Heat-treated PVC-plastic panel

Abstract

The present invention relates to a method of treating PVC plates as well as plates and panels manufactured by this method. Further, the invention relates to plates and panels, in particular wall, ceiling or floor panels, comprising a heat-treated carrier plate (12) based on polyvinyl chloride with a density of, for example, 900 to 2,500 kg/m.sup.3 and a film (17) applied thereon. The film is a thin PVC-film and comprises a decorative pattern (18) directly printed thereon.

Claims

1. A method of treating a polyvinyl chloride (PVC) plate comprising the following steps in the given order: providing a PVC plate; heating the PVC plate in an oven to at least 70° C.; cooling the heated plate.

2. The method according to claim 1, wherein the plate is heated to at least its glass transition temperature.

3. The method according to claim 1, wherein the plate is kept at the minimum temperature for at least 3 minutes.

4. The method according to claim 1, wherein the plate is heated with a heating gradient of 2° C./min to 20° C./min on average.

5. The method according to claim 1, wherein the plate is cooled down in a controlled manner, in a cooling oven, with a cooling gradient of 3° C./min to 20° C./min on average.

6. The method according to claim 5, wherein the PVC plate is fed through the oven on a conveyor and the oven is a continuous oven, and the cooling of the heated plate occurs in the continuous oven.

7. The method according to claim 1, wherein the PVC plate is provided with a PVC film having a thickness of 0.04 to 0.2 mm before or after the heat treatment.

8. A panel, comprising a polyvinyl chloride plate and a film attached thereto, wherein the film is a PVC film having a thickness of 0.04 to 0.2 mm and comprising a decorative pattern directly printed thereon, and a cured polymer layer is provided over the PVC film, and wherein the polyvinyl chloride plate contains no plasticizers.

9. The panel according to claim 8, wherein the polymer layer comprises a hardness gradient, so that the hardness of the polymer layer decreases essentially continuously with increasing depth as seen from the surface of the polymer layer.

10. The panel according to claim 8, wherein the printing ink used for printing the decorative pattern (18) is solvent based and a UV printing ink, and contains a polymerizable acrylate and/or N-vinylcaprolactam.

11. The panel according to claim 8, wherein the PVC film has a thickness from 0.05 to 0.15 mm.

12. The panel according to claim 8, wherein the PVC plate comprises a thickness between 3 and 20 mm.

13. The panel according to claim 8, wherein a layer comprising a UV primer is provided on the PVC film.

14. The panel according to claim 8, wherein the PVC film is glued or thermally welded to the plate.

15. A method for manufacturing of a panel, comprising the following steps: performing a method according to claim 1, wherein a PVC film having a thickness of 0.04 to 0.2 mm is applied to the PVC plate before or after the heat treatment; printing a decorative pattern directly on the PVC film; applying at least a first polymer layer to the PVC film; and curing the polymer layer.

16. The method according to claim 15, wherein a heated calender is used for applying the PVC film in such a way that the PVC film is thermally welded to the carrier plate.

17. The method according to claim 15, wherein the decorative pattern is directly printed on the PVC film by means of digital printing.

18. The method according to claim 15, wherein the PVC film has a thickness of 0.05 to 0.15 mm.

19. The panel according to claim 8, wherein the polyvinyl chloride plate consists of PVC-U.

Description

4. DESCRIPTION OF PREFERRED EMBODIMENTS

(1) In the following, the invention is explained in more detail using the figures, wherein:

(2) FIG. 1a schematically shows a device for the heat treatment of a PVC plate;

(3) FIG. 1b schematically shows the temperature curve in the device;

(4) FIG. 2 shows a schematic diagram of a plate 10 with a carrier plate 12 made of polyvinyl chloride;

(5) FIG. 3 shows a schematic view of a coating device; and

(6) FIG. 4 schematically shows an experimental setup for the comparison of treated and untreated panels.

