Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – To produce printing surface
Reexamination Certificate
1997-12-10
2001-03-27
Dote, Janis L. (Department: 1753)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
To produce printing surface
C430S056000, C430S069000, C430S902000
Reexamination Certificate
active
06207332
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing a lithographic printing plate. More specifically, it relates to a process for producing a lithographic printing plate using an electrophotographic method, which can suppress non-uniform charging to thereby obtain a desirable toner image having low fogging.
A conventional process for producing a lithographic printing plate by an electrophotographic method comprises corona-charging an original plate for lithographic printing comprising a water-resistant support having a layer containing zinc oxide and a binder provided thereon, imagewise exposing, toner developing, fixing and etching.
The above-described water resistant support used is a paper to which water resistant property has been imparted, metal foil, or the composite thereof.
Where a paper is used as the support, in order to impart conductivity to the paper, a so-called conductive agent, such as a coating liquid containing an inorganic electrolyte such as sodium chloride, potassium chloride or calcium chloride, or an organic polymer electrolyte such as quaternary ammonium, is used and a paper is impregnated or coated therewith. In this case, the paper is adjusted so as to have a volume electric resistance of about 1×10
9
&OHgr;·cm.
However, where an original plate for lithographic printing is produced using the paper having been subjected to such a conductivity treatment as a substrate, even if a water resistance treatment has been applied to the paper, due to addition of dampening water during printing, the paper is inevitably partially elongated on a roll during printing, viz., the plate elongation cannot be avoided. Thus, various problems may occur during printing such that wrinkles happen on backedge and resister changes by slipping of printing plate during printing.
As a structure for protecting the paper support from water influence, it has been attempted to use a paper support having, for example, a conductive filler-containing polyethylene layer, laminated thereon i.e., to use a conductive laminate paper, as described in, for example, JP-A-58-57994 and 59-64395 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”).
However, such a laminate paper involves the disadvantages that a conductive treatment must be applied to a paper support or a resin film, so that the production cost of the support increases, which may undesirably invite high cost of the entire printing plate.
Further, it has been attempted to use a paper having a metal foil, such as aluminum, zinc or copper, adhered thereon (hereinafter referred to as a “metal foil laminate paper”) as described in, for example, JP-B-38-17249, 41-2426 and 41-12432 (The term “JP-B” as used herein means an “examined published Japanese patent publication”). In any case, a paper which is impregnated with the above-described conductive agent is used as a paper to be laminated.
When this metal foil laminate paper is used, a paper must be subjected to a conductive treatment. Further, a metal foil is required to adhere to one side or both sides of the paper. Thus, this attempt has the disadvantage that a production cost is higher than that in the above-described laminate paper.
In this case, it is considered to use a support obtained by forming a conductive layer such as a metal foil on an ordinary base such as a polyester base or a polyethylene laminate paper and further forming a photoconductive layer thereon. However, such a support, although being inexpensive, has a low conductivity as the entire support, so that it cannot be practically used. This point will be explained below.
In a lithographic printing plate by an electro-photographic method, the plate is produced according to a plate making method as shown in
FIG. 4
that corona charge is applied to both sides of the original plate. In this drawing, master
1
′ is charged negatively and positively above and below the photoconductive layer by a negative corona discharge unit
12
and a positive corona discharge unit
19
, respectively, prior to entering an exposure part
20
. In the exposure part
20
, the charged master
1
′ is exposed to imagewise exposure, so that the charge in the exposed area disappears by the conduction of the photoconductive layer, remaining only in the unexposed area. Thus, a static latent image is formed.
However, in the plate making method having the construction as shown in
FIG. 4
, if a support has a low conductivity, a discharge phenomenon does not occur well, so that an image deteriorates. It is considered that a conductive layer is directly contacted with a conductor so as to ground, thereby charging. In the case of a lithographic printing plate, however, the plate is not repeatedly used, and a fresh plate is always used. Therefore, it is mechanically impossible that the conductor is directly contacted with the conductive layer interposed between a support and a photoconductive layer.
In the plate making method shown in
FIG. 4
, exposing light irradiated from a light source is condensed by the lens
18
in the exposure part
20
. The condensed exposing light forms an image on the master
1
′ located in the exposure part
20
between guide rollers
15
and
16
, which was supplied from the paper supply part
11
by a carrying means and was subjected to the above-described charging treatment. The master
1
′ is imagewise exposed form an image. This master
1
′ which has been exposed to light is carried to the developing and fixing part
17
by a carrying means, where toner is adhered to the unexposed part, followed by development. The developed image is fixed, subjected to a desensitizing treatment, and dried to produce the lithographic printing plate.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a process for producing a lithographic printing plate which is inexpensive, is not elongated, can be readily handled and can provide a uniform image.
The above-described object can be achieved by the following constitution.
The process for producing a lithographic printing plate according to the present invention comprises the steps of:
using an original plate for lithographic printing comprising a support having a volume electric resistance of more than 1×10
10
&OHgr;·cm, a conductive layer having a volume electric resistance of 1×10
5
&OHgr;·cm or less, provided on one surface of the support, and a photoconductive layer containing zinc oxide and a binder, provided on the conductive layer,
conducting negative corona discharge from the side of the photoconductive layer of the original plate for lithographic printing, and
during this corona discharge, contacting a conductor having earth potential with at least the support of the original plate, thereby charging the photoconductive layer of the original plate for lithographic printing.
Thus, it has been found in the present invention that even if a support itself has a low conductivity of a volume electric resistance of more than 1×10
10
&OHgr;·cm, if a conductive layer is provided between a support and a photoconductive layer and a conductor having an earth potential is contacted with the back side of the support, a necessary charge can be obtained by the discharge between them. The present invention has been completed based on this finding.
REFERENCES:
patent: 3866096 (1975-02-01), Metcalfe et al.
patent: 6022654 (2000-02-01), Nakayama et al.
patent: 387448 (1965-05-01), None
patent: 1295886 (1962-11-01), None
patent: 2201491 (1974-04-01), None
patent: 912836 (1962-12-01), None
patent: 912845 (1962-12-01), None
patent: 1006117 (1965-09-01), None
patent: 995491 (1996-06-01), None
Patent Abstracts of Japan, vol. 15, No. 245, & JP 03 077981A—Matsushita, published Aug. 21, 1989.
Patent Abstracts of Japan, vol. 7, No. 15 & 57 171356 A (Ricoh), published Oct. 21, 1982.
Dan Shigeyuki
Hattori Hideyuki
Itakura Ryousuke
Nakayama Takao
Tashiro Hiroshi
Dote Janis L.
Fuji Photo Film Co. , Ltd.
Reed Smith LLP
LandOfFree
Process for producing lithographic printing plate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for producing lithographic printing plate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing lithographic printing plate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2509078