Method for manufacturing fluororesin sheet and method for manufacturing metal-clad fluororesin substrate
Patent Information
- Application Number
- JP2024509434
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Priority Date
- 2023-02-22
- Filing Date
- 2023-11-13
- Publication Date
- 2025-01-29
- Estimated Expiration
- 2043-11-13
AI Technical Summary
Conventional fluororesin sheets are prone to tearing and have poor handling properties, limiting their use in high-frequency communication boards and densely packed information terminals.
A fluororesin sheet is manufactured by mixing an aqueous dispersion of fluoropolymer and inorganic filler, followed by repeated lamination and press-forming at specific pressures to orient the fluoropolymer in the plane direction, entangling it with the inorganic filler, and eliminating interfacial peeling, resulting in a laminated structure with high tensile strength and elongation.
The resulting fluororesin sheet exhibits high tensile strength and elongation, allowing easy handling and compatibility with high-frequency circuit boards, with improved dielectric and thermal properties.
Smart Images
Figure 00000010_0000 
Figure 00000010_0001 
Figure 00000011_0000
Abstract
Description
[Technical field]
[0001] The present invention relates to a fluororesin sheet that is useful for printed wiring boards for high-speed communication using high frequencies such as millimeter waves and microwaves. of Manufacturing method and metal-clad fluororesin substrate Manufacturing method Regarding. [Background technology]
[0002] Currently, with the advancement of high-speed communications such as 5G, there is a strong demand for high-speed communication boards and antenna boards that have low transmission loss even when using high frequencies such as millimeter waves. In addition, there has been a remarkable progress in high-density mounting and ultra-thinning of wiring boards in information terminals such as smartphones. For high-speed communications such as 5G, printed circuit boards are widely used, which are made by laminating prepregs obtained by impregnating low-dielectric glass cloth such as D glass, NE glass, and L glass with thermoplastic resins such as fluororesin and polyphenylene ether, and further with thermosetting resins such as low-dielectric epoxy resin and low-dielectric maleimide resin, and then curing them under heat and pressure. Patent Document 1 proposes mixing a low molecular weight polytetrafluoroethylene fine powder and an inorganic filler with a fluororesin, impregnating the mixture into a glass fiber cloth to produce a fluororesin prepreg. Patent Document 2 proposes hydrophilizing the surface of the fluororesin prepreg impregnated into the glass fiber cloth by providing amino and hydroxyl groups, and then laminating the surface to a metal foil. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] JP 2020-50860 A [Patent Document 2] JP 2022-114351 A Summary of the Invention [Problem to be solved by the invention]
[0004] However, fluororesin sheets have the problem of being easily torn and difficult to handle. Although Patent Documents 1 and 2 improve the handleability by impregnating a glass fiber cloth with the fluororesin to form a fluororesin prepreg, there has been a demand for a fluororesin sheet that does not use a glass fiber cloth and that is easy to handle by itself, and a metal-clad fluororesin substrate including the same.
