JP2024055769A - Composition, fluororesin sheet and method for producing same - Google Patents

Abstract

The present invention provides a composition for obtaining a fluororesin sheet having excellent performance in terms of low dielectric constant, low loss, and low thermal expansion, a fluororesin sheet, and a method for producing the same.
The composition includes a fluororesin and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035.
[Selection diagram] None

Description

This disclosure relates to a composition, a fluororesin sheet, and a method for producing the same.

There is a demand for high-frequency printed wiring boards with low transmission loss. It is known that fluororesin films are used in such high-frequency printed wiring boards (Patent Document 1, etc.). In addition, Patent Documents 2 and 3 describe the use of fluororesin containing filler as a wiring board material.

Furthermore, Patent Document 4 discloses that a fluororesin composition in which spherical silica particles are blended with a fluororesin is used for circuit boards.

Patent Publication No. 2015-8260 Japanese Patent Application Laid-Open No. 63-259907 Special table 2022-510017 International Publication No. 2020/145133

The present disclosure aims to provide a composition for obtaining a fluororesin sheet having excellent performance in terms of low dielectric constant, low loss, and low thermal expansion, a thin fluororesin sheet, and a method for producing the same.

The present disclosure relates to
The composition is characterized by comprising a fluororesin and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035.
The fluororesin is preferably a polytetrafluoroethylene resin.
The fluororesin is preferably non-melt moldable.

The polytetrafluoroethylene resin preferably has an SSG of 2.0 to 2.3.
The polytetrafluoroethylene resin preferably has a refractive index of 1.2 to 1.6.
The fluororesin preferably has a primary particle size of 0.05 to 10 μm.
The fluororesin preferably has a volume-based cumulative 50% diameter of 0.05 to 40 μm.

The filler is preferably silica particles.
The content of the filler in the total amount of the composition is preferably 50 wt % or more.
The filler preferably has an average particle size of 0.5 to 250 μm.
The above filler is preferably one whose surface is coated with a silane coupling agent.
The composition preferably has a dielectric loss tangent value at 10 GHz of 0.0015 or less.

The present disclosure also provides a fluororesin sheet comprising a composition containing a fluororesin and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035.
The fluororesin sheet preferably has a thickness of 5 to 250 μm.

The present disclosure also relates to a method for producing the above-mentioned fluororesin sheet, which is characterized by having a step of mixing fluororesin particles and a filler to form a film.
In the above-mentioned production method, it is preferable to form a film by mixing only the fluororesin particles and the inorganic filler, without adding any other components.

The present disclosure also relates to a copper clad laminate having a copper foil and the above-mentioned fluororesin film as essential layers.
The present disclosure also relates to a circuit board comprising the above-mentioned copper clad laminate.

The fluororesin sheet obtained from the composition of the present disclosure has excellent performance in terms of low dielectric constant, low loss, and low thermal expansion. In addition, the sheet can be made thin.

The present disclosure will be described in detail below.
Many studies have been conducted on compositions in which a filler is blended with a fluororesin. Meanwhile, in the field of high-frequency printed wiring boards, increasingly high levels of performance, such as low dielectric constant, low loss, and low expansion, have been required in recent years. However, there has not been sufficient research into achieving such high levels of low dielectric constant, low loss, and low expansion.

The objective of this disclosure is to provide a composition for obtaining a fluororesin sheet with unprecedentedly high levels of low dielectric constant, low loss, and low expansion.

(Filler)
The composition of the present disclosure is characterized by comprising a fluororesin and a filler, and having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00035 to 0.00001. In other words, the composition is characterized by using a filler that satisfies the above-mentioned specific parameters.

The dielectric tangent of the filler is greatly affected by the polar functional groups on the surface. For example, in the case of silica, the amount of Si-OH groups on the surface affects the dielectric tangent. More specifically, the greater the amount of Si-OH groups on the surface, the greater the dielectric tangent of the filler. For this reason, in the present disclosure, it is preferable to reduce the amount of Si-OH on the surface.

From this viewpoint, the ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler ( ^m2 /g)) is an index showing the amount of surface polar functional groups per unit surface area of the filler. The present inventors have found that when the amount of such surface polar functional groups is reduced to within the above-mentioned specified range, a fluororesin sheet having particularly excellent low dielectric constant, low loss and low expansion can be obtained, and have completed the present disclosure.

In order to obtain a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler ( ^m2 /g)) within the above-mentioned range, in addition to selecting the filler to be used, it is necessary to perform a surface treatment. That is, the polar functional groups present on the filler surface are reacted by the surface treatment to reduce the amount of the polar functional groups, thereby making it possible to obtain a filler within the above-mentioned range. Such surface treatments will be described in detail below.

The upper limit of the above-mentioned (dielectric loss tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) is more preferably 0.00030, and further preferably 0.00025.

In this disclosure, the dielectric loss tangent of the filler measured at 10 GHz was measured using a cylindrical cavity resonator and a network analyzer by filling a filler powder sample into a quartz tube and loading it into the resonator. The characteristics of the resonator (resonant frequency and Q value) were obtained before and after inserting the sample, and the dielectric loss tangent was calculated from the results. This measurement method complies with the Japanese Industrial Standard JIS 2565 Microwave Ferrite Core Test Method, and measurements were performed in an environment with a room temperature of 25°C and a humidity of 40%.

