Fluororesin sheet-shaped material and laminate containing same

Abstract

Provided is a fluororesin sheet-shaped material which exhibits excellent adhesion to a metal layer even if bonded at a temperature that is equal to or lower than the melting point of the fluororesin. The fluororesin sheet-shaped material is a sheet-shaped material which contains a fluororesin, at least one surface of which satisfies the following general formula (A). (A): O ≥ E + 0.5 In the formula, O is the elemental oxygen ratio obtained from measurements by a scanning X-ray photoelectron spectroscopic analyzer (XPS), and E is the difference between the surface elastic modulus at the time when the cumulative relative frequency reaches 0.99 and the surface elastic modulus at the time when the cumulative relative frequency reaches 0.01 in a multipoint measurement of the surface elastic modulus by a scanning atomic force microscope at 120°C.

Description

Fluororesin sheet material and laminate containing same

[0001] The present disclosure relates to a fluororesin sheet material and a laminate including the same.

[0002] To realize high-speed communication by next-generation information communication (high-frequency 5G), dielectrics (insulating materials) of printed circuit boards used in antennas and transmission paths are required to have low transmission loss characteristics. Against this background, fluororesin materials (PTFE, PFA, etc.) with excellent electrical properties have attracted attention as insulating materials for printed circuit boards. However, fluororesin materials generally have poor adhesion to other materials, so surface modification techniques such as plasma treatment are used to improve adhesion (see, for example, Patent Document 1).

[0003] Patent Document 2 describes that by subjecting a fluororesin film to a surface treatment and an annealing treatment and adjusting the dimensional change rate and oxygen atomic ratio of the fluororesin film to specific ranges, defects during lamination of the fluororesin film and copper foil can be reduced and a fluororesin film with excellent adhesion to the copper foil can be obtained.

[0004] Furthermore, Patent Document 3 describes that by subjecting the surface of a heat-resistant film such as aramid to a surface modification treatment by corona discharge to make the surface elastic modulus 1.5 GPa or more, the adhesion between the heat-resistant film and the adhesive resin is improved and a thinner film can be achieved. Furthermore, Patent Document 4 describes that by making the surface elastic modulus of a release polyester film for a semiconductor encapsulation process within a specific range, the occurrence of cracks in the release polyester film is suppressed and the transfer of resin flow marks to the surface of the release film is prevented.

[0005] Japanese Patent Application Publication No. 2019-181735 International Patent Application Publication No. 2022 / 158524 Japanese Patent Application Publication No. 2004-123928 Japanese Patent Application Publication No. 2023-116512

[0006] An object of the present disclosure is to provide a fluororesin sheet material that has excellent adhesion to a metal layer even when bonded at a temperature below the melting point of the fluororesin.

[0007] The present disclosure relates to a sheet material containing a fluororesin, wherein the following general formula (A) is satisfied on at least one surface: O≧E+0.5 (A), where O is the oxygen element ratio obtained when measured with a scanning X-ray photoelectron spectroscopy (XPS), and E is the difference between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 in multipoint measurement of the surface elastic modulus with a scanning atomic force microscope at 120°C.

[0008] Furthermore, it is preferable that the difference E between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 is 0.35 GPa≦E≦3.0 GPa. It is also preferable that the oxygen element ratio O is 1.35 atomic %<O<20 atomic %.

[0009] The present disclosure also provides a sheet-like material containing a fluororesin, wherein, on at least one surface, when heated from 25°C to 120°C, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more in multipoint measurements of the surface elastic modulus at 25°C and 120°C using a scanning atomic force microscope.

[0010] The present disclosure relates to a sheet material containing a fluororesin, wherein the following general formula (A) holds on at least one surface, and further, on at least one surface, when heated from 25°C to 120°C, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more in multi-point measurements of the surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C: O≧E+0.5 (A), where O: oxygen element ratio obtained when measured using a scanning X-ray photoelectron spectroscopy (XPS), E: the difference between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 in multi-point measurements of the surface elastic modulus using a scanning atomic force microscope at 120°C.

[0011] The fluororesin is preferably tetrafluoroethylene-perfluoroalkylvinyl ether (PFA) or tetrafluoroethylene-hexafluoropropylene (FEP).

[0012] The present disclosure also provides a laminate including a fluororesin sheet material and a metal layer. In the laminate of the present disclosure, it is preferable that the adhesive strength between the measurement surface of the fluororesin sheet material and the metal layer is 0.5 N / cm or more.

[0013] It is preferable that the laminate further comprises a layer other than the fluororesin sheet material and the metal layer, and that the layer other than the fluororesin sheet material and the metal layer provided on the surface of the fluororesin sheet material is a layer made of at least one material selected from the group consisting of polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, divinylbenzene, and polybutadiene.

[0014] The fluororesin sheet material of the present disclosure has excellent adhesiveness to a metal layer even when bonded at a temperature below the melting point of the fluororesin.

[0015] The present disclosure is described in detail below. Conventionally, in the surface modification of fluororesin sheets by plasma treatment, there have been a number of patents specifying the amount of oxygen element or the amount of specific functional groups as requirements for achieving good adhesion. However, in adhesion below the melting point, these requirements alone do not provide satisfactory adhesion. Insufficient adhesion can lead to peeling in subsequent processes and reduced reliability of the substrate.

[0016] The inventors have discovered that by improving the in-plane uniformity of the surface treatment of a fluororesin sheet material, adhesion to metals such as copper foil can be improved when the material is bonded at a temperature below the melting point of the fluororesin. Furthermore, they evaluated not only the oxygen element content of the fluororesin sheet material but also the in-plane uniformity of the surface elastic modulus, and identified two parameters that can be used to obtain high adhesion.

[0017] One of them is that the following general formula (A) is satisfied on at least one surface of the sheet-like material containing a fluororesin: O≧E+0.5 (A), where O is the oxygen element ratio obtained when measured with a scanning X-ray photoelectron spectroscopy (XPS), and E is the difference between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 in multipoint measurement of the surface elastic modulus with a scanning atomic force microscope at 120°C.

