JP7687202B2 - Foam molded article made of thermoplastic polyester elastomer resin composition, and sound absorbing material - Google Patents

Description

The present invention relates to a foam molded article made of a thermoplastic polyester elastomer resin composition having excellent cushioning properties and sound absorption characteristics. More specifically, the foam molded article made of the thermoplastic polyester elastomer resin composition of the present invention is thin and lightweight, has excellent cushioning properties, and is capable of controlling high sound absorption properties from low to high frequencies.

Thermoplastic polyester elastomers are materials that have excellent injection and extrusion moldability, high mechanical strength, rubber-like properties such as elastic recovery, impact resistance, and flexibility, and excellent cold resistance, and are used in applications such as automotive parts, electrical and electronic parts, fibers, films, and sports parts.

Thermoplastic polyester elastomers have excellent resistance to heat aging, light resistance, and abrasion, and are therefore used in automotive parts, particularly parts used in high-temperature environments and automotive interior parts. Furthermore, in recent years, efforts have been made not only to reduce the weight of plastic parts, but also to impart cushioning and sound-absorbing properties, and the use of foam-molded products can be cited as one means of achieving this goal.

In Patent Document 1, high-quality foam molded products are produced by controlling the melt tension of the polyester elastomer composition and suppressing gelation. However, the density of the foam molded products is high, and it has not yet been possible to produce a foam with a low density that is satisfactory for reducing weight. Furthermore, no consideration is given at all to the cushioning and resilience required for foam molded products.

Incidentally, a soft polyurethane foam that has high hysteresis loss and excellent resilience as a cushioning property is preferably used as a foam for automobile seats, and a manufacturing method thereof is proposed in Patent Document 2. However, the manufacturing method is not simple, and urethane foam generates cyanide gas and the like when burned, which poses the problem of environmental pollution.

Traditionally, sound-absorbing materials have been used in a variety of products, including automobiles, houses, and electrical appliances, primarily to reduce noise. However, because the frequency of sound generated by each product is different, it is necessary to apply sound-absorbing materials with a high sound absorption rate at frequencies appropriate for each product.

Conventionally, fibrous materials such as glass wool and felt, and foam materials such as urethane foam have been widely used as sound-absorbing materials. However, although these materials exhibit sound-absorbing properties in the high frequency range, their sound-absorbing properties are poor in the low to mid frequency range, and in order to obtain sufficient sound-absorbing properties at low frequencies, it is necessary to use a thick material (Patent Document 3).

In addition, in automotive applications, there is a trend towards greater heat resistance due to engine downsizing, but materials that are excellent in heat resistance, sound absorption, and cushioning properties have yet to be developed.

JP 2012-140532 A JP 2006-008774 A JP 2018-92131 A

The objective of the present invention is to provide a foamed molded article of a thermoplastic polyester elastomer resin composition that is thin and lightweight, has comfortable cushioning properties, and has high sound absorption properties that can be controlled from low to high frequencies.

The present inventors have conducted extensive research to provide a foam molded product of a thermoplastic polyester elastomer resin composition that has comfortable cushioning properties while allowing control of sound absorption properties in the low to high frequency range. As a result, they have found that it is possible to produce a foam with comfortable cushioning properties by adding a thermoplastic elastomer with a high loss tangent other than a thermoplastic polyester elastomer to a thermoplastic polyester elastomer and controlling the resilience modulus and surface hardness. Furthermore, they have found that in the foam molded product of the above-mentioned thermoplastic polyester elastomer resin composition, by changing the ratio of hard and soft segments of the thermoplastic polyester elastomer and the amount of thermoplastic elastomer added, it is possible to control the sound absorption coefficient to have a peak frequency of a predetermined value or more in the frequency range of 0.4 kHz to 5.0 kHz, leading to the completion of the present invention.

That is, the present invention comprises the following [1] to [10].
[1] A foam-molded product made from a thermoplastic polyester elastomer resin composition, comprising a thermoplastic polyester elastomer (A) and a thermoplastic elastomer (B) other than (A) in a mass ratio of (A)/(B) = 95/5 to 50/50.
[2] The foamed molded article according to [1], having a loss tangent (tan δ) at 23° C. of 0.10 or more.
[3] The foamed molded article according to [1] or [2], wherein the thermoplastic polyester elastomer (A) is a thermoplastic polyester elastomer in which a hard segment made of a polyester having an aromatic dicarboxylic acid and an aliphatic and/or alicyclic diol as constituent components is bonded to at least one soft segment selected from an aliphatic polyether, an aliphatic polyester, and an aliphatic polycarbonate, and the soft segment content is 40 to 90 mass%.
[4] The foam-molded product according to any one of [1] to [3], wherein the thermoplastic elastomer (B) is at least one selected from the group consisting of thermoplastic polyolefin-based elastomers and thermoplastic styrene-based elastomers.
[5] The foam molded article according to any one of [1] to [4], having a rebound resilience of 30 to 60%.
[6] The foamed molded article according to any one of [1] to [5], having a surface hardness of 10 to 55C.
[7] The foamed molded article according to any one of [1] to [6], having an average cell diameter of 10 to 900 μm.
[8] The foamed molded article according to any one of [1] to [7], having a density of 0.1 to 0.35 g/ ^cm3 .
[9] The foam molded article according to any one of [1] to [8], which has a non-foamed skin layer having a thickness of 100 to 800 μm as a surface layer, a foamed layer consisting of foamed cells having an average cell diameter of 10 to 900 μm independent of a resin continuous phase as an inner layer, and has a sandwich structure of the non-foamed skin layer and the foamed layer in the thickness direction.
[10] A sound-absorbing material comprising the foam molded article according to any one of [1] to [9], characterized in that when the normal incidence sound absorption coefficient of the foam molded article is measured in a frequency range of 0.4 kHz to 5.0 kHz in accordance with JIS A1405-2 (2007), the normal incidence sound absorption coefficient has a peak frequency in the frequency range of 0.4 kHz to 5.0 kHz at which the normal incidence sound absorption coefficient is 40% or more.

