Abstract:
An extruded seal member having a corrugated axial surface exhibiting alternating peaks and valleys extending longitudinally along the axial surface of the seal member; a method for manufacturing the seal member which comprises extruding a tubular structure having a corrugated axial surface, crosslinking the extrude tubular structure, cutting the tubular structure to provide a plurality of uniform seal members and recovering the seal members; and a method of using such multilayer seal members, are described.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to seals, and more particularly to multilayer, extruded seals having improved physical characteristics and reduced permeability to fuel vapors, and to a method for the manufacture of such seals as well as to the use of such seals in automotive fuel system components such as an air intake manifold. 
     In recent years there have been numerous restrictions and regulations imposed upon manufacturing industries in general and particularly upon automotive manufacturers, which are intended to reduce the amount of potentially harmful contaminates from being released into the environment by such industries. In the automotive industry, such regulations and restrictions severely limit the amount of hydrocarbon fuel vapor and other chemical materials that can permeate from of motor vehicles. Typically, the various seals employed in the automotive industry are used in grooves for maintaining the seal member in place. Typically, the seal members are molded and are composed of fluoroelastomer rubber materials. However, these molded fluoroelastomer seal members are expensive to manufacture due, in part, to the slow production cycling time and, in part, to the expensive tooling required for the manufacture of such molded seal members. For example, molded seal members typically have retention features located on both the inside and outside of the part for retaining the seal member in a seal groove. This works well, but creates more exacting tolerances in the width of the seal member as well as the height of the seal. Since it is the height of the seal, rather than the width, that is responsible for the sealing function, exact width tolerances are not critical in most sealing functions. Furthermore, such molded seals are prone to excess parting line flash which can lead to a separate operation to remove the parting flash from each individual seal. In some instances the parting flash may be severe enough to lead to total rejection of the seal members. 
     Accordingly, there is a need in the automotive industry for an improved fuel system seal which meets industry standards and a method for manufacturing automotive seals which overcomes the high costs and manufacturing problems associated with the manufacture of prior seal members. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a rigid seal member having the desired characteristics which meet the present industry permeation standards and which is relatively inexpensive to manufacture is provided by extruding a tubular structure wherein the tubular structure has a corrugated axial surface exhibiting a plurality of alternating peaks and valleys longitudinally around the axial surface of the tubular structure; crosslinking the tubular structure; and cutting the tubular structure to obtain a seal member having an irregular profile configuration which exhibits alternating peaks and valleys in an axial direction circumferentially around the inner and outer surfaces of the seal member. 
     The materials employed in the manufacture of the seal member in accordance with the invention, is one of those materials that will provide the desired performance characteristics to the seal member. Generally, the seal member will comprise a fluoroelastomer. Typically, the seal member of the present invention will comprise a single layer of fluoroelastomer; however, other layer may be employed. For example, the seal member may comprise a first layer of an fluoroelastomer and a second elastomeric layer which is typically a non-fluoroelastomer disposed on the outer surface of the first fluoroelastomer layer. 
     The seal member is manufactured by extruding an elongated, tubular structure having a corrugated circumferential surface, i.e., a circumferential surface that exhibits a plurality of alternating peaks and valleys extending longitudinally along the X-axis. The term tubular structure as used herein is meant to include a structure exhibiting annular, oval, elliptical, rectangular, square or any other shape along its longitudinal axis. After the tubular structure has been formed, it is crosslinked and then cut to form a seal member having a predetermined corrugated structure exhibiting a plurality of alternating peaks and valleys extending along and defining the inner and outer surfaces of the seal member in an axial direction. 
