WO2021013679A1

WO2021013679A1 - Method for producing a structure on a surface

Info

Publication number: WO2021013679A1
Application number: PCT/EP2020/070113
Authority: WO
Inventors: Stefan Hörnicke
Original assignee: Achilles Veredelt Nord Gmbh
Priority date: 2019-07-19
Filing date: 2020-07-16
Publication date: 2021-01-28
Also published as: EP3999358B1; EP3999358A1

Abstract

The present invention relates to a method for producing a structured surface on a flat workpiece, wherein existing tools can be used in conventional production plants, and which is flexible enough that the tool (the roller or the press plate) does not have to be changed in the event of a structure change. The method according to the invention additionally relates to the possibility of producing nanostructures and microstructures on the workpiece surface. In the method, a surface of the flat workpiece is varnished, a transfer film having a fine structure is applied to the varnished surface before the varnish cures, such that the fine structure contacts the varnished surface of the flat workpiece, the varnishing of the varnished surface cures or is allowed to cure in contact with the transfer film and the transfer film is removed from the cured, varnished surface, such that a copied structure is left behind on the target surface.

Description

METHOD FOR PRODUCING A STRUCTURE ON A SURFACE

The present invention relates to a method for the produc- tion of a structure on a surface of a flat, in particular rigid workpiece, in particular a furniture part, a cladding part, a structural part, a floor element, a component or the like.

BACKGROUND OF THE INVENTION

Structured surfaces are widely used, for example, in the furniture industry and in the construction industry, for example for finishing kitchen fronts, furniture panels and building materials. In the industrial production of flat workpieces, e.g. in the coating and finishing of chipboard, MDF boards for furniture, floors, interior and exterior cladding, and in the cement fiber board industry, surface finishing, especially with a replica of a structure, is common nowadays. These replicas of structures can be simulated wood pores, simulated stone surfaces or fantasy structures. There are various processes for producing these surface structures that are tailored to the coating process for the surface. Different embossing matrices are used, which are pressed into the surface by pressing melamine, for example, or a structure that is painted onto the surface. For example, a paper that has been printed with a wood look is impregnated with a melamine resin, dried and then pressed onto a chipboard in a heating press with an embossing plate. On the surface, the embossing plate results in structures with a depth of about 20 gm to 150 gm.

In addition to this so-called melamine pressing process, there are other processes for coating wood-based panels. In another known method, for example, a wood-based panel is painted, printed and then provided with a transparen th top coat. In order to obtain a corresponding surface structure here too, there is the option of applying a structure with a structured topcoat roller. Such a method is described, for example, in DE 10 2007 019 871 A1.

All of these methods of structuring a surface have in common that they are relatively inflexible with regard to adaptation to the 3D topography and are limited to the processing of flat surfaces. In addition, if a structure is changed, the respective tool (the roller or the press plate) must be changed. But especially with workpieces that are rigid, i.e. workpieces such as kitchen fronts, furniture panels and building materials, but also floor panels, interior and exterior cladding, aircraft wings, boat hulls, industrial panels and the like, a high degree of flexibility is required due to the required design flexibility. Such workpieces are characterized in particular by the fact that they have a high degree of rigidity and dimensional stability, so that they are dimensionally stable in actual language usage or when used generically.

In order to circumvent these disadvantages, methods for the digital application of a structure have been proposed. One such is the ben described for example in DE 10 2009 044 802 A1. However, this digital method also has disadvantages: it uses a large amount of radiation-curing ink, which is very expensive.

EP 3 109 056 B1 finally describes a method for producing a structure on a surface, in which, in a first step, the surface of a workpiece to be coated is coated with a liquid base layer and in a second step a structure is created in this still liquid base layer with the help of sprayed-on liquid droplets, which is later fixed. This method is also comparatively complex and requires elaborately manufactured tools.

The disadvantage of all these processes is that no nanostructures can be produced on the flat workpieces. If nanostructures are applied with an embossing roller, there is a risk of the structure ripping off or flowing. The structures applied by means of the inkjet process have elevations of 5 gm to 300 gm. Finer structures cannot be achieved due to a lack of resolution.

