JP2019028078A - Method of inspecting gas diffusion electrode, and gas diffusion electrode - Google Patents

Abstract

To provide an automatic inspecting method for appearance defect that targets a long-sized, rolled gas diffusion electrode as a principal object and can automatically and continuously inspect, in continuous conveyance thereof, many kinds of appearance defect with high precision in an optical manner.SOLUTION: The present invention relates to a method of inspecting a gas diffusion electrode, having a finely porous layer at least on one side of a porous carbon electrode base material, that inspects appearance defects on a surface of the gas diffusion electrode while continuously conveying the gas diffusion electrode, the method of inspecting the gas diffusion electrode having: a process of irradiating the surface of the gas diffusion electrode with light; an imaging process of receiving one of reflected light and transmitted light from the surface of the gas diffusion electrode; a data processing process of processing image data obtained by imaging means; and a process of recording information on at least the kind, size, or area and position of a defect thereof.SELECTED DRAWING: Figure 1

Description

  A fuel cell is a mechanism that electrically extracts the energy generated when water is produced by reacting hydrogen and oxygen. It is highly energy efficient and has only water, so it is expected to spread as clean energy. Has been. The present invention relates to a method for automatically inspecting an appearance defect of a gas diffusion electrode used in a fuel cell and the gas diffusion electrode.

  A fuel cell, for example, a polymer electrolyte fuel cell, supplies a reaction gas (a fuel gas and an oxidant gas) via a gas diffusion electrode to a membrane electrode assembly in which a polymer electrolyte membrane is sandwiched between a pair of catalyst layers. By causing an electrochemical reaction, the chemical energy of the substance is directly converted into electrical energy.

  In a gas diffusion electrode of a fuel cell, a porous carbon electrode substrate such as carbon paper is subjected to a water repellent treatment, and a microporous layer is provided on the surface in contact with the catalyst layer.

  In the microporous layer, various appearance defects that occur during the production also cause a problem that the performance of the fuel cell is lowered and the originally required function cannot be sufficiently exhibited. The appearance defect referred to here is, for example, that a lump of conductive fine particles such as carbon black contained in a coating solution for forming a microporous layer (hereinafter referred to as a microporous layer coating solution) is present on the surface of the microporous layer. There are various types, such as holes in the microporous layer, and fluff of the carbon fiber of the porous carbon electrode substrate can be seen on the surface of the microporous layer.

  Therefore, an appearance inspection is performed to detect various appearance defects generated in the microporous layer of the gas diffusion electrode. However, conventionally, the inspection repeatedly performed in the manufacturing process of the gas diffusion electrode has been performed by human visual inspection. When a long gas diffusion electrode transported continuously is targeted, the inspection object itself In addition to being black, the appearance defects are also many black, and it is also a burden for the inspector to accurately determine the slight difference in color and gloss on the surface, and there are individual differences depending on the inspector. For this reason, there is a problem that the inspection results vary, and the appearance inspection cannot be performed quantitatively and accurately.

  For example, in Patent Document 1, a long sheet member that moves is inspected using an inspection device disposed on the side of the microporous layer from an irradiation unit disposed on the surface side opposite to the microporous layer. , The inspection light is reflected by a roll, and a continuous inspection method for detecting inspection light transmitted from the surface of the sheet member opposite to the microporous layer to the microporous layer side has been proposed.

  On the other hand, for example, Patent Document 2 discloses an appearance defect by imaging a coating layer of a fuel cell electrode with a high-definition camera using a transmission illumination optical system, binarizing the image, and providing an appropriate threshold value. There has been proposed an inspection method for performing a comprehensive pass / fail judgment.

JP 2014-190706 A JP 2016-225059 A

The surface defect inspection methods disclosed in Patent Documents 1 and 2 are all inspections by transmitted light inspection means, so that if it is effective to inspect a single type of defect, It was difficult to simultaneously inspect various types of appearance defects having different colors, glosses, sizes, and areas with high accuracy.

  The present invention has been made to solve the above-mentioned problems, and is mainly intended for a long, roll-shaped gas diffusion electrode. An object of the present invention is to provide an automatic inspection method for appearance defects capable of automatically and continuously inspecting with accuracy.

The first main configuration of the present invention is a gas for inspecting appearance defects on the surface of the microporous layer while continuously conveying a gas diffusion electrode having a microporous layer on at least one surface of the porous carbon electrode substrate. A method for inspecting a diffusion electrode, comprising the step of irradiating light on the surface of the gas diffusion electrode, and the step of receiving and imaging at least one of reflected light or transmitted light from the surface of the gas diffusion electrode The gas diffusion electrode inspection method includes a data processing step of processing image data obtained by the imaging means, and at least a step of recording information on the type, size, area, and position of the defect.
Further, the second main configuration of the present invention is a gas having at least an inspection record in which the type and / or position of the defect by the appearance defect automatic inspection method for the gas diffusion electrode which is the first main configuration is recorded. It is a diffusion electrode. Here, it is desirable that the type of the defect includes at least one of a protrusion, a foreign object, a fluff, a dent, a crack, a hole in a microporous layer, a through hole, a chipped end, and a streak.

According to the present invention, in a gas diffusion electrode having a microporous layer on at least one surface of a porous carbon electrode substrate, these inspection means are adopted even if it is an appearance defect that is difficult to detect by normal visual inspection. As a result, the type of defect, the color, gloss, shape, size, area, and position specific to each defect can be determined simultaneously and accurately, and highly reliable and highly accurate inspection is possible.
In addition, if the gas diffusion electrode of the present invention has the inspection record, it is possible to easily identify the type, location, size, and area of appearance defects that affect performance, and to easily remove the appearance defect portion. Become.

2 is an example of a schematic side view of an inspection apparatus suitably used in an inspection method for a gas diffusion electrode 6. It is the side outline of another example of the inspection apparatus used suitably for the inspection method of the gas diffusion electrode 6. It is the schematic which shows the data processing means and data classification means which concern on this invention. It is the photograph which image | photographed the surface of the gas diffusion electrode which concerns on one form of this invention with the camera.

