ABRASION-RESISTANT DECOR SHEET

Abstract: An abrasion-resistant decor sheet comprising a resin impregnated paper containing abrasion resisting particles and a protective cover sheet comprising at least one layer of a non pre-impregnated sheet, a method of producing the decor sheet, a decor laminate comprising the decor sheet and a method of producing the decor laminate.

Description: ABRASION-RESISTANT DECOR SHEET The present invention relates to an abrasion-resistant decor sheet, a method of producing the sheet, a decor laminate containing the sheet and a method of producing the laminate. The decor sheet according to the present invention comprises a protective coversheet of at least one layer of a non pre-impregnated sheet. Abrasion-resistant decorative thermosetting laminates are well known in the art and used for instance as surface material for such applications where a high abrasion resistance is required. This is especially the case for flooring laminates, but also to a certain extent for desktop and tabletop laminates. These laminates usually comprise a top surface or overlay consisting of an impregnated paper containing abrasive particles imparting abrasion resistance to the finished product. The abrasive particles used are hard particles having normally an average particle size of about 50 μm, which is advantageous for the abrasion resistance but not for the press plates used during the lamination stage. The press plates are scratched by the relatively big particles in the surface of the laminate. These plates are very expensive and manufactured of high quality steel. Intermediate layers of aluminium foil are often used to protect these press plates which will affect the production cost. An attempt to solve the above mentioned problem with the press plates is described in WO 97/00172 A1. A process for manufacturing an abrasion- and scratch- resistant decorative thermosetting laminate is disclosed, wherein the surface layer of the laminate, consisting of an overlay of a paper web or sheet, is first impregnated with a melamine-formaldehyde resin, then coated on one side with abrasive particles with an average particle size of 30-90 μm, and whereafter the resin is dried. Then the other side of the sheet, or alternatively another sheet is coated with a melamine-formaldehyde resin containing abrasive particles with an average particle size of 1-15 μm, whereafter the resin is dried. The surface containing the smaller particles is placed outwards on the top of the laminate, while the larger particles are incorporated in the lower side of the surface sheet, or on the topside of the sheet directly under the surface sheet. This arrangement will give a good abrasion resistance to the finished product. However, technical solutions are still sought for the need to increase the abrasion resistance of decor sheets and decrease the wear of the press plates during the lamination step and at the same time keep the production cost low. According to the invention it has been found that the use of a protective cover sheet of a non pre-impregnated sheet in a decor sheet significantly improves the abrasion resistance of the resulting decor sheet, does not affect transparency and diminishes wear of the press plates. In addition, the handling is simplified and the cost reduced, since the protective cover sheet is applied on the impregnated paper in one single step and there is no need of an extra impregnation and drying step. The present invention accordingly provides an abrasive-resistant decor sheet, a method of producing this sheet, a laminate comprising the sheet and a method of producing this laminate, by which the above mentioned problems are overcome. The decor sheet according to the invention is defined in the appended claims. It comprises a resin-impregnated paper containing abrasion resisting particles and a protective cover sheet comprising at least one layer of a non pre-impregnated sheet. The non pre-impregnated sheet should suitably be thin enough to be able to be applied directly onto the impregnated paper, without needing a separate impregnation route itself. This normally means that the sheet will be quickly wetted by the resin in the impregnated paper without having absorbed too much resin. If the cover sheet absorbs too much resin from the impregnated substrate, there will not be enough left resin to give a satisfactory adhesion between the sheets, with delamination as a result. In addition, another possible problem might be air inclusion giving rise to a poor surface finish. The non pre-impregnated sheet may consist of a paper having a surface weight of up to about 50 g/m 2 , more suitable of up to about 30 g/m 2 , preferably of up to about 20 g/m 2 , and most preferably of up to about 10 g/m 2 . Furthermore, the non pre- impregnated sheet may also consist of a non-woven. For example non-woven defined according to ISO 9092/EN 29092 can be used. Suitably, thin paper such as that used in tea bags and absorbing non-woven may be used. Preferably tissue paper is used. Suitable curable resins for use in the present invention are thermosetting resins, such as melamine resins, for example, melamine-formaldehyde, urea resins, for example, urea-formaldehyde, phenolic resins, for example, phenol-formaldehyde, or mixtures thereof. The abrasion resisting particles that are incorporated in the decor sheet according to the invention may consist of many different