Composite sheet and method for manufacturing a composite sheet

Abstract

A composite sheet comprising woven or nonwoven fabric of a liquid-crystal polymer and, infiltrated into the woven or nonwoven fabric of a liquid-crystal polymer, a heat-fusible tetrafluoroethylene-based polymer having an oxygen-containing polar group.

Description

[Technical Field]

[0001] This disclosure relates to a composite sheet and a method for manufacturing 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 composite sheet comprising a woven or nonwoven fabric of a heat-meltable liquid crystal polymer, and a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups impregnated into the woven or nonwoven fabric of the liquid crystal polymer. <2> The oxygen-containing polar group is a hydroxyl group-containing group or a carbonyl group-containing group. <1> The composite sheet described above. <3> The liquid crystal polymer includes a liquid crystal aromatic polyester. <1> or <2> The composite sheet described above. <4> The melting point of the tetrafluoroethylene polymer is 260 to 320°C. <1> ~ <3> A composite sheet as described in any one of the items. <5> The melting point of the liquid crystal polymer is 230 to 350°C. <1> ~ <4> A composite sheet as described in any one of the items. <6> The absolute difference between the melting point of the tetrafluoroethylene polymer and the melting point of the liquid crystal polymer is 30°C or less. <1> ~ <5> A composite sheet as described in any one of the items. <7> The polymer further contains a polymer different from the aforementioned tetrafluoroethylene polymer, <1> ~ <6> A composite sheet as described in any one of the items. <8> It further contains inorganic particles, <1> ~ <7> A composite sheet as described in any one of the items. <9> The composite sheet contains at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles, wherein the total content of the at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and the inorganic particles is greater than 5% by mass of the total mass of the composite sheet. <1> ~ <8> A composite sheet as described in any one of the items. <10> The system comprises at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles, wherein the ratio of the total mass of the at least one selected from the group consisting of the polymer different from the tetrafluoroethylene polymer and the inorganic particles to the mass of the tetrafluoroethylene polymer is 0.1 or more. <1> ~ <9> A composite sheet as described in any one of the items. <11> The thickness is less than 50 μm. <1> ~ <10> A composite sheet as described in any one of the items. <12> A method for producing a composite sheet, comprising heat-pressing a sheet containing a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups with a woven or nonwoven fabric of a liquid crystal polymer to obtain a composite sheet. <13> The sheet is formed from a dispersion containing particles of the tetrafluoroethylene polymer. <12> The manufacturing method described above. <14> A method for producing a composite sheet, comprising impregnating a liquid crystal polymer woven or nonwoven fabric with a dispersion containing particles of a heat-meltable tetrafluoroethylene polymer having oxygen-containing polar groups to obtain a composite sheet. <15> The dispersion further contains at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles. <14> The manufacturing method described above. [Effects of the Invention]

[0006] This disclosure provides a composite sheet with excellent electrical properties and low linear expansion, and a method for manufacturing the composite sheet. [Modes for carrying out the invention]

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

[0008] In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the term "layer" includes cases where, when observing the region in which the layer or film exists, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable. In this disclosure, "composite sheet" means a sheet comprising a polymer and a liquid crystal polymer woven or nonwoven fabric. In this disclosure, "volume-average particle diameter (D50)" is the volume-based cumulative 50% diameter of a particle, 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 determined with the total volume of the particle collection set to 100%, and D50 is the particle diameter at the point on that cumulative curve where the cumulative volume is 50%. The D50 particle size distribution analyzer measures particles dispersed in water using a laser diffraction / scattering type particle size distribution analyzer. It is determined by analysis using the laser diffraction / scattering method with a LA-920 measuring instrument manufactured by Horiba, Ltd. In this disclosure, "specific surface area" is a value calculated by measuring particles using the gas adsorption (constant volume) BET multipoint method, and is determined using NOVA4200e (manufactured by Quantachrome Instruments). In this disclosure, the "melting point of the tetrafluoroethylene polymer" is the temperature corresponding to the maximum value of the polymer's melting peak measured by differential scanning calorimetry (DSC). In the present disclosure, the "melting point of the liquid crystal polymer" is the temperature at which an endothermic peak appears when a film of the liquid crystal polymer is heated at a rate of 20 °C / min to be completely melted using a differential scanning calorimeter, then the melt is rapidly cooled to 50 °C at a rate of 50 °C / min, and then heated again at a rate of 20 °C / min. In the present disclosure, the "melt flow rate" means the melt mass flow rate of the polymer as 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, the "viscosity" is determined by measuring the dispersion liquid at 25 °C under the condition that the rotation speed is 30 rpm using a B-type viscometer. The measurement is repeated three times, and the average value of the three measurement values is taken. In the present disclosure, the "thixotropy ratio" is a value calculated by dividing the viscosity η1 of the dispersion liquid measured under the condition that the rotation speed is 30 rpm by the viscosity η2 measured under the condition that the rotation speed is 60 rpm. The measurement of each viscosity is repeated three times, and the average value of the three measurement values is taken. 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 the present disclosure, the "unit" in a polymer means an atomic group based on the monomer formed by polymerization of the monomer. The unit may be a unit directly formed by a polymerization reaction, or a unit in which a part of the unit is converted into another structure by treating the polymer. Hereinafter, the unit based on monomer a is also simply referred to as "monomer a unit".

