Method for manufacturing foamed beads, amorphous resin foamed beads, crystalline resin foamed beads, and foamed molded articles

Abstract

The purpose of the present invention is to provide a method for efficiently producing foam beads which exhibit excellent expansibility when the foam beads are expanded into a foam molded body, and which enable the production of a foam molded body that has a small dimensional change after a long-term high-temperature treatment. A method for producing foam beads according to the present invention is characterized by comprising: a bead foaming step in which a bead starting material that contains a resin is foamed; and a bead annealing step in which a heat treatment is performed at a temperature that is not less than (the glass transition temperature of the bead starting material minus 30°C) but not more than (the glass transition temperature of the bead starting material plus 30°C) after the bead foaming step.

Description

[Technical Field]

[0001] The present invention relates to a method for producing foamed beads, amorphous resin foamed beads, crystalline resin foamed beads, and foamed molded articles. [Background technology]

[0002] Bead foaming is a well-known technique for manufacturing foamed resins. In bead foaming, foamable resin particles are foamed to form foamed beads, and then these foamed beads are foamed again to fuse them together and obtain a foamed molded product. Bead foaming has advantages such as allowing for easy control of product shape and easy acquisition of foamed molded products with high foaming ratios, and is widely used in industries such as automotive peripheral components and electronic equipment peripheral components. Methods for manufacturing foamed beads used in the bead foaming process are known, including those described in Patent Documents 1 and 2. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-164676 [Patent Document 2] Japanese Patent Publication No. 2006-265305 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, in fields such as automotive peripheral components and electronic equipment peripheral components, the demand for resin foams that do not change dimensions even after prolonged high-temperature heat treatment has been increasing due to the demand for higher power output, larger capacity, and larger size. Furthermore, with the thinning of parts and the increasing complexity of shapes, there is a growing demand for resin foams with high dimensional accuracy and processability, such as thin-wall moldability. The inventors of this invention have found that bead foams (foamed molded articles), which have excellent shapeability and processability among resin foams, have a problem in that they tend to undergo large dimensional changes (shrinkage) due to residual stress in the molded product generated during the molding process.

[0005] Patent Document 1 describes a method for producing foamed beads that have good foaming properties while maintaining crystalline properties, specifically a method for controlling the crystallinity of the resin contained in the raw material composition of the foamed beads. Patent Document 2 describes a method for producing foamed beads that exhibit little dimensional change even when used at high temperatures by heat-treating an extruded foam to remove residual stress from the extrusion foaming process. However, conventional methods for preparing foam raw materials and foam after manufacturing, as described in Patent Documents 1 and 2, etc., are insufficient to remove residual stress generated in the resin molded body, resulting in insufficient dimensional stability after long-term high-temperature treatment. Furthermore, conventional methods cannot remove residual stress generated in the foam beads, resulting in poor expansion capacity of the foam beads and insufficient moldability.

[0006] Therefore, the object of the present invention is to provide an efficient method for producing foamed beads that have excellent expansion ability when expanding from foamed beads to foamed molded bodies and that exhibit small dimensional changes after long-term high-temperature treatment. [Means for solving the problem]

[0007] In other words, the present invention is as follows: [1] The resin-containing bead material is foamed. to obtain pre-foamed beads The bead foaming process, After the bead foaming process, the bead raw material is subjected to a temperature of (glass transition temperature -30)°C or higher and (glass transition temperature +30)°C or lower. The aforementioned pre-foamed beads Includes a heat treatment bead annealing process. fruit, The ratio of the bulk ratio of the foamed beads after the bead annealing process to the bulk ratio of the pre-foamed beads before the bead annealing process (100%) is 30% or more and 99% or less. The aforementioned resin is an amorphous resin. A method for manufacturing foamed beads, characterized by the following: [2] In the bead annealing step, the heat treatment is performed using steam, [1 ] The manufacturing method of the expanded beads described. [3] In the bead annealing step, the heat treatment is performed using hot air, [1 ] The manufacturing method of the expanded beads described. [4] The bead foaming step and the bead annealing step are performed in the same apparatus, [1 ] The manufacturing method of the expanded beads described. [5] The time of the heat treatment is 10 seconds or more and 600 seconds or less, [1]~ 4] any of the following The manufacturing method of the expanded beads described in. [6] In the bead annealing process, the rate of change in the bulk ratio of the pre-foamed beads per second is -0.5 cm. 3 / g or more -0.001cm 3 A method for producing foamed beads according to any of [1] to [5], wherein the amount is less than or equal to / g. [7] Expanded beads obtained by foaming a bead raw material containing an amorphous resin, wherein the heat shrinkage rate when heated at (glass transition temperature + 10) °C for 5 minutes of the bead raw material is 25% or less. Amorphous resin expanded beads, characterized in that. [8] The expansion ability is 2.3 or more. [7] The amorphous resin expanded beads described in. [9] [7] or [8] Formed from the amorphous resin expanded beads described in. An expanded molded body, characterized in that. 。

Advantages of the Invention

[0008] In the method for producing expanded beads of the present invention, it is possible to efficiently produce expanded beads that are excellent in expansion ability when expanding from expanded beads to an expanded molded body and that have a small dimensional change after long-term high-temperature treatment, and it is possible to efficiently produce expanded molded bodies. [Modes for carrying out the invention]

[0009] The following describes in detail embodiments for carrying out the present invention (hereinafter referred to as "this embodiment"). The present invention is not limited to the following description and can be implemented in various modifications within the scope of its gist.

[0010] [Method for manufacturing foam beads] The method for manufacturing foamed beads according to this embodiment includes a bead foaming step of foaming a bead raw material containing resin, and a bead annealing step of heat-treating the bead material at a predetermined temperature after the bead foaming step. The method for manufacturing foamed beads in this embodiment is preferably a method comprising a bead foaming step of foaming a bead raw material containing resin, and a bead annealing step of heat-treating the bead raw material at a temperature of (glass transition temperature - 30)°C or higher and (glass transition temperature + 30)°C or lower after the bead foaming step (this method may be referred to as "Method A for manufacturing foamed beads" in this specification), or a method comprising a bead foaming step of foaming a bead raw material containing resin, and a bead annealing step of heat-treating the bead raw material at a temperature of (softening point temperature - 30)°C or higher and (softening point temperature + 30)°C or lower after the bead foaming step (this method may be referred to as "Method B for manufacturing foamed beads" in this specification). The method for manufacturing foamed beads in this embodiment may consist only of the bead foaming step and the bead annealing step described above, or it may include other steps as well. In this specification, foamed particles obtained after the bead foaming process and before the bead annealing process may be referred to as "pre-foamed beads." Furthermore, "foamed beads" can be manufactured from pre-foamed beads through the bead annealing process.

[0011] [Bead foaming process] The above bead foaming process is a process of impregnating the bead raw material with a foaming agent and foaming it to obtain pre-foamed beads.

