Foamed acrylic resin particles

Abstract

To provide foamable acrylic resin particles which enable production of acrylic resin foam particles that are excellent in in-mold moldability.SOLUTION: Foamable acrylic resin particles contain chain type saturated hydrocarbon, alicyclic hydrocarbon, and carboxylate that is ester of a carboxylic acid and alcohol. The total carbon number of the carboxylate is 10 or more and 40 or less. The total of the content of the alicyclic hydrocarbon and the content of the carboxylate in the foamable acrylic resin particles is 1 pts.mass or more and 4 pts.mass or less with respect to 100 pts.mass of the resin component contained in the foamable acrylic resin particles. A mass ratio of the content of the carboxylate with respect to the content of the alicyclic hydrocarbon is 0.1 or more and 1.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to foamed acrylic resin particles. [Background technology]

[0002] Conventionally, foamed resin molded bodies have been used as lost-wax models for casting. Specifically, foamed resin molded bodies are used in the following casting method: First, a foamed resin molded body of the desired shape is embedded in sand that serves as a mold. Next, molten metal is poured into the foamed resin molded body in the sand. At this time, the foamed resin molded body is thermally decomposed and replaced by the molten metal. Subsequently, by cooling and solidifying the molten metal, a metal casting having a shape similar to that of the foamed resin molded body can be obtained.

[0003] For lost-wax resin molded products, foamed particle molded products made of acrylic resin are used. This type of foamed particle molded product is obtained by a method called in-mold molding, in which acrylic resin foamed particles are filled into a mold equipped with a molding cavity corresponding to the shape of the desired molded product, and then the acrylic resin foamed particles inside the mold are heated with a heating medium to fuse them together.

[0004] Furthermore, acrylic resin foam particles used in the manufacture of foamed particle molded articles are obtained by foaming foamable acrylic resin particles (for example, Patent Document 1) containing an acrylic resin and a physical foaming agent. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-84040 [Overview of the project] [Problems that the invention aims to solve]

[0006] As mentioned above, in casting using a lost-wax model, it is possible to obtain a casting with the same shape as the lost-wax model. Therefore, when the desired shape of the casting is complex, a lost-wax model with a complex shape corresponding to the casting shape may be required. In recent years, there has been a desire to cast castings with more complex shapes using lost-wax models. To meet this demand and manufacture lost-wax models with more complex shapes, it has been desirable to further improve the in-moldability of acrylic resin foam particles.

[0007] This invention was made in view of the above background, and aims to provide foamable acrylic resin particles that can be produced as acrylic resin foam particles with excellent in-mold moldability. [Means for solving the problem]

[0008] One aspect of the present invention relates to foamed acrylic resin particles according to the following [1] to [7]. [1] Foamed acrylic resin particles, The foamed acrylic resin particles contain a chain-type saturated hydrocarbon, an alicyclic hydrocarbon, and a carboxylic acid ester which is an ester of a carboxylic acid and an alcohol. The total number of carbon atoms in the carboxylic acid ester is 10 or more and 40 or less. The total amount of the alicyclic hydrocarbon and the carboxylic acid ester in the foamed acrylic resin particles is 1 part by mass or more and 4 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particles. Foaming acrylic resin particles in which the mass ratio of the carboxylic acid ester content to the alicyclic hydrocarbon content is 0.1 or more and 1.0 or less.

[0009] [2] The foamed acrylic resin particles according to [1], wherein the average particle diameter of the foamed acrylic resin particles is 0.3 mm or more and 0.5 mm or less. [3] The foaming acrylic resin particles according to [1] or [2], wherein the carboxylic acid ester is an ester of a carboxylic acid having 5 to 20 carbon atoms and an alcohol having 2 to 10 carbon atoms. [4] The foamed acrylic resin particles according to any one of [1] to [3], wherein the content of the carboxylic acid ester in the foamed acrylic resin particles is 0.2 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particles.

[0010] [5] Foaming acrylic resin particles according to any one of [1] to [4], wherein the chain-type saturated hydrocarbon has 3 to 6 carbon atoms and the alicyclic hydrocarbon has 5 to 7 carbon atoms. [6] The foamed acrylic resin particle according to any one of [1] to [5], wherein the content of the chain-type saturated hydrocarbon in the foamed acrylic resin particle is 5 parts by mass or more and 9 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particle. [7] Foaming acrylic resin particles according to any one of [1] to [6], wherein the mass ratio of the total content of the alicyclic hydrocarbon and the carboxylic acid ester to the content of the chain-type saturated hydrocarbon is 0.1 or more and 0.4 or less. [Effects of the Invention]

[0011] According to the above embodiment, it is possible to provide foamable acrylic resin particles that can be manufactured to produce acrylic resin foam particles with excellent in-moldability. [Modes for carrying out the invention]

[0012] (Foamed acrylic resin particles) The foamed acrylic resin particles (hereinafter referred to as "foamed resin particles") contain an acrylic resin as a base resin, a chain-type saturated hydrocarbon, an alicyclic hydrocarbon, and a carboxylic acid ester.

[0013] • Acrylic resin The acrylic resin constituting the foamed resin particles is a polymer obtained by polymerizing (meth)acrylic acid ester monomers. That is, the acrylic resin constituting the foamed resin particles contains at least a (meth)acrylic acid ester component. Note that the expression "(meth)acrylic acid" mentioned above is a concept that encompasses both acrylic acid and methacrylic acid. For example, the acrylic resin may be a polymer of methacrylic acid ester or a polymer of acrylic acid ester. Furthermore, the acrylic resin may be a copolymer of methacrylic acid ester and acrylic acid ester. In addition, the acrylic resin may be a copolymer of methacrylic acid ester and / or acrylic acid ester with another monomer copolymerizable with (meth)acrylic acid ester monomers.

[0014] As methacrylic acid esters, for example, alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate, or methacrylic acid esters having polycyclic saturated hydrocarbon groups such as isobornyl methacrylate and dicyclopentanyl methacrylate can be used. As acrylic acid esters, for example, alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, or acrylic acid esters having polycyclic saturated hydrocarbon groups such as isobornyl acrylate and dicyclopentanyl acrylate can be used. The acrylic resin may contain constituent units derived from one type of (meth)acrylic acid ester, or it may contain constituent units derived from two or more types of (meth)acrylic acid esters.

[0015] The acrylic resin preferably contains a methyl methacrylate component as a main component. In this case, the casting property of the finally obtained foamed particle molded body (hereinafter referred to as "molded body") can be further enhanced. From the viewpoint of more surely obtaining such an effect, the proportion of the methyl methacrylate component in the component derived from the (meth)acrylic acid ester monomer is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 80 mol% or more.

[0016] Further, examples of other monomers copolymerizable with the (meth)acrylic acid ester include styrene and α-methylstyrene. The content of the component derived from the other monomer in the acrylic resin can be appropriately set within a range that does not impair the above-described effects. For example, the content of the component derived from the other monomer in the acrylic resin may be generally 30 parts by mass or less with respect to 100 parts by mass of the component derived from the (meth)acrylic acid ester monomer. The content of the component derived from the other monomer in the acrylic resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less with respect to 100 parts by mass of the component derived from the (meth)acrylic acid ester monomer. In this case, the amount of soot generated when the foamed particle molded body is burned can be more easily reduced.

[0017] The acrylic resin constituting the foaming resin particles is a copolymer of a methacrylic acid ester and an acrylic acid ester, and the molar ratio of the methacrylic acid ester component to the total of 100 mol% of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin is 85 mol% or more and 99 mol% or less, and at least one of the methacrylic acid ester component and the acrylic acid ester component preferably has a polycyclic saturated hydrocarbon group.

