WO1988005262A1

WO1988005262A1 - A means for prolonging the life of cut flowers

Info

Publication number: WO1988005262A1
Application number: PCT/SE1988/000018
Authority: WO
Inventors: Lars Zetterquist
Original assignee: Lars Zetterquist
Priority date: 1987-01-23
Filing date: 1988-01-22
Publication date: 1988-07-28
Also published as: AU1187788A; EP0344187B1; JPH02501885A; ATE83604T1; SE8700259D0; DE3876982D1; SE456391B; EP0344187A1; SE8700259L; JPH0685664B2; DE3876982T2; US5102715A

Abstract

A means for keeping fresh cut flowers placed in water, which is in the form of a label (1) applicable to one or more stalks of the cut flowers. The label comprises a water insoluble carrier layer (2), a coat (4) applied to the same which comprises an active material and a barrier layer (5) for water applied to this coat (4). The active material comprises at least one active substance which sets free bactericidal and/or bacterial inhibiting agent in the presence of water. In accordance with the invention the barrier layer in cooperation with the carrier layer regulates the size of the total contact surface of the water with the active material and consequently the release time for the active substance when the label is immersed into the water.

Description

A MEANS FOR PROLONGING THE LIFE OF CUT FLOWERS

The present invention relates to a means for prolonging the life of cut flowers standing in water. The means is in the form of a label which comprises a water-insoluble carrier layer and a coat applied to the same, the coat containing an active material with at least one substance setting free bactericidal and/or bacterial inhibiting agents in the presence of water.

A plant contains a network of ducts for the transport from the roots to the shoot of water and substances dissolved therein. When a flower-stalk is cut off these ducts are opened, so that during the remaining life of the flov/er the water, which normally comes from the roots and which is constantly supplied to leaves and flowers so that they should not wilt, now has to be absorbed through the cut wound formed. It is of the greatest importance for the keeping quality of cut flowers, therefore, that the ducts in the stalks should be kept open as long -as possible after the cutting, so as to make possible this transport of water and of substances possibly dissolved in the water. Choking up of the ducts may occur through bacteria and algae penetrating into them or through scar substances which are formed by the plants inside the ducts, or through the actual cut surface receiving a coating of microorganisms.

The impaired water absorption of cut flowers which have been placed in a vase indicated in the preceding paragraph as a rule causes them to wilt much earlier than if they had been allowed to remain on the plant. Through frequent cutting off of the flower stalks and daily changing of the water, the life can be prolonged to some extent, but since such measures necessitate both care and effort, they are frequently neglected. By using a so-called preservative agent which is dissolved in the vase water it is possible, however, without too much effort to prolong the life. In this way one of the causes for the early wilting and death of the flowers is acted upon, namely the aforementioned choking up. In cut flowers which have been cut off from the mother plant the nutrient reserve (consisting primarily of sugar) in leaves and flowers rapidly becomes exhausted, whereupon the flowers wilt. If this starvation can be prevented in that a nutrient substance, e.g. usually sugar, is supplied from the outside via the vase water, an appreciable prolongation of life becomes feasible. Hov/ever, the possibility of a supply of sugar from the outside too will depend, of course, on being able to keep open the ducts in the stalks. Since sugar solution is an excellent substrate also for bacterial grov/th, the addition of sugar to the vase water entails the risk, though, of the stopping up of the ducts being increased. This too can be prevented by the addition of a so-called preservative agent (bacte¬ ricidal agent) to the vase water as a result of which the duct openings remain open and nutrient supplied to the vase water can be absorbed by the cut flowers.

The presence of large quantities of bacteria in vases with cut flowers has been established many times. A bacteria count of up to 10^3 _m ^~\-1 has been reported. Attention has been drawn in parti- cular to the occurrence of so-called gram-negative pathogens in flower vases in a hospital environment.

Means of the type referred to in the introduction are known from US patent specification No. 4 167 832. According to this the coat v/hich contains active material is adapted for direct contact with the water so that on immersion of the label in the water a reaction is started in connection with the whole surface of the coat releasing chlorine from the layer. The quantity of chlorine which at any given time is present in the water is determined partly by the rate of reaction, partly by the consumption and evaporation of chlorine from the liquid surface. On application of the technique described in the patent specification it is found that when the label is immersed in the water, a very rapid liberation of chlorine sets in which leads to a rapidly increasing chlorine concentration in the water. According to the patent specification this agrees with the effect aimed at, since it is the intention through a rapidly increased concentration of chlorine to kill quickly all bacteria in the vase water and prevent thereby any stopping up of the liquid and nutrient ducts ending at the cut surface.

