| 摘要 |
1,157,688. Electrostatic screen printing. MONSANTO CO. 19 July, 1966 [19 July, 1965], No. 32319/66. Heading B6C. Articles having surfaces formed by rotation of a planar line about an axis are printed by means of a patterned screen between which and the article an electrostatic field is set up, electroscopic powder ink being fed to the screen, and the article and screen being rotated or oscillated in unison so that the surfaces of the screen and article approach one another tangentially and so that printing occurs along the line where the surfaces are closest to one another. In one embodiment, Fig. 7, a conical container 53 to be printed is mounted on a mandrel 51 and a conical screen 54 is mounted on a shaft 60 for oscillation or rotation in unison. At the line where the surfaces of the screen and article are closest to one another, a roller 69 covered with mohair pile fabric supplies ink particles to the screen, and an electric field is set up between the roller and the mandrel so that the ink particles pass through the screen on to the article. The ink particles are supplied to the roller 69 from a hopper 62 by an intermediate roller 65. A shield 73 of plate glass and having a gap along the printing line may be provided between the screen and the article. There may be a small gap between the screen and the article at the printing line or light contact may occur. A flat reciprocating screen may be used for printing on cylindrical or conical articles mounted on an oscillating mandrel. Arcuate screens oscillating about an axis may be employed and arrangements are described for using such screens for printing on cylindrical, conical and hyperboloid articles, and in the latter case, the screen is suitably shaped to be a counterpart of the article surface, and the article is supported on an expanding mandrel. Another apparatus for supplying ink particles to the screen 24, Fig. 4, comprises a trough 21 vibrated electrically and having a feed plate 22 at its lower end and a hopper 13 at its upper end. Heavy spring wires 19 attached to an adjustable plate 17 terminate near the wall 14 of the hopper 13 to provide a feed slot 20. The wires 19 are connected to a high voltage source to provide a corona discharge so that the ink particles passing the wires are triboelectrically charged. As shown in Fig. 3, ink particles are carried from a hopper 28 into a space 31 by a roller 30 having a surface of a relatively thick brush-like material. Air-pressure means carry the particles from the space 31 to a tube 33 feeding the particles to the screen 36. A metallic shield, or corona discharge wires, may charge the particles in their passage through the tube 33 An endless band 47, Fig. 6 (not shown), of relatively thick pile fabric may be used to feed ink particles to the screen, and a trough similar to that shown in Fig. 4 may be employed to supply particles to the band.
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