METHOD FOR FINISHING A WOOD BOARD

Abstract

The invention relates to a method for finishing a wood board with an upper face and a lower face. A layer of liquid synthetic resin is first applied at least onto the upper face or the lower face, and at least one paper ply soaked with a synthetic resin is then applied. The structure is then pressed in a press under high pressure and at a high temperature, wherein the synthetic resin melts and is connected to the upper face or the lower face of the wood board. The invention is characterized in that the upper face and/or the lower face is provided while still having a press skin and in an ungrounded state, and the layer is applied so thinly that the liquid synthetic resin is completely drawn into the press skin, the layer is not actively dried, and the paper ply is positioned on the press skin.

Claims

1. A process for the finishing of a wooden composite board with an upper side and an underside, comprising a layer of liquid synthetic resin applied at least to an upper side or an underside, then at least one paper ply impregnated with a synthetic resin is applied, and the synthetic resin and the paper ply are then pressed in a press under high pressure and at high temperature, where the synthetic resin melts and bonds to the upper side or the underside of a wooden composite board, wherein the upper side and/or the underside retain a press skin and are provided without surface-grinding, and the layer applied is such a thickness that all of the synthetic resin enters the press skin, no active drying of the layer takes place, and the paper ply is placed onto the press skin.

2. The process as claimed in claim 1, wherein finishing process is carried out identically on both the upper side and the underside.

3. The process as claimed in claim 1, wherein the liquid synthetic resin is applied by rolling, spreading, trowelling or spraying.

4. The process as claimed in claim 1, wherein a quantity applied of the synthetic resin is from 5 to 100 g/m.sup.2.

5. The process as claimed in claim 4, wherein a quantity applied of the synthetic resin is from 5 to 50 g/m.sup.2.

6. The process as claimed in claim 5, wherein a quantity applied of the synthetic resin is from 5 to 25 g/m.sup.2.

7. The process as claimed in claim 1, wherein the liquid synthetic resin is a melamine resin or a urea resin or a melamine-urea-resin mixture.

8. The process as claimed in claim 1, wherein the ratio of the synthetic resin to water is (60:40) with a tolerance of ±10%.

9. The process as claimed in claim 1, wherein the synthetic resin comprises additives.

10. The process as claimed in claim 9, wherein the synthetic resin comprises hardeners and/or wetting agents and/or thermoplastic polymers.

11. The process as claimed in claim 1, wherein at least one paper ply is a decorative paper.

12. The process as claimed in claim 1, wherein before the pressing procedure, the paper ply is covered with a wear layer made of synthetic resin.

13. The process as claimed in claim 12, further comprising an overlay paper placed onto the paper ply.

Description

[0013] The problem is solved in the case of a process of the generic type in that the upper side and/or the underside retain a press skin and are provided without surface grinding, and the layer applied is so thin that all of the liquid synthetic resin enters the press skin, no active drying of the layer takes place, and the paper ply is placed onto the press skin.

[0014] It has been shown, wholly surprisingly, that this application of synthetic resin, which is known per se from direct printing technology, leads to a substantial improvement in the adhesion of the paper ply to the upper side and/or the underside of the wooden composite board. Because the paper, which is generally a decorative paper, is impregnated with a synthetic resin, it could be assumed that this better adhesion occurs simply because more resin is used in the lamination. This assumption is not correct, however, because delamination phenomena are known to occur even when the decorative paper is saturated with resin and a paper that is very absorbent is used, so that the amount of synthetic resin that enters the laminate structure is increased. Delamination cannot reliably be prevented with such a structure.

[0015] Tests have shown that the resin with which the paper ply is impregnated does not begin to dissolve, as it does in EP 2 743 094 A1. The synthetic resin drawn completely into the press skin is inactive here.

[0016] The improved adhesion is probably attributable to the fact that the upper side and/or the underside is provided without surface processing, that is to say untreated and with the full press skin. The synthetic resin applied in liquid form penetrates into the press skin and thus forms, together with the press skin, an optimum base for the decorative paper applied subsequently.

[0017] The liquid synthetic resin can be applied by rolling, spreading, trowelling or spraying.

[0018] By omitting active drying, the manufacturing process is accelerated and, in addition, a significant energy saving is achieved.