(7) FIG. 1 schematically shows a device for the heat treatment of a PVC plate. The device essentially consists of an oven 1, which in the example shown is a continuous oven. The oven is equipped with a conveyor 2 which moves the parts to be treated through the oven in the direction of arrow 3. The reference sign 12 indicates PVC plates which are conveyed through the oven from left to right. Reference number 10 indicates finished panels which have already been coated or provided with films as described below. Such coated panels 10 can also be subjected to a heat treatment in order to treat the respective carrier plates 12 of the panels 10 accordingly. The oven 1 comprises seven zones O1 to O7 in which different temperatures are present. Of course the shown device is only exemplary and also devices with more or less zones as well as devices with completely different temperature profiles as presented herein are possible. The plates 12 or panels 10 enter the first zone O1 of the oven. The temperature within the first zone O1 rises continuously in the conveying direction of the oven.

(8) The temperature course or the temperature profile within the individual zones of the oven is shown in FIG. 1b. The temperature is shown on the vertical axis and the horizontal axis corresponds to the course along the length of the oven (L.sub.Oven). The dotted lines indicate the transition between the different zones O1 to O7. In the example shown, the temperature within zone O1 rises continuously with a relatively low rate of increase. The reason for this is that the panels or plates have a relatively low temperature when entering the oven, such as room temperature, and therefore even relatively low oven temperatures lead to rapid heating of the plates. This is because the speed at which the body is heated depends fundamentally on the temperature difference between the body and the surrounding air, for example. As the skilled person knows, large temperature differences lead to a greater transfer of heat energy and thus to a faster heating of the body. By a suitable selection of the temperature profile in the conveying direction of the oven, the temporal course of the heating of the plates can be controlled. It is desirable that the heating should be as homogeneous as possible, i.e. the heating or cooling gradient should be as constant as possible during treatment.

(9) In zone O2, the temperature rises relatively more in the conveying direction than in zone O1. In zone O3 the temperature is kept constant and the plates or panels are kept at the desired target temperature for a few minutes during transport through zone O3.

(10) In zone O4, the temperature in the oven is slowly lowered in the conveying direction, as can be seen from the relatively flat temperature course in FIG. 2b. In the following zones O5 to O7 the temperature then drops further and further, so that the plates or panels are slowly cooled down to a temperature close to the room temperature (e.g. 30 or 35° C.). The cooling phase is advantageous, as shown, longer than the heating phase, i.e. cooling should preferably take place relatively slowly. After the plates have left the oven, they can be stored or further processed as required.

(11) FIG. 2 shows a panel 10 that is provided with several films or layers and can be used, for example, as a floor panel. The panel 10 comprises a plate (carrier plate) made of PVC 12, which has tongue and groove connections at its respective edges, which allow individual panels 10 to be connected with each other. The carrier plate consists of an extruded hard PVC (PVC-U) and can, for example, be heat-treated using one of the methods described herein.

(12) Above the (carrier) plate 12 a PVC film 17 is arranged. A decorative pattern (décor layer) 18 is printed on the top side of film 17, preferably by means of a digital printing process. This decorative pattern can be any pattern, depending on the application.

(13) Above the PVC film and the décor layer, a UV-curable polymer layer system 19 is provided. The illustration is not true to scale and the layers are shown here at a distance from each other not present in the real product in order to make them more clearly visible. In particular, the plate 12 is considerably thicker than the layers applied to it, namely in the range of several mm, whereas the layers applied to it represent only a fraction of a mm in total.

(14) In the following, FIG. 3 is used as an example to describe the manufacture of a panel according to the invention or the method required for this. FIG. 3 schematically shows a coating device for the coating of plates 12 or for the production of panels 10. The plates 12 consist of hard PVC with a thickness of 4-8 mm and were first subjected to the heat treatment described herein. Alternatively, the heat treatment described herein can also be carried out subsequently on the finished panel 10 or an intermediate product. The plates 12 are guided by a roller conveyor 21 through the various stations of the coating device. The coating stations shown are not to be understood conclusively, but serve only as examples to explain the method according to the invention and are shown purely schematically. In front of, behind and between the stations shown, further processing stations may be provided, such as further drying stations, stations for applying primers, stations for applying fillers, etc. The first station 30 is intended to be a calender unit used to apply the PVC film 17 to the top of the plates 12. The film is unwound from a supply roll 31 and attached to the top of the plates 12 by a heated calender roll 32. The film is cut to size using suitable cutting means known to a person skilled in the art (not shown).

