Resin sheet, its manufacturing method, copper-clad laminate and circuit board

Abstract

To provide a resin sheet including a fluororesin with excellent thermal expansion characteristics in the thickness direction.SOLUTION: This resin sheet includes a fluororesin and an anisotropic filler, and the anisotropic filler is uniaxially oriented in the film thickness direction and is randomly distributed in the surface direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a resin sheet, a method for producing the same, a copper-clad laminate, and a circuit board. [Background technology]

[0002] Resin sheets used in printed wiring boards and the like are required to have high dimensional stability. That is, they are required to have a low coefficient of thermal expansion, and for this reason, fillers are often blended into them. As such fillers, those containing anisotropic fillers whose shapes are anisotropic may be used.

[0003] Patent Document 1 discloses that in the production of a resin sheet containing an anisotropic filler, the filler is oriented by applying a magnetic field. Patent Documents 2 and 3 disclose methods for obtaining the orientation of anisotropic fillers other than by applying a magnetic field. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2002-80617 [Patent Document 2] International Publication No. 2020 / 225678 [Patent Document 3] Patent Publication No. 2022-60242 [Patent Document 4] International Publication No. 2020 / 145133 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a resin sheet that uses a fluororesin and has excellent low thermal expansion properties in the thickness direction. [Means for solving the problem]

[0006] The present disclosure provides: The resin sheet contains a fluororesin and an anisotropic filler, and is characterized in that the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the plane direction.

[0007] The fluororesin is preferably a perfluoro-based fluororesin, and particularly preferably at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / hexafluoropropylene copolymer. The anisotropic filler preferably has an aspect ratio of 1 or more and 200 or less.

[0008] The anisotropic filler preferably has an average particle size of 0.1 to 50 μm. The anisotropic filler is preferably talc or boron nitride. In the resin sheet, the anisotropic filler is talc, and in an X-ray diffraction pattern obtained by irradiating the sheet with X-rays in the cross-sectional direction, the talc in the sheet thickness direction is <020> For the surface <001> Intensity ratio of the diffraction peaks of the plane ( <001> / <020> ) is 300 or less, or the anisotropic filler is boron nitride, and in an X-ray diffraction pattern obtained by irradiating X-rays in the cross-sectional direction of the sheet, the <100> For the surface <002> Intensity ratio of the diffraction peaks of the plane ( <002> / <100> ) is preferably 20 or less. The resin sheet preferably contains silica or glass fiber in addition to the anisotropic filler.

[0009] The silica is preferably amorphous. The resin sheet preferably has a thickness of 0.1 to 2 mm. The resin sheet is preferably an insulating material for a circuit board.

[0010] The present disclosure also relates to a copper clad laminate having a copper foil and the above-described resin sheet as essential layers. The present disclosure also provides a circuit board having the above-described resin sheet and a conductive layer. The conductive layer is preferably made of a metal. The metal preferably has a surface roughness Rz of 2.0 μm or less on the surface that comes into contact with the resin sheet.

[0011] The metal 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.

[0012] The present disclosure provides: A step (1) of applying a dispersion containing a fluororesin and anisotropic filler onto a substrate to form a coating. Step (2) of drying the film obtained in step (1) while applying a magnetic field to form a dry film. Step (3) of firing the dried coating obtained in step (2). The method for producing a resin sheet is characterized by comprising the steps of:

[0013] In the above-mentioned method for producing a resin sheet, in step (2), the linear expansion coefficient in the film thickness direction is preferably half or less than that of a resin sheet obtained by firing a dried film that has been dried without applying a magnetic field.

[0014] In the above method for producing a resin sheet, the strength of the magnetic field is preferably 0.1 to 10T. In the method for producing a resin sheet, the total solid concentration of the fluororesin and the anisotropic filler in the dispersion is preferably 5 to 70 wt %. The weight ratio of the fluororesin to the anisotropic filler in the dispersion is preferably 90 / 10 to 30 / 70. [Effects of the Invention]

[0015] The resin sheet of the present disclosure has anisotropic fillers oriented in the sheet thickness direction, which reduces thermal expansion in the thickness direction and provides highly uniform thermal expansion performance in the planar direction, thereby solving the conventional problem of cracks occurring in the copper plating in the direction perpendicular to the sheet plane. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing a method for producing a resin sheet containing an anisotropic filler according to a conventional technique. [Figure 2] 1A and 1B are schematic diagrams illustrating a method for producing a resin sheet containing an anisotropic filler according to the present disclosure. [Figure 3] FIG. 1 is a schematic diagram showing an example of a method for applying a magnetic field in the present disclosure. [Figure 4] FIG. 1 is a schematic diagram showing a method for measuring X-ray diffraction. [Figure 5] FIG. 2 is a schematic diagram showing a state when a resin sheet according to the present disclosure is subjected to X-ray diffraction measurement. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present disclosure will be described in detail below. Resin components generally tend to expand when heated, which has been a problem in obtaining dimensional stability for resin molded products. To solve this problem, it is common to add inorganic fillers with low thermal expansion.

[0018] As such inorganic fillers, inorganic fillers having a highly anisotropic shape (e.g., plate-like) are widely used. It is widely known that such highly anisotropic inorganic fillers, when formed into a sheet, are oriented in the planar direction of the sheet (Fig. 1). In Fig. 1, (1) represents the state immediately after the dispersion is applied to the substrate, (2) represents the state after drying, and (3) represents the state after firing.

[0019] This orientation of the inorganic filler makes it difficult to suppress the thermal expansion of the resin sheet in the thickness direction due to the incorporation of the inorganic filler. To solve this problem, Patent Documents 2 and 3 use methods completely different from those of the present application to obtain resin sheets in which the inorganic filler is oriented in the thickness direction of the sheet. However, these methods also result in orientation in the planar direction, reducing randomness, resulting in anisotropy of linear expansion in the planar direction, and thermal expansion causes cracks in the copper foil in only specific directions.