  First, a gas diffusion electrode that is an inspection object of the present invention will be described. As a porous carbon electrode base material used for a gas diffusion electrode, a sheet-like material made from short fibers including short carbon fibers, a woven or non-woven fabric containing carbon fibers, or carbon fibers are aligned in one or more directions. Examples of the sheet-like material include a carbon fiber sheet-like material in which these fibers are bound with a matrix resin, and the present invention is preferably applied to a long sheet-like material. Furthermore, examples of the carbon fiber sheet include porous carbon sheet obtained by carbonizing the matrix resin in an inert atmosphere. Examples of porous carbon sheet such as film, woven fabric, nonwoven fabric, paper, etc. There is no particular limitation on the form. In particular, a porous carbon electrode base material in which dispersed carbon short fibers are bound with resin and / or organic carbide has a high flexural modulus, a high coefficient of static friction, and is brittle. An apparatus and a manufacturing method using the apparatus are preferably applied. Here, the dispersed state is often a state in which the short carbon fibers do not have a remarkable orientation in the sheet surface and are present almost randomly, for example, in a random direction. The fiber length of the short carbon fiber is preferably 3 to 20 mm, more preferably 5 to 15 mm. By setting the fiber length of the short carbon fiber within the above range, when the short carbon fiber is dispersed and paper is obtained to obtain a carbon fiber sheet, the dispersibility of the short carbon fiber can be improved and the basis weight variation can be suppressed.

  As the porous carbon electrode base material used for the gas diffusion electrode which is an inspection object of the present invention, a porous carbon electrode base material that has been subjected to water repellent treatment by applying a fluororesin is preferably used. That is, since the fluororesin acts as a water repellent resin, the porous carbon electrode substrate used in the present invention preferably contains a water repellent resin such as a fluororesin. As the water-repellent resin contained in the porous carbon electrode substrate, that is, the fluororesin contained in the porous carbon electrode substrate, PTFE (polytetrafluoroethylene) (for example, “Teflon” (registered trademark)), FEP (tetrafluoroethylene) Hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluoride resin), ETFE (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc. are strong, but strong PTFE or FEP that exhibits water repellency is preferred.

  The amount of the water-repellent resin is not particularly limited, but it is appropriate that it is contained in an amount of 0.1% by mass or more and 20% by mass or less in the entire 100% by mass of the porous carbon electrode substrate. If the amount is less than 0.1% by mass, the water repellency may not be sufficiently exerted. If the amount exceeds 20% by mass, pores serving as gas diffusion paths or drainage paths may be blocked, and electrical resistance may increase. is there.

  The method of water-repellent treatment of a porous carbon electrode base material is generally known by a processing technique of immersing the porous carbon electrode base material in a dispersion containing a water-repellent resin, by die coating, spray coating, etc. An application technique for applying a water-repellent resin to the porous carbon electrode substrate is also applicable. Further, processing by a dry process such as sputtering of a fluororesin can also be applied. In addition, you may add a drying process and also a sintering process as needed after water-repellent treatment.

In the present invention, the porous carbon electrode substrate has a microporous layer on at least one side.
The microporous layer has a high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, and a high drainage property for discharging the water generated by the electrochemical reaction to the porous electrode substrate. It is necessary to have high conductivity for extracting current. For this reason, it has electroconductivity, Preferably the thing of an average pore diameter of 0.01-10 micrometers is mentioned.
The number of microporous layers may be single or plural, and is not particularly limited. However, from the viewpoint of process management and cost, a single layer or two layers are preferable. Hereinafter, first, common matters regarding the microporous layer will be described.
The microporous layer used for the gas diffusion electrode to be inspected according to the present invention preferably contains a carbon material, and conductive fine particles such as carbon black, carbon nanotube, carbon nanofiber, carbon fiber chopped fiber, graphene, and graphite are used. It is an included layer. As the conductive fine particles, carbon black is preferably used from the viewpoint of low cost and safety and stability of product quality. As the carbon black contained in the microporous layer, acetylene black is preferably used in that it has few impurities and hardly reduces the activity of the catalyst. Moreover, ash is mentioned as a standard of the impurity content of carbon black, but it is preferable to use carbon black having an ash content of 0.1% by mass or less. The ash content in the carbon black is preferably as small as possible, and carbon black having an ash content of 0% by mass, that is, carbon black containing no ash is particularly preferable.

  In addition, the microporous layer has characteristics such as conductivity, gas diffusivity, water drainage, moisture retention, and thermal conductivity, as well as strong acid resistance on the anode side inside the fuel cell and oxidation resistance on the cathode side. Therefore, the microporous layer preferably contains a water-repellent resin such as a fluororesin in addition to the conductive fine particles. As the fluororesin contained in the microporous layer, polytetrafluoroethylene (PTFE), perfluoroethylene-propene copolymer (FEP), perfluoroethylene, which is suitably used for water repellency of the porous carbon electrode substrate, is used. Examples thereof include fluoroalkoxyalkane (PFA), ethylene-tetrafluoroethylene copolymer (ETFE) and the like. PTFE or FEP is preferred because of its particularly high water repellency.

  In order for the gas diffusion electrode to have a microporous layer, it is common to apply a coating liquid for forming the microporous layer, that is, a microporous layer coating liquid, to the porous carbon electrode substrate. The microporous layer coating liquid usually comprises the above-mentioned conductive fine particles and a dispersion medium such as water or alcohol, and a surfactant or the like is often blended as a dispersant for dispersing the conductive fine particles. When the water repellent resin is included in the microporous layer, it is preferable that the water repellent resin is included in advance in the microporous layer coating liquid.

  As a method of forming the microporous layer, a method of applying a microporous layer coating liquid to a porous carbon electrode substrate is preferable.

