Resin sheet, method for producing same, copper-clad laminate, and circuit board

Abstract

Provided is a resin sheet which uses a fluororesin and has excellent thermal expansion characteristics in the thickness direction. A resin sheet which contains a fluororesin and an anisotropic filler, and wherein the anisotropic filler is uniaxially oriented in the film thickness direction and is random in the planar direction.

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 substrate. Background Art

[0002] The resin sheets used in printed wiring boards and the like require high dimensional stability. In other words, they require a low coefficient of thermal expansion, and therefore, are often mixed with fillers. As such fillers, fillers containing anisotropic fillers having anisotropic shapes are sometimes used.

[0003] Patent Document 1 discloses orienting the filler by applying a magnetic field during the production of a resin sheet containing an anisotropic filler. Patent Documents 2 and 3 disclose orienting the anisotropic filler by methods other than applying a magnetic field.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-80617

[0007] Patent Document 2: International Publication No. 2020 / 225678

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 2022-60242

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

[0010] Problems to be solved by the invention

[0011] An object of the present disclosure is to provide a resin sheet using a fluororesin and having excellent low thermal expansion properties in the thickness direction.

[0012] Means for solving problems

[0013] The present disclosure provides a resin sheet comprising a fluororesin and an anisotropic filler, wherein the anisotropic filler is uniaxially oriented in the film thickness direction and is random in the plane direction.

[0014] The fluororesin is preferably a perfluororesin, and particularly preferably at least one selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymers, and tetrafluoroethylene / hexafluoropropylene copolymers.

[0015] The aspect ratio of the anisotropic filler is preferably 1 or more and 200 or less.

[0016] The average particle size of the anisotropic filler is preferably 0.1 to 50 μm or less.

[0017] The anisotropic filler is preferably talc or boron nitride.

[0018] Preferably, the anisotropic filler is talc, and in the X-ray diffraction pattern obtained by irradiating the cross-section of the sheet with X-rays, the talc in the sheet thickness direction is <001> Face relative to <020> The diffraction peak intensity ratio of the surface ( <001> / <020> ) is 300 or less; or, the anisotropic filler is boron nitride, in the cross-sectional direction of the sheet irradiated with X-rays and obtained X-ray diffraction pattern, the boron nitride in the thickness direction of the sheet <002> Face relative to <100> The diffraction peak intensity ratio of the surface ( <002> / <100> ) is less than 20.

[0019] The resin sheet preferably contains silica or glass fiber in addition to the anisotropic filler.

[0020] The silicon dioxide is preferably amorphous.

[0021] The resin sheet preferably has a thickness of 0.1 to 2 mm.

[0022] The resin sheet is preferably an insulating material for a circuit board.

[0023] The present disclosure also relates to a copper-clad laminate having copper foil and the above-mentioned resin sheet as essential layers.

[0024] The present disclosure also relates to a circuit substrate, characterized by comprising the above-mentioned resin sheet and a conductive layer.

[0025] The conductive layer is preferably made of metal.

[0026] The surface roughness Rz of the metal surface in contact with the resin sheet is preferably 2.0 μm or less.

[0027] The above-mentioned metal is preferably copper.

[0028] The copper is preferably rolled copper or electrolytic copper.

[0029] The circuit substrate is preferably a printed circuit board, a laminated circuit board or a high-frequency board.

[0030] The present disclosure relates to a method for manufacturing a resin sheet, characterized by comprising the following steps:

[0031] A step (1) of applying a dispersion containing a fluororesin and an anisotropic filler on a substrate to form a film;

[0032] Step (2) of drying the film obtained in step (1) while applying a magnetic field to obtain a dry film;

[0033] A step (3) of calcining the dried film obtained in the step (2).

[0034] In the above-mentioned method for producing a resin sheet, preferably, in step (2), the linear expansion coefficient in the film thickness direction is 1 / 2 or less compared to a resin sheet obtained by baking a dried film dried without applying a magnetic field.

[0035] In the above-mentioned method for producing a resin sheet, it is preferable that the intensity of the magnetic field is 0.1 to 10T.

[0036] In the method for producing a resin sheet, it is preferred that the total solid concentration of the fluororesin and the anisotropic filler in the dispersion liquid is 5 wt % to 70 wt %.

[0037] The weight ratio of the fluororesin to the anisotropic filler in the dispersion is preferably 90 / 10 to 30 / 70.

