Method of manufacturing composite sheet, and composite sheet

Abstract

A method for manufacturing a composite sheet and the aforementioned composite sheet, wherein the method for manufacturing the composite sheet involves impregnating a woven or nonwoven fabric containing a hot-melt tetrafluoroethylene polymer with a liquid crystal polymer to obtain the composite sheet, wherein the hot-melt tetrafluoroethylene polymer has oxygen atoms.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing composite sheets and composite sheets. [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 method for manufacturing a composite sheet, wherein a composite sheet is obtained by impregnating a film containing a thermoplastic tetrafluoroethylene polymer into a woven or nonwoven fabric containing a liquid crystal polymer, wherein the thermoplastic tetrafluoroethylene polymer has oxygen atoms. <2> The manufacturing method of <1>, wherein the melt flow rate of the aforementioned tetrafluoroethylene polymer is 1 to 30 g / min under a load of 49 N. <3> The manufacturing method of <1> or <2>, wherein the melt temperature of the aforementioned tetrafluoroethylene polymer is 260°C or higher. <4> The manufacturing method of any one of <1> to <3>, wherein the aforementioned tetrafluoroethylene polymer has an oxygen-containing polar group, and the aforementioned oxygen-containing polar group is a hydroxyl-containing group or a carbonyl-containing group. <5> The manufacturing method of any one of <1> to <4>, wherein the aforementioned tetrafluoroethylene polymer has oxygen-containing polar groups, and the number of the aforementioned oxygen-containing polar groups in the aforementioned tetrafluoroethylene polymer, based on the number of carbon atoms in the main chain, is 10 to 5000 per 1×10⁶ main chain carbons. <6> The manufacturing method of any one of <1> to <5>, wherein the aforementioned tetrafluoroethylene polymer comprises units mainly composed of perfluorinated (alkyl vinyl ethers), and the content of the aforementioned units mainly composed of perfluorinated (alkyl vinyl ethers) in all units of the aforementioned tetrafluoroethylene polymer is greater than 2 mol%. <7> The manufacturing method of any one of <1> to <6>, wherein the load flexural temperature of the aforementioned liquid crystal polymer is 240°C or higher. <8> The manufacturing method of any one of <1> to <7>, wherein the aforementioned liquid crystal polymer comprises a liquid crystal aromatic polyester. <9> The manufacturing method of <8>, wherein the aromatic ring content of the aforementioned aromatic polyester is 55% by mass or more. <10> The manufacturing method of any one of <1> to <9>, wherein the thickness of the aforementioned composite sheet is 200µm or less. <11> The manufacturing method of any one of <1> to <10>, wherein the aforementioned film is impregnated by heat-pressing it with the aforementioned woven or non-woven fabric. <12> The manufacturing method of <11>, wherein the heat-pressing temperature is within ±30°C of the melting temperature of the aforementioned tetrafluoroethylene-based polymer. <13> The manufacturing method of <11> or <12>, wherein the heat-pressing pressure is 1MPa or more. <14> The manufacturing method of any one of <11> to <13>, wherein the aforementioned heat-pressing is performed under reduced pressure. <15> A composite sheet comprising a woven or nonwoven fabric containing a liquid crystal polymer and a thermoplastic tetrafluoroethylene polymer having oxygen atoms, wherein the thermoplastic tetrafluoroethylene polymer is impregnated in the aforementioned woven or nonwoven fabric.

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

Implementation Method

[0007] The following details 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 element procedures, etc.) are not necessary unless specifically stated otherwise. The same applies to numerical values ​​and their ranges; the embodiments of this disclosure are not limited thereto.

[0008] In this disclosure, the numerical ranges indicated by "~" include the minimum and maximum values ​​recorded before and after "~". In this disclosure, each component may also contain multiple substances equivalent to it. When multiple substances equivalent to each component exist in the composition, unless otherwise specified, the content or percentage of each component 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, unless otherwise specified, the particle size of each component refers to the value of the mixture of the multiple particles present in the composition. In this disclosure, "composite sheet" refers to a sheet of woven or non-woven fabric containing polymer and liquid crystal polymer. In this disclosure, "film" and "sheet" are interchangeable, and their thickness is not particularly limited. 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" refers to the stacking of layers; two or more layers can be bonded together or detachable. The "average particle size (D50)" in this disclosure is the particle size accumulated at 50% of the particle volume using laser diffraction. That is, by measuring particle size distribution using laser diffraction, and calculating the accumulation curve with the total volume of the particle group at 100%, the particle size at the point where the accumulated volume on the accumulation curve reaches 50%. 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 Manufacturing Co., Ltd., LA-920 measuring instrument). In this disclosure, "specific surface area" is a value calculated by measuring particles using the BET multipoint method (constant volume method), obtained using a NOVA4200e (manufactured by Quantachrome Instruments). "Melting temperature" refers to the temperature corresponding to the maximum value of the polymer's melting peak as determined by differential scanning calorimetry (DSC). "Melting flow rate" 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)" refers to the value measured by analyzing the polymer using dynamic viscoelasticity (DMA) analysis. In this disclosure, "polymer" is a compound formed by the polymerization of monomers. That is, a "polymer" has a plurality of units primarily composed of monomers. The term "unit" in a polymer refers to a group of atoms primarily composed of the aforementioned monomers, formed by the polymerization of monomers. The unit can be a unit formed directly through a polymerization reaction, or it can be a unit that is processed by treating the polymer to transform one part of the aforementioned unit into a unit with another structure.In the following, the unit with monomer a as its main component will be simply referred to as "monomer a unit".

