Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-12-14
2002-12-24
Jagannathan, Vasu (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S560000, C524S577000, C347S100000
Reexamination Certificate
active
06498202
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to aqueous ink jet ink compositions which include latex binder and which exhibit an advantageous combination of good optical density, good print quality and good wet-rub resistance. The present invention is also directed to latex binders for use in aqueous ink jet ink compositions and ink jet printing methods, and to methods of ink jet printing, which methods provide printed mediums having an advantageous combination of good optical density, good print quality and good wet-rub resistance.
BACKGROUND OF THE INVENTION
Ink jet printing is a well known process and generally comprises ejecting a droplet of an ink composition through a fine nozzle to record images on a surface of a recording medium. Typically, paper recording mediums are employed although other polymer based film recording mediums have also been used. High quality printing and relatively low noise operation have made ink jet printers particularly advantageous.
Dyes and/or pigments are typically used as colorants in ink jet ink compositions. While dyes often provide very good color properties immediately after printing, they are often light sensitive so that printed images tend to fade after time. Dyes can also remain water soluble after printing, whereby printed images smear when contacted with moisture. On the other hand, pigment colorants often exhibit improved light-fastness and water-fastness as compared with dyes. Typically, a pigment is employed in combination with one or more polymeric dispersants in ink jet ink compositions in order to form a stable dispersion of the pigment particles in the ink.
While inks containing pigment colorants generally exhibit improved water-fastness as compared with inks containing water-soluble dyes, it is often desirable to further improve the water-fastness of pigment-containing ink jet ink compositions, particularly for end-use applications where a printed recording medium may be exposed to high moisture and/or humidity conditions. The water-fastness is often measured as wet-rub resistance.
Recently, various latex binders have been employed in attempts to improve the water-fastness of ink jet ink compositions which contain pigment colorants. Oftentimes, however, a latex binder which improves the wet-rub resistance of an ink jet ink composition is not suitable for use in the ink jet print head nozzles and causes printer maintenance problems. Typically, the print head nozzles have diameters of less than about 30 &mgr;m and relatively high temperatures are employed to eject the ink compositions from the nozzles. Under the high temperature conditions, many latex binders form a film on the nozzle plate, resulting in clogging of the nozzle and printhead failure, so that extra maintenance of the printer is often required.
Accordingly, pigment-containing ink jet ink compositions which exhibit good printing properties, particularly in terms of print quality and optical density, which have improved wet-rub resistance, and which are suitable for substantially maintenance-free use in conventional ink jet printing systems are desired. Additionally, substantially maintenance-free printing methods which provide printed recording mediums having good print quality, good optical density, and good wet-rub resistance are desired.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide improved ink jet ink compositions. It is a more specific object of the invention to provide ink jet ink compositions which exhibit good optical density and good print quality. It is a further object of the invention to provide such ink jet ink compositions which also exhibit improved wet rub resistance. It is a related object of the invention to provide latex binders for use in ink jet ink compositions and, particularly, for improving wet rub resistance of ink jet ink compositions. It is a further object of the invention to provide improved methods for ink jet printing, which methods employ pigment-containing ink jet ink compositions having latex binder therein.
These and additional objects and advantages are provided by the present invention. In a first embodiment, the invention is directed to aqueous ink jet ink compositions which comprise pigment, humectant, dispersant and a latex binder. The latex binder is formed from first monomer having a glass transition temperature Tg greater than about 70° C. and comprising styrene, substituted styrene, methyl methacrylate, or a mixture thereof, second monomer having a glass transition temperature Tg less than about 0° C. and comprising a C
2
-C
10
alkyl acrylate, charge stabilizing agent, emulsifier and initiator. The latex binder has a glass transition temperature Tg of from about 0° C. to about 70° C., an average particle size of from about 150 nm to about 350 nm, and a surface tension of from about 40 dynes/cm to about 60 dynes/cm. In a further embodiment, the invention is directed to methods of ink jet printing, which methods comprise ejecting a droplet of an aqueous ink jet ink composition as described through a nozzle and onto a surface of a paper recording medium. These compositions and methods provide an advantageous combination of good optical density, print quality and wet-rub resistance.
The present invention is also directed to latex binders formed by emulsion polymerization and suitable for use in ink jet ink compositions. The latex binders are formed by emulsion polymerization of first monomer having a glass transition temperature Tg greater than about 70° C. and comprising styrene, substituted styrene, methyl methacrylate or a mixture thereof, second monomer having a glass transition temperature Tg less than about 0° C. and comprising a C
2
-C
10
alkyl acrylate, charge stabilizing agent, emulsifier and initiator. The latex binders have a glass transition temperature Tg of from about 0° C. to about 70° C., an average particle size from about 150 nm to about 350 nm, and a surface tension of from about 40 dynes/cm to about 60 dynes/cm.
In a further embodiment, the invention is directed to methods of ink jet printing, which methods comprise ejecting a droplet of an aqueous ink jet ink composition through a nozzle and onto a surface of a paper recording medium, and passing the paper recording medium with the aqueous ink jet ink composition on a surface thereof through a fuser system. The fuser system is operated at a temperature greater than about 100° C., and the paper recording medium is passed through the fuser system for about 5 to about 100 seconds. The aqueous ink jet composition employed in these methods comprises, by weight, from about 1% to about 20% pigment, from about 5% to about 50% humectant, from about 0.01% to about 10% dispersant, and from about 1% to about 20% of an emulsion polymerized latex binder having a glass transition temperature Tg of from about 0° C. to about 70° C. and a particle size of from about 150 nm to about 350 nm. These methods provide printed recorded mediums having an advantageous combination of good optical density, good print quality and good wet-rub resistance.
Additional embodiments, objects and advantages of the present invention will be more further apparent in view of the following detailed description.
DETAILED DESCRIPTION
The aqueous ink jet ink compositions and the ink jet printing methods according to the present invention provide printed recording mediums which exhibit good optical density, good print quality and good wet-rub resistance.
The aqueous ink jet ink compositions comprise pigment, humectant, dispersant and latex binder in an aqueous medium. The aqueous medium may comprise water, preferably distilled and/or deionized water, or may comprise water in combination with one or more water-miscible organic oils or solvents. In a preferred embodiment, the aqueous medium is deionized water.
A wide variety of organic and inorganic pigments are known in the art for use in ink jet printing systems and are suitable for use in the compositions of the present invention, alone or in combination. The pigment dispersion particles mu
Sun Jing X.
Suthar Ajay K.
Daspit Jacqueline M.
Dinsmore & Shohl LLP
Jagannathan Vasu
Lexmark International Inc
Shosho Callie E.
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