JP6972683B2 - Method for manufacturing porous carbon sheet - Google Patents

Description

The present invention relates to a porous carbon sheet and a method for producing the same, which can be suitably used as a material for a gas diffuser of a polymer electrolyte fuel cell.

The polymer electrolyte fuel cell is a stack of a plurality of membrane-electrode junctions (MEA) sandwiched between separators on both sides via gaskets. The MEA consists of an anode and a cathode electrodes in which a reaction responsible for power generation occurs, and a solid polymer electrolyte membrane sandwiched between the electrodes. The electrode consists of a catalyst layer and a gas diffusion electrode base material. The gas diffusion electrode base material is composed of a gas diffusion layer and a microporous layer.

In a solid polymer fuel cell, a fuel gas containing hydrogen is supplied to an anode, an oxidation gas containing oxygen is supplied to a cathode, and an electromotive force is obtained by an electrochemical reaction occurring at both poles. The porous carbon sheet used as the gas diffusion layer of a solid polymer fuel cell has high gas diffusivity for diffusing the gas supplied from the separator to the catalyst layer, and the water generated by the electrochemical reaction is separated. A porous carbon sheet made of carbon fiber is widely used because it requires high drainage property for discharging to and high conductivity for extracting the generated current.

In the porous carbon sheet used for these gas diffusion layers, there is a problem that various defects generated during manufacturing have an adverse effect when used as an electrode base material and cannot fully exhibit the originally required functions. The drawbacks referred to here occur, for example, when impurities contained in the raw material are mixed in, impurities floating in the manufacturing process are attached, and carbon short fibers are not dispersed and are solidified in a bundle.

Therefore, inspections are conducted to detect various defects generated in the porous carbon sheet, and markings are applied so that the defective portions can be identified. However, conventionally, marking that is repeatedly performed in the manufacturing process of a porous carbon sheet is performed by a person, which places a heavy burden on the operator and causes marking errors, so that marking cannot be performed quantitatively and accurately. There was a problem.

Therefore, it is required to introduce an automatic marking technology for identification on a porous carbon sheet for the purpose of labor saving and improvement of accuracy. For example, Patent Document 1 proposes a laser marking technique for a gas diffusion layer containing conductive carbon particles and a polymer resin as main components.

Japanese Unexamined Patent Publication No. 2014-191867

However, the gas diffusion layer mainly composed of carbon fibers is carbonized and graphitized at a high temperature of 1000 ° C. or higher, and is more difficult to form than the gas diffusion layer mainly composed of conductive carbon particles and a polymer resin. It was extremely difficult to improve the detectability of marking by the method described in Patent Document 1 described above.

Therefore, the present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to provide a porous carbon sheet in which markings for identification having excellent detectability are formed and a method for producing the same.

In order to solve the above problems, the porous carbon sheet of the present invention has the following constitution. That is, in the porous carbon sheet on which the marking is formed, the ratio of the number of oxygen atoms to the carbon atom (the number of oxygen atoms / the number of carbon atoms) at the place where the marking is formed (hereinafter referred to as the marking portion) is , 0.046 or more is a porous carbon sheet.

Further, the method for producing a porous carbon sheet of the present invention has the following constitution. That is, it is as follows.

A method for manufacturing a porous carbon sheet on which markings are formed.
A method for producing a porous carbon sheet, which comprises irradiating the porous carbon sheet with a fiber laser to form markings (hereinafter referred to as a marking step).

Since the porous carbon sheet of the present invention is formed with markings for identification with good detectability, it is possible to automatically detect defective parts with an inspection device with few false detections and undetected parts. , The gas diffusion electrode and its junction can be efficiently manufactured.

It is a photograph which took the surface of the porous carbon sheet which concerns on one form of this invention with a camera. It is a photograph (magnification 100 times) which took the surface of the marking part of the porous carbon sheet which concerns on one embodiment of this invention with a microscope.

(About marking)
In the porous carbon sheet of the present invention, markings are formed, and the ratio of the number of oxygen atoms to carbon atoms (number of oxygen atoms / number of carbon atoms) at the location where the markings are formed (marking portion) is 0. A porous carbon sheet of .046 or higher.

The marking unit is used for identification, but the purpose of the identification is not particularly limited, and examples thereof include identification of a defect position of a porous carbon sheet, identification of a product number, identification of a product orientation, and the like. can. Further, the shape of the marking portion is not particularly limited.