[0009] The present invention discloses a method for manufacturing composite sheets by impregnating a thin film containing a thermoplastic tetrafluoroethylene polymer (hereinafter also referred to as "F polymer") into a woven or nonwoven fabric containing a liquid crystal polymer to obtain a composite sheet, wherein the thermoplastic tetrafluoroethylene polymer contains oxygen atoms. The composite sheet manufactured by the method 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. Conventional composite sheets using TEF polymers do not exhibit sufficient low linear expansion. Furthermore, in the composite sheet of Patent Document 1, a thermoplastic TEF polymer is impregnated into a nonwoven fabric containing a liquid crystal polymer, 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 have diligently researched and discovered a composite sheet obtained by impregnating a thin film of a thermoplastic TEF polymer containing oxygen atoms into a woven or nonwoven fabric containing a liquid crystal polymer. This composite sheet exhibits excellent electrical properties and low linear expansion, and also excellent peel strength after lamination with the substrate. The reason for this is not yet clear, but we believe it to be as follows. In the aforementioned impregnation process, the oxygen atoms contained in the tetrafluoroethylene (TEF) polymer affect the configuration of the TEF polymer, thereby improving the adhesion between the TEF polymer and the woven or non-woven fabric of the liquid crystal polymer. We believe that, through this, the linear expansion of the TEF polymer is buffered by the woven or non-woven fabric of the liquid crystal polymer, while the polymer properties of both are exhibited in a highly balanced manner. Furthermore, the oxygen atoms in the TEF polymer can also enhance adhesion to the substrate. We believe that, through these properties, it is possible to provide a material that is effective as a low-transmission-loss material.

[0011] The method for manufacturing the composite sheet disclosed herein uses a woven or non-woven fabric of a liquid crystal polymer. The liquid crystal polymer is preferably a thermotropic liquid crystal polymer that exhibits liquid crystal properties in the molten state. 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 is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 100% by mass or more.

[0012] 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. 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 and 2-hydroxy-6-naphthoic acid. As long as liquid crystal properties are exhibited, in addition to these aromatic dicarboxylic acids, aromatic diols, and aromatic hydroxycarboxylic acids, components such as aliphatic dicarboxylic acids, aliphatic diols, and aliphatic hydroxycarboxylic acids may also be used. Examples of aliphatic diols include ethylene glycol.

[0013] 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 60% by mass or more. The aromatic ring content is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% 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 oxygen atoms and thus high configurational freedom, it has high affinity with the liquid crystal polymer, and therefore easily bonds well with the liquid crystal polymer with a high aromatic ring content.

[0014] 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%

[0015] 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.

[0016] 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 polymer F has oxygen atoms and thus a higher degree of configurational freedom, it readily bonds well with liquid crystal polymers with high load flexural temperatures, i.e., it readily bonds well with liquid crystal polymers with low configurational freedom and difficulty in interacting with other polymers. Also, the load flexural temperature of the liquid crystal polymer should preferably be greater than the melting temperature of polymer F. At this temperature, under high-temperature exposure, a high degree of matrix structure between the liquid crystal polymer and polymer F is easily formed, thereby more easily improving the electrical properties and low linear expansion of the composite sheet. In addition, the load flexural temperature is the value measured according to ASTM D648, with a load set at 0.46 MPa.

[0017] The average fiber diameter of the liquid crystal polymer nonwoven fabric is preferably 0.01~20µm, more preferably 0.05~10µm, and even more preferably 0.1~4µm. The average fiber diameter is determined by observing 200 fibers using an electron microscope, removing the data from the 10 finest and 10 thickest fibers, and then calculating the average value. The unit area volume of the liquid crystal polymer nonwoven fabric is preferably 3~100cm³ / m², more preferably 5~60cm³ / m², and even more preferably 10~40cm³ / m². Furthermore, the unit area volume of the liquid crystal polymer nonwoven fabric is obtained by dividing the unit area weight of the liquid crystal polymer nonwoven fabric by its specific gravity.

[0018] Liquid crystal polymer nonwoven fabrics can be manufactured or pre-made. The molding of liquid crystal polymer nonwoven fabrics can be performed using either dry or wet methods. When forming nonwoven fabrics using a dry method, especially by melting, the crystalline structure generally breaks down at a temperature higher than the glass transition temperature and at a temperature higher than the temperature range where the liquid crystal structure exists in a non-flowing state, thus forming in a temperature range without a defined orientation. Although this varies depending on the chemical structure of the liquid crystal polymer, melt molding can, for example, be performed at a molding temperature of 200-400°C. Melt molding methods for liquid crystal polymer nonwoven fabrics include spunbond and meltblown methods, and for example, the molding method described in International Publication No. 2010 / 098400. The wet process can also form nonwoven fabric by using pre-spun liquid crystal polymer fibers as raw materials, cutting them into short fibers of a certain length, and then forming the obtained short fibers onto a sheet using a papermaking method as illustrated in Japanese Patent Application Publication No. 2012-36538, thereby forming a nonwoven fabric. Liquid crystal polymer nonwoven fabric can be formed by electrospinning a solution containing liquid crystal polymer, or by using the method illustrated in Japanese Patent Application Publication No. 2010-196228, that is, by extending the long filaments of liquid crystal polymer while heating them with a laser. In this case, a nonwoven fabric containing liquid crystal polymer fibers with a fine average fiber diameter can be obtained.

