Jet ink with amine surfactant

Abstract: A liquid ink composition comprising at least one water soluble dye, water dissolving said dye, a volatile base bringing said ink to basic pH, and a minor amount of a surfactant, said surfactant being a tertiary amine having two polyethoxylate substituents, with the number of ethoxy groups being in the range of 5 to 25, and a third substituent of a straight chain alkyl, an ester, a fat or a fatty acid. The static surface tension is less than 40 dynes/cm while the dynamic surface tension is about 65 dynes/cm. Satellites and splatter in thermal drop on demand printing are greatly reduced, and drop misdirection is reduced.

Description: Technical Field This invention relates to aqueous liquid ink applied from nozzles, commonly termed jet inks. The inks of this invention exhibit cohesive ink placement during use. Background of the Invention Jet inks commonly contain water, an organic co-solvent, such as tetraethyleneglycol, one or more dyes dissolved in the water, and a surfactant to facilitate penetration of the ink. The dyes are typically soluble in a basic solution and the ink contains a base such as ammonia, which leaves the ink after printing, leaving a printed dye resistant to ordinary water (termed waterfast printing). Other standard ingredients are a chelant for mineral control, such as tetrasodium ethylene diamine tetraacetic acid, a wetting agent such as glycerol, a biocide, and buffers, such as equal parts of sodium phosphate and sodium tetraborate. US-A-5,352,283 has inks which incorporate much of such prior art. This invention also employs the same black dye as employed as the single dye in the embodiments of the foregoing patent 5,352,283. That dye is the direct subject of US-A-5,198,002. US-A-5,062,892 discloses buffers such as used in these formulations. US 4,508,570 discloses aqueous inks for ink-jet printing comprising (i) a water-soluble dye and/or acid dye, (ii) a polyhydric alcohol and/or an alkyl ether thereof, (iii) water, and (iv) at least one water-soluble non-ionic surface active agent selected from the group consisting of a polyoxyethylene alkyl amine, a polyoxyethylene alkyl phenyl ether and a polyoxyethylene alkyl ether. US 5,254,158 discloses aqueous inks comprising an aqueous liquid vehicle, a colorant, and an additive material selected from the group consisting of amine alkoxylates, sorbitan monoester alkoxylates, alkylene oxide adducts of glycerine, and mixtures thereof. This invention employs an ethoxylated amine surfactant believed to be a novel incorporation in jet inks. The jet inks print conventionally with minimal splatter or separation into small adjoining dots (which will be termed satellites). The novel surfactant is a tertiary dipolyethoxylated amine with the third substituent being a stearyl group. Trispolyoxylated amines in jet inks are disclosed in US-A-5,389,134. No comparable prior art with respect to the novel surfactant of this invention is known. A prior art ink comparable in performance to the ink of this invention has a static surface tension of more than 45 dynes/cm and a dynamic surface tension of about 65 dynes/cm. The ink of this invention has a static surface tension of less than 40 dynes/cm and a dynamic surface tension also of about 65 dynes/cm. Disclosure of the Invention The novel surfactant in aqueous jet inks of this invention is a tertiary amine having two polyethoxylated substituents, in which the total number of ethoxy groups is 5 to 10, each polyethoxylate substituent has at least two ethoxy groups and the third substituent is a stearyl group. The jet ink of this invention prints with few separated small dots experienced during conventional drop on demand printing by thermal vaporization of the ink. Such outlying dots can be identified as either satellites or splatter. In accordance with this invention, both of these characteristics are greatly reduced in size and compared to such printing with inks of the same formulation except for employing different surfactants. In addition, horizontal line quality is improved. There is less drop misdirection and lines appear to be straighter and less fuzzy. Best Mode for Carrying Out the Invention The preferred ink formula is as follows: INGREDIENT FUNCTION % BY WT. Black Dye (See Note 1 below) Colorant 2 Yellow dye (Direct Yellow 132) Colorant for Blackness Improvement 0.25 Tetrasodium ethylenediamine tetraacetic acid (EDTA) Chelating Agent for Calcium Control 0.10 Glycerol Spread Control/ Humectant 5 Tetraethylene Glycol Co-Solvent 1.25 Proxel GXL (trademark) Biocide 0.2 t-amine (See Note 2 below) Surface Tension Adjustment 0.05-0.1 (0.05 preferred) Na 2 HPO 4 7H 2 O Buffer/Kogation Reduction 0.25 NaB 4 O 7 10H 2 O Buffer 0.25 Triethanolamine Nozzle Start-up (Improve printing at start-up) 1 Ammonium hydroxide to adjust pH to 8.65 Water Balance Note 1: This dye is the single dye used in the formulas disclosed in US-A-5,352,283 and is a direct subject for patenting of US-A-5,198,002. Note 2: R-N(C 2 H 4 O) x H(C 2 H 4 O) y H, where x + y (the number of polyoxyethylene groups) is from 5 to 10, with each x and y at least 2, and R is a stearyl. Specifically, functioning well in accordance with this invention are the following: the material where R is stearyl and x+y is 5, which is sold commercially as Chemeen (trademark) 18-5; x+y is 6, which is sold as Chemeen 18-6; x+y is 8, which is sold as Chemeen 18-8; and x+y is 10, which is sold commercially as Chemeen 18-10. Dynamic surface tension can be measured by bubbling nitrogen gas into the liquid ink at varying rates while observing the pressure on the gas to achieve those rates. Higher pressure at a given rate correlates with higher dynamic surface tension. Certain surfactants in formulas according to the foregoing preferred formula have been observed to increase notably in surface tension over increasing bubble rates (establishing high dynamic surface), whereas the same ink with 0.10% hexylcarbitol by weight as the only surfactant has relatively the same surface tension across all bubble rates (establishing low dynamic surface tension.) At least one prior art ink having low satellites and splatter, as true for this ink, also has comparably high dynamic surface tension. The inventive ink has a static surface tension of 40 dynes/cm or less while that ink has a static surface tension of more than 45 dynes/cm. Both have dynamic surface tension of about 65 dynes/cm. The foregoing preferred formula is optimized for use in the ExecJet (trademark) IIc printer sold commercially by the applicant of this invention which prints by drop on demand through nozzles by vaporizing the ink with heat, as is generally standard. Using the same ink as just described but replacing the amine surfactant with the hexylcarbitol and, separately, using the same ink but replacing the amine surfactant with Chemeen 18-2, which is like Chemeen 18-5 except x+y=2, both showed much higher satellites and splatter in normal use over that of the ink of this invention when printed by that ExceJet printer. Variations within the foregoing description of this invention can be anticipated.

