Method for manufacturing a composite sheet and composite sheet

Abstract

Provided are: a method for producing a composite sheet, that yields a composite sheet by impregnating a woven or nonwoven fabric of a liquid-crystal polymer with a film comprising a heat-fusible tetrafluoroethylene polymer that contains the oxygen atom; and said composite sheet.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a composite sheet and to a composite sheet. [Background technology]

[0002] In recent years, the field of information and communication has seen a demand for improved performance of materials used in printed circuit boards and the like due to advancements in communication technologies such as high-frequency communication. Fluoropolymers, particularly tetrafluoroethylene polymers, are suitable for use in printed circuit boards because they possess excellent electrical properties and heat resistance. Patent Document 1 describes a composite sheet comprising a liquid crystal polymer nonwoven fabric on the opposing surfaces of a layer containing a liquid crystal polymer and a layer containing a tetrafluoroethylene polymer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-119378 [Overview of the project] [Problems that the invention aims to solve]

[0004] Tetrafluoroethylene polymers have excellent electrical properties but a high coefficient of thermal expansion. Therefore, when processing laminates of composite sheets and substrates as described in Patent Document 1 at high temperatures, for example, when subjected to a reflow process in the manufacture of wiring boards, the composite sheet tends to expand due to heat, causing the composite sheet and substrate to delaminate. This disclosure relates to the provision of a composite sheet with excellent electrical properties and low thermal expansion, and a method for manufacturing the composite sheet. [Means for solving the problem]

[0005] The means for solving the above problems include the following embodiments. <1> A method for producing a composite sheet, comprising impregnating a liquid crystal polymer woven or nonwoven fabric with a film containing a heat-meltable tetrafluoroethylene polymer having oxygen atoms to obtain a composite sheet. <2> The melt flow velocity of the tetrafluoroethylene polymer is 1 to 30 g / min under a load of 49 N. <1> The manufacturing method described above. <3> The melting temperature of the tetrafluoroethylene polymer is 260°C or higher. <1> or <2> The manufacturing method described above. <4> The tetrafluoroethylene polymer has an oxygen-containing polar group, and the oxygen-containing polar group is a hydroxyl group-containing group or a carbonyl group-containing group. <1> ~ <3> A manufacturing method described in any one of the following items. <5> The tetrafluoroethylene polymer has oxygen-containing polar groups, and the number of oxygen-containing polar groups in the tetrafluoroethylene polymer is equal to the number of carbon atoms in the main chain (1 × 10). 6 Each unit contains 10 to 5000 pieces. <1> ~ <4> A manufacturing method described in any one of the following items. <6> The tetrafluoroethylene polymer contains units based on perfluoro(alkyl vinyl ether), and the content of the units based on perfluoro(alkyl vinyl ether) in relation to the total units in the tetrafluoroethylene polymer is greater than 2 mol%. <1> ~ <5> A manufacturing method described in any one of the following items. <7> The load deflection temperature of the liquid crystal polymer is 240°C or higher. <1> ~ <6> A manufacturing method described in any one of the following items. <8> The liquid crystal polymer includes a liquid crystal aromatic polyester. <1> ~ <7> Noi The manufacturing method described in item 1. <9> The aromatic ring content of the aforementioned aromatic polyester is 55% by mass or more. <8> The manufacturing method described above. <10> The thickness of the composite sheet is 200 μm or less. <1> ~ <9> A manufacturing method described in any one of the following items. <11> The film and the woven or nonwoven fabric are heat-pressed together to impregnate the film. <1> ~ <10> A manufacturing method described in any one of the following items. <12> The manufacturing method according to <11>, wherein the crimping temperature in the thermocompression bonding is within ±30°C of the melting temperature of the tetrafluoroethylene-based polymer. <13> The manufacturing method according to <11> or <12>, wherein the crimping pressure in the thermocompression bonding is 1 MPa or more. <14> The manufacturing method according to any one of <11> to <13>, wherein the thermocompression bonding is performed under reduced pressure. <15> A composite sheet containing a woven or non-woven fabric of a liquid crystal polymer and a heat-meltable tetrafluoroethylene-based polymer having an oxygen atom, which is impregnated in the woven or non-woven fabric.

Advantages of the Invention

[0006] According to the present disclosure, there are provided a manufacturing method and a composite sheet of a composite sheet excellent in electrical characteristics and low linear expansion properties.

Embodiments for Carrying Out the Invention

[0007] Hereinafter, embodiments for carrying out the present disclosure will be described in detail. However, the embodiments of the present disclosure are not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the embodiments of the present disclosure.

[0008] In the present disclosure, in the numerical range indicated by "~", the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content or content rate of each component means the total content or content rate of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may include a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for a mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the "composite sheet" is a sheet including a polymer and a woven or non-woven fabric of a liquid crystal polymer. In the present disclosure, the terms "film" and "sheet" are used interchangeably, and their thickness is not particularly limited. In the present disclosure, the term "layer" includes not only the case where the layer or film is formed over the entire area when observing the area where the layer or film exists, but also the case where it is formed only in a part of the area. In the present disclosure, the term "lamination" indicates stacking layers, and two or more layers may be bonded, and two or more layers may be detachable. In the present disclosure, the "average particle diameter (D50)" is the volume-based cumulative 50% diameter of particles determined by the laser diffraction / scattering method. That is, the particle size distribution is measured by the laser diffraction / scattering method, the cumulative curve is obtained with the total volume of the particle population as 100%, and it is the particle diameter at the point where the cumulative volume becomes 50% on the cumulative curve. The D50 of the particles is determined by analyzing them by the laser diffraction / scattering method using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba, Ltd., LA-920 measuring instrument) with the particles dispersed in water. In the present disclosure, the "specific surface area" is a value calculated by measuring particles by the gas adsorption (constant volume method) BET multi-point method, and is determined using NOVA4200e (manufactured by Quantachrome Instruments). In the present disclosure, the "melting temperature" is the temperature corresponding to the maximum value of the melting peak of the polymer measured by the differential scanning calorimetry (DSC) method. In the present disclosure, the "melt flow rate" means the melt mass flow rate of the polymer defined in JIS K 7210-1:2014 (ISO1133-1:2011). In the present disclosure, the "glass transition point (Tg)" is a value measured by analyzing the polymer by the dynamic viscoelasticity measurement (DMA) method. In the present disclosure, a "polymer" is a compound formed by polymerization of monomers. That is, a "polymer" has a plurality of units based on monomers. In this disclosure, "unit" in a polymer means an atomic group based on a monomer formed by the polymerization of a monomer. A unit may be a unit directly formed by a polymerization reaction, or a unit in which a portion of the unit is converted to a different structure by processing the polymer. Hereinafter, a unit based on monomer a will also be simply referred to as "monomer a unit".

