Method for producing a surface-coated fluororesin substrate, surface treatment apparatus, and fluororesin-elastomer composite

Abstract

To provide a method for producing a surface-coated fluororesin substrate which can form a uniform surface coating layer on the surface of fluororesin.SOLUTION: A method for producing a surface-coated fluororesin substrate includes a surface treatment step for applying plasma treatment to the surface of a fluororesin substrate with atmospheric-pressure plasma by dielectric barrier discharge in a gas passage with a flowing gas containing inert gas, and forming a surface coating layer on the surface with steam of organic compounds.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a surface-coated fluororesin substrate, a surface treatment apparatus, and a fluororesin-elastomer composite.

Background Art

[0002] Fluororesins such as PTFE, PCTFE, and PFA have excellent performance in terms of heat resistance, chemical resistance, weather resistance, gas barrier properties, etc., and are used in various applications. However, fluororesins have low adhesion to other materials and are likely to peel off at the bonding interface. As a surface treatment method for fluororesins, a method of performing atmospheric pressure plasma polymerization treatment is known (see, for example, Patent Documents 1 and 2). By performing such atmospheric pressure plasma polymerization treatment on the surface of a fluororesin, the adhesion of the fluororesin can be improved. In Patent Document 1, while supplying a mixed gas (a mixed gas of acrylic acid monomer vapor and argon gas) generated by bubbling argon gas into a liquid acrylic acid monomer in a liquid tank to a discharge nozzle, the surface of a PTFE plate is treated with plasma by corona discharge generated at the discharge nozzle. In Patent Document 2, the vapor of acrylic acid is supplied into a treatment chamber by heating liquid acrylic acid in a monomer gas supply device installed in the treatment chamber to 60°C, and the surface of a PTFE film is treated with plasma by corona discharge in this treatment chamber.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When performing surface treatment of fluororesin using plasma generated by corona discharge, the plasma torch is moved while treating the surface of the fluororesin. Therefore, it is difficult to form a homogeneous surface coating layer on the surface of the fluororesin. The present invention has been made in view of these circumstances, and provides a method for producing a surface-coated fluororesin substrate that can form a homogeneous surface coating layer on the surface of the fluororesin. [Means for solving the problem]

[0005] The present invention provides a method for manufacturing a surface-coated fluororesin substrate, characterized by including a surface treatment step in which the surface of a fluororesin substrate is plasma-treated by atmospheric pressure plasma generated by dielectric barrier discharge in a gas channel through which a gas containing an inert gas flows, and a surface coating layer is formed on the surface by vapor of an organic compound. [Effects of the Invention]

[0006] By placing a dielectric fluororesin substrate between electrodes, atmospheric pressure plasma can be generated by dielectric barrier discharge. High-energy electrons generated in this plasma can collide with the fluororesin substrate, generating radicals. These radicals on the fluororesin substrate react with an organic compound, causing the organic compound to chemically bond with the surface of the fluororesin substrate. This allows for the formation of a firmly bonded surface coating layer on the surface of the fluororesin substrate, improving its adhesion. Furthermore, because the surface coating layer is formed from an organic compound, the effect of the surface treatment can be sustained for a long period of time. In dielectric barrier discharges in gas channels through which an inert gas flows, a stable and uniform atmospheric pressure plasma can be generated. Therefore, a homogeneous surface coating layer can be formed on the surface of the fluororesin substrate, suppressing unevenness in the adhesion of the fluororesin substrate. [Brief explanation of the drawing]

[0007] [Figure 1]This is a schematic cross-sectional view of a surface treatment apparatus of one embodiment of the present invention. [Figure 2] Figure 1 is a schematic cross-sectional view of the surface treatment apparatus along the dotted line EE or dotted line FF. [Figure 3] (a) to (d) are schematic cross-sectional views of the steam generator tank. [Figure 4] This is an explanatory diagram for the manufacturing method of fluororesin-elastomer composites. [Figure 5] This is a schematic cross-sectional view of a fluororesin-elastomer composite. [Figure 6] This is an explanatory diagram for the peel test. [Figure 7] This is an explanatory diagram of the acrylic acid concentration measurement location. [Figure 8] This graph shows the results of the acrylic acid concentration measurement. [Figure 9] This table shows the results of contact angle measurement and acrylic acid concentration measurement. [Figure 10] This is a schematic cross-sectional view of the fluororesin substrate showing the position of the sample for the peel test. [Modes for carrying out the invention]

[0008] The present invention provides a method for manufacturing a surface-coated fluororesin substrate, characterized by including a surface treatment step in which the surface of the fluororesin substrate is plasma-treated by atmospheric pressure plasma produced by dielectric barrier discharge in a gas channel through which a gas containing an inert gas flows, and a surface coating layer is formed on the surface by vapor of an organic compound.

