JP5159101B2 - Polymer electrolyte laminated film - Google Patents

Description

  The present invention relates to a polymer electrolyte membrane for a polymer electrolyte fuel cell.

A fuel cell obtains electric energy by electrochemical reaction from a fuel (hydrogen source) and an oxidant (oxygen) in the cell. In other words, the chemical energy of the fuel is directly converted into electrical energy. As the fuel source, pure hydrogen and other oils containing hydrogen elements, natural gas (methane, etc.), methanol, and the like can be used.
Since the fuel cell itself has no mechanical part, it generates less noise, and is characterized in that it can generate electric power semi-permanently by continuing to supply external fuel and oxidant.
Electrolytes are classified into liquid electrolytes and solid electrolytes. Among them, a polymer electrolyte fuel cell is one that uses a polymer electrolyte membrane as an electrolyte.
In particular, since the polymer electrolyte fuel cell operates at a low temperature as compared with others, it is expected as an alternative power source such as an automobile, a household cogeneration system, and a portable generator.
The polymer electrolyte fuel cell includes at least a membrane / electrode assembly in which a gas diffusion electrode in which an electrode catalyst layer and a gas diffusion layer are laminated is bonded to both surfaces of a polymer electrolyte membrane. The polymer electrolyte membrane referred to here is a material having a strongly acidic group such as a sulfonic acid group or a carboxylic acid group in a polymer chain and a property of selectively transmitting protons. As such a polymer electrolyte membrane, a perfluoro proton exchange resin membrane represented by Nafion (registered trademark, manufactured by DuPont, USA) having high chemical stability is preferably used.

Such a polymer electrolyte membrane is generally a thin film having a thickness of 20 to 100 μm, and wrinkles and scratches are likely to occur when it is handled as a thin film. Therefore, it is desirable to adhere on a resin film (Backing Film 1) as shown in Non-Patent Document 1 from the viewpoint of storage and handling until a membrane / electrode assembly is produced.
By the way, the polymer electrolyte membrane generally has extremely high water absorption, and the membrane swells under high humidity. Therefore, when the adhesiveness between the polymer electrolyte membrane and the resin film is poor, there is a problem that the polymer electrolyte membrane is easily peeled off from the resin film or bubbles are likely to enter in a high humidity environment in summer. When such a problem occurs, there is a problem that the polymer electrolyte membrane becomes a defective product with defects and other defects, and cannot be used for a fuel cell.

Dennis E. Curtin, Robert D. et al. Lousenberg, Timothy J. et al. Henry, Paul C.H. Tageman, Monica E. et al. Tisack, J. et al. Power Sources, 131 (2004), 41-48

  An object of the present invention is to provide a method for facilitating handling without increasing defects such as wrinkles even when the polymer electrolyte membrane is stored for a long period of time.

The present inventors diligently studied to solve the above problems. As a result, a polymer electrolyte laminate film having a moderately improved adhesion between the resin film and the polymer electrolyte membrane can be obtained by applying a corona discharge treatment or a plasma discharge treatment on the resin film. It has been found that problems such as peeling do not occur even when stored. This is presumably because the familiarity with the highly hydrophilic polymer electrolyte membrane was improved by making the surface of the resin film hydrophilic.
At the same time, it was found that the use of polyethylene terephthalate as such a resin film facilitates peeling of the polymer electrolyte membrane from the end of the polymer electrolyte laminate film during the production of the membrane / electrode assembly, which is preferable in handling. Furthermore, it has been found that a polymer electrolyte laminated film as described above can be obtained by laminating a polymer electrolyte membrane at 30 to 200 ° C. on a resin film that has been subjected to corona discharge treatment or plasma discharge treatment. . That is, the present invention is as follows.

(1) A polymer electrolyte membrane having a thickness of 1 to 500 μm is laminated and laminated on a resin film having a thickness of 5 to 500 μm and a wettability of 40 to 100 mN / m , which has been subjected to corona discharge treatment or plasma discharge treatment. A polymer electrolyte laminate film characterized by that.
(2) The polymer electrolyte laminate film as described in (1) above, wherein the resin film is made of polyethylene terephthalate.
(3) A polymer electrolyte membrane is laminated at 30 to 200 ° C. on a resin film having a thickness of 5 to 500 μm and a wettability of 40 to 100 mN / m that has been subjected to corona discharge treatment or plasma discharge treatment. A method for producing a polyelectrolyte laminate film, which is characterized.

  The polymer electrolyte laminate film of the present invention does not peel off from the resin film (Backing Film 1) even when stored for a long time, and can provide ease of handling without increasing defects such as wrinkles of the polymer electrolyte membrane.