The marking unit is used for the purpose of identifying the defect position, identifying the product number, identifying the orientation of the product, and the like. Therefore, the shape of the marking portion is not particularly limited, but it may be a line, a circle, an ellipse, a polygon, various symbols that can identify the defect position, or a number or an alphabet that can identify the product number may be written. However, it may be an arrow that can identify the orientation of the product. Further, as will be described later, it is preferable that the marking portions such as lines, circles, ellipses, polygons, symbols, numbers, alphabets, and arrows are composed of multiple lines.

The method for forming the marking on the porous carbon sheet is not particularly limited, and the marking can be formed by irradiating _{the porous carbon sheet with a laser such as a fiber laser or a CO 2 laser.} Hereinafter, the step of irradiating the porous carbon sheet with a laser to form markings is simply referred to as a marking step. By irradiating with a laser, the porous carbon sheet can be cut, engraved or oxidized by heat to discolor it, so that it is possible to form a marking portion with good detectability. Above all, it is preferable to use a fiber laser as a method for forming markings because it is possible to prevent the porous carbon sheet from being deformed and shaving by irradiating with a focused focus.

In the present invention, as shown in FIG. 1, in the porous carbon sheet, the portion where the marking for identification is formed is a marking portion, and the portion other than the marking portion is a non-marking portion. Further, as shown in FIG. 2, the marking portion includes not only the portion cut by the laser irradiation but also the portion discolored by the irradiation heat of the laser (thermal discoloration portion).

In the present invention, it is important that the ratio of the number of oxygen atoms to carbon atoms (number of oxygen atoms / number of carbon atoms) of the marking portion is 0.046 or more. Further, the higher the ratio of the number of oxygen atoms to carbon atoms (number of oxygen atoms / number of carbon atoms) in the marking portion, the better the detectability, but from the viewpoint of suppressing the decrease in bending strength of the porous carbon sheet, from the viewpoint of suppressing the decrease in bending strength of the porous carbon sheet. The upper limit is preferably 0.07 or less.

On the other hand, the porous carbon sheet of the present invention is preferably graphitized at a high temperature of 1000 ° C. or higher, and in the case of such a porous carbon sheet, the composition of the non-marking portion is formed only by carbon atoms. Therefore, the composition of the non-marking portion is preferably 100% carbon atoms (based on the number). Then, by irradiating the porous carbon sheet having the composition of the non-marking portion with 100% carbon atoms (based on the number) with a high-power laser, the porous carbon sheet is oxidized and the number ratio of oxygen atoms becomes large. If the ratio of the number of oxygen atoms to carbon atoms in the marking part (number of oxygen atoms / number of carbon atoms) is 0.046 or more, the difference in color density between the marking part and the non-marking part becomes large, and the detectability is good. It becomes a marking part.

The number ratio of oxygen atoms to carbon atoms (number of oxygen atoms / number of carbon atoms) can be measured by X-ray photoelectron analysis (XPS). It can be measured with Quantera SXM (manufactured by PKI) or its equivalent. The measurement conditions are that the excited X-rays are Monochromatic Al Kα _{1 and 2} rays (1486.6 eV), the X-ray diameter is 200 μm, and the photoelectron escape angle is 45 °. For data processing, smoothing was set to 9point smoothing, and horizontal axis correction was set to 284.6 eV for the C1s main peak (CHx, C—C, C = C).

Using the value of the number ratio of oxygen atoms (%) and the value of the number ratio of carbon atoms (%) obtained from the XPS measurement, the number ratio of oxygen atoms to carbon atoms (hereinafter, number ratio (number of oxygen atoms / number of oxygen atoms /) The number of carbon atoms)) can be calculated according to the following formula (also abbreviated as O / C).

O / C = value of the number ratio of oxygen atoms / value of the number ratio of carbon atoms The measurement of whether the composition of the non-marking part is 100% carbon atoms (number basis) is the number of oxygen atoms and carbon atoms. Similar to the ratio (number of oxygen atoms / number of carbon atoms), it can be measured by X-ray photoelectron analysis (XPS). That is, it is determined whether or not the value (%) of the number ratio of carbon atoms obtained from the XPS measurement is 100%.

