Lithographic printing plate precursor

Details Lithographic printing plate precursor Lithographic printing plate precursor

2000-03-20

2002-09-24

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

C430S138000, C430S273100, C101S130000, C101S453000, C101S467000

Reexamination Certificate

active

06455222

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a directly thermosensitive lithographic printing plate precursor for offset printing requiring no development and having excellent press life. More particularly, the present invention relates to a lithographic printing plate precursor that can record images by scanning exposure based on digital signals and can be water developed, or can be mounted on a printing press (hereinafter, sometimes called “a printing machine”) as such without development to conduct printing.
BACKGROUND OF THE INVENTION
In general, lithographic printing plates comprise lipophilic image areas receiving ink in the printing process and hydrophilic non-image areas receiving fountain solution. As lithographic printing plate precursor, presensitized plates have hitherto been widely used in which lipophilic light-sensitive resin layers are formed on hydrophilic supports. In methods for making the plates, the non-image areas are usually removed by dissolving them in developing solutions after exposure through images of lithographic films or the like, thereby obtaining the desired printing plates.
The processes for making the conventional presensitized plates requires the operation of removing the non-image areas by dissolution after exposure, and it is one problem that has been desired to be improved with respect to the prior art to make unnecessary or simplify such additional wet treatment. In particular, the disposal of waste liquid discharged by the wet treatment has recently become a matter of concern in the whole industry from the consideration to the earth circumstances, so that a request for an improvement in this respect has become stronger.
As one of the simple plate-making methods meeting this request, a method is proposed in which such image recording layers that the non-image areas of the lithographic printing precursors can be removed in the usual printing process are used and developed on a printing machine (i.e., a printing press) after exposure to obtain final printing plates. The plate-making system of the lithographic printing plates due to such a method is called an “on-press developing system”. Specific examples thereof include the use of image recording layers soluble in fountain solutions or ink solvents and mechanical removal of image recording layers by contact with an impression cylinder or a blanket cylinder in the printing machine. However, a large problem of the on-press developing system is that it is necessary to employ, for example, a troublesome method of keeping the printing plate precursor in a completely light-shaded state or under constant-temperature conditions until the printing plate precursors are mounted on the printing machine, because the image recording layers of the printing plate precursors are not fixed even after exposure.
On the other hand, as another recent trend in this field, digital conversion techniques of electronically processing, accumulating and outputting image information by the use of computers have been widely applied, and various new image output systems corresponding to such digital conversion techniques have come in practice- Associated therewith, computer-to-plate techniques have been noted in which high convergent radiations such as laser beams bear digitized image information, and printing plate precursors are scan-exposed to the radiations to directly produce printing plates through no lithographic films. Resulting therefrom, it becomes an important problem to obtain printing plate precursors adapted to this object.
Accordingly, simplification, conversion to a dry system and dispensing with treatment of the plate-making operation have been desired more strongly than before, from both the above-mentioned circumstance problem and adaption to digital conversion.
Recently, solid lasers such as semiconductor lasers and YAG lasers, which are high in output, have become available at low cost. Accordingly, the prospects of the plate-making methods using these lasers as image recording means have become particularly encouraging, as the methods for producing the printing plates by scan-exposure that can be easily incorporated in the digital conversion techniques. In the conventional plate-making methods, low- to medium-illuminance imagewise exposure is given to light-sensitive printing plate precursor to carry out image recording according to imagewise physical property changes of printing plate precursor faces by the photochemical reaction. However, in the methods using high power density exposure using high output lasers, exposure regions are intensively irradiated with a large amount of light energy during momentary exposure time to efficiently convert light energy to heat energy, and heat changes such as chemical changes, phase changes and changes in shape or structure are allowed to occur by that heat to utilize those changes for image recording. That is to say, although image information is inputted by light energy of the laser beams, image recording is conducted by the reaction due to heat energy. Usually, the recording system utilizing heat generation caused by such high power density exposure is called heat mode recording, and conversion of light energy to heat energy is called light-heat conversion.
The great advantage of the plate-making methods using heat mode recording means is that the printing plate precursors are not sensitive to light of the usual illuminance level such as room illumination, and that fixing is not indispensable to images recorded by high illuminance exposure. That is to say, when heat mode light-sensitive materials are used in image recording, they are safe to room light before exposure, and the fixing of images is not indispensable also after exposure. Accordingly, when the plate-making process of using, for example, image recording layers insolubilized or solubilized by heat mode exposure, and removing the exposed image recording layers imagewise to form printing plates is carried out by the on-press developing system, such printing systems that images are not influenced by development (removal of non-image areas) for a certain period of time after image exposure, for example, even if exposed to room environmental light, become possible.
It is therefore expected that the use of the heat mode recording will make it possible to obtain lithographic printing plate precursors desirable for the on-press developing system.
As one of the preferred methods for producing the lithographic printing plates based on the heat mode recording, a method is proposed in which hydrophobic image recording layers are provided on hydrophilic substrates and subjected to imagewise heat mode exposure to change the solubility and dispersibility of the hydrophobic layers, and non-image areas are removed by wet development as needed.
As an example of the method using such printing plate precursors, JP-B-46-27919 (the term “JP-B” as used herein means an “examined Japanese patent publication”) discloses a method in which printing plate precursors comprising hydrophilic supports having provided thereon recording layers improved in solubility by heat, exhibiting the so-called positive action, specifically recording layers having specific compositions including saccharides and melamine-formaldehyde resins, are subjected to heat mode recording, thereby obtaining printing plates.
However, all the recording layers disclosed are not sufficient in thermosensitivity, so that the sensitivity is very insufficient for heat mode scanning exposure. Further, the small discrimination of the hydrophobicity/hydrophilicity before and after exposure, that is to say, small changes in solubility, also practically introduces a problem. The poor discrimination substantially makes it difficult to perform the plate-making by the on-press developing system.
Furthermore, WO98/40212 discloses lithographic printing plate precorsors comprising substrates having provided thereon lipophilic image recording layers containing transition metal oxide colloids, the plate-making of which can be carried out without development. How

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