The present invention is described in detail below.
As the polymer electrolyte membrane constituting the polymer electrolyte laminate film of the present invention, the most preferred is a fluorine-based polymer electrolyte as shown below.
The fluorine-based polymer electrolyte is not particularly limited, but Nafion (registered trademark; manufactured by DuPont, USA), Aciplex (registered trademark; manufactured by Asahi Kasei Chemicals Corporation, Japan), Flemion (registered trademark; Asahi Glass Company, Japan) A typical example is a perfluorocarbon polymer having a proton exchange group represented by the following chemical formula (1) represented by the following chemical formula (1). ^{_{[CF 2 CX 1 X 2]}} a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3
^{_{)) B -Oc - (CFR 1}} ) d - (CFR 2) e - (CF 2) f -X 4)] g
... (1)
(Wherein X ¹ , X ² and X ³ are each independently a halogen element or a perfluoroalkyl group having 1 to 3 carbon atoms, 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, 0 ≦ b. ≦ 8, c is 0 or 1, d, e and f are each independently a number in the range of 0-6 (where d + e + f is not equal to 0), R ¹ and R ² are each independently a halogen element, A C 1-10 perfluoroalkyl group or fluorochloroalkyl group, and X ⁴ is —COOH, —SO ₃ H, —PO ₃ H ₂ , —PO ₃ HZ (Z is a hydrogen atom, a metal atom (Na , K, Ca, etc.) or amines (NH ₄ , NH ₃ R, NH ₂ R ₂ , NHR ₃ , NR ₄ (R is an alkyl group or arene group))

Among these, a perfluorocarbon polymer represented by the following chemical formula (2) or (3) is preferable because of high proton conductivity.
_{[CF 2 CF 2] a -} [CF 2 -CF (-O- (CF 2 -CF (CF 3)) b -O- (CF 2) f -X 4)] g ··· (2)
(Where 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, 1 ≦ b ≦ 3, 1 ≦ f ≦ 8, and X ⁴ represents —COOH, —SO ₃ H, —PO ₃ H ₂ or — PO ₃ H.)
_{[CF 2 CF 2] a -} [CF 2 -CF (-O- (CF 2) f -X 4)] g ··· (3)
(Where 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, 1 ≦ f ≦ 8, and X ⁴ is —COOH, —SO ₃ H, —PO ₃ H ₂ or —PO ₃ H. )

The perfluorocarbon polymer as described above may be a copolymer further including units derived from a perfluoroolefin such as hexafluoropropylene or chlorotrifluoroethylene, or a comonomer such as perfluoroalkyl vinyl ether.
A method for producing a fluorine-based polymer electrolyte used in the present invention is, for example, US Pat. No. 5,281,
No. 680, Japanese Patent Application Laid-Open No. 7-252322, and US Pat. No. 5,608,022.

  Examples of the polymer electrolyte membrane include polyethersulfone resin, polyetheretherketone resin, phenol-formaldehyde resin, polystyrene resin, polytrifluorostyrene resin, trifluorostyrene resin, poly (2,3-diphenyl-1, 4-phenylene oxide) resin, poly (allyl ether ketone) resin, poly (allyl ether sulfone) resin, poly (phenylquinosan phosphorus) resin, poly (benzylsilane) resin, polystyrene-graft-ethylenetetrafluoroethylene resin, polystyrene- A sulfonic acid group or a carboxylic acid group was introduced into a polymer having a hydrocarbon moiety such as graft-polyvinylidene fluoride resin, polystyrene-graft-tetrafluoroethylene resin, polyimide resin, polybenzimidazole resin. Also applicable to.

The proton exchange capacity of the polymer electrolyte membrane is not particularly limited, but is preferably 0.5 to 4.0 milliequivalents per gram, more preferably 0.8 to 4.0 milliequivalents, most preferably 0.9 to 1.5 milliequivalents. The use of a polymer electrolyte membrane having a larger proton exchange capacity exhibits higher proton conductivity under high temperature and low humidification conditions, and when used in a fuel cell, a higher output can be obtained during operation.
The thickness of the polymer electrolyte membrane is 1 to 500 μm, preferably 2 to 200 μm, more preferably 5 to 100 μm, and most preferably 10 to 50 μm. The thicker the film thickness, the better the durability and the worse the initial characteristics. Therefore, it is preferable to set the film thickness within the above range.

