Plate-like composite material and method for producing same

Abstract

The following is provided as a plate-like composite material which enables continuous extrusion and rolling, and has excellent appearance and excellent yield despite its long size.　A plate-like composite material containing fibrils comprising a fluorine-based resin and a filler, wherein the ratio (Ct / Cm) of the cohesive force (Cm) in an MD direction to the cohesive force (Ct) in a TD direction orthogonal to the MD direction is 0.7-1.5.

Description

Plate-shaped composite material and its manufacturing method

[0001] The present invention relates to a plate-shaped composite material suitable for use as a substrate for a microstrip patch antenna used in millimeter-wave radar or the like.

[0002] In recent years, the automotive industry has been actively researching and developing ADAS (Advanced Driver Assistance Systems) and autonomous driving, and millimeter-wave radar is becoming increasingly important as a sensing technology that supports these technologies. From the perspectives of compact size, high performance, and low cost, the use of "microstrip patch antennas," which are planar antennas with antenna elements (patches) printed on a resin substrate, is a promising option for automotive millimeter-wave radar, and studies are underway on antenna pattern designs and substrate materials to improve performance.

[0003] One of the most promising substrate materials used for these antennas is polytetrafluoroethylene (PTFE), which has a small dielectric dissipation factor. In order to further improve the mechanical, thermal, and electrical properties, it has been proposed to incorporate granular fillers such as boron nitride, silicon dioxide (silica), and titanium oxide (titania), as well as fillers such as glass fiber and carbon fiber (see Patent Documents 1 and 2).

[0004] However, in low-dielectric substrates containing fluororesin and filler, a high filler loading is necessary to maximize the filler's properties. However, high loading reduces the fluororesin content, raising concerns that the strength (particularly cohesive strength) of the composite material may decrease.

[0005] Furthermore, in continuous production methods such as extrusion and rolling, shear is applied only in the flow direction (MD) of the sheet, which results in anisotropy of the cohesive force with respect to the width direction (TD) of the sheet, and there is a concern that voids or breakage may occur when the thickness is reduced by rolling.

[0006] Currently, in order to stabilize the characteristics of low-dielectric substrate products, a batch production technology has been disclosed in which the substrate is cut to a predetermined length during rolling, rotated 90° and rolled (TD rolling) (Patent Document 3).

[0007] JP 03-212987 JP 06-119810 JP 2017-171898

[0008] However, batch-type rolling tends to reduce yields due to uneven tension within the rolling surface and variations in the rolling performance between batches. Furthermore, continuous production is still required from the viewpoint of productivity.

[0009] Therefore, the present invention provides a plate-shaped composite material that can be extruded or rolled continuously and that has an excellent appearance and a high yield despite being long.

[0010] In view of these circumstances, the present inventors have conducted extensive research and have found that, in a low dielectric substrate containing a fluorine-based resin and a filler, continuous extrusion and rolling are possible, and an excellent appearance and high yield can be achieved, by keeping the ratio of the cohesive force in the MD direction to the cohesive force in the TD direction perpendicular to the MD direction within a specific range.

[0011] That is, the present invention has the following aspects. [1] A plate-shaped composite material containing fibrils made of a fluororesin and a filler, wherein the ratio (Ct / Cm) of the cohesive strength in the MD direction (Cm) to the cohesive strength in the TD direction perpendicular to the MD direction (Ct) is 0.7 to 1.5. [2] The plate-shaped composite material according to [1], which has a length of 5 m or more. [3] The plate-shaped composite material according to [1] or [2], which is rolled using a corrugated roll in the rolling step. [4] The plate-shaped composite material according to any of [1] to [3], wherein the content of the fluororesin is 10 to 70 vol%. [5] The plate-shaped composite material according to any of [1] to [4], wherein the fluororesin contains polytetrafluoroethylene. [6] The plate-shaped composite material according to any of [1] to [5], wherein the porosity is 10 to 90 vol%. [7] A method for producing the plate-shaped composite material according to any one of [1] to [6], wherein the plate-shaped composite material is continuously produced. [8] A method for producing the plate-shaped composite material according to [7], comprising a molding step of a composite material composition, a rough rolling step, and a high-precision rolling step, wherein the roll surface of the rolling roll used in the rough rolling step has a wavy structure in the TD direction.

[0012] According to the present invention, continuous extrusion and rolling can be performed, and a long plate-shaped composite material can be obtained that has an excellent appearance and a high yield.

[0013] Fig. 1 is an SEM image (photograph substitute for drawing) of a porous inorganic fine particle aggregate formed by agglomeration of inorganic fine particles having an average primary particle size of 5 to 200 nm. Fig. 2 is a perspective view showing the appearance of a corrugated rolling roll used in one embodiment of the present invention. Fig. 3(A) is a cross-sectional view of one corrugated rolling roll of Fig. 2. Fig. 3(B) is an enlarged view of one waveform cycle of the waveforms in the cross-sectional view of Fig. 3(A). Fig. 4 is a perspective view showing the appearance of a flat rolling roll used in one embodiment of the present invention.

[0014] The present invention will be described below based on examples of embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below.

[0015] In this specification, "p and / or q (p and q are any configuration)" means at least one of p and q, and can mean three things: p only, q only, or p and q. In this specification, when "P or more" (P is any number) or "Q or less" (Q is any number) is expressed, it also means "preferably greater than P" or "preferably less than Q." In this specification, "P and / or Q (P and Q are any configuration)" means at least one of P and Q, and can mean three things: P only, Q only, or P and Q. In this specification, for numerical ranges described in stages, the upper or lower limit of a numerical range in one stage can be arbitrarily combined with the upper or lower limit of a numerical range in another stage. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range can also be replaced with the values ​​shown in the examples.

[0016] <Plate-Like Composite Material> A plate-like composite material (hereinafter sometimes simply referred to as "composite material") according to one embodiment of the present invention is a plate-like composite material containing fibrils made of a fluororesin and a filler, and has a ratio (Ct / Cm) of the cohesive strength in the MD direction (Cm) to the cohesive strength in the TD direction (Ct) perpendicular to the MD direction of 0.7 to 1.5.

[0017] In order to improve the strength (particularly cohesive strength) of a composite material containing a fluorine-based resin and a filler, the present inventors have conducted extensive research into a plate-shaped composite material that can be used as a substrate for a microstrip patch antenna or the like. As a result, they have found that it is necessary to apply a shear force to the composite material composition to promote fibrillation of the fluorine-based resin. However, with ordinary extrusion or rolling methods, shear is applied only in the machine direction (MD) of the sheet, resulting in anisotropy of the cohesive strength with respect to the width direction (TD) of the sheet. However, they have found that the production method of this embodiment suppresses the anisotropy of the cohesive strength and makes it possible to obtain a plate-shaped composite material that is long but has excellent appearance and high yield.

[0018] The "fluororesin" and "filler" constituting the composite material composition will be described in detail below.

[0019] <Fluorine-based resin> The type of fluorine-based resin is not particularly limited, and can be suitably adopted as the fluorine-based resin used for substrate etc. As fluorine-based resin, generally, polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polychlorotrifluoroethylene (PCTEF), tetrafluoroethylene-ethylene copolymer (ETFE), chlorotrifluoroethylene-ethylene copolymer (ECTFE), polyvinylidene fluoride (PVDF) can be listed, and PTFE is particularly preferred.These can be used alone or in combination of two or more kinds.

[0020] The fluororesin is preferably "fibrillated (fibrous microstructured)." It is more preferable that the fibrillated fibers are oriented not only in one direction but in multiple directions, and it is particularly preferable that the fibrils are linked to the inorganic fine particle aggregates described below to form a "three-dimensional micromesh structure." When the fluororesin is fibrillated, particularly when a three-dimensional micromesh structure is formed, the composite material can ensure excellent mechanical strength and dimensional stability. The fibrillation of the fluororesin can be confirmed by surface observation using an SEM or the like. The fibrillation of the fluororesin can be promoted, for example, by applying a shear force. More specifically, it can be carried out by multi-stage rolling, which will be described later. Furthermore, the three-dimensional micromesh structure can be formed by anti-directional multi-stage rolling, which will be described later.