[0009] The present disclosure is a method for manufacturing a composite sheet, which involves impregnating a woven or nonwoven fabric of a liquid crystal polymer with a film containing a heat-meltable tetrafluoroethylene polymer having oxygen atoms (hereinafter also referred to as "F polymer") to obtain a composite sheet. The composite sheet manufactured by the present disclosure has excellent electrical properties and low linear expansion.

[0010] Generally, tetrafluoroethylene polymers have excellent electrical properties such as low dielectric constant and low dielectric loss tangent, but they have a large coefficient of linear expansion. Conventional composite sheets using tetrafluoroethylene polymers do not have sufficient low linear expansion properties. Furthermore, in the composite sheet of Patent Document 1, the tetrafluoroethylene polymer is impregnated into a liquid crystal polymer nonwoven fabric, and the two are merely intertwined and bonded together, resulting in insufficient adhesion at the interface. As a result, the laminate of the composite sheet and the substrate had problems such as thermal expansion when processed at high temperatures, causing it to delaminate from the substrate. The inventors conducted thorough research and found that a composite sheet obtained by impregnating a liquid crystal polymer woven or nonwoven fabric with a film of a heat-meltable tetrafluoroethylene polymer containing oxygen atoms exhibits excellent electrical properties and low linear expansion, as well as excellent peel strength when laminated with a substrate. The reason for this is not entirely clear, but it is thought to be as follows. In the aforementioned impregnation process, oxygen atoms contained in the tetrafluoroethylene polymer affect the conformation of the tetrafluoroethylene polymer, improving the adhesion at the interface between the tetrafluoroethylene polymer and the liquid crystal polymer woven or nonwoven fabric. As a result, the linear expansion of the tetrafluoroethylene polymer is buffered by the liquid crystal polymer woven or nonwoven fabric, and it is believed that the polymer properties of both materials are expressed in a highly balanced manner. Furthermore, the oxygen atoms in the tetrafluoroethylene polymer are thought to improve adhesion to the substrate, and these properties are expected to provide a material that is useful, for example, as a low transmission loss material.

[0011] The method for manufacturing the composite sheet of this disclosure uses a woven or nonwoven fabric of a liquid crystal polymer. A thermotropic liquid crystal polymer that exhibits liquid crystal properties in a molten state is preferred as the liquid crystal polymer. One type of liquid crystal polymer may be used, or two or more types may be used. The liquid crystal polymer woven or nonwoven fabric may be any woven or nonwoven fabric containing liquid crystal polymer, and may also contain other materials. The liquid crystal polymer content relative to the total mass of the liquid crystal polymer woven or nonwoven fabric is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 100% by mass.

[0012] As the liquid crystal polymer, liquid crystal polyester is preferred. The liquid crystal polyester may be liquid crystal polyesteramide, liquid crystal polyester ether, liquid crystal polyester carbonate, or liquid crystal polyester imide. As the liquid crystal polyester, liquid crystal aromatic polyesters are preferred, and specifically, examples include polycondensates of aromatic dicarboxylic acids and aromatic diols or aromatic hydroxycarboxylic acids, and polycondensates of aromatic dicarboxylic acids, aromatic diols and aromatic hydroxycarboxylic acids. 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 parahydroxybenzoic acid and 2-hydroxy-6-naphthoic acid. As long as they exhibit liquid crystalline properties, in addition to these aromatic dicarboxylic acids, aromatic diols, and aromatic hydroxycarboxylic acids, other components such as aliphatic dicarboxylic acids, aliphatic diols, and aliphatic hydroxycarboxylic acids may also be used in combination. Ethylene glycol is an example of an aliphatic diol.

[0013] In particular, as a liquid crystal polymer, a liquid crystalline aromatic polyester having an aromatic ring content of 55% by mass or more is preferred from the viewpoint of excellent heat resistance. The aromatic ring content of the liquid crystalline aromatic polyester is more 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. Such liquid crystal polymers have a small degree of conformational freedom and excellent heat resistance, but they do not interact well with other polymers. However, in this disclosure, the F polymer has oxygen atoms and has a relatively high degree of conformational freedom and high affinity with liquid crystal polymers, so it adheres well to liquid crystal polymers with a high aromatic ring content.

[0014] In this disclosure, the aromatic ring content is determined by the following formula. Note that carbon atoms included in substituents bonded to the aromatic ring are not included in the carbon atoms that form the aromatic ring. Aromatic ring content (mass%) = 100 × [Mass of carbon atoms forming aromatic rings in the polymer backbone (g) / Total mass of polymer (g)] For example, the aromatic ring content in typical units contained in liquid crystalline aromatic polyesters is as follows, and the aromatic ring content of liquid crystalline aromatic polyesters 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-Naphthalenedicarboxylic acid: 66%

[0015] Examples of liquid crystal polyesteramides include aromatic polyesteramides obtained by copolymerizing the liquid crystal aromatic polyester with aminophenol. Specific examples of liquid crystal polymers include those described in paragraphs 0032 to 0039 of Japanese Patent Publication No. 2017-119378.

