Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Reexamination Certificate
1999-03-12
2001-07-10
Cole, Elizabeth M. (Department: 1771)
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
C442S006000, C442S007000, C442S015000, C442S016000, C442S052000, C428S216000
Reexamination Certificate
active
06258445
ABSTRACT:
The invention concerns a printing apparatus with a flexible screen printing form comprising plastic cloth in a printing frame as set forth in the classifying portion of claim
1
. The invention also concerns a screen printing form with screen printing cloth comprising mutually crossing plastic yarns as a carrier for a coating comprising an—in particular photosensitive—emulsion, as set forth in the classifying portion of claim
1
.
U.S. Pat. No. 5,111,743 describes a printing apparatus with a flexible screen printing plate comprising a textile-like cloth which is made from silk, nylon, polyester or the like yarns or however from stainless steel wires. Metal plates with a hole system etched therein are also mentioned. That screen printing plate is clamped at two parallel edge regions into a printing frame, between which a rubber scrubber can be reciprocated for applying ink.
The one edge of the plate is fixed with screws which engage through one side of the frame, while the opposite edge of the plate can be displaced by means of a frame member which is fixed thereto and which is mounted with play in the printing frame; for that purpose, provided on the displaceable frame member is a central bar which with its outwardly facing free end engages through the adjacent side of the frame, against the outside surface of which it bears by means of coil spring.
Centuries after it was first used in China the screen printing process has been known in Europe approximately since the 19th Century; a fine-mesh textile cloth or wire mesh material is stretched out in a screen printing frame and covered at the image-free regions so as to be impermeable to ink. Besides manual cut stencils—for example for labelling or writing—nowadays preferably photographically produced direct or indirect stencils are the usual practice; the choice of the kind of stencil adopted—in the case of direct stencils those with emulsion, with direct film and emulsion or with direct film and water—is left to the discretion of the screen printer.
A plurality of steps are usually required to produce a screen printing form. Firstly a screen printing cloth is stretched out over a clamping frame of light metal or alloy, wood or the like, and is glued to the frame in its stretched position. Cleaning of the cloth permits the subsequent application of a photosensitive emulsion, for example using a coating channel manually or by machine with an automatic coating apparatus. As the coating thereon cannot be produced exactly as far as the inward side of the frame, the remaining surface area must be subsequently sealed off using screen filler. The coated surface is now exposed by means of a copy original (film) corresponding to the print image. The regions of the print image which are not exposed are washed out.
After the washing-out operation, what is produced is the actual screen printing stencil, the edge zones of which often still have to be covered over. When those covering portions are also dried, printing can be effected with the stencil. In addition the individual items of equipment which are used for the respective stencil production steps have to be cleaned. Thus the amount of work involved in the production of a screen printing stencil and in particular an individual stencil is relatively great.
For certain areas of use, it is known, when dealing with plastic meshes, to settle palladium nuclei or seeds on the surface by a chemical treatment of the surface, and to metallise the filaments. Those chemical treatment procedures involve a plurality of stages and are to be matched in terms of their compositions and operating procedures to the respective plastic material involved. Limitations in regard to the choice of material are predetermined on the basis of poor or unsuitable materials. The known expensive preliminary treatments can be followed by expensive chemical metal deposition processes; because of its inadequate conductivity, the pre-treated plastic cloth surface cannot be directly covered with a galvanic metal deposit.
A further aspect is that the stencil carriers which are used nowadays in screen printing, prior to mounting of the actual stencil, have to be braced and glued on a frame on all sides. In that respect the quality of the printing is dependent on the correct cloth tension, relaxation of the cloth, the adjusted deflection effect, the squeegee pressure or the like factors. So that the adjusted deflection effect as between the cloth and the object being printed upon can be overcome, stretching of the stencil is necessary. In the case of stencil carriers without natural stretch or with only a very low degree of natural stretch, that results in high alternating tensile loadings which can result in the stencil carriers suffering from rapid fatigue effects or possibly can result in destruction thereof.
As printing can satisfactorily occur with those low-stretch stencil carriers in a flat screen printing process, a printing or clamping frame is necessary which is capable of compensating for the variations in length caused by the deflection effect.
U.S. Pat. No. 3,303,777 describes a holding arrangement for a stencil on a screen printing machine, in which it is to be fixed and tensioned at two parallel regions—which cross the direction of movement of a displaceable squeegee which presses the printing inks through screen meshes.
In consideration of those factors the inventor set himself the aim of considerably simplifying manufacture and handling of screen printing forms or stencils, making the use thereof in printing mechanisms more operator-friendly and increasing their register accuracy—even with high numbers of print runs. In addition the inventions seeks to provide that the print quality is optimised in the case of fine lines and patterns by homogenous coating, with a constant structure.
In regard to the printing or clamping frame, the invention seeks to make it possible to use stencil carriers without natural stretch while seeking to eliminate the changes in length caused by the above-mentioned deflection effect—and therewith changes in tension of the stencil. Minimum stencil tightening tensions are intended to permit minimum squeegee pressures, which results in a reduced amount of wear of the stencil and the squeegee. Tightening the screen printing stencil in only one direction permits a constant specific squeegee pressure over the printing width.
In accordance with the invention the plastic threads or yarns are coated with a casing layer which is produced thereon by vapour deposition and which in turn is covered over by a metal coating which carries the emulsion and which is produced by galvanisation. In accordance with another feature of the invention the plastic cloth can also be prepared for the galvanisation operation by so-called sputtering or cathode sputtering with the casing layer.
As misprinting can definitely occur with those low-stretch stencil carriers in a flat screen printing process, a printing or clamping frame is necessary which is capable of compensating for the variations in length caused by the deflection effect.
U.S. Pat. No. 3,303,777 describes a holding arrangement for a stencil on a screen printing machine, in which it is to be fixed and tensioned at two parallel regions—which cross the direction of movement of a displaceable squeegee which presses the printing inks through screen meshes.
U.S. Pat. No. 1,934,643 dating from the year 1930 describes a cloth of electrically conductive material, the surface of which is provided with a non-metallic cover layer or a cover layer of pure metal or an alloy, in particular with nickel or chromium, by spraying, plating or a chemical or galvanic process.
U.S. Pat. No. 4,042,466 discloses a process for the production of a cloth web which is made from a textile cloth for use as a screen printing stencil, the web being provided with a metallic cover layer. For that purpose the plastic yarns are coated with a thin metal layer of for example copper of a thickness of 1 to 2 &mgr;m as a conductive intermediate layer and a nickel layer of 25 &mgr;m is applie
Baumann Horst
Lehner Martin
Schilling Christian
Bachman & LaPointe P.C.
Cole Elizabeth M.
Ruddock Ula
Sefar AG
LandOfFree
Screen printing form and flexible screen printing form... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Screen printing form and flexible screen printing form..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Screen printing form and flexible screen printing form... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2551133