Sheet material, shaped body thereof, and acoustic diaphragm

Abstract

Provided is a sheet material which comprises a fiber structure comprising fibers comprising a first resin, and comprises a second resin with which the fiber structure is impregnated, said second resin comprising a liquid crystal polymer. When the first resin comprises a thermoplastic liquid crystal polymer and the second resin comprises a thermoplastic liquid crystal polymer, the fibers comprising the first resin may have higher heat resistance than the second resin.

Description

Sheet material, molded body thereof, and acoustic diaphragm Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-063617, filed April 10, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a sheet material including a fiber structure impregnated with a liquid crystal polymer resin, a molded article using the sheet material, and an acoustic diaphragm.

[0003] Liquid crystal polymers such as liquid crystal polyesters are used as engineering plastics in a variety of technical fields. For example, because they have a high elastic modulus and internal loss, they are also used as acoustic diaphragms such as speaker diaphragms.

[0004] When using liquid crystal polymers as materials for acoustic diaphragms, various materials have been investigated with the aim of improving the elastic modulus, internal loss, and processability. For example, Patent Document 1 (JP 3-50255 A) describes a resin composition comprising a liquid crystal polymer and 5% by weight or more but less than 20% by weight of a fibrous material, and a speaker diaphragm comprising the resin composition. In the examples, pellets obtained by kneading the liquid crystal polymer with carbon fiber or potassium titanate fiber are injection molded to evaluate their properties. Furthermore, Patent Document 2 (JP Patent No. 6124764 A) describes a speaker diaphragm molded by injection molding of a resin material containing 57% by weight or more but less than 90% by weight of a carbon fiber-reinforced liquid crystal polymer and 10% by weight or more but less than 38% by weight of a cyclic olefin-based resin, and also containing carbon nanotubes.

[0005] Japanese Patent Application Publication No. 3-50255 Patent No. 6124764

[0006] Patent Document 1 describes that blending a fibrous substance can improve the fluidity and modulus of elasticity of a liquid crystal polymer while suppressing a decrease in heat resistance. However, in materials in which a filler is added to a liquid crystal polymer, the improvement in modulus of elasticity and the improvement in internal loss are generally in a trade-off relationship, such as an increase in modulus of elasticity but a decrease in internal loss, or an increase in internal loss but a decrease in modulus of elasticity. Furthermore, diaphragms using liquid crystal polymers are generally formed by injection molding as described in Patent Documents 1 and 2. In this case, although the filler is oriented in the resin flow direction to obtain a high modulus of elasticity, the modulus of elasticity is low in the direction perpendicular to the flow, making it difficult to obtain isotropic performance.

[0007] The present invention aims to provide a sheet-like material (sheet material) that is composed of multiple materials including a liquid crystal polymer resin and that achieves both an improved elastic modulus and an improved internal loss. Another object of the present invention is to provide a sheet-like material that achieves both an improved elastic modulus and an improved internal loss and that suppresses the directional dependence of the elastic modulus and the internal loss within the sheet plane.

[0008] The present invention can take the following aspects: [Aspect 1] A sheet material comprising: a fiber structure including fibers containing a first resin; and a second resin impregnated into the fiber structure, wherein the second resin contains a liquid crystal polymer. [Aspect 2] The sheet material of Aspect 1, wherein the first resin contains a liquid crystal polymer.

[0009] [Aspect 3] The sheet material according to aspect 1 or 2, wherein the fiber structure is at least one selected from a woven fabric, a knitted fabric, and a nonwoven fabric. [Aspect 4] The sheet material according to any one of aspects 1 to 3, wherein the second resin comprises a thermoplastic liquid crystal polymer. [Aspect 5] The sheet material according to any one of aspects 1 to 4, wherein the fibers have higher heat resistance than the second resin.

[0010] [Aspect 6] The sheet material according to any one of Aspects 1 to 5, having a laminated structure including a composite layer containing the first resin and the second resin, and a resin layer present on at least one side of the composite layer and made of the second resin.

[0011] [Aspect 7] A sheet material having a dynamic viscoelastic modulus at 35°C of 4000 MPa or more in both a first direction along the sheet surface and a second direction along the sheet surface perpendicular to the first direction, an internal loss of 0.04 or more, and an internal loss of 0.07 or more (preferably 0.09 or more) in at least one direction. This sheet material may be the sheet material described in any one of Aspects 1 to 6. [Aspect 8] The sheet material of Aspect 7, wherein the dynamic viscoelastic modulus at 80°C of 4000 MPa or more in both a first direction along the sheet surface and a second direction along the sheet surface perpendicular to the first direction.

[0012] [Aspect 9] A molded article molded from the sheet material according to any one of Aspects 1 to 8. [Aspect 10] An acoustic diaphragm including the sheet material according to any one of Aspects 1 to 8.

[0013] It should be noted that any combination of at least two elements disclosed in the claims and / or the specification and / or the drawings is included in the present invention, and in particular any combination of two or more of the claims set forth in the claims is included in the present invention.

[0014] The sheet material of the present invention can improve the elastic modulus and also the internal loss, compared to when a sheet made of a liquid crystal polymer resin alone is used.

[0015] FIG. 1 is a schematic cross-sectional view showing the layering arrangement of materials for a sheet material in one embodiment of the present invention, illustrating a state in which a fiber structure is sandwiched between two liquid crystal polymer films. FIG. 2 is a schematic cross-sectional view showing a state in which a fiber structure is integrated by being impregnated with a liquid crystal polymer. FIG. 3 is a schematic cross-sectional view showing the configuration of an apparatus used to evaluate the processability of a sheet material. FIG. 4 is a schematic cross-sectional view showing a state in which a sheet material is deformed by the apparatus shown in FIG. 3. FIG. 5 is a diagram showing the state in which a cross-section of a sheet material produced in Example 1 is observed using a polarized mode stereomicroscope. FIG. 6 is an SEM image obtained by photographing the sample shown in FIG. 5 using a scanning electron microscope. FIG. 7 is a diagram showing the state in which a cross-section of a laminate produced in Comparative Example 7 is observed using a stereomicroscope. FIG. 8 is a schematic view showing the cross-sectional structure of a laminate produced in Comparative Example 7.

[0016] The sheet material of the present invention is a sheet-like material (composite sheet) including a fiber structure containing fibers containing a first resin and a second resin impregnated into the fiber structure, the second resin including a liquid crystal polymer. The inventors discovered that impregnating a fiber structure containing organic fibers with a liquid crystal polymer can achieve both improved elastic modulus and improved internal loss, thereby providing a sheet-like material suitable for acoustic diaphragms, and thus completed the present invention. In this specification, the first resin and the second resin contain a polymer as an organic compound, and it is preferable that each of the first resin and the second resin contains the polymer as an organic compound as a main component (50 wt % or more in the resin). Furthermore, the first resin and the second resin may contain components other than the polymer as the main component (a component comprising 50 wt % or more in each resin).

[0017] The first resin is preferably a resin capable of spinning fibers with a high elastic modulus. The polymer contained in the first resin is preferably a liquid crystal polymer, more preferably a thermoplastic liquid crystal polymer. Note that a liquid crystal polymer is a polymer capable of forming an optically anisotropic molten phase. The fiber structure may be a woven fabric, a knitted fabric, or a nonwoven fabric.

[0018] The fiber structure is impregnated with a second resin containing a liquid crystal polymer. That is, the second resin is filled into at least a portion of the voids in the fiber structure, forming a sheet material containing the first resin and the second resin. The impregnation method is not particularly limited, and may involve immersing the fiber structure in a melt or solution of the second resin containing the liquid crystal polymer. However, it is preferable to fill the voids in the fiber structure with the second resin containing the plasticized liquid crystal polymer by pressure injection. Therefore, it is preferable that the second resin contains a thermoplastic liquid crystal polymer as a polymer that is the main component, and that it has lower heat resistance than the fibers that constitute the first resin.

[0019] The second resin may have different components from the first resin, or may have the same components. Even if the first resin and the second resin have the same components (for example, the same combination of structural units and their content), the heat resistance of the fiber containing the first resin can be made higher than that of the second resin by adjusting the degree of polymerization, crystallinity, crystal structure, etc. of the polymer that makes up the fiber. Here, heat resistance can be determined by the melting point of the polymer that is the main component contained in each resin.

