Expandable styrene resin particles

Abstract

To provide foamable styrene resin particles that prevent blocking during the foaming process, even for foamed particles with low bulk density, enable their molding in efficient cycles, and yield a foamed particle molded product with superior flexural strength.SOLUTION: A foamable styrene resin particle includes a styrene resin particle body (A) and a coating agent (B) that coats it. The coating agent (B) includes a higher fatty acid metal salt (B1), a glycerol higher fatty acid triester (B2), a glycerol higher fatty acid monoester (B3), a pentaerythritol higher fatty acid ester (B4), and dimethylpolysiloxane (B5). The components that make up the coating agent (B) are each adjusted according to a predetermined relationship with respect to the coating levels.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to foamed styrene-based resin particles. [Background technology]

[0002] Foamed styrene resin particles are manufactured by foaming foamable styrene resin particles, which use styrene resin as the base resin. By foaming foamable styrene resin particles, foamed styrene resin particles with low bulk density can be obtained. Furthermore, by heating the foamed particles in a mold and performing secondary foaming to fuse the foamed particles together, a molded foam particle body can be obtained. Molded foam particle bodies obtained using foamable styrene resin particles are lightweight and have excellent mechanical properties. For these reasons, molded foam particle bodies are used in various fields such as automotive materials, construction materials, and logistics materials.

[0003] For example, Patent Documents 1 and 2 propose a technique for coating foamed styrene resin particles with a predetermined coating agent in order to prevent the foaming of foamed styrene resin particles from adhering to each other (i.e., blocking) during foaming and to improve in-moldability. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-66720 [Patent Document 2] Japanese Patent Application Publication No. 51-49261 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] On the other hand, with conventional foamed styrene resin particles coated with a coating agent, attempting to obtain foamed particles with lower bulk density sometimes resulted in insufficient prevention of blocking, leading to an increase in the amount of foamed particle agglomeration (i.e., the amount of blocking). Furthermore, it became difficult to sufficiently fuse the foamed particles together during in-mold molding while preventing the occurrence of blocking, making it impossible to obtain foamed particle molded articles with high flexural strength. Moreover, from the viewpoint of increasing the productivity of foamed particle molded articles, it is preferable to shorten the cooling time during in-mold molding and shorten the molding cycle, but conventional technology had room for improvement in shortening the cooling time while simultaneously preventing the occurrence of blocking and ensuring good fusion of foamed particles.

[0006] This invention has been made in view of the above background, and aims to provide foamable styrene-based resin particles that can prevent blocking during foaming even when obtaining foamed particles with low bulk density, enable molding in an excellent molding cycle, and produce foamed particle molded articles with excellent flexural strength. [Means for solving the problem]

[0007] One aspect of the present invention relates to foamed styrene resin particles according to the following [1] to [4]. [1] Foaming styrene resin particles having a styrene resin particle body (A) and a coating agent (B) that covers the particle body (A), The above coating agent (B) comprises a higher fatty acid metal salt (B1), a glycerin higher fatty acid triester (B2), a glycerin higher fatty acid monoester (B3), a pentaerythritol higher fatty acid ester (B4), and dimethylpolysiloxane (B5). The total amount of coating by the glycerin higher fatty acid triester (B2), the glycerin higher fatty acid monoester (B3), and the pentaerythritol higher fatty acid ester (B4) per 100 parts by mass of the particle body (A) is 0.02 parts by mass or more and 0.3 parts by mass or less. The amount of dimethylpolysiloxane (B5) coating per 100 parts by mass of the above particle body (A) is 0.01 parts by mass or more and 0.2 parts by mass or less. The total mass ratio of the above glycerin higher fatty acid monoester (B3) and the above pentaerythritol higher fatty acid ester (B4) to the above glycerin higher fatty acid triester (B2) is 0.1 or more and 2.0 or less. Expandable styrene resin particles in which the mass ratio of the pentaerythritol higher fatty acid ester (B4) to the glycerin higher fatty acid monoester (B3) is 0.01 or more and 0.5 or less.

[0008] [2] The foamable styrene-based resin particles according to [1], wherein the mass ratio of dimethylpolysiloxane (B5) to the sum of the glycerin higher fatty acid triester (B2), the glycerin higher fatty acid monoester (B3), and the pentaerythritol higher fatty acid ester (B4) is 0.1 or more and 1 or less.

[0009] [3] The foamable styrene resin particle according to [1] or [2], wherein the amount of coating of the higher fatty acid metal salt (B1) per 100 parts by mass of the particle body (A) is 0.03 parts by mass or more and 0.4 parts by mass or less. [4] The foamed styrene resin particles described in any of [1] to [3], wherein the average particle diameter of the foamed styrene resin particles is 0.6 mm or more and 2 mm or less. [Effects of the Invention]

[0010] According to the above-mentioned foamed styrene resin particles, for example, 15 kg / m³ 3 Even when obtaining foamed particles with low bulk density, such as those described below, blocking during foaming can be prevented, the cooling time during molding can be shortened, and molding with an excellent molding cycle can be achieved. Furthermore, using the above-mentioned foamable styrene-based resin particles, it is possible to obtain a foamed particle molded article with excellent flexural strength. [Modes for carrying out the invention]

[0011] In this specification, letters and numbers enclosed in parentheses do not limit the present invention in any way. Furthermore, "expandable styrene-based resin particles" may be referred to as "expandable resin particles," "styrene-based foamed particles" as "foamed particles," and "foamed particle molded articles" as "molded articles." In addition, when the expression "~" is used in this specification, it is intended to include the numerical or physical values ​​described before and after it.

[0012] Foamable resin particles can be foamed by heating with a heating medium such as steam, thereby obtaining foamed particles. In other words, foamable resin particles are used to obtain foamed particles.

[0013] Furthermore, by molding a large number of foam particles in a mold, a foam particle molded body can be obtained in which the foam particles are fused to each other. In-mold molding of foam particles can be performed, for example, by filling a mold having a cavity corresponding to the desired molded body shape with foam particles, supplying a heating medium such as steam into the cavity, and heating the foam particles while causing secondary foaming to fuse the foam particles together.

