Stock material or miscellaneous articles – Structurally defined web or sheet – Including grain – strips – or filamentary elements in...
Patent
1990-08-20
1991-10-22
Sluby, P. C.
Stock material or miscellaneous articles
Structurally defined web or sheet
Including grain, strips, or filamentary elements in...
428 57, 428114, 428535, 156 622, 156297, B32B 512, B32B 202, B27N 302
Patent
active
050594664
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the manufacture of chipboard, or particle board, comprising a centre layer of coarse chips and outer layers of chips whose fibres are positioned in the plane of the board.
Conventional chipboard comprised of a centre layer of coarse wood chips and sandwiching outer layers of finer wood chips are generally characterised by a high density. This high density can be ascribed primarily to the fact that the fibres in the centre layer are positioned parallel with the longitudinal axes of the chips, i.e. in a plane which extends substantially parallel to the plane of the manufactured board, and that the chips during the compression step required to form glue joints between the chips are compressed to an appreciable extent such that the density of the board will be substantially higher than the intrinsic density of the starting material. In the case of conventional chipboard manufacture, this increase in density will reach about 50%, such as to obtain a characteristic profile which corresponds to a given chipboard standard, for instance SIS 234 801.
A high density, however, results in chipboard of lower moisture stability, primarily thickness swelling. Furthermore, because of its high density, chipboard is normally considered to be heavy and difficult to handle. The manufacture of conventional chipboard also involves high costs for starting materials, i.e. chips, and glue, in addition to energy costs.
Against the background of the afore-described known technique, there is a desire for a method by means of which the density of chipboard can be reduced, and therewith a reduction in the consumption of starting materials, while retaining the same characteristic profile in general, or while improving said profile.
A method which touches partially upon this problem is described in SE-B-346 945. It is stated in this document (page 10, line 27 to page 22, line 27) that the size of the chips, the direction of chip fibres and the positioning or orientation of the chips in the board influences the properties of the finished chipboard, for instance such properties as density, swelling, mechanical strength, etc. For example, it has been found that when the longitudinal axes of the chip fibres are located transversely to the plane of the board, the board will be less compressible as a whole after being formed and the smaller particles located in the outer layers will be compressed to a greater extent than the particles located in the core of the board. For the purpose of obtaining chipboard in which a greater percentage of fibres are located with the longitudinal axes of the fibres extending transversely to or at an angle to the plane of the board, it has been proposed in accordance with SE-B-346 945 to use very short, essentially cubic chips as conventional wood chips, which because of their short lengths can be positioned with the long axes of the fibres extending both vertically and horizontally and in positions there between. There is obtained in this way random orientation of fibres in all directions.
For the purpose of reducing density and consumption of starting materials still further, while retaining the conventional, useful properties of the finished chipboard, or even improving the level of such properties, there is proposed in accordance with the invention a method which will impart a more refined and positive orientation of the chip fibres in the centre layer in a direction perpendicular to the plane of the finished board. To this end, it is proposed in accordance with the present invention that the chips used for the centre layer of the board are end-grain cut, flake-like chips whose fibres are oriented in the thickness direction of said chips, the chips fibres in the centre layer of the board being orientated substantially transversely to the plane of the board. By flake-shaped is meant here the shape of a body whose width and length are substantially greater than the thickness of the body. When using such flake-shaped chips, the chips will settle naturally on their re
Institutet for Trateknisk Forskning
Sluby P. C.
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