Patent Application
20090234057
The invention relates to the use of a rubber compound as a material in the area of application of fuel cells.
European patent application EP 1 075 034 A1 describes the use of polyisobutylene or perfluoropolyether, crosslinked by hydrosilylation, as a sealing material in fuel cells.
U.S. Pat. No. 6,743,862 B2 discloses a crosslinkable rubber composition, preferably consisting of ethylene propylene diene monomer, with a compound having at least two SiH groups and optionally with a platinum catalyst, and it describes its use as a sealing material.
European patent application EP 1 277 804 A1 discloses compositions made of a vinyl polymer having at least one alkenyl group that can be crosslinked by hydrosilylation, of a compound with a component containing hydrosilyl groups, of a hydrosilylation catalyst as well as of an aliphatic unsaturated compound having a molecular weight of not more than 600 g/mol.
Terminal double bonds are decisive when a rubber is crosslinked by hydrosilylation. No undesired decomposition products that could migrate are created during the crosslinking. Consequently, these rubber compositions are usually suitable for applications in which a clean environment is especially important such as, for example, in fuel cells, in the medical sector or in the realm of food packaging.
Moreover, an improvement in the mechanical properties of the employed rubber types, especially those relating to tensile strength, elongation at break and/or compression set, is desirable in order to do justice to the specific loads encountered in the cited areas of application.
So far, a reduction of the compression set has been achieved by increasing the crosslinking density. This causes an increase in the hardness. However, the elongation at break often decreases at the same time, which causes problems in many applications.
The invention is based on the objective of proposing the use of a rubber compound with which an improvement of the mechanical properties of rubbers is achieved, especially an increase in the elongation at break and/or in the tensile strength and/or in the tear propagation resistance, along with a concurrent reduction in the compression set.
The envisaged objective is achieved by the features of claim 1.
For use in the area of application of fuel cells, according to the invention, the rubber compound comprises a rubber (A) having at least two functional groups that can be crosslinked by hydrosilylation, it also comprises, as the crosslinking agent (B), a hydrosiloxane or hydrosiloxane derivative or a mixture of several hydrosiloxanes or hydrosiloxane derivatives that, on average, have at least two SiH groups per molecule, and it comprises a hydrosilylation catalyst system (C), at least one filler (D) and a co-agent (E) that can be crosslinked by hydrosilylation.
The subordinate claims constitute advantageous refinements of the subject matter of the invention.
In a preferred embodiment, the rubber compound additionally comprises at least one additive (G).
In order to improve the mechanical properties of rubbers, especially in order to increase the elongation at break, the tensile strength and/or the tear propagation resistance, while concurrently reducing the compression set, it is advantageous to use the following for the rubber compound:
In a preferred embodiment, the rubber compound additionally contains 0.1 to 20 phr of the at least one additive (F).
The abbreviation phr means parts per hundred of rubber; in other words it indicates the parts by weight per hundred parts by weight of rubber.
Preferred rubber compounds have proven to be those for which rubber (A) is selected from among
An especially preferred rubber compound contains, as rubber (A), ethylene propylene diene monomer rubber (EPDM) having a vinyl group in the diene or polyisobutylene (PIB) having two terminal vinyl groups.
Advantageously, the mean molecular weight of rubber (A) is between 5000 and 100,000 g/mol, preferably between 5000 and 60,000 g/mol.
The following are preferably used as the crosslinking agent (B):
a compound containing SiH and having the Formula (I):
wherein R1 stands for a saturated hydrocarbon group or for an aromatic hydrocarbon group that is monovalent, that has 1 to 10 carbon atoms and that is substituted or unsubstituted, whereby a stands for integers ranging from 0 to 20 and b stands for integers ranging from 0 to 20, and R2 stands for a bivalent organic group having 1 to 30 carbon atoms or oxygen atoms,
a compound containing SiH and having the Formula (II):
and/or
a compound containing SiH and having the Formula (III):
The crosslinking agent (B) is especially selected from among poly(dimethyl siloxane co-methyl hydrosiloxane), tris(dimethyl silyoxy)phenyl silane, bis(dimethyl silyloxy)diphenyl silane, polyphenyl(dimethyl hydrosiloxy)siloxane, methyl hydrosiloxane phenyl methyl siloxane copolymer, methyl hydrosiloxane alkyl methyl siloxane copolymer, polyalkyl hydrosiloxane, methyl hydrosiloxane diphenyl siloxane alkyl methyl siloxane copolymer and/or polyphenyl methyl siloxane methyl hydrosiloxane.
Poly(dimethyl siloxane co-methyl hydrosiloxane) has proven to be especially well-suited for building networks for difunctional vinyl rubbers such as, for example, polyisobutylene having two terminal double bonds.
