EP2497650B1 - Method for processing a structured surface of an embossing tool - Google Patents

Description

The invention relates to a method for processing a structured surface of an embossing tool, in which the surface is provided with a first metallic coating over the entire surface and has at least one further metallic coating with a different degree of gloss in selected areas.

Generic embossing tools are required in the wood processing industry, especially in the production of wood-based panels. With the help of the embossing tools, the visible surface of the wood-based panels is embossed to the extent that a desired motif, preferably a true-to-life replica of a natural surface structure, can be produced. For this purpose, resin films, for example, are placed on wood-based panels, which are preferably made from pressboard, which are then pressed into the wood-based panel under pressure and temperature in hydraulic heating press systems. During the pressing process, the resin film becomes liquid under pressure and temperature and polycondensation occurs. The pressing time and temperature determine the degree of crosslinking of the resins and their surface quality. After the pressing time has elapsed, the resin has reached the desired degree of crosslinking and is in a solid phase. During this process, the resin surface takes on the desired natural surface due to the surface structure of the embossing tool. Duroplast resins are used as the coating material, for example melamine, phenol or melamine/urea resins. To design the surface, a structured metallic pressed sheet, preferably a steel sheet, is used as an embossing tool. In order to improve the wear resistance and release properties of the metal surface, the embossing tools are additionally provided with a coating. This process preferably uses embossing tools that were produced using digital printing technology, so that the decorative papers used are also produced true to scale and in line with the digital printing process can. A precise arrangement of the decorative paper and the embossed structure can thus be achieved, which means that significantly better results can be achieved than with the prior art.

Embossing tools in the form of pressed sheets or endless belts are manufactured according to the state of the art by appropriate processing of the surface, namely by producing a desired surface structure. In the past, for this purpose, the pretreated sheet was provided with a matrix, for example by means of a screen printing process, so that the sheet could then be etched. The sheet metal is etched only in the areas that are not covered by the matrix. Due to the size of the sheet metal used, very precise processing and in particular conformal processing is required if the surface structure is produced in several work steps. All areas that are later to form the raised surface structure are repeatedly covered by the mask, so that surface etching only takes place in the areas that can be directly attacked by the etching liquid. The etched areas then form the profile valleys of the desired structure, with the surfaces being cleaned and the mask removed after the respective etching process has ended. This procedure can be repeated several times, although the accuracy of screen printing processes usually causes considerable difficulties in applying additional masks precisely to the passage.

An alternative method is to first apply a photo layer, which is then subjected to exposure, in order to subject the press sheets or endless belts to a rinsing process after the final development of the photo layer, so that only the parts of the photo layer remain that form the mask for the later etching process . The reproducibility of the masks produced in this way is very difficult and problematic because the negative or positive used to expose the light-sensitive layer must always be arranged in exactly the same position relative to the existing structuring. Around For example, to recreate complicated three-dimensional structures on the surface of the pressed sheet or the endless belt, several exposure and etching processes are required. Due to the fact that these are extremely large-format pressed sheets, even the slightest deviations lead to significant displacements of the structures. The reproducibility of the application of the mask is therefore associated with considerable difficulties, particularly in the photographic process to achieve high imaging accuracy. The difficulties can increase further if a three-dimensional structure has to be achieved through several consecutive exposure and etching processes and there is a need to apply several masks one after the other and to carry out an etching process between each mask application. Due to the precise positioning required and the required number of corresponding masks, the production of the pressed sheets or endless belts is very complex and cost-intensive. The results that can be achieved also depend very much on the processes used, with complex handling having to be taken into account due to the size of the pressed plates or endless belts.

Alternatively, it is known from the prior art to produce a mask by applying wax using a print head instead of a screen printing process. The wax application is chemically resistant to the etching agents used, so that etching can be carried out in areas where the surface is not covered by the wax. For this purpose, a spray head is used, which sprays the wax onto the surface and can be moved along an x and y axis to recreate the required structure. However, the use of wax to apply a matrix has proven to be disadvantageous because the wax is difficult to remove from the surface and the cleaning work required is very costly. The resulting costs and the dissolution of a wax matrix have led to the need for further digitized printing techniques. For example, it is known to apply a UV varnish to the surface of the embossing tools to be processed, in particular press sheets, using a print head or to apply endless tapes. The particular advantage of digitized printing technology is that almost identical masks can be applied again and again to existing structures and thus several etching processes can be carried out one after the other with precise passage, for example in order to achieve a deep structure.

From the DE 102 24 128 A1 For example, a method for applying coatings to surfaces is known in which a nozzle head is used and the individual nozzles are controlled by control signals. Either the nozzle head can be moved over the surface or the surface to be treated is moved relative to the nozzle head. A UV varnish is preferably used here, which is hardened after application to the surface by irradiation with UV light.

