Printing – Stenciling – Stencils
Patent
1991-07-26
1995-10-10
Burr, Edgar S.
Printing
Stenciling
Stencils
101128, 1011281, B05C 1704
Patent
active
054561736
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a device for fixing end rings in the ends of a rotary screen printing stencil, in which means are present for positioning the stencil and the end rings relative to each other, thus forming an assembly thereof, and heating means to make adhesive, which can be applied to the adhesive edge of each of the end rings for the formation of a connection between a stencil and an end ring, form said connection through adhesion.
BACKGROUND OF THE INVENTION
Such a device is known and is used for fixing end rings in a rotary screen printing stencil. A rotary screen printing stencil is generally a seamless, metal perforated cylinder, for example of electrodeposited nickel which is covered pattern-wise with a lacquer, and in which the parts not covered correspond to the pattern which is required to be printed on a substrate, for example textiles. In order to print such a pattern, the rotary screen printing stencil is brought rotating into contact with a substrate to be provided with a pattern, while the peripheral speed of the stencil and the speed of movement of the substrate are essentially the same. Inside the stencil a printing paste is fed in and is pressed by means of a fixed squeegee through the perforations of the stencil and thus arrives on the substrate. For the fixing of a rotary screen printing stencil in a printing machine, the stencil has fixed in it so-called end rings which at one side have an adhesive edge which is connected by gluing to the inside of the stencil and at the other side have a clamping edge or bayonet edge which is connected to stencil fixing heads which are located on the machine and grip the stencil at the two ends, and which exert tensile force in the lengthwise direction of the stencil. The stencil sheads fixed on the printing machine are driven by means of the machine drive, and in these ways the stencil can be given a speed of rotation in which the peripheral speed is essentially the same as the speed of movement of the substrate. The commonly used end rings are made of aluminium injection mouldings and are used on a wide scale.
During operation of the known device described above the end rings used and the inside edge of the stencil are provided with a coating of adhesive and subsequently positioned relative to the stencil and pushed from that position to a position in which the adhesive edge present on the end rings falls within the periphery on the two ends of the stencil in question. A heating element is then placed inside the end rings in contact with the material of said end rings. The heat produced by the heating elements is conveyed by convection to the border area between the adhesive edge and the stencil where there is a quantity of adhesive which under the influence of heat can produce a connection between the stencil and an end ring by gelling and/or polymerization of the adhesive. Such an adhesive is often a thermosetting adhesive such as a thermosetting epoxy resin system. Such a heating possibility was considered necessary in the known devices on account of the relatively great heat sensitivity of, for example, the nickel material of such rotary screen printing stencils. Heating of such a material above, for example, 250.degree. C. for certain types of stencil produced the risk of an embrittlement of the nickel material, which had a very adverse effect on the service life of the stencil material in question. By introducing the heat in a controlled manner via the end ring which had a relatively great mass, it was possible to make sure that a temperature below 250.degree. was maintained.
Such heating of an adhesive by introducing heat through convection via the end ring cannot, however, be carried out with the use of, for example, plastic end rings. In such cases use was generally made of so-called cold-setting adhesives such as, for example, cold-setting epoxy resin/hardener systems. However, such cold-setting adhesive systems have the disadvantage that they are not resistant to certain solvent systems or chemicals foun
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Burr Edgar S.
Hilten John S.
Stork Screens B.V.
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