Tris(dimethyl silyoxy)phenyl silane or bis(dimethyl silyloxy)diphenyl silane have proven to be especially suitable as crosslinking agents for rubbers having more than two functional groups in the molecule that can be crosslinked by hydrosilylation such as, for example, for ethylene propylene diene monomer rubber (EPDM) with 5-vinyl-2-norbomene as the diene.
The hydrosilylation catalyst system (C) is preferably selected from among platinum(0)-1,3-divinyl-1,1,3,3,-tetramethyl disiloxane complex, hexachloroplatinic acid, dichloro(1,5-cyclooctadiene)platinum(II), dichloro(dicyclopentadienyl)-platinum(II), tetrakis(triphenyl phosphine)platinum(0), chloro(1,5-cyclooctadiene)rhodium(I)dimer, chlorotris(triphenyl phosphine)rhodium(I) and/or dichloro(1,5-cyclooctadiene)palladium(II), optionally in combination with a kinetics regulator selected from among dialkyl maleate, especially dimethyl maleate, 1,3,5,7-tetramethyl-1,3,5,7-tetravinyl cyclosiloxane, 2-methyl-3-butin-2-ol and/or l-ethinyl cyclohexanol.
The at least one filler (D) is advantageously selected from furnace, flame and/or channel black, silicic acid, metal oxide, metal hydroxide, carbonate, silicate, surface-modified or hydrophobized, precipitated and/or pyrogenic silicic acid, surface-modified metal oxide, surface-modified metal hydroxide, surface-modified carbonate, such as chalk or dolomite, surface-modified silicate, such as kaolin, calcinated kaolin, talcum, quartz powder, siliceous earth, layer silicate, glass beads, fibers and/or organic fillers such as, for example, wood flour and/or cellulose.
Hydrophobized or hydrophobic silicic acids can be incorporated especially well into non-polar rubbers and translate into a lesser increase in viscosity as well as better mechanical values in comparison to unmodified silicic acids.
The co-agent (E) is advantageously selected from among 2,4,6-tris(allyloxy)-1,3,5-triazine (TAC), triallyl isocyanurate (TAIC), 1,2-polybutadiene, 1,2-polybutadiene derivatives, diacrylates, triacrylates, especially trimethyl propane triacrylate, dimethacrylates and/or trimethacrylates, especially trimethylol propane trimethacrylate (TRIM), triallyl phosphonic acid esters and/or butadiene styrene copolymers having at least two functional groups that bond to rubber (A) by hydrosilylation.
The following are used as additive (F):
The method for the production of such a rubber compound does not generate any by-products during the crosslinking that have to be removed in a laborious procedure. No decomposition products are released that can migrate and that can be problematic for applications in the realm of fuel cells. Moreover, the crosslinking with a relatively small amount of hydrosilylation catalyst system takes place more quickly than with conventional materials.
In order to produce the rubber compounds described, first of all, rubber (A), the at least one filler (D) and the co-agent (E) and/or the at least one additive (F) are mixed, the crosslinking agent (B) and the hydrosilylation catalyst system (C) are added as a one-component system or as a two-component system and all of the components are mixed.
In the case of a one-component system, the crosslinking agent (B) and the hydrosilylation catalyst system (C) are added to the above-mentioned other components in a system or in a container. In contrast, with the two-component system, the crosslinking agent (B) and the hydrosilylation catalyst system (C) are mixed separately from each other, that is to say, in two systems or containers, each at first with part of a mixture of the other components, until they are homogeneously blended, before the two systems, that is to say, the mixture with the crosslinking agent (B) and the mixture with the hydrosilylation catalyst system (C), are combined with each other, and all of the components are mixed together. The two-component system has the advantage that the two mixtures, in which the crosslinking agent (B) and the hydrosilylation catalyst system (C) are separate from each other, can be stored for a longer period of time than a mixture that contains the crosslinking agent (B) as well as the hydrosilylation catalyst system (C).
Subsequently, the product is processed by an injection-molding or (liquid) injection-molding method ((L)IM), by a compression-molding method (CM), by a transfer-molding method (TM) or by a method derived from any of these, by a printing process such as, for example, silkscreen printing, by bead application, dip-molding or spraying.
The above-mentioned rubber compounds are used as material in the area of application of fuel cells.
Preferably, the rubber compounds are used as a material for seals such as loose or integrated seals, for instance, O-rings or chevron-type sealing rings, adhesive seals, soft-metal seals or impregnations, for coatings, membranes or adhesive compounds for hoses, valves, pumps, filters, humidifiers, reformers, storage tanks, vibration absorbers, for coatings of fabrics and/or non-wovens.
