DE102011001905A1 - Method and device for surface coating of three-dimensionally deformed components - Google Patents

Abstract

The invention relates to a method for surface coating a three-dimensionally deformed component (11) which is positioned in the area of its surface (13) to be coated at a distance from a wall (23) of a molded part (14) and is located between the surface (13) to be coated and the wall (23) forms a gap (16), wherein liquid surface coating material is filled into the gap (16) and cured under irradiation by means of a radiation source (20), the surface coating material comprising a radiation-curable acrylate or methacrylate prepolymers or oligomers Is resin and the molded part (14) is light-scattering, light-directing or beam-expanding for the radiation.

Description

The present invention relates to a method and a device for coating the surfaces of three-dimensionally deformed components or substrates, in which at least one visible side is provided with a preferably transparent surface layer.

A three-dimensionally deformed component is understood to mean any component which has a shape deviating from a plane to be coated in the third dimension, for example curved.

The present invention relates in particular to the coating of three-dimensionally deformed components, substrates or interior components for the automotive industry, household articles, medical technology or electrical appliances. Under component are understood below all these components, substrates or interior components.

The components to be coated may consist, for example, of wood, wood materials, plastic, fiber composite materials (MDF, HDFR, WPC) and, if desired, be coated in particular with wood or a film.

In addition to the application of the liquid coating material by spraying or painting, the coating of the component can also be carried out by IMC (in-mold coating). In this case, the component is inserted into a cavity of a mold part, wherein between the surface to be coated of the component and the wall of the mold part, a gap is formed, in which the liquid surface coating material is filled. By filling the mold a large part of the air or possibly other gases or gas mixtures is displaced from the gap. The coating material in the cavity is substantially closed in shape to corresponding atmospheric contact.

Subsequently, the surface coating material is cured within the gap space, for which - as in the DE 43 20 893 C1 and the DE 199 61 992 S1 described - UV radiation can be used. For this purpose, the molding is preferably formed at least in the region of the surface to be coated UV radiation permeable. The height of the gap, which corresponds to the thickness of the paint layer produced, is generally from 300 .mu.m to 1000 .mu.m.

The EP 1 239 975 B1 teaches to introduce the UV radiation via optical fibers in the gap space, wherein it is preferred to irradiate the filled into the gap space surface coating material by a radiation-permeable molded part. The molded parts which are irradiated are made of plastic, glass, in particular quartz glass, and of low absorption for UV radiation. In order to avoid radiation losses, a UV radiation source with high intensity is used.

With in-mold coating, the entire layer is applied in a single step.

Radiation curable coatings comprise a resin component and an initiator which dissociates with the energy radiated in. The irradiation generates radicals from the initiator which trigger a chain reaction, which is subsequently maintained even when irradiation no longer takes place. The radiation-activated surface coating material can then cure within a few minutes, for example less than three minutes, at least to the extent that the component provided with the surface layer can be detached from the molding and can be handled.

In general, UV radiation is used for irradiation. However, for example, a coating with electron radiation or with short-wave visible radiation is possible if an initiator sensitive to this irradiation is selected.

The known IMC methods are used in particular for coating components with polyester resins, wherein polyester resins can also be used to achieve crack-free and continuously hardened thick layers on three-dimensionally deformed components, even with layer thicknesses of 300 .mu.m to 1,000 .mu.m.

UV-curable surface coating coatings in IMC systems which comprise acrylate or methacrylate prepolymers or oligomers as resin components are known, for example, from US Pat EP 1 888 701 B1 the applicant known. With these paints are transparent coatings that after curing or after appropriate stress (heat, exposure, climate) have no turbidity and show no visible changes compared to the unloaded reference part (delivery condition), provided that the coated molded part is a substantially two-dimensional having coating surface.

The use of such UV-curable acrylate-based resins, however, leads in the hitherto known IMC systems in the coating of three-dimensionally deformed components to non-homogeneously through-hardened layers and at the latest at normal load for crack formation.

The object of the present invention is to provide a method and a device which allows the production of radiation-cured polyacrylate coatings without cracking on three-dimensionally deformed components.

This object is achieved in that the molding for the wavelength of the irradiated radiation light scattering, light directing or at least the beam is expanding or the radiation source is a diffuse radiation source.

In this way, it is possible to achieve a more intense irradiation of the acrylate resin or a steering / guidance of the radiation into the edge regions in the edge region of the component, and thus a crack-free, well-cured polyacrylate coating.

Applicants, it was found that by a diffuse UV irradiation of the acrylate resin in the gap space or irradiation with a widened beam and / or the guidance / direction of the beam, the areas in the gap space can be sufficiently irradiated, which in a conventional non-diffuse or unexpanded radiation tends to crack.

