Abstract:
A multi-component composite extrusion includes various combinations of a hollow, high density profile filled in with a foamed, thermoplastic core. A further low density foamed profile can alternately surround the high density, hollow component. A capstock can be provided on either embodiment of the multi-component extrusion. All of the components are preferably substantially simultaneously extruded in a single multi-plate extrusion die, so that the various components are substantially laterally coextensive with one another and molecularly bonded to the adjacent component. The thin wall, high density component and the adjacent low density foamed thermoplastic component may optionally be provided with substantial wood fiber content to alter the macroscopic properties of the resulting multi-component extrusion. The extrusion has utility in the fenestration, decking, and remodeling industries. The method disclosed for making the extrusion permits the extrusion designer to vary the type of thermoplastic material used with respect to each component and the presence or absence of wood fiber in the components to vary the macroscopic properties of the entire composite extrusion, surface characteristics of the extrusion, and weatherability of the extrusion.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to methods and apparatus for forming a multiple component, composite polymer/wood fiber extrusion and a method for making the same. More specifically, the invention relates to a composite extrusion of the type described above having a multiplicity of components, including a high density, substantially hollow extrusion profile having inner and/or outer components having a different density coextruded with the high density component.  
         BACKGROUND OF THE INVENTION  
         [0002]    Milled wood products have formed the foundation for the fenestration, decking and remodeling industries for many years. Historically, ponderosa pine, fir, red wood, cedar and other coniferous varieties of soft woods have been employed with respect to the manufacture of residential window frames, residential siding and outer decking. Wood products of this type inherently possess the advantageous characteristics of high flexural modulus, good screw retention, easy workability (e.g., milling, cutting, paintability), and for many years, low cost. Conversely, wood products of this type have also suffered from poor weatherability in harsh climates, potential insect infestation such as termites, and high thermal conductivity. In addition to these inherent disadvantages, virgin wood resources have become scarce, thus the raw material cost for milled wood products has become correspondingly expensive.  
           [0003]    In response to the above described disadvantages of milled wood products, the fenestration industry, in particular, adopted polyvinyl chloride as a raw material for the manufacture of hollow, lineal extrusions for subsequent assembly into window frames. Window frames manufactured from such lineal extrusions became an enormous commercial success, particularly at the lower end of the price spectrum. Window frames manufactured from hollow, lineal polyvinyl chloride (PVC) extrusions exhibited superior thermal conductivity, water absorption resistance (and thus rot resistance), insect resistance, and ultraviolet radiation resistance compared to painted ponderosa pine. Although such extrusions further enjoyed a significant cost advantage over comparable milled wood products, these polymer based products had a significantly lower flexural modulus. (i.e., bending moment), were difficult if not impossible to paint effectively, and had a significantly higher coefficient of thermal expansion. By the mid  1990   s , a number of window and door frame manufacturers attempted to combine the most desirable characteristics of extruded thermoplastic polymers and solid wood frame members by alloying PVC with wood fiber in an extruded product.  
           [0004]    U.S. Pat. No. 5,486,553 to Deaner et al. discloses an extruded polymer/wood fiber thermoplastic composite structural member, suitable for use as a replacement for a wood structural member, such as for window frame components. The preferred thermoplastic component is polyvinyl chloride (PVC), and the preferred wood fiber component is sawdust. In a preferred embodiment of the invention, a double hung window unit is disclosed having cell, jamb and header portions comprising hollow, multi-compartment lineal extrusions which can be made from the disclosed thermoplastic polymer/wood fiber composite. The resulting extrusion has mechanical properties which are similar to wood, but have superior dimensional stability, and resistance to rot and insect damage as compared to conventional wood products.  
