Carbon fiber-resin composite sheet

Abstract

To provide a novel carbon fiber-resin composite sheet having good electrical conductivity.SOLUTION: As shown in FIG. 1, a carbon fiber-resin composite sheet 10 has a thermoplastic resin 12, and carbon fibers 14 dispersed in the thermoplastic resin 12. In the carbon fiber-resin composite sheet 10, on at least one surface of the carbon fiber-resin composite sheet 10, a cross section 14a of the carbon fibers 14 is exposed on a surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon fiber-resin composite sheet, and more particularly to a carbon fiber-resin composite sheet that can be used as a separator for a fuel cell, a bipolar plate for a redox flow battery, a bipolar plate for a water electrolysis device, etc. [Background technology]

[0002] Conventionally, fuel cell separators made of metal materials and carbon materials have been developed. Fuel cell separators made of carbon materials are advantageous in terms of lighter weight and chemical resistance compared to separators primarily made of metal materials. However, such fuel cell separators sometimes lack sufficient strength, and are more susceptible to gas leaks due to cracking than metal separators. Furthermore, increasing the amount of binder components, such as resins, to prevent cracking results in reduced electrical conductivity. Various proposals have been made to address these issues.

[0003] Patent Document 1 discloses a fuel cell separator characterized by having a conductive gas blocking layer (B) on a conductive layer (A) made of conductive fibers bound and solidified with a synthetic resin.

[0004] Patent Document 2 discloses a fuel cell separator comprising a substrate, the substrate including a first conductive layer containing a conductive first carbon material and formed in a resin material, and a second conductive layer containing a conductive second carbon material, formed adjacent to the first conductive layer on at least one side in the thickness direction of the first conductive layer, and bonded to the first conductive layer via the resin material.

[0005] Patent document 3 discloses an electrically conductive article for use as an electrode in a fuel cell, which comprises electrically conductive reinforcement fibers contained in a matrix having a thickness with the fibers mechanically oriented to be parallel to the thickness.

[0006] Patent document 4 discloses a method for manufacturing a fuel cell separator, which includes the steps of: manufacturing a stampable sheet containing a conductive filler and a polymer material; supplying the stampable sheet to a molding machine equipped with a pair of molds engraved with the shape of a fuel cell separator; and thermoforming the stampable sheet supplied to the molding machine into the shape of the separator.

[0007] Patent Document 5 discloses a method for manufacturing a separator for a fuel cell, which includes providing a raw material sheet having a fiber sheet and carbon particles and resin applied to the fiber sheet, and pressing the raw material sheet to have an uneven shape that forms a flow path for gas flow, thereby obtaining the top portion and the transition portion, and pressing the raw material sheet so that the reduction rate of the top portion is higher than the reduction rate of the transition portion. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-15131 [Patent Document 2] Japanese Patent Publication No. 2021-170524 [Patent Document 3] Special Publication No. 2005-527092 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-269313 [Patent Document 5] Japanese Patent Publication No. 2022-29802 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a novel carbon fiber-resin composite sheet having good electrical conductivity. [Means for solving the problem]

[0010] The present inventors have conducted extensive research and found that the above problems can be solved by the following means, and have completed the present invention. That is, the present invention is as follows: <Aspect 1> A carbon fiber-resin composite sheet having a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin, On at least one surface of the carbon fiber-resin composite sheet, the cross section of the carbon fiber is exposed on the surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet. Carbon fiber-resin composite sheet. Aspect 2: The carbon fiber-resin composite sheet according to Aspect 1, wherein the arithmetic mean roughness of the at least one surface of the carbon fiber-resin composite sheet is 1.0 μm or less. <Aspect 3> The carbon fiber-resin composite sheet according to Aspect 1 or 2, wherein the thermoplastic resin is polyamide. <Aspect 4> A fuel cell separator, which is made of the carbon fiber-resin composite sheet according to any one of aspects 1 to 3. <Aspect 5> A fuel cell comprising the fuel cell separator according to aspect 4. <Aspect 6> Providing a carbon fiber-resin composite sheet precursor having a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin, The carbon fiber-resin composite sheet precursor is polished with sandpaper so that the cross section of the carbon fiber is flush with the surface of the carbon fiber-resin composite sheet on at least one side of the carbon fiber-resin composite sheet, thereby exposing the carbon fiber on the surface of the carbon fiber-resin composite sheet. A method for producing a carbon fiber-resin composite sheet, comprising: Aspect 7: The method for producing a carbon fiber-resin composite sheet according to Aspect 6, wherein the ratio of the arithmetic mean roughness Ra of the polished surface of the sandpaper measured from a profile curve obtained in a measurement range of 2 mm in accordance with JIS B 0601 to the average fiber diameter of the carbon fibers measured by image analysis using a transmission electron microscope is 1.0 or less. Aspect 8: The method for producing a carbon fiber-resin composite sheet according to aspect 6 or 7, wherein the carbon fibers have an average fiber diameter of 3 μm to 10 μm as measured by image analysis using a transmission electron microscope. [Effects of the Invention]

