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

Abstract

The present invention addresses the problem of providing expandable methyl-methacrylate-based resin particles with which it is possible to provide a molded foam of a methyl-methacrylate-based resin having excellent surface beauty qualities. The above problem is solved by using expandable methyl-methacrylate-based resin particles containing a base resin that contains methyl methacrylate units and acrylic acid ester units, and a foaming agent, the expandable methyl-methacrylate-based resin particles having (a) a specific volume average particle size, peak top particle size, and foamability, or (b) a specific structural unit ratio, volume average particle size, peak top particle size, and weight average molecular weight.

Description

Technical Field

[0001] The present invention relates to expandable methyl methacrylate resin particles, methyl methacrylate resin foam particles, methyl methacrylate resin foam molded articles, and expendable molds.

Background Art

[0002] When performing metal casting, a lost foam casting method (full mold method) for casting a casting is known, in which a mold made of a foam molded article is buried in casting sand, and molten metal is poured into the foam molded article to replace the foam molded article with metal. In the full mold method, a foam molded article of a methyl methacrylate polymer is often used as a lost foam mold.

[0003] As expandable methyl methacrylate resin particles for producing a foam molded article of a methyl methacrylate polymer, for example, Patent Document 1 discloses expandable methyl methacrylate resin particles containing a base resin containing a methyl methacrylate unit, an acrylic acid ester unit, and a structural unit derived from a crosslinking agent as structural units, and a foaming agent.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the above-mentioned conventional technology has room for improvement from the viewpoint of the surface beauty of the methyl methacrylate resin foam molded article.

[0006] One aspect of the present invention is to provide expandable methyl methacrylate resin particles that can provide a methyl methacrylate resin foam molded article excellent in surface beauty.

Means for Solving the Problems

[0007] The inventors, after diligent study to solve the aforementioned problems, have completed the present invention. That is, one embodiment of the present invention includes the following configuration.

[0008] Foamable methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the foamable methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and when the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to reach foamed methyl methacrylate resin particles with a bulk ratio of 50 times is less than 80 seconds.

[0009] 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 acrylic acid ester units are butyl acrylate units, and when the total content of the methyl methacrylate units and butyl acrylate units in the base resin is 100 parts by weight, the content of the methyl methacrylate units is 93.0 parts by weight to 98.0 parts by weight, and the content of the butyl acrylate units is 2.0 parts by weight to 7.0 parts by weight, and the foaming methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and the weight average molecular weight of the base resin is 175,000 to 285,000. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide foamable methyl methacrylate resin particles that can provide a foamed molded article of methyl methacrylate resin with excellent surface aesthetics. [Modes for carrying out the invention]

[0011] 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)."

[0012] 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."

[0013] [1. Technical Concept of One Embodiment of an Embodiment] The foamed molded article obtained using the foamed resin particles disclosed in Patent Document 1 has room for improvement in terms of surface aesthetics.

[0014] As a result of diligent research, the inventors have independently discovered the following novel aspects and completed the present invention: (i) Foaming methyl methacrylate resin particles in which the peak top particle diameter of the particle size distribution is within a specific range have little variation in particle size, i.e., excellent uniformity; (ii) Foaming methyl methacrylate resin particles having a specific amount of specific constituent units and a small weight-average molecular weight of the base resin have excellent foaming properties; (ii) Foaming methyl methacrylate resin particles with a small volume-average particle diameter are obtained by foaming them. (iii) The methyl methacrylate resin foam particles have excellent filling properties for molded objects of various shapes (for example, narrow areas with a width of several mm), and the methyl methacrylate resin foam particles obtained by foaming foamable methyl methacrylate resin particles, which have excellent uniformity and foaming properties and a small volume average particle diameter, have improved surface aesthetics of the resulting methyl methacrylate resin foam molded product because the surface of the methyl methacrylate resin foam molded product stretches during the molding process when using the methyl methacrylate resin foam particles in mold molding.

[0015] If the packing performance of methyl methacrylate resin foam particles is poor, when these foam particles are filled into a mold, regions with high and low packing densities of the foam particles will be formed within the mold. When in-mold molding is performed under these conditions, the regions with low packing densities will need to foam more to fill the gaps compared to the regions with high packing densities. In other words, the degree of foaming of the foam particles (in other words, the size of the foam particles constituting the methyl methacrylate resin foam molded article) will differ between the regions with low and high packing densities, resulting in a decrease in the surface aesthetics of the resulting methyl methacrylate resin foam molded article. Therefore, "packing performance of methyl methacrylate resin foam particles" can be one of the indicators for evaluating the surface aesthetics of a methyl methacrylate resin foam molded article, as described in the examples below.

[0016] When the peak-top particle diameter of foamed methyl methacrylate resin particles is large, the variation in particle size is large, and the variation in particle size of the foamed methyl methacrylate resin particles derived from those foamed methyl methacrylate resin particles is also large. When in-mold molding is performed using foamed methyl methacrylate resin particles with large variation in particle size, the size of the foamed particles constituting the resulting foamed methyl methacrylate resin molded body will differ, resulting in a decrease in the surface aesthetics of the foamed methyl methacrylate resin molded body. Therefore, the "peak-top particle diameter of foamed methyl methacrylate resin particles" can be one of the indicators for evaluating the surface aesthetics of a foamed methyl methacrylate resin molded body, as described in the examples below.

[0017] [2. Foaming methyl methacrylate resin particles] The foamed methyl methacrylate resin particles according to one embodiment of the present invention are foamed methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the foamed methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and when the foamed methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) in which the foamed methyl methacrylate resin particles reach foamed methyl methacrylate resin particles with a bulk ratio of 50 is less than 80 seconds.

[0018] The foamed methyl methacrylate resin particles according to one embodiment of the present invention are foamed methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the acrylic acid ester units are butyl acrylate units, and when the total content of the methyl methacrylate units and butyl acrylate units in the base resin is 100 parts by weight, the content of the methyl methacrylate units is 93.0 parts by weight to 98.0 parts by weight, and the content of the butyl acrylate units is 2.0 parts by weight to 7.0 parts by weight, the foamed methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and the weight average molecular weight of the base resin is 175,000 to 285,000.

