JP7783106B2 - Thermoplastic polyester elastomer resin foam molded article and method for producing same - Google Patents

Description

The present invention relates to a foam molded thermoplastic polyester elastomer resin.

Polyester block copolymers, which have crystalline aromatic polyester units as hard segments and aliphatic polyether units such as poly(alkylene oxide) glycol or aliphatic polyester units such as polylactone as soft segments, are excellent in many respects, including moldability, impact resistance, elastic recovery, flexibility, and other mechanical properties, as well as heat resistance. Because of their excellent balance of these properties (moldability, mechanical properties, and heat resistance), their applications have expanded to include industrial materials such as sheets, films, and fibers, as well as automobiles and electrical and electronic parts.

For impact absorption and vibration-damping applications, materials are required that are flexible, have a low impact resilience, and have excellent impact absorption properties. Furthermore, since sound absorption properties may be required depending on the location of use of the impact absorption and vibration-damping materials, excellent sound absorption properties are also desirable.

Theoretically, polyester block copolymers can be made more flexible by increasing the mass ratio of the soft segment, but at the same time, the impact resilience increases. Furthermore, a surface Shore D hardness of 30 is the practical limit for flexibility, and in terms of flexibility, they are positioned as the hardest elastomers among engineering plastic elastomers and general-purpose elastomers, which limits their potential applications.

Furthermore, efforts to reduce the weight of plastic parts have been progressing in recent years, and one way to achieve this is through the use of foam molded products.

Conventionally, a method of using a supercritical inert gas as a physical blowing agent to obtain foamed polyester block copolymers has been proposed, making it possible to obtain foamed molded articles with excellent lightness and a high expansion ratio (for example, Patent Documents 1 and 2). Patent Documents 1 and 2 disclose foamed molded articles with excellent lightness and a high expansion ratio obtained by impregnating a low-hardness polyester elastomer with a supercritical inert gas.

Patent No. 6380638 Patent No. 6358368

However, the compositions disclosed in Patent Documents 1 and 2 use a polyester elastomer with a high mass ratio of soft segments, which results in a high rebound resilience modulus for the resulting foam molded article, making it difficult to obtain a flexible foam molded article with a high expansion ratio and a rebound resilience modulus of less than 60%.

As a result of extensive research to achieve the above-mentioned objective, the inventors have succeeded in producing a thermoplastic polyester elastomer resin foam molded article with a high expansion ratio that is flexible, has a low rebound resilience, and is lightweight. By controlling the mass ratio of each component in a composition that simultaneously blends a specific polyester block copolymer with a core-shell copolymer, the core of which is a polymer primarily composed of butyl acrylate or a mixture of butyl acrylate and 2-ethylhexyl acrylate and obtained by emulsion polymerization of a specific group of compounds, and the shell of which is a polymer primarily composed of an aromatic vinyl compound and a vinyl cyanide compound and obtained by polymerization of a specific compound, the inventors have succeeded in producing a thermoplastic polyester elastomer resin foam molded article with a high expansion ratio that is flexible, has a low rebound resilience, and is lightweight.

That is, the present invention constitutes [1] to [6].
[1] A polyester block copolymer (A) having as its main components a high-melting crystalline segment (a-1) mainly composed of crystalline aromatic polyester units and a low-melting polymer segment (a-2) mainly composed of aliphatic polyether units and/or aliphatic polyester units, in an amount of 20 to 95% by mass, with butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1), at least one compound (b-2) selected from alkyl acrylates having an alkyl group of 1 to 4 carbon atoms and alkyl methacrylates having an alkyl group of 1 to 4 carbon atoms, a vinyl cyan compound (b-3), and a copolymer represented by the following structural formula (I): a thermoplastic polyester elastomer resin foam molded article having foam cells, and a density (apparent density) of less than 0.70 g/cm3, an expansion ratio of 2.0 or more, and a rebound resilience of 60% or less, the thermoplastic polyester elastomer resin composition comprising 5 to 80 mass% of a core-shell copolymer (B) having a core formed by emulsion polymerization of a maleic acid monoalkyl ester compound (b-4) and a crosslinking agent (b-5), and a shell formed by polymerization of an aromatic vinyl compound (b-6), a vinyl cyan compound (b- ^{3), and a crosslinking agent (b-5} ); and 0 to 40 mass% of a hydrogenated styrene block copolymer (C) comprising at least one vinyl aromatic compound polymer block (c1) and at least one conjugated diene block (c2).
[2] The thermoplastic polyester elastomer resin foam molded article according to [1], wherein the foam cells have an average cell diameter of 10 to 600 μm.
[3] The thermoplastic polyester elastomer resin foam molded article according to [1] or [2], characterized in that the surface hardness measured according to the method described in JIS K7215 is 90A or less.
[4] A method for producing a thermoplastic polyester elastomer resin foam molded article according to any one of [1] to [3], comprising: injecting the thermoplastic polyester elastomer resin composition in a molten state together with a chemical foaming agent (E) and/or an inert gas (D) in a supercritical state into a cavity of a mold comprising a fixed mold and a movable mold that can move forward and backward to any position, and then moving the movable mold in the mold opening direction to expand the volume of the cavity and cause foaming.
[5] A method for producing a thermoplastic polyester elastomer resin foam molded article according to [4], characterized in that the thermoplastic polyester elastomer resin composition in a molten state is injected and filled together with an inert gas (D) in a supercritical state.
[6] The method for producing a thermoplastic polyester elastomer resin foam molded article according to [4] or [5], characterized in that the inert gas (D) is nitrogen.

The thermoplastic polyester elastomer resin foam molded article of the present invention is not only lightweight, but also flexible and exhibits a low rebound resilience. Furthermore, despite a high expansion ratio, it maintains a uniform foaming state and exhibits high heat resistance, water resistance, sound absorption properties, and molding stability, making it possible to provide a thermoplastic polyester elastomer resin foam molded article that can be used in parts that require high reliability.