[0020] In light of these problems, the present inventors have solved these problems by making at least a portion of the anisotropic filler exist in a direction perpendicular to the plane of the resin sheet, thereby obtaining a resin sheet with low thermal expansion in the thickness direction, which prevents cracks in the copper foil in the thickness direction when used in a circuit board.

[0021] An example of a manufacturing method for obtaining such a resin sheet includes a step (1) of applying a dispersion containing a fluororesin and an anisotropic filler to a substrate to form a film, a step (2) of drying the film obtained in step (1) while applying a magnetic field to form a dried film, and a step (3) of firing the dried film obtained in step (2). A schematic diagram of such a manufacturing method is shown in Figure 2. In Figure 2, (1) to (3) represent the above steps (1) to (3), respectively.

[0022] The resin sheet of the present disclosure is characterized in that the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the planar direction. This state can be confirmed by measuring the intensity ratio of diffraction peaks in an X-ray diffraction diagram obtained by irradiating the sheet with X-rays in the thickness direction.

[0023] The resin sheet of the present disclosure contains a fluororesin and an anisotropic filler, which will be described in detail below.

[0024] (anisotropic filler) The anisotropic filler used in the present disclosure is a particle having an anisotropic shape (having a diameter that varies depending on the direction), excluding glass fiber, crushed silica, and ceramics. For example, it is made of inorganic compounds such as carbon, inorganic oxides, inorganic nitrides, and inorganic carbides, or resins, etc. Specific examples include metal oxides such as boron nitride, aluminum nitride, aluminum oxide, zinc oxide, silicon carbide, and aluminum hydroxide, metal nitrides, metal carbides, and metal hydroxides; metals and alloys; carbon materials such as graphite, graphite, and diamond; and highly thermally conductive resins, and may be fibrous, needle-like, scale-like, or whisker-like particles.

[0025] Among these, talc or boron nitride is preferred from the viewpoint of electrical properties, and examples of the shape thereof include flat, flaky, plate-like, linear, tabular, granular, fibrous, and whisker-like shapes, preferably flaky, plate-like, or linear, more preferably flaky or plate-like, and particularly preferably plate-like. In this embodiment, only one type of anisotropic filler may be used, or two or more types of anisotropic fillers may be contained within a range that does not impair the effects of the present invention. For example, talc and other anisotropic fillers may be used in combination.

[0026] The anisotropic filler is preferably talc or boron nitride, from the viewpoint of low hardness and excellent magnetic field alignment.

[0027] The anisotropic filler preferably has an aspect ratio of 1 or more and 2000 or less. Use of an anisotropic filler having such a shape is preferable in that it can reduce thermal expansion (linear expansion) in the thickness direction. The aspect ratio is the value obtained by dividing the average particle diameter of the anisotropic filler measured with an electron microscope by the average minor axis (average value of the length in the shorter direction). The lower limit of the aspect ratio is more preferably 10, and even more preferably 20. The upper limit of the aspect ratio is more preferably 1000, and even more preferably 200.

[0028] The average particle size of the anisotropic filler is preferably 0.1 μm or more and 50 μm or less. Using an anisotropic filler with such an average particle size is preferable because it is more effective in reducing linear expansion. The average particle size is the D50 value measured by laser analysis / scattering. The lower limit of the average particle size is more preferably 1 μm or more, and even more preferably 3 μm or more. The upper limit of the average particle size is more preferably 30 μm, and even more preferably 20 μm.

[0029] (Fluorine resin) The resin sheet of the present disclosure contains a fluororesin, which has low dielectric properties and can therefore be suitably used for the purposes of the present disclosure.

[0030] Although the fluororesin that can be used in the present disclosure is not particularly limited, perfluororesins are preferred. 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). These fluororesins may be used alone or in combination of two or more. From the viewpoint of low dielectric constant, the fluororesin is preferably a perfluororesin, and particularly preferably polytetrafluoroethylene resin (PTFE), tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer (FEP), or TFE / alkyl vinyl ether copolymer (PFA). Among these, polytetrafluoroethylene resin (PTFE) and TFE / alkyl vinyl ether copolymer (PFA) are more preferable.

[0031] (polytetrafluoroethylene) The PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or a mixture of modified PTFE and homoPTFE. From the viewpoint of maintaining good moldability of polytetrafluoroethylene, the content of modified PTFE in the polymeric PTFE is preferably 10% by weight or more and 98% by weight or less, and more preferably 50% by weight or more and 95% by weight 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 Nos. 57-135, 63-137906, 2000-143727, 2002-201217, WO 2007 / 046345, WO 2007 / 119829, WO 2010 / 113950, etc. is preferred.

[0032] The modified PTFE is composed of TFE and a monomer other than TFE (hereinafter referred to as a modified monomer). Modified PTFE includes, but is not limited to, PTFE uniformly modified with the modified monomer, PTFE modified at the beginning of the polymerization reaction, and PTFE modified at the end of the polymerization reaction. The modified PTFE is preferably a TFE copolymer obtained by polymerizing a small amount of a monomer other than TFE together with TFE within a range that does not significantly impair the properties of the TFE homopolymer. Modified PTFEs that can be suitably used include those disclosed in, for example, 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, and the like. Among these, modified PTFEs having high stretchability and disclosed in JP-A Nos. 61-16907, 62-104816, 64-1711, 1999-240917, WO 2003 / 033555, WO 2005 / 061567, WO 2007 / 005361, WO 2011 / 055824, etc. are preferred.

[0033] The modified PTFE contains TFE units derived from TFE and modified monomer units derived from a modified monomer. The modified monomer units are a part of the molecular structure of the modified PTFE and are derived from the modified monomer. The modified PTFE preferably contains the modified monomer units in an amount of 0.001 to 0.500% by weight, more preferably 0.01 to 0.30% by weight, of the total monomer units. The total monomer units are the parts derived from all monomers in the molecular structure of the modified PTFE.