[0009] In conventional methods for generating organic compound vapor by bubbling (e.g., Patent Document 1), bubbling generates a mist of the organic compound, which can mix with the gas containing the organic compound vapor, potentially increasing the concentration of the organic compound. In this case, this high concentration of organic compound affects the plasma treatment, making it difficult to stably improve the adhesion of the fluororesin substrate. Furthermore, in conventional methods for placing an open container holding liquid organic compound inside a discharge reactor (e.g., Patent Document 2), the concentration of the organic compound inside the discharge reactor changes over time, making it difficult to precisely control the concentration of the organic compound. Additionally, it is difficult to switch the gas inside the discharge reactor between an inert gas containing organic compound vapor and an inert gas that does not contain organic compound vapor. In the surface treatment step of the manufacturing method of the present invention, it is preferable to inject an inert gas into the headspace of a vapor generator tank containing a liquid organic compound, thereby supplying the gas containing the vapor of the organic compound discharged from the headspace to the gas flow path. This makes it possible to supply an inert gas containing the vapor of the organic compound at a stable concentration to the gas flow path of the discharge reactor, thereby enabling stable improvement of the adhesion of the fluororesin substrate by plasma treatment. In the surface treatment step described above, it is preferable to inject an inert gas parallel to the surface of the organic compound into the headspace of the steam generator tank containing the liquid organic compound. This prevents the inert gas introduced into the headspace from being blown onto the surface of the organic compound, thereby preventing the surface from becoming turbulent and generating bubbles or mist. As a result, it is possible to prevent the concentration of the organic compound in the gas supplied to the gas flow path of the discharge reactor from becoming abnormally high, and to supply an inert gas containing the vapor of the organic compound at a stable concentration to the gas flow path of the discharge reactor.

[0010] It is preferable to control the amount of organic compound vapor supplied to the gas flow path by adjusting the surface area of ​​the liquid of the organic compound in the vapor generation tank or the temperature of the liquid. This makes it possible to supply an inert gas containing organic compound vapor at an appropriate concentration to the gas flow path. Preferably, the organic compound is a monomer having a double bond in the molecule, the surface coating layer is a resin layer, and the surface treatment step is a step of forming the resin layer by plasma graft polymerization. Since this resin layer is chemically bonded to the surface of the fluororesin substrate, it is difficult to peel off from the fluororesin substrate. Therefore, it becomes possible to firmly bond the fluororesin substrate and another member via the resin layer. Preferably, the organic compound is a (meth)acrylic monomer, the surface coating layer is a (meth)acrylic resin layer, and the surface treatment step is a step of forming the (meth)acrylic resin layer by plasma graft polymerization. Since this (meth)acrylic resin layer is chemically bonded to the surface of the fluororesin substrate, it is difficult to peel off from the fluororesin substrate. Therefore, it becomes possible to firmly bond the fluororesin substrate and another member via the (meth)acrylic resin layer.

[0011] The present invention also provides a surface treatment apparatus including a discharge reactor having a first electrode and a second electrode, a power supply device electrically connected to at least one of the first and second electrodes, an inert gas supply unit provided to supply an inert gas to the discharge reactor, and a vapor generation tank provided to supply a vapor of an organic compound to the discharge reactor. The discharge reactor is provided to dispose a fluororesin substrate, which is an object to be treated, between the first electrode and the second electrode. The vapor generation tank and the inert gas supply unit are provided to supply a gas containing the vapor of the organic compound discharged from the head space to the discharge reactor by injecting an inert gas into the head space of the vapor generation tank storing the organic compound. Since the discharge reactor is provided to dispose a fluororesin substrate, which is an object to be treated, between the first electrode and the second electrode, it is possible to generate atmospheric pressure plasma by dielectric barrier discharge in a gas flow path adjacent to the fluororesin substrate. The vapor generation tank and the inert gas supply unit are provided to supply a gas containing the vapor of the organic compound discharged from the headspace to the discharge reactor by supplying an inert gas to the headspace above the liquid surface of the organic compound. Therefore, an inert gas containing the vapor of the organic compound at a stable concentration can be supplied to the gas flow path of the discharge reactor, and the adhesiveness of the fluororesin substrate can be stably improved by plasma treatment.

[0012] The vapor generation tank preferably includes a gas injection port provided to inject an inert gas into the vapor generation tank and a gas discharge port provided to discharge the gas in the vapor generation tank. The gas injection port and the gas discharge port are preferably provided such that the inert gas flows parallel to the liquid surface of the organic compound in the headspace. This enables an inert gas containing the vapor of the organic compound at a stable concentration to be supplied to the gas flow path of the discharge reactor, and the adhesiveness of the fluororesin substrate can be stably improved by plasma treatment.

[0013] Preferably, the discharge reactor has an outer cylinder, the fluororesin substrate has a tubular shape and is disposed inside the outer cylinder, the second electrode is disposed inside the fluororesin substrate, the first electrode is disposed on the outer surface of the outer cylinder, and the inert gas supply unit and the vapor generation tank are provided to supply the vapor of the organic compound and the inert gas to the gas flow path between the outer cylinder and the fluororesin substrate. This allows the distance between the first electrode and the second electrode to be shortened and the first electrode and the second electrode to be arranged in parallel, and a stable atmospheric pressure plasma can be generated in the gas flow path. The surface of the fluororesin substrate can be homogeneously plasma-treated by this atmospheric pressure plasma. The present invention also provides a fluororesin-elastomer composite comprising a fluororesin substrate, a (meth)acrylic resin layer covering the surface of the fluororesin substrate, and an elastomer member bonded to the fluororesin substrate via the (meth)acrylic resin layer. This fluororesin-elastomer composite has elastomer properties and its surface has the properties of fluororesin, and can therefore be used in a variety of applications.

[0014] One embodiment of the present invention will be described below with reference to the drawings. The configurations shown in the drawings and the following description are illustrative, and the scope of the present invention is not limited to those shown in the drawings and the following description.

[0015] Figure 1 is a schematic cross-sectional view of the surface treatment apparatus according to this embodiment, and Figure 2 is a schematic cross-sectional view of the surface treatment apparatus along the dotted line EE or dotted line FF in Figure 1. The method for manufacturing the surface-coated fluororesin substrate 17 of this embodiment is characterized by including a surface treatment step in which the surface of the fluororesin substrate 5 is plasma-treated by atmospheric pressure plasma produced by dielectric barrier discharge in a gas channel 20 through which a gas containing an inert gas flows, and a surface coating layer 6 is formed on the surface by vapor of an organic compound.

