Composite sheet and method of manufacturing composite sheet

Abstract

A composite sheet comprising a woven or non-woven fabric of a liquid crystal polymer and a thermoplastic tetrafluoroethylene polymer having oxygen-containing polar groups, wherein the thermoplastic tetrafluoroethylene polymer is impregnated in the aforementioned woven or non-woven fabric of the liquid crystal polymer.

Description

[Technical Field]

[0001] This disclosure relates to a composite sheet and a method for manufacturing the composite sheet. [Previous Technology]

[0002] In recent years, the information and communication field has seen advancements in communication technologies such as high-frequency communication, leading to a demand for improved performance in materials used in printed wiring boards. Fluoropolymers, particularly tetrafluoroethylene-based polymers, are suitable for use in printed wiring boards due to their excellent electrical properties and heat resistance. Patent Document 1 describes a composite sheet in which a nonwoven fabric containing a liquid crystal polymer is applied to the opposing surfaces of a layer containing a liquid crystal polymer and a layer containing a tetrafluoroethylene-based polymer. (Prior Art Documents, Patent Documents)

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-119378 [Summary of the Invention]

[0004] The problem this invention aims to solve is that while tetrafluoroethylene-based polymers have excellent electrical properties, they also have a high coefficient of linear expansion. Therefore, when processing the laminate of the composite sheet and substrate described in Patent Document 1 at high temperatures, such as during the reflow step of manufacturing a wiring board, the composite sheet will thermally expand, making it easy for the composite sheet and substrate to peel off. This disclosure relates to providing a composite sheet with excellent electrical properties and low linear expansion, and a method for manufacturing the composite sheet.

[0005] Means for Solving the Problems Means for solving the above-mentioned problems include the following forms: <1> A composite sheet comprising a woven or nonwoven fabric containing a thermoplastic liquid crystal polymer and a thermoplastic tetrafluoroethylene polymer having an oxygen-containing polar group, wherein the thermoplastic tetrafluoroethylene polymer is impregnated into the woven or nonwoven fabric containing the liquid crystal polymer. <2> The composite sheet of <1>, wherein the aforementioned oxygen-containing polar group is a hydroxyl-containing group or a carbonyl-containing group. <3> The composite sheet of <1> or <2>, wherein the aforementioned liquid crystal polymer comprises a liquid crystal aromatic polyester. <4> The composite sheet of any one of <1> to <3>, wherein the melting point of the aforementioned tetrafluoroethylene polymer is 260~320°C. <5> The composite sheet of any one of <1> to <4>, wherein the melting point of the aforementioned liquid crystal polymer is 230~350°C. <6> The composite sheet of any one of <1> to <5>, wherein the absolute value of the difference between the melting point of the aforementioned tetrafluoroethylene polymer and the melting point of the aforementioned liquid crystal polymer is 30°C or less. <7> The composite sheet of any one of <1> to <6> further contains a polymer different from the aforementioned tetrafluoroethylene polymer. <8> The composite sheet of any one of <1> to <7> further contains inorganic particles. <9> The composite sheet of any one of <1> to <8> comprises at least one selected from the group consisting of a polymer different from the aforementioned tetrafluoroethylene polymer and inorganic particles; and, relative to the total mass of the aforementioned composite sheet, the total content of at least one selected from the group consisting of a polymer different from the aforementioned tetrafluoroethylene polymer and the aforementioned inorganic particles is greater than 5% by mass. <10> A composite sheet as described in any one of <1> to <9>, comprising at least one selected from the group consisting of polymers different from the aforementioned tetrafluoroethylene-based polymers and inorganic particles; and the total mass of the selected polymers different from the aforementioned tetrafluoroethylene-based polymers and inorganic particles is at least 0.1 times the mass of the aforementioned tetrafluoroethylene-based polymer. <11> A composite sheet as described in any one of <1> to <10>, having a thickness of less than 50 µm. <12> A method for manufacturing a composite sheet, comprising hot-pressing a sheet containing a thermoplastic tetrafluoroethylene-based polymer with a woven or nonwoven fabric of a liquid crystal polymer to obtain a composite sheet, wherein the thermoplastic tetrafluoroethylene-based polymer has oxygen-containing polar groups. <13> A manufacturing method as described in <12>, wherein the aforementioned sheet is formed from a dispersion containing particles of the aforementioned tetrafluoroethylene-based polymer. <14> A method for manufacturing a composite sheet involves impregnating a dispersion containing particles of a thermoplastic tetrafluoroethylene polymer into a woven or nonwoven fabric of a liquid crystal polymer to obtain the composite sheet, wherein the thermoplastic tetrafluoroethylene polymer has oxygen-containing polar groups. <15> The manufacturing method of <14> further comprises at least one selected from the group consisting of polymers different from the aforementioned tetrafluoroethylene polymer and inorganic particles.

[0006] Effects of the invention According to the present disclosure, a composite sheet with excellent electrical properties and low linear expansion and a method for manufacturing the composite sheet are provided.

Implementation Method

[0007] The following is a detailed description of the embodiments used to implement this disclosure. However, the embodiments of this disclosure are not limited to the following embodiments. In the following embodiments, the constituent elements (including process elements, etc.) are not necessary unless otherwise specified. The same applies to numerical values ​​and their ranges, which are not intended to limit the embodiments of this disclosure.

[0008] In this disclosure, the numerical range indicated by "~" includes the minimum and maximum values ​​recorded before and after "~". Each component in this disclosure may also contain multiple substances equivalent to it. When multiple substances equivalent to each component exist in the composition, the content or percentage of each component, unless otherwise specified, refers to the total content or percentage of the multiple substances present in the composition. This disclosure may also contain multiple particles equivalent to each component. When multiple particles equivalent to each component exist in the composition, the particle size of each component, unless otherwise specified, refers to the value of the mixture of the multiple particles present in the composition. In this disclosure, the term "layer" refers to the presence of a layer or film in a region, including not only the formation of the entire region but also the formation of only a portion of the region. The term "layering" in this disclosure indicates the stacking of layers; two or more layers may be bonded together or detachable. The term "composite sheet" in this disclosure refers to a woven or non-woven sheet containing both polymer and liquid crystal polymer. The "volume average particle size (D50)" in this disclosure is the particle size at the 50% volume threshold obtained by laser diffraction. That is, by measuring particle size distribution using laser diffraction, and calculating the cumulative curve with the total volume of the particle group as 100%, the particle size at the point where the cumulative volume reaches 50% on that curve is determined. The D50 of a particle can be obtained by dispersing the particles in water and analyzing them using a laser diffraction particle size distribution measuring device (Horiba Seisakusho, LA-920 measuring instrument). The "specific surface area" in this disclosure is a value calculated by measuring particles using the gas adsorption (constant volume method) BET multi-point method, obtained using a NOVA4200e (Quantachrome Instruments). In this disclosure, "melting point of tetrafluoroethylene-based polymers" refers to the temperature corresponding to the maximum value of the melting peak of the polymer as determined by differential scanning calorimetry (DSC). "Melting point of liquid crystal polymers" refers to the temperature of the endothermic peak displayed by a differential scanning calorimeter after the liquid crystal polymer film is heated to complete melting at a rate of 20°C / min, then rapidly cooled to 50°C at a rate of 50°C / min, and then heated again at a rate of 20°C / min. "Melting flow rate" in this disclosure refers to the melt mass-flow rate of the polymer as specified in JIS K 7210-1:2014 (ISO 1133-1:2011). "Glass transition point (Tg)" in this disclosure refers to the value measured by dynamic viscoelasticity determination (DMA) of the polymer. "Viscosity" in this disclosure is obtained by measuring the dispersion using a type B viscometer at 25°C and a rotational speed of 30 rpm. After repeating the measurement three times, the average of the three measurements is taken.The "thixotropic ratio" in this disclosure refers to the value calculated by dividing the viscosity η1 of the dispersion measured at 30 rpm by the viscosity η2 measured at 60 rpm. Each viscosity measurement was repeated three times, and the average of the three measurements was taken. In this disclosure, a "polymer" is a compound formed by the polymerization of monomers. That is, a "polymer" has a plurality of units primarily composed of monomers. The "unit" of a polymer in this disclosure refers to a group of atoms primarily composed of the aforementioned monomers, formed by the polymerization of monomers. A unit can be a unit formed directly through a polymerization reaction, or it can be a unit whose structure is transformed by processing the polymer. Hereinafter, a unit primarily composed of monomer a will be simply referred to as "monomer a unit".

