Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1996-12-27
2001-05-15
Copenheaver, Blaine (Department: 1771)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S505000, C524S533000, C524S555000, C524S556000
Reexamination Certificate
active
06232369
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to aqueous inks for ink jet printers, and more particularly, to aqueous ink jet inks containing hydrosols as additives to improve smear resistance of the ink.
Ink jet printing is a non-impact printing process in which droplets of ink are deposited on a substrate such as paper or transparency film in response to an electronic signal. Low cost and high quality of the output, combined with relatively noise free operation, have made ink jet printers a popular option to other types of printers used with computers. Both dyes and pigments have been used as ink colorants for ink jet printers. The dye-based inks while in general superior in color properties, have several disadvantages as compared to pigment based inks. The dyes are usually water soluble and remain so after drying on the substrate. They are easily redissolved by water spills, and the image smears on contact with felt pen markers. In addition, the dyes exhibit poor light stability relative to pigments and are known to fade even under office lighting. Thus, dye-based inks are often unsuitable for use in applications requiring moisture resistance and greater light stability. The pigments are preferred colorants provided the pigment dispersion can be made resistant to flocculation and settling.
Polymeric additives may be added to the pigmented inks to further improve their resistance to smear/smudge or general handling. However, such additives have a great tendency towards generating problems for the ink jet printing process. The most common ones include 1). aggravating the pigment dispersion stability; 2). building up solids around the nozzle plate resulting in misdirection of the ink drop or complete blockage of the ink delivery; and 3). interfering with the ink drop generation, especially in the bubble formation in a thermal ink jet device.
There exists a need for ink jet inks which have good water resistance and smear fastness. In particular, with pigment based inks there is a need to maintain the stability of the dispersion and pen reliability while improving water and smear fastness.
SUMMARY OF THE INVENTION
The present invention provides an ink jet ink composition comprising:
(a) an aqueous carrier medium;
(b) an aqueous carrier medium insoluble colorant;
(c) polymeric dispersant; and
(d) a hydrosol polymer.
Preferably, the hydrosol polymer is an acrylic hydrosol polymer. The inks of the invention are stable, have low viscosity, exhibit excellent print quality, provide excellent smear resistance after drying and good decap or crusting time. They may be used with a variety of ink jet printers such as continuous, piezoelectric, drop-on-demand and thermal or bubble jet drop-on-demand, and are particularly adapted for use in thermal ink jet printers. These inks may also be useful in air brush printing devices.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The invention provides an ink jet ink composition which is particularly suited for use in ink jet printers in general, and thermal ink jet printers in particular. Essentially, the ink composition comprises an aqueous carrier medium, a colorant that is insoluble in the aqueous medium, a polymeric dispersant (preferably a structured polymeric dispersant); and a hydrosol polymer, preferably an acrylic hydrosol polymer. The inks may be adapted to the requirements of a particular ink jet printer to provide a balance of light stability, smear resistance, viscosity, surface tension, high optical density, and crust resistance.
Aqueous Carrier Medium
The aqueous carrier medium is water or a mixture of water and at least one water soluble organic solvent. Selection of a suitable mixture depends on requirements of the specific application, such as desired surface tension and viscosity, the selected colorant, drying time of the ink, and the type of substrate onto which the ink will be printed. Representative water-soluble organic solvents that may be selected are disclosed in U.S. Pat. No. 5,085,698. A mixture of water and a polyhydric alcohol, such as diethylene glycol, is preferred as the aqueous carrier medium.
If a mixture of water and a water-soluble solvent is used, the aqueous carrier medium usually contains from about 30% to about 95% water with the balance (i.e., 70 to 5%) being the water-soluble solvent. Preferably, the aqueous carrier medium is 60-95%, by weight, water. The aqueous carrier medium comprises 70 to 99.8%, by weight of the total ink composition, depending on the type of colorant selected. Preferably, the aqueous carrier medium comprises 94-99.8% when an organic pigment is selected; 70 to 99.8% when an inorganic pigment is selected; and 80 to 99.8% when a dye is selected.
Colorants
The colorant is either a dye or a pigment that is insoluble in the aqueous carrier medium. By the term “dye” we mean a colorant that becomes soluble at some point during the printing process. By “pigment” we mean a colorant that is insoluble (i.e., in particulate or crystalline form) throughout the printing process. Pigments are the preferred colorants for use in the compositions of this invention.
Pigments
Useful pigments comprise a wide variety of organic and inorganic pigments, alone or in combination. The pigment particles are sufficiently small to permit free flow of the ink through the ink jet printing device, especially at the ejecting nozzles that usually have a diameter ranging from 10 micron to 50 micron. The particle size also has an influence on the pigment dispersion stability, which is critical throughout the life of the ink. Brownian motion of minute particles will help prevent the particles from settling. It is also desirable to use small particles for maximum color strength. The range of useful particle size is approximately 0.005 micron to 15 microns, preferably 0.005 to 5 microns, and most preferably from 0.01 to 0.3 micron.
The selected pigment may be used in dry or wet (i.e., presscake) form. In presscake form, the pigment is not aggregated to the extent that it is in dry form and therefore do not require as much deaggregation in the process of preparing the inks. Representative commercial dry and presscake pigments that may be used in practicing the invention are disclosed in U.S. Pat. No. 5,085,698 issued Feb. 4, 1992.
Fine particles of metal or metal oxides also may be used to practice the invention. For example, metal and metal oxides are suitable for the preparation of magnetic ink jet inks. Fine particle size oxides, such as silica, alumina, titania, and the like, also may be selected. Furthermore, finely divided metal particles, such as copper, iron, steel, aluminum and alloys, may be selected for appropriate applications.
In the case of organic pigments, the ink may contain up to approximately 30% pigment by weight, but will generally be in the range of approximately 1 to 15%, preferably approximately 1 to 8%, by weight of the total ink composition for most ink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of the pigment than with comparable inks employing organic pigment, and may be as high as approximately 50% because inorganic pigments generally have higher specific gravities than the organic pigments.
Dyes
The color and amount of dye present in the ink composition is largely a function of choice, being primarily dependent upon the desired color of the print achieved with the ink, the purity of the dye and its strength. Low concentrations of dye may not give adequate color vividness whereas high concentrations may result in poor printhead performance or unacceptably dark colors. Generally, the dye will be present in the amount of 0.01 to 20%, preferably 0.05 to 8%, and most preferably 1 to 5%, by weight, based on the total weight of the ink composition.
Dispersant
Polymeric dispersants suitable for practicing the invention include random polymers and structured polymeric dispersants such as block copolymers and branched-type polymers. The polymers may be anionic, cationic, or non-ionic in nature.
Random polymers are not as effective
Anton Waifong Liew
Ma Sheau-Hwa
Copenheaver Blaine
E. I. Du Pont de Nemours and Company
Guarriello John J.
Tessari Joseph A.
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