CA2152546A1

CA2152546A1 - Electrochromatic coloring system

Info

Publication number: CA2152546A1
Application number: CA 2152546
Authority: CA
Inventors: Richard E. Miller; Robert C. Dereamus
Original assignee: Individual
Current assignee: Binney and Smith Inc
Priority date: 1994-07-05
Filing date: 1995-06-23
Publication date: 1996-01-06

Abstract

A coloring system containing an aqueous coloring composition whose coloring effect is changed upon application of an electric current is disclosed. The coloring system comprises a marking instrument containing an aqueous coloring composition whose color may be modified upon application of an electric current; and a source of electric current for modifying the color of said aqueous coloring composition. The aqueous coloring composition may include a PH-sensitive dye or reactants that are oxidized or reduced at an electrode to effect a color change. The electric current may be used either to generate hydroxyl ions, thereby increasing the local pH of the aqueous solution, or to directly oxidize or reduce the reactants of the coloring composition.

Description

215~5g6 ~CTROCEROMIC COT9P~ 8Y8TEM

R~hATBD APP$ICATION8 This application is a continuation-in-part of previous United States Patent Application Serial No. 08/089,503 which was a continuation-in-part of previous United States Patent Application Serial No. 07/923,308 which issued as United States Patent No. 5,232,494 on August 3, lg93. This application is also a continuation-in-part of United States Patent Application Serial No. 08/078,722 which was a continuation of previous United States Patent Application Serial No. 07/923,308 which issued as United States Patent No. 5,232,494 on August 3, 1993.

FI~D OP TH~ l~v~ ON
This invention relates generally to the field of coloring compositions and more particularly to coloring systems containing coloring compositions whose color may be modified upon the application of an electric current.
BAC~GRO~ND OF THB l~.V~ .lON
Children enjoy various drawing and coloring activities using a variety of mediums. Useful in such activities are markers containing inks, crayons, pencils of various colors, and various paints including water colors, oil paints and acrylic paints. However, children would often like to change the color of a mark after they have made the mark.
One instance would be the desire to add a yellow sun over a previously colored blue sky.
Coloring compositions generally are mixtures of a coloring matter dispersed or dissolved in a carrier fluid.
The colorant, if readily dissolving in the carrier fluid, is termed a dye. An insoluble coloring material is termed a pigment. Pigments are finely ground solid materials and the nature and amount of pigment contained in an ink determines its color. Coloring composition may also optionally include 21~254~ -such ingredients as humectants, preservatives, bittering agents, and drying agents. Humectants function to improve freeze/thaw stability and to control drying out of the tip when the coloring composition is used as a marker ink.
Preservatives serve the obvious function of preventing spoilage of the ink during the expected shelf life of the marker product. Drying agents speed drying of a mark laid down by a marker. Bittering agents impart the coloring composition with an unpleasant taste, so that children and animals will not consume the coloring composition.
Changing the color of a mark is not readily done with the typical children's coloring instruments and compositions such as those described. In the past, children changed the marks by placing the mark of one color over the mark of another color. When performing this using traditional marking pens, the marks produced are often not the desired colors and the tips of the markers get soiled with the other inks, rendering the marker useless. If attempted with traditional children's paints, the colors tend to bleed together resulting in undesirable color smears. Therefore, there has been a long felt need for coloring compositions, including markers containing such compositions, which produce marks of a first color that can be readily changed into a wide variety of second colors.
There further exists a need for a marking instrument that is capable of producing marks of various colors from a single instrument. Preferably, the marking instrument sh~uld be able to produce variously colored marks from a single nib, using a single ink reservoir. Although marking instruments capable of creating variously colored marks are known, these instruments include multiple ink reservoirs and multiple nibs or other dispensing devices, thus compounding the complexity of the ink storage and delivery system.
, In one available marker application, a child is able to change a specific initial mark laid down to a second ~152546 specific color by applying a reducing agent to the first mark yielding a change in color. The marker inks used in these markers are typically prepared by blending a reducing agent (sometimes termed a bleaching agent) or pH sensitive dye with a dye that is stable in reducing agent or high pH.
For example, German Patent Specification No. 2724820 (hereinafter "the German Patent") concerns the combining of a chemically stable dye and a chemically unstable dye in an ink formulation. Once a mark using this combination of stable and unstable dyes is laid down, the mark may be overwritten with a clear reducing agent solution, eliminating the color contribution of the unstable dye. The resulting mark of the stable dye, with its characteristic color, remains.
There are several drawbacks to such a marking system.
First, there are strict limitations on the number of color changes which may be produced. Specifically, in formulations made according to the German Patent, the particular ink composition may only be changed from a first color to a fixed second color. For example, a green mark may only be changed to a violet color as the inks are described in the practice of the German Patent. In addition, since one of the required pair of markers contains only the reducing agent, that reducing agent marker cannot render a visible mark and may only be used in combination with the base color marker. Once the base color marker is used up, the reducing agent marker is of no use. Or, once the reducing agent marker is used up, the base color marker may only be used for the color which it initially marks with. A further disadvantage of the marking process of the German Patent is that the nib of the reducing agent marker tends to get soiled by picking up the colors of the base coloring composition, thus tainting the color of subsequent marks.

