Fluororesin film and composites containing the same

Abstract

The present invention provides a fluororesin film that suppresses the content of perfluorocarboxylic acids with 9 to 14 carbon atoms while maintaining excellent adhesive properties. [Solution] The present invention relates to a fluororesin film 1 containing a fluororesin. The nitrogen element ratio when the surface included in at least one main surface 11a of the fluororesin film 1 is measured by X-ray photoelectron spectroscopy is 1.2 at.% or more and 30 at.% or less, and the amount of perfluorocarboxylic acids with 9 to 14 carbon atoms contained in the fluororesin film 1 is 25 ppb or less.

Description

Technical Field

[0001] The present invention relates to a fluororesin film and a composite including the same.

Background Art

[0002] Fluororesin films containing fluororesins such as polytetrafluoroethylene have high chemical and thermal stability. Therefore, fluororesin films are used in various applications, such as sheets for the exterior of power storage devices such as batteries and capacitors, protective films for outdoor use devices such as solar cells, and films for coating the surface of rubber-containing base materials.

[0003] On the other hand, the adhesiveness of fluororesin films to other substances and members is generally low. Therefore, conventionally, as a technique for improving the adhesiveness of fluororesin films, it has been proposed to perform plasma treatment such as sputter etching treatment on the surface of fluororesin films. For example, Patent Document 1 proposes a technique for introducing a nitrogen element into the surface of a fluororesin film by performing plasma treatment on the surface of the fluororesin film under atmospheric pressure to improve the adhesion stability of the fluororesin film. Further, Patent Document 2 proposes improving the adhesiveness of a fluororesin film by performing sputter etching treatment on the surface of the fluororesin film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, perfluorocarboxylic acids (PFCAs), which are organofluorine compounds with 9 to 14 carbon atoms, have become subject to environmental regulations as hazardous substances. When the surface of a fluororesin film is modified using conventional plasma treatments such as sputter etching, even if the adhesion of the fluororesin film is improved, there is a possibility that PFCAs will be generated at the same time. Therefore, if sputter etching is performed under conditions that reduce damage to the film surface due to surface modification, for example, in order to reduce the generation of PFCAs, the improvement in the adhesion of the fluororesin film becomes insufficient. Thus, with conventional technology, it has been difficult to provide a fluororesin film with excellent adhesion while suppressing the PFCA content.

[0006] Therefore, the present invention aims to provide a fluororesin film with excellent adhesion while suppressing the content of PFCAs. Furthermore, the present invention also aims to provide a composite in which the fluororesin film and other materials are strongly bonded together while suppressing the content of PFCAs. [Means for solving the problem]

[0007] The present invention A fluororesin film containing fluororesin, When the surface included in at least one main surface of the fluororesin film is measured by X-ray photoelectron spectroscopy, the ratio of nitrogen to the total amount of all elements is 1.2 at.% or more and 30 at.% or less. The PFCAs contained in the aforementioned fluororesin film are 25 ppb or less. We provide fluororesin films.

[0008] From another perspective, the present invention is The above-mentioned fluororesin film of the present invention, A substrate made of a material different from the aforementioned fluororesin film and bonded to the aforementioned fluororesin film, including, Provide a composite. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a fluororesin film with excellent adhesive properties while suppressing the content of PFCAs. Furthermore, according to the present invention, it is also possible to provide a composite in which the fluororesin film and other materials are strongly bonded together while suppressing the content of PFCAs. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of the fluororesin film of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of the composite of the present invention. [Figure 3] This is a perspective view showing the positional relationship between the low-inductance antenna and the object to be plasma-treated in the plasma processing chamber used in Examples 1 and 2 and Comparative Example 1. [Figure 4] This is a cross-sectional view showing the positional relationship between the low-inductance antenna and the object to be plasma-treated in the plasma processing chamber used in Examples 1 and 2 and Comparative Example 1. [Figure 5] This is a schematic diagram showing the equipment used in the sputter etching performed in Comparative Examples 2 and 3. [Modes for carrying out the invention]

[0011] A fluororesin film according to a first aspect of the present invention is a fluororesin film containing a fluororesin, When the surface included in at least one main surface of the fluororesin film is measured by X-ray photoelectron spectroscopy, the ratio of nitrogen to the total amount of all elements is 1.2 at.% or more and 30 at.% or less. The PFCAs contained in the aforementioned fluororesin film are 25 ppb or less.

