Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Finishing or perfecting composition or product
Reexamination Certificate
2001-05-11
2003-04-01
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Finishing or perfecting composition or product
C430S486000
Reexamination Certificate
active
06541188
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. In particular, this invention relates to a developing system for both positive-working and negative-working imageable elements useful as alkaline-developable lithographic printing plates and to a method for its use.
BACKGROUND OF THE INVENTION
In lithographic printing, ink receptive regions, 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 regions 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.
Imageable elements useful as lithographic printing plates, sometimes called printing plate precursors or printing forms, typically comprise an imageable layer applied over the surface of a hydrophilic substrate. The imageable 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 regions, it is necessary to remove regions of an imaged imageable element. The most common method for removing the undesired regions is to contact the imaged element with a developer. If after exposure to radiation the exposed regions of the layer are removed by the developer revealing the underlying hydrophilic surface of the substrate, the element is a positive-working printing element. Conversely, if the unexposed regions are removed, the element is a negative-working element. In each instance, the regions of the imageable 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 imageable elements comprise a light sensitive layer comprising a phenolic resin, such as a novolac resin, on a hydrophilic substrate, typically a specially treated aluminum sheet. In one type of element, for example, the light sensitive layer comprises 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 developer penetrates and removes the exposed, or image regions of the imageable layer, revealing the underlying hydrophilic surface of the substrate, without substantially affecting the complimentary unexposed regions.
Certain negative-working printing plates contain novolac resins, a cross-linking agent, and a radiation-sensitive component that produces acid on exposure. Subsequent heating cures the exposed regions, so that only the unexposed areas can be removed by an alkaline developer. The exposed regions, which remain after development, are oleophilic and will accept ink.
In both types of printing plates, an alkaline developer can attack the imageable layer, front side (aluminum oxide) and/or the backside (aluminum) of the imageable element. Developers for imageable elements that contain phenolic or similar resins typically comprise components that suppress the attack of the high alkaline developer either on the substrate or on the imageable layer. Often there are problems of miscibility of these components in the alkaline developer. Typically, silicate solutions (either as meta silicate or water glass) are used to protect aluminum substrates. In practice, this leads to problems caused by silicate deposits on developed plates.
In addition, the activity of developers based on meta-silicates cannot be monitored by conductivity measurements. Therefore, a top-up mode is required leading to a high volume of wasted developer. In this mode, only the developer is used to keep the activity of the developer in the developing section of a processor constant. This requires about 150 to 250 mL of developer per square meter of plate treated, from which about 100 to 200 mL are removed by an overflow device of the processor.
Therefore, a need exists for a developing system that protects the substrate from attack by an alkaline developer, that does not cause undesirable deposits on the developed printing plate, that requires only a small number of components, and whose activity can be monitored by conductivity measurements.
SUMMARY OF THE INVENTION
The invention is a developing system for both positive-working and negative-working imageable elements useful as lithographic printing plates. The developing system comprises both a developer and a replenisher.
The developer comprises an aqueous alkaline solution of one of more water-soluble suppressors of the following structure:
R
1
(CHOH)
n
R
2
in which n is 4 to 7; and
either (i) R
1
is hydrogen, aryl, or CH
2
OH; and R
2
is alkyl group having 1 to 4 carbon atoms, CH
2
OR
3
in which R
3
is an alkyl group having 1 to 4 carbon atoms, CH
2
N(R
4
R
5
) in which R
4
and R
5
are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or CO
2
H; or (ii) R
1
and R
2
together form a carbon-carbon single bond. These suppressors prevent attack by the alkaline developer on both the image and on the aluminum substrate.
The aqueous alkaline solution has a pH of about 10.0, typically greater than about 11.0, to about 14.0; and the one or more suppressors together comprise about 10 wt % to about 30 wt % of the developer.
Although the developer may be used as its own replenisher, typically a specially formulated replenisher, which comprises all the ingredients of the developer but which has a higher concentration of base is used as the replenisher.
preferred positive-working imageable element for use with the developing system of the invention comprises an aluminum substrate and an imageable layer that comprises a phenolic resin, preferably a novolac resin. Preferred suppressors include N-methyl-glucamin, meso-inosit, gulonic acid gamma-lactone, and mixtures thereof.
In another aspect, the invention is a method for forming an image using the developing system. In another aspect, the invention is an image formed by the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Developing System
Attack both on the imageable layer and on an aluminum or aluminum alloy substrate by a developer having a pH of greater than about 10 can be suppressed by water-soluble organic compounds, or suppressors, having the following structure:
R
1
(CHOH)
n
R
2
in which n is 4 to 7; and
either (i) R
1
is H, aryl, or CH
2
OH; and R
2
is alkyl group having 1 to 4 carbon atoms, CH
2
OR
3
in which R
3
is an alkyl group having 1 to 4 carbon atoms, CH
2
N(R
4
R
5
) in which R
4
and R
5
are each independently H or an alkyl group having 1 to 4 carbon atoms, or CO
2
H; or (ii) R
1
and R
2
together form a carbon-carbon single bond.
Either a single suppressor or a mixture of suppressors may be used. The suppressor or the mixture of suppressors comprises about 10 wt % to about 30 wt % of the developer.
In one group of suppressors, R
1
and R
2
together form a carbon-carbon single bond. Included are carbocyclic compounds of the structure: (CHOH)
n
, in which n is 4 to 7. In a preferred group of suppressors, n is 5 or 6, more preferably 6. There are nine possible stereoisomers of 1,2,3,4,5,6-hexahydroxycyclohexane, several of which are naturally occurring. A preferred suppressor is meso-inosit (cis-1,2,3,5-trans-4,6-hexahydroxycyclohexane). meso-Inosit can be isolated from corn steep liquor.
In another group of suppressors, R
1
is H, aryl, or CH
2
OH; and R
2
is alkyl group having 1 to 4 carbon atoms, CH
2
OR
3
in which R
3
is an alkyl group having 1 to 4 carbon atoms, CH
2
N(R
4
R
5
) i
Fiebag Ulrich
Timpe Hans-Joachim
Tondock Uwe
Vihs Andreas
Kodak Polychrome Graphics LLC
Le Hoa Van
RatnerPrestia
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