[0021] <Filler> The composite material preferably contains inorganic particle aggregates and nonporous inorganic particles as fillers. Specifically, inorganic particle aggregates are as shown in the SEM image of FIG. 1, and refer to aggregates formed by fusion of multiple inorganic particles, with voids between the inorganic particles, making them porous. The inorganic particles in the aggregates may be fused at the time of formulation, and the fusion may be released by subsequent mixing with a fluorine-based resin, for example. Meanwhile, the "nonporous" term for nonporous inorganic particles refers to the opposite of the "porous" characteristic of inorganic particles, and nonporous inorganic particles may be inorganic particles that are not "porous." In other words, nonporous inorganic particles do not need to be completely pore-free, and may have pores to the extent that they are not recognized as "porous." Below, "inorganic particle aggregates" and "nonporous inorganic particles" will be described in detail.

[0022] (Inorganic Fine Particle Aggregate) The material of the inorganic fine particles in the inorganic fine particle aggregate is typically an oxide (including composite oxides) of a typical element such as silicon oxide (silicon monoxide, silicon dioxide (silica), etc.) or aluminum oxide (alumina); a transition metal oxide (including composite oxides) such as titanium oxide (titanium dioxide (titania), etc.), iron oxide, or zirconium oxide (zirconium dioxide (zirconia)); or a nitride of a typical element such as boron nitride or silicon nitride. Of these, an oxide of a typical element is preferred, and silicon dioxide (silica) is particularly preferred. The oxide of a typical element can keep the dielectric constant of the composite material extremely low, and the composite material can be produced at lower cost. The crystallinity of the inorganic fine particles is not particularly limited, but silicon dioxide is usually amorphous.

[0023] The average primary particle diameter of the inorganic fine particles in the inorganic fine particle aggregate is typically 5 to 200 nm, but is preferably 10 nm or more, more preferably 15 nm or more, even more preferably 20 nm or more, and preferably 150 nm or less, more preferably 120 nm or less, even more preferably 100 nm or less, particularly preferably 80 nm or less, and most preferably 70 nm or less. Within this range, the inorganic fine particle aggregate is less likely to be broken even during processing such as mixing, molding, or rolling, ensuring good voids between the inorganic fine particles and making it easier to ensure a smooth surface as a plate-shaped composite material. The average primary particle diameter of the inorganic fine particles in the inorganic fine particle aggregate is a value obtained by measuring particle diameters through SEM observation and averaging the measured values. Specifically, the procedure involves randomly selecting 100 inorganic fine particle aggregates, measuring the particle diameter (the major axis of each particle) of each, and averaging the obtained particle diameters to obtain a numerical value.

[0024] The average particle size of the primary aggregates of inorganic fine particles in the inorganic fine particle aggregate is usually 100 nm or more, preferably 120 nm or more, more preferably 150 nm or more, and usually 400 nm or less, preferably 380 nm or less, more preferably 350 nm or less. The average particle size of the secondary aggregates of inorganic fine particles (aggregates of primary aggregates) in the inorganic fine particle aggregate is usually 0.1 μm or more, preferably 1 μm or more, more preferably 2 μm or more, and usually 100 μm or less, preferably 90 μm or less, more preferably 80 μm or less. The inorganic fine particle aggregates in the composite material are preferably in the form of secondary aggregates. In the form of secondary aggregates, the aforementioned three-dimensional fine network structure is easily formed. The average particle size of the primary aggregates and the average particle size of the secondary aggregates can be calculated using the same method as for the average primary particle size of the inorganic fine particles in the inorganic fine particle aggregate.

[0025] The BET specific surface area of ​​the inorganic fine particle aggregate is usually 10 m ２ / g or more, preferably 20m ２ / g or more, more preferably 30m ２ / g or more, more preferably 40m ２ / g or more, and usually 250m ２ / g or less, preferably 240m２ / g or less, more preferably 210m ２ / g or less, more preferably 150m ２ / g or less, particularly preferably 80m ２ / g or less. Within this range, a high porosity can be ensured for the composite material, and an increase in the dielectric loss tangent can be suppressed. In particular, if the BET specific surface area is too high, the dielectric loss tangent of the composite material tends to be high. The BET specific surface area of ​​the inorganic fine particle aggregate is a value calculated by substituting the gas adsorption amount measured by a gas adsorption method (particularly nitrogen adsorption isotherm) into the BET formula, and is expressed as a value before use in producing a composite material.

[0026] The apparent specific gravity of the inorganic fine particle aggregate is usually 10 g / L or more, preferably 20 g / L or more, more preferably 30 g / L or more, and even more preferably 40 g / L or more, and usually 100 g / L or less, preferably 90 g / L or less, more preferably 80 g / L or less, even more preferably 70 g / L or less, and particularly preferably 60 g / L or less. Within this range, a high porosity can be ensured as a composite material, and the inorganic fine particle aggregate is less likely to break. The apparent specific gravity of the inorganic fine particle aggregate is determined by filling the inorganic fine particle aggregate into a container capable of measuring volume, such as a 250 mL measuring cylinder, measuring the filling mass (X g) and filling volume (Y mL) of the inorganic fine particle aggregate, and dividing the filling mass by the filling volume ([apparent specific gravity (g / L)] = X / Y × 1000).

[0027] As the inorganic fine particle aggregate, commercially available products such as the Mizukasil series (manufactured by Mizusawa Industrial Chemicals), the Sylysia series (manufactured by Fuji Silysia Chemicals), the AEROSIL series (manufactured by Nippon Aerosil Co., Ltd.), and the Nipseal series (manufactured by Tosoh Silica Corporation) can be suitably used, and among these, fumed silica from the AEROSIL series (manufactured by Nippon Aerosil Co., Ltd.) is particularly preferred.

[0028] (Nonporous inorganic fine particles) Materials for the nonporous inorganic fine particles include oxides of typical elements such as silicon oxide (silicon monoxide, silicon dioxide (silica), etc.) and aluminum oxide (alumina) (including composite oxides); transition metal oxides such as titanium oxide (titanium dioxide (titania), etc.), iron oxide, and zirconium oxide (zirconium dioxide (zirconia)) (including composite oxides); and nitrides of typical elements such as boron nitride and silicon nitride, with silicon oxide being preferred. Examples of composite oxides include cordierite, talc, wollastonite, mullite, steatite, and forsterite. The material for the nonporous inorganic fine particles is not limited to one type, and two or more types may be combined.

[0029] The average primary particle diameter of the nonporous inorganic fine particles is typically 0.2 to 50 μm, but is preferably 0.3 μm or more, more preferably 0.4 μm or more, even more preferably 0.5 μm or more, and preferably 40 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, particularly preferably 10 μm or less, and most preferably 5 μm or less. Within the above range, a suitable specific surface area can be achieved, ensuring a good dielectric loss tangent, and the surface of the composite material can be made smooth, making it more suitable for use as a substrate for high frequencies. The average primary particle diameter of the nonporous inorganic fine particles is determined by measuring particle diameters through SEM observation and averaging the measured values. Specifically, the procedure involves randomly selecting 100 inorganic fine particle aggregates, measuring the particle diameter (the longest diameter of each particle) for each, and averaging the particle diameters obtained.

[0030] The BET specific surface area of ​​non-porous inorganic fine particles is usually 0.1 m ２ / g or more, preferably 0.5m ２ / g or more, more preferably 1m ２ / g or more, more preferably 2m ２ / g or more, and is usually 30m ２ / g or less, preferably 25m ２ / g or less, more preferably 20m ２ / g or less, more preferably 15m ２ / g or less, particularly preferably 10m ２ / g or less. Within this range, a good dielectric loss tangent can be ensured, and the surface of the composite material is more easily made smooth, making the material more suitable for use as a substrate for high frequencies. The BET specific surface area of ​​the nonporous inorganic fine particles is a value calculated by substituting the gas adsorption amount measured by a gas adsorption method (particularly nitrogen adsorption isotherm) into the BET formula, and is expressed as a value before use in producing a composite material.

[0031] The dielectric constant of the nonporous inorganic fine particles is usually 10 or less, preferably 8 or less, more preferably 7 or less, even more preferably 6 or less, particularly preferably 5 or less, and is usually 3 or more. The dielectric constant of the nonporous inorganic fine particles is a value determined by a method in accordance with Japanese Industrial Standard JIS C2565.

