Directly printed, coated panel

Abstract

The present invention relates to a panel, in particular a wall-, ceiling or floor-panel, comprising a carrier layer (71) with a front side and a rear side, wherein the carrier layer (71) comprises at least at its front side as seen from the front side the following layers: a primer layer (72); a decor layer (73), comprising a polymerizable print color; and a polymer layer (74), which preferably comprises a hardness gradient.

Claims

1. A panel for use as a wall, ceiling or floor panel, comprising a carrier layer having a front side and a rear side, the carrier layer having on the front side at least the following layers in the following order: a primer layer; a decor layer comprising a polymerizable print color; and a polymer layer having a front surface and a rear surface, wherein the polymer layer has a hardness gradient such that the hardness of the polymer layer continuously decreases with increasing depth from the front surface of the polymer layer, wherein the print color of the decor layer is crosslinked with the polymer layer at an interface of the decor layer and the polymer layer.

2. The panel according to claim 1, wherein the print color is based on a polymerizable acrylate.

3. The panel according to claim 1, wherein the print color of the decor layer and the polymer layer have been cured in one common step together.

4. The panel according to claim 1, wherein the decor layer has been applied by digital printing.

5. The panel according to claim 1, wherein between the decor layer and the polymer layer no further layer is present.

6. The panel according to claim 1, wherein the hardness gradient in general follows the following relation:
(3.0.Math.x)+CY(x)(0.2.Math.x)+C wherein x is the absolute value of the depth in micrometer of the coating as seen from the front surface of the coating; Y(x) is the absolute value of the hardness in N/mm.sup.2 at a specific depth x; and C is the absolute value of the initial hardness in N/mm.sup.2 of the coating at about x0-5 m depth.

7. The panel according to claim 6, wherein the hardness gradient corresponds in general to the following relation:
(2.5.Math.x)+CY(x)(0.4.Math.x)+C(2,0.Math.x)+CY(x)(0.6.Math.x)+C.

8. The panel according to claim 1, wherein the polymer layer comprises a thickness of 20-300 m.

9. The panel according to claim 1, wherein the primer layer comprises a thickness of 20-300 m.

10. The panel according to claim 1, wherein the primer layer is no UV-curing lacquer.

11. The panel according to claim 1, wherein the primer layer is based on an aqueous acrylate system.

12. The panel according to claim 1, wherein the primer layer has been applied by a curtain coating method.

13. The panel according to claim 1, wherein the polymer layer is based on one or more of the following acrylates: 1,6 hexandioldiacrylate, polyesteracrylate, polyurethanacrylacidester and dipropylenglycoldiacrylate.

14. The panel according to claim 1, wherein the front surface of the polymer layer achieves in the grid cut test according to DIN ISO 2409 a grid cut parameter of at least 2.

15. A method for the coating of a panel, comprising the following steps: (i) providing a carrier board; (ii) applying a primer layer on the carrier board; (iii) applying on the primer layer a decor layer including a polymerizable print color; (iv) optionally: partially curing the print color; (v) applying a first liquid coating agent onto the incompletely cured print color; (vi) applying at least a second liquid coating agent onto the still wet first coating agent so that a partial mixing of the coating agents takes place; and (vii) curing at least the applied coating agents and the print color in one common step together by using radiation, such that the cured coating agents comprise a hardness gradient, wherein the hardness of the cured coating agents decreases with increasing depth from a front surface of the resulting coating and wherein the print color of the decor layer is crosslinked with the first liquid coating agent at an interface of the decor layer and the first liquid coating agent.

16. The method according to claim 15, wherein the primer layer in step (ii) is applied by a curtain coating method.

17. The method according to claim 15, wherein the primer layer is dried after step (ii) and before step (iii).

18. The method according to claim 15, wherein the decor layer is applied by digital printing.

19. The method according to claim 15, wherein the coating agents are directly applied onto the decor layer.

20. The method according to claim 15, wherein the hardness gradient in general corresponds to the following relation:
(3.0.Math.x)+CY(x)(0.2.Math.x)+C wherein: x is the absolute value of the depth in micrometer of the coating as seen from the front surface of the coating; Y(x) is the absolute value of the hardness in N/mm.sup.2 at a specific depth x; and C is the absolute value of the initial hardness in N/mm.sup.2 of the coating at about x0-5 m depth.

