NO337077B1 - System and method of coating wood fiberboard - Google Patents

Description

The present invention relates to the surface treatment of machined wood fiber boards. The surface treatment includes applying a layer of primer, and removing a portion of the primer using rollers after application. The surface treatment gives an approximately equal surface quality on both the machined and the unmachined areas of the wood fiber boards. Both a system for surface treatment of wood fiber boards and a method for treating such boards are described. Furthermore, a procedure for writing/printing on such a disc is described.

The plates are typically used inside buildings, and are delivered with a finished surface treatment so that the assembly process is completed immediately after assembly. In this way, you can avoid spalling and painting during the installation of internal wall panels and ceilings. This means that surface-treated wood fiber boards are very economical to use, while at the same time you get a uniform and predictable surface quality.

The boards can be milled so as to have a surface reminiscent of a painted wooden panel with different profiles and patterns, and this gives a finished surface that is considered appealing. Machining is usually carried out with a CNC-controlled milling machine, which gives great freedom in the choice of profiling, or with fixed milling machines based on a given structure.

Milling can include milling out grooves and tongues along the edges of the wood fiber board so that several boards can be joined together without the joint having to be finished, for example by sandblasting and painting.

Wood fiberboard in this context is intended to include chipboard, MDF boards (Medium-density fiberboard or fiberboard with medium density), HDF boards (High-density fiberboard, fiberboard with high density), particleboard and other boards made of wood fibers that are used in buildings, especially internal.

During surface treatment of machined wood fibreboards, there is a problem that the machined areas take up primer unlike the unmachined areas. The machined areas often have a somewhat rougher surface than the unmachined areas. The machined areas will therefore take up more, or need more priming, than the areas that are not machined. At the same time, one does not want to apply more primer than necessary, especially for cost reasons.

Applying excessive amounts of primer means that an unnecessarily large volume of primer is used. Too much primer also results in unnecessarily high energy consumption for curing, and the time it takes for the primer to harden becomes unnecessarily long.

From US 3050415 A, a method and device for applying a liquid for surface treatment on panels of wood or cellulose appears. The device is intended for applying a penetrating, sealing composition to a plate with grooves, and comprises a roller with an elastic coating.

The primer layer can form the basis for applying graphics or printing, and is well suited for writing or "printing" with a suitable ink printer or "printer" connected to a unit for inputting and processing graphic files. For the application of such pressure, it is important that the surface to which pressure is applied has a uniform roughness or surface quality to give a nice result without, for example, light being reflected differently from machined and unmachined areas. With UV curing ink, however, it is a challenge to get the ink to harden if the layer of ink is too thin. Applying a layer of ink that is thick enough to provide good curing is, however, expensive and presents other challenges in connection with flow between the colors in the ink, in connection with correct color saturation, etc. It is therefore also an object of the invention to provide a process where the amount of ink used is not dictated by the required thickness to provide a good curing process.

The graphics can typically include imitation wood, or can be any other image, pattern, figures, etc.

The graphic can be given a protective layer of clear lacquer which is preferably cured with ultraviolet light. The clear coat should be overpaintable in consideration of any subsequent refurbishing needs.

The present invention thus relates to a method for surface treatment of a machined wooden fiber board with an unmachined main surface and machined recesses with pores or uneven surfaces. The method comprises at least one first step of applying at least one layer of UV curing primer of a type that must be processed in at least one dedicated curing step to be cured, and at least one step of removing an excess amount of primer with at least one roller from at least the main surface. The UV-curing primer is then cured in a UV curing unit by irradiation with ultraviolet light. The method further comprises a step of writing a decoration with a UV-curable printer ink on the primed surface with an inkjet writing unit in a thin, separate layer of at least partially uncured UV-curable primer applied to the at least one layer of cured primer, and curing the printer ink and made uncured primer in a common curing step.

The excess amount of primer removed from at least the main surface by at least one roller can be fed to a step for applying a layer of primer.