[0019] 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.

[0020] The woven or non-woven fabric of the liquid crystal polymer should preferably undergo surface treatment. This improves the affinity between the woven or non-woven fabric and the F polymer, thereby easily improving the adhesion between them. Furthermore, the F polymer easily penetrates the fine pores of the woven or non-woven fabric of the liquid crystal polymer, thereby easily improving the mechanical properties of the resulting composite sheet. Surface treatments include corona treatment and plasma treatment. Plasma treatments include vacuum plasma treatment and atmospheric pressure plasma treatment, with vacuum plasma treatment being preferable. Vacuum plasma treatment is preferably carried out in a gaseous environment containing argon, oxygen, or a gaseous environment containing hydrogen and nitrogen.

[0021] The manufacturing method disclosed herein uses a film containing an F polymer (hereinafter also referred to as an F film). One type of F polymer may be used, or two or more types may be used. Tetrafluoroethylene-based polymers are polymers containing units (hereinafter also referred to as "TFE units") primarily composed of tetrafluoroethylene (hereinafter also referred to as "TFE units"). From the viewpoint of suitably exhibiting the characteristics brought about by TFE units, the content of TFE units in the tetrafluoroethylene-based polymer should preferably be 50 mol% or more, and more preferably 90 mol% or more, relative to all units in the tetrafluoroethylene-based polymer. The above content can be 99 mol% or less, or 98 mol% or less.

[0022] The F polymer contains oxygen atoms. According to the manufacturing method disclosed herein using the F polymer, a composite sheet with excellent electrical properties and low linear expansion can be obtained. Furthermore, the composite sheet made using the F polymer tends to have excellent adhesion to a substrate. In this disclosure, "polymer containing oxygen atoms" means a polymer that has oxygen atoms intended to be constituent atoms of the polymer; even if oxygen atoms are unavoidably introduced during the manufacturing process, such polymers containing oxygen atoms are not included in the category of "polymers containing oxygen atoms".

[0023] In one state, the F polymer can be a thermoplastic tetrafluoroethylene-based polymer having an oxygen-containing polar group. In this case, the oxygen-containing polar group in the F polymer interacts with the liquid crystal polymer or the substrate, thus the composite sheet readily exhibits excellent low linear expansion and adhesion to the substrate. Examples of oxygen-containing polar groups include hydroxyl-containing groups, carbonyl-containing groups, epoxy-containing groups, and phosphonyl-containing groups, preferably hydroxyl-containing groups or carbonyl-containing groups, with carbonyl-containing groups being more preferred. The F polymer can have one or more types of oxygen-containing polar groups. The hydroxyl-containing group is preferably a group containing an alcoholic hydroxyl group, more preferably -CF2CH2OH and -C(CF3)2OH. The carbonyl group should preferably be a carboxyl group, alkoxycarbonyl group, amide group, isocyanate group, carbamate group (-OC(O)NH2), acid anhydride residue (-C(O)OC(O)-), amide imine residue (-C(O)NHC(O)-, etc.) and carbonate group (-OC(O)O-), with acid anhydride residue being more preferred.

[0024] The number of oxygen-containing polar groups in polymer F is preferably 10 to 5000 per 1×106 main chain carbons, more preferably 100 to 3000. In addition, the number of oxygen-containing polar groups can be quantified by means of the polymer composition or by means of the method described in International Publication No. 2020 / 145133.

[0025] The oxygen-containing polar group can be contained in the monomer-based unit of the F polymer, or it can be contained in the terminal group of the main chain of the F polymer, 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. On the other hand, the F polymer or its film can also be a surface-treated product that has not undergone plasma treatment or ionizing radiation treatment.

[0026] 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 viewpoint that the resulting composite sheet has excellent adhesion, NAH is more preferred.

[0027] The F polymer having oxygen-containing polar groups is preferably polytetrafluoroethylene (PTFE), a polymer containing TFE units and ethylene-based units (ETFE), a polymer containing TFE units and propylene-based units, a polymer containing TFE units and perfluoro(alkyl vinyl ether) (PAVE)-based units (PAVE units) (PFA), or a polymer containing TFE units and hexafluoropropylene-based units (HFP units) (FEP), preferably PFA and FEP having oxygen-containing polar groups, and more preferably PFA having oxygen-containing polar groups. These polymers may also further contain units based on other comonomers.

[0028] The F polymer is preferably a polymer containing carbonyl groups, including TFE units and PAVE units; more preferably, it contains TFE units, PAVE units, and units mainly composed of monomers containing carbonyl groups; even more preferably, it is a polymer containing TFE units, PAVE units, and units mainly composed of monomers containing carbonyl groups, and containing such units in the following order: 90-99 mol%, 0.99-9.97 mol%, and 0.01-3 mol%, relative to all units; or, containing such units in the following order: 87-96 mol%, 0.99-9.97 mol%, and 3-6 mol%, relative to all units. The former is preferable because it readily yields composite sheets with excellent heat resistance. The latter is preferable because it readily yields composite sheets with excellent adhesion to woven or nonwoven fabrics of the F polymer and the liquid crystal polymer. Specific examples of the F polymer can be found in the polymer described in International Publication No. 2018 / 016644.

