Compression molding of synthetic wood material

This application is a continuation of U.S. patent application Ser. No. 08/739,416 filed Oct. 29, 1996, now U.S. Pat. No. 6,180,257.

The present invention relates generally to wood replacement materials. In particular, the present invention relates to a wood-polymer composite material suitable for use in place of natural wood. The present invention describes a process for manufacturing the composite materials.

For several reasons, there is a need to find materials that exhibit the look and feel of natural wood. One reason has to do with the supply of good wood for construction purposes from the world's forest. This supply of wood from mature trees has become an important issue in recent years and as a result the cost of wood has risen.

Several attempts have been made by others to find a wood like material. Many of these efforts have failed due to the qualities of the resultant product.

In addition to natural wood, other materials such as particle board, wafer board, and the like may be replaced by the synthetic wood of the present invention. One noticeable improvement over these materials is that synthetic wood has enhanced moisture resistance.

The present invention overcomes many of the disadvantages of the prior art attempts at a quality wood replacement material that is capable of being produced in a commercially practicable production environment. The present invention includes the combining of cellulosic material with a thermoplastic material and optionally with a cross-linking agent to form a combined product.

In the present invention conventional compression molding equipment is used to fuse the combined product under sufficient conditions to blend the combined product into a homogeneous mixture and a completed useable synthetic wood material component.

In a preferred material composition of the present invention, the synthetic wood material includes approximately two-thirds organic fibrous or cellulosic material and approximately one-third thermoplastic material in combination. The resultant product has an appearance similar to wood and may be sawed, sanded, shaped, turned, fastened and/or finished in the same manner as natural wood. The resultant product is resistant to rot and decay as well as termite attack. The resultant product may be used for example as, decorative moldings inside or outside of a house, picture frames, furniture, porch decks, window moldings, window components, door components, roofing systems, and any other type of use where structural requirements do not exceed the physical properties of the resultant material.

More particularly, in a preferred embodiment of the present invention, it is useful in conjunction with the synthetic wood composition and method as described in U.S. Pat. No. 5,516,472 which issued on May 14, 1996, entitled EXTRUDED SYNTHETIC WOOD COMPOSITION AND METHOD FOR MAKING SAME.

FIG. 1 is a schematic diagram illustrating the process of the present invention;

FIG. 2 is a schematic representation of a first embodiment of a resultant product of the present invention; and

FIG. 3 is a schematic representation of a second embodiment of a resultant product of the present invention.

The present invention is directed toward synthetic wood compositions of the type in which synthetic wood material composites are compression molded.

The cellulosic fibrous-polymer composite material used in the present invention may have a higher cellulosic fiber content then normally recognized. The overall process may include the mixing of raw materials including cellulosic fibers, thermoplastic materials, cross-linking agents and process lubricants. The cellulosic material may be any one or more cellulosic materials such as sawdust, newspapers, alfalfa, wheat pulp, wood chips, wood fibers, wood particles, ground wood, wood flour, wood flakes, wood veneers, wood laminates, paper, cardboard, straw, cotton, rice hulls, coconut shells, peanut shells, bagass, plant fibers, bamboo or palm fiber, and kenaf. Cellulosic material is first dried to a low moisture content. Although apparently not critical a preferred moisture content is about 1%-10%. Thermoplastic materials may include multilayer films, polyethylene, polypropylene, polyvinyl chloride (PVC), low density polyethylene (LDPE), ethyl-vinyl acetate, other polyethylene copolymers and other thermoplastics.

Examples of cross-linking agents include polyurethanes, such as isocynate, phenolic resins, unsaturated polyesters and epoxy resins and combinations of the same. Lubricants may be added as a process aid. Examples of lubricants include zinc stearate or wax. Other materials may be added which are known to the art and include accelerators, inhibitors, enhancers, compatibilizers and blowing agents.

In the preferred embodiment of the present invention, as shown in FIG. 1, the cellulosic fiber, thermoplastic raw materials, and other minor ingredients are physically mixed or blended by any simple or conventional mixing or blending device. The preferred process temperature at the compression mold is about 350° F. Several well known compression molding machines may be used in the present invention.

The composition achieved surprising results when it was compression molded to form flat boards or other three dimensional shapes. The powder blended composition was placed in a compression mold under heat and pressure to form a three dimensional shaped article as shown in FIG. 2 .

The compression molding device into which the composition is loaded includes one or more mold cavities, a hydraulic press, temperature controls, and cooling features.

As shown in FIG. 3, an optional film or sheet layer may be added to adhere to the wood composite material to provide a different aesthetic and functional surface appearance. The compatible films or sheets may include such weatherable polymer films as PVC, CPVC, S-RPVC, fluoropolymer, acrylic, and acrylic-fluoropolymer alloys appropriately selected to match compatibility with the substrate wood-like composite material. These films may naturally adhere to the compression molded composite substrate when compressed onto the substrate while in the compression mold under the temperature and pressure provided by the compression mold process, or they may be later secured to the substrate by using adhesives or compatibilizers such as EVA, EMA, and caprolactone for example.

48″×120″ synthetic wood boards were compression molded on a 4000 ton Dominion slab-sided Hydraulic press which was manufactured around 1955. The platen dimensions of the press were 3″×62″×148″.

The loose material was loaded by weight into a ¾″ sheet mold which was lined with a ¾″ thick wooden frame. The height of the frame was between 2 to 2.375 inches. The area inside the wooden frame was 50″×124″.

The material was loaded in the mold and distributed evenly (leveled) in the mold by the use of a straight bar which is indexed equally off the sides of the mold so as to provide an even distribution.

A flat aluminum plate (lid) was placed on top of the synthetic wood material and the mold was loaded into an unheated press.

The press was closed to a line pressure of 700 PSI, and the operating temperature was set at 350° F.

The molds were heated for (1) hour and (5) minutes including the heat-up time. (Heat-up time would be approximately 25 minutes.) After the heat cycle, the press was cooled for approximately one hour and the sheets were done.

Below is a summary of some pertinent facts:

Inside dimension of mold: ¾″×51.5″×125.5″

Mold dimension inside wooden frame: 50″×124″

Weight loaded: 203 lbs. per mold

Height of wooden frame: Approximately 2″

Height of leveled pile before processing: 2.7″

Compressed thickness of finished sheet: 0.903″-0.911″

Total length of heat cycle including 25 minute heat-up period: 1 hour-5 minutes.

Processing temperature: 350° F.

Internal temperature of the material at the end of the heat cycle: 330° F.

Processing pressure: 700 PSI line pressure for the entire heat and cool phase of the cycle.

Processing pressure on the work (specific pressure): 355 PSI

Length of cool cycle: Approximately 1 hour.

Press used: Dominion. 4000 ton slab-sided hydraulic press. Manufacture approximately 1955.

Platen size: 3″×62″X148″

Bulk density of the loose material was: 21 lbs./ft. 3

Density of the finished product was: 62.4 lbs./ft. 3

The above described advantages and features of the present invention are offered as an example of the way in which the present invention may be commercially implemented. The embodiments listed herein are, therefore, exemplary in nature and are not intended to unnecessarily limit the scope of the following claims.