Carbon fiber sheet and method for producing carbon fiber sheet

Abstract

Air permeability in the thickness direction of the carbon fiber sheet can be enhanced.SOLUTION: The carbon fiber sheet 10 contains carbon fibers 21 obtained by carbonizing cellulose fibers. A surface direction and a thickness direction of the carbon fiber sheet 10 are defined as a surface direction and a thickness direction, respectively. The carbon fiber sheet 10 has a plurality of elongated first portions 20 provided side by side in the plane direction. The carbon fibers 21 constituting the first portion 20 include carbon fibers which are oriented in the thickness direction and are flat in the longitudinal direction of the first portion 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon fiber sheet and a method for producing a carbon fiber sheet. [Background technology]

[0002] A polymer electrolyte fuel cell is constructed by stacking a plurality of unit cells (see, for example, Patent Document 1). Each unit cell includes an electrolyte membrane, anode-side and cathode-side catalyst layers sandwiching the electrolyte membrane, anode-side and cathode-side gas diffusion layers sandwiching the anode-side and cathode-side catalyst layers, and anode-side and cathode-side separators sandwiching the anode-side and cathode-side gas diffusion layers.

[0003] The gas diffusion layer is gas permeable and is made of, for example, a carbon fiber nonwoven fabric, which is obtained by spinning a pitch-based material or a PAN-based material into a nonwoven fabric, and then baking the nonwoven fabric in an inert gas atmosphere to carbonize it.

[0004] Further, there is a conventional method for obtaining a carbon fiber sheet by baking a sheet formed by papermaking cellulose fibers, i.e., paper, in an inert gas atmosphere to carbonize it. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-48833 Summary of the Invention [Problem to be solved by the invention]

[0006] Cellulose fibers are flat. Therefore, in a sheet formed by papermaking cellulose fibers, the flat cellulose fibers overlap each other in the thickness direction of the sheet. In a carbon fiber sheet formed by burning and carbonizing such a sheet, the flat carbon fibers also overlap each other in the thickness direction of the carbon fiber sheet, resulting in low air permeability in the thickness direction. Therefore, when using such a carbon fiber sheet as, for example, a gas diffusion layer of a fuel cell, it is necessary to improve the air permeability of the carbon fiber sheet in the thickness direction.

[0007] These problems are not limited to carbon fiber sheets used as gas diffusion layers in fuel cells, but are common to all carbon fiber sheets that are required to have high air permeability in the thickness direction. [Means for solving the problem]

[0008] A carbon fiber sheet for solving the above problem is a carbon fiber sheet containing carbon fibers formed by carbonizing cellulose fibers, and when the surface direction and thickness direction of the carbon fiber sheet are defined as the surface direction and thickness direction, respectively, the carbon fiber sheet has a plurality of elongated first portions arranged side by side in the surface direction, and the carbon fibers constituting the first portions are oriented in the thickness direction and flat in the longitudinal direction of the first portions.

[0009] According to this configuration, the carbon fiber sheet has a plurality of elongated first portions arranged side by side in the surface direction. The carbon fibers constituting the first portions are oriented in the thickness direction and include those that are flat in the longitudinal direction of the first portions. Therefore, in the first portions, overlapping of the carbon fibers in the thickness direction is less likely to occur, thereby improving the breathability in the thickness direction. Therefore, the breathability in the thickness direction of the carbon fiber sheet can be improved.

[0010] In addition, a method for manufacturing a carbon fiber sheet to solve the above problem includes a first sheet preparation step of preparing a first sheet formed by papermaking cellulose fibers, a laminate formation step of stacking a plurality of the first sheets to form a laminate, a second sheet formation step of cutting the laminate into sheets along the stacking direction of the laminate to form a second sheet, and a firing step of firing the second sheet at 1200 degrees or higher in an inert gas atmosphere to carbonize it, thereby forming a carbon fiber sheet.

[0011] According to this method, the cellulose fibers constituting the first sheet extend along the surface direction of the first sheet. The laminate is formed by stacking multiple first sheets. The second sheet is formed by cutting the laminate into sheets along the stacking direction of the laminate. Therefore, the cellulose fibers constituting the second sheet include those oriented in the thickness direction of the second sheet. Then, by baking and carbonizing the second sheet at 1200 degrees or higher in an inert gas atmosphere, a carbon fiber sheet is formed having a plurality of elongated first portions arranged side by side in the surface direction, and the carbon fibers constituting the first portions are oriented in the thickness direction. Therefore, a carbon fiber sheet with high breathability in the thickness direction can be produced. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view of a carbon fiber sheet according to one embodiment. [Figure 2] FIG. 2 is an SEM image of the first sheet used in the production of the carbon fiber sheet of FIG. [Figure 3] FIG. 3(a) is a perspective view of the first sheet and the adhesive layer, FIG. 3(b) is a perspective view of the laminate, and FIG. 3(c) is a perspective view of the second sheet. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, one embodiment of a carbon fiber sheet and a method for producing the same will be described with reference to FIGS. Hereinafter, the surface direction and thickness direction of the carbon fiber sheet 10 will be referred to as the surface direction and thickness direction, respectively.