  On the other hand, as the resin film constituting the polymer electrolyte laminate film of the present invention, polyethylene terephthalate, polyethylene naphthalate, polystyrene, polyethylene, polypropylene, polycarbonate, polyimide, polyetheretherketone, polyvinylidene fluoride, polytetrafluoroethylene, etc. All of the general resin films correspond to this, and among them, in the case of a resin film made of polyethylene terephthalate, the polymer electrolyte membrane can be easily peeled when the membrane / electrode assembly is produced, which is preferable in handling.

The thickness of such a resin film is 5 to 500 μm, preferably 2 to 200 μm, more preferably 5 to 100 μm, and most preferably 10 to 50 μm.
Moreover, such a resin film is characterized by being subjected to corona discharge treatment or plasma discharge treatment.
The corona discharge treatment referred to here is a discharge handbook (published by Ohm, revised in 1982, edited by the Electrotechnical Society Discharge Handbook Publishing Committee) p. As described in 102 to 106, a counter electrode such as a stainless steel wire or a tungsten wire is placed on the resin film surface, a high frequency and a high voltage are applied, and a corona discharge is generated in the atmosphere, thereby generating The process etc. which directly irradiate a resin film with the functional group and electron which are made.

In addition, the plasma discharge treatment referred to here is a discharge handbook (published by Ohm, revised in 1982, edited by the Institute of Electrical Engineers of Japan Discharge Handbook) p. As described in 281 to 329, plasma discharge is generated in the atmosphere by high-voltage arc plasma discharge, activated by irradiating the surface of the resin film with plasma discharge electrons, and generated by discharge activated oxygen. The treatment which gives the functional polar group to the resin film surface.
The discharge electron irradiation amount in the corona discharge treatment or plasma discharge treatment as described above, a 0.01~1000W ^/ m 2 ^/ min, preferably 0.1~500W ^/ m 2 ^/ min, more preferably 1 to 200 W / m ² / min, most preferably ^{2 to} 100 W / m ² / min.
The wettability of the resin film subjected to corona discharge treatment or plasma discharge treatment is preferably 40 to 100 mN / m, more preferably 50 to 90 mN / m, and most preferably 60 to 80 mN / m.

(Production example of the polymer electrolyte laminate film of the present invention)
An example using a polymer electrolyte membrane made of a fluorine-based polymer electrolyte will be described below as a method for producing the polymer electrolyte laminated film of the present invention, but is not particularly limited.
The polymer electrolyte membrane of the present invention can be produced, for example, by the following method.
The fluorine-based polymer electrolyte can be produced by polymerizing a precursor polymer represented by the following chemical formula (4) by the following method, followed by hydrolysis and acid treatment.
^{_{[CF 2 CX 1 X 2]}} a - [CF 2 -CF (-O- (CF 2 -CF (CF 2 X 3)) b -O c - (CFR 1) d - (CFR 2) e - (CF ₂ ) _f- X ⁵ )] _g
... (4)
(Wherein X ¹ , X ² and X ³ are each independently a halogen element or a C 1-3 perfluoroalkyl group, 0 ≦ a <1, 0 <g ≦ 1, a + g = 1, b is 0 to 8, c is 0 or 1, d, e and f are each independently a number from 0 to 6 (where d + e + f is not equal to 0), R ¹ and R ² are each independently a halogen element , A C 1-10 perfluoroalkyl group or fluorochloroalkyl group, X ⁵ is —COOR ³ , —COR ⁴ or —SO ₂ R ⁴ (R ³ is a C 1-3 alkyl group (fluorinated Not R), R ⁴ is a halogen element))
The precursor polymer represented by the chemical formula (4) is produced by copolymerizing a fluorinated olefin and a vinyl fluoride compound. As a specific fluorinated olefin, CF ₂
= CF ₂ , CF ₂ = CFCl, CF ₂ = CCl _{2 and the} like. Specific fluorinated vinyl _{compounds, CF 2 = CFO (CF 2} ) z -SO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) z -SO 2 F, CF 2 = CF ( _{CF 2) z -SO 2 F,} CF 2 F (OCF 2 CF (CF 3)) z - (CF 2) z-1 -SO 2
_{F, CF 2 = CFO (CF} 2) z -CO 2 R, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) z -CO 2 R, CF 2 = CF (CF 2) z -CO 2 R , CF _{2
= CF (OCF 2 CF (CF} 3)) z - a _{(CF 2) 2 -CO 2 R} (Z is an integer of 1 to 8, R represents those not alkyl groups (fluorine-substituted 1 to 3 carbon atoms) For example).