[0034] The modifying monomer is not particularly limited as long as it is copolymerizable 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 ethers, perfluoroalkylethylenes (PFAE), ethylene, etc. The modifying monomer used may be one type or multiple types.

[0035] The perfluorovinyl ether is not particularly limited, and may be, for example, a perfluorovinyl ether represented by the following general formula (1): perfluorounsaturated compounds. CF2 = CF-ORf (1)

[0036] In the formula, Rf represents a perfluoroorganic group.

[0037] 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.

[0038] An example of perfluorovinyl ether is perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (1) 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 perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Preferred PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0039] The perfluoroalkylethylene (PFAE) is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE), and the like.

[0040] The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0041] (Melt-moldable fluororesin) The fluororesin of the present disclosure may be a melt-moldable fluororesin, which will also be described in detail below.

[0042] The fluororesin may be a melt-processable fluororesin, and examples thereof include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), copolymers having chlorotrifluoroethylene (CTFE) units (CTFE copolymers), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer (THV), tetrafluoroethylene-vinylidene fluoride copolymer, and the like. Among these melt-moldable fluororesins, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferred.

[0043] The resin constituting the resin sheet preferably has a glass transition temperature of 40°C or higher. A temperature of 40°C or higher is preferable because, for example, when a roll film is stored at room temperature, deformation at ambient temperatures is unlikely to occur, and a temperature of 60°C or higher is more preferable, and a temperature of 80°C or higher is even more preferable. The upper limit is not particularly limited, but from the viewpoint of adhesiveness, it is preferably 200°C or lower, more preferably 160°C or lower, and even more preferably 120°C or lower. The glass transition temperature is a value obtained by dynamic viscoelasticity measurement.

[0044] The melting point of the PFA is preferably 180 to 340° C., more preferably 230 to 330° C., and even more preferably 280 to 320° C. The melting point is the temperature corresponding to the maximum value on the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC).

[0045] The PFA is not particularly limited, but a copolymer having a molar ratio of TFE units to PAVE units (TFE units / PAVE units) of 70 / 30 or more but less than 99.5 / 0.5 is preferred. A more preferred molar ratio is 70 / 30 or more but less than 98.9 / 1.1, and an even more preferred molar ratio is 80 / 20 or more but less than 98.5 / 1.5. If the TFE units are too few, the mechanical properties tend to decrease, while if they are too many, the melting point tends to become too high and moldability tends to decrease. The PFA may be a copolymer consisting of only TFE and PAVE, or it is also preferred to be a copolymer having 0.1 to 10 mol% of monomer units derived from monomers copolymerizable with TFE and PAVE, and a total of 90 to 99.9 mol% of TFE units and PAVE units. Monomers copolymerizable with TFE and PAVE include HFP, CZ 3 Z 4 =CZ 5 (CF2) n Z 6 (In the formula, Z 3 , Z 4 and Z 5 are the same or different and represent a hydrogen atom or a fluorine atom; Z 6represents a hydrogen atom, a fluorine atom or a chlorine atom, and n represents an integer of 2 to 10.) and a vinyl monomer represented by CF2=CF-OCH2-Rf 7 (In the formula, Rf 7 represents a perfluoroalkyl group having 1 to 5 carbon atoms. ) and alkyl perfluorovinyl ether derivatives represented by the formula (I) are included. Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group, and examples of acid anhydride monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, and maleic anhydride. One type of acid anhydride monomer may be used alone, or two or more types may be used in combination.

[0046] The PFA preferably has a melt flow rate (MFR) of 0.1 to 100 g / 10 min, more preferably 0.5 to 90 g / 10 min, and even more preferably 1.0 to 85 g / 10 min. In this specification, the MFR is a value measured in accordance with ASTM D3307 at a temperature of 372°C and a load of 5.0 kg.

[0047] Although the FEP is not particularly limited, a copolymer having a molar ratio of TFE units to HFP units (TFE units / HFP units) of 70 / 30 or more and less than 99 / 1 is preferred. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and an even more preferred molar ratio is 80 / 20 or more and 97 / 3 or less. If the TFE unit content is too low, mechanical properties tend to decrease, while if the TFE unit content is too high, the melting point tends to become too high and moldability tends to decrease. It is also preferred that the FEP is a copolymer containing 0.1 to 10 mol % of monomer units derived from monomers copolymerizable with TFE and HFP, and 90 to 99.9 mol % of TFE units and HFP units in total. Examples of monomers copolymerizable with TFE and HFP include alkyl perfluorovinyl ether derivatives. Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group, and examples of acid anhydride monomers include itaconic anhydride, citraconic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, maleic anhydride, etc. One type of acid anhydride monomer may be used alone, or two or more types may be used in combination.

[0048] The melting point of the FEP is preferably 150 to 320° C., more preferably 200 to 300° C., and even more preferably 240 to 280° C. The melting point is the temperature corresponding to the maximum value on the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimeter (DSC). The FEP preferably has an MFR of 0.01 to 100 g / 10 min, more preferably 0.1 to 80 g / 10 min, further preferably 1 to 60 g / 10 min, and particularly preferably 1 to 50 g / 10 min.

[0049] The fewer functional groups the fluororesin has, the fewer unstable terminal groups it has. Such fluororesins can be produced by adjusting the conditions during production (polymerization reaction), or by subjecting the fluororesin after polymerization to fluorine gas treatment, heat treatment, supercritical gas extraction, or other methods to reduce the number of unstable terminal groups. Fluorine gas treatment is preferred because it has excellent treatment efficiency and converts some or all of the unstable terminal groups to —CF3, resulting in stable terminal groups. The use of a fluororesin with a reduced number of unstable terminal groups is preferred because it reduces the electrostatic dissipation factor and reduces electrical signal loss.

[0050] The number of unstable terminal groups is not particularly limited, but is preferably 1×10 6 The number of particles per particle is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. In consideration of the effect of reducing the dielectric loss tangent, the number is preferably less than 10, and more preferably 5 or less.

