Abstract:
A composite siding comprising a binder and a wood-based filler. The composite siding is preferably produced by a pultrusion process and exhibits great dimensional stability, aging resistance to damage characteristics while maintaining high product stiffness and strength.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to composite siding and more particularly to composite siding comprising wood fiber in a polymeric binder.  
         BACKGROUND OF THE INVENTION  
         [0002]    Composite products comprising a binding agent such as a polymer or other extrudable plastic into which is incorporated a filler have been produced by both an extrusion and a pultrusion process. An example of existing extrusion processes are described in U.S. Pat. No. 5,169,589 to Francoeur et al., U.S. Pat. No. 5,204,045 to Courval et al. and U.S. Pat. No. 5,169,587 to Courval. The pultrusion process is known in the art and comprises the extrusion of the composite material through a die while simultaneously pulling the thus extruded material in its longitudinal direction to provide polymer and filler orientation to a desired degree. An example of an existing pultrusion process is disclosed in PCT Application WO 01/45915A1, published Jun. 28, 2001. Pultrusion processes have been used to make a variety of different materials; however, none have been employed to produce a composite siding composed of a binding agent and wood fiber that meets the high standards of the building industry.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention therefore provides a composite siding comprising a binder and a wood filler. Preferably, the wood filler comprises wood flour or sawdust. The wood siding has superior conventional characteristics, for example stability, weather aging, combustibility characteristics, and resistance to damage in use set forth in Table 1 below while maintaining high product stiffness and product strength.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0005]    [0005]FIG. 1 is a perspective view of a piece of composite siding having the characteristics set forth herein. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0006]    The composite siding of the present invention comprise a binding agent and a filler that is extruded and preferably lengthened using a pultrusion process. The filler and binding agent are placed in a feeder, which in turn feeds a predetermined volume of filler and binding agent into a melt extruder. The filler and the binding agent are mixed in the melt extruder to form a feed stock as is well known to those of ordinary skill in the art. As shown in FIG. 1, the feedstock then passes to an extruder and is extruded through a die  14  to produce a product  10  of composite material. While being extruded, the composite material is grasped by a mechanical clamp  16  or other pulling means and pulled in the longitudinal direction of extrusion. This orients the polymeric and wood fiber to produce a composite wood-like siding product.  
         [0007]    The filler can be a natural fiber such as wood and agricultural fibers such as hemp, flax, straw or wheat; a synthetic fiber such as nylon, polyethylene terephthalate, glass or polypropylene fiber with a polyethylene matrix. The filler can also be a mineral based filler such as slate, talc, vermiculite, mica or nanoclay. Combinations of fillers may also be used. In a presently preferred embodiment, the filler is a wood fiber in the form of sawdust wood flour, wood particles or pulp. All types of bleached or unbleached pulp produced by any of the conventional pulping processes may be employed. In addition, the pulp may be cross-linked or otherwise bleached in ways known in the art. The most preferred wood fiber is wood flour, processed by grinding planer shavings, chips and sawdust, having a mesh in the range of 10 to 300, and more preferably in the range 10 to 150. In the presently preferred embodiment filler has a mesh size of 60.  
         [0008]    The binding agent is a polymer or other suitable extrudable polymer, such as polypropylene, polyethylene, polyvinyl chloride or other known extrudable polymer. It may be virgin or recycled polymer. The binding agent may form approximately 40% to 80% by weight of feedstock  20 , and more preferably from 60% to 80% by weight. The balance of the feedstock comprises the filler.  
         [0009]    Additives to improve material properties or to enhance the production process may also be added, for example, lubricants, Ultra Violet radiation stabilizers, and anti-bacterials.  
         [0010]    All of the components, i.e., filler, binding agent and additives may be combined prior to extrusion by compounding into pellet form or by pre-mixing.  
         [0011]    The pultrusion process is the preferred method for producing the siding of the present invention, although conventional extrusion processes may be employed. The pultrusion process produces a highly oriented polymer profile. The resultant composite material, produced by this process, generally has a higher tensile and flexural strength and modulus than the extrudate. In the presently preferred embodiment an oriented product of composite material, formed with a wood-fiber concentrate filler may be produced in standard widths of 2 inches, 3 inches or 6 inches (5.08cm, 7.62cm or 15.24cm), or for that matter any other desired width producible by the pultrusion process.  