21. The method according to claim 15, wherein the hardness gradient corresponds in general to the following relation:
(2.5.Math.x)+CY(x)(0.4.Math.x)+C.

22. The method according to claim 15, wherein the coating agents comprise a total thickness of 20-300 m.

23. The method according to claim 15, wherein the primer layer comprises a thickness of 20-300 m.

24. The method according to claim 15, wherein the primer layer is no UV-curing lacquer.

25. The method according to claim 15, wherein the coating agents are based on one or more of the following acrylates: 1,6 hexandioldiacrylate, polyesteracrylate, polyurethanacrylacidester and dipropylenglycoldiacrylate.

26. The method according to claim 1, wherein the decor layer consists of print color.

Description

4. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(1) In the following, now a detailed description of exemplary embodiments is given by means of the accompanying diagrams and figures. Herein, the production of a polymer layer with a hardness gradient will be described by means of the FIGS. 1 to 6 analog to WO 2008/061791 A1.

(2) FIG. 1 is a schematic view of a coating process for the manufacturing of a polymer layer with a hardness gradient according to the prior art;

(3) FIGS. 2A to 2C are schematic views, wherein the process of the mixing of two liquid layers is shown;

(4) FIGS. 3 to 5 are diagrams, which show the gradient of the hardness depending on the depth of the coating; and

(5) FIG. 6 shows an exemplary panel according to the invention in a schematic view.

(6) In FIG. 1 a coating machine for the coating of wood material boards 10 is schematically shown. The wood material boards 10, like for instance solid wood boards, HDF-, MDF- or chip boards, are guided by a roller conveyor 12 through different stations of the coating machine. In a first coating station 14 a first liquid coating agent 20 is applied by means of a rotating application drum 15 onto the wood material boards 10 by means of a passage coating. The application drum 15 is supplied with a coating agent by a supply device 16. In the second coating station 17 a second liquid coating agent 21 is applied onto the still wet first coating agent 20 by means of a further rotating application drum 18. The application drum 18 is supplied with the second liquid coating agent by means of a supply device 19. Of course, the application can be also carried out with any other suitable application method, like for instance by spraying or by a coating knife and the like. It is only important that the application of the second layer is carried out while the first layer is still wet enough so that a partial mixing of the layers takes place. Moreover, of course further coating stations may be provided after the second station 17, in order to apply for instance a third liquid coating agent onto the still wet second coating agent 21 or also additional stations, in order to apply abrasion resistant particles onto or into the wet layers.

(7) After leaving the coating station 17, the coated boards 10 are transported to a curing station 30, where the layers are cured by means of UV-radiators 31. On their way from the coating station 17 to the curing station 30 the partial mixing of the liquid coating agents 20 and 21 takes place, which happens particularly in the border area of the two coating agents. In general, the mixing rate is the larger the nearer the point of interest is located at the border of the two layers. By the curing of the layers in the curing station 30, the mixing process is stopped and the set mixing ratio, and thus the mechanical properties of the generated coating, is fixed. The dimension of the mixing in the border areawhich happens on its own terms and preferably without any mechanical impact from outsidedepends on the duration, which passes between the application of the second coating agent 21 onto the still wet first coating agent 20 and the curing at the curing station 30. In addition, the mixing of the two coating agents is also influenced by the specific viscosities of the coating agents, wherein it is seen as a rule of thumb that the higher the viscosity is the lower the mixing per time unit is.