[0014] The foamed resin particles comprise a styrene-based resin particle body (A), a coating agent (B) that coats the particle body, and a foaming agent. The coating agent includes a higher fatty acid metal salt (B1), a glycerin higher fatty acid triester (B2), a glycerin higher fatty acid monoester (B3), a pentaerythritol higher fatty acid ester (B4), and dimethylpolysiloxane (B5). The total coating amounts of (B2) to (B4), the coating amount of (B5), the ratio of the total coating amounts of (B3) and (B4) to the coating amount of (B2), and the ratio of the coating amount of (B4) to the coating amount of (B3) are adjusted to a predetermined range. As described above, the particle body is coated with a coating agent composed of five predetermined components, and the components contained in the coating agent are adjusted to have a predetermined coating amount relationship. Therefore, the foamed resin particles can prevent blocking during foaming, that is, the phenomenon of foamed particles fusing together and forming clumps, over a wide range of bulk densities from high to low, for example, 15 kg / m³.3 Blocking during foaming can be prevented even when obtaining expanded particles having a low bulk density as described below. Furthermore, the cooling time during in-mold molding of the obtained expanded particles can be shortened, enabling molding with an excellent molding cycle. In addition, a molded article excellent in fusion bonding between the expanded particles and excellent in bending strength can be obtained.

[0015] The total (b2+b3+b4) of the coating amount (b2) of glycerin higher fatty acid triester (B2), the coating amount (b3) of glycerin higher fatty acid monoester (B3), and the coating amount (b4) of pentaerythritol higher fatty acid ester (B4) is 0.02 parts by mass or more and 0.3 parts by mass or less based on 100 parts by mass of the particle body (A). If the total coating amount (b2+b3+b4) of glycerin higher fatty acid triester (B2), glycerin higher fatty acid monoester (B3), and pentaerythritol higher fatty acid ester (B4) is too small, the fusion rate in the molded article will decrease, the appearance (specifically, the surface properties of the molded article) will deteriorate, and the bending strength may decrease. On the other hand, if the total coating amount (b2+b3+b4) is too large, the fusion rate of the molded article will also decrease, the appearance will deteriorate, and the bending strength may decrease. From the viewpoint of stably obtaining a molded article with a good fusion state and stably obtaining a molded article excellent in appearance and bending strength, the total coating amount (b2+b3+b4) based on 100 parts by mass of the particle body (A) is preferably 0.04 parts by mass or more and 0.2 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.2 parts by mass or less. Note that 100 parts by mass of the particle body (A) refers to the mass of the particle body (mass of styrene resin or the like) that does not contain a blowing agent, and the same applies to the description of the particle body (A) regarding the coating agent described later.

[0016] The coating amount (b5) of dimethylpolysiloxane (B5) relative to 100 parts by mass of the particle body (A) is 0.01 parts by mass or more and 0.2 parts by mass or less. If the coating amount (b5) of dimethylpolysiloxane (B5) is too small, the releasability of the molded article will deteriorate during molding, and there is a risk that the molded article may be damaged. In addition, in this case, blocking tends to easily occur when obtaining expanded particles with low bulk density. Furthermore, in this case, the cooling time during molding becomes longer, and there is a risk that the molding cycle becomes longer. On the other hand, if the coating amount (b5) of dimethylpolysiloxane (B5) is too large, the fusion bondability between expanded particles decreases, and there is a risk that the bending strength of the molded article decreases. From the viewpoint of preventing blocking, shortening the cooling time, and stably obtaining a molded article with excellent bending strength, the coating amount (b5) of dimethylpolysiloxane (B5) relative to 100 parts by mass of the particle body (A) is preferably 0.02 parts by mass or more and 0.1 parts by mass or less, and more preferably 0.02 parts by mass or more and 0.06 parts by mass or less.

[0017] Dimethylpolysiloxane (B5) is a compound that is oily at normal temperature, and is a type of substance called silicone oil composed of organopolysiloxane. Even if the coating agent (B) contains other silicone oils other than dimethylpolysiloxane (B5), if it does not contain at least dimethylpolysiloxane (B5), blocking tends to easily occur when obtaining expanded particles with low bulk density, and the amount of blocking tends to increase. In addition, in this case, the cooling time during molding tends to become longer, and the molding cycle tends to become longer.

[0018] The mass ratio ((b3+b4) / b2) of the total of glycerin higher fatty acid monoester (B3) and pentaerythritol higher fatty acid ester (B4) to glycerin higher fatty acid triester (B2) is between 0.1 and 2.0. If the mass ratio ((b3+b4) / b2) is too small, blocking may occur when obtaining foamed particles with low bulk density. In this case, the cooling time during molding may be prolonged, and the molding cycle may be extended. On the other hand, if the mass ratio ((b3+b4) / b2) is too large, the fusion rate of the molded article will be low, resulting in a poor appearance and a decrease in bending strength. From the viewpoint of further preventing blocking and shortening the cooling time during molding, the mass ratio ((b3+b4) / b2) is preferably between 0.2 and 1.5, and more preferably between 0.2 and 1.0.

[0019] The mass ratio (b4 / b3) of pentaerythritol higher fatty acid ester (B4) to glycerin higher fatty acid monoester (B3) is 0.01 or more and 0.5 or less. If the mass ratio (b4 / b3) is too small, the cooling time during molding will be longer, which may lengthen the molding cycle. Also, blocking may be more likely to occur when obtaining foamed particles with low bulk density. On the other hand, if the mass ratio (b4 / b3) is too large, the fusion properties between foamed particles will decrease, which may reduce the bending strength of the molded article. From the viewpoint of suppressing the occurrence of blocking, stably shortening the cooling time during molding, and stably obtaining a molded article with excellent bending strength, the mass ratio (b4 / b3) is preferably 0.02 or more and 0.2 or less, and more preferably 0.03 or more and 0.1 or less.