[0012] <Bead materials> The above bead material may contain resin and may also contain other components.

[0013] (resin) The above resin may be a crystalline resin, an amorphous resin, or a mixture thereof. Furthermore, the above resin may be used alone or as a mixture of multiple types. In foam bead manufacturing method A, the above resin is preferably an amorphous resin, and in foam bead manufacturing method B, the above resin is preferably an amorphous resin and / or a crystalline resin, and more preferably a crystalline resin.

[0014] The amorphous resin described above generally undergoes significant dimensional changes when subjected to long-term high-temperature treatment. Since particularly excellent effects can be obtained when using foamed beads produced by the manufacturing method of this embodiment, it is preferable that the resin mainly consists of amorphous resin. More preferably, the mass ratio of amorphous resin to 100% of the total mass of the resins contained in the bead raw material is 50% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and especially preferably 95% by mass or more. It is particularly preferable that the resin consists solely of amorphous resin. Furthermore, the mass ratio of crystalline resin to 100% of the total mass of the resins contained in the bead raw material may be 50% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or the resin may consist solely of crystalline resin.

[0015] -Amorphous resin- The amorphous resins mentioned above 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); polycarbonate resins such as polycarbonate resin, polycarbonate resin / ABS resin alloy, and polycarbonate resin / polybutylene terephthalate resin alloy; polyvinyl chloride; polymethyl methacrylate; polyethersulfone, polyetherimide; polyamideimide; and the like. In particular, polyphenylene ether resins or polystyrene resins are preferred, with polyphenylene ether resin / polystyrene resin / high-impact polystyrene resin alloys, modified polyphenylene ether resins, and polystyrene resins being more preferred, from the viewpoint of further reducing dimensional changes after long-term high-temperature treatment of the foamed molded product and further increasing the expansion capacity of the foamed beads. The reduced dimensional changes of these resins after long-term high-temperature treatment make the resin foams applicable to automotive and information and communication applications.

[0016] --Polyphenylene ether 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.

[0017] The polyphenylene ether resin refers to a polymer containing repeating units (structural units) represented by the following formula (I). Examples include a homopolymer consisting only of repeating units represented by the following formula (I), and a copolymer containing repeating units represented by the following general formula (I). The copolymer is a copolymer in which the repeating units represented by the following formula (I) are the main repeating units (for example, a copolymer in which the mass ratio of repeating units represented by the following formula (I) is more than 50% by mass (preferably 70% by mass or more) per 100% by mass of the copolymer). The polyphenylene ether may be used alone or in combination of two or more types. The repeating units represented by the following formula (I) contained in the polyphenylene ether may be one type or multiple types. [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. The number of carbon atoms in the alkyl group or alkoxy group may be 1 to 7.

[0018] Specific examples of the polyphenylene ether resin 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-didodecyl-1,4-phenylene) ether, poly(2,6-diphenyl-1,4-diphenylene) ether, poly(2,6-dimethoxy-1,4-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., but are not limited thereto. Among these, particularly, in the general formula (I), R 1 and R 2 are alkyl groups having 1 to 4 carbon atoms, and R 3 and R 4 are hydrogen or alkyl groups having 1 to 4 carbon atoms are preferred.

[0019] 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.

[0020] As the above-mentioned polyphenylene ether resin, a modified polyphenylene ether resin can be used in which some or all of the constituent units of the polyphenylene ether resin are modified with an unsaturated or saturated carboxylic acid or a derivative thereof. Examples of the above-mentioned modified polyphenylene ether resins include those described in Japanese Patent Publication No. 2-276823 (US Patent No. 5159027, US Reissue 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.

[0021] 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.

[0022] 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.

[0023] When the polyphenylene ether resin is a polymer alloy, from the viewpoint of foam molding processability, the polyphenylene ether resin content is preferably 40 to 99% by mass, more preferably 50 to 95% by mass, and even more preferably 70 to 90% by mass, per 100% by mass of the polymer alloy.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The mass ratio of the polyphenylene ether resin to 100% by mass of the above bead raw material is preferably 60 to 100% by mass, more preferably 70 to 99% by mass, and even more preferably 80 to 95% by mass. When the mass ratio of the polyphenylene ether resin is within the above range, foamed beads that produce foamed molded articles with small dimensional changes after long-term high-temperature treatment are easily obtained.

[0028] --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.

[0029] 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.

[0030] The polystyrene resin may be manufactured by any conventionally known manufacturing method.

[0031] --Polycarbonate resin-- Examples of polycarbonate-based resins include 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.

[0032] 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.

[0033] Furthermore, the polycarbonate resin may be linear polycarbonate, branched polycarbonate polymerized with trifunctional phenols, or copolymerized polycarbonate polymerized with aliphatic dicarboxylic acid, aromatic dicarboxylic acid, or divalent aliphatic or alicyclic alcohol.

[0034] The polycarbonate resin may be manufactured by any conventionally known manufacturing method.

[0035] The above bead material preferably contains a resin that includes aromatic monomer units. Including a resin that includes aromatic monomer units tends to yield a foamed molded article with good flame retardancy. Examples of resins containing aromatic monomer units include aromatic polyamide resins, polycarbonate resins, polyethylene terephthalate resins, polyimide resins, polyphenylene ether resins, and styrene resins. The mass percentage of aromatic monomer units in the above-mentioned resin is preferably 20% by mass or more, more preferably 25-100% by mass, even more preferably 30-100% by mass, and even more preferably 50-100% by mass, based on 100% by mass of the resin. This is because the resin is more likely to carbonize during combustion, thus making it easier to suppress ignition and flame of the resin, and also because it 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 resin can be calculated by averaging according to the mass percentage of each resin mixed. Furthermore, if the structure is unknown, aromatic monomer units can be estimated and calculated using NMR, IR, etc.

[0036] Furthermore, the foamed molded articles obtained from the foamed beads 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 include selecting a resin with low density, low polarity, and few polar groups at the end of the molecular chain as the resin before foaming in the bead raw material. From this viewpoint, particularly suitable resins include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluororesins, liquid crystal polymers, 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, in order to avoid water absorption when manufacturing foamed beads and foamed molded products, methods to reduce the water absorption of the bead raw materials include reducing the polarity of the constituent units in the resin and reducing the polar groups at the ends of the molecular chains. From this viewpoint, suitable resins include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluororesins, liquid crystal polymers, 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.

[0037] -Crystalline resin- The above-mentioned crystalline resins are not particularly limited as long as they are crystalline resins, and examples include polyethylene resin, polypropylene resin, polyvinylidene chloride resin, polyamide resin, polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polyphenylene sulfide resin, polyether ether ketone resin, liquid crystal polymer, polytetrafluoroethylene resin, etc. Among these, polyamide resin, polyacetal resin, polybutylene terephthalate resin, and polyphenylene sulfide resin are preferred from the viewpoint of heat resistance, flame retardancy, and moldability.