[0005] In order to solve the above-mentioned problems, the present invention provides a fluororesin sheet that is easy to handle by itself. of Manufacturing method and metal-clad fluororesin substrate Manufacturing method to provide. [Means for solving the problem]
[0006] The fluororesin sheet of the present invention is Contains fluoropolymers and inorganic fillers A method for producing a fluororesin sheet, comprising the steps of: A first step is mixing an aqueous dispersion of a fluoropolymer with an inorganic filler to form a compound, which is then press-molded into a sheet; The method includes a second step of laminating the sheets and press-molding the sheets again to obtain a sheet, the press molding in the second step is performed at room temperature (room temperature) and a pressure of 0.15 to 2.5 MPa, and lamination and press molding are repeated at this time, the lamination is at least one lamination selected from the group consisting of unidirectional lamination (parallel lamination), multidirectional lamination (cross lamination) and a combination thereof, the fluoropolymer is laminated in the thickness direction of the fluororesin sheet, and the fluoropolymer is oriented in the plane direction and entangled with the inorganic filler to cover the inorganic filler, and the lamination and press molding are repeated until there is no interfacial peeling between the inorganic filler and the fluoropolymer, The resulting sheet is rolled and dried, and then 、 Degreasing at 200-300℃ for 5-24 hours By including the third step of forming a degreased sheet, The fluororesin sheet contains a fluoropolymer and an inorganic filler, the fluororesin sheet is a degreased sheet in which a plurality of sheets are laminated in the thickness direction, the fluoropolymer is oriented in the plane direction of the fluororesin sheet and is entangled with the inorganic filler to coat the inorganic filler, there is no interfacial peeling between the inorganic filler and the fluoropolymer, and the fluororesin sheet has a tensile strength of 6 MPa or more in both the length direction and the width direction and a breaking elongation of 10% or more in both the length direction and the width direction. It is characterized by:
[0007] The metal-clad fluororesin substrate of the present invention Manufacturing method is characterized in that a metal foil is laminated to at least one surface of the fluororesin sheet. Effect of the Invention
[0009] The present invention can provide a fluororesin sheet which contains a fluoropolymer and an inorganic filler, and in which the fluoropolymer is oriented in the planar direction of the fluororesin sheet, and which is therefore easy to handle as a single unit, a method for producing the same, and a metal-clad fluororesin substrate including the same. [Brief description of the drawings]
[0010] [Figure 1] FIG. 1 is an SEM cross-sectional photograph (magnification: 500 times) of a fluororesin sheet according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an SEM cross-sectional photograph (magnification: 1000 times) of a fluororesin sheet according to one embodiment of the present invention. [Diagram 3] FIG. 3 is an SEM cross-sectional photograph (magnification: 500 times) of the fluororesin sheet of the comparative example. [Figure 4] FIG. 4 is an SEM cross-sectional photograph (magnification: 1000 times) of the fluororesin sheet of the comparative example. [Diagram 5] FIG. 5 is a schematic perspective view of a copper-clad fluororesin substrate according to one embodiment of the present invention. [Figure 6] 6A to 6D are schematic perspective views showing a method for producing a fluororesin sheet according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0011] The present inventors have studied the problems of conventional fluororesin sheets laminated with glass fiber cloth and metal-clad fluororesin substrates containing the same, and have found that conventional products have problems such as the difficulty of forming a thin film due to the restriction on the thickness of the glass fiber cloth, and also in terms of physical properties, the difference in volume balance between fluororesin and glass fiber cloth causes the dielectric constant to fluctuate, tending to result in poorer transmission characteristics at high frequencies compared to clothless, and the fact that fluororesin has a high viscosity and is therefore difficult to impregnate to the inside, which may lead to air entrapment. The present invention was completed based on these ideas.
[0012] The present invention is a fluororesin sheet containing a fluoropolymer and an inorganic filler. The fluororesin sheet may be made of a fluoropolymer and an inorganic filler, or additives other than the fluoropolymer and the inorganic filler, such as pigments, stabilizers, oils, alcohols, and resins, may be added. The fluoropolymer is oriented in the plane direction of the fluororesin sheet. That is, the fluororesin sheet has a laminated structure when viewed from the cross-sectional direction. This structure provides high tensile strength in multiple directions, and the fluororesin sheet alone has good handleability even without using glass fiber cloth. Of course, the use of glass fiber cloth is not excluded, and it may be laminated at any location. Preferably, the fluororesin sheet alone is used without using glass fiber cloth. It is preferable that this fluororesin sheet has a structure in which fluoropolymers are laminated in layers in the thickness direction. The above structure provides high strength in various directions and improves handleability.
[0013] The fluororesin sheet has high tensile strength in both the length and width directions. Degree Each of the upper limit values is preferably 5 MPa or more, more preferably more than 5 MPa, and even more preferably 6 MPa or more. The higher the upper limit value, the better, but in practice, it is preferably 100 MPa or less, and even more preferably 95 MPa or less. This provides high strength in various directions and improves handling.
[0014] The fluororesin sheet preferably has a breaking elongation in both the length direction and the width direction of 1% or more, 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 provides high elongation in various directions and improves handling.
[0015] The fluoropolymer is preferably at least one selected from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymer (PFA), and perfluoroethylenepropene copolymer (FEP). In particular, a combination of PTFE as a main component at 50% by mass or more and PFA and / or FEP as subcomponents at less than 50% by mass is preferred.
