Lexmark Issued Patent for Aqueous Pigmented Yellow Ink

[Anonymous]

Lexmark Issued Patent for Aqueous Pigmented Yellow Ink

Patent Issued for Aqueous Pigmented Yellow Inkjet Ink Composition
Lexmark International, Inc.NewsRx.com

By a News Reporter-Staff News Editor at Journal of Engineering — According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Zimmer, Agnes (Lexington, KY); Bogale, Rahel (Lexington, KY), filed on September 30, 2011, was published online on April 30, 2013.

The assignee for this patent, patent number 8431631, is Lexmark International, Inc. (Lexington, KY).

Reporters obtained the following quote from the background information supplied by the inventors: "Field of Disclosure

"Ink jet printing is accomplished by ejecting ink from a nozzle toward paper or another print medium. The ink may be driven toward the medium in a variety of ways. For example, in electrostatic printing, the ink is driven from a nozzle toward a medium by an electrostatic field. Another ink jet printing procedure, known as squeeze tube, employs a piezoelectric element in the ink nozzle. Electrically-caused distortions of the piezoelectric element pump the ink through the nozzle and toward the print medium. In still another ink jet printing procedure, known as thermal or bubble ink jet printing, the ink is driven from the nozzle toward the print medium by the formation of an expanding vapor phase bubble in the nozzle. These various printing methods are described in ‘Output Hard Copy Devices,’ edited by Durbeck and Sherr, Academic Press, 1988 (see particularly chapter 13, entitled ‘Ink Jet Printing’).

"Ink jet printers are well known. One common type of ink jet printer uses a replaceable print cartridge having a printhead and a supply of ink contained within the cartridge. The printhead is installed in a printhead carrier, which positions the printhead along a printing zone. When the supply of ink contained within the print cartridge is depleted, the print cartridge is disposed of and a new print cartridge is installed in the printhead carrier. In contrast, off-carrier inkjet printers deliver ink through supply tubes connected from a refillable off-carrier ink supply tank to an ink jet printhead positioned on the printhead carrier. This inkjet printhead is not disposable but permanent or semi-permanent in nature. Naturally consumers expect that these permanent or semi-permanent printheads have a longer life compared to a disposable printhead. When the supply of ink is exhausted, the consumer will purchase a new tank filled with ink as opposed to purchasing a brand new printhead containing the same supply of ink. Purchasing a tank of ink is a more economical option for the consumer. Therefore it is imperative that a permanent or semi-permanent printhead does not fail in their operations prematurely because consumers expect that permanent and semi-permanent printheads will have a longer life compared to a disposable printhead.

"Ink being jetted over the life of permanent or semi-permanent printheads can cause many problems which affect the overall performance of the printhead. One of the most common problems is kogation. During the millions of firing of drops of ink from the printhead, the layer of ink covering the surface of the heating element of the printhead can reach a very high temperature, usually over 300.degree. C. At this high temperature, ink decomposes, thereby depositing a residue onto the surface of the heater. This phenomenon is called kogation. The presence of this residue negatively affects the volume, mass, shape and velocity of each ejected drop of ink jetted from the printhead, thereby reducing the quality and the expected life of a thermal inkjet printhead. A loss of drop mass over the life of the printhead negatively reduces the accuracy of drop placement onto the print media. In extreme cases, kogation causes the printhead to stop working altogether. Therefore, it is necessary to have an ink that does not cause the undesirable kogation in a printhead.

"Another undesirable problem is paper curl. The use of water in high concentrations in inkjet ink formulations induces the water to negatively react with the paper, thereby causing the edges of the paper migrate towards the center of the paper. Curl may appear immediately after printing or it may take a couple of days to manifest itself. In its final state, the paper may curl so much that it resembles a roll, scroll or a tube. Curled paper cannot be stacked nor can it successfully be duplexed in a print job.