[0016] The deflection temperature under load of the liquid crystal polymer is preferably 240°C or higher, more preferably 270°C or higher, and even more preferably 300°C or higher. A deflection temperature of 400°C or lower is preferable. In this case, the composite sheet is preferable because it tends to have excellent heat resistance. Furthermore, since the F polymer contains oxygen atoms and has a relatively high degree of conformational freedom, it readily adheres well to liquid crystal polymers with high deflection temperatures, i.e., those with a low degree of conformational freedom and less interaction with other polymers. Furthermore, it is preferable that the load deflection temperature of the liquid crystal polymer is above the melting temperature of the F polymer. In this case, a sophisticated matrix structure of the liquid crystal polymer and the F polymer is more easily formed under high-temperature exposure, and the electrical properties and low linear expansion properties of the composite sheet are further improved. The temperature deflection under load is measured according to ASTM D648, with a load of 0.46 MPa.

[0017] The average fiber diameter of the liquid crystal polymer nonwoven fabric is preferably 0.01 to 20 μm, more preferably 0.05 to 10 μm, and most preferably 0.1 to 4 μm. The average fiber diameter is determined by measuring the fiber diameter of 200 fibers by electron microscopy, and excluding the data of the 10 thinnest and 10 thickest fibers, and then taking the average value. The volume basis weight of liquid crystal polymer nonwoven fabrics is 3 to 100 cm². 3 / m 2 Preferably, 5-60cm 3 / m 2 More preferably, 10-40cm 3 / m 2 That is even more preferable. The volume basis weight of a liquid crystal polymer nonwoven fabric is determined by dividing the basis weight of the liquid crystal polymer nonwoven fabric by its specific gravity.

[0018] The liquid crystal polymer nonwoven fabric may be fabricated or may be an off-the-shelf product. The nonwoven fabric of the liquid crystal polymer may be formed using either a dry method or a wet method. In dry molding, particularly when forming nonwoven fabrics by melting, molding can generally be performed in a temperature range higher than the glass transition temperature, and even higher than the temperature range in which the liquid crystal structure exists in a non-flowing state, at which point the liquid crystal structure breaks down and random orientation occurs. Depending on the chemical structure of the liquid crystal polymer, melt molding is possible at, for example, a molding temperature of 200 to 400°C. Examples of melt molding methods for liquid crystal polymer nonwoven fabrics include the spunbond method and the melt-blown method, for example, the molding method described in International Publication No. 2010 / 098400. As a wet process, nonwoven fabrics can also be formed by using pre-spun liquid crystal polymer fibers as raw materials, cutting them to a certain length, and then forming the resulting short fibers onto a sheet using a papermaking method as exemplified in Japanese Patent Application Publication No. 2012-36538. The liquid crystal polymer nonwoven fabric may be formed by electrospinning a solution containing the liquid crystal polymer, or by the method exemplified in Japanese Patent Application Publication No. 2010-196228, namely, by stretching the liquid crystal polymer filaments 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] Liquid crystal polymer fabrics can also be considered as fabrics made of liquid crystal polymer fibers, and a specific example is a plain weave fabric. The warp density of the plain weave fabric of liquid crystal polymer is preferably 2 to 80 threads / cm, and more preferably 4 to 60 threads / cm. The weft density of the liquid crystal polymer plain weave fabric is preferably 2 to 80 threads / cm, and more preferably 4 to 60 threads / cm. The liquid crystal polymer fibers are preferably those obtained by melt spinning the liquid crystal polymer. The liquid crystal polymer fibers obtained by melt spinning may be further heat-treated to improve their strength. The liquid crystal polymer fibers may consist of one type of liquid crystal polymer, or they may consist of two or more types of liquid crystal polymers. The liquid crystal polymer fibers may be core-sheath composite fibers having 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] It is preferable that the woven or nonwoven fabric of the liquid crystal polymer is surface-treated. In this case, the affinity between the liquid crystal polymer woven or nonwoven fabric and the F polymer is improved, and the adhesion between the liquid crystal polymer woven or nonwoven fabric and the F polymer tends to improve. In addition, the F polymer is more easily impregnated into the fine voids of the liquid crystal polymer woven or nonwoven fabric, and the mechanical properties of the resulting composite sheet tend to improve. Surface treatments include corona treatment and plasma treatment. Plasma treatments include vacuum plasma treatment and atmospheric pressure plasma treatment, with vacuum plasma treatment being preferred. Vacuum plasma treatment is preferably performed in an atmosphere containing argon gas, an atmosphere containing oxygen gas, or an atmosphere containing hydrogen gas and nitrogen gas.

[0021] The manufacturing method disclosed herein uses a film containing an F polymer (hereinafter also referred to as F film). One type of F polymer may be used, or two or more types may be used. Tetrafluoroethylene polymers are polymers containing units based on tetrafluoroethylene (hereinafter also referred to as "TFE") (hereinafter also referred to as "TFE units"). From the viewpoint of suitably expressing the properties of TFE units, the content of TFE units in the tetrafluoroethylene polymer is preferably 50 mol% or more, and more preferably 90 mol% or more, relative to the total units in the tetrafluoroethylene polymer. The above content may be 99 mol% or less, or 98 mol% or less.

[0022] The F polymer contains oxygen atoms. According to the manufacturing method of this disclosure using the F polymer, a composite sheet with excellent electrical properties and low linear expansion can be obtained. Furthermore, composite sheets made using the F polymer tend to have excellent adhesion to the substrate. In this disclosure, the term "polymer having oxygen atoms" means a polymer having oxygen atoms intended as constituent atoms of the polymer. Even if oxygen atoms are inevitably introduced during the manufacturing process, polymers containing such oxygen atoms are not included in the definition of "polymer having oxygen atoms."