[0020] The mass ratio of dimethylpolysiloxane (B5) to the sum of glycerin higher fatty acid triester (B2), glycerin higher fatty acid monoester (B3), and pentaerythritol higher fatty acid ester (B4) (b5 / (b2+3+4)) is preferably 0.1 or more and 1 or less. In this case, the molded article can be stably demolded during molding, and the effects of suppressing blocking when obtaining foamed particles, shortening the cooling time during molding, and ensuring the bending strength of the molded article can be stably obtained. From this viewpoint, the mass ratio (b5 / (b2+3+4)) is more preferably 0.1 or more and 0.8 or less, and even more preferably 0.1 or more and 0.6 or less.

[0021] In the terms "higher fatty acid" in higher fatty acid metal salts (B1), glycerol higher fatty acid triesters (B2), glycerol higher fatty acid monoesters (B3), and pentaerythritol higher fatty acid esters (B4), "higher fatty acid" refers to fatty acids with 12 to 24 carbon atoms.

[0022] Examples of higher fatty acid metal salts (B1) that can be used include metal stearate salts such as zinc stearate, magnesium stearate, calcium stearate, barium stearate, aluminum stearate, and lithium stearate, as well as metal laurate salts such as zinc laurate and barium laurate. These higher fatty acid metal salts (B1) may be used alone or in combination of two or more. From the viewpoint of enabling in-mold molding at a lower molding pressure while further preventing blocking during foaming, it is preferable that the higher fatty acid metal salt (B1) contains zinc stearate as the main component. More specifically, it is preferable that the proportion of zinc stearate in the higher fatty acid metal salt (B1) is 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0023] The amount of higher fatty acid metal salt (B1) coating (b1) per 100 parts by mass of particle body (A) is preferably 0.03 parts by mass or more and 0.4 parts by mass or less. In this case, blocking during foaming of the foamable resin particles can be stably suppressed while ensuring good bending strength of the molded article. From this viewpoint, the amount of higher fatty acid metal salt (B1) coating (b1) per 100 parts by mass of particle body (A) is more preferably 0.04 parts by mass or more and 0.3 parts by mass or less, and even more preferably 0.05 parts by mass or more and 0.2 parts by mass or less.

[0024] Glycerin higher fatty acid triesters (B2) are triesters of glycerin and higher fatty acids. Examples of glycerin higher fatty acid triesters (B2) include glycerin trilaurate, glycerin trimyristate, glycerin tripalmitate, glycerin tristearate, glycerin trilicinolate, and glycerin tri-12-hydroxystearate. These glycerin higher fatty acid triesters (B2) may be used individually or in combination of two or more. From the viewpoint of minimizing blocking during foaming of foamed resin particles and improving the fusion properties between foamed particles, it is preferable that glycerin higher fatty acid triesters (B2) contain glycerin tri-12-hydroxystearate as the main component. More specifically, it is preferable that the proportion of glycerin tri-12-hydroxystearate in the glycerin higher fatty acid triesters (B2) be 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. Furthermore, as the glycerin higher fatty acid triester (B2), hydrogenated castor oil, hydrogenated beef tallow, etc., may be used. Here, hydrogenated castor oil is a substance obtained by adding hydrogen to castor oil through hydrogenation treatment. The main component of castor oil is glycerin trilicinolate, and the main component of hydrogenated castor oil is glycerin tri-12-hydroxystearate.

[0025] The amount of glycerin higher fatty acid triester (B2) coating (b2) per 100 parts by mass of particle body (A) is preferably 0.02 parts by mass or more and 0.2 parts by mass or less. In this case, the blocking prevention effect at low bulk density during foaming, the effect of improving the molding cycle, and the effect of improving the bending strength of the molded article can be stably expressed. From this viewpoint, the amount of glycerin higher fatty acid triester (B2) coating (b2) per 100 parts by mass of particle body (A) is more preferably 0.03 parts by mass or more and 0.2 parts by mass or less, and even more preferably 0.04 parts by mass or more and 0.1 parts by mass or less.

[0026] Glycerin higher fatty acid monoester (B3) is a monoester of glycerin and a higher fatty acid. Examples of glycerin higher fatty acid monoester (B3) that can be used include glycerin monolaurate, glycerin monomyristate, glycerin monopalmitate, glycerin monostearate, and glycerin monoricinolate. These glycerin higher fatty acid monoesters (B3) may be used individually or in combination of two or more. From the viewpoint of suppressing aggregation of foaming resin particles due to electrostatic charge and making it easier to suppress blocking during foaming of foaming resin particles, it is preferable that the glycerin higher fatty acid monoester (B3) contains glycerin monostearate as its main component. More specifically, it is preferable that the proportion of glycerin monostearate in the glycerin higher fatty acid monoester (B3) be 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more.

[0027] The amount of glycerin higher fatty acid monoester (B3) coating (b3) per 100 parts by mass of particle body (A) is preferably 0.003 parts by mass or more and 0.1 parts by mass or less. In this case, the blocking prevention effect at low bulk density during foaming, the effect of improving the molding cycle, and the effect of improving the bending strength of the molded article can be stably expressed. From this viewpoint, the amount of glycerin higher fatty acid monoester (B3) coating (b3) per 100 parts by mass of particle body (A) is more preferably 0.005 parts by mass or more and 0.09 parts by mass or less, and even more preferably 0.006 parts by mass or more and 0.08 parts by mass or less.

[0028] Pentaerythritol higher fatty acid ester (B4) is an ester of pentaerythritol and a higher fatty acid, such as a monoester of pentaerythritol and a higher fatty acid, or a diester of pentaerythritol and a higher fatty acid. Examples of monoesters of pentaerythritol and a higher fatty acid include pentaerythritol monooleate, pentaerythritol monopalmitate, and pentaerythritol monostearate. Examples of diesters of pentaerythritol and a higher fatty acid include pentaerythritol dioleate, pentaerythritol dipalmitate, and pentaerythritol distearate. These pentaerythritol higher fatty acid esters (B4) may be used individually or in combination of two or more. From the viewpoint of ensuring good flexural strength of the molded article, stably suppressing blocking during foaming of foamable resin particles, and stably shortening the cooling time during molding, it is preferable that pentaerythritol higher fatty acid ester (B4) has pentaerythritol distearate as its main component. More specifically, it is preferable that the proportion of pentaerythritol distearate in the pentaerythritol higher fatty acid ester (B4) is 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0029] The amount of pentaerythritol higher fatty acid ester (B4) coating (b4) per 100 parts by mass of particle body (A) is preferably 0.0005 parts by mass or more and 0.008 parts by mass or less. In this case, the blocking prevention effect at low bulk density during foaming, the effect of improving the molding cycle, and the effect of improving the bending strength of the molded article can be stably expressed. From this viewpoint, the amount of glycerin higher fatty acid monoester (B3) coating (b3) per 100 parts by mass of particle body (A) is more preferably 0.0006 parts by mass or more and 0.007 parts by mass or less, and even more preferably 0.0008 parts by mass or more and 0.006 parts by mass or less.