The present invention is described below.

The thermoplastic polyester elastomer resin foam molded article of the present invention comprises 20 to 95 mass % of a polyester block copolymer (A) having as its main components a high-melting point crystalline polymer segment (a-1) mainly composed of a crystalline aromatic polyester and a low-melting point polymer segment (a-2) mainly composed of an aliphatic polyether unit and/or an aliphatic polyester unit, and a mixture of butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1), at least one compound (b-2) selected from an alkyl acrylate having an alkyl group of 1 to 4 carbon atoms and an alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, a vinyl cyan compound ( a core-shell copolymer (B) having a core formed by emulsion polymerization of a maleic acid monoalkyl ester compound (b-4) represented by the following structural formula (I) and a crosslinking agent (b-5), and a shell formed by polymerization of an aromatic vinyl compound (b-6), a vinyl cyan compound (b-3), and a crosslinking agent (b-5); and a thermoplastic polyester elastomer resin foam molded article comprising a thermoplastic polyester elastomer resin composition characterized by blending 5 to 80 mass% of a core-shell copolymer (B) having a core formed by emulsion polymerization of a maleic acid monoalkyl ester compound (b-4) represented by the following structural formula (I) and a crosslinking agent (b-5), and 0 to 40 mass% of a hydrogenated styrene block copolymer (C) comprising at least one vinyl aromatic compound polymer block (c-1) and at least one conjugated diene block (c- ² ), the thermoplastic polyester elastomer resin foam molded article having foam cells, a density (apparent density) of less than 0.7 g/cm3, an expansion ratio of 2.0 or more, and a rebound resilience of 60% or less.

The polyester block copolymer (A) used in the present invention is primarily composed of a high-melting crystalline segment (a-1) primarily composed of crystalline aromatic polyester units and a low-melting polymer segment (a-2) primarily composed of aliphatic polyether units and/or aliphatic polyester units. The high-melting crystalline polymer segment (a-1) is a polyester formed primarily from an aromatic dicarboxylic acid or its ester-forming derivative and a diol or its ester-forming derivative. Specific examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, anthracene dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenoxyethane dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 5-sulfoisophthalic acid, and sodium 3-sulfoisophthalate.

Aromatic dicarboxylic acids are primarily used for the high-melting point crystalline polymer segment (a-1). However, if necessary, some of the aromatic dicarboxylic acids may be substituted with alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid, cyclopentanedicarboxylic acid, and 4,4'-dicyclohexyldicarboxylic acid, or aliphatic dicarboxylic acids such as adipic acid, succinic acid, oxalic acid, sebacic acid, dodecanedioic acid, and dimer acid. Ester-forming derivatives of dicarboxylic acids, such as lower alkyl esters, aryl esters, carbonate esters, and acid halides, can also be used.

Preferred diols include those with a molecular weight of 400 or less, such as aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, and decamethylene glycol; alicyclic diols such as 1,1-cyclohexanedimethanol, 1,4-dicyclohexanedimethanol, and tricyclodecanedimethanol; and aromatic diols such as xylylene glycol, bis(p-hydroxy)diphenyl, bis(p-hydroxyphenyl)propane, 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, bis[4-(2-hydroxy)phenyl]sulfone, 1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane, 4,4'-dihydroxy-p-terphenyl, and 4,4'-dihydroxy-p-quaterphenyl. These diols can also be used in the form of ester-forming derivatives, such as acetylated forms and alkali metal salts.

Two or more of these dicarboxylic acids and their derivatives or diol components may also be used in combination.

The most preferred example of the high-melting-point crystalline polymer segment (a-1) is polybutylene terephthalate derived from terephthalic acid and/or dimethyl terephthalate and 1,4-butanediol.

The low-melting point polymer segment (a-2) of the polyester block copolymer (A) used in the present invention is an aliphatic polyether and/or an aliphatic polyester. Examples of aliphatic polyethers include poly(ethylene oxide) glycol, poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide adducts of poly(propylene oxide) glycol, and copolymers of ethylene oxide and tetrahydrofuran. Examples of aliphatic polyesters include poly(ε-caprolactone), polyenantholactone, polycaprylolactone, and polybutylene adipate. Among these aliphatic polyethers and/or aliphatic polyesters, poly(tetramethylene oxide) glycol, ethylene oxide adducts of poly(propylene oxide) glycol, poly(ε-caprolactone), polybutylene adipate, etc. are preferred due to the elastic properties of the resulting polyester block copolymers, and of these, ethylene oxide adducts of poly(propylene oxide) glycol are particularly preferred.

The copolymerization amount of the low-melting point polymer segment (a-2) in the polyester block copolymer (A) used in the present invention is typically 10 to 90% by mass, preferably 15 to 85% by mass, and more preferably 20 to 80% by mass. In particular, if it is 10% by mass or less, flexibility will be insufficient, and if it is 90% by mass or more, crystallinity will be low and moldability will be poor.

Two or more polyester block copolymers with different compositions may also be used in combination.

The polyester block copolymer (A) used in the present invention can be produced by known methods. For example, any of the following methods may be used: transesterification of a lower alcohol diester of a dicarboxylic acid, an excess amount of a low-molecular-weight glycol, and a low-melting polymer segment component in the presence of a catalyst, followed by polycondensation of the resulting reaction product; esterification of a dicarboxylic acid, an excess amount of a glycol, and a low-melting polymer segment component in the presence of a catalyst, followed by condensation of the resulting reaction product; randomization of a high-melting crystalline segment by pre-forming it and then adding a low-melting segment component to it through a transesterification reaction; linking a high-melting crystalline segment and a low-melting polymer segment with a chain linking agent; or addition reaction of a high-melting crystalline segment with an ε-caprolactone monomer when poly(ε-caprolactone) is used for the low-melting polymer segment.