[0029] In another embodiment, the F polymer can be a hot-melt tetrafluoroethylene polymer containing PAVE units. In this case, due to the presence of PAVE units, the configurational freedom of the F polymer can be increased while maintaining the excellent electrical properties of the tetrafluoroethylene polymer. This results in the composite sheet readily possessing excellent electrical properties, low linear expansion, and adhesion to the substrate, which is preferable. The hot-melt tetrafluoroethylene polymer containing PAVE units can be one without carbonyl groups, or it can be one without units primarily composed of monomers containing carbonyl groups. PAVE is preferably CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (hereinafter also denoted as PPVE), with PPVE being more preferred.

[0030] In the F polymer containing PAVE units, the content of PAVE units among all units in the F polymer should preferably be 1.0 mol% or more, more preferably 2.0 mol% or more, and even more preferably 2.3 mol% or more. It can be inferred that if the content of PAVE units is above the aforementioned lower limit, the melt flowability of the F polymer will be improved, and it will be easier to form microspheres, thereby improving the adhesion. From the viewpoint of heat resistance, the content of PAVE units among all units in the F polymer should preferably be 10.0 mol% or less, more preferably 5.0 mol% or less.

[0031] The F polymer, which contains PAVE units and in which the content of PAVE units in all units is 2.0 mol% or more, is preferably terminally fluorinated. The number of oxygen-containing polar groups in the F polymer, calculated by the number of carbon atoms in the main chain, is preferably less than 500 per 1×10⁶ carbon atoms, more preferably less than 100, and even more preferably 0. In this case, the crystallization of the F polymer promotes the formation of a lamellar structure and facilitates the generation of microspheres, thereby improving the adhesion to woven or non-woven fabrics or substrates of the liquid crystal polymer. The polymer is preferably composed of TFE units and PPVE units, with the content of TFE units being 95.0~98.0 mol% and the content of PPVE units being 2.0~5.0 mol%.

[0032] 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.

[0033] From the perspective of improving the heat resistance of composite sheets, the melting temperature of polymer F should preferably be above 200°C, and more preferably above 260°C. From the perspective of effectively impregnating liquid crystal polymers into woven or nonwoven fabrics, the melting temperature of polymer F should preferably be below 325°C, and more preferably below 320°C.

[0034] From the viewpoint of improving the heat resistance of composite sheets, 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 woven or nonwoven fabrics with liquid crystal polymers, the glass transition point of polymer F should preferably be below 150°C, and more preferably below 125°C.

[0035] From the perspective of improving the electrical properties and heat resistance of composite sheets, the fluorine content of polymer F should preferably be above 70% by mass, and more preferably 72-76% by mass. In addition, the fluorine content is determined from the composition of the polymer.

[0036] 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 the presence of oxygen atoms, 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.

[0037] The F film may be composed solely of the F polymer, or it may contain components other than the F polymer. The content of the F polymer in the F film is preferably 50% by mass or more, and more preferably 80% by mass. The content of the F polymer is preferably 100% by mass or less.

[0038] The F film may also contain polymers different from the F polymer (hereinafter also referred to as "different polymers"). Examples of dissimilar polymers include: tetrafluoroethylene polymers without oxygen atoms, non-thermally fusible tetrafluoroethylene polymers, epoxy resins, polyimide resins, polyamide precursors of polyimide, polyamide-imide resins, precursors of polyamide-imide resins, acrylic resins, phenolic resins, liquid crystal polyester resins, polyolefin resins, modified polyphenylene ether resins, polyfunctional cyanate resins, polyfunctional maleimide-cyanate resins, polyfunctional maleimide resins, vinyl ester resins, urea resins, diallyl phthalate resins, melamine resins, guanidine resins, melamine-urea cocondensation resins, styrene resins, polycarbonate resins, polyarylate resins, polyurethane, polyaryl urethane, polyamide resins, polyetheramide, polyphenylene sulfide, polyaryl ether ketone, polyphenylene ether, and polytetrafluoroethylene. The dissimilar polymers should preferably be non-thermally meltable tetrafluoroethylene-based polymers and aromatic polymers. One or more dissimilar polymers may be used.

[0039] Examples of tetrafluoroethylene polymers without oxygen atoms include PTFE, ETFE, polymers containing TFE units and propylene-based units, and FEP. These polymers may further contain units based on other comonomers, or they may not. However, the polymers exemplified above do not have oxygen atoms. Examples of non-meltable tetrafluoroethylene polymers include non-meltable PTFE.

[0040] Aromatic polymers are preferably precursors of aromatic polyimides, aromatic polyamides, aromatic polyamides, and aromatic polyamides. Specific examples of aromatic polymers include: the "UPIA-AT" series (manufactured by Ube Industries), the "Neopulim" series (manufactured by MITSUBISHI GAS CHEMICAL), the "SPIXAREA" series (manufactured by SOMAR), the "Q-PILON" series (manufactured by PI Technology Research Institute), the "WINGO" series (manufactured by Wingo Technology), the "Tohmide" series (manufactured by T&K TOKA), the "KPI-MX" series (manufactured by Kawamura Industries), "HPC-1000", and "HPC-2100D" (all manufactured by SHOWA DENKO MATERIALS).