[0051] Specific examples of unstable terminal groups include functional groups such as -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), hydroxyl groups (such as -CHOH), -CONH, -COOR (such as R = CH), -CFH, and -OCOO-R (such as normal propyl carbonate).

[0052] Specifically, the number of unstable terminal groups is measured by the following method. First, the fluororesin is melted and compression-molded to produce a film with a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the fluororesin, and a difference spectrum is obtained from the base spectrum, which is completely fluorinated and has no functional groups. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of carbon atoms in the main chain of the fluororesin is calculated according to the following formula (A): 6 The number of unstable terminal groups per unit is calculated. N=I×K / t (A) I: Absorbance K: Correction coefficient t: film thickness (mm)

[0053] For reference, the absorption frequencies, molar absorption coefficients, and correction coefficients for the unstable terminal groups in this specification are shown in Table 1. The molar absorption coefficients were determined from FT-IR measurement data of low molecular weight model compounds.

[0054] [Table 1]

[0055] The fluorine gas treatment can be carried out by contacting a fluorine-containing compound with a fluorine resin that has not been treated with fluorine gas.

[0056] The fluorine-containing compound is not particularly limited, but examples thereof include fluorine radical sources that generate fluorine radicals under fluorine gas treatment conditions, such as F2 gas, CoF3, AgF2, UF6, OF2, N2F2, CF3OF, and halogen fluorides (e.g., IF5, ClF3).

[0057] The fluorine radical source such as F2 gas may be 100% concentrated, but from a safety standpoint, it is preferably mixed with an inert gas and diluted to 5 to 50 mass %, more preferably 15 to 30 mass % for use. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, with nitrogen gas being preferred from an economical standpoint.

[0058] The conditions for the fluorine gas treatment are not particularly limited, and the molten fluororesin may be contacted with the fluorine-containing compound, but the treatment is usually carried out at a temperature below the melting point of the fluororesin, preferably 20 to 220°C, more preferably 100 to 200°C. The fluorine gas treatment is generally carried out for 1 to 30 hours, preferably 5 to 25 hours. The fluorination treatment is preferably carried out by contacting a fluororesin that has not been treated with fluorine gas with fluorine gas (F2 gas).

[0059] In this specification, the content of each monomer unit constituting the fluororesin can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0060] (mixing ratio) The resin sheet of the present disclosure preferably contains 10 to 80% by mass of the anisotropic filler relative to the total amount of the fluororesin and the anisotropic filler. This range is preferable in that it achieves both the effect of low linear expansion and the strength of the material itself. The lower limit is more preferably 15% by mass, and even more preferably 20% by mass. The lower limit is more preferably 70% by mass, and even more preferably 60% by mass.

[0061] (Other fillers) The resin sheet of the present disclosure may further contain silica or glass fiber. The silica or glass fiber may be a mixture of both.

[0062] When the "other fillers" are blended, they are preferably contained in a proportion of 1 to 40% by mass relative to the total amount of the resin sheet. A content within this range is preferred in that it is possible to achieve a balance between the effects of reducing linear expansion in the thickness direction and the plane direction. The lower limit is more preferably 3% by mass, and even more preferably 5% by mass. The lower limit is more preferably 35% by mass, and even more preferably 30% by mass.

[0063] (Other ingredients) The resin sheet of the present disclosure may contain other components as needed, such as additives such as UV absorbers, fillers, crosslinking agents, antistatic agents, heat stabilizers, foaming agents, foam nucleating agents, antioxidants, surfactants, photopolymerization initiators, anti-wear agents, surface modifiers, and liquid crystal polymers.

[0064] When the above-mentioned other components are blended, the blending amount is preferably such that the content of the fluororesin, anisotropic filler, and other fillers is 95 mass% or more relative to the total amount of the resin sheet. Blending of an excessive amount of other components is not preferable because it may not be possible to obtain the desired physical properties.

[0065] (resin sheet) The resin sheet of the present disclosure is made of the above-mentioned components and preferably has a film thickness of 0.1 to 2 mm. The thickness here is a value measured with a film thickness meter. Setting the thickness within this range is preferable in that it can achieve both sheet strength and flexibility.

[0066] In the resin sheet of the present disclosure, the anisotropic filler is talc, and in an X-ray diffraction pattern obtained by irradiating the sheet with X-rays in the cross-sectional direction, the talc in the sheet thickness direction is <020> For the surface <001> Intensity ratio of the diffraction peaks of the plane ( <001> / <020> ) is 300 or less, or the anisotropic filler is boron nitride, and in the X-ray diffraction pattern obtained by irradiating X-rays in the cross-sectional direction of the sheet, <100> For the surface <002> Intensity ratio of the diffraction peaks of the plane ( <002> / <100> ) is preferably 20 or less. The X-ray diffraction measurement method here can be carried out according to the method shown in the Examples.

[0067] The X-ray diffraction pattern of the present disclosure is measured in the state shown in the schematic diagram of FIG. 4. The sample sheet cross section 5 in FIG. 4 is the sheet of the present disclosure. The resin sheet of the present disclosure is in the state shown in the schematic diagram of FIG. 5(a), or in a state close to that. Since X-ray diffraction is performed in this state, the X-ray diffraction has peaks at 90° and 270°. On the other hand, a conventional resin sheet is in the state shown in the schematic diagram of FIG. 5(b), or in a state close to that. Therefore, the X-ray diffraction has peaks at 0° and 180°.

[0068] From this point of view, when the diffraction peak intensity ratio of the X-ray diffraction described above is within a specific range, it can be determined that the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the plane direction. From this point of view, the parameters of the diffraction peak intensity ratio described above are set, and a resin sheet is obtained in which these fall within the specific range.

[0069] The thickness of the sheet is <020> For the surface <001> Intensity ratio of the diffraction peaks of the plane ( <001> / <020> ) is more preferably 300 or less, and even more preferably 100 or less. <100> For the surface <002> Intensity ratio of the diffraction peaks of the plane ( <002> / <100> ) is more preferably 20 or less, and even more preferably 10 or less.

