Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
1999-06-23
2001-03-27
Acquah, Samuel A. (Department: 1711)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C525S054400, C525S423000, C106S031130, C106S031410, C106S237000
Reexamination Certificate
active
06206960
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to heatset lithographic printing ink compositions having low rub-off properties.
BACKGROUND OF THE INVENTION
Inks having low rub-off properties are known in the prior art. Such inks typically contain waxes of various types and the resultant inks will exhibit improved mar-resistance and better slip and water repellency properties. Wax of a controlled fine particle size can be mixed or ground into the batch along with pigments or may be introduced during the final blending operations. Alternatively, the wax may be compounded into a “wax media” by dispersing or melting the wax into varnishes and/or solvents and adding these to the ink.
It is generally well-known that the non-rub qualities imparted by an individual wax are a function of both the particle size and the hardness as well as the melting temperature of any particular wax. However, the addition of wax to solve the rub-off problem introduces other problems. First, on a scale of 100 which represents an ink having no rub-off, when wax is added to ink the result is a reduction in rub-off to a level of only about 60. Second, with the heat and movement imparted by the friction of constant rubbing under pressure, particles of the ink film can ball up and mark unprinted areas. Additionally, introducing more wax to improve rub resistance properties only introduces more problems with respect to gloss and hardness characteristics. The addition of wax to ink almost invariably decreases the ink's level of gloss. Accordingly, a compromise must be achieved between the desired level of non-rub properties and gloss. Finally, wax only provides minimal rub-off reduction in news ink formulations.
Synthetic waxes such as polyethylene wax and polytetrafluoroethylene wax are the most popular waxes used in the ink industry. Such waxes are usually added in the form of “non-rub” or “slip” media which are fine dispersions of the wax in the solvents, oils and resins of the particular type of ink formulation in which it is to be incorporated. Waxes prepared from polytetrafluoroethylene powders are suitable for all types of printing inks, but are especially ideal for heatset inks, where the temperature of the drying apparatus does not cause the wax to soften or melt. Polytetrafluoroethylene-based waxes can also be stirred into finished inks to improve their rub and scuff resistance. Nevertheless, the problem is not completely eliminated by these strategies, particularly with regards to transit marking rub-off of magazine covers.
Another method used in the prior art to remedy the rub-off that may occur during transit is the use of insoluble resin, or oxidative chemistry based on oxidizable resin, drying oil and metallic driers.
Heatset inks that employ commercially available lithographic solvent soluble resin chemistry have not been able to eliminate the rub off problem, particularly when they are used to print on highly oil absorbent paper. In order to solve the problem, oxidative chemistry is utilized to achieve a degree of polymerization necessary to render an ink film that will not resoften twenty four (24) to forty eight (48) hours after heatset drying due to the hydrocarbon solvents being trapped within the printed substrate.
One problem associated with inks prepared by heatset oxidative chemistry is skin formation. Skin formation occurs, for example, when the ink is placed in tote bins and pumped to the printing press. A layer or ink film will form in the tote bins or in the pumping lines that feed the press.
Another solution to solving the ink rub-off problem is to use free radical polymerized ink resins suitable for use with ultraviolet or electron beam curable inks. These inks contain no volatile solvent and achieve a high molecular weight cross-link density when cured. However, the use of curable inks is expensive and thus not widely used.
SUMMARY OF THE INVENTION
The present invention relates to heatset lithographic printing ink compositions containing a resin cross-linked with a polyepoxide compound and solubilized with an aliphatic alcohol having at least 12 carbon atoms that exhibit superior rub-off resistant properties and avoid the aforementioned problems.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that the objectives of this invention are realized by cross-linking a resin with a polyepoxide compound and solubilizing the cross-linked resins with an aliphatic alcohol having at least 12 carbon atoms.
The resin of this invention preferably comprises polyester which is reaction product of four components, namely (a) a polyol, (b) a monobasic aliphatic carboxylic acid, (c) a rosin or modified-rosin acid, and (d) a polycarboxylic acid and/or anhydride thereof.
The polyols found most suitable for producing the polyesters of the present invention are triols. Examples include but are not limited to trimethylolethane, trimethylolpropane, glycerol, and hexane triol.
The most useful monobasic aliphatic carboxylic acids are those having about 8 to 20 carbon atoms, such as for example stearic acid, lauric acid, palmitic acid, oleic acid, and refined tall oil fatty acid.
The rosin or modified rosin may be selected from tall oil rosin, wood rosin, hydrogenated rosin, dehydrogenated rosin, and the like.
The polycarboxylic acids or anhydrides (d) include phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, maleic anhydride, isophthalic acid, fumaric acid, mixtures thereof and the like.
The polyesters of this invention are generally prepared by a two-step process whereby in the first step, the polyol, the monobasic aliphatic carboxylic acid, and the rosin or modified rosin are reacted at temperatures ranging from about 250° C. to 290° C., and preferably between about 260° C. and 280° C., to an acid number between about 1 to 10. In the second step, the polycarboxylic acid or anhydride is then added and the reaction is continued at temperatures ranging from about 150° C. to 220 ° C. and preferably between about 170° C. and 200° C., to an acid number between about 20 to 90, and preferably between about 20 and 50. Thus, as a result, all of the monobasic aliphatic carboxylic acid groups and most of the rosin carboxylic acid groups are reacted at about 250° C. to 290 ° C. and the aromatic carboxylic groups as pendant groups are added at about 150° C. to 210° C. Polyesters typically prepared from this synthetic route include phenolic modified rosin ester resins and maleic modified rosin ester resins.
The printing inks and overprint varnishes of the invention are prepared by grafting a polyepoxide onto carboxyl groups available on, for example, a phenolic or maleic modified rosin ester resin. The molecular weight number average for the maleic or phenolic resin is typically from about 1,500 to 3,000. The polyepoxide is preferably a diepoxide, and more preferably an aromatatic or cycloaliphatic diepoxide, and most preferably bisphenol A diepoxide. The molecular weight of the polyepoxide is up to 560 daltons, and preferably from 100 to 500 daltons, and more preferably from 300 to 500 daltons.
Grafting of the polyepoxide onto the ink resin leaves the resulting polymer oil insoluble which enhances squalene (skin oil) resistance, facilitates solvent release for improved heatset drying by comparison to prior art, and also by comparison with commercially available, rosin based resins currently used for offset printing.
Since the cross-linked resins of the invention are more insoluble, they are kept in solution in the presence of an aliphatic alcohol having at least 12 carbon atoms, and preferably 12 to 24 carbon atoms, and more preferably 12 to 13 carbons such as Neodol 23 (Shell Oil Co.). Furthermore, in order to achieve ink roller stability required for high speed, lithographic web printing, a high boiling petroleum distillate varnish solvent is preferred such as Magie 500 (Magie Bros.).
The aliphatic alcohol is used to keep the resin in solution with the hydrocarbon solvent which may be selected, for example, from Magie 500 and Magie 470 (hydrocarbon solvents available from Magi
Glesias Walter
Hirota Noritaka
Smith Kenneth
Acquah Samuel A.
Sidley Persley, Esq.
Sun Chemical Corporation
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