[0038] --Polyamide resin-- The polyamide resin is not particularly limited, and any known polyamide resin can be used. Examples of polyamide resins include polyamide homopolymers and polyamide copolymers. Examples of polyamide homopolymers include nylon 66, nylon 610, nylon 612, nylon 46, nylon 1212, etc., obtained by polycondensation of diamines and dicarboxylic acids; and nylon 6, nylon 12, etc., obtained by ring-opening polymerization of lactams. Examples of polyamide copolymers include nylon 6 / 66, nylon 66 / 6, nylon 66 / 610, nylon 66 / 612, and the like. As the polyamide resin, aliphatic polyamides are preferred, and nylon 6, nylon 66, nylon 6 / 66, nylon 66 / 6, etc., are more preferred.

[0039] The glass transition temperature of the above resin is preferably 80 to 250°C, more preferably 100 to 230°C, and even more preferably 120 to 220°C, from the viewpoint of minimizing dimensional changes under long-term high-temperature treatment. From the viewpoint of minimizing dimensional changes under long-term high-temperature processing, the glass transition temperature of the bead raw material is preferably 80 to 180°C, more preferably 100 to 170°C, and even more preferably 120 to 160°C. If multiple glass transition temperatures are observed when using a material as a bead raw material, the highest glass transition temperature will be used as the glass transition temperature of the bead raw material. The above glass transition temperature can be measured by the method described in the examples below.

[0040] The softening point temperature of the above resin is preferably 80 to 250°C, more preferably 100 to 230°C, and even more preferably 120 to 220°C, from the viewpoint of minimizing dimensional changes under long-term high-temperature treatment. The softening point temperature of the bead material is preferably 80 to 180°C, more preferably 100 to 170°C, and even more preferably 120 to 160°C, from the viewpoint of minimizing dimensional changes under long-term high-temperature treatment. The softening point temperature Tm shall be the melting peak temperature obtained by differential scanning calorimetry (DSC) in accordance with JIS K7121. If multiple melting peaks appear, the temperature of the peak with the highest temperature shall be taken as Tm. Furthermore, if a clear melting peak cannot be obtained by DSC (i.e., if a peak with a melting enthalpy change of 1 J / g or more cannot be confirmed), such as when amorphous resin is included, the temperature at which the loss tangent tanδ observed during the glass transition is maximum in dynamic viscoelasticity measurement shall be taken as Tm. If there are multiple temperatures at which the loss tangent tanδ observed during the glass transition is maximum in dynamic viscoelasticity measurement, the temperature with the highest temperature shall be taken as Tm. Specifically, this can be measured by the method described in the examples below.

[0041] The mass percentage of the above resin in 100% by mass of the above bead raw material is preferably 50 to 100% by mass, more preferably 60 to 95% by mass, even more preferably 70 to 92% by mass, and particularly preferably 80 to 90% by mass.

[0042] (Other ingredients) Other components mentioned above 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, etc., and can be added insofar as they do not impair the effects of the present invention. Other components mentioned above may be components other than resins.

[0043] The mass ratio of the other components in the bead raw material is preferably 0 to 40 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 10 to 20 parts by mass, based on 100 parts by mass of the resin. The mass percentage of the above-mentioned other components in 100% by mass of the above-mentioned bead raw material is preferably greater than 0% by mass and 50% by mass or less, more preferably 5 to 40% by mass, even more preferably 8 to 30% by mass, and particularly preferably 10 to 20% by mass.

[0044] Examples of the above-mentioned flame retardants 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.

[0045] Among the above-mentioned flame retardants, from the viewpoint of environmental impact, non-halogenated organic flame retardants are preferred, and phosphorus-based or silicone-based flame retardants are more preferred.

[0046] 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, triphenylphosphine oxides, and the like. 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 such as bisphenol A bisphosphate, 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.

[0047] 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, methyl, ethyl, 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.

[0048] The mass percentage of the above flame retardant in 100% by mass of the above bead raw material is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass. Furthermore, the mass ratio of the flame retardant to 100 parts by mass of the resin is preferably 5 to 30 parts by mass, and more preferably 10 to 25 parts by mass.

[0049] Examples of the rubber components mentioned above 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 a 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 adding rubber components, the content of the rubber components is 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, per 100 parts by mass of the above resin. When the content is 0.3 parts by mass or more, the resin exhibits excellent flexibility and elongation, the foam cell film is less likely to rupture during foaming, and a foam with excellent moldability and mechanical strength is easily obtained.

[0050] To improve the flame retardancy of the foamed molded article obtained by molding the above-mentioned foamed beads, it is preferable to add more flame retardant to the bead raw material. However, increasing the amount of flame retardant negatively affects the foaming properties. In such cases, rubber components are suitably used to impart foaming properties to the bead raw material. In particular, the above-mentioned rubber components are important in bead foaming, where the temperature is gradually increased from room temperature to foam the resin in a non-molten state.

[0051] Examples of the inorganic fillers mentioned above include fibrous inorganic fillers such as glass fibers, potassium titanate fibers, gypsum fibers, brass fibers, stainless steel fibers, steel fibers, ceramic fibers, and boron whisker fibers; plate-like inorganic fillers such as mica, talc, kaolin, calcined kaolin, and glass flakes; granular inorganic fillers such as titanium oxide, apatite, glass beads, silica, calcium carbonate, and carbon black; and needle-like inorganic fillers such as wollastonite and xonotlite. Among these, fibrous inorganic fillers, plate-like inorganic fillers, and needle-like inorganic fillers are preferred, and glass fibers, glass flakes, mica, and talc are more preferred. The inorganic fillers described above may be used individually or in combination of two or more types. The mass percentage of the inorganic filler in 100% by mass of the above bead raw material is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 3% by mass.

[0052] <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.

[0053] 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 foam 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 in that excellent heat resistance is easily exhibited from an earlier stage after molding. Moreover, inorganic gases are less soluble in resin than organic gases such as hydrocarbons, and they dissipate easily from the pellet surface during foaming, which is also preferable because it makes it easier to form a skin layer and makes it less prone to rupture. Among inorganic gases, carbon dioxide is preferred from the viewpoint of solubility in resin and ease of handling.

[0054] In the bead foaming process, a method for foaming bead raw materials by impregnating them with a foaming agent (i.e., a method for obtaining pre-foamed beads) is, for example, the method described in Example 1 of Japanese Patent Publication No. 4-372630, in which bead raw materials (pellets, beads, etc.) are 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 bead raw materials with the foaming agent (gas), the pressure is released and the bead raw material pellets are transferred from the pressure vessel to a foaming furnace, and the bead raw material pellets are heated with pressurized steam while stirring blades are rotated in the foaming furnace to cause foaming, thereby producing pre-foamed beads.

[0055] Methods for incorporating a foaming agent into the bead material can be generally applied. These include methods using an aqueous medium such as water (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 bead material in a liquid phase under an atmosphere of pressure above critical pressure (liquid phase impregnation), and methods in which a gas is brought into contact with the bead material in a gas phase 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.

