Manufacturing method of fluororesin film

Abstract

The present invention provides a method for producing a fluororesin film with excellent adhesive properties while suppressing the content of perfluorocarboxylic acids having 9 to 14 carbon atoms. [Solution] The present invention provides a method for producing a fluororesin film, which involves plasma treatment of at least one main surface of a raw film containing fluororesin under reduced pressure conditions to obtain a fluororesin film. The plasma treatment is performed using inductively coupled plasma of a nitrogen-containing gas generated by applying high-frequency power to a low-inductance antenna.

Description

[Technical Field]

[0001] This invention relates to a method for producing a fluororesin film. [Background technology]

[0002] Fluoropolymer films, including those made from polytetrafluoroethylene and other fluororesins, possess high chemical and thermal stability. Therefore, fluoropolymer films are used in a wide range of applications, such as casings for energy storage devices like batteries and capacitors, protective films for outdoor devices like solar cells, and films for coating the surfaces of rubber-containing substrates.

[0003] On the other hand, the adhesion of fluororesin films to other materials and components is generally low. Therefore, conventionally, plasma treatment, including sputter etching, has been proposed as a technique to improve the adhesion of fluororesin films. For example, Patent Document 1 proposes a technique to improve the adhesion of a molded body containing organic polymer compounds such as fluororesin by performing plasma treatment under atmospheric pressure on the surface of the molded body to introduce peroxide radicals. Patent Document 2 also proposes improving the adhesion of a fluororesin film by applying sputter etching to the surface of the fluororesin film. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-56363 [Patent Document 2] Japanese Patent Publication No. 2022-62589 [Overview of the project] [Problems that the invention aims to solve]

[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 provides a method for producing a fluororesin film that has excellent adhesive properties while suppressing the content of PFCAs. [Means for solving the problem]

[0007] The present invention The method includes obtaining a fluororesin film by plasma treatment of at least one main surface of a base film containing fluororesin under reduced pressure. The aforementioned plasma treatment is a treatment using inductively coupled plasma of a nitrogen-containing gas, generated by applying high-frequency power to a low-inductance antenna. The present invention provides a method for manufacturing fluororesin films. [Effects of the Invention]

[0008] According to the present invention, a manufacturing method is provided for producing a fluororesin film with excellent adhesive properties while suppressing the content of PFCAs. [Brief explanation of the drawing]

[0009] [Figure 1] This is a flowchart showing a method for manufacturing a fluororesin film according to one embodiment of the present invention. [Figure 2]This is a diagram for explaining a method for manufacturing a fluororesin film according to an embodiment of the present invention. [Figure 3] This is a schematic configuration diagram showing an example of an apparatus for performing plasma treatment in a method for manufacturing a fluororesin film according to an embodiment of the present invention. [Figure 4] This is a schematic configuration diagram showing a modified example of an apparatus for performing plasma treatment in a method for manufacturing a fluororesin film according to an embodiment of the present invention. [Figure 5] This is a perspective view showing the positional relationship between the low-inductance antenna and the raw film in the plasma treatment chamber shown in FIG. 3. [Figure 6] This is a cross-sectional view showing the positional relationship between the low-inductance antenna and the raw film in the plasma treatment chamber shown in FIG. 3. [Figure 7] This is a schematic configuration diagram showing the apparatus used for sputter etching performed in Comparative Examples 2 and 3.

Mode for Carrying Out the Invention

[0010] The method for manufacturing a fluororesin film according to the first aspect of the present invention includes: obtaining a fluororesin film by subjecting at least one main surface of a raw film containing a fluororesin to plasma treatment in a reduced-pressure environment, where the plasma treatment is treatment by inductively coupled plasma of a nitrogen-containing gas generated by applying high-frequency power to a low-inductance antenna.

[0011] In the second aspect of the present invention, for example, in the manufacturing method according to the first aspect, the high-frequency power in the plasma treatment is 4.5 kW or less.

[0012] In the third aspect of the present invention, for example, in the manufacturing method according to the first or second aspect, in the plasma treatment, the intensity I of the maximum emission peak within the range of a wavelength of 336 nm or more and 338 nm or less

[0012] , , , B with respect to the intensity I of the maximum emission peak within the range of a wavelength of 390.5 nm or more and 392.5 nm or lessA Ratio I A / I B Set it to 1.0 or less.

