Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2002-01-24
2004-04-20
Huff, Mark E (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S171000, C430S176000, C430S905000, C430S330000, C430S958000, C430S964000
Reexamination Certificate
active
06723495
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lithographic printing. In particular, this invention relates to negative-working, water-developable, infrared and ultraviolet imageable elements useful as lithographic printing plate precursors.
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, which is typically an aqueous alkaline solution. 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 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.
During the development process, the developer becomes loaded with components of the imageable layer that have been removed during development. 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 alkaline developers, many of which also contain organic solvents, must be treated before disposal to render them non-hazardous. If the imageable element could be developed with water, rather with an alkaline developer, it would be unnecessary to treat alkaline developers before disposal. Thus, a need exists for imageable elements that can be developed with water, rather than with alkaline developers.
SUMMARY OF THE INVENTION
In one aspect the invention is a method for forming an image using a water-developable negative-working ultraviolet and infrared imageable element. The method comprises the steps of:
(a) imaging the imageable element and forming an imaged imageable element comprising imaged regions and unimaged regions in an imageable layer;
in which:
the imageable element is imaged either with ultraviolet radiation, with infrared radiation, or with heat,
the imageable element comprises:
a substrate comprising a hydrophilic surface, and
the imageable layer over the hydrophilic surface, and
the imageable layer comprises an imageable composition that comprises:
a latent Brönsted acid,
a water-soluble or water-dispersible binder, and
an acid-activated cross-linking agent;
(b) heating the imaged imageable element; and
(c) developing the imaged imageable element with water and removing the unimaged regions.
When the element is imaged with infrared radiation, the imageable composition typically additionally comprises a photothermal conversion material.
DETAILED DESCRIPTION OF THE INVENTION
Imageable Elements
The imageable elements comprise an imageable layer over the hydrophilic surface of a substrate. Preferably the imageable layer is on the hydrophilic surface of the substrate. Preferably no other layers are present.
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 imageable elements useful as 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, for example, polymeric films such as polyethylene terephthalate film, ceramics, metals, or stiff papers, or a lamination of any of these materials. Metal supports include aluminum, zinc, titanium, and alloys thereof.
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 subsequent coated layers. Examples of subbing layer materials are adhesion-promoting materials, such as alkoxysilanes, amino-propyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers, as well as conventional subbing materials used on polyester bases in photographic films.
The surface of an aluminum support may be treated by techniques known in the art, including physical graining, electrochemical graining, chemical graining, and anodizing. The substrate should be of sufficient thickness to sustain the wear from printing and be thin enough to wrap around a printing form, typically from about 100 to about 860 &mgr;m. Typically, the substrate comprises an interlayer between the aluminum support and the imageable layer. The interlayer may be formed by treatment of the support with, for example, silicate, dextrine, hexafluorosilicic acid, phosphate/fluoride, polyvinyl phosphonic acid (PVPA) or polyvinyl phosphonic acid copolymers.
The back side of the substrate (i.e., the side opposite the underlayer and imageable layer) may be coated with an antistatic agent and/or a slipping layer or matte layer to improve handling and “feel” of the imageable element.
Imageable Layer
The imageable layer comprises an imageable composition. The imageable composition comprises a latent Brönsted acid which is capable of forming a Brönsted acid by the action of either heat or light, a water-soluble or water-dispersible binder, an acid-activated cross-linking agent, and optionally and typically a photothermal conversion material.
Useful latent Brönsted acids are precursors that form a Brönsted acid both by thermally initiated decomposition and by photochemically initiated decomposition. Latent Brönsted acids include, for example, onium salts in which the cation is iodonium, sulphonium, diazonium, phosphonium, oxysulphoxonium, oxysulphonium, sulphoxonium, selenonium, arsonium, or ammonium, and the anion is a non-nucleophilic anion selected from, for example, tetrafluoroborate, hexafluorophosphate, hexafluoroantimonate, triflate, tetrakis(pentafluorophenyl)-borate, pentafluoroethyl sulfonate, p-methyl-benzyl sulfonate, ethyl sulfonate, trifluoromethyl acetate, and pentafluoroethyl acetate. Non-ionic latent Brönsted acids include, for example, haloalkyl-substituted s-triazines, which are described, for example, in Smith, U.S. Pat. No. 3,779,778. Examples of onium salts are diphenyliodonium hexafluorophosphate; triphenylsulfonium hexafluoroantimonate; and phenylmethyl-ocyanobenzylsulfonium trifluoromethane sulfonate. Water-soluble latent Brönsted acids, such as water-soluble onium salts, are preferred.
Water soluble diazonium salts that comprise one diazonium group (i.e., non-polymeric diazonium salts), such as 2-methoxy-4-aminophenyl diazonium hexafluorophosphate, 4-(dimethylam
Kitson Paul
Ray Kevin
Chacko-Davis Daborah
Huff Mark E
Kodak Polychrome Graphics LLC
RatnerPrestia
LandOfFree
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