[0009] The composite sheet disclosed herein contains a woven or nonwoven fabric of a hot-melt liquid crystal polymer (hereinafter referred to only as "liquid crystal polymer") and a hot-melt tetrafluoroethylene polymer (hereinafter referred to as "F polymer") having oxygen-containing polar groups, wherein the hot-melt tetrafluoroethylene polymer impregnates the aforementioned woven or nonwoven fabric of the liquid crystal polymer. The composite sheet disclosed herein has excellent electrical properties and low linear expansion.

[0010] Generally speaking, tetrafluoroethylene (TEF) polymers have excellent electrical properties such as low dielectric constant and low dielectric tangent, but on the other hand, they have a large coefficient of linear expansion. The low linear expansion of conventional composite sheets using TEF polymers is insufficient. Furthermore, in conventional composite sheets, the thermally fusible TEF polymer is impregnated into woven or non-woven fabrics containing liquid crystal polymers, and the two are only wound together, resulting in insufficient interfacial adhesion. As a result, the laminate between the composite sheet and the substrate expands thermally during high-temperature processing, leading to problems such as peeling from the substrate. The inventors of this invention have diligently researched and discovered that composite sheets impregnated with TEF polymers into woven or non-woven fabrics containing liquid crystal polymers possess excellent electrical properties and low linear expansion.

[0011] We believe that the composite sheet disclosed herein improves the adhesion between the F polymer and the liquid crystal polymer through the good interaction between the oxygen-containing polar groups in the F polymer and the liquid crystal polymer. Furthermore, the linear expansion of the F polymer is well buffered by the woven or non-woven fabric of the liquid crystal polymer, while the polymer properties of both polymers are exhibited in a highly balanced manner. Moreover, the oxygen-containing polar groups in the tetrafluoroethylene polymer can also improve adhesion to the substrate. We believe that these properties, for example, can provide a material that is effective as a low-transmission-loss material. In addition to the woven or non-woven fabric of the liquid crystal polymer and the F polymer, the composite sheet may also contain polymers different from the F polymer, inorganic particles, various additives, etc. The components of the composite sheet will be explained below.

[0012] The composite sheet disclosed herein contains an F polymer, which is a thermoplastic tetrafluoroethylene polymer having oxygen-containing polar groups. One or more F polymers may be used. In the composite sheet, the F polymer may be granular or non-granular, but the latter is preferred. The F polymer in the composite sheet is preferably sintered. From the viewpoint of excellent adhesion between the F polymer and the liquid crystal polymer in woven or non-woven fabrics, the F polymer in the composite sheet is preferably a sintered product of F polymer particles.

[0013] Tetrafluoroethylene-based polymers are polymers containing units (hereinafter also referred to as "TFE units") with tetrafluoroethylene (hereinafter also referred to as "TFE units") as the main component. From the viewpoint of suitably exhibiting the characteristics brought about by TFE units, the content of TFE units in tetrafluoroethylene-based polymers should preferably be 50 mol% or more, and more preferably 90 mol% or more, relative to all units in the polymer. The above content can be 99 mol% or less, or 98 mol% or less.

[0014] Polymer F has an oxygen-containing polar group. Examples of oxygen-containing polar groups include hydroxyl groups, carbonyl groups, and phosphonyl groups, preferably hydroxyl or carbonyl groups, with carbonyl groups being more preferred. Polymer F may have one or more types of oxygen-containing polar groups. The hydroxyl group is preferably an alcoholic hydroxyl group, preferably -CF2CH2OH and -C(CF3)2OH. The carbonyl group is preferably a carboxyl group, alkoxycarbonyl group, amide group, isocyanate group, carbamate group (-OC(O)NH2), anhydride residue (-C(O)OC(O)-), amide imine residue (-C(O)NHC(O)-, etc.), and carbonate group (-OC(O)O-), with anhydride residues being more preferred.

[0015] The number of oxygen-containing polar groups in polymer F, measured by the number of carbon atoms in the main chain, is preferably 10 to 5000 per 1×10⁶ carbon atoms, more preferably 100 to 3000. Furthermore, the number of oxygen-containing polar groups can be quantified by the composition of the polymer or by the method described in International Publication No. 2020 / 145133. Oxygen-containing polar groups can be contained in monomer-dominated units of polymer F, or in the terminal groups of the main chain of polymer F, preferably the former. Examples of the latter include: tetrafluoroethylene-based polymers having oxygen-containing polar groups as terminal groups derived from polymerization initiators, chain transfer agents, etc., and polymers obtained by plasma treatment or ionizing radiation treatment of tetrafluoroethylene-based polymers.

[0016] As a monomer having a carbonyl group, itaconic anhydride, citraconic anhydride and 5-norconene-2,3-dicarboxylic anhydride (hereinafter also referred to as "NAH") are preferred. From the point of view of excellent adhesion to liquid crystal polymers, NAH is more preferred.

[0017] The F polymer system comprises polymers with oxygen-containing polar groups, preferably: polytetrafluoroethylene (PTFE), polymers containing TFE units and ethylene-based units (ETFE), polymers containing TFE units and propylene-based units, polymers containing TFE units and perfluoro(alkyl vinyl ether) (PAVE)-based units (PAVE units) (PFA), and polymers containing TFE units and hexafluoropropylene-based units (FEP). PFA and FEP with oxygen-containing polar groups are more preferred, and PFA with oxygen-containing polar groups is even more preferred. As PAVE units, CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (hereinafter also denoted as PPVE) are preferred, with PPVE being more preferred. These polymers may also further contain units based on other comonomers.

[0018] Polymer F is preferably a polymer containing carbonyl groups, comprising TFE units and PAVE units; more preferably, it comprises TFE units, PAVE units, and units mainly composed of monomers containing carbonyl groups; even more preferably, it is a polymer comprising TFE units, PAVE units, and units mainly composed of monomers containing carbonyl groups, and, relative to all units, comprises such units in the following order: 90-99 mol%, 0.99-9.97 mol%, and 0.01-3 mol%. Specific examples of polymer F may be found in International Publication No. 2018 / 016644.

[0019] Polymer F is thermomeltable. A thermomeltable polymer is defined as a polymer that exhibits a melt flow rate of 1-1000 g / 10 minutes under a load of 49 N. From the viewpoint of effectively impregnating woven or nonwoven fabrics with liquid crystal polymers using polymer F, under a load of 49 N, the melt flow rate of polymer F should preferably be 1-30 g / min, and more preferably 5-30 g / min.

[0020] From the viewpoint of improving the heat resistance of the composite sheet, the melting point of polymer F should preferably be above 200°C, and more preferably above 260°C. From the viewpoint of effectively impregnating the liquid crystal polymer into woven or non-woven fabrics, the melting point of polymer F should preferably be below 325°C, and more preferably below 320°C. From the viewpoint of improving the heat resistance of the composite sheet, the glass transition point of polymer F should preferably be above 50°C, and more preferably above 75°C. From the viewpoint of effectively impregnating the liquid crystal polymer into woven or non-woven fabrics, the glass transition point of polymer F should preferably be below 150°C, and more preferably below 125°C. From the viewpoint of improving the electrical properties and heat resistance of the composite sheet, the fluorine content of polymer F should preferably be above 70% by mass, and more preferably 72-76% by mass. Furthermore, the fluorine content is determined from the composition of the polymer.

