Printing – Print plate feeding or delivering
Reexamination Certificate
2002-11-06
2004-08-17
Evanisko, Leslie J. (Department: 2854)
Printing
Print plate feeding or delivering
C101S415100
Reexamination Certificate
active
06776096
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for attaching a printing plate onto a plate cylinder of a printing press. Specifically, the invention relates to a method and apparatus for attaching a flexible printing plate prepared by digital plate making.
BACKGROUND OF THE INVENTION
In a printing press for lithographic printing, it is a common practice to wind and fix a printing plate around a plate cylinder and carry out printing with the plate kept in such a condition.
However, a lithographic printing plate, which is inexpensive and easy to handle and at least the rear surface of which is made of a material other than metal (hereinafter referred to as a flexible printing plate), has a drawback in dimensional stability. For example, the flexible printing plate has a problem in that distortion may occur by handling of the printing plate at the plate attachment or by a frictional force generated between the printing plate and a blanket cylinder during printing and as a result, the print dimension and the accuracy in the printed position relative to printing paper are degraded.
Accordingly, the use of such a flexible printing plate has been limited to a simple printing for a relatively small number of prints wherein a high registration accuracy in the resulting print is not so severely required, and such flexible printing plates have not been used for multi-color high-quality printing and printing using a large printing press.
The above-mentioned distortion of a flexible printing plate caused by the handling at the plate attachment is described in detail below. In
FIG. 16
, a typical plate-attaching unit
60
is shown.
FIG. 16
shows a view of the plate-attaching unit when it is viewed from the direction of the arrow X in FIG.
15
.
FIG. 15
is a cross-sectional view taken along the line Y—Y shown in FIG.
16
.
As is shown in
FIG. 15
, a plate cylinder
61
of the printing press has such a shape as being obtained by cutting off a part of a cylinder along the axial direction thereof and providing a groove
65
in a substantially flat plane (hereinafter referred to as a flat portion
61
a
), which is the cut edge of cylinder. In the groove
65
are provided a plate front end clamping mechanism
62
that clamps and holds the front end or leading edge of a printing plate
70
and a plate rear end clamping mechanism
63
that clamps and holds the rear end or trailing edge of the printing plate
70
. Each of the clamping mechanisms
62
and
63
is provided with a lower tooth
62
b
or
63
b
the upper surface of which constitutes substantially the same level as the flat portion
61
a
, and an upper tooth
62
a
or
63
a
which is rotatably supported by the bottom tooth and capable of clamping and holding the front end of printing plate between the upper surface of the bottom tooth and itself. Further, a position-adjusting mechanism (not shown), which can control the positions of the plate front end clamping mechanism
62
and the plate rear end clamping mechanism
63
in the forward-backward, left-right or oblique direction is provided on the bottom plane of the groove
65
.
There is formed a ridge portion
61
c
between the flat portion
61
a
and a curved portion
61
b
of the plate cylinder
61
. Though not shown, there is known a plate cylinder in which, for example, the upper surface of the lower tooth in the clamping mechanism, instead of the flat portion, forms a ridge portion together with the curved portion therebetween.
Usually, the portion where the flat portion
61
a
and the curved portion
61
b
are bounded is rounded to form a curved surface with a radius of 5 to 30 mm. Such a rounded portion is also referred to as the ridge portion in the specification.
As shown in
FIG. 16
, on the upper surface of the lower tooth
62
b
of the plate front end clamping mechanism, protruding registration pins
64
are provided at two positions with a spacing in the axial direction of the plate cylinder
61
. At the positions of the upper tooth
62
a
of the plate front end clamping mechanism corresponding to those of the registration pins
64
, notches
66
are formed respectively. Further, in a plate front end
70
a
of the printing plate
70
shown by a two-dot chained line in the figure, notches
71
at the positions corresponding to those of registration pins
64
.
In the case where a flexible printing plate
70
is attached onto the plate cylinder
61
using, for example, the plate-attaching unit
60
described above, an operator pushes the plate front end
70
a
of the printing plate into a gap between the upper tooth
62
a
and the lower tooth
62
b
of the plate front end clamping mechanism so that the plate front end comes into contact with the two registration pins
64
while the operator holds the plate rear end
70
b
in his hand. At that time, it accidentally happens that the plate front end
70
a
is deformed and fixed in such a deformed state. Specifically, since distance between the two registration pins
64
aligned on plate cylinder
61
is considerably large in the plate cylinder capable of attaching a printing plate of a half-kiku size (approximately 670 mm in width and 560 mm in length) or larger, when the operator pushes a flexible printing plate
70
even slightly in excess at the plate attachment, deformation of the printing plate
70
occurs in such a manner that the plate front end
70
a
protrudes from the spacing between the two registration pins
64
in the pushed direction. However, when the printing plate
70
is pushed insufficiently with care of preventing such deformation, accurate positioning of the printing plate is impossible.
Moreover, as shown in
FIG. 15
, in the vicinity of the ridge portion
61
c
formed between the flat portion
61
a
and the curved portion
61
b
of the plate cylinder
61
, the flexible printing plate
70
is difficult to adjust itself to the outer periphery of plate cylinder
61
, and tends to float from the outer periphery of the plate cylinder.
To prevent such floating of the printing plate
70
, the operator wraps and attaches the printing plate
70
by rotating the plate cylinder while strongly pulling the plate rear end of the printing plate whose front end has been clamped and held by the plate front end clamping mechanism
62
. However, during such operation, the pulled portion in the plate rear end of the flexible printing plate
70
is elongated.
After winding and attaching the printing plate by pulling the plate rear end thereof as described above, the plate rear end of the printing plate is pushed into a gap between the upper and lower teeth of the plate rear end clamping mechanism and fixed by rotating the upper tooth. Then, by moving the plate rear end clamping mechanism in such a direction as to impart tension to the printing plate using a tension-applying mechanism (not shown), the printing plate is brought into close contact with the periphery of plate cylinder, whereby the plate attachment is completed.
In a conventional plate-attaching device, such a tension-applying mechanism for bringing a printing plate into close contact with the peripheral surface of plate cylinder is designed in conformity with a printing plate having a metal substrate such as aluminum. Accordingly, in the case of a flexible printing plate, the plate is elongated to an extent more than necessary.
On the other hand, when the tension-imparting mechanism is designed so as to apply a low tension adapted for flexible printing plates, the tension is not enough and the printing plate fails to get in close contact with the plate cylinder. Even when the printing plate is favorably attached without floating from the plate cylinder, under such a weak tension the printing plate is moved by the frictional force between the blanket cylinder and itself during printing.
As means for resolving the above-described problem of moving printing plate (hereinafter referred to as “plate slippage”), there have been proposed a method of immobilizing the plate on the plate cylinder using a spray paste (Japanese Patent Laid
Kasai Seishi
Naniwa Mutsumi
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