Fluororesin sheet, method for producing the same, and metal-clad fluororesin substrate including the same

Abstract

The fluororesin sheet of the present invention contains a fluoropolymer and an inorganic filler. The fluoropolymer is oriented in the plane direction of the fluororesin sheet, the inorganic filler is surface-treated, and it is a degreased sheet. The metal-clad laminate of the present invention has a metal foil laminated on at least one surface of the fluororesin sheet. The method of the present invention includes a step of mixing an aqueous dispersion of a fluoropolymer and an inorganic filler that has been surface-treated in advance to form a compound, press-molding it into a sheet, a step of laminating the sheets and press-molding them into a sheet, a step of rolling and then drying the obtained sheet, and a step of degreasing at a temperature of 200°C or higher and less than 300°C for 5 to 24 hours. Thereby, a fluororesin sheet with good handleability as a single unit is provided.

Description

Technical Field

[0001] The present invention relates to a fluororesin sheet useful for a printed wiring board for high-speed communication using high frequencies such as millimeter waves and microwaves, a method for manufacturing the same, and a method for manufacturing a metal-clad fluororesin substrate including the same.

Background Art

[0002] Currently, with the development of high-speed communication such as 5G, there is a strong demand for high-speed communication substrates and antenna substrates with low transmission loss even when using high frequencies such as millimeter waves. In addition, in information terminals such as smartphones, the high-density mounting and ultra-thinning of wiring boards have been progressing significantly. For high-speed communication such as 5G, printed boards obtained by laminating prepregs obtained by impregnating low-dielectric glass cloths such as D glass, NE glass, and L glass with thermoplastic resins such as fluororesin and polyphenylene ether, and further thermosetting resins such as low-dielectric epoxy resin and low-dielectric maleimide resin, and heating and pressurizing to cure are widely used. Patent Document 1 proposes mixing fine powder of low molecular weight polytetrafluoroethylene and an inorganic filler with a fluororesin and impregnating a glass fiber cloth therewith to obtain a fluororesin prepreg. Patent Document 2 proposes hydrophilically treating the surface of a fluororesin prepreg impregnated with a glass fiber cloth with amino groups and hydroxyl groups and laminating it with a metal foil. Patent Documents 3 to 7 propose laminating fluororesin sheets by multi-stage rolling forming.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the fluororesin sheet has a problem that it is easily torn and has poor handleability. The above Patent Documents 1 to 2 are impregnated with a glass fiber cloth to form a fluororesin prepreg, which improves the handleability. However, there has been a demand for a fluororesin sheet that can be handled alone with good handleability and a metal-clad fluororesin substrate containing the same without using a glass fiber cloth. Patent Documents 3 to 7 have a problem of containing unnecessary organic substances in the fluororesin sheet, and when heated to the hot press temperature in the copper foil pasting process, there is a problem that defects due to bubbles are likely to occur.

[0005] In order to solve the above conventional problems, the present invention provides a fluororesin sheet that has good handleability alone and is less likely to generate bubbles even when heated to the hot press temperature in the copper foil pasting process, a method for manufacturing the same, and a metal-clad fluororesin substrate containing the same.

Means for Solving the Problems

[0006] One embodiment of the present invention is a fluororesin sheet containing a fluoropolymer and an inorganic filler, the inorganic filler has a median diameter of 0.1 to 90 μm, and R(CH3) a Si(OR’) 4-a (R is an unsubstituted or substituted organic group having 1 to 20 carbon atoms, R’ is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1) is a surface-treated alkylalkoxysilane compound or a partial hydrolyzate thereof, the surface treatment agent is provided in an amount of 0.05 to 4 parts by mass per 100 parts by mass of the inorganic filler, The fluoropolymer is oriented in the plane direction of the fluororesin sheet, has a laminated structure when viewed from the cross-sectional direction of the fluororesin sheet, and is a press-molded product. The fluoropolymer is entangled with the inorganic filler and coats the inorganic filler, and has a structure in which there is no interfacial peeling between the inorganic filler and the fluoropolymer. Relates to a fluororesin sheet.

[0007] Another embodiment of the present invention relates to a metal-clad laminate in which a metal foil is laminated on at least one surface of the fluororesin sheet.