[0023] In one embodiment, the F polymer is a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups. In this case, the oxygen-containing polar groups in the F polymer interact with the liquid crystal polymer and the substrate, making the composite sheet more likely to exhibit low linear expansion and excellent adhesion to the substrate, which is preferable. Examples of oxygen-containing polar groups include hydroxyl group-containing groups, carbonyl group-containing groups, epoxy group-containing groups, and phosphono group-containing groups, with hydroxyl group-containing groups or carbonyl group-containing groups being preferred, and carbonyl group-containing groups being more preferred. The F polymer may have one or more types of oxygen-containing polar groups. The hydroxyl group-containing group is preferably a group containing an alcoholic hydroxyl group, and -CF2CH2OH and -C(CF3)2OH are more preferred. The carbonyl group-containing groups are preferably carboxyl groups, alkoxycarbonyl groups, amide groups, isocyanate groups, carbamate groups (-OC(O)NH2), acid anhydride residues (-C(O)OC(O)-), imide residues (-C(O)NHC(O)-, etc.), and carbonate groups (-OC(O)O-), with acid anhydride residues being more preferred.

[0024] The number of oxygen-containing polar groups in F polymer is 1 × 10⁶ carbon atoms in the main chain. 6 The number of oxygen-containing polar groups per polymer is preferably 10 to 5000, and more preferably 100 to 3000. The number of oxygen-containing polar groups can be quantified by the polymer composition or by the method described in International Publication No. 2020 / 145133.

[0025] The oxygen-containing polar group may be included in the monomer-based units in the F polymer, or it may be included in the terminal groups of the main chain of the F polymer, with the former being preferred. Examples of the latter include tetrafluoroethylene polymers having oxygen-containing polar groups as terminal groups derived from polymerization initiators, chain transfer agents, etc., and polymers obtained by plasma treatment or ionization treatment of tetrafluoroethylene polymers. On the other hand, the F polymer or its film may not be subjected to surface treatment such as plasma treatment or ionization treatment.

[0026] Preferred monomers having a carbonyl group include itaconic anhydride, citraconic anhydride, and 5-norbornene-2,3-dicarboxylic acid anhydride (hereinafter also referred to as "NAH"), and NAH is more preferred from the viewpoint of excellent adhesion of the resulting composite sheet.

[0027] Preferred F polymers having oxygen-containing polar groups include 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), or polymers containing TFE units and hexafluoropropylene-based units (HFP units) (FEP), with PFA and FEP being more preferred, and PFA being even more preferred. These polymers may further contain units based on other comonomers.

[0028] The F polymer is preferably a polymer having carbonyl group-containing groups, including TFE units and PAVE units; more preferably, it includes TFE units, PAVE units, and units based on monomers having carbonyl group-containing groups; and even more preferably, it is a polymer containing 90-99 mol%, 0.99-9.97 mol%, and 0.01-3 mol% of these units in that order relative to the total number of units, or 87-96 mol%, 0.99-9.97 mol%, and 3-6 mol%. The former is preferable because it is easier to obtain a composite sheet with excellent heat resistance. The latter is preferable because it is easier to obtain a composite sheet with excellent adhesion between the F polymer and the liquid crystal polymer woven or nonwoven fabric. A specific example of such an F polymer is the polymer described in International Publication No. 2018 / 016644.

[0029] In yet another aspect, examples of the F polymer include a thermoplastic tetrafluoroethylene-based polymer containing PAVE units. In this case, by having PAVE units, it is possible to improve the degree of freedom of the conformation of the F polymer while maintaining the excellent electrical properties of the tetrafluoroethylene-based polymer, and the composite sheet is likely to be excellent in electrical properties, low linear expansibility, and adhesion to the substrate, which is preferable. The thermoplastic tetrafluoroethylene-based polymer containing PAVE units may not have a carbonyl group-containing group, and may not contain a unit based on a monomer having a carbonyl group-containing group. PAVE is preferably CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (hereinafter also referred to as PPVE), and more preferably PPVE.

[0030] In the F polymer containing PAVE units, the content rate of the PAVE units in all the units in the F polymer is preferably 1.0 mol% or more, more preferably 2.0 mol% or more, and even more preferably 2.3 mol% or more. When the content rate of the PAVE units is at least the above lower limit value, it is considered that the melt fluidity of the F polymer increases, and it is easy to form fine spherulites and the adhesive force improves. From the viewpoint of heat resistance, the content rate of the PAVE units in all the units in the F polymer is preferably 10.0 mol% or less, and more preferably 5.0 mol% or less.

[0031] The F polymer containing PAVE units and having a content rate of the PAVE units in all the units in the F polymer of 2.0 mol% or more is preferably end-fluorinated, and the number of oxygen-containing polar groups in the F polymer is preferably 500 or less, more preferably 100 or less, and even more preferably 0 per 1×10 carbon atoms in the main chain. 6 In this case, during the crystallization of the F polymer, the formation of a lamellar structure is promoted and fine spherulites are likely to be generated, and the adhesion to the woven or non-woven fabric of the liquid crystal polymer or the substrate is likely to be further enhanced. This polymer is composed of TFE units and PPVE units, and preferably has a TFE unit content rate of 95.0 to 98.0 mol% and a PPVE unit content rate of 2.0 to 5.0 mol%. ​

[0032] F polymer is thermally meltable. A heat-meltable polymer refers to a polymer that, under a load of 49N, has a temperature at which the melt flow velocity is between 1 and 1000 g / 10 minutes. From the viewpoint of properly impregnating the liquid crystal polymer with the F polymer, the melt flow rate of the F polymer is preferably 1 to 30 g / min under a load of 49 N, and 5 to 30 g / min is preferable. More preferable.

[0033] From the viewpoint of improving the heat resistance of the composite sheet, the melting temperature of the F polymer is preferably 200°C or higher, and more preferably 260°C or higher. From the viewpoint of good impregnation of the F polymer into the liquid crystal polymer woven or nonwoven fabric, the melting temperature of the F polymer is preferably 325°C or lower, and more preferably 320°C or lower.

[0034] From the viewpoint of improving the heat resistance of the composite sheet, the glass transition temperature of the F polymer is preferably 50°C or higher, and more preferably 75°C or higher. From the viewpoint of good impregnation of the liquid crystal polymer woven or nonwoven fabric, the glass transition temperature of the F polymer is preferably 150°C or lower, and more preferably 125°C or lower.

