OF PRODUCING GRANULATE

The present invention relates to granulate comprising granules of thermoplastic material.

In addition, the present invention relates to a granulator comprising a sieve or mould containing openings for pressing through thermoplastic material in order to form granules.

Furthermore, the present invention also comprises a method of producing granulate.

Granulate to which the present invention relates is more specifically used to form mouldings by means of thermoplastic processes, such as pressing, extruding, co- extruding, injection-moulding, rotational moulding, etc. In these processes, granulate is pressurized and/or heated by means of heating elements and/or heated up through friction, resulting in a rise in temperature which is such that the granules melt. The melted material can thus assume a desired shape and subsequently be cured in this desired shape.

It is the object of the present invention to provide improved granulate.

This object of the invention is firstly achieved by providing granulate comprising granules of thermoplastic material in which the granulate comprises granules of different sizes or different shapes or a combination of both. With existing granulates, the granules contained in a granulate are of virtually the same shape and size.

Granulate according to the invention comprises granules of different sizes and/or shapes. If the granules contained in such a granulate are homogeneously mixed with each other, it is possible to achieve better results when producing mouldings, such as plates, profiled sections, injection-moulded products, etc. than using granulate comprising granules of virtually the same shape and size. Due to the different sizes and/or shapes, granulate according to the invention can be distributed more evenly. Mouldings produced therewith can thus be made more even. The bulk density of the granulate is higher than with existing granulate. Fewer openings remain between the granules when producing mouldings. As a result thereof, less air is present between the granules, so that less venting has to take place during the process. The stress on the resulting mouldings is thus reduced.

Due to the different sizes and/or shapes, the granules melt at different points in time during the production of mouldings.

When producing mouldings in a press, the press is thus not heavily loaded all at once, but distributed over a period of time during which the different mouldings start to melt in succession. This results in better end products.

When extruding or injection-moulding mouldings, the screws in the machine which melts and pressurizes the granulates are susceptible to a high degree of wear in a certain zone. This is mainly the zone where the granules change from solid form to liquid form. Due to the different sizes and/or shapes of granules, the latter will now change from solid to liquid or less solid form at different points in time. As a result thereof, this zone becomes larger, thus reducing the load thereon locally. Wear now occurs in a larger zone, but this is significantly less strong, thus greatly increasing the total service life of the screws.

A preferred embodiment of granulate according to the present invention comprises first granules having a first size as the largest size and second granules having a second size as the largest size, wherein the first size differs by more than 0.2 mm from the second size. Preferably, this first size differs by more than 0.5 mm from the second size. More preferably, the first size differs essentially by 1 mm from the second size.

A specific embodiment of granulate according to the present invention comprises essentially 25% of granules whose largest size is 1 mm, essentially 25% of granules whose largest size is 2 mm, essentially 25% of granules whose largest size is 3 mm and essentially 25% of granules whose largest size is 4 mm. Alternatively, two or more different types of granules of different sizes and/or different shapes may be provided in these or other ratios.

The granules of granulate according to the present invention may have all kinds of shapes. More specifically, these may be, for example, spherical or cylindrical or cubical, conical or more bar- shaped, etc. The same granulate may contain granules having one shape in different sizes or also granules having different shapes with respect to each other. In a specific embodiment of granulate according to the present invention, the granules are essentially cylindrical.

Granules of granulate according to the present invention may be made of all kinds of thermoplastic materials. In a particularly preferred embodiment, the granules are made of a composite. More specifically, this composite may comprise, for example, mineral and/or vegetable fibres, such as for example talcum, calcium, carbonate, etc. and/or hemp, bamboo, wood, straw, sisal, coconut, peas, etc. Still more specifically, the composite may be, for example, a wood composite (wood/plastic composite). More specifically, the granules may in this case be made using polyolefin as the plastic. Still more specifically, the granules may in this case be made using thermally modified wood as the wood.

The object of the present invention is furthermore also achieved by providing a granulator comprising a sieve or mould containing openings for pressing through thermoplastic material in order to form granules, wherein the sieve comprises openings of different sizes and/or shapes.

By means of such a granulator, it is possible to directly produce granulate according to the present invention.

In a preferred embodiment of a granulator according to the present invention, the openings comprise first openings having a first size as the largest size and second openings having a second size as the largest size, wherein the first size differs by more than 0.2 mm from the second size. Preferably, this first size differs by more than 0.5 mm from the second size. More preferably, the first size differs essentially by 1 mm from the second size.

In a specific embodiment of a granulator according to the present invention, the openings comprise essentially 25% of openings whose largest size is 1 mm, essentially 25% of openings whose largest size is 2 mm, essentially 25% of openings whose largest size is 3 mm and essentially 25% of openings whose largest size is 4 mm.

Alternatively, two or more different types of openings of different sizes and/or different shapes may be provided in these or other ratios.

The object of the present invention is furthermore also achieved by providing a method of producing granulate, wherein granules having a first size as the largest size are mixed with granules having a second size as the largest size to form a homogeneous mixture. By means of such a method, it is possible to produce granulate according to the present invention.

In addition, the object of the invention is also achieved by providing a method of producing a granulate, wherein granules of a first shape are mixed with granules of a second shape, different from the first shape, to form a homogeneous mixture. By means of such a method, it is also possible to produce granulate according to the present invention.

Finally, the object of the present invention is also achieved by providing a method of producing granulate, wherein said granulate is produced by means of a granulator according to the present invention. Also by means of such a method according to the present invention, it is possible to produce granulate according to the present invention. The present invention will now be explained in more detail by means of the following detailed description of some embodiments of granulate, a granulator and a method according to the present invention. The sole aim of this description is to give illustrative examples and to indicate further advantages and particulars, and can therefore by no means be interpreted as a limitation of the area of application of the invention or of patent rights defined in the claims. The indicated examples illustrate that granulate, granulators and methods according to the present invention may be provided in an endless number of variants.

Example 1

A number of pill- shaped granules having a size of essentially 3 mm between the extremities of the pill shape are provided.

In addition, an amount of spherical granules is provided having a diameter of essentially 1 mm.

Both types of granules are produced by mixing particles of wood fibres and cured binding agent, which originate from MDF or HDF mouldings, with a polymer.

The ratio between the amounts is as follows: 1/3 of pill-shaped granules is added to 2/3 of spherical granules. These granules are homogeneously mixed with each other to form a granulate according to the present invention.

In alternative examples, it is also possible to mix granules having different sizes and/or having different shapes and/or in different ratios and/or made of different materials, etc. with one another in order to produce a granulate according to the present invention.

Example 2

A sieve or mould for a granulator is provided with 40% of round openings having a 4 mm diameter, 30% of round openings having a 2 mm diameter and 30% of round openings having a 1 mm diameter, all evenly distributed. This sieve or mould is placed in a granulator. Into this granulator, thermoplastic material, comprising essentially 50% thermally modified wood and essentially 50% polyolefin, is introduced and granulated to form granules. The granules which are produced in this way form a granulate according to the present invention. In alternative examples, the sieve may also be provided with openings having different shapes and/or different sizes and/or in different ratios and/or differently distributed, etc. and the granulated material may be different from thermoplastic material.