[0008] Yet another embodiment of the present invention is a method for manufacturing the fluororesin sheet, an aqueous dispersion of a fluoropolymer, and R(CH3) a Si(OR’) 4-a (where R is an unsubstituted or substituted organic group having 1 to 20 carbon atoms, R’ is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1), or an inorganic filler previously surface-treated with a partial hydrolyzate thereof, are mixed to form a compound, and pressed Molding in a first step to form a sheet, the sheet is After performing at least one lamination selected from the group consisting of cross lamination and parallel lamination, press molding is performed. formed into a sheet in a second step, a third step of drying the obtained sheet, and a fourth step of degreasing at a temperature of 200°C or higher and less than 300°C for 5 to 24 hours, relating to a method for manufacturing a fluororesin sheet.

Advantages of the Invention

[0009] The present invention includes a fluoropolymer and an inorganic filler. The fluoropolymer is oriented in the plane direction of the fluororesin sheet, the inorganic filler is surface-treated, and the fluororesin sheet is a degreased sheet. Thus, it is possible to provide a fluororesin sheet with good handleability as a single body, a manufacturing method thereof, and a metal-clad fluororesin substrate including the same, to reduce the water absorption rate (moisture absorption rate), and to improve the electrical stability. In particular, since it is a degreased sheet, unnecessary organic substances can be removed, and defects due to bubbles can be prevented even when heated to the hot press temperature (near the melting point of the fluororesin, 326°C) in the copper foil lamination process.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] The inventors of the present invention studied the problems of conventional fluororesin sheets laminated with glass fiber cloth and metal-clad fluororesin substrates containing the same. As a result, it was found that conventional products are difficult to form into thin films due to the limitations of the thickness of the glass fiber cloth. Also, in terms of physical properties, since the volume balance between the fluororesin and the glass fiber cloth is different, the dielectric constant fluctuates, and the transmission characteristics tend to deteriorate compared to crossless at high frequencies. In addition, since the fluororesin has a high viscosity, it is difficult to impregnate to the inside, and there is a possibility of air entrainment. The present invention has been completed based on such an idea.

[0012] The fluororesin sheet of the present invention contains a fluoropolymer and an inorganic filler, and the inorganic filler is surface-treated (pre-treated). The inorganic filler is preferably silicon oxide, aluminum oxide, titanium oxide, aluminum nitride, boron nitride, silicon nitride, barium titanate, barium sulfate, magnesium hydroxide, glass particles, ceramic particles, and combinations thereof. These inorganic fillers can enhance the reinforcing effect of the fluororesin sheet. The pre-treatment means fixing a surface treatment agent to the surface of the inorganic filler in advance before mixing the fluoropolymer and the inorganic filler.

[0013] The surface treatment agent is preferably a silane coupling agent, an aluminate coupling agent, or a titanate coupling agent. These surface treatment agents have a high affinity for fluoropolymers. Even when a large amount of inorganic filler is added to the fluoropolymer, the mixing property is good and the handleability is improved. In addition, when the humidity increases, there is a problem that the inorganic filler absorbs moisture and the dielectric tangent increases. However, by surface-treating the inorganic filler, moisture absorption can be suppressed and an increase in the dielectric tangent can be suppressed. Specifically, moisture absorption can be prevented by blocking the hydroxyl groups (-OH groups) on the surface of the inorganic filler with a surface treatment agent. The water absorption rate is preferably 0.06% or less, more preferably 0.01 to 0.06%. Thereby, even when the humidity changes, a decrease in transmission characteristics at high frequencies can be prevented. Among the surface treatment agents, a silane coupling agent is preferred. As the silane coupling agent, R(CH3) a Si(OR’) 4-a (where R is an unsubstituted or substituted organic group having 1 to 20 carbon atoms, R’ is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1), or a partial hydrolyzate thereof. Examples include methyltrimethoxysilane, n-propyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, methyltriethoxysilane, n-propyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, and the like. Examples of the aluminate coupling agent include aluminum alkyl acetoacetate diisopropylate, and examples of the titanate coupling agent include triisostearoyl oxy-isopropoxytitanium. The coupling agents can be used alone or in combination of two or more.

[0014] The surface treatment agent is preferably added in an amount of 0.05 to 4 parts by mass, more preferably 0.07 to 3.5 parts by mass, and even more preferably 1 to 3 parts by mass per 100 parts by mass of the inorganic filler. Thereby, even when a large amount of inorganic filler is added to the fluoropolymer, the mixing property is good and the handleability is improved.

[0015] In addition to the fluoropolymer and the surface-treated inorganic filler, other additives such as pigments, stabilizers, oils, alcohols, resins, etc. may be added.

