WO2021235460A1 - Fluororesin sheet, multilayer sheet, and shield material - Google Patents

Abstract

The fluororesin sheet according to the present invention contains a polytetrafluoroethylene and a filler. The weight average molecular weight Mw of the polytetrafluoroethylene is 1,000,000 or more. The mass ratio of the filler with respect to the polytetrafluoroethylene is 1.0 or more. The tensile elongation of the fluororesin sheet is 50% or more.

Description

Fluororesin sheet, multi-layer sheet and shield material

The present disclosure relates to fluororesin sheets, multilayer sheets and shielding materials.
This application claims priority based on Japanese Application No. 2020-87053 filed on May 18, 2020, and incorporates all the contents described in the above Japanese application.

A printed wiring board having a fluororesin base material is known. Since the fluororesin has a lower dielectric constant than the epoxy resin, a printed wiring board having a fluororesin base material is used as a circuit board for high-frequency signal processing (see, for example, Japanese Patent Application Laid-Open No. 2001-7466). ). Further, wiring materials such as electric wires and bus bars, shield materials, and heat dissipation materials using the heat resistance and electrical characteristics of fluororesin are known.
Further, since the fluororesin has excellent wear resistance, a sliding member having a fluororesin base material has also been proposed (see, for example, Japanese Patent Application Laid-Open No. 2000-326441).

Japanese Unexamined Patent Publication No. 2001-7466 Japanese Unexamined Patent Publication No. 2000-326441

The fluororesin sheet according to one aspect of the present disclosure contains polytetrafluoroethylene and a filler, the weight average molecular weight Mw of the polytetrafluoroethylene is 1 million or more, and the filler with respect to the polytetrafluoroethylene is used. The mass ratio is 1.0 or more, and the tensile elongation is 50% or more.

FIG. 1 is a schematic cross-sectional view showing a fluororesin sheet according to one aspect of the present disclosure. FIG. 2 is a schematic cross-sectional view showing a multilayer sheet according to one aspect of the present disclosure.

[Problems to be solved by this disclosure]
It can be said that the conventional fluororesin base material meets the requirements in that it can be used as a circuit board for high-frequency communication, a wiring material, a shield material, a heat radiating material, and a sliding member. However, the conventional fluororesin base material is required to be further improved in functions such as control of relative permittivity and heat dissipation, and a technique for adding a filler to the fluororesin is known. In order to reduce the price by using high frequency characteristics, heat dissipation, shielding properties, and inexpensive filler, it is desirable to add a large amount of filler so that the mass ratio of the filler to the fluororesin is 1.0 or more. .. However, in this case, there is a problem that the surface texture and the physical characteristics of elongation are significantly deteriorated and it becomes difficult to mold. Further, the fluororesin base material is often used in a form in which a fluorine sheet and a base material such as metal are integrated, but it is not easy to bond the base material to the fluororesin sheet.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a fluororesin sheet having excellent sheet properties and moldability.

[Effect of this disclosure]
According to the present disclosure, it is possible to provide a fluororesin sheet having excellent sheet properties and moldability.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

The fluororesin sheet according to one aspect of the present disclosure contains polytetrafluoroethylene and a filler, the weight average molecular weight Mw of the polytetrafluoroethylene is 1 million or more, and the filler with respect to the polytetrafluoroethylene is used. The mass ratio is 1.0 or more, and the tensile elongation is 50% or more.

Since the fluororesin sheet contains polytetrafluoroethylene, it has low transmission loss and heat resistance. Further, when the weight average molecular weight Mw of the polytetrafluoroethylene is 1 million or more, the polytetrafluoroethylene molecules are easily entangled with each other by shearing, so that the fibers can be efficiently fiberized. Therefore, even if a large amount of filler is contained, the mass ratio of the filler to polytetrafluoroethylene is 1.0 or more, the properties of the resin sheet are good, and the tensile elongation of the fluororesin sheet is 50% or more. Since the physical properties can be obtained, the flexibility is increased and the moldability can be ensured. Therefore, it is possible to obtain the effect that the range of industrial application can be expanded, such as post-processing such as circuit formation, adhesion to a base material, and use in a bent state. Further, when the mass ratio of the filler to the polytetrafluoroethylene is 1.0 or more, the content of the filler can be dramatically increased, so that the fluororesin sheet is excellent in sheet properties and moldability. .. Here, the "weight average molecular weight Mw of polytetrafluoroethylene" can be calculated by measuring the heat of crystallization by the differential scanning calorimetry (DSC) method. "Tensile elongation" means the elongation ratio measured in accordance with JIS-K7161-1: 2014 "Plastic-How to determine tensile properties-Part 1: General rules". The polytetrafluoroethylene also includes modified polytetrafluoroethylene. The "modified polytetrafluoroethylene" is a small amount of hexafluoropropylene (HFP), alkyl vinyl ether (AVE), chlorotrifluoroethylene (CTFE), etc., preferably 1/50 (molar ratio) or less with respect to tetrafluoroethylene. Copolymerized polytetrafluoroethylene.

In the fluororesin sheet, it is preferable that the Asker A hardness is 20 or more. When the Ascar A hardness of the fluororesin sheet is 20 or more, the fibrosis of polytetrafluoroethylene can be confirmed. Further, the strength as a resin sheet required for the above-mentioned applications becomes good. Here, "Asker A hardness" means the hardness measured by a type A durometer based on JIS-K6253-3 (2012).