In the present disclosure, the dielectric tangent of the filler measured at 10 GHz is not particularly limited, but is preferably 0.0015 or less. This value is preferable in that the fluororesin sheet has low loss. The upper limit is more preferably 0.0025, and even more preferably 0.002.

In the present disclosure, the surface area (m ² /g) of the filler is not particularly limited, but is preferably 1 to 10. By setting it within the above range, it is preferable in that the fluororesin sheet has a good balance between low loss and low linear expansion. The lower limit is more preferably 1.2, and even more preferably 1.5. The upper limit is more preferably 9, and even more preferably 7.

In the present disclosure, the surface area (m ² /g) of the filler is a value based on the BET method, and can be measured using a specific surface area measuring device such as "Macsorb HM model-1208" (manufactured by MACSORB Co., Ltd.). When the fluororesin sheet of the present disclosure contains two or more types of fillers, the surface area measured for the entire blended fillers falls within the above-mentioned range.

In the present disclosure, the filler preferably has an average particle size of 0.5 to 250 μm. The average particle size here is the D50 value measured by a laser analysis particle size distribution analyzer.
If the average particle size is less than 0.5 μm, the filler will aggregate, making it difficult to obtain a sufficient effect, which is undesirable.

The filler that can be used in the present disclosure is not particularly limited, and examples thereof include organic fillers that are one or more selected from aramid fibers, polyphenyl esters, polyphenylene sulfide, polyimides, polyether ether ketones, polyphenylenes, polyamides, and wholly aromatic polyester resins, and inorganic fillers that are one or more selected from ceramics, talc, mica, aluminum oxide, zinc oxide, tin oxide, titanium oxide, silicon oxide, calcium carbonate, calcium oxide, magnesium oxide, potassium titanate, glass fibers, glass chips, glass beads, silicon carbide, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers. Two or more of these may be used in combination.

The filler is not particularly limited in shape, but it is particularly preferred that it be spherical. A spherical shape is preferred because it is easier to process uniformly during drilling, has a small specific surface area, and has low transmission loss.

Of these, it is particularly preferable to use silica, and it is most preferable to use spherical silica particles.

The spherical silica particles mentioned above refer to particles whose particle shape is close to a perfect sphere. Specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.95 or more. The sphericity is calculated by taking a photograph with an SEM and calculating the value from the area and perimeter of the particle observed, as follows: (sphericity) = {4π x (area) ÷ (perimeter)2}. The closer to 1, the closer to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Corporation: FPIA-3000) is used.

The spherical silica particles used in this disclosure preferably have a D90/D10 of 2 or more (preferably 2.3 or more, 2.5 or more) and a D50 of 10 μm or less when the volume is accumulated from the smallest particle size. Furthermore, it is preferable that the D90/D50 is 1.5 or more (more preferably 1.6 or more). It is preferable that the D50/D10 is 1.5 or more (more preferably 1.6 or more). It is more preferable that the D50 is 5 μm or less. Since the small particle size spherical silica particles can enter the gaps between the large particle size spherical silica particles, it is possible to achieve excellent filling properties and high fluidity. In particular, it is preferable that the particle size distribution has a higher frequency on the small particle size side compared to a Gaussian curve. The particle size can be measured by a laser diffraction scattering type particle size distribution measuring device. In addition, since coarse particles make it difficult to form a thin sheet, it is preferable that the coarse particles having a particle size of a certain size or more have been removed by a filter or the like.

The above-mentioned spherical silica particles preferably have a water absorption of 1.0% or less, and more preferably 0.5% or less. The water absorption is based on the mass of the silica particles when dry. The water absorption is measured by leaving a dry sample at 40°C and 80% RH for 1 hour, and measuring and calculating the water generated by heating at 200°C using a Karl Fischer moisture meter.

The spherical silica particles can also be measured using the above-mentioned methods after the fluororesin sheet is heated in an air atmosphere at 600°C for 30 minutes to burn off the fluororesin and extract the spherical silica particles.

The silica particles are surface-treated. By performing the surface treatment in advance, the aggregation of the silica particles can be suppressed, and the silica particles can be well dispersed in the resin composition. In addition, it is also preferable that the ratio of the dielectric loss tangent of the filler measured at 10 GHz to the surface area of the filler (m ² /g) can be set within a predetermined range.

The above surface treatment can be carried out by appropriately selecting the type and amount of surface treatment agent so that the ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler ( ^m2 /g)) can be within a predetermined range.

The above surface treatment is not particularly limited, and any known treatment can be used. Specific examples include treatment with a silane coupling agent such as epoxy silane, amino silane, isocyanate silane, vinyl silane, acrylic silane, hydrophobic alkyl silane, phenyl silane, and fluorinated alkyl silane having a reactive functional group, plasma treatment, and fluorination treatment.

Examples of the silane coupling agent include epoxy silanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino silanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, isocyanate silanes such as 3-isocyanatepropyltrimethoxysilane, vinyl silanes such as vinyltrimethoxysilane, and acrylic silanes such as acryloxytrimethoxysilane.

