HK1145344B - Process for machining a structured surface - Google Patents

Description

Method for machining structured surfaces

Technical Field

The invention relates to a method for producing a structured surface of an embossing tool, wherein the surface is provided over its entire surface with a first metal coating.

Background

In the coating of wood panels with thermosetting plastic resins, there is a constant attempt to reproduce the surface from nature as substantially realistic as possible. Melamine resins, phenolic resins or melamine/urea resins are among the thermosetting plastic resins used. The surface profiling of thin layers of melamine resin, for example, is carried out under pressure and temperature in a hydraulic hot-pressing device. For example, a structured metal pressing plate, for example a thin steel plate, is used as the embossing tool as the surface pressure applicator. In order to improve the wear resistance and separation properties of the metal surface, the embossing tool is additionally provided with a coating. During the extrusion process, under pressure and temperature, the melamine resin becomes liquid and further polycondensation takes place. The extrusion time and temperature determine the degree of crosslinking of the melamine resin and its surface quality. After the extrusion time has elapsed, the melamine resin has reached the desired degree of crosslinking and has turned into the solid phase. In this process, the melamine resin surface also realistically has the surface of the embossing tool.

According to the prior art, embossing tools and continuous strips in the form of extruded sheets are produced from sheet steel, which are correspondingly machined to obtain a surface structure. For this purpose, a pretreated sheet steel is provided with a base layer which is applied, for example, by means of a screen printing method, so that subsequently etching of the sheet steel can be carried out in order to obtain a surface structure. In this case, the steel sheet used has a very large specification, so that it depends on a very precise machining and in particular a consistent-coverage machining, generally requiring a plurality of working steps. In this case, all the regions of the surface structure which are to form the projections are covered by a mask, so that the surface etching is carried out only in those regions which can be directly attacked by the etching liquid. The individual etched regions then form the valleys of the desired structure, wherein after the etching process has ended, the surface is cleaned and in particular the mask is removed.

Alternatively, it is possible to first apply a photosensitive layer, which is subsequently exposed, so that after the development of the photosensitive layer has been completed, the pressure plate or the continuous strip is subjected to a rinsing process, so that only those parts of the photosensitive layer which constitute a mask for the subsequent etching process remain. The reproducibility of masks produced in this way is difficult and problematic, since the negative or positive film used for exposing the photosensitive layer must always be positioned precisely in the same position relative to the existing structures, if, for example, more than one exposure and etching process is to be carried out in order to thus apply complex three-dimensional structures on the surface of a pressing plate or continuous strip. In this case, it is also to be taken into account that, in the case of very large-format extruded plates, very small deviations can already lead to a very large deflection of the structure. The reproducibility of the mask application is therefore very difficult especially in the case of the photosensitive method in order to obtain a high degree of accuracy of the simulation. In this case, difficulties may arise if a three-dimensional structure is to be obtained by a plurality of exposure and etching processes which are carried out one after the other and for which a plurality of masks must be applied, with one etching process being carried out between each mask application. The production of the press plate or the continuous strip is therefore very costly and expensive due to the precise positioning and the corresponding number of masks required. And the achievable resolution strongly depends on the method used. Furthermore, a large number of work steps are required, which require a complex handling, in particular due to the size of the press plate or the continuous strip.

It is also known from the prior art to produce, instead of the screen printing method, a mask by means of a wax coating (Wachsauftrag), which is chemically resistant to the etchant used and can therefore be etched in the regions of the surface not covered by wax. In this method, a spray head that sprays beeswax onto a surface is moved along an X-axis and Y-axis to coat the desired structure. However, it has proven to be disadvantageous in the application of beeswax coatings that the beeswax can only be removed again from the surface with difficulty and at a high cost. Although great progress can thus be made in this process, it has been found in practice that the removal of the beeswax layer is difficult to solve, since the beeswax cannot be removed by chemical treatment and therefore the cleaning of the steel sheet after the etching process is extremely difficult, for example only with a high-pressure cleaner.

