COVER DEVICE

Description

[0001] The invention relates to a covering device for liquid containers, in particular for swimming pools, which protects the container from heat loss as well as from steam escape and from the penetration of foreign bodies or contaminants.

[0002] Such cover devices are known and designed to assume a space-saving configuration when not in use. The prior art describes cover devices that can be rolled up or folded to assume the space-saving configuration. Cover devices are also known that are designed as a roof arranged at a distance from the liquid surface and that can be telescoped into one another when not in use.

[0003] Such pool covers are generally essentially vapor-tight, but unlike rollable or foldable solutions, they are bulky. Furthermore, the vapor space between the liquid surface and the cover usually results in significant heat loss. Covers constructed as foils take up less space and can be placed directly on the water surface, preventing heat loss through evaporation. However, to save space when stored, these are usually quite thin and therefore usually have poor thermal insulation properties.

[0004] Lamellar covering devices are also known. These offer a greater thickness of insulating material and can be rolled up, but due to their hinged connecting elements, they are not vapor-tight, which in turn results in heat loss.

[0005] Disadvantages of known constructions are therefore at least that the thermal insulation properties are insufficient or that they cannot be configured to save space when not in use.

[0006] The publications CH 580 733 A5 and DE 84 29 962 U1 show swimming pool covers. GB 2 253 184 A shows a weatherproof cover for buildings.

[0007] One object of the invention is, among other things, to overcome this conflict of objectives and to provide a covering device which, on the one hand, has good thermal insulation properties and, on the other hand, can be stored easily and in a space-saving manner.

[0008] These and other objects of the invention are achieved by a device according to the independent patent claim.

[0009] A covering device according to the invention comprises a carrier layer and an insulating layer, wherein the covering device is flexible and can be brought from a rolled-up state into a flat state for covering the liquid container. In the flat state, the carrier layer and the insulating layer extend along a main extension plane of the covering device. According to the invention, the insulating layer has a plurality of transverse slits which, in the flat state, extend essentially parallel to one another and orthogonal to the main extension plane. Here, the term "parallel" also includes curved transverse slits having identical curvature.

[0010] The insulation layer is divided into a plurality of insulation layer segments by the transverse slots. The insulation layer segments are preferably of substantially equal size. The main extension plane of the covering device is any parallel plane spanned in space by the length and width of a covering device.

[0011] The thickness direction, in which the thickness of a layer extends, runs orthogonally to the main plane of extension. Thus, for example, the geometric shape of a rolled-out layer in a specific embodiment can be understood as a flat cuboid, with the thickness being many times smaller than the length and width of the cuboid. The thickness direction, length direction, and width direction form an orthogonal coordinate system in three-dimensional space, with the covering device preferably being designed to be rolled up along the length direction, and the transverse slits preferably running in the width direction.

[0012] The inventive design ensures that the cover device has good thermal insulation in the flat state, since the insulation layer segments are only slightly spaced apart or even abut one another in this state. At the same time, the cover device can be easily rolled up to save space, since in this state the transverse slits, which reduce the flexural rigidity of the cover device, allow it to be bent. Furthermore, the insulation layer segments, which are in contact in the flat state, lead to increased flexural rigidity of the cover device with respect to an internal curvature.

[0013] Where appropriate, the transverse slots form transverse slot surfaces, with the transverse slot surfaces of adjacent insulation layer segments running essentially parallel to one another in the flat state and preferably being in direct contact with one another. When rolled up, the transverse slot surfaces are spaced apart and not parallel. This provides the necessary flexibility to achieve the respective configurations with minimal force exerted by the user. Where appropriate, the transverse slots have a depth that is less than or equal to the thickness of the insulation layer. This avoids design-critical notch stress in the carrier layer.

[0014] If necessary, the carrier layer and insulation layer are formed integrally from a common material. Alternatively, the carrier layer and insulation layer can also be formed from different materials.

[0015] The carrier layer and the insulation layer can be connected to one another in a planar manner, wherein the insulation layer segments are preferably formed as separate insulation elements arranged on the carrier layer.

[0016] If necessary, the insulation layer segments are compressively stressed in the flat state by surface pressure of the transverse slots in the main extension plane, in particular with at least 2 N / cm 2 , preferably with at least 5 N / cm 2 . In particular, the volume of the insulation layer segments increases with increasing temperature. For example, the insulation layer segments can be compressively stressed in the flat state at a temperature above 20 °C, and not compressively stressed at a lower temperature, for example below 10 °C or below 0 °C. If the temperature rises, the insulation layer segments therefore stress themselves and ensure an increased thermal insulation effect. This effect can be achieved during production of the insulation layer segments by creating the transverse slots at a low temperature, for example below 10 °C.