[0012] In a second embodiment of the present invention, for example, in the fluororesin film according to the first embodiment, the nitrogen element ratio is 2.5 at.% or more.

[0013] In a third aspect of the present invention, for example, in the fluororesin film according to the first or second aspect, the nitrogen element ratio is 15 at.% or less.

[0014] In a fourth aspect of the present invention, for example, in the fluororesin film according to any one of the first to third aspects, the fluorine / carbon element ratio (F / C ratio) when the surface is measured by X-ray photoelectron spectroscopy is more than 0.7 and 2.0 or less.

[0015] In a fifth aspect of the present invention, for example, in the fluororesin film according to any one of the first to fourth aspects, the surface is a modified surface, and the nitrogen element ratio on the surface is larger than the nitrogen element ratio inside the fluororesin film.

[0016] In a sixth aspect of the present invention, for example, in the fluororesin film according to any one of the first to fifth aspects, the fluororesin is polytetrafluoroethylene.

[0017] The composite according to the seventh aspect of the present invention a fluororesin film according to any one of the first to sixth aspects, an adherend made of a material different from the fluororesin film and adhered to the fluororesin film, and includes.

[0018] In an eighth aspect of the present invention, for example, in the composite according to the seventh aspect, the adherend includes a polyolefin.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments.

[0020] [Fluororesin Film] Figure 1 shows the fluororesin film of this embodiment. The fluororesin film 1 in Figure 1 contains fluororesin. When the surface included in at least one of the main surfaces 11a of the fluororesin film 1 in Figure 1 is measured by X-ray photoelectron spectroscopy (hereinafter referred to as XPS), the nitrogen element ratio to the total element is 1.2 at.% or more and 30 at.% or less. The PFCAs contained in the fluororesin film 1 is 25 ppb or less. Hereinafter, the main surface 11a whose nitrogen element ratio satisfies the above range will be referred to as the first main surface 11a.

[0021] The fluororesin film 1 shown in Figure 1 has excellent adhesion because its first main surface 11a includes a surface into which nitrogen atoms have been introduced such that the nitrogen element ratio is in the range of 1.2 at.% or more and 30 at.% or less. Furthermore, the amount of PFCAs contained in the fluororesin film 1 is kept below 25 ppb. Therefore, the fluororesin film 1 can have excellent adhesion while suppressing the PFCA content with the above configuration. In this specification, the adhesion of a fluororesin film refers to the adhesion of the fluororesin film to other substances or components.

[0022] To achieve better adhesion, the nitrogen element ratio on the first main surface 11a of the fluororesin film 1 may be 1.5 at.% or more, 2.0 at.% or more, or 2.5 at.% or more.

[0023] To achieve better adhesion, the nitrogen element ratio on the first main surface 11a of the fluororesin film 1 may be 25 at.% or less, 20 at.% or less, or 15 at.% or less.

[0024] The fluorine / carbon ratio (hereinafter referred to as the F / C ratio) of the surface included in the first main surface 11a, measured by XPS, may be greater than 0.7 and less than or equal to 2.0. Even when the F / C ratio on the first main surface 11a of the fluororesin film 1 satisfies this range, that is, even when the proportion of fluorine on the first main surface 11a of the fluororesin film 1 is relatively high, excellent adhesion can be achieved by setting the nitrogen ratio to 1.2 at.% or more and 30 at.% or less. The F / C ratio may be 0.8 or more. The F / C ratio may be 1.5 or less.

[0025] The PFCAs content in the fluororesin film 1 is preferably 20 ppb or less, and more preferably 15 ppb or less.

[0026] The surface included in the first main surface 11a is, for example, a modified surface. The nitrogen element ratio on the modified surface is, for example, greater than the nitrogen element ratio inside the fluororesin film 1. In this specification, the nitrogen element ratio inside the fluororesin film 1 is the nitrogen element ratio at a depth of 1 μm from the surface of the fluororesin film 1. The nitrogen element ratio at a depth of 1 μm from the surface of the fluororesin film 1 can be determined, for example, by exposing the area at a depth of 1 μm from the surface of the fluororesin film 1 and measuring the nitrogen element ratio on the exposed surface by XPS. The nitrogen element ratio inside the fluororesin film 1 can be considered to be substantially the same as the nitrogen element ratio on the surface of the fluororesin film before surface modification (hereinafter referred to as the original film). Therefore, if the original film is available, the nitrogen element ratio on the surface of the original film may be used as the nitrogen element ratio at a depth of 1 μm from the surface of the fluororesin film 1.