For the above reasons, it is therefore necessary to apply a mask directly to the pressure plate or the continuous strip or to expose the photosensitive layer present in part by means of a digital printing technique, in order to be able to carry out the etching immediately after the cleaning has been carried out. A particular advantage in digital printing technology is that by using the same database a very precise knowledge of the structure is possible, so that a plurality of etching processes can be carried out in succession with precision, for example in order to obtain a deep structure.

DE 10224128 a1 discloses a method for applying a coating to a surface, wherein the device used comprises a nozzle head having at least one nozzle which can be controlled by means of a control signal. In this case, the method sets either the surface to be coated to move or the nozzle head to move. A fluid coating material is applied to the surface by means of the nozzle, wherein a selected coating of selected regions is provided with liquid or gaseous materials, which may also be, for example, magics. The use of UV lacquers is exemplified. The method is particularly useful for etching of surfaces, wherein a chemical is applied to the surface.

After the surface structuring is completed, the press plate and the continuous strip are subjected to a plurality of cleaning processes and may additionally be coated with a nickel layer which is subsequently modified by further metal coatings in such a way that the surface has a desired degree of gloss and the required surface hardness. The gloss is responsible here for the fact that, after the extrusion of the material to be processed by means of the extrusion plate or the continuous strip, the extruded structure is given different degrees of depth and tone mirror effect (farbspiegelung).

Disclosure of Invention

Starting from this prior art, the object of the invention is to continue to increase the shaping possibilities of the surface structure and to adapt the synthetic resin to the greatest possible extent to a painted real wood surface.

According to the invention, for the purpose of the method, at least one further metal coating is provided on the first coating in predetermined regions, the gloss of the first coating differing from the gloss of the further coating. Preferably, a protective layer is partially coated on the first coating layer. Preferably, the protective layer is applied by means of a digital printing technique.

In contrast to the prior art, it is provided that after the structure and a first metal coating have been applied, a further coating is applied in part, the gloss of the first coating differing from the gloss of the further coating. The gloss levels of an embossing tool, in particular a press plate or a continuous strip, can thus differ from one another at least partially in local regions. By this measure, it is possible to provide the projecting structures or, if appropriate, the deeper structures with a different gloss level, for example, in order to make the structures particularly prominent. This measure permanently improves the visual impression and leads to a surface which, because of the exact printing pattern and the exact application of the substrate, can be applied in a covering manner, which in turn makes it possible to obtain not only a different deep structure but also a different gloss in order to highlight defined structure regions. In this case, the gloss difference can be selectively set, for example, the areas of the protrusions can have a higher gloss than the deeper areas or vice versa.

For example, a painted real wood surface can be simulated, wherein the surface of the protrusions has a certain dullness and the deeper wood pores, which depend on the reflection of light, show areas that shine.

For this purpose, wood cellular structures are produced according to known etching processes, which are matched to precisely match the wood decor printing.

In order to achieve this, a precisely adapted protective layer is applied to this end, which in a subsequent working process makes it possible to apply a further partial coating in the region not covered by the protective layer. In order to achieve the high precision required for the precise arrangement and covering of the respective structures, a digital printing technique is used, so that, on the one hand, a complementary structuring can be realized on an existing structure and, after the application of a protective layer, a gloss change can also be carried out.

Preferably, chromium plating is carried out as the metal coating, wherein a high-gloss chromium plating or a matt chromium plating is involved. However, the method is not limited to the chrome plating of the surface, but other metal coatings can also be applied. It is imperative, for example, to carry out a chromium plating in such a way that the protective layer used here is made of a material resistant to chromic acid, so that the protective layer is not damaged during the chromium plating process.

In order to better adhere the protective layer to the existing chromium coating, a baking of the protective layer can be provided as a further intermediate step in the process, wherein the protective layer is completely removed after the second metal coating has been completed. In order to produce the surface structure, a deep etching is generally carried out first and then a circular etching is carried out in order to highlight the shape of the microporous structure. A mechanical polishing can then be achieved before the surface is cleaned and degreased. For better adhesion of the metal coatings, in particular the chromium layer, the structured surface can additionally be activated before the application of the respective coating or another coating ensuring better adhesion, for example a nickel layer, can be applied.