[0038] Effects of the Invention

[0039] The resin sheet disclosed herein features anisotropic fillers oriented along the sheet's thickness, resulting in reduced thermal expansion in the thickness direction and highly uniform thermal expansion in the planar direction. This solves the conventional problem of cracking in the copper plating perpendicular to the sheet's plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a schematic diagram illustrating a conventional method for producing a resin sheet containing an anisotropic filler.

[0041] Figure 2 This is a schematic diagram illustrating a method for producing a resin sheet containing an anisotropic filler in the present disclosure.

[0042] Figure 3 Schematic diagram showing an example of a method of applying a magnetic field in the present disclosure.

[0043] Figure 4 It is a schematic diagram showing the measurement method of X-ray diffraction.

[0044] Figure 5 This is a schematic diagram showing a state when the resin sheet of the present disclosure is subjected to X-ray diffraction measurement. DETAILED DESCRIPTION

[0045] Hereinafter, the present disclosure will be described in detail.

[0046] Resin components generally expand easily when heated, which poses a problem in terms of dimensional stability of the resulting resin molded product. To improve this problem, inorganic fillers with low thermal expansion are usually blended.

[0047] As such inorganic fillers, inorganic fillers having a highly anisotropic shape (e.g., plate-like) are widely used. As is known to all, when such an anisotropic inorganic filler is formed into a sheet, it is oriented in a manner that becomes the plane direction of the sheet ( Figure 1 ). Figure 1 In the figures, (1) shows the state immediately after the dispersion is applied to the substrate, (2) shows the state after drying, and (3) shows the state after firing.

[0048] This orientation of the inorganic filler makes it difficult to achieve the effect of suppressing thermal expansion of the resin sheet in the thickness direction by mixing the inorganic filler. To address this problem, Patent Documents 2 and 3 use methods completely different from those of the present application to produce resin sheets in which the inorganic filler is oriented in the thickness direction. However, these methods also produce orientation in the planar direction, reducing randomness. This results in anisotropy of linear expansion within the planar direction, causing cracks in the copper foil to occur only in specific directions due to thermal expansion.

[0049] In view of this problem, the present inventors solved this problem by aligning at least a portion of the anisotropic filler in a direction perpendicular to the plane of the resin sheet, thereby obtaining a resin sheet with low thermal expansion in the thickness direction. This can suppress cracking of the copper foil in the thickness direction when used as a circuit board.

[0050] As an example of a method for producing such a resin sheet, there can be cited a method for producing a resin sheet having the following steps: step (1) of applying a dispersion containing a fluororesin and an anisotropic filler on a substrate to form a film; step (2) of drying the film obtained in step (1) while applying a magnetic field to the film to form a dry film; and step (3) of calcining the dry film obtained in step (2). A schematic diagram of such a production method is shown in FIG. Figure 2 . Figure 2 (1) to (3) in the figure represent the above-mentioned steps (1) to (3), respectively.

[0051] The resin sheet disclosed herein is characterized in that the anisotropic filler is uniaxially oriented in the film thickness direction and randomly oriented in the planar direction. This state is confirmed by measuring the intensity ratio of diffraction peaks in an X-ray diffraction pattern obtained by irradiating the sheet with X-rays in the thickness direction.

[0052] The resin sheet disclosed herein contains a fluororesin and an anisotropic filler, which will be described in detail below.

[0053] (Anisotropic filler)

[0054] Anisotropic fillers used in this disclosure are particles having anisotropic shapes (diameters that vary depending on the direction), excluding glass fibers, crushed silica, and ceramics. For example, they are composed of inorganic compounds such as carbon, inorganic oxides, inorganic nitrides, and inorganic carbides, and resins. Specific examples include fibrous, needle-like, flaky, and whisker-like particles composed of metal oxides, metal nitrides, metal carbides, and metal hydroxides such as boron nitride, aluminum nitride, aluminum oxide, zinc oxide, silicon carbide, and aluminum hydroxide; metals and alloys; carbon materials such as graphite, graphite, and diamond; and highly thermally conductive resins.

[0055] Among these, talc or boron nitride are preferred from the perspective of electrical properties. Examples of their shapes include flat, flaky, plate-like, linear, flat, granular, fibrous, and whisker-like. Flakes, plates, or lines are preferred, flaky or plate-like is more preferred, and plate-like is particularly preferred. In this embodiment, only one anisotropic filler may be used, or two or more anisotropic fillers may be included within a range that does not impair the effects of the present disclosure. For example, talc and other anisotropic fillers may be used in combination.

[0056] The anisotropic filler is preferably talc or boron nitride from the viewpoint of low hardness and excellent magnetic field orientation.

