Bead foams and foam particles, and methods for producing the same.

Abstract

This bead foam body is characterized by comprising foam particles formed by foaming a base material resin composition containing a noncrystalline resin. The glass transition temperature Tg of the base material resin composition is 120°C or more; the low-temperature side half-value width of the loss tangent (tanδ) of the base material resin composition obtained by measuring the dynamic viscoelasticity is less than 9°C; and the flame retardancy at a 10 mm thickness as measured according to the UL-94 vertical method (20 mm vertical burn test) in the UL standards is V-2 or more.

Description

[Technical Field]

[0001] The present invention relates to bead foams, foam particles, and methods for producing the same. [Background technology]

[0002] Generally, in automotive components and electronic equipment components (especially devices that transmit and receive radio waves), there is a need for materials that are highly heat-resistant and flame-retardant, as they require resistance to high ambient temperatures and safety. Due to their excellent lightweight properties, heat insulation properties, and low dielectric properties, resin foams are being considered for a wide range of applications, including those in automotive peripheral components and electronic equipment peripheral components. Among foams, bead foams are attracting particular attention for their excellent shapeability (for example, Patent Document 1). Since foamed beads are generally molded by heating with steam, increasing the vapor pressure is necessary to heat them to high temperatures. Increasing the vapor pressure requires redesigning the pressure resistance of the mold and molding machine, so molding is generally done at a temperature slightly higher than the glass transition temperature (Tg) of the base resin composition. Therefore, if a base resin composition with a high glass transition temperature is used to improve heat resistance and flame retardancy, it becomes necessary to increase the vapor pressure in order to raise the molding temperature, and this can lead to problems such as the molding machine being unable to cope with the high vapor pressure, making molding difficult. Furthermore, it is generally known that foams tend to have poor flame retardancy because they contain resin and air. Methods to improve flame retardancy include adjusting the type of resin and adding flame retardants, but in particular, when flame retardants are added, the plasticizing effect of the flame retardant can worsen the heat resistance of the molded product. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2011-019057 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Therefore, the present invention aims to provide bead foams and foam particles that are flame-retardant, have high heat resistance and good moldability, as well as methods for producing the same. [Means for solving the problem]

[0005] The present invention is as follows: [1] From foamed particles obtained by foaming a base resin composition containing amorphous resin. It is a bead foam , The glass transition temperature Tg of the aforementioned base resin composition is 120°C or higher. The low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition obtained by dynamic viscoelasticity measurement is less than 9°C. The flame retardancy, measured according to the UL standard UL-94 vertical method (10mm vertical combustion test), is V-2 or higher at a thickness of 10mm. The difference between the glass transition temperature Tg of the base resin composition and the temperature Ts at which the dimensional change rate of the bead foam becomes 1% after heating for 24 hours (1% dimensional change temperature) is 40°C or less. The base resin composition contains a non-halogenated flame retardant having a melting point of 30°C or higher. A bead foam characterized by the following features. [2] The bead foam according to [1], wherein the base resin composition contains a flame retardant having a decomposition temperature of 200°C or higher. [3] The bead foam according to [1] or [2], wherein the melting point of the non-halogenated flame retardant is higher than the temperature at which the dimensional change rate becomes 1% when the bead foam is heated for 24 hours (1% dimensional change temperature) Ts-50℃. [4] These are foamed particles obtained by foaming a base resin composition containing an amorphous resin. The glass transition temperature Tg of the aforementioned base resin composition is 120°C or higher. The low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition obtained by dynamic viscoelasticity measurement is less than 9°C, the flame retardancy of the bead foam obtained by molding the foam particles, measured in accordance with the UL-94 vertical method (10 mm vertical combustion test) of the UL standard, is V-2 or higher at a thickness of 10 mm of the bead foam, the difference Tg-Ts between the glass transition temperature Tg of the base resin composition and the temperature (1% dimensional change temperature) Ts at which the dimensional change rate becomes 1% when the bead foam is heated for 24 hours is 40°C or lower, the base resin composition contains a non-halogenated flame retardant having a melting point of 30°C or higher The foam particles, characterized by the above. [5] The foam particles according to [4], wherein the heat shrinkage rate when heated at the glass transition temperature Tg+10°C of the base resin composition for 5 minutes is 25% or less. [6] A bead foam formed by molding the foam particles according to [4] or [5]. [7] A bead foaming step of foaming a base resin composition containing an amorphous resin, after the bead foaming step, a bead annealing step of heat-treating at a temperature of glass transition temperature Tg-30°C or higher and glass transition temperature Tg+30°C or lower of the base resin composition, The method for producing foam particles according to [4] or [5], characterized by the above. [8] A molding step of filling the mold with the foam particles obtained by foaming the base resin composition and heating to obtain a bead foam, after the molding step, a foam annealing step of heating the obtained bead foam at a temperature not higher than the glass transition temperature Tg of the base resin composition, The method for producing a bead foam according to any one of [1] to [3], characterized by the above. [9] including a molding step of filling the mold with the foam particles obtained by foaming the base resin composition and heating to obtain a bead foam, In the shaping process, the heating includes heating at a high temperature exceeding the glass transition temperature Tg of the base resin composition, or heating for a long time exceeding 40 seconds at a temperature equal to or higher than the glass transition temperature Tg of the base resin composition. The method for producing a bead foam according to any one of [1] to [3], characterized by the above.

Advantages of the Invention

[0006] According to the present invention, it is possible to provide a bead foam, expanded particles having flame retardancy, high heat resistance, and good moldability, and a method for producing the same.

Brief Description of the Drawings

[0007] [Figure 1] It is a diagram showing a loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition constituting the bead foams of the examples and comparative examples.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments for carrying out the present invention (hereinafter also referred to as "the present embodiments") will be described in detail. Note that the present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist thereof.

[0009] [Bead Foam] The bead foam of the present embodiment is made of a base resin composition containing an amorphous resin, the glass transition temperature obtained by dynamic viscoelasticity measurement of the base resin composition is 120°C or higher, the low-temperature side half-value width of the loss tangent (tanδ) peak of the base resin composition is less than 9°C, and the flame retardancy measured in accordance with the UL-94 vertical method (10 mm vertical combustion test) of the UL standard is V-2 or higher at a thickness of 10 mm. Bead foam is a foam composed of foamed particles and can be manufactured by the bead foaming method described below. Advantages of bead foam include good formability, the elimination of secondary processing of the foam by pre-shaping, reduced dust generation due to the absence of exposed cut surfaces, improved thermal insulation and mechanical strength due to its closed-cell structure, and ease of controlling cell diameter and distribution. On the other hand, since bead foam is generally foamed by heating with steam, it foams at a temperature relatively close to the glass transition temperature (Tg) of the base resin composition, unlike extrusion foaming which can be foamed at high temperatures. Therefore, it tends to retain residual strain and is prone to large dimensional changes. The bead foam of this embodiment may be obtained by foaming a base resin composition that includes an amorphous resin as the base resin and optionally further contains additives such as a flame retardant.

[0010] [Base resin composition] The base resin constituting the base resin composition preferably contains an amorphous resin, with the amorphous resin being the main component (i.e., when the total mass of resin components in the base resin composition is taken as 100% by mass, the amorphous resin accounts for 50% or more by mass). When the base resin contains an amorphous resin, it is easier to obtain a base resin composition with a small difference (Tg-Ts) between the glass transition temperature Tg of the base resin composition (described later) and the 1% dimensional change temperature (also called the heat resistance temperature) Ts of the bead foam, and a bead foam with high heat resistance tends to be obtained.

[0011] The content of the base resin is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on 100% by mass of the base resin composition. Furthermore, it is preferably 100% by mass or less, more preferably 98% by mass or less, and even more preferably 95% by mass or less.

[0012] (Amorphous resin) Amorphous resins are not particularly limited as long as they are amorphous resins, and examples include polyphenylene ether (PPE) resins such as polyphenylene ether (PPE) resin, polyphenylene ether resin / polystyrene resin alloy, polyphenylene ether resin / high-impact polystyrene resin alloy, polyphenylene ether resin / polystyrene resin / high-impact polystyrene resin alloy, and polyphenylene ether resin / polypropylene resin alloy; polystyrene resins such as polystyrene resin, rubber-reinforced polystyrene resin (high-impact polystyrene resin), and acrylonitrile-butadiene-styrene copolymer (ABS resin); and polycarbonate resins such as polycarbonate resin, polycarbonate resin / ABS resin alloy, and polycarbonate resin / polybutylene terephthalate resin alloy. In particular, from the viewpoint of heat resistance and flame retardancy, polyphenylene ether resins are preferred, and polyphenylene ether resins, polyphenylene ether resins / polystyrene resin alloys, polyphenylene ether resins / high-impact polystyrene resin alloys, or polyphenylene ether resins / polystyrene resins / high-impact polystyrene resin alloys are more preferred. Amorphous resins are preferred as the base resin composition of this embodiment because, compared to crystalline resins, they have no melting point, exhibit a gradual change in viscosity with respect to temperature, resulting in excellent foaming properties, and their processability and heat resistance can be easily adjusted by controlling the glass transition temperature (or heat deflection temperature, Vicat softening point).