  The concentration of the conductive fine particles in the microporous layer coating liquid is preferably 5% by mass or more, more preferably 10% by mass or more from the viewpoint of productivity. If the viscosity, dispersion stability of the conductive particles, and coating properties of the coating liquid are suitable, there is no upper limit for the concentration, but in practice, the concentration of the conductive fine particles in the microporous layer coating liquid exceeds 50% by mass. And suitability as a coating liquid may be impaired. In particular, when acetylene black is used as the conductive fine particles, in the study by the present inventors, in the case of an aqueous coating liquid, the upper limit of the concentration of acetylene black in the microporous layer coating liquid is about 25% by mass. When the concentration is exceeded, acetylene blacks reaggregate, so-called percolation occurs, and the applicability of the coating liquid is impaired due to a sudden increase in viscosity.

The role of the microporous layer is as follows: (1) protection of the catalyst, (2) re-dressing effect to prevent the rough porous carbon electrode substrate surface from being transferred to the electrolyte membrane, and (3) water vapor generated at the cathode. The effect of preventing condensation is mentioned.
In addition, the types of appearance defects occurring in the microporous layer used for the gas diffusion electrode to be inspected include protrusions, foreign matter, fluff, dents, cracks, holes in the microporous layer, through holes, chipped ends, streaks, etc. Can be mentioned. Here, each defect will be briefly described.
The protrusion is a part of a lump in which conductive fine particles such as carbon black contained in the microporous layer coating liquid are aggregated, and when irradiated with light for inspection, the protrusion looks blacker than the surroundings.
The foreign matter is a portion where dust or the like floating in the manufacturing process is attached, and looks white or black.
The fluff may be seen on the surface of the microporous layer of the carbon single fiber or multiple carbon fibers of the porous carbon electrode base material, or may be seen where the carbon fiber fluff floating in the manufacturing process is attached. Looks white or black.
The dent is where the air contained in the microporous layer coating liquid is present or where the microporous layer coating liquid sinks into the porous carbon electrode substrate, and appears darker than the surroundings.
The crack is an elongated crack portion of the microporous layer generated by shrinkage during drying of the microporous layer coating liquid, and appears blacker than the surroundings.

  The hole in the microporous layer is a portion that occurs when the microporous layer coating liquid sinks into the porous carbon electrode substrate or when the microporous layer coating liquid breaks during coating, and appears black from the surroundings.

The through-hole is a portion where a hole is formed in the porous carbon electrode base material due to burning of foreign matters or the like in the porous carbon electrode base material during firing, and looks black from the surroundings.
The end chipping is a portion where the end of the gas diffusion electrode is chipped due to contact or the like during the manufacturing process.

Lines are clogged with foreign matter between the discharge port of the microporous layer coating liquid on the coater and the porous carbon electrode base material during coating, and are continuously generated in the flow direction of the conveyance. Looks black.
From here, based on the illustrated embodiment, an automatic appearance defect inspection method for the gas diffusion electrode 1 according to the present invention and the inspected gas diffusion electrode will be specifically described.
FIG. 1 shows an example of a schematic side view of an inspection apparatus that is preferably used for the inspection method of the gas diffusion electrode 6. The gas diffusion electrode 6 is conveyed in a state in contact with the conveyance roll 7 along the longitudinal direction MD of the gas diffusion electrode 6 indicated by an arrow A, and at a predetermined position above the gas diffusion electrode 6 in contact with the conveyance roll 7, The illuminating means 1 is arranged so as to irradiate the surface of the gas diffusion electrode 6 with a predetermined angle with respect to the gas diffusion electrode 6. Further, the imaging means 2 is arranged on the same side as the illumination means 1 so as to receive the reflected light generated on the surface of the gas diffusion electrode 6. The image picked up by the image pickup means 2 is input to the image input means 3, and further, analysis and defect determination are performed by the image analysis means 4. The results analyzed and determined by the image analysis means 4 are stored in the image recording means 5. When the illumination means 1 is specularly reflected light or scattered light, it can be suitably used particularly for protrusions, foreign substances, fluff, dents, cracks, and holes in a microporous layer.

The angle at which the illumination unit 1 in the present invention irradiates the surface of the gas diffusion electrode 6 is preferably an angle at which it is scattered or regularly reflected by the imaging unit 2 described later.
In particular, the direction of irradiation from the illuminating means 1 to the surface of the gas diffusion electrode 6 and the direction perpendicular to the plane that is irradiated on the gas diffusion electrode 6 and that is in contact with the curved surface on the transport roll 7. Is preferably 0 ° to 60 °.

  Further, the illumination means 1 has an irradiation surface having a line shape or a planar shape and is orthogonal to the longitudinal direction MD of the gas diffusion electrode 6, or the irradiation light is entirely in the width direction TD of the gas diffusion electrode 6. It is preferable that it is arrange | positioned so that it can cover. This is because, when the entire width direction TD of the gas diffusion electrode 6 is inspected at a time, the irradiation surface has a linear or planar illumination rather than the spot-like illumination arranged side by side in the width direction TD. This is because arranging the gas diffusion electrode 6 at a position orthogonal to the longitudinal direction MD can uniformly irradiate the surface of the gas diffusion electrode 6 and prevent a decrease in detection accuracy due to uneven illumination. .

  The imaging means 2 in the present invention is arranged on the same side as the illuminating means 1 with respect to the gas diffusion electrode 6 but in a different direction so as to receive specularly reflected light or scattered light generated on the surface of the gas diffusion electrode 6. ing. In this inspection method, the illumination unit 1 irradiates the surface of the gas diffusion electrode 6 with light, and the imaging unit 2 captures the surface image of the gas diffusion electrode 6 by the specularly reflected light or scattered light generated on the surface of the gas diffusion electrode 6. Take an image with. Thereby, the image data of the predetermined range of the gas diffusion electrode 6 can be obtained. For example, a CCD line sensor camera or the like is preferably used as the imaging unit 2. Further, the direction in which reflected light from the surface of the gas diffusion electrode 6 enters the imaging means 2 and the surface irradiated with the gas diffusion electrode 6 that is perpendicular to the plane that is in contact with the curved surface on the transport roll 7. The angle θ2 from the direction is preferably 0 ° to 60 °.

