Fluororesin sheet material and laminate containing the same

Abstract

To provide a fluororesin sheet-like material excellent in adhesive properties with a metal layer even in the case of adhesion at a temperature below a melting point of fluororesin.SOLUTION: A fluororesin sheet-like material is a sheet-like material including fluororesin and the following general formula (A) holds for at least one surface. O≥E+0.5 ... (A) where O is an oxygen element ratio obtained by measurement by a scanning X-ray photoelectron spectrometer, and E is a difference between a surface elastic modulus when a cumulative relative frequency reaches 0.99 and a surface elastic modulus when the cumulative relative frequency reaches 0.01 in multipoint measurement of surface elastic modulus by a scanning atomic force microscope at 120°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a fluororesin sheet material and a laminate containing the same. [Background technology]

[0002] To realize high-speed communication using next-generation information and communication (high-frequency 5G), the dielectric (insulating material) of printed circuit boards used in antennas and transmission lines is required to have low transmission loss characteristics. Against this backdrop, fluoropolymer materials (PTFE, PFA, etc.) with excellent electrical properties are attracting attention as insulating materials for printed circuit boards. On the other hand, fluoropolymer materials generally have poor adhesion to other materials, so surface modification technologies such as plasma treatment are used to improve adhesion (Patent Document 1, etc.).

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

[0004] Furthermore, Patent Document 3 describes how surface modification treatment can be applied to the surface of a heat-resistant film such as aramid by corona discharge to achieve a surface modulus of 1.5 GPa or higher, thereby improving the adhesion between the heat-resistant film and the adhesive resin and enabling thinner designs. Furthermore, Patent Document 4 describes how setting the surface modulus of a release polyester film for semiconductor encapsulation processes within a specific range can suppress the occurrence of cracks in the release polyester film and prevent the transfer of resin flow marks to the surface of the release film. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-181735 [Patent Document 2] International Publication No. 2022 / 158524 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-123928 [Patent Document 4] Japanese Patent Application Laid-Open No. 2023-116512 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] An object of the present disclosure is to provide a fluororesin sheet-like material having excellent adhesion to a metal layer even when adhered at a temperature below the melting point of the fluororesin. [Means for Solving the Problems]

[0007] The present disclosure is a sheet-like material containing a fluororesin, and is a fluororesin sheet-like material in which the following general formula (A) holds on at least one surface. O≧E + 0.5 (A) O: Oxygen element ratio obtained when measured by a scanning X-ray photoelectron spectrometer (XPS) E: 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 the multi-point measurement of the surface elastic modulus by 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 satisfies 0.35 GPa ≦ E ≦ 3.0 GPa. Furthermore, it is preferable that the oxygen element ratio O satisfies 1.35 atomic% < O < 20 atomic%.

[0009] The present disclosure is a sheet-like material containing a fluororesin, and on at least one surface Even in a fluororesin sheet-like material, when measured by multi-point measurement of surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C after heating 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.

[0010] The present disclosure relates to a sheet-like material containing a fluororesin, which is a fluororesin sheet-like material satisfying the following general formula (A) on at least one surface, and further, on at least one surface, Even in a fluororesin sheet-like material, when measured by multi-point measurement of surface elastic modulus using a scanning atomic force microscope at 25°C and 120°C after heating 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. O≧E + 0.5 (A) O: Oxygen element ratio obtained when measured by a scanning X-ray photoelectron spectrometer (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 the multi-point measurement of the surface elastic modulus by a scanning atomic force microscope at 120°C.

[0011] It is preferable that the fluororesin is tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) or tetrafluoroethylene-hexafluoropropylene (FEP).

[0012] The present disclosure also relates to a laminate including a fluororesin sheet-like material and a metal layer. <{ It is preferable that the adhesion strength between the measurement surface of the fluororesin sheet-like material and the metal layer in the laminate of the present disclosure is 0.5 N / cm or more.

[0013] In the above laminate, further, it has a layer other than the fluororesin sheet-like material and the metal layer, The layer provided on the surface of the fluororesin sheet-like material, other than the fluororesin sheet-like material and the metal layer, is preferably a layer made of at least one 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. [Effects of the Invention]

[0014] The fluororesin sheet material of this disclosure exhibits excellent adhesion to metal layers even when bonded at a temperature below the melting point of the fluororesin. [Modes for carrying out the invention]

[0015] The details of this disclosure are described below. Conventionally, in the surface modification of fluororesin sheets by plasma treatment, patents specifying the amount of oxygen element and the amount of specific functional groups as requirements for obtaining good adhesion are occasionally seen. However, for adhesion below the melting point, these requirements alone are insufficient to obtain satisfactory adhesion. Insufficient adhesion can lead to peeling and a decrease in the reliability of the substrate in subsequent processes.

