Foaming methyl methacrylate resin particles, foamed methyl methacrylate resin particles, foamed methyl methacrylate resin molded article, lost-wax model, and method for producing foaming methyl methacrylate resin particles

Abstract

The present invention addresses the problem of providing expandable methyl methacrylate-based resin particles that can provide expanded particles having an excellent mold-filling behavior and that can provide foam molded articles that exhibit excellent surface aesthetics. Provided are expandable methyl methacrylate-based resin particles that comprise a blowing agent and a base resin comprising the methyl methacrylate unit and an acrylate ester unit as constituent units, and that have a volume-average particle diameter of 0.30-0.50 mm and a particle size distribution (UT) of not more than 2.30.

Description

Technical Field

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

Background Art

[0002] When performing metal casting, a lost mold casting method (full mold method) is known in which a mold made of a foam molded body is buried in casting sand, and molten metal is poured into the foam molded body to replace the foam molded body with metal to cast a casting. In the full mold method, a foam molded body of a methyl methacrylate polymer is used from the viewpoint of reducing residues during casting.

[0003] As conventional techniques for expandable methyl methacrylate resin particles for producing a foam molded body of a methyl methacrylate polymer, there are techniques as shown in Patent Documents 1 to 4 below. Patent Document 1 discloses expandable methyl methacrylate resin particles having an average particle diameter of 0.6 to 1.0 mm and a narrow particle size distribution. Further, Patent Documents 2 to 4 describe separating expandable methyl methacrylate resin particles having a smaller particle size by sieving.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the conventional techniques described above, when using foamed particles obtained by foaming foamed resin particles to produce molded articles, have room for improvement in terms of the ability of the foamed particles to fill the mold and the surface aesthetics of the foamed articles.

[0006] In view of the above circumstances, an object of one embodiment of the present invention is to provide foamable methyl methacrylate resin particles that can provide foamed particles with excellent mold-filling properties and foamed molded articles with excellent surface aesthetics. [Means for solving the problem]

[0007] The inventors diligently studied to solve the aforementioned problems and have now completed the present invention. Specifically, the foamed methyl methacrylate resin particles according to one embodiment of the present invention include a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, with a volume-average particle diameter of 0.30 mm to 0.50 mm and a particle size distribution (UT) of 2.30 or less. [Effects of the Invention]

[0008] According to one embodiment of the present invention, it is possible to provide foamed methyl methacrylate resin particles that can provide foamed particles with excellent mold filling properties and foamed molded articles with excellent surface aesthetics. [Modes for carrying out the invention]

[0009] One embodiment of the present invention is described below, but the present invention is not limited thereto. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic and patent documents mentioned herein are incorporated herein by reference. Furthermore, unless otherwise specified herein, "A to B" representing a numerical range means "A or greater (including A and greater than A) and B or less (including B and less than B)."

[0010] In this specification, "foaming methyl methacrylate resin particles" may also be referred to as "foaming resin particles," "foaming methyl methacrylate resin particles" may also be referred to as "foaming particles," and "foaming molded articles of methyl methacrylate resin" may also be referred to as "foaming molded articles."

[0011] [1. Technical Concept of One Embodiment of an Embodiment] Generally, lost-wax casting models are made by machining a block-shaped foam molded body of about 1 cubic meter. However, when manufacturing castings with complex shapes and / or small sizes, a foam molded body with a similar shape and size to the casting is created and used as the lost-wax casting model.

[0012] As a result of diligent research by the present inventors, it has been found that the foaming methyl methacrylate resin particles described in the above-mentioned Patent Documents 1 to 4 have room for improvement when used to produce foamed molded bodies for lost-wax models, as described below.

[0013] The foamed methyl methacrylate resin particles described in Patent Document 1 exhibit suitable foaming and moldability for manufacturing large block-shaped foamed molded articles due to their narrow particle size distribution and average particle diameter of 0.6 to 1.0 mm. However, when foamed particles obtained by foaming these foamed methyl methacrylate resin particles are used to manufacture complex-shaped and / or small foamed molded articles, there is room for improvement in their ability to fill thin-walled areas (for example, narrow areas with a thickness of a few mm) within the mold.

[0014] Furthermore, the foaming methyl methacrylate resin particles described in Patent Documents 2 to 4 have room for improvement in terms of the surface aesthetics of the molded articles obtained from these particles.

[0015] In view of the above circumstances, the inventors diligently conducted research with the aim of providing foamed methyl methacrylate resin particles that can provide foamed particles with excellent mold filling properties and foamed molded articles with excellent surface aesthetics.

[0016] The inventors, through diligent research, have newly discovered the following points and completed the present invention: (a) Foamed methyl methacrylate resin particles obtained by foaming foamed methyl methacrylate resin particles having a small volume average particle diameter have good fillability into molds; and (b) Foamed molded articles obtained by molding foamed methyl methacrylate resin particles, which have a narrow particle size distribution and small particle size variation, have excellent surface aesthetics.

[0017] Although Patent Document 4 attempts to narrow the particle size distribution of foamed resin particles, there is still room for improvement in terms of the uniformity of the particle size of the foamed resin particles, that is, in terms of the surface beauty of the resulting molded article.

[0018] [2. Foaming methyl methacrylate resin particles] The foaming methyl methacrylate resin particles according to an embodiment of the present invention include a base resin containing a methyl methacrylate unit and an acrylate unit as constituent units, and a foaming agent, and (a) the volume average particle diameter is 0.30 mm to 0.50 mm, and (b) the particle size distribution (UT) is 2.30 or less.

[0019] The "foaming methyl methacrylate resin particles according to an embodiment of the present invention" may also be referred to as "the present foaming resin particles" hereinafter.

[0020] By foaming the present foaming resin particles by a known method, foamed particles can be provided. By molding the foamed particles obtained by foaming the present foaming resin particles in a mold by a known method, a foamed molded body can be provided.

[0021] Since the present foaming resin particles have the above configuration, they have the advantage of being able to provide foamed particles with excellent filling properties into a mold and a foamed molded body with excellent surface appearance. In particular, since the volume average particle diameter is 0.30 mm to 0.50 mm, the present foaming resin particles can provide foamed particles with excellent filling into a mold. Further, since the particle size distribution (UT) is 2.30 or less, the foamed particles obtained by foaming the present foaming resin particles can provide a foamed molded body with excellent surface appearance.

[0022] In this specification, "excellent filling properties" means that when foamed particles are filled into a mold and in-mold molding is performed, it is intended that filling defects are less likely to occur. Further, "excellent surface appearance" means that the particle diameters of the foamed particles observed on the surface of the foamed molded body are substantially uniform, preferably uniform, and that there are few gaps between the foamed particles on the surface, preferably, there are substantially no gaps. A foamed molded body with excellent surface appearance can be obtained by in-mold molding of foamed particles having a substantially uniform or uniform particle diameter and good surface elongation. In this specification, "good surface elongation" means that there is little foam breakage on the surface of the foamed particles, and thus the foaming power does not decrease, so that the surface of the foamed particles is likely to elongate.

[0023] Furthermore, it is preferable that the volume-average particle diameter of the foamed resin particles is the volume-average particle diameter measured immediately after the manufacturing of the foamed resin particles. By sieving the foamed resin particles, it is possible to obtain an apparent volume-average particle diameter that is the desired one. For example, in Patent Documents 2 to 4, foamed resin particles within the desired particle size range are separated by sieving the foamed resin particles. Here, we will explain the case where the volume-average particle diameter of the foamed resin particles immediately after manufacturing is outside the desired particle size range, and / or the particle size distribution (UT) is wide. In this case, even if the foamed resin particles are sieved to separate foamed resin particles within the desired particle size range, (a) it is difficult to make the particle size distribution (UT) of the separated foamed resin particles 2.30 or less, and (b) a large amount of foamed resin particles are removed by sieving, i.e., the loss of foamed resin particles becomes large. Therefore, from the viewpoint of achieving both packing performance and yield of foamed resin particles obtained by foaming foamed resin particles, it is preferable that the volume-average particle diameter of the foamed resin particles immediately after production (before sieving) is 0.30 mm to 0.50 mm.

