Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2002-01-24
2004-08-31
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...
C190S114000, C190S114000, C190S114000, C190S030000, C190S030000, C190S030000
Reexamination Certificate
active
06783911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive working imageable composition, which includes a hydroxyfunctional resin having a covalently bound radiation sensitive group and an isocyanate crosslinking agent. More particularly, the present invention relates to a positive working imageable element, which includes a substrate and a positive working imageable composition according to the present invention, as well as a method of producing the imaged element.
2. Description of the Prior Art
Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water, will not accept the ink. In the art of photolithography, a photographic material is made imagewise receptive to oily inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophilic background. The areas which accept ink form the printing image areas and the ink-rejecting areas form the background areas.
Lithographic printing plate precursors, i.e., imageable elements, typically include a radiation-sensitive coating applied over the hydrophilic surface of a support material. If after exposure to radiation, the exposed regions of the coating become soluble and are removed in the developing process, revealing the underlying hydrophilic surface of the support, the plate is called a positive-working printing plate. Conversely, if exposed regions become insoluble in the developer and the unexposed regions are removed by the developing process, the plate is called a negative-working plate. In each instance, the regions of the radiation-sensitive layer that remain (i.e., the image areas) are ink-receptive and the regions of the hydrophilic surface revealed by the developer are ink-repellent.
Upon imagewise exposure of the light-sensitive layer in a positive working system, the exposed image areas become soluble and the unexposed areas become insoluble. The plate is then developed with a suitable liquid to remove the photosensitive composition from the exposed areas.
Common difficulties encountered by practitioners of lithography include the poor solubility of the layer components in the solvents selected for the preparation of the coating solutions, insufficient differentiation between the image areas and the non-image areas, poor developability, undesirable scumming during printing, low practical light-sensitivity, poor adhesion of the imaging layer, low resistance to delamination under humid conditions, poor resistance to press chemicals and short press life.
U.S. Pat. No. 4,189,320 describes polymers derived from phenol formaldehyde novolak resin and organic isocyanates that are used in conventionally exposed positive working plates. While the adhesion of the coating to the support is improved, the image contrast and edge sharpness deteriorate during the developing process, particularly when the development is carried out using aggressive developers. The coating does not survive and is lost in the aggressive developer. There is no disclosure of a positive working imageable composition including a hydroxyfunctional resin that has a covalently bound radiation sensitive group. In addition, there is no disclosure of how to maintain the coating edges with little or no loss of the imageable composition under prolonged development in aggressive developers.
International Patent Application WO 9512837 discloses a photoreactive polymeric binder. The binder is derived from an isopropenyldimethyl benzyl isocyanate derivatised with hydroxyalkyl acrylate. The printing plate that uses this polymer exhibits improved runlength. The crosslinking in these systems is achieved by vinylic polymerization of the acrylic group, not by crosslinking of a hydroxyfunctional resin having a covalently bound radiation sensitive group with an isocyanate crosslinking agent.
Japanese Patent Document JP 55045017 describes a negative working printing plate containing a diazo resin and a resin binder with an isocyanate regenerator (stable at room temperature). After imaging and developing, the plate is baked crosslinked with the available resin. Coatings having enhanced runlengths are obtained. This patent document does not disclose positive working systems that have improved developer resistance of the unexposed coating to aggressive developers.
Japanese Patent Document JP 275834 discloses a composition having a blocked isocyanate group, an aqueous binder resin and an IR absorber. On thermal exposure, the isocyanate crosslinks with the binder resin. After development with water, a negative image results. This is a negatively working system. It does not disclose positive working systems that have improved developer resistance of the unexposed coating to aggressive developers.
Japanese Patent Document JP 62164049 discloses a thermal, negative working, non pre-heat plate system. There is no teaching of a negative working system that has an improved resistance to aggressive developers.
Japanese Patent Document JP 089451 discloses a thermally sensitive, positively working composition containing a phenolic resin, IR absorber and a multivalent isocyanate. There is no disclosure of an imageable composition which includes a hydroxyfunctional resin that has a covalently bound radiation sensitive group. In addition, there is no disclosure of resistance of the imageable composition aggressive developers under prolonged development conditions.
Thus, none of the above references discloses an imageable composition which includes a hydroxyfunctional resin that has a covalently bound radiation sensitive group and which is resistant to aggressive developers under prolonged development conditions.
Accordingly, it is an object of the present invention to provide an imagable composition, which includes an isocyanate crosslinking agent and a hydroxyfunctional resin having covalently bound radiation sensitive group.
It is another object of the present invention to provide an imagable composition, which is resistant to aggressive developers in the unexposed regions.
It is still another object of the present invention to provide an imagable composition, which enables coating edges to be maintained with little or no loss of material from the unexposed regions under prolonged development in aggressive developers.
The present invention provides such an imageable composition the unexposed regions of which are resistant to aggressive developers under prolonged development conditions.
SUMMARY OF THE INVENTION
The present invention provides a positive working imageable composition, including:
a hydroxyfunctional resin including a covalently bound radiation sensitive group capable of increasing the solubility of the imageable composition in an alkaline developer upon exposure to radiation; and
an isocyanate crosslinking agent.
The present invention also provides an imageable element including:
a substrate; and
a positive working imageable composition coated on a surface of the substrate, the composition including: a hydroxyfunctional resin including a covalently bound radiation sensitive group capable of increasing the solubility of the imageable composition in an alkaline developer upon exposure to radiation; and an isocyanate crosslinking agent.
The present invention further provides a method of producing an imaged element including the steps of:
providing an imageable element including a substrate and a positive working imageable composition coated on a surface of the substrate, the composition including: a hydroxyfunctional resin including a covalently bound radiation sensitive group capable of increasing the solubility of the imageable composition in an alkaline developer upon exposure to radiation; and a blocked or unblocked isocyanate crosslinking agent;
heating the imageable element at a temperature and length of time sufficient to produce a crosslinked imageable element;
imagewise exposing the crosslinked imageable element to produce an imagewise exposed element having exposed and un
Chu John S.
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
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