In the porous carbon sheet of the present invention, it is preferable that the warp height of the portion where the marking portion is formed is 1 cm or less. The warp height of the marking part is the height from the flat plate at the most raised position of the porous carbon sheet when the porous carbon sheet including the part where the marking is formed is cut out to each 10 cm and placed on the flat plate. Is the warp height. The smaller the warp height is, the more preferable it is, and it is particularly preferable that the warp height is 0 cm. In order to obtain a porous carbon sheet with a warp height of 1 cm or less at the location where the marking portion is formed, a fiber laser is used as a laser in the step of irradiating the porous carbon sheet with a laser to form markings. Can be mentioned as a method using.

In the porous carbon sheet of the present invention, the difference in color density between the marking portion and the non-marking portion (color density of the marking portion-color density of the non-marking portion) is preferably 0.15 or more. When the difference in color density between the marking portion and the non-marking portion is 0.15 or more, the marking has good detectability. The higher the difference in color density, the better the detectability, but from the viewpoint of suppressing the decrease in bending strength of the porous carbon sheet, the upper limit is preferably 0.26 or less, preferably 0.24 or less. Is even more preferable.

The color density is a value calculated from the ratio of the amount of light emitted and the amount of light reflected or transmitted, and is defined by the following formula 3.

Color density = log ₁₀ (incident light intensity / reflected light intensity) ・ ・ ・ Equation 3
The color density can be measured using a formula difference meter (DensiEye100, X-Rite) or an equivalent product thereof.

(Porous carbon sheet)
As the porous carbon sheet, for example, a carbon fiber woven fabric or a carbon fiber non-woven fabric such as a carbon fiber papermaking body may be used as it is, but the porous carbon sheet of the present invention binds dispersed carbon short fibers. It is preferable that the sheet is made of carbonized material. Here, the state in which the carbon short fibers are dispersed is often a state in which the carbon short fibers do not have a remarkable orientation in the sheet surface and exist in a substantially random manner, for example, in a random direction. Regarding the state in which the carbon short fibers are dispersed, specifically, the state in which the short fibers are dispersed by the papermaking method described later. The binder carbide is a carbide in which carbon short fibers are bonded to each other in a porous carbon sheet, and includes resin carbide and pulp carbide described later.

The average fiber diameter of the carbon short fibers constituting the porous carbon sheet of the present invention is preferably 3 to 20 μm, more preferably 4 to 16 μm, and even more preferably 5 to 13 μm. Here, the average fiber diameter of the single fibers in the carbon short fibers is 30 different single fibers randomly obtained by magnifying the carbon fibers by 1,000 times or more with a microscope such as a scanning electron microscope. Was selected, its diameter was measured, and its average value was calculated. As the scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent product thereof can be used.

As the carbon short fibers, polyacrylonitrile (PAN) -based, pitch-based, rayon-based and other carbon short fibers can be used. Among them, it is preferable to use PAN-based or pitch-based, particularly PAN-based carbon short fibers, because a porous carbon sheet having excellent mechanical strength and excellent handleability having appropriate flexibility can be obtained. ..

The porous carbon sheet of the present invention preferably contains carbonaceous particles. By including carbonaceous particles, the conductivity of the porous carbon sheet itself is improved. The average particle size of the carbonaceous particles is preferably 0.01 to 10 μm, more preferably 1 to 8 μm, still more preferably 3 to 6 μm. Further, the carbonaceous particles are preferably graphite or carbon black powder, and more preferably graphite powder. The average particle size of the carbonaceous particles can be obtained from the number average of the particle size distribution obtained by performing dynamic light scattering measurement.

If the density is low, the strength of the marking portion tends to decrease. Therefore, the porous carbon sheet of the present invention has a density of 0.2 to 0.4 g / cm ³ in order to achieve both detectability and bending strength. Is preferable, and 0.25 to 0.35 g / cm ³ is more preferable.

Here, the density of the above-mentioned porous carbon sheet refers to the apparent density, and is calculated from the thickness and basis weight (mass per unit area) of the porous carbon sheet. The thickness of the porous carbon sheet is measured by applying a surface pressure of 0.15 MPa in the thickness direction of the sheet using a micrometer.

In the porous carbon sheet of the present invention, the bending strength of the non-marking portion is preferably 18 MPa or more and 60 MPa or less, and more preferably 20 MPa or more and 60 MPa or less. When the bending strength of the non-marking portion is less than 18 MPa, the porous carbon sheet may be destroyed by the bending force received from the separator when assembled as a fuel cell stack, or the porous carbon sheet for a polymer electrolyte fuel cell may be destroyed. Handleability during manufacturing and higher-order processing is reduced. The higher the bending strength, the more preferable, but when the density of the porous carbon sheet ^{is as small as 0.2 to 0.4 g / cm 3} , the limit is usually about 60 MPa.