[0056] 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 bead material 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 bead material, considering the balance between these factors.

[0057] The amount of foaming agent impregnated is preferably 3 to 13% by mass relative to the resin contained in the bead raw material, 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.

[0058] The method of foaming the bead material in the bead foaming process is not particularly limited, but examples include a method of rapidly releasing the material 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 material 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 material 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 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 bead material 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.

[0059] 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 beads. However, according to the method of this embodiment, a bead annealing process is provided, making it possible to obtain foamed beads with low residual stress. In the bead foaming process, it is preferable to use hot air for heating and foaming, particularly from the viewpoint of obtaining a foamed molded product with excellent heat shrinkage rate. In this context, "steam" refers to pressurized water vapor that has been pressurized and heated to a pressure higher than atmospheric pressure. "Hot air" refers to dry air with a relative humidity of less than 10% that has been heated to a temperature of 50°C or higher.

[0060] In the bead foaming process, the foaming temperature is preferably above the glass transition temperature Tg -25°C of the bead material, and more preferably above Tg -20°C. Furthermore, the foaming temperature is preferably below the glass transition temperature Tg +30°C of the bead material, and more preferably below Tg +20°C. By foaming at the above foaming temperatures, the bead material becomes more easily foamed and expanded. In the bead foaming process, when steam is used for heating and foaming, the temperature of the pressurized steam is preferably (glass transition temperature of the bead material Tg-30)°C to (glass transition temperature of the bead material Tg+10)°C, more preferably (glass transition temperature of the bead material Tg-20)°C to (glass transition temperature of the bead material Tg+5)°C, and even more preferably (glass transition temperature of the bead material Tg-10)°C to the glass transition temperature of the bead material Tg. In the bead foaming process, the foaming temperature is preferably above the softening point temperature Tm - 25°C of the bead material, and more preferably above Tm - 20°C. Furthermore, the foaming temperature is preferably below the softening point temperature Tm + 30°C, and more preferably below Tm + 20°C. By foaming at the above foaming temperatures, the bead material becomes more easily foamed and expanded. In the bead foaming process, when steam is used for heating and foaming, the temperature of the pressurized steam is preferably (softening point temperature Tm-30)°C to (softening point temperature Tm+10)°C, more preferably (softening point temperature Tm-20)°C to (softening point temperature Tm+5)°C, and even more preferably (softening point temperature Tm-10)°C to the softening point temperature Tm, from the viewpoint of efficiently obtaining pre-foamed beads with a magnification greater than or equal to that of the foamed beads. The glass transition temperature and softening point temperature of the bead material can be determined by the method described in the examples below. The foaming temperature mentioned above may be the maximum temperature in the bead foaming process.

[0061] 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.

[0062] When foaming foam beads to a desired foaming ratio, the foaming may be done 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 reserve beads (beads that have not undergone the final foaming stage, etc.) 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. Furthermore, the foaming conditions before each stage may be the same or different. In this specification, the bead foaming process refers to the process in which the bulk density of the bead material gradually increases after foaming begins, and includes the period up to just 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 / g or more 100cm 3 This refers to a process where the increase is within a range of less than / g.

[0063] [Bead annealing process] The pre-foamed beads obtained in the above bead foaming process can be heat-treated in the bead annealing process to produce foamed beads. 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 pre-foamed beads by heat-treating them after foaming is complete, and is different from the foaming process or the process of leaving the beads untreated without intentional heat treatment. When processing resins into beads or foamed molded products, the resin is stretched and then cooled and fixed, which tends to leave residual stress in the beads or foamed molded products. Therefore, when the foamed molded product is heated to near its softening point, the molecular chains begin to move and attempt to rearrange themselves into molecular arrangements with lower free energy, resulting in shrinkage of the molded product. In particular, amorphous resins tend to retain residual stress more easily than crystalline resins, and the dimensional change rate when the foamed molded product is heated is greater, so the bead annealing process is preferable as it can be expected to reduce residual stress. On the other hand, while some residual stress can be relieved during crystallization of crystalline resins, the lower the degree of crystallinity of the crystalline resin, the greater the residual stress reduction effect of the bead annealing process, which is preferable. 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 bulk ratio per second of the pre-foamed beads is set to -0.5 to -0.001 cm from the viewpoint of obtaining excellent expansion ability. 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.

[0064] Examples of the above heat treatments include heating with steam (preferably pressurized steam or steam), heating with hot air, and heating with a heater. Among these, heat treatment using steam is preferable from the viewpoint of good thermal conductivity and the ability to anneal in a short time. On the other hand, heat treatment using hot air is preferable from the viewpoint of obtaining a foamed molded product with particularly excellent heat shrinkage rate.

[0065] The temperature for the heat treatment described above is preferably between -30°C and +30°C, the glass transition temperature of the bead raw material. More preferably, the temperature is between -25°C and +25°C, and even more preferably between -20°C and +20°C, from the viewpoint of excellent dimensional change after long-term high-temperature treatment and even better expansion capacity. 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.

[0066] The temperature for the heat treatment described above is preferably between -30°C and +30°C of the softening point of the bead material. More preferably, from the viewpoint of excellent dimensional change after long-term high-temperature treatment and even better expansion capacity, the temperature is between -25°C and +25°C, and even more preferably between -20°C and +20°C. The heat treatment may be performed at a constant temperature or at a variable temperature. When the temperature is varied, it is preferable to vary the temperature within the above range.

[0067] In particular, when the resin contained in the bead material is an amorphous resin, the heat treatment temperature is preferably between -30°C and +30°C, which is the glass transition temperature of the bead material. More preferably, the temperature is between -25°C and +25°C, and even more preferably between -20°C and +20°C, which is the glass transition temperature. The heat treatment may be performed at a constant temperature or at a variable temperature. When the temperature is varied, it is preferable to vary the temperature within the above range.

[0068] 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. If the heat treatment time is less than 10 seconds, the effect of removing residual stress is not sufficiently obtained, the thermal shrinkage rate of the foam beads increases, and as a result the dimensional change rate of the resulting foamed molded product is large, which is undesirable. If the heat treatment time exceeds 600 seconds, the foam beads will shrink significantly, leading to an extreme decrease in the foaming ratio, which is undesirable.

[0069] The temperature of the steam used in the above heat treatment is preferably between -30°C and +30°C, more preferably between -25°C and +10°C, and even more preferably between -20°C and +5°C. Furthermore, the softening point temperature of the bead material is preferably between -30°C and +30°C, more preferably between -25°C and +10°C, and even more preferably between -20°C and +5°C. The temperature of the hot air used in the above heat treatment is preferably between -30°C and +30°C, more preferably between -20°C and +20°C, and even more preferably between -10°C and +10°C. Furthermore, the softening point temperature of the bead material is preferably between -30°C and +30°C, more preferably between -20°C and +20°C, and even more preferably between -10°C and +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.