The foam molded article made from the thermoplastic polyester elastomer resin composition of the present invention is not only thin and lightweight, but also has comfortable cushioning properties and can control extremely high sound absorption properties from low to high frequencies. Furthermore, despite its high expansion ratio, it has a uniform foaming state, high heat resistance, water resistance, and molding stability, making it possible to provide a foam molded article made from the polyester elastomer resin composition that can be used in parts that require high reliability.

FIG. 1 is a schematic diagram for explaining an example of a method for producing a foamed molded article of the present invention.

The foamed molded article made from the thermoplastic polyester elastomer resin composition of the present invention is described in detail below.

The normal incidence sound absorption coefficient of the foamed molded body made of the thermoplastic polyester elastomer resin composition of this embodiment at the peak frequency of 0.4 kHz to 5.0 kHz, which is the main frequency range of automobile noise, measured according to a method conforming to JIS A1405-2 (2007), is 40% or more, preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. By satisfying this characteristic, the foamed molded body made of the thermoplastic polyester elastomer resin composition of the present invention can improve the balance between its lightness and sound absorption characteristics. In addition, the upper limit of the normal incidence sound absorption coefficient of the foamed molded body at 0.4 kHz to 5.0 kHz is not particularly limited, but is measured to be 100% or less. The normal incidence sound absorption coefficient described above can be measured using, for example, a normal incidence sound absorption coefficient measurement system WinZacMTX manufactured by Nihon Acoustic Engineering Co., Ltd.

In addition, in the foamed molded article made of the thermoplastic polyester elastomer resin composition of this embodiment, the peak frequency range is preferably 0.4 kHz to 4 kHz, more preferably 0.4 kHz to 3.5 kHz, even more preferably 0.4 kHz to 3 kHz, particularly preferably 0.4 kHz to 2.5 kHz, and most preferably 0.4 kHz to 2 kHz. The sound-absorbing material of the present invention is characterized in that the peak frequency can be controlled, particularly in the low frequency range (0.4 kHz to 4 kHz).

The foam molded article made from the thermoplastic polyester elastomer resin composition of the present invention may be used to form a sound-absorbing material either alone or in combination with other materials to form a sound-absorbing material.

[Thermoplastic polyester elastomer (A)]
The thermoplastic polyester elastomer (A) used in the present invention is formed by bonding a hard segment and a soft segment. The hard segment is made of a polyester, and is preferably made of a polyester having an aromatic dicarboxylic acid and an aliphatic and/or alicyclic diol as constituent components. As the aromatic dicarboxylic acid constituting the polyester of the hard segment, a normal aromatic dicarboxylic acid is widely used and is not particularly limited, but it is desirable that the main aromatic dicarboxylic acid is terephthalic acid or naphthalenedicarboxylic acid (among isomers, 2,6-naphthalenedicarboxylic acid is preferred). The content of these aromatic dicarboxylic acids is preferably 70 mol% or more, more preferably 80 mol% or more, of the total dicarboxylic acids constituting the polyester of the hard segment. Examples of other dicarboxylic acid components include aromatic dicarboxylic acids such as diphenyldicarboxylic acid, isophthalic acid, and 5-sodium sulfoisophthalic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and tetrahydrophthalic anhydride, and aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, and hydrogenated dimer acid. These can be used in an amount that does not significantly lower the melting point of the resin, and the amount is preferably 30 mol % or less, more preferably 20 mol % or less, of the total acid components.

In the thermoplastic polyester elastomer (A) used in the present invention, the aliphatic or alicyclic diol constituting the polyester of the hard segment is generally aliphatic or alicyclic diol, and although there is no particular limitation, it is preferable that it is mainly an alkylene glycol having 2 to 8 carbon atoms. Specific examples include ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol. Of these, either ethylene glycol or 1,4-butanediol is preferable.

As the components constituting the polyester of the above hard segments, those consisting of butylene terephthalate units (units consisting of terephthalic acid and 1,4-butanediol) or butylene naphthalate units (units consisting of 2,6-naphthalenedicarboxylic acid and 1,4-butanediol) are preferred in terms of physical properties, moldability, and cost performance.

In addition, when an aromatic polyester suitable as the polyester constituting the hard segment in the thermoplastic polyester elastomer (A) used in the present invention is produced in advance and then copolymerized with the soft segment component, the aromatic polyester can be easily obtained according to a normal polyester production method. In addition, such a polyester preferably has a number average molecular weight of 10,000 to 40,000.

The soft segment of the thermoplastic polyester elastomer (A) used in the present invention is at least one selected from aliphatic polyethers, aliphatic polyesters, and aliphatic polycarbonates.

Examples of aliphatic polyethers include poly(ethylene oxide) glycol, poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, poly(trimethylene oxide) glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide adducts of poly(propylene oxide) glycol, copolymers of ethylene oxide and tetrahydrofuran, etc. Among these, poly(tetramethylene oxide) glycol and ethylene oxide adducts of poly(propylene oxide) glycol are preferred from the viewpoint of elastic properties.

Aliphatic polyesters include poly(ε-caprolactone), polyenantholactone, polycaprylolactone, polybutylene adipate, etc. Among these, poly(ε-caprolactone) and polybutylene adipate are preferred from the viewpoint of elastic properties.

