Printing press and printing press control method

Details Printing press and printing press control method Printing press and printing press control method

2001-05-16

2003-09-09

Nolan, Jr., Charles H. (Department: 2854)

Printing

Processes

C101S365000, C101S467000, C101S478000, C101S484000

Reexamination Certificate

active

06615725

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a printing press and, more particularly, to a printing press having a on-machine plate making function of exposing an image on a printing plate mounted on a plate cylinder and an ink film thickness control function.
[On-machine Plate Making]
Recently, to improve the efficiency of plate making and register accuracy, a printing press has been designed to directly perform plate making by using a plate making apparatus incorporated in the printing press itself. That is, a graphic pattern (image) is exposed on a printing plate (raw plate) mounted on a plate cylinder by irradiating it with a laser beam from the head of a plate making apparatus incorporated in a printing unit instead of using a plate making apparatus provided independently of the printing press. This operation is called on-machine plate making.
More specifically, the printing press is accelerated to a designated rotational speed. When the rotational speed is stabilized, laser radiation (exposure) from the head to a raw plate is started. Thereafter, the head is moved in the axial direction of the plate cylinder during exposure to expose an image on the entire plate. The exposure time is determined by the size of the plate and the designated rotational speed during exposure. As a technique of exposing an image on a raw plate by laser radiation, the technique disclosed in U.S. Pat. No. 5,379,698 (reference 1) is incorporated in this specification.
FIG. 8
shows how plate making apparatuses are incorporated in a four-color web offset printing press. Referring to
FIG. 8
, reference numerals
1
-
1
to
1
-
4
denote printing units for the respective ink colors. Plate making apparatuses
2
-
1
to
2
-
4
are respectively incorporated in the printing units
1
-
1
to
1
-
4
. The plate making apparatuses
2
-
1
to
2
-
4
are normally located at the positions indicated by the chain double-dashed lines in FIG.
8
and brought near to plate cylinders
3
in the printing units
1
-
1
to
1
-
4
when exposure is performed. Reference numeral
4
denotes a blanket cylinder which is in contact opposite to the plate cylinder and on which a blanket is mounted. Impression cylinders (not shown) are respectively placed below the blanket cylinders
4
.
FIG. 9
shows the main part of a plate making apparatus
2
. The plate making apparatus
2
includes an exposure apparatus
2
b
having a head
2
a
. The exposure apparatus
2
b
is fixed on a table
2
c
. The table
2
c
moves in the axial direction (the direction indicated by arrows A and B in
FIG. 9
) of the plate cylinder
3
while being guided by rails
2
f
1
and
2
f
2
on a stage
2
f
. A raw plate
5
before plate making is mounted on the plate cylinder
3
.
[Ink Film Thickness Control]
To adjust the amount of ink to be supplied and decrease the number of times of test printing until a desired tone is obtained, an ink film thickness control method like that disclosed in U.S. Pat. Nos. 5,884,562 (reference 2) and 5,921,184 (reference 3) has been proposed. These references disclose ink film thickness control methods called “pre-inking 1” and “pre-inking 2”. According to the ink film thickness control methods disclosed in these references, when a printing plate is set in the plate cylinder for the first time, an ink film thickness distribution is formed in the inking device by “pre-inking 1”. When an old printing plate is to be changed to a new printing plate, an ink film thickness distribution is formed in the inking device by “pre-inking 2”. The technique disclosed in references 1 and 2 is incorporated in this specification.
FIG. 10
shows the main part of the inking device (inker) in a printing unit
1
. Reference numeral
6
denotes an ink fountain;
7
, an ink stored in the ink fountain
6
;
8
, an ink fountain roller;
9
, a plurality of ink fountains aligned in the axial direction of the ink fountain roller
8
;
10
, an ink ductor roller;
11
, an ink roller group; and
12
, a printing plate on which an image has already been exposed.
In the inking device having this arrangement, the ink
7
is supplied from the ink fountain
6
onto the surface of the ink fountain roller
8
through a portion between the ink fountain key
9
and the ink fountain roller
8
. The ink supplied to the ink fountain roller
8
is supplied to the printing plate
12
via the ink roller group
11
upon ink feed operation of the ink ductor roller
10
. The ink supplied to the printing plate
12
is printed on printing paper.
When the old printing plate is changed to the new printing plate
12
, the opening amount of the ink fountain key
9
, the rotation amount of the ink fountain roller
8
, and the like are preset to values corresponding to the image on the printing plate
12
. More specifically, by setting the opening amount of the ink fountain key
9
, the rotation amount of the ink fountain roller
8
, and the like to the values corresponding to the image on the printing plate
12
, the ink
7
in the ink fountain
6
is supplied to the printing plate
12
via the ink roller group
11
. In this case, test printing is performed before final printing to obtain a satisfactory tone while adjusting the amount of ink to be supplied. With this operation, a desired ink film thickness distribution (ink film thickness gradient) is formed on the ink roller group
11
.
When the old printing plate is changed to the new printing plate
12
, the ink film thickness distribution is left on the ink roller group
11
. For the new printing plate
12
, this ink film thickness distribution for the old printing plate must be gradually changed to an ink film thickness distribution suited to the new printing plate
12
. For this reason, to obtain a satisfactory tone, adjustment of the amount of ink to be supplied and test printing are required to excessive degrees, resulting in problems, e.g., an increase in printing preparation time, an increase in work load, a waste of printing materials, a decrease in production efficiency, and an increase in cost.
According to references 2 and 3 described above, when the old printing plate is to be changed to the printing plate
12
, ink removing operation is performed first. More specifically, ink removing is selected on a display (not shown) after a printing unit is selected. In ink removing operation, the ink feed operation of the ink ductor roller
10
is set in the OFF state, and the printing press is driven while the old printing plate is mounted to print out a predetermined number of sheets. With this operation, as shown in
FIG. 11A
, a minimum ink film thickness distribution Ma required during printing is left on the ink roller group
11
, which decreases in thickness from upstream to downstream. That is, the basic ink film thickness distribution Ma corresponding to a portion of the printing plate
12
which has no image is left.
Pre-inking 2 is then selected on the display to perform operation of pre-inking 2. In pre-inking 2, after the opening amount of the ink fountain key
9
, the rotation amount of the ink fountain roller
8
, and the like are preset to values corresponding to the image on the printing plate
12
, the printing press is driven, and the ink feed operation of the ink ductor roller
10
is performed a predetermined number of times. With this operation, as shown in
FIG. 11B
, an ink film thickness distribution (to be referred to as image ink film thickness distribution hereinafter) Mb corresponding to the image on the printing plate
12
is superimposed on the basic ink film thickness distribution Ma left on the ink roller group
11
.
After the image ink film thickness distribution Mb is superimposed on the basic ink film thickness distribution Ma, test printing corresponding to a predetermined number of sheets is performed while the printing plate is changed to the new printing plate
12
, thereby performing density checks on printing products produced by test printing. In the density checks, if a satisfactory tone is obtained, ink film thickness control by “pre-inking

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