The spherical silica particles may be commercially available silica particles that satisfy the above-mentioned properties. Examples of commercially available silica particles include Denka Fused Silica FB Grade (manufactured by Denka Company Ltd.), Denka Fused Silica SFP Grade (manufactured by Denka Company Ltd.), Exelica (manufactured by Tokuyama Corporation), high-purity synthetic spherical silica particles Admafine (manufactured by Admatechs Co., Ltd.), Admanano (manufactured by Admatechs Co., Ltd.), Admafuse (manufactured by Admatechs Co., Ltd.), etc.

The value of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) can be adjusted by the shape of the filler, the size of the filler, the presence or absence of surface treatment, and the like. More specifically, it is preferable to use the spherical silica particles of a predetermined size as the above-mentioned, and further to subject them to surface treatment. The type of surface treatment agent when performing surface treatment also affects the above parameters. More specifically, it is particularly preferable to perform surface treatment with aminopropyltriethoxysilane, aminosilane, vinylsilane, hydrophobic alkylsilane, phenylsilane, 3-mercaptopropylsilane, 3-acryloxypropylsilane, 3-methacryloxypropylsilane, p-styrylsilane, silylpropylsuccinic anhydride, 3-isocyanatopropylsilane, 2-(3,4-epoxycyclohexyl)ethylsilane, or the like. By performing surface treatment with these silane coupling agents, the polar functional groups present on the filler surface react, and the amount of polar functional groups is reduced, resulting in excellent electrical properties.

The filler is preferably contained in a proportion of 50% by weight or more relative to the sheet weight. This amount is preferable in that it provides low thermal expansion while maintaining a low dielectric constant and low loss. The amount is more preferably 53% by weight or more, and even more preferably 56% by weight or more. There is no particular upper limit to the amount of filler contained, but it is preferably 68% by weight or less, and even more preferably 65% by weight or less.

(Fluorine resin)
The composition of the present disclosure contains a fluororesin. Since fluororesin has low dielectric properties, it can be suitably used for the purpose of the present disclosure.

The fluororesin that can be used in the present disclosure is not particularly limited, but examples thereof include polytetrafluoroethylene (PTFE), tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] copolymer [FEP], TFE/alkyl vinyl ether copolymer [PFA], TFE/HFP/alkyl vinyl ether copolymer [EPA], TFE/chlorotrifluoroethylene [CTFE] copolymer, TFE/ethylene copolymer [ETFE], polyvinylidene fluoride [PVdF], and tetrafluoroethylene with a molecular weight of 300,000 or less [LMW-PTFE]. One type may be used, or two or more types may be mixed. From the viewpoint of low dielectric properties, polytetrafluoroethylene resin (PTFE) is particularly preferable. PTFE having fibrillation properties is preferable. PTFE having fibrillation properties means PTFE that can be paste-extruded from unsintered polymer powder.

PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or a mixture of modified PTFE and homoPTFE. In addition, the content of modified PTFE in the polymer PTFE is preferably 10% by weight or more and 98% by weight or less, more preferably 50% by weight or more and 95% by weight or less, from the viewpoint of maintaining good moldability of polytetrafluoroethylene. The homo-PTFE is not particularly limited, and homo-PTFE disclosed in JP-A-53-60979, JP-A-57-135, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007/046345 pamphlet, WO 2007/119829 pamphlet, WO 2009/001894 pamphlet, WO 2010/113950 pamphlet, WO 2013/027850 pamphlet, etc. can be suitably used. Among these, homo-PTFE having high stretchability and disclosed in JP-A-57-135, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007/046345, WO 2007/119829, WO 2010/113950, etc. is preferred.

Modified PTFE is composed of TFE and a monomer other than TFE (hereinafter referred to as modified monomer). Modified PTFE includes, but is not limited to, those uniformly modified with modified monomer, those modified at the beginning of the polymerization reaction, and those modified at the end of the polymerization reaction. The modified PTFE is preferably a TFE copolymer obtained by subjecting TFE to polymerization together with a small amount of a monomer other than TFE, within a range that does not significantly impair the properties of the TFE homopolymer. The modified PTFE may be, for example, those disclosed in JP-A-60-42446, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-64-1711, JP-A-2-261810, JP-A-11-240917, JP-A-11-240918, WO 2003/033555 pamphlet, WO 2005/061567 pamphlet, WO 2007/005361 pamphlet, WO 2011/055824 pamphlet, WO 2013/027850 pamphlet, etc., which can be suitably used. Among these, modified PTFEs having high stretchability and disclosed in JP-A-61-16907, JP-A-62-104816, JP-A-64-1711, JP-A-11-240917, WO 2003/033555, WO 2005/061567, WO 2007/005361, WO 2011/055824, etc. are preferred.

The modified PTFE contains TFE units based on TFE and modified monomer units based on modified monomers. The modified monomer units are a part of the molecular structure of the modified PTFE that is derived from the modified monomer. The modified PTFE preferably contains modified monomer units in an amount of 0.001 to 0.500% by weight, and more preferably 0.01 to 0.30% by weight, of the total monomer units. The total monomer units are the part derived from all monomers in the molecular structure of the modified PTFE.

The modified monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP); chlorofluoroolefins such as chlorotrifluoroethylene (CTFE); hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF); perfluorovinyl ether; perfluoroalkylethylene (PFAE), ethylene, etc. The modified monomer used may be one type or multiple types.

