COATING MATERIAL FOR THE SURFACES OF PLATES

Description

[0001] The invention relates to a coating material for the surfaces of panels, in particular wood panels, wood-based panels, plastic panels or panels made of a wood-plastic mixture, consisting of a single, resin-impregnated cellulose layer provided with a decoration on one side, which is provided with a transparent covering layer of a radiation-curable acrylate lacquer covering the decoration.

[0002] This coating material can be referred to as a thin laminate and is known, for example, from EP 3 351 682 A1 or EP 2 042 344 A2.

[0003] Boards used in furniture construction, for example, can be coated with real wood veneer or with a plastic film or laminate. So-called continuous pressure laminates (CPL) are high-quality decorative materials produced in continuously operating double-belt presses. They consist of a resin-impregnated decorative paper and a multi-layered backing paper made of parchment or kraft paper. These individual layers are stacked on top of each other and bonded together in a hot press using high pressure and high temperature. This strengthens the fiber structure of the paper, creating a dense material with a closed surface. Thin CPL laminates are well suited for surfaces subject to intensive wear and tear. The melamine resin film formed during the production process protects the laminate and makes the board surface resilient and durable.

[0004] A method for producing a high-pressure laminate is known, for example, from EP 3 296 107 A1.

[0005] US 2001 / 0046594 A1 discloses a decorative film that exhibits good anti-transfer properties onto a cellophane pressure-sensitive adhesive tape and can also be manufactured stably. The film comprises a substrate and a surface protective layer applied thereto, formed from a crosslinked cured product of a radiation-curable resin composition. This composition comprises, as an additive, a combination of silicone acrylate with an organic polyorganosiloxane copolymer.

[0006] It's also known to use finish foil or wrapping film, which consists of a paper web treated with a lacquer finish. The lacquer is cured, for example, by UV radiation. The paper is not completely penetrated by the lacquer, resulting in only a limited scratch resistance of the surface.

[0007] From DE 10 2013 112 275 B4, it is known to digitally print a decoration on unresin-treated, but white parchment paper coming from a roll. A UV-curing digital printing ink is used for this purpose. After printing and the ink has cured, the parchment paper is rewound onto a roll. In a second step, the printed roll with the parchment paper is unwound and fed to a double-belt press together with a translucent overlay paper that becomes completely transparent after pressing. At a pressure of 15 to 25 bar and a temperature of 150 to 210 °C, the melamine resin in the overlay paper is first liquefied, then penetrates the paper layer and hardens as a whole. The unresin-treated printed parchment paper and the melamine resin-impregnated overlay paper are thus unwound from two different rolls and fed to a continuously operating double-belt press.The surface tension of the resin-free parchment paper used is such that aqueous inks, such as those commonly used in decorative gravure printing, exhibit poor or no adhesion to the parchment. Therefore, a UV-curable ink must be used. Production involves considerable engineering effort. Due to the asymmetrical structure of the laminate, it is subject to a strong tendency to curl, which complicates further processing, for example, when coating the panels.

[0008] Based on this, a coating material is to be created that is characterized by good processability, is as thin as possible and has high abrasion resistance.

[0009] To solve this problem, a generic coating material is characterized by the fact that the impregnation with synthetic resin amounts to 50 to 75% based on the weight of the cellulose layer.

[0010] The radiation-curable acrylic varnish can consist of a UV varnish.

[0011] Preferably, the cellulose layer is designed as a printing base paper with a weight of 60 to 100 g / m 2<, preferably 70 to 90 g / m 2< and particularly preferably 70 g / m 2<.

[0012] The cellulose layer is preferably impregnated with a urea-formaldehyde resin, a melamine-formaldehyde resin, a mixture of urea-formaldehyde resin and melamine-formaldehyde resin or with a polyurethane.

[0013] A process for producing a coating material is characterized by the following steps: a) Providing a cellulose layer, b) Printing a surface (top side) of the cellulose layer with a decoration, c) Impregnating the cellulose layer with a liquid synthetic resin in an amount based on the weight of the cellulose layer of 50 to 75%, d) Drying the impregnated cellulose layer, e) Applying a liquid cover layer made of a radiation-curable acrylate lacquer to the surface (top side) printed with the decoration, f) Partially curing the applied cover layer and then g) Pressing the structure consisting of the cellulose layer and the cover layer in a hot press.