[0032] Examples of commercially available nonporous inorganic fine particles include fused silica such as SFP-130MC, SFP-30M, and FB-3SDC manufactured by Denka Co., Ltd.; cordierite such as cordierite powder FINE type, ELP-150N, and ELP-325N manufactured by AGC Ceramics Co., Ltd.; boron nitride such as FS-1, HP-P1, and HP40J series manufactured by Mizushima Ferroalloy Co., Ltd.; and talc such as Nano Ace D-600, D-800, D-1000, and FG-15 manufactured by Nippon Talc Co., Ltd.

[0033] (Other fillers) The composite material may contain fillers that do not fall under the category of inorganic particle aggregates and nonporous inorganic particles (hereinafter, sometimes abbreviated as "other fillers"). It is also preferable that the filler consists only of inorganic particle aggregates and nonporous inorganic particles. Examples of other fillers include granular fillers and fibrous fillers. Examples of granular fillers include solid carbon such as carbon black and graphite; hollow inorganic particles such as silica balloons and glass balloons; and examples of fibrous fillers include glass fiber and carbon fiber. The other fillers are not limited to one type, and two or more types may be combined.

[0034] The filler (including inorganic fine particle aggregates and nonporous inorganic fine particles) is preferably surface-modified with a surface modifier having a hydrophobic group (hereinafter, sometimes abbreviated as "surface modifier"). Modification with a "surface modifier" will be described in detail below.

[0035] The hydrophobic group of the surface modifier may be a fluoro group (-F), a hydrocarbon group (-C n H 2n+1 (n = 1 to 30)), etc., with fluoro groups being particularly preferred because they exhibit liquid repellency not only to water but also to oils. The surface modifier may be one that chemically adsorbs (reacts) with the surface of the filler, or one that physically adsorbs with the surface of the filler, and may be a low molecular weight compound or a high molecular weight compound. Surface modifiers that chemically adsorb (react) with the surface of the filler typically have a reactive functional group that reacts with the surface functional group of the filler (such as a hydroxyl group (-OH)). Examples of the reactive functional group include an alkoxysilyl group (-SiOR (where R has 1 to 6 carbon atoms)), a chlorosilyl group (-SiCl), a bromosilyl group (-SiBr), and a hydrosilyl group (-SiH). The method for modifying the surface of the filler with a surface modifier can be any known method, but one example is to bring the filler into contact with the surface modifier.

[0036] The surface modifier may be used alone or in combination of two or more. For example, a surface modifier of a low molecular weight compound having a reactive functional group may be reacted with the surface of the filler, and then a surface modifier of a high molecular weight compound having a hydrophobic group may be physically adsorbed onto the surface. If the filler material is silicon dioxide (silica) or the like, it may dissolve (decompose) when exposed to a basic aqueous solution, but by modifying it in this way, it is possible to increase its resistance to the basic aqueous solution.

[0037] The thermal decomposition temperature of the surface modifier is usually 250°C or higher, preferably 300°C or higher, more preferably 350°C or higher, even more preferably 360°C or higher, and particularly preferably 370°C or higher. Within this range, decomposition can be suppressed even when treatment such as high-temperature heating is performed. The thermal decomposition temperature of the surface modifier is defined as the temperature at which a 5% weight loss occurs when the temperature is increased at a rate of 20°C / min, as measured by thermogravimetry-dependent temperature change analysis (TG-DTA).

[0038] Examples of surface modifiers that are low molecular weight compounds having a fluoro group and a reactive functional group include those represented by the following formula: The compounds represented by the following formula are commercially available and can be obtained as appropriate and used as surface modifiers.

[0039] Examples of the surface modifying agent of a polymer compound having a fluoro group include those represented by the following formula:

[0040] A commercially available solution may be used as the surface modifier, and suitable examples include T1770 manufactured by Tokyo Chemical Industry Co., Ltd. and Novec (registered trademark) 2202 manufactured by 3M. Novec (registered trademark) 2202 contains a polymer compound having a fluoro group, and has been publicly disclosed as containing a "fluoroalkylsilane polymer." When Novec (registered trademark) 2202 is used as a surface modifier, it has the advantage of making it easier to keep the critical liquid repellency tension of the composite material low with a relatively simple operation.

[0041] The content of the surface modifier in the filler (content of organic matter) is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and particularly preferably 4% by mass or more, and is usually 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

[0042] <Composite Material> The composite material is produced using a composite material composition containing fibrils made of the above-mentioned fluororesin and a filler, and optionally containing other raw materials. The composite material will be described below.

[0043] The composite material preferably has a total content of inorganic fine particle aggregates and nonporous inorganic fine particles of 20 to 90% by mass, more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and more preferably 80% by mass or less, even more preferably 75% by mass or less, particularly preferably 70% by mass or less.

[0044] Here, "total content" refers to the total content of inorganic particle aggregates and nonporous inorganic particles when the composite material is taken as 100% by mass. When two or more types of inorganic particle aggregates and / or nonporous inorganic particles are included, this refers to the total content of all of them. Furthermore, when the total of the fluororesin, inorganic particle aggregates, and nonporous inorganic particles is taken as 100% by mass, the total content of the inorganic particle aggregates and nonporous inorganic particles is typically 20 to 90% by mass, more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, more preferably 80% by mass or less, even more preferably 75% by mass or less, and particularly preferably 70% by mass or less. Within this range, various properties such as the dielectric constant and dielectric loss tangent are easily balanced.

[0045] The composite material preferably has a mass ratio of the content of the nonporous inorganic fine particles to the total content of the inorganic fine particle aggregates and the nonporous inorganic fine particles [content of the nonporous inorganic fine particles / (content of the inorganic fine particle aggregates+content of the nonporous inorganic fine particles)] of 0.15 to 0.90, more preferably 0.2 or more, even more preferably 0.3 or more, particularly preferably 0.4 or more, and most preferably 0.5 or more, and more preferably 0.8 or less, even more preferably 0.75 or less, particularly preferably 0.7 or less, and most preferably 0.65 or less.

[0046] The total content of the filler in the composite material is usually 20 to 90% by mass, preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0047] When the total of the fluororesin and the filler is taken as 100% by mass, the total content of the filler is usually preferably 20 to 90% by mass, more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and more preferably 80% by mass or less, even more preferably 75% by mass or less, particularly preferably 70% by mass or less. Within this range, various properties such as the dielectric constant and the dielectric loss tangent can be easily balanced.

[0048] The composite material may contain materials other than the above-mentioned fluororesin and filler (including inorganic fine particle aggregates and nonporous inorganic fine particles), but the total content of the fluororesin and filler in the composite material is usually 60 mass % or more, preferably 70 mass % or more, more preferably 80 mass % or more, even more preferably 90 mass % or more, and particularly preferably 100 mass %.

[0049] The composite material has a plate-like shape, and its thickness is usually 2.0 to 3000 μm, preferably 10 μm or more, more preferably 50 μm or more, even more preferably 80 μm or more, and most preferably 90 μm or more, and is preferably 2000 μm or less, more preferably 1000 μm or less, even more preferably 800 μm or less, particularly preferably 600 μm or less, and most preferably 400 μm or less. Within the above ranges, a good relative dielectric constant and the like of the composite material can be ensured.

[0050] The smaller the thickness variation of the composite material, the more preferable, specifically, it is preferably ±17 μm or less, more preferably ±16 μm or less, and even more preferably ±15 μm or less. The lower limit is usually 0 μm.

[0051] The length (MD direction) of the composite material is preferably 5 m or more, more preferably 5 to 50 m, even more preferably 50 to 100 m, and particularly preferably 100 to 500 m. A long sheet can be obtained by continuous production, but such a long sheet cannot be obtained by veneer rolling, which involves rolling and then rotating the sheet 90°.

[0052] The width (TD direction) of the composite material is usually 20 to 1500 mm, preferably 30 mm or more, more preferably 40 mm or more, even more preferably 50 mm or more, and most preferably 60 mm or more, and is preferably 1400 mm or less, more preferably 1300 mm or less.

[0053] The composite material contains pores, and the porosity of the composite material is usually 10 to 90% by volume, preferably 15% by volume or more, more preferably 20% by volume or more, even more preferably 30% by volume or more, particularly preferably 40% by volume or more, and is preferably 80% by volume or less, more preferably 70% by volume or less, even more preferably 60% by volume or less, particularly preferably 55% by volume or less. When the porosity is within the above range, the composite material can ensure good properties such as dielectric constant and thermal expansion coefficient.

