Decorative sheet and processes for the production of sheets

Abstract

A decorative sheet arranged on the outside or inside of buildings is composed of a compression-molded core made from one or more core layers. The core comprises cellulose fibers and / or wood fibers, bound to one another by a hot-curing resin. Each core layer is composed of wood fibers and / or of cellulose fibers having lengths from 0.3 to 30 mm, and is containing pigments or is without pigments. The pigments are uniformly distributed within the core layer, and their proportion by weight is from above 0 to 20% by weight of the mixture made from pigments and from wood fibers and / or cellulose fibers. The pigments are colorfast, and weathering of the wood fibers and / or cellulose fibers at the surfaces of the sheet causes the original coloration of the core surfaces to change so that, when dry, the core is covered by a gray-silver patina, but substantially regains its original coloration when wet.

Description

[0001] 1. Field of the Invention[0002] The invention relates to a decorative sheet comprising a compression-molded core having one or more core layers, said core layers being prefabricated layers made from wood fibers and / or of cellulose fibers, surrounded and bound by hot-curing resin, and also to the use of a sheet of this type, and to processes for the production of the sheets.[0003] 2. Description of the Related Art[0004] Sheets made from wood chips and wood fibers with a matrix of amino plastic or of phenolic resins or cement are known from the prior art, as are plywood sheets, these having uniform density and being suitable for outdoor use or use in damp indoor areas. However, unlike laminate sheets, sheets of this type are not maintenance-free, and their marked absorption of water through the unsealed surface means that they regularly require comprehensive treatment. Absorption of water can cause severe swelling with an increase in the thickness of the sheet. These sheets the...

AI Technical Summary

Benefits of technology

[0014] In using the sheets of the invention as a facade cladding in the form of a curtain facade, of a panel screening a wall or roof, or of cladding for a balcony, or of a parapet panel or apron panel, the sheets are subjected to direct external weathering which causes slight weathering changes in the resin and the wood fibers and / or cellulose fibers which are directly arranged at the surfaces of the sheets, changing the original color of the sheets. Specifically, the slight weathering changes in the resin release some of the fibers at the surfaces of the sheets and cause due to this release some slight color changes to the sheets, but not any noticeable change in the physical, mechanical or chemical properties of the sheets. During this process, the surfaces of the sheets are given a patina effect, caused by a translucent gray-silver color which overlays the surfaces. When dry, the sheets then have the appearance of sheets of solid natural wood with a patina effect. If the sheets becomes moist or wet as a result of weathering, this patina effect disappears and the sheets is given their original color. The color change on the transition from the dry state to the wet state of a sheet is explained by the different reflection properties of the sheet in these states. In the dry state, the irregular surface with its slight weathering changes reflects the light nonuniformly and nondirectionally. In the wet state, the surface of the sheet has been moistened and becomes uniform, reflecting the light more directionally and producing a perceived color similar to that of the sheet prior to its slight change by weathering. As a result of these color changes, the sheet gives the impression that it is natural wood and certainly not a laminate made from a variety of layers press-molded to one another. It has all of the technical and physical advantages of a laminated sheet composed of layers and press-molded at high pressure and temperature, for example high strength, low tendency to split on impact, dimensional stability and low moisture absorption. Various types of natural wood can be imitated by appropriately selecting and combining or mixing the pigments added.

Problems solved by technology

However, unlike laminate sheets, sheets of this type are not maintenance-free, and their marked absorption of water through the unsealed surface means that they regularly require comprehensive treatment.

Absorption of water can cause severe swelling with an increase in the thickness of the sheet.

These sheets then have low strength and are unsightly.

The weathering resistance of this molding is unsatisfactory.

In weathering tests there is marked absorption of water with associated edge swelling and splitting of the compression-molded core, causing surface cracking after just a few weeks.

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