[0009] The composite sheet of the present disclosure contains a woven or non-woven fabric of a thermally fusible liquid crystal polymer (hereinafter, also simply referred to as "liquid crystal polymer"), and a thermally fusible tetrafluoroethylene-based polymer having an oxygen-containing polar group (hereinafter, also referred to as "F polymer") impregnated in the woven or non-woven fabric of the liquid crystal polymer. The composite sheet of the present disclosure is excellent in electrical properties and low linear expansibility.

[0010] Generally, tetrafluoroethylene-based polymers are excellent in electrical properties such as low dielectric constant and low dielectric tangent, but have a large coefficient of linear expansion. In conventional composite sheets using tetrafluoroethylene-based polymers, the low linear expansion property is not sufficient. In addition, in conventional composite sheets, the tetrafluoroethylene-based polymer is merely impregnated into a woven or non-woven fabric of a liquid crystal polymer, and the two are only intertwined and adhered, and the adhesiveness of the interface is insufficient. As a result, the laminate of the composite sheet and the base material has problems such as thermal expansion during processing at high temperatures and peeling from the base material. The inventors have intensively studied and found that a composite sheet in which an F polymer is impregnated into a woven or non-woven fabric of a liquid crystal polymer is excellent in electrical properties and low linear expansion property.

[0011] In the composite sheet of the present disclosure, the oxygen-containing polar group in the F polymer interacts well with the liquid crystal polymer, so that the adhesiveness between the F polymer and the liquid crystal polymer is improved, and the linear expansion property of the F polymer is better buffered by the woven or non-woven fabric of the liquid crystal polymer, and it is considered that the polymer physical properties of both are highly balanced and expressed. In addition, the oxygen-containing polar group in the tetrafluoroethylene-based polymer is considered to also improve the adhesion to the base material, and these properties are considered to provide a material useful as, for example, a low transmission loss material. In addition to the woven or non-woven fabric of the liquid crystal polymer and the F polymer, the composite sheet may contain a polymer different from the F polymer, inorganic particles, various additives, and the like. Hereinafter, each component of the composite sheet will be described.

[0012] The composite sheet of the present disclosure contains an F polymer which is a thermoplastic tetrafluoroethylene-based polymer having an oxygen-containing polar group. One type of F polymer may be used, or two or more types may be used. The F polymer may be particulate or non-particulate in the composite sheet, and the latter is preferred. The F polymer in the composite sheet is preferably fired. From the viewpoint of excellent adhesion between the F polymer and the woven or non-woven fabric of the liquid crystal polymer, the F polymer in the composite sheet is preferably a fired product of the F polymer particles.

[0013] 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 number of units in the polymer. The above content may also be 99 mol% or less, or 98 mol% or less.

[0014] The F polymer has an oxygen-containing polar group. Examples of oxygen-containing polar groups include hydroxyl group-containing groups, carbonyl 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.

[0015] 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. 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 group of the main chain of the F polymer, with the former being preferred. Examples of the latter include tetrafluoroethylene polymers having an oxygen-containing polar group as a terminal group derived from a polymerization initiator, chain transfer agent, etc., and polymers obtained by plasma treatment or ionization treatment of a tetrafluoroethylene polymer.

[0016] 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"), with NAH being more preferred from the viewpoint of excellent adhesion to liquid crystal polymers.

[0017] The F polymer is a polymer having an oxygen-containing polar group, and 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 (FEP). PFA and FEP, which have oxygen-containing polar groups, are more preferred, and PFA, which has oxygen-containing polar groups, is even more preferred. As PAVE units, CF2=CFOCF3, CF2=CFOCF2CF3, and CF2=CFOCF2CF2CF3 (hereinafter also referred to as PPVE) are preferred, and PPVE is more preferred. These polymers may further contain units based on other comonomers.

[0018] The F polymer is preferably a polymer having carbonyl group-containing groups, including TFE units and PAVE units; more preferably, it includes units based on TFE units, PAVE units, and monomers having carbonyl group-containing groups; and even more preferably, it is a polymer containing TFE units, PAVE units, and units based on monomers having carbonyl group-containing groups, with these units present in the following proportions relative to the total number of units: 90-99 mol%, 0.99-9.97 mol%, and 0.01-3 mol%. A specific example of such an F polymer is the polymer described in International Publication No. 2018 / 016644.

[0019] 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 effectively impregnating the liquid crystal polymer with the F polymer, the melt flow rate of the F polymer is preferably 1 to 30 g / min, and more preferably 5 to 30 g / min, under a load of 49 N.

[0020] From the viewpoint of improving the heat resistance of the composite sheet, the melting point 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 point of the F polymer is preferably 325°C or lower, and more preferably 320°C or lower. 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. 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.

[0021] 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 exhibit excellent adhesion to woven or nonwoven liquid crystal polymer fabrics because they contain oxygen-containing polar groups. 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.

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

[0023] The composite sheet of this disclosure contains a woven or nonwoven fabric of a liquid crystal polymer. A thermotropic liquid crystal polymer 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, and more preferably 80% by mass or more.

[0024] 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.

[0025] Examples of aromatic dicarboxylic acids include terephthalic acid and 2,6-naphthalenedicarboxylic acid. Examples of aromatic diols include 4,4'-dihydroxybiphenyl and bisphenol A. Examples of aromatic hydroxycarboxylic acids include parahydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, and 6-hydroxy-2-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.