It is preferable that the filler contains silica, titanium oxide, alumina, forsterite or a combination thereof. When the filler contains silica, titanium oxide, alumina, forsterite or a combination thereof, the fluororesin sheet can further improve transmission performance such as relative permittivity.

It is preferable that the filler contains the silica and the mass ratio of the silica to the polytetrafluoroethylene is 1.0 or more and 2.0 or less. When the filler contains the silica and the mass ratio to the polytetrafluoroethylene is in the above range, the fluororesin sheet can further enhance the transmission performance. Further, since the coefficient of linear expansion can be reduced to bring it closer to copper, the accuracy and durability of the circuit can be improved. The "coefficient of linear expansion" is a coefficient of linear expansion measured according to the test method for dynamic mechanical properties described in JIS-K7424-4 (1999).

It is preferable that the filler contains ferrite, sendust, a conductive filler, or a combination thereof. When the filler contains ferrite, sendust, a conductive filler, or a combination thereof, the fluororesin sheet can improve the conductivity.

It is preferable that the filler contains ferrite, sendust, or a combination thereof. When the filler contains ferrite, sendust, or a combination thereof, the fluororesin sheet can improve the electromagnetic wave shielding performance.

It is preferable that the filler contains alumina, boron nitride, aluminum nitride, sendust, or a combination thereof. When the filler contains alumina, boron nitride, aluminum nitride, silicon nitride or a combination thereof, the fluororesin sheet can improve heat dissipation.

The multilayer sheet according to another aspect of the present disclosure includes the fluororesin sheet, the conductive layer laminated on both sides of the fluororesin sheet, and the adhesive layer laminated between the fluororesin sheet and the conductive layer. And prepare. Since the multilayer sheet contains the fluororesin sheet, the transmission loss in a high frequency signal is low, and the multilayer sheet can be suitably used as a printed wiring board for high frequency. Further, since it is excellent in the effect of reducing the coefficient of linear expansion, heat dissipation, electromagnetic wave shielding performance, and economy, it can be suitably used as an electric wire, a bus bar, an electromagnetic wave shielding component, a heat radiating component, and a sliding component.

It is preferable that the total average thickness of the adhesive layers is 0.1 μm or more and 50 μm or less. When the total average thickness of the adhesive layers is within the above range, the adhesive strength can be improved and deterioration of transmission performance, heat dissipation and electromagnetic wave shielding performance can be suppressed. Here, the "total average thickness" is a value obtained by totaling the average thickness of each layer in the plurality of adhesive layers.

The shield material according to another aspect of the present disclosure includes the fluororesin sheet. The fluororesin sheet provided in the shielding material contains ferrite, sendust, or a combination thereof as the filler. Since the fluororesin sheet provided in the shield material contains ferrite, sendust, or a combination thereof as a filler, the shield material has good electromagnetic wave shielding performance.

[Details of Embodiments of the present disclosure]
Hereinafter, an embodiment of the fluororesin sheet, the multilayer sheet and the shielding material according to the present disclosure will be described in detail with reference to the drawings.

<Fluororesin sheet>
The fluororesin sheet 1 of FIG. 1 contains polytetrafluoroethylene and a filler.

As the lower limit of the Asker A hardness of the fluororesin sheet 1, 20 is preferable, 30 is more preferable, and 40 is further preferable. When the Asker A hardness of the fluororesin sheet is 20 or more, the strength becomes good. On the other hand, when the hardness of Asker A is less than 20, the sheet shape is not formed, molding is impossible, and the shape may not be maintained by its own weight.

The lower limit of the average thickness of the fluororesin sheet 1 is preferably 10 μm, more preferably 50 μm. The upper limit of the average thickness of the fluororesin sheet 1 is preferably 3000 μm, more preferably 1500 μm. If the average thickness of the fluororesin sheet 1 is less than the above lower limit, the effect of reducing the relative permittivity may be insufficient. On the other hand, when the average thickness of the fluororesin sheet 1 exceeds the above upper limit, the temperature dependence of the transmission performance of the fluororesin sheet 1 may increase or the thickness may become unnecessarily large. Here, the "average thickness" means a value obtained by measuring the thickness of an arbitrary portion at five points and averaging the thickness.

(Polytetrafluoroethylene)
Since the fluororesin sheet contains polytetrafluoroethylene (hereinafter, also referred to as PTFE) having a low relative permittivity, the transmission loss is low and the fluororesin sheet has heat resistance.

The lower limit of the weight average molecular weight Mw of the PTFE is 1 million, preferably 4 million, more preferably 8 million, and even more preferably 10 million. On the other hand, the upper limit of the weight average molecular weight Mw of the PTFE is preferably 20 million. When the weight average molecular weight Mw of the PTFE is in the above range, the formability of the fluororesin sheet having the mass ratio of the filler to the PTFE of 1.0 or more is excellent.