[0018] The foamed resin particles made of such an acrylic resin can reduce the amount of soot generated when the finally obtained molded body is burned. Therefore, by performing casting using a lost mold made of such a molded body, the generation of soot during casting can be reduced. Further, by setting the molar ratio of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin within the specific range, an excessive increase in the generation rate of pyrolysis gas generated from the lost mold during casting can be more reliably avoided. Thereby, an excessive increase in the pressure inside the mold can be more reliably avoided, and the casting property can be further improved.

[0019] From the viewpoint of further enhancing these effects, it is more preferable that the main component of the methacrylic acid ester component in the acrylic resin is the methyl methacrylate component, and the main component of the acrylic acid ester component is the methyl acrylate component. From the same viewpoint, the acrylic resin is a copolymer of methyl methacrylate, methyl acrylate, and a (meth)acrylic acid ester having a polycyclic saturated hydrocarbon, and the molar ratio of the methacrylic acid ester component to the total 100 mol% of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin is more preferably 85 mol% or more and 99 mol% or less.

[0020] Also, by introducing a component having a polycyclic saturated hydrocarbon group into the acrylic resin, the foaming property of the foamed resin particles can be improved, and the in-mold formability of the acrylic resin foamed particles (hereinafter referred to as "foamed particles") obtained by foaming the foamed resin particles can be further improved.

[0021] From the viewpoint of further enhancing the casting property, the polycyclic saturated hydrocarbon group contained in the copolymer is preferably one or more polycyclic saturated hydrocarbon groups selected from the group consisting of a dicyclopentanyl group, an adamantyl group, a norbornyl group, and an isobornyl group.

[0022] Furthermore, the content of the polycyclic saturated hydrocarbon group component in the acrylic resin is preferably 2 mol% to 20 mol%, and more preferably 3 mol% to 15 mol%, relative to 100 mol% of the total of the methacrylic acid ester component and the acrylic acid ester component in the acrylic resin. In this case, the aforementioned effects can be more reliably achieved.

[0023] The glass transition temperature of the methanol-insoluble portion of the acrylic resin is preferably 112°C to 125°C. In this case, foamed particles with a low apparent density can be produced more easily. Furthermore, molded articles with a smooth surface can be produced more easily.

[0024] The weight-average molecular weight of the acrylic resin is preferably between 50,000 and 140,000. By setting the weight-average molecular weight of the acrylic resin within this range, the melting of the resin on the surface can be suppressed. In this case, the foam particles fuse together sufficiently, the gaps between the foam particles are small, and a molded article with a smooth surface can be obtained more easily. From the viewpoint of further enhancing these effects, the weight-average molecular weight of the acrylic resin is more preferably between 60,000 and 120,000, and even more preferably between 80,000 and 110,000.

[0025] The weight-average molecular weight of the acrylic resin is the polystyrene-equivalent molecular weight measured by gel permeation chromatography using polystyrene as the standard substance. The method for measuring the weight-average molecular weight of the acrylic resin will be explained in more detail in the examples.

[0026] Chain-type saturated hydrocarbons The chain-type saturated hydrocarbons in the foamable resin particles primarily act as physical foaming agents, and by heating the foamable resin particles, a large number of bubbles can be formed within the resin particles, thereby creating foamed particles. Examples of chain-type saturated hydrocarbons that can be used include propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, etc. The foamable resin particles may contain one type of chain-type saturated hydrocarbon, or two or more types of chain-type saturated hydrocarbons. From the viewpoint of further enhancing the foaming properties of the foamable resin particles, it is preferable that the number of carbon atoms in the chain-type saturated hydrocarbons contained in the foamable resin particles is between 3 and 6.

[0027] The content of chain-type saturated hydrocarbons in the foamed resin particles is preferably 5 parts by mass or more and 9 parts by mass or less, and more preferably 6 parts by mass or more and 8 parts by mass or less, per 100 parts by mass of the total resin components contained in the foamed resin particles, i.e., acrylic resin and, if necessary, other resins other than acrylic resin contained in the foamed resin particles. In this case, the foaming properties of the foamed resin particles can be further enhanced.

[0028] • Alicyclic hydrocarbons and carboxylic acid esters The foamed resin particles contain alicyclic hydrocarbons and carboxylic acid esters having a total carbon number of 10 to 40. The total content of alicyclic hydrocarbons and carboxylic acid esters in the foamed resin particles is between 1 and 4 parts by mass per 100 parts by mass of the resin component in the foamed resin particles. Furthermore, the mass ratio of carboxylic acid esters to alicyclic hydrocarbons in the foamed resin particles is between 0.1 and 1.0.

[0029] If carboxylic acid esters are not included in the foamed resin particles, the effect of improving in-moldability will be reduced, and depending on the desired shape of the molded product, areas where the foamed particles are not sufficiently fused together may easily form in the molded product. In this case, the range of molding pressures in which a good molded product can be produced may be narrowed. On the other hand, if alicyclic hydrocarbons are not included in the foamed resin particles, the foaming ability of the foamed resin particles will decrease, and the heating time required to obtain foamed resin particles with the desired bulk density may be increased. In addition, a phenomenon called blocking, in which foamed resin particles fuse together and form clumps, is more likely to occur when foaming the foamed resin particles. Furthermore, in this case, the in-moldability of the foamed particles is also likely to be insufficient.

[0030] In contrast, as mentioned above, by including both alicyclic hydrocarbons and carboxylic acid esters in the foamed resin particles in the specific ratios described above, blocking during foaming can be suppressed while improving the in-moldability of the foamed particles. Furthermore, with foamed particles obtained by foaming such foamed resin particles, even when the foamed particles have a complex shape, they fuse well with each other, making it easy to obtain a molded article with a good appearance. Moreover, with these foamed particles, a good molded article can be obtained over a wide range of molding pressures.

[0031] The following are some possible reasons why such effects can be obtained by using alicyclic hydrocarbons and carboxylic acid esters in combination.

[0032] Alicyclic hydrocarbons have the effect of plasticizing resins as well as acting as physical blowing agents. Therefore, when using only alicyclic hydrocarbons among alicyclic hydrocarbons and carboxylic acid esters, it is thought that the foamed particles will easily expand due to secondary foaming when the foamed particles are molded in the mold. In this case, depending on the shape of the molding cavity, there will be areas that are relatively easy to heat and areas that are not easily heated, and it is thought that secondary foaming of the foamed particles will proceed earlier in the areas that are relatively easy to heat. If the secondary foaming force of the foamed particles becomes excessively high, it is thought that secondary foaming of the foamed particles will proceed earlier in the areas that are easily heated in the molding cavity before a sufficient amount of heating medium is supplied to the entire molding cavity, and the foamed particles will not be sufficiently heated in the areas that are not easily heated in the molding cavity.

[0033] Based on the above results, it is thought that, depending on the desired shape of the molded product, areas where the foam particles are not sufficiently fused together may easily occur when molded at relatively low molding pressures. Furthermore, when molded at relatively high molding pressures, the foam particles, which are excessively heated during in-mold molding, tend to melt easily, which is thought to easily lead to a deterioration in the appearance of the resulting molded product. It should be noted that this tendency is thought to be more pronounced, for example, when manufacturing molded products with thin sections or more complex shapes.

