A mixing method for raw materials of a composite bipolar plate

Abstract

The present invention relates to a method for mixing raw materials of a composite bipolar plate. S1: Heat the curing agent and the accelerator to a temperature above the softening point to make them in a state of lower viscosity; S2: Add flexible graphite and the softened curing agent and accelerator into a mixer; S3: Mix the first mixture of flexible graphite, curing agent, and accelerator; S4: Cool the first mixture to room temperature; S5: Add the first mixture into a crusher for crushing; S6: Add the crushed first mixture into a vibrating screen machine for screening; S7: Add the screened first mixture and resin into the mixer in a certain proportion for the second mixing; S8: After the second mixture is mixed, obtain the raw materials of the graphite / resin composite bipolar plate. This solution fully improves the uniformity of the current multi-solid-phase mixing of graphite / resin, making it have more excellent strength, electrical conductivity, thermal conductivity, and performance distribution uniformity.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a method for mixing raw materials of a composite bipolar plate. Background Art

[0002] The bipolar plate is a key component of a proton exchange membrane fuel cell, and its main functions include isolating hydrogen and oxygen, connecting circuits in series, and supporting the battery structure, etc. The mass, volume, and cost of the bipolar plate account for 60% - 80% of the proton exchange membrane fuel cell. Therefore, in order to industrialize fuel cells, it is necessary to break through the materials and processing technologies of the bipolar plate. The graphite / resin composite bipolar plate is formed by powder molding and has characteristics such as good strength, corrosion resistance, thermal conductivity, and easy mass production. However, due to the differences in the physical and chemical properties of the multi-phase raw materials before molding, the mixing effect is poor, which affects the performance and uniformity of the composite bipolar plate after molding, making it an important obstacle in the manufacturing of current graphite / resin composite bipolar plates.

[0003] In order to overcome the above deficiencies, the present invention provides a method for mixing raw materials of a composite bipolar plate. Summary of the Invention

[0004] The object of the present invention is to solve the problem that due to the differences in the physical and chemical properties of the multi-phase raw materials of the existing graphite / resin composite bipolar plate, the mixing effect is poor, which affects the performance and uniformity of the composite bipolar plate after molding. The specific solution is as follows:

[0005] A method for mixing raw materials of a composite bipolar plate, comprising the following steps:

[0006] Step 1: Heat the curing agent and the accelerator to a temperature W1 above the softening point, and keep them at a low viscosity state for a period of time T1.

[0007] Step 2: Add the flexible graphite and the softened curing agent and accelerator into a mixer.

[0008] Step 3: Mix the first mixture of the flexible graphite, the curing agent, and the accelerator for a certain period of time T2, and heat or keep warm to a temperature W2 at the same time.

[0009] Step 4: Cool the first mixture to room temperature.

[0010] Step 5: Add the first mixture into a crusher for crushing.

[0011] Step 6: Add the crushed first mixture into a vibrating screen for screening.

[0012] Step 7: Add the screened first mixture and the resin into a mixer in a certain proportion for mixing the second mixture.

[0013] Step 8, after the second mixture is mixed for a certain time T3, a raw material of a graphite / resin composite bipolar plate with a higher mixing degree is obtained.

[0014] Furthermore, the flexible graphite has a carbon content greater than 99.9%, the particle size of the flexible graphite is 10 - 200 μm, and the resin is a thermosetting resin with a content of 10 - 45 wt%.

[0015] Furthermore, the thermosetting resin is any one of epoxy resin, polyester resin, or phenolic resin. The thermosetting resin is a solid powder with a particle size of 10 - 200 μm.

[0016] Furthermore, both the curing agent and the accelerator are solids; the temperature W1 in Step 1 is 50 - 300 °C, the time T1 is 10 - 100 min, and the weight ratio of the curing agent to the accelerator is 5:1 - 50:1.

[0017] Furthermore, the weight ratio of the flexible graphite to the mixture of the curing agent and the accelerator in Step 2 is 5:1 - 20:1, and the mixer is any one of a double-cone mixer, a pneumatic stirring mixer, a three-dimensional motion mixer, or a V-type mixer.

[0018] Furthermore, the time T2 in Step 3 is 5 - 15 min, and the temperature W2 is 50 - 300 °C.

[0019] Furthermore, the pulverizer in Step 5 is any one of a pneumatic pulverizer, a mechanical pulverizer, or a grinder, and the pulverizing time is 5 - 15 min.

