Screen printing processes are known in which, for using thermoplastic printing inks, a chrome-nickel steel screen is used which is electrically heated by joining its opposite sides to a current supply. For functioning, such steel screens have to be insulated at the positions where they are supported and fixed in position, this being done by having an insulating material, such as rubber or plastics, between the frame and the screen, this making for a complex screen fixing system designed for pulling the screen tight on the one hand and at the same time stopping any danger of electric shocks. For this reason it is normal for non-conducting lengths of fabric to be stitched on to the two sides of the edges of the steel screen and these strips are then fixed to the frame mechanically with or without a system for pulling the screen tight on later use, while the two other opposite sides of the steel screen or fabric are loosely rested or guided over insulating bridges on the frame and run to points on which they are joined with an electrically insulated system for pulling the screen tight. A screen fixing system, with which the screen may be pulled tight later as desired, is better, because, when the screen is heated, it becomes extended, that is to say less tight. In a simple system the metal screen is directly fixed to a wood frame. However screens have been bedded or seated in thermosetting (that is to say not thermoplastic) synthetic resin screen frames. No suggestion has been made so far for using adhesives without a mechanical join at the same time, because adhesives are generally thermoplastic and the heated screen would, it would seem, then become loose.
USPTO Backgrounds
USPTO Backgrounds