[0011] According to the present invention, a novel carbon fiber-resin composite sheet having good electrical conductivity can be provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional side view of a carbon fiber-resin composite sheet of the present invention. [Figure 2] FIG. 2 is a cross-sectional side view of another embodiment of the carbon fiber-resin composite sheet of the present invention. [Figure 3] FIG. 3 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Example 1 obtained by a scanning electron microscope (SEM). [Figure 4] FIG. 4 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Example 2 obtained by a scanning electron microscope (SEM). [Figure 5] FIG. 5 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Example 3 obtained by a scanning electron microscope (SEM). [Figure 6] FIG. 6 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Comparative Example 1, obtained by a scanning electron microscope (SEM). [Figure 7] FIG. 7 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Comparative Example 2 obtained by a scanning electron microscope (SEM). [Figure 8] FIG. 8 is an enlarged photograph of the surface of the carbon fiber-resin composite sheet of Comparative Example 3, obtained by a scanning electron microscope (SEM). DETAILED DESCRIPTION OF THE INVENTION

[0013] Carbon fiber-resin composite sheet As shown in FIG. 1, the carbon fiber-resin composite sheet 10 of the present invention is A carbon fiber-resin composite sheet 10 having a thermoplastic resin 12 and carbon fibers 14 dispersed in the thermoplastic resin 12, On at least one side of the carbon fiber-resin composite sheet 10, the cross section 14a of the carbon fiber 14 is exposed on the surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet 10.

[0014] The present inventors have found that by exposing the carbon fibers on the surface of the carbon fiber-resin composite sheet so that their cross sections are flush with the surface of the carbon fiber-resin composite sheet on at least one side of the sheet, i.e., so that the cross sections of the carbon fibers and the surface of the carbon fiber-resin composite sheet are on the same plane, the proportion of carbon fibers on this at least one side can be increased, thereby providing good electrical conductivity.

[0015] From the viewpoint of electrical conductivity, the arithmetic mean roughness Ra of at least one surface of the carbon fiber-resin composite sheet is preferably 1.0 μm or less. This arithmetic mean roughness Ra may be 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less, or may be 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, or 0.4 μm or more.

[0016] The arithmetic mean roughness Ra can be measured in accordance with JIS B 0601 using a stylus surface profiler (Dektak 6M, ULVAC) from a profile curve obtained under the following conditions: Stylus Radius: 12.5 μm Measurement range (Length): 2mm Measurement time (Duration): 12 seconds Resolution: 0.556 μm / sample Load (Force): 4mg

[0017] From the viewpoint of electrical conductivity, it is preferable that the cross sections of the carbon fibers are exposed on the surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet on both sides of the carbon fiber-resin composite sheet.

[0018] The carbon fiber-resin composite sheet of the present invention can be used particularly as a separator for a fuel cell, and can also be used as a bipolar plate for a redox flow battery or a water electrolysis device.

[0019] The carbon fiber-resin composite sheet of the present invention may be in a flat plate shape, or may be in a corrugated shape that integrally forms an uneven shape as shown in Fig. 2. In particular, fuel cell separators or bipolar plates for redox flow batteries or water electrolysis devices may have flow paths on their surfaces for passing liquids or gases. When the carbon fiber-resin composite sheet of the present invention is used in these applications, the corrugated shape described above may be useful.