[0016] The inorganic filler is preferably 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, and magnesium hydroxide. These serve as reinforcing materials and / or thermally conductive materials. The reinforcing materials can increase the strength of the sheet, and the thermally conductive materials can transfer heat from heat-generating components such as semiconductors to heat-dissipating materials.
[0017] In the fluororesin sheet, the inorganic filler is preferably 100 to 1000 parts by volume, more preferably 150 to 900 parts by volume, and even more preferably 200 to 800 parts by volume, per 100 parts by volume of the fluororesin, which improves reinforcement and / or thermal conductivity. Each particle of the inorganic filler 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 cumulative particle size distribution by volume measured by a laser diffraction light scattering method, which improves reinforcement and / or thermal conductivity.
[0018] The thermal conductivity of the fluororesin sheet is preferably 0.1 to 10 W / m·K, more preferably 0.2 to 10 W / m·K, and further preferably 0.3 to 10 W / m·K, thereby providing favorable thermal conductivity.
[0019] 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, which makes it compatible with a variety of circuit boards.
[0020] The mass per unit area of the fluororesin sheet is 80 to 40,000 g / m 2 and more preferably 160 to 30,000 g / m 2 and more preferably 200 to 20,000 g / m 2 This makes it possible to create circuit boards with different characteristics.
[0021] The fluororesin sheet can be adhered to a metal foil having a surface roughness of Rz 0.85 or more and 2.0 or less, and the peel strength of the adhesive strength with the metal foil is preferably a maximum of 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. This allows it to be used with a variety of circuit boards. In addition, the solder heat resistance is preferably such that the copper foil does not peel off or swell when a 50 mm square copper-clad fluororesin board sample is floated in a solder bath at 288°C for 10 minutes. This improves the process passability in the soldering work.
[0022] The metal-clad fluororesin substrate of the present invention has a metal foil laminated to at least one surface of any of the above-mentioned fluororesin sheets, preferably laminated to both surfaces or in multiple layers, making it suitable for use in many circuit boards.
[0023] The metal-clad fluororesin substrate preferably has a dielectric loss tangent at a frequency of 10 GHz of 0.0001 to 0.003.The metal-clad fluororesin substrate preferably has a relative dielectric constant at a frequency of 10 GHz of 1.5 to 20.This makes it suitable for use as a high-frequency circuit board.
[0024] The metal foil is preferably a copper foil, which is suitable for use in high-frequency circuit boards.
[0025] The manufacturing method of the present invention includes the following steps. (1) First step Aqueous dispersion of fluoropolymer and inorganic filler are mixed, compounded, and press molded into a sheet. Here, compound has the same meaning as green body. Press molding is preferably performed at room temperature (room temperature) and pressure of 0.5 to 4.0 MPa. Compounding can be performed using a mixing method such as planetary mixing, kneader kneading, shaking, three-roll mill, or pot mill. (2)Second process The sheets are laminated and press molded again to obtain a sheet. The press molding is preferably performed at a pressure of 0.15 to 2.5 MPa at room temperature. At this time, lamination and press molding may be repeated multiple times. The multiple times is preferably 2 to 20 times, more preferably 3 to 15 times. The lamination is preferably at least one selected from the group consisting of unidirectional lamination (parallel lamination), multidirectional lamination (cross lamination), and a combination thereof. As a result, the fluoropolymer is laminated in the thickness direction of the fluororesin sheet and oriented in the plane direction. In addition, by repeating lamination and press molding multiple times, the fluoropolymer is entangled with the inorganic filler and covers the inorganic filler. As a result, a structure is obtained in which interfacial peeling between the inorganic filler and the fluoropolymer does not occur. As described above, the structure in which the fluororesin sheet is laminated in the thickness direction and oriented in the plane direction, and the structure in which interfacial peeling between the inorganic filler and the fluoropolymer does not occur synergistically provide a fluororesin sheet with high tensile strength in multiple directions and good handleability even without using glass fiber cloth. (3) Rolling, drying, and degreasing processes The sheet obtained as described above is rolled, dried, and degreased. Rolling is preferably performed by roll rolling. Drying is preferably performed by natural drying (air drying at room temperature). Degreasing is preferably performed by heat treatment at 200 to 300°C for 5 to 24 hours. This removes unnecessary organic matter.
