Patent Application
20080032070
The invention relates to a transfer film comprising a carrier film having a first side and a second side, a release layer being arranged on the first side of the carrier film and a transfer layer being arranged on the side of the release layer facing away from the carrier film, and to its use. The invention also relates to two processes for the production of a plastic article which is decorated with a transfer layer of a transfer film and which has three-dimensional structuring in the region of the transfer layer, using such a transfer film.
Transfer films of the type mentioned above and suitable processes for the decoration of plastic articles with a transfer layer, three-dimensional structuring being produced in the region of the transfer layer, are known.
For example, JP 2002264268 A discloses what is known as an in-mold process for the production of an injection molded article decorated with a decorative film, having three-dimensional structuring in the region of the decorative film. In this case, an unstructured decorative film is arranged in an injection mold, of which the surface is structured. After the injection mold has been closed, according to FIG. 2 of JP 2002264268 A the decorative film has a plastic injection molding compound injected behind it, the decorative film being forced against the structured wall of the injection mold. In the process, structuring of the layer of the decorative film that faces the wall and which has thermoplastic properties and a glass transition temperature of 130° C. or less takes place. As a result of the contact between the hot injection molding compound and the decorative film, the thermoplastic layer softens and is shaped in accordance with the structuring of the injection mold.
With the process disclosed in JP 2002264268 A, differently configured structuring of the injection molded article can be achieved only if a further injection mold with changed structuring of the inner wall is provided. In addition, unstructured injection molded articles cannot be produced by using the structured injection mold. Since the production of an injection molding tool and the structuring thereof are generally costly and time-consuming, undesirably high costs and regular machine stoppages arise in the event of a change in the decorative structuring according to the process of JP 2002264268 A, even if the general shape of the injection molded article is intended to be maintained.
It is, then, an object of the invention to provide a transfer film for the decoration of a plastic article which has three-dimensional structuring in the region of the transfer layer which permits faster and more cost-effective changing of be three-dimensional structuring. Furthermore, two cost-effective processes are to be provided for the decoration of a plastic article with a transfer layer which has three-dimensional structuring in the region of the transfer layer, which processes permit faster and more cost-effective changing of the three-dimensional structuring by using the transfer film according to the invention.
For the transfer film which comprises a carrier film having a first side and a second side, a release layer being arranged on the first side of the carrier film and a transfer layer being arranged on the side of the release layer facing away from the carrier film, the object is achieved in that, either on the second side of the carrier film or on the side of the transfer film opposite the second side of the carrier film there is partially arranged a structured layer with a layer thickness of at least approximately 9 μm of a structuring varnish, whose compressive strength is substantially constant at least up to a temperature of 200° C.
If such a transfer film is used in an in-mold injection molding process or during hot pressing, the structured layer is not deformed or deformed only insignificantly, since injection molding compounds are normally injected at temperatures below 200 to 300° C. into molds having a temperature of about 30 to 70° C., and hot embossing is only likewise carried out below 270° C. The use of the transfer film according to the invention for the in-mold injection or hot pressing permits the formation of three-dimensional structures in the region of the transfer layer on a plastic article decorated with one such, it being possible for a three-dimensional positive or negative image of the structured layer to be produced on the plastic article and on the transfer layer connected thereto, depending on the arrangement of the structured layer.
In this case, the structured layer can be produced on the carrier film in a simple and cost-effective manner in the required thickness by a printing process such as gravure printing, pad printing or screen printing. The formation of the structured layer by means of screen printing is preferred in this case, since particularly high layer thicknesses can be formed therewith. Here, flat screens or rotary screens can be used. The screen material should permit a maximum application of the structured layer for the desired printed image. To this end, stainless steel fabrics with a fineness of, for example, 110 threads per cm are preferably used. Depending on the desired printing resolution, this value can be reduced further, which leads to a further increase in the layer thickness that can be achieved.
In the event of a change in the decoration of the three-dimensional structuring of a plastic article decorated with the transfer layer of the transfer film according to the invention, the necessary steps are accordingly restricted to the provision of a changed printing original for the structured layer. If no more three-dimensional structuring is desired, the application of the structured layer can be dispensed with and a decorative plastic article with a smooth surface can immediately be fabricated in the injection molding tool previously used. Neither the transfer layer used nor the apparatus used hitherto, such as injection molds or embossing rolls, needs to be changed. This minimizes the costs and the changeover times in the event of a change in the decoration. How the process of forming three-dimensional structuring by using the transfer film according to the invention is carried out in detail is explained in the following text in relation to the process according to the invention.