[0034] On the other hand, carboxylic acid esters with a total carbon number within the aforementioned specific range have a lower ability to plasticize resins compared to alicyclic hydrocarbons, and are less likely to act as physical blowing agents. Therefore, when using only carboxylic acid esters among alicyclic hydrocarbons and carboxylic acid esters, the foaming ability of the foamable resin particles will be lower, and a longer time will be required to foam them to the desired bulk density. Furthermore, it is thought that the longer heating time when foaming the foamable resin particles will make blocking more likely to occur. In addition, in this case, secondary foaming during in-mold molding is likely to be insufficient, and gaps are likely to form between the foamed particles in the molded product after in-mold molding.

[0035] Therefore, by setting the total content of alicyclic hydrocarbons and carboxylic acid esters to 1 to 4 parts by mass per 100 parts by mass of resin components, and the mass ratio of carboxylic acid esters to alicyclic hydrocarbons to 0.1 to 1.0, it is considered possible to ensure sufficient foaming during foaming while adjusting the secondary foaming force of foamed particles during in-mold molding to an appropriate range. Furthermore, since such foamable resin particles can be foamed in a relatively short time, it is considered possible to suppress the occurrence of blocking during foaming.

[0036] Furthermore, since the foamed particles obtained by foaming the aforementioned foamable resin particles have a moderately high secondary foaming force, it is believed that the heating medium is more easily supplied throughout the entire mold during in-mold molding. Therefore, even when the shape is complex, the foamed particles fuse together sufficiently, and it is believed that a molded product with a good appearance can be easily obtained. In addition, it is believed that a good molded product can be easily obtained with such foamed particles over a wide range of molding pressures.

[0037] From the viewpoint of more reliably obtaining the effects described above, the total content of alicyclic hydrocarbons and carboxylic acid esters is preferably 1.2 parts by mass or more, more preferably 1.4 parts by mass or more, and even more preferably 1.5 parts by mass or more, per 100 parts by mass of resin components in the foamed resin particles. Furthermore, the total content of alicyclic hydrocarbons and carboxylic acid esters is preferably 3.5 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.8 parts by mass or less, per 100 parts by mass of resin components in the foamed resin particles. Furthermore, the total content of alicyclic hydrocarbons and carboxylic acid esters is preferably 1.2 parts by mass or more and 3.5 parts by mass or less, more preferably 1.4 parts by mass or more and 3.0 parts by mass or less, and even more preferably 1.5 parts by mass or more and 2.8 parts by mass or less, per 100 parts by mass of resin components in the foamed resin particles.

[0038] From the viewpoint of obtaining foamed resin particles that can produce good molded articles over a wide range of molding pressures while ensuring sufficient foaming properties of the foamed resin particles, the mass ratio of the carboxylic acid ester content to the alicyclic hydrocarbon content is preferably 0.2 to 0.9, and more preferably 0.3 to 0.8.

[0039] Furthermore, from the viewpoint of further improving the balance between the foaming properties of the foamed resin particles and the in-moldability of the foamed particles, the mass ratio of the total content of alicyclic hydrocarbons and the carboxylic acid esters to the content of chain-type saturated hydrocarbons is preferably 0.1 or more and 0.4 or less, and more preferably 0.2 or more and 0.4 or less.

[0040] As the alicyclic hydrocarbon contained in the foamed resin particles, for example, alicyclic saturated hydrocarbons such as cyclopentane, cyclohexane, and cycloheptane can be used. The foamed resin particles may contain one type of alicyclic hydrocarbon, or two or more types of alicyclic hydrocarbons. Preferably, the number of carbon atoms in the alicyclic hydrocarbon contained in the foamed resin particles is 5 to 7. In this case, the in-moldability of the foamed particles obtained by foaming the foamed resin particles can be further improved. Furthermore, the alicyclic hydrocarbon contained in the foamed resin particles is preferably an alicyclic saturated hydrocarbon, and more preferably cyclohexane. In this case, a foamed particle molded article with excellent castability can be stably obtained while improving the in-moldability of the foamed particles obtained by foaming the foamed resin particles.

[0041] The content of alicyclic hydrocarbons in the foamed resin particles is preferably 0.6 parts by mass or more, more preferably 0.9 parts by mass or more, even more preferably 1.1 parts by mass or more, and particularly preferably 1.2 parts by mass or more, per 100 parts by mass of the resin component in the foamed resin particles. On the other hand, the content of alicyclic hydrocarbons in the foamed resin particles is preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.6 parts by mass or less, and particularly preferably 1.5 parts by mass or less, per 100 parts by mass of the resin component in the foamed resin particles. Furthermore, the content of alicyclic hydrocarbons in the foamed resin particles is preferably 0.6 parts by mass or more and 2.5 parts by mass or less, more preferably 0.9 parts by mass or more and 2.0 parts by mass or less, even more preferably 1.1 parts by mass or more and 1.6 parts by mass or less, and particularly preferably 1.2 parts by mass or more and 1.5 parts by mass or less, per 100 parts by mass of the resin component in the foamed resin particles.

[0042] From the viewpoint of improving the foaming properties of foamed resin particles and the in-moldability of foamed resin particles in a more balanced manner, it is preferable that the mass ratio of the content of alicyclic hydrocarbons to the content of chain-type saturated hydrocarbons in foamed resin particles is 0.1 or more and 0.3 or less.

[0043] Examples of carboxylic acid esters that can be included in the foamed resin particles include dicarboxylic acid esters, which are esters of dicarboxylic acid and alcohol, and monocarboxylic acid esters, which are esters of monocarboxylic acid and alcohol. Examples of dicarboxylic acid esters include dioctyl succinate, dioctyl adipate, dibutyl adipate, diisobutyl adipate, diisononyl adipate, diisodecyl adipate, dibutyl sebacate, dioctyl sebacate, and diisononyl 1,2-cyclohexanedicarboxylic acid. Examples of monocarboxylic acid esters include butyl stearate, isopropyl palmitate, ethylhexyl palmitate, isopropyl myristate, and ethylhexyl isononanoate. In addition, esters of carboxylic acid and polyhydric alcohols can also be used as carboxylic acid esters. The foamed resin particles may contain one type of carboxylic acid ester, or two or more types of carboxylic acid esters.

[0044] The content of carboxylic acid ester in the foamed resin particles is preferably 0.2 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the resin component in the foamed resin particles. On the other hand, the content of carboxylic acid ester in the foamed resin particles is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 1.2 parts by mass or less, and particularly preferably 0.7 parts by mass or less, per 100 parts by mass of the resin component in the foamed resin particles. Furthermore, the content of carboxylic acid ester in the foamed resin particles is preferably 0.2 parts by mass or more and 2.0 parts by mass or less, more preferably 0.3 parts by mass or more and 1.5 parts by mass or less, even more preferably 0.4 parts by mass or more and 1.2 parts by mass or less, and particularly preferably 0.4 parts by mass or more and 0.7 parts by mass or less, per 100 parts by mass of the resin component in the foamed resin particles.

[0045] The boiling point of the carboxylic acid ester contained in the foamed resin particles is preferably 150°C or higher, more preferably 200°C or higher, and even more preferably 250°C or higher. By using such a carboxylic acid ester, the dissipation of the carboxylic acid ester from the foamed particles during molding is suppressed, and the state of the acrylic resin constituting the foamed particles can be easily maintained in a state suitable for molding from the initial to the later stages of molding. The upper limit of the boiling point of the carboxylic acid ester contained in the foamed resin particles is approximately 400°C.

