Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-01-08
2004-01-27
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031610, C106S031580, C106S031860
Reexamination Certificate
active
06682587
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a meltable ink composition, for use in printing devices in which ink drops are ejected from ink ducts. Inks of this kind, which are also known as hot melt inks or phase change inks, are solid at room temperature and liquid at elevated temperatures. In a printing device, for example, an ink jet printer, the ink is melted and transferred to substantially closed ink ducts which lead at one end into a nozzle. As a result of a sudden pressure rise in the duct, produced for example by rapidly reducing the volume of the duct or rapidly evaporating some of the ink in the duct, a drop of ink can be ejected from the duct through the nozzle. In this way an image can be built up from individual ink drops on a receiving material. Meltable inks contain a carrier material with a melting point higher than room temperature so that the ink melted in the printing device is practically not subject to evaporation when the printing device is not printing. This prevents the nozzles of the ink ducts from becoming clogged. In addition, inks of this kind have the advantage that they set rapidly on the receiving material, so that the print quality, particularly the edge sharpness, is less dependent on the type of receiving material.
U.S. Pat. No. 4,851,045 discloses oxidized montan waxes which are the reaction product of aliphatic diols and C25-35 fatty acids. These waxes have the disadvantage that their melting temperature is relatively low, so that printed ink images may result in blocking at elevated temperature or bleeding through the paper. In addition, the crystallized waxes are relatively soft, so that printed images may feel “waxy” and be less resistant to mechanical stresses. Finally, the viscosity of these esterified montan waxes is relatively high, so that it is difficult to use them in ink compositions for ink jet printers.
U.S. Pat. No. 4,931,095 discloses benzoates as a component of meltable inks. Compounds of this kind are formed by esterifying benzoic acid, an unsubstituted aromatic acid, with a suitable alcohol. From the patent specification it is known to use polyalcohols, such as pentaerythritrol, sucrose and glycerol for this purpose. These benzoates have the disadvantage that they set amorphously when they cool rapidly from a melted state, particularly when a liquid ink drop is transferred to a relatively cold receiving material. As a result, the solidified ink drops are to some extent tacky at room temperature, particularly when mechanically stressed. By gumming, scratching or rubbing over a printed image, for example, the ink may block. In addition, the compounds may subsequently crystallize after being transferred to a receiving material, so that quality of the image, particularly the visual quality, deteriorates in the course of time.
EP 0 856 565 A1 discloses the toluate and anisylate esters of pentaerythritol as a component of a meltable ink. These compounds differ from the benzoates due to the presence of a substituent on the aromatic benzene ring. As a result, the physical and chemical properties of these compounds differ from those of the benzoates. These toluates and anisolates, however, also have the disadvantage that they solidify amorphously when cooled rapidly. In addition, the compounds have a relatively intensive after-crystallization. They also have the disadvantage that their melting temperature is relatively high, thus making them less suitable as a component for a meltable ink. A higher melting temperature makes much higher demands of the printing device itself.
The toluate and anisylate esters of 2,2′-bisphenol are known from EP 0 978 548 A1. These substances result in inks which exhibit a deterioration in copy quality if the prints are stored for a long time, for example some months. This is probably the result of a slow after-crystallization from an amorphous state.
A specific 1,4-bis-[(substituted)-benzoyloxymethyl]-cyclohexane is known from JP 2076786 as a sensitivity improver for a color developer in a sheet suitable for thermal transfer. This patent does not indicate or suggest that these compounds can also be used in meltable inks suitable for ink jet printers. The latter inks are subject to totally different requirements from inks for thermal transfer. Ink jet printers differ from thermal printers in that the liquid ink in the form of individual ink drops ejected through air over a certain distance, is transferred to a receiving material. As already indicated hereinbefore, the print heads used for this purpose have ink ducts provided with nozzles and means for ejecting one ink drop at a time from a specific nozzle. To achieve this drop formation, the physical properties of the ink, particularly the viscosity and surface tension, must lie within narrow limits. In addition, meltable ink is frequently heated a number of times in an ink jet printer and then cooled again to room temperature before actually being transferred to a receiving material. This places high demands on the thermal stability of the ink. All this makes the development of meltable inks for ink jet printers a particularly complex area.
High-boiling organic solvents for use in a silver halide photographic material are known from U.S. Pat. No. 4,923,783, in accordance with formula I
(ArCOO)
n
—L (I)
wherein Ar is an aryl group with 6 to 24 carbon atoms, L is a 2-valent to 6-valent alkylene with 2 to 24 carbon atoms possibly containing one or more ether bonds and n is an integer between 2 and 6. Compounds of this kind reduce the reductive bleaching of cyan dyes as a result of damp and heat. This patent contains no suggestion that these substances can be used as a component in a meltable ink.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a meltable ink composition having advantageous properties for use in printing devices in which the ink is ejected in the form of drops from ink ducts. Another object of the present invention is to provide ink compositions which result in printed images having a good and stable print quality. A further object of the present invention is to provide inexpensive ink compositions. To this end, an ink composition has been discovered which contains a compound in accordance with the following formula II
where R
1
and R′
1
are the same or different and are selected from a C1-8 alkyl group or a C1-8 alkoxy group, R
2
is a C1-12 linear alkane diyl or a C5-12 alkane diyl which contains an alicyclic group, and n is 1, 2, or 3. These bis-ester compounds have melting temperatures suitable for forming a meltable ink composition usable in an ink jet printer. The melt viscosity of the compounds is also sufficiently low, typically lower than 20 cP, at the regular jet temperatures. The compounds are also such that they can result in inks sufficiently resistant to mechanical stress. Finally, these compounds are stable in the solidified state, so that the risk of deterioration of the copy quality of printed images is reduced. Compounds of this kind can advantageously be used in meltable ink compositions. In this way the present invention counters the disadvantages of the prior art ink compositions as described above.
Advantageously, R
1
and R′
1
are selected from a C1-6 alkyl group or a C1-6 alkoxy group. With these compounds it is possible to obtain ink compositions which are less waxy. With ink compositions of this kind, therefore, it is possible to obtain images which are more resistant to mechanical stress such as rubbing, scratching, gumming or folding. More preferably, R
1
and R′
1
are selected from a C1-4 alkyl group or a C1-4 alkoxy group. These compounds are even less waxy and can thus result in ink compositions for printing images which are even more resistant to mechanical stresses.
In one preferred embodiment, R
1
is equal to R′
1
. In this way, better-defined compounds can be obtained, the properties of which can be more satisfactorily controlled. In this way it is possible to obtain an ink composition which is better a
Hendricks Danny Hendrik maria
Huinck Marcus Petrus Leonardus
Suilen Frederik Leonardus Everardus
Bell Mark L.
Birch & Stewart Kolasch & Birch, LLP
Faison Veronica F.
Oce--Technologies B.V.
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