The fluororesin sheet 1 may contain a fluororesin other than PTFE. Examples of the fluororesin other than PTFE include tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-ethylene copolymer (ETFE). , Polyvinylidene fluoride (PVdF), fluororubber, thermoplastic fluororesin (THV) formed from three kinds of monomers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride, and other copolymers of tetrafluoroethylene. And so on. The upper limit of the mass ratio of the fluororesin other than PTFE to PTFE is preferably 1.0, more preferably 0.2. Further, the fluororesin sheet may contain a resin other than the above-mentioned fluororesin. Examples of such a resin include polyetheretherketone (PEEK), polyamideimide (PAI), polyethersulphon (PES), polyimide (PI), liquid crystal polymer (LCP), etc., which have excellent heat resistance. can.

(Filler)
The fluororesin sheet can dramatically increase the content of the filler. The lower limit of the mass ratio of the filler to the polytetrafluoroethylene is 1.0, preferably 1.2, and preferably 1.5. When the lower limit of the mass ratio of the filler is within the above range, the fluororesin sheet is excellent in sheet properties and moldability. On the other hand, as the upper limit of the mass ratio of the filler, 35.0 is preferable, and 20.0 is more preferable. When the upper limit of the mass ratio of the filler is within the above range, the sheet properties of the fluororesin sheet can be maintained satisfactorily.

The lower limit of the average particle size of the filler is preferably 0.01 μm, more preferably 0.10 μnm. The upper limit of the average particle size of the filler is preferably 300 μm, more preferably 150 μm. When the average particle size of the filler is less than the lower limit, the filler tends to aggregate when contained in the fluororesin sheet 1, and the dispersion of particles may become non-uniform. On the other hand, when the average particle size of the filler exceeds the upper limit, unevenness is likely to occur on the outer surface of the fluororesin sheet 1 and molding of the fluororesin sheet 1 may be difficult. Here, the "average particle size" means a value (D50) of an integrated value of 50% in the integrated distribution of the average particle size on a volume basis. The integrated distribution is created based on the value obtained by volume-converting the value of the circular radius measured by image analysis of 500 particles observed with a scanning electron microscope (SEM).

It is preferable that the filler contains silica, titanium oxide, alumina, forsterite or a combination thereof. When the filler contains silica, titanium oxide, alumina, forsterite or a combination thereof, the fluororesin sheet can further improve transmission performance such as relative permittivity. When the filler contains silica, titanium oxide, alumina, forsterite or a combination thereof, the lower limit of the mass ratio of the silica, titanium oxide, alumina, forsterite or a combination thereof to the polytetrafluoroethylene is 1. 0 is preferable, 1.3 is more preferable, and 1.9 is even more preferable. On the other hand, 99.0 is preferable as the upper limit of the mass ratio of the above silica, titanium oxide, alumina, forsterite or a combination thereof. 10.0 is more preferable. When the range of the mass ratio of the silica, titanium oxide, alumina, forsterite or a combination thereof is within the above range, the fluororesin sheet can further enhance the transmission performance.

From the viewpoint of imparting high insulation, reducing the coefficient of linear expansion, and low dielectric constant to the fluororesin sheet and further enhancing the transmission performance, it is preferable that the filler contains silica. When the filler contains silica, the lower limit of the mass ratio of the silica to the polytetrafluoroethylene is preferably 1.0, more preferably 1.3. On the other hand, as the upper limit of the mass ratio of the silica, 2.0 is preferable, and 1.8 is more preferable. When the range of the mass ratio of the silica is in the above range, the fluororesin sheet can further enhance the transmission performance. Further, since the coefficient of linear expansion can be reduced to bring it closer to copper, the accuracy and durability of the circuit can be improved. The "coefficient of linear expansion" is a coefficient of linear expansion measured according to the test method for dynamic mechanical properties described in JIS-K7424-4 (1999).

As the silica, synthetic silica, natural silica, crushed silica, silica coated with a hydrophobic coating agent on the surface of these silicas, silica reacted with a silane coupling agent, and the like can be used.

In the fluororesin sheet, the transmission loss at 25 ° C. and 80 GHz is preferably −7 [dB / 0.1 m] (25 ° C., 80 GHz) or more from the viewpoint of improving the transmission performance. Further, from the viewpoint of improving the transmission performance, a material having a small temperature dependence is required, the rate of change in dielectric constant at −40 ° C. to 120 ° C. is less than 2%, and transmission at −40 ° C. to 120 ° C. It is more preferable that the amount of change in loss is less than 3 dB.

When the filler contains silica, the filler further contains titanium oxide, so that the temperature dependence of the transmission performance can be reduced. When the filler contains silica and titanium oxide, the mass ratio of the titanium oxide to the polytetrafluoroethylene is preferably 0.05 or more and 10 or less.

From the viewpoint of improving the conductivity of the fluororesin sheet, it is preferable that the filler contains ferrite, sendust, a conductive filler, or a combination thereof. When the filler contains a ferrite, a sendust, a conductive filler or a combination thereof, 1.0 is preferable as the lower limit of the mass ratio of the ferrite, the sendust, the conductive filler or a combination thereof to the polytetrafluoroethylene. 2.0 is more preferable. On the other hand, 99.0 is preferable as the upper limit of the mass ratio of the above-mentioned ferrite, sendust, conductive filler or a combination thereof. When the range of the mass ratio of the ferrite, the sendust, the conductive filler or a combination thereof is within the above range, the fluororesin sheet can further enhance the conductivity.

