the content of (b) methyl methacrylate units is more than 97.0 parts by weight. It is more preferably 98.5 parts by weight or less, and the content of the acrylic acid ester unit is 1.5 parts by weight or more and less than 3.0 parts by weight. 0 parts by weight or more and 98.0 parts by weight or less, and the content of the acrylic acid ester unit is more preferably 2.0 parts by weight or more and less than 3.0 parts by weight, and (d) the methyl methacrylate unit is 97.5 parts by weight, and the content of acrylate units is particularly preferably 2.5 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 particle are within the respective ranges described above, the expandable resin particle has good internal fusion bondability and castability. It has the advantage of being able to efficiently provide a foamed molded article having excellent properties. More specifically, in the base resin, when the content of the acrylate unit is 1.0 parts by weight or more with respect to 100 parts by weight of the total amount of the methyl methacrylate unit and the acrylate unit, the expandable resin particles are expanded. tend to be superior. In the base resin, when the content of the acrylate unit is 3.0 parts by weight or less with respect to 100 parts by weight of the total amount of the methyl methacrylate unit and the acrylate unit, (a) the expandable resin particles are expanded to (b) The glass transition temperature of the base resin tends to be 114.5° C. or higher, so the castability of the finally obtained foamed product tends to be excellent. be.

Acrylate ester units according to one embodiment of the present invention include methyl acrylate units, ethyl acrylate units, propyl acrylate units, butyl acrylate units, and the like. A butyl acrylate unit is particularly preferred as the acrylate unit. According to this configuration, it is possible to provide expandable resin beads that are excellent in foamability and moldability (for example, shrinkage-suppressing property of expanded beads). In addition, the butyl acrylate unit has a large effect of lowering the glass transition temperature of the base resin, and has a large effect of improving castability.

The base resin of the present expandable resin particles may contain structural units derived from a cross-linking agent (hereinafter also referred to as cross-linking agent units). When the base resin of the expandable resin bead contains a cross-linking agent unit, (a) the expandable resin bead has excellent expandability, and (b) the expanded bead obtained by expanding the expandable resin bead has low expandability. Furthermore, (c) a foamed molded article obtained by molding the foamed particles in a mold has excellent internal fusion bonding and has excellent castability due to less residue at the time of combustion. have advantages. Moreover, the expandable resin particles containing a base resin containing a structural unit derived from a cross-linking agent as a structural unit also has the advantage that the molecular weight can be easily adjusted in the manufacturing process.

Examples of cross-linking agents include compounds having two or more functional groups exhibiting radical reactivity. Among compounds having two or more functional groups exhibiting radical reactivity, it is preferable to use a bifunctional monomer having two functional groups as the cross-linking agent. In other words, the base resin of the present expandable resin particles preferably contains a bifunctional monomer unit, which is a structural unit derived from a bifunctional monomer, as a structural unit derived from a cross-linking agent. According to this configuration, (a) the expandable resin particles have superior expandability, (b) the expanded beads obtained by expanding the expandable resin particles have lower expandability and superior shrinkage suppression properties, and (c ) A foamed molded product obtained by molding the foamed particles in a mold has the advantage of being excellent in internal fusion bondability and being excellent in castability due to less residue during combustion.

Examples of the bifunctional monomer include (a) ethylene glycol such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate, and oligomers of the ethylene glycol. (b) neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate (e.g. 1,6-hexanediol diacrylate), butanediol di( Examples include meth) acrylates and other dihydric alcohols whose hydroxyl groups are esterified with acrylic acid or methacrylic acid, and (c) aryl compounds having two alkenyl groups such as divinylbenzene. As the bifunctional monomer, hexanediol di(meth)acrylate is preferred because of ease of molecular weight adjustment. In addition, in this specification, "(meth)acrylate" intends "acrylate and/or methacrylate." For example, hexanediol di(meth)acrylate is intended as hexanediol diacrylate and/or hexanediol dimethacrylate.

The content of the 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 with respect to 100 parts by weight of the total content of the methyl methacrylate units and the acrylic acid ester units. 0.08 parts by weight or more and 0.13 parts by weight is more preferable. According to the above configuration, (a) the expandable resin particles are more excellent in expandability, (b) the expanded beads obtained by expanding the expandable resin particles are even lower in expandability and more excellent in shrinkage suppression, and (c) A foamed molded product obtained by molding the foamed particles in a mold has the advantage of being more excellent in internal fusion bondability and being more excellent in castability due to further reduced residue during combustion.

The base resin of the present expandable resin particles may further contain, as structural units, structural units derived from aromatic monomers (aromatic units). Examples of aromatic monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene and chlorostyrene. When the base resin of the present expandable resin particles contains an aromatic unit, a foam molded article having excellent strength can be obtained.

On the other hand, from the viewpoint of obtaining a foamed molded product with little residue upon combustion, it is preferable that the amount of the structure (for example, aromatic ring) derived from the aromatic monomer contained in the present expandable resin particles is as small as possible. Specifically, the amount of aromatic units contained in the base resin of the expandable resin particles is preferably as small as possible. For example, the amount of aromatic units contained in the base resin of the expandable resin particles is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, with respect to 100 parts by weight of the base resin. 0 parts by weight or less is more preferred, 1.5 parts by weight or less is more preferred, 1.0 parts by weight or less is even more preferred, and 0 parts by weight is particularly preferred. That is, it is particularly preferable that the base resin of the expandable resin particles does not contain aromatic units.

The types and amounts of the structural units contained in the base resin are the same as the types and amounts of the monomers contained in the monomer mixture used in the polymerization of the base resin (for example, the copolymerization step described later). (However, when the polymerization conversion rate is 100%).

(foaming agent)
The foaming agent contained in the present expandable resin particles is not particularly limited. Examples of foaming agents include (a) aliphatic hydrocarbons having 3 to 5 carbon atoms such as propane, isobutane, normal butane, isopentane, normal pentane, and neopentane; and (b) difluoroethane and tetrafluoro Volatile foaming agents such as hydrofluorocarbons with zero ozone depletion potential such as ethane can be mentioned. One of these foaming agents may be used alone, or two or more of them may be used in combination.

In the present expandable resin particles, the content of the foaming agent is preferably 5 to 12 parts by weight, more preferably 7 to 10 parts by weight, based on 100 parts by weight of the base resin. This configuration has the advantage of being able to provide expandable resin particles having sufficient expandability and of eliminating the need for heavy polymerization equipment.

(Other additives)
The expandable resin particles may optionally contain other additives in addition to the base resin and the foaming agent. Examples of the other additives include cell control agents, solvents, plasticizers, flame retardants, flame retardant aids, heat radiation inhibitors, pigments, dyes and antistatic agents.

Solvents and plasticizers are described in [3. Method for producing expandable methyl methacrylate-based resin particles] section. The contents of the solvent and the plasticizer in the expandable resin particles may be the same amounts as the amounts of the solvent and the plasticizer used, which will be described later.

(Air bubble control agent)
Examples of cell control agents include (a) aliphatic bisamides such as methylenebisstearate amide and ethylenebisstearate amide, and (b) polyethylene wax. The content of the cell control agent is preferably 0.01 to 0.50 parts by weight with respect to 100 parts by weight of the base resin.

(Weight average molecular weight)
The weight average molecular weight of the base resin contained in the present expandable resin particles is preferably 220,000 to 310,000, more preferably 230,000 to 310,000, and 24.0. It is more preferably 10,000 to 300,000. According to this configuration, surprisingly, (a) the expandable resin particles have good expandability, and (b) the expanded beads obtained by expanding the expandable resin particles have low expandability and shrinkage-suppressing properties. Furthermore, there is an advantage that (c) a foam molded article obtained by molding the foamed particles in a mold has excellent internal fusion bondability. As a result of intensive studies, the present inventors have found that, in addition to adjusting the amount of methyl methacrylate units and the amount of acrylic acid ester units in the base resin, the weight average molecular weight is set to 310,000 or less. As a matter of fact, the present inventors have obtained new knowledge that a foam molded article having excellent internal fusion bondability can be efficiently provided.

In this specification, the weight average molecular weight obtained by measuring by the following method is defined as the weight average molecular weight of the base resin contained in the expandable resin particles: (1) 0.02 g of expandable resin particles is added to tetrahydrofuran (hereinafter referred to as (sometimes abbreviated as “THF”)) is dissolved in 20 ml; (2) then the gel component in the resulting solution is filtered; (4) Calculate the weight average molecular weight (Mw) and number average molecular weight (Mn) from the GPC measurement chart obtained by GPC measurement. . The weight average molecular weight (Mw) and number average molecular weight (Mn) are relative values in terms of polystyrene.

