CA1109287A - Dye in chemical temperature indicating device - Google Patents

Abstract

DYE IN CHEMICAL TEMPERATURE INDICATING DEVICE

ABSTRACT
There is provided a temperature indicating device such as a disposable thermometer. The thermometer includes a thermally conductive sheet as a carrier layer having one or more cavities formed by depressions in the sheet material. At least one of the cavities is filled with a solid mixture which melts at a pre-determined temperature. The mixture includes the combination of ortho-chloronitrobenzene, ortho-bromonitrobenzene and a dyestuff.
An indicator layer of absorbent material is superimposed on the solid mixture, and a transparent cover layer seals the cavities and their contents.

Description

BACKGROUND OF THE INVENTION
This invention relates to a temperature indicatiny device. More particularly it relates to a temperature indi-cating device used as a disposable thermometer.
Reference is made to my Canadian Patent Application Serial No. 302,322 filed on May 1, 1978 and entitled "Tempera-ture Indicating Device Using a Pressure Sensitive Adhesive Seal".
Temperature indicating devices which utilize ther-mally responsive mixtures of ortho-chloronitrobenzene and orthobromonitrobenzene are known and one such device is des-cribed in U.S. Patent 3,704,9~5. The device described in the above patent includes a layer having a dye impregnated therein which is separated from the thermally responsive mixture. It would be desirable to include a dye in the mixture, however, it has never been applied in practice because it had not been possible to find suitable dyestuffs which meet particular re-quirements. These requirements are: no detrimental effect on the melting point of the mixture of ortho-chloronitrobenzene and ortho-bromonitrobenzene, a distinctly perceptible color change of the indicator layer upon the melting of said mixture and, particularly, good durability without premature discolora-tion of the indicator layer.
Owing to the lack of suitable dyestuffs recourse was made in practice to the use of special constructions in which a shield was positioned between the meltable solid mixture and the indicator layer, which shield is removed just prior to use of the temperature indicating device. Such a construction is des-cribed in U.S~ Patent 3,674,176. Although such a temperature indicating device can very well be used, the above described shield causes production and use thereof to be complicated and expensive. Particular dyestuffs have now been found which eliminate the need for making use of a shield.

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OnJI~CTS ()F 1'11~ VI~ TIOM
..
I It is one object of this invention to provide an im~roved temperature indicatin~ clevice.
It is another object of the invention to provide~ a temperature indicating device which is simpler and cheaper to manufacture than prior art devices.
It is another object of this invention to provide a temPerature indicating device which utilizes thermally responsive chemicals mixed with a dye which vields accurate temperature information. -'1~ SUMMARV OF TH~ INVEN'rION
_ _ , In accordance with one form of this invention, there is i¦provided a temperature indicating device which includes a , ¦thermally conductive sheet,as a carrier layer provided with one , lor more cavities formed by depressions in the sheet material. At least one of the cavities is illed with a solid mixture which melts at a predetermined temperature and includes ortho-chloro-nitrobenzene, ortho-brornonitrobenzene and a dyestuff. An indicator layer of absorbent material is superimposed on the ~0 ¦solid mixture. A transparent cover layer seals the cavities and their contents.
The dyestuff applied is selected from the group of dyestuffs which in accordance with the Colour Index are referred !
to as solvent blue 10, solvent blue 44~ solvent hlue 45 solvent ~blue 49, solvent blue 67, solvent r~d 90, solvent orange 59 and I
solvent green 19.
The temperature indicating device according to the I
invention is of simple construction and has surprisingly good durabil ty. Morè~ve-, its indlcation of the temperature is