[0018] A fluororesin sheet material having a specific relationship between the oxygen element ratio O and the difference E in surface elastic modulus as shown in the general formula (A) exhibits good adhesion to metal foil when bonded at a temperature below the melting point of the fluororesin, resulting in no poor appearance or peeling, and improved reliability as a circuit substrate. By enabling bonding at a temperature below the melting point of the fluororesin, warping of the metal foil is less likely to occur, resulting in a good appearance. Furthermore, by reducing peeling resistance, surface smoothness is maintained, thereby maintaining low transmission loss characteristics. Furthermore, lowering the bonding temperature facilitates manufacturing and improves production efficiency.

[0019] Here, the oxygen element ratio was determined by the following method. (Method for measuring oxygen element ratio) Using a scanning X-ray photoelectron spectroscopic analyzer (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.), the oxygen element ratio on the surface of the fluororesin sheet material was measured under the conditions shown below. Carbon, oxygen, fluorine, nitrogen, and silicon were detected, and the oxygen element ratio was determined from the composition ratio of C1s, O1s, F1s, N1s, and Si2p. Radiation source: Monochromated AlKα Beam diameter: 100 μm X-ray output: 25 W Measurement area: 1000 μm × 300 μm Pass energy: 23.5 eV Detection angle: 45°

[0020] The surface elasticity was measured at 64 x 32 points in a 20 μm x 10 μm area using a scanning atomic force microscope (AFM5300E, manufactured by Hitachi High-Tech Science Corporation) in force curve mapping mode. A histogram was created for the surface elasticity at a total of 2,048 points, with a 0.01 GPa pitch, and the difference between the class value when the cumulative relative frequency reached 0.99 and the class value when the cumulative relative frequency reached 0.01 was taken as the distribution width. E represents the distribution width at a measurement temperature of 120°C, and the smaller the value, the higher the uniformity of the treated surface.

[0021] Although the mechanism by which the above results are obtained is unclear, in order to form a bond with a metal, for example, it is important to bring as many functional groups on the metal surface as possible into close proximity, and it is presumed that by making the surface elastic modulus of the fluororesin sheet material uniform within the plane when heated and eliminating the gap between hard and soft areas, adhesion to the metal foil surface is improved and adhesive strength is improved even at low temperatures, even without softening it by heating it to near the melting point of the fluororesin. Furthermore, in addition to the uniformity of the surface elastic modulus upon heating, adhesiveness is improved when the relationship with the oxygen element ratio of the fluororesin sheet material is specific.

[0022] Furthermore, the difference E between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 in the above general formula (A) is preferably 0.35 GPa≦E≦3.0 GPa. The lower limit of E is more preferably 0.4 GPa or more, even more preferably 0.5 GPa or more, and most preferably 0.6 GPa or more. The upper limit of E is more preferably 2.0 GPa or less, even more preferably 1.5 GPa or less, and most preferably 1.0 GPa or less. When E is within the above range, there is no difference in the surface elastic modulus within the plane, and it can be said that in-plane uniformity is ensured, so that adhesion to metals such as copper foil is good when bonding at a temperature below the melting point of the fluororesin.

[0023] Furthermore, the oxygen element ratio O is preferably 1.35 atomic%<O<20 atomic%. The lower limit of the oxygen element ratio O is more preferably 1.5 atomic% or more, even more preferably 1.8 atomic% or more, and most preferably 2.0 atomic% or more. The upper limit of the oxygen element ratio O is more preferably 25 atomic% or less, even more preferably 20 atomic% or less, and most preferably 15 atomic% or less. An oxygen element ratio within the above range is advantageous in that the functional groups that contribute to adhesion are present in an appropriate amount.

[0024] Another parameter discovered in the present disclosure is that when at least one surface of a fluororesin sheet material is heated from 25°C to 120°C, the median value of the surface elastic modulus (the value at which the cumulative relative frequency reaches 0.50) decreases by 20% or more in multipoint measurements of the surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C. Thus, when the fluororesin sheet material is heated from room temperature to 120°C, the median value of the surface elastic modulus decreases by 20% or more. In other words, it is presumed that the surface tends to soften even at adhesion temperatures below the melting point of the fluororesin, making it easier to form a distance suitable for bonding with functional groups present on the surface of the object to be bonded.

[0025] Furthermore, it is preferable that the fluororesin sheet material of the present disclosure simultaneously satisfy the above two parameters, since this makes it easier to come into close proximity with the surface to be bonded, thereby allowing the functional groups present on each surface to be efficiently utilized in bond formation.

[0026] The fluororesin sheet material of the present disclosure, which satisfies the above-mentioned physical properties, can be surface-treated by corona discharge, for example, using nitrogen gas, argon, and carbon dioxide gas as inert gases, and by imparting functional groups with the carbon dioxide gas, the in-plane uniformity of the surface treatment can be improved. Details of the surface treatment method will be described later.

[0027] (Fluororesin) The fluororesin contained in the fluororesin sheet material of the present disclosure is not particularly limited as long as it is a resin containing fluorine, and any known fluororesin can be used. Among them, tetrafluoroethylene (TFE)-(per)fluoro(alkyl vinyl ether) copolymer (PFA) or tetrafluoroethylene-hexafluoropropylene (HFP) copolymer (FEP) is preferred.

[0028] The (per)fluoro(alkyl vinyl ether) (PAVE) may be either a fluoroalkyl vinyl ether or a perfluoro(alkyl vinyl ether). In the present disclosure, the term "perfluoro(alkyl vinyl ether)" refers to an alkyl vinyl ether that does not contain a C—H bond. Examples of the PAVE constituting the PAVE unit include those represented by the general formula (1): CF ２ = CFO (CF ２ CFY １ O) ｐ -(CF ２ CF ２ CF ２ O) ｑ -R ｆ (1) (wherein, Y １ is F or CF ３ represents R ｆ represents a perfluoroalkyl group having 1 to 5 carbon atoms, p represents an integer of 0 to 5, and q represents an integer of 0 to 5.) and a monomer represented by the general formula (2): CFX=CXOCF ２ OR １ (2) (Wherein, X may be the same or different and is H, F or CF ３ represents R １ represents a linear or branched fluoroalkyl group having 1 to 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I, or a cyclic fluoroalkyl group having 5 or 6 carbon atoms which may contain 1 to 2 atoms of at least one type selected from the group consisting of H, Cl, Br and I.

