Compositions: coating or plastic – Coating or plastic compositions – Marking
Utility Patent
1998-12-22
2001-01-02
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031660, C106S031850
Utility Patent
active
06168656
ABSTRACT:
The present invention concerns a pigmented inkjet ink with improved anti-wetting properties.
A distinction is made between two types of ink which are employed for so-called inkjet printers (inkjet print). Involved are, on the one side, inks where the coloring substance is dissolved as a dye in a solvent, on the other side, dispersed inks, where the coloring agent is dispersed in a dilution agent in the form of a pigment.
Depending upon the material to be printed or the printing method to be employed (continuous or drop-on-demand) (DOD) method, the ink properties must satisfy certain criteria, such as required invariability of ink, high degree of endurance and optical density and similar. In order to meet these specifications, pigmented inks are being employed in increasing measure for improvement of print quality.
Pigmented inks on the basis of high-boiling aliphatic hydrocarbons are less likely to clog the inkjet nozzles, since they do not dry up in the nozzle area during stops in printing.
They can be reliably employed on porous substrates because of quick migration and their water-proof behavior. Such inks are not electrically conductive and have a non-corrosive effect upon the metal components of the print head.
In order to increase the stability of these dispersions, preferential use is made of ionic dispersants such as macro-molecular, poly-ionic compounds from poly or oligomer systems with acid or alkaline groups as repetitive structural units. Such dispersants are also specifically employable with non-watery or essentially non-watery inks. Polyesteramines are known for example as dispersants with acid or alkaline groups, such as SOLSPERESE (brand name of the Zeneca colors) and EFKA (polyamine dispersant, brand of Efka Chemicals).
It has been shown the aforementioned dispersants, specifically with respect to the polyamine-aliphatic acid condensates that they have a skin and eye irritation effect when used as dispersants in the specified inks. In addition, during storage, raw material and ink release ammonia. As a rule, addition of another additive is required, which prevents wetting of the print head nozzle plates in the inkjet printers, but which has a detrimental effect upon the dispersion stability.
Solvents employed in non-watery pigmented inks comprise, aside from polar solvents, also homopolar solvents, such as aliphatic hydrocarbons, for example EXXSOL (brand name of Exxon Chemical GmbH, Cologne for a fraction from distillation of natural or synthetic hydrocarbon mixtures) or aromatic hydrocarbons, for example SOLVESSO (brand name of Exxon Chemical GmbH for aromatic compounds) as well as their mixtures in long-chained alcohols, esters and ethers, commonly used are homopolar solvents with at least six carbon atoms.
From DE 197 26 043, a pigmented ink is known of at least 80% homopolar solvent with therein dispersed pigment and also one co-polymer of vinyl-pyrrolidone with one or several long-chained alpha-olefins having at least 6 carbon atoms. This ink, however, does not always have totally satisfactory anti-wetting properties.
With the use of such inks in inkjet printers, problems occur in such manner that a portion of the ejected droplets is split off and collects in the area surrounding the jet plate.
While it is true that the ink is able to flow back into the nozzle and become part of the next ejected ink drop, there forms, however, when stops in printing are reduced and with increased ink expulsion frequency, more ink residue that can flow back, which then accumulates on the nozzle plate. Even worse is the formation of a cohesive ink film on the nozzle plate, which obstructs the nozzles. The drops cannot be propelled through this film. The printing process fails.
In order to achieve an improvement in the anti-wetting property of the ink on the nozzle plate, it is possible to apply a so-called de-wetting coating or anti-wetting coating on the surface of the nozzle plate, which is formed, for example, of fluorocarbon or fluo-silane. The above mentioned problems can be reduced by this coating. Formation and run off of ink droplets is improved, but essential improvement of the anti-wetting behavior of the ink is not yet obtained in sufficient measure.
Another problem occurs with providing multi-colored images by inkjet print, because an accumulation of ink on the surface of the nozzle plate may lead, with further expulsion of ink, to mixing together or running together of different colored inks.
One possibility of diminishing the surface wetting of the nozzle plate by the ink is the addition of a compound which will neutralize the acid or alkaline groups of the dispersant in the ink in such quantity that will not destabilize the dispersion. This neutralization prevents the ink from accumulating on the nozzle plate, with concurrent increase in the run-off speed of the drops on the nozzle plate surface. The neutralizing agent can be a small molecule or a polymer. If the dispersant is a polyamine, an acid is employed as a neutralizing agent. Examples for this are organic carbonic acids, such as acetic or citric acid, organic sulfonic acids, phenols or novolaks, such as Uravar FN5. If the dispersant contains acid groups, the neutralizing agent is appropriately an amine. Preferred as solvents are homopolar organic solvents and compounds with small amounts of polar solvents. Such inks are described in WO 97/15633.
The known inks, however, have a number of drawbacks. The employed dispersants and additives irritate the eyes, the skin and the mucous membranes.
Furthermore, the dispersion stability of the known inks on the basis of homopolar hydrocarbons is not sufficient, since the addition of further additives it is possible to improve other properties, such as the anti-wetting property of the ink, but, at the same time, there is a decrease in the stability of the dispersion phase of the ink. With extended storage, this may lead to inhomogeneities and sediment formation.
The invention is therefore based on the object of making available an ink for use in inkjet printers which has the indicated drawbacks of the state of the art to only a reduced extent, which specifically demonstrates improved dispersion stability, even with extended storage, and which has, at the same time, improved anti-wetting capability of the homopolar pigmented ink on the nozzle plate of an inkjet print head. Furthermore, the anti-wetting additive should have no toxic properties, specifically it should not be irritating to the skin and eyes. In addition, such ink should permit the beneficial imprinting of absorbent materials, such as paper and cardboard, with excellent functional capability.
According to the invention, this object is solved by an inkjet ink containing:
a) a solvent which has at least 80% of a homopolar, non-watery solvent.
b) a pigment dispersed in the solvent, and
c) one or several phospholipides.
Consequently, necessary components of the inkjet ink according to the invention are: solvents, pigments and one or several phospholipides.
It has now been shown, quite unexpectedly, that the addition of at least one phospholipide to the pigmented inkjet ink clearly improves the anti-wetting property of the ink. This behavior might be attributed to the amphiphilic properties of the phospholipides. Phospholipides have special properties based on their hydrophilic head group and their hydrophobic aliphatic acid chain.
The phospholipides can form so-called liposomes—mostly spherical structures with a double membrane from the lipid molecules, whereby the lyophilic portions of the molecule point toward the interior of the liposome and form its surface, while the lyophobic portions of the molecule in the membrane point towards each other. Within the scope of the invention, such vesicles are very well suited for encapsulations of pigment particles and therefore act not only as anti-wetting additive but also as stabilizer.
Phospholipides occur in all animal and vegetable food items and belong to the complex lipides which are subdivided into the sphingo-phospholipides and glycero-phospholipides.
Griebel Thomas
Howald Nicole
Schulz Matthias
Fay Sharpe Fagan Minnich & McKee LLP
Klemanski Helene
Pelikan Produktions AG
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