Process for the provision of a mark or design in a plastic film, and stencil suitable for that purpose

Abstract: A process is described for the provision of a mark or design in a plastic film (2) in the form of a relief pattern, in which the film is at least partially deformed under the influence of heat and pressure by providing recesses which may or may not be perforated, using a stencil (1) provided with perforations (3, 4), and the mark or design is formed in the plastic film (2) by deforming the film material at least along the periphery of the mark or design, in such a way that the mark or design, unlike the deformed part of the film, is not perforated, said relief being provided by using a perforated stencil (1) whose non-perforated surfaces are raised parts formed on the stencil (1), comprising a coating (5) applied to the stencil (1). The coating is preferably a photoresist layer.

Description: The invention relates to a stencil which is suitable for the provision of a mark or design in a plastic film, said stencil comprising raised parts and at least partially being provided with perforations. Such a stencil is known from US-A-4.609.518, and is made by utilizing the laminar construction techniques, if desired followed by laser drilling techniques. Due to these rather sophisticated techniques, this known stencil must be expensive. Moreover, such a stencil cannot be adapted very easily for the provision of a different mark or design. A stencil with a coating having a desired pattern which can be produced easier, faster and more reproducible than a pattern in a stencil according to US-A-4.609.518, has now been found. The stencil according to the invention is characterized in that said stencil is completely perforated and comprises raised parts consisting of a coating covering perforated parts of said stencil. The mesh number of the stencil used, which constitutes a measure for the pitch and diameter of the perforations, can of course be selected freely. However, if the mesh number is high, for example greater than 125 mesh, the perforations have become so small that the film is no longer perforated; while a low mesh number leads to perforations in the film which are of such large diameter that the pattern obtained becomes coarse and therefore aesthetically unattractive, although this constitutes no problem at all for certain applications. Although the thickness of the coating can generally be varied between 0 and 100 µ, a thickness of approximately 15 µ has been found to be particularly suitable for the present purpose. The coating is expediently a through-polymerizable resist system, in particular a photoresist. Such a coating layer has the advantage that a certain pattern can be applied easily to the stencil, using known techniques, such as, for example, by etching or photographic techniques, or by using high-energy (laser) radiation. The invention also relates to a process for the provision of a mark or design in a plastic film, in which the film is at least partially deformed under the influence of heat and pressure by providing recesses which may or may not be perforated, using a stencil comprising raised parts and at least partially being provided with perforations and the mark or design is formed in the plastic film by deforming the film material at least along the periphery of the mark or design, in such a way that the mark or design, unlike the deformed part of the film, is not perforated, said process being characterized in that a relief pattern is provided by using a stencil which has completely been perforated and comprises raised parts consisting of a coating covering perforated parts of said stencil. The coating is preferably a through-polymerizable resist system, such as a photoresist. The film is expediently a thermoplastic film, in particular a polyalkene film, preferably a polyethylene or polypropylene film. Although such polyalkenes are preferable on account of their plastic deformability, the invention is not restricted to these materials. Other plastics can, of course, also be used. It is pointed out that the term thermoplastic is understood to mean any plastic which can be softened or plasticized under heating, but plastics which are plastic at low temperature (for example, room temperature) and can be hardened, can also be used. The film preferably has a thickness of at most 250 µ, more particularly approximately 10 µ to 150 µ. Such a thickness of the film makes it possible to deform said film in such a way that a mark or design or design can be discerned particularly clearly in the film in relief relative to the deformed part. According to a preferred embodiment, the film is also provided with a supporting layer. The selection of the supporting layer to be used will depend on the envisaged use, and it can be connected to the plastic film locally if desired. The deformed surface of the plastic film is preferably provided with a microstructure. The specific microstructure can be selected depending on the envisaged use and the film material concerned. The film, apart from the design or mark, can thus be given a modified surface structure which, due to the fact that the mark or design retains a smooth and shiny surface, means that the pictorial information becomes more clearly discernible in the film. The film is preferably deformed by vacuum deep-drawing. This deep-drawing expediently takes place under the influence of heat. More particularly, such deformation is produced by guiding the film material, directly after the formation of the film at elevated temperature, and therefore in the phase in which optimum deformability of the film is possible, over a perforated stencil which is connected to a vacuum source. The deformations thus formed will then consist of recesses which may or may not be perforated, depending on the partial vacuum applied. Of couse, it is also possible to make the deformations by exerting pressure on the film when it is being guided over the stencil. The deformations are preferably made under the application of heat which is fed in by means of a hot gas, in particular hot air. Through a suitable choice of the cross-section of the deformations present, it is also possible for a certain matting to occur at the site of the deformations. The stencil used in the process of the invention is perforated at least corresponding to the periphery of the pattern to be applied to the film. Through the application of a partial vacuum in the stencil or through pressing the film against the stencil, it thus becomes possible to place the desired pictorial information in relief in the plastic film. Of course, the temperature of the film must be sufficiently high here to permit such deformation, and it is therefore selected depending on the plastic used. The invention is explained in greater detail below with reference to the appended drawing, in which: Fig. 1 shows a cross-section through a part of a preferred embodiment of a cylindrical stencil during the formation of a plastic film according to the invention; and Figs. 2 - 6 show various embodiments of the deformed part of a plastic film according to the invention. In Fig. 1 the arrows a indicate the direction of movement of the plastic film 2 which is conveyed over the surface of a cylindrical stencil 1 for the provision of a mark or design. The arrows b indicate the direction in which pressure is exerted on the film material. This pressure can be a partial vacuum set in the cylindrical stencil, or a partial overpressure exerted on the surface of the film which is not in contact with the stencil. During the deformation of the plastic film, the latter is at a sufficiently high temperature to permit permanent deformation of the film material, using slight pressure, within the residence time set by the process. For the provision of a mark or design, the stencil is provided with perforations such as 3 and also locally provided with a coating 5. The coating 5 preferably comprises a through-polymerizable resist system, for example a photoresist. The use of such a system makes it possible to apply the desired mark or design to the stencil in relief with great accuracy by known techniques. The pattern corresponding to the mark or design to be applied is therefore provided on the surface of the stencil. The stencil used is preferably perforated over the entire surface. The perforations 4 are covered by the coating, but the perforations such as 3 are not. The recesses 6 will be formed at the uncovered perforations under the influence of heat and pressure, in order to obtain the desired mark or design. The film material used can be any plastic which is deformable under the influence of heat and/or pressure. A polyalkene, more particularly a polyethylene or polypropylene, is preferably used for the film material. Of course, the invention is not restricted to these materials. A number of embodiments of the deformations to be applied are shown in cross-section in Figs. 2 - 6. More particularly, the deformations are in the form of recesses, as shown perforated in Fig. 2, unlike Fig. 3 in which the recesses are not perforated. Figs. 2a and 3a show deformations corresponding to those of Figs. 2 and 3, but the surface of the film is provided with a microstructure. Figs. 4, 5 and 6 show a number of other variants of the deformations to be made in the film. The raised parts are shown by 7. The height of these parts 7 is, of course, determined by the thickness of the resist layer present on the stencil. The thickness of the resist layer lies expediently between 0 and 100 µ, but it is preferably approximately 15 µ. The invention is, of course, not restricted to the variants shown, while combinations of these variants are also possible.