[0013] In a fourth embodiment of the present invention, for example, in a manufacturing method according to any one of the first to third embodiments, the plasma treatment is performed while the raw film is being transported by rollers that are in contact with the raw film.

[0014] In a fifth aspect of the present invention, for example, in a manufacturing method according to any one of the first to fourth aspects, the ratio Ra2 / Ra1 of the arithmetic mean roughness Ra1 of the main surface of the raw film, as defined in JIS B0601:2001, to the arithmetic mean roughness Ra2 of the main surface of the fluororesin film corresponding to the main surface of the raw film, as defined in JIS B0601:2001, is 5.0 or less.

[0015] In a sixth aspect of the present invention, for example, in a manufacturing method according to any one of the first to fifth aspects, the ratio Rzjis2 / Rzjis1 of the ten-point average roughness Rzjis1 of the main surface of the fluororesin film corresponding to the main surface of the original film, as defined in JIS B0601:2001, to the ten-point average roughness Rzjis1 of the main surface of the original film, as defined in JIS B0601:2001, is 4.0 or less.

[0016] In a seventh embodiment of the present invention, for example, in a manufacturing method according to any one of the first to sixth embodiments, the fluororesin is polytetrafluoroethylene.

[0017] Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

[0018] [Method for manufacturing fluororesin film] The method for manufacturing a fluororesin film according to this embodiment includes obtaining a fluororesin film 2 by plasma treatment of at least one main surface 1a of a raw film 1 containing fluororesin under reduced pressure (S1), as shown in Figures 1 and 2. The plasma treatment performed here is a treatment using inductively coupled plasma of a nitrogen-containing gas generated by applying high-frequency power to a low-inductance antenna.

[0019] In the manufacturing method of this embodiment, as described above, the first main surface 1a of the original film 1 is plasma-treated by inductively coupled plasma (ICP) of a nitrogen-containing gas generated by applying high-frequency power to a low-inductance antenna. Compared to the sputter etching treatment conventionally used for surface modification of fluororesin films, plasma treatment using ICP with a low-inductance antenna can moderately modify the first main surface 1a of the original film 1 while suppressing excessive damage to the first main surface 1a. Moderate modification of the first main surface 1a includes, for example, the introduction of nitrogen elements into the first main surface 1a or moderate crosslinking of surface molecules of the first main surface 1a. For example, by efficiently introducing nitrogen elements into the first main surface 1a while suppressing excessive damage, the first main surface 2a of the resulting fluororesin film 2 can have excellent adhesion. Furthermore, by appropriately crosslinking the surface molecules of the first main surface 1a, the elasticity of the first main surface 2a of the resulting fluororesin film 2 can be increased, and as a result, the first main surface 2a of the fluororesin film 2 can have excellent adhesion.

[0020] Conventional sputter etching is typically performed by applying a high-frequency voltage to a chamber containing the original film while simultaneously reducing the pressure 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 the 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, when used on original film 1, it is presumed that the main chains of the fluororesin contained on the surface of original 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. Furthermore, because of the significant damage to the surface being modified, the elastic modulus of the surface is also reduced. In contrast, plasma treatment using ICP with a low-inductance antenna, as described above, 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 by ICP using 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, it is presumed that if a nitrogen-containing gas is used, many of the generated carbon radicals will react with nitrogen plasma species and disappear, further reducing the amount of generated PFCAs.

[0021] Based on the above, the manufacturing method of this embodiment makes it possible to produce a fluororesin film with excellent adhesive properties while suppressing the content of PFCAs.

[0022] The manufacturing method of this embodiment will be described in more detail below.

[0023] (Original film) Original film 1 is a precursor of fluororesin film 2 and contains fluororesin.

[0024] 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.

[0025] The base 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 base 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 base film 1 may contain two or more types of fluororesin.

[0026] The base film 1 may contain materials other than fluororesin. Examples of other materials in the base 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.

[0027] The thickness of the base film 1 can be appropriately determined according to the desired thickness of the fluororesin film 2, and is not particularly limited. For example, the thickness of the fluororesin film 2 may be 10 to 300 μm, 30 to 250 μm, or 50 to 200 μm.

[0028] The original film 1 shown in Figure 2 is a single layer. However, the original film 1 may be a laminate of two or more layers.

