JP2015108051A - Porous film production method and reinforcement polymer electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress blockage of a pore in a drawing step of a porous film.SOLUTION: The porous film production method comprises a step for drawing a sheet member having synthetic resin in atmosphere in which temperature is less than melting start temperature of the sheet member.

Description

  The present invention relates to a method for producing a porous membrane and a reinforced electrolyte membrane.

  A porous membrane having pores formed in a synthetic resin is used, for example, as a reinforcing membrane that reinforces an electrolyte membrane of a fuel cell. As a method for producing a porous membrane, Patent Document 1 discloses a multistage stretching of a resin composition mainly composed of a polyolefin resin (C) composed of crystalline polypropylene (A) and a propylene-α-olefin copolymer (B). A method is disclosed. In this method, a temperature lower than the melting point of the propylene-α-olefin copolymer (B) is used as the first stage stretching temperature, and a temperature lower than the melting point of the crystalline polypropylene (A) is used as the second stage stretching temperature. It is done. Thus, the blockage | closure of the space | gap (pore) of a porous membrane is suppressed by making extending | stretching temperature the temperature below melting | fusing point.

JP 2008-150628 A

  In the production of a porous membrane, the present inventors have found that even if the stretching temperature is lower than the melting point, the synthetic resin may melt and the pores may be blocked if the melting temperature is higher than the melting start temperature. It was. If the electrolyte membrane of the fuel cell is reinforced by such a porous membrane, the conduction of hydrogen ions (protons) may be inhibited in the fuel cell. Therefore, a technique for suppressing the clogging of the pores during the stretching process has been desired. In addition, in the conventional method for producing a porous membrane, it has been desired to simplify the production and reduce the cost.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.

(1) According to one aspect of the present invention, a method for producing a porous membrane is provided. This manufacturing method includes a step of stretching a sheet member having a synthetic resin in an atmosphere lower than the melting start temperature of the sheet member. With the method for producing a porous membrane having such a form, stretching is performed in an atmosphere lower than the melting start temperature of the sheet member, so that blockage of pores due to local melting of the sheet member can be suppressed.

(2) In the method for producing a porous membrane according to the above aspect, the sheet member includes, as the synthetic resin, a polyolefin resin, a cellulose resin, a fluorine resin, a polyethersulfone, a polycarbonate, a polyamide, a polyimide, a polyamideimide, an aroma. You may contain at least any one among group polyamide resin. Among these, in particular, a porous member having a high chemical stability can be obtained if the sheet member contains a fluororesin.

(3) In the method for manufacturing a porous membrane of the above aspect, the melting start temperature may be obtained based on an inspection scanning calorimetry of the sheet member. If it is the manufacturing method of the porous membrane of such a form, the melting start temperature of a sheet | seat member can be calculated | required appropriately.

(4) In the manufacturing method of the porous membrane of the said form, you may have the secondary extending process which extends | stretches the said sheet | seat member further after extending | stretching in the atmosphere below the said melting start temperature. In the case of performing multi-stage stretching, since the density of the synthetic resin in the sheet member is high in the first stretching, the pores are likely to be blocked by melting of the synthetic resin during stretching. However, if it is a manufacturing method of a porous membrane of such a form, even when performing multi-stage stretching, since stretching is performed in a temperature atmosphere lower than the melting start temperature at least in the first stretching, Occlusion of pores due to melting of the synthetic resin can be suppressed.

(5) According to another aspect of the present invention, there is provided a reinforced electrolyte membrane comprising a porous membrane produced by any one of the above aspects (1) to (4). With such a reinforced electrolyte membrane, the electrolyte membrane can be reinforced with a porous membrane in which pore blocking is suppressed. Therefore, a fuel cell having improved strength and power generation performance can be obtained.

  The present invention can also be realized in various forms other than the manufacturing method described above. For example, it can be realized in the form of a porous membrane, a method for producing a reinforced electrolyte membrane, a fuel cell including a porous membrane or a reinforced electrolyte membrane, and the like.

It is a figure which shows a reinforced type electrolyte membrane. It is a flowchart which shows the manufacturing method of a reinforced type electrolyte membrane. It is a flowchart which shows the manufacturing method of a porous membrane. It is a figure shown about the primary extending | stretching temperature of samples 1-3. It is a flowchart shown about the calculation method of the melting start temperature of a sheet | seat member. It is a figure which shows the DSC measurement result of a sheet | seat member.

