JP7256981B2 - Sound absorbing material made of thermoplastic polyester elastomer resin foam - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sound absorbing material made of a thermoplastic polyester elastomer resin foam having excellent sound absorbing properties. More specifically, the sound absorbing material made of the thermoplastic polyester elastomer resin foam of the present invention is thin and lightweight, and can control high sound absorption in the low to high frequency range.

Thermoplastic polyester elastomers have excellent injection moldability and extrusion moldability, high mechanical strength, rubber-like properties such as elastic recovery, impact resistance, and flexibility, as well as excellent cold resistance. It is used in applications such as electronic parts, textiles, films, and sports parts.

Thermoplastic polyester elastomers are excellent in heat aging resistance, light resistance, and abrasion resistance, so they are used in automobile parts, especially parts used in high-temperature environments and automobile interior parts. Furthermore, in recent years, efforts have been made to reduce the weight of resin parts and to provide them with sound absorbing properties.

Conventionally, sound absorbing materials have been used in various products, such as automobiles, houses, and electrical appliances, mainly to reduce noise. It is necessary to apply a sound absorbing material with a high modulus.

Conventionally, fiber 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 absorption in the high frequency range, they have poor sound absorption in low to medium frequencies. Reference 1).

In addition, in automotive applications, there is a tendency to demand greater heat resistance due to the downsizing of engines, etc., but materials with excellent heat resistance and sound absorption have not yet been developed.

By the way, urethane foam used as a sound absorbing material generates cyanide gas and the like when burned, so there is a problem of environmental pollution.

JP 2018-92131 A

An object of the present invention is to provide a sound absorbing material made of a thermoplastic polyester elastomer resin foam which is thin and light and is capable of controlling high sound absorption in the low to high frequency range.

The inventors of the present invention have made intensive studies to provide a foamed sound absorbing material capable of controlling sound absorption characteristics in the low to high frequency range. As a result, in the thermoplastic polyester elastomer resin foam, by changing the ratio of the hard segment and the soft segment of the thermoplastic polyester elastomer and the foaming ratio, the sound absorption coefficient increased in the frequency range of 0.4 kHz to 5.0 kHz. The inventors have found that it is possible to control the peak frequency to be equal to or higher than a predetermined value, and have completed the present invention.

That is, the present invention constitutes the following [1] to [ 4 ].
[1] A sound absorbing material made of thermoplastic polyester elastomer resin foam, measuring the normal incident sound absorption coefficient of the foam in the frequency range of 0.4 kHz to 5.0 kHz according to JIS A1405-2 (2007). In the sound absorbing material having a peak frequency at which the normal incidence sound absorption coefficient is 40% or more in the frequency range of 0.4 kHz to 5.0 kHz when / or a hard segment made of a polyester containing an alicyclic diol as a constituent component and at least one soft segment selected from aliphatic polyethers, aliphatic polyesters, and aliphatic polycarbonates are combined to contain the soft segment A sound absorbing material characterized by comprising a thermoplastic polyester elastomer resin in an amount of 55 to 90% by mass .
[2] The sound absorbing material according to [1] , wherein the foam has an average cell diameter of 10 to 400 μm.
[3] The sound absorbing material according to [1] or [2], wherein the foam has a density of 0.1 to 0.35 g/cm ³ .
[4] The foam has a non-foamed skin layer with a thickness of 100 to 800 μm on the surface layer, and a foamed layer consisting of foamed cells with an average cell diameter of 10 to 400 μm independent of the resin continuous phase on the inner layer, and has a thickness direction. The sound absorbing material according to any one of [1] to [ 3 ], which is a foam having a sandwich structure of a non-foamed skin layer and a foamed layer.

The sound absorbing material made of the thermoplastic polyester elastomer resin foam of the present invention is not only excellent in thinness and lightness, but also capable of controlling extremely high sound absorption in the low to high frequency range. In addition, it is made of polyester elastomer resin foam that can be applied to parts that require high reliability because it has a uniform foaming state, high heat resistance, water resistance, and molding stability despite its high expansion ratio Acoustic material can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram for demonstrating an example of the manufacturing method of the foam molding of this invention.

The sound absorbing material made of the thermoplastic polyester elastomer resin foam of the present invention will be described in detail below.

For the sound absorbing material made of the foam of this embodiment, the peak of the foam at 0.4 kHz to 5.0 kHz, which is the main frequency range of automobile noise, measured by a method based on JIS A1405-2 (2007). The normal incidence sound absorption coefficient for frequencies is 40% or more, preferably 50% or more, more preferably 60% or more, and still more preferably 70% or more. By satisfying these characteristics, the sound absorbing material made of the foam of the present invention can improve the balance between its lightness and sound absorbing properties. The upper limit of the normal incidence sound absorption coefficient of the foam at 0.4 kHz to 5.0 kHz is not particularly limited, but is 100% or less in terms of measurement. The normal incidence sound absorption coefficient described above can be measured, for example, using a normal incidence sound absorption coefficient measurement system WinZacMTX manufactured by Nippon Onkyo Engineering Co., Ltd.

