TIME DURATION INDICATOR SYSTEMS, AND ALSO PRODUCTS CONTAINING SUCH INDICATOR SYSTEMS HAVING A LIMITED DURATION OF USE OR LIFE

Abstract: Time duration indicator systems comprising a porous inert carrier (4) and a volatile liquid, capable of reversibly changing the visual properties of the carrier. Such indicator systems can be used for products (1) having a limited duration of use or life.

Description: The invention relates to indicator systems which indicate the end of a predetermined time duration and also to products with a limited duration of use or life which contain such time duration indicator systems. More particularly, the invention relates to indicator systems for once-only use which, in the case of a product with a limited duration of life, indicate when said life has come to an end. In the case of many products with a limited dura­ tion of life it is not possible, or barely possible, for the consumer to detect when said duration of life has come to an end and there is therefore no purpose in mak­ ing further use of the product. The end of said duration of life cannot be indi­ cated by printing on a date during the production since the duration of life only begins at the moment when the consumer actually starts to use the product. In such cases there is a need for an indicator system which is activated at the moment the product is put into use, and which undergoes a clearly visible change at the end of the duration of life. Other products have a limited durability from the moment of production. In these cases a final date of use is generally indicated on the packaging. Said date is often difficult for the consumer to find or poorly legible. In these cases too, an eye-catching indicator could be used with advantage. Typical examples of products with a limited dura­ tion of life from the moment they are put into use by the consumer are so-called air-treatment products. Such pro­ ducts are intended to disperse one or more volatile com­ ponents, such as perfumes, deodorant components, insect­ icides, pheromones or repellants in the atmosphere by evaporation. If perfumes or deodorant components are in­ volved, said air-treatment products are usually termed air fresheners. Indicator systems specially intended for air-­ freshener systems are, for example, described in the U.S. Patent 4,128,508 and the Japanese Patent Applications 56,053,461 and 56,131,681. These are based on the change in colour of a pH indicator combined with a slowly evap­ orating acid or base. Such systems have the disadvan­ tage that the choice of suitable volatile acids and bases is limited, inter alia, because they often have a strong and usually undesirable smell of their own. Fur­ thermore, many are not completely harmless to health and, in addition, volatile acids may have a corrosive effect on metals in the surroundings. Other colour indicator systems, which are described in the Japanese Patent Ap­ lication 55,027,200, are based on the slow oxidation or reduction of organic pigments by added oxidation or re­ duction agents respectively, or by atmospheric oxygen. Such systems have hitherto only proved suitable for add­ ing to, for example, shampoo, depilatories, toothpastes and the like in order to indicate action times from a few minutes to a few tens of minutes. For products with a duration of life of a few days to a few months, such sys­ tems are completely unsuitable. It has now been found that duration-of-life indi­ cators which function effectively can be manufactured by impregnating a porous material, hereinafter termed the "carrier", with a volatile liquid, as a result of which a visible change occurs in the visual properties of the carrier. As a result of evaporation of the volatile im­ pregnating liquid, the original visual properties of the carrier return again after the expiry of a certain time. The time lapse between the beginning of the evaporation and the return of the original properties, hereinafter termed the "indication duration" is therefore chosen in such a manner that it coincides with the duration of life of the product to which the indicator is attached. The change in the visual properties of the car­ rier can be achieved in various ways. Thus, a transpa­ rent porous carrier material can be impregnated with a coloured volatile liquid in a manner such that the carrier remains transparent but acquires a different colour. As a result of the evaporation of the coloured liquid, the original colour of the carrier returns after expiry of the indication duration. A clear carrier material can also be impregnated with a volatile liquid, whether co­ loured or not, such that the carrier becomes cloudy. In that case the change in the indicator is indicated by the carrier becoming clear again, which may or may not be com­ bined with the alteration of the colour. Finally, a carrier material which diffusely re­ flects light in a dry state can be impregnated with a volatile liquid, whether coloured or not, as a result of which the carrier, which was previously not translucent or only slightly translucent, becomes translucent. In this last case the change in the indicator is indicated by the carrier becoming (almost) opaque again, which may or may not be combined with the alteration of the colour. The indication duration is determined, inter alia, by the quantity of volatile liquid which is available for evaporation. At the same time this does not need to be limited to the quantity which can be absorbed by the car­ rier. It is also possible to use a reservoir containing volatile liquid with which the carrier makes contact and from which liquid can be taken up by capillary action. In this manner, a longer indication time can be achieved than would be possible with the quantity of liquid absorbed in the carrier only. Furthermore, the indication duration is determined by the volatility of the liquid and, in par­ ticular, in a manner