Moreover, the illumination means 1 in this invention can also be made into oblique illumination. This is applied when detecting irregularities on the surface by irradiating light obliquely in a direction parallel to the longitudinal direction MD of the gas diffusion electrode 6, and particularly suitable for detecting streaks generated in the longitudinal direction MD of the gas diffusion electrode 6. Used for.
FIG. 2 shows a schematic side view of another example of an inspection apparatus suitably used for the inspection method of the gas diffusion electrode 6. The gas diffusion electrode 6 is conveyed along the longitudinal direction MD of the gas diffusion electrode 6 indicated by an arrow A. A predetermined position above the gas diffusion electrode 6 between the transport roll 10 and the transport roll 11 is illuminated so that light is applied to the surface of the gas diffusion electrode 6 from an angle perpendicular to the surface of the gas diffusion electrode 6. Means 8 are arranged. Further, an imaging means 9 is arranged on the opposite side of the illumination means 8 so as to receive transmitted light generated on the surface of the gas diffusion electrode 6. The image picked up by the image pickup means 9 is input to the image input means 3, and further, analysis and defect determination are performed by the image analysis means 4. The results analyzed and determined by the image analysis means 4 are stored in the image recording means 5. In this case, it is particularly preferably used for detecting holes, through-holes and end chippings in the microporous layer.

  The illumination means 8 has an irradiation surface in a line shape or a planar shape, and is disposed at a position orthogonal to the longitudinal direction MD of the gas diffusion electrode 6 as shown in FIG. It is preferable that the diffusion electrode 6 is disposed at a position covering the entire width direction TD. This is because, in the case where the width direction TD of the gas diffusion electrode 6 is inspected at the same time, the illumination in which the irradiation surface is linear or planar is arranged in the longitudinal direction of the gas diffusion electrode 6 rather than arranging the spot-like illumination side by side in the width direction TD. This is because the arrangement at the position orthogonal to the MD can uniformly irradiate the surface of the gas diffusion electrode 6 and prevent a decrease in detection accuracy due to uneven illumination.

The image pickup means 9 in the present invention preferably uses, for example, a CCD line sensor camera or the like. Further, the angle of the imaging means 9 with respect to the surface of the gas diffusion electrode 6 is preferably vertical as shown in FIG.
In describing the data processing means and data sorting means in the present invention, an example of the flow of image input, image analysis, and image storage will be briefly described.

  The image input means 3 sequentially inputs image data obtained by imaging the gas diffusion electrode 6 illuminated by the illumination means 1 with the imaging means 2.

  The image data input to the image input means 3 is supplied to the image analysis means 4 and analyzed in time series. Then, the analysis result in the image analysis means 4, the presence / absence of a defect based on the analysis result, the type of defect, and the position of the defect are detected, and the analysis ends.

  When the analysis is completed, information input to the image storage unit 5 and analyzed and determined by the image analysis unit 4 is stored. An analysis (detection) processing method and a result determination method will be described later.

As described above, a series of examinations of lighting, imaging, analysis, result determination, and storage are repeated,
A continuous automatic inspection is performed along the longitudinal direction MD of the gas diffusion electrode 6. Further, in this inspection method, at least one or more of projections, foreign matters, fluff, dents, cracks, microporous layer holes, through-holes, end cuts, and streaks on the surface of the gas diffusion electrode 6 to be inspected. Can be detected.

  As shown in FIG. 3, the image analysis unit 12 in the present invention includes a first data processing unit 31, a second data processing unit 32, and a data sorting unit 33.

  The first data processing unit 31 is a data processing unit that extracts defect candidates from image data obtained by the imaging unit 2 or the imaging unit 9.

  The second data processing unit 32 is a data processing unit that calculates the feature amount of the defect candidate from the image data of the defect candidate obtained by the first data processing unit.

  The data disposal classification means 33 is a data classification means for extracting defects from the defect candidate feature quantities obtained by the second data processing means and sorting them.

  Here, each data processing means and data separation in the image analysis means 12 will be described in detail.

  First, the first data processing unit 31 extracts defect candidates from the image data obtained by the imaging unit 2 and the imaging unit 9. Since the image data obtained by the imaging unit 2 and the imaging unit 9 here may include a defect candidate other than the defect candidate to be detected (for example, the background of the imaging region), the image data A process of extracting only defect candidates to be detected from data is performed. As a method of such extraction processing, there is generally binarization, and if a pixel in the image data is brighter than a preset brightness (threshold), it is extracted as bright part data, and if dark, it is extracted as dark part data.

  In the inspection method of the gas diffusion electrode 6 according to the present invention, the defect candidate is brighter than the background by receiving the light emitted from the illumination unit 1 or the illumination unit 8 as reflected light by the imaging unit 2 or the imaging unit 9. Or since it can image darkly, a binarization process can be applied. By executing such processing on all the pixels in the image data, the defect candidates are extracted as bright part data or dark part data.

  In addition, when the image data includes noise (for example, tumbling noise called sesame salt noise), before performing the above extraction process, an averaging filter, a Gaussian filter, It is preferable to perform a filtering process such as a median filter to reduce noise so that a defect candidate can be easily extracted as bright part data or dark part data.

The second data processing means 32 calculates the feature amount of the defect candidate from the defect candidate image data obtained by the first data processing means 31. Typical features here include a center of gravity, a circumscribed rectangle, an area, a perimeter, and a circularity. Each feature amount will be briefly described. The center of gravity is the center of the weight of the entire region when it is assumed that the pixels in the extracted region have an equal weight. The circumscribed rectangle is the smallest rectangle that touches the extracted area, and is used to know the approximate size of the area. The area is the number of pixels constituting the extracted region. The perimeter is the number of pixels around the extracted area. The circularity represents how close the extracted region is to a circle, and is obtained by 4πS / L ² where S is the area and L is the perimeter.
When the object is a circle, the maximum circularity is 1, and the further away from the circle, the smaller the value. Such feature amounts are calculated and used for extraction and separation processing by a data separation means described later. Since the defects generated in the gas diffusion electrode 6 in the present invention have different characteristics, the accuracy of detecting the defects can be improved by applying one or more kinds of feature amounts suitable for each defect. It becomes possible.