The weight average molecular weight of the base resin depends on the composition (type and amount) of the monomers used in the polymerization (copolymerization) process of the base resin, the type and amount of the chain transfer agent, the polymerization temperature and time, and the type of initiator. and amount, and by changing the type and amount of the cross-linking agent.

(Glass-transition temperature)
The base resin contained in the present expandable resin particles has a glass transition temperature of 114.5° C. or higher. With this configuration, the present expandable resin particles have the advantage of being able to provide a foam molded article with excellent castability. The glass transition temperature is preferably 114.6° C. or higher, more preferably 114.8° C. or higher, and particularly preferably 115.0° C. or higher, since a foamed molded article having excellent castability can be provided. From the viewpoint of castability, a higher glass transition temperature is more preferable, and the upper limit is not particularly limited.

In this specification, the glass transition temperature obtained by measuring by the following method is defined as the glass transition temperature of the base resin contained in the expandable resin particles: (1) Dry treatment of the expandable resin particles at 150° C. for 30 minutes. (2) After placing 4 mg of the sample in an aluminum container, attach an aluminum lid to the aluminum container using a compressor to obtain a measurement sample; (3) About the measurement sample , Using a DSC measuring machine (for example, Hitachi DSC7000X), the temperature was raised from 50 ° C. to 150 ° C. (heating rate 10 ° C./min), and the temperature was lowered from 150 ° C. to 50 ° C. (cooling rate 10 ° C./min). , again from 50° C. to 150° C. (heating rate of 10° C./min); (4) using the DSC curve obtained at the second heating, the glass transition temperature is calculated. In addition, the glass transition temperature here intends the midpoint glass transition temperature defined in JIS K7121.

The glass transition temperature of the base resin can be adjusted by changing the composition (kind and amount) of the monomers used in the polymerization (copolymerization) process of the base resin.

In the expanded beads produced using the expandable resin beads, the structure of the expandable resin beads changes, but the composition of the expandable resin beads does not change. In addition, in the foamed molded article manufactured using the expanded beads, the structure of the expanded beads changes, but the composition of the expanded beads does not change. Therefore, the weight-average molecular weight and glass transition temperature of the foamed beads or the foamed molded product are regarded as the weight-average molecular weight and the glass transition temperature of the base resin contained in the expandable resin beads, which are the raw materials of the foamed beads or the foamed molded product. can be made. The weight-average molecular weight of the expanded beads or the foamed molded product is determined by changing the term "expanded resin particles" to "expanded beads" or "expanded molded body" in the method for measuring the weight-average molecular weight of the base resin of the expandable resin beads described above. It can be measured by the measurement method replaced with Further, the glass transition temperature of the expanded beads or the foamed molded article is determined by changing the term "expanded resin particles" to "expanded particles" or "expanded molded article" in the method for measuring the glass transition temperature of the base resin of the expandable resin particles described above. It can be measured by the measurement method replaced with

(Volume average particle size)
The volume average particle diameter of the expandable resin particles is preferably 0.5 mm to 1.4 mm, more preferably 0.6 mm to 1.2 mm, and more than 0.6 mm and 1.0 mm or less. is more preferable, and 0.7 mm to 0.9 mm is more preferable. When the volume average particle diameter is 0.5 mm or more, the expandability of the expandable resin particles during expansion does not decrease and/or blocking does not increase. When the volume average particle diameter is 1.4 mm or less, there is no fear that the expandability of the expanded beads obtained by expanding the expandable resin beads will be too high, and the surface of the molded article will slowly rise during molding using the expanded beads. Steam enters into the inside of the foamed molded body by forming. As a result, the fusion-bondability inside the foam molded article is improved. In the present specification, the volume average particle diameter of the expandable resin particles is defined by measuring the particle size of the expandable resin particles on a volume basis using a particle size analyzer (for example, an image processing type Millitrac JPA particle size analyzer). The obtained results are expressed in terms of cumulative distribution, and the particle diameter at which the volume cumulative volume is 50%.

In some cases, the expandable methyl methacrylate-based resin particles are sieved to separate the expandable methyl methacrylate-based resin particles having a particle size of 0.5 mm to 1.4 mm. In this case, the volume-average particle diameter of the fractionated expandable methyl methacrylate-based resin particles is in the range of 0.5 mm to 1.4 mm.

(Expandability of expandable methyl methacrylate-based resin particles)
The present expandable resin particles have a bulk density (A) of 0.0285 g/cm ³ or less and are excellent in expandability. The expanded beads can be efficiently provided (for example, in a shorter time), and as a result, the foamed molded article can be provided efficiently (for example, in a shorter time), so the bulk density (A) is 0.0260 g/cm ³ The following is preferable, 0.0250 g/cm ³ or less is more preferable, and 0.0222 g/cm ³ or less is particularly preferable. The lower the bulk density (A), the better, and the lower limit thereof is not particularly limited, but the bulk density (A) exceeds at least 0.0000 g/cm ³ . Moreover, the expandable methyl methacrylate-based resin particles used for measuring the bulk density (A) may be those coated with an antiblocking agent on the surface thereof.

In this specification, the bulk density of expanded beads is a value obtained by sequentially performing the following (1) to (4): (1) a certain amount of expanded beads (for example, measurement of bulk density (A) (2) Put the total amount of the foamed particles into a graduated cylinder of ^{1000 cm3} ; (3) Measure the volume of the foamed particles from the scale of the graduated cylinder; 4) Calculate the bulk density of the expanded particles by the following formula;
Bulk density (g/cm ³ )=weight of expanded beads (g)/volume of expanded beads (cm ³ ).

Alternatively, the weight of the expandable resin particles used for measuring the bulk density (A) may be measured in advance and used as the weight of the obtained expanded particles. The weight of the expandable resin particles used for measuring bulk density (A) is, for example, 10 g.

An example of the expansion method of the expandable resin particles in the measurement of the bulk density (A) is shown below in (1) to (3): (1) A certain amount (for example, 10 g) of the expandable resin particles is weighed, and the expandable resin particles are measured. (2) Putting the expandable resin particles into a steamer having an outlet; (3) Supplying steam at 100° C. to the steamer so that 300 The expanded particles are obtained by heating for a second.

The expanded beads obtained by expanding the present expandable resin beads have a volume (B) of 140 cm ³ or less and have low expandability. The volume (B) is preferably 138 cm ³ or less, more preferably 135 cm ³ or less, and particularly preferably 130 cm ³ or less, since it is possible to provide a foamed molded article having excellent internal fusion bondability. The smaller the volume (B), the better, and the lower limit is not particularly limited, but the volume (B) exceeds at least 100 cm ³ .

Here, the method for measuring the volume (B) of the expanded beads obtained by expanding the present expandable resin beads is not particularly limited, but for example, a method of performing the following (1) to (6) in order: (1) Expand the present expandable resin particles to a bulk ratio of 60 ^times to prepare expanded beads having a bulk ratio of 60 times; (3) Supply steam at 100°C to the steamer to heat the expanded beads for 30 seconds; (4) After heating, remove the expanded beads from the steamer and leave at 25°C for 1 minute; (5) Foam Place the particles into a graduated cylinder of 1000 cm ³ ; (6) Measure the volume (B) of the expanded particles from the scale of the graduated cylinder.

The expanded beads obtained by expanding the present expandable resin beads have a volume (C) of more than 160 cm ³ and are excellent in shrinkage suppressing properties. The volume (C) is preferably 165 cm ³ or more, more preferably 168 cm ³ or more, and particularly preferably 170 cm ³ or more, because it is possible to provide a foam molded article having excellent internal fusion bondability.

Here, the method for measuring the volume (C) of the expanded beads obtained by expanding the present expandable resin beads is not particularly limited. (1) Expand the present expandable resin particles to a bulk ratio of 60 ^times to prepare expanded beads having a bulk ratio of 60 times; (3) Supply steam at 100°C to the steamer to heat the expanded beads for 180 seconds; (4) After heating, remove the expanded beads from the steamer and leave at 25°C for 1 minute; (5) Foam Place the particles into a graduated cylinder of 1000 cm ³ ; (6) Measure the volume (C) of the expanded particles from the scale of the graduated cylinder.

In this specification, the bulk ratio of the expanded beads is a value obtained by sequentially performing the following (1) to (3): (1) 10 g of expanded beads are weighed and put into a graduated cylinder of 1000 cm ³ ; (2) Measure the volume of 10 g of expanded beads from the scale of the graduated cylinder; (3) Calculate the bulk magnification of the expanded beads by the following formula;
Bulk magnification (times)=volume of foamed particles (cm ³ )/10 g.

