Ink compositions comprising salts with polyvalent ions

An ink composition and, in particular, an ink jet ink composition, comprising a liquid vehicle, at least one modified pigment having attached at least one functional group, at least one salt having a polyvalent ion, and at least one polymer is disclosed. Methods of generating an image using this ink composition are also described.

EXAMPLES Examples 1-4 For Examples 1-4, the following general procedure was used. The solutions of styrene-co-maleic acid polymer used in the following examples were prepared by base hydrolysis of an aqueous acetone solution of poly(styrene-co-maleic anhydride). Thus, the styrene-maleic anhydride polymer (commericially available from Monomer/Polymer and DAJAC Labs, Feasterville, Pa.) was added to 1 liter of acetone in a 2 liter flask fitted with a heating mantle and reflux condenser. The mixture was stirred and heated to fully dissolve the polymer. Once dissolved, a solution of sodium hydroxide in 200 mL water was added over one hour. The mixture was stirred for an additional 2 hours at 30° C. at which time the reflux condenser was replaced with a simple distillation head and the acetone was removed by distillation. A total of 600 mL deionized water was added over the course of the distillation so that the solution remained easy to stir. The distillation was continued to remove several grams of water to ensure that all of the acetone had been removed. The resulting solution was characterized by % solids, pH, and thermogravimetric analysis (TGA). Amounts used to prepare the polymer solutions and results are shown in Table 1 below. 1 TABLE 1 % solid SMA NaOH of Polymer composition (g) (g) solution pH of solution 50:50, 1600 MW 70 30 24.5 10.2 75:25, 1900 MW 100 21.4 17.6 10.2 A freshly prepared solution of zinc chloride (1.36% solids) was added in one portion to a 20 mL vial containing Cab-O-Jet® 300 black dispersion (a 15% aqueous dispersion of a pigment black with a BET surface area 200 m 2 /g with attached carboxyphenyl groups commercially available from Cabot Corporation). This mixture was then shaken with ceramic grinding media (¼″) for 2 minutes and then allowed to stand for 2 hours. To this thick dispersion was added a solution of a styrene-co-maleic acid polymer (prepared as described above). This mixture was shaken intermittently for 20 minutes and then allowed to stand overnight. The amounts of components added for each of these examples is shown in Table 2 below. 2 TABLE 2 Cab-O-Jet ® 300 Zinc Polymer Example dispersion chloride solution Number (g) (g) (g) Polymer type 1 6.67 2.43 2.54 g Hydrolyzed 75/25 poly (styrene-co-maleic anhydride) (1900 MW, 17.6% solids) 2 6.67 2.43 0.846 g Hydrolyzed 75/25 poly (styrene-co-maleic anhydride) (1900 MW, 17.6% solids) 3 6.67 2.43 1.53 g Hydrolyzed 50/50 poly (styrene-co-maleic anhydride) (1600 MW, 24.5% solids) 4 6.67 2.43 0.510 g Hydrolyzed 50/50 poly (styrene-co-maleic anhydride) (1600 MW, 24.5% solids) A sample of the resulting dispersion was removed for particle size analysis, and the remaining material was dialyzed using a 300,000 MW cutoff dialysis tubing (cellulose ester tubing available from Spectrum Laboratories, Rancho Dominguez, Calif.) sealed to form a bag. The dialysis was run against 1 liter of deionized water at room temperature for 24 hours. After 24 hours, the water was replaced with fresh water and the dialysis continued. This procedure was repeated for 1 more day (total of 3 days). After removing a sample for particle size analysis, the remainder of the resulting dialyzed dispersion was concentrated to about 5% solids by evaporation in an oven. The performance of these compositions was evaluated based on a 3 mil wet film drawdown on Xerox 4024 DP paper. The results are summarized in Table 3 below. 