[0029] Among these, the PAVE is preferably a monomer represented by general formula (1), more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) (PPVE), and even more preferably PPVE.

[0030] The content of PAVE units in the TFE / PAVE copolymer is preferably 1.0 to 10% by mass, more preferably 2.0% by mass or more, even more preferably 3.5% by mass or more, particularly preferably 4.0% by mass or more, most preferably 5.0% by mass or more, more preferably 8.0% by mass or less, even more preferably 7.0% by mass or less, particularly preferably 6.5% by mass or less, and most preferably 6.0% by mass or less, based on the total amount of the PAVE units. １９ The TFE / PAVE copolymer may be a copolymer consisting of only TFE units and PAVE units.

[0031] When the fluororesin sheet material is made of a TFE / PAVE copolymer, the melting point is preferably 280 to 322°C, more preferably 290°C or higher, and more preferably 315°C or lower.

[0032] When the fluororesin sheet material is made of a TFE / PAVE copolymer, the glass transition temperature (Tg) is preferably 70 to 110° C., more preferably 80° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0033] The TFE / HFP copolymer contains TFE units and HFP units. The content of the TFE units in the TFE / HFP copolymer is preferably 70% by mass or more, more preferably 85% by mass or more, and is preferably 99.8% by mass or less, more preferably 99% by mass or less, and even more preferably 98% by mass or less, based on the total monomer units.

[0034] The TFE / HFP copolymer preferably has a mass ratio of TFE units to HFP units (TFE / HFP) of 70 to 99 / 1 to 30 (mass %), more preferably 85 to 95 / 5 to 15 (mass %).

[0035] The TFE / HFP copolymer can further contain (per)fluoro(alkyl vinyl ether) (PAVE) units.The PAVE units contained in the TFE / HFP copolymer can be the same as the PAVE units described above.The TFE / PAVE copolymer does not contain HFP units, so in this respect it is different from the TFE / HFP / PAVE copolymer.

[0036] When the TFE / HFP copolymer is a copolymer containing TFE units, HFP units, and PAVE units (hereinafter also referred to as "TFE / HFP / PAVE copolymer"), the mass ratio (TFE / HFP / PAVE) is preferably 70-99.8 / 0.1-25 / 0.1-25 (mass%). The mass ratio (TFE / HFP / PAVE) is more preferably 75-98 / 1.0-15 / 1.0-10 (mass%). The TFE / HFP / PAVE copolymer preferably contains 1 mass% or more of HFP units and PAVE units in total relative to all monomer units.

[0037] In the TFE / HFP / PAVE copolymer, the HFP unit is preferably 25% by mass or less of the total monomer units. The content of the HFP unit is more preferably 20% by mass or less, even more preferably 18% by mass or less, and particularly preferably 15% by mass or less. The content of the HFP unit is preferably 0.1% by mass or more, more preferably 1% by mass or more, and particularly preferably 2% by mass or more. The content of the HFP unit is １９ It can be measured by F-NMR.

[0038] The content of PAVE units is more preferably 20% by mass or less, further preferably 10% by mass or less, and particularly preferably 3% by mass or less. The content of PAVE units is preferably 0.1% by mass or more, more preferably 1% by mass or more. The content of PAVE units is １９ It can be measured by F-NMR.

[0039] The TFE / PAVE copolymer and the TFE / HFP copolymer may further contain other ethylenic monomer (α) units. The other ethylenic monomer (α) units are not particularly limited as long as they are monomer units copolymerizable with TFE, HFP, and PAVE, and examples thereof include fluorine-containing ethylenic monomers such as vinyl fluoride (VF), vinylidene fluoride (VdF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE), as well as non-fluorinated ethylenic monomers such as ethylene, propylene, and alkyl vinyl ethers. The content of the other ethylenic monomer (α) units is preferably 0 to 25% by mass, more preferably 0.1 to 25% by mass.

[0040] When the copolymer is a TFE / HFP / PAVE / other ethylenic monomer (α) copolymer, the mass ratio (TFE / HFP / PAVE / other ethylenic monomer (α)) is preferably 70 to 98 / 0.1 to 25 / 0.1 to 25 / 0.1 to 25 (mass %). The TFE / HFP / PAVE / other ethylenic monomer (α) copolymer preferably contains 1 mass % or more of monomer units other than TFE units in total.

[0041] The melting point of the TFE / HFP copolymer is preferably 200 to 322°C, more preferably above 200°C, even more preferably 220°C or higher, more preferably 300°C or lower, and even more preferably 280°C or lower.

[0042] The glass transition temperature (Tg) of the TFE / HFP copolymer is preferably 60 to 110° C., more preferably 65° C. or higher, and more preferably 100° C. or lower. The glass transition temperature is a value obtained by measuring dynamic viscoelasticity.

[0043] The fluororesin can be produced by a conventionally known method, such as emulsion polymerization or suspension polymerization, by appropriately mixing monomers that constitute the fluororesin and additives such as a polymerization initiator. Of these, emulsion polymerization is more preferred.

[0044] The fluororesin preferably has a melt flow rate of 1 to 50 g / 10 min at 372° C. and a load of 49 N.

[0045] The fewer functional groups the fluororesin has, the less unstable terminal groups it has. Such fluororesins can be produced by adjusting the conditions during production (polymerization reaction), or by subjecting the fluororesin after polymerization to fluorine gas treatment, heat treatment, supercritical gas extraction treatment, etc. The number of unstable terminal groups can be reduced by using methods such as: excellent treatment efficiency; ３ The fluorine gas treatment is preferable because the fluorine resin having a reduced number of unstable terminal groups is converted into a stable terminal group. The use of such a fluororesin having a reduced number of unstable terminal groups is preferable because it reduces the electrostatic dissipation factor and the loss of electrical signals.

[0046] The number of unstable terminal groups is not particularly limited, but is preferably 10 or more, and more preferably 10 or more, and most .... ６ The number per particle is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. In consideration of the effect of reducing the dielectric loss tangent, the number per particle is preferably less than 10, and more preferably 5 or less.

