Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1997-05-13
2001-07-31
Cole, Elizabeth M. (Department: 1771)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C523S161000, C523S351000, C260SDIG031, C427S218000, C347S100000, C106S031650, C106S412000
Reexamination Certificate
active
06267807
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a novel method for grinding a colorant agglomerate. More particularly, the instant invention is directed to a method for dispersing a pigment agglomerate in a carrier liquid by grinding said pigment agglomerate in the carrier liquid with a mill and a small size grain ceramic medium.
BACKGROUND OF THE INVENTION
Ink jet printing is a conventional technique by which printing is normally accomplished without contact between the printing apparatus and the substrate on which the desired print characters are deposited. Such printing is accomplished by ejecting ink from an ink jet printhead of the printing apparatus via numerous methods which employ, for example, pressurized nozzles, electrostatic fields, piezo-electric elements and/or heaters for vapor phase bubble formation.
The ink compositions used in ink jet printing typically employ, for example, water, colorants and low molecular weight water-miscible solvents. The colorants which may be employed include dyes or pigments. Pigments often are preferred and they are generally characterized as colorants that are not soluble in the desired liquid vehicle of an ink composition. In order to prepare a pigment-based ink, therefore, pigment agglomerates typically are dispersed in a dispersant so that the resulting colorant concentrate can be added to the liquid vehicle to produce an ink.
When preparing the colorant concentrate, pigment agglomerates are typically reduced in size and dispersed in a dispersant. This often is achieved by mixing the pigments with the dispersant, followed by a grinding step. The grinding step may take place in commercially available ink preparation mills like ball and pebble mills. When grinding in these types of mills, conventional grinding media such as glass, stainless steel and zirconium oxide often are employed in order to enhance the grinding process. Unfortunately, however, conventional grinding media enhance the grinding process while simultaneously decreasing the purity of the resulting colorant concentrate, or the subsequent ink composition prepared therefrom. Such a decrease in purity can result in ink discolorations, ink pH alterations and malfunction of printing apparatuses.
It is of increasing interest to prepare colorant concentrates that are substantially pure. This invention, therefore, is directed to a novel method for grinding colorants with, for example, a small grain size grinding medium, to unexpectedly produce a substantially pure colorant concentrate. “Substantially pure”, as used herein, is defined to mean less than 0.04%, and preferably, less than about 0.03%, and most preferably, less than about 0.025% impurities by weight, based on total weight of the colorant concentrate, as determined by Inductively Coupled Plasma-Atomic Emission Spectroscopy. Such impurities originate from the grinding media and/or the mill employed.
DESCRIPTION OF THE PRIOR ART
Efforts have been disclosed for preparing pigment-based ink compositions. In U.S. Pat. No. 5,589,522, assigned to Lexmark International, Inc., aqueous pigment based ink compositions comprising a compositions. In U.S. patent application Ser. No. 08/667,268, now U.S. Pat. No. 5,656,071 assigned to Lexmark International, Inc., pigment-based ink compositions comprising a diol-containing cosolvent are described.
SUMMARY OF THE INVENTION
In a first aspect, the instant invention is directed to a method for making a colorant concentrate comprising the steps of:
(a) combining a colorant and a carrier liquid to produce a premix; and
(b) grinding said premix in a mill comprising a grinding medium having a grain size of less than about 1.35 microns.
In a second aspect, the instant invention is directed to a colorant concentrate made by the novel method described in the first aspect of this invention.
In a third aspect, the instant invention is directed to an ink composition prepared from the colorant concentrates described above.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
“Colorant” is defined herein to mean an insoluble additive capable of generating a color in a liquid and/or on a substrate. Preferred colorants which may be employed in this invention include pigments. There is no limitation with respect to the pigments that may be employed in this invention other than that they are capable of resulting in an ink. Any of the commonly employed organic or inorganic pigments may be used. An illustrative list of the pigments which may be employed in this invention includes azo pigments such as condensed and chelate azo pigments, and polycyclic pigments such as phthalocyanines, anthraquinones, quinacridones, thioindigoids, isoindolinones, and quinophthalones. Still other pigments which may be employed include, for example, nitro pigments, daylight fluorescent pigments, carbonates, chromates, titanium oxides, zinc oxides, iron oxides and carbon black. Preferred pigments employed in this invention include carbon black and pigments capable of generating a cyan, magenta and yellow ink. The pigments employable in this invention may be prepared via conventional techniques, are typically commercially available, and often listed as, for example, a specific yellow, orange, red, blue, green, violet or black on the Colour Index.
It should be further noted herein that the colorants employed in this invention may be referred to as colorant agglomerates or agglomerates, whereby agglomerate is meant to mean a combination or cluster of colorant particles. The colorant agglomerates, prior to grinding, typically have an approximate diameter of about 700 nm to about 1,100 nm. “Carrier liquid”, as defined herein, is meant to mean any liquid, including mixtures, capable of suspending the colorant. The carrier liquid may be aqueous or non-aqueous. When an aqueous carrier is preferred, it is often selected from the group consisting of water, distilled water and deionized water. The aqueous carrier may also include mixtures having at least two members selected from the group consisting of water, distilled water, deionized water and a miscible organic solvent. An illustrative list of the miscible organic solvents which may be employed include glycols (like ethylene glycol), alcohols (like 1-propanol), glycol-ethers (like polyethylene glycol), diols (like propane diol), or mixtures prepared therefrom. The preferred aqueous carrier is deionized water.
There is essentially no limitation with respect to the non-aqueous carrier liquids which may be employed in this invention other than that they are capable of suspending the colorant. An illustrative list of the non-aqueous carrier liquids that may be employed in this invention include oils such as mineral oil, tung oil, and soybean oil as well as organic solvents such as polyethylene glycol, glycerol and 2-pyrrolidinone.
When the colorant and the carrier liquid are combined (e.g., in a beaker or a conventional mixing vessel), the resulting mixture is referred to as a premix. Formation of the premix may be enhanced by, for example, stirring, mixing, shaking or agitating (via any art-recognized technique) the colorant and carrier liquid to ensure that the colorant is wetted and suspended therein.
When the carrier liquid is a mixture, it typically has from about 5.0% to about 95.0%, and preferably, from about 10.0% to about 80.0%, and most preferably, from about 20.0% to about 70.0% by weight miscible organic solvent, based on total weight of the carrier liquid, including all ranges subsumed therein.
The premix typically comprises no more than about 35.0%, and preferably, no more than about 20.0%, and most preferably, no more than about 10.0% by weight of colorant agglomerate (e.g., pigment) based on total weight of the premix.
Subsequent to premix preparation, the premix is added to a mill such as one conventionally used for making ink compositions. An illustrative list of the mills which may be employed include, for example, ball mills, pebble mills, fine media mills, bead mills, as well as shot mills. Such mills are commercially available and described in texts such as
Paint
Harshbarger Kenneth James
Suthar Ajay Kanubhai
Watkins Richard Barber
Wickline Austin Keith
Brady John A.
Cole Elizabeth M.
Guarriello John J.
Lexmark International Inc.
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