[0046] The melting point of the carboxylic acid ester contained in the foamed resin particles is preferably 30°C or lower, more preferably 5°C or lower, and even more preferably -30°C or lower. By using such a carboxylic acid ester, the carboxylic acid ester can be more easily dispersed homogeneously in the acrylic resin, and foamed particles with excellent in-moldability can be obtained more stably. The lower limit of the melting point of the carboxylic acid ester contained in the foamed resin particles is approximately -100°C.

[0047] The carboxylic acid ester contained in the foamed resin particles is preferably a monocarboxylic acid ester and / or a dicarboxylic acid ester, and more preferably a dicarboxylic acid ester. In this case, the total number of carbon atoms in the carboxylic acid ester is preferably 12 to 36, more preferably 16 to 30, and even more preferably 18 to 26. By using such a carboxylic acid ester, the acrylic resin constituting the foamed particles can be appropriately plasticized during in-mold molding, thereby further enhancing the effect of improving the in-moldability of the foamed particles.

[0048] From a similar viewpoint, the carboxylic acid ester contained in the foamed resin particles is preferably an ester of a carboxylic acid having 5 to 20 carbon atoms and an alcohol having 2 to 10 carbon atoms, and more preferably an ester of a carboxylic acid having 6 to 18 carbon atoms and an alcohol having 4 to 8 carbon atoms. Furthermore, the carboxylic acid ester contained in the foamed resin particles is preferably an ester of a saturated carboxylic acid and an alcohol.

[0049] Other ingredients Other resins and additives may be blended into the foamed resin particles, as long as they do not hinder the objectives of the present invention. The content of other components is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, per 100 parts by mass of acrylic resin. Furthermore, it is particularly preferable that the resin component in the foamed resin particles is composed of acrylic resin and does not contain any other resins besides acrylic resin.

[0050] • Average particle size of foamed resin particles The average particle diameter of the foamed resin particles is preferably 0.3 mm or more and 0.5 mm or less. By foaming such foamed resin particles, foamed particles can be obtained that have excellent in-moldability and even better filling properties, and that can be easily filled even when the molding cavity of the mold has thin parts or a more complex shape. From the viewpoint of further improving the filling properties into the molding cavity, the average particle diameter of the foamed resin particles is more preferably 0.48 mm or less, more preferably 0.45 mm or less, and even more preferably 0.42 mm or less.

[0051] The average particle size of the foamed resin particles mentioned above is the cumulative 63% diameter (d63) in the mass-based particle size distribution. The specific method for measuring the average particle size of the foamed resin particles will be explained in the examples.

[0052] • Coating agent The surface of the foamed resin particles may be covered with a coating agent such as an anti-blocking agent or an antistatic agent. By covering the surface of the foamed resin particles with a coating agent, effects such as suppressing blocking during foaming and suppressing the charging of the foamed resin particles and foamed particles can be achieved.

[0053] As antiblocking agents, for example, metal stearate salts such as magnesium stearate, calcium stearate, zinc stearate, barium stearate, aluminum stearate, and lithium stearate, and metal laurate salts such as zinc laurate and barium laurate, can be used, which are metal salts of fatty acids with 12 to 24 carbon atoms. In addition, as antistatic agents, glycerin fatty acid esters such as glycerin monostearate and alkyldiethanolamines can be used.

[0054] From the viewpoint of preventing blocking of foamed resin particles during foaming and improving the fusion properties of foamed particles during in-mold molding, the amount of the blocking prevention agent coating is preferably 0.005 parts by mass or more and 0.3 parts by mass or less, more preferably 0.01 parts by mass or more and 0.2 parts by mass or less, and even more preferably 0.02 parts by mass or more and 0.1 parts by mass or less, per 100 parts by mass of the resin component in the foamed resin particles.

[0055] Furthermore, the amount of antistatic agent coating is preferably approximately 0.005 parts by mass or more and 0.06 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.05 parts by mass or less, per 100 parts by mass of resin component in the foamed resin particles.

[0056] (Method for manufacturing foamed resin particles) The foamed resin particles can be produced by known methods, such as suspension polymerization. More specifically, the method for producing the foamed resin particles comprises a suspension polymerization step of obtaining an acrylic resin by suspension polymerization of (meth)acrylic acid ester monomers, and is a method for producing foamed acrylic resin particles containing a chain-type saturated hydrocarbon, an alicyclic hydrocarbon, and a carboxylic acid ester, The total number of carbon atoms in the carboxylic acid ester is 10 or more and 40 or less. The sum of the amount of alicyclic hydrocarbon added and the amount of carboxylic acid ester added is 1 part by mass or more and 4 parts by mass or less per 100 parts by mass of the (meth)acrylic acid ester monomer. It is preferable that the mass ratio of the amount of carboxylic acid ester added to the amount of alicyclic hydrocarbon added is 0.1 or more and 1.0 or less.

[0057] A specific embodiment of the suspension polymerization process is as follows: First, in a sealed container equipped with a stirring device, a suitable suspension agent and suspension aid are dispersed in an aqueous medium, to which a monomer component such as a (meth)acrylic acid ester monomer is added together with a polymerization initiator, a chain transfer agent, etc., to disperse the monomer component in the aqueous medium. At this time, if necessary, alicyclic hydrocarbons and / or carboxylic acid esters may be added to the aqueous medium. From the viewpoint of reliably impregnating the foamable resin particles with alicyclic hydrocarbons and carboxylic acid esters, it is preferable to add the alicyclic hydrocarbons and carboxylic acid esters to the aqueous medium before the start of the polymerization reaction.

[0058] Next, the polymerization reaction of the monomer component is started. The polymerization reaction of the monomer component may be carried out in one step or in two or more steps. Then, during or after polymerization, a chain-type saturated hydrocarbon is added to the sealed container and impregnated into the acrylic resin polymer produced by the polymerization reaction. At this time, if necessary, alicyclic hydrocarbons and / or carboxylic acid esters may also be added to the sealed container and these substances may be impregnated into the acrylic resin. By doing so, the foamed resin particles can be obtained.

[0059] Since the monomer components used in the suspension polymerization process are the same as the monomer components of the acrylic resin that constitutes the foamed resin particles described above, the explanation regarding the monomer components that constitute the acrylic resin can be referred to as appropriate. Furthermore, since the chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters used in the suspension polymerization process are the same as the chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters contained in the foamed resin particles described above, the explanation regarding the chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters contained in the foamed resin particles can be referred to as appropriate.

[0060] Furthermore, the amounts of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters added can be appropriately set within the aforementioned range, depending on the desired content of alicyclic hydrocarbons and carboxylic acid esters in the foamed resin particles.

[0061] The weight-average molecular weight of an acrylic resin can be adjusted by the amount of chain transfer agent added during polymerization. When a chain transfer agent is used, the amount of the chain transfer agent added is preferably approximately 0.20 parts by mass to 0.60 parts by mass, and more preferably 0.25 parts by mass to 0.50 parts by mass, per 100 parts by mass of monomer components added to the aqueous medium. By setting the amount of the chain transfer agent to the above-mentioned specific range, it is possible to easily adjust the weight-average molecular weight of the acrylic resin to the above-mentioned specific range.

[0062] Conventional known chain transfer agents such as n-octyl mercaptan and α-methylstyrene dimer can be used as the chain transfer agent, but the use of n-octyl mercaptan is more preferable.

[0063] When coating the surface of foamed resin particles with a coating agent, for example, the foamed resin particles obtained by the above method and the coating agent can be stirred in a container. As a stirring device, for example, a tumbler mixer can be used.

