Gel-forming inks for use in the alleviation of bleed

Abstract: A method for controlling color bleed between adjacent multi-color ink regions on a print medium is disclosed. Color bleed involves the migration of color agents between adjacent zones in a multicolored printed image on a print medium. A first composition containing a gel-forming species and a color agent is brought into contact on a region of the print medium with a second composition having a color agent and a gel-initiating species or chemical conditions which bring about gelation. In alternative embodiments, the print medium may be pretreated with either a gel-initiating species or a gel-forming species (with no colorant), followed by treatment with a gel-forming species or gel-initiating species (with colorant), respectively. The formation of the gel upon the print medium impedes the movement of the color agent or agents and thus reduces the color bleed between adjacent zones.

Description: The present invention relates to inks employed in ink-jet printing, especially in thermal ink-jet printing, and, more particularly, to colored compositions in which color bleed is substantially reduced or even eliminated. Heavy dye loads on bond paper of various colored inks can lead to bleed and reduction of waterfastness. Bleed, as used herein, is the invasion of one color into another color on paper or other print medium. This is in contradiction to uses of the term in the prior art, which tend to define "bleed" in the context of ink of a single color following the fibers of the paper. Thermal ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen. In operation, each resistor element is connected via a conductive trace to a micro-processor, where current carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which is expelled through the nozzle toward the print medium. In this way, firing of a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fill, and provides other print capabilities on the medium. Many inks that are described for use in ink-jet printing are usually associated with non-thermal ink-jet printing. An example of such non-thermal ink-jet printing is piezoelectric ink-jet printing, which employs a piezoelectric element to expel droplets of ink to the medium. Inks suitably employed in such non-thermal applications often cannot be used in thermal ink-jet printing, due to the effect of heating on the composition. JP-A-61231287 describes a method of printing with reduced color bleed, comprising pre-impregnating the fiber structure of the paper substrate with a gelling agent for polyvinyl alcohol (PVA), followed by printing on the substrate with an ink containing PVA. The gelling agent is composed of boric acid, borax and a titanium compound. EP-A-0586079 describes a method for preventing color bleed in multi-ink printing systems by incorporating a precipitating agent (e.g. a multi-valent metal salt) in at least one of the ink compositions. The precipitating agent is designed to react with the coloring agent in the other ink composition at the interface between adjacent printed regions to form a precipitate which prevents ink migration between adjacent the printed regions. A need remains for compositions for use in ink-jet printing, particularly thermal ink-jet printing, which do not evidence bleed, as defined herein, and yet which possess relatively long shelf life and other desirable properties of such inks. The present invention provides an improved method for printing multi-color images on a print medium in which color bleed between adjacent colored regions is controlled comprising the steps of: (a) providing two compositions, a first composition comprising a gel-forming species and a second composition comprising a gel-initiating species which is capable of reacting with the first composition in order to form a gel therefrom, provided that each of the two compositions includes at least one coloring agent; (b) applying the first composition to the print medium in a first region thereon; (c) applying the second composition to the print medium in a second region thereon, the second region being directly adjacent and in contact with the first region; and (d) allowing the gel-initiating species in the second composition to react with the gel-forming species in the first composition at a position on the print medium where the first region comes in contact with the second region so that the gel is formed at the position in order to prevent color bleed between the first composition in the first region and the second composition in the second region. The inks of the invention evidence little or no color bleed when printed on a print medium and possess relatively long shelf life. The present invention described is also applicable to other ink-jet technologies. In accordance with the present invention, a unique and highly effective method for controlling color bleed between adjacent multi-color ink regions on a print medium is described herein. Color bleed involves the