Abstract:
A multi layer thermoplastic polymer alloy is provided. The multi layer alloy includes a skin of thermoplastic polymer alloy having non-polar segments and a tie-layer having non-polar segments and polar functional groups. The non-polar segments of the tie-layer are bondable with the non-polar segments of the thermoplastic polymer alloy skin. Similarly, the polar functional groups of the tie-layer are bondable or reactable with a surface layer.

Description:
TECHNICAL FIELD 
     This application relates to multi layer thermoplastic polymer alloy compositions including one or more tie-layers. This application further relates to methods of manufacturing such multi layer thermoplastic polymer alloy compositions. 
     BACKGROUND 
     Thermoplastic polymer alloy compositions have been developed to replace polyvinyl chloride for the fabrication of many articles. In the automotive field, thermoplastic polymer alloy (hereinafter TPA) compositions have been used for the fabrication of articles such as interior sheathing, including instrument panel skins, door panels, air bag covers, roof liners, and seat covers. In these applications, the interior sheathing includes a sheet or skin (hereinafter skin) made of the TPA composition. 
     The bottom surface of the skin is commonly adhered to a layer of foam padding, typically urethane foam. Similarly, the top surface of the skin is commonly painted to provide a desired appearance and scuff resistance. Prior to applying either the layer of foam or paint, the top and bottom surfaces of the skin are primed to increase adhesion with the foam and/or the paint. 
     The layer of foam padding is adhered to the skin by, for example, a foam-in-place process. During such a foam-in-place process, the skin is placed on mold cavity of a molding tool and the foam is introduced into the molding tool to fill the gap between the skin and a plastic retainer which is pre-inserted into the mold core. 
     SUMMARY 
     A multi layer thermoplastic polymer alloy is provided. The multi layer alloy includes a skin of thermoplastic polymer alloy having non-polar segments and a tie-layer having non-polar segments and polar functional groups. The non-polar segments of the tie-layer are bondable with the non-polar segments of the thermoplastic polymer alloy skin. Similarly, the polar functional groups of the tie-layer are bondable or reactable with a surface layer. 
     An interior sheathing for a vehicle is provided. The sheathing includes a multi-layer skin having a first layer and a second layer, and a layer of urethane foam. The first layer of the multi-layer skin is a layer of thermoplastic polymer alloy. The second layer of the multi-layer skin is a tie-layer. The thermoplastic polymer alloy layer has non-polar segments on a first side and a second side. The tie-layer has non-polar segments and polar functional groups. The non-polar segments of the tie-layer are bonded with the non-polar segments of the first side of the thermoplastic polymer alloy. The polar functional groups of the tie-layer are bonded to or reacted with the layer of urethane foam. 
     A method of forming a multi layer thermoplastic polymer alloy is provided. The method includes providing a thermoplastic polymer alloy skin, providing a tie-layer, disposing the tie-layer on a lower surface of the thermoplastic polymer alloy skin, and exposing the thermoplastic polymer alloy skin and the tie-layer to heat and pressure. The thermoplastic polymer alloy skin has non-polar segments. The tie-layer has non-polar segments and polar functional groups. The non-polar segments of the tie-layer are bondable with the non-polar segments of said thermoplastic polymer alloy skin. Similarly, the polar functional groups of the tie-layer are bondable or reactable with a layer of foam. 
     The above-described and other features and advantages of the present application will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic depiction of a paintable skin manufacturing process; 
     FIG. 2 is a cross sectional view of an interior sheathing using the paintable skin manufactured according to FIG. 1; 
     FIG. 3 is a schematic depiction of a paintless skin manufacturing process; 
     FIG. 4 is a cross sectional view of an interior sheathing using the paintless skin manufactured according to FIG. 3; 
     FIG. 5 is a schematic depiction of an exemplary embodiment of a multi-layer skin manufacturing process for co-extruding top and bottom tie-layers; 
     FIG. 6 is a schematic depiction of an alternate exemplary embodiment of a multi-layer skin manufacturing process for laminating top and bottom tie-layers; 
     FIG. 7 is a cross sectional view of an interior sheathing using the multi-layer skin manufactured according to FIG. 5 or  6 ; 
     FIG. 8 is a schematic depiction of an alternate exemplary embodiment of a multi-layer skin manufacturing process for co-extruding a bottom tie-layer; 
     FIG. 9 is a schematic depiction of an alternate exemplary embodiment of a multi-layer skin manufacturing process for laminating a bottom tie-layer; and 
     FIG. 10 is a cross sectional view of an interior sheathing using the multi-layer skin manufactured according to FIG. 8 or  9 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Some TPA skins are painted (e.g., paintable skins) before forming the interior sheathing. The painting process is labor intensive and accordingly adds to the overall manufacturing costs (e.g. labor, equipment and materials). The painting process includes applying a primer on a bottom surface of the skin, heat curing, applying a primer on a top surface of the skin, heat curing again, applying a paint coat and heat curing again. The primer on the top surface aids with adhesion of the paint coat to the skin, while the layer of primer on the bottom surface aids with adhesion of the layer of foam to the skin. 
