Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1998-11-09
2004-08-17
Huff, Mark F. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S272100, C430S273100, C430S302000, C430S303000, C430S309000, C430S003000
Reexamination Certificate
active
06777156
ABSTRACT:
The present invention relates to directly imageable planodgraphic printing plate precursor, sometimes referred to as “raw plate”, which can be directly processed by laser light and, in particular, it relates to a directly imageable waterless planographic printing plate precursor which enables printing to be conducted without using dampening water.
The direct manufacture of an offset printing plate from an original image without using a plate making film, that is to say directly imageable plate making, is beginning to become popular not only in short run printing fields but also more generally in the offset printing and gravure printing fields on account of its special features such as its simplicity and lack of requirement for skill, its speediness in that the printing plate is obtained in a short time, and its rationality in making possible selection from diverse systems according to quality and cost.
In particular, very recently, as a result of rapid advances in output systems such as prepress systems, image setters and laser printers, etc, new types of various directly imageable planographic printing plates have been developed.
Classifying these planographic printing plates by the plate making method employed, such methods include the method of irradiating with laser light, the method of inscribing with a thermal head, the method of locally applying voltage with a pin electrode, and the method of forming an ink repellent layer or ink receptive layer with an ink jet. Of these, the method employing laser light is more outstanding than the other systems in terms of resolution and the plate making speed, and there are many varieties thereof.
The printing plates employing laser light may be further divided into two types, the photon mode type which depends on photo-reaction and the heat mode type in which light-to-heat conversion takes place and a thermal reaction brought about. In particular, with the heat mode type there is the advantage that handling is possible in a bright room and, furthermore, due to rapid advances in the semiconductor lasers which serve as the light source, recently a fresh look has been taken at the usefulness thereof.
For example, in U.S. Pat. No. 5,339,737, U.S. Pat. No. 5,353,705, U.S. Pat. No. 5,378,580, U.S. Pat. No. 5,487,338, U.S. Pat. No. 5,385,092, U.S. Pat. No. 5,649,486, U.S Pat. No. 5,704,291 and U.S. Pat. No. 5,570,636, there are described directly imageable waterless planographic printing plate precursors which use laser light as the light source, together with their plate making methods.
The heat sensitive layer in this kind of thermal-breakdown type printing plate precursor uses primarily carbon black as the laser light absorbing compound and nitrocellulose as the thermally-decomposing compound and has, applied to its surface, a silicone rubber layer. The carbon black absorbs the laser light, converting it into heat energy, and the heat sensitive layer is broken down by this heat. Moreover, finally, these regions are eliminated by developing, as a result of which the surface silicone rubber layer separates away at the same time and ink-receptive regions are formed.
However, with these printing plates, since the image is formed by breakdown of the heat sensitive layer, the image ditch cells are deepened, so that problems arise in that the ink receptiveness at the minute halftone dots is impaired and the ink mileage is poor. Furthermore, in order that the heat sensitive layer readily undergoes thermal breakdown, a crosslinked structure is formed and so there is also the problem that the durability of the printing plate is poor. If the heat sensitive layer is made more flexible, the sensitivity drops markedly and indeed making the heat sensitive layer flexible has been difficult. Moreover, with such a printing plate, the sensitivity being low, there is also the problem that a high laser intensity is needed to break down the heat sensitive layer.
In JP-A-09-146264, there is proposed a negative type laser-sensitive waterless planographic printing plate precursor which has, in the light-to-heat conversion layer, a compound which converts laser light to heat, a polymeric compound with film forming capability, a photopolymerization initiator and an ethylenically unsaturated compound which can be photopolymerized, and by carrying out exposure of the entire face by UV irradiation following the formation of the silicone rubber layer, reaction takes place between the light-to-heat conversion layer and the silicone rubber layer.
In this printing plate, by carrying out exposure of the entire face following the application of the silicone rubber layer, the adhesive strength between the silicone rubber layer and the light sensitive layer is increased, with the result that a printing plate of outstanding image reproducibility and scratch resistance is obtained. However, as stated above, there is a trade-off between the flexibility of the light sensitive layer and sensitivity, and this has presented the problem in particular of low sensitivity.
In JP-A-09-239942, a peeling development type printing plate is proposed which contains, in a laser-responsive layer, a material which generates acid and a polymeric compound which is decomposed by the action of the acid, but since two steps are required, namely a laser irradiation step and a heating step, the process becomes more complex and there is also the inherent problem of peeling development in that the reproducibility of minute half tone dots is poor.
In U.S. Pat. No. 5,379,698 there is described a directly imageable waterless planographic printing plate which employs a thin metal film as a heat sensitive layer. With this printing plate, the heat sensitive layer is rather thin, so a very sharp image is obtained and this is advantageous in terms of the degree of resolution of the printing plate. However, the adhesion between the base material and the heat sensitive layer is poor and the heat sensitive layer in non-image regions separates away during the printing and this has presented the problem that ink adheres thereto, producing faults on the printed material. Moreover, with this printing plate, the image is also formed by breakdown of the heat sensitive layer, and again this presents the problem that the image ditch cells are deepened and the ink acceptance and ink mileage are impaired.
As well as the aforesaid negative type planographic printing plates, in particular in relation to directly imageable waterless planographic printing plates, positive type directly imageable waterless planographic printing plates may also be considered.
With this type of printing plate, the silicone rubber layer in the laser irradiated regions is selectively retained, and serves to provide the non-image regions. The mechanism thereof comprises some form of enhancement in the adhesive strength between the silicone rubber layer and laser-responsive layer due to the laser irradiation, or an enhancement in the adhesive strength of the laser-responsive layer and the substrate below, with the result that the unirradiated silicone rubber layer, or silicone rubber layer and laser-responsive layer, is/are selectively removed by the subsequent treatment.
The printing plate proposed in JP-A-09-120157 is one where an acid generated by laser irradiation acts as a catalyst to promote the reaction of the light sensitive layer, so that image reproduction is realized. However, a separate heat treatment step is necessary to promote the reaction following the acid generation, so the process becomes more complex. Moreover, following the acid generation, the time which elapses up to the heat treatment exerts an influence on the image reproducibility and this presents the problem that this image reproducibility is unstable.
The present invention seeks to provide positive and negative type directly imageable printing plate precursors which overcome the aforesaid disadvantages, do not require a complex process following the laser irradiation, and provide printing plates having high sensitivity and high image reproducibility.
In order to solve th
Goto Kazuki
Ichikawa Michihiko
Ikeda Norimasa
Gilliam Barbara
Huff Mark F.
Morrison & Foerster / LLP
Toray Industries Inc.
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