[0016] The surface treatment apparatus 40 used in the method for manufacturing the surface-coated fluororesin substrate 17 of this embodiment comprises a discharge reactor 4 having a first electrode 2 and a second electrode 3, a power supply device 10 electrically connected to at least one of the first electrode 2 and the second electrode 3, an inert gas supply unit 11 provided to supply an inert gas to the discharge reactor 4, and a steam generating tank 7 provided to supply vapor of an organic compound to the discharge reactor 4. The discharge reactor 4 is provided so as to place the fluororesin substrate 5, which is the object to be processed, between the first electrode 2 and the second electrode 3, and the steam generating tank 7 and the inert gas supply unit 11 are provided so as to supply gas containing vapor of an organic compound discharged from the headspace 9 by supplying an inert gas to the headspace 9 above the liquid surface of the organic compound 8 to the discharge reactor 4.

[0017] Dielectric barrier discharge is a type of discharge in which plasma is generated in a gas channel between electrodes by applying an AC voltage to the electrodes while a dielectric material (for example, an outer cylinder 15 and a fluororesin substrate 5) is placed between the electrodes. Atmospheric pressure plasma is a type of plasma generated by setting the pressure in the gas channel between the electrodes to atmospheric pressure or a pressure close to atmospheric pressure. Atmospheric pressure plasma generated by dielectric barrier discharge can be generated, for example, using a surface treatment apparatus 40 as shown in Figure 1.

[0018] The discharge reactor 4 is a reactor for surface-treating a fluororesin substrate 5 by generating atmospheric pressure plasma in a gas channel 20. The discharge reactor 4 includes a first electrode 2 and a second electrode 3. The first electrode 2 and the second electrode 3 are electrodes for generating atmospheric pressure plasma in the gas channel 20 between the electrodes, and atmospheric pressure plasma can be generated in the gas channel 20 by applying an AC voltage between the first electrode 2 and the second electrode 3 using a power supply device 10. The gas channel 20 can be formed, for example, between the fluororesin substrate 5 and the outer cylinder 15. The first electrode 2 can also be placed on the outer surface of the outer cylinder 15. The first electrode 2 may be a metal film or a metal mesh. The material of the first electrode 2 may be silver, copper, aluminum, etc.

[0019] The outer cylinder 15 may include tubes made of dielectric material, for example, glass tubes, preferably quartz glass tubes. The outer cylinder 15 is preferably translucent. This allows the state of the atmospheric pressure plasma to be visually confirmed. The outer cylinder may also be formed by joining multiple tubes using joints. In this case, glass tubes having a metal film (first electrode 2) on their outer surface can be joined to other tubes using joints. The outer cylinder 15 may have an inlet and an outlet. The inlet and outlet may be configured so that the gas injected into the discharge reactor 4 from the inlet flows through the gas flow path 20 between the fluororesin substrate 5 and the outer cylinder 15 (the gas flow path 20 between the first electrode 2 and the second electrode 3) and is discharged from the outlet.

[0020] The second electrode 3 is positioned inside the outer cylinder 15 and is positioned opposite the first electrode 2, with the outer cylinder 15 and the fluororesin substrate 5 in between. The second electrode 3 can also be made of a metal tube, specifically a stainless steel tube. In this case, the second electrode 3 can be positioned so that the outer cylinder 15 and the second electrode 3 form a double tube, creating a gas flow path 20 between the outer cylinder 15 and the second electrode 3.

[0021] The fluororesin substrate 5 is a substrate containing fluororesin, such as a fluororesin tube or a fluororesin sheet. The thickness of the fluororesin substrate 5 is, for example, 10 μm or more and 3 mm or less. The material of the fluororesin substrate 5 is, for example, a fluororesin such as PTFE, modified PTFE, PFA, PCTFE, PVDF, PVF, FEP, ETFE, or ECTFE.

[0022] The fluororesin substrate 5 can be placed between the second electrode 3 and the outer cylinder 15. Alternatively, the fluororesin substrate 5 can be positioned such that a gas flow path 20 is formed between the fluororesin substrate 5 and the outer cylinder 15. The fluororesin substrate 5 can have a tubular shape. In this case, the second electrode 3 is placed inside the fluororesin substrate 5 and functions as a mandrel for the fluororesin substrate 5. Furthermore, the inner circumferential surface of the fluororesin substrate 5 may be in close contact with the outer circumferential surface of the second electrode 3. This allows for the formation of a gas flow path 20 between the outer circumferential surface of the fluororesin substrate 5 and the inner circumferential surface of the outer cylinder 15.

[0023] The power supply unit 10 is, for example, a high-frequency power supply unit, and is configured to apply an AC voltage between the first electrode 2 and the second electrode 3. For example, the output terminal of the power supply unit 10 can be electrically connected to the first electrode 2, and the second electrode 3 can be connected to ground. The output of the power supply unit 10 can be, for example, 50W or more and 300W or less. The output frequency of the power supply unit 10 can be, for example, 20kHz or more and 35kHz or less.