In addition, in the sound absorbing material made of the foam of the present embodiment, the peak frequency range is preferably a frequency range of 0.4 kHz to 4 kHz, more preferably a frequency range of 0.4 kHz to 3.5 kHz. More preferably, the frequency range is from 0.4 kHz to 3 kHz, particularly preferably from 0.4 kHz to 2.5 kHz, and most preferably from 0.4 kHz to 2 kHz. be. The sound absorbing material of the present invention is characterized in that the peak frequency can be controlled even in the low frequency range.

The sound absorbing material of the present invention may be formed only from a thermoplastic polyester elastomer resin foam, or may be formed by combining a thermoplastic polyester elastomer resin foam with another material to form a sound absorbing material.

[Thermoplastic polyester elastomer resin]
In the present invention, the thermoplastic polyester elastomer resin may refer only to the thermoplastic polyester elastomer, but may also include a cross-linking agent and additives, which will be described later. If it contains components other than the thermoplastic polyester elastomer, it is appropriate to call it a "composition". In the present invention, the term "thermoplastic polyester elastomer resin" is used both when the thermoplastic polyester elastomer is used alone and when the thermoplastic polyester elastomer includes a cross-linking agent and additives.

First, the thermoplastic polyester elastomer alone will be described. Here, it is referred to as "thermoplastic polyester elastomer".
The thermoplastic polyester elastomer used in the present invention is formed by bonding hard segments and soft segments. The hard segment consists of polyester. As the aromatic dicarboxylic acid that constitutes the polyester of the hard segment, ordinary aromatic dicarboxylic acids are widely used and are not particularly limited. 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 hard segment polyester. Other dicarboxylic acid components include aromatic dicarboxylic acids such as diphenyldicarboxylic acid, isophthalic acid and 5-sodiumsulfoisophthalic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and tetrahydrophthalic anhydride, succinic acid, glutaric acid, Aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, dimer acid, hydrogenated dimer acid, and the like are included. These can be used within a range that does not significantly lower the melting point of the resin, and the amount thereof is 30 mol % or less, preferably 20 mol % or less of the total acid component.

Further, in the thermoplastic polyester elastomer used in the present invention, general aliphatic or alicyclic diols are widely used as the aliphatic or alicyclic diol constituting the polyester of the hard segment, and are not particularly limited, but mainly Alkylene glycols having 2 to 8 carbon atoms are desirable. Specific examples include ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol and the like. Among these, ethylene glycol or 1,4-butanediol is preferable.

The components constituting the hard segment polyester include butylene terephthalate units (units composed of terephthalic acid and 1,4-butanediol) or butylene naphthalate units (2,6-naphthalenedicarboxylic acid and 1,4-butanediol unit) is preferable from the viewpoint of physical properties, moldability and cost performance.

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

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

Aliphatic polyethers include poly(ethylene oxide) glycol, poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, poly(trimethylene oxide) glycol, co-polymer of ethylene oxide and propylene oxide. polymers, ethylene oxide adducts of poly(propylene oxide) glycol, copolymers of ethylene oxide and tetrahydrofuran, and the like. 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, polycaprylollactone, polybutylene adipate and the like. Among these, poly(ε-caprolactone) and polybutylene adipate are preferred from the viewpoint of elastic properties.

The aliphatic polycarbonate preferably consists mainly of aliphatic diol residues 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, 2-methyl-1,8- octanediol and the like. In particular, aliphatic diols having 5 to 12 carbon atoms are preferred from the viewpoint of the flexibility and low-temperature properties of the resulting thermoplastic polyester elastomer. These components may be used alone, or two or more of them may be used in combination according to the cases described below.

As the aliphatic polycarbonate diol having good low-temperature properties, which constitutes the soft segment of the thermoplastic polyester elastomer used in the present invention, those having a low melting point (for example, 70° C. or lower) and a low glass transition temperature are preferred. In general, an aliphatic polycarbonate diol composed of 1,6-hexanediol, which is used to form the soft segment of a thermoplastic polyester elastomer, has a low glass transition temperature of around -60°C and a melting point of around 50°C. Good low temperature characteristics are obtained. In addition, an aliphatic polycarbonate diol obtained by copolymerizing an appropriate amount of, for example, 3-methyl-1,5-pentanediol with the above aliphatic polycarbonate diol has a glass transition point higher than that of the original aliphatic polycarbonate diol. is slightly higher, but the melting point is lowered or becomes amorphous. In addition, for example, an aliphatic polycarbonate diol composed 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. , which corresponds to aliphatic polycarbonate diols with good low-temperature properties.

From the viewpoint of solving the problems of the present invention, aliphatic polyethers are preferred as the soft segment of the thermoplastic polyester elastomer used in the present invention.

The thermoplastic polyester elastomer used in the present invention is preferably a copolymer containing terephthalic acid, 1,4-butanediol, and poly(tetramethylene oxide) glycol as main components. Among the dicarboxylic acid components constituting the thermoplastic polyester elastomer, terephthalic acid is preferably 40 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and 90 mol%. It is particularly preferable that it is above. Among the glycol components constituting the thermoplastic polyester elastomer, the total amount of 1,4-butanediol and poly(tetramethylene oxide) glycol is preferably 40 mol% or more, more preferably 70 mol% or more, and 80 It is more preferably mol % or more, and particularly preferably 90 mol % or more.