A. Embodiment:
A-1. Configuration of reinforced electrolyte membrane:
FIG. 1 is a view showing a reinforced electrolyte membrane 10 as one embodiment of the present invention. The reinforced electrolyte membrane 10 is a membrane in which the electrolyte membrane 20 and the porous membranes 30 and 40 disposed on both surfaces of the electrolyte membrane 20 are integrated, and is used, for example, in a fuel cell. Part of the electrolyte of the electrolyte membrane 20 is impregnated in the pores of the porous membranes 30 and 40.

A-2. Manufacturing method of reinforced electrolyte membrane:
FIG. 2 is a flowchart showing a method for manufacturing the reinforced electrolyte membrane 10. In the manufacture of the reinforced electrolyte membrane 10, first, the porous membranes 30 and 40 are prepared (step S100). The porous films 30 and 40 in the present embodiment are made by stretching polytetrafluoroethylene (PTFE), which is a fluorine-based synthetic resin, to make it porous. Fluorocarbon resins have high chemical stability among synthetic resins. Details of the manufacturing method of the porous membranes 30 and 40 will be described later.

Next, the electrolyte membrane 20 is prepared (step S110). The electrolyte membrane 20 is produced by extruding a synthetic resin whose side chain end group is —SO ₂ F with a molding machine.

  Next, the porous membranes 30 and 40 and the electrolyte membrane 20 are bonded together (step S120). In step S120, the porous membranes 30 and 40 are respectively placed on both surfaces of the electrolyte membrane 20, and then heated to 230 ° C. and pressed at 0.5 MPa. By doing so, a part of the electrolyte of the electrolyte membrane 20 is impregnated into the pores of the porous membranes 30 and 40, and the electrolyte membrane 20 and the porous membranes 30 and 40 are integrated.

Next, the integrated electrolyte membrane 20 and porous membranes 30 and 40 are hydrolyzed from —SO ₂ F to SO ₃ Na in a 1 (mol / L) aqueous sodium hydroxide solution (step S 130). . Ionic conductivity is imparted to the integrated electrolyte membrane 20 and porous membranes 30 and 40 by hydrolysis.

Thereafter, the hydrolyzed electrolyte membrane 20 and the porous membranes 30 and 40 are acid-treated with a 1 (mol / L) nitric acid aqueous solution (step S140). By step S140, the side chain end groups of the electrolyte membrane 20 and the porous membranes 30 and 40 are replaced with —SO ₃ Na acid type from —SO ₃ Na.

  Next, the acid-treated electrolyte membrane 20 and the porous membranes 30 and 40 are washed with ion-exchanged water and dried (step S150). As described above, the reinforced electrolyte membrane 10 reinforced with the porous membranes 30 and 40 is manufactured. In addition, the specific example shown here is an example of the manufacturing method of a reinforced type electrolyte membrane, and a reinforced type electrolytic membrane can be produced also by cast film forming etc.

A-3. Production method of porous membrane:
FIG. 3 is a flowchart showing a method for manufacturing the porous membranes 30 and 40. When manufacturing the porous films 30 and 40, a sheet member is prepared (step S10). A sheet | seat member can be produced as follows, for example. First, a paste-like mixture in which naphtha as a liquid lubricant is uniformly dispersed in PTFE fine powder is prepared, and the prepared mixture is preformed. A bead is produced by paste extrusion of the preformed mixture, and a long sheet member is produced by passing the bead between a pair of metal rolling rolls. The produced sheet member exhibits high anisotropy.

  Next, the sheet member is primarily stretched (step S30). In step S30, the sheet member is stretched uniaxially in the longitudinal direction (longitudinal stretching) in a temperature atmosphere in which the sheet member can be stretched (for example, a temperature atmosphere of room temperature or higher) and a temperature atmosphere lower than a previously calculated melting start temperature Tms. ) In this embodiment, the melting start temperature Tms of the sheet member is 273 ° C., and the primary stretching temperature is 250 ° C. A method for calculating the melting start temperature Tms will be described later.

  Next, the first stretched sheet member is secondarily stretched (step S50). In secondary stretching, the sheet member is stretched (laterally stretched) in a direction perpendicular to the longitudinal direction. In the present embodiment, the secondary stretching is performed in a temperature atmosphere lower than the melting start temperature Tms of the sheet member. As described above, the porous membranes 30 and 40 are manufactured.

  The both sides of the reinforced electrolyte membrane 10 including the porous membranes 30 and 40 thus manufactured include conductive particles such as carbon particles carrying a catalyst such as platinum or a platinum alloy, and an electrolyte resin. A catalyst layer is formed, and gas diffusion layers are formed on both sides of the catalyst layer. Furthermore, a fuel cell can be manufactured by providing a separator on both surfaces of the gas diffusion layer and forming a gas flow path between the gas diffusion layer and the separator.