[0013] (Polyphenylene ether-based resin) Examples of polyphenylene ether resins include, as mentioned above, polyphenylene ether resin, polyphenylene ether resin / polystyrene resin alloy, polyphenylene ether resin / high-impact polystyrene resin alloy, or polyphenylene ether resin / polystyrene resin / high-impact polystyrene resin alloy. These can be used individually or in combination of two or more.

[0014] Polyphenylene ether resins refer to polymers containing repeating units (structural units) represented by the following general formula (I). Examples include homopolymers consisting of repeating units represented by the following general formula (I), and copolymers containing repeating units represented by the following general formula (I). [ka] In general formula (I), R 1 , R 2 , R 3 and R 4 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a phenyl group, or a haloalkyl group or haloalkoxy group having at least two carbon atoms between the halogen atom and the benzene ring in general formula (I), without a third α-carbon atom. In general formula (I), n is an integer representing the degree of polymerization.

[0015] Specific examples of polyphenylene ether resins include poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,4-phenylene) ether, poly(2-methyl-6-propyl-1,4-phenylene) ether, poly(2,6-dipropyl-1,4-phenylene) ether, poly(2-ethyl-6-propyl-1,4-phenylene) ether, poly(2,6-dibutyl-1,4-phenylene) ether, poly(2,6-dilauryl-1,4-phenylene) ether, poly(2,6-diphenyl-1,4-diphenylene) ether, and poly(2,6-dimethoxy-1 Examples include, but are not limited to, ,4-phenylene) ether, poly(2,6-diethoxy-1,4-phenylene) ether, poly(2-methoxy-6-ethoxy-1,4-phenylene) ether, poly(2-ethyl-6-stearyloxy-1,4-phenylene) ether, poly(2,6-dichloro-1,4-phenylene) ether, poly(2-methyl-6-phenyl-1,4-phenylene) ether, poly(2,6-dibenzyl-1,4-phenylene) ether, poly(2-ethoxy-1,4-phenylene) ether, poly(2-chloro-1,4-phenylene) ether, poly(2,6-dibromo-1,4-phenylene) ether, etc. In particular, in general formula (I), R 1 and R 2 is an alkyl group having 1 to 4 carbon atoms, and R 3 and R 4 Preferably, the element is hydrogen or an alkyl group having 1 to 4 carbon atoms.

[0016] The above-mentioned polyphenylene ether resin is not particularly limited and can be produced by known methods. For example, it can be easily produced by oxidative polymerization of 2,6-xylenol using Hay's cuprous salt and amine complex as a catalyst, as described in U.S. Patent No. 3,306,874. Other methods include those described in U.S. Patent No. 3,306,875, U.S. Patent No. 3,257,357, U.S. Patent No. 3,257,358, Japanese Patent Publication No. 52-17880, Japanese Unexamined Patent Publication No. 50-51197, and Japanese Unexamined Patent Publication No. 63-152628.

[0017] Furthermore, in this embodiment, a modified polyphenylene ether resin can be used as the polyphenylene ether resin, in which some or all of the constituent units of the polyphenylene ether resin are modified with an unsaturated or saturated carboxylic acid or its derivative. Examples of the above-mentioned modified polyphenylene ether resins include those described in Japanese Patent Publication No. 2-276823 (US Patent No. 5159027, US Reissued Patent No. 35695), Japanese Patent Publication No. 63-108059 (US Patent No. 5214109, US Patent No. 5216089), Japanese Patent Publication No. 59-59724, and others. Modified polyphenylene ether resins are produced, for example, by melt-kneading and reacting a polyphenylene ether resin with an unsaturated or saturated carboxylic acid or its derivative in the presence or absence of a radical initiator. Alternatively, they are produced by dissolving a polyphenylene ether resin and an unsaturated or saturated carboxylic acid or its derivative in an organic solvent in the presence or absence of a radical initiator and reacting them in solution.

[0018] Examples of unsaturated carboxylic acids or their derivatives include maleic acid, fumaric acid, itaconic acid, halogenated maleic acid, cis-4-cyclohexene 1,2-dicarboxylic acid, endo-cis-bicyclo(2,2,1)-5-heptene-2,3-dicarboxylic acid, as well as acid anhydrides, esters, amides, and imides of these dicarboxylic acids, and also acrylic acid, methacrylic acid, as well as esters and amides of these monocarboxylic acids.

[0019] Furthermore, saturated carboxylic acids or their derivatives include, for example, compounds that undergo thermal decomposition at the reaction temperature used to produce modified polyphenylene ether resins, and can become derivatives of the modified polyphenylene ether resin. Specifically, examples include malic acid and citric acid.

[0020] The polyphenylene ether resin may consist solely of a polyphenylene ether resin in which the above-mentioned polyphenylene ether resin makes up 100% by mass, or it may be a polymer alloy as described above. In the case of a polymer alloy, the polyphenylene ether resin content is preferably 20 to 99% by mass, more preferably 25 to 95% by mass, and even more preferably 30 to 90% by mass in 100% by mass of the polymer alloy. Generally, the higher the proportion of polyphenylene ether resin, the better the heat resistance and flame retardancy, but the more moldability tends to deteriorate, requiring higher processing temperatures.

[0021] Examples of polystyrene resins that can be used in polyphenylene ether resins include homopolymers of styrene compounds, copolymers of two or more styrene compounds, and rubber-modified styrene resins (high-impact polystyrene resins) in which rubbery polymers are dispersed in particulate form within a matrix of polymers of styrene compounds. Examples of styrene compounds that yield these polymers include styrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, α-methylstyrene, ethylstyrene, α-methyl-p-methylstyrene, 2,4-dimethylstyrene, monochlorostyrene, and p-tert-butylstyrene.

[0022] When using the polymer alloy described above as the polyphenylene ether resin, the polystyrene resin contained in the polyphenylene ether resin may be a copolymer obtained by using two or more styrene compounds in combination or a high-impact polystyrene resin, but among these, polystyrene resin obtained by polymerization using styrene alone is preferred. Polystyrene resins having a stereoregular structure, such as atactic polystyrene and syndiotactic polystyrene, can be effectively used as the polyphenylene ether resin.

[0023] The weight-average molecular weight (Mw) of the polyphenylene ether resin is preferably between 20,000 and 60,000. The weight-average molecular weight (Mw) is determined by measuring the molecular weight of the resin using gel permeation chromatography (GPC), and then using a calibration curve (created using the peak molecular weight of standard polystyrene) derived from measurements of commercially available standard polystyrene.

[0024] The polyphenylene ether resin content is as follows, relative to 100% by mass of the base resin composition: The content is preferably 50-100% by mass, more preferably 60-99% by mass, and even more preferably 70-95% by mass. A higher content of polyphenylene ether resin tends to result in a higher glass transition temperature, leading to a bead foam with excellent heat resistance and flame retardancy, but this tends to worsen moldability as it requires a higher processing temperature.

[0025] (Polystyrene resin) Polystyrene resin refers to a homopolymer of styrene and styrene derivatives, or a copolymer in which styrene and styrene derivatives are the main components (components present in the polystyrene resin at a concentration of 50% by mass or more). Examples of styrene derivatives include o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, α-methylstyrene, β-methylstyrene, diphenylethylene, chlorostyrene, and bromostyrene.

[0026] Examples of polystyrene-based homopolymer resins include polystyrene, poly-α-methylstyrene, and polychlorostyrene. Examples of polystyrene-based copolymer resins include binary copolymers such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, styrene-maleimide copolymer, styrene-N-phenylmaleimide copolymer, styrene-N-alkylmaleimide copolymer, styrene-N-alkyl-substituted phenylmaleimide copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-n-alkyl acrylate copolymer, styrene-n-alkyl methacrylate copolymer, and ethyl vinylbenzene-divinylbenzene copolymer; terpolymers such as ABS and butadiene-acrylonitrile-α-methylbenzene copolymer; and graft copolymers such as styrene-grafted polyethylene, styrene-grafted ethylene-vinyl acetate copolymer, (styrene-acrylic acid) grafted polyethylene, and styrene-grafted polyamide. These can be used individually or in combination of two or more.

[0027] The polystyrene resin may be manufactured by any conventionally known manufacturing method.

[0028] (Polycarbonate resin) Examples of polycarbonate-based resins include, as mentioned above, polycarbonate resin, polycarbonate resin / ABS resin alloy, and polycarbonate resin / polybutylene terephthalate resin alloy. These can be used individually or in combination of two or more.

[0029] The polycarbonate resin may be bisphenol A type polycarbonate polymerized using bisphenol A, or various polycarbonates with high heat resistance or low water absorption polymerized using other divalent phenolic compounds. Other divalent phenolic compounds mentioned above include, for example, hydroquinone, 4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)ketone, bis(4-hydroxyphenyl)ether, and halogenated bisphenols such as 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane.

[0030] Furthermore, the polycarbonate resin may be linear polycarbonate, branched polycarbonate obtained by polymerizing trifunctional phenols, or copolymerized polycarbonate obtained by copolymerizing aliphatic dicarboxylic acid, aromatic dicarboxylic acid, or divalent aliphatic or alicyclic alcohol.

[0031] The polycarbonate resin may be manufactured by any conventionally known manufacturing method.

