INK JET INK COMPOSITION

Abstract: A non-aqueous ink jet ink composition suitable for being discharged from an ink jet apparatus at a temperature above ambient, comprises stearic acid. The composition preferably also contains oleic acid and/or a dye. The stearic acid is in waxy form and other natural and/or synthetic waxes may also be present,

Description: INK JET INK COMPOSITION This invention relates to an ink jet ink composition suitable for discharging from an ink jet apparatus at a temperature above ambient temperature, which is normally a temperature of from 200C to 250C. Known ink jet inks often provide marginal print quality. This is because water-based jet inks are generally incompatible with paper, having poor penetration and drying characteristics with respect to the paper. On the other hand, oil-based inks which are more compatible with paper, have low surface tensions and usually provide ink dots which are too large to give good print quality. It is an object of the present invention to provide an improved ink jet ink. According to the present invention there is provided a nonaqueous ink jet ink composition which is suitable for being discharged from an ink jet apparatus at a temperature above ambient temperature, characterised by containing stearic acid. Preferably the ink jet ink composition contains from 50.0 to 99.0 wt % of stearic acid. Stearic acid of commercial quality may be considered a wax or mixture of waxes, synthetic or natural, and is normally a mixture of fatty acids in which stearic acid predominates. Commercial stearic acids are chiefly produced from saponified and distilled animal fatty acids. These fatty acids are usually composed of approximately 60% liquid and 40% solid acid. The bulk of the liquid acids is separated from the solid acids by hydraulic pressing. From the first pressing single-pressed stearic acid is obtained, from the second pressing, double-pressed stearic acids, and from the third pressing, triple pressed stearic acids. Each successive pressing removes additional liquid fatty acids, thus increasing the purity and quality of the resulting solid stearic acid. The liquid acids present are unsaturated and the solid acids, saturated. Within the scope of waxy stearic acids useable in the invention are compounded or chemically modified waxes which may include natural or synthetic materials, for example, resins. A definition of waxes can be found in Industrial Waxes by H. Bennett; Volumes 1 and 2; Chemical Publishing Company, Inc., New York, NY (1975). Bennett defines a wax as "an unctuous solid with varying degrees of gloss, slipperiness and plasticity, which melts readily". Natural waxes may be of vegetable, animal or mineral origin. Modified waxes are natural waxes that have been treated chemically to change their nature and properties. Synthetic waxes are made by the reaction or polymerization of chemicals. Compounded waxes are mixtures of various waxes or of waxes with resins or other compounds added thereto. The term "Wax-Natural" is also describec on page 1094 of the 10th Edition of the Condensed Chemical Dictionary, Van Nostrand Reinhold Company, New York. The term "Wax-Synthetic" is also described on page 1094 of the above-referred to Dictionary. The term "Natural Wax" as used herein will include Japan wax, candelilla wax and carnauba wax. It does not include materials such as kauri gum, wool wax or cocoa butter. Wax-containing ink jet inks are usually solids or semi-solids at ambient temperature, and therefore, require to be discharged from an ink jet apparatus at elevated temperatures. The heated ink fluid will solidify when it comes in contact with its paper target. The rate of solidification of the wax-containing ink will control the degree of penetration into the paper, usually a small circular dot will result. As a general rule, inks containing wax as a major component thereof, will have less penetration into the paper than inks containing additive amounts of wax. A hot-melt ink for use in an ink jet apparatus is taught in United States Patents, Nos 3,653,932 and 3,715,219, respectively. The major component of the hot melt ink is a didodecyl-sebacate which is a highly viscous, synthetic substance. As compared with the present invention, the didodecyl-sebacate is a synthetic substance which is generally too viscous to provide good jetability in an impulse ink jet apparatus. In a Japanese Abstract, Rico J56166-274, the use of stearic acid in an oil-in-water emulsion ink fluid is suggested. This aqueous ink uses only small amounts of fatty acids in its formulations, and is not meant to operate as a hot melt (wax) ink. The ink composition of the present invention suitably further contains oleic acid. The stearic acid may be the basic fluid vehicle of the ink or may be used as an additive to other fluidic vehicles such as fatty acids, and more particularly oleic acid, and oleic acid with benzyl ether, etc. A suitable dye or coloring agent, for example, an oil-or-solventsoluble dye may also be present in the ink composition for visibility. Examples are Typophor Black and Calco Nigrosine Base, manufactured respectively by BASF and American Cyanamid. Preferably the ink jet ink composition of this invention has a maximum viscosity of 35 x 10 Pa.s (35 centipoises)ata temperature in the range 400C to 900C. Stearic acid as an ink jet ink vehicle has been found to have the advantage of good dye solubility, viscosity vs temperature relationship and good compatibility to a wide range of vehicles. The stearic acid also has a functional group, COOH, which has good affinity to paper Thus, it will prevent the ink flaking off from the paper. The stearic acid can be used in a hot melt ink. Because the ink changes from liquid to solid when it hits the paper, the ink/paper interaction has been minimized The dots are very consistent so that it gives good print quality on almost any kind of paper. An ink composition according to this invention gives a good print quality. Print quality is generally a measure of the circularity of an ink dot. An ink of this invention provides highly repetitive dots of small size and high measure of circularity thus giving good edge definition and contrast Circularities of 0.7 or better are attainable (as measured by the technique described in our European Patent Publication No.62 444 Al). The ink formulations of this invention find particular applicability in an ink jet apparatus of the impulse type, but are not limited thereto. Specific ink formulations which have been found to provide the above described good ink dot circularity are presented in Table I below by way of non-limitative examples. All parts are parts by weight. Table I Stearic Acid 85 97 60 60 65 75 Oleic Acid -- -- 20 20 -- - Typophor Black 15 -- 20 40 15 - Calco Nigrosine Base -- 3 -- -- -- 5 Vis. Solid/Room Temp. 11.4 1.4 10.5 10.1 -- - (75 C) (70 C) (75 C) (75 C) Wax &num;2** -- -- -- -- -- 20 Wax &num;3** -- -- -- -- -- 20 Viscosity-- 65 C -- -- -- 65 C 18.4 9.0 (Pa.s x 10-3) -- -- -- -- 13.4 7.7 (7@ C) (70 C) -- -- -- 85 C 10.2 Dot Size* 4 mil/ 4 mil/ 2 mil 2 mil orifice orifice 6 mil/ 3 mil orifice *The dot size data is generally independent of target substrate materials (paper) but will vary to a slight degree with different ink jet apparatuses. **The waxes designated No. 2 and No. 3 are the product of Strahl & Pitsch, Inc. 230 Great East Neck Road, West Babylon, N.Y. 11704. The above ink formulations provide dots which produce characters approaching typewriter quality printing. As such, the above formulations are believed to provide inks which result in the finest print quality in the ink jet art. Other natural waxes such as Japan wax, can del lila wax and/or carnuauba wax can be blended with stearic acid to produce an acceptable ink for an ink jet apparatus. The above formulations are, however, meant to be only exemplary, and are meant to provide a general teaching and understanding of the invention.

