GB2165646A - Temperature indicators - Google Patents

Abstract

A unit having a plurality of cells (4) ... (8) which include a light filter and a liquid crystal composition, and which are characterized in that each cell displays a color in response to exposure to a temperature in a predetermined narrow range which is above about 27 DEG C and below about 38 DEG C, and otherwise appears dark; the color that each cell displays is different from the colors that the other cells display; and no more than two of the cells display color at any given temperature. The device is used to determine skin temperature. <IMAGE>

Description

SPECIFICATION Temperature-responsive color device This invention relates to devices which respond to exposure to a given temperature, or range of temperature, by exhibiting characteristic colors. Simple examples of such devices include the well-known "mood-rings" and similar objects. The known devices generally have the drawback that when they are stimulated to produce a display of colors, the display changes uncontrollably through a wide range of several colors. There is a need for devices which respond to a given temperature by exhibiting a characteristic color, or at most a range of colors in a relatively tight range of frequencies, and in which the exhibited color(s) remain stable as long as the temperature remains relatively unchanged.In particular, there is a need for such devices in which the temperatures in question range above 80"F to body temperature.

The present invention comprises a temperature-responsive color display unit which has a plurality of cells each of which includes a light filter and a liquid crystal composition. Each cell displays color in response to exposure to a temperature in a predetermined narrow range which is above about 80"F and below about 100"F, and otherwise appears indigo or black; the color that each cell displays is different from the colors that the other cells display; and no more than two of the cells display color at any given temperature.

In particular preferred embodiments of this invention, the unit is further characterized in that at all temperatures between the lower limit of the lowest of said predetermined narrow ranges and the upper limit of the highest of said predetermined narrow ranges, at least one cell displays color.

In accordance with the accompanying drawings, Figure 1 is a front view of one embodiment of the invention. Figure 2 is a view of the embodiment of Figure 1, seen on the cross-section along line 2'-2' of Figure 1. Figure 3 is a perspective view of another embodiment of the invention.

Devices made in accordance with this invention are useful for detecting temperature changes, such as changes in body-skin temperature. One appiication is diagnostic or medical uses where it is necessary to measure body temperature or to detect changes in temperature. Another is in point-of-purchase sales efforts, in which the device is used to detect the temperature of a customer's skin and to exhibit a characteristic color in response to that temperature; then the sales effort is coordinated around that color, for instance by correlating the exhibited color to an individual's emotional or physiological state and then persuading that individual to purchase particular products designed to complement that state.

One embodiment of the invention is illustrated in Figure 1. Unit 1 comprises a thin, multi-layer film 2 which includes region 3 which is preferably permanently opaque and dark. Unit 1 also contains a plurality of cells, which are denoted by reference numerals 4, 5, 6, 7 and 8 in Figure 1. While five such cells are depicted, other numbers of cells (2 or more) can be employed in this invention.

Each cell exhibits a characteristic color under certain conditions, as described more fully below. Of course, each cell can take any desired geometric shape in the film, i.e. a circle, star, ellipse, triangle, and so forth.

Figure 2 is an expanded cross-sectional view of cell 6 in unit 1, showing the layers which are employed in a preferred embodiment of this invention. The other cells have the same set of layers, although the particular materials are varied to provide the desired variety of colors.

Layer 9 is a clear, inert, transparent, flexible film which serves as the outside front surface of the unit. A satisfactory material is 4 milthick polyester film such as that sold under the name "Melinex" by ICI Americas, Inc.

Other equivalent materials can easily be used instead; examples would be cellulose acetate, or other polymeric materials such as polyethylene, polyvinylchloride, and the like.

Layer 10 comprises a color filter. A different color filter is used for each cell. This layer must cover the cell area 6. Each color filter is a transparent, colored film preferably comprising an ink or a mixture of inks. Commercial acrylic inks are quite satisfactory. The colors of the color filters are selected so as to be distinctive one from another, and preferably easily noticeable against a surrounding background which is black.

Layer 11 is a black, opaque layer which extends throughout the unit 1 except not over the cell areas. This layer can preferably be any commercially available black lacquer or ink.

Layer 12 can be a latex emulsion or other thin film effective to promote adhesion between the layers on each side of this layer.

Layer 12 should extend over the entire unit 1, preferably at least over the cell area.