[0016] The present inventors have found that by improving the in-plane uniformity of the surface treatment when surface-treating a fluororesin sheet material, the adhesion to metals such as copper foil is improved when bonded at a temperature below the melting point of the fluororesin. Furthermore, by evaluating not only the oxygen content of the fluororesin sheet material but also the in-plane uniformity of the surface modulus, we identified two parameters that enable high adhesion.

[0017] One of these conditions is that the following general formula (A) holds true on at least one surface of the sheet-like material containing fluororesin. O≧E+0.5···(A) O: Oxygen element ratio obtained when measured by scanning X-ray photoelectron spectroscopy (XPS) E: The difference between the surface modulus at which the cumulative relative frequency reaches 0.99 and the surface modulus at which the cumulative relative frequency reaches 0.01, measured at multiple points using 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 modulus, as shown in the general formula (A) above, exhibits good adhesion to metal foil when bonded at a temperature below the melting point of the fluororesin. As a result, defects in appearance and peeling are eliminated, improving the reliability of the circuit board. By enabling bonding at temperatures below the melting point of fluororesin, warping of the metal foil is reduced, resulting in a better appearance. Furthermore, reduced peeling maintains surface smoothness, thus preserving low transmission loss characteristics. Lower bonding temperatures also simplify manufacturing and increase production efficiency.

[0019] Here, the oxygen element ratio is determined by the following method. (Method for measuring the oxygen element ratio) The oxygen element ratio on the surface of a fluororesin sheet material was measured using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.) under the conditions described 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: Monochromatized AlKα Beam diameter: 100 μm X-ray output: 25W Measurement area: 1000μm x 300μm Pass energy: 23.5 eV Detection angle: 45°

[0020] Furthermore, the above surface modulus was obtained by measuring 64 points × 32 points in a 20 μm × 10 μm area using the force curve mapping mode of a scanning atomic force microscope AFM5300E (manufactured by Hitachi High-Tech Science Corporation). For the 2048 surface moduli obtained in this way, histograms were created at a class pitch 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 defined as the width of the distribution. The above value E represents the width of the distribution at a measurement temperature of 120°C, and a smaller value indicates higher uniformity of the treated surface.

[0021] Although the mechanism by which the above results are obtained is not clear, in order to form a bond with a metal, it is important to bring the functional groups on the surface of the metal as close together as possible. It is presumed that by making the surface modulus of the fluororesin sheet material uniform across the surface when heated, and eliminating the gap between hard and soft areas, the adhesion to the metal foil surface is improved even without heating it to near the melting point of the fluororesin to soften it, and the adhesive strength is improved even at low temperatures. Furthermore, in addition to the uniformity of the surface modulus in the plane during heating, adhesion is improved when the relationship with the oxygen element ratio of the fluororesin sheet material is specific.

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

[0023] Also, it is preferable that the above oxygen element ratio O satisfies 1.35 atomic% < O < 20 atomic%. The lower limit of the above oxygen element ratio O is more preferably 1.5 atomic% or more, still more preferably 1.8 atomic% or more, and most preferably 2.0 atomic% or more. Also, the upper limit of the above oxygen element ratio O is more preferably 25 atomic% or less, still more preferably 20 atomic% or less, and most preferably 15 atomic% or less. If the oxygen element ratio is within the above range, it is advantageous in that the functional groups contributing to adhesion are in a suitable amount.

[0024] Another parameter found in the present disclosure is that, in the multi-point measurement of the surface elastic modulus by a scanning atomic force microscope at 25°C and 120°C when heating from 25°C to 120°C on at least one surface of the fluororesin sheet-like material, the median value of the surface elastic modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more. Thus, the median value of the surface elastic modulus when heating the fluororesin sheet-like material from room temperature level to 120°C decreases by 20% or more. That is, it is presumed that even at an adhesion temperature below the melting point of the fluororesin, the surface tends to become soft and is more likely to be at an appropriate distance for forming bonds with the functional groups present on the surface of the adhesion target.

[0025] Also, it is preferable that the fluororesin sheet-like material of the present disclosure simultaneously satisfies the above two parameters because it is more likely to be close to the surface of the adhesion target, and thereby the functional groups present on their respective surfaces can be efficiently utilized for bond formation.