[0020] The sheet material may have a laminated structure including a composite layer containing the first resin and the second resin, and a resin layer containing the second resin present on at least one side of the composite layer. That is, the sheet material may have a laminated structure including a composite layer in which a fiber structure containing fibers containing the first resin is impregnated with the second resin, and a resin layer containing the second resin laminated on one or both sides of the composite layer. Such a structure can be formed by disposing a film containing the second resin on one or both sides of the fiber structure and pressing the second resin, which has been plasticized by heating, into the voids of the fiber structure.

[0021] In the present invention, a fiber structure (e.g., a woven fabric, knitted fabric, nonwoven fabric, etc.) composed of fibers (preferably long fibers) and capable of independently forming a sheet-like shape is impregnated with a second resin containing a liquid crystal polymer, thereby improving strength compared to a film made of a liquid crystal polymer alone. The impregnated liquid crystal polymer (second resin) forms multiple contact interfaces with the fibers, thereby improving internal loss. Furthermore, because the liquid crystal polymer (second resin) is impregnated into a fiber structure with fibers oriented in multiple directions (multidirectionally in the case of nonwoven fabrics), anisotropy of the modulus of elasticity and loss factor within the sheet plane can be reduced compared to conventional acoustic panel composites formed by injection molding a liquid crystal polymer containing fibers as a filler. For example, the present invention can provide a sheet material having a dynamic viscoelastic modulus of elasticity of 4000 MPa or more in both a first direction along the sheet surface and a second direction along the sheet surface perpendicular to the first direction, and an internal loss of 0.04 or more, with 0.07 or more in at least one direction. The structure of the sheet material of the present invention will be described in more detail below.

[0022] [Fibers containing first resin] The fibers containing the first resin are not particularly limited as long as they do not impair the elastic modulus or internal loss of the liquid crystal polymer (second resin) impregnated into the fiber structure, and examples thereof include polyolefin fibers formed from polyolefin resins such as polyethylene and polypropylene; polyester fibers formed from polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polylactic acid; polyamide fibers formed from polyamide resins such as polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamide 610, and polyamide 612; and various heat-resistant fibers. These fibers may be used alone or in combination of two or more.

[0023] The fiber containing the first resin preferably has higher heat resistance than the second resin, and is preferably a heat-resistant fiber. Examples of heat-resistant fibers include liquid crystal polymer fibers formed from liquid crystal polymers; amorphous polyarylate fibers formed from amorphous polyarylate; wholly aromatic polyamide fibers formed from wholly aromatic polyamides such as para-aramid and meta-aramid; polybenzazole fibers formed from polybenzazoles such as polybenzoxazole, polybenzothiazole, and polybenzimidazole; polyimide fibers formed from polyimide resins such as polyimide, polyetherimide, and polyamideimide; polyetherketone fibers formed from polyetherketone resins such as polyetheretherketone, polyetherketone, and polyetherketoneketone; polyphenylene sulfide fibers formed from polyphenylene sulfide; and fluorine-based resin fibers formed from fluorine-based resins such as polytetrafluoroethylene. Among these, liquid crystal polymer fibers and wholly aromatic polyamide fibers are preferred.

[0024] The liquid crystal polymer used as the first resin may be, for example, a liquid crystal polyester composed of structural units derived from aromatic diols, aromatic dicarboxylic acids, aromatic hydroxycarboxylic acids, etc. The structural units derived from aromatic diols, aromatic dicarboxylic acids, and aromatic hydroxycarboxylic acids are not particularly limited in chemical structure as long as the effects of the present invention are not impaired. Furthermore, the liquid crystal polymer may be a liquid crystal polyester amide containing structural units derived from aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids, provided that the effects of the present invention are not impaired. The liquid crystal polymer is preferably a wholly aromatic liquid crystal polyester or wholly aromatic liquid crystal polyester amide in which all structural units contain aromatic groups in the main chain. For example, preferred structural units include those shown in Table 1.

[0025]

[0026] In the structural units in Table 1, m is an integer of 0 to 2, and Y in the formula, in the range of 1 to the maximum number of possible substitutions, each independently represents a hydrogen atom, a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (for example, an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (for example, a methoxy group, an ethoxy group, an isopropoxy group, a n-butoxy group, etc.), an aryl group (for example, a phenyl group, a naphthyl group, etc.), an aralkyl group (for example, a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (for example, a phenoxy group), an aralkyloxy group (for example, a benzyloxy group), etc.

[0027] More preferred structural units include the structural units described in Examples (1) to (20) shown in the following Tables 2, 3, and 4. When the structural unit in the formula is a structural unit that can exhibit multiple structures, two or more of such structural units may be combined and used as structural units that constitute the polymer.

[0028]

[0029]

[0030]

[0031] In the structural units of Tables 2, 3 and 4, n is an integer of 1 or 2, and each structural unit n=1 and n=2 may exist alone or in combination; Y １ and Y ２may each independently be a hydrogen atom, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc.), an alkyl group (e.g., an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, an isopropyl group, a t-butyl group, etc.), an alkoxy group (e.g., a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, etc.), an aryl group (e.g., a phenyl group, a naphthyl group, etc.), an aralkyl group (e.g., a benzyl group (phenylmethyl group), a phenethyl group (phenylethyl group), etc.), an aryloxy group (e.g., a phenoxy group), an aralkyloxy group (e.g., a benzyloxy group), etc. Of these, a hydrogen atom, a chlorine atom, a bromine atom, or a methyl group is preferred.

[0032] Examples of Z include substituents represented by the following formulas.

[0033]

[0034] The liquid crystal polymer is preferably a copolymer containing at least a structural unit (A) derived from hydroxybenzoic acid and / or a structural unit (B) derived from hydroxynaphthoic acid. For example, the structural unit (A) can be a structural unit derived from 4-hydroxybenzoic acid, represented by the following formula (A), and the structural unit (B) can be a structural unit derived from 6-hydroxy-2-naphthoic acid, represented by the following formula (B).

[0035]

[0036]

[0037] The wholly aromatic polyamide is composed of constituent units derived from, for example, aromatic diamines, aromatic dicarboxylic acids, aromatic aminocarboxylic acids, etc., and the constituent units derived from aromatic diamines, aromatic dicarboxylic acids, and aromatic aminocarboxylic acids are not particularly limited in terms of their chemical constitution, as long as the effects of the present invention are not impaired.

[0038] Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, etc. Also included are derivatives in which hydrogen atoms on the aromatic rings of these aromatic diamines are substituted with halogen atoms, alkyl groups, alkoxy groups, aryl groups, aralkyl groups, aryloxy groups, aralkyloxy groups, etc., such as 2-chloro-p-phenylenediamine, 2,5-dichloro-p-phenylenediamine, 2,6-dichloro-p-phenylenediamine, 2-chloro-m-phenylenediamine, 4-chloro-m-phenylenediamine, 2-methyl-p-phenylenediamine, 2-methyl-m-phenylenediamine, 4-methyl-m-phenylenediamine, etc.

[0039] Examples of aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, etc. Also included are derivatives in which hydrogen atoms on the aromatic rings of these aromatic dicarboxylic acids are substituted with halogen atoms, alkyl groups, alkoxy groups, phenyl groups, etc., such as 2-chloroterephthalic acid, 2,5-dichloroterephthalic acid, 2,6-dichloroterephthalic acid, 3-chloroisophthalic acid, and 3-methoxyisophthalic acid.

[0040] The wholly aromatic polyamide may preferably be poly(p-phenylene terephthalamide) containing structural units derived from p-phenylenediamine and structural units derived from terephthalic acid; poly(m-phenylene isophthalamide) containing structural units derived from m-phenylenediamine and structural units derived from isophthalic acid; or copoly(p-phenylene-3,4'-oxydiphenylene terephthalamide) containing structural units derived from p-phenylenediamine and structural units derived from 3,4'-diaminodiphenyl ether as aromatic diamines, and structural units derived from terephthalic acid as aromatic dicarboxylic acid.