           [0005]    Problems relating to co-extrusion of wood fibers and a thermoplastic polymer component are well explained in U.S. Pat. No. 5,851,469 to Muller et al. issued Dec. 22, 1998, the disclosure of which is incorporated herein by reference. Muller et al. described the typical prior art steps for co-extruding a thermoplastic polymer with wood fiber. In a first step, the wood fiber is dried using conventional techniques to a moisture content of less than 8% by weight. In a second step the wood fiber and plastic material are preheated to a temperature of approximately 176° F. to 320° F. In a third step, the materials are mixed or kneaded at a temperature of 248° F. to 482° F. to form a paste. In a fourth and final step, the paste is either injection molded or extruded into a final form. If the paste is extruded, the extrudate must be calibrated and cooled. The Muller et al. reference specifically addresses the problem of controlling the temperature of the extrudate through various stages of the extrusion process to prevent undesirable sheer stresses from arising during the extrusion process. Muller et al. also teach that a particular problem involved with wood fiber/thermoplastic composite extrudates involves volatiles in the wood component boiling off at extrusion temperatures causing an undesirable foaming of the extrudate.  
           [0006]    In addition, extruded polymer/wood thermoplastic composite structural members allowed manufacturers to limit the amount of expensive thermoplastic materials used in the extrusion by increasing the percentage of low cost waste wood product incorporated into the process. Substantial advancements have been made in this art whereas as of the filing date of this application, concentrations of wood fiber in a hollow core, thermoplastic extrusion up to 30 to 40 percent are known. Unfortunately, adding significant quantities of wood fiber to the thermoplastic polymer/wood fiber composite degrades the flexural modulus (i.e., bending moment) of the extrusion. Thus, manufacturers often resort to the use of U-shaped metal channels which reside inside hollow sections of the longitudinal extrusion to provide increased stiffness, as well as angled metal members incorporated into interior components of such structures and corners thereof. The use of such additional structural members disadvantageously increases the cost of assembling products of this type, as well as decreases the thermal efficiency of these products.  
           [0007]    Some manufacturers have moved in a different direction by preparing foamed lineal extrusions, with and without a wood fiber content. Such extrusions address the difficulties in connecting thin wall, hollow extrusions at corners (typically done by thermal welding) by providing a large surface area for joining. In addition, screw retention and thermal efficiency may be substantially improved in foamed extrusions of this type. Further yet, foamed extrusions containing a high wood fiber content are readily paintable and can be provided with a surface texture which mimics solid wood. The assignee of the present invention has developed improved techniques for increasing the wood fiber content of such foamed extrusions as disclosed in U.S. patent application Ser. No. 09/452,906, entitled “Wood Fiber Polymer Composite Extrusion and Method”, filed Dec. 1, 1999, the disclosure of which is incorporated herein by reference. Unfortunately, while such foamed lineal extrusions advantageously exhibit improved heat deflection, Vicat softening point, screw retention, and lower density (i.e., decreased raw material cost) as opposed to rigid, hollow core PVC extrusions, foamed extrudates typically have a lower flexural modulus than comparable rigid, thin walled, hollow core PVC extrusions.  
           [0008]    In an attempt to combine the specific structural advantages of different types of polymers, at least one manufacturer in the fenestration industry has attempted to produce a multi-component extrusion having an extruded foamed material as one component, flexible flanges as another component, and a partial capstock as a third component. An example of an extrusion of this type is disclosed in U.S. Pat. No. 5,538,777 to Pauley et al. entitled “Triple Extruded Frame. Profiles”, issued Jul. 23, 1996. That patent discloses a three-component extrusion for a window sash. The main component of the extrusion in cross-section is a polyvinyl chloride foam core, optionally including a fiber component. The core has a recess forming a U-shaped channel for receipt of glass panes. The panes are held in place by flexible flanges extending normal to the inside of the channel in the form of a flexible material which is used to form the flexible flanges and/or seals. Dupont Alcryn™ is disclosed as an appropriate material for the flanges. The extrusion is also disclosed as having a partial capstock, preferably acrylic styrene acrylonitrile (ASA) which is provided only on the portion of the exterior of the extrusion which will be exposed to weathering. Although this extrusion enjoys the low cost advantages of a foamed, thermoplastic/wood fiber core and the weatherability of a partial capstock, it is believed that an extrusion of this type has insufficient flexural modulus for use in anything other than as a sash portion of a window assembly. That is, it is believed that metallic channel stiffeners, and the like, would still be necessary if this type of extrusion construction was employed as a main frame element.  
