Multi-layered composite article

Abstract

A composite article is used in commercial and residential decking. The composite article includes a first layer including a thermoplastic resin and a cellulosic fiber. The composite article also includes a second layer including a styrene butadiene copolymer that is disposed in contact with the first layer. The composite article further includes a third layer consisting essentially of styrene acrylonitriles and disposed in contact with the second layer as an outermost layer of the composite article. The thermoplastic resin and cellulosic fiber contribute to shear strength and compressive strength. The styrene butadiene copolymer, as a tie layer, contributes to an ability of the first layer to bond to the third layer. The styrene acrylonitriles contribute to ultraviolet light resistance, moisture resistance, mold resistance, weatherability, and resistance to warping and surface distortion, and allow the composite article to be used in outdoor environments.

Description

FIELD OF THE INVENTION

The present invention generally relates to a multi-layered composite article. More specifically, the present invention relates to a unique multi-layered composite article used as a deck board which includes a first layer of a thermoplastic resin and a reinforcing fiber, a second layer including a styrene butadiene copolymer, and a third layer consisting essentially of styrene acrylonitriles.

DESCRIPTION OF THE RELATED ART

Various composite articles have been used in commercial and residential construction as boards, planks, posts, and joists. Other composite articles have been used as exterior siding, roofs, shutters, doors, and window lineals. Some of the composite articles include thermoplastic and/or thermoset resins and do not effectively weather or resist fading, staining, scratching and marring, or mold and mildew.

Efforts have been made in the past to increase weatherability of composite articles. However, these efforts have not included composite articles used in either commercial or residential decking applications. One effort is disclosed in U.S. Pat. No. 5,306,548 to Zabrocki et al. The '548 patent discloses a multi-layered film including polystyrene and polyethylene in a first layer, styrene butadiene copolymer in a second layer, and acrylonitrile styrene acrylate in a third layer. The multi-layered film is used as vinyl siding, plastic shutters, doors, and windows. There is no reinforcing fiber included in the first layer and the multi-layered film is not used in commercial or residential decking applications. The lack of the reinforcing fiber in the first layer hinders an ability of the film to be used in load bearing applications such as boards, planks, posts, and joists due to insufficient structural stability and potential failure. As such, the multi-layered film is not suitable for use in decking applications.

Another similar effort is disclosed in U.S. Pat. No. 5,334,450, also to Zabrocki et al. The '450 patent discloses a multi-layered film applied to a substrate. The film includes an ethylene copolymer adhesive in a first layer, styrene butadiene copolymer in a second layer, and acrylonitrile styrene acrylate in a third layer. The substrate to which the multi-layered film is applied includes wood, plastic, or polymers. The multi-layered film and substrate are used in exterior siding, in metal roofs, in plastic shutters, door, window lineals, and in automotive coatings. There is no reinforcing fiber included in the first layer and the multi-layered film is not used in load bearing applications or in commercial or residential decking applications. Like the '548 patent, the lack of the reinforcing fiber in the first layer hinders an ability of the film to be used in load bearing application such as boards, planks, posts, and joists due to insufficient structural stability and potential collapse. As such, the multi-layered film is not suitable for use in decking applications.

Yet another effort is disclosed in U.S. Pat. No. 6,844,071 to Wang et al. The '071 patent discloses a multi-layer article including polypropylene and a reinforcing fiber in a first layer, styrene butadiene copolymer in a second layer, and a mixture of polycarbonate and acrylonitrile styrene acrylate in a third layer. The polycarbonate of the third layer materially affects the basic and novel weathering characteristics of the acrylonitrile styrene acrylate, when blended, thereby reducing the weatherability of the acrylonitrile styrene acrylate and reducing an ability of the blend to be used in outdoor environments. When used in building and construction applications, the polycarbonate does not effectively resist weathering. In fact, the polycarbonate fades easily over time. The multi-layer article is not used in commercial or residential decking applications or as posts, beams, or joists. Instead, the multi-layer article is used in building and construction applications including flooring. Although use of the multi-layer article in flooring is disclosed, the '071 patent focuses on use of the multi-layered article in non-load bearing applications such as in panels and housings.

An additional effort is disclosed in U.S. patent application Ser. No. 2004/0175593 to Davis et al. The '593 publication discloses a multi-layer laminate bonded to a substrate. The multi-layer laminate includes a first layer including resorcinol, a second layer including acrylonitrile styrene acrylate, a third layer including styrene butadiene copolymer. The substrate includes a thermoplastic material and includes reinforcing fibers. The multi-layer laminate is used in exterior automotive panels such as door panels, roofs, and hoods. The multi-layered laminate is not used in commercial or residential decking applications or in load bearing applications such as posts, beams, or joists. The multi-layered laminate does not have an outer layer including the acrylonitrile styrene acrylate. Specifically, resorcinol, like the polycarbonate described above, does not resist fading or staining, and does not resist mold and mildew growth over time. Therefore, the multi-layered laminate is not desirable for use in outdoor environments because it does not have suitable weatherability.

Aside from weatherability, efforts have also been made in the past to increase strength of composite articles that are used in decking applications. One effort is disclose in U.S. Pat. No. 6,844,040 to Pabedinskas et al. The '040 patent discloses a composite article having first and third layers including a thermoplastic material and the third layer including reinforcing fibers. The '040 patent also discloses a second layer that functions as a tie layer between the first and third layers. The thermoplastic material of the first and/or third layers includes polycarbonate, polyetheretherketone, polyoxymethylene, polyphenylene sulfide, polyethylene, polypropylene, polystyrene, and/or polyvinyl chloride. However, styrene butadiene copolymer is not used in the second layer and styrene acrylonitriles are not used in the third layer. Specifically, the thermoplastic materials fade and stain and are subject to scratching, marring, and the growth of mold and mildew. Therefore, the composite article is not desirable for use in outdoor environments.

Although composite articles have been used in commercial and residential construction in the past, there remains an opportunity for a composite article to be formed that has excellent physical properties such as structural stability including shear and compressive strength, chemical resistance, impact resistance, heat stability, scratch and mar resistance, moisture, mold, and mildew resistance, ultraviolet light resistance, fade resistance, stain resistance, and resistance to warping and surface distortion. There also remains an opportunity for the composite article to be easily processed.