[0020] Furthermore, the vibrating screen in Step 6 is any one of a linear vibrating screen, a circular vibrating screen, or a high-frequency vibrating screen, and the particle size of the screened material is 50 - 150 μm.

[0021] Furthermore, the ratio of the first mixture to the resin in Step 7 is 9:1 - 1:1; the time T3 in Step 8 is 10 - 30 min.

[0022] In summary, adopting the technical solution of the present invention has the following beneficial effects:

[0023] This solution solves the problem that due to the differences in the physical and chemical properties of the raw materials of the existing graphite / resin composite bipolar plates, the mixing effect is poor, which affects the performance and uniformity of the composite bipolar plates after forming. In the present invention, the curing agent and the accelerator are liquefied, so that they first reach a very high mixing degree with the flexible graphite powder, and after cooling, they are adhered to the surface of the graphite powder to reach a relatively stable mixing state, and then they are crushed and mixed with the thermosetting resin together to achieve a better mixing effect; the polymerization reaction position of the resin and the curing agent is mainly around the curing agent. When the resin system cures, since the curing agent and the accelerator are evenly distributed around the graphite, the polymerization reaction of the resin system occurring around the graphite is more uniform. This solution fully improves the uniformity of the current multi-solid phase mixing of graphite / resin, making it have more excellent strength, electrical conductivity, thermal conductivity and performance distribution uniformity. Therefore, this mixing method has very good application prospects in fuel cell composite bipolar plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Appendix Figure 1 is a step diagram of a method for mixing raw materials of a composite bipolar plate according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Hereinafter, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0026] As Figure 1 shown, a method for mixing raw materials of a composite bipolar plate adopts the following steps:

[0027] Step S1, heating the curing agent and the accelerator to a temperature W1 above the softening point for a period of time T1 to make them in a state of lower viscosity;

[0028] Step S2, adding the flexible graphite and the softened curing agent and accelerator into a mixer;

[0029] Step S3, mixing the first mixture of the flexible graphite, the curing agent and the accelerator for a certain period of time T2, and heating or keeping warm to a temperature W2 at the same time;

[0030] Step S4, cooling the first mixture to room temperature;

[0031] Step S5, adding the first mixture into a crusher for crushing;

[0032] Step S6, adding the crushed first mixture into a vibrating screen machine for sieving;

[0033] Step S7, add the first screened mixture and resin into a mixer in a certain proportion to perform the mixing of the second mixture.

[0034] Step S8, after mixing the second mixture for a certain time T3, a raw material of a graphite / resin composite bipolar plate with a higher mixing degree is obtained.

[0035] Further, the flexible graphite has a carbon content greater than 99.9%, the particle size of the flexible graphite is 10 - 200 μm, and the resin is a thermosetting resin with a content of 10 - 45 wt%.

[0036] Further, the thermosetting resin is any one of epoxy resin, polyester resin, and phenolic resin. This thermosetting resin is a solid powder with a particle size of 10 - 200 μm.

[0037] Further, both the curing agent and the accelerator are solids; in step 1, the temperature W1 is 50 - 300 °C, the time T1 is 10 - 100 min, and the weight ratio of the curing agent to the accelerator is 5:1 - 50:1.

[0038] Further, in step 2, the weight ratio of the flexible graphite to the mixture of the curing agent and the accelerator is 5:1 - 20:1, and the mixer is any one of a double-cone mixer, an air-flow stirring mixer, a three-dimensional motion mixer, and a V-type mixer.

[0039] Further, in step 3, the time T2 is 5 - 15 min, and the temperature W2 is 50 - 300 °C.

[0040] Further, in step 5, the pulverizer is any one of an air-flow pulverizer, a mechanical pulverizer, and a grinder, and the pulverizing time is 5 - 15 min.

[0041] Further, in step 6, the vibrating screen is any one of a linear vibrating screen, a circular vibrating screen, and a high-frequency vibrating screen, and the particle size of the screened material is 50 - 150 μm.

[0042] Further, in step 7, the certain proportion of the first mixture and the resin is 9:1 - 1:1; in step 8, the time T3 is 10 - 30 min.