[0054] The porosity of the composite material is a value calculated by measuring the volume of the composite material, the specific gravity and mass of the fluororesin (blended mass), and the specific gravity and mass of the filler (blended mass), and substituting these values ​​into the following formula: [Porosity (volume %)] = ([volume of composite material] - [mass of fluororesin / specific gravity of fluororesin] - [mass of filler / specific gravity of filler]) / [volume of composite material] x 100

[0055] The cohesive strength of the composite material is such that the ratio (Ct / Cm) of the cohesive strength in the MD direction (Cm) to the cohesive strength in the TD direction perpendicular to the MD direction (Ct) is 1.5 or less, preferably 1.45 or less, more preferably 1.4 or less, and even more preferably 1.3 or less. The lower limit is usually 0.7 or more, preferably 0.8 or more, and more preferably 0.85 or more.

[0056] The cohesive strength (Cm) of the composite material in the MD direction is preferably 0.7 to 1.8 kN / mm, more preferably 0.8 to 1.6 kN / mm, and even more preferably 0.9 to 1.4 kN / mm, while the cohesive strength (Ct) in the TD direction is preferably 0.9 to 2.0 kN / mm, more preferably 1.0 to 1.8 kN / mm, and even more preferably 1.1 to 1.6 kN / mm.

[0057] The cohesive strength (peel strength) of the composite material is a value measured in accordance with the method specified in the copper-clad laminate test for printed wiring boards in accordance with Japanese Industrial Standard JIS C6481:1996 (see below for detailed conditions).

[0058] The tensile strength of the composite material is usually 1 to 50 MPa, preferably 5 MPa or more, more preferably 7 MPa or more, and even more preferably 10 MPa or more, and is preferably 45 MPa or less, more preferably 40 MPa or less, and even more preferably 35 MPa or less. The tensile strength is a value measured in accordance with the method specified in Japanese Industrial Standard JIS K7161 (see below for detailed conditions).

[0059] The tensile modulus of the composite material before lamination pressing is such that the ratio (Em / Et) of the tensile modulus in the MD direction (Em) to the tensile modulus in the TD direction (Et) is 0.8 to 3.6, preferably 3.4 or less, more preferably 3.3 or less, and even more preferably 3.2 or less. The lower limit is usually 1.2 or more, preferably 1.5 or more, and more preferably 1.8 or more. Here, the composite material before lamination pressing refers to the composite material after rolling and before lamination pressing of the resin layer, metal layer, etc., specifically the composite material after compression and after removing additives such as volatilizers by drying in the "additive removal step" described below. Furthermore, if the "heat compression step" described below is performed, it refers to the composite material before the heat compression step.

[0060] The tensile modulus in the MD direction is usually 5 to 100 MPa, preferably 10 MPa or more, more preferably 20 MPa or more, and even more preferably 30 MPa or more, and preferably 90 MPa or less, more preferably 80 MPa or less, and even more preferably 70 MPa or less. On the other hand, the tensile modulus in the TD direction is usually 5 to 100 MPa, preferably 8 MPa or more, more preferably 10 MPa or more, and even more preferably 15 MPa or more, and preferably 60 MPa or less, more preferably 50 MPa or less, and even more preferably 40 MPa or less.

[0061] The tensile modulus of the composite material is a value measured in accordance with the method specified in Japanese Industrial Standard JIS K7161 (see below for detailed conditions).

[0062] The dielectric constant (frequency: 10 GHz) of the composite material is usually 3.0 or less, preferably 2.60 or less, more preferably 2.40 or less, even more preferably 2.00 or less, particularly preferably 1.80 or less, and is usually 1.55 or more. The dielectric constant of the composite material is the numerical value of the real part (εr') calculated by measuring the complex dielectric constant by a cavity resonator perturbation method (measurement frequency: 10 GHz).

[0063] The dielectric loss tangent (frequency: 10 GHz) of the composite material is usually 0.01 or less, preferably 0.008 or less, more preferably 0.006 or less, even more preferably 0.004 or less, particularly preferably 0.002 or less, and is usually 0.0005 or more. The relative permittivity of the composite material is defined as the ratio (εr" / εr') of the imaginary part (εr") to the real part (εr') calculated by measuring the complex permittivity by a cavity resonator perturbation method (measurement frequency: 10 GHz).

[0064] The thermal expansion coefficient (in the Z-axis direction) of the composite material is usually 100 ppm / K or less, preferably 90 ppm / K or less, more preferably 80 ppm / K or less, even more preferably 70 ppm / K or less, particularly preferably 60 ppm / K or less, and most preferably 50 ppm / K or less, and is usually 5 ppm / K or more. The thermal expansion coefficient (in the Z-axis direction) of the composite material is a value calculated from a formula in accordance with Japanese Industrial Standard JIS R3251:1990 using laser interferometry (laser thermal dilatometer, measurement temperature range: −50 to 200°C, heating rate: 2°C / min, atmosphere: He, load: 17 g).

[0065] <Applications of Composite Material> Applications of the composite material are not particularly limited, but examples thereof include preferably electronic circuit boards, more preferably circuit boards for mobile phones, computers, etc., and substrates for microstrip patch antennas for millimeter-wave radars. That is, a substrate (hereinafter sometimes abbreviated as "substrate") containing the composite material described above also constitutes one embodiment of the present invention.

[0066] The substrate comprises a composite material, and preferably has a layer comprising a thermoplastic resin (hereinafter sometimes abbreviated as "resin layer") attached to one or both sides of the composite material, with fluorine-based resins being particularly preferred as the thermoplastic resin. Examples of fluorine-based resins include polytetrafluoroethylene (PTFE, melting point: 327°C), perfluoroalkoxyalkane (PFA, melting point: 310°C), tetrafluoroethylene-hexafluoropropylene copolymer (FEP, melting point: 260°C), polychlorotrifluoroethylene (PCTEF, melting point: 220°C), tetrafluoroethylene-ethylene copolymer (ETFE, melting point: 270°C), chlorotrifluoroethylene-ethylene copolymer (ECTFE, melting point: 270°C), and polyvinylidene fluoride (PVDF, melting point: 151-178°C), with PTFE and PFA being particularly preferred. These may be used alone or in combination of two or more.

[0067] The thickness of the resin layer is typically 0.050 to 30 μm, preferably 0.100 μm or more, more preferably 0.40 μm or more, even more preferably 1.0 μm or more, and most preferably 1.5 μm or more, and preferably 20 μm or less, more preferably 10 μm or less, even more preferably 8.0 μm or less, particularly preferably 6.0 μm or less, and most preferably 5.0 μm or less. Substrates are exposed to various chemicals used in the manufacturing process of antennas and the like. For example, exposure to highly penetrating treatment solutions can cause the treatment solution to penetrate the substrate, resulting in poor appearance and changes in characteristics. Since the resin layer also functions to suppress the penetration of treatment solutions, a thickness within the above range can effectively suppress peeling of metal layers and the like, and is less likely to cause poor appearance and changes in characteristics even when exposed to highly penetrating treatment solutions used in the manufacture of electronic circuit boards. The thickness of the resin layer refers to the average value of 5 to 10 measurements taken from the end of the resin layer in the thickness direction to the interface between the composite material and the resin layer.

[0068] The resin layer may be laminated (attached) not only to one side of the composite material, but also to both sides of the composite material.

[0069] The peel strength between the composite material and the resin layer is typically 0.2 to 2.5 N / mm, preferably 0.3 N / mm or more, more preferably 0.4 N / mm or more, and even more preferably 0.5 N / mm or more, and is preferably 2.4 N / mm or less, more preferably 2.2 N / mm or less, and even more preferably 2 N / mm or less. The peel strength is a value measured in accordance with the method specified in Japanese Industrial Standard JIS C6481:1996 (see below for detailed conditions). The peel strength here corresponds to the cohesive strength described in the Examples below. When the composite material undergoes cohesive failure when the conductor layer or resin layer is peeled from the composite material, in that case, the "peel strength" equals the "cohesive strength of the composite material."