[0024] The inert gas supply unit 11 is a part provided to supply inert gas to the gas flow path 20 of the discharge reactor 4. The inert gas supply unit 11 may include, for example, gas cylinders, gas piping, flow control valves, pressure regulating valves, flow meters, and flow controllers that are necessary for gas supply. The inert gas supply unit 11 may also supply inert gas to the headspace 9 of the steam generator 7. In this case, by supplying inert gas to the headspace 9, the gas containing organic compound vapor and inert gas discharged from the headspace 9 is supplied to the gas flow path 20 of the discharge reactor 4. The inert gas supplied to the gas flow path 20 by the inert gas supply unit 11 is, for example, argon gas (Ar) or helium gas (He). The inert gas supply unit 11 may also include a switching valve provided to switch the gas supplied to the gas flow path 20 between a mixture of organic compound vapor and inert gas, inert gas alone, or both.

[0025] The steam generator tank 7 is a liquid tank that generates steam from the organic compound 8. Figures 3(a) and 3(d) are schematic cross-sectional views of the steam generator tank 7, Figure 3(b) is a schematic cross-sectional view of the steam generator tank 7 along the dotted line AA in Figure 3(a), and Figure 3(c) is a schematic cross-sectional view of the steam generator tank 7 along the dashed line BB in Figure 3(a). The steam generator 7 can be a sealed liquid tank comprising a liquid tank for storing liquid organic compounds, a gas inlet 12 provided for supplying inert gas to the headspace 9 above the liquid surface, and a gas outlet 13 provided for discharging gas from the headspace 9. The headspace 9 is the space including the headspace above the liquid surface of the organic compounds. The gas outlet 13 is connected to the inlet of the outer cylinder 15 so that the exhaust gas is supplied to the gas flow path 20 of the discharge reactor 4. Furthermore, the gas inlet 12 and gas outlet 13 in the steam generator 7 can be configured so that the inert gas flows in a direction parallel to the liquid surface of the organic compounds. This prevents the inert gas introduced into the headspace 9 from being blown onto the liquid surface of the organic compounds, thereby preventing the liquid surface from becoming wavy and generating bubbles or mist. As a result, it is possible to prevent the concentration of organic compounds in the gas supplied to the gas flow path 20 from becoming abnormally high, and to supply inert gas containing organic compound vapor at a stable concentration to the gas flow path 20 of the discharge reactor 4.

[0026] The organic compounds stored in the steam generator 7 are organic compounds that are in a liquid state at room temperature, such as monomers having double bonds in their molecules, methanol, ethanol, propanol, acetic acid, and formic acid. Examples of monomers having double bonds in their molecules include (meth)acrylic monomers (e.g., acrylic acid, acrylic acid esters, acrylic acid derivatives, methacrylic acid, methacrylic acid esters, methacrylic acid derivatives, etc.) and styrene monomers. When the surface coating layer 6 is a resin layer, the organic compound can be a monomer having double bonds in its molecule. When the surface coating layer 6 is a (meth)acrylic resin layer 16, the organic compound can be a (meth)acrylic monomer. Furthermore, the (meth)acrylic resin layer 16 is a layer derived from the polymerization reaction of (meth)acrylic monomers. Also, when the organic compound is methanol, ethanol, propanol, acetic acid, formic acid, etc., the surface coating layer 6 can be a monolayer of the organic compound.

[0027] The steam generator 7 may be equipped with a temperature measuring unit (e.g., a thermocouple 28) for measuring the temperature of the liquid organic compound. The steam generator 7 may also have a heating unit for heating the liquid organic compound inside the tank. Furthermore, the steam generator 7 may be equipped with a control unit that uses the temperature measuring unit and the heating unit to control the temperature of the liquid organic compound. By controlling the temperature of the liquid organic compound 8 with this control unit, the vapor pressure of the liquid organic compound 8 can be controlled, and the amount of organic compound vapor supplied from the liquid organic compound 8 to the headspace 9 can be controlled.

[0028] The steam generator 7 may comprise a rectangular parallelepiped liquid tank 25 with an open top and a top cover 26 that covers the upper opening of the liquid tank 25. The gap between the liquid tank 25 and the top cover 26 can be sealed with a rubber packing 27. The top cover 26 may also have a rectangular parallelepiped shape with an open bottom. A gas inlet 12 can be provided on one side of the top cover 26, and a gas outlet 13 can be provided on the side opposite to the side on which the gas inlet 12 is located. This allows the inert gas to flow in a direction parallel to the liquid surface, suppressing turbulence in the headspace 9. Furthermore, a gas containing organic compounds can be discharged from the gas outlet 13 at a stable concentration and supplied to the gas flow path 20 of the discharge reactor 4.

[0029] The steam generator tank 7 (liquid tank 25) can be configured to store liquid organic compounds in a space of length L × width W × depth D. The ratio of length L to width W (L / W) can be, for example, 10 / 1 or more and 20 / 1 or less. The gas inlet 12 and gas outlet 13 can be configured so that inert gas flows in the longitudinal direction of the steam generator tank 7 (from one end of length L to the other). This suppresses turbulence in the headspace 9, and allows a gas containing organic compounds at a stable concentration to be discharged from the gas outlet 13 and supplied to the gas flow path 20 of the discharge reactor 4. In addition, a sufficient amount of organic compound vapor can be supplied from the liquid organic compound 8 into the inert gas flowing through the headspace 9, and a gas containing organic compounds at an appropriate concentration can be stably discharged from the gas outlet 13 and supplied to the gas flow path 20 of the discharge reactor 4.

[0030] If the steam generator 7 includes a liquid tank 25 and a top cover 26, a block 29 having a width W (the top surface of the block is higher than the liquid level of the liquid organic compound) can be placed in the space of the liquid tank 25. This allows the size of the liquid surface to be adjusted by the length of the block 29, and the amount of organic compound vapor supplied from the liquid organic compound to the inert gas flowing through the headspace can be controlled. The block 29 is, for example, an aluminum block. In the steam generator 7 shown in Figure 3(d), the size of the liquid surface is narrower than that of the steam generator 7 shown in Figure 3(a) using the block 29.