A serious disadvantage associated with a large quantity of chlorine being released into the vase water during a very short period is that the high chlorine concentration which arises in the vase water causes damage to cut flowers with sensitive foliage and sensitive stalks.

It is a further disadvantage that the active agent is consumed relatively quickly which in turn leads to the chlorine concentration of the water diminishing prematurely, that is to say the flowers wilt earlier than would be the case with a better distribution in time of the setting free of the chlorine.

The label in accordance with the patent specification cited in the foregoing paragraph has the further disadvantage that the active substance is set free when the label comes into contact with water during transport or storage. If the active substance specified in the patent is chlorine, a strong smell of chlorine will ensure. On skin contact with the label skin irritations easily can occur which may cause problems for persons frequently handling the product, e.g. employees in flower shops. There is also a risk that clothes might be damaged on coming into contact.

It is the object of the invention to reduce to a substantial degree the above entioned problems and to provide a means which makes it possible to keep the flowers fresh in the water for a longer time than has been possible hitherto.

The novelty of the invention consists essentially in that the coat of active material is surrounded on each of its two sides by at least one substantially water-impermeable layer and that between the water-impermeable layers located closest to the coat, and/or through passages provided in the layers, regions for contact of the water with the active material are formed.

In accordance with a preferred embodiment of the invention a coat of active material includes a substance which sets free chlorine, sodium dichloroisocyanurate having proved to be particularly suitable.

In accordance with a preferred embodiment the water-impermeable barrier layer is formed by a lacquer based on at least one acrylic compound. This is selected from a group consisting of acrylate derivative, diacrylate derivative, triacrylate derivative and acrylo-epoxide compounds, the lacquer containing moreover a photo- initiator which initiates the hardening of the lacquer under the influence of UV-light.

The dependent claims refer to further appropriate embodiments of the invention.

The invention will be described in greater detail with reference to the drawing, wherein

Fig. 1 shows schematically a means in accordance with the invention, Fig. 2 shows an alternative embodiment of a means in accordance with the invention, and Fig. 3 shows a curve diagram v/ith the results from comparative experiments.

In Fig. 1 is shown schematically an embodiment of the invention where a means in the form of a label 1 comprises a carrier layer 2, which in accordance with a preferred embodiment consists of a water- insoluble and, substantially, water-impermeable flexible material, preferably a plastic material, e.g. polyvinyl chloride, polypropylene or similar material. The carrier layer as a rule is relatively thin, and a thickness of approx. 0.1 mm has proved to be sufficient. Alternatively, the carrier layer consists of some other material with a certain capacity of allowing the passage of liquid or the drawing up or absorbing of the same, e.g. paper or cardboard.

The carrier layer of the label is covered on its upper side with a coat 4 which contains an active material containing at least one active substance which sets free bactericidal and/or bacterial inhibiting agents in the presence of moisture or water. Such a preferred active substance, which is used in an embodiment of the invention, is sodium dichloroisocyanurate. The coat 4 comprises further a carrier material for the active material in the form of a plastic binder. On application, the plastic binder and the active material are mixed to a paste with which the solid carrier layer 2 is coated.

The label is shown in Fig. 1 in an embodiment where the underside of the carrier layer, and consequently of the label, is covered with a binder layer 3. The binder layer in accordance with a preferred embodiment consists of a rubber-based binder, e.g. that which is known in the trade as Beiersdorf B4. In certain applications the binder layer consists of a water-impermeable material. This latter embodiment is used especially when the carrier layer is water- permeable and the binder layer is used in order to protect the surface of the carrier layer from contact with the water, which otherwise easily could pass the carrier layer and make contact with the coat 4 comprising active material.

The coat 4 which contains active material is coated on its upper side with a layer 5, referred to hereinafter as barrier layer 5, of sub- stantially water-impermeable material. When the label is lowered into the water, the barrier layer hinders the water from coming into contact with the surface of the coat 4. Through the placing and design of the barrier layer and the carrier layer, alternatively the binder layer, the extent of the surface of the coat 4 is regulated with which the water makes, or is able to make, contact, and conse¬ quently the quantity of bactericidal agent which on each occasion is released. Active substance diffuses out continuously, but at a rate diminishing in time, from the surfaces which are not covered by layers representing barriers against the water. In certain appli- layer 2 and the coat 4 and/or between the coat 4 and the barrier layer 5 in order to improve the release of active substance from central parts of the label.