The core-shell copolymer (B) used in the present invention is a core-shell copolymer having a core formed by emulsion polymerization of butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1), at least one compound (b-2) selected from an alkyl acrylate having an alkyl group of 1 to 4 carbon atoms and an alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, a vinyl cyanide compound (b-3), a maleic acid monoalkyl ester compound (b-4) represented by the following structural formula (I), and a crosslinking agent (b-5), and a shell formed by further polymerization of an aromatic vinyl compound (b-6), a vinyl cyanide compound (b-3), and a crosslinking agent (b-5).

Examples of the acrylic acid ester having an alkyl group with 1 to 4 carbon atoms and the methacrylic acid ester having an alkyl group with 1 to 4 carbon atoms (b-2) that constitute the core of the core-shell copolymer (B) include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate, with methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate being preferred.

(In the formula, the substituent R represents a saturated aliphatic hydrocarbon group having 10 to 24 carbon atoms, an unsaturated aliphatic hydrocarbon group, or an aromatic hydrocarbon group.)
The vinyl cyanide compound (b-3) constituting the core-shell copolymer (B) used in the present invention can be acrylonitrile, methacrylonitrile, etc. The vinyl cyanide compound (b-3) used in the core and the vinyl cyanide compound (b-3) used in the shell may be the same or different, but when they are the same, the core-shell copolymer (B) can be easily obtained.

The maleic acid monoalkyl ester compound (b-4) constituting the core-shell copolymer (B) used in the present invention is represented by the structural formula (I) above. Examples of saturated aliphatic hydrocarbon groups include lauryl, undecanyl, myristyl, palmityl, heptadecanyl, stearyl, arachidyl, and behenyl groups. Examples of unsaturated aliphatic hydrocarbon groups include palmitoleic, heptadecenyl, oleyl, eicosenyl, erucyl, linoleic, and linolenic groups. Examples of aromatic hydrocarbon groups include phenylpropane, phenylsulfone, xylyl, and naphthyl groups. Examples of alkali metals include sodium and potassium.

Examples of the crosslinking agent (b-5) constituting the core-shell copolymer (B) used in the present invention include diacrylates and/or triacrylates of polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propanediol, 1,4-butanediol, and glycerin, dimethacrylates and/or trimethacrylates of similar polyhydric alcohols, and aromatic divinyl compounds such as divinylbenzene and divinyltoluene. The crosslinking agent (b-5) used for the core and the crosslinking agent (b-5) used for the shell may be the same or different, but if they are the same, the core-shell copolymer (B) can be obtained more easily.

Examples of the aromatic vinyl compound (b-6) constituting the core-shell copolymer (B) used in the present invention include styrene, α-methylstyrene, o-methylstyrene, m-methoxystyrene, and N,N-dimethyl-p-aminostyrene.

The copolymerization amount of butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1) constituting the core-shell copolymer (B) used in the present invention is preferably 40 to 80% by mass per 100% by mass of the core-shell copolymer (B). If the copolymerization amount of butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1) is less than 40% by mass, the flexibility of the core-shell copolymer (B) will be insufficient, and the objective of the present invention to achieve flexible thermoplastic polyester elastomer resin foam molded articles will not be fully achieved. Furthermore, if the copolymerization amount of butyl acrylate alone or a mixture of 2-ethylhexyl acrylate (b-1) exceeds 80% by mass, the stickiness of the core-shell copolymer (B) will be significant, resulting in sticky thermoplastic polyester elastomer resin foam molded articles of the present invention, and the desired improved handleability and pleasant feel to the touch will not be achieved.

The amount of 2-ethylhexyl acrylate in the butyl acrylate alone or the mixture (b-1) of butyl acrylate and 2-ethylhexyl acrylate that constitutes the core-shell copolymer (B) used in the present invention is preferably 40% by mass or less. If the amount of 2-ethylhexyl acrylate exceeds 40% by mass, the core-shell copolymer (B) becomes significantly tacky, resulting in the thermoplastic polyester elastomer resin foam molded article of the present invention becoming tacky, and the desired improved handleability and pleasant feel to the touch cannot be achieved.

The shell constituting the core-shell copolymer (B) used in the present invention is preferably obtained by polymerizing 6 to 20 parts by mass of an aromatic vinyl compound (b-6), 3 to 12 parts by mass of a vinyl cyan compound (b-3), and 0.05 to 1 part by mass of a crosslinking agent (b-5) per 100 parts by mass of the core polymer. If the amount of aromatic vinyl compound (b-6) or vinyl cyan compound (b-3) constituting the shell polymer is small, the dispersion of the core-shell copolymer (B) in the polyester block copolymer (A) will be poor, resulting in a significant decrease in the strength of the thermoplastic polyester elastomer resin foam molded article. Furthermore, if the amount of aromatic vinyl compound (b-6) or vinyl cyan compound (b-3) constituting the shell polymer is large, the flexibility of the core-shell copolymer (B) will be insufficient, and the objective of this invention to improve the flexibility of the thermoplastic polyester elastomer resin foam molded article will not be fully achieved.

Two or more types of core-shell copolymers (B) with different compositions may also be used in combination.

The core-shell copolymer (B) used in the present invention can be produced by a known two-step reaction. For example, butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1), at least one compound selected from alkyl acrylates and alkyl methacrylates having an alkyl group containing 1 to 4 carbon atoms (b-2), a vinyl cyanide compound (b-3), a monoalkyl maleate (b-4), and a crosslinking agent (b-5) are charged into a reaction vessel together with a solvent such as water, a surfactant such as sodium alkylbenzene sulfonate, and a radical initiator such as di-t-butyl peroxide, and emulsion polymerization is carried out at a predetermined temperature to produce a core polymer latex. The desired core-shell copolymer can be obtained by further reacting an aromatic vinyl compound (b-6), a vinyl cyanide compound (b-3), and a crosslinking agent (b-5) into the reaction vessel containing this core polymer latex. The resulting core-shell copolymer (B) latex is then added with a coagulant such as calcium chloride, washed, and dried to isolate the core-shell copolymer (B).

