Patent GB-644474-A (GB)
Title: Improvements in or relating to screen printing apparatus
Inventor: WHEELWRIGHT JOHN SYLVESTER
IPC: B41F15/08
Filed: 1948-01-27
Abstract: 644,474. Stencilling-apparatus. WHEELWRIGHT & CO., Ltd., J. Jan. 27, 1948, No. 2468. [Classes 100 (i) and 100 (ii)] In a screen printing apparatus, the web of paper or textile material 1, Fig. 1, to be printed is advanced stepwise over a printing bed 14 and downwardly through a transverse slot 15 therein, the screen being so positioned that one edge of the pattern thereon coincides with the edge of the slot nearest the end of the bed whence the web is fed. The slot 15 may be formed by the provision of the bed 14 in two sections, one section being adjustably mounted to determine the width of the slot. The web passes over a roller 5 at the rear end of the table 6 supporting the bed, and under a tensioning device consisting of a suitably loaded felt pad 11a carried on a pivoted arm 12, and after passing through the slot it is supported by a roller 24. The screen frame 16 is pivoted at its end near the slot, and is mounted so that during printing its transverse member at that end is supported on the bed to the left of the slot, and is longitudinally adjustable to register the pattern with the slot, or the screen may be adjustably mounted in the frame. The frame 16 has at its right-hand edge a spring-pressed gripping member to hold the web against the bed during printing. The squeegee blades comprises a continuous strip of rubber 17, Fig. 2, in the form of a substantially rectangular trough open at top and bottom to contain a liquid printing medium, the strip 17 being held in rigid parallel channels 19 secured together by curved connecting parts 20, and during printing the leading blade trails rearwardly to retain the liquid, while the other blade is supported by an adjustable bar 18 to assume a suitable printing angle. The rigid squeegee frame 22 has rollers 23 running in rails on the frame 16, which rails are upwardly inclined at their ends to cause the blades to relax tension on while remaining in contact with the screen at either end of the travel of the frame 22. The web is dried while passing from the roller 24 to a take-up roll 29. Where textile fabric is to be printed, an endless band or belt of backing cloth may be provided to which the web is caused to adhere, a carding roller adjacent a roller 25 stripping the web from the backing, which is then passed through a cleaning zone comprising scrubbers or brushes in a trough containing a detergent solution before passing back to the feed end of the bed 14. Feeding webs.-The web 1 is fed from a roll 2 between a driven roller 4 and an idle roller 3 to the roller 5, and from the roller 24 to the roll 29 over rollers 25, 27, 28. A loop 8 is kept at a predetermined length by a roller 9 carried on pivoted arms 10,.and a loop between 27, 28 is tensioned by a weight-loaded roller 26. A slider vertically movable on guides 32 comprises a flat surface 31 and brake-shoe type grippers 33 on either side thereof to grip the edges of the web against the surface 31. The travel of the slider is limited by adjustable stops to the length of one pattern unit on the web. When the frame 16 is raised sufficiently to separate the screen from the web, it actuates a switch to cause a motor to rotate a crank 34 through one revolution to lower and raise the slider, a cam on the crank spindle actuating the grippers 33 to grip the web only on the downward stroke. During the feed of the web by the slider the loop 8 is shortened, and on lowering of the frame 16 a switch is actuated to cause a motor to drive the roller 4, and when the loop 8 regains its predetermined length, the arm 10 operates a switch to stop the roller 4. The length of web advanced by the slider is taken up by the roller 26, and on lowering of the screen, a motor driving the roll 29 is switched on to take up the length and draw down the roller 26, the roller 29 being stopped by a switch operated by the weight loading the roller 26. Alternatively, the frame 16 and crank 34 may be linked, whereby manually raising the frame actuates the slider.