It is evident from Fig. 1 that in the embodiment shown in the Figure the traverse edge surfaces of the label are devoid of protective layers. In other embodiments where it is desired to reduce the exposed contact surface, at least some edges are coated wholly or partly with protective layer. In certain embodiments the barrier layer 5 does not cover the whole coat, but leaves regions adjoining the edges of the label uncovered. In yet other embodiments the exposed contact surface is increased by means of one or several through-going holes in the label.

The embodiment where all edges are without protective layers has advantages from a point of view of manufacture, since the individual labels can be punched out from a larger plate containing the coat 4 with active material as well as all the layers surrounding the coat.

Fig. 2 shows an embodiment of the invention according to which the barrier layer 5 is provided with passages 6 which allow direct contact between the coat 4 of active material and the environment. As is evident from the Figure the number of passages, and consequently the contact surface of the active material per surface unit, in certain embodiments is greater in connection with the edges of the label. This distribution of passages is chosen in applications where there is a need for a more rapid release of bactericidal means as soon as the label has been placed in the water and for a complete release of active substance from the coat 4 of active material within a certain time. In the Figure the passages are shown as round holes, but alternative designs of the passages, e.g. slots, perforations etc., of course, are likewise within the concept of the invention. Although in Figure 2 passages are only shown on the barrier layer, in certain applications the carrier layer and/or the binder layer too are provided with passages. The latter alternative relates in parti¬ cular to applications where the binder layer 3 does not permit the passage of v/ater and of bactericidal and/or bacterial inhibiting means. This latter embodiment, of course, is feasible only in cases where the label is let down into the vase v/ater or in applications where the flowers tolerate the high concentrations of bactericidal and/or bacterial inhibiting agents which occur in connection with passages in the carrier layer.

Prior to use, the label is stored appropriately on a protective foil to which the label is fixed detachably, with its binder layer 3 lying against the protective foil.

According to a practical realization of the label, it has a size of about 20x50 mm and contains in its coat 4 a chlorine salt of the type indicated in a quantity of about 40-50 mg (dry weight). When the label is to be used, it is detached from the protective foil and fitted e.g. around one or more flower stalks with surfaces of the binder layer 3 stuck to one another or it is lowered down separately into the water.

The said barrier layer 5 in accordance with the present invention is constituted of a specially selected surface lacquer, which is based on at least one acrylic compound, and which is applied to the coat 4 of active material in the form of a mixture preferably containing several acrylic compounds and a photoinitiator which hardens the lacquer under the influence of UV-light. The mixture is applied appropriately in a quantity of 25-35 g/m calculated on dry weight.

The surface lacquer proposed in accordance with the invention forms a barrier layer which reduces the risk of a release of the bactericidal and bacterial inhibiting agent, e.g. chlorine, in a moist environ¬ ment. Furthermore, the risk of skin irritations in persons handling the labels is reduced as the agent cannot issue forth through the surface lacquer. The danger of the bactericidal and/or bacterial inhibiting agent coming into contact with clothing and damaging the same is also eliminated. This applies also to embodiments of the invention where the label is provided with passages. If e.g. during transport or storage of a bouquet, water accidentally should get onto the label kept therein, and the active agent chosen for the label is, for example, chlorine, little chlorine smell v/ould develop. If the label is manipulated with wet hands, there is no risk of skin irrita¬ tion either, since release of active substance through e.g. perfora- ^' tions occurs only after several minutes complete immersion in water. The most tangible effect of the means in accordance with the invention, however, is that the release of the bactericidal and/or bacterial inhibiting agent in the v/ater takes place over a longer period and in a more controllable manner than would be the case in labels of a similar type known hitherto. This is achieved by the material of the barrier layer not allowing v/ater and bactericidal and/or bacterial inhibiting agent to pass through to an appreciable extent, but by these being released on the whole only via the regions which are not protected by barrier layers, e.g. one or more of the lateral edges of the label and possible passages which have been provided in the surrounding layers. As a result of the regulated, and by comparison with previous technique greatly reduced, rate of release after immersion in the v/ater, the burning damages on the foliage, especially on sensitive species of flowers, encountered frequently on using e.g. chlorine according to previously applied techniques are avoided. Moreover, the flowers keep fresh for a longer time compared with flowers standing in water into which has been downed a label which lacks a barrier layer.