(15) In Station 60, a decorative décor, in particular a real wood décor, is printed on PVC film 17 using digital printing. After printing, a polymer layer is applied in the coating station 70. The polymer layer is applied with a hardness gradient, so that the hardness of the polymer layer decreases essentially continuously with increasing depth as seen from the surface of the polymer layer. For this purpose, a first polymer layer based on a polymerizable acrylate system is applied in a first coating unit 71. A further wet-on-wet polymer layer is applied to this first polymer layer in Station 72. The second polymer layer, for example, has a higher double bond content, as described in detail in the above-mentioned application on the hardness gradient. The two polymer layers are applied wet-on-wet in stations 71 and 72, so that partial mixing occurs at the interface of the two layers. In Station 73, the two polymer layers are cured together under the influence of UV radiation.

(16) Station 60 is preferably a digital printing station and uses a printing ink based on a polymerizable acrylate. In this case, it is preferable that no curing of the ink takes place between stations 60 and 70, but at most an intermediate drying step during which some moisture is removed from the polymerizable acrylate of the ink. In the curing station 73, the printing ink and the first and second polymer layers are then cured together, resulting in a particularly resistant surface.

(17) Comparison of Standard PVC and Heat-Treated PVC

(18) The effect of heat treatment according to the invention was investigated experimentally. For this purpose, a PVC carrier plate with a density of 2,050 kg/m.sup.3 was extruded on a twin-screw extruder. This plate was then provided with a decorative high-performance layer and processed into floor panels 510. Panels manufactured in this way were laid to a test area of approx. 2×4 m (“standard PVC”) as sketched in FIG. 4. As a comparison, after cooling to approx. 40° C., an identically extruded plate was heated again to 85° C. in an oven in accordance with the invention and then slowly cooled again (“heat-treated PVC”). Afterwards the same coating, panel production and laying to a second test area as in the case of the untreated panels 510 was carried out.

(19) Both test areas were irradiated in an area of approx. 1 m.sup.2 from above with four IR radiators 501 (as a simulation of solar radiation through deep-drawn windows, e.g. in a winter garden). The radiators heated the surfaces of the floors or panels at a rate of approx. 1° C./min up to a surface temperature of approx. 80° C. During irradiation, the maximum curvature of the panels was measured and recorded. The results of this test are summarized in the table below:

(20) TABLE-US-00001 Standard-PVC Treated PVC Start curvature after t 25 None in min: Start curvature at 50 None temperature in ° C.: Maximum curvature 9.46 None in mm Maximum curvature at 68.6 None temperature in ° C.: T.sub.max during test 75.6 81 in ° C. Duration of irradiation 127 124 in min

(21) In the case of non-heat-treated PVC (“standard PVC”), the floor beneath the 501 infrared lamps began to curve significantly after 25 minutes at a surface temperature of 50° C. The curvature occurred over a large area, as indicated by circle 502 in FIG. 4. The floor of treated PVC plates showed no visible curvature. The untreated floor (“Standard-PVC”) reaches its maximum curvature of 9.5 mm at a surface temperature of 68.6° C. The floor of treated PVC plates showed no change at this temperature. The test was aborted after 127 min and a surface temperature of 81° C.

(22) Throughout the area investigated, the floor of treated PVC plates was stable and showed no curvature behaviour. The surface temperatures achieved in the test correspond to those that can be achieved in practice when floors are exposed to direct sunlight, especially with dark decors. The problems with the standard PVC regularly lead to complaints, so that a number of panel manufacturers point out on their packaging that the products are “not suitable for e.g. winter gardens and places with direct sunlight”. The plates treated according to the invention do not show such problems.