REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application of PCT/EP2019/075834, filed Sep. 25, 2019, which claims the benefit of European Application No. 18199040.9, filed Oct. 8, 2018, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The invention relates to an effervescent developer precursor for processing a printing plate precursor.

BACKGROUND ART

Lithographic printing typically involves the use of a so-called printing master such as a printing plate which is mounted on a cylinder of a rotary printing press. The master carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper. In conventional lithographic printing, ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of photopolymer oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas. In so-called driographic printing, the lithographic image consists of ink-accepting and ink-adhesive (ink-repelling) areas and during driographic printing, only ink is supplied to the master.

Lithographic printing masters are generally obtained by the image-wise exposure and processing of a radiation sensitive layer on a lithographic support. Imaging and processing renders the so-called lithographic printing plate precursor into a printing plate or master. Image-wise exposure of the radiation sensitive coating to heat or light, typically by means of a digitally modulated exposure device such as a laser, triggers a (physico-)chemical process, such as ablation, polymerization, insolubilization by cross-linking of a polymer or by particle coagulation of a thermoplastic polymer latex, solubilization by the destruction of intermolecular interactions or by increasing the penetrability of a development barrier layer. Although some plate precursors are capable of producing a lithographic image immediately after exposure, the most popular lithographic plate precursors require wet processing since the exposure produces a difference in solubility or difference in rate of dissolution in a developer between the exposed and the non-exposed areas of the coating. In positive working lithographic plate precursors, the exposed areas of the coating dissolve in the developer while the non-exposed areas remain resistant to the developer. In negative working lithographic plate precursors, the non-exposed areas of the coating dissolve in the developer while the exposed areas remain resistant to the developer. Most lithographic plate precursors contain a hydrophobic coating on a hydrophilic support, so that the areas which remain resistant to the developer define the ink-accepting, hence printing areas of the plate while the hydrophilic support is revealed by the dissolution of the coating in the developer at the non-printing areas.

Conventionally, a plate material is developed by applying a developer solution—for example by immersing it in, or spraying it with a developer—as it passes through the processing apparatus. Typically the material is also subjected to mechanical rubbing with e.g. one or more rotating brushes or specified roller(s)—after a while or after being treated with the developer.

After development, the plate is typically rinsed with water to remove any remaining developer and then gummed. Gumming, sometimes also called finishing or desensitizing, involves the application of a protective coating on the lithographic image, especially the non-printing areas, to avoid contamination or oxidation of the aluminum substrate. Gum solution can be applied by immersion, by spraying or by jetting as disclosed for example in EP 1 524 113.

An important trend in lithographic platemaking is related to ecology and sustainability. Systems and methods which enable a low consumption of processing liquids such as developer, rinse water and/or gum solution, or which allow processing with aqueous developers comprising no hazardous chemicals and/or which have a pH close to 7 (neutral developer), have attracted a lot of attention in the marketplace. A convenient method which has become popular involves the use of a gum solution as developer, whereby the plate is developed and gummed in a single step.

During processing the developer becomes loaded with components of the coating that have been removed during development and the amount of material in the developer increases as more plates are developed. Due to the increasing amount of dissolved and/or dispersed material in the developer, the activity of the developer decreases resulting in a reduced ability of removing the non-printing areas of the lithographic image. In addition, the activity of the developer which is typically applied from an open vessel, may further decrease with time due to dissolution of carbon dioxide from the atmosphere into the developer. Especially silicate free developers which come into contact with air are more sensitive towards such carbonisation. As a result, the efficiency of the developer highly reduces as soon as the recipient containing such a developer is opened. If the period of time before the developer in the processor needs renewal is too long, fresh developer in the recipient under the processor may have become out of specification due to such carbonisation. A solution provided in the art includes for example the use of flexible packaging which avoid air contact with the developer. However, flexible packaging is more expensive than commonly used containers. Alternatively, packaging which contains the adjusted amount of developer required to fill only one tank has been suggested, however, too many packaging sizes would be required.

Nowadays, developers and/or gumming solutions are prepared and then shipped worldwide whereby transportation has a major negative impact on both economy and ecology.

EP 1 434 102 discloses a silicate-free development composition for photosensitive printing plates which is in the form of a paste, powder or granules.

JP2005/153644 discloses a method for processing a photosensitive printing plate including the step of dissolving a solified developer. The solidified developer only dissolves in a liquid upon agitating and/or churning of the liquid.

SUMMARY OF INVENTION

It is an object of the present invention to provide a solidified developer which is able to completely dissolve in a liquid, even without stirring and/or agitating the liquid.

This object is realised by the effervescent developer precursor for preparing a developer solution defined in the independent claims, with preferred embodiments defined in the dependent claims. The invention has the specific feature that the effervescent developer precursor includes an effervescence generating compound and dissolves sufficiently fast and homogenously into a liquid without the need for stirring and/or agitation. The effervescent developer precursor may be used for instant preparation of a developing solution and/or for regeneration of a development solution during processing. The use of the effervescent developer precursor highly contributes to the reduction of waste liquids and/or required stockroom, makes the processing job less labour intensive and prevents mistakes as the operator needs to handle only one type of developer. Therefore, the current invention is not only convenient and cost-efficient, but is also favorable from an environmental point of view. In addition, transportation, distribution and packaging requirements are less stringent for effervescent developer precursors than for liquids.

It is a further object of the present invention to provide a method for making a developing solution for developing a lithographic printing plate comprising the step of dissolving the effervescent developer precursor in a liquid.

Other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention. Specific embodiments of the invention are also defined in the dependent claims.