[0019] "Foamable methyl methacrylate resin particles according to one embodiment of the present invention" may also be referred to as "the foamable resin particles" below.

[0020] Foamed resin particles can be provided by foaming them using a known method. Foamed molded articles can be provided by in-mold molding the foamed resin particles using a known method.

[0021] Since the expandable resin particles have the above-described configuration, they have the advantage of being able to provide a methyl methacrylate-based resin foam molded article excellent in surface beauty. Specifically, the expandable resin particles have a peak top particle diameter of the particle size distribution within a specific range. Therefore, the expandable resin particles have the advantage of having little variation in particle size, that is, being excellent in uniformity. Further, the expandable resin particles according to one embodiment of the present invention are excellent in expandability. Also, the expandable resin particles according to another embodiment of the present invention surprisingly have excellent expandability because they have a specific amount of a specific structural unit and a small weight average molecular weight of the base resin. Further, since the expandable resin particles have a small volume average particle diameter, the expanded particles formed by expanding the expandable resin particles also have the advantage of having a small particle diameter. The expanded particles having a small particle diameter have the advantage of being excellent in filling properties into moldings of various shapes (for example, a narrow portion having a width of about several millimeters). Also, the expanded particles formed by expanding expandable resin particles excellent in uniformity and expandability and having a small volume average particle diameter have the advantage of being able to provide a foam molded article excellent in surface beauty as a result of the surface of the methyl methacrylate-based resin foam molded article during molding stretching when using the expanded particles in in-mold molding.

[0022] (Base resin) The base resin contained in the expandable resin particles includes a methyl methacrylate unit and an acrylate unit as structural units. In the present specification, the "methyl methacrylate unit" is a structural unit derived from a methyl methacrylate monomer, and the "acrylate unit" is a structural unit derived from an acrylate monomer. In the present specification, the notation of "monomer" may be omitted. Therefore, in the present specification, for example, when simply denoted as "methyl methacrylate" and "acrylate", they respectively intend "methyl methacrylate monomer" and "acrylate monomer".

[0023] In the base resin contained in the expandable resin particles, with respect to a total of 100 parts by weight of methyl methacrylate units and acrylate units, (a) the content of methyl methacrylate units is 93.0 to 98.0 parts by weight, and the content of acrylate units can be 2.0 to 7.0 parts by weight; (b) it is preferable that the content of methyl methacrylate units is 93.5 to 98.0 parts by weight, and the content of acrylate units is 2.0 to 6.5 parts by weight; (c) it is more preferable that the content of methyl methacrylate units is 94.0 to 98.0 parts by weight, and the content of acrylate units is 2.0 to 6.0 parts by weight; (d) it is even more preferable that the content of methyl methacrylate units is 94.5 to 98.0 parts by weight, and the content of acrylate units is 2.0 to 5.5 parts by weight; (e) it is particularly preferable that the content of methyl methacrylate units is 95.0 to 97.5 parts by weight, and the content of acrylate units is 2.5 to 5.0 parts by weight.

[0024] In the base resin, when the content of acrylate units with respect to a total of 100 parts by weight of methyl methacrylate units and acrylate units is within the above-mentioned range, the expandable resin particles have the advantage of being excellent in foamability. As a result, the expandable resin particles (foamed particles) have the advantage of being able to provide a foamed molded body with excellent surface beauty.

[0025] Examples of the acrylate according to one embodiment of the present invention include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, etc. As the acrylate, butyl acrylate is particularly preferable. In other words, it is particularly preferable that the acrylate unit is a butyl acrylate unit derived from a butyl acrylate monomer. Butyl acrylate has a great effect of lowering the glass transition temperature of the base resin. Therefore, according to this configuration, the expandable resin particles have the advantage of being excellent in foamability. As a result, the expandable resin particles (foamed particles) have the advantage of being able to provide a foamed molded body with excellent surface beauty.

[0026] 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 advantage of providing foamed particles with excellent shrinkage suppression and excellent foaming properties.

[0027] Examples of crosslinking agents include compounds having two or more functional groups that exhibit radical reactivity. Among compounds having two or more functional groups that exhibit radical reactivity, it is preferable to use a difunctional monomer having two functional groups as the crosslinking agent. In other words, it is preferable that the base resin of the foamed resin particles contains a difunctional monomer unit, which is a constituent unit derived from a difunctional monomer, as the crosslinking agent unit. 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.

[0028] 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 / or 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 groups 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, are esterified with acrylic acid or methacrylic acid, and (c) aryl compounds having two alkenyl groups, such as divinylbenzene. Hexanediol di(meth)acrylate is preferred as a bifunctional monomer because it is easy to adjust the molecular weight of the base resin. In this specification, "(meth)acrylate" refers to methacrylate and / or acrylate, and "(meth)acrylic acid" refers to methacrylic acid and / or acrylic acid.

[0029] In the base resin, the content of crosslinking agent units per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units is 0 parts by weight or more and less than 0.20 parts by weight, preferably 0 to 0.19 parts by weight, more preferably 0 to 0.17 parts by weight or less, more preferably 0 to 0.15 parts by weight or less, and even more preferably 0 to 0.13 parts by weight. According to the above configuration, (a) the foamed resin particles have excellent foaming properties, (b) the foamed particles obtained by foaming the foamed resin particles have excellent shrinkage suppression properties, and (c) the foamed molded body obtained by in-mold molding the foamed particles has excellent surface beauty properties. In the base resin, the content of crosslinking agent units per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units may be 0.01 parts by weight or more, 0.03 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

[0030] 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.

[0031] 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, more preferably 1.5 parts by weight or less, even more preferably 1.0 part by weight or less, even more preferably 0.5 parts 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.

[0032] (Foaming agent) The foaming agent contained in these foamed resin particles is not particularly limited. Examples of foaming agents include (a) aliphatic hydrocarbons having 3 to 5 carbon atoms, such as propane, isobutane, n-butane, isopentane, n-pentane, and neopentane, and (b) 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.

