Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-10-16
2002-08-20
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S944000
Reexamination Certificate
active
06436596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a quality control method for a planographic printing plate recordable by an infrared laser for so-called direct plate formation in which a plate can be formed directly by scanning an infrared laser based on digital signals from a computer or the like, and that is usable as an offset printing master.
2. Description of the Related Art
The development of lasers in recent years has been remarkable. In particular, the development of high-output, compact solid-state lasers and semiconductor lasers that have a light emission region in an infrared region from near infrared rays is advancing. These infrared lasers are extremely useful as a recording light source at the time a printing plate is formed directly on the basis of digital data from a computer or the like.
The positive type planographic printing plate material for an infrared laser, which material uses as an exposure light source an infrared laser having a light emitting region in an infrared region, is a planographic printing plate material having as essential components thereof a binder resin soluble in an aqueous alkali solution and an IR dye or the like that absorbs light to generate heat.
When the positive type planographic printing plate material for an infrared laser is exposed to the infrared laser, at non-exposed portions (image portions), the IR dye or the like in the positive type planographic printing plate material for the infrared laser works as a solution inhibitor to substantially reduce the solubility of the binder resin by interacting with the binder resin. In contrast, at exposed portions (non-image portions), since the IR dye or the like absorbs light to generate heat, interaction of the IR dye or the like with the binder resin becomes weak. Accordingly, exposed portions (non-image portions) are dissolved in an alkaline developing solution at the time of development, whereby the planographic printing plate is formed.
However, in such a positive type planographic printing plate material for an infrared laser, a latitude with respect to an activity of the developing solution is narrow in comparison with that of material of a positive type planographic printing plate made by exposure to an ultraviolet ray (UV). Therefore, there are problems in that, when the activity becomes high, reduction in the concentration of image portions and deterioration in printing durability are triggered, and when the activity becomes low, deficiencies in development are triggered.
These problems are caused by the following essential difference between the plate-making mechanisms of the positive type planographic printing plate material for the infrared laser and the material of the positive type planographic printing plate made by exposure to an ultraviolet ray.
The material of the positive type planographic printing plate made by exposure to an ultraviolet ray has as essential components thereof a binder resin soluble in an aqueous alkali solution and an onium salt, a quinone diazide compound and the like. Here, when the material of the positive type planographic printing plate made by exposure to an ultraviolet ray is exposed, at non-exposed portions (image portions), the onium salt or quinone diazide compound operates as a solution inhibitor in the same manner as those of the positive type planographic printing plate material for the infrared laser. Further, at exposed portions (non-image portions), the onium salt or quinone diazide compound is decomposed by light to produce an acid, thus operating, unlike those of the positive type planographic printing plate material for the infrared laser, as a dissolution accelerator for the binder resin. Consequently, in the material of the positive type planographic printing plate made by exposure to an ultraviolet ray, the difference between the solubility of the exposed portions and solubility of the non-exposed portions with respect to an alkaline developing solution is extremely large.
In contrast, in the positive type planographic printing plate material for the infrared laser, although the interaction between the IR dye or the like and the binder resin becomes weak at exposed portions (non-image portions) at the time of exposure, the difference between the solubility of exposed portions and the solubility of non-exposed portions is small because the IR dye cannot operate as a dissolution accelerator for the binder resin.
Process control for the purpose of continuously forming stable images by using an image forming material having a narrow latitude with respect to the activity of the developing solution is extremely difficult.
Ordinarily, an automatic developing machine having a replenishment mechanism to maintain developing solution sensitivity as constant as possible is used in developing the positive type planographic printing plate material for the infrared laser. The replenishment mechanism adds a replenishing solution having a high activity in order to prevent a decrease in the pH of the developing solution and deterioration of developability due to development processings of the plate or absorption of CO
2
. Specifically, in an ordinary PS plate processing system, a method in which a replenishing solution is added to control conductivity so that it is kept constant, and a method in which a predetermined amount of replenishing solution is periodically added every time the number of plates for which development processing has been administered reaches a fixed numerical value or after a lapse of a fixed processing time have been proposed.
However, in the method in which conductivity is controlled, when the number of plates for which development processing has been administered increases and much of the composition of the photosensitive layer is dissolved, the pH of the developing solution becomes different even if the value of conductivity is the same as it was at the starting time, whereby a difference in developability arises.
Moreover, in the method in which a predetermined amount of replenishing solution is added at a fixed interval such as a fixed time or a number of planographic printing plates for which development processing has been completed, the composition amount of the photosensitive layer dissolved in the developing solution varies according to image area because the replenishment amount per unit area of the plate is prescribed. Further, the amount of CO
2
absorbed over time varies depending upon the installation environment of the automatic developing machine (i.e., temperature, humidity, CO
2
concentration or the like). Due to these factors, conditions change slightly. Hence, it has been difficult to continuously obtain uniform developability with a control at a fixed value.
The issues described above do not pose too much of a problem with an ordinary planographic printing plate that uses ultraviolet exposure since the latitude thereof is wide. However, because a positive type planographic printing plate material for an infrared laser has a narrow latitude, image forming properties become markedly different due to changes in the activity ratio of the developing solution, thus leading to problems relating to the quality of the planographic printing plate.
However, a method that is applicable to a generalized positive type planographic printing plate material for an infrared laser, and that can effectively prevent with a simple process control reduction in the concentration of image portions, deterioration in printing durability and deficiencies in development has yet to be discovered.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a quality control method for simply evaluating and easily determining plate making conditions of a positive type planographic printing plate material for an infrared laser for use in direct plate making, in particular, an active state of a developing solution, feeding back the evaluation results to exposure/development processes, keeping the quality of a planographic printing plate constant, and continuously forming unifo
Aono Koichiro
Kawauchi Ikuo
Okuno Kei
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Hamilton Cynthia
LandOfFree
Quality control method for a planographic 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 Quality control method for a planographic printing plate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Quality control method for a planographic printing plate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2913692