One-pack type adhesive and fuel cell separator

Abstract

Provided is a one-pack type adhesive which contains (A) an epoxy resin, (B) a curing agent, (C) a curing accelerator, (D) an inorganic filler and (E) a polycarbodiimide compound, and wherein: the curing agent (B) contains at least one amine-based curing agent; the curing accelerator (C) contains at least one capsule type curing accelerator; the inorganic filler (D) contains at least one flake-like inorganic filler; and the content of the inorganic filler (D) is 10-200 parts by mass relative to 100 parts by mass of the epoxy resin (A).

Claims

1. A one-part adhesive comprising (A) an epoxy resin, (B) a curing agent, (C) a curing accelerator, (D) an inorganic filler and (E) a polycarbodiimide compound, wherein the curing agent (B) includes at least one amine-type curing agent, the curing accelerator (C) includes at least one capsule-type curing accelerator, the inorganic filler (D) includes at least one flaky inorganic filler, and the content of the inorganic filler (D) is from 10 to 200 parts by weight per 100 parts by weight of the epoxy resin (A).

2. The one-part adhesive of claim 1, wherein the epoxy resin (A) is liquid at 10° C.

3. The one-part adhesive of claim 1, wherein the flaky inorganic filler accounts for 5 to 100 wt % of the inorganic filler (D).

4. The one-part adhesive of claim 1, wherein the inorganic filler (D) is of at least one type selected from the group consisting of talc, silica, mica and graphite.

5. The one-part adhesive of claim 1, wherein the amine curing agent is dicyandiamide or diaminodiphenylmethane.

6. The one-part adhesive of claim 1, wherein the capsule curing accelerator is a capsule-type imidazole.

7. The one-part adhesive of claim 1, wherein the curing accelerator (C) includes a capsule curing accelerator and an imidazole compound.

8. The one-part adhesive of claim 1, further comprising (F) a coupling agent.

9. The one-part adhesive of claim 8, wherein the coupling agent (F) is a silane coupling agent.

10. An adhesive for fuel cell separators which comprises the one-part adhesive of claim 1.

11. A fuel cell separator obtained by bonding a plurality of fuel cell separators using the fuel cell separator adhesive of claim 10.

12. A fuel cell separator/membrane electrode assembly monolith obtained by bonding a fuel cell separator with a membrane electrode assembly using the fuel cell separator adhesive of claim 10.

13. A fuel cell unit cell obtained by bonding a fuel cell separator to each of the two sides of a membrane electrode assembly using the fuel cell separator adhesive of claim 10.

14. A fuel cell unit cell obtained using the fuel cell separator adhesive of claim 10.

15. A fuel cell comprising the fuel cell separator of claim 11.

16. A fuel cell comprising the fuel cell separator/membrane electrode assembly monolith of claim 12.

17. A fuel cell comprising the fuel cell unit cell of claim 13.

18. A method for producing fuel cell separators, comprising the steps of applying the fuel cell separator adhesive of claim 10 onto a portion of a first fuel cell separator, and bonding a second fuel cell separator to the first fuel cell separator.

19. A method for producing a fuel cell separator/membrane electrode assembly monolith, comprising the steps of applying the fuel cell separator adhesive of claim 10 onto a portion of a fuel cell separator, and bonding thereto a membrane electrode assembly.

20. The fuel cell separator production method of claim 18, wherein the adhesive is applied by a screen printing process.

21. A method for producing a fuel cell unit cell, comprising the step of bonding a fuel cell separator with a membrane electrode assembly using the fuel cell separator adhesive of claim 10.

Description

EXAMPLES

(1) Examples and Comparative Examples are given below by way of illustration, although the invention is not limited by these Examples. The reagents used in the Examples below were as follows.