[0057] The aspect ratio of the anisotropic filler is preferably from 1 to 2000. Using an anisotropic filler of this shape is preferred in terms of reducing thermal expansion (linear expansion) in the thickness direction. The aspect ratio is the value obtained by dividing the average particle size of the anisotropic filler by the average minor diameter (the average value of the length in the short side direction) as measured using an electron microscope. 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.

[0058] The average particle size of the anisotropic filler is preferably at least 0.1 μm and no more than 50 μm. Using such an average particle size is preferred because it is more effective in achieving low linear expansion. This average particle size is the D50 value measured by laser analysis / scattering. Furthermore, the lower limit of the average particle size is more preferably at least 1 μm, and even more preferably at least 3 μm. The upper limit of the average particle size is more preferably 30 μm, and even more preferably 20 μm.

[0059] (Fluororesin)

[0060] The resin sheet of the present disclosure contains a fluororesin. Since the fluororesin has low dielectric properties, it can be suitably used for the purpose of the present disclosure.

[0061] Fluororesin that can be used in the present disclosure is not particularly limited, preferably perfluorinated fluororesin.For example, 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), tetrafluoroethylene (LMW-PTFE) with a molecular weight of less than 300,000 etc. can be enumerated. These fluororesins can use one, or two or more can be mixed. From the viewpoint of low dielectric constant, above-mentioned fluororesin is preferably perfluorinated fluororesin, particularly preferably polytetrafluoroethylene (PTFE), tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer [FEP], TFE / alkyl vinyl ether copolymer [PFA]. Among these, more preferably polytetrafluoroethylene (PTFE), TFE / alkyl vinyl ether copolymer [PFA].

[0062] (polytetrafluoroethylene)

[0063] 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.

[0064] Modified PTFE comprises TFE units based on TFE and modified monomer units based on the modified monomer. The modified monomer units are part of the molecular structure of the modified PTFE and are derived from the modified monomer. The modified PTFE preferably comprises 0.001 to 0.500 weight percent of the total monomer units, and more preferably 0.01 to 0.30 weight percent of the total monomer units. The total monomer units are derived from all monomers in the molecular structure of the modified PTFE.

[0065] The modifying monomer is not particularly limited as long as it can copolymerize with TFE. 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. The modifying monomers used may be one or more.

[0066] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorounsaturated compounds represented by the following general formula (1).

[0067] CF2=CF-ORf…(1)

[0068] In the formula, Rf represents a perfluoro organic group.

[0069] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to carbon atoms are replaced by fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0070] Examples of perfluorovinyl ethers include perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms. Examples of perfluoroalkyl groups in PAVE include perfluoromethyl, perfluoroethyl, perfluoropropyl, perfluorobutyl, perfluoropentyl, and perfluorohexyl. Preferred PAVEs include perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0071] The perfluoroalkylethylene (PFAE) is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE) and perfluorohexylethylene (PFHE).

[0072] 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.

[0073] (Fluororesin that can be melt-molded)

[0074] The fluororesin disclosed herein may be a melt-moldable fluororesin. The melt-moldable fluororesin will be described in detail below.

[0075] The fluororesin may be a fluororesin that can be melt-molded, and examples thereof include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), a copolymer having chlorotrifluoroethylene (CTFE) units (CTFE copolymer), 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, etc.

[0076] Among these melt-moldable fluororesins, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP) are preferred.

[0077] As the above-mentioned PFA, there is no particular limitation, but a copolymer in which the molar ratio of TFE units to PAVE units (TFE units / PAVE units) is 70 / 30 or more and less than 99.5 / 0.5 is preferred. A more preferred molar ratio is 70 / 30 or more and 98.9 / 1.1 or less, and a further preferred molar ratio is 80 / 20 or more and 98.5 / 1.5 or less. If the TFE unit is too little, the mechanical properties tend to decrease; if it is too much, the melting point is too high and the moldability tends to decrease. The above-mentioned PFA may be a copolymer consisting only of TFE and PAVE, and is also preferably a copolymer in which the monomer units from monomers copolymerizable with TFE and PAVE are 0.1 mol% to 10 mol%, and the total of TFE units and PAVE units is 90 mol% to 99.9 mol%. As monomers copolymerizable with TFE and PAVE, HFP, CZ3Z4=CZ5(CF2) can be cited. n A vinyl monomer represented by Z6 (wherein Z3, Z4, and Z5 are the same or different and represent a hydrogen atom or a fluorine atom, Z6 represents a hydrogen atom, a fluorine atom, or a chlorine atom, and n represents an integer from 2 to 10), and an alkyl perfluorovinyl ether derivative represented by CF2=CF-OCH2-Rf7 (wherein Rf7 represents a perfluoroalkyl group having 1 to 5 carbon atoms). Other copolymerizable monomers include, for example, cyclic hydrocarbon monomers having an acid anhydride group. 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.