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

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

[0028] (Per)fluoro(alkyl vinyl ether) (PAVE) may be a fluoroalkyl vinyl ether or a perfluoro(alkyl vinyl ether). In this disclosure, "perfluoro(alkyl vinyl ether)" means an alkyl vinyl ether that does not contain a CH bond. The PAVE that constitutes the above PAVE unit is given by the general formula (1): CF2 = CFO(CF2CFY 1 O) p -(CF2CF2CF2O) q -R f (1) (In the formula, Y 1 represents F or CF3, and R f represents a perfluoroalkyl group having 1 to 5 carbon atoms. p represents an integer from 0 to 5, and q represents an integer from 0 to 5. ) Monomers represented by general formula (2): CFX=CXOCF2OR 1 (2) (In the formula, X represents the same or different H, F, or CF3, and R represents the same or different H, F, or CF3.) 1represents a linear or branched fluoroalkyl group having 1 to 6 carbon atoms which may contain 1 or 2 atoms 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 or 2 atoms selected from the group consisting of H, Cl, Br, and I. At least one monomer selected from the group consisting of monomers represented by ) can be mentioned.

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

[0030] The content of the PAVE unit in the above TFE / PAVE copolymer is preferably 1.0 to 10% by mass, more preferably 2.0% by mass or more, further 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, further preferably 7.0% by mass or less, particularly preferably 6.5% by mass or less, and most preferably 6.0% by mass or less with respect to all monomer units. The amount of the above PAVE unit is 19 measured by the F-NMR method. The above TFE / PAVE copolymer may be a copolymer consisting only of TFE units and PAVE units.

[0031] When the above fluororesin sheet-like 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 above-mentioned 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 above-mentioned glass transition temperature is a value obtained by dynamic viscoelasticity measurement.

[0033] The above TFE / HFP copolymer contains TFE units and HFP units. The TFE unit content in the above TFE / HFP copolymer is preferably 70% by mass or more, more preferably 85% by mass or more, 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 above TFE / HFP copolymer preferably has a mass ratio (TFE / HFP) of 70-99 / 1-30 (mass%) of TFE units to HFP units. More preferably, the above mass ratio (TFE / HFP) is 85-95 / 5-15 (mass%).

[0035] The above TFE / HFP copolymer may further contain (per)fluoro(alkyl vinyl ether) (PAVE) units. Examples of PAVE units included in the above TFE / HFP copolymer are the same as those described above. The above TFE / PAVE copolymer does not contain HFP units, and therefore differs from the TFE / HFP / PAVE copolymer in this respect.

[0036] When the above TFE / HFP copolymer is a copolymer containing TFE units, HFP units, and PAVE units (hereinafter also referred to as "TFE / HFP / PAVE copolymer"), it is preferable that the mass ratio (TFE / HFP / PAVE) is 70-99.8 / 0.1-25 / 0.1-25 (mass%). It is more preferable that the above mass ratio (TFE / HFP / PAVE) is 75-98 / 1.0-15 / 1.0-10 (mass%). It is preferable that the above TFE / HFP / PAVE copolymer contains 1% by mass or more of HFP units and PAVE units in total with respect to the total monomer units.

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

[0038] The PAVE unit content is more preferably 20% by mass or less, even more preferably 10% by mass or less, and particularly preferably 3% by mass or less. Furthermore, the PAVE unit content is preferably 0.1% by mass or more, and more preferably 1% by mass or more. Note that the PAVE unit content is 19 It can be measured by the 1F-NMR method.

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

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

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

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

[0043] The above-mentioned fluororesin can be produced by conventionally known methods, such as emulsion polymerization or suspension polymerization, by appropriately mixing monomers that form its constituent units and additives such as polymerization initiators. Among these, it is more preferable that it is obtained by emulsion polymerization.

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

[0045] The above-mentioned fluororesin is preferable to have fewer functional groups, and in particular, a lower number of unstable end groups. Such fluororesins can be produced by adjusting the conditions during manufacturing (polymerization reaction), or by reducing the number of unstable end groups by performing fluorine gas treatment, heat treatment, or supercritical gas extraction treatment on the polymerized fluororesin. Fluorine gas treatment is preferred due to its excellent processing efficiency and the fact that some or all of the unstable end groups are converted to -CF3, which becomes a stable end group. Using a fluororesin with a reduced number of unstable end groups in this way is preferable because it lowers the electrostatic loss tangent and reduces the loss of electrical signals.

[0046] The number of unstable end groups mentioned above is not particularly limited, but for fluororesins with a main chain of 10 carbon atoms... 6 The value per unit is preferably 450 or less, more preferably 250 or less, even more preferably 100 or less, and most preferably 50 or less. Considering the effect of reducing dielectric loss tangent, it is preferably less than 10, and even more preferably 5 or less.

[0047] Examples of unstable end groups include functional groups such as -COF, -COOH free (free COOH), -COOH bonded (associated -COOH), hydroxyl groups (-CH2OH, etc.), -CONH2, -COOR (R=CH3, etc.), -CF2H, and -OCOO-R (n-propyl carbonate, etc.).