[0016] The fluoropolymer is oriented in the plane direction of the fluororesin sheet. This structure is achieved by repeatedly laminating and press-molding a sheet of a compound (mixture) of the fluoropolymer and the surface-treated inorganic filler multiple times in parallel lamination or cross lamination. In addition, by repeatedly laminating and press-molding multiple times, the fluoropolymer becomes a structure that wraps around the inorganic filler and coats the inorganic filler. This results in a structure where there is no interfacial peeling between the inorganic filler and the fluoropolymer. Since the fluoropolymer is oriented in the plane direction and there is no interfacial peeling between the inorganic filler and the fluoropolymer, the tensile strength is high in multiple directions, and a fluororesin sheet with good handleability can be obtained without using a glass fiber cloth. Due to this structure, the tensile strength is high in the plane direction, and the handleability of the fluororesin sheet alone is improved without using a glass fiber cloth. Of course, the use of a glass fiber cloth is not excluded and it may be laminated at any location, but preferably, the glass fiber cloth is not used and it is preferably a single fluororesin sheet.

[0017] The fluororesin sheet preferably has a tensile strength of 5 MPa or more in both the length direction and the width direction, more preferably exceeding 5 MPa, and even more preferably 6 MPa or more. Also, the higher the upper limit value, the better, but practically, it is preferably 100 MPa or less, and even more preferably 95 MPa or less. This makes the strength high in various directions and improves the handleability.

[0018] The fluororesin sheet preferably has a breaking elongation of 1% or more in both the length and width directions, more preferably 5% or more, and even more preferably 10% or more. The upper limit is preferably 500% or less, and even more preferably 400% or less. This results in high elongation in various directions and improved handleability.

[0019] The fluoropolymer is preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymer (PFA), and perfluoroethylene propene copolymer (FEP). In particular, a combination with PTFE as the main component of 50% by mass or more and PFA and / or FEP as the sub-components of less than 50% by mass is preferred.

[0020] For the fluororesin sheet, the inorganic filler is preferably 10 to 4000 parts by mass, more preferably 30 to 3800 parts by mass, and even more preferably 50 to 3500 parts by mass with respect to 100 parts by mass of the fluororesin.

[0021] Each particle of the inorganic filler preferably has a D50 (median diameter) of 0.01 to 100 μm, more preferably 0.1 to 90 μm, and even more preferably 0.1 to 80 μm in the cumulative particle size distribution based on volume by the laser diffraction light scattering method. This improves the reinforcing property.

[0022] The thickness of the fluororesin sheet is preferably 0.05 to 10.0 mm, more preferably 0.1 to 9 mm, and even more preferably 0.12 to 8 mm. This enables it to be compatible with various circuit boards.

[0023] The mass per unit area of the fluororesin sheet is preferably 80 to 40000 g / m 2 more preferably 160 to 30000 g / m 2 and even more preferably 200 to 20000 g / m 2 This allows the production of circuit boards with different characteristics.

[0024] The fluororesin sheet can be adhered to a metal foil with a surface roughness of Rz of 0.85 or more and 2.0 or less, and the adhesive strength with the metal foil is preferably a peel strength of at most 40 N / cm. More preferably, the peel strength is 5.0 to 40 N / cm, and even more preferably 5.3 to 40 N / cm. Thereby, it can be applied to various circuit boards. Also, for solder heat resistance, it is preferable that when a sample of a 50 mm square copper-clad fluororesin substrate is floated in a solder bath at a temperature of 288°C for 10 minutes, the copper foil does not peel off or bulge. Thereby, the process passability in the soldering operation can be improved.

[0025] In the metal-clad fluororesin substrate of the present invention, a metal foil is laminated on at least one surface of any of the above-mentioned fluororesin sheets. Preferably, it is laminated on both sides or in multiple layers. Thereby, it can be applied to many circuit boards.

[0026] The metal-clad fluororesin substrate preferably has a dielectric tangent of 0.0001 to 0.003 at a frequency of 10 GHz. The metal-clad fluororesin substrate preferably has a relative dielectric constant of 1.5 to 20 at a frequency of 10 GHz. Thereby, it can be applied to high-frequency circuit boards.

[0027] The metal foil is preferably a copper foil. Thereby, it can be applied to high-frequency circuit boards.