[0031] The surface treatment process in which the surface coating layer 6 is formed will be described below. In the surface treatment process, the surface of the fluororesin substrate 5 is plasma-treated to react with an organic compound to radicals formed on the fluororesin substrate 5, thereby forming a surface coating layer 6. The plasma treatment of the surface of the fluororesin substrate 5 may be performed while an inert gas and a vapor of an organic compound are flowing through the gas channel 20. Alternatively, the plasma treatment (pretreatment) may be performed while an inert gas is flowing through the gas channel 20, and then the radicals on the surface of the fluororesin substrate 5 may be reacted with the organic compound.

[0032] This section describes a plasma treatment process performed while an inert gas and organic compound vapor are flowing through the gas channel 20. As shown in Figure 1, a tubular fluororesin substrate 5 is set inside the outer cylinder 15 and sealed with a sealing member 22. Then, an inert gas is supplied to the headspace 9 of the steam generation tank 7 which stores liquid organic compounds, and the inert gas is flowed parallel to the liquid surface. The inert gas containing organic compound vapor is discharged from the gas outlet 13, and this discharged gas is supplied to the gas flow path 20 from the inlet of the outer cylinder 15. Alternatively, the inert gas containing organic compound vapor discharged from the gas outlet 13 may be diluted with another inert gas and supplied to the gas flow path 20. Alternatively, inert gas may be supplied to the gas flow path 20 from another inlet, and the dilution of the inert gas containing organic compound vapor may be performed in the gas flow path 20.

[0033] An inert gas containing organic compound vapor flows through a gas channel 20 (the gas channel 20 between the first electrode 2 and the second electrode 3) between the outer surface of the fluororesin substrate 5 and the inner surface of the outer cylinder 15, and is then discharged from the outlet of the outer cylinder 15. The concentration of organic compound in the gas flowing through the gas channel 20 can be between 500 ppm and 4000 ppm. With the inert gas containing organic compound vapor flowing through the gas channel 20 in this state, an AC voltage is applied between the first electrode 2 and the second electrode 3 using the power supply unit 10 to generate atmospheric pressure plasma (organic compound vapor plasma) in the mixed gas flowing through the gas channel 20. The output of the power supply unit 10 can be, for example, between 50 W and 300 W. The output frequency of the power supply unit 10 can be, for example, between 20 kHz and 35 kHz. The voltage application time for generating atmospheric pressure plasma can be, for example, between 0.5 seconds and 20 seconds.

[0034] In an atmospheric pressure plasma, the strong electric field causes ionization of inert gases or organic compounds, resulting in the presence of electrons and ions. When these plasma electrons collide with the surface of the fluororesin substrate 5, radicals (atoms or molecules with unpaired electrons) are generated on the surface of the fluororesin substrate 5. For example, as shown in equation (1), the CF bond of the fluororesin substrate 5 is broken, generating radicals. In equation (1), R is the fluororesin main chain containing carbon atoms, hydrogen atoms, oxygen atoms, and fluorine atoms. Equation (1): RF → R· + F·

[0035] When the organic compound flowing through the gas channel 20 reacts with radicals on the surface of the fluororesin substrate 5, a surface coating layer 6 is formed that is chemically bonded to the fluororesin substrate 5. When the organic compound is methanol, ethanol, propanol, acetic acid, formic acid, etc., a monolayer, which is the surface coating layer, is formed on the surface of the fluororesin substrate 5. When the organic compound is a monomer having a double bond in its molecule, a graft polymerization reaction (gas-phase polymerization reaction) proceeds when the monomer flowing through the gas channel 20 reacts with radicals on the surface of the fluororesin substrate 5, forming a resin layer, which is a surface coating layer 6 chemically bonded to the fluororesin substrate 5. Similarly, when the organic compound is a (meth)acrylic monomer, a graft polymerization reaction (gas-phase polymerization reaction) proceeds when the (meth)acrylic monomer flowing through the gas channel 20 reacts with radicals on the surface of the fluororesin substrate 5, forming a (meth)acrylic resin layer 16, which is a surface coating layer 6 chemically bonded to the fluororesin substrate 5. For example, when acrylic acid reacts with a radical (initial radical) on the surface of the fluororesin substrate 5, as shown in equation (2), the radical adds to the double bond of the acrylic acid, generating a growing radical. This growing radical repeatedly adds to the double bond of the acrylic acid, causing the polymerization reaction to proceed (for example, equation (3)), and forming the (meth)acrylic resin layer 16. Formula (2): R + CH2=CHCOOH → R-CH2-C·HCOOH Formula (3): R + n(CH2=CHCOOH) → R-(CH2-CHCOOH) n In this way, a surface coating layer 6 can be formed on the surface of the fluororesin substrate 5.

[0036] Next, we will describe a method in which plasma treatment is performed as a pretreatment, followed by the formation of the surface coating layer 6. As shown in Figure 1, a tubular fluororesin substrate 5 is set inside the outer cylinder 15 and sealed with a sealing member 22. Then, an inert gas (for example, argon gas, helium gas, or a mixture thereof) is supplied to the gas channel 20 from the inlet of the outer cylinder 15. The inert gas flows through the gas channel 20 between the outer surface of the fluororesin substrate 5 and the inner surface of the outer cylinder 15 (the gas channel 20 between the first electrode 2 and the second electrode 3), and is then discharged from the outlet of the outer cylinder 15. With the inert gas flowing through the gas channel 20 in this state, an AC voltage is applied between the first electrode 2 and the second electrode 3 using the power supply device 10, generating atmospheric pressure plasma (argon plasma, helium plasma, etc.) in the gas flowing through the gas channel 20. In the atmospheric pressure plasma, the strong electric field causes ionization of the inert gas, resulting in the presence of electrons and ions. When these plasma electrons collide with the surface of the fluororesin substrate 5, radicals (atoms or molecules with unpaired electrons) are generated on the surface of the fluororesin substrate 5. For example, as shown in equation (1), the CF bond of the fluororesin substrate 5 is cleaved, and radicals are generated.

