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
2000-06-26
2002-10-15
Hamilton, Cynthia (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
C430S275100, C430S272100, C430S276100, C430S944000, C430S954000, C430S302000, C101S456000, C101S463100, C101S451000
Reexamination Certificate
active
06465152
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to lithographic imaging members, and particularly to heat-sensitive imaging members that can be used with or without wet processing after imaging. The invention also relates to a method of digitally imaging such imaging members, and to a method of printing using them.
BACKGROUND OF THE INVENTION
The art of lithographic printing is based upon the immiscibility of oil and water, wherein an oily material or ink is preferentially retained by an imaged area and the water or fountain solution is preferentially retained by the nonimaged areas. When a suitably prepared surface is moistened with water, and ink is then applied, the background or nonimaged areas retain the water and repel the ink while the imaged areas accept the ink and repel the water. The ink is eventually transferred to the surface of a suitable substrate, such as cloth, paper or metal, thereby reproducing the image.
Very common lithographic printing plates include a metal or polymer support having thereon an imaging layer sensitive to visible or UV light. Both positive- and negative-working printing plates can be prepared in this fashion. Upon exposure, and perhaps post-exposure heating, either imaged or nonimaged areas are removed using wet processing chemistries.
Thermally sensitive printing plates are less common. Examples of such plates are described in U.S. Pat. No. 5,372,915 (Haley et al). They include an imaging layer comprising a mixture of dissolvable polymers and an infrared radiation absorbing compound. While these plates can be imaged using lasers and digital information, they require wet processing using alkaline developer solutions.
It has been recognized that a lithographic printing plate could be created containing an IR absorbing layer. For example, Canadian 1,050,805 (Eames) discloses a dry planographic printing plate comprising an ink receptive substrate, an overlying silicone rubber layer, and an interposed layer comprised of laser energy absorbing particles (such as carbon particles) in a self-oxidizing binder (such as nitrocellulose). Such plates were exposed to focused near IR radiation with a Nd
++
YAG laser. The absorbing layer converted the infrared energy to heat thus partially loosening, vaporizing or ablating the absorber layer and the overlying silicone rubber. The plate was developed by applying naphtha solvent to remove debris from the exposed image areas. Similar plates are described in
Research Disclosure
19201, 1980 as having vacuum-evaporated metal layers to absorb laser radiation in order to facilitate the removal of a silicone rubber overcoated layer. These plates were developed by wetting with hexane and rubbing. CO
2
lasers are described for ablation of silicone layers by Nechiporenko & Markova, PrePrint 15th International IARIGAI Conference, June 1979, Lillehaminer, Norway, Pira Abstract 02-79-02834. Typically, such printing plates require at least two layers on a support, one or more being formed of ablatable materials. Other ablation imaging processes are described for example in U.S. Pat. No. 5,385,092 (Lewis et al), U.S. Pat. No. 5,339,737 (Lewis et al), U.S. Pat. No. 5,353,705 (Lewis et al), U.S. Pat. No. Reissue 35,512 (Nowak et al) and U.S. Pat. No. 5,378,580 (Leenders).
While the noted printing plates used for digital, processless printing have a number of advantages over the more conventional photosensitive printing plates, there are a number of disadvantages with their use. The process of ablation creates debris and vaporized materials that must be collected. The laser power required for ablation can be considerably high, and the components of such printing plates may be expensive, difficult to coat, or unacceptable in resulting printing quality. Such plates generally require at least two coated layers on a support.
Thermally switchable polymers have been described for use as imaging materials in printing plates. By “switchable” is meant that the polymer is rendered from hydrophilic to relatively more hydrophobic, or from hydrophobic to relatively more hydrophilic, upon exposure to heat.
U.S. Pat. No. 4,634,659 (Esumi et al) describes imagewise irradiating hydrophobic polymer coatings to render exposed regions more hydrophilic in nature. While this concept was one of the early applications of converting surface characteristics in printing plates, it has the disadvantages of requiring long UV light exposure times (up to 60 minutes) and the plate's use is in a positive-working mode only.
In addition, EP-A 0 652 483 (Ellis et al) describes lithographic printing plates imageable using IR lasers, and which do not require wet processing. These plates comprise an imaging layer that becomes more hydrophilic upon the imagewise exposure to heat. This coating contains a polymer having pendant groups (such as t-alkyl carboxylates) that are capable of reacting under heat or acid to form more polar, hydrophilic groups. Imaging such compositions converts the imaged areas from hydrophobic to relatively more hydrophilic in nature, and thus requires imaging the background of the plate, which is generally a larger area. This can be a problem when imaging to the edge of the printing plate is desired.
Positive-working photoresists and printing plates having crosslinked, UV-sensitive polymers are described in EP-A 0 293 058 (Shirai et al). The polymers contain pendant iminosulfonate groups that are decomposed upon UV exposure, generating a sulfonic group and providing polymer solubility.
U.S. Pat. No. 5,512,418 (Ma) describes the use of polymers containing pendant ammonium groups for thermally induced imaging. U.S. Pat. No. 4,693,958 (Schwartz et al) also describes a method of preparing printing plates that are wet processed. The imaging layers contain polyamic acids and vinyl polymers containing quaternary ammonium groups. Japanese Kokai 9-197,671 describes a negative-working printing plate and imaging method in which the imaging layer includes a sulfonate-containing polymer, an IR radiation absorber, a novolak resin and a resole resin.
EP 0 830940A (Vershueren et al) and EP 0 830,941 (Vershueren et al) describe titanium-containing layers on the back sides of metal or polyester supports in driographic printing plates.
U.S. Pat. No. 5,985,514 (Zheng et al) describes useful heat-sensitive imaging thiosulfate polymers that can be used successfully to prepare printing plates. The graphic arts industry is continually seeking improved printing plates for either short or long run length, improved photospeed, faster roll-up, longer shelf life and more invariance in coating formulations.
SUMMARY OF THE INVENTION
The problems noted above are overcome with an imaging member comprising a support having thereon a hydrophilic imaging layer comprising a hydrophilic heat-sensitive thiosulfate polymer, and
disposed between the support and the hydrophilic imaging layer, an interlayer comprising a Group IVB element compound.
In preferred embodiments, the heat-sensitive thiosulfate polymer comprises recurring units comprising a heat-activatable thiosulfate group that is represented by structure I:
wherein X is a divalent linking group, and Y is hydrogen or a cation.
This invention also includes a method of imaging comprising:
A) providing the imaging member described above, and
B) imagewise exposing the imaging member to provide exposed and unexposed areas in the imaging layer of the imaging member, whereby the exposed areas are rendered more hydrophobic than the unexposed areas by the heat generated by the imagewise exposing.
An additional method includes steps A and B noted above as well as:
C) in the presence of water or a fountain solution, contacting the imagewise exposed imaging member with a lithographic printing ink, and imagewise transferring the printing ink from the imaging member to a receiving material.
The imaging member of this invention has a number of advantages, thereby avoiding the problems of known printing plates. Specifically, the problems and concerns associated with ablation imaging (that is, imagewise remo
DoMinh Thap
Kersten Jennifer R.
Zheng Shiying
Baker & Botts L.L.P.
Hamilton Cynthia
Kodak Polychrome Graphics LLC
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