Method and apparatus for making products from polymer wood fiber composite

Abstract

A method and apparatus for making products from polymer wood fiber composite is described. The method includes the steps of providing a extruder having two counter-rotating non-intermeshing screws, supplying to the extruder fiber material and polymer material, mixing and heating the fiber material and polymer material in the extruder for form a mixture, removing the mixture from the extruder and placing the mixture in a press, and compression molding the mixture in the press to form the product.

Description

FIELD OF INVENTION [0001] The present invention relates to a method and apparatus for the continuous manufacture of products from a mixture of a fiber material, particularly wood fiber, and a polymer binder, and more particularly to a method and apparatus that allows large sized wood fiber particles to be used. BACKGROUND OF THE INVENTION [0002] A large number of processes have been proposed for combining wood fiber with a polymer resin binder to produce materials for making various types of finished products. The advantages of such materials include their cost and appearance, and its ability to be used as substitutes for lumber. Extensive applications have been made of these materials in making extruded components for the manufacture of windows and doors. [0003] In many prior art processes, the wood has been supplied only in the form of a wood flour having a small particle size and specific moisture properties. The small size, limited size range and limited moisture content have be...

AI Technical Summary

Benefits of technology

[0040] The counter-rotating non-intermeshing twin screw extruder has unique distributive mixing capabilities that make it highly desirable for this application. The counter-rotating screws that are non-intermeshing (or at least non-self wiping) reduce destruction to the fibers. This provides an advantage of the present invention, since fiber length is maintained, and long fibers that can be used in the present invention are retained to improve the quality of the finished product. This provides increased tensile strength and flex modulus to the finished product. Other processes in which fibers are destroyed result in shortened fiber lengths and associated decreases in tensile and shear strengths and flex modulus.

[0041] The method of the present invention has shown to be particularly useful in the manufacture of pallet skids, and replaces the manufacture of pallets made by nailing up pieces of lumber. However, the method can also be used to make any items that can be molded, and it is particularly useful in making decking, panels, privacy fences, boat docks, playground equipment, trailer inner walls, and railroad ties. Products made using the method of the present invention are especially useful as structural components, since the resulting products have a high tensile strength.

Problems solved by technology

If the wood particle sizes were too large or if the particle sizes varied too greatly or if the moisture content of the wood particles was too great, the resulting mixture with the polymer resin would be inconsistent, and the quality of the resulting product would suffer.

This increased the cost of wood material used, and thus increased the overall cost of the finished product.

Furthermore, it has been difficult to obtain desired physical properties in the finished products.

However, in manufacturing wood / polymer composite replacement products, the size of the wood particles has been very limited, so that the products made of these replacement materials have not been able to achieve comparable tensile strength.

As a result many of these products have been relatively brittle and inferior to those made of actual lumber.

Another problem with prior art processes is that most of them are not continuous.

Making material in batches or providing an intermediate step of forming pellets does not provide a continuous process and can result in inconsistencies in product properties and inefficiencies resulting from starting and stopping the process.

Discontinuous processes are also energy inefficient, since the material must be heated and cooled more than once.

Furthermore, the processing of the wood fiber polymer mixture into pellets or other intermediate products can result in degradation of the fiber size in the mixture, which can adversely affect the desired physical properties of the finished products.

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