3 TABLE 3 Particle Size 1 Highlighter Before Dialysis After Dialysis Smear 3 100% 100%< % Dry Ex. &num; mv (&mgr;m) mv (&mgr;m) Solids O.D WF 2 rub 1 h 24 h 1 0.1280 0.3437 0.1331 0.4088 4.6 1.57 <1 good 3 2 min 2 0.1334 0.4088 0.1392 0.4088 4.9 1.68 <1 fair 5 5 min 3 0.1340 0.3437 0.1500 0.4861 4.6 1.72 >1 h fair 5 5 4 0.1308 0.3437 0.1368 0.4088 4.7 1.71 >1 h poor 5 5 1 Particle size was measured using a Leeds Northrup Microtrac Particle Size Analyzer. 2 Waterfastness was evaluated by dripping water across the drawdown at the specified time intervals. 3 Highlighter smear was evaluated on a 6 point scale where 6 is bad smearing and 1 is no smearing. The results show that several polymer types and levels can be used along with a modified pigment having attached functional groups and a polyvalent ion to give ink compositions with acceptable overall performance. It is also expected that a range of different polymers types and levels can be used in the present invention. Examples 5-6 For the following examples, the procedure used for Example 1 was followed, except the order of addition was changed. The polymer type and the amount of polymer, salt, and dispersion were the same as for Example 1, as shown in Table 4 below. 4 TABLE 4 Cab-O-Jet ® 300 Zinc Polymer Example dispersion chloride solution Number (g) (g) (g) Order of Addition 1 6.67 2.43 2.54 Mixed pigment dispersion and zinc chloride solution, then added polymer solution 5 6.67 2.43 2.54 g Mixed polymer and zinc chloride solution, then added pigment dispersion 6 6.67 2.43 2.54 g Mixed polymer solution and pigment dispersion, then added zinc chloride solution These samples were dialyzed in the same manner as in Example 1. The results of particle size analysis and drawdown performance are shown in Table 5. 5 TABLE 5 Particle Size After Dialysis and Concentration Highlighter Ex. 100% % Smear &num; mv (&mgr;m) Solids O.D. WF Dry rub 1 h 24 h 1 0.1331 0.4088 4.6 1.57 <1 min good 3 2 5 0.1350 0.4088 5.0 1.65 <3 min fair 4 4 6 0.1259 0.3437 4.9 1.63 <1 min fair 4 3 The data for Example 1 is taken from Table 3 and repeated here. These examples show that ink compositions with acceptable performance can be prepared by any order of addition of the components. Comparative Example 1 For the following example, the procedure used for Example 1 was followed, except that no zinc chloride was added. The polymer type and the amount of polymer, and dispersion were the same as for Example 1, as shown in Table 6 below. 6 TABLE 6 Cab-O-Jet ® 300 Zinc Polymer dispersion chloride solution Ex. &num; (g) (g) (g) Order of Addition 1 6.67 2.43 2.54 Mixed pigment dispersion and zinc chloride solution, then added polymer solution Comp 6.67 0.0 2.54 Mixed polymer and pigment 1 dispersion with no added zinc chloride solution These samples were dialyzed in the same manner as in Example 1. The results of particle size analysis and drawdown performance are shown in Table 7. 7 TABLE 7 Particle Size After Dialysis and Concentration Highlighter Ex. 100% % Dry Smear &num; mv (&mgr;m) Solids O.D. WF rub 1 h 24 h 1 0.1331 0.4088 4.6 1.57 <1 good 3 2 min Comp 0.1301 0.4088 4.9 1.62 3 min fair 5 4 1 The data for Example 1 is taken from Table 3 and repeated here. These results show that the combination of a modified pigment having an attached organic group, a salt having a polyvalent ion, and a polymer gives an ink composition with overall better performance than one in which no salt is added. In addition, this combination gives rise to far improved stability over a composition in which only a modified pigment and a salt are combined (based on the observations made in Example 1 in which the addition of the salt and a modified pigment gave rise to coagulation). The foregoing description of preferred embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.