[0024] (Base resin) The base resin contained in these foamed resin particles contains methyl methacrylate units and acrylic acid ester units as constituent units. In this specification, "methyl methacrylate unit" refers to a constituent unit derived from methyl methacrylate monomer, and "acrylic acid ester unit" refers to a constituent unit derived from acrylic acid ester monomer. In this specification, the term "monomer" may be omitted. Therefore, in this specification, for example, when simply "methyl methacrylate" and "acrylic acid ester" are used, they refer to "methyl methacrylate monomer" and "acrylic acid ester monomer," respectively.

[0025] In the base resin contained in these foamed resin particles, (a) the content of methyl methacrylate units is preferably 90.0 to 99.0 parts by weight and the content of acrylic acid ester units is preferably 1.0 to 10.0 parts by weight per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units, (b) the content of methyl methacrylate units is preferably 91.0 to 99.0 parts by weight and the content of acrylic acid ester units is preferably 1.0 to 9.0 parts by weight, and (c) the content of methyl methacrylate units is preferably 92.0 to 97.0 parts by weight and the content of acrylic acid ester units is preferably (d) The content is more preferably 3.0 to 8.0 parts by weight, (e) the content of methyl methacrylate units is more preferably 93.0 to 96.0 parts by weight and the content of acrylic acid ester units is more preferably 4.0 to 7.0 parts by weight, (f) the content of methyl methacrylate units is more preferably 94.0 to 96.0 parts by weight and the content of acrylic acid ester units is more preferably 4.0 to 6.0 parts by weight, and (f) the content of methyl methacrylate units is more preferably 94.5 to 95.0 parts by weight and the content of acrylic acid ester units is more preferably 5.0 to 5.5 parts by weight.

[0026] In the base resin, when the content of methyl methacrylate units per 100 parts by weight of the total amount of methyl methacrylate units and acrylic ester units is 99.0 parts by weight or less, the foaming properties and moldability of the foamed resin particles tend to improve. As a result, the foamed molded articles obtained from these foamed resin particles may have further improved surface aesthetics. In the base resin, when the content of acrylic ester units per 100 parts by weight of the total amount of methyl methacrylate units and acrylic ester units is 10.0 parts by weight or less, the foamed particles tend to shrink less, i.e., the shrinkage suppression properties improve. As a result, the foamed molded articles obtained from these foamed particles may have further improved surface aesthetics.

[0027] Examples of acrylic acid esters according to one embodiment of the present invention include methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate. Among the acrylic acid esters, butyl acrylate is particularly preferred.

[0028] In other words, it is particularly preferable that the acrylic acid ester units are butyl acrylate units derived from butyl acrylate monomers. Butyl acrylate has a significant effect in lowering the glass transition temperature of the base resin. Therefore, this configuration makes it possible to provide foamable resin particles with excellent foaming properties.

[0029] The base resin of these foamed resin particles may contain constituent units derived from a crosslinking agent (hereinafter also referred to as crosslinking agent units). When the base resin of these foamed resin particles contains crosslinking agent units, the foamed resin particles have the advantages of (a) excellent foaming properties and (b) excellent shrinkage suppression properties when foamed.

[0030] Examples of crosslinking agents include compounds having two or more functional groups that exhibit radical reactivity. Among compounds having two or more functional groups that exhibit radical reactivity, it is preferable to use a difunctional monomer having two functional groups as the crosslinking agent. In other words, it is preferable that the base resin of the foamed resin particles contains difunctional monomer units, which are constituent units derived from difunctional monomers, as crosslinking agent units. With this configuration, (a) the foamed resin particles have superior foaming properties, (b) the foamed particles obtained by foaming the foamed resin particles have superior shrinkage suppression properties, and (c) the foamed molded body obtained by in-mold molding the foamed particles has superior surface beauty.

[0031] Examples of bifunctional monomers include (a) compounds in which both terminal hydroxyl groups of ethylene glycol, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate, are esterified with (meth)acrylic acid, and compounds in which both terminal hydroxyl groups of the oligomer of the ethylene glycol are esterified with (meth)acrylic acid, (b) compounds in which the hydroxyl group of a divalent alcohol, such as neopentyl glycol di(meth)acrylate, hexanediol di(meth)acrylate (e.g., 1,6-hexanediol diacrylate), and butanediol di(meth)acrylate, is esterified with acrylic acid or methacrylic acid, and (c) aryl compounds having two alkenyl groups, such as divinylbenzene. Hexanediol di(meth)acrylate makes it easy to adjust the molecular weight of the base resin. For this reason, hexanediol di(meth)acrylate, such as 1,6-hexanediol diacrylate, is preferred as the bifunctional monomer. In this specification, "(meth)acrylate" refers to methacrylate and / or acrylate, and "(meth)acrylic acid" refers to methacrylic acid and / or acrylic acid.

[0032] When the base resin contains constituent units derived from a crosslinking agent, the content of crosslinking agent units (e.g., bifunctional monomer units) in the foamed resin particles (base resin) is preferably 0.05 parts by weight or more and less than 0.20 parts by weight, more preferably 0.05 to 0.19 parts by weight, more preferably 0.05 to 0.17 parts by weight or less, more preferably 0.08 to 0.15 parts by weight or less, and even more preferably 0.08 to 0.13 parts by weight, based on 100 parts by weight of the total content of methyl methacrylate units and acrylic acid ester units. The above configuration has the advantages that (a) the foamed resin particles have superior foaming properties, (b) the foamed particles obtained by foaming the foamed resin particles have superior shrinkage suppression properties, and (c) the foamed molded article obtained by in-mold molding the foamed particles has superior surface quality. The above configuration also has the advantages that the foamed molded article has superior strength and less residue when burned.

[0033] The base resin of these foamed resin particles may further contain constituent units derived from aromatic monomers (hereinafter also referred to as aromatic units) as constituent units. Examples of aromatic monomers include aromatic vinyl compounds such as styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene. When the base resin of these foamed resin particles contains aromatic units, a foamed molded article with excellent strength can be obtained.

[0034] On the other hand, from the viewpoint of obtaining a foamed molded article with less residue during combustion, it is preferable that the amount of structures derived from aromatic monomers (e.g., aromatic rings) contained in the base resin of the foamed resin particles be as small as possible. For example, the amount of aromatic units contained in the base resin of the foamed resin particles is 2.5 parts by weight or less per 100 parts by weight of the base resin, preferably less than 2.5 parts by weight, more preferably 2.0 parts by weight or less, even more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, and particularly preferably 0 parts by weight. In other words, it is particularly preferable that the base resin of these foamed resin particles does not contain aromatic units.

[0035] In other words, in one embodiment of the present invention, it is preferable that the base resin does not contain aromatic units, or that it contains more than 0 parts by weight and 2.5 parts by weight or less of aromatic units per 100 parts by weight of the base resin.

[0036] The base resin of these foamed resin particles may be composed of one type of resin having the same composition of constituent units, or it may be composed of two or more types of resins having different compositions of constituent units. If the base resin is composed of two or more types of resins, the base resin may also include resins that do not contain methyl methacrylate units and / or acrylic acid ester units, as long as it includes resins that contain methyl methacrylate units and acrylic acid ester units as constituent units.

[0037] (Foaming agent) The foaming agent contained in these foamed resin particles is not particularly limited. Examples of foaming agents include (a) aliphatic hydrocarbons with 3 to 5 carbon atoms, such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentane, and (b) volatile foaming agents such as hydrofluorocarbons with zero ozone depletion potential, such as difluoroethane and tetrafluoroethane. These foaming agents may be used individually or in combination of two or more.

[0038] In these foamed resin particles, the foaming agent content is preferably 5 to 12 parts by weight, and more preferably 7 to 10 parts by weight, per 100 parts by weight of the base resin. This configuration has the advantage of providing foamed resin particles with sufficient foaming properties and eliminating the need for heavy polymerization equipment.

[0039] (Other additives) These foamed resin particles may optionally contain other additives in addition to the base resin and foaming agent. Examples of these other additives include foam regulators, solvents, plasticizers, flame retardants, flame retardant enhancers, heat radiation inhibitors, pigments, dyes, and antistatic agents.