The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorounsaturated compounds represented by the following general formula (1).
CF ₂ ═CF-ORf (1)

In the formula, Rf represents a perfluoro organic group.

In this specification, a perfluoro organic group is an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoro organic group may have an ether oxygen.

The perfluorovinyl ether may, for example, be perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (1) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group. Preferred examples of PAVE include perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

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

The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE and ethylene.

The above fluororesin is preferably not melt moldable. "Not melt moldable" means that the resin does not have sufficient fluidity even when heated above its melting point, and cannot be molded by the melt molding techniques commonly used for resins. PTFE falls into this category.

In the present disclosure, it is preferable to use such a fluororesin that cannot be melt molded, and to make it into a fluororesin sheet by a molding method that fibrillates it. The molding method will be described later.

The PTFE preferably has an SSG of 2.0 to 2.3. When such PTFE is used, it is easy to obtain a PTFE membrane with high strength (cohesion and puncture strength per unit thickness). PTFE with a large molecular weight has long molecular chains, so it is difficult to form a structure in which the molecular chains are regularly arranged. In this case, the length of the amorphous part increases, and the degree of entanglement between molecules increases. When the degree of entanglement between molecules is high, the PTFE membrane is unlikely to deform under an applied load and is thought to exhibit excellent mechanical strength. In addition, when PTFE with a large molecular weight is used, it is easy to obtain a PTFE membrane with a small average pore size.

The lower limit of the SSG is preferably 2.05, and more preferably 2.1. The upper limit of the SSG is preferably 2.25, and more preferably 2.2.

Standard specific gravity [SSG] was measured by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the resulting sample using the water displacement method.

In this embodiment, the molecular weight (number average molecular weight) of the PTFE constituting the PTFE powder is, for example, in the range of 2 to 12 million. The lower limit of the molecular weight of PTFE may be 3 million or 4 million. The upper limit of the molecular weight of PTFE may be 10 million.

The number average molecular weight of PTFE can be measured by determining it from the standard specific gravity, or by measuring it from dynamic viscoelasticity when melted. The method of determining it from the standard specific gravity can be carried out by using a sample molded in accordance with ASTM D-4895 98 and the water displacement method in accordance with ASTM D-792. The method of measuring it from dynamic viscoelasticity is explained, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538 and the same reference, 1989, Vol. 29, 273.

The PTFE preferably has a refractive index in the range of 1.2 to 1.6. Having such a refractive index is preferable in terms of low dielectric constant. The refractive index can be adjusted to be within the above range by adjusting the polarizability or flexibility of the main chain. The lower limit of the refractive index is more preferably 1.25, more preferably 1.30, and most preferably 1.32. The upper limit of the refractive index is more preferably 1.55, more preferably 1.50, and most preferably 1.45.

The refractive indexes above were measured using a refractometer (Abbemat 300).

Furthermore, it is preferable that the maximum endothermic peak temperature (crystalline melting point) of the above PTFE is 340±7°C.

The PTFE may be low-melting-point PTFE, which has a maximum peak temperature of 338°C or less on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter, or high-melting-point PTFE, which has a maximum peak temperature of 342°C or more on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter.

The low melting point PTFE is a powder produced by polymerization using an emulsion polymerization method, and has the above-mentioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.08 to 2.2, and a dielectric tangent (tan δ) of 1.9×10 ⁻⁴ to 4.0×10 ⁻⁴ . Commercially available products include Polyflon Fine Powder F201, F203, F205, F301, and F302 manufactured by Daikin Industries, Ltd.; CD090 and CD076 manufactured by Asahi Glass Industry Co., Ltd.; and TF6C, TF62, and TF40 manufactured by DuPont.

The high melting point PTFE powder is also a powder produced by polymerization using an emulsion polymerization method, and has the above-mentioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.0 to 2.1, and a dielectric tangent (tan δ) of 1.6×10 ⁻⁴ to 2.2×10 ⁻⁴ , which are generally low. Commercially available products include Polyflon Fine Powder F104 and F106 manufactured by Daikin Industries, Ltd., CD1, CD141, and CD123 manufactured by Asahi Glass Co., Ltd., and TF6 and TF65 manufactured by DuPont.

The average particle size of the powder formed by secondary aggregation of both PTFE polymer particles is usually preferably 250 to 2000 μm. In particular, granulated powder obtained by granulation using a solvent is preferred because it improves fluidity when filling a mold during preforming.

Powdered PTFE that satisfies the above-mentioned parameters can be obtained by conventional manufacturing methods. For example, it can be manufactured by following the manufacturing methods described in International Publication No. 2015-080291 and International Publication No. 2012-086710.

(Composition)
The composition of the present disclosure contains the above-mentioned filler and fluororesin. If necessary, it may contain components other than the filler and fluororesin, or may consist of only the filler and fluororesin. The content of components other than the filler and fluororesin is preferably 10% by weight or less.

The composition of the present disclosure preferably has a filler content of 70% by weight or less relative to the total amount of the composition. By including the filler in such a range, the linear expansion coefficient can be lowered, which is preferable in that the composition is easy to mold. The lower limit of the amount of the filler is not particularly limited, but is preferably 40% by weight from the viewpoint of lowering the linear expansion coefficient. The upper limit is more preferably 68% by weight, and even more preferably 65% by weight. The lower limit is more preferably 40% by weight, and even more preferably 45% by weight.