[0026] In particular, as the liquid crystal polymer, a liquid crystal 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 crystal aromatic polyester is more preferably 65% ​​by mass or more. The aromatic ring content is preferably 80% 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, since the F polymer has a high affinity for liquid crystal polymers, it adheres well to such liquid crystal polymers with a high aromatic ring content.

[0027] 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%

[0028] 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.

[0029] 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, because the F polymer has oxygen-containing polar groups, it adheres well to liquid crystal polymers with high deflection temperatures, i.e., those with small conformational degrees of freedom and less interaction with other polymers. The temperature deflection under load is measured according to ASTM D648, with a load of 0.46 MPa.

[0030] The melting point of the liquid crystal polymer is preferably 230°C or higher, and more preferably 280°C or higher. The melting point of the liquid crystal polymer is preferably 350°C or lower, and more preferably 330°C or lower. The melting point of the liquid crystal polymer may also be adjusted by heat treatment. Liquid crystal polymers with such melting points not only have excellent heat resistance on their own, but also tend to interact more readily with F polymers under high-temperature exposure, further improving the low linear expansion properties of the composite sheet.

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

[0032] The specific gravity of the liquid crystal polymer nonwoven fabric is preferably 1.0 to 3.0, and more preferably 1.5 to 2.0. The average fiber diameter of the liquid crystal polymer nonwoven fabric is preferably 0.01 to 20 μm, and more preferably 3 to 10 μm. The average fiber diameter is determined by measuring the fiber diameter of 200 fibers using electron microscopy, and excluding the data of the 10 thinnest and 10 thickest fibers, and then taking the average value. The basis weight (mass per unit area) of liquid crystal polymer nonwoven fabrics ranges from 1 to 300 g / m². 2 Preferably, 3-30 g / m 2This is preferable.

[0033] The liquid crystal polymer nonwoven fabric may be fabricated or may be an off-the-shelf product. Nonwoven fabrics made from liquid crystal polymers can be molded, for example, at a molding temperature of 300-400°C. Methods for forming nonwoven fabrics of liquid crystal polymers include the spunbond method and the melt-blown method, for example, the molding method described in International Publication No. 2010 / 098400. Specific examples of liquid crystal polymers include the "Veculus" series (manufactured by Kuraray Claflex Co., Ltd.), the "Vectran" series (manufactured by Kuraray Co., Ltd.), and the "UENO LCP" series (manufactured by Ueno Pharmaceutical Co., Ltd.).

[0034] 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.

[0035] The composite sheet may further contain inorganic particles. One type of inorganic particle may be used, or two or more types may be used. In the composite sheet, it is preferable that the inorganic particles are dispersed in the F polymer. The inorganic particles are preferably spherical, needle-shaped, fibrous, or plate-shaped, preferably spherical, flaky, or layered, and more preferably spherical or flaky. The inorganic particles may also be hollow. The spherical inorganic particles are preferably nearly spherical. Nearly spherical means that, when observed with a scanning electron microscope (SEM), the proportion of inorganic particles 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 particles is preferably 2 or greater, and preferably 5 or greater. An aspect ratio of 10,000 or less is also preferred.

[0036] The material of the inorganic particles is preferably carbon, inorganic nitride, or inorganic oxide, more preferably carbon, boron nitride, aluminum nitride, beryllia, silica, wollastonite, talc, cerium oxide, aluminum oxide, magnesium oxide, zinc oxide, or titanium oxide, and even more preferably boron nitride or silica.

[0037] The D50 of the inorganic particles 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 particles is 1 to 20 m². 2 / g is preferable.

[0038] The surface of the inorganic particles may be surface-treated with a silane coupling agent. Preferred silane coupling agents include those having functional groups such as 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-isocyanatetopropyltriethoxysilane.

[0039] Specific examples of silica particles 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 particles is the "FINEX" series (manufactured by Sakai Chemical Industry Co., Ltd.). Specific examples of titanium dioxide particles include the "Typake®" series (manufactured by Ishihara Sangyo Co., Ltd.) and the "JMT" series (manufactured by Teika Co., Ltd.). A concrete example of talc particles is the "SG" series (manufactured by Nippon Talc Co., Ltd.). A specific example of steatite particles is the "BST" series (manufactured by Nippon Talc Co., Ltd.). Specific examples of boron nitride particles include the "UHP" series (manufactured by Showa Denko Corporation) and the "GP" and "HGP" grades of the "Denka Boron Nitride" series (manufactured by Denka Corporation).

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

[0041] The composite sheet of this disclosure may further contain a polymer different from the F polymer (hereinafter also referred to as "different polymer"). The different polymers may be thermosetting or thermoplastic. One or more different polymers may be used. The different polymers may be contained in the woven or nonwoven liquid crystal polymer fabric, or they may be dispersed in the F polymer, with the latter being preferred.

[0042] Examples of different polymers include tetrafluoroethylene polymers other than F polymers, polyester resins (such as liquid crystalline aromatic polyesters), imide resins, epoxy resins, maleimide resins, urethane resins, polyphenylene ether resins, polyphenylene oxide resins, and polyphenylene sulfide resins.