[0021] The surface tension of the F polymer should preferably be 16~26 mN / m. Surface tension can be measured by placing a droplet of wettability index reagent (manufactured by FUJIFILM Wako Pure Chemical Corporation) on a plate made of the F polymer. Even with low surface tension, the F polymer, due to its oxygen-containing polar groups, readily exhibits excellent adhesion to woven or non-woven fabrics of liquid crystal polymers. From the viewpoint of adhesion to woven or non-woven fabrics and substrates of liquid crystal polymers, the spherulite radius of the F polymer in the composite sheet should preferably be 0.2~10µm, more preferably 0.5~5µm.

[0022] From the viewpoint of electrical properties, the content of polymer F relative to the total mass of the composite sheet should preferably be 10% by mass or more, and more preferably 30% by mass or more. From the viewpoint of low linear expansion, the aforementioned content should preferably be 80% by mass or less, and more preferably 60% by mass or less. From the viewpoint of electrical properties, in the composite sheet, relative to the total mass of woven or nonwoven fabric excluding liquid crystal polymer, the content of polymer F should preferably be 30% by mass or more, and more preferably 50% by mass or more. The aforementioned content should preferably be 100% by mass or less, and more preferably 80% by mass or less.

[0023] This disclosure discloses composite sheets containing woven or non-woven fabrics of liquid crystal polymers. The liquid crystal polymer is preferably a thermotropic liquid crystal polymer. One type of liquid crystal polymer may be used, or two or more types may be used. The woven or non-woven fabric containing the liquid crystal polymer may also contain other materials. The content of the liquid crystal polymer relative to the total mass of the woven or non-woven fabric should preferably be 50% by mass or more, and more preferably 80% by mass or more.

[0024] The liquid crystal polymer is preferably a liquid crystal polyester. The liquid crystal polyester may also be a liquid crystal polyester amide, a liquid crystal polyester ether, a liquid crystal polyester carbonate, or a liquid crystal polyester amide. The liquid crystal polyester is preferably a liquid crystal aromatic polyester, specifically, examples include condensation polymers of aromatic dicarboxylic acids and aromatic diols or aromatic hydroxycarboxylic acids; condensation polymers of aromatic dicarboxylic acids, aromatic diols, and aromatic hydroxycarboxylic acids, etc.

[0025] Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of aromatic diols include 4,4'-dihydroxybiphenyl and bisphenol A. Examples of aromatic hydroxycarboxylic acids include p-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and 6-hydroxy-2-naphthoic acid. As long as liquid crystal properties are exhibited, in addition to these aromatic dicarboxylic acids, aromatic diols, and aromatic hydroxycarboxylic acids, aliphatic dicarboxylic acids, aliphatic diols, and aliphatic hydroxycarboxylic acids may also be used. Examples of aliphatic diols include ethylene glycol.

[0026] From the viewpoint of excellent heat resistance, the liquid crystal polymer is preferably a liquid crystal aromatic polyester with an aromatic ring content of 55% by mass or more. The aromatic ring content of the liquid crystal aromatic polyester is preferably 65% ​​by mass or more. The aromatic ring content is preferably 80% by mass or less. This liquid crystal polymer has low configurational freedom and excellent heat resistance, but on the other hand, it is difficult to interact with other polymers. However, in this disclosure, because the F polymer has high affinity with the liquid crystal polymer, it is also easy to bond well with this liquid crystal polymer with a high aromatic ring content.

[0027] In this disclosure, the aromatic ring content is obtained by the following formula. Furthermore, the carbon atoms contained in the substituents bonded to the aromatic ring are not included in the carbon atoms forming the aromatic ring. Aromatic ring content (mass %) = 100 × [mass of carbon atoms forming the aromatic ring in the polymer backbone (g) / total mass of the polymer (g)] For example, the aromatic ring content in typical units of a liquid crystal aromatic polyester is shown below, and the aromatic ring content of the liquid crystal aromatic polyester can be calculated based on the copolymerization ratio (molar ratio) of each unit. 2-Hydroxy-6-naphthoic acid: 71% 4,4'-Dihydroxybiphenyl: 78% Terephthalic acid: 54% 2,6-Naphthoic acid: 66%

[0028] As a liquid crystal polyester amide, an aromatic polyester amide formed by copolymerizing amine phenol with the aforementioned liquid crystal aromatic polyester can be cited. As a liquid crystal polymer, specifically, the liquid crystal polymer described in paragraphs 0032 to 0039 of Japanese Patent Application Publication No. 2017-119378 can be cited.

[0029] The load flexural temperature of the liquid crystal polymer should preferably be above 240°C, more preferably above 270°C, and even more preferably above 300°C. The load flexural temperature should preferably be below 400°C. At this temperature, the composite sheet is more likely to exhibit excellent heat resistance. Furthermore, because the F polymer contains oxygen-containing polar groups, it readily bonds well with liquid crystal polymers with high load flexural temperatures, that is, it readily bonds well with liquid crystal polymers that have limited configurational freedom and are difficult to interact with other polymers. In addition, the load flexural temperature is a value determined according to ASTM D648, with a load set at 0.46 MPa.

[0030] The melting point of the liquid crystal polymer is preferably above 230°C, and more preferably above 280°C. The melting point of the liquid crystal polymer is preferably below 350°C, and more preferably below 330°C. The melting point of the liquid crystal polymer can also be adjusted by heat treatment. Liquid crystal polymers with the aforementioned melting points not only have excellent heat resistance individually, but also exhibit enhanced interaction with F polymers under high-temperature exposure, and the low linear expansion of the composite sheet is more easily improved.

[0031] In particular, when the absolute value of the difference between the melting point of polymer F and the melting point of liquid crystal polymer is less than 30°C, this tendency tends to become more pronounced because the interaction between the polar groups of the polymer softened by high-temperature exposure is enhanced. The aforementioned difference (absolute value) should preferably be less than 25°C, and more preferably less than 20°C. The aforementioned difference (absolute value) should preferably be greater than 0°C.

[0032] The specific gravity of the liquid crystal polymer nonwoven fabric is preferably 1.0~3.0, more preferably 1.5~2.0. The average fiber diameter of the liquid crystal polymer nonwoven fabric is preferably 0.01~20µm, more preferably 3~10µm. The average fiber diameter is determined by observing with an electron microscope, measuring the diameter of 200 fibers, and removing the data of the 10 thinnest and 10 thickest fibers to obtain the average value. The unit area weight (mass per unit) of the liquid crystal polymer nonwoven fabric is preferably 1~300g / m2, more preferably 3~30g / m2.

[0033] Liquid crystal polymer nonwoven fabrics can be manufactured or pre-made. The molding of liquid crystal polymer nonwoven fabrics can, for example, be carried out at a molding temperature of 300-400°C. Molding methods for liquid crystal polymer nonwoven fabrics include spunbonding and meltblowing, and for example, the molding method described in International Publication No. 2010 / 098400. Specific examples of liquid crystal polymers include: the "Vecrus" series (manufactured by Kuraray Kuraflex), the "Vectran" series (manufactured by Kuraray), and the "UENO LCP" series (manufactured by Ueno Pharmaceutical Co., Ltd.).

[0034] Fabrics made of liquid crystal polymers can also be considered as fabrics made of liquid crystal polymer fibers, specifically plain weave fabrics. The warp density of plain weave fabrics made of liquid crystal polymers is preferably 2-80 yarns / cm, more preferably 4-60 yarns / cm. The weft density of plain weave fabrics made of liquid crystal polymers is preferably 2-80 yarns / cm, more preferably 4-60 yarns / cm. The fibers of liquid crystal polymers are preferably fibers obtained by melt spinning of liquid crystal polymers. To improve the strength, the fibers of liquid crystal polymers obtained by melt spinning may also be further heat-treated. The fibers of liquid crystal polymers may be composed of one type of liquid crystal polymer, or may be composed of two or more types of liquid crystal polymers. The fibers of liquid crystal polymers may also be core-sheath composite fibers with a core-sheath structure. In this case, the liquid crystal polymer may be included as a core component, as a sheath component, or as both a core component and a sheath component.

