Traditionally, printing screens have been mounted in large rectangular frames by a flexible, perforate sheet, typically a woven mesh of polypropylene or stainless steel strands, which acts to tension the printing screen.
Whilst the above-described mounting system has been well used, the mounting system does exhibit a number of drawbacks, notably in not allowing the printing screen to be detached from the frame without permanently damaging the perforate sheet, which requires the printing screens to be maintained in the mounted state, and thus requires a large storage facility for storing a large number of mounted printing screens.
More recently, as disclosed in WO-A-1997/003833, a mounting system has been developed which enables the printing screen to be demounted after use, and thus enables the use of a single frame with a large number of printing screens, thereby obviating the problem of the earlier mounting system regarding storage. In this mounting system, the printing screen, which comprises a thin, stiff metal sheet, typically of stainless steel, includes a plurality of fixing apertures at the opposite edges thereof by which the printing screen is mounted to a frame by mechanical tensioning mechanisms which engage the fixing apertures in the printing screen and act to tension the printing screen, with the tensioning force typically being provided by hydraulic, pneumatic or spring means.
Whilst the above-described mounting system has also been well used, this mounting system does suffer from a number of drawbacks. In particular, as the printing screens are very thin, typically having a thickness of from 0.1 to 0.25 mm, the edges thereof are razor sharp, which can lead to personal injury to a user if not handled with the utmost care.
Still more recently, as disclosed in WO-A-2003/093012 and illustrated in FIGS. 1 to 3, a mounting system has been developed which enables a printing screen to be demounted after use, and also, in utilizing an attachment frame, typically in the form of extrusions, shields the edges of the printing screen and thus prevents the possibility of personal injury to a user as could be caused by the sharp edges of a printing screen.
The above-described mounting system has been widely accepted. However, this mounting system does suffer from the drawback of requiring the edges of the printing screen to be cut and formed, typically by bending, to allow for the fitting of the attachment frame. Such cutting and forming adds both to the time and the cost in fabricating the resulting printing screen units.
USPTO Backgrounds
USPTO Backgrounds