[0027] A modified surface refers to a surface whose chemical or physical surface properties have been altered by physical, chemical, or other methods, resulting in properties different from those of the original state.

[0028] In the fluororesin film 1 shown in Figure 1, only a portion of the first main surface 11a may satisfy the above-mentioned nitrogen element ratio characteristics. The entire first main surface 11a of the fluororesin film 1 shown in Figure 1 may satisfy the above-mentioned nitrogen element ratio characteristics, and may also satisfy the above-mentioned F / C ratio characteristics, in order to have a suppressed PFCAs content and excellent adhesion.

[0029] When adhesion is required on both sides of the fluororesin film 1 in Figure 1, the surface included in the second main surface 11b, which is the other main surface, may satisfy the above-mentioned nitrogen element ratio characteristics in the same way as the first main surface 11a, and may also satisfy the above-mentioned F / C ratio characteristics.

[0030] The thickness of the fluororesin film 1 is, for example, 10 to 300 μm, and may also be 30 to 250 μm or 50 to 200 μm.

[0031] The fluororesin film 1 shown in Figure 1 is a single layer. However, the fluororesin film in this embodiment may be a laminate of two or more layers, as long as it has a first main surface 11a that satisfies the above-mentioned PFCAs content and the above-mentioned nitrogen element ratio characteristics.

[0032] Examples of fluororesins include at least one selected from ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polychlorotrifluoroethylene (PCTFE), and polytetrafluoroethylene (PTFE). The fluororesin may also be PTFE.

[0033] The fluororesin film 1 may contain fluororesin as its main component. In this specification, "main component" means the component with the highest content. The fluororesin content in the fluororesin film 1 may be, for example, 50% by mass or more, and may be 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or even 99% by mass or more. The fluororesin film 1 may be composed of fluororesin. The fluororesin film 1 may contain two or more types of fluororesin.

[0034] The fluororesin film 1 may contain materials other than fluororesin. Examples of other materials in the fluororesin film 1 are resins other than fluororesin. Examples of such resins are polyolefins such as polyethylene and polypropylene, and polyvinylidene chloride. The content of other materials in the fluororesin film 1 may be, for example, 20% by mass or less, and may be 10% by mass or less, 5% by mass or less, 3% by mass or less, or even 1% by mass or less.

[0035] The shape of the fluororesin film 1 may be, for example, a polygon including squares and rectangles, a circle, an ellipse, or a strip. The corners of the polygon may be rounded. However, the shape of the fluororesin film 1 is not limited to the above examples. Polygonal, circular, and elliptical fluororesin films 1 can be distributed as individual sheets, while strip-shaped fluororesin films 1 can be distributed as rolls wound around a core. The width of the strip-shaped fluororesin film 1 and the width of the roll in which the strip-shaped fluororesin film 1 is wound can be freely set.

[0036] The fluororesin film 1 is usually non-porous. The fluororesin film 1 may be a non-porous film that does not have pores connecting both main surfaces, at least in the area of ​​use.

[0037] The fluororesin film 1 may be an impermeable film that does not allow fluids such as water, aqueous solutions, oils, and organic liquids to permeate in the thickness direction, based on the high liquid-repellent (water-repellent and oil-repellent) properties of the fluororesin. Alternatively, the fluororesin film 1 may be an insulating film (non-conductive film) based on the high insulating properties of the fluororesin. For example, the insulating properties may be 1 × 10⁻⁶. 14 It is expressed as a surface resistivity of Ω / □ or greater.