[0030] The coating agent (B) may contain other coating agents other than (B1) to (B5) to the extent that the intended objectives of the present invention can be achieved. Specifically, the coating agent (B) may contain, for example, glycerin as another coating agent. In this case, aggregation due to electrostatic charge of the foamed resin particles can be suppressed, and for example, accumulation of foamed resin particles in pipes, etc., when the foamed resin particles are pneumatically transported can be suppressed. From this viewpoint, the amount of glycerin coating per 100 parts by mass of the particle body (A) is preferably 0.005 parts by mass or more and 0.05 parts by mass or less, and more preferably 0.01 parts by mass or more and 0.03 parts by mass or less. Furthermore, from the viewpoint of stably exhibiting the effects of the present invention, the amount of coating agent (B) per 100 parts by mass of particle body (A) is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less.

[0031] The particle body (A) contains a styrene-based resin as a base resin. The styrene-based resin may be a polymer of styrene-based monomers, or a copolymer of styrene-based monomers and other monomers. Preferably, the styrene-based resin is a polymer of styrene-based monomers. Examples of styrene-based monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-methoxystyrene, pn-butylstyrene, pt-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, 2,4,6-tribromostyrene, etc. These styrene-based monomers may be used individually or in combination of two or more. Preferably, the styrene-based monomer contains at least styrene, with styrene being the main component. More specifically, it is preferable that the proportion of styrene in the styrene-based monomer is 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. In this case, it is possible to stably obtain a molded article that has good foaming properties and moldability of foamed resin particles, as well as good flexural strength.

[0032] Examples of monomers copolymerizable with styrene monomers include (meth)acrylic acid esters. Examples of (meth)acrylic acid esters include acrylic acid esters such as methyl acrylate, ethyl acrylate, and butyl acrylate, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, and butyl methacrylate. These monomers copolymerizable with styrene monomers may be used individually or in combination of two or more. Other monomers as described above may be used to the extent that the intended purpose of the present invention can be achieved, in which case the content of the other monomer is preferably about 20 parts by mass or less, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of styrene monomer.

[0033] From the viewpoint of making it easier to foam the foamable resin particles to a high magnification and improving the in-moldability of the foamed particles under low molding pressure conditions, the particle body (A) may contain a plasticizer. Examples of plasticizers include liquid paraffin, carboxylic acid esters such as di-2-ethylhexyl phthalate and di-2-ethylhexyl adipate, alkyl (meth)acrylate esters such as butyl stearate, and higher fatty acid esters such as glycerin tristearate. Furthermore, from the viewpoint of making it easier to foam the foamable resin particles to a higher magnification, it is preferable that the particle body (A) contains butyl stearate. In this case, the butyl stearate content in the particle body (A) is preferably 0.1% by mass or more and 0.5% by mass or less, and more preferably 0.2% by mass or more and 0.4% by mass or less. In the past, when the particle body (A) contains butyl stearate, problems arose such as blocking easily occurring during foaming and a prolonged cooling time during molding, resulting in a poor molding cycle. However, with foamable resin particles in which the particle body (A) is coated with the above-mentioned coating agent (B), blocking can be prevented, and foamable particles with an excellent molding cycle can be obtained.

[0034] The foamed styrene resin particles contain a foaming agent. The foamed styrene resin particles are obtained by impregnating the particle body (A) with a foaming agent. Preferably, a hydrocarbon-based foaming agent can be used. Examples of hydrocarbon-based foaming agents include chain-type aliphatic hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, neopentane, and n-hexane, and cyclic aliphatic hydrocarbons such as cyclohexane. These foaming agents may be used alone, or two or more foaming agents may be used in combination. The foaming agent content in the foamed styrene resin particles is preferably 3% by mass or more and 9% by mass or less, and more preferably 4% by mass or more and 8% by mass or less.

[0035] The particle body (A) may contain additives such as bubble regulators, chain transfer agents, antioxidants, ultraviolet absorbers, and light stabilizers, to the extent that the intended objectives of the present invention can be achieved.

[0036] As foam regulators, polyethylene wax, methyl methacrylate copolymers, talc, silica, ethylene bisstearylamide, etc., can be used.

[0037] Examples of chain transfer agents that can be used include octyl mercaptan, dodecyl mercaptan, and α-methylstyrene dimer.

[0038] As antioxidants, phenolic antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, etc., can be used. As ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, and the like can be used. Hindered amine compounds and the like can be used as light stabilizers.

[0039] One method for producing foamed resin particles is as follows: First, in a pressure vessel equipped with a stirring device, styrene monomers are dispersed in an aqueous solvent in the presence of a suitable suspension agent, along with additives such as foam regulators and plasticizers, and polymerization initiators.

[0040] Next, the polymerization reaction of the styrene monomer is initiated. As this polymerization reaction progresses, particle bodies are formed in the aqueous solvent. By adding a foaming agent to a sealed container during or after polymerization, the particle bodies are impregnated with the foaming agent. In this way, foamed resin particles before coating with the coating agent can be obtained. In the following explanation, the foamed resin particles before coating with the coating agent will be referred to as "foamed resin particles (α)" as appropriate.

[0041] As polymerization initiators, initiators soluble in styrene monomers can be used. Specifically, examples include azo compounds such as azobisisobutyronitrile, cumenehydroperoxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxybenzoate, benzoyl peroxide, t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl monocarbonate, 1,1-dimethylpropylperoxy-2-ethylhexyl monocarbonate, 1,1-dimethylbutylperoxy-2-ethylhexyl monocarbonate, pentylperoxy-2-ethylhexyl monocarbonate, hexylperoxy-2-ethylhexyl monocarbonate, lauroyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-di-t-butylperoxy-2-methylcyclohexane. These polymerization initiators may be used individually or in combination of two or more. The amount of polymerization initiator used is preferably 0.01 to 3 parts by mass per 100 parts by mass of the total of the styrene monomer and the monomer copolymerizable with the styrene monomer.