[0035] From the viewpoint of improving the electrical properties and heat resistance of the composite sheet, the fluorine content of the F polymer is preferably 70% by mass or more, and more preferably 72-76% by mass. The fluorine content can be determined from the composition of the polymer.

[0036] The surface tension of F polymer is preferably 16 to 26 mN / m. Surface tension can be measured by placing a droplet of wetting index reagent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) on a flat plate made of F polymer. Even F polymers with low surface tension tend to have excellent adhesion to liquid crystal polymer woven or nonwoven fabrics because they contain oxygen atoms. From the viewpoint of adhesion of the liquid crystal polymer to the woven or nonwoven fabric and substrate, the spherulite radius of the F polymer in the composite sheet is preferably 0.2 to 10 μm, and more preferably 0.5 to 5 μm.

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

[0038] The F film may contain polymers different from the F polymer (hereinafter also referred to as "different polymers"). Examples of different polymers include tetrafluoroethylene polymers without oxygen atoms, non-thermally fused tetrafluoroethylene polymers, epoxy resins, polyimide resins, polyamic acid which is a polyimide precursor, polyamide-imide resins, precursors of polyamide-imide resins, acrylic resins, phenolic resins, liquid crystalline polyester resins, polyolefin resins, modified polyphenylene ether resins, polyfunctional cyanate ester resins, polyfunctional maleimide-cyanate ester resins, polyfunctional maleimide resins, vinyl ester resins, urea resins, diallyl phthalate resins, melamine resins, guanamine resins, melamine-urea cocondensation resins, styrene resins, polycarbonate resins, polyarylate resins, polysulfones, polyallyl sulfones, polyamide resins, polyetheramides, polyphenylene sulfide, polyaryl ether ketones, polyphenylene ethers, and polytetrafluoroethylene. Preferred different polymers are non-thermally fused tetrafluoroethylene polymers and aromatic polymers. One or more different polymers may be used.

[0039] Examples of tetrafluoroethylene-based polymers that do not contain oxygen atoms include PTFE, ETFE, polymers containing TFE units and propylene-based units, and FEP. These polymers may or may not contain units based on other comonomers. However, the polymers exemplified above do not contain oxygen atoms. Non-thermally soluble tetrafluoroethylene polymers include non-thermally soluble PTFE.

[0040] As aromatic polymers, aromatic polyimides, aromatic polyamic acids, aromatic polyamideimides, and precursors of aromatic polyamideimides are more preferred. Specific examples of aromatic polymers include the "Yupia-AT" series (manufactured by Ube Industries), the "Neoprim®" series (manufactured by Mitsubishi Gas Chemical Company), the "Spixeria®" series (manufactured by Somar), the "Q-PILON®" series (manufactured by PI Technical Research Institute), the "WINGO" series (manufactured by Wingo Technology), the "Tomide®" 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).

[0041] When the F film contains different polymers, the content of the different polymers relative to the total mass of the F film is preferably 0.1 to 60% by mass, and more preferably 1 to 40% by mass. When the different polymers are non-thermally soluble tetrafluoroethylene polymers, the content of the non-thermally soluble tetrafluoroethylene polymer relative to the total mass of the F film is preferably 10 to 60% by mass, and more preferably 20 to 50% by mass. When the different polymers are aromatic polymers, the content of the aromatic polymer relative to the total mass of the F film is preferably 0.1 to 30% by mass, and more preferably 1 to 10% by mass.

[0042] The F film may contain inorganic fillers. Preferred inorganic fillers are carbon fillers, inorganic nitride fillers, or inorganic oxide fillers, more preferably carbon fiber fillers, glass fiber fillers, boron nitride fillers, aluminum nitride fillers, beryllia fillers, silica fillers, wollastonite fillers, talc fillers, cerium oxide fillers, aluminum oxide fillers, magnesium oxide fillers, zinc oxide fillers, or titanium oxide fillers, and even more preferably boron nitride fillers or silica fillers. One or more inorganic fillers may be used.

[0043] The D50 of the inorganic filler is preferably 20 μm or less, and more preferably 10 μm or less. The D50 is preferably 0.01 μm or more, and more preferably 0.1 μm or more. The specific surface area of ​​inorganic fillers is 1 to 20 m². 2 / g is preferable.

[0044] The surface of the inorganic filler may be surface-treated with a silane coupling agent. Preferred silane coupling agents include silane coupling agents having functional groups, such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-isocyanatetopropyltriethoxysilane.

[0045] The inorganic filler is preferably spherical, needle-shaped, fibrous, or plate-shaped, preferably spherical, flaky, or layered, and more preferably spherical or flaky. The spherical inorganic fillers are preferably nearly spherical. Nearly spherical means that, when observed with a scanning electron microscope (SEM), the proportion of inorganic fillers with a ratio of minor axis to major axis of 0.7 or more is 95 percent or more. The aspect ratio of the non-spherical inorganic filler is preferably 2 or greater, and more preferably 5 or greater. The aspect ratio is preferably 10,000 or less.

[0046] Specific examples of silica fillers include the "AdmaFine" series (manufactured by Admatex), the "SFP" series (manufactured by Denka), the "E-SPHERES" series (manufactured by Taiheiyo Cement Corporation), and the "Q" series (manufactured by Ginet). A specific example of zinc oxide filler is the "FINEX" series (manufactured by Sakai Chemical Industry Co., Ltd.). Specific examples of titanium dioxide fillers include the "Typake®" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Teika Co., Ltd.). A concrete example of talc filler is the "SG" series (manufactured by Nippon Talc Co., Ltd.). A specific example of steatite filler is the "BST" series (manufactured by Nippon Talc Co., Ltd.). 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] If the F film contains an inorganic filler, the inorganic filler content relative to the total mass of the F film is preferably 1 to 50% by mass, and more preferably 5 to 20% by mass.

[0048] In addition to the components described above, the F film may also contain other components such as organic fillers, thixotropic agents, defoaming agents, 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, and flame retardants. The content of components other than the F polymer, polymers other than the F polymer, and inorganic fillers in the total mass of the F film is preferably 0 to 10% by mass.