[0029] The shape of the base 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 base film 1 is not limited to the above examples. Polygonal, circular, and elliptical fluororesin films 1 can be distributed as sheets, while the strip-shaped base film 1 can be distributed as a roll wound around a core. The width of the strip-shaped base film 1 and the width of the roll wound around the strip-shaped base film 1 can be freely set.

[0030] The base film 1 is usually non-porous. The base film 1 may be a non-porous film that does not have pores connecting both main surfaces, at least in the area of ​​use.

[0031] The base 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 base film 1 may be an insulating film (non-conductive film) based on the high insulating properties of the fluororesin. The insulating properties are, for example, 1 × 10⁻⁶. 14 It is expressed as a surface resistivity of Ω / □ or greater.

[0032] (Plasma processing using ICP with a low-inductance antenna) In the manufacturing method of this embodiment, the ICP used when plasma treating the first main surface 1a of the original film 1 is an ICP using a low-inductance antenna. The plasma treatment method is not particularly limited, but the plasma treatment may be performed while transporting the original film 1 in a roll-to-roll manner, or it may be performed in a batch manner.

[0033] 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.

[0034] The frequency of the high-frequency power applied during plasma processing by ICP using a low-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 plasma damage to the first main surface 1a of the original film 1. 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, even more preferably 6 kW or lower, and particularly preferably 4.5 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 plasma damage to the first main surface 1a of the original film 1 can be suppressed.

[0035] As mentioned above, the gas used for plasma treatment contains nitrogen. The gas used for plasma treatment may also contain other gases, such as oxygen.

[0036] In the plasma treatment of the first main surface 1a of the original 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, particularly preferably 0.3 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 of the first main surface 1a of the original film 1 can be formed in the plasma treatment chamber during the plasma treatment. When the pressure is below the upper limit, thermal damage to the original film 1 caused by excessively high-density plasma, and further thermal deformation of the original film 1, can be suppressed. The pressure can be adjusted, for example, by the amount of gas supplied to the plasma treatment chamber.

[0037] In the plasma treatment for forming the first main surface 2a of the fluororesin film 2, the plasma treatment time is preferably 5 seconds or more, 10 seconds or more, 30 seconds or more, more preferably 40 seconds or more, even more preferably 50 seconds or more, 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 can be produced on the first main surface 1a of the original film 1 for the formation of the fluororesin film 2 by plasma treatment. When the plasma treatment time is below the upper limit, thermal damage to the original film 1 caused by excessively high-density plasma, and further thermal deformation of the original film 1, can be suppressed.

[0038] The plasma treatment of the first main surface 1a of the original film 1 may be carried out while cooling or heating the original film 1. This allows for suppressing heat-induced damage to the original film 1 by cooling it during plasma treatment, or enhancing the effects of plasma treatment by heating the original film 1 during plasma treatment.

[0039] The plasma treatment of the original film 1 may be carried out, for example, in a roll-to-roll manner under a reduced pressure atmosphere while the original film 1, which is the object to be plasma treated, is being transported. In the following, the details of the plasma treatment will be explained using the roll-to-roll method as an example. However, the configuration of the low-inductance antenna provided in the plasma treatment chamber C2 described later, the positional relationship between the low-inductance antenna and the original film, and the processing conditions for the plasma treatment carried out in the plasma treatment chamber C2 are not limited to the roll-to-roll method and can also be applied to batch plasma treatment.

[0040] The apparatus 30 shown in Figure 3 is an example of an apparatus for performing plasma treatment on the original film 1. The apparatus 30 comprises, for example, a feeding chamber R1, a winding chamber R2, a connection chamber C1, a plasma treatment chamber C2, a connection chamber C3, and a PEM device (not shown).

[0041] The feeding chamber R1 is equipped with a feeding roller 31 for feeding out the object to be plasma-treated 100 (original film 1). A roll of the long object to be plasma-treated 100 is attached to the feeding roller 31. In addition, a predetermined number of guide rollers G for guiding the object to be plasma-treated 100 are provided inside the feeding chamber R1.

[0042] The winding chamber R2 is equipped with a winding roller 32 for winding up the object 100 to be treated with plasma. A predetermined number of guide rollers G are provided inside the winding chamber R2 for guiding the object 100 to be treated with plasma.