The composition of the present disclosure preferably has a dielectric tangent of 0.0001 to 0.0015 at 10 GHz. Having the dielectric tangent within this range is preferable in that it results in low loss.

Furthermore, the composition of the present disclosure may have a dielectric loss tangent of 0.0001 to 0.0018 at 80 GHz as a composition. It is preferable that the composition has a low dielectric loss tangent over such a wide frequency range, resulting in low loss. In addition, a low dielectric loss tangent at 80 GHz is preferable because it improves the gain of the millimeter wave antenna.

(Fluororesin sheet)
The fluororesin sheet of the present disclosure contains a fluororesin and a filler in which the ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) is 0.00001 to 0.00035.
The fluororesin sheet is preferably less than 300 μm. Even if the fluororesin sheet of the present disclosure is thin, it can fully achieve its purpose. From this viewpoint, it is more preferably less than 200 μm, and even more preferably less than 150 μm. In addition, if it can be processed to a thickness of 100 μm or less as necessary, it can be widely applied to substrates of various thicknesses, which is preferable.

The fluororesin sheet of the present disclosure preferably has a linear expansion coefficient of 10 to 100 (ppm/°C). The above range is preferable in that the fluororesin sheet has low shrinkage and excellent dimensional stability. The upper limit is more preferably 90, and even more preferably 80. The lower limit is more preferably 12, and even more preferably 15. The linear expansion coefficient in this specification was determined by performing TMA measurement in tension mode using a TMA-7100 (manufactured by Hitachi High-Tech Science Corporation), using a sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm as a sample piece, setting the chuck distance to 10 mm, and applying a load of 49 mN at a heating rate of 2°C/min from the displacement of the sample at -10 to 160°C.

The fluororesin sheet of the present disclosure preferably has a rate of change in relative dielectric constant in the temperature range of -50 to 150°C of 0.025 or less, more preferably 0.023 or less, and even more preferably 0.021 or less. If it is within such a range, there is little change in electrical properties due to temperature, which is preferable in that stable performance can be obtained when used in high-frequency printed circuit boards.

(Method of manufacturing fluororesin sheet)
The fluororesin sheet of the present disclosure can be obtained by mixing the above-mentioned fluororesin particles and a filler and forming a film. The manufacturing method is not limited, but can be paste extrusion molding, powder rolling molding, etc.

As described above, it is preferable to use a fluororesin that cannot be melt molded as the fluororesin used in the fluororesin sheet of the present disclosure. When using such a fluororesin, if it is to be molded into a sheet, it is preferable to mold it by fibrillating powdered PTFE as a raw material.

The powdered PTFE preferably has a primary particle size of 0.05 to 10 μm. Using such a powder has the advantage of excellent moldability and dispersibility. The primary particle size here is a value measured in accordance with ASTM D 4895.

The powdered PTFE preferably contains 50% by mass or more, and more preferably 80% by mass or more, of polytetrafluoroethylene resin having a secondary particle diameter of 500 μm or more. By having PTFE having a secondary particle diameter of 500 μm or more within this range, it is advantageous in that a composite sheet with high strength can be produced. By using PTFE having a secondary particle diameter of 500 μm or more, a composite sheet with lower resistance and excellent toughness can be obtained.

The lower limit of the secondary particle diameter is more preferably 300 μm, and even more preferably 350 μm. The upper limit of the secondary particle diameter is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle diameter can be determined, for example, by a sieving method.

The powdered PTFE preferably has an average primary particle diameter of 50 nm or more, since this allows the production of a fluororesin sheet with higher strength and excellent homogeneity. More preferably, it is 100 nm or more, even more preferably 150 nm or more, and particularly preferably 200 nm or more. The larger the average primary particle diameter of PTFE, the more suppressed the increase in paste extrusion pressure when the powder is used for paste extrusion molding, and the more excellent the moldability. There is no particular upper limit, but it may be 500 nm. From the viewpoint of productivity in the polymerization process, it is preferable that it is 350 nm.

The above average primary particle diameter can be determined by preparing a calibration curve between the transmittance of 550 nm projected light per unit length of an aqueous dispersion of PTFE obtained by polymerization, in which the polymer concentration has been adjusted to 0.22% by mass, and the average primary particle diameter determined by measuring the unidirectional diameter in a transmission electron microscope photograph, and then measuring the transmittance for the aqueous dispersion to be measured, and then based on the calibration curve.

The PTFE used in the present disclosure may have a core-shell structure. Examples of PTFE having a core-shell structure include modified polytetrafluoroethylene, which contains a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene in the particles. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in JP-A-2005-527652.

The specific methods for paste extrusion molding and powder rolling molding are not particularly limited, but the general methods are described below.

(Paste extrusion molding)
The method for producing the sheet may include the steps of: (1a) mixing the PTFE powder obtained by using a hydrocarbon surfactant with an extrusion aid; (1b) paste-extrusion molding the mixture; (1c) rolling the extrudate obtained by extrusion; (1d) drying the sheet after rolling; and (1e) firing the sheet after drying to obtain a molded product. The paste extrusion molding may also be performed by adding conventionally known additives such as pigments and fillers to the PTFE powder.

The extrusion aid is not particularly limited, and any commonly known extrusion aid can be used. For example, hydrocarbon oils can be used.

