Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-12-05
2003-03-04
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...
C430S271100, C430S302000
Reexamination Certificate
active
06528228
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to light-sensitive imageable elements useful in lithographic printing. More particularly, this invention relates multilayer photoimageable elements, useful for forming lithographic printing members, that comprises a chemical resistant underlayer.
BACKGROUND OF THE INVENTION
The art of lithographic printing is based on the immiscibility of oil and water. Ink receptive areas are generated on the surface of a hydrophilic surface. When the surface is moistened with water and then ink is applied, the hydrophilic background areas retain the water and repel the ink and the ink receptive areas 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.
Lithographic printing plates typically comprise a radiation-sensitive coating applied to a support. If after exposure to radiation, the exposed portions of the coating become soluble and are removed in the developing process, the plate is called as a positive-working printing plate. Conversely, if exposed portion of the plate become insoluble in the developer and the unexposed portions are removed by the developing process, the plate is called a negative-working plate. In each instance, the portions of the radiation-sensitive layer (i.e., the image areas) that remain are ink-receptive.
Nagashima, GB 2,124,399, discloses a printing plate comprising one or more light-sensitive layer or layers positioned on a support. The layer or layers comprise an o-diazonaphthoquinone compound and an alkali soluble resin, in which the concentration of the o-diazonaphthoquinone compound decreases in the direction of the support.
In use, a lithographic printing member is often subjected to aggressive blanket washes, such as a “UV wash” to remove ultraviolet curable inks. The areas of the radiation-sensitive coating that remain after development must resist these aggressive blanket washes. Thus, a need exists for improved imageable elements, useful as lithographic printing members, that are robust and are resistance to aggressive washes.
SUMMARY OF THE INVENTION
The invention is a multilayer photoimageable element that comprises a chemical resistant underlayer. The element comprises:
a) a substrate, the substrate comprising a hydrophilic surface;
b) an underlayer over the hydrophilic surface; and
c) a top layer over the underlayer:
wherein:
the top layer is ink receptive;
the underlayer is soluble in aqueous alkaline developer;
the top layer comprises a material that comprises a o-diazonaphthoquinone moiety;
the underlayer is essentially free of material that comprises the o-diazonaphthoquinone moiety; and
the underlayer has a one-minute soak loss in 80 wt % diacetone alcohol/20 wt % water of less than 20 wt %.
In another embodiment, the invention is an exposed and developed element, which can be used as a lithographic printing member. In another embodiment, the invention is a process for forming the lithographic printing member. In still another embodiment, the invention is a method of printing using the lithographic printing member.
DETAILED DESCRIPTION OF THE INVENTION
The multilayer imageable element (sometimes referred to as a printing plate precursor) comprises a hydrophilic substrate, typically comprising an aluminum or polyester support; a chemically resistant underlayer; and an ink-receptive top layer. Although other layers, such as radiation absorbing layers may be present, typically no other layers are present. The element has increased speed and is very robust, developing well in a broad spectrum of positive and negative developers.
Hydrophilic Substrate
The hydrophilic substrate, i.e., the substrate comprising at least one hydrophilic surface, comprises a support, which may be any material conventionally used to prepare 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 polymeric films, ceramics, metals, or stiff papers, or a lamination of any of these materials. Paper supports are typically “saturated” with polymerics to impart water resistance, dimensional stability and strength.
Metal supports include aluminum, zinc, titanium, and alloys thereof. A preferred metal support is an aluminum sheet. The surface of the aluminum sheet may be treated by techniques known in the art, including physical graining, electrochemical graining, chemical graining, and anodizing, and then conditioned by chemical means, for example by treatment with water, a solution of phosphate or silicate salt, or a polycarboxylic acid to produce the hydrophilic surface.
If the surface is roughened, the average roughness Ra is preferably in the range 0.1 &mgr;m to 0.8 &mgr;m. Roughened substrates in which the surface has a surface roughness of 0.1 &mgr;m to 2 &mgr;m are disclosed in Bhambra, WO97/19819 (PCT/GB96/02883); Bhambra, WO98/52769 (PCT/GB98/01500); and Bhambra, WO98/52768 (PCT/GB/98/01496). In these substrates the support is coated with a hydrophilic layer that comprises a mixture of two particulate materials, preferably alumina and titanium dioxide. The mean particle size of the alumina particles is preferably in the range of 1 &mgr;m to 5 &mgr;m; the mean particle size of the titanium dioxide particles is preferably in the range of 0.1 &mgr;m to 0.5 &mgr;m.
Useful polymeric films include polyester films (such as Mylar® polyethylene terephthalate film sold by E.I. du Pont de Nemours Co., Wilmington, Del., and polyethylene naphthanate). A preferred polymeric film is polyethylene terephthalate.
The substrate may consist only of the support, or it may additionally comprise one or more optional subbing and/or adhesion layers. 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, aminopropyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers, as well as conventional subbing materials used on polyester bases in photographic films.
The back side of the substrate (i.e., the side opposite the underlayer and top 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.
The support should be of sufficient thickness to sustain the wear from printing and be thin enough to wrap around a printing form. Polyethylene terephthalate or polyethylene naphthanate, typically has a thickness of from about 100 to about 310 &mgr;m, preferably about 175 &mgr;m. Aluminum sheet typically has a thickness of from about 100 to about 600 &mgr;m.
Underlayer
The underlayer, or first layer, is over the hydrophilic surface of the hydrophilic substrate. After imaging, it is removed by the developer to expose the underlying hydrophilic surface of the substrate. It is preferably soluble in the aqueous alkaline developer to prevent sludging of the developer. Preferably it is soluble in a wholly aqueous developer, i.e., one that does not include added organic solvents.
The underlayer has one-minute soak loss in 80 wt % diacetone alcohol/20 wt % water of less than about 20 wt %, preferably less than 10 wt %, and more preferably less than about 5 wt %. In favorable cases a soak loss of less than about 2 wt % in 80 wt % diacetone alcohol/20 wt % water may be obtained.
The resistance of an underlayer to aggressive washes, such as a UV wash, can be tested by a one-minute soak loss in 80 wt % diacetone alcohol/20
Hauck Celin-Savariar
Hauck Gerhard
Chu John S.
Kodak Polychrome Graphics LLC
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