Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2001-06-11
2003-11-18
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...
C430S166000, C430S270100, C430S278100, C430S302000, C430S331000
Reexamination Certificate
active
06649319
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. In particular, this invention relates to a method of processing imagewise-exposed imageable elements useful as alkaline-developable lithographic printing plates using an aqueous alkaline developing-gumming solution.
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 imageable 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.
Typically, after development the imaged element must be treated with a specially formulated gumming or finisher solution to desensitize the non-image areas to assure that they will not accept ink upon printing. When a metal support is used for the imageable layer, the finisher also prevents oxidation of the non-image areas of the element during storage or while waiting for press mounting.
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.
The conventional method for processing imageable elements useful as lithographic printing plates comprises the following steps: imagewise exposure, developing, rinsing, gumming, and drying. In case of conventional negative-working plates, “2 in 1 processing,” which is described, for example, in Dhillon U.S. Pat. No. 4,873,174, can also be used. This method consists of the steps: exposure, development/gumming, drying, where development/gumming is carried-out with one solution and in one processor section. However, this method cannot be used for positive-working plates that comprise novolacs or similar resins due to the high alkalinity of the developer required for the dissolution of such resins in aqueous solutions. Residues of alkaline ingredients remaining at both image and non-image areas would lead to problems during printing and/or storage of the plates. Attempts have been made to prepare a single solution that simultaneously develops and gums positive-working plates by simply mixing typical developer and finisher compositions. However, such attempts suffer from several drawbacks, mainly from incompatibility of the components. Therefore, for positive-working plates, conventional processing is still required.
Thus, a need exists for a method for processing imageable elements useful as lithographic printing plates, especially for positive-working elements that comprise novolacs or similar resins, that does not require separate rinsing and gumming steps.
SUMMARY OF THE INVENTION
The invention is a method for forming an image. The method comprises the steps of:
(a) imaging an imageable element, the imageable element comprising an imageable layer over a hydrophilic support, and forming an imaged element comprising exposed regions and unexposed regions in the imageable layer; and
(b) simultaneously developing and gumming the imaged element by contacting the imaged element with an aqueous alkaline developing-gumming solution and removing one of the exposed regions and the unexposed regions of the imageable layer;
in which:
the aqueous alkaline developing-gumming solution comprises one or more water-soluble polyhydroxy compounds 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 hydrogen, alkyl group having 1 to 4 carbon atoms, CH
2
OR
3
in which R
3
is hydrogen or 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;
the aqueous alkaline developing-gumming solution has a pH of about 10.0 to about 14; and
the one or more polyhydroxy compounds comprise about 10 wt % to about 30 wt % of the aqueous alkaline developing-gumming solution.
Preferably, the method does not comprise either a rinsing step or a further gumming step following step (b). Preferably, the imageable layer comprises (i) at least one phenolic resin or at least one polymeric compound having pendent sulfonamide groups, and (ii) the hydrophilic support comprises aluminum or an aluminum alloy.
In another aspect, the invention is an imaged element useful as a lithographic printing plate formed by the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Developing and Gumming
The aqueous alkaline developing-gumming solution comprises one or more water-soluble polyhydroxy compounds having 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 hydrogen, alkyl group having 1 to 4 carbon atoms, CH
2
OR
3
in which R
3
is hydrogen or 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.
In one group of polyhydroxy compounds, R
1
is hydrogen or CH
2
OH and R
2
is hydrogen. In a preferred group of these polyhydroxy compounds, n is 5 or 6. This group includes the sugar alcohols, compounds of the structure H(CHOH)
n
H, which do not carry a free aldehyde or ketone group and do not show a reducing property. The sugar alcohols may be obtained from natural sources or prepared by hydrogenation of reducing sugars. Preferred sugar alcohols include mannitol, sorbitol, xylitol, ribitol, and arabitol. Other sugar alcohols include, for example, talitol, dulcitol, and allodulcitol.
In another group of polyhydroxy compounds, 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 these polyhydroxy compounds, n is 5 or 6, more preferably
Fiebag Ulrich
Timpe Hans-Joachim
Todock Uwe
Vihs Anfreas
Chu John S.
Kodak Polychrome Graphics LLC
RatnerPrestia
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