Sheet, copper-clad laminate, circuit board, and production method for sheet

Abstract

Provided is a sheet that exhibits little change in dielectric loss tangent during water absorption. The sheet contains a fluororesin and a filler, and has a specific gravity of 2.05-2.19.

Description

Sheet, copper clad laminate, circuit board, and method for manufacturing the sheet

[0001] The present disclosure relates to a sheet, a copper clad laminate, a circuit board, and a method for manufacturing the sheet.

[0002] There is a demand for high-frequency printed wiring boards with low transmission loss. The use of fluororesin films in such high-frequency printed wiring boards is known (see, for example, Patent Document 1). Patent Documents 2 and 3 also describe the use of fluororesins containing fillers as wiring board materials.

[0003] Furthermore, Patent Document 4 discloses that a fluororesin composition in which spherical silica particles are blended with a fluororesin is used for a circuit board.

[0004] JP 2015-8260 JP 63-259907 A JP 2022-510017 WO 2020 / 145133

[0005] An object of the present disclosure is to provide a sheet that exhibits a small rate of change in dielectric loss tangent upon water absorption.

[0006] The present disclosure relates to a sheet comprising a fluororesin and a filler, the sheet having a specific gravity of 2.05 or more and 2.19 or less. The fluororesin is preferably polytetrafluoroethylene resin. The filler is preferably silica. The silica is preferably spherical silica. The silica preferably has a particle size of 0.1 to 3 μm. The silica content is preferably 20 to 80 mass% based on the sheet weight. The silica preferably has a surface treated with a surface treatment agent. The fluororesin is polytetrafluoroethylene resin having a standard specific gravity of 2.0 to 2.3, the filler is spherical silica, the particle size of the spherical silica is 0.5 to 2.1 μm, the polytetrafluoroethylene resin content is 40 to 60 mass% based on the sheet weight, and the spherical silica content is preferably 40 to 60 mass% based on the sheet weight.

[0007] The present disclosure also provides a sheet containing 20 to 80 mass% of polytetrafluoroethylene resin relative to the sheet weight and surface-treated spherical silica having a particle size of 0.1 to 3 μm, wherein the silica content is 20 to 80 mass% relative to the sheet weight and the sheet has a specific gravity of 2.05 or more and 2.19 or less.

[0008] The sheet preferably has a water absorption rate of 0.10% or less. The sheet is preferably obtained by a manufacturing process including a densification step that increases the specific gravity of the sheet by 1% or more. When comparing the rate of change in the dielectric tangent of the sheet before and after water absorption, the rate of change in the dielectric tangent of the sheet after densification is preferably lower than that before densification.

[0009] The sheet preferably has a linear expansion coefficient of 120 ppm / K or less, a thickness of 0.1 to 2 mm, and is preferably an insulating material for a circuit board.

[0010] The present disclosure also relates to a metal clad laminate having a metal layer and the above-mentioned sheet as essential layers. The metal layer is preferably copper foil. The present disclosure also relates to a circuit board characterized by having the above-mentioned sheet and a metal layer. The metal constituting the metal layer is preferably copper. The copper is preferably rolled copper or electrolytic copper. The circuit board is preferably a printed circuit board, a laminated circuit board, or a high-frequency board.

[0011] The present disclosure also provides a method for producing the sheet, comprising step (1) of mixing the fluororesin and the filler and rolling the mixture into a sheet, and step (2) of densifying the rolled sheet obtained by step (1). In step (2), the rolled sheet is pressurized so that the specific gravity of the rolled sheet increases by 1% or more, and the fluororesin is preferably polytetrafluoroethylene resin having a standard specific gravity of 2.0 to 2.3, the filler is preferably spherical silica having a particle size of 0.5 to 2.1 μm, the polytetrafluoroethylene resin content is 40 to 60 mass% of the sheet weight, and the spherical silica content is 40 to 60 mass% of the sheet weight.

[0012] The sheet of the present disclosure has a small rate of change in dielectric loss tangent when absorbing water.

[0013] The present disclosure will be described in detail below. Many studies have been conducted on compositions containing fluororesins and fillers. Meanwhile, in the field of high-frequency printed wiring boards, increasingly high levels of performance, such as low dielectric constant, low loss, and low expansion, have been required in recent years.

[0014] In such applications, the electrochemical properties of the sheet must be stable and not affected by the surrounding environment. However, sheets made of filler and fluororesin are prone to change in dielectric tangent when they absorb water. Since sheets containing fluororesin are required to have low dielectric constant and low loss, it is preferable that the sheet containing fluororesin has low water absorption in order to achieve stable low loss. Low water absorption makes it possible to reduce the rate of change in dielectric tangent when absorbing water.

[0015] In the present disclosure, the density is increased in order to reduce the rate of change in the dielectric loss tangent upon water absorption. That is, by reducing the voids in the resin sheet, the intrusion of water into the sheet upon water absorption is prevented, thereby achieving the above-mentioned object.

[0016] Resin compositions containing a large amount of filler are prone to gaps at the interface between the resin and the filler, and when formed into a sheet by a conventional molding method, voids are likely to form. Also, voids are generated when the molding aid is removed from the fluororesin. Therefore, it is presumed that water gets into the voids, causing the above-mentioned problems.

[0017] Therefore, for example, by carrying out a densification treatment after molding, the voids can be reduced to form a high-density sheet, thereby solving this problem.

[0018] In view of the above, the sheet of the present disclosure contains a fluororesin and a filler, and has a specific gravity of 2.05 to 2.19. The specific gravity in the present disclosure is a value measured by the density and specific gravity measurement method by the submerged weighing method in accordance with JIS Z 8807 (Methods for measuring density and specific gravity of solids) 8.

[0019] If the specific gravity is less than 2.05, the problem of a low rate of change in dielectric tangent upon water absorption cannot be sufficiently achieved. Furthermore, if the specific gravity exceeds 2.19, the relative dielectric constant becomes undesirably high.

[0020] The lower limit of the specific gravity is more preferably 2.05. The upper limit of the specific gravity is preferably 2.18, more preferably 2.17, and even more preferably 2.16. A sheet having such a specific gravity has a low porosity, thereby achieving the above-mentioned effects.

[0021] The sheet of the present disclosure preferably has a water absorption rate of 0.10% or less, more preferably 0.08% or less, and even more preferably 0.06% or less. By setting the specific gravity within the above range, the sheet of the present disclosure has a low porosity. It is preferable to reduce the porosity and achieve the water absorption rate described above. A water absorption rate of the above value is preferable in that it can suitably achieve the goal of reducing the rate of change of the dielectric loss tangent upon water absorption.