An especially advantageous embodiment of the rubber compounds is their use as seals for fuel cell stacks in the form of, for example, profiled or unprofiled seals. Preferably, the rubber compounds according to the invention are also used on a bipolar plate, a membrane, a gas diffusion layer or in profiled or unprofiled seals integrated into a membrane-electrode unit.
The subject matter of the invention will be explained below with reference to a number of examples.
A rubber (A), a filler (D) and a co-agent (E) are mixed in a mnixer, namely, a SpeedMixer DAC 400 FVZ made by the Hausschild & Co. KG company, at temperatures between 30° C. and 60° C. [86° F. and 140° F.] until the components are homogeneously mixed. Subsequently, a crosslinking agent (B) and a hydrosilylation catalyst system (C) are added, and the mixture is further mixed until the components are homogeneously blended.
This mixture is then compression-molded under vulcanization conditions at 150° C. [302° F.], for example, in a press, to form 2 mm-thick plates.
Ethylene propylene 5-vinyl-2-norbornene rubber made by the Mitsui Chemicals company and having a norbomene content of 5.3% by weight and a mean molecular weight of 31,000 g/mol (Mitsui EPDM) or polyisobutylene (PE:B) having two vinyl groups made by the Kaneka company and having a mean molecular weight of 16,000 g/mol (EPION-PIB (EP 400)) is used as rubber (A).
Tris(dimethylsilyloxy)phenyl silane made by the Shin Etsu company is used as the hydrosilylation crosslinking agent (B) for the Mitsui EPDM. This crosslinking agent is especially well-suited for rubbers that have more than two vinyl groups in the molecule.
2,5-Dimethyl-2,5-di(tert-butyl peroxy)hexane made by Arkema Inc. (Luperox 101 XL-45) is used as the peroxide crosslinking agent for the Mitsui EPDM.
Poly(dimethyl siloxane co-methyl hydrosiloxane) made by the Kaneka company (CR 300) is used as the hydrosilylation crosslinking agent (B) for the polyisobutylene terminal-functionalized with two vinyl groups (EPION-PIB (EP 400)). CR 300 has more than 3 SiH groups per molecule and is thus especially well-suited for building networks for difunctional vinyl rubbers such as polyisobutylene having two vinyl groups.
A so-called Karstedt catalyst is used as the hydrosilylation catalyst system (C), namely, platinum(0)-1,3-divinyl-1,1,3,3,-tetramethyl disiloxane complex, that has been dissolved in a 5% concentration in xylene and that is used in combination with dimethyl maleate as a kinetics regulator.
Hydrophobized pyrogenic silicic acid made by the Degussa company (Aerosil R8200) is used as the filler (D). Hydrophobized or hydrophobic silicic acids can be incorporated especially well into non-polar rubbers and cause a lesser increase in viscosity as well as a better compression set in comparison to silicic acids that have not been surface-modified.
Triallyl isocyanurate (TAIC) made by the Nordmann, Rassmann GmbH company or else 1,2-polybutadiene (Nisso PB B-3000) made by Nippon Soda Co., Ltd. or trimethylol propane triacrylate (Saret 519) made by the Sartomer company is used as the co-agent (E) that can be crosslinked by hydrosilylation.
The invention can be better understood with reference to the following examples from Tables I to IV.
The rubber compounds with and without a co-agent undergo the following tests:
Tables Ia and Ib give examples, whereby ethylene propylene 5-vinyl-2-norbomene rubber made by the Mitsui Chemicals company is used as rubber (A).
Tris(dimethyl silyoxy)phenyl silane is used as the hydrosilylation crosslinking agent (B) for the Mitsui EPDM in a dose that is adapted to the double bonds supplied by the co-agent (E).
As is known, a number of secondary reactions can occur during the crosslinking of EPDM with peroxides, some of which can be suppressed by the use of co-agents.
Moreover, by increasing the crosslinking density, the addition of a co-agent such as, for instance, 1,2-polybutadiene (Nisso PB B-3000) or triallyl isocyanurate (TAIC) during peroxide crosslinking of Mitsui EPDM translates into an increase in the hardness and a decrease in the compression set, but also an undesired decrease in the elongation at break.
In the case of Mitsui EPDM crosslinked by hydrosilylation, the increase in the crosslinking density due to the addition of the co-agent 1,2-polybutadiene (Nisso PB B-3000) or of triallyl isocyanurate (TAIC) translates into an increase in the hardness and an increase in the tensile strength. The addition of a co-agent (E) also brings about a marked reduction in a permanent deformation of the rubber under load, that is to say, a decrease in the compression set value.