  In addition, the above-mentioned feature amount is focused on the shape feature of the pixels constituting the extracted region, but there is also a feature amount focused on the luminance value of the pixels constituting the extracted region. It can also be applied. Typical examples include a minimum luminance value and a maximum luminance value. The minimum luminance value is the value with the lowest luminance among the pixels constituting the extracted region, and the maximum luminance value is the value with the highest luminance among the pixels constituting the extracted region. For example, in the case of a hole in the microporous layer, this defect looks blacker than the normal part of the gas diffusion electrode 6, so that the luminance value of the pixel constituting the defective part is smaller than the luminance value of the pixel constituting the normal part. It should be. Therefore, in this case, the minimum luminance value can be applied. In this way, the luminance feature amount can be applied, and by applying these in combination with the shape feature amount described above, it is possible to further improve the defect detection accuracy.

The data classification means 33 extracts defects from the defect candidate feature quantities obtained by the second data processing means 32 and classifies them. The feature amount calculated by the second data processing means 32 is compared with a preset threshold value, and if the feature amount is equal to or greater than the threshold value or less than the threshold value, it is extracted as a defect. In addition, since the shape characteristics and luminance characteristics are different for each defect, the optimal feature amount is selected in advance according to the defect feature to be detected, and a threshold is set to compare the defect candidates for each defect. It becomes possible to do. For example, for cracks, the shape is narrower than other defects, so the circularity is selected as the feature quantity, and the threshold value is set to a value close to 0 (because the value gets closer to 0 as the distance from the circle increases). Thus, it is possible to accurately distinguish from other defects.
Next, image analysis conditions set so as to be detected by the defect size or area measured by the laser microscope of the gas diffusion electrode in the present invention will be described.
Since the size or area of the image of the defect candidate taken is changed depending on the angle and distance between the gas diffusion electrode, the illumination unit, and the imaging unit, it may not match the actual size or area of the defect candidate. First, the actual size or area of a defect candidate is measured with a laser microscope in advance, and the defect candidate is inspected with an inspection apparatus. Next, the relationship between the actual size or area measured by the laser microscope and the size or area detected by the inspection apparatus (regression equation of linear approximation, etc.) is found, and by applying the relationship to the size or area in the captured image, The area can be calculated with high accuracy. The sizes of defect candidates listed here include circumscribed circles (major axis) and inscribed circles (minor axis) as examples. The maximum and minimum values of each size and defect type according to the purpose. Etc. are appropriately selected.

Next, a suitable inspection position of the gas diffusion electrode 6 in the present invention will be described.
When the gas diffusion electrode 6 is conveyed, in the case of FIG. 2, the gas diffusion electrode 6 vibrates up and down due to meandering of the roll, a slight difference in tension in the width direction, and the like in the portion not in contact with the conveyance roll. Sometimes. Due to the vibration, the distance between the gas diffusion electrode 6 and the imaging unit 9 varies, and the imaging unit 9 may not be in focus. On the other hand, in the case of FIG. 1, since the gas diffusion electrode 6 does not vibrate up and down because it is in contact with the transport roll, stable imaging can be performed. For this reason, it is preferable to inspect a portion of the gas diffusion electrode 6 that is in contact with the transport roll from the viewpoint of stably imaging.

  Next, the deposits present on the surface of the gas diffusion electrode 6 in the present invention and the mechanism for removing the deposits will be described.

  Examples of the deposit include dust present in the air and short carbon fibers generated from the gas diffusion electrode 6. These deposits may adhere during the manufacturing process or during transportation, and may be detected as an appearance defect when the inspection method of the present invention is used for inspection. Here, the adhering substance refers to an object that can be confirmed on the surface of the gas diffusion electrode 6 but is not completely fixed. When these deposits exist at the time of inspection and come off after the inspection, a portion that is not an appearance defect is regarded as a defect. On the other hand, if these deposits do not come off, they may be pressed and fixed to the surface of the gas diffusion electrode 6 when they are wound up as a roll.

  As a method for removing these deposits, the deposit on the surface of the gas diffusion electrode 6 is blown off by air, and the blown deposit is sucked and removed. The static electricity of the gas diffusion electrode 6 and surrounding deposits is removed. And the like, and the like.

  Next, a gas diffusion electrode having an inspection record that records at least the type of defect and / or its position in the present invention will be described.

Here, the inspection record includes a recording sheet, a recording medium such as a CD-ROM or flash memory in which the inspection record is recorded as an electronic file, and an electronic file itself.
If they are present together with the gas diffusion electrode, the type and / or position of the defects that affect performance can be easily identified, so that the defect part can be removed and assembled at the fuel cell assembly site. High-performance and high-quality cell assembly becomes easy.

The defect position in the length direction of the gas diffusion electrode can be obtained by detecting the number of rotations of the axis of the conveyance roll contacting the gas diffusion electrode to be conveyed with an encoder and converting it to the conveyance length. Further, the defect position in the width direction of the gas diffusion electrode can be obtained by calculation from imaging data obtained by each imaging device arranged linearly in the width direction.
Next, the marking that can determine the defect position of the gas diffusion electrode 6 in the present invention will be described.

  In addition to the inspection record, it is preferable that the surface of the gas diffusion electrode is marked so that a defective portion of the gas diffusion electrode can be easily identified.

Examples of the marking include those based on ink jet and laser marking.
In the case of inkjet, it is preferable to use an organic pigment-based ink from the viewpoint of preventing metal contamination that causes a decrease in fuel cell performance.
In the case of laser marking, it is preferable to have a mechanism for collecting and processing harmful gas generated by decomposition by laser irradiation.

  The marking part 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 gas diffusion electrode, identification of a product number, identification of a product direction, and the like. . The shape of the marking part is not particularly limited, but may be a line, circle, ellipse, polygon, various symbols that can identify the defect position, or a number or alphabet that can identify the product number. It is good also as an arrow etc. which can identify the direction of a product.