B. Experimental result:
B-1. Observation of pores:
Hereinafter, the grounds for extending the sheet member in a temperature atmosphere lower than the melting start temperature Tms in step S30 of FIG. 3 will be described based on some experimental results. In the experiment, first, a sheet member made of polytetrafluoroethylene prepared in Step S10 (FIG. 3) described above was prepared, and Samples 1 to 3 having different primary stretching temperatures in Step S30 (FIG. 3) were prepared. .

  FIG. 4 is a diagram showing the primary stretching temperatures of Samples 1 to 3. The melting start temperature Tms of Samples 1 to 3 is 273 ° C. The primary stretching temperature of sample 1 is 250 ° C., the primary stretching temperature of sample 2 is 200 ° C., and the primary stretching temperature of sample 3 is 330 ° C. The primary stretching temperature of Samples 1 and 2 is lower than the melting start temperature Tms. The primary stretching temperature of sample 3 is equal to or higher than the melting start temperature Tms and lower than the melting point Tm. Note that the secondary stretching temperature was an atmosphere having a melting start temperature of less than Tms for all of Samples 1 to 3.

  The pores of Samples 1 to 3 thus produced were observed using a 3D-SEM (three Dimensional Scanning Electron Microscope), and primary stretching was performed in a temperature atmosphere below the melting start temperature Tms. In sample 1 performed, no blockage of pores was observed. In Sample 2 that was subjected to primary stretching in a lower temperature atmosphere than Sample 1, as in Sample 1, no pore clogging was observed. However, in the sample 3 subjected to primary stretching in an atmosphere having a temperature higher than the melting start temperature Tms and lower than the melting point Tm, local pore blockage was observed. It should be noted that the pores being blocked means that the pores of the porous membrane are blocked in such a shape that the flow of gas or water can stay.

  From the SEM observation results of the above pores, in the porous membranes (Samples 1 and 2) that were stretched in a temperature atmosphere lower than the melting start temperature Tms, the stretching was performed in a temperature atmosphere lower than the melting point Tm and higher than the melting start temperature Tms. It was shown that pore blockage was suppressed compared to the porous membrane performed (Sample 3). If the melting start temperature Tms or higher, local melting of the sheet member starts. Therefore, even if the melting point is lower than the melting point Tm of the sheet member, it is considered that in the sample 3 subjected to the primary stretching at the melting start temperature Tms or more, melting of the synthetic resin started and local pore blockage was observed.

B-2. Fuel cell test:
Next, a power generation test was performed at a cell temperature of 83 ° C. and a current density of 1.2 (A / cm ² ) using the reinforced electrolyte membranes using Samples 1 to 3, respectively. As a result, the cell resistance was 11 (mΩ) in the power generation test using Sample 1 that was subjected to primary stretching in a temperature atmosphere lower than the melting start temperature Tms. Similarly, in the power generation test using Sample 2 that was subjected to primary stretching at a lower temperature than Sample 1, the cell resistance was 11 (mΩ). However, the cell resistance was 19 (mΩ) in the power generation test using Sample 3 in which the primary stretching was performed at a temperature equal to or higher than the melting start temperature Tms and lower than the melting point Tm. The cell resistance in the power generation test using Sample 3 was about 1.7 times higher than the cell resistance in the power generation test using Samples 1 and 2.

From the results of the power generation test described above, in the reinforced electrolyte membrane using the porous membrane (sample 1) that was stretched in a temperature atmosphere below the melting start temperature Tms, the temperature atmosphere is below the melting point Tm and above the melting start temperature Tms. Compared to the reinforced electrolyte membranes using the porous membranes (samples 1 and 2) that were stretched in step 1, the cell resistance was low and the proton conductivity was high when used in fuel cells. . This is presumably because Samples 1 and 2 were not clogged with pores like Sample 3 and proton (H ⁺ ) conduction was not inhibited.

C. effect:
As described above, the porous film is manufactured by stretching in an atmosphere below the melting start Tms temperature of the sheet member, as described for the method for producing the porous film and the experimental results. It is possible to suppress clogging of the pores due to. In addition, in the primary stretching where the density of the synthetic resin contained in the sheet member is relatively high and pore clogging is likely to occur, stretching is performed below the melting start temperature of the sheet member. can do. Furthermore, since the porous film contains a fluororesin, a chemically stable porous film can be produced. In addition, if such a reinforced electrolyte membrane using a porous membrane is used in a fuel cell, proton (H ⁺ ) conduction inhibition in the fuel cell can be reduced, and the performance of the fuel cell can be improved.