The hydrogenated styrene-butadiene block copolymer (C) used in the present invention is a hydrogenated styrene-butadiene block copolymer, and this styrene-butadiene block copolymer is a diblock copolymer, triblock copolymer, radial block copolymer, or the like, consisting of a styrene block and a butadiene block.

At least one vinyl aromatic compound polymer block (c-1) of the hydrogenated styrene block copolymer (C) used in the present invention is a block polymerized from styrene, α-methylstyrene, vinyltoluene, p-methylstyrene, p-t-butylstyrene, o-ethylstyrene, o,p-dichlorostyrene, or the like, with styrene being preferred among these.

At least one conjugated diene block (c-2) of the hydrogenated styrene block copolymer (C) used in the present invention is a block polymerized from butadiene, isoprene, butadiene/isoprene copolymer, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 3-butyl-1,3-octadiene, chloroprene, or the like. Of these, styrene-butadiene block copolymers, styrene-isoprene block copolymers, and styrene-isoprene/butadiene block copolymers are preferably used.

The hydrogenated styrene block copolymer (C) may be modified with an unsaturated carboxylic acid or its anhydride, or an epoxy group-containing monomer. Specific examples include modified styrene-hydrogenated butadiene diblock copolymers and modified styrene-hydrogenated butadiene-styrene triblock copolymers (modified styrene-ethylene-butylene-styrene block copolymers: modified SEBS).

Furthermore, two or more types of hydrogenated styrene-butadiene block copolymers (C) having different compositions may be used.

The blending ratios of each component in the thermoplastic polyester elastomer resin composition of the present invention are 20 to 95% by mass, more preferably 20 to 90% by mass, preferably 25 to 85% by mass, and even more preferably 30 to 80% by mass of the polyester block copolymer (A), 5 to 80% by mass, preferably 5 to 75% by mass of the core-shell copolymer (B), and 0 to 40% by mass, preferably 0 to 25% by mass of the hydrogenated styrene block copolymer (C). The hydrogenated styrene block copolymer (C) is an optional component.

If the polyester block copolymer (A) is less than 20% by mass, the melt tension of the thermoplastic polyester polymer decreases, making the bubbles more likely to break and forming coarse cells. If it exceeds 95% by mass, flexibility will be lost.

If the core-shell copolymer (B) is less than 5% by mass, sufficient flexibility cannot be achieved. If it exceeds 80% by mass, the melt tension of the thermoplastic polyester polymer decreases, making the bubbles more likely to break and resulting in the formation of coarse cells.

When using hydrogenated styrene block copolymer (C), if the amount exceeds 40% by mass, the melt tension of the thermoplastic polyester polymer decreases, making the cells more likely to break and resulting in the formation of coarse cells.

The thermoplastic polyester elastomer resin composition of the present invention preferably has a surface hardness of 90A or less, and more preferably 80A or less, measured according to the method described in JIS K7215.

The thermoplastic polyester elastomer of the present invention may optionally contain or exclude, to the extent that the performance of the thermoplastic polyester elastomer of the present invention is not impaired, known antioxidants such as hindered phenols, phosphites, thioethers, and aromatic amines; light stabilizers such as benzophenones, benzotriazoles, and hindered amines; thickeners such as epoxy compounds and isocyanate compounds; colorants such as dyes and pigments; UV screeners such as titanium oxide and carbon black; reinforcing agents such as glass fiber, carbon fiber, and potassium titanate fiber; fillers such as silica, clay, calcium carbonate, zinc oxide, magnesium oxide, calcium sulfate, and glass beads; liquid polyisobutene, liquid polybutene, liquid (hydrogenated) polyisoprene, liquid (hydrogenated) polybutadiene, paraffinic oil, naphthenic oil, epoxy plasticizers, plasticizers such as phosphate esters, phthalates, aliphatic dibasic acid esters, and glycol esters; nucleating agents such as talc; tackifiers; flame retardants; fluorescent agents; crosslinking agents; surfactants.

The thermoplastic polyester elastomer resin foam molded article of the present invention is obtained using the thermoplastic polyester elastomer resin composition of the present invention described above. The thermoplastic polyester elastomer resin foam molded article of the present invention has a non-foamed skin layer present on the surface and a foamed layer present on the inner layer. Because the non-foamed skin layer and the foamed layer are formed from the thermoplastic polyester elastomer resin composition of the present invention described above, the article has a foam structure with uniform and fine foam cells, and exhibits excellent light weight, low resilience, and flexibility. The foamed layer is composed of a resin continuous phase and independent foam cells. Here, the resin continuous phase refers to the portion of the cured polyester elastomer resin composition that does not have voids.

As long as the diameter (cell diameter) of the foam cells of the thermoplastic polyester elastomer resin foam molded article of the present invention is uniform and without variation, the properties will vary depending on the size. A smaller cell diameter is advantageous for achieving flexibility and low impact resilience, and specifically, an average cell diameter of 10 to 600 μm is preferred. If the average cell diameter is less than 10 μm, the internal pressure of the foam molded article will be low, resulting in insufficient pressure when forming the non-foamed skin layer, and poor appearance such as sink marks will tend to occur. On the other hand, if the average cell diameter exceeds 600 μm, the tensile strength will be low and the mechanical properties will tend to be poor.