(8) The principle of mixing of the two applied coating agents can be seen at its best from the schematic views of the FIGS. 2A to 2C. Herein, FIG. 2A shows the state of the two coating agents 20 and 21, which have been applied onto a wood material board 10, directly after the application of the second coating agent 21. At that point of time, no mentionable mixing has taken place. The coating agents 20 and 21 are in that case polymers, which each comprise different numbers of CC carbon-double bonds. As schematically indicated in FIG. 2A, the first coating agent 20 comprises a lower number of CC double bonds than the second coating agent 21. Due to the larger number of CC double bonds in the second coating agent 21, the second coating agent 21 will comprise a higher hardness than the first coating agent 20, which comprises less CC double bonds after the curing.

(9) Since both coating agents 20 and 21 are applied wet-in-wet, a mixing happens starting from the border 22 between the two layers, as it is indicated in FIG. 2B. That means, that in the area near to the border 22 of the lower layer more double bonds are present and accordingly in the area near to the border 22 of the upper layer less double bonds are located than prior to the mixing due to the mixing process. FIG. 2C shows the two layers after the mixing is a little more progressed and has reached a sufficient degree of mixing. When the curing of the coating agents, like for instance by means LTV-radiation, is carried out at that point of time, this degree of mixing is fixed, since in the cured layers no more mixing can happen.

(10) In the diagram of FIG. 3 a gradient of the hardness of the coating with hardness gradient and of the coating without hardness gradient (labeled with: prior art) is shown. The example with hardness gradient was a grinded wood material board, which was provided with a primer layer on which two different coating agents have been applied wet-in-wet. The first applied coating agent comprised about 35% 1,6-hexandioldiacrylate and about 65% polyestheracrylate and has been applied in a thickness of 45 g/m.sup.2. The second coating agent, which has been applied onto the still wet first layer comprised about 70% polyurethanacrylacidesther and about 30% dipropylendiglycoldiarcylate and was applied in a thickness of about 40 g/m.sup.2. After the application of the second layer, it has been waited for 10 seconds in order to give the viscose liquid materials the chance to mix themselves. In the following the two layers have been completely cured in one single common step. The example without hardness gradient consisted of a common coating, wherein several thin material layers have been individually applied and wherein between the specific application processes, the layer, which has been applied before, has been cured. The lower three layers consisted of a mixture, comprising 70% polyestheracrylate and 30% 1,6-hexandioldiacrylate with a thickness of each of about 12 g/m.sup.2. The two upper layers consisted of 70% polyurethanglycoldiarcylate and 30% dipropylenarcylacidesther and the two upper layers comprised 15% corundum with the mean particle size of D 50 of 25 m.

(11) The test has been carried out according to the European standard for laminate floorings DIN EN 13329 with a Tabor Abraser Measurement System 5151 of the company Tabor Industries. After 200 rotations with S-41-sanding paper, the hardness and the depth of the grooves of the samples has been determined. The determination of the Martens hardness (registering hardness examination under the impact of a test force) has been carried out according to DIN EN ISO 14577. A Fischerscope H100 of the Helmut Fischer GmbH has been used as measurement system. The following test parameters have been used: maximum force 50/30 mN and test duration 20 seconds. The determination of the groove depth has been carried out by means of a mechanical stylus measurement instrument. A perthometer S3P of the company Perthen has been used as measurement system.

(12) During the examination of the samples it has been shown that more or less large deviations in the hardness occur for a given layer depth due to the used relatively weak materials. It is thus necessary to measure at several points in order to get reliant and representative data by means of a mean value calculation. During the carried out measurements, the hardness as well as the groove depth has been measured after 200 rotations of the sanding paper each at four points. It has been shown that four measurement points provide in most cases a sufficient validity. Of course, more valid measurement results can be achieved, when more than four measurement points are used, like for instance eight.

(13) In the table shown below, the single measurement values for the sample of the example according to the invention are listed. The measurement has been carried out with completely cured coatings, i. e. in the state, in which the corresponding products would be also used in realty as flooring panels.