     The seals of the present invention are rigid, have stability over a wide temperature range and exhibit a low compression set resistance. Since it is the width of the seal member, not the circumference, which creates the seal, the seal member doe not require exact circumferential tolerances. In accordance with the invention, the present corrugated seal members not only have the ability to readily adjust to the shape of the seal-groove upon being disposed therein, but the corrugated configuration allows the seal member to exert resilient pressure at sequential points along both sides of the seal-groove providing a rigid and stable seal between the air intake manifold and the engine. Therefore, the need for expensive tooling and other costly manufacturing procedures associated with molded seal members can be eliminated. For example, the extruded seals of the present invention are free of excess flashing commonly associated with the manufacture of molded seals. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a single layer seal member of the present invention; 
         FIG. 2  is a fragmentary perspective view of a single layer tubular structure on a mandrel with portions of the single layer of the tubular structure broken for purposes of illustration; 
         FIG. 3  is a plan view illustrating the formation of the seal member of  FIG. 1  from the tubular structure of  FIG. 2  using a lathe; 
         FIG. 4  is a cross sectional view of a multilayer layer seal member of the present invention; 
         FIG. 5  is a fragmentary perspective view of a Multilayer layer tubular structure on a mandrel with portions of the various layers of the tubular structure broken for purposes of illustration; 
         FIG. 6  is a plan view illustrating the formation of the seal member of  FIG. 4  from the tubular structure of  FIG. 5  using a lathe; 
         FIG. 7  is a cross-sectional plan view of a typical air intake manifold port having a seal member of the present invention disposed therein; and 
         FIG. 8 . illustrates an automotive air intake manifold sealed to an automotive engine using a seal member of the present invention disposed therein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Elastomeric seal members for use in automotive fuel systems to prevent the release of hydrocarbon fuel vapors into the atmosphere are generally made out of a fluoroelastomer material by a molding process which is expensive and requires time-consuming steps. The automotive seal members of the present invention are extruded multilayer seals which are not only superior to prior art seals, but are more economical to produce, are more rigid while still retaining sufficient resilience to provide excellent sealing characteristics. Furthermore, it is widely known that seal members are typically employed in a seal groove to secure the seal member in place. Prior to the present invention the only way that the seal member could be secured in the seal-groove was through modification of the seal-groove. This solution is unacceptable because of the high cost of such modifications. It has now been found that if the seal member is manufactured to have an irregular surface such as an alternating peak and valleys profile around the outer and inner surfaces of the seal member, exact tolerances of the width of the seal member is unnecessary because the peaks and valleys which make up the axial outer surface of the seals allow the seal to easily seat in the groove even if the seal member does not exactly meet the tolerances of the groove. 
     According to the invention, a first manifestation of the seal member comprises an extruded fluoroelastomer tubular seal member exhibiting a plurality of alternating peaks and valleys such that the seal has a corrugated shape. The seal also has a first tubular rim surface forming a first lateral side of the seal, a second tubular rim surface forming a second lateral side of the seal, wherein the first lateral side is diametrically opposite the second lateral side. In a second manifestation of the present invention, the seal member is an extruded multilayer seal member comprising a first inner fluoroelastomer and a second outer elastomer which is typically a non-fluoroelastomer disposed adjacent the first inner fluoroelastomer. Each of the first fluoroelastomer and the second elastomer exhibit a corrugated surface having alternating peaks and valleys in an axial relationship around the seal member. Typically, a fluoroelastomer material having a very low hydrocarbon fuel permeation rate forms the inner structural surface of the seal which is nearest to the hydrocarbon fuel of the automotive fuel system. The second elastomer is formed adjacent the inner fluoroelastomer material and exhibits improved physical characteristics. 
     Referring to the drawings,  FIGS. 1-3  are representative of one embodiment of the invention where a seal member  10  exhibits a generally rectangular configuration and exhibiting a corrugated profile having a plurality of alternating peaks  20  and valleys  22  in the axial direction. While the seal member  10  is shown as having a rectangular configuration, it may take any other desirable shape or configuration as described below. The seal member  10  comprises a fluoroelastomer material  12  forming a corrugated surface  14  of the seal member  10 . The seal member  10 , as shown in  FIG. 1 , exhibits an annular profile having a notch  24  which represents a deviation from the otherwise corrugated interior and exterior surfaces. The notch  24  may or may not be present in every seal member and may or may not take the shape illustrated in  FIG. 1 . It is to be understood that the notch  24  and its particular shape will be determined by the general shape of the fuel injector  42  ( FIG. 7 ) in the fuel system component for accepting the seal  10 , and may be different from that shown in  FIG. 1 . 