migration of color agents between adjacent zones in a multi-colored printed image on a print medium. Color bleed substantially decreases print quality and resolution, and prevents distinct boundaries from being produced between adjacent color regions. According to the invention, one pen contains a gel-forming species and the other pen contains a gel-initiating species. Gelation occurs between a first composition comprising the gel-forming species and a coloring agent and a second composition comprising the gel-initiating species and a coloring agent. As an example, the first composition containing the gel-forming species and the color agent is brought into contact on a region of the print medium with the second composition having a color agent and the gel-initiating species. The formation of the gel on the print medium impedes the movement of the color agents between the two inks and thus reduces the color to color bleed. Exemplary gel-forming species employed in the practice of the present invention include, but are not limited, to agar, algin, carrageenan, fucoidan, laminaran, gum arabic, corn hull gum, gum ghatti, guar gum, karaya gum, locust bean gum, pectin, dextrans, starches, carboxymethylcellulose, and polyvinyl alcohol. Many of these gel-formers are commercially available under such tradenames as Kelzon, Crodyne BY19, Kelcogel PC, Mannucol LB, Kelgin QL, Keltone LV, and Keltone HV. Exemplary gel-initiating species employed in the practice of the present invention include, but are not limited to, (1) sodium borate, (2) typical mineral acids such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, phosphorous acid, and sulfurous acid, (3) typical organic acids such as acetic acid, propionic acid, benzoic acid, and phthalic acid, and (4) protonated tertiary amines such as trimethyl ammonium hydrochloride. Exemplary coloring agents employed in the practice of the present invention include sulfonate or carboxylate water-soluble dyes, such as C.I. Acid Blue 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. Direct Blue 199, and C.I. Direct Yellow 86, and Food Black 2. Accordingly, the present invention also provides a thermal ink-jet set comprising two compositions, a first composition consisting essentially of: (a) 0.1 to 1 wt.% of guar gum; (b) at least one water-soluble dye; and (c) the balance water; and a second composition consisting essentially of: (a) 0.1 to 3 wt.% of sodium borate; (b) sufficient base to adjust the pH greater than 8, (c) at least one water soluble dye, and (d) the balance water. The present invention further provides a thermal ink-jet ink set comprising two compositions, a first composition comprising: (a) 0.1 to 1 wt.% of a gel-forming species, (b) at least one water-soluble dye; and (c) the balance water, and a second composition having a pH less than 5 and comprising: (a) 0.1 to 3 wt.% of a gel-initiating species; (b) at least one water-soluble dye; and (c) the balance water. The gel-forming species comprises one of the gel-forming species described above, preferably carboxymethylcellulose. The second component comprises a gel initiating species of sufficient acidity to bring about gelation of the gel-forming species. In these compositions, other substances commonly added to inks, such as biocides and the like, which do not affect the material properties of the ink disclosed herein, may be included. Exemplary situations are provided, involving the control of color bleed between two compositions (herein-after "Composition 1" and "Composition 2"), with the preferred formulations as follows: Example 1 Gel-forming species in one pen and gel-initiating species in the other. Composition 1 : Composition 1 comprises (a) about 0.01 to 10 wt% of a gel-forming species selected from the group consisting of agar, algin, carrageenan, fucoidan, laminaran, gum arabic, corn hull gum, gum ghatti, guar gum, karaya gum, locust bean gum, pectin, dextrans, starches, carboxymethylcellulose, polyvinyl alcohol, Kelzon, Crodyne BY19, Kelcogel PC, Mannucol LB, Kelgin QL, Keltone LV, and Keltone HV, (b) one or more water-soluble dyes selected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. Direct Blue 199, C.I. Direct Yellow 86, and Food Black 2, and (c) the balance water. In a preferred embodiment, the gel-forming species consists essentially of about 0.1 to 1 wt% of guar gum. Composition 2 : Composition 2 comprises a gel-initiating species comprising about 0.01 to 10 wt% of sodium borate, with sufficient base to adjust the pH greater than 8, one or more water-soluble dyes selected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. Direct Blue 199, C.I. Direct Yellow 86, and Food Black 2, and the balance water. In a preferred embodiment, the gel-initiating species consists essentially of about 0.1 to 3 wt% of sodium borate. Example 2 Gel-forming species in one pen and gel-initiating species of sufficient acidity to bring about gelation of gel-forming species in the other. In a preferred embodiment, the pH of the gel-initiating