[0042] As a suspension agent, hydrophilic polymers such as polyvinyl alcohol, methylcellulose, and polyvinylpyrrolidone, or poorly water-soluble inorganic salts such as tricalcium phosphate and magnesium pyrophosphate can be used. Alternatively, a suspension agent and a surfactant may be used in combination as needed. When using poorly water-soluble inorganic salts, it is preferable to use an anionic surfactant such as sodium alkyl sulfonate or sodium dodecylbenzenesulfonate as the surfactant.

[0043] The amount of suspension agent used is preferably 0.01 to 5 parts by mass per 100 parts by mass of the total styrene monomer and monomers copolymerizable with the styrene monomer as needed. When using a poorly water-soluble inorganic salt and an anionic surfactant in combination, it is preferable to use 0.05 to 3 parts by mass of the poorly water-soluble inorganic salt and 0.0001 to 0.5 parts by mass of the anionic surfactant per 100 parts by mass of the total styrene monomer and monomers copolymerizable with the styrene monomer, or per 100 parts by mass of the total styrene monomer (A1) and alkyl acrylate (A2).

[0044] During the polymerization reaction of styrene monomers, the above-mentioned additives may be added to the aqueous solvent as needed.

[0045] The foamed resin particles (α) obtained as described above are removed from the aqueous solvent and dried. Afterward, if necessary, the foamed resin particles (α) may be classified. By mixing the dried foamed resin particles (α) with the coating agent (B) described above, the coating agent (B) can be attached to the surface of the particle body (A) (i.e., the foamed resin particles (α)). As a result, foamed resin particles in which the particle body (A) is coated with the coating agent can be obtained.

[0046] The average particle size of the foamed resin particles is preferably 0.6 mm or larger. In this case, the foamed resin particles can be foamed to a higher degree, for example, 15 kg / m³. 3It is possible to stably obtain foamed particles with a low bulk density as follows. Furthermore, even when foamed resin particles are foamed to become foamed particles with such a low bulk density, the presence of coating agent (B) prevents blocking, and it is possible to stably obtain foamed particles that can be molded into molded articles with a short molding cycle and high flexural strength. From this viewpoint, it is more preferable that the average particle diameter of the foamed resin particles be 0.7 mm or more, and even more preferable that it be 0.8 mm or more. It is also preferable that the average particle diameter of the foamed resin particles be 2 mm or less. In this case, it is possible to prevent the average particle diameter of the foamed particles from becoming too large, to fill the mold well with foamed particles, and to improve the in-moldability of the foamed particles. From this viewpoint, it is more preferable that the average particle diameter of the foamed resin particles be 1.5 mm or less, and even more preferable that it be 1.2 mm or less. The average particle size of foamed resin particles is calculated by measuring the particle size distribution of the foamed resin particles using a particle size distribution analyzer, and determining the particle size (d63) at 63% of the volume integrated value in the measured particle size distribution. For example, the "Millitrack JPA" manufactured by Nikkiso Co., Ltd. can be used as a particle size distribution analyzer.

[0047] Foamed resin particles can be obtained by foaming the foamed resin particles obtained as described above. One method of foaming is to heat and foam the foamed resin particles by supplying a heating medium such as steam to the foamed resin particles in a cylindrical foaming machine equipped with a stirring device.

[0048] The bulk density of the foamed particles is, for example, 10 kg / m³. 3 More than 200kg / m 3 The following conditions are acceptable. Furthermore, according to the foamed resin particles of this disclosure, the bulk density is 15 kg / m³. 3 The following foamed particles can be obtained. In this case, the above-mentioned blocking prevention effect of the coating agent (B) becomes significant. In other words, normally, when foaming foamed resin particles at a high magnification to obtain foamed particles with a lower bulk density, blocking tends to occur more easily during foaming, and conventional foamed resin particles have a bulk density of 15 kg / m³. 3When attempting to obtain expanded particles with a bulk density of 15 kg / m 3 or lower, blocking tends to occur easily. However, in the case of producing expanded particles with a bulk density of 15 kg / m 3 or lower, the above-mentioned expandable resin particles coated with the coating agent (B) can prevent blocking. Therefore, by expanding the expandable resin particles in which the particle body (A) is coated with the aforementioned coating agent (B), expanded particles with low bulk density can be obtained while preventing blocking. Further, with the obtained expanded particles, a molded article having good flexural strength can be obtained by in-mold molding, and in-mold molding can be performed in a short cooling time.

[0049] The expanded particles are used, for example, in the production of molded articles. Specifically, by subjecting a large number of expanded particles to in-mold molding, a molded article in which the large number of expanded particles are mutually fused can be obtained. In-mold molding is produced, for example, by filling a large number of expanded particles into a mold having a cavity of a desired molded article shape, and heating the expanded particles with a heating medium such as steam. That is, the expanded particles expand by heating, and the expanded particles mutually fuse together. After fusing, the molded article is cooled. Thereby, the molded article is obtained. By using expanded particles obtained by expanding expandable resin particles in which the particle body (A) is coated with the aforementioned coating agent (B), a molded article having a short cooling time during molding, a high fusion rate, good appearance and high flexural strength can be obtained.

[0050] The apparent density of the molded article is 10 to 200 kg / m 3 , which is preferable. In this case, the molded article can be lightweight and have good mechanical properties such as flexural strength. From the viewpoint of further improving light weight, the apparent density of the molded article is 100 kg / m 3 or lower, more preferably 50 kg / m 3 or lower, still more preferably 30 kg / m 3 or lower, and particularly preferably.

Examples

[0051] Examples and comparative examples of foamed resin particles are described below. In this example, the foamed resin particles shown in Tables 1 to 3 were produced by the following method.