[0032] The base resin composition of this embodiment preferably contains a resin containing aromatic monomer units as the base resin. Including a resin containing aromatic monomer units tends to yield a bead foam with good flame retardancy. Examples of resins containing aromatic monomer units include aromatic polyamide resins, polycarbonate resins, polyethylene terefrate resins, polyimide resins, polyphenylene ether resins, and styrene resins. The mass percentage of aromatic monomer units in the above-mentioned base resin is preferably 20% by mass or more, more preferably 25 to 100% by mass, even more preferably 30 to 100% by mass, and even more preferably 50 to 100% by mass, based on 100% by mass of the base resin. This is because the base resin is easily carbonized during combustion, making it easier to suppress ignition and flame in the resin, and also suppresses the generation of flammable gases, thereby further improving its non-flammability. The mass percentage of aromatic monomer units can be calculated from the molecular structure of the constituent units if the molecular structure is known. Even when multiple resins are included, the same calculation can be performed for each resin and additive, and the mass percentage of aromatic monomer units in the entire base resin can be calculated by averaging according to the mass percentage of each resin and additive mixed. Furthermore, if the structure is unknown, aromatic monomer units can be estimated and calculated using NMR, IR, etc.

[0033] Furthermore, the bead foam of this embodiment may be used in electronic devices, but when used in devices that transmit and receive radio waves, for example, it may be required to reduce the relative permittivity and dielectric loss tangent. In this case, methods for reducing the relative permittivity and dielectric loss tangent of the base resin composition include selecting a base resin with low density of unfoamed resin, low polarity of unfoamed resin, and few polar groups at the end of the molecular chain. From this viewpoint, particularly suitable resins include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluororesins, polymer liquid crystal resins, and polyphenylene sulfide resins. Among these, polyolefin resins, polystyrene resins, and polyphenylene ether resins are preferred from the viewpoints of processability, cost, and flame retardancy. Furthermore, as will be described later, it is preferable that the base resin composition has low water absorption. Methods for reducing the water absorption rate of the base resin composition in a high-temperature and high-humidity environment include reducing the polarity of the base resin and reducing the polar groups at the ends of the molecular chain. From this viewpoint, suitable resins include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluororesins, polymer liquid crystal resins, and polyphenylene sulfide resins. Among these, polyolefin resins, polystyrene resins, and polyphenylene ether resins are preferred from the viewpoints of processability, cost, and flame retardancy.

[0034] (Additives) Examples of additives include flame retardants, flame retardant enhancers, heat stabilizers, antioxidants, antistatic agents, inorganic fillers, anti-dripping agents, ultraviolet absorbers, light absorbers, plasticizers, mold release agents, dyes and pigments, rubber components, resins other than the base resin mentioned above, and can be added within a range that does not impair the effects of the present invention.

[0035] The additive content is preferably 0 to 40 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 20 parts by mass, relative to 100 parts by mass of the base resin.

[0036] Here, the flame retardant is not particularly limited, but examples include organic flame retardants and inorganic flame retardants. Examples of organic flame retardants include halogen compounds such as bromine compounds, phosphorus compounds, and non-halogen compounds such as silicone compounds. Examples of inorganic flame retardants include metal hydroxides such as aluminum hydroxide and magnesium hydroxide, and antimony compounds such as antimony trioxide and antimony pentoxide. These can be used individually or in combination of two or more.

[0037] Among the above flame retardants, from an environmental standpoint, organic flame retardants, specifically non-halogenated flame retardants, are preferred, and phosphorus-based and silicone-based flame retardants are more preferred.

[0038] Phosphorus-based flame retardants can include those containing phosphorus or phosphorus compounds. Red phosphorus is an example of phosphorus. Examples of phosphorus compounds include phosphate esters, phosphazene compounds having a phosphorus-nitrogen bond in the main chain, trialkylphosphine oxides, and triphenylphosphine oxides. Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, dimethyl ethyl phosphate, methyl dibutyl phosphate, ethyl dipropyl phosphate, hydroxyphenyl diphenyl phosphate, resorcinol bis-diphenyl phosphate, and others. Other examples include phosphate ester compounds modified with various substituents, various condensation-type phosphate ester compounds, and phosphate ester compounds having a cyclic structure. Among these, phosphazene compounds, triphenyl phosphates, condensation-type phosphate ester compounds, and phosphate ester compounds having a cyclic structure are preferred from the viewpoint of heat resistance, flame retardancy, and foaming properties. These can be used individually or in combination of two or more.

[0039] Furthermore, (mono or poly)organosiloxanes can be used as silicone-based flame retardants. Examples of (mono or poly)organosiloxanes include monoorganosiloxanes such as dimethylsiloxane and phenylmethylsiloxane; polydimethylsiloxane and polyphenylmethylsiloxane obtained by polymerizing these; and organopolysiloxanes such as copolymers thereof. In the case of organopolysiloxanes, the bonding groups of the main chain and branched side chains are hydrogen, alkyl groups, and phenyl groups, preferably phenyl groups, methyl groups, ethyl groups, and propyl groups, but are not limited to these. Terminal bonding groups may be hydroxyl groups, alkoxy groups, alkyl groups, and phenyl groups. There are no particular restrictions on the form of the silicones, and any form such as oil, gum, varnish, powder, or pellet can be used. These can be used individually or in combination of two or more.

[0040] The flame retardant content may be within the range of the additive content, but is preferably 0 to 40 parts by mass, more preferably 1 to 30 parts by mass, and even more preferably 3 to 25 parts by mass, based on 100 parts by mass of the base resin. While a higher flame retardant content improves the flame retardancy of the bead foam, those with a plasticizing effect on the resin tend to lower the glass transition temperature of the base resin composition, leading to a decrease in heat resistance.

[0041] In bead foams containing amorphous resins, when using a resin with poor fluidity, such as polyphenylene ether resin, as part of the base resin composition, it is generally easier to improve processability (easier to process at lower temperatures) by using a flame retardant with a low melting point, but this tends to lower the heat resistance temperature Ts of the bead foam. The melting point of the flame retardant is not particularly limited, but is preferably 30°C or higher, more preferably 50°C or higher, and even more preferably 100°C or higher (or has no melting point). Furthermore, the melting point of the flame retardant is preferably higher than the heat resistance temperature Ts-50°C of the bead foam described later, more preferably Ts-40°C or higher, and even more preferably Ts-30°C or higher. When the melting point of the flame retardant is within the above range, the decrease in the glass transition temperature of the base resin composition due to the plasticizing effect when the flame retardant is added tends to be suppressed, and the low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition described later tends to be reduced, improving the heat resistance temperature of the bead foam and reducing the difference between the glass transition temperature of the base resin composition and the heat resistance temperature Ts of the bead foam.

[0042] The decomposition temperature of the flame retardant is not particularly limited, but is preferably 200°C or higher, more preferably 250°C or higher, and even more preferably 280°C or higher. From the viewpoint of improving manufacturing stability in the manufacturing process of the base resin composition, reducing the low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition, and enhancing flame retardancy, it is preferable that the decomposition temperature be within the above range. The decomposition temperature can be defined as the 5 wt% weight loss temperature, and can be measured, for example, by measuring weight loss using a differential thermal and thermogravimetric analyzer (TG-DTA).

[0043] Examples of rubber components include butadiene, isoprene, and 1,3-pentadiene, but are not limited to these. These are preferably dispersed in particulate form in a continuous phase made of polystyrene resin. As for the method of adding these rubber components, the rubber components themselves may be added, or resins such as styrene elastomers and styrene-butadiene copolymers may be used as rubber component sources. When rubber components are added, the content of the rubber components may be within the range of the additive content, but preferably 0.3 to 15 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the base resin. When the amount is 0.3 parts by mass or more, the resin has excellent flexibility and elongation, the foam cell film is less likely to break during foaming, and a foam with excellent moldability and mechanical strength is easily obtained.

[0044] In this embodiment, it is preferable to add more flame retardant to the resin composition in order to improve the flame retardancy of the foam, but increasing the amount of flame retardant adversely affects foamability. In such cases, a rubber component is suitably used to impart foamability to the base resin composition. In particular, the rubber component is important in bead foaming, in which the resin is foamed in a non-molten state by gradually raising the temperature from room temperature.

[0045] [Glass transition temperature of the base resin composition] The base resin composition of this embodiment has a glass transition temperature of 120°C or higher, preferably 125°C or higher, and more preferably 130°C or higher. When the glass transition temperature Tg is 120°C or higher, a bead foam with excellent heat resistance can be obtained. Furthermore, the glass transition temperature is preferably 230°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower. When the glass transition temperature is 230°C or lower, the moldable temperature during foaming of the bead foam does not become too high, and the bead foam tends to be easier to mold. The glass transition temperature of a base resin composition can be adjusted by mixing resins with different glass transition temperatures. For example, increasing the mixing ratio of a resin with a high glass transition temperature will raise the glass transition temperature of the base resin composition. The glass transition temperature of the base resin composition is the peak temperature of the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement, and can be measured by the method described in the examples below.