[0020] Each component of the present invention will be described below.

[0021] <Thermoplastic resin> The thermoplastic resin may be a resin in any form, for example, a resin fiber aggregate.

[0022] The thermoplastic resin preferably has the properties of being resistant to the chemical environment of the fuel cell, not softening or melting at the reaction temperature of the fuel cell, and softening or melting during press molding. Examples of such resins include polypropylene, polyethylene, polyamide, polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polyetherimide (PEI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), liquid crystal polymer (LCP), polyimide (PI), polycarbonate (PC), polyphenylene ether (PPE), polysulfone (PSU), polyethersulfone (PES), and polyetheretherketone (PEEK), as well as polymers or mixtures of two or more of the above.

[0023] (Resin: Resin fiber aggregate) The resin fiber aggregate can be obtained by melting the resin fibers, particularly by partially melting them by hot pressing. The resin constituting the resin fibers may be any of the resins described above.

[0024] <Carbon fiber> As the carbon fiber, for example, milled fiber, chopped fiber, etc. can be used. These may be used alone or in combination.

[0025] The average length of the carbon fibers can be, for example, 100 μm or more, 300 μm or more, 500 μm or more, 1.0 mm or more, 1.5 mm or more, 2.0 mm or more, 2.5 mm or more, or 2.8 mm or more, and can be 10.0 mm or less, 8.0 mm or less, 5.0 mm or less, 4.0 mm or less, or 3.5 mm or less.

[0026] The average fiber diameter of the carbon fibers can be 1 μm or more, 3 μm or more, or 5 μm or more, and can be 50 μm or less, 40 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less.

[0027] The average length and average fiber diameter of the carbon fibers can be measured by image analysis using a transmission electron microscope (TEM).

[0028] The carbon fiber content may be 10% by mass or more, 15% by mass or more, 20% by mass or more, or 23% by mass or more, and may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 27% by mass or less, relative to the mass of the carbon fiber-resin composite sheet.

[0029] <Fuel cell separator> The fuel cell separator of the present invention is composed of the above carbon fiber-resin composite sheet.

[0030] 《Fuel Cell》 The fuel cell of the present invention has the above-described fuel cell separator.

[0031] The fuel cell may have a general configuration as long as it has the above-mentioned fuel cell separator, and may, for example, have a fuel cell separator, a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer, and a fuel cell separator in this order.

[0032] Any known material used as a cathode gas diffusion layer, a cathode catalyst electrode layer, an electrolyte layer, an anode catalyst electrode layer, or a fuel cell can be used.

[0033] <Method for manufacturing carbon fiber-resin composite sheet> The method of the present invention for producing a carbon fiber-resin composite sheet includes the steps of: providing a carbon fiber-resin composite sheet precursor having a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin; The carbon fiber-resin composite sheet precursor is polished with sandpaper so that the cross section of the carbon fiber is flush with the surface of the carbon fiber-resin composite sheet on at least one side of the carbon fiber-resin composite sheet, thereby exposing the carbon fiber on the surface of the carbon fiber-resin composite sheet. Includes:

[0034] Each step of the method of the present invention will now be described.

[0035] <Provision of carbon fiber-resin composite sheet precursor> The carbon fiber-resin composite sheet precursor has a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin. In particular, in this specification, the carbon fiber-resin composite sheet precursor refers to a carbon fiber-resin composite sheet before being subjected to polishing, which will be described later.

[0036] The carbon fiber-resin composite sheet precursor can be obtained by a method including the following: Obtaining a precursor structure comprising a thermoplastic resin and carbon fibers; pressing the precursor structure; While pressure is applied by pressing, the precursor structure is heated to soften or melt the thermoplastic resin and maintained in this state, then cooled to solidify the thermoplastic resin, and the pressure is released to obtain a carbon fiber-resin composite sheet precursor.

[0037] (Preparation of precursor structures) The precursor structure includes a thermoplastic resin and carbon fibers. In particular, when the thermoplastic resin is a thermoplastic resin fiber, the precursor structure may be a precursor fiber structure.

