Abstract:
A system and method for extruding composite material and the composite material therefrom. The composite material consists of a filler mixed with a binding agent. The composite material is extruded as billets with enhanced physical properties, such as colour, texture, electrical conductivity and fire retardancy, and contains a dispersion pattern of the filler material. A system and method are also provided for drawing the composite material through a die and a composite material produced thereby. The drawn composite material exhibits a density reduction over the density of the starting material and enhanced physical properties. A particularly useful tongue and groove arrangement are also provided for joining adjacent strips of a composite material made according to the extrusion process.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to extrusion processes. In particular, the present invention relates to an extrusion method and apparatus for composite material.  
       BACKGROUND OF THE INVENTION  
       [0002]     The process of solid-state extrusion is known. Extrusion processes that are used include ram extrusion and hydrostatic extrusion. Ram extrusion utilises a chamber in which polymer billets are placed, one end of which contains a die and the other an axially mobile ram. The billet is placed within the chamber such that the sides of the billet are touching the sides of the chamber. The mobile ram pushes the billets and forces them through the die.  
         [0003]     In hydrostatic extrusion processes, the billet is of a smaller size than the chamber and does not come into contact with the sides of the chamber. The chamber contains a pressure generating device at one end and a die at the other. The space between the billet and the chamber is filled with a hydraulic fluid, pumped into the chamber at the end containing the pressure generating device. During operation pressure is increased on the hydraulic fluid and this in turn transmits pressure to the surface of the billet. As the billet passes through the die some of the hydraulic fluid adheres to the surface of the billet, providing additional lubrication to the process.  
         [0004]     Both processes produce a polymer that is oriented in a longitudinal direction, having increased mechanical properties, such as tensile strength and stiffness. However, the orientation in a longitudinal direction can also make the polymer weak and subject to transverse cracking or fibrillation under abrasion. The process of pushing the polymer through a die can also create surface imperfections caused by frictional forces.  
         [0005]     U.S. Pat. No. 5,204,045 to Courval et al. discloses a process for extruding polymer shapes with smooth, unbroken surfaces. The process includes heating the polymer shape to below the melting point of the polymer and then extruding the polymer through a die that is heated to a temperature at least as high as the temperature of the polymer. The process also involves melting a thin surface layer of the polymer to form a thin, smooth surface layer. The process produces a material of a uniform appearance and subsequent commercial applications are limited as a result.  
       SUMMARY OF THE INVENTION  
       [0006]     A composite material comprising an oriented polymer and a particulate filler dispersed throughout the oriented polymer. The composite material has a reduced density which is less than the combined masses of the oriented polymer and a particulate filler divided by their combined respective volumes.  
         [0007]     The oriented polymer maybe of plastic and the particulate filler may be selected from the group consisting of wood, slate, talc, vermiculite and mica.  
         [0008]     The plastic may be polypropylene, polyethylene and polyvinyl chloride and present in an amount of from 95% to 60% by weight as compared to the particulate filler.  
         [0009]     According to one embodiment, the oriented polymer is polypropylene and the particulate filler is wood sawdust having a particle size of about 60 mesh and present in amount of from 20% to 30% by weight as compared to the weight of the oriented polymer.  
         [0010]     A process for producing an oriented composite material, said process comprising the steps  
         [0000]     of combining:  
         [0000]    
       
         
           
              (i) an extrudable polymer with a particulate filler to form a starting material;  
              (ii) heating and extruding said starting material into a first column;  
              (iii) adjusting the temperature of said first column to a drawing temperature;  
              (iv) presenting said first column to a drawing die and causing said first column to exit said drawing die in a second column having a cross-sectional area less than that of said first column;  
              (v) applying a pulling force to said second column to draw said first column through said drawing die at a rate sufficient to cause orientation of said polymer and to cause said second column diminish in density to form said composite material.  