[0043] Example 1

[0044] Heat and soften the aromatic curing agent and accelerator with a weight ratio of 5:1 - 30:1. The heating temperature is 50 - 300 °C, and the heating time is 15 - 60 min. Ensure that the viscosity of the cured agent and accelerator after softening is low enough and reduce the heating time. The heating temperature needs to be 50 °C or more above the softening point temperature of the curing agent and accelerator.

[0045] Flexible graphite with a carbon content of over 99.9% and a particle size of 10 - 100 μm, and a mixture of softened aromatic curing agent and accelerator are added to a mixer at a weight ratio of 5:1 - 10:1, heated and mixed for 5 - 15 min, and then cooled to room temperature. The cooled mixture of flexible graphite, aromatic curing agent, and accelerator is added to a mechanical grinder or mill and pulverized for 5 - 15 min; the pulverized mixture is screened through a vibrating sieve to obtain a powder of flexible graphite, aromatic curing agent, and accelerator with a particle size of 50 - 100 μm;

[0046] The powder of flexible graphite, aromatic curing agent, and accelerator with a particle size of 50 - 100 μm obtained by screening and epoxy resin powder with a particle size of 50 - 100 μm are added to a three-dimensional mixer or V-shaped mixer at a weight ratio of 7:1 - 4:1 and mixed for 10 - 30 min.

[0047] The weight ratio of the final bipolar plate raw material mixture is flexible graphite: epoxy resin: curing agent: accelerator = 75:17:7:1.

[0048] Example 2

[0049] A phenolic resin curing agent and an accelerator with a weight ratio of 10:1 - 40:1 are heated and softened at a heating temperature of 50 - 280 °C for 10 - 50 min to ensure that the viscosity of the softened curing agent and accelerator is low enough and the heating time is reduced. The heating temperature needs to be 50 °C or more above the softening point temperature of the curing agent and accelerator.

[0050] Flexible graphite with a carbon content of over 99.9% and a particle size of 30 - 150 μm, and a mixture of softened phenolic resin curing agent and accelerator are added to a mixer at a weight ratio of 8:1 - 15:1, heated and mixed for 5 - 15 min, and then cooled to room temperature.

[0051] The cooled mixture of flexible graphite, phenolic resin curing agent, and accelerator is added to a mechanical grinder or mill and pulverized for 5 - 15 min; the pulverized mixture is screened through a vibrating sieve to obtain a powder of flexible graphite, phenolic resin curing agent, and accelerator with a particle size of 50 - 100 μm;

[0052] The powder of flexible graphite, phenolic resin curing agent, and accelerator with a particle size of 50 - 100 μm obtained by screening and epoxy resin powder with a particle size of 50 - 100 μm are added to a three-dimensional mixer or V-shaped mixer at a weight ratio of 9:1 - 5:1 and mixed for 10 - 30 min.

[0053] The weight ratio of the final bipolar plate raw material mixture is flexible graphite: epoxy resin: curing agent: accelerator = 75:16:8.45:0.55.

[0054] Example 3

[0055] Heat and soften an aromatic curing agent and an accelerator with a weight ratio of 7:1 to 35:1. The heating temperature is 60 to 300 °C, and the heating time is 12 to 70 min. Ensure that the viscosity of the cured agent and the accelerator after softening is low enough and reduce the heating time. The heating temperature needs to be increased by more than 50 °C above the softening point temperature of the curing agent and the accelerator.

[0056] Add flexible graphite with a carbon content of more than 99.9% and a particle size of 20 - 130 μm to the softened mixture of the aromatic curing agent and the accelerator at a weight ratio of 5:1 to 15:1 into a mixer, heat and mix for 5 to 15 min, and then cool to room temperature.

[0057] Add the cooled mixture of flexible graphite, aromatic curing agent, and accelerator into a mechanical crusher or grinder and crush for 5 to 15 min; screen the crushed mixture through a vibrating sieve to obtain a powder mixture of flexible graphite, aromatic curing agent, and accelerator with a particle size of 60 - 120 μm;

[0058] Add the screened powder mixture of flexible graphite, aromatic curing agent, and accelerator with a particle size of 60 - 120 μm and epoxy resin powder with a particle size of 60 - 120 μm into a three-dimensional mixer or V-type mixer at a weight ratio of 8:1 to 4:1 and mix for 10 to 30 min.

[0059] The weight ratio of the final bipolar plate raw material mixture is flexible graphite: epoxy resin: curing agent: accelerator = 70:16:13:1.

