GB2231056A - Ink compositions for ink jet printers - Google Patents

Abstract

ink compositions have been formulated that have low wetting properties and other characteristics that lend themselves for use in an ink jet printer with stainless steel orifice plates. The ink composition includes polar organic solvents and a dye or combination of dyes matched for optimum properties. The polar organic solvent has a dipole moment of 2.3 to 5.0 debyes, a surface tension of 38 to 50 dynes/cm and Hildebrand solubility parameter of delta >10. Exemplified solvents are diethylene glycol, dimethylsulphoxide, N-methyl pyrrolidone, 1.2 propylene glycol, 1.3 propylene glycol, ethylene carbonate, propylene carbonate and 2-pyrrolidone.

Description

INK QOMPOSITIONS FOR INK JET PRINTERS Ink jet systems, particularly impulse ink jet systems, are well known in the art. The principle behind an impulse ink jet is the displacement of ink and the subsequent emission of ink droplets from an ink chamber through a nozzle by means of a driver mechanism which consists of a transducer, usually a piezoceramic material, bonded to a thin diaphragm. when voltage is applied to the transducer, the transducer attempts to change its planar dimensions, but because it is securely and rigidly attached to the diaphragm, bending occurs. This bending displaces ink in the chamber, causing outward flow, both through an inlet from the ink supply, or restrictor, and through an outlet or nozzle of the ink jet printhead. One of the popular materials used for the orifice plate of the printhead is stainless steel.Unfortunately, the use of stainless steel for this purpose presents certain wetting problems because of its high surface energy. This wetting problem, with most inks, prevents a stable performance of the inks in the ink jet especially at high frequencies. As a result of this wetting problem, inks must be specially formulated in order to meet the high requirements of jet performance, which presently commercially available inks will not satisfy. It obviously would be desirable to have ink compositions that lend themselves well to the use in ink jet printers having stainless steel orifice plates.

Ink compositions have been formulated that have properties suitable for ink jet printing and can be used in ink jet printers having stainless steel orifice plates.

These ink compositions are generally non-wetting, have a long shelf life, have stable viscosity and their surface tension is high enough to form stable droplets. In addition, they are non-toxic and non-volatile. They have viscosity coefficients in the range of 12 to 16 cps at 250C and surface tension values of 38-50 dynes/cm at 25doc.

The solvents of these ink formulations are polar organic with Hildebrand solubility parameters of 6 > 10 H units and medium to strong hydrogen bonding properties.

These solvents have a dipole moment in the range of 2.3 to 5 debyes.

The dyes of the ink formulation contain ionic groups covalently bound to the hydrophobic backbone of the dye.

The ionic groups can be of the sulfonate type (So3 ) or quaternary ammonium type (NR4+). Additionally, a combination of dyes can be used where one component has a high surface activity because of its chemical structure and a second dye component with smaller molecules and higher polarity that compensates for the deficiencies of the first dye.

Description Of The Preferred Embodiments Ink jet printers having orifice plates made of stainless steel experience wetting problems with prior commercially available inks because of the high surface energy of stainless steel. These stainless steel surfaces are easily wet by a large range of solvents and wetting of the orifice plate is not conducive to stable printhead performance and is therefore a serious problem. Inks for ink jet printing should be non-toxic and have good storage properties. Additionally, surface tension, polarity and rheological properties of the ink are all important in print head performance.

Inks have been formulated based upon selecting the ink components that tend to resolve the wetting problem associated with use with stainless steel. As with other ink jet inks, the ink compositions of the instant invention include at least one solvent, dyes and additives. The solvents of the ink formulations are polar organic with Hildebrand solubility parameters of 6 > 10 H units. These solvents have a dipole moment in the range of 2.3 to 5 debyes. Table I shows solvents exhibiting such properties.