[0040] The solvent is not particularly limited, but a solvent with a boiling point of 50°C or higher is preferred. Examples of solvents with a boiling point of 50°C or higher include (a) aliphatic hydrocarbons having 6 or more carbon atoms (C6 or higher), such as toluene, hexane, and heptane, and (b) alicyclic hydrocarbons with 6 or more carbon atoms, such as cyclohexane and cyclooctane. Toluene and / or cyclohexane are preferred as solvents with a boiling point of 50°C or higher, as they allow for the production of foamable resin particles with excellent foaming properties. In these foamable resin particles, the solvent content per 100 parts by weight of the base resin is preferably 1.0 to 3.0 parts by weight, and more preferably 1.5 to 3.0 parts by weight. When the solvent content per 100 parts by weight of the base resin is (a) 1.0 part by weight or more, foamable resin particles with sufficient foaming power can be obtained, and when it is (b) 3.0 parts by weight or less, a foamed molded article with suppressed surface expansion, i.e., excellent dimensional stability, can be obtained.

[0041] The plasticizer is not particularly limited, but a high-boiling-point plasticizer having a boiling point of 200°C or higher is preferred. Examples of the high-boiling-point plasticizer include (a) fatty acid glycers such as triglyceride stearate, triglyceride palmitate, triglyceride laurate, diglyceride stearate, and monoglyceride stearate; (b) vegetable oils such as coconut oil, palm oil, and palm kernel oil; (c) aliphatic esters such as dioctyl adipate and dibutyl sebacate; and (d) organic hydrocarbons such as liquid paraffin and cyclohexane.

[0042] In these foamed resin particles, the plasticizer content per 100 parts by weight of the base resin is preferably 0.40 to 4.00 parts by weight, more preferably 0.50 to 3.50 parts by weight, more preferably 0.60 to 3.00 parts by weight, more preferably 0.70 to 2.70 parts by weight, more preferably 0.80 to 2.40 parts by weight, more preferably 0.90 to 2.10 parts by weight, even more preferably 1.00 to 1.80 parts by weight, and particularly preferably 1.20 to 1.50 parts by weight. This configuration has the advantage of providing foamed resin particles with excellent foaming properties and excellent shrinkage properties.

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

[0044] (Weight average molecular weight) The foamed resin particles are preferably measured by gel permeation chromatography (GPC) and have a weight-average molecular weight converted to polystyrene of 100,000 to 400,000. This configuration makes it possible to obtain a foamed molded article with excellent surface quality and low residue during combustion.

[0045] (Volume-average particle size) The volume-average particle diameter of the foamed resin particles is 0.30 mm to 0.50 mm, preferably 0.35 to 0.45 mm, and more preferably 0.40 mm to 0.45 mm. If the volume-average particle diameter of the foamed resin particles is less than 0.30 mm, the foamed resin particles tend to result in a decrease in foaming ability and / or an increase in blocking during foaming. If the volume-average particle diameter of the foamed resin particles is greater than 0.50 mm, the foamed particles obtained by foaming the foamed resin particles have poor filling ability into narrow spaces when the foamed particles are filled into a molding machine. Note that narrow spaces in the molding machine correspond to thin areas in the resulting foamed molded article. In this specification, the volume-average particle diameter of the foamed resin particles is defined as the particle size at which the volume cumulative distribution reaches 50% (i.e., D50), obtained by measuring the particle size of the foamed resin particles on a volume basis using a particle size analyzer (e.g., an image processing type Millitrack JPA particle size analyzer), displaying the obtained results as a cumulative distribution, and determining the particle size at which the volume cumulative distribution reaches 50%.

[0046] The volume-average particle size of the foamed resin particles can be adjusted by selecting the droplet polymerization method described later as the method for producing foamed methyl methacrylate resin particles, and by changing the diameter and number of outlets of the droplet generation nozzle, the frequency of vibration applied to the droplet generation nozzle, and the flow rate (supply rate of monomer mixture) in the droplet polymerization method.

[0047] (Particle size distribution (UT)) The particle size distribution (also referred to as UT) of the foamed resin particles is 2.30 or less, preferably 2.25 or less, more preferably 2.20 or less, even more preferably 2.19 or less, and particularly preferably 2.18 or less. If the particle size distribution (UT) of the foamed resin particles is greater than 2.30, the foamed resin particles will have poor uniformity in particle size, and the foamed molded article obtained from these foamed resin particles will have poor surface aesthetics.

[0048] In this specification, the particle size distribution (UT) is calculated from a distribution table showing the cumulative distribution of particle sizes measured on a volume basis. Specifically, when the particle sizes at which the cumulative volume percentages are 90%, 60%, 40%, and 10% are defined as D90, D60, D40, and D10, respectively, the value obtained by the following formula is defined as the particle size distribution (UT). Particle size distribution (UT)=(D90 / D40)+(D60 / D10) Furthermore, if all particles have exactly the same particle size, the particle size distribution (UT) will be 2.00. Therefore, the lower limit of the particle size distribution (UT) for these foamed resin particles is 2.00 or higher.

[0049] The particle size distribution (UT) of the foamed resin particles can be adjusted by selecting the droplet polymerization method described later as the method for producing foamed methyl methacrylate resin particles, and by changing the diameter and number of outlets of the droplet generation nozzle, the frequency of vibration applied to the droplet generation nozzle, and the flow rate (supply rate of monomer mixture) in the droplet polymerization method.

[0050] [3. Method for producing foaming methyl methacrylate resin particles] A method for producing foamed methyl methacrylate resin particles according to one embodiment of the present invention includes a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer by a droplet polymerization method, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, wherein the volume average particle diameter of the foamed methyl methacrylate resin particles is 0.30 mm to 0.50 mm, and the particle size distribution (UT) is 2.30 or less.

[0051] The "Method for Producing Foaming Methyl Methacrylate Resin Particles According to One Embodiment of the Precedent" may also be referred to as "the present manufacturing method" below.

[0052] This manufacturing method has the advantage of being able to provide foamed methyl methacrylate resin particles that have excellent mold-filling properties and foamed molded articles with excellent surface aesthetics, due to the aforementioned configuration. Furthermore, this manufacturing method has the advantage of being able to provide foamed resin particles with a volume-average particle diameter of 0.30 mm to 0.50 mm immediately after manufacturing and a particle size distribution (UT) of 2.30 or less. As a result, it is not necessary to sieve the obtained foamed resin particles, or the amount of foamed resin particles discarded by sieving can be reduced, and as a result, the loss of foamed resin particles due to sieving can be significantly reduced.

[0053] Furthermore, because this manufacturing method has the above-described configuration, it has the advantage of being able to provide the foamed resin particles described in section [2. Foamed Methyl Methacrylate Resin Particles]. In other words, this manufacturing method is suitably used to produce the foamed resin particles described in section [2. Foamed Methyl Methacrylate Resin Particles].

[0054] The following describes each step of the manufacturing method. Except for matters detailed below, refer to the section [2. Foaming Methyl Methacrylate Resin Particles] as appropriate. Furthermore, while the foaming resin particles described in section [2. Foaming Methyl Methacrylate Resin Particles] are preferably manufactured by this method, they may also be manufactured by other methods. In other words, the method for manufacturing the foaming resin particles is not limited to the embodiments of this method described below.

[0055] (Droplet generation polymerization method) Conventionally, suspension polymerization has been used as a method for producing foamed methyl methacrylate resin particles. The process for producing foamed resin particles by suspension polymerization includes, for example, the following steps (1) to (4): (1) Mixing water, monomer components, polymerization initiator, and optionally other additives to prepare an aqueous suspension; (2) Next, raising the temperature of the aqueous suspension to a predetermined polymerization temperature; (3) Next, carrying out a polymerization reaction by reacting the aqueous suspension at the predetermined polymerization temperature for a predetermined polymerization time to obtain a polymer; (4) Adding a foaming agent to the aqueous suspension during or after step (3) to impregnate the polymer with the foaming agent. Steps (1) to (4) are usually carried out under vigorous stirring (e.g., more than 200 rpm) to disperse the droplets in the aqueous medium.

[0056] In suspension polymerization, droplets dispersed in an aqueous medium by vigorous stirring are prone to adhesion and additional dispersion. Therefore, foamed resin particles produced by suspension polymerization tend to have a broad particle size distribution.

