Composition, fluororesin sheet, and method for producing same

Abstract

Provided are: a composition for obtaining a fluororesin sheet having excellent performance from the viewpoints of low dielectric constant, low loss, and low thermal expansion; a fluororesin sheet; and a method for producing the fluororesin sheet. A composition containing a fluororesin and a filler in which the ratio of (dielectric loss tangent of the filler as measured at 10 GHz) / (surface area of the filler (m2 / g)) is 0.00001-0.00035.

Description

Technical Field

[0001] The present disclosure relates to a composition, a fluororesin sheet, and a method for manufacturing the same. Background Art

[0002] In high-frequency printed wiring boards, high-frequency printed wiring boards with low transmission loss are required. In such high-frequency printed wiring boards, it is known to use fluororesin films (Patent Document 1, etc.). In addition, Patent Documents 2 and 3 describe the use of a fluororesin mixed with a filler as a wiring board material.

[0003] Furthermore, Patent Document 4 discloses the use of a fluororesin composition in which spherical silica particles are mixed in a fluororesin for a circuit substrate.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-8260

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 63-259907

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2022-510017

[0009] Patent Document 4: International Publication No. 2020 / 145133 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] An object of the present disclosure is to provide a composition, a fluororesin sheet made thin, and a method for manufacturing the same, which are used to obtain a fluororesin sheet having excellent properties from the viewpoints of low dielectric constant, low loss, and low thermal expansion.

[0012] Means for Solving the Problems

[0013] The present disclosure relates to a composition, characterized in that it contains:

[0014] a fluororesin; and

[0015] (The dielectric loss tangent of the filler measured at 10 GHz) / (the specific surface area of the filler (m 2 / g)) ratio is a filler of 0.00001 to 0.00035.

[0016] The above fluororesin is preferably a polytetrafluoroethylene resin.

[0017] The above fluororesin is preferably not melt-moldable.

[0018] The SSG of the above polytetrafluoroethylene resin is preferably 2.0 to 2.3.

[0019] The refractive index of the above-mentioned polytetrafluoroethylene resin is preferably 1.2 to 1.6.

[0020] The primary particle size of the above-mentioned fluororesin is preferably 0.05 μm to 10 μm.

[0021] The volume-based cumulative 50% diameter of the above-mentioned fluororesin is preferably 0.05 μm to 40 μm.

[0022] The above-mentioned filler is preferably silica particles.

[0023] The content of the above-mentioned filler relative to the total amount of the composition is 50 wt% or more.

[0024] The average particle size of the above-mentioned filler is preferably 0.5 μm to 250 μm.

[0025] The above-mentioned filler is preferably a filler whose surface is coated with a silane coupling agent.

[0026] The value of the dielectric loss tangent of the above-mentioned composition at 10 GHz is preferably 0.0015 or less.

[0027] The present disclosure also relates to a fluororesin sheet, which is characterized in that it is composed of a composition, and the above-mentioned composition includes: a fluororesin; and a filler having a ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (specific surface area of the filler (m 2 / g)) of 0.00001 to 0.00035.

[0028] The thickness of the above-mentioned fluororesin sheet is preferably 5 μm to 250 μm.

[0029] The present disclosure also relates to a method for manufacturing the above-mentioned fluororesin sheet, which is characterized in that it has a step of mixing fluororesin particles and a filler and forming a film.

[0030] The above-mentioned manufacturing method preferably only mixes fluororesin particles and an inorganic filler and forms a film without adding other components.

[0031] The present disclosure also relates to a copper-clad laminate, which uses a copper foil and the above-mentioned fluororesin sheet as essential layers.

[0032] The present disclosure also relates to a circuit board, which is characterized in that it has the above-mentioned copper-clad laminate.

[0033] Effects of the Invention

[0034] The fluororesin sheet obtained from the composition of the present disclosure has excellent properties in terms of low dielectric constant, low loss, and low thermal expansion. In addition, the sheet can be made thinner. Detailed Description

[0035] The following provides a detailed description of the present disclosure.

[0036] A great deal of research has been conducted on compositions in which fillers are mixed with fluororesins. On the other hand, in fields such as high-frequency printed wiring boards, in recent years, there has been an increasing demand for high-level properties such as low dielectric constant, low loss, and low expansion. Research on obtaining such high-level low dielectric constant, low loss, and low expansion has not been sufficient.

[0037] An object of the present disclosure is to provide a composition for obtaining a fluororesin sheet having a high level of low dielectric constant, low loss, and low expansion that has not been achieved in the past.

[0038] (Filler)

[0039] The composition of the present disclosure is characterized in that it contains a fluororesin and a filler, and the ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2 / g)) is 0.00035 to 0.00001. That is, it is characterized by using a filler that satisfies the above specific parameters.

[0040] The dielectric loss tangent of the filler is greatly affected by polar functional groups on the surface. For example, in the case of silica, the amount of Si-OH groups on the surface affects the dielectric loss tangent. More specifically, the larger the amount of Si-OH groups on the surface, the larger the dielectric loss tangent of the filler. Therefore, in the present disclosure, it is preferable to reduce the amount of Si-OH on the surface.

[0041] From such an aspect, the ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2 / g)) becomes an index indicating the amount of surface polar functional groups per unit surface area of the filler. The present inventors found that when the amount of such surface polar functional groups is reduced to be within the above specified range, a fluororesin sheet having particularly excellent low dielectric constant, low loss, and low expansion can be obtained, thereby completing the present disclosure.

[0042] In order to produce a filler having a ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2 / g)) within the above range, in addition to selecting the filler to be used, surface treatment is also required. That is, through surface treatment, the polar functional groups present on the surface of the filler react to reduce the amount of polar functional groups, thereby enabling it to be within the above range. The following provides a detailed description of such surface treatment.

[0043] The above ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2The upper limit of ( / g) is more preferably 0.00030, and even more preferably 0.00025.

[0044] In the present disclosure, regarding the dielectric loss tangent of the filler measured at 10 GHz, using a cylindrical cavity resonator and a network analyzer, the filler powder sample is filled in a quartz tube and loaded into the resonator for measurement. The characteristics (resonance frequency and Q value) of the resonator before and after inserting the sample are obtained, and the dielectric loss tangent is calculated based on the results. This measurement method is carried out in an environment of room temperature 25°C and humidity 40% in accordance with Japanese Industrial Standard JIS 2565 Test Method for Ferrite Cores for Microwaves.

