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
2001-04-17
2004-06-15
Huff, Mark F. (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
C430S302000, C430S303000
Reexamination Certificate
active
06749984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive-type planographic printing plate precursor, and more particularly to a positive-type planographic printing plate precursor that can be written by heat from an infrared laser, a thermal head or the like, and used for so-called direct plate-making in which a plate can be made directly from digital signals from a computer, or the like.
2. Description of the Related Art
In recent years, as advances have been made in solid state lasers and semiconductor lasers having a light emission range in the near infrared to infrared range, attention has been focused on systems that employ these infrared lasers for direct plate-making from computer digital data.
A positive-type planographic printing plate material to be used with an infrared laser for direct plate making is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-285275. This invention is an image recording material which is produced by adding a substance which absorbs light and generates heat, and a positive-type photosensitive compound such as a quinonediazide compound, or the like, to a resin soluble in an aqueous alkali solution. In the image portion of the image recording material, the positive-type photosensitive compound works as a dissolution inhibitor to substantially lower the solubility of the resin soluble in an aqueous alkali solution. In the non-image portion of the image recording material, this positive-type photosensitive compound is rendered incapable of inhibiting dissolution by being decomposed by heat, and can be removed by development to thereby form an image.
The present inventors have found through examination that positive images can be obtained even when the quinonediazide compound is not added to an image recording material. However, the image recording material which is produced simply without the quinonediazide compound has a drawback in that stability of sensitivity thereof with respect to concentration of a developing solution, i.e., development latitude thereof, is poor. The development latitude used herein refers to a latitude within which good images can be formed when an alkali concentration in the alkaline developing solution is changed.
On the other hand, onium salts and alkali-insoluble hydrogen-bondable compounds are known to have an alkali dissolution-inhibiting action on alkali-soluble polymers. Particularly, with the image forming materials that are used with an infrared laser and disclosed in JP-A No. 10-268512, JP-A No. 11-44956, WO 98/42507, WO 99/1795 and WO 99/11458, it is known that a good positive action is obtained by employing a cyanine dye in a photosensitive composition, whereby discrimination between an image portion and a non-image portion in imaging is improved. The positive action is an action in which an infrared absorbing colorant absorbs laser light, and the heat thus generated eliminates the dissolution inhibiting effect of the polymer film in the irradiated portion to form an image.
These positive-type imaging materials are superior in image formability. However, it has been found that developing properties thereof largely vary depending on drying conditions at the time a photosensitive layer coating solution is coated and dried to form a photosensitive layer. That is, there has been the problem that developing properties of planographic printing plates provided with the same photosensitive layers largely vary by changing only a thickness of the aluminum substrate which is a hydrophilic support, and therefore stable plate-making cannot be carried out with such planographic printing plates. That is, when the thickness of the support is changed in order to improve the support's ability to be accommodated to a printer or the like, it becomes impossible to obtain the desired planographic printing plate due to variation in the developing properties thereof, and it becomes necessary to select appropriate exposure and developing conditions. This creates problems in that, not only does processing of the planographic printing plates become complicated, but significant losses in time and costs can occur.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a positive-type planographic printing plate precursor which has high sensitivity, is superior in image formability and has a good developing stability in that the sensitivity does not vary even when a thickness of the support is changed.
The present inventors have found through examination that the variation of developing properties can be prevented by selecting a solvent used in forming a photosensitive layer and a cyanine dye as a light-heat converting agent.
A first aspect of the present invention is a positive-type planographic printing plate precursor including a photosensitive layer which is obtained by coating and drying on a support a photosensitive layer coating solution formed by a photosensitive composition containing a cyanine dye represented in the following general formula (I) and a polymer insoluble in water and soluble in an aqueous alkali solution which are dissolved or dispersed in a solvent system containing 80% by weight or more of a solvent having a boiling point lower than 100° C. in a solvent having a boiling point lower than 200° C.; and solubility in an aqueous alkali solution of the photosensitive layer is enhanced by an exposure to an infrared laser:
wherein, each of Y
1
and Y
2
represents a dialkylmethylene group or a sulfur atom; each of R
3
and R
4
represents an alkyl group, alkenyl group, alkynyl group or phenyl group which may be substituted; L
2
represents a trimethine group, pentamethine group or heptamethine group which may be substituted, and two substituents of the pentamethine group or the heptamethine group may be combined with each other to form a cycloalkene ring having 5 to 7 carbon atoms; each of R
5
through R
8
represents a hydrogen atom or an alkyl group, alkenyl group, alkoxy group, cycloalkyl group or aryl group which may be substituted, and R
5
and R
6
, and R
7
and R
8
may be respectively combined with each other to form a ring structure. X
−
represents an anion.
A second aspect of the present invention is a method for producing a positive-type planographic printing plate precursor including the steps of: preparing a photosensitive composition containing a cyanine dye represented in the general formula (I) and a polymer insoluble in water and soluble in an aqueous alkali solution; preparing a photosensitive layer coating solution by dissolving or dispersing the photosensitive composition in a solvent system containing 80% by weight or more of a solvent having a boiling point lower than 100° C. in a solvent having a boiling point lower than 200° C.; and coating and drying the photosensitive coating solution on a support to form a photosensitive layer.
In the step of coating and drying the photosensitive coating solution, when the thickness of the aluminum support, which has high thermal conductivity, is changed, a temperature rise, i.e., a thermal load at the photosensitive layer, largely differs, and the amount of the residual solvent in the photosensitive layer varies under the same drying conditions. Since the solvent used in the photosensitive layer coating solution has a sufficient interaction capability to dissolve components such as polymers in the photosensitive layer, the solvent remaining after the formation of the coating film causes interaction which competes with interactions between polymers as well as between polymers and an infrared absorbing agent, thereby affecting the desired interactions between the polymers as well as between the polymers and the infrared absorbing agent.
The mechanism resulting in the working of the present invention is not altogether clear. However, the mechanism is believed to be as follows. A particular cyanine dye that can form a strong interaction between the polymers used to form the coating film is used in the photosensitive layer coating solution. An amount of solvent having a relati
Burns Doane Swecker & Mathis L.L.P.
Fuji Photo Film Co. , Ltd.
Huff Mark F.
Walke Amanda
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