TABLE I Solvent Hildebrand Solubility Surface Tension Dipole Parameter (dynes/cm) Moment (Hildebrand Units) (debyes) diethylene glycol 12.02 48.50 2.31 dimethyl sulfoxide 12.02 43.50 3.96 N methyl pyrrolidone 11.30 38.90 4.09 1,2 propylene glycol 14.76 36.00 2.25 1,3 propylene glycol 10.70 47.40 2.50 ethylene carbonate 14.70 48.30 4.87 propylene carbonate 13.30 40.70 4.98 2 pyrrolidone 14.70 37.60 3.55 The dyes of the ink formulations are selected on the basis of their chemical structure and compatibility with the solvents. The general types are 1) direct or acid dyes which contain ionic groups covalently bound to the hydrophobic backbone of the dye with at least 3 sulfonic groups (SO3 ) or basic dyes that have quaternary ammonium groups such as NR . The dye could be of the azo type, but should not contain a bulky hydrophobic aromatic backbone.

The ratio of the ionic groups to the aromatic backbone should be high. Such dyes do not have a tendency of aggregation, and therefore do not have a strong tendency for phase separation in solution. Examples of dyes that can be used in this formulation are color index C.I. direct dye #163, C.I. direct dye 8168 or acid dye, C. I. food black n2.

The inks formulated with these dyes include low concentrations of an additive to improve the non-wetting characteristics, increase the surface tension and further assist prevention of aggregation.

There is a class of direct dyes which is not suitable for making jet ink formulations. Examples of this class are: C.I. direct dye #19, #22 or #171. These dyes have bulky hydrophobic aromatic backbones and a low ratio of ionic groups and show greater tendency for aggregation which adversely affects the surface tension and viscosity of inks.

This is detrimental to ink jet performance. But these dyes can be used in combination with compensating dyes. The second dye compensates effectively for the deficiency of the first above mentioned direct dyes. The second dye could be a reactive metal complex dye. This second dye has a smaller molecule and forms intermolecular bonds with the direct dye, thus preventing aggregation. The interaction also improves light fastness and water fastness of prints, and reduces feathering. The concept of mixing dyes to improve print quality of aqueous inks is not unknown but exploiting specific chemical structures and intermolecular forces to modify bulk properties is innovative, especially with non-aqueous solvents.

In another embodiment there are three dye components.

Two of them are basic dyes with quaternary groups of the type (NR4+) and the third is a solvent dye such as C.I solvent red #49. Once again, the solvent dye has a relatively small molecule and it has no polar groups. The compatibility of this non-polar group dye with the other two dyes yields a neutral black. This third dye also effectively prevents aggregation of the other two dyes iri the final formulation. The combination of dyes mentioned here also produces larger spot sizes than the direct dye formulations. Thus, a tool is given to the formulator to control spot size as needed. The inks further show less feathering, thus enhancing the quality of the print.

Generally, aqueous inks need biocides, but biocides are corrosive and hence unsuitable for stainless steel print heads. The non-aqueous inks of the instant invention do not require such biocides.

Examples of ink formulations having a polar organic solvent and a direct dye with suitable properties are as follows: Example I Components/Description Source Weight-percent Cartablack 2 GT direct dye Sandoz Chemicals Charlotte, N.C. 28205 10.0 Diethylene glycol (DEG) Aldrich Chemical Co.

Milwaukee, WS 33.0 Dimethyl Sulfoxide (DMSO) Aldrich Chemical Co. 56.9 (Approx.) Lithium Hydroxide (LiOH) Manufacturing Chemists < 0.1 Inc. (MCB) Dermstadt, Germany Properties at 25"C The above ink exhibited the following properties: viscosity coefficient, centipoise (cps) 13.90 kinematic viscosity, centistokes (cs) 12.20 Apparent pH 9.04 Surface tension (dynes/cm) 41.50 Density (gm/cm3) 1.14 Example II Components/Description Source Weight percent Special black 7984 WDP acid dye Mobay Corp. 9.7 Pittsburgh, PA 15205 DEG Aldrich Chemical 36.2 DMSO Aldrich Chemical 54.1 Properties at 250C viscosity coefficient (cps) 14.20 kinematic viscosity (cs) 12.40 Apparent pH 8.70 Surface tension (dynes/cm) 44.70 Density (gm/cm3) 1.14 Example III Components/Description Source Weight percent C.I. direct black 168 direct dye ICI Americas, Inc.