[0060] Example 4

[0061] Heat and soften a phenolic resin curing agent and an accelerator with a weight ratio of 8:1 to 45:1. The heating temperature is 60 to 280 °C, and the heating time is 10 to 65 min. Ensure that the viscosity of the cured agent and the accelerator after softening is low enough and reduce the heating time. The heating temperature needs to be increased by more than 50 °C above the softening point temperature of the curing agent and the accelerator.

[0062] Add flexible graphite with a carbon content of more than 99.9% and a particle size of 25 - 140 μm to the softened mixture of the phenolic resin curing agent and the accelerator at a weight ratio of 8:1 to 20:1 into a mixer, heat and mix for 5 to 15 min, and then cool to room temperature.

[0063] Add the cooled mixture of flexible graphite, phenolic resin curing agent, and accelerator into a mechanical crusher or grinder and crush for 5 to 15 min; screen the crushed mixture through a vibrating sieve to obtain a powder mixture of flexible graphite, phenolic resin curing agent, and accelerator with a particle size of 60 - 150 μm;

[0064] The powder mixture of flexible graphite with a particle size of 60 - 150 μm, phenolic resin curing agent, and accelerator and epoxy resin powder with a particle size of 60 - 150 μm is added to a three-dimensional mixer or V-type mixer at a weight ratio of 8:1 - 4:1 and mixed for 10 - 30 min.

[0065] The weight ratio of the final bipolar plate raw material mixture is flexible graphite: epoxy resin: curing agent: accelerator = 72:19:8.4:0.6.

[0066] The following four comparative examples are four experiments of direct mixing (i.e., the existing ordinary dry mixing method) without using the mixing method of this solution:

[0067] Comparative Example 1

[0068] Flexible graphite with a particle size of 50 - 100 μm, epoxy resin, aromatic curing agent, and accelerator are directly added to a three-dimensional mixer or V-type mixer at a weight ratio of 75:17:7:1 without other operations and mixed for 10 - 30 min.

[0069] Comparative Example 2

[0070] Flexible graphite with a particle size of 50 - 100 μm, epoxy resin, phenolic resin curing agent, accelerator, and epoxy resin are directly added to a three-dimensional mixer or V-type mixer at a weight ratio of 75:16:8.45:0.55 without other operations and mixed for 10 - 30 min.

[0071] Comparative Example 3

[0072] Flexible graphite with a particle size of 60 - 120 μm, epoxy resin, aromatic curing agent, and accelerator are directly added to a three-dimensional mixer or V-type mixer at a weight ratio of 70:16:13:1 without other operations and mixed for 10 - 30 min.

[0073] Comparative Example 4

[0074] Flexible graphite with a particle size of 60 - 150 μm, epoxy resin, phenolic resin curing agent, and accelerator are directly added to a three-dimensional mixer or V-type mixer at a weight ratio of 72:19:8.4:0.6 without other operations and mixed for 10 - 30 min.

[0075] The standard deviation can reflect the dispersion degree of a data set or the stability / uniformity degree of a physical quantity, that is, the dispersion degree of a set of data from its average value. In this experiment, the surface conductivity standard deviation is used to characterize the distribution uniformity of the performance after bipolar plate molding. The smaller the surface conductivity standard deviation, the better the uniformity; on the contrary, the larger the surface conductivity standard deviation, the worse the uniformity.

[0076] To fully verify the beneficial effects of the present invention and demonstrate the improvement in the material mixing uniformity of the present invention, the present invention is compared with the existing ordinary dry mixing method. The graphite / resin mixtures prepared in Examples 1-4 and Comparative Examples 1-4 are respectively molded and cured to obtain bipolar plate samples, and relevant performance tests and analyses are carried out. The results are shown in Table 1 as follows:

[0077] Table 1 List of bipolar plate samples prepared from the mixtures of Examples 1-4 and Comparative Examples 1-4

[0078]

[0079]

[0080] Note: The weight ratios of raw materials in Example 1 and Comparative Example 1 are the same, the weight ratios of raw materials in Example 2 and Comparative Example 2 are the same, the weight ratios of raw materials in Example 3 and Comparative Example 3 are the same, and the weight ratios of raw materials in Example 4 and Comparative Example 4 are the same.