215254~

Therefore, an object of the present invention is to provide a coloring composition system which is capable of enhanced multiple color changing abilities.
A further object of the present invention is to provide a coloring system including a marking instrument that is capable of producing a plurality of colors utilizing a single ink reservoir and single nib.
These and other objects will become apparent to those skilled in the art to which the invention pertains.
8VMMARY OF T~ Ih~ ON
The present invention overcomes the drawbacks associated with prior coloring systems in that the particular coloring composition made according to the invention may be changed to multiple second colors, depending upon the dye present in the coloring composition employed in the coloring system. According to the present invention, the color of the coloring composition is modified by using an electric current.
In general, the present invention is a coloring system whose coloring effect may be changed by using an electric current. The coloring system comprises:
(a) an aqueous coloring composition whose color may be modified upon application of an electric current;
(b) a source of electric current for modifying the color of said agueous coloring composition; and (c) means for applying said electric current to said coloring~composition.
In a preferred embodiment, the coloring system comprises:
(a) a marking instrument including an aqueous coloring composition whose color may be modified upon application of an electric current;
(b) a source of electric current; and ~1~2~6 tc) means for applying the electric current to the aqueous coloring composition.
The agueous coloring composition may comprise, for example, a pH-sensitive dye whose coloring ability is destroyed or modified in the presence of a pH of about 10 or greater, or may include reactants that are oxidized or reduced at an electrode to effect a color change.
In one emhoAiment of the present invention, the source of electric current may be a battery contained within the marking instrument, or may be a snap-on power device, such as a battery or AC/DC adaptor. In another embodiment of the present invention, the coloring system includes a marking instrument containing a suitable aqueous coloring composition and an external electrode in the form of a receptacle. The marking instrument may be used in the same manner as a conventional marking instrument. When a color change is desired, the user briefly inserts the nib of the marking instrument into the receptacle, thereby effecting a color change of the coloring composition in the marking instrument.

BRIFF DESCRIPTION OF T~E DRA~ING8 Fig. 1 is a schematic illustration of a coloring system according to the present invention in the form of a marker including an internal power source.

Fig. 2 is a schematic illustration of a coloring system according to the present invention in the form of a marker having internal electrodes for use with an external power source.

Fig. 3 is a perspective view of a two-pointed nib useful in the coloring system of the present invention.

Fig. 4 is a top elevational view of the two-pointed nib illustrated in Fig. 3.

Fig. 5 i8 a first alternative cross-sectional view of the two-pointed nib illustrated in Fig. 3. taken along line 4-4 in Fig. 3.

Fig. 6 is an exploded view of a coloring system according to the present invention including an external power source and external electrodes.

Fig. 7 is a top plan view of the external electrode illustrated in the coloring system shown in Fig. 6.

lS Fig. 8 is a cross-sectional view of the external electrode illustrated in Fig. 7. taken along line 8-8 in Fig. 7, further illustrating contact between the nib of a marking instrument and the external electrodes.

Fig. 9 is a second alternative cross-sectional view of the two-pointed nib illustrated in Fig. 3. taken along line 9-9 in Fig. 3.

Fig. 10 is a perspective view of a chisel nib useful in the coloring system of the present invention.

Fig. 11 is a top elevational view of the chisel nib illustrated in Fig. 10.

Fig. 12 is a first alternative cross-sectional view of the chisel nib illustrated in Fig. 11. taken along line 12-12 in Fig. 10.

Fig. 13 is a second alternative cross-sectional view of the chisel nib illustrated in Fig. 10. taken along line 13--2152~4~ -13 in Fig. 10.

D8TaI~D ~88CRIPTION OF T~8 INV8NTION
The present invention imparts the desirable ease of application and convenience of use of traditional color changer systems while avoiding the strict limitations of current color change markers. The coloring system of the present invention therefore imparts improved and convenient coloring properties. A coloring system according to the present invention comprises a marking instrument containing an agueous coloring composition whose color may be modified upon application of an electric current, a source of electric current for modifying the color of the aqueous coloring composition, and means for applying the electric current to the aqueous coloring composition. The coloring composition may be in any suitable form, such as a paint or an ink. Preferably, the coloring composition is provided in the form of an ink.
Typically, an ink suitable for use in a marker comprises a colorant, such as a pigment or dye, in an agueous carrier. With reference to the agueous coloring composition, it is only necessary that the coloring composition be one whose color may be modified upon application of an electric current. To achieve the color-changing effects, the ink should include as a colorant atleast one dye that is color-sensitive to pH, or should include reactants that may be directly oxidized or reduced at an electrode using an electric current to effect a color change. When the dye is a pH-sensitive dye, the electrolysis of water according to the following reaction provides the driving force behind the color change:

2H2O + 2 e H2 + OH-~1~2546 Thus, the electric current is used to generate hydroxyl ions at the cathode, thereby increasing the local pH of the ink composition and causing the dye to change color.
Any dye or indicator that changes color as pH increases may be used in the aqueous coloring compositions of the present invention as a pH-sensitive dye. For example, dyes and indicators that change color or become colorless as pH
increases may be used. Especially suitable for use as pH-sensitive dyes in the aqueous coloring composition are those polymethine dyes, triphenylmethane dyes, cyanine dyes, methine dyes, and azo dyes which are unstable in the presence of a pH of about 10 or greater. Such dyes include the dyes marketed under the tradenames BASACRYL X-RL yELLowr (Basic Yellow 49), marketed by the BASF Corporation, ASTRAZON BLUE FRR~ (Basic Blue 69), ASTRAZON BRILLIANT RED
4G~ (Basic Red 14), and ASTRAZON PINX FBB~ (8asic Red 49) by ~iles(Mobay); and the dyes marketed under the tradenames Acid Green 3 by International Dyestuffs Corporation, Acid Blue 93 and Acid Violet 19 marketed by Spectra Color Corporation as well as mixtures thereof. Further useful in the aqueous coloring compositions are dyes such as Direct Yellow 4, manufactured by Crompton & Xnowles (changing from yellow to red at high pH); PYRANINE 120~ marketed by Miles(Mobay), and phenolpthalien.
Dyes such as Acid Violet 19, Acid Blue 93, Acid Green 3, Basic Red 14, and Basic Yellow 49 have the effect of becoming colorless at high pH, whereas Pyranine 120 changes from colorless to fluorescent yellow. Direct yellow 4 changes from yellow to red at high pH, and phenolpthalien changes from colorless to red at high pH. Thus, for example, a coloring composition may include Pyranine 120 and Acid Blue 93. This composition would initially be blue.
However, upon the application of an electric current, the increase in local pH surrounding the electrode would cause the color of the composition to change from blue to 2152~46 fluorescent yellow.
The listed ASTRAZON dyes are classified as polymethine dyes. Polymethine dyes are colored substances in which a series of -CH= (methine) ~GU~ connect to terminal groups of a chromophore. Polymethine and cyanine are often used interchangeably as generic terms for all polymethine dyes.
The previous primary usage for polymethine dyes are dying acetate rayon as well as polyacrylonitrile and polyacrylamide. Acid Green 3, Acid Blue 93 and Acid Violet 19 are triphenylmethane dyes. Acid Green 3 is commonly used in making pulp colors or lakes. Acid Violet dyes are primarily fashion colors.
In addition to dyes that change color in response to a high pH, the aqueous coloring composition may include reactants that are oxidized or reduced by an electric current to effect a color change. For example, many dyes or indicators may be directly oxidized or reduced at an electrode to thereby effect a color change. Dyes that change color when oxidized or reduced are sometimes termed ~redox dyes. n In addition, the solution may contain other reactants that may be oxidized or reduced at an electrode to effect a color change. For example, the solution may contain potassium iodide and starch. Iodine is oxidized at the anode to form free iodine, which reacts with the starch to form a dark blue color.
The following table lists a number of redox dyes, their redox potential, and their colors in the oxidized and reduced states.

