Printing – Flexible-sheet-securing devices
Reexamination Certificate
2001-02-21
2004-05-18
Evanisko, Leslie J. (Department: 2854)
Printing
Flexible-sheet-securing devices
C101S378000, C101S382100, C101S384000
Reexamination Certificate
active
06736065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a plate-mounting member which is used to mount a plate onto a plate cylinder disposed in a printing apparatus or a plate-making apparatus. The present invention also relates to method and apparatus for mounting a printing plate, especially, a digitally made flexible printing plate, onto a plate cylinder of a printing apparatus.
DESCRIPTION OF THE RELATED ART
In a lithographic printing apparatus, generally, a printing plate is wound around and fixed to a plate cylinder and, in this state, printing is executed.
However, a lithographic printing plate (in the present specification, this is referred to as a flexible printing plate), which uses as a support member a member formed of other material than metal inexpensive and easy to handle (for example, a plastic film or paper), has a weak point in dimensional stability. For example, the flexible printing plate can be deformed depending on the way of handling of the flexible printing plate when it is mounted or due to a frictional force between a rubber cylinder and itself during printing, which can degrade the printing dimension as well as the printing position accuracy with respect to paper.
Therefore, use of the flexible printing plate of the above type, conventionally, is limited to a simple printing which prints a relatively small number of printings and does not require the high matching accuracy of the printings; that is, such flexible printing plate has not been employed in a high-quality printing using multiple colors and requiring great delicacy or in a full-dress printing using a large-scale printing machine.
Here, description will be given in detail of the above-mentioned deformation that is caused depending on the way of handling of the flexible printing plate when it is mounted. In
FIGS. 19 and 20
, there is shown a typical printing plate-mounting apparatus. Specifically,
FIG. 20
is a view of the printing plate-mounting apparatus when it is viewed from the direction of the arrow mark X shown in
FIG. 19
; and,
FIG. 19
is a section view taken along the line Y—Y shown in FIG.
20
.
As shown in
FIG. 19
, the plate cylinder
61
of the printing machine is structured such that a portion of a cylinder is cut away along the axial direction of the cylinder and, in a substantially flat surface (which is hereinafter referred to as a flat surface portion
61
a,
which is the cut face of the cutaway portion of the cylinder), there is formed a groove portion
65
. And, within the groove portion
65
, there are disposed a plate front end clamp mechanism
62
for holding the front end or leading end of a printing plate
70
, and a plate rear end clamp mechanism
63
for holding the rear end or trailing end of the printing plate
70
. The clamp mechanisms
62
and
63
respectively include lower teeth
62
b
and
63
b
(the upper surfaces of which are substantially flush with the flat surface portions
61
a
), and upper teeth
62
a
and
63
a
which are rotatably supported by their respective lower teeth and are capable of holding the plate front end or rear end between the upper surfaces of their respective lower teeth and themselves. Further, there is disposed a position adjusting mechanism (not shown) which is capable of adjusting the positions of the plate front end clamp mechanism
62
and plate rear end clamp mechanism
63
in the back-and-forth direction, in the right-and-left direction and in the oblique direction on the bottom surface of the groove portion
65
.
Between the two flat surface portions
61
a
and curved surface portion
61
b
of the plate cylinder
61
, there are formed top portions
61
c
respectively. Although not shown, there is known another type of plate cylinder in which there are formed top portions between the upper surfaces of the lower teeth of the clamp mechanisms, instead of the flat surface portions, and the curved portion of the plate cylinder.
Normally, the portions of the plate cylinder
61
, where the two flat surface portions
61
a
and curved surface portion
61
b
cross each other, are each rounded to thereby provide a curved surface having a radius of 5-30 mm. It should be noted here that, in the present specification, such curved surface portions are also referred to as top portions.
And, as shown in
FIG. 20
, two positioning pins
64
are respectively provided on and projected from the upper surface of the lower tooth
62
b
of the plate front end clamp mechanism; specifically, at two positions of the lower tooth
62
b
upper surface which are spaced from each other in the axial direction of the plate cylinder
61
. At the positions of the upper surface
62
of the plate front end clamp mechanism that correspond to the positioning pins
64
, there are formed notches
66
respectively. Also, in the front end portion
70
a
of the printing plate
70
which is shown by a two-dot chained line in
FIG. 20
; specifically, at the positions of the front end portion
70
a
that correspond to the positioning pins
64
, there are also formed two notches
71
respectively.
Recently, as printings have been turned into small lots and diversified, there has increased the need for a plate (which, in the present specification, is referred to as a flexible plate comprising a support member formed of material which is inexpensive and easy to handle (for example, plastic film, paper) other than metal, and a photosensitive layer disposed on such support member. However, since such plate is high in flexibility, there arise several problems when it is mounted on the plate cylinder.
For example, there is generally known a case where the flexible printing plate
70
is mounted onto the plate cylinder
61
using the printing plate-mounting apparatus shown in
FIGS. 7 and 8
. Specifically, in this case, when, while holding the plate rear end
70
b,
an operator pushes the plate front end
70
a
of the printing plate between the upper tooth
62
a
and lower tooth
62
b
of the plate front end clamp mechanism to thereby bring the plate front end
70
a
into contact with two positioning pins
64
, there is a fear that the plate front end
70
a
can be deformed and can be fixed in such deformed state. That is, in a plate cylinder capable of mounting thereon a printing plate of a half-kiku size or more, the distance between the two positioning pins
64
in the plate cylinder
61
is fairly wide; and, therefore, when mounting the printing plate
70
onto the plate cylinder
61
, in case where the operator overpushes the printing plate
70
even slightly, the printing plate
70
can be deformed in such a manner that the plate front end
70
a
is projected in the pushing direction from between the two positioning pins
64
. However, in case where the operator pushes the printing plate
70
insufficiently in order to avoid such deformation of the printing plate
70
, the printing plate
70
cannot be positioned accurately.
As described above, the mountability of the flexible plate onto the plate cylinder is poor and thus it is difficult to always mount the flexible plate onto the plate cylinder in a constant state. Therefore, there are necessary a plurality of plate cylinders and thus, in case where the flexible plate is used in a multicolor printing (for example, four-color printing) which requires strict matching between the plate cylinders, mismatching can occur.
Also, as shown in
FIG. 19
, in the vicinity of the top portions
61
c
respectively formed between the flat surface portions
61
a
and curved portion
61
b
of the plate cylinder
61
, the flexible printing plate
70
does not easily stick to the outer peripheral surface of the plate cylinder
61
but the flexible printing plate
70
tends to float up from the outer peripheral surface of the plate cylinder
61
.
In order to prevent such flotation of the printing plate
70
, an operator, while pulling strongly the plate rear end of the printing plate
70
with the plate front end thereof held by the plate front end clamp mechanism
62
, rotates the plate cylinder to thereby wind the printing plate
7
Naniwa Mutsumi
Oishi Chikashi
Evanisko Leslie J.
Fuji Photo Film Co. , Ltd.
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