Highly conductive molding compounds for use as fuel cell plates and the resulting products

Abstract

A conductive polymer is disclosed which is suitable for use in applications which require corrosion resistance including resistance to corrosion when subjected to acidic flow at temperature ranging from −40 to 140 degrees Fahrenheit and which can be molded such as by compression and/or injection molding techniques, into highly intricate and thin specimens without significant post machining. and which exhibit consistent conductivity, sufficient strength and flexibility, and appropriate surface characteristics. In particular the invention involves molding resin composition, which have high loadings of conductive fillers. Further the compositions may include rheological modifiers such as Group II oxides and hydroxides; carbodiamides; aziridines; polyisocyanates; polytetrafluorethylene (PTFE); perfluoropolyether (PFPE), and polyethylene. In an additional embodiment of the invention, an anti-shrink additive is added to improve the characteristics of the molded fuel cell plate.

What is claimed is:  
     
         1 . A process for making a fuel cell plate having an intricate flow pattern molded therein comprising the steps of mixing a composition comprising; 
 a) an unsaturated prepolymer resin which comprises one or more of unsaturated polyester and vinyl ester resin;    b) an unsaturated material copolymerizable with said resin and including a terminal ethylene group;    c) an inorganic conductive filler in an amount sufficient to provide a bulk conductivity of at least 40 S/cm to the resulting fuel cell plate; and    d) an initiator to initiate said copolymerization; and    molding the composition to form said fuel cell plate having the pattern therein substantially without machining the pattern.    
     
     
         2 . A process as set forth in  claim 1  wherein the conductive filler is a particulate filler and the amount of said conductive filler is at least 60 weight percent.  
     
     
         3 . A process as set forth in  claim 2  wherein the filler is a graphite filler and the amount of said conductive filler is at least 65 weight percent.  
     
     
         4 . A process as set forth in  claim 1  wherein the molding step is an injection or compression molding step or a combination thereof.  
     
     
         5 . An electrochemical cell flow field plate comprising 
 a molded thermosetting resin composition having an intricate fuel flow pattern molded therein and having a thickness from about 0.050 to about 0.200 inches and a bulk conductivity of at least 55 S/cm, said molded thermosetting resin composition being the reaction product of at least: 
 a) an unsaturated prepolymer resin which comprises one or more of unsaturated polyester and vinyl ester resin;  
 b) an unsaturated material copolymerizable with said resin and including a terminal ethylene group;  
 c) a conductive filler in an amount sufficient to provide a bulk conductivity of at least 40 S/cm to the resulting fuel cell plate; and  
 d) an initiator to initiate said copolymerization.  
   
     
     
         6 . An electrochemical cell flow field plate as set forth in  claim 5  further comprising an effective amount of a rheological modifier to prevent phase separation between said resin and said conductive filler during molding, said Theological modifier being one or more compositions selected from the group consisting of Group II oxides and hydroxides, carbodiamides, aziridines, polyisocyanates, polytetrafluorethylene, perfluoropolyether, polyethylene and fumed silica.  
     
     
         7 . An electrochemical cell flow field plate as set forth in  claim 6  wherein the effective amount of said rheological modifier is from about 0.5% to about 15% by total weight of the system.  
     
     
         8 . An electrochemical cell flow field plate as set forth in  claim 5  wherein said conductive filler is an inorganic particulate filler and the amount of said conductive filler is at least 50 weight percent.  
     
     
         9 . An electrochemical cell flow field plate as set forth in  claim 8  wherein the filler is a graphite filler and the amount of said conductive filler is at least 65 weight percent.  
     
     
         10 . An electrochemical cell flow field plate as set forth in  claim 6 , wherein said Theological modifier comprises one or more of magnesium oxide, calcium oxide, magnesium hydroxide, and calcium hydroxide; and said effective amount is from about 0.1 to about 2 weight percent based on the weight of said composition.  
     
     
         11 . An electrochemical cell flow field plate as set forth in  claim 6 , wherein said Theological modifier is one or more of aziridine, carbodiamides, and an isocyanate and said effective amount is from about 1 to about 10 weight percent based on the weight of said composition.  
     
     
         12 . An electrochemical cell flow field plate as set forth in  claim 6 , wherein said effective amount of rheological modifier is an effective amount to prevent cracking of a part molded at a pressure from about 100 to about 5000 psi and to a thickness of from about 0.050 to about 0.200 inches.  
     
     
         13 . An electrochemical cell flow field plate as set forth in  claim 6 , wherein said Theological modifier comprises one or more of polytetrafluorethylene, and perfluoropolyether and said effective amount is from about 0.1 to about 5 weight percent based on the weight of said molding composition.  
     
     
         14 . An electrochemical cell flow field plate as set forth in  claim 6 , wherein said rheological modifier is an isocyanate and said effective amount is from about 2 to about 8 weight percent based on the weight of said molding composition.  
     
     
         15 . An electrochemical cell flow field plate as set forth in  claim 5  wherein said conductive filler is one or more of a synthetic crystalline graphite particle and a crystalline graphite particle, and said unsaturated prepolymer resin is one or more resins selected from the group consisting of epoxy vinyl resin, bisphenol fumarate resin, modified bisphenol fumarate polyester resin, unsaturated polyester resin, urethane modified vinyl ester resin, bisphenol-epoxy vinylester resin, elastomer-modified vinyl ester resin, epoxy novolac vinyl ester resin and unsaturated isocyanurate vinyl ester resin.  
     