[0048] The number of unstable end groups is measured specifically by the following method. First, the above-mentioned fluororesin is melted and compressed to produce a film with a thickness of 0.25 to 0.3 mm. This film is analyzed by Fourier transform infrared spectroscopy to obtain the infrared absorption spectrum of the above-mentioned fluororesin, and a difference spectrum is obtained from the base spectrum, which is completely fluorinated and does not contain any functional groups. From the absorption peak of a specific functional group that appears in this difference spectrum, the number of carbon atoms in the above-mentioned fluororesin is calculated according to the following formula (A): 1 × 10 6 Calculate the number of unstable terminals per unit. N = I × K / t (A) I: Absorbance K: Correction coefficient t: Film thickness (mm)

[0049] For reference, Table 1 shows the absorption frequency, molar extinction coefficient, and correction factor for the unstable end groups used in this specification. The molar extinction coefficient was determined from FT-IR measurement data of a small molecule model compound.

[0050] [Table 1]

[0051] The above fluorination treatment can be carried out by bringing an unfluorinated fluororesin into contact with a fluorine-containing compound.

[0052] The fluorine-containing compounds mentioned above are not particularly limited, but include fluorine radical sources that generate fluorine radicals under fluorination treatment conditions. Examples of fluorine radical sources include F2 gas, CoF3, AgF2, UF6, OF2, N2F2, CF3OF, and halogenated fluorides (e.g., IF5, ClF3).

[0053] The fluorine radical source, such as F2 gas, may be at 100% concentration, but it is preferable to mix it with an active gas and dilute it to 5-50% by mass before use, and more preferably to 15-30% by mass before use. Examples of the inert gas include nitrogen gas, helium gas, and argon gas, but nitrogen gas is preferred from an economic standpoint.

[0054] The conditions for the above fluorination treatment are not particularly limited, and the fluororesin may be brought into contact with a fluorine-containing compound in a molten state. However, it is usually carried out at a temperature below the melting point of the fluororesin, preferably 20 to 220°C, and more preferably 100 to 200°C. The above fluorination treatment is generally carried out for 1 to 30 hours, preferably 5 to 25 hours. The above fluorination treatment preferably involves bringing an unfluorinated fluororesin into contact with fluorine gas (F2 gas).

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

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

[0057] The fluororesin sheet material of this 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 above-mentioned fluororesin sheet material was measured using the reflection spectroscopy method of the film thickness measurement system F20 (manufactured by Filmetrics).

[0059] The arithmetic mean roughness (Ra) of the fluororesin sheet material of this 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. If the above Ra is within the above range, it is preferable because it has high smoothness and the surface treatment is applied more uniformly within the plane, resulting in better adhesion to the surface to be bonded. The above Ra value is obtained by the measurement method described below. (Ra (arithmetic mean roughness) of fluororesin sheet material) Using a scanning atomic force microscope (AFM5000, manufactured by Hitachi High-Tech Corporation), the surface Ra of the surface-treated film and copper foil in a 30 μm × 30 μm area was measured under the conditions described below. Cantilever: SI-DF20 (tip radius < 10 nm, spring constant 15 N / m) Measurement mode: AC mode Scanning frequency: 1Hz Pixel count: 256 x 256

[0060] Furthermore, it is preferable that the difference between the oxygen element ratio of the fluororesin sheet material of this disclosure measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) on its surface and the oxygen element ratio measured by scanning X-ray photoelectron spectroscopy (XPS / ESCA) after etching the fluororesin sheet material with an argon gas cluster ion beam at an incident angle of 45° in the depth direction for 15 minutes is 1.0 atomic% or more. Increasing the difference in the oxygen element ratio from the surface to the depth direction is preferable because it allows for obtaining a predetermined transmission loss while maintaining adhesion.

[0061] The oxygen element ratio after etching, as described above, represents the oxygen element ratio on the surface of the fluororesin sheet material before surface treatment. Therefore, the difference in the oxygen element ratio above represents the increase in the oxygen element ratio due to the surface treatment.

[0062] The above-mentioned fluororesin sheet material preferably has an adhesive strength greater than 30 N / m when two sheets of the same surface are bonded together at 200°C, either on one side or both sides. Having such an adhesive strength ensures that the fluororesin sheet material maintains excellent adhesion when used in combination with various other substrates, even after heat treatment. The above adhesive strength is more preferably greater than 50 N / m, and even more preferably greater than 100 N / m.