           [0009]    Thus, a need exists for a lineal extrusion for use in the fenestration, decking and remodeling industries which combines a low raw material cost with high tensile, compressive, bending moment, and impact strength; improved weldability with respect to hollow core extrusions; high wood fiber content (reduced cost); and high workability (e.g., millable, paintable, and good screw retention). In addition, there is a need for an extrusion of the type described above which is highly durable, being-resistant to rot, mildew, and ultraviolet degradation.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of the present invention to provide a continuous, lineal multi-component polymer composite extrusion having low raw material cost; high tensile, compressive, bending moment, and impact strength; improved weldability with respect to hollow core extrusions; high wood fiber content; and high workability.  
           [0011]    It is a further object of the present invention to achieve the above object by a method and apparatus which provides a continuous, lineal multi-component polymer composite extrusion which is highly durable, being resistant to rot, mildew, and ultraviolet degradation.  
           [0012]    It is yet a further object of the invention to achieve the above objects with a manufacturing process capable of varying the ultimate macroscopic properties of the resulting extrudate so as to closely match the differing physical requirements of the fenestration, decking and siding markets.  
           [0013]    The invention achieves the above objects and advantages, and other objects and advantages which will become apparent from the description which follows, by providing a multi-component, longitudinally continuous extrusion having a first, high density, thin wall composite member having a thermoplastic component and a cellulosic fiber component. The inventive extrusion further has a second, low density foamed member, consisting of a foamed, thermoplastic polymer coextruded with the first member in a plastic state, substantially contemporaneously with the first member, in an extrusion die so as to be laterally coextensive with, and molecularly bonded to, either an inside hollow portion of the first, thin wall high density member, an outside of the first, thin wall, high density member, or both.  
           [0014]    In the preferred embodiment, the inventive extrusion may be capped with a thin layer of acrylic styrene acrylonitrile (ASA) or polyvinyl chloride (PVC).  
           [0015]    In alternate embodiments of the invention, the low density foamed member may include a substantial wood fiber content, particularly when the second, low density foamed member is on the outside of the first, thin wall, high density composite member and a thermoplastic cap is not employed. The thermoplastic cap may be provided with a highly weatherable, thermoplastic polymer on one side of the extrusion (to be exposed to the outdoor portion of a building) and a highly paintable thermoplastic polymer on an opposite side of the extrusion, to be exposed to an indoor portion of the building.  
           [0016]    The invention includes apparatus in the form of a multi-plate extrusion die for manufacturing the above extrusions, including an introductory plate for passage therethrough of a primary extrudate from a principal extruder, a mandrel plate downstream of the introductory plate for receipt of the primary extrudate which will become the first, thin wall, high density composite member. The mandrel plate has suspended within an aperture therein a first elongated mandrel wherein the first mandrel is substantially hollow and has therein a second mandrel substantially suspended therein in a spaced apart relationship from the side walls of the first elongated mandrel so as to form an elongated, hollow interstitial void between the first and second mandrels. The interstitial void is thus available for introduction of the second, low density foamed material which can become laterally coextensive with, and molecularly bonded to, one of the inner side walls of the first member. Finally, a secondary plate is positioned between the introductory and mandrel plates so that in one alternate, preferred embodiment of the invention the second, low density foamed extrudate can be provided on the outer side wall of the first, thin wall, high density composite member so that foamed material can be provided on both the inside and the outside of the thin wall extrusion, as well as on the inside or the outside of the hollow core extrusion exclusively. A capstock plate can be provided downstream of the mandrel plate for adding a third extrudate in the form of a capstock to the final extrudate. Elongated, tapered fins are preferably provided to support the first elongated mandrel with respect to the aperture in the mandrel and also to support the second mandrel in a spaced apart relationship with respect to inner side walls of the first hollow mandrel.  