When the filler contains ferrite, sendust, a conductive filler, or a combination thereof, the upper limit of the volume resistivity of the fluororesin sheet 1 ^{is preferably 3 × 10 13} Ωcm, more preferably 1 × 10 ⁹ Ωcm, and 1 × 10 ³ Ωcm is more preferable. If the volume resistivity of the fluororesin sheet 1 exceeds the above upper limit, the conductivity may decrease. The volume resistivity means a value measured according to JIS-C2139-3-1 (2018). The larger the volume resistivity, the higher the conductivity.

Examples of the conductive filler include metals such as copper, silver, aluminum, nickel, iron, and stainless steel, tin oxide-doped indium oxide (ITO), fluorine-doped indium oxide (FTO), tin oxide (IO), and neodymium barium indium. The surface of metal oxides such as oxides, polythiophene-based, polypyrrole-based, polyaniline-based, oligothiophene-based organic substances, inorganic insulators such as alumina and glass, and polymers such as polyethylene and polystyrene is coated with a conductive substance. However, carbon-based materials such as carbon black, graphite, graphene, carbon nanotubes, fullerene, graphene oxide, and acetylene black are not limited thereto. These may be used alone or in combination of two or more.

It is preferable that the filler contains ferrite, sendust, or a combination thereof. When the filler contains ferrite, sendust, or a combination thereof, the fluororesin sheet can improve the electromagnetic wave shielding performance. In particular, flat sendust is particularly preferable because it can improve the electromagnetic wave shielding performance. When the filler contains the ferrite, sendust or a combination thereof, the lower limit of the mass ratio of the ferrite, sendust or a combination thereof to the polytetrafluoroethylene is preferably 1.0, more preferably 2.0. 9.8 is more preferable. Further, as the upper limit of the mass ratio of the above-mentioned ferrite, sendust or a combination thereof to the above-mentioned polytetrafluoroethylene, 95.0 is preferable. When the range of the mass ratio of the above-mentioned ferrite, sendust or a combination thereof is within the above-mentioned range, the fluororesin sheet can further enhance the electromagnetic wave shielding performance.

When the filler contains the ferrite, sendust, or a combination thereof, the upper limit of the signal attenuation [dB] in the range of 10 MHz to 100 MHz of the fluororesin sheet 1 is preferably −8 dB, more preferably −15 dB. If the signal attenuation of the fluororesin sheet 1 exceeds the above upper limit, a sufficient electromagnetic wave shielding effect may not be obtained.

From the viewpoint of improving the heat dissipation of the fluororesin sheet, it is preferable that the filler contains alumina, boron nitride, aluminum nitride, sendust or a combination thereof. When the filler contains alumina, boron nitride, aluminum nitride, sendust or a combination thereof, the fluororesin sheet can improve heat dissipation. When the filler contains alumina, boron nitride, aluminum nitride, sendust or a combination thereof, as the lower limit of the mass ratio of the alumina, boron nitride, aluminum nitride, sendust or a combination thereof to the polytetrafluoroethylene or a combination thereof. Is preferably 1.0, more preferably 2.0. Further, 95.0 is preferable as the upper limit of the mass ratio of the alumina, boron nitride, aluminum nitride, sendust or a combination thereof to the polytetrafluoroethylene. When the range of the mass ratio of the alumina, boron nitride, aluminum nitride, sendust or a combination thereof is within the above range, the fluororesin sheet can further enhance the heat dissipation.

When the filler contains alumina, boron nitride, aluminum nitride, sendust, or a combination thereof, the lower limit of the thermal conductivity of the fluororesin sheet 1 is preferably 0.6 W / m · K, preferably 1.0 W / m · K. K is more preferable. If the thermal conductivity of the fluororesin sheet 1 does not reach the above lower limit, the thermal conductivity may be insufficient. The "thermal conductivity" is a value measured by the laser flash method defined in JIS-R1611 (2010).

When the filler contains the above alumina, boron nitride, aluminum nitride, sendust, or a combination thereof, the heat dissipation can be further improved by combining the filler having a large average particle size and the filler having a small average particle size. In this case, the average particle size of the large filler is preferably 10 μm or more, and the average particle size of the small filler is preferably 5 μm or less.

The fluororesin sheet 1 may contain components (arbitrary components) other than the above-mentioned PTFE and the filler. Examples of this optional component include a dielectric property-imparting agent such as barium titanate and potassium titanate, a thermal conductivity-imparting agent, a linear expansion coefficient inhibitor, a flame retardant, a flame retardant aid, a pigment, an antioxidant, and a reflection-imparting agent. Examples include agents, hiding agents, lubricants, processing stabilizers, plasticizers, foaming agents and the like. As these, various known substances can be used, and the upper limit of the content of the arbitrary component is preferably 10% by mass, more preferably 1% by mass, based on the fluororesin sheet 1.

[Manufacturing method of fluororesin sheet]
The method for producing the fluororesin sheet is, for example, a step of producing a mixed powder of PTFE or modified PTFE powder and a filler (hereinafter, also referred to as a mixing step), and molding the mixed powder obtained in the above mixing step into a sheet. (Hereinafter, also referred to as a molding step), a step of firing the sheet-shaped molded product by heating above the melting point of PTFE or a modified PTFE (hereinafter, also referred to as a baking step), and a sheet-like molding after the baking step. It is preferable to have a step of cooling the product (hereinafter, also referred to as a cooling step). As described above, by producing the fluororesin sheet by the above-mentioned step, the content of the filler in the fluororesin sheet can be dramatically increased.