[0043] Examples of tetrafluoroethylene polymers other than F polymers include heat-meltable PTFE, ETFE, PFA, FEP, and non-heat-meltable PTFE, which do not have oxygen-containing polar groups, with non-heat-meltable PTFE being preferred. Non-heat-meltable PTFE may be included in the composite sheet as particles or in non-particulate form.

[0044] Preferred different polymers include aromatic polymers and tetrafluoroethylene-based polymers other than F polymers, such as aromatic polyimides, aromatic polyamic acids, and aromatic polyamides. At least one aromatic imide polymer selected from the group consisting of imides and aromatic polyamide-imide precursors, and non-thermally fused PTFE are more preferred.

[0045] Specific examples of aromatic polyimides include the "Yupia-AT" series (manufactured by Ube Industries, Ltd.), the "Neoprim®" series (manufactured by Mitsubishi Gas Chemical Company, Ltd.), the "Spixeria®" series (manufactured by Somar Corporation), the "Q-PILON®" series (manufactured by PI Technical Research Institute, Ltd.), the "WINGO" series (manufactured by Wingo Technology Co., Ltd.), the "Tomide®" series (manufactured by T&K TOKA Corporation), the "KPI-MX" series (manufactured by Kawamura Industries Co., Ltd.), and "HPC-1000" and "HPC-2100D" (both manufactured by Showa Denko Materials Co., Ltd.).

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

[0047] When the composite sheet contains non-thermally fused PTFE as a different polymer, the content of non-thermally fused PTFE relative to the total mass of the composite sheet is preferably 10 to 60% by mass, and more preferably 20 to 40% by mass. In the composite sheet, the ratio of the mass of non-thermally fused PTFE to the mass of F polymer is preferably 0.5 to 5, and more preferably 1 to 4. When the content of non-thermally fused PTFE falls within a certain range, composite sheets tend to exhibit superior electrical properties.

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

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

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

[0051] In addition to the components mentioned above, the composite sheet may also contain other components such as organic particles, 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. Furthermore, the composite sheet may also contain components derived from the dispersion described later.

[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, and more preferably 100 μm or less. 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, and more preferably 30 ppm / °C or less. The lower limit of the coefficient of linear expansion is 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] The method for manufacturing the composite sheet is not particularly limited as long as the composite sheet of this disclosure is obtained. The composite sheet may be manufactured using sheets or dispersions containing each of the above-mentioned components, or it may be manufactured by the manufacturing method described later.

[0057] A method for manufacturing a composite sheet according to one aspect of this disclosure involves heat-pressing a sheet containing an F polymer with a woven or nonwoven fabric of a liquid crystal polymer to obtain a composite sheet. Hereinafter, this manufacturing method will also be referred to as the "heat-pressing method."

[0058] When using the heat-sealing method, the sheet containing the F polymer may be an existing product or may be newly manufactured. The thickness of the sheet containing F polymer is preferably 1 to 200 μm. A sheet containing F polymer may be formed from a dispersion containing F polymer particles. For example, a sheet containing F polymer may be formed by a method comprising: 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 removing the temporary substrate from the laminate.

[0059] A method for heating the temporary substrate to which the dispersion has been applied is the same as the heating method in the dispersion impregnation method described later, and a preferred embodiment thereof is also the same. Examples of temporary substrates include metal foil and resin film, and methods for removing the temporary substrate include peeling and etching.

[0060] Sheets containing F polymer may be formed by melt-extruding the F polymer. Sheets further containing different polymers or inorganic particles can be formed by melt-kneading the F polymer with the different polymers or inorganic particles and then extruding them.

[0061] The heat-sealing process can be carried out by overlapping a sheet containing F polymer with a woven or nonwoven liquid crystal polymer 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 ensuring good impregnation of the F polymer into the woven or nonwoven liquid crystal polymer fabric, the heat-sealing temperature is preferably above the melting point of the F polymer, and more preferably above the melting point + 20°C. The heat-sealing temperature is preferably 300 to 380°C. The heat-sealing pressure is preferably 0.2 to 10 MPa. 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.

[0062] A further embodiment of the present disclosure provides a method for producing a composite sheet, comprising impregnating a liquid crystal polymer woven or nonwoven fabric with a dispersion containing F polymer particles. Hereinafter, this method will also be referred to as the "dispersion impregnation method." In one embodiment, the method for producing a composite sheet by the dispersion impregnation method may include impregnating a liquid crystal polymer woven or nonwoven fabric with a dispersion containing F polymer particles, and heating the liquid crystal polymer woven or nonwoven fabric impregnated with the dispersion to obtain a composite sheet. When manufacturing a composite sheet by a dispersion impregnation method, the F polymer is easily impregnated between the fibers of the liquid crystal polymer woven or nonwoven fabric. As a result, the adhesion between the liquid crystal polymer woven or nonwoven fabric and the F polymer tends to increase, which is preferable.

[0063] Impregnation can be carried out by placing the dispersion on the surface of the liquid crystal polymer woven or nonwoven fabric. Methods of impregnation include coating, droplet dispensing, and immersion, with roll coating, knife coating, bar coating, die coating, roller immersion, or spraying being preferred, and roller immersion being more preferred.