(2) (A) Epoxy Resin

(3) (A-1) YD-8125: a bisphenol A-type epoxy resin (Nippon Steel & Sumikin Chemical Co., Ltd.) (A-2) EPICLON® EXAS35LV: a bisphenol A/F mixed epoxy resin (DIC Corporation) (A-3) YH434L: a glycidyl amine-type epoxy resin (Nippon Steel & Sumikin Chemical Co., Ltd.) (A-4) EPICLON N740: a phenolic noyolak-type epoxy resin (DIC Corporation)
(B) Curing Agent (B-1) jERCURE® DICY7: dicyandiamide (Mitsubishi Chemical Corporation) (B-2) Diaminodiphenylmethane (Tokyo Chemical industry Co., Ltd.) (B-3) EPICLON B-570H: methyltetrahydrophthalic anhydride (DIC Corporation)
(C) Curing Accelerator (C-1) Curezol 2MZ-A: an imidazole-type curing accelerator (Shikoku Chemicals Corporation) (C-2) Novacure HX3722: a capsule-type curing accelerator (Asahi Kasei Corporation)
(D) Inorganic Filler (D-1) MK-100: mica from Katakura & Co-op Agri Corporation; average particle size, 5 μm; flaky; aspect ratio, 30 to 50) (D-2) i-Naflecs®: silica (from Nippon Sheet Glass Co., Ltd.; average particle size, 10 μm; flaky; aspect ratio, (D-3) BF-10A: graphite (from Shin-Etsu Kasei Kogyo Co., Ltd.; average particle size, 10 μm; flaky; aspect ratio 10) (D-4) SA31: alumina powder (Nippon Light Metal Co., Ltd.; to average particle size, 5 μm; blocky) (D-5) FB940: (Denka Co., Ltd.; average particle size, 15 μm; spherical)
(E) Polycarbodiimide (E-1) Carbodilite V-05: a polycarbodiimide compound (Nisshinbo Chemical Inc.)
(F) Coupling Agent (F-1) KBM403: an epoxy group-containing, silane coupling agent (Shin-Etsu Chemical Co., Ltd.) (F-2) KBE-903: an amino group-containing silane coupling agent (Shin-Etsu Chemical Co., Ltd.)
Fabrication of Fuel Cell Separator Sample

(4) A fuel cell separator composition was prepared by charging a Henschel mixer with 100 parts by weight of synthetic graphite powder (average particle size: particle size distribution d.sub.50, 100 μm), 20.5 parts by weight of an o-cresol novolak-type epoxy resin (epoxy equivalent weight, 204 g/eq, ICI viscosity at 150° C., 0.65 Pa.Math.s) and 10.5 parts by weight of a novolak-type phenolic resin (hydroxyl group equivalent weight, 103 g/eq; ICI viscosity at 150° C., 0.22 Pa.Math.s) and 0.3 part by weight of 2-phenylimidazole as the binder ingredients, and 0.2 part by weight of carnauba wax as an internal mold release to agent; and mixing at 800 rpm for 3 minutes.

(5) The resulting composition was charged into a 200 mm×200 mm mold for fabricating fuel cell separators, and was press-molded at a mold temperature of 185° C., a molding pressure of 30 MPa and a molding time of 30 seconds, thereby obtaining a fuel cell separator preform having on one side grooves intended to serve as gas flow channels.

(6) Both sides of the resulting preform (the gas flow channel side and the opposite side) were subjected to surface roughening treatment by wet-blasting with using alumina abrasive grains (average particle size: particle size distribution (d.sub.50, 6 μm) at a discharge pressure of 0.22 MPa, thereby giving a fuel cell separator sample.

(7) [2] Preparation of Adhesive

Example 1

(8) The following were coarsely mixed together and then passed through a three-roll mill: 70 parts by weight of epoxy resin (A-1), 30 parts by weight of epoxy resin (A-3) and 6 parts by weight of curing agent (B-1). To the resulting mixture were added 10 parts by weight of curing accelerator (C-2), 100 parts by weight of inorganic filler (D-1), 3 parts by weight of polycarbodiimide compound (E-1) and 1 part by weight of silane coupling agent (F-1), and mixing was carried out for 3 minutes using a planetary stirrer/deaerator (Mazerustar KK-400W from Kurabo Industries, Ltd.), thereby giving a light yellow-colored pasty adhesive.

Examples 2 to 8, Comparative Examples 1 to 6

(9) Based on the formulations in Table 1 below, adhesives were prepared in the same way as in Example 1.

(10) [3] Evaluation of Adhesive

(11) (1) Screen Printability

(12) Using a screen printer (a semi-automatic screen printer from Seria Corporation) and an 80-mesh (openings, 210 μm) screen, the adhesives prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were printed onto fuel cell separator samples (120 mm×120 mm) at a squeegee load of 30 kg and a squeegee speed of 50 mm/s, following which the presence or absence of residual adhesive in the mesh openings of the screen used was determined by visual examination.

(13) The criteria for rating the screen printability were as follows. G: No adhesive remains in mesh openings of screen after printing N: Adhesive remains in mesh openings of screen after printing
(2) Rapid Curability

(14) The adhesives prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were heated for 1 minute at 180° C. within a dryer, following which they were removed from the dryer and, using a differential scanning calorimeter (DSC6200, from Seiko Instruments Inc.), the presence or absence of an exothermic peak at a temperature rise rate of 10° C./min was determined.

(15) The criteria for rating the rapid curability were as follows. G: No exothermic peak N: Exothermic peak is present

(16) An exothermic peak represents adhesive curing reactions, which indicates that curing under the 180° C./1 minute conditions was inadequate.