[0022] In the present disclosure, the water absorption rate is a value obtained by drying a 50 × 50 (mm) sheet at 110°C for 1 hour, cooling it to 23°C in a desiccator, and then immersing it in water at 23°C for 24 hours, and calculating the water absorption rate from the weight before and after immersion in water.

[0023] The water absorption is more preferably 0.08% or less, and even more preferably 0.07% or less. Since a low water absorption does not cause any particular problems, the lower limit is not particularly limited and may be 0%. The lower limit is preferably 0.001%.

[0024] The sheet of the present disclosure preferably has a linear expansion coefficient of 120 ppm / K or less. By using such a linear expansion coefficient, it is possible to obtain a dielectric sheet with low shrinkage and excellent dimensional stability. The linear expansion coefficient is more preferably 70 ppm / K or less, and even more preferably 50 ppm / K or less.

[0025] The lower limit of the linear expansion coefficient is not particularly limited, but is more preferably 5 ppm / K, and even more preferably 10 ppm / K.

[0026] The linear expansion coefficient in this specification was determined by performing TMA measurement using a TMA-7100 (manufactured by Hitachi High-Tech Science Corporation) in a tensile mode, using a sheet cut out to a length of 20 mm, a width of 5 mm, and a thickness of 150 μm as a sample piece, setting the distance between chucks at 10 mm, and applying a load of 49 mN at a heating rate of 2°C / min from -10 to 160°C, and measuring the displacement of the sample length.

[0027] The sheet of the present disclosure preferably has a film thickness of 0.03 to 2 mm. By achieving a film thickness within this range, the sheet becomes suitable for applications described in detail below in this disclosure. The lower limit is more preferably 0.05 mm, and even more preferably 0.1 mm. The upper limit is more preferably 1 mm, and even more preferably 0.5 mm.

[0028] The film thickness in this disclosure is a value measured with a film thickness meter.

[0029] The sheet of the present disclosure preferably has a rate of change in relative dielectric constant of 0.025 or less, more preferably 0.023 or less, and even more preferably 0.021 or less in the temperature range of −50 to 150° C. A value within this range is preferred in that changes in electrical properties due to temperature are minimal, and stable performance can be obtained when used in high-frequency printed circuit boards.

[0030] As described above, the sheet of the present disclosure contains a fluororesin and a filler. Sheets containing these have a low dielectric constant, resulting in low transmission loss and making them particularly suitable for use as printed wiring boards. These components constituting the sheet of the present disclosure are described in detail below.

[0031] (Fluororesin) The composition of the present disclosure contains a fluororesin. Fluororesin has low dielectric properties and can therefore be suitably used for the purposes of the present disclosure.

[0032] The fluororesin that can be used in the present disclosure is not particularly limited, but examples include polytetrafluoroethylene (PTFE), tetrafluoroethylene [TFE] / hexafluoropropylene [HFP] copolymer [FEP], TFE / alkyl vinyl ether copolymer [PFA], TFE / HFP / alkyl vinyl ether copolymer [EPA], TFE / chlorotrifluoroethylene [CTFE] copolymer, TFE / ethylene copolymer [ETFE], polyvinylidene fluoride [PVdF], and tetrafluoroethylene having a molecular weight of 300,000 or less [LMW-PTFE]. One type may be used, or two or more types may be mixed. From the viewpoint of low dielectric constant, polytetrafluoroethylene resin (PTFE) is particularly preferred. PTFE having fibrillar properties is preferred. Fibrillar PTFE refers to PTFE that can be paste-extruded from unsintered polymer powder.

[0033] PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), may be homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or may be a mixture of modified PTFE and homoPTFE. Note that, from the viewpoint of maintaining good moldability of polytetrafluoroethylene, the content ratio of modified PTFE in polymeric PTFE is preferably 10% by mass or more and 98% by mass or less, more preferably 50% by mass or more and 95% by mass or less. The homo-PTFE is not particularly limited, and homo-PTFE disclosed in JP-A-53-60979, JP-A-57-135, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007 / 046345 pamphlet, WO 2007 / 119829 pamphlet, WO 2009 / 001894 pamphlet, WO 2010 / 113950 pamphlet, WO 2013 / 027850 pamphlet, etc. can be suitably used. Among these, homo-PTFE having high stretchability and disclosed in JP-A-57-135, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007 / 046345, WO 2007 / 119829, WO 2010 / 113950, etc. is preferred.

[0034] Modified PTFE is made up of TFE and monomer other than TFE (hereinafter referred to as modified monomer).Modified PTFE can include, but is not limited to, the one that is uniformly modified by modified monomer, the one that is modified at the beginning of polymerization reaction, or the one that is modified at the end of polymerization reaction.Modified PTFE is preferably the TFE copolymer obtained by subjecting TFE and a small amount of monomer other than TFE to polymerization within the range that does not significantly impair the properties of TFE homopolymer. The modified PTFE can be suitably used, for example, those disclosed in JP-A-60-42446, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-64-1711, JP-A-2-261810, JP-A-11-240917, JP-A-11-240918, WO 2003 / 033555 pamphlet, WO 2005 / 061567 pamphlet, WO 2007 / 005361 pamphlet, WO 2011 / 055824 pamphlet, WO 2013 / 027850 pamphlet, etc. Among these, modified PTFE having high stretchability and disclosed in JP-A-61-16907, JP-A-62-104816, JP-A-64-1711, JP-A-11-240917, WO 2003 / 033555, WO 2005 / 061567, WO 2007 / 005361, WO 2011 / 055824, etc. are preferred.

[0035] The modified PTFE contains TFE units based on TFE and modified monomer units based on a modified monomer. The modified monomer units are a part of the molecular structure of the modified PTFE that is derived from the modified monomer. The modified PTFE preferably contains modified monomer units in an amount of 0.001 to 0.500 mass% of the total monomer units, and more preferably 0.01 to 0.30 mass%. The total monomer units are the parts derived from all monomers in the molecular structure of the modified PTFE.

[0036] The modified monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluorovinyl ether; perfluoroalkylethylene (PFAE), ethylene, etc. The modified monomer used may be one kind or multiple kinds.

[0037] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorounsaturated compounds represented by the following general formula (1): CF ２ =CF-ORf...(1)

[0038] In the formula, Rf represents a perfluoroorganic group.

[0039] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0040] An example of a perfluorovinyl ether is perfluoro(alkyl vinyl ether) (PAVE), which is represented by the above general formula (1) and in which Rf is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. Preferred PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0041] The perfluoroalkylethylene (PFAE) is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE).

[0042] The modifying monomer in the modified PTFE is preferably at least one (for example, 1 to 6) selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0043] The fluororesin is preferably non-melt-moldable. "Non-melt-moldable" means that the resin does not have sufficient fluidity even when heated above its melting point, and cannot be molded by melt-molding techniques commonly used for resins. PTFE falls into this category.