[0041] For example, the polymer that is the main component contained in the first resin may contain at least one structural unit selected from the group consisting of structural units represented by the following formulas (I) to (III) (structural units (I) to (III)): １ -CO- (I) -CO-Ar ２ -CO- (II) -X-Ar ３ -Y- (III) (In formulas (I) to (III), Ar １ is a phenylene group, a naphthylene group, or a biphenylylene group, and Ar ２ and Ar ３ are each independently a phenylene group, a naphthylene group, a biphenylylene group, a diphenyletherdiyl group, a diphenylmethyldiyl group, or a diphenylsulfondiyl group, and Ar １ , Ar ２ and Ar ３ Each hydrogen atom in the aromatic ring may be independently substituted with a halogen atom, an alkyl group, an alkoxy group, an aryl group, an aralkyl group, an aryloxy group, or an aralkyloxy group, and each of X and Y is independently an oxygen atom or a secondary amino group (—NH—).

[0042] The structural unit (I) is a structural unit derived from an aromatic hydroxycarboxylic acid, the structural unit (II) is a structural unit derived from an aromatic dicarboxylic acid, and the structural unit (III) is a structural unit derived from an aromatic diol (X and Y are oxygen atoms), an aromatic diamine (X and Y are secondary amino groups), or an aromatic hydroxyamine (one of X and Y is an oxygen atom, and the other is a secondary amino group).

[0043] The polymer that is the main component contained in the first resin may contain one type of each of the structural units (I) to (III), or may contain two or more types. The polymer that is the main component contained in the first resin may have a total content of the structural units (I) to (III) of, for example, 90 mol % or more, preferably 95 mol % or more, more preferably 99 mol % or more, and even more preferably 100 mol %, based on the total amount of all structural units.

[0044] The first resin may contain at least one polymer selected from the group consisting of a liquid crystal polyester having the structural unit (I) as a main component, a liquid crystal polyester having the structural units (I) to (III), and a wholly aromatic polyamide having the structural units (II) and (III).

[0045] For example, the polymer that is the main component contained in the first resin may be a liquid crystal polyester having two or more types of structural unit (I). １ Examples of structural units include a 1,4-phenylene group (structural unit (A) derived from 4-hydroxybenzoic acid) and a 2,6-naphthylene group (structural unit (B) derived from 6-hydroxy-2-naphthoic acid). Preferably, the structural unit (A) may be a copolymer containing the structural unit (B). For example, from the viewpoint of improving melt moldability, the ratio (A) / (B) of the structural unit (A) to the structural unit (B) may be preferably in the range of 9 / 1 to 1 / 1, more preferably 7 / 1 to 1 / 1, and even more preferably 5 / 1 to 1 / 1.

[0046] The total amount of the structural units (A) and (B) may be, for example, 65 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more, based on all structural units. The liquid crystal polymer may contain 4 to 45 mol % of the structural unit (B) based on all structural units.

[0047] The liquid crystal polymer may contain the structural unit (A) in an amount of preferably 50 mol% or more, more preferably 53 mol% or more, even more preferably 60 mol% or more, even more preferably 65 mol% or more, and particularly preferably 70 mol% or more, based on the total structural units. The upper limit of the content of the structural unit (A) in the liquid crystal polymer is not particularly limited, but may be, for example, 90 mol% or less, preferably 88 mol% or less, and more preferably 85 mol% or less.

[0048] The polymer that is the main component contained in the first resin may be a liquid crystal polyester having structural units (I) to (III), and for example, a copolymer containing a structural unit (I) derived from an aromatic hydroxycarboxylic acid, such as a structural unit (A) derived from 4-hydroxybenzoic acid and / or a structural unit (B) derived from 6-hydroxy-2-naphthoic acid, a structural unit (II) derived from at least one type of aromatic dicarboxylic acid, and a structural unit (III) derived from at least one type of aromatic diol and / or aromatic hydroxyamine is preferred.

[0049] The structural unit (II) is Ar ２ However, preferred are 1,4-phenylene group structural units (structural units derived from terephthalic acid), 1,3-phenylene group structural units (structural units derived from isophthalic acid), 2,6-naphthylene group structural units (structural units derived from 2,6-naphthalenedicarboxylic acid), 4,4'-biphenylylene group structural units (structural units derived from 4,4'-biphenyldicarboxylic acid), and diphenylether-4,4'-diyl group structural units (structural units derived from diphenylether-4,4'-dicarboxylic acid).

[0050] The structural unit (III) as an aromatic diol is Ar ３ However, preferred are structural units which are 1,4-phenylene groups (structural units derived from hydroquinone), structural units which are 4,4'-biphenylylene groups (structural units derived from 4,4'-dihydroxybiphenyl), structural units which are phenyl-1,4-phenylene groups (structural units derived from phenylhydroquinone), and structural units which are diphenylether-4,4'-diyl groups (structural units derived from 4,4'-dihydroxydiphenyl ether).

[0051] The aromatic hydroxyamine structural unit (III) is Ar ３ However, a structural unit which is a 1,4-phenylene group (a structural unit derived from 4-aminophenol) and a structural unit which is a 4,4'-biphenylylene group (a structural unit derived from 4-amino-4'-hydroxybiphenyl) are preferred.

[0052] The content of the structural unit (I) in the liquid crystal polymer may be 20 to 80 mol %, preferably 30 to 75 mol %, and more preferably 40 to 70 mol %, based on the total amount of all structural units.

[0053] The content of the structural unit (II) in the liquid crystal polymer may be 10 to 40 mol %, preferably 12.5 to 35 mol %, and more preferably 15 to 30 mol %, based on the total amount of all structural units.

[0054] The content of the structural unit (III) in the liquid crystal polymer may be 10 to 40 mol %, preferably 12.5 to 35 mol %, and more preferably 15 to 30 mol %, based on the total amount of all structural units.

[0055] From the viewpoint of easily increasing the molecular weight of the liquid crystal polymer and improving its mechanical properties, the molar ratio of the content of the structural unit (II) to the content of the structural unit (III), (II) / (III), may be 90 / 100 to 100 / 90, preferably 95 / 100 to 100 / 95, more preferably 98 / 100 to 100 / 98, and even more preferably 100 / 100.

[0056] The polymer that is the main component contained in the first resin may be a wholly aromatic polyamide having structural units (II) and (III), and is preferably, for example, a copolymer containing structural units (II) derived from an aromatic dicarboxylic acid, such as structural units derived from terephthalic acid and / or structural units derived from isophthalic acid, and structural units (III) derived from at least one type of aromatic diamine.

[0057] The aromatic diamine structural unit (III) is Ar ３However, preferred are structural units which are 1,4-phenylene groups (structural units derived from p-phenylenediamine), structural units which are 1,3-phenylene groups (structural units derived from m-phenylenediamine), structural units which are diphenylether-3,4'-diyl groups (structural units derived from 3,4'-diaminodiphenyl ether), structural units which are diphenylether-4,4'-diyl groups (structural units derived from 4,4'-diaminodiphenyl ether), structural units which are diphenylmethyl-4,4'-diyl groups (structural units derived from 4,4'-diaminodiphenylmethane), and structural units which are diphenylsulfone-3,4'-diyl groups (structural units derived from 3,4'-diaminodiphenyl sulfone).

[0058] The fiber containing the first resin may be a fiber made of the first resin. Alternatively, it may be a fiber made of a composition containing the first resin as a main component polymer and other components. For example, in the description of this specification, "polyolefin-based fiber" may be a fiber containing a polyolefin-based resin as a main component and other components. The same applies when the first resin is another resin. For example, the fiber containing the first resin may contain various additives such as inorganic substances such as titanium oxide, kaolin, silica, and barium oxide, colorants such as carbon black, dyes and pigments, antioxidants, UV absorbers, and light stabilizers, as well as other resin components. In one embodiment, the fiber containing the first resin may contain 50% by weight or more of the main component polymer, preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more. As the polymer that is the main component, for example, the above-mentioned liquid crystal polymer, amorphous polyarylate, wholly aromatic polyamide, polybenzazole, polyimide resin, polyether ketone resin, polyphenylene sulfide, fluorine resin, etc. are preferable.

[0059] The single fiber fineness of the fiber containing the first resin can be appropriately selected depending on the type of fiber structure, etc. For example, the single fiber fineness may be 50 dtex or less, preferably 15 dtex or less, and more preferably 10 dtex or less. The lower limit of the single fiber fineness is not particularly limited, but may be, for example, about 0.01 dtex. The single fiber fineness is a value measured by the method described in the Examples below.

