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
2002-03-11
2003-09-23
Baxter, Janet (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
C430S281100, C430S288100, C430S944000, C430S964000, C101S453000, C101S467000
Reexamination Certificate
active
06623910
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a planographic printing plate precursor capable of being exposed by an IR laser for image formation thereon. More specifically, the present invention relates to such planographic printing plate precursor having a negative recording layer of high recording sensitivity.
2. Description of the Related Art
The recent development of laser technology has been remarkable, and high-power, small-sized solid lasers and semiconductor lasers for emitting near-IR and IR rays have become readily available. For light sources for directly processing printing plate precursors from digital data of computers or the like, these lasers are extremely useful.
Negative planographic printing plate materials for IR lasers, that is, materials to be processed for image formation thereon, with an IR laser capable of emitting IR rays as a light source, generally have a photosensitive layer that comprises an IR absorbent, a polymerization initiator capable of generating a radical when exposed to light or heat, and a polymerizable compound.
One example of such negative image recording materials is described in U.S. Pat. No. 5,340,699, which features an IR absorbent, an acid generator, a resol resin and a novolak resin. However, negative image recording materials of this type require heat treatment at 140 to 200° C. for 50 to 120 seconds or so, after exposure to a laser for image formation thereon, and this heat treatment often requires a large, complicated device and much energy.
Japanese Patent Application Publication (JP-B) No. 7-103171 discloses a recording material that includes a cyanine dye having a specific structure, an iodonium salt, and an ethylenically unsaturated double bond-having addition-polymerizable compound. This does not require heat treatment after imagewise exposure to light. However, the recording material disclosed is problematic in that the polymerization of the polymerizable compound therein is often retarded by oxygen in air, and therefore sensitivity is not satisfactory. Japanese Patent Application Laid-Open (JP-A) No. 8-108621 discloses an image-recording medium that features an ordinary thermal polymerization initiator, which is an organic peroxide or azobisisobutyronitrile compound, and a thermo-polymerizable resin. Regarding image-recording sensitivity, however, this medium requires an energy level of at least 200 mJ/cm
2
. Accordingly, to increase sensitivity, the medium must be pre-heated before exposure to light. At present, no one has succeeded in realizing high-sensitivity recording materials satisfactory for practical use.
SUMMARY OF THE PRESENT INVENTION
An object of the present invention is to provide a negative planographic printing plate precursor of high sensitivity, which can be imagewise exposed by IR rays from an IR-emitting solid laser or semiconductor laser for direct image formation thereon from digital data of a computer or the like, without requiring a heat treatment after this exposure to light for image formation.
Having specifically noted the constituent components of negative image-recording materials and having assiduously studied them, the present inventors have found that, when an onium salt whose counter anion has a divalent anionic structure is used for a polymerization initiator, the recording sensitivity of an image-recording material can be increased. On the basis of this finding, we have completed the present invention.
Specifically, the present invention provides a negative planographic printing plate precursor for a heat-mode exposure system, the plate precursor having, on a support, a photosensitive layer that is exposable with an IR laser, the photosensitive layer including: (A) a light-to-heat conversion agent; (B) a polymerizable unsaturated group-having compound; and (C) a polyvalent anionic onium salt having a counter anion that has a valency of at least two.
Although not clear, the mechanism of the planographic printing plate precursor of the present invention is thought to be as follows: In the plate precursor, the counter anion of the onium salt that serves as an initiator, such as a sulfonium, iodonium, diazonium or azinium salt, has a divalent anionic structure. Therefore, the electron density of the counter anion is high, and thermal decomposition of the onium salt is thereby facilitated. In addition, an ordinary light-to-heat conversion agent such as an electrically-charged cyanine dye or oxonole dye can readily interact with an onium salt of this type, and therefore the dye and the initiator are readily localized to thereby increase light-to-heat conversion efficiency of the plate precursor. Accordingly, the initiator can be efficiently decomposed, increasing the recording sensitivity of the plate precursor.
The planographic printing plate precursor of the present invention may be for a “heat-mode exposure system”, which means that the plate precursor may be subjected to heat-mode exposure for image formation thereon. A definition of heat-mode exposure is now described in detail. As described by Hans-Joachim Timpe (IS & Ts NIP 15:1999
International Conference on Digital Printing Technologies
, page 209), it is known that a process featuring photo-excitation of a light-absorbing substance (e.g., dye) in a photographic material followed by a chemical or physical change thereof for image formation in a photosensitive layer of the material (that is, a process of image formation comprising photo-excitation of the light-absorbing substance followed by the chemical or physical change thereof includes two major modes. Specifically, one is a photon mode in which the photo-excited light-absorbing substance in the photographic material is inactivated through some photo-chemical interaction (for example, energy transfer or electron transfer) with another reactive substance in the material, and the reactive substance, having been thus activated as a result of the interaction, undergoes the chemical or physical change necessary for image formation in the photosensitive layer of the material. The other mode is a heat mode in which the photo-excited light-absorbing substance in the photographic material generates heat and is thus inactivated by the heat generation, and the other reactive substance in the material receives the heat and undergoes the chemical or physical change necessary for image formation in the photosensitive layer of the material. Other minor modes of the process, for example, ablation, in which the substances in a photographic material are explosively scattered by locally focused light energy, and poly-photon absorption, in which one molecule in a photographic material absorbs a number of photons at the same time, are omitted herein.
The exposure processes of the modes are referred to as photon-mode exposure and heat-mode exposure. A technical difference between photon-mode exposure and heat-mode exposure is whether or not the energy quantities from a plurality of photons for exposure can be added up for the intended reaction. For example, referred to is a reaction through exposure to a number of photons n. In photon-mode exposure, which takes advantage of photo-chemical interaction of the substances in the photographic material, the energy quantities from n photons cannot be added up for the reaction, because of the laws of quantum energy and momentum conservation. In other words, every reaction through photon-mode exposure requires the condition “quantity of energy of one photon≧quantity of energy for one reaction”. On the other hand, in heat-mode exposure, the light-absorbing substance in the photographic material is first photo-excited to generate heat, and the heat, having been thus converted from light energy, serves for the reaction for image formation in the photosensitive layer of the material. Accordingly, in heat-mode exposure, the energy quantities of all n photons can be added up for image formation. Therefore, the condition “energy quantities of n photons≧energy quantity for one reaction” is sufficient fo
Shimada Kazuto
Sorori Tadahiro
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilliam Barbara
LandOfFree
Planographic 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 Planographic printing plate precursor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Planographic printing plate precursor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3052880