[0033] 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.

[0034] (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 solvents, plasticizers, foam regulators, flame retardants, flame retardant enhancers, heat radiation inhibitors, pigments, dyes, and antistatic agents.

[0035] 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 this allows 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 1.5 to 3.0 parts by weight. When the solvent content per 100 parts by weight of the base resin is (a) 1.5 parts 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.

[0036] 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.

[0037] In these foamed resin particles, the content of plasticizer per 100 parts by weight of 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 suppression properties.

[0038] 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.

[0039] (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%.

[0040] The volume-average particle size of foamed resin particles can be adjusted by changing (a) the amount of initial dispersant (e.g., tricalcium phosphate, sodium α-olefin sulfonate), (b) the amount of dispersant added during polymerization (e.g., tricalcium phosphate), and (c) the timing of dispersant addition during polymerization (e.g., the time from the start of polymerization to the addition of the dispersant).

[0041] (Particle size distribution peak top particle diameter) The peak top particle diameter of the particle size distribution of this foamed resin particle is 0.33 mm to 0.47 mm, preferably 0.35 mm to 0.47 mm, and more preferably 0.40 mm to 0.45 mm.

[0042] In this specification, the peak-top particle diameter of the particle size distribution of foamed resin particles is defined as the particle size of the foamed resin particles measured on a volume basis using a particle size analyzer (e.g., an image processing type MilliTrac JPA particle size analyzer), and the obtained results are displayed as a distribution with particle diameter (0.1 mm intervals) on the horizontal axis and volume frequency on the vertical axis. The region (particle diameter) with the highest frequency in the obtained particle size distribution is defined as the peak-top particle diameter.

[0043] (Foaming properties of foaming methyl methacrylate resin particles) When these foamable resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to reach a bulk ratio of 50 times may be less than 80 seconds. Preferably, the time (A) is 70 seconds or less, and more preferably 50 seconds or less. The lower limit of time (A) is not limited, but it must be at least greater than 0 seconds. If the time (A) is less than 80 seconds, the foamable resin particles can be said to have excellent foaming properties.

[0044] Here, the method for measuring the time (A) (foaming rate) of foamed resin particles is not particularly limited, but for example, the following method can be used, in order: (1) Put the foamed resin particles into a pressurized foaming machine (for example, a BHP manufactured by Daikai Kogyo Co., Ltd.); (2) Next, steam (for example, water vapor) is blown into the foaming machine under conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed resin particles; (3) At regular intervals, the foamed particles formed from the foamed resin particles are removed from the foaming machine and the bulk ratio of the foamed particles is measured; (4) Measure the time (A) (which can also be called the heating time (A)) from when steam is blown into the foamed resin particles until foamed particles with a bulk ratio of 50 are obtained.

[0045] Compared to heating foamed resin particles at a steam injection pressure of 0.10 MPa, heating them at a steam injection pressure of 0.16 MPa slightly reduces the time required to obtain foamed particles with a bulk ratio of 50, but it is virtually unchanged. In this specification, time (A) is defined as the time required to obtain foamed resin particles with a bulk ratio of 50 when heated under the conditions of a steam injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa.

[0046] In this specification, the bulk ratio of the foamed particles shall be the value obtained by performing the following steps (1) to (3) in order: (1) Weigh out 10 g of foamed particles and measure 1000 cm² 3 (1) Place the foam particles into a graduated cylinder; (2) Measure the volume of 10g of foam particles from the scale on the graduated cylinder; (3) Calculate the bulk ratio of the foam particles using the following formula; Bulk magnification (cm 3 ( / g) = Volume of foamed particles (cm³) 3 ) / 10g.

[0047] In this specification, the bulk ratio of foamed particles can also be called the foaming ratio. Furthermore, the unit of the bulk ratio is actually cm based on the formula described above. 3 Although the unit is / g, for convenience, in this specification the unit of bulk ratio will be expressed as "times".

[0048] (Weight average molecular weight) The weight-average molecular weight of the base resin contained in these foamed resin particles can range from 175,000 to 285,000. Surprisingly, when the weight-average molecular weight of the base resin is 285,000 or less, the foamed resin particles have the advantage of excellent foaming properties. As a result, the foamed resin particles (foamed particles) have the advantage of being able to provide foamed molded articles with excellent surface beauty. When the weight-average molecular weight of the base resin is 175,000 or more, the foamed particles shrink less, making it less likely for gaps to form between particles when molded into an article, and thus having excellent surface elongation. The weight-average molecular weight is preferably 200,000 to 260,000, and more preferably 230,000 to 250,000.

[0049] In this specification, the weight-average molecular weight obtained by the following method is defined as the weight-average molecular weight of the base resin contained in the foamed resin particles: (1) Dissolve 0.02 g of foamed resin particles in 20 ml of tetrahydrofuran (hereinafter sometimes abbreviated as "THF"); (2) Filter the gel component in the resulting solution; (3) Then, using only the components soluble in THF (i.e., the filtrate) as a sample, perform GPC measurement using a gel permeation chromatograph (GPC); (4) Calculate the weight-average molecular weight (Mw) and number-average molecular weight (Mn) from the GPC measurement chart obtained by the GPC measurement. Note that the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are relative values ​​on a polystyrene basis.

[0050] The weight-average molecular weight of the base resin can be adjusted by changing the composition (type and amount) of monomers used in the polymerization (copolymerization) process of the base resin, the type and amount of chain transfer agent, the polymerization temperature and time, the type and amount of initiator, and the type and amount of crosslinking agent.