           [0017]    The invention includes a method of making the above described multi-component, longitudinally continuous extrusion with the above described introductory, mandrel, and secondary die plates which includes the steps of preparing a thermoplastic primary extrudate and a secondary thermoplastic extrudate, introducing the primary extrudate in a plastic state into the introductory plate, positioning a mandrel plate downstream of the introductory plate, and introducing the secondary extrudate in a plastic state into a void between the first and second, coaxially spaced mandrels in the mandrel plate, so that an elongated final extrudate having at least two different longitudinally continuous, molecularly bonded thermoplastic components exit the mandrel plate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is an environmental view of a first embodiment of a multi-component, polymer composite extrusion of the present invention.  
         [0019]    [0019]FIG. 2 is a an exploded schematic representation of a plurality of extrusion die plates employed in the manufacture of the extrusion shown in FIG. 1.  
         [0020]    [0020]FIG. 3 is a left hand, environmental view of a mandrel plate die of the die shown in FIG. 2.  
         [0021]    [0021]FIG. 4 a  is a right hand perspective view of the mandrel plate die shown in FIG. 3.  
         [0022]    [0022]FIG. 4 b  is a left hand perspective view of a floating mandrel of the mandrel die shown in FIG. 4 a.    
         [0023]    [0023]FIG. 4 c  is a right hand perspective view of the floating mandrel shown in the mandrel die of FIG. 4 a.    
         [0024]    [0024]FIG. 5 is a schematic representation of a polymer flow in a plastic state in the die assembly shown in FIG. 2.  
         [0025]    [0025]FIG. 6 is an environmental view of a second embodiment of a multi-component, polymer composite extrusion of the present invention.  
         [0026]    [0026]FIG. 7 a  is a right hand, perspective view of a mandrel plate having a dual floating mandrel therein for manufacture of the extrudate shown in FIG. 6 in conjunction with some of the die plates shown in the die plate assembly of FIG. 2.  
         [0027]    [0027]FIG. 7 b  is a left hand environmental view of a mandrel plate having a dual floating mandrel therein for manufacture of the extrudate shown in FIG. 6 in conjunction with some of the die plates shown in the die plate assembly of FIG. 2.  
         [0028]    [0028]FIG. 8 a  is an enlarged, right hand perspective view of the dual floating mandrel shown in FIG. 7 a.    
         [0029]    [0029]FIG. 8 b  is a left hand perspective view of the dual floating mandrel shown in corresponding FIG. 7 b.    
         [0030]    [0030]FIG. 9 is a schematic representation of a third alternate embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    A first preferred embodiment of a multi-component, composite polymer/wood fiber continuous lineal extrusion of the present invention is generally indicated at reference numeral  10  of FIG. 1. The extrusion includes a first, high density, thin wall component  12 , having an inner side wall  14  defining at least one hollow section in profile. The multi-component extrusion  10  further has a second, low density foamed thermoplastic member  16  which is coextruded with, and substantially fills, the hollow section defined by inner side wall  14 . As will be described in further detail hereinbelow, the second component  16  is preferably formed of a foamed thermoplastic member which is molecularly bonded to, and substantially laterally coextensive with, the inner sidewall  14 . In this preferred embodiment, the first component  12  has an outer side wall  18  defining the exterior surface of the first component. In this first preferred embodiment, the outer side wall  18  supports a thermoplastic cap  20  which is substantially coextruded with the first and second components  12 ,  14 , so as to be molecularly bonded to the outer side wall  18 . The thermoplastic cap is preferably formed from a highly weatherable, thermoplastic polymer such as polyvinyl chloride (PVC).  