It is preferable that the aliphatic polycarbonate is mainly composed of an aliphatic diol residue having 2 to 12 carbon atoms. Examples of these aliphatic diols include ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,9-nonanediol, and 2-methyl-1,8-octanediol. In particular, aliphatic diols having 5 to 12 carbon atoms are preferable in terms of the flexibility and low-temperature properties of the resulting thermoplastic polyester elastomer. These components may be used alone or in combination of two or more types as necessary, based on the examples described below.

As the aliphatic polycarbonate diol with good low-temperature properties that constitutes the soft segment of the thermoplastic polyester elastomer (A) used in the present invention, it is preferable that it has a low melting point (for example, 70°C or less) and a low glass transition temperature. In general, the aliphatic polycarbonate diol made of 1,6-hexanediol used to form the soft segment of the thermoplastic polyester elastomer has a low glass transition temperature of about -60°C and a melting point of about 50°C, so that it has good low-temperature properties. In addition, an aliphatic polycarbonate diol obtained by copolymerizing, for example, an appropriate amount of 3-methyl-1,5-pentanediol with the above aliphatic polycarbonate diol has a slightly higher glass transition point than the original aliphatic polycarbonate diol, but has a lower melting point or is amorphous, so that it corresponds to an aliphatic polycarbonate diol with good low-temperature properties. Furthermore, for example, an aliphatic polycarbonate diol made of 1,9-nonanediol and 2-methyl-1,8-octanediol has a melting point of about 30° C. and a glass transition temperature of about −70° C., which are sufficiently low, and corresponds to an aliphatic polycarbonate diol having good low-temperature properties.

From the viewpoint of solving the problems of the present invention, an aliphatic polyether is preferred as the soft segment of the thermoplastic polyester elastomer (A) used in the present invention.

The thermoplastic polyester elastomer (A) used in the present invention is preferably a copolymer mainly composed of terephthalic acid, 1,4-butanediol, and poly(tetramethylene oxide) glycol. Of the dicarboxylic acid components constituting the thermoplastic polyester elastomer (A), terephthalic acid is preferably 40 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. Of the glycol components constituting the thermoplastic polyester elastomer (A), the sum of 1,4-butanediol and poly(tetramethylene oxide) glycol is preferably 40 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

The number average molecular weight of the poly(tetramethylene oxide) glycol is preferably 500 to 4000. If the number average molecular weight is less than 500, it may be difficult to exhibit elastomeric properties. On the other hand, if the number average molecular weight exceeds 4000, compatibility with the hard segment component decreases, making it difficult to copolymerize in a block form. The number average molecular weight of the poly(tetramethylene oxide) glycol is more preferably 800 to 3000, and even more preferably 1000 to 2500.

In the thermoplastic polyester elastomer (A) used in the present invention, the content of the soft segment is preferably 40 to 90% by mass, more preferably 45 to 90% by mass, even more preferably 55 to 90% by mass, and particularly preferably 65 to 90% by mass. If the content of the soft segment is lower than 40% by mass, the surface hardness becomes high and the cushioning property becomes poor. Furthermore, the lower the surface hardness, the easier the material vibrates, so the sound absorption performance in the low frequency range improves. If the content of the soft segment is lower than 40% by mass, the surface hardness becomes low and the sound absorption peak frequency appears in the high frequency range, and if it exceeds 90% by mass, the crystallinity decreases too much, so the foam moldability tends to be poor. The surface hardness of the thermoplastic polyester elastomer (A) is preferably 10 to 60C, more preferably 10 to 50C, and even more preferably 10 to 40C. In the present invention, the surface hardness is measured using a C-type hardness tester, and for convenience, it is described as 10C, 60C, etc.

By changing the ratio of hard and soft segments of the thermoplastic polyester elastomer (A) and the expansion ratio, it is possible to control the peak frequency at which the sound absorption coefficient is equal to or greater than a specified value. However, if the soft segment content is 40 to 90% by mass, this control is possible without increasing the expansion ratio.

The thermoplastic polyester elastomer (A) used in the present invention can be produced by known methods. For example, any of the following methods may be used: a method of transesterifying a lower alcohol diester of a dicarboxylic acid, an excess of a low molecular weight glycol, and a soft segment component in the presence of a catalyst, and polycondensing the resulting reaction product; a method of esterifying a dicarboxylic acid, an excess of a glycol, and a soft segment component in the presence of a catalyst, and polycondensing the resulting reaction product; a method of preparing a polyester of hard segments in advance, adding a soft segment component to the polyester, and randomizing the polyester by transesterification; a method of connecting hard segments and soft segments with a chain linking agent; and, when poly(ε-caprolactone) is used for the soft segment, a method of adding an ε-caprolactone monomer to the hard segment.

A crosslinking agent may be blended into the thermoplastic polyester elastomer (A) as necessary, as long as the effect of the present invention is not impaired. Such crosslinking agents are not particularly limited as long as they react with the hydroxyl groups or carboxyl groups of the thermoplastic polyester elastomer, and examples thereof include epoxy-based crosslinking agents, carbodiimide-based crosslinking agents, isocyanate-based crosslinking agents, acid anhydride-based crosslinking agents, silanol-based crosslinking agents, melamine resin-based crosslinking agents, metal salt-based crosslinking agents, metal chelate-based crosslinking agents, and amino resin-based crosslinking agents. The crosslinking agents may be used alone or in combination of two or more.

The amount (content) of the crosslinking agent used is adjusted appropriately depending on the extrusion conditions, the desired expansion ratio, etc., but for example, it is preferably 0.1 to 4.5 parts by mass, more preferably 0.1 to 4 parts by mass, and even more preferably 0.1 to 3 parts by mass per 100 parts by mass of thermoplastic polyester elastomer (A).