[0038] [Measurement of elemental content on the surface of fluoropolymer film] The amount of each element contained on the surface of fluororesin film 1 is measured by XPS. Specifically, first, a wide-scan measurement is performed on the surface. Then, a narrow-scan measurement is performed on the peak of each element to obtain the integrated intensity (area) of the peak of each element. From the obtained integrated intensities, the proportion (at.%) of each element on the surface of fluororesin film 1 is calculated. Using the obtained proportions of each element, the nitrogen element ratio and F / C ratio are calculated. The conditions for the wide-scan and narrow-scan measurements are as follows. X-ray source: Monochrome AlKα rays, X-ray output: 25W (acceleration voltage 15kV) X-ray beam diameter: 100 μmφ Photoelectron extraction angle: 45° relative to the evaluation surface Charge neutralization: Use of neutralization gun and Ar ion gun (neutralization mode) in combination. Binding energy correction: Charge correction is applied to the peak originating from the CF binding in the F1s spectrum to 689.7 eV.

[0039] [Measurement of PFCAs content in fluoropolymer films] The PFCAs content in fluororesin film 1 is measured by the following method: After freeze-grinding a sample of fluororesin film 1, a predetermined amount (e.g., about 0.1 g) is weighed out, and a known amount of surrogate substance is added to it. Methanol is added, and ultrasonic extraction is performed. The resulting extract is concentrated, water is added, and the amount of PFCAs is measured using a liquid chromatograph-tandem mass spectrometer (LC-MS / MS). The amounts of the substances shown in Table 1 below are measured as PFCAs. From the obtained amount of PFCAs, the PFCAs content in fluororesin film 1 is determined. The surrogate substance is a substance such as perfluorooctanoic acid (PFOA) added to confirm and correct the recovery rate in the above measurement. 13 It is a 1C stable isotope-labeled compound.

[0040] [Table 1]

[0041] [Method for manufacturing fluororesin film] The fluororesin film 1 can be manufactured, for example, by applying a modification treatment to a surface included in at least one main surface (the main surface corresponding to the first main surface 11a of the fluororesin film 1) of a raw film containing fluororesin.

[0042] An example of the above method is shown below. However, the method for producing fluororesin film 1 is not limited to the above method or the following example.

[0043] The original film is typically a film having the same structure as the fluororesin film 1, except that it does not have a first main surface 11a that includes a surface satisfying the above-mentioned nitrogen element ratio characteristics, and does not contain PFCAs that may be generated by the modification treatment.

[0044] The modification treatment of the surface included in at least one main surface of the original film is, for example, plasma treatment by inductively coupled plasma (ICP). Preferably, the ICP used is an ICP using a low-inductance antenna. That is, the modification treatment performed on the surface of the original film to be modified is preferably plasma treatment by ICP generated by applying high-frequency power to a low-inductance antenna. As the gas used for plasma treatment by ICP using a low-inductance antenna, for example, a gas containing nitrogen is used. The method of plasma treatment by ICP using a low-inductance antenna is not particularly limited, but the plasma treatment may be performed while conveying the original film in a roll-to-roll manner, or the plasma treatment may be performed in a batch manner.

[0045] Here, a low-inductance antenna refers to an antenna that has a low inductance of 7.5 μH or less and can generate inductively coupled plasma by applying high-frequency power. High-frequency power refers to the power from a high-frequency power supply (RF power supply) used to excite plasma discharge.

[0046] Plasma treatment using ICP with a low-inductance antenna allows for efficient introduction of nitrogen elements to the surface of the original film to be modified, and reduces the amount of PFCAs generated during the modification process. Therefore, plasma treatment using ICP with a low-inductance antenna allows for the formation of a surface with a specific configuration, i.e., a surface satisfying the above-mentioned nitrogen element ratio, on the original film while suppressing the amount of PFCAs generated by the modification process. In other words, plasma treatment using ICP with a low-inductance antenna allows for the easy production of a fluororesin film 1 having a surface with a nitrogen element ratio of 1.2 at.% or more and 30 at.% or less, and a PFCAs content of 25 ppb or less.