[0045] In the present disclosure, the dielectric loss tangent of the filler measured at 10 GHz is not particularly limited, and is preferably 0.0015 or less. By being such a value, it is preferable in terms of the fluororesin sheet having low loss. The above upper limit is more preferably 0.0025, and even more preferably 0.002.

[0046] In the present disclosure, the surface area (m 2 / g) of the filler is not particularly limited, and is preferably 1 to 10. By being within the above range, it is preferable in terms of the good balance between low loss and low linear expansion of the fluororesin sheet. The above lower limit is more preferably 1.2, and even more preferably 1.5. The above upper limit is more preferably 9, and even more preferably 7.

[0047] In the present disclosure, the surface area (m 2 / g), that is, the specific surface area of the filler is a value based on the BET method. As a specific surface area measuring machine, “Macsorb HM model-1208” (manufactured by MACSORB Co., Ltd.) can be used for measurement. It should be noted that when the fluororesin sheet of the present disclosure contains two or more kinds of fillers, the surface area measured with respect to the entire mixed fillers is within the above range.

[0048] In the present disclosure, the average particle size of the filler is preferably 0.5 μm to 250 μm. It should be noted that the average particle size here is the D50 value measured by a laser analysis type particle size distribution meter.

[0049] If the average particle size is less than 0.5 μm, agglomeration of the filler occurs, and thus sufficient effects cannot be obtained, which is not preferable in this regard.

[0050] The filler that can be used in the present disclosure is not particularly limited, and examples thereof include one or more organic filler materials selected from aromatic polyamide fibers, polyphenylene esters, polyphenylene sulfides, polyimides, polyether ether ketones, polyphenylenes, polyamides, and wholly aromatic polyester resins; one or more inorganic filler materials selected from ceramics, talc, mica, alumina, zinc oxide, tin oxide, titanium oxide, silicon oxide, calcium carbonate, calcium oxide, magnesium oxide, potassium titanate, glass fibers, glass flakes, glass beads, silicon carbide, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers; and the like. Two or more of them can also be used in combination.

[0051] The shape of the above-mentioned filler is not particularly limited, and spherical shape is particularly preferred. If it is spherical, it is preferred in terms of being easily processed uniformly during hole opening processing, having a small specific surface area, and low transmission loss.

[0052] Among them, silica is particularly preferably used, and spherical silica particles are most preferably used.

[0053] The above-mentioned spherical silica particles refer to particles whose particle shape is close to a perfect sphere. Specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, further preferably 0.90 or more, and most preferably 0.95 or more. Regarding the sphericity, a photograph is taken by SEM, and based on the area and perimeter of the observed particles, it is calculated as the value calculated by (sphericity) = {4π×(area)÷(perimeter)²}. The closer it is to 1, the closer it is to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Co., Ltd.: FPIA-3000) is adopted.

[0054] For the spherical silica particles used in the present disclosure, when integrating the volume from the smaller particle size side, D90 / D10 is preferably 2 or more (preferably 2.3 or more, 2.5 or more), and D50 is preferably 10 μm or less. Furthermore, D90 / D50 is preferably 1.5 or more (more preferably 1.6 or more). D50 / D10 is preferably 1.5 or more (more preferably 1.6 or more). Furthermore, D50 is more preferably 5 μm or less. Since spherical silica particles with a small particle size may enter the gaps between spherical silica particles with a large particle size, the filling property is excellent, and the fluidity can be improved. In particular, as the particle size distribution, it is preferred that the frequency on the smaller particle size side is larger compared to the Gaussian curve. The particle size can be measured using a laser diffraction scattering type particle size distribution measuring device. In addition, since coarse particles make it difficult to thin the film of the sheet, it is preferred to remove coarse particles having a specified particle size or more using a filter or the like.

[0055] The water absorbency of the above spherical silica particles is preferably 1.0% or less, more preferably 0.5% or less. The water absorbency is based on the mass of the silica particles in the dry state. In the measurement of the water absorbency, a sample in a dry state is placed at 40°C and 80% RH for 1 hour, and the water generated by heating at 200°C is measured using a Karl Fischer moisture analyzer, and thus calculated.

[0056] In addition, for the above spherical silica particles, the fluororesin sheet can be heated in an air atmosphere at 600°C for 30 minutes to burn off the fluororesin. After taking out the spherical silica particles, the above parameters can be measured by the above method.

[0057] The above silica particles are surface-treated. By performing surface treatment in advance, aggregation of the silica particles can be suppressed, and the silica particles can be well dispersed in the resin composition. In addition, it is also preferable in terms of making the ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2 / g)) within a specified range.

[0058] The above surface treatment can be appropriately selected in terms of the type of surface treatment agent and the treatment amount so that the ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (surface area of the filler (m 2 / g)) is within a specified range.

[0059] There is no particular limitation on the above surface treatment, and any known surface treatment can be used. Specifically, for example, treatment with a silane coupling agent such as an epoxy silane, an amino silane, an isocyanate silane, a vinyl silane, an acrylic silane, a hydrophobic alkyl silane, a phenyl silane, a fluorinated alkyl silane, etc. having a reactive functional group, plasma treatment, fluorination treatment, etc. can be mentioned.

[0060] Examples of the above silane coupling agents include epoxy silanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino silanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, isocyanate silanes such as 3-isocyanatopropyltrimethoxysilane, vinyl silanes such as vinyltrimethoxysilane, and acryloyl silanes such as acryloyloxytrimethoxysilane.

[0061] The above spherical silica particles can use commercially available silica particles that satisfy the above properties. Examples of commercially available silica particles include Denka fused silica FB grade (manufactured by Denka Co., Ltd.), Denka fused silica SFP grade (manufactured by Denka Co., Ltd.), EXCELICA (manufactured by Tokuyama Corporation), high-purity synthetic spherical silica ADMAFINE (manufactured by Admatechs Co., Ltd.), ADMANANO (manufactured by Admatechs Co., Ltd.), ADMAFUSE (manufactured by Admatechs Co., Ltd.), and the like.