In this specification, the bulk ratio of the expanded particles can also be said to be the expansion ratio. Also, the unit of the bulk ratio is actually cm ³ /g based on the above formula, but in this specification, the unit of the bulk ratio is expressed as “times” for convenience.

The method for producing the expanded beads with a bulk ratio of 60 times used for measuring the volume (B) and the volume (C) is not particularly limited. (2) a steam injection pressure of 0.10 MPa to 0.16 MPa and an internal pressure of 0.005 MPa to 0.030 MPa; Blowing steam (e.g. water vapor) into the foaming machine under the above conditions to heat the expandable resin particles; Foaming is performed to obtain foamed particles. The expandable resin particles used for the production of the expanded particles with a bulk ratio of 60 times used for measuring the volume (B) and the volume (C) were obtained by sieving an expandable resin having a particle diameter of 0.5 mm to 1.4 mm. It may be made into particles.

(Modification 1)
The inventors of the present invention have been in the process of intensive studies with the aim of providing expandable methyl methacrylate resin particles that can efficiently provide a methyl methacrylate resin foam molded article excellent in internal fusion bondability and castability. Furthermore, the following findings were also independently found: (i) the higher the content of acrylic acid ester units in the base material of the expandable resin particles, the higher the expansion rate of the expandable resin particles, that is, the higher the expandability. (ii) On the other hand, the larger the content of acrylic acid ester units in the base material of the expandable resin particles, the more the expandable resin particles expand. (iii) when the content of acrylic acid ester units in the base material of the expandable resin particles is too high (exceeds a certain value), The expansion speed of the expanded beads obtained by expanding the expandable resin beads is increased, and the shrinkage of the expanded beads after heating is increased. (iv) that the lower the content of the acrylic acid ester unit in the base material of the expandable resin bead, the slower the expansion rate of the expanded bead obtained by expanding the expandable resin bead; If the content of the acrylate unit in the base material of the expandable resin bead is too low (below a certain value), the foaming speed of the expandable resin bead becomes too slow. The foamed beads do not expand sufficiently during the molding process, and as a result, the foamed molded article provided by the foamed beads is inferior in internal fusion bondability. That is, only by adjusting the ratio of the methyl methacrylate unit and the acrylate unit in the base resin (in other words, the glass transition temperature of the base resin), methyl methacrylate having excellent internal fusion bondability and castability can be obtained. However, it was not possible to provide expandable methyl methacrylate-based resin particles capable of efficiently providing a system resin foam molded product.

Therefore, the inventors of the present invention conducted further intensive studies. As a result, it was newly found that the above-mentioned problems can be achieved by adjusting not only the glass transition temperature of the base resin containing methyl methacrylate units and acrylic acid ester units, but also the weight average molecular weight of the base resin. Another embodiment of the invention has been completed. Specifically, the present inventors have found the following new knowledge: By setting the weight average molecular weight of the base resin contained in the expandable resin particles within a specific range and setting the glass transition temperature to a certain temperature or higher, It is possible to provide expandable resin particles that can efficiently provide a foamed molded article having excellent internal fusion bondability and castability; Further, by setting the glass transition temperature to a certain temperature or higher, (a) the expandable resin particles are excellent in expandability, and (b) the expansion speed of the expanded particles obtained by expanding the expandable resin particles is slow, and (c) The expanded particles can provide expandable resin particles that shrink less after heating.

That is, an expandable methyl methacrylate-based resin particle according to another embodiment of the present invention has the following configuration: a base resin containing methyl methacrylate units and acrylic acid ester units as structural units; agent, the base resin has a weight average molecular weight of 220,000 to 310,000, and the glass transition temperature of the base resin is 114.5° C. or higher. particle.

Since the expandable methyl methacrylate-based resin particles according to another embodiment of the present invention have the above-described configuration, they are (a) excellent in foamability and (b) low in foamability and excellent in shrinkage suppression. It has the advantage of being able to provide expanded particles. In addition, the expandable resin particles having the above-described structure have the advantage of being able to efficiently provide a foam molded article having excellent internal fusion bondability and castability.

For other aspects of the expandable methyl methacrylate-based resin particles according to another embodiment of the present invention, the above description is appropriately incorporated.

(Modification 2)
The present expandable resin particles can provide a foam molded article having excellent internal fusion bondability. The internal fusion bondability of a foamed molded product can be evaluated by the ratio of the foamed particles that are fractured outside the boundaries of the foamed particles in the fracture surface obtained by breaking the foamed molded product. For example, in the fracture surface of the expanded molded article obtained by breaking the expanded molded article obtained by molding the expanded particles obtained by expanding the present expandable resin particles, all the expanded particles ( 100%), when the ratio (D) of the expanded beads that are fractured outside the interface of the expanded beads is 85% or more, it can be said that the foam molded article has excellent internal fusion bondability.

That is, an expandable methyl methacrylate-based resin particle according to another embodiment of the present invention has the following configuration: a base resin containing methyl methacrylate units and acrylic acid ester units as structural units; and an expandable methyl methacrylate-based resin particle that satisfies (a) to (e) below:
(a) The bulk density (A) of the expanded methyl methacrylate resin particles obtained by heating the expandable methyl methacrylate resin particles with water vapor at 100° C. for 300 seconds is 0.0285 g/cm ³ or less;
(b) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 30 seconds, and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. The volume (B) of the expanded resin particles is 140 cm ³ or less;
(c) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 180 seconds and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. (d) the glass transition temperature of the base resin is 114.5° C. ^or higher; and (e) the expandable methyl methacrylate-based resin particles are In the fracture surface of the methyl methacrylate-based resin foamed molded product obtained by breaking the methyl methacrylate-based resin foamed molded product obtained by molding the expanded methyl methacrylate-based resin foamed particles, the methyl methacrylate-based resin The proportion (D) of the methyl methacrylate-based resin foamed beads that are broken outside the interface of the foamed beads is 90% or more.

Here, the method for measuring the ratio (D) in the fracture surface of the expanded molded product obtained by molding the expanded particles obtained by expanding the present expandable resin particles in a mold is not particularly limited, but for example, the following ( A method of performing 1) to (4) in order can be mentioned: (1) Expanded beads obtained by expanding expandable resin beads are placed in a mold (for example, having a molding space with a length of 2000 mm, a width of 1000 mm and a thickness of 525 mm). Mold) is used to perform in-mold molding to prepare a foamed molded product; Cut the foamed molded body perpendicular to the thickness direction; (3) Cut the middle one of the five divisions (a portion of the foamed molded body in the thickness direction of 210 mm to 315 mm before cutting) perpendicular to the thickness direction (4) Visually observe the obtained fracture surface, and all particles and particle interfaces constituting the fracture surface Measure the number of foamed particles that are broken outside, and calculate the ratio (D) based on the following formula;
Proportion (D) (%)=number of particles in fractured surface that are fractured outside of particle interface/number of particles that constitute fractured surface×100.

The method for producing the foamed molded article used for measuring the proportion (D) is not particularly limited, but includes, for example, a method in which the following (1) to (8) are performed in order: (1) expandable resin particles are pressurized; Put into a foaming machine (for example, BHP manufactured by Daikai Kogyo Co., Ltd.); (3) By the above (2), the expandable resin particles are expanded to a desired expansion ratio (for example, a bulk ratio of 60 times); (4) The obtained (5) Mold (for example, a metal mold having a molding space of 2000 mm in length, 1000 mm in width and 525 mm in thickness). A molding machine (for example, Daisen PEONY-205DS) having a mold) is filled with foamed particles having a bulk ratio of 60 times; (6) Steam (for example, steam ) is blown into the mold, and under the condition that the pressure in the mold is 0.030 MPa to 0.060 MPa, molding is performed in the mold by vacuum suction heating until the foaming pressure reaches 0.070 MPa to 0.080 MPa, and the expanded particles are fused together. (7) After the foaming pressure reaches 0.070 MPa to 0.080 MPa, it is left in the mold at 80 ° C. to 110 ° C. for 1000 seconds, and then the foamed molded product is taken out; The molded article is left at 60° C. for 3 days to obtain a foam molded article. The expandable resin particles used in the production of the foamed molded article used for measuring the ratio (D) may be those obtained by sieving into expandable resin particles having a particle diameter of 0.5 mm to 1.4 mm. .

The ratio (D) can also be said to be a fusion rate. The ratio (D) is preferably 85% or more because it is more excellent in internal fusion bondability.