         [0032]    The multi-component, composite polymer/wood fiber extrusion  10  shown in FIG. 1 is suitable for use as vertical and horizontal members of a window sash. The extrusion defines a substantially U-shaped channel, generally indicated at reference numeral  22 , for the receipt of weatherstripping material, and the like (not shown). The extrusion  10  shown in FIG. 1 also has on the upper portion thereof a substantially L-shaped surface  24 , having a lower ledge  26  and at right angles thereto a vertical edge  28 . When assembled into a window sash, the extrusion  10  is cut into four desired lengths, having each end of each section mitered at an appropriate angle. The mitered edges are then thermally welded in a manner well known to those of ordinary skill in the art so as to form a complete sash frame. Extrusion  10  of the present invention advantageously presents a cross-section at each miter joint having a substantially continuous surface of thermoplastic material. Thus, the entire cross-sectional surface area available for thermal welding is substantially greater than that of a continuous lineal extrusion being substantially hollow in profile. In addition, it is relatively easy to align adjacent members of the sash because of the large, surface area available for welding.  
         [0033]    In the context of a complete sash structure, the lower edge  26  of the extrusion  10  is well adapted to receive edges of glass panes (not shown) in a moveable or fixed sash. Vertical edge  28  provides a support surface for a rearward pane member of, for example, a double-pane sash. The extrusion  10  is also provided on a forward edge thereof with a bead pocket, generally indicated at reference numeral  30 , for receipt of a bead (not shown) for retaining an outer pane of a double pane window sash. Thus, the completed sash defines an exterior surface  32  for the sash and an interior surface  34 . In this embodiment, the exterior surface  32  is exposed to weathering, while the interior surface  34  [extending from the vertical edge  28  around the rear (hidden in FIG. 1) surface of the thermoplastic cap  20 ] is exposed to the interior of a home or the like. The thermoplastic cap  20  may therefore be preferably provided with the interior surface  34  being extruded from a thermoplastic polymer that is highly paintable, whereas the exterior surface  32  is extruded with a thermoplastic polymer that is highly weatherable.  
         [0034]    [0034]FIG. 2 illustrates a die assembly  40  consisting of a series of individual die plates,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56 , and  58 , for manufacturing the multi-component extrusion  10  shown in FIG. 1. The manner of use of such dies is well known to those of ordinary skill in the thermoplastic extrusion art and is well described in U.S. patent application Ser. No. 09/452,906, entitled “Wood Fiber Polymer Composite Extrusion and Method” assigned to the assignee of the present invention. Disclosure of that application is incorporated herein by reference. Nevertheless, it is sufficient to state that the die assembly  40  shown in FIG. 2 is intended for use with a plurality of conventional extruders, such as conventional twin screw extruders, each of which includes a hopper or mixer for accepting a feed stock consisting of a thermoplastic polymer and/or wood composite pelletized material, a conduit for connecting the hopper with a preheater for controlling the temperature of an admixture of the feed stock in the hopper, and optionally an inlet for introducing foaming agents in the case of a foamed component. The preheater is fluidly connected to a multi-screw chamber for admixing feedstock with the foaming agent (if present) and other conditioners to be described hereinbelow under controlled conditions of temperature and pressure. The multi-screw chamber of each extruder is connected to an appropriate one of the die assembly plates shown in FIG. 2 for producing the multi-component extrusion  10  shown in FIG. 1. The extrudate is then preferably calibrated in a conventional calibrator to result in a final product shown in FIG. 1. Appropriate extruding machines are available from Cincinnati Millacron Corporation, Batavia, Ohio, USA.  