[0052] (Example 1) "Manufacturing of foamed resin particles" 275 kg of deionized water, 0.81 kg of tricalcium phosphate, 0.11 kg of disodium hydrogen phosphate, and 3.3 g of potassium persulfate were added to a 760 L autoclave (sealed container) equipped with a stirring device. Next, while stirring the contents of the autoclave, 0.179 kg of a foam regulator (specifically, polyethylene wax 1000 manufactured by Toyo Chem Co., Ltd.), 0.38 kg of a higher fatty acid ester (specifically, glycerin tristearate), and 0.922 kg of butyl stearate (butyl stearate) were added to the autoclave.

[0053] Furthermore, 5.31 kg of cyclohexane as a foaming agent, and 275 kg of polymerization initiator and styrene were added to the autoclave. As the polymerization initiator, 0.868 kg of benzoyl peroxide (NOF Corporation's "NIPER® BW") and 0.164 kg of t-butyl peroxy 2-ethylhexyl monocarbonate (NOF Corporation's "Perbutyl® E") were used in combination.

[0054] The contents of the autoclave were stirred at room temperature for 5 minutes, and then the temperature inside the autoclave was raised to 90°C over 30 minutes. After the temperature inside the autoclave reached 90°C, this temperature was maintained for 330 minutes (first half of the pre-polymerization process). Next, the temperature inside the autoclave was heated to 96°C over 25 minutes and maintained for 52 minutes (second half of the pre-polymerization process). Next, the temperature inside the autoclave was raised to 120°C over 96 minutes and maintained for 200 minutes (second-stage polymerization process). After that, the temperature inside the autoclave was cooled to 25°C over 140 minutes. In addition, a blowing agent (specifically butane) was supplied to the autoclave during the second half of the pre-polymerization process. Specifically, the supply of the blowing agent to the autoclave began 364 minutes after the temperature inside the autoclave reached 90°C and ended 60 minutes later. As the blowing agent supplied in the latter half of the preceding polymerization process, 19.25 kg of butane (a mixture of approximately 70% by mass of n-butane and approximately 30% by mass of isobutane) was used.

[0055] As described above, the styrene in the autoclave was polymerized to obtain particle body (A). The butyl stearate content in particle body (A) was 0.3% by mass. Then, the particle body (A) was impregnated with a foaming agent to obtain foamed resin particles (α). After the autoclave had cooled completely, the foamed resin particles (α) were removed from the autoclave. Next, the foamed resin particles (α) were dehydrated and washed using a centrifuge.

[0056] Subsequently, the foamed resin particles (α) were dried by blowing air through them using an airflow drying apparatus. The temperature of the airflow blown onto the foamed resin particles (α) was adjusted to 40°C. In the following, this drying process will be referred to as primary drying.

[0057] Next, the foamed resin particles (α) after primary drying were transferred to a fluidized bed dryer. By supplying 40°C air into the dryer chamber, the foamed resin particles were suspended within the chamber and dried in this state for 60 minutes or more. In the following, this drying process will be referred to as secondary drying.

[0058] Next, the foamed resin particles (α) after secondary drying were subjected to a classifier to obtain foamed resin particles (α) with an average particle size of 0.9 mm. Next, to 100 parts by mass of particle body (A) (in other words, 100 parts by mass of foaming resin particles (α) excluding the amount of foaming agent, which is a volatile component, more specifically the amount of cyclohexane and butane), 0.086 parts by mass of higher fatty acid metal salt (specifically, zinc stearate), 0.049 parts by mass of glycerin higher fatty acid triester (specifically, hydrogenated castor oil (main component: glycerin tri-12-hydroxystearate)), 0.011 parts by mass of glycerin higher fatty acid monoester (specifically, glycerin monostearate), 0.001 parts by mass of pentaerythritol higher fatty acid ester (specifically, pentaerythritol distearate), 0.027 parts by mass of dimethylpolysiloxane, and 0.015 parts by mass of glycerin were added and mixed in a mixer, and the surface of the foaming resin particles (α) (particle body (A)) was coated with coating agent (B). As a result, foaming resin particles were obtained.

[0059] The average particle size of the foamed resin particles (α) was measured using the "Millitrack JPA" particle size distribution analyzer manufactured by Nikkiso Co., Ltd., as follows. First, 30 g of foamed resin particles (α) were supplied to the sample supply section of the analyzer. Next, the foamed resin particles (α) were allowed to free-fall from the sample supply section, and the projection image of the foamed resin particles (α) during free-fall was captured by a CCD camera. The particle size distribution of the foamed resin particles (α) was measured under the conditions of an image analysis method that sequentially performs calculation and merging processing on the image information thus captured and outputs the particle size distribution result. The particle size (d63) mm of each particle at a volume integrated value of 63% in the obtained particle size distribution was determined, and this was taken as the average particle size of the foamed resin particles (α). Note that the average particle size of the foamed resin particles does not change much before and after coating with the coating agent, so the average particle size of the foamed resin particles (α) can be considered as the average particle size of the foamed resin particles.

[0060] The formulation of the coating agent for the foamed resin particles in Example 1 is shown in Table 1. In Tables 1 to 3, "b1" indicates the amount of higher fatty acid metal salt coating per 100 parts by mass of the particle body (A) as follows. Furthermore, "b2" indicates the amount of glycerin higher fatty acid triester coating per 100 parts by mass of the particle body (A). Furthermore, "b3" indicates the amount of glycerin higher fatty acid monoester coating per 100 parts by mass of the particle body (A). Furthermore, "b4" indicates the amount of pentaerythritol higher fatty acid ester coating per 100 parts by mass of the particle body (A). Furthermore, "b5" indicates the amount of dimethylpolysiloxane coating per 100 parts by mass of the particle body (A). Furthermore, "c" indicates the amount of methylphenylpolysiloxane coating per 100 parts by mass of the particle body (A).

[0061] (Examples 2-7, Comparative Examples 1-11) Foamed resin particles were prepared in the same manner as in Example 1, except that the formulation of the coating agent relative to 100 parts by mass of the particle body was changed as shown in Tables 1 to 3.