In addition to the crosslinking agent, the thermoplastic polyester elastomer (A) used in the present invention can also contain various additives depending on the purpose. The type of additive is not particularly limited, and various additives commonly used in foam molding can be used. Specifically, additives include known hindered phenol, sulfur, phosphorus, and amine antioxidants, hindered amines, as well as benzotriazole, benzophenone, benzoate, triazole, nickel, and salicylic light stabilizers, lubricants, fillers, flame retardants, flame retardant assistants, mold release agents, antistatic agents, molecular regulators such as peroxides, metal deactivators, organic and inorganic nucleating agents, neutralizing agents, antacids, antibacterial agents, fluorescent brighteners, organic and inorganic pigments, as well as organic and inorganic phosphorus compounds used for the purpose of imparting flame retardancy or thermal stability. The amount of additive can be appropriately selected within a range that does not impair the formation of bubbles, and the amount used in molding of ordinary thermoplastic resins can be adopted.

The MFR value of the thermoplastic polyester elastomer (A) used in the present invention at 230°C is preferably 10 to 20 g/10 min. By having the MFR in this range, it is possible to maintain optimal fluidity and foaming characteristics.

The composition and composition ratio of the thermoplastic polyester elastomer (A) used in the present invention can be determined by calculating from the proton integral ratio of ¹ H-NMR measured by dissolving a sample in a solvent such as deuterated chloroform.

[Thermoplastic elastomer (B)]
The thermoplastic elastomer (B) in the present invention may be any thermoplastic elastomer other than the thermoplastic polyester elastomer (A), but is preferably an elastomer other than a polyester-based elastomer. For example, a thermoplastic polyolefin-based elastomer or a thermoplastic styrene-based elastomer may be mentioned. The thermoplastic elastomer (B) is preferably at least one selected from a thermoplastic polyolefin-based elastomer and a thermoplastic styrene-based elastomer.
As the thermoplastic polyolefin-based elastomer, an α-olefin copolymer is preferably used. Specific examples of the α-olefin copolymer include ethylene-propylene copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene-1 copolymer, ethylene-ethyl acrylate copolymer, ethylene-methacrylate copolymer, ethylene-propylene-diene terpolymer, isoprene rubber, nitrile rubber, polybutene rubber, etc.
As the thermoplastic styrene elastomer, a styrene block copolymer composed of a polystyrene block and an elastomer block having a polyolefin structure is preferably used. Specific examples of the styrene block copolymer include styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene propylene-styrene block copolymer (SEPS), styrene-ethylene butylene-styrene block copolymer (SEBS), styrene-ethylene ethylene/propylene-styrene block copolymer (SEEPS), etc.
From the viewpoint of obtaining soft cushioning properties, it is particularly desirable for the thermoplastic elastomer (B) to be a thermoplastic styrene-based elastomer.

In the present invention, the thermoplastic elastomer (B) preferably has a high loss tangent/tan δ (δ is the loss angle) at 23°C near room temperature. The impact absorption properties of the foamed molded product can be evaluated by dynamic viscoelasticity measurement. The loss tangent (tan δ) indicates the scale at which external vibration energy is converted into thermal energy by internal friction, and can be used to evaluate the impact absorption properties. It is known that tan δ shows a maximum value near the glass transition temperature (Tg) of each resin, and the impact absorption properties are most exhibited near this maximum peak temperature. By increasing the value of tan δ and widening the temperature range, it is possible to exhibit impact absorption properties over a wide temperature range. By dispersing a thermoplastic elastomer (B) with a high loss tangent (tan δ) in the thermoplastic polyester elastomer (A) and expressing impact absorption properties, the rebound elasticity is lowered, and by suppressing the rebound force, flexibility as a cushion can be obtained. The loss tangent (tan δ) of the thermoplastic elastomer (B) at 23° C. around room temperature is preferably 0.20 or more, more preferably 0.30 or more, further preferably 0.40 or more, and particularly preferably 0.50 or more.

By dispersing a thermoplastic elastomer (B) with a high loss tangent (tan δ) in a thermoplastic polyester elastomer (A), it is possible to improve sound absorption characteristics in the low frequency range. When sound enters a foam molded body, it is transmitted through the skeleton of the foam molded body and diffuses as solid-borne sound. If the skeleton made of a thermoplastic polyester elastomer resin composition has a high loss tangent tan δ, external sound energy can be converted into thermal energy through internal friction, making it possible to absorb low-frequency sound that easily propagates through solids.

[Thermoplastic polyester elastomer resin composition]
In the present invention, the thermoplastic polyester elastomer resin composition contains the thermoplastic polyester elastomer (A) and the thermoplastic elastomer (B) in a mass ratio of (A)/(B)=95/5 to 50/50. The mass ratio is preferably (A)/(B)=90/10 to 60/40. If the mass ratio of the thermoplastic elastomer (B) is less than 5, the elastic modulus at low temperatures is high, the use environment is limited, and the vibration damping performance is poor. If the mass ratio of the thermoplastic elastomer (B) is more than 50, crystallization may be delayed, resulting in a decrease in moldability or a decrease in mechanical strength, which is not preferable.

The thermoplastic polyester elastomer resin composition may contain the above-mentioned crosslinking agent and various additives as necessary. In the thermoplastic polyester elastomer resin composition of the present invention, the total proportion of the thermoplastic polyester elastomer (A) and the thermoplastic elastomer (B) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[Foam molded product]
The foamed molded article of the present invention is obtained by using the above-mentioned thermoplastic polyester elastomer resin composition. The foamed molded article of the present invention preferably has a non-foamed skin layer present on the surface and a foamed layer present on the inner layer. Since the non-foamed skin layer and the foamed layer are formed of the above-mentioned thermoplastic polyester elastomer resin composition, they have a uniform cell-state foam structure and can exhibit excellent light weight, cushioning properties, and sound absorption properties.