[0028] The manufacturing method of the present invention includes the following steps. (1) First step An aqueous dispersion of a fluoropolymer and an inorganic filler are mixed, compounded, and press-molded into a sheet. Here, compounding has the same meaning as green body. For the press molding, a pressure of 0.5 to 4.0 MPa at room temperature (ambient temperature) is preferable. For compounding, mixing methods such as self-revolution mixing, kneader kneading, shaking, three-roll, and pot mill can be adopted. (2) Second step Stack the sheets and press-mold them into a sheet. The press molding is preferably carried out at room temperature (ambient temperature) with a pressure of 0.15 to 2.5 MPa. At this time, the stacking and press molding may be repeated a plurality of times. The plurality of times is preferably 2 to 20 times, more preferably 3 to 15 times. Also, the stacking may be performed in one direction (parallel stacking) or in multiple directions (cross stacking). As a result, the fluoropolymer has a structure in which it is laminated in the thickness direction of the fluororesin sheet and oriented in the plane direction. In addition, by repeating the stacking and press molding a plurality of times, the fluoropolymer has a structure in which it wraps around the inorganic filler and coats the inorganic filler. As a result, a structure is obtained in which there is no interfacial peeling between the inorganic filler and the fluoropolymer. As described above, the structure laminated in the thickness direction of the fluororesin sheet and oriented in the plane direction, and the structure in which there is no interfacial peeling between the inorganic filler and the fluoropolymer combine to synergistically provide high tensile strength in a plurality of directions, and a fluororesin sheet that can be handled alone without using a glass fiber cloth and has good handleability is obtained. (3) Third step Next, the obtained sheet is rolled and then dried. The rolling is preferably roll rolling. The drying is preferably natural drying (air drying at room temperature) or heating at 150 °C for 30 minutes. (4) Fourth step Next, the obtained sheet is degreased. The heating temperature during degreasing is 200 °C or higher and less than 300 °C, preferably 210 to 280 °C, more preferably 220 to 260 °C. If it is less than 200 °C, substances that cannot be degreased remain, and if it is 300 °C or higher, there are problems such as the surface treatment agent decomposing and its effect decreasing, and the decomposition amount of the fluoropolymer also increasing. When degreasing, the treatment time is preferably 10 minutes to 24 hours of heat treatment, more preferably 30 minutes to 20 hours, and even more preferably 1 to 16 hours. The size of the fluororesin sheet when degreasing is preferably a length of 30 to 30000 mm, a width of 20 to 1000 mm, and a thickness of 70 to 11000 μm. The degreasing treatment is preferably carried out by exposing at least one side, preferably both sides, of the fluororesin sheet to air. Thereby, unnecessary organic substances such as stabilizers, oils, alcohols, and dispersants are removed. If unnecessary organic substances remain in the fluororesin sheet, when heated to the hot press temperature (near the melting point of the fluororesin, 326 °C) in the subsequent copper foil pasting process, the organic substances will become bubbles and cause defects. Also, the substances that have become bubbles will corrode the copper foil and reduce the peel strength. By degreasing in the present invention, unnecessary organic substances can be removed, and defects caused by bubbles can be prevented even when heated to the hot press temperature (near the melting point of the fluororesin, 326 °C) in the subsequent copper foil pasting process. The degreasing treatment may be carried out under a reduced pressure of 0.1 to 10 kPa. As the degreasing device, there are an electric heating oven, a blowing type circulation heating oven, an IR oven, etc., and it may be a batch type or a continuous method. The IR oven can obtain a degreasing effect equal to or better than that of an electric heating oven in a short time. The IR oven enables continuous degreasing and can also handle long lengths. Since thick sheets require time for degreasing, it is preferable to heat with an electric heating oven and then reduce the pressure after sufficient heating.

[0029] The following will be described with reference to the drawings. In the following drawings, the same reference numerals indicate the same objects. FIG. 1 is a scanning electron microscope (SEM) cross-sectional photograph (magnification 40 times) of the fluororesin sheet 1 of Example 1 of the present invention. The fluoropolymer is oriented in the plane direction of the fluororesin sheet. That is, the fluoropolymer is arranged in the horizontal direction. Also, it can be observed that this fluororesin sheet has a structure in which the fluoropolymers are laminated in layers in the thickness direction. That is, it has a laminated structure when viewed from the cross-sectional direction.

[0030] FIG. 2 is an SEM photograph (magnification 40 times) of the fluororesin sheet of Comparative Example 1. This fluororesin sheet was produced by a method without the second step (lamination press step) of the method of the present invention, and no orientation of the fluoropolymer is observed.

[0031] Figure 3 is a schematic perspective view of a copper-clad fluororesin substrate 1 according to an embodiment of the present invention. In this copper-clad fluororesin substrate 1, copper foils 3a and 3b are attached to both surfaces of a fluororesin sheet 2. The fluororesin sheet 2 is heated to a temperature near 326°C and attached to the copper foils 3a and 3b by hot pressing. An adhesive may be used at this time.