[0014] The topcoat is preferably applied with a roller or a roll. It can also be sprayed on.

[0015] It is advantageous if the covering layer is dried before the structure is pressed.

[0016] When the structure is pressed together, the covering layer then hardens completely.

[0017] The decoration can be applied using analog and / or digital printing. Water-based digital printing ink is preferred.

[0018] Based on the weight of the cellulose layer, a quantity of 50 to 75% synthetic resin is used for impregnation. Preferably, 75% synthetic resin is used based on the paper weight. With core impregnation, the decorated and core-impregnated paper preferably reaches a weight of approximately 100 g / m².

[0019] The surface opposite the decoration (underside) of the core-impregnated cellulose layer can also be provided with a cover layer. The cover layer preferably has a weight of 5 to 100 g / m². Particularly preferably, the cover layer has a weight of 10 to 60 g / m², and most preferably 30 g / m².

[0020] The drying and / or curing of the impregnated cellulose layer and also of the cover layer is stopped in time so that, although residual activity remains, the cellulose layer or the printed paper can be wound up, stacked, stored and / or transported without contacting layers sticking together. An exemplary embodiment of the invention is described in more detail below: The coating material consists of a cellulose layer designed as a printing base paper with a weight of approximately 60 to 120 g / m². In contrast to parchment paper, the printing base paper has an open structure. Printing base papers are usually white or beige and therefore already form a good printing base for a decoration. Alternatively, the printing base papers can also have a solid-colored decoration.

[0021] A decoration is printed onto the upper side of the base paper, preferably using single-pass digital printing and water-based digital printing inks (CMYK or, even better, CRYK). The decorated base paper is core-impregnated in a conventional impregnation system. Core impregnation involves extensive filling of the structural spaces between the cellulose fibers of the base paper. Core impregnation can be carried out with urea-formaldehyde resin, melamine-formaldehyde resin, or a combination of urea-melamine-formaldehyde resin, or with polyurethane. A conventional polyurethane, such as a thermoset polyurethane, is used as the polyurethane. 50 to 60% synthetic resin, based on the paper weight, is used for core impregnation. With core impregnation, the decorated and core-impregnated paper achieves a weight of approximately 100 g / m².

[0022] A cover layer weighing approximately 5 to 100 g / m² is then rolled or sprayed onto at least the decorated side of the core-impregnated printing base paper. The cover layer consists of a conventional acrylic varnish, which can be partially cured and / or fully cured using high-energy radiation, e.g., UV radiation.

[0023] The printing base paper, covered with the partially cured acrylic varnish, is pressed in a short-cycle press or a continuous hot press at a pressure of approximately 30 to 70 N / cm² and a temperature of 130 to 200 °C. A pressure of 60 N / cm² and a temperature of 150 °C are preferred. The pressing time is approximately 0.6 to 2 s / mm² (sheet thickness), preferably 1.2 s / mm². The temperature in the press is measured on the surface of the press plate.

[0024] In order to ensure that residual reactivity remains and to allow the impregnated paper to be wound up, stacked, stored and / or transported, the drying and / or curing of both the core impregnation and the cover layer is stopped in good time.

[0025] If a short-cycle press is used to produce the coating material, the core impregnation is more likely to contain only polyurethane components and consist primarily of urea and / or melamine-formaldehyde resin. In this case, the coating material will preferably be used on furniture surfaces. When using short-cycle presses, it is important to ensure that they have sufficiently high pressing pressures.

[0026] Structuring of the surface of the cover layer can be integrated into the process, as described, for example, in EP 3 296 107 A1. The structuring agent is then inserted between the press plate and the structure to be laminated. It remains there during lamination and is subsequently peeled off the structured surface. Particular preference is given to producing so-called nano- or microstructures, which facilitate cleaning of the surface of the coating material and also counteract fingerprints, for example (anti-fingerprint). The use of microfolding carried out with an excimer emitter has proven particularly suitable for the anti-fingerprint effect. Microfolding is based on the following principle: 172 nm radiation causes free radicals to form in acrylates, which trigger polymerization and crosslinking.The penetration depth of the 172 nm photons into the acrylates is between 0.1 and 0.5 nm, so that only a thin surface layer is crosslinked. The shrinkage caused by polymerization then leads to microstructures. A wrinkled skin floats on the liquid film, which is then completely cured with a second radiation source. This can be a mercury UV lamp, an electron beam source, or a long-wave excimer lamp at 308 nm. To avoid ozone formation, irradiation usually takes place in a nitrogen atmosphere. A process for adjusting the gloss level of decorative and functional surfaces is described, for example, in DE 10 2006 042 063 A1.