The method for forming the marking on the gas diffusion electrode is not particularly limited, and the marking can be formed by irradiating the gas diffusion electrode with a laser such as a fiber laser, a CO ₂ laser, a YVO ₄ laser, or a UV laser. . Hereinafter, the process of forming a marking by irradiating the gas diffusion electrode with a laser is simply referred to as a marking process. By irradiating the laser, the gas diffusion electrode can be cut, engraved or oxidized by heat and discolored, so that it is possible to form a marking portion with good detectability. Among them, the YVO ₄ laser has a high peak power (the instantaneous value of the laser is high), and printing is possible even with short-time irradiation, so that thermal damage to the substrate irradiated with the laser can be reduced. In addition, since there is an advantage in that fine processing is possible, it is preferable to use a YVO ₄ laser as a method for forming the marking.

  In the present invention, as shown in FIG. 4, in the gas diffusion electrode, the part where the marking for identification is formed is the marking part 41, and the part other than the marking part is the non-marking part 42. Further, the marking portion 41 includes not only a portion irradiated with the laser and cut, but also a portion (thermal discoloration portion) that is discolored by the irradiation heat of the laser.

  In the present invention, the number ratio of oxygen atoms in the marking portion to the total of carbon atoms and fluorine atoms (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)) is preferably 0.042 or more, It is more preferably 0.048 or more, and further preferably 0.054 or more. In addition, the higher the number ratio of oxygen atoms in the marking part to the total number of carbon atoms and fluorine atoms (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)), the better the detection, but the gas From the viewpoint of suppressing a decrease in the tensile strength of the diffusion electrode, the upper limit is preferably 0.085 or less. Also, if the laser output becomes too high, the cutting becomes deeper and reaches the microporous layer, so that the carbon material of the microporous layer is detected as the number of carbon atoms and the fluororesin is detected as the number of fluorine atoms. This is not preferable because the ratio of the number of oxygen atoms is relatively reduced.

  If the number ratio (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)) of oxygen atoms in the marking part to the total of carbon atoms and fluorine atoms is 0.042 or more, the marking part and the non-marking part The difference in color density is increased, resulting in a marking portion with good detectability.

  The number ratio of oxygen atoms to the total number of carbon atoms and fluorine atoms (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)) can be measured by X-ray photoelectron analysis (XPS). It can be measured with Quantera SXM (manufactured by PHI) or its equivalent. The measurement conditions are such that the excitation X-ray is Monochromatic Al Kα1,2 (1486.6 eV), the X-ray diameter is 200 μm, and the photoelectron detection angle is 45 °. In the data processing, smoothing can be 9-point smoothing, and in the horizontal axis correction, the C1s main peak (CHx, CC, C = C) can be 284.6 eV.

Using the oxygen atom number ratio value (%), carbon atom number ratio value (%), and fluorine atom number ratio value (%) obtained from XPS measurement, the oxygen atom carbon atom and fluorine atom The number ratio (hereinafter, the number ratio (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)) is also abbreviated as O / (C + F)) can be calculated according to the following formula.
O / (C + F) = number ratio of oxygen atoms / (number ratio of carbon atoms + value ratio of fluorine atoms)
In addition, the marking portion in the gas diffusion electrode is imaged with an image processing software after an observation image is captured with an optical microscope using incident light. As the optical microscope, M205C (manufactured by Leica) or equivalent is used. A clear image can be obtained by imaging at a magnification of about 20 times.
Image processing is performed by binarization using Jtrim, ImageJ, or equivalent software. At that time, the case where all of the theoretically marked area is discolored by the marking process and is completely filled by the binarization by the image processing is defined as a marking portion discolored area ratio of 100%. Specifically, the area of the marking shape set by the marking device can be used as the “theoretical marking area”. Moreover, the marking portion can be measured visually using a ruler, or can be magnified and measured with an optical microscope to calculate the area. The discolored portion of the marking portion is regarded as an area to be painted by binarization, assuming that the luminance of 0 to 255 gradations set by the image processing software has changed from 0 to 30 gradations to black. The 31st to 255th gradations are regarded as undiscolored portions. The discolored area ratio of the marking part can be calculated according to the following formula. In addition, about the marking selected arbitrarily, it measures 5 times each and takes the average value.
Marking part discoloration area ratio (%) = area where the discoloration part caused by marking is painted by binarization of image processing / theoretical area of the marking part × 100
In the gas diffusion electrode of the present invention, the marking area discoloration area ratio is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more. The higher the marking portion discolored area ratio, the better the detectability. However, if it is 30% or more, the difference in color density between the marking portion and the non-marking portion becomes large, and the marking portion has good detectability.
The gas diffusion electrode of the present invention preferably has a tensile strength of 2.4 N / mm or more, more preferably 2.7 N / mm or more, and further preferably 3.0 N / mm or more. When the tensile strength is less than 2.4 N / mm, breakage may occur during handling of the gas diffusion electrode, or handling may be deteriorated. The larger the tensile strength, the more preferable. However, in the case of a long and roll-shaped gas diffusion electrode, the limit is usually about 7 N / mm.

  The tensile strength of the gas diffusion electrode is determined in accordance with the method specified in JIS P 8113: 2006 “Paper and paperboard—Test method for tensile properties—Part 2: Constant speed extension method”. At this time, the width of the test piece is 15 mm, the length is 150 mm, and the grip interval is 60 mm. The tensile speed is 2 mm / min. In addition, when the gas diffusion electrode has anisotropy, the test is performed 10 times in the longitudinal direction MD, and the average thereof is taken as the tensile strength of the gas diffusion electrode.

    Hereinafter, the present invention will be described specifically by way of examples. The materials used in the examples, the porous carbon electrode substrate, the method for producing the microporous layer, the gas diffusion electrode inspection method, and the marking method on the gas diffusion electrode are shown below.