[0017] Optionally, the carrier layer is formed from a flexible polymer that comprises a UV stabilizer and / or is UV stabilized.

[0018] The insulation layer can comprise or consist of a closed-cell plastic material, such as polyethylene foam or chloroprene rubber. This ensures the longevity of the cover and allows the cover to be designed to float on water. Furthermore, due to its chemically inert nature, closed-cell plastic material is suitable for use in humid, oxygen-containing environments with seasonal temperature fluctuations.

[0019] If necessary, the insulation layer also has longitudinal slots in addition to the transverse slots, which divide the insulation layer segments into further segments and, together with the transverse slots, form a grid pattern. This allows the covering device to be wound around non-cylindrical winding devices, for example, barrel-shaped ones, with centering if necessary.

[0020] Furthermore, the insulation layer can comprise an elastic film or mesh covering the transverse slots, which may be connected to the insulation layer segments via fastening means. The film preferably covers the transverse slots both in the flat and rolled-up state to protect the transverse slots from contamination. This allows, in particular, gentle rolling up of the covering device on both sides.

[0021] The invention further extends to an arrangement comprising a winding device and a covering device, wherein the winding device comprises a peripheral surface for contact with the covering device. In the wound state of the covering device, the carrier layer rests against the peripheral surface of the winding device. This allows the winding device to assume a space-saving configuration with as little force as possible.

[0022] Where appropriate, the winding device is designed as a substantially rotationally symmetrical, particularly cylindrical, body. This reduces the risk of wrinkling during winding.

[0023] If necessary, the winding device is designed as a substantially barrel-shaped body. This achieves a self-centering effect during the winding process.

[0024] The insulation layer may be in contact with the water surface when unrolled. However, the carrier layer may also be in contact with the water surface when unrolled.

[0025] The entire covering device is preferably designed to be substantially fluid-tight, and optionally vapor- and / or watertight. The carrier layer preferably forms the water- and vapor-impermeable layer of the covering device and also serves to support the insulation layer. The insulation layer serves to reduce heat loss from the container to be covered. The insulation layer can have a thickness of at least 1 cm, preferably 3 cm, or at least about 10 cm. Furthermore, the thickness of the covering device can be at least 1 cm, preferably at least 3 cm, or at least 6 cm.

[0026] Both the insulation layer and the carrier layer can be made of or comprise a plastic, in particular a hydrophobic plastic. Preferably, the covering device floats independently on water and therefore has an average density of less than 1.0 g / cm3.

[0027] This prevents the formation of steam under the cover device, which could subsequently lead to critical ice formation under the cover device at an ambient temperature below 0°C.

[0028] The carrier layer may comprise or consist of a flexible plastic material, such as polyethylene, with or without stabilizing mesh inserts. The insulation layer segments may have a length in the direction of the main extension plane of approximately 3 cm to 15 cm, preferably approximately 5 cm or approximately 8 cm. This achieves a flexibility of the cover device that is suitable for swimming pools.

[0029] The carrier layer can be thinner than the insulation layer. Preferably, the carrier layer is at least 70% thinner, in particular at least 85% thinner, than the insulation layer. The carrier layer thickness can be, for example, less than 2 cm, preferably less than 1 cm.

[0030] The transverse slots can be designed to have a depth that is smaller than the thickness of the insulation layer, or they can have a depth that is equal to the thickness of the insulation layer. This positions the structurally critical points of the transverse slot notches either in the insulation layer or at the transition area between the carrier layer and the insulation layer. Consequently, the magnitude of the maximum notch foot stresses is reduced. The transverse slots can be designed as incisions in the material.

[0031] It can be provided that the carrier layer and the insulation layer are made of different materials, which are preferably bonded to one another over a large area, for example by a material bond, a form fit, and / or a friction fit. A material bond is preferably created by gluing or welding, while a form fit is preferably created by mechanical fasteners such as screws or bolts.

[0032] Optionally, in an embodiment with different materials for the carrier layer and insulation layer, the carrier layer is made of a material with higher tensile strength than that of the insulation layer. This allows two different materials to be selected for the carrier layer and insulation layer, optimizing the fluid tightness, thermal insulation capacity, and fatigue strength of the covering device.