[0026] The following description will be given 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: 500 times) of a fluororesin sheet 1 according to one embodiment of the present invention. The fluoropolymer 2 is oriented in the surface direction of the fluororesin sheet 1. That is, it is the fluoropolymer 2 that is arranged in the horizontal direction. This fluoropolymer 2 is entangled with the inorganic filler 3 and coats the inorganic filler, and no clear sea-island structure is observed between the inorganic filler 3 and the fluoropolymer 2. In addition, the vertical lines in FIG. 1 are cut scratches when the cross section is cut by ion milling. It can also be observed that this fluororesin sheet 1 has a structure in which the fluoropolymer 2 is layered in the thickness direction. That is, it has a layered structure when viewed from the cross-sectional direction. FIG. 2 is a SEM cross-sectional photograph (magnification: 1000 times) of a fluororesin sheet according to one embodiment of the present invention.
[0027] Fig. 3 is an SEM photograph (magnification 500x) of a fluororesin sheet 4 of a comparative example. This fluororesin sheet 4 was produced by a method that does not include the second step (lamination press step) of the method of the present invention. The fluoropolymer 5 and inorganic filler 6 form a clear sea-island structure, and no orientation of the fluoropolymer 5 is observed. The interface between the inorganic filler 6 and the fluoropolymer 5 can be clearly observed, and there are some areas where interfacial peeling can be seen. In Fig. 3, the vertical lines are cut scratches made when the cross section was cut by ion milling. Fig. 4 is an SEM cross-sectional photograph (magnification 1000x) of the fluororesin sheet of the comparative example.
[0028] 5 is a schematic perspective view of a copper-clad fluororesin substrate 7 according to one embodiment of the present invention. This copper-clad fluororesin substrate 7 has copper foils 8a, 8b attached to both sides of a fluororesin sheet 1. The fluororesin sheet 1 is heated to a temperature near its melting point of 326° C., and is attached to the copper foils 8a, 8b by heat pressing. An adhesive may be used at this time.
[0029] 6A-D are schematic perspective views showing a method for producing a fluororesin sheet according to one embodiment of the present invention. FIG. 6A shows a fluororesin sheet 9 obtained in the first step of the method of the present invention. FIG. 6B shows an example in which the fluororesin sheet 9 is cross-laminated as indicated by the arrows 10 and 11. The folding angle is arbitrary. FIG. 6C shows the fluororesin sheet 9 being parallel-laminated as indicated by the arrows 10 and 11. The cross lamination of FIG. 6B and the parallel lamination of FIG. 6C may be mixed to form a mixed lamination. The fluororesin sheet 9 laminated in this manner is pressed with press plates 14 and 15 as shown in FIG. 6D. Next, the fluororesin sheet of the present invention is obtained through the rolling, drying and degreasing steps as described above. EXAMPLES
[0030] The present invention will be described below with reference to examples, but is not limited to these examples. Various parameters were measured by the following methods. <Dielectric constant, dielectric loss tangent> Measurements were performed using a network analyzer (Keysight Technologies) using the cavity resonator perturbation method. <Effective relative dielectric constant, transmission loss> The transmission loss was measured using a network analyzer (Keysight). <Peel strength> The peel-off strength was measured by peeling at 90° according to JIS C6481 (1996) using a tensile tester (manufactured by Shimadzu Corporation). <Tensile strength, elongation> Tensile tests and elongation tests were performed using a tensile testing machine (Shimadzu Corporation) in accordance with ASTM D638 (1995). The tensile strength and elongation were measured on a 5 cm wide sample and converted to per cm. Elongation refers to the elongation at break. <Specific gravity> The specific gravity was measured using a hydrometer (Mettler Toledo) according to ASTM D792:20 (2020). The liquid used was ethanol. <Thermal resistance, thermal conductivity> The thermal resistance was measured according to a method compliant with ASTM D5470 (2017) (a sample was sandwiched between aluminum blocks, a load of 5 kgf was applied, and the thermal resistance was measured from the temperature difference between the top and bottom and the electric power, and the thermal conductivity was calculated from the thermal resistance value). The thermal conductivity was also calculated from the slope. <Solder heat resistance> The solder heat resistance was confirmed by floating a 50 mm square copper-clad fluororesin substrate sample in a solder bath at 288°C for 10 minutes and checking whether the copper foil peeled off or blistered. <Other physical properties> Measured according to industry standard tests.