The technical effect of labels with or without barrier layer in accordance with the present invention is evident from the following experiments. In all these experiments the label v/as of the same size. Likewise identical were the quantity of active material, the quantity of v/ater (1 litre) and the water temperature (24°C. In all the expe- riments the carrier layer consisted of water-impermeable material and, more particularly, of polyvinyl chloride in a thickness of approximately 0.1 mm. The barrier layer consisted of an acrylic-based UV-lacquer (referred to hereinafter as UV 25-35) of a total thickness corresponding to 25-35 g/m and containing several acrylic com- pounds and a photoinitiator which causes the lacquer to be set in approximately 1 s. The active substance consisted of sodium dichloroisocyanurate. The containers wherein the water as kept were adapted so as to minimize the discharge of chlorine to the environ¬ ment. In Figure 3 are indicated on the Y-axis the quantity in mg of chlorine released which is found in the v/ater per litre water, and on the X-axis the time in hours. Experiment 1 The experiment (cf. curve A) was intended to determine the rate of release of active substance from a label without a barrier layer, but whose carrier layer was water-impermeable. The curve indicatesthat after approximately 12 hours substantially all the chlorine had been released. Thereafter the chlorine content in the water diminished slowly owing to losses to the environment.

Experiment 2 A corresponding experiment (cf. curve B) was carried out with a label where the coat 4 with active material was covered on its upper side with a barrier layer which had no passages (corresponding to the embodiment described in connection with Fig. 1). The label, for the rest, was of the same dimensions and build-up as the label in experiment 1. The active material thus was accessible for contact with the water only along the transverse edge surfaces of the label. The quantity of chlorine in the water increased continuously during the 96 hours of the experiment. After 96 hours the increase was very moderate. It was found that only after approximately 36 hours the chlorine content was sufficiently high to achieve an inhibiting effect on the bacterial growth which v/ould influence the life of the flowers. During the first 18 hours the bacterial growth continued substantially without any reduction.

Experiment 3

The barrier layer of the label was perforated, the perforations being distributed substantially uniformly over the surface of the barrier layer. For the rest the label corresponded to that which was used in experiment 2. It is evident from the result (curve C) that the quan- tity of chlorine released after 12 hours already corresponded to the quantity which had been released after 36 hours on using a barrier layer without holes. It is further evident from the curve that the total quantity of chlorine given off after 96 hours exceeds the quantity v/hich has been given off by the label in experiment 2 and approaches the total quantity which is discharged by the label without a barrier layer. The differences in the releasing effect are clearly evident. When the barrier layer is absent, the release takes place so rapidly that after approximately 6 hours all the chlorine in the active material has been released. With a barrier layer and without the provision of holes the chlorine is released very slowly from the active coat and not even after 96 hours attains an accumulated quantity corresponding to the quantity which is released from the label without a barrier layer. The explanation for this is that in the absence of a barrier layer all the active material in the coat 4 will be accessible for contact with water. By contrast it is found that the label in accordance with experiment 2 after 96 hours releases only a limited amount of chlorine which can be explained by the fact that chlorine is released from the coat only in a region close to the edges of the label, whereas the more centrally located material on the whole does not release any chlorine. The width of the region of release at the edges of the label can be increased to a certain extent by raising the thickness of the coat 4 with active material which also brings about an increase in the rate of release during the first phase of the release process. On the other hand it takes such a long time for the water to release chlorine from the centrally situated material portions, that the contribution to the quantity of chlorine in the water which can be furnished from these regions is without real significance.

During the first phase of the release process the rate of release of the label provided with passages can be increased by increasing the number of passages (exposed surface on the coat 4 with active material) in the region nearest the edges of the label. In this way the release process can be directed so that the curve C is given a steeper gradient in the starting phase and a more gentle gradient thereafter. By reducing the exposed surface, e.g. the number of passages in the edge regions of the label it is possible instead to reduce the rate of release during the first part of the release process so that the curve C obtains a weaker gradient in the starting phase. After substantially all the accessible chlorine has been released from the edge region of the label, the subsequent supply of chlorine to the water takes place on the whole merely via the passages in the central portion of the label. It is obvious, therefore, that by providing a certain number and a certain defined layout of the passages in the barrier layer, a regulation of the rate of release in time, and thereby also a regulation of the amount of chlorine which is present in the vase v/ater, will be achieved.

