Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1998-08-06
2002-05-07
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031280, C106S031860
Reexamination Certificate
active
06383277
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink set for utilization in inkjet printers.
Inkjet printing finds growing distribution, specifically for so-called “Desk Top Publishing” application which is particularly attributable to its capacity to produce multi-colored prints by application of three or more primary inks onto a substrate in one single pass through.
Other printing methods generally require one pass through the printer for each primary color. An important benefit of the inkjet printers is, furthermore, their favorable price.
Thermal inkjet printing systems play a particularly important role. They have an ink reservoir, connected in liquid-conducting fashion with the print head, on which are located a plurality of resistors. The selective activation of the resistors provokes thermal excitation of the ink and its outward propulsion. Exemplary thermal inkjet print systems are described in the U.S. Pat. Nos. 5,500,895 and 4,794,409. Other systems are based on the so called Piezo-technology, in which a piezo element is excited via a current impulse causing outward propulsion of a drop of ink.
Creation of multi-colored images is possible by application of special inkjet print heads having a plurality of individual ink compartments. Each compartment holds a selected ink having special color properties. By combining these ink materials on one substrate, for example paper, in different configurations and quantities, it is possible to produce multi-colored images having high resolution and clarity.
When producing multi-colored images via inkjet print, there occurs, however, a problem if an ink of one color is applied onto or in the immediate proximity to an ink of a different color. This problem expresses itself in a mixing or “running together” of the two inks at their border areas, as a result of which the borderline between the inks becomes blurred, for example, at the outer edges. If, for example, a black image area is printed directly next to a yellow image area, one notes, in most cases, a diffusion of the black ink into the yellow ink. One obtains unsatisfactory images having poor resolution. This phenomenon is known to persons skilled in the art of print technology under the term “color bleeding”. Furthermore, problems of “running together” of color in multiple ink systems can be caused by capillary forces, which originate with the commonly used paper substrates. The capillary forces result in the print inks being sucked into neighboring areas. This also results in a printout of poor quality and resolution.
Several methods have already been suggested to reduce or prevent the “running together” of the inks at the contact lines. Thus, the bleeding problem was to be minimized by more rapid penetration of the inks into the medium to be imprinted. Such more rapid penetration can be obtained by adding to the printing inks, surface active substances, such as tensides, wetting agents, alcohols, solvents and similar. This is proposed, for example, in U.S. Pat. Nos. 5,106,416 and 5,196,056. This attempt at solving the problem results in only insufficient reduction of the bleeding. Additional drawbacks consist in greater “feathering”, i.e., the inks show greater tendency to run alongside the paper fibers. By more rapid penetration into the paper, the portion of the coloring substance, available on the surface of the paper, becomes smaller. This leads to reduction in the optical density and is particularly noticeable with black ink on white paper. Cohesive color areas no longer appear deep black, but gray.
In a modification of said method, a rapidly penetrating ink is printed at the contact surfaces under a slowly penetrating ink. As a result, in these spots the slow penetrating ink penetrates also more quickly into the paper, and bleeding is reduced. The printing process is hereby controlled by specially programmed software. Preferably, the black ink is the slowly penetrating ink and a colored ink, the rapidly penetrating ink. With this modification, bleeding overall is also little diminished. Additionally, one obtains a weaker and variable black color shade.
In another modification, all colors are printed above each other at the contact surfaces, with the colored inks being rapidly penetrating inks and the black ink a slowly penetrating ink. In this proposal also, the optical density of the black ink is again reduced by the more rapid penetration; this is, however, complimented by the mixed color of the colored inks, which, based on the subtractive color mixtures, leads to a black color shade. The drawbacks consist here also in insufficient reduction of the bleeding and in the variable shade of black.
Another suggestion is presented in EP 0 705 889 A1, which makes use of gel-forming inks. An ink, preferably the black ink, contains a gel-forming reagent and another ink, preferably the colored ink, a gel-initiating reagent. When making contact at the contact line, there forms between the two inks a gel barrier. The formed gel, however, dries extremely slow, as a result of which wipe resistance is decreased. In addition, the inks have insufficient shelf life because greater instability risk is caused by the presence of the gel-forming or the gel-initiating reagent. With drying of ink at the print nozzle, viscosity, furthermore, greatly increases, which leads to increased clogging risk.
A commercially available inkset product is also known where a first ink contains a coloring substance which can be precipitated by a precipitation reagent. A second ink contains the precipitation reagent in addition to a second coloring substance. It is, hereby, of disadvantage that the precipitation reagent of the second ink must be admixed in high concentration, which carries with it significant risk of instability or risk of cogation. The high percentage of precipitation reagent can also lead to corrosion problems. Precipitation agents, for example metallic salts of higher valence such as Ca
2
+, Cu
2
+, Co
2
+, Ni
2
+, etc. The selection of coloring substances, which may be present in the second ink, is highly limited, since only such coloring substances come under consideration that will remain soluble or dispersed over an extended period of time in the presence of the precipitation reagent.
The present invention was, therefore, based on the object of providing a multi-color inkjet print method, which does not have the previously described drawbacks, and for which specifically the bleeding has been sufficiently reduced at the contact lines of different colors, whereby the color shade of the printed ink does not undergo change, high optical density of the inks is retained and the employed printing inks have adequate shelf life.
The applicant, surprisingly, has found that these problems are prevented or greatly minimized if an inkset is used where a first ink contains a watery ink medium—if necessary with assistance from a dispersing agent—a dispersed first color pigment and the coloring substance of a second ink acts as precipitation agent for the first color pigment.
Accordingly, the invention concerns in one specific embodiment an inkset for utilization in inkjet printers, comprising a) a first ink, which contains: (a1) a watery ink medium, (a2) an in-the-ink medium dispersed first color pigment and (a3) optionally, a first dispersing agent, whereby the first color pigment and/or the first dispersing agent carry ionic groups b) a second ink, which contains: (b1) a watery ink medium and b2) an in the ink medium soluble coloring substance whereby the soluble coloring substance acts as precipitation agent for the first color pigment water insoluble, solvent-dissolved solvent dye, optionally with an emulsifier for this system, whereby the solvent dye, the emulsifier and/or the in water insoluble solvent act as precipitation medium for the first color pigment.
In another specific embodiment, the invention concerns an inkset for utilization in inkjet printers, comprising (a) a first ink, which contains: (a1) a watery ink medium, (a2) an in-the-ink medium di
Bell Mark L.
Faison Veronica F.
Fay Sharpe Fagan Minnich & McKee LLP
Pelikan Produktions AG
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