[0044] In the present disclosure, it is preferable to use such a fluororesin that cannot be melt-molded and to form the fluororesin sheet by a molding method that fibrillates the fluororesin. The molding method will be described later.

[0045] The PTFE preferably has an SSG of 2.0 to 2.3. The use of such PTFE facilitates the production of PTFE membranes with high strength (cohesion and puncture strength per unit thickness). PTFE with a large molecular weight has long molecular chains, making it difficult to form a structure in which the molecular chains are regularly arranged. In this case, the length of the amorphous portion increases, and the degree of entanglement between molecules increases. It is believed that when the degree of entanglement between molecules is high, the PTFE membrane is less likely to deform under an applied load and exhibits excellent mechanical strength. Furthermore, the use of PTFE with a large molecular weight facilitates the production of PTFE membranes with small average pore sizes.

[0046] The lower limit of the SSG is more preferably 2.05, and even more preferably 2.1. The upper limit of the SSG is more preferably 2.25, and even more preferably 2.2.

[0047] The standard specific gravity [SSG] was measured by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample by the water displacement method.

[0048] In this embodiment, the molecular weight (number average molecular weight) of the PTFE constituting the PTFE powder is, for example, in the range of 2 million to 12 million. The lower limit of the molecular weight of PTFE may be 3 million or 4 million. The upper limit of the molecular weight of PTFE may be 10 million.

[0049] Methods for measuring the number average molecular weight of PTFE include a method determining it from standard specific gravity and a measurement method based on dynamic viscoelasticity in the melt. The method for determining it from standard specific gravity can be carried out by using a sample molded in accordance with ASTM D-4895 98 and a water displacement method based on ASTM D-792. The measurement method based on dynamic viscoelasticity is explained, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538 and the same document, 1989, Vol. 29, 273.

[0050] The refractive index of the PTFE is preferably in the range of 1.2 to 1.6. Having such a refractive index is preferable in terms of low dielectric constant. The refractive index can be adjusted to within the above range by adjusting the polarizability or the flexibility of the main chain. The lower limit of the refractive index is more preferably 1.25, more preferably 1.30, and most preferably 1.32. The upper limit of the refractive index is more preferably 1.55, more preferably 1.50, and most preferably 1.45.

[0051] The refractive index is a value measured using a refractometer (Abbemat 300).

[0052] The PTFE preferably has a maximum endothermic peak temperature (crystalline melting point) of 340±7°C.

[0053] The PTFE may be a low-melting-point PTFE having a maximum peak temperature of 338°C or lower on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter, or a high-melting-point PTFE having a maximum peak temperature of 342°C or higher on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter.

[0054] The low-melting-point PTFE is a powder produced by emulsion polymerization, has the maximum endothermic peak temperature (crystalline melting point) mentioned above, a dielectric constant (ε) of 2.08 to 2.2, and a dielectric loss tangent (tan δ) of 1.9 × 10 －４ ~4.0 x 10 －４ Examples of commercially available products include Polyflon fine powders F201, F203, F205, F301, and F302 manufactured by Daikin Industries, Ltd., CD090 and CD076 manufactured by Asahi Glass Co., Ltd., and TF6C, TF62, and TF40 manufactured by DuPont.

[0055] The high melting point PTFE powder is also a powder produced by emulsion polymerization, and has the above-mentioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.0 to 2.1, and a dielectric loss tangent (tan δ) of 1.6 × 10 －４ ~2.2 × 10 －４ Examples of commercially available products include Polyflon fine powders F104 and F106 manufactured by Daikin Industries, Ltd., CD1, CD141, and CD123 manufactured by Asahi Glass Co., Ltd., and TF6 and TF65 manufactured by DuPont.

[0056] Powdered PTFE satisfying the above-described parameters can be obtained by conventional manufacturing methods, such as those described in International Publication Nos. 2015-080291 and 2012-086710.

[0057] (Filler) The filler that can be used in the present disclosure is not particularly limited, and examples thereof include organic fillers that are one or more selected from aramid fibers, polyphenyl esters, polyphenylene sulfide, polyimides, polyether ether ketones, polyphenylenes, polyamides, and wholly aromatic polyester resins, and inorganic fillers that are one or more selected from ceramics, talc, mica, aluminum oxide, zinc oxide, tin oxide, titanium oxide, silica, calcium carbonate, calcium oxide, magnesium oxide, potassium titanate, glass fibers, glass chips, glass beads, silicon carbide, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers. Two or more of these fillers may also be used in combination.

[0058] The filler is not particularly limited in shape, but is preferably a spherical filler, which is preferable because it is easy to process uniformly during drilling and has a small specific surface area and therefore low transmission loss.

[0059] Among these, it is particularly preferable to use silica, and it is most preferable to use spherical silica particles.

[0060] The spherical silica particles mentioned above mean particles whose particle shape is close to a perfect sphere, and specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.95 or more. The sphericity is calculated by taking a photograph with an SEM and calculating the value from the area and perimeter of the observed particle using the formula (sphericity) = {4π × (area) ÷ (perimeter)2}. The closer to 1, the closer to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (FPIA-3000, Spectris Inc.) is used.

[0061] The spherical silica particles used in the present disclosure preferably have a D90 / D10 of 2 or more (preferably 2.3 or more, 2.5 or more) and a D50 of 10 μm or less when the volume is calculated from the smallest particle size. Furthermore, it is preferable that the D90 / D50 is 1.5 or more (more preferably 1.6 or more). It is preferable that the D50 / D10 is 1.5 or more (more preferably 1.6 or more). Furthermore, it is more preferable that the D50 is 5 μm or less. Since small-sized spherical silica particles can enter the gaps between large-sized spherical silica particles, excellent filling properties and high fluidity can be achieved. In particular, it is preferable that the particle size distribution has a higher frequency on the small particle size side compared to a Gaussian curve. The particle size can be measured using a laser diffraction / scattering particle size distribution analyzer. Furthermore, since coarse particles make it difficult to form a thin sheet, it is preferable that coarse particles having a particle size above a certain size have been removed using a filter or the like.

[0062] The spherical silica particles preferably have a water absorption of 1.0% or less, more preferably 0.5% or less. The water absorption is based on the mass of the silica particles when dry. The water absorption is measured by leaving a dry sample at 40°C and 80% RH for 1 hour, and measuring the water content generated by heating at 200°C using a Karl Fischer moisture content analyzer.