For a first process for the production of an injection molded article decorated with a transfer layer of a transfer of film, which has three-dimensional structuring in the region of the transfer layer, the object is achieved by the following steps:
As the injection mold, which has no kind of structuring on its inner wall, is filled with plastic injection molding compound, in the case in which the structured layer is arranged directly on the transfer film, the structured layer and, at the same time, the regions of the carrier film free of the structured layer are forced against the normally rigid inner wall of and injection mold. In the regions free of the structured layer, the carrier film runs along the inner wall of the injection mold and, in the regions in which there is a structured layer, leads away from the inner wall of the injection mold or is spaced apart from the inner wall of the injection mold by the structured layer. The decorated injection molded article formed has three-dimensional structuring which can be detected by touch in the region of the transfer layer.
If a transfer film is used whose structured layer is arranged on the side of the transfer film opposite the carrier film, the structured layer produces either three-dimensional structuring which is only visible but cannot be detected by touch, by means of the structuring varnish itself, that is to say on the side of the transfer layer which faces away from the observer and which is filled by the injection molding compound, or structuring in the region of the transfer layer which can be detected by touch.
If the inner wall of the injection mold is formed in such a way, for example by means of elastic inlays, that it can be deformed under injection molding conditions, then structuring which can be detected by touch is produced, since regions with structuring varnish effect more intense deformation of the inner wall of the injection mold than regions without structuring varnish. In this case, elastic inlays can be formed of silicone, for example. If, on the other hand, the inner wall of the injection mold is formed in such a way that it cannot be deformed under injection molding conditions, then structuring which is merely visible is produced, since no deformation of the inner wall of the injection mold takes place and thus the regions between the structuring varnish regions are merely filled without the transfer layer being deformed in the process. The surface of the transfer layer and of the injection molded article decorated therewith remains smooth in this case.
It has proven to be advantageous if the plastic injection molding compound is formed of ABS, an ABS/PC mixture, PC, PA, SAN, ASA, TPO, PMMA, PP or a mixture of at least two of these materials, if these are compatible with each other. Plastic materials of this type can be processed reliably on injection molding machines.
For a second process for the production of a thermoplastic article which is decorated with a transfer layer of a transfer film by means of hot embossing and which has three-dimensional structuring in the region of the transfer layer, the object is achieved by the following steps:
For an embossing tool and an opposing pressure surface, between which the transfer film and the thermoplastic article are led during hot embossing, different materials can be used, depending on the application. For example, on the one hand an embossing tool, for example an embossing roll, can be rigid and an opposing pressure surface to the embossing tool, for example likewise a roll, can be elastic, or else the opposing pressure surface can be rigid and the embossing tool elastic, or both the embossing tool and the opposing pressure surface can be rigid or elastic.
In this case, the elasticity should be designed experimentally, matching the application-specific pressure conditions. Here, neither the embossing tool nor the opposing pressure surface has a surface structure; instead both are designed to be smooth on their contact surfaces with respect to the transfer film and with respect to the thermoplastic article. However, the material selection must be made such that an adequate heat transfer to the transfer film and the plastic article is ensured during hot embossing. The following exemplary embodiments assume that, during hot embossing, the embossing tool is in contact with the transfer film, while the opposing pressure surface is in contact with the thermoplastic article. However, this is not absolutely necessary and is intended here to serve only to illustrate the effects that can be achieved.
If a rigid, for example metallic, embossing tool is pressed against the transfer film, the plastic article and a rigid, for example likewise metallic, opposing pressure surface, in the case in which the structured layer is arranged directly on the transfer film, the structured layer and, at the same time, also the regions of the carrier film free of the structured layer are pressed against the smooth surface of the embossing tool. Accordingly, in the regions free of the structured layer, the carrier film runs along the surface of the embossing tool and, in the regions in which the structured layer is present, is led away from the surface of the embossing tool or spaced apart from the surface of the embossing tool by the structured layer. The decorated plastic article formed has three-dimensional structuring that can be detected by touch in the region of the transfer layer.