[0046] [Low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition] Regarding the heat resistance and moldability of bead foams, in the loss loss tangent (tanδ) obtained by dynamic viscoelasticity measurement of the base resin composition, for example, if the glass transition temperature (peak temperature of tanδ) is the same, a narrower peak width on the low-temperature side improves heat resistance because the temperature at which dimensional changes begin to occur in the resulting bead foam (dimensional change onset temperature) is higher, but the moldable temperature also increases, making molding more difficult. On the other hand, a wider peak width on the low-temperature side improves moldability because the temperature at which dimensional changes begin in the resulting bead foam is lower, but the heat resistance of the bead foam deteriorates because dimensional changes begin to occur at a lower temperature. Focusing on the above characteristics, the inventors have achieved improved heat resistance while maintaining good moldability, even in bead foams, which are difficult to improve by increasing the glass transition temperature of the base resin composition due to limitations in the rise of the molding temperature compared to other foam molding methods such as extrusion foam molding. This is achieved by controlling the low-temperature half-width of the loss tangent tanδ peak. The base resin composition of this embodiment has a low-temperature half-width (FWHM) of the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement of less than 9°C, preferably 8°C or less, and more preferably 7°C or less. When the low-temperature FWHM of the loss tangent (tanδ) peak is less than 9°C, the difference between the glass transition temperature of the base resin composition and the heat resistance temperature Ts of the bead foam described later becomes small, making it possible to obtain a bead foam with excellent heat resistance while maintaining good moldability. Furthermore, the lower limit of the low-temperature FWHM is not particularly limited, but is preferably 2°C or higher, more preferably 3°C or higher, and even more preferably 4°C or higher. When the low-temperature FWHM is 2°C or higher, the moldable temperature does not become too high, and the bead foam tends to have good moldability. The low-temperature half-width of the base resin composition can be determined by the method described in the examples below.

[0047] [Water absorption rate of base resin composition] The base resin composition of this embodiment preferably has a water absorption rate of 3.0% or less under high temperature and high humidity conditions, more preferably 2.2% or less, and even more preferably 2.0% or less. When the water absorption rate of the base resin composition is 3.0% or less, dimensional changes due to moisture absorption tend to be suppressed. The water absorption rate of the base resin composition in a high-temperature and high-humidity environment is the water absorption rate measured at a temperature of 60°C and a relative humidity of 85%, and can be specifically measured by the method described in the examples below.

[0048] [Flame retardancy of foamed beads] The foamed beads of this embodiment have a flame retardancy of V-2 or higher at a thickness of 10 mm, as measured in accordance with the UL standard UL-94 vertical method (10 mm vertical combustion test), preferably V-1 or higher, and more preferably V-0. The flame retardancy of the bead foam can be evaluated by the method described in the examples below.

[0049] [Temperature Ts of 1% dimensional change of bead foam] In this embodiment, the bead foam preferably has a temperature Ts at which the dimensional change rate becomes 1% after 24 hours of heating (referred to as the 1% dimensional change temperature or heat resistance temperature) of 80 to 200°C, more preferably 100 to 180°C, and even more preferably 110 to 150°C. When the 1% dimensional change temperature Ts is within the above range, it tends to be possible to obtain a bead foam with excellent heat resistance while maintaining good moldability. Generally, Ts is lower than the glass transition temperature (Tg) of the base resin composition. Furthermore, in this embodiment, the difference (Tg-Ts) between the glass transition temperature (Tg) of the base resin composition constituting the bead foam and the 1% dimensional change temperature (Ts) of the bead foam is preferably 40°C or less, more preferably 38°C or less, and even more preferably 35°C or less. When Tg-Ts is 40°C or less, the low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition is narrow, and the moldable temperature and the 1% dimensional change temperature (Ts) of the bead foam become closer (the dimensional change onset temperature becomes higher), so it tends to be possible to obtain a bead foam with high heat resistance while maintaining moldability. Also, Tg-Ts is preferably 10°C or more, more preferably 15°C or more, and even more preferably 20°C or more. When Tg-Ts is 10°C or more, molding becomes possible from a lower temperature than the glass transition temperature (Tg), so it tends to be easier to mold the bead foam.

[0050] Methods for adjusting the Ts of bead foam include, for example, adjusting the Tg of the base resin composition and removing residual stress from the foam particles and bead foam. The value of Ts can generally be designed by the Tg of the base resin composition, but even when using a base resin composition with the same Tg, it is possible to further increase Ts by reducing the residual stress remaining in the foam particles and bead foam. In order to reduce the residual stress of foam particles and bead foam, it is necessary to leave them in an environment with a sufficiently high temperature for a sufficient amount of time. For example, this can be achieved by increasing the heating time at a sufficiently high heating temperature when foaming the base resin composition (such as applying the bead annealing process described later), increasing the heating temperature or extending the heating time in the molding process during the production of bead foam, or heat-treating the bead foam after the molding process (such as applying the foam annealing process described later).

[0051] [Method for manufacturing foam beads] The bead foam of this embodiment is manufactured by the bead foaming method (in-mold foaming method). The bead foaming method (in-mold foaming method) is a method for obtaining a foam by filling a mold with foamed particles, which are made by foaming a base resin composition, and heating them with steam or the like to expand the foamed particles and simultaneously heat-fuse the foamed particles together. The bead foaming method involves creating a mold of the desired shape and filling it with foam particles, making it easier to form foams into finer and more complex shapes. Furthermore, the bead foaming method makes it easier to increase the foaming ratio of the foam, and the resulting foam tends to exhibit flexibility in addition to thermal insulation properties.

[0052] The blowing agent is not particularly limited, and commonly used gases can be used. Examples include inorganic gases such as air, carbon dioxide, nitrogen, oxygen, ammonia, hydrogen, argon, helium, and neon; fluorocarbons such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane (R22), tetrachlorodifluoroethane (R112), dichlorofluoroethane (R141b), chlorodifluoroethane (R142b), difluoroethane (R152a), HFC-245fa, HFC-236ea, HFC-245ca, and HFC-225ca; saturated hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and neopentane; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, and flu. Examples include ethers such as fural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; ketones such as dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, and ethyl n-butyl ketone; alcohols such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, and t-butyl alcohol; carboxylic acid esters such as methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl propionate, and ethyl propionate; and chlorinated hydrocarbons such as methyl chloride and ethyl chloride. These can be used individually or in combination of two or more.

[0053] From the viewpoint of flame retardancy, it is preferable that the blowing agent is non-flammable and has little or no combustion-supporting properties, and from the viewpoint of gas safety, inorganic gases are more preferable. Furthermore, inorganic gases are less soluble in resin than organic gases such as hydrocarbons, and the gas escapes easily from the resin after the foaming or molding process, which has the advantage of providing better dimensional stability of the foam over time after molding. In addition, when inorganic gases are used, plasticization of the resin due to residual gas is less likely to occur, and there is an advantage that excellent heat resistance can be easily achieved at an earlier stage without going through processes such as maturation. Among inorganic gases, carbon dioxide is preferred from the viewpoint of solubility in resin and ease of handling. Furthermore, hydrocarbon-based organic gases are generally highly flammable, and if they remain in the foam, the flame retardancy tends to deteriorate.

[0054] Foamed particles used in the bead foaming method can be obtained by impregnating a base resin composition with a foaming agent to generate foam (this process is called the "bead foaming process"). Specifically, for example, a method can be used in accordance with the method described in Example 1 of Japanese Patent Application Publication No. 4-372630, in which a base resin composition (pellet form, bead form, etc.) is placed in a pressure vessel, the gas in the vessel is replaced with dry air, a foaming agent (gas) is injected under pressure to impregnate the base resin composition with the foaming agent (gas), the pressure is released and the base resin composition pellets are transferred from the pressure vessel to a foaming furnace, and the base resin composition pellets are heated with pressurized steam while stirring blades are rotated in the foaming furnace to generate foamed particles. The conditions for impregnating the base resin composition with a foaming agent (gas) are not particularly limited, but from the viewpoint of more efficiently impregnating the base resin composition with the foaming agent (gas), it is preferable that the impregnation pressure is 0.3 to 30 MPa, the impregnation temperature is -20 to 100°C, and the impregnation time is 10 minutes to 96 hours. Furthermore, from the viewpoint of easily obtaining the desired magnification and improving the appearance, it is preferable that the maximum vapor pressure of the pressurized steam in the foaming furnace be 30 to 700 kPa·G. In the above method for producing foamed particles, the time from the completion of depressurization (release of impregnation pressure) in the pressure vessel to the start of heating with pressurized steam in the foaming furnace is preferably less than 600 seconds, more preferably within 300 seconds, even more preferably within 120 seconds, and particularly preferably within 60 seconds. If this time is within the above range, it is possible to suppress the uneven diffusion of the gas impregnated into the base resin composition, thereby making the bubble diameter uniform and preventing an increase in the bubble diameter.

[0055] The method for forming a foam using foam particles is not particularly limited, but for example, one method involves filling the cavity of a molding die with foam particles, heating to cause expansion and thermal fusion of the foam particles, and then cooling to solidify the product and form it (this process is also called the "forming process"). The method for filling the foam particles is not particularly limited, and known methods can be used.

[0056] It is preferable to apply a gas pressurization treatment to the foam particles before filling them into the cavity of the molding die. By applying a constant gas pressure to the bubbles of the foam particles, the foam particles constituting the resulting foam can be firmly fused together, improving the rigidity and appearance of the molded product. The gas used for the pressurization treatment is not particularly limited, but air and inorganic gases are preferred from the viewpoint of ease of handling and economy. The method of pressurization treatment is not particularly limited, but examples include filling the foam particles into a pressurized container, introducing pressurized gas, and supplying gas to the pressurized container by increasing the pressure to a maximum pressure of 0.1 to 20 MPa over 10 minutes to 96 hours.