The effect described in the foregoing paragraph is obtained in an alternative embodiment through variation of the opening area of the passages. Through selection of the number of passages and/or the size of the passages the rate of release is thus controlled and in this way the rate of release and the accumulated quantity of chlorine can be varied in time so as to adapt to the tolerance different cut flowers present towards chlorine. Naturally the method is not limited to being applied only to the release of chlorine, but the method is generally applicable to the release of bactericidal and/or bacterial inhibiting agent from the coat 4 comprising active material.

In the diagram has also been included a curve D which indicates how chlorine has been discharged to the atmosphere during 96 hours if the quantity of chlorine at the start was 100 mg. The experiment was carried out under corresponding conditions as experiments 1-3 where¬ fore the curve D also constitutes an indication of losses to the environment during experiments A-C. The slope of the curve D corre¬ sponds to a loss of approximately 3 % chlorine per day. It should be noted that on application of the invention the amount of chlorine decreases more rapidly because of the reactions which ensue in the vase water betv/een chlorine and substances and/or organisms occurring in the vase water.

The experiments were completed by placing a drop of pure water on a dry label and noting that a reagent powder for chlorine

(N,N-diethyl-p-phenylenediamine sulphate) was instantly coloured red when the barrier layer v/as absent v/hilst it remained unaffected when a barrier layer without passages was in position. When a sprinkle of pure water was brought onto a dry label with UV— 5—35 lacquer and a test with reagent powder v/as carried out, no discharge of any chlo¬ rine could be detected, not even when the powder was rubbed in for a few minutes. This confirms that on the label in accordance with the present invention the barrier layer prevents chlorine from passing into the water. Experiment 4 The effect of different preservative agents on cut flowers v/as examined. In each test five stalks were used in a vase with 0.5 litre of water. In the Table which follows the symbols used have the following meanings:

KONT = No preservative agent UV-N = Label without barrier layer and with carrier layer covered by an active coat containing sodium dichloroisocyanurate, this label being used jointly v/ith two lumps of sugar. UV-A = Label with barrier layer lacking passages and consisting of

UV-25-35 lacquer comprising several (three) acrylic compounds and with sodium dichloroisocyanurate in the active layer, this label being used jointly v/ith tv/o lumps of sugar.

KRIS = Krislite, which is the trade name of another preservative agent and which is used in the specified quantity.

The quality of the cut flowers is assessed on a scale 0-5, where 5 is the highest quality.

TABLE

Date of Assessment

Species Treatment 7/12 9/12 10/12 13/12 21/12

KONT 5 4 3 1

Rose UV-N 5 5 4 4*

Gabriela UV-A 5 5 5 5

KRIS 5 5 4 3**

KONT 5 3 3 0

Gerbera UV-N 5 5 1 0

UV-A 5 3 0

KRIS 5 5 3 0

KONT 5 5 1 0 0

"Green" UV-M 5 2 0 0 0

Ad anthu UV-A 5 3 3 2 0

KRIS 5 2 0 0 0

^"") Green leaves wither

"^'*) Green leaves turn yellow It is clearly evident from the above results that preservative agents have a beneficial effect on the keeping quality of the flowers and that UV-A (acrylic compound lacquer-label in accordance with the invention) is superior to the label without barrier layer and, for certain flowers, is also better than the preservative agent called Krislite.

The active coat, beside containing a chlorine salt as a preservative, may include other active substances, such as other bactericides, one or more bacterial inhibiting substances, one or more surface-active substances and one or more nutrients. Examples of substances which in certain applications are included in the active coat by themselves or in combination are silver thiosulphate or compounds containing nickel, copper or aluminium.

A preferred UV-lacquer in accordance v/ith the invention contains as acrylic compound components an acrylate derivative, hexanediol diacrylate, trimethylolpropane triacrylate and acrylo-epoxide derivative.

Acrylic lacquers of a diversity of compositions are suitable to be used. Examples of lacquers are those acrylic lacquers which contain photoinitiators of a composition which entails a hardening of the lacquer within a short time, as a rule v/ithin approximately 3 s, and preferably 1 s, when the lacquer is exposed to ultraviolet light exceeding a certain intensity.

It has been found appropriate to select as a barrier layer an acrylic compound which has been chosen from a group consisting of acrylate derivative, diacrylate derivative, triacrylate derivative and acrylo-epoxide compound and to allow photoinitiators according to the above to enter into the lacquer.