[0070] (Method of manufacturing resin sheet) The method for producing a resin sheet according to the present disclosure includes: A step (1) of applying a dispersion containing a fluororesin and anisotropic filler onto a substrate to form a coating. Step (2) of drying the film obtained in step (1) while applying a magnetic field to form a dry film. Step (3) of firing the dried coating obtained in step (2). It has the following characteristics.

[0071] That is, after the dispersion is applied to the substrate, in step (2) of forming a dried film, the film is dried while a magnetic field is applied. By doing so, at least a portion of the anisotropic filler is oriented by the action of the magnetic field and aligned in a direction closer to perpendicular to the thickness direction of the coating, thereby achieving the above-mentioned object.

[0072] Talc, boron nitride, and other materials commonly used as anisotropic fillers are diamagnetic and generally considered to have no magnetic properties. However, they do in fact possess weak magnetic properties, and can become oriented when an external magnetic field is applied. While melt molding is also widely known as a molding method for fluororesin, it requires high temperatures, which cannot be achieved depending on the type of magnet. Also, due to the high viscosity of the molten material, it is not easy to orient anisotropic fillers by melt molding in the presence of a magnetic field.

[0073] On the other hand, when forming a film by applying a dispersion, such problems do not occur. Furthermore, in the early stages of the drying process, the anisotropic filler can move relatively freely in the coating film, and can easily move under the action of a magnetic field. Therefore, this method is suitable as a method for obtaining the resin sheet of the present disclosure. This allows the object of the present disclosure to be achieved in a simple manner.

[0074] Hereinafter, the method for producing a resin sheet according to the present disclosure will be described in detail according to each step. (Process (1)) Step (1) is a step of applying a dispersion containing a fluororesin and an anisotropic filler onto a substrate to form a coating. In the step (1), a dispersion containing a fluororesin and an anisotropic filler is used. The fluororesin and anisotropic filler used here are as described above.

[0075] The dispersion liquid is a dispersion of a fluororesin and an anisotropic filler in a liquid medium. The liquid medium is not particularly limited, and preferably contains water or a water-soluble solvent in combination with water. The water-soluble solvent has the function of wetting the fluororesin, and those with a high boiling point also act as a drying retarder that bonds the resin together during drying after coating and prevents cracks from occurring. Even high-boiling point solvents evaporate at the baking temperature of the fluororesin, so they do not adversely affect the coating film.

[0076] Specific examples of the water-soluble solvent include low-boiling organic solvents having a boiling point of up to 100°C, such as methanol, ethanol, isopropanol, sec-butanol, t-butanol, acetone, and methyl ethyl ketone; medium-boiling organic solvents having a boiling point of 100 to 150°C, such as methyl cellosolve and ethyl cellosolve; and high-boiling organic solvents having a boiling point of 150°C or higher, such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, 3-butoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N-dimethylformamide, ethylene glycol, propylene glycol, glycerin, dimethylcarbitol, butylcarbitol, butyl dicarbitol, butyl cellosolve, 1,4-butanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, and diethylene glycol monomethyl ether. These water-soluble solvents may be used alone or in combination. As the water-soluble solvent, a high-boiling organic solvent is preferred, and among these, a glycol-based solvent is more preferred in terms of dispersion stability and safety. The glycol-based solvent preferably contains at least one selected from the group consisting of ethylene glycol, diethylene glycol monomethyl ether, glycerin, and butyl carbitol.

[0077] The blending amount of the water-soluble solvent is preferably 0.5 to 50% by mass, more preferably 1 to 30% by mass, of the total amount of water and water-soluble solvent. In the case of low-boiling-point organic solvents, too little blending can easily cause bubble entrapment, while too much can make the entire composition flammable, diminishing the benefits of the aqueous dispersion composition. In the case of medium-boiling-point organic solvents, too much blending can remain in the coating film after baking and cause adverse effects, while too little can cause the fluororesin to revert to powder during drying after application, making baking impossible. In the case of high-boiling-point organic solvents, too much blending can remain in the coating film after baking and cause adverse effects. It is preferable to select a water-soluble solvent that is easily volatile or adjust the blending amount so that it does not remain in the coating film after baking of the fluororesin. The absence of glycol-based solvents after baking of the fluororesin can be confirmed by scraping off the coating film after baking and performing TG / DTA analysis to determine whether there is any weight loss near the boiling point of the glycol-based solvent.

[0078] The fluororesin dispersed in water may be an emulsion resin obtained by emulsion polymerization or a dispersion of fluororesin powder in a liquid medium, but is preferably an emulsion resin.

[0079] The anisotropic filler can be dispersed in the liquid medium by shaking the mixture.

[0080] The dispersion preferably contains the liquid medium in a proportion of 20 to 80% by mass.

[0081] The dispersion may contain an emulsifier and the like in addition to the components constituting the sheet and the liquid medium.

[0082] Such a dispersion is applied to a substrate to form a film. Here, the substrate is not particularly limited, and examples thereof include metals such as copper foil, iron, stainless steel, copper, aluminum, and brass; glass products such as glass plates and glass fiber woven and nonwoven fabrics; molded and coated products of general-purpose and heat-resistant resins such as polypropylene, polyoxymethylene, polyimide, modified polyimide, polyamideimide, polysulfone, polyethersulfone, polyetheretherketone, and liquid crystal polymers; molded and coated products of general-purpose rubbers such as SBR, butyl rubber, NBR, and EPDM, silicone rubber, and heat-resistant rubbers such as fluororubber; woven and nonwoven fabrics of natural and synthetic fibers; and laminated substrates formed by combining these. The article substrate may be surface-treated. Examples of the surface treatment include roughening to a desired roughness using sandblasting, roughening by adhering particles, and metal oxidation prevention treatment. Examples of the coating formation method include spray coating, roll coating, coating with a doctor blade, dip coating, impregnation coating, spin flow coating, curtain flow coating, coating with a bar coater, gravure coating, microgravure coating, etc.