[0037] After stopping the application of the AC voltage, an inert gas is supplied to the headspace 9 of the steam generator tank 7, which stores liquid organic compounds. The inert gas flows parallel to the liquid surface, and the inert gas containing organic compound vapor is discharged from the gas outlet 13. This discharged gas is then supplied to the gas flow path 20 from the inlet of the outer cylinder 15. This supplied gas may be diluted with inert gas. The inert gas containing organic compound vapor flows through the gas flow path 20 (the gas flow path 20 between the first electrode 2 and the second electrode 3) between the outer surface of the fluororesin substrate 5 and the inner surface of the outer cylinder 15, and is then discharged from the outlet of the outer cylinder 15.

[0038] When radicals on the surface of the fluororesin substrate 5, generated by the plasma treatment pretreatment, react with the organic compound flowing through the gas channel 20, a surface coating layer 6 is formed that is chemically bonded to the fluororesin substrate 5. When the organic compound is methanol, ethanol, propanol, acetic acid, formic acid, etc., a monolayer, which is the surface coating layer 6, is formed on the surface of the fluororesin substrate 5. When the organic compound is a (meth)acrylic monomer, a graft polymerization reaction occurs when the (meth)acrylic monomer flowing through the gas channel 20 reacts with radicals on the surface of the fluororesin substrate 5, forming a (meth)acrylic resin layer 16, which is the surface coating layer 6. For example, when acrylic acid reacts with a radical (initial radical) on the surface of the fluororesin substrate 5, as shown in equation (2), the radical adds to the double bond of the acrylic acid, generating a growing radical. This growing radical repeatedly adds to the double bond of the acrylic acid, causing the polymerization reaction to proceed (for example, equation (3)), and forming the (meth)acrylic resin layer 16. In this way, a surface coating layer 6 can be formed on the surface of the fluororesin substrate 5.

[0039] Next, we will describe the fluororesin-elastomer composite 50. Figure 4 is an explanatory diagram of the manufacturing method of the fluororesin-elastomer composite, Figure 5 is a schematic cross-sectional view of the fluororesin-elastomer composite, and Figure 6 is an explanatory diagram of the peel test. The fluororesin-elastomer composite 50 comprises a fluororesin substrate 5, a (meth)acrylic resin layer 16 (surface coating layer 6) covering the surface of the fluororesin substrate 5, and an elastomer member 18 bonded to the fluororesin substrate 5 via the (meth)acrylic resin layer 16. The acrylic resin layer 16 (surface coating layer 6) can be formed by the method described above. The elastomer member 18 is a member having rubber elasticity, and may be a thermosetting elastomer, a thermoplastic elastomer, or rubber. The elastomer member 18 is, for example, butyl rubber (type: IIR).

[0040] The elastomer member 18 can be bonded to a fluororesin substrate 5 having a (meth)acrylic resin layer 16 using, for example, a crosslinking agent. For example, the crosslinking reaction can be promoted by applying heat and pressure to a laminate of raw rubber and a fluororesin substrate 5 so that the raw rubber (elastomer member 18) containing a crosslinking agent comes into contact with the (meth)acrylic resin layer 16. This crosslinking reaction crosslinks the elastomer member 18 and the (meth)acrylic resin layer 16, allowing the fluororesin substrate 5 and the elastomer member 18 to be joined via the (meth)acrylic resin layer 16, thereby producing a fluororesin-elastomer composite 50. For example, as shown in Figure 4, the elastomer member 18 and the (meth)acrylic resin layer 16 can be joined by pressurizing and heating the laminate of raw rubber and fluororesin substrate 5 using a press machine. Examples of crosslinking agents that can be used include sulfur, organic peroxides, alkylphenol resin oligomers, and p-benzoquinone dioxime. The elastomer member 18 may also contain vulcanization accelerators, vulcanization accelerators, activators, etc. Furthermore, the peel adhesion strength between the elastomer member 18 and the fluororesin substrate 5 can be measured using a peel test apparatus as shown in Figure 6.

[0041] Acrylic acid concentration measurement and plasma treatment Tests No. 1 to No. 9 were conducted using a surface treatment apparatus 40 as shown in Figures 1 and 2, and the acrylic acid concentration in the gas flow path 20 and other areas was measured (see Table 1). In addition, plasma treatment was performed on the surface of the fluororesin substrate 5 in tests No. 5 to No. 9. A PFA tube was used for the fluororesin substrate 5. A quartz glass tube (outer diameter: 55 mm, inner diameter: 50 mm) was used in the part of the outer cylinder 15 where the first electrode 2 (metal film electrode) was placed, and the width (discharge width) of each of the first electrodes 2 was set to 100 mm. A steam generator tank 7 (length L: 295.5 mm, width W: 20.5 mm) as shown in Figures 3(a) to (d) was used. The second electrode 3 (stainless steel tube) was connected to ground, and the first electrode 2 was connected to the output terminal of the high-frequency high-voltage generator (power supply unit 10).