           
         
       
     
         [0016]     The extrudable polymer may be of plastic, such as polypropylene, polyethylene or polyvinyl chloride.  
         [0017]     The particulate filler may be wood, slate, talc, vermiculite or mica.  
         [0018]     The extruable polymer may be present in an amount of from 95% to 60% by weight in the starting material.  
         [0019]     According to one embodiment, the extruable polymer is polypropylene, the particulate filler is wood sawdust having a particle size of about 60 mesh, the wood sawdust being present in an amount from about 20% to 30% by weight in the starting material.  
         [0020]     The rate of drawing through the drawing die may be sufficient to cause the composite material to have a density of from 0.5 to 0.9 of the density of the starting material.  
         [0021]     A composite material is provided which includes a filler for enhancing the physical properties of the composite material and a binding agent mixed with the filler for permitting extrusion of the composite material in a plastic extrusion process to provide a predetermined dispersion pattern of the filler in the composite material.  
         [0022]     The filler may be natural or synthetic fiber and the binding agent may be a polymer.  
         [0023]     A composite material is provided which comprises a particulate material dispersed in an oriented polymer.  
         [0024]     The particulate material may be wood sawdust having a particle size of about 60 mesh. The oriented polymer may be polyethylene with the oriented polymer forming from 60% to 95% by weight of the composite material.  
         [0025]     A strip of composite material is provided, suitable for strip flooring and having parallel upper and lower faces with first and second parallel edges extending between the upper and lower faces. The first edge has a tongue extending therefrom with parallel upper and lower curved surfaces. The second edge has a groove extending thereinto with curved parallel opposite sides. The tongue and the groove are of complimentary curvature for the tongue of a first strip to be rotatable into registration with the groove of an adjacent strip to resist lateral separation between the first strip, and the adjacent strips by interference between the upper and lower curved surfaces and the curved parallel opposite sides. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:  
         [0027]      FIG. 1  illustrates a method of extruding a composite material according to the present invention;  
         [0028]      FIG. 2  illustrates an extruder for extruding same;  
         [0029]      FIG. 3  illustrates an extruded billet of the composite material;  
         [0030]      FIG. 4  is an end elevation of a tongue and groove joint which may be formed in the extrusion method of the present invention;  
         [0031]      FIG. 5  is a cross-sectional illustration of an alternate forming method according to the present invention; and  
         [0032]      FIG. 6  is a schematic illustration of an automated process of the method of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Referring now to  FIG. 1 a  method of extruding a composite material is shown generally at  10 . A filler  12  and a binding agent  14  are placed in a feeder  16 . Feeder  16  feeds a predetermined volume of filler  12  and binding agent  14  into melt extruder  18 . In an embodiment, feeder  16  is a gravimetric feeder controlled by an external CPU  17 . Melt extruder  18  mixes filler  12  and binding agent  14  to form feedstock  20 , as is well known to those of skill in the art. Feedstock  20  then passes to an extruder  22 , and is extruded to produce a composite material  24 .  
         [0034]     Filler  12  can be a natural fibre, such as wood and agricultural fibres such as hemp, flax, straw or wheat; a synthetic fibre such as nylon, polyethylene terephthalate, glass or polypropylene fibre with a polyethylene matrix. Filler  12  can also be a mineral based filler such as slate, talc, vermiculite or mica. In a presently preferred embodiment, filler  12  is a wood fibre concentrate. Filler  12  has a mesh in the range of 10-300, more preferably in the range  10 - 150 . In the presently preferred embodiment filler  12  has a 60 mesh.  
         [0035]     Binding agent  14  is a polymer or other suitable extrudable plastic, such as polypropylene (PP), polyethylene (PE) or polyvinyl chloride (PVC). Binding agent  14  forms approximately 55-95% by weight of feedstock  20 . Other ranges for the % weight of binding agent  14  in feedstock  20  may be appropriate depending on the filler chosen. More limited ranges of 60-95% or 70-90% may be required depending on the chosen filler  12 .  