An approach known from the prior art for producing actually finer structures is known from CA 2 709 564 A1, which, however, relates to a method for applying holograms to flexible substrates, ie lottery tickets. Here, the flexible substrate is provided with a layer of lacquer. A film with a microstructure is applied to the lacquer layer. After a curing process using UV light, in which the paint layer hardens, the film is removed. This document describes the application of fine structures to flexible substrates in a printing machine with inline printing and coating units and an integrated perforating station, which is not suitable for finishing workpieces such as furniture, cladding parts and the like. In addition, this document is limited to transferring the fine structure to the paper and therefore does not offer a solution as to how the fine structure has to be molded into the film when coating flat pieces of furniture in order to achieve the best possible result for work pieces such as pieces of furniture. In contrast, WO 2019/0185832 A1 describes an embossing die referred to as a master film web, by means of which fine structures are embossed into a further film web. The master film web is provided on a transfer surface with a master lacquer layer in which negative forms of the structures to be transferred are formed. The master film web and the film web to which the structures are to be transferred run through a pressure roller-pressure roller arrangement and are pressed against one another, whereby the structure of the master film web is transferred to the film web. Before the embossing process, the film web is provided with a layer of lacquer on its surface. The structure is later embossed into the applied lacquer layer by means of the master film web and cured by means of UV light. To produce the master film web, a film web is also provided with a layer of lacquer. The film web then runs through an embossing calender in which the structure is embossed into the film web. The lacquer coating is cured using UV light. A major disadvantage of this method is in particular that the foil web is first coated with a curable varnish, which is then embossed and cured. With this approach, there is basically the risk of the structure in the lacquer layer ripping off or flowing away, which considerably impairs the precision of the fine structure. Nor can it be guaranteed that the lacquer layer on the film web is always constant for the embossing process. It has been shown that there is also considerable potential for cost savings compared to this multi-level embossing approach.

EP 2 025 413 A2 relates to a method for producing a surface on a flat workpiece, in which the workpiece is first powder-coated. A structured film-like transfer medium is then pressed against the uncured powder coating and the powder coating is cured. To produce the structured Transmission medium, it is proposed that the film-like transmission medium first be provided with a coating. The desired structure is then mechanically embossed into the lacquer layer and the lacquer layer is cured by irradiation. Here, too, there is a risk in the use of curable lacquer for foil stamping, which can lead to the fine structure being plucked out or flowing. In addition, with an uncured powder coating against which the transmission medium is pressed, there is always the risk that particle accumulations, voids or sink marks occur, which have a negative impact on the overall result.

In view of the lack of satisfactory solutions for producing a structure on surfaces of, in particular, rigid workpieces, such as furniture surfaces, kitchen and floor panels or structural elements and the like, the object of the present invention is to provide a method for producing a structure on a surface of a workpiece , in which existing tools can be used in conventional production systems and which is sufficiently flexible so that when a structure is changed, the respective tool (the roller or the press plate) does not have to be changed. In addition, the method according to the invention should also offer the possibility of producing nanostructures (e.g. holographic surfaces) on the workpiece surface with high accuracy and cost-effectiveness.

This object is achieved by the features of claim 1. Preferred embodiments are given in the subclaims. SUMMARY OF THE INVENTION

The method according to the invention for producing a structure on a surface of a flat workpiece comprises the following steps:

(a) A transfer film with a fine structure is produced by embossing a fine structure with a profile depth of 100 nm to 150 gm into the transfer film using a structured cylinder or a structured sleeve, the surface of the transfer film being free of a curable lacquer coating and the fine structure is embossed into the transfer film thermally or by means of ultrasound,

(b) a surface of the flat workpiece is coated with a hardenable coating,

(c) A structured transfer film is applied to the surface coated in (b) before the coating hardens, so that the structure is in contact with the coated surface of the flat workpiece,

(d) the coating of the coated surface is cured or allowed to cure in contact with the transfer film,

(e) the transfer film is removed from the cured, coated surface, so that a copied structure is left on the target surface.

With the method according to the invention, a structure is generated on the workpiece surface by means of a transfer film, on the surface of which there is an original fine structure. In connection with the present invention, a structured surface is to be understood as a three-dimensional structure. In contrast to the state of the art, as it is For example, as described in EP 2 025 413 A2, neither a powder-coated substrate is used, nor is the fine structure introduced into the absorbent film using a lacquer coating. The application of lacquers to the transfer film can be dispensed with in the context of the process according to the invention, which brings considerable advantages from an economic point of view. When using additives such as paints, there is always the risk of contamination and unwanted accumulations of material that have a negative impact on the overall result. According to the invention, the fine structure is introduced into the transfer film exclusively by thermal embossing or by means of ultrasonic embossing of the transfer film, without additional substances for structuring being applied to the transfer film prior to the embossing process.