[0042] [Table 1]

[0043] After placing an aluminum block 29 (width: 19 mm, height: 35 mm, length: 280.5 mm) into the steam generating tank 7, 26.07 g of acrylic acid (CH2=CHCOOH) (organic compound 8) (acrylic acid surface area: 307.5 mm²) was added. 2 A liquid (26 mm deep) was added. After letting the inside of the steam generator tank 7 remain at room temperature for 15 minutes, argon gas (Q) was supplied to the headspace 9 of the steam generator tank 7 using the inert gas supply unit 11 for the purging time shown in Table 1. 1.1 A gas flow rate of 2.0 L / min was supplied, and a mixed gas of helium gas (Q3 = 6.5 L / min) and argon gas (Q4 = 4.5 L / min) was supplied to the gas channel 20. Tests No. 1 to No. 9 each had different purge times, which were gradually increased. In addition, in tests No. 1 to No. 4, after the purge time had elapsed, the acrylic acid concentration at spots A, B, and C shown in Figures 1 and 7 was measured. Figure 7 is a schematic cross-sectional view of the discharge reactor 4 along the dashed line GG in Figure 1, and is an explanatory diagram of the positions of spots A and B. In tests No. 5 to No. 9, after the purge time had elapsed, an AC voltage was applied between the first electrode 2 and the second electrode 3 using a high-frequency high-voltage generator (output: 150 W, applied voltage: approximately 15 kV, frequency: 25.2 kHz, application time: 5 seconds), and atmospheric pressure plasma was generated in the gas channel 20 between the first electrode 2 and the second electrode 3 to perform surface treatment of the fluororesin substrate 5. Subsequently, the acrylic acid concentrations at spots A and B, shown in Figures 1 and 7, were measured. In Test No. 9, the acrylic acid concentration at spot D was also measured. Note that "Ac" in Figures 7, 8, and 10 represents acrylic acid.

[0044] Acrylic acid concentration was measured by collecting a mixed gas from spots A, B, or D using a syringe-type dilution container, diluting it 100-fold with air, and then measuring the acrylic acid concentration using a detector tube (Acetic Acid 81, manufactured by Gastec Co., Ltd.). The measurement results are shown in Table 1 and Figure 8. Table 1 also shows the chamber temperature (temperature of gas flow path 20), monomer temperature (temperature of liquid acrylic acid in the acrylic acid bath), wet-bulb temperature, purge time, discharge output, and plasma treatment time. Figure 8 shows the flow rate (Q) of the inert gas (argon gas and helium gas). 1.1 Q3, Q4), and monomer temperature (temperature of liquid acrylic acid in the acrylic acid bath) are also shown. Because the argon gas containing acrylic acid was diluted in gas flow path 20, there was variation in the acrylic acid concentration at spots A, B, and C. However, even when the purging time was changed, the acrylic acid concentration at spot A remained between 1400 ppm and 2200 ppm and did not fluctuate significantly.

[0045] contact angle measurement After measuring the acrylic acid concentration in tests No. 5 to No. 9, the fluororesin substrate 5 was removed from the discharge reactor 4, and water was dropped onto the plasma-treated surface of the fluororesin substrate 5 (at locations θ=230° to 244° (see Figures 7 and 10)). The contact angle was measured after 1 minute. The measurement results are shown in Figure 9. Figure 9 also shows the contact angle, purge time, and acrylic acid concentration of the fluororesin substrate without plasma treatment. The contact angle of the fluororesin substrate obtained in tests No. 5 to No. 9 was smaller than that of the untreated fluororesin substrate. Therefore, it was found that the hydrophilicity of the fluororesin substrate was improved by plasma treatment. This is thought to be because an acrylic resin layer is formed on the surface of the fluororesin substrate.

[0046] Fabrication of fluororesin-elastomer composites After measuring the acrylic acid concentration in tests No. 5 to No. 9, the fluororesin substrate 5 was removed from the discharge reactor 4, and the plasma-treated portion of the fluororesin substrate 5 was cut out. In addition, fluororesin substrate samples were prepared by cutting it into the parts (1) to (10) shown in Figure 10 (sample size: length 100 mm x width 50 mm). Note that θ in Figure 10 is the same angle as in Figure 7. Furthermore, an elastomer member 18 containing a crosslinking agent (type: IIR, hardness [rubber hardness tester type A]: 40, tensile strength: 9.2 MPa, elongation: 1000%) was cut into pieces of length 100 mm x width 50 mm x thickness approximately 4 mm. Then, as shown in Figure 4, the fluororesin substrate sample and the elastomer member 18 were stacked so that the plasma-treated surface of the fluororesin substrate sample was in contact with the elastomer member 18, and the resulting pieces were set in the mold 30 and subjected to a heat press treatment (load 10 kN, vulcanization temperature 150 °C, vulcanization time 60 minutes). This resulted in the creation of a fluororesin-elastomer composite in which a fluororesin substrate sample and an elastomer member 18 were bonded together via an acrylic resin layer. In order to form the gripping portion for the grippers 35 and 36 in the peel test, a polymer film measuring 50 mm in length, 10 mm in width, and 0.2 mm in thickness was sandwiched between the fluororesin substrate sample and the elastomer member, forming a gripping portion at the end of the fluororesin-elastomer composite.