Layer 13 is a nematic chiral ester liquid crystal. This composition is placed in the cell area; a different composition is placed in each different cell area. Each liquid crystal composition is characterized in that at temperatures below a certain minimum temperature T the composition appears dark or nearly black, and at temperatures above a certain maximum temperature Tax the composition appears indigo, or black. Each composition, when exposed to a temperature between its Trnrn and TmaX, exhibits color (i.e. not black) which can be any color (or colors) in the visible spectrum including white and off-white.The range between the Trnn and T,, for any composition is generally 1-4"F, preferably 2-3"F. To compose a unit in accordance with this invention, each of the two or more compositions are selected so that the Tmax of any one composition is about the same as, or up to about 1"F higher than, the Tm of one other composition (except of course for the min composition with the highest Tom,,) Thus, when a unit is made with compositions selected in this way, exposure of the unit to a temperature below the lowest T - leaves the unit looking dark; as the temperature is slowly raised, only the composition having the lowest Tm, will exhibit color; then, as the Tm,, of that composition is reached, that composition loses color. However, at the same time, the Tm of the composition having the next lowest Tm,n, will have been reached, causing that composition to exhibit color; if the temperature continues to increase, that second composition will lose color and the composition (if there is one) with the third lowest T will begin to exhibit color, and so on until the temperature exceeds the highest Tm,, at which point all cells will appear indigo or dark. Thus, at any temperature above the lowest Tm,, one or at most two cells will exhibit color.As indicated previously, the lowest T . is 80"F or higher, and the highest Tm,, is 100"F or less.

Nematic, chiral-ester liquid crystal compositions useful in this invention and meeting the above criteria can readily be identified by those familiar with standard sources of supply in this area. They can be obtained from Djinnii Industries, Inc., Dayton, Ohio. These compositions are of the type described in U.S. Patents Nos. 4,002,670; 4,012,434; 4,130,501; 4,154,697; 4,229,378; 4,268,829; 4,330,426; and 4,331,552; and British Patents Nos. 1,556,994; 1,596,012; 1,596,013; 1,596,014; and 1,592,161. The compositions are preferably microencapsulated by ordinary methods in gelatin or equivalent clear, inert material.

Returning to Figure 2, layer 14 is opaque, preferably black enamel ink, and covers the entire surface of the unit 1. This layer serves as the "back" of the unit; that is the surface which is placed against the object whose temperature is to be detected. Any commercially available black lacquer ink is quite satisfactory.

The following is an example of the preparation of a unit in accordance with this invention. This example is for purposes of illustration, and is not to be taken as the only embodiment of the invention.

EXAMPLE On a 1.75" X 1.75" piece of 4-mil polyester film, 0.25" X 1.75" stripe borders were screen printed at the top and bottom edges of one side of the film in black lacquer ink (opaque black (DLW-710) Flexible Decal Lacquer, Advance-Excello Company, Color and Chemical Division). In the clear 1.25" X 1.75" space remaining between the two black borders, five transparent color filters (0.25" X 1.75" each) were screen printed side by side.

From bottom to top they were (1) Indigo: formed by mixing 40 vol. % ABS-455 Permanent Blue (RS), 20 vol % ABS576 Permanent Rose Red, and 40 vol. % ABS-800 Clear Acrylic Base; (2) Pink: formed by mixing 40 vol. ABS-576 Permanent Rose Red and 60 vol. % ABS-800 Clear Acrylic Base; (3) Emerald: formed by mixing 40 vol. ABS304 Monastral Green, 10 vol. % ABS-455 Permanent Blue (RS), and 50 vol. % ABS-800 Clear Acrylic Base; (4) Scarlet: formed by mixing 40 vol. % ABS-503 Permanent Red Y, 10 vol. % ABS576 Permanent Rose Red, and 50 vol. % ABS-800 Clear Acrylic Base; (5) Light Blue: formed by mixing 30 vol. % ABS-455 Permanent Blue (RS), 10 vol. % ABS-576 Permanent Rose Red, and 60 vol. % ABS-800 Clear Acrylic Base.

All the components of the color filters were Multi-Vac Acrylic Inks (ABS Series), products of AdvanceExcello Company, Color and Chemical Division.

Next, black lacquer ink (same as above) was screen printed to cover all of the unit but a 1.25" X 0.375" space directly in the center of the unit. This exposed a 0.25" X 0.375" window for each of the color filter windows.

A clear latex emulsion was then screen printed over the entire surface to provide a protective coating and to facilitate adhesion between the color filters and the liquid crystals.

Next, a different and specific microencapsulated chiral ester liquid crystal ink was screen printed on each color filter window. From bottom to top, the five compositions were (temperature measurements are + 0.5"F): (1) Composition known generally in this art as R29C1W, characterized in that it appears black below about 83"F, exhibits color between about 83.1"F and about 86.7"F, and appears black at temperatures above that.

(2) Composition known generally in this art as R31CIW, characterized in that it appears black below about 86.5"F, exhibits color between about 86.5"F and about 88.9"F, and appears indigo above about 88.9"F.