The thermoplastic polyester elastomer resin foam molded article of the present invention is characterized by having a density (apparent density) of less than 0.70 g/cm ^3. Since the density of a typical polyester elastomer is approximately 1.0 to 1.4 g/cm ³ , it can be said that the foam molded article of the present invention is sufficiently lightweight. On the other hand, if the density exceeds 0.70 g/cm ³ , sufficient flexibility cannot be obtained.

The thermoplastic polyester elastomer resin foam molded article of the present invention is characterized by a rebound resilience of 60% or less, more preferably 50% or less. If the rebound resilience exceeds 60%, the resilience is too great and sufficient impact absorption cannot be achieved.

The thermoplastic polyester elastomer resin foam molded article of the present invention is characterized by having foam cells and an expansion ratio of 2.0 or more. If the expansion ratio is less than 2.0, the low impact resilience and light weight of the foam molded article will be insufficient. An expansion ratio of 4 or more is more preferable. Furthermore, from the viewpoint of extensibility, which allows the edge surfaces of the foam molded article to be formed faithfully to the mold, an expansion ratio of 6 or less is preferable.

For the thermoplastic polyester elastomer resin foam molded article of the present invention, the normal incidence sound absorption coefficient at the sound absorption peak frequency (hereinafter sometimes referred to as "peak frequency sound absorption coefficient") measured in the frequency range of 0.4 kHz to 5.0 kHz, which is generally the main frequency range where noise problems occur, according to a method in accordance with JIS A1405 (2007) is preferably 0.3% or more, more preferably 0.4% or more, even more preferably 0.5% or more, and particularly preferably 0.6% or more. The peak frequency sound absorption coefficient can be measured, for example, using the WinZac MTX normal incidence sound absorption coefficient measurement system manufactured by Nihon Onkyo Engineering Co., Ltd.

The sound absorption peak frequency is preferably 0.4 kHz to 4.0 kHz, more preferably 0.4 kHz to 3.5 kHz, even more preferably 0.4 kHz to 3.0 kHz, particularly preferably 0.4 kHz to 2.5 kHz, and most preferably 0.4 kHz to 2.0 kHz. The thermoplastic polyester elastomer resin foam molded product of the present invention preferably has the sound absorption peak frequency in the low frequency range.

The expansion ratio in the present invention is calculated from the density of the thermoplastic polyester elastomer resin composition before foaming/the density of the thermoplastic polyester elastomer resin foam molded product. The density of the thermoplastic polyester elastomer resin composition before foaming and the density of the thermoplastic polyester elastomer resin foam molded product can be determined according to ASTM D792.

The foaming method for the foamed molded article of the present invention is not particularly limited, but a foaming method in which a resin composition is impregnated with a high-pressure gas and then the pressure is reduced (the pressure is released) is preferred. Among these, a method in which a foamed molded article is obtained by expanding the volume of the cavity when the blowing agent and the polyester elastomer resin composition of the present invention are melt-mixed and injection-molded is preferred, as this molding method is advantageous in terms of molding cycle time, cost, and ability to produce homogeneous foam.

Specifically, this method involves injecting a molten thermoplastic polyester elastomer resin composition together with a chemical foaming agent (E) and/or a supercritical inert gas (D) into a cavity formed by a mold consisting of multiple clamped fixed molds and a movable mold that can move forward and backward to any position, filling the cavity. Once a non-foamed skin layer has been formed, at least one movable mold is moved in the mold opening direction to expand the cavity volume and cause foaming, thereby obtaining a thermoplastic polyester elastomer resin foam molded article. Among these, the use of a supercritical inert gas (D) is preferred.

The distance traveled in the mold opening direction is the core-back amount, and by setting the core-back amount, it is possible to adjust the desired thickness of the foam molded product. Furthermore, during foam molding, the molding temperature, cooling time, the time from when the thermoplastic polyester elastomer resin composition is filled into the mold cavity until it is core-backed (core-back delay time), and the time from when core-back begins to be completed (core-back transition time) can be adjusted appropriately depending on the material to obtain an optimal foam molded product. The thermoplastic polyester elastomer resin composition for foam molding, the chemical blowing agent (E) and/or the supercritical inert gas (D) can be mixed in the plasticization zone of the injection molding machine before being filled into the cavity.

The chemical foaming agent (E) that can be used to obtain the foamed molded article of the present invention is added to the molten resin in the resin melting zone of the molding machine as a gas component or source that serves as the foam nuclei. Specifically, examples of chemical foaming agents that can be used include inorganic compounds such as ammonium carbonate and sodium bicarbonate, and organic compounds such as azo compounds, sulfohydrazide compounds, nitroso compounds, and azide compounds.

Examples of the azo compounds include diazocarbonamide (ADCA), 2,2-azoisobutyronitrile, azohexahydrobenzonitrile, and diazoaminobenzene, with ADCA being the most preferred. Examples of the sulfohydrazide compounds include benzenesulfohydrazide, benzene 1,3-disulfohydrazide, diphenylsulfone-3,3-disulfonhydrazide, and diphenyloxide-4,4-disulfonhydrazide. Examples of the nitroso compounds include N,N-dinitrosopentaethylenetetramine (DNPT). Examples of the azide compounds include terephthalazide and p-tert-butylbenzazide.

A variety of gases are produced from chemical blowing agents (E). For example, diazocarbonamide (ADCA) produces thermal decomposition products, primarily nitrogen, carbon monoxide, and carbon dioxide, as well as trace amounts of ammonia gas. Biurea, cyanuric acid, and urazole may also remain as decomposition residues. These thermal decomposition products and decomposition residues can be identified using pyrolysis gas chromatography, infrared spectroscopy, and mass spectrometry.