Wilmington, DL 19897 8.5 DEG Aldrich Chemical 56.8 (Approx.) DMSO Aldrich Chemical 34.6 LiOH Manufacturing Chemists, Inc. (MCB) Darmstadt, Germany < 0.1 Properties at 250C viscosity coefficient (cps) 13.90 kinematic viscosity (cs) 12.20 Apparent pH 9.80 Surface tension (dynes/cm) 42.70 3 Density (gm/cm3) 1.14 Examples of ink compositions with a direct dye and a compensatory dye are as follows: Example IV Components/Description Source Weight percent Duasyne HSF direct dye Hoechst Celanese Corp.

Coventry, R.I.

02816 3.64 Duasyn RL reactive dye Hoechst Celanese Corp. 1.22 DEG Aldrich Chemical 51.74 DMSO Aldrich Chemical 42.40 Triethanol Amine Fisher Scientific Pittsburg, PA.

15205 < 1.00 Properties at 250C viscosity coefficient (cps) 13.80 kinematic viscosity (cs) 12.20 Apparent pH 8.15 Surface tension (dynes/cm) 47.80 Density (gmjcm3) 1.12 Example V Components/Description Source Weight percent C.I. direct dye 168 ICI 6.0 (Approx.) Neptune Red 543 solvent dye BASF 0.4 (Approx.) 1,3 Propylene Glycol Fluka 35.5 (Approx.) N-methyl pyrrolidone Aldrich 58.0 LiOH MCB < 0.1 Properties at 250C viscosity coefficient (cps) 13.20 kinematic viscosity (cs) 12.40 Apparent pH 8.80 Surface Tension (dynes/cm) 41.40 3 Density (gm/cm3) 1.06 An example of a 3 dye component ink formulation is as follows: Example VI Components/Description Source Weight percent Flexo yellow N B 117 (C.I. basic yellow #65) BASF Corp.

Holland, MI 49423 6.0 Flexo blue 630 Basic dye BASF Corp. 2.50 Neptune Red 543 (C.I. solvent red #49) BASF Corp. 1.50 DEG Aldrich Chemical 52.00 DMSO Aldrich Chemical 38.00 Properties at 250C viscosity coefficient (cps) 12.80 kinematic viscosity (cs) 11.30 Apparent pH 7.33 Surfact Tension (dynes/cm) 45.10 3 Density (gm/cm3)

Claims (2)

1. An ink composition suitable for use with an ink jet printer having a stainless steel print head, comprising: a polar organic solvent having a dipole moment of

2.3 to 5.0 debyes, a surface tension of 38 to 50 dynes/cm and a Hildebrand solubility parameter of 6 > 10 and at least one dye containing ionic groups covalently bound to the hydrophobic backbone of the dye.

2. The ink composition of claim 1 including at least one of lithium hydroxide and sodium acetate.

3. The ink composition of claim 1 wherein said dye is one of an acid dye having at least three sulfonic groups, a basic dye having quatenary ammonium groups and an azo dye.

4. An ink composition suitable for ink jet printing comprising: a polar organic solvent with a dipole moment of

2.3 to 5.0 debyes, a surface tension of 38 to 50 dynes/cm and a Hildebrand solubility parameter of 8 > 10 H units and medium to strong hydrogen bond capability, two basic dyes, and a third dye which is a solvent dye with a free base.

2.3 to 5.0 debyes, a surface tension of 38 to 50 dynes/cm and a Hildebrand solubility parameter of 6 > 10, a basic dye having bulky aromatic backbone and a low ratio of ionic groups and a second dye having a higher polarity and smaller molecules than said first dye.

5. The ink composition of claim 4 wherein said ink composition includes an additive selected from lithium hydroxide and sodium acetate.

6. An ink composition suitable for ink jet printing comprising: a polar organic solvent with a dipole moment of