Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Coating selected area
Patent
1996-09-20
1999-10-26
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Coating selected area
205122, B41C 308
Patent
active
059721944
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing a base mold for electrolytically producing seamless rotary screen printing stencils, in particular of nickel, wherein a metallic mold base member with a cylindrical generated surface is provided at the outer circumference thereof with depressions distributed in a regular grid with the depressions having a round or polygonal contour and in-between grid webs forming a regular net, and wherein subsequently the depressions are filled flush to the height of the grid webs with an electrically non-conductive filling compound, whereafter repeatedly screen printing stencils may be generated by electrolytically coating with metal and axially removing the sleeve thus produced.
In practical experience base molds for the purpose mentioned hitherto have been produced by a roll embossing method. Therein the desired grid of depressions is pressed into the generated surface of the mold base member by a grooved roller. The grooved roller is a relatively small roller being rolled at the circumference of the mold base member along a helix under strong pressure. The grooved roller at the generated surface thereof carries projections in form of the desired grid which produce a negative image of the desired depressions for the mold base.
Disadvantages of the roll embossing method are that it involves lengthy process times, requires high tooling effort and must be performed by highly skilled operators to produce acceptable methods. In particular, it is very difficult, and in fact only possible for an operator with extensive experience, to roll the grooved roller at the generated surface of the mold base member such, that the helix extending along the generated surface of the mold base member as seen in longitudinal and circumferential direction of the mold base member has no offset in the grid image. Furthermore the production of grooved rollers is very costly as extensive steps in mechanical machining are necessary. Each change in the grid requires the production of an adapted grooved roller. A further disadvantage is such, that the material for the mold base member must be relatively soft to enable the desired pressing or rolling of the depressions by the grooved roller. Therefore for practical reasons only copper has been used for mold base members which is provided with a thin chroming at the surface thereof. For raising the stability which is necessary for rolling the grooved roller under high pressure the mold base member furthermore has to have a sturdy steel core which makes the mold base member as such very heavy and therefore difficult to handle and to transport.
The depressions generated by roll embossing may only have the shape of truncated pyramids or cones with relatively flat inclined flanks. This leads to the disadvantage, that the electrically non-conductive filling compounds situated in the depressions are very thin at the edges of the depressions and may break. During the later electrolytical coating of metal on the mold base for shaping the screen printing stencil this may lead to a damage of the surface of the mold base by metal tappets protruding inwardly from the stencil when removing the electrolytically finished stencil with the tappets resulting from broken areas of the filling compound. Since furthermore, the mold base consists of relatively soft copper, in contrast to e.g., nickel as a relatively hard and preferred material for screen printing stencils marks may be produced in the longitudinal direction of the mold base in spite of the chroming however, which is relatively thin, with the marks leading to relatively few production operations with the base mold for producing screen printing stencils.
Processes other than the mechanical roll embossing method for producing base molds for use in forming screen printing stencils are disclosed in EP 0 030 774 A1. As a first known process for producing a mold base member it is disclosed, that the depressions which are to be filled with non-conductive material are generated by etching. It is not disclosed in the
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Saueressig Karl-Wilhelm
Schepers Hans-Georg
Gorgos Kathryn
Smith-Hicks Erica
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