[0063] Alternatively, the spherical silica particles can be measured using the above-mentioned methods after the fluororesin sheet is heated at 600°C for 30 minutes in an air atmosphere to burn off the fluororesin and the spherical silica particles are removed.

[0064] The silica particles are preferably surface-treated, which is preferable because the silica particles can be prevented from aggregating and can be well dispersed in the resin composition.

[0065] The surface treatment is not particularly limited, and any known treatment can be used. Specific examples include treatment with a silane coupling agent such as an epoxy silane, amino silane, isocyanate silane, vinyl silane, acrylic silane, hydrophobic alkyl silane, phenyl silane, or fluorinated alkyl silane, which has a reactive functional group; plasma treatment; and fluorination treatment.

[0066] Examples of the silane coupling agent 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-isocyanatepropyltrimethoxysilane, vinyl silanes such as vinyltrimethoxysilane, and acrylic silanes such as acryloxytrimethoxysilane.

[0067] The spherical silica particles may be commercially available silica particles that satisfy the above-mentioned properties. Examples of commercially available silica particles include Denka fused silica FB grade (manufactured by Denka Company Ltd.), Denka fused silica SFP grade (manufactured by Denka Company Ltd.), Excelica (manufactured by Tokuyama Corporation), high-purity synthetic spherical silica particles Admafine (manufactured by Admatechs Co., Ltd.), Admanano (manufactured by Admatechs Co., Ltd.), and Admafuse (manufactured by Admatechs Co., Ltd.).

[0068] As used in this disclosure, the filler is defined as (dielectric tangent of the filler measured at 10 GHz) / (surface area of ​​the filler (m ２ / g)) is preferably 0.00001 to 0.00035. Use of a filler that satisfies this relationship is preferred in that it allows for the production of a sheet that has particularly excellent low dielectric constant, low loss, and low expansion.

[0069] (Dielectric loss tangent of the filler measured at 10 GHz) / (surface area of ​​the filler (m ２ The value of ( / g)) can be adjusted by the shape and size of the filler, the presence or absence of surface treatment, and the like. More specifically, it is preferable to use spherical silica particles of a predetermined size as the above-mentioned spherical silica particles and further subject them to surface treatment. The surface of the silica is preferably treated with a surface treatment agent. When surface treatment is performed, the type of surface treatment agent also affects the above parameters. More specifically, it is particularly preferable to subject the filler to surface treatment with aminopropyltriethoxysilane, aminosilane, vinylsilane, hydrophobic alkylsilane, phenylsilane, 3-mercaptopropylsilane, 3-acryloxypropylsilane, 3-methacryloxypropylsilane, p-styrylsilane, silylpropylsuccinic anhydride, 3-isocyanatopropylsilane, 2-(3,4-epoxycyclohexyl)ethylsilane, or the like. By performing surface treatment with these silane coupling agents, polar functional groups present on the filler surface react, reducing the amount of polar functional groups, resulting in excellent electrical properties.

[0070] The filler is preferably contained in a proportion of 20 to 80% by mass relative to the sheet weight. This amount is preferable in that it achieves low thermal expansion while maintaining a low dielectric constant and low loss. The amount is more preferably 40% by mass or more, even more preferably 53% by mass or more, and even more preferably 56% by mass or more. There is no particular upper limit to the filler amount, but it is preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, and even more preferably 60% by mass or less.

[0071] (Dielectric tangent of the filler measured at 10 GHz) / (surface area of ​​the filler (m ２ The upper limit of the saturation coefficient (μm / g) is more preferably 0.00030, and even more preferably 0.00025.

[0072] In this disclosure, the dielectric loss tangent of the filler measured at 10 GHz was measured using a cylindrical cavity resonator and a network analyzer. A filler powder sample was filled into a quartz tube and loaded into the resonator. The characteristics of the resonator (resonance frequency and Q value) were obtained before and after inserting the sample, and the dielectric loss tangent was calculated from the results. This measurement method complies with the Japanese Industrial Standard JIS 2565 Microwave Ferrite Core Test Method, and measurements were performed in an environment of room temperature of 25°C and humidity of 40%.

[0073] In the present disclosure, the dielectric loss tangent of the filler measured at 10 GHz is not particularly limited, but is preferably 0.0015 or less. This value is preferable in that the fluororesin sheet has low loss. The upper limit is more preferably 0.0025, and even more preferably 0.002.

[0074] In the present disclosure, the surface area (m ２ / g) is not particularly limited, but is preferably 1 to 10. Setting it within the above range is preferable in that the fluororesin sheet has a good balance between low loss and low linear expansion. The lower limit is more preferably 1.2, and even more preferably 1.5. The upper limit is more preferably 9, and even more preferably 7.

[0075] In the present disclosure, the surface area (m ２ / g) is a value based on the BET method, and can be measured using a "Macsorb HM model-1208" (manufactured by MACSORB) as a specific surface area measuring device. When the fluororesin sheet of the present disclosure contains two or more types of fillers, the surface area measured for all of the blended fillers falls within the above-mentioned range.

[0076] In the present disclosure, the average particle size of the filler is preferably 0.1 μm or more, more preferably 0.5 μm or more. In the present disclosure, the average particle size of the filler is preferably 250 μm or less, more preferably 100 μm or less, even more preferably 10 μm or less, even more preferably 3 μm or less, even more preferably 2.5 μm or less, and particularly preferably 2.1 μm or less.

[0077] In the present disclosure, the filler may have an average particle size of 0.5 to 250 μm. The average particle size here is the D50 value measured using a laser analysis particle size distribution analyzer. If the average particle size is 0.5 μm or more, the filler is less likely to aggregate, and a sufficient effect tends to be obtained.

[0078] (Regarding Composition) The sheet of the present disclosure contains the above-described filler and fluororesin. If necessary, it may contain components other than the filler and fluororesin, or may consist solely of the filler and fluororesin. The content of components other than the filler and fluororesin is preferably 10% by mass or less (0% by mass, i.e., not contained, or greater than 0% by mass and 10% by mass or less). In other words, the total content of the fluororesin and filler is preferably, for example, 90% by mass or more and 100% by mass or less relative to the sheet weight. The ratio Wf / Wr of the mass of the filler Wf to the mass Wr of the fluororesin may be, for example, 0.6 to 1.5.

[0079] The sheet of the present disclosure preferably has a fluororesin content of 20 to 80% by mass relative to the total amount of the sheet. By incorporating a filler in this range, the linear expansion coefficient can be lowered, which is preferable in that it is easy to mold. The lower limit of the amount of the filler is not particularly limited, but from the viewpoint of being able to lower the linear expansion coefficient, it is preferably 30% by mass, and more preferably 40% by mass. The upper limit is more preferably 75% by mass, even more preferably 70% by mass, even more preferably 65% ​​by mass, and even more preferably 60% by mass.