SUMMARY OF THE INVENTION AND ADVANTAGES

The present invention provides a composite article. The composite article includes first, second, and third layers. The first layer includes a thermoplastic resin and a reinforcing fiber. The second layer includes a styrene butadiene copolymer. The third layer consists essentially of styrene acrylonitriles. The second layer is disposed on the first layer and the third layer is disposed on the second layer as an outermost layer of the composite article.

In an alternative embodiment, the first layer includes a cellulosic fiber. The second layer is disposed in contact with the first layer. The third layer disposed is disposed in contact with the second layer as the outermost layer of the composite article.

The present invention further provides a method of making the composite article. The method includes the step of forming the first layer including the thermoplastic resin and the reinforcing fiber. The method also includes the step of forming the second layer including the styrene butadiene copolymer, on the first layer. The method further includes forming the third layer on the second layer. The third layer consists essentially of styrene acrylonitriles and is an outermost layer of the composite article.

The composite article of the present invention has excellent physical properties including structural stability including shear and compressive strength, chemical resistance, impact resistance, heat stability, scratch and mar resistance, moisture, mold, and mildew resistance, ultraviolet light resistance, fade resistance, stain resistance, and resistance to warping and surface distortion. The composite article is also easily processed. The thermoplastic resin and the reinforcing fiber in the first layer contribute to the shear strength and compressive strength of the composite article. The styrene butadiene copolymer in the second layer contributes to an ability of the first layer to bond to the third layer, with the second layer as a tie layer. The styrene acrylonitriles in the third layer contribute to the chemical resistance, impact resistance, heat stability, scratch and mar resistance, moisture, mold, and mildew resistance, ultraviolet light resistance, fade resistance, stain resistance, and resistance to warping and surface distortion, of the composite article. The styrene acrylonitriles in the third layer also contribute to an ability of the composite article to be used in outdoor environments. The particular first, second, and third layers all contribute to the ease of processing of the composite article.

The styrene acrylonitriles allow the composite article of the present invention to be utilized in both indoor environments and outdoor environments. Such outdoor environments include, but not limited to, tropical, dry, and temperate climates. The composite article may be utilized in horizontal, angled, or vertical positions, in load-bearing and in non load-bearing applications, and is resistant to shearing, compression, and bending.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is an environmental view of a deck including a composite article according to the present invention;

FIG. 2 is a cross-sectional view of the deck of FIG. 1 including the composite article;

FIG. 3 is an exploded cross-sectional view of a first embodiment of the present invention;

FIG. 4 is an exploded cross-sectional view of a second embodiment of the present invention;

FIG. 5 is a partial cross-sectional perspective view of a third embodiment of the present invention;

FIG. 6 is a partial cross-sectional perspective view of a fourth embodiment of the present invention;

FIG. 7 is a partial cross-sectional perspective view of a fifth embodiment of the present invention;

FIG. 8 is a partial cross-sectional perspective view of a sixth embodiment of the present invention;

FIG. 9 is a bar graph illustrating a color shift of the composite article and comparative articles as a function of months of weathering exposure;

FIG. 10 is a bar graph illustrating a stain value of the composite article and the comparative articles as a function of stain type; and

FIG. 11 is a bar graph illustrating a scratch value of the composite article and the comparative articles as a function of weight.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a composite article (20) and a method of forming the composite article (20). The method of forming the composite article (20) is described in greater detail below. The composite article (20) may be used in a wide variety of industries including, but not limited to, commercial and residential construction and decking applications, and may be a deck board. The composite article (20) may be used alone or may be used as a component in larger structures, may be hollow, semi-solid, or solid, and may be utilized in horizontal, angled, or vertical positions, in both load-bearing and non load-bearing applications. The composite article (20) may also be used in both indoor environments and outdoor environments. The outdoor environments include, but are not limited to, tropical, dry, and temperate climates. In various embodiments of the present invention, the composite article (20) may include, but is not limited to, boards (42), footings, posts (44), beams, joists, planks, rails (46), spindles (48), stringers (50), studs, balusters, caps (52), panels (54), doors, fascia, and combinations thereof. In one embodiment, as shown in FIG. 1, the composite article (20) includes boards (42), posts (44), rails (46), spindles (48), a stringer (50), a cap (52), and panels (54) of a deck (40). The composite article (20) may also be any shape including, but not limited to, cubic, trapezoidal, and cylindrical. In one embodiment, the composite article (20) mimics common shapes of commercially available lumber, as is known in the art. One skilled in the art will select an appropriate shape based on necessity, aesthetic qualities, and desire.

The composite article (20) includes a first layer (22), a second layer (28), and a third layer (34), as shown in FIGS. 2 through 8. The first layer (22) includes a thermoplastic resin and a reinforcing fiber. The thermoplastic resin may be included in the first layer (22) in any amount. In various embodiments, it is contemplated that the thermoplastic resin may be included in the first layer (22) in amounts of greater than 30 parts by weight per 100 parts by weight of the first layer (22). Preferably, the thermoplastic resin may be included in the first layer (22) in an amount of from 30 to 90, more preferably of from 40 to 80, and most preferably of from 40 to 60, parts by weight per 100 parts by weight of the first layer (22).

The thermoplastic resin may include any thermoplastic resin known in the art. However, the thermoplastic resin is preferably selected from the group of polyalkylenes, polyaromatics, and combinations thereof. It is contemplated that the polyaromatics include, but are not limited to, aromatic compounds that have been polymerized. More preferably, the thermoplastic resin is selected from the group of polyethylene, polypropylene, and combinations thereof. In one embodiment, the thermoplastic resin includes polyethylene. The polyethylene is commercially available from Dow Chemical of Midland, Mich., under the trade name of Dow HDPE. In another embodiment, the thermoplastic resin includes polypropylene. The polypropylene is commercially available from Basell Service Company B.V of Hoofddorp, Netherlands, under the trade name of Profax. In yet another embodiment, the thermoplastic resin includes polystyrene. The polystyrene is commercially available from Chevron Phillips Chemical Company of Woodlands, Tex., under the trade name of Chevron PS.