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

A preferred embodiment of the method for producing the present expandable resin particles includes, for example, the following method: 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, wherein the copolymerization step includes: (a) 0.08 parts by weight to 0.08 part by weight per 100 parts by weight of the monomer mixture. an initiation step of initiating copolymerization of the monomer mixture in the presence of 20 parts by weight of the first sparingly water-soluble inorganic salt; , an addition step of adding 0.08 parts by weight to 0.50 parts by weight of the second poorly water-soluble inorganic salt to the reaction mixture with respect to 100 parts by weight of the monomer mixture, and the copolymerization A method for producing expandable methyl methacrylate-based resin particles, wherein the copolymer obtained in the step has a weight average molecular weight of 220,000 to 310,000 and a glass transition temperature of 114.5° C. or higher.

As used herein, "sparingly water-soluble inorganic salt" means an inorganic salt having a solubility in water at 25°C of 0.1 mg/ml or less.

A preferable aspect of the method for producing the present expandable resin particles described above is also an embodiment of the present invention. A preferred embodiment of the above-described method for producing expandable resin particles, that is, a method for producing expandable methyl methacrylate-based resin particles according to one embodiment of the present invention will be described below. Matters other than those described in detail below may be appropriately described in [2. expandable methyl methacrylate-based resin particles]. Further, hereinafter, the copolymer (also referred to as base resin) obtained in the copolymerization step may be simply referred to as "resin particles". Further, in this specification, the "method for producing expandable methyl methacrylate-based resin particles according to one embodiment of the present invention" may be referred to as "this production method".

The “aqueous suspension” in one embodiment of the present invention refers to a liquid in which monomer droplets and/or resin particles are dispersed in water or an aqueous solution using a stirrer or the like. The aqueous suspension may contain (a) a water-soluble surfactant and a monomer dissolved therein, and (b) a water-insoluble dispersant, a polymerization initiator, a chain transfer agent, and a cross-linking agent. , a cell control agent, a flame retardant, a solvent, etc. may be dispersed together with the monomer.

In the aqueous suspension, the weight ratio of the monomer and polymer (methyl methacrylate-based resin, also referred to as a copolymer) to water or the aqueous solution is the obtained methyl methacrylate-based resin/water or The aqueous solution ratio is preferably 1.0/0.6 to 1.0/3.0. In addition, the "aqueous solution" referred to here intends a solution consisting of water and components other than the methyl methacrylate-based resin.

In the copolymerization step according to one embodiment of the present invention, the monomers are An initiation step is included to initiate copolymerization of the mixture. The starting step is, for example, (a) water, (b) a monomer mixture containing methyl methacrylate monomer and acrylic acid ester monomer, (c) 0.08 per 100 parts by weight of the monomer mixture. parts by weight to 0.20 parts by weight of a first sparingly water-soluble inorganic salt, and optionally (d) a cross-linking agent, a polymerization initiator, a surfactant, a dispersant other than a sparingly water-soluble inorganic salt, a chain transfer agent, air bubbles An aqueous suspension containing modifiers, flame retardants, etc. is used to initiate the copolymerization of the monomer mixture.

In the present specification, "before the initiation step", that is, "before initiation of the polymerization reaction" may be referred to as "initial stage of polymerization". The first sparingly water-soluble inorganic salt blended (added) to the aqueous suspension in the initiation step and the optionally blended polymerization initiator can be said to be substances (raw materials) used at the initial stage of polymerization.

In the initiation step, the first sparingly water-soluble inorganic salt can function as a dispersant. Examples of the first sparingly water-soluble inorganic salt used in the initiation step, that is, the initial stage of polymerization include tribasic calcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin.

Also, in the initiation step according to one embodiment of the present invention, (a) a water-soluble polymer such as polyvinyl alcohol, methylcellulose, polyacrylamide, polyvinylpyrrolidone, and/or (b) sodium α-olefin sulfonate, dodecylbenzene sulfone An anionic surfactant such as acid soda may be used in combination with the first sparingly water-soluble inorganic salt.

As the first sparingly water-soluble inorganic salt used in the starting step according to one embodiment of the present invention, tribasic calcium phosphate is preferable from the viewpoint of the ability to protect droplets of resin particles and/or monomers. From the viewpoint of the dispersion stability of the droplets, the initiation step is to prepare the monomer mixture in the presence of the first sparingly water-soluble inorganic salt, tribasic calcium phosphate, and the anionic surfactant, sodium α-olefin sulfonate. The step of initiating copolymerization is preferred.

The initiation step according to one embodiment of the present invention is preferably 0.08 to 0.20 parts by weight, more preferably 0.10 to 0.19 parts by weight, relative to 100 parts by weight of the monomer mixture. The step of initiating copolymerization of the monomer mixture in the presence of the first sparingly water-soluble inorganic salt of part 3 is preferred. When starting the copolymerization of the monomer mixture in the presence of 0.08 parts by weight or more of the first sparingly water-soluble inorganic salt with respect to 100 parts by weight of the monomer mixture, the volume average particle size of the resulting expandable resin particles There is no risk of the diameter becoming too large. When starting the copolymerization of the monomer mixture in the presence of 0.20 parts by weight or less of the first sparingly water-soluble inorganic salt with respect to 100 parts by weight of the monomer mixture, many fine particles of expandable resin particles are generated. No fear. That is, by initiating copolymerization of the monomer mixture in the presence of the first sparingly water-soluble inorganic salt in an amount within the range described above, expandable resin particles having a desired volume average particle diameter are obtained at a high yield. Obtainable.

A case where a water-soluble polymer and/or an anionic surfactant is used in combination with a first sparingly water-soluble inorganic salt in the initiation step according to one embodiment of the present invention 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 based on the concentration of the monomer mixture (1,000,000 ppm).

In the copolymerization step, after the initiation step, when the polymerization conversion rate is 35% to 70%, 0.08 parts by weight to 0.50 parts by weight of the second poorly water-soluble Preferably, an addition step is included in which an inorganic salt is added to the reaction mixture.

In the present specification, "after the initiation step", that is, "after initiation of the polymerization reaction" may be referred to as "during 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.

In the copolymerization step according to one embodiment of the present invention, when the monomer mixture is polymerized (copolymerized) by suspension polymerization, the reaction mixture in the addition step can be said to be an aqueous suspension.

In the adding step according to one embodiment of the present invention, the second sparingly water-soluble inorganic salt can function as a dispersant. As the second sparingly water-soluble inorganic salt used in the addition step, that is, during the polymerization, the substances already exemplified as the first sparingly water-soluble inorganic salt can be mentioned. The second sparingly water-soluble inorganic salt is preferably one or more selected from the group consisting of tribasic calcium phosphate, hydroxyapatite and kaolin, more preferably tribasic calcium phosphate. According to this configuration, it is possible to prevent the coalescence of the resin particles after the addition (addition) of the dispersant, and there is an advantage that the expandable resin particles having the target (desired) volume average particle diameter can be easily obtained. .

In the addition step, after the initiation step, when the polymerization conversion rate is 35% to 70%, 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, still more preferably 0.10 to 0.30 parts by weight, particularly preferably 0.10 to 0.10 parts by weight Preferably, the step of adding 0.20 parts by weight of the second sparingly water-soluble inorganic salt to the reaction mixture. In the addition step, when 0.08 parts by weight or more of the second poorly water-soluble inorganic salt is added to the reaction mixture with respect to 100 parts by weight of the monomer mixture, the resulting expandable resin particles have a volume average particle diameter of There is no danger of it becoming 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 amount of the poorly water-soluble inorganic salt used should not be excessive. can reduce production costs. That is, in the addition step, by adding the second sparingly water-soluble inorganic salt in an amount within the range described above to the reaction mixture, expandable resin particles having a desired volume-average particle size can be obtained at low production cost. be able to.

In the addition step, preferably when the polymerization conversion is 35% to 70%, more preferably when the polymerization conversion is 35% to 60%, and more preferably when the polymerization conversion is 40% to 50%. A second sparingly water-soluble inorganic salt is preferably added to the reaction mixture. In the addition step, when the second sparingly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is 35% or more, there is no possibility that the resulting expandable resin particles will have an excessively small volume average particle size. In the addition step, when the second sparingly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is 70% or less, there is no possibility that the resulting expandable resin particles will have an excessively large volume average particle diameter. That is, in the addition step, when the second sparingly water-soluble inorganic salt is added to the reaction mixture when the polymerization conversion rate is within the above range, expandable resin particles having a desired volume average particle size can be easily obtained. be able to. The method for measuring the polymerization conversion in the present specification will be described in detail in the examples below.