[0051] [3. Method for producing foaming methyl methacrylate resin particles] A method for producing foaming methyl methacrylate resin particles according to one embodiment of the present invention may include a copolymerization step of copolymerizing a monomer mixture containing a methyl methacrylate monomer and an acrylic acid ester monomer, and a foaming agent impregnation step of impregnating the obtained copolymer with a foaming agent. The copolymerization step further includes (a) an initiation step of starting copolymerization of the monomer mixture in the presence of 0.20 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, and (b) an addition step of adding 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture to the reaction mixture after the initiation step when the polymerization conversion rate is 35% to 70%. In the copolymerization step, it is preferable that the amount of methyl methacrylate monomer used is 93.0 to 98.0 parts by weight and the amount of acrylic acid ester monomer used is 2.0 to 7.0 parts by weight, relative to 100 parts by weight of the total amount of methyl methacrylate monomer and acrylic acid ester monomer used.

[0052] In this specification, "poorly water-soluble inorganic salt" refers to an inorganic salt whose solubility in water at 25°C is 0.1 mg / ml or less.

[0053] 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.

[0054] Because this manufacturing method has the above configuration, it is possible to provide foamed methyl methacrylate resin particles that can provide a foamed molded article of methyl methacrylate resin with excellent surface beauty. Because this manufacturing method has the above configuration, it is possible to provide foamed methyl methacrylate resin particles according to one embodiment of the present invention, as described in section [2. Foamed Methyl Methacrylate Resin Particles]. This manufacturing method is suitably used to produce the foamed resin particles described in section [2. Foamed Methyl Methacrylate Resin Particles]. In this manufacturing method, "polymer" corresponds to the "base resin" contained in the foamed resin particles described in section [2. Foamed Methyl Methacrylate Resin Particles].

[0055] 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.

[0056] (3-1.Copolymerization process) The copolymerization step in this manufacturing method is suspension polymerization, in which a monomer mixture is polymerized in an aqueous suspension. Hereinafter, the copolymer (base resin) obtained in the copolymerization step may simply be referred to as "resin particles."

[0057] In the present invention, "aqueous suspension" refers to a liquid in which monomer droplets and / or resin particles are dispersed in water or an aqueous solution by stirring or the like. The aqueous suspension may contain (a) water-soluble surfactants and monomers, or (b) water-insoluble dispersants, polymerization initiators, chain transfer agents, crosslinking agents, foam regulators, flame retardants, solvents, plasticizers, etc., dispersed together with the monomers.

[0058] The weight ratio of monomers and polymers (resins) to water or aqueous solution in the aqueous suspension is preferably 1.0 / 0.6 to 1.0 / 3.0 as the ratio of the resulting methyl methacrylate resin to water or aqueous solution. The term "aqueous solution" as used herein refers to a solution consisting of water and components other than the methyl methacrylate resin.

[0059] The copolymerization step includes an initiation step in which copolymerization of the monomer mixture is initiated in the presence of 0.20 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture. The initiation step is a step in which copolymerization of the monomer mixture is initiated using an aqueous suspension containing, for example, (a) water, (b) a monomer mixture containing methyl methacrylate monomer and acrylic acid ester monomer, (c) 0.20 to 1.20 parts by weight of a first poorly water-soluble inorganic salt per 100 parts by weight of the monomer mixture, (d) a crosslinking agent, and optionally (e) a polymerization initiator, surfactant, dispersant other than the poorly water-soluble inorganic salt, chain transfer agent, foam regulator, flame retardant, solvent and plasticizer, etc.

[0060] In this specification, the period "before the start of the polymerization reaction" may also be referred to as the "initial polymerization stage." The first poorly water-soluble inorganic salt added to the aqueous suspension in the initiation step, and optionally added polymerization initiators, can be considered substances (raw materials) used in the initial polymerization stage.

[0061] In the initial step, the first poorly water-soluble inorganic salt can function as a dispersant. Examples of the first poorly water-soluble inorganic salt used in the initial step, i.e., the initial stage of polymerization, include tricalcium phosphate, magnesium pyrophosphate, hydroxyapatite, and kaolin.

[0062] Furthermore, in the initial step, (a) a water-soluble polymer such as polyvinyl alcohol, methylcellulose, polyacrylamide, or polyvinylpyrrolidone, and / or (b) an anionic surfactant such as sodium α-olefin sulfonate or sodium dodecylbenzenesulfonate may be used in combination with the first poorly water-soluble inorganic salt.

[0063] As the first poorly water-soluble inorganic salt used in the initiation step, tricalcium phosphate is preferred from the viewpoint of protecting resin particles and / or monomer droplets. From the viewpoint of droplet dispersion stability, the initiation step is preferably a step in which copolymerization of the monomer mixture is started in the presence of tricalcium phosphate, which is a poorly water-soluble inorganic salt, and sodium α-olefin sulfonate, which is an anionic surfactant.

[0064] The starting step is preferably a step in which copolymerization of the monomer mixture is started in the presence of a first poorly water-soluble inorganic salt in an amount of preferably 0.20 to 1.20 parts by weight, more preferably 0.20 to 1.10 parts by weight, and even more preferably 0.40 to 1.10 parts by weight, per 100 parts by weight of the monomer mixture. When copolymerization of the monomer mixture is started in the presence of a first poorly water-soluble inorganic salt of 0.20 parts by weight or more per 100 parts by weight of the monomer mixture, there is no risk that the volume average particle size of the resulting foamed resin particles will be too large. When copolymerization of the monomer mixture is started in the presence of a first poorly water-soluble inorganic salt of 1.10 parts by weight or less per 100 parts by weight of the monomer mixture, there is no risk that a large amount of fine particles will be generated in the foamed resin particles. In other words, by starting copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt in an amount within the above range, foamed resin particles having a desired volume average particle size can be obtained in good yield.

[0065] When a water-soluble polymer and / or anionic surfactant is used in combination with a first poorly water-soluble inorganic salt in the initial step, 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.

[0066] The copolymerization step includes an addition step in which, after the initiation step, when the polymerization conversion rate is 35% to 70%, 0.08 to 0.50 parts by weight of a second poorly water-soluble inorganic salt is added to the reaction mixture per 100 parts by weight of the monomer mixture.

[0067] In this specification, "after the start of the polymerization reaction" may also be referred to as "during polymerization." The second poorly water-soluble inorganic salt added to the reaction mixture during the addition step can be considered a substance (raw material) used during polymerization.