(17) (3) Bleedability

(18) The adhesives prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were printed onto fuel cell separator samples (120 mm×120 mm) by the same method as that described above for evaluating the screen printability, following which the separator was placed on the printed surface of another separator and 30 minutes of heating was carried out at 150° C. under an applied load of 1 MPa in a dryer, thereby producing bonded separator samples. These were taken out of the dryer and visually examined for bleeding of the adhesive in the areas where adhesive was printed.

(19) The criteria for rating the bleedability were as follows. G: No bleedout of adhesive outside of areas where adhesive was printed N: Adhesive bleedout observed outside of areas where adhesive was printed
(4) Moist Heat Resistance

(20) The adhesives prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were heated at 150° C. for 30 minutes in a dryer and completely cured, thereby giving samples of cured adhesive measuring 4 mm×18 mm×2 mm. The glass transition temperatures (Tg) of these cured adhesives were measured using a differential scanning calorimeter (DSC6200, from Seiko Instruments Inc.). Measurement of the glass transition temperature (Tg) was carried out at a temperature rise rate of 3° C./min while applying a tensile load straining the sample 10 μm at a frequency of 1 Hz. The temperature that gives the maximum value for the tan δ ratio between the two resulting elastic moduli (loss modulus, storage modulus), expressed as “loss modulus/storage modulus,” was treated as the glass transition temperature (Tg). In addition, the cured adhesives were held under the following moist heat conditions. Condition 1: 2,000 hours of immersion in hot (80° C.) water Condition 2: 2,000 hours of immersion in a hot (80° C.) water/ethylene glycol mixture (mixing ratio, 1:1)

(21) The criteria firm rating the moist heat resistance were as follows. G: The glass transition temperature (Tg) after immersion under both Condition 1 and Condition 2 was at least 90° C. N: The glass transition temperature (Tg) after immersion under at least one of Condition 1 and Condition 2 was less than 90° C.
(5) Gas Leakage Test (Room Temperature)

(22) Air (0.1 MPa) was passed through the interior of the bonded portion of bonded separator samples fabricated in the same way as described above for evaluating bleedability, and the samples were checked for the presence or absence of air leaks.

(23) The rating criteria for this gas leakage test (room temperature) were as follows. G: No leakage of air N: Air leakage occurred
(6) Gas Leakage Test (Following Hot Water Immersion)

(24) Bonded separator samples fabricated in the same way as described above for evaluating bleedability were immersed for 2,000 hours in hot (90° C.) water, following which 0.1 MPa air was passed through the interior of the bonded portion of the bonded separator samples and the samples were checked for the presence or absence of air leaks.

(25) The rating criteria for this gas leakage test (following hot water immersion) were as follows. G: No leakage of air N: Air leakage occurred

(26) These evaluation results are presented in Table 1.

(27) TABLE-US-00001 TABLE 1 Example Comparative Example Ingredients (pbw) 1 2 3 4 5 6 7 8 1 2 3 4 5 6 (A) Epoxy resin A-1 70 60 70 85 70 70 70 70 80 70 A-2 40 80 100 60 100 A-3 30 30 30 30 40 30 30 20 30 A-4 20 15 (B) Curing agent B-1 6 6 8 10 6 6 6 6 6 6 6 6 B-2 25 B-3 70 (C) Curing accelerator C-1 3 1 1 5 3 3 3 1 3 3 3 3 C-2 10 20 30 5 15 10 10 15 20 10 10 10 10 (D) Inorganic filler D-1 100 10 50 30 100 100 5 80 D-2 80 D-3 40 40 40 D-4 100 80 D-5 100 100 (E) Polycarbortiimide E-1 3 2 5 2 2 3 3 3 3 3 3 3 3 (F) Coupling agent F-1 1 1 2 1 1 1 0.1 1 1 F-2 1 1 Evaluation Screen printability G G G G G G G G N G N G N G results Rapid curability G G G G G G G G G N G N G G Bleedability G G G G G G G G G N G N G G Moist Initial Tg (° C.) 185 157 191 179 173 146 181 173 193 171 183 166 187 144 heat Tg (° C.) after 158 114 170 148 139 112 151 143 162 108 152 110 153 83 resist- Condition 1 ance Tg (° C.) after 167 120 178 157 147 125 160 151 169 115 163 115 161 88 Condition 2 Rating G G G G G G G G G G G G G N Gas leakage test (initial) G G G G G G G G N G N G N G Gas leakage test (following 2,000 hrs G G G G G G G G N N N G N N immersion)

(28) The results in Table 1 demonstrate that this invention is able to provide one-part adhesives which have an excellent productivity (screen printability, rapid curability) and moist heat resistance and also have a high reliability, particularly one-part adhesives suitable for fuel cell separator bonding applications.