[0031] Example 1 <Raw materials> The cumulative particle size distribution by volume based on the laser diffraction light scattering method (D50: 13.5 μm median diameter) of silica (LS-44: manufactured by Marukama Kamado Toryo Co., Ltd.) was added to the container at 132 volume parts. Then, an aqueous dispersion (60% concentration) of polytetrafluoroethylene (31-JR: manufactured by Mitsui Chemours) was added to the container at a resin content of 95 volume parts. To An aqueous dispersion (56% concentration) of perfluoroethylene (335-JR: manufactured by Mitsui Chemours) was added so that the resin content was 5 parts by volume. To The mixture was added so as to obtain a dispersion liquid. <Mixed> The dispersion obtained above was stirred for 2 minutes with a propeller machine adjusted to a rotation speed of 60 to 70 rpm, and then stirred for 2 minutes with a propeller machine adjusted to a rotation speed of 60 to 70 rpm. <Solidification> The dispersion thus obtained was allowed to solidify. <Compounding (making clay)> The solidified dispersion liquid was scooped out with a spatula or the like and kneaded. <Molding> The clay thus obtained was placed in a metal frame having an inner frame of 14 cm square and a thickness of 1.5 cm, and press molded at room temperature under a pressure of 2.0 MPa. <Laminated press> The molded body that had been soaked for a sufficient time was placed in a metal frame with an inner frame of 21 cm square and 0.65 cm thick, and press molded at room temperature at a pressure of 1.5 MPa. After that, lamination shown in Fig. 6A and lamination shown in Fig. 6B were performed once each, and then press molded at room temperature at a pressure of 1.0 MPa. <Rolling> The molded body obtained above was placed on a 100 μm thick polyethylene terephthalate (PET) film and rolled with a roll gap of 3.5 mm. At this time, it is preferable to set the rolling reduction rate to a low level. Rolling was repeated until the desired thickness (about 0.16 mm) was obtained. <Drying> The sheet obtained by the rolling was dried while still placed on the PET film. <Degreasing> The resulting dried sheet was cut to a specified size and placed in an oven and heated at 250° C. for 12 hours. <Heat pressing> The long degreased sheet obtained in the degreasing process was cut to a specified size (for example, 200 mm length, 300 mm width), and copper foil (manufactured by Fukuda Metal Foil and Powder Co., Ltd., product name "CF-T4X-SV18") / degreased sheet / copper foil were stacked in this order, gradually heated to a temperature of 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. The size of the obtained copper-clad fluororesin substrate was 200 mm length, 300 mm width, 0.127 mm thickness, and 555 g / m mass per unit area. 2 It was. The fluororesin sheet for evaluation was prepared by pressing only the sheet without using copper foil under the same conditions as above. The size of the obtained fluororesin sheet was 200 mm long, 300 mm wide, 0.127 mm thick, and had a mass per unit area of 272 g / m. 2 It was.
[0032] Comparative Example 1 The same procedure as in Example 1 was carried out except that the lamination press process was not performed. However, the process passability after rolling was poor, and it was difficult to obtain a long fluororesin sheet. The reason for this was that without the lamination press process, the fluororesin sheet was weak and easily torn in the longitudinal direction. Although a long fluororesin sheet could not be obtained, a small sheet measuring approximately 100 mm in length and 60 mm in width was obtained. The sheet was then rolled, dried, degreased, and hot pressed in the same manner as in Example 1 to obtain a single fluororesin sheet for evaluation.
