Detailed Description Of Printing Inks
One preferred embodiment of the printing ink 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 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; 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"). Also, a resin which is obtained by further denaturing the conventional varnish with acid, amine or alcohol so as to gel in an ink solvent used commonly in a printing ink may be applied for the same purpose. "Gelation" termed herein designates the state in which the denatured resin as noted above lacks in fluidity in a non-polar ink solvent.
The conventional varnish to be used as a film-forming substance indispensable to a
printing 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. Therefore, the degree of denaturation thereof has conventionally been limited to a certain range as is well known.
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.
Next a second preferred embodiment of this invention will be described. In this embodiment, the oxidation polymerization type resin does not show fluidity in the non-polar ink solvent since the conventional varnish is subjected to acid-denaturation, amine-denaturation or alcohol denaturation to a high degree so as to set to gel. In the case of an acid-denatured resin, such a gelable resin can easily be produced by subjecting the conventional varnish to anti-denaturation so as to gel the varnish in the non-polar ink solvent through the agency of a polyvalent fatty acid such as maleic acid, fumaric acid and citric acid; a polyvalent carboxylic acid of polyvalent aromatic acid such as terephtalic acid, phthalic acid, isophthalic acid and trimellitic acid. In the case of an amine-denatured resin, the gelable resin is likewise produced by subjecting the conventional varnish to amine-denaturation so as to allow the varnish to gel in the non-polar ink solvent through the agency of a polyvalent amine such as higher aliphatic monoamine, ethylene diamine, propylene diamine, hexamethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentamethylene tetramine, tetramethylene diamine, or the like. Further, in the case of an alcohol-denatured resin (in this invention, epoxy-denaturation is also termed as alcohol-denaturation), the gelable resin is likewise obtained by subjecting the conventional varnish to alcohol-denaturation so as to gel the varnish in the non-polar ink solvent through the agency of a polyalcohol such as ethylene glycol, propylene glycol, trimethylolpropane, pentaerythritol or the like, or various kinds of epoxy resins, e.g. EPOMIC R-140, R-301, R-304K and R-307 made by Mitsui Petrochemical Industries, Ltd. of Japan.
As mentioned above, the oxidation polymerization type resin in this invention sets to gel in the non-polar ink solvent, and therefore, cannot be used for a printing ink as it is. However, it was proved by the studies conducted by the inventors of this invention that the oxidation polymerization type resin capable of setting to gel in the non-polar ink solvent is prevented from gelatinizing to keep sufficient fluidity in an ink solvent by using a non-volatile polar solvent instead of all or part of the non-polar ink solvent. The oxidation polymerization type resin which acquires fluidity owing to the non-volatile polar solvent as mentioned above can maintain sufficient fluidity in a container or on non-absorbent printing members such as a printing plate in a printing machine. On the contrary, when the oxidation polymerization type resin is applied onto an absorbent printing object such as paper, it is absorbed by the printing object to decrease the ink solvent in quantity in the
printing ink, whereby the printing ink sets to gel in an instant and dries quickly.
by: ericfu
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