[0047] Peel test A peel test was performed on a fluororesin-elastomer composite using a peel test apparatus (INSTRON®, model: 33R4444) as shown in Figure 6 (in accordance with JIS K 6256-1 "Vulcanized rubber and thermoplastic rubber - Determination of adhesion - Part 1: Peel strength to cloth", 180° peel, specimen width: 10 mm). Specifically, the gripping portion of the fluororesin-elastomer composite was grasped by the first and second grippers 35 and 36, and the first gripper 35 was raised at 50 mm / min to measure the maximum peel strength (N / mm). The peel test was terminated when the displacement reached 350 mm or when the rubber or resin broke. The rubber peel ratio (the percentage of the peeled surface where the elastomer component is broken) was also visually confirmed. The measurement results are shown in Table 2.

[0048] [Table 2]

[0049] The maximum peel strength of the fluororesin-elastomer composite fabricated using the surface-treated fluororesin substrate in Tests No. 5 and No. 7 exceeded 10 N / mm, and the rubber fracture rate was between 70% and 100%. Therefore, it was found that this composite can firmly bond the fluororesin substrate and the elastomer component. On the other hand, the maximum peel strength of the fluororesin-elastomer composites made using the surface-treated fluororesin substrates in Tests No. 6 and No. 9 was low, indicating that the fluororesin substrate and elastomer component easily separated. Furthermore, the maximum peel strength of the fluororesin-elastomer composite made using the surface-treated fluororesin substrate in Test No. 8 was found to vary depending on the location. The reason for this is unclear, but it is thought that the dilution of argon gas containing acrylic acid in the gas channel 20 caused variations in the acrylic acid concentration during plasma treatment, and that these variations affected the formation of the acrylic resin layer. [Explanation of symbols]

[0050] 2: First electrode 3: Second electrode 4: Discharge reactor 5: Fluororesin substrate 6: Surface coating layer 7: Steam generator 8: Organic compound 9: Headspace 10: Power supply unit 11: Inert gas supply unit 12: Gas inlet 13: Gas outlet 15: Outer cylinder 16: (Meth)acrylic resin layer 17: Surface coating fluororesin substrate 18: Elastomer component 20: Gas flow path 22: Seal component 25: Liquid tank 26: Top cover 27: Rubber gasket 28: Thermocouple 29: Block 30: Mold 31: First plate for pressing 32: Second plate for pressing 35: First gripper 36: Second gripper 40: Surface treatment device 50: Fluororesin-elastomer composite

Claims

1. The process includes a surface treatment step in which the surface of a fluororesin substrate is plasma-treated by atmospheric pressure plasma produced by dielectric barrier discharge in the gas flow path of a discharge reactor through which a gas containing an inert gas flows, and a surface coating layer is formed on the surface by vapor of an organic compound. In the surface treatment step, an inert gas is introduced into the headspace of a vapor generator tank containing the liquid organic compound, thereby supplying the gas containing the vapor of the organic compound discharged from the headspace to the gas flow path of the discharge reactor, and generating atmospheric pressure plasma by dielectric barrier discharge in the gas flow path of the discharge reactor. The aforementioned organic compound is a monomer having a double bond within its molecule. The aforementioned surface coating layer is a resin layer, A method for producing a surface-coated fluororesin substrate, characterized in that the surface treatment step is a step of forming the resin layer by plasma graft polymerization.

2. The manufacturing method according to claim 1, which controls the amount of organic compound vapor supplied to the gas channel by adjusting the surface area of ​​the liquid of the organic compound in the steam generating tank or the temperature of the liquid.

3. The aforementioned organic compound is a (meth)acrylic monomer, The aforementioned surface coating layer is a (meth)acrylic resin layer. The manufacturing method according to claim 1 or 2, wherein the surface treatment step is a step of forming the (meth)acrylic resin layer by plasma graft polymerization.

4. A discharge reactor having a first electrode and a second electrode for generating a dielectric barrier discharge; a power supply device electrically connected to at least one of the first and second electrodes; an inert gas supply unit provided for supplying an inert gas to the discharge reactor; and a steam generating tank provided for supplying a vapor of an organic compound to the discharge reactor. The discharge reactor is provided such that the fluororesin substrate, which is the material to be processed, is placed between the first electrode and the second electrode. The steam generating tank and the inert gas supply unit are provided to supply the gas containing the vapor of the organic compound discharged from the headspace to the discharge reactor by introducing an inert gas into the headspace of the steam generating tank where the organic compound is stored. A gas containing the vapor of the organic compound is supplied to the discharge reactor, and an atmospheric pressure plasma is generated by the dielectric barrier discharge. The aforementioned organic compound is a monomer having a double bond within its molecule. A surface treatment apparatus characterized by forming a resin layer on the fluororesin substrate by plasma graft polymerization.

5. The steam generating tank comprises a gas inlet provided for introducing inert gas into the steam generating tank, and a gas outlet provided for discharging the gas inside the steam generating tank. The surface treatment apparatus according to claim 4, wherein the gas inlet and gas outlet are provided such that an inert gas flows parallel to the liquid surface of the organic compound in the headspace.

6. The discharge reactor has an outer cylinder, The fluororesin substrate has a tubular shape and is disposed inside the outer cylinder. The second electrode is placed inside the fluororesin substrate. The first electrode is positioned on the outer surface of the outer cylinder. The surface treatment apparatus according to claim 4 or 5, wherein the inert gas supply unit and the steam generating tank are provided to supply the steam of the organic compound and the inert gas to the gas flow path between the outer cylinder and the fluororesin substrate.

7. A method for producing a fluororesin-elastomer composite, comprising the steps of: producing a surface-coated fluororesin substrate having a (meth)acrylic resin layer formed on the surface of the fluororesin substrate by the method for producing a surface-coated fluororesin substrate described in claim 1; and joining the fluororesin substrate and an elastomer member via the (meth)acrylic resin layer.

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