[0064] (Foaming particles) Foamed particles are obtained by foaming foamable resin particles. The method for foaming foamable resin particles is not particularly limited. For example, foamable resin particles can be foamed by supplying them with a heating medium such as steam and heating them. One such method involves using a cylindrical foaming machine equipped with a stirring device to heat and foam the foamable resin particles with steam or the like.

[0065] (Foam particle molded body) A foamed particle molded body is obtained by in-mold molding of foamed particles. The method for in-mold molding of foamed particles is not particularly limited. For example, foamed particles are filled into a mold having a molding cavity corresponding to the shape of the desired molded body, and a large number of foamed particles are heated in the mold using a heating medium such as steam. The foamed particles in the molding cavity foam up further upon heating and fuse together with each other. As a result, a large number of foamed particles become integrated, and a foamed particle molded body corresponding to the shape of the molding cavity is obtained. [Examples]

[0066] Examples and comparative examples of the foamed acrylic resin particles described above are explained below. In this example, the foamed resin particles shown in the examples in Tables 1 and 2 and the comparative examples in Tables 3 to 6 were produced by the following method.

[0067] (Example 1) First, the internal volume with the stirring device is 1 m³ 3 576 kg of deionized water, 3.35 kg of suspension agent, 0.35 g of surfactant, 0.86 g of sodium acetate as an electrolyte, and 0.2 g of suspension aid were added to the autoclave. Specifically, the suspension agent was a 20.5% by mass tricalcium phosphate slurry (manufactured by Taihei Chemical Industry Co., Ltd.). Specifically, the surfactant was a 10% by mass disodium dodecyldiphenyl ethersulfonate aqueous solution (specifically, "Perex® SSH" manufactured by Kao Corporation). Specifically, the suspension aid was potassium persulfate.

[0068] A mixture of 343 kg of methyl methacrylate, 40 kg of isobornyl methacrylate, and 20 kg of methyl acrylate was prepared as monomer components. To this mixture, 0.54 kg of t-butyl peroxy-2-ethylhexanoate (specifically, "Perbutyl® O" manufactured by NOF Corporation) and 0.54 kg of t-butyl peroxy-2-ethylhexyl monocarbonate (specifically, "Perbutyl® E" manufactured by NOF Corporation) were dissolved as polymerization initiators, 0.97 kg of n-octyl mercaptan (manufactured by Chevron) was dissolved as a chain transfer agent, 8.1 kg of cyclohexane was dissolved as an alicyclic hydrocarbon, and 2.0 kg of dioctyl adipicate (total carbon number: 22, melting point: -70°C, boiling point: 335°C) was dissolved as a carboxylic acid ester.

[0069] After replacing the air inside the autoclave with nitrogen, the autoclave was sealed. Next, the temperature inside the autoclave was raised to 70°C while stirring at a stirring speed of 100 rpm, and the temperature was maintained at 70°C for 6 hours to carry out the preliminary polymerization process. In the preliminary polymerization process, pentane (specifically, a mixture of n-pentane and i-pentane) as a physical blowing agent was added 5 hours after the temperature inside the autoclave reached 70°C. The amount of pentane added was 48.4 kg, and the time required from the start to the completion of the addition was approximately 1 hour. Immediately after the addition of the physical blowing agent was completed, the stirring speed was reduced to 80 rpm.

[0070] After the initial polymerization step was completed, the temperature inside the autoclave was raised to 115°C over 4 hours, and the temperature was maintained at 115°C for 5 hours for the subsequent polymerization step. After the subsequent polymerization step was completed, the temperature inside the autoclave was cooled to 35°C over 4 hours, and then further cooled to room temperature.

[0071] After cooling, the foamed resin particles were removed from the autoclave contents. These foamed resin particles were washed with nitric acid to dissolve the tricalcium phosphate adhering to their surface. Subsequently, the foamed resin particles were dehydrated and washed using a centrifuge, and then any remaining moisture adhering to the surface of the foamed resin particles was removed using an air-flow dryer.

[0072] Next, the foamed resin particles were sieved to extract foamed resin particles with a diameter of 0.30 mm or more and 0.54 mm or less. Then, the foamed resin particles and 0.04 parts by mass of alkyldiethanolamine per 100 parts by mass of foamed resin particles were supplied to a drum tumbler. Furthermore, 0.10 parts by mass of zinc stearate, 0.10 parts by mass of calcium stearate, and 0.02 parts by mass of glycerin monostearate per 100 parts by mass of foamed resin particles were supplied to the drum tumbler, and these were stirred and mixed to coat the surface of the foamed resin particles with the coating agent.

[0073] Based on the above, foamable resin particles were obtained containing an acrylic resin as the base resin, n-pentane and i-pentane as chain-type saturated hydrocarbons, cyclohexane as an alicyclic hydrocarbon, and dioctyl adipate as a carboxylic acid ester. The molar ratio of each monomer component to the total monomer components used in the suspension polymerization step (i.e., the molar ratio of each component to the total of 100 mol% of methacrylate ester components and acrylic acid ester components in the acrylic resin) was methyl methacrylate: 89 mol%, isobornyl methacrylate: 5 mol%, and methyl acrylate: 6 mol%, with the proportion of monomer components having polycyclic saturated hydrocarbon groups being 5 mol%.

[0074] (Example 2) The foamed resin particles in this example have the same composition as the foamed resin particles of Example 1, except that they contain cyclopentane instead of cyclohexane as an alicyclic hydrocarbon. The method for producing the foamed resin particles in this example is the same as the method for producing the foamed resin particles of Example 1, except that cyclopentane is used instead of cyclohexane in the suspension polymerization step.

[0075] (Example 3) The foamed resin particles in this example have the same composition as the foamed resin particles of Example 1, except that they contain butyl stearate (total carbon number: 22, melting point: 23°C, boiling point: 220°C) instead of dioctyl adipicate as the carboxylic acid ester. The method for producing the foamed resin particles in this example is the same as the method for producing the foamed resin particles of Example 1, except that butyl stearate is used instead of dioctyl adipicate in the suspension polymerization step.

[0076] (Examples 4-5) The foamed resin particles of Examples 4 and 5 have the same composition as the foamed resin particles of Example 1, except that the ratio of alicyclic hydrocarbons to carboxylic acid esters is changed. The method for producing the foamed resin particles of these examples is the same as the method for producing the foamed resin particles of Example 1, except that the amount of cyclohexane and butyl stearate added in the suspension polymerization step is changed as shown in Table 1.

[0077] (Example 6) The foamed resin particles in this example have the same composition as the foamed resin particles of Example 1, except that they contain diethyl sebacate (total carbon number: 14, melting point: 2°C, boiling point: 309°C) as the carboxylic acid ester instead of dioctyl adipate. The method for producing the foamed resin particles in this example is the same as the method for producing the foamed resin particles of Example 1, except that diethyl sebacate is used instead of dioctyl adipate in the suspension polymerization step.

[0078] (Example 7) The foamed resin particles in this example have the same composition as the foamed resin particles of Example 1, except that they contain diethyl phthalate (total carbon number: 12, melting point: -4°C, boiling point: 295°C) instead of dioctyl adipate as the carboxylic acid ester. The method for producing the foamed resin particles in this example is the same as the method for producing the foamed resin particles of Example 1, except that diethyl phthalate is used instead of dioctyl adipate in the suspension polymerization step.

[0079] (Comparative Examples 1-2) The foamed resin particles of Comparative Example 1 and Comparative Example 2 have the same composition as the foamed resin particles of Example 1, except that they do not contain carboxylic acid esters. The method for producing the foamed resin particles of these comparative examples is the same as the method for producing the foamed resin particles of Example 1, except that carboxylic acid esters are not added in the suspension polymerization step and the amounts of chain-type saturated hydrocarbons and alicyclic hydrocarbons added are changed, as shown in Table 3.