-3-.' accurate and reproducible, and distinctly visible. Of the blue dyestuffs according to the invention solvent blue 49 is pre-ferred. Under certain circumstances it is preferred that, because of its red color, solvent red 90 be used.
The indicator layer of absorbent material applied to the solid mixture is preferably constituted of paper made from cellulose fibers. Because of its lower sensitivity to the influence of moisture it is preferred that under certain circum--stances use should be made of an indicator layer consisting of paper made from synthetic fibers. In view of the desired high absorptivity and high porosity of the indicator layer, it is preferred that this indicator layer should be of a coarse filter paper~
The temperature indicating device according to the invention is excellently suitable for clinical use and is preferably so constructed then that the carrier layer consists of aluminium sheet provided with a number of cavities which contain solid mixtures having different melting points, and the transparent cover layer consists of polyester film. The polyes-ter film is preferably bonded to the aluminium film by means of a pressure-sensitive adhesive agent. Preferably, polyisobutylene is used as the pressure sensitive adhesive agent According to a broad aspect of the present invention, there is provided a temperature indicating device which com-prises a thermally conductive sheet as carrier layer provided with one or more cavities formed by depressions in -the sheet material. At least one of the depressions is filled with a solid mixture which melts at a predetermined temperature and is composed of ortho-chloronitrobenzene, orthobromonitroben-zene and a dyestuff. An indicator layer of absorbent materialis superimposed on the solid mixture. A transparent cover layer seals the cavities and their contents and it is charac-_ 4 _ P?

, terized in that the dyestuff used is selected from the group consisting of dyestuffs which in accordance with the Colour Index are referred to as solvent blue 10, solvent blue 44, solvent blue 45, solvent blue 49, solvent blue 67, soLvent red 90, solvent orange 59 and solvent green 19.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is further described with reference to the accompanying drawings.
-~ Figure 1 is a plan view of a temperature indicating device according to the invention.
Figure 2 is a vertical section along the line A-A' given in Figure 1.

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D~SCRIPTIOl`~ OF lHl~ PRT~FF,RT~D F,'l~ ODI~ TS
In Figure 1 the temperature indicatiny device has a portion 1 which serves as a handle and an indicator portion 2 adapted to be inserted into the mouth for oral temperature measurement. The indicator portion 2 is provided with a number of suitably spaced cavities 3. ~ach cavity is filled with a solia mixture 4 (Figure ~) which melts at a known temperature.
In the adjacent cavities the melting temperature may, for instance, be 0.1C higher or lower, which can be realized by a ¦proper choice of the composition of the solid mixture.
¦ Although in Figure 1 a series of cavities 3 are shown, there is only need for one cavity if the temperature indicating device is used to establish whether or not a certain temperature value has been exceeded. The cavities 3 are formed by depression lof the thermally conductive sheet material, which serves as ' carrier layer 5. Although the thermally conductive sheet i material may very well be of aluminium, also other flexible ther- j mally conductive materials may be used. On the solid mixture ¦and in intimate contact therewith is an irldicator layer 6 of I
labsorbent material, which is usually an absorbent paper having a ¦
high porosity and a high absorptivity, so that when the solid mixture melts, the indicator layer is immediately wetted by the I
liquid phase formed. A transparent cover layer 7 seals the !
cavities 3 and their contents. The cover layer 7 is of film material which is sufficiently impervious to the substances present in the cavities, and to substances, for example moisture, which may unfavorably influence temperature indication. It is I
preferred that the transparent cover layer should be o !
polyester, more particularly of the polyethylene tere~hthalate !
type. The thickness of the transparent cover layer is preferably !
20-100 microns.

.

The cover layer 7 is bonded to the carrier layer 5 by an adhesive layer 8. This adhesive layer ~3 consists of an adhesive agent which can be applied without the melt tem~era-ture of the solid mixtures being exceeded. For this purpose use may be made of a pressure-sensitive adhesive or a bonding agent with which the cover layer 7 and the carrier layer 5 may be welded together ultrasonically. It is preferred that the adhesive layer 8 should be of polyisobutylene.
The E'igures 1 and 2 show a special embodiment of the temperature indicating device according to the invention. It will be clear that within the scope of the invention it is possible for a man skilled in the art to realize many other embodiments and/or modifications. The nature of the thermally conductive material for the carrier layer, the number, the dimensions and the arrangement of the cavities provided therein, the weight ratio of ortho-chloronitrobenzene and ortho-bromo-nitrobenzene in the solid mixture and the choice of the material of the transparent cover layer can immediately be derived from the state of the art by a man skilled in the same art. The same applies to the amount of -the solid mixture in each of the cavities and the way of filling the cavities. When use is made of the temperature indicating device according to the in-vention, the melt temperature of the solid mixture will be ex-ceeded in one or more cavities, depending on the level of the temperature to be measured, so that the respective mixture will pass from the solid into the liquid state. The liquid formed is then sucked up by the absorbent material of the indicator layer. The dyestuff contained in the liquid causes a visually perceptible discoloration of the indicator layer. From the position of the border between cavities having a colored and those not having a colored indicator layer immediately the value of the temperature to be determined can be read.