Example 1
<Material>
A: PAN-based carbon fiber “TORAYCA” (registered trademark) T300 (average diameter: 7 μm) manufactured by Toray Industries, Inc., a porous carbon electrode substrate, is cut into an average length of 12 mm of short fibers, dispersed in water, and wet papermaking Paper was continuously made by the method. Furthermore, a 10% by mass aqueous solution of polyvinyl alcohol as a binder was applied to the paper and dried to prepare a carbon short fiber sheet having a carbon short fiber basis weight of 26 g / m ² . The adhesion amount of polyvinyl alcohol was 18 parts by mass with respect to 100 parts by mass of the carbon fiber.

  Next, a phenolic resin in which a resol type phenolic resin and a novolac type phenolic resin are mixed as a thermosetting resin so as to have a mass ratio of non-volatile content of 1: 1, and scaly graphite powder (average particle size 5 μm) as a carbon powder Then, methanol is used as a solvent, and these are mixed at a blending ratio of thermosetting resin (non-volatile content) / carbon powder / solvent = 10 parts by mass / 1 part by mass / 35 parts by mass, and uniformly dispersed resin composition ( A mixed solution) was obtained.

  Next, the carbon short fiber sheet was continuously immersed in the mixed solution of the above resin composition, and after undergoing a resin impregnation step in which the carbon short fiber sheet was sandwiched and squeezed between a pair of rolls, it was wound into a roll shape to obtain a precursor fiber sheet. At this time, a certain clearance was provided between the rolls, a pair of rolls were horizontally arranged, and the carbon short fiber sheet was pulled up vertically to adjust the total amount of the resin composition. In addition, one of the two rolls was a smooth metal roll having a structure capable of removing excess resin composition with a doctor blade, and the other roll was a roll having a rugged gravure roll. . By sandwiching one surface side of the carbon short fiber sheet with a metal roll and the other surface side with a gravure roll and squeezing the impregnating solution of the resin composition, the resin composition of one surface and the other surface of the carbon short fiber sheet A difference was made in the amount of deposits. The adhesion amount of the phenol resin in the precursor fiber sheet was 104 parts by mass with respect to 100 parts by mass of the short carbon fibers.

The hot plate was set in a press molding machine so as to be parallel to each other, a spacer was disposed on the lower hot plate, and the resin-impregnated carbon fiber paper sandwiched between release papers from above and below was intermittently conveyed and compressed. In that case, the space | interval of an up-and-down press face plate was adjusted so that it might become a precursor fiber sheet which has a desired short carbon fiber density after a pressurization process. Moreover, the compression process was performed by repeating heating and pressurization, mold opening, and sending of carbon fiber, and it wound up in roll shape.
The precursor fiber sheet subjected to the pressure treatment was introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere, and passed through a carbonization step of firing while continuously running in the heating furnace. It wound up in roll shape and obtained the porous carbon electrode base material. The obtained porous carbon electrode substrate had a density of 0.29 g / cm ³ .

  Then, the preparation method of a microporous layer is shown.

<Material>
B: Carbon black 1 with a structure index of 3.0 or higher
: DBP oil absorption 140 cc / 100 g, BET specific surface area 41 m ² / g, structure index 3.4
Carbon black 2 with a structure index of 3.0 or higher
: DBP oil absorption 125 cc / 100 g, 41 m ² / g, structure index 3.1

C: Carbon black 3 with a structure index of less than 3.0
DBP oil absorption 175 cc / 100 g, BET specific surface area 67 m ² / g, structure index 2.6)

D: Water repellent resin “Neofluon” (registered trademark) FEP dispersion ND-110 (FEP resin, manufactured by Daikin Industries, Ltd.)
E: Surfactant “TRITON” (registered trademark) X-100 (manufactured by Nacalai Tesque)
<Measurement of thickness of porous carbon electrode substrate and gas diffusion electrode>
About the thickness of a porous carbon electrode base material and a gas diffusion electrode, it measured, applying a 0.15 MPa load, using the dial gauge of the measuring element of diameter 5mm (phi).
<Measurement of the thickness of the microporous layer>
About the thickness of the microporous layer, it computed from the difference of the thickness of the porous carbon fiber base material and gas diffusion electrode at the time of 0.15 MPa pressurization calculated | required by the above.

<Marking area discoloration area ratio>
The theoretical area of marking was defined as the area of the marking shape set by the marking device, and the discolored area ratio of the marking portion was calculated according to the following formula. In each example, five measurements were performed for two arbitrarily selected markings, and the average value was taken.
Marking part discoloration area ratio (%) = area where the discoloration part caused by marking is painted by binarization of image processing / theoretical area of the marking part × 100
<Production of gas diffusion electrode>
A water repellent resin disperser in which a porous carbon electrode base material having a thickness of 136 μm wound in a roll shape is dispersed in water so as to have a fluororesin concentration of 5 mass% while being transported using a wind-up transport device. It was immersed in a dipping tank filled with John to perform water repellent treatment, dried with a drier set at 100 ° C. and wound up with a winder to obtain a water-repellent porous carbon electrode substrate. As the water-repellent resin dispersion, FEP dispersion ND-110 diluted with water so that the FEP concentration was 5% by mass was used.

  Next, a winding-type continuous coater provided with two die coaters, a dryer and a sintering machine was prepared in a conveying device equipped with an unwinder, an interleaf paper unwinder, and a winder.

  As the water-repellent treated porous carbon electrode base material, a raw material obtained by winding a porous carbon electrode base material having a thickness of 136 μm and a width of about 400 mm into a 400-m roll was set in an unwinding machine.

  The surface on which the microporous layer was applied was used as the surface on the layer X side, and the raw material was conveyed by drive rolls installed in the unwinding unit, the winding unit, and the coater unit. First, the first microporous layer coating solution is applied using the first die coater, and then the second microporous layer coating solution is continuously applied by the second die coater. In a sintering machine in which moisture was dried with hot air and the temperature was set to 350 ° C., sintering was performed, and then winding was performed with a winder.

  The microporous layer coating solution was prepared as follows.

First microporous layer coating solution:
15 parts by mass of carbon black 1 having a structure index of 3.0 or more, or 15 parts by mass of carbon black 2 having a structure index of 3.0 or more, 5 parts by mass of FEP dispersion (“Neoflon” (registered trademark) ND-110), a surfactant ( 15 parts by mass of “TRITON” (registered trademark) X-100) and 65 parts by mass of purified water were kneaded with a planetary mixer to prepare a coating solution.