In order to obtain a consistently high-quality structured surface on the workpiece, a further embodiment of the invention provides that the structured cylinder or the structured sleeve for embossing the transfer film is seamless. A seamless or seamlessly structured sleeve is shaped, for example, in the manner of a sleeve and has a seamless, in particular continuously smooth surface structure into which the embossed structure is molded. The particular advantage is that, unlike shim systems, ie embossing systems in which plate-shaped shims are welded to form a cylindrical embossing mold, no images of weld seams are formed in the substrate running on the embossing mold. In particular, the embossed structure can also be made seamless, ie the embossed structure also has no seams or the like, but is molded directly into the structured sleeve or the structured cylinder. By using a seamless textured cylinder or a seamless textured one Sleeves can effectively create a seamless structure on the surface of a workpiece.

The invention is particularly aimed at providing workpieces of a rigid nature with a structured surface. According to the invention, the workpiece is therefore preferably a rigid workpiece or a rigid substrate. According to the invention, a rigid workpiece is understood to mean in particular one which has a high degree of rigidity and dimensional stability, so that it is not bent or deformed in actual parlance or when used generically, ie is dimensionally stable. This includes in particular kitchen fronts, furniture panels and building materials, but also floor panels, indoor and outdoor cladding, industrial panels and the like. In principle, however, flexible workpieces, i.e. flexible substrates, can also be provided with a structured surface within the scope of the invention.

According to a further embodiment, the workpiece is a furniture part, a cladding part, a structural part, a floor element, a component or the like.

The structured transfer film is made of a material that is suitable for this purpose, for example of thermoplastic plastic. The structured transfer sheet used in the method can be made as part of the process of manufacturing the fine structure of the target surface, or a transfer sheet that has been previously made or procured elsewhere that has the desired original fine structure can be used in the method.

The surface can basically be any surface of a workpiece, such as a wooden surface, a plastic surface, a metal surface or a layered paper surface on a particularly otherwise rigid workpiece. The target surface can be flat or curved (sheet or roll goods).

The coating can be a lacquer, a paint or another curable coating. Acrylic lacquers are preferred. Lacquers that are UV-curable are very particularly preferred.

The selected transfer film is placed on the target surface in such a way that its original fine structure touches the target surface while the coating has not yet hardened. After the coating has cured, the transfer film is removed from the surface of the workpiece. The mate rial of the transfer film, which adheres to the target surface, creates a copied fine structure that is a mirror image of the original fine structure of the transfer film.

The height of the copied fine structure generated on the target surface is preferably slightly smaller in the direction of the normal to the target surface than the height of the original fine structure. With the method according to the invention, surface structures with a profile depth of, for example, 100 nm to 500 nm, preferably 100 nm to 200 nm, more preferably 120 nm to 150 nm can be produced without the structures ripping out or flowing. With the method according to the invention, however, haptic structures can also be produced which preferably have a profile depth of 10 μm to 150 μm without the need to use special profiled rollers. A wide variety of functional surface structures such as lotus blossom effects, moth eye effects or shark skin effects, light deflection effects, retroreflection, backlight effects with a profile depth of 100 nm to 50 μm, preferably 350 nm to 20 μm, can be generated on the flat workpieces with the method according to the invention. According to a further embodiment of the invention, the structured transfer films can be transparent or opaque, in particular if the lacquer underneath can be cured by irradiation, such as by UV irradiation.

A further embodiment of the invention provides that in step (b) the surface of the flat workpiece is provided with a coating and that in step (d) the coating is cured in contact with the transfer film by means of radiation, preferably UV radiation. The irradiation preferably takes place through the transfer film from the side of the transfer film facing away from the workpiece.

According to a further embodiment, the material of the transfer film can be acetyl cellulose or paper.

Another embodiment of the invention provides that the material of the transfer film is cellulose diacetate or cellulose triacetate.