The copolymerization process according to one embodiment of the present invention is preferably carried out in at least two stages with varying polymerization temperatures. For convenience, the two copolymerization steps with different polymerization temperatures are hereinafter referred to as the first copolymerization step and the second copolymerization step. It can also be said that the copolymerization step preferably includes a continuous first copolymerization step and a second copolymerization step with different polymerization temperatures.

The copolymerization step according to one embodiment of the present invention includes, for example, (a) a first copolymerization step performed at a polymerization temperature of 70 ° C. to 90 ° C. and using a low temperature decomposition type polymerization initiator; b) A second step which is carried out continuously with the first copolymerization step, at a polymerization temperature higher than that of the first copolymerization step (for example, 90° C. to 110° C.), and using a high-temperature decomposable polymerization initiator. 2 copolymerization steps. In the copolymerization step, it is preferable that the main polymerization reaction is carried out in the above-described first copolymerization step, and the residual monomer is reduced in the above-described second copolymerization step. In addition, (i) the temperature in the first copolymerization step may be 70° C. or more and less than 90° C., and the temperature in the second copolymerization step may be 90° C. to 110° C., and (ii) the first copolymerization step may be 70° C. to 90° C., and the temperature in the second copolymerization step may be above 90° C. and 110° C. or less.

As the polymerization initiator, radical-generating polymerization initiators generally used for producing thermoplastic polymers can be used. Typical radical-generating polymerization initiators include, for example, (a) benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy oxy-2-ethylhexanoate, t-butyl perpivalate, t-butylperoxyisopropyl carbonate, di-t-butylperoxyhexahydroterephthalate, 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-butylperoxy-2 - organic peroxides such as ethylhexyl monocarbonate, and (b) azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile. These polymerization initiators may be used individually by 1 type, and may be used in combination of 2 or more type.

Among the radical-generating polymerization initiators described above, (a) benzoyl peroxide, lauroyl peroxide, t-butyl perpivalate, di-t-butyl peroxyhexahydroterephthalate, azobisisobutyronitrile and azobisdimethyl Valeronitrile is a low-temperature decomposing polymerization initiator, and (b) t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butylperoxy isopropyl carbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethyl Cyclohexane, 1,1-bis(t-butylperoxy)cyclohexane and t-butylperoxy-2-ethylhexyl monocarbonate are high temperature decomposition type polymerization initiators.

The amount of the polymerization initiator used is the sum of the amount used in the first copolymerization step and the amount used in the second copolymerization step, for example, 0.1 part by weight to 0.1 part by weight with respect to 100 parts by weight of the monomer mixture. .5 parts by weight or less is preferred. According to this configuration, expandable resin particles having excellent expandability can be obtained.

The initiation step according to one embodiment of the present invention includes (a) copolymerization of a monomer mixture in the presence of a first sparingly water-soluble inorganic salt, a low-temperature decomposing polymerization initiator, and a high-temperature decomposing polymerization initiator. or (b) initiating copolymerization of the monomer mixture in the presence of the first sparingly water-soluble inorganic salt and a low-temperature decomposable polymerization initiator. When the initiation step is a step of initiating copolymerization of the monomer mixture in the presence of the first sparingly water-soluble inorganic salt and the low temperature decomposable polymerization initiator, the high temperature decomposable polymerization initiator is added after the initiation step, i.e. It may be added to the reaction mixture (aqueous suspension) during the polymerization.

The initiation step may be carried out (initiated) at a polymerization temperature of 70°C to 90°C or 70°C to 90°C. When the initiation step is a step of initiating copolymerization of the monomer mixture at a polymerization temperature of 70° C. to 90° C. or 70° C. or more and less than 90° C., after the initiation step, that is, during the polymerization, the polymerization temperature is set higher than at the start of polymerization. It may be changed to a higher temperature (eg, higher than 90° C. and 110° C. or lower, or 90° C. to 110° C.).

A chain transfer agent is preferably used in the copolymerization step according to one embodiment of the present invention. The chain transfer agent is not particularly limited, and known substances used for polymerization of methyl methacrylate resins can be used. Examples of chain transfer agents include (a) monofunctional chain transfer agents such as alkylmercaptans and thioglycolic acid esters, and (b) polyhydric alcohols (e.g., ethylene glycol, neopentyl glycol, trimethylolpropane, sorbitol, etc.). ) is esterified with thioglycolic acid or 3-mercaptopropionic acid. Alkylmercaptans include n-octylmercaptan, n-dodecylmercaptan and t-dodecylmercaptan. As the chain transfer agent, n-dodecylmercaptan is preferred because it facilitates molecular weight control.

By changing the amount of the chain transfer agent used in the copolymerization step, the molecular weight of the resulting expandable resin particles can be adjusted. The amount of the chain transfer agent used is, for example, preferably 0.100 parts by weight or more and less than 0.500 parts by weight, more preferably 0.200 parts by weight to 0.400 parts by weight, based on 100 parts by weight of the monomer mixture. More preferably 0.250 to 0.300 parts by weight.

In the step of impregnating a foaming agent according to one embodiment of the present invention, the methyl methacrylate-based resin particles, which are the copolymer obtained in the copolymerization step, are impregnated with a foaming agent to obtain expandable methyl methacrylate-based resin particles. can be obtained.

The blowing agent impregnation step according to one embodiment of the present invention can be performed at any time, for example it can be performed with the second copolymerization step or after the second copolymerization step.

In the step of impregnating the foaming agent according to one embodiment of the present invention, the obtained copolymer can be impregnated with the foaming agent when the polymerization conversion rate from the monomer to the copolymer is 80% to 95%. preferable. When the copolymer is impregnated with the foaming agent when the polymerization conversion rate is 80% or more, the copolymer is moderately impregnated with the foaming agent. There is no risk of occurrence, and the production yield is good. When the copolymer is impregnated with the foaming agent when the polymerization conversion rate is 95% or less, the copolymer is sufficiently impregnated with the foaming agent, so that the obtained expandable resin particles are expanded. There is no risk of forming a double cell structure (hard core) in the As a result, by in-mold molding the expanded particles, it is possible to obtain an expanded molded article having excellent surface quality.

In the foaming agent impregnation step according to an embodiment of the present invention, the amount (use amount) of the foaming agent with which the copolymer methyl methacrylate-based resin particles are impregnated includes preferable aspects, and [2. It is the same as the content of the foaming agent in the foaming resin particles described in the section (Blowing agent) of Expandable methyl methacrylate-based resin particles]. According to this configuration, expandable resin particles having sufficient expandability can be obtained, and expandable resin particles can be safely produced without causing cohesion of the copolymer in the step of impregnating the blowing agent.

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

In the step of impregnating the foaming agent according to one embodiment of the present invention, the impregnation temperature at which the copolymer is impregnated with the foaming agent is preferably 95° C. to 120° C. or less, more preferably 100° C. to 117° C. or less. When the impregnation temperature is 95° C. or higher, the foaming agent is sufficiently impregnated into the interior of the copolymer, so that the methyl methacrylate-based resin foamed particles obtained by foaming the obtained expandable resin particles have a double cell structure. (hard core) is not likely to be formed. As a result, by in-mold molding the foamed particles, a foamed molded article having excellent surface quality can be obtained. When the impregnation temperature is 120° C. or less, the pressure in the polymerization machine does not become too high, so that expanded particles having a uniform cell structure can be provided without requiring heavy impregnation equipment capable of withstanding high pressure. Expandable resin particles can be obtained.

In order to obtain expandable resin particles capable of providing a foam molded article having excellent strength, in the present production method, aromatic monomers (e.g., styrene, α-methylstyrene, paramethylstyrene, aromatic vinyl compounds such as t-butylstyrene and chlorostyrene) may also be used.

On the other hand, in order to obtain expandable resin particles capable of providing foamed molded articles with little residue upon combustion, it is preferable that the amount of the aromatic monomer used in the present production method is as small as possible. In this production method, the content of the aromatic monomer in 100 parts by weight of the monomer mixture is preferably 2.5 parts by weight or less, more preferably less than 2.5 parts by weight, and 2.0 parts by weight or less. is more preferably 1.5 parts by weight or less, more preferably 1.0 parts by weight or less, and particularly preferably 0 parts by weight. That is, it is particularly preferable that the monomer mixture in the present production method does not contain aromatic monomers.

In this production method, a solvent may also be used. As the solvent, compounds having a boiling point of 50° C. or higher are preferred. Examples include (a) C6 or higher (C6 or higher) aliphatic hydrocarbons such as toluene, hexane and heptane, and (b) cyclohexane, cyclooctane and the like. C6 or higher alicyclic hydrocarbons, and the like. As the solvent, toluene and/or cyclohexane are preferable for obtaining expandable resin particles having excellent expandability.