The poly(tetramethylene oxide) glycol preferably has a number average molecular weight of 500-4000. If the number average molecular weight is less than 500, it may be difficult to develop elastomeric properties. On the other hand, if the number average molecular weight exceeds 4,000, the compatibility with the hard segment component may be lowered, making block-like copolymerization difficult. The number average molecular weight of poly(tetramethylene oxide) glycol is more preferably 800 or more and 3000 or less, further preferably 1000 or more and 2500 or less.

In the thermoplastic polyester elastomer used in the present invention, the soft segment content is preferably 25 to 90% by mass, more preferably 45 to 90% by mass, still more preferably 55 to 90% by mass, particularly preferably 65 to 90% by mass. % by mass. Here, when the content of the soft segment is large, the repulsive force of the resin foam of the polyester elastomer resin increases, which makes the material more likely to vibrate, thereby improving the sound absorbing performance in the low frequency range. If the content of the soft segment is less than 25% by mass, the impact resilience will be low and the sound absorption peak frequency will appear in the high frequency region. tend to be inferior. The rebound resilience is preferably 50-90%, more preferably 60-90%, still more preferably 70-90%.

By changing the ratio of the hard segment to the soft segment and the expansion ratio of the thermoplastic polyester elastomer, it is possible to control the peak frequency at which the sound absorption coefficient becomes a predetermined value or more. If it is 45 to 90% by mass, this control becomes possible without particularly increasing the expansion ratio.

The thermoplastic polyester elastomer used in the present invention can be produced by known methods. For example, a lower alcohol diester of a dicarboxylic acid, an excessive amount of a low molecular weight glycol, and a soft segment component are transesterified in the presence of a catalyst, and the resulting reaction product is polycondensed. A method of subjecting segment components to an esterification reaction in the presence of a catalyst and polycondensing the resulting reaction product. A hard segment polyester is prepared in advance, and a soft segment component is added to this to randomize it by transesterification. method, a method of linking the hard segment and the soft segment with a chain linking agent, and when poly(ε-caprolactone) is used for the soft segment, a method of adding the ε-caprolactone monomer to the hard segment. .

The thermoplastic polyester elastomer (resin) may optionally contain a cross-linking agent within a range that does not impair the effects of the present invention. Such a cross-linking agent is not particularly limited as long as it is a cross-linking agent that reacts with the hydroxyl group or carboxyl group of the thermoplastic polyester elastomer. Examples include epoxy cross-linking agents, carbodiimide cross-linking agents, isocyanate cross-linking agents, and acid anhydrides cross-linking agents, silanol-based cross-linking agents, melamine resin-based cross-linking agents, metal salt-based cross-linking agents, metal chelate-based cross-linking agents, amino resin-based cross-linking agents, and the like. In addition, a crosslinking agent can be used individually or in combination of 2 or more types.

The epoxy-based cross-linking agent is not particularly limited as long as it is a polyfunctional epoxy compound having two or more epoxy groups (glycidyl groups) in the molecule, and specifically, 1,6-dihydroxynaphthalene having two epoxy groups. Diglycidyl ether, 1,3-bis(oxiranylmethoxy)benzene, 1,3,5-tris(2,3-epoxypropyl)-1,3,5-triazine-2,4 with three epoxy groups ,6(1H,3H,5H)-trione and diglycerol triglycidyl ether, 1-chloro-2,3-epoxypropane・formaldehyde・2,7-naphthalenediol polycondensate having four epoxy groups and pentaerythritol poly Glycidyl ethers may be mentioned. Among them, a polyfunctional epoxy compound having heat resistance in its skeleton is preferable. Particularly preferred are bifunctional or tetrafunctional epoxy compounds having a naphthalene structure in the skeleton, or trifunctional epoxy compounds having a triazine structure in the skeleton. Considering the degree of increase in the solution viscosity of the thermoplastic polyester elastomer, the effect of efficiently lowering the acid value of the thermoplastic polyester elastomer, and the degree of gelation due to aggregation and solidification of the epoxy itself, Functional epoxy compounds are preferred.

In addition, it contains two or more glycidyl groups per molecule and has a weight average molecular weight of 4000 to 25000, and (X) 20 to 99% by mass of a vinyl aromatic monomer, (Y) 1 to 80% by mass of glycidyl ( Examples include meth)acrylates and (Z) styrenic copolymers composed of vinyl group-containing monomers other than (X) containing no epoxy groups in an amount of 0 to 79% by mass. More preferably, (X) is 20 to 99% by mass, (Y) is 1 to 80% by mass, and (Z) is 0 to 40% by mass. 10 to 75% by mass of (Y) and 0 to 35% by mass of (Z). Examples of the vinyl aromatic monomer (X) include styrene and α-methylstyrene. Examples of the (Y) glycidyl (meth)acrylate include glycidyl (meth)acrylate, (meth)acrylic acid ester having a cyclohexene oxide structure, (meth)acrylic glycidyl ether, etc. Among these, reactive glycidyl (meth)acrylate is preferred in terms of high Examples of (Z) other vinyl group-containing monomers include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (Meth)acryl having an alkyl group having 1 to 22 carbon atoms (the alkyl group may be linear or branched) such as cyclohexyl (meth)acrylate, stearyl (meth)acrylate, methoxyethyl (meth)acrylate, etc. acid alkyl esters, (meth)acrylic acid polyalkylene glycol esters, (meth)acrylic acid alkoxyalkyl esters, (meth)acrylic acid hydroxyalkyl esters, (meth)acrylic acid dialkylaminoalkyl esters, (meth)acrylic acid benzyl esters, (Meth)acrylic acid phenoxyalkyl ester, (meth)acrylic acid isobornyl ester, (meth)acrylic acid alkoxysilylalkyl ester and the like. In addition, (meth)acrylamide, (meth)acryldialkylamide, vinyl esters such as vinyl acetate, aromatic vinyl monomers such as vinyl ethers and (meth)allyl ethers, α-olefin monomers such as ethylene and propylene etc. can also be used as (Z) other vinyl group-containing monomers.
The weight average molecular weight of the copolymer is preferably 4,000 to 25,000. The weight average molecular weight is more preferably 5000-15000. The epoxy value of the copolymer is preferably 400 to 2500 equivalents/1×10 ⁶ g, more preferably 500 to 1500 equivalents/1×10 ⁶ g, still more preferably 600 to 1000 equivalents/1×10 ⁶ is g.