[0064] It is preferable to heat the liquid crystal polymer woven or nonwoven fabric impregnated with the dispersion to remove the dispersion medium, and then heat it further to calcine the F polymer. In this case, a composite sheet is obtained in which the calcined F polymer is impregnated into the liquid crystal polymer woven or nonwoven fabric. Heating to remove the dispersion medium is preferably carried out at 100-200°C for 0.1-30 minutes. Additionally, during heating, air may be blown in to promote the removal of the liquid dispersion medium by air drying. The heating for firing the F polymer is preferably carried out at a temperature above the melting point of the F polymer, and more preferably at 300-400°C for 0.1-30 minutes. Examples of heating devices for each heating process include ovens and forced-air drying ovens. The heat source in the device may be a contact-type heat source (hot air, hot plate, etc.) or a non-contact heat source (infrared radiation, etc.). Furthermore, each heating process may be carried out under normal pressure or under reduced pressure. Furthermore, the atmosphere used for each heating process may be either an air atmosphere or an inert gas atmosphere (such as helium, neon, argon, or nitrogen).

[0065] The impregnation and heating of the dispersion may be repeated two or more times. For example, the dispersion may be placed on the surface of a liquid crystal polymer woven or nonwoven fabric and heated to remove the liquid dispersion medium and bake the F polymer, thereby obtaining a composite sheet impregnated with the F polymer. Subsequently, the dispersion may be placed on the surface of the sheet and heated to remove the liquid dispersion medium and bake the F polymer, thereby obtaining a composite sheet further impregnated with the F polymer. When the impregnation and heating of the dispersion are repeated, it is preferable to repeat the impregnation and heating of the dispersion 2 to 8 times. When the impregnation and heating of the dispersion are repeated, the same type of dispersion may be used, or different types of dispersions may be used. Furthermore, when the impregnation and heating of the dispersion are repeated, it is sufficient to use a dispersion containing F polymer particles (hereinafter also referred to as "F particles") at least once.

[0066] When impregnation and heating of the dispersion are repeated, the dispersion used in the first impregnation is preferably one containing F particles. In this case, the components such as F particles contained in subsequent dispersions are more easily retained by the liquid crystal polymer woven or nonwoven fabric. Furthermore, the dispersion used in the first impregnation is more preferably one containing F particles and non-heat-meltable PTFE particles (hereinafter also referred to as "PTFE particles"). In this case, the components such as F particles contained in subsequent dispersions are even more easily retained by the liquid crystal polymer woven or nonwoven fabric. For the final impregnation, a dispersion containing F particles is preferable. In this case, the surface of the composite sheet tends to have excellent smoothness and adhesion. Furthermore, for the final impregnation, a dispersion containing both F particles and PTFE particles is more preferable. In this case, the surface of the composite sheet not only has excellent smoothness and adhesion, but also tends to possess a higher degree of PTFE properties. For impregnation steps other than the first and last, a dispersion containing PTFE particles is preferable. In this case, the composite sheet is more likely to possess high levels of PTFE properties, such as electrical characteristics.

[0067] The composite sheet is preferably a composite sheet in which a liquid crystal polymer woven or nonwoven fabric is impregnated with F polymer, non-thermally fused PTFE, and F polymer in that order. In this case, the composite sheet tends to have excellent low linear expansion, adhesion to other substrates, and electrical properties. One method for manufacturing such a composite sheet involves first impregnating a liquid crystal polymer woven or nonwoven fabric with a dispersion containing F particles and heating it, then impregnating it with a dispersion containing PTFE particles and heating it, and finally impregnating it with a dispersion containing F particles and heating it. Preferably, the dispersion used first and the dispersion used last are dispersions containing F particles and PTFE particles, respectively. Furthermore, it is preferable to perform the impregnation and heating of the dispersion containing PTFE particles multiple times.

[0068] In the thermocompression bonding method or dispersion impregnation method described above, it is preferable that the melting point of the F polymer, the melting point of the liquid crystal polymer, and the absolute value of the difference between the melting points of the F polymer and the liquid crystal polymer are within the range described above. In this case, during heating in both methods, the interaction between the polar groups of the softened polymer tends to increase, forming a dense matrix structure of the F polymer and liquid crystal polymer, which further improves the electrical properties and low linear expansion of the composite sheet. Furthermore, if the composite sheet contains inorganic particles, the support of the inorganic particles tends to improve. The following describes a dispersion containing F particles that may be used in the heat-compression bonding method or the dispersion impregnation method.

[0069] The dispersion is a mixture of F particles dispersed in a liquid dispersion medium. The dispersion may also contain inorganic particles, polymers other than the F polymer, and other components as described for the composite sheet. If the dispersion contains different polymers, these polymers may be dispersed as particulate matter in the dispersion or dissolved in the liquid dispersion medium. The dispersion may also contain surfactants and silane coupling agents.

[0070] From the viewpoint of dispersion stability, the D50 of F particles is preferably 0.1 μm or larger, more preferably 0.3 μm or larger, and even more preferably 1 μm or larger. From the viewpoint of dispersion stability, the D50 of F particles is preferably 25 μm or smaller, more preferably 10 μm or smaller, and even more preferably 8 μm or smaller. The specific surface area of ​​F particles is 1 to 25 m². 2 / g is preferable. One type of F particle may be used, or two or more types may be used.

[0071] F particles are particles containing F polymer, and may consist solely of F polymer. The F particles may contain polymers other than the F polymer, inorganic compounds, etc., and may form a core-shell structure with the F polymer as the core and a polymer other than the F polymer or an inorganic compound as the shell, or may form a core-shell structure with the F polymer as the shell and a polymer or inorganic compound different from the F polymer as the core. Examples of polymers other than F polymers include aromatic polyesters, polyamide-imides, polyimides, and maleimides. Examples of inorganic compounds include silica and boron nitride.