[0060] The fiber containing the first resin may be a monofilament or a multifilament. In the case of a multifilament, the number of filaments can be appropriately selected depending on the application, etc. For example, the number of filaments may be 2 to 5,000, preferably 3 to 4,000, and more preferably 5 to 3,000.

[0061] The total fineness of the fibers containing the first resin can be appropriately selected depending on the type of fiber structure, etc., and may be, for example, 50,000 dtex or less, preferably 10,000 dtex or less, more preferably 5,000 dtex or less, and even more preferably 2,000 dtex or less. The lower limit of the total fineness is not particularly limited, but may be, for example, about 1 dtex.

[0062] Fibers containing the first resin can be obtained by a known spinning method depending on the type of the first resin. For example, liquid crystal polymer fibers can be obtained by melt spinning, and wholly aromatic polyamide fibers can be obtained by solution spinning such as dry spinning, wet spinning, or dry-wet spinning.

[0063] For example, when a liquid crystal polymer fiber is produced by melt spinning and then subjected to a heat treatment, solid-state polymerization can be promoted to improve the mechanical properties of the fiber, such as strength and elastic modulus, and the thermal properties, such as the melting point. A known method can be used for the heat treatment, and various properties may be adjusted by adjusting the atmosphere, heat treatment temperature, heat treatment time, etc.

[0064] For example, the raw spinning yarn of the wholly aromatic polyamide fiber may be subjected to heat drawing and, if necessary, heat treatment.

[0065] The fiber containing the first resin preferably has higher heat resistance than the second resin. For example, the melting point may be 260°C or higher, preferably 290°C or higher, and more preferably 320°C or higher. The upper limit of the melting point is not particularly limited, but may be 500°C or lower. In this specification, the melting point of the fiber containing the first resin is the main absorption peak temperature observed when measured using a differential scanning calorimeter (DSC) in accordance with the JIS K 7121 test method. Specifically, 4 to 6 mg of a sample is placed in an aluminum pan and sealed in a DSC apparatus. Nitrogen is flowed as a carrier gas at a flow rate of 200 mL / min, and the endothermic peak is measured when the temperature is increased from room temperature (e.g., 25°C) at a rate of 10°C / min. If a clear peak does not appear in the first run of DSC measurement due to the type of polymer, the polymer should be heated at a rate of 50°C / min to a temperature 50°C higher than the expected flow temperature, completely melted at that temperature for 3 minutes, then cooled to 50°C at a rate of 80°C / min, and then the endothermic peak should be measured at a heating rate of 10°C / min.

[0066] [Fiber structure] Fibers containing the first resin (e.g., liquid crystal polymer fibers) constitute a fiber structure containing the first resin at least in part. In the present invention, the fiber structure is preferably a sheet-like fiber structure (fabric) such as a woven fabric, knitted fabric, or nonwoven fabric. Such a fiber structure can be produced by a known method. The fiber structure preferably contains long fibers containing the first resin. In this specification, long fibers are fibers that are continuous to a certain length, and examples include filaments and spun yarns. In addition, fibers that constitute long-fiber nonwoven fabrics obtained by melt-blowing or spunbonding are considered to be long fibers.

[0067] The form of the woven or knitted fabric is not particularly limited, and for example, in the case of a woven fabric, the weave may be plain weave, twill weave, satin weave, etc. In the case of a knitted fabric, it may be weft knitting, circular knitting, warp knitting, etc., and any known knitting structure can be selected. The nonwoven fabric is not particularly limited, and may be, for example, a wet-laid nonwoven fabric, a dry-laid nonwoven fabric, a long-fiber nonwoven fabric, etc., but a long-fiber nonwoven fabric is preferred. A long-fiber nonwoven fabric is a nonwoven fabric made of fibers that are continuous to a certain length, and can be distinguished from a nonwoven fabric made of short fibers that are intentionally cut to a predetermined fiber length, and examples thereof include meltblown nonwoven fabrics and spunbond nonwoven fabrics.

[0068] The fiber structure may contain a combination of multiple types of fibers containing the first resin, as long as the effects of the present invention are not impaired. For example, composite fibers containing liquid crystal polymer fibers and other fibers (e.g., blended yarns containing liquid crystal polymer fibers and other fibers) can be used. Furthermore, composite fabrics containing liquid crystal polymer fibers and other fibers, or different types of liquid crystal polymer fibers (e.g., blended fabrics containing multiple types of fibers) can be used.

[0069] The fiber structure was 5 cm long before being impregnated with the second resin. ３ / cm ２ ・S or more, 950cm ３ / cm ２ It is preferable that the air permeability is 5 cm or less. ３ / cm ２ If the thickness is less than 950 cm, the second resin made of a liquid crystal polymer tends not to be sufficiently impregnated. ３ / cm ２ If the thickness exceeds 5 cm, the sheet material tends to be unable to be given sufficient strength. ３ / cm ２ ・S or more, 950cm ３ / cm ２ s or less, more preferably 10 cm ３ / cm ２ ・S or more, 700cm ３ / cm ２It is more preferable that the air permeability of the fiber structure is .s or less. The air permeability of the fiber structure can be adjusted to within the above range by selecting the shape or average fiber diameter of the fibers constituting the fiber structure, or by processing the fiber structure, etc. The air permeability can be measured in accordance with the Frazier method in 6.8 of JIS L 1913:2010 "General nonwoven fabric testing methods."

[0070] The weight of the fiber structure is, for example, 15 to 400 g / m ２ and preferably 20 to 300 g / m ２ When the basis weight is within the above range, it is easy to impregnate the second resin made of a liquid crystal polymer, and sufficient strength can be imparted to the sheet material. The basis weight of the fiber structure can be adjusted to within the above range by selecting the form or average fiber diameter of the fibers constituting the fiber structure, or by processing the fiber substrate. The basis weight can be measured in accordance with JIS P 8124 "Method for measuring the metric basis weight of paper."

[0071] The thickness of the fiber structure may be, for example, 20 to 1000 μm, and preferably 40 to 1000 μm. When the thickness is within the above range, lightness or flexibility is easily achieved. The thickness can be measured using a thickness meter.

[0072] The fiber structure may be subjected to one or more known post-processing or post-treatments, such as one or more of calendaring, embossing, spunlace (water needle) treatment, etc., as needed.

[0073] [Second Resin] The second resin includes a liquid crystal polymer. As described above, a liquid crystal polymer is a polymer capable of forming an optically anisotropic melt phase. The second resin preferably includes a thermoplastic liquid crystal polymer that can be melt-molded. As described below, a film containing a thermoplastic liquid crystal polymer is heated to a predetermined temperature to increase its plasticity, and then pressed into a fiber structure, thereby impregnating the fiber structure with the thermoplastic liquid crystal polymer. The chemical structure of the liquid crystal polymer is not particularly limited, but examples thereof include liquid crystal polyester and liquid crystal polyesteramide in which an amide bond is introduced therein.

[0074] The liquid crystal polymer may also be a polymer in which an isocyanate-derived bond such as an imide bond, a carbonate bond, a carbodiimide bond or an isocyanurate bond is further introduced into an aromatic polyester or an aromatic polyester amide.

[0075] Specific examples of the liquid crystal polymer used as the second resin include known liquid crystal polyesters and liquid crystal polyesteramides derived from the compounds classified as (1) to (4) below and their derivatives. However, it goes without saying that there is an appropriate range for the combination of various raw material compounds in order to form a polymer capable of forming an optically anisotropic molten phase.

[0076] (1) Aromatic or aliphatic diol (see Table 5 for representative examples)

[0077] (2) Aromatic or aliphatic dicarboxylic acids (see Table 6 for representative examples)

[0078] (3) Aromatic hydroxycarboxylic acids (see Table 7 for representative examples)

[0079] (4) Aromatic diamines, aromatic hydroxyamines, or aromatic aminocarboxylic acids (see Table 8 for representative examples)

[0080] Representative examples of liquid crystal polymers obtained from these raw material compounds include copolymers having structural units shown in Tables 9 and 10.