         [0035]    As best seen in FIG. 2, one of the hereinabove described extruders (not shown) is fluidly connected to an introductory plate  44  for introduction of a primary extrudate which will become the hollow high density component  12  shown in FIG. 1. The primary extrudate is introduced through a primary aperture  60  in the introductory plate  44 . A first shaping plate  46  has a plurality of internal conduits  47  for directing the flow of the primary extrudate to corresponding conduits in a secondary extrudate die plate  48 . Secondary extrudate die plate  48  has an inlet  49  for introduction of a secondary extrudate which will become the second, low density foamed thermoplastic component  16  of the extrusion shown in FIG. 1. The inlet  49  is fluidly connected to a secondary shaping die plate  50  by way of an internal secondary conduit  51 . Both the internal primary and secondary conduits  47 ,  51  are in fluid communication with a mandrel plate  52  which supports a first mandrel  53 ( a ) by means of a plurality of longitudinally elongated fins  53 ( b ) within the internal primary conduit  47 . An external surface  53 ( c ) of the first mandrel  53 ( a ) is the inner forming surface for the primary extrudate. As best seen in FIGS.  3  &amp;  4 ( a )- 4 ( c ), the first mandrel  53 ( a ) is substantially hollow and has suspended therein a second mandrel  53 ( d ). The second mandrel  53 ( d ) is suspended within the hollow interior of the first mandrel  53 ( a ) by elongated, longitudinally tapering fins  53 ( e ). Thus, the first and second mandrels  53  (a) and  53 ( d ) form a two-stage floating mandrel within the internal primary conduit  47 . The secondary extrudate which will ultimately comprise the second, low density foamed thermoplastic component  16  of the multi-component extrusion  10  of FIG. 1 enters the die assembly  40  of FIG. 2 through the secondary extrudate inlet  49 , the internal secondary conduit  51 , and then the voids formed between the first and second mandrels. A mandrel shaping plate  54  is positioned adjacent to the mandrel plate  52  and is in fluid communication therewith for further shaping the principal extrudate about the external surface  53 ( c ) of the first mandrel  53 ( a ). The tapering fins  53 ( e ) taper in thickness from the maximum thickness shown in FIG. 4 b  to a thin edge (hidden from view) approximately one-quarter of the length of the first and second mandrels in a manner well known to those of ordinary skill in the art so that at the exit end of the first and second mandrels the fins end and are absent from the void  55 . The die assembly  40  further includes first and second capstocking dies  56 ,  58 , having corresponding first and second internal channels  57 ,  59  for introduction of a third extrudate in the form of a capstock from a third extruder (not shown) through capstocking inlet  62  in first capstock die  56 , as best seen in FIG. 5.  
         [0036]    [0036]FIG. 5 is a schematic representation of extrudate flow through die assembly  40 , illustrating flow of the primary extrudate  64 , the secondary extrudate  66 , and the third extrudate  68 . As stated above, the primary extrudate forms the thin wall, high density, hollow component  12 ; the secondary extrudate forms the second, low density foamed thermoplastic component  16 ; and the third extrudate forms the thermoplastic cap  20  of the extrusion  10  shown in FIG. 1.  
         [0037]    Table 1 hereinbelow illustrates one preferred formulation used for the principal extrudate used in the production of the thin wall, high density hollow component  12 , shown in FIG. 1. In this preferred embodiment, the thin wall, high density hollow component  12  consists of a polyvinyl chloride (PVC)/wood flour composite. The inclusion of wood flour is preferred, but nevertheless is optional.  
                                                           TABLE 1                           PVC/Wood Flour Composite            INGREDIENT   PERCENT   SUPPLIER   CITY   STATE                    PVC resin   50.25   Shintech   Freeport   Texas       Stabilizer   0.75   Witco   Taft   Louisiana       Plasticizer   1.51   Kalama   Kalama   Washington       Process Aid   1.96   Struktol   Stow   Ohio       TR-060       Lubricant   0.50   Morton   Cincinnati   Ohio       PCS-351E       Modifier   5.03   GE   Morgantown   West       B-360               Virginia       Wood Flour   40.00   American   Schofield   Wisconsin       (60 Mesh       Wood       Pine)       Fiber                  
 
         [0038]    The secondary extrudate  66  which forms the second, low density foamed thermoplastic component  16  in the preferred embodiment shown in FIG. 1 consists of a polyvinyl chloride (PVC) foamed core. Table II illustrates one preferred formulation of the secondary extrudate  66 .  