[0038] In particular, the precursor fiber structure can be obtained by a method comprising: Dispersing thermoplastic resin fibers and carbon fibers in water to obtain a precursor fiber aqueous dispersion; and The obtained aqueous dispersion of precursor fibers is cast into a sheet, which is then dehydrated and dried.

[0039] (Pressing of precursor structure) The precursor structure may be pressed at a pressure of, for example, 6 MPa or more, 7 MPa or more, 8 MPa or more, or 9 MPa or more, or 15 MPa or less, 14 MPa or less, 13 MPa or less, 12 MPa or less, or 11 MPa or less. For example, the precursor structure may be pressed at a pressure of 6 MPa or more and 15 MPa or less.

[0040] (Heating and Cooling of Precursor Structure) The precursor structure is heated and cooled by heating the precursor fiber structure under pressure from a press to soften or melt the thermoplastic resin and maintaining it in this state, then cooling it to solidify the thermoplastic resin, and then releasing the pressure.

[0041] The heating temperature is not particularly limited as long as it is higher than the softening temperature or melting point of the thermoplastic resin and lower than the thermal decomposition temperature of the thermoplastic resin, and may be, for example, 150° C. or higher, 170° C. or higher, 200° C. or higher, 220° C. or higher, or 240° C. or higher, or 300° C. or lower, 290° C. or lower, 280° C. or lower, 270° C. or lower, or 260° C. For example, the heating temperature may be 150° C. or higher and 300° C. or lower.

[0042] The cooling temperature is not particularly limited as long as it is a temperature that can solidify the thermoplastic resin, and may be, for example, 100° C. or lower, 90° C. or lower, 80° C. or lower, 75° C. or lower, 70° C. or lower, or 60° C. or lower, or may be 15° C. or higher, 20° C. or higher, or 25° C. or higher. For example, the cooling temperature may be 15° C. or higher and 100° C. or lower.

[0043] <Polishing of carbon fiber-resin composite sheet precursor> The carbon fiber-resin composite sheet precursor is polished with sandpaper, so that the cross sections of the carbon fibers on at least one surface of the carbon fiber-resin composite sheet are flush with the surface of the carbon fiber-resin composite sheet and exposed on the surface of the carbon fiber-resin composite sheet.

[0044] Sandpaper of #800 or higher is preferred from the viewpoint of exposing the cross sections of the carbon fibers on the surface of the carbon fiber-resin composite sheet as described above. Sandpaper of #800 or higher, #900 or higher, #1000 or higher, #1200 or higher, #1500 or higher, or #1800 or higher is preferred from the viewpoint of maintaining the carbon fiber network while moderately scraping the thermoplastic resin on the surface, thereby exposing the cross sections of the carbon fibers on the surface of the carbon fiber-resin composite sheet as described above. Sandpaper of, for example, #20,000 or lower, 15,000 or lower, 12,000 or lower, or 10,000 or lower may be used. It is known that the larger the grit (#) number of sandpaper, the smaller the surface roughness of the polished surface; the surface roughness Ra of the polished surface of #800 sandpaper is known to be approximately 6.3 μm.

[0045] The ratio of the surface roughness of the abrasive surface of the sandpaper to the average fiber diameter of the carbon fibers may be 0.1 or more and 1.0 or less. This ratio allows the cross sections of the carbon fibers to be exposed on the surface as described above. This ratio may be, for example, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, or 0.6 or less, or may be 0.1 or more, 0.2 or more, or 0.3 or more. [Example]

[0046] The present invention will be specifically explained with reference to examples and comparative examples, but the present invention is not limited to these.

[0047] Example 1 75 parts by mass of 6-Nylon® fiber as a thermoplastic resin and 25 parts by mass of carbon fiber (average length 3 mm, average fiber diameter 7 μm) were dispersed in water to obtain a precursor fiber aqueous dispersion. The precursor fiber aqueous dispersion was then dehydrated on a wire mesh and then dried to produce a precursor fiber structure. The resulting precursor fiber structure was then heated to a temperature of 250°C and held at this temperature for 1 minute. The precursor fiber structure was then cooled to 70°C or below while maintaining the pressure, to obtain a carbon fiber-resin composite sheet precursor. The surface was then polished using sandpaper #2000 to obtain a carbon fiber-resin composite sheet.

