Latent image ink

Details Latent image ink Latent image ink

1994-05-27

1995-08-22

Klemanski, Helene

Compositions: coating or plastic

Coating or plastic compositions

Metal-depositing composition or substrate-sensitizing...

106 21R, C09D 1110

Patent

active

054436290

DESCRIPTION:

BRIEF SUMMARY
This invention relates to printing inks, and more particularly to latent image inks used in producing games, coloring books, forms, and the like. Typically, such games and books include both visible and "invisible" images; the "development" of the latent image is at least in part an object of the
It is desirable to use conventional lithographic printing methods including oleoresinous inks, "wet" offset presses and standard grade offset paper in order to be able to manufacture games and the like at reasonable cost. Reusable games have been suggested. Manufacture of such games, however, could require more complex printing, developing and erasure techniques. Further, this might not be entirely cost effective, particularly if the game is usually discarded after use, for example during travel. Currently available children's game books (e.g. as disclosed in Lee, U.S. Pat. No. 3,826,449 and Lenkoff, U.S. Pat. No. 3,850,649) utilize a water-based printing ink for the printing of the latent image portions. Printing of each of the latent and visible images requires the use of different print methods. The games are printed in two passes on two different machines. Use of oleoresinous offset inks to print the latent image would be advantageous, in that both the latent and the visible images could be printed in one pass using a conventional two color (or four color) "wet" offset press.
Problems that may be encountered in the development of printed latent images include premature detection of the latent images ("clueing"), that is, when a distinction between background and latent print areas can be seen with the naked eye because of yellowing or different light reflectance of the ink and paper. Inadvertent development of latent ink images may also be caused by impurities in the ink by substances in the paper, by contamination during the printing process, or by heating of the printed latent image during print drying.
A further potential problem is that of long development time for converting the colorless image to a colored reaction product which is clearly visible. Development should preferably be relatively fast.
Other problems not encountered in letter press printing must be overcome to provide a latent image ink suitable for high speed "wet" offset printing techniques.
Canadian Patent No. 974,004 discusses the problems to be overcome in using offset presses without extensive modification. The ink vehicle and the color-forming reactant preferably should be specifically adapted to conventional lithographic offset techniques. Undesirable chemical side reactions caused by conventional metal salt "driers" should preferably be avoided. Some phenolic color-forming reactants tend to inhibit oxidation and/or polymerization of conventional offset vehicles. Finally, invisible ink penetration and migration within the paper should preferably be prevented without resorting to resin coated low porosity or other high reflectance sheets which could cause clueing. The proposed solution in that patent was the use of an ink composition in which the primary components, including the color forming reactant, had little or no solubility in water and were resistant to emulsification in water.
Canadian Patent No. 974,004 proposed the use of relatively large quantities of organic, water insoluble, hydrophobic compounds as the color forming reactant in the latent image ink, combined with conventional lithographic ink components.
Canadian Patent No. 1,148,782 deals with latent image inks suitable for dry offset printing only, i.e. inks that are water soluble and are not suited to "wet" offset printing.
It would therefore be advantageous to have a lithographic ink that permits the use of highly desirable conventional lithographic printing methods to print both the visible and invisible entries on a suitable offset grade paper. Thus, standard "wet" offset lithographic press equipment could be used, avoiding the necessity of printing the visible and latent (i.e. "invisible") images in separate operations. If latent images which are to consist of mor

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