The amount of the solvent used is not particularly limited, but it is preferably 1.5 parts by weight or more and 3.0 parts by weight or less per 100 parts by weight of the monomer. When the amount of the solvent used is within this range, expandable resin particles having excellent foamability can be obtained, and the expanded particles obtained by expanding the expandable resin particles can be used for foam molding having excellent internal fusion bonding properties. you can get a body

In this production method, the timing of using the solvent is not particularly limited, and it can be used in the copolymerization step, the foaming agent impregnation step, or both the copolymerization step and the foaming agent impregnation step. As for the timing of adding the solvent to the reaction mixture (aqueous suspension), the solvent may be added to the reaction mixture immediately before the foaming agent is impregnated into the resin particles (that is, immediately before the foaming agent impregnation step), or the solvent may be added to the reaction mixture together with the foaming agent. Simultaneous addition to the reaction mixture is preferred.

In this production method, a plasticizer may also be used. As the plasticizer, a high boiling point plasticizer having a boiling point of 200° C. or higher is preferable. oil, vegetable oils such as 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.

The amount of the plasticizer used and the timing of using the plasticizer are not particularly limited, and may be set as appropriate.

A fatty acid metal salt, a fusion promoter, an antistatic agent, and the like may be applied to the surfaces of the expandable resin particles obtained through the above-described copolymerization step and blowing agent impregnation step. That is, the production method may further include a coating step of coating the surface of the expandable resin particles obtained in the foaming agent impregnation step with a fatty acid metal salt, a fusion promoter, an antistatic agent, and the like. A fatty acid metal salt, a fusion promoter, an antistatic agent, and the like that are applied to the surface of the expandable resin particles are sometimes referred to as "external additives."

By applying the fatty acid metal salt to the surfaces of the expandable resin particles, there is an advantage of suppressing mutual adhesion (hereinafter referred to as blocking) between the expandable resin particles and/or the expanded particles during the manufacturing process of the expanded particles. Fatty acid metal salts include zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc oleate, magnesium oleate, zinc laurate and calcium laurate. These fatty acid metal salts may be used singly or in combination of two or more. Zinc stearate and magnesium stearate are preferable as the fatty acid metal salt from the viewpoints of affinity with the methyl methacrylate unit contained in the base resin, anti-blocking effect, and adhesion of the foam molded product. is particularly preferred.

By applying the fusion accelerator to the surface of the expandable resin particles, there is an advantage that the fusion during molding can be ensured even when the antiblocking agent is applied to the surfaces of the expandable resin particles. Examples of fusion promoters include (a) fatty acid triglycerides such as lauric triglyceride, stearic triglyceride, linoleic acid triglyceride, and hydroxystearic triglyceride; (b) fatty acid diglycerides such as lauric acid diglyceride, stearic acid diglyceride, and linoleic acid diglyceride; (c) fatty acid monoglycerides such as lauric acid monoglyceride, stearic acid monoglyceride, and linoleic acid monoglyceride; and (d) vegetable oils such as castor hydrogenated oil. These fusion promoters may be used singly or in combination of two or more. As the fusion promoter, hydrogenated castor oil and triglyceride stearate are preferred, and hydrogenated castor oil is particularly preferred, because of their affinity with the methyl methacrylate unit contained in the base resin and their excellent fusion promotion effect.

By applying an antistatic agent to the surface of the expandable resin particles, it is possible to suppress the inhibition due to static electricity during raw material feeding, and it is possible to suppress adhesion of the expanded particles to the silo. . Antistatic agents include commonly used N-hydroxyethyl-N-(2-hydroxyalkyl)amine, N,N-bis(hydroxyethyl)dodecylamine, N,N-bis(hydroxyethyl)tetra Decylamine, N,N-bis(hydroxyethyl)hexadecylamine, N,N-bis(hydroxyethyl)octadecylamine, N-hydroxyethyl-N-(2-hydroxytetradecyl)amine, N-hydroxyethyl-N -(2-hydroxyhexadecyl)amine, N-hydroxyethyl-N-(2-hydroxyoctadecyl)amine, N-hydroxypropyl-N-(2-hydroxytetradecyl)amine, N-hydroxybutyl-N-(2 -hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxytetradecyl)amine, N-hydroxypentyl-N-(2-hydroxyhexadecyl)amine, N-hydroxypentyl-N-(2-hydroxy octadecyl)amine, N,N-bis(2-hydroxyethyl)dodecylamine, N,N-bis(2-hydroxyethyl)tetradecylamine, N,N-bis(2-hydroxyethyl)hexadecylamine, N, 1-amino-2-hydroxy compounds such as N-bis(2-hydroxyethyl)octadecylamine, glycerin, fatty acid monoglycerides, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters and the like. One of these antistatic agents may be used alone, or two or more thereof may be used in combination. N-hydroxyethyl-N-(2-hydroxyalkyl)amine is particularly preferred as the antistatic agent because of its best antistatic performance.

[4. Methyl methacrylate-based resin expanded particles]
[2. expandable methyl methacrylate-based resin particles], or the expandable methyl methacrylate-based resin particles described in [3. Method for producing expandable methyl methacrylate-based resin particles]. Expanded particles obtained by expanding the expandable methyl methacrylate-based resin particles produced by the production method described in the above section are also an embodiment of the present invention. .

The "methyl methacrylate-based resin expanded beads according to one embodiment of the present invention" may be hereinafter referred to as "present expanded beads".

The present expandable resin particles can be made into expanded particles by a general expansion method. Specifically, for example, methyl methacrylate-based resin expanded beads can be obtained by performing the following operations (1) to (3) in order: (2) Steam (for example, steam) is introduced into the foaming machine under the conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a pressure inside the foaming machine of 0.005 MPa to 0.030 MPa. (3) According to (2) above, the expandable resin particles are expanded to a desired expansion ratio (for example, a bulk ratio of 60) to obtain expanded beads.

The expansion of the expandable methyl methacrylate-based resin particles can be said to be preliminary expansion for obtaining a methyl methacrylate-based resin expansion molded article to be described later from the expandable methyl methacrylate-based resin particles. Therefore, the expansion of the expandable methyl methacrylate-based resin particles is sometimes referred to as "pre-expansion", and the expanded methyl methacrylate-based resin particles are sometimes referred to as "methyl methacrylate-based pre-expanded particles". A foaming machine used for foaming the expandable methyl methacrylate-based resin particles (for example, a foaming machine used for measuring the bulk density (A)) is sometimes called a "pre-foaming machine".

Since the foamed beads have the above-described structure, the volume (B) is 140 cm ³ or less, and therefore the foaming speed is low. Moreover, since the foamed beads have the above-described structure, the volume (C) is more than 160 cm ³ , and therefore, the foamed beads are excellent in shrinkage suppressing properties. That is, the present foamed beads have the advantage of being able to provide a foamed molded article with excellent internal fusion bondability and castability.

Regarding the expanded beads, other than the matters described above, [2. Expandable methyl methacrylate-based resin particles] and [3. Method for producing expandable methyl methacrylate-based resin particles].

[5. Methyl methacrylate-based resin foam molded product]
[4. Methyl methacrylate-based resin foamed particles] is also an embodiment of the present invention.

The "methyl methacrylate-based resin foam molded article according to one embodiment of the present invention" may be hereinafter referred to as the "present foam molded article".

The foamed particles can be formed into a foamed molded article by molding by a general in-mold molding method. Specifically, for example, by performing the following operations (1) to (3) in order, a foamed molded article can be obtained: (1) a molding machine having a mold (for example, PEONY-205DS manufactured by Daisen Co., Ltd.); (2) Blow steam (for example, steam) into the mold at a steam blowing pressure of 0.15 MPa to 0.25 MPa, and under the condition that the pressure in the mold is 0.030 MPa to 0.060 MPa (3) After the foaming pressure reaches 0.070 MPa to 0.080 MPa, molding is performed in the mold by vacuum suction heating until the foaming pressure reaches 0.070 MPa to 0.080 MPa, and the foamed particles are fused together; It is left in a mold at 80° C. to 110° C. for 1000 seconds and then taken out to obtain a foamed molded product.

Since the present foam molded article has the above-described structure, it is excellent in internal fusion bondability and castability. In particular, it is preferable that the content of (D) in the present foam molded article is 85% or more. As a result, the present foam molded article can be suitably used as a disappearance model.