     Paintable skins are commonly a blend of polypropylene, ethylene copolymer ionomer resin, ethylene glycidyl acrylate or methacrylate copolymer, and uncrosslinked ethylene propylene rubber. Alternately, paintable skins are a blend of polypropylene, ethylene copolymer ionomer resin, ethylene glycidyl acrylate or methacrylate copolymer, uncrosslinked ethylene propylene rubber, acid or anhydride grafted polypropylene, an agent for crosslinking the rubber and/or catalyzing an epoxide/acid reaction, and optionally, a poly-.alpha.-olefin. 
     Other TPA skins do not require painting (e.g., paintless skins). However, such paintless skins still require a primer on the bottom surface to aid adhesion with the layer of foam. These skins do not require further priming and painting of the top surface since the paintless skin provides the desired appearance and scuff and scratch resistance. The primer on the bottom surface of the skin aids with adhesion of the layer of urethane foam to the skin. The priming process, similar to painting process described above, is labor intensive and accordingly adds to the overall manufacturing costs (e.g. labor, equipment, and materials). 
     Paintless skins are commonly a blend of polypropylene, uncrosslinked ethylene copolymer, ionomeric copolymer of ethylene and .alpha.,.beta.-unsaturated C 3 -C 8  carboxylic acid, crosslinking agent, silicone elastomer, and may further comprise particulate filler, color concentrate and/or coloring pigment. 
     Referring now to the Figures and in particular to FIG. 1, a schematic depiction of a paintable skin manufacturing process is illustrated. In this process, components of the TPA are melt blended and pelletized to form pellets in precompounding extruder  10  to form pellets. In a separate step, the formed pellets are coextruded with, for example, color pigment, through extruders  12  and extruder  14 . 
     The extrudate  17  is passed through die  16  and embossing rollers  18  to form a skin  20 . Here, die  16  is a manifold die. Alternately and as shown in phantom, extrudate  17  is passed through a feed block  15 , then through die  16  and embossing rollers  18  to form skin  20 . 
     In order to provide the desired appearance and scuff and scratch resistance to skin  20  and in order to provide the skin with the desired adhesion capabilities to the foam, the skin is primed and painted. A primer  22  is applied to a bottom surface  24  of skin  20  followed by heating in an oven. A primer  26  is then applied to a top surface  28  of skin  20  followed by heating in an oven. Following application of the primer coats  22  and  26 , a topcoat of paint  30  is applied to top surface  28  of skin  20 , followed again by heating. Skin  20  is then transferred to rolls for forming articles therefrom. 
     An example of skin  20  used in the manufacture of an interior sheath  40  is illustrated in FIG.  2 . In this example, the rolls are then transferred to a foam-in-place process where a layer of foam  32  is integrated with skin  20  at primer  22 . Thus, primer  22  of skin  20  promotes adhesion of the skin with paint  30  and foam  32 . 
     Similarly, FIG. 3 is a schematic depiction of two alternate embodiments of a paintless skin manufacturing process. In a first embodiment, the TPA is compounded and co-extruded through extruder  52  and extruder  54 . Here, extruder  52  uses virgin or new material to form a cap layer, while extruder  54  uses regrind or recycled material to form a base layer. In a second embodiment, the TPA is compounded and co-extruded only with virgin material through extruder  52 . 
     In either embodiment, extrudate  57  is passed from extruder  52  and optionally extruder  54  through layer die  58  and through embossing rollers  18  to form skin  120 . Here, die  58  is a manifold die. Alternately and as shown in phantom, extrudate  57  is passed through a feed block  55 , then through die  58  and embossing rollers  18  to form skin  120 . 
     Skin  120  is transferred to rolls for forming articles of manufacture therefrom. Due to the inherent properties of the TPA, skin  120  provides the desired level of appearance and scuff and scratch resistance. Hence, skin  120  is a paintless skin. 
     An example of skin  120  used in the manufacture of an interior sheath  140  is illustrated in FIG.  4 . In this embodiment, skin  120  includes a bottom surface  124  and a top surface  128 . As discussed above, top surface  128  imparts sufficient color and wear characteristics to skin  120  so as to eliminate the need for expensive, time consuming priming steps for the top surface of the skin. However, a primer  122  is required at bottom surface  124  to promote the adhesion of skin  120  and a layer of foam  132 . Thus, skin  120  is provided to a foam-in-place process where layer of foam  132  is adhered to skin  120  at primer  122 . 