[0033] Example 2 <Raw materials> 100g of alumina with a D50 median diameter of 2 μm and 265 volume parts of alumina with a D50 median diameter of 10 μm were added to the container. Then, an aqueous dispersion (60% concentration) of polytetrafluoroethylene (31-JR: manufactured by Mitsui Chemours) was added to the container so that the resin content was 95 volume parts. To An aqueous dispersion (56% concentration) of perfluoroethylene (335-JR: manufactured by Mitsui Chemours) was added so that the resin content was 5 parts by volume. To The mixture was added so as to obtain a dispersion liquid. <Mixed> The resulting dispersion was stirred for 2 minutes with a propeller machine adjusted to a rotation speed of 60 to 70 rpm. <Solidification> The dispersion thus obtained was allowed to solidify. <Compounding (making clay)> The solidified dispersion liquid was scooped out with a spatula or the like and kneaded. <Molding> The clay thus obtained was placed in a metal frame having an inner frame of 14 cm square and a thickness of 1.5 cm, and press molded at room temperature under a pressure of 0.65 MPa. <Laminated press> The molded body that had been soaked for a sufficient time was placed in a metal frame with an inner frame of 21 cm square and 0.65 cm thick, and press molded at room temperature at a pressure of 0.40 MPa. After that, lamination shown in Figure 6A and lamination shown in Figure 6B were performed twice each, and then press molded at room temperature at a pressure of 0.35 MPa. <Rolling> The molded body obtained above was placed on a 100 μm thick polyethylene terephthalate (PET) film and rolled with a roll gap of 3.5 mm. At this time, it is preferable to set the rolling reduction rate to a low level. Rolling was repeated until the desired thickness (approximately 0.127 mm) was obtained. <Drying> The sheet obtained by the rolling was dried while still placed on the PET film. <Degreasing> The resulting dried sheet was cut to a specified size and placed in an oven and heated at 250° C. for 12 hours. <Heat pressing> The long degreased sheet obtained in the degreasing process was cut to a specified size, and the copper foil (manufactured by Fukuda Metal Foil and Powder Co., Ltd., product name "CF-T4X-SV18") / degreased sheet / copper foil were stacked in this order, gradually heated to a temperature of 350°C, and vacuum hot-pressed at a vacuum degree of 0.9 kPa and a pressure of 8 MPa to form a laminate. The size of the obtained copper-clad fluororesin substrate was 200 mm long, 300 mm wide, 0.127 mm thick, and 693 g / m mass per unit area. 2 It was. The fluororesin sheet for evaluation was prepared by pressing only the sheet under the same conditions as above, without using copper foil. The size of the obtained fluororesin sheet was 200 mm long, 300 mm wide, 0.127 mm thick, and had a mass per unit area of 410 g / m 2 It was. A scanning electron microscope (SEM) cross-sectional photograph (magnification 500x) of this fluororesin sheet alone is shown in Figure 1. As is clear from Figure 1, the fluoropolymer 2 was laminated in the thickness direction of the fluororesin sheet 1 and was oriented in the plane direction. In other words, it is the fluoropolymer 2 that is aligned in the horizontal direction. This fluoropolymer 2 is entangled with and coats the inorganic filler 3, and no clear sea-island structure is observed between the inorganic filler 3 and the fluoropolymer 2. As is clear from Figures 1 and 2, it can also be confirmed that there is a laminated structure.
[0034] Comparative Example 2 The same procedure as in Example 2 was carried out except that the lamination press process was not performed. However, the process passability after rolling was poor, and it was difficult to obtain a long fluororesin sheet. The reason for this was that without the lamination press process, the fluororesin sheet was weak and easily torn in the longitudinal direction. Although a long fluororesin sheet could not be obtained, a small sheet measuring approximately 100 mm in length and 60 mm in width was obtained. This was then rolled, dried, degreased, and hot-pressed in the same manner as in Example 2 to obtain a single fluororesin sheet for evaluation. A scanning electron microscope (SEM) cross-sectional photograph (magnification 500x) of this fluororesin sheet alone is shown in Figure 3. As is clear from Figure 3, the fluoropolymer 5 and inorganic filler 6 form a clear sea-island structure, and no orientation of the fluoropolymer 5 was observed. In addition, the interface between the inorganic filler 6 and the fluoropolymer 5 could be clearly observed, and there were some areas where interfacial peeling was observed. This state can also be confirmed from Figure 4. The physical properties of the fluororesin sheet alone and the physical properties of the copper-clad fluororesin substrate are shown in Table 1 and Table 2, respectively.
