Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-10-30
2002-10-22
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S031600, C106S499000, C106S505000
Reexamination Certificate
active
06468340
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink composition used in inkjet printing, and, more specifically, to enabling solubilization of laked dye pigments in water by a chelating process.
BACKGROUND OF INVENTION
The use of ink-jet printing systems has grown dramatically in recent years. This growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost. Today's ink-jet printers offer acceptable print quality for many commercial, business, and household applications at costs fully an order of magnitude lower than comparable products available just a few years ago. Notwithstanding their recent success, intensive research and development efforts continue toward improving ink-jet print quality, while further lowering cost to the consumer.
An ink-jet image is formed when a precise pattern of dots is ejected from a drop-generating device known as a “printhead” onto a printing medium.
Inks normally used in ink-jet recording are commonly composed of water-soluble organic solvents (humectants, etc.), surfactants, and colorants in a predominantly aqueous fluid. When printed on “plain paper”, the colorants retain some mobility, which can be manifest in poor bleed, edge acuity, feathering, and inferior optical density/chroma (due to penetration of the paper). These features adversely impact text and image quality.
The evaporation rate of water-based inks is slow and smearing of the printed image can occur. The use of pigments can improve ink jet printing attributes such as drytime, waterfastness, smearfastness, chroma and optical density. However, pigments by themselves are not soluble in aqueous thermal ink jet (TIJ) vehicles. A dispersant is conventionally used to render the pigment water-soluble. This conventional stabilization of the dispersion has disadvantages because unless properly designed the dispersion is unstable to time and temperature fluctuations.
U.S. Pat. No. 4,597,794 discloses stabilizing the pigments in the printing inks with polymeric dispersants constructed of ionically hydrophilic and aromatically hydrophobic segments.
EP-A 518 225 and EP-A556 649 describe acrylic block copolymers of the type AB, BAB and ABC for use as dispersants for pigments in printing inks.
U.S. Pat. Nos. 5,750,592 and 5,913,971 both disclose dispersing a pigment for a water-based inkjet ink with a water-soluble resin,
Similarly, U.S. Pat. No. 5,969,002 discloses an inkjet ink in which a pigment is dispersed in a water-based inkjet ink with a water-soluble polyisocyanate addition product.
As a further example, U.S. Pat. No. 5,958,999 discloses an ink for use in inkjet printing in which a pigment is combined with a polyvinylimidazole, a polyvinylpyridine or a polyethyleneimine to form aqueous dispersions.
All of the above means to achieve the dispersion of pigment in water for inkjet ink printing tend to be expensive. Furthermore, they introduce other complications into the inkjet ink.
For example, pigments as conventionally used in paints have excellent water resistance and lightfastness. However, when pigments, in an aqueous vehicle together with the dispersing agent, are inkjetted onto a medium, the water resistance and colorfastness of the pigment is noticeably decreased. Thus, in making a pigment dispersible for use in inkjet printing ink, the pigment's most positive qualities are diminished.
A way is needed to achieve inkjettability of pigments by solubilizing the pigment in the aqueous inkjet ink vehicle. It would be particularly advantageous if this could be achieved without resorting to organic dispersing agents which significantly diminish the waterfastness and lightfastness of the pigment on the media, which in turn decreases the overall print quality and chroma.
SUMMARY OF THE INVENTION
The present invention relates to a method of increasing solubility of a laked dye pigment in an aqueous vehicle, comprising the steps of:
a) adding a sufficient amount of chelating agent to the aqueous vehicle to chelate and remove precipitating cations bound to surface anionic solubilizing groups from the laked dye pigment; and
b) removing chelating agent from the aqueous vehicle.
The present invention also relates to a laked dye pigment at least partially soluble in a aqueous vehicle produced by the method comprising the steps of:
a) adding a sufficient amount of chelating agent to the aqueous vehicle to chelate and remove precipitating cations bound to surface anionic solubilizing groups from the laked dye pigment; and
b) removing chelating agent from the aqueous vehicle.
The present invention additionally relates to an ink-jet printing apparatus, comprising:
at least one printhead portion including an ink composition comprising
at least one pigment particle complex;
at least one chelating agent; and
an aqueous solvent;
wherein the at least one pigment particle complex is made by the method comprising the steps of:
a) adding a sufficient amount of chelating agent to the aqueous vehicle to chelate and remove precipitating cations bound to surface anionic solubilizing groups from the laked dye pigment; and
b) removing chelating agent from the aqueous vehicle.
The present invention also relates to a water soluble laked dye pigment having a zeta potential in the range from 5 to 5000 mVolts.
The present invention also relates to a water soluble laked dye pigment having a particle size in the range from 0.005 to 12 microns.
DETAILED DESCRIPTION OF THE INVENTION
The present invention described herein is directed to ink-jet inks for printing ink-jet images using commercially available ink-jet printers such as, for example but not limited to, HP DeskJet® printers, manufactured by Hewlett-Packard Company, of Palo Alto, Calif. The inks enable production of near photographic images having little or no coalescence, excellent waterfastness, and reduced dry time, on a range of print media, in particular, for example but not limited to, plain white, 8½″×11″, 20 lb. weight, printer paper conventionally used for office and home computers.
In particular, the present invention relates to laked dye pigments such as calcium, magnesium, aluminium lakes of sulpho-and/or carboxyl-containing dyes. As with other pigments such as organic pigments (azo, disazo, polyazo, anthraquinone, thioindigo series; phthalocyanine, quinacridone, dioxazine, isoindolinone, naphthalenetetracarboxylic acid and perylene and perylenetetracarboxylic acid series; perinone, indigoid, thioindigoid, diketopyrrolopyrrole series; and metal complex pigments of azo azomethine or methine dyes), laked dyes are not readily dispersible in aqueous solvent. Organic solvent dispersants are needed to use these pigments in inkjet printing inks.
As discussed above in the background section, the use of organic dispersants with pigments, including the laked dye pigments, has the effect of decreasing water resistance and lightfastness in media images inkjet-printed with pigment-containing inks.
The present inventors have discovered how to make the laked dye pigments soluble in the aqueous vehicle used in inkjet ink. This alleviates the necessity of using organic dispersants in the inks. Thus, water resistance and lightfastness are improved on media images inkjet printed with such laked dye pigment-containing inks.
In summary, the present invention relates to a method of increasing solubility of a laked dye pigment in an aqueous vehicle, comprising the steps of:
a) adding a sufficient amount of chelating agent to the aqueous vehicle to chelate and remove precipitating cations bound to surface anionic solubilizing groups from the laked dye pigment; and
b) removing chelating agent from the aqueous vehicle.
In the method of making the above-described water-soluble laked dye pigment, the chelating agent may be removed from the aqueous vehicle using semi-permeable membranes by a method such as microfiltration (which may be ultrafiltration), reverse osmosis and dialysis. Membrane processes for purification of pigments (specifically, macromolec
Moffatt John R
Tsang Joseph W
Green Anthony J.
Hewlett--Packard Company
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