[0047] Specific examples of unstable terminal groups include -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), and hydroxyl groups (-CH ２ OH, etc.), -CONH ２ , -COOR(R=CH ３ etc.), -CF ２ Examples of functional groups include H and —OCOO—R (normal propyl carbonate, etc.).

[0048] Specifically, the number of unstable terminal groups is measured by the following method. First, the fluororesin is melted and compression-molded to produce a film having a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain an infrared absorption spectrum of the fluororesin, and a difference spectrum is obtained from a base spectrum in which the fluororesin is completely fluorinated and no functional groups are present. From the absorption peaks of specific functional groups that appear in this difference spectrum, the number of carbon atoms in the fluororesin is calculated according to the following formula (A): ６ The number of unstable terminal groups per unit is calculated as follows: N = I x K / t (A) I: absorbance K: correction coefficient t: film thickness (mm)

[0049] For reference, the absorption frequencies, molar absorption coefficients, and correction coefficients for the unstable terminal groups in this specification are shown in Table 1. The molar absorption coefficients were determined from the FT-IR measurement data of low molecular weight model compounds.

[0050]

[0051] The fluorination treatment can be carried out by contacting a non-fluorination-treated fluororesin with a fluorine-containing compound.

[0052] The fluorine-containing compound is not particularly limited, but may be a fluorine radical source that generates fluorine radicals under fluorination treatment conditions. ２ Gas, CoF ３ , AgF ２ , U.F. ６ , OF ２ , N ２ F ２ , C.F. ３ OF, halogen fluorides (e.g., IF ５ , ClF ３ ) etc.

[0053] Above F ２The fluorine radical source such as a gas may be of 100% concentration, but is preferably mixed with an active gas and diluted to 5 to 50 mass %, more preferably 15 to 30 mass % for use. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, with nitrogen gas being preferred from an economical standpoint.

[0054] The conditions for the fluorination treatment are not particularly limited, and the molten fluororesin may be brought into contact with the fluorine-containing compound, but the treatment is usually carried out at a temperature below the melting point of the fluororesin, preferably 20 to 220°C, more preferably 100 to 200°C. The fluorination treatment is generally carried out for 1 to 30 hours, preferably 5 to 25 hours. The fluorination treatment is carried out by exposing an unfluorinated fluororesin to fluorine gas (F ２ It is preferable to contact the catalyst with a gas.

[0055] In this specification, the content of each monomer unit constituting the fluororesin can be calculated by an appropriate combination of NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0056] The fluororesin sheet material of the present disclosure may contain components other than the fluororesin. The components that can be contained are not particularly limited, and examples thereof include fillers such as silica particles and short glass fibers, and fluorine-free thermosetting resins and thermoplastic resins. The content of components other than the fluororesin is not particularly limited, but is preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0057] The fluororesin sheet material of the present disclosure preferably has a thickness of 1 to 100 μm. The upper limit is more preferably 50 μm or less, and even more preferably 30 μm or less. The lower limit is more preferably 3 μm or more, and even more preferably 5 μm or more.

[0058] The thickness of the fluororesin sheet material is a value measured by reflection spectroscopy using a film thickness measurement system F20 (manufactured by Filmetrics).

[0059] The Ra (arithmetic mean roughness) of the fluororesin sheet material of the present disclosure in a 30 μm × 30 μm area is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less. The lower limit is not particularly limited, but is preferably 5 nm or more. A Ra within the above range is preferable in that the smoothness is high and the surface treatment is more uniform within the surface, thereby improving adhesion to the surface to be bonded when bonding. The Ra is a value obtained by the measurement method described below. (Ra (arithmetic mean roughness) of fluororesin sheet material) The surface Ra of the surface-treated film surface and the copper foil in a 30 μm × 30 μm area was measured using a scanning atomic force microscope AFM5000 (manufactured by Hitachi High-Technologies Corporation) under the conditions shown below. Cantilever: SI-DF20 (tip R<10 nm, spring constant 15 N / m) Measurement mode: AC mode Scanning frequency: 1 Hz Number of pixels: 256 x 256

[0060] Furthermore, the fluororesin sheet material of the present disclosure preferably has a difference of 1.0 atomic % or more between the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) for the surface state thereof and the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) for the fluororesin sheet material after etching the fluororesin sheet material in the depth direction at an incident angle of 45° with an argon gas cluster ion beam for 15 minutes. A larger difference in the oxygen element ratio from the surface to the depth direction is preferable in terms of being able to obtain a predetermined transmission loss while maintaining adhesion.

[0061] The oxygen element ratio after etching is the oxygen element ratio on the surface of the fluororesin sheet material before the surface treatment, and therefore the difference in the oxygen element ratio represents the increase in the oxygen element ratio due to the surface treatment.

[0062] The fluororesin sheet material preferably has an adhesive strength of more than 30 N / m on one or both sides when the sheet materials are bonded together in the same plane at 200° C. By having such an adhesive strength, the fluororesin sheet material will have excellent adhesiveness when used in combination with various other substrates even after heat treatment, and the adhesive strength is more preferably more than 50 N / m, and even more preferably more than 100 N / m.

[0063] More specifically, the adhesive strength was measured by overlapping the surface-treated surfaces of the fluororesin sheet material together and heat pressing (200°C, 0.1 MPa, 60 s) to produce a sample, which was then cut into a 10 mm wide strip. Using a precision universal testing machine Autograph AGS-X 100N (manufactured by Shimadzu Corporation), the unbonded portion of the strip sample was gripped between the upper and lower chucks of the Autograph and pulled at a rate of 100 mm per minute to measure the peel strength, and the obtained value was taken as the adhesive strength.

[0064] The resin sheet material of the present disclosure preferably has a dielectric dissipation factor of less than 0.0015 at 10 GHz. A dielectric dissipation factor within this range is preferable because it can minimize electrical signal loss in circuits. The dielectric dissipation factor is more preferably less than 0.0013, even more preferably less than 0.0010, and most preferably 0.00050 or less. Furthermore, considering signal transmission and antenna transmission / reception at higher frequencies, the dielectric dissipation factor at 40 GHz is preferably less than 0.0015, more preferably less than 0.0013, even more preferably less than 0.0010, and most preferably 0.00050 or less. To achieve a dielectric dissipation factor within the above range, it is preferable to use a resin with few unstable terminal groups, and it is more preferable to use a fluororesin that has been subjected to a terminal fluorination treatment.

