Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-06-07
2003-01-14
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...
C430S270100, C430S302000, C525S227000, C525S330500, C525S256000, C525S259000, C525S359200
Reexamination Certificate
active
06506533
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to novel polymers and to their use in imagable products. The invention relates further to the synthesis of the novel polymers.
Imagable products of particular interest in the context of this invention are lithographic printing form precursors i.e. coated printing forms (or plates) prior to exposure and development). The background to the invention will be described with reference to the lithographic printing field, from which this invention derived, but it is to be understood that the invention is not limited to this field. The novel polymers may find application in the lithographic printing field and in other fields.
2. Background Information
The art of lithographic printing is based on the immiscibility of ink, generally an oily formulation, and water, wherein in the traditional method the ink is preferentially retained by the image or pattern area and the water or fountain solution is preferentially retained by the non-image or non-pattern area. When a suitably prepared surface is moistened with water and an ink is then applied, the background or non-image area retains the water while the image area accepts ink and repels the water. The ink on the image area is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth and the like. Commonly the ink is transferred to an intermediate material called the blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
A generally used type of lithographic printing form precursor has a radiation sensitive coating applied to an aluminum substrate. Negative working lithographic printing form precursors have a radiation sensitive coating which when imagewise exposed to radiation of a suitable wavelength hardens in the exposed areas. On development, the non-exposed areas of the coated composition are removed leaving the image. On the other hand positive working lithographic printing form precursors have a radiation sensitive coating, which after imagewise exposure to radiation of a suitable wavelength becomes more soluble in the exposed areas than in the non-exposed areas, in a developer. In both cases only the image area on the printing form itself is ink-receptive.
The differentiation between image and non-image areas is made in the exposure process where a film is applied to the printing form precursor with a vacuum to ensure good contact. The printing form precursor is then exposed to a radiation source; conventionally this has been a UV radiation source. In the case where a positive form precursor is used, the area of the film that corresponds to the image in the printing form precursor is opaque so that no light will strike the printing form precursor, whereas the area on the film that corresponds to the non-image area is clear and permits the transmission of light to the coating which becomes more soluble and is removed on development.
Many positive working systems rely on the inhibition of the inherent solubility of phenolic resins, in suitable developers. Traditionally this has been achieved through the use of diazide moieties, especially naphthoquinone diazide (NQD) moieties, to provide compositions which only following exposure to UV radiation are soluble in the developer.
As demands on the performance of UV-sensitive positive working coatings have increased, so NQD technology has become limiting. In addition, digital and laser imaging technology is making new demands on coatings for lithographic printing.
It is known from G.B. 1245924 that the solubility of phenolic resins in lithographic developers may be increased by the application of heat. The heat may be delivered by infra-red radiation, assisted by radiation absorbing components such as carbon black or Milori Blue (C.I. Pigment Blue 27). However the developer resistance of the non-exposed areas to commercial developers is low, and the solubility differential is low compared to the commercial UV sensitive compositions containing NQD moieties.
Additional positive working heat sensitive systems have been developed to meet the new demands. Such systems and methods are disclosed, for example, in EP 825927B, WO 99/01795 and WO 99/01796.
EP 825927B describes commercially-successful positive working thermal printing form technology. Imagable coatings disclosed in EP 825927B comprise a polymeric substance, an infra-red absorbing compound and a compound which acts to inhibit the polymeric substance from dissolving in a developer liquid. The infra-red absorbing compound may be admixed within the coating, or may form a separate layer within the coating. Where heated, the inhibition effect is lost and the polymeric substance is able to dissolve in the developer liquid. Infra-red radiation is used for imaging. In imaged areas the infra-red absorbing compound absorbs the radiation and generates the required heat. EP 825927B discloses that certain compounds may be infra-red absorbing compounds and also have the reversible dissolution effect. However the most effective examples use two separate compounds to perform these functions.
WO 99/01796 discloses that imagable lithographic coatings composed of a polymeric substance and diazide moieties, such as naphthoquinone diazide (NQD) moieties—previously used in traditional ultra-violet exposure methods—may be insolubilized by heat. Again, it is disclosed that the heat may be delivered by infra-red radiation, acting on an infra-red absorbing compound admixed within the coating, or forming a separate layer within the coating.
WO 99/01795 discloses imagable lithographic coatings comprising an infra-red absorbing compound—once again admixed or in a separate layer—and a polymeric substance modified to carry functional groups which act to inhibit the dissolution of the modified polymeric substance in a developer liquid, compared with the corresponding unmodified polymeric substance.
The technology described above has been successful, but the need for a plurality of compounds has some implications for manufacturing and storage. Errors may occur in manufacturing, leading to products which are not optimal, or which are not wholly consistent, from batch to batch. After manufacture, there is a possibility that migration of separate components, for example the infra-red absorbing compounds, can occur.
SUMMARY OF THE INVENTION
The polymer of this invention has at least one pendent infra-red absorbing group, and the polymer initially does not dissolve in a developer liquid. However, when the polymer is subjected to infra-red radiation, the polymer dissolves in the developer liquid. In one preferred embodiment, the polymer has functional groups independently selected from —SONHR, —NHR, —SH and —OH, where R is H or a C
1
-C
4
alkyl group, and the polymer additionally has pendent groups which absorb infra-red radiation, such as polymethine dye and cyanine dye residues. The polymer may be prepared by reacting a parent polymer with an infra-red absorbing compound.
The thermally imageable composition of this invention comprises the above-described polymer, such that when the composition is applied as a dry coating to a substrate, the composition initially does not dissolve in a developer liquid, but upon exposure of regions of the coating to infra-red radiation, the coating dissolves in the developer liquid. The lithographic printing form precursor of this invention comprises a substrate having the above-described coating applied thereon.
The lithographic printing form of this invention is prepared by a method which comprises: (a) providing the above-described precursor; (b) imagewise exposing areas of the thermally imageable composition applied to the substrate via infra-red radiation; and (c) contacting the precursor with a developer liquid to remove the exposed areas of the composition.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that a polymer may be manufactured which itself has the means to absorb infra-red radiation, to generate the heat required to alter its s
Glatt Hans-Horst
Hilgart Stefan
Kottmair Eduard
West Paul
Chu John S.
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
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