Detalled description of the printing inks

One preferred embodiment of the printing inks according to this invention will now be described hereinafter. 

The printing ink according to this invention comprises an oxidation polymerization type resin, a coloring agent, and an offset printing ink solvent. As the oxidation polymerization type resin used in the ink according to this invention, there may be used a mixture obtained by combining at the specific rate a drying oil such as a linseed oil and a semidrying oil such as a soja bean oil which are generally used as an ink for offset printing inks; an unsaturated aliphatic acid obtained from the aforesaid drying oil or semidrying oil; various denatured substances obtained by denaturing the aforesaid substances with acid, amine or alcohol; and a denatured synthetic resin such as phenolic resin, xylene resin and alkyd resin which are denatured with the drying oil, semidrying oil, unsaturated aliphatic acid or the like (hereinafter referred to simply as "conventional varnish"). 

The conventional varnish to be used as a film-forming substance indispensable to a sheetfed offset ink is per se required to have sufficient fluidity. The ink solvent used for an offset printing ink is of, for example, a non-polar petroleum solvent, i.e. an aliphatic hydrocarbon, aromatic hydrocarbon or a mixture thereof (hereinafter referred to as a non-polar solvent). In case where the varnish is denatured with acid, amine, alcohol or the like to exhibit sufficient fluidity in the non-polar ink solvent as noted above, the varnish is reduced in its affinity relative to the non-polar ink solvent to be gelatinized when the degree of denaturation is too high, thereby to be deprived of its fluidity. 

The oxidation polymerization type resin used in this invention is primarily characterized in that at least a part thereof sets to gel in the non-polar ink solvent as mentioned above. One preferred example of the oxidation polymerization type resin is a mixture of an acid-denatured resin and an amine-denatured resin as used in a conventional printing ink. When the known acid-denatured resin and amine-denatured resin are together used in a mixture, it could not been so far expected from a conventional technique of printing inks that they set to gel in the non-polar ink solvent due to acid base bonding or hydrogen bonding brought about therebetween. Though the oxidation polymerization type resin does not set to gel under certain circumstances according to the mixing ratio thereof, this invention is not applicable to such a condition.