[0070] 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 (for example, the highest temperature in the 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. When the above bead annealing process is carried out with hot air, the heat treatment temperature is preferably below the foaming temperature in the above bead foaming process, more preferably 2°C or more lower than the foaming temperature, 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. 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.

[0071] The bulk ratio of the pre-foamed beads obtained in the bead foaming process may decrease after the bead annealing process. The ratio of the bulk ratio of the foamed beads after the bead annealing process to the bulk ratio of the pre-foamed beads before the bead annealing process (100%) is preferably 30-99%, and more preferably 40-95%. From the viewpoint of weight reduction, the lower limit of the final bulk ratio after the bead foaming process is preferably 2 cc / g or more, more preferably 3 cc / g or more, and even more preferably 5 cc / g or more. From the viewpoint of maintaining the strength of the molded product, the upper limit of the final bulk ratio after the bead foaming process is preferably 30 cc / g or less, more preferably 20 cc / g or less, and even more preferably 15 cc / g or less. During the bead annealing process described above, the bulk ratio of the foamed beads may be gradually reduced. The bead annealing process may be a process in which the bulk ratio of the beads remains the same or decreases (preferably decreases) during the process. The bulk density of the pre-foamed beads and foamed beads can be measured by the method described in the examples below.

[0072] In the method for manufacturing foamed beads of this embodiment, the bulk ratio of the pre-foamed beads decreases after the bead annealing process. Therefore, taking into account the decrease in bulk ratio during the bead annealing process, it is preferable to continue foaming the beads in the foaming process until the bulk ratio is higher than the planned bulk ratio of the foamed beads. For example, a step may be provided to measure in advance the percentage of the bulk ratio that will be reduced in the bead annealing process and to determine the planned bulk ratio after the foaming process.

[0073] In the method for manufacturing foamed beads 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 beads by continuously annealing the pre-foamed beads without removing them 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. In the foam bead manufacturing method of this embodiment, it is preferable to connect multiple impregnation tanks in parallel from the viewpoint of increasing productivity. This allows the impregnation process to be carried out efficiently. Furthermore, in the foam bead manufacturing method of this embodiment, it is preferable to connect multiple foaming tanks in parallel from the viewpoint of increasing productivity. This eliminates the rate-limiting factor of the foaming tank when the bead foaming process and the bead annealing process are carried out in the same equipment, making it possible to carry out the bead annealing process efficiently.

[0074] [Foam molding process] The foam molding process described above is a process for manufacturing a foamed molded product from foamed beads obtained in the bead annealing process. For example, a foamed molded product can be obtained by filling a mold with foamed beads obtained in the bead annealing process, heating them with steam or the like to expand the foamed beads, and simultaneously heat-fusing the foamed beads together. The bead foaming method allows for the creation of molds of the desired shape, into which foam beads are filled and molded. This makes it easier to form foamed molded products into finer and more complex shapes. Furthermore, the bead foaming method makes it easier to increase the foaming ratio of the foamed molded product, resulting in a foamed molded product that exhibits flexibility in addition to thermal insulation properties.

[0075] The foamed beads obtained in the bead annealing process may be used continuously in the foam molding process, or they may be used in the foam molding process at intervals.

[0076] Methods for filling foam beads include, for example, the cracking method, in which the mold is filled with the beads while slightly open; the compression method, in which the beads are compressed under pressure while the mold is closed and then filled; and the compression-cracking method, in which the beads are compressed and then cracked.

[0077] It is preferable to perform a pressurization step in which the foam beads are subjected to pressure treatment under an inorganic gas atmosphere before filling. This is because pressurization treatment allows a constant gas pressure to be applied to the air bubbles within the foam beads, making it easier to achieve more uniform foaming and molding. The pressure source used when performing pressurized treatment is not particularly limited, but it is preferable to use the inorganic gases mentioned above. Examples of inorganic gases include air, carbon dioxide, nitrogen, oxygen, ammonia, hydrogen, argon, helium, and neon. From the viewpoint of ease of handling and economic efficiency, carbon dioxide and air are preferred. The method of pressurization is not particularly limited, but one example is to fill a pressurized tank with foam beads, supply inorganic gas to the tank, and increase the pressure to a maximum of 0.1 to 20 MPa over 10 minutes to 96 hours.

[0078] Using the foamed beads obtained by the manufacturing method of this embodiment, it is possible to manufacture foamed molded bodies with fine or complex shapes using known in-mold molding methods, which broadens the range of applications for which they can be used. Conventional foam molding processes often employ a cracking method, where the mold is slightly open and a large amount of foam beads are filled in, because foam beads do not expand sufficiently in the corners or thin cavity spaces (thin molded body spaces) within the mold. However, the foam beads produced by the manufacturing method of the present invention have high expansion capacity, allowing them to fill gaps between beads and corners within the mold even with a small amount of foam beads, enabling foam molding to be performed with the mold closed. The cracking method involves filling the mold with beads while it is slightly open, resulting in a large amount of foam beads being filled into the mold. This increases the weight per unit volume of the resulting foamed molded product, sometimes causing it to differ from the intended foaming ratio. By filling the mold with beads while it is closed (zero cracking rate), it is possible to obtain a foamed molded product with excellent shape, without gaps even in areas where it is difficult to fill the mold with foam beads, such as thin-walled sections, ribs, and corners. Furthermore, even with simple plate-shaped molded bodies, when molding large boards with a large molding area, increasing the amount of beads filled by cracking requires a greater force to compress the beads when closing the mold, resulting in the mold not closing completely and poor thickness accuracy. The foamed beads obtained by the manufacturing method of this embodiment have excellent expansion ability, so fewer foamed beads need to be filled into the mold, allowing molding with the mold completely closed and obtaining a foamed molded body with excellent thickness accuracy. Moreover, even in foamed molded bodies with areas of varying thickness, it is possible to obtain a foamed molded body with small variation in the expansion ratio. In addition, it is possible to achieve both the lightweight properties and the freedom of shape design that are advantages of foamed materials.

[0079] As a method for molding the foamed beads obtained by the manufacturing method of this embodiment, for example, there is a vacuum molding method (for example, Japanese Patent Publication No. 46-38359) in which a pair of molds for conventional in-mold molding of foamed beads is used, the foamed beads are filled into the mold cavity under pressurized atmospheric pressure or reduced pressure, the mold is closed and compressed so that the volume of the mold cavity is reduced by 0 to 70%, and then a heat medium such as steam is supplied into the mold to heat and fuse the foamed beads, and so on. Furthermore, the foam beads can also be molded by a compression filling molding method (Japanese Patent Publication No. 4-46217), in which foam beads pressurized to a pressure exceeding atmospheric pressure are filled into a cavity pressurized to a pressure exceeding atmospheric pressure using compressed gas, and then a heat transfer medium such as steam is supplied into the cavity to heat and fuse the foam beads. In addition, the foam beads can also be molded by an atmospheric pressure filling molding method (Japanese Patent Publication No. 6-49795), in which the secondary foaming force of the foam beads is increased under special conditions, the foam beads are filled into a pair of mold cavities under atmospheric pressure or reduced pressure, and then a heat transfer medium such as steam is supplied to heat and fuse the foam beads, or by a method combining the above methods (Japanese Patent Publication No. 6-22919).

