Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-12-01
2002-01-01
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S446000, C524S447000, C524S451000, C524S492000, C524S493000, C524S497000, C524S494000, C524S551000, C524S555000, C524S556000, C524S563000, C524S557000, C524S577000, C524S575000
Reexamination Certificate
active
06335395
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of preparation of a stable coating for a pigment-coated ink jet recording element.
BACKGROUND OF THE INVENTION
In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof.
An ink jet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness.
It is well known that in order to achieve and maintain photographic-quality images on such an image-recording element, an ink jet recording element must:
Be readily wetted so there is no puddling, i.e., coalescence of adjacent ink dots, which leads to nonuniform density
Exhibit no image bleeding
Exhibit the ability to absorb high concentrations of ink and dry quickly to avoid elements blocking together when stacked against subsequent prints or other surfaces
Exhibit no discontinuities or defects due to interactions between the support and/or layer(s), such as cracking, repellencies, comb lines and the like
Not allow unabsorbed dyes to aggregate at the free surface causing dye crystallization, which results in bloom or bronzing effects in the imaged areas
Have an optimized image fastness to avoid fade from contact with water or radiation by daylight, tungsten light, or fluorescent light
An ink jet recording element that simultaneously provides an almost instantaneous ink dry time and good image quality is desirable. However, given the wide range of ink compositions and ink volumes that a recording element needs to accommodate, these requirements of ink jet recording media are difficult to achieve simultaneously.
Ink jet recording elements are known that employ porous or non-porous single layer or multilayer coatings that act as suitable image receiving layers on one or both sides of a porous or non-porous support. Recording elements that use non-porous coatings typically have good image quality but exhibit poor ink dry time. Recording elements that use porous coatings typically have poorer image quality but exhibit superior dry times.
Simultaneous quick dry time and good image quality may be obtained by improving image quality of recording elements using porous coatings. The quality of images printed using ink jet printers on porous coatings is usually poor because ink jet ink dyes, upon application, tend to migrate through the pores away from the surface of the recording element resulting in poor image quality. In order to obtain good image quality and high optical density, it is necessary to maintain the ink dyes at or near the surface of the recording element. This may be achieved through the use of a component in the coating that will trap the dye molecule at or near the surface of the recording element. Since most ink jet ink dyes are anionic, a suitable cationic material may be used to trap the dye molecules at or near the surface of the recording element. Such a material is referred to in the art as a mordant.
Porous coatings are created by applying a coating containing inorganic anionic pigments, organic anionic binders, and anionic or non-ionic additives onto a substrate such as paper. Since such coatings are predominantly anionic, addition of a cationic mordant increases the viscosity to the point that the coating is no longer coatable using standard techniques.
German Patent DE 19,534,327A1 relates to an ink jet coating comprising an inorganic, modified cationic pigment and an organic, cationic binder. The patent discloses a cationic dispersion with pH in the range 5 to 12. There is a problem with this coating, however, in that it requires the use of cationic binders, instead of anionic binders which are more readily available.
It is an object of this invention to provide a process for making a stable coating containing a cationic mordant, an anionic pigment and anionic binder while maintaining a constant viscosity so that it can be coated using standard techniques.
SUMMARY OF THE INVENTION
This and other objects are achieved using the present invention which comprises a process for making a stable coating comprising an inorganic, anionic pigment, an organic, anionic binder and an organic, cationic mordant comprising:
a) mixing the inorganic, anionic pigment with the organic, cationic mordant;
b) lowering the pH of the mixture to below about 4; and
c) adding the organic, anionic binder to the mixture, thus providing a coating composition which has an approximately constant viscosity over a period of time.
The ink jet recording elements made from the coating of the invention provide good image quality and fast ink dry times.
DETAILED DESCRIPTION OF THE INVENTION
As noted above, cationic mordants may be used to trap dyes at or near the surface of a recording element to improve image quality. However, the addition of a cationic mordant to a predominantly anionic coating results in the aggregation of oppositely charged particles, which in turn results in a rapid increase in coating viscosity to the point that the coating is no longer coatable using standard techniques.
During the coating preparation, it is important that the mordant retain its cationic charge to preserve its function to trap the anionic ink jet dyes. By lowering the coating pH, such as by using nitric acid, the anionic charge on the pigment and binder can be significantly reduced while maintaining the cationic charge on the mordant. Thus, the cationic mordant interacts less with the weakly anionic pigment and binder, thereby rendering the coating capable of being coated using standard coating techniques.
In a preferred embodiment of the invention, the pH is lowered to a range from 2-4, preferably approximately 3.
The inorganic, anionic pigment useful in the invention may be a kaolin clay, a calcined clay, titanium dioxide, talc or a silicate. In a preferred embodiment of the invention, the inorganic, anionic pigment is a kaolin clay sold under the trade name Hydragloss® 92 (J.M.Huber Company). The amount of inorganic, anionic pigment used may range from about 10% to about 50% of the coating, preferably from about 15% to about 30%.
The organic, anionic binder useful in the invention may be a styrene acrylic latex, a styrene butadiene latex, a poly(vinyl alcohol) or a poly(vinyl acetate). A commercially-available styrene acrylic latex useful in the invention is Acronal® S-728 (BASF Corp.). A commercially-available styrene butadiene latex useful in the invention is Styronal® BN 4606X (BASF Corp.). A commercially-available poly(vinyl alcohol) useful in the invention is Airvol® 21-205 (Air Products Inc.). A commercially-available poly(vinyl acetate) useful in the invention is Vinac® 884 (Air Products Inc.).
The organic, anionic binder may be used in an amount of from about 1% to about 10% of the coating, preferably from about 2% to about 4% of the coating. In general, good results are obtained when the ratio of pigment to binder is from about 3:1 to about 8:1.
The organic, cationic mordant useful in the invention may be a polymer latex dispersion or a water-soluble polymer solution. Examples of mordants useful in the invention are disclosed in U.S. Pat No. 5,474,843. Other useful mordants include cationic urethane dispersions sold under the trade name Witcobond® W-213 and Witcobond® W-215 (Witco Corporation).
In a preferred
Mollon Craig T.
Oakland Michelle M.
Sadasivan Sridhar
Samons Elwood C.
Sunderrajan Suresh
Cole Harold E.
Eastman Kodak Company
Reddick Judy M.
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