[0065] (Method for manufacturing fluororesin sheet material) An example of a method for manufacturing the fluororesin sheet material of the present disclosure described above will be described in detail below. Note that the fluororesin sheet material of the present disclosure is not limited to those manufactured by the following manufacturing method. The fluororesin sheet material of the present disclosure is not particularly limited to a method for forming into a sheet, but examples include a melt molding method such as extrusion molding, and a casting method in which a solution or dispersion containing a fluororesin is prepared and then applied to a substrate and dried. Furthermore, the sheet may be stretched by a uniaxial or biaxial stretching method, or may be an unstretched sheet.

[0066] By subjecting one or both sides of the fluororesin sheet material obtained by this method to surface treatment under appropriate conditions, a fluororesin sheet material that satisfies the above two parameters can be obtained.

[0067] The specific method for the surface modification is not particularly limited, but specific examples are described in detail below. Conventional discharge treatments such as corona discharge, glow discharge, plasma discharge, and sputtering can be used to modify the surface of fluororesin sheet materials. Corona discharge treatment is particularly preferred. For example, surface free energy can be controlled by introducing oxygen gas, nitrogen gas, hydrogen gas, carbon dioxide gas, methane gas, or ethylene gas into a discharge atmosphere. Alternatively, the surface to be modified can be exposed to an atmosphere of an organic compound-containing inert gas, which is an inert gas containing an organic compound, and a high-frequency voltage is applied between electrodes to generate a discharge, thereby generating active species on the surface. Surface modification can then be achieved by introducing functional groups from the organic compound or graft-polymerizing a polymerizable organic compound. Examples of inert gases include nitrogen gas, helium gas, and argon gas.

[0068] In particular, it is preferable to use nitrogen gas and argon gas in combination. Furthermore, it is preferable to use carbon dioxide gas. The ratio (volume) of nitrogen gas to argon gas is preferably 30 / 70 to 100 / 0, more preferably 40 / 60 to 80 / 20, and even more preferably 50 / 50 to 70 / 30. A ratio of nitrogen gas to argon gas within the above range is advantageous in that discharge is stable and more uniform in-plane surface modification is possible. Furthermore, the carbon dioxide gas content is preferably 0.05 to 5% by volume, more preferably 0.1 to 2% by volume, relative to the nitrogen gas / argon gas ratio. A carbon dioxide gas content within the above range is advantageous in that functional groups contributing to adhesiveness on the surface of the fluororesin sheet material are imparted within a suitable range.

[0069] Examples of the organic compound in the organic compound-containing inert gas include polymerizable or non-polymerizable organic compounds containing oxygen atoms, such as vinyl esters such as vinyl acetate and vinyl formate; acrylic esters such as glycidyl methacrylate; ethers such as vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids such as acetic acid and formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; carboxylic esters such as ethyl acetate and ethyl formate; acrylic acids such as acrylic acid and methacrylic acid. Among these, vinyl esters, acrylic esters, and ketones are preferred because the modified surface is less likely to be deactivated, i.e., has a long lifespan, and is easy to handle. Vinyl acetate and glycidyl methacrylate are particularly preferred.

[0070] The concentration of the organic compound in the organic compound-containing inert gas varies depending on the type of organic compound, the type of fluororesin to be surface-modified, etc., but is usually 0.1 to 3.0% by volume, preferably 0.1 to 1.0% by volume, more preferably 0.15 to 1.0% by volume, and even more preferably 0.30 to 1.0% by volume. The discharge conditions may be appropriately selected depending on the desired degree of surface modification, the type of fluororesin, the type and concentration of the organic compound, etc. The discharge rate is usually 50 to 1500 W·min / m ２ , preferably 100 W·min / m２ More than 1400W・min / m ２ Less than 200 W·min / m ２ More than 1300W・min / m ２ The discharge treatment is performed within the following range. The treatment temperature can be any temperature in the range of 0°C to 100°C. Due to concerns about stretching and wrinkling of the fluororesin sheet material, a temperature of 80°C or less is preferable. Considering that oxygen elements on the surface are deactivated by heat applied during lamination with metal foil or the like, resulting in a decrease in adhesive ability, the degree of surface modification of the fluororesin sheet material is such that the oxygen element abundance ratio observed by ESCA is 1.5% or more, preferably 1.75% or more, more preferably 2.0% or more, and even more preferably 2.5% or more. There is no particular upper limit, but in consideration of the impact on productivity and other physical properties, it is preferably 25.0% or less. The nitrogen element abundance ratio is not particularly specified, but is preferably 0.1% or more.

[0071] During the surface modification, the discharge degree, which indicates the output per unit area, is 1.0 to 10 W / cm ２ It is preferable to perform discharge treatment within this range, adjusting the gas concentration / line speed ratio to a range of 0.005 to 0.05 L / m. The gas concentration / line speed ratio here refers to the ratio of the organic compound concentration in the organic compound-containing inert gas divided by the line speed. If the gas concentration / line speed ratio is lower than 0.005 L / m, the space is not filled with sufficient gas relative to the transport speed, making it difficult for the activated gas to contact the surface of the fluororesin sheet material, which tends to reduce in-plane uniformity. If the gas concentration is higher than 0.05 L / m, the surface is over-treated and damaged, resulting in the formation of low-molecular-weight compounds on the surface, forming a brittle layer and, in turn, reducing adhesive strength. Therefore, treatment within this range is particularly preferred because it is expected to result in more uniform treatment within the surface of the fluororesin sheet material and achieve the desired adhesiveness.

[0072] Furthermore, in the above-mentioned method, it is preferable that the fluororesin sheet material is surface-treated so that the difference between the oxygen element ratio when the surface condition of one or both sides is measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) and the oxygen element ratio when the fluororesin-containing layer is etched in the depth direction with an argon gas cluster ion beam at an incident angle of 45° for 15 minutes and then measured by a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) is 1.0 atomic % or more.