[0062] (The dielectric loss tangent of the filler measured at 10 GHz) / (the surface area of the filler (m 2 / g)) value can be adjusted by the filler shape, the size of the filler, the presence or absence of surface treatment, etc. More specifically, as the above spherical silica particles, particles of a specified size are preferably used, and surface treatment is further performed. The type of surface treatment agent during surface treatment also affects the above parameters. More specifically, it is particularly preferred to perform surface treatment using aminopropyltriethoxysilane, aminosilane, vinylsilane, hydrophobic alkylsilane, phenylsilane, 3-mercaptopropylsilane, 3-acryloxypropylsilane, 3-methacryloxypropylsilane, p-styrylsilane, silylpropyl succinic anhydride, 3-isocyanatepropylsilane, 2-(3,4-epoxycyclohexyl)ethylsilane, and the like. By performing surface treatment using these silane coupling agents, the polar functional groups present on the surface of the filler react, and the amount of polar functional groups decreases, so the electrical properties are excellent.

[0063] The above filler is preferably contained in a proportion of 50% by weight or more based on the weight of the sheet. Such a blending amount is preferable from the aspect of being low thermal expansion while maintaining a low dielectric constant and low loss. The above blending amount is more preferably 53% by weight or more, and further preferably 56% by weight or more. The upper limit of the blending amount of the filler is not particularly limited, and is preferably 68% by weight or less, and further preferably 65% by weight or less.

[0064] (fluororesin)

[0065] The composition of the present disclosure contains a fluororesin. Since the fluororesin has low dielectric properties, it can be suitably used for the purpose of the present disclosure.

[0066] The fluororesin that can be used in the present disclosure is not particularly limited, and examples thereof include polytetrafluoroethylene (PTFE), tetrafluoroethylene [TFE] / hexafluoropropylene [HFP] copolymer [FEP], TFE / alkyl vinyl ether copolymer [PFA], TFE / HFP / alkyl vinyl ether copolymer [EPA], TFE / trifluorochloroethylene [CTFE] copolymer, TFE / ethylene copolymer [ETFE], polyvinylidene fluoride [PVdF], tetrafluoroethylene with a molecular weight of 300,000 or less [LMW-PTFE], etc. One kind can be used, or two or more kinds can be mixed. From the aspect of low dielectric properties, polytetrafluoroethylene resin (PTFE) is particularly preferred. PTFE preferably has fibrillarity. PTFE with fibrillarity refers to PTFE that can perform paste extrusion on unfired polymer powder.

[0067] PTFE can be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), or homopolymer polytetrafluoroethylene (hereinafter referred to as homopolymer PTFE), or a mixture of modified PTFE and homopolymer PTFE. It should be noted that from the aspect of maintaining the moldability of polytetrafluoroethylene well, the content ratio of modified PTFE in high-molecular PTFE is preferably 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less. The homopolymer PTFE is not particularly limited, and the homopolymer PTFE disclosed in Japanese Patent Laid-Open No. 53-60979, Japanese Patent Laid-Open No. 57-135, Japanese Patent Laid-Open No. 61-16907, Japanese Patent Laid-Open No. 62-104816, Japanese Patent Laid-Open No. 62-190206, Japanese Patent Laid-Open No. 63-137906, Japanese Patent Laid-Open No. 2000-143727, Japanese Patent Laid-Open No. 2002-201217, International Publication No. 2007 / 046345 pamphlet, International Publication No. 2007 / 119829 pamphlet, International Publication No. 2009 / 001894 pamphlet, International Publication No. 2010 / 113950 pamphlet, International Publication No. 2013 / 027850 pamphlet, etc. can be preferably used. Among them, the homopolymer PTFE disclosed in Japanese Patent Laid-Open No. 57-135, Japanese Patent Laid-Open No. 63-137906, Japanese Patent Laid-Open No. 2000-143727, Japanese Patent Laid-Open No. 2002-201217, International Publication No. 2007 / 046345 pamphlet, International Publication No. 2007 / 119829 pamphlet, International Publication No. 2010 / 113950 pamphlet, etc., which has high tensile properties, is preferred.

[0068] The modified PTFE is composed of TFE and monomers other than TFE (hereinafter referred to as modified monomers). Examples of the modified PTFE include PTFE uniformly modified with a modified monomer, PTFE modified in the initial stage of the polymerization reaction, and PTFE modified in the final stage of the polymerization reaction, and there is no particular limitation. The modified PTFE is preferably a TFE copolymer obtained by supplying a trace amount of monomers other than TFE together with TFE for polymerization within a range that does not significantly impair the properties of the TFE homopolymer. For example, the modified PTFE disclosed in Japanese Patent Application Laid-Open No. 60-42446, Japanese Patent Application Laid-Open No. 61-16907, Japanese Patent Application Laid-Open No. 62-104816, Japanese Patent Application Laid-Open No. 62-190206, Japanese Patent Application Laid-Open No. 64-1711, Japanese Patent Application Laid-Open No. 2-261810, Japanese Patent Application Laid-Open No. 11-240917, Japanese Patent Application Laid-Open No. 11-240918, Pamphlet of International Publication No. 2003 / 033555, Pamphlet of International Publication No. 2005 / 061567, Pamphlet of International Publication No. 2007 / 005361, Pamphlet of International Publication No. 2011 / 055824, Pamphlet of International Publication No. 2013 / 027850, etc. can be preferably used. Among them, the modified PTFE disclosed in Japanese Patent Application Laid-Open No. 61-16907, Japanese Patent Application Laid-Open No. 62-104816, Japanese Patent Application Laid-Open No. 64-1711, Japanese Patent Application Laid-Open No. 11-240917, Pamphlet of International Publication No. 2003 / 033555, Pamphlet of International Publication No. 2005 / 061567, Pamphlet of International Publication No. 2007 / 005361, Pamphlet of International Publication No. 2011 / 055824, etc., which has high tensile properties, is preferred.

