Background of Invention Over the last 20 years, clinical thermometry has developed single-use, handheld thermometers that use precise quantities of different compositions of solid solutions of two thermally responsive materials in a plurality of cavities on a single strip of laminated material, each composition in each cavity alterable at a different temperature. The precision of the different compositions responsive to the different temperatures has permitted these chemical thermometers to be truly qualified as clinical devices.

A number of patents describe the advances made to this field of clinical thermometry. Among these patents are those issued to Hof et al. such as U. S. Pat.

Nos. 4,232,552; 4,299,727; 4,345,470; and 4,397,570, which describe improvements to the temperature indicating compositions of matter, the all-plastic construction of the thermometer, and the like.

Automated assembly of the clinical thermometer reduces costs, improves productivity, improves quality assurance, and provides other benefits. In the assembly of a clinical thermometer where as many as 45 different compositions are being deposited in 45 separate cavities on the thermometer surface, precise metering and delivery of the compositions to the cavities, in registration, is essential for productive assembly ofthe clinical thermometers. U.S. Pat. No. 3,810,779 (Pickett et al.) discloses a method and apparatus for depositing precisely metered quantities of

liquid on a surface, particularly temperature indicating compositions ot matter on to the surface of a clinical thermometer. The method and apparatus disclosed in Pickett et al. has formed a basis for the construction of automated machinery to measure and deliver 45 different compositions to the 45 cavities for detecting temperatures ranging from 96.00F to 104.80F for the American market (35.5"C to 40.40C for international markets).

Clinical thermometry has enjoyed the advances disclosed by the Hof et al. patents and the Pickett et al. patent because the thermometers can be precisely manufactured inexpensively and because the inexpensive clinical thermometers can be disposed of after a single use. The clinical thermometer can be taken, then the instrument disposed to avoid the transmission of viruses, bacteria, and other germs that unfortunately plague reusable thermometer devices.

Clinical thermometry also is benefitting from advances in the nature of the temperature indicating compositions of matter whereby the amount of energy and time needed to reverse the "firing" of one of the compositions in one of the cavities from freezing temperatures overnight to freezing temperatures for a few hours. Some of these new reversible thermometer compositions employ an emulsion of a thermally responsive material, means for observing a change in state of the material such as a dye, and a matrix forming material in which the thermally responsive material is dispersed.

Reversible thermometer compositions of this type are disclosed in European Patent Publication 0 684 463 (Al) (Hof).

Summarv of Invention While this Hof innovation is truly unexpected and remarkable, unexpected improvements have been developed that further assure the control of "firing" of the reversible chemical composition and the color change of each chemical composition in a cavity on the thermometer.

One aspect of the present invention is a chemical thermometer composition comprising the incorporation of a compatible thixotropic agent into an

emulsion of a thermally responsive material, means for observing a cnange in state ot the material such as a dye, and a matrix forming material in which the thermally responsive material is dispersed.

"Compatible thixotropic agent" means a thixotropic agent that provides thixotropic properties to the reversible chemical composition without adversely affecting the "firing" of the chemical composition at a predetermined temperature range and without adversely affecting the reversing of a "fired" chemical composition.

Thixotropy is the property of a fluid to exhibit a reduction in viscosity with an increase in shear force. Conversely, reductions in shear force are accompanied by an increase in viscosity. More particularly, thixotropy is exhibited by certain gels of liquefying when stirred or shaken and returning to the hardened state upon standing.

Another aspect of the present invention is a chemical thermometer composition comprising the incorporation of a contrast enhancing agent to an emulsion of a thermally responsive material, means for observing a change in state of the material such as a dye, and a matrix forming material in which the thermally responsive material is dispersed.

"Contrast enhancing agent" means any dye or pigment that more dramatically increases visual perception of a "fired" chemical composition in a cavity of a multiple cavity reversible chemical thermometer.

The present invention contemplates incorporation of either or both agents into the reversible chemical composition disclosed in European Patent Publication 0 684 463 (Al) (Hof).

A feature of the invention is the ability to improve assurance of the reliability of a Hof reversible chemical composition by enhancing a more visually perceptible "firing" of the reversible chemical composition in a cavity of the thermometer.