[0032] Figures 4A - D are schematic perspective views showing a method for manufacturing a fluororesin sheet according to an embodiment of the present invention. Figure 4A shows a fluororesin sheet 4 obtained in the first step of the method of the present invention. Figure 4B shows an example of cross-laminating this fluororesin sheet 4 as indicated by arrows 5 and 6. The folding angle is arbitrary. Figure 4C shows parallel lamination of the fluororesin sheet 4 as indicated by arrows 7 and 8. A mixed lamination by mixing the cross-lamination of Figure 4B and the parallel lamination of Figure 4C may be performed. The fluororesin sheet 4 laminated in this way is pressed with press plates 10 and 11 as shown in Figure 4D. Next, through the rolling, drying, and degreasing processes as described above, the fluororesin sheet of the present invention is obtained.

Examples

[0033] The following examples are used for explanation. The present invention is not limited to the examples. In the following examples, unless otherwise specified, "parts" refers to parts by mass, and "%" refers to mass %. Various parameters were measured by the following methods. <Effective relative dielectric constant, transmission loss> A network analyzer (manufactured by Keysight Technologies) was used to measure the transmission loss. <Peel strength (peel-off strength)> A tensile testing machine (manufactured by Shimadzu Corporation) was used to perform a 90° peel in accordance with JIS C6481:1996 to measure the peel-off strength. <Tensile strength, tensile elongation> A tensile testing machine (manufactured by Shimadzu Corporation) was used to perform a tensile strength test and a tensile elongation test in accordance with ASTM D638:1995. Note that the tensile strength and tensile elongation were measured with a sample width of 5 cm and converted per centimeter. The elongation refers to the elongation at break. <Thermal resistance, thermal conductivity> The thermal resistance was measured according to the method in accordance with ASTM D5470 (clamping the sample between aluminum blocks, applying a load of 5 kgf, measuring the thermal resistance value from the temperature difference and power between the upper and lower parts, and calculating the thermal conductivity from the thermal resistance value). Also, the thermal conductivity was calculated from the slope. <Soldering heat resistance> For soldering heat resistance, a sample of a 50 mm square copper-clad fluororesin substrate was floated in a solder bath at 288°C for 10 minutes to check whether the copper foil peeled off or bulged. <Water absorption> The water absorption was measured in accordance with IPC-TM-650 2.6.2.1 (1986). <Presence or absence of bubbles in the copper foil attachment process> The presence or absence of bubble generation when heated to the hot press temperature (near the melting point of fluororesin, 326°C) in the copper foil attachment process was carried out by visual observation. <Other physical properties> Measured according to the standard inspection of the industry.

[0034] (Example 1) <Raw materials> To 100 parts of silicon oxide (F-40: manufactured by Maru Kama Kido Ceramics Co., Ltd.) with a D50 (median diameter) of 5.6 μm in the cumulative particle size distribution based on the laser diffraction light scattering method and volume standard, 0.7 part of trimethoxymethylsilane (DOWSIL SZ 6070 Silan, manufactured by Toray Industries, Inc.) and 24 parts of normal propanol were mixed, and the mixture was dropped. The mixture was mixed with a Henschel mixer for 30 minutes and then heated in an oven at 100°C for 60 minutes to obtain a surface-treated filler. To 132 parts of the above surface-treated filler, an aqueous dispersion (60% concentration) of polytetrafluoroethylene (31-JR: manufactured by Mitsui Chemicals, Inc.) was added so that the resin content was 95 parts by volume, and an aqueous dispersion (60% concentration) of perfluoroethylene (335-JR: manufactured by Mitsui Chemicals, Inc.) was added so that the resin content was 5 parts by volume, and the mixture was stirred to obtain a dispersion. <Mixing> The dispersion obtained above was stirred for 2 minutes with a propeller mixer adjusted to a rotation speed of 60 to 70 rpm. Next, it was stirred for 2 minutes with a propeller mixer at a rotation speed of 60 to 70 rpm. <Solidification> The dispersion obtained above was solidified. <Compounding (clay forming)> The solidified dispersion obtained above was scooped out with a spatula or the like and kneaded. <Molding> The clay obtained above was placed in a metal frame with an inner frame of 14 cm square and a thickness of 1.5 cm, and press-molded at a pressure of 2.0 MPa at room temperature. <Laminated press> The molded body soaked for a sufficient time above was placed in a metal frame with an inner frame of 21 cm square and a thickness of 0.65 cm, and press-molded at a pressure of 1.5 MPa at room temperature. Then, the lamination shown in FIG. 4A and the lamination shown in FIG. 4B were each performed once, and then press-molded at a pressure of 1.0 MPa at room temperature. <Rolling> The molded body obtained above was placed on a polyethylene terephthalate (PET) film with a thickness of 100 μm and rolled at a roll interval of 3.5 mm. At this time, it is desirable to set the reduction ratio low. Rolling was repeated until a predetermined thickness (about 0.16 mm) was obtained. <Drying> The sheet obtained by the rolling was dried while placed on the PET film. <Defatting> The obtained dried sheet was cut into a predetermined size and placed in an electric heating oven and heated at 250 ° C for 12 hours. The size of the sheet was 10000 mm in length, 500 mm in width, and 100 μm in thickness. The defatting treatment was performed by exposing at least one side of the fluororesin sheet to air. <Heating press> The long defatted sheet obtained in the defatting process was cut into a predetermined size (for example, 200 mm in length and 300 mm in width), and copper foil (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., product name "CF-T4X-SV18" surface roughness Rz: 1.0 μm) / defatted sheet / copper foil were stacked in this order, gradually heated to a temperature of 350 ° C, and vacuum heated and pressed at a vacuum degree of 0.9 kPa and a pressing force of 8.0 MPa to form a laminate. Figure 1 is a cross-sectional scanning electron microscope (SEM) photograph (magnification: 40 times) of the fluororesin sheet 1 of Example 1. It can be confirmed that the fluoropolymer is oriented in the plane direction of the fluororesin sheet. That is, the fluoropolymer is arranged horizontally. Further, it can be observed that this fluororesin sheet has a structure in which the fluoropolymers are laminated in layers in the thickness direction. That is, it has a laminated structure when viewed from the cross-sectional direction.