[0014] <Carbon fiber sheet 10> As shown in FIG. 1, the carbon fiber sheet 10 includes carbon fibers 21 formed by carbonizing cellulose fibers.

[0015] The carbon fiber sheet 10 has a plurality of elongated first portions 20 arranged side by side in the surface direction, and elongated second portions 30 arranged alternately with the first portions 20 in the surface direction. The carbon fibers 21 constituting the first portion 20 are oriented in the thickness direction, and include those that are flat in the longitudinal direction of the first portion 20.

[0016] The carbon fibers 31 constituting the second portion 30 include those that connect the carbon fibers 21 of the first portion 20. The diameter of the carbon fibers 31 is smaller than the diameter of the carbon fibers 21. The second portion 30 has a lower density than the first portion 20 .

[0017] <Method of manufacturing carbon fiber sheet 10> The method for producing the carbon fiber sheet 10 includes a first sheet preparation step, a laminate formation step, a second sheet formation step, and a firing step.

[0018] As shown in Figures 2 and 3(a), in the first sheet preparation step, a first sheet 40 is prepared by papermaking cellulose fibers 41. Note that Figure 3(a) schematically shows the first sheet 40. The cellulose fibers 41 constituting the first sheet 40 extend along the surface direction of the first sheet 40.

[0019] As shown in FIG. 3(b), in the laminate formation step, a plurality of first sheets 40 are laminated to form a laminate 50. In the laminate formation step, the first sheets 40 are bonded together with the adhesive layer 80 made of resin to form the laminate 50.

[0020] As shown in FIG. 3(a), the adhesive layer 80 contains carbon fibers 82. That is, the adhesive layer 80 contains a resin 81, which is the main component of the adhesive, and the carbon fibers 82. The resin 81 in this embodiment is polyethylene (PE). The diameter of the carbon fibers 82 is smaller than the diameter of the cellulose fibers 41. The carbon fibers 82 in this embodiment are PAN-based carbon fibers. Note that the carbon fibers 82 may also be pitch-based carbon fibers.

[0021] As shown in FIGS. 3(b) and 3(c), in the second sheet forming step, the laminate 50 is cut into sheets along the lamination direction of the laminate 50 to form second sheets 60. 3(c), the second sheet 60 has a plurality of elongated first portions 70 arranged side by side in the surface direction of the second sheet 60, and elongated adhesive layers 80 arranged alternately with the first portions 70 in the surface direction. The cellulose fibers 41 constituting the first portions 70 are oriented in the thickness direction of the second sheet 60, and include cellulose fibers that are flat in the longitudinal direction of the first portions 70.

[0022] In the firing step, the second sheet 60 is fired at 1200°C or higher in an inert gas atmosphere to carbonize it, thereby forming the carbon fiber sheet 10. In this embodiment, the second sheet 60 is fired at 1250°C. This forms the carbon fiber sheet 10, which has a plurality of elongated first portions 20 arranged side by side in the planar direction, and in which the carbon fibers 21 constituting the first portions 20 are oriented in the thickness direction.

[0023] Furthermore, in the baking process, the resin 81 that constitutes the adhesive layer 80 is burned away, and the carbon fibers 82 contained in the adhesive layer 80 are assimilated with the carbon fibers 21 that constitute the first portion 20, thereby connecting the carbon fibers 21 in the first portion 20. That is, the carbon fibers 82 become the carbon fibers 31 that constitute the second portion 30 of the carbon fiber sheet 10 through the baking process.

[0024] <Operation of this embodiment> The carbon fiber sheet 10 has a plurality of elongated first portions 20 arranged side by side in the plane direction. The carbon fibers 21 constituting the first portions 20 are oriented in the thickness direction, and some of the first portions 20 are flat in the longitudinal direction of the first portions 20. Therefore, in the first portions 20, overlapping of the carbon fibers 21 in the thickness direction is less likely to occur, thereby improving breathability in the thickness direction (the above is effect 1).

[0025] The second portion 30 has a lower density than the first portion 20, and therefore the breathability in the thickness direction is improved (the above is effect 2). <Effects of this embodiment> (1) The carbon fiber sheet 10 includes carbon fibers 21 formed by carbonizing cellulose fibers 41. The carbon fiber sheet 10 has a plurality of elongated first portions 20 arranged side by side in the planar direction. The carbon fibers 21 constituting the first portions 20 are oriented in the thickness direction and include those that are flat in the longitudinal direction of the first portions 20.

