Printing – Stenciling – Stencils
Reexamination Certificate
2000-01-04
2001-05-15
Yan, Ren (Department: 2854)
Printing
Stenciling
Stencils
Reexamination Certificate
active
06230618
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing a screen-printing stencil in which a covering layer is applied to only some regions of a fine-mesh screen. The stencil printing device includes a bearing device, a coating device, and an elastic hollow body.
2. Description of the Background Art
A method of producing a screen-printing stencil is already generally known, in which a covering layer is applied to only some regions of a fine-mesh screen in accordance with a desired printing pattern.
However, it has been shown that screen openings can often not be filled completely by a liquid substance that is used for forming the covering layer. In other situations where the edge of the printing pattern is intended to end between two screen webs, the covering layer may not be built up to a sufficient extent. One cause of this is the fact that the liquid substance does not adhere to the structure that are already present but passes through the screen. This leads to faulty printing patterns on the stencil and hence ultimately to prints which are of reduced quality.
SUMMARY OF THE INVENTION
The invention is based on the object of developing a method of the type mentioned at the beginning such that printing patterns may be produced more accurately on the stencil. Furthermore, it is an object of the invention to specify a device suitable for this.
The method according to the invention of producing a screen-printing stencil, in which a covering layer is applied to only some regions of a fine-mesh screen in accordance with a desired printing pattern, is characterized by the fact that, for the application of the covering layer, the screen is closed on the rear side by a support.
This support prevents the liquid substance that is used to build up the covering layer from passing through the screen. As a result, the screen openings may always be filled completely, specifically even when the screen has a relatively course mesh. Furthermore, edges of the covering layer which end in the region between two screen webs are supported by the support with the result that they can be relatively projecting. The covering layers produced in this way allow the printing patterns to be modeled better, which leads to a higher-grade quality print.
All of the common screens can be used for forming stencils such as plastic screens, screens made of wire fabric or screens produced by electroplating, nickel screens, and the like. After the application of the covering layer to the screen, the support is removed once more from them, so that the finished screen-printing stencil is present. In this case, care must be taken that the material used for forming the covering layer does not adhere too strongly to the support or does not adhere at all in order to avoid damage to the applied covering layer when separating the screen and support. In this case, a material which only has a low affinity with the material of the support is selected for the covering layer.
According to one embodiment of the invention, the separation of screen and support is effected after risk of damaging the covering layer when removing the support from the screen is thus reduced. In this case, the type of solidification of the covering layer is effected according to the material used f or forming the covering layer.
The material for forming the covering layer can be, for example, a viscid liquid, for example an aqueous emulsion of a synthetic resin lacquer, an aqueous suspension of pigment or wax. However, molten metal or a molten metal alloy, for example Wood's metal, is also considered as the liquid substance for forming the covering layer. Wood's metal has a relatively low melting point and can therefore be used in particular in the case of metallic screens. The use of paints or the use of ink for forming the covering layers is also possible.
The solidification of these materials is dependent on the type of composition of the materials. If a polymerizable lacquer is employed then the latter may be cured or cross-linked by heating and/or exposing using radiation of suitable wavelength. In the case of paints or inks or in the case of wax, the covering layer only needs to be heated. Metals or metal alloys can be solidified by cooling. Annealing steps could follow this if appropriate.
In another embodiment of the invention, the covering layer may be sprayed on to the screen. This also applied to specific metals or metal alloys (Wood's metal). However, the spreading of appropriate materials onto the screen for forming the covering layer is also possible. However, the latter can also be applied to the screen by a transfer-printing method such as using liquid plastics, lacquers, paints and inks. Last but not least, the covering layer may also be applied to the screen by a doctoring or dipping method, if specific regions of the screen have previously been treated in such a way that no covering material remains adhering to them. Before carrying out the doctoring or dipping method, these regions could be greased.
The screens used can quite generally be flat screens, cylindrical screens or screens of any other arbitrary shape. What is important is only that they may be closed on the rear side by the support. For the purpose of coating with the covering layer, a flat shape, for example into a cylindrical shape, by being placed onto the circumferential surface of a cylinder and then treated.
Rigid orelastic supports are used as the support, which for example can also be pressed against the rear side of the screen. In the case of a screen cylinder, the support may be an expandable hollow body, which is arranged in the interior of the screen cylinder and may be pressed by expansion against the inner circumferential surface of the screen cylinder. After the covering layer has been applied, the hollow body is evacuated once more, as a result of which it is detached from the screen cylinder.
The material for the support can be selected in accordance with the material of the screen and that of the covering layer. Thus, for example, a support may comprise metal, rubber, unvulcanized rubber, plastic and the like. Natural materials, such as wood, stone, glass, etc. are also possible. Certain materials are ruled out, however, if the support has to be elastic.
A device according to the invention for producing a printing stencil has at least the following: a bearing device for the rotatable mounting of a hollow cylinder about its longitudinal axis; a coating device for the application of a covering layer to the outer circumferential surface of the hollow cylinder, as defined by a pattern; and an elastic hollow body, which can be pressed by expansion against the inner circumferential surface of the hollow cylinder.
When using a device of this type, it is possible to coat not only screens with a covering layer in accordance with the method of the present invention, but also hollow cylinders which have a closed circumferential surface. These may be, for example, flexographic printing forms, which have a continuous photoelastomer layer on their outer circumferential surface. This can be covered as defined by a pattern, in order subsequently to be exposed. However, a hollow cylinder may also be metallic cylinder, which is covered with an insulating layer, as defined by a pattern, in order subsequently to apply a metal screen to it by way of electroplating. Other hollow cylinders can also be coated as defined by a pattern, for example screen cylinders closed by a continuous lacquer layer, the lacquer layer being photosensitive. After coating, the cylinder is exposed in order to expose screen openings, as defined by a pattern, by means of a subsequent development operation.
According to another embodiment of the invention, the hollow body may be designed as a tube that can be inflated in the radial direction of the hollow cylinder. The hollow body is placed from the inside against the wall of the hollow cylinder and thus stabilizes the concentric running of the hollow cylinder. If the hollow cylinder is a scre
Birch & Stewart Kolasch & Birch, LLP
Schablonentechnik Kufstein Aktiengesellschaft
Yan Ren
LandOfFree
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