[0080] (Comparative Examples 3-5) The foamed resin particles of Comparative Examples 3 to 5 have the same composition as the foamed resin particles of Example 1, except that they do not contain alicyclic hydrocarbons. The method for producing the foamed resin particles of these comparative examples is the same as the method for producing the foamed resin particles of Example 1, except that alicyclic hydrocarbons are not added in the suspension polymerization step and the amounts of chain-type saturated hydrocarbons and carboxylic acid esters added are changed, as shown in Table 3.

[0081] (Comparative Examples 6-7) The foamed resin particles of Comparative Examples 6 and 7 have the same composition as the foamed resin particles of Example 1, except that the ratio of alicyclic hydrocarbon content to carboxylic acid ester content is different. The method for producing the foamed resin particles of these comparative examples is the same as the method for producing the foamed resin particles of Example 1, except that the amount of cyclohexane and dioctyl adipate added in the suspension polymerization step is changed, as shown in Table 5.

[0082] (Comparative Example 8) The foamed resin particles of Comparative Example 8 have the same composition as the foamed resin particles of Example 1, except that they do not contain alicyclic hydrocarbons and do contain toluene. The method for producing the foamed resin particles of Comparative Example 8 is the same as the method for producing the foamed resin particles of Example 1, except that alicyclic hydrocarbons are not added in the suspension polymerization step, as shown in Table 5.

[0083] (Comparative Examples 9-10) The foamed resin particles of Comparative Examples 9 and 10 have the same composition as the foamed resin particles of Example 1, except that they do not contain carboxylic acid esters with a total carbon number of 10 to 40, and do contain carboxylic acid esters with a total carbon number outside the specified range. The method for producing the foamed resin particles of these comparative examples is the same as the method for producing the foamed resin particles of Example 1, except that in the suspension polymerization step, carboxylic acid esters with a total carbon number of 10 to 40, as shown in Table 5, are not added, and methyl acetate (total carbon number: 3, melting point: -98°C, boiling point: 57°C) or glyceryl tristearate (total carbon number: 57, melting point: 73°C, boiling point: 260°C) is added.

[0084] The properties of the foamed resin particles described above were evaluated using the following method.

[0085] (Average particle size of foamed resin particles) Using a test sieve conforming to JIS Z 8801, the foamed resin particles were sieved and classified according to their particle size range. By measuring the mass of the foamed resin particles remaining on the sieve, the mass fraction of foamed resin particles in each particle size range was calculated. After determining the particle size distribution from these mass fractions using the Rosin-Rammler distribution formula, the particle size (i.e., d63) at which the cumulative percentage below the sieve, that is, the cumulative value of the mass fraction accumulated from the smallest particle side, becomes 63% by mass was calculated based on the obtained particle size distribution. This value was taken as the average particle diameter of the foamed resin particles. The average particle diameters of the foamed resin particles in the examples and comparative examples are shown in Tables 2, 4, and 6.

[0086] (Weight-average molecular weight of acrylic resins) Chromatograms of acrylic resins were obtained using gel permeation chromatography (GPC) with polystyrene as the standard substance. Based on the obtained chromatograms, the weight-average molecular weight (Mw) of the acrylic resins was calculated.

[0087] To obtain chromatograms, we used the HLC-8320GPC EcoSEC manufactured by Tosoh Corporation. After preparing a 0.1 wt% sample solution by dissolving foamed resin particles, which were to be measured, in tetrahydrofuran (THF), we used a column consisting of one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H connected in series. Under separation conditions of eluent: tetrahydrofuran (THF) and THF flow rate: 0.6 ml / min, we separated the measured samples by molecular weight using gel permeation chromatography (GPC) to obtain chromatograms.

[0088] Then, the retention time in the chromatogram obtained using a calibration curve prepared with standard polystyrene was converted to molecular weight, and a differential molecular weight distribution curve was obtained. The weight-average molecular weight Mw of the acrylic resin was calculated from this differential molecular weight distribution curve. The weight-average molecular weight Mw of the acrylic resin in the foamed resin particles of the examples and comparative examples are shown in Tables 2, 4, and 6.

[0089] (Glass transition temperature of methanol-insoluble components in acrylic resins) Methanol-insoluble components were extracted from acrylic resins by reprecipitation purification using methanol. Specifically, first, 1 g of foamed resin particles were dissolved in 10 mL of methyl ethyl ketone. Next, the obtained methyl ethyl ketone solution was added dropwise to 500 mL of methanol to precipitate the methanol-insoluble components containing the acrylic resin. Then, the filtered methanol-insoluble components were air-dried at room temperature, and further vacuum-dried until a constant weight was obtained.

[0090] Next, 2 mg of methanol-insoluble matter extracted from the foamed resin particles was weighed and DSC was performed in accordance with JIS K 7121:1987. A differential scanning calorimeter (TA Instruments "Q1000") was used as the measuring instrument, and the heating rate was set to 10°C / min. The glass transition temperature at the midpoint of the DSC curve obtained by DSC was defined as the glass transition temperature Tg of the methanol-insoluble matter. The glass transition temperatures Tg of the methanol-insoluble matter are shown in Tables 2, 4, and 6.

[0091] (Content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in foamed resin particles) A sample solution was prepared by dissolving 1 g of precisely weighed foamed resin particles in 25 ml of N,N-dimethylformamide (DMF). This sample solution was then used for gas chromatography (GC) measurements to quantify the content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in the foamed resin particles. The content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters per 100 parts by mass of resin component in the foamed resin particles is shown in Tables 1, 3, and 5.

[0092] The measurement conditions for gas chromatography are as follows: Measurement device: Shimadzu Corporation gas chromatograph GC-9A Column material: Glass column with an inner diameter of 3 mm and a length of 3000 mm. Column packing material: [Liquid phase name] PEG-20M [Liquid phase impregnation rate] 25% by mass [Carrier particle size] 60 / 80 mesh [Carrier treatment method] AW-DMCS (washing with water, calcination, acid treatment, silane treatment) Carrier gas: N2 Detector: FID (Flame Ionization Detector) Quantification method: internal standard method

[0093] (Effervescent) The foaming properties of foamable resin particles were evaluated based on the bulk density obtained when foamed using a shelf-type foaming machine, and the time required for foaming when foamed using a pre-foaming device.

[0094] The foaming properties using a shelf-type foaming machine were evaluated as follows: First, steam at a gauge pressure of 3 kPa(G) was supplied into the shelf-type foaming machine (manufactured by FESTO) and heated for 270 seconds to foam the foamable resin particles and obtain foamed particles. Next, the foamed particles were air-dried at room temperature for one day.

[0095] These foamed particles were filled into a graduated cylinder so that they would naturally accumulate, and the bulk volume (in L) of the foamed particle group was read from the scale of the graduated cylinder. Then, the mass (in g) of the foamed particle group in the graduated cylinder was divided by the aforementioned bulk volume, and the bulk density (in kg / m³) of the foamed particles was obtained by further unit conversion. 3 The bulk density of the foamed particles measured in this way is shown in the "Shelf-type foaming (270 seconds)" column of Tables 2, 4, and 6. In evaluating foaming performance using a shelf-type foaming machine, a lower bulk density indicates better foaming performance.