In the porous carbon sheet of the present invention, the bending strength of the marking portion is lowered due to the influence of cutting by a fiber laser and oxidation by heat. The marking part is usually for identifying the defect position and is not assembled in the final product fuel cell stack, but if the bending strength is low, it is porous when manufacturing a porous carbon sheet or performing higher-order processing. The quality carbon sheet may be destroyed. Therefore, the porous carbon sheet of the present invention preferably has a bending strength of 18 MPa or more, more preferably 20 MPa or more and 40 MPa or less at the marking portion.

The bending strength of the porous carbon sheet is obtained by a three-point bending test, and is performed according to the method specified in JIS K 7074-1988. At this time, the width of the test piece is 12.7 mm, the length is 70 mm, and the distance between the fulcrums is 30 mm. The radius of the fulcrum is 3R, the radius of the indenter is 1/8 inch R, and the load application speed is 5 mm / min. If the porous carbon sheet has anisotropy with respect to the maximum load and flexural modulus, two tests are performed in each of the vertical and horizontal directions, and the average of them is the bending of the porous carbon sheet. Let it be strength.

When measuring the bending strength of the marking portion, sampling is performed so that the marking line crosses the width direction of the test piece. By sampling so that the marking line crosses the width direction of the test piece, it is possible to measure the bending strength at the portion where the strength is most reduced by the marking.

The porous carbon sheet of the present invention preferably has a thickness of 100 to 250 μm, more preferably 120 to 230 μm, and even more preferably 140 to 210 μm. If the thickness is less than 100 μm, the porous carbon sheet will be destroyed by the force received from the separator when assembled as a fuel cell stack, and the handleability during manufacturing and higher-order processing of the porous carbon sheet will deteriorate. It may happen. If the thickness exceeds 250 μm, the flexibility of the porous carbon sheet is greatly reduced, and it may be difficult to wind the porous carbon sheet into a roll. Further, the thinner the thickness, the easier it is for the strength of the marking portion to decrease, and it becomes difficult to achieve both detectability and bending strength.

The porous carbon sheet of the present invention can be produced by firing a precursor fiber sheet containing carbon short fibers and a resin at a high temperature with the carbon short fibers and the resin having an appropriate grain size. Next, a method suitable for producing the porous carbon sheet of the present invention will be specifically described.

When a sheet formed by binding dispersed carbon short fibers with a binder carbide is used as the porous carbon sheet, the method for producing a porous carbon sheet of the present invention is a precursor containing carbon short fibers and a resin. It has a compression step of pressurizing the body fiber sheet and a carbonization step of heating the pressure-treated precursor fiber sheet to convert the resin into a binder carbide.

The precursor fiber sheet may contain pulp. In that case, the content of the pulp contained is preferably 5 to 100 parts by mass, more preferably 20 to 80 parts by mass, and particularly preferably 30 to 60 parts by mass with respect to 100 parts by mass of the carbon short fibers.

The precursor fiber sheet can be produced through a paper making step of making carbon fiber paper by making paper using carbon short fibers and pulp, and a resin impregnation step of impregnating carbon fiber paper with a thermosetting resin.

In the papermaking process, for example, carbon short fibers and pulp having the above-mentioned average fiber length are uniformly dispersed in water, the dispersed carbon short fibers and pulp are made on a net, and the papermaking sheet is dispersed in an aqueous system of polyvinyl alcohol. Immerse in the liquid and pull up the soaked sheet to dry. In the precursor fiber sheet, the basis weight of the carbon short fibers is preferably ^{10 to 35 g / m 2.}

In the resin impregnation step, the precursor fiber sheet is produced by immersing the carbon fiber paper in the resin solution, pulling up the soaked carbon fiber paper, and drying it.

Examples of the resin contained in the precursor fiber sheet include thermocurable resins such as epoxy resin, unsaturated polyester resin, phenol resin, polyimide resin and melamine resin, acrylic resin, polyvinylidene chloride resin and polytetrafluoroethylene resin. Thermoplastic resin can be used. Usually, a thermosetting resin is used, and it is more preferable to use a thermosetting resin having a high carbonization yield of the resin in the carbonization step, and it is further preferable to use a phenol resin.

