Flexographic printing process with wet on wet capability

Abstract

The invention refers to a flexographic printing process with wet on wet capability based on controlled polymer or polymer segment precipitation that leads to gel formation of ink compounds by controlling the solubility parameter of the ink system. The mechanism to obtain a desirable wet on wet color trapping is the formation and / or presence of a gel in the applied ink film due to a controlled physicochemical mechanism of resin precipitation. This is accomplished either by controlling a change in the Hansen Solubility Parameter of the liquid in the ink through evaporation of some or all of a non-reactive and volatile solvent, or alternatively by use of a polymer comprised of two distinct and separate segments one of which is soluble in the monomer / oligomer mix and the other of which is not. The insoluble segments form a reversible gel that is broken to a liquid by shear in the application process, allowing application of a liquid ink, and is reestablished in the applied ink film in such a manner and with such strength as to allow overprinting in the wet on wet flexographic printing process.

Description

FIELD OF THE INVENTION[0001]This invention concerns to a flexographic printing process with wet on wet capability that is made possible by controlled gel formation based on precipitation of a polymer or segments thereof in ink formulations, causing formation of a gel with suitable mechanical strength to allow the required color trapping for a wet on wet flexographic printing process. This controlled precipitation is accomplished by controlling the Hansen Solubility Parameter of the ink system at all times. The wet on wet printing process is possible with or without intermediate air drying, with greatly reduction or no emission of VOLATILE ORGANIC COMPOUNDS (VOC), greatly reduced use of energy, and with a single final curing step by UV or EB radiation. The invention also concerns an ink and a printing apparatus for carrying out the process. The process is also suitable for letterpress printing.BACKGROUND OF THE INVENTION[0002]Flexographic printing has become the major printing proces...

AI Technical Summary

Benefits of technology

[0019]It is an object of this invention to provide a flexographic printing system and process with the overprint color process without solvent or with a reduced amount of solvents, and at the same time providing inks that have higher color strength and exhibit a good adhesion to major substrates currently on the market.

[0021]The object of this patent may be achieved by providing a flexographic printing process involving gelation of the ink once applied to the substrate, said process being characterized by two important principles: the gelation or gel formation of the ink on the substrate and the use of Hansen Solubility Parameter to reach this gelation. This process is an overprint color process that uses reduced VOLATILE ORGANIC COMPOUNDS (VOC) content that means a reduced amount of solvents, and at the same time providing inks that have higher color strength and exhibit a good adhesion to major substrates currently on the market.

Problems solved by technology

The controlled gel results from formation of a polymer chain network, or polymer segment precipitation forming such a network, because of a lack of solvency in the liquid media.

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