[0083] (Process (2)) In step (2), the film obtained in step (1) is dried while applying a magnetic field to form a dried film. A schematic diagram showing an example of a method for applying a magnetic field when performing step (2) is shown in Figure 3.

[0084] The apparatus shown in Figure 3 has a conductive coil installed on the outer periphery of a cylindrical shape and a sample installation section in the center. The article having a coating formed on a substrate obtained in the above step (1) is placed on this section and dried while a magnetic field is applied.

[0085] When the dispersion contains talc, the dispersion is arranged in a magnetic field atmosphere so that the direction of the magnetic field lines corresponds to the desired orientation direction of the talc. In this way, by arranging the dispersion so that the direction of the magnetic field lines corresponds to the desired orientation direction, it is possible to orient the talc in any direction.

[0086] The applied magnetic field is preferably 0.1 to 10 T. Such a magnetic field is a value obtained by measuring the magnetic field density using a gaussmeter. Setting the magnetic field within this range is preferable in that the orientation of the anisotropic filler proceeds favorably. The lower limit of the applied magnetic field is more preferably 0.3 T, and even more preferably 0.5 T. There is no particular upper limit to the applied magnetic field.

[0087] The magnet for applying such a magnetic field is not particularly limited, but a permanent magnet or a superconducting magnet is particularly preferred.

[0088] The drying in step (2) is preferably carried out under heated conditions, and the drying temperature is preferably within the range of 1 to 80°C. If the drying temperature is too high, the filler will dry before it is oriented, which is undesirable. On the other hand, if the drying temperature is too low, the evaporation temperature of the liquid medium will be too low, which is undesirable because it will reduce efficiency. The drying method is not particularly limited, but a method that can control the temperature on the sample stage may be used.

[0089] (Step (3)) Step (3) is a step of heating and baking the dried film obtained in step (2). A resin sheet is formed by this step. Step (3) can be performed under general conditions for obtaining a resin sheet by such a method. Specifically, it can be performed at 300 to 400°C.

[0090] The above-mentioned steps (1) to (3) may be carried out continuously on a line by sequentially installing means for carrying out the above-mentioned steps (1) to (3) on the line, or may be carried out in a batch system for each step.

[0091] In the method for producing a resin sheet according to the present disclosure, in step (2), the linear expansion in the film thickness direction is preferably half or less of that of a resin sheet obtained by baking a dried film dried without applying a magnetic field. By adopting such a method, the effects of the present disclosure can be satisfactorily exhibited.

[0092] (circuit board) The sheet-shaped resin composition of the present disclosure can be suitably used in circuit board applications by being laminated with a conductive layer.

[0093] The present disclosure also provides a circuit board having a conductive layer of metal or the like on one or both sides of the resin sheet described above. As described above, the resin sheet of the present disclosure is particularly suitable for use in printed wiring board applications, and can therefore be suitably used as such a laminate. The conductive layer is preferably copper foil.

[0094] The circuit board may be manufactured using a metal foil as the conductive layer and laminated with a resin sheet, or may be manufactured by adhering a metal foil to the resin sheet to form a laminate.

[0095] The copper foil preferably has an Rz of 1.6 μm or less. That is, the fluororesin composition of the present disclosure also has excellent adhesion to copper foil with a high smoothness of 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 is bonded to the resin sheet, and there are no particular restrictions on the Rz value of the other surface. The Rz is the sum of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The Rz is the ten-point average roughness specified in JIS-B0601. In this specification, the Rz is measured using a surface roughness meter (product name: Surfcom) with a measurement length of 4 mm. The values ​​were measured using a 470A (Tokyo Seiki Co., Ltd.).

[0096] 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.

[0097] The copper foil is not particularly limited, and specific examples include rolled copper foil and electrolytic copper foil.

[0098] 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.).

[0099] The copper foil may be surface-treated to increase the adhesive strength with the resin sheet of the present disclosure.

[0100] The surface treatment is not particularly limited, but may be a silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, or the like. 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 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 may include 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 (such as an oxide film such as chromate), a heat-resistant layer, or the like formed thereon.

[0101] 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.

[0102] The copper foil may have a roughened layer on the surface from the viewpoint of improving adhesion to the resin sheet. If the roughening treatment is likely to degrade 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 roughening treatment may not be performed at all.

[0103] In order to improve various properties, one or more layers selected from the group consisting of a heat-resistant layer, a rust-proofing layer, and a chromate-treated layer may be provided between the copper foil and the surface-treated layer. These layers may be a single layer or multiple layers.

[0104] The circuit board of the present disclosure may further include layers other than the copper foil and the resin sheet. The layers other than the copper foil and the resin sheet are 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 ether, polyphenylene ether, and polybutadiene.

[0105] The layers other than the copper foil and the resin sheet are not particularly limited as long as they are made of the above-mentioned resins, and the thickness of the layers other than the copper foil and the resin sheet is preferably within the range of 12.5 to 260 μm.

[0106] In the circuit board of the present disclosure, the copper layer may be formed on one side or both sides. Methods for forming the copper layer include laminating (adhering) copper foil to the surface of a resin sheet, vapor deposition, plating, etc. Methods for laminating copper foil include a method using heat pressing. The heat pressing temperature may be from the melting point of the resin sheet -150°C to the melting point of the resin sheet +40°C. The heat pressing time is, for example, 1 to 30 minutes. The circuit board can be manufactured using a method in which the heat pressing pressure is 0.1 to 10 MPa.

[0107] A circuit board is a plate-like component that electrically connects electronic components such as semiconductors and capacitor chips while simultaneously arranging and fixing them in a limited space. There are no particular limitations on the configuration of the circuit board having a resin sheet layer of the present disclosure. The circuit board may be any of a rigid board, a flexible board, and a rigid-flexible board. The circuit board may be any of a single-sided board, a board, a double-sided board, and 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 circuit board for high frequencies of 10 GHz or higher.