When using a chemical blowing agent (E), the chemical blowing agent (E) can be used as a blowing agent masterbatch based on a thermoplastic resin with a melting point lower than the decomposition temperature of the thermally decomposable blowing agent in order to uniformly disperse the chemical blowing agent (E) in the thermoplastic polyester elastomer of the present invention. The base thermoplastic resin is not particularly limited as long as it has a melting point lower than the decomposition temperature of the chemical blowing agent (E), and examples include polystyrene (PS), polyethylene (PE), and polypropylene (PP). In this case, the blending ratio of the chemical blowing agent (E) to the thermoplastic resin is preferably 10 to 100 parts by weight of the thermally decomposable blowing agent per 100 parts by weight of the thermoplastic resin. If the chemical blowing agent (E) is less than 10 parts by weight, the amount of masterbatch relative to the thermoplastic polyester elastomer of the present invention may be too high, potentially resulting in a deterioration in physical properties. If the amount exceeds 100 parts by weight, masterbatch formation becomes difficult due to issues with the dispersibility of the chemical blowing agent (E).

Other additives can be used with these chemical foaming agents (E) as needed. For example, to stabilize and uniformly fine the cells in the foamed molded article, organic acids such as citric acid, which promote gas generation, or metal salts of organic acids such as sodium citrate can be used or added in combination. Nucleating agents such as talc and inorganic fine particles such as lithium carbonate can also be added. Particularly preferred are sodium bicarbonate, a combination of sodium bicarbonate and sodium citrate, and a combination of sodium bicarbonate and citric acid.

The amount of chemical blowing agent (E) in the thermoplastic polyester elastomer resin composition of the present invention is preferably 1.0 to 5.0 parts by mass, and more preferably 1.0 to 3.5 parts by mass, per 100 parts by mass of the thermoplastic polyester elastomer resin composition. If the amount of chemical blowing agent (E) is 1.0 part by mass or less, foaming performance may be poor. If it exceeds 5.0 parts by mass, the amount of foaming gas will be excessive, and the bubbles may interfere with each other, making it easier for open cells to form, resulting in a non-uniform foam.

The supercritical inert gas (D) is not particularly limited as long as it can be dissolved in the thermoplastic polyester elastomer resin composition and is inert, but carbon dioxide and nitrogen are preferred from the standpoints of safety and cost. The supercritical inert gas (D) is preferably used in an amount of 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, per 100 parts by mass of the thermoplastic polyester elastomer resin composition.

The supercritical inert gas (D) is preferably impregnated into the molten thermoplastic polyester elastomer resin composition in a kneader. Examples of methods for this include injecting the gaseous supercritical inert gas (D) directly or under pressure or pressure into the kneader, or injecting the liquid supercritical inert gas (D) into the kneader using a plunger pump or similar. When impregnating the thermoplastic polyester elastomer resin with the supercritical inert gas (D), the gas pressure is maintained at or above the critical pressure of the supercritical inert gas (D) being impregnated, at least until the mold is filled with the thermoplastic polyester elastomer resin composition. To further improve the impregnation rate, the gas pressure is preferably 1 MPa or higher, more preferably 5 MPa or higher.

While carbon dioxide or nitrogen can be used alone as the supercritical inert gas (D), a mixture of carbon dioxide and nitrogen may also be used. Nitrogen tends to be more suitable for forming finer closed cells in thermoplastic polyester elastomer compositions, while carbon dioxide allows for a larger gas injection amount, making it suitable for achieving a higher expansion ratio.

Nitrogen is more preferred as the supercritical inert gas (D) used in the present invention, from the viewpoint of forming closed cells with a uniform and desirable cell diameter of 10 to 600 μm.

To inject the molten thermoplastic polyester elastomer composition into the cavity together with the chemical blowing agent (E) and/or the inert gas (D) in a supercritical state, the molten thermoplastic polyester elastomer composition can be mixed with the chemical blowing agent (E) and/or the inert gas (D) in a supercritical state in the plasticizing zone of the injection molding machine. When using a chemical blowing agent (E), it is desirable to mix it with the thermoplastic polyester elastomer pellets beforehand.

When using supercritical carbon dioxide and/or nitrogen, a method can be used in which gaseous carbon dioxide and/or nitrogen are injected into the injection molding machine directly from a gas cylinder or pressurized using a booster pump. From the standpoint of solubility, permeability, and diffusibility in the molten thermoplastic polyester elastomer composition, the carbon dioxide and/or nitrogen must be in a supercritical state inside the injection molding machine.

Here, the term "supercritical state" refers to a state in which, when the temperature and pressure of a substance that exists in both gas and liquid phases are increased, the distinction between the gas and liquid phases can be eliminated within a certain temperature and pressure range; the temperature and pressure at this point are called the critical temperature and critical pressure. In other words, in a supercritical state, a substance possesses the properties of both a gas and a liquid, and the fluid that occurs in this state is called a critical fluid. Such critical fluids have a higher density than a gas and a lower viscosity than a liquid, making them extremely easy to diffuse within a substance.

The effects of the present invention will be explained below using examples. Note that all parts in the examples are by mass unless otherwise specified. The physical properties shown in the examples were measured as follows.

[Density (apparent density)]
The obtained foamed molded article was cut into a rectangular parallelepiped, the dimensions of which were measured with a vernier caliper, and the mass was measured with an electronic balance and calculated using the following formula.
Density (g/cm ³ ) = mass of test piece/volume of test piece.

[Expansion ratio]
The density of the thermoplastic polyester elastomer resin foam molded product sample was divided by the density of the thermoplastic polyester elastomer resin composition, and the value rounded to one decimal place was used as the expansion ratio. The density of the thermoplastic polyester elastomer resin composition before foaming and the density of the thermoplastic polyester elastomer resin foam molded product were determined according to ASTM D792.