such that a higher volatility leads to a shorter indication duration. The same applies to an increase in the evaporating surface of the carrier. Finally, the indication duration can be very accu­ rately regulated by covering the carrier impregnated with volatile liquid, with a polymer film which is permeable to the vapour of the volatile liquid. Provided other con­ ditions remain the same, the degree of permeability of a chosen film to the vapour of a chosen liquid determines the rate of evaporation and, consequently, the indication duration. In its turn, permeability is determined by the thickness of the film, the nature of the polymer and the nature of the liquid. If said film is situated on the observer's side of the indicator, it must, of course, be sufficiently transparent in order for it to be possible to detect the change in the indicator which indicates the end of the duration of life. The change in the visual properties of the impreg­ nated carrier and, consequently, the change in the indi­ cator, can be detected both by transmitted and by incident light. In the first case a translucent layer in a colour differing from that of the carrier material and/or the impregnating liquid is preferably provided behind the carrier, as a result of which the change in the indicator from cloudy to clear or from translucent to opaque is accompanied by a change in colour. The initial and final colour can be chosen as desired by optionally colouring the carrier material itself. Even if the indicator is intended to be used with incident light, it is advisable to provide the carrier with a coloured layer on the side facing away from the observer, which coloured layer can be observed through the carrier in the clear or translu­ cent state of the carrier and cannot be, or virtually cannot be, observed in the cloudy or opaque state. In this latter state only, or principally, the carrier it­ self is observable. If incident light is used, however, the coloured layer does not need to be translucent, but a fluorescent or strongly reflecting material is preferably chosen so that as good use as possible is made of the quantity of instant light. Such a coloured layer may, for example, consist of fluorescent paint or paper, glass, metal, plastic or another material coated with such paint. Said paint must not be soluble in the vola­ tile liquid. Finally, it is also possible to mix a car­ rier, which is opaque in the dry state, homogeneously with a colourant. Such a carrier is very clearly and detect­ ably coloured in the impregnated state, but during the change the colour largely disappears before the eye and only a slightly coloured carrier remains behind. The assessment of whether the indicator has or has not changed can be appreciably simplified by provid­ ing an object with the same exterior as the indicator after change in the immediate vicinity of the indicator for comparison. For this purpose, for example, the same indicator may be used from which the volatile liquid has been om­ itted. It is also possible to give the wrapping of the product to be indicated the colour of the indicator after change so that the latter does in fact stand out from its surroundings before change, but no longer does so after change. The change in the indicator usually occurs even before 100% evaporation of the volatile liquid has taken place. The residual quantity which is still left after the change, depends on the specific design of the indica­ tor and the materials used in it, but is independent of the quantity of liquid at the beginning of the indication duration provided the latter exceeds the residual quantity. The residual quantity is simple to determine ex­ perimentally by weighing the indicator before impregna­ tion with liquid and shortly after complete change. It is constant for a combination of a chosen embodiment of the indicator and a chosen liquid. For a chosen embodi­ ment and liquid, the indication duration is approximately directly proportional to the quantity of liquid. Many different materials are suitable for acting as a carrier material for the indicator. For the indica­ tor systems which are based on the principle that an op­ aque carrier becomes translucent by impregnation with volatile liquid and becomes opaque again by evaporation, for example, paper, textiles, felt-type materials, porous, non-transparent polymers, porous ceramic materials, pow­ ders, whether compacted or not, bonded or sintered, such as synthetic or natural polymer powders, silica gel, alu­ minium oxide and the like are suitable. In order to be satisfactorily translucent in the impregnated state, a thin layer of carrier material should be used. In the case of uniformly coloured carriers, however, in which the change is based on the colour difference in the carrier itself in the impregnated and in the dry state, thick layers or carriers in the form of pills or tablets may also be used. For the indicator systems, which are based on the principle that a clear carrier material becomes cloudy and/or changes colour on impregnating with a liquid and, after evaporation of the liquid regains its original colour again and/or becomes clear again, clear porous polymers are primarily very suitable. Many types of volatile liquids are likewise suit­ able for acting as an impregnating liquid. Here the term "volatile liquid" is used to mean a liquid with a vola­ tility such that, after being applied to a carrier, it has evaporated within a year at 20°C. The volatile liquid to be used should be harmless to health and not have any undesired smell in the concentrations released during evaporation from the indicator. Furthermore, the carrier and the polymer covering film optionally to be provided must not dissolve in the liquid or react with it. Suitable liquids may be, for example, water, alcohols, diols, polyols and low-molecular polymers thereof, such as polyethylene glycols, polypropylene