[0041] When the F film contains a dissimilar polymer, the content of the dissimilar polymer relative to the total mass of the F film is preferably 0.1~60% by mass, more preferably 1~40% by mass. When the dissimilar polymer is a non-thermally fusible tetrafluoroethylene-based polymer, the content of the non-thermally fusible tetrafluoroethylene-based polymer relative to the total mass of the F film is preferably 10~60% by mass, more preferably 20~50% by mass. When the dissimilar polymer is an aromatic polymer, the content of the aromatic polymer relative to the total mass of the F film is preferably 0.1~30% by mass, more preferably 1~10% by mass.

[0042] The F-film may also contain inorganic fillers. The inorganic fillers are preferably carbon fillers, inorganic nitride fillers, or inorganic oxide fillers, with carbon fiber fillers, glass fiber fillers, boron nitride fillers, aluminum nitride fillers, beryllium oxide fillers, silica fillers, silash fillers, talc fillers, cerium oxide fillers, alumina fillers, magnesium oxide fillers, zinc oxide fillers, or titanium oxide fillers being more suitable. Boron nitride fillers or silica fillers are even more suitable. One type of inorganic filler may be used, or two or more types may be used.

[0043] The D50 of inorganic packing 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 packing should preferably be 1~20m2 / g.

[0044] The surface of the inorganic filler 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.

[0045] The shape of inorganic packing material should preferably be spherical, needle-like, fibrous, or plate-like, and preferably spherical, scaly, or layered, more preferably spherical or scaly. Spherical inorganic packing material should preferably be substantially spherical. "Substantially spherical" means that, when observed using a scanning electron microscope (SEM), the proportion of inorganic packing material with a minor axis to major axis ratio of 0.7 or higher is 95% or higher. The aspect ratio of non-spherical inorganic packing material should preferably be 2 or higher, and preferably 5 or higher. The aspect ratio should preferably be 10,000 or lower.

[0046] Specific examples of silica fillers 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 fillers include the "FINEX" series (manufactured by Sakai Chemical Industry Co., Ltd.). Specific examples of titanium oxide fillers include the "TIPAQUE (registered trademark)" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Tayca Corporation). Specific examples of talc fillers include the "SG" series (manufactured by Nippon Talc). Specific examples of block talc fillers include the "BST" series (manufactured by Nippon Talc). Specific examples of boron nitride fillers 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).

[0047] When the F film contains inorganic fillers, the content of inorganic fillers relative to the total mass of the F film should preferably be 1 to 50% by mass, and more preferably 5 to 20% by mass.

[0048] In addition to the above-mentioned components, the F film may also contain: organic fillers, thixotropic agents, defoamers, silane coupling agents, dehydrating agents, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive materials, mold release agents, surface treatment agents, viscosity modifiers, flame retardants, and other components. The content of components other than the F polymer, polymers different from the F polymer, and inorganic fillers in the total mass of the F film should preferably be 0 to 10% by mass.

[0049] The thickness of the F film is preferably 1~200µm. The F film can also be surface-treated with a silane coupling agent. As the silane coupling agent, the same silane coupling agent as described above that can also be used for the surface treatment of inorganic fillers can be used. In this case, it is preferable to easily improve the adhesion of the woven or nonwoven interface between the F polymer and the liquid crystal polymer, or the adhesion of the composite sheet to the substrate.

[0050] The F-film can also be formed by melt extrusion of the F polymer. In this case, sheets containing dissimilar polymers, inorganic fillers, or other components can be formed simply by melt-kneading and extruding the F polymer with the dissimilar polymer, inorganic fillers, or other components. The F-film can also be formed from a dispersion of particles containing the F polymer and a liquid dispersion medium. For example, the F-film can also be formed by applying a dispersion of F polymer particles to the surface of a temporary substrate, heating the temporary substrate to which the dispersion has been applied, and obtaining a laminate having the temporary substrate and a layer containing the F polymer, and then removing the temporary substrate from the laminate. The heating of the temporary substrate to which the dispersion has been applied should preferably be performed in two stages: heating to remove the liquid dispersion medium and heating to calcify the F polymer. Examples of temporary substrates include metal foils and resin films, and methods for removing the temporary substrate include peeling and etching. At this point, sheets containing dissimilar polymers, inorganic fillers, or other components can be formed simply by using a dispersion containing particles of polymer F and a liquid dispersion medium, and further containing dissimilar polymers, inorganic fillers, or other components.

[0051] When the volume concentration of the liquid crystal polymer in the woven or nonwoven fabric is 1, the ratio of the volume concentration of polymer F in the composite sheet to the volume concentration of the liquid crystal polymer in the woven or nonwoven fabric should preferably be 0.6 or more, and more preferably 1 or more. This ratio should preferably be 4 or less, and more preferably 3 or less.

[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, more preferably less than 100µm, and may also be less than 50µm. The composite sheet may 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 / ℃, more preferably below 50 ppm / ℃, even more preferably below 30 ppm / ℃, and especially preferably below 20 ppm / ℃. The lower limit of the coefficient of linear expansion is, for example, 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] The method for manufacturing the composite sheet disclosed herein involves impregnating a film containing an F polymer into a woven or non-woven fabric of a liquid crystal polymer. Impregnation can be performed by impregnating one surface of the woven or non-woven fabric of the liquid crystal polymer with the F film, or by impregnating both surfaces of the woven or non-woven fabric of the liquid crystal polymer with the F film. Impregnation is preferably performed by heat-pressing the film containing the F polymer with the aforementioned woven or non-woven fabric of the liquid crystal polymer. In this case, the F polymer easily penetrates between the fibers of the woven or non-woven fabric of the liquid crystal polymer. As a result, it is preferable to easily improve the adhesion between the woven or non-woven fabric of the liquid crystal polymer and the F polymer.