According to the invention, in order to obtain a high gloss, a method is provided which consists of the following steps:

applying a first mask to the surface by means of a digital printing technique,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a second mask, which is precisely matched, again to the chemically machined surface by means of a digital printing technique,

-the surface provided with the second mask is again chemically processed,

-polishing the chemically machined surface,

-activating the polished surface,

-cleaning the activated surface,

-chrome-plating the clean surface,

applying a third, precisely fitting mask again to the chrome-plated surface, and

-again chrome-plating the chrome-plated surface provided with the mask,

wherein the structured surface has coatings produced by chrome plating with different gloss levels.

The above-described method describes the processing of the surface of an embossing tool, in particular a press plate or a continuous strip, from the application of a first mask to the surface by means of a digital printing technique and subsequent chemical processing in order to obtain the surface structure, wherein the structuring can be repeated by applying a mask and an etching process several times before the finished structured surface is subjected to a cleaning step by polishing and activation and then a first coating is applied by chrome plating, wherein subsequently a mask in the form of a protective layer is applied again in order to be able to achieve a further chrome plating with different gloss in a final method step.

Alternatively, it is possible to supplement the method by further steps which provide for multiple application of masks and processing of the surface in order to obtain the surface structure, i.e. to obtain the surface structure

Applying a first mask to the surface by means of a digital printing technique for fine structuring,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a second, precisely fitting mask to the surface by means of a digital printing technique for the structuring of the pores,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a third mask, which is precisely matched, again to the chemically machined surface by means of a digital printing technique,

-the surface provided with the third mask is again chemically processed,

-polishing the chemically machined surface,

-activating the polished surface,

-cleaning the activated surface,

-chrome-plating the clean surface,

applying a fourth, precisely fitting mask again to the chrome-plated surface, and

-again chrome-plating the chrome-plated surface provided with the mask,

wherein the structured surface has coatings produced by chrome plating with different gloss levels.

An essential point in order to obtain a suitably precise arrangement of the structures and the subsequent gloss is that the first, second and third masks and the finally applied protective layer are applied precisely in a suitable manner by means of a digital printing technique, so that a structurally uniform covering layer is present and no structural deviations occur over the entire surface of the press plate or the continuous strip.

The method according to the invention results in an embossing tool having at least one structured surface, wherein a metallic coating of a first material is provided over the entire surface of the structured surface and a metallic coating of a second material is provided in its upper part, wherein the gloss of the coatings is different. The material coating preferably used is chromium, since it is particularly hard and is then suitable for the extrusion process to be carried out. However, depending on the intended use, it is also possible to achieve particular effects by means of corresponding partial chromium coatings having different hardness and gloss, provided, for example, that no particularly high hardness is present or that the surface thereof is formed as a resilient or soft material is pressed.

The method according to the invention and the embossing tool produced therewith have the particular advantage that the structure predefined there is simulated identically on the material to be processed by means of the embossing tool, wherein the existing gloss level, that is to say at least in double layers, is simultaneously visible directly on the material to be processed. In this case, the defined regions, for example the raised regions or also the deeper regions, can additionally be provided with different gloss levels by means of different gloss levels, so that the structure is presented exactly and a visual effect is produced which results in a material surface which, for example, is hardly distinguishable from the growing wood. Other realistic surfaces can likewise be simulated in this way.

Drawings

The invention is explained below with the aid of the figures. Wherein:

FIG. 1 is a perspective view of a stripper plate according to the invention

Fig. 2 is an enlarged side view of the structures present on the surface of the press plate.

Detailed Description

Fig. 1 shows a perspective view of a press plate 1 according to the invention, which in the exemplary embodiment shown is designed to be planar. However, in the case of a continuous belt, the embossing tool can also be of arched design. The extruded panel 1 exhibits a texture 2 which imitates the shape of a wood structure. However, it is conceivable to produce different textures or different surface structures in this way by means of the method according to the invention and the etching method required for this purpose.