[0043] The connection chamber C1 is located after the feed chamber R1 and before the plasma processing chamber C2 in the direction of travel of the object to be plasma processed 100. A predetermined number of guide rollers G are provided inside the connection chamber C1 to guide the object to be plasma processed 100. The connection chamber C1 is connected to a vacuum pump (not shown) and is configured to allow adjustment of the chamber pressure. When the apparatus 30 is in operation, the pressure inside the connection chamber C1 is maintained at a predetermined pressure between the pressure inside the feed chamber R1 and the pressure inside the plasma processing chamber C2. This ensures a differential pressure between the feed chamber R1 and the plasma processing chamber C2.

[0044] Plasma processing chamber C2 is located between connection chamber C1 and connection chamber C3 in the direction of travel of the object to be plasma processed 100. Plasma processing is performed in plasma processing chamber C2 as described below.

[0045] In this embodiment, the plasma processing chamber C2 is equipped with a plurality of low-inductance antennas (LAs) 51. In this embodiment, the LAs 51 are arranged inside the plasma processing chamber C2, supported by mounting fixtures 52, as shown in Figures 5 and 6. Here, the case where there are four LAs 51 is illustrated as an example.

[0046] Multiple LA51s are arranged in alignment so as to be aligned in the direction of travel of the object 100 to be plasma-treated and in a direction perpendicular to the direction of travel (the width direction of the object 100 to be plasma-treated). The mounting fixture 52 is a vacuum flange. As shown in Figure 6, the LA51s are fixed to the mounting fixture 52 via a field-through 53. As shown in Figure 3, the mounting fixture 52 is assembled into an opening 55 provided in the wall of the plasma-treatment chamber C2. Specifically, the mounting fixture 52 is assembled to the opening 55 with a sealing member (not shown) sandwiched between the wall of the plasma-treatment chamber C2 and the mounting fixture 52. Outside the plasma-treatment chamber C2, the LA51s are electrically connected to a high-frequency power supply (RF power supply) via an impedance matching device. Such LA51s are formed of a conductor. Examples of conductors include copper and silver, with copper being preferred. The LA51s may be covered with an insulator. Examples of insulators include glass and quartz.

[0047] As shown in Figure 5, in this embodiment, LA51 has an open-loop shape. Having an open-loop shape for LA51 is advantageous for lowering the inductance of LA51. Therefore, with an open-loop shaped LA51, it is possible to suppress the increase in voltage due to an increase in the power applied to LA51. This suppresses abnormal discharge during plasma processing, which will be described later. By suppressing abnormal discharge, damage to the plasma-processed object 100 can be suppressed. Specifically, LA51 has a U-shape with two free ends. For each LA51, the two free ends are fixed to the mounting fixture 52 so that they are aligned in the width direction of the plasma-processed object 100. In addition, in this embodiment, LA51 has an extension portion 51a on the side opposite to the two free ends. The extension portion 51a extends parallel to the plasma-processed object 100 passing through the plasma processing chamber C2. The extension portion 51a extends in the width direction of the plasma-processed object 100. Each extension 51a may extend in the direction of travel of the object 100 to be plasma-treated, and four LA51 may be arranged in this manner. The length of the extension 51a is, for example, 50 to 150 mm. Figure 5 illustrates an example where the length of the extension 51a is the same as the maximum length d2 of LA51 described later. LA51 may have a coil shape instead of an open-loop shape.

[0048] LA51 extends from the mounting fixture 52 toward the object to be plasma-treated 100. Preferably, LA51 extends perpendicularly to the mounting fixture 52. The extension length d1 of LA51 from the mounting fixture 52 is, for example, 30 to 150 mm. The maximum length d2 of LA51 in the planar direction of the object to be plasma-treated 100 is, for example, 50 to 150 mm. The separation distance d3 (shown in Figure 6) between LA51 and the object to be plasma-treated 100 is, for example, 50 to 200 mm. Preferably, the extension length d1 and the separation distance d3 are the same. The ratio of the separation distance d3 to the extension length d1 (d3 / d1) is, for example, 0.5 to 3.5. The number of LA51s (rows) spaced apart in the direction of travel of the plasma-treated object 100 may be 1, 2, or 3, or 4 or more if necessary, depending on the travel speed (i.e., plasma treatment time) of the plasma-treated object 100. The distance d4 between the centers of adjacent LA51s in the direction of travel of the plasma-treated object 100 is, for example, 100 to 500 mm. The distance d5 between the centers of adjacent LA51s in the width direction of the plasma-treated object 100 is, for example, 200 to 500 mm. By adjusting the distance d5 between centers, the uniformity of the plasma density in the width direction of the plasma-treated object 100 can be controlled. It is preferable that the distances d4 and d5 between centers are the same. The ratio of the distance d5 to the distance d4 (d5 / d4) is, for example, 0.5 to 2.0. Preferably, the center points of the extensions 51a of the four LA51s form a square as vertices. Such a set of LA51s can generate a plasma with high in-plane uniformity and high density. As the LA51, for example, a high-frequency antenna for plasma generation described in Japanese Patent Application Publication No. 2013-258153 may be used.