[0078] The melt flow rate (MFR) of the PFA is preferably 0.1 g / 10 min to 100 g / 10 min, more preferably 0.5 g / 10 min to 90 g / 10 min, and even more preferably 1.0 g / 10 min to 85 g / 10 min. It should be noted that 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.

[0079] (Mixing ratio)

[0080] The resin sheet disclosed herein preferably contains an anisotropic filler in a ratio of 10% to 80% by mass relative to the total amount of the fluororesin and the anisotropic filler. This range is preferred for achieving a balance between 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.

[0081] (Other fillers)

[0082] The resin sheet of the present disclosure may further contain silica or glass fiber. Silica or glass fiber may be mixed with both.

[0083] When the "other fillers" are mixed, they are preferably included in a ratio of 1 to 40% by mass relative to the total amount of the resin sheet. This range is preferred because it allows for a balance between the effects of reducing linear expansion in the film thickness direction and in the planar 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.

[0084] (Other ingredients)

[0085] The resin sheet of the present disclosure may contain other components as needed. Examples of such other components include additives such as UV absorbers, fillers, crosslinking agents, antistatic agents, heat stabilizers, foaming agents, foaming nucleating agents, antioxidants, surfactants, photopolymerization initiators, anti-wear agents, surface modifiers, and liquid crystal polymers.

[0086] When other components are added, the content of the fluororesin, anisotropic filler, and other fillers is preferably 95% by mass or more relative to the total amount of the resin sheet. Excessive addition of other components may not achieve the desired physical properties, which is not preferred.

[0087] (resin sheet)

[0088] The resin sheet disclosed herein preferably contains the above-mentioned components and has a thickness of 0.1 to 2 mm. The thickness herein is a value measured using a film thickness meter. Setting the thickness within this range is preferred in terms of achieving a balance between sheet strength and flexibility.

[0089] In the resin sheet of the present disclosure, it is preferred that the anisotropic filler is talc, and in an X-ray diffraction pattern obtained by irradiating the cross-sectional direction of the sheet with X-rays, the talc in the sheet thickness direction is <001> Face relative to <020> The diffraction peak intensity ratio of the surface ( <001> / <020> ) is 300 or less; or, the anisotropic filler is boron nitride, in the cross-sectional direction of the sheet irradiated with X-rays and obtained X-ray diffraction pattern, the boron nitride in the thickness direction of the sheet <002> The diffraction peak of the surface is relative to <100> Surface strength ratio ( <002> / <100> ) is 20 or less. It should be noted that the X-ray diffraction measurement method here can be carried out according to the method shown in the Examples.

[0090] The X-ray diffraction patterns in this disclosure are Figure 4 The measurement is performed under the state shown in the schematic diagram. Figure 4 The cross section 5 of the sample in the figure is the sheet disclosed herein. The resin sheet disclosed herein becomes Figure 5Since X-ray diffraction is performed in such a state, peaks are present at 90° and 270° in the X-ray diffraction. On the other hand, the conventional resin sheet becomes Figure 5 Therefore, there are peaks at 0° and 180°.

[0091] From this perspective, when the X-ray diffraction peak intensity ratio 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 perspective, the parameters for the diffraction peak intensity ratio are set as described above to obtain a resin sheet having these parameters within the specific range.

[0092] The thickness of the talc in the thickness direction of the sheet <001> Face relative to <020> The intensity ratio of the diffraction peak of the surface ( <001> / <020> ) is more preferably 300 or less, and further preferably 100 or less. <002> Face relative to <100> The intensity ratio of the diffraction peak of the surface ( <002> / <100> ) is more preferably 20 or less, and further preferably 10 or less.

[0093] (Method for producing resin sheet)

[0094] The method for producing a resin sheet disclosed herein includes the following steps:

[0095] A step (1) of applying a dispersion containing a fluororesin and an anisotropic filler on a substrate to form a film;

[0096] Step (2) of drying the film obtained in step (1) while applying a magnetic field to obtain a dry film;

[0097] A step (3) of calcining the dried film obtained in the step (2).

[0098] That is, the method is characterized in that after the dispersion is applied to the substrate, in the step (2) of forming a dry film, the dispersion is dried while applying a magnetic field.

[0099] Thus, at least a portion of the anisotropic filler is oriented by the action of the magnetic field and arranged in a direction close to the vertical direction with respect to the thickness direction of the film.

