Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-05-25
2001-07-24
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
Reexamination Certificate
active
06265049
ABSTRACT:
Inkjet printing media are frequently made by coating a substrate with an aqueous coating composition containing organic polymer followed by drying the applied coating composition to provide an ink-receiving coating on the substrate. The aqueous coating composition may be formulated so that the final printed printing media exhibit desirable gloss, low coalescence, and low bleed. Although the quality of the printed images as measured by one or more of these characteristics may be satisfactory, the inkjet printing media, whether before or after printing, often exhibit unacceptable curl.
“Gloss” is the ratio of luminous flux reflected in the mirror direction from a printing medium, whether or not printed, to the luminous flux reflected from a standard surface under the same geometric conditions. Usually visual comparisons of surface shininess are satisfactory. When more objective quantification is either desirable or necessary, the procedure of ASTM D 523-85 employing 60° geometry is used.
“Coalescence” is the phenomenon wherein wet ink droplets applied to an inkjet printing medium fail to spread sufficiently to eliminate the unprinted space between the droplets.
“Bleed”, also known as “bloom”, is migration of ink, after printing and substantial drying, from its original locations on printed media, thereby resulting in unsatisfactory images. such migration is especially prevalent under conditions of high temperature and high humidity, such as for example, 35° C. and 80 percent relative humidity.
“Curl” is the inability of a printing medium to lie flat under its own weight when placed on a flat surface. Small amounts of curl which do not seriously interfere with the intended use of the printing medium, whether before or after printing, are usually acceptable. However greater amounts of curl which significantly interfere with such use are unsatisfactory.
In an effort to reduce curl, various plasticizers of one type or another have been included in the aqueous coating composition. While some of the plasticizers have reduced curl, they have concomitantly reduced gloss unacceptably and/or increased coalescence. In many instances they have also increased bleed.
It has now been found that the presence of substantially water-insoluble plasticizer reduces curl while neither unacceptably reducing gloss nor materially increasing coalescence, and while not materially increasing bleed.
Accordingly, one embodiment of the invention is a coating composition comprising: (a) a volatile aqueous liquid medium; and (b) binder dissolved or dispersed in the volatile aqueous liquid medium, the binder comprising: (1) water-soluble or water-dispersible film-forming organic polymer which is substantially free of ammonium groups wherein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes from 10 to 100 percent by weight of the water-soluble or water-dispersible film-forming organic polymer which is substantially free of ammonium groups, (2) water-soluble or water-dispersible first cationic addition polymer consisting essentially of quaternary ammonium-containing mer units and ammonium-free mer units, (3) water-soluble or water-dispersible second cationic addition polymer consisting essentially of secondary, tertiary, or both secondary and tertiary ammonium-containing mer units and ammonium-free mer units, and (4) substantially water-insoluble plasticizer having a solubility in water at 25°C. of less than 1000 ppm, wherein the binder constitutes from 20 to 90 percent by weight of the solids of the coating composition; and (c) finely divided substantially water-insoluble pseudoboehmite particles which have a maximum dimension of less than 500 nanometers and constitute from 10 to 80 percent by weight of the solids of the coating composition.
A second embodiment of the invention is a printing medium comprising a substrate having at least one surface and a coating on the surface wherein the coating comprises: (a) binder comprising: (1) organic polymer which is substantially free of ammonium groups wherein poly(ethylene oxide) having a weight average molecular weight in the range of from 100,000 to 3,000,000 constitutes from 10 to 100 percent by weight of the organic polymer which is substantially free of ammonium groups, (2) first cationic addition polymer consisting essentially of quaternary ammonium-containing mer units and ammonium-free mer units, (3) second cationic addition polymer consisting essentially of secondary, tertiary, or both secondary and tertiary ammonium-containing mer units and ammonium-free mer units, and (4) plasticizer having a solubility in water at 25° C. of less than 1000 ppm, wherein the binder constitutes from 20 to 90 percent by weight of the coating; and (b) finely divided substantially water-insoluble pseudoboehmite particles which have a maximum dimension of less than 500 nanometers, are distributed throughout the binder, and constitute from 10 to 80 percent by weight of the coating.
Yet another embodiment of the invention is a printing process which comprises applying liquid ink droplets to the printing medium of the second embodiment.
The printing media of the invention may be made by coating a surface of a substrate with the coating composition of the invention and thereafter substantially removing the aqueous liquid medium.
The coating composition can be in the form of an aqueous solution in which case the volatile aqueous liquid medium is a volatile aqueous solvent for the polymer of the binder, or the coating composition can be in the form of an aqueous dispersion in which instance the volatile aqueous liquid medium is a volatile aqueous dispersion liquid for at least some of the polymer of the binder.
The volatile aqueous liquid medium is predominately water. Small amounts of low boiling volatile water-miscible organic liquids may be intentionally added for particular purposes. Examples of such low boiling volatile water-miscible organic liquids solvents include methanol [CAS 67-56-1], ethanol [CAS 64-17-5], 1-propanol, [CAS 71-23-8], 2-propanol [CAS 67-63-0], 2-butanol [CAS 78-92-2], 2-methyl-2-propanol [CAS 75-65-0], 2-propanone [CAS 67-64-1], and 2-butanone [CAS 78-93-3]. The listing of such liquids is by no means exhaustive.
It is preferred that substantially no low boiling volatile water-miscible organic liquids be intentionally added to the system in order to minimize organic emissions upon drying the coating.
Similarly, water-miscible organic liquids which themselves are of low, moderate, or even negligible volatility may be intentionally added for particular purposes, such as for example, retardation of evaporation. Examples of such organic liquids include 2-methyl-1-propanol [CAS 78-83-1], 1-butanol [CAS 71-36-3], 1,2-ethanediol [CAS 107-21-1], and 1,2,3-propanetriol [CAS 56-81-5]. The listing of such liquids is by no means exhaustive.
It is preferred that substantially no water-miscible organic liquids which are of low, moderate, or negligible volatility be intentionally added to the system.
Notwithstanding the above, those materials which, although not intentionally added for any particular purpose, are normally present as impurities in one or more of the components of the coating compositions of the invention and which become components of the volatile aqueous liquid medium, may be present at low concentrations.
In most instances water constitutes at least 80 percent by weight of the volatile aqueous liquid medium. Often water constitutes at least 95 percent by weight of the volatile aqueous liquid medium. Preferably water constitutes substantially all of the volatile aqueous liquid medium.
The amount of volatile aqueous liquid medium present in the coating composition may vary widely. The minimum amount is that which will produce a coating composition having a viscosity low enough to apply as a coating. The maximum amount is not governed by any theory, but by practical consideratio
Li Huawen
Swisher Robert G.
Grendzynski Michael E.
Hess Bruce H.
Hewlett--Packard Company
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