The carbodiimide-based cross-linking agent is not particularly limited as long as it is a polycarbodiimide having two or more carbodiimide groups (-N=C=N- structure) in one molecule. Carbodiimides, aromatic polycarbodiimides, copolymers thereof, and the like can be mentioned. Aliphatic polycarbodiimide compounds or alicyclic polycarbodiimide compounds are preferred.

A polycarbodiimide compound can be obtained, for example, by a decarbonization reaction of a diisocyanate compound. Diisocyanate compounds that can be used here include, for example, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, and 2,4-tolylene diisocyanate. , 2,6-tolylene diisocyanate, 1,5-naphthylene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane diisocyanate, tetramethylxylylene diisocyanate, 1,3,5-triisopropylphenylene-2,4-diisocyanate and the like. These may be used alone, or two or more may be copolymerized and used. Also, a branched structure may be introduced, or a functional group other than a carbodiimide group or an isocyanate group may be introduced by copolymerization. Furthermore, although the terminal isocyanate can be used as it is, the degree of polymerization may be controlled by reacting the terminal isocyanate, or a portion of the terminal isocyanate may be blocked.

As the polycarbodiimide compound, alicyclic polycarbodiimides derived from dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, isophorone diisocyanate and the like are particularly preferred, and polycarbodiimides derived from dicyclohexylmethane diisocyanate and isophorone diisocyanate are particularly preferred.

The polycarbodiimide compound preferably contains 2 to 50 carbodiimide groups per molecule in terms of stability and handleability. More preferably, it contains 5 to 30 carbodiimide groups per molecule. The number of carbodiimides in a polycarbodiimide molecule (that is, the number of carbodiimide groups) corresponds to the degree of polymerization in the case of polycarbodiimide obtained from a diisocyanate compound. For example, the degree of polymerization of polycarbodiimide obtained by connecting 21 diisocyanate compounds in a chain is 20, and the number of carbodiimide groups in the molecular chain is 20. Generally, polycarbodiimide compounds are mixtures of molecules of various lengths and the number of carbodiimide groups is expressed as an average value. If it has the number of carbodiimide groups in the above range and is solid at around room temperature, it can be pulverized, so that it has excellent workability and compatibility when mixed with the thermoplastic polyester elastomer (A), uniform reactivity, and bleed-out resistance. is also preferable. The number of carbodiimide groups can be measured, for example, by a conventional method (method of dissolving with amine and performing back titration with hydrochloric acid).

The polycarbodiimide compound preferably has an isocyanate group at its end and an isocyanate group content of 0.5 to 4% by mass from the viewpoint of stability and handleability. More preferably, the isocyanate group content is 1-3% by mass. In particular, polycarbodiimide derived from dicyclohexylmethane diisocyanate or isophorone diisocyanate and having an isocyanate group content within the above range is preferred. The isocyanate group content can be measured by a conventional method (method of dissolving with amine and performing back titration with hydrochloric acid).

Examples of the isocyanate-based cross-linking agent include the above-described polycarbodiimide compound containing an isocyanate group and the isocyanate compound that is a raw material for the above-described polycarbodiimide compound.

As the acid anhydride cross-linking agent, a compound containing 2 to 4 anhydrides per molecule is preferable from the viewpoint of stability and handleability. Examples of such compounds include phthalic anhydride, trimellitic anhydride, and pyromellitic anhydride.

The amount (content) of the cross-linking agent used is appropriately adjusted depending on the extrusion conditions, the desired expansion ratio, etc., and is, for example, 0.1 to 4.5 parts by mass with respect to 100 parts by mass of the thermoplastic polyester elastomer. is preferred, more preferably 0.1 to 4 parts by mass, and still more preferably 0.1 to 3 parts by mass.