[0026] According to this configuration, the above-mentioned effect 1 is achieved, and therefore the air permeability in the thickness direction of the carbon fiber sheet 10 can be improved. (2) The carbon fiber sheet 10 has elongated second portions 30 arranged alternately with the first portions 20 in the planar direction. The carbon fibers 31 constituting the second portions 30 include those that connect the carbon fibers 21 of the first portions 20 together. The second portions 30 have a lower density than the first portions 20.

[0027] According to this configuration, the above-mentioned effect 2 is achieved, and the air permeability in the thickness direction of the carbon fiber sheet 10 can be further improved. Furthermore, since the second portion 30 has a lower density than the first portion 20, the breathability in the extending direction of the second portion 30 among the planar directions is improved.

[0028] (3) The method for producing the carbon fiber sheet 10 includes a first sheet preparation step, a laminate formation step, a second sheet formation step, and a firing step. According to this method, the cellulose fibers 41 constituting the first sheet 40 extend along the surface direction of the first sheet 40. The laminate 50 is formed by stacking a plurality of first sheets 40. The second sheet 60 is formed by cutting the laminate 50 into sheets along the stacking direction of the laminate 50. Therefore, the cellulose fibers 41 constituting the second sheet 60 include fibers oriented in the thickness direction of the second sheet 60. The second sheet 60 is then fired at 1200°C or higher in an inert gas atmosphere to be carbonized. This forms a carbon fiber sheet 10 having a plurality of elongated first portions 20 arranged side by side in the surface direction, with the carbon fibers 21 constituting the first portions 20 oriented in the thickness direction. Therefore, a carbon fiber sheet 10 with high breathability in the thickness direction can be manufactured.

[0029] (4) The laminate formation step is to form the laminate 50 by bonding the first sheets 40 together with a resin adhesive layer 80. The adhesive layer 80 contains carbon fibers 82.

[0030] According to this method, the resin 81 constituting the adhesive layer 80 is burned away in the baking process, and the carbon fibers 82 contained in the adhesive layer 80 are assimilated with the carbon fibers 21 constituting the first portion 20, thereby connecting the carbon fibers 21 of the first portion 20 together. In this way, the carbon fiber sheet 10 can be manufactured.

[0031] Furthermore, the first sheets 40 constituting the laminate 50 are bonded together by the adhesive layer 80. Therefore, in the second sheet formation step, the laminate 50 can be cut to easily form the second sheets 60. Furthermore, since the shape of the second sheets 60 can be made more stable, the second sheets 60 can be easily handled in the firing step, for example, when being moved into a furnace.

[0032] <Modification> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0033] The resin 81 that constitutes the adhesive layer 80 is not limited to polyethylene (PE), but may be other resins such as polyvinyl alcohol (PVA). In the above embodiment, the adhesive layer 80 contains the carbon fibers 82, but the adhesive layer 80 may contain a precursor material that becomes carbon fibers by carbonization in the firing process in addition to or instead of the carbon fibers 82. Even in this case, the same effect as in (4) above can be achieved.

[0034] In the above embodiment, the laminate 50 is formed by bonding the first sheets 40 together with the adhesive layer 80, but the adhesive layer 80 may be omitted. The carbon fiber sheet 10 is not limited to having the second portion 30, and may not have the second portion 30. In other words, the carbon fiber sheet 10 may have only a plurality of first portions 20 arranged side by side in the planar direction. [Explanation of symbols]

[0035] 10...Carbon fiber sheet 20…Part 1 21...Carbon fiber 30…Second part 31...Carbon fiber 40...1st seat 41...Cellulose fiber 50...Laminate 60...Second seat 70…Part 1 80...Adhesive layer 81...Resin 82...Carbon fiber

Claims

1. A carbon fiber sheet containing carbon fibers obtained by carbonizing cellulose fibers, When the plane direction and thickness direction of the carbon fiber sheet are defined as the plane direction and thickness direction, respectively, a plurality of elongated first portions arranged side by side in the planar direction; The carbon fibers constituting the first portion include those oriented in the thickness direction and flattened in the longitudinal direction of the first portion. Carbon fiber sheet.

2. The second portions have elongated shapes and are alternately arranged with the first portions in the planar direction, The carbon fibers constituting the second portion include those that connect the carbon fibers of the first portion to each other, the second portion being less dense than the first portion; The carbon fiber sheet according to claim 1 .

3. a first sheet preparation step of preparing a first sheet formed by papermaking cellulose fibers; a laminate forming step of laminating a plurality of the first sheets to form a laminate; a second sheet forming step of cutting the laminate into sheets along a stacking direction of the laminate; and a firing step of firing the second sheet at 1200°C or higher in an inert gas atmosphere to carbonize it, thereby forming a carbon fiber sheet. Manufacturing method of carbon fiber sheet.

4. the laminate forming step forms the laminate by bonding the first sheets together via a resin adhesive layer; The adhesive layer contains at least one of carbon fiber and a material that becomes carbon fiber when carbonized in the baking step. The method for producing the carbon fiber sheet according to claim 3.

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