[0068] When the polymerization of monomer mixtures in the copolymerization process is carried out by suspension polymerization, the reaction mixture in the addition step can be described as an aqueous suspension.

[0069] In the addition step, the second poorly water-soluble inorganic salt can function as a dispersant. Examples of the second poorly water-soluble inorganic salt used in the addition step, i.e., during polymerization, include the substances already exemplified as the first poorly water-soluble inorganic salt. The second poorly water-soluble inorganic salt is preferably one or more selected from the group consisting of tricalcium phosphate, hydroxyapatite, and kaolin, and more preferably tricalcium phosphate. This configuration has the advantage of preventing the resin particles from coalescing after the addition of the dispersant, thereby obtaining resin particles of the desired particle size.

[0070] The addition step is preferably a step in which, after the initiation step, when the polymerization conversion rate is 35% to 70%, a second poorly water-soluble inorganic salt is added to the reaction mixture in an amount of preferably 0.08 to 0.50 parts by weight, more preferably 0.10 to 0.50 parts by weight, more preferably 0.10 to 0.40 parts by weight, even more preferably 0.10 to 0.30 parts by weight, and particularly preferably 0.10 to 0.20 parts by weight, per 100 parts by weight of the monomer mixture. When 0.08 parts by weight or more of the second poorly water-soluble inorganic salt is added to the reaction mixture per 100 parts by weight of the monomer mixture in the addition step, there is no risk that the volume average particle size of the resulting foamed resin particles will become too large. When 0.50 parts by weight or less of the second poorly water-soluble inorganic salt is added to the reaction mixture per 100 parts by weight of the monomer mixture in the addition step, the production cost will increase due to the excessive use of the poorly water-soluble inorganic salt. In other words, by adding a second poorly water-soluble inorganic salt in the amount within the above range to the reaction mixture during the addition step, foamed resin particles having a desired volume-average particle size can be obtained at a low production cost.

[0071] The addition step preferably involves adding the second poorly water-soluble inorganic salt to the reaction mixture when the polymerization conversion rate is 35% to 70%, more preferably when the polymerization conversion rate is 40% to 50%. This configuration allows for the production of foamed resin particles having a desired volume-average particle size. The method for measuring the polymerization conversion rate in this specification will be described in detail in the following examples.

[0072] The copolymerization process is preferably carried out in at least two stages by varying the polymerization temperature. For convenience, the two polymerization stages with different polymerization temperatures will be referred to below as the first polymerization stage and the second polymerization stage. It can also be said that the copolymerization process preferably includes consecutive first and second polymerization stages with different polymerization temperatures.

[0073] The copolymerization process preferably includes, for example, (a) a first polymerization step carried out at a polymerization temperature of 70°C to 90°C using a low-temperature decomposition type polymerization initiator, and (b) a second polymerization step carried out continuously with the first polymerization step at a higher polymerization temperature (e.g., 90°C to 110°C) than the first polymerization step and using a high-temperature decomposition type polymerization initiator. In the copolymerization process, it is preferable that the main polymerization reaction takes place in the first polymerization step described above, and that the remaining monomers are reduced in the second polymerization step described above.

[0074] As polymerization initiators, radical-generating polymerization initiators commonly used in the production of thermoplastic polymers can be used. Typical radical-generating polymerization initiators include, for example, (a) organic peroxides such as benzoyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, isopropyl-t-butyl peroxycarbonate, butyl perbenzoate, t-butyl peroxy-2-ethylhexanoate, t-butyl perpivalate, t-butyl peroxyisopropyl carbonate, di-t-butyl peroxyhexahydroterephthalate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-amylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, and t-butyl peroxy-2-ethylhexyl monocarbonate, and (b) azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used individually or in combination of two or more.

[0075] 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.

[0076] The amount of polymerization initiator used is preferably 0.05 to 0.5 parts by weight or less per 100 parts by weight of monomer mixture, when totaled in the first polymerization step and the second polymerization step. This configuration yields foamable resin particles with excellent foaming properties.

[0077] The initiation step may be (a) a step of initiating copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt, a low-temperature decomposition type polymerization initiator, and a high-temperature decomposition type polymerization initiator, or (b) a step of initiating copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt and a low-temperature decomposition type polymerization initiator. If the initiation step is a step of initiating copolymerization of the monomer mixture in the presence of a first poorly water-soluble inorganic salt and a low-temperature decomposition type polymerization initiator, the high-temperature decomposition type polymerization initiator may be added to the reaction mixture (aqueous suspension) after the initiation step, i.e., during polymerization.

[0078] In the copolymerization process, it is preferable to use a chain transfer agent. The chain transfer agent is not particularly limited, and well-known substances used in the polymerization of methyl methacrylate resins can be used. Examples of chain transfer agents include (a) monofunctional chain transfer agents such as alkyl mercaptans and thioglycolic acid esters, and (b) polyfunctional chain transfer agents 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. The amount of chain transfer agent used is preferably 0.100 parts by weight or more and less than 0.500 parts by weight, and more preferably 0.270 parts by weight or more and less than 0.340 parts by weight, per 100 parts by weight of the base resin.

[0079] (3-2. Foaming agent impregnation process) In the foaming agent impregnation step, foamable methyl methacrylate resin particles can be obtained by impregnating the methyl methacrylate resin particles, which are copolymers obtained in the copolymerization step, with a foaming agent.

[0080] The foaming agent impregnation step can be performed at any time, for example, together with the second polymerization step or after the second polymerization step.

[0081] 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 beauty can be obtained.

[0082] 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.

[0083] 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.

[0084] 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 particles obtained by foaming the resulting foamed resin particles. As a result, a foamed molded article with excellent surface beauty 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.

[0085] In this manufacturing method, when using a solvent (for example, a solvent with a boiling point of 50°C or higher), it is preferable to add the solvent to the reaction mixture (aqueous suspension) immediately before or simultaneously with the foaming agent impregnation step.

[0086] [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].

[0087] "Methyl methacrylate-based resin foamed particles according to one embodiment of the present invention" may also be referred to as "the foamed particles" below.