[0062] "Manufacturing of foamed particles" Next, foamed resin particles were produced by foaming the foamed resin particles of the examples and comparative examples, and molded articles were made using these foamed particles. Specifically, first, 2.5 kg of foamed resin particles were placed in a pressurized pre-foaming machine (DYHL-500-U manufactured by Daisen Corporation) (internal dimensions: 300 mm x 300 mm x 50 mm). Then, by supplying steam into the pre-foaming machine while stirring the foamed resin particles, the foamed resin particles were foamed at a heating pressure of 0.014 MPa (G: gauge pressure). In this way, foamed particles with the bulk densities shown in Tables 1 to 3 were obtained. The method for measuring bulk density will be described later.

[0063] "Manufacturing of molded products" The foamed particles obtained as described above were left at room temperature for one day to mature, and then filled into the cavity of a mold for a molding machine. The mold used in this example has a cavity capable of molding a plate-shaped molded body measuring 350 mm in length, 300 mm in width, and 25 mm in thickness. Next, the foamed particles were heated at a predetermined molding pressure for 15 seconds by supplying steam into the cavity (main heating). After that, water for cooling was sprayed onto the mold for 10 seconds, and then the pressure inside the mold was reduced to cool the mold. After cooling until the pressure (surface pressure) on the molding surface of the mold reached 0.02 MPa, the mold was opened and the molded body was removed. The obtained molded body was dried at a temperature of 40°C for one day.

[0064] Using the foamed particles and molded articles obtained in this manner, the bulk density of the foamed particles, the amount of blocking during foaming, the moldability, the molding cycle (specifically, the cooling time), and the bending strength of the molded articles were measured using the following methods. The results are shown in Tables 1 to 3.

[0065] "Bulk density of foamed particles" After air-drying the foam particles for one day, the foam particles were filled into a graduated cylinder, and the cylinder was lightly tapped several times against the floor with its bottom to adjust the height of the foam particles to the 1L mark on the cylinder. The mass of the foam particles per 1L volume was then measured in grams. The bulk density (kg / m³) was then calculated by converting the mass per 1L volume to its units. 3 ) was calculated.

[0066] "Blocking amount" After air-drying the foamed particles for one day, 500g of the foamed particles were classified using a sieve with a mesh size of 10mm. The mass of the foamed particles remaining on the sieve was measured, and the blocking amount (unit: mass %) was calculated by dividing this mass by the total amount of foamed particles (i.e., 500g) and expressing the result as a percentage.

[0067] "Moldability" The moldability during in-mold molding can be evaluated based on the fusion rate between foam particles and the surface properties (i.e., appearance) of the molded body. For the evaluation of moldability, molded bodies were prepared by setting the pressure of the steam supplied into the cavity during in-mold molding (i.e., molding pressure) to two levels (0.05 MPa and 0.06 MPa). The following evaluations were performed using these molded bodies. Note that all molding pressures are gauge pressures (G). The density of the obtained molded bodies was 14.6 kg / m³. 3 That was the case.

[0068] "Molded object density" The mass of the molded body (in grams) is divided by the volume (in liters) obtained from the external dimensions of the molded body, and then the density of the molded body (in kg / m³) is calculated by converting the units. 3 ) was calculated.

[0069] "Measurement of fusion rate" A test specimen was prepared by forming a linear cut with a depth of 2 mm and passing through the center in the longitudinal direction of a plate-shaped molded body measuring 350 mm in length, 65 mm in width, and 25 mm in thickness on one surface (i.e., one side measuring 340 mm in length and 65 mm in width) along the entire width of the molded body. Next, the test specimen was bent in the direction of widening the cut until the test specimen broke or the ends of the test specimen touched each other. Then, the cross-section of the test specimen was visually observed, and the number of foamed particles that broke (material fracture) and the number of foamed particles that detached at the interface between foamed particles were measured. Next, the ratio of broken foamed particles to the total number of foamed particles that broke and foamed particles that detached at the interface was calculated and expressed as a percentage to determine the fusion rate (%). The fusion rate is preferably 80% or higher, and more preferably 90% or higher.

[0070] "Evaluation of surface properties (appearance)" The condition of the molded body was observed visually, and its appearance was judged according to the following criteria. ○: When there are almost no interparticle gaps on the surface of the molded body, and the molded body is smooth. △: When interparticle gaps are observed on the surface of the molded product. ×: When the surface gap on the molded body surface is significant.

[0071] "Cooling time" In the manufacturing of molded articles, the time (cooling time) was measured from the point when the heating of the foam particles at a predetermined molding pressure was completed (the point when the main heating was completed) until the surface pressure of the mold became 0.02 MPa and the mold was opened. The cooling time is preferably 36 seconds or less for molding at a molding pressure of 0.05 MPa, and preferably 105 seconds or less for molding at a molding pressure of 0.06 MPa.

[0072] "Bending strength" A plate-shaped test specimen measuring 350 mm in length, 65 mm in width, and 25 mm in thickness was taken from the molded body. Using this specimen, a three-point bending test was performed in accordance with the bending test method described in JIS K7221-2:2006, and a stress-strain curve was obtained. The bending strength at the maximum load calculated based on this stress-strain curve was defined as the bending strength of the molded body. A universal testing machine ("Autograph®" manufactured by Shimadzu Corporation) was used for the three-point bending test, and the test was performed under the conditions of a lower support distance of 300 mm and a test speed of 20 mm / min. The bending strength is preferably 230 kPa or higher for molding at a molding pressure of 0.05 MPa, and preferably 240 kPa or higher for molding at a molding pressure of 0.06 MPa.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] As can be seen from Table 1, Examples 1 to 7 use foamed resin particles coated with fatty acid higher fatty acid salts, glycerin higher fatty acid triesters, glycerin higher fatty acid monoesters, pentaerythritol higher fatty acid esters, and dimethylpolysiloxane in predetermined coating amounts. As a result, foamed particles with low bulk density were obtained while preventing blocking during foaming. Furthermore, in Examples 1 to 7, the cooling time during in-mold molding was shortened, enabling molding in an excellent molding cycle, and foamed particle molded articles with excellent flexural strength were obtained.