Second microporous layer coating solution:
5 parts by mass of carbon black 35 having a structure index of less than 3.0, 2 parts by mass of FEP dispersion (“Neofluon” (registered trademark) ND-110), 7 parts by mass of surfactant (“TRITON” (registered trademark) X-100) Part and 86 parts by mass of purified water were kneaded with a planetary mixer to prepare a coating solution. The kneading conditions in the planetary mixer were adjusted to increase the degree of dispersion of the conductive fine particles.

  In applying the first microporous layer coating liquid, the basis weight of the microporous layer after sintering was adjusted to 22 g / m2. At this time, the thickness of the first microporous layer was 31 μm. Furthermore, in applying the second microporous layer coating solution, the thickness of the second microporous layer was adjusted to 6 μm.

<Gas diffusion electrode inspection method and gas diffusion electrode marking method>
Next, the conveyance inspection apparatus provided with the unwinding machine, LED line type illumination, the line sensor camera, the image analysis means, and the winding machine was prepared.

  The raw material which wound the gas diffusion electrode which has the said microporous layer in 400-m roll shape was set to the unwinding machine.

While irradiating the surface having the microporous layer with LED line illumination, images were taken continuously with a line sensor camera, and wound with a winder while being processed with image analysis means.
At that time, using the YVO ₄ laser marker MH-D1500 (output 25W) manufactured by Keyence Corporation in the vicinity of the detected defect, the porosity of the gas diffusion electrode is 30% output, the printing speed is 1000 m / sec, and the frequency is 140 KHz. The carbon electrode substrate surface was irradiated with a laser to form a circular marking. There was no defocusing, and irradiation was performed in a focused state. In this way, a gas diffusion electrode having a marking formed thereon was obtained.
(Example 2)
A gas diffusion electrode with markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 40%.
(Example 3)
A gas diffusion electrode with markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 20%.

Example 4
A gas diffusion electrode with markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 50%.
(Example 5)
A gas diffusion electrode with markings was obtained in the same manner as in Example 1 except that the output percentage was changed to 10%.
(Reference Example 1)
The non-marking part in the gas diffusion electrode formed with the marking obtained in Example 1 was evaluated in the same manner as in Example 1.

  The irradiation conditions and evaluation results of the above Examples and Reference Examples are shown in Table 1.

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

◎: Very dark marking ○: Dark marking △: Light marking

In the table, “O / (C + F)” means “number ratio (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)”).

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

DESCRIPTION OF SYMBOLS 1 Illumination means 2 Imaging means 3 Image input means 4 Image analysis means 5 Image recording means 6 Gas diffusion electrode 7 Transport roll 8 Illumination means 9 Imaging means 10 Transport roll 11 Transport roll 31 First data processing means 32 Second data processing Means 33 Data sorting means A Longitudinal direction MD of gas diffusion electrode 6
41 Non-marking part 42 Marking part

Claims (15)

A gas diffusion electrode inspection method for inspecting appearance defects on the surface of the gas diffusion electrode while continuously conveying a gas diffusion electrode having a microporous layer on at least one surface of a porous carbon electrode substrate,
Irradiating the gas diffusion electrode surface with light,
An imaging step of receiving at least one of reflected light and transmitted light from the surface of the gas diffusion electrode;
A data processing step of processing image data obtained by the imaging means;
And the inspection method of a gas diffusion electrode which has the process of recording the information of the kind, size, area, and position of the fault at least. The gas diffusion electrode inspection method according to claim 1, wherein the reflected light is at least one selected from the group consisting of scattered light, oblique light reflection, and regular reflection light. The method for inspecting a gas diffusion electrode according to claim 1 or 2, wherein the type of the defect includes any one of a protrusion, a foreign substance, a fluff, a dent, a crack, a hole in a microporous layer, a through hole, a chipped end, and a streak. .   The gas diffusion electrode inspection method according to claim 1, wherein the microporous layer contains a carbon material.   The size and area of the defect in the image obtained by the imaging means are calculated using image analysis conditions that are set based on the correlation with the size and area of the defect measured by a laser microscope. The gas diffusion electrode inspection method according to claim 1, wherein the gas diffusion electrode is detected. The inspection method of the gas diffusion electrode according to claim 1, wherein the defect in the portion where the gas diffusion electrode is in contact with the transport roll is inspected. The gas diffusion electrode inspection method according to any one of claims 1 to 6, wherein deposits existing on a surface of the gas diffusion electrode are removed before the gas diffusion electrode is inspected. The inspection method of the gas diffusion electrode according to any one of claims 1 to 7, wherein after the inspection of the gas diffusion electrode, marking capable of determining a defect position is performed. The gas diffusion electrode inspection method according to claim 8, wherein the marking is performed on one side or both sides of the gas diffusion electrode by ink jet or laser. The gas diffusion electrode inspection method according to claim 9, wherein the laser is a YVO ₄ laser. A gas diffusion electrode having an inspection record in which at least the type and / or position of the defect is recorded among the defect information obtained by the gas diffusion electrode inspection method according to claim 1. The gas diffusion electrode which has the marking which can identify the fault position obtained by the inspection method of the gas diffusion electrode in any one of Claims 8-11 on one side or both surfaces. The number ratio of oxygen atoms to the total number of carbon atoms and fluorine atoms (number of oxygen atoms / (number of carbon atoms + number of fluorine atoms)) in the marking portion where the marking is formed is 0.042 or more. The gas diffusion electrode according to claim 12. The ratio of the area occupied by the discolored portion obtained by the image processing in the marking portion (the area where the discolored portion due to marking is painted by binarization of the image processing / theoretical area of the marking portion × 100) is 30% or more. The gas diffusion electrode according to claim 12 or 13. The gas diffusion electrode according to any one of claims 12 to 14, wherein the marking portion has a tensile strength of 2.4 N / mm or more.