         [0036]     Once filler  12  and binding agent  14  have been fed to feeder  16 , they pass to melt extruder  18 . A predetermined volume of filler  12 , in accordance with the % weight of binding agent  14  that is used, and binding agent  14  are mixed in melt extruder  18  and extruded in a conventional manner to produce feedstock  20 . The resultant feedstock  20  is fed by melt extruder  18  to extruder  22 .  
         [0037]      FIG. 2  illustrates a preferred embodiment of extruder  22 . Extruder  22  has a ram  34 , a pressure chamber  30  and a die  38 . The method and apparatus of the extrusion process are detailed 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 contents of which are incorporated herein by reference. The method of the extrusion process produces a highly oriented polymer profile. The resultant composite material  24 , produced by this process, generally has a higher tensile strength and modulus than feedstock  20 . In the presently preferred embodiment an oriented product  48  of composite material  24 , formed with a wood-fibre concentrate filler is produced in standard widths of 2 inches, 3 inches or 6 inches (5.08 cm, 7.62 cm or 15.24 cm).  
         [0038]      FIG. 3  illustrates an oriented product  48  of composite material  24 . Produced in the manner outlined above, composite material  24  has striations  50  of filler  12 , formed in a dispersion pattern with a wood-grain appearance. The resultant oriented product  48  resembles hard wood flooring and can be adapted to be used in commercial applications as such. Appropriate attaching means, such as a tongue and groove, or snap lock, can be subsequently tooled in to the oriented material to create a product that can be attached in series in a commercial application, such as flooring or furniture manufacturing. Surface treatment can also be applied to the billet for increasing the surface properties of the billet, such as adding a protective coating, such as polyurethane, to protect the surface layer from scratching.  
         [0039]     By varying parameters of the ram extrusion process, such as temperature, pressure and die contours, properties of composite material  24  can be changed. The properties of composite material  24  can also be changed by varying amounts of filler  12 , and by changing the composition of filler  12 . This will affect the physical properties of composite material  24 , such as colour, texture, electrical conductivity, glow in the dark and fire retardancy.  
         [0040]     The oriented product  48  of composite material  24  can be manipulated in order to meet a manufacturer&#39;s specifications with regards to the final commercial application. Oriented product  48  can be cut and shaped during the ram extruding process. In the presently preferred embodiment, composite material  24  is extruded as oriented product  48  of varying specifications, however it can also be extruded as a sheet for use in commercial applications such as indoor and outdoor furniture manufacturing.  
         [0041]     The present invention provides a new composite material, and a method and apparatus for extruding the composite material. The invention includes the initial mixing of a binding agent and a filler to produce a feedstock which is subsequently extruded as a billet of a composite material. The composite material is stronger and more durable then the starting materials. The composite material also contains striations of the filler which allows the manufacturer to produce a composite material that can reflect the image of a natural product and can be used in commercial applications such as floor coverings. The properties of the composite material can also be changed, in order to met the requirements for the commercial application of the product, by the incorporation of different types of filler and by varying the amount of filler used.  
         [0042]      FIG. 4  is an end elevation showing a particularly advantageous tongue and groove configuration which can be formed along opposite edges of the oriented product  48  of the composite material  24 . A first edge  50  has a tongue  52  formed thereon having an upper concave face  54  and a lower convex face  56 . The opposite edge  60  has a groove  62  with an upper convex edge  64  and a lower concave edge  66 . The tongue  52  and the groove  62  register to allow the tongue to be initially inserted into the groove  62  of an adjacent strip of oriented product  48  at a relative angle on the order of 45° between the adjacent strips of oriented product  48  and then rotated into place in the direction of arrow  70  so that the tongue  52  nests in the groove  62  with the adjacent strips of oriented product in a parallel side by side configuration.  