[0077] In contrast, as can be seen from Table 2, Comparative Example 1 did not contain dimethylpolysiloxane as a coating agent, nor did it contain any other silicone oils. As a result, in Comparative Example 1, mold release failure occurred during in-mold molding, and the molded body was damaged when it was removed from the mold. Furthermore, in Comparative Example 2, the coating agent did not contain glycerin higher fatty acid monoester or pentaerythritol higher fatty acid ester. As a result, the amount of blocking during foaming increased in Comparative Example 2. In addition, the cooling time during in-mold molding became longer, worsening the molding cycle.

[0078] In Comparative Example 3, the coating agent did not contain pentaerythritol higher fatty acid ester, resulting in a longer cooling time during in-mold molding and a deterioration of the molding cycle. In Comparative Example 4, the coating agent did not contain glycerol-based higher fatty acid monoester, resulting in a lower bending strength for the resulting molded article.

[0079] In Comparative Example 5, the coating agent did not contain glycerin-based higher fatty acid triester, resulting in a low fusion rate and low bending strength of the molded article. In Comparative Example 6, the total mass ratio ((b3+b4) / b2) of the glycerin higher fatty acid monoester and pentaerythritol higher fatty acid ester to the glycerin higher fatty acid triester is excessively high. As a result, in Comparative Example 6, the fusion rate of the molded article is low, and the bending strength is low.

[0080] Furthermore, as can be seen from Table 3, in Comparative Example 7, the total mass ratio ((b3+b4 / b2)) of glycerin higher fatty acid monoester and pentaerythritol higher fatty acid ester to glycerin higher fatty acid triester is excessively high. As a result, in Comparative Example 7, the fusion rate of the molded article is low, and the bending strength is low. In Comparative Example 8, the total mass ratio ((b3+b4 / b2)) of the glycerin higher fatty acid monoester and pentaerythritol higher fatty acid ester to the glycerin higher fatty acid triester was excessively low. As a result, in Comparative Example 8, the amount of blocking during foaming increased, and the cooling time during in-mold molding became longer, resulting in a deterioration of the molding cycle.

[0081] Comparative Example 9 is an example using the same coating agent as in Example 1, except that methylphenylsiloxane was used as the silicone oil in the coating agent, and dimethylpolysiloxane was not used. In Comparative Example 9, the amount of blocking during foaming increased, and the cooling time during in-mold molding became longer, resulting in a deterioration of the molding cycle. Comparative Example 10 is an example using the same coating agent as in Example 2, except that methylphenylsiloxane was used as the silicone oil in the coating agent, and dimethylpolysiloxane was not used. In Comparative Example 10, the amount of blocking during foaming increased, and the cooling time during in-mold molding became longer, resulting in a deterioration of the molding cycle.

[0082] Comparative Example 11 is an example using the same coating agent as in Example 7, except that methylphenylsiloxane was used as the silicone oil in the coating agent, and dimethylpolysiloxane was not used. In Comparative Example 11, the amount of blocking during foaming increased. Also in Comparative Example 11, molding at low molding pressure resulted in a longer cooling time during in-mold molding, worsening the molding cycle and decreasing flexural strength. On the other hand, increasing the molding pressure during in-mold molding improved flexural strength, but increased the cooling time.

[0083] From the above results, it can be understood that, in the example in which the surface of the particle body (A) of the foamed styrene resin particles is coated with the above-mentioned specific coating agent (B), blocking during foaming can be prevented even when obtaining foamed particles with a low bulk density.

[0084] Furthermore, using the foamed resin particles of the examples shortens the cooling time during in-mold molding, resulting in an improved molding cycle. Moreover, even at low molding pressures, the foamed particles exhibit excellent fusion properties, and a foamed particle molded article with superior mechanical properties can be obtained. Therefore, with the foamed resin particles of the examples, in-mold molding can be performed even at low molding pressures, reducing the energy consumption when producing the foamed particle molded article. The foamed particle molded article produced using the foamed resin particles of the examples is particularly suitable for packaging materials such as fish boxes and food containers.

Claims

1. A foamed styrene resin particle having a styrene resin particle body (A) and a coating agent (B) that covers the particle body (A), The above coating agent (B) comprises a higher fatty acid metal salt (B1), a glycerin higher fatty acid triester (B2), a glycerin higher fatty acid monoester (B3), a pentaerythritol higher fatty acid ester (B4), and dimethylpolysiloxane (B5). The higher fatty acids in the above-mentioned higher fatty acid metal salt (B1), the above-mentioned glycerol higher fatty acid triester (B2), the above-mentioned glycerol higher fatty acid monoester (B3), and the above-mentioned pentaerythritol higher fatty acid ester (B4) are fatty acids having 12 to 24 carbon atoms. The total amount of coating by the glycerin higher fatty acid triester (B2), the glycerin higher fatty acid monoester (B3), and the pentaerythritol higher fatty acid ester (B4) per 100 parts by mass of the particle body (A) is 0.02 parts by mass or more and 0.3 parts by mass or less. The amount of dimethylpolysiloxane (B5) coating per 100 parts by mass of the particle body (A) is 0.01 parts by mass or more and 0.2 parts by mass or less. The total mass ratio of the above glycerin higher fatty acid monoester (B3) and the above pentaerythritol higher fatty acid ester (B4) to the above glycerin higher fatty acid triester (B2) is 0.1 or more and 2.0 or less. Expandable styrene resin particles in which the mass ratio of the pentaerythritol higher fatty acid ester (B4) to the glycerin higher fatty acid monoester (B3) is 0.01 or more and 0.5 or less.

2. The foamed styrene-based resin particles according to claim 1, wherein the mass ratio of dimethylpolysiloxane (B5) to the sum of the glycerin higher fatty acid triester (B2), the glycerin higher fatty acid monoester (B3), and the pentaerythritol higher fatty acid ester (B4) is 0.1 or more and 1 or less.

3. The foamed styrene-based resin particle according to claim 1 or 2, wherein the amount of coating of the higher fatty acid metal salt (B1) per 100 parts by mass of the particle body (A) is 0.03 parts by mass or more and 0.4 parts by mass or less.

4. The foamed styrene resin particles according to claim 1 or 2, wherein the average particle diameter of the foamed styrene resin particles is 0.6 mm or more and 2 mm or less.

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