[0063] More specifically, the above adhesive strength was determined by overlapping the surface-treated surfaces of two fluororesin sheet materials and preparing a sample using heat pressing (200°C, 0.1 MPa, 60 s). This sample was then cut into 10 mm wide strips, and the peel strength was measured using a precision universal testing machine, Autograph AGS-X 100N (manufactured by Shimadzu Corporation). The unbonded portion of the strip sample was grasped by the upper and lower chucks of the Autograph and pulled at a speed of 100 mm per minute. The resulting value was defined as the adhesive strength.

[0064] The resin sheet material of this disclosure preferably has a dielectric loss tangent of less than 0.0015 at 10 GHz. This is preferable because it can keep the loss of electrical signals in the circuit low. The dielectric loss tangent is more preferably less than 0.0013, even more preferably less than 0.0010, and most preferably 0.00050 or less. Furthermore, assuming that signals are transmitted at higher frequencies and antennas are transmitted and received, the dielectric loss tangent 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. In order to keep the dielectric loss tangent within the above range, it is preferable to use a resin with few unstable end groups, and more preferably to use a fluororesin that has undergone end fluorination treatment.

[0065] (Method for manufacturing fluororesin sheet material) The following details an example of a method for manufacturing the fluororesin sheet material of the present disclosure described above. However, the fluororesin sheet material of the present disclosure is not limited to those manufactured by the following manufacturing method. The fluororesin sheet material of this disclosure is not limited in terms of the molding method used to form the sheet, but examples include a melt molding method such as extrusion molding, and a casting method in which a solution or dispersion containing fluororesin is prepared and then applied and dried on a substrate. Furthermore, the sheet may be stretched by a uniaxial stretching or biaxial stretching method, or it may be an unstretched sheet.

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

[0067] The specific methods for surface modification described above are not limited, but some specific examples are detailed below. Surface modification of fluororesin sheet materials can be performed using conventional discharge treatments such as corona discharge treatment, glow discharge treatment, plasma discharge treatment, and sputtering treatment. 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, ethylene gas, etc., into the discharge atmosphere. Alternatively, surface modification can be performed by exposing the surface to be modified to an atmosphere of an inert gas containing organic compounds, applying a high-frequency voltage between electrodes to induce a discharge, thereby generating active species on the surface, and then introducing functional groups of organic compounds or graft polymerization of polymerizable organic compounds. Examples of the above-mentioned 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. If the ratio of nitrogen gas to argon gas is within the above range, it is advantageous in that the discharge is stable and more uniform surface modification can be achieved within the plane. Furthermore, the amount of carbon dioxide is preferably 0.05 to 5% by volume, and more preferably 0.1 to 2% by volume, relative to the nitrogen gas / argon gas. If the carbon dioxide content is within the above range, it is advantageous in that functional groups contributing to adhesion on the surface of the fluororesin sheet material are introduced within a suitable range.

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

[0070] The concentration of the organic compound in the inert gas containing the organic compound varies depending on its type, 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 should be appropriately selected depending on the desired degree of surface modification, the type of fluororesin, and the type and concentration of organic compounds. Typically, the discharge rate is 50-1500 W·min / m 2 Preferably 100 W·min / m 2 More than 1400W min / m 2 More preferably, 200 W·min / m 2 More than 1300W min / m 2 Discharge treatment will be performed within the following range. The processing temperature can be any temperature within the range of 0°C to 100°C. However, it is preferable to keep the temperature below 80°C due to concerns about stretching and wrinkling of the fluororesin sheet material. The degree of surface modification of the fluororesin sheet material is such that, considering the deactivation of oxygen elements on the surface due to heat during lamination with metal foil, etc., and the resulting decrease in adhesive strength, the oxygen element abundance observed by ESCA is preferably 1.5% or more, more preferably 1.75% or more, more preferably 2.0% or more, and even more preferably 2.5% or more. There is no specific upper limit, but considering the impact on productivity and other physical properties, it is preferable that it be 25.0% or less. While there are no specific requirements regarding the relative abundance of nitrogen, it is preferable that it be 0.1% or higher.

[0071] In the above surface modification process, the discharge rate, which indicates the output per unit area, should be 1.0 to 10 W / cm². 2 It is preferable to perform the discharge treatment within the specified range and adjust the gas concentration / line velocity ratio to a range of 0.005 to 0.05 L / m. The gas concentration / line velocity ratio referred to here is the ratio obtained by dividing the concentration of the organic compound in the organic compound-containing inert gas by the line velocity. If the flow rate is lower than 0.005 L / m, the space will not be sufficiently filled with gas relative to the transport speed, making it difficult for the activated gas to come into contact with the surface of the fluororesin sheet material, and the uniformity within the surface tends to decrease. If the flow rate is higher than 0.05 L / m, the surface will be overtreated and damaged, causing low molecular weight compounds to form on the surface, which will create a brittle layer and conversely lead to a decrease in adhesive strength. Therefore, it is presumed that the surface of the fluororesin sheet material will be treated more uniformly and the desired adhesive strength will be obtained, so treatment within this range is particularly preferable.

