Printing – Planographic – Lithographic printing plates
Reexamination Certificate
2001-04-13
2003-02-04
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic printing plates
C101S462000, C430S302000
Reexamination Certificate
active
06513433
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a negative-working lithographic printing plate precursor. More particularly, the present invention relates to a lithographic printing plate precursor which allows scanning exposure on the basis of digital signal to make a printing plate, exhibits a high sensitivity and a high impression capacity that can give a stain-free printed matter, and can be mounted undeveloped on the printing machine for printing.
BACKGROUND OF THE INVENTION
Many studies have been made of computer-to-plate system printing plates, which have recently shown a remarkable development. Under these circumstances, studies have been made of development-free lithographic printing plate precursors which can be mounted undeveloped on a printing machine after exposure so that it can be directly used for printing, aiming at further rationalization of procedure and solution to problem of disposal of waste liquid. Various methods have been proposed.
One of methods for eliminating these processing steps is a so-called on-the-machine development which comprises supplying a fountain solution and an ink onto an exposed printing plate precursor mounted on the cylinder of a printing machine while the cylinder is being rotated to remove the non-image area from the printing plate precursor. In accordance with the on-the-machine development process, all the processing steps are completed during ordinary printing procedure after the mounting of the exposed printing plate precursor on the printing machine.
The lithographic printing plate precursor suitable for such an on-the-machine development process needs to have a light-sensitive layer soluble in the fountain solution or ink solvent as well as daylight handleability suitable for development on the printing machine installed in daylight.
For example, Japanese Patent No. 2,938,397 discloses a lithographic printing plate precursor comprising a hydrophilic support having a light-sensitive layer having a particulate thermoplastic hydrophobic polymer dispersed in a hydrophilic binder polymer provided thereon. It is described in the above cited patent that the lithographic printing plate precursor is arranged such that when exposed to light from an infrared laser, thermal coalescence of the particulate thermoplastic hydrophobic polymer occurs to give a printing plate having an image formed thereon which is then mounted on the cylinder of a printing machine where it is then subjected to development with a fountain solution and/or ink.
However, the method involving the mere thermal coalescence allowing the formation of an image gives a good on-the-machine developability but is disadvantageous in that the resulting image strength gives an insufficient impression capacity. Further, when the heat-sensitive layer is provided directly on an aluminum substrate, the resulting heat is absorbed by the aluminum substrate, making it impossible to cause thermal coalescence on the substrate-heat-sensitive layer interface and hence giving an insufficient impression capacity.
JP-A-9-127683 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-9-123387, JP-A-9-123388, JP-A-9-131850, and WO99-10186, too, disclose a method which comprises thermal coalescence of thermoplastic particles followed by on-the-machine development allowing the preparation of a printing plate. However, this approach, too, is disadvantageous in that the resulting image strength is weak, giving an insufficient impression capacity.
JP-A-8-48020 discloses a method which comprises subjecting a lipophilic heat-sensitive layer provided on a porous hydrophilic support to exposure to light from an infrared laser so that the lipophilic heat-sensitive layer is fixed to the substrate. However, this approach is disadvantageous in that such a lipophilic film exhibits a deteriorated on-the-machine developability, causing tailings of the lipophilic heat-sensitive layer to be attached to the ink roller or printed matters.
SUMMARY OF THE INVENTION
An object of the invention is to provide a lithographic printing plate precursor which can overcome the foregoing disadvantages of the prior art, i.e., lithographic printing plate precursor having a good on-the-machine developability, a high sensitivity and a high impression capacity.
In other words, the present invention provides a lithographic printing plate precursor comprising a hydrophilic support having thereon a heat-sensitive layer containing a thermoplastic particulate polymer having Tg of not lower than 60° C., and at least one of a particulate polymer having a heat-reactive group and a microcapsule containing a compound having a heat-reactive group incorporated therein.
It is thought that when subjected to heat mode exposure, the lithographic printing plate precursor according to the invention undergoes heat reaction of the microcapsules containing a particulate polymer having a heat-reactive group or a compound having a heat-reactive group incorporated in the heat-sensitive layer to enhance the strength on the image area and hence provide an excellent impression capacity. It is also thought that the thermoplastic particulate polymer which has once been melted becomes solidified when the temperature returns to ordinary value after exposure, whereby the strength can be further enhanced on the image area which has been exposed in a heat mode, providing better impression capacity.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be further described hereinafter.
The heat-sensitive layer to be incorporated in the lithographic printing plate precursor of the invention will be described first.
[Thermoplastic Particulate Polymer]
Preferred examples of the thermoplastic particulate polymer having Tg of not lower than 60° C. (hereinafter occasionally referred simply to as “thermoplastic particulate polymer”) to be contained in the heat-sensitive layer of the lithographic printing plate of the invention include those disclosed in Research Disclosure No. 33303, January 1992, JP -A-9-123387, JP-A-9-131850, JP-A-9-171249, JP-A-9-171250, and EP931647. Specific examples of these thermoplastic particulate polymers include homopolymer and copolymer of monomers such as ethylene, styrene, vinyl chloride, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, vinylidene chloride, acrylonitrile and vinylcarbazole, and mixture thereof. Preferred among these polymers are polystyrene, and methyl polymethacrylate.
The thermoplastic particulate polymer to be contained in the heat-sensitive layer of the lithographic printing plate precursor of the invention preferably comprises at least two thermoplastic particulate polymers having different particle sizes or different Tg values.
In this arrangement, the resulting image area exhibits further improvement of hardness. The lithographic printing plate thus obtained exhibits further improvement of impression capacity.
For example, if the thermoplastic particulate polymer comprises particulate polymers having the same particle size, there is some void between the thermoplastic particulate polymer particles. Thus, even if the thermoplastic particulate polymer is subjected to exposure in a heat mode or the like to undergo melt-solidification, the resulting layer occasionally cannot have desired hardness. However, if the thermoplastic particulate polymer comprises particulate polymers having different particle sizes, the void between the thermoplastic particulate polymer particles can be reduced, making it possible to improve the hardness of the image area after exposure in a heat mode.
Further, in the case where the thermoplastic particulate polymer comprises particulate polymers having the same Tg value, if the rise of temperature of the heat-sensitive layer by exposure in a heat mode or the like is insufficient, the thermoplastic particulate polymer cannot undergo sufficient melt-solidification. Thus, the resulting layer cannot exhibit desired hardness. On the contrary, in the case where the thermoplastic particulate polymer co
Inoue Nobuaki
Maemoto Kazuo
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Funk Stephen R.
LandOfFree
Lithographic printing plate precursor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Lithographic printing plate precursor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lithographic printing plate precursor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3177080