[0070] A metal layer is usually provided on the substrate. When a resin layer is provided, the metal layer is laminated on the resin layer. Metal species of the metal layer include gold (Au), silver (Ag), platinum (Pt), copper (Cu), aluminum (Al), and alloys containing these metal species. The thickness of the metal layer is usually 5 μm or more, preferably 10 μm or more, and more preferably 15 μm or more, and usually 50 μm or less, preferably 45 μm or less, and more preferably 40 μm or less.

[0071] The maximum height Rz of the contact surface of the metal layer with the composite material or resin layer is usually 0.020 μm or more, preferably 0.050 μm or more, more preferably 0.10 μm or more, even more preferably 0.20 μm or more, and particularly preferably 0.30 μm or more, and is usually 10.0 μm or less, preferably 8.0 μm or less, more preferably 6.0 μm or less, even more preferably 4.0 μm or less, and particularly preferably 2.0 μm or less. Note that "maximum height Rz" refers to a value determined by a method conforming to Japanese Industrial Standard JIS B0601:2013 (a Japanese Industrial Standard created without technical changes to the International Organization for Standardization standard ISO 4287). Furthermore, "the maximum height Rz of the contact surface of the metal layer with the composite material or resin layer" can be measured directly, or it can be considered using the maximum height Rz of the material used for the metal layer as is.

[0072] The thickness obtained by subtracting the maximum height Rz of the metal layer from the thickness of the resin layer ((thickness of resin layer) - (maximum height Rz of metal layer)) is usually 0.005 μm or more, preferably 0.010 μm or more, more preferably 0.050 μm or more, even more preferably 0.10 μm or more, and particularly preferably 0.50 μm or more, and is usually 29.98 μm or less, preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5.0 μm or less. If it is within the above range, the thickness of the resin layer is sufficiently ensured, making it less likely to suffer from poor appearance or changes in characteristics even when exposed to highly penetrating treatment solutions, etc., used in the manufacture of electronic circuit boards.

[0073] <Method for producing composite material> The composite material is preferably produced by a production method including the following resin preparation step, filler preparation step, mixing step, molding step, and rolling step: - A resin preparation step of preparing a fluororesin (hereinafter sometimes abbreviated as the "resin preparation step"); - A filler preparation step of preparing a filler (hereinafter sometimes abbreviated as the "filler preparation step"); - A mixing step of mixing the fluororesin, the filler, and a volatile additive to obtain a precursor composition (hereinafter sometimes abbreviated as the "mixing step"); - A molding step of molding the precursor composition to obtain a rollable object (hereinafter sometimes abbreviated as the "molding step"); - A rolling step of rolling the object to be rolled to obtain a composite material (hereinafter sometimes abbreviated as the "rolling step").

[0074] The "resin preparation step," "filler preparation step," "mixing step," "molding step," "rolling step," etc. will be described in detail below.

[0075] The resin preparation step is a step of preparing a fluororesin, which may be procured or produced by the process itself. The average particle size (median diameter d50) of the prepared fluororesin granules (particles of secondary particles and beyond) is usually 0.5 μm or more, preferably 1.0 μm or more, more preferably 10 μm or more, and even more preferably 30 μm or more, and usually 700 μm or less, preferably 300 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. Within the above range, the fluororesin and filler can be easily dispersed uniformly. The fluororesin granules can be determined by a method conforming to Japanese Industrial Standard JIS Z8825:2001.

[0076] The filler preparation step is a step of preparing a filler, and the filler (including inorganic fine particle aggregates and nonporous inorganic fine particles) may be obtained or manufactured by the process itself. The average particle diameter (median diameter d50) of the prepared filler, particularly the granulated inorganic fine particle aggregates (particles of secondary particles or later) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more, and usually 500 μm or less, preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and particularly preferably 20 μm or less. The average particle diameter (median diameter d50) of the granulated nonporous inorganic fine particles (particles of secondary particles or later) is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, and usually 2000 μm or less, preferably 1000 μm or less, more preferably 500 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less. Within the above range, the fluororesin and the filler can be easily dispersed uniformly. The granulated filler can be determined by a method conforming to Japanese Industrial Standard JIS Z8825:2001. The surface of the filler is preferably modified with the above-mentioned surface modifier.

[0077] The particle size ratio of the average particle sizes of the prepared fluororesin granules and the inorganic fine particle aggregate granules [average particle size (median size d50) of fluororesin / average particle size (median size d50) of inorganic fine particle aggregates] is usually 150 or less, preferably 100 or less, more preferably 60 or less, even more preferably 40 or less, particularly preferably 30 or less, most preferably 10 or less, and usually 1 or more. The particle size ratio of the average particle sizes of the prepared fluororesin granules and the nonporous inorganic fine particles (average particle size (median size d50) of fluororesin / average particle size (median size d50) of nonporous inorganic fine particles) is usually 500 or less, preferably 300 or less, more preferably 200 or less, even more preferably 100 or less, particularly preferably 50 or less, most preferably 30 or less, and usually 0.01 or more. Within the above range, the fluororesin and filler can be easily dispersed uniformly.

[0078] The mixing step is a step of mixing a fluororesin, a filler, and a volatile additive to obtain a precursor composition. Mixing can be carried out by appropriately employing a known method such as a dry method or a wet method, or by using a mixer, etc. In the case of a dry method, the rotation speed (peripheral speed) of the agitator, etc. is usually 0.5 m / sec or more, preferably 1 m / sec or more, more preferably 5 m / sec or more, even more preferably 10 m / sec or more, and particularly preferably 15 m / sec or more, and is usually 200 m / sec or less, preferably 180 m / sec or less, more preferably 140 m / sec or less, even more preferably 100 m / sec or less, particularly preferably 50 m / sec or less, and most preferably 20 m / sec or less. Within the above range, the fluororesin and the filler can be easily dispersed uniformly.

[0079] In the case of dry mixing, the mixing time is usually 10 seconds or more, preferably 20 seconds or more, more preferably 30 seconds or more, even more preferably 40 seconds or more, particularly preferably 1 minute or more, and most preferably 5 minutes or more, and is usually 60 minutes or less, preferably 50 minutes or less, more preferably 40 minutes or less, even more preferably 30 minutes or less, particularly preferably 20 minutes or less, and most preferably 15 minutes or less. Within the above range, the fluororesin and filler can be easily dispersed uniformly.

[0080] In the case of a wet method, the rotation speed (peripheral speed) of the agitator or the like is usually 1 m / sec or more, preferably 5 m / sec or more, more preferably 10 m / sec or more, even more preferably 15 m / sec or more, particularly preferably 20 m / sec or more, and most preferably 25 m / sec or more, and is usually 160 m / sec or less, preferably 130 m / sec or less, more preferably 100 m / sec or less, even more preferably 80 m / sec or less, particularly preferably 60 m / sec or less, and most preferably 40 m / sec or less. Within the above range, the fluororesin and filler can be easily dispersed uniformly.

[0081] In the case of a wet mixing method, the mixing time is usually 5 seconds or more, preferably 10 seconds or more, more preferably 20 seconds or more, even more preferably 30 seconds or more, particularly preferably 40 seconds or more, and most preferably 50 seconds or more, and is usually 60 minutes or less, preferably 50 minutes or less, more preferably 40 minutes or less, even more preferably 20 minutes or less, particularly preferably 10 minutes or less, and most preferably 5 minutes or less. Within the above range, the fluororesin and filler can be easily dispersed uniformly.

[0082] The volatile additive serves to encapsulate sufficient pores in the composite material by finally volatilizing and removing it. The volatile additive refers to a compound that has a boiling point of 30 to 300°C and is liquid at room temperature (25°C). The boiling point of the volatile additive is preferably 50°C or higher, more preferably 100°C or higher, and even more preferably 200°C or higher, and is preferably 280°C or lower, more preferably 260°C or lower, and even more preferably 240°C or lower.

[0083] Examples of volatile additives include low-reactivity hydrocarbons, ethers, esters, and alcohols, but aliphatic saturated hydrocarbons are preferred. Specific examples include hexane (boiling point: 69°C), heptane (boiling point: 98°C), octane (boiling point: 126°C), nonane (boiling point: 151°C), decane (boiling point: 174°C), undecane (boiling point: 196°C), dodecane (boiling point: 215°C), tridecane (boiling point: 234°C), and tetradecane (boiling point: 254°C). These additives may be used alone or in combination of two or more.