(3) Composition known generally in this art as R32C1W, characterized in that it appears black below about 87.5"F, exhibits color between about 87.5"F and about 90.3"F, and appears indigo above about 90.3"F.

(4) Composition known generally in this art as R33C1W, characterized in that it appears black below about 89.2"F, exhibits color between about 89.2"F and about 91.9"F, and appears indigo above about 91.9"F.

(5) Composition known generally in this art as R34C1W, characterized in that it appears black below about 92.1"F, exhibits color be tween about 92.1"F and about 94.1"F, and appears indigo above about 94.1"F.

Finally, black enamel ink was screen printed over the entire back surface.

This device exhibited the following color profile.

Cell number (1) was black at temperatures below about 83.1"F. It appeared indigo between about 83.1"F and about 86.7"F, and black above that temperature. With a filter of a different color, this cell would exhibit a color from about 83.1-86.70F and appear indigo above 86.7"F.

Cell number (2) appeared black at temperatures below about 86.5"F. It turned pink at that temperature, gradually changing to light blue at about 88.3"F, passing to indigo at about 88.9"F and above.

Cell number (3) appeared black at temperatures below about 87.6"F, at which point it appeared deep green, changing gradually to blue-green at about 89.6"F, and to indigo at about 90.3"F and above.

Cell number (4) appeared black below about 89.2"F, at which point it turned scarlet. This color changed gradually to become maroon at about 89.9"F, red at about 90.5"F, faded-red at about 91.6"F, and purpleindigo at about 92"F and above.

Cell number (5) appeared black below about 92"F, at which point it became gray-blue. The color changed gradually to become powder blue at about 93"F, bright blue at about 93.7"F, becoming indigo at about 94.1"F and above.

This unit can be used as is, but preferably it is mounted in a frame, bracelet, or other relatively rigid device so that the user can hold the unit against the surface whose temperature is being measured, and so that the unit does not inadvertently respond to the temperature of the user's own fingers. To use the device, one simply holds it against the surface whose temperature is being measured, and notes which (if any) of the cells displays color.

Since the user already knows the temperature range within which each cell displays color, the user knows that the surface has a temperature which is within the range for the cell that displays color. When two cells display color, the user knows that the temperature is near the one cell's Tm and the other cell's Tmax Preferably the unit is incorporated into a clip or bracelet, of the sort shown on Figure 3, which is dimensioned so that a person's wrist fits snugly between points 15 and 16. The clip or bracelet thereby holds itself in place.

The back surface of the color-sensitive unit is thereby held against the wearer's skin and the front surface 17 is visible so that one can observe the color produced by the skin temperature.

The units are novel in that when a cell is exposed to a temperature which causes it to display a color, the displayed color lies in a relatively narrow range of wavelengths, each range being unique for a given cell. This is preferable to having each cell pass through the range from, say, red-to-green-to-blue.

Claims (11)

1. A temperature-responsive device comprising: (a) a plurality of cells each of which has a light filter (10) and a liquid crystal composition (13); (b) each cell displays color only in response to exposure to a temperature in a predetermined narrow range which falls within the broad range of about 80"F to about 100"F, and otherwise appears indigo or black; (c) the colors that each cell can display are different from the colors that the other cells can display; and (d) no more than two of the cells display color at any given temperature.

2. The device of claim 1, further characterized in that upon exposure of the device to any temperature between the lower limit of the lowest of said predetermined narrow ranges and the upper limit of the highest of said predetermined narrow ranges, at least one cell displays color.

3. The device according to claims 1 or 2 having four or five cells.

4. The device according to claims 1 or 2 having five cells.

5. The device of any one of the preceding claims wherein said broad range is about 83"F to about 94"F.

6. The device of any one of the preceding claims wherein said broad range is about 86"F to about 94"F.

7. The device according to any one of the preceding claims wherein each color filter of each cell displays a different color from the other filters of each cell.

8. The device according to any one of the preceding claims wherein the liquid crystal composition for each cell is selected to be responsive to a temperature range different from liquid crystal composition of each other cell to display a color when the cell is exposed to a temperature within the selected range.

9. The device according to 10 wherein said liquid crystal compositions are selected so that Tm, of any one composition is about the same as, or up to 1"F higher than the Tm,n of one other composition except for the composition with the highest Tm,,.

10. The device of any one of the preceding claims further including a transparent film outer front surface, a black opaque region extending throughout the device except for the cell areas, and a black opaque back surface.

11. A method of detecting the approximate temperature of a surface having a temperature between about 80 F and about 100"F, com prising (a) contacting said surface with a device according--to claim 2, (b) observing which cell or cells display co lor in response to said contact, and (c) identifying the predetermined narrow range of temperature which corresponds to the cell or cells displaying color.