If a rigid, for example metallic, embossing tool is pressed against the transfer film, the plastic article and an elastic opposing pressure surface, for example silicone, in the case in which the structured layer is arranged directly on the carrier film, the structured layer and, at the same time, also the regions of the carrier film free of the structured layer are pressed against the smooth surface of the embossing tool. Accordingly, in regions free of then structured layer, the carrier film runs along the surface of the embossing tool and, in the regions in which the structured layer is present, is led away from the surface of the embossing tool or spaced apart from the surface of the embossing tool by the structured layer, the adjacent region of the plastic article being pressed into the elastic opposing pressure surface and the latter being deformed. The decorated plastic article formed has three-dimensional structuring that can be detected by touch in the region of the undecorated surface of the plastic article opposite the transfer layer and in the region of the transfer layer.
If, then, a transfer film is used whose structured layer is arranged on the side of the transfer film opposite the carrier film, the structured layer produces either three-dimensional structuring that is merely visible but cannot be detected by touch or three-dimensional structuring which can be detected by touch.
If a rigid embossing tool is pressed against the transfer film, the plastic article and a rigid opposing pressure surface, the structured layer arranged directly on the transfer layer is pressed into the thermoplastic article. The decorated plastic article formed has structuring which is merely visible in the region of the structuring layer and which results on the waviness of the surface of the thermoplastic article which adjoins the transfer layer. This surface must accordingly be visible either from the transfer layer or from the surface of the plastic article opposite the transfer layer.
If a rigid embossing tool is pressed against the transfer film, the plastic article and an elastic opposing pressure surface, the structured layer being arranged directly on the transfer layer, the structured layer is pressed in the direction of the elastic opposing pressure surface and deforms the latter. The decorated plastic article formed has three-dimensional structuring which can be detected by touch in the region of the free surface of the plastic article opposite the transfer layer.
If an elastic embossing tool is pressed against the transfer film, the plastic article and a rigid opposing pressure surface, the structured layer being arranged directly on the transfer layer, the structured layer is pressed in the direction of the elastic embossing tool and deforms the latter. The decorated plastic article formed has three-dimensional structuring that can be detected by touch in the region of the surface of the plastic article covered by the transfer layer.
If an elastic embossing tool is pressed against the transfer film, the plastic article and an elastic opposing pressure surface, the structured layer being arranged directly on the transfer layer, the structured layer leads both to deformation of the elastic embossing tool and of the elastic opposing pressure surface. In this case, an elastic material should be used for the embossing tool and/or the opposing pressure surface which is capable of transmitting the quantity of heat required for hot embossing to the thermoplastic article and the transfer film. The decorated plastic article has in each case three-dimensional structuring that can be detected by touch in the region of the surface of the plastic article covered by the transfer layer and also in the surface opposite the transfer layer, but structure depth is naturally lower by at least a half with regard to the aforementioned procedures.
For the depth of the three-dimensional structuring that can be produced, in general the layer thickness of the structured layer is critical for the process according to the invention. In order to achieve three-dimensional structuring that can be detected by touch, a structured layer with at least 20 μm thickness is required, which cannot be deformed or can be deformed only little under the processing conditions for the transfer film. Of course, the thickness of the structured layer on a carrier film can be formed differently in this case, so that three-dimensional structures of different depths can be produced simultaneously.
It has proven particularly worthwhile if the structuring varnish has a thermosetting plastic or a thermoplastic with a glass transition temperature Tg above 200° C. However, the use of a structuring varnish made of a non cross-linked varnish system filled with a filler, the filler preferably being formed of inorganic fillers such as titanium dioxide, has proven worthwhile. Structuring varnishes of this type are dimensionally stable and pressure-resistant up to high temperatures, so that deformation of the structured layer under injection molding conditions does not take place or takes place only to an extremely low extent.
Here, it has proven particularly worthwhile if the structuring vanish is a radiation-curable, ESH-curable, epoxy-curable, isocyanate-curable or acid-curable varnish. Such crosslinking varnishes exhibit the required dimensional and pressure stability at high processing temperatures and can also be processed easily with a high solids content.
