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
2001-04-04
2004-02-17
Baxter, Janet (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
C430S302000, C430S303000
Reexamination Certificate
active
06692890
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imageable element and a method of producing an imaged element that can be used in lithographic printing plates. More particularly, the present invention relates to an imageable element comprising a hydrophilic anodized aluminum base and coated thereon an image-forming layer comprising polymer particles and a method of producing the same.
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.
In the production of common lithographic printing plates, also called surface litho plates or planographic printing plates, a support that has affinity to water or obtains such affinity by chemical treatment is coated with a thin layer of a photosensitive composition. Coatings for that purpose include light-sensitive polymer layers containing diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers, particularly diazo-sensitized systems, which are widely used. Upon image-wise exposure of the light-sensitive layer the exposed image areas become insoluble and the unexposed areas remain soluble. The plate is then developed with a suitable liquid to remove the diazonium salt or diazo resin in the unexposed areas.
Eurpean Patent Application No. 849,091 A1 and U.S. Pat. No. 6,001,536 disclose thermal coalescence of imageable compositions, including on-press developable compositions. These patent do not contain any disclosure regarding the oxide pore size on the surface of the substrate or the relationship of the oxide pore size to the particle size of the polymer in the image-forming layer.
U.S. Pat. No. 4,990,428 discloses an aluminum substrate having an oxide layer with 35-100 nm pore diameters, obtained by using phosphoric acid as the main electrolyte in the anodization process. When this substrate is overcoated with a free radical photo-polymerizable composition containing carboxylic acid groups and cured, the resulting lithographic plate exhibits superior press life. As above, this patent also does not contain any disclosure regarding the relationship of pore size to particle size of the polymer in the image-forming layer.
U.S. Pat. No. 4,865,951 discloses a bilayer anodic surface produced in a 2-stage process, which affords average pore size diameters of 10-75 nm in the upper layer and substantially greater diameters in the lower layer. A lithographic printing plate comprising an imageable layer on this support is shown to improve stain resistance. However, there is no disclosure regarding the relationship of pore size to particle size.
U.S. Pat. No. 5,922,507 discloses a photosensitive imaging element having a two-phase layer on a support. The two-phase layer has a hydrophilic continuous phase containing a hardened hydrophilic polymer and a dispersed hydrophobic photopolymerizable phase that has a multifunctionally polymerizable monomer and a photoinitiator. The hydrophobic photopolymerizable phase is formed of particles having an average particle size comprised between 0.1 and 10 &mgr;m, i.e., 100-10,000 nm. Neither pore size on the support nor pore size/imaging layer particle size matching are mentioned.
The present invention provides average pore diameter to average particle diameter ratios that can enhance adhesion, which enhances the sensitivity and the press life of the printing plates prepared therefrom.
SUMMARY OF THE INVENTION
The present invention includes a radiation-imageable element for lithographic printing. The radiation-imageable ellement comprises a hydrophilic anodized aluminum base having a surface comprising pores, and coated thereon, an image-forming layer comprising polymer particles, the ratio of said average pore diameter to said average particle diameter being from about 0.4:1 to about 10:1.
The present invention also includes a method of producing an imaged element. The method comprises the steps of:
providing a radiation-imageable element for lithographic printing comprising: a hydrophilic anodized aluminum base having a surface comprising pores; and coated thereon, an image-forming layer comprising polymer particles, the ratio of the average pore diameter to the average particle diameter being from about 0.4:1 to about 10:1; and
imagewise exposing the radiation-imageable element to radiation to produce exposed and unexposed regions.
The present invention further includes a method of producing an imaged element having complementary ink receiving and ink rejecting regions. The method comprises the steps of:
providing a radiation-imageable element for lithographic printing comprising: a hydrophilic anodized aluminum base having a surface comprising pores; and coated thereon, an image-forming layer comprising polymer particles, the ratio of the average pore diameter to the average particle diameter being from about 0.4:1 to about 10:1;
imagewise exposing the radiation-imageable element to radiation to produce exposed and unexposed regions; and
contacting said imagewise exposed radiation-imageable element and a developer to selectively remove said exposed or said unexposed regions.
The present invention provides average pore diameter to average particle diameter ratios that can enhance the interaction of the image-forming layer with the substrate surface layer following thermal imaging by allowing the polymer particles to enter into the oxide pores of the substrate, thereby enhancing adhesion. The enhanced adhesion, in turn, will enhance the sensitivity and the press life of the printing plates.
DETAILED DESCRIPTION OF THE INVENTION
Lithographic printing is based on the immiscibility of oil and water. Ink receptive areas are generated on the surface of a hydrophilic surface. When the surface is moistened with water and then ink is applied, the hydrophilic background areas retain the water and repel the ink. The ink receptive areas accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. Typically, the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is thereafter reproduced.
Lithographic printing plate precursors, i.e., imageable elements, typically include an imageable coating applied over the hydrophilic surface of a support material. If after exposure to radiation, the exposed regions of the coating become the ink-receptive image regions, the plate is called a negative-working printing plate. Conversely, if the unexposed regions of the coating become the ink-receptive image regions, the plate is called a positive-working plate. In the present invention, the imagewise exposed regions are rendered less soluble or dispersible in a developer and become the ink-receptive image areas. The unexposed regions, being more readily soluble or dispersible in the developer, are removed in the development process, thereby revealing a hydriphilic surface, which readily accepts water and becomes the ink-repellant image area.
The term “graft” polymer or copolymer in the context of the present invention refers to a polymer which has as a side chain a group having a molecular weight of at least 200. Such graft copolymers can be obtained, for example, by anionic, cationic, non-ionic, or free radical grafting methods, or they can be obtained by polymerizing or co-polymerizing monomers, which contain such groups.
The term “polymer” in the context of the present invention refers to high and low molecular weight polymers, including oligomers, and includes homopolymers and copolymers. The te
Huang Jen-Chi
Pappas S. Peter
Saraiya Shashikant
Zhong Xing-Fu
Baxter Janet
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
Walke Amanda C.
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