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

[0073] The liquid dispersion medium is a compound that is liquid at atmospheric pressure and 25°C, and preferably has a boiling point of 50 to 240°C. One liquid dispersion medium may be used, or two or more liquid dispersion mediums may be used. When two or more liquid dispersion mediums are used, it is preferable that the two or more liquid dispersion mediums are mutually compatible.

[0074] The liquid dispersion medium is preferably a compound selected from the group consisting of water, amides, ketones, and esters, and more preferably water. Examples of amides include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropanamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N-diethylformamide, hexamethylphosphoric triamide, and 1,3-dimethyl-2-imidazolidinone. Examples of ketones include acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl n-pentyl ketone, methyl isopentyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, and cycloheptanone. Examples of esters include methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethyl 3-ethoxypropionate, γ-butyrolactone, and γ-valerolactone.

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

[0076] The dispersion may contain inorganic particles. Details of the inorganic particles are as described above. If the dispersion contains inorganic particles, the inorganic particle content relative to the total volume of the dispersion is preferably 10 to 40% by mass, and more preferably 10 to 30% by mass.

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

[0078] If the different polymers are non-thermally soluble PTFE, the non-thermally soluble PTFE is preferably contained in the dispersion as particles. The D50 of the non-thermally soluble PTFE particles is preferably 0.1 to 1 μm. The content of non-thermally soluble PTFE particles relative to the total volume of the dispersion is preferably 20 to 60% by mass. In the dispersion, the ratio of the mass of non-thermally soluble PTFE particles to the mass of F particles is preferably 0.5 to 5, and more preferably 1 to 3. In this case, it is easier to obtain a composite sheet with excellent electrical properties.

[0079] If the different polymers are aromatic polymers, it is preferable that the aromatic polymers be dissolved in a liquid dispersion medium and included in the dispersion. The content of aromatic polymer relative to the total volume of the dispersion is preferably 0.1 to 30% by mass, and more preferably 0.3 to 10% by mass. In this case, it is easy to obtain a composite sheet with low linear expansion and excellent adhesion to the substrate.

[0080] The dispersion preferably contains a surfactant. A nonionic surfactant is preferred. Preferred nonionic surfactants include glycol-based surfactants, acetylene-based surfactants, silicone-based surfactants, or fluorine-based surfactants, with silicone-based surfactants being more preferred. One nonionic surfactant may be used, or two or more may be used. When two nonionic surfactants are used, it is preferable that they be a silicone-based surfactant and a glycol-based surfactant.

[0081] Specific examples of nonionic surfactants include the "Futergent®" series (manufactured by Neos Corporation), the "Surflon®" series (manufactured by AGC Seimi Chemical Co., Ltd.), the "Megafac®" series (manufactured by DIC Corporation), the "Unidyne®" series (manufactured by Daikin Industries Ltd.), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by Bic Chemie Japan Co., Ltd.), "KF-6011", "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.), and the "Tergitol" series (manufactured by Dow Chemical Corporation, such as "Tergitol TMN-100X").

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

[0083] The dispersion may further contain a silane coupling agent. In this case, the silane coupling agent acts as a binder for the F particles, making it easier for the F polymer to be well impregnated into the liquid crystal polymer woven or nonwoven fabric. Examples of silane coupling agents include those similar to the silane coupling agents that may be used for the surface treatment of the inorganic particles described above. If the dispersion contains a silane coupling agent, the content of the silane coupling agent in the dispersion is preferably 1 to 10% by mass.

[0084] The dispersion may further contain a pH adjuster or pH buffer to adjust the pH. Examples of pH adjusters include amines, ammonia, and citric acid. Examples of pH buffers include tris(hydroxymethyl)aminomethane, ethylenediaminetetraacetic acid, ammonium bicarbonate, ammonium carbonate, and ammonium acetate. The dispersion may further contain the other components mentioned above as components of the composite sheet.

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

[0086] The dispersion can be prepared by mixing F particles with a liquid dispersion medium. If the dispersion further contains other components such as inorganic particles or particles of different polymers, the dispersion may be prepared by adding the F particles and other components to the liquid dispersion medium all at once and mixing; adding the F particles and other components to the liquid dispersion medium sequentially and mixing; mixing the F particles and the liquid dispersion medium, and the other components and the liquid dispersion medium separately before mixing; or mixing the F particles and other components before mixing the liquid dispersion medium. It is preferable to manufacture the product by mixing it with a dispersion medium. These mixing processes may be carried out in batches or continuously.

[0087] Mixing devices include agitators equipped with blades (Henschel mixers, pressure kneaders, Banbury mixers, planetary mixers, etc.), grinding devices equipped with media (ball mills, attritors, basket mills, sand mills, sand grinders, Dino mills, dispermats, SC mills, spike mills, or agitator mills, etc.), and dispersion devices equipped with other mechanisms (microfluidizers, nanomizers, ultimateizers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impellers, rotating and revolving agitators, and thin-film swirling high-speed mixers, etc.).