[0057] Heating methods for molding foam particles include heating with a heat transfer medium such as steam, heating with a heater such as an IR heater, and heating with microwaves. When heating with a heat transfer medium, a general-purpose heat transfer medium is suitable, and steam is preferred from the viewpoint of efficiently heating the resin. A method for molding bead foam using steam (steam foam molding) generally involves using a mold with steam vents and may include steps such as replacing the air inside the mold and between the foam particles with steam, known as one-sided heating, introducing steam from both sides of the mold to sufficiently heat the foam particles and fuse them together, known as double-sided heating, and a cooling step of spraying water to cool the heated product. In particular, since the double-sided heating step tends to generate the highest temperatures, the residual stress in the bead foam can be controlled by controlling the temperature and time of the double-sided heating step.

[0058] Higher heating temperatures for foam particles tend to cause them to fuse together more easily, reducing residual stress in the bead foam and improving moldability and heat resistance. However, excessively high heating temperatures tend to cause shrinkage and warping of the bead foam. Similarly, longer heating times also tend to improve moldability and heat resistance by causing the foam particles to fuse together more easily and reducing residual stress in the bead foam. However, excessively long heating times can cause shrinkage and warping of the bead foam, worsen the cycle time, and degrade moldability. From the above viewpoint, the heating temperature of the foamed particles in the molding process is preferably Tg-30°C or higher, may be Tg-20°C or higher, may be Tg-10°C or higher, may be Tg or higher, or may be greater than Tg. Furthermore, the heating temperature of the foamed particles in the molding process is preferably Tg+50°C or lower, may be Tg+30°C or lower, or may be Tg+20°C or lower. Furthermore, from the above viewpoint, the heating time of the foamed particles in the molding process is preferably 10 seconds or more, may be 20 seconds or more, may be 40 seconds or more, and may be greater than 40 seconds. Also, the heating time of the foamed particles in the molding process is preferably 180 seconds or less, may be 120 seconds or less, and may be 90 seconds or less. For example, the molding process may include heating at a temperature above Tg, or heating at or above Tg for a long period of time exceeding 40 seconds.

[0059] The expansion ratio of the bead foam is preferably 1.5 cm 3 / g or more, more preferably 2.0 cm 3 / g or more, still more preferably 2.5 cm 3 / g or more. Also, the expansion ratio of the bead foam is preferably 50 cm 3 / g or less, more preferably 30 cm 3 / g or less, still more preferably 20 cm 3 / g or less, from the viewpoints of improving mechanical strength and flame retardancy.

[0060] [Foam Annealing Process] After forming the bead foam (after the forming process), by further adding a foam annealing process for the formed bead foam, the residual stress of the bead foam can be reduced, and the above-mentioned 1% dimensional change temperature Ts can be increased. As the foam annealing process, the higher the heating temperature and the longer the heating time, the higher the effect tends to be. However, if the heating temperature is too high or the heating time is too long, large dimensional changes will occur, resulting in deterioration of dimensional accuracy and warpage. Therefore, the heating temperature in the foam annealing process is preferably not higher than the Tg of the base resin composition, more preferably not lower than Tg - 70°C and not higher than Tg, and still more preferably not lower than Tg - 50°C and not higher than Tg - 10°C. Also, the heating time in the foam annealing process may be within 1 month, preferably 1 hour or more and within 1 week, more preferably 1 hour or more and within 3 days.

[0061] [Expanded Particles] The expanded particles of the present embodiment are expanded particles obtained by expanding a base resin composition containing an amorphous resin. The glass transition temperature Tg of the base resin composition is 120°C or higher, the low-temperature side half-value width of the loss tangent (tanδ) peak of the base resin composition obtained by dynamic viscoelasticity measurement is less than 9°C, and the flame retardancy of the bead foam obtained by molding the expanded particles, measured in accordance with the UL-94 vertical method (10 mm vertical combustion test) of the UL standard, is V-2 or higher at a bead foam thickness of 10 mm. The foamed particles of this embodiment may be obtained by foaming a base resin composition that includes an amorphous resin as the base resin and optionally further contains additives such as a flame retardant. The same base resin composition as described above can be used as the base resin composition. The foamed particles of this embodiment can be produced, for example, by a manufacturing method described later, which involves foaming a base resin composition.

[0062] The foamed particles described above preferably have a heat shrinkage rate of 25% or less, more preferably 20% or less, and even more preferably 18% or less, when heated at the glass transition temperature Tg + 10°C of the base resin composition for 5 minutes, from the viewpoint of excellent dimensional stability after long-term high-temperature treatment. The above heat shrinkage rate can be adjusted, for example, by the conditions of the bead annealing process described later (e.g., the type of heating medium used, heating temperature, heating time, pressure, etc.). Residual strain occurs in the foamed particles during the manufacturing process. If this residual strain remains in the bead foam obtained by molding these foamed particles, the heat resistance deteriorates because the aforementioned 1% dimensional change temperature Ts becomes lower, even if the bead foam uses the same base resin composition. Therefore, reducing the residual stress remaining in the foamed particles during the manufacturing process tends to improve the heat resistance of the molded bead foam. Furthermore, foamed particles with low residual stress tend to expand easily when heated during the molding process of the bead foam, resulting in superior appearance and moldability. The above heat shrinkage rate can be measured specifically by the method described in the examples below.

[0063] [Method for producing foamed particles] The method for producing foamed particles in this embodiment includes a bead foaming step in which a base resin composition containing an amorphous resin is foamed.

[0064] [Bead foaming process] In the bead foaming process, for example, as described in the [Method for Manufacturing Bead Foam] above, a foaming agent is impregnated into the base resin composition, and then foaming is generated by heating, thereby obtaining foamed particles.

[0065] Methods for incorporating a foaming agent into a base resin composition can be generally applied. Examples include methods using an aqueous medium such as a suspension system (suspension impregnation), methods using a thermal decomposition type foaming agent such as sodium bicarbonate (foaming agent decomposition method), methods in which a gas is brought into contact with the base resin composition in a liquid phase state under an atmosphere of pressure above critical pressure (liquid phase impregnation), and methods in which a gas is brought into contact with the base resin composition in a gas phase state under a high-pressure atmosphere below critical pressure (gas phase impregnation). Among these methods, the method of impregnating the gas phase under a high-pressure atmosphere below critical pressure is particularly preferred. Compared to suspension impregnation, which is performed under high-temperature conditions, gas-phase impregnation offers better gas solubility in the resin, making it easier to achieve a higher foaming agent content. Therefore, it is easier to achieve a high foaming ratio and uniform bubble size. The foaming agent decomposition method is performed under high-temperature conditions, and not all of the added thermally decomposed foaming agent turns into gas, resulting in relatively less gas generation. Therefore, gas-phase impregnation has the advantage of allowing for a higher foaming agent content. Furthermore, compared to liquid-phase impregnation, gas-phase impregnation allows for more compact equipment such as pressure-resistant and cooling systems, resulting in lower equipment costs.

[0066] The gas-phase impregnation conditions are not particularly limited, but the ambient pressure is preferably 0.5 to 6.0 MPa, and more preferably 1.0 to 5.0 MPa. The ambient temperature is preferably 5 to 30°C, and more preferably 7 to 15°C. The impregnation time is preferably 0.5 to 48 hours, and more preferably 1 to 24 hours. When the ambient pressure, ambient temperature, and impregnation time are within the above ranges, gas dissolution into the base resin composition proceeds more efficiently. In particular, if the ambient temperature is low, the amount of impregnation increases but the impregnation rate slows down, and if the ambient temperature is high, the amount of impregnation decreases but the impregnation rate tends to speed up. Therefore, it is preferable to set the ambient temperature as described above to efficiently promote gas dissolution into the base resin composition.

[0067] The amount of foaming agent impregnated is preferably 3 to 13% by mass relative to the resin contained in the base resin composition, and more preferably 3.5 to 10% by mass. When the impregnation amount of a foaming agent (e.g., carbon dioxide) is 3% by mass or more, it becomes easier to achieve a higher foaming ratio, and the variation in bubble size is reduced, making it easier to suppress variations in the foaming ratio. Furthermore, when it is 13% by mass or less, the bubble size becomes appropriate, making it easier to suppress the decrease in the percentage of closed cells due to over-foaming.

[0068] The method for foaming the base resin composition in the bead foaming process is not particularly limited, but examples include a method of rapidly releasing the resin from high-pressure conditions to a low-pressure atmosphere to expand the foaming agent (e.g., gas) dissolved in the resin, or a method of heating the resin with pressurized steam or hot air to expand the foaming agent (e.g., gas) dissolved in the resin. Among these, the method of heating to foam is particularly preferred. This is because, compared to the method of rapidly releasing the resin from high-pressure conditions to a low-pressure atmosphere, the bubble size inside the resin tends to become more uniform. It also has the advantage of making it easier to control the foaming ratio, especially the low foaming ratio. Furthermore, when the pressure is suddenly released from high-pressure conditions to a low-pressure atmosphere, foaming begins simultaneously from all points, which has the disadvantage of making it difficult to form a skin layer. On the other hand, with heat foaming, the foaming gas dissipates from the surface of the base resin composition while the resin is heated to the foaming start temperature, making it easier to form a skin layer. In addition, there is the advantage that the thickness of the skin layer can be adjusted by adjusting the heating rate and heating temperature, and the faster the heating rate and the higher the heating temperature, the thinner the skin layer tends to be.