The method for evaluating the castability of the foam molded article will be described in detail in the following examples. In the full-molding method, residual defects tend to accumulate on the surface of the casting. Therefore, generally, a foam-molding body that is larger than the product size with a processing allowance is used for casting. After casting, the casting is cut to remove residual defects from the casting along with the machining allowance. At this time, if the residual defects are large, the residual defects may not be completely removed from the casting. If there are residual defects in the casting, the mechanical properties such as strength are affected, and the casting may be damaged after a short period of use, which is not preferable. If there are no residual defects in the casting, these problems can be solved, so that a casting with good durability can be efficiently provided.

Regarding the present foam molded article, other than the matters described above, [2. Expandable methyl methacrylate-based resin particles], [3. Method for producing expandable methyl methacrylate-based resin particles] and [4. Methyl methacrylate-based resin expanded particles] section is incorporated.

[6. disappearance model]
[5. Methyl methacrylate-based resin foam molded article] is also an embodiment of the present invention.

INDUSTRIAL APPLICABILITY The disappearance pattern according to one embodiment of the present invention is excellent in internal fusion bondability and castability, and thus can be suitably used for various metal castings.

EXAMPLES 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 to these.

(Polymerization conversion rate of expandable methyl methacrylate-based resin particles)
The aqueous suspension was sampled during the polymerization and filtered. The weight of the resin component remaining on the filter paper was weighed, and the obtained weight was defined as the weight before heating. Then, after adding a polymerization inhibitor to the resin component, the resin component was heated at 150° C. for 30 minutes to remove volatile components. After that, the weight of the obtained resin component was measured, and the obtained weight was defined 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.

(Glass-transition temperature)
The glass transition temperature obtained by measuring by the following method was defined as the glass transition temperature of the base resin contained in the expandable resin particles: (1) The expandable resin particles were dried at 150°C for 30 minutes. (2) After placing 4 mg of the sample in an aluminum container, an aluminum lid was attached to the aluminum container using a compressor to obtain a measurement sample; (3) The measurement sample was subjected to DSC Using a measuring machine (Hitachi DSC7000X), the temperature was raised from 50 ° C. to 150 ° C. (temperature increase rate 10 ° C./min), the temperature was lowered from 150 ° C. to 50 ° C. (temperature decrease rate 10 ° C./min), and again 50 ° C. (4) The glass transition temperature was calculated using the DSC curve obtained during the second temperature increase. In addition, the glass transition temperature here intends the midpoint glass transition temperature defined in JIS K7121.

(Weight average molecular weight)
The weight average molecular weight obtained by measuring by the following method was used as the weight average molecular weight of the base resin contained in the expandable resin particles: (1) 0.02 g of expandable resin particles was dissolved in 20 ml of THF; (2) After that, the gel component in the obtained solution was filtered; (3) Then, using only the component soluble in THF (that is, the filtrate) as a sample, using gel permeation chromatography (GPC), GPC measurement was performed under the following conditions; (4) Weight average molecular weight (Mw) and number average molecular weight (Mn) were calculated from the GPC measurement chart obtained by GPC measurement. The weight average molecular weight (Mw) and number average molecular weight (Mn) are relative values in terms of polystyrene.
<Conditions for GPC measurement>
Measurement device: Tosoh Corporation, high-speed GPC device HLC-8220
Column used: Tosoh Corporation, SuperHZM-H × 2, SuperH-RC × 2 Column temperature: 40 ° C., mobile phase: THF (tetrahydrofuran)
Flow rate: 0.35 ml/min, injection volume: 10 μl
Detector: RI.

(Expandability of expandable methyl methacrylate-based resin particles)
The following (1) to (6) were performed in order to calculate the bulk density (A) of the expandable resin particles: (1) 10 g of the expandable resin particles were weighed, and an antiblocking agent was applied to the surfaces of the expandable resin particles; (2) The expandable resin particles were put into a steamer having an outlet; (3) Steam at 100°C was supplied to the steamer and the expandable resin particles were heated for 300 seconds to obtain expanded particles. (4) The obtained expanded beads were placed in a measuring cylinder of 1000 cm ³ ; (5) The volume (cm ³ ) of the expanded beads was measured from the scale of the measuring cylinder; The bulk density of the particles was calculated;
Bulk density (g/cm ³ )=10 (g)/volume of expanded beads (cm ³ ).

Based on the following criteria, the expandability of the expandable resin particles was evaluated from the obtained bulk density (A).
○ (Good): Bulk density (A) is 0.0285 g/cm ³ or less × (Poor): Bulk density (A) is greater than 0.0285 g/cm ³ and 0.0333 g/cm ³ or less XX (Very poor ): Bulk density (A) exceeds 0.0333 g/cm ³ .

(Expandability of expanded methyl methacrylate-based resin particles)
The expandable resin particles were sieved to separate expandable resin particles having a particle size of 0.5 mm to 1.4 mm. Using the collected expandable resin particles, the following steps (1) to (3) were performed in order to obtain expanded beads having a bulk ratio of 60: (2) Steam was blown into the foaming machine under the conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and an internal pressure of the foaming machine of 0.005 MPa to 0.030 MPa to form expandable resin particles. (3) According to (2) above, the expandable resin particles were expanded to a bulk ratio of 60 times to obtain expanded beads having a bulk ratio of 60 times.

Using the obtained expanded beads, the following (1) to (5) were performed in order to measure the volume (B) of the expanded beads: (1) 100 cm ³ of expanded beads with a bulk ratio of 60 were weighed; (2) Steam at 100°C was supplied to the steamer to heat the expanded beads for 30 seconds; (3) After heating, the expanded beads were removed from the steamer and left at 25°C for 1 minute. (4) The expanded beads were put into a graduated cylinder of 1000 cm ³ ; (5) The volume (B) of the expanded beads was measured from the scale of the graduated cylinder. Based on the following criteria, the foamability of the expanded beads was evaluated from the obtained volume (B). The smaller the volume (B), that is, the lower the expandability of the expanded beads, the higher the evaluation.
○ (Good): Volume (B) is 140 cm ³ or less × (Poor): Volume (B) is more than 140 cm ³ and less than 150 cm ³ XX (Very Poor): Volume (B) is 150 cm ³ or more.

(Shrinkage suppression property of expanded methyl methacrylate resin particles)
Expanded beads having a bulk ratio of 60 times were obtained by the method described in the section (Expandability of methyl methacrylate-based resin expanded beads). Using the obtained expanded beads, the following (1) to (5) were performed in order to measure the volume (C) of the expanded beads: (1) 100 cm ³ of expanded beads with a bulk ratio of 60 were weighed; (2) Steam at 100°C was supplied to the steamer to heat the expanded beads for 180 seconds; (3) After heating, the expanded beads were removed from the steamer and allowed to stand at 25°C for 1 minute. (4) The foamed beads were put into a 1000 cm ³ graduated cylinder; (5) The volume (C) of the foamed beads was measured from the scale of the graduated cylinder. Based on the following criteria, the shrinkage suppression property of the expanded beads was evaluated from the obtained volume (C).
○ (Good): Volume (C) is over 160 cm ³ × (Bad): Volume (C) is over 155 cm ³ and 160 cm ³ or less XX (Very Poor): Volume (C) is 155 cm ³ or less.

(Internal fusion bondability of methyl methacrylate-based resin foam molded product)
The expandable resin particles were sieved to separate expandable resin particles having a particle size of 0.5 mm to 1.4 mm.

Using the collected expandable resin particles, the following (1) to (8) were carried out in order to obtain a molded foam: (2) Steam was blown into the foaming machine under the conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and an internal pressure of the foaming machine of 0.005 MPa to 0.030 MPa to heat the expandable resin particles. (3) According to (2) above, the expandable resin beads were expanded to a bulk ratio of 60 times; (5) A molding machine (PEONY-205DS manufactured by Daisen) having a mold with a length of 2000 mm, a width of 1000 mm and a thickness of 525 mm was filled with expanded particles having a bulk ratio of 60 times; (6) Steam is blown into the mold at a steam blowing pressure of 0.15 MPa to 0.25 MPa, and the pressure inside the mold is 0.030 MPa to 0.060 MPa, and the foaming pressure is 0.070 MPa to 0.080 MPa. (7) After the foaming pressure reaches 0.070 MPa to 0.080 MPa, it is placed in the mold at 80 ° C. to 110 ° C. for 1000 seconds. (8) The removed foam-molded article was allowed to stand at 60° C. for 3 days to obtain a foam-molded article. The obtained foam molded article had a length of 2000 mm, a width of 1000 mm and a thickness of 525 mm.