The crack formation which occurs in the case of acrylate resin is attributed, on the applicant side, to the fact that the higher activity of the acrylic double bond results in uneven curing due to spatially different irradiation intensities. The resulting hardness gradients lead to stresses in the cured polyacrylate layer and thus to the undesirable cracking. This effect occurs in particular in areas which are difficult to access for UV light, such as undercuts, edge areas or deformations.

The scattering of the radiation, in particular the UV radiation through the molded part can be achieved in different ways. Thus, instead of the conventionally transparent non-diffusing molding, molding materials having embedded scattering centers may be used. In this case, the scattering centers can be distributed statistically over the entire layer thickness of the molded part or the scattering centers can be provided only in partial areas of the molded part, for example, near the molded part upper side facing in the direction of the radiation source.

It is also possible to coat the upper side and / or lower side of the molded part, for example with a scattering coating.

Instead of a scattering coating, the molded part top can also have scattering surface structures, which can be produced, for example, by a laser. Such irregular surface structures cause a widening of the beam and a "broader" more diffuse radiation distribution in the molded part and thus ultimately in the resin layer to be irradiated.

It is particularly preferred to form the structure on the surface of the molded part in such a way that the radiation incident on the structured surface is increasingly directed in the direction of the edge regions of the gap space. The radiation is directed and guided by these structured surface structures. The surface structures directing or directing the radiation may be applied to the surface of the molding, for example by lasering or milling, wherein the structure of the surface is preferably calculated or simulated.

Such structured light-guiding surfaces are advantageous over scattering systems, since guided radiation is more concentrated and thus better captured and relayed. For guiding / guiding the radiation, the surface may be structured in accordance with a Fresnel lens.

It is also possible to form the top and / or bottom of the molding partially reflective, z. B. as a semitransparent mirror. With this variant, an amplification of the radiation in the direction of the edge regions of the gap space can be achieved, which, however, is associated with a weakening of the radiation intensity that primarily enters the layer of the molded part.

A higher irradiation intensity in the edge regions of the gap can be achieved with a light-guiding coating of the molded part.

It is also possible to form such semi-transparent and / or scattering surfaces only in individual areas of the upper or lower side of the molded part, for example in the areas of maximum light intensity, and thereby to direct the light into the areas of lower intensity.

Beam expansion or scattering is in principle also possible because the molded part is provided with a retardation plate (eg λ / 4 or λ / 2-plate).

As an alternative or in addition to the use of light-scattering or jet-expanding molded parts, it is also possible to use a radiation source that radiates at least partially diffusely. Such a diffuse radiation source can be, for example, using an Ulbricht sphere or reflection of the primary radiation at a reflecting and / or light-scattering, correspondingly curved Reflector, for example, coated with BaSO ₄ or MgO can be achieved.

In order to further improve the irradiation of edge regions of the gap, the radiation source can additionally be moved along the upper side of the molded part and swiveled if necessary. The radiation source can be filled along the surface by a robot, wherein, for example, in the case of the structured surface of the molded part, the lamp movement can also be adapted to the specific course of the surface structure.

It is also possible to provide a plurality of directional radiation sources and to position them so that the proportion of radiation in the edge regions is high. An arrangement of two or more radiation sources is desired in particular when using light-guiding surfaces or coatings of the molded part, since the targeted irradiation of the light-directing structures can thereby be achieved.

The weakening of the primary radiation caused by the scattering and possibly also the reflection of the radiation on / in the molding layer is quite desirable since it has been found that a less intensive, diffuse irradiation of the liquid resin causes a more homogeneous and hence stress-free curing of the acrylate resin and thus the undesired radiation Cracking avoids cracking.

In the hitherto known methods, by contrast, the irradiation direction of the layer of the molded part was irradiated with a very high UV intensity, so that the acrylate resin present in the main irradiation direction hardened immediately due to the high irradiation intensity, whereas the irradiation in the edge regions was insufficient.

The molding which diffuses the radiation or the UV light or expands the beam can be made of different materials as long as they are resistant to the acrylate resin and do not completely absorb the irradiated radiation, for example glass, in particular quartz glass or silicone.

Quartz glass is characterized by high permeability of UV radiation. The molding may also be made of a combination of these materials.

Silicone is characterized by a high radiation permeability. In addition, the cured polyacrylate can be removed from the silicone surface very well.

As scattering centers for UV radiation, for example BaSO ₄ , TiO ₂ , MgO, Al ₂ O ₃ or SiO ₂ can be used. These have a lower absorption for UV light and generally a scattering efficiency of more than 50 cm ^-1 .

In the context of the present invention, the radiation source is preferably a UV light source and the radiation is preferably UV radiation.

The paint films obtained by the process according to the invention are characterized by the use of in the EP 1 888 701 B1 Moreover, polyacrylate resin described by high transparency, high surface scratch resistance and very low yellowing tendency.