[0069] The modified PTFE contains TFE units based on TFE and modified monomer units based on the modified monomer. The modified monomer units are part of the molecular structure of the modified PTFE and are parts derived from the modified monomer. The modified PTFE preferably contains 0.001% by weight to 0.500% by weight of the modified monomer units based on all the monomer units, and preferably contains 0.01% by weight to 0.30% by weight. All the monomer units are parts derived from all the monomers in the molecular structure of the modified PTFE.

[0070] The modified monomer is not particularly limited as long as it can copolymerize with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); fluorochloroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing fluorinated olefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluoro vinyl ethers; perfluoroalkyl ethylene (PFAE), ethylene, etc. The modified monomer used may be one kind or a plurality of kinds.

[0071] The perfluoro vinyl ether is not particularly limited. For example, perfluoro unsaturated compounds represented by the following general formula (1) can be cited, etc.

[0072] CF 2 =CF-ORf…(1)

[0073] In the formula, Rf represents a perfluoro organic group.

[0074] In this specification, the perfluoro organic group is an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The above perfluoro organic group may have an ether oxygen.

[0075] As the perfluoro vinyl ether, for example, perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms can be cited. The number of carbon atoms of the perfluoroalkyl group is preferably 1 to 5. As the perfluoroalkyl group in PAVE, for example, perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, perfluorohexyl, etc. can be cited. As PAVE, perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE) are preferred.

[0076] The above perfluoroalkyl ethylene (PFAE) is not particularly limited. For example, perfluorobutyl ethylene (PFBE), perfluorohexyl ethylene (PFHE), etc. can be cited.

[0077] As the modifying monomer in the modified PTFE, at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene is preferred.

[0078] The above fluororesin is preferably not melt-moldable. Not being melt-moldable means that even when heated above the melting point, the resin does not have sufficient fluidity and cannot be molded by the melt-molding methods commonly used in resins. PTFE conforms to this situation.

[0079] In the present disclosure, it is preferred to use such a non-melt-moldable fluororesin and form a fluororesin sheet by a fibrillation molding method. This molding method will be described later.

[0080] The above PTFE preferably has an SSG of 2.0 to 2.3. If such PTFE is used, it is easy to obtain a PTFE film having high strength (cohesion and puncture strength per unit thickness). PTFE having a large molecular weight has long molecular chains, so it is difficult to form a structure in which the molecular chains are regularly arranged. In this case, the length of the amorphous part increases and the degree of entanglement of the molecules increases. It is considered that when the degree of entanglement of the molecules is high, the PTFE film is not easily deformed by the applied load and exhibits excellent mechanical strength. In addition, if PTFE having a large molecular weight is used, it is easy to obtain a PTFE film having a small average pore size.

[0081] The lower limit of the above SSG is more preferably 2.05, and further preferably 2.1. The upper limit of the above SSG is more preferably 2.25, and further preferably 2.2.

[0082] The standard specific gravity [SSG] is obtained by preparing a specimen in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained specimen by the water displacement method.

[0083] In the present embodiment, the molecular weight (number average molecular weight) of PTFE constituting the PTFE powder is, for example, in the range of 2 million to 12 million. The lower limit value of the molecular weight of PTFE may be 3 million or 4 million. The upper limit value of the molecular weight of PTFE may be 10 million.

[0084] As a method for measuring the number average molecular weight of PTFE, there are a method obtained from the standard specific gravity (Standard Specific Gravity) and a measurement method using the dynamic viscoelasticity during melting. The method obtained from the standard specific gravity can be implemented by using a sample molded in accordance with ASTM D-4895 98 and the water displacement method according to ASTM D-792. The measurement method using dynamic viscoelasticity is described, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538 and this literature 1989, Vol. 29, 273.

[0085] The refractive index of the above PTFE is preferably in the range of 1.2 to 1.6. By having such a refractive index, it is preferable from the aspect of low dielectric. The refractive index can be made within the above range by methods such as adjusting the polarizability and the flexibility of the main chain. The lower limit of the above refractive index is more preferably 1.25, more preferably 1.30, and most preferably 1.32. The upper limit of the above refractive index is more preferably 1.55, more preferably 1.50, and most preferably 1.45.

[0086] The above refractive index is a value measured using a refractometer (Abbemat 300).

[0087] In addition, the maximum endothermic peak temperature (crystal melting point) of the above PTFE is preferably 340 ± 7°C.

[0088] PTFE can be low melting point PTFE with a maximum peak temperature of the endothermic curve on the crystal melting curve measured by a differential scanning calorimeter of 338°C or less, and high melting point PTFE with a maximum peak temperature of the endothermic curve on the crystal melting curve measured by a differential scanning calorimeter of 342°C or more.

[0089] Low melting point PTFE is a powder manufactured by polymerization through the emulsion polymerization method, having the above-mentioned maximum endothermic peak temperature (crystal melting point), with a dielectric constant (ε) of 2.08 - 2.2 and a dielectric loss tangent (tanδ) of 1.9×10 -4 ~4.0×10 -4 . As commercially available products, for example, POLYFLON FINE POWDER F201, F203, F205, F301, F302 manufactured by Daikin Industries, Ltd.; CD090, CD076 manufactured by Asahi Glass Co., Ltd.; TF6C, TF62, TF40, etc. manufactured by DuPont Corporation can be cited.

[0090] High melting point PTFE powder is also a powder manufactured by polymerization through the emulsion polymerization method, having the above-mentioned maximum endothermic peak temperature (crystal melting point), with a dielectric constant (ε) of 2.0 - 2.1 and a dielectric loss tangent (tanδ) of 1.6×10 -4 ~2.2×10 -4 , being low overall. As commercially available products, for example, POLYFLON FINE POWDER F104, F106 manufactured by Daikin Industries, Ltd.; CD1, CD141, CD123 manufactured by Asahi Glass Co., Ltd.; TF6, TF65, etc. manufactured by DuPont Corporation can be cited.

[0091] It should be noted that the average particle size of the powder formed by the secondary aggregation of the two PTFE polymer particles is usually preferably 250 μm - 2000 μm. In particular, from the aspect of improving the fluidity during mold filling at the time of preforming, granulated powder obtained by granulating using a solvent is preferably used.