The reinforcing fiber may be any reinforcing fiber known in the art. Preferably, the reinforcing fiber is selected from the group of glass fibers, carbon fibers, metallic fibers, thermoplastic fibers, cellulosic fibers, polymeric fibers, fiberglass fibers, and combinations thereof. Most preferably, the reinforcing fiber includes cellulosic fibers including, but not limited to, wood fibers. The reinforcing fiber may be present in the first layer (22) in any amount. Preferably, the reinforcing fiber is present in the first layer in an amount of from 20 to 70 and more preferably of from 20 to 60, parts by weight per 100 parts by weight of the first layer.

The first layer (22) may have any thickness. However, the first layer (22) preferably has a thickness of less than 6.5 inches. If the composite article (20) is used in commercial and/or residential construction, it is contemplated that the first layer (22) may have thicknesses of approximately one, two, four, or six inches, and widths of approximately two, four, six, eight, ten, or twelve inches, to mimic common shapes of commercially available lumber as is known in the art. More preferably, the first layer (22) has a thickness of less than 2.5, and most preferably of from 0.12 to 2, inches.

Additionally, the first layer (22) includes a first top face (24) and a first bottom face (26) as shown in FIGS. 3 and 4. The first top and bottom faces (24, 26) may be corrugated. One skilled in the art will select whether to corrugate the first top and/or bottom faces (24, 26) of the first layer (22) based on application and aesthetic considerations. Without intending to be bound by any particular theory, it is believed that if the first bottom face (26) of the first layer (22) is corrugated, the first bottom face (26) of the first layer (22) may more effectively bond to a second top face (30) of the second layer (28), described in greater detail below.

Referring now to the second layer (28), first introduced above, the second layer (28) includes a styrene butadiene copolymer. The styrene butadiene copolymer may be included in the second layer (28) in any amount. In various embodiments, it is contemplated that the styrene butadiene copolymer may included in the second layer (28) in amounts of greater than 85, 90, 95, and 98, parts by weight per 100 parts by weight of the second layer (28). In one embodiment, the styrene butadiene copolymer is present in the second layer (28) in an amount of greater than 99.5 parts by weight per 100 parts by weight of the second layer (28). The styrene butadiene copolymer preferably includes a reaction product of a styrene monomer polymerized with a 1,3-butadiene. However, any butadiene known in the art may be included. It is contemplated that the styrene butadiene copolymer may include a styrene butadiene block copolymer. It is to be understood that the terminology “block copolymer” refers to the styrene butadiene copolymer including repeating sequences of two or more distinct units, such as a styrene monomer. Typically, the styrene butadiene copolymer includes at least 50 weight percent of styrene, from 5 to 50 weight percent of the butadiene, and up to 10 weight percent of additional polymers. More typically, the styrene butadiene copolymer includes of from 60 to 90 and most typically of from 65 to 80, parts by weight of styrene per 100 parts by weight of the styrene butadiene copolymer. Also, the styrene butadiene copolymer more typically includes of from 10 to 40 and most typically of from 20 to 35, parts by weight of the butadiene per 100 parts by weight of the styrene butadiene copolymer.

Styrene butadiene copolymers are typically synthesized using anionic polymerization techniques including use of an alkylmetallic initiator and a coupling agent. Most typically, the alkylmetallic initiator includes an alkyllithium initiator and the coupling agent includes, but is not limited to, alcohols, organohalogens, esters, chlorosilanes, divinylbenzene, and combinations thereof. Examples of typical styrene butadiene copolymers and methods of synthesis are described in U.S. Pat. No. 4,086,298, incorporated herein by reference.

The preferred styrene butadiene copolymer used in the present invention is commercially available from BASF Corporation under the trade name of Styrolux®. Preferred examples of the styrene butadiene copolymer include Styrolux® 684D, Styrolux® 3G33, Styrolux® 3G55, and Styrolux® 656C. However, other styrene butadiene copolymers are also commercially available originally from Shell Chemicals of Houston, Tex., and Chevron Phillips Chemical Company of Woodlands, Tex., under the trade names of Kraton® D-1401-P, and K Resin, respectively. Those skilled in the art will choose a suitable styrene butadiene copolymer based on desirable properties, economics and suitability.

The second layer (28), like the first layer (22), may have any thickness. However, the second layer (28) preferably has a thickness of from 1 to 30, more preferably of from 1 to 15, even more preferably of from 2 to 10, and most preferably of from 2 to 5 mils. If the composite article (20) is used in commercial and/or residential construction, it is contemplated that the second layer (28) may have widths of approximately two, four, six, eight, ten, or twelve inches, to mimic common shapes of commercially available lumber as is known in the art.

Additionally, the second layer (28) includes the second top face (30), as first introduced above, and a second bottom face (32), as shown in FIGS. 3 and 4. The second top and bottom faces (30, 32) of the second layer (28) may be corrugated as is shown in FIGS. 4, 7, and 8. One skilled in the art will select whether to corrugate the second top and/or bottom faces (30, 32) of the second layer (28) based on application and aesthetic consideration. Without intending to be bound by any particular theory, it is believed that if the second bottom face (32) of the second layer (28) is corrugated, the second bottom face (32) of the second layer (28) may more effectively bond to the first top face (24) of the first layer (22). That is, the bond between the first layer (22) and the second layer (28) may be strengthened due to an increased contact area between the first top face (24) of the first layer (22) and the second bottom face (32) of the second layer (28).

The second layer (28) is disposed on the first layer (22) which, in the context of the present invention, does not have to be in direct contact with the first layer (22). However, it is contemplated that the second layer (28) may be disposed in contact with the first layer (22) and may function as a tie layer to bond the first layer (22) to the third layer (34), as is shown in FIGS. 2 through 8. It is also contemplated that the second layer (28) may completely surround the first layer (22), as is shown in FIGS. 2, 6, and 8.

Referring now to the third layer (34) first introduced above, the third layer (34) is disposed on the second layer (28) as the outermost layer of the composite article (20) to sandwich the second layer (28) between the first and third layers (22, 34), as is shown in FIGS. 2 through 8. It is also contemplated that the third layer (34) may completely surround the first and second layers (22, 28) and serve as the outer layer of the composite article (20), as is shown in FIGS. 2, 6, and 8. Additionally, the third layer (34) may be disposed in contact with the second layer (28), as is shown in FIGS. 2, and 5 through 8. If so, the second layer (28) may serve as the tie layer, as first introduced above. If the second layer (28) serves as a tie layer, the first and the third layers (22, 34) sandwich the second layer (28) because the styrene butadiene copolymer included in the second layer (28) contributes to an ability of the first layer (22) to bond to the third layer (34). Also, the first layer (22) is subject to degradation if exposed to chemicals, impact, heat, scratches and mars, moisture, mold, and mildew, ultraviolet light, and stains. However, the styrene acrylonitriles included in the third layer (34) are resistant and therefore protect the first layer (22) from degradation.

