Summary of the printing ink

The invention provides a printing ink composition that includes a branched vinyl resin. The term “vinyl resin” when used in conjunction with the present invention includes polymers prepared by chain reaction polymerization, or addition polymerization, through carbon-carbon double bonds, using vinyl monomers such as acrylic and methacrylic monomers, vinyl aromatic monomers including styrene, and monomers compatible with these. By “branched vinyl resin” it is meant that, while the vinyl polymer is branched, it nonetheless remains usefully soluble. By “soluble” it is meant that the polymer can be diluted with one or more solvents. (By contrast, polymers may be crosslinked into insoluble, three-dimensional network structures that are only be swelled by solvents.) The branched vinyl resins of the invention unexpectedly retain solubility in spite of significant branching. 

The branched vinyl polymers of the invention preferably include at least about 0.008 equivalents, per 100 grams of monomer polymerized, of at least one monomer having at least two ethylenically unsaturated polymerizable bonds or at least about 0.004 equivalents per 100 grams of monomer polymerized of each of two ethylenically unsaturated polymerizable monomers having mutually reactive groups other than the polymerizable double bonds. The branched vinyl resin typically has a low number average molecular weight and a broad polydispersity. In a preferred embodiment, the branched vinyl resin of the invention has a polydispersity of at least about 15, as determined by gel permeation chromatography calibrated with polystyrene standards according to well-known methods. 

The invention also provides a method of making an offset printing ink composition with the branched vinyl resin. In another aspect of the invention, the offest printing inks are modified by the addition of another vehicle resin. The invention further provides a method of polymerizing a branched vinyl resin in which substantially no monomer remains unpolymerized. The printing inks also provides a method of printing using the compositions of the invention. 

Ink formulations including the branched vinyl vehicle of the sheetfed offset inks have unexpectedly improved misting and slinging properties. The inks using the branched vinyl polymer have reduced tack at higher viscosities relative to comparable inks made with linear vinyl polymer vehicles. The invention reduces the amount of misting and slinging and improves the tack/body balance as compared to what would be expected for previous inks formulated with vinyl vehicles that would provide body by increasing tack or nonvolatile content or both. Incorporation of the branched vinyl vehicles of the invention into ink compositions also lends a certain amount of elastic character to the inks, which in many cases is beneficial to ink properties. News inks that include the branched vinyl polymer of the invention have improved rub-off properties. 

Finally, the inks of the invention containing the branched vinyl can be formulated as single-fluid printing inks. The single-fluid printing ink of the invention is advantageously employed in lithographic printing processes.