Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-12-22
2001-09-25
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S166000, C430S275100, C430S302000, C430S014000, C525S203000, C525S205000, C525S217000, C525S218000, C525S221000, C525S222000, C525S238000
Reexamination Certificate
active
06294311
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to imageable elements useful in lithographic printing. More particularly, this invention relates to multilayer elements useful as lithographic printing members in which the underlayer comprises a combination of polymeric materials that provides resistance both to fountain solution and to aggressive washes.
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.
Infrared-sensitive imaging elements for the preparation of positive-working lithographic printing plates have been disclosed comprising a substrate, an aqueous alkali soluble underlayer, and a radiation-sensitive top layer. On exposure, the exposed areas of the top layer become soluble or permeable in aqueous alkali so that the developer can penetrate the top layer and remove the underlayer, exposing the underlying substrate. Systems have been produced in which a developer insoluble top layer is coated over a developer soluble underlayer. Following exposure both layers are removed by the developer in the exposed region, revealing the hydrophilic surface of the underlying substrate.
In use, a lithographic printing member comes in contact with fountain solution. In addition, the printing member is often subjected to aggressive blanket washes, such as a “UV wash” to remove ultraviolet curable inks. However, many of these systems have limited resistance to either fountain solution and/or aggressive blanket washes. Thus, a need exists for an improved imageable element, useful as a lithographic printing member, that does not suffer from these disadvantages.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a multilayer imageable element, useful as a precursor for a lithographic printing member, in which the underlayer is resistant both to fountain solution and to aggressive washes, such as a UV wash.
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 underlayer comprises a combination of at least a first polymeric material and a second polymeric material;
the top layer comprises a third polymeric material; and
the chemical resistance parameter for the underlayer is greater than about 0.4.
Depending primarily on the nature of the top layer, the element may be imaged photochemically or thermally. Although other layers, such as radiation absorbing layers may be present in the element, typically no other layers are present.
In another embodiment the invention is a composition useful as the underlayer for an imageable element. 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 invention is an imageable element useful as precursor for a lithographic printing plate. The element comprises a hydrophilic substrate, an underlayer, and a top layer. The underlayer comprises a unique combination of polymeric materials that surprisingly provides resistance both to fountain solution and to aggressive washes, such as a UV wash. Any top layer known in the art of lithographic printing may be used with the underlayer of the invention.
If the element is to be imaged by imagewise exposure with a beam of radiation, typically in the range of about 800 nm to about 1200 nm, the element absorbs imaging radiation. Either the top layer, the underlayer, or both may absorb the imaging radiation, and/or a separate imaging radiation absorbing layer may be present in the element. If the element is to be imaged photochemically or by exposure with a thermal head, it is unnecessary that the element absorb radiation in the range of 800 nm to 1200 nm.
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, WO097/19819 (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
Huang Jianbing
Jarek Mathias
Merchant Nishith
Patel Jayanti
Shimazu Ken-ichi
Chu John S.
Kodak Polychrome Graphics LLC
Ratner & Prestia
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