[0049] The thickness of the F film is preferably 1 to 200 μm. The F film may be surface-treated with a silane coupling agent. Examples of silane coupling agents include those similar to those used for surface treatment of the inorganic filler described above. In this case, the adhesion at the interface between the F polymer and the liquid crystal polymer woven or nonwoven fabric, and the adhesion of the composite sheet to the substrate are easily improved, which is preferable.

[0050] The F film may be formed by melt-extruding the F polymer. In this case, sheets further containing different polymers, inorganic fillers, and other components can be formed by melt-kneading the F polymer with the different polymers, inorganic fillers, and other components, and then extruding them. The F film may be formed from a dispersion containing F polymer particles and a liquid dispersion medium. For example, the F film may be formed by applying a dispersion containing F polymer 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 F polymer, and then removing the temporary substrate from the laminate. It is preferable to heat the temporary substrate to which the dispersion has been applied in two stages: heating to remove the liquid dispersion medium and heating to bake the F polymer. Examples of temporary substrates include metal foil and resin film, and methods for removing the temporary substrate include peeling and etching. In this case, sheets further containing different polymers, inorganic fillers, and other components can be formed using F polymer particles and a liquid dispersion medium, and further dispersions containing different polymers, inorganic fillers, and other components.

[0051] In the composite sheet, the ratio of the volume concentration of F polymer to the volume concentration of the liquid crystal polymer woven or nonwoven fabric is preferably 0.6 or higher, more preferably 1 or higher, with the volume concentration of the liquid crystal polymer woven or nonwoven fabric being 1. Such a ratio is preferably 4 or lower, and more preferably 3 or lower.

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

[0053] The thickness of the composite sheet is preferably 5 μm or more, and more preferably 10 μm or more. The thickness of the composite sheet is preferably 200 μm or less, more preferably 100 μm or less, and may be less than 50 μm. The composite sheet may be in the form of a roll or a single sheet.

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

[0055] The coefficient of linear expansion of the composite sheet is preferably 80 ppm / °C or less, more preferably 50 ppm / °C or less, even more preferably 30 ppm / °C or less, and particularly preferably 20 ppm / °C or less. The lower limit of the coefficient of linear expansion is, for example, 5 ppm / °C. The coefficient of linear expansion is measured by the method specified in JIS C 6471:1995. Specifically, it is measured by the method described in the examples.

[0056] In the method for manufacturing a composite sheet according to the present disclosure, a film containing an F polymer is impregnated into a woven or nonwoven fabric of a liquid crystal polymer. The impregnation may be performed by impregnating one surface of the woven or nonwoven fabric of the liquid crystal polymer with the F film, or by impregnating both surfaces of the woven or nonwoven fabric of the liquid crystal polymer with the F film. The impregnation is preferably carried out by heat-pressing a film containing the F polymer with a woven or nonwoven fabric of the liquid crystal polymer. In this case, the F polymer is easily impregnated between the fibers of the woven or nonwoven fabric of the liquid crystal polymer. As a result, the adhesion between the woven or nonwoven fabric of the liquid crystal polymer and the F polymer tends to be increased, which is preferable.

[0057] The heat-sealing process can be carried out, for example, by overlapping the film with a liquid crystal polymer woven or nonwoven fabric and passing it between a pair of heated rolls, by sandwiching it between a pair of opposing hot plates and applying pressure, or by sandwiching it between a hot plate and rolls and applying pressure. From the viewpoint of facilitating good impregnation of the liquid crystal polymer into the woven or nonwoven fabric, the sealing temperature in the heat-sealing process is preferably 30°C or higher than the melting temperature of the F polymer, and more preferably above the melting temperature of the F polymer. The sealing temperature is preferably 30°C or lower than the melting temperature of the F polymer. The heat-sealing temperature is preferably 280 to 380°C, and more preferably 300 to 330°C.

[0058] The bonding pressure in heat sealing is preferably 0.2 MPa or higher, more preferably 1 MPa or higher, and even more preferably 10 MPa or higher. The bonding pressure is preferably 1000 MPa or lower, and more preferably 300 MPa or lower. From the viewpoint of obtaining a composite sheet with reduced air bubbles, it is preferable to perform the heat-sealing under reduced pressure. When performing heat-sealing under reduced pressure, the atmospheric pressure is preferably 10 kPa or less, and more preferably 1 kPa or less.

[0059] The composite sheet may be laminated with a substrate to form a laminate. The composite sheet of this disclosure exhibits excellent adhesion to the substrate. Furthermore, because the composite sheet of this disclosure exhibits excellent low linear expansion, it is less likely to peel 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, polyallyl ether ketone, polyamide-imide, liquid crystalline polyester, and tetrafluoroethylene polymers), prepreg substrates (precursors of fiber-reinforced resin substrates), ceramic substrates (ceramic substrates such as silicon carbide, aluminum nitride, and silicon nitride), and glass substrates.

[0060] The substrate can be flat, curved, or uneven. Furthermore, the substrate may be foil-like, plate-like, film-like, or fibrous. The surface roughness of the substrate with a ten-point average is preferably 0.01 to 0.05 μm. The surface of the substrate may be surface-treated with a silane coupling agent or plasma-treated. One method for laminating the composite sheet and the substrate is thermocompression bonding. The thermocompression bonding method is the same as the thermocompression bonding method used in the manufacturing of the composite sheet described above.