[0048] Comparative Example 1 A carbon fiber-resin composite sheet of Comparative Example 1 was obtained in the same manner as in Example 1, except that the surface was not polished.

[0049] Example 2 and Comparative Examples 2 to 3 Carbon fiber-resin composite sheets of Example 2 and Comparative Examples 2 and 3 were obtained in the same manner as in Example 1, except that the grit size of the sandpaper used was changed as shown in Table 1.

[0050] The arithmetic mean roughness Ra of the obtained carbon fiber-resin composite sheet was measured in accordance with JIS B 0601 from a profile curve obtained under the condition of a measurement range of 2 mm.

[0051] "evaluation" <Surface observation> The surfaces of the carbon fiber-resin composite sheets were magnified and observed using a transmission electron microscope. The correspondence between the obtained magnified images and each carbon fiber-resin composite sheet is shown in Table 1.

[0052] <Resistance measurement> Carbon paper was placed on both sides of the carbon fiber-resin composite sheet, which was then sandwiched between gold-plated flat electrodes and a pressure of 1 MPa was applied. A current of 1 A was then applied to the flat electrodes, and the voltage between the electrodes was measured. The resistance at the interface between the carbon fiber-resin composite sheet and the carbon paper was then measured by subtracting the resistance at the interface between the flat electrodes and the carbon paper from the resistance obtained.

[0053] The configurations and evaluation results of the examples and comparative examples are shown in Table 1 and FIGS.

[0054] [Table 1]

[0055] 3 to 5, it can be seen that in the carbon fiber-resin composite sheets of Examples 1 to 3, the cross sections 14a of the carbon fibers are exposed on the surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet. It can be seen that these resistance values ​​were better than those of the carbon fiber-resin composite sheet of Comparative Example.

[0056] In contrast, the carbon fiber-resin composite sheets of Comparative Examples 1 to 3 maintain the outer shape of the carbon fibers 14 and do not expose the cross sections of the carbon fibers, as shown in Figures 6 to 8, and therefore it can be understood that these are not included in the present invention. [Explanation of symbols]

[0057] 10 Carbon fiber-resin composite sheet 12 Thermoplastic resin 14 Carbon Fiber 14a Cross section of carbon fiber

Claims

1. A carbon fiber-resin composite sheet having a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin, On at least one surface of the carbon fiber-resin composite sheet, the cross section of the carbon fiber is exposed on the surface of the carbon fiber-resin composite sheet so as to be flush with the surface of the carbon fiber-resin composite sheet. Carbon fiber-resin composite sheet.

2. The carbon fiber-resin composite sheet according to claim 1, wherein the arithmetic mean roughness of the at least one surface of the carbon fiber-resin composite sheet is 1.0 μm or less.

3. The carbon fiber-resin composite sheet according to claim 1 or 2, wherein the thermoplastic resin is polyamide.

4. A fuel cell separator comprising the carbon fiber-resin composite sheet according to claim 1 or 2.

5. A fuel cell comprising the fuel cell separator according to claim 4.

6. providing a carbon fiber-resin composite sheet precursor having a thermoplastic resin and carbon fibers dispersed in the thermoplastic resin; The carbon fiber-resin composite sheet precursor is polished with sandpaper so that the cross section of the carbon fiber is flush with the surface of the carbon fiber-resin composite sheet on at least one side of the carbon fiber-resin composite sheet, exposing the carbon fiber on the surface of the carbon fiber-resin composite sheet. A method for producing a carbon fiber-resin composite sheet, comprising:

7. 7. The method for producing a carbon fiber-resin composite sheet according to claim 6, wherein the ratio of the arithmetic mean roughness Ra of the polished surface of the sandpaper measured from a profile curve obtained in a measurement range of 2 mm in accordance with JIS B 0601 to the average fiber diameter of the carbon fibers measured by image analysis using a transmission electron microscope is 1.0 or less.

8. The method for producing a carbon fiber-resin composite sheet according to claim 6 or 7, wherein the average fiber diameter of the carbon fibers measured by image analysis using a transmission electron microscope is 3 μm to 10 μm.

Images