FR2472461A1 - Dry blending and fusion of reground thermoplastics - and wood-based particles, to produce cheap granules for reprocessing by moulding or extrusion - Google Patents

Abstract

A composite moulding material comprises a blend of chopped wood particles and reground thermoplastic material contg. 40-80% wt. of the wood-based material, where the particles have a mean length of 5-7mm and none has a section greater than 1 sq.mm. The particles are blended and bound by fusion of the thermoplastic constituents. The components are dry belded cold under shear conditions which fuse the thermoplastic constituents without involving external heating, pref. using a screw extrusion blender opt. fitted with a face cutting die to produce composite granules. Additives such as colourants, stabilisers, fire-retardants may also be added during blending. For re-use of sawdust, chopped savings, chopped packaging films etc., to produce a composite granulate suitable for injection moulding, extrusion, milling, thermoforming etc.

Description

The present invention relates to a new composite material based in particular on wood and plastic waste and its production process.

 The object of the invention is the recovery of certain plastic waste materials such as sheets or films used for packaging, overwrapping, the production of greenhouses etc ... as well as wood waste, in order to achieve a composite material of low cost price and susceptible of numerous applications thanks to its good qualities and mechanical properties in particular.

To this end, the subject of the invention is a composite material of the type based on wood or the like and of plastic material characterized in that it comprises between 40 and 802d by weight of wood or the like in the form of particles not exceeding 1 mm2 in cross-section and 5 to 7 mm in their largest dimension and between 60 and 20% by weight of plastic material intimately mixed with said particles and agglomerated by heat alone, said plastic material coming from shredding or reduction into plots or particles of various products in recycled thermoplastics.

 The wood used comes from leaves or conifers and is advantageously obtained from wood residues such as sawdust, shavings, split wood, etc.

 These wood residues are screened beforehand and possibly shredded, crushed or prepared (notably split wood) with a view to accepting acceptable particle size conditions.

Whether it is round wood grains (sawdust) or elongated fibers (splintered wood) the section of the particles should not preferably exceed i min2 while the largest dimension of these elongated particles must not exceed 5 to 7 mm.

The plastic material comes from the recovery of waste thermoplastic materials of heterogeneous compositions and from various sources. This waste is in particular sheets or films of high or low pressure polyethylene, retractable or not, of polyvinyl chloride etc ... having been used for various packaging, overpackaging, materials for the production of greenhouses, coatings for cultivation outside soil, protective films, covers etc ... these various products are now commonly used in agriculture, horticulture and transport.

The present invention also relates to a process for obtaining such a composite product from in particular the above basic products.

 To this end, the particles of wood, after preparation and screening in order to obtain the required particle size conditions and, after drying, are intimately mixed in the proportions by weight also required, with particles or plots of said plastic films or sheets .

These particles or plots are obtained for example by passing a thermoplastic sheet through a knife mill after possible washing and drying thereof. It is of course possible to shred the sheets using other means, for example depending on the nature and shape of the plastic recovery products.

 It is desirable in the case of shredding the sheets not to obtain plots of dimensions greater than 5 to 7 mm.

 Said mixing is carried out dry and cold.

 The mixture thus obtained is then sent to a densifier advantageously constituted by a screw granulator. I1 is a well known device comprising, inside a cylindrical chamber perforated with holes, a rotor compressing said mixture against the wall of the chamber. This treatment causes intense friction generating sufficient heating to soften the plastics which amalgamate with the particles of wood, the paste thus formed passing through the calibrated holes of said cylindrical chamber. One or more knives applied against the external wall of the chamber cut small dough strands which exit therefrom and thus form granules.

 The granules are then transported to a storage and conditioning station after passing through an air cooling circuit.

 It is particularly advantageous to market the composite product according to the invention in the form of granules.

Such a semi-finished product is indeed easy to package, transport and store. It is then implemented on site using injection presses, extruders, etc., in order to produce specific products defined and varied according to the applications envisaged.

The amalgam of particles of wood and plastic by softening them is preferably done by friction without heat input (by a densifier or the like) because it avoids the heat input that would require a fusion which makes the even more economical.

The composite product obtained in accordance with the invention is thermoformable, solid and water-repellent with varying degrees depending on the load of plastics.

It can be used for the production of molded parts, sheets which may be thermoformed later, packaging angles, etc.

By varying the proportions of wood and plastic, we thus obtain different degrees of flexibility or hardness,
Additives can be provided, for example a dye or a flame retardant, added during the implementation of the granules (extension, injection) or after the implementation in the form of introduction into the mass of the finished product.

Other additives tending to improve certain mechanical or presentation characteristics can be envisaged (addition before extrusion or injection).

 One thus realizes the interest of the process of the invention, which makes it possible in a particularly economic way, to recover waste which, without that, would be useless, lost and bulky, with a view to obtaining a cheap and susceptible material many practical applications.

Of course, the invention is not limited to the above examples but on the contrary covers all variants.

This is how wood waste could be replaced by similar waste such as paper, chopped straw, etc.

as for plastic waste they can be of different origins, plastic materials, provided that they are not thermosetting, can be mixed.

Claims (7)

CLAIMS.  1. Composite material of the type based on wood or the like and plastics, characterized in that it comprises between 40 and 80% by weight of wood or the like in the form of per 2 sheets not exceeding 1 mm in cross section and S at 7 mm in their largest dimension and between 60 and 20% by weight of plastic material intimately mixed with said particles and agglomerated by heat alone, said plastic material coming from shredding or reduction or plots or particles of various thermoplastic products of recovery.  2. Composite material according to claim 1 charac terized in that it is made from thermoplastic materials of various kinds or not, in the form of sheets or thin films shredded into plots whose largest dimensions do not exceed 5 to 7 mm.  3. Composite material according to claim 1 or 2 characterized in that it further comprises one or more additives such as dye, flame retardant, etc. ... incorporated in the mass.  4. Composite material according to one of claims 1 to 3 characterized in that it is in the form of granules used subsequently by extrusion, injection, thermoforming etc ... 5. Method for obtaining the composite material according to one of claims 1 to 3-characterized in that it consists in preparing, on the one hand, the wood particles, in screening them and optionally drying them in order to to give them the required particle size, to prepare, on the other hand, the plastic particles, with a view to giving them the required particle size, then to mix these two constituents in the proportions by weight required and to agglomerate or amalgamate them with softening of plastic particles.  6. Method according to claim 5 characterized in that the amalgamation of said particles of the two constituents is carried out by friction without the addition of external heat.  7. Method according to claim 6, more particularly intended for obtaining the material according to claim 4, characterized in that said friction is operated by passage through a densifier constituted by a screw granulator.