[0081]

[0082] Among these copolymers, copolymers containing at least p-hydroxybenzoic acid and / or 6-hydroxy-2-naphthoic acid as structural units are preferred, and in particular, (i) copolymers containing structural units of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, or (ii) copolymers containing structural units of at least one aromatic hydroxycarboxylic acid selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, at least one aromatic diol, and at least one aromatic dicarboxylic acid are preferred.

[0083] When the liquid crystal polymer is a copolymer containing structural units of p-hydroxybenzoic acid (A) and 6-hydroxy-2-naphthoic acid (B), the molar ratio (A) / (B) is preferably (A) / (B)=10 / 90 to 90 / 10, more preferably 50 / 50 to 90 / 10, even more preferably 75 / 25 to 90 / 10, still more preferably 75 / 25 to 85 / 15, and particularly preferably 77 / 23 to 80 / 20.

[0084] For example, in the case of the copolymer (i), in addition to the constituent units of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, from the viewpoint of adjusting the molecular weight, etc., it may contain constituent units constituted by an aromatic diol or an aromatic dicarboxylic acid (for example, terephthalic acid).

[0085] Furthermore, in the case of the copolymer (ii), it may be a copolymer containing structural units of at least one aromatic hydroxycarboxylic acid selected from the group consisting of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, at least one aromatic diol selected from the group consisting of 4,4'-dihydroxybiphenyl, hydroquinone, phenylhydroquinone, and 4,4'-dihydroxydiphenyl ether, and at least one aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid.

[0086] The ability to form an optically anisotropic molten phase in the present invention can be confirmed, for example, by placing a sample on a hot stage, heating it in a nitrogen atmosphere, and observing the light transmitted through the sample.

[0087] The liquid crystal polymer has a melting point (Tm ０ ) may be, for example, in the range of 200 to 360 ° C., more preferably in the range of 250 to 340 ° C. The melting point of the liquid crystal polymer can be measured using a differential scanning calorimeter by placing a portion of the thermoplastic liquid crystal polymer in a sample container, heating it from room temperature (e.g., 25 ° C.) to a predetermined temperature (e.g., 400 ° C.) at a predetermined heating rate (e.g., 10 ° C. / min), cooling it to room temperature at a predetermined cooling rate (e.g., 10 ° C. / min), and then heating it again from room temperature to the predetermined temperature (e.g., 400 ° C.) at a predetermined heating rate (e.g., 10 ° C. / min). The position of the endothermic peak that appears when this is measured as the melting point.

[0088] Furthermore, from the viewpoint of melt moldability, the liquid crystal polymer may have, for example, a melt viscosity of 30 to 120 Pa·s at a shear rate of 1000 / s at (melting point + 20) ° C., and preferably a melt viscosity of 50 to 100 Pa·s.

[0089] The second resin preferably contains a liquid crystal polymer as a main component. It may also contain polymers other than liquid crystal polymers, such as polyethylene terephthalate, modified polyethylene terephthalate, polyolefin, polycarbonate, polyarylate, polyamide, polyphenylene sulfide, polyether ether ketone, and fluororesin, as long as the effects of the present invention are not impaired. If necessary, the second resin may contain various additives, such as colorants (e.g., dyes and pigments), antioxidants, UV absorbers, and light stabilizers. A filler may be dispersed in the resin impregnated into the fibers and / or fiber structure, as long as the filler maintains the properties of the present invention. Alternatively, the fiber structure may be impregnated with a resin composition containing a filler or the like in the second resin. The second resin may contain 50 wt % or more of the liquid crystal polymer, preferably 80 wt % or more, more preferably 90 wt % or more, even more preferably 95 wt % or more, even more preferably 98 wt % or more, and particularly preferably 99.9 wt %.

[0090] [Thermoplastic Liquid Crystal Polymer Film] For example, a film containing a melt-moldable thermoplastic liquid crystal polymer can be used as the second resin. The thermoplastic liquid crystal polymer can be impregnated into a fiber structure by heating the film to a predetermined temperature to increase its plasticity and then pressing it into the fiber structure. The method for producing the thermoplastic liquid crystal polymer film is not particularly limited. For example, the thermoplastic liquid crystal polymer can be cast to obtain a film, or a melt-kneaded mixture of the thermoplastic liquid crystal polymer can be extruded to obtain a film. Any extrusion molding method can be used, but well-known methods such as the T-die method and inflation method are industrially advantageous. In particular, inflation method applies stress not only to the thermoplastic liquid crystal polymer film in the machine axis direction (hereinafter abbreviated as MD direction) but also in the direction perpendicular to it (hereinafter abbreviated as TD direction), allowing for uniform stretching in both the MD and TD directions, resulting in a thermoplastic liquid crystal polymer film with controlled molecular orientation in both the MD and TD directions. Therefore, when using a thermoplastic liquid crystal polymer film to impregnate a fiber structure with a second resin, it is possible to impart isotropic properties to the sheet material.

[0091] For example, in extrusion molding using the T-die method, the molten sheet extruded from the T-die may be stretched not only in the MD direction of the thermoplastic liquid crystal polymer film but also in both the TD direction and the MD direction simultaneously to form a film, or the molten sheet extruded from the T-die may be stretched first in the MD direction and then in the TD direction to form a film.

[0092] In addition, in extrusion molding by the inflation method, a cylindrical sheet melt-extruded from a ring die may be stretched at a predetermined draw ratio (corresponding to the stretch ratio in the MD direction) and blow ratio (corresponding to the stretch ratio in the TD direction) to form a film.

[0093] The stretching ratio in such extrusion molding, as a stretching ratio (or draw ratio) in the MD direction, may be, for example, about 1.0 to 10, preferably about 1.2 to 7, and more preferably about 1.3 to 7. Furthermore, the stretching ratio (or blow ratio) in the TD direction may be, for example, about 1.5 to 20, preferably about 2 to 15, and more preferably about 2.5 to 14.

[0094] The melting point of the thermoplastic liquid crystal polymer film may be in the range of 200 to 360°C, preferably in the range of 250 to 330°C, and more preferably in the range of 280 to 320°C. The melting point of the thermoplastic liquid crystal polymer film can be determined by using the film as a measurement sample in the method described above. The melting point of the film is approximately the same as the melting point of the raw material resin unless a separate heat treatment for heat resistance is performed after the above-mentioned extrusion molding.

[0095] The heat distortion temperature of the thermoplastic liquid crystal polymer film is preferably 180 to 320° C., more preferably 200 to 300° C. The heat distortion temperature can be measured by the method described in the examples below.

[0096] [Method for manufacturing sheet material] The method for impregnating a fiber structure containing fibers containing a first resin with a second resin is not particularly limited, and a method of immersing the fiber structure in a solution of a second resin containing a liquid crystal polymer may be used. However, when the second resin contains a thermoplastic liquid crystal polymer, or when the first resin contains a liquid crystal polymer and the second resin contains a thermoplastic liquid crystal polymer, a method of heating the second resin to increase its plasticity and then pressurizing it into the fiber structure is preferred. Note that when the second resin contains resins other than the liquid crystal polymer or various additives, these are also impregnated into the fiber structure. Furthermore, when impregnation is performed using a resin composition containing a second resin and a filler, at least a portion of the filler may be impregnated into the fiber structure as long as the characteristics of the present invention are not impaired.

[0097] A method for manufacturing a sheet material according to one embodiment is described below with reference to the schematic diagrams shown in Figures 1 and 2. (1) First, a fiber structure 1 containing fibers containing a first resin and a thermoplastic liquid crystal polymer film 2 containing a thermoplastic liquid crystal polymer as a second resin are prepared, and a laminate 10 is formed by sandwiching the fiber structure 1 between two thermoplastic liquid crystal polymer films 2 (Figure 1). Note that the fiber structure 1 in Figure 1 is an example of a woven fabric, and the illustration of the fiber structure 1 is a schematic cross-sectional view of the woven fabric. (2) Next, the thermoplastic liquid crystal polymer film is heated and pressurized from both sides, thereby plasticizing and forcing at least a portion of the resin constituting the thermoplastic liquid crystal polymer film 2 into the voids in the fiber structure 1. The sheet material 20 thus formed comprises at least a composite 20a containing the first resin and the second resin, and optionally comprises resin layers 20b containing the second resin (thermoplastic liquid crystal polymer) on both sides (Figure 2).