[0035] The composite sheet may also contain inorganic particles. One type of inorganic particle may be used, or two or more types may be used. In the composite sheet, the inorganic particles are preferably dispersed in the F polymer. The shape of the inorganic particles is preferably spherical, needle-like, fibrous, or plate-like, and preferably spherical, scaly, or layered, more preferably spherical or scaly. The inorganic particles may also be hollow. Spherical inorganic particles are preferably substantially spherical. "Substantially spherical" means that when observed with a scanning electron microscope (SEM), the proportion of inorganic particles with a minor axis to major axis ratio of 0.7 or higher is 95% or higher. The aspect ratio of non-spherical inorganic particles is preferably 2 or higher, and preferably 5 or higher. The aspect ratio is preferably 10,000 or lower.

[0036] The material used as inorganic particles should preferably be carbon, inorganic nitrides or inorganic oxides, and more preferably carbon, boron nitride, aluminum nitride, beryllium oxide, silicon dioxide, silash, talc, cerium oxide, aluminum oxide, magnesium oxide, zinc oxide or titanium oxide, and even more preferably boron nitride or silicon dioxide.

[0037] The D50 of inorganic particles should preferably be below 20µm, and more preferably below 10µm. The D50 should preferably be above 0.01µm, and more preferably above 0.1µm. The specific surface area of ​​inorganic particles should preferably be 1~20m2 / g.

[0038] The surface of inorganic particles can also be surface-treated with a silane coupling agent. Suitable silane coupling agents include 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-epoxypropoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-isocyanatepropyltriethoxysilane, which are silane coupling agents with functional groups.

[0039] Specific examples of silicon dioxide particles include: the "Admafine" series (manufactured by Admatechs), the "SFP" series (manufactured by Denka), the "E-SPHERES" series (manufactured by Pacific Cement Corporation), and the "Q" series (manufactured by Ginet). Specific examples of zinc oxide particles include the "FINEX" series (manufactured by Sakai Chemical Industry Co., Ltd.). Specific examples of titanium dioxide particles include the "TIPAQUE (registered trademark)" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Tayca Corporation). Specific examples of talc particles include the "SG" series (manufactured by Nippon Talc). Specific examples of block talc particles include the "BST" series (manufactured by Nippon Talc). Specific examples of boron nitride particles include the "UHP" series (manufactured by Showa Denko Corporation) and the "GP" and "HGP" grades of the "Denka Boron Nitride" series (manufactured by Denka Corporation).

[0040] When the composite sheet contains inorganic particles, from the viewpoint of the strength and low linear expansion of the composite sheet, the content of inorganic particles relative to the total mass of the composite sheet should preferably be 5% by mass or more, and may also be 10% by mass or more. From the viewpoint of suitably exhibiting the properties of the polymer containing polymer F, the aforementioned content should preferably be 40% by mass or less, and more preferably 20% by mass or less. From the viewpoint of the strength and low linear expansion of the composite sheet, the ratio of the mass of inorganic particles to the mass of polymer F in the composite sheet should preferably be 0.1 or more, and more preferably 0.2 or more. The aforementioned ratio should preferably be 1 or less, and more preferably 0.6 or less.

[0041] The composite sheet disclosed herein may also contain polymers different from polymer F (hereinafter also referred to as "dissimilar polymers"). The dissimilar polymers may be thermosetting or thermoplastic. One dissimilar polymer may be used, or two or more dissimilar polymers may be used. The dissimilar polymers may be contained in the woven or nonwoven fabric of the liquid crystal polymer, or may be dispersed in polymer F, preferably the latter.

[0042] As dissimilar polymers, examples include: tetrafluoroethylene-based polymers other than polymer F, polyester resins (such as liquid crystal aromatic polyesters), acetilime resins, epoxy resins, maleimide resins, ethyl carbamate resins, polyphenylene ether resins, polyoxyphenylene oxide resins, polyphenylene sulfide resins, etc.

[0043] As a tetrafluoroethylene-based polymer other than F polymer, examples include hot-melt PTFE, ETFE, PFA, FEP, and non-hot-melt PTFE that do not have oxygen-containing polar groups, with non-hot-melt PTFE being preferable. Non-hot-melt PTFE can be contained in the composite sheet in particle form or it can be non-granular.

[0044] The dissimilar polymer is preferably a tetrafluoroethylene polymer other than aromatic polymers and F polymers, and is more preferably an aromatic polyimide polymer selected from the group consisting of aromatic polyimides, aromatic polyamides, aromatic polyamides and precursors of aromatic polyamides, and non-thermally meltable PTFE.

[0045] Specific examples of aromatic polyimides include: the “UPIA-AT” series (manufactured by Ube Industries), the “Neopulim (registered trademark)” series (manufactured by MITSUBISHI GAS CHEMICAL), the “SPIXAREA (registered trademark)” series (manufactured by SOMAR), the “Q-PILON (registered trademark)” series (manufactured by PI Technology Research Institute), the “WINGO” series (manufactured by Wingo Technology), the “Tohmide (registered trademark)” series (manufactured by T&K TOKA), the “KPI-MX” series (manufactured by Kawamura Industries), and “HPC-1000” and “HPC-2100D” (both manufactured by SHOWA DENKO MATERIALS).

[0046] The content of dissimilar polymers can be adjusted according to the desired properties to be obtained. When the composite sheet contains dissimilar polymers, the content of dissimilar polymers relative to the total mass of the composite sheet is preferably 0.1% by mass or more, and more preferably 3% by mass or more. The aforementioned content is preferably 60% by mass or less, and more preferably 40% by mass or less. In the composite sheet, the mass ratio of the dissimilar polymer to the mass of polymer F is preferably 0.005 or more, and more preferably 0.05 or more. The aforementioned ratio is preferably 5 or less, and more preferably 4 or less.

[0047] When the composite sheet contains non-thermally fusible PTFE as a dissimilar polymer, the content of non-thermally fusible PTFE relative to the total mass of the composite sheet is preferably 10-60% by mass, more preferably 20-40% by mass. In the composite sheet, the mass ratio of non-thermally fusible PTFE to the mass of polymer F is preferably 0.5-5, more preferably 1-4. When the content of non-thermally fusible PTFE is within the above range, the composite sheet tends to have excellent electrical properties.

[0048] When the composite sheet contains an aromatic polymer as a dissimilar polymer, the content of the aromatic polymer relative to the total mass of the composite sheet is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass. In the composite sheet, the mass ratio of the aromatic polymer to the F polymer is preferably 0.01 to 0.2, more preferably 0.05 to 0.1. When the content of the aromatic polymer is within the above range, the composite sheet tends to have excellent low linear expansion or adhesion.

[0049] When the composite sheet contains at least one selected from the group consisting of dissimilar polymers and inorganic particles, the total content of the group consisting of at least one selected from the group consisting of dissimilar polymers and inorganic particles relative to the total mass of the composite sheet shall preferably be greater than 5% by mass, and more preferably 15% by mass or more. The aforementioned content shall preferably be 50% by mass or less, and more preferably 30% by mass or less.

[0050] When the composite sheet comprises at least one selected from the group consisting of dissimilar polymers and inorganic particles, the ratio of the total mass of the group consisting of at least one selected from the group consisting of dissimilar polymers and inorganic particles to the mass of polymer F is preferably 0.1 or more, and more preferably 0.3 or more. The aforementioned ratio is preferably 0.7 or less, and more preferably 0.5 or less.