Claims: A liquid ink composition comprising at least one water soluble dye, water dissolving said dye, a volatile base bringing said ink to basic pH, and 0.05 to 0.1% by weight of a surfactant, said surfactant being a tertiary amine having two polyethoxylate substituents, in which the total number of ethoxy groups is 5 to 10, each polyethoxylate substituent has at least two ethoxy groups and the third substituent is a stearyl group. An ink of claim 1 in which the total number of ethoxy groups in the tertiary amine is 5. An ink of claim 1 in which the total number of ethoxy groups in the tertiary amine is 6. An ink as in any preceding claim also comprising tetraethylene glycerol as a co-solvent. An ink as in any preceding claim also comprising glycerol as a humectant. An ink as in any preceding claim also comprising triethanolamine to improve printing at start-up. An ink as in claim 1 which contains about 2.3 percent by weight of said dye, about 5 percent by weight of glycerol, about 1.25 percent by weight of tetraethylene glycol, and about 0.5 percent by weight of buffers, said base is ammonium hydroxide and said pH is about 8.7. An ink as in claim 7 which contains about 0.05% by weight of said tertiary amine.

Inventors: MRVOS JAMES M, PIEKUNKA ANN M, WATKINS RICHARD B, MRVOS, JAMES M., PIEKUNKA, ANN M., WATKINS, RICHARD B.
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1996
Main classification: C09D11
IPC codes: C09D11