Heat mode sensitive imaging element for making positive working printing plates

Abstract

According to the present invention there is provided a heat mode imaging element for making a lithographic printing plate having on a lithographic base with a hydrophilic surface a first layer including a polymer soluble in an aqueous alkaline solution, and a top layer on the same side of the lithographic base as the first layer that is IR-sensitive and unpenetrable for an aqueous alkaline developer wherein said first layer and said top layer may be one and the same layer; characterized in that the surface of said element upon exposure and treatment with an aqueous alkaline developer is such that a) the contact angle between the unexposed areas of the imaging element and the aqueous alkaline developer changes for at most 6° during the first minute of contact with said developer; b) the contact angle between the exposed areas of the imaging element and the aqueous alkaline developer changes more than 15° during the first minute of contact with said developer; c) the difference in contact angle between on the one side the unexposed areas and on the other side the exposed areas of the imaging element with the aqueous alkaline solution at the onset of the measurement is not higher than 10°.

Description

DESCRIPTION[0001] The present invention relates to a heat mode imaging element for preparing a lithographic printing plate.[0002] More specifically the invention is related to a heat mode imaging element for preparing a lithographic printing plate whereof the difference in the top layer of being penetrated and / or solubilised in the exposed areas and in the non-exposed areas by an aqueous developer is increased.[0003] Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water, will not accept the ink. The areas which accept ink form the printing image areas and the ink-rejecting areas form the background areas.[0004] In the art of photolithography, a photographic material is made imagewise receptive to oily or greasy inks in the photo-exposed (negative-working) or in the non-exposed areas (positive-working) on a hydrophilic background.[0005] In the production of...

AI Technical Summary

Benefits of technology

[0021] It is another object of the invention to provide a heat mode sensitive imaging element for making positive lithographic printing plates having excellent printing properties, developable in a selective, rapid, convenient and ecological way.

[0089] The diptime in the developing solution was 22 seconds. Printing this material results in a good ink-uptake, runlength, dotrendering and processing latitude.

Problems solved by technology

Lithography is the process of printing from specially prepared surfaces, some areas of which are capable of accepting lithographic ink, whereas other areas, when moistened with water, will not accept the ink.

Such method of working is cumbersome and labor intensive.

However the photosensitive coating is not sensitive enough to be directly exposed with a laser.

Such method is disclosed in for example JP-A-60-61 752 but has the disadvantage that a complex development and associated developing liquids are needed.

This method however still has the disadvantage that the image mask has to be removed prior to development of the photosensitive layer by a cumbersome processing.

A particular disadvantage of photosensitive imaging elements such as described above for making a printing plate is that they have to be shielded from the light.

Furthermore they have a problem of sensitivity in view of the storage stability and they show a lower resolution.

A disadvantage of this method is that the printing plate obtained is easily damaged since the non-printing areas may become ink accepting when some pressure is applied thereto.

Moreover, under critical conditions, the lithographic performance of such a printing plate may be poor and accordingly such printing plate has little lithographic printing latitude.

The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.

The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.

The printing results of a lithographic plate obtained by irradiating and developing said imaging element are poor.

Said last three heat-mode imaging element have the disadvantage that the difference between the solubility in the exposed areas and in the non-exposed aqreas is not very great so that also non-exposed areas are dissolved during the processing of said element so that said plates could not be used as lithographic plates.

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