Time-Color Indicators

Europaisches Patentamt 0 309 173 J European Patent Office (") Publication number: A2 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 88308644.9 mt. CIA G01 N 31/22 © Date of filing: 19.09.88 © Priority: 23.09.87 GB 8722379 0 Applicant: S.C. JOHNSON & SON, INC. 1525 Howe Street @ Date of publication of application: Racine, Wisconsin 53403(US) 29.03.89 Bulletin 89/13 @ Inventor: Kelly, Petrina Mary © Designated Contracting States: 8 Paul Court Hythe Park Road AT BE CH DE ES FR GB GR IT LI LU NL SE Egham Surrey. TW20 8DG.(GB) Inventor: Berrido, Colin No.10 Gloucester Gardens Bagshot Surrey. GU19 5NU.(GB) © Representative: Baillie, lain Cameron et ai c/o Ladas & Parry Isartorpiatz 5 D-8000 Munchen 2(DE) © Time-color indicators. © Disclosed are end point indicator compositions and devices containing them, particularly useful as air freshener devices, comprise compositions containing a polar indicator dye which assumes a first color or is colorless in the presence of a room temperature volatilizable solvent which is initially present in excess and a small amount of a proton donating compound. The indicator dye assumes a second color visually distinct from the first color in the presence of the proton donating compound after the majority of the solvent escapes from the remainder of the composition. Optionally, the compositions further include color change developers and/or secondary dyes to render the change to the second color, indicating attainment of the end point, more apparent to a user. < CO rs a o CO o LJJ Xerox Copy Centre EP 0 309 173 A2 TIME-COLOR INDICATORS Background of the Invention 5 1 . Field of the Invention This invention relates to an end point indicator composition, particularly for air fresheners, which allows the user to determine whether an associated product is still effective by visually inspecting the product. This invention further relates to the use of an indicator composition which includes a polar indicator dye 70 which assumes a first color or is colorless in the presence of a volatile solvent which is initially present in excess. The indicator composition further includes a small amount of a proton donating compound wherein the indicator dye assumes a second color visually distinct from the first in the presence of that compound. The dye progressively assumes the second color as the solvent evaporates until when the second color is at its highest intensity, the solvent is essentially exhausted and the associated product should be replaced. 75 2. Description of the Prior Art Kydonieus et al., U.S. Patent No. 4,212,153 discloses a laminated indicator which changes in a visually 20 perceptible mode with the passage of time and a method of making such an indicator. The indicator of Kydonieus et al. includes the migration of a dye of the migration of an acid or base within the laminated structure so that it is carried with the evaporation or the use of the product so that when the product is completely used up, the dye is visible to the user. The time-color indicator of Kydonieus et al. is dependent upon the pH of the solution. After the solvent substrate is exhausted, a pH change occurs whereby, for 25 example, the substrate turns from acidic to basic and the color is elicited, thereby alerting the user that the composition is exhausted. In another embodiment, there is a migration of the dye through various substrates along with the perfumes or fragrances whereby the dye builds up upon a polyester film and when the fragrance is exhausted, the dye is built up to a point where it is visible to the user. 30 The present invention differs from Kydonieus et al. in that it does not rely on the migration of an acid or base through at least two layers to cause a pH change which provides a visual color change perceptible to the user. The present invention relies on the change in concentration of a solvent relative to a polar proton donating compound to visually indicate an end point of a product. When the solvent is at its lowest concentration in the present invention, the proton donating compound is at its highest concentration and 35 thus the second color is at its highest intensity. The present invention requires no multiple layers and also provides an indicator composition which can be visually transparent to a user. Munden in U.S. Patent No. 4,128,508 relates to a color change perfume system in which the color changes when the perfume is effectively exhausted into the atmosphere. Munden also teaches air fresheners consisting of porous carriers impregnated with the perfume coloring system. 40 Munden differs from the present invention in that it requires a volatile acid or base and a pH indicator whereby the acid or base volatilizes at the same rate as the perfume. The pH indicator changes color when the acid or base, and thus the perfume, is essentially exhausted from the system. Munden also con- templates use of aqueous systems although he mentions that the system can be made up largely of the essential components. The indicator composition of the present invention is nonaqueous and requires a 45 combination of a major amount of a nonaqueous solvent, a minor amount of a proton donating compound which can be an ester, a dye and a perfume, none of which are required to be acidic or basic. McNeely in U.S. Patent No. 4,248,597 is a time watch or depletion indicator for removable substances and relies on a pH indicator in close proximity to the substance to be delivered. As the substance being delivered passes through a permeable membrane or porous substance, as in Example 1 of McNeely, a pH 50 change occurs and the color of the pH indicator changes and indicates that the substance being delivered is exhausted. McNeely relies on pH changes and pH indicator compounds to signal the user when depletion occurs. As noted above, the present invention does not require that an acidic or basic compound be present, but requires that both a solvent and a proton donating compound be present, as well as a polar dye, where the dye has one color in the solvent and a second color in the presence of the proton donating compound. EP 0 309 173 A2 Summary of the Invention The present invention relates to the use of an indicator composition which includes an effective amount, preferably at least 0.0002% of the total weight of the composition, of a polar indicator dye which assumes a 5 first color or, preferably is colorless, in the presence of a room temperature volatilizabie nonaqueous solvent which is initially present in excess. The indicator composition further includes an effective amount, preferably at least 0.0002% of the total weight of the composition, of a proton donating compound such as linalyl acetate or a polyhydric alcohol wherein the indicator dye assumes a second color visually distinct from the first in the presence of that compound. The indicator dye progressively assumes the second color w as the solvent evaporates and the concentration of the proton donating compound increases until when the second color is at its highest intensity or level of difference from that of the first color, the solvent is essentially exhausted and the associated product should be replaced. The solvent is selected with the product to be depleted in mind so that the evaporation rate of the solvent substantially corresponds with the depletion rate of the product such as a perfume. 75 One advantage of the present invention is that although one can be present, the proton donating compound does not have to be an acid such as a carboxylic acid. It thus permits essentially neutral compositions to be made unlike other indicator systems which rely on pH changes such as basic to acidic to generate a color change. Other advantages of the present invention are that the compositions are simple to manufacture and use, and provide a wide range of time spans by appropriate choice of solvents and 20 means for releasing the same from the compositions. The indicator dyes contemplated for use are the Xanthene dyes, and particularly the Rhodamine dye series. In a preferred embodiment, a color change developer such as a 1 ,2-propylene glycol is includes in an amount which is at least 0.005% by weight of the total composition to produce a more noticeable color change when the product is exhausted. In a more preferred embodiment, the indicator composition further 25 includes an effective amount of a second dye which renders the second color change more apparent to a user. Detailed Description of the Preferred Embodiment 30 Without wishing to be bound by any theory of operation, the following explanation is presented to assist others in practicing this invention. The present invention provides an indicator composition which comprises a polar indicator dye which assumes a color in the presence of a proton donating compound. The higher the concentration of the proton donating compound, the more the indicator dye becomes colored. By proper 35 choice of a room temperature volatilizabie nonaqueous solvent in which the indicator dye is soluble, the dye will assume a color different from the color exhibited in the presence of a proton donating solvent. More preferably, the dye is colorless in the presence of such a solvent. In the presence of the highly polar compound water, the indicator dye may remain strongly colored, even in the presence of a nonaqueous solvent. Therefore, aqueous solutions are to be avoided as are proton donating compounds which so 40 strongly associate with the dye that they do not permit the indicator dye to assume a different color in the presence of a large amount of the solvent relative to the amount of the proton donating compound.

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