The third layer (34) consists essentially of styrene acrylonitriles. However, in one embodiment, the third layer (34) consists of styrene acrylonitriles. That is, in one embodiment, the third layer (34) includes approximately one-hundred percent of styrene acrylonitriles. The styrene acrylonitriles include any compound including a styrene group and an acrylonitrile group. Preferably the styrene acrylonitriles include, but are not limited to, acrylonitrile styrene acrylate, styrene acrylonitrile copolymer, olefin-styrene-acrylonitriles, acrylonitrile-EPDM-styrene, and combinations thereof. The styrene acrylonitrile copolymer is commercially available from BASF Corporation under the trade name of Luran®. The acrylonitrile-EPDM-styrene is commercially available from Lanxess AG of Leverkusen, Germany, under the trade name of Centrex®. Most preferably, the styrene acrylonitriles include acrylonitrile styrene acrylate, commercially available from BASF Corporation under the trade name of Luran®S. It is to be appreciated by those of ordinary skill in the art that the terminology “styrene acrylonitriles” is not limited to styrene-acrylonitrile copolymer, commonly known as SAN.

The styrene acrylonitriles may be formed by any method known in the art including, but not limited to, but not limited to, in mass, solution, suspension, and/or aqueous emulsion. In one embodiment, the styrene acrylonitriles are formed from a styrene monomer which is polymerized with an ethylenically unsaturated compound. Illustrative examples of the styrene monomer include, but are not limited to, styrene, β-methylstyrene, o-methylstyrene, p-methylstyrene, m-methylstyrene, 1,3-dimethylstyrene, tertbutylstyrene, and combinations thereof. Illustrative examples of the ethylenically unsaturated compound include, but are not limited to, vinyl cyanides such as acrylonitrile, and methacrylonitrile, and alkylacrylates including alkylmethacrylates having from 1 to 4 carbon atoms in an alkyl moiety, acrylic acid, methacrylic acid, and combinations thereof.

The third layer (34), like the first and second layers (22, 28), may have any thickness. However, the third layer (34) preferably has a thickness of from 1 to 50, more preferably of from 1 to 40, and most preferably of from 4 to 25, mils. If the composite article (20) is used in commercial and/or residential construction, it is contemplated that the third layer (34) may have widths of approximately two, four, six, eight, ten, or twelve inches, to mimic common shapes of commercially available lumber as is known in the art.

The third layer (34) also includes third top and bottom faces (36, 38), as shown in FIGS. 3 and 4. The third top and/or bottom faces (36, 38) of the third layer (34) may be corrugated. One skilled in the art will select whether to corrugate the third top and/or bottom faces (36, 38) of the third layer (34) based on application and aesthetic considerations. Without intending to be bound by any particular theory, it is believed that if the third bottom face (38) of the third layer (34) is corrugated, the third bottom face (38) of the third layer (34) may more effectively bond to the second top face (30) of the second layer (28). That is, the bond between the third bottom face (38) of the third layer (34) and the second top face (30) of the second layer (28) may be strengthened due to an increased contact area between the third bottom face (38) of the third layer (34) and the second top face (30) of the second layer (28).

Any of the first, second, and third layers (22, 28, 34) may include an additive. If an additive is included, the additive is preferably selected from the group of oxidative and thermal stabilizers, impact modifiers, lubricants, release agents, flame-retarding agents, oxidation inhibitors, oxidation scavengers, neutralizers, antiblock agents, anti-fading agents, dyes, pigments and other coloring agents, ultraviolet light absorbers and stabilizers, organic and inorganic fillers including particulate and fibrous fillers, reinforcing agents, nucleators, plasticizers, waxes, and combinations thereof. Particularly suitable reinforcing agents as the additive include, but are not limited to, talc, mica, calcium carbonate, clay, and combinations thereof. Particularly suitable anti-fading agents as the additive include benzotriazoles, benzophenones, and combinations thereof. However, any additive known in the art may be used.

If the additive is included in any or all of the first, second, and/or third layers (22, 28, 34), the additive may be included in any amount. Preferably, if the additive includes the ultraviolet light stabilizer, and the additive is included in the first, second, and/or third layers (22, 28, 34), the additive is preferably included in an amount of from 0.1 to 2, more preferably of from 0.1 to 1, and most preferably of from 0.2 to 0.7, parts by weight per 100 parts by weight of the thermoplastic resin, the styrene butadiene copolymer, and the styrene acrylonitriles, of the first, second, and third layers (22, 28, 34), respectively.

Referring now to the method of forming the composite article (20) first introduced above, the method includes the steps of forming the first layer (22) including the thermoplastic resin and the reinforcing fiber. The method also includes the step of forming the second layer (28) including the styrene butadiene copolymer on the first layer (22). The method further includes forming the third layer (34) consisting essentially of styrene acrylonitriles on the second layer (28) as an outermost layer of the composite article (20). The second layer (28) may be formed in contact with the first layer (22) and/or in contact with the third layer (34).

Preferably, to form the first, second, and third layers (22, 28, 34), the thermoplastic resin, the styrene butadiene copolymer and the styrene acrylonitriles are introduced into an extruder which may be a single screw extruder. Most preferably, the thermoplastic resin, the styrene butadiene copolymer and the styrene acrylonitriles are introduced into three in-feed hoppers of a first, second, and third extruder, a first extruder handling the thermoplastic resin for the first layer (22), a second extruder handling the styrene butadiene copolymer for the second layer (28), and a third extruder handling the styrene acrylonitriles for the third layer (34). The first, second, and third extruders preferably melt and plasticize the thermoplastic resin, the styrene butadiene copolymer and the styrene acrylonitriles , respectively.

