Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2001-08-06
2003-07-01
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031860, C106S031750, C106S031900
Reexamination Certificate
active
06585818
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to improved ink formulations and methods for making ink formulations for ink jet printers.
BACKGROUND OF THE INVENTION
Ink jet printing methods use printheads having orifices which eject ink droplets onto a print medium. For higher quality, higher resolution printing applications, the orifices of the printheads have been increased in number and their diameter significantly reduced in size. As the size of the nozzles decrease improved print quality is obtained by use of different ink formulations. Some ink formulations contain only dyes while other formulations contain only pigments or mixtures of pigments and dyes. Pigments have become increasingly useful in ink formulations, particularly black ink formulations to improve the image quality including optical density of the printed image. However, while pigmented ink formulations have some advantages over dye-based ink formulations, pigment-based formulations are often less stable over time than dye-based formulations resulting in operating problems, particularly with higher quality, higher speed ink jet printers which demand significantly better print performance. Accordingly, improved pigment ink formulations and methods for making the formulations are needed to meet the demands of ever improving ink jet printer technology.
SUMMARY OF THE INVENTION
With regard to the above and other objects and advantages thereof, the invention provides ink jet printer ink formulation and method for making the ink formulation. The formulation includes from about 50 to about 85 percent by weight water, humectant, an organic solvent and a chemically modified carbon black pigment, wherein the chemically modified carbon black pigment contains steric inducing groups on a surface of the carbon black which groups are derived from a steric inducing compound, the compound being substantially soluble in the humectant and the compound being reactive with an organic acid halide. The ink jet printer ink formulation containing the chemically modified carbon black has an idle time of greater than about 15 seconds in an ink jet printhead.
In another aspect the invention provides a method for making an ink formulation for an ink jet printer. The method includes mixing from about 1 to about 10 percent by weight of a chemically modified carbon black pigment containing steric inducing groups on a surface of the carbon black with from about 50 to about 85 percent by weight water, humectant and an organic solvent to provide an ink formulation having improved idle time. The steric inducing groups on the carbon black surface are derived from a steric inducing compound, the compound being substantially soluble in the humectant and the compound being reactive with an organic acid halide. The chemically modified carbon black pigment used in the ink formulation has an acid number ranging from about 0.1 to about 0.7.
An important advantage of the invention is the significant increase in idle time exhibited by ink formulations made according to the invention. Without desiring to be bound by theoretical considerations, it is believed that as water evaporates from the ink adjacent the nozzles of a printhead, the properties of the ink composition in the printhead change. Ink formulations used in ink jet printers are a mixture of water, self-dispersing pigment and organic components such as humectants, binders, penetrants, organic solvent and the like. As water evaporates from the ink, the percentage of organic components in the ink formulation increases so that the ink becomes less hydrophilic. As the ink becomes less hydrophilic, the self-dispersing pigment which is strongly hydrophilic is pulled back into the bulk aqueous phase. Idle time is used to measure the short term reliability of the ink. “Idle time” means the time between nozzle firings just before the printhead produces delayed or misdirected ink droplets. Historically, self-dispersing carbon blacks exhibit poor idle times in ink jet printers. The invention greatly improves the idle time of the ink formulation by modifying the surface of the pigment particles so that the particles remain substantially dispersed in the organic components as well as the aqueous components of the ink formulation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Ink compositions of the invention are generally referred to as “aqueous ink formulations” because a major component of the ink formulation is water, preferably dionized water. Water is preferably present in the ink formulation in an amount ranging from about 50 to about 85 percent by weight based on the total weight of the ink formulation. All of the other components in the ink formulation are present in an amount of less than about 50 percent by weight, hence the majority of the ink formulation is water. The ink formulation, however, preferably contains organic components which are soluble or dispersible in water. These organic components include binders, humectants, penetrants, and other components which enhance the print quality and durability of images printed with the ink formulation.
An important component of the ink formulation is a chemically modified carbon black pigment. The carbon black pigment modified according to the invention is preferably a self-dispersing carbon black pigment. Methods for making self-dispersing 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 carbon black is preferably in a range of 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 self-dispersing carbon black and the disclosure of the '632 patent is incorporated by reference as if fully set forth herein. A particularly preferred carbon black for making a self-dispersing carbon black is a neutral carbon black available from Cabot Corporation of Billerica, Mass. under the trade name MONARCH 880.
As a result of the reaction between carbon black and sodium hypochlorite, the surface of the carbon black contains carboxyl, hydroxyl and/or carbonyl groups. The carboxyl groups on the surface of the carbon black provide sites for reaction with steric inducing compounds to provide a chemically modified carbon black pigment which exhibits improved idle time in ink formulations containing the carbon black. A process for reacting a self-dispersing carbon black with a compound selected to provide steric inducing groups on the surface of the carbon black is described in more detail below.
Steric inducing groups are attached to the surface of an oxidized carbon black by first reacting a self-dispersing carbon black with an amount of thionyl halide such as thionyl chloride to provide organic acid halide groups on the surface of the carbon black. The acid halide groups are then reacted with a compound which is soluble in the humectant described below and which is reactive with the organic acid halide group on the surface of the carbon black. The compound preferably contains only one terminal group reactive with the acid halide. Such reactive terminal groups include hydroxyl groups, amino groups, thiol groups, and the like.
A preferred class of steric inducing compounds containing one reactive terminal group include monoalkoxy-terminated polyalkylene glycol compounds having an alkylene group containing from 2 to 6 carbon atoms and an alkyl group containing from 1 to 6 carbon atoms. Representative monoalkoxy-terminated polyalkylene glycol compounds include, but are not limited to triethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethyleneglycol monoethyl ether, diethylene glycol monoethyl ether, triethylene glycol monopropyl ether, diethylene glycol monopropyl ether, triethylene glycol monobutyl ether, diethylene glycol monobutyl ether and the like and mixtures thereof. Other mono-terminated glycol reactants may be used to modify self-dispersible carbon black by lowering the acid number of the carbon black without adversely af
Sun Jing X.
Thakkar Sharad Ramanlal
Bell Mark L.
Daspit Jacqueline M.
Faison Veronica F.
LaRose David
Lexmark International Inc.
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