(Powder rolling molding)
The sheet can also be formed by powder rolling. Powder rolling is a method of applying a shear force to resin powder to fibrillate it and form it into a sheet. The method may then include a step of sintering the powder to obtain a molded product. More specifically,
A step (1) of applying a shear force to a raw material composition containing a fluororesin and a filler while mixing the raw material composition.
a step (2) of forming the mixture obtained in the step (1) into a bulk form, and a step (3) of rolling the bulk form of the mixture obtained in the step (2) into a sheet form.
When a sheet is formed by such powder rolling molding, it is preferable to mix only the fluororesin particles and the inorganic filler and mold the mixture.

(Laminate)
The sheet-shaped resin composition of the present disclosure can be used by laminating it with other substrates as a sheet for printed wiring boards.

The present disclosure also relates to a copper-clad laminate characterized by having copper foil adhered to one or both sides of the above-mentioned fluororesin film. As described above, the film containing the fluororesin of the present disclosure is particularly suitable for use in printed wiring board applications, and therefore can be suitably used as such a copper-clad laminate.

The copper foil preferably has an Rz of 1.6 μm or less. That is, the fluororesin composition of the present disclosure has excellent adhesion to copper foil with a high smoothness of Rz of 1.6 μm or less. Furthermore, the copper foil only needs to have a surface that is adhered to the above-mentioned fluororesin film of 1.6 μm or less, and the Rz value of the other surface is not particularly limited. The Rz is the sum of the highest part (maximum peak height: Rp) and the deepest part (maximum valley depth: Rv). The surface roughness is the ten-point average roughness defined in JIS-B0601. In this specification, the Rz is a value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

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

The copper foil is not particularly limited, and specific examples include rolled copper foil and electrolytic copper foil.

There are no particular limitations on the copper foil with an Rz of 1.6 μm or less, and commercially available products can be used. Examples of commercially available copper foil with an Rz of 1.6 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm/Rz 0.85 μm) (manufactured by Fukuda Metal Foil and Powder Co., Ltd.).

The copper foil may be surface-treated to increase the adhesive strength with the fluororesin film of the present disclosure.

The above surface treatment is not particularly limited, but may be a silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, etc. The reactive functional group of the silane coupling agent is not particularly limited, but from the viewpoint of adhesion to the resin substrate, it is preferable that the reactive functional group has at least one selected from an amino group, a (meth)acrylic group, a mercapto group, and an epoxy group at the end. In addition, the hydrolyzable group is not particularly limited, but may be an alkoxy group such as a methoxy group or an ethoxy group. The copper foil used in the present disclosure may have an anti-rust layer (such as an oxide film such as chromate), a heat-resistant layer, etc. formed thereon.

A surface-treated copper foil having a surface treatment layer of the above-mentioned silane compound on the copper foil surface can be produced by preparing a solution containing the silane compound and then surface treating the copper foil with this solution.

The copper foil may have a roughening treatment layer on the surface thereof from the viewpoint of improving adhesion to a resin substrate.
In addition, if there is a risk that the roughening treatment will degrade the performance required in the present disclosure, the amount of roughening particles electrodeposited on the copper foil surface can be reduced as necessary, or the roughening treatment can be omitted.

In order to improve various properties, one or more layers selected from the group consisting of a heat-resistant layer, a rust-proofing layer, and a chromate-treated layer may be provided between the copper foil and the surface treatment layer. These layers may be a single layer or multiple layers.

The copper-clad laminate of the present disclosure may further include layers other than the copper foil and the fluororesin film.
The layers other than the copper foil and the fluororesin film are preferably at least one selected from the group consisting of polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene.

The layers other than the copper foil and the fluororesin film are not particularly limited as long as they are made of the above-mentioned resins. In addition, it is preferable that the layers other than the copper foil and the fluororesin film have a thickness in the range of 12.5 to 260 μm.

In the copper-clad laminate of the present disclosure, the copper layer may be formed on one or both sides of the roll film. Methods for forming the copper layer include laminating (adhering) copper foil to the surface of the roll film, vapor deposition, plating, and the like. Methods for laminating copper foil include a method using heat pressing. The heat pressing temperature may be from the melting point of the dielectric film -150°C to the melting point of the dielectric film +40°C. The heat pressing time is, for example, 1 to 30 minutes. The plate can be manufactured using a method in which the heat pressing pressure is 0.1 to 10 MPa.

The copper clad laminate of the present disclosure is used as a circuit board without any particular limitations on its application. A printed circuit board is a plate-shaped component for electrically connecting electronic components such as semiconductors and capacitor chips while at the same time arranging and fixing them in a limited space. There are no particular limitations on the configuration of the printed circuit board formed from the present copper clad laminate. The printed circuit board may be any of a rigid board, a flexible board, and a rigid-flexible board. The printed circuit board may be any of a single-sided board, a board, a double-sided board, and a multilayer board (such as a pulled-up board). In particular, it can be suitably used for flexible boards and rigid boards. In particular, it can be suitably used as a printed circuit board for high frequencies of 10 GHz or more.

The circuit board is not particularly limited, and can be manufactured by a general method using the copper-clad laminate described above.

