JP2009301792A - Water-repellent paste for gas diffusion layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide water-repellent paste for a gas diffusion layer capable of being manufactured in a simple component composition, securing coating performance without adding a thickener giving rise to calcination residues, and that, with due consideration not involving air at its filling in a coating head or the like. <P>SOLUTION: As to the water-repellent paste for a gas diffusion layer of an embodiment 1 in which a nonionic surfactant A (polyoxyethylene tridecyl ether) of HLB=10.5 is added as a surfactant in a mixture of carbon black slurry and PTFE dispersion, a yield value at 25°C is 12.5 Pa, and a yield value at 10°C is 2.6 Pa, that at ambient temperatures being large and that at low temperature being small. Therefore, the paste is to be cooled at filling and put back to ambient temperatures at coating on a base material with the use of the characteristics, whereby, generation of pinholes on a coated face and soaking into the base material after coating can be surely prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water repellent paste for a gas diffusion layer for forming a gas diffusion layer of an electrode used in a polymer electrolyte fuel cell.

  In a polymer electrolyte fuel cell, a cathode side electrode and an anode side electrode are formed on both sides of a polymer electrolyte membrane. Usually, the cathode side electrode and the anode side electrode are carbon carrying a catalyst such as platinum. Electrocatalyst layer composed of black and ion exchange resin, carbon black powder for imparting conductivity to carbon substrate such as carbon cloth and carbon paper, polytetrafluoroethylene dispersion for imparting water repellency, etc. It is comprised by the gas diffusion layer formed by coating the water-repellent paste which knead | mixed.

  Here, the water repellent paste for forming the gas diffusion layer is adjusted to an appropriate viscosity by adding a polymer thickener in order to prevent sagging after coating and penetration into the carbon substrate. It is necessary to increase the yield value to some extent in order to prevent the penetration of the sagging / carbon base material after coating, but water repellent paste having such a high yield value is used for containers and coatings. Air is easily caught when filling the work head or the like, causing pinholes on the coated surface. Moreover, in order to obtain water repellency, it is necessary to perform baking after coating. However, since the added polymer thickener generates a baking residue, there is a possibility of adversely affecting battery performance.

  Therefore, for the purpose of adjusting the viscosity of the water-repellent paste without adding a polymer thickener, in Patent Document 1, the carbon slurry and the fluororesin dispersion are not easily soluble in water and easily dissolved in water. A solvent is mixed, and in particular, an alcohol having a molecular weight of 70 or more is used as the former, and an ethylene oxide addition surfactant having an alcohol having a hydrophilic / lipophilic balance (HLB) of 8 to 13 is used as the latter. An invention of water paste is disclosed. This allows the fluororesin to not be fiberized with relatively low shearing forces in the piping and pumps of the mixing process and coating process, but can be made to fiberize on the substrate when applied with a high shearing force. It is said that a water-repellent paste for a gas diffusion layer excellent in binding power as a binder, water repellency, moderate penetrability to a substrate, and planar uniformity is obtained.

In Patent Document 2, as a slurry in which carbon black is dispersed, a fluorine resin dispersion, a fibrous filler (VGCF) slurry, a biodegradable polymer compound (polylactic acid) pore-forming agent, and a thickener A technique for manufacturing a gas diffusion layer by applying a water-repellent paste mixed with a nonionic surfactant (polyoxyethylene alkyl ether) on a base layer, drying and baking the same is disclosed. As a result, the viscosity can be adjusted without adding a polymer thickener, and while maintaining conductivity and water repellency, the occurrence of cracks during drying is reliably prevented, and the catalyst layer is uniformly formed. It is said that the water-repellent paste can be supplied with gas and can further improve battery performance.
JP 2004-247148 A JP 2006-294559 A

  However, in the technique described in Patent Document 1, there is only a description that an ethylene oxide addition surfactant of alcohol having a hydrophilic / lipophilic balance (HLB) of 8 to 13 is used as a solvent that is easily soluble in water. , “Alcohol ethylene oxide addition surfactant” alone does not specify a specific compound, but even a specific compound group, so it is surely used for an excellent gas diffusion layer having the above-described characteristics. It is difficult to obtain a water repellent paste.