       FIG. 2  illustrates a tubular structure  26  from which the seal member  10  of  FIG. 1  is formed, on a mandrel  28 . A conventional extrusion process such as co-extrusion or tandem extrusion forms the tubular structure  26 , from which the seal members  10  are fabricated. According to the invention, the extruded tubular structure  26  is placed on a mandrel  28  having the desired configuration for forming the corrugated seal member  10 . The tubular structure  26  is crosslinked on the mandrel  28  to set the shape of the tubular structure  26  and the tubular structure  26  is then cut into a plurality of seal members  10  having the desired shape and width. 
     As illustrates in  FIG. 3 , a tubular structure  26  is cut into a plurality of seal members  10  using a lathe  30  having a blade  32  associated therewith. According to the invention, the extruded tubular structure  26  of  FIG. 2  is placed on a mandrel  28  having the requisite configuration for forming the seal member  10 . The tubular structure  26  is crosslinked on the mandrel  28  to set the shape of the tubular structure  26  and the tubular structure is then cut into a plurality of seal members  10  having the desired shape and dimensions. The tubular member  26  may be cut sequentially to form the seal members  10  one at a time using a single blade, or a plurality of the seal members may be formed simultaneously using a plurality of precisely spaced apart blades. 
       FIG. 4  illustrates another embodiment of the invention where the seal member is a multilayer seal member where seal member  10 ′ exhibits a generally rectangular configuration and exhibiting a corrugated profile having a plurality of alternating peaks  20 ′ and valleys  22 ′ in the axial direction. Again, while the seal member  10 ′ is shown as having a rectangular configuration, it may take any other desirable shape or configuration. The seal member  10 ′ comprises first elastomer material  12 ′ forming an interior corrugated surface  14 ′ of the seal member  10 ′ and a second non-fluoroelastomer material  16 ′ forming an exterior corrugated surface  18 ′ of the seal member  10 ′, and an optional intermediate layer  17 ′ of a fluoroplastic material between the first fluoroelastomer layer  12 ′ and the second non-fluoroelastomer layer  16 ′. The seal member  10 ′, as shown in  FIG. 4 , exhibits an annular profile having a notch  24 ′ which represents a deviation from the otherwise corrugated interior and exterior surfaces. The notch  24 ′ may or may not be present in every seal member and may or may not take the shape illustrated in  FIG. 4 . It is to be understood that the notch  24 ′ and its particular shape will be determined by the general shape of the fuel injector  42  ( FIG. 7 ) in the fuel system component for accepting the seal  10 ′, and may be different from that shown in  FIG. 4 . 
       FIG. 5  illustrates the formation of an extruded multilayer structure  26 ′ having an inner fluoroelastomer layer  12 ′, an outer elastomer layer  16 ′ and an optional intermediate fluoroplastic barrier layer  17 ′ is placed around a mandrel  28 ′ having the desired corrugated configuration and the tubular structure  26 ′ is then crosslinked to permanently establish the desired configuration. 
     The tubular structure  26 ′ has a longitudinal axis X from which the multilayer seal member  10 ′ of  FIG. 4  is formed. A conventional extrusion process such as co-extrusion or tandem extrusion forms the tubular structure  26 ′, from which the seal members  10 ′ are fabricated. According to the invention, the extruded multilayer tubular structure  26 ′ is placed on a mandrel  28 ′ having the desired configuration for forming the corrugated seal member  10 ′. The tubular structure  26 ′ is crosslinked on the mandrel  28 ′ to set the shape of the tubular structure  26 ′ and the tubular structure  26 ′ is then cut into a plurality of seal members  10 ′ having the desired shape and width. 