[0069] In the bead foaming process, there are no particular restrictions on the heat source for heating and foaming, such as steam, hot air, or heaters. However, from the viewpoint of shortening the foaming time by taking advantage of its high thermal conductivity, heat treatment using steam (preferably pressurized steam) is preferred. Generally, residual stress is generated inside the beads after foaming, which tends to increase the heat shrinkage rate of the foamed particles. However, by providing the bead annealing process described later, the residual stress can be reduced.

[0070] The foaming temperature in the bead foaming process is preferably above the glass transition temperature Tg -25°C of the base resin composition, and more preferably above Tg -20°C. Furthermore, the foaming temperature is preferably below the glass transition temperature Tg +30°C of the base resin composition, and more preferably below Tg +20°C. By foaming at the above foaming temperatures, the base resin composition becomes more easily foamed and expanded. In the bead foaming process, from the viewpoint of efficiently obtaining foamed particles with the desired bulk ratio, and from the viewpoint of easily reducing the residual stress of the foamed particles by heating and shrinking them in the bead annealing process after increasing the foaming ratio to a bulk ratio greater than or equal to the desired foamed particle size when carrying out the bead annealing process described later, the heating temperature is preferably between the glass transition temperature Tg -30°C and the glass transition temperature Tg +30°C of the base resin composition, more preferably between the glass transition temperature Tg -30°C and the glass transition temperature Tg +10°C of the base resin composition, even more preferably between the glass transition temperature Tg -20°C and the glass transition temperature Tg +5°C of the base resin composition, and even more preferably between the glass transition temperature Tg -10°C and the glass transition temperature Tg of the base resin composition.

[0071] The foaming time in the bead foaming process is not particularly limited as it depends on the foaming temperature, but it is generally preferably 5 to 120 seconds, more preferably 10 to 60 seconds, and even more preferably 15 to 45 seconds. The glass transition temperature of the base resin composition can be determined by the method described in the examples below.

[0072] When foaming foamed particles to a desired foaming ratio, the foaming may be performed in a single stage, or in multiple stages such as secondary and tertiary foaming. When foaming in multiple stages, it is preferable to include a bead annealing process, as described later, after each stage. Furthermore, it is preferable to apply pressure treatment with an inorganic gas or the like to the preliminary beads (beads that have not undergone the final foaming stage) before foaming in each stage. In the case of multi-stage foaming, the conditions for the bead annealing process after each stage may be the same or different. Also, the gas used before each stage may be the same or different, but it is preferable to use the same gas. In this specification, the bead foaming process refers to the process in which the bulk density of the base resin composition gradually increases after foaming begins, and includes the period up to immediately before the transition to a state in which the bulk density does not change or gradually decreases. In this invention, the bead foaming process is defined as a process with a bulking ratio of 0.1 cm per second. 3 This refers to a process that increases the weight by more than / g.

[0073] <Foaming agent> As the foaming agent mentioned above, commonly used gases can be used. Examples include inorganic gases such as air, carbon dioxide, nitrogen, oxygen, ammonia, hydrogen, argon, helium, and neon; fluorocarbons such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane (R22), tetrachlorodifluoroethane (R112), dichlorofluoroethane (R141b), chlorodifluoroethane (R142b), difluoroethane (R152a), HFC-245fa, HFC-236ea, HFC-245ca, and HFC-225ca; saturated hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and neopentane; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, and flu. Examples include ethers such as fural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; ketones such as dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, and ethyl n-butyl ketone; alcohols such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, and t-butyl alcohol; carboxylic acid esters such as methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl propionate, and ethyl propionate; and chlorinated hydrocarbons such as methyl chloride and ethyl chloride. These can be used individually or in combination of two or more.

[0074] As the foaming agent, inorganic gases are preferred from the viewpoint of maintaining moldability and excellent flame retardancy. Furthermore, inorganic gases are less soluble in resin than organic gases such as hydrocarbons, and the gas escapes easily from the resin after the bead foaming process or the molding process of the bead foam, which has the advantage of providing better dimensional stability of the foam over time after molding. In addition, when inorganic gases are used, plasticization of the resin due to residual gas is less likely to occur, and there is also the advantage that excellent heat resistance can be achieved at an earlier stage after molding. Among inorganic gases, carbon dioxide is preferred from the viewpoint of solubility in resin and ease of handling.

[0075] [Bead annealing process] The foamed particles obtained in the above bead foaming process may be further heat-treated in a bead annealing process. The bead annealing process described above may be performed immediately after the bead foaming process, or it may be performed after the bead foaming process with a time gap in between. The bead annealing process described above is intended to remove residual stress inside the foamed particles by heat-treating the foamed particles after foaming is complete, and is a different process from the foaming process itself. The bead annealing process described above refers to the process that includes both the bead foaming process and the bead annealing process, but with the portion corresponding to the bead foaming process removed. In the bead annealing process described above, the rate of change in the bulk ratio of the foamed particles per second is set to -0.5 to -0.001 cm from the viewpoint of appropriately reducing residual stress. 3 It is preferable that the value is / g, and -0.2 to -0.005 cm 3 It is more preferable that the value is / g, and -0.08 to -0.01 cm 3 It is even more preferable that it be / g.

[0076] Examples of the above heat treatments include heating with steam (preferably pressurized steam), heating with hot air, and heating with a heater. Among these, heat treatment using steam is preferred from the viewpoint of good thermal conductivity and the ability to anneal in a short time.

[0077] The temperature for the heat treatment described above is between the glass transition temperature Tg -30°C and Tg +30°C of the base resin composition. From the viewpoint of having excellent dimensional change after long-term high-temperature treatment and even better expansion capacity, it is preferably between the glass transition temperature Tg -25°C and Tg +25°C, and more preferably between the glass transition temperature Tg -20°C and Tg +20°C. The above heat treatment may be performed at a constant temperature or at a variable temperature. If the temperature is varied, it is preferable to vary it within the above range.

[0078] The duration of the above heat treatment is preferably 10 to 600 seconds, more preferably 20 to 300 seconds, and even more preferably 30 to 120 seconds, from the viewpoint of excellent dimensional change after long-term high-temperature treatment and even better expansion capacity.

[0079] The temperature of the steam used in the above heat treatment is preferably between Tg -30°C and Tg +30°C, more preferably between Tg -25°C and Tg +10°C, and even more preferably between Tg -20°C and Tg +5°C. The temperature of the hot air used in the above heat treatment is preferably between Tg -30°C and Tg +30°C, more preferably between Tg -20°C and Tg +20°C, and even more preferably between Tg -10°C and Tg +10°C. The temperatures of the steam and hot air mentioned above may be constant or varied. When varying the temperatures, it is preferable to vary them within the above range.

[0080] When the above bead annealing process is carried out using pressurized steam, the heat treatment temperature is preferably lower than the foaming temperature in the above bead foaming process, more preferably 2°C or more lower, and even more preferably 4°C or more lower, from the viewpoint of having excellent dimensional change after long-term high-temperature treatment and even better expansion capacity. When the bead annealing process is carried out using pressurized steam, the heat treatment temperature is preferably kept at a constant temperature, gradually increased from a low temperature to a high temperature, or a combination of these. In particular, a temperature program that gradually increases the temperature during the bead annealing process is preferred because it can be expected to shorten the process time. If the heat treatment temperature in the bead annealing process is 20°C or more lower than the foaming temperature in the bead foaming process, it is undesirable because it will require an extremely long time for annealing. The heat treatment temperature in the bead annealing process described above may be lower than the foaming temperature at the end of the bead foaming process described above. Furthermore, the heat treatment temperature in the bead annealing process described above may be lower than the maximum foaming temperature of the bead foaming process described above.

[0081] The bulk ratio of the foamed particles obtained in the bead foaming process may decrease after the bead annealing process. The ratio of the bulk ratio of the foamed particles after the bead annealing process to the bulk ratio of the foamed particles before the bead annealing process (100%) is preferably 30-99%, and more preferably 40-95%. During the bead annealing process described above, the bulk ratio of the foamed particles may gradually decrease. The bead annealing process may be a process in which the bulk ratio of the foamed particles remains the same or decreases (preferably decreases) during the process. The bulk density of the foamed particles can be measured by the method described in the examples below.

[0082] If the method for producing foamed particles in this embodiment includes a bead annealing step, the bulk ratio of the foamed particles decreases after the bead annealing step. Therefore, taking into account the decrease in bulk ratio in the bead annealing step, it is preferable to continue foaming in the bead foaming step until the bulk ratio of the foamed particles is higher than the planned bulk ratio. For example, a step may be provided to measure in advance the percentage of bulk ratio reduction in the bead annealing step and determine the planned bulk ratio after the bead foaming step.

[0083] In the method for producing foamed particles according to this embodiment, the bead foaming step and the bead annealing step may be performed in different equipment or in the same equipment. In particular, it is preferable to perform the steps in the same equipment, as this simplifies the process and makes it easier to control the bulk ratio of the resulting foamed particles by continuously annealing the beads without removing the foamed particles from the equipment. Furthermore, when performing multi-stage foaming, it is preferable to carry out all stages of foaming and annealing in the same equipment.