[0049] In this embodiment, the plasma processing chamber C2 further includes a transport roller 33. The transport roller 33 is a main guide roller for transporting the object to be plasma processed 100 within the plasma processing chamber C2. The transport roller 33 has a temperature control function that allows for heating or cooling of the object to be plasma processed 100, for example. That is, the transport roller 33 may be a transport roller with a temperature control function. When the apparatus 30 is in operation, the transport roller 33 transports the original film 1, which is the object to be plasma processed 100, while in contact with the original film 1. At this time, the transport roller 33 is in contact with the second main surface 1b, which is opposite to the first main surface 1a, which is the surface of the original film 1 that is to be plasma processed. LA51 is positioned opposite the transport roller 33. With the apparatus 30 equipped with such a plasma processing chamber C2, plasma processing can be performed on the original film 1 while cooling or heating the original film 1 with the transport roller 33 that is in contact with the original film 1. By controlling the temperature of the base film 1, thermal deformation of the base film 1 can be suppressed, and the influence of such thermal deformation on the transport of the base film 1 can also be suppressed.

[0050] By using the transport roller 33 with the temperature control function described above, it is possible to, for example, cool the raw film 1 during plasma treatment to suppress damage to the raw film 1 due to heat, or to heat the raw film 1 during plasma treatment to enhance the effect of plasma treatment.

[0051] The PEM apparatus is a device for performing plasma emission monitoring (PEM) during plasma processing, and comprises a main unit and an optical fiber for collecting light. One end of the optical fiber is positioned between the object to be plasma processed 100 and LA51 in the direction of separation within the plasma processing chamber C2. The other end of the optical fiber is connected to the main unit. In addition, a first line L1 with a flow control valve for introducing gas into the plasma processing chamber C2 is connected to the plasma processing chamber C2.

[0052] The connection chamber C3 is located next to the plasma processing chamber C2 in the direction of travel of the object to be plasma processed 100. A predetermined number of guide rollers G are provided inside the connection chamber C3 to guide the object to be plasma processed 100. The connection chamber C3 is connected to a vacuum pump (not shown) and is configured to allow adjustment of the chamber pressure. When the apparatus 30 is in operation, the pressure inside the connection chamber C3 is maintained at a predetermined pressure between the pressure inside the plasma processing chamber C2 and the pressure inside the winding chamber R2. This ensures a differential pressure between the plasma processing chamber C2 and the winding chamber R2.

[0053] The apparatus 30 described above can be used to perform plasma treatment on the original film 1. Specifically, it is as follows:

[0054] The plasma-treated object 100 is unfurled from the unfurling chamber R1. After being unfurled from the unfurling chamber R1, the plasma-treated object 100 sequentially passes through the connection chamber C1, the plasma treatment chamber C2, and the connection chamber C3, and is wound up in the winding chamber R2. The travel speed of the plasma-treated object 100 is preferably 0.1 m / min or more, more preferably 0.5 m / min or more, even more preferably 0.7 m / min or more, and particularly preferably 0.9 m / min or more. The travel speed of the plasma-treated object 100 is, for example, 10 m / min or less. When the travel speed of the plasma-treated object 100 is above the lower limit, the manufacturing efficiency of the fluororesin film can be ensured. When the travel speed of the plasma-treated object 100 is below the upper limit, variations in the quality of the fluororesin film can be suppressed. Furthermore, the entire line from the unfurling chamber R1 to the winding chamber R2 is not opened to the atmosphere along the way, and the process is carried out in a reduced-pressure atmosphere in this line. A reduced pressure atmosphere is preferably a vacuum. A vacuum preferably means a reduced pressure atmosphere of 10 Pa or less.