The application of at least one layer of primer may include spraying the primer onto the wood fiberboard.

Application of at least one coat of primer may include application in a low pressure chamber with primer mist.

The step of applying at least one coat of primer may include rolling the primer with a roller.

The primer can be a UV-curing primer, and the curing of the primer in a curing unit can then include irradiation with ultraviolet light (UV light).

The method may further comprise a step of writing a decoration with printing ink on the primed surface with an ink printing unit.

The step of writing on the primed surface with an inkjet printing unit may comprise writing with the printer ink in a thin layer of at least partially uncured primer applied to the at least one layer of hardened primer.

The application of the thin layer of at least partially uncured primer may comprise the application of primer in a primer unit, and the removal of excess primer in a roller unit.

The primer applied to printer ink can be a clear primer.

The printer ink can be cured in a dedicated curing step. Alternatively, both the printer ink and the uncured primer can be cured in a common curing step. The printer ink can be UV-curing ink.

The method can further include applying a layer of clear lacquer with a lacquer unit, the lacquer unit being of a type that must be processed in at least one dedicated curing step to be hardened on the surface with printer ink, removing an excess amount of lacquer with at least one roller from at least the main surface. The varnish is then cured in a curing unit.

The varnish is typically a UV-curing varnish, in that the curing of the varnish in a curing unit includes irradiation with ultraviolet light.

The invention also includes a method for producing wall or ceiling panels. The method includes providing a fiberboard, machining tongue and groove along the edges of the fiberboard, machining indentations in the surface of the fiberboard, applying a layer of UV curing primer in an amount in excess of the amount required to fill pores formed during machining, removing an excess amount of primer with at least one roller, and return the excess amount of primer that is removed to a primer application unit. The layered UV-curing primer is then cured by irradiation with ultraviolet light, a separate layer of uncured UV-curing primer is applied to the at least one layer of cured primer, a decoration is written with a UV-curing printer ink on the separate layer of uncured UV-curing primer applied to it at least one layer of cured primer, and the printer ink and the separate layer of uncured primer are cured in a common curing step.

The invention also includes a system for surface treatment of machined wood fiber boards. The system comprises a first priming unit for applying a primer to the wood fiber boards, a first hard roller for removing a portion of the primer, a first UV curing unit, a first sanding unit, a second priming unit, a second hard roller for removing a portion of the primer and a second UV curing unit.

The system can further comprise a third priming unit, a first soft roller for removing a portion of the primer, a third UV curing unit, a second grinding unit, a second soft roller for removing a portion of the primer, a second soft roller for applying U -cured layer for fusion with printing, an inkjet printer, a fourth UV curing unit, a coating unit, and a fifth UV curing unit.

A third soft roller for applying clear coat and a sixth curing unit are also described.

Brief description of the attached figures:

Fig 1 is a schematic diagram showing an embodiment of a system according to the invention; Fig. 2 shows a cross-section of a wood fiber board that can be treated according to the invention; Fig. 3 is a schematic representation of a wood fiber board that has been treated according to the invention, where different layers appear; Fig. 4 is a schematic diagram showing another embodiment of a system or a production line according to the invention;

Fig. 5 is a schematic diagram of a device for applying agents; and

Fig. 6 is a schematic diagram of a device for applying and removing means.

Detailed description of embodiments of the invention with reference to the attached figures: Figure 1 shows a system or a production line according to the invention which can be used in a method for surface treatment according to the invention. From fig. 1 shows a wooden fiber board 1 with machined grooves 2 so that the board imitates a wall panel of profiled boards. After the plate 1 has been sanded / brushed to remove irregularities etc. from the machining process and dust and other impurities have been removed, the plate enters a priming unit 3 for the application of UV curing primer in an amount greater than the amount desired on the fully primed plate. Put another way, the primer made is thicker than the thickness of the primer you want on the finished product. The primer is applied in an amount typically from 20 - 100 g/m<2>, preferably 40 - 80 g/m<2>.