[0073] The fluororesin sheet material surface-treated by the above method may be annealed to remove residual stress in advance. This reduces dimensional changes in the fluororesin film caused by heat from the pressure roll during the process of laminating it with metal foil to produce a laminate, allowing it to be bonded without wrinkles, thereby suppressing poor appearance of the laminate. Because these heat treatments reduce the amount of oxygen on the surface of the fluororesin sheet material, it is preferable to carry out surface modification under conditions that ensure a sufficient amount of surface oxygen at the time the fluororesin sheet material and metal foil are bonded together.

[0074] The annealing treatment can be carried out by heat treatment. The heat treatment can be carried out, for example, by passing the material through a heating furnace using a roll-to-roll method. The heat treatment can also be carried out by placing the material in a batch-type drying furnace.

[0075] The annealing temperature is preferably not less than the glass transition temperature of the fluororesin minus 20° C. and less than the melting point, more preferably not less than the glass transition temperature of the fluororesin minus 20° C., and even more preferably not less than the glass transition temperature of the fluororesin minus 60° C. The annealing time is not particularly limited, but may be adjusted as appropriate within the range of, for example, 0.5 to 60 minutes.

[0076] When heating is performed by the roll-to-roll method, the tension may be adjusted appropriately depending on the thickness of the fluororesin sheet material, the set temperature, etc., but is preferably 20 N / m or less. Heating under such conditions is preferable in that it can sufficiently relieve internal stress and does not cause dimensional changes, etc.

[0077] The order of the surface treatment and annealing treatment is not particularly limited, and the number of times each step is performed is not limited to one, but each step may be performed two or more times.

[0078] (Laminate) The fluororesin sheet material of the present disclosure is suitably used to form a laminate with a metal or resin substrate, etc. The present disclosure also relates to a laminate including the fluororesin sheet material and a metal layer. The laminate of the present disclosure is suitably configured such that the surface of the fluororesin sheet material having the above properties is in contact with the metal layer.

[0079] (Metal Layer) In the present disclosure, examples of metal species constituting the metal layer include copper, aluminum, SUS, nickel, and gold. Alloys of these metals can also be used. From the viewpoints of conductivity and circuit processability, it is preferable to use copper foil.

[0080] The copper foil preferably has an Rz of 1.5 μm or less. In other words, the fluororesin sheet material of the present disclosure also has excellent adhesion to copper foil, which has a high smoothness of Rz of 1.5 μm or less. Furthermore, the copper foil only needs to have an Rz of 1.5 μm or less on at least the surface that adheres to the fluororesin film; the Rz value of the other surface is not particularly limited. The Rz is the sum of the values ​​of the highest point (maximum peak height: Rp) and the deepest point (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.

[0081] 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 in the range of 9 to 35 μm.

[0082] The copper foil is not particularly limited, and specific examples include rolled copper foil and electrolytic copper foil.

[0083] The copper foil having an Rz of 1.5 μm or less is not particularly limited, and commercially available products can be used. Examples of commercially available copper foils having an Rz of 1.5 μm or less include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

[0084] The copper foil may be surface-treated to enhance the adhesive strength with the fluororesin sheet material of the present disclosure.

[0085] The 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 fluororesin sheet material, 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 terminal. Furthermore, the hydrolyzable group is not particularly limited, but may include alkoxy groups such as a methoxy group and an ethoxy group. The copper foil used in the present disclosure may have a rust prevention layer (such as an oxide film such as chromate), a heat-resistant layer, etc. formed thereon.

[0086] The 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.

[0087] The copper foil may have a roughened layer on its surface from the viewpoint of improving adhesion to the fluororesin sheet material, etc. If the roughening treatment is likely to deteriorate the performance required in the present disclosure, the amount of roughening particles electrodeposited on the copper foil surface may be reduced as needed, or the copper foil may not be roughened at all.

[0088] Between the copper foil and the surface treatment layer, one or more layers selected from the group consisting of a heat-resistant treatment layer (nickel plating, titanium plating, etc.), a rust-proofing treatment layer, and a chromate treatment layer may be provided in order to improve various properties. These layers may be a single layer or multiple layers.

[0089] The laminate of the present disclosure preferably has an adhesive strength of 0.5 N / cm or more between the metal layer and the fluororesin sheet material. Such adhesive strength can be achieved by adhering the metal layer to a surface of the fluororesin sheet material of the present disclosure where the general formula (A) holds, and / or a surface of the fluororesin sheet material of the present disclosure where, when heated from 25°C to 120°C, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more in multipoint measurements of the surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C. By achieving an adhesive strength of 1 N / cm or more, or even 2 N / cm or more, the laminate can be suitably used as a copper-clad laminate or a circuit board. The adhesive strength here refers to the adhesive strength measured under the conditions described in the examples.

[0090] (Layer Structure of Laminate) The laminate of the present disclosure may have a two-layer structure consisting of the above-mentioned fluororesin sheet material and metal layer, or may have a three-layer or more structure having two or more layers of either or both of these. Furthermore, it may have a three-layer or more structure having a layer (X) other than the metal layer and the fluororesin sheet material.

[0091] Examples of the layer (X) other than the metal layer and the fluororesin sheet material include polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, etc. Examples of the thermosetting resin include those containing epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, divinylbenzene, polybutadiene, etc.

[0092] When the laminate of the present disclosure has the layer (X), the layer configuration can be a metal layer / fluororesin sheet material layer / layer (X). A fluororesin sheet material layer / metal layer laminate may be provided on one or both sides of the layer (X). In the present disclosure, it is preferable to provide the layer (X) on the surface of the fluororesin sheet material.

[0093] In addition, in the case of a laminate in which copper foil is bonded to the surface-treated surface of a fluororesin sheet material that has been surface-treated on only one side, the surface of the fluororesin sheet material that has not been surface-treated may be separately surface-modified in order to improve the adhesion between the laminate and other materials.

[0094] (Method for manufacturing laminate) A method for manufacturing a laminate of the present disclosure is described in detail below. To obtain the laminate of the present disclosure, it is preferable that the metal foil used as a material has high smoothness, and further, that the conditions for the step of bonding the metal foil to the fluororesin sheet material are adjusted.