[0055] Plasma processing is performed in plasma processing chamber C2. In plasma processing, for example, the first main surface 1a of the original film 1 is plasma-treated in a reduced-pressure atmosphere inside plasma processing chamber C2 (chamber). Plasma processing may be performed while detecting the plasma emission intensity.

[0056] During plasma processing, nitrogen is supplied to the plasma processing chamber C2 via the first line L1. Other gases besides nitrogen may be supplied to the plasma processing chamber C2. Examples of other gases include oxygen, hydrogen, and water vapor. The nitrogen concentration (N2 concentration) in the gas (nitrogen-containing gas) in the plasma processing chamber C2 is preferably 50 volume% or more, more preferably 65 volume% or more, even more preferably 80 volume% or more, even more preferably 90 volume% or more, even more preferably 95 volume% or more, and particularly preferably 100 volume%.

[0057] The pressure inside the plasma processing chamber C2 during plasma processing is preferably 0.05 Pa or higher, more preferably 0.1 Pa or higher, even more preferably 0.2 Pa or higher, particularly preferably 0.3 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. When the pressure inside the plasma processing chamber C2 is above the lower limit, a plasma environment with sufficient density for surface modification treatment of the first main surface 1a of the original film 1 can be formed inside the plasma processing chamber C2 during plasma processing. When the pressure inside the plasma processing chamber C2 is below the upper limit, thermal damage to the original film 1 caused by excessively high-density plasma can be suppressed during plasma processing, and thermal deformation of the original film 1 can also be suppressed. The pressure inside the plasma processing chamber C2 can be adjusted, for example, by the amount of gas supplied into the plasma processing chamber C2.

[0058] The frequency of the high-frequency power applied to LA51 during the plasma treatment by ICP using a low-inductance antenna is preferably 1 MHz or higher, more preferably 5 MHz or higher, still more preferably 10 MHz or higher, and is preferably 100 MHz or lower, more preferably 80 MHz or lower, still more preferably 60 MHz or lower. When the frequency is not less than the above lower limit value, while increasing the plasma current density, the plasma discharge can be stabilized. When the frequency is not more than the above upper limit value, the antenna potential can be suppressed, and thus, damage to the original film 1 by the plasma can be suppressed. Further, the high-frequency power is preferably 0.1 kW or higher, more preferably 0.3 kW or higher, still more preferably 1.0 kW or higher, and is preferably 10 kW or lower, more preferably 8 kW or lower, still more preferably 6 kW or lower, particularly preferably 4.5 kW or lower. When the high-frequency power is not less than the above lower limit value, in the plasma treatment by inductively coupled plasma, a high-density plasma environment can be formed in the plasma treatment chamber C2. When the high-frequency power is not more than the above upper limit value, excessive damage to the original film 1 by the plasma can be suppressed.

[0059] In the plasma treatment, the plasma emission intensity in the plasma treatment may be monitored by a PEM device. For example, based on the monitoring result, the intensity I of the emission peak within the range of 336 nm or more and 338 nm or less B with respect to the intensity I of the emission peak within the range of 390.5 nm or more and 392.5 nm or less A of the ratio (I A / I B ) is controlled to be 1.0 or less, preferably 0.50 or less, more preferably 0.45 or less. The maximum emission peak within the range of 390.5 nm or more and 392.5 nm or less is an emission peak derived from the electron transition in nitrogen molecular ions. The maximum emission peak within the range of 336 nm or more and 338 nm or less is an emission peak derived from the electron transition within neutral nitrogen molecules. The fact that the ratio (I A / I B ) is 1.0 or less indicates that the kinetic energy of nitrogen particles in the plasma is suppressed. The ratio (I A / I BIf the ratio (I) is below the above upper limit, the excessive increase in the kinetic energy of nitrogen particles in the plasma can be controlled, and damage to the surface of the plasma-treated object can be suppressed. A / I B The ratio (I) is preferably 0.01 or higher, more preferably 0.10 or higher, and even more preferably 0.20 or higher. A / I B If the value is above the lower limit mentioned above, moderately active movement of nitrogen particles is ensured, and the activation of the surface of the plasma treatment target can be promoted. Methods for controlling the plasma emission intensity include, for example, adjusting the amount of nitrogen-containing gas introduced into the plasma treatment chamber C2, adjusting the frequency of the high-frequency power in the high-frequency power supply, and adjusting the magnitude of the applied power.