[0080] In the foam molding process, the maximum vapor pressure of the pressurized steam inside the mold (inside the foaming furnace) is preferably 30 to 700 kPa, from the viewpoint of easily obtaining the desired magnification and improving the appearance.

[0081] [Foam beads] The foamed beads of this embodiment can be manufactured by the manufacturing method of this embodiment described above. Examples of the foamed beads include amorphous resin foamed beads and crystalline resin foamed beads, which will be described later.

[0082] The foamed beads described above are preferably foamed beads obtained by foaming a bead material containing an amorphous resin. Amorphous resin foamed beads are preferred in which the heat shrinkage rate when heated at the glass transition temperature of the bead material containing the amorphous resin + 10°C for 5 minutes is 25% or less. The amorphous resin described above is one example, and an amorphous resin similar to that described above is preferred. The bead material described above is one example, and the same as that described above is preferred.

[0083] The foamed beads described above are preferably foamed beads obtained by foaming a bead material containing a crystalline resin. The foamed beads described above are preferably crystalline resin foamed beads in which the heat shrinkage rate when heated for 5 minutes at the softening point temperature of the bead material containing the crystalline resin is -10°C is 25% or less. The amorphous resin described above is one of the above, and an amorphous resin similar to that described above is preferred. The bead material described above is one of the above, and the same as that described above is preferred.

[0084] The heat shrinkage rate of the foamed beads described above is preferably 25% or less, more preferably 20% or less, and even more preferably 18% or less, from the viewpoint of excellent dimensional stability after long-term high-temperature treatment. The heat shrinkage rate can be adjusted by the conditions of the bead annealing process (for example, the type of medium used for heating, heating temperature, heating time, pressure, etc.). The above heat shrinkage rate can be measured by the method described in the examples below.

[0085] The expansion capacity of the above-mentioned foamed beads (for example, amorphous resin foamed beads or crystalline resin foamed beads) is preferably 2.3 or higher, more preferably 2.5 to 10.0, and even more preferably 3.0 to 5.0, from the viewpoint of excellent moldability. The above expansion capacity can be adjusted by the conditions of the bead annealing process (for example, the type of medium used for heating, heating temperature, heating time, pressure, etc.). The above expansion capacity can be measured by the method described in the examples below.

[0086] [Foam molded product] The foamed molded body of this embodiment can be obtained by foaming and molding the foamed beads of this embodiment described above. The foamed molded article described above is preferably a foamed molded article made by molding amorphous resin foam beads having a heat shrinkage rate of 25% or less when heated for 5 minutes at a temperature of "glass transition temperature of the bead raw material containing amorphous resin + 10" °C, or a foamed molded article made by molding crystalline resin foam beads having a heat shrinkage rate of 25% or less when heated for 5 minutes at a temperature of "softening point temperature of the bead raw material containing crystalline resin - 10" °C. The above-mentioned foamed molded body can be suitably used, for example, as a peripheral component for automobiles, a peripheral component for electronic equipment, and the like. [Examples]

[0087] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0088] The measurement and evaluation methods used in the examples and comparative examples are described below.

[0089] (Glass transition temperature of bead raw materials) Dynamic viscoelasticity measurements were performed on the bead material using a rheometer (Anton Paar's "Physica MCR301") under the following conditions, and the peak temperature (°C) of the loss tangent (tanδ) was defined as the glass transition temperature (Tg) of the bead material. Measuring jig: SRF10 Measurement mode: vibration φ, γ Strain: Swing angle γ = 0.015% Frequency: 1Hz Measurement temperature: 20℃~200℃ Heating rate: 2°C / min Normal force: -0.3N Measurement points: 180 Time unit: s

[0090] (Softening point temperature of bead material) For the bead raw materials, the melting peak temperature (°C) was measured using a differential scanning calorimetry system (PerkinElmer "DSC8500") under the following conditions, and this was defined as the softening point temperature. Sample amount: 10 mg Bread: Aluminum crimped pan Atmosphere: Nitrogen Measurement temperature: 50℃~220℃ Temperature increase / decrease rate: 10℃ / min Measurement cycle: 2 cycles In the above measurements, a change in enthalpy of melting of 1 J / g or more during the heating process of the second run was defined as the softening point temperature. If a change in enthalpy of melting of 1 J / g or more was not observed during the heating process of the second run, the glass transition temperature measured by the following evaluation method was defined as the softening point temperature (Tm). Dynamic viscoelasticity measurements were performed on the bead material using a rheometer (Anton Paar's "Physica MCR301") under the following conditions, and the peak temperature (°C) of the loss tangent (tanδ) was defined as the glass transition temperature (Tg) and softening point temperature (Tm) of the bead material. Measuring jig: SRF10 Measurement mode: vibration φ, γ Strain: Swing angle γ = 0.015% Frequency: 1Hz Measurement temperature: 20℃~200℃ Heating rate: 2°C / min Normal force: -0.3N Measurement points: 180 Time unit: s

[0091] (Bulk ratio of pre-foamed beads and foamed beads) After measuring the mass W (g) of the pre-foamed beads and foamed beads, the volume V (cc) is measured by the immersion method, and the value is given by the following formula: (V / 0.63) / W(cm³). 3 The bulk ratio was defined as ( / g).

[0092] (Heat shrinkage rate of amorphous resin foam beads) 20cm of polystyrene beads 3 The materials were placed on a metal tray in a non-overlapping manner and placed in an oven set to the glass transition temperature Tg + 10°C of the bead material. After 5 minutes, they were removed. After cooling to room temperature, the bulk ratio after heating was determined, and the heat 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] (Heat shrinkage rate of crystalline resin foam beads) 20cm of polystyrene beads 3 The materials were placed on a metal tray in a non-overlapping manner and placed in an oven set to the softening point (melting point, Tm) of the bead material - 10°C. After 5 minutes, they were removed. After cooling to room temperature, the bulk ratio after heating was determined, and the heat 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)