[0095] Heating is required to bond the metal foil and the fluororesin sheet material. In the production of the laminate of the present disclosure, a temperature below the melting point of the fluororesin is preferred. Specifically, the heating temperature is preferably 70 to 300°C. Preferably, it is 70 to 250°C, and even more preferably, 70 to 200°C. The fluororesin sheet material of the present disclosure exhibits excellent adhesion to the metal layer even when bonded at a temperature below the melting point of the fluororesin. The heat treatment process may be a roll-to-roll lamination method or a method in which a fluororesin coated on a metal foil is heat-treated. In other words, a low heating temperature is preferable in that it suppresses warping of the metal foil and minimizes loss of smoothness of the bonding surface during the process of bonding the metal foil layer and the fluororesin sheet material. As a result, poor appearance and peeling are eliminated, improving the reliability of the circuit board.

[0096] In producing the laminate of the present disclosure, the method for bonding the metal foil and the fluororesin sheet material is not particularly limited, but from the viewpoint of excellent production efficiency, a roll-to-roll lamination method is particularly preferred.

[0097] The roll-to-roll method is also preferable in that it reduces costs and allows a long laminate to be obtained. When producing a laminate by such a method, the width of the laminate is not particularly limited, but is preferably 200 mm or more.

[0098] The laminate of the present disclosure has good adhesion between the metal layer and the fluororesin sheet material, making them less likely to peel off. Therefore, the surface smoothness of the adhesive surface can be maintained, resulting in low transmission loss. Therefore, it is suitable for use in circuit boards, etc., and is particularly suitable for use in circuit boards for high-frequency circuits.

[0099] In this disclosure, the term "high-frequency circuit" refers not only to a circuit that simply transmits only high-frequency signals, but also to a circuit that also includes a transmission line that converts a high-frequency signal into a low-frequency signal and outputs the generated low-frequency signal to the outside, a transmission line for supplying power to drive high-frequency compatible components, and other transmission lines that transmit signals other than high-frequency signals, all of which are installed on the same plane.The circuit can also be used as a circuit board for an antenna, a filter, etc.

[0100] The present disclosure will be specifically described below based on examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0101] (Example 1) [Method for manufacturing a fluororesin sheet material] PFA was charged into an extruder at 360°C, extruded through a 1700 mm wide T-die, taken up on a metal cooling roll, and further wound around a winding core to obtain a roll sheet with a width of 1300 mm and a thickness of 12 μm. The PFA was a TFE / PPVE copolymer, with a composition of TFE / PPVE=95.4 / 4.6 (mass%), MFR of 15.8 g / 10 min, a melting point of 305°C, and a number of unstable terminal groups of 10 main chain carbon atoms. ６ 297 pieces per piece were used.

[0102] [Number of Unstable Terminal Groups] Analysis was carried out using an FT-IR Spectrometer 1760X (manufactured by Perkin-Elmer).

[0103] [Surface Treatment] Surface treatment was performed on both sides of the roll sheet (while an inert gas (nitrogen / Ar ratio 75 / 25) containing 0.50% by volume of vinyl acetate and 0.25% by volume of carbon dioxide was flowed near the discharge electrode and roll-shaped ground electrode of a corona discharge device, the sheet was continuously passed along the roll-shaped ground electrode, and a discharge amount of 150 W min / m was obtained. ２The sheet was then wound into a roll to obtain a surface-treated sample. The oxygen element ratio and surface elastic modulus were then evaluated as described below.

[0104] [Method for manufacturing laminate] The obtained fluororesin sheet material and electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) were used to cut out each of them, and then the copper foil, the fluororesin sheet material, and the copper foil were stacked in this order, with the unroughened side of the copper foil in contact with the fluororesin sheet material and with the inner surface of the fluororesin sheet material after surface treatment facing up, and the laminate was heat-pressed in a vacuum heat press (model number: MKP-1000HVWH-S7 / manufactured by Mikado Technos Co., Ltd.) at a press temperature of 120°C, a preheat time of 120 seconds, a pressure of 10 MPa, and a press time of 600 seconds.

[0105] (Example 2) Discharge amount: 200 W·min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0106] Example 3 A surface-treated sample was obtained in the same manner as in Example 1, except that the carbon dioxide gas concentration was changed to 0.5% by volume, and then the sample was evaluated.

[0107] Example 4 A surface-treated sample was obtained in the same manner as in Example 1, except that the nitrogen / Ar ratio was set to 65 / 35, and then the sample was evaluated.

[0108] Example 5 A surface-treated sample was obtained in the same manner as in Example 1, except that the nitrogen / Ar ratio was 65 / 35 and the carbon dioxide gas was 0.5% by volume, and then the sample was evaluated.

[0109] (Example 6) Nitrogen / Ar ratio 65 / 35, carbon dioxide gas 0.5% by volume, discharge amount 200 W min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0110] (Example 7) As a fluororesin, fluorinated PFA1 (TFE / PPVE copolymer, composition: TFE / PPVE=94.1 / 5.9 (mass%), MFR: 16.2 g / 10 min, melting point: 305°C, number of unstable terminal groups: undetectable (main chain carbon number: 10 ６ A surface-treated sample was obtained in the same manner as in Example 1, except that the nitrogen / Ar ratio was changed to 55 / 45, and then evaluation was performed.