[0092] PTFE in the form of powder satisfying the above various parameters can be obtained by existing manufacturing methods. For example, it can be manufactured according to the manufacturing methods described in International Publication No. WO2015 / 080291 pamphlet, International Publication No. WO2012 / 086710 pamphlet, etc.

[0093] (Composition)

[0094] The composition of the present disclosure contains the above-mentioned filler and fluororesin. As needed, it may contain components other than the filler and fluororesin, or may be composed only of the filler and fluororesin. The content of components other than the filler and fluororesin is preferably 10% by weight or less.

[0095] In the composition of the present disclosure, the content of the filler is preferably 70% by weight or less relative to the total amount of the composition. By containing the filler in such a range, the linear expansion coefficient can be reduced, which is preferable in terms of easy molding. The lower limit of the compounding amount of the above filler is not particularly limited, and from the aspect of being able to reduce the linear expansion coefficient, it is preferably 40% by weight. The above upper limit is more preferably 68% by weight, and further preferably 65% by weight. The above lower limit is more preferably 40% by weight, and further preferably 45% by weight.

[0096] The composition of the present disclosure preferably has a dielectric loss tangent of 0.0001 to 0.0015 at 10 GHz as the composition. By being within such a range, it is preferable in terms of achieving low loss.

[0097] Furthermore, the dielectric loss tangent of the composition of the present disclosure at 80 GHz as the composition can be 0.0001 to 0.0018. It is preferably to have a low dielectric loss tangent in such a wide frequency region to achieve low loss. In addition, when the dielectric loss tangent at 80 GHz is low, the gain of the millimeter-wave antenna increases, so it is preferable.

[0098] (Fluororesin sheet)

[0099] The fluororesin sheet of the present disclosure contains a fluororesin and a filler having a ratio of (dielectric loss tangent of the filler measured at 10 GHz) / (specific surface area of the filler (m 2 / g)) of 0.00001 to 0.00035.

[0100] The above fluororesin sheet is preferably less than 300 μm. Even if the fluororesin sheet of the present disclosure is thin, its purpose can be fully achieved. From such an aspect, it is more preferably less than 200 μm, and further preferably less than 150 μm. In addition, if it can be processed into a thickness of 100 μm or less as needed, it can be widely applied to substrates of various thicknesses, which is preferable.

[0101] The linear expansion coefficient of the fluororesin sheet of the present disclosure is preferably 10 to 100 (ppm / °C). By being within the above range, it is preferable in terms of becoming a fluororesin sheet with low shrinkage and excellent dimensional stability. The above upper limit is more preferably 90, and further preferably 80. The above lower limit is more preferably 12, and further preferably 15. Regarding the linear expansion coefficient in this specification, TMA measurement using TMA-7100 (manufactured by Hitachi High-Tech Science Corporation) was performed in the tensile mode. As the sample sheet, a sheet with a length of 20 mm, a width of 5 mm, and a thickness of 150 μm was used, the distance between the chucks was set to 10 mm, and the linear expansion rate was obtained from the displacement amount of the sample at -10°C to 160°C while applying a load of 49 mN at a heating rate of 2°C / minute.

[0102] The rate of change of the relative dielectric constant of the fluororesin sheet of the present disclosure in the temperature range of -50°C to 150°C is preferably 0.025 or less, more preferably 0.023 or less, and still more preferably 0.021 or less. If it is within such a range, the change in electrical properties caused by temperature is small, and stable performance can be obtained when used for high-frequency printed circuit boards, which is preferable from this point of view.

[0103] (Manufacturing method of fluororesin sheet)

[0104] The fluororesin sheet of the present disclosure can be obtained by mixing the above-mentioned fluororesin particles with a filler and forming a film. Its manufacturing method is not limited, and it can be carried out by paste extrusion molding, powder calendering molding, etc.

[0105] As described above, as the fluororesin used in the fluororesin sheet of the present disclosure, a fluororesin that cannot be melt-molded is preferably used. In the case of using such a fluororesin and molding it into a sheet shape, it is preferably formed by fibrillating powdery PTFE as a raw material.

[0106] The above-mentioned powdery PTFE preferably uses PTFE having a primary particle size of 0.05 μm to 10 μm. By using such PTFE, it has the advantages of excellent moldability and dispersibility. It should be noted that the primary particle size here is the value measured according to ASTM D 4895.

[0107] The above-mentioned powdery PTFE preferably contains 50% by mass or more of polytetrafluoroethylene resin having a secondary particle size of 500 μm or more, and more preferably contains 80% by mass or more. By making the PTFE having a secondary particle size of 500 μm or more within this range, a binder sheet with high strength can be produced, which has advantages in this regard. By using PTFE having a secondary particle size of 500 μm or more, a binder sheet with lower resistance and greater toughness can be obtained.

[0108] The lower limit of the above-mentioned secondary particle size is more preferably 300 μm, and still more preferably 350 μm. The upper limit of the above-mentioned secondary particle size is more preferably 700 μm or less, and still more preferably 600 μm or less. The secondary particle size can be obtained by, for example, a sieving method.

[0109] From the aspect of obtaining a fluororesin sheet with higher strength and excellent homogeneity, the average primary particle diameter of the above-mentioned powdered PTFE is preferably 50 nm or more. More preferably 100 nm or more, further preferably 150 nm or more, and particularly preferably 200 nm or more. The larger the average primary particle diameter of PTFE, the more the increase in the paste extrusion pressure can be suppressed during paste extrusion molding using this powder, and the more excellent the moldability. The upper limit is not particularly limited and can be 500 nm. From the aspect of productivity in the polymerization process, it is preferably 350 nm.

[0110] Regarding the above average primary particle diameter, using an aqueous dispersion of PTFE obtained by polymerization, a calibration curve of the transmittance of 550 nm projection light per unit length of an aqueous dispersion with the polymer concentration adjusted to 0.22% by mass and the average primary particle diameter determined by measuring the orientation diameter in a transmission electron microscope photograph is produced. By measuring the above transmittance of the aqueous dispersion to be measured, it can be determined based on the above calibration curve.

[0111] The PTFE used in the present disclosure may have a core-shell structure. As PTFE having a core-shell structure, for example, modified PTFE containing a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene in particles can be cited. As such modified PTFE, for example, the polytetrafluoroethylene described in Japanese Patent Application Laid-Open No. 2005-527652 can be cited.