Preferably, the step of forming the first layer (22) includes extruding the first layer (22). Also, the step of forming the second layer (28) preferably includes extruding the second layer (28). Further, the step of forming the third layer (34) preferably includes extruding the third layer (34). Most preferably, the first, second, and third layers (22, 28, 34) are simultaneously extruded. However, it is also contemplated that the first, second, and third layers (22, 28, 34) may be extruded in any order and at different times. The first, second, and third layers (22, 28, 34) are preferably co-extruded.

Most preferably, the first, second, and third extruders form three separate streams of the thermoplastic resin, the styrene butadiene copolymer and the styrene acrylonitriles , respectively. Preferably, each of the first, second, and third extruders includes at least one temperature zone. However, each of the first, second, and third extruders may include more than one temperature zone. Although each of the temperature zones may be heated to any temperature, the temperature zone of the first, second, and third extruders is preferably heated to a temperature from 160 to 250° C.

The streams from the first, second, and third extruders are preferably fed into a single manifold extrusion die or a multi manifold co-extrusion die to form the first, second, and third layers (22, 28, 34) of the composite article (20). While in the co-extrusion die, the first, second, and third layers (22, 28, 34) are preferably juxtaposed and combined, and emerge from the co-extrusion die as the composite article (20) of the present invention. However, it is also contemplated that the composite article (20) can be formed using a single manifold extrusion die utilizing feedblock technology.

It is further contemplated that the first, second, and third layers (22, 28, 34) may be melt-bonded together. Melt-bonding includes directly applying a subject layer to at least one object layer wherein both the subject and object layers are in a partially softened or molten form. A suitable melt-bonding technique includes lamination techniques known in the art.

After exiting the die, the composite article (20) preferably enters a first of a series of calibrators. The calibrators preferably help shape and cool the composite article (20) to final dimensions. The calibrators may have any length and are preferably water cooled. Preferably, the calibrators have a length of 2 to 10 feet. After exiting the calibrators, the composite article (20) preferably enters a first of a series of water baths to finalize cooling and to retain consistent shape. The water baths may have any length and preferably have a length of 10 to 40 feet. Although the composite article (20) may be formed by co-extrusion, it is contemplated that the composite article (20) may be formed by any method known in the art. The following examples illustrating formation of and use of the composite article (20), as presented herein, are intended to illustrate and not limit the invention.

EXAMPLES

A Composite Article (20) is formed according to the present invention. The first layer (22) includes polyethylene as the thermoplastic resin and a cellulosic fiber as the reinforcing fiber. The second layer (28) includes the styrene butadiene copolymer. The third layer (34) consists essentially of acrylonitrile styrene acrylate. Additionally, a series of comparative articles, Comparative Articles 1 through 5, are obtained from various manufacturers and do not include acrylonitrile styrene acrylate at all. Rather, the Comparative Articles 1 through 5 include wood filled polyethylene, wood filled polypropylene, wood filled polyvinyl chloride, polystyrene, or polyvinyl chloride, as a single layer, respectively. Specifically, the Comparative Article 1 including the wood filled polyethylene is commercially available from Louisiana Pacific Corporation of Nashville, Tenn., under the trade name of Weatherbest®. The Comparative article 2 including the wood filled polypropylene is commercially available from Correct Building Products of Biddeford, Me, under the trade name of CorrectDeck®. The Comparative Article 3 including the wood filled polyvinyl chloride is commercially available from CertainTeed of Valley Forge, Pa., under the trade name of Boardwalk®. The Comparative Article 4 including the polystyrene is commercially available from CPI Plastics Group Ltd. of Mississauga, Ontario under the trade name of EON®. The Comparative Article 5 including the polyvinyl chloride is commercially available from Veka Innovations of Fombell, Pa., under the trade name of VEKAdeck®. The Composite Article (20) and the Comparative Articles 1 through 5 are tested and color retention, stain resistance, and scratch resistance are determined by ASTM D1435, Practice G147, a visual stain resistance determination, and a visual scratch resistance determination.

The Composite Article (20) of the present invention is formed from simultaneous extrusion of the first, second, and third layers (22, 28, 34) of the Composite Article (20). The first layer (22) is extruded from a first extruder including four temperature zones, including a first temperature zone, a second temperature zone, a third temperature zone, and a fourth temperature zone. The thermoplastic resin of the first layer (22) passes through the four temperature zones sequentially. The first temperature zone is maintained at a temperature of 165° C. The second temperature zone is maintained at a temperature of 170° C. The third temperature zone is maintained at a temperature of 180° C. The fourth temperature zone is maintained at a temperature of 185° C. After the thermoplastic resin passes through the fourth temperature zone, the thermoplastic resin exits the first extruder at a temperature of 190° C.

The second layer (28) is extruded from a second extruder at the same time as the first layer (22) is extruded from the first extruder. The second extruder, like the first extruder, includes four temperature zones, including a first temperature zone, a second temperature zone, a third temperature zone, and a fourth temperature zone. The styrene butadiene copolymer of the second layer (28) also passes through the four temperature zones sequentially. The first temperature zone is maintained at a temperature of 185° C. The second temperature zone is maintained at a temperature of 190° C. The third temperature zone is maintained at a temperature of 195° C. The fourth temperature zone is maintained at a temperature of 195° C. After the styrene butadiene copolymer passes through the fourth temperature zone, the styrene butadiene copolymer exits the second extruder at a temperature of 205° C.

The third layer (34) is extruded from a third extruder at the same time as the first layer (22) and second layer (28) are extruded from the first and second extruders. The third extruder, like the first and second extruders, includes four temperature zones, including a first temperature zone, a second temperature zone, a third temperature zone, and a fourth temperature zone. The styrene acrylonitriles of the third layer (34) also passes through the four temperature zones sequentially. The first temperature zone is maintained at a temperature of 185° C. The second temperature zone is maintained at a temperature of 190° C. The third temperature zone is maintained at a temperature of 195° C. The fourth temperature zone is maintained at a temperature of 200° C. After the styrene acrylonitriles pass through the fourth temperature zone, the styrene acrylonitriles exit the third extruder at a temperature of 205° C.

After formation, samples of the Composite Article (20) and the Comparative Articles 1 through 5 are tested for color retention, stain resistance, and scratch resistance. Color retention is tested to simulate fading of color of the Composite Article (20) and the Comparative Articles 1 through 5 after exposure to actual outdoor environments. Stain resistance is tested to simulate removal of common household stains from the Composite Article (20) and the Comparative Articles 1 through 5. The scratch resistance is tested to simulate dragging heavy objects, such as chairs and tables, across the Composite Article (20) and the Comparative Articles 1 through 5.