[0060] In the plasma treatment, the plasma current density at the intermediate position between LA51 and the original film 1 is preferably 1.0 mA / cm². 3 More preferably, 2.0 mA / cm² 3 More preferably, 3.0 mA / cm² 3 In addition, preferably 10 mA / cm² 3 More preferably, 8 mA / cm 3 More preferably, 4 mA / cm 3 The following applies: When the plasma current density is above the lower limit, sufficient plasma particles (e.g., plasma nitrogen particles) can be secured in the plasma treatment chamber C2 during plasma treatment, and the first main surface 1a of the original film 1 can be appropriately surface modified. When the plasma current density is below the upper limit, damage to the first main surface 1a due to excessively high density of plasma particles can be suppressed during plasma treatment. Methods for adjusting the plasma current density include, for example, adjusting the amount of gas introduced into the plasma treatment chamber C2, adjusting the frequency of the high-frequency power in the high-frequency power supply, and adjusting the magnitude of the applied power.

[0061] The apparatus used for plasma processing may be an apparatus 40 equipped with a plasma processing chamber C2' instead of the plasma processing chamber C2 (see Figure 3) in the apparatus 30 shown in Figure 3, as shown in Figure 4. Plasma processing chamber C2' differs from plasma processing chamber C2 in that it does not have a transport roller 33. In other words, it is also possible to use an apparatus 40 that does not have a transport roller 33.

[0062] The fluororesin film 2 produced by the manufacturing method of this embodiment has a suppressed PFCAs content and excellent adhesive properties.

[0063] The manufacturing method of this embodiment results in less roughening of the film surface than the conventional sputter etching method. Therefore, in the manufacturing method of this embodiment, the ratio Ra2 / Ra1 of the arithmetic mean roughness Ra1 of the first main surface 1a of the original film 1 to the arithmetic mean roughness Ra2 of the first main surface 2a of the fluororesin film 2 corresponding to the first main surface 1a of the original film 1, as defined in JIS B0601:2001, can be set to, for example, 5.0 or less.

[0064] Furthermore, in the manufacturing method of this embodiment, the ratio Rzjis2 / Rzjis1 of the ten-point average roughness Rzjis1 of the first main surface 1a of the original film 1 to the ten-point average roughness Rzjis2 of the first main surface 2a of the fluororesin film 2 corresponding to the first main surface 1a of the original film 1, as defined in JIS B0601:2001, can be, for example, 4.0 or less. [Examples]

[0065] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

[0066] First, we will describe the evaluation method for fluoropolymer films.

[0067] [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.

[0068] [Measurement of PFCAs content in fluoropolymer films] The PFCAs content in fluororesin films was measured by the following method. After freeze-grinding a sample of fluororesin film 1, a predetermined amount (approximately 0.1 g) was weighed out, and a known amount of surrogate substance was added to it. Methanol was added, and ultrasonic extraction was performed. The resulting extract was concentrated, water was added, and the amount of PFCAs was measured using a liquid chromatograph-tandem mass spectrometer (LC-MS / MS). The amounts of the substances shown in Table 1 below were measured as PFCAs. From the obtained PFCAs amounts, the PFCAs content in fluororesin film 1 was determined. The surrogate substance mentioned above is perfluorooctanoic acid (PFOA), etc., which is added to confirm and correct the recovery rate in the above measurement. 13This is a 1C stable isotope-labeled compound. 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+).

[0069] [Table 1]

[0070] [Surface roughness measurement] The surface roughness of the first main surface of the fluoropolymer film was measured using a scanning probe microscope (AFM). The measurement sample was prepared by cutting the fluoropolymer film to be measured into a 30 mm x 30 mm size. This measurement sample was fixed to the sample stage of the measuring apparatus, and the surface roughness was measured. The measuring apparatus and measurement conditions used are as follows: Measurement device: Hitachi High-Tech Science Co., Ltd., "AFM5300E" Measurement mode: DFM mode Cantilever: AC160TS (equivalent to a spring constant of 40 N / m) Measurement range: 5 μm square scan Measurement atmosphere: Air Measurement temperature: room temperature

[0071] (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.