As a method for polymerizing such a precursor polymer, a solution polymerization method in which a vinyl fluoride compound is dissolved in a solvent such as chlorofluorocarbon and then reacted with a tetrafluoroethylene gas to perform polymerization. Polymerization is performed without using a solvent such as chlorofluorocarbon. Examples thereof include a bulk polymerization method, and an emulsion polymerization method in which a vinyl fluoride compound is charged with water in a surfactant and emulsified, and then reacted with tetrafluoroethylene gas for polymerization. In any of the above polymerization methods, the reaction temperature is preferably 30 to 90 ° C., and the reaction pressure is preferably 280 to 1100 kPa.
The melt index MI (g / 10 minutes) measured at 270 ° C., load 2.16 kgf, orifice inner diameter 2.09 mm based on JIS K-7210 of the precursor polymer thus produced is not limited. It is preferably 0.001 or more and 1000 or less, more preferably 0.01 or more and 100 or less, and most preferably 0.1 or more and 10 or less.

In order to form such a precursor polymer into a film, a general melt extrusion method (T-die method, inflation method, calendar method, etc.) is used.
The precursor polymer thus molded is brought into contact with the reaction liquid to hydrolyze the ion exchange group precursor to produce a polymer electrolyte membrane. In this case, the hydrolysis of the ion-exchange group precursor can be carried out in an aqueous alkali hydroxide solution, and it is advantageous to use a relatively high temperature solution in order to further increase the hydrolysis reaction rate. For example, this is a method of hydrolyzing at 70 to 90 ° C. for 16 hours using an aqueous solution containing 20 to 25% sodium hydroxide as disclosed in JP-A 61-19638. Further, in order to swell the membrane and accelerate the hydrolysis reaction rate, the mixture is hydrolyzed with a mixture of an alkali hydroxide aqueous solution and an alcohol solvent such as methyl alcohol, ethyl alcohol or propyl alcohol or a water-soluble organic solvent such as dimethyl sulfoxide. A method of decomposing is used. For example, a method of hydrolyzing at 90 ° C. for 1 hour using an aqueous solution containing 11 to 13% potassium hydroxide and 30% dimethyl sulfoxide disclosed in JP-A-57-139127, JP-A-3-6240 This is a method of hydrolyzing at 60 to 130 ° C. for 20 minutes to 24 hours using an aqueous solution containing 15 to 50 wt% of alkali hydroxide and 0.1 to 30 wt% of a water-soluble organic compound.

Thus, after forming an ion exchange group by hydrolysis treatment, a polymer electrolyte membrane can be produced by further acid treatment with an inorganic acid such as hydrochloric acid.
As a method for producing a polymer electrolyte laminated film using the polymer electrolyte membrane produced by the above method and a resin film subjected to corona discharge treatment or plasma discharge treatment, a hot press is performed in a state in which these are laminated. Examples thereof include a method of joining by using a known press technique such as a roll press or a vacuum press or a lamination technique. Among these, on a resin film having a thickness of 5～500Myu m, method of lamination a polymer electrolyte membrane at 30 to 200 ° C. it is preferable to be able to produce a more moderate polyelectrolyte multilayer film.

The polymer electrolyte laminate film of the present invention can also be used for chloralkali electrolysis, water electrolysis, hydrohalic acid electrolysis, salt electrolysis, oxygen concentrator, humidity sensor, gas sensor and the like. For a method of using the polymer electrolyte membrane for the oxygen concentrator, see, for example, Chemical Engineering, 56 (3), p. 178-180 (1992) and U.S. Pat. No. 4,879,016. For a method of using a polymer electrolyte membrane for a humidity sensor, see, for example, Journal of the Japan Ion Exchange Society, 8 (3), p. 154-165 (1997) and J.A. Fang et al. , Macromolecules, 35, 6070 (2002). For a method of using a polymer electrolyte membrane for a gas sensor, see, for example, Analytical Chemistry, 50 (9), p. 585-594 (2001), X. Yang, S.M. Johnson, J.M.
Shi, T .; Holesinger, B.H. Swanson: Sens. Actuators B, 45, 887 (1997).