[Average cell diameter]
Observation was performed using a scanning electron microscope (FE-SEM) manufactured by JEOL Ltd. 100 voids (foam cells) were randomly selected, and the equivalent circle diameter of adjacent foam cells was measured with a vernier caliper as the cell diameter of the foam cells. The average value of these 100 voids was calculated, and this was repeated at three random locations in the foamed molded article sample. The average value of the three average values obtained at the three locations was used as the average cell diameter.

[Tensile strength]
The obtained foamed molded sample was cut into a JIS K7113 No. 2 dumbbell test piece shape using a punching blade, and the strength was measured in accordance with JIS K7113 (1995 edition).

[Rebound elasticity]
The obtained foamed molded sample was cut into 8 x 50 mm strips and measured in accordance with BS903. Using a Tripso type rebound resilience tester, a hammer was dropped onto the test piece from a specified angle, and the maximum rebound angle was read. Three measurements were performed, and the median value was calculated to calculate the rebound resilience.

[Sound absorption peak frequency and peak frequency sound absorption coefficient]
The obtained foam molded articles were cut into circular shapes with a diameter of 39.5 mm using a punching blade, and the normal incidence sound absorption coefficient in the frequency range of 0.4 kHz to 5.0 kHz was measured for each of Examples 1 to 8 and Comparative Examples 1 to 4 using a normal incidence sound absorption coefficient measurement system, WinZacMTX, manufactured by Nippon Engineering Co., Ltd., in accordance with a method in accordance with JIS A1405 (2007). The lowest frequency peak was taken as the sound absorption peak, and this frequency was read as the sound absorption peak frequency. The normal incidence sound absorption coefficient at this sound absorption peak frequency was taken as the peak frequency sound absorption coefficient.

[Compounds used in the examples]
[Production of Thermoplastic Polyester Elastomer (A-1)]
273 parts of dimethyl terephthalate, 120 parts of 1,4-butanediol, and 723 parts of poly(tetramethylene oxide) glycol having a number-average molecular weight of approximately 2,000 were charged into a reaction vessel equipped with a helical ribbon stirrer along with 3 parts of titanium tetrabutoxide and 3 parts of trimellitic anhydride, and heated at 210°C for 2 hours and 30 minutes to distill off 95% by mass of the theoretical amount of methanol. After adding 0.5 parts of "Irganox" 1330 (a hindered phenol-based antioxidant manufactured by Ciba-Geigy), the reaction mixture was heated to 245°C, and the pressure in the system was reduced to 27 Pa over 50 minutes. Polymerization was carried out under these conditions for 1 hour and 50 minutes. The resulting polymer was extruded into water in the form of strands and cut into pellets.

[Production of thermoplastic polyester elastomer (A-2)]
340 parts of terephthalic acid, 100 parts of isophthalic acid, 394 parts of 1,4-butanediol, and 495 parts of poly(tetramethylene oxide) glycol having a number-average molecular weight of approximately 1,400 were charged together with 2 parts of titanium tetrabutoxide into a reaction vessel equipped with a helical ribbon-type stirring blade, and the mixture was heated at 190 to 225°C for 3 hours to carry out an esterification reaction while distilling the reaction water out of the system. After adding 0.5 parts of "Irganox" 1098 (a hindered phenol-based antioxidant manufactured by Ciba-Geigy), the reaction mixture was heated to 245°C, and the pressure in the system was reduced to 27 Pa over 50 minutes, and polymerization was carried out under these conditions for 2 hours and 45 minutes. The resulting polymer was discharged into water in the form of strands and cut into pellets.

[Production of thermoplastic polyester elastomer (A-3)]
348 parts of terephthalic acid, 340 parts of 1,4-butanediol, and 645 parts of poly(tetramethylene oxide) glycol having a number-average molecular weight of approximately 1,400 were charged together with 0.2 parts of titanium tetrabutoxide into a reaction vessel equipped with a helical ribbon-type stirring blade, and the mixture was heated at 190 to 225°C for 3 hours to carry out an esterification reaction while distilling the reaction water out of the system. After adding 0.5 parts of "Irganox" 1098 (a hindered phenol-based antioxidant manufactured by Ciba-Geigy), the reaction mixture was heated to 245°C, and the pressure in the system was reduced to 27 Pa over 50 minutes, and polymerization was carried out under these conditions for 2 hours and 45 minutes. The resulting polymer was discharged into water in the form of strands and cut into pellets.

[Production of Core-Shell Copolymer (B)]
37.3 kg of water, 0.46 kg of maleic acid hexadecyl monoester, 0.16 kg of a 50% by weight aqueous solution of potassium hydroxide, 0.031 kg of sodium dodecylbenzenesulfonate, 9 kg of butyl acrylate, 2.6 kg of methyl acrylate, 1.3 kg of acrylonitrile, 0.19 kg of 1,4-butanediol dimethacrylate, 0.039 kg of t-dodecyl mercaptan, and 0.029 kg of potassium persulfate were charged into a reaction vessel and reacted at 60°C for 2 hours and 30 minutes to obtain a core polymer latex. Furthermore, 301.7 kg of styrene, 0.74 kg of acrylonitrile, 0.025 kg of divinylbenzene, and 0.005 kg of t-dodecyl mercaptan were added to the reaction vessel, and the reaction was continued to obtain a core-shell copolymer (B). The obtained core-shell copolymer (B) latex was destroyed by salting out, washed, and dried to obtain a powder.

[Hydrogenated styrene block copolymer (C)]
Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) "Tuftec" H1272 manufactured by Asahi Kasei Corporation.

[Supercritical inert gas (D)]
nitrogen.

[Chemical foaming agent (E)]
"Cellmic Masterbatch" 1023 (containing 30% by mass of the thermal decomposition type foaming agent azodicarbonamide (ADCA)) manufactured by Sankyo Kasei Co., Ltd.