[0072] Furthermore, in the above method, it is preferable to perform a surface treatment on the fluororesin sheet material such that the difference between the oxygen element ratio measured on one or both sides of the surface state using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) and the oxygen element ratio measured after etching the fluororesin-containing layer with an argon gas cluster ion beam at an incident angle of 45° in the depth direction for 15 minutes, and then measuring it using a scanning X-ray photoelectron spectroscopy (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 beforehand. This reduces dimensional changes in the fluororesin film due to heat from the pressure roll during the lamination process with metal foil to manufacture a laminate, allowing for wrinkling-free bonding and thus suppressing defects in the appearance of the laminate. Since these heat treatments reduce the oxygen content on the surface of the fluororesin sheet material, it is preferable to perform surface modification under conditions that ensure a sufficient amount of surface oxygen is obtained when the fluororesin sheet material and metal foil are bonded together.

[0074] Annealing can be carried out by heat treatment. This heat treatment can be performed, for example, by passing the material through a heating furnace in a roll-to-roll manner. Heat treatment may also be performed in a batch-type drying oven.

[0075] The annealing temperature is preferably above the glass transition temperature of the fluororesin - 20°C and below the melting point, more preferably above the glass transition temperature of the fluororesin and below the melting point - 20°C, and even more preferably above the glass transition temperature of the fluororesin and below the melting point - 60°C. The annealing time is not particularly limited, but can be appropriately adjusted, for example, between 0.5 and 60 minutes.

[0076] When heating using the roll-to-roll method described above, the tension can be adjusted appropriately depending on the thickness of the fluororesin sheet material and the set temperature, but it is preferable to keep it at 20 N / m or less. Heating under these conditions is preferable because it allows for sufficient relaxation of internal stress and prevents dimensional changes.

[0077] The above surface treatment and annealing treatments are not limited to any particular order, nor are they limited to being performed only once; they may be performed two or more times.

[0078] (Laminated structure) The fluororesin sheet material of this disclosure is suitably used to form laminates with metals, resin substrates, and the like. This disclosure also relates to a laminate comprising the above-mentioned fluororesin sheet material and a metal layer. The laminate of the present disclosure is preferably configured such that a surface of the fluororesin sheet material having the above-mentioned properties is in contact with a metal layer.

[0079] (metal layer) Examples of metal species constituting the metal layer in this disclosure include copper, aluminum, stainless steel, nickel, and gold. Alloys of these can be used. From the viewpoint of conductivity and circuit processability, copper foil is preferred.

[0080] The copper foil described above preferably has an Rz of 1.5 μm or less. That is, the fluororesin sheet material of this disclosure has excellent adhesion to copper foil with 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 described above, and the Rz value of the other surface is not particularly limited. The above Rz is the sum of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The above surface roughness is the ten-point average roughness specified in JIS-B0601. In this specification, the above Rz is the 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 foils mentioned above are not particularly limited; for example, rolled copper foil, electrolytic copper foil, etc., are examples.

[0083] The copper foil with an Rz of 1.5 μm or less is not particularly limited, and commercially available foils can be used. Examples of commercially available copper foils with 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 Industry Co., Ltd.).

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

[0085] The above surface treatment is not particularly limited, but may include 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 it has at least one selected from amino groups, (meth)acrylic groups, mercapto groups, and epoxy groups at its terminal end. The hydrolyzable group is not particularly limited, but may include alkoxy groups such as methoxy groups and ethoxy groups. The copper foil used in this disclosure may have a rust-preventive layer (such as an oxide film like chromate), a heat-resistant layer, etc. formed on it.

[0086] Surface-treated copper foil having a surface treatment layer of the above-mentioned silane compound on the surface of the copper foil can be manufactured by preparing a solution containing the silane compound and then surface-treating the copper foil with this solution.

[0087] The copper foil described above may have a roughened layer on its surface, for example, to improve adhesion with the fluororesin sheet material. Furthermore, if the roughening treatment is likely to degrade the performance required in this disclosure, the amount of roughening particles electrodeposited onto the copper foil surface may be reduced or the roughening treatment may be omitted as necessary.

[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-preventive treatment layer, and a chromate treatment layer may be provided from the viewpoint of improving various properties. These layers may be a single layer or multiple layers.