  Moreover, in the technique described in the said patent document 2, the specific characteristic of the nonionic surfactant (polyoxyethylene alkyl ether) as a thickener, especially hydrophilic lipophilic balance (HLB) are specified. Therefore, the viscosity cannot be reliably adjusted, the manufacturing process of the water repellent paste and the gas diffusion layer is complicated, and there are many kinds of components used in the water repellent paste, which increases the manufacturing cost. There was a problem of end.

  Therefore, in the present invention, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and when filling a coating head or the like. An object of the present invention is to provide a water-repellent paste for a gas diffusion layer that does not involve air.

  The water-repellent paste for gas diffusion layer according to the invention of claim 1 is a water-repellent paste for gas diffusion layer for forming a gas diffusion layer of a polymer electrolyte fuel cell composed mainly of a polymer electrolyte membrane. The carbon black slurry, the fluororesin dispersion, and the surfactant are mixed, and the yield value at 25 ° C. is in the range of 6 Pa to 20 Pa, more preferably in the range of 10 Pa to 20 Pa, and 10 The yield value at 0 ° C. is in the range of 0.1 Pa to 5 Pa, more preferably in the range of 1 Pa to 3 Pa.

  However, the yield value is: measuring instrument: viscometer with spring relaxation measuring function, cone rotor cone angle: 1 ° 34 ', measurement mode: spring relaxation mode, spring winding rate: 50%, measurement time: 200 seconds It is measured under measurement conditions. Here, specific examples of the “viscosity with spring relaxation measurement function” include RE550L, RE550H, RE550R, and RE550U as R550 type viscometers manufactured by Toki Sangyo Co., Ltd., for example.

  The water repellent paste for a gas diffusion layer according to the invention of claim 2 is the polyethylene glycol type nonionic composition according to claim 1, wherein the surfactant has a hydrophilic / lipophilic balance (HLB) in the range of 10-11. It is a surfactant.

  The water repellent paste for a gas diffusion layer according to the invention of claim 3 is the structure of claim 1 or claim 2, wherein the surfactant is a polyoxyethylene alkyl ether as a polyethylene glycol type nonionic surfactant. Is.

  The water repellent paste for a gas diffusion layer according to the invention of claim 4 is the structure of claim 3, wherein the polyoxyethylene alkyl ether has an alkyl group having a carbon number in the range of 10 to 15 and ethylene oxide. The added mole number is in the range of 3-7.

  The water repellent paste for a gas diffusion layer according to the invention of claim 5 is the structure of claims 1 to 4, wherein the fluororesin dispersion is added to 100 parts by weight of carbon black solid content in the carbon black slurry. In the range of 5 to 80 parts by weight of the fluororesin solid content, more preferably in the range of 10 to 40 parts by weight, and the surfactant in the range of 3 to 30 parts by weight, more preferably Each of them is mixed within the range of 5 to 20 parts by weight.

  The water repellent paste for a gas diffusion layer according to claim 1 is formed by mixing carbon black slurry, a fluororesin dispersion, and a surfactant, and is composed of three components and has a very simple composition. At the same time, since no polymer thickener is contained, no baking residue is produced. And since the yield value in 25 degreeC is in the range of 6 Pa-20 Pa, and the yield value in normal temperature is large, it does not produce sagging after application | coating or a carbon base material. Furthermore, since the yield value at 10 ° C. is in the range of 0.1 Pa to 5 Pa, the yield value can be reduced by cooling to around 10 ° C. during filling, and air is used when filling the coating head or the like. Can be reliably prevented.

  Here, if the yield value at 25 ° C. of the water-repellent paste for gas diffusion layer is within the range of 10 Pa to 20 Pa, it is possible to more reliably prevent penetration into the sagging and carbon substrate after coating, More preferred. In addition, if the yield value at 10 ° C. is in the range of 1 Pa to 3 Pa, the situation where air is involved when filling the coating head or the like by cooling the water repellent paste for gas diffusion layer to around 10 ° C. during filling. Is more preferable because it can be surely prevented.