Another feature of the invention is the use of thixotropic agents and contrast enhancing agents that otherwise do not affect the chemical performance of the reversible chemical composition in its intended use discussed in Hof.

An advantage of the present invention is the ease and economy of incorporation of both agents into the Hof reversible chemical compositions.

Another advantage of the present invention is the formation of a more visually perceptible clinical, single-use chemical thermometer than previously known in the art.

Further features and advantages will be discussed with respect to embodiments of the invention.

Embodiments of Invention Chemical Composition U.S. Pat. Nos. 4,232,552; 4,299,727; 4,345,470; and 4,397,570, (all Hof et al.) and European Patent Publication 0 684 463 (Al) (Hof) identify many possible chemical compositions for use in single use, clinical thermometers. Each of these compositions are theoretically reversible with differing degrees of effort and energy required.

References in the Hof et al. patents and the Hof EPO publication to polyisobutylene should be deemed to include any composition of polybutene that has at least a minor component of polyisobutylene. The ability of commercial manufacturers to provide pure polyisobutylene is not yet proven. Those skilled in the art will recognize that, often as a shorthand expression, references to a polymer composition allows for the possibility of other isomers of a desired polymeric composition to also be present.

Of all of these compositions, the reversible chemical compositions identified in European Patent Publication 0 684 463 (Al) (Hof) are particularly preferred. For emphasis, these compositions are an emulsion of a thermally responsive material, means for observing a change in state of the material such as a dye, and a matrix forming material in which the thermally responsive material is dispersed, where the composition of the thermally responsive material is altered with calibration to a predetermined temperature. The typical formulation identified in the table of

components and quantities in the Examples section of the HofEPO publication are more particularly preferred.

Therefore, a reversible chemical composition comprises a thermally sensitive material dispersed in a matrix forming material wherein the matrix forming material is insoluble in and inert to the thermally sensitive material. The composition is preferably reversibly responsive to changes in temperature at a predetermined temperature. The composition can further comprise a means for visually observing a change in state of the thermally sensitive material from a solid to a liquid substantially at a predetermined temperature. The composition more particularly includes a dye or an organic moiety as the means for visual observing. The matrix forming material can be selected from polybutyene isomers, low density polyethylene, amorphous polypropylene, and mixtures thereof, and preferably comprising at least a minor component of polyisobutylene. More particularly, the thermally sensitive material comprises a solid solution of o-chloronitrobenzene and o-bromonitrobenzene, preferably with a minor amount of a nucleating agent. The nucleating agent can comprise an anthraquinone. Most preferably, the means for visually observing is an organic moiety selected from the group consisting of pinacyanol iodide, a mixture of ethyl red and bromophenol red, a mixture of ethyl red and bromocresolpurple, and a mixture of ethyl red and bromophenol blue.

Compatible Thixotropic Agent "Compatible Thixotropic Agent" refers to the compatibility of the thixotropic agent with the remainder of the chemical composition of the present invention. While different color change dyes can have different compatibilities with different thixotropic agents, an important aspect of the invention to one skilled in the art is the ability to tailor which thixotropic agent is preferable for which chemical composition system.

For example, it has been observed with the Hof et al. European Publication compositions that relative incompatibility is found in the change of the color of the solid temperature indicating compositions of matter with the dye as having a color change in the solid from a rose/tan solid to a bluish solid. This change in color can mask the actual change from rose/tan solid to a blue liquid, the actual solid/liquid color contrast that is important in observing the result of a temperature measurement.

Therefore, compatibility of a thixotropic agent within a given chemical composition is needed to minimize changes in solid-to-solid in order to maximize the appearance of changes in solid-to-liquid upon which the chemical thermometry is founded.

Moreover, compatibility is concentration dependent. Higher concentrations of a thixotropic agent will produce more of a color aberration than lower concentrations. Very high concentrations of thixotropic agent do begin to discolor the chemical composition.

An effective amount of thixotropic agent is determined by the degree of thermal abuse to which the thermometers are expected to be exposed. The determination of an effective amount for the preferred thixotropic agents of the present invention occurred by challenge testing to the likely commercial conditions of use.

More particularly, the challenge testing comprised about 7-10 cycles of slow heating and cooling (the most deleterious of possible usage conditions) from room temperature to about 50"C and about 3-5 days of continuous storage at that elevated temperature.