From the DE 102 117 919 A1 a press for laminate panels is known, in which a press sheet is used to structure the surface of the panels. The pressed sheet metal is chrome-plated over the entire surface and more or less polished in order to obtain different surface roughness. Especially for fine subdivisions and different levels of gloss, pressed sheet metal production in the manner of an offset printing plate with a galvanic coating is proposed, whereby the coating is exposed and removed in the areas that are not required. The decorative image can be projected directly onto the press sheet. The areas that are not required can be removed by etching, as is the case in the production of printing plates.

Regardless of the form in which the surfaces of the pressed sheets or endless belts are structured, they are subjected to several cleaning processes and can also be coated with a nickel layer, which is then refined with further metallic coatings. The metallic coatings give the surface a desired level of gloss and the necessary surface hardness. The degree of gloss is responsible for the fact that after the materials to be processed have been pressed using the press sheets or Endless belts give the pressed structure different shades and color reflections.

To improve the appearance, it was also proposed to provide partial areas of the surface with different metallic coatings in order to vary the level of gloss. This measure allows desired shading effects to be achieved.

The present invention is based on the object of demonstrating a further improved embossing tool and a method for producing the same in order to enable a variety of shading options with corresponding transfer to a wood material.

According to the invention, in order to solve the problem, it is provided that different levels of gloss are produced on the first coating in several selected areas, the levels of gloss being produced by a combination of metallic coatings, mechanical or chemical post-treatments. Further advantageous process steps can be found in the subclaims.

In order to produce a variety of gloss levels on an embossing tool and to keep costs as low as possible, it is proposed, in addition to the use of metallic coatings of different gloss levels, to carry out a partial post-treatment of individual areas of the surface using mechanical or chemical processes. It is therefore a combination of individual treatment processes in order to provide certain areas of a structured surface of the embossing tool, which are represented, for example, by the wood grain of the surface, with a certain level of gloss and other areas with different levels of gloss, with several different levels of gloss on one Surface can be present. On the one hand, these gloss levels are achieved by a metallic coating and on the other hand by mechanical ones or chemical processing, whereby a digitized mask is applied between the individual treatment steps in order to process or coat only the areas that should receive a different level of gloss. This means that after the structuring measures have been completed, it is possible to first apply hard chrome plating with a certain level of gloss over the entire surface. Then, after applying a matrix, part of this surface can be achieved with a different level of gloss by mechanical, chemical or, if necessary, a further application of a metallic coating. Subsequently, a mask can be applied at least once, if necessary several times, in order to provide further partial areas of the surface structure with further gloss levels that deviate from the first gloss levels. In individual cases, a metallic coating can also be applied, but a mechanical or chemical treatment process can also be used. The combination of the different treatment processes results in the particular advantage that the finest differences in gloss levels can be produced and, moreover, cost-effective production is possible even with multiple gloss levels.

In order to achieve the different levels of gloss, a digital printing technology is used to apply the protective layer (mask), which ensures that the protective layer is applied precisely even after multiple repetitions. The protective layer can be applied in subsequent work steps in such a way that it is applied at least partially overlapping or not overlapping the already finished areas. Depending on the existing structuring of the surface of the pressing tool, it may be necessary for the partial areas with different degrees of gloss to be arranged next to one another, but there is also the possibility that an overlap is desired for aesthetic reasons.

By applying a second partial coating or mechanical or chemical treatment to an existing first coating, different levels of gloss can be achieved, the level of gloss being determined by an embossing tool, in particular a pressed sheet or an endless belt, at least partially differs from one another in partial areas. This measure makes it possible to provide raised structures or, if necessary, deeper structures with a different degree of gloss in order to particularly emphasize the structure. This measure sustainably improves the visual impression and leads to a surface which, thanks to the passage-accurate print templates and passage-accurate matrix, can be designed to conform to the coverage and thus not only a different depth structure can be achieved, but also a different level of gloss in order to highlight certain structural areas. This difference in gloss level can be optionally provided, for example the raised areas can have a higher level of gloss than the lower areas or vice versa. By applying different levels of gloss multiple times, whether through additional coatings or through mechanical or chemical processes, the structured areas of the surface of the pressed sheet or endless belt can be highlighted even more clearly than was previously possible. This makes a significant improvement in detailed structuring possible. For example, a painted real wood surface can be modeled, with the raised surfaces having a certain degree of mattness and the deeper wood pores showing a shiny area due to the light reflection. The wood pore structures required here are produced using the precise matrix and well-known etching technologies. By using digital printing technology, it is possible to arrange and cover the respective structure multiple times, so that a variety of gloss levels can be achieved on an existing structured profile, which leaves nothing to be desired. For example, a variation in the degree of gloss can be provided on an individual wood pore. It is also possible to provide individual wood pores with different degrees of gloss, which are either arranged adjacently or are at greater distances from one another. This makes it possible to provide several neighboring wood pores with a different level of gloss in order to improve the overall appearance.

