Printing – Stenciling – Traveling-inker machines
Reexamination Certificate
2001-12-20
2004-02-03
Yan, Ren (Department: 2854)
Printing
Stenciling
Traveling-inker machines
C101S120000
Reexamination Certificate
active
06684766
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wiper blades for screen printing, and has particular, though not exclusive, application to screen printing apparatus of the kind disclosed in WO-98/16387 which applies a pasty product to a printing screen by applied pressure.
BACKGROUND OF THE INVENTION
WO-98/16387 discloses a screen printing apparatus for screen printing a pasty product onto a workpiece. As illustrated in
FIG. 7
, this screen printing apparatus comprises a printing head
100
which is moveable bi-directionally over a printing screen
101
, as indicated by arrows A and B. The printing head
100
comprises a main body
102
, first and second wiper blades
103
, which contact the printing screen
101
and together with the main body
102
define a chamber
104
containing a pasty product
105
, a grille
106
located at the lower end of the main body
102
, and a piston
107
for applying a downward pressure on the pasty product
105
. In use, the printing head
100
is moved in one of the two opposite printing directions which causes the wiper blades
103
, which are pressed against the printing screen
101
by the force imparted on the pasty product
105
by the piston
107
, to act to lift the pasty product
105
from the region above the printing screen
101
, as illustrated by the curved arrows, causing the pasty product
105
to pass upwardly through the grille
106
, which pasty product is subsequently forced back downwardly through the grille
106
by the action of the pressure developed by the piston
107
. This working of the pasty product
105
confers the pasty product
105
with rheological qualities suitable for its application, and is particularly important when the pasty product
105
is a mixture of particles of different densities, such as for example solder paste which comprises balls of metal in a flux paste.
It is important to restrict the thickness of the wiper blades so as not to be unduly stiff and allow the same to be pressed downwardly by the pressure applied to the pasty product such that the free edges of the wiper blades can conform to the surface of the printing screen so as to ensure good shearing of the pasty material over the stencil apertures and good gasketting of the printing screen to an underlying workpiece being screen printed, thereby to prevent pasty product bleeding out and giving a smeared print.
It is also important that the wiper blades can conform to sealing members provided at the ends of the main body to prevent any leakage of pasty product onto the stencil.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a wiper blade for a screen printing head in which pasty product to be screen printed is biased towards a printing screen under pressure, the wiper blade comprising an elongate blade element having a thickness of between 0.1 and 0.5 mm, one edge of the blade element being configured to be fixed to a screen printing head and the other edge of the blade element being a forwardly-directed free edge which in use contacts a printing screen, and a strip fixed to the upper, non-screen contacting surface of the blade element along the free edge thereof, wherein the strip and the free edge of the blade element together define a leading face which has a height of from 1 to 2.5 mm and encloses an acute angle with the printing screen.
Preferably, the blade element comprises a generally rectangular strip of sheet material.
More preferably, the sheet material is a stainless steel sheet material.
Preferably, the strip is formed of a flexible material.
Preferably, the strip is formed of a plastics material.
More preferably, the plastics material is a polyester material, still more preferably Mylar (RTM).
Preferably, the blade element has a thickness of about 0.25 mm and the leading face of the wiper blade has a height of about 1.6 mm.
Preferably, the leading edge of the strip at the free edge of the blade element is inclined upwardly and forwardly so as to meet the surface of the blade element at an acute angle.
Preferably, the trailing edge of the strip is inclined downwardly and rearwardly so as to meet the surface of the blade element at an obtuse angle.
Preferably, the strip extends the full length of the blade element except for the distal end regions.
The present invention also provides a screen printing head for applying a pasty product to a printing screen, comprising a main body and first and second wiper blades, wherein the wiper blades are inwardly and downwardly directed and at least one of the first and second wiper blades has the construction of the above-described wiper blade.
Preferably, the first and second wiper blades have the construction of the above-described wiper blades.
By means of the invention, a wiper blade formed from a thin flexible sheet, preferably of stainless steel, can, without significantly reducing the flexibility at the free edge of the wiper blade, be given a side face to the leading edge which is highly effective in ensuring complete filling with pasty product of apertures in the printing screen while maintaining effective shearing of pasty product at the upper face of the printing screen, thus avoiding wedging, dog-earring and rippling at the upper surface of the product in the apertures in the printing screen, while enhancing the working of the product immediately above the printing screen in front of the side face of the leading edge of the wiper blade to improve the rheological condition of the pasty product.
REFERENCES:
patent: 2445140 (1948-07-01), Hanington
patent: 3884145 (1975-05-01), Datwyler
patent: 4753163 (1988-06-01), Blaak
patent: 4823161 (1989-04-01), Yamada et al.
patent: 5001979 (1991-03-01), Kürten
patent: 5078061 (1992-01-01), Messerschmitt
patent: 5715748 (1998-02-01), Murakami et al.
patent: 5775219 (1998-07-01), Shimazu et al.
patent: 0 167 906 (1986-01-01), None
patent: 2 334 479 (1999-08-01), None
patent: WO98/16387 (1998-04-01), None
Clasper Simon Garry
Macraild Neil MacMillan
Dek International GmbH
Shanks & Herbert
Yan Ren
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