[0035] (Comparative Example 1) It was carried out in the same manner as in Example 1 except that the surface of the inorganic filler was not treated and degreasing was not performed. Figure 2 is an SEM photograph (magnification: 40 times) of the fluororesin sheet of Comparative Example 1. This fluororesin sheet was produced by a method without the second step (lamination pressing step) of the method of the present invention, and no orientation of the fluoropolymer was observed.

[0036] (Example 2) <Raw materials> To 100 parts of silicon oxide (LS-44: manufactured by Maru Kama Kido Ceramics Co., Ltd.) with a D50 (median diameter) of 13.5 μm in the cumulative particle size distribution based on volume by the laser diffraction light scattering method, 0.3 part of trimethoxymethylsilane (DOWSIL SZ 6070 Silan, manufactured by Toray Industries, Inc.) and 7 parts of normal propanol were mixed, and the resulting liquid was dropped and mixed with a Henschel mixer for 30 minutes. The mixed filler was heated in an oven at 100 °C for 60 minutes to obtain a surface-treated filler. To 132 parts of the above surface-treated filler, an aqueous dispersion (60% concentration) of polytetrafluoroethylene (31-JR: manufactured by Mitsui Chemicals, Inc.) was added so that the resin content was 95 parts by volume, and an aqueous dispersion (60% concentration) of perfluoroethylene (335-JR: manufactured by Mitsui Chemicals, Inc.) was added so that the resin content was 5 parts by volume, and the mixture was stirred to obtain a dispersion. <Mixing> The dispersion obtained as described above was stirred with a propeller machine adjusted to a rotation speed of 60 to 70 rpm for 2 minutes. Next, it was stirred with a propeller machine at a rotation speed of 60 to 70 rpm for 2 minutes. <Solidification> The dispersion obtained as described above was solidified. <Compounding (soil hardening)> The solidified dispersion was scooped out with a spatula or the like and kneaded. <Molding> The soil obtained as described above was placed in a metal frame with an inner frame of 14 cm square and a thickness of 1.5 cm, and press-molded at a pressure of 2.0 MPa at room temperature. <Laminated press> The molded body soaked for a sufficient time as described above was placed in a metal frame with an inner frame of 21 cm square and a thickness of 0.65 cm, and press-molded at a pressure of 1.5 MPa at room temperature. Then, the lamination shown in Fig. 4A and the lamination shown in Fig. 4B were each performed once, and then press-molded at a pressure of 1.0 MPa at room temperature. <Rolling> The molded body obtained as described above was placed on a polyethylene terephthalate (PET) film with a thickness of 100 μm and rolled at a roll interval of 3.5 mm. At this time, it is desirable to set the rolling reduction rate low. Rolling was repeated until a predetermined thickness (about 0.16 mm) was reached. <Drying> The sheet obtained by the rolling was dried while placed on the PET film. <Debinding> The obtained dried sheet was cut into a predetermined size and placed in an electric heating oven and heated at 250 °C for 12 hours. The size of the sheet was 10000 mm in length, 500 mm in width, and 100 μm in thickness. The debinding treatment was performed with at least one side of the fluororesin sheet exposed to air. <Hot press> The long debound sheet obtained in the debinding step was cut into a predetermined size (for example, 200 mm in length and 300 mm in width), and copper foil (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., product name "CF-T4X-SV18" surface roughness Rz: 1.0 μm) / debound sheet / copper foil were stacked in this order, gradually heated to 350 °C, and vacuum hot pressed at a vacuum degree of 0.9 kPa and a pressure of 8.0 MPa to form a laminate.