It is particularly preferred in this case if the structuring varnish has a solids content of at least 40%, preferably of 100%. The high solids content increases the achievable layer thickness of the structured layer and improves the transcription capability of the structured payer. Thus, the achievable depth of the three-dimensional structures is increased.
If the structured layer is arranged on the second side of the carrier film, it has proven to be advantageous if the structuring vanish is colored differently from the carrier film. This permits visual checking of the structured layer, for example with regard to its completeness, and simpler and more accurate, also automatic, positioning of the transfer of film in the selected processing method.
If the structured layer is arranged on the side of the transfer film arranged opposite the second side of the carrier film, the structuring varnish can be both colorless or colored. Whether coloration is desired of course also depends on whether the transfer layer used enables a view at all of the structured layer remaining between plastic article and transfer layer.
The structured layer is preferably formed on the carrier film in the form of a regular or irregular pattern and/or in the form of alphanumeric characters and/or in the form of pictorial illustrations. The design selected for the structured layer will be a positive or negative for the pattern, the alphanumeric characters or the pictorial illustration, depending on the arrangement of the structured layer and of the transfer film. If the carrier film including the structured layer is removed, then a negative image of the structured layer remains as three-dimensional structuring, which means that the regions of the transfer layer in which the carrier film was free of the structured layer represents the elevated regions, while the regions of the transfer layer in which the structured layer was provided represent the—possibly differently—depressed regions.
A thickness of the carrier film of the transfer film according to the invention in the range from 12 to 100 μm has proven to be worthwhile. In the case of hot embossing, thin carrier films in the range from about 19 to 23 μm are normally used. A suitable material for the carrier film is, for example, PET, but also other plastic materials.
The three-dimensional structuring of the decorated plastic article is approximately wider by twice the thickness of the carrier film than the width of the structured layer which, together with the maximum print resolution for printing structured layers, limits the resolving power of the process. With a thickness of about 75 μm of the PET carrier film 1, a structured layer 9 applied thereto in the screen printing process and a desired depth of the three-dimensional structuring of about 25 μm, about a minimum line width of 350 μm can be applied. The spacing between two three-dimensional structures in the finally decorated plastic article should likewise be of this order of magnitude. If thinner carrier films or amorphous films, unstretched films or BOPP films (biaxially oriented polypropylene) are used, this value can be reduced further in order to increase the resolution.
In order to be used as a decorative element, the transfer film of the transfer film according to the invention comprises at least one protective layer and/or a decorative layer having a decorative effect. Such a decorative effect can be produced inter alia by an at least partly arranged, possibly mirror-reflective metal layer and/or an at least partly arranged interference layer and/or an at least partly arranged replication layer having relief structures such as macroscopic relief structures, diffractive structures or holograms and/or an at least partly arranged colored layer and/or an at least partly arranged pigmented layer, which has fluorescent, phosphorescent, thermochromic or photochromic pigments or pigments with color changing effects that depend on the viewing angle.
If a suitable material which can easily be separated from the transfer layer is chosen for the transfer film, it is possible to dispense with an additional release layer, since one surface of the carrier film then already forms the release layer.
The hot embossing according to the second process according to the invention is preferably carried out by rolling heated rolls on the transfer film or, in the reciprocating process, by means of heated surface or shaped dies.
If the plastic article used in the hot pressing forms a film web, then it has proven worthwhile if the film web decorated with the transfer layer is processed further by means of thermoformimg or punching to form a semifinished product. The semifinished product can finally be inserted into an injection mold and sprayed with a plastic injection molding compound, at least on one of its two sides. A process of this type is normally designated an insert-molding process.
In general, it has proven worthwhile if at least the three-dimensional structuring produced in the process according to the invention has an injection molding compound sprayed over it in a subsequent injection molding process, so that specific article depth effects result.
The use of a transfer film according to the invention for the production of a plastic article which is decorated with a transfer layer and which has three-dimensional structuring in the region of the transfer layer is ideal. Such decorated plastic articles are preferably used as decorative components for the interior and exterior of a motor vehicle, for domestic appliances, radios, televisions, monitors, PCs or (mobile radio) telephones. Innumerable further possible applications are conceivable.
