Laminate production method

Abstract

A method for producing an impregnated article comprising a cellulose layer which is impregnated with a melamine resin in order for a core impregnation to be formed is characterized in that a layer of a liquid medium having a moiety of isocyanate groups is applied to the top face and/or the bottom face of the core-impregnated cellulose layer.

Claims

1. A process for the production of a cellulose ply comprising: impregnating a core of the cellulose ply with a melamine resin to form a core-impregnation cellulose ply; and applying a layer made of a liquid medium having a proportion of isocyanate groups to at least one of an upper side and underside of the core-impregnated cellulose ply wherein the isocyanate groups react with either a -cellulose in the core-impregnated cellulose ply or with the melamine resin.

2. The process as claimed in claim 1, wherein the liquid medium is applied in the form of dispersion with from 50% to 60% solids content, the remainder being water, and is then dried to give a layer.

3. The process as claimed in claim 1, wherein the liquid medium is applied in the form of heated hotmelt with 100% solids content and the isocyanate groups, and during the subsequent cooling spontaneously forms a layer.

4. The process as claimed claim 1, wherein the liquid medium comprises wear-inhibiting particles.

5. The process as claimed in claim 1, wherein a quantity of the liquid medium is from 50 g/m.sup.2 to 300 g/m.sup.2.

6. The process as claimed claim 1, wherein at least one protective covering layer is applied to the layer on the upper side.

7. The process as claimed in claim 6, wherein the protective covering layer comprises nanoparticles to improve resistance to microscratching, and/or agents having antistatic effect and/or agents having antibacterial effect provided.

8. The process as claimed in claim 1, wherein the melamine resin takes the form of mixture of melamine resin and urea resin.

9. The process as claimed in claim 4, wherein the liquid medium comprises corundum particles.

10. The process as claimed in claim 1, wherein the isocyanate groups react either with OH group of the -cellulose in the cellulose ply or with a NH group or a methylol group of the melamine resin of the core-impregnation system of the cellulose ply.

11. The process as claimed in claim 10, wherein solids content of the liquid medium is from 50% to 60%, with water as solvent.

12. The process as claimed in claim 10, wherein solids content of the liquid medium is from 50% to 60%, with organic solvents or additions.

13. The process as claimed in claim 12, wherein the organic solvents or additions are one of dispersing agents, release agents, wetting agents, and antifoams.

14. The process as claimed in claim 3, wherein prior to the hotmelt being applied to the core-impregnated cellulose ply, the liquid medium is heated and melted and the hotmelt is applied either by using a slot die or by spray application.

15. The process as claimed in claim 3, further comprising applying to an upper side of a dried layer of the liquid medium, or of re-hardened hotmelt, at least one protective covering layer composed of a UV lacquer, which comprises admixed nanoparticles.

16. The process as claimed in claim 10, wherein the melamine resin is pure melamine resin.

17. The process as claimed in claim 10, wherein the melamine resin is a melamine resin mixture made of pure melamine resin and urea resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in more detail below with the aid of a drawing.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(2) The single FIGURE shows an impregnate with a cellulose ply 4, which can be used as decorative paper, as overlay, as counterbalancing material, and/or as underlay. This impregnate can take the form of sheet product or roll product. The cellulose ply 4 has been core-impregnated with a pure melamine resin or with a melamine resin mixture made of pure melamine resin and urea resin. To this end, the cellulose ply 4 can be drawn through a trough containing liquid, or the resin can be applied by rolling and/or spraying. A particularly advantageous method here has proven to be impregnation via single-side contact with liquid. Excess quantities of resin on the upper side and underside O, U can be removed by drawing a doctor blade across the cellulose ply 4. Drying of the impregnated cellulose ply 4 to a defined residual moisture content does not cause formation of any melamine-resin layers 3, 5 on the upper side O and underside U thereof; instead, the core-impregnation system fills the cellulose ply 4.

(3) A liquid medium comprising isocyanate groups is applied at least to the upper side O or underside U of the cellulose ply 4. The solids content of the liquid medium is preferably from 50% to 60%, with water as solvent. It is moreover possible to use not only water but also organic solvents or additions, for example dispersing agents, release agents, wetting agents, and antifoams. The dispersion, the applied quantity of which is from 50 to 300 g/m.sup.2, is then dried to give a layer 2. After the drying process, a protective covering layer 1 composed of a UV lacquer is applied to the upper side O of the layer 2. This UV lacquer preferably comprises nanoparticles 7 based on silica in order to increase resistance to microscratching.

(4) In order to increase abrasion resistance, the liquid medium can comprise wear-inhibiting particles 6, in particular corundum particles, which have either been mixed into the medium before application or have been scattered onto the upper side O and, respectively, underside U after application.

(5) Instead of application of the liquid medium in the form of dispersion to the upper side O and, respectively, underside U of the cellulose ply 4, followed by active drying, another possibility is use of a hotmelt (hotmelt adhesive) which has isocyanate groups. The hotmelt, like the dispersion, can also be applied additionally to the underside U of the cellulose ply 4. Before application, the hotmelt is heated and becomes liquid, and then on cooling spontaneously forms a layer 2 having isocyanate groups. Here again, there can also be wear-inhibiting particles 6, in particular corundum particles, added to the hotmelt, or these can be scattered onto the upper side O of the liquid hotmelt after application.

(6) The quantity of the dispersion or hotmelt applied is about 50 to 300 g/m.sup.2 in solid form. Added to the protective covering layer 1 there can also be, alongside the nanoparticles 7, agents having antistatic effect and/or agents having antibacterial effect. Again, these agents can have been admixed with the liquid material or scattered onto the layer 1 while it remains liquid after application.

(7) An example of a hotmelt that can be used is the product PUR HC717.5 marketed by Kleiberit. The isocyanate groups in the hotmelt or in the dried dispersion are reactive, and react with the OH group of the -cellulose in the cellulose ply 4 and/or with the methylol group of the melamine resin from the core-impregnated cellulose ply 4 to give a polyurethane, and/or with the NH group to give a urea derivative. Another possibility is the reaction with water to give amine and further reaction with free isocyanate groups to give urea derivatives. Anchoring of the dried dispersion or of the hotmelt on the impregnate is thus achieved. A layer 2 is thus formed which, in comparison with a conventional melamine-resin layer, is softer, but nevertheless wear-resistant, has warmer haptic properties, and produces less noise.

(8) If the intention is to use said impregnate as overlay, it can be pressed in short-cycle presses in combination with conventional melamine-resin-impregnated decorative papers and counterbalancing materials. The isocyanate groups react with the melamine resin in the cellulose ply 4 and/or with the -cellulose in the cellulose ply 4, and the individual layers thus become bonded, and by way of the melamine present in the cellulose ply 4 the overlay becomes bonded to the other melamine-resin-impregnated papers.

(9) It has been found in a comparative test in practice that there are no discernible color differences of any kind between a product with a melamine overlay and a product with the overlay of the invention.

(10) The cellulose ply 4 can be a paper, in particular a printed decorative paper. During the subsequent pressing of the laminate structure it is possible to emboss, into the protective covering layer 1, a structure that is synchronous with the decorative effect (synchronous pore). The press plates engraved with the structure, usually designed for a build based on melamine resin, can be used without modification.

(11) The resultant impregnate can be pressed with a wooden board, for example MDF or HDF, other impregnates, and in particular specialty papers or kraft papers, to give a laminate.

(12) The wooden board coated with one or more impregnates can in particular be used to produce floor panels which, at opposite lateral edges, have profiling that permits connection of a plurality of panels to one another and interlocking of same with one another.