gly­ cols, copolymers thereof and ethers derived therefrom, other single and multiple ethers, ketones, aldehydes, nitriles, esters etc. Such liquids are known, for example, as industrial solvents or raw materials. Covering film which is permeable to vapour and suitable for regulating the rate of evaporation of the volatile liquid may be of natural, semisynthetic or syn­ thetic origin. Very suitable, for example, are poly­ ethylene, polypropylene, ethylene/vinyl acetate copolymer, polyvinyl chloride, and polyurethane films. If the indicator is intended to indicate the dura­ tion of life of a product from the moment it is put into use by the consumer, the packaging of the indicator should be impermeable to the vapour of the volatile liquid. In a preferably used embodiment of the indicator a small disc of impregnated carrier is completely wrapped in a packaging material which is not permeable to vapour, for example a thin metal foil or plastic material which is not per­ meable to vapour, whereafter, when the indicator is put into use, said packaging material is completely or par­ tially removed on at least one side, preferably in one operation with the removal of the packaging of the pro­ duct to be indicated. An example of an indicator con­ structed in this way is shown in Figure 1 in which (1) represents a product with limited duration of life, (2) a packaging material which is impermeable to vapour, (3) a film which is permeable to vapour, (4) an impregnated carrier and (5) a coloured and/or reflecting layer. The indicator systems described above are especi­ ally suitable for indicating the duration of life of air-­ treatment products such as air fresheners and insecticide spreaders, in which the active component is released to the atmosphere by evaporation from a carrier material. Said carrier material may be of a completely different type to the carrier material which is used for the life duration indicator. The duration of life of such air-­ treatment products may be considerably affected by exter­ nal factors, such as the ambient temperature, the degree of ventilation and the degree of humidity of the room in which the product is set up, and the presence of air cur­ rents flowing past the products. Since the action of such products and of the life duration indicator according to the invention are based on the same principle, said external factors affect the duration of life of the preparation and the indication duration of the indicator in a corresponding manner, as a result of which a precise indication of the duration of life is obtained under varying circumstances. Some air-treatment products are provided with a packaging with a variable opening, with which the rate of evaporation of the active components can be regulated. By also providing the space in which the life duration indicator is situated with such a variable opening and coupling the mechanisms for opening and closing the two openings together, the precise indication duration can also be obtained for said products. An example of such a system is shown in Figure 2, in which (11) represents a container of the air-treatment product (front view), (12) and (13) represent rotatable segments on a single spindle, (14) represents an opening behind which the life duration indicator is situated, and (15) represents an evaporation opening for the air-treatment product. It will be clear to those skilled in the art, that many dif­ ferent embodiments are conceivable for such systems. Many air-treatment products consist of a porous carrier material from which the active components are released by evaporation. In such cases it is possible in principle to make the entire air-treatment product it­ self, or a part thereof, act as a life duration indica­ tor, for example by providing a coloured layer at the back as been described above, the colour being visible through the product during the duration of life. In prac­ tice it is often more expedient to provide a separately manufactured duration of life indicator. The following examples serve to illustrate the principle of the invention and some possible applications. The invention is, however, not limited thereto. Example I The effect of a number of covering films on the rate of evaporation of various volatile liquids was in­ vestigated. For this purpose, a carrier consisting of a small sheet of porous polypropylene film with an area of 25 cm² and 163 µm thick and having a 75% pore volume was impregnated with 0.3 g of liquid and covered with one of the following vapour-permeable films: A) Polyurethane film, type PS 8010 thickness: 100 µm B) As above thickness: 225 µm C) Ethylene/vinyl acetate copolymer film, type H-4/M 1436 thickness: 80 µm D) Polyvinyl chloride film, type MTAS thickness: 100 µm E) As above thickness: 150 µm F) As above thickness: 200 µm G) Polyvinyl chloride film, type DTAS thickness: 90 µm H) As above thickness: 120 µm I) As above thickness: 170 µm The films A and B are marketed by Deerfield Ure­ thane Co., South Deerfield, USA; film C by Plate Neder­ land, Soest; films D to I incl. by Draka, Amsterdam/­ Enkhuizen; the porous polypropylene film type accurel by Enka, Obernburg, West Germany. The evaporation (at 21°C and a relative humidity of 45%) was tracked by measuring the decrease in weight as a consequence of evaporation 3 days after impregnation and subsequently at intervals of 5 days. As a compari­ son, the evaporation from the same uncovered carrier was determined under the same conditions. The results have been summarized in the table be­ low for the volatile liquids mentioned therein. The de­ crease in weight is specified as a percentage of the ori­ ginal quantity of liquid. Example II The indication duration of indicators consisting of a carrier of porous polypropylene film described in Example I having an area of 0.4 cm² and coated on the reverse side with fluorescent paint was