[0072] 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, the apparatus 30 shown in Figure 3, which can perform a roll-to-roll process on the raw film, was used. In this embodiment, a roll of general-purpose PET film was set on the feed roller 31 as a carrier film for transporting the raw film. The plasma treatment chamber C2 was equipped with a transport roller 33 with a temperature control function and four low-inductance antennas 51. The positional relationship between the low-inductance antennas and the object to be plasma treated in the plasma treatment chamber C2 used in this embodiment was the same as the positional relationship shown in Figures 5 and 6. Each low-inductance antenna 51 had an extension 51a parallel to the object to be plasma treated 100. In the four low-inductance antennas 51, the extension length d1 was 88 mm, the maximum length d2 (extension length) 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 51 was electrically connected to a high-frequency power supply (RF power supply, frequency 13.56 MHz) via an impedance matching device outside the plasma processing chamber C2.

[0073] 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.

[0074] The plasma treatment conditions were as follows: The ultimate vacuum level in the plasma treatment chamber was 1.0 × 10⁻⁶. -4After 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.

[0075] 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.

[0076] (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.

[0077] (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.

[0078] (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.

[0079] In the sputter etching process performed in Comparative Example 2, the apparatus shown in Figure 7 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 200 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 200. 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 feed section 105a and a winding section 105b, and the film 200 was transported while in contact with a roll-shaped cathode 104. When a dark area was formed in the space near the film 200 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 200, and sputter etching was performed by the impact.

[0080] 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.

[0081] (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.

[0082] (Comparative Example 4) The raw film prepared in Example 1 was used as the fluororesin film in Comparative Example 4.

[0083] The evaluation results for each fluororesin film are shown in Table 2 below.

[0084] [Table 2]

[0085] As shown in Table 2, the fluororesin films of Examples 1 and 2, which underwent plasma treatment by ICP using a low-inductance antenna with a nitrogen-containing gas, 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 produced by the manufacturing methods of Examples 1 and 2 satisfied both suppressed PFCAs content and excellent adhesion. In contrast, the fluororesin film of Comparative Example 1, which underwent plasma treatment by ICP using a low-inductance antenna with argon gas, had poor adhesion and a PFCAs content exceeding 25 ppb. The fluororesin film of Comparative Example 2, whose surface was modified by sputter etching using nitrogen gas, had poor adhesion. The fluororesin film of Comparative Example 3, whose surface was modified by water vapor 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 had very low adhesion. [Industrial applicability]

[0086] 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]

[0087] 1 Original film 2. Fluororesin film

Claims

1. The method includes obtaining a fluororesin film by plasma treatment of at least one main surface of a base film containing fluororesin under reduced pressure. The aforementioned plasma treatment is a treatment using inductively coupled plasma of a nitrogen-containing gas, generated by applying high-frequency power to a low-inductance antenna. A method for manufacturing fluororesin film.

2. The high-frequency power in the plasma processing is 4.5 kW or less. A method for producing a fluororesin film according to claim 1.

3. In the plasma treatment described above, the intensity of the maximum emission peak in the wavelength range of 336 nm or more and 338 nm or less is I B The intensity I of the maximum emission peak within the wavelength range of 390.5 nm or higher and 392.5 nm or lower. A Ratio I A / I B Set it to 1.0 or less. A method for producing a fluororesin film according to claim 1.

4. The plasma treatment is performed while the original film is being transported by rollers that come into contact with the original film. A method for producing a fluororesin film according to claim 1.

5. The ratio Ra2 / Ra1 of the arithmetic mean roughness Ra2 of the main surface of the fluororesin film corresponding to the main surface of the original film, to the arithmetic mean roughness Ra1 of the main surface of the original film, as defined in JIS B0601:2001, is 5.0 or less. A method for producing a fluororesin film according to claim 1.

6. The ratio Rzjis2 / Rzjis1 of the ten-point average roughness Rzjis1 of the main surface of the original film, as defined in JIS B0601:2001, to the ten-point average roughness Rzjis2 of the main surface of the fluororesin film corresponding to the main surface of the original film, as defined in JIS B0601:2001, is 4.0 or less. A method for producing a fluororesin film according to claim 1.

7. The fluororesin is polytetrafluoroethylene. A method for producing a fluororesin film according to claim 1.

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