[0037] (Comparative Example 2) The same procedure as in Example 2 was carried out except that the surface treatment of the inorganic filler was not performed and debinding was not performed.

[0038] (Example 3) <Raw materials> To 100 parts of silicon oxide (LS-44, manufactured by Maru Kama Kido Ceramics Co., Ltd.) with a D50 (median diameter) of 13.5 μm in the cumulative particle size distribution based on volume by the laser diffraction light scattering method, 1.0 part of triisostearoyl oxy-isopropoxytitanium (TTS, manufactured by Ajinomoto Fine-Techno Co., Inc.) and 8 parts of xylene were mixed, and the resulting liquid was dropped and mixed with a Henschel mixer for 30 minutes. The mixed filler was heated in an oven at 150 °C for 60 minutes to obtain a surface-treated filler. To 132 parts of the above surface-treated filler, an aqueous dispersion (60% concentration) of polytetrafluoroethylene (31-JR, manufactured by Mitsui Chemicals) was added so that the resin content was 95 parts by volume, and an aqueous dispersion (60% concentration) of perfluoroethylene (335-JR, manufactured by Mitsui Chemicals) was added so that the resin content was 5 parts by volume, and the mixture was stirred to obtain a dispersion. <Mixing> The dispersion obtained above was stirred with a propeller machine adjusted to a rotation speed of 60-70 rpm for 2 minutes. Next, it was stirred with a propeller machine at a rotation speed of 60-70 rpm for 2 minutes. <Solidification> The dispersion obtained above was solidified. <Compounding (claying)> The solidified dispersion obtained above was scooped out with a spatula and kneaded. <Molding> The clay obtained above was placed in a metal frame with an inner frame of 14 cm square and a thickness of 1.5 cm, and press-molded at a pressure of 2.0 MPa at room temperature. <Laminated press> The molded body soaked for a sufficient time above was placed in a metal frame with an inner frame of 21 cm square and a thickness of 0.65 cm, and press-molded at a pressure of 1.5 MPa at room temperature. Then, the lamination shown in Figure 4A and the lamination shown in Figure 4B were each performed once, and then press-molded at a pressure of 1.0 MPa at room temperature. <Rolling> The molded body obtained above was placed on a polyethylene terephthalate (PET) film with a thickness of 100 μm and rolled at a roll interval of 3.5 mm. At this time, it is desirable to set the rolling reduction rate low. Rolling was repeated until a predetermined thickness (about 0.16 mm) was reached. <Drying> The sheet obtained by the rolling was dried while placed on a PET film. <Degreasing> The obtained dried sheet was cut into a predetermined size and placed in an electric oven and heated at 250 °C for 12 hours. The size of the sheet was 10,000 mm in length, 500 mm in width, and 100 μm in thickness. The degreasing treatment was performed by exposing at least one side of the fluororesin sheet to air. <Hot pressing> The long degreased sheet obtained in the degreasing process was cut into a predetermined size (for example, 200 mm in length and 300 mm in width), and copper foil (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., product name "CF-T4X-SV18" surface roughness Rz: 1.0 μm) / degreased sheet / copper foil were stacked in this order, gradually heated up to 350 °C, and vacuum hot pressed at a vacuum degree of 0.9 kPa and a pressing force of 8.0 MPa to obtain a laminate.

[0039] (Comparative Example 3) The same procedure as in Example 3 was carried out except that the surface treatment of the inorganic filler was not performed and degreasing was not performed. The above results are summarized in Table 1.

[0040]

Table 1

[0041] As is clear from Table 1, in Examples 1-3, no bubbles were generated in the copper foil sticking process, and a copper foil-stuck laminate without defects was obtained. Also, it was confirmed that the fluororesin sheets of Examples 1-3 had a low water absorption rate and were less affected by humidity due to the surface treatment of the inorganic filler. Furthermore, it was confirmed that the fluororesin sheets of Examples 1-3 could obtain a fluororesin sheet with good handleability without using a glass fiber cloth, and both the physical properties and electrical properties were good.