[0108] The circuit board of the present disclosure is not particularly limited in its application, but is preferably used as a printed circuit board, a laminated circuit board, or a high-frequency board. The circuit board is not particularly limited and can be produced by a general method.

[0109] The laminate for a circuit board is also a laminate characterized by having a copper foil layer, the above-mentioned resin sheet, and a base layer. The base layer is not particularly limited, but preferably has a fabric layer made of glass fiber and a resin sheet layer.

[0110] The glass fiber fabric layer is a layer made of glass cloth, glass nonwoven fabric, or the like. Commercially available glass cloths can be used, and those treated with a silane coupling agent are 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 or twill. The thickness of the glass cloth is typically 5 to 90 μm, preferably 10 to 75 μm, but it is preferable to use glass cloths that are thinner than the resin sheet of the present disclosure.

[0111] The laminate may use a glass nonwoven fabric as a fabric layer made of glass fibers. The 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 usually 3 to 15 mass% based on the weight of 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 usually 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.

[0112] 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.

[0113] 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.

[0114] The laminate may have a glass fiber fabric layer and a resin sheet bonded at the interface, or the glass fiber fabric layer may be partially or entirely impregnated with the resin sheet. Furthermore, the laminate may be a prepreg produced by impregnating a glass fiber fabric with a fluororesin composition. The prepreg thus produced may further be laminated with a resin sheet according to the present disclosure. In this case, the fluororesin composition used to produce the prepreg is not particularly limited, and the resin sheet according to the present disclosure may also be used.

[0115] The resin sheet used as the substrate layer is preferably a heat-resistant resin sheet or a thermosetting resin sheet. Examples of heat-resistant resin sheets include polyimide, modified polyimide, liquid crystal polymer, and polyphenylene sulfide. Examples of thermosetting resins include those containing epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene. The heat-resistant resin sheet and the thermosetting resin sheet may contain reinforcing fibers. While the reinforcing fibers are not particularly limited, glass cloth, particularly low-dielectric type fibers, are preferred.

[0116] The heat-resistant resin sheet and the thermosetting resin sheet are not particularly limited in terms of dielectric properties, linear expansion coefficient, water absorption, and other properties. 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. It is preferable that the linear expansion coefficient in the thickness direction satisfies the above values. [Example]

[0117] 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.

[0118] The materials used in the examples are as follows: (Fluororesin water dispersion) PFA aqueous dispersion 1: average particle size: 336 nm, PFA component: 64.5% PTFE aqueous dispersion 1: average particle size: 250nm, PTFE component: 60.0%

[0119] (Fluorocarbon powder) PFA powder 1: Average particle size: 504 nm, MFR: 27.0

[0120] (additives) Surfactant 1: Polyether type surface modifier

[0121] (filler) Talc 1: Average particle size: 5 μm, aspect ratio: 40-45 Talc 2: Average particle size: 7 μm, aspect ratio: 30, surface treatment: treated with aminosilane (amino group-containing silane coupling agent) Talc 3: Average particle size: 5 μm, aspect ratio: 40-45, surface treatment: treated with aminosilane (amino group-containing silane coupling agent) Boron nitride 1: Average particle size: 10 μm, Shape: scaly Silica 1: Average particle size: 2.1 μm, Shape: Spherical

[0122] Example 1 <Preparation of the mixed solution> 5.0 g of PFA aqueous dispersion, 3.3 g of talc, 4.3 g of water, and 0.5 g of surfactant were mixed and stirred with a mix rotor at room temperature for 10 hours. <Magnetic field application and preliminary drying> 4.4 g of the obtained mixture was placed in a glass petri dish with a diameter (inner diameter) of 48 mm, and it was left to stand for 70 minutes on a hot stage heated to 60 °C while applying a magnetic field of 10 T using a magnetic field application device (manufactured by Japan Superconductor Technology Co., Ltd., model: JMTD10T 100) until it lost its fluidity and was pre-dried. <Drying> To remove the volatile components in the obtained solid content, it was further dried at 130 °C for 30 minutes. <Firing> The dried film was fired at 330 °C for 30 minutes to obtain a sample with a thickness of 0.4 mm.

[0123] <Linear expansion rate measurement> Using a sample cut out into a 5 mm square from the resin sheet obtained by firing, the linear expansion rate was measured with a thermomechanical analyzer (manufactured by Hitachi High-Tech Science Corporation, model: TMA-7100). The linear expansion rate was determined from the displacement amount of the sample at 20 - 200 °C at a heating rate of 2 °C / min while applying a load of 49 mN.

[0124] <X-ray diffraction measurement (wide-angle X-ray scattering method)> Various samples were observed using the WAXS method. The WAXS method was carried out at the High Energy Accelerator Research Organization (JASRI) SPring-8, beamline BL40B2. The wavelength (λ) of the X-ray was λ = 0.0709 nm, the camera length (R) was R = 323 mm, and a PLATUS 3M (manufactured by Dectris) was used as the detector at room temperature of 25 °C. The resin sheet obtained by firing was cut into a thickness of 0.2 mm, placed in a sample holder so that the thickness direction was horizontal, and the beam was irradiated on the cross-section (edge) (Figure 4). The exposure time of the X-ray was 60 seconds.

[0125] (Examples 2 - 8, 10) A dispersion was prepared with the composition as shown in Table 2, and samples were obtained and the linear expansion rate was measured in the same manner as in Example 1 except that a magnetic field strength was applied. Examples 2, 3, 8, and 10 were subjected to X-ray measurement in the same manner as in Example 1.

[0126] (Example 9) A sample was obtained in the same manner as in Example 1, except that in the step of <magnetic field application and pre-drying>, the mixed solution was poured after placing a copper foil (surface roughness Rz 1.4 μm) with a thickness of 18 μm and a diameter of 48 mm in a glass petri dish, and then the linear expansion coefficient was measured. The results show that the anisotropic filler is also oriented by the application of a magnetic field in the laminate laminated with the copper foil.