Surprisingly, the elongation at break increases with Mitsui EPDM crosslinked by hydrosilylation in contrast to Mitsui EPDM crosslinked by peroxide, especially after the addition of 1,2-polybutadiene (Nisso PB B-3000) as the co-agent. This positive effect opens up improved application possibilities to use this rubber compound in numerous areas of application.
In particular, the elongation at break is also increased as a result of the addition of diacrylates, for example, of 1,6-hexane dioldiacrylate (SR 238) made by the Sartomer company, as is shown in Table Ib.
Table IIa shows examples, whereby polyisobutylene (PIB) having two vinyl groups made by the Kaneka company (EPION-PIB (EP 400)) is used as rubber (A).
Poly(dimethyl siloxane co-methyl hydrosiloxane) made by the Kaneka company (CR 300) is used as the hydrosilylation crosslinking agent (B) for the polyisobutylene terminal-functionalized with two vinyl groups (EPION-PIB (EP 400)) in a dose that is adapted to the double bonds supplied by the co-agent (E).
In the case of polyisobutylene having two vinyl groups (EPION-PIB (EP 400)) crosslinked by hydrosilylation, the addition of trimethylol propane triacrylate (Saret 519) as the co-agent (E) translates into an increase in the tensile strength and a decrease in the compression set at 120° C. [248° F.].
Surprisingly, when the co-agent (E) is added, the elongation at break increases in the case of polyisobutylene having two vinyl groups (EPION-PIB (EP 400)) crosslinked by hydrosilylation. The tear propagation resistance also increases when the co-agent (E) is added.
Table IIb shows the effect of the addition of the co-agent 1,2-polybutadiene (Nisso PB B-3000) or of triallyl isocyanurate (TAIC) on various mechanical properties.
With the addition of these co-agents (E) as well, the hydrosilylation compound with polyisobutylene displays increased tensile strength values and, exactly like with the addition of trimethylol propane triacrylate (Saret 519), surprisingly improved elongation at break properties.
In particular, the compression set values after 24 hours at 120° C. [248° F.] in air can also be lowered as a result of the addition of acrylate and triallyl isocyanurate (TAIC).
Acrylonitrile butadiene rubber (NBR) made by the Lanxess company (Perbunan 2845 F) is used in the examples compiled in Table III.
In addition to rubber (A) without a co-agent and with the co-agent (E), the data of Table III turns to the example of the use of the co-agent triallyl isocyanurate (TAIC) or 1,2-polybutadiene (Nisso PB B-3000) to show how the mechanical properties are influenced by the addition of a co-agent (E) that can be crosslinked by hydrosilylation.
The hardness values are increased as a result of the addition of a co-agent (E) and so are the tensile strength values. The same applies to the tear propagation resistance when the co-agent (E) is added.
In this context, the hydrosilylation compounds with the co-agent triallyl isocyanurate (TAIC) display even somewhat higher tensile strength, elongation at break and tear propagation resistance values as well as a somewhat lower compression set in comparison to those with the co-agent 1,2-polybutadiene (Nisso PB B-3000).
Moreover, the measured data compiled in Table IV for the comparative examples with hydrosilylation compounds with acrylate rubber (ACM OR 100 A) made by the Kaneka company as rubber (A) without a co-agent and with the co-agent (E), for example, using the co-agent triallyl isocyanurate (TAIC), triacrylate (Saret 519) or 1,2-polybutadiene (Nisso PB B-3000), shows how the mechanical properties are influenced by the addition of a co-agent (E) that can be crosslinked by hydrosilylation.
The hardness values here are increased as a result of the addition of a co-agent (E) and so are the tensile strength values. Noteworthy here is the improvement of the compression set after 70 hours at 150° C. [302° F.] as a result of the addition of a co-agent from the group of acrylates, as shown with the triacrylate (Saret 519), and especially as a result of the addition of the co-agent triallyl isocyanurate (TAIC).
The examples compiled in the tables show that the rubber compounds that contain ethylene propylene diene monomer rubber (EDPM), polyisobutylene (PIB), acrylonitrile butadiene rubber (NBR) or acrylate rubber (ACM) as rubber (A), and that contain triallyl isocyanurate (TAIC), 1,2-polybutadiene, triacrylates (Saret 519) or diacrylates such as, for example, 1,6-hexane dioldiacrylate (SR 238) as co-agent (E) have especially advantageous mechanical properties.
Hydrosilylation compounds containing 1,2-polybutadiene or ether groups as co-agents tend towards slightly worse mechanical properties, especially in terms of thermal ageing, which is evident from the compression set values at 120° C. [248° F.] and higher temperatures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 045 167.5 | Sep 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/009036 | 9/16/2006 | WO | 00 | 3/20/2008 |