[0088] These foamed resin particles can be produced by a general foaming method. Specifically, for example, methyl methacrylate-based resin foamed particles can be obtained by performing the following steps (1) to (3) in order: (1) Place the foamed methyl methacrylate-based resin particles in a container equipped with a stirrer; (2) Heat the foamed methyl methacrylate-based resin particles with a heat source such as steam; (3) Perform foaming to the desired foaming ratio using the method described in (2) to obtain methyl methacrylate-based resin foamed particles.

[0089] The foaming of foamed methyl methacrylate resin particles can be described as preliminary foaming performed in order to obtain a foamed methyl methacrylate resin molded product, which will be described later, from said foamed methyl methacrylate resin particles. For this reason, the foaming of foamed methyl methacrylate resin particles is sometimes referred to as "pre-foaming," and the foamed methyl methacrylate resin particles are sometimes referred to as "pre-foamed methyl methacrylate resin particles."

[0090] These foamed particles exhibit excellent packing properties. The packing properties of the foamed particles can be evaluated by performing the following steps (1) to (5) in order. (1) Leave the foamed particles (for example, foamed particles with a bulk ratio of 50 times) at room temperature (for example, 25°C) (for example, leave for 3 days); (2) Fill a molding machine having a mold measuring 450 mm in length, 300 mm in width, and 30 mm in thickness with the foamed particles; (3) Blow steam into the mold at a steam blowing pressure of 0.10 MPa to 0.50 MPa, and perform in-mold molding by vacuum suction heating under conditions where the pressure inside the mold is 0.030 MPa to 0.100 MPa, until the foaming pressure reaches 0.100 MPa to 0.180 MPa, thereby fusing the foamed particles together; (4) After the foaming pressure reaches 0.100 MPa to 0.180 MPa, leave the mold for 200 seconds, and then remove the foamed molded body; (5) Visually inspect the obtained foamed molded body for any areas with filling defects.

[0091] [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].

[0092] 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.

[0093] 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.

[0094] A methyl methacrylate-based resin foam molded article according to one embodiment of the present invention has the advantages of excellent surface aesthetics and low residue during combustion. For these reasons, a methyl methacrylate-based resin foam molded article according to one embodiment of the present invention can be suitably used as a lost-wax model.

[0095] [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].

[0096] The lost-wax model according to one embodiment of the present invention has excellent surface aesthetics and can therefore be suitably used in various metal castings.

[0097] [7. Other] The present invention can be configured as follows.

[0098] [1] Foamable methyl methacrylate resin particles comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, wherein the foamable methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and when the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to become foamed methyl methacrylate resin particles with a bulk ratio of 50 times is less than 80 seconds.

[0099] [2] The foaming methyl methacrylate resin particles according to [1], wherein the acrylic acid ester unit is a butyl acrylate unit.

[0100] [3] Foaming methyl methacrylate resin particles according to [1] or [2], wherein the weight-average molecular weight of the base resin is 175,000 to 285,000.

[0101] [4] 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 acrylic acid ester units are butyl acrylate units, and when the total content of the methyl methacrylate units and butyl acrylate units in the base resin is 100 parts by weight, the content of the methyl methacrylate units is 93.0 parts by weight to 98.0 parts by weight, and the content of the butyl acrylate units is 2.0 parts by weight to 7.0 parts by weight, and the foaming methyl methacrylate resin particles have a volume average particle diameter of 0.30 mm to 0.50 mm and a peak top particle diameter of 0.33 mm to 0.47 mm, and the weight average molecular weight of the base resin is 175,000 to 285,000.

[0102] [5] The foaming agent comprises (a) an aliphatic hydrocarbon having 3 to 5 carbon atoms, and / or (b) a volatile foaming agent, as described in any of [1] to [4].

[0103] [6] Foaming methyl methacrylate resin particles according to any one of [1] to [5], wherein the content of the foaming agent per 100 parts by weight of the base resin is 5 to 12 parts by weight.

[0104] [7] The base resin is foamed methyl methacrylate resin particles according to any one of [1] to [6], comprising structural units derived from a crosslinking agent.

[0105] [8] The foaming methyl methacrylate resin particles according to [7], wherein the base resin includes a difunctional monomer unit, which is a constituent unit derived from a difunctional monomer, as a constituent unit derived from the crosslinking agent.

[0106] [9] The foaming methyl methacrylate resin particles according to [7] or [8], wherein the content of constituent units derived from the crosslinking agent is 0 parts by weight or more and less than 0.20 parts by weight per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units in the base resin.

[0107]

[10] Foaming methyl methacrylate resin particles according to any one of [1] to [9], further comprising a plasticizer.

[0108]

[11] The foaming methyl methacrylate resin particles according to

[10] , wherein the content of the plasticizer per 100 parts by weight of the base resin is 0.40 parts by weight to 4.00 parts by weight.

[0109]

[12] Foaming methyl methacrylate resin particles obtained by foaming the foaming methyl methacrylate resin particles described in any of [1] to

[11] .

[0110] A methyl methacrylate resin foamed molded article obtained by in-mold molding the methyl methacrylate resin foamed particles described in

[13] and

[12] .

[0111] Loss-wax model comprising a methyl methacrylate-based resin foam molded product as described in

[14] and

[13] . [Examples]

[0112] One embodiment of the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0113] (Volume average particle diameter, peak top particle diameter, and uniformity of foamed methyl methacrylate resin particles) The particle size of foamed methyl methacrylate resin particles was measured using an image processing type Millitrack JPA particle size analyzer, based on volume, at cut width intervals of 0.005 mm. The obtained results were displayed as a cumulative distribution, and the particle size at which the volume cumulative distribution reached 50% was defined as the volume-average particle size. The region with the highest frequency in the obtained particle size distribution was defined as the peak-top particle size.

[0114] Based on the following indicators, the uniformity of the foaming methyl methacrylate resin particles was evaluated: A (very good): The peak top particle size is 0.33 mm to 0.47 mm B (poor): The peak top particle size is less than 0.33 mm or exceeds 0.47 mm.