As the cross-linking agent, an epoxy-based cross-linking agent, in particular, a vinyl aromatic monomer containing two or more glycidyl groups per molecule and having a weight average molecular weight of 4,000 to 25,000, and (X) 20 to 99% by mass, (Y ) 1 to 80% by mass of glycidyl (meth)acrylate and (Z) 0 to 79% by mass of a vinyl group-containing monomer other than (X) that does not contain an epoxy group is preferred. However, when a compound having a highly reactive functional group such as a carbodiimide group is used in combination with an epoxy compound, the molecular weight distribution of the resin composition after cross-linking tends to be narrow. Therefore, there is a possibility that the injection pressure during injection molding increases, the foam nuclei disappear, and the expansion ratio decreases. Therefore, in the resin composition used in the present invention, it is preferable not to use both an epoxy-based cross-linking agent and a carbodiimide-based cross-linking agent as cross-linking agents.

Furthermore, the thermoplastic polyester elastomer (resin) used in the present invention may contain various additives in addition to the above-described crosslinking agent, depending on the purpose. The types of such additives are not particularly limited, and various additives commonly used in foam molding can be used. Specifically, additives include known hindered phenol-based, sulfur-based, phosphorus-based, and amine-based antioxidants, hindered amine-based antioxidants, benzotriazole-based, benzophenone-based, benzoate-based, triazole-based, nickel-based, and salicyl antioxidants. Light stabilizers such as systems, lubricants, fillers, flame retardants, flame retardant aids, release agents, antistatic agents, molecular modifiers such as peroxides, metal deactivators, organic and inorganic nucleating agents, In addition to neutralizers, antacids, antibacterial agents, fluorescent brighteners, organic and inorganic pigments, organic and inorganic phosphorus compounds used for the purpose of imparting flame retardancy and thermal stability, etc. mentioned. The amount of the additive to be added can be appropriately selected within a range that does not impair the formation of air bubbles, etc., and the amount to be added used for molding ordinary thermoplastic resins can be employed. In the present invention, the content of the thermoplastic polyester elastomer in the thermoplastic polyester elastomer resin is preferably 90% by mass or more, more preferably 95% by mass or more.

The MFR value at 230° C. of the thermoplastic polyester elastomer resin used in the present invention is preferably 10 to 30 g/10 min, more preferably 10 to 20 g/10 min. With the MFR in this range, optimum fluidity and foaming properties can be maintained.

As a method for determining the composition and composition ratio of the polyester elastomer resin used in the present invention, it is also possible to calculate from the proton integral ratio of ¹ H-NMR measured by dissolving a sample in a solvent such as heavy chloroform.

[Foam]
The foam in the present invention is obtained using the polyester elastomer resin of the present invention described above. The foam of the present invention preferably comprises 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-described thermoplastic polyester elastomer resin, they have a uniform cell-state foamed structure and can exhibit excellent lightness and sound absorption.

The foam in the present invention usually has a sandwich structure in which non-foamed skin layers are provided on both sides of a foamed layer (in other words, a structure in which a foamed layer is sandwiched between non-foamed skin layers on both sides). The size of the foam is not particularly limited, but the thickness direction of the sandwich structure is assumed 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 having no cavities formed of a cured thermoplastic polyester elastomer resin. The average cell diameter of foamed cells is preferably 10 to 400 μm. If the average cell diameter is less than 10 μm, the internal pressure of the foam 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, when the average cell diameter exceeds 400 μm, the load resistance is lowered. As the foaming ratio increases, the diameter of the foamed cells (cell diameter) becomes coarser and the impact resilience of the material increases, so the sound absorption peak frequency appears at a lower frequency. , the average cell diameter is more preferably 100 to 400 μm, more preferably 200 to 400 μm. A foam having an average cell diameter within the above range can be obtained by applying an appropriate pressure to the non-foamed skin layer from inside the foam.

The non-foamed skin layer is laminated on the foamed layer, and preferably has a thickness of 100 to 800 μm. When the thickness of the non-foamed skin layer is less than 100 µm, there is a tendency that a good appearance cannot be obtained. 01-0.35 g/cm ³ , there is a tendency not to obtain a foamed structure with a uniform cell state.

The thermoplastic polyester elastomer resin foam 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-frequency sound with a material of limited thickness, it is possible to obtain a low-frequency sound-absorbing effect through resonance. and Helmholtz sound absorber type sound absorption using slits and perforated plates. The foam of the thermoplastic polyester elastomer resin has a non-foamed layer, so that it exhibits a plate vibration type, and can exhibit high sound absorbing properties even at low frequencies. 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 high frequencies, so having the non-foamed skin layer is advantageous for low-frequency sound absorption. However, even if the non-foamed skin layer is removed, the sound absorption peak frequency only changes, and the sound absorption characteristics such as the sound absorption coefficient do not decrease. The thickness of the non-foamed skin layer is more preferably 200-600 μm, still more preferably 200-400 μm, and particularly preferably 300-400 μm.

The density of the foam in the present invention is preferably 0.01-0.35 g/cm ³ . Since the density of general polyester elastomers is around 1.0 to 1.4 g/cm ³ , it can be said that the foam of the present invention is sufficiently light in weight. More preferably from 0.1 to 0.35 g/cm ³ , still more preferably from 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 the mechanical properties tend to be inferior. In order to achieve both excellent strength and high sound absorption properties, the density of the foam is more preferably 0.01 to 0.25 g/cm ³ , more preferably 0.1 to 0.25 g/cm ³ . More preferred. Density is apparent density, the measurement method of which is shown in the Examples section.

