Patent Publication Number: US-2009239046-A1

Title: Method for Printing a Surface

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application under 35 U.S.C. § 371 of PCT International Application No. PCT/EP 2007/001709, filed Feb. 28, 2007, which claims priority to German Application No. 10 2006 011983.5, filed Mar. 16, 2006. The contents of each of these applications are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     The invention relates to a method for printing a surface, in particular a plastic surface, by hot embossing, in particular hot-film embossing, and a film backing and a toothbrush. 
     BACKGROUND 
     For decorating and printing plastic surfaces, hot embossing methods are used. In hot-film embossing, for example, a prefabricated embossing film comprised of multiple layers is used, carrying the information that is to be applied to the surface, e.g., in the form of unicolored or multicolor images, characters, logos and the like. 
     The ink pigments contained in an ink layer of the embossing film are transferred from the film to the surface to be printed, which requires a supply of heat. This serves to release the ink layer from the embossing film and also to secure the ink layer on the plastic surface to be printed. 
     The heat is input in general via a heatable hot embossing ram. The heat emanating from this stamp is passed through the entire film when printing the surface. 
     DE 103 18 909 A1, for example, discloses the fact that the hot embossing ram comprises a heatable aluminum backing with a silicone coating for equalizing irregularities in the plastic part to be printed. Due to the poor heat transfer properties of silicone, the aluminum backing must be heated to relatively high temperatures, so that the heat input into the embossing film is sufficient for printing the surface. Consequently, there is often a relatively high temperature gradient between the aluminum backing and the silicone outer surface of the hot embossing ram. 
     Temperature regulation of the hot embossing ram is of course relatively inert due to the thermal conduction properties of the materials to be heated. A high temperature gradient in the area of the silicone coating is reflected in a short lifetime of this coating. 
     SUMMARY 
     In one aspect, a method for printing a surface, in particular a plastic surface, is a hot-film embossing method in which the embossing film has at least one ink layer and at least one melt layer. To apply an ink layer to the surface that is to be printed, an embossing ram is used, pressing he embossing film and thus also the ink layer that carries the information against the surface that is to be printed. 
     The at least one melt layer is designed as a hot-melt adhesive layer or as a release layer. Both layers, namely the release layer and the hot-melt adhesive layer, melt during the embossing operation due to the input of heat, so that the pattern layer or ink layer is secured on the substrate to be printed and a backing film of the embossing film is released from the pattern attached to the surface. 
     In some implementations, the heat input into the at least one hot-melt layer is achieved by means of high-frequency radiation. At least the hot-melt layer is designed so that it undergoes heating when exposed to high-frequency radiation. In this way, targeted input of heat into the layer to be melted in the embossing process can be achieved without requiring a heatable embossing ram for this purpose. 
     Here again, the heat must not be supplied to the embossing film from the outside. Due to irradiation with high-frequency waves, local heating is supplied directly into the layers that are to be heated. Depending on the radiation exposure, uniform and rapid heating of the hot-melt layer can thus be achieved with at the same time minimal stress on the backing film, the embossing device and the substrate that is to be printed. 
     In addition, by using high-frequency radiation, it is possible to achieve suitable heating of the melt layer. By direct introduction of the thermal energy into the melt layer, the embossing process can be made completely independent of the other materials and the geometry of the embossed film, in particular its thickness. Furthermore, the targeted and more controllable introduction of thermal energy into the melt layer ultimately leads to better attachment and adhesion of the pattern layer or ink layer to the plastic surface. 
     According to a first advantageous embodiment, metal particles are added to the melt layer. Such an addition already takes place, for example, during the production of the embossing film, so that the metal particles are already present inside the embossing film before the actual embossing operation. The melt layer, which may be designed both as a hot-melt adhesive layer and as a release layer, experiences almost instantaneous heating in the HF field due to the interaction of the metal particles with the high-frequency (HF) radiation according to the distribution of the metal particles in the layer. 
     According to another embodiment, the metal particles are distributed essentially uniformly in the melt layer. This uniform distribution of metal particles or metal pigments with uniform action of HF radiation leads to uniform heating of the melt layer. 
     According to another embodiment, the melt layer is heated to a temperature between 30° C. and 250° C., preferably to a temperature between 80° C. and 120° C. Owing to the targeted and direct input of heat into the melt layer, the embossing ram may be designed as a so-called cold embossing ram, i.e., not being actively heatable. 
     Thermal conduction effects within the embossing film may therefore be essentially disregarded, so that a predetermined temperature can be adjusted accurately based only on the radiation power, the duration of radiation and the properties of the melt layer, in particular the density of the metal particles contained in it. Measurement of a temperature of the melt layer during the embossing process as part of process control can therefore be eliminated in a manner that saves on costs. 
     According to another aspect, the surface to be printed is part of a toothbrush made of plastic. The method for printing a plastic surface is therefore provided for printing toothbrushes. 
     According to another aspect, an embossing film for printing a surface, in particular a plastic surface, is featured. The embossing film has at least one pattern layer or ink layer to be applied to the surface and has at least one melt layer, whereby at least the melt layer contains metal particles that can be heated by high-frequency radiation. 
     In addition, a toothbrush with which the handle in particular is printed according to the above process features is described. 
     Advantages of the method described herein include simplification and optimization of a hot-film embossing process for printing plastic surfaces, and a film backing and a toothbrush printed accordingly. Furthermore, stress on the material of the embossing ram as well as the surface to be printed can be minimized. As described herein, available cycle times and embossing times may be shortened, so that the entire embossing operation can be optimized with regard to cost and time. In addition, better adhesion of the decoration and/or the pattern or image to the plastic surface that is to be printed can be achieved. 
     Additional goals, advantages and features and advantageous possible applications are derived from the following description of an exemplary embodiment on the basis of the drawings. All the features described here and/or illustrated in the figures form the subject matter of the present description, even independently of the patent claims or their reference back to previous claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embossing ram, an embossing film and a substrate in cross section. 
     
    
    
     DETAILED DESCRIPTION 
     The embossing ram  30  illustrated in  FIG. 1  has a backing  10 , preferably made of aluminum, with a silicone coating  12 , which is provided for equalizing irregularities in the substrate  26  that is to be printed. 
     The embossing film  40  consists of multiple layers, namely backing film  14 , release layer  16 , clear lacquer layer  18 , ink or patterned layer  20  and hot-melt adhesive layer  22 . At least the hot-melt adhesive layer  22  but preferably also the release layer  16  are melt layers in the sense of the present embodiment. 
     In the hot press operation, the embossing film  40  is printed by means of the embossing ram  30  on the surface  24  of the substrate  26  that is to be printed. The heat input required for melting the hot-melt adhesive layer  22  and release layer  16  is accomplished here via high-frequency radiation  28 , which interacts with the metal particles present in the layers  16  and  22  and thus leads to a targeted and local heating of these layers which are provided for melting. 
     The heating of the hot-melt adhesive layer  22  leads to joining and securing of the patterned layer or ink layer  20  at the surface  24  of the substrate  26 , which can be made of polypropylene. 
     The heating of the release layer  16  results in the backing film  14  being releasable from the ink layer and/or pattern layer  20  and a clear lacquer layer  18  provided above it. At the end of the embossing operation, the clear lacquer layer  18  thus forms a surface of the substrate  26  that is to be printed and protects the ink layer or patterned layer  20 .