[0100] Talc, boron nitride, and other materials commonly used as anisotropic fillers are diamagnetic and generally considered to have no magnetism. However, they actually possess magnetism, albeit weakly, and are oriented by applying an external magnetic field.

[0101] Melt molding is also a widely known method for molding fluororesins. However, melt molding requires high temperatures, which cannot be achieved with certain magnet types. Furthermore, due to the high viscosity of the melt, it is difficult to orient anisotropic fillers using melt molding in the presence of a magnetic field.

[0102] On the other hand, when forming a film by coating a dispersion, such problems do not arise. Furthermore, in the initial stages of the drying process, the anisotropic filler can move relatively freely within the coating, and thus can be easily moved by the action of a magnetic field. Therefore, this method is suitable for obtaining the resin sheet disclosed herein. Thus, the objectives of this disclosure can be achieved using a simple method.

[0103] Hereinafter, the method for producing a resin sheet of the present disclosure will be described in detail according to each step.

[0104] (Process (1))

[0105] Step (1) is a step of applying a dispersion containing a fluororesin and an anisotropic filler onto a substrate to form a film.

[0106] In the above step (1), a dispersion containing a fluororesin and an anisotropic filler is used. The fluororesin and anisotropic filler used here are as described above.

[0107] The dispersion disperses the fluororesin and anisotropic filler in a liquid medium. While the liquid medium is not particularly limited, it preferably contains water or a water-soluble solvent suitable for hydration. The water-soluble solvent wets the fluororesin, while the high-boiling-point solvent acts as a drying retardant to prevent cracks by connecting the resins during drying after coating. Even high-boiling-point solvents evaporate at the fluororesin's firing temperature, thus not adversely affecting the coating.

[0108] The fluororesin dispersed in water may be an emulsion resin obtained by emulsion polymerization or a resin obtained by dispersing fluororesin powder in a liquid medium, but is preferably an emulsion resin.

[0109] The dispersion of the anisotropic filler in the liquid medium can be carried out by shaking the mixed liquid.

[0110] The dispersion preferably contains the liquid medium in a ratio of 20% by mass to 80% by mass.

[0111] The dispersion may contain an emulsifier and the like in addition to the components constituting the sheet and the liquid medium.

[0112] The dispersion is applied to a substrate to form a film. The substrate is not particularly limited and may include metals such as copper foil, iron, stainless steel, copper, aluminum, and brass; glass products such as glass plates and woven and nonwoven glass fiber fabrics; molded articles and coverings of general-purpose and heat-resistant resins such as polypropylene, polyoxymethylene, polyimide, modified polyimide, polyamide-imide, polysulfone, polyethersulfone, polyetheretherketone, and liquid crystal polymers; molded articles and coverings of general-purpose rubbers such as SBR, butyl rubber, NBR, and EPDM, and heat-resistant rubbers such as silicone rubber and fluororubber; woven and nonwoven natural and synthetic fiber fabrics; or laminated substrates formed from combinations thereof.

[0113] The substrate may be a substrate that has been surface-processed. Examples of the surface processing include surface processing using sandblasting to a desired roughness, surface processing roughened by particle attachment, and surface processing that has undergone metal anti-oxidation treatment. The film may be formed by spraying, roller coating, coating with a scraper, dip coating, impregnation coating, rotary flow coating, curtain flow coating, coating with a rod coater, gravure coating, micro-gravure coating, and the like.

[0114] (Process (2))

[0115] Step (2) is a step of drying the film obtained by step (1) while applying a magnetic field to the film to obtain a dry film. A schematic diagram showing an example of a method for applying a magnetic field when performing such step (2) is shown in FIG. Figure 3 .

[0116] Figure 3 The device shown has a conductive coil provided on the outer periphery of the cylindrical shape and a sample setting portion provided in the center thereof. The article having a film formed on the substrate obtained in the above step (1) is placed therein and dried while applying a magnetic field.

[0117] When the dispersion contains talc, the dispersion is arranged so that the direction of the magnetic lines of force in the magnetic field atmosphere corresponds to the desired orientation direction of the talc. Thus, by arranging the dispersion so that the direction of the magnetic lines of force corresponds to the desired orientation direction, the talc can be oriented in any direction.

[0118] The applied magnetic field is preferably 0.1 to 10 T. This magnetic field is a value obtained by measuring the magnetic field density using a gaussmeter. Setting it within this range is preferred in terms of properly orienting the anisotropic filler. The lower limit of the applied magnetic field is more preferably 0.3 T, and even more preferably 0.5 T. The upper limit of the applied magnetic field is not particularly limited.