TABLE

S INDICATOR R~vu~ OXIDI~D ~
Indigo monosulfonate Colorless Blue 0.26 Phenosafranine Colorle6s Blue 0.28 Methylene blue Colorle6s Green-~lue 0.36l-Naphthol-2-6ulfonlc acid indophenol Colorles6 Red 0.54 3,3'Dimethylnapht~ ne Colorle~6 Red-Purple 0.71Diphenylamine Colorles6 Violet 0.76 3,3'Dimethylnaphthadine sulfonate Colorle6s Red-Purple 0.80Diphenylamine sulfonic acid Colorle~s Violet 0.84 15 N,N'-Tetramethylbenzidine-3-~ulfonic acid Colorles~ Yellow . 0.88 Ferrous 2,2'-bipyridine sulfate Red Blue 0.97 Erioglaucine A Red Green 1.00 Ferrous 5-methyl-1,10-phenanthroline Red Blue 1.02 sulfonate Ferrous 1~10-phQnanthroline (ferroin) Red Blue 1.06p-Nitrodiphenylamine Colorless Violet 1.06Ferrous 5-nitro-1,10- Red Blue 1.25 phenanthroline(nitroferroin) Ruthenium tridipyridine dichloride Colorless Yellow 1.33 In addition to the color-changing dye, a color-stable colorant, i.e., a colorant whose coloring ability is not modified upon application of an electric current, may be used in the aqueous coloring composition to obtain final coloring composition colors that are a result of the combination of the color-changing dye and the color-stable colorant. With respect to dyes, a limited number of dye colorants meet this criteria. Color-stable dyes to be used in the coloring composition must be highly resistant to chemical attack such as from an electric current or high pH
conditions. Specific dyes meeting this criteria include those xanthene dyes, pthalocyanine dyes, and azo dyes which are stable in the presence of a pH of about 10 or greater.
Specific suitable dyes which have been found to meet these criteria include, for example, Acid Red 52, a colorant for plastics marketed by Carolina Color. In addition, Food Red 14, also known as FD&C Red No. 3, is commercially available under the tradenames Erythrosine and Erythrosine Bluish and marketed by Hilton-Davis, and may be used. Food Red 14 is the disodium salt of 9(o-carboxyphenyl)-6-hydroxy-2,4,5,7-tetraiodo-3H-xanthen-3-one, which contains smaller amounts of lower iodinated fluoresceins. BASANTOL GREEN
910~ marketed by BASF is another suitable dye. Acid Red 87 marketed by Hilton-Davis, Acid Red 92 marketed by International Dyestuffs Corporation, Acid Red 388 and Direct Blue 199 marketed by Crompton & Knowles may further be used.
Acid Red dyes, classified as xanthene dyes, are generally used as colorants for foods, drugs and cosmetics.
Specifically, Acid Red 87, is the disodium salt of 2,4,5,7 -tetrabromo-9-o-carboxyphenyl-6-hydroxy -3-isoxanthone. Acid Red 87 is also called D ~ C Red No. 22 by the Food and Drug Administration ("FDA"), and sold under the tradenames Eosine YS and Eosine G. In addition, Acid Red 92, the disodium salt of 2,4,5,7-tetrabromo-9-3,4,5,6 tetrachloro-o-carboxylphenyl)-6-hydroxy-3-isoxanthone, is called D & C Red No. 28 by th~ , and sold under the tradename Phloxine B.
Mixtures of any of the foregoing dyes, as well as any suitable other color-changing dyes or indicators may be used.
To achieve good coloring of the aqueous coloring composition, the minimum concentration of dye which will produce a workable ink is governed by the color intensity desired, though as little as 0.1% dye may be sufficient for certain applic~tions. The maximum workable concentration of dye is determined largely by the ability to maintain a stable composition and the depth of color desired and can vary widely depending upon the concentration of other components. It is also a function of the characteristics of the desired end product, though a practical upper limit in lS the formulatior; of, for example, a marker ink, is about 15%
by weight. The preferred concentration range for most applications is from about 1% to about 6% dye by weight of the composition. A concentration of about 1.5% to about 4%
is even more preferred when the aqueous coloring composition is to be used as an ink for a typical marker to ensure good coloration.
In addition, pigments may be used as excellent color-stable colorants in the coloring compositions of the invention. To achieve good coloring of the coloring composition and promote compatibility with the remaining ink components, the pigment is utilized in the form of an aqueous dispersion, inasmuch as pigments are by definition insoluble materials. Aqueous pigment dispersions are commercially a~ailable which are combinations of a pigment, and a surfactant or dispersant system. A pigment dispersion may also be prepared specifically for use in the overcolor coloring composition of the invention. From the standpoint of convenience, a commercial pigment dispersion is preferred for use in the present invention. Typical commercial dispersions contain 30 to 74% by weight active pigment 2~5~S46 ingredients.
In general, a workable pigment dispersion may have a wide or narrow particle size range depending upon the use to which the ink will be put. The lower limit on pigment particle size is determined not by any functional characteristic of the aqueous coloring composition, but by the ability to form a stable dispersion. Similarly, the upper limit on pigment particle size is determined by the type of applicator by which the aqueous coloring composition is to be applied or dispense~, since pigment particle size determines the ability of pigment particles to flow through, for example, the matrix of a marker nib where the coloring composition is in the form of an ink.
Indeed, relatively larger pigment particles can restrict ink flow through many types of nibs utilized in the instruments of the present invention, ultimately rendering them inoperable. Larger particle sizes may, however, may be used where the aqueous coloring composition is to be used in, for example, a paint marker, in which the composition is dispensed through a valve assembly, or in a roller ball pen or where there composition is used in the form of a paint and a brush is used to distribute the coloring composition.
Pigments having a mean particle size range from about 0.05 to about 2.0 microns have been found to work well in compositions of the invention.
In choosing the most suitable pigment particle size when coloring compositions of the invention are to be used in the form of, for instance, an ink, one must be guided by the partic~ ar nib type to be utilized in the marking instrument in which the ink will be placed. A pigment particle size must be selected which will allow the passage of the composition through the nib being used. Further, the pigment particle size should be selected to promote capillary flow through the particular nib being used in the marking instrument. In general, the size of pigment particles should be kept as low as possible while maintaining the stability of the composition. For example, it has been found that an ink to be utilized in a marking instrument having either a porous plastic nib or a bonded fiber nib, an ultra fine pigment dispersion having a mean particle size in the range of from about 0.05 to about 0.5 microns provides acceptable results. A more preferred ultra fine pigment dispersion for such applications has a mean particle size in the range from about 0.05 to about 0.25 microns, since such a dispersion promotes better wicking or capillary flow through the nib. Examples of suitable pigment dispersions, which are especially suited for compositions of the invention used in the form of an ink include Hostafine Rubine F6B (C.I. Pigment Red 184 dispersion), Blue B2G (Pigment Blue 15-3) and Black 7 (Pigment Black T), marketed by Hoescht Celanese Corporation under the tradename "Hostafines Dispersionsn.
The minimum concentration of pigment which will produce a workable coloring composition is governed by the color intensity desired, though as little as 0.1% active pigment may be sufficient for certain applications. The maximum workable concentration of pigment is determined largely by the ability to maintain a stable composition, and can vary widely depending upon the concentration of other components.
The maximum concentration of pigment usable is also a function of the characteristics of the desired end product, though a practical upper limit in the formulation of the agueous coloring composition used, for example, as a marker ink, is about 30% by weight since higher concentrations may cause ink instability and undesirably high viscosity.
When a commercial pigment dispersion is utilized, as it preferably is, a practical limit is imposed by the concentration of pigment in the dispersion, which, as previously noted, is typically in the range of about 30% to 74% pigment by the weight of dispersion. The preferred -21525~