[0098] In the above method, the heating temperature of the thermoplastic liquid crystal polymer film 2 is preferably higher than the heat distortion temperature of the thermoplastic liquid crystal polymer film and lower than the melting point of the fibers containing the first resin that constitute the fiber structure 1. The pressure during pressing is not particularly limited, but a pressure of approximately 1.5 MPa to 6 MPa can be used, for example. A batch press such as a vacuum heat press can be used for heating and pressing. However, considering productivity, heating and pressing can also be performed using at least a pair of rolls while feeding a fiber structure such as a woven fabric, knitted fabric, or nonwoven fabric unwound from a roll between two thermoplastic liquid crystal polymer films unwound from a roll. In some cases, the thermoplastic liquid crystal polymer film may be placed on only one side of the fiber structure.

[0099] However, the method of impregnating the fiber structure with the second resin is not limited to pressurization, and impregnation may be performed by applying a solution in which the second resin containing a liquid crystal polymer is dissolved to the fiber structure or by immersing the fiber structure in the solution.

[0100] [Sheet Material] The fiber structure of the present invention, such as a woven fabric, knitted fabric, or nonwoven fabric, is impregnated with a second resin containing a liquid crystal polymer. Since the long fibers constituting the fiber structure are oriented in multiple directions, in-plane anisotropy of the elastic modulus can be suppressed. For example, in the sheet material, the dynamic viscoelastic modulus at 35 ° C can be 4000 MPa or more, preferably 4500 MPa or more, and more preferably 5000 MPa or more in both the first direction along the sheet surface and the second direction perpendicular to the first direction along the sheet surface. Furthermore, the dynamic viscoelastic modulus at 80 ° C can be 2700 MPa or more, preferably 3500 MPa or more, and more preferably 4000 MPa or more in both the first and second directions. When a thermoplastic liquid crystal polymer film is used for impregnation with the second resin, the first direction can be the MD direction of the thermoplastic liquid crystal polymer film (the winding direction of the raw film), and the second direction can be the TD direction perpendicular to the MD direction.

[0101] Furthermore, since the sheet material of the present invention forms many interfaces between the fibers constituting the fiber structure and the second resin impregnated into the fiber structure, it is possible to improve the internal loss compared to a sheet made of the second resin alone. For example, the internal loss in both the first direction can be 0.04 or more, and in at least one direction can be 0.07 or more, preferably 0.09 or more. It is also possible to make the internal loss at 35°C 0.07 or more in both the first direction and the second direction.

[0102] In the sheet material of the present invention, the weight percentage of the fiber structure is preferably greater than 8 wt %, and more preferably 20 wt % or more. The weight percentage of the fiber structure may be, for example, 5 to 60 wt %, and preferably 10 to 40 wt %. When the sheet material has a laminate structure having a composite layer and a resin layer, the thickness of the composite layer may be 5 to 95% of the total thickness of the sheet material, and preferably 20 to 70%. The thickness of the composite layer can be measured as the distance between the upper and lower ends of the cross section of the sheet material where the fiber cross sections are observed.

[0103] In the sheet material of the present invention, the fiber structure containing fibers containing a first resin is preferably a fiber structure containing thermoplastic liquid crystal polymer fibers, and the second resin is preferably a thermoplastic liquid crystal polymer. In this case, the thermoplastic liquid crystal polymer constituting the fiber structure and the second resin may have the same composition (e.g., the combination of structural units and their content). When the fiber structure is a thermoplastic liquid crystal polymer fiber and the resin impregnated therein is a thermoplastic liquid crystal polymer, and particularly when they have the same composition, the sheet material can be a recyclable high-strength sheet material.

[0104] In another aspect of the present invention, the sheet material has a dynamic viscoelastic modulus at 35°C of 4000 MPa or more in both a first direction along the sheet surface and a second direction along the sheet surface perpendicular to the first direction, an internal loss of 0.04 or more, and 0.07 or more in at least one direction. In another aspect of the present invention, the sheet material has a dynamic viscoelastic modulus at 35°C of 4500 MPa or more, and more preferably 5000 MPa or more, in both the first and second directions. In another aspect of the present invention, the sheet material has a dynamic viscoelastic modulus at 35°C of 0.07 or more, and more preferably 0.09 or more, in both the first and second directions.

[0105] In another embodiment of the present invention, the sheet material may have a dynamic viscoelastic modulus at 80° C. of 2700 MPa or more, preferably 3500 MPa or more, more preferably 4000 MPa or more in both the first direction and the second direction.

[0106] The sheet material in this embodiment of the present invention is not particularly limited to any particular material as long as it has the above-mentioned dynamic viscoelastic modulus and internal loss at 35° C., but preferably contains a liquid crystal polymer.

[0107] [Molded body, acoustic diaphragm] The sheet material described above exhibits a high elastic modulus and internal loss, and is therefore suitable for applications such as acoustic diaphragms, etc. In particular, when the liquid crystal polymer impregnated into the fiber structure is a thermoplastic liquid crystal polymer, the sheet-like material can be molded into any shape by heating it to an appropriate temperature, deforming it into a desired shape, and then cooling it.

[0108] Examples of molding methods include various thermoforming methods such as pressure forming, vacuum forming, and press forming. For example, a desired shape may be imparted using a mold by pressure forming or vacuum forming to form the shape required for the acoustic diaphragm. Pressure forming refers to a method in which a sheet material is softened and then pressed against a mold by applying pressure to the sheet material using air pressure or the like to form the shape. Vacuum forming refers to a method in which a sheet material is softened and then drawn into a mold by creating a vacuum in the gap between the mold and the sheet material to form the shape.

[0109] The acoustic diaphragm can be used in acoustic devices, such as devices in which a receiver holds an acoustic device directly to his / her ear to receive sound (e.g., headphones, earphones, etc.), devices in which a receiver holds an acoustic device close to his / her ear to receive sound (e.g., mobile phones, smartphones, etc.), and devices in which a receiver receives sound from an acoustic device while standing a predetermined distance away (e.g., speakers, audio equipment, radios, televisions, personal computers, car audio equipment, etc.).

[0110] The present invention will be explained in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0111] (Heat distortion temperature of thermoplastic liquid crystal polymer film) A sample of 5 mm wide and 20 mm long was taken from the thermoplastic liquid crystal polymer film, and a tensile load of 1 g was applied to both ends of the sample using a thermomechanical analyzer (TMA). The temperature was raised from room temperature at a rate of 5°C / min until the film broke. The heat distortion temperature was measured as the temperature at which a sudden expansion (elongation) occurred, and the temperature at the intersection of the tangent to the high-temperature side baseline and the tangent to the low-temperature side baseline in the temperature-deformation curve.

[0112] (Density of Sheet Material) The density of the sheet material obtained in the Examples or Comparative Examples was measured in accordance with JIS K 7112 using a hexane / carbon tetrachloride density gradient tube.

[0113] (Evaluation of Workability of Sheet Material) Figure 3 shows a schematic cross-sectional view of the apparatus configuration used in the workability evaluation test of the sheet material. An upper 90° folding mold 4a was installed on the upper platen 3a of a press (not shown in its entirety), and a lower 90° folding mold 4b was installed on the lower platen 3b, with the sheet material 20 or its counterpart placed between the two molds 4a and 4b. A sample measuring 4 cm wide and 12 cm long was taken from the sheet material. The mold was then pressed against the sheet material with a pressure of 2 MPa for 15 minutes, and the molds were evaluated as A for those that bent, and B for those that did not bend, as shown in Figure 4.

[0114] (Dynamic viscoelasticity measurement (DMA) of sheet material) Using a dynamic viscoelasticity measuring device (Rheology Corporation "DVE V4 FT Rheospectr"), measurements were performed at a frequency of 10 Hz, a heating rate of 3 ° C. / min (10 ° C. to 300 ° C.), and a strain of 0.025%. The real part (E': storage modulus) and imaginary part (E": complex modulus) of the obtained complex modulus were determined at 35 ° C. and 80 ° C., and the internal loss (tan δ) was further calculated from the ratio (E" / E'). The obtained storage modulus E' was used as the elastic modulus (MPa) of the sheet material. Regarding the elastic modulus, if the elastic modulus at 35 ° C. was 4000 MPa or more in both the MD direction and the TD direction, it was rated as A, and if this was not met, it was rated as B. Furthermore, the internal loss was rated as A if the internal loss at 35°C was 0.04 or more in both the MD and TD directions and the internal loss in either direction was 0.07 or more, and if this was not met, it was rated as B. The specific elastic modulus was calculated by dividing the storage modulus E' in the MD direction at 35°C by the density of the sheet material measured above. The sound velocity was calculated as the square root of the storage modulus E' in the MD direction at 35°C divided by the density of the sheet material.