To produce the surface structure, a deep etching is usually carried out first and then a circular etching to highlight the shape of the pore structure. Mechanical polishing can then be carried out before the surface is cleaned and degreased. For better adhesion of the metallic layers, in particular the chrome layer, the structured surface can be additionally activated before the coatings are applied or other coatings that ensure better adhesion, for example a nickel layer, can be applied.

A first applied metallic coating usually consists of chrome plating, which can be high-gloss chrome plating or matt-gloss chrome plating. In any case, it is conceivable that other metal coatings are used instead of chrome plating. However, if a first coating was applied using chrome plating, it is imperative that the protective layer (mask) to be applied consists of a chromic acid-resistant material so that the protective layer is not affected during the chrome plating or further chrome plating steps.

To improve the adhesion of the protective layer to the existing chrome plating, a further intermediate step can be to bake the protective layer, with the protective layer being completely removed after the second treatment. To achieve the respective levels of gloss, in addition to a metallic coating, a process step involving matt etching, sandblasting or mechanical polishing can be provided.

The aforementioned methods are characterized by the fact that there is a structure-conform covering and there is no deviation from the desired structure over the entire surface of the pressed sheets or endless belts. The number of masks is determined by the number of processing steps required, with the focus being on structuring the surface in order to then be able to set the desired gloss level. According to the invention, at least a first degree of gloss is provided by metallic coating is specified, while further partial gloss levels are given a different gloss level either by metallic coating or by mechanical or chemical treatment processes. The frequency of masks and processing operations to be applied essentially depends on the surface structuring, for example whether it is a true-to-life replica of a wood pore or a rock surface or whether graphic artificial structures are to be reproduced in detail.

The application of the method according to the invention leads to an embossing tool with a structured surface on which a metallic coating made of a first material and partially a metallic coating made of a second material is arranged in selected areas, or further areas by mechanical polishing, matt etching, sandblasting or chemical treatment have a gloss level and the gloss levels of the areas differ from one another, with the peaks of the heights of the structured surface having gloss levels that differ from the valleys. For this purpose, the material is often coated with chrome, as this is particularly hard and is best suited for the pressing processes to be carried out. However, it is easily possible to press other materials that do not have a particularly high degree of hardness and whose surface is elastic and soft, so that other metallic coatings can also be used to achieve different levels of gloss.

The particular advantage of the method according to the invention and the embossing tool presented here is to produce identical structures, such as those known from nature, with different degrees of gloss, which have a particularly attractive look and feel, so that the impression is created that they are, for example, grown natural wood. Due to the different degrees of gloss, certain areas, for example raised areas or deeper areas, can also be provided with several different degrees of gloss, so that the structure stands out very clearly and creates an optical effect that leads to a material surface that is hardly similar to that of grown wood, for example is to be distinguished. Alternatively, it is possible to recreate other, more natural surfaces.

The invention is explained again below with reference to the figures.

Fig. 1

in einer perspektivischen Ansicht ein erfindungsgemäßes Pressblech und

Fig. 2

in einer vergrößerten Seitenansicht die vorhandene Struktur auf der Pressblechoberfläche mit unterschiedlichen Glanzgraden.

It shows

Fig. 1

in a perspective view a pressed sheet according to the invention and

Fig. 2

an enlarged side view of the existing structure on the pressed sheet metal surface with different levels of gloss.

Figure 1 shows a perspective view of a press plate 1 according to the invention, which is flat in the exemplary embodiment shown. In the case of an endless belt, however, this embossing tool can also be curved. The pressed sheet 1 shows a grain 2 which is modeled on the shape of a wooden structure. However, it is conceivable that other grains or other surface properties can be produced in this way using the method according to the invention and the etching process required for this.

Figure 2 shows an enlarged side view of part of the front edge area of the pressed sheet 1 and the structure 3 located thereon, which has a mountain-like surface with valleys 4 and heights 5. The surface is produced by one or more etching processes, after which a matrix has previously been applied using a standard process or a digitized printing technique, with the areas that should not be subjected to the etching processes being covered by the mask. With the help of etching processes, for example, fine surface structures and deep structures can be produced, which can then be additionally rounded off using mechanical processing or etching processes. After the surface has been etched, the surface structure is completed by further chemical processing, polishing and, if necessary, activation of the polished surface, so that cleaning is then carried out before a first metallic coating 6 with a certain level of gloss is applied.