Fig. 2 shows an enlarged side view of a part of the front edge region of the compression plate 1 and the structures 3 lying thereon, which have a kind of mountain-like surface with valleys 4 and peaks 5. In this case, after a substrate is first applied by a standard method or a digital printing technique, the surface is produced by one or more etching processes, wherein the regions which are not subjected to the etching process are to be covered by a mask. By means of etching methods, for example, fine surface structures and deep structures can be produced, which are then possibly additionally rounded by machining. After the surface etching, the surface structure is finished by further chemical processing, polishing and, if necessary, activation of the polished surface, in order to clean it immediately before applying a chromium coating 6 with a certain gloss, and then to cover a part of the chromium-coated surface by means of a further mask, so that the uncovered areas can be subsequently chromium-coated again with a chromium coating 7, more precisely with a gloss different from that of the first chromium coating 6.

Instead of chromium plating, different surface finishes may also be carried out in some sections, wherein the surfaces are provided in some sections with different gloss levels by applying the method according to the invention. In general, by using an etching method to simulate a wood structure on the compression plate 1, it is possible, for example, to provide the surface 6 of the protrusions with a dull gloss, while the deeper regions that form the pores of the wood are provided with a higher gloss. This measure particularly highlights the wood cell structure, which fit is exactly coordinated with the wood decor printing and gives the appearance of a very natural product with the real wood properties of the product made with the press plate.

List of reference numerals

1 extrusion plate

2 texture

3 structure

4 grains

5 Peak

6 chromium coating

7 chromium coating

Claims (12)

1. Method for producing a structured surface of an embossing tool, wherein the surface is provided over its entire surface with a first metal coating (6), characterized in that at least one further metal coating (7) is provided on the first metal coating (6) in predetermined regions, wherein the gloss of the first metal coating (6) differs from the gloss of the further metal coating (7).

2. A method according to claim 1, characterized in that a protective layer is partly applied on the first metal coating (6).

3. A method according to claim 2, characterized in that the protective layer is applied by means of a digital printing technique.

4. Method according to one of the preceding claims 1 to 3, characterized in that said first metal coating (6) and said further metal coating (7) are produced by chrome plating.

5. A method according to any one of claims 2 to 3, wherein a chromic acid resistant material is used for the protective layer.

6. A method according to any one of claims 2 to 3, characterized in that the protective layer is baked into the first metal coating (6).

7. A method according to any of claims 1 to 3, wherein the structured surface is activated before applying said first metal coating (6) and said further metal coating (7).

8. A method for processing a surface of an embossing tool, comprising the steps of:

applying a first mask to the surface by means of a digital printing technique,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a second mask, which is precisely matched, again to the chemically machined surface by means of a digital printing technique,

-the surface provided with the second mask is again chemically processed,

-polishing the chemically machined surface,

-activating the polished surface,

-cleaning the activated surface,

-chrome-plating the clean surface,

applying a third, precisely fitting mask again to the chrome-plated surface, and

-again chrome-plating the chrome-plated surface provided with the mask,

wherein the structured surface has coatings produced by chrome plating with different gloss levels.

9. Method according to claim 8, characterized in that the first mask, the second mask and the third mask in the form of the protective layer are applied precisely in cooperation by means of a digital printing technique.

10. A method for processing a surface of an embossing tool, comprising the steps of:

applying a first mask to the surface by means of a digital printing technique for fine structuring,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a second mask, which is precisely matched, to the surface by means of a digital printing technique for the structuring of the pores,

-chemically processing the surface provided with the mask in order to obtain a surface structure,

applying a third mask, which is precisely matched, again to the chemically machined surface by means of a digital printing technique,

-the surface provided with the third mask is again chemically processed,

-polishing the chemically machined surface,

-activating the polished surface,

-cleaning the activated surface,

-chrome-plating the clean surface,

applying a fourth, precisely fitting mask again to the chrome-plated surface, and

-again chrome-plating the chrome-plated surface provided with the mask,

wherein the structured surface has coatings produced by chrome plating with different gloss levels.

11. Method according to claim 10, characterized in that the first mask, the second mask and the third mask and the fourth mask in the form of the protective layer are applied precisely in cooperation by means of a digital printing technique.

12. Embossing tool comprising at least one structured surface, characterized in that a metal coating (6) of a first material is provided over the entire surface of the structured surface and a metal coating (7) of a second material is provided in its upper part, wherein the gloss of the metal coatings (6, 7) differs.