         [0012]    [0012]FIG. 1 illustrates the oriented product  10  of composite material. Produced in the manner outlined above, the composite material may have striations  12  of filler, formed in a dispersion pattern with a wood-grain appearance. The resultant oriented product resembles soft wood siding and can be used in residential and commercial applications as such. Appropriate attaching means, such as a tongue and groove, or snap lock, can be incorporated in the die or subsequently tooled in to the oriented material to create a product that can be attached in overlapping relation like conventional siding. Surface treatment can also be applied to the oriented product for increasing the surface properties of the product, for example adding a protective coating, such as polyurethane, to protect the surface layer from scratching. Other coatings may be employed, for example, to enhance the paintability of the siding. Embossing means can be used to add texture or smoothness to the product surfaces.  
         [0013]    By varying parameters of the pultrusion process, such as temperature, the pressure and die contours, properties of composite product can be changed. The properties of composite material can also be changed by varying amounts of the filler, and by changing the composition of the filler(s). These variations in processing parameters will affect the physical properties of composite product, such as colour, texture, electrical conductivity, and fire retardancy, and the other desired properties set forth below.  
         [0014]    The oriented product of composite material can be manipulated in order to meet a manufacturer&#39;s specifications with regards to the final commercial application. Oriented product can be cut and shaped during the pultrusion process. In the presently preferred embodiment, composite material is extruded as oriented product of varying specifications, however it can also be extruded as a sheet for use in commercial applications other than siding.  
         [0015]    Extrusion rates for the composite material will vary depending on various factors such as the particular binders and fillers selected, the degree of reduction, and the cross-sectional area of the extruded strip or column. Extrusion rates are however rather slow and rates on the order of six inches per minute (6 in./min.) to three feet per minute (3 ft./min) are not atypical.  
         [0016]    As stated above, the composite material may also be drawn through a die, or simultaneously pushed (extruded) and drawn through a die by conventional pultrusion processes. One manner of drawing the composite material through a die is to initially commence by extrusion, as discussed above. Once an end of the oriented product begins to emerge from the die, the end may be grasped, such as by a mechanical clamp and pulled. The pulling may be done with no further extrusion force being applied to yield an oriented end product 10. Pulling rates of up to 14 ft./min. (fourteen feet per minute) have been achieved. Pulling rates of 20 ft./min. (twenty feet per minute) are entirely feasible.  
         [0017]    The properties of the oriented end product produced by drawing have properties that are different from those produced by extrusion alone. By way of example, a starting billet formed by combining a wood fiber-plastic concentrate containing 30% by weight wood particles of about 60 mesh size and 70% by weight virgin polypropylene. This combination yields a composition having a specific gravity of 0.51 that is much lower than expected without the introduction of air voids. The volume ratio of wood, polypropylene and air in the composition is 11%, 40% and 49%, respectively. The resulting combination was heated and extruded to form the billet.  
         [0018]    The billet is of rectangular cross-section measuring about one inch by five inches. The billet is heated in an oven to about 150° C. (i.e., close to but below, the melting point of polypropylene which is about 160° C.) and is transferred to a pressure chamber and initially forced through a die. The extruded material is then grasped using the clamp and drawn at a rate of about four feet per minute. Once it is entirely drawn through the die  38 , it is allowed to cool into the oriented end product. The draw ratio (i.e., the initial cross-sectional area divided by the final cross-sectional area) is about 8.  
         [0019]    The oriented end product bears a remarkable similarity both in look and in feel to wood. The oriented end product is diminished in density by about half compared to the starting billet. The density of the oriented end product is about 0.510 g/cc (grams per cubic centimeter) compared to a density of about 0.80 g/cc for the starting billet.  
         [0020]    The oriented end product can be shaped as if it were wood and in planing and sawing behaves very much like wood, producing shavings remarkably like wood shavings and sawdust remarkably like wood sawdust. The oriented end product receives both nails and screws much like wood but without splitting.  
         [0021]    In testing, the oriented end product is found to have a density and flexural strength not unlike wood and a modulus of elasticity equal to that of low density wood or ⅓ that of grade 2 lumber. Typical desired properties are set forth in the Table below.  