[0047] Conventionally, sputter etching, a method used for surface modification of fluororesin films, is typically performed by applying a high-frequency voltage to the original film while simultaneously reducing the pressure in a chamber containing the original film and introducing an atmospheric gas into the chamber. The high-frequency voltage can be applied, for example, using a cathode in contact with the original film and an anode spaced apart from the original film. In such sputter etching, ions generated by plasma are accelerated by an electric field and collide with the surface of the original film, thereby roughening the surface of the original film and introducing elements such as oxygen into the surface. Such sputter etching causes significant damage to the surface being modified. For example, it is presumed that the main chains of the fluororesin contained in the surface of fluororesin film 1 are cut, and the resulting carbon radicals react with oxygen and water vapor in the atmosphere, making it easy for PFCAs to be generated. If the sputter etching conditions are adjusted to reduce the amount of PFCAs generated by minimizing damage to the surface being modified, it is thought that the introduction of the target elements into the surface will be insufficient, and sufficient improvement in adhesion will not be achieved. In contrast, plasma treatment using ICP with a low-inductance antenna causes less damage to the surface being modified and has a higher surface modification effect than conventional plasma treatments such as sputter etching. Therefore, it is presumed that on the surface of a fluororesin film treated with plasma using ICP with a low-inductance antenna, the amount of cleavage of the fluororesin's main chain is reduced, resulting in fewer carbon radicals being generated, thus keeping the amount of generated PFCAs low. Furthermore, if a gas containing nitrogen is used, it is presumed that many of the generated carbon radicals will react with nitrogen plasma species and disappear, further reducing the amount of generated PFCAs.

[0048] The frequency of the high-frequency power applied during plasma processing by ICP using an inductance antenna is preferably 1 MHz or higher, more preferably 5 MHz or higher, even more preferably 10 MHz or higher, and also preferably 100 MHz or lower, more preferably 80 MHz or lower, and even more preferably 60 MHz or lower. When the frequency is above the lower limit, the plasma discharge can be stabilized while increasing the plasma current density. When the frequency is below the upper limit, the antenna potential can be suppressed, thereby suppressing damage to the fluororesin film 1 by the plasma. The high-frequency power is preferably 0.1 kW or higher, more preferably 0.3 kW or higher, even more preferably 1.0 kW or higher, and also preferably 10 kW or lower, more preferably 8 kW or lower, and even more preferably 6 kW or lower. When the high-frequency power is above the lower limit, a high-density plasma environment can be formed in the plasma processing chamber during plasma processing by ICP. When the high-frequency power is below the upper limit, excessive damage to the fluororesin film 1 by the plasma can be suppressed.

[0049] The plasma treatment gas for forming the fluororesin film 1 includes, as described above, nitrogen, for example. The plasma treatment gas may also contain gases other than nitrogen, such as oxygen.

[0050] In plasma treatment using ICP with an inductance antenna for the manufacture of fluororesin film 1, the pressure in the plasma treatment chamber is preferably 0.05 Pa or higher, more preferably 0.1 Pa or higher, even more preferably 0.2 Pa or higher, and also preferably 10 Pa or lower, more preferably 7 Pa or lower, even more preferably 5 Pa or lower, particularly preferably 3 Pa or lower, and even more preferably 1 Pa or lower. When the pressure is above the lower limit, a plasma environment with sufficient density for surface modification treatment for the manufacture of fluororesin film 1 can be formed in the plasma treatment chamber during plasma treatment. When the pressure is below the upper limit, thermal damage to the fluororesin film 1 caused by excessively high-density plasma can be suppressed during plasma treatment, and thermal deformation of the fluororesin film 1 can also be suppressed. The pressure can be adjusted, for example, by the amount of gas supplied to the plasma treatment chamber.

[0051] In plasma treatment using ICP with an inductance antenna for the manufacture of fluororesin film 1, the plasma treatment time is preferably 5 seconds or more, more preferably 10 seconds or more, even more preferably 30 seconds or more, particularly preferably 40 seconds or more, even more preferably 50 seconds or more, and also preferably 200 seconds or less, more preferably 150 seconds or less, and even more preferably 120 seconds or less. When the plasma treatment time is above the lower limit, sufficient surface modification for the manufacture of fluororesin film 1 by plasma treatment can be achieved. When the plasma treatment time is below the upper limit, thermal damage to the fluororesin film 1 caused by excessively high-density plasma can be suppressed during plasma treatment, and thermal deformation of the fluororesin film 1 can also be suppressed.

[0052] [complex] The composite of this embodiment includes a fluororesin film of this embodiment and an adherend composed of a material different from the fluororesin film and bonded to the fluororesin film. The material different from the fluororesin film includes, for example, a material with different constituent components from the material of the fluororesin film, or a material with the same constituent components as the material of the fluororesin film but with different component ratios, and other materials with different components or composition ratios from the material of the fluororesin film.