[0119] The magnet for applying such a magnetic field is not particularly limited, but a permanent magnet or a superconducting magnet is particularly preferable.

[0120] The drying in step (2) is preferably carried out under heating conditions, and the drying temperature is preferably in the range of 1°C to 80°C. If the drying temperature is too high, the filler dries before orientation, which is not preferred. On the other hand, if the drying temperature is too low, the volatilization temperature of the liquid medium becomes too low, which reduces the efficiency, which is not preferred. The drying method is not particularly limited, and may be a method that can be temperature-controlled using a sample stand.

[0121] (Process (3))

[0122] Step (3) is a step of heating and calcining the dried film obtained in step (2). This step forms a resin sheet. Step (3) can be performed under the general conditions used to obtain a resin sheet using this method. Specifically, it can be performed at 300 to 400°C.

[0123] The above steps (1) to (3) can be performed continuously on the production line by sequentially setting up a mechanism for performing the above steps (1) to (3), or can be performed in batches for each step.

[0124] The method for producing a resin sheet disclosed herein preferably has a linear expansion in the film thickness direction of 1 / 2 or less compared to a resin sheet obtained by calcining a dry film dried without applying a magnetic field in step (2).

[0125] (Circuit Board)

[0126] The sheet-like resin composition of the present disclosure can be laminated with a conductive layer and can be suitably used for circuit board applications.

[0127] The present disclosure also relates to a circuit substrate having a conductive layer of metal or the like on one or both sides of the aforementioned resin sheet. 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 more preferably copper foil.

[0128] The circuit board may be produced by using a metal foil as the conductive layer to form a laminate with a resin sheet, or by bonding the metal foil and the resin sheet to form a laminate.

[0129] 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 a copper foil having an Rz of 1.6 μm or less and high smoothness.

[0130] Furthermore, the copper foil can be formed with a surface Rz of at least 1.6 μm or less on the surface bonded to the resin sheet. The Rz value of the other surface is not particularly limited. The Rz value is the sum of the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv). The Rz value is the ten-point average roughness specified in JIS-B0601. In this specification, the Rz value is measured using a surface roughness meter (trade name: SURFCOM 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0131] The thickness of the copper foil is not particularly limited, but is preferably in the range of 1 μm to 100 μm, more preferably in the range of 5 μm to 50 μm, and even more preferably in the range of 9 μm to 35 μm.

[0132] The copper foil is not particularly limited, and specific examples thereof include rolled copper foil and electrolytic copper foil.

[0133] 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 foil 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 Co., Ltd.).

[0134] The copper foil may be surface-treated in order to improve the bonding strength with the resin sheet of the present disclosure.

[0135] The circuit board of the present disclosure may further include layers other than the copper foil and the resin sheet.

[0136] In the circuit substrate disclosed herein, the copper layer may be formed on one side or on both sides. As a method for forming the copper layer, a method of laminating (bonding) copper foil on the surface of a resin sheet, a vapor deposition method, a plating method, etc. may be cited. As a method for laminating copper foil, a method using hot pressing may be cited. The hot pressing temperature may be -150°C, the melting point of the resin sheet, to +40°C, the melting point of the resin sheet. The hot pressing time is, for example, 1 minute to 30 minutes. The method can be manufactured by a method in which the hot pressing pressure is 0.1 to 10 MPa.

[0137] The application of the circuit substrate disclosed herein is not particularly limited, but it is preferably used as a printed circuit board, a laminated circuit board, or a high-frequency board.

[0138] The circuit substrate is not particularly limited and can be produced by a general method.

[0139] The laminate for circuit board is also characterized by comprising a copper foil layer, the above-mentioned resin sheet and a base material layer. The base material layer is not particularly limited, but preferably comprises a cloth layer composed of glass fiber and a resin sheet layer.

[0140] Example

[0141] The present disclosure will be described in detail below based on Examples. In the following Examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0142] The materials used in the examples are as follows.