[0115] (Weight average molecular weight of the base resin) The weight average molecular weight obtained by measuring according to the following method was taken as the weight average molecular weight of the base resin contained in the foaming resin particles: (1) 0.02 g of the foaming resin particles was dissolved in 20 ml of THF; (2) Then, the gel component in the obtained solution was filtered; (3) Next, only the component soluble in THF (i.e., the filtrate) was used as a sample, and GPC measurement was performed under the following conditions using gel permeation chromatography (GPC); (4) From the GPC measurement chart obtained by GPC measurement, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were calculated. The weight average molecular weight (Mw) and the number average molecular weight (Mn) are relative values in terms of polystyrene conversion. <GPC measurement conditions> Measurement device: High-speed GPC device HLC-8220 manufactured by Tosoh Corporation Columns used: Two SuperHZM-H columns and two SuperH-RC columns manufactured by Tosoh Corporation Column temperature: 40 °C, mobile phase: THF (tetrahydrofuran) Flow rate: 0.35 ml / min, injection volume: 10 μl Detector: RI.

[0116] (Foaming property of the methyl methacrylate resin foaming particles) Using foamed methyl methacrylate resin particles, the following steps (1) to (3) were performed in order to obtain foamed methyl methacrylate resin particles with a bulk ratio of 50: (1) Foamed methyl methacrylate resin particles were placed into a pressurized foaming machine, the BHP110, manufactured by Daikai Kogyo Co., Ltd.; (2) Steam was blown into the foaming machine under conditions of a steam blowing pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa to heat the foamed methyl methacrylate resin particles; (3) The foamed methyl methacrylate resin particles were foamed according to (2) until a bulk ratio of 50 was obtained, thereby obtaining foamed methyl methacrylate resin particles with a bulk ratio of 50. The heating time required for the foamed methyl methacrylate resin particles to reach a bulk ratio of 50 was also measured.

[0117] The foaming properties of methyl methacrylate-based resin foam particles were evaluated based on the following indicators: A (Excellent): Heating time 70 seconds or less B (Good): Heating time 80 seconds or less C (defective): Heating time exceeds 80 seconds.

[0118] (Filling properties of methyl methacrylate-based resin foam particles) Using methyl methacrylate-based resin foam particles, the following steps (1) to (4) were carried out in order to obtain a methyl methacrylate-based resin foam molded article: (1) Methyl methacrylate-based resin foam particles with a bulk ratio of 50 times were left at room temperature (25°C) for 3 days; (2) Methyl methacrylate-based resin foam particles with a bulk ratio of 50 times were filled into a molding machine (DAISEN KR-57) having a mold with dimensions of 450 mm in length, 300 mm in width, and 10 mm in thickness; (3) Steam injection (4) After the foaming pressure reached 0.10 MPa to 0.180 MPa, steam was blown into the mold at a pressure of 0.10 MPa to 0.50 MPa, and in-mold molding was performed by vacuum suction heating under conditions where the pressure inside the mold was 0.030 MPa to 0.100 MPa, fusing the methyl methacrylate resin foam particles together.

[0119] 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: A (Good): No areas with filling defects. B (Defective): There are areas with filling defects.

[0120] (Surface aesthetics of methyl methacrylate-based resin foam molded products) The surface of the methyl methacrylate resin foam molded article was observed visually, and its surface aesthetics were evaluated based on the following indicators. The degree of gaps between the methyl methacrylate resin foam particles constituting the methyl methacrylate resin foam molded article was evaluated on a scale of 0 (gaps between particles are not filled at all) to 5 (gaps between particles are completely filled), with increments of 0.25 points. A (Excellent): The gap between foamed particles is 4.50 or higher, and the packing performance and peak top particle size are excellent. B (Good): The gap between foamed particles is 4.25 or higher and less than 4.50, and the packing performance and peak top particle size are very good. C (Poor): The gap between foamed particles is less than 4.25 points, the peak top particle size is poor, or the filling performance is poor.

[0121] (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.

[0122] (Example 1) In a 6L autoclave equipped with a stirrer, 150 parts by weight of water, 0.53 parts by weight of tricalcium phosphate as the first poorly water-soluble inorganic salt, 0.0075 parts by weight of sodium α-olefin sulfonate, 0.08 parts by weight of lauroyl peroxide, 0.1 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane as the first poorly water-soluble inorganic salt, 0.1 parts by weight of 1,6-hexanediol diacrylate as a crosslinking agent, 0.300 parts by weight of n-dodecyl mercaptan, and 0.03 parts by weight of sumisorb were charged to prepare a mixture containing the first poorly water-soluble inorganic salt. 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 charged into the mixture as a monomer mixture to prepare an aqueous suspension. Next, the temperature of the aqueous suspension was raised to 80°C to start polymerization, i.e., the initiation step was carried out. One hour and forty-five minutes after the start of polymerization (after the initiation step), the polymerization conversion rate was measured to be 40% to 50%. One hour and forty-five minutes after the start of polymerization (after the initiation step), 0.12 parts by weight of tricalcium phosphate was added to the reaction mixture (aqueous suspension) as a second poorly water-soluble inorganic salt, and the addition step was carried out.

[0123] After a further 2 hours and 35 minutes, 1.5 parts by weight of cyclohexane as a plasticizer and 9 parts by weight of n-rich butane (the weight ratio of n-butane to isobutane in the n-rich butane (n-butane / isobutane) is 70 / 30) as a blowing agent were charged into the aqueous suspension. The temperature of the aqueous suspension was then raised to 101°C. Next, the temperature of the aqueous suspension was maintained at 101°C for 10 hours to carry out copolymerization and impregnation of the copolymer with the blowing agent (copolymerization step and blowing agent impregnation step). The aqueous suspension was then cooled. After cooling the aqueous suspension, the obtained product was washed, dehydrated, and dried to obtain blowing methyl methacrylate resin particles.