It should be understood by those skilled in the art that less aggressive challenge testing for less dramatic possible usage conditions could provide a more expanded list of compatible thixotropic agents.

For the present invention, but not limited thereto, the choice of thixotropic agents concern fumed silicas which have reacted with reagents to modify their surfaces with attached moieties. Most of the reagents are silicone derivatives, preferably also containing a basic nitrogen group. The nitrogen group (or other basic group) contributes to compatibility with the preferred organic moieties as the means for

visually observing a change in state of the thermally responsive matertlal because the organic moiety has basic characteristics also, i.e., pinacyanol iodide is a basic dye.

While a surface modified silica having basic characteristics is presently preferred, the invention is not so limited. If one skilled in the art desired to employ a different means for observing that contained more acidic characteristics, then the preferred surface modified silica could be selected from those thixotropic agents that have acidic characteristics.

Based on this selection criteria for a compatible thixotropic agent, a presently preferred compatible thixotropic agent useful in the present invention a silane- surface-modified fumed silica thixotropic agent sold by Degussa Corporation of Ridgefield Park, NJ, USA under the trade designation of"Aerosils R-504 Fumed Silica" In this instance, the surface modification is provided by triethoxy-propyl- amino silanes and heamethyl-di-silanes.

The amount of compatible thixotropic agent can range from about 0.14 to about 1.5 weight percent of the total chemical composition, and preferably from about 0.7 to about 1.415 weight percent.

Contrast Enhancing Agent Contrast enhancing agents can be dye-based inks or toners depending the extent of miscibility of the solvent and the extent of inertness of the dye(s) with the Reversible Chemical Composition identified above. Nonlimiting examples of contrast enhancing agents include Oil Red 0 and Oil Red EGN dyes from commercial laboratory supply companies such as Aldrich Chemical Co. and ACROS Chemcal Company (formerly Kodak Chemical). Particularly preferred as a contrast enhancing agent is the Oil Red EGN dye The amount of contrast enhancing agent can range from about 0.003 to about 0.01 weight percent ofthe total chemical composition, and preferably from about 0.006to about 0.009weight percent.

Method of Making Either of the Compatible Thixotropic Agent or Contrast Enhancing Agent, or both, can be incorporated into a Chemical Compositions during its preparation. For example, the Examples section of the Hof EPO application provides a description of the preferred method of making the composition of the present invention, with the addition of the Compatible Thixotropic Agent or Contrast Enhancing Agent, or both.

Method of Using Each chemical thermometer composition can be prepared in a droplet form and deposited on to a surface of clinical chemical thermometer device, as disclosed in U. S. Pat. No 4,345,470 (Hof et al.). Depending on the viscosity of the chemical thermometer composition, one skilled in the art can use either the teachings of U.S. Pat. No. 3,810,779 (Pickett et al.) and copending, coassigned, PCT Pat. Appln.

Serial No. ~~~~~~~~~ (Attorney Docket No. 53167PCT7A), for dispensing and delivery of each composition to each designated cavity of the thermometer device.

Such a thermometer can comprise a heat conducting carrier having a multiplicity of different compositions thereon, wherein each composition comprises one chemical thermometer composition of the present invention.

Examples The method of the Examples in the HofEPO publication were generally employed.

Table 1 shows a preferred chemical thermometer composition. Each of the three premixes were made according to the following conditions using a Ross PD-2 power mixer: The Contrast Enhancing Agent Premix began with the addition of ingredients of the Thermally Responsive Material into a NalgeneTM bottle. The Contrast Enhancing Agent was then added and the bottle shaken vigorously. The

bottle was placed in an oven at about 50"C until further use. The polybutene was heated in a bowl at 650C for at least 30 minutes. Then the contents of the bottle were added to the bowl, following by a three stage sequence of mixing with a planetary blade for about 10 minutes each at 20, 35 and 60 Hz. After this sequence, a high speed blade was added (without turning of the planetary blade) for 2 minutes at 30 Hz. The mixing was interrupted for scraping the resumed for an additional 3 minutes with the planetary blade rotating at 60 Hz and the high speed blade rotating at 20 Hz.

The other Premixes followed this general premixing procedure.