[0096] The foaming properties were evaluated using a pre-foaming device as follows: First, foaming resin particles were placed in a pre-foaming device (DAISEN "DYHL-500U"), and the foaming resin particles were heated by supplying steam at a gauge pressure of 0.01 MPa (G) to induce foaming. At this time, the bulk density of the foamed particles was 20 kg / m³ after the steam was supplied. 3 The time required to reach the target temperature (heating time) was measured. See Tables 2, 4, and 6 for "bulk density 20 kg / m³". 3 In the "Heating time" column, the bulk density measured in this way was 20 kg / m³. 3 This indicates the heating time required to reach the specified state. Note that in the evaluation of foaming properties using a pre-foaming device, the bulk density was 20 kg / m³. 3 The shorter the heating time required to reach this point, the better the foaming performance can be judged to be.

[0097] (Blocking rate) Using the same method as described above for evaluating foaming properties with the pre-foaming device, foamable resin particles with a bulk density of 20 kg / m³ were obtained. 3 The foamed particles were foamed in the manner described above. The foamed particles obtained in this way were sieved using a sieve with a mesh size of 10 mm to remove clumps of foamed particles formed by blocking. The blocking rate, which is the ratio of the mass of clumps of foamed particles formed by blocking to the total mass of foamed particles after foaming, is shown in Tables 2, 4, and 6. In evaluating the blocking rate, a lower blocking rate indicates that blocking is suppressed.

[0098] (Content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in foamed particles) Except for using foamed particles instead of foamed resin particles, the content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in the foamed particles was quantified using the same method as described above for measuring the content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in the foamed resin particles. The content of chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acid esters in the foamed particles per 100 parts by mass of resin component is shown in Tables 2, 4, and 6.

[0099] (Moldable range) In evaluating the minimum molding pressure and the moldable range, molded bodies were produced by performing in-mold molding while varying the molding pressure during heating in increments of 0.01 MPa between 0.04 and 0.10 MPa (G). The moldable range was determined based on the surface properties, fusion properties, and presence or absence of melt marks of the obtained molded bodies.

[0100] The method for manufacturing the molded body is as follows. The mold used in this example has a first mold and a second mold, and is configured to form a molding cavity between the first mold and the second mold. The molding cavity has a main body that is a rectangular parallelepiped with a length of 300 mm, a width of 300 mm, and a thickness of 15 mm, and four thin-walled parts that protrude from the main body in one direction in the thickness direction. The thin-walled parts are provided near the center of the 300 mm length side and the 300 mm width side of the main body, and each thin-walled part is configured to form a foamed particle molded body having a rectangular shape with a width of 30 mm, a height of 90 mm, and a thickness of 4 mm. Of the two molds that make up the mold, the first mold is positioned on the side of the molded body that has the thin-walled parts, and the second mold is positioned on the back side of the surface of the molded body where the thin-walled parts are provided. The foam particle filling hole for supplying foam particles into the molding cavity is located in the second mold, at a position corresponding to the lateral center of the main body of the molded body, 40 mm away from the 300 mm side, and has a circular shape with a diameter of 20 mm.

[0101] The mold was positioned such that the vertical direction of the main body of the molded body was vertical, the horizontal direction was horizontal, and the side closest to the foam particle filling hole was facing upwards, and the foam particles were then filled into the mold.

[0102] Next, in-mold molding was performed by supplying steam into the mold. In the in-mold molding, first, preheating was performed by supplying steam into the mold for 5 seconds with the drain valve of the mold open. Then, the drain valve of the first mold in the mold was closed, and steam was supplied to the molding cavity from the first mold side for 5 seconds to perform the first one-sided heating. Next, the drain valve of the first mold was opened, the drain valve of the second mold was closed, and steam was supplied to the molding cavity from the second mold side for 5 seconds to perform the second one-sided heating. After that, the drain valve of the first mold was closed, and the main heating was performed by supplying steam from both the first and second mold sides until the molding pressure for the main heating was reached. After the main heating was completed, the pressure inside the mold was released, and the molded body was cooled inside the mold until the surface pressure due to the foaming force of the molded body reached 0.02 MPa (G).

[0103] Subsequently, the foam particle molded body removed from the mold was left to cure in a 40°C drying chamber for 24 hours. The surface properties, fusion properties, and presence or absence of melt marks of the foam particle molded body after the curing process were evaluated according to the evaluation criteria described later. The range of molding pressures in which a molded body that passed all items (i.e., a good molded body) was obtained was defined as the moldable range. The "Moldable Range" column in Tables 2, 4, and 6 shows the moldable range of the foam particles for the examples and comparative examples. If a good molded body could not be obtained at any molding pressure, "None" was written in the "Moldable Range" column. In evaluating the moldable range, a wider range of molding pressures in which a good molded body can be formed indicates superior in-moldability.

[0104] The evaluation methods for surface properties, fusion properties, and the presence or absence of melt marks in the assessment of the moldable range are as follows.

[0105] ·Superficiality The foamed particle molded body was visually observed. When there were almost no gaps between the foamed particles present on the surface, it was judged as qualified because the surface property was good. When obvious gaps were present between the foamed particles present on the surface, it was judged as unqualified because the surface property was inferior.

[0106] ·Fusibility A thin-walled portion of the foamed particle molded body was cut off from the main body portion and broken so as to be roughly equally divided in the height direction. More than 100 foamed particles randomly selected from the foamed particles exposed on the fracture surface were visually observed to determine whether they were foamed particles broken inside the particles (that is, foamed particles with material fracture) or foamed particles broken at the interface between the foamed particles. Then, the ratio of the number of foamed particles broken inside the particles to the total number of observed foamed particles, expressed as a percentage (that is, the material fracture rate), was calculated, and this value was taken as the fusion rate. When the fusion rate was 80% or more, it was judged as qualified, and when it was less than 80%, it was judged as unqualified.

[0107] ·Presence or absence of melting marks The foamed particle molded body was visually observed. When there were almost no marks of resin melting on the surface of the foamed particle molded body, it was judged as qualified. When marks of resin melting were scattered on the surface of the foamed particle molded body, it was judged as unqualified.

[0108] (Density of the foamed particle molded body) In the evaluation of the above-mentioned moldable range, a measurement sample was cut out from the molded body obtained by performing in-mold molding at the lowest molding pressure among the molding pressures at which good products could be obtained. After dividing the mass (unit: g) of this measurement sample by the volume (unit: cm 3 ), the density of the molded body (unit: kg / m 3 ) was calculated by converting the unit. The densities of the molded bodies in the examples and comparative examples were as shown in Tables 2, 4, and 6. For the foamed particles without a moldable range, since the density evaluation could not be performed, the symbol "-" was described in the "Density" column of Tables 2, 4, and 6.

[0109] (Maximum bending stress of the foamed particle molded body) A mold with a molding cavity capable of forming a foam particle molded body having a rectangular parallelepiped shape with dimensions of 300 mm in length, 75 mm in width, and 25 mm in thickness was used. In the evaluation of the moldable range described above, the foam particle molded body was obtained by performing in-mold molding at the lowest molding pressure at which good products could be obtained. A three-point bending test was performed on this molded body in accordance with JIS K 7221-2:2006, under the conditions of a support distance of 200 mm, a pressure wedge of 10R and a support base of 10R, and a pressure wedge descent rate of 10 mm / min, and the bending strength was measured. A stress-strain curve was created from the stress (unit: kPa) and strain (unit: %) obtained from the measurement, and the maximum bending stress (bending strength), which is the point at which the molded body exhibits the greatest stress, was calculated based on this stress-strain curve. The maximum bending stress of the molded bodies in the examples and comparative examples is shown in Tables 2, 4, and 6.