materials having a hardness of 7 or more on the Moh hardness scale. Such materials as silicon dioxide, aluminium oxide, silicon carbide, ceramic particles, and mixtures thereof may be used. Depending on which material the abrasive particles are based on and the end-use properties desired in the laminates to be manufactured using the decor sheet of this invention, the particle size could range from 10 to150 microns, suitably from 30 to 90 microns and preferably from 40 to 70 microns. The particles incorporated into the decor sheet should be in a sufficient quantity to impart the desired degree of abrasion resistance to the finished product. Suitably 5-70 g/m 2 of particles, preferably 10-50 g/m 2 , and most preferably 20-40 g/m 2 are incorporated into the impregnated paper. The decor sheet according to the present invention is particularly suitable for use where a high abrasion resistance is required, for example, for flooring, desktop, or tabletop laminates. The method according to the present invention is defined in the appended claims and comprises the steps of applying onto the surface of a wet paper impregnated with a curable resin and containing abrasion resisting particles, a protective cover sheet of at least one layer of a non pre-impregnated sheet, whereafter the decor sheet is dried. The substrate used in the method of the invention for making resin impregnated paper, though usually paper, may be any type of impregnable substrate, including such as woven and non-woven textiles. The substrate is normally printed, coloured or otherwise decorated, if it is intended for decorative purposes. The paper that is used normally has a weight of about 20 to about 250 g/m 2 , more typically about 60 to about 100 g/m 2 . The substrate can be impregnated with resin by various conventional techniques of applying resin compositions, such as baths, rollers, doctor blades, air knife, metering roll, doctor bars, etc. The resin compositions can be applied in one or more steps with drying and/or partial curing between the application stages. The abrasive particles can be incorporated into the resin impregnating paper by various methods known in the art. The particles can be added to the paper during impregnation of the paper with a curable resin containing the particles, or they can be applied onto the paper after it has been impregnated with a curable resin. It is also possible to incorporate the particles into the paper before it is impregnated with a curable resin. The non pre-impregnated sheet is applied onto the resin-impregnated paper after the impregnation step and before drying the resin. Thereafter, the resin- impregnated paper and the protective cover sheet are put together, for example, by calande ng, banana rolls and/or pressing. The coversheet adheres to the substrate without air inclusions forming a uniform surface. The sheet covered with the non pre-impregnated cover sheet is suitably sequentially dried and the curable resin is at least partially cured. Sheets that are partially cured are usually bonded to a core by laminating under heat and pressure, whereby final curing of the resin takes place. However, within the scope of the invention are also included sheets that are completely cured, so-called foils. These are normally bonded to a core by gluing with commercially available glues. The core of the laminate may be of any desired type, and such cores as wood, particle-board, fibre-board, plywood and the like can be used, as well as a number of conventional dry prepreg webs or sheets impregnated with resins such as phenol- formaldehyde or phenol-urea-formaldehyde resins. The abrasion-resistant decor sheets obtainable by the method according to the present invention can be used for both high-pressure and low-pressure laminates. The present invention is illustrated by means of a non-limiting example below, showing one embodiment of the present invention. EXAMPLE A paper sheet was impregnated with melamin-formaldehyde resin (MF) and applied with abrasive particles of aluminium oxide. Whereafter a non-impregnated tissue paper with a surface weight of 28 g/m 2 and a Gurley value of less than 1 second, was applied onto the still wet surface of the impregnated paper, on the side containing the abrasive particles. Normal rolls were used to ensure that the tissue paper was properly adhered to the paper web. The combined sheets were subsequently dried, whereby the resin was transformed to the so-called B-stage. As a comparison another sheet was produced in the same manner but without a protective layer of a tissue paper. Pieces of the two sheets were pressed on MDF(Medium density fibre)-board under the same process conditions, P=2.0 N/mm 2 and T=185 °C, for 30 seconds, whereby the resin was completely cured. The pressed products showed the same transparency with or without a protective layer of a tissue paper. The abrasion resistance of the finished decor laminates, expressed in Taber values, was measured according to DIN 53798 (1986). The abrasive paper stripes (Taber S-42) were renewed every 200 cycles. Three different experiments were carried out at different times but in the same fashion. The results are shown in a table below. Table As shown by the test results above, the use of a protective cover sheet comprising a paper tissue in accordance with the present invention unexpectedly increases the abrasion resistance of the finished decor laminate.