(Mixing process)
In the mixing step, a powder of PTFE or modified PTFE and a filler are mixed to prepare a mixed powder. In this step, first, the powder of PTFE or modified PTFE is mixed with the filler. The above-mentioned "PTFE or modified PTFE powder" is a powder composed of fine particles of PTFE or modified PTFE. The powder of PTFE or modified PTFE is, for example, a powder composed of fine particles of PTFE or modified PTFE, a fine powder of PTFE or modified PTFE produced by emulsion polymerization, or a PTFE or modified PTFE produced by suspension polymerization. Molding powder can be mentioned.

(Molding process)
In the molding step, the mixed powder obtained in the above mixing step is molded into a sheet. In this step, the mixed powder obtained in the above mixing step is used as a raw material and molded into a sheet to obtain a sheet-shaped molded product having a predetermined shape and size. First, a sheet-forming composition obtained by blending a fine powder of PTFE or modified PTFE with a liquid lubricant is kneaded, and then compression-molded and preformed into a primary molded body. Usually, the mass ratio of the liquid lubricant to PTFE or modified PTFE is preferably 0.1 or more and 10.0 or less, and preferably 0.3 or more and 5.0 or less. In the preforming, the sheet-forming composition is compression-molded at a pressure of, for example, about 10 kPa to 500 kPa to form a primary molded product such as a sheet. Specifically, the molded product obtained by preforming is extruded by a paste extruder, rolled by a calender roll or the like, or rolled after being extruded to form a sheet-like primary molding having a shape that can be stretched. Manufacture the body.

As the liquid lubricant, various known lubricants can be used. For example, petroleum-based solvents such as solvent naphtha and white oil, hydrocarbon oils such as nonan and undecane, aromatic hydrocarbons such as toluol and xylol, alcohols, ketones, esters, silicone oils and fluorochlorocarbon oils. , A solution in which a polymer such as polyisobutylene or polyisoprene is dissolved in these solvents, or a water or an aqueous solution containing a mixture thereof and a surfactant can be mentioned. In addition to the liquid lubricant, other substances may be added depending on the purpose.

The above molding process is usually performed near room temperature. After extrusion molding, the liquid lubricant is removed from the molded body. The liquid lubricant may be removed before the firing step, which will be described later, and may be removed after the stretching step, but it is more preferable to remove the liquid lubricant before the stretching step. The liquid lubricant is removed by heating, extraction, dissolution, or the like, and is preferably performed by heating.

(Baking process)
In the firing step, the sheet-shaped primary molded product is fired by heating above the melting point of PTFE or modified PTFE. In the firing step, the sheet-shaped molded product is heated to a temperature equal to or higher than the melting point of PTFE or modified PTFE to obtain a non-porous sheet-shaped molded product. Further, the heating temperature is preferably 450 ° C. or lower in order to suppress the decomposition and denaturation of the resin. The sheet-shaped molded product obtained by compacting the PTFE particles or the modified PTFE particles produced by emulsion polymerization or the like has pores or voids due to the gaps between the particles or the removal of the auxiliary agent, but the PTFE or modified PTFE powder is completely contained. By melting, these pores and voids disappear or the substantially continuous voids are minimized. As a result, a non-porous sheet-shaped molded product is produced.

(Cooling process)
After the firing step, it is preferable to perform a step of cooling the PTFE or the modified PTFE by slowly cooling it. In this way, the fluororesin sheet can be manufactured.

The fluororesin sheet can dramatically increase the filler content. As a result, the fluororesin sheet is excellent in sheet properties and moldability.

<Multi-layer sheet>
The multilayer sheet 10 shown in FIG. 2 is laminated between the fluororesin sheet 1, the conductive layer 2 laminated on both sides of the fluororesin sheet 1, and the fluororesin sheet 1 and the conductive layer 2, respectively. It is provided with a two-layer adhesive layer 4. Since the multilayer sheet contains the fluororesin sheet, the transmission loss in a high frequency signal is low, and the multilayer sheet can be suitably used as a printed wiring board for high frequency. In FIG. 2, the same elements as those of the fluororesin sheet of FIG. 1 are designated by the same reference numerals, and the duplicate description thereof will be omitted below.

[Conductive layer]
The conductive layer 2 is formed into a desired planar shape (pattern) by an existing method such as etching the conductive layer laminated on the outer surface of the fluororesin sheet 1 or printing with conductive ink. The conductive layer 2 can be formed of a material having conductivity, but from the viewpoint of further enhancing the transmission performance, the material used for the conductive layer 2 is preferably a foil such as copper, silver, or gold. Further, from the viewpoint of improving heat dissipation, the material used for the conductive layer 2 preferably has a thermal conductivity of 10 [W / m · k] or more, and specifically, stainless steel, iron, aluminum, silver, copper, etc. Foil is preferred. Further, conductive carbon can also be used as the conductive layer.

From the viewpoint of further enhancing transmission performance and heat dissipation, the average thickness of the total of the two conductive layers is preferably 2 μm or more and 30 μm or less.