                                                                                   Range of Values           Characteristic   Measure   Test Standard   (for patent application)   Target                   Maintains   Linear expansion   Temperature: ASTM   1/32″ to 1/16″ in 8 ft   3/64″ to 1/16″ in 8 ft       dimensional stability   along the length   D696   (0.07%) for 3/8 in   length, for 3/8″       (40° F. to 125° F.)       Moisture: ASTM   material   material (40° F. to       (20% RH to 90% RH)       D1037, Sections   Thermal coef of   125° F. temperature               107-110   expansion (TCOE) =   change)                   2 × 10 −6  to 9 × 10 −6     TCOE = 6 × 10 −6  to                   in/in/° F.   8 × 10 −6  in/in/° F.           Linear expansion   Temperature: ASTM   0.005″ to 0.015″ in 8″   1/64″ in 8″ width, for           along the width   D1037 Sec 107-110   in width or 3/8″   3/8″ material                   for samples prep   material                   Moisture: ASTM                   D1037, Sections 107-110           Thickness swell   Temperature: ASTM   0.00541  to 0.0 15″ for   less than 3% for 3/8″               D1037 Sec 107-110   3/8″ material   material               for samples prep               Moisture: ASTM               D1037, Sections 107-110           Sag between supports   N/A   0.005″ to 0.35″ in 24″   Less than 0.0035″                   span between studs   (24″ stud c.c.                       spacing)       Withstands Weather   Freeze-thaw cycling   ICBO AC 174/   70% to 100% of   85-95% of       and Aging   (structural   ASIM Std D6662   unconditioned value   unconditioned value       (low maintenance,   degradation due to       (50% relative   (50% relative       does not fade over   hygrothermal   ANSI Standard 135,   humidity; 70° F.)   humidity; 70° F.)       time, holds paint   cycling)   Section 4.2       well)   Weatherability of       1% to 15% max   1-5% max residual           substrate       residual swell   swell           (Physical change due               to hygrothermal               cycling)               Weatherability of   ANSI Standard 135,   No checking, erosion,   No checking, erosion,           primed substrate   Sec 4.2   flaking, fiber raising.   flaking, fiber raising.           (Physical change due       Adhesion: 1/16″ to   Adhesion: 1/16″ to           to hygrothermal       3/16″ of coating   1/8″ of coating           cycling)       picked-up   picked-up           Permeability of   ASTM Standard E96   0.2-08 perms.   0.2 to 0.4 perms           substrate           Water absorption -   ANSI Standard 135   3% to 15% by weight   5-10% by weight           24 hrs   ASTM Standard               D1037 Sec 163, 164           Thickness swell due   ANSI Standard 135   2% to 8%   Less than 3%           to H 2 O absorption -   ASTM Standard           24 hrs   D1037 Sec 163, 164           Surface H 2 O   ASTM Standard   4-300 g/100 in 2     5-10 g 100 in 2             absorption - Cobb   C473, Sec 82-87           ring       Non combustible   Ignition temperature:   ASTM D1929   400-800° F.   Greater than 550° F.           Lowest air           temperature that will           cause self ignition       Resistant to Damage   Hardness: Resistance   ASTM D143/ASTM   200-1200 lbs   300-500 lbs       in Use   to indentations and   D1037, section 68-73           wear   ANSI 135           Load req&#39;d to press a           0.44″ dia. ball to a           depth of 0.222 in           Impact: Index of   ASTM Standard   5-10 in   7-9 in           resistance to impact.   D1037 Sec 91-95           Failure is reached   ANSI Standard 135           when a visible           fracture occurs at the           bottom surface of the           specimen.           Nail-head pull-   ANSI Standard 135   150-400 lbs   180 lbs           through   and ASTM Standard               D1037 Sec 54-60           Lateral nail resistance   ANSI Standard 135   150-300 lbs   150-300 lbs           (along strong   and ASTM Standard           direction)   D1037 Sec 54-60       Can be carried in 16′   Product stiffness, EI   ASTM Standard   150-68,500 Ibs-   15500-36900 lbs-       length as a plank       D1037, Sec 11   in 2 /ft of width   in 2 /ft of width       Capable of resisting       ladder and wind       loads with minimal       residual deflection       Can be carried in 16′   Product bending   ASTM Standard   49-190 ft-lbs/ft of   80-165 ft-lbs/ft of       length as a plank   strength, M   D1037 Sec 155-158   width   width       without breaking       ANSI Standard 135       Capable of resisting       ladder and wind       loads without       breaking                  
 
         [0022]    The measuring and testing methods used to evaluate the products of the present invention are set forth under the column labeled “Test Standard.” All standards are conventional ASTM or ANSI standards.  
         [0023]    While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.