In the precursor fiber sheet, the basis weight of the resin was 20 to 35 g / ^{m 2,} is preferably 22~34g / ^{m 2,} and more preferably 25~33g / ^{m 2.}

In the resin impregnation step, it is preferable to add carbonaceous particles to the solution of the thermosetting resin. The carbonaceous particles are preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass, still more preferably 20 to 50 parts by mass with respect to 100 parts by mass of the thermosetting resin.

In the compression step, the precursor fiber sheet is pressure-treated, usually while being heated. For the compression step, an intermittent press device having a pair of hot plates located parallel to each other, a continuous heating press device having a pair of endless belts, or a continuous roll press device can be used.

Next, the precursor fiber sheet that has undergone the compression step is subjected to a carbonization step and carbonized in an atmosphere of an inert gas such as nitrogen to convert the pulp contained in the precursor fiber sheet into pulp carbide and the resin into resin carbide. Thereby, a porous carbon sheet is obtained.

In the method for producing a porous carbon sheet of the present invention, the maximum heating temperature in the carbonization step is preferably in the range of 2200 to 2700 ° C.

The method for producing a porous carbon sheet of the present invention includes a step of detecting defects (defect detection step) before the marking step, and a fiber laser is provided for the porous carbon sheet according to the detected defect location. It is preferable to form markings by irradiating with. Defects detected in the defect detection process include carbon short fiber bundles, holes, foreign matter, and defects due to charring. Further, as a method for detecting defects, there are visual inspections and automatic inspections that can detect defects by irradiating with X-rays, ultraviolet rays, infrared rays, and visible light. In the case of automatic inspection, it is preferable to send the detected foreign matter position information to the marking device because it is possible to automatically mark defects. In any case, it is preferable to form markings in the marking step so that the defective parts detected in the defect detecting step can be identified.

Next, the formation of markings for identification will be described. The method for forming markings on the porous carbon sheet of the present invention is not particularly limited, but in the method for producing a porous carbon sheet of the present invention, it is important to irradiate a laser to form markings (marking step). .. As described above, it is preferable to use a fiber laser as the laser used in the marking process. The fiber laser is not particularly limited, but can be formed by using, for example, a fiber laser marker 7510 (output 50 W, lens f420) manufactured by VideoJet or an equivalent product thereof.

In the porous carbon sheet of the present invention, it is preferable that the marking portion is composed of multiple lines. When the marking portion is a multi-line, it is preferable because the heat-discolored portions of the adjacent lines overlap each other, so that the detectability of the marking portion can be improved. Further, in order to improve the detectability with a single wire, it is possible to cut the porous carbon sheet deeper. In this case, although the bending strength tends to decrease, if the marking portion is made of multiple wires, bending is possible. Since it is possible to improve the detectability without lowering the strength, it is preferable that the marking portion is composed of multiple lines.

Further, the marking may be formed by printing the same portion over and over again. That is, in the marking step, the fiber laser may be irradiated to the same place a plurality of times.

The irradiation conditions of the fiber laser in the marking process include output percentage, printing speed, line pitch, and frequency, which will be described in detail below.

The output percentage of the fiber laser in the marking process is a parameter of what percentage of the fiber laser is irradiated to the device output. The higher the value, the darker the print, and the lower the value, the lighter the print.

The printing speed of the fiber laser in the marking process is the moving speed of the laser scan of the fiber laser. The larger the value, the lighter the printing, and the smaller the value, the darker the printing.

The pitch of the lines of the fiber laser in the marking process is the interval between adjacent lines when printing with multiple lines, and the higher the value, the less the heat-discolored portions of the adjacent lines overlap. On the other hand, the lower the value of the line pitch of the fiber laser, the more easily the heat-discolored portions of the adjacent lines overlap, but if the value is too small, the porous carbon sheet is easily cut and the bending strength is easily lowered. For the above reasons, the line pitch of the fiber laser is preferably 0.3 to 0.7 mm.

The frequency of the fiber laser in the marking process is the period of the fiber laser irradiated by the pulse. The larger the value, the darker the print, and the lower the value, the lighter the print. In the manufacturing method of the present invention, the frequency of the fiber laser is preferably 20 to 90 kHz. By setting the frequency of the fiber laser to 20 to 90 kHz in the marking step, it is possible to suppress deformation of the porous carbon sheet and form a marking portion having good detectability.

In the present invention, the parameter X combined with the irradiation conditions of the fiber laser is defined by the following equation 1.