[Adhesive layer]
The adhesive constituting the adhesive layer 3 is not particularly limited, but is a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer having high thermal fluidity. It is preferable to use (PFA) or a combination thereof. As described above, by including the above FEP and PFA as the adhesive, the adhesiveness to the fluororesin sheet and the conductive layer is excellent. Further, by including the above FEP and PFA as the adhesive, it is possible to obtain better transmission performance and reduce the temperature dependence of the transmission performance. It is presumed that this is because FEP and PFA have a small crystallinity, and the change in transmission performance due to a change in the crystal structure is small.

It is preferable that the adhesive contains 50% by mass or more of a tetrafluoroethylene-hexafluoropropylene copolymer (FEP), a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), or a combination thereof. By including FEP and PFA as the main components of the adhesive layer in this way, it is possible to obtain better transmission performance and reduce the temperature dependence of the transmission performance. It is presumed that this is because FEP and PFA have a small crystallinity, and the change in transmission performance due to a change in the crystal structure due to a temperature change is small.

The lower limit of the total average thickness of the two adhesive layers is preferably 0.1 μm, more preferably 2 μm. The upper limit of the total average thickness of the two adhesive layers is preferably 50 μm, more preferably 40 μm. If the total average thickness of the two adhesive layers is less than the above lower limit, the adhesive strength to the fluororesin sheet and the conductive layer may be insufficient. On the other hand, if the total average thickness of the two adhesive layers exceeds the above upper limit, the transmission performance, heat dissipation and electromagnetic wave shielding performance may deteriorate, the multilayer sheet may become unnecessarily thick, and linear expansion in the thickness direction may occur. The coefficient may increase, the temperature dependence of the dielectric constant may increase, and the through-hole plating may break after a heat cycle.

[Manufacturing method of multilayer sheet]
As a method for manufacturing the multilayer sheet, for example, a step of laminating a conductive layer on both side surfaces of a fluororesin sheet (hereinafter, also referred to as a conductive layer laminating step) is provided.

(Conductive layer laminating process)
In the conductive layer laminating step, as shown in FIG. 2, the conductive layer 2 having conductivity is laminated on both side surfaces of the fluororesin layer 1. As the material used for the conductive layer 2, as described above, foils such as copper, silver, gold, stainless steel, iron, aluminum, and conductive carbon can be used depending on the purpose.

As a method of laminating the conductive layer 2 in the conductive layer laminating step, for example, it can be formed by adhering a foil-shaped conductor to both sides of the fluororesin layer 1 using an adhesive. As the adhesive, the adhesive constituting the above-mentioned adhesive layer 3 can be used. As a method for laminating the adhesive layer 3, fusion of a resin film, resin coating, or the like can be used.

Since the multilayer sheet contains the fluororesin sheet, the transmission loss in a high frequency signal is low, and the multilayer sheet can be suitably used as a printed wiring board for high frequency. Further, since it is excellent in the effect of reducing the coefficient of linear expansion, heat dissipation, electromagnetic wave shielding performance, and economy, it can be suitably used as an electric wire, a bus bar, an electromagnetic wave shielding component, a heat radiating component, and a sliding component.

<Shield material>
The shield material includes the fluororesin sheet. The fluororesin sheet provided in the shielding material contains alumina, boron nitride, aluminum nitride or a combination thereof as the filler. Since the fluororesin sheet provided in the shield material contains alumina, boron nitride, aluminum nitride or a combination thereof as a filler, the shield material has good electromagnetic wave shielding performance.

[Other embodiments]
It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present disclosure is not limited to the configuration of the above embodiment, but is indicated by the scope of claims and is intended to include all modifications within the meaning and scope equivalent to the scope of claims. NS.

The fluororesin sheet may be a porous sheet having a fine hollow structure. Having a hollow structure can reduce the relative permittivity, so that transmission loss can be suppressed more effectively. Such a hollow structure can be obtained by stretching the sheet-shaped molded product after the molding step. In the stretching step, it is preferable to stretch in the axial direction and the circumferential direction. The size and shape of the pores of the fluororesin sheet can be adjusted by adjusting the stretching conditions such as the stretching temperature and the stretching rate. Hollow fillers can also be used.

Hereinafter, the present disclosure will be specifically described based on examples, but the present disclosure is not limited to these examples.

[Fluororesin sheet No. 1 to No. 10]
The PTFE powder or the mixed powder of the PFA powder and the filler having the mass ratio shown in Table 1 was mixed using a container rotary mixer to prepare a mixed powder (mixing step).

Next, the mixed powder obtained in the above mixing step was molded by a roll machine at a temperature of 50 ° C., and the molecules were entangled to promote fibrosis and molded into a sheet (molding step). Idemitsu nonane having the mass ratio shown in Table 1 was added as a liquid lubricant. The pressure during compression molding was 10 kPa.

Next, the sheet-shaped molded product was fired by heating (firing step). The firing temperature profile was 90 minutes at a temperature of 350 ° C. under the condition of a pressure of 4.9 MPa. Then, under the condition of the pressure of 4.9 MPa, the sheet-shaped molded product after the firing step was cooled to prepare a fluororesin sheet.