[0057] In contrast, this manufacturing method includes a copolymerization step to obtain a copolymer (i.e., a base resin) by a droplet polymerization method. The copolymer (base resin) can also be called resin particles, and the methyl methacrylate copolymer can also be called methyl methacrylate resin particles. In this specification, the droplet polymerization method refers to a method for producing resin particles in which a monomer mixture containing at least monomer components and polymerization initiators, and optionally other additives, is passed through a droplet generation nozzle under regular vibration to disperse it as a group of droplets in an aqueous medium, and polymerized without causing adhesion and additional dispersion (or with a significant reduction in the occurrence of adhesion and additional dispersion).

[0058] In other words, the process of producing a copolymer (base resin) by droplet polymerization may include the following steps (1) to (3): (1) A dispersion step in which a monomer mixture containing at least monomer components and polymerization initiators, and optionally other additives, is passed through a droplet-generating nozzle under regular vibration to disperse it as a group of droplets in an aqueous medium containing water to prepare an aqueous suspension; (2) Next, a heating step in which the aqueous suspension is heated to a predetermined polymerization temperature; (3) Next, a polymerization step in which the aqueous suspension is reacted at a predetermined polymerization temperature for a predetermined polymerization time to carry out a polymerization reaction and obtain a copolymer. Steps (1) to (3) above are usually carried out under gentle stirring (for example, 200 rpm or less).

[0059] In droplet polymerization, droplets are dispersed in an aqueous medium by passing them through a droplet generation nozzle under regular vibrations, making it unlikely or impossible for droplets to adhere to each other or to undergo additional dispersion. Therefore, resin particles produced by droplet polymerization tend to have a narrow particle size distribution and excellent particle size uniformity.

[0060] (Device) The apparatus used in this manufacturing method preferably comprises a polymerization reactor, a droplet generation unit, and a foaming agent impregnation reactor. The polymerization reactor and the foaming agent impregnation reactor may be in the same container or in separate containers. In other words, the copolymerization step and the foaming agent impregnation step may be carried out consecutively in the same container or in separate containers.

[0061] The polymerization reactor is not particularly limited, except that it is equipped with a droplet inlet for introducing droplets into the polymerization reactor; a reactor commonly used for polymerization reactions can be used. Preferably, the polymerization reactor is equipped with a stirrer.

[0062] The droplet generation unit is equipped with a droplet generation nozzle and a vibrator, and is connected to the droplet inlet of the polymerization reactor via a droplet introduction tube.

[0063] The droplet generation unit may further include a dispersant aqueous solution inlet for introducing the dispersant aqueous solution into the droplet generation unit.

[0064] A droplet-generating nozzle is a nozzle that discharges a monomer mixture as droplets. There may be one or more droplet-generating nozzles. For example, a droplet-generating nozzle consists of a nozzle plate with an outlet for discharging the monomer mixture and a nozzle box with a monomer mixture inlet for introducing the monomer mixture. There may be one or more outlets.

[0065] By adjusting the number of discharge ports, the particle size and particle size distribution (UT) of the foamed resin particles can be controlled. Furthermore, by adjusting the diameter of the discharge ports, the droplet size can be controlled, and consequently, the particle size and particle size distribution (UT) of the foamed resin particles can be controlled.

[0066] The vibration exciter includes a vibrating section that applies regular vibrations to the droplet generation nozzle.

[0067] The reactor for impregnating with the foaming agent is not particularly limited, but it is preferably a container that can withstand the foaming temperature and foaming pressure described later, and for example, a pressure-resistant container is preferred.

[0068] (Dispersion process) The dispersion step in droplet polymerization involves dispersing a monomer mixture, which includes monomer components, polymerization initiators, and optionally other additives, as droplets in an aqueous medium containing water by passing it through a nozzle under regular vibration, thereby preparing an aqueous suspension.

[0069] In this specification, “monomer components” refers to the monomers used in the polymerization process. Specifically, “monomer components” refers to the (a) methyl methacrylate monomer and (b) acrylic acid ester monomer used in the polymerization process, as well as (c) other monomers different from the methyl methacrylate monomer and acrylic acid ester monomer, which may be used optionally.

[0070] As the polymerization initiator included in the monomer mixture, a radical-generating polymerization initiator, which is generally used in the production of thermoplastic polymers, can be used. Examples of typical radical-generating polymerization initiators include (a) organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl monocarbonate, and (b) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used individually or in combination of two or more.

[0071] Of the radical-generating polymerization initiators mentioned above, (a) benzoyl peroxide, lauroyl peroxide, t-butyl perpivalate, di-t-butyl peroxyhexahydroterephthalate, azobisisobutyronitrile, and azobisdimethylvaleronitrile are low-temperature decomposition polymerization initiators, and (b) t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxyisopropyl carbonate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl monocarbonate are high-temperature decomposition polymerization initiators.

[0072] In this manufacturing method, it is preferable to use a combination of at least one low-temperature decomposition type polymerization initiator and at least one high-temperature decomposition type polymerization initiator as the polymerization initiator. In other words, in the copolymerization step, a polymerization initiator is used, and it is preferable that the polymerization initiator contains at least one low-temperature decomposition type polymerization initiator and at least one high-temperature decomposition type polymerization initiator. These configurations have the advantage of being able to control the molecular weight and / or the amount of residual monomer while controlling the reaction rate.

[0073] The amount of polymerization initiator used is preferably 0.1 to 0.5 parts by weight, and more preferably 0.15 to 0.25 parts by weight, per 100 parts by weight of monomer components contained in the monomer mixture. With this configuration, foamable resin particles with excellent foaming properties can be obtained.

[0074] Other additives included in monomer mixtures include chain transfer agents, light stabilizers, plasticizers, and solvents.

[0075] In this manufacturing method, it is preferable to use a chain transfer agent; in other words, it is preferable that the monomer mixture contains a chain transfer agent. The chain transfer agent is not particularly limited, and well-known substances used in the polymerization of methyl methacrylate resins can be used. Examples of chain transfer agents include (a) monofunctional chain transfer agents such as alkyl mercaptans and thioglycolic acid esters, and (b) polyfunctional chain transfer agents in which the hydroxyl group of a polyhydric alcohol such as ethylene glycol, neopentyl glycol, trimethylolpropane, or sorbitol is esterified with thioglycolic acid or 3-mercaptopropionic acid. Examples of alkyl mercaptans include n-octyl mercaptan, n-dodecyl mercaptan, and t-dodecyl mercaptan. These chain transfer agents may be used individually or in combination of two or more. The amount of chain transfer agent used is preferably 0.10 parts by weight or more and less than 0.50 parts by weight, and more preferably 0.20 parts by weight to 0.35 parts by weight, per 100 parts by weight of monomer components contained in the monomer mixture.

[0076] The light stabilizer is not particularly limited as long as it is a generally known one. Commercially available light stabilizers such as Sumisorp® (manufactured by Sumitomo Chemical Co., Ltd.) can also be used. The amount of light stabilizer used is preferably 0.01 to 0.05 parts by weight per 100 parts by weight of monomer components contained in the monomer mixture.

[0077] The aqueous medium preferably contains a dispersant to enhance the dispersibility of the monomer mixture in water. The dispersant is not particularly limited, and well-known substances can be used. Examples of dispersants include (a) poorly water-soluble inorganic salts such as tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin; (b) water-soluble polymers such as polyvinyl alcohol, methylcellulose, polyacrylamide, and polyvinylpyrrolidone; and (c) water-soluble inorganic salts such as sodium nitrite and sodium chloride. These dispersants may be used individually or in combination of two or more.

[0078] Furthermore, a surfactant may be used in combination with the dispersant. Examples of surfactants include anionic surfactants such as sodium α-olefin sulfonate and sodium dodecylbenzenesulfonate. These surfactants may be used individually or in combination of two or more.

[0079] The amount of dispersant used is not particularly limited, but for example, 0.2 to 2.0 parts by weight, and more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of monomer components contained in the aqueous suspension.

[0080] The amount of surfactant used is not particularly limited, but for example, 0.001 to 0.010 parts by weight, and more preferably 0.003 to 0.008 parts by weight, per 100 parts by weight of monomer components contained in the aqueous suspension.

[0081] The aqueous medium may optionally contain other additives in addition to the dispersant and surfactant.

[0082] In the dispersion process, the monomer mixture introduced into the nozzle box from the monomer mixture inlet is discharged from the nozzle plate outlet. At this time, the vibrating part of the vibrator applies regular vibrations to the droplet generation nozzle, causing the monomer mixture discharged from the outlet to disperse as droplets in the aqueous medium. The aqueous medium containing the droplets is introduced into the polymerization reactor containing the aqueous medium via the droplet introduction tube and the droplet inlet.