Claims: CLAIMS I. An abrasion-resistant decor sheet comprising a resin impregnated paper containing abrasion resisting particles, characte rised in that it comprises a protective cover sheet comprising at least one layer of a non pre-impregnated sheet. 2. An abrasion-resistant decor sheet according to claim 1, ch a racte rised in that the non pre-impregnated sheet is a paper having a surface weight of less than about 50 g/m 2 . 3. An abrasion-resistant decor sheet according to claim 2, ch a ra cteri sed in that the non pre-impregnated sheet is a paper having a surface weight of less than about 30 g/m 2 . 4. An abrasion resistant decor sheet according to any preceding claim, ch a racte rised in that the non pre-impregnated sheet is a tissue paper. 5. An abrasion resistant decor sheet according to claim 1, ch a racte rised in that the non pre-impregnated sheet is a non-woven. 6. A method of producing an abrasion-resistant decor sheet comprising the steps of applying onto the surface of a wet paper impregnated with a curable resin and containing abrasion resisting particles, a protective cover sheet comprising at least one layer of a non pre-impregnated sheet , whereafter the decor sheet is dried. 7. A method according to claim 6, characterised in that it further comprises at least partially curing the curable resin in the decor sheet. 8. A method according to claim 6, ch aracte rised in that the non pre- impregnated sheet is a paper having a surface weight of less than about 50 g/m 2 . 9. A method according to claim 6 or 8, ch aracterised in that the non pre-impregnated sheet is a paper having a surface weight of less than about 30 g/m 2 . 10. A method according to any of claims 6 or 8-9, characterised in that the non-pre-impregnated sheet is a tissue paper. I I . A method according to claim 6, ch aracterised in that the non pre-impregnated sheet is a non-woven. 12. A method according to claim 6, cha racterised in that the curable resin is a melamine-formaldehyde resin, a urea-formaldehyde resin, a phenolic resin, and mixtures thereof. 13. A method according to claim 6, ch aracterised in that the abrasion resisting particles consist of aluminium oxide, silicon carbide, ceramic materials and mixtures thereof. 14. A method according to claim 13, ch aracterised in that the abrasion resisting particles have an average particle size of about 40-70 μm. 15. A method according to any of claims 6 or 13-14, c h a r a c t e r i s e d in that the abrasion resisting particles are added to the paper during impregnation of this with a curable resin containing the particles. 16. A method according to any of claims 6 or 13-14, c h a r a c t e r i s e d in that the abrasion resisting particles are incorporated into the paper before it is impregnated with the curable resin. 17. A method according to any of claims 6 or 13-14, c h a r a c t e r i s e d in that the abrasion resisting particles are applied onto the surface of the paper after it has been impregnated with a curable resin. 18. An abrasion-resistant decor sheet obtainable by the method according to any of claims 6-17. 19. An abrasion-resistant decor laminate comprising a core of at least one layer and an overlay of an abrasion resistant decor sheet according to any of the preceding claims. 20. A method of producing an abrasion-resistant decor laminate, wherein the abrasion-resistant sheet according to any of claims 1-15 is bonded to the core by gluing or laminating under heat and pressure.

Inventors: HILBERT THOMAS, STAUDT JOCHEN GEORG, HILBERT, THOMAS, STAUDT, JOCHEN, GEORG
Applicants: AKZO NOBEL NV, CASCO PRODUCTS AB, HILBERT THOMAS, STAUDT JOCHEN GEORG, AKZO NOBEL N.V., HILBERT, THOMAS, STAUDT, JOCHEN, GEORG
Application year: 2000
Main classification: B32B29
IPC codes: B32B29, B44C5, D21H27