[0080] (Method for Manufacturing Sheet) The method for manufacturing a sheet of the present disclosure is not particularly limited, but an example will be described. The method for manufacturing a sheet of the present disclosure includes, for example, step (1) of mixing the fluororesin and the filler and rolling them into a sheet; and step (2) of densifying the rolled sheet obtained by step (1). More specifically, the sheet of the present disclosure can be obtained by mixing fluororesin particles and a filler to form a film in step (1), and rolling the sheet obtained by the film formation in step (2). By rolling, the amount of voids in the sheet is reduced, thereby enabling densification. The method for forming a film on the sheet in step (1) is not limited, but can be performed by paste extrusion molding, powder rolling molding, etc.

[0081] As described above, it is preferable to use a fluororesin that cannot be melt-molded as the fluororesin used in the sheet of the present disclosure. When such a fluororesin is used and is molded into a sheet, it is preferable to mold it by fibrillating powdered PTFE as a raw material.

[0082] The powdered PTFE preferably has a primary particle size of 0.05 to 10 μm. The use of such a powder offers the advantages of excellent moldability and dispersibility. The primary particle size here is a value measured in accordance with ASTM D 4895.

[0083] The powdered PTFE preferably contains 50% by mass or more, more preferably 80% by mass or more, of polytetrafluoroethylene resin having a secondary particle diameter of 500 μm or more.The PTFE having a secondary particle diameter of 500 μm or more within this range has the advantage of being able to produce a sheet with high strength.By using PTFE having a secondary particle diameter of 500 μm or more, a sheet with lower resistance and excellent toughness can be obtained.

[0084] The lower limit of the secondary particle diameter is more preferably 300 μm, and even more preferably 350 μm. The upper limit of the secondary particle diameter is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle diameter can be determined, for example, by a sieving method.

[0085] The powdered PTFE preferably has an average primary particle diameter of 50 nm or more, since a sheet with higher strength and excellent homogeneity can be obtained. More preferably, it is 100 nm or more, even more preferably 150 nm or more, and particularly preferably 200 nm or more. The larger the average primary particle diameter of PTFE, the more suppressed the increase in paste extrusion pressure when using the powder for paste extrusion molding, and the better the moldability. The upper limit is not particularly limited, but may be 500 nm. From the viewpoint of productivity in the polymerization process, it is preferably 350 nm.

[0086] The average primary particle diameter can be determined by preparing a calibration curve of the transmittance of 550 nm projected light per unit length of an aqueous dispersion of PTFE obtained by polymerization, the polymer concentration of which is adjusted to 0.22% by mass, and the average primary particle diameter determined by measuring the unidirectional diameter in a transmission electron microscope photograph, and measuring the transmittance of the aqueous dispersion to be measured, and then using the calibration curve.

[0087] The PTFE used in the present disclosure may have a core-shell structure. Examples of PTFE with a core-shell structure include modified polytetrafluoroethylene particles, which contain a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in JP-A-2005-527652.

[0088] The specific methods for paste extrusion molding and powder rolling molding in step (1) are not particularly limited, but the following general methods will be described.

[0089] (Paste extrusion molding) The method for producing the sheet may include the steps of: mixing the PTFE powder obtained using a hydrocarbon surfactant with an extrusion aid (1a), paste extrusion molding the resulting mixture (1b), rolling the extrudate obtained by extrusion molding (1c), drying the rolled sheet (1d), and firing the dried sheet to obtain a molded body (1e). The paste extrusion molding can also be carried out by adding conventionally known additives such as pigments and fillers to the PTFE powder.

[0090] The extrusion aid is not particularly limited, and any commonly known extrusion aid can be used, such as hydrocarbon oil.

[0091] (Powder Rolling Molding) The sheet can also be formed by powder rolling molding. Powder rolling molding is a method of applying shear force to resin powder to fibrillate it and thereby form it into a sheet. This method may then include a step of sintering the powder to obtain a molded product. More specifically, the sheet can be obtained by a production method including: a step (1-1) of applying shear force while mixing a raw material composition containing a fluororesin and a filler; a step (1-2) of forming the mixture obtained by the step (1-1) into a bulk shape; and a step (1-3) of rolling the bulk mixture obtained by the step (1-2) into a sheet shape. When forming a sheet by such powder rolling molding, it is preferable to mix and mold only the fluororesin particles and the inorganic filler.

[0092] (Densification Treatment) In order to obtain the sheet of the present disclosure, it is preferable to perform the above-mentioned densification treatment in step (2). The densification treatment is not particularly limited, and specific examples thereof include pressure using a pressure roll or a pressure press.

[0093] The densification treatment preferably increases the specific gravity of the sheet by 1% or more. More specifically, in step (2), the rolled sheet obtained in step (1) is preferably pressurized so that the specific gravity of the rolled sheet increases by 1% or more. Increasing the specific gravity in this manner allows the object of the present disclosure to be successfully achieved. To achieve such an increase rate, it is preferable to appropriately adjust the pressure, temperature, pressurization time, etc. The upper limit of the increase rate of the specific gravity is not particularly limited, but is, for example, 10% or less.

[0094] Furthermore, when comparing the rate of change in dielectric loss tangent before and after water absorption, the densification treatment preferably results in a lower rate of change in the dielectric loss tangent of the densified sheet compared to the sheet before water absorption. That is, the dielectric loss tangent of the sheet before and after water absorption is measured, respectively. The rate of change in the dielectric loss tangent due to water absorption is then calculated for each of the sheets before and after the densification treatment. In this case, it means that the densified sheet has a smaller rate of change in the dielectric loss tangent. Note that the water absorption here is measured using the same method as the water absorption rate measurement method described above.

[0095] In order to fully obtain the advantages of the densification treatment, the ratio R2 / R1 of the rate of change R2 of the dielectric tangent of the sheet after the densification treatment before and after water absorption to the rate of change R1 of the dielectric tangent of the sheet before the densification treatment before and after water absorption is preferably 0.8 or less, more preferably 0.7 or less. The lower the ratio R2 / R1, the better, and there is no particular lower limit, but it may be, for example, 0.0 or more.

[0096] The pressure roll directly contacts the sheet passing through the press-fitting mechanism and applies pressure to it. This is particularly preferred because it increases the density of the sheet. The pressure roll is preferably a rubber roll, a resin roll, or a metal roll. In particular, a pair of rolls, one of which is a metal roll and the other of which is a rubber-coated roll on a metal core, can be used to apply an appropriate amount of pressure. The material of the metal roll is not particularly limited, and examples include iron, stainless steel (SUS304, SUS430, SUS410, SUS403, etc.), copper, etc. Furthermore, the surface of the metal roll may be subjected to various surface treatments to improve durability and processability. The surface treatment is not particularly limited, and may include plating treatments such as chrome plating, copper plating, nickel plating, or composite plating of these, mechanical treatments such as embossing and grooving, and treatments to improve release properties such as fluorine coating and silicone coating.