The invention further provides a device for surface coating of a three-dimensionally deformed component, in which the molded part is scattered for the irradiated radiation and / or the beam is widened and / or the radiation source is at least partially diffuse. In general, the gap width in such an IMC system is between 300 μm and 1000 μm, preferably between 700 μm and 900 μm.

The invention will be described in more detail below with reference to exemplary embodiments. It shows:

1 : A schematic representation of a first embodiment of an apparatus for coating three-dimensionally deformed components with scattering centers in the molding and

2 : A schematic representation of a second embodiment with scattering molding surface.

1 shows a device for coating a component 11 , which may be, for example, an interior fitting for motor vehicles.

The component 11 can on its surface 13 with a decorative layer of wood, foil o. Ä. be provided.

The device comprises a molding 14 which has little absorption for UV radiation and a UV radiation source 20 , On the radiation source 20 opposite lower side 23 of the molding 14 is located - spaced by a gap 16 - The component to be coated 11 that with the molding 14 can be tense.

The gap space 16 serves to be filled with liquid surface coating material. The hardening of the in the gap space 16 located liquid coating material is carried out by UV irradiation with the radiation source 20 , wherein the UV light passes through the molded part 14 through to the in the gap 16 located coating material meets.

So when filling the surface coating material in the gap 16 air can escape is in the component 11 preferably additionally provided an outlet opening.

The surface to be coated 13 of the component 11 lies on a curved surface, ie the component is deformed three-dimensionally. The side areas pointing in + x and - x direction 21 of the component extend in the edge region in the -z direction, ie in the edge regions, the surface 13 of the component 11 also a component in -z direction.

The production of UV radiation transmissive moldings for components, extending in the -z direction edge areas 21 have, is very complex and costly.

Because of this, the border areas become 15 of the molding 14 often made of metal or wood. Although the desired shape for the coating of the component in the edge region can be achieved with these materials. The disadvantage, however, is the lack of transparency of the peripheral areas 15 of the molding 14 for UV radiation, leaving the coating material in the edge areas 17 of the gap 16 ultimately not sufficiently harden and the resulting coating tends to crack, especially when using acrylic resins.

This hitherto insufficient irradiation in the edge area 17 of the gap 16 is now improved by a diffused and / or expanded irradiation of the gap.

In the in 1 illustrated embodiment, the molding comprises 14 , which may be made of quartz, for example, a plurality of scattering centers S, at which the incident UV light is scattered.

In the layer of the molding 14 Due to the scattering at the scattering centers S, a large number of processes occur, including further scattering, total reflection at the interface 22 . 23 the molding layer 14 when the critical angle .alpha. of total reflection is reached, the re-emergence of the UV radiation from the layer of the molding 14 in the direction of the radiation source 20 , for exit from the layer of the molding 14 in the direction of the gap 16 and thus irradiation of the liquid coating material and optionally also for the (unwanted) absorption of the UV photon in the layer of the molding 14 ,

Due to the additional scattering of the UV photons in the layer of the molding 14 is the mean path length of the UV photons in the layer of the molding 14 extended and a more diffuse irradiation and an increase in the relative UV photon density in the peripheral areas 17 the space filled with surface coating material gap 16 reached.

Through the scattering centers S is in the layer of the molding 14 also increases the proportion of total reflected light in the layer and thus a migration / conduction of the generally center of the component irradiated light in the edge regions.

In addition to the possibility of statistical distribution of the scattering centers S in the layer of the molding 14 The scattering centers can also be in a specific layer segment of the molding 14 be arranged. In this variant, the molding 14 For example, consist of three layers, two transparent quartz layers, between which a scattering layer is provided.

Another variant of the invention, namely with a UV light scattering surface 22 of the molding 14 , is in 2 shown. Instead of the scattering centers S within the layer of the molding 14 is the surface 22 of the molding 14 UV light scattering, resulting in a more diffuse and expanded course of the irradiated UV light in the layer of the molding 14 and subsequently also to a more diffuse and expanded irradiation of the gap 16 and a higher UV light intensity in the peripheral areas 17 leads.

The production of such a scattering surface 22 of the molding 14 can be done for example by means of laser or by etching.

Another variant of the invention provides that the upper 22 and / or bottom 23 of the molding 14 (see. 1 ) to be provided with a reflective, photoconductive and / or scattering coating. (The coatings on the top 22 or bottom 23 of the molding 14 are in 1 not shown.)

The use of semi-transparent reflective coatings can be used in the molded part layer 14 incoming UV beam also widened and more towards the inaccessible side areas 17 be reflected.

In a further variant, for coating the upper 22 or bottom 23 of the molding 14 a delay plate can be used.