(14) TABLE-US-00001 TABLE 1 Example with hardness gradient Depth of the hardness Martens hardness Depth of groove in m measurement in m in N/mm.sup.2 Rotation 1 2 3 4 1 2 3 4 1 2 3 4 3.6 3.8 3.3 3.4 134.8 118.7 159.0 150.6 MW 3.5 140.8 200 20.0 20.0 20.0 20.0 3.5 3.7 4.3 3.9 139.7 125.2 93.5 112.2 MW 20.0 3.9 117.7 400 20.0 20.0 20.0 25.0 4.5 5.0 4.0 3.9 85.9 69.9 108.9 113.2 MW 21.3 4.4 84.5 600 25.0 25.0 25.0 30.0 4.7 4.7 4.3 4.0 80.5 79.6 95.0 106.1 MW 26.3 4.4 90.3 800 30.0 30.0 30.0 35.0 4.1 4.1 4.0 4.2 103.8 103.1 109.7 100.3 MW 31.3 4.1 104.2 1000 40.0 40.0 40.0 45.0 4.7 4.2 3.9 4.5 78.5 99.3 112.0 87.5 MW 41.3 4.3 94.3 1200 50.0 50.0 50.0 50.0 4.3 5.4 4.2 4.6 93.7 59.8 98.5 82.8 MW 50.0 4.6 83.7 1400 55.0 55.0 60.0 60.0 5.4 4.5 4.0 5.0 60.1 85.0 106.7 70.8 MW 57.5 4.7 80.7 1600 60.0 65.0 70.0 70.0 4.7 4.4 4.3 4.6 47.8 53.6 55.5 48.9 MW 66.3 4.5 51.5 1800 65.0 70.0 75.0 75.0 4.0 4.6 4.9 5.3 64.5 50.1 43.7 37.1 MW 71.3 4.7 48.9 2000 75.0 80.0 80.0 75.0 5.8 4.9 6.2 5.0 31.3 43.6 27.3 41.6 MW 77.5 5.5 36.0 2200 95.0 105.0 105.0 100.0 4.5 5.1 6.1 4.9 51.4 40.8 28.1 43.7 MW 101.3 5.2 41.0

(15) In the table shown above, the column rotation lists the number of rotations which have been carried out by means of the Tabor Abraser Measurement System. The column depth of the groove lists, how many micrometers of material of the coating has been abrased starting from the original surface at the four measurement points 1-4. The column depth of hardness measurement lists, how many micrometers the test probe penetrates into the coating at the four measurement points 1-4. In the column Martens hardness then the hardness in Newton per mm.sup.2 is listed for the four measurement points 1-4. Beyond the single values the corresponding mean value is listed for the four measurement points. It can be gathered well from the table shown above that the Martens hardness decreases the deeper the cured, finished layer is penetrated. It can be also gathered that at 800 and 1000 (complete) rotations a slight increase of the Martens hardness is determined. This is based on an inhomogenious mixing of the two used coating agents, which is in practice difficult to avoid completely.

(16) Nevertheless, it can be gathered from the chart of FIG. 3 dearly that in the example with hardness gradient all in all a nearly continuous hardness decrease without large steps is on hand. The comparison example without hardness gradient shows contrary to that no such continuous gradient of the hardness, but shows at a depth of 60 to 80 m a significant step up to the original initial hardness.

(17) The mean values of the sample are listed in table 2 below.

(18) TABLE-US-00002 TABLE 2 Mean values of the example with hardness gradient Standard Martens hardness deviation of the Martens Rotation Depth in m in N/mm.sup.2 hardness in N/mm.sup.2 3.5 140.8 15.4 200 23.9 117.7 17.0 400 25.6 94.5 17.6 600 30.7 90.3 11.0 800 42.1 104.2 3.4 1000 45.8 87.5 12.6 1200 54.6 82.8 14.9 1400 62.2 80.7 17.4 1600 70.8 51.4 3.2 1800 76.0 48.9 10.1 2000 83.0 35.9 6.8 2200 106.4 41.0 8.4

(19) The values of the comparison example without hardness gradient are listed in tables 3 and 4 below.