[0097] The linear pressure applied to the sheet by the pressure roll is preferably 30 to 500 kg / cm, more preferably 40 to 400 kg / cm, and even more preferably 50 to 300 kg / cm. This range is preferable because it makes it easier to obtain a sheet having the above-mentioned predetermined density.

[0098] The pressure applied by the pressure roll may be heated in an electric furnace or by the pressure roll itself. The temperature range of the sheet is preferably 10 to 250°C, more preferably 15 to 150°C, and even more preferably 20 to 100°C. By using such pressure conditions, the sheets can be more easily integrated, and the object of the present disclosure can be suitably achieved. The pressure rolls may have different diameters and rotation speeds facing each other. By using such a design, the shear force applied to the sheet can be changed.

[0099] Known methods can be applied as the pressure roll press-in means. More specifically, for example, a pair of two rolls as described in Japanese Patent No. 6590350, a two-stage rolling mill as described in Japanese Patent No. 5087646, a cluster mill as described in International Publication No. 2020 / 204070, a planetary rolling mill as described in Japanese Patent Laid-Open No. 62-275508, and the like can be exemplified. The pressure roll may be equipped with a cleaning mechanism. The cleaning mechanism is not particularly limited, and examples thereof include an adhesive roll.

[0100] The pressure press directly contacts the sheet with a press-fitting mechanism and applies pressure. This is particularly preferred because it increases the density of the sheet. The pressure press is preferably a rubber plate, a resin plate, or a metal plate. Using a metal plate, in particular, allows for the application of a moderate amount of pressure. The material of the metal plate is not particularly limited, and examples include iron, stainless steel (SUS304, SUS430, SUS410, SUS403, etc.), copper, etc. Furthermore, various surface treatments may be performed on the sheet surface to improve durability and processability. The surface treatment is not particularly limited, and may include plating treatments such as chrome plating, copper plating, nickel plating, or composite plating of these, mechanical treatments such as embossing and grooving, and treatments to improve releasability such as fluorine coating and silicone coating.

[0101] The pressure applied by the pressure press is preferably 1 to 200 MPa, more preferably 5 to 100 MPa, and even more preferably 10 to 80 MPa. This range is preferable because it makes it easier to obtain a sheet having the above-mentioned predetermined density.

[0102] The pressure applied by the pressure press may be achieved by heating the electric furnace or the pressure plate itself. The temperature range of the sheets is preferably 10 to 250°C, more preferably 15 to 150°C, and even more preferably 20 to 100°C. By using such pressure conditions, the sheets can be more easily integrated, and the object of the present disclosure can be suitably achieved.

[0103] (Laminate) The sheet-shaped resin composition of the present disclosure can be used by laminating it with other substrates as a sheet for printed wiring boards, that is, it can be suitably used as an insulating material for circuit boards.

[0104] The present disclosure also relates to a metal clad laminate having a metal layer and the above-mentioned sheet as essential layers. The metal clad laminate of the present disclosure is, for example, a metal clad laminate characterized in that a metal layer is bonded to one or both sides of the above-mentioned sheet (e.g., a fluororesin film). As described above, the fluororesin-containing film of the present disclosure is particularly suitable for use in printed wiring board applications, and therefore can be suitably used as such a metal clad laminate.

[0105] In the present disclosure, examples of metal species constituting the metal layer include copper (e.g., rolled copper, electrolytic copper, etc.), aluminum, SUS, nickel, gold, etc. Alloys of these can also be used. Copper is preferably used from the viewpoint of electrical conductivity and circuit processability. A heat-resistant layer (nickel plating, titanium plating, etc.) or a rust-preventive layer (chromate treatment layer, etc.) may be formed on the copper surface. Furthermore, the surface may be chemically treated with a silane coupling agent. Among these, it is preferable to use copper foil as the metal layer.

[0106] The copper foil preferably has an Rz of 1.6 μm or less. That is, the sheet of the present disclosure also has excellent adhesion to highly smooth copper foil with an Rz of 1.6 μm or less. Furthermore, the copper foil only needs to have an Rz of 1.6 μm or less on at least the surface that adheres to the fluororesin film, and the Rz value of the other surface is not particularly limited. The Rz is the sum of the values ​​of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The surface roughness is the ten-point average roughness defined in JIS-B0601. In this specification, the Rz is a value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0107] The thickness of the copper foil is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm, and even more preferably in the range of 9 to 35 μm.

[0108] The copper foil is not particularly limited, and specific examples include rolled copper foil and electrolytic copper foil.

[0109] The copper foil having an Rz of 1.6 μm or less is not particularly limited, and commercially available products can be used. Examples of commercially available copper foils having an Rz of 1.6 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

[0110] The copper foil may be surface-treated to enhance the adhesive strength with the fluororesin film of the present disclosure.

[0111] The surface treatment is not particularly limited, but includes 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, but from the viewpoint of adhesion to the resin substrate, it is preferable that the reactive functional group has at least one (e.g., 1 to 4) selected from an amino group, a (meth)acrylic group, a mercapto group, and an epoxy group at the terminal. Furthermore, the hydrolyzable group is not particularly limited, but includes alkoxy groups such as a methoxy group and an ethoxy group. The copper foil used in the present disclosure may have a rust-preventive layer (e.g., an oxide film such as chromate), a heat-resistant layer, etc. formed thereon.

[0112] The surface-treated copper foil having a surface treatment layer of the above-mentioned silane compound on the copper foil surface can be produced by preparing a solution containing the silane compound and then surface treating the copper foil with this solution.

[0113] The copper foil may have a roughened layer on its surface from the viewpoint of improving adhesion to a resin substrate, etc. If the roughened layer may deteriorate the performance required in the present disclosure, the amount of roughening particles electrodeposited on the copper foil surface may be reduced as needed, or the copper foil may not be roughened at all.

[0114] Between the metal layer and the surface treatment layer, one or more layers selected from the group consisting of a heat-resistant treatment layer, a rust-proofing treatment layer, and a chromate treatment layer may be provided in order to improve various properties. These layers may be a single layer or multiple layers.

[0115] The metal-clad laminate of the present disclosure may further include a layer other than the metal layer and the fluororesin film. The layer other than the metal layer and the fluororesin film is preferably at least one (e.g., 1 to 12) selected from the group consisting of polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene.