concentration -ange for most applications is from about 1%
to about 10% active pigment by weight of the composition. A
concentration of about 3% by weight of active pigment is ordinarily required to ensure good coloration in a typical marker ink and most preferred is a concentration of active pigment in a concentration range of about 1.5% to about 5%
by weight of the composition.
Optionally, two ~r more colorants may be used in the marking instrument. For example, two or more color-changing dyes may be incorporated into the aqueous coloring composition. Alternately, the color-changing dye may be blended with one or more color-stable colorants. Indeed, any possible combination of color-stable and color-changing dyes may be incorporated into the agueous coloring composition used in the coloring system of the present invention. It is only necessary that the color of the coloring composition be modifiable upon application of an electric current. Preferably, the coloring composition is modifiable from a first color to a second color upon the application of an electric current. However, the coloring composition may also be formulated such that it changes from a colored composition to a colorless composition upon application of an electric current. Similarly, the composition may be formulated such that it changes from a colorless composition to a colored composition upon application of an electric current.
Where the coloring composition contains two or more dyes that may be directly oxidized or reduced, the coloring system may ~nclude a potentiometer or other means for regulating the voltage applied to the coloring composition.
If the dyes have different redox potentials, then the effect of applying electric current at different potentials will be to allow the coloring composition to undergo a plurality of color changes. A single coloring composition may then be used to provide a number of colors, by adjusting the voltage -21~i2S~6 applied to the coloring composition.
The water used in the aqueous coloring composition of the present invention is preferably deionized water. The amount of water present in undercolor coloring compositions is typically from about 10% to about 90% and this amount is in large part determined by the amount of other components included in the undercolor color composition. To achieve a desirable viscosity when the coloring composition is used in the form of, for example, an ink, water is preferably present in an amount of from about 20% to about 80%, and most preferably from about 45% to about 60% by weight of the composition.
Optionally, the aqueous coloring composition may further comprise such additives as humectants, drying agents, bittering agents, preservatives such as biocides and fungicides, and conduction-enhancing agents. Preferably, the coloring composition does not include a base or other reducing agent.
Addition of a humectant ensures that coloring compositions of the invention, when in the form of an ink, do not prematurely dry in a capillary marking system, such as a bonded f~er marking nib. Typical humectants which may be employed in the coloring compositions of the present invention include polyhydric alcohols such as ethylene glycol, propylene glycol, hexylene glycol and poly(ethylene glycol), and hydroxylated starches. The humectant is preferably glycerin.
The-humectant is generally used in an amount of from about 0% to ~ ut 30% by weight of the composition, though this range is by no means critical. The amount of humectant to be added is determined by the type of nib used in the marking instrument to be employed and the protection time period desired. In one preferred composition, the humectant, glycerin, is added in an amount of from about 15%
to about 25% by weight of the coloring composition.

21~54~

To achieve a more rapid drying rate and to improve marking characteristics upon nonporous materials, a drying agent may be added to increase the overall volatility and therefore the evaporation rate of the water and the pH
regulant. Any compatible material which performs this function may be used. The drying agent should be added in an amount ranging from 5% to about 20% by weight of the composition, as determined by the overall formulation of the composition. Of course, this range is by no means critical.
The drying agent preferably should be a volatile polar material so as to ensure compatibility with the primary components of the marker ink. Straight chain C2-C4 alcohols are good, highly volatile drying agents, and of these, ethanol is preferred because of its relatively low cost and because it does not contribute any unpleasant odor to the composition. Alcohols can also provide added benefits, such as reducing surface tension, increasing adherence of the ink to porous surfaces, and providing bactericidal activity when added to the ink composition.
To discourage improper usage of the marker ink, such as ingesting the ink, the alcohol may contain a bittering agent or a conventional denaturant. An alcohol utilizing a bittering agent will discourage such improper usage of the ink by simply imparting a disagreeable taste, while not requiring the use of toxic denaturants as methanol or benzene, and is therefore preferred. A conventional denatured alcohol may, of course, also be utilized. The most preferred drying agent is an ethyl alcohol which contains a bittering agent and which is sold under the trade name SDA 4OB, manufactured by Aaper Alcohol.
When utilized, the drying agent preferably is added from about 5% up to about 30% by weignt, with the most preferred concentration being about 8-10% by weight, though these amounts are not critical to the practice of the lnvention. About 8% per weight of drying agent is 21525~