     
         16 . An electrochemical cell flow field plate as set forth in  claim 15  wherein said copolymerizable material is one or more monomers selected from the group consisting of styrene, alpha-methyl styrene, chloro-styrene, vinyl toluene, divinyl benzene, diallylphthalate, and methyl methacrylate, and mixture thereof.  
     
     
         17 . An electrochemical cell flow field plate as set forth in  claim 16  wherein said copolymerizable material is one or more monomers selected from the group consisting of styrene and methyl methacrylate.  
     
     
         18 . An electrochemical cell flow field plate as set forth in  claim 5  wherein said initiator is a free radical initiator.  
     
     
         19 . An electrochemical cell flow field plate as set forth in  claim 18  wherein said initiator is selected from the group consisting of peroxides, hydroperoxides, redox systems, diazo compounds, persulfates, and perbenzoates, and is used in amounts of about 0.05 to about 5 weight percent based on the total weight of the system.  
     
     
         20 . An electrochemical cell flow field plate as set forth in  claim 19  further comprising carbon black.  
     
     
         21 . An electrochemical cell flow field plate as set forth in  claim 20  further comprising reinforcing fillers.  
     
     
         22 . A process for making a fuel cell plate having an intricate flow pattern molded therein comprising the steps of mixing a composition comprising; 
 a) an unsaturated prepolymer resin which comprises one or more of unsaturated polyester and vinyl ester resin;    b) an unsaturated material copolymerizable with said resin and including a terminal ethylene group;    c) an inorganic conductive filler in an amount sufficient to provide a bulk conductivity of at least 40 S/cm to the resulting fuel cell plate;    d) an initiator to initiate said copolymerization of said composition; and    e) a low profile additive; and    molding the composition to form said fuel cell plate having the pattern therein substantially without machining the pattern.    
     
     
         23 . A process as set forth in  claim 22  wherein said low profile additive is selected from the group selected from homopolymers of ethylene, styrene, vinyl toluene, alkyl methacrylates, polythylene ether, polyphenylene oxide and alkyl acrylates, vinyl chloride, vinyl acetate, acrylonitrile, and butadiene  
     
     
         24 . A process as set forth in  claim 22  wherein said low profile additive is selected from the group selected from copolymers of vinyl chloride and vinyl acetate; styrene and acrylonitrile; methyl methacrylate and alkyl esters of acrylic acid; methyl methacrylate and styrene; methyl methacrylate and acrylamide; and SBS block copolymers.  
     
     
         25 . A process as set forth in  claim 22  wherein said low profile additive is present in the amount of 10 to 50 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         26 . A process as set forth in  claim 22  wherein said low profile additive is present in the amount of 20 to 45 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         27 . A process as set forth in  claim 22  wherein said low profile additive is present in the amount of 30 to 40 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         28 . A process for making a fuel cell plate having an intricate flow pattern molded therein comprising the steps of mixing a composition comprising; 
 a) an unsaturated prepolymer resin which comprises one or more of unsaturated polyester and vinyl ester resin;    b) an unsaturated material copolymerizable with said resin and including a terminal ethylene group;    c) an inorganic conductive filler in an amount sufficient to provide a bulk conductivity of at least 40 S/cm to the resulting fuel cell plate;    d) a rheological modifier to prevent phase separation between said resin and said conductive filler during molding, said rheological modifier being one or more compositions selected from the group consisting of Group II oxides and hydroxides, carbodiamides, aziridines, polyisocyanates, polytetrafluorethylene, perfluoropolyether, polyethylene and fumed silica;    e) an initiator to initiate said copolymerization of said composition;    f) a low profile additive; and molding the composition to form said fuel cell plate having the pattern therein substantially without machining the pattern.    
     
     
         29 . A process as set forth in  claim 28  wherein said low profile additive is selected from the group selected from homopolymers of ethylene, styrene, vinyl toluene, alkyl methacrylates, polythylene ether, polyphenylene oxide and alkyl acrylates, vinyl chloride, vinyl acetate, acrylonitrile, and butadiene  
     
     
         30 . A process as set forth in  claim 28  wherein said low profile additive is selected from the group selected from copolymers of vinyl chloride and vinyl acetate; styrene and acrylonitrile; methyl methacrylate and alkyl esters of acrylic acid; methyl methacrylate and styrene; methyl methacrylate and acrylamide; and SBS block copolymers.  
     
     
         31 . A process as set forth in  claim 22  wherein said low profile additive is present in the amount of 10 to 50 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         32 . A process as set forth in  claim 28  wherein said low profile additive is present in the amount of 20 to 45 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         33 . A process as set forth in  claim 31  wherein said low profile additive is present in the amount of 30 to 40 weight percent based on the total weight of the additive and the resin system, i.e. the resin and any monomers.  
     
     
         34 . A process for making a fuel cell plate having an intricate flow pattern molded therein comprising the steps of mixing a composition comprising; 
 a) an unsaturated prepolymer resin which comprises one or more of unsaturated polyester and vinyl ester resin;    b) an unsaturated material copolymerizable with said resin and including a terminal ethylene group;    c) an inorganic conductive filler in an amount sufficient to provide a bulk conductivity of at least 40 S/cm to the resulting fuel cell plate; and    d) a mold release agent; and molding the composition to form said fuel cell plate having the pattern therein substantially without machining the pattern.    
     
     
         35 . A process as set forth in  claim 33  wherein said mold release agent comprises one or more of calcium stearate and zinc stearate.