[0084] The amount of the volatile additive added, when the total of the fluororesin and filler is taken as 100% by mass, is usually 1% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 30% by mass or more, and is usually 200% by mass or less, preferably 150% by mass or less, more preferably 130% by mass or less, even more preferably 110% by mass or less, and particularly preferably 100% by mass or less. Within this range, a good porosity can be ensured as a composite material.

[0085] In the mixing step, a solvent is preferably added to the fluorine-based resin, filler, and volatile additive, and mixed. The solvent functions to make the precursor composition into a paste and enable uniform dispersion. Examples of the solvent include water and lower alcohols such as methanol, ethanol, isopropanol, and butanol. These can be used alone or in combination of two or more.

[0086] The molding step is a step of molding the precursor composition to obtain a rollable object, and examples of molding machines used in the molding step include an FT die (fishtail extrusion die), a press, an extrusion molding machine, a calender roll, etc. An FT die is particularly preferred.

[0087] The rolling process is a process in which a rolled object is rolled to obtain a composite material, and it is preferable that the rolling process be a "multi-stage rolling" in which the obtained rolled object is stacked and rolled into the rolled object, and this process is repeated multiple times. Specifically, it is preferable that the rolling process include a "rough rolling process" and a "high-precision rolling process."

[0088] The rough rolling process refers to a process in which a shear force is also applied in the TD direction using a corrugated rolling roll 1 whose roll surface has a corrugated structure in the TD direction, as shown in Figure 2, for example. Such corrugated rolling rolls 1 are arranged in two stages, each having a corrugated concave-convex structure, and are arranged opposite each other so that the convex portions of one corrugated rolling roll 1 face the concave portions of the other corrugated rolling roll, and the rolled object 2 is rolled and formed according to the shape of the gap between the convex portions and concave portions of the rolls. Since the rolled object 2 discharged from such corrugated rolling rolls 1 is in a corrugated state, it is flattened into a flat rolled object through a high-precision rolling process in which it is rolled using a rolling roll with a flat roll surface, as shown in Figure 4, for example.

[0089] As shown in FIG. 3, the shape of the corrugated rolling roll 1 used in the rough rolling process is such that the wave depth is "a", the length of the wave's hypotenuse is "b", the wave's curvature radius is "R", and the creeping distance (pitch) from the crest of the wave to the apex of the trough is "h". By adjusting these, various wave shapes can be realized. For example, in a corrugated design, the longer the wave's hypotenuse b, the more likely the sheet will elongate in the TD direction during rolling. The greater the wave depth a, the longer the hypotenuse b will be, which tends to make it easier for elongation to occur in the TD direction.

[0090] Furthermore, the pitch h is usually the same from the concave portion to the convex portion and from the convex portion to the concave portion, and is uniform from one end of the roll to the other. However, in reality, since the center of the sheet tends to stretch more easily in the TD direction, it may be preferable for the pitch to be smaller in the center of the roll.

[0091] Examples of materials that can be used for the corrugated rolls used in the rough rolling step include iron, stainless steel, epoxy resin, polyphenylene ether resin, and rubber materials, and among these, iron plated with nickel or hard chrome is preferred.

[0092] Normally, in continuous production methods such as extrusion and rolling, shear force is applied only in the flow direction of the sheet (MD direction), promoting fibrillation, resulting in anisotropy of cohesive force with the width direction of the sheet (TD direction).However, by undergoing this rough rolling process, shear force is also applied in the TD direction, promoting fibrillation, thereby reducing the anisotropy of cohesive force between the MD and TD directions.

[0093] The high-precision rolling process refers to a process of precisely uniforming the sheet thickness using, for example, flat rolling rolls as shown in Figure 4. To achieve precise rolling, it is preferable that the opening precision between the rolling rolls is such that there is no variation in opening in the width direction of the rolling rolls or during roll rotation. The opening precision is +0.01 mm to -0.01 mm, preferably +0.005 mm to -0.005 mm, and particularly preferably +0.001 mm to -0.001 mm, relative to the normal set value.

[0094] The number of layers of the rolled product in the multi-stage rolling is usually 2 or more, preferably 3 or more, more preferably 4 or more, even more preferably 10 or more, and particularly preferably 30 or more, and is usually 10,000 or less, preferably 2,500 or less, more preferably 700 or less, even more preferably 500 or less, and particularly preferably 300 or less.

[0095] The rolling ratio in the rolling step is usually 10 or more, preferably 20 or more, more preferably 40 or more, even more preferably 50 or more, and particularly preferably 100 or more, and is usually 20,000 or less, preferably 15,000 or less, more preferably 10,000 or less, even more preferably 5,000 or less, and particularly preferably 3,000 or less.

[0096] Examples of the apparatus used in the rolling step include a press, an extruder, and a rolling roll (for example, a calender roll).

[0097] The method for producing a composite material or a substrate may include other steps, specifically the following: an additive removal step of removing the volatile additive from the rolled material (hereinafter may be abbreviated as "additive removal step"); a heat compression step of heat compressing the rolled material (hereinafter may be abbreviated as "heat compression step"); a resin layer formation step of forming a resin layer containing a fluorine-based resin on one or both sides of the composite material (hereinafter may be abbreviated as "resin layer formation step"); an other layer formation step of forming a metal layer on one or both sides of the composite material (hereinafter may be abbreviated as "metal layer formation step"); a patterning step of patterning the metal layer (hereinafter may be abbreviated as "patterning step").

[0098] The "additive removing step," "heat compression step," "resin layer forming step," "metal layer forming step," and "patterning step" will be described in detail below.

[0099] The additive removal step is a step of removing the volatile additive from the rolled product, and typically involves heating the rolled product in a heating furnace that can be used for drying. The heating conditions can be appropriately selected depending on the boiling point of the volatile additive, etc.

[0100] The hot compression step is a step of hot compressing the rolled product, and typically includes a method of hot compressing using a press, etc. Hot compression conditions can be appropriately selected, but it is preferable to apply pressure uniformly within the surface of the rolled product.

[0101] The resin layer forming step is a step of forming a resin layer containing a fluororesin on one or both sides of the composite material, and the resin layer can be formed by a method in which a resin film containing a fluororesin is heated and pressurized using a press or the like to adhere to the composite material, and it is more preferable to heat and pressurize the metal layer to adhere to the composite material via such a resin film. By heating and pressurizing the metal layer to the composite material via the resin film containing a fluororesin, the fluororesin permeates the composite material, effectively preventing peeling of the metal layer and ensuring a good dielectric constant and the like for the composite material.

[0102] The thickness of the resin film containing a fluorine-based resin is usually 0.050 μm or more, preferably 0.10 μm or more, more preferably 0.40 μm or more, even more preferably 1.0 μm or more, and particularly preferably 1.5 μm or more, and is usually 30 μm or less, preferably 20 μm or less, more preferably 10 μm or less, even more preferably 8.0 μm or less, particularly preferably 6.0 μm or less, and most preferably 5.0 μm or less.

[0103] The pressure in the resin layer formation step is usually 0.01 MPa or more, preferably 0.10 MPa or more, more preferably 0.50 MPa or more, even more preferably 0.80 MPa or more, and particularly preferably 1.00 MPa or more, and is usually 50 MPa or less, preferably 40 MPa or less, more preferably 30 MPa or less, even more preferably 20 MPa or less, and particularly preferably 10 MPa or less. Within this range, peeling of the metal layer and the like can be effectively suppressed, and a good relative dielectric constant and the like of the composite material can be ensured.

[0104] The temperature in the resin layer formation step is usually 250° C. or higher, preferably 280° C. or higher, more preferably 300° C. or higher, even more preferably 320° C. or higher, and particularly preferably 340° C. or higher, and usually 500° C. or lower, preferably 480° C. or lower, more preferably 460° C. or lower, even more preferably 440° C. or lower, and particularly preferably 420° C. or lower. Within the above range, peeling of the metal layer or the like can be effectively suppressed, and a good relative dielectric constant and the like of the composite material can be ensured.