  Conventional pastes generally have a yield value that increases as the temperature decreases.As such, pastes that have a large yield value at normal temperature and a low yield value at low temperature It was not. And, in this way, by controlling the yield value of the water-repellent paste for gas diffusion layer to be large at room temperature and small at low temperature, it prevents penetration into the sagging / carbon base material after coating and maintains coating performance. However, the technical idea of preventing air entrainment during filling was first created by the present inventors.

  In this way, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and air is filled when filling the coating head or the like. It becomes a water-repellent paste for a gas diffusion layer that does not get involved.

  In the water-repellent paste for gas diffusion layer according to claim 2, since a polyethylene glycol type nonionic surfactant having a hydrophilic / lipophilic balance (HLB) in the range of 10 to 11 is used as the surfactant, The yield value of the water-repellent paste for gas diffusion layer can be reliably controlled to be large at normal temperature and small at low temperature.

  That is, as a result of accumulating earnest experimental research, the present inventors have determined that the yield value of the water-repellent paste for gas diffusion layer formed by mixing carbon black slurry, fluororesin dispersion, and surfactant is In order to have an unprecedented property of increasing with increasing, it is preferable to use a polyethylene glycol type nonionic surfactant as the surfactant, provided that the HLB of the polyethylene glycol type nonionic surfactant is 10 It is found that the yield value is too small when the ratio is less than 1, and the yield value is too small when the HLB exceeds 11, and the present invention has been completed based on this finding.

  In this way, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and air is filled when filling the coating head or the like. It becomes a water-repellent paste for a gas diffusion layer that does not get involved.

  In the water repellent paste for gas diffusion layer according to claim 3, since polyoxyethylene alkyl ether is used as the surfactant among the polyethylene glycol type nonionic surfactants, the water repellent for gas diffusion layer is surely provided. The yield value of the paste can be controlled to be large at room temperature and small at low temperature.

  As a result of accumulating earnest experimental research, the present inventors have found that the yield value of the water-repellent paste for gas diffusion layer formed by mixing carbon black slurry, fluororesin dispersion, and surfactant increases with increasing temperature. In order to have an unprecedented characteristic of increasing, it has been found that it is preferable to use polyoxyethylene alkyl ether as a surfactant, and the present invention has been completed based on this finding.

  In this way, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and air is filled when filling the coating head or the like. It becomes a water-repellent paste for a gas diffusion layer that does not get involved.

  In the water-repellent paste for gas diffusion layer according to claim 4, as polyoxyethylene alkyl ether, the carbon number of the alkyl group is in the range of 10 to 15 and the added mole number of ethylene oxide is in the range of 3 to 7. Therefore, the yield value of the water-repellent paste for gas diffusion layer can be reliably controlled to be large at normal temperature and small at low temperature.

  That is, the present inventors have conducted extensive experimental research, and as a result, water-repellent paste for gas diffusion layers formed by mixing carbon black slurry, fluororesin dispersion, and polyoxyethylene alkyl ether as a surfactant. In order to give an unprecedented characteristic that the yield value increases as the temperature rises, the carbon number of the alkyl group of the polyoxyethylene alkyl ether is within the range of 10 to 15 and addition of ethylene oxide The inventors have found that the number of moles is preferably in the range of 3 to 7, and have completed the present invention based on this finding.

  In this way, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and air is filled when filling the coating head or the like. It becomes a water-repellent paste for a gas diffusion layer that does not get involved.

  The water repellent paste for a gas diffusion layer according to claim 5 has a fluororesin dispersion within a range of 5 to 80 parts by weight of fluororesin dispersion with respect to 100 parts by weight of carbon black solids in the carbon black slurry. Since the surfactant is mixed within the range of 3 to 30 parts by weight, the yield value of the water-repellent paste for gas diffusion layer can be more reliably controlled to be large at normal temperature and small at low temperature.

  That is, as a result of accumulating earnest experimental research, the present inventors have determined that the yield value of the water-repellent paste for gas diffusion layer formed by mixing carbon black slurry, fluororesin dispersion, and surfactant is In order to give an unprecedented property of increasing as the amount increases, the fluororesin dispersion is 5 to 80 parts by weight in terms of solids of fluororesin with respect to 100 parts by weight of carbon black solids in the carbon black slurry. It has been found that it is more preferable that the surfactant be within the range of 3 to 30 parts by weight, and the present invention has been completed based on this finding.