[0124] The obtained foamed methyl methacrylate resin particles were sieved using sieves with mesh sizes of 0.235 mm and 0.600 mm. Through this procedure, foamed methyl methacrylate resin particles with particle sizes ranging from 0.235 mm to 0.600 mm were collected. Subsequently, 0.40 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 foamed methyl methacrylate resin particles.

[0125] Following the method described above, each evaluation item (volume-average particle diameter, peak-top particle diameter, uniformity, foaming properties, and filling properties of foamed methyl methacrylate resin particles, as well as the surface aesthetics of the methyl methacrylate resin foam molded article) was evaluated. The evaluation results are shown in Table 1.

[0126] (Example 2) Except for changing the monomer mixture used to 96.5 parts by weight of methyl methacrylate and 3.5 parts by weight of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0127] (Example 3) Except for changing the monomer mixture used to 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0128] (Example 4) Except for changing the monomer mixture used to 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate, and changing the amount of n-dodecyl mercaptan used to 0.340 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0129] (Example 5) Except for changing the amount of n-dodecyl mercaptan used to 0.275 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0130] (Example 6) Except for changing the amount of n-dodecyl mercaptan used to 0.340 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0131] (Comparative Example 1) Except for changing the amount of n-dodecyl mercaptan used to 0.240 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0132] (Comparative Example 2) Except for changing the amount of tricalcium phosphate used as the first poorly water-soluble inorganic salt to 0.15 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0133] (Comparative Example 3) Except for changing the monomer mixture used to 97.5 parts by weight of methyl methacrylate and 2.5 parts by weight of butyl acrylate, and changing the amount of n-dodecyl mercaptan used to 0.265 parts by weight, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0134] (Comparative Example 4) Except for changing the amount of tricalcium phosphate used as the first poorly water-soluble inorganic salt to 0.15 parts by weight, and changing the mesh size of the sieve used for sieving the foamed methyl methacrylate resin particles to 0.50 mm to 1.40 mm, the same procedure as in Example 1 was followed to obtain foamed methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0135] (Comparative Example 5) Except for changing the monomer mixture used to 91.5 parts by weight of methyl methacrylate and 8.5 parts by weight of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0136] (Comparative Example 6) Except for changing the monomer mixture used to 98.5 parts by weight of methyl methacrylate and 1.5 parts by weight of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate-based resin particles. Each evaluation item was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0137] (Comparative Example 7) Except for using methyl acrylate instead of butyl acrylate, the same procedure as in Example 1 was followed to obtain foaming methyl methacrylate resin particles. Each evaluation item was evaluated using the same method as in Example 1. The evaluation results are shown in Table 1.

[0138] (result) As is clear from Table 1, Examples 1-6 received high ratings for "uniformity," "foaming properties," and "filling properties," and consequently, also received high ratings for "surface aesthetics." [Table 1] [Industrial applicability]

[0139] According to one embodiment of the present invention, foamable methyl methacrylate resin particles can be provided that can provide a foamed molded article of methyl methacrylate resin 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-molding method.

Claims

1. A foaming methyl methacrylate resin particle comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, The foamed methyl methacrylate resin particles have a volume-average particle diameter of 0.30 mm to 0.50 mm, and a peak-top particle diameter of 0.33 mm to 0.47 mm in the particle size distribution. When the foamable methyl methacrylate resin particles are foamed under conditions of a vapor injection pressure of 0.10 MPa to 0.16 MPa and a foaming machine internal pressure of 0.005 MPa to 0.030 MPa, the time (A) for the foamable methyl methacrylate resin particles to become foamed methyl methacrylate resin particles with a bulk ratio of 50 is less than 80 seconds. Foaming methyl methacrylate resin particles, wherein the weight-average molecular weight of the base resin is 175,000 to 240,000.

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

3. A foaming methyl methacrylate resin particle comprising a base resin containing methyl methacrylate units and acrylic acid ester units as constituent units, and a foaming agent, The aforementioned acrylic acid ester unit is a butyl acrylate unit. When the total content of methyl methacrylate units and butyl acrylate units in the base resin is 100 parts by weight, the content of methyl methacrylate units is 93.0 to 98.0 parts by weight, and the content of butyl acrylate units is 2.0 to 7.0 parts by weight. The foamed methyl methacrylate resin particles have a volume-average particle diameter of 0.30 mm to 0.50 mm, and a peak-top particle diameter of 0.33 mm to 0.47 mm in the particle size distribution. Foaming methyl methacrylate resin particles, wherein the weight-average molecular weight of the base resin is 175,000 to 240,000.

4. The foaming agent comprises (a) an aliphatic hydrocarbon having 3 to 5 carbon atoms, and / or (b) a volatile foaming agent, as described in claim 1 or 3.

5. The foaming methyl methacrylate resin particles according to claim 1 or 3, wherein the content of the foaming agent per 100 parts by weight of the base resin is 5 to 12 parts by weight.

6. The foaming methyl methacrylate resin particles according to claim 1 or 3, wherein the base resin includes constituent units derived from a crosslinking agent.

7. The foamable methyl methacrylate resin particles according to claim 6, wherein the base resin includes a difunctional monomer unit, which is a constituent unit derived from a difunctional monomer, as a constituent unit derived from the crosslinking agent.

8. The foaming methyl methacrylate resin particles according to claim 6, wherein the content of constituent units derived from the crosslinking agent is 0 parts by weight or more and less than 0.20 parts by weight per 100 parts by weight of the total amount of methyl methacrylate units and acrylic acid ester units in the base resin.

9. The foaming methyl methacrylate resin particles according to claim 1 or 3, further comprising a plasticizer.

10. The foaming methyl methacrylate resin particles according to claim 9, wherein the content of the plasticizer per 100 parts by weight of the base resin is 0.40 parts by weight to 4.00 parts by weight.

11. Foamed methyl methacrylate resin particles obtained by foaming the foamable methyl methacrylate resin particles described in claim 1 or 3.

12. A methyl methacrylate-based resin foamed molded article obtained by in-mold molding the methyl methacrylate-based resin foamed particles described in claim 11.

13. A lost-wax model comprising a methyl methacrylate-based resin foam molded body as described in claim 12.

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