Claims: CLAIMS: 1. A non-aqueous ink jet ink composition which is suitable for being discharged from an ink jet apparatus at a temperature above ambient temperature, characterised by containing stearic acid. 2. An ink jet ink composition as claimed in claim 1, wherein the stearic acid is contained in a weight percentage range of from 50,0 to 99.0. 3. An ink jet ink composition as claimed in claim 1 or claim 2, wherein the stearic acid is present in the form of a wax or a mixture of waxes. 4. An ink jet ink composition as -claimed in claim 3, wherein the composition comprises a chemically modified or compounded wax. 5. An ink jet ink composition as claimed in any one of claims 1 to 3, wherein the composition comprises a natural wax in combination with said stearic acid. 6. An ink jet ink composition as claimed in claim 5, wherein the natural wax is selected from Japan wax, candelilla wax, and carnauba wax. 7. An ink jet ink composition as claimed in any preceding claim, wherein the composition further contains oleic acid. 8. An ink jet ink composition as claimed in any preceding claim, wherein the composition further contains at least one dye or coloring agent. 9. An ink jet ink composition as claimed in any preceding claim, wherein the composition has a maximum viscosity of 35 x 10 Pa.s at a temperature in the range of 400C to 900C. 10. A method of ink jet printing employing an ink jet printer from which ink is discharged at above ambient temperature, characterised by employing an ink composition defined in any preceding claim.

Inventors: COOKE, THEODORE MICHAEL, LIN, AN-CHUNG ROBERT, WHITFIELD, RICHARD GEORGE
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1983
Main classification: C09D11
IPC codes: C09D11