[0083] By adjusting the supply rate (flow rate) of the monomer mixture to the nozzle box of the droplet generation nozzle, the particle size and particle size distribution (UT) of the foamed resin particles can be controlled.

[0084] The particle size and particle size distribution (UT) of the foamed resin particles can be controlled by adjusting the frequency of vibration applied to the droplet generation nozzle through which the monomer mixture passes. The frequency is preferably, for example, 200 Hz to 3000 Hz, more preferably 500 Hz to 2500 Hz, even more preferably 500 Hz to 2000 Hz, even more preferably 500 Hz to 1500 Hz, and particularly preferably 500 Hz to 1000 Hz.

[0085] As described above, the particle size and particle size distribution (UT) of the foamed resin particles can be controlled by appropriately adjusting the diameter and number of outlets of the droplet generation nozzle, the frequency of vibration applied to the droplet generation nozzle, and the flow rate (supply rate of the monomer mixture). Therefore, the diameter and number of outlets of the droplet generation nozzle, the frequency of vibration applied to the droplet generation nozzle, and the flow rate (supply rate of the monomer mixture) can be appropriately adjusted according to their respective settings so that the volume average particle size of the foamed resin particles is 0.30 mm to 0.50 mm and the particle size distribution (UT) is 2.30 or less. In addition, the diameter and number of outlets of the droplet generation nozzle, the frequency of vibration applied to the droplet generation nozzle, and the flow rate (supply rate of the monomer mixture) may be appropriately adjusted according to the viscosity of the monomer mixture.

[0086] In the dispersion process, the mixing ratio of the monomer mixture to the aqueous medium (weight of monomer mixture / weight of aqueous medium) is preferably 1.0 / 1.0 to 1.0 / 2.0.

[0087] In the dispersion process, a dispersant aqueous solution may be prepared separately from the monomer mixture, and this dispersant aqueous solution may be introduced into the droplet generation unit. The dispersant aqueous solution is, for example, an aqueous solution obtained by mixing a dispersant such as a water-soluble polymer and a water-soluble inorganic salt with an aqueous medium (e.g., water).

[0088] In the copolymerization process (for example, the dispersion process and the heating and polymerization processes described later), the aqueous suspension in the polymerization reactor may be gently stirred. The stirring speed is preferably 200 rpm or less, and more preferably 150 rpm or less, in order to prevent droplet adhesion and further dispersion. The lower limit of the stirring speed is not particularly limited, but from the viewpoint of preventing droplet adhesion, it is preferably 50 rpm or more, and more preferably 60 rpm or more.

[0089] (Heating process) The heating step is a process of raising the temperature of the aqueous suspension to a predetermined polymerization temperature in order to initiate polymerization. In the heating step, the temperature of the aqueous suspension is raised to the polymerization temperature of the polymerization step described later. The heating rate is not particularly limited.

[0090] (Polymerization process) The polymerization process is a step in which a copolymer is obtained by reacting an aqueous suspension at a predetermined polymerization temperature for a predetermined polymerization time to carry out a polymerization reaction. By holding (maintaining) the aqueous suspension at a predetermined polymerization temperature for a predetermined polymerization time, the polymerization reaction proceeds in the aqueous suspension. In the polymerization process, the polymerization reaction is carried out until the polymerization conversion rate reaches a value suitable for the foaming agent impregnation process described later.

[0091] The polymerization temperature in the polymerization process can be adjusted depending on the type and amount of monomer components, polymerization initiators, and other additives used, but is, for example, 60°C to 100°C, preferably 70°C to 90°C.

[0092] The polymerization time in the polymerization process is the time required to reach the desired polymerization conversion rate. The polymerization time can be adjusted depending on the type and amount of monomer components, polymerization initiators, and other additives used, but is typically 1 to 8 hours, preferably 3 to 5 hours.

[0093] When the desired polymerization conversion rate is reached, the polymerization can be completed (the polymerization reaction can be terminated) by cooling the aqueous suspension in the polymerization reactor. Next, it is preferable to recover the copolymer from the cooled aqueous suspension using a solid-liquid separation means or the like and subject it to the foaming agent impregnation step described later. This has advantages over the case where the foaming agent impregnation step is performed immediately without recovering the copolymer from the aqueous suspension, in that (a) a polymerization reactor with high pressure resistance is not required and the equipment can be simplified, and (b) the copolymer (resin particles) can be stored in the state before the foaming agent impregnation step.

[0094] As described above, the copolymerization step may include a dispersion step, a heating step, and a polymerization step. In other words, the copolymerization step in this manufacturing method may include, as an example, (a) a dispersion step in which a monomer mixture containing monomer components and a polymerization initiator is passed through a droplet-generating nozzle under vibration to form droplets and dispersed in an aqueous medium containing water to prepare an aqueous suspension; (b) a heating step in which the aqueous suspension is heated to the polymerization temperature; and (c) a polymerization step in which the polymerization reaction is carried out by maintaining the aqueous suspension at the polymerization temperature.

[0095] (Foaming agent impregnation process) The foaming agent impregnation process is a process of obtaining foamable resin particles by impregnating the copolymer with a foaming agent.

[0096] The foaming agent impregnation step includes, for example, the following (1) to (3): (1) In a foaming agent impregnation reactor, an aqueous medium containing water and the copolymer obtained by the copolymerization step are mixed to prepare an aqueous suspension; (2) Next, the aqueous suspension is heated to a predetermined impregnation temperature; (3) Next, at the predetermined impregnation temperature, the foaming agent is added to the aqueous suspension and the foaming agent is impregnated for a predetermined impregnation time.

[0097] In the foaming agent impregnation step, the stirring speed of the aqueous suspension is not particularly limited, but it is preferable to stir it at, for example, 200 rpm to 400 rpm.

[0098] In the foaming agent impregnation step, it is preferable to impregnate the obtained copolymer with the foaming agent when the polymerization conversion rate from monomer to copolymer is 80% to 95%. When the foaming agent is impregnated into the copolymer when the polymerization conversion rate is 80% or higher, the foaming agent is adequately impregnated into the interior of the copolymer, so there is no risk of aggregation of copolymers due to softening of the copolymer, and the production yield is good. When the foaming agent is impregnated into the copolymer when the polymerization conversion rate is 95% or lower, the foaming agent is sufficiently impregnated into the interior of the copolymer, so there is no risk of a double-cell structure (hard core) being formed in the foamed particles obtained by foaming the resulting foamed resin particles. As a result, by in-mold molding the foamed particles, a foamed molded article with excellent surface quality can be obtained.

[0099] In the foaming agent impregnation step, the aqueous medium preferably contains a dispersant to enhance the dispersibility of the copolymer in water. The type and amount of dispersant contained in the aqueous medium are the same as those described in the (dispersion step) section above.

[0100] Furthermore, a surfactant may be used in combination with the dispersant. The type and amount of surfactant used are the same as those described in the (dispersion step) section above.

[0101] In the foaming agent impregnation step, the amount of foaming agent impregnated into the methyl methacrylate resin particles, which are copolymers, includes preferred embodiments and is the same as the foaming agent content in foamed resin particles as described in the (Foaming Agent) section of [2. Foamed Methyl Methacrylate Resin Particles]. With this configuration, foamed resin particles with sufficient foaming properties can be obtained, and foamed resin particles can be safely manufactured without causing aggregation of the copolymer in the foaming agent impregnation step.

[0102] In the foaming agent impregnation process, the processing temperature (also referred to as the impregnation temperature) and processing time (also referred to as the impregnation time) when impregnating the copolymer with the foaming agent are not particularly limited.

[0103] In the foaming agent impregnation process, the impregnation temperature when impregnating the copolymer with the foaming agent is preferably 95°C to 120°C or lower, and more preferably 100°C to 117°C or lower. When the impregnation temperature is 95°C or higher, the foaming agent is sufficiently impregnated into the interior of the copolymer, so there is no risk of a double-cell structure (hard core) being formed in the foamed resin particles obtained by foaming. As a result, a foamed molded article with excellent surface quality can be obtained by in-mold molding of the foamed particles. When the impregnation temperature is 120°C or lower, the pressure inside the polymerization machine does not become too high, so foamed resin particles with a uniform cell structure can be obtained without requiring heavy-duty impregnation equipment that can withstand high pressure.