[0115] (Method for observing cross sections of samples) A ​​sample of the sheet material was embedded in epoxy resin, and a cross section was cut out using a polishing machine (manufactured by Struers, "Labopol 20"), and observed using a digital microscope (manufactured by Olympus Corporation, "DSX1000"). Next, platinum was vapor-deposited on the cross section of the sample, and an SEM image was observed using a scanning electron microscope (manufactured by JEOL Ltd., tabletop scanning electron microscope "JCM-7000").

[0116] (Method of measuring melting point) The melting points of the thermoplastic liquid crystal polymer film, fiber structure, and sheet material were measured using a differential scanning calorimeter DSC ("Q2000" manufactured by TA Instruments Japan Co., Ltd.).

[0117] Melting point of thermoplastic liquid crystal polymer film For the thermoplastic liquid crystal polymer film, the film sample was heated to 400°C at a heating rate of 10°C / min, then cooled to 50°C at a cooling rate of 10°C / min, and heated again at a rate of 10°C / min. The position of the endothermic peak that appeared after this was recorded as the melting point of the thermoplastic liquid crystal polymer (second resin).

[0118] For the measurement of the melting point of the fiber structure, finely cut thermoplastic liquid crystal polymer fibers were used to improve thermal conductivity. The measurement was performed by heating the fiber from room temperature at a rate of 10°C / min, and the position of the endothermic peak that appeared was recorded as the melting point of the fiber containing the thermoplastic liquid crystal polymer (first resin).

[0119] Melting point of sheet material (impregnated body) The melting point of the sheet material was determined by recording the position of the endothermic peak that appeared when the temperature was raised from room temperature at a rate of 10°C / min, and peaks were confirmed near the melting points of the film alone and the fiber structure alone.If peaks were present in two places, it was determined that the properties of the film and the fiber structure were maintained in the sheet material.

[0120] A thermotropic liquid crystalline polyester consisting of 23 mol parts of 6-hydroxy-2-naphthoic acid units and 77 mol parts of p-hydroxybenzoic acid units was polymerized and extruded through an inflation die to obtain a thermoplastic liquid crystal polymer film having a thickness of 100 μm. The resulting thermoplastic liquid crystal polymer film had a melting point of 310°C and a heat distortion temperature of 280°C.

[0121] Film Production Example 2 A thermotropic liquid crystalline polyester consisting of 27 mol parts of 6-hydroxy-2-naphthoic acid units and 73 mol parts of p-hydroxybenzoic acid units was polymerized and extruded through an inflation die to obtain a 100 μm thick thermoplastic liquid crystal polymer film. The resulting thermoplastic liquid crystal polymer film had a melting point of 280 ° C and a heat distortion temperature of 230 ° C. In both Production Examples 1 and 2, the film was not subjected to heat treatment for heat resistance after extrusion molding, so the measured melting point and heat distortion temperature can be considered to correspond to the melting point and heat distortion temperature of the raw material resin (thermoplastic liquid crystal polymer as the second resin).

[0122] Example 1 The thermoplastic liquid crystal polymer film of Production Example 1 was used as the film containing the second resin, and the fiber structure was a plain weave fabric of thermoplastic liquid crystal polymer fibers, "Vectran (registered trademark)" fabric manufactured by Kuraray Co., Ltd., product number HT1020 (weave structure: plain weave, both warp and weft yarns used were HT-1100 dtex, weave density 20 threads / inch, thickness 0.33 mm, basis weight 179 g / m ２ A woven fabric (having a melting point of 330°C) was prepared. As shown in the configuration of Figure 1, a fiber structure was placed between two thermoplastic liquid crystal polymer films, and impregnation with the thermoplastic liquid crystal polymer was carried out using a vacuum batch press (Kitagawa Seiki Co., Ltd., "VH2-2325"). Specifically, the upper and lower surfaces of the laminate were pressurized at a pressure of 3 MPa for 30 minutes at a vacuum degree of 100 Pa and 300°C, and the resin constituting the upper and lower thermoplastic liquid crystal polymer films was plasticized and impregnated into the fiber structure.

[0123] Figure 5 shows the cross section of the sheet material 20 prepared in Example 1 embedded in epoxy resin 5, observed in polarized mode with a digital microscope (digital stereomicroscope). It can be seen that a sheet material 20 approximately 250 μm thick is formed, with a composite layer 20a and resin layers 20b on both sides. Figure 6 shows an SEM image of the same cross section polished and observed with a scanning electron microscope (scale: 100 μm). It can be seen that most of the voids in the fiber structure made of thermoplastic liquid crystal polymer fibers are filled with the thermoplastic liquid crystal polymer, forming a structure with very few voids. To confirm whether the heat resistance properties of the fiber and film were maintained, the prepared impregnated body was measured using DSC. Two melting point peaks were confirmed in the DSC curve, confirming that the properties of the film and fiber were maintained even when the fiber structure was impregnated with resin. The measurement results of the physical properties of the obtained sheet material are shown in Table 11.

[0124] [Example 2] The fiber structure used was a plain weave fabric of thermoplastic liquid crystal polymer fiber, "Vectran (registered trademark)" fabric manufactured by Kuraray Co., Ltd., product number HT-0235 (weave structure: plain weave, warp and weft yarns are both HT-220 dtex, weave density is 35 threads / inch, thickness is 0.11 mm, basis weight is 62 g / m ２ Impregnation was carried out under the same conditions as in Example 1, except that the fiber and film were changed to a woven fabric (melting point 330°C). To confirm whether the heat resistance properties of the fiber and film were maintained, the prepared composite material was measured by DSC. Two melting point peaks were confirmed in the DSC curve, confirming that the properties of the film and fiber were maintained. The measurement results of the physical properties of the obtained sheet material are shown in Table 11.

[0125] [Example 3] The thermoplastic liquid crystal polymer film of Production Example 2 was used as the film containing the second resin, and impregnation was carried out under the same conditions as in Example 1, except that the lamination temperature was 270 ° C. To confirm whether the heat resistance properties of the fiber and film were maintained, the prepared sheet material was measured by DSC. Two melting point peaks were confirmed in the DSC curve, confirming that the properties of the film and fiber were maintained. The measurement results of the physical properties of the obtained sheet material are shown in Table 11.

[0126] [Example 4] The film of Production Example 2 was used as the thermoplastic liquid crystal polymer film, and the fiber structure was a nonwoven fabric of liquid crystal polymer fibers, polyarylate melt-blown nonwoven fabric "Veculus (registered trademark)" manufactured by Kuraray Co., Ltd. (nonwoven fabric thickness: 100 μm, basis weight: 40 g / m ２ A sheet material was produced under the same conditions as in Example 1, except that a cellulose acylate (cellulose acetate, melting point 330°C) was used. The produced impregnated body was measured by DSC to confirm whether the heat resistance properties of the fiber and film were maintained. Two melting point peaks were confirmed in the DSC curve, confirming that the properties of the film and fiber were maintained. The measurement results of the physical properties of the obtained sheet material are shown in Table 11.

[0127] Example 5: The liquid crystal polymer film prepared in Production Example 2 was pulverized using a freeze pulverizer and dissolved in pentafluorophenol (PFP) heated to 60°C at a weight concentration of 2.0% while stirring to prepare a solution containing a liquid crystal polymer. The solution was then cast onto Kuraray Co., Ltd.'s "Vectran (registered trademark)" fabric, product number HT1020, and dried. By repeating the casting and drying process, the fiber structure was completely impregnated with the liquid crystal polymer (second resin). The impregnated body was measured using DSC to confirm whether the heat resistance characteristics of the fibers and the second resin constituting the liquid crystal polymer film were maintained. Two melting point peaks were observed in the DSC curve, confirming that the properties of the second resin and fiber were maintained. The measurement results of the physical properties of the obtained sheet material are shown in Table 11.