"In order to reduce paper curl it is helpful to understand the mechanism of paper curl and determine which particular ink components have an effect on this paper curl. Media tends to curl after a large quantity of ink is deposited onto the surface of the printing substrate. Plain paper substrates are comprised mainly of cellulose fibers, along with varying levels of inorganic fillers. It is the interaction of the water in the inkjet inks with these cellulose fibers that leads to the phenomenon of paper curl. The absorption of water by the cellulose fibers causes swelling and then breaking of the interfiber cellulose bonds in the paper.

"Upon drying there are differential stresses between the printed and non-printed surfaces. These differential stresses manifest themselves as paper curl, whereby the substrate tends to curl towards the surface from which moisture was last removed (the imaged surface). An ink formulation with a reduced level of water in addition to humectants with high boiling points effectively eliminates the typical end user problems of stacking and displaying printed images with unacceptable levels of paper curl.

"Another important factor considered when formulating inks is idle time. Idle time is used to measure the short term reliability of an ink. Idle time is measured as the time between nozzle firings just before the printhead produces delayed or misdirected ink droplets. Often yellow inks exhibit poor idle times.

"Ink formulations used in ink jet printers generally comprise deionized water, a water-soluble or water-miscible organic solvent, and a colorant. Generally, the colorant is a soluble dye. Unfortunately, inks comprising soluble dyes can exhibit many problems, such as poor water-fastness, poor light-fastness, clogging of the jetting channels as a result of solvent evaporation and changes in the dye’s solubility, dye crystallization, poor print quality including ink bleeding and feathering, poor thermal stability, chemical instability, and ease of oxidation.

"Many of these problems can be overcome by replacing the soluble dyes used in the ink formulations with insoluble pigments. In general, pigments have superior properties when compared to dyes, particularly in terms of water-fastness, light-fastness, thermal stability, oxidative stability, and compatibility with both coated/treated and plain papers. However, a new set of problems arises because the pigments are insoluble in the ink composition and must be present in the ink as a dispersion. Stability of the ink is critical, both in terms of maintaining uniformity of properties and assuring that the pigment does not clog the ink jets during long periods of idle in usage. The ideal, both for stability and cost reasons, of course, would be to utilize the minimum amount of pigment necessary in the ink composition. However, decreasing the amount of pigment in the ink compositions can lead to images having poor optical densities. Further, because of the compositional balancing required to assure the necessary stability, it is also important to assure that the composition has an appropriate viscosity for use in an ink jet printer, as well as good printing properties such as good water-fastness, light-fastness, and minimized running and feathering when applied to the paper. Appropriate viscosity is vital, especially when the ink is used in an off-carrier printer. Low viscosity is needed to increase the ink penetration and image drying speeds. Usually a desirably viscosity at 25 C is in the range of 2.5-3.0 cps. However, many solvents and antikogation agents negatively increase the viscosity of the ink. This causes great difficulty in jetting the ink, especially after the printhead is idle, and consequently leads to clogging of the printhead, difficulty in jetting the ink and ultimately to the printhead failing prematurely.

"As discussed above, it has been very difficult to develop a yellow ink formulation which optimizes all of these desired ink printing properties simultaneously. Therefore, many trade-offs arise when trying to formulate an acceptable yellow ink formulation. Often the inclusion of an ink component meant to fix and or control one of the above discussed problems can prevent another printing property from being met. The general approach has been to balance and optimize these often competing properties. Thus, most yellow inks are a compromise in an attempt to achieve most of the above listed printing property requirements.

"Prior to the present invention, however, an ink formulation which optimizes all of these desired ink printing properties had not been achieved. For example, increasing the pigment load in the inkjet ink formulation improves the optical density and gamut of the ink but it also has a negative impact on jetting and heater kogation. Many solvents help kogation but they negatively increase the viscosity of the ink which can lead to jetting failure in the printhead. Humectants (also termed cosolvents) can be added to the ink composition to aid in maintaining the colorant in the ink composition and to enhance the performance of the ink. However, often the addition of particular humectants can negatively impact the print quality of the ink. Unfortunately, high quantities of humectants adversely affect the yellow ink in terms of viscosity, dry time and smudging. Consequently, there is a need to balance these competing factors when deciding exactly which components to include and at what percentage each component should be used in a yellow ink formulation, wherein the ink formulation would minimize kogation and paper curl while still have acceptable print quality and print properties. The yellow inkjet ink of the present invention balances these many trade-offs to formulate an optimized yellow inkjet ink formulation. More particularly, additional development work done by the inventors has determined a particular group of cosolvents which reduce paper curl and kogation, maintain printhead function while still provide acceptable print quality.