(20) TABLE-US-00003 TABLE 3 Samples without hardness gradient Depth of the hardness Martens hardness Depth of groove in m measurement in m in N/mm.sup.2 Rotation 1 2 3 4 1 2 3 4 1 2 3 4 3.1 3.5 3.1 3.0 180.6 141.8 173.1 192.4 MW 3.2 172.0 200 30.0 25.0 25.0 25.0 4.2 4.2 3.7 4.7 99.9 99.6 124.5 79.3 MW 26.3 4.2 100.8 400 35.0 35.0 35.0 35.0 3.7 3.8 4.0 4.1 126.9 117.2 110.1 105.3 MW 35.0 3.9 114.9 600 45.0 45.0 45.0 45.0 3.7 3.8 4.6 4.8 128.4 122.2 83.2 74.7 MW 45.0 4.2 102.1 800 50.0 50.0 50.0 50.0 4.0 4.7 4.8 4.0 108.2 80.8 75.4 110.9 MW 50.0 4.4 93.8 1000 60.0 60.0 60.0 60.0 3.5 3.1 4.0 3.6 143.7 177.4 108.0 129.9 MW 60.0 3.6 139.8 1200 66.0 70.0 70.0 70.0 3.3 3.4 3.6 3.0 160.7 145.1 135.0 185.1 MW 68.8 3.3 156.5 1400 70.0 75.0 75.0 75.0 3.3 3.0 3.1 3.8 157.7 191.6 178.0 119.3 MW 73.8 3.3 161.7 1600 75.0 80.0 80.0 80.0 2.3 2.9 2.6 2.4 183.8 124.8 147.9 174.4 MW 78.8 2.6 157.7 1800 80.0 85.0 85.0 85.0 3.8 3.0 3.4 3.1 71.4 112.3 88.6 107.0 MW 83.8 3.3 94.8 2000 85.0 90.0 85.0 85.0 5.1 3.5 2.6 3.0 40.9 82.3 146.4 112.6 MW 86.3 3.6 95.6 2200 85.0 95.0 90.0 90.0 3.6 3.0 3.0 2.7 81.2 116.0 114.5 137.5 MW 90.0 3.1 112.3 2400 90.0 100.0 100.0 95.0 3.7 5.2 3.1 3.0 77.6 39.7 108.2 111.8 MW 96.3 3.8 84.3 2600 100.0 100.0 105.0 100.0 5.3 3.3 5.0 3.9 37.8 92.6 42.4 67.7 MW 101.3 4.4 60.1

(21) TABLE-US-00004 TABLE 4 Mean values of the sample without hardness gradient Standard Martens hardness deviation of the Martens Rotation Depth in m in N/mm.sup.2 hardness in N/mm.sup.2 3.2 172.0 18.7 200 30.4 100.8 16.0 400 38.9 114.9 8.1 600 49.2 102.1 23.5 800 54.4 93.8 15.9 1000 63.6 139.8 25.2 1200 72.1 156.5 18.9 1400 77.1 169.7 27.3 1600 81.3 157.7 23.1 1800 87.1 94.8 16.1 2000 89.8 95.6 38.9 2200 93.1 112.3 20.1 2400 100.0 84.3 29.0 2600 105.7 60.1 21.9

(22) It has been shown by way of experiments that particularly good mechanical properties of the completely finished coating can be achieved when the hardness gradient of the finished entire coatingas it is exemplarily shown in FIG. 3corresponds in general to the following relation:
(3.0.Math.x)+CY(x)(0.2.Math.x)+C
wherein: is the total value of the depth in m of the coating as seen from the surface of the coating; Y(x) is the total value of the hardness in N/mm.sup.2 at a specific depth x; and C is the total value of the initial hardness in N/mm.sup.2 of the coating at a depth of x05 m.

(23) The total values have to be understood in that only the pure numbers are used for the above mentioned formula, i. e. without the corresponding units m or N/mm.sup.2. When for example the initial value of the above mentioned example with hardness gradient is 140.8 N/mm.sup.2 (cf. table 2) so in the above mentioned formula only the absolute values are used, i. e. C=140.8. In the same way for x only the absolute values, i. e. for example x=3.5 is used. Thus, for example upper and lower limits result for Y(x=3.5) of 140.1 and respectively of 130.3. At a depth of x=40 m then results for example 132.8 for the upper limit and respectively 20.8 for the lower limit. These upper and lower limits of Y(x) have the unit N/mm.sup.2. It is important that the absolute values are used starting from the mentioned unit m or N/mm.sup.2 in the formula and not for instance starting from mm or N/m.sup.2. It should be clear to the person skilled in the art that the above mentioned formula is no mathematic formula for the description of the hardness gradient itself, but it rather defines a range, in which it shall be located.