[0027] High-gloss surfaces can also be achieved if high-gloss press belts or press plates are used.

[0028] Instead of using a texturer, the press belts and / or press plates can also be textured. Preferably, the textures are at least partially synchronized with the decor, with complete synchronization being the goal.

[0029] Due to the single-layer structure of the coating material, it is very thin, which offers the great advantage during further processing of being able to safely coat even modern small radii < 1.0 mm.

[0030] Continuous pressing can be achieved, for example, with a double-belt press used by Hymmen for the production of HPL laminates. This press operates according to the isobaric pressure principle. Adjustment to the product thickness is achieved by a fixed lower and an upper, height-adjustable pressure frame. To protect the product from premature exposure to temperature without pressure in the press, cooling zones are installed at the inlet of the double-belt presses to prevent pre-reaction of the material. The raw material is pressed by the two circulating steel belts, which pass through shared heating and pressing zones. In the pressing zones, gaseous pressure media generate the surface pressure required for the process against the steel belts and thus against the material. The heat energy is generated by a thermal oil system.The belt drums and the upper and lower heating plates are heated to the required temperature via separately controllable heat transfer oil circuits. The surface pressure in the reaction zone is generated by compressed air cushions pressing against the steel belts. This eliminates friction between the steel belts and the heating platen. The required pressure is generated by high-pressure compressors and supplied via special pressure controls in the double-belt press.

[0031] Instead of a double belt press, a C-HPL hot press or a short-cycle press can also be used.

Claims

1. A coating material for the surfaces of panels, especially panels made of wood, wood-based material, plastic or a wood / plastic mixed material, comprised of a single resin-impregnated cellulose layer with a decor on one side, said layer being equipped with a transparent cover layer that covers the decor made of an acrylate lacquer which can be cured by radiation, characterised in that the impregnation with synthetic resin is 50 to 75% in relation to the weight of the cellulose layer.

2. The coating material according to one of the preceding claims, characterised in that the cellulose layer is made as a print base paper with a weight of 60 to 120 g / m2, preferably 70 to 90 g / m2, especially preferably 70 g / m2.

3. The coating material according to one of the preceding layers, characterised in that the cellulose layer is impregnated with a urea-formaldehyde resin, a melamine-formaldehyde resin, a mixture of urea-formaldehyde resin and melamine-formaldehyde resin or with a polyurethane.

4. The coating material according to one of the preceding claims, characterised in that the impregnation with synthetic resin is 75% in relation to the weight of the cellulose layer.

5. A method for producing a coating material, comprising the following steps: a) providing a cellulose layer, b) printing a decor onto a surface of the cellulose layer, c) impregnating the cellulose layer with a liquid synthetic resin in a quantity of 50 to 75% in relation to the weight of the cellulose layer, d) drying the impregnated cellulose layer, e) applying a liquid cover layer made of an acrylate lacquer which can be cured by radiation to the surface with the printed decor, f) partially curing the applied cover layer and subsequently g) pressing the resulting structure composed of the cellulose layer and the cover layer in a hot press.

6. The method according to claim 5, characterised in that the cover layer is applied with a drum or a roller.

7. The method according to claim 5, characterised in that the cover layer is sprayed on.

8. The method according to one of the preceding claims 5 to 7, characterised in that the impregnation with synthetic resin is applied in an amount of 75% in relation to the weight of the cellulose layer.

9. The method according to one of the claims 5 to 8, characterised in that the cover layer is fully cured during pressing of the structure.

10. The method according to one of the claims 5 to 9, characterised in that the decor is printed on by analogue and / or digital printing.

11. The method according to claim 10, characterised in that a water-based digital printing ink is used.