[0143] (Aqueous dispersion of fluororesin)

[0144] PFA aqueous dispersion 1: average particle size: 336 nm, PFA content: 64.5%

[0145] PTFE aqueous dispersion 1: average particle size: 250nm, PTFE content: 60.0%

[0146] (Fluororesin powder)

[0147] PFA powder 1: average particle size: 504 nm, MFR: 27.0

[0148] (additive)

[0149] Surfactant 1: Polyether surface modifier

[0150] (filler)

[0151] Talc 1: average particle size: 5 μm, aspect ratio: 40-45

[0152] Talc 2: average particle size: 7 μm, aspect ratio: 30, surface treatment: treated with aminosilane (silane coupling agent containing amino group)

[0153] Talc 3: average particle size: 5μm, aspect ratio: 40-45, surface treatment: treated with aminosilane (silane coupling agent containing amino group)

[0154] Boron nitride 1: average particle size: 10 μm, shape: scaly

[0155] Silica 1: Average particle size: 2.1 μm, shape: spherical

[0156] (Example 1)

[0157] <Preparation of Mixed Solution>

[0158] 1:5.0 g of a PFA aqueous dispersion, 1:3.3 g of talc, 4.3 g of water, and 1:0.5 g of a surfactant were mixed, and stirred at room temperature for 10 hours using a mixing rotor.

[0159] <Magnetic Field Application and Pre-Drying>

[0160] Put 4.4 g of the obtained mixture into a glass dish with a diameter (inner diameter) of 48 mm. Using a magnetic field application device (manufactured by Japan Super Conductor Technology Co., Ltd., model: JMTD10T 100), place it on a hot plate heated to 60 °C for 70 minutes while applying a magnetic field of 10 T, and perform pre-drying until the fluidity disappears.

[0161] <Drying>

[0162] In order to remove the volatile components in the obtained solid component, further dry it at 130 °C for 30 minutes.

[0163] <Firing>

[0164] Fire the dried film at 330 °C for 30 minutes to obtain a sample with a thickness of 0.4 mm.

[0165] <Linear expansion rate measurement>

[0166] Use a sample obtained by cutting the fired resin sheet into a square with a side length of 5 mm, and measure the linear expansion rate with a thermomechanical analysis device (manufactured by Hitachi High-Technologies Corporation, model: TMA-7100). Measure the linear expansion rate from the displacement of the sample at 20 °C to 200 °C at a heating rate of 2 °C / min while applying a load of 49 mN.

[0167] <X-ray diffraction measurement (wide-angle X-ray scattering method)>

[0168] Observe various samples using the WAXS method. The WAXS method is carried out as follows: Using the SPring-8 of the Japan Synchrotron Radiation Research Institute (JASRI), beam line BL40B2, the wavelength (λ) of the X-ray is λ = 0.0709 nm, the camera length (R) is R = 323 mm, and the detector uses PLATUS 3M (manufactured by Dectris), and perform it at room temperature of 25 °C.

[0169] Cut out a 0.2-mm-thick resin sheet obtained by firing, set it on the sample stage with the thickness direction as the horizontal direction, and irradiate the cross-section (edge) with a light beam ( Figure 4 ). The exposure time of the X-ray is 60 seconds.

[0170] (Examples 2 to 8, Example 10)

[0171] Prepare a dispersion liquid with the composition shown in Table 1, apply a magnetic field intensity, and otherwise obtain a sample in the same manner as in Example 1, and measure the linear expansion rate. Examples 2, 3, 8, and 10 were subjected to X-ray measurement in the same manner as in Example 1.

[0172] (Example 9)

[0173] In the <Magnetic Field Application and Pre-Drying> step, a copper foil (surface roughness Rz 1.4 μm) with a thickness of 18 μm and a diameter of 48 mm was placed in a glass dish before the mixed solution was added. Samples were obtained and their linear expansion coefficients were measured in the same manner as in Example 1. These results indicate that the anisotropic filler was oriented in the laminated body with the copper foil as well by the application of a magnetic field.

[0174] (Comparative Examples 1 to 8, Comparative Example 11)

[0175] Dispersions were prepared using the compositions shown in Table 2. Samples were obtained and their linear expansion coefficients were measured in the same manner as in Example 1, except that no magnetic field was applied in the <Magnetic Field Application and Pre-Drying> step. X-ray measurements were performed in the same manner as in Example 1 for Comparative Examples 2 to 4 and 11.

[0176] (Comparative Example 9)

[0177] A dispersion having the composition shown in Table 2 was prepared, and a sample was obtained in the same manner as in Example 1 except that no magnetic field was applied in the <Magnetic Field Application and Preliminary Drying> step and a magnetic field was applied after the <Drying> step, and the linear expansion coefficient was measured.

[0178] (Comparative Example 10)

[0179] A Labo Plastomill mixer was used to melt-knead PFA powder (1:71.4g) and talc (1:31.6g) (600 seconds, 350°C) and then allowed to cool to obtain a solid composition. The resulting solid composition was crushed and pelletized. The pellets were press-molded at 350°C to obtain a 0.5mm thick resin sheet. The resin sheet was cut into 5mm squares, and the linear expansion coefficient was measured.