[0127] (Comparative Examples 1 to 8, 11) A dispersion liquid was prepared with the composition shown in Table 3, and samples were obtained and measured for linear expansion coefficient in the same manner as in Example 1, except that a magnetic field was not applied in the step of <magnetic field application and pre-drying>. Comparative Examples 2 to 4 and 11 were subjected to X-ray measurement in the same manner as in Example 1.

[0128] (Comparative Example 9) A dispersion liquid was prepared with the composition shown in Table 3, and samples were obtained in the same manner as in Example 1 except that a magnetic field was not applied in the <magnetic field application and pre-drying> step and a magnetic field was applied after the <drying> step, and the linear expansion coefficient was measured.

[0129] (Comparative Example 10) PFA powder (1:71.4 g) and talc (1:31.6 g) were melt-kneaded using a Labo Plastomill Mixer (time: 600 seconds, temperature: 350°C), and then naturally cooled to obtain a solid composition. The resulting solid composition was crushed and pelletized. The resulting pellets were press-molded at 350°C to obtain a resin sheet with a thickness of 0.5 mm. This resin sheet was cut into 5 mm squares, and the linear expansion coefficient was measured.

[0130] [Table 2]

[0131] [Table 3]

[0132] The relationship between the above-mentioned Examples and Comparative Examples is shown in Table 4 below, where the Comparative Example is a resin sheet obtained by baking a dried film that has been dried without applying a magnetic field to each Example. Based on this comparison, the ratio of the linear expansion coefficient in the film thickness direction (linear expansion coefficient in the film thickness direction of the resin sheet to which a magnetic field has been applied / linear expansion coefficient of the resin sheet to which a magnetic field has not been applied) was calculated, and the values ​​are shown in Table 4.

[0133] [Table 4]

[0134] From the results of each example in Tables 2 to 4 above, it is clear that the resin sheet of the present disclosure has excellent heat shrinkage properties in the thickness direction. [Industrial Applicability]

[0135] The resin sheet of the present disclosure can be suitably used in circuit board applications. [Explanation of symbols]

[0136] 1 Superconducting coil 2 Sample stage 3. Sample 4 magnetic field 5 Sheet cross section 6 Sheet thickness direction 7 Beam irradiation position 8 holes 9 Sample Holder

Claims

1. A resin sheet comprising a perfluoro-based fluororesin and an anisotropic filler, wherein the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the plane direction, and the anisotropic filler has an anisotropic shape with a diameter that varies depending on the direction, and the resin sheet contains the anisotropic filler in a proportion of 10 to 80 mass% with respect to the total amount of the perfluoro-based fluororesin and the anisotropic filler.

2. 2. The resin sheet according to claim 1, wherein the perfluoro-based fluororesin is at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer, and tetrafluoroethylene / hexafluoropropylene copolymer.

3. 3. The resin sheet according to claim 1, wherein the anisotropic filler has an aspect ratio of 10 or more and 200 or less.

4. 3. The resin sheet according to claim 1, wherein the anisotropic filler has an average particle size of 0.1 μm or more and 50 μm or less.

5. 3. The resin sheet according to claim 1, wherein the anisotropic filler is talc or boron nitride.

6. 6. The resin sheet according to claim 5, wherein the anisotropic filler is talc, and in an X-ray diffraction diagram obtained by irradiating the sheet with X-rays in the cross-sectional direction, the intensity ratio (<001> / <020>) of the diffraction peak of the <001> plane to the <020> plane of the talc in the thickness direction of the sheet is 300 or less; or the anisotropic filler is boron nitride, and the intensity ratio (<002> / <100>) of the diffraction peak of the <002> plane to the <100> plane of the boron nitride in the thickness direction of the sheet is 20 or less.

7. 3. The resin sheet according to claim 1, further comprising silica or glass fiber in addition to the anisotropic filler.

8. The resin sheet according to claim 7 , wherein the silica is amorphous.

9. 3. The resin sheet according to claim 1, wherein the thickness is 0.1 to 2 mm.

10. 3. The resin sheet according to claim 1, which is an insulating material for a circuit board.

11. A copper clad laminate comprising a copper foil and the resin sheet according to claim 1 or 2 as essential layers.

12. A circuit board comprising the resin sheet according to claim 1 or 2 and a conductive layer.

13. 13. The circuit board according to claim 12, wherein the conductive layer is a metal.

14. 14. The circuit board according to claim 13, wherein the metal has a surface that comes into contact with the resin sheet and has a surface roughness Rz of 2.0 [mu]m or less.

15. 14. The circuit board of claim 13, wherein the metal is copper.

16. 16. The circuit board according to claim 15, wherein the copper is rolled copper or electrolytic copper.

17. The circuit board according to claim 12, which is a printed circuit board, a multilayer circuit board or a high-frequency board.

18. Step (1) of applying a dispersion containing a perfluororesin and an anisotropic filler onto a substrate to form a coating. Step (2) of drying the film obtained in step (1) while applying a magnetic field to form a dried film. Step (3) of firing the dried coating obtained in step (2). and A method for producing a resin sheet, characterized in that the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the plane direction, the anisotropic filler has an anisotropic shape whose diameter varies depending on the direction, and the anisotropic filler is contained in a proportion of 10 to 80 mass% with respect to the total amount of the perfluoro-based fluororesin and the anisotropic filler.

19. The method for producing a resin sheet according to claim 18, wherein in step (2), the linear expansion coefficient in the film thickness direction is ½ or less compared to a resin sheet obtained by firing a dried film dried without applying a magnetic field.

20. The method for producing a resin sheet according to claim 18 or 19, wherein the strength of the magnetic field is 0.1 to 10 T.

21. 20. The method for producing a resin sheet according to claim 18, wherein the total solid concentration of the perfluoro-based fluororesin and the anisotropic filler in the dispersion is 5 to 70 wt %.

22. 20. The method for producing a resin sheet according to claim 18, wherein a weight ratio of the perfluororesin to the anisotropic filler in the dispersion is 90 / 10 to 30 / 70.

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