Claims: A stencil (1), in particular suitable for the provision of a mark or design in a relief pattern in a plastic film (2), said stencil comprising raised parts (5) and at least partially being provided with perforations (3, 4), characterized in that said stencil (1) is completely perforated and comprises raised parts (5) consisting of a coating covering perforated parts (3, 4) of said stencil (1). A stencil according to claim 1, characterized in that the coating is a through-polymerizable resist system, in particular a photoresist. A process for the provision of a mark or design in a plastic film (2) in the form of a relief pattern, in which the film is at least partially deformed under the influence of heat and pressure by providing recesses which may or may not be perforated, using a stencil (1) comprising raised parts (5) and at least partially being provided with perforations (3, 4) and the mark or design is formed in the plastic film (2) by deforming the film material at least along the periphery of the mark or design, in such a way that the mark or design, unlike the deformed part of the film, is not perforated, characterized in that a relief pattern is provided by using a stencil (1) which has completely been perforated and comprises raised parts (5) consisting of a coating covering perforated parts (3, 4) of said stencil (1). A process according to claim 3, characterized in that, the film (2) is a thermoplastic film. A process according to claim 4, characterized in that, the film (2) is a polyethylene or polypropylene film. A process according to one or more of the claims 3 to 5, characterized in that, the film (2) has a thickness of at most 250 µ. A process according to claim 6, characterized in that, the film (2) has a thickness of approximately 10 µ to 150 µ. A process according to one or more of the claims 3 to 7, characterized in that, the film (2) is provided with a supporting layer.

Inventors: BOOGERS MICHAEL PETRUS JOHANNE, MEIJER WILLEM HUBERT, BOOGERS, MICHAEL  PETRUS JOHANNES, MEIJER, WILLEM HUBERT, BOOGERS, MICHAEL PETRUS JOHANNES
Applicants: TREDEGAR FILM PRODUCTS B V, TREDEGAR FILM PRODUCTS B.V.
Application year: 1990
Main classification: B29C51
IPC codes: B29C51, B29C59