Parameter X = Fiber laser output (W) ÷ Line pitch (mm) ・ ・ ・ Equation 1
Here, the output (W) of the fiber laser is divided by 100 by multiplying the output (W) of the device and the "output percentage" that sets the percentage of the output of the device to be irradiated with the fiber laser. It is a thing. In the method for producing a porous carbon sheet of the present invention, when the marking portion is composed of multiple lines, the value of the parameter X represented by the formula 1 is preferably 50 or more. By setting the value of the parameter X to 50 or more, it is possible to form a marking with a dark print and good detectability. The larger the parameter X is, the more preferable it is, but in consideration of the decrease in the strength of the porous carbon sheet, the parameter X is usually limited to about 400.

In the present invention, the parameter Y combined with the irradiation conditions of the fiber laser is defined by the following equation 2.

Parameter Y = Fiber laser output (W) ÷ Printing speed (mm / sec) ÷ Line pitch (mm) ・ ・ ・ Equation 2
In the method for producing a porous carbon sheet of the present invention, when the marking portion is composed of multiple lines, the value of the parameter Y represented by the formula 2 is preferably 0.04 or more. By setting the value of the parameter Y to 0.04 or more, it is possible to form markings with dark printing, good detectability, and little decrease in strength of the porous carbon sheet. The larger the parameter Y is, the more preferable it is, but in consideration of the decrease in the strength of the porous carbon sheet, the parameter Y is usually limited to about 0.6.

In the present invention, the porous carbon sheet preferably contains a water-repellent resin. The water-repellent resin is not particularly limited, and examples thereof include fluororesins such as polytetrafluoroethylene resin (PTFE), polyvinylidene fluoride resin (PVDF), and a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP). The amount of the water-repellent resin applied is preferably 1 to 50 parts by mass with respect to 100 parts by mass of the porous carbon sheet before the water-repellent resin is applied.

The gas diffusion electrode base material of the present invention has the porous carbon sheet and the microporous layer of the present invention. In order to obtain the gas diffusion electrode base material of the present invention, it is possible to form a microporous layer containing carbonaceous particles on the above-mentioned porous carbon sheet of the present invention. It is usually preferable that the microporous layer contains 5 to 95% by mass of carbonaceous particles with respect to 100% by mass of the microporous layer.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)
Polyacrylonitrile carbon fiber "Treca (registered trademark)" T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6,000) manufactured by Toray Co., Ltd. is cut to a length of 6 mm and made by Nippon Paper Co., Ltd. ) Papermaking process of continuously making water as a papermaking medium together with broad-leaved sulphite pulp (LDPT), immersing it in a 10% by mass aqueous solution of polyvinyl alcohol, and drying it. A long carbon fiber paper having a fiber texture of 30 g / m ^{2 was obtained.} The amount of added pulp corresponds to 40 parts by mass and the amount of polyvinyl alcohol attached corresponds to 20 parts by mass with respect to 100 parts by mass of carbon fiber paper.

A dispersion prepared by mixing scaly graphite BF-5A (average particle size 5 μm), phenol resin and methanol manufactured by Chuetsu Graphite Industry Co., Ltd. in a mass ratio of 2: 3: 25 was prepared. The carbon fiber paper is continuously impregnated with the dispersion liquid so that the resin impregnation amount is 96 parts by mass of the phenol resin with respect to 100 parts by mass of the carbon short fibers, and dried at a temperature of 90 ° C. for 3 minutes. After undergoing the resin impregnation step, the carbon fiber paper impregnated with resin was obtained by winding it into a roll. The phenol resin is a mixture of a resole-type phenol resin KP-743K manufactured by Arakawa Chemical Industry Co., Ltd. and a novolak-type phenol resin Tamanol (registered trademark) 759 manufactured by Arakawa Chemical Industry Co., Ltd. in a mass ratio of 1: 1. Was used.

Set the hot plates parallel to each other on a 100t press manufactured by Kawajiri Co., Ltd., place spacers on the lower hot plate, and raise and lower the press repeatedly at a hot plate temperature of 170 ° C and a surface pressure of 0.8 MPa. While intermittently transporting the resin-impregnated carbon fiber paper sandwiched between the hot plates, the same portion was subjected to compression treatment so that the same portion was heated and pressed for a total of 6 minutes. The effective pressure length LP of the hot plate was 1200 mm, the feed amount LF of the precursor fiber sheet when intermittently conveyed was 100 mm, and LF / LP = 0.08. That is, the compression treatment was performed by repeating heating and pressurizing for 30 seconds, mold opening, and feeding of carbon fiber paper (100 mm), and the material was wound into a roll.