[0061] In the method for manufacturing a composite sheet according to this disclosure, a composite sheet may be formed by impregnating a liquid crystal polymer woven or nonwoven fabric with an F film, and at the same time, it may be laminated with a substrate to obtain a laminate of the composite sheet and the substrate. For example, a laminate of the composite sheet and the substrate can be obtained by stacking the liquid crystal polymer woven or nonwoven fabric, the F film, and the substrate in this order and heat-pressing them together. The heat-pressing method can be the same as the heat-pressing method used in the manufacturing of the composite sheet described above. In the method for manufacturing a composite sheet according to this disclosure, a composite sheet may be formed by impregnating a liquid crystal polymer woven or nonwoven fabric with an F film, and at the same time, laminating it with a copper foil to obtain a copper-clad laminate in which the composite sheet and the copper foil are bonded together. For example, by layering a liquid crystal polymer woven or nonwoven fabric, an F film, and a copper foil in this order and heat-pressing them together, a copper-clad laminate in which the composite sheet and the copper foil are bonded together can be obtained. The heat-pressing method may be the same as the heat-pressing method used in the manufacturing of the composite sheet described above. The substrate may be removed from the laminate to obtain a single composite sheet. The peel strength between the composite sheet and the substrate in the laminate is preferably 10 to 100 N / cm, and more preferably 12 to 100 N / cm.

[0062] The applications of composite sheets are not particularly limited. Composite sheets are useful as antenna components, printed circuit boards, aircraft parts, automotive parts, sports equipment, food industry products, heat dissipation components, etc. Specifically, these include wire insulation materials (aircraft wires, etc.), enamel wire insulation materials used in motors for electric vehicles, etc., electrical insulation tapes, insulating tapes for oil drilling, oil transport hoses, hydrogen tanks, printed circuit board materials, separation membranes (microfiltration membranes, ultrafiltration membranes, reverse osmosis membranes, ion exchange membranes, dialysis membranes, gas separation membranes, etc.), electrode binders (for lithium secondary batteries, fuel cells, etc.), copy rolls, furniture, car dashboards, covers for home appliances, sliding components (load bearings, yaw bearings, sliding shafts, valves, bearings, bushings, seals, sliding shafts). It is useful in applications such as tow washers, wear rings, pistons, slide switches, gears, cams, belt conveyors, food transport belts, etc., tension ropes, wear pads, wear strips, tube lamps, test sockets, wafer guides, wear parts for centrifugal pumps, chemical and water supply pumps, tools (shovels, files, drills, saws, etc.), boilers, hoppers, pipes, ovens, baking molds, chutes, racket strings, dies, toilets, container coverings, power devices, transistors, thyristors, rectifiers, transformers, power MOS FETs, CPUs, heat sinks, metal heat sinks, blades for wind turbines, wind power generation equipment and aircraft, casings for personal computers and displays, electronic device materials, interior and exterior parts for automobiles, sealing materials for processing machines and vacuum ovens that perform heat treatment under low oxygen conditions, plasma processing equipment, heat dissipation components in processing units such as sputtering and various dry etching equipment, electromagnetic shielding, process films for semiconductor sintering processes, and release films for high-temperature sealing of power semiconductors.

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

[0064] A composite sheet in one aspect of the present disclosure comprises a woven or nonwoven fabric of a liquid crystal polymer and a liquid crystal polymer The composite sheet contains an F polymer impregnated into a woven or nonwoven fabric. The characteristics of the composite sheet are such that the above-mentioned matters apply. Preferably, the composite sheet is manufactured by the manufacturing method of the present disclosure described above. [Examples]

[0065] The embodiments of this disclosure will be described in detail below with reference to examples, but the embodiments of this disclosure are not limited to these.

[0066] 1. Preparation of each component [film] Film 1: Contains TFE units, NAH units, and PPVE units in the following order: 97.9 mol%, 0.1 mol%, and 2.0 mol%, respectively, and contains acid anhydride groups, which are carbonyl group-containing groups, with a main chain of 1 × 10¹⁶ carbon atoms. 6 A film (thickness: 12 μm) of polymer 1 (melting temperature: 300°C, melt flow rate: 20 g / 10 min) with 1000 polymer molecules per unit. Film 2: Contains TFE units, NAH units, and PPVE units in the following order: 94.9 mol%, 0.1 mol%, and 5.0 mol%, respectively, and contains acid anhydride groups, which are carbonyl group-containing groups, with a main chain of 1 × 10¹⁶ carbon atoms. 6 A film (thickness: 12 μm) of polymer 2 (melting temperature: 260°C, melt flow rate: 20 g / 10 min) with 1000 polymer molecules per unit. Film 3: A film (thickness: 12 μm) of polymer 3 (melt temperature: 305°C, melt flow rate: 25 g / 10 min) containing 97.5 mol% and 2.5 mol% of TFE units and PPVE units, respectively, and having been fluorinated at the ends, substantially lacking functional groups (i.e., substantially lacking functional groups intended to be components of the polymer). Film 4: A film (thickness: 12 μm) of polymer 4 (melting temperature: 260°C, melt flow rate: 24 g / 10 min) containing 75 mol% TFE units and 25 mol% HFP units in that order, and substantially free of oxygen atoms (i.e., free of oxygen atoms intended as constituent atoms of the polymer). Film 5: Contains TFE units, NAH units, and PPVE units in the following order: 97.9 mol%, 0.1 mol%, and 2.0 mol%, respectively, and contains acid anhydride groups, which are carbonyl group-containing groups, with a main chain of 1 × 10¹⁶ carbon atoms. 6 A film (thickness: 50 μm) of polymer 1, which has 1000 molecules per unit (melting temperature: 300°C, melt flow rate: 20 g / 10 min).