[0081] As can be seen from Table 1, through the comparison between Comparative Example 1 and Example 1, Comparative Example 2 and Example 2, Comparative Example 3 and Example 3, and Comparative Example 4 and Example 4, it can be known that the mixing method adopted in the present invention has no obvious effect on the density and gas permeability of the graphite / resin composite bipolar plate after molding, but effectively improves the flexural strength, surface conductivity and bipolar plate uniformity of the graphite / resin composite bipolar plate after molding.

[0082] In summary, adopting the technical solution of the present invention has the following beneficial effects:

[0083] This solution solves the problem that the mixing effect of the raw materials of the existing graphite / resin composite bipolar plate is poor due to the differences in the physical and chemical properties of multiple phases, which affects the performance and uniformity of the composite bipolar plate after molding. The present invention liquefies the curing agent and the accelerator, makes them first reach a very high mixing degree with the flexible graphite powder, adheres to the surface of the graphite powder after cooling, reaches a relatively stable mixing state, and then is crushed and mixed with the thermosetting resin together to achieve a better mixing effect; the polymerization reaction position of the resin and the curing agent is mainly around the curing agent. When the resin system cures, since the curing agent and the accelerator are fully and evenly distributed around the graphite, the polymerization reaction of the resin system occurring around the graphite is more uniform. This solution fully improves the mixing uniformity of the current graphite / resin multi-solid phase, making it have more excellent strength, conductivity, thermal conductivity and performance distribution uniformity. Therefore, this mixing method has a very good application prospect in fuel cell composite bipolar plates.

[0084] The above-described embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the above embodiments shall be included within the protection scope of the technical solution.

Claims

1. A mixing method for raw materials of a composite bipolar plate, characterized in that, Adopt the following steps: Step 1: Heat the curing agent and accelerator to a temperature W1 above the softening point for a period of time T1 to keep them in a state of lower viscosity. Step 2: Add the flexible graphite and the softened curing agent and accelerator into a mixer. Step 3: Mix the first mixture of flexible graphite, curing agent, and accelerator for a certain period of time T2, and heat or keep it warm to a temperature W2 simultaneously. Step 4: Cool the first mixture to room temperature. Step 5: Add the first mixture into a crusher for crushing. Step 6: Add the crushed first mixture into a vibrating screen for sieving. Step 7: Add the sieved first mixture and resin into a mixer in a certain proportion for mixing the second mixture. Step 8: After mixing the second mixture for a certain period of time T3, obtain a graphite / resin composite bipolar plate raw material with a higher degree of mixing. In Step 1, the temperature W1 is 50 - 300 °C, the time T1 is 10 - 100 min, and the weight ratio of the curing agent to the accelerator is 5:1 - 50:

1. In Step 2, the weight ratio of the flexible graphite to the mixture of the curing agent and accelerator is 5:1 - 20:

1. In Step 3, the time T2 is 5 - 15 min, and the temperature W2 is 50 - 300 °C. In Step 5, the crushing time is 5 - 15 min. In Step 7, the proportion of the first mixture to the resin is 9:1 - 1:1; in Step 8, the time T3 is 10 - 30 min.

2. The mixing method of a composite bipolar plate raw material according to claim 1, wherein: The flexible graphite has a carbon content greater than 99.9%, and the particle size of the flexible graphite is 10 - 200 μm. The resin is a thermosetting resin with a content of 10 - 45 wt%.

3. The mixing method of a composite bipolar plate raw material according to claim 2, characterized in that: The thermosetting resin is any one of epoxy resin, polyester resin, or phenolic resin. This thermosetting resin is a solid powder with a particle size of 10 - 200 μm.

4. The mixing method of a composite bipolar plate raw material according to claim 1, characterized in that: Both the curing agent and the accelerator are solids.

5. The mixing method of a composite bipolar plate raw material according to claim 1, characterized in that: The mixer is any one of a double-cone mixer, a pneumatic stirring mixer, a three-dimensional motion mixer, or a V-type mixer.

6. The mixing method of a composite bipolar plate raw material according to claim 1, characterized in that: In Step 5, the crusher is any one of a pneumatic crusher, a mechanical crusher, or a grinder.

7. The mixing method of a composite bipolar plate raw material according to claim 1, characterized in that: In Step 6, the vibrating screen is any one of a linear vibrating screen, a circular vibrating screen, or a high-frequency vibrating screen, and the particle size of the sieved material is 50 - 150 μm.

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