The foam molded article of the present invention usually has a sandwich structure in which non-foamed skin layers are provided on both sides of the foam layer (in other words, a structure in which the foam layer is sandwiched between non-foamed skin layers on both sides). There are no particular limitations on the size of the foam molded article, but the thickness of the sandwich structure is expected to be about 1 to 30 mm.

The foam layer is composed of a resin continuous phase and independent foam cells. Here, the resin continuous phase means a portion formed of the cured thermoplastic polyester elastomer resin composition that does not have a cavity. The average cell diameter of the foam cells is preferably 10 to 900 μm. If the average cell diameter is less than 10 μm, the internal pressure of the foamed molded body is low, and the pressure during the formation of the non-foamed skin layer is insufficient, which tends to result in poor appearance such as sink marks. On the other hand, if the average cell diameter exceeds 900 μm, the load resistance is reduced. As the expansion ratio increases, the diameter (cell diameter) of the foam cells becomes coarse and the surface hardness of the material decreases, improving cushioning properties and causing the sound absorption peak frequency to appear in the low frequency range. To further improve cushioning properties and cause the sound absorption peak frequency to appear in the low frequency range, the average cell diameter is more preferably 100 to 900 μm, and even more preferably 200 to 900 μm. By applying an appropriate pressure to the non-foamed skin layer from inside the foamed molded article, a foamed molded article having an average cell diameter in the above-mentioned range can be obtained.

The rebound resilience of the foam molded article of the present invention is preferably 30 to 60%. If the rebound resilience exceeds 60%, the rebound force is too strong, making it difficult to obtain the flexibility required for a cushion. If the rebound resilience is less than 30%, bottoming out may occur when a high load is applied, or when the foam molded article is thinned. The rebound resilience of the foam molded article is preferably 30 to 60%, more preferably 35 to 55%, and even more preferably 35 to 50%.

The surface hardness of the foam molded article of the present invention is preferably 10 to 55C. As with the above-mentioned resilience modulus, if the surface hardness exceeds 55C, it is difficult to obtain the flexibility required for a cushion. If the surface hardness is less than 10C, bottoming out may occur when a high load is applied, or when the foam molded article is thinned. The surface hardness of the foam molded article is preferably 10 to 55C, more preferably 15 to 50C, and even more preferably 20 to 45C. The description of the surface hardness is the same as above.

The flexibility, resistance to settling, and lack of bottoming out of the foamed molded article of the present invention as a cushion are determined by the balance between the aforementioned resilience modulus and surface hardness.

The non-foamed skin layer is laminated on the foamed layer and preferably has a thickness of 100 to 800 μm. If the thickness of the non-foamed skin layer is less than 100 μm, a good appearance tends not to be obtained, while if it exceeds 800 μm, the specific gravity of the foamed layer becomes too low, and it tends not to be possible to obtain a foam structure having a density of 0.01 to 0.35 g/cm ³ as the entire foamed molded article in a uniform cell state.

The foamed molded product of the thermoplastic polyester elastomer resin composition has a plate vibration type sound absorption mechanism by laminating a non-foamed skin layer on a foamed layer. Here, in order to absorb low frequencies with a material of limited thickness, a low-frequency sound absorption effect can be obtained by resonance (resonance), and examples of such a method include plate vibration type sound absorption using a plate or membrane, and Helmholtz sound absorber type sound absorption using a slit or perforated plate. The foamed molded product of the thermoplastic polyester elastomer resin composition exhibits a plate vibration type by having a non-foamed layer, and can exhibit high sound absorption characteristics even in the low-frequency range. When the non-foamed skin layer is removed and the sound absorption coefficient of only the foamed layer is measured, the sound absorption peak frequency shifts to a high frequency, so having a non-foamed skin layer is advantageous for low-frequency sound absorption. However, even if the non-foamed skin layer is removed, only the sound absorption peak frequency changes, and sound absorption characteristics such as the sound absorption coefficient do not decrease. The thickness of the non-foamed skin layer is more preferably 200 to 600 μm, further preferably 200 to 400 μm, and particularly preferably 300 to 400 μm.

The foamed molded product of the thermoplastic polyester elastomer resin composition has a high loss tangent (tan δ) at 23°C near room temperature, and therefore can improve sound absorption characteristics in the low frequency range. When sound enters the foamed molded product, it is transmitted through the skeleton of the foamed molded product and diffuses as solid-borne sound. If the skeleton made of the thermoplastic polyester elastomer resin composition has a high loss tangent (tan δ), sound energy from the outside can be converted into thermal energy by internal friction, and low-frequency sound that easily propagates through solids can be absorbed. The loss tangent (tan δ) of the foamed molded product at 23°C near room temperature is preferably 0.10 or more, more preferably 0.15 or more, and even more preferably 0.20 or more. The upper limit of the loss tangent (tan δ) is about 0.50.

The density of the foamed molded article of the present invention is preferably 0.01 to 0.35 g/cm ^3. Since the density of a typical polyester elastomer is about 1.0 to 1.4 g/cm ³ , it can be said that the foamed molded article of the present invention is sufficiently lightweight. More preferably, it is 0.1 to 0.35 g/cm ³ , and even more preferably, it is 0.1 to 0.25 g/cm ^3. If the density is less than 0.01 g/cm ³ , sufficient strength cannot be obtained and mechanical properties tend to be poor, and if the density exceeds 0.35 g/cm ³ , the sound absorption peak frequency appears in the high frequency range. In order to achieve both excellent strength and high sound absorption properties, the density of the foamed molded article is more preferably 0.01 to 0.25 g/cm ³ , and even more preferably 0.1 to 0.25 g/cm ^3. The density is an apparent density, the measurement method of which is shown in the Examples section.