[0116] The layers other than the metal layer and the fluororesin film are not particularly limited as long as they are made of the above-mentioned resins. The thickness of the layers other than the copper foil and the fluororesin film is preferably within the range of 12.5 to 260 μm.

[0117] In the metal-clad laminate of the present disclosure, the metal layer may be formed on one or both sides of the roll film. Methods for forming the metal layer include laminating (adhering) metal foil to the surface of the roll film, vapor deposition, plating, etc. Methods for laminating copper foil include a heat press method. The heat press temperature may be from the melting point of the dielectric film −150°C to the melting point of the dielectric film +40°C. The heat press time is, for example, 1 to 30 minutes. The laminate can be produced using a heat press pressure of 0.1 to 10 MPa.

[0118] The present disclosure also relates to a circuit board comprising the above-described sheet and a metal layer. The above-described metal-clad laminate is not particularly limited in its application and is used as a circuit board. Examples of circuit boards include printed circuit boards, laminated circuit boards, and high-frequency boards. A printed circuit board is a plate-shaped component that electrically connects electronic components such as semiconductors and capacitor chips while simultaneously arranging and fixing them in a limited space. The configuration of a printed circuit board formed from this metal-clad laminate is not particularly limited. The printed circuit board may be a rigid board, a flexible board, or a rigid-flexible board. The printed circuit board may be a single-sided board, a board, a double-sided board, or a multilayer board (such as a built-up board). It is particularly suitable for use as a flexible board or a rigid board. It is particularly suitable for use as a high-frequency printed circuit board of 10 GHz or more.

[0119] The circuit board is not particularly limited, and can be produced by a general method using the above-mentioned metal-clad laminate.

[0120] The laminate for a circuit board is also a laminate characterized by having a metal layer, the above-mentioned fluororesin film, and a substrate layer. The substrate layer is not particularly limited, but preferably has a fabric layer made of glass fiber and a resin film layer.

[0121] The glass fiber fabric layer is a layer made of glass cloth, glass nonwoven fabric, or the like. Commercially available glass cloth can be used, and glass cloth treated with a silane coupling agent is preferred to enhance affinity with the fluororesin. Examples of glass cloth materials include E-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, and low-dielectric-constant glass, with E-glass, S-glass, and NE-glass being preferred due to their ease of availability. The fiber weave may be plain weave or twill weave. The thickness of the glass cloth is typically 5 to 90 μm, preferably 10 to 75 μm, but it is preferable to use glass cloth that is thinner than the fluororesin film used.

[0122] The laminate may use a glass nonwoven fabric as a fabric layer made of glass fibers. Glass nonwoven fabric is a fabric in which short glass fibers are fixed with a small amount of a binder compound (resin or inorganic substance), or a fabric in which the shape is maintained by entanglement of the short glass fibers without the use of a binder compound. Commercially available glass nonwoven fabrics can be used. The diameter of the short glass fibers is preferably 0.5 to 30 μm, and the fiber length is preferably 5 to 30 mm. Specific examples of binder compounds include resins such as epoxy resins, acrylic resins, cellulose, polyvinyl alcohol, and fluororesins, as well as inorganic substances such as silica compounds. The amount of binder compound used is typically 3 to 15 mass% relative to the short glass fibers. Examples of materials for the short glass fibers include E-glass, C-glass, A-glass, S-glass, D-glass, NE-glass, and low-dielectric-constant glass. The thickness of the glass nonwoven fabric is typically 50 to 1000 μm, preferably 100 to 900 μm. The thickness of the glass nonwoven fabric in this application refers to a value measured in accordance with JIS P8118:1998 using a digital gauge DG-925 (load 110 grams, face diameter 10 mm) manufactured by Ono Sokki Co., Ltd. In order to increase the affinity with the fluororesin, the glass nonwoven fabric may be treated with a silane coupling agent.

[0123] Since most glass nonwoven fabrics have a very high porosity of 80% or more, it is preferable to use a sheet that is thicker than a sheet made of fluororesin and compress it under pressure.

[0124] The glass fiber fabric layer may be a layer formed by laminating a glass cloth and a glass nonwoven fabric. This allows the properties of each to be combined to obtain suitable properties. The glass fiber fabric layer may be in the form of a prepreg impregnated with a resin.

[0125] The laminate may have a glass fiber fabric layer and a fluororesin film bonded at the interface, or the glass fiber fabric layer may be partially or entirely impregnated with the fluororesin film. Furthermore, the laminate may be one in which a glass fiber fabric is impregnated with a fluororesin composition to produce a prepreg. The prepreg thus obtained may further be laminated with the fluororesin film of the present disclosure. In this case, the fluororesin composition used to produce the prepreg is not particularly limited, and the fluororesin film of the present disclosure may also be used.

[0126] The resin film used as the substrate layer is preferably a heat-resistant resin film or a thermosetting resin film. Examples of heat-resistant resin films include polyimide, modified polyimide, liquid crystal polymer, and polyphenylene sulfide. Examples of thermosetting resins include epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene. The heat-resistant resin film and thermosetting resin film may contain reinforcing fibers. While the reinforcing fibers are not particularly limited, glass cloth, particularly low-dielectric fibers, are preferred. The dielectric properties, linear expansion coefficient, water absorption, and other characteristics of the heat-resistant resin film and 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 even more preferably 3.0 or less. The dielectric loss tangent at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and even more preferably 0.0020 or less. The linear expansion coefficient is preferably 100 ppm / ° C. or less, more preferably 70 ppm / ° C. or less, and even more preferably 40 ppm / ° C. or less. The water absorption is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

[0127] The present disclosure will be specifically described below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0128] The raw materials are as follows: PTFE: PTFE having the following properties was used: Particle size: 500 μm Apparent density: 460 g / L Standard specific gravity: 2.17 Melting point: 327° C.

[0129] Silica 1 to 6: For silicas 1, 3 to 6, SC-6500SQ (particle size 2.1 μm, spherical) manufactured by Admatechs Co., Ltd. was used. For silica 2, SC-2500SQ (particle size 0.5 μm, spherical) manufactured by Admatechs Co., Ltd. was used. The silicas were subjected to the following surface treatments. Silica 3: Aminopropyl, treatment amount 1.0% Silica 4: Aminopropyl, treatment amount 0.2% Silica 5: Phenylamino, treatment amount 0.4% Silica 6: Isocyanate, treatment amount 0.2%

[0130] The treating agents used in the surface treatment are as follows: Aminopropyl: 3-aminopropyltriethoxysilane Phenylamino: N-phenyl-3-aminopropyltrimethoxysilane Isocyanate: 3-isocyanatepropyltriethoxysilane

[0131] (Sheet Production) Each sheet in the Examples and Comparative Examples listed in Table 1 was produced according to the production method detailed below. The PTFE and silica were weighed to the blending ratios shown in Table 1 and mixed in a mixer in the presence of dry ice. The temperature during mixing was −10°C or below. The resulting powder was left at room temperature for 2 hours, then placed in a plastic container, and 19 parts of a processing aid, hydrocarbon oil (product name: IP2028, manufactured by Idemitsu Kosan Co., Ltd.), were added (19 parts hydrocarbon oil per 100 parts PTFE and silica combined). The mixture was mixed for 3 minutes, left in a thermostatic oven at 25°C for 2 hours, and then heated to 40°C using a mold with a flat outlet to extrude the paste. The resulting sheet was rolled between two metal rolls to obtain a sample with a thickness of 125 μm, which was then dried at 200°C for 2 hours.