Examples 1 to 8, Comparative Examples 1 to 4
According to the compounding compositions shown in Table 1, various components were melt-kneaded with a thermoplastic polyester elastomer using a twin-screw extruder, and then pelletized to obtain pellets of Examples 1 to 8 and Comparative Examples 1 to 4.

Next, a foam molded article was produced using the mold expansion method described above. The mold used was a flat plate production mold consisting of a fixed mold and a movable mold. When clamped, it was possible to form a cavity measuring 150 mm in width, 150 mm in length, and 2 mm in thickness. When cored back in the mold opening direction, it was possible to form a cavity of the same width and length, but with a thickness of 2 mm + the cored back amount (mm).

Specifically, using a Japan Steel Works, Ltd. J110AD-180H-MuCell, pellets of the resulting thermoplastic polyester elastomer were mixed with a chemical blowing agent (E) and/or a supercritical inert gas (nitrogen gas) (D) in the plasticizing zone of an injection molding machine. The mixture was then injected into a mold whose surface temperature was controlled at 50°C. Once a non-foamed skin layer was formed by external injection pressure and internal foaming pressure, the operating mold was moved in the mold opening direction by the core-back distance (mm) listed in Table 1 to expand the cavity volume and produce a foamed molded article. The properties of the resulting foam were investigated, and the results are shown in Table 1. The chemical blowing agent (E) was dry-blended with the pellets in advance, and the supercritical inert gas (nitrogen gas) (D) was injected into the injection molding machine by pressurizing gaseous nitrogen from a gas cylinder using a booster pump.

From the above results, it can be confirmed that the thermoplastic polyester elastomers shown in Examples 1 to 8 are highly lightweight with a density of less than 0.70 ^g /cm, are flexible with a surface hardness of 75 A or less, and have a rebound resilience of 60% or less.

Comparative Examples 1 and 2, which are thermoplastic polyester elastomer resin foam molded articles composed only of polyester block copolymer (A), have a high rebound resilience.

Furthermore, in Comparative Example 3, in which the part by mass of core-shell copolymer (B) was large, a foamed molded article with a high expansion ratio exceeding 2.0 could not be obtained. Furthermore, in Comparative Example 4, in which the part by mass of hydrogenated styrene block copolymer (C) was large, the average cell diameter became large, and a foamed molded article with the target average cell diameter could not be obtained.

Furthermore, Examples 1-8 and Comparative Examples 1-2 all have sound absorption peak frequencies between 0.4 kHz and 5.0 kHz, and peak frequency sound absorption coefficients of 0.3% or greater. Compared to Comparative Examples 1 and 2, which are thermoplastic polyester elastomer resin foam molded articles composed solely of polyester block copolymer (A), Examples 1-4 and 7, which are composed of polyester block copolymer (A) and core-shell copolymer (B), and Examples 5-6 and 8, which are composed of polyester block copolymer (A), core-shell copolymer (B), and hydrogenated styrene block copolymer (C), show no significant differences in sound absorption peak frequencies or peak frequency sound absorption coefficients. Comparative Example 3 has a low expansion ratio, resulting in a high proportion of the skin layer inside the foam molded article, and therefore a low peak frequency sound absorption coefficient of 0.3% or less. Furthermore, Comparative Example 4 has a large cell diameter, resulting in a low peak frequency sound absorption coefficient of 0.3% or less.

Claims (6)

The polyester block copolymer (A) mainly comprises a high-melting crystalline segment (a-1) composed of a crystalline aromatic polyester unit and a low-melting polymer segment (a-2) composed of an aliphatic polyether unit and/or an aliphatic polyester unit, and the polyester block copolymer (A) is mixed with 20 to 95% by mass of butyl acrylate alone or a mixture of butyl acrylate and 2-ethylhexyl acrylate (b-1), at least one compound (b-2) selected from an alkyl acrylate having an alkyl group of 1 to 4 carbon atoms and an alkyl methacrylate having an alkyl group of 1 to 4 carbon atoms, a vinyl cyan compound (b-3), and a copolymer represented by the following structural formula (I): a thermoplastic polyester elastomer resin foam molded article having foam cells, and a density (apparent density) of less than 0.70 g/cm3, an expansion ratio of 2.0 or more, and a rebound resilience of 60% or less, the thermoplastic polyester elastomer resin composition comprising 5 to 80 mass% of a core-shell copolymer (B) having a core formed by emulsion polymerization of a maleic acid monoalkyl ester compound (b-4) and a crosslinking agent (b-5), and a shell formed by polymerization of an aromatic vinyl compound (b-6), a vinyl cyan compound (b- ^{3), and a crosslinking agent (b-5} ); and 0 to 40 mass% of a hydrogenated styrene block copolymer (C) comprising at least one vinyl aromatic compound polymer block (c1) and at least one conjugated diene block (c2). The thermoplastic polyester elastomer resin foam molded article according to claim 1, characterized in that the average cell diameter of the foam cells is 10 to 600 μm. The thermoplastic polyester elastomer resin foam molded article according to claim 1 or 2, characterized in that the surface hardness measured according to the method described in JIS K7215 is 90A or less. A method for producing a thermoplastic polyester elastomer resin foam molded article according to any one of claims 1 to 3, comprising injecting and filling the molten thermoplastic polyester elastomer resin composition together with a chemical foaming agent (E) and/or a supercritical inert gas (D) into a cavity of a mold consisting of a fixed mold and a movable mold that can move forward and backward to any position, and then moving the movable mold in the mold opening direction to expand the volume of the cavity and cause foaming. The method for producing a thermoplastic polyester elastomer resin foam molded article according to claim 4, characterized in that the thermoplastic polyester elastomer resin composition in a molten state is injected and filled together with an inert gas (D) in a supercritical state. The method for producing a thermoplastic polyester elastomer resin foam molded article according to claim 4 or 5, characterized in that the inert gas (D) is nitrogen.