For color retention, delta E is measured. Delta E is a color shift measurement obtained by measuring a color of the Composite Article (20) and Comparative Articles 1 through 5 before and after weathering exposure. The color shift is measured using a portable hand-held colorimeter, commercially available from X-Rite Incorporated of Grandville, Mich., under the trade name of X-Rite SP 60 Series. Specifically, the colorimeter measures L, a*, and b*. L is a measure of a lightness/darkness. a* is a measure of red/green and b* is a measure of yellow/blue. The delta E is calculated by taking a square root of a sum of the squares of (delta L+delta a*+delta b*).

Samples of the Composite Article (20), Samples 1 through 4, and samples of the Comparative Articles 1 through 5, Comparative Samples 1 through 20, respectively, are measured for color retention. Control measurements for L, a*, and b* of the Samples 1 through 4 and the Comparative Samples 1 through 20 are measured before weathering. After the L, a*, and b* are measured, the Samples 1 through 4 and the Comparative Samples 1 through 20 are exposed to weathering for either one, two, three, or four months, outside in Wyandotte, Mich., between the months of March and July. Specifically, Sample 1 and Comparative Samples 1, 5, 9, 13, and 17, are exposed during March and during a portion of April. Sample 2 and Comparative Samples 2, 6, 10, 14, and 18, are exposed during March and April and during a portion of May. Sample 3 and Comparative Samples 3, 7, 11, 15, and 19, are exposed during March, April, May, and during a portion of June. Sample 4 and Comparative Samples 4, 8, 12, 16, and 20 are exposed during March, April, May, June, and during a portion of July.

After exposure, the Samples 1 through 4 and the Comparative Samples 1 through 20 are measured for L, a*, and b* using the colorimeter and the Delta E is calculated. Specifically, each of L, a*, and b* are measured by the colorimeter twice in the same location on the each of the Samples 1 through 4 and the Comparative Samples 1 through 20, to ensure accuracy of measurement. The color retention is set forth in set forth in Table 1, below. In Table 1, the color retention is set forth as an average of two calculations of Delta E for each of the Samples 1 through 4 and the Comparative Samples 1 through 20.

TABLE 1
Time of Test	Sample 1	Sample 2	Sample 3	Sample 4
Months of	1	2	3	4
Exposure
Delta E	0.21	0.15	0.25	0.33
	Comparative	Comparative	Comparative	Comparative
Time of Test	Sample 1	Sample 2	Sample 3	Sample 4
Months of	1	2	3	4
Exposure
Delta E	4.22	5.15	6.32	6.68
	Comparative	Comparative	Comparative	Comparative
Time of Test	Sample 5	Sample 6	Sample 7	Sample 8
Months of	1	2	3	4
Exposure
Delta E	2.36	6.41	7.67	8.34
	Comparative	Comparative	Comparative	Comparative
Time of Test	Sample 9	Sample 10	Sample 11	Sample 12
Months of	1	2	3	4
Exposure
Delta E	1.46	4.18	5.27	7.24
	Comparative	Comparative	Comparative	Comparative
Time of Test	Sample 13	Sample 14	Sample 15	Sample 16
Months of	1	2	3	4
Exposure
Delta E	1.67	1.76	2.31	3.52
	Comparative	Comparative	Comparative	Comparative
Time of Test	Sample 17	Sample 18	Sample 19	Sample 20
Months of	1	2	3	4
Exposure
Delta E	0.82	1.12	0.53	1.32

Samples 1 through 4 are samples of the Composite Article (20) of the present invention. The first layer (22) of the Composite Article (20) includes polyethylene as the thermoplastic resin and a cellulosic fiber as the reinforcing fiber. The second layer (28) of the Composite Article (20) includes the styrene butadiene copolymer commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Styrolux®. The third layer (34) of the Composite Article (20) consists essentially of acrylonitrile styrene acrylate commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Luran® S.

Comparative Samples 1 through 4 are samples of Comparative Article 1 and include wood filled polyethylene.

Comparative Samples 5 through 8 are samples of Comparative Article 2 and include wood filled polypropylene.

Comparative Samples 9 through 12 are samples of Comparative Article 3 and include wood filled polyvinyl chloride.

Comparative Samples 13 through 16 are samples of Comparative Article 4 and include polystyrene.

Comparative Samples 17 through 20 are samples of Comparative Article 5 and include polyvinyl chloride.

Upon testing, it is determined that the Samples 1 through 4 exhibit excellent delta E values of less than 0.4, as shown in FIG. 9. This indicates that, after exposure, any color change of the Samples 1 through 4 is not perceptible to the human eye. Additionally, the delta E values of the Samples 1 through 4 are lower than the delta E values of the Comparative Samples 1 through 20 indicating that the Composite Article (20) of the present invention is more fade resistant than articles known in the art such as Comparative Articles 1 through 5, as also shown in FIG. 9.

Additional samples of the Composite Article (20), Samples 5 through 7, and additional samples of the Comparative Articles 1 through 5, Comparative Samples 21 through 35, respectively, are visually measured for stain resistance. Specifically, 3 drop samples of 15 agents are utilized to determine stain resistance. The 15 agents are classified into three categories including oils, condiments, and drinks. The oil category includes BBQ Sauce, Marinade, Italian Dressing, Cooking Oil, and Suntan Oil. The condiment category includes Ketchup, Mustard, Mayonnaise, Pizza Sauce, and Chocolate Syrup. The drink category includes Cola, Red Wine, Red Fruit Drink, Grape Juice, and Coffee. The 15 agents are applied to the Samples 5 through 7 and the Comparative Samples 21 through 35 in an outdoor environment in Wyandotte, Mich., at noon, at approximately 86° F., in July. The Samples 5 through 7 and the Comparative Samples 21 through 35 are exposed to an outdoor environment in July in Wyandotte, Mich., for approximately 20 hours. After approximately 20 hours, the 15 agents are manually removed and the Samples 5 through 7 and the Comparative Samples 21 through 35 are visually assessed on a scale of 1 through 5 for any stain remaining. A value of 1 indicates no stain visually detected after 20 scrubs with water and a brush. A value of 2 indicates no stain visually detected after 20 scrubs with soap, water, and a brush. A value of 3 indicates no stain visually detected after 20 scrubs with a commercial soap, commercially available from SC Johnson of Racine, Wis., under the trade name of Fantastik®, water and a brush. A value of 4 indicates no stain visually detected after 20 scrubs with a deck cleaner, commercially available from PPG Architectural Finishes, Inc. of Pittsburgh, Pa., under the trade name of Olympic Premium Deck Cleaner, water and a brush. A value of 5 indicates that a stain is visually detected after all of the aforementioned cleaning attempts are performed. It is to be understood that decimal values between 1 and 5 are possible. The stain resistance is set forth in Table 2 as an average of the agents in each category and an average of ten measurements of the Samples 5 through 7 and the Comparative Samples 21 through 35.

