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
2001-03-13
2003-09-02
Hamilton, Cynthia (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
C430S162000, C430S155000, C430S273100, C430S165000, C101S456000, C101S457000
Reexamination Certificate
active
06613494
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. In particular, this invention relates to imageable elements having a protective overlayer and to methods for their preparation.
BACKGROUND OF THE INVENTION
In lithographic printing, ink receptive areas, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and 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 to be reproduced.
Lithographic printing plates, sometimes called printing plate precursors or printing forms, typically comprise a radiation-sensitive layer applied over the surface of a hydrophilic support. The radiation-sensitive layer includes one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material.
To obtain a printing plate with imagewise distribution of printable areas, it is necessary to remove areas of an imaged printing plate. The most common method for removing the undesired areas is to contact the imaged plate with a developer solution. If after exposure to radiation the exposed regions of the layer are removed by the developer revealing the underlying hydrophilic surface of the support, the plate is a positive-working printing plate. Conversely, if the unexposed regions are removed, the plate is a negative-working plate. In each instance, the regions of the radiation-sensitive layer (i.e., the image areas) that remain after development are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
Many alkaline-developable positive-working printing plates have a light sensitive layer comprising a novolac resin and a radiation-sensitive o-diazoquinone or diazonaphthoquinone compound, such as a naphthoquinonediazide sulfonic acid ester of a novolac resin. Upon exposure to light, the radiation-sensitive diazonaphthoquinone is converted to the corresponding carboxylic acid. The alkaline developer removes only the exposed regions of the radiation-sensitive layer, revealing the underlying hydrophilic surface of the support.
The amount of diazonaphthoquinone compound in a radiation-sensitive layer determines its photospeed. Diazonaphthoquinone inhibits attack by the developer. When more diazonaphthoquinone is present in the layer, more radiation is required to covert the diazonaphthoquinone to alkali soluble acid. Thus, photospeed can be increased by decreasing the amount of diazonaphthoquinone in the layer.
However, reducing the amount of diazonaphthoquinone compound in the layer also reduces the resistance of the unimaged regions to attack by the developer. Consequently, photospeed cannot be increased by reducing the amount of diazonaphthoquinone in the radiation-sensitive layer without reducing the resistance of the unimaged regions to developers.
Developer resistance can be enhanced by heating the unexposed printing plate in an oven for a prolonged period of time. Because printers require printing plates with consistent properties, this is generally done by the manufacturer, increasing the cost of manufacture of the printing plates.
Developer resistance can also be enhanced by applying a developer-resistant top layer over the radiation-sensitive layer. Van Damme, EP 0 950 518, discloses a two-layer heat mode imaging element in which the top layer comprises an infra-red dye or pigment, a binder resin, and a surfactant. However, the material added to the top layer must be soluble in the solvent used to apply the top layer. In addition, the material used in this layer sometimes tends to form insoluble residues in the developer bath. The throughput for the developer is reduced, and the bath may require extensive cleaning to remove the residues.
Thus, a need exists for a printing plate that has improved photospeed but in which the unexposed regions are resistant to alkaline developers and do not require a prolonged conditioning step as part of the manufacturing process. In addition, undesirable residues should be formed in the developer bath.
SUMMARY OF THE INVENTION
In one aspect, the invention is a method for preparing a positive working imageable element, the element comprising, in order:
a hydrophilic substrate;
a bottom layer; and
an overlayer comprising an overlayer material; the method comprising:
applying the overlayer over the bottom layer of a precursor comprising the bottom layer and the hydrophilic substrate, and forming the imageable element;
in which:
the overlayer is applied from a solution of the overlayer material in a solvent;
the bottom layer comprises a positive working photosensitive composition;
the positive working photosensitive composition comprises a phenolic resin;
the overlayer material reduces the alkali solubility of the phenolic resin;
the bottom layer is essentially insoluble in the solvent; and
the overlayer is less than about 0.01 &mgr;m thick.
In one embodiment, the overlayer is applied by dipping or immersing the precursor in a solution comprising the overlayer material and the solvent. In another embodiment, a solution of the overlayer material is applied to, or coated over, the bottom layer.
In another aspect, the invention is the imageable element. In one embodiment, the overlayer consists essentially of the overlayer material.
DETAILED DESCRIPTION OF THE INVENTION
Hydrophilic Substrate
The hydrophilic substrate, i.e., a substrate that comprises at least one hydrophilic surface, comprises a support, which may be any material conventionally used to prepare lithographic printing plates. The support is preferably strong, stable and flexible. It should resist dimensional change under conditions of use so that color records will register in a full-color image. Typically, it can be any self-supporting material, including polymeric films, ceramics, metals, or stiff papers, or a lamination of any of these materials. Paper supports are typically “saturated” with a polymeric material to impart water resistance, dimensional stability, and strength.
Metal supports include aluminum, zinc, titanium, and alloys thereof. A preferred metal support is an aluminum sheet. To produce the hydrophilic surface, the surface of the aluminum sheet may be treated by techniques well known in the art. These include, for example, physical graining, electrochemical graining, chemical graining, and anodizing, followed by chemical conditioning, for example by treatment with water, a solution of phosphate or silicate salt, or a polycarboxylic acid. Roughened substrates in which the surface has a surface roughness of 0.1 &mgr;m to 2 &mgr;m are disclosed in Bhambra, U.S. Pat. No. 6,105,500; WO98/52769; and WO98/01496.
Useful polymeric films include polyester films (such as MYLAR® polyethylene terephthalate film sold by E.I. du Pont de Nemours and Co., Wilmington, Del.) and polyethylene naphthanate. A preferred polymeric film is polyethylene terephthalate.
The substrate may consist only of the support, or it may additionally comprise one or more optional subbing and/or adhesion layers. Typically, polymeric films contain a sub-coating on one or both surfaces to modify the surface characteristics to enhance the hydrophilicity of the surface, to improve adhesion to subsequent layers, to improve planarity of paper substrates, and the like. The nature of this layer or layers depends upon the substrate and the composition of subsequently applied layers. Examples of subbing layer materials are adhesion-promoting materials, such as alkoxysilanes, aminopropyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers, as well as conventional subbing materials used on polyester bas
Fiebag Ulrich
Frank Dietmar
Hauck Gerhard
Savariar-Hauck Celin
Hamilton Cynthia
Kodak Polychrome Graphics LLC
LandOfFree
Imageable element having a protective overlayer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Imageable element having a protective overlayer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Imageable element having a protective overlayer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3111806