Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Readily visible image formation
Reexamination Certificate
2002-10-17
2003-12-09
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Readily visible image formation
C430S302000
Reexamination Certificate
active
06660454
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to additive compositions suitable for rinse water used for processing lithographic printing plates, particularly to additive compositions for rinse water in water recycling systems. Further, the invention refers to aqueous concentrates of said additive compositions, to a method of processing an imagewise exposed lithographic printing plate by using rinse water containing said additive composition, and to printing plates obtained by said method.
BACKGROUND OF THE INVENTION
The art of lithographic printing is based upon the immiscibility of oil and water, in which oily material or ink is preferentially retained by the image areas and the water or fountain solution is preferentially retained by the non-image areas of the printing plate. When a suitably prepared surface is moistened with water and ink is applied, the background or non-image areas retain the water and repel the ink while the image areas accept the ink and repel the water. The ink on the image areas is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth and plastics. 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.
Lithographic printing plates can be either negative-working or positive-working, and comprise one or more radiation-sensitive layers on a suitable substrate, such as metal or polymeric support. The radiation-sensitive layer generally includes one or more radiation-sensitive components that may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material. Certain useful printing plates can be used either as positive-working or negative-working.
A negative-working printing plate generally has a light sensitive layer composed of a radiation-sensitive component such as an unsaturated resin on a suitable substrate. Upon imagewise exposure to light, the exposed areas are hardened, leaving non-exposed areas removable during development. Certain negative-working printing plates contain novolac resins, a cross-linking agent, and a radiation-sensitive component that produces acid on exposure. By subsequently heating the plate, only the exposed areas are cured and the unexposed areas can be removed by a developer. The exposed, hardened areas are therefore oleophilic and will accept ink while the non-exposed underlying areas of the substrate are hydrophilic.
An alkaline developable positive-working printing plate generally has a light sensitive layer comprising a novolac resin and a radiation-sensitive component such as an o-diazoquinone or diazonaphthoquinone compound. Upon imagewise exposure to imaging radiation, the radiation-sensitive component is converted to the corresponding carboxylic acid. The use of an alkaline developer will remove only the exposed areas of the radiation-sensitive layer, leaving the surface of the support. Because the surface of the support is hydrophilic, the uncovered non-image area attracts water and repels the oily ink. The image area remaining after development is oleophilic thereby repelling water and attracting the printing ink.
After subjecting the imagewise exposed printing plate to a suitable developer solution the plate is rinsed with water (“rinse water”) in order to remove the developer solution adhering thereto. Subsequently, the plate is usually subjected to a gumming step in order to protect the plate against air and pollution during storage before being used for printing.
The rinsing of the plate with fresh water results in a high consumption of water. In addition to the high costs for the fresh water, there is an additional high cost for waste-water treatment, because a large amount of waste water contaminated with both the organic substances of the radiation-sensitive layer and the ingredients of the used developer has to be treated. Therefore, there is a tendency to use a water recycling system in order to save water and costs. This means that the printing plates are no longer rinsed with fresh water (like tap water and well water) but with water that is permanently in circulation. However, due to the permanent recycling the water quality decreases by the uptake of developer solution and coating components during the rinsing step; consequently the rinsing efficiency decreases and the image and non-image areas of the plate might be interfered.
Furthermore, it is time consuming to carry out the rinsing and gumming subsequently in separate process steps. Therefore, it would be desirable to overcome the necessity of a separate gumming step.
Therefore, a need exists for a method of processing an imagewise exposed printing plate in which the rinse water can be recirculated without a decrease of rinsing efficiency, which does not require of a separate gumming step, and which can be carried out by the use of conventional processors, i.e. which does not require new and/or additional equipment.
SUMMARY OF THE INVENTION
The invention is an additive composition that can be added to the rinse water used to rinse an imagewise exposed and developed lithographic printing plate (also known as a printing plate precursor), an aqueous concentrate comprising the additive composition, a rinse water, a method of for processing an imagewise exposed lithographic printing plate using the rinse water, and an exposed and developed lithographic printing plate (also called a printing form) produced by the method of the invention. The additive composition comprises:
(a) at least one water-soluble film-forming polymer; and
(b) at least one compound selected from the group consisting of phosphonic acid derivatives of formula I
in which X is C
2
-C
6
alkylene or
in which: k is 0 or 1; m is 1, 2, or 3; p is 1, 2, or 3; r is an integer from 10 to 20; R
1
and R
3
are each independently H or C
1
-C
4
alkyl; R
2
and R
4
are each independently H, OH or C
1
-C
4
alkoxy; and Y is —R
6
N—(CH
2
)
n
—(NR
5
)
q
—, in which q is 0 or 1, n is an integer from 0 to 8, and R
5
and R
6
are each independently H, C
1
-C
4
alkyl, or —CH
2
—P(O)(OH)
2
. Preferably, the additive composition further comprises at least one pH regulating agent capable of maintaining the pH value of an aqueous solution at about 7 or below.
DETAILED DESCRIPTION OF THE INVENTION
One essential component of the additive composition is at least one film-forming water-soluble polymer. Typical examples of such polymers include natural substances and modified products thereof like gum arabic, starch derivatives, for instance, dextrin, wasted dextrine, enzyme-modified dextrin, etherified enzyme-modified dextrin, carboxymethylated starch and starch phosphate, octenyl succinated starch, alginates or cellulose derivatives, for instance, carboxymethyl cellulose, carboxyethyl cellulose, hydroxyethyl cellulose, methyl cellulose and hydroxypropyl methyl cellulose; and synthetic substances like polyvinyl alcohol and derivatives thereof, polyvinyl pyrrolidone, polyacrylamide and copolymers thereof, polyacrylic acid and copolymers thereof, styrene/maleic anhydride copolymers, vinyl methyl ether/maleic anhydride copolymer and vinyl acetate/maleic anhydride copolymers. These water-soluble polymers may be used alone or in combination and the amount thereof in the additive composition of the invention preferably ranges from about 0.1 to 80% by weight, more preferably about 5 to 30% by weight on the basis of the total amount of additives.
Another essential component of the additive composition is at least one component selected from the group consisting of phosphonic acid derivatives of formula I
in which X is C
2
-C
6
alkylene or
in which: k is 0 or 1; m is 1, 2, or 3; p is 1, 2, or 3; r is an integer from 10 to 20; R
1
and R
3
are each independently H or C
1
-C
4
alkyl; R
2
and R
4
are each independently H, OH or C
1
-C
4
alkoxy; and Y is —R
6
N—(CH
2
)
n
—(NR
5
)
q
—, in which q is 0 or 1, n is an integer from 0 to 8, and R
5
and R
6
are each independentl
Kodak Polychrome Graphics LLC
Le Hoa Van
RatnerPrestia
LandOfFree
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