The foam in 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, so that it has a uniform and fine cell structure. As a result, it is possible to control high sound absorption characteristics in a wide frequency range.

The foam in the present invention can have different thicknesses, weights, and densities depending on the expansion ratio. When the same thermoplastic polyester elastomer resin is used, the sound absorption peak frequency changes depending on the expansion ratio, but the sound absorption characteristics such as the sound absorption coefficient are hardly affected. In addition, when the same thermoplastic polyester elastomer resin is used for the foam in the present invention, if the density is the same, even if the thickness and weight change, the sound absorption characteristics such as the sound absorption peak frequency and the sound absorption coefficient are hardly affected. .

The foaming method of the foam in the present invention is not particularly limited, but a foaming method of impregnating the resin with a high-pressure gas and then reducing the pressure (releasing the pressure) is preferable. Among them, as a molding method that can achieve molding cycleability, cost, and uniform foaming, a method of obtaining a foamed molded product by expanding the volume of the cavity during injection molding by melt-mixing a foaming agent and a thermoplastic polyester elastomer resin. preferable. Specifically, as shown in FIG. 1, a molten thermoplastic polyester elastomer resin is added to a cavity 3 formed by a plurality of clamped molds 1 and 2 in a chemical blowing agent and/or in a supercritical state. of inert gas (hereinafter collectively referred to as “foaming agent”), and at the stage where a non-foaming skin layer having a thickness of 100 to 800 μm is formed on the surface layer, at least one mold 2 is formed. In this method, a foam is obtained by moving in the opening direction to expand the volume of the cavity 3 . Specifically, after the cavity 3 is filled with the thermoplastic polyester elastomer resin and the foaming agent, it is cooled at a predetermined temperature to form a non-foamed skin layer on the surface layer of the thermoplastic polyester elastomer resin filled in the cavity 3. be done. When the 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 and the foaming agent can be mixed in the plasticizing area 4 a of the injection molding machine 4 before filling the cavity 3 .

The chemical foaming agent that can be used to obtain the foam in the present invention is added to the resin that is melted in the resin melting zone of the molding machine as a gas component that serves as foam nuclei or as a source of the gas.
Specifically, as chemical foaming agents, inorganic compounds such as ammonium carbonate, sodium bicarbonate, and azide compounds, and organic compounds such as azo compounds, sulfhydrazide compounds, and nitroso compounds, and the like can be used. Examples of the azide compound include terephthalazide and p-tert-butylbenzazide. Furthermore, examples of the azo compound include diazocarbonamide (ADCA), 2,2-azoisobutyronitrile, azohexahydrobenzonitrile, and diazoaminobenzene, among which ADCA is preferred and utilized. 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) and the like.

When a chemical blowing agent is used as the blowing agent, the chemical blowing agent is based on a thermoplastic resin whose melting point is lower than the decomposition temperature of the chemical blowing agent in order to uniformly disperse it in the thermoplastic polyester elastomer resin. It can also be used as a masterbatch. 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. Examples thereof include polystyrene (PS), polyethylene (PE), and polypropylene (PP). In this case, the mixing ratio of the chemical foaming agent and 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 amount of the chemical blowing agent is less than 10 parts by mass, the amount of the masterbatch for the thermoplastic polyester elastomer resin may be too large, resulting in deterioration of physical properties. If it exceeds 100 parts by mass, it becomes difficult to form a masterbatch due to the problem of dispersibility of the chemical blowing agent.

When a supercritical inert gas is used as the blowing 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 thereof is preferably 0.05 to 30 parts by mass, preferably 0.1 to 20 parts by mass, per 100 parts by mass of the thermoplastic polyester elastomer resin. is more preferable. If the amount of supercritical carbon dioxide and/or nitrogen is less than 0.05 parts by mass, it will be difficult to obtain uniform and fine foamed cells, and if it exceeds 30 parts by mass, the surface appearance of the molded article will tend to be impaired.

Carbon dioxide or nitrogen in a supercritical state used as a blowing agent can be used alone, but carbon dioxide and nitrogen may be mixed and used. Nitrogen tends to be suitable for forming finer cells with respect to thermoplastic polyester elastomer resins, and carbon dioxide is suitable for obtaining a higher expansion ratio because a relatively large amount of gas can be injected. Therefore, they may be arbitrarily mixed in order to adjust the state of the foamed structure, and the mixing ratio in the case of mixing is preferably in the range of 1:9 to 9:1 in terms of molar ratio.

As the foaming agent used in the present invention, nitrogen in a supercritical state is more preferable from the viewpoint of uniform fine foaming.

In order to inject the molten thermoplastic polyester elastomer resin together with the foaming agent into the cavity 3, the molten thermoplastic polyester elastomer resin and the foaming agent may be mixed in the plasticizing region 4a of the injection molding machine 4. In particular, when supercritical carbon dioxide and/or nitrogen is used as the foaming agent, for example, as shown in FIG. A method of injecting into the injection molding machine 4 or the like can be adopted. These 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.

Here, the supercritical state means that when the temperature and pressure of a substance that produces a gas phase and a liquid phase are increased, the distinction between the gas phase and the liquid phase can be lost in a certain temperature range and pressure range. The temperature and pressure at this time are called critical temperature and critical pressure. In other words, a substance in a supercritical state has the properties of both gas and liquid, so the fluid produced 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, so it has the property of diffusing in a substance very easily.