The priming unit 3 can be a spray painting unit or a vacuum/mist unit for applying the primer. The device can alternatively use a bath, rollers or other application methods. The primer must be able to be applied in the quantities specified above.

After application of primer, plate 1 passes to a roller unit 4 for removal of excess primer. The roller unit comprises a rigid roller which removes primer from the plate, but so that the primer remains in the machined grooves typically in an amount of 40-80 g/m<2>.

The roller unit 4 contains rollers 5. There are typically two rollers that rotate against each other and collect excess primer. The surface of the rollers is smooth and hard so that the removal effect in the grooves 2 is less than on the surface between the grooves 2. Excess primer is collected with a unit that runs along the length of the rollers and is stored in a separate container, or fed directly back to the primer unit 3 via a hose 6. This return entails a significant cost reduction in that there is very little wastage of priming.

After removal of the primer on the top surface, the layer with primer is cured with UV rays in a curing unit 7.

The curing unit 7 will normally be a unit that illuminates the primer with high-intensity ultraviolet light if a UV-curing primer is used.

From fig. 2 shows a machined wooden fiber board 1 with machined grooves 2 which can be surface treated with a system and a method according to the present invention. From fig. 2 it is clear how the machined grooves 2 lie lower than the main surface so that the roller removes less primer from these than from the main surface. Plate 1 is also shown with groove 9 and spring 8.

In the following description, the reference numbers 1, 2, 20, 30a, 30b, 30c, 31, 32a and 32b refer to figure 3, which is a schematic representation of a wood fiber board treated according to the invention, where different layers appear. The other reference numbers refer to figure 4 which is a schematic diagram showing an embodiment of a system or a production line according to the invention in which the units for the various processes are shown.

Figure 4 shows a first unit which in principle appears from Figure 6. The unit 40 performs steps A, B and comprises three rollers (Fig. 6) where the first two rollers 10, II (seen in a direction of travel for a plate to be processed from left to right in figures 4 and 6) applies a layer of primer, in step A. The first of these two rollers 11 applies primer to the plate to be surface treated, and the second roller 10 ensures the application of the correct amount of primer and distribution of priming on the first roller 11 which lays the primer on the plate. The first roller 11 is soft, so that it applies primer to the entire surface, including the grooves. A third roller 12 in the unit 40 removes excess primer from the plate in step B so that only one layer of primer 30a remains in the grooves (grooves 2, fig. 2) in the plate due to the grooves being lower than the main surface of the plate 1/ top surface. The third roller 12 in stage B is hard, so that it does not remove primer from the grooves.

This is advantageous because the machining of the grooves 2 means that the grooves 2 have a rougher surface than the main surface of the plate 1 (Fig. 2). In addition, fibers from the plate tend to rise, which gives a more uneven surface in the grooves 2. This is why there is a need for more priming in the grooves. Steel scraper 13, 14 scrapes the primer of the roller 12 (fig. 6).

The surface is then semi-hardened in a step C in a hardening unit 41 for hardening the primer. The curing unit 41 is a unit that exposes the primer to UV rays. Semi-hardening in this context means that the primer only partially hardens.

The surface is then sanded in a sanding unit 42 which polishes the surface in a step D.

The surface is then primed again in a step E with a priming and removal unit 43 which then removes some primer in a step F. The unit 43 is schematically shown in figure 6. In step F a hard roller is used which leaves more primer in the grooves than on the main surface between the tracks. The units 40 and 43 can be the same, and thus the plate can actually be run twice through the same unit. However, this is not efficient in a production line. The process leaves a layer 30b.

The primer is then semi-cured once again in a new curing unit 44 in a curing step G. Again, this process could have been carried out in the curing unit 41, but again this would be less efficient.

A new layer of primer is then applied with a primer unit 45 in a step H with a primer unit corresponding to the unit shown in fig. 5. The priming unit 45 has a soft roller which lays a thin layer of primer 30c over the entire surface.