                                                           TABLE II                           PVC Foam Core            INGREDIENT   PERCENT   SUPPLIER   CITY   STATE                    PVC resin SE 650   77.97   Shintech   Freeport   Texas       Stablizer   1.25   Witco   Taft   Louisiana       MK 1915       Lubricant   1.55   Cognis   Kanakee   Illinois       VGE-1875       Calcium   0.39   Synpro   Cleveland   Ohio       Stearate       Lubricant   0.12   Cognis   Kanakee   Illinois       AC-629A       Modifier   4.68   Kaneka   Pasadena   Texas       PA-40       Titanium   0.78   Huntsman   Lake   Louisiana       Dioxide       Tioxide   Charles       Filler UFT   2.34   OMYA   Florence   Vermont       Foaming   9.36   Clariant   Charlotte   North       Agent                   Hydrocerol       Process Aid   1.56   Struktol   Stow   Ohio       TR-060                  
 
         [0039]    A preferred formulation used for the third extrudate  68 , forming the thermoplastic cap  20  in the multi-component extrusion  10  of FIG. 1, is illustrated in Table III, wherein the thermoplastic has favorable weatherability characteristics.  
                                                           TABLE III                           PVC Cap            INGREDIENT   PERCENT   SUPPLIER   CITY   STATE                    PVC Resin   76.161   Shintech   Freeport   Texas       SE-650       Stabilizer   0.610   Witco   Taft   Louisiana       401P   0.228   PQ Corp.   Kansas City   Kansas       Lubricant   2.44   Cognis   Kanakee   Illinois       VGE-3041       Anti-stat   0.38   Clariant       Germany       Modifier K-   4.95   Kaneka   Pasadena   Texas       37       Calcium   3.04   OMYA   Florence   Vermont       Carbonate       TiO2   7.62   Huntsman   Lake   Louisiana               Tioxide   Charles       Calcined   4.57   Burgess   Sanders-   Georgia       Clay           ville                  
 
         [0040]    Alternatively, thermoplastic component  20  may be provided by an alternate formulation of the third extrudate  68  in the form of a highly paintable thermoplastic cap  20 . A preferred extrudate formulation is illustrated in Table IV, wherein the principal ingredients of that extrudate are Styrene Acrylonitrile (SAN) and Acrylic Styrene Acrylonitrile (ASA).  
                                                           TABLE IV                           ASA Cap            INGREDIENT   PERCENT   SUPPLIER   CITY   STATE                    SAN B-578   69.125   GE   Morgantown   West                       Virginia       ASA B-984   29.625   GE   Morgantown   West                       Virginia       EBS Advawax 280   0.50   Morton   Cincinnati   Ohio       Calcium   0.50   Synpro   Cleveland   Ohio       Stearate       UV Absorber   0.25   GE   Morgantown   West                       Virginia                  
 
         [0041]    An alternate embodiment of the multi-composite polymer/wood fiber extrusion  10 ′ is shown in FIG. 6. This alternate embodiment employs a first thin wall, high density, hollow component  12 , substantially identical to the corresponding component of FIG. 1. In addition, a second, low density foamed thermoplastic component  16  is employed which is also identical to that shown in FIG. 1, with a corresponding reference numeral. However, the extrusion  10 ′ of FIG. 6 has a first component  12 , having a slightly different shape in profile, including an intermediate web portion  80 , dividing the interior cavity  14  shown in FIG. 1 into twin cavities in which the second, low density foamed thermoplastic component  16  resides. The alternate embodiment 10′ also includes a thermoplastic cap  20  identical to that shown with respect to the first embodiment 10 shown in FIG. 1. However, the alternate embodiment 10′ is provided with a further, low density foamed thermoplastic component  82 , intermediate the thermoplastic cap  20  and the exterior surface  18  of the thin wall, high density component  12 . The further, low density foamed component  82  may be formed from an extrudate having a composition identical to the second, low density foamed thermoplastic component  16 , as shown in Table II hereinabove.  