Examples are given below to demonstrate the effects of the present invention, but the present invention is not limited to these examples.

The following raw materials were used in the following examples and comparative examples.
[Thermoplastic polyester elastomer]
(Polyester elastomer A)
According to the method described in JP-A-9-59491, dimethyl terephthalate, 1,4-butanediol, and poly (tetramethylene oxide) glycol having a number average molecular weight of 2000 are used as raw materials, and the soft segment content is 83% by mass. A thermoplastic polyester elastomer was produced and designated as Polyester Elastomer A.
(Polyester elastomer B)
According to the method described in JP-A-9-59491, dimethyl terephthalate, 1,4-butanediol, and poly (tetramethylene oxide) glycol having a number average molecular weight of 2000 are used as raw materials, and the soft segment content is 76% by mass. A thermoplastic polyester elastomer was produced and designated as Polyester Elastomer B.
(Polyester elastomer C)
According to the method described in JP-A-9-59491, using dimethyl terephthalate, 1,4-butanediol, and poly(tetramethylene oxide) glycol having a number average molecular weight of 1000 as raw materials, the soft segment content is 55% by mass. A thermoplastic polyester elastomer was produced and designated as Polyester Elastomer C.
(Polyester elastomer D)
According to the method described in JP-A-9-59491, dimethyl terephthalate, 1,4-butanediol, and poly (tetramethylene oxide) glycol having a number average molecular weight of 1000 are used as raw materials, and the soft segment content is 49% by mass. A thermoplastic polyester elastomer was produced and designated Polyester Elastomer D.
(Polyester elastomer E)
According to the method described in JP-A-9-59491, dimethyl terephthalate, 1,4-butanediol, and poly (tetramethylene oxide) glycol having a number average molecular weight of 1000 as raw materials, the soft segment content is 28% by mass. A thermoplastic polyester elastomer was produced, and this was designated as Polyester Elastomer E.
[Polybutylene terephthalate resin]
(polybutylene terephthalate)
Polybutylene terephthalate (PBT) having an intrinsic viscosity of 0.75 dl/g manufactured by Toyobo Co., Ltd. was used.

[Crosslinking agent]
(styrene copolymer)
The oil jacket temperature of a 1 liter pressurized stirred tank reactor equipped with an oil jacket was kept at 200°C. On the other hand, a monomer mixture consisting of 89 parts by weight of styrene (St), 11 parts by weight of glycidyl methacrylate (GMA), 15 parts by weight of xylene (Xy) and 0.5 parts by weight of ditertiarybutyl peroxide (DTBP) as a polymerization initiator. The liquid was charged into the raw material tank. This was continuously supplied from the raw material tank to the reactor at a constant supply rate (48 g/min, residence time: 12 minutes), and the reaction liquid was discharged from the outlet of the reactor so that the content liquid mass of the reactor was constant at about 580 g. continuously extracted from The internal temperature of the reactor at that time was kept at about 210°C. After 36 minutes have passed since the temperature inside the reactor has stabilized, the extracted reaction liquid is led to a thin film evaporator kept at a pressure reduction of 30 kPa and a temperature of 250 ° C., and volatile components are continuously removed. A polymer was obtained. This styrene-based copolymer had a mass average molecular weight of 8,500 and a number average molecular weight of 3,300 according to GPC analysis (converted to polystyrene). Further, according to the following measurement method, the epoxy value is 670 equivalents/1×10 ⁶ g, the epoxy value (average number of epoxy groups per molecule) is 2.2, and the glycidyl group is It has two or more.

[Thermoplastic polyester elastomer resin]
According to the formulation shown in Table 1, 100 parts by mass of a thermoplastic polyester elastomer is melted and kneaded with a styrene copolymer using a twin-screw extruder, and then pelletized to obtain a thermoplastic polyester elastomer resin A'. ~E' pellets were obtained. As the thermoplastic polyester elastomer resin A, the pellets of the polyester elastomer A were used as they were for evaluation. MFR (melt flow rate) was obtained by the following measurements.

[MFR]
The MFR of the thermoplastic polyester elastomer resin was measured at a load of 2,160 g and a measurement temperature of 230° C. according to the measurement method described in ASTM D1238.

[Examples 1 to 8, Reference Examples 1 and 2 , Comparative Examples 1 and 2]
Next, using the above resin component (thermoplastic polyester elastomer resin, PBT), a foam was produced by the above-described mold expansion method. As for the mold, when the mold is clamped, a cavity with a width of 100 mm, a length of 100 mm, and a thickness of 2.5 mm or 3.0 mm can be formed. A mold for producing a flat plate was used, which consists of a fixed mold and an operating mold capable of forming a cavity of 0.5 mm (or 3.0 mm) + core-back amount (mm). Specifically, in the plasticizing region of an electric injection molding machine having a screw with a mold clamping force of 1800 kN, a screw diameter of 40 mm, and a screw stroke of 180 mm, nitrogen in a supercritical state was injected to bring the surface temperature to 50 ° C. After injection filling into the temperature-controlled mold, at the stage where a non-foamed skin layer of 100 to 800 μm is formed by the injection external pressure and the foaming pressure from the inside, the operating mold is opened in the mold opening direction, and the core is backed as shown in Table 2. A foam was obtained by moving the length indicated as amount (mm) to enlarge the volume of the cavity.