[0057] Hot pressing can be performed, for example, by laminating the aforementioned film with a woven or non-woven fabric of the liquid crystal polymer using the following methods: 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 of easily and effectively impregnating the woven or non-woven fabric of the liquid crystal polymer, the pressing temperature of hot pressing is preferably above -30°C of the melting temperature of the polymer F, and more preferably above the melting temperature of the polymer F. The pressing temperature is preferably below +30°C of the melting temperature of the polymer F. The hot pressing temperature is preferably 280~380°C, and more preferably 300~330°C.

[0058] The pressing pressure for hot pressing should preferably be 0.2 MPa or higher, more preferably 1 MPa or higher, and even more preferably 10 MPa or higher. The pressing pressure should preferably be 1000 MPa or lower, more preferably 300 MPa or lower. 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 lower, more preferably 1 kPa or lower.

[0059] The composite sheet can also be laminated with a substrate to form a laminate. The composite sheet disclosed herein readily exhibits excellent adhesion to the substrate. Furthermore, due to its excellent low linear expansion, the composite sheet disclosed herein is not easily peeled off from the substrate even when the laminate is subjected to high-temperature processing. 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.

[0060] The shape of the substrate can be planar, curved, or uneven. Furthermore, the shape of the substrate can 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 can be surface-treated with a silane coupling agent or plasma. The method of bonding the laminated composite sheet to the substrate can be a hot-pressing method. The hot-pressing method can be the same as the hot-pressing method used in the manufacture of the composite sheet described above.

[0061] In the method for manufacturing the composite sheet disclosed herein, a composite sheet can also be formed by impregnating an F film with a woven or non-woven fabric of a liquid crystal polymer, and simultaneously laminated with a substrate to obtain a laminate of the composite sheet and the substrate. For example, by sequentially stacking the woven or non-woven fabric of the liquid crystal polymer, the F film, and the substrate and then hot-pressing them together, a laminate of the composite sheet and the substrate can be obtained. The hot-pressing method can be the same as the hot-pressing method used in the manufacturing of the composite sheet described above. In the method for manufacturing the composite sheet disclosed herein, a copper-clad laminate formed by impregnating an F film with a woven or non-woven fabric of a liquid crystal polymer, and simultaneously laminated with a copper foil, can be obtained. For example, by sequentially stacking the woven or non-woven fabric of the liquid crystal polymer, the F film, and the copper foil and then hot-pressing them together, a laminate of the composite sheet and the copper foil can be obtained. The hot-pressing method can be the same as the hot-pressing method used in the manufacturing of the composite sheet described above. Alternatively, a separate composite sheet can be obtained by removing the substrate from the laminate. The peel strength between the composite sheet and the substrate in the laminate should preferably be 10~100 N / cm, more preferably 12~100 N / cm.

[0062] There are no particular limitations on the applications of composite sheets. Composite sheets can be effectively used as antenna parts, printed circuit boards, aircraft parts, automotive parts, sporting goods, food industry supplies, heat dissipation parts, etc. Specifically, they can be effectively used as: wire sheathing materials (aircraft wires, etc.), enameled wire sheathing materials for motors used in 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, bearing 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 under 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, engineering thin films for semiconductor sintering processes, and release films for high-temperature sealing of power semiconductors, etc.

[0063] Composite sheets are suitable for applications where the desired properties are desired due to their excellent electrical properties and low linear expansion. For example, composite sheets are suitable for use as materials in copper-clad laminates and other printed wiring boards.

[0064] The composite sheet in one embodiment of this disclosure comprises a woven or nonwoven fabric containing a liquid crystal polymer and an F polymer, wherein the F polymer is impregnated into the woven or nonwoven fabric containing the liquid crystal polymer. The characteristics of the composite sheet are applicable to the foregoing. The composite sheet is preferably manufactured by the aforementioned manufacturing method of this disclosure.

[0065] Examples The following examples illustrate the implementation of the present disclosure in detail, but the implementation of the present disclosure is not limited thereto.

[0066] 1. Preparation of each component [film] Film 1: Film of polymer 1 (melting temperature: 300℃, melt flow rate: 20g / 10min) (thickness: 12µm), which contains TFE units, NAH units and PPVE units in sequence at 97.9 mol%, 0.1 mol%, and 2.0 mol%, and has anhydride groups with 1000 carbonyl groups per 1×106 main chain carbons. Film 2: Film of polymer 2 (melting temperature: 260℃, melt flow rate: 20g / 10min) (thickness: 12µm), which contains TFE units, NAH units and PPVE units in sequence at 94.9 mol%, 0.1 mol%, and 2.0 mol%, respectively. A film (thickness: 12µm) of polymer 3 (melting temperature: 305℃, melt flow rate: 25g / 10min) containing TFE, NAH and PPVE units, and having 1000 carbonyl groups per 1×106 main chain carbons, comprising 97.5 mol% and 2.5 mol% of TFE and PPVE units respectively, and substantially lacking terminally fluorinated functional groups (i.e., substantially lacking functional groups intended to be part of the polymer). Film 4: A film (thickness: 12µm) of polymer 4 (melt temperature: 260℃, melt flow rate: 24g / 10min), containing TFE units and HFP units in sequence at 75 mol% and 25 mol%, and substantially lacking oxygen atoms (i.e., lacking oxygen atoms intended to be constituent atoms of the polymer). Film 5: A film (thickness: 50µm) of polymer 1 (melt temperature: 300℃, melt flow rate: 20g / 10min), containing TFE units, NAH units, and PPVE units in sequence at 97.9 mol%, 0.1 mol%, and 2.0 mol%, and having 1000 carbonyl-containing anhydride groups per 1×106 carbon atoms in the main chain.