[0112] The specific methods of paste extrusion molding and powder calendering molding are not particularly limited, and general methods are described below.

[0113] (Paste Extrusion Molding)

[0114] The manufacturing method of the above sheet may include: step (1a) of mixing PTFE powder obtained using a hydrocarbon surfactant and an extrusion aid; step (1b) of subjecting the obtained mixture to paste extrusion molding; step (1c) of calendering the extrudate obtained by extrusion molding; step (1d) of drying the calendered sheet; and step (1e) of firing the dried sheet to obtain a molded body. The above paste extrusion molding can also be carried out by adding pigments, fillers and other conventionally known additives to the above PTFE powder.

[0115] The above extrusion aid is not particularly limited, and generally known extrusion aids can be used. For example, hydrocarbon oils and the like can be cited.

[0116] (Powder Calendering Molding)

[0117] The above-mentioned sheet can also be formed by powder calendering. Powder calendering is a method of fibrillating resin powder by applying a shearing force thereto and then forming it into a sheet. Thereafter, a step of firing to obtain a formed body may be included.

[0118] More specifically, it can be obtained by the following manufacturing method, which includes:

[0119] Step (1) of applying a shearing force while mixing a raw material composition containing a fluororesin and a filler;

[0120] Step (2) of forming the mixture obtained in the above step (1) into a block; and

[0121] Step (3) of calendering the block-shaped mixture obtained in the above step (2) into a sheet.

[0122] It should be noted that when forming a sheet by such powder calendering, it is preferable to form by mixing only fluororesin particles and an inorganic filler.

[0123] (Laminate)

[0124] The sheet-shaped resin composition of the present disclosure can be used as a sheet for a printed wiring board and laminated with other base materials.

[0125] The present disclosure also relates to a copper-clad laminate, characterized in that a copper foil is adhered to one or both sides of the above-mentioned fluororesin film. As described above, the film containing the fluororesin of the present disclosure is particularly suitable for use in printed wiring board applications, and thus can be suitably used as such a copper-clad laminate.

[0126] The Rz of the above-mentioned copper foil is preferably 1.6 μm or less. That is, the fluororesin composition of the present disclosure also has excellent adhesiveness to a copper foil with high smoothness having an Rz of 1.6 μm or less.

[0127] Furthermore, it is sufficient that at least the surface of the copper foil adhered to the above-mentioned fluororesin film is 1.6 μm or less, and the Rz value of the other side is not particularly limited. The above-mentioned Rz is the value of the sum of the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv). The above-mentioned surface roughness is the ten-point average roughness specified in JIS-B0601. In this specification, the above-mentioned Rz is a value measured using a surface roughness meter (trade name: SURFCOM 470A, manufactured by Tokyo Seimitsu Co., Ltd.) with a measurement length of 4 mm.

[0128] The thickness of the above-mentioned copper foil is not particularly limited, and is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm, and further preferably in the range of 9 μm to 35 μm.

[0129] The above copper foil is not particularly limited. Specifically, for example, rolled copper foil, electrolytic copper foil, etc. can be cited.

[0130] As the copper foil with Rz of 1.6 μm or less, there is no particular limitation, and commercially available products can be used. As the commercially available copper foil with Rz of 1.6 μm or less, for example, electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) etc. can be cited.

[0131] In order to improve the adhesive strength with the fluororesin film of the present disclosure, the above copper foil can be subjected to surface treatment.

[0132] The above surface treatment is not particularly limited, and examples include silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, etc. The reactive functional group of the silane coupling agent is not particularly limited, and from the aspect of adhesiveness to the resin substrate, it is preferably at least one selected from amino group, (meth)acryloyl group, mercapto group, and epoxy group at the terminal. In addition, the hydrolyzable group is not particularly limited, and examples include alkoxy groups such as methoxy group and ethoxy group. The copper foil used in the present disclosure can be formed with an anti-rust layer (oxide film such as chromate, etc.), a heat-resistant layer, etc.

[0133] The surface-treated copper foil having a surface treatment layer formed of the above silane compound on the copper foil surface can be manufactured as follows: After preparing a solution containing the silane compound, the copper foil is surface-treated with this solution, thereby manufacturing.

[0134] From the aspect of improving adhesiveness to the resin substrate, etc., the above copper foil can have a roughened treatment layer on the surface.

[0135] It should be noted that when the roughening treatment may reduce the performance required by the present disclosure, the roughening particles electrodeposited on the copper foil surface can be reduced as needed, or a method of not performing the roughening treatment can be adopted.

[0136] From the aspect of improving various properties, one or more layers selected from the group consisting of a heat-resistant treatment layer, an anti-rust treatment layer, and a chromate treatment layer can be provided between the copper foil and the surface treatment layer. These layers can be single layers or multiple layers.

[0137] The copper-clad laminate of the present disclosure can further have layers other than the copper foil and the fluororesin film.

[0138] The layer other than the copper foil and the fluororesin film is preferably at least one selected from the group consisting of polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene oxide, polyphenylene ether, and polybutadiene.

[0139] Layers other than these copper foils and fluororesin films are not particularly limited as long as they are made of the above-mentioned resin. In addition, the thickness of the layers other than the copper foils and fluororesin films is preferably in the range of 12.5 μm to 260 μm.

[0140] In the copper-clad laminate of the present disclosure, the copper layer can be formed on one side or both sides of the rolled film. As a method for forming the copper layer, methods such as laminating (bonding) a copper foil on the surface of the rolled film, evaporation plating method, plating method, etc. can be cited. As a method for laminating the copper foil, a method using hot pressing can be cited. The hot pressing temperature can be cited as the melting point of the dielectric film - 150°C to the melting point of the dielectric film + 40°C. The hot pressing time is, for example, 1 minute to 30 minutes. It can be manufactured by a method with a hot pressing pressure of 0.1 MPa to 10 MPa.