species is less than 5. Composition 1: Composition 1 comprises (a) about 0.01 to 10 wt% of a gel-forming species selected from the group consisting of agar, algin, carrageenan, fucoidan, laminaran, gum arabic, corn hull gum, gum ghatti, guar gum, karaya gum, locust bean gum, pectin, dextrans, starches, carboxymethylcellulose, polyvinyl alcohol, Kelzon, Crodyne BY19, Kelcogel PC, Mannucol LB, Kelgin QL, Keltone LV, and Keltone HV, (b) one or more water-soluble dyes selected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. Direct Blue 199, C.I. Direct Yellow 86, and Food Black 2, and (c) the balance water. In a preferred embodiment, the gel-forming species consists essentially of about 0.1 to 1% of carboxymethylcellulose. Composition 2 : Composition 2 comprises (a) a gel-initiating species selected from the group consisting of sodium borate and typical mineral acids such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, phosphorous acid, and sulfurous acid, and typical organic acids such as acetic acid, propionic acid, benzoic acid, and phthalic acid, and protonated tertiary amines such as trimethyl ammonium hydrochloride, having sufficient acidity to bring about gelation of the gel-forming species, (b) one or more water-soluble dyes selected from the group consisting of C.I. Acid Blue 9, C.I. Acid Red 18, C.I. Acid Red 27, C.I. Acid Red 52, C.I. Acid Yellow 23, C.I. Direct Blue 199, and C.I. Direct Yellow 86, and (c) the balance water. In a preferred embodiment, the gel-initiating species has a pH less than 5. The present invention represents an advance in the art of thermal ink-jet printing technology. Use of the invention as described herein avoids color bleed problems in multi-color ink systems, thereby allowing the production of clear and distinct printed images. Having herein described preferred embodiments of the present invention, it is anticipated that suitable modifications may be made to the invention by individuals skilled in the art which nonetheless remain within the scope of the invention as defined in the accompanying claims.

Claims: A method for printing multi-color images on a print medium in which color bleed between adjacent colored regions is controlled comprising the steps of: (a) providing two compositions, a first composition comprising a gel-forming species and a second composition comprising a gel-initiating species which is capable of reacting with said first composition in order to form a gel therefrom, provided that each of said two compositions includes at least one coloring agent; (b) applying said first composition to said print medium in a first region thereon; (c) applying said second composition to said print medium in a second region thereon, said second region being directly adjacent to and in contact with said first region; and (d) allowing said gel-initiating species in said second composition to react with said gel-forming species in said first composition at a position on said print medium where said first region comes in contact with said second region so that said gel is formed at said position in order to prevent color bleed between said first composition in said first region and said second composition in said second region. The method of claim 1 wherein said gel-forming species is selected from the group consisting of agar, algin, carrageenan, fucoidan, laminaran, gum arabic, corn hull gum, gum ghatti, guar gum, karaya gum, locust bean gum, pectin, dextrans, starches, carboxymethylcellulose, and polyvinyl alcohol and wherein said gel-initiating species is selected from the group consisting of sodium borate, mineral acids, organic acids, and protonated tertiary amines. The method of claim 2 wherein said mineral acids are selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, phosphorous acid, and sulfurous acid, said organic acids are selected from the group consisting of acetic acid, propionic acid, benzoic acid, phthalic acid, and said protonated tertiary amine consists essentially of trimethyl ammonium hydrochloride. A thermal ink-jet ink set comprising two compositions, a first composition consisting essentially of: (a) 0.1 to 1 wt.% of guar gum; (b) at least one water-soluble dye; and (c) the balance water; and a second composition consisting essentially of: (a) 0.1 to 3 wt.% of sodium borate; (b) sufficient base to adjust the pH greater than 8, (c) at least one water soluble dye, and (d) the balance water. A thermal ink-jet ink set comprising two compositions, a first composition comprising: (a) 0.1 to 1 wt.% of a gel-forming species, (b) at least one water-soluble dye; and (c) the balance water, and a second composition having a pH less than 5 and comprising: (a) 0.1 to 3 wt.% of a gel-initiating species; (b) at least one water-soluble dye; and (c) the balance water.

Inventors: MOFFATT JOHN R, SHIELDS JAMES P, MOFFATT, JOHN R., SHIELDS, JAMES P.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1995
Main classification: C09D11
IPC codes: C09D11, B41M5, B41M3, B41J2