D. Calculation method of melting start temperature of sheet member:
Below, the calculation method of the melting start temperature Tms of a sheet | seat member is demonstrated.
FIG. 5 is a flowchart showing a method for calculating the melting start temperature Tms of the sheet member. FIG. 6 is a diagram illustrating a DSC measurement result of the sheet member. Hereinafter, a method for calculating the melting start temperature Tms will be described with reference to FIGS. 5 and 6. In order to calculate the melting start temperature Tms of the sheet member, first, a DSC (Differential scanning calorimetry) profile of the sheet member is acquired (step S12).

  FIG. 6A shows a DSC measurement result of the sheet member. FIG. 6A shows a DSC profile of the sheet member with the heat flow W on the vertical axis and the temperature T on the horizontal axis. The DSC profile is obtained by using DSC Q100 manufactured by TA instruments and raising the temperature of about 5 mg of the sheet member produced in the above-described step S10 (FIG. 3) from 25 ° C. to 400 ° C. at 10 ° C./min. I got it. The endothermic peak shown in FIG. 6A is the melting point Tm of the sheet member.

  Next, the change amount (dw / dt, ΔW) of the heat flow W is obtained at each temperature in FIG. 6A (FIG. 5, step S14). In step S14, as shown in the inset of FIG. 6A, a change amount ΔW of the heat flow W when the temperature T changes by 1 ° C. is obtained. Note that the change amount ΔW can be obtained by the following equation (1).

ΔW = (W at T + 1 ° C.) − (W at T ° C.) Expression (1)
W: heat flow, T: temperature

  FIG. 6B is a diagram showing the amount of change in heat flow at each temperature T.

Next, a temperature T ₀ that is equal to or higher than the melting point Tm and at which the heat flow variation ΔW is ₀ is obtained (FIG. 5, step S16). FIG. 6A shows the temperature T ₀ at which the heat flow change ΔW obtained from FIG. 6B becomes _zero .

When the temperature T ₀ is obtained, a straight line N is drawn from the temperature T ₀ to the low temperature side in parallel with the horizontal axis on the DSC profile in FIG. 6A (step S18 in FIG. 5). Then, the intersection of this straight line N and the DSC profile is calculated as the melting start temperature Tms (FIG. 5, step S20). In this way, the melting start temperature Tms of the sheet member can be obtained appropriately.

E. Variation:
In the above embodiment, the melting start temperature Tms is obtained by DSC measurement. On the other hand, the melting start temperature Tms may be obtained by another measuring method capable of measuring the endothermic peak of the synthetic resin.

  In the above-described embodiment, the porous film is manufactured using polytetrafluoroethylene, which is a fluororesin, as the synthetic resin. On the other hand, as a synthetic resin, a porous film is manufactured using at least one of polyolefin resin, cellulose resin, fluorine resin, polyethersulfone, polycarbonate, polyamide, polyimide, polyamideimide, and aromatic polyamide resin. May be. Further, as the polyolefin resin, for example, polyethylene, polypropylene or the like may be used, and as the cellulose resin, for example, cellulose acetate, acetyl cellulose, cellulose acetate or the like may be used. For example, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, PFA, FEP, ETFE or the like may be used as the fluorine-based resin, and for example, aramid or the like may be used as the aromatic polyamide resin.

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and the modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Reinforcement type electrolyte membrane 20 ... Electrolyte membrane 30, 40 ... Porous membrane

Claims (5)

A method for producing a porous membrane, comprising:
Stretching a sheet member having a synthetic resin in an atmosphere lower than the melting start temperature of the sheet member;
A method for producing a porous membrane. It is a manufacturing method of the porous membrane according to claim 1,
The sheet member contains at least one of a polyolefin resin, a cellulose resin, a fluorine resin, a polyether sulfone, a polycarbonate, a polyamide, a polyimide, a polyamideimide, and an aromatic polyamide resin as the synthetic resin. A method for producing a membrane. It is a manufacturing method of the porous membrane according to claim 1 or 2,
The said melting start temperature is a manufacturing method of the porous membrane calculated | required based on the scanning scanning calorimetry of the said sheet | seat member. It is a manufacturing method of the porous membrane according to any one of claims 1 to 3,
A method for producing a porous membrane, further comprising a secondary stretching step of stretching the sheet member after stretching in an atmosphere below the melting start temperature.   A reinforced electrolyte membrane comprising a porous membrane produced by the method for producing a porous membrane according to any one of claims 1 to 4.

Images