The foamed molded product of the present invention has an average cell diameter within a specific range, a density within a specific range, and a non-foamed skin layer thickness within a specific range, and therefore has a uniform and fine cell structure, making it possible to control high sound absorption characteristics over a wide frequency range.

The foamed molded article of the present invention can have different thicknesses, weights, and even densities depending on the expansion ratio. The sound absorption peak frequency changes depending on the expansion ratio, but sound absorption properties such as the sound absorption coefficient are hardly affected.

The foaming method of the foamed molded product of the present invention is not particularly limited, but a foaming method in which the resin is impregnated with a high-pressure gas and then the pressure is reduced (pressure is released) is preferred as a molding method that can obtain homogeneous foaming, cost, and molding cycle properties. In particular, a method in which the volume of the cavity is expanded when the foaming agent and the thermoplastic polyester elastomer resin composition are melt-mixed and injection-molded to obtain a foamed molded product is preferred as a molding method that can obtain homogeneous foaming, cost, and molding cycle properties. Specifically, as shown in FIG. 1, a molten thermoplastic polyester elastomer resin composition is injected and filled into a cavity 3 formed by multiple clamped molds 1 and 2 together with a chemical foaming agent and/or a supercritical inert gas (hereinafter, collectively referred to as "foaming agent"). At the stage when a non-foamed skin layer having a thickness of 100 to 800 μm is formed on the surface layer, at least one mold 2 is moved in the mold opening direction to expand the volume of the cavity 3, thereby obtaining a foamed molded product. Specifically, after the thermoplastic polyester elastomer resin composition and the foaming agent are filled into the cavity 3, the cavity 3 is cooled at a predetermined temperature, thereby forming a non-foamed skin layer on the surface of the thermoplastic polyester elastomer resin composition filled into the cavity 3. When this non-foamed skin layer reaches a predetermined thickness (100 to 800 μm), the mold 2 is moved in the mold opening direction to expand the volume of the cavity 3. The thermoplastic polyester elastomer resin composition and the foaming agent can be mixed in the plasticization region 4a of the injection molding machine 4 before being filled into the cavity 3.

The chemical foaming agent 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 a molding machine as a gas component that becomes the foaming nucleus or as a source of the gas component.
Specifically, examples of chemical foaming agents that can be used include inorganic compounds such as ammonium carbonate, sodium bicarbonate, and azide compounds, as well as organic compounds such as azo compounds, sulfohydrazide compounds, and nitroso compounds. Examples of the azide compounds include terephthalazide and p-tert-butylbenzazide. Examples of the azo compounds include diazocarbonamide (ADCA), 2,2-azoisobutyronitrile, azohexahydrobenzonitrile, and diazoaminobenzene, among which ADCA is preferred. Examples of the sulfohydrazide compounds include benzenesulfohydrazide, benzene 1,3-disulfohydrazide, diphenylsulfone-3,3-disulfonehydrazide, and diphenyloxide-4,4-disulfonehydrazide. Examples of the nitroso compounds include N,N-dinitrosopentaethylenetetramine (DNPT).

When a chemical foaming agent is used as the foaming agent, the chemical foaming agent can be used as a foaming agent masterbatch based on a thermoplastic resin having a melting point lower than the decomposition temperature of the chemical foaming agent in order to disperse the agent uniformly in the thermoplastic polyester elastomer resin composition. The base thermoplastic resin is not particularly limited as long as it has a melting point lower than the decomposition temperature of the chemical foaming agent, and examples of the base thermoplastic resin include polystyrene (PS), polyethylene (PE), and polypropylene (PP). In this case, the blending ratio of the chemical foaming agent to the thermoplastic resin is preferably 10 to 100 parts by mass of the chemical foaming agent per 100 parts by mass of the thermoplastic resin. If the chemical foaming agent is less than 10 parts by mass, the amount of the masterbatch relative to the thermoplastic polyester elastomer resin composition may be too large, resulting in a decrease in physical properties. If the amount exceeds 100 parts by mass, it becomes difficult to make a masterbatch due to the problem of dispersibility of the chemical foaming agent.

When a supercritical inert gas is used as the foaming agent, carbon dioxide and/or nitrogen can be used as the inert gas. When supercritical carbon dioxide and/or nitrogen are used as the foaming agent, the amount is preferably 0.05 to 30 parts by mass, and more preferably 0.1 to 20 parts by mass, per 100 parts by mass of the thermoplastic polyester elastomer resin composition. If the amount of supercritical carbon dioxide and/or nitrogen is less than 0.05 parts by mass, it becomes difficult to obtain uniform and fine foam cells, and if it exceeds 30 parts by mass, the appearance of the molded body surface tends to be impaired.

Although the supercritical carbon dioxide or nitrogen used as the foaming agent can be used alone, a mixture of carbon dioxide and nitrogen may also be used. Nitrogen tends to be suitable for forming finer cells in a thermoplastic polyester elastomer resin composition, while carbon dioxide allows for a relatively larger amount of gas to be injected and is suitable for obtaining a higher expansion ratio. Therefore, they may be mixed as desired to adjust the state of the foam structure, and when mixed, the mixing ratio is preferably in the range of 1:9 to 9:1 in molar ratio.

From the viewpoint of achieving uniform fine foaming, supercritical nitrogen is more preferred as the foaming agent used in the present invention.

To inject the molten thermoplastic polyester elastomer resin composition together with the blowing agent into the cavity 3, the molten thermoplastic polyester elastomer resin composition and the blowing agent may be mixed in the plasticization area 4a of the injection molding machine 4. In particular, when supercritical carbon dioxide and/or nitrogen are used as the blowing agent, a method of injecting gaseous carbon dioxide and/or nitrogen directly from a gas cylinder 5 or pressurized by a booster pump 6 into the injection molding machine 4 as shown in FIG. 1 can be used. The carbon dioxide and/or nitrogen must be in a supercritical state inside the molding machine from the viewpoint of solubility, permeability, and diffusibility in the molten thermoplastic polyester elastomer resin composition.