The resins and fillers used are as follows.
(Fluororesin)
(1) PTFE: Asahi Glass Co., Ltd. "CD141E", weight average molecular weight Mw 4 million (2) PTFE: Mitsui-Kemers Fluoro Products Co., Ltd. "F650J", weight average molecular weight Mw 20 million (3) PTFE: Daikin Co., Ltd. "Lubron L" -5 ”, Weight average molecular weight Mw 400,000 (4) PTFE: Daikin Corporation“ F181 ”, Weight average molecular weight Mw 7 million (5) PFA: Daikin Corporation“ AD-2CERR ”, Weight average molecular weight 400,000 (liquid crystal polymer)
"Vecstar CTQ-100" manufactured by Kuraray
(Filler)
(1) Silica: "SC2500-SQ" manufactured by Admatex, average particle size 0.5 μm
(2) Alumina: "AZ4-75" manufactured by Nittetsu Chemical & Materials Co., Ltd., average particle size 4 μm

[Multilayer sheet No. 11-No. 16]
No. 11, No. 12, No. 14-No. For No. 16, the fluororesin sheet No. 16 was used by using the resin, filler and liquid lubricant having the mass ratio shown in Table 2. A resin sheet was produced by the same procedure as in the production method of 2. No. The fluororesin sheet of No. 13 used a liquid crystal polymer as a resin and did not add a filler.

Next, the conductive layers shown in Table 2 were laminated on both sides of the resin sheet. Multi-layer sheet No. 11-No. 12 and No. 15-No. In No. 16, a conductive layer was laminated on both sides of the resin sheet via the adhesive layer shown in Table 2. In addition, the multilayer sheet No. 13-No. In No. 14, the conductive layer was laminated by hand laying up.

[Fluororesin sheet No. 17-No. 26]
No. 18-No. For No. 26, the fluororesin sheet No. 26 was prepared by using the resin, filler and liquid lubricant having the mass ratios shown in Table 3. A resin sheet was produced by the same procedure as in the production method of 2. No. No. 17 produced a resin sheet without adding a filler.

[Fluororesin sheet No. 27-No. 36]
No. 28-No. For 36, the fluororesin sheet No. 36 was used with the resin, filler and liquid lubricant having the mass ratio shown in Table 4. A resin sheet was produced by the same procedure as in the production method of 2. No. No. 27 produced a resin sheet without adding a filler.

[evaluation]
The above No. 1 to No. Ten fluororesin sheets were evaluated for tensile elongation, Asker A hardness, and sheet properties. The above No. 11-No. Tensile elongation, sheet properties, relative permittivity, transmission loss, change in dielectric constant, change in transmission loss, coefficient of linear expansion and peel strength were measured for 16 multilayer sheets. In addition, No. 17-No. With respect to the fluororesin sheet of No. 26, tensile elongation, sheet properties, volume resistivity and input signal attenuation were evaluated, and No. 27-No. Thirty-six fluororesin sheets were evaluated for tensile elongation, sheet properties, and heat dissipation.

(Asker A hardness)
Asker A hardness was measured based on JIS-K6253-3 (2012). Specifically, a test piece of a fluororesin sheet having a thickness of 1.0 mm was prepared, and the hardness was measured by a type A durometer.

(Sheet properties)
The sheet properties of the fluororesin sheet were evaluated on the basis that the sheet did not break due to its own weight or no holes were visually observed. It was judged to be good when the sheet did not break due to its own weight and no holes were visually observed.

(Relative permittivity)
The relative permittivity at 25 ° C. and 80 GHz was measured according to the measuring method specified in JIS-C-2138 (2007).

(Transmission loss)
Strip lines with various line lengths such as 100 mm were formed, and the transmission loss [dB / 0.1 m] at 25 ° C. and 80 GHz was measured using a network analyzer.

(Amount of change in permittivity)
Using a cylindrical cavity resonator (10 GHz), the rate of change in dielectric constant [%] from −40 ° C. to 120 ° C. was measured.

(Change in transmission loss)
Using a cylindrical cavity resonator (10 GHz), the amount of change in transmission loss [dB] from −40 ° C. to 120 ° C. was measured.

(Linear expansion coefficient)
The coefficient of linear expansion XY (planar direction) [ ^10-6 / K] and the coefficient of linear expansion Z (thickness direction) [ ^10-6 / K] are used for viscoelasticity measuring devices (for example, "DVA-220" manufactured by IT Measurement Control Co., Ltd.). ”), Calculated from the dimensional change of the multilayer sheet with respect to the temperature change under the conditions of the tensile mode, the temperature range of −55 ° C. to 210 ° C., the heating rate of 5 ° C./min, and the load of 5 gf (49.03 mN). ..
The linear expansion coefficient XY and the linear expansion coefficient Z are preferably 100 or less, more preferably 60 or less, still more preferably 20 or less.

(Peeling strength)
The peel strength [N / cm] was measured by a method according to JIS-K6854-2 (1999) "Adhesive-Peeling Adhesive Strength Test Method-2 Part: 180 Degree Peeling".
The peel strength is preferably 5.0 N / cm or more.

(Tensile elongation)
The tensile elongation was measured at a tensile speed of 50 mm / min at room temperature in accordance with JIS-K7161-1: 2014 "Plastic-How to determine tensile properties-Part 1: General rules".

(Volume resistivity)
The volume resistivity was measured according to JIS-C2139-3-1 (2018).