         [0042]    The alternate embodiment 10′ of the multi-component extrusion shown in FIG. 6 is manufactured utilizing a modified form of the die assembly  40  shown in FIG. 2. In this alternate embodiment, the mandrel plate  52  is replaced with an alternate mandrel plate design  52 ′, shown in FIGS. 7 a  and  7   b . In this alternate embodiment, the first mandrel  53 ( a )′ is provided with a first section  84  and a second section  86 , interconnected by a fin  88 . Each of the sections includes an outer, hollow mandrel  90  and an inner, floating mandrel.  92 , having a solid cross-section. Each of the mandrels is supported by a plurality of fins, shown with respect to the first embodiment. In addition, the alternate embodiment of the mandrel plate  52 ′ is provided with a tertiary extrudate inlet  94 , which is in fluid communication with an internal tertiary conduit  96  for introduction of a tertiary extrudate which will result in the further, low density foamed component  82 , shown in FIG. 6. The tertiary extrudate may have the same formulation as shown in Table II with respect to the secondary extrudate  66  and second, low density foamed thermoplastic component  16  of the first embodiment 10.  
         [0043]    Further alternate embodiments of the invention are contemplated. By way of example and not limitation, the capstock material  20  of alternate embodiment 10′ may be eliminated, and the tertiary extrudate which forms the further, low density foamed component  82  may be replaced with a formulation having a significant wood flour component and improved paintability characteristics resulting from the formulation illustrated in Table V, below, in which the principal thermoplastic component is Styrene Acrylonitrile (SAN) polymer resin.  
                                     TABLE V                           SAN/Wood Flour Foamed Composite                PERCENT                        (by       INGREDIENT   weight)   SUPPLIER   CITY   STATE               SAN Resin   70-90   Kumho       South                       Korea       Wood Flour    5-25   American   Schofield   Wisconsin               Wood Fiber       ABS   2-8   GE   Morgantown   West       Modifier               Virginia       Lubricant   0.1-0.5   Synpro   Cleveland   Ohio       Foaming   0.5-3.0   Color   Cleveland   Ohio       Agent       Matrix       80-428-1                  
 
         [0044]    In each of the above-described embodiments, all of the components exit the second capstocking die plate  58  in a molten (i.e. plastic) state and are introduced into a calibration unit (not shown) where the extrudate is cooled to shape. The resulting multi-component extrusion is preferably cooled further in a conventional cooling tank. Subsequent thereto the resulting extrudate enters a puller before it is cut to length by a saw subsequent to assembly into a window frame or the like.  
         [0045]    The above described methods and apparatus are also applicable for the production of decking and siding. By way of example, a third, alternate embodiment of the invention is generally indicated at reference numeral  10 ″ in FIG. 9. This embodiment employs a component structure substantially identical with respect to the second embodiment 10′ shown in FIG. 6 where like reference numerals refer to like structure. As will be appreciated by those of ordinary skill in the art, appropriate materials can be selected from those shown in Tables I through V above to achieve the desired macroscopic mechanical properties and weather resistance of the resulting multi-component extrusion  10 ″. Similarly, a decking material can be provided in the form shown with respect to the first preferred embodiment 10, shown in FIG. 1. In this alternate embodiment the cross-sectional shape of the extrusion is substantially identical to decking in the form of standard dimensional lumber wherein the multi-component composite decking extrusion has a foam composite core shown at reference numeral  16  in FIG. 1, surrounded by a composite shell core corresponding to reference numeral  12  of FIG. 1, and a cap corresponding to reference numeral  20  in FIG. 1.  
         [0046]    In view of the above, the invention is not to be limited by the above disclosure but is to be determined in scope by the claims which follow.