Here, the term "supercritical state" refers to a state in which, when the temperature and pressure of a substance that has gas and liquid phases are increased, the distinction between the gas and liquid phases can be eliminated in a certain temperature and pressure range, and the temperature and pressure at this point are called the critical temperature and critical pressure. In other words, in a supercritical state, a substance has the properties of both a gas and a liquid, so the fluid that occurs in this state is called a critical fluid. Such a critical fluid has a higher density than a gas and a lower viscosity than a liquid, and therefore has the property of being extremely easy to diffuse through a substance.

The following examples are provided to demonstrate the effects of the present invention, but the present invention is not limited to these examples in any way.

In the following examples and comparative examples, the following raw materials were used.
[Thermoplastic polyester elastomer (A)]
(Polyester elastomer A-1)
According to the method described in JP-A-9-59491, a thermoplastic polyester elastomer having a soft segment content of 83% by mass was produced using dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a number average molecular weight of 2000 as raw materials, and this was designated as polyester elastomer A-1.
(Polyester elastomer A-2)
According to the method described in JP-A-9-59491, a thermoplastic polyester elastomer having a soft segment content of 76% by mass was produced using dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a number average molecular weight of 2000 as raw materials, and this was designated as polyester elastomer A-2.
(Polyester elastomer A-3)
According to the method described in JP-A-9-59491, a thermoplastic polyester elastomer having a soft segment content of 55% by mass was produced using dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a number average molecular weight of 1,000 as raw materials, and this was designated as polyester elastomer A-3.
(Polyester elastomer A-4)
According to the method described in JP-A-9-59491, a thermoplastic polyester elastomer having a soft segment content of 49% by mass was produced using dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a number average molecular weight of 1,000 as raw materials, and this was designated as polyester elastomer A-4.
[Thermoplastic elastomer (B)]
(Styrene-based elastomer B-1)
The thermoplastic styrene-based elastomer "Tuftec H1221" manufactured by Asahi Kasei Corporation was used.
(Olefin elastomer B-2)
An α-olefin copolymer "Absoutomer EP1001" manufactured by Mitsui Chemicals was used.

Using (A) and (B) having the loss tangent (tan δ) shown in Table 1, the various components were melt-kneaded using a twin-screw extruder according to the composition shown in Table 2, and then pelletized to obtain the pellets of Examples 1 to 8 and Comparative Examples 1 to 6.

[Examples 1 to 8 (Example 7 is a reference example) , Comparative Examples 1 to 6]
Next, the above resin component (thermoplastic polyester elastomer resin composition) was used to produce a foamed molded product by the above-mentioned mold expansion method. The mold used was a flat plate production mold consisting of a fixed mold and a working mold, which can form a cavity with a width of 100 mm, a length of 100 mm, and a thickness of 3.0 mm when clamped, and can form a cavity with the same width and length and a thickness of 3.0 mm + core back amount (mm) when cored back in the mold opening direction. Specifically, supercritical nitrogen was injected in the plasticization region of an electric injection molding machine with a screw having a clamping force of 1800 kN, a screw diameter of 40 mm, and a screw stroke of 180 mm, and the mold was injected and filled at a surface temperature of 50°C. At the stage where a non-foamed skin layer of 100 to 800 μm was formed by the injection external pressure and the foaming pressure from the inside, the working mold was moved in the mold opening direction by the length shown as the core back amount (mm) in Table 2 to expand the volume of the cavity, and a foamed molded product was obtained.

The foamed molded articles obtained from the thermoplastic polyester elastomer resin compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 6 were evaluated as follows. The results are shown in Table 2.

[Density (apparent density)]
The dimensions of the foamed molded product were measured with a vernier caliper, and the mass was measured with an electronic balance, and calculated according to the following formula.
Density (g/cm ³ )=mass of test piece/volume of test piece

[Average cell diameter]
A photograph of the foam cross section of the sample for cross section observation taken with a scanning electron microscope SU1510 manufactured by Hitachi High-Technologies Corporation was processed, and the circle equivalent diameter of at least 100 adjacent cells was taken as the cell diameter, which was then measured with a vernier caliper. The average of the 100 cells was calculated, and this was performed at any three locations, and the average of the three average values obtained at the three locations was taken as the average cell diameter.

[Skin layer thickness]
A photograph of the foamed cross section of the sample for cross-section observation taken with a scanning electron microscope SU1510 manufactured by Hitachi High-Technologies was processed, and the thickness of the integrated non-foamed layer observed in the surface layer portion was measured as the skin layer thickness.

[Rebound elasticity]
The measurement was carried out according to the method described in JIS K 6400. Using a manual measuring tester, a steel ball was dropped onto the test piece from a specified height, and the maximum rebound height was read. Three measurements were taken within one minute, and the median value was calculated to calculate the rebound resilience.

[Surface hardness]
The center of the foam molded article (obtained above) having a length of 100 mm and a width of 100 mm was measured in accordance with JIS K 7312:1996 using a C-type hardness tester (Asker Rubber Hardness Tester Type C, manufactured by Kobunshi Keiki Co., Ltd.).

