Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-15
2002-10-15
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S190000, C524S577000, C523S160000, C528S205000
Reexamination Certificate
active
06465567
ABSTRACT:
The present invention relates to pigment preparations for inkjet printing comprising pigment, a dispersant from the group consisting of optionally ionically modified phenol-styrene polyglycol ethers and a surface-active agent from the group consisting of oxalkylated acetylene glycols or of optionally modified alkyl (aryl)polyglycol ethers, to a process for preparing them and to their use as inks for inkjet printing.
In recent years, the use of inkjet printing, as a “non-impact”, computer-controlled printing method, has increased greatly. Inkjet printers are “drop-on-demand” printers, in which by means of an electronic signal drops of liquid inks are generated and are sprayed onto suitable substrates such as paper or films, where they generate the desired image. With the use of inks based on 4 primary colours such as black, yellow, cyan and magenta, and the computer technique for generating, altering and storing image, text or graphic information, images of high resolution can be produced in virtually the entire visual colour space. The header “drop-on-demand” encompasses two different printing systems, as described, for example, in U.S. Pat. No. 4,597,794.
In thermal inkjet printing, drops are produced by introducing thermal energy into the ink liquid. The systems available today are distinguished by a high technical standard for colour images of high optical quality, up to photo quality, and are also suitable for large-format prints and high printing speeds.
In piezo inkjet printing, the drops are generated by means of a piezoelectric element which by application of an electrical voltage is stimulated and ejects the ink continuously, or on demand. Today, this system too has reached a similarly high standard to the thermal system.
In both systems the inks used most widely to date have been based on solutions of water-soluble dyes in an aqueous-organic medium. The advantages of dye-based inks, such as high brilliance and optical density of the prints, however, are countered by a number of disadvantages. Those that may be mentioned include the inadequate light fastness of the dyes, the penetration into the paper fibres and running in the paper (feathering, inadequate edge definition), and inadequate smear resistance and water resistance of the prints, owing to the water solubility of the dyes. For this reason, high-quality prints are in many cases obtained only on special papers.
One alternative is represented by water-based inks comprising as their colouring components organic colour pigments in their particulate form. Given an appropriate choice of pigments, pigment-based ink systems possess markedly better fastness properties, especially light fastness and weather fastness, so that there is particular interest in their use in applications where this property is particularly prized, such as, for example, for prints for posters and displays, and for photographic reproductions.
The pigmented inks currently available on the market, however, still have a number of disadvantages. In terms of colour brilliance, they have still not attained the quality of dye inks. Furthermore, the tendency of the suspended particles to agglomerate means that problems such as long-term storage stability of the inks and undisrupted printing behaviour have not yet been satisfactorily solved. These defects can be caused, for example, by clogging of the fine nozzle apertures, deposits, or settling of the particles or ingredients of the inks on the printing head materials, especially the heating elements, and also drying or deposits at the nozzle outlet.
In order to eleminate the said problems, especially those relating to the agglomeration behaviour, particular importance is attached to the physical stabilization of the pigment particles in the aqueous-organic carrier medium of the inks. It is the state of the art here to use dispersants which stabilize the particles electrostatically and/or sterically. Effective stabilization is achieved with steric dispersants, whose molecules generally possess both hydrophobic moieties, which have affinity for the pigment surfaces, and hydrophilic, long-chain moieties, which bring about the actual steric hindrance in the aqueous-organic medium.
In accordance with U.S. Pat. No. 4,597,794, polymeric dispersants, especially random copolymers, are preferred for inkjet printing, or very specific block copolymers as used in EP 518 225. Although polymeric dispersants are often considered superior to the oligomeric dispersants for aqueous pigmented printing inks, their widespread use does not yet appear to have been successful. In particular, there are still a number of disadvantages to be overcome, in relation to adverse interactions of these agents in the ink formulations or the recording material or the elements of the printing head.
For example, the organic solvents used in the aqueous-organic carrier media of the inks may, depending on their nature and proportions, impair the storage stability of the inks. This applies even to surface-active agents which are used in the inks as additional ink constituents in order to improve the drying properties on the substrates. Since agents of this kind may form micelles in the inks, they may impair the affinity of the polymers for the pigment surface and/or for the aqueous-organic carrier medium as well and so may lead to reagglomeration of the pigment particles.
Furthermore, it is known from, for example, WO 97/43351 that there are other problems with printing inks when using polymeric dispersants, such as, for example, a non-uniform printed image in the case of prolonged printing, owing to cogation—that is, deposits on the heating elements of the printing cartridge.
In order to overcome the disadvantages mentioned, WO 97/43351 recommends the use of oligomeric dispersants based on N-substituted amino acids, which are rendered water-soluble by the introduction of ionic groups and can be understood as electrostatically acting dispersants. Nevertheless, the examples show that stable inks cannot be prepared with all of the pigments in question.
The abovementioned prior art also mentions, as additional ink constituents, surface-active agents (wetting agents) with which the surface tension of the inks and, in particular, the wetting and drying behaviour of the inks on the substrates can be adjusted. Suitable such agents include alkylphenol oxalkylates (WO 97/43351) and, inter alia, acetylenediol derivatives, Na sulphosuccinates and also alkylaryl polyethers (EP 0 518 225).
The fact is, however, as already remarked above, that the use of just such agents affects a large number of parameters, so that it is not simple to find an appropriate combination.
Particular importance is also attached to the selection of the pigments for the establishment of a trichromatic system in the primary colours such as, for example, magenta, cyan and yellow and, if desired, further colours in order to establish an extended colour space. Suitable pigments, and printing inks produced from them, are required to satisfy very stringent requirements in terms of colour brilliance, transparency and light fastness. The pigmented printing inks produced in accordance with the prior art are not yet entirely satisfactory in this respect. This applies in particular to the colour locus yellow. In order to achieve sufficient transparency and brilliance, and also good printing properties, the pigments must be present stably in very fine distribution (very small particles) in the printing inks, which for many pigments, especially in the yellow region, is associated with a deterioration in light fastness. For example, commercially available pigmented inks exhibit a poorer light fastness in the yellow hue than in cyan and magenta, which may lead to unwanted changes in colour (greying) and loss of brilliance under the effect of light.
The colour brilliance achievable is, furthermore, not dependent solely on the particle fineness but also on the wetting characteristics of the inks on the substrate. In this respect there is still considerable room for improvement, especially for p
Grobe Michael
Krause Michael
Kutschkau Karina
Nyssen Peter-Roger
Pfützenreuter Dirk
Bayer Akgiengesellschaft
Gil Joseph C.
Henderson Richard E. L.
Jagannathan Vasu
Shosho Callie E.
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