[0094] (Expansion capacity of foam beads) 20cm of polystyrene beads 3 The material was placed in a pressure-resistant container with a pressure relief valve, and pressurized by introducing pressurized air (pressurized to 0.4 MPa over 4 hours, then held at 0.4 MPa for 16 hours) to perform pressurization. The pressure relief valve was fully opened, and the foam beads were moved from the pressure-resistant container to the foaming machine. Five minutes after the pressure relief valve was fully opened, the pressure was increased at a constant rate over 20 seconds using steam from 0 kPa to a predetermined pressure determined by the following formula, causing the beads to expand. The bulk ratio of the expanded foam beads was determined, and the expansion capacity was calculated using the following formula. The predetermined pressure was determined by considering the glass transition temperature if the resin contained in the bead material is amorphous, and the softening point temperature if it is crystalline, as shown in the following formula. Pressure: 8 × (glass transition temperature Tg or softening point temperature Tm of the bead material) - 756 (kPa) (wherein Tg is used if the resin contained in the bead material is amorphous, and Tm is used if it is crystalline) Expansion capacity: Xc / Xa Xa: Bulk ratio of the foam beads before heating (before expansion) (cm 3 / g) Xc: Bulk ratio of expanded foam beads (cm)3 / g)

[0095] (Moldability) A foamed molded body measuring 150 mm x 150 mm x 3 mm thick was produced using the method described in the examples and comparative examples below, under conditions of 0% cracking rate. The obtained foamed molded body was visually inspected, and its moldability was evaluated according to the following criteria. A: No filling defects were observed at the edges of the foamed molded product. B: Filling defects are observed at the edges of the foamed molded product.

[0096] (Rate of dimensional change) A 150mm x 150mm x 3mm thick foamed molded body test specimen was prepared using the method described in the examples and comparative examples below. This test specimen was dried for 24 hours in a 60°C drying oven (Satake Safe Bend Dryer N50-S5) to remove moisture from the specimen. Referring to the high-temperature dimensional stability test (Method B) described in JIS K6767, three 100mm long straight lines were drawn in a grid pattern in the center of the test specimen, both vertically and horizontally, parallel to each other, at 50mm intervals. The test specimen was then placed in the drying oven (Satake Safe Bend Dryer N50-S5) and heated for 168 hours at the "glass transition temperature Tg -32°C" if the resin contained in the bead raw material was amorphous resin, and at the "softening point temperature Tm -32°C" if it was crystalline resin. The lengths of the three vertical and three horizontal lines drawn on the test specimen were measured before and after the heating test, and the average value was calculated. The dimensional change rate was then calculated according to the following formula. Dimensional change rate (%) = {(L2-L1) / L1} × 100 (In the formula, L1 represents the average value of the line dimensions [mm] before the heating test, and L2 represents the average value of the line dimensions [mm] after the heating test.)

[0097] (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. Cases falling under any of the above categories V-0, V-1, or V-2 were classified as good (A), and cases falling under none of the above were classified as poor (B).

[0098] The raw materials used in the examples and comparative examples are described below.

[0099] (Reference example 1) Bead material pellet A was prepared by extruding a mixture of 87.5% by mass of modified polyphenylene ether resin ("SX-101" manufactured by Asahi Kasei Corporation) and 12.5% ​​by mass of a phosphazene-based flame retardant ("Rabitol FP-110" manufactured by Fushimi Pharmaceutical Co., Ltd.) as a non-halogenated flame retardant after heating, melting, and kneading in an extruder.

[0100] (Reference example 2) To 100 parts by mass of thermoplastic resin consisting of 73% by mass of S201A (manufactured by Asahi Kasei Corporation) as polyphenylene ether resin (PPE), 12% by mass of high-impact polystyrene resin (HIPS) with a rubber concentration of 6% by mass (rubber component content in the base resin is 0.6%), and 15% by mass of GP685 (manufactured by PS Japan Co., Ltd.) as general-purpose polystyrene resin (PS), 22 parts by mass of bisphenol A-bis(diphenyl phosphate) (BDP) as a non-halogenated flame retardant was added, and after heating, melting, and kneading in an extruder, the mixture was extruded to produce bead raw material pellet B.

[0101] (Reference example 3) Bead material pellet C was produced by extruding 40% by mass of polyphenylene ether resin (PPE) S201A (manufactured by Asahi Kasei Corporation) and 60% by mass of general-purpose polystyrene resin (PS) GP685 (manufactured by PS Japan Co., Ltd.) after heating, melting, and kneading in an extruder.

[0102] (Reference example 4) Bead raw material pellet D was produced by extruding general-purpose polystyrene resin (PS) GP685 (manufactured by PS Japan Co., Ltd.) after heating, melting, and kneading in an extruder.

[0103] (Reference example 5) Bead material pellets E:PA 100 parts by mass of a copolymer of nylon 6 and nylon 66 (product name: Novamid 2430A, manufactured by DSM) as a polyamide resin and 0.8 parts by mass of talc as a nucleating agent were heated, melt-mixed, and then extruded in an extruder to produce bead raw material pellets E.

[0104] (Reference example 6) Bead material pellets F: PLA 100 parts by weight of polylactic acid (Cargill Japan) with an L / D ratio of 88.5 / 11.5, 2.0 parts by weight of isocyanate compound (Millionate MR-200, Nippon Polyurethane Industry Co., Ltd.), and 3.0 parts by weight of talc (LMP-100, Fuji Talc Industry Co., Ltd.) were heated, melt-mixed, and then extruded in an extruder to produce bead material pellets F.

[0105] (Example 1) Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, the bead raw material pellets shown in Table 1 were placed in a pressure vessel, the gas in the pressure 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 bead raw material pellets were impregnated with carbon dioxide for 3 hours. Immediately after removing them from the pressure vessel, the bead raw material pellets were transferred and foamed with pressurized steam in a foaming furnace while rotating the stirring blades at 77 rpm according to the pressure program shown in Table 2. The bead foaming process and annealing bead process were then performed to obtain foamed beads. The hydrocarbon gas content of the foamed beads was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). In the bead foaming process shown in Table 2, the increase in bulk ratio per second is 0.1 cm. 3 / g or more 100cm 3 Although the value was less than / g, the bulk ratio decreased during the bead annealing process. Subsequently, these foam beads 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 (cracking rate 0%), heated with steam to expand and fuse the foam beads together, cooled, and removed from the molding die to obtain a foamed molded body made of foam beads. The measurement and evaluation results of each physical property are shown in Table 1.

[0106] (Examples 2-5, 16-17, Comparative Example 2) A foamed molded body was obtained in the same manner as in Example 1, except that the pressure program for pressurized steam used when manufacturing foamed beads from bead raw materials was set as shown in Table 2. The measurement and evaluation results of each physical property are shown in Table 1. In Examples 2-5, 16-17, and Comparative Example 2, the increase in bulk ratio per second in the bead foaming process shown in Table 2 was 0.1 cm. 3 / g or more 100cm 3 Although the value was less than / g, the bulk ratio decreased during the bead annealing process.