[0051] In addition to the above-mentioned components, the composite sheet may also contain: organic particles, thixotropic agents, defoamers, silane coupling agents, dehydrating agents, plasticizers, weather-resistant agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive materials, release agents, surface treatment agents, viscosity modifiers, flame retardants, and other components. Furthermore, the composite sheet may also contain components derived from the dispersion described below.

[0052] The relative permittivity of the composite sheet is preferably 3.0 or less, and more preferably 2.5 or less. The relative permittivity is preferably 1.5 or more. The dielectric tangent of the composite sheet is preferably 0.0100 or less, and more preferably 0.0010 or less. The dielectric tangent is preferably 0.0001 or more. The relative permittivity and dielectric tangent are measured at a frequency of 10 GHz using the SPDR (Split-Post Dielectric Resonator) method.

[0053] The thickness of the composite sheet should preferably be 5µm or more, and more preferably 10µm or more. The thickness of the composite sheet should preferably be less than 200µm, and more preferably less than 100µm. The composite sheet can be in roll form or in single sheet form.

[0054] The composite sheet can also be surface treated. Examples of surface treatments include: corona discharge treatment, plasma treatment, plasma graft polymerization treatment, electron beam irradiation, excimer UV light irradiation, ITRO treatment using flame, and wet etching treatment using metallic sodium. Through these surface treatments, polar functional groups such as hydroxyl, carbonyl, and carboxyl groups can be introduced onto the surface of the composite sheet.

[0055] The coefficient of linear expansion of the composite sheet should preferably be below 80 ppm / ℃, and more preferably below 30 ppm / ℃. The lower limit of the coefficient of linear expansion is 5 ppm / ℃. The coefficient of linear expansion is determined by the method specified in JIS C 6471:1995. Specifically, it is determined by the method described in the examples.

[0056] There are no particular limitations on the manufacturing method of the composite sheet if the composite sheet disclosed herein can be obtained. The composite sheet may be manufactured using a sheet or dispersion containing the above-mentioned components, or it may be manufactured by the manufacturing method described later.

[0057] The method for manufacturing the composite sheet in one embodiment disclosed herein is a method of obtaining the composite sheet by hot-pressing a sheet containing polymer F and a woven or non-woven fabric of liquid crystal polymer together. Hereinafter, this manufacturing method will also be referred to as the "hot-pressing method".

[0058] When using the hot-pressing method, the sheet containing polymer F can be a pre-made product or a newly manufactured one. The thickness of the sheet containing polymer F is preferably 1~200µm. The sheet containing polymer F can also be formed from a dispersion of polymer F particles. For example, the sheet containing polymer F can also be formed by a method including the following steps: applying a dispersion of polymer F particles to the surface of a temporary substrate; heating the temporary substrate to which the dispersion has been applied to obtain a laminate having the temporary substrate and a layer containing polymer F; and removing the temporary substrate from the laminate.

[0059] The method of heating the temporary substrate to which the aforementioned dispersion is applied can be the same as the heating method in the dispersion impregnation method described later, and the suitable conditions are also the same. Examples of temporary substrates include metal foil, resin film, etc., and methods for removing the temporary substrate include peeling, etching, etc.

[0060] Sheets containing polymer F can also be formed by melt extrusion of polymer F. Sheets containing dissimilar polymers or inorganic particles can be formed by melt kneading and extruding polymer F with dissimilar polymers or inorganic particles.

[0061] Hot pressing can be performed by: laminating a sheet containing polymer F with a woven or non-woven fabric of liquid crystal polymer, and then pressing it by: passing it between a pair of heated rollers, clamping it with a pair of opposing heated plates, or clamping it with heated plates and rollers. From the viewpoint that the impregnation of polymer F into the woven or non-woven fabric of liquid crystal polymer is easy and good, the temperature of hot pressing should preferably be above the melting point of polymer F, preferably above the melting point +20°C. The temperature of hot pressing should preferably be 300~380°C. The pressure of hot pressing should preferably be 0.2~10MPa. From the viewpoint of obtaining a composite sheet with reduced air bubbles, hot pressing should preferably be performed under reduced pressure. When hot pressing is performed under reduced pressure, the gas environment pressure should preferably be 10 kPa or less, preferably 1 kPa or less.

[0062] This invention discloses another method for manufacturing a composite sheet, comprising the following steps: impregnating a woven or nonwoven fabric containing F polymer particles with a dispersion of liquid crystal polymer. This manufacturing method will also be referred to below as the "dispersion impregnation method". In one embodiment, the method for manufacturing a composite sheet by the dispersion impregnation method may also include the following steps: impregnating a woven or nonwoven fabric containing F polymer particles with a dispersion of liquid crystal polymer; and heating the aforementioned woven or nonwoven fabric impregnated with the dispersion to obtain the composite sheet. When manufacturing a composite sheet by the dispersion impregnation method, the F polymer easily impregnates between the fibers of the woven or nonwoven fabric containing the liquid crystal polymer. As a result, it is preferable to easily improve the adhesion between the woven or nonwoven fabric containing the liquid crystal polymer and the F polymer.

[0063] Impregnation can be carried out by applying the dispersion to the surface of the liquid crystal polymer in woven or non-woven fabric. Impregnation methods include coating, droplet ejection, and immersion. Roller coating, knife coating, bar coating, mold coating, roller immersion, or spraying are preferred, with roller immersion being the most suitable.

[0064] The woven or non-woven fabric impregnated with the liquid crystal polymer dispersion should be heated to remove the dispersion medium, and then further heated to calcine the F polymer. At this point, a composite sheet of woven or non-woven fabric impregnated with the F polymer can be obtained. The heating for removing the dispersion medium should preferably be carried out at 100-200°C for 0.1-30 minutes. Furthermore, air can be blown during heating to promote the removal of the liquid dispersion medium through air drying. The heating for calcifying the F polymer should preferably be carried out at a temperature above the melting point of the F polymer, preferably at 300-400°C for 0.1-30 minutes. Regarding the heating devices, ovens, ventilated drying furnaces, etc., are suitable. The heat source in the device can be a contact heat source (hot air, heating plate, etc.) or a non-contact heat source (infrared rays, etc.). Furthermore, the heating can be carried out under normal pressure or under reduced pressure. Furthermore, the gas environment during each heating process can be either an air environment or an inactive gas environment (helium, neon, argon, nitrogen, etc.).

[0065] The impregnation and heating of the dispersion can be repeated more than twice. For example, a dispersion is applied to the surface of a woven or nonwoven fabric containing a liquid crystal polymer and heated to remove the liquid dispersion medium and calcine the F polymer, thereby obtaining a composite sheet impregnated with the F polymer. Alternatively, a dispersion can be applied to the surface of the aforementioned sheet and heated to remove the liquid dispersion medium and calcine the F polymer, thereby obtaining a composite sheet further impregnated with the F polymer. When repeating the impregnation and heating of the dispersion, the impregnation and heating of the dispersion should preferably be repeated 2 to 8 times. When repeating the impregnation and heating of the dispersion, the same type of dispersion or different types of dispersion can be used. Furthermore, when repeating the impregnation and heating of the dispersion, at least one dispersion containing F polymer particles (hereinafter also referred to as "F particles") is sufficient.

[0066] When repeatedly impregnating and heating the dispersion, the dispersion used for the initial impregnation should preferably be a dispersion containing F particles. In this case, the F particles and other components contained in subsequent dispersions are more easily retained in the woven or non-woven fabric of the liquid crystal polymer. Furthermore, the dispersion used for the initial impregnation should preferably be a dispersion containing both F particles and non-thermally fusible PTFE particles (hereinafter also referred to as "PTFE particles"). In this case, the F particles and other components contained in subsequent dispersions are more easily retained in the woven or non-woven fabric of the liquid crystal polymer. The dispersion used for the final impregnation should preferably be a dispersion containing F particles. In this case, the surface of the composite sheet tends to have excellent smoothness and adhesion. Furthermore, the dispersion used for the final impregnation should preferably be a dispersion containing both F particles and PTFE particles. In this case, the surface of the composite sheet not only has excellent smoothness and adhesion, but also tends to possess a higher degree of PTFE properties. The dispersion used for impregnation other than the initial and final impregnation should preferably be a dispersion containing PTFE particles. In this case, the composite sheet can easily possess the physical properties of PTFE, such as electrical properties.