[0053] In the composite of this embodiment, the adherend may contain polyolefin.

[0054] Figure 2 shows an example of a composite of this embodiment, in which the adherend is a resin film 2, and a laminate 3 is formed by laminating a fluororesin film 1 and a resin film 2. The resin film 2 is made of a different resin material than the fluororesin film 1. The resin film 2 may be, for example, a film containing polyolefins such as polyethylene and polypropylene.

[0055] In the laminate 3, the first main surface 11a of the fluororesin film 1 is bonded to the resin film 2. As described above, the fluororesin film 1 has a suppressed PFCAs content, and furthermore, the first main surface 11a of the fluororesin film 1 has a surface with excellent adhesive properties. Therefore, the laminate 3 shown in Figure 2 is a highly reliable composite in which the PFCAs content is suppressed and the fluororesin film 1 and the resin film 2 are firmly bonded.

[0056] The laminate 3 can be manufactured, for example, by overlapping a fluororesin film 1 and a resin film 2 in a orientation where the first main surface 11a of the fluororesin film 1 is in contact with the resin film 2, and then joining the fluororesin film 1 and the resin film 2 together by heating and pressing. [Examples]

[0057] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0058] First, we will describe the evaluation method for fluoropolymer films.

[0059] [Measurement of elemental content on the surface of fluoropolymer film] The elemental content on the surface of the fluororesin film was measured by the method described above. The fluororesin films prepared in the examples and comparative examples were cut into approximately 1 cm squares and used as measurement samples. The instrument used for the measurements was an X-ray photoelectron spectrometer (ULVAC-PHI, Quantum2000).

[0060] [Measurement of PFCAs content in fluoropolymer films] The PFCAs content in the fluoropolymer film was measured by the method described above. The instruments used for the measurement were a liquid chromatograph (AB Sci-X, Exion LC) and a tandem mass spectrometer (AB Sci-X, TripleQuad 5500+). The surrogate substance used was PFOA. 13 It was a 1C stable isotope-labeled compound.

[0061] [Peeling force] The peel strength of the fluororesin film was evaluated by a T-type peel test. A fluororesin film and a polyethylene film (manufactured by Tokyo Glass Instruments, 100 μm thick) were overlapped with the modified surface of the fluororesin film in contact with the polyethylene film. The fluororesin film and polyethylene film were bonded by heating and pressing, and the resulting laminate was heated in an oven at 200°C for 10 minutes. From this laminate, a rectangle with a width of 15 mm and a length of 100 mm was cut out as a test specimen. However, this test specimen was made so that the fluororesin film and polyethylene film were not bonded at the edges. The above heating and pressing was performed using a hydraulic vacuum press (manufactured by Imoto Seisakusho) under the conditions of a temperature of 160°C, a pressure of 8 MPa, a pressing time of 60 seconds, and an atmospheric pressure of 0.1 MPa. At the edges of the test specimen where the fluororesin film and polyethylene film were not bonded, the fluororesin film and polyethylene film were each attached to the grips of a tensile testing machine, and a peel test was performed by peeling them 180° at a peeling speed of 50 mm / min. The measured 180° peel force was defined as the peel force of the fluoropolymer film. The measurement was performed three times, and the average value was used as the peel force. The peel test was conducted at room temperature. The tensile testing machine used was the Shimadzu AGX-V2.

[0062] (Example 1) A PTFE film was prepared as the base film. To a PTFE dispersion (PTFE powder concentration of 40% by mass, average particle size of PTFE powder of 0.2 μm, containing 6 parts by mass of nonionic surfactant per 100 parts by mass of PTFE), 1 part by mass of a fluorine-based surfactant (DIC, Megafac F-142D) was added per 100 parts by mass of PTFE. Next, a long polyimide film (thickness 125 μm) was immersed in the PTFE dispersion and pulled out to form a coating film of PTFE dispersion on the polyimide film. The thickness of the coating film was set to 20 μm using a measuring bar. Next, the entire film was heated at 100°C for 1 minute, followed by 390°C for 1 minute to remove water contained in the coating film and to bind the PTFE powder particles together to form a film. After repeating the above immersion and heating process 13 more times, the film was peeled off from the polyimide film to obtain a cast film of PTFE (thickness approximately 100 μm), which was the base film.