The laminate for the circuit board is also a laminate characterized by having a copper foil layer, the above-mentioned fluororesin film, and a substrate layer. The substrate layer is not particularly limited, but preferably has a fabric layer made of glass fiber and a resin film layer.

The fabric layer made of glass fibers is a layer made of glass cloth, glass nonwoven fabric, or the like.
The glass cloth may be commercially available, and is preferably treated with a silane coupling agent to enhance affinity with the fluororesin. The glass cloth may be made of E glass, C glass, A glass, S glass, D glass, NE glass, low dielectric constant glass, etc., and is preferably made of E glass, S glass, or NE glass because of its easy availability. The fiber may be woven in either plain or twill weave. The thickness of the glass cloth is usually 5 to 90 μm, preferably 10 to 75 μm, but it is preferable to use a glass cloth thinner than the fluororesin film to be used.

The laminate may use a glass nonwoven fabric as a fabric layer made of glass fibers. The glass nonwoven fabric is a fabric in which short glass fibers are fixed with a small amount of a binder compound (resin or inorganic substance), or a fabric in which the shape is maintained by entangling short glass fibers without using a binder compound, and a commercially available product can be used. The diameter of the short glass fibers is preferably 0.5 to 30 μm, and the fiber length is preferably 5 to 30 mm.
Specific examples of the binder compound include resins such as epoxy resins, acrylic resins, cellulose, polyvinyl alcohol, and fluororesins, and inorganic substances such as silica compounds. The amount of the binder compound used is usually 3 to 15% by mass based on the glass short fibers. Examples of the material of the glass short fibers include E glass, C glass, A glass, S glass, D glass, NE glass, and low dielectric constant glass. The thickness of the glass nonwoven fabric is usually 50 μm to 1000 μm, and preferably 100 to 900 μm. The thickness of the glass nonwoven fabric in this application means a value measured using a digital gauge DG-925 (load 110 grams, surface diameter 10 mm) manufactured by Ono Sokki Co., Ltd. in accordance with JIS P8118:1998. In order to increase the affinity with the fluororesin, the glass nonwoven fabric may be treated with a silane coupling agent.

Since most glass nonwoven fabrics have a very high porosity of 80% or more, it is preferable to use a sheet that is thicker than a sheet made of fluororesin and compress it using pressure.

The glass fiber fabric layer may be a layer in which a glass cloth and a glass nonwoven fabric are laminated together, whereby the properties of the two fabrics are combined to obtain suitable properties.
The glass fiber fabric layer may be in the form of a prepreg impregnated with a resin.

In the above laminate, the glass fiber fabric layer and the fluororesin film may be bonded at the interface, or the glass fiber fabric layer may be partially or entirely impregnated with the fluororesin film.
Furthermore, a prepreg may be prepared by impregnating a fabric made of glass fibers with the fluororesin composition. The prepreg thus obtained may be further laminated with the fluororesin film of the present disclosure. In this case, the fluororesin composition used in preparing the prepreg is not particularly limited, and the fluororesin film of the present disclosure may also be used.

The resin film used as the substrate layer is preferably a heat-resistant resin film or a thermosetting resin film. Examples of the heat-resistant resin film include polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, etc. Examples of the thermosetting resin include those containing epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, polybutadiene, etc.
The heat-resistant resin film and the thermosetting resin film may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but for example, glass cloth, particularly low dielectric type, is preferable.
The heat-resistant resin film and the thermosetting resin film are not particularly limited in terms of dielectric properties, linear expansion coefficient, water absorption rate, and other properties, but for example, the dielectric constant at 20 GHz is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably 3.0 or less. The dielectric loss tangent at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and even more preferably 0.0020 or less. The linear expansion coefficient is preferably 100 ppm/°C or less, more preferably 70 ppm/°C or less, and even more preferably 40 ppm/°C or less. The water absorption rate is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

The present disclosure will now be described in detail with reference to examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

In the following examples and comparative examples, the following silicas were used:

In the table, ZA-30 phenyl+amino is a mixture of phenyltrimethoxysilane and aminoethylaminopropyltrimethoxysilane in a ratio of 9:1.

The evaluation of each sample in Table 1 above was carried out based on the following methods.
[Df (dielectric tangent) of filler]
The dielectric loss tangent of the filler measured at 10 GHz was measured using a cylindrical cavity resonator and a network analyzer by filling a filler powder sample into a quartz tube and loading it into the resonator. The characteristics of the resonator (resonant frequency and Q value) were obtained before and after inserting the sample, and the dielectric loss tangent was calculated from the results.
This assumed method complies with the Japanese Industrial Standard JIS 2565 Microwave Ferrite Core Test Method.

[D50]
The measurement was performed using a laser analysis particle size distribution analyzer.

[Specific surface area of filler]
The value is based on the BET method, and the specific surface area was measured using a "Macsorb HM model-1208" (manufactured by MACSORB).

Example 1
Sheet manufacturing method 1 (paste extrusion molding)
The PTFE powder (average particle size: 500 μm, apparent density: 460 g/L, standard specific gravity: 2.17) and silica were weighed out in the proportions shown in Table 1 and mixed in a mixer in the presence of dry ice. The temperature during mixing was -10° C. or lower.
Oil (IP Solvent 2028) was added to the resulting mixed powder at 18 to 23 wt %, mixed, and aged for about 5 hours.
The aged composition was preformed under a pressure of 3 MPa, and the preformed body was extruded under conditions of 40°C and 50 mm/min to obtain an extrusion sample. The extrusion sample was rolled with two rolls to obtain a sample with a thickness of 125 μm, which was dried at 200°C for 2 hours and baked at 360°C for 15 minutes to obtain a sheet. The pressure of the two rolls was further adjusted to produce a sample with a thickness of 30 μm, and the presence or absence of holes or cracks was observed.