(24) The initial value of the hardness of the coating is the value in the first few micrometers of the coating. Due to the commonly used measurement method by means of a probe pin, which enters some micrometers into the coating, it is difficult to determine the hardness for the entering depth 0 m. The phrase in general is thus chosen, because it is difficult to achieve a perfectly homogenous mixing of the materials so that in reality again and again small outliers occur, like for instance the hardness value of 140.2 N/mm.sup.2 at a depth of 42.1 m (cf. table 2) of the example with hardness gradient as discussed above. Moreover, the values, which are located extremely near to the surface of the wood material board are often inaccurate, since the remaining layer thickness to be measured has to comprise a specific minimum thickness in order to allow reliant measurements. The remaining layer thickness should thus be at least 5 m, preferably 10 m and even more preferred at least 20 m for reliant measurements. In other words, the last 20 m of the layer near to the wood material plate do not have necessarily to follow the above discussed preferred hardness gradient, but this is of course preferred.

(25) In a further preferred embodiment, the hardness gradient fulfills in general the following relation:
(2.5.Math.x)+CY(x)(0.4.Math.x)+C

(26) And in an even more preferred embodiment in general:
(2.0.Math.x)+CY(x)(0.6.Math.x)+C

(27) In the FIGS. 4 to 6 the importance of the above mentioned relationships of the hardness gradients are explained by means of the example with hardness gradient. It should be clear that the discussed absolute values for the hardness and depth are just to be understood by way of example. Of course, it is also possible to apply entire layers with significantly larger thicknesses or lower thicknesses. Moreover, the absolute value of the hardness depends of course on the used materials and can be also larger or lower than the values of the example with hardness gradient. But the order of magnitude of the mentioned values for the example with hardness gradient are particularly preferred and suitable for the use in a floor panel.

(28) FIG. 6 shows in a schematic view a panel according to the invention. The shown panel is a floor panel and comprises a carrier layer 71 made of MDF. FIG. 7 is not true to scale: the carrier layer 71 comprises in practice a thickness of several millimeters, whereas the layers, which are provided on the front side thereof, comprise just an overall thickness of several hundred micrometers. At the front side of the carrier layer 71 a primer layer 72 is applied. The primer layer 72 bases on an aqueous acrylate system and is preferably applied by means of a curtain coating method. After the drying of the primer layer 72 the decor layer 73 is applied by means of digital printing by the use of a polymerizable print color. Optionally, between the primer layer 72 and decor layer 73 further layers can be provided, like for instance a suitable priming coat. In the same way, optional further layers may be provided between the carrier layer 71 and the primer layer 72, like for instance filler layers, but also further priming coats in order to increase the adhesion of the primer layer 72 at the front side of the carrier layer 71. Such further primer- and filler layers are known to the person skilled in the art so that a more detailed description thereof is omitted. As initially explained, a polymer layer 74 is applied directly onto the decor layer 73, for which a polymerizable print color has been used, like for instance basing on a polymerizable acrylate comprising a hardness gradient. The decor layer 73 as well as the polymer layer 74 have been cured together in one single common step. Preferably, the layers comprise therefore photoinitiators, so that for instance a polymerization and thus a curing of the two layers 73 and 74 is carried out by radiation with UV-radiation. Optionally, a further thin layer 75 made of high gloss lacquer is applied.

(29) At the rear side of the carrier layer 71, a thin layer of a footfall sound insolation 76 is provided. The footfall sound insolation may be for instance a thin fiber fleece of 1 to 2 mm. As finishing layer at the rear side of the carrier layer in addition a foil 77 is provided, which serves as humidity protection.