Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-04-11
2003-10-28
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031580, C106S031860, C106S031490, C106S031780, C106S472000
Reexamination Certificate
active
06638350
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to improved ink compositions containing dyes and pigments and to methods for making improved ink formulations, particularly for ink jet printers.
BACKGROUND OF THE INVENTION
Ink jet recording is an advantageous print method used in many commercial products. Beneficial characteristics include small size, high speed, low cost, and adaptability to various substrates. A common problem with ink jet recording systems involves the formulation of an ink composition that has desirable print characteristics. Ink compositions for ink jet printer applications may be based on dyes or pigment colorants. Dyes are often used in ink compositions because of their stability over time, vibrant color, and excellent dry times. But images printed with dyes are prone to fading and poor water fastness which adversely effect print quality. Ink compositions based on pigment type colorants have improved light fastness and water fastness. However, many pigments are not readily soluble in aqueous solutions and often require the presence of polymeric dispersing agents to improve their dispersibility. Unfortunately, the polymeric dispersing agent tends to increase the viscosity and dry time of the ink and decreases the wettability of the ink with respect to the print media.
As print speed increases for ink jet printers there is a need for improved ink formulations which have acceptable dry times and can produce print with high optical density without decreasing the stability of the ink or idling maintenance time.
SUMMARY OF THE INVENTION
The present invention relates to an ink jet ink composition including an ink vehicle, from about 0.1 to about 10% by weight self-dispersed ink pigment and from about 0.1 to about 10% by weight ink dye. The ink composition also includes a humectant selected from the group consisting of dipropylene glycol, tripropylene glycol, triethylene glycol, tetraethylene glycol, 1,(2,-hydroxyethyl)-2-pyrrolidone, trimethyolpropane, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, 2-pyrrolidone, polyethylene glycol, diethylene glycol, 2,2-thiodiethanol, and mixtures thereof; and a penetrant selected from the group consisting of 1,2-hexandiol, hexyl carbitol, diethylene glycol butyl ether, diethylene glycol benzyl ether, n-propyl alcohol, secondary alcohol ethoxylates, ethoxylated acetylenic diols, polyalkyleneoxide modified heptamethyltrisiloxane, and mixtures thereof. The weight ratio of pigment to dye in the ink composition preferably ranges from greater than about 0.75:1 to less than about 2.5:1.
In another aspect the invention provides a method for improving the printing characteristics of an ink jet ink composition. The method includes preparing an ink formulation containing from about 0.1 to about 10% by weight self-dispersed ink pigment, from about 0.1 to about 10% by weight dye, and water. A humectant, a penetrant, and optionally a biocide are mixed with the ink formulation to provide an ink composition. In the composition, the weight ratio of ink pigment to dye ranges from greater than about 0.75:1 to less than about 2.5:1.
An advantage of the invention is that the ink composition exhibits substantially improved permanence and higher optical density than ink compositions containing only dye or only pigment. The ink composition of the invention also dries faster than a conventional ink containing only pigment as the colorant thereby enabling use of the ink on a wider variety of print media than can be used with a conventional ink made only with dye or pigment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Ink compositions according to the invention include an ink vehicle, preferably water. However, the invention is not limited to use of water as an ink vehicle and thus may be applicable to ink compositions made with organic-based ink vehicles.
An important component of the ink composition is a self-dispersed ink pigment, such as self-dispersed carbon black. Self-dispersed carbon blacks include oxidized carbon blacks, surface modified carbon blacks, and a combination of oxidized and surface modified carbon blacks. Methods for making oxidized carbon black are well known and include reacting carbon black with sodium hypochlorite in an aqueous medium. The proportion by weight of sodium hypochlorite to provide an oxidized carbon black is preferably in a range from about 0.4 to about 5.25 parts hypochlorite per part carbon black by weight. U.S. Pat. No. 3,347,632 to Parker describes a preferred method for making oxidized carbon black and the disclosure is incorporated by reference as if fully set forth herein. A particularly preferred carbon black for making oxidized carbon black is a neutral carbon black available from Cabot Corporation of Billerica, Mass. under the trade name MONARCH 880.
Other self-dispersed pigment concentrates useful for the ink formulations of the invention are available from Cabot Corporation of Boston Mass. under the trade names CAB-O-JET 250 (cyan), CAB-O-JET 260 (magenta), CAB-O-JET 270 (yellow), CAB-O-JET 200 (black), and CAB-O-JET 300 (black), and from Orient Chemicals Industries, Ltd. Of Osaka, Japan under the trade names BONJET BLACK CW-1 and BONJET BLACK CW-2. The foregoing pigments are believed to have surface modification which enables the pigments to readily disperse in an aqueous medium without a dispersant.
The self-dispersed ink pigments may be further improved to increase the idle time of the ink formulation by further modifying the surface of the ink pigment. In the case of oxidized carbon black as the self-dispersed pigment, the surface of the oxidized carbon black is preferably further modified by adding steric inducing groups to the surface of the carbon black. Carbon black pigment oxidized with sodium hypochlorite contains carboxyl, hydroxyl, and/or carbonyl groups on its surface. The carboxyl groups on the surface of the carbon black provide sites for reaction with steric inducing compounds. Oxidized carbon black for reaction with such steric inducing compounds preferably has an acid number ranging from about 0.01 to about 1.5 milliequivalents COOH/gram of carbon black, more preferably from about 0.1 to about 0.7 millequivalents COOH/gram of carbon black.
In one step of the reaction, oxidized carbon black is reacted with an amount of thionyl halide to provide organic acid halide groups on the surface of the carbon black. The halide groups of the thionyl halide may be a chloride, bromide, iodide, or fluoride group. Of the thionyl halides, thionyl chloride is a preferred thionyl halide which provides organic acid chloride groups on the surface of the carbon black. The amount of thionyl halide reacted with the carbon black preferably ranges from about 1 to about 20 mole equivalents per COOH group on the carbon black with approximately 10 mole equivalents per COOH group on the carbon black being most preferred. It is preferred to react all of the acid groups on the carbon black with thionyl halide, hence the use of excess thionyl halide is preferred which may also act as a solvent for the reaction.
The reaction between the oxidized carbon black and the thionyl halide is preferably carried out in the presence of a solvent. The preferred solvent is an inert organic solvent. The particularly preferred solvents include, but are not limited to, methylene chloride, tetrahydrofuran, xylene, chloroform, 1,4-dioxane, toluene and other aprotic solvents.
While the order of reactant addition is not limited, the preferred order includes the addition of the thionyl halide to the solvent. Subsequently, this solution is added to a reaction vessel containing the oxidized carbon black.
The reaction is preferably conducted under an atmosphere of inert gas. A particularly preferred inert gas atmosphere for conducting the reaction is a nitrogen gas atmosphere. During the reaction, the temperature of the reaction mass is preferably controlled at a range from about 30° C. to about 55° C. Depending upon the solvent used, reflux may occur. Reaction times may range from about 4 to about 8 hours during which the reaction
Butler Susan Hardin
Sun Jing X.
Bell Mark L.
Faison Veronica F.
Lexmark International Inc.
Luedeka Neely & Graham P.C.
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