ordinarily required to ensure rapid drying of the ink on a nonporous surface, while amounts in excess of about 30% by weight may adversely affect stability of the ink and may cause flocculation of the pigment unless other stabilizing additives are employed.
To maintain the shelf life of the composition, a preservative may be added. The preservative preferably serves as both a bactericide and a fungicide, and is added in any effective amount, though a typical concentration range is from about 0.1% up to about 5.0% by weight. The use of preservatives in levels greater than about 5% by weight may cause the ink to become toxic or unstable and may, in any event, be unnecessary. Should alcohol be added to the composition as a drying agent, that alcohol will function as a preservative to some extent also.
Any conventional preservative may be utilized in the invention as long as there is compatibility with the remaining ink components. For example, preservatives manufactured by Dow Chemical Co. and sold under the trademarks Dowicil 75 (1-(3-chloroallyl)-3,5,7-triaza-1-azoniaadamantane chloride) and Dowicil 200 (3-chlorovinyl-hexamethylene tetrammonium chloride) or a preservative manufactured by Rohm and Haas and sold under the trademark Kathon PFM (isothiazolinones), or a preservative manufactured by Sutton Labs and sold under the trademark Germall II (imazolidinyl urea), or a preservative manufactured by Merck and sold under the trademark Tektamer 38 (1,2 dibromo-2,4-dicyanobutane), will work in the composition of the invention.
Other acceptable preservatives include TROYSAN
POLYPHASE P100~, a 3-Iodo-2-Propynyl Butyl Carbamate sold by Troy Chemical and which is commonly solubilized in PVP X-30~, a 2-Pyrrolidinone, l-Ethenyl-, Homopolymer solubilizer ((C~gNO)~ sold by ISP Technologies Inc., and M-PYROL~, a 1-~1~2546 Methyl-Pyrrolidinone solubilizer sold by GAF Chemicals Corporation. Addition of preservatives to the coloring compositions inhibits the growth of bacteria and fungi in water-based products.
To enha~ce the conductivity of the ink, a conduction-~n~ncing agent should further be added. Preferably, the conduction-enhancing agent is a water-soluble salt. The specific salt chosen is not critical. Preferably, a pH-neutral salt is used as the conduction-enhancing agent; most preferably, sodium sulfate (Na2SO~) is used. The conduction-enhancing agent preferably is present in an amount ranging from 0-10%; most preferably, it is present in an amount of about 5%.
The coloring system of the present invention further includes a source of electric current and means for applying the current to the coloring composition. With regard to the source of electric current, the selection of this source is by no means critical, and any suitable source of direct current may be used. For example, the source of electric current may be a battery. Alternately, the source of electric current may be an AC/DC adaptor or converter.
Preferably, the source of electric current is of sufficiently low power to be safely usable by children. The power source should produce current at a low voltage, such as from 1 to 12 volts. For example, commonly available household batteries may be used in the coloring system of the present invention, as well as batteries used in such devices a-s watches.
With reaard to the means for applying the electric current to ~_ aqueous coloring composition, any suitable means may be used. Preferably, however, the means for applying the current to the coloring composition includes a pair of electrodes. For example, the coloring composition may be applied to a substrate, such as a sheet of paper, and 21525~6 one or more electrodes may be attached to the substrate to effectuate a color change of the coloring composition. In the preferred embodiments of the present invention, the coloring system takes the form of a marking instrument.
Most preferably, the coloring system is in the form of a marker, as illustrated in the Figures.
As generally defined in the art, a marker comprises a handle, a reservoir for storing a coloring composition, and a wicking nib in fluid communication with the fluid reservoir. With reference to Fig. 1, the coloring system 10 comprises a marker 12 having a battery 14, a handle 18, a fluid reservoir 16 having a proximal end and a distal end, and a nib 20 located at the proximal end of the fluid reservoir 16 and in fluid communication with the fluid reservoir 16. Internal electrodes 22, 24 are included in the nib 20 and the fluid reservoir 16. Preferably, the positive electrode 24 is included at the distal end of the fluid reservoir 16, and the negative electrode 22 near the tip of the nib 20. A switch 26, which is preferably a push-button switch, controls the flow of current to the coloring composition. Optionally, means for regulating the voltage applied to the coloring composition may be included. For example, as illustrated in Fig. 1, a potentiometer 28 may be used as a voltage regulator.
Fig. 2 illustrates a second embodiment of the coloring system of the present invention. In this embodiment, the marker 12 includes a socket 30 for receiving power from an external power source 32. The external power source 32 may be, for examrie, a battery or an AC/DC adaptor of the type commonly used for childrens' toys. A potentiometer or other voltage regulator may also be included with the external power source 32, or may be included within the marker 12.
The external power source 32 may be connected to the marker 12 by means of a snap-on connection device (not shown).
35 ~ The fluid reservoir 16 of the marker 12 may be designed 21S2~6 in any suitable fashion. As is well-known in the pertinent art, a fluid reservoir may contain a transorb, i.e., an absorbent body that is inserted into the fluid reservoir and which contacts the nib to effectuate a fluid connection between the nib and the reservoir. In the context of the present coloring systems, the transorb is preferably made of polyester or polypropylene fibers.
The nib 20 may be made of any suitable capillary material. Suitable materials include felt nibs, bonded fiber nibs, and sintered plastic nibs. Preferably, the nib is made from sintered ultra high molecular weight polyethylene powder. To increase the surface area and conductivity within the nib, a fibrous material, such as carbon fibrils available from Hyperion Catalysis International, or silver-plated polyester fibers may be incorporated into the nib.
As shown in Fig. 3, the nib 20 has a fluid receiving end 42, in contact with the fluid reservoir 16, and a fluid dispensing end 44. Where the nib incorporates a self-contained or internal electrode 22, the electrode is preferably inserted into the nib close to the fluid dispensing end 44.
The nib can be designed in any suitable fashion. With respect to the shape of the nib, the nib may have the shape of a chisel or other suitable shape. For example, Figs. 10-13 illustrate a nib having a chisel or wedge design. Nibs having a plurality of points are conventionally known, and are further useful in the coloring systems of the present inventioh. Figs. 3-5 and 9 illustrate a nib having two points.
If external electrodes are used as the means to apply electric current to the nib, no electrode need be present in the nib. If the electrodes are contained within the marking instrument, one or more electrodes may be contained on or within the nib. The electrode may optionally be insulated such that electric current flows only from one point on the - 21525~6 electrode, such as the tip. For example, when a two-pointed nib i8 used, the nib may contain one electrode, as illustrated in Figs. 1, 2, and 5. The other electrode would be positioned at the distal end of the fluid reservoir, as illustrated in Figs. 1 and 2. Application of an electric rent to the coloring composition would cause the color of the coloring composition in the first point 46 to change, as illustrated in Fig. 5. Alternatively, two electrodes may be positioned within the two-pointed nib, as illustrated in Fig. 9. Thus, for example, a positive and a negative electrode may be positioned within the nib. Using such an arrangement, two different colors can be produced using a single nib. Alternately, the components of the coloring composition can be chosen such that, in using a double-pointed nib, one point of the nib makes a mark that theother point of the nib can erase. Alternatively, a multi-pointed nib can be used with one or more electrodes to produce a plurality of colors at the nib.
Where the nib is a chisel nib, as illustrated in Figs.
10-13, the nib may further contain one or more electrodes.
For example, if the nib contains a positive and a negative electrode, as illustrated in Fig. 13. Especially if the nib is canted, the change in color of the coloring composition may be observed along the width of the mark produced by the marking instrument. Particularly if the coloring composition contains a color-stable dye along with a color-changing colorant, the visual effect of this change is striking, and provides great enjoyment value for a child.
Of course, the chisel nib need not contain two electrodes.
For example, as illustrated in Fig. 12, the chisel nib may contain one electrode.
Figs. 6-8 illustrate a third embodiment of the coloring system of the present invention. The external electrodes 34, 36 are connected to a power source (not shown), and, optionally, a voltage regulator such as a potentiometer (not - 21~2546 shown). Preferably, the external electrodes 34, 36 are contained within a housing 38. No electrodes need be present within the marker 12. When the user desires to change the color of the coloring composition, the user inserts the marker 12 into funnel 40, thus guiding the nib 20 to the position illustrated in Fig. 8. Current flows through the coloring composition, thus effectuating a color change.
In employing the embodiment illustrated in Figs. 6-8, the user may thus use the marker in the same manner as an ordinary marker would be used. If a color change is desired, the user briefly inserts the marker into the housing 38, thus causing the coloring composition at the tip of the nib 20 to change color. The external electrodes thus simulate an "inkwell" as the ink is changed to a colored ink, thus ~nhA~cing the play value of the coloring systems for a child.
The following Examples illustrate coloring compositions suitable for use in the coloring systems of the present invention. These examples are presented for illustration purposes, and are not to be construed as limiting the scope of the present invention.