Z~7 The dyestuffs to be used according to the invention are dissolved in mixtures of ortho-chloronitrobenzene and ortho-bromonitrobenzene in an amount which is usually about 0.05 - 0.2 percent by weight. Al-though it is possible to use amounts smaller than 0.05 percent by weight, the color change in the indicatox layer will be less clearly perceptible then.
On the other hand, if the dyestuff is used in an amount con-siderably higher than 0.2 percent by weight, an undesirable change of the melting point of the particular solid mixtures will take place. In the above-mentioned range of 0.05 - 0.2 percent by weight there will be no detrimental change of the melt temperature of the solid mixtures used. The dyestuffs used according to the invention are known in themselves and are referred to under the names mentioned in the colour Index, ; 3rd Edition (1971), published by the Society of Dyers and Colourists, Great Britain (five volumes).
Solvent blue 10 is marketed, for instance, by the firm of Sandoz, Switzerland, under the registered trademark Savinyl Blue B.
Solvent blue 44 is marketed, fGr instance, by the firm of Sandoz, under the registered trademark Savinyl Blue GLS.
Solvent blue 45 is marketed, for instance, by the firm of Sandoz under the registered trademark Savinyl Blue RS.
Solvent blue 49 is marketed by the firm of Ciba-Geigy, Switzerland, under the registered trademark Orasol Blue BLN.
Solvent blue 67 is marketed by Ciba-Geigy under the re~gistered trademark Orasol Blue GN.
Solvent red 90 is marketed by the firm of Sandoz under the registered trademark Savinyl Red BLSN.
Solvent orange 59 is marketed, for instance, by Ciba-Geigy under the registered trademark orasol Orange RLN.

Solvent green 19 is marketed, for ins-tance, by the firm of Sandoz under the registered trademark Savinyl Green B.
The dyestuffs used according to the invention are remarkable particularly for the speed at which they migrate from the solid mixture to the indicator layer. This means that there is no premature discoloration of the indicator layer, in spite of the fact that the indicator layer and the dyestuff-containing solid mixture are constantly in contact with each other also during storage. Because of this resis-tance to premature discoloration the durability is excellent.
All solid mixtures that are present in the various cavities of the temperature indicating device may contain one and the same dyestuff. It is also possible to use different dyes.
For instance, the use of a blue dyestuff may be combined with that of a red one to clearly indicate that a particular temperature value is exceeded.
Suitable materials for the indicator layer are cellulose paper and paper from synthetic starting materials, for instance polyester. It is preferred that the paper used should be opaque, have a uniform structure and evenly discolor upon getting into contact with the melted solid mixture. It has been found that these requirements are fully met by coarse filter paper (No~ 589') supplied by~the firm of Schleicher &
Schull and by chromatography paper No. 1 supplied by the firm of r~hatman. The transparent cover layer consists of a material which does not change -the melting point of the solid mixture contained in the cavities, and is not adversely affected by said mixture and is sufficiently impervious to the various substances~ It is preferred that the transparent layer should consist of polyester film, for instance Melinex (registered trademark) film supplied by I.C.I., Great Britain.

~,~f Bonding the transparent cover layer to the carrier layer should be carried out at such a low temperature that the melting temperature of the solid mixtures present in the cavities is not exceeded. The cavities must then be sealed off from each o-ther as well as from the ambient air. The ad-hesive agent used should be properly resistant to the chem-ical substances present in the cavities, not influence their melting point, and hardly absorb chemical substance nor allow the passage thereof. It has been found that polyisobutylene is a very suitable pressure-sensitive adhesive agent. Alter-natively, the cover layer and the carrier layer may be bonded to each other by a short ultrasonic welding treatment, use being made of an ionomer, for instance, Surlyn (registered trademark), as adhesive agent.
The temperature indicating device according to the invention is particularly suitable to be applied as disposable thermometer for single clinical use. As the temperature indi-cation is irreversible, it should be taken care that prior to actual use, for example, during transport and storage, the temperature indicating device is protected from exposure to temperatures which are higher than the temperature to be mea-sured. The invention will be further described in the follow-ing examples.
EX~MPLE 1 A mixture of equal parts by weigh-t of ortho-chloro-nitrobenzene and ortho~bromonitrobenzene in which 0.1% by weight of a dyestuff has been dissolved i5 poured inside a metal ring which is closed off on one side with polyester film tMelinex, registered trademark, I.C.I., Great Britain) coated with polyisobutylene (Oppanol D 3061, registered trademark, BASF, ,~ `.