[0067] The composite sheet is preferably a composite sheet formed by sequentially impregnating a liquid crystal polymer with an F polymer, a non-thermally meltable PTFE, and an F polymer into a woven or non-woven fabric. In this case, the composite sheet readily exhibits excellent low linear expansion, adhesion to other substrates, and electrical properties. As a method for manufacturing this composite sheet, the following method can be adopted: first, impregnate a liquid crystal polymer-containing dispersion into a woven or non-woven fabric and heat it; then, impregnate a liquid crystal polymer-containing dispersion into a PTFE-containing dispersion and heat it; finally, impregnate a liquid crystal polymer-containing dispersion into a ...

[0068] In the above-described hot-pressing method or dispersion impregnation method, the absolute values ​​of the melting point of the F polymer, the melting point of the liquid crystal polymer, and the difference between the melting points of the F polymer and the liquid crystal polymer should preferably be within the aforementioned range. In this case, during heating in both methods, the interaction between the polar groups of the softened polymer is easily enhanced, forming a fine matrix structure of the F polymer and the liquid crystal polymer, thereby making it easier to improve the electrical properties and low linear expansion of the composite sheet. Furthermore, when the composite sheet contains inorganic particles, the carrying capacity of the inorganic particles is easily improved. The following description addresses dispersions containing F particles that can also be used in the hot-pressing method or dispersion impregnation method.

[0069] The dispersion is a liquid in which F particles are dispersed in a liquid dispersion medium. The dispersion may also contain inorganic particles as described as components of the composite sheet, polymers different from F polymers, and other components. When the dispersion contains dissimilar polymers, the dissimilar polymers may be dispersed in the dispersion in particulate form or dissolved in the liquid dispersion medium. Furthermore, the dispersion may also contain surfactants or silane coupling agents.

[0070] From the perspective of dispersion stability, the D50 of F particles should preferably be greater than 0.1µm, more preferably greater than 0.3µm, and even more preferably greater than 1µm. From the perspective of dispersion stability, the D50 of F particles should preferably be less than 25µm, more preferably less than 10µm, and even more preferably less than 8µm. The specific surface area of ​​F particles should preferably be 1~25m² / g. One type of F particles can be used, or two or more types can be used.

[0071] The F particles include particles of the F polymer, or may be composed of the F polymer. The F particles may contain polymers other than the F polymer, inorganic compounds, etc., and can form a core-shell structure with the F polymer as the core and a polymer or inorganic compound other than the F polymer as the shell, or a core-shell structure with the F polymer as the shell and a polymer or inorganic compound different from the F polymer as the core. Examples of polymers other than the F polymer include aromatic polyesters, polyamide-imide, polyamide, and maleimide. Examples of inorganic compounds include silicon dioxide and boron nitride.

[0072] From the viewpoint of impregnating a sufficient amount of F polymer into a woven or nonwoven fabric of liquid crystal polymer, the content of F particles relative to the total amount of dispersion should preferably be 10% by mass or more, and more preferably 20% by mass or more. From the viewpoint of dispersion stability of the dispersion medium, the content of F particles relative to the total amount of dispersion should preferably be 60% by mass or less, and more preferably 40% by mass or less.

[0073] The liquid dispersion medium is a compound that is liquid at atmospheric pressure and 25°C, and preferably a compound with a boiling point of 50~240°C. One type of liquid dispersion medium may be used, or two or more types may be used. When two or more liquid dispersion media are used, they should preferably be miscible.

[0074] The liquid dispersion medium is preferably a compound selected from the group consisting of water, amides, ketones, and esters, with water being more preferred. Examples of amides include: N-methyl-2-pyrrolidone, N,N-dimethylmethoxymethylene, N,N-dimethylacetylamine, N,N-dimethylpropionic acid, 3-methoxy-N,N-dimethylpropionic acid, 3-butoxy-N,N-dimethylpropionic acid, N,N-diethylmethoxymethylene, hexamethylphosphonic acid triamide, and 1,3-dimethyl-2-imidazolidineone. Examples of ketones include: acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl n-pentyl ketone, methyl isopentyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, and cycloheptanone. Examples of esters include: methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethyl 3-ethoxypropionate, γ-butyrolactone, and γ-valerolactone.

[0075] The content of liquid dispersion medium relative to the total amount of dispersion liquid should preferably be 40% by mass or more, and more preferably 50% by mass or more. The content of liquid dispersion medium relative to the total amount of dispersion liquid should preferably be 90% by mass or less, and more preferably 80% by mass or less.

[0076] The dispersion may also contain inorganic particles. Details of the inorganic particles are as described above. When the dispersion contains inorganic particles, the content of inorganic particles relative to the total amount of the dispersion should preferably be 10-40% by mass, and more preferably 10-30% by mass.

[0077] The dispersion may also contain a different polymer. Details of the polymer, which is different from polymer F, are as described above. The different polymer may be contained in the dispersion in the form of particles or dissolved in the liquid dispersion medium. When the dispersion contains a different polymer, the content of the different polymer relative to the total amount of the dispersion should preferably be 0.1% by mass or more, and more preferably 0.3% by mass or more. The aforementioned content should preferably be 60% by mass or less, and more preferably 40% by mass or less.

[0078] When the dissimilar polymer is non-thermally fusible PTFE, the non-thermally fusible PTFE should preferably be contained in the dispersion in the form of particles. The D50 of the non-thermally fusible PTFE particles should preferably be 0.1~1µm. The content of non-thermally fusible PTFE particles relative to the total amount of the dispersion should preferably be 20~60% by mass. In the dispersion, the mass ratio of the non-thermally fusible PTFE particles to the mass of the PTFE particles should preferably be 0.5~5, more preferably 1~3. At this time, it is easy to obtain a composite sheet with excellent electrical properties.

[0079] When the dissimilar polymer is an aromatic polymer, the aromatic polymer should preferably be dissolved in a liquid dispersion medium and contained in the dispersion. The content of the aromatic polymer relative to the total amount of the dispersion should preferably be 0.1 to 30% by mass, and preferably 0.3 to 10% by mass. At this point, it is easy to obtain a composite sheet with low linear expansion and excellent adhesion to the substrate.

[0080] The dispersion should preferably contain a surfactant. The surfactant should preferably be a nonionic surfactant. As a nonionic surfactant, it is preferably an ethylene glycol-based surfactant, an acetylene-based surfactant, a polysiloxane-based surfactant, or a fluorinated surfactant, with a preference for polysiloxane-based surfactants. One or more nonionic surfactants may be used. When using two nonionic surfactants, the nonionic surfactants should preferably be a polysiloxane-based surfactant and an ethylene glycol-based surfactant.

[0081] Specific examples of nonionic surfactants include: the "Ftergent" series (manufactured by NEOS Corporation), the "Surflon" series (manufactured by AGC SEIMI CHEMICAL Corporation), the "MEGAFACE" series (manufactured by DIC Corporation), the "UNIDYNE" series (manufactured by Daikin Industries, Ltd.), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by BYK Japan Corporation), "KF-6011", "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by Dow Chemical Company, "Tergitol TMN-100X", etc.).

[0082] When the dispersion contains a nonionic surfactant, the content of the nonionic surfactant in the dispersion should preferably be 1 to 15% by mass.