The foams obtained from the thermoplastic polyester elastomer resins obtained in Examples 1 to 8, Reference Examples 1 and 2, and Comparative Examples 1 and 2, and the foams obtained from polybutylene terephthalate were evaluated as follows. did Table 2 shows the results. Example 4 is obtained by removing (cutting) the skin layer from the same thermoplastic polyester elastomer resin foam as in Example 3.

[Density (apparent density)]
The dimensions of the foam were measured with vernier calipers, and the mass was measured with an electronic balance and calculated by the following formula.
Density (g/cm ³ ) = mass of test piece/volume of test piece

[Average cell diameter]
A photograph of a cross-section of a foamed sample for cross-section observation taken with a scanning electron microscope SU1510 manufactured by Hitachi High-Technologies Corporation was subjected to image processing, and the circle equivalent diameter of at least 100 adjacent cells was taken as the cell diameter and measured with a vernier caliper. An average value of 100 of them was determined, and this was performed at arbitrary three locations, and the average value of the three average values obtained at the three locations was taken as the average cell diameter.

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

[Rebound resilience]
Measurement was carried out by the method described in JIS K 6400. Using a manual measurement tester, a steel ball was dropped from a specified height onto the test piece, and the maximum rebound height was read. The measurement was performed three times within one minute, the median value was obtained, and the rebound resilience was calculated.

[Sound absorption characteristics]
JIS A1405-2 (2007) for each of Examples 1 to 8, Reference Examples 1 and 2, and Comparative Examples 1 and 2 using the normal incidence sound absorption coefficient measurement system WinZacMTX manufactured by Nippon Onkyo Engineering Co., Ltd. , 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. At this time, the first peak appearing from the low frequency at which 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, and exhibit a sound absorption peak frequency with a high sound absorption coefficient in the frequency range of 0.4 kHz to 5.0 kHz. . Comparing Examples 3 , 7 and 8 with Reference Examples 1 and 2, as the soft segment content increases, the sound absorption peak frequency appears at a low frequency, and in Example 3, it is 2.1 kHz. In Examples 1 and 2, in which the expansion ratio is increased from that of Example 3, the sound absorption peak frequency appears at a low frequency due to the increase in the expansion ratio. Furthermore, in Example 4, the skin layer was removed from the same thermoplastic polyester elastomer resin foam as in Example 3, and the sound absorption peak frequency shifted to a higher frequency than in Example 3. From the comparison between Example 3 and Example 4, it can be seen that the presence of the skin layer enables the sound absorption peak frequency to appear at lower frequencies. Example 5 has more cavities than Example 3 and has the same foaming ratio. It can be seen that even if the thickness of the molded product increases, there is no great difference in the sound absorbing properties. Reference Example 2 and Comparative Example 1 have the same soft segment content and different expansion ratios. However, in Reference Example 2 , since the modulus of rebound resilience is high, the sound absorption peak frequency appears at 5.0 kHz or less. Furthermore, Comparative Example 2 is polybutylene terephthalate, and the sound absorption peak frequency exceeds 5.0 kHz.

The sound absorbing material made of the thermoplastic polyester elastomer resin foam of the present invention is not only excellent in thinness and lightness, but also capable of controlling high sound absorption in the low to high frequency range. In addition, despite its high expansion ratio, it has a uniform foaming state, high heat resistance, water resistance, and molding stability, so it can be used for parts that require high reliability. It is possible to provide a sound absorbing material consisting of

1 mold (for fixing)
2 Mold (for operation)
3 cavity 4 injection molding machine 4a plasticizing region 5 gas cylinder 6 booster pump 7 pressure control valve

Claims (4)

A sound absorbing material made of a thermoplastic polyester elastomer resin foam, when measuring the normal incident sound absorption coefficient of the foam in the frequency range of 0.4 kHz to 5.0 kHz according to JIS A1405-2 (2007) , a sound absorbing material having a peak frequency at which the normal incident sound absorption coefficient is 40% or more in the frequency range of 0.4 kHz to 5.0 kHz, wherein the thermoplastic polyester elastomer resin is an aromatic dicarboxylic acid and an aliphatic and/or fatty acid. A hard segment made of a polyester containing a cyclic diol as a component and at least one soft segment selected from aliphatic polyethers, aliphatic polyesters, and aliphatic polycarbonates are bonded, and the content of the soft segment is 55 A sound absorbing material characterized by being a thermoplastic polyester elastomer resin having a content of up to 90% by mass . 2. The sound absorbing material according to claim 1, wherein said foam has an average cell diameter of 10 to 400 μm. 3. The sound absorbing material according to claim 1, wherein the foam has a density of 0.1 to 0.35 g/cm ³ . The foam has a non-foamed skin layer with a thickness of 100 to 800 μm on the surface layer, and a foamed layer consisting of foamed cells with an average cell diameter of 10 to 400 μm independent of the resin continuous phase on the inner layer, and is non-foamed in the thickness direction. The sound absorbing material according to any one of claims 1 to 3 , which is a foam having a sandwich structure of a skin layer and a foam layer.

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