Time duration indicator systems, and also products containing such indicator systems having a limited duration of use or life

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

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. 
BACKGROUND OF THE INVENTION 
In the case of many products with a limited duration 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 
making further use of the product. 
The end of said duration of life cannot be indicated 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 duration of life from the 
moment they are put into use by the consumer are so-called air-treatment 
products. Such products are intended to disperse one or more volatile 
components, such as perfumes, deodorant components, insecticides, 
pheromones or repellants in the atmosphere by evaporation. If perfumes or 
deodorant components are involved, said air-treatment products are usually 
termed air fresheners. 
Indicator systems specially intended for airfreshener systems are, for 
example, described in the U.S. Pat. No. 4,128,508 and the Japanese Patent 
applications Nos. 56,053,461 and 56,131,681. These are based on the change 
in colour of a pH indicator combined with a slowly evaporating acid or 
base. Such systems have the disadvantage 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. Furthermore, 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 application 
No. 55,027,200, are based on the slow oxidation or reduction of organic 
pigments by added oxidation or reduction agents respectively, or by 
atmospheric oxygen. Such systems have hitherto only proved suitable for 
adding to, for example, shampoo, depilitories, 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 systems are completely unsuitable. 
SUMMARY OF THE INVENTION 
It has now been found that duration-of-life indicators 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 impregnating 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.

