Radiation imagery chemistry: process – composition – or product th – Regenerating image processing composition – Developer
Reexamination Certificate
2001-11-14
2004-07-06
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Regenerating image processing composition
Developer
C430S302000, C210S732000, C210S746000
Reexamination Certificate
active
06759185
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. In particular, this invention relates to a method for the reuse of loaded developers.
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, also called printing plate precursors, 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 an imageable layer comprising a phenolic resin, such as a novolac resin, on a hydrophilic substrate, typically a specially treated aluminum sheet. For example, in one type of element the light sensitive layer comprises a novolac resin and a o-diazoquinone or diazonaphthoquinone, such as a naphthoquinonediazide sulfonic acid ester of a novolac resin. Upon exposure to ultraviolet light, the diazonaphthoquinone is converted to the corresponding carboxylic acid. The developer penetrates and removes the exposed regions of the imageable layer, revealing the underlying hydrophilic surface of the substrate, without substantially affecting the complimentary unexposed regions. During the printing process, the unexposed regions act as the image regions and accept ink.
The imageable layers of certain negative-working printing plates comprise a novolac resin, 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.
During the development process, the developer becomes loaded with components of the imageable layer that have been removed during development. Although some of the partly loaded developer is removed from the developing bath with the developed printing plates (drag-out) and is replaced with a replenisher, the amount of material in the developer increases as more imageable elements are developed. Once the developer becomes fully loaded, scum will form on the developed printing plates and on the components of the processor. The developer then must be replaced with fresh developer and the loaded developer disposed of.
Because of environmental considerations, the loaded developer must be treated before disposal to render it non-hazardous. If the loaded developer could be reused, it would be unnecessary to dispose of loaded developer and to prepare fresh developer. Thus, a need exists for a method for reusing loaded developer.
SUMMARY OF THE INVENTION
The invention is a method for producing a refreshed developer from a loaded developer. The method comprises the steps of:
(a) adding about 0.8 wt % to about 5.0 wt % of a water-soluble polyoxyalkylene derivative to a loaded silicate-containing developer,
in which:
the polyoxyalkylene derivative comprises recurring units of the —(CH
2
—CHR—O)— structural unit, in which each R is independently hydrogen or methyl;
the loaded developer comprises loaded solids; and
the loaded developer has a loaded solids content of about 0.1 wt % to about 10 wt %;
(b) separating insoluble material from the developer and producing an essentially colorless liquid, in which the insoluble material comprises material dispersed in the loaded developer, a precipitate formed in step (a), or a combination thereof; and
(c) adjusting the alkalinity level of the essentially colorless liquid and producing the refreshed developer.
The refreshed developer may be used to develop imaged imageable elements. Or it may be mixed with fresh developer and used to develop imaged imageable elements.
DETAILED DESCRIPTION OF THE INVENTION
Production of the Refreshed Developer
In one aspect, the invention is a method for the recovery and reuse of loaded developer. Imaging, as described below, produces an imaged precursor, which comprises a latent image of image regions and non-image regions in an imageable layer. Development of the imaged precursor to form a printing plate, or printing form, converts the latent image to an image by removing the non-image regions, revealing the hydrophilic surface of the underlying substrate.
As described below, the imageable layer of imageable elements comprises materials that are soluble or dispersible in aqueous base, such as phenolic polymers, carboxylic acid polymers, and/or sulfonamide polymers. The developers used in the process of the invention have a pH before loading of greater than about 12, typically about 12 to about 14, more typically from about 12.5 to about 13.7. In addition, the developers comprise of silicates. Typically these developers comprise about 1 wt % to about 20 wt %, based on the weight of the developer, of a silicate. The silicate is typically sodium silicate, potassium silicate, sodium waterglass or potassium waterglass, i.e. silicates with a molar ratio of SiO
2
to M
2
O (with M=alkali metal) of 2 or more. Developers that comprise silicates are disclosed, for example, in Yamasue, U.S. Pat. No. 4,259,434; Seino, U.S. Pat. No. 4,452,880; Miller, U.S. Pat. No. 5,851,735; Eckler, U.S. Pat. No. 5,998,102; Miro, EP-A-0 732 628; Toyama,GB-A-2,276,729 (DE-A-4 411 176); and Fiebag, U.S. Pat. No. 6,143,479.
The alkalinity is provided using a suitable concentration of any suitable chemical base, such as an alkali metal hydroxide, such as sodium hydroxide, lithium hydroxide or potassium hydroxide. The alkalinity level is defined as the volume of 0.5 N hydrochloric acid (HCl) in mL needed to reach the first inflection point in the titration of 5 mL of developer. The developer typically has an alkalinity level of about 4.5 to about 10.0, preferably about 5.5 to about 8.0.
In addition, the developer may comprise one or more components that suppress the attack of the alkali on the substrate and/or the imageable layer, for example phosphonic acid derivatives such as the sodium salt of hydroxyethane diphosphonic acid and the potassium salt of hexamethylene diamino-tetramethylenephosphonic acid (typically about 0.01 to about 5 wt %; more typically about 0.1 to about 1 wt %, based on the weight of the developer), and glycols such as ethylene glycol and propylene glycol. Other optional components include one or more surfactants (anionic, nonionic and/or amphoteric) in a suitable amount (for example up to 5 wt % based on the total composition weight), chelating agents (such as ethylenediaminetetraacetic acid,diethylene-triaminepentaacetic acid, triethylenetetraaminehexaacetic acid, hydro
Fiebag Ulrich
Timpe Hans-Joachim
Tondock Uwe
Vihs Andreas
Chu John S.
Kodak Polychrome Graphics LLC
RatnerPrestia
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