[0111] (Example 8) As a fluororesin, fluorinated PFA1 (TFE / PPVE copolymer, composition: TFE / PPVE=94.1 / 5.9 (mass%), MFR: 16.2 g / 10 min, melting point: 305° C., number of unstable terminal groups: undetectable (main chain carbon number: 10 ６ The nitrogen / Ar ratio was 55 / 45, and the discharge amount was 200 W min / m. ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0112] (Example 9) As a fluororesin, fluorinated PFA1 (TFE / PPVE copolymer, composition: TFE / PPVE=94.1 / 5.9 (mass%), MFR: 16.2 g / 10 min, melting point: 305°C, number of unstable terminal groups: undetectable (main chain carbon number: 10 ６ The nitrogen / Ar ratio was 55 / 45 and the discharge amount was 250 W min / m. ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0113] (Example 10) As a fluororesin, fluorinated PFA2 (TFE / PPVE copolymer, composition: TFE / PPVE=96.1 / 3.9 (mass%), MFR: 16.0 g / 10 min, melting point: 305°C, number of unstable terminal groups: undetectable (main chain carbon number: 10 ６ The nitrogen / Ar ratio was 55 / 45 and the discharge amount was 250 W min / m. ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0114] (Comparative Example 1) The nitrogen / Ar ratio was 100 / 0, vinyl acetate was not added, carbon dioxide gas was not added, and the discharge amount was 80 W·min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0115] (Comparative Example 2) The nitrogen / Ar ratio was 100 / 0, vinyl acetate was not added, carbon dioxide gas was not added, and the discharge amount was 200 W·min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0116] (Comparative Example 3) Nitrogen / Ar ratio 100 / 0, carbon dioxide gas 0.25% by volume, discharge amount 80 W·min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0117] (Comparative Example 4) The nitrogen / Ar ratio was 100 / 0, no carbon dioxide gas was added, and the discharge amount was 200 W·min / m ２ A surface-treated sample was obtained in the same manner as in Example 1, except that the above-mentioned conditions were changed, and then the sample was evaluated.

[0118] (Method for measuring oxygen element ratio) The measurement sample was obtained by cutting out a fluororesin sheet material for laminate production, and cutting out a 1 cm x 1 cm square from a location adjacent to the cut-out portion. Using a scanning X-ray photoelectron spectroscopy analyzer (XPS / ESCA) PHI5000 VersaProbe II (manufactured by ULVAC-PHI Inc.), the oxygen element ratio on the inner surface of a roll of surface-treated fluororesin sheet material was measured under the conditions shown below. Carbon, oxygen, fluorine, nitrogen, and silicon were detected, and the oxygen element ratio was determined from the composition ratio of C1s, O1s, F1s, N1s, and Si2p. Radiation source: Monochromated AlKα Beam diameter: 100 μm X-ray output: 25 W Measurement area: 1000 μm x 300 μm Pass energy: 23.5 eV Detection angle: 45°

[0119] (Method for measuring surface elastic modulus) When a fluororesin sheet material for laminate production was cut out, a measurement sample was obtained by cutting out a 1 cm x 1 cm square from a location adjacent to the cut-out portion. The surface elastic modulus was measured on the inner surface of a roll of surface-treated fluororesin sheet material using a scanning atomic force microscope AFM5300E (manufactured by Hitachi High-Tech Science Corporation) under the following conditions. Cantilever: Si cantilever (with Al coating on the back, manufactured by Hitachi High-Tech Fielding Corporation, tip R≦10 nm, spring constant 2 N / m) Indentation load: 10 nN Measurement mode: Force curve mapping (FCM) mode Measurement environment: Air, 120°C Measurement field of view: 20 μm x 10 μm (64 points x 32 points)

[0120] (Method of calculating the distribution width of the surface elastic modulus) A histogram was created for the surface elastic modulus at a total of 2,048 points obtained as described above, with a class interval of 0.01 GPa, and the difference between the class value when the cumulative relative frequency reached 0.99 and the class value when the cumulative relative frequency reached 0.01 was taken as the distribution width. The distribution width was evaluated at 120°C, which is the assumed bonding temperature.

[0121] (Method of calculating the rate of decrease in surface elastic modulus) The class value (median value) when the cumulative relative frequency obtained from the histogram obtained above reached 0.50 was evaluated for the rate of decrease in the median value when heated from room temperature (25°C) to 120°C.

[0122] (Adhesion strength between copper foil and fluororesin sheet material) An aluminum plate was attached to the underside of the laminate with adhesive tape, and a 10 mm wide copper foil was gripped and pulled at a speed of 50 mm per minute in a direction 90° to the plane of the laminate using a Tensilon universal testing machine (manufactured by Shimadzu Corporation) to measure the peel strength of the copper foil, and the obtained value was taken as the adhesive strength. The measurement results are shown in Table 2.

[0123]

[0124] From the results in Table 2, it can be seen that the fluororesin sheet materials of the examples had good adhesiveness at temperatures below the melting point of the fluororesin.

[0125] The fluororesin sheet material of the present disclosure can be suitably used as a circuit substrate.

Claims

1. A sheet material containing a fluororesin, wherein the following general formula (A) is satisfied on at least one surface: O≧E+0.5 (A), where O is the oxygen element ratio obtained when measured with a scanning X-ray photoelectron spectroscopy (XPS), and E is the difference between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 in a multipoint measurement of the surface elastic modulus at 120°C using a scanning atomic force microscope.

2. The fluororesin sheet material according to claim 1, wherein the difference E between the surface elastic modulus when the cumulative relative frequency reaches 0.99 and the surface elastic modulus when the cumulative relative frequency reaches 0.01 satisfies the condition 0.35 GPa≦E≦3.0 GPa.

3. A fluororesin sheet material according to claim 1 or 2, wherein the oxygen element ratio O is 1.35 atomic % < O < 20 atomic %.

4. A sheet material containing fluororesin, in which, on at least one surface, when heated from 25°C to 120°C, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more in multipoint measurements of the surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C.

5. A fluororesin sheet material according to any one of claims 1 to 3, which comprises a fluororesin, and on at least one surface, when heated from 25°C to 120°C, in multipoint measurements of the surface elastic modulus at 25°C and 120°C using a scanning atomic force microscope, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more.

6. A fluororesin sheet material according to any one of claims 1 to 5, wherein the fluororesin is tetrafluoroethylene-perfluoroalkylvinyl ether (PFA) or tetrafluoroethylene-hexafluoropropylene (FEP).

7. A laminate comprising the fluororesin sheet material according to any one of claims 1 to 6 and a metal layer.

8. The laminate according to claim 7, wherein the adhesive strength between the measurement surface of the fluororesin sheet material and the metal layer is 0.5 N / cm or more.

9. The laminate according to claim 7 or 8, further comprising a layer other than the fluororesin sheet material and the metal layer, wherein the layer other than the fluororesin sheet material and the metal layer provided on the surface of the fluororesin sheet material is a layer made of at least one material selected from the group consisting of polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, polyphenylene ether, divinylbenzene, and polybutadiene.

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