[0104] In this manufacturing method, when a solvent (for example, a solvent with a boiling point of 50°C or higher) is used, it is preferable to add the solvent to the reaction mixture (aqueous suspension) immediately before or simultaneously with the addition of the blowing agent. In other words, when a solvent is used in this manufacturing method, it is preferable to use (add) the solvent in the blowing agent impregnation step, and it is even more preferable to use the solvent only in the blowing agent impregnation step (i.e., not use the solvent in the copolymerization step).

[0105] [4. Methyl methacrylate-based resin foamed particles] The methyl methacrylate resin foam particles according to one embodiment of the present invention are foam particles obtained by foaming foam methyl methacrylate resin particles described in section [2. Foaming methyl methacrylate resin particles] or foaming methyl methacrylate resin particles produced by the manufacturing method described in section [3. Method for producing foaming methyl methacrylate resin particles]. The "methyl methacrylate resin foam particles according to one embodiment of the present invention" may also be referred to as "the foam particles" below.

[0106] Because these foamed particles have the above-described structure, they have the advantage of providing foamed molded articles that are excellent in terms of filling into molds and have excellent surface aesthetics.

[0107] These foamed resin particles can be produced by a general foaming method. Specifically, for example, methyl methacrylate resin foamed particles can be obtained by performing the following operations (1) to (3) in order: (1) Place the foamed methyl methacrylate resin particles in a container equipped with a stirrer; (2) While stirring the foamed methyl methacrylate resin particles, heat the foamed methyl methacrylate resin particles with a heat source such as steam; (3) Perform foaming to the desired foaming ratio as in (2) to obtain methyl methacrylate resin foamed particles.

[0108] The foaming of foamed methyl methacrylate resin particles can be considered a preliminary foaming process performed in order to obtain a methyl methacrylate resin foam molded product, as described later, from these foamed methyl methacrylate resin particles. Therefore, the foaming of foamed methyl methacrylate resin particles is sometimes referred to as "pre-foaming," and the methyl methacrylate resin foam particles are sometimes referred to as "methyl methacrylate pre-foamed particles."

[0109] Since these foamed particles are formed by foaming foamable resin particles having a particle size distribution (UT) of 2.30 or less, the particle size distribution (UT) of these foamed particles can also be 2.30 or less.

[0110] The particle size distribution (UT) of the foamed particles is preferably 2.30 or less, more preferably 2.25 or less, even more preferably 2.20 or less, even more preferably 2.19 or less, and particularly preferably 2.18 or less. When the particle size distribution (UT) of the foamed particles is 2.30 or less, the surface beauty of the foamed molded article obtained from the foamed particles can be further improved.

[0111] With regard to these foamed particles, the descriptions in sections [2. Foamed Methyl Methacrylate Resin Particles] and [3. Method for Producing Foamed Methyl Methacrylate Resin Particles] shall be applied as appropriate, except for the matters described above.

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

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

[0114] Because this foamed molded body has the above-described structure, it has the advantage of having excellent surface aesthetics. Furthermore, the methyl methacrylate-based resin foamed molded body according to one embodiment of the present invention has the advantage of producing less residue compared to aromatic resin foamed molded bodies (for example, foamed molded bodies made of styrene-based resin) when the foamed molded body is buried in casting sand and molten metal is poured into the foamed molded body to replace the metal. For these reasons, the methyl methacrylate-based resin foamed molded body according to one embodiment of the present invention can be suitably used as a lost-wax mold.

[0115] These foamed particles can be molded into a foamed molded article by a general in-mold molding method. Specifically, a methyl methacrylate-based resin foamed molded article can be obtained by performing the following operations (1) to (3) in order: (1) Fill a mold that can be closed but cannot be airtight with methyl methacrylate-based resin foamed particles; (2) Heat the methyl methacrylate-based resin foamed particles with steam; (3) Fuse the methyl methacrylate-based resin foamed particles together as in (2) to obtain a methyl methacrylate-based resin foamed molded article.

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

[0117] The lost-wax casting model according to one embodiment of the present invention has excellent surface aesthetics and produces less residue during combustion compared to lost-wax casting models containing aromatic resin foam molded bodies, making it suitable for use in various metal casting applications.

[0118] One embodiment of the present invention may have the following configuration.

[0119] [1] Foaming methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the volume average particle diameter is 0.30 mm to 0.50 mm and the particle size distribution (UT) is 2.30 or less.

[0120] [2] The foaming methyl methacrylate resin particles according to [1], wherein the content of methyl methacrylate units in the base resin is 90.0 to 99.0 parts by weight and the content of acrylic acid ester units is 1.0 to 10.0 parts by weight, per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units.

[0121] [3] The foaming methyl methacrylate resin particles according to [1] or [2], wherein the acrylic acid ester unit is a butyl acrylate unit.

[0122] [4] The foaming methyl methacrylate resin particle according to any one of [1] to [3], wherein the base resin further contains crosslinking agent units, and the content of the crosslinking agent units is 0.05 parts by weight or more and less than 0.20 parts by weight per 100 parts by weight of the total amount of the methyl methacrylate units and the acrylic acid ester units in the base resin.

[0123] [5] The foaming methyl methacrylate resin particles according to any one of [1] to [4], wherein the base resin does not contain aromatic units, or contains more than 0 parts by weight and 2.5 parts by weight or less of aromatic units in 100 parts by weight of the base resin.

[0124] [6] The foaming methyl methacrylate resin particles according to any one of [1] to [5], wherein the foaming methyl methacrylate resin particles further contain a solvent, and the content of the solvent in the foaming methyl methacrylate resin particles is 1.0 to 3.0 parts by weight per 100 parts by weight of the base resin.

[0125] [7] [1] to [6] Foamed methyl methacrylate resin particles obtained by foaming the foamed methyl methacrylate resin particles described in any one of these.

[0126] A methyl methacrylate resin foam molded article obtained by in-mold molding the methyl methacrylate resin foam particles described in [8] and [7].

[0127] Loss-wax model comprising a methyl methacrylate resin foam molded product as described in [9] and [8].

[0128]

[10] A method for producing foaming methyl methacrylate resin particles, comprising a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer by a droplet polymerization method, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, wherein the volume average particle diameter of the foaming methyl methacrylate resin particles is 0.30 mm to 0.50 mm and the particle size distribution (UT) is 2.30 or less.

[0129]

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

[10] , wherein the copolymerization step comprises (a) a dispersion step of dispersing a monomer mixture containing monomer components and a polymerization initiator as a group of droplets in an aqueous medium containing water by passing it through a droplet-generating nozzle under vibration to produce an aqueous suspension; (b) a heating step of raising the aqueous suspension to a polymerization temperature; and (c) a polymerization step of allowing the polymerization reaction to proceed by maintaining the aqueous suspension at the polymerization temperature.

[0130]

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

[11] , wherein the frequency of the vibration in the dispersion step is 200 Hz to 3000 Hz.

[0131]

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

[11] or

[12] , wherein in the copolymerization step, the aqueous suspension is stirred at a speed of 200 rpm or less.

[0132]

[14] A method for producing foaming methyl methacrylate resin particles according to any one of

[10] to

[13] , wherein the content of the methyl methacrylate monomer in the monomer mixture is 90.0 to 99.0 parts by weight and the content of the acrylic acid ester monomer is 1.0 to 10.0 parts by weight, based on 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic acid ester monomer.

[0133]

[15] The method for producing foaming methyl methacrylate resin particles according to any one of

[10] to

[14] , wherein the acrylic acid ester monomer is butyl acrylate.

[0134]

[16] The method for producing foaming methyl methacrylate resin particles according to any one of

[10] to

[15] , wherein the monomer mixture further contains a crosslinking agent, and the content of the crosslinking agent in the monomer mixture is 0.05 parts by weight or more and less than 0.20 parts by weight per 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic acid ester monomer,

[0135]

[17] A method for producing foaming methyl methacrylate resin particles according to any one of

[10] to

[16] , wherein the monomer mixture does not contain an aromatic monomer, or contains more than 0 parts by weight and 2.5 parts by weight or less of the aromatic monomer in 100 parts by weight of the monomer mixture.