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

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

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

[0092] If the laminate of the present disclosure has the above layer (X), the layer configuration may be metal layer / fluororesin sheet-like material layer / layer (X). The laminate of fluororesin sheet-like material layer / metal layer may be present on one or both sides of layer (X). In this disclosure, it is preferable to provide a layer (X) on the surface of the fluororesin sheet material.

[0093] Furthermore, in the case of a laminate formed by bonding copper foil to the surface-treated surface of a fluororesin sheet material that has been surface-treated on only one side, surface modification may be performed separately on the untreated surface of the fluororesin sheet material to improve the adhesion between the laminate and other materials.

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

[0095] When bonding the above-mentioned metal foil and fluororesin sheet material, heating is required, but in the manufacture of the laminate according to this disclosure, it is preferable to use a temperature below the melting point of the fluororesin. Specifically, it is preferable to set the heating temperature to 70 to 300°C. Preferably, it is 70 to 250°C, and even more preferably, 70 to 200°C. The fluororesin sheet material of this disclosure exhibits excellent adhesion to metal layers even when bonded at a temperature below the melting point of the fluororesin. The heat treatment process may involve a roll-to-roll lamination method, or a heat treatment method for a fluororesin coating applied to a metal foil. In other words, by using a low heating temperature, warping of the metal foil is suppressed, and the smoothness of the bonding surface is less likely to be impaired during the process of bonding the metal foil layer to the fluororesin sheet material, which is preferable. As a result, cosmetic defects and peeling are eliminated, improving the reliability of the circuit board.

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

[0097] Manufactured by roll-to-roll is preferable because it reduces costs and allows for the production of long laminates. When manufacturing laminates in this way, the width of the laminate is not particularly limited, but it is preferable to be 200 mm or more.

[0098] The laminate of this disclosure exhibits good adhesion between the metal layer and the fluororesin sheet-like material, making it resistant to peeling. Therefore, it has the advantage of low transmission loss because the surface smoothness of the adhesive surface can be maintained. For this reason, it can be suitably used in circuit boards and the like. In particular, it can be especially suitably used in circuit boards for high-frequency circuits.

[0099] In this disclosure, a high-frequency circuit includes not only circuits that transmit only high-frequency signals, but also circuits that have transmission lines for transmitting non-high-frequency signals on the same plane, such as transmission lines that convert high-frequency signals to low-frequency signals and output the generated low-frequency signals to the outside, and transmission lines that supply power for driving high-frequency compatible components. It can also be used as a circuit board for antennas, filters, etc. [Examples]

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

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

[0102] [Number of unstable terminal groups] FT-IR Spectrometer 1760X (manufactured by Perkin-Elmer) The analysis was performed using [this method].

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

[0104] [Method for manufacturing laminates] Using 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 Industry Co., Ltd.), after cutting out each, the copper foil, fluororesin sheet material, and copper foil were stacked in that order, with the unroughened surface of the copper foil in contact with the fluororesin sheet material, and the inner surface of the roll after surface treatment facing upwards for the fluororesin sheet material. The materials were then heat-pressed using a vacuum heat press (model number: MKP-1000HVWH-S7 / manufactured by Mikado Technos Co., Ltd.) at a press temperature of 120°C, a preheating time of 120 seconds, a pressing pressure of 10 MPa, and a pressing time of 600 seconds.

[0105] (Example 2) Discharge rate: 200W·min / m2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0106] (Example 3) Samples were obtained with the same surface treatment as in Example 1, except that the amount of carbon dioxide was set to 0.5% by volume, and then evaluated.

[0107] (Example 4) Samples were obtained with surface treatment in the same manner as in Example 1, except that the nitrogen / Ar ratio was set to 65 / 35, and then evaluated.

[0108] (Example 5) Samples were obtained with surface treatment in the same manner as in Example 1, except that the nitrogen / Ar ratio was set to 65 / 35 and the carbon dioxide content was 0.5% by volume, and then evaluated.

[0109] (Example 6) Nitrogen / Ar ratio 65 / 35, carbon dioxide 0.5% by volume, discharge rate 200 W·min / m 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0110] (Example 7) As a fluororesin, F-modified 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 end groups: undetectable (main chain carbon number: 10) 6 Samples were obtained and evaluated in the same manner as in Example 1, except that samples with less than one particle per sample were used and the nitrogen / Ar ratio was set to 55 / 45.