     As illustrated in  FIG. 6 , a tubular structure  26 ′ which includes a barrier layer  17 ′ between the fluoroelastomer layer  12 ′ and the non-fluoroelastomer layer  16 ′ is cut to provide a single member  10 ′ using a lathe  20 ′. The tubular structure  26 ′ having a longitudinal axis X from which the seal member  10 ′ of  FIG. 2  is formed by conventional extrusion such as co-extrusion or tandem extrusion. According to the invention, the extruded multilayer tubular structure  26 ′ of  FIG. 5  is placed on a mandrel having the requisite configuration for forming the seal member  10 ′. The tubular structure  26 ′ is crosslinked on the mandrel  28 ′ to set the shape of the tubular structure  26 ′ and the tubular structure is then cut into a plurality of seal members  10 ′ having the desired shape and width. The tubular member  26 ′ may be cut sequentially to form the seal members one at a time ( FIG. 6 ) using a single blade, or a plurality of the seal members may be formed simultaneously using a plurality of precisely spaced apart blades. 
     The extruded multilayer tubular structure  26 ′ having an inner fluoroelastomer layer  12 ′, an outer elatomer layer  16 ′ and an optional intermediate fluoroplastic barrier layer  17 ′ is placed around a mandrel  28 ′ having the desired corrugated configuration and the tubular structure  26 ′ is then crosslinked to permanently establish the desired configuration. 
       FIG. 7  shows the seal member  10  in a seal groove  36  wherein said seal member  10  is positioned in the groove  36  for sealing an air intake manifold  38  to an automotive engine  40 . The seal member  10  includes a notch  24  having a general shape corresponding to a fuel injector  42 . 
     The individual layers of the extruded multilayer tubular structure and the seal members manufactured there from include at least one fluoropolymer material and at least one non-fluoropolymer material. Preferably, the first polymer layer is an FKM fluoropolymer and the second polymer layer, or outer layer, is a non-fluoropolymer. 
       FIG. 8  illustrates an automotive air intake manifold  38  sealed to an automotive engine  40  wherein the seal member  10  is disposed in the air intake manifold groove  36 . 
     The polymeric material, that forms the extruded tubular structure and, ultimately, the seal member, is a fluoroelastomer such as an FKM fluoroelastomer. FKM fluoropolymers are commonly referred to as fluoroelastomers or fluoro rubbers of the polymethylene type that utilizes vinylidene fluoride as a co-monomer and has substituent fluoro, alkyl, perfluoroalkyl or perfluroalkoxy groups on the polymer chain with or without a cure site monomer (having a reactive cure site). Generally, FKM fluoropolymers include dipolymers of hexafluoropropylene and vinylidene fluoride; terpolymers of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene; terpolymers of tetrafluoroethylene, fluorinated vinyl ether and vinylidene fluoride; terpolymers of tetrafluoroethylene, propylene and vinylidene fluoride; and pentaflluoropolymers of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, ethylene, and a fluorinated vinyl ether. Preferably, the FKM fluoropolymers of the present invention are fluoroelastomers selected from the group consisting of a polyvinylidene tetrafluoride, polyvinylidene trifluoride, polyvinylidene difluoride, polyvinyl Amendments to the Drawings are shown at page 7 of this paper. 
     In some instances, it may be desirable to use certain fluoroelastomers which have an affinity for hydrocarbons, such as fluorosilicone elastomer, as an inner material covered with a second fluoroelstomer material to provide the first fluoroelastomer layer of the seal member, and a non-fluoroelastomer as the outer layer of the seal member, whereby the fluorosilicone material would adsorb the hydrocarbons which would then be purged from the fluorosilicone when the engine is running. 
     The non-fluoropolymer material which forms the outer surface of the extruded tubular structure and, ultimately, the seal member is an elastomer selected from the group consisting of an ethylene-acrylic copolymer (AEM), a polyacrylate (ACM), an ethylene-vinyl acetate rubber (EVM), a nitrile-butadiene rubber (NBR), a hydrogenated nitrile-butadiene rubber (HNBR), an ethylene-propylene-diene terpolymer (EPDM), a polybutadiene, a polyisoprene, a silicone rubber, and the like, and blends thereof. Preferably, the second elastomer that forms the outer layer of the seal member is an ethylene-acrylic copolymer. 