     It has been determined that a thin tie-layer can be added to skin  20  or  120  to form a multi-layer skin to eliminate the priming steps described above. Thus, skin  20  or  120  is provided with a multi-layer format that includes not only the skin, but also the tie-layer(s). In the use of paintable skin  20 , the tie-layer is disposed on the top and bottom of the skin where it is needed to aid with adhesion of a layer of foam and a layer of paint. However, in the use of paintless skin  120 , the tie-layer is disposed only on the bottom of the skin where it is needed to aid with adhesion of the layer of foam. 
     The tie-layer has dual functionality, namely it includes a high molecular weight polymeric chain that has non-polar segments, which bond with the non-polar segments of skin  20  or  120 , and it includes polar functional groups, which can either bond or react with the paint or layer of foam. 
     Accordingly, skin  20  or  120  with the tie-layer(s) eliminates the need for expensive, time consuming priming steps for the top and bottom surfaces of the skin. In the embodiment using paintable skin  20 , the incorporation of a top tie-layer and a bottom tie-layer eliminates the need for priming the top and the bottom sides of the skin. However in the embodiment using paintless skin  120 , the incorporation of the tie-layer is only needed at the bottom of the skin and eliminates the need for priming the bottom. 
     The tie-layer is a thin layer of a copolymer that is adapted to function as an adhesion promoter. More specifically, the tie-layer is a layer having a thickness between about 0.001 inches and about 0.01 inches disposed on the top surface and bottom surface of skin  20 , or disposed on the bottom surface of skin  120 , where the skin  20  and  120  has a thickness of about 0.04 inches. Preferably, the tie-layer has a thickness between about 0.001 inches and about 0.002 inches. 
     Of course, it should be recognized that as other applications require skin  20  and  120  and/or the tie-layer having thickness larger or smaller than described above are considered within the scope of the present invention 
     The tie-layer includes a polymeric chain that bonds with skins  20  and  120 . Moreover, in the application where skins  20  and  120  are used in conjunction with a urethane foam layer and/or a layer of paint, the tie-layer includes a polymeric chain that bonds or reacts with the urethane foam and/or the layer of paint. 
     In a first embodiment, the tie-layer is a styrenic copolymer such as, but not limited to, ethylene-styrene copolymers, generic acid copolymer and terpolymers, and vinyl acetate copolymers. In an alternate embodiment, the tie-layer is a copolymer having a reactive functional (di-function or tri-function) group. For example, the tie-layer is a copolymer having a reactive functional group such as, but not limited to, hydroxyl, maleic anhydride, amine, ionomer, urethane, isocyanate functional groups and epoxy. In a preferred embodiment, the tie-layer is maleic anhydride functionalized styrenic block copolymers and terpolymers. Accordingly, the tie-layer eliminates the need for expensive, time consuming priming steps for the top and bottom surfaces of skin  20  and for the bottom surface of skin  120 . 
     The tie-layer is disposed on the top and bottom surface of skin  20  and is disposed on the bottom surface of skin  120  by means such as, but not limited to co-extrusion, lamination, roller coating, spray coating and the like. 
     Referring now to FIG. 5, an exemplary embodiment of a co-extrusion process for a multi-layer skin  220  having the tie-layer described above and paintable skin  20  is illustrated. In this embodiment, multi-layer skin  220  includes paintable skin  20  co-extruded with a top tie-layer  222  and a bottom tie-layer  224 . 
     As described above with respect to FIG. 1, the components of skin  20  are precompounded in extruder  10  to form pellets. Additionally, the components of tie-layers  222  and  224  are precompounded in separate precompounding extruders  210  to form pellets. In a separate step, the formed pellets are co-extruded through extruders  12 ,  14  and  212 , respectively. 
     The extrudate  17 , which includes skin  20  and tie-layers  222  and  224 , is passed through die  16  and embossing rollers  18  to form multi-layer skin  220  consisting of skin  20 , tie-layer  222 , and tie-layer  224 . Here, die  16  is a manifold die. Alternately and as shown in phantom, extrudate  17  is passed through a feed block  15 , then through die  16  and embossing rollers  18  to form skin  220 . 
     Apart from the chemical bond formed between tie layers  222  and  224  and skin  20 , a mechanical bond is formed as a result of the heat and pressure multi-layer skin  220  is subjected to during processing by die  16  and embossing rollers  18 . 