[0180]

[0181]

[0182] Regarding the relationship between the above-mentioned Examples and Comparative Examples, a resin sheet obtained by calcining a dried film dried without applying a magnetic field, relative to each Example, served as a comparative example, resulting in a comparison as shown in Table 3 below. Based on this comparison, the ratio of the linear expansion coefficients in the film thickness direction (linear expansion coefficient in the film thickness direction of the resin sheet with a magnetic field applied / linear expansion coefficient of the resin sheet without a magnetic field applied) was calculated, and the values ​​are shown in Table 3.

[0183]

[0184] As can be seen from the results of the respective Examples in Tables 1 to 3 above, the resin sheet of the present disclosure is excellent in heat shrinkage properties in the thickness direction.

[0185] Industrial applicability

[0186] The resin sheet of the present disclosure can be suitably used for circuit substrate applications.

[0187] Explanation of symbols

[0188] 1 Superconducting coil

[0189] 2. Sample table

[0190] 3. Samples

[0191] 4 Magnetic Field

[0192] 5-piece cross section

[0193] 6 sheets in thickness direction

[0194] 7 Beam irradiation position

[0195] 8 holes

[0196] 9 Sample racks

Claims

1. A resin sheet, characterized in that The resin sheet contains a fluororesin and an anisotropic filler. The anisotropic filler is uniaxially oriented in the film thickness direction and is random in the plane direction.

2. The resin sheet according to claim 1, wherein The fluororesin is a perfluorinated fluororesin.

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

4. The resin sheet according to any one of claims 1 to 3, wherein The aspect ratio of the anisotropic filler is 1 or more and 200 or less.

5. The resin sheet according to any one of claims 1 to 4, wherein The average particle size of the anisotropic filler is 0.1 μm to 50 μm or less.

6. The resin sheet according to any one of claims 1 to 5, wherein The anisotropic filler is talc or boron nitride.

7. The resin sheet according to claim 6, wherein The anisotropic filler is talc. In the X-ray diffraction pattern obtained by irradiating the cross section of the sheet with X-rays, the talc in the sheet thickness direction is <001> Face relative to <020> The diffraction peak intensity ratio of the surface, that is, <001> / <020> 300 or less; or, the anisotropic filler is boron nitride, the boron nitride in the thickness direction of the sheet <002> Face relative to <100> The diffraction peak intensity ratio of the surface, that is, <002> / <100> Below 20.

8. The resin sheet according to any one of claims 1 to 7, wherein In addition to the anisotropic filler, silica or glass fibers are also contained.

9. The resin sheet according to claim 8, wherein The silicon dioxide is amorphous. 10 . The resin sheet according to claim 1 , wherein the thickness is 0.1 mm to 2 mm. 11 . The resin sheet according to claim 1 , which is an insulating material for a circuit board. 12 . A copper-clad laminate comprising a copper foil and the resin sheet according to claim 1 as essential layers.

13. A circuit substrate, characterized in that: The invention comprises the resin sheet according to any one of claims 1 to 11 and a conductive layer.

14. The circuit substrate according to claim 13, wherein: The conductive layer is metal.

15. The circuit substrate according to claim 14, wherein The surface roughness Rz of the metal surface in contact with the resin sheet is 2.0 μm or less.

16. The circuit substrate according to claim 14 or 15, wherein: The metal is copper.

17. The circuit substrate according to claim 16, wherein: The copper is rolled copper or electrolytic copper. 18 . The circuit substrate according to claim 13 , which is a printed circuit board, a laminated circuit board, or a high-frequency board.

19. A method for producing a resin sheet, characterized in that: The process includes the following steps: A step (1) of applying a dispersion containing a fluororesin and an anisotropic filler on a substrate to form a film; Step (2) of drying the film obtained in step (1) while applying a magnetic field to obtain a dry film; A step (3) of calcining the dried film obtained in the step (2).

20. The method for producing a resin sheet according to claim 19, wherein In step (2), the linear expansion coefficient in the film thickness direction is 1 / 2 or less compared to a resin sheet obtained by baking a dry film dried without applying a magnetic field.

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

22. The method for producing a resin sheet according to any one of claims 19 to 21, wherein The total solid concentration of the fluororesin and the anisotropic filler in the dispersion is 5 wt % to 70 wt %.

23. The method for producing a resin sheet according to any one of claims 19 to 22, wherein The weight ratio of the fluororesin to the anisotropic filler in the dispersion is 90 / 10 to 30 / 70.

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