Industrial Applicability

[0042] The fluororesin sheet of the present invention and the metal-clad fluororesin substrate including the same are useful for wiring boards such as IoT devices, wearable devices, high-speed transmission FPCs, transceivers, high-speed communication boards, antenna boards, smartphones, smartwatches, communication base station antennas, collision sensors, distance sensors, in-train monitoring system sensors, satellite communication antennas, intersection inspection sensors, security image sensors, runway foreign object detection systems, river water level monitoring sensors, etc., which have little transmission loss even when using high frequencies such as millimeter waves.

Explanation of Signs

[0043] 1 Copper-clad fluororesin substrate 2,4 Fluororesin sheet 3a,3b Copper foil 5,6,7,8 Folding direction 9,10 Press plate

Claims

1. A fluororesin sheet containing a fluoropolymer and an inorganic filler, wherein the fluoropolymer is oriented in the plane direction of the fluororesin sheet, The inorganic filler has a median diameter of 0.1 to 90 μm, and R(CH 3 ), a Si(OR') 4-a (where R is an unsubstituted or substituted organic group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1), or a partial hydrolyzate thereof, and has been surface-treated in advance. the surface treatment agent is provided in an amount of 0.05 to 4 parts by mass per 100 parts by mass of the inorganic filler, the fluororesin sheet is a press-molded product in which a plurality of sheets are laminated in the thickness direction and is a degreased sheet, the fluoropolymer is wound around the inorganic filler and covers the inorganic filler, and has a structure in which there is no interfacial peeling between the inorganic filler and the fluoropolymer, a fluororesin sheet characterized by this.

2. The fluororesin sheet according to claim 1, wherein the inorganic filler is at least one selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide, aluminum nitride, boron nitride, silicon nitride, barium titanate, barium sulfate, magnesium hydroxide, glass particles, and other ceramic particles.

3. The fluororesin sheet according to claim 1, wherein the fluororesin sheet has a tensile strength of 5 MPa or more in both the length direction and the width direction.

4. The fluororesin sheet according to claim 1, wherein the fluoropolymer is at least one selected from the group consisting of polytetrafluoroethylene: PTFE, perfluoroalkoxyalkane polymer: PFA, and perfluoroethylene propene copolymer: FEP.

5. The fluororesin sheet according to claim 1, wherein the inorganic filler is 10 to 4000 parts by mass with respect to 100 parts by mass of the fluororesin.

6. The fluororesin sheet according to claim 1, wherein each particle of the inorganic filler has a D50: median diameter of 0.01 to 100 μm in the cumulative particle size distribution based on volume by the laser diffraction light scattering method.

7. The fluororesin sheet according to claim 1, wherein the thickness of the fluororesin sheet is 0.005 to 10.0 mm.

8. The fluororesin sheet according to claim 1, wherein the fluororesin sheet can be adhered to a metal foil having a surface roughness: Rz of 0.6 or more and 2.0 or less, and the adhesion strength with the metal foil is a peel strength of at most 40 N / cm.

9. A metal-clad fluororesin substrate, characterized in that a metal foil is laminated on at least one surface of the fluororesin sheet according to any one of claims 1 to 8.

10. The metal-clad fluororesin substrate is the metal-clad fluororesin substrate according to claim 9, having a dielectric tangent of 0.0001 to 0.003 at a frequency of 10 GHz.

11. The metal-clad fluororesin substrate is the metal-clad fluororesin substrate according to claim 9, having a relative dielectric constant of 1.5 to 20 at a frequency of 10 GHz.

12. The metal foil is a copper foil in the metal-clad fluororesin substrate according to claim 9.

13. A method for manufacturing a fluororesin sheet according to any one of claims 1 to 12, An aqueous dispersion of a fluoropolymer and an inorganic filler surface-treated in advance with an alkylalkoxysilane compound represented by R(CH 3 )( a Si(OR') 4-a (wherein R is an unsubstituted or substituted organic group having 1 to 20 carbon atoms, R' is an alkyl group having 1 to 4 carbon atoms, and a is 0 or 1), or a partial hydrolyzate thereof, are mixed to form a compound, which is press-molded into a sheet in a first step; a second step of subjecting the sheet to at least one lamination selected from the group consisting of cross-lamination and parallel-lamination and then press-molding the sheet into a sheet; a third step of drying the obtained sheet; and a fourth step of degreasing at a temperature of 200 °C or higher and less than 300 °C for 5 to 24 hours. A method for manufacturing a fluororesin sheet, characterized by including the above steps.

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