[0067] [Nonwoven Fabrics of Liquid Crystal Polymers] Nonwoven Fabric 1: A film-like nonwoven fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or more (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 7µm, unit area volume: 9.9cm3 / m2) Nonwoven Fabric 2: A film-like nonwoven fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or more (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 7µm, unit area volume: 28.2cm3 / m2) Nonwoven Fabric 3: A film-like nonwoven fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or more (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 3µm, unit area volume: 4.2cm3 / m2) Nonwoven fabric 4: A film-like nonwoven fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or more (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 3µm, unit area volume: 16.9cm3 / m2)

[0068] [Cloth of Liquid Crystal Polymer] Cloth 1: Plain weave fabric of liquid crystal aromatic polyester with an aromatic ring content of 60% by mass or more (load flexural temperature: 300℃, specific gravity: 1.42g / cm3, fiber diameter: 7µm, thickness: 123µm, unit area volume: 32cm3 / m2, warp density: 20 yarns / cm, weft density: 20 yarns / cm) Cloth 2: Plain weave fabric of liquid crystal aromatic polyester (load flexural temperature: 350℃, unit area weight: 45g / m2, manufactured by Kuraray Co., Ltd. "Vectran (registered trademark)") [Copper Foil] Copper Foil 1: Copper foil (thickness: 18µm, average roughness of ten points on the surface: 0.8µm)

[0069] 2. Manufacturing of copper-clad laminate [Example 1] Two films 1 are laminated on each side of a nonwoven fabric 1, and copper foil 1 is further laminated on both sides to obtain a laminate 1 having copper foil 1 / film 1 / film 1 / nonwoven fabric 1 / film 1 / film 1 / copper foil 1 in sequence. The laminate 1 is hot-pressed under reduced pressure at a temperature of 320°C, a pressure of 10MPa, and a time of 10 minutes, so that the film 1 is impregnated from both surfaces of the nonwoven fabric 1 to obtain a copper-clad laminate 1 (thickness: 94µm) containing nonwoven fabric 1, polymer 1 impregnated with nonwoven fabric 1, and copper foil 1 laminated on both outer sides. [Example 2] One film 1 is laminated on each side of a nonwoven fabric 2, and copper foil 1 is further laminated on both outer sides to obtain a laminate 2 having copper foil 1 / film 1 / nonwoven fabric 2 / film 1 / copper foil 1 in sequence. The laminate 2 was hot-pressed under reduced pressure at a temperature of 320°C, a pressure of 10 MPa, and a time of 10 minutes, so that the film 1 impregnated from both surfaces of the nonwoven fabric 2, thereby obtaining a copper-clad laminate 2 (thickness: 88 µm) containing the nonwoven fabric 2, the polymer 1 impregnated with the nonwoven fabric 2, and copper foils laminated on both outer sides thereof. [Example 3] Except that the nonwoven fabric 1 was replaced with nonwoven fabric 3, a copper-clad laminate 3 (thickness: 89 µm) was obtained in the same manner as in Example 1. [Example 4] Except that the nonwoven fabric 1 was replaced with nonwoven fabric 4, a copper-clad laminate 4 (thickness: 77 µm) was obtained in the same manner as in Example 2. [Example 5] Except that the film 1 was replaced with film 2 and the hot-pressing temperature was set to 290°C, a copper-clad laminate 5 (thickness: 94 µm) was obtained in the same manner as in Example 1. [Example 6] A copper-clad laminate 6 (thickness: 94µm) was obtained in the same manner as in Example 1, except that film 1 was replaced with film 3. [Example 7] A copper-clad laminate 7 (thickness: 94µm) was obtained in the same manner as in Example 1, except that film 1 was replaced with film 4. [Example 8] A copper-clad laminate 8 (thickness: 130µm) was obtained in the same manner as in Example 1, except that film 1 was replaced with film 5 and nonwoven fabric 1 was replaced with woven fabric 1. [Example 9] A copper-clad laminate 9 (thickness: 130µm) was obtained in the same manner as in Example 1, except that film 1 was replaced with film 5 and nonwoven fabric 1 was replaced with woven fabric 2.

[0070] 3. Manufacturing of composite sheet: For copper-clad laminate 1, copper foil is removed by etching with ferric chloride aqueous solution, and then dried by heating in an oven at 100°C for 1 hour to obtain composite sheet 1. Except that copper-clad laminate 1 is changed to copper-clad laminate 2 to 9, composite sheets 2 to 9 are obtained in the same manner as composite sheet 1.

[0071] 4. Evaluation 4-1. Peel Strength Rectangular test pieces, 100 mm long and 10 mm wide, were cut from each copper-clad laminate. After fixing the test piece at a position 50 mm from one end along its length, the copper foil was peeled from the composite sheet at a stretching speed of 50 mm / min from one end along its length at a 90° angle relative to the test piece. The maximum load causing the peel was taken as the peel strength (N / cm). The peel strengths of the copper-clad laminates are as follows: [Evaluation Criteria] A: 12 N / cm or more. B: 10 N / cm or more but less than 12 N / cm. C: Less than 10 N / cm.