Another embodiment of the invention provides that a fine structure is generated in a surface of a flat workpiece which has a height in the direction of the normal to the target surface of 100 nm to 500 nm, preferably 100 nm to 200 nm, more preferably 120 nm to 150 nm nm.

Another embodiment of the invention provides that a fine structure is produced in the surface of a flat workpiece, which creates a holographic optical effect.

Another embodiment of the invention provides that a fine structure is produced in the surface of a flat workpiece, which creates a lotus blossom effect. Another embodiment of the invention provides that a fine structure is produced in the surface of a flat workpiece, which creates a moth-eye effect.

According to a further embodiment of the invention, the transfer film with a fine structure is used on both sides, in that it is applied in a second pass of the method to a further flat workpiece with the opposite side of the previous pass, whereby the front and back of the transfer film can comprise different fine structures . In this embodiment, care must be taken that the depth of the fine structures on both sides of the transfer film and the film thickness of the transfer film are selected such that the fine structures are spaced apart in a direction perpendicular to the film surface, ie in the film thickness direction. In order to emboss the transfer film on both sides, for example in the roll-to-roll process, first one side of the transfer film can be embossed and then the transfer film can be rolled up onto a roll. For the second embossing process on the other side of the transfer film, the transfer film can be unrolled again from the roll and brought back into contact with the surface of the embossing cylinder or embossing sleeve. With this re-embossing, however, an additional deflection roller can be provided over which the transfer film runs. This deflection roller is arranged in such a way that the transfer film is turned before it comes into contact again with the surface of the embossing cylinder or the embossing sleeve in order to form the second embossing. In order to use the transfer foil on both sides, the transfer foil is removed from the workpiece after the first pass, turned and placed with the other side on a prepared workpiece in order to shape the second fine structure into the workpiece. DETAILED DESCRIPTION OF THE INVENTION

The fine structure with a profile depth of 100 nm to 150 mpi is embossed into the transfer film using a structured cylinder or a structured sleeve. For this purpose, it is explicitly not provided that the transfer film is first coated with a curable lacquer, which is then embossed and cured, because with such a procedure there would be the risk of the structure ripping off or flowing. However, the transfer film can have more layers. The cylinders or sleeves for embossing the transfer film can be made of nickel, copper or chrome, for example. Exemplary methods for imparting the structured surface on the cylinders or sleeves include electron beam lithography, laser technology, such as the use of pico or nano lasers and engraving, chemical or plasma etching. According to the invention, the structure is transferred to the film by thermal embossing or ultrasonic embossing. Thermal embossing can be done with a roll-to-roll printing machine or by static embossing. According to the invention, thermal structure embossing or hot embossing is understood to mean a method in which a prefabricated structure on a stamp, i.e. in the context of the invention on the structured cylinder or the structured sleeve, is transferred to the transfer film to be embossed under the influence of heat. The structure embossing of the substrate is preferably carried out in the context of the invention in the roll-to-roll process at embossing surface temperatures of 50 ° to 130 ° C.

The structured transfer films can be transparent or opaque, in particular if the lacquer underneath can be cured by exposure to radiation, such as by UV radiation, as will be explained later. The material of the transfer film can be selected, for example, from polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyester, polycarbonate, cellophane. Other synthetic materials, such as bio-based plastics, for example polycactide, cellulose acetates and starch blends, can also be used as the material of the transfer film. Preferred plastics are cellulose acetates, such as cellulose diacetate or cellulose triacetate. Composite materials of different foils or foil / paper are also suitable for the transfer foils. The connection of two materials to produce a composite material can be done, for example, by gluing using dispersion, LF or LH adhesives, co-extrusion or ultrasound.

The film thickness of the transfer film is preferably 10 μm to 250 μm. Most preferred is a film thickness between 50 μm and 90 μm so that the transfer film has an advantageous stiffness and yet sufficient balance between flexibility and stiffness to be used in the inventive method . To improve the rigidity of thinner films, the structured transfer film can also have a thermoreactive adhesive layer, for example made of EVA / PE. Foil thicknesses between 60 μm and 80 μm are preferred for structuring furniture surfaces. Foil widths can be from 10 mm to 2500 mm. Foil widths of 800 mm to 2100 mm are provided for structuring furniture surfaces.