[0141] The use of the copper-clad laminate of the present disclosure is not particularly limited, and it is used as a circuit board. A printed circuit board refers to a board-like component used for electrically connecting and disposing and fixing electronic components such as semiconductors and capacitor chips in a limited space. The configuration of the printed circuit board formed from the present copper-clad laminate is not particularly limited. The printed circuit board can be any one of a rigid board, a flexible board, and a rigid-flexible board. The printed circuit board can be any one of a single-sided board, a double-sided board, and a multi-layer board (such as an additive board). In particular, it is suitable for use in flexible boards and rigid boards. In particular, it is suitable for use as a printed circuit board for high frequencies above 10 GHz.

[0142] There is no particular limitation as a circuit board, and the above-mentioned copper-clad laminate can be used and manufactured by a general method.

[0143] The laminate for a circuit board can also be the following laminate, which is characterized by having a copper foil layer, the above-mentioned fluororesin film, and a base material layer. There is no particular limitation as the base material layer, and it preferably has a cloth layer and a resin film layer made of glass fiber.

[0144] The cloth layer made of the above-mentioned glass fiber is a layer composed of glass cloth, glass non-woven fabric, etc.

[0145] As the glass cloth, commercially available glass cloth can be used, and in order to improve the affinity with the fluororesin, it is preferably subjected to a silane coupling agent treatment. As the material of the glass cloth, E glass, C glass, A glass, S glass, D glass, NE glass, low dielectric constant glass, etc. can be cited. From the aspect of easy availability, E glass, S glass, and NE glass are preferred. As the weaving method of the fiber, it can be plain weave or twill weave. The thickness of the glass cloth is usually 5 μm to 90 μm, preferably 10 μm to 75 μm, and it is preferable to use a glass cloth thinner than the fluororesin film used.

[0146] The above laminate may use glass nonwoven fabric as the fabric layer composed of glass fibers. The glass nonwoven fabric is a material obtained by bonding short glass fibers with a small amount of binder compound (resin or inorganic substance), or a material that maintains its shape by winding short glass fibers without using a binder compound, and commercially available products can be used. The diameter of the short glass fibers is preferably 0.5 μm to 30 μm, and the fiber length is preferably 5 mm to 30 mm.

[0147] Specific examples of the binder compound include resins such as epoxy resin, acrylic resin, cellulose, polyvinyl alcohol, fluororesin, or inorganic substances such as silica compounds. The amount of the binder compound relative to the short glass fibers is usually 3% by mass to 15% by mass. Examples of the material of the short glass fibers include E glass, C glass, A glass, S glass, D glass, NE glass, low dielectric constant glass, etc. The thickness of the glass nonwoven fabric is usually 50 μm to 1000 μm, preferably 100 μm to 900 μm. It should be noted that the thickness of the glass nonwoven fabric in this application refers to the value measured in accordance with JIS P8118:1998 using a digital gauge DG-925 (load 110 g, face diameter 10 mm) manufactured by Ono Sokki Co., Ltd. In order to improve the affinity with the fluororesin, the glass nonwoven fabric can be subjected to a silane coupling agent treatment.

[0148] Most of the glass nonwoven fabrics have a porosity of 80% or more, which is very high. Therefore, it is preferable to use a glass nonwoven fabric thicker than the sheet made of fluororesin and use it under compression.

[0149] The above fabric layer composed of glass fibers may be a layer formed by laminating a glass cloth and a glass nonwoven fabric. Thus, the properties of each other are combined, and appropriate properties can be obtained.

[0150] The above fabric layer composed of glass fibers may be in the state of a prepreg impregnated with resin.

[0151] In the above laminate, the fabric layer composed of glass fibers and the fluororesin film may be bonded at the interface, and the fluororesin film may also partially or entirely infiltrate into the fabric layer composed of glass fibers.

[0152] In addition, a fluororesin composition may be infiltrated into the fabric composed of glass fibers to make a prepreg. For the prepreg thus obtained, the fluororesin film of the present disclosure may be further laminated. In this case, there is no particular limitation on the fluororesin composition used when making the prepreg, and the fluororesin film of the present disclosure may also be used.

[0153] As the resin film used as the above-mentioned base material layer, a heat-resistant resin film and a thermosetting resin film are preferred. Examples of the heat-resistant resin film include polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, etc. Examples of the thermosetting resin include thermosetting resins containing epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, polybutadiene, etc.

[0154] The heat-resistant resin film and the thermosetting resin film may contain reinforcing fibers. There is no particular limitation on the reinforcing fibers, and glass cloth, particularly a reinforcing fiber of a low dielectric constant type, is preferably used, for example.

[0155] The properties such as dielectric characteristics, linear expansion coefficient, water absorption rate, etc. of the heat-resistant resin film and the thermosetting resin film are not particularly limited. For example, the dielectric constant at 20 GHz is preferably 3.8 or less, more preferably 3.4 or less, and further preferably 3.0 or less. The tangent of the dielectric loss angle at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and further preferably 0.0020 or less. The linear expansion coefficient is preferably 100 ppm / °C or less, more preferably 70 ppm / °C or less, and further preferably 40 ppm / °C or less. The water absorption rate is preferably 1.0% or less, more preferably 0.5% or less, and further preferably 0.1% or less.

[0156] Examples

[0157] The present disclosure will be specifically described based on the examples below. In the following examples, unless otherwise specified, "parts" and "%" respectively represent "parts by mass" and "mass %".

[0158] In the following examples and comparative examples, the following silica was used.

[0159]

[0160] In the table, the phenyl + amino group of ZA-30 is a mixture of phenyltrimethoxysilane and aminoethylaminopropyltrimethoxysilane in a ratio of 9:1.

[0161] The evaluation of each sample in Table 1 above was carried out based on the following method.

[0162] [Df (tangent of dielectric loss angle) of the filler]

[0163] Regarding the tangent of the dielectric loss angle of the filler measured at 10 GHz, a cylindrical cavity resonator and a network analyzer were used. The filler powder sample was filled in a quartz tube and loaded into the resonator for measurement. The characteristics (resonance frequency and Q value) of the resonator before and after inserting the sample were obtained, and the tangent of the dielectric loss angle was calculated based on the results.

[0164] This measurement method is based on the test method for ferrite cores for microwaves specified in Japanese Industrial Standard JIS 2565.

[0165] [D50]

[0166] Measurement is carried out using a laser diffraction particle size distribution analyzer.