  Here, with respect to 100 parts by weight of carbon black solids in the carbon black slurry, the fluororesin dispersion is within the range of 10 to 40 parts by weight of fluororesin solids, and the surfactant is 5 to 20 parts by weight. By setting it within the range of parts by weight, it is more preferable because it can have an unprecedented characteristic that the yield value of the water-repellent paste for gas diffusion layer increases more reliably as the temperature increases.

  In this way, it can be produced with a simple component composition, coating performance can be ensured without adding a thickening agent that produces a baking residue, and air is filled when filling the coating head or the like. It becomes a water-repellent paste for a gas diffusion layer that does not get involved.

  Hereinafter, a water-repellent paste for a gas diffusion layer used for a polymer electrolyte fuel cell electrode according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a graph showing a change in viscosity with respect to temperature of a water repellent paste for a gas diffusion layer according to an embodiment of the present invention in comparison with a comparative example.

  Initially, the manufacturing method of the water repellent paste for gas diffusion layers which concerns on embodiment of this invention is demonstrated. The water repellent paste for gas diffusion layer according to the present embodiment was produced as follows. First, carbon black was dispersed in water to prepare a 19% concentration carbon black slurry. Polytetrafluoroethylene (hereinafter referred to as “4% to 49% concentration) with respect to 74.0 parts by weight of the carbon black slurry. PTFE ") A polyoxyethylene tridecyl ether serving as a nonionic surfactant A having a hydrophilic / lipophilic balance (HLB) of 10.5 was mixed with a dispersion of 19.1 parts by weight. It was added at a ratio of 6.9 parts by weight, and was thickened to form a paste.

  That is, in the water-repellent paste for gas diffusion layer according to the present embodiment, the surfactant is polyoxyethylene alkyl ether, the alkyl group has 13 carbon atoms, and the number of added moles of ethylene oxide is 5 is used. Further, the solid content (carbon black) of the carbon black slurry is 19% by weight of the carbon black slurry, and the solid content (PTFE) of the PTFE dispersion is 48% to 49% by weight of the PTFE dispersion.

  For comparison, the carbon black slurry and the PTFE dispersion are mixed in the same amount, and the surfactant is a nonionic surfactant B having an HLB of 8.6, or a nonionic interface having an HLB of 12.4. Comparative example in which activator C was added, and polymer type thickeners A and B were added instead of surfactant, or n-butanol was added together with nonionic surfactant A having an HLB of 10.5 A water-repellent paste for gas diffusion layer was produced in the same manner. The composition of each water-repellent paste for gas diffusion layer is shown in the upper part of Table 1.

  The characteristics of the water repellent paste for gas diffusion layer of Example 1 and the water repellent paste for gas diffusion layers of Comparative Examples 1 to 5 according to the present embodiment shown in Table 1 were evaluated. As evaluation items, the yield value at 25 ° C. and the yield value at 10 ° C. are measured, and further, the presence or absence of pinholes on the coated surface when the paste is applied to the substrate, and the presence or absence of penetration into the substrate Was observed.

  Specifically, for the water-repellent paste for gas diffusion layers of Example 1 and Comparative Examples 1 to 5, the paste was cooled to 10 ° C. and filled in the coating head, and the temperature became 20 ° C. to 25 ° C. Later, coating on the substrate was carried out, and pinholes on the coated surface and penetration into the substrate were confirmed.

  The yield value at 25 ° C. and the yield value at 10 ° C. are as follows: Measuring instrument: viscometer with spring relaxation measuring function, cone rotor cone angle: 1 ° 34 ′, measurement mode: spring relaxation mode, spring winding rate: 50% Measurement time: 200 seconds. As a viscometer with a spring relaxation measuring function, RE550R was used among R550 type viscometers manufactured by Toki Sangyo Co., Ltd. The evaluation result of each evaluation item is shown in the lower part of Table 1.