[0110] (Castability) Castability was evaluated based on the surface finish and amount of soot in the casting. First, using a mold with a molding cavity capable of forming a foam particle molded body having a rectangular parallelepiped shape of 300 mm in length, 75 mm in width, and 25 mm in thickness, an in-mold molding was performed at the lowest molding pressure among those that yielded good products in the aforementioned evaluation of the moldable range, thereby obtaining a foam particle molded body consisting of the foam particles of the example. A test specimen exhibiting a rectangular parallelepiped shape of 150 mm in length, 75 mm in width, and 25 mm in thickness was taken from this molded body.

[0111] This specimen was used as a lost-wax model, and metal casting was performed using the full-mold casting method. Specifically, first, the specimen coated with a zircon-based mold agent was placed in the casting frame along with the runner and weir. Then, sand to serve as the mold was filled into the casting frame. The sand used was an alkali phenol gas-cured binder resin (Kao Corporation's "Kaostep® C-800").

[0112] Next, carbon dioxide gas was filled into the entire mold to harden the sand. After installing the sprue and relief opening, molten metal was poured in through the sprue and casting was performed. Spheroidal graphite cast iron (i.e., FCD) was used as the molten metal. The temperature of the molten metal during casting was approximately 1400°C. After casting was completed, the metal solidified within the mold, forming a casting in the shape corresponding to the test specimen. After the temperature of the casting had sufficiently decreased within the mold, the casting was removed from the mold and shot blasted.

[0113] The surface finish and amount of soot of the castings obtained as described above were evaluated according to the evaluation criteria described later. If all items were deemed satisfactory, the casting properties were judged to be good, and the symbol "A" was entered in the "Castiability" column of Tables 2, 4, and 6. Note that the casting properties of the comparative example molded body made of foamed particles were not evaluated.

[0114] • Evaluation of casting surface The castings were visually inspected to evaluate the presence or absence of soot defects. Soot defects are cavities or indentations on the casting surface or inside the casting, caused by the failure of thermal decomposition products of the test specimen (i.e., the lost-wax model) to be properly discharged and remain in the sand mold during casting. The absence or small number of soot defects means that little to no soot was generated during combustion. In evaluating the casting surface, a casting without soot defects was judged as acceptable, while a casting with soot defects was judged as unacceptable.

[0115] • Amount of soot From the aforementioned test specimen, a test piece measuring 75 mm in length, 25 mm in width, and 25 mm in thickness was cut out, excluding the skin surface. This test piece was mounted horizontally in a clamp, and a flame was brought into contact with it. The amount of soot generated was visually observed. A test was judged to pass if there was almost no soot generated, and to fail if there was a clear amount of soot generated.

[0116] [Table 1]

[0117] [Table 2]

[0118] [Table 3]

[0119] [Table 4]

[0120] [Table 5]

[0121] [Table 6]

[0122] As shown in Tables 1 and 2, the foamed resin particles of Examples 1 to 7 contain chain-type saturated hydrocarbons, alicyclic hydrocarbons, and carboxylic acids with a total carbon number of 4 to 10 in the specified proportions. Therefore, these foamed resin particles can be used to obtain foamed particles with excellent in-moldability, even when producing molded articles with complex shapes.

[0123] On the other hand, the foamed resin particles of Comparative Example 1 shown in Tables 3 and 4 did not contain carboxylic acid esters, resulting in a narrow moldable range and poor in-moldability.

[0124] Although the foamed resin particles of Comparative Example 2 had a higher amount of alicyclic hydrocarbons added compared to Comparative Example 1, they did not contain carboxylic acid esters, resulting in similar in-moldability to Comparative Example 1.

[0125] The foamed resin particles of Comparative Example 3 lacked alicyclic hydrocarbons and therefore exhibited poor foaming properties. Furthermore, significant blocking occurred when the foamed resin particles of Comparative Example 3 were foamed. Moreover, the foamed particles obtained by foaming the foamed resin particles of Comparative Example 3 could not yield a good molded product through in-mold molding.

[0126] Although the foaming resin particles of Comparative Examples 4 and 5 had a higher amount of carboxylic acid ester added compared to Comparative Example 3, they did not contain alicyclic hydrocarbons, and therefore could not sufficiently improve their foaming properties.

[0127] In Comparative Example 6, shown in Tables 5 and 6, the foaming resin particles had an excessively high mass ratio of carboxylic acid ester content to alicyclic hydrocarbon content, resulting in insufficient effect from the alicyclic hydrocarbons. Consequently, the foaming resin particles of Comparative Example 6 exhibited poor foaming properties.

[0128] In Comparative Example 7, the foamed resin particles had an insufficient effect from the carboxylic acid ester because the mass ratio of carboxylic acid ester content to alicyclic hydrocarbon content was too low. As a result, the foamed resin particles of Comparative Example 7 had poor in-moldability.

[0129] The foaming resin particles of Comparative Example 8 did not contain alicyclic hydrocarbons and contained toluene, an aromatic hydrocarbon, so the effect of alicyclic hydrocarbons was not obtained. As a result, the foaming resin particles of Comparative Example 8 had inferior foaming properties.

[0130] In Comparative Examples 9 and 10, the foamed resin particles used carboxylic acid esters with a total carbon number outside the specified range, resulting in insufficient effect from the carboxylic acid esters. Consequently, the foamed resin particles of these comparative examples exhibited poor in-moldability.

[0131] Although specific embodiments of the foamed acrylic resin particles according to the present invention have been described above based on examples, the embodiments of the foamed acrylic resin particles according to the present invention are not limited to those of the examples, and the configuration can be appropriately modified without impairing the spirit of the present invention.

Claims

1. Foamed acrylic resin particles, The foamed acrylic resin particles contain a chain-type saturated hydrocarbon, an alicyclic hydrocarbon, and a carboxylic acid ester which is an ester of a carboxylic acid and an alcohol. The total number of carbon atoms in the carboxylic acid ester is 10 or more and 40 or less. The total amount of the alicyclic hydrocarbon and the carboxylic acid ester in the foamed acrylic resin particles is 1 part by mass or more and 4 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particles. The content of the carboxylic acid ester in the foamed acrylic resin particles is 0.2 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particles. Foaming acrylic resin particles in which the mass ratio of the carboxylic acid ester content to the alicyclic hydrocarbon content is 0.2 or more and 1.0 or less.

2. The foamed acrylic resin particles according to claim 1, wherein the average particle diameter of the foamed acrylic resin particles is 0.3 mm or more and 0.5 mm or less.

3. The foamable acrylic resin particles according to claim 1 or 2, wherein the carboxylic acid ester is an ester of a carboxylic acid having 5 to 20 carbon atoms and an alcohol having 2 to 10 carbon atoms.

4. The foamed acrylic resin particles according to claim 1 or 2, wherein the number of carbon atoms in the chain-type saturated hydrocarbon is 3 to 6, and the number of carbon atoms in the alicyclic hydrocarbon is 5 to 7.

5. The foamed acrylic resin particles according to claim 1 or 2, wherein the content of the chain-type saturated hydrocarbon in the foamed acrylic resin particles is 5 parts by mass or more and 9 parts by mass or less per 100 parts by mass of the resin component contained in the foamed acrylic resin particles.

6. The foamable acrylic resin particles according to claim 1 or 2, wherein the mass ratio of the total content of the alicyclic hydrocarbon and the carboxylic acid ester to the content of the chain-type saturated hydrocarbon is 0.1 or more and 0.4 or less.

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