determined. Each carrier was impregnated with approximately 0.05 ml of volatile liquid. The indication duration was determined at room temperature. The impregnated carriers were not covered with a polymer film. The table below lists the volatile liquids used, followed by the indication duration obtained. The figures obtained are not intended to provide more than an indica­ tion of the indication duration which can be achieved under similar circumstances: Ethyl decanoate 3 days Propyl decanoate 4 days Isobutyl decanoate 12 days n-Butyl decanoate 14 days Isoamyl decanoate 14 days Methyl undecanoate 3 days Ethyl undecanoate 5 days Isoamyl undecanoate 10 days Phenylethyl undecanoate >90 days Ethyl dodecanoate >90 days Ethyl tridecanoate >90 days Ethyl pentadecanoate >90 days Undecane <1 day Dodecane <1 day Tridecane <1 day Tetradecane 1 day Pentadecene 4 days Hexadecene 8 days Example III Three indicators were manufactured by sticking red-coloured paper of type "Normacolor 022.200" made by Mecanorma, France over the reverse side of small white sheets of porous polypropylene film described in Example I, area 25 cm². The paper was sprayed beforehand with varnish of the type "Protecting Spray 16" made by Talens, a varnish based on acrylate resins. The carriers manufactured in this way were impreg­ nated with 0.5, 0.6 and 0.7 g respectively of isobornyl acetate, as a result of which the colour of the indicator changed from white to red. The impregnated carriers were covered with film A from Example I. The indication duration and the range of change was determined at 21°C and a relative humidity of 45%. The range of change (the time duration between the begin­ ing of detectable colour change and complete change) var­ ied from 3 days for 0.5 g of liquid to 4 days with 0.7 g of liquid. Complete colour change to white was reached after 16 days with 0.5 g, after 25 days with 0.6 g, and after 35 days with 0.7 g. After complete colour change approximately 0.35 g of liquid proved to be present in all 3 indicators so that approximately 0.15, 0.25 and 0.35 g, respectively, of liquid were available for evaporation. As appears from the results, in the indicator system de­ scribed here, approximately 0.1 g of liquid more than the residual quantity is required for each 10 days of indica­ tion duration if isobornyl acetate is used as the vola­ tile liquid.

Claims: 1. Time duration indicator system, characterized by a porous inert carrier and by a volatile liquid, which is capable of reversibly changing the visual properties of the carrier, impregnated into said carrier. 2. Time duration indicator system according to Claim 1, characterized in that the carrier is transparent and the volatile impregnating liquid has a colour differ­ ent from that of the carrier. 3. Time duration indicator system according to Claim 1, characterized in that the carrier is clear and the volatile impregnating liquid, which may or may not be coloured, produces a cloudiness in the carrier. 4. Time duration indicator system according to Claim 1, characterized in that the carrier reflects light diffusely in the dry state and the impregnating liquid, which may or may not be coloured, renders the carrier translucent. 5. Time duration indicator system according to one or more of Claims 1-4, characterized in that the system is provided with a reservoir for the volatile impregnat­ ing liquid, which reservoir is connected to the carrier. 6. Time duration indicator system according to one or more of Claims 1-5, characterized in that the evapora­ tion surface of the carrier is provided with a vapour-­ permeable film, which film is at least partially trans­ parent. 7. Time duration indicator system according to Claim 6, characterized in that the vapour-permeable film is a plastic-material film. 8. Time duration indicator system according to one or more of Claims 1-7, characterized in that the reverse side of the carrier is provided with an inert translucent layer having a different colour from the carrier material and/or volatile impregnating liquid. 9. Time duration indicator system according to one or more of Claims 1-7, characterized in that the reverse side of the carrier is provided with an inert opaque layer having a colour different from the carrier material and/or volatile impregnating liquid. 10. Time duration indicator system according to Claim 9, characterized in that the opaque layer is embo­ died in a fluorescent or reflecting material. 11. Time duration indicator system according to one or more of Claims 1-10, characterized in that the evapo­ ration surface of the indicator system is provided with a detachable film which is not permeable to the volatile impregnating liquid. 12. Product with a limited duration of use or life, provided with a time duration indicator system according to one or more of Claims 1-11, it being understood that the duration of use and of life and the indication dura­ tion of the indicator system are matched to each other. 13. Product according to Claim 12, characterized in that the product is also provided with an indication sign based on the carrier used in the indicator system in non-­ impregnated form. 14. Product according to Claim 12 or 13, character­ ized in that the impermeable film of the indicator system according to Claim 11 forms part of the packaging to be removed from the product before use. 15. Product according to one or more of Claims 12-14, characterized in that the product is an air-treatment product which contains one or more volatile substances as active components. 16. Product according to Claim 15, characterized in that the product contains a regulating element with which both the evaporation surface of the product and of the indicator system is adjusted.

Inventors: TRAAS, PETRUS CORNELIS
Applicants: NAARDEN INTERNATIONAL N.V.
Application year: 1986
Main classification: G07C1
IPC codes: G09F3, G04F1, G07C1, G01K3, C09K3