"It is believed that the yellow ink of the present invention uses a unique group of cosolvents which surprisingly produces an optimal ink formulation which minimize kogation and paper curl while still has acceptable print quality. With the increased usage of off carrier inkjet printing systems having permanent and semi-permanent printheads, this type of yellow inkjet ink formulation greatly needed.

"It has now been discovered that the use of a very specific cosolvent mixture containing: 1) a terminal C.sub.2-C.sub.8 terminal alkanediol; 2) a polyol/alkylene oxide condensate; 3) a trihydric alcohol; and 4) a cyclic amide and its derivative in an aqueous inkjet ink composition containing a dispersion of an insoluble yellow pigment provides a unique blend of optimized properties needed and desired for a yellow pigmented ink. Specifically, this yellow ink composition provides excellent printing properties in terms of stability, optical density (even when low levels of pigment are utilized), viscosity, paper curl, printing characteristics (water-fastness, minimized feathering, minimized running of ink on the printed page), and printer maintenance problems (i.e., minimized clogging of the printhead during gaps in printer usage). The inventors are not aware of any prior art that describes or suggests the specific cosolvent combinations of the present invention.

"It is, therefore, an object of the present invention to provide an improved yellow pigmented ink composition for ink jet printers having very specific cosolvent system which produces an inkjet ink having optimal printing properties while simultaneously reducing paper curl and kogation and improving idle times. The yellow inkjet ink of the present invention is especially suitable for use in permanent or semi permanent printheads. Other objects and advantages of the present invention will become apparent from the following disclosure."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors’ summary information for this patent: "The present invention relates to an aqueous ink composition suitable for use in ink jet printers comprising: (a) from about 1.0% to about 5.0% of an insoluble yellow pigment; (b) from about 0.5% to about 2.0% of a polymeric dispersant for the yellow pigment; from about 0.1% to about 3% of a surfactant; (d) from about 15.0% to about 25.0% of a cosolvent mixture comprising (1) a C.sub.2 to C.sub.8 terminal alkanediol; (2) a trihydric alcohol; (3) a polyol/alkylene oxide condensate having the formula

"##STR00001## wherein X is H or C.sub.1-C.sub.6 alkyl, R is H, C.sub.1-C.sub.6 alkyl or CH.sub.2O(CH.sub.2CH.sub.2O).sub.eH, b is 0 or 1, a+d+f (c+e) is from about 2 to about 100, and f is from about 1 to about 6; (4) a cyclic amide and its derivative; and (e) the balance an aqueous carrier.

"The weight ratio of the yellow pigment to the polymeric dispersant is 3:1 to 5:1, preferably 3.5:1. Optionally, the yellow inkjet ink of the present invention may contain a biocide. All percentages used herein are ‘by weight’ unless otherwise specified and are based on the overall yellow inkjet ink composition. All molecular weights, used herein, are number average molecular weights unless otherwise specified. A C.sub.2-C.sub.8 terminal alkanediol is defined to mean a diol having hydroxyl groups at each end like, for example, an alkanediol having the formula: HO–CH.sub.2(CH.sub.2).sub.tCH.sub.2–OH, wherein t is about 0 to about 6."

For more information, see this patent: Zimmer, Agnes; Bogale, Rahel. Aqueous Pigmented Yellow Inkjet Ink Composition. U.S. Patent Number 8431631, filed September 30, 2011, and published online on April 30, 2013. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=63&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3142&f=G&l=50&co1=AND&d=PTXT&s1=20130430.PD.&OS=ISD/20130430&RS=ISD/20130430

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May 9, 2013 at 8:45 AM