[0035] [Table 1]
[0036] [Table 2]
[0037] As is clear from Table 1-2, in Examples 1 and 2, it was confirmed that a fluororesin sheet with good handleability could be obtained without using a glass fiber cloth, and that both the physical properties and the electrical properties were good. [Industrial Applicability]
[0038] The fluororesin sheet of the present invention and metal-clad fluororesin substrates containing the same are useful for wiring substrates such as IoT devices and wearable devices which have low transmission loss even when using high frequencies such as millimeter waves, high-speed transmission FPCs, transceivers, high-speed communication substrates, antenna substrates, smartphones, smart watches, communication base station antennas, collision sensors, distance sensors, sensors in train monitoring systems, satellite communication antennas, intersection inspection sensors, security image sensors, runway foreign object detection systems, and river water level monitoring sensors. [Explanation of symbols]
[0039] 1,4,9 Fluorine resin sheet 2,5 Fluoropolymers 3,6 Inorganic filler 7 Copper-clad fluororesin substrate 8a,8b copper foil 14,15 Press plate
Claims
1. A fluororesin sheet containing a fluoropolymer and an inorganic filler, the fluoropolymer is oriented in the plane direction of the fluororesin sheet and is entangled with the inorganic filler to coat the inorganic filler, and no interfacial peeling occurs between the inorganic filler and the fluoropolymer; The fluororesin sheet has a tensile strength of 6 MPa or more in both the length direction and the width direction, and a breaking elongation of 10% or more in both the length direction and the width direction. Fluororesin sheet characterized by:
2. 2. 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 perfluoroethylenepropene copolymer (FEP).
3. 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, and magnesium hydroxide.
4. 2. The fluororesin sheet according to claim 1, wherein the fluororesin sheet contains 100 to 1000 parts by volume of the inorganic filler relative to 100 parts by volume of the fluororesin.
5. 2. 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 cumulative particle size distribution on a volume basis as measured by a laser diffraction light scattering method.
6. 2. The fluororesin sheet according to claim 1, wherein the thermal conductivity of the fluororesin sheet is 0.1 to 10 W / m·K.
7. 2. The fluororesin sheet according to claim 1, wherein the thickness of the fluororesin sheet is 0.05 to 10.0 mm.
8. The mass per unit area of the fluororesin sheet is 80 to 40,000 g / m 2 2. The fluororesin sheet according to claim 1,
9. 2. The fluororesin sheet according to claim 1, which is capable of adhering to a metal foil having a surface roughness of Rz 0.85 or more and 2.0 or less, and has an adhesive strength with the metal foil of a maximum peel strength of 40 N / cm.
10. A metal-clad fluororesin substrate comprising the fluororesin sheet according to any one of claims 1 and 3 to 10, and a metal foil laminated to at least one surface of the sheet.
11. 11. The metal-clad fluororesin substrate according to claim 10, wherein the metal-clad fluororesin substrate has a dielectric loss tangent at a frequency of 10 GHz of 0.0001 to 0.
003.
12. 11. The metal-clad fluororesin substrate according to claim 10, wherein the metal-clad fluororesin substrate has a relative dielectric constant of 1.5 to 20 at a frequency of 10 GHz.
13. 11. The metal-clad fluororesin substrate according to claim 10, wherein the metal foil is a copper foil.
14. A method for producing a fluororesin sheet according to any one of claims 1 to 9, A first step of mixing an aqueous dispersion of a fluoropolymer with an inorganic filler to form a compound, and then pressing the compound into a sheet; The method includes a second step of laminating the sheets and press-molding the sheets again to obtain a sheet, the press molding in the second step is performed at room temperature (room temperature) and a pressure of 0.15 to 2.5 MPa, and lamination and press molding are repeated at this time, the lamination is at least one lamination selected from the group consisting of unidirectional lamination (parallel lamination), multidirectional lamination (cross lamination) and combinations thereof, the fluoropolymer is laminated in the thickness direction of the fluororesin sheet, and the fluoropolymer is oriented in the plane direction and entangled with the inorganic filler to cover the inorganic filler, and the lamination and press molding are repeated until there is no interfacial peeling between the inorganic filler and the fluoropolymer, The method for producing a fluororesin sheet comprises rolling the obtained sheet, drying and degreasing the same.