[0128] [Comparative Example 1] As a fiber structure, a glass cloth, greige cloth manufactured by Unitika Glass Fiber Co., Ltd. (product number: H105F107 (warp count 22.5 tex, weft count 22.5 tex, mass 107 g / m ２ A sheet material was produced under the same conditions as in Example 1, except that a sheet material having a thickness of 0.10 mm was used. The results of measuring the physical properties of the obtained sheet material are shown in Table 11.

[0129] Comparative Example 2 The same fiber structure as in Example 1, Vectran fabric manufactured by Kuraray Co., Ltd., product number HT1020, was used. A polyester resin for FRP (Toughseal #50 manufactured by Nippon Tokushu Toryo Co., Ltd.) was mixed with a curing agent and applied to both the front and back surfaces of the fabric to produce a resin-impregnated sheet. The measurement results of the physical properties of the obtained sheet material are shown in Table 11. Because a curable resin was used, the sheet was not bent in the processability evaluation.

[0130] Comparative Example 3 The same fiber structure as in Example 4, a polyarylate meltblown nonwoven fabric "Veculus (registered trademark)" manufactured by Kuraray Co., Ltd., was used, and a polyester resin for FRP (Tafseal #50 manufactured by Nippon Tokushu Toryo Co., Ltd.) was mixed with a curing agent and applied to both the front and back surfaces of the fabric to produce a resin-impregnated sheet. The measurement results of the physical properties of the obtained sheet material are shown in Table 11. Because a curable resin was used, the sheet did not bend in the processability evaluation.

[0131] Comparative Example 4 The physical properties of the thermoplastic liquid crystal polymer film prepared in Production Example 1 were evaluated by the same measuring methods as in the examples.

[0132] Comparative Example 5: As a fiber structure, a polyethylene terephthalate nonwoven fabric (a spunlace nonwoven fabric "NISSELON (registered trademark)" manufactured by Nissei Corporation, product number: 8021, basis weight: 81 g / m) was used. ２ An attempt was made to produce a sheet material under the same conditions as in Example 1, except that a nonwoven fabric (a fibrous structure with a heat distortion temperature of 230°C and a melting point of 260°C) was used. However, the nonwoven fabric melted when heated and pressed, and a structure in which the fiber structure was impregnated with resin was not obtained. The measurement results of the physical properties of the obtained material are shown in Table 11.

[0133] [Comparative Example 6] Using the same materials as in Example 1, an attempt was made to produce a sheet material by changing the conditions in the vacuum batch press to a vacuum of 100 Pa, 280 ° C, and applying a pressure of 2 MPa to the top and bottom of the laminate for 15 minutes. As a result, the resin of the thermoplastic liquid crystal polymer film was not impregnated into the fiber structure, and a laminate was obtained in which the thermoplastic liquid crystal polymer film was simply pressed onto both sides of the fiber structure. The measurement results of the physical properties of the laminate are shown in Table 11.

[0134] Comparative Example 7: The thermoplastic liquid crystal polymer film (melting point 280°C) of Production Example 2 and the product number HT1020 used in Example 1 were prepared as the fiber structure. As shown in the configuration of Figure 1, the fiber structure was placed between two thermoplastic liquid crystal polymer films and pressed in a vacuum batch press at a temperature of 270°C, a pressure of 1 MPa, and a lamination time of 10 minutes. Figure 7 shows the result of photographing the cross section of the obtained sample with a reflected light microscope. As a result, no impregnation was observed, and as shown in Figure 8, a laminate structure 10 was formed in which the fiber structure 1 was simply sandwiched between the thermoplastic liquid crystal polymer films 2, and no resin impregnation into the fiber structure 1 was observed. Therefore, the physical properties of the integrated sheet material were not evaluated.

[0135]

[0136] Comparing Examples 1, 2, and 4 with Comparative Example 4, it can be seen that by impregnating a fiber structure made of highly heat-resistant fibers with the resin constituting the thermoplastic liquid crystal polymer film to form a sheet, the elastic modulus in both mutually perpendicular directions (MD and TD) is significantly improved, and the internal loss is also generally improved, compared to when a thermoplastic liquid crystal polymer film alone is used. Furthermore, Example 5, in which the liquid crystal polymer is impregnated into a fiber structure in the form of a solution, also achieves a relatively high elastic modulus and internal loss. In Examples 1 to 5, the dynamic viscoelastic modulus at 35°C in both the MD and TD directions is 4000 MPa or more, and the internal loss is 0.04 or more. In Examples 1 to 5, the internal loss in the MD direction is 0.09 or more, and in Examples 1 and 3, the internal loss is 0.09 or more. Furthermore, in Examples 1 and 3, the elastic modulus at 80°C is also 4000 MPa or more in both the MD and TD directions.

[0137] In Comparative Example 1, the modulus of elasticity was improved due to the properties of the glass cloth, but the internal loss was inferior to that of Example 1. Comparative Example 2, which used a curable resin as the second resin, was inferior to Example 1 in terms of internal loss and processability, and also in terms of the modulus of elasticity at 80°C. Comparative Example 3, which used a nonwoven fabric as the fiber structure and a curable resin as the second resin, also had inferior modulus of elasticity and internal loss, and poor processability, compared to Example 4. In Comparative Example 5, a nonwoven fabric made of a resin with low heat resistance was used as the fiber structure, and the fibers melted and the fiber structure was lost when heated and pressurized. As a result, the obtained properties were almost identical to those of the thermoplastic liquid crystal polymer film shown in Comparative Example 4. Comparative Example 6, which was a three-layer laminate in which a thermoplastic liquid crystal polymer film and a fiber structure were pressure-bonded, tended to have a lower modulus of elasticity and inferior internal loss compared to Example 1, which used the same materials. Furthermore, in Comparative Example 6, the fiber structure was not impregnated with the second resin, so part of the structure was crushed in the processability evaluation, and the processability was also poor. In Comparative Example 7, the same materials as in Example 3 were used and heated at the same temperature. However, the pressure applied during heating and pressurization was low and the time was short, so the resin did not impregnate the fiber structure, and no integral sheet was obtained.

[0138] As described above, the preferred embodiment of the present invention has been described, but various additions, modifications, or deletions can be made without departing from the spirit of the present invention, and such additions, modifications, or deletions are also included within the scope of the present invention.

[0139] According to the present invention, it is possible to provide a sheet-like material that achieves both an improvement in elastic modulus and an improvement in internal loss, and in which the directional dependency of the elastic modulus and internal loss within the sheet plane is suppressed, and the material is highly useful for applications such as acoustic diaphragms in acoustic equipment.

[0140] REFERENCE SIGNS LIST 1 Fiber structure 2 Thermoplastic liquid crystal polymer film 3a Upper platen 3b Lower platen 4a 90° folding upper mold 4b 90° folding lower mold 10 Laminate 20 Sheet material 20a Composite layer 20b Resin layer

Claims

1. A sheet material comprising: a fiber structure including fibers containing a first resin; and a second resin impregnated into the fiber structure, wherein the second resin contains a liquid crystal polymer.

2. The sheet material according to claim 1, wherein said first resin comprises a liquid crystal polymer.

3. The sheet material according to claim 1, wherein the fiber structure is at least one selected from the group consisting of woven fabrics, knitted fabrics, and nonwoven fabrics.

4. The sheet material according to claim 1, wherein said second resin comprises a thermoplastic liquid crystal polymer.

5. The sheet material according to claim 1, wherein said fibers have a higher heat resistance than said second resin.

6. The sheet material according to claim 1, having a laminated structure including a composite layer containing the first resin and the second resin, and a resin layer present on at least one side of the composite layer and containing the second resin.

7. A sheet material having a dynamic viscoelastic modulus at 35°C of 4000 MPa or more in both a first direction along the surface of the sheet and a second direction along the surface of the sheet perpendicular to the first direction, an internal loss of 0.04 or more, and 0.07 or more in at least one direction.

8. The sheet material according to claim 7, wherein the modulus of dynamic viscoelasticity at 80°C is 4000 MPa or more in both a first direction along the surface of the sheet and a second direction along the surface of the sheet perpendicular to the first direction.

9. A molded article formed from the sheet material according to any one of claims 1 to 8.

10. An acoustic diaphragm comprising the sheet material according to any one of claims 1 to 8.

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