  As shown in the lower part of Table 1, nonionic surfactant A (polyoxyethylene tridecyl ether) with HLB = 10.5 was added as a surfactant to the mixture of carbon black slurry and PTFE dispersion. In the water-repellent paste for gas diffusion layer of Example 1, the yield value at 25 ° C. is 12.5 Pa, the yield value at 10 ° C. is 2.6 Pa, the yield value at room temperature is large, and the yield value at low temperature. Is getting smaller.

  On the other hand, in Comparative Example 1 in which the polymer type thickener A was added instead of the surfactant, the yield value at 25 ° C. was 14.3 Pa, the yield value at 10 ° C. was 14.5 Pa, and the temperature Regardless of the large yield value. Further, in Comparative Example 2 in which the polymer type thickener B was added instead of the surfactant, the yield value at 25 ° C. was 0.9 Pa, and the yield value at 10 ° C. was 1.0 Pa, regardless of the temperature. It showed a small yield value.

  Further, Comparative Example 3 in which nonionic surfactant B with HLB = 8.6 was added as a surfactant, and Comparative Example 4 in which nonionic surfactant C with HLB = 12.4 was added as a surfactant. In both cases, the viscosity was too small and the yield value could not be measured. Further, in Comparative Example 5 in which n-butanol was added together with the nonionic surfactant A, the yield value at 25 ° C. was 14.8 Pa, the yield value at 10 ° C. was 15.5 Pa, and the yield was large regardless of the temperature. The value is shown.

  For reference, the relationship between temperature and viscosity of the water-repellent paste for gas diffusion layer of Example 1, Comparative Example 1, and Comparative Example 2 was measured. The viscosity was measured at a shear rate of 50 [1 / s]. FIG. 1 is a graph showing the results. As shown in FIG. 1, the water-repellent paste for gas diffusion layer of Example 1 has a unique property that the viscosity greatly increases as the temperature rises.

  On the other hand, the water repellent paste for gas diffusion layer of Comparative Example 1 and Comparative Example 2 has a characteristic that the viscosity hardly changes or slightly decreases even when the temperature changes. I understand. The water repellent paste for gas diffusion layer of Comparative Example 2 had a small yield value, but in the viscosity measurement with a large shear rate, the viscosity value was almost constant regardless of the temperature.

  As a result, as shown in the lower part of Table 1, in the water repellent paste for gas diffusion layer of Example 1, since the yield value at 10 ° C. is small, air is not involved when filling the coating head, Pinholes on the coated surface did not occur (evaluation: ◯), and since the yield value at 25 ° C. was large, very good results were obtained that penetration into the substrate did not occur (evaluation: ◯).

  On the other hand, in Comparative Example 1 and Comparative Example 5, since the yield value at 25 ° C. and the yield value at 10 ° C. are both large, no penetration into the base material occurred (evaluation: ◯), As a result of easy air entrainment when filling the coating head, pinholes are generated on the coated surface (evaluation: x). In Comparative Example 2, Comparative Example 3 and Comparative Example 4, since the yield value at 25 ° C. and the yield value at 10 ° C. are both small (or cannot be measured), air is supplied when filling the coating head. No pinholes on the coated surface occur because it is not involved (evaluation: ◯), but penetration into the substrate has occurred (evaluation: x).

  As described above, in the water repellent paste for gas diffusion layer according to Example 1 of the present embodiment, polyoxyethylene alkyl ether which is a nonionic surfactant with HLB = 10.5 is used as the surfactant. By adding polyoxyethylene tridecyl ether as a base material, it is possible to give an unprecedented characteristic that the yield value increases as the temperature rises. By returning to room temperature during coating, pinholes on the coated surface and penetration into the substrate after coating can be reliably prevented.

  In this way, the water-repellent paste for gas diffusion layer according to the present embodiment can be manufactured with a simple component composition, and ensures coating performance without adding a thickener that produces a firing residue. In addition, a water repellent paste for a diffusion layer that does not entrain air when filling a coating head or the like is obtained.