[0105] The heating and pressing time in the resin layer forming step is usually 1 second or more, preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 2 minutes or more, and particularly preferably 3 minutes or more, and is usually 180 minutes or less, preferably 120 minutes or less, more preferably 60 minutes or less, even more preferably 30 minutes or less, and particularly preferably 20 minutes or less. When it is within this range, peeling of the metal layer or the like can be effectively suppressed, and a good relative dielectric constant, etc. of the composite material can be ensured.

[0106] Examples of the apparatus used in the resin layer forming step include a press, a heat roll laminator, and a belt press.

[0107] The metal layer forming step is a step of forming a metal layer on one or both sides of the composite material. Methods for forming the metal layer include sputtering, plating, pressure bonding of metal foil, adhesion by heating and pressure, lamination, etc., and as described above, it is more preferable to heat and pressurize the metal layer to be adhered to the composite material via a resin film that will later become the resin layer.

[0108] The pressure in the metal layer formation step is usually 0.01 MPa or more, preferably 0.10 MPa or more, more preferably 0.50 MPa or more, even more preferably 0.80 MPa or more, and particularly preferably 1.00 MPa or more, and is usually 50 MPa or less, preferably 40 MPa or less, more preferably 30 MPa or less, even more preferably 20 MPa or less, and particularly preferably 10 MPa or less. Within this range, peeling of the metal layer and the like can be effectively suppressed, and a good relative dielectric constant and the like of the composite material can be ensured.

[0109] The temperature in the metal layer formation step is usually 250° C. or higher, preferably 280° C. or higher, more preferably 300° C. or higher, even more preferably 320° C. or higher, and particularly preferably 340° C. or higher, and usually 500° C. or lower, preferably 480° C. or lower, more preferably 460° C. or lower, even more preferably 440° C. or lower, and particularly preferably 420° C. or lower. Within the above range, peeling of the metal layer and the like can be effectively suppressed, and a good relative dielectric constant and the like of the composite material can be ensured.

[0110] The heating and pressing time in the metal layer forming step is usually 1 second or more, preferably 30 seconds or more, more preferably 1 minute or more, even more preferably 2 minutes or more, and particularly preferably 3 minutes or more, and is usually 180 minutes or less, preferably 120 minutes or less, more preferably 60 minutes or less, even more preferably 30 minutes or less, and particularly preferably 20 minutes or less. When it is within this range, peeling of the metal layer and the like can be effectively suppressed, and a good relative dielectric constant and the like of the composite material can be ensured.

[0111] Examples of the apparatus used for heating and pressurizing in the metal layer forming step include a press, a hot roll laminator, and a belt press.

[0112] Cooling in the metal layer formation step is preferably carried out slowly, and the cooling rate is preferably 3° C. / min or less, more preferably 2° C. / min or less, and even more preferably 1° C. / min or less, and is usually 0.01° C. / min or more, preferably 0.05° C. / min or more, and more preferably 0.1° C. / min or more. Within the above range, residual strain generated during cooling is reduced, making it possible to suppress expansion and contraction due to strain release by etching, and as a result, dimensional changes during circuit processing can be suppressed.

[0113] As a cooling method, low-temperature air, water, oil, etc. are used. For example, when the heat transfer medium is oil, it can be mixed with low-temperature oil in a predetermined ratio, or the cooling rate of water or air can be appropriately controlled by controlling the flow rate.

[0114] The patterning step is a step of patterning the metal layer, and known etching methods can be used as the patterning method. The etching method may be either wet etching or dry etching, but wet etching is preferred from the viewpoint of production efficiency.

[0115] In wet etching, for example, a covering portion (masking tape, photoresist, etc.) is placed on the metal layer so as to correspond to the patterned portion and the non-patterned portion, and the metal layer (non-patterned portion) exposed from the covering portion is etched using an etching solution.

[0116] Examples of etching solutions include acids such as hydrochloric acid, sulfuric acid, nitric acid, acetic acid, oxalic acid, phosphoric acid, and mixed acids thereof, with aqueous ferric chloride being preferred. These may be used alone or in combination. The coating is then removed from the top surface of the metal layer by, for example, peeling.

[0117] The specific cohesive force in this embodiment can be achieved by appropriately selecting the manufacturing steps such as the above-mentioned "molding step," "rolling step," "heat compression step," "resin layer forming step," and "metal layer forming step." In particular, the rolling step can be preferably controlled by including a rough rolling step in which rolling is performed using a corrugated rolling roll whose roll surface has a corrugated structure in the TD direction.

[0118] The present invention will be explained in more detail below by way of examples, but modifications can be made as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0119] [Example 1] Hydrophilic fumed silica (manufactured by Nippon Aerosil Co., Ltd., product number "AEROSIL50", BET specific surface area 50±15 m) was used as inorganic fine particle aggregate. 2 / g, average primary particle size 40 nm, average particle size of secondary aggregates 0.2 μm) was modified with triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane (manufactured by Tokyo Chemical Industry Co., Ltd., product number "T1770") represented by the following formula as a surface modifier.

[0120] Specifically, 40.8 g of the surface modifier, 22.1 g of acetic acid, 43.2 g of pure water, and 80 g of inorganic fine particle aggregates were added to 832.9 g of isopropanol, and the mixture was stirred for 24 hours to obtain a dispersion of inorganic fine particle aggregates. The dispersion was then heated at 100° C. for 1 hour and then at 200° C. for 2 hours to obtain surface-modified inorganic fine particle aggregates.

[0121] Next, fused silica (manufactured by Denka Co., Ltd., product number "SFP-130MC", BET specific surface area 6.2 m) was used as non-porous inorganic fine particles. 2 / g, average primary particle diameter 0.6 μm) was modified using triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane (Tokyo Chemical Industry Co., Ltd., product number "T1770") as a surface modifier.

[0122] Specifically, 6.8 g of the surface modifier, 2.1 g of acetic acid, 4.3 g of pure water, and 80 g of nonporous inorganic fine particles were added to 83.3 g of isopropanol and stirred for 24 hours to obtain a dispersion of nonporous inorganic fine particles. The dispersion was then heated at 100°C for 1 hour and then further heated at 200°C for 2 hours to obtain surface-modified nonporous inorganic fine particles.

[0123] Next, using a high-speed fluid mixer, polytetrafluoroethylene (hereinafter sometimes abbreviated as "PTFE"), inorganic fine particle aggregates, nonporous inorganic fine particles, and a volatile additive were mixed. Specifically, polytetrafluoroethylene (manufactured by Daikin Corporation, product number "Polyflon PTFE F-104", average particle size 550 μm) was prepared, and taking into account the solid content, polytetrafluoroethylene, surface-modified inorganic fine particle aggregates, and nonporous inorganic fine particles were added so that the mass ratio was 38:37:25, and after stirring and mixing for 1 minute at a rotation speed of 14 m / sec and a temperature of 24 ° C, a hydrocarbon oil (manufactured by Exxon Mobil Corporation, product number "Isopar M") was added as a volatile additive so that the total amount of polytetrafluoroethylene, inorganic fine particle aggregates, and nonporous inorganic fine particles was 65 mass % when the total amount of polytetrafluoroethylene, inorganic fine particle aggregates, and nonporous inorganic fine particles was 100 mass %, and the mixture was mixed for 5 minutes at a rotation speed of 3 m / sec and a temperature of 24 ° C to obtain a paste.

[0124] The paste was extruded using an extrusion molding machine to produce a long sheet having a thickness of 2 mm, a width of 10 m, and a length of 100 m, and then wound around a roll to produce a plurality of roll-shaped sheets. Two of the obtained roll-shaped sheets were passed through a laminating roll to produce a plurality of first roll-shaped rolled laminate sheets (1) having a two-layer structure. The obtained roll-shaped rolled laminate sheet (1) was passed through a corrugated roll having the radius of curvature, pitch, and depth shown in Table 1 below to roll in the TD direction to produce a first roll-shaped rolled laminate sheet (1'). Next, two of the obtained first rolled laminate sheets (1') were passed through a laminating roll to produce a plurality of second roll-shaped rolled laminate sheets (2) having a total four-layer structure. The obtained roll-shaped laminate roll (2) was passed through a corrugated roll having the radius of curvature, pitch, and depth shown in Table 1 below to roll in the TD direction to produce a second roll-shaped rolled laminate sheet (2'). In this way, a series of steps of stacking the sheets, rolling them, and passing them through the corrugated rolling roll was repeated several times to produce a third rolled laminated sheet (3') (number of constituent layers: 2048) rolled in the TD direction.

