Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making printing plates
Reexamination Certificate
2000-08-14
2003-04-29
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making printing plates
C430S270100, C430S271100, C430S273100, C430S281100, C430S283100, C430S286100, C430S348000, C430S944000, C430S945000, C101S453000, C101S463100, C101S465000
Reexamination Certificate
active
06555291
ABSTRACT:
FIELD OF THE INVENTION
The invention relates lithographic printing. More particularly, this invention relates to thermally imageable elements useful as lithographic printing plates and to a method for forming an image using a thermally imageable element.
BACKGROUND OF THE INVENTION
In lithographic printing, ink receptive areas, 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 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 plate precursors typically comprise a radiation-sensitive coating applied over the hydrophilic surface of a support. If after exposure to radiation the exposed regions of the coating become soluble or dispersible and are removed in the developing process revealing the underlying hydrophilic surface of the support, the plate is called a positive-working printing plate. Conversely, if the exposed regions of the plate become insoluble in the developer, and the unexposed regions are removed by the developing process, the plate is called a negative-working plate. In each instance, the regions of the radiation-sensitive layer (i.e., the image areas) that remain are ink-receptive and the regions of the hydrophilic surface revealed by the developing process accept water, typically a fountain solution, and repel ink.
Direct digital imaging of lithographic printing plate precursors, which obviates the need for exposure through a negative, is becoming increasingly important in the printing industry. Thermally imageable systems have been developed in which it has been suggested that a thermally frangible complex is formed between a polymeric material and a solubility-suppressing component that reversibly suppresses the solubility of the polymeric material in the developer. After imagewise thermal exposure, the rate of removal of the exposed regions by the developer is greater that the rate of removal of the unexposed regions so that the exposed regions are removed by the developer to form an image. Such systems are disclosed in, for example, Parsons, WO 97/39894 and U.S. Pat. No. 6,280,899; Nagasaka, EP 0 823 327; Miyake, EP 0 909 627; West, WO 98/42507 and U.S. Pat. No. 6,090,532; and Nguyen, WO 99/11458, and U.S. Pat. No. 6,060,217. However, in these systems it is necessary to use a solubility-suppressing component for the polymeric material in the top. Thus, a need exists for an improved thermally imageable element, useful as a lithographic printing member, that does not suffer from this disadvantage.
SUMMARY OF THE INVENTION
In one embodiment, the invention is a method for forming an image using a thermally imageable element comprising a top layer that does not comprise a compound that acts as a solubility-suppressing component. The method comprises the steps of:
a) thermally imaging the thermally imageable element and producing exposed and unexposed regions in the thermally imageable element; and
b) developing the thermally imageable element with an aqueous alkaline developer and removing the exposed regions;
in which:
the thermally imageable element comprises, in order:
a top layer;
an underlayer; and
a hydrophilic substrate;
the underlayer comprises a first polymeric material;
the top layer comprises a second polymeric material;
the second polymeric material is removable by the aqueous alkaline developer;
the top layer is free of materials that function as a solubility-suppressing component for the second polymeric material;
the top layer is ink-receptive; and
the aqueous alkaline developer has a pH of at least 7 to about 11.
In another embodiment, the invention is a thermally imageable element. In still another embodiment, the invention is a method of printing using an imaged and developed thermally imageable element.
The top layer does not require a compound that functions as a solubility-suppressing component for the second polymeric material. Consequently, the top layer is free of materials that function as a solubility-suppressing component for the second polymeric material. Typically, the aqueous alkaline developer has a pH of about 10. In one embodiment, the top layer consists essentially of the second polymeric material. In a preferred embodiment, the second polymeric material is a phenolic resin or a sulphonanide resin, more preferably a novolac resin or a resole resin.
DETAILED DESCRIPTION OF THE INVENTION
The thermally imageable element (sometimes referred to as a precursor for a lithographic printing plate or a lithographic printing member) comprises a substrate with a hydrophilic surface, an underlayer comprising a first polymeric material, and an ink-receptive top layer comprising a second polymeric material. The underlayer is over the hydrophilic surface, and the top layer over the underlayer. The top layer does not comprise a solubility inhibitor for the second polymeric material. Although other layers, such as radiation absorbing layers may be present, typically no other layers are present. The thermally imageable element is thermally exposed and developed with an aqueous alkaline developer having a pH between 7 and 11 to remove the exposed regions without removing the unexposed regions. The imaged element is useful as a lithographic printing plate or a lithographic printing member.
Hydrophilic Substrate
The hydrophilic substrate, i.e., the substrate that comprises 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 and 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
Baxter Janet
Gilliam Barbara
Kodak Polychrome Graphics LLC
LandOfFree
Thermal digital lithographic printing plate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermal digital lithographic printing plate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermal digital lithographic printing plate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017317