[0083] The dispersion may further contain a silane coupling agent. In this case, the silane coupling agent acts as a binder for the F particles, thereby allowing the F polymer to easily and effectively impregnate the woven or non-woven fabric of the liquid crystal polymer. As the silane coupling agent, examples similar to those described above that can also be used for the surface treatment of inorganic particles can be used. When the dispersion contains a silane coupling agent, the content of the silane coupling agent in the dispersion should preferably be 1 to 10% by mass.

[0084] To adjust the pH, the dispersion may further contain a pH adjuster or a pH buffer. Examples of pH adjusters include amines, ammonia, and citric acid. Examples of pH buffers include trimethylolamine methane, ethylenediaminetetraacetic acid, ammonium bicarbonate, ammonium carbonate, and ammonium acetate. The dispersion may also contain other components mentioned above as components of the composite sheet.

[0085] The viscosity of the dispersion should preferably be 10 mPa·s or higher, and more preferably 100 mPa·s or higher. The viscosity of the dispersion should preferably be 10,000 mPa·s or lower, and more preferably 3,000 mPa·s or lower. The viscosity of the dispersion is measured using a type B viscometer at 25°C and a rotation speed of 30 rpm. The measurement is repeated three times, and the average of the three measurements is taken. The thixotropic ratio of the dispersion should preferably be 1.0 to 3.0. The pH of the dispersion should preferably be 5 to 10, and more preferably 8 to 10.

[0086] The dispersion can be manufactured by mixing F particles with a liquid dispersion medium. When the dispersion contains other components such as inorganic particles or particles of dissimilar polymers, the dispersion is preferably manufactured using the following methods: a method of adding the F particles and other components together into the liquid dispersion medium for mixing; a method of adding the F particles and other components sequentially into the liquid dispersion medium for mixing; a method of pre-mixing the F particles with the liquid dispersion medium and the other components with the liquid dispersion medium separately, and then mixing them; or a method of mixing the F particles with other components and then mixing them with the liquid dispersion medium. Such mixing can be carried out in batches or continuously.

[0087] As a mixing device, examples include: stirring devices with blades (Heinz mixers, pressure kneaders, Bambury closed mixers, planetary mixers, etc.), grinding devices with media (ball mills, grinding mills, basket mills, sand mixers, sand mills, Dyno-Mills, DISPERMAT, SC-Mills, spiked mills or stirred mills, etc.), and dispersing devices with other mechanisms (microfluid homogenizers, nanomizers, ultramizers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impeller dispersers, self-rotating and revolution-rotating mixers, and thin-film rotary high-speed mixers, etc.).

[0088] A suitable method for manufacturing the dispersion is as follows: a kneading compound is obtained by pre-kneading F particles and a portion of a liquid dispersion medium, and the kneading compound is further added to the remaining liquid dispersion medium to obtain the dispersion. The liquid dispersion medium used during kneading and addition can be the same type of liquid dispersion medium or different types of liquid dispersion media. When the dispersion contains other components such as inorganic particles or particles of a polymer different from the F polymer, these other components can be mixed during kneading or during addition.

[0089] The kneaded mixture obtained by kneading can be in the form of a paste (a paste with a viscosity of 1,000 to 100,000 mPa·s, etc.) or in the form of a wet powder (a wet powder with a viscosity of 10,000 to 100,000 Pa·s, etc., as measured by a capillary rheometer).

[0090] Furthermore, the viscosity measured by the capillary rheometer refers to the value measured using a capillary with a length of 10 mm and a radius of 1 mm, with the furnace diameter set to 9.55 mm, the load cell capacity set to 2 t, the temperature set to 25 °C, and the shear rate set to 1 s⁻¹.

[0091] The mixing during kneading should be carried out by a planetary mixer. A planetary mixer is a mixing device with two shaft stirring blades that rotate on their own axis and revolve around the sun.

[0092] The mixing during addition should be carried out by a thin-film rotary high-speed mixer. A thin-film rotary high-speed mixer is a stirring device that spreads F particles and liquid dispersion media into a thin film on the inner wall of a cylindrical stirring tank and rotates it to mix them under centrifugal force.

[0093] The composite sheet can also be laminated with a substrate to form a laminate. The composite sheet disclosed herein has an excellent coefficient of linear expansion, so even when the laminate is subjected to high-temperature processing, the composite sheet is not easily peeled off from the substrate. Examples of substrates include: metal substrates (metal foils such as copper, nickel, aluminum, titanium, and their alloys), heat-resistant resin films (heat-resistant resin films such as polyimide, polyamide, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyamide-amide, liquid crystal polyester, and tetrafluoroethylene polymers), prepreg substrates (precursors to fiber-reinforced resin substrates), ceramic substrates (ceramic substrates such as silicon carbide, aluminum nitride, and silicon nitride), and glass substrates.

[0094] The shape of the substrate may be planar, curved, or uneven. Furthermore, the shape of the substrate may also be any of the following: foil, plate, film, or fibrous. The average roughness of the substrate surface at ten points is preferably 0.01~0.05µm. The surface of the substrate may be surface-treated with a silane coupling agent or plasma treatment. The laminated composite sheet and the substrate may be joined by hot pressing. The hot pressing method may be the same as the hot pressing method described above. The peel strength between the composite sheet and the substrate in the laminate is preferably 10~100N / cm.

[0095] The uses of the composite sheet disclosed herein are not particularly limited. The composite sheet disclosed herein can be effectively used as antenna parts, printed circuit boards, aircraft parts, automotive parts, sporting goods, food industry supplies, heat dissipation parts, etc. Specifically, it can be effectively used as: wire sheathing materials (aircraft wires, etc.), enameled wire sheathing materials used in motors of electric vehicles, electrical insulating tape, oil drilling insulating tape, oil delivery hoses, hydrogen tanks, materials for printed circuit boards, separation membranes (microporous filter membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, gas separation membranes, etc.), electrode adhesives (for lithium batteries, fuel cells, etc.), copy rolls, housings for furniture, automotive dashboards, and home appliances, sliding components (load bearings, yaw bearings, sliding shafts, valves, bearings, bushings, seals, thrust washers, wear rings, pistons, slide switches, gears, cams, conveyor belts, food conveyor belts, etc.), tension cables, wear pads, wear strips, lamps, test sockets, wafer guides. (guide), wear parts of centrifugal pumps, chemical pumps and water pumps, tools (shovels, files, cones, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, molds, toilets, container coverings, power devices, transistors, thyristors, rectifiers, transformers, power MOSFETs, CPUs, heat sinks, metal heat sinks, blades of windmills or wind power generation equipment or aircraft, housings of computers or monitors, electronic device materials, automotive interior and exterior parts, processing machines or vacuum ovens that undergo heat treatment in low oxygen conditions, sealing materials for plasma treatment devices, heat dissipation parts in processing units of sputtering or various dry etching devices, electromagnetic wave shielding components, etc.

[0096] The composite sheet disclosed herein is suitable for applications where the desired characteristics are desired due to its excellent electrical properties and low linear expansion. For example, the composite sheet is suitable for use as a material in copper-clad laminates and other printed wiring boards.

[0097] Examples The following examples illustrate the implementation of the present disclosure in detail, but the implementation of the present disclosure is not limited thereto.

[0098] 1. Preparation of each component of the dispersion [F particles] F particle 1: Particles of thermomeltable polymer 1 (melting point: 300℃, melt flow rate: 25g / 10min) (D50: 2.1µm), which contain TFE units, NAH units and PPVE units in sequence at 97.9 mol%, 0.1 mol%, and 2.0 mol%, and have 1000 carbonyl groups per 1×106 main chain carbons. F particle 2: Particles of thermomeltable polymer 2 (melting point: 300℃, melt flow rate: 22g / 10min) without oxygen-containing polar groups (D50: 2.4µm), which contain TFE units and PPVE units in sequence at 98.5 mol% and 1.5 mol%. [Inorganic particles] Inorganic particle 1: Spherical silicon dioxide (D50: 1µm) [Woven or non-woven fabric of liquid crystal polymer] Non-woven fabric 1: Kuraray Kuraflex's "Vecrus" (area weight: 9g / m2) fabrics are categorized as follows: Fabric 1: Plain weave fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or higher (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 7µm, thickness: 123µm, area volume: 32cm3 / m2, warp density: 20 ends / cm, weft density: 20 ends / cm). Fabric 2: Fabric of liquid crystal aromatic polyester (melting point: 320℃) (load flexural temperature: 350℃, area weight: 45g / cm2). Fabric 3: Fabric of liquid crystal aromatic polyester (melting point: 230℃) (area weight: 41g / cm2).