[0067] [Liquid crystal polymer nonwoven fabric] Nonwoven fabric 1: A film-like nonwoven fabric of liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300℃, specific gravity: 1.42 g / cm³) 3 Fiber diameter: 7 μm, Basis weight: 9.9 cm² 3 / m 2 ) Nonwoven fabric 2: A film-like nonwoven fabric of liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300℃, specific gravity: 1.42 g / cm³) 3 Fiber diameter: 7 μm, volume basis weight: 28.2 cm² 3 / m 2 ) Nonwoven fabric 3: A film-like nonwoven fabric of liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300℃, specific gravity: 1.42 g / cm³) 3 Fiber diameter: 3 μm, Basis weight: 4.2 cm 3 / m 2 ) Nonwoven fabric 4: A film-like nonwoven fabric of liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300℃, specific gravity: 1.42 g / cm³) 3 Fiber diameter: 3 μm, volume basis weight: 16.9 cm² 3 / m 2 )

[0068] [Liquid crystal polymer woven fabric] Fabric 1: Plain weave fabric of liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300℃, specific gravity: 1.42 g / cm²) 3 Fiber diameter: 7 μm, Thickness: 123 μm, Volume basis weight: 32 cm² 3 / m 2 (Warp density: 20 threads / cm, Weft density: 20 threads / cm) Woven fabric 2: Plain weave of liquid crystalline aromatic polyester (load deflection temperature: 350℃, basis weight: 45g / m²) 2 (Vectran (registered trademark) manufactured by Kuraray Co., Ltd.) [copper foil] Copper foil 1: Copper foil (thickness: 18 μm, average surface roughness at 10 points: 0.8 μm)

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

[0070] 3. Manufacturing of composite sheets For the copper-clad laminate 1, the copper foil is removed by etching with an aqueous ferric chloride solution, and then the laminate is heated in an oven at 100°C for 1 hour to dry it and obtain a composite sheet 1. Composite sheets 2 to 9 are obtained in the same manner as composite sheet 1, except that copper-clad laminate 1 is replaced with copper-clad laminates 2 to 9.

[0071] 4. Evaluation 4-1. Peel strength Rectangular test specimens measuring 100 mm in length and 10 mm in width were cut from each copper-clad laminate. The specimen was fixed 50 mm from one end in the longitudinal direction, and the copper foil and composite sheet were peeled off at a tensile speed of 50 mm / min, at a 90° angle to the specimen from the other end in the longitudinal direction. The maximum load at which peeling occurred was defined as the peel strength (N / cm). The peel strengths of the copper-clad laminates were as follows: [Evaluation Criteria] A: It is 12 N / cm or higher. B: 10 N / cm or more, and less than 12 N / cm. C: Less than 10 N / cm

[0072] 4-2. Coefficient of linear expansion For each composite sheet, a 180mm square test piece was cut out and measured according to JIS C The coefficient of linear thermal expansion of the test specimen was measured in the range of 25°C to 260°C according to the measurement method specified in 6471:1995. As a result, the coefficient of linear thermal expansion of the composite sheet is as follows. [Evaluation Criteria] AA: 20 ppm / ℃ or less. A: It is greater than 20 ppm / °C and less than or equal to 30 ppm / °C. B: Greater than 30 ppm / °C and less than or equal to 50 ppm / °C. C: Over 50 ppm / ℃.

[0073] 4-3. Electrical Characteristics For each composite sheet, a sample measuring 10 cm in length and 5 cm in width was cut out, and the relative permittivity and dielectric loss tangent (measurement frequency: 10 GHz) were measured using the SPDR (Split Post Dielectric Resonance) method. The electrical properties of the composite sheets are as follows. Note that composite sheet 7 was not measured because it has a high coefficient of thermal expansion and low adhesion to the copper foil in the copper-clad laminate 7. [Evaluation Criteria] AA: The relative permittivity is 2.2 or less, and the dielectric loss tangent is less than 0.0010. A: The relative permittivity is 2.2 or less, and the dielectric loss tangent is 0.0010 or more and less than 0.0020. The relative permittivity is greater than 2.2 and less than or equal to 2.4, and the dielectric loss tangent is less than 0.0010. B: The relative permittivity is greater than 2.2 and less than or equal to 2.4, and the dielectric loss tangent is 0.0010 or greater and less than 0.0020.

[0074] Table 1 below summarizes the materials used in the manufacture of each copper-clad laminate and composite sheet, as well as 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, with composite sheet 9 being particularly excellent in low linear expansion. Furthermore, composite sheets 1-6, 8, and 9 also exhibit excellent peel strength from copper foil.

[0077] The disclosures of Japanese Patent Applications Nos. 2021-119740 and 2021-172597 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted as being incorporated by reference.

Claims

1. A method for producing a composite sheet, comprising impregnating a woven or nonwoven liquid crystal polymer with a film containing a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups selected from the group consisting of alcoholic hydroxyl group-containing groups and carbonyl group-containing groups to obtain a composite sheet.

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

3. The manufacturing method according to claim 1 or 2, wherein the melting temperature of the tetrafluoroethylene polymer is 260°C or higher.

4. The number of oxygen-containing polar groups in the tetrafluoroethylene polymer is 1 × 10 carbon atoms in the main chain. ６ The manufacturing method according to claim 1 or 2, wherein the quantity per unit is 10 to 5,000 units.

5. The manufacturing method according to claim 1 or 2, wherein the tetrafluoroethylene polymer contains units based on perfluoro(alkyl vinyl ether), and the content of the units based on perfluoro(alkyl vinyl ether) in the total units within the tetrafluoroethylene polymer is greater than 2 mol%.

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

7. The manufacturing method according to claim 1 or 2, wherein the liquid crystal polymer includes a liquid crystalline aromatic polyester.

8. The manufacturing method according to claim 7, wherein the aromatic ring content of the aromatic polyester is 55% by mass or more.

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

10. The manufacturing method according to claim 1 or 2, wherein the film and the woven fabric or nonwoven fabric are heat-pressed together to impregnate the film.

11. The manufacturing method according to claim 10, wherein the bonding temperature in the heat bonding is within ±30°C of the melting temperature of the tetrafluoroethylene polymer.

12. The manufacturing method according to claim 10, wherein the pressing pressure in the heat-pressure bonding is 1 MPa or more.

13. The manufacturing method according to claim 10, wherein the heat-pressing is performed under reduced pressure.

14. The manufacturing method according to claim 1 or 2, wherein the composite sheet is used in a copper-clad laminate of a printed wiring board.

15. A composite sheet comprising a woven or nonwoven liquid crystal polymer and a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups selected from the group consisting of alcoholic hydroxyl group-containing groups and carbonyl group-containing groups, impregnated into the woven or nonwoven fabric.

16. The composite sheet according to claim 15, used in a copper-clad laminate for a printed circuit board.

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