E~AMPLE~
Examples of coloring compositions of the present invention when formulated as an ink are as follows.
Quantities are in percent by weight of the total composition.

2i~4~

Example 1 Example 2 Blue Ink Red Ink Component % %
Deionized Water 73.60 72.07 Glycerin 24.20 24.48 Preservative Germall II 0.70 045 Dye Basic Blue 69 1.50 ----Basic Red 14 ---- 3.00 Example 3 Example 4 Violet Ink Blue Ink Component % %
Deionized Water 70.5 70.7 Glycerin 24.5 24.5 Preservatives Nuosept 95 0.5 0.3 Troysan Polyphase P-100 0.05 0.05 PVP-K30 0.05 0.05 M-Pyrol 2.4 2.4 Dye Acid Violet 192.0 ----Basic Blue 69 ---- 2.00 Example 5 Example 6 Blue Ink Yellow Ink Component % %
Deionized Water 70.5 70-5 Glycerin 24.5 24.5 Preservative Nuosept 95 0.5 0.5 Troysan Polyphase P-100 0.05 0.05 PVP-K30 0.05 0-05 M-Pyrol 2.4 2.4 Dye Acid Blue 93 2.00 ----Basic Yellow 49 ---- 2.00 The inks of examples 1 through 6 had acceptable working properties. For examples 1 through 6, the pH ranged from 2 ~o 7 and the density ranged from 8.5 to 9.1 pounds per 2~52546 gallon. For examples 1 through 6, the viscosity ranged from 1.5 to 3 centipoise. Because these coloring compositions turn clear at high pH, they are suitable as coloring compositions within the meaning of the present invention.
Addition of a color-stable compound to the inks of Examples 1-6 would create coloring compositions that change from a first color to a second color upon the application of an electric current. Addition of sodium sulfate to the inks of Examples 1-6 would improve the conductivity of these inks.
Exzmple 7 % BY Wei~ht Water 69.67 Glycerine 23.23 Acid Violet 19 1.0 Pyranine 170 1.0 Sodium Sulfate 5.0 Preservative 0.1 The ink of Example 72 has a pH of about 7 when formulated. Because Pyranine 120 is essentially colorless at this pH, the ink has a magenta color. When an electric current is applied, sodium hydroxide is produced at the cathode. The high pH causes the Acid Violet 19 to become colorless, and, at the same time, the Pyranine 120 develops into a fluorescent yellow color.