[0072] 4-2. Coefficient of Linear Expansion For each composite sheet, 180mm square test pieces were cut. Following the testing method specified in JIS C6471:1995, the coefficient of linear expansion of the test pieces was measured in the range of 25°C to 260°C. The results show that the coefficient of linear expansion of the composite sheets is as follows: [Evaluation Criteria] AA: Below 20ppm / °C. A: Greater than 20ppm / °C and below 30ppm / °C. B: Greater than 30ppm / °C and below 50ppm / °C. C: Greater than 50ppm / °C.

[0073] 4-3. Electrical Properties Samples measuring 10cm in length and 5cm in width were cut from each composite sheet. The relative permittivity and dielectric tangent were measured using the SPDR (Split-Post Dielectric Resonator) method (measurement frequency: 10GHz). The electrical properties of the composite sheets are as follows. Furthermore, composite sheet 7 has a high coefficient of linear expansion and low adhesion to the copper foil in the copper-clad laminate 7; therefore, no measurement was performed. [Evaluation Criteria] AA: Relative permittivity ≤ 2.2, and dielectric tangent < 0.0010. A: Relative permittivity ≤ 2.2, and dielectric tangent > 0.0010 and < 0.0020; or relative permittivity > 2.2 and ≤ 2.4, and dielectric tangent < 0.0010. B: The relative permittivity is greater than 2.2 and less than 2.4, and the dielectric tangent is greater than 0.0010 and less than 0.0020.

[0074] Table 1 below summarizes and displays the materials used to manufacture each copper-clad laminate and composite sheet, the thickness of the copper-clad laminate, and the evaluation results.

[0075] [Table 1]

[0076] As shown in the table, composite sheets 1-6, 8 and 9 exhibit excellent electrical properties and low linear expansion, especially composite sheet 9, which exhibits excellent low linear expansion. Furthermore, composite sheets 1-6, 8 and 9 also possess excellent peel strength from copper foil.

[0077] This specification is incorporated herein by reference to the entire disclosure of Japanese Patent Application Nos. 2021-119740 and 2021-172597. 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 and individually described by reference.

Claims

1. A method for manufacturing a composite sheet, comprising impregnating a woven or nonwoven fabric containing a hot-melt tetrafluoroethylene polymer with a liquid crystal polymer to obtain a composite sheet, wherein the hot-melt tetrafluoroethylene polymer has oxygen atoms; the aforementioned tetrafluoroethylene polymer has an oxygen-containing polar group, wherein the aforementioned oxygen-containing polar group is a hydroxyl-containing group or a carbonyl-containing group.

2. The manufacturing method of claim 1, wherein the melt flow rate of the aforementioned tetrafluoroethylene polymer is 1 to 30 g / min under a load of 49 N.

3. The manufacturing method as claimed in claim 1 or 2, wherein the melting temperature of the aforementioned tetrafluoroethylene polymer is above 260°C.

4. The manufacturing method of claim 1 or 2, wherein the aforementioned tetrafluoroethylene polymer has oxygen-containing polar groups, and the number of the aforementioned oxygen-containing polar groups in the aforementioned tetrafluoroethylene polymer is calculated based on the number of carbon atoms in the main chain, with each 1×10⁶ main chain carbon atom having 10 to 5000 atom numbers.

5. The manufacturing method of claim 1 or 2, wherein the aforementioned tetrafluoroethylene polymer comprises units mainly composed of perfluoro(alkyl vinyl ether), and the content of the aforementioned units mainly composed of perfluoro(alkyl vinyl ether) in all units of the aforementioned tetrafluoroethylene polymer is greater than 2 moles.

6. The manufacturing method of claim 1 or 2, wherein the load flexural temperature of the aforementioned liquid crystal polymer is 240°C or higher.

7. The manufacturing method of claim 1 or 2, wherein the aforementioned liquid crystal polymer comprises a liquid crystal aromatic polyester.

8. The manufacturing method as described in claim 7, wherein the aromatic ring content of the aforementioned aromatic polyester is 55% by mass or more.

9. The manufacturing method of claim 1 or 2, wherein the thickness of the aforementioned composite sheet is less than 200µm.

10. The manufacturing method of claim 1 or 2, wherein the aforementioned film is heat-pressed onto the aforementioned woven or non-woven fabric to impregnate the aforementioned film.

11. The manufacturing method of claim 10, wherein the pressing temperature of the aforementioned hot pressing is within ±30°C of the melting temperature of the aforementioned tetrafluoroethylene polymer.

12. The manufacturing method of claim 10, wherein the pressing pressure of the aforementioned hot pressing is 1 MPa or more.

13. The manufacturing method of claim 10, wherein the aforementioned heat pressing is performed under reduced pressure.

14. A composite sheet comprising a woven or nonwoven fabric containing a liquid crystal polymer and a thermoplastic tetrafluoroethylene polymer having oxygen atoms, wherein the thermoplastic tetrafluoroethylene polymer is impregnated in the woven or nonwoven fabric; wherein the tetrafluoroethylene polymer has an oxygen-containing polar group, and the oxygen-containing polar group is a hydroxyl-containing group or a carbonyl-containing group.