DETAILED DESCRIPTION OF THE INVENTION 
The change in the visual properties of the carrier can be achieved in 
various ways. Thus, a transparent 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 coloured 
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 combined with the alteration of the colour. 
Finally, a carrier material which diffusely reflects 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 
carrier. 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 particular, 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 accurately 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 
conditions 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 impregnated carrier and, 
consequently, the change in the indicator, 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 translucent 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 
itself 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 volatile liquid. Finally, it is also possible to mix a carrier, which 
is opaque in the dry state, homogeneously with a colourant. Such a carrier 
is very clearly and detectably 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 providing 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 omitted. 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 indicator 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 experimentally by weighing the 
indicator before impregnation 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 embodiment 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 indicator systems which are based on the principle 
that an opaque 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, powders, whether compacted or not, bonded or sintered, 
such as synthetic or natural polymer powders, silica gel, aluminum 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 use 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 suitable for acting as an 
impregnating liquid. Here the term "volatile liquid" is used to mean a 
liquid with a volatility Such that, after being applied to a carrier, it 
has evaporated within a year at 20.degree. 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 glycols, 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 synthetic origin. Very suitable, for example, are 
polyethylene, polypropylene, ethylene/vinyl acetate copolymer, polyvinyl 
chloride, and polyurethane films. 
If the indicator is intended to indicate the duration 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 permeable to vapour, whereafter, when the indicator is put 
into use, said packaging material is completely or partially removed on at 
least one side, preferably in one operation with the removal of the 
packaging of the product to be indicated. An example of an indicator 
constructed in this way is shoen in FIG. 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 especially 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 
external 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 currents flowing past the products. 
Since the action of such products and of the way 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 FIG. 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 different embodiments are conceivable for such 
systems. 
Many air-treatment products consist of a porous carrier from which the 
active components are released by evaporation. In such cases it is 
possible in principle to make the entire air-treatment product itself, or 
in part thereof, act as a life duration indicator, for example by 
providing a coloured layer at the back as been described above, the colour 
bring visible through the product during the duration of life. In practice 
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 investigated. For this purpose, a carrier 
consisting of a small sheet of porous polypropylene film with an area of 
25 cm.sup.2 and 163 .mu.m 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 .mu.m 
(B) As above:thickness : 225 .mu.m 
(C) Ethylene/vinyl acetate copolymer film, type H-4/M 1436 thickness: 80 
.mu.m 
(D) Polyvinyl chloride film, type MTAS: thickness: 100 .mu.m 
(E) As above:thickness: 150 .mu.m 
(F) As above:thickness: 200 .mu.m 
(G) Polyvinyl chloride film, type DTAS:thickness: 90 .mu.m 
(H) As above:thickness: 120 .mu.m 
(I) As above:thickness: 170 .mu.m 
The films A and B are marketed by Deerfield Urethane Co., South Deerfield, 
USA; film C by Plate Nederland, 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.degree. 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 comparison, the evaporation from the same uncovered carrier was 
determined under the same conditions. 
The results have been summarized in the table below for the volatile 
liquids mentioned therein. The decrease in weight is specified as a 
percentage of the original quantity of liquid. 
______________________________________ 
Effects of various types of film on evaporation 
HEXANOL 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 49 94 100 100 100 
B 13 47 75 93 100 
C 93 100 100 100 100 
D 22 44 60 72 81 
E 11 35 52 68 79 
F 10 33 51 63 70 
G 3 6 12 16 18 
H 0 1 4 6 10 
I 0 0 0 4 7 
none 100 100 100 100 100 
______________________________________ 
______________________________________ 
HEPTANOL 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 40 100 100 100 100 
B 6 35 62 86 93 
C 96 100 100 100 100 
D 18 46 62 74 84 
E 11 32 48 63 69 
F 6 29 47 61 67 
G 1 10 18 24 29 
H 0 6 11 15 16 
I 0 0 0 4 7 
none 100 100 100 100 100 
______________________________________ 
______________________________________ 
OCTANOL 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 19 47 84 92 92 
B 1 18 34 51 68 
C 65 100 100 100 100 
D 5 27 39 54 61 
E 5 25 35 45 55 
F 2 20 29 38 46 
G 1 4 5 9 10 
H 0 0 1 4 5 
I 0 0 0 1 3 
none 100 100 100 100 100 
______________________________________ 
______________________________________ 
NONANOL 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 4 16 27 39 43 
B 0 8 18 27 36 
C 20 65 97 100 100 
D 5 21 31 40 45 
E 4 15 21 30 37 
F 0 10 15 23 30 
G 0 0 3 6 10 
H 0 0 2 3 5 
I 0 0 0 2 5 
none 29 95 100 100 100 
______________________________________ 
______________________________________ 
DECANOL 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 85 98 100 100 100 
B 0 1 3 8 12 
C 17 54 90 100 100 
D 38 87 100 100 100 
E 29 65 93 100 100 
F 26 56 86 90 93 
G 19 61 87 100 100 
H 15 43 74 87 89 
I 11 39 66 79 85 
none 100 100 100 100 100 
______________________________________ 
______________________________________ 
DIETHYLENE GLYCOL MONOETHYL ETHER 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 77 100 100 100 100 
B 25 75 85 89 91 
C 19 60 95 100 100 
D 40 91 100 100 100 
E 31 79 94 97 100 
F 27 70 92 96 100 
G 18 54 85 92 94 
H 18 46 76 86 92 
I 13 38 64 82 86 
none 100 100 100 100 100 
______________________________________ 
______________________________________ 
ISOBORNYL ACETATE 
% evaporation after 
Film 3 days 8 days 13 days 18 days 
23 days 
______________________________________ 
A 2 16 24 33 47 
B 0 0 4 8 12 
C 77 96 98 98 98 
D 58 77 82 86 89 
E 44 65 70 75 80 
F 21 45 54 58 63 
G 31 54 59 63 67 
H 8 44 50 54 58 
I 0 22 32 38 43 
none 100 100 100 100 100 
______________________________________ 
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 cm.sup.2 
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 indication 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:&gt;90 days 
Ethyl dodecanoate:&gt;90 days 
Ethyl tridecanoate:&gt;90 days 
Ethyl pentadecanoate:&gt;90 days 
Undecane:&lt;1 day 
Dodecane:&lt;1 day 
Tridecane:&lt;1 day 
Tetradecane:1 day 
Pentadecene:4 days 
Hexadecene:8 days 
EXAMPLE III 
Three indicators were manufactured by sticking red-colored 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 cm.sup.2. The paper was sprayed beforehand with varnish of the 
type "Protecting Spray 16" made by Talnes, a varnish based on acrylate 
resins. 
The carriers manufactured in this way were impregnated with 0.5, 0.6 and 
0.7 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 rate of change was determined at 21.degree. 
C. and a relative humidity of 45%. The range of change (the time duration 
between the beginning of detectable colour change and complete change) 
varied 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 described here, approximately 0.1 g of liquid more than 
the residual quantity is required for each 10 days of indication duration 
if isobornyl acetate is used as the volatile liquid.