Each of the obtained samples was evaluated based on the following criteria.
[Sheet Df]
Df was measured at 25° C., 10 GHz and 80 GHz using a split cylinder type dielectric constant/dielectric loss tangent measuring device (manufactured by EM Lab).

[Linear expansion]
TMA measurement was performed in tensile mode using a TMA-7100 (Hitachi High-Tech Science Corporation). A sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm was used as a sample piece. The chuck distance was set to 10 mm, and the linear expansion coefficient was calculated from the displacement of the sample from 0 to 150° C. at a heating rate of 2° C./min while applying a load of 49 mN.

[Thinning to 30 μm]
In the composition shown in Table 2 below, in which the PTFE/silica ratio was 40/60, a film having a thickness of 30 μm was formed without holes or tears, and an X was given to those in which a film could not be formed.
The results are shown in Table 2.

From the above results, the fluororesin sheet of the present disclosure has excellent performance in terms of low dielectric constant, low loss, and low thermal expansion. Furthermore, the Df at 80 GHz for Example 8 with a PTFE/silica ratio of 40/60 is 0.0008, and the sheet has excellent performance even at 80 GHz.

For the sheets of Examples 1 and 8 with a PTFE/silica ratio of 40/60, the rate of change in the relative dielectric constant in the temperature range of -50 to 150°C was measured using the following method. The results are shown in Table 3.

(Method for measuring the rate of change in dielectric constant in the temperature range of -50 to 150°C)
Using a split cylinder type dielectric constant/dielectric loss tangent measuring device (manufactured by EM Lab), Dk at 10 GHz was measured at 10°C intervals from -50°C to 150°C.
The rate of change from -50°C to 150°C was calculated from the difference between the maximum and minimum measured Dk values.

The results in Table 3 clearly show that the fluororesin sheet of the present disclosure has a small rate of change in relative dielectric constant in the temperature range of -50 to 150°C.

The fluororesin sheets disclosed herein are particularly suitable for use in high-frequency printed circuit boards.

The present disclosure relates to
The composition is characterized in that it contains a fluororesin that is not melt-moldable and a filler in which the ratio of (dielectric dissipation factor of the filler measured at 10 GHz)/(surface area of the filler (m2/g)) is 0.00001 to 0.00035 , and the filler has a dielectric dissipation factor of 0.0015 or less at 10 GHz .
The fluororesin is preferably a polytetrafluoroethylene resin .

The filler is preferably silica particles.
The content of the filler in the total amount of the composition is preferably 50 wt % or more.
The filler preferably has an average particle size of 0.5 to 250 μm.
The above filler is preferably one whose surface is coated with a silane coupling agent .

The present disclosure includes a fluororesin that is not melt-moldable and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035 ;
The filler is also a fluororesin sheet characterized in that it is made of a composition having a dielectric loss tangent value of 0.0015 or less at 10 GHz .
The fluororesin sheet preferably has a thickness of 5 to 250 μm.

Claims (18)

A composition comprising a fluororesin and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035. The composition according to claim 1, wherein the fluororesin is polytetrafluoroethylene resin. The composition according to claim 1 or 2, wherein the fluororesin is not melt moldable. The composition according to claim 2, wherein the polytetrafluoroethylene resin has an SSG of 2.0 to 2.3. The composition according to claim 2, wherein the polytetrafluoroethylene resin has a refractive index of 1.2 to 1.6. The composition according to claim 1 or 2, wherein the fluororesin has a primary particle size of 0.05 to 10 μm. The composition according to claim 1 or 2, wherein the fluororesin has a volume-based cumulative 50% diameter of 0.05 to 40 μm. The composition according to claim 1 or 2, wherein the filler is silica particles. The composition according to claim 1 or 2, wherein the filler is present in an amount of 50 wt% or more relative to the total amount of the composition. The composition according to claim 1 or 2, wherein the filler has an average particle size of 0.5 to 250 μm. The composition according to claim 1 or 2, wherein the filler has a surface coated with a silane coupling agent. The composition according to claim 1 or 2, which has a dielectric tangent value of 0.0015 or less at 10 GHz. A fluororesin sheet comprising a composition containing a fluororesin and a filler having a ratio of (dielectric tangent of the filler measured at 10 GHz)/(surface area of the filler (m ² /g)) of 0.00001 to 0.00035. The fluororesin sheet according to claim 13, having a thickness of 5 to 250 μm. The method for producing a fluororesin sheet according to claim 13 or 14, characterized in that it includes a step of mixing fluororesin particles and a filler to form a film. The method for producing a sheet-shaped composition according to claim 15, characterized in that only fluororesin particles and inorganic filler are mixed and a film is formed without adding other components. A copper-clad laminate having copper foil and the fluororesin sheet according to claim 13 or 14 as essential layers. A circuit board comprising the copper clad laminate according to claim 17.