[0167] [Specific surface area of the filler]

[0168] The value is based on the BET method. As a specific surface area measuring instrument, "Macsorb HM model-1208" (manufactured by MACSORB Co., Ltd.) is used for measurement.

[0169] (Example 1)

[0170] Sheet production method 1 (paste extrusion molding)

[0171] Weigh a specified amount of PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17) and silica in the proportions shown in Table 1, and mix them using a mixer in the presence of dry ice. The temperature during mixing is -10°C or lower.

[0172] Add 18 wt% - 23 wt% of oil (IP solvent 2028) to the obtained mixed powder, mix it, and cure for about 5 hours.

[0173] Preform the cured composition under a pressure of 3 MPa, extrude the preformed body at 40°C and 50 mm / min to obtain an extruded sample. Roll the extruded sample using a two-roll calender to obtain a sample with a film thickness of 125 μm, dry it at 200°C for 2 hours, and sinter it at 360°C for 15 minutes to obtain a sheet. Furthermore, adjust the pressure of the two-roll calender to produce a sample with a film thickness of 30 μm, and observe whether there are any holes or cracks.

[0174] For each of the obtained samples, evaluation is carried out based on the following criteria.

[0175] [Sheet Df]

[0176] Using a split cylinder type dielectric constant and dielectric loss tangent measuring device (manufactured by EM lab Co., Ltd.), measure the Df at 25°C, 10 GHz, and 80 GHz.

[0177] [Coefficient of linear expansion]

[0178] TMA measurement using TMA-7100 (manufactured by Hitachi High-Tech Science Corporation) was performed in the tensile mode. As the sample piece, a piece cut to a length of 20 mm, a width of 5 mm, and a thickness of 150 μm was used. The distance between the chucks was set to 10 mm, and while applying a load of 49 mN, the linear expansion rate was determined from the displacement amount of the sample at 0 to 150°C at a heating rate of 2°C / minute.

[0179] [Thin-film formation to 30 μm]

[0180] In the compositions shown in Table 2 below, in the composition of PTFE / silica = 40 / 60, the case where a film can be formed without holes or cracks at a thickness of 30 μm is marked as 〇, and the case where a film cannot be formed is marked as ×.

[0181] The results are shown in Table 2.

[0182]

[0183] Based on the above results, the fluororesin sheet of the present disclosure has excellent properties from the viewpoints of low dielectric constant, low loss, and low thermal expansion. In addition, the Df of Example 8 with PTFE / silica = 40 / 60 (mass ratio) at 80 GHz is 0.0008, and it also has excellent properties at 80 GHz.

[0184] For the sheets of PTFE / silica = 40 / 60 in Examples 1 and 8 above, the rate of change of the relative dielectric constant in the temperature range of -50°C to 150°C was measured based on the following method. The results are shown in Table 3.

[0185] (Method for measuring the rate of change of the relative dielectric constant in the temperature range of -50°C to 150°C)

[0186] Using a split cylinder type dielectric constant and dielectric loss tangent measuring device (manufactured by EM lab), Dk at 10 GHz was measured at every 10°C scale from -50°C to 150°C.

[0187] The rate of change from -50°C to 150°C was calculated from the difference between the maximum value and the minimum value of the measured Dk values.

[0188] [Table 3]

[0189] The change rate of the relative dielectric constant in the temperature range of -50°C to 150°C Example 1 0.023 Example 8 0.021

[0190] From the results in Table 3, it can be seen that the rate of change of the relative dielectric constant of the fluororesin sheet of the present disclosure in the temperature range of -50°C to 150°C is small.

[0191] Industrial Applicability

[0192] The fluororesin sheet of the present disclosure is particularly suitable for use in high-frequency printed circuit boards.

Claims

1. A composition, characterized in that, it comprises: a fluororesin; and a filler having a ratio of the dielectric loss tangent of the filler to the surface area of the filler measured at 10 GHz of 0.00001 to 0.00035, The unit of the surface area of the filler is m 2 / g.

2. The composition according to claim 1, wherein, the fluororesin is a polytetrafluoroethylene resin.

3. The composition according to claim 1 or 2, wherein, the fluororesin cannot be melt-molded.

4. The composition according to claim 2, wherein, the SSG of the polytetrafluoroethylene resin is 2.0 to 2.

3.

5. The composition according to claim 2 or 4, wherein, the refractive index of the polytetrafluoroethylene resin is 1.2 to 1.

6.

6. The composition according to any one of claims 1 to 5, wherein, the primary particle size of the fluororesin is 0.05 μm to 10 μm.

7. The composition according to any one of claims 1 to 6, wherein, the volume-based cumulative 50% diameter of the fluororesin is 0.05 μm to 40 μm.

8. The composition according to any one of claims 1 to 7, wherein, the filler is silica particles.

9. The composition according to any one of claims 1 to 8, wherein, the content of the filler relative to the total amount of the composition is 50 wt% or more.

10. The composition according to any one of claims 1 to 9, wherein, the average particle size of the filler is 0.5 μm to 250 μm.

11. The composition according to any one of claims 1 to 10, wherein, the filler is a filler having its surface coated with a silane coupling agent.

12. The composition according to any one of claims 1 to 11, wherein, the value of the dielectric loss tangent at 10 GHz is 0.0015 or less.

13. A fluororesin sheet, characterized in that, it is composed of a composition comprising: a fluororesin; and a filler having a ratio of the dielectric loss tangent of the filler to the surface area of the filler measured at 10 GHz of 0.00001 to 0.00035, The unit of the surface area of the filler is m 2 / g.

14. The fluororesin sheet according to claim 13, having a thickness of 5 μm to 250 μm.

15. A method for manufacturing the fluororesin sheet according to claim 13 or 14, characterized in that, it has a step of mixing fluororesin particles and a filler and forming a film.

16. The method for manufacturing the sheet-like composition according to claim 15, characterized in that, only fluororesin particles and an inorganic filler are mixed and a film is formed without adding other components.

17. A copper-clad laminate having a copper foil and the fluororesin sheet according to claim 13 or 14 as essential layers.

18. A circuit board, characterized in that, it has the copper-clad laminate according to claim 17.

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