Eradicable inks

Details Eradicable inks Eradicable inks

1999-04-28

2001-04-24

Parker, Fred J. (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Chemical agent applied to treat coating

C427S340000

Reexamination Certificate

active

06221432

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to eradicable inks.
Ink eradicator systems generally include two components. One component is an aqueous ink that includes a dye—typically a triarylmethane—that can be converted to a colorless form when contacted with a substance such as a sulfite reducing agent or an amine. The second component is an aqueous eradicator fluid that includes a substance that can cause the dye to convert to a colorless form. A user writes with the ink and, if correction is necessary, applies the eradicator fluid to the ink marking to decolorize the dye.
Aqueous inks used in eradicator systems often are not waterfast. In addition, aqueous inks may have a low viscosity, and low viscosity inks can be more prone to leakage than higher viscosity inks. Finally, writing instruments containing aqueous inks often include a cap so that the ink does not dry out when the pen is not being used.
Inks that are used in ball-point pens typically include largely non-volatile organic solvents, such as benzyl alcohol, phenyl cellosolve, diethylene glycol monoethyl ether, dipropylene glycol, glycerin, and propylene glycol. Ball-point pen inks tend to have a relatively high viscosity (e.g., greater than 10,000 cps).
An example of a triarylmethane that has been used in aqueous eradicable inks is Acid Blue 93, which has the following structure:
Acid Blue 93 is not significantly soluble in many of the non-volatile organic solvents commonly used in ball-point pen inks.
SUMMARY OF THE INVENTION
The invention features an eradicable ink that can be used, for example, in ball-point pens. The ink contains a colorant, preferably a triarylmethane dye, that changes color (e.g., decolorizes) when contacted with a chemical agent such as a sulfite or an amine. The preferred colorants are soluble in common non-volatile organic solvents used in ball pen ink, like benzyl alcohol, phenyl cellosolve, diethylene glycol, monoethyl ether, dipropylene glycol, glycerin, and/or propylene glycol. Because the colorant can be dissolved in non-volatile organic solvents, the colorant can be incorporated into an eradicable ink that can be used effectively in ball-point pens. The solvent preferably contains essentially no water. Preferred inks containing essentially no water are waterfast and are not prone to dry out. The eradicable ink also has a viscosity, for example, of greater than 10,000 cps at 25° C., and as a result, preferred inks can be used in ball-point pens without significant leakage.
The invention also features the combination of the eradicable ink and an eradicator fluid. The eradicator fluid may include an aqueous solvent and/or a non-aqueous solvent and a chemical agent like a sulfite or an amine that can cause the dye in the ink to change color (e.g., decolorize).
The invention also features triarylmethane dyes that can be used in eradicable inks containing non-volatile organic solvents. The dyes include a counterion—preferably a hydrophobic counterion—that provides the dye with solubility in the non-volatile organic solvents. Examples of preferred counterions include n-alkylpyridinium salts, tetraalkyl ammonium salts, and tetraalkyl phosphonium salts.
The invention also features a method of synthesizing a colorant that is soluble in a selected organic solvent, for example, a non-volatile organic solvent that can be used in a ball-point pen ink, from a colorant that is insoluble in the organic solvent. The starting colorant contains an ionic colorant portion and a counterion. The method includes replacing the counterion in the starting colorant with a counterion that renders the colorant soluble in the organic solvent.
The invention also features a method of synthesizing a water insoluble colorant from a water soluble colorant. The starting colorant contains an ionic portion and a counterion, and the method involves replacing the counterion with a different counterion that is sufficiently hydrophobic to render the colorant insoluble in water.
“Triarylmethane dye”, as used herein, means a dye that includes three aryl groups covalently bonded to a methyl group. Each aryl group may have, for example, a sulfonate group (SO
3
−
) attached.
“Changes color if contacted with a sulfite or an amine”, as used herein, means that the colorant changes to a different color or decolorizes if contacted with a sulfite and/or an amine.
“Insoluble”, as used herein, means that the dye does not dissolve in the solvent in sufficient quantity to cause a significant color change in the solvent.
“Soluble”, as used herein, means that the dye dissolves in solvent in sufficient quantity to cause a significant color change in the solvent at 25° C.
“Eradication system”, as used herein, means that an eradicable ink and an eradicator fluid combination are stored unmixed in the same general packaging. For example, the ink can be in one container and the eradicator fluid in another, but the two containers are included in the same package.
“Non-volatile organic solvent”, as used herein, means an organic solvent that exhibits no appreciable mass loss due to vaporization at up to 100° F. at 1 atm.
“Essentially non-aqueous solvent”, as used herein, means a solvent that contains less than 10% water by weight. Preferred solvents for the eradicable inks contain less than 5% water by weight, more preferably less than 2% water by weight, and most preferably no water.
Other features and advantages of the invention will be apparent from the description of the preferred embodiment thereof, and from the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred eradicable ink contains a non-volatile organic solvent, a triarylmethane dye dissolved in the non-volatile organic solvent, a polymer, and an organic acid. The ink may also include ingredients like surfactants, anti-oxidants, preservatives, etc. It does not contain water.
Enough non-volatile organic solvent should be included in the ink to dissolve the other components and provide the ink with the desired viscosity. Preferred inks have a viscosity of between 10,000 cps and 18,000 cps, and more preferably have a viscosity of between 14,000 cps and 16,000 cps, at 25° C. Preferred inks include between 40% and 80% of the non-volatile organic solvent by weight. Examples of suitable non-volatile organic solvents include benzyl alcohol, phenyl cellosolve, diethylene glycol monoethyl ether, dipropylene glycol, glycerin, and propylene glycol. The non-volatile organic solvent may consist of a single solvent or mixtures of two or more solvents.
The polymer provides adhesion between the ink and the writing surface, and can also be used to adjust the viscosity of the ink. Enough polymer should be included in the ink to provide the desired benefit, but not so much should be included that the viscosity of the ink becomes undesirably high. Inks may include, for example, between 5% and 30% of the polymer by weight. The quantity of polymer used can depend in part on the molecular weight and rheology properties of the particular polymer. Examples of suitable polymers include ketone formaldehyde resins.
The organic acid increases the acidity of the eradicable ink and as a result increases the color intensity of the triarylmethane dye. Examples of organic acids include citric acid and tartaric acid. A sufficient quantity of the organic acid should be included to provide an ink including a dye of the desired intensity. Preferred inks may include between 1% and 3%, and more preferably approximately 2%, of the organic acid by weight.
The triarylmethane dye decolorizes when contacted with a sulfite or an amine. Enough dye should be included in the ink to provide the desired color intensity, but not so much that large quantities of eradicator fluid must be applied to a mark made with the ink to cause it to decolorize. Preferred inks may include between 10% and 45%, more preferably approximately 20% to 35%, and most preferably about 30%, of the triarylmethane dye by weight.
The triarylmethane dye includes a relatively hydrophobic counterion that renders the dye soluble in the non-volatile

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