Again, the primer is semi-cured in a curing unit 46 in a step I. The curing unit 46, like the other curing units, is a unit that processes the curing with UV rays.

The surface is polished or sanded in a sanding unit 47 in a step J. This sanding is also considered an intermediate sanding.

The layers of primer in the previous steps are typically a white primer.

A new thin layer of primer 30d is laid over the entire surface with a priming unit 48 with a soft roller in step K. This layer of primer is a clear primer.

This layer is intended for fusing with ink in a subsequent print/write step.

This layer can be applied in an amount of 2-12g/m<2>, preferably 3-6 g/m<2>.

The entire surface is printed with a desired image or pattern in a printer unit 49 in a printing step L which forms an ink layer 31.

It is a problem that thin layers of UV-curing materials such as primer or ink do not harden or harden more slowly if the layer is too thin. In this context, the layer of print/ink is too thin to harden well enough on its own. Printing in an uncured primer means that the layered primer and ink together will be thick enough for the curing process to be good. Alternatively, more ink could be used in the printing process, but this is problematic for print-technical reasons and is unnecessarily expensive because printer ink is more expensive than primer. Consequently, it is an advantage to print in a thin layer of uncured primer.

Alternatively, increased time in a UV curing unit would help complete the curing of the ink, but this makes the process slower and more energy intensive.

The layers of primer and the ink layer 31 are then fully cured in a curing unit 50 in a step M. The curing unit 50 is also a unit that irradiates the plate with UV rays.

A layer of clear lacquer 32a is then applied over the entire surface with a lacquer unit 51 in a step N. The lacquer unit 51 can be of the same type as the primer units.

The clear coat is then semi-cured in a new curing unit 52 in a step 0 before applying another layer of clear coat 32b in a lacquer unit 53 with a soft roller in a step P before fully curing in a curing unit 54 in a step Q.

The surface is then primed again in a new priming unit which may correspond to the priming unit in the first step, or may be passed through the first unit again for a new application of a primer.

The primer in layer 30c is clear/transparent.

Clearcoat is applied in another layer 32a a unit and removed with a stiff roller before half-hardening in a curing unit.

Finally, a final layer 32b of clear lacquer is applied which is fully cured.

The total amount of primer is typically 40-60 g/m<2>on the main surface and 100-120 g/m<2>in the millings.

Figure 5 shows a schematic diagram of a priming unit or varnish unit (application unit) that can be used in the present invention. The application unit comprises a first rotating roller 11 which is applied with the agent to be applied to the underlying plate 2 and a second rotating roller 10 which distributes the agent on the first roller 11. The second roller 10 also helps to regulate the amount of agent applied to the first roller 11.

Figure 6 shows a schematic diagram of a combined application unit and removal unit, where the first roller 11 and the second roller 10 have the same function and mode of operation as explained above in connection with claim 5. The combined priming unit and removal unit, however, also includes a rotating removal roller 12 for removing agent from the surface 2. The agent that is removed from the surface with the removal roller 12 is dragged along by it and scraped by the removal roller 12 with two scrapers 13, 14. The agent that is scraped off can be used again in an application unit somewhere in the production line.

In this statement, the term "application unit" is intended to cover "priming unit" and "coating unit".

In the described embodiment, UV-curing varnish and primer and units for irradiation with UV rays are indicated. It is important to use agents that do not harden under production conditions before the agents are subjected to a dedicated treatment for hardening. By using agents that do not harden, the agents that are removed as excess agent can be returned to the process for reuse. At the same time, curing can take place quickly when curing is desired, and this is important to achieve an efficient process. It is also an advantage that agents are used that harden without emitting large amounts of solvents for the sake of the working environment. Finally, such agents significantly facilitate their use in the machinery because they do not harden during the process, and because it does not harden when the machinery is not in operation.