[0088] A preferred method for producing the dispersion is to pre-mix F particles and a portion of the liquid dispersion medium to obtain a mixture, and then add the mixture to the remaining liquid dispersion medium to obtain the dispersion. The liquid dispersion medium used during mixing and addition may be of the same type or of a different type. If the dispersion further contains other components such as inorganic particles or particles of a polymer different from the F polymer, these other components may be mixed during mixing or during addition.

[0089] The kneaded product obtained by kneading may be in the form of a paste (such as a paste with a viscosity of 1,000 to 100,000 mPa·s) or a wet powder (such as a wet powder with a viscosity of 10,000 to 100,000 Pa·s as measured by a capillograph).

[0090] The viscosity measured by the capillary graph is calculated using a capillary with a length of 10 mm and a radius of 1 mm, with a furnace diameter of 9.55 mm, a load cell capacity of 2 t, a temperature of 25°C, and a shear rate of 1 s. -1 This is the value measured as such.

[0091] Mixing in the kneading process is preferably carried out using a planetary mixer. A planetary mixer is a stirring device having two stirring blades that rotate on their own axis and revolve around each other.

[0092] Mixing during the addition process is preferably carried out using a thin-film swirling high-speed mixer. A thin-film swirling high-speed mixer is a stirring device that spreads F particles and a liquid dispersion medium in a thin film on the inner wall surface of a cylindrical stirring tank and mixes them while swirling and applying centrifugal force.

[0093] The composite sheet may be in the form of a laminate formed by laminating it with a substrate. Because the composite sheet of this disclosure has an excellent coefficient of 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.

[0094] 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 a composite sheet and a substrate is thermocompression bonding. The thermocompression bonding method is the same as that described above. The peel strength between the composite sheet and the substrate in the laminate is preferably 10 to 100 N / cm.

[0095] The applications of the composite sheets disclosed herein are not particularly limited. The composite sheets disclosed herein are useful as antenna components, printed circuit boards, aircraft components, automotive components, sports equipment, food industry products, heat dissipation components, and the like. 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, and electromagnetic shielding.

[0096] Since the composite sheet of the present disclosure is excellent in electrical properties and low linear expansion properties, it is suitably used in applications where such properties are desired. For example, the composite sheet is suitably used as a material such as a copper-clad laminate of a printed wiring board.

Example

[0097] Hereinafter, embodiments of the present disclosure will be described in detail by way of examples, but the embodiments of the present disclosure are not limited thereto.

[0098] 1. Preparation of each component of the dispersion [F particles] F particle 1: Contains 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units in this order, and has a carbonyl group with 1000 per main chain carbon atom 6 Particles (D50: 2.1 μm) of a thermoplastic polymer 1 (melting point: 300 ° C, melt flow rate: 25 g / 10 min) F particle 2: Particles (D50: 2.4 μm) of a thermoplastic polymer 2 (melting point: 300 ° C, melt flow rate: 22 g / 10 min) that contains 98.5 mol% and 1.5 mol% of TFE units and PPVE units in this order and does not have an oxygen-containing polar group [Inorganic particles] Inorganic particle 1: Spherical silica (D50: 1 μm) [Woven or non-woven fabric of liquid crystal polymer] Non-woven fabric 1: "Vecroes" manufactured by Kuraray Co., Ltd. (basis weight: 9 g / m 2 ) Woven fabric 1: Plain weave of a liquid crystalline aromatic polyester with an aromatic ring content of 60% by mass or more (load deflection temperature: 300 ° C, specific gravity: 1.42 g / cm 3 , fiber diameter: 7 μm, thickness: 123 μm, volume basis weight: 32 cm 3 / m 2 , warp density: 20 threads / cm, weft density: 20 threads / cm) Woven fabric 2: Woven fabric of a liquid crystalline aromatic polyester (melting point: 320 ° C) (load deflection temperature 350 ° C, basis weight: 45 g / cm 2 ) Woven fabric 3: Woven fabric of a liquid crystalline aromatic polyester (melting point: 230 ° C) (basis weight: 41 g / cm 2)

[0099] 2. Manufacturing of composite sheets (Example 1) 30 parts by mass of F particles 1, 15 parts by mass of inorganic particles 1, 1 part by mass of silicone-based surfactant, and 64 parts by mass of water are placed in a pot, and zirconia balls are added. The pot is then rolled at 150 rpm for 1 hour to obtain dispersion 1 (viscosity: 200 mPa·s). The obtained dispersion 1 is placed on the nonwoven fabric 1 by the roller immersion method, and then heated and dried in a drying oven at 120°C for 5 minutes. After that, it is heated and baked in a far-infrared oven at 340°C for 10 minutes to obtain a composite sheet 1 (thickness: 40 μm) in which the baked F particles 1 are impregnated into the nonwoven fabric 1. In the composite sheet 1, the content of inorganic particles 1 is 16% by mass, and the mass ratio of the content of inorganic particles 1 to the content of polymer 1 is 0.5. (Example 2) A composite sheet 2 (thickness: 140 μm) is obtained in which the woven fabric 1 is impregnated with a calcined product of F particles 1, in the same manner as in Example 1, except that the nonwoven fabric 1 is changed to woven fabric 1. In the composite sheet 2, the content of inorganic particles 1 is 7% by mass, and the mass ratio of the content of inorganic particles 1 to the content of polymer 1 is 0.5. (Example 3) A composite sheet 3 (thickness: 140 μm) is obtained in which the woven fabric 2 is impregnated with a fired product of F particles 1, in the same manner as in Example 1, except that the nonwoven fabric 1 is changed to woven fabric 2. In the composite sheet 3, the content of inorganic particles 1 is 7% by mass, and the mass ratio of the content of inorganic particles 1 to the content of polymer 1 is 0.5. (Example 4) In the preparation of dispersion 1, inorganic particles 1 are not used, and the nonwoven fabric 1 is replaced with woven fabric 2, but otherwise the same procedure as in Example 1 is followed to obtain a composite sheet 4 (thickness: 140 μm) in which the woven fabric 2 is impregnated with a calcined product of F particles 1. (Example 5) In the preparation of dispersion 1, inorganic particles 1 are not used, and the nonwoven fabric 1 is replaced with woven fabric 3, otherwise the procedure is the same as in Example 1, to obtain a composite sheet 5 (thickness: 140 μm) in which the woven fabric 3 is impregnated with calcined F particles 1. (Example 6: Comparative Example) A composite sheet 6 (thickness: 140 μm) is obtained by impregnating woven fabric 1 with fired F particles 2, in the same manner as in Example 1, except that F particle 1 is changed to F particle 2. During the drying and firing processes in the manufacture of the composite sheet 6, inorganic particles 1 are detached.

