Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-05-12
2001-11-06
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S096000, C347S100000
Reexamination Certificate
active
06312100
ABSTRACT:
The present invention concerns an inkjet print method and an inkset for multicolor inkjet print.
Inkjet print specifically for so-called desk top publishing application finds growing use, which is particularly attributable to its capacity of producing in a single pass multicolored prints by means of application of three or more primary inks on one substrate. Other printing methods generally require one pass through the printer for each primary color. An important benefit of the inkjet printers is also their price.
Thermal inkjet printing systems play a particularly significant role. These have an ink reservoir with liquid-conducting connection to a print head, on which are arranged a plurality of resistors. Selective activation of resistors causes thermal excitation of the ink and its outward propulsion. Exemplary thermal inkjet print systems are described in 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 by a current impulse and a droplet of ink is thereby flung out.
By using special inkjet print heads with a plurality of individual ink compartments, it is possible to produce multicolored images. Each compartment holds a selected ink with special color properties. By combining these ink materials in varying configurations and quantities on one substrate, for example, paper, multicolored images can be produced having high resolution and clarity.
When producing multicolored images by inkjet print, a problem, however, arises if an ink of one color is applied on or in the immediate vicinity next to an ink of a different color.
The problem expresses itself by intermingling or running together of the two inks at their border region, whereby the border line between the inks becomes less sharp, 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. Unsatisfactory images with poor resolution are obtained. This phenomenon is also known to experts skilled in the area of print technology under the term “color bleeding.” In addition, problems of colors running together in multiple ink systems can also be caused by capillary forces, which originate from the traditionally employed paper substrates.
These capillary forces lead to print inks being sucked into neighboring areas. This also results in a printout of poor quality and dissolution.
Different methods have already been proposed for reducing or eliminating the running together of inks at the contact lines. Thus, by more rapid penetration of ink into the to-be-printed medium, the bleeding problem should be minimized. Such more rapid penetration can be attained by addition of surface-active agents to the inks, such as Tenside wetting agents, alcohols, solvents and similar. This is proposed, for example, in U.S. Pat. Nos. 5 106 416 and 5 196 056. Such attempt of solving the problem, however, leads only to insufficient reduction of bleeding. Additional drawbacks lie in an increased “feathering,” i.e., the inks now have an even greater tendency to run along the paper fibers. By more rapid penetration into the paper, that portion of the coloring material which is available on the surface of the paper becomes smaller. This leads to a reduction of the optical density and is particularly noticeable with black ink on white paper. Cohesive color surfaces no longer appear deep black but gray.
In a modification of this method, a rapidly penetrating ink is printed at the contact areas below a slowly penetrating ink. As a result, the slowly penetrating ink also penetrates at these locations more rapidly into the paper and bleeding is reduced. The printing process is hereby controlled via a special software program. The black ink is preferably the slow penetrating ink and a colored ink the rapidly penetrating ink. With this modification, overall bleeding is also insufficiently reduced. In addition, a less intensive, uneven shade of black is obtained.
In another modification, all colors are printed on top of each other at the contact areas, whereby the colored inks are quickly penetrating inks and the black inks are slowly penetrating ink. In this proposal, the optical density of the black ink is also reduced because of the more rapid penetration, which is, however, supplemented by the mixed color of the colored inks, which, based on subtractive color mixing, leads to a shade of black. The drawbacks lie here also in insufficient reduction of bleeding and in an uneven shade of black.
Another proposal is introduced 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, contains a gel-initiating reagent. With contact at the contact line, a gel barrier is formed between the two inks. The formed gel, however, dries rather slowly, which results in reduced rub-off resistance. In addition, the inks have an inadequate shelf life, since the presence of gel-forming or gel-initiating reagents causes higher risk of instability. Also, when ink dries up at the nozzle of the printer, the viscosity increases greatly, which leads to higher clogging risk.
Another “core product” is known, namely an ink set where a first ink contains a coloring substance which can be precipitated by means of a precipitation reagent. A second ink contains the precipitation reagent in addition to a second coloring substance. It is, however, of disadvantage that the precipitation reagent of the second ink must be added in high concentration, which carries with it considerable risk of instability or agglutination. The high percentage of precipitation reagent may also lead to corrosion problems. The precipitation agents are, for example, metallic salts of higher valence such as Ca
2+
, Cu
2+
, Co
2+
, Ni
2+
, etc. Selection of dyes which can be present in the second ink is very limited, since consideration can be given to only such dyes which will remain soluble or dispersed for an extended period of time in the presence of the precipitation reagent.
The present invention was therefore based on the object of making available a multicolor inkjet printing method, which does not have the above described drawbacks and for which specifically the bleeding at the contact lines of different colors has been sufficiently reduced, whereby the color shade of the printed ink is not changed, high optical density of the inks remains preserved, and the employed printing inks have adequate storage stability.
According to the invention, this task is solved by an inkjet printing method where a first, a second and, selectively, a third or additional ink is printed simultaneously or successively or immediately next to each other, whereby
i) the first ink contains a via-precipitation reagent precipitable coloring substance
ii) the first or the second ink contains the precipitation reagent in temporarily passivated form, and
iii) the first, second or third ink contains an activator for the temporarily passivated precipitation provided that the temporarily passivated precipitation reagent and the activator are not present in the same ink.
The following combinations are possible within the scope of the invention:
(a) the precipitable coloring substance and the temporarily passivated precipitation reagent can be contained in the first ink and the activator in the second ink
(b) the precipitable coloring substance and the activator can be contained in the first ink and the temporarily passivated precipitation reagent in the second ink
(c) the precipitable coloring substance can be contained in the first ink, the temporarily passivated precipitation reagent in the second ink and the activator in the third ink.
A coloring substance is a chemical compound which is used in order to provide a printing ink with a desired color characteristic. The coloring substance can be a water-soluble dye, a pigment dispersion or a micro-emulsion. Water-soluble pigments are known substanc
Drescher Peter
Loosli Daniel
Mancini Bruno
Schudel Markus
Barlow John
Fay Sharpe Fagan Minnich & McKee LLP
Pelikan Produktions AG
Shah Manish S.
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