  In the present embodiment, the case where the yield value at 25 ° C. of the water-repellent paste for gas diffusion layer is 12.5 Pa and the yield value at 10 ° C. is 2.6 Pa is explained. However, the yield value is limited to these values. The yield value at 25 ° C. is in the range of 6 Pa to 20 Pa, and the yield value at 10 ° C. is in the range of 0.1 Pa to 5 Pa. In addition, it is more preferable that the yield value in 25 degreeC is in the range of 10 Pa-20Pa, and the yield value in 10 degreeC is in the range of 1 Pa-3 Pa.

  In the present embodiment, polyoxyethylene tridecyl ether (carbon number of alkyl group) as a polyethylene glycol-type nonionic surfactant having a hydrophilic / lipophilic balance (HLB) of 10.5 as a surfactant. However, the case where the number of added moles of ethylene oxide is 5) has been described, but the surfactant is not limited thereto.

  As the surfactant, polyoxyethylene alkyl ether is preferably used, and the number of carbon atoms of the alkyl group of polyoxyethylene alkyl ether is within a range of 10 to 15 and the number of moles of ethylene oxide added is 3 to 7. It is more preferable to be within the range. Further, as the surfactant, it is preferable to use a polyethylene glycol type nonionic surfactant having an HLB in the range of 10 to 11.

  Furthermore, in this embodiment, 6.9 wt.% Of surfactant is added to a mixture of PTFE dispersion in a proportion of 19.1 wt. Parts with respect to 74.0 wt. However, the concentration of the carbon black slurry and the blending ratio of the PTFE dispersion and the surfactant are not limited to these.

  In addition, with respect to 100 parts by weight of carbon black solids in the carbon black slurry, the fluororesin dispersion is within the range of 5 to 80 parts by weight of fluororesin solids, and the surfactant is 3 to 30 parts by weight. It is preferable to be within the range of parts. Further, the fluororesin dispersion is within the range of 10 to 40 parts by weight of the fluororesin solid content with respect to 100 parts by weight of the carbon black solid content in the carbon black slurry, and the surfactant is 5 to 20 parts by weight. More preferably, it is within the range of parts.

  In carrying out the present invention, other configurations, components, materials, blending, shapes, sizes, manufacturing methods, etc. of the water-repellent paste for gas diffusion layers are not limited to the present embodiment. In addition, since the numerical value raised in the embodiment of the present invention does not indicate a critical value but indicates a preferable value suitable for implementation, even if the numerical value is slightly changed, implementation is not denied. Absent.

FIG. 1 is a graph showing a change in viscosity with respect to temperature of a water repellent paste for a gas diffusion layer according to an embodiment of the present invention in comparison with a comparative example.

Claims (5)

A water-repellent paste for a gas diffusion layer for forming a gas diffusion layer of a polymer electrolyte fuel cell mainly composed of a polymer electrolyte membrane,
Carbon black slurry, fluororesin dispersion, and surfactant are mixed,
A water repellent paste for a gas diffusion layer, wherein a yield value at 25 ° C. is in a range of 6 Pa to 20 Pa, and a yield value at 10 ° C. is in a range of 0.1 Pa to 5 Pa.
However, the yield value is measured by the following method.
Measuring instrument: Viscometer with spring relaxation measuring function Cone rotor cone angle: 1 ° 34 '
Measurement mode: Spring relaxation mode Spring winding rate: 50%
Measurement time: 200 seconds   The water-repellent paste for gas diffusion layers according to claim 1, wherein the surfactant is a polyethylene glycol type nonionic surfactant having a hydrophilic / lipophilic balance (HLB) in the range of 10 to 11. .   The water-repellent paste for gas diffusion layers according to claim 1 or 2, wherein the surfactant is polyoxyethylene alkyl ether as a polyethylene glycol type nonionic surfactant.   4. The polyoxyethylene alkyl ether according to claim 3, wherein the carbon number of the alkyl group is in the range of 10 to 15 and the number of added moles of ethylene oxide is in the range of 3 to 7. 5. Water repellent paste for gas diffusion layer.   The fluororesin dispersion is within the range of 5 to 80 parts by weight of the fluororesin dispersion with respect to 100 parts by weight of the carbon black solid content in the carbon black slurry, and 3 to 30 parts by weight of the surfactant. The water repellent paste for a gas diffusion layer according to any one of claims 1 to 4, wherein the water repellent paste is mixed within a range of parts by weight.

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