Fabric (woven – knitted – or nonwoven textile or cloth – etc.) – Woven fabric – Including a free metal or alloy constituent
Reexamination Certificate
1999-03-12
2001-09-04
Wong, Edna (Department: 1741)
Fabric (woven, knitted, or nonwoven textile or cloth, etc.)
Woven fabric
Including a free metal or alloy constituent
C442S131000, C442S232000, C205S150000, C205S159000, C205S165000, C174S034000
Reexamination Certificate
active
06284679
ABSTRACT:
The invention concerns a process for the production of a cloth web, in particular for use as a screen printing form comprising a non-metallic cloth which is provided with a casing layer and then galvanically coated with a metal coating. The invention also concerns a cloth comprising mutually crossing strands, in particular a screen printing cloth produced by that process.
Centuries after it was first used in China the screen printing process has been known in Europe approximately since the
19
th 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 operation of drying the stencil, a retouching operation is effected, and the edges are covered over with screen filler.
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.
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, using 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 produced for use as a screen printing stencil from a textile cloth, the cloth 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 layer of 1 to 2 &mgr;m as a conductive intermediate layer and a nickel layer of 25 &mgr;m is applied thereto by galvanization.
Finally DE 32 43 190 A1 is concerned with a continuous process for the production of metallized textile flat structures which are coated with an electrically conductive metal layer and then galvanically reinforced. The first metal layer can be applied by means of a wet-chemical, current-less process or by vapor deposition. The result obtained is a metallized, textile surface structure with still textile properties. Gluing of the mesh intersections is undesirable.
In consideration of that state of the art, the inventor set himself the aim of so improving the process as set forth in the opening part of this specification that, while avoiding the known disadvantages, operationally reliable cloth webs are produced inexpensively, in particular for use in screen printing, under a high loading they result in a substantially lesser degree of stretch in comparison with the state of the art, and they can no longer be displaced or deformed. The invention seeks to provide that expensive metal cloths can be replaced by metallized plastic cloths of corresponding properties.
That object is attained by the teachings of the independent claims; the appendant claims set forth advantageous developments.
In accordance with the invention a plastic cloth is prepared from both sides thereof in a multiple procedure by vapor deposition or so-called sputtering—using cathodic atomisation—for the galvanization operation, that is to say it is provided with a metallic casing layer of a surface resistance of 0.2 ohm/2 to 200 ohm/2 and is then galvanically coated.
Finally, such a preparation procedure by means of vacuum plasma spraying is also in accordance with the invention.
In accordance with the invention all vapor deposition materials can be freely selected and are to be matched to the subsequent galvanization procedure. However nickel in particular is preferred because of its chemical resistance; other substances which are advantageously used here are gold, silver, copper, steel or a light metal—in particular aluminum—alone or as an alloy.
The vapor deposition, sputtering process or spray process is to be implemented on both sides, and it can also be repeated a plurality of times. In that respect, layer thicknesses of about 5 to over 200 nanometers—in particular over 50 nm—, are produced.
Electrical conductivity of the cloth is afforded by the dry process step of vapor deposition, cathode sputtering as mentioned above or vacuum plasma spraying.
The mechanical properties of the metallized cloth are primarily determined by the galvanization operation; stretching is strikingly reduced, with an increased level of strength of the cloth, and—irrespective of the nature of the initial cloths—the resistance to slip of the cloth is increased to an extraordinary degree. The metallizing substances contribute in particular to the strength at the bonding locations of the cloth of plastic base materials and form a conductive surface. It thus becomes possible to replace expensive metallic cloths by metallized plastic cloths with similar properties.
Therefore, the basis used for the screen printing form which is produced in a finished condition and which is provided with a coating is a metallized plastic cloth, preferably with a metal coating of nickel because of its general strength. The metallic surface of the screen printing plate reduces the wear of the stencil, whereby it is possible to achieve very high numbers of print copies with the latter. The conductive surface of the screen printing plate prevents static charging phenomena. Limitations in regard to materials to be printed or inks, due to problems with static, can be practically eliminated.
The metallized plastic cloth according to the invention guarantees very minimal stretch phenomena with an adequate level of basic strength and provides that there are scarcely measurable register differences on the stencil, irrespective of the set clamping tension.
The fact that the limitedly flexible metallized cloth is coated over its full surface area provides for a high, reproducible stencil quality with excellent edge sharpness and accurate ink metering. A protective foil which is applied if necessary reduces improper manipulation operations which could cause impairment of the quality of coating. As the coating is effected on the endless roll of cloth, there is no need for covering operations, as are the conventional practice at the present time.
To sum up, the advantages achieved are as follows:
the metal vapor deposition operation, the sputtering operation or the vacuum plasma spraying operation on cloths—in particular plastic cloths—is effected inexpensively and continuously and provides a conductive c
Gmür Hugo
Lehner Martin
Schilling Christian
Bachman & LaPointe P.C.
Sefar AG
Wong Edna
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