[0084] A bead foam can be obtained by further molding the foam particles of this embodiment in a molding process. For the molding process, the same method as the molding process in the above-described [Method for Manufacturing Bead Foam] can be used. The foam particles obtained by the above-described method for manufacturing foam particles may be used in the molding process continuously or at intervals. [Examples]

[0085] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way to the following examples.

[0086] The measurement and evaluation methods used in the examples and comparative examples are described below.

[0087] [Foaming ratio of foam] Based on the manufacturing methods for each foam, samples were prepared with dimensions of approximately 30 mm square and 10 mm thickness. The mass W (g) of the sample was measured, and the volume V (cm³) of the sample was calculated. 3 The value V / W obtained by dividing ) by the mass W is the expansion ratio (cm 3 ( / g)

[0088] [Flame retardant] The foam was tested in accordance with the UL-94 vertical method (10mm vertical combustion test) of the US UL standard to evaluate its flame retardancy. The details of the measurement method are shown below. Five test specimens, each 125 mm long, 13 mm wide, and 10 mm thick, were prepared and used based on the methods described in the examples and comparative examples below. The test specimens were mounted vertically on clamps, and two 10-second indirect flame tests were performed using a 10 mm flame. The combustion behavior was then evaluated to determine whether the specimens were V-0, V-1, or V-2. V-0: In both the first and second trials, the duration of flamed combustion was within 10 seconds. Furthermore, the sum of the duration of flamed combustion and flameless combustion in the second trial was within 30 seconds. Additionally, the sum of the flamed combustion times of the five test specimens was within 50 seconds. No samples burned up to the position of the fixing clamp, and there was no cotton ignition by burning debris. V-1: In both the first and second trials, the duration of flamed combustion was within 30 seconds. Furthermore, the sum of the duration of flamed and flameless combustion in the second trial was within 60 seconds. Additionally, the sum of the flamed combustion times of the five test specimens was within 250 seconds. No samples burned up to the position of the fixing clamp, and there was no cotton ignition by burning debris. V-2: In both the first and second trials, the duration of flamed combustion was within 30 seconds. Furthermore, the sum of the duration of flamed and flameless combustion in the second trial was within 60 seconds. Additionally, the sum of the duration of flamed combustion for all five test specimens was within 250 seconds. No samples burned up to the position of the fixing clamp. Cotton ignition occurred due to falling combustion material. Any item that does not fall under any of the above categories V-0, V-1, or V-2 was marked as non-compliant (×).

[0089] [Dynamic viscoelasticity measurement of base resin compositions] Dynamic viscoelasticity measurements were performed on the base resin composition using a rheometer (Anton Paar "Physica MCR301") under the following conditions to determine the low-temperature half-width (°C) of the loss tangent (tanδ). The peak temperature (°C) of the loss tangent (tanδ) was defined as the glass transition temperature (Tg) of the base resin composition. Furthermore, the low-temperature half-width of tanδ was defined as the temperature at which the value of tanδ is half of tanδ(MAX), where tanδ(MAX) is the maximum value of tanδ during the glass transition, and Tg is lower than Tg (the temperature at which tanδ(MAX) occurs). 低1 / 2 ) calculate (Tg-T 低1 / 2 The value of ) was used. Measuring jig: SRF10 Measurement mode: vibration φ, γ Strain: Swing angle γ = 0.015% Frequency: 1 Hz Measurement temperature: 20°C to 200°C Temperature rising rate: 2°C / min Normal force: -0.3 N Measurement point: 180 Time unit: s

[0090] [1% dimensional change temperature Ts] Referring to the methods described in the examples and comparative examples below, a test piece of a foam with a size of 150 × 150 mm × thickness 5 mm was prepared. This test piece was dried in a drying oven at 60°C (Satake Safe Bend Dryer N50 - S5) for 24 hours to remove the moisture contained in the test piece. For this test piece, referring to the dimensional stability test (Method B) at high temperature described in JIS K6767, three straight lines each with a length of 100 mm were marked in parallel to each other in the vertical and horizontal directions in the shape of a "field" character at 50 mm intervals in the central part of the test piece. Then, it was placed in a drying oven (Satake Safe Bend Dryer N50 - S5) and heated at a predetermined temperature for 24 hours. For the test piece before and after the heating test, the lengths of the three vertical and three horizontal lines marked were measured respectively, and the average value was obtained. Then, the dimensional change rate was calculated according to the following formula. The same test was carried out while changing the heating temperature, and the temperature at which the dimensional change rate exceeded 1% was defined as the 1% dimensional change temperature Ts (°C). Dimensional change rate (%) = {(L2 - L1) / L1} × 100 (In the formula, L1 represents the average value of the dimension [mm] of the line before the heating test, and L2 represents the average value of the dimension [mm] of the line after the heating test.)

[0091] [Water absorption rate of the base resin composition] The water absorption rate of the base resin composition was measured according to the following method. First, using the base resin composition, a sheet with a thickness of 1.0 mm × length of 100 mm × width of 100 mm was prepared by the hot pressing method. Next, the sheet obtained above was placed in a 60°C oven for one day to dry, and its mass after drying was measured. Then, it was allowed to absorb water for 8 hours in a constant temperature and humidity chamber adjusted to 60°C and 85% relative humidity. After the water absorption was complete, any water droplets around the sheet were quickly wiped off, and its mass was measured. The water absorption rate (mass %) was calculated using the following formula. Water absorption rate (mass %) = 100 × {mass after water absorption - mass after drying (before water absorption)} / mass after drying (before water absorption)

[0092] [Heat shrinkage rate of foamed particles] Foam particles 20cm 3 The samples were placed on a metal tray without overlapping and placed in an oven set to the glass transition temperature Tg + 10°C of the base resin composition. After 5 minutes, they were removed. After cooling to room temperature, the bulk ratio after heating was determined, and the thermal shrinkage rate (%) was calculated using the following formula. (1-Xb / Xa)×100(%) Xa: Volume ratio before heating (cm) 3 / g) Xb: Volume increase after heating (cm) 3 / g)

[0093] (Example 1) A base resin composition pellet was prepared by extruding a mixture of 90% by mass of modified polyphenylene ether resin ("SX-101" manufactured by Asahi Kasei Corporation) and 10% by mass of a phosphazene-based flame retardant ("Rabitol FP-110" manufactured by Fushimi Pharmaceutical Co., Ltd. (decomposition temperature: 300°C or higher)) as a non-halogenated flame retardant after heating, melting, and kneading in an extruder. Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, a base resin composition pellet was placed in a pressure vessel, the gas in the vessel was replaced with dry air, and carbon dioxide (gas) was injected as a blowing agent. Under conditions of a pressure of 3.0 MPa and a temperature of 10°C, the base resin composition pellet was impregnated with carbon dioxide for 3 hours. Immediately after removing it from the pressure vessel, the base resin composition pellet was transferred and foamed in a foaming furnace with pressurized steam at a maximum of 400 kPa·G while rotating the stirring blade at 77 rpm to obtain foamed particles. The hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). Subsequently, these foamed particles were placed in a container and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, and then held at 0.4 MPa for 16 hours). This was then filled into an in-mold molding die with steam vents, heated with steam to cause the foamed particles to expand and fuse together, cooled, and removed from the molding die to obtain a bead foam composed of the foamed particles. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0094] (Example 2) A bead foam was obtained in the same manner as in Example 1, except that the amount of modified polyphenylene ether resin SX-101 was set to 87.5% by mass, the amount of flame retardant FP-110 was set to 12.5% ​​by mass, and the pressure of the pressurized steam used to produce foamed particles from the base resin composition was changed to 350 kPa·G. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0095] (Example 3) A bead foam was obtained in the same manner as in Example 1, except that the amount of modified polyphenylene ether resin SX-101 was set to 87.5% by mass, the amount of flame retardant FP-110 was set to 12.5% ​​by mass, and the pressure of the pressurized steam used to produce foamed particles from the base resin composition was changed to 400 kPa·G. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0096] (Example 4) A bead foam was obtained in the same manner as in Example 1, except that the amount of modified polyphenylene ether resin SX-101 was set to 85% by mass, the amount of flame retardant FP-110 was set to 15% by mass, and the pressure of the pressurized steam used to produce foamed particles from the base resin composition was changed to 300 kPa·G. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0097] (Example 5) A bead foam was obtained in the same manner as in Example 1, except that the amount of modified polyphenylene ether resin SX-101 was set to 80% by mass, the amount of flame retardant FP-110 was set to 20% by mass, and the pressure of the pressurized steam used to produce foamed particles from the base resin composition was changed to 260 kPa·G. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0098] (Example 6) Foamed particles and bead foam were obtained in the same manner as in Example 2, except that the foaming conditions were changed to the following heating conditions when producing foamed particles from the base resin composition, and the molding process for the bead foam was changed as follows. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition. The heat shrinkage rate of the obtained foamed particles was 49%. • Manufacturing procedure for foamed particles: Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, a base resin composition pellet was placed in a pressure vessel, the gas in the vessel was replaced with dry air, carbon dioxide (gas) was injected as a blowing agent, and the base resin composition pellet was impregnated with carbon dioxide for 3 hours under conditions of a pressure of 3.0 MPa and a temperature of 10°C. After that, the base resin composition pellet was removed from the pressure vessel and immediately transferred. The base resin composition pellet was heated in a foaming furnace while rotating a stirring blade at 77 rpm in the following steps to obtain foamed particles: (1) the water vapor pressure was increased to 315 kPa·G in 0 to 10 seconds from the start of heating (heating temperature 144.2°C), (2) the water vapor pressure was increased to 350 kPa·G in 10 to 20 seconds from the start of heating (heating temperature 147.0°C), and (3) the water vapor pressure was maintained at 350 kPa·G (heating temperature 147.0°C) for 20 to 30 seconds from the start of heating. • Molding process for bead foam: The foamed particles were placed in a container and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, then held at 0.4 MPa for 16 hours). This was then filled into an in-mold molding die with steam vents, and the foamed particles were heated in a double-sided heating process under conditions of steam pressure of 500 kPa·G (heating temperature 157.6°C) for 40 seconds to cause them to expand and fuse together. After cooling, the mixture was removed from the molding die to obtain a bead foam composed of the foamed particles.