The metallic coating 6 has a certain level of gloss, which depends on the customer's wishes. A mask is then applied again to this first metallic coating 6, which covers the areas that should not be subjected to any further treatment. In contrast, the exposed areas can be provided with a different level of gloss by further processing methods, for example matt etching, sandblasting or mechanical polishing or repeated application of a metallic coating. The method according to the invention provides that a mask is applied for certain partial areas and the exposed areas are subjected to a further treatment process. After removing the applied mask, this process can be repeated several times, so that the structure 3 of the pressed sheet 1 has different degrees of gloss in selected areas.

In the exemplary embodiment shown, different degrees of gloss are created on the first metallic coating 6 by applying different masks and subsequent treatment processes. In the area of the valleys 4, for example, no treatment has been carried out, so that the areas 7 marked in white have the gloss level of the first metallic coating 6, while the peaks of the heights 5 have different gloss levels. These different levels of gloss are characterized by completely colored areas 8 and hatched areas 9 and 10. In the transition areas of the valleys 4 and heights 5, a different level of gloss was created by applying a corresponding mask in a subsequent process step. These areas 11 are shown in dotted lines.

In deviation from the exemplary embodiment, however, there is the freedom to provide all heights 5 with a uniform level of gloss or, if necessary, to equip the transition areas with different levels of gloss. In principle, the present invention enables the application of a digitized mask and the process steps provided for this purpose to generate a level of gloss Possibility to vary the arrangement of the individual gloss levels as desired. If a wood structure is reproduced on the pressed sheet 1 by the etching process used, it is possible, for example, to provide the raised surfaces 7 with a matt level of gloss and to provide the deeper areas that form the wood pores with a higher level of gloss. Due to the possibility of applying several masks and achieving a certain level of gloss in a subsequent process step, raised areas lying next to one another can, for example, be provided with different levels of gloss. It is also possible to give the flanks of individual raised areas a different level of gloss in order to clearly express the appearance of the wood pores. This measure particularly highlights the wood pore structures, which match the wood decor print precisely, and gives the products made with the pressed sheets the appearance of a real wood character, which is very close to the natural product.

Reference symbol list

1

Pressed sheet metal

2

Grain

3

structure

4

valley

5

Height

6

Coating

7

Area

8th

Area

9

Area

10

Area

11

Area

Claims (11)

1. A method for processing a structured surface of an embossing tool, in which the surface is provided with a first metallic coating (6) over the entire area, and has at least one further metallic coating having a different degree of gloss in selected areas (7, 8, 9, 10, 11),
   characterized in that,
   on the first coating (6) different degrees of gloss are produced in multiple selected areas (7, 8, 9, 10, 11), wherein a protective layer (mask) is partially applied on the first coating (6) by means of a digital printing technique to define the selected areas (7, 8, 9, 10, 11) and the degrees of gloss are produced by a combination of metallic coatings, mechanical, or chemical subsequent treatments.
2. The method according to claim 1,
   characterized in that
   in the subsequent work steps, the protective layer is applied to the areas (7, 8, 9, 10, 11) that have already been completed so as to at least partially overlap or to not overlap.
3. The method according to claim 2,
   characterized in that
   a material resistant to chromic acid is used for the protective layer.
4. The method according to one of the preceding claims,
   characterized in that
   the protective layer is burned into the first coating (6).
5. The method according to one of claims 2 to 4,
   characterized in that
   the metallic coatings (6) are produced by chromium plating.
6. The method according to one of claims 2 to 5,
   characterized in that
   further degrees of gloss are obtained by matte etching, sandblasting, or mechanical polishing.
7. The method according to one of the claims 2 to 6,
   characterized in that
   the degrees of gloss are partly arranged to be at least partially adjacent, or that the degrees of gloss run at least partially distanced from one another.
8. The method according to one of the preceding claims,
   characterized in that
   the structured surface is activated before the application of the coatings (6).
9. An embossing tool having at least one structured surface,
   characterized in that

   a metallic coating (6) of a first material is arranged over the entire area of the structured surface,
   and

   a metallic coating of a second material is partially arranged thereon in selected areas (7, 8, 9, 10, 11),
   or

   further areas (7, 8, 9, 10, 11) receive a degree of gloss by mechanical polishing, matte etching, sandblasting, or chemical treatments, and the degrees of gloss of the areas (7, 8, 9, 10, 11) differ from one another, wherein the peaks of the heights (5) of the structured surface have degrees of gloss which differ from the valleys (4).
10. The embossing tool according to claim 9,
    characterized in that
    the peaks of the heights (5) have different degrees of gloss or that all heights (5) are provided with a uniform degree of gloss.
11. The embossing tool according to claim 9 or 10,
    characterized in that
    the regions of the valleys (4) have the degree of gloss of the metallic coating (6) of the first material.

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