In applications where passages are absent experiments have shown that in certain compositions the coat 4, which includes the active material, rapidly sets free bactericidal agents immediately after immersion in the water, but that thereafter the discharge of agent becomes slower and gradually ceases altogether. This phenomenon is made use of in certain of the aforementioned applications of the invention in order to control the discharge of bactericidal and/or bacterial inhibiting agent in time through e.g. selective distribu¬ tion of the layout of the pssages in the barrier layer or of through- going holes in the label. By the selection described earlier of the size of the passages or of the through-going holes and the number of passages or through-going holes per surface unit, the contact sur¬ faces between water and active material are regulated, as a result of which the active material which is located away from the edges of the label or from the through-going holes will continue to discharge bactericidal material, even after the discharge via the active mate¬ rial exposed at the edges of the label or at the holes has substan¬ tially ceased. In the region adjoining the passages too the depth of effectiveness in the active material for the penetrant water is limit- ed. In certain applications the discharge of bactericidal and/or bac¬ terial inhibiting agents directly after letting the label down into water is accelerated by increasing the number of passages or through- going holes and/or the size of the these passages or holes close to the edges of the label, whereas in other applications the supply of bactericidal and/or bacterial inhibiting agent is kept to a lower level by placing passages only in the central parts of the label.

One phenomenon occuring on application of barrier layer which contains acrylic compound components and where the lacquer applied is hardened with the help of ultraviolet light, is that the lacquer easily wrinkles during hardening, a phenomenon which is particularly common in thick lacquer layers. Such a wrinkling frequently results in the lacquer layer becoming water-permeable. In accordance with the invention, therefore, the barrier layer is applied in several succes- sive courses and the lacquer is allowed to harden between each course. In this v/ay the lacquer is kept at such a thickness each time that wrinkling is avoided.

When using acrylic lacquers which contain photoinitiators a thickness corresponding to 25-35 g/m is required so that the barrier layer after hardening prevents the passage of water. The above description referred only to a limited number of embodi¬ ments of the invention, but it will be readily understood by those versed in the art that the invention encompasses a large number of embodiments within the scope of the subsequent claims.

Claims

1. A means for prolonging the life of cut flowers placed in water, which is in the form of a label (1) comprising a carrier layer (2) v/ith an upper side and a lower side, and a material coat (4) applied to the upper side of the carrier layer wherein the coat contains an active material with at least one active substance setting free bactericidal and/or bacterial inhibiting agent in the presence of v/ater, c h a r a c t e r i z e d in that the coat (4) is surrounded on each of its two sides by at least one substantially waterimpermeable layer (2,3,5) and that between the water-impermeable layers located closest to the coat, and/or through passages (6) provided in the layers, regions for contact of the water with the active material are formed.

2. A means in accordance v/ith claim 1, c h a r a c t e r i z e d in that the carrier layer (2) and/or a binder layer (3) applied to the lower side of the carrier forms at least one substantially waterimpermeable layer and/or that the substantially water¬ impermeable layer (5) opposite the carrier layer (2) is in direct contact with the coat (4) comprising active material.

3. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the coat (4) comprising active material is in direct contact with the environment of the label in the regions in connection with the edges of the label.

4. A means in accordance v/ith anyone of the preceding claims, c h a r a c t e r i z e d in that the passages (6) in the substantially water-impermeable layers are adapted as perfo¬ rations or as holes.

5. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the passages (6) are provided only in the barrier layer (5).

6. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the regions for contact of the water with the active material formed by means of the passages (6) have a larger surface per surface unit adjoining the edges of the label than in the regions nearer the centre of the label.

7. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the active material is sodium dichloroisocyanurate.

8. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the barrier layer (5) is constituted of a lacquer of an acrylic compound which has been selected from a group consisting of acrylate derivative, diacrylate derivative, triacrylate derivative and acryloepoxide compound and that the lacquer contains a photoinitiator which initiates hardening of the lacquer under the influence of UV- ight.

9. A means in accordance with claim 8, c h a r a c t e r i z e d in that- the acrylic compound enters in a quantity of 25-35 g/m2 calculated on dry weight.

10. A means in accordance with anyone of the preceding claims, c h a r a c t e r i z e d in that the barrier layer (5) is constituted of several layers of lacquer which are applied with intervening hardening so as to avoid any wrinkling of the lacquer coat which would make it permeable to water.