Printing press with mechanical development of imaged plate

Abstract

On-press development of an imaged printing plate on a plate cylinder, in which ink is applied by an ink form roll, a blanket roll is in contact with the plate, a rubber roll is opposed to the blanket roll, and printable media passes between the blanket roll and the rubber roll. The plate comprises a substrate carrying an imaged coating, in which nonimage areas have cohesion C1, adhesion to the substrate A1, and adhesion to the applied ink A3 and image areas have cohesion C2, adhesion to the substrate A2, and adhesion to the applied ink A4. The ink has cohesion C3 and adhesion A5 to the blanket roll. The nonimage areas have adhesion A6 to the printable medium and the ink has adhesion A7 to the medium. The adhesions and cohesions are such that the blanket roll pulls the ink from the plate and the ink pulls the nonimage areas from the substrate as undissolved particles that are transferred by the blanket with the ink to the printable media.

Description

RELATED APPLICATIONS[0001]This is a divisional of U.S. application Ser. No. 12 / 799,568 filed Apr. 27, 2010 for “Processless Development of Printing Plate”, which is a continuation-in-part of U.S. application Ser. No. 12 / 586,764 filed Sep. 28, 2009 for “Non-Chemical Development of Printing Plates”, which is a continuation-in-part of U.S. application Ser. No. 11 / 493,183 filed Jul. 26, 2006 for “Imagable Printing Plate for On-Press Development”, which claims priority under 35 U.S.C. §119(e) from U.S. Provisional Application No. 60 / 704,140 filed Jul. 29, 2005, for “Imagable Printing Plate for On-Press Development”, and benefit under 35 U.S.C. §120 is also claimed from U.S. application Ser. No. 11 / 821,721 filed Jun. 25, 2007 for “Water Spray Development of Planographic Plates” and U.S. application Ser. No. 12 / 215,124 filed Jun. 25, 2008 for “Heated Water Spray Processor”. The complete disclosures of these applications are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]...

AI Technical Summary

Benefits of technology

[0015]The most evident advantage is that no separate developing equipment or step is required between the imager and the press. A second significant advantage, whether or not the plate is passed through a pre-press water processor, is that there is little or no chemical treatment required of the waste stream associated with developing the plate. A third significant advantage is that because dissolution of the polymer resin is not relied upon for processing the plate, higher molecular weight resins can be used in the imagable coating, thereby producing more durable oleophilic areas and longer plate life on press.

[0019]Practitioners in this field had no reason to investigate or optimize the difference in adhesion of non-aqueous photopolymerizable resins as a basis for non-chemical, and especially mechanical, removal of the nonimage areas. Because it was the established practice that nonimage areas of the imaged plate could be substantially completely dissolved by the non aqueous developer solution, the main objective for improving coatings has been to increase the adhesion, cohesion, and durability of the imaged areas and thereby enable the plate to better withstand the rigors of the printing press. Any desired relationship between the imaged and unimaged areas was based on relative solubility, not relative mechanical adhesion, to minimize incidental dissolution of any of the exposed surface the imaged areas while the developer solution dissolved substantially all of the non image areas.

[0020]With the present invention, several techniques are available for facilitating or increasing the speed of the removal of the unimaged areas in solidus, i.e., without dissolution or dispersion.

[0022]According to another technique, the plates are heated after imaging to increase the difference in cohesion and adhesion of the coating to the substrate as between the imaged and unimaged areas, such that a greater force can be applied to the plates to dislodge only the unimaged areas. In particular, a thermally imagable negative working plate can be exposed to heat for a short period of time after imaging, whereby the imaged portions become more stable and tougher, while the portions of the coating that are to be removed are not significantly affected. The heating step preferably, but not necessarily, immediately follows the imaging step, but can be at a different location from the imaging step.

[0024]In a further preference, the water soluble top coat conventionally used to protect photosensitive (PS) coatings is washed off the PS coating after imaging (and after any subsequent heating step) and the plates stored temporarily until mounted on press. The top coat is typically a water soluble film former (such as PVOH) that prevents atmospheric oxygen from diffusing into the coating and quenching the free radicals necessary for inducing polymerization. The removal of this topcoat has been found to substantially immunize the imaged coating from further polymerization in the unimaged areas due to ambient light. Thus, the plates need not be handled in yellow or other special light between imaging and mounting on press.

Problems solved by technology

Not only is a high level of energy required for imaging such plates, but the rate of imaging is slow and the resolution is low.

Images