[0019] Preferably, the liquid synthetic resin is applied in a quantity of from 5 to 100 g/m.sup.2, in particular from 5 to 50 g/m.sup.2 and more particularly preferably from 5 to 25 g/m.sup.2.

[0020] The synthetic resin is preferably a melamine resin or a urea resin or a melamine-urea-resin mixture.

[0021] Good results have been achieved with a coating in which the ratio of synthetic resin to water is (60:40) with a tolerance of ±10%.

[0022] The synthetic resin can comprise additives, in particular hardeners and/or wetting agents and/or thermoplastic polymers.

[0023] The paper ply is preferably covered with a wear layer made of synthetic resin before the pressing procedure. This wear layer can be produced by an overlay paper impregnated with a synthetic resin. The paper ply is preferably a decorative paper. The wear layer can, however, also be applied in liquid form. It is also conceivable to scatter synthetic resin particles onto the paper ply for the wear layer.

[0024] The wooden composite board finished by the process according to the invention corresponds to a conventional laminate having a paper structure on the upper side, with the fundamental difference that the adhesion between the paper structure and the wooden composite board is significantly improved by the previously applied liquid synthetic resin layer. The wear layer can thus comprise abrasion-resistant particles, for example corundum, in order to increase the abrasion resistance of the laminate. A structure can be embossed in the wear layer during pressing of the laminate structure. This structure can correspond to the decoration (“synchronous pore”). The decoration can be a wood grain or a tile effect. In the case of a wood grain, the structure then corresponds to the pattern of the grain, the knotholes or pores in the reproduced wood surface. In the case of a tile effect, the structure corresponds to the joints.

[0025] The improvement achieved compared to a conventional laminate structure having paper plies can readily be seen in the figures. The figures each show an apparent density profile of a coated MDF board from the upper side (0 mm) to the middle of the wooden composite core (3 mm).

[0026] FIG. 1 shows the laminate structure with a standard MDF board, the upper side of which has been ground in order to remove the press skin completely. A synthetic-resin-impregnated decorative paper ply has been placed on the ground upper side, and an overlay paper ply has been placed thereon and pressed. The delamination strength of the top layer is 2.0±0.1 N/m.sup.2. The high apparent density of 1900 kg/m.sup.3 results on the upper side from the paper structure. The apparent density falls continuously towards the middle of the wooden composite core.

[0027] In the case of the diagram shown in FIG. 2, a standard MDF board with an unground upper side has been used, that is to say an MDF board with a complete press skin, on which a synthetic-resin-impregnated decorative ply and an overlay paper ply have been placed and pressed. The abrasion resistance of the top layer is 1.5±0.3 N/m. The apparent density is here lower at the peak, but it is also formed by the paper layers. The apparent density initially falls continuously, the increase at a depth of about 0.25 mm results from the press skin, which has not been removed from the upper side. Here there is a risk of delamination, because the bond between the paper structure and the wooden composite board is poor.

[0028] The board tested according to FIG. 3 is a standard MDF board treated according to the invention, which was made available with an unprocessed upper side and coated with 50 g/m.sup.2 melamine resin before a synthetic-resin-impregnated decorative paper and overlay paper ply were placed on and pressed. The abrasion resistance of the top layer was 1.9±0.1 N/mm.sup.2. It can be seen that the maximum apparent density reaches almost the value of the standard board (FIG. 1), but this then falls continuously and, although the press skin was not removed, no further increase in the apparent density is to be noted. As can be seen from a comparison of FIGS. 2 and 3, the defect which can lead to delamination phenomena could largely be avoided, so that a largely closed curve shape is established. Although the delamination strength of the top layer is at the level of the standard structure according to FIG. 1, it is to be taken into consideration that the production time is shortened significantly simply because the press skin does not have to be ground off, a cost saving is thereby achieved, and the region of the upper side that is to be ground off does not have to be compensated for beforehand by the introduction of more material during production of the MDF board. It will be seen that delamination is reliably avoided according to the invention, and in some cases the resin-coating of the impregnated paper plies can also be reduced because the synthetic resin necessary for bonding is possibly provided beforehand by the introduction of synthetic resin into the press skin. The underside of the wooden composite board can be finished in exactly the same way as the upper side. The upper side and the underside can also be treated identically. Both sides are then preferably finished at the same time.