The structured transfer foils can be applied to the upper surface of a flat workpiece, for example with commercially available calander coating inert machines, as is practiced, for example, in the furniture industry for the production of high-gloss surfaces. Such calander coating inert machines are for example from the company Hymmen GmbH (Hamm, Germany) and Cefla sc (Imola, Italy en) available. In this industrial coating process for the panel industry, UV lacquers are applied in a rolling process. Then a film or tape smooths the still liquid paint surface. The curing takes place through the film by means of UV radiation with direct surface contact. Then the film is removed from the upper surface. It is not necessary to adapt the calendar coating inert machines.

With the help of the structured transfer film, decorative or functional structures can be transferred to the surfaces of a flat workpiece. The flat workpiece as a format or rolled goods can be chipboard, MDF boards (for example for furniture), HDF boards, raw chipboard, veneer, floors, interior and exterior cladding and / or cement fiber boards, but also aircraft, automobile and railroad parts. For example, the invention provides for functional structures to be transferred to aircraft wings and tail units with the aid of the method according to the invention, so that, for example, their air flow (shark skin) is favorably influenced, a self-cleaning effect (lotus blossoms) or an anti-reflective coating (moth's eye effect) is achieved.

Another application of the structured surfaces according to the invention is the provision with test marks such as holograms or hidden security features based on micro or nano scripts or images, which can facilitate the identification of counterfeit products. Of course, the method according to the invention can also be used to produce decorative optical or haptic effects on the surfaces of the workpieces.

Transfer effects can be applied over the whole area or partially. The coating applied to the surface of the flat workpiece is preferably a thermally and / or UV-curing lacquer or a thermally and / or UV-curing paint. If a UV-curing lacquer is used, the film is preferably transparent, so that curing with UV light is facilitated. Conventional varnishes or paints based on polyacrylate or those based on alkyd resins are preferred. The paints or paints can be those with or without electrical conductivity. The conductivity can be produced, for example, by mixing with polyanilline in the paint composition. Polyaniline is a polymer with excellent electrical conductivity that has an anti-corrosive effect due to its passivation. If biodegradability is desired, varnishes based on vegetable oils can also be used. In principle, there are no limits to the use of certain paints in the process according to the invention.

Claims

1. A method for producing a structure on a surface of a flat workpiece with the following steps:

(b) a surface of the flat workpiece is coated with a hardenable coating,

2. The method according to any one of the preceding claims, characterized in that the surface of the flat work piece is a rigid substrate which is dimensionally stable when used as intended.

3. The method according to claim 1, characterized in that the transfer film is transparent or opaque.

4. The method according to any one of the preceding claims, characterized in that in step (b) the surface of the flat workpiece is provided with a coating and that in step (d) the coating in contact with the transfer film by means of irradiation, preferably UV irradiation, is cured.

5. The method according to any one of the preceding claims, characterized in that the structured cylinder or the structured sleeve are seamless.

6. The method according to any one of the preceding claims, characterized in that the workpiece is a furniture part, a clothing part Ver, a structural part, a floor element, a component or the like.

7. The method according to any one of the preceding claims, characterized in that the material of the transfer film is acetyl cellulose or paper.

8. The method according to claim 7, characterized in that the material of the transfer film is cellulose diacetate or cellulose triacetate.

9. The method according to any one of the preceding claims, characterized in that a fine structure is generated in a surface of a flat workpiece which has a height in the direction of the normal to the target surface of 100 nm to 500 nm, preferably 100 nm to 200 nm, more preferably 120 nm to 150 nm.

10. The method according to any one of the preceding claims, characterized in that a fine structure in the surface a flat workpiece is generated, which creates a decorative optical effect.

11. The method according to any one of the preceding claims, characterized in that a fine structure is generated in the surface of a flat workpiece, which causes a holographic optical effect.

12. The method according to any one of the preceding claims, characterized in that a fine structure is produced in the surface of a flat workpiece, which causes a lotus blossom effect.

13. The method according to any one of the preceding claims, characterized in that a fine structure is generated in the surface of a flat workpiece, which causes a moth-eye effect.

14. The method according to any one of the preceding claims, characterized in that transfer film with a fine structure is used on both sides by being applied in a second pass of the method on a further flat workpiece with the opposite side of the previous pass, with the front and back of the Transfer film can include different fine structures.