A further variant of the invention provides for the irradiation with an at least partially diffuse radiation source 20 make. For this purpose, the radiation source 20 at least partially from a UV-scattering reflector 18 ( 1 . 2 ) surrounded by the radiation source 20 emitted to the reflector 18 incident light diffused on the molding 14 scatters back.

In addition, another reflector 19 in the beam path between the radiation source 20 and molding 14 be provided, which is the emitted primary light in the reflector 18 reflected, so as to ensure that no emitted primary light without scattering on the molding 14 falls.

As the 1 and 2 show, are different shapes of the reflector 18 possible.

To a higher irradiation intensity in the border areas 17 the surface 13 of the component 11 The lamp can be reached 20 additionally during the irradiation along the component 11 moved and possibly also swung. The speed of the radiation source 20 can also vary depending on the position to be irradiated.

In a further variant of the invention (not shown), the molded part 14 a light directing surface 22 on, wherein the steering of the radiation, which should take place in particular in the edge regions, for example, by Fresnel lenses corresponding surface structures can be achieved.

Instead of a light-guiding surface structure, the molded part 14 Of course, be provided with a light-directing surface coating similar to a Fresnel lens.

The irradiation of the light-guiding surface of the molding 14 preferably takes place with at least one radiation source 20 that emits directed radiation. In order to achieve increased irradiation of the edge regions, in this embodiment preferably at least two radiation sources 20 used or moved the radiation source.

The position and orientation of the radiation source (s) should be matched to the specific structure of the light directing surface.

Of course, the different variants described above can increase the radiation intensity in the edge region 17 of the gap 16 can also be combined.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4320893 C1 [0006]
• DE 19961992 S1 [0006]
• EP 1239975 B1 [0007]
• EP 1888701 B1 [0012, 0038]

Claims (11)

Process for the surface coating of a three-dimensionally deformed component ( 11 ), which in the region of its surface to be coated ( 13 ) at a distance to a wall ( 23 ) of a molded part ( 14 ) and between the surface to be coated ( 13 ) and the wall ( 23 ) a gap space ( 16 ), wherein in the gap space ( 16 ) liquid surface coating material and under irradiation by means of a radiation source ( 20 ), characterized in that the surface-coating material is a resin comprising radiation-curable acrylate or methacrylate prepolymers or oligomers and the molding ( 14 ) is for the radiation light scattering, light directing or Strahlaufweitend. A method according to claim 1, characterized in that in the material of the molded part ( 14 ) Scattering centers S are embedded. A method according to claim 2, characterized in that the scattering centers S over the entire layer thickness of the molding material distributed randomly or only in partial areas of the molding ( 14 ) are provided. Method according to one of the preceding claims, characterized in that the upper side ( 22 ) and / or underside ( 23 ) of the molded part ( 14 ) is coated, in particular with a semitransparent, scattering, radiation directing and / or reflective coating. Method according to one of the preceding claims, characterized in that the upper side ( 22 ) of the molded part ( 14 ) has scattering or radiation-guiding surface structures. Method according to one of the preceding claims, characterized in that the upper ( 22 ) and / or underside ( 23 ) of the molded part ( 14 ) is designed as a semitransparent mirror. Method according to one of the preceding claims, characterized in that the radiation source ( 20 ) is a UV radiation source and the radiation is UV radiation. Process for the surface coating of a three-dimensionally deformed component ( 11 ), in particular according to one of claims 1 to 7, which in the region of its surface to be coated ( 13 ) at a distance to a wall ( 23 ) of a molded part ( 14 ) and between the surface to be coated ( 13 ) and the wall ( 23 ) a gap space ( 16 ), wherein in the gap space ( 16 ) liquid surface coating material and under irradiation by means of a radiation source ( 20 ) is cured with UV radiation, characterized in that the surface coating material is a resin comprising UV-curable acrylate or methacrylate prepolymers or oligomers and the radiation source ( 20 ) an at least partially diffuse radiation source ( 20 ). Device for the surface coating of a three-dimensionally deformed component ( 11 ) with a molded part ( 14 ) to which the component to be coated ( 11 ) forming a gap space ( 16 ) and a radiation source ( 20 ), wherein the molded part ( 14 ) is at least partially transparent to the radiation, characterized in that the molded part ( 14 ) is for the radiation light scattering, light directing or Strahlaufweitend. Apparatus according to claim 9, characterized in that the molded part ( 14 ) or its coating are light-directing and that at least two directional radiation sources ( 20 ) are provided. Device for the surface coating of a three-dimensionally deformed component ( 11 ) with a molded part ( 14 ) to which the component to be coated ( 11 ) forming a gap space ( 16 ) and a radiation source ( 20 ), wherein the molded part ( 14 ) is at least partially transparent to the radiation, characterized in that the radiation source ( 20 ) of at least one reflector ( 18 . 19 ) is surrounded and at least partially diffuse.

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