[0136]

[18] A method for producing foaming methyl methacrylate resin particles according to any one of

[10] to

[17] , wherein in the foaming agent impregnation step, a solvent is further used, and the amount of the solvent used per 100 parts by weight of the copolymer is 1.0 to 3.0 parts by weight. [Examples]

[0137] Examples and comparative examples are given below, but the present invention is not limited thereto.

[0138] The various measurement and evaluation methods for foamed methyl methacrylate resin particles, methyl methacrylate resin foam particles, and methyl methacrylate resin foam molded articles in the examples and comparative examples are as follows. Unless otherwise specified, "parts" and "%" are based on weight.

[0139] (Polymerization and conversion rate of foamed methyl methacrylate resin particles) During polymerization, an aqueous suspension was sampled and filtered. The weight of the resin component remaining on the filter paper was measured and taken as the weight before heating. Next, a polymerization inhibitor was added to the resin component, and the resin component was heated at 150°C for 30 minutes to remove volatile components. After that, the weight of the resulting resin component was measured and taken as the weight after heating. The polymerization conversion rate was calculated using the following formula. Polymerization conversion rate (%) = Weight after heating / Weight before heating × 100.

[0140] (Volume-average particle size and particle size distribution (UT) of foamed methyl methacrylate resin particles) The particle size of foamed methyl methacrylate resin particles was measured on a volume basis using an image processing type Millitrack JPA particle size analyzer. A distribution table was created showing the obtained results as a cumulative distribution, and the particle size at which the volume cumulative distribution reaches 50% (D50) was defined as the volume-average particle diameter. Furthermore, using this distribution table, the particle size distribution (UT) of the foamed methyl methacrylate resin particles was calculated according to the definition described above.

[0141] (Foaming properties of foaming methyl methacrylate resin particles) The bulk density of the foamed resin particles obtained by foaming the foamed resin particles was calculated by following steps (1) to (6) below in order: (1) 10 g of foamed resin particles was weighed out and an anti-blocking agent was applied to the surface of the foamed resin particles; (2) The foamed resin particles were placed in a steamer with a blower outlet; (3) 100°C steam was supplied to the steamer and the foamed resin particles were heated for 180 seconds to obtain foamed particles; (4) The obtained foamed particles were heated to 1000 cm 3 (5) Place the foam particles into the graduated cylinder; (5) From the scale of the graduated cylinder, determine the volume of the foam particles (cm³ 3 (6) The bulk density of the foamed particles was calculated using the following formula: Bulk density (g / cm³) 3 ) = 10(g) / volume of foamed particles (cm³) 3 ).

[0142] Based on the following criteria, the foaming properties of the foamed resin particles were evaluated from the obtained bulk density. ○ (Good): Bulk density (A) is 0.0182 g / cm³ 3 below × (Defective): Bulk density (A) is 0.0182 g / cm³ 3 It exceeds.

[0143] (Filling properties of methyl methacrylate-based resin foam particles) A blocking inhibitor was applied to foamed methyl methacrylate resin particles. The foamed methyl methacrylate resin particles were then placed in a steamer at 100°C. Next, the foamed methyl methacrylate resin particles were heated while adjusting the heating time to obtain foamed methyl methacrylate resin particles with a foaming ratio of 50. The obtained foamed methyl methacrylate resin particles were filled into a mold (flat plate shape, size: 450mm long, 300mm wide, 10mm thick). In-mold molding was performed using a molding machine (Daisen Co., Ltd., KR-57) under molding conditions of a blown vapor pressure of 0.04~0.10 MPa to obtain a foamed methyl methacrylate resin molded body.

[0144] The resulting methyl methacrylate-based resin foam molded articles were visually inspected for areas with filling defects, and the filling performance of the methyl methacrylate-based resin foam particles was evaluated based on the following indicators. ○ (Good): No areas with filling defects. × (Defective): There are areas with filling defects.

[0145] (Surface elongation of methyl methacrylate-based resin foam particles) Using the methyl methacrylate resin foam molded article obtained by the method described in the section above (Filling properties of methyl methacrylate resin foam particles), the surface elongation of the methyl methacrylate resin foam particles was evaluated based on the size of the gaps between the foam particles on the surface of the molded article, according to the following indicators. ○ (Good): There are no or very few gaps between the foam particles. × (Defective): There are slight gaps between the foam particles (more than "very few"). ×× (Very poor): There are many gaps between the foam particles.

[0146] (Surface aesthetics of methyl methacrylate-based resin foam molded products) Using the methyl methacrylate resin foam molded article obtained by the method described in the section on (filling properties of methyl methacrylate resin foam particles) above, the uniformity of particle size of the foam particles observed on the surface of the foam molded article was visually evaluated. The uniformity of particle size of the foam particles observed on the surface of the foam molded article showed a high correlation with the particle size distribution (UT) of the foamed methyl methacrylate resin particles, and the lower the value of the particle size distribution (UT), the better the uniformity.

[0147] The surface aesthetics of methyl methacrylate-based resin foam molded articles were evaluated based on the following indicators. ○ (Good): There are no or very few gaps between foam particles, and the particle size is uniform or nearly uniform. × (Poor): There are small gaps between the foam particles (more than "very few"), and the particle size is uniform or nearly uniform. ×× (Very Poor): (a) There are small gaps between foam particles (more than "Very Small") and the particle size is non-uniform, or (b) There are many gaps between foam particles.

[0148] In Examples 1-3 and Comparative Example 3 below, a 6L polymer reactor was used as the polymerization reactor, which had a droplet inlet at the bottom communicating with the droplet generation unit and was equipped with a flat plate stirrer. In the following Examples and Comparative Example, the droplet generation unit used was equipped with (i) a droplet generation nozzle consisting of one nozzle plate and a nozzle box (having a monomer mixture inlet), (ii) a vibrator, and (iii) a dispersant aqueous solution inlet. In Examples 1-3 and Comparative Example 3, the diameter of the nozzle plate's discharge port was 0.17 mmφ, and the number of discharge ports on the nozzle plate was 45.

[0149] (Example 1) 1.5 L of aqueous dispersion medium, prepared in pure water to contain 11,000 ppm tricalcium phosphate and 110 ppm sodium dodecylbenzenesulfonate, was added to the polymerization reactor, and stirring of the raw materials was started at 60 rpm.

[0150] Next, an aqueous dispersant solution prepared by dissolving 530 g of 3% polyvinyl alcohol and 20 g of sodium nitrite in 5000 g of pure water was introduced into the droplet generation unit at a rate of 80 mL / min. Simultaneously, the following (i) and (ii) were performed in order to generate droplets (droplet groups) of the monomer mixture in the droplet generation unit: (i) In the nozzle box of the droplet generation nozzle, a monomer component consisting of 95.0 parts by weight of methyl methacrylate and 5.0 parts by weight of butyl acrylate, 0.03 parts by weight of Sumisorp® (manufactured by Sumitomo Chemical Co., Ltd., product number [B]NL-0682), and 0.08 parts by weight of lauroyl peroxide and 1,1-bis(t-butylperoxy)cyclohexane as polymerization initiators were added. (ii) A monomer mixture consisting of 0.1 parts by weight of 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent and 0.3 parts by weight of n-dodecyl mercaptan as a chain transfer agent was supplied from the monomer mixture inlet at a rate of 90 mL / min; (ii) Along with the supply of the monomer mixture to the nozzle box, the monomer mixture was discharged from the nozzle plate outlet while applying regular vibrations of 800 Hz to the droplet generation nozzle using a vibrator, and the monomer mixture was formed as droplets in the dispersant aqueous solution of the droplet generation section. The droplets formed in the droplet generation section were transferred from the droplet inlet to the 6 L polymerization reactor via the droplet introduction tube to prepare an aqueous suspension (dispersion step).

[0151] When a group of 1500 g of monomer mixture droplets was introduced into a 6 L polymerization reactor, droplet formation was stopped. After changing the stirring speed to 100 rpm, the aqueous suspension in the 6 L polymerization reactor was heated (heating step), and polymerization was started at 80°C. Four hours after the start of polymerization, the aqueous suspension was cooled to complete the polymerization (polymerization step). The polymerization conversion rate was 88%. The copolymer was obtained (recovered) by dehydrating and drying the cooled aqueous suspension (copolymerization step).