         [0043]     Once the tongue  52  and the groove  62  are nested, removal in a lateral direction indicated by arrows  80  is prevented first by interference between an upper edge  58  of the tongue and a depending edge  68  of the groove. Lateral separation is further inhibited by an upwardly extending edge  69  of the groove  62  interfering with a lowermost portion  59  of the tongue  52 .  
         [0044]     Extrusion rates for the composite material  24  will vary depending on various factors such as the particular composite material  24  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.) are not atypical.  
         [0045]     It has been found that rather than extruding the composite material  24 , by pressing it through the die  38 , the composite material may be drawn through the die  38 .  FIG. 5  illustrates such a drawing process.  
         [0046]     One manner of drawing the composite material through the die  38  is to initially commence by extrusion, as discussed above. Once an end  100  of the oriented product  48  begins to emerge from the die  38 , the end may be grasped, such as by a clamp  102  and pulled. The pulling would typically be done with no further pressing force being applied and yields an oriented end product  104 .  
         [0047]     In tests, pulling rates of up to 14 ft./min. (fourteen feet per minute) have been achieved which was limited by machine capacity. It is expected that pulling rates of 20 ft./min. (twenty feet per minute) are entirely feasible.  
         [0048]     The properties of the oriented end product  104  produced by drawing are significantly different than those produced by extrusion. By way of example, a starting billet  110  was first formed by combining a wood fiber plastic concentrate containing 60% wood particles of about 60 mesh size and 50% polypropylene with virgin polypropylene in a 1:1 ratio. This yielded a composition having about 30% wood fiber and 70% polypropylene. The resulting combination was heated and extruded to form the billet  110 .  
         [0049]     The billet  110  was of rectangular cross-section measuring about two inches by two inches (2″×2″). The billet  110  was heated in an oven to about 150° C. (ie. close to but below the melting point of polypropylene which is about 160° C.) and transferred to the pressure chamber  30  and initially forced through the die  38 . The extruded material was then grasped using the clamp  102  and drawn at a rate of about 4 ft./min. (Four feet per minute) and once it had been entirely drawn through the die  38 , allowed to cool into the oriented end product  104 . The draw ratio (i.e. the initial cross-sectional area divided by the final cross-sectional area) was 10:4.  
         [0050]     The oriented end product  104  bore a remarkable similarity both in look and in feel to wood. The oriented end product  104  diminished in density by about half compared to the starting billet  110 . The density of the oriented end product  104  was about 0.59 g/cc (grams per cubic centimeter) compared to a density of about 1 g/cc for the starting billet  110 .  
         [0051]     The oriented end product  104  could be shaped as if it were wood and in planing and sawing behaved very much like wood producing shavings remarkably like wood shavings and sawdust remarkably like wood sawdust. The oriented end product  104  received both nails and screws without splitting much like wood.  
         [0052]     In testing, the oriented end product was found to have a density and flexural strength not unlike wood and a modulus of elasticity of about half that of wood. Typical properties were a density of 0.059 g/cc, flexural strength of 6,353 lb/in 2  and a modulus of elasticity of 799,298 lb/in 2 . Unlike wood however the oriented product  104  was virtually non adsorptive to water.  
         [0053]     Although testing was carried out using a starting billet  110 , the process can no doubt be automated as schematically illustrated in  FIG. 6 .  FIG. 6  shows an extruder  120  in which feed materials  121  may be blended and extruded through a die  122  into a first column  124 . The first column  124  is fed through a first haul off  125  into a continuous furnace  126  where its temperature is adjusted to a drawing temperature. The first haul off  125  acts against the extrusion direction to maintain extrusion pressure and to support the column  124 . The temperature adjusted first column  124  is fed into a drawing die  128  at the exit of which it is reduced in size to a second column  130 . The second column  130  is grasped by a suitable haul off  132  such as sold under the trademark CATERPILLAR as it exits the drawing die  128 . The haul off  132  then pulls the second column  130  at a desired rate to form an oriented product  138 .  
         [0054]     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.