     It should be recognized that co-extrusion of tie-layers  222  and  224  with skin  20  is an example of the formation of multi-layer skin  220 . Of course, and as other applications require, tie-layers  222  and  224  are disposed on skin  20  by other methods. For example, tie-layers  222  and  224  disposed on the top and bottom surface of skin  20  by means such as, but not limited to lamination, roller coating, spray coating and the like are considered within the scope of the present invention. 
     Referring now to FIG. 6, an exemplary embodiment of a laminating process for multi-layer skin  220  is illustrated. Here, tie-layer  222  and tie-layer  224  are formed into rolls separate from the extrusion of skin  20 . Tie-layers  222  and  224  are then fed into die  16  (or feed block  15  and then die  16 ) concurrent with the extrusion of extrudate  17  (e.g., skin  20 ) from extruders  12  and  14 . Again, apart from the chemical bond formed between tie layers  222  and  224  and skin  20 , a mechanical bond is formed as a result of the heat and pressure multi-layer skin  220  is subjected to during processing by die  16  and embossing rollers  18 . 
     Referring now to FIG. 7, an interior sheath  240  of multi-layer skin  220  is illustrated. Here, top tie-layer  222  is adapted to bond or react with a coat of paint  230  and bottom tie-layer  224  is adapted to bond or react with a foam layer  232 . Of course, it should be recognized that top tie-layer  222  being of either the same material as bottom tie-layer, or of differed material from that of bottom tie-layer  224  are considered within the scope of the present invention. Accordingly, it is seen that multi-layer skin  220  having top tie-layer  222  and bottom tie-layer  224  disposed on skin  20  eliminates the need for expensive, time consuming priming steps for the top and bottom surfaces. 
     Referring now to FIG. 8, an exemplary embodiment of a co-extrusion process for a multi-layer skin  320  incorporating the tie-layer described above and paintless skin  120  is illustrated. Multi-layer skin  320  includes paintless skin  120  having a bottom tie-layer  324 . 
     As described above with respect to FIG. 3, the components of skin  120  are compounded and co-extruded through either extruders  52  and  54  (e.g., cap of virgin material and a base of regrind material) or extruder  52  only (e.g., skin  120  of complete virgin material). The components of tie-layer  324  are compounded in extruder  352 . 
     In either embodiment, extrudate  57 , which includes tie-layer  324 , is passed from extruders  52 ,  54 , and  352  through layer die  58  and through embossing rollers  18  to form multi-layer skin  320 . Here, die  58  is a manifold die. Alternately and as shown in phantom, extrudate  57  is passed through a feed block  55 , then through die  58  and embossing rollers  18  to form skin  120 . 
     Apart from the chemical bond formed between tie layer  324  and skin  120 , a mechanical bond is formed as a result of the heat and pressure multi-layer skin  320  is subjected to during processing by die  58  and embossing rollers  18 . 
     Referring now to FIG. 9, an exemplary embodiment of a laminating process for multi-layer skin  320  is illustrated. Here, tie-layer  324  is formed into rolls separate from the extrusion of skin  120 . Tie-layer  324  is then fed into die  58  (or feed block  55  and then die  58 ) concurrent with the extrusion of extrudate  57  (e.g., skin  120 ) from extruders  52  and  54  (or only extruder  52 ). Again, apart from the chemical bond formed between tie layer  324  and skin  120 , a mechanical bond is formed as a result of the heat and pressure multi-layer skin  320  is subjected to during processing by die  58  and embossing rollers  18 . 
     It should be recognize that disposal of the tie-layer on the bottom surface of skin  120  is described above by way of example as a co-extrusion or a lamination process. Of course, and as other applications require the tie-layer is disposed on the bottom surface of skin  120  by means such as, but not limited to roller coating, spray coating, and the like. 
     Referring now to FIG. 10, multi-layer skin  320  used in an interior sheath  340  is illustrated. Here, bottom tie-layer  324  is adapted to bond or react with a foam layer  332 . Accordingly, it is seen that multi-layer skin  320  having bottom tie-layer  324  disposed on skin  120  eliminates the need for expensive, time consuming priming steps for the bottom surface. 
     By way of example, adhesion between the skin and the foam layer is tested using a peel test, where the skin is peeled from the foam at an angle of 180°. The adhesion is deemed acceptable if the foam layer splits or tears when pulled away from the skin (e.g., some of the foam remains adhered to the skin). Such peel tests are often performed after exposure to temperature cycles commonly experienced by automotive interiors. Thus, tie-layer  224  and  324  provides adhesion to foam layer  232  and  332  sufficient to meet and exceed such post exposure cycling peel tests. 
     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.