FIGS. 1 to 4 are intended to explain the invention by way of example. Thus:
a shows a commercially available transfer film in cross section,
b shows a transfer film according to the invention in cross section,
a to 2c show a schematic flow diagram relating to the first process according to the invention,
a shows a commercially available IMD-capable (IMD=inmold decoration) transfer film in cross section, as is often used for inmold injection molding processes. The transfer film has a carrier film 1, a release layer 2, a transparent protective varnish layer 3, at least one decorative layer 4, a backing layer 5 and a primer or adhesive layer 6. The release layer 2, the transparent protective layer 3, the at least one decorative layer 4, the backing layer 5 and the primer or adhesive layer 6 can be applied to the carrier film 1 by means of a printing or coating process. The carrier film 1 and the release layer 2 form a first layer system 8 which, after the application of the transfer layer 7 formed by the transparent protective varnish layer 3, the at least one decorative layer 4, the backing layer 5 and the primer or adhesive layer 6 to a basic element to be decorated, is pulled off the transfer layer 7. This is done only at a time, since the primer or adhesive layer 6 is already mechanically connected to the base element.
b shows a transfer film 10 according to the invention in cross section. The transfer film 10 has, in addition to the commercially available transfer film illustrated in
Here, the following melamine-crosslinking composition is used as a structuring varnish for forming the structured layer 9 in gravure printing technology:
Alternatively, the following UV-curing composition can be used as a structuring varnish for forming the structured layer 9 in a screen printing process:
Additionally, the following crosslinking structuring varnish can be used:
Furthermore, the following non crosslinked structuring varnish highly filled with an inorganic filler can be used:
A structuring varnish according to the above compositions exhibits good adhesion to a carrier film 1 of PET and is so flexible that the deformations of the carrier film 1 possibly occurring during the processing of the transfer film are withstood without flaking off or tearing. A particularly suitable carrier film for carrying out the process according to the invention has an extension at tear in the range from about 110 to 135%, a tensile strength in the range from about 27 to 31 kpsi and a modulus of elasticity in the region of about 500 kpsi.
The structuring vanish is formed partly in the form of a pattern, a layer thickness of the cured structured layer in the range from 9 to 35 μm being produced.
The release layer 2 can also be a functional layer of the transfer layer 7 here, which permits the transfer layer 7 to be released from the carrier film 1. For example, the protective varnish layer 3 can simultaneously provide the function of the release layer and thus be used as a release layer. However, it is equally possible for a suitable carrier film 1 to provide the function of a release layer at the surface, and thus no separate release layer is required between carrier film 1 and transfer layer 7.
a now shows in schematic form how the transfer film 10 is used in an inmold injection molding process. It shows schematically a detail of an injection mold 20, against whose rigid inner wall the transfer film 10 is placed, the structured layer 9 and/or carrier film 1 being in contact with the injection mold 20. After the injection mold 20 has been closed, a plastic injection molding compound, symbolized by the arrow illustrating, is injected into the injection mold 20 and the injection mold 20 is therefore filled. In the process, the transfer film 10 is pressed against the injection mold 20.
In
c shows the demolding step, in which the first layer system 8, consisting of the carrier film 1 and the release layer 2, including the structured layer 9, are pulled simultaneously off the transfer layer 7.
The injection molded article 13 decorated with the transfer layer 7 formed as a decorative element has three-dimensional structuring 12 in the region of the decorative element, elevations being formed in the regions in which there was no structured layer 9 and valleys being firmed in the regions in which the structured layer 9 was arranged. If a carrier film 1 of PET is used with a thickness of 75 μm and a structured layer 9 of 35 μm, the profile depth produced here of the three-dimensional structuring 12 on the decorated injection molded article 13 is about 25 μm. As can be seen from
By means of skillful selection of transparency and color for the plastic article to be decorated in combination with the decorations provided by the at least one decorative layer of the transfer layer, visually striking effects can be achieved. For example, colorations of the plastic articles can be detected through transparent regions in the transfer layer. Superimposition of the three-dimensional structure produced in the region of the decorative element with relief structures such as diffractive structures or holograms in the at least one decorative layer can achieve further visual effects. Three-dimensional structures which are arranged in register with at least one decoration of a decorative layer appear particularly striking.
Those skilled in the art will readily discover, in a non-inventive way, diverse further possible configurations, which are covered by the idea of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004041868.3 | Aug 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP05/08667 | 8/10/2005 | WO | 3/23/2007 |