[0063] Next, the surface of the fabricated raw film was plasma treated. In this embodiment, plasma treatment by ICP using a low-inductance antenna was performed on the surface of the raw film while the raw film was being transported in a roll-to-roll manner. Specifically, an apparatus capable of performing a roll-to-roll process on the raw film was used. This apparatus consisted of a feeding chamber, a plasma treatment chamber, and a winding chamber, which were arranged in this order and were in communication with each other. The feeding chamber was equipped with a feeding roller. A roll of general-purpose PET film was set on the feeding roller as a carrier film for transporting the raw film. The plasma treatment chamber was equipped with a transport roller with a temperature control function and four low-inductance antennas. Figure 3 is a perspective view showing the positional relationship between the low-inductance antenna and the object to be plasma treated (i.e., the raw film in this embodiment) in the plasma treatment chamber used in this embodiment. Figure 4 is a cross-sectional view showing the positional relationship between the low-inductance antenna and the object to be plasma treated in the plasma treatment chamber used in this embodiment. Each low-inductance antenna 21 had an extension 21a parallel to the object 20 being processed by plasma. For the four low-inductance antennas 21, the extension length d1 was 88 mm, the maximum length d2 (length of the extension) was 100 mm, the separation distance d3 was 112 mm, the center-to-center distance d4 was 290 mm, and the center-to-center distance d5 was 280 mm. Each low-inductance antenna 21 was electrically connected to a high-frequency power supply (RF power supply, frequency 13.56 MHz) outside the plasma processing room via an impedance matching device. In Figures 3 and 4, 22 is a mounting fixture, and 23 is a field-through; the low-inductance antenna 21 was fixed to the mounting fixture 22 via the field-through 23.

[0064] The original film, which was to be subjected to plasma treatment, was cut to A4 size and bonded to a general-purpose PET film carrier film using tape so that the main surface of the original film that was not to be modified was in contact with it. This roll was set in the feeding chamber, and while the carrier film was transported from the feeding chamber to the winding chamber using a roll-to-roll method, plasma treatment was performed on the main surface of the original film that was to be modified in the plasma treatment chamber.

[0065] The plasma treatment conditions were as follows: The ultimate vacuum level in the plasma treatment chamber was 1.0 × 10⁻⁶. -4 After evacuating the apparatus to a pressure of 0.2 Pa, nitrogen (N2) gas was introduced into the plasma processing chamber to set the atmospheric pressure to 0.2 Pa. A 4 kW power supply was applied to four low-inductance antennas using a 13.56 MHz high-frequency power supply (RF power supply) to form an inductively coupled plasma of nitrogen-containing gas around the four antennas. The carrier film travel speed was set to 0.5 m / min. The temperature of the temperature-controlled transport roller was set to -8°C. The plasma processing conditions are shown in Table 2.

[0066] The main surface of the raw film subjected to the plasma treatment described above became the first main surface of the fluororesin film, and the fluororesin film of Example 1 was fabricated.

[0067] (Example 2) The fluororesin film of Example 2 was prepared in the same manner as in Example 1, except that the plasma treatment conditions were changed as shown in Table 2.

[0068] (Comparative Example 1) A fluororesin film of Comparative Example 1 was prepared in the same manner as in Example 1, except that argon (Ar) gas was introduced into the plasma treatment chamber instead of nitrogen (N2) gas, and the plasma treatment conditions were changed as shown in Table 2.

[0069] (Comparative Example 2) A fluororesin film of Comparative Example 2 was prepared in the same manner as in Example 1, except that the surface modification treatment of the original film was changed from plasma treatment using ICP with a low-inductance antenna to sputter etching.

