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
2000-02-23
2002-06-25
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
C430S286100
Reexamination Certificate
active
06410203
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a positive-type planographic printing plate which is sensitive to light having a wavelength in the infrared region. More particularly, the present invention relates to a positive-type planographic printing plate which can be directly formed by using an infrared laser based on digital signals output from a computer or the like.
2. Description of the Related Art
In recent years, laser technologies have developed remarkably. In particular, high output and compact solid-state lasers and semiconductor lasers emitting infrared rays of a wavelength of 760 nm to 1,200 nm (hereinafter occasionally referred to as “infrared lasers”) are readily available. These infrared lasers are very useful as light sources for recording in the direct production of printing plates from digital computer data. Accordingly, recently, the demand has increased for image recording materials which are highly sensitive to such infrared light sources for recording, i.e., image recording materials in which a photochemical reaction or the like is caused by infrared irradiation and the solubility in a developer is thereby greatly changed.
As an example of such image recording materials on which images can be recorded by using an infrared laser, a recording material comprising an onium salt, a phenol resin and a spectral sensitizing agent is disclosed in U.S. Pat. No. 4,708,925. This image recording material is a positive-type image recording material utilizing a dissolution suppressing effect with respect to the developer, which effect is due to the onium salt and the phenol resin.
The energy of an infrared ray is lower than that of an ultraviolet ray which has been conventionally used as a light source for exposure. Therefore, it is difficult to initiate, by exposure to infrared rays, a light reaction or the like of a compound, which light reaction causes a great change in the solubility of an image recording material with respect to a developer. For example, in WO 97/39894, there is disclosed an image recording material comprising an infrared absorbing agent and a polymeric binder which is soluble in an alkaline aqueous solution. The surface of the image recording material onto which a laser is irradiated has excellent positive action (i.e., development is suppressed in unexposed portions, and development is suppressed only a little or not at all in exposed portions) as a result of the photothermal effect. However, heat generated near the surface of the image recording material does not sufficiently reach the deep portions of the material, and therefore, the positive action at the deep portions is not sufficient. Consequently, even if development is carried out with an alkali developer, the discrimination between the unexposed portions and the exposed portions is not clear, and drawbacks arise in terms of sensitivity and development latitude.
Further, Japanese Patent Application Laid-Open (hereinafter abbreviated as “JP-A”) No. 7-20629 proposes an image recording material in which a diazonium salt having a high ability to decompose due to heat is added as a photothermal decomposition material. Although the image recording material has improved sensitivity to infrared lasers and development latitude, the storage stability thereof is poor, and the material has drawbacks in terms of product control.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above-described conventional drawbacks and to achieve the following object. Namely, the object of the present invention is to provide a positive-type planographic printing material which makes it possible to directly make a printing plate from digital data such as from a computer by using a solid state laser or a semiconductor laser emitting an infrared ray, and which exhibits high sensitivity to infrared lasers and has excellent development latitude and storage stability.
The present inventors focused on the constituent components of positive-type planographic materials which allow direct formation of printing plates by irradiation of infrared rays, and achieved the present invention after learning, as a result of intensive studies, that by lowering the pK
a
value of phenolic hydroxyl groups in a polymeric binder, interactions between hydroxyl groups and interactions between a hydroxyl group and an infrared absorbing agent or the like can be improved, changes of the material with the passage of time after forming of a film can be suppressed, and furthermore, the solubility of the material in an alkali developer at the exposed portions can be improved.
The means for achieving the above-mentioned object is as follows. Namely, there is provided a positive-type planographic printing material comprising: (A) a water-insoluble and alkaline water-soluble polymer including a main chain and a side chain and having a phenol structure at at least one of the main chain and the side chain, the phenol structure having an aromatic ring and at least one electron-withdrawing substituent on the aromatic ring; and (B) an infrared absorbing agent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the positive-type planographic printing material in accordance with the present invention will be described in more detail.
The positive-type planographic printing material in accordance with the present invention comprises at least (A) a water-insoluble and alkaline water-soluble polymer including a main chain and a side chain and having a phenol structure at at least one of the main chain and the side chain, the phenol structure having an aromatic ring and at least one electron-withdrawing substituent on the aromatic ring (hereinafter referred to as the “specific alkaline water-soluble polymer”), (B) an infrared absorbing agent, and other components as occasion demands.
(A) Specific Alkaline Water-soluble Polymer
The present invention is characterized in that the specific alkaline water-soluble polymer has, at at least one of the main chain and a side chain, a phenol structure which has an electron-withdrawing substituent.
The electron-withdrawing substituent serves to lower the pK
a
value of a phenolic hydroxyl group in the specific alkaline water-soluble polymer. By lowering the pK
a
value of the phenolic hydroxyl group, the interactions between the hydroxyl groups and the interactions between the hydroxyl group and the infrared absorbing agent or the like become strong, and therefore, dense network of bondings can be formed. Further, by lowering the pK
a
value of the phenolic hydroxyl group, the solubility of the positive-type planographic printing material in an alkali developer at the exposed portions of the material can be improved, and high sensitivity and high development latitude can be obtained. Furthermore, since the phenolic hydroxyl groups in a film have strong interactions in a reticular form, the material is hardly affected by external factors such as humidity and temperature and can be maintained in a stable state in terms of energy. As a result, storage stability over a long period of time can be improved.
As described above, the electron-withdrawing substituent serves to lower the pK
a
value of the phenolic hydroxyl groups in the specific alkaline water-soluble polymer. The pK
a
value of the phenolic hydroxyl groups is preferably 9.5 or less, and more preferably 9.0 or less.
When the pK
a
value exceeds 9.5, the interactions between the phenolic hydroxyl groups become weak, and it becomes difficult to maintain a stable state. Consequently, storage stability may deteriorate.
The electron-withdrawing substituent is not particularly limited as long as it attracts more electrons than hydrogen. However, the substituent preferably has a Hammett's substituent constant &sgr;
para
(hereinafter simply referred to as the “&sgr; value”) of 0.05 or more, and more preferably 0.20 or more.
When the electron-withdrawing substituent has a &sgr; value of less than 0.05, it may be difficult to achieve a pK
a
value of the phenolic hydroxyl group of 9.5 or less
Baxter Janet
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Gilmore Barbara
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