Stencil printing

Stencil printing apparatus especially useful for printing on a curved or irregular underlying surface is described. It features a peripheral, elastically compressible and deformable stencil supporting wall and a flexible stencil screen having its outer peripheral edge sealingly mounted on the supporting wall, the stencil screen being deformable into continuous contact with the underlying surface with the supporting wall elastically compressed thereby for extrusion of printing fluid through the stencil screen onto the underlying surface to be printed.

This invention relates to stencil printing apparatus, and more particularly 
to such apparatus capable of printing on a curved or irregular underlying 
surface. 
In Tripp, U.S. Pat. No. 3,372,638, there is shown and described stencil 
printing apparatus especially useful for printing on plastic containers, 
such as those used in the dairy field and other segments of the food 
industry, consumer information such as the last date of sale. Although the 
apparatus disclosed in that patent has been successfully commercialized, 
its use is limited to printing the consumer codes on the vertical sides of 
the bottles. This has proved to be a disadvantage, since the printed codes 
cannot be viewed from above and so are frequently blocked from view when 
the bottles are stored in a dairy case. 
Furthermore, the apparatus of that patent required the use of a vacuum 
source for holding the stencil against the surface to be printed and such 
a source was not always readily available and was also expensive. 
It is a major object of the present invention to provide novel stencil 
printing apparatus capable of printing on a curved or irregular surface, 
particularly on the rounded shoulders of plastic bottles so that the code 
can be seen from above when the bottles are stacked in a conventional 
store diary case. 
It is another object of the present invention to provide novel stencil 
printing apparatus which does not require a source of vacuum. 
Accordingly, the present invention provides a novel stencil printing 
apparatus adapted for printing on a curved or irregular underlying 
surface, comprising a rigid member, elastically compressible and 
deformable supporting wall means mounted on one end of the rigid member 
and extending axially therebeyond, and a flexible stencil screen having 
its outer peripheral edge sealingly mounted on the outer edge of the 
supporting wall means and extending thereacross, the stencil screen being 
deformable into continuous contact with the underlying surface and with 
the supporting wall means being elastically compressed thereby for 
extrusion of printing fluid through the stencil screen onto the underlying 
surface to be printed. 
In preferred embodiments of the present invention, the rigid member has 
side wall means providing a chamber for enclosing a quantity of printing 
fluid and the supporting wall means provides an axial extension of the 
chamber side wall means, the outer edge of the supporting wall means being 
normally generally perpendicular to the side wall means of the chamber, 
with the flexible stencil screen normally generally perpendicular to the 
side wall means of the chamber to form an end wall of the chamber. 
Preferably, piston means are mounted in the chamber adjacent the other end 
of the housing member for transmitting pressure to the printing fluid to 
extrude the printing fluid through the stencil screen onto the underlying 
surface when the stencil screen is in contact with the surface to be 
printed.

Referring to the drawings, in general, the stencil printing apparatus of 
the invention includes a cylindrical rigid housing member, generally 
designated 12, an elastically compressible and deformable wall, generally 
designated 14, mounted on one end of housing member 12 and a flexible 
stencil screen, generally designated 16, mounted on the outer edge of wall 
14. 
More specifically, cylindrical rigid housing member 12 has side wall 18 
which provides a chamber 20 for enclosing a quantity of printing fluid. 
The elastically compressible and deformable wall 14 is mounted on one end 
of housing member 12 and extends around the housing member and axially 
beyond its side wall 18 providing an extension of chamber 20. The outer 
edge 22 of deformable wall 14 is normally generally perpendicular to side 
wall 18 of chamber 20. Deformable wall 14 is frusto-conical with its 
smaller diameter end mounted on housing member 12 and the other end 
flaring outwardly therebeyond. A revised flare or a bellows configuration 
could be used as well. 
The flexible stencil screen 16 has its outer peripheral edge sealingly 
mounted on outer edge 22 of the deformable wall 14. The flexible stencil 
screen extends across deformable wall 14 and is normally generally 
perpendicular to side wall 18 of chamber 20 in forming an end wall of 
chamber 20. Flexible stencil screen 16, including its outer peripheral 
edge, is deformable into continuous contact with an underlying surface 
when the deformable wall 14 is elastically compressed onto the underlying 
surface. 
A piston 24 is mounted in chamber 20 adjacent the other end of housing 
member 12 for transmitting pressure to a printing fluid therewithin to 
extrude it through flexible stencil screen 16 onto the underlying surface 
when flexible stencil screen 16 is in contact with the underlying surface 
to be printed. A cap 25 secures the deformable wall 14 along with its 
flexible stencil screen 16 onto the housing member 12. 
Referring to FIG. 1, housing member 12 is mounted on frame 26 which in turn 
is mounted on ink pressure cylinder 28 and print cylinder 30. Ink pressure 
cylinder 28 transmits pressure to piston 24 for extruding through stencil 
screen 16 the printing fluid contained in chamber 20. Print cylinder 30 is 
mounted on machine frame 32. 
A controller 34 is provided for actuating the ink pressure cylinder 28 and 
the print cylinder 30. Controller 34 communicates with a bottle sensor 36, 
the print cylinder 30 and the ink pressure cylinder 28. 
In operation, referring to FIG. 1, a plastic milk bottle B is moved into 
position to be printed and its presence is detected by bottle sensor 36. A 
signal is then transmitted to controller 34, which then transmits signals 
to actuate the ink pressure cylinder 28 and the print cylinder 30. 
Print cylinder 30 then moves frame 26 into printing position, deforming 
both deformable wall 14 and the flexible stencil screen 16 so that the 
latter is in contact with the rounded shoulder of milk bottle B, as shown 
in dotted lines in FIG. 1. Controller 34 then transmits a signal to the 
ink pressure cylinder 28, which depresses piston 24. The pressure exerted 
by piston 24 extrudes the printing fluid contained in chamber 20 through 
the flexible stencil screen 16, and the image on the stencil screen is 
transferred onto the surface of the rounded milk bottle shoulder. Print 
cylinder 30 is then retracted and the printed bottle removed, in readiness 
for a succeeding printing cycle.