[0099] (Example 7) Foamed particles and bead foam were obtained in the same manner as in Example 6, except that the foaming conditions were changed to the following heating conditions when producing foamed particles from the base resin composition. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition. The heat shrinkage rate of the obtained foamed particles was 24%. Furthermore, the resulting bead foam exhibited excellent appearance, with the foam particles well fused together, even in areas that were difficult to heat during the molding process, such as the corners of the mold. • Manufacturing procedure for foamed particles: Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, the base resin composition pellets were placed in a pressure vessel, the gas in the vessel was replaced with dry air, carbon dioxide (gas) was injected as a blowing agent, and the base resin composition pellets were impregnated with carbon dioxide for 3 hours under conditions of a pressure of 3.0 MPa and a temperature of 10°C. After that, the base resin composition pellets were removed from the pressure vessel and immediately transferred, and the base resin composition pellets were heated in a foaming furnace while rotating the stirring blade at 77 rpm, (1) a water vapor pressure of 37 was reached in 0 to 10 seconds from the start of heating. The heating process was carried out in the following steps to obtain foamed particles: (1) increase the pressure to 8 kPa·G (heating temperature 149.2°C), (2) increase the steam pressure to 420 kPa·G 10 to 20 seconds after the start of heating (heating temperature 152.3°C), (3) maintain the steam pressure at 420 kPa·G (heating temperature 152.3°C) for 20 to 30 seconds after the start of heating, (4) decrease the steam pressure to 350 kPa·G 300 seconds after the start of heating (heating temperature 147.0°C), and (5) maintain the steam pressure at 350 kPa·G (heating temperature 147.0°C) for 40 to 120 seconds after the start of heating. Steps (4) and (5) correspond to the bead annealing process.

[0100] (Example 8) After obtaining the bead foam, a bead foam was obtained in the same manner as in Example 6, except that the following foam annealing step was added. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition. • Foam annealing process: The resulting bead foam was heated (aged) in a drying oven (Safe Bend Dryer N50-S5, manufactured by Satake Multimix Co., Ltd.) at 125°C for 24 hours. The heating temperature was set to Tg-32°C of the base resin composition.

[0101] (Example 9) A bead foam was obtained in the same manner as in Example 8, except that the molding method for the bead foam was changed as follows. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition. • Molding process for bead foam: The foamed particles were placed in a container and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, then held at 0.4 MPa for 16 hours). This was then filled into an in-mold molding die with steam vents, and the foamed particles were heated in a double-sided heating process under conditions of steam pressure of 500 kPa·G (heating temperature 157.6°C) for 50 seconds to cause them to expand and fuse together. After cooling, the mixture was removed from the molding die to obtain a bead foam composed of the foamed particles.

[0102] (Example 10) A bead foam was obtained in the same manner as in Example 8, except that the molding method for the bead foam was changed as follows. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition. • Molding process for bead foam: The foamed particles were placed in a container and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, then held at 0.4 MPa for 16 hours). This was then filled into an in-mold molding die with steam vents, and the foamed particles were heated in a double-sided heating process under conditions of steam pressure of 520 kPa·G (heating temperature 158.9°C) for 40 seconds to cause them to expand and fuse together. After cooling, the mixture was removed from the molding die to obtain a bead foam composed of the foamed particles.

[0103] (Comparative Example 1) A base resin composition pellet was prepared by adding 60% by mass of polyphenylene ether resin (Asahi Kasei Corporation's "S201A"), 15% by mass of bisphenol A-bis(diphenyl phosphate) (BBP) (melting point below 20°C) as a non-halogenated flame retardant, 10% by mass of high-impact polystyrene resin (HIPS) with a rubber concentration of 6% by mass, and 15% by mass of GP685 (PS Japan Co., Ltd.) as a general-purpose polystyrene resin (PS). The mixture was heated, melted, kneaded, and then extruded in an extruder. Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, a base resin composition pellet was placed in a pressure vessel, the gas in the vessel was replaced with dry air, and carbon dioxide (gas) was injected as a blowing agent. Under conditions of a pressure of 3.0 MPa and a temperature of 10°C, the base resin composition pellet was impregnated with carbon dioxide for 3 hours. Immediately after removing it from the pressure vessel, the base resin composition pellet was transferred and foamed in a foaming furnace with pressurized steam at a maximum of 330 kPa·G while rotating the stirring blade at 77 rpm to obtain foamed particles. The hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). Subsequently, these foamed particles were placed in a container and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, and then held at 0.4 MPa for 16 hours). This was then filled into an in-mold molding die with steam vents, heated with steam to cause the foamed particles to expand and fuse together, cooled, and removed from the molding die to obtain a foam made of foamed particles. Table 1 shows the measurement and evaluation results for each physical property. Figure 1 also shows the loss tangent (tanδ) peak obtained by dynamic viscoelasticity measurement for the base resin composition.

[0104] [Table 1] [Industrial applicability]

[0105] The foamed beads of the present invention are flame-retardant and have high heat resistance, making them suitable for use in automotive peripheral components, electronic equipment peripheral components, and the like.

Claims

1. A bead foam comprising foamed particles obtained by foaming a base resin composition containing an amorphous resin, The glass transition temperature Tg of the aforementioned base resin composition is 120°C or higher. The low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition obtained by dynamic viscoelasticity measurement is less than 9°C. The flame retardancy, measured according to the UL standard UL-94 vertical method (10 mm vertical combustion test), is V-2 or higher at a thickness of 10 mm. The difference between the glass transition temperature Tg of the base resin composition and the temperature Ts at which the dimensional change rate of the bead foam becomes 1% after heating for 24 hours (1% dimensional change temperature) is 40°C or less. The base resin composition contains a non-halogenated flame retardant having a melting point of 30°C or higher. A bead foam characterized by the following features.

2. The bead foam according to claim 1, wherein the base resin composition contains a flame retardant having a decomposition temperature of 200°C or higher.

3. The bead foam according to claim 1 or 2, wherein the melting point of the non-halogenated flame retardant is higher than the temperature at which the dimensional change rate becomes 1% when the bead foam is heated for 24 hours (1% dimensional change temperature) Ts-50°C.

4. These are foamed particles obtained by foaming a base resin composition containing an amorphous resin. The glass transition temperature Tg of the aforementioned base resin composition is 120°C or higher. The low-temperature half-width of the loss tangent (tanδ) peak of the base resin composition obtained by dynamic viscoelasticity measurement is less than 9°C. The flame retardancy of the bead foam obtained by molding the aforementioned foam particles is V-2 or higher at a thickness of 10 mm, as measured in accordance with the UL standard UL-94 vertical method (10 mm vertical combustion test). The difference between the glass transition temperature Tg of the base resin composition and the temperature Ts at which the dimensional change rate of the bead foam becomes 1% after heating for 24 hours (1% dimensional change temperature) is 40°C or less. The base resin composition contains a non-halogenated flame retardant having a melting point of 30°C or higher. Foaming particles characterized by the following features.

5. The foamed particle according to claim 4, wherein the heat shrinkage rate when the base resin composition is heated at a glass transition temperature Tg + 10°C for 5 minutes is 25% or less.

6. A bead foam obtained by molding the foam particles described in claim 4 or 5.

7. A bead foaming process for foaming a base resin composition containing an amorphous resin, The bead foaming step includes a bead annealing step in which the base resin composition is heat-treated at a temperature of glass transition temperature Tg - 30°C or higher and glass transition temperature Tg + 30°C or lower after the bead foaming step. A method for producing foamed particles according to claim 4 or 5, characterized in that

8. A molding process for a bead foam, in which foamed particles obtained by foaming the aforementioned base resin composition are filled into a mold and heated to obtain a bead foam, The process includes a foam annealing step in which the obtained bead foam is heated at a temperature below the glass transition temperature Tg of the base resin composition after the molding step. A method for producing a foamed bead product according to claim 1 or 2, characterized in that

9. The process includes a molding step for a bead foam, in which foamed particles obtained by foaming the base resin composition are filled into a mold and heated to obtain a bead foam, The molding process includes heating at a high temperature exceeding the glass transition temperature Tg of the base resin composition, or heating at or above the glass transition temperature Tg of the base resin composition for a long period of time exceeding 40 seconds. A method for producing a foamed bead product according to claim 1 or 2, characterized in that

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