Using the obtained foamed molded article, the following (1) to (3) were performed in order, and the ratio (D) in the fracture surface of the foamed molded article was measured: (1) The foamed molded article is uniform in the thickness direction The foamed molded article was cut perpendicularly to the thickness direction of the foamed molded article using a hot wire slicer so as to be divided into 5 parts; 210 mm to 315 mm in the thickness direction of the molded body), the surface perpendicular to the thickness direction was bent along the width direction at the center in the length direction and the foamed molded body was broken; The cross section was visually observed, all the particles forming the fractured surface and the number of expanded particles fractured outside the particle interface were counted, and the ratio (D) was calculated based on the following formula;
Proportion (D) (%)=number of particles in fractured surface that are fractured outside of particle interface/number of particles that constitute fractured surface×100.

Based on the obtained ratio (D), the internal fusion bondability of the foam molded product was evaluated according to the following criteria.
○ (excellent): ratio (D) is 85% or more × (poor): ratio (D) is 75% or more and less than 85% XX (very poor): ratio (D) is less than 75%.

(Castability of methyl methacrylate-based resin foam molded product)
The castability of the foam-molded article was measured and evaluated by the following methods: (1) A foam-molded article having a length of 2,000 mm, a width of 1,000 mm, and a thickness of 500 mm was produced using expanded particles; A foamed model (disappearing model) was produced by processing: (3) Using the obtained foamed model, a casting was produced (casting) by a full mold method. Here, the material to be poured was FCD700; (4) the surface of the obtained casting was shot-blasted to remove the casting sand used during casting; (6) Then, whether or not there was a casting defect such as a residue in the center of the casting was confirmed by visual inspection and magnetic particle inspection. Based on the obtained results, castability was evaluated according to the following criteria.

(Castability evaluation)
The castability of the methyl methacrylate-based resin foam molded product was evaluated according to the following criteria.
○ (excellent): when there are no residual defects in the casting × (poor): when there are residual defects in the casting XX (very poor): when there are many residual defects in the casting (Example 1)
In a 6 L autoclave equipped with a stirrer, 150 parts by weight of water, 0.15 parts by weight of tribasic calcium phosphate as the first poorly water-soluble inorganic salt, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.3 parts by weight of NaCl, lauroyl par Oxide 0.08 parts by weight, 1,1-bis(t-butylperoxy)cyclohexane 0.1 parts by weight, 1,6-hexanediol diacrylate 0.1 parts by weight as a cross-linking agent, n-dodecyl as a chain transfer agent 0.265 parts by weight of mercaptan and 0.026 parts by weight of benzotriazole as an ultraviolet absorber were charged to prepare a mixture containing the first sparingly water-soluble inorganic salt. After that, 1.0 part by weight of toluene and 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate as a monomer mixture were added to the mixed solution to prepare an aqueous suspension. . The temperature of the aqueous suspension was then raised to 80° C. to initiate the polymerization, ie the initiation step was performed. One hour and 45 minutes after the initiation of polymerization (after the initiation step), the polymerization conversion rate was measured to be 40% to 50%. After 1 hour and 45 minutes from the initiation of the polymerization (after the initiation step), 0.10 parts by weight of tribasic calcium phosphate is added to the reaction mixture (aqueous suspension) as the second sparingly water-soluble inorganic salt, and the addition step is performed. bottom. The initiation step and addition step described above can also be referred to as a first copolymerization step.

After 2 hours and 35 minutes, 0.24 parts by weight of tribasic calcium phosphate, 1.5 parts by weight of cyclohexane and normal-rich butane as a blowing agent (weight ratio of normal-butane and iso-butane in normal-rich butane (normal-butane/isobutane ) is 70/30.) 9 parts by weight were charged into the aqueous suspension. After that, 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, the copolymerization and impregnation of the foaming agent into the copolymer (copolymerization step (also referred to as a second copolymerization step) and foaming agent impregnation step ) was performed. The aqueous suspension was then cooled. After cooling the aqueous suspension, the resulting product was washed, dehydrated and dried to obtain expandable methyl methacrylate-based resin particles.

The resulting expandable methyl methacrylate-based resin particles were sieved with sieves having mesh sizes of 0.500 mm and 1.400 mm. Through this operation, expandable methyl methacrylate-based resin particles having a particle diameter of 0.500 mm to 1.400 mm were collected.

Next, 0.20 parts by weight of zinc stearate as a fatty acid metal salt and 0.05 parts by weight of hardened castor oil as a fusion accelerator were applied to the surface of the obtained expandable methyl methacrylate resin particles.

Subsequently, according to the above-described method, the expandability of the expandable methyl methacrylate resin particles, the expandability and shrinkage inhibition properties of the methyl methacrylate resin expandable particles, and the internal fusion bondability of the methyl methacrylate resin expansion molded product are determined. and castability were evaluated. The evaluation results are shown in Table 1.

(Example 2)
The procedure of Example 1 was repeated except that the amount of n-dodecyl mercaptan was changed to 0.300 parts by weight. 400 mm expandable methyl methacrylate-based resin particles were obtained. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

(Comparative example 1)
Example 1 except that the monomer mixture used was changed to 95.0 parts by weight of methyl methacrylate and 5.0 parts by weight of butyl acrylate, and the amount of n-dodecyl mercaptan was changed to 0.240 parts by weight. The same operation was performed to obtain expandable methyl methacrylate-based resin particles having a particle diameter of 0.500 mm to 1.400 mm, the surfaces of which were coated with zinc stearate and castor hardened oil. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

(Comparative example 2)
Example 1 except that the monomer mixture used was changed to 96.5 parts by weight of methyl methacrylate and 3.5 parts by weight of butyl acrylate, and the amount of n-dodecyl mercaptan was changed to 0.240 parts by weight. The same operation was performed to obtain expandable methyl methacrylate-based resin particles having a particle diameter of 0.500 mm to 1.400 mm, the surfaces of which were coated with zinc stearate and castor hardened oil. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 3)
The procedure of Example 1 was repeated except that the amount of n-dodecyl mercaptan was changed to 0.240 parts by weight. 400 mm expandable methyl methacrylate-based resin particles were obtained. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 4)
The same operation as in Example 1 was performed except that the amount of n-dodecyl mercaptan was changed to 0.330 parts by weight. 400 mm expandable methyl methacrylate-based resin particles were obtained. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 5)
Example 1 except that the monomer mixture used was changed to 97.0 parts by weight of methyl methacrylate and 3.0 parts by weight of butyl acrylate, and the amount of n-dodecyl mercaptan was changed to 0.250 parts by weight. By performing the same operation, expandable methyl methacrylate-based resin particles having a particle size of 0.500 mm to 1.400 mm were obtained. Each evaluation item was evaluated by the same method as in Example 1. The evaluation results are shown in Table 1.

According to one embodiment of the present invention, it is possible to provide expandable methyl methacrylate-based resin particles that can efficiently provide a foam molded article having excellent internal fusion bondability. Therefore, one embodiment of the present invention can be suitably used as a disappearing model when performing metal casting by the full mold method.

Claims (5)

Expandable methyl methacrylate-based resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as structural units, and a foaming agent, and satisfying the following (a) to (d):
(a) The bulk density (A) of the expanded methyl methacrylate resin particles obtained by heating the expandable methyl methacrylate resin particles with water vapor at 100° C. for 300 seconds is 0.0285 g/cm ³ or less;
(b) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 30 seconds, and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. The volume (B) of the expanded resin particles is 140 cm ³ or less;
(c) Methyl methacrylate obtained by heating 100 cm ³ of methyl methacrylate-based resin foamed particles obtained by expanding the expandable methyl methacrylate-based resin particles with water vapor at 100° C. for 180 seconds and then leaving the foamed methyl methacrylate-based resin particles at 25° C. for 1 minute. and (d) the base resin has a glass transition temperature of 114.5° C. ^or higher. 2. The expandable methyl methacrylate resin particles according to claim 1, wherein the base resin has a weight average molecular weight of 220,000 to 310,000. A base resin containing methyl methacrylate units and acrylate units as structural units, and a foaming agent,
The weight average molecular weight of the base resin is 220,000 to 310,000,
The expandable methyl methacrylate-based resin particles, wherein the base resin has a glass transition temperature of 114.5° C. or higher. 4. The expandable methyl methacrylate-based resin particles according to any one of claims 1 to 3, wherein the acrylate unit is a butyl acrylate unit. In the base resin,
(a) the content of the methyl methacrylate unit is more than 97.0 parts by weight and not more than 99.0 parts by weight, and (b) The expandable methyl methacrylate-based resin particles according to any one of claims 1 to 4, wherein the content of the acrylate unit is 1.0 parts by weight or more and less than 3.0 parts by weight.