[0099] 2. Manufacturing of Composite Sheet (Example 1) 30 parts by mass of F particles 1, 15 parts by mass of inorganic particles 1, 1 part by mass of polysiloxane surfactant, and 64 parts by mass of water were placed in a container, and zirconia balls were added. The container was then rotated at 150 rpm for 1 hour to obtain dispersion 1 (viscosity: 200 mPa·s). The obtained dispersion 1 was applied to nonwoven fabric 1 using a roller impregnation method, and then passed through a drying oven at 120°C for 5 minutes and heated to dry. Afterwards, it was fired in a far-infrared furnace at 340°C for 10 minutes to obtain composite sheet 1 (thickness: 40 µm) impregnated with the fired product of F particles 1. In composite sheet 1, the content of inorganic particles 1 is 16% by mass, and the mass ratio of the content of inorganic particles 1 to the content of the aforementioned polymer 1 is 0.5. (Example 2) Except that non-woven fabric 1 is replaced with woven fabric 1, a composite sheet 2 (thickness: 140µm) of sintered product of F particles 1 impregnated with woven fabric 1 is obtained in the same manner as in Example 1. In composite sheet 2, the content of inorganic particles 1 is 7% by mass, and the mass ratio of the content of inorganic particles 1 to the content of the aforementioned polymer 1 is 0.5. (Example 3) Except that non-woven fabric 1 is replaced with woven fabric 2, a composite sheet 3 (thickness: 140µm) of sintered product of F particles 1 impregnated with woven fabric 2 is obtained in the same manner as in Example 1. In composite sheet 3, the content of inorganic particles 1 is 7% by mass, and the mass ratio of the content of inorganic particles 1 to the content of the aforementioned polymer 1 is 0.5. (Example 4) Except that inorganic particles 1 are not used in the preparation of dispersion liquid 1 and non-woven fabric 1 is replaced with woven fabric 2, a composite sheet 4 (thickness: 140µm) of sintered product of F particles 1 impregnated with woven fabric 2 is obtained in the same manner as in Example 1. (Example 5) Except that inorganic particles 1 are not used in the preparation of dispersion 1 and nonwoven fabric 1 is replaced with woven fabric 3, a composite sheet 5 (thickness: 140µm) in which the sintered product of F particles 1 is impregnated with woven fabric 3 is obtained in the same manner as in Example 1. (Example 6: Comparative Example) Except that F particles 1 is replaced with F particles 2, a composite sheet 6 (thickness: 140µm) in which the sintered product of F particles 2 is impregnated with woven fabric 1 is obtained in the same manner as in Example 1. During the drying and firing processes in the manufacture of composite sheet 6, inorganic particles 1 peel off.

[0100] 3. Evaluation of Composite Sheets 3-1. Peel Strength The obtained composite sheets are each heat-pressed and bonded to copper foil to create copper-clad laminates. Rectangular test pieces with a length of 100 mm and a width of 10 mm are cut from the copper-clad laminates. After fixing the test piece at a position 50 mm from one end along its length, the copper foil is peeled from the composite sheet at a tensile speed of 50 mm / min at a 90° angle relative to the test piece. The maximum load causing the peel is taken as the peel strength (N / cm), and the following evaluation criteria are used for evaluation. [Evaluation Criteria] A: 12 N / cm or more. B: Less than 12 N / cm. 3-2. Coefficient of Linear Expansion: For the obtained composite sheets, 180mm square test pieces were cut. Following the testing method specified in JIS C 6471:1995, the coefficient of linear expansion of the test pieces was measured in the range of 25°C to 260°C, and evaluated according to the following evaluation criteria: AA: Below 20ppm / °C; A: Greater than 20ppm / °C and below 30ppm / °C; B: Greater than 30ppm / °C and below 40ppm / °C; C: Greater than 40ppm / °C.

[0101] 3-3. Electrical Properties Samples measuring 10cm in length and 5cm in width were cut from the obtained composite sheets. The relative permittivity and dielectric tangent were measured using the SPDR (Split-Post Dielectric Resonator) method (measurement frequency: 10GHz), and evaluated according to the following evaluation criteria: [Evaluation Criteria] A: Relative permittivity below 2.2, and dielectric tangent less than 0.0010. B: Relative permittivity below 2.2, and dielectric tangent greater than 0.0010 and less than 0.0020; or relative permittivity greater than 2.2 and below 2.4, and dielectric tangent less than 0.0010. C: Relative permittivity greater than 2.2 and below 2.4, and dielectric tangent greater than 0.0010 and less than 0.0020. The evaluation results for each composite sheet are summarized and displayed in Table 1 below. As shown in the table below, composite sheets 1-5 exhibit excellent electrical properties and low linear expansion. Furthermore, the peel strength of composite sheets 1-5 is also satisfactory.

[0102] [Table 1]

[0103] This specification is incorporated herein by reference to the entire disclosure of Japanese Patent Application Nos. 2021-119739 and 2021-172596. All documents, patent applications and technical specifications described in this specification are referenced in this specification to the same extent as the contents of each document, patent application and technical specification specifically described and incorporated herein by reference.

Claims

1. A composite sheet comprising: a woven or nonwoven fabric of a thermomeltable liquid crystal polymer having a melting point of 230-350°C; and a thermomeltable tetrafluoroethylene-based polymer impregnated with the aforementioned liquid crystal polymer, having an oxygen-containing polar group and a melting point of 260-320°C, comprising a polymer containing units mainly composed of tetrafluoroethylene and units mainly composed of perfluoro(alkyl vinyl ether); and wherein the absolute value of the difference between the melting point of the aforementioned tetrafluoroethylene-based polymer and the melting point of the aforementioned liquid crystal polymer is less than 30°C.

2. The composite sheet as claimed in claim 1, wherein the aforementioned oxygen-containing polar group is a hydroxyl-containing group or a carbonyl-containing group.

3. The composite sheet as claimed in claim 1 or 2, wherein the aforementioned oxygen-containing polar group is a group containing an alcoholic hydroxyl group or a group containing a carbonyl group.

4. The composite sheet as claimed in claim 1 or 2, wherein the aforementioned oxygen-containing polar group is a carbonyl group.

5. The composite sheet as claimed in claim 1 or 2, wherein the aforementioned liquid crystal polymer comprises a liquid crystal aromatic polyester.

6. The composite sheet of claim 1 or 2 further contains a polymer that is different from the aforementioned tetrafluoroethylene-based polymer.

7. The composite sheet as requested in item 1 or 2 further contains inorganic particles.

8. The composite sheet of claim 1 or 2, comprising at least one selected from the group consisting of polymers and inorganic particles that are different from the aforementioned tetrafluoroethylene-based polymers; and, relative to the total mass of the aforementioned composite sheet, the total content of at least one selected from the group consisting of polymers and inorganic particles that are different from the aforementioned tetrafluoroethylene-based polymers is greater than 5% by mass.

9. The composite sheet of claim 1 or 2, comprising at least one selected from the group consisting of polymers and inorganic particles that are different from the aforementioned tetrafluoroethylene polymers; and the total mass of the selected polymers and inorganic particles is at least 0.1 times the mass of the aforementioned tetrafluoroethylene polymer.

10. The composite sheet of request item 1 or 2 has a thickness of less than 50µm.