The compressed carbon fiber paper was used as a precursor fiber sheet and introduced into a heating furnace with a maximum temperature of 2400 ° C, which was maintained in a nitrogen gas atmosphere, and was continuously run in the heating furnace at about 500 ° C / min. After undergoing a carbonization step of firing at a heating rate of (400 ° C./min up to 650 ° C. and 550 ° C./min at temperatures exceeding 650 ° C.), the carbonized carbon sheet was wound into a roll to obtain a porous carbon sheet.

Using a fiber laser marker 7510 (output 50W, lens f420) manufactured by VideoJet, the output percentage is 95%, the printing speed is 1200 mm / sec, the frequency is 75 KHz, the line pitch is 0.5 mm, the number of lines is 10, and the number of overprints is 1. The porous carbon sheet was irradiated with a laser to form a circle having an outer diameter of 54 mm as a marking for identification. There was no defocus, and irradiation was performed in a focused state. In this way, a porous carbon sheet on which identification markings were formed was obtained.

(Example 2)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 85%.

(Example 3)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 75%.

(Example 4)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 65%.

(Example 5)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 55%.

(Example 6)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 500 mm / sec.

(Example 7)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 750 mm / sec.

(Example 8)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 1000 mm / sec.

(Example 9)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 1500 mm / sec.

(Example 10)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 1750 mm / sec.

(Example 11)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 0.2 mm.

(Example 12)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 0.3 mm.

(Example 13)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 0.4 mm.

(Example 14)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 0.6 mm.

(Example 15)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the frequency was changed to 25 kHz.

(Example 16)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the frequency was changed to 50 kHz.

(Example 17)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 45%.

(Example 18)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the printing speed was changed to 3000 mm / sec.

(Example 19)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 0.8 mm.

(Example 20)
A porous carbon sheet having identification markings was obtained in the same manner as in Example 3 except that the line pitch was changed to 1.0 mm.

(Example 21)
_{The laser was changed to a CO 2} laser marker 7310 (output 20W) manufactured by VideoJet, and the output percentage was 100%, the printing speed was 100 mm / sec, the frequency was 5 KHz, the line pitch was 1.0 mm, the number of lines was 10, and the number of overprints was 1. A porous carbon sheet on which identification markings were formed was obtained in the same manner as in Example 1 except that the value was changed to.

Table 1 shows the irradiation conditions and evaluation results of the above Examples and Comparative Examples.

[Detectability]
The detectability was visually evaluated according to the following criteria.

⊚: Very dark marking ○: Dark marking △: Light marking [ warp height]
The warp height of the portion where the marking portion was formed was evaluated according to the following criteria.

○: 1 cm or less ×: greater than 1 cm

In the table, "O / C" means "number ratio (number of oxygen atoms / number of carbon atoms)".

MD means the longitudinal direction, and TD means the width direction.

XPS (C) means the value (%) of the number ratio of carbon atoms obtained from the XPS measurement, and XPS (O) means the value (%) of the number ratio of oxygen atoms obtained from the XPS measurement. ..

1 Non-marking part 2 Marking part 3 Thermal discoloration part 4 Laser irradiation (cutting) part

Claims (4)

A method for manufacturing a porous carbon sheet on which markings are formed.
With respect to the porous carbon sheet, forming a marking by irradiating laser (hereinafter, referred to as the marking step) have, when the location where the marking is formed and a marking unit, the marking unit from the multiplet A method for producing a porous carbon sheet, wherein a fiber laser is used as the laser and the value of the parameter X represented by the formula 1 is 50 or more.
Parameter X = Fiber laser output (W) ÷ Line pitch (mm) ・ ・ ・ Equation 1 The value of parameter Y of formula 2 is 0.04 or more, the porous carbon sheet production method of claim 1.
Parameter Y = Fiber laser output (W) ÷ Printing speed (mm / sec) ÷ Line pitch (mm) ・ ・ ・ Equation 2 The method for producing a porous carbon sheet according to claim 1 or 2 , wherein the frequency of the fiber laser is 20 to 90 kHz. Prior to the marking step, a step of detecting defects is provided.
The method for producing a porous carbon sheet according to any one of claims 1 to 3 , wherein a marking is formed by irradiating the porous carbon sheet with a laser according to the detected defective portion.

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