[0132] (Sheet Densification) The dried sheet was rolled at room temperature and 25°C using a pair of rolls, one of which was a metal roll and the other of which was a rubber-coated roll with a metal core. The sheet was then baked at 360°C for 15 minutes to obtain a sheet. The obtained sheet was evaluated according to the following criteria. The results are shown in Table 1.

[0133] (Specific Gravity of Sheet) JIS Z 8807 (Methods for measuring density and specific gravity of solids) 8 Measurement was carried out according to the method for measuring density and specific gravity by the submerged weighing method.

[0134] Furthermore, the rate of change in specific gravity of the sheet before and after densification was calculated as follows: Rate of change = (specific gravity after densification - specific gravity before densification) * 100 / specific gravity before densification.

[0135] (Water absorption test) The sheet was cut into a 5 cm x 5 cm square. After wiping off any dirt on the surface of this sheet, it was dried at 110°C for one hour. Immediately after drying, it was allowed to cool naturally in a desiccator. When the sample had cooled to room temperature, it was weighed and this weight was designated as W1. Next, it was immersed in water at room temperature for 24 hours to allow it to absorb water. After wiping off the moisture from the sheet after water absorption, its weight was measured (W2). The water absorption rate was calculated by the following formula: Water absorption rate = [(W2 - W1) / W1] x 100.

[0136] (Dielectric Loss Tangent) Df was measured at 25°C and 10 GHz using a split cylinder type dielectric constant / dielectric loss tangent measuring device (manufactured by EM Lab). The dielectric loss tangent was measured for a normal sheet and a sheet after water absorption under the same conditions as the water absorption test. Furthermore, the rate of change in the dielectric loss tangent before and after water absorption was also calculated. The rate of change was calculated as follows: Rate of change = (Dielectric loss tangent after water absorption - Dielectric loss tangent before water absorption) * 100 / Dielectric loss tangent before water absorption.

[0137] (Linear expansion coefficient) TMA measurement was carried out using a TMA-7100 (manufactured by Hitachi High-Tech Science Corporation) in a tensile mode. A sheet cut into a length of 20 mm, a width of 5 mm, and a thickness of 150 μm was used as a sample piece. The distance between chucks was set to 10 mm, and the linear expansion coefficient was determined from the displacement of the sample at a temperature rise rate of 2° C. / min from 0 to 150° C. while applying a load of 49 mN.

[0138]

[0139] The sheet of the present disclosure can be suitably used in particular for high-frequency printed circuit boards.

Claims

1. A sheet containing a fluororesin and a filler, and having a specific gravity of 2.05 or more and 2.19 or less.

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

3. A sheet according to claim 1 or 2, wherein the filler is silica.

4. The sheet according to claim 3, wherein the silica is spherical silica.

5. A sheet according to claim 3 or 4, wherein the silica has a particle size of 0.1 to 3 μm.

6. A sheet according to any one of claims 3 to 5, wherein the silica content is 20 to 80 mass % based on the weight of the sheet.

7. A sheet according to any one of claims 3 to 6, wherein the surface of the silica is treated with a surface treatment agent.

8. A sheet according to any one of claims 1 to 7, wherein the fluororesin is polytetrafluoroethylene resin having a standard specific gravity of 2.0 to 2.3, the filler is spherical silica, the particle size of the spherical silica being 0.5 to 2.1 μm, the content of the polytetrafluoroethylene resin is 40 to 60 mass% relative to the weight of the sheet, and the content of the spherical silica is 40 to 60 mass% relative to the weight of the sheet.

9. A sheet comprising 20 to 80% by mass of polytetrafluoroethylene resin relative to the sheet weight and surface-treated spherical silica having a particle size of 0.1 to 3 μm, wherein the silica content is 20 to 80% by mass relative to the sheet weight and the specific gravity is 2.05 or more and 2.19 or less.

10. The sheet according to any one of claims 1 to 9, which has a water absorption rate of 0.10% or less.

11. The sheet according to any one of claims 1 to 10, obtained by a manufacturing process including a densification step that increases the specific gravity of the sheet by 1% or more.

12. The sheet according to claim 11, wherein when the rate of change in the dielectric loss tangent before and after water absorption is compared, the rate of change in the dielectric loss tangent after densification is lower than that before densification.

13. The sheet according to any one of claims 1 to 12, which has a linear expansion coefficient of 120 ppm / K or less.

14. The sheet according to any one of claims 1 to 13, having a thickness of 0.1 to 2 mm.

15. The sheet according to any one of claims 1 to 14, which is an insulating material for circuit boards.

16. A metal clad laminate comprising a metal layer and a sheet according to any one of claims 1 to 15 as essential layers.

17. The metal clad laminate according to claim 16, wherein the metal layer is copper foil.

18. A circuit board comprising the sheet according to any one of claims 1 to 15 and a metal layer.

19. The circuit board according to claim 18, wherein the metal constituting the metal layer is copper.

20. The circuit board according to claim 19, wherein the copper is rolled copper or electrolytic copper.

21. The circuit board according to any one of claims 18 to 20, which is a printed circuit board, a multilayer circuit board, or a high-frequency board.

22. A method for manufacturing a sheet according to any one of claims 1 to 15, comprising: a step (1) of mixing the fluororesin and the filler and rolling the mixture into a sheet; and a step (2) of densifying the rolled sheet obtained by step (1).

23. A method for manufacturing a sheet as described in claim 22, wherein in the densification step (2), the rolled sheet is pressurized so that the specific gravity of the rolled sheet increases by 1% or more, the fluororesin is polytetrafluoroethylene resin having a standard specific gravity of 2.0 to 2.3, the filler is spherical silica, the particle size of the spherical silica being 0.5 to 2.1 μm, the content of the polytetrafluoroethylene resin is 40 to 60 mass% of the sheet weight, and the content of the spherical silica is 40 to 60 mass% of the sheet weight.