Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1999-01-11
2001-06-19
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031470, C106S031490, C106S031570, C106S031580, C106S031590
Reexamination Certificate
active
06248161
ABSTRACT:
TECHNICAL FIELD
The present invention is directed to ink-jet ink printing, and, more particularly, to providing ink compositions containing water-soluble dyes that are color-permanent, particularly, water-fast.
BACKGROUND ART
A number of ink-jet ink sets utilize water-soluble dyes, which are highly soluble in water, in order to achieve the right color gamut. Examples of patents that are directed to ink-jet ink sets for achieving the desired color gamut include U.S. Pat. No. 5,108,504, issued Apr. 28, 1992, to Loren E. Johnson et al and entitled “High Chroma Color Dye-Set for Use in Ink-Jet Inks Employing Polysaccharide-Containing Vehicles”; U.S. Pat. No. 5,143,547, issued Sep. 1, 1992, to William D. Kappele and entitled “Specific Dye Set for Thermal Ink-Jet Printing on Plain and Coated Papers”; U.S. Pat. No. 5,145,519, issued Sep. 8, 1992, to William D. Kappele and entitled “Specific Dye Set for Thermal Ink-Jet Printing”; U.S. Pat. No. 5,185,034, issued Feb. 9, 1993 and entitled “Ink-Jet Inks with Improved Colors and Plain Paper Capacity”; and U.S. Pat. No. 5,534,051, issued Jul. 9, 1996, to Hiang P. Lauw and entitled “Specific Dye Set for Thermal Ink-Jet Printing”; all of the foregoing cited patents are assigned to the same assignee as the present application.
However, many dye-based inks, after being printed, exhibit poor water-fastness. There is an increased demand by consumers on the permanence or durability of ink-jet print, including water-fastness, light-fastness, smear-fastness, smudge-fastness, etc. The purpose of the present invention is to improve the durability of water-soluble dye-based inks, especially the water-fastness, smear-fastness, smudge-fastness, and light-fastness, lumped together under the term “color permanence”, of such inks.
DISCLOSURE OF INVENTION
In accordance with the present invention, color permanence in ink-jet inks containing water-soluble dyes is achieved by using a specific ionic species having a charge opposite to that on the dye molecule. In most ink-jet inks, the dyes employed are anionic dyes. Such anionic dyes typically contain one or more sulfonate or carboxylate anionic groups. Using a specific ionic species of opposite charge, namely, phosphonium salts, causes the colorant components to “crash” or precipitate out of the water-based ink onto the print medium due to the formation of a suitable charge complex between the ionic parts of the dye and the opposite charge of the counter-ion species.
The phosphonium salt may be used alone to achieve improved color permanence. Alternatively, the phosphonium salt may be combined with other phosphonium salts or other cationic salts, such as quaternary ammonium salts, carbonium salts, iodonium salts, sulfonium salts, and pyrillium salts to improve aqueous dispersion stability and thus printability. Further, other cationic species, such as cationic polymers and polyfunctional cationic salts may be so combined with the phosphonium salt(s). Such additional cationic species partially replace the phosphonium salt(s). Alternatively, certain surfactants, such as aromatic ethoxylates, polyethylene oxide ethers, or polypropylene oxide ethers may be used to improve print quality.
BEST MODES FOR CARRYING OUT THE INVENTION
(A) Water-fast Phosphonium Salt Additives
The present invention discloses a novel method of achieving color permanence, and, more particularly, water-fastness ink components from water-soluble dyes. In this invention, the water solubility of the dye molecules is particularly enhanced by anionic groups such as sulfonates or carboxylates attached to the dye molecule.
In accordance with the present invention, a specific phosphonium salt can form a complex with anionic dye (water soluble) due to the charge exchange between anionic dye and cationic phosphonium ion. The so-called dye-complex becomes essentially hydrophobic and render a permanent print which can resist against water (water-fastness), solvent (smear-fastness), mechanical rubbing with liquid (smudge-fastness) and, in some case, against the lighting condition where the print is exposed (light-fastness).
On the other hand, due to the increased hydrophobicity, the dye-complex is occasionally susceptible to precipitation, even in the ink, and causes a problem for printability. The present invention also provides a solution for good printability with such kind of dye-complex by a suitable selection and design of chemistry, concentration of phosphonium salt molecule so that minimized intermolecular collision in the ink and maximized intermolecular collision in the print can be achieved. The minimized collision between the cationic salt and anionic dyes is found effective to maximize the pen performance including stable jettability (no decap, no kogation). In some cases, the addition of a third component such as surfactants or other cationic salts, including a second phosphonium and/or non-phosphonium salt, is required to gain this kind of minimal interaction and stable printability. The maximized collision between phosphonium salt and anionic dye in the print is achieved when the ink vehicle (water, solvents, etc.) disappears, such as by penetration into the print media or by evaporation, and it does provide the highest yield of dye-complex formation, required for the print permanence, including primarily water-fastness and secondarily other physical properties such as smear-fastness, smudge-fastness, and light-fastness.
The following mechanism likely occurs in the present invention associated with phosphonium salt and anionic dyes:
(a) Step 1: Aqueous Dispersion
Dispersion of the dye molecule in water occurs due to its hydrophilicity associated with anionic functional groups. Dispersion of the phosphonium salt in water occurs due to its hydrophilicity associated with cationic salt part. However, the hydrophobic part of the phosphonium salt molecule tends to cause the reduction of this dispersion. So, water-miscible co-solvents are helpful to gain back the aqueous dispersion. The collision between aqueous active dye and salt molecule is essentially prohibited with the practical concentration of dye and salt in the printable ink.
(b) Step 2: Molecular Collision
Collision between the anionic dye and the cationic phosphonium salt must occur due to a shortened collision distance when the water/co-solvent concentration in the print is reduced, as by penetration into the print media or by evaporation.
(c) Step 3: Charge Exchange
Complex formation between the anionic dye and the cationic phosphonium salt must occur in order to gain hydrophobicity. This process must be irreversible to insure the water-fastness of a dried print. In order to form the dye-salt complex, there must be a right oxidation potential and reduction potential between two molecules because one will act as electron donor and the other will act as electron acceptor. The hydrophobic interaction will lock the complex and prohibit the molecules from going back to the free form. If the redox potential is not right, the collision will not end up with a charge exchange and then the complex will not be strongly formed. The complex force will be destroyed again in a dried print and the water-fastness of the print will be poor.
(d) Step 4: Complex Stabilization
The stability or stabilization process occurs by hydrophobic interaction and charge stabilization, as mentioned above.
Here, it is necessary to clarify the electrochemical stability of the complex, required for permanent print and the stability of the water dispersion of the complex, and required for good printability. The term “stable complex” described in Step 4 means “electrochemically stable complex”, which is formed when the cationic species is ready to gain back its electron from the anionic species and when the anionic species is ready to give away its electron to the cationic species in order to form a neutral species. Such a stable complex is not easily re-ionized by water in the solid state. Another contributing factor to the stable complex is the strong hydrophobic interaction between bulky cationic species and bulky
Adamic Raymond J
Ganapathiappan Sivapackia
Nguyen Khe C
Hewlett--Packard Company
Klemanski Helene
LandOfFree
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