Example 8 % By Weight Water 68.7 ~ Glycerine 23.0 Acid Blue 93 1.0 Acid Yellow 17 2.0 Sodium Sulfate 5.0 Preservative 0.3 The ink of Example 8 turns from green to yellow due to reduction of the Acid Blue 93 at the cathode. If a chisel - 21~2546 nib is used with two electrodes, the gradual change from blue to yellow can be observed along the width of the mark made by the marking instrument.

Example 9 % 8y ~eight Water 69.7 Glycerine 23.0 Direct Yellow ~4 2.0 Sodium Sulfate 5.0 Preservative 0.3 The ink of Example 9 turns from yellow to red upon application of an electric current. The marking system illustrated in Fig. 12 could deliver red and yellow lines from different sides of the same nib.
Example 10 % By Wei~ht Water 70.2 Glycerine 23.0 Basic Red 14 1.5 Sodium Sulfate 5.0 Preser~ative 1.0 Use of the ink of Example 10 is a dual-tipped nib would result in a nib in which one tip produces a mark and the other tip eradicates the mark.
Thus, a coloring system including a marking instrument that is capable of producing a plurality of colors utilizing a single ink reservoir and single nib is provided by the present invention. The coloring system may be used in conjunction with the underwriters and overwriters disclosed in United States Patent Applications Serial No. 08/089,503 and 08/078,722 and United States Patent No. 5,232,494. For example, the coloring system may serve as an underwriter before the color of the coloring composition has been ohanged with an electric current. Alternately, the coloring - 21~2~4~ .

system may be used as an overwriter after the color of the coloring composition has been changed with an electric current, provided that the pH of the coloring composition is sufficiently high.
While only certain embodiments of the coloring systems of the present invention have been set forth, alternative embodiments and various modifications will be apparent to those skilled in the art. For example, a marking instrument containing a reversible electrical system whereby the anode and cathode may be reversed thereby causing the color change to reverse could be designed. These and other alternatives are considered equivalents and within the spirit and scope of the present invention. All references and previous patent applications cited herein are hereby incorporated by reference in their entireties.

Claims

1. A coloring system comprising:
(a) a marking instrument containing an aqueous coloring composition whose color may be modified upon application of an electric current;
(b) a source of electric current for modifying the color of said aqueous coloring composition; and (c) means for applying said electric current to said aqueous coloring composition.

2. A coloring system according to claim 1, wherein said aqueous coloring composition contains a compound selected from the group consisting of a pH-sensitive dye and a reactant that is oxidized or reduced at an electrode to effect a color change.

3. A coloring system according to claim 2, wherein said aqueous coloring composition contains a pH-sensitive dye.

4. A coloring system according to claim 3, wherein said pH-sensitive dye changes color upon an increase in pH.

5. A coloring system according to claim 4, wherein said pH-sensitive dye is selected from the group consisting of polymethine dyes, triphenylmethane dyes, cyanine dyes, methine dyes, and azo dyes which are unstable in the presence of a pH of about 10 or greater.

6. A coloring system according to claim 4, wherein said pH-sensitive dye is selected from the group consisting of Basic Yellow 49, Basic Blue 69, Basic Red 14, Basic Red 49, Acid Green 3, Acid Blue 93, and Acid Violet 19.

7. A coloring system according to claim 2, wherein said aqueous coloring composition contains a reactant that is oxidized or reduced at an electrode to effect a color change.

8. A coloring system according to claim 7, wherein said reactant is a dye.

9. A coloring system according to claim 8, further comprising a humectant.

10. A coloring system according to claim 9, further comprising a drying agent.

11. A coloring system according to claim 7, wherein said reactant is not a dye.

12. A coloring system according to claim 11, wherein said reactant is iodine ion.

13. A coloring system according to claim 2, further comprising a conduction-enhancing agent.

14. A coloring system according to claim 13, further comprising a dye that is stable upon application of an electric current.

15. A coloring system according to claim 13, further comprising a humectant.

16. A coloring system according to claim 13, further comprising a drying agent.

17. A coloring system according to claim 13, further comprising a preservative.

18. A coloring system according to claim 1, wherein said source of electric current is a battery.

19. A coloring system according to claim 18, wherein said battery is contained within said marking instrument.

20. A coloring system according to claim 1, wherein said source of electric current is an AC/DC adaptor.

21. A coloring system according to claim 1, wherein said marking instrument terminates at a nib.

22. A coloring system according to claim 21, wherein said nib has a plurality of points

23. A coloring system according to claim 21, wherein said nib is a sintered ultra-high-molecular-weight polyethylene nib.

24. A coloring system according to claim 21, wherein said nib is a chisel nib.

25. A coloring system according to claim 21, wherein said means for applying said electric current to said coloring composition comprises a first electrode and a second electrode, wherein said first and second electrodes are separated by a gap, wherein the width of said gap is less than the width of said nib.

26. A coloring system according to claim 21, wherein said means for applying said electric current to said coloring composition comprises a first electrode and a second electrode, wherein said first electrode is contained within said nib.

27. A coloring system comprising:

(a) an aqueous coloring composition whose color may be modified upon application of an electric current;
(b) a source of electric current for modifying the color of said aqueous coloring composition; and (c) means for applying said electric current to said coloring composition.