Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
1999-05-11
2002-04-23
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S190000, C430S191000, C430S192000, C430S193000, C430S302000
Reexamination Certificate
active
06376150
ABSTRACT:
FIELD OF THE INVENTION
This application is based on application No. MI98A 0001023 filed in Italy, the content of which is incorporated hereinto by reference.
The present invention relates to an IR- and UV-radiation-sensitive Composition and to a lithographic plate.
In particular, the invention relates to an IR- and UV-radiation-sensitive composition which is useful for producing a positive-type lithographic plate.
BACKGROUND OF THE INVENTION
As is known, the technique of printing using a lithographic plate is based on the distinct partition fatty substances and water. The fatty substance or ink is preferably retained by the image area and the water is preferably retained by the non-image area. When the surface of a suitably prepared lithographic plate is moistened with water and then coated with ink, the non-image area retains the water and repels the ink, while the image area accepts the ink and repels the water. Then, the ink on the image area is transferred onto the surface of a material on which it is desired to reproduce the image, such as, for example, card, fabric and the like.
In general, the lithographic plates used in printing processes are formed of an aluminium support coated with a light-sensitive (photosensitive) composition. When this composition reacts to light of a suitable wavelength, such that the portion exposed to the light becomes soluble and thus able to be removed during the developing process, the printing process is referred to as a “positive” process. In contrast, when the portion exposed to the light becomes insoluble, the printing process is referred to as a “negative” process. In both cases, the remaining image area is lipophilic and thus accepts the ink, whereas the non-image area is hydrophilic and accepts the water.
Recent developments in the field of lithographic plates are oriented towards the search for compositions that are sensitive to laser light, preferably in the near-IR region, in particular to a laser light controlled by software, so as to transfer the image created by computer directly onto the surface of the plate. This technique has the advantage of dispensing with photographic films, with a consequent reduction in the pollution resulting from the chemical substances used to prepare and produce these films, and elimination of all the problems encountered in transferring the image onto the plate via photographic films.
Firstly, a composition which is sensitive to IR radiation emitted by a laser might make the system more reliable.
Secondly, it would be possible to work in ambient light, thus dispensing with the need for automatic loading systems and darkrooms.
Patent application WO 96/20429 describes a method for forming a lithographic printing matrix by means of the heat-printing method. This method includes the following stages: (i) coating a support, which can be used as a lithographic support, with a positive-type photosensitive composition comprising a naphthoquinonediazide ester of a phenolic resin or a naphthoquinonediazide ester and a phenolic resin and at least one substance capable of absorbing in the IR region, (ii) exposing the system to ultraviolet light (UV) so as to enable the photosensitive composition to be developed, (iii) imprinting on the plate with IR radiation emitted by a laser, and (iv) developing the plate in order to remove those areas of the photosensitive composition that have not been exposed to the laser.
In addition, in the course of the description, it is stated that the combination of the stages of exposure to light (UV) and of heating (by IR radiation) is essential for forming the image (page 7, lines 1-3).
Patent application WO 97/39894 describes a heat-sensitive olefinic composition comprising a polymer substance which is soluble in aqueous developer and a compound which reduces the solubility of the polymer substance in aqueous developer, characterized in that the solubility of the composition in aqueous developer is increased by heating but is not increased by the incident UV radiation (see Claim 1). In other words, the said plate is sensitive to IR but not to UV.
Preferably, the heat-sensitive composition comprises no UV-sensitive components (page 17, lines 17-18).
EP-A-0 833 204 discloses an infrared radiation sensitive imaging composition contains two essential component, namely an infrared radiation absorbing material, and a phenolic resin that is either mixed or reacted with an o-diazonaphthoquinone derivative. These compositions are useful in imaging elements such as lithographic printing plates that can be used to provide either positive or negative images using laser imaging, and that can be adapted to direct-to-plate imaging procedures. However, none of the examples of EP-A-0 833 204 relates to the use of said composition in a process for obtaining an image after UV exposure only.
Photosensitive plates which, like those of the abovementioned patent applications WO 96/20429 and WO 97/39894, necessarily require exposure to IR light, are currently seldom used since plants capable of printing on a lithographic plate with laser light are still very expensive. Thus, a period of transition is currently being experienced during which many operators are still using the old technique of printing on the plate by exposure to UV lamps by means of a master image, while a few—those who already have the necessary equipment—require plates that are sensitive to IR light.
Patent application EP 0 672 954 attempts to address this requirement, disclosing a photosensitive coating for a lithographic plate which is sensitive to both UV and IR radiation and is capable of functioning in both positive and negative modes. The said coating includes a resol resin, a novolac resin, an s-triazine substituted with a haloalkyl group and an IR absorber. The solubility of the abovementioned composition in a solution of alkaline aqueous developer is reduced in the exposed area and increased in the unexposed area during the stages of (i) exposure to the radiation which forms the image, and (ii) heating. In the course of the description, it is specified that in order to be able to use the plate in negative mode, it is essential that both resol and novolac resins are present (page 4, lines 10-13).
The inventors of the present invention have used a plate according to patent application EP 0 672 954 to form UV-positive images and have found that the image thus obtained shows little resistance either to the alkaline developer solution or to the isopropyl alcohol in the bathing solution used during the printing, and in addition the said image also shows little resistance to mechanical abrasion.
OBJECTS OF THE INVENTION
A first object of the present invention is to provide a composition which is sensitive to both IR and UV radiation.
A second object of the present invention is that the said composition should give good results during alkaline developing, irrespective of the system (UV or IR) used to imprint it.
A third object of the present invention is that the said composition should give an image which, after developing, has good resistance to the solvents used in printing processes and, in particular, to isopropyl alcohol.
A fourth object of the present invention is to provide a lithographic plate comprising a composition having the abovementioned characteristics.
DEFINITIONS
The term “lithographic plate” is understood to refer to a support coated with a photosensitive coating which, after having been appropriately exposed and developed, is used as a planographic matrix in printing processes in which there is a distinct partition fatty substances and water.
Typical examples of support materials are aluminium, zinc and copper, polymeric supports such as polyester, and paper coated with a polymer.
Even more typically, the support is a metal sheet, made of electrograined aluminium, which has been oxidized and suitably treated to receive the photosensitive composition.
The term “positive type” is understood to mean that that portion of photosensitive coating exposed to the radiation becomes soluble so that it can be removed during
Bolli Angelo
Peveri Paolo
Tettamanti Andrea
Chu John S.
Lastra S.p.A.
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