[0125] Next, the obtained third rolled laminate sheet (3') was passed through a high-precision rolling roll (flat roll, material: iron + nickel plating, roll diameter φ: 300 mm) to laminate and roll, and the gap between the rolling rolls was narrowed by 0.5 mm each time, and rolling was performed multiple times to obtain a rolled laminated cohesive sheet with a thickness of approximately 150 μm. The obtained rolled laminated cohesive sheet was heated at 150 ° C for 20 minutes to remove volatile additives, and a composite material sheet was produced wound around a roll.

[0126] [Examples 2 to 4, Comparative Example 2] Composite material sheets were produced in the same manner as in Example 1, except that the corrugation of the corrugated rolling roll was changed to have the radius of curvature, pitch, and depth shown in Table 1. However, in Comparative Example 2, the sheet thickness was set to a level that would allow measurement of cohesive strength and tensile modulus, because rolling to a thickness of 150 μm would cause the sheet itself to break due to voids, etc.

[0127] [Comparative Example 1] Instead of producing a long sheet using the paste prepared in Example 1, the paste was passed through a pair of rolling rolls to form an oval-shaped base sheet (sheet-shaped molded body) having a thickness of 3 mm, a width of 10 to 50 mm, and a length of 150 mm, and multiple base sheets were produced. Next, two of these base sheets were stacked with the same rolling direction, and this stack was rolled by passing it between the rolling rolls in the same rolling direction to produce multiple first rolled laminate sheets. Next, four first rolled laminate sheets were stacked with the same rolling direction, and rolled in the same direction to produce a second rolled laminate sheet. In this way, the process of stacking and rolling the sheets was repeated a total of five times, counting from the stacking and rolling of the base sheet, to produce a third rolled laminate sheet (512 constituent layers). Next, four third rolled laminate sheets were stacked, and the laminate sheets were rotated 90 degrees from the previous rolling direction while keeping the sheet surfaces parallel, and rolled through the rolls. The gap between the rolls was narrowed by 0.5 mm increments, and rolled multiple times to obtain a sheet with a thickness of approximately 150 μm. The resulting rolled laminate sheet was heated at 150° C. for 20 minutes to remove the volatile additives, and a composite material sheet was produced.

[0128] Comparative Example 3 A composite material sheet was produced in the same manner as in Example 1, except for omitting the step of passing through a corrugated rolling roll in Example 1. However, in Comparative Example 3, the sheet thickness was set to a level that would allow measurement of cohesive strength and tensile modulus, because rolling to a thickness of 150 μm would cause the sheet itself to break due to voids and the like.

[0129] The physical properties of each of the composite material sheets obtained were measured and evaluated as follows, and the results are shown in Table 1 below.

[0130] <Yield> When the composite material sheet was made to a thickness of 200 μm or less, the yield (those that did not break during rolling and had a thickness variation of ±30 μm or less) was evaluated according to the following criteria: ◯ (Very good): Yield of 90% or more △ (Good): Yield of 30% or more but less than 90% × (Poor): Yield of less than 30%

[0131] <Continuous Production> The continuous production of the composite material sheet was evaluated according to the following criteria: ◯ (Very good): Continuous production is possible using a roll-to-roll process or the like. × (Poor): Continuous production is not possible.

[0132] <Appearance> The appearance of the composite material sheet when rolled to a thickness of 150 μm was visually evaluated according to the following criteria: ◯ (Very good): Almost no thickness unevenness △ (Good): Thickness unevenness is observed, but no breaks or streaks or voids are observed × (Poor): Breaks and / or streaks or voids are observed

[0133] <Cohesion in MD and TD (peel strength)> The composite material sheet was subjected to a copper-clad laminate test for printed wiring boards in accordance with Japanese Industrial Standard JIS C6481: 1996. A test piece approximately 100 mm long was prepared with a conductor layer laminated to a width of 10 mm, and the conductor layer was peeled off in a 90° direction at a rate of 50 mm / min, and the average value of the load was measured as the cohesion (peel strength, unit: kN / m).

[0134] <Tensile modulus in MD and TD> The tensile modulus of the composite material before lamination pressing was measured in accordance with the method specified in Japanese Industrial Standard JIS K7161. More specifically, a bench-top precision universal testing machine, Autograph AGS-X (manufactured by Shimadzu Corporation), was used as the tensile tester, and tensile tests were performed on test pieces shaped like dumbbell No. 1 or dumbbell No. 2 (with a parallel portion width of 10 mm) under the following measurement conditions: a measurement temperature of 25°C, a tensile speed of 100 mm / min, and an initial grip distance of 10 mm. Note that for each experimental example, a test piece for tension in the MD direction and a test piece for tension in the TD direction were prepared and tested. The maximum tensile force recorded until the test piece was broken was determined, and the value obtained by dividing this by the cross-sectional area of ​​the test piece was taken as the tensile strength (unit: MPa). The slope of the stress / strain curve corresponding to the two points of strain, 0.05% and 0.25% during the tensile test, was taken as the tensile modulus (unit: MPa).

[0135] <Porosity> The porosity was calculated by measuring the volume of the composite material, the specific gravity and mass (blended mass) of polytetrafluoroethylene (PTFE), the specific gravity and mass (blended mass) of the inorganic fine particle aggregate, the specific gravity and mass (blended mass) of the nonporous inorganic fine particles, and the specific gravity and mass (blended mass) of the other fillers, and substituting these values ​​into the following formula: Porosity (volume %) = [volume of composite material - (mass of PTFE / specific gravity of PTFE) - (mass of inorganic fine particle aggregate / specific gravity of inorganic fine particle aggregate) - (mass of nonporous inorganic fine particles / specific gravity of nonporous inorganic fine particles) - (mass of other fillers / specific gravity of other fillers)] / volume of composite material x 100

[0136]

[0137] The composite materials of Examples 1 to 4, whose ratio of cohesive strength in the MD direction to that in the TD direction was within the specific range specified by the present invention, enabled continuous roll-to-roll extrusion and rolling, and despite their long lengths, exhibited excellent appearance and yield. In contrast, Comparative Example 1 required cutting into single sheets of a size that could be rotated 90° in order to be rolled in the TD direction, which precluded continuous extrusion and rolling, resulting in variations from batch to batch and from face to face. Furthermore, Comparative Examples 2 and 3, whose ratio of cohesive strength in the MD direction to that in the TD direction was outside the specific range specified by the present invention, exhibited poor appearance and yield, and could not be thinned due to breakage.

[0138] Although the above examples show specific embodiments of the present invention, the examples are merely illustrative and should not be construed as limiting. Various modifications that are obvious to those skilled in the art are intended to fall within the scope of the present invention.

[0139] The composite material according to one embodiment of the present invention can be used as a circuit board for a mobile phone, a computer, or the like, or as a substrate for a microstrip patch antenna for a millimeter-wave radar.

[0140] 1 Corrugated rolling roll 2 Rolled object

Claims

1. A plate-shaped composite material containing fibrils made of fluororesin and a filler, in which the ratio (Ct / Cm) of the cohesive strength in the MD direction (Cm) to the cohesive strength in the TD direction (Ct) perpendicular to the MD direction is 0.7 to 1.

5.

2. The plate-shaped composite material according to claim 1, having a length of 5 m or more.

3. The plate-shaped composite material according to claim 1 or 2, which is rolled using a corrugated rolling roll in the rolling step.

4. A plate-shaped composite material according to any one of claims 1 to 3, wherein the content of the fluororesin is 10 to 70% by volume.

5. A composite material plate according to any one of claims 1 to 4, wherein the fluororesin comprises polytetrafluoroethylene.

6. A plate-shaped composite material according to any one of claims 1 to 5, having a porosity of 10 to 90% by volume.

7. A method for producing a plate-shaped composite material according to any one of claims 1 to 6, wherein the plate-shaped composite material is produced continuously.

8. A method for producing a plate-shaped composite material, comprising a molding step of a composite material composition, a rough rolling step, and a high-precision rolling step, wherein the roll surface of the rolling roll used in the rough rolling step has a wavy structure in the TD direction.

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