Process for developing positive photosensitive lithographic prin

Details Process for developing positive photosensitive lithographic prin Process for developing positive photosensitive lithographic prin

1982-05-18

1984-06-05

Downey, Mary F.

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making printing plates

430302, 430331, 430165, 430190, G03F 708, G03C 534

Patent

active

044528809

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for developing a positive photosensitive lithographic printing plate (also referred to as positive pre-sensitized plate or abbreviated as positive PS plate), and more particularly to a developing method suitable for treating a positive PS plate comprising a photosensitive layer containing, as the photosensitive constituent, an o-quinonediazide compound provided on an aluminium substrate by use of an automatic developing machine.


DESCRIPTION OF THE PRIOR ART

Conventional positive PS plates which are most widely used comprise a photosensitive layer containing, as the photosensitive constituent, an o-naphthoquinonediazide compound provided on an aluminium substrate. The photosensitive constituent in said photosensitive layer contains a structural unit ##STR1## as the photosensitive group. This structural unit is decomposed by an active light ray to form an alkali-soluble group, resulting in an increase in the solubility in an alkali and a difference in the solubility between the exposed area and the unexposed area. In this way, a positive image is obtained by developing the exposed photosensitive layer by use of an aqueous alkali solution.
Recently, an automatic developing machine for a PS plate is widely used for the purpose of rationalizing and standardizing the printing plate making work in the printing industry. In one of the automatic developing machines most widely used for positive PS plates, the developing solution is jeted from a pipe having a plurality of nozzles to the surface of the PS plate, and the used developing solution is recovered through a filter to a tank. In the development of the positive PS plate by use of such an automatic developing machine, an aqueous solution of sodium silicate is generally used as the developing solution. However, this method has disadvantage in that it is impossible to treat many PS plates. To solve this problem, it has been proposed in Japanese Provisional Patent Publication No. 22759/1980 to adopt a replenishing system and use, as the developing solution, an aqueous solution of alkali metal silicates in which the ratio [SiO.sub.2 ]/[M], (provided that [SiO.sub.2 ] denotes the content of SiO.sub.2 in the unit volume when the amount of SiO.sub.2 is expressed in terms of gram molecule unit and [M] denotes the content of alkali metals in the unit volume when the amount of M is expressed in terms of gram atom unit), is within the range between 0.5 and 0.75, the concentration of SiO.sub.2 is within the range between 1% and 4% by weight, and at least 20 atomic % of the alkali metal based on gram atom is constituted by potassium. In this developing method, an aqueous solution of alkali metal silicates having a ratio [SiO.sub.2 ]/[M] within the range of 0.25 to 0.75 is used as the replenishing solution so as to treat many positive PS plates.
However, it has been found that, with the developing method just described above, insolubles are formed in the developing solution when a larger quantity of positive PS plates comprising an aluminium substrate are treated. The insolubles formed stick to the PS plate carrying roller and clog the nozzles and plug the pores in a filter. In addition, the developing solution is exhausted very quickly due to the absorption of carbon dioxide gas from ambient air. With the developing process, therefore, a high accuracy is required with respect to the replenishment.
Therefore, an object of the present invention is to provide a developing process which can achieve development treatment of a large quantity of positive PS plates without changing the developing solution for a long period.
Another object of the present invention is to provide a developing process which can achieve development of a large quantity of positive PS plates by use of a generally used type of automatic developing machine, in which the developing solution is jeted from a spray unit to the surface of the photosensitive layer, without changing the developing solution in the tank for a long period and without cau

REFERENCES:
patent: 3471289 (1969-10-01), Herrick
patent: 3615480 (1971-10-01), Lam
patent: 3905816 (1975-09-01), Boardman et al.
patent: 3907564 (1975-09-01), Boardman et al.
patent: 4259434 (1981-03-01), Yamasue et al.
patent: 4282301 (1981-08-01), Ohta

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