W-Germany). After the surface of the tablet thus formed has been smooth, the tablet is placed on coarse, white filter paper in such a way that the mixture of chemicals and dyestuff is in contact with the paper. It is determined how long it will take for the paper to display discoloration at a storage temperature of 28C. The results are listed in Table I.

TABI,r I

Num~er o~ days the , paper remains nyes--tuff/supplier Color Index uncolored at 28C
. .
savinyl blue GLS solvent blue 44 ~ 28 Sandoz orasol blue BLN solvent blue 49 ~ 28 Ciba-Geigy orasol blue GN solvent blue 67 > 28 Ciba-Geigy .
savinyl red BLSN solvent red 90 ~ 28 Sandoz -¦ savinyl blue RS solvent blue 45 > 28 : ¦ Sandoz savinyl b].ue B solvent blue 10 ~28 Sandoz savinyl green B solvent green 19 >28 Sandoz orasol orange RLM solvent orange 59 > 28 Ciba-Geigy orasol navy blue 2RB solvent blue 53 7 Ciba-Geigy D~C green 6 solvent green 3 . 7 blue VIF organol JN solvent blue 63 Ugine ~uhlmann C.I. Mo. 61250 : irgalith violet MNC pigment violet 3 t~- Ciba-Geigy C.I, No. 42535 . fettrot ~S solvent red 24 Sandoz C.I. ~lo. ~6105 ~- 30 irgalith ~ink TYNC pigment red 81~
Ciba-Geigy - C.I~ No. 45160:2 irgalith blue TNC pigment blue 1 Ciba-Ge y C.I. Mo. 42595:Z

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~ 2~ 7 It appears that the dyestu~fs to be used according to~
the invention, viz. solvent blue 10, solvent blue 44, solvent~
blue ~5, solvent blue ~9, solvent blue 67, solvent red 90, !
solvent orange 59 and solvent green 19 still do not cause any discoloration of the filter paper after 28 days' storage at 28C.
By contrast, the majority of the other dyestuffs examined cause discoloration of the paper already after one day.
Also, the solvent green 3 employed in the known single-use thermometers causes discoloration of the paper already afterl seven days and is therefore not quite suitable. ~
EXA~IPLE 2 In this example the suitability as absorbent indicator material ahsorben~ oE various makes of paper is demonstrated.
j The test procedure is as follows. Six cavities formed in an . I aluminium carrier layer are filled with a mixture of ortho-j ¦ chloronitrobenzene and ortho-bromonitrobenzene having a melting point of 38.5~C in which 0.1~ by weight of orasol blue BLM
~solvent blue 49) is dissoIved. In three of the cavities thus, filled the solid mixture is covered by the kind of paper to be examined, and the other three cavities are covered by a reference paper. The reference paper is of a type used in known tempera-, ture indicatin~ devices. Subsequently, the cavities are sealed !
with polyester film (Melinex) coated with a pressure-sensitive adhesive layer of polyisobutylene (Oppanol D 3061). The test objects thus rnade are placed in water of 37.5C. The temperaturej is then increased at a rate of 0.25C/min.
The ternperature at which in the first and in the last~
of the three cavities the paper is fully discolored are written down both for the paper to be examined and for the reference paper. Table II gives:

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a. shift in the temperature level at which dis-coloration occurs with respect to the reference paper (differences between the avera~e values of ~he paper to be examined and the reference paper);
b. spread of the measured ternperatures in the three cavities;
c. rating of discoloration.