The system according to the invention is particularly suitable for UV curing because with UV curing agents there is no danger of the primer/agents hardening on the rollers or during the return to the primer unit 3. This could change the viscosity of the primer and could therefore cause problems. Controlled hardening of the primer also greatly simplifies cleaning, maintenance, service interruptions, etc. when the primer does not dry. Reversing the primer is significantly more complicated without a UV-hardening primer.

In Table 1, the various steps in the production line according to the invention are set up schematically.

Claims (13)

1. Process for surface treatment of a machined wood fiber board (1) with an unmachined main surface and machined recesses (2) with pores or uneven surface, comprising at least one first step of applying at least one layer of UV-hardening primer of a type that must be treated in at least one dedicated curing stage to be cured, characterized by: at least one step (B) of removing an excess amount of primer with at least one roller from at least the main surface; curing the UV curing primer in a UV curing unit by irradiation with ultraviolet light, the method further comprising a step of writing a decoration with a UV curing printing ink on the primed surface with an ink writing unit in a thin, separate layer of i the at least partially uncured UV curing primer applied to the at least one layer of cured primer; and curing of the printer ink and the uncured primer made in a common curing step. 2. Method according to claim 1, further comprising guiding the excess quantity of primer which is removed from at least the main surface with at least one roller, to a step for applying a layer of primer. 3. Method according to claim 1, further comprising that the step of applying at least one layer of primer comprises spraying the primer on the wood fiber board (1). 4. Method according to claim 1, further comprising that the step of applying at least one layer of primer comprises application in a low-pressure chamber with primer mist. 5. Method according to claim 1, further comprising that the step of applying at least one layer of primer comprises rolling on the primer with a roller. 6. Method according to claim 1 in which the application of the thin layer of at least partially uncured primer comprises the application of primer in a primer unit, and the removal of excess primer in a roller unit. 7. Method according to claim 1 or 6, in which the primer is a clear primer. 8. Method according to one of claims 1, 6 or 7 in which at least the printer ink is hardened in a dedicated hardening step. 9. Method according to claim 1, further comprising applying a layer of clear varnish of a type which must be processed in at least one dedicated curing step to be cured on the surface with printer ink, with a varnish unit; removing an excess amount of varnish with at least one roller from at least the main surface; and curing the varnish in a curing unit. 10. Method according to claim 9, further comprising that the varnish is a UV-curing primer, in that the curing of the varnish in a curing unit comprises irradiation with ultraviolet light. 11. Method for the production of wall or ceiling panels comprising: providing a wood fiber board (1); machining of grooves (9) and tongues (8) along the edges of the wood fiberboard (1); machining recesses (2) in the surface of the wood fiber board (1); applying a layer of UV curing primer in an amount in excess of the amount needed to fill pores formed during machining; characterized by: removing an excess amount of primer with at least one roller; returning the excess amount of primer removed to a primer application unit; hardening of the layered UV-hardening primer by irradiation with ultraviolet light; applying a separate layer of uncured UV curing primer to the at least one layer of cured primer; writing a decoration with a UV-curing printer ink on the separate layer of uncured UV-curing primer applied to the at least one layer of cured primer; and curing the printer ink and the separate layer of uncured primer in a common curing step. 12. System for surface treatment of engineered wood fiberboard (1) comprising; a first primer unit (40) for applying a primer to the wood fiber boards (1); a first hard roller for removing a portion of the primer; a first UV curing unit (41); a first grinding unit (42); a second priming unit (43); a second hard roller for removing a portion of the primer; and a second UV curing unit (44). 13. System according to claim 12, further comprising: a third priming unit (45); a first soft roller for removing a portion of the primer; a third UV curing unit (46); a second grinding unit (47); a second soft roller for removing a portion of the primer; a second soft roller for applying the U-hardened layer for fusion by printing an inkjet printer (49); a fourth UV curing unit (50); a sheet unit (51); and a fifth UV curing unit (52).