[0107] (Examples 6-10) Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, the bead raw material pellets shown in Table 1 were 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 bead raw material pellets were impregnated with carbon dioxide for 3 hours. Immediately after removing them from the pressure vessel, the bead raw material pellets were transferred and foamed in a foaming furnace with pressurized steam using the pressure program shown in Table 2 while rotating the stirring blades at 77 rpm, thereby obtaining pre-foamed beads. The hydrocarbon gas content of the foamed beads was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). Next, the obtained pre-foamed beads were placed in a hot air dryer and heated at the temperatures and times shown in Table 3 to obtain foamed beads. In Examples 6-10, the increase in bulk ratio per second in the bead foaming process shown in Table 2 was 0.1 cm. 3 / g or more 100cm 3 Although the value was less than / g, the bulk ratio decreased during the bead annealing process. Subsequently, these foam beads 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 (cracking rate 0%), heated with steam to expand and fuse the foam beads together, cooled, and removed from the molding die to obtain a foamed molded body made of foam beads. The measurement and evaluation results of each physical property are shown in Table 1.

[0108] (Examples 11-12, 14) Following the method described in Example 1 of Japanese Patent Publication No. 4-372630, the bead raw material resin pellets shown in Table 1 were placed in a pressure-resistant container, the gas inside the container was replaced with dry air, and then 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 bead raw material resin pellets were impregnated with carbon dioxide for 3 hours. Next, the bead raw material resin pellets were placed in a mesh basket and heated with hot air while stirring under the conditions shown in Table 4 to obtain foamed and annealed beads. Subsequently, these foam beads 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 (cracking rate 0%), heated with steam to expand and fuse the foam beads together, cooled, and removed from the molding die to obtain a foamed molded body made of foam beads. The measurement and evaluation results of each physical property are shown in Table 1.

[0109] (Example 13) A foamed molded body was obtained in the same manner as in Example 1, except that the bead raw materials were changed as shown in Table 1 and the pressure program for pressurized steam used to produce foamed beads from the bead raw materials was set as shown in Table 2. The measurement and evaluation results of each physical property are shown in Table 1. In the bead foaming process shown in Table 2, the increase in bulk ratio per second is 0.1 cm. 3 / g or more 100cm 3 Although the value was less than / g, the bulk ratio decreased during the bead annealing process.

[0110] (Example 15) Carbon dioxide was added to the resin pellet E as a foaming agent in accordance with the method described in the examples of Japanese Patent Publication No. 2011-105879. Foamed beads were then obtained by heating and foaming the resin pellet containing carbon dioxide. This was filled into an in-mold molding die with steam vents (cracking rate 0%), heated with steam to expand and fuse the foam beads together, then cooled and removed from the molding die to obtain a foamed molded body made of foam beads. The measurement and evaluation results of each physical property are shown in Table 1. In the bead foaming process shown in Table 4, the increase in bulk ratio per second is 0.1 cm. 3 / g or more 100cm 3 Although the value was less than / g, the bulk ratio decreased during the bead annealing process.

[0111] (Comparative Example 1) Except for the absence of the bead annealing process, foamed beads and foamed molded articles were obtained using the program shown in Table 2, in the same manner as in Example 1. The measurement and evaluation results of each physical property are shown in Table 1.

[0112] (Comparative Example 7) Foamed beads and foamed molded articles were obtained using the program shown in Table 4, in the same manner as in Example 15, except that the bead annealing process was omitted. The measurement and evaluation results of each physical property are shown in Table 1.

[0113] (Comparative Example 3) Except for the absence of the bead annealing process, foamed beads and foamed molded articles were obtained using the program shown in Table 2, in the same manner as in Example 9. The measurement and evaluation results of each physical property are shown in Table 1.

[0114] (Comparative Example 4) To 100 parts by weight of the same bead raw material resin pellets as in Example 1, 10 parts by weight of n-pentane (boiling point 36.1°C) was added as a foaming agent, and the mixture was heated and kneaded in an extruder to obtain unfoamed particles. These resin particles were heated in a foaming furnace with pressurized steam while rotating a stirring blade at 77 rpm to foam them and obtain foamed beads. The foaming temperature at this time was 155°C. Subsequently, without performing bead annealing, we attempted to apply pressure and mold the material in the same manner as in Example 1, but we were unable to obtain a foamed molded body due to insufficient bead fusion. The measurement and evaluation results of each physical property are shown in Table 1.

[0115] (Comparative Example 5) Foamed beads and foamed molded articles were obtained using the program shown in Table 4, in the same manner as in Example 11, except that the bead annealing process was omitted. The measurement and evaluation results of each physical property are shown in Table 1.

[0116] (Comparative Example 6) 100 parts by weight of bead raw material pellets F were mixed with 40 parts by weight of isobutane and 4.8 parts by weight of methanol, sealed, and heated to 85°C for 3 hours. After cooling to 25°C, the mixture was removed and expanded with steam (94°C for 1 minute) to obtain expanded beads. After aging at 30°C for 1 day, the mixture was filled into an in-mold molding die with steam vents (cracking rate 0%), and an attempt was made to mold the expanded beads by heating with steam, but due to insufficient fusion of the beads, a expanded molded body could not be obtained. The measurement and evaluation results of each physical property are shown in Table 1.

[0117] [Table 1]

[0118] [Table 2]

[0119] [Table 3]

[0120] [Table 4] [Industrial applicability]

[0121] The foamed molded articles obtained from the foamed beads manufactured by the manufacturing method of this embodiment can be suitably used as automotive peripheral components, electronic equipment peripheral components, and the like.

Claims

1. A bead foaming process involves foaming a resin-containing bead material to obtain pre-foamed beads, The process includes a bead annealing step in which the pre-foamed beads are heat-treated at a temperature of (glass transition temperature - 30)°C or higher and (glass transition temperature + 30)°C or lower after the bead foaming step, The ratio of the bulk ratio of the foamed beads after the bead annealing process to the bulk ratio of the pre-foamed beads before the bead annealing process (100%) is 30% or more and 99% or less. The aforementioned resin is an amorphous resin. A method for manufacturing foamed beads, characterized by the following features.

2. The method for producing foamed beads according to claim 1, wherein the heat treatment is performed using steam in the bead annealing step.

3. The method for producing foamed beads according to claim 1, wherein the heat treatment is performed using hot air in the bead annealing step.

4. A method for manufacturing foamed beads according to claim 1, wherein the bead foaming step and the bead annealing step are performed in the same apparatus.

5. The method for producing foamed beads according to claim 1, wherein the heat treatment time is 10 seconds or more and 600 seconds or less.

6. The method for producing foamed beads according to Claim 1, wherein in the bead annealing step, the rate of change of the bulk ratio of the pre-foamed beads per second is -0.5 cm³ / g or more and -0.001 cm³ / g or less.

7. A foamed bead obtained by foaming a bead material containing an amorphous resin, wherein the heat shrinkage rate when heated at (glass transition temperature + 10)°C for 5 minutes is 25% or less. Amorphous resin foam beads characterized by the following features.

8. The amorphous resin foam beads according to claim 7, wherein the expansion capacity is 2.3 or more.

9. A material obtained by molding amorphous resin foam beads according to claim 7 or 8, A foamed molded article characterized by the following features.

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