[0100] 3. Evaluation of composite sheets 3-1. Peel strength Each of the obtained composite sheets is heat-pressed and bonded to the copper foil to create a copper-clad laminate, and a rectangular test piece measuring 100 mm in length and 10 mm in width is cut from the copper-clad laminate. The test piece is fixed 50 mm from one end in the longitudinal direction, and the copper foil and composite sheet are peeled off at a tensile speed of 50 mm / min at a 90° angle to the test piece from the other end in the longitudinal direction. The maximum load at which peeling occurs is defined as the peel strength (N / cm), and is evaluated according to the following evaluation criteria. [Evaluation Criteria] A: It is 12 N / cm or higher. B: Less than 12 N / cm 3-2. Coefficient of linear expansion For each of the obtained composite sheets, a 180 mm square test specimen is cut out, and the coefficient of linear expansion of the test specimen in the range of 25°C to 260°C is measured according to the measurement method specified in JIS C 6471:1995, and evaluated according to the following evaluation criteria. AA:20ppm / ℃ or less A: More than 20ppm / ℃ and below 30ppm / ℃ B: More than 30ppm / ℃ and less than 40ppm / ℃ C: More than 40ppm / ℃

[0101] 3-3. Electrical Characteristics For each of the obtained composite sheets, a sample measuring 10 cm in length and 5 cm in width is cut out, and the relative permittivity and dielectric loss tangent (measurement frequency: 10 GHz) are measured using the SPDR (Split Post Dielectric Resonance) method, and evaluated according to the following evaluation criteria. [Evaluation Criteria] A: The relative permittivity is 2.2 or less, and the dielectric loss tangent is less than 0.0010. B: The relative permittivity is 2.2 or less and the dielectric loss tangent is 0.0010 or more and less than 0.0020, or the relative permittivity is greater than 2.2 and 2.4 or less and the dielectric loss tangent is less than 0.0010. C: 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. Table 1 below summarizes the evaluation results for each composite sheet. As shown in the table below, composite sheets 1 to 5 exhibit excellent electrical properties and low linear expansion. Furthermore, composite sheets 1 to 5 also showed good evaluation of peel strength.

[0102] [Table 1]

[0103] The disclosures of Japanese Patent Applications Nos. 2021-119739 and 2021-172596 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 woven or nonwoven fabric of a heat-meltable liquid crystal polymer having a melting point of 230 to 350°C, The liquid crystal polymer woven or nonwoven fabric is impregnated with a heat-meltable tetrafluoroethylene-based polymer having oxygen-containing polar groups and a melting point of 260 to 320°C, and containing units based on tetrafluoroethylene and units based on perfluoro(alkyl vinyl ether). A composite sheet in which the absolute difference between the melting point of the tetrafluoroethylene polymer and the melting point of the liquid crystal polymer is 30°C or less.

2. The composite sheet according to claim 1, wherein the oxygen-containing polar group is a hydroxyl group-containing group or a carbonyl group-containing group.

3. The composite sheet according to claim 1 or 2, wherein the oxygen-containing polar group is an alcoholic hydroxyl group-containing group or a carbonyl group-containing group.

4. The composite sheet according to claim 1 or 2, wherein the oxygen-containing polar group is a carbonyl group-containing group.

5. The composite sheet according to claim 1 or 2, wherein the liquid crystal polymer includes a liquid crystal aromatic polyester.

6. The composite sheet according to claim 1 or 2, further containing a polymer different from the tetrafluoroethylene polymer.

7. The composite sheet according to claim 1 or 2, further containing inorganic particles.

8. The composite sheet according to claim 1 or 2, comprising at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles, wherein the total content of the at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles is greater than 5% by mass with respect to the total mass of the composite sheet.

9. The composite sheet according to claim 1 or 2, comprising at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and inorganic particles, wherein the ratio of the total mass of the at least one selected from the group consisting of a polymer different from the tetrafluoroethylene polymer and the inorganic particles to the mass of the tetrafluoroethylene polymer is 0.1 or more.

10. The composite sheet according to claim 1 or 2, wherein the thickness is less than 50 μm.

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