(Input signal attenuation)
The input signal attenuation [dB] in the range of 10 MHz to 100 MHz was measured using a current probe. The input signal attenuation was evaluated by calculating the difference between the input signal intensity to the probe when the fluororesin sheet was not arranged and the input signal intensity to the probe when each fluororesin sheet was arranged.

(Thermal conductivity)
It was measured by the laser flash method specified in JIS-R1611 (2010).

No. 1 to No. The evaluation results of the fluororesin sheet of No. 10 are shown in Table 1, and No. 11-No. Table 2 shows the evaluation results of the transmission performance of the 16 multilayer sheets. In addition, No. 17-No. The evaluation results of the fluororesin sheets of No. 26 are shown in Table 3, and No. 27-No. Table 4 shows the evaluation results of the 36 fluororesin sheets. In addition, "-" indicates that the corresponding component is not included.

From the results in Table 1, No. 1 in which the weight average molecular weight Mw of polytetrafluoroethylene is 1 million or more. 2-No. The fluororesin sheet of No. 7 contains no filler even though the filler content is high. Similar to No. 1, good sheet properties and elongation properties were obtained.
On the other hand, No. 1 in which the weight average molecular weight Mw of polytetrafluoroethylene is less than 1 million. 8 to No. The fluororesin sheet of No. 11 could not be produced.

From the results in Table 2, the fluororesin sheet using the fluororesin sheet having a weight average molecular weight Mw of polytetrafluoroethylene of 1 million or more and a mass ratio of the filler to the polytetrafluoroethylene of 1.0 or more was used. 11-No. 12 and No. 14-No. The 16 multilayer sheets obtained good transmission performance.
On the other hand, No. 1 in which a liquid crystal polymer was used as the resin and a fluororesin sheet to which no filler was added was used. The multi-layer sheet of 13 had very poor transmission performance. In addition, No. 1 containing polytetrafluoroethylene but not having an adhesive layer. The multi-layer sheet of 14 had a very low peel strength even though the compression press was performed.

From the results in Table 3, the weight average molecular weight Mw of polytetrafluoroethylene is 1 million or more, and the mass ratio of sendust or ferrite to the polytetrafluoroethylene is 1.0 or more. 18-No. 22 and No. 25-No. The fluororesin sheet of 26 was shown to have good conductivity and electromagnetic wave shielding performance. Further, No. 1 using a fluororesin sheet having a mass ratio of Ni-based ferrite or Mn-based ferrite filler to the above polytetrafluoroethylene of 1.0 or more. 23-No. 24 was also shown to have good electromagnetic shielding performance.
On the other hand, No. which does not contain a filler. 17 was inferior in conductivity and electromagnetic wave shielding performance.

From the results in Table 4, the fluororesin sheet has a weight average molecular weight Mw of polytetrafluoroethylene of 1 million or more, and the mass ratio of alumina, boron nitride, aluminum nitride, and sentust to the polytetrafluoroethylene is 1.0 or more. No. using No. 28-No. No. The fluororesin sheet of 36 was shown to have good heat dissipation.
On the other hand, No. which does not contain a filler. 27 was inferior in heat dissipation.

As described above, the fluororesin sheet can dramatically increase the filler content. Therefore, the multilayer sheet provided with the fluororesin sheet can effectively reduce the transmission loss in the high frequency signal, and can be suitably used as a double-sided printed wiring board for high frequency. In addition, the fluororesin sheet has excellent performance such as moldability, conductivity, electromagnetic wave shielding, and heat dissipation.

1 Fluororesin sheet 2 Conductive layer 3 Adhesive layer 10 Multilayer sheet

Claims (10)

1. Contains polytetrafluoroethylene and filler,
   The weight average molecular weight Mw of the above polytetrafluoroethylene is 1 million or more.
   The mass ratio of the filler to the polytetrafluoroethylene is 1.0 or more, and the mass ratio is 1.0 or more.
   Fluororesin sheet with a tensile elongation of 50% or more.
2. The fluororesin sheet according to claim 1, which has an Asker A hardness of 20 or more.
3. The fluororesin sheet according to claim 1 or 2, wherein the filler contains silica, titanium oxide, alumina, forsterite, or a combination thereof.
4. The filler contains silica and
   The fluororesin sheet according to claim 3, wherein the mass ratio of the silica to the polytetrafluoroethylene is 1.0 or more and 2.0 or less.
5. The fluororesin sheet according to any one of claims 1 to 4, wherein the filler contains a ferrite, a sendust, a conductive filler, or a combination thereof.
6. The fluororesin sheet according to any one of claims 1 to 5, wherein the filler contains ferrite, sendust, or a combination thereof.
7. The fluororesin sheet according to any one of claims 1 to 6, wherein the filler contains alumina, boron nitride, aluminum nitride, sendust, or a combination thereof.
8. The fluororesin sheet according to any one of claims 1 to 7.
   The conductive layers laminated on both sides of the fluororesin sheet and
   A multilayer sheet provided with an adhesive layer laminated between the fluororesin sheet and the conductive layer.
9. The multilayer sheet according to claim 8, wherein the total average thickness of the adhesive layers is 0.1 μm or more and 50 μm or less.
10. A shield material provided with the fluororesin sheet according to claim 6.
    

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