The three premixes were then combined with the remainder chemicals and mixed to produce a preferred chemical thermometer composition of the present invention using the following procedure: After heating the mixing bowl at 470C for about 30 minutes prior to mixing, the polybutene and then the Thermally Responsive Material were added, followed by a three stage mixing sequence of about 12, 10, and 8 minutes at 20, 35, 60 Hz, respectively using the planetary paddle. Without stopping the planetary paddle, the high speed blade was turned on for 4 minutes at 20 Hz. The mixing was stopped and the bowl was stopped and scraped. The high speed blade was removed and the contents were cooled for about 50 minutes by running ice-cold water about the bowl.

Then the planetary paddle was run for 3 minutes at 45 Hz. A vacuum was initiated to between 20 and 30 Inches Hg. The speed of the mixer was slowed to 30 Hz, the cold water was stopped, and the mixer continued for 8 minutes. The mixing stopped and the contents were scraped. Then all of the Premixes were added and mixed at 30 Hz for 10 minutes. Once again the mixing was stopped for a scraping ofthe paddle and sides and then resumed at 30 Hz for 10 minutes.

Table 1 Premix Wt. Percent of Total Composition Premix Wt. Percent of Total Composition Contrast Enhancing Agent Premix Polybutene (Parapol 2500 from Exxon) 5.421 Thermally Responsive Material 0.406 (OBNB/OCNB Solid Solution)1 Contrast Enhancing Agent 0.009 (Oil Red EGN) Nucleating Agent Premix 9,10-anthraquinone 0.071 (Fluka, 99%) Parapol 2500 14.149 Thixotropic Agent Premix Fumed Silica 1.415 (Aerosil R 504 from Degussa) Parapol 2500 14.149 Remainder Mixed with Premixes OCNB/OBNB 19.435 Color Change Agent 0.021 (pinacyananol iodide) Parapol 2500 58.366 Total - 100 Ratio varies with predetermined temperature desired

The result of this mixture then can employ the apparatus disclosed m copending, coassigned, PCT Pat. Appln. Serial No. ~~~~~~~~~ (53 (53167PCT7A) to dispense dollops of the emulsion on to cavities of a plastic thermometer disclosed in U.S. Pat. No. 4,345,470 (Hof et al.), except that an ionomer layer covering the nylon on the base web has been removed and the nylon thickness has been increased to about 0.05 mm. The nylon is bonded on one side by a 0.15 mm layer of amorphous polyester and on the side contacting the reversible composition in the cavity by a 0.012 mm low density polyethylene layer. According to the teachings of U.S. Pat. No. 4,397,570 (Hof et al.), the cavity and composition are covered by a 0.025 layer of polyisobutylene-containing adhesive having a number average molecular weight of about 2500, a 0.012 mm layer of a biaxially oriented polyester, and a 0.025 layer of low density polypropylene.

In each dollop of the emulsion, one can find a continuous phase of the matrix forming material and dye, in which are dispersed as discontinuous phases, discrete quantities of the thermally responsive material, nucleating agent, and a contrast enhancing agent, thixotropic agent, or both.

Use of the compatible thixotropic agent in compositions of the present invention minimizes the gradual aggregration and then coalescence of the discrete quantities of the thermally responsive material and contrast enhancing agent in the matrix forming material, thereby avoiding the the possibility of change in color appearance of the dollop in the cavity of the thermometer. Not being limited to any particular theory, it is believed that the compatible thixotropic agent acts by forming a weakly bonded three dimensional net within the fluid in which it is dispersed. When subjected to shear stress, the network breaks down and the fluid flows more easily.

Compositions of the present invention can effectively and essentially withstand weeks of repeated slow heating and cooling with only limited amounts of coalescence within the matrix forming material.

Use of the contrast enhancing agent can be exposed to interference with and by the means for changing color, because particularly with an organic moiety such

as pinacyananol iodide is a basic dye. Quantities of the contrast enhancing agent of less than about 0.07 weight percent are preferred because higher amounts can mask the reading contrast necessary to determine when the temperature responsive material "fires" at a predetermined temperature.

Also without being limited to a particular theory, it is believed that chemical thermometer compositions ofthe present invention The invention is not limited to the above embodiments. The claims follow.