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not restrict | limited to an Example. Evaluation methods and measurement methods used in the present invention are as follows.
[Example 1]
As the polymer electrolyte membrane, a perfluorosulfonic acid polymer represented by [CF ₂ CF ₂ ] _0.812- [CF ₂ -CF (—O— (CF ₂ ) ₂ —SO ₃ H)] _0.188 ( Hereinafter, a polymer electrolyte membrane having a proton exchange capacity of 1.22 meq / g and a film thickness of 50 μm composed of “PFS” was produced as follows.
First, as a PFS precursor polymer, a perfluorocarbon polymer (MI: 3.0) made of a copolymer of tetrafluoroethylene and CF ₂ ═CFO (CF ₂ ) ₂ —SO ₂ F was produced. A film formed by melt extrusion of this precursor polymer to a thickness of about 50 μm is brought into contact with a reaction liquid containing 15 wt% potassium hydroxide, 30 wt% dimethyl sulfoxide and 55 wt% water at 60 ° C. for 4 hours. Then, the hydrolysis treatment was performed. Thereafter, the film was immersed in 60 ° C. water for 4 hours and then immersed in a 2N hydrochloric acid aqueous solution at 60 ° C. for 3 hours, and then the acid was washed out with ion-exchanged water to obtain a polymer electrolyte membrane.
As the resin film, a polyethylene terephthalate film subjected to corona discharge treatment was used as follows.
As the polyethylene terephthalate film, Teijin ^TM Tetron Film ^TM G2 manufactured by Teijin DuPont Films Co., Ltd. having a thickness of 38 μm was used (hereinafter referred to as PET film).
The wettability of the resin film before treatment was 30 mN / m (based on JIS K-6768).

In such a corona discharge treatment of the PET film, a corona discharge treatment was performed at a dose of 100 W / m ² / min using a corona discharge surface treatment system manufactured by Kasuga Electric Co., Ltd.
The wettability of this resin film was 70 mN / m (based on JIS K-6768).
Next, a 10 cm square polymer electrolyte membrane and a corona discharge-treated PET film were laminated, and both sides thereof were sandwiched between Kapton (registered trademark, DuPont) films (300H, film thickness 75 μm). This was set in a compression molding machine (manufactured by Shinfuji Kogyo Co., Ltd., VSF-10), heated to 100 ° C., and pressed at 10 kgf / cm ^{2 for} 10 minutes. After completion of pressing, the pressure was released and the temperature was lowered to 30 ° C., and then a sample was taken out to obtain a polymer electrolyte laminated film of the present invention laminated on a PET film subjected to corona discharge treatment.
This polymer electrolyte laminated film was placed in a constant temperature and humidity chamber, and a dry / wet cycle test was performed at 30 ° C. and 95% RH for 3 hours to 10 ° C. and 30% RH for 3 hours. When the polymer electrolyte laminate film of the present invention was taken out after 400 cycles, the polymer electrolyte membrane was not peeled off from the corona discharge treated PET film.
When an attempt was made to peel the polymer electrolyte membrane from the polymer electrolyte laminated film by hand from the end, it was easily peeled off.

[Example 2]
The example of the polymer electrolyte laminated film produced using the same polymer electrolyte membrane as Example 1 and the PET film which performed the following plasma discharge processes is shown below.
For plasma discharge treatment of the PET film, a plasma irradiation surface modification device (PS-601S) manufactured by Kasuga Electric Co., Ltd. was used, and the treatment was performed at an irradiation amount of 100 W / m ² / min.
The wettability of this resin film was 66 mN / m (based on JIS K-6768).
Next, the same laminating treatment as in Example 1 was performed to obtain the polymer electrolyte laminated film of the present invention. When this polymer electrolyte laminated film was subjected to a dry and wet cycle test in the same manner as in Example 1, the polymer electrolyte membrane was not peeled off from the plasma discharge treated PET film.
When an attempt was made to peel the polymer electrolyte membrane from the polymer electrolyte laminated film by hand from the end, it was easily peeled off.

[Comparative Example 1]
A polymer electrolyte laminate film was obtained in the same manner as in Example 1 except that a PET film not subjected to corona discharge treatment was used. When this polymer electrolyte laminated film was subjected to a dry and wet cycle test in the same manner as in Example 1, the polymer electrolyte membrane was peeled off from the PET film.
When an attempt was made to peel the polymer electrolyte membrane from the polymer electrolyte laminated film by hand from the end, it was easily peeled off.

The polymer electrolyte laminate film of the present invention is a resin film (Backin) even when stored for a long time.
It is possible to provide a method for facilitating handling without delamination from g Film 1) and without increasing defects such as wrinkles of the polymer electrolyte membrane.

Claims (3)

A polymer electrolyte membrane having a thickness of 1 to 500 μm is laminated and laminated on a resin film having a thickness of 5 to 500 μm and a wettability of 40 to 100 mN / m , which has been subjected to corona discharge treatment or plasma discharge treatment. A polymer electrolyte laminate film.   The polymer electrolyte laminate film according to claim 1, wherein the resin film is made of polyethylene terephthalate. A polymer electrolyte membrane is laminated at 30 to 200 ° C. on a resin film having a thickness of 5 to 500 μm and a wettability of 40 to 100 mN / m that has been subjected to corona discharge treatment or plasma discharge treatment. A method for producing a polymer electrolyte laminated film.