Printing process, apparatus, and materials for the reduction of paper curl

Claim 1

A process for the reduction of curl in duplex ink jet printing comprising the steps of: (a) applying at least one first aqueous ink in an image-wise fashion to a first side of a substrate to provide a first visible image, (b) applying at least one first clear aqueous liquid to a second, opposite side of the substrate, (c) applying at least one second aqueous ink in an image-wise fashion to the second, opposite side of the substrate to provide a second visible image, and (d) applying at least one second clear aqueous liquid to the first side of the substrate, wherein the first and second aqueous inks are the same or different and comprise water, a colorant of dye or pigment, and at least one ingredient selected from the group consisting of anticurl agent, biocide, pH buffering agent, antioxidant, antikogation agent, anticockling agent, penetrant, bubble nucleation aid, microwave coupling agent or salt, surfactant and dispersing agent, and wherein the first clear aqueous liquid comprises water and at least one ingredient, the at least one ingredient being the same as the at least one ingredient of the first aqueous ink with the exception that the first clear aqueous liquid does not contain any colorant, and wherein the second clear aqueous liquid comprises water and at least one ingredient, the at least one ingredient being the same as the at least one ingredient of the second aqueous ink with the exception that the second clear aqueous liquid does not contain any colorant.