     An optional barrier layer may be employed between the first FKM fluoroelastomer layer and the second elastomer layer to prevent or significantly reduce the permeation of hydrocarbon fuel vapors to the atmosphere. Typically, the intermediate barrier layer is a thin layer of a fluoroplastic material such as tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV), polyvinylidene fluoride, ethylene-fluoroethylene-propylene (EFEP), fluoroethylene-propylene (EFP), ethylene-tetrafluoroethylene (ETFE), and the like. Preferably, the intermediate barrier layer is a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (THV). 
     It may be desirable, in some instances, to further enhance the adherence of the first FKM fluoroelastomer layer to the THV fluoroplastic intermediate barrier layer, and/or between the THV fluoroplastic barrier layer and the second non-fluoroelaxtomer layer by applying a suitable adhesive between such layers. The adhesive may be any of those adhesives conventionally used to adhere such polymeric structures together. Typically, the adhesive is an amine-based adhesive. 
     The thicknesses of the various layers of the seal member depend upon the extrusion process and are not considered to be absolutely critical to the effectiveness of the seal. However, the first polymer layer which preferably is a fluoroelastomer forming the inner layer of the tubular structure, typically has a thickness of about 0.1 to 5 mm and, preferably about 0.2 to 2 mm; and the second polymer layer which, preferably is an elastomer forming the outer layer of the tubular structure, typically has a thickness of about 0.1 to 5 mm and, preferably, about 0.2 to 2 mm. 
     The width of the seal member which is responsible for the effectiveness of the seal is predetermined and depends upon the particular use of the seal member. The width of the seal member is measured from the outer rim surface of one lateral side of the seal member to the outer rim surface of the other lateral side of the seal member. To be effective, the seal member has a width which is greater than the depth of the seal groove. Typically, the width of the seal member ranges from about 1 to 30 mm and, preferably about 3 to 20 mm. 
     According to a preferred method for the manufacture of the seal members of the invention, a multilayer tubular structure having an irregular surface is first extruded to form a multilayer tubular structure having the desired irregular surface, crosslinked, and then cut into individual seal members wherein each of the seal members exhibit an inner surface and an outer surface configuration having a plurality of alternating peaks and valleys in the axial direction. 
     After the multilayer tubular structure is formed, the structure is crosslinked in the presence of a peroxide, a polyol, a dihydroxy, a bisphenol, a polyamine, and the like, or a mixture thereof. Preferably, the crosslinking agent is a peroxide selected from the group consisting of dicumyl peroxide, 2,5-dimethyl-2,5(t-butylperoxy)-hexene-3; 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, 1,1-bis(t-butylperoxy)-hexene-3, t-butylperoxybenzoate, dibenzoyl peroxide; t-butylperbenzoate; and mixtures thereof. In some instances it may be desirable to use a co-agent in combination with the peroxide crosslinking agent. Suitable co-agents include triallyl cyanurate, triallyl isocyanate, tri-methallyl-isocyanate, tris (diallylamine-s-triazine, triallyl) phosphate, and the like and mixtures thereof. 
     Upon being crosslinked, the multilayer tubular structure is uniformly cut into a plurality of predetermined seal members as described above wherein each of the seal members exhibit an inner surface and an outer surface having a plurality of alternating peaks and valleys, configurations, and recovered for use in various applications requiring little or no hydrocarbon fuel vapor permeation. The seal members of the present invention having stability at wide temperature ranges and low compression set resistance are useful in the automotive industry, particularly in automotive fuel systems where reliability and reduced hydrocarbon fuel vapor permeation are desired. A preferred application for the seal members of the invention is in an automotive fuel system wherein the seal is disposed between the air intake manifold and the automotive engine. 
     Various pigments and/or other colorants as well as other conventional additives may be added to the first fluoroelastomer material and/or to the second elastomer material to meet certain desirable specifications. For example, one of the elastomer layers may be colored a particular color and the other elastomer layer colored a different color. Typically, the outer elastomer layer is black and the inner fluoroelastomer layer is of a color other than black. 
     While the present invention has been fully described and illustrated herein, it is to be understood that certain variations, changes and modifications may be made to the invention without departing from the spirit and scope of the invention as defined by the appended claims.