[0111] (Example 8) As a fluororesin, F-modified 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 end groups: undetectable (main chain carbon number: 10) 6Using less than one atom per unit, and further setting the nitrogen / Ar ratio to 55 / 45 and the discharge rate to 200 W·min / m², 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0112] (Example 9) As a fluororesin, F-modified 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 end groups: undetectable (main chain carbon number: 10) 6 Using less than one atom per unit, and further setting the nitrogen / Ar ratio to 55 / 45 and the discharge rate to 250 W·min / m², 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0113] (Example 10) As a fluororesin, F-modified 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 end groups: undetectable (main chain carbon number 10) 6 Using less than one atom per unit, and further setting the nitrogen / Ar ratio to 55 / 45 and the discharge rate to 250 W·min / m², 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0114] (Comparative Example 1) With a nitrogen / Ar ratio of 100 / 0, no vinyl acetate added, no carbon dioxide added, and a discharge rate of 80 W·min / m². 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0115] (Comparative Example 2) The nitrogen / Ar ratio was set to 100 / 0, no vinyl acetate was added, no carbon dioxide was added, and the discharge rate was 200 W·min / m². 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0116] (Comparative Example 3) Nitrogen / Ar ratio 100 / 0, carbon dioxide 0.25% by volume, discharge rate 80 W·min / m 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0117] (Comparative Example 4) The nitrogen / Ar ratio was set to 100 / 0, no carbon dioxide was added, and the discharge rate was 200 W·min / m². 2 Except for the above, a surface-treated sample was obtained in the same manner as in Example 1, and then evaluated.

[0118] (Method for measuring the oxygen element ratio) The measurement samples were obtained by cutting a 1cm x 1cm square from an area adjacent to the cut portion of a fluororesin sheet material used for laminate manufacturing. Using a scanning X-ray photoelectron spectroscopy (XPS / ESCA) PHI5000VersaProbeII (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 described 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: Monochromatized AlKα Beam diameter: 100 μm X-ray output: 25W Measurement area: 1000μm x 300μm Pass energy: 23.5 eV Detection angle: 45°

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

[0120] (Method for calculating the surface modulus distribution width) For the 2048 surface modulus values ​​obtained as described above, histograms were created at class intervals of 0.01 GPa. The difference between the class value at which the cumulative relative frequency reached 0.99 and the class value at which the cumulative relative frequency reached 0.01 was defined as the width of the distribution. The width of the distribution at 120°C, which is assumed to be the bonding temperature, was evaluated.

[0121] (Method for calculating the reduction rate of surface modulus) The percentage decrease in the median value (class value) when the cumulative relative frequency obtained from the histogram as described above reached 0.50 was evaluated when the temperature was increased 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 bottom surface of the laminate with adhesive tape, and using a Tensilon universal testing machine (manufactured by Shimadzu Corporation), a 10 mm wide copper foil was grasped and pulled at a speed of 50 mm per minute in a direction 90° to the plane of the laminate. The peel strength of the copper foil was measured, and the obtained value was defined as the adhesive strength. The results of each measurement are shown in Table 2.

[0123] [Table 2]

[0124] The results in Table 2 show that the fluororesin sheet material of the example exhibited good adhesion at temperatures below the melting point of the fluororesin. [Industrial applicability]

[0125] The fluororesin sheet material of this disclosure can be suitably used as a circuit board.

Claims

1. A sheet-like material containing a fluororesin, wherein the following general formula (A) holds true on at least one surface, and furthermore, the difference E between the surface modulus when the cumulative relative frequency reaches 0.99 and the surface modulus when the cumulative relative frequency reaches 0.01 is 0.35 GPa ≤ E ≤ 2.0 GPa. O≧E+0.5...(A) O: Oxygen element ratio obtained when measured by scanning X-ray photoelectron spectroscopy (XPS) E: The difference between the surface modulus at which the cumulative relative frequency reaches 0.99 and the surface modulus at which the cumulative relative frequency reaches 0.01, in multi-point measurements of surface modulus using a scanning atomic force microscope at 120°C.

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

3. A sheet-like material containing fluororesin, wherein at least one surface, The fluororesin sheet material according to claim 1, wherein, in multi-point measurements of the surface modulus using a scanning atomic force microscope at 25°C and 120°C when heated from 25°C to 120°C, the median value of the surface modulus (the value when the cumulative relative frequency reaches 0.50) decreases by 20% or more.

4. The fluororesin sheet material according to claim 3, wherein the fluororesin is tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) or tetrafluoroethylene-hexafluoropropylene (FEP).

5. A laminate comprising a fluororesin sheet-like material and a metal layer as described in claim 3 or 4.

6. The laminate according to claim 5, wherein the adhesive strength between the above-mentioned measuring surface of the fluororesin sheet material and the metal layer is 0.5 N / cm or more.

7. Furthermore, it has layers other than a fluororesin sheet material and a metal layer, The laminate according to claim 5, wherein the layer provided on the surface of the fluororesin sheet-like material, other than the fluororesin sheet-like material and the metal layer, is a layer made of at least one 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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