	TABLE 2
	Sample 5	Sample 6	Sample 7
Category of Stain	Oils	Condiments	Drinks
Stain Value	1	1.5	1
	Comparative	Comparative	Comparative
	Sample 21	Sample 22	Sample 23
Category of Stain	Oils	Condiments	Drinks
Stain Value	4.4	3.3	3.4
	Comparative	Comparative	Comparative
	Sample 24	Sample 25	Sample 26
Category of Stain	Oils	Condiments	Drinks
Stain Value	4.2	2.8	3.2
	Comparative	Comparative	Comparative
	Sample 27	Sample 28	Sample 29
Category of Stain	Oils	Condiments	Drinks
Stain Value	3.8	2.6	2
	Comparative	Comparative	Comparative
	Sample 30	Sample 31	Sample 32
Category of Stain	Oils	Condiments	Drinks
Stain Value	1.7	1	1
	Comparative	Comparative	Comparative
	Sample 33	Sample 34	Sample 35
Category of Stain	Oils	Condiments	Drinks
Stain Value	1	1.5	1

Samples 5 through 7 are samples of the Composite Article (20) of the present invention. The first layer (22) of the Composite Article (20) includes polyethylene as the thermoplastic resin and the cellulosic fiber as the reinforcing fiber. The second layer (28) of the Composite Article (20) includes the styrene butadiene copolymer commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Styrolux®. The third layer (34) of the Composite Article (20) consists essentially of acrylonitrile styrene acrylate commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Luran® S.

Comparative Samples 21 through 23 are samples of Comparative Article 1 and include wood filled polyethylene.

Comparative Samples 24 through 26 are samples of Comparative Article 2 and include wood filled polypropylene.

Comparative Samples 27 through 29 are samples of Comparative Article 3 and include wood filled polyvinyl chloride.

Comparative Samples 30 through 32 are samples of Comparative Article 4 and include polystyrene.

Comparative Samples 33 through 35 are samples of Comparative Article 5 and include polyvinyl chloride.

Upon testing, it is determined that the Samples 5 through 7 exhibit excellent stain values of 1.5 or less, as shown in FIG. 10. This indicates that, after application of stain and subsequent washing, no stain is visually detectable. Additionally, the stain values of the Samples 5 through 7 are generally lower than the stain values of the Comparative Samples 21 through 35 indicating that the Composite Article (20) of the present invention is more stain resistant than articles known in the art such as Comparative Articles 1 through 5, as also shown in FIG. 10.

Additional samples of the Composite Article (20), Samples 8 through 11, and additional samples of the Comparative Articles 1 through 5, Comparative Samples 36 through 55, respectively, are measured for scratch resistance with visual determination. Various weights of 1,000, 2,500, 5,000, and 10,000 grams are dragged across the Samples 8 through 11 using a scratch and mar tester commercially available from BYK-Gardener USA of Columbia, Md., under the trade name of Balance Beam Scrape Adhesion and Mar Tester. Specifically, the scratch and mar tester includes an arm declined at approximately 45° downward from horizontal and a 0.25 inch diameter hook. The various weights are loaded onto the arm and the Samples 8 through 11 and the Comparative Samples 36 through 55 are placed on a sled. The Samples 8 through 11 and the Comparative Samples 36 through 55 are then dragged on the sled under the loaded arm and hook at approximately 10-20 feet per second to create scratches. After the scratches are created, a severity of the scratch is visually determined according to a scratch value scale including values from 1 to 5. A value of 1 indicates that there is no detectable scratch. A value of 2 indicates that there is a slight scratch. A value of 3 indicates that there is a moderate scratch. A value of 4 indicates that there is a significant scratch. A value of 5 indicates that there is a severe scratch. It is to be understood that decimal values between 1 and 5 are possible. The scratch resistance is set forth in Table 3 as an average of approximately three measurements of the Samples 8 through 11 and the Comparative Samples 36 through 55.

	TABLE 3
	Sample 8	Sample 9	Sample 10	Sample 11
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	1	1.5	1.8	2
	Comparative	Comparative	Comparative	Comparative
	Sample 36	Sample 37	Sample 38	Sample 39
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	2	2.8	3.3	3.8
	Comparative	Comparative	Comparative	Comparative
	Sample 40	Sample 41	Sample 42	Sample 43
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	2	2	2	4
	Comparative	Comparative	Comparative	Comparative
	Sample 44	Sample 45	Sample 46	Sample 47
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	1	2	2	3
	Comparative	Comparative	Comparative	Comparative
	Sample 48	Sample 49	Sample 50	Sample 51
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	1	2	3	5
	Comparative	Comparative	Comparative	Comparative
	Sample 52	Sample 53	Sample 54	Sample 55
Weight (g)	1,000	2,500	5,000	10,000
Scratch Value	1	2	2	2.4

Samples 8 through 1 are samples of the Composite Article (20) of the present invention. The first layer (22) of the Composite Article (20) includes polyethylene as the thermoplastic resin and the cellulosic fiber as the reinforcing fiber. The second layer (28) of the Composite Article (20) includes the styrene butadiene copolymer commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Styrolux®. The third layer (34) of the Composite Article (20) consists essentially of acrylonitrile styrene acrylate commercially available from BASF Corporation of Wyandotte, Mich., under the trade name of Luran® S.

Comparative Samples 36 through 39 are samples of Comparative Article 1 and include wood filled polyethylene.