[0152] In a 6L autoclave equipped with a stirrer, 92 parts by weight of pure water, 0.38 parts by weight of tricalcium phosphate, 0.0104 parts by weight of sodium α-olefin sulfonate, 0.1 parts by weight of sodium chloride, and 100 parts by weight of the copolymer obtained by the copolymerization process were charged. The raw materials were then stirred at 250 rpm to prepare an aqueous suspension. Subsequently, the temperature of the aqueous suspension was raised to 80°C, and then 9 parts by weight of n-rich butane (the weight ratio of n-butane to isobutane in the n-rich butane is 70 / 30) and 1.5 parts by weight of cyclohexane as a solvent were charged into the aqueous suspension. The temperature of the aqueous suspension was then raised to 101°C. Subsequently, the temperature of the aqueous suspension was maintained at 101°C for 10 hours to impregnate the copolymer with the blowing agent (blowing agent impregnation process). Subsequently, the aqueous suspension was cooled to room temperature, and the resulting product was washed, dehydrated, and dried to obtain foamed methyl methacrylate resin particles. 0.4 parts by weight of zinc stearate as a fatty acid metal salt and 0.05 parts by weight of hydrogenated castor oil as a fusion accelerator were applied to the surface of the obtained foamed methyl methacrylate resin particles.

[0153] Using the obtained foamed methyl methacrylate resin particles, the volume-average particle size, particle size distribution (UT), and foaming properties of the foamed methyl methacrylate resin particles, as well as the filling properties and surface elongation of the foamed methyl methacrylate resin particles, and the surface aesthetics of the foamed methyl methacrylate resin molded article were evaluated according to the method described above. The evaluation results are shown in Table 1.

[0154] (Example 2) Except for changing the amount of butyl acrylate used in the monomer mixture to 2.5 parts by weight, the same procedure as in Example 1 was followed to obtain foamed resin particles, foamed particles, and foamed molded articles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0155] (Example 3) Except for changing the amount of butyl acrylate used in the monomer mixture to 7.0 parts by weight, the same procedure as in Example 1 was followed to obtain foamed resin particles, foamed particles, and foamed molded articles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0156] (Comparative Example 1) A mixture was prepared by charging 150 parts by weight of water, 0.15 parts by weight of tricalcium phosphate, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide, 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane, 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, 0.03 parts by weight of Sumisorp® ([B]NL-0682), and 0.24 parts by weight of n-dodecyl mercaptan into a 6L autoclave equipped with a stirrer. Subsequently, 95.0 parts by weight of methyl methacrylate, 5.0 parts by weight of butyl acrylate, and 1.0 part by weight of toluene were added to the mixture as a monomer mixture to prepare an aqueous suspension. The temperature of the aqueous suspension was then raised to 80°C to start polymerization. After 1 hour and 45 minutes from the start of polymerization, the polymerization conversion rate was measured to be 40% to 50%. One hour and forty-five minutes after the start of polymerization, 0.12 parts by weight of tricalcium phosphate was added to the reaction mixture (aqueous suspension).

[0157] After a further 2 hours and 35 minutes, 1.5 parts by weight of cyclohexane and 9 parts by weight of n-rich butane (with a weight ratio of n-butane to isobutane (n-butane / isobutane) of 70 / 30) were added to the aqueous suspension. The temperature of the aqueous suspension was then raised to 101°C. The aqueous suspension was then maintained at 101°C for 10 hours to impregnate the copolymer with the blowing agent. The aqueous suspension was then cooled. After cooling, the resulting product was washed, dehydrated, and dried to obtain blown methyl methacrylate resin particles.

[0158] The obtained foamed methyl methacrylate resin particles were sieved using sieves with mesh sizes of 0.500 mm and 1.400 mm. Through this procedure, foamed methyl methacrylate resin particles with a particle size of 0.500 mm to 1.400 mm were collected. 0.2 parts by weight of zinc stearate as a fatty acid metal salt and 0.05 parts by weight of hydrogenated castor oil as a fusion accelerator were applied to the surface of the obtained foamed methyl methacrylate resin particles.

[0159] Using the obtained foamed methyl methacrylate resin particles, foamed particles and foamed molded articles were obtained according to the method described above. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0160] (Comparative Example 2) Except for sieving with mesh sizes of 0.355 mm and 0.500 mm to collect foamed methyl methacrylate resin particles with a particle size of 0.355 mm to 0.500 mm, the same procedure as in Comparative Example 1 was followed to obtain foamed resin particles, foamed particles, and foamed molded articles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0161] (Comparative Example 3) Except for changing the supply rate of the monomer mixture to 380 mL / min, the same procedure as in Example 1 was followed to obtain foamed resin particles, foamed particles, and foamed molded articles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1. [Table 1] [Industrial applicability]

[0162] According to one embodiment of the present invention, foamable methyl methacrylate resin particles can be provided that provide foamed particles with excellent mold filling properties and foamed molded articles with excellent surface aesthetics. Therefore, one embodiment of the present invention can be suitably used as a lost-wax model when performing metal casting by the full-mold method, and in particular can be suitably used as a lost-wax model when manufacturing castings that have complex shapes and / or are small in size.

Claims

1. The base resin contains methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent. The volume-average particle size is 0.30 mm to 0.50 mm, and the particle size distribution (UT) is 2.30 or less. In the base resin, the content of methyl methacrylate units is 90.0 to 99.0 parts by weight, and the content of acrylic acid ester units is 1.0 to 10.0 parts by weight, relative to 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units. The aforementioned base resin further comprises crosslinking agent units, Foaming methyl methacrylate resin particles, wherein the content of the crosslinking agent unit is 0.05 parts by weight or more and less than 0.20 parts by weight per 100 parts by weight of the total amount of the methyl methacrylate unit and the acrylic acid ester unit in the base resin.

2. The foaming methyl methacrylate resin particles according to claim 1, wherein the acrylic acid ester unit is a butyl acrylate unit.

3. The foamable methyl methacrylate resin particles according to claim 1, wherein the base resin does not contain aromatic units, or contains more than 0 parts by weight and 2.5 parts by weight or less of aromatic units in 100 parts by weight of the base resin.

4. The foaming methyl methacrylate resin particles further contain a solvent, The foamed methyl methacrylate resin particles according to claim 1, wherein the content of the solvent in the foamed methyl methacrylate resin particles is 1.0 to 3.0 parts by weight relative to 100 parts by weight of the base resin.

5. Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles described in any one of claims 1 to 4.

6. A methyl methacrylate-based resin foamed molded article obtained by in-mold molding the methyl methacrylate-based resin foamed particles described in claim 5.

7. A lost-wax model comprising a methyl methacrylate-based resin foam molded body as described in claim 6.

8. A method for producing foaming methyl methacrylate resin particles, comprising a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer by a droplet polymerization method, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent, The volume-average particle diameter of the foamed methyl methacrylate resin particles is 0.30 mm to 0.50 mm, and the particle size distribution (UT) is 2.30 or less. In the monomer mixture, the content of the methyl methacrylate monomer is 90.0 to 99.0 parts by weight, and the content of the acrylic acid ester monomer is 1.0 to 10.0 parts by weight, relative to 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic acid ester monomer. The monomer mixture further comprises a crosslinking agent, A method for producing foaming methyl methacrylate resin particles, wherein the amount of the crosslinking agent in the monomer mixture is 0.05 parts by weight or more and less than 0.20 parts by weight, relative to 100 parts by weight of the total amount of the methyl methacrylate monomer and the acrylic acid ester monomer.

9. The copolymerization step is, (a) A dispersion step in which a monomer mixture containing monomer components and polymerization initiators is passed through a droplet-generating nozzle under vibration to form droplets, which are then dispersed in an aqueous medium containing water to prepare an aqueous suspension; (b) A heating step of raising the aqueous suspension to the polymerization temperature, (c) A method for producing foaming methyl methacrylate resin particles according to claim 8, comprising a polymerization step of carrying out a polymerization reaction by maintaining an aqueous suspension at a polymerization temperature.

10. The method for producing foamed methyl methacrylate resin particles according to claim 9, wherein the frequency of the vibration in the dispersion step is 200 Hz to 3000 Hz.

11. The method for producing foaming methyl methacrylate resin particles according to claim 9 or 10, wherein the copolymerization step involves stirring the aqueous suspension at a speed of 200 rpm or less.

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