[Loss tangent (tanδ)]
The foamed molded article was cut into a size of 5 mm in width, 25 mm in length, and 0.1 to 0.5 mm in thickness, and the dynamic viscoelasticity was measured under the following conditions using a Rheogel-E4000 manufactured by UBM with a clamping distance of 15 mm, and tan δ at 23° C. was read. The non-foamed skin layer of the foamed molded article was cut and sampled.
Measurement temperature range: -100 to 150°C
Temperature increase condition: 2° C./min
Here, tan δ refers to the loss angle in the relationship expressed by the following formula when a periodic stimulus of 11 Hz is applied to a test piece and the strain (or stress) is observed as the response.
tan δ=E'' (dynamic loss modulus)/E' (dynamic storage modulus)

[Moldability]
The moldability of the foam molded body was evaluated from the thickness of the foam molded body produced by the above-mentioned mold expansion method. In Examples 1 to 8 and Comparative Examples 1 to 6, in a mold that forms a cavity with a width of 100 mm, a length of 100 mm, and a thickness of 3.0 mm when the mold is closed, the volume of the cavity was expanded by core backing 12.0 mm in the mold opening direction to obtain a foam molded body. In this case, a foam molded body with a thickness of 15.0 mm was finally obtained, but if the moldability of the resin is poor, the thickness will be small. The moldability was evaluated as follows.
◯: The thickness of the foam molded article is 14.0 mm or more. △: The thickness of the foam molded article is 10.0 mm or more and less than 14.0 mm. ×: The thickness of the foam molded article is less than 10.0 mm.

[Sound absorption characteristics]
The normal incidence sound absorption coefficient was measured in the frequency range of 0.4 kHz to 5.0 kHz, which is the main frequency of automobile noise as defined in JIS A1405-2 (2007), for each of Examples 1 to 8 and Comparative Examples 1 to 6 using a normal incidence sound absorption coefficient measurement system WinZacMTX manufactured by Nihon Onkyo Engineering Co., Ltd. At this time, the first peak that appears from the low frequencies where the sound absorption coefficient is 40% or more was read as the sound absorption peak frequency.

As is clear from Table 2, all of Examples 1 to 8 within the scope of the present invention are thin and lightweight, have a highly flexible cushioning property with a resilience modulus of 30 to 60% and a surface hardness of 10C to 55C, and show a high sound absorption peak frequency in the frequency range of 0.4 kHz to 5.0 kHz. Comparisons between Examples 1 to 4 and Comparative Examples 1 and 2, and between Example 8 and Comparative Example 1, show that as the content of thermoplastic elastomer (B) increases, the resilience modulus and surface hardness decrease, and soft cushioning property is shown, and further, as the loss tangent tan δ increases, the sound absorption peak frequency appears in the low frequency region. However, in Comparative Example 3, in which the content of thermoplastic elastomer (B) is 65 parts by mass, the resin does not follow during foam molding, and moldability is poor. Even in Examples 5 to 7 and Comparative Examples 4 to 6, in which the soft segment content of thermoplastic polyester elastomer (A) is low, the aforementioned tendency of cushioning property and sound absorption characteristics is shown. From a comparison between Example 2 and Example 8, it can be said that from the viewpoint of soft cushioning properties, the thermoplastic elastomer (B) is preferably a styrene-based elastomer.

Possible industrial applications

The foam molded article made from the thermoplastic polyester elastomer resin composition of the present invention is not only thin and lightweight, but also has comfortable cushioning properties and can control extremely high sound absorption properties from low to high frequencies. Furthermore, despite its high expansion ratio, it has a uniform foaming state, high heat resistance, water resistance, and molding stability, making it possible to provide a foam molded article made from the polyester elastomer resin composition that can be used in parts that require high reliability.

1. Mold (for fixing)
2. Mold (for operation)
3 Cavity 4 Injection molding machine 4a Plasticization area 5 Gas cylinder 6 Booster pump 7 Pressure control valve

Claims (9)

The thermoplastic polyester elastomer (A) and the thermoplastic elastomer (B) other than (A) are contained in a mass ratio of (A)/(B)=95/5 to 50/50,
A foamed molded article made of a thermoplastic polyester elastomer resin composition, characterized in that the soft segment content of the thermoplastic polyester elastomer (A) is 55 to 90 mass %,
A foamed molded article having a surface non-foamed skin layer having a thickness of 100 to 800 μm, an inner layer made of foamed cells having an average cell diameter of 10 to 900 μm that are independent of the resin continuous phase, and a sandwich structure of the non-foamed skin layer and the foamed layer in the thickness direction. The foamed molded article according to claim 1, which has a loss tangent (tan δ) at 23°C of 0.10 or more. 3. The foamed molded article according to claim 1 or 2, wherein the thermoplastic polyester elastomer (A) is a thermoplastic polyester elastomer in which a hard segment made of a polyester having an aromatic dicarboxylic acid and an aliphatic and/or alicyclic diol as constituent components is bonded to at least one soft segment selected from an aliphatic polyether, an aliphatic polyester, and an aliphatic polycarbonate, and the soft segment content is 55 to 90 mass%. The foamed molded article according to any one of claims 1 to 3, wherein the thermoplastic elastomer (B) is at least one selected from a thermoplastic polyolefin-based elastomer and a thermoplastic styrene-based elastomer. The foam molded article according to any one of claims 1 to 4, having a resilience modulus of 30 to 60%. The foam molded article according to any one of claims 1 to 5, having a surface hardness of 10 to 55C. The foamed molded article according to any one of claims 1 to 6, having an average cell diameter of 10 to 900 μm. The foamed molded article according to any one of claims 1 to 7, having a density of 0.1 to 0.35 g/ ^cm3 . A sound-absorbing material comprising the foamed molded article according to any one of claims 1 to 8 , characterized in that, when the normal incidence sound absorption coefficient of the foamed molded article is measured in a frequency range of 0.4 kHz to 5.0 kHz in accordance with JIS A1405-2 (2007), the sound-absorbing material has a peak frequency in the frequency range of 0.4 kHz to 5.0 kHz at which the normal incidence sound absorption coefficient is 40% or more.