[0070] In the sputter etching process performed in Comparative Example 2, the apparatus shown in Figure 5 was used. This apparatus consisted of four elements: a high-voltage application means for forming a low-temperature plasma, a vacuum chamber 102 for maintaining gas concentration and pressure, a supply and exhaust means for introducing and exhausting gas, and a transport mechanism for transporting, unwinding, and winding the film 100 to be processed. The high-voltage application means consisted of a cathode 104, an anode 109, and a high-frequency power supply 107 for applying an AC voltage between the two electrodes. The cathode 104 was formed in a roll shape and configured to rotate in synchronization with the transport of the film 100. The cathode 104 was also partially covered with a shielding material 108, allowing processing only at openings. The vacuum chamber 102 could be supplied with atmospheric gas via a valve 103, and exhaust could be performed from an exhaust pipe 101 using a vacuum pump or the like. The atmospheric pressure at that time could be determined by a pressure gauge 110. The transport mechanism consisted of a film feeding section 105a and a winding section 105b, and the film 100 was transported while in contact with a roll-shaped cathode 104. When a dark area was formed in the space near the film 100 by the high-voltage application means, and a plasma area was formed on the anode 109 side, positive ions were accelerated toward the cathode 104 and collided with the surface of the film 100, and sputter etching was performed by the impact.

[0071] In Comparative Example 2, no specific temperature control was performed, and the discharge energy was 1.86 W / cm² at room temperature, atmospheric pressure of 6.0 Pa, frequency of 13.56 MHz, and discharge energy of 1.86 W / cm². 2 Sputter etching was performed at a speed of 1 m / min.

[0072] (Comparative Example 3) The fluororesin film of Comparative Example 3 was prepared in the same manner as in Comparative Example 2, except that water vapor (H2O) was introduced into the sputter etching chamber instead of nitrogen (N2) gas.

[0073] (Comparative Example 4) The raw film prepared in Example 1 was used as the fluororesin film in Comparative Example 4.

[0074] The evaluation results for each fluororesin film are shown in Table 2 below.

[0075] [Table 2]

[0076] As shown in Table 2, the fluororesin films of Examples 1 and 2, which had surfaces with a nitrogen element ratio within the range of 1.2 at.% to 30 at.%, exhibited excellent adhesion. Furthermore, the fluororesin films of Examples 1 and 2 had a PFCAs content of 25 ppb or less, indicating suppressed PFCAs content. Thus, the fluororesin films of Examples 1 and 2 satisfied both suppressed PFCAs content and excellent adhesion. In contrast, the fluororesin films of Comparative Examples 1 and 2 did not have surfaces with a nitrogen element ratio within the range of 1.2 at.% to 30 at.%, and therefore exhibited low adhesion. Furthermore, the fluororesin films of Comparative Examples 1 and 2 also had PFCAs content exceeding 25 ppb. The fluororesin film of Comparative Example 3, whose surface was modified by steam sputter etching, exhibited excellent adhesion, but had a high PFCAs content, failing to achieve both suppressed PFCAs content and excellent adhesion. The untreated fluororesin film of Comparative Example 4 exhibited very low adhesion. [Industrial applicability]

[0077] The fluororesin film of the present invention can be used in a wide range of applications as a film requiring excellent adhesion, such as a sheet for the exterior of energy storage devices such as batteries and capacitors, a protective film for outdoor devices such as solar cells, and a film for covering the surface of rubber-containing substrates. [Explanation of symbols]

[0078] 1. Fluororesin film 2. Resin film 3. Laminate 11a 1st main surface 11b 2nd principal surface

Claims

1. A fluororesin film containing fluororesin, When the surface included in at least one main surface of the fluororesin film is measured by X-ray photoelectron spectroscopy, the ratio of nitrogen to the total amount of all elements is 1.2 at.% or more and 30 at.% or less. The amount of perfluorocarboxylic acids with 9 to 14 carbon atoms contained in the fluororesin film is 25 ppb or less. Fluoropolymer film.

2. The nitrogen element ratio is 2.5 at.% or more. The fluororesin film according to claim 1.

3. The nitrogen element ratio is 15 at.% or less. The fluororesin film according to claim 1.

4. The fluorine / carbon ratio (F / C ratio) of the aforementioned surface, measured by X-ray photoelectron spectroscopy, is greater than 0.7 and less than or equal to 2.

0. The fluororesin film according to claim 1.

5. The aforementioned surface is a modified surface, The nitrogen element ratio on the surface is greater than the nitrogen element ratio inside the fluororesin film. The fluororesin film according to claim 1.

6. The fluororesin is polytetrafluoroethylene. The fluororesin film according to claim 1.

7. A fluororesin film according to any one of claims 1 to 6, A substrate made of a material different from the aforementioned fluororesin film and bonded to the aforementioned fluororesin film, A complex that includes this.

8. The adherend comprises a polyolefin, The composite according to claim 7.

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