Comparative Samples 40 through 43 are samples of Comparative Article 2 and include wood filled polypropylene.

Comparative Sample 44 through 47 are samples of Comparative Article 3 and include wood filled polyvinyl chloride.

Comparative Samples 48 through 51 are samples of Comparative Article 4 and include polystyrene.

Comparative Samples 52 through 55 are samples of Comparative Article 5 and include polyvinyl chloride.

Upon testing, it is determined that the Samples 8 through 11 exhibit excellent scratch values of 2 or less, as shown in FIG. 11. This indicates that, after contacted with the scratch and mar tester, the Samples 8 through 11 exhibit slight or no scratching. Additionally, the scratch values of the Samples 8 through 11 are generally lower than the scratch values of the Comparative Samples 36 through 55 indicating that the Composite Article (20) of the present invention is generally more scratch and mar resistant than articles known in the art such as Comparative Articles 1 through 5, as also shown in FIG. 11.

The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.

Claims

1. A composite article comprising:

A. a first layer comprising a thermoplastic resin and a reinforcing fiber;

B. a second layer comprising a styrene butadiene copolymer and disposed on said first layer; and

C. a third layer consisting essentially of styrene acrylonitriles and disposed on said second layer as an outermost layer of said composite article.

2. A composite article as set forth in claim 1 wherein said first, second, and third layers are co-extruded.

3. A composite article as set forth in claim 1 wherein said thermoplastic resin is selected from the group of polyalkylenes, polyaromatics, and combinations thereof.

4. A composite article as set forth in claim 1 wherein said thermoplastic resin is selected from the group of polyethylene, polypropylene, and combinations thereof.

5. A composite article as set forth in claim 1 wherein said thermoplastic resin comprises polystyrene.

6. A composite article as set forth in claim 1 wherein said reinforcing fiber is selected from the group of glass fibers, carbon fibers, metallic fibers, thermoplastic fibers, cellulosic fibers, polymeric fibers, fiberglass fibers, and combinations thereof.

7. A composite article as set forth in claim 1 wherein said styrene acrylonitriles comprise acrylonitrile styrene acrylate.

8. A composite article as set forth in claim 1 wherein said second layer is disposed in contact with said first layer.

9. A composite article as set forth in claim 8 wherein said third layer is disposed in contact with said second layer.

10. A composite article as set forth in claim 1 wherein said third layer is disposed in contact with said second layer.

11. A composite article as set forth in claim 1 wherein said first layer has a thickness of less than 2.5 inches.

12. A composite article as set forth in claim 1 wherein said second layer has a thickness of from 2 to 10 mils.

13. A composite article as set forth in claim 1 wherein said third layer has a thickness of from 1 to 40 mils.

14. A composite article as set forth in claim 1 wherein said first, second, and third layers each have top and bottom surfaces and at least one of said top and bottom surfaces is corrugated

15. A composite article as set forth in claim 1 further comprising an additive selected from the group of oxidative and thermal stabilizers, impact modifiers, lubricants, release agents, flame-retarding agents, oxidation inhibitors, oxidation scavengers, neutralizers, antiblock agents, dyes, pigments and other coloring agents, ultraviolet light absorbers and stabilizers, organic and inorganic fillers including particulate and fibrous fillers, reinforcing agents, nucleators, plasticizers, waxes, hot melt adhesives, and combinations thereof.

16. A composite article as set forth in claim 1 wherein said reinforcing fiber is present in said first layer in an amount of from 20 to 60 parts by weight per 100 parts by weight of said first layer and said second layer consists essentially of said styrene butadiene copolymer.

17. A composite article as set forth in claim 1 wherein said composite article is selected from the group of boards, footings, posts, beams, joists, planks, rails, spindles, stringers, studs, balusters, caps, panels, doors, fascia, and combinations thereof.

18. A composite article comprising:

A. a first layer comprising a thermoplastic resin and a cellulosic fiber;

B. a second layer comprising a styrene butadiene copolymer and disposed in contact with said first layer; and

C. a third layer consisting essentially of acrylonitrile styrene acrylate and disposed in contact with said second layer as an outermost layer of said composite article.

19. A composite article as set forth in claim 18 wherein said first layer has a thickness of from 0.12 to 2 inches.

20. A composite article as set forth in claim 18 wherein said second layer has a thickness of from 2 to 5 mils.

21. A composite article as set forth in claim 18 wherein said third layer has a thickness of from 20 to 40 mils.

22. A composite article as set forth in claim 18 wherein said first, second, and third layers each have top and bottom surfaces and at least one of said top and bottom surfaces is corrugated.

23. A composite article as set forth in claim 18 further comprising an additive selected from the group of oxidative and thermal stabilizers, impact modifiers, lubricants, release agents, flame-retarding agents, oxidation inhibitors, oxidation scavengers, neutralizers, antiblock agents, dyes, pigments and other coloring agents, ultraviolet light absorbers and stabilizers, organic and inorganic fillers including particulate and fibrous fillers, reinforcing agents, nucleators, plasticizers, waxes, hot melt adhesives, and combinations thereof.

24. A composite article as set forth in claim 18 wherein said reinforcing fiber is present in said first layer in an amount of from 20 to 60 parts by weight per 100 parts by weight of said first layer and said second layer consists essentially of said styrene butadiene copolymer.

25. A composite article as set forth in claim 18 wherein said composite article is a board.

26. A method of making a composite article, said method comprising the steps of:

forming a first layer comprising a thermoplastic resin and a reinforcing fiber;

forming a second layer comprising a styrene butadiene copolymer on the first layer; and

forming a third layer consisting essentially of styrene acrylonitriles on the second layer as an outermost layer of the composite article.

27. A method as set forth in claim 26 wherein the step of forming the first layer comprises extruding the first layer, the step of forming the second layer comprises extruding the second layer, and the step of forming the third layer comprises extruding the third layer.

28. A method as set forth in claim 27 wherein the first, second, and third layers are simultaneously extruded.

29. A method as set forth in claim 26 further comprising the step of melt-bonding the first, second, and third layers.

30. A method as set forth in claim 26 wherein the second layer is formed in contact with the first layer.

31. A method as set forth in claim 30 wherein the third layer is formed in contact with the second layer.

32. A method as set forth in claim 26 wherein the third layer is formed in contact with the second layer.