~2~

TA~LE I I

Discolor-ation temp. Spread Paper relative to of disc. ~iscolor-reference temp. ation No. Name/firm type (C) (C) ratinq 1 Schleicher & cellu- -0.20 0.07 good, ! Shcull lose uniform chromatogra- color phy pa~er No. 2040 a 2 ditto cellu- -0.14 0.06 good color No. 2043 a lose 3 ditto cellu- -0.14 0.07 qood color No. 2045 a lose

4 Schleicher & cellu- -0.11 0.04 good color Schull lose filter paper (coarse) No. 589' Tyvek style polypro- +0.08 0.10 poor color 6 Pellon* polyester - - very 7450 transp.
paper, no distinct color change 7 Pellon* polyester -0.52 0.06 good color 8 Pellon polyester -0.28 0.14 good color 9 reference cellu- - 0.08 good color paper lose *Registered Trademark ,~ `. .

2~t7 From Table II it can be concluded that paper No. 4 (Schleicher & Schull, coarse filter paper, No. 589') is to be preferred because of its small spread of discoloration tempera-ture. Unsuitabie for use is paper No. 6 (Pellon 7450, registered trademark), which because of its transparency does not display a clearly perceptible color change.

In this example the reproducibility of the tempera-ture indication is demonstrated. A number of cavities formed in an aluminium carrier layer are filled with a series of mix-tures of ortho-chloronitrobenzene, ortho-bromonitrobenzene and 0.1% by weight of Orasol Blue BLN, registered trademark, (solvent blue 49), whose melting temperatures progressively increase by 0.1C. The cavities thus filled are covered with Whatman chromatographypaper No. 1 and subsequently with poly-ester film (Melinex, registered trademark), provided with a pressure-sensitive adhesive coating of polyisobutylene. The test objects are stored at 28C. and after 3, 7 and 10 weeks, respectively, placed in a water bath of a particular tempera-ture to measure the temperature at which discoloration of the indicator layer takes place. The results obtained as average values of 4 temperature indicating devices are listed in Table III.
TABLE III
Temperature at which discoloration occurs (C~
after 0 weeks 36.40 3 weeks 36.45 7 weeks 36.48 10 weeks 36.50 It appears that the temperature indication as a function of times does not or hardly undergo any change.

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g2~7 From the foregoing description of the em~odiments o~
the invention it ~ill be apparent that many modifications may be made therein. It will he understood that these embodiments of' the invention are intended as an exemplification of the invention only, and the invention is not limited thereto. It is to bej understood there~ore that it is intended in the appended claims !
to cover all such modifications which fall ~ithin the true scope and spirit of the invention.

Claims (9)

I The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A temperature indicating device comprising:
a) a thermally conductive sheet as carrier layer provided with one or more cavities formed by depressions in the sheet material, at least one of which depressions is filled with a solid mixture which melts at a predetermined temperature and is composed of ortho-chloronitrobenzene, ortho-bromonitrobenzene and a dyestuff, and b) an indicator layer of absorbent material super-imposed on said solid mixture, and c) a transparent cover layer sealing said cavities and their contents, characterized in that said dyestuff used is selected from the group consisting of dyestuffs which in accordance with the Colour Index are referred to as solvent blue 10, solvent blue 44, solvent blue 45, solvent blue 49, solvent blue 67, solvent red 90, solvent orange 59 and solvent green 19.

2. A temperature indicating device according to Claim 1, characterized in that said dyestuff used is solvent blue 49.

3. A temperature indicating device according to Claim 1, characterized in that said dyestuff used is solvent red 90.

4. A temperature indicating device according to Claim 1, characterized in that said indicator layer is a paper made from cellulose fibers.

5. A temperature indicating device according to Claim 1, characterized in that said indicator layer is paper made from synthetic fibers.

6. A temperature indicating device according to Claim 1, characterized in that said indicator layer is a coarse filter paper.

7. A temperature indicating device according to Claim 1, characterized in that said carrier layer includes an aluminium sheet provided with a number of cavities, which cavities contain solid mixtures having different melting points, and said trans-parent cover layer is of polyester film.

8. A temperature indicating device according to Claim 7, characterized in that said polyester film is bonded to the aluminium sheet by means of a pressure-sensitive adhesive agent.

9. A temperature indicating device according to Claim 8, characterized in that said pressure-sensitive adhesive agent is polyisobutylene.