[0033] The insulation layer segments or insulation elements are preferably cuboidal or prismatic. This allows the insulation layer to be formed on the carrier layer in a flat state using joining technology, and the insulation elements can be applied to the carrier layer in a prestressed state.

[0034] For this purpose, the insulation segments are applied to the carrier layer either with a prestress or at a lower temperature. If necessary, the insulation layer can also be attached to the carrier layer in a compressed form along the main plane of extension.

[0035] In the former case, the prestress leads to elastic deformation of the insulation elements. This prestress remains even after joining, as the insulation elements cannot repel each other and relax due to their connection to the carrier layer.

[0036] The elastic deformation and the limited degrees of freedom of the insulation elements lead to compressive stress in the insulation layer material and to surface pressure at the transverse slot surfaces. Compressive stress and surface pressure may decrease with decreasing temperature, especially if the thermal expansion coefficient of the carrier layer is higher than that of the insulation layer. Surface pressure and compressive prestress result in a larger temperature range, down to below freezing, in which the transverse slots expand. This prevents increased heat loss at low ambient temperatures, where the insulation effect is particularly important.

[0037] In the latter case, the insulation layer is applied to the carrier layer at a lower temperature than the substrate layer. After the substrate layer and insulation layer are bonded, compressive stress develops in the insulation layer as soon as the two layers reach thermal equilibrium and the degrees of freedom of the insulation layer segments are restricted. The insulation layer segments are subject to compressive stress, analogous to the insulation elements in the first case.

[0038] Furthermore, it can be provided that the cover device has at least one edge region on which no insulation layer is provided. The edge region runs within the outer contour of the cover device and extends in the lengthwise or widthwise direction. This results in at least one possibly bulging sealing lip which is sufficiently elastic and flexible to cushion and also seal movements of the cover device in the lengthwise and / or widthwise direction towards a container edge. This can improve the vapor-tightness and insulation effect in the edge region of the cover device. If necessary, two edge regions can also be provided which extend along two opposite sides of the cover device, wherein the edge regions possibly run essentially orthogonally to the transverse slots.A double edge area centers the cover device on the liquid surface of the liquid container and simultaneously acts as a sealing lip against the inside of the container.

[0039] If necessary, at least one edge area has a sealing strip designed as a tube or cord. Alternatively, a sealing body with a row of sealing lips can be provided there. These parts can be made of rubber or include rubber. This ensures excellent thermal insulation even in the edge area.

[0040] In addition, it can be provided that the thermal transmittance of the covering device, in particular the thermal transmittance of the insulation layer, is less than 5 W / m 2 < K, in particular less than 2 W / m 2 < K, preferably less than 1 W / m 2 < K. By means of a covering device or an insulation layer with said thermal transmittance, the heat loss of the covered container to the environment is reduced to a minimum.

[0041] It can be provided that the width of the transverse slots in the flat state at a temperature below 10°C is less than 500 µm, preferably less than 200 µm. The width of the transverse slots refers to the normal distance between the transverse slot surfaces. In a preferred limiting case, the width can also be zero; in this limiting case, the transverse slot surfaces are in contact with each other.

[0042] According to the invention, the covering device can be formed by providing a one-piece starting material for a carrier layer, connecting a one-piece starting material for an insulation layer to the carrier layer, and producing a plurality of transverse slits arranged parallel to one another by cutting into the starting material for the insulation layer, wherein the transverse slits run substantially along the thickness direction of the starting material.

[0043] Furthermore, the covering device can be formed by providing a one-piece starting material for a carrier layer, connecting individual insulation elements for an insulation layer to the carrier layer, so that transverse slots extending substantially parallel to one another are formed between the insulation elements.

[0044] Furthermore, the covering device can be formed by providing a common one-piece starting material for a carrier layer and an insulation layer and creating a plurality of transverse slits arranged parallel to one another by cutting the starting material, wherein the transverse slits run substantially along the thickness direction of the starting material.

[0045] The manufacturing method of a covering device according to the invention can also comprise features of the first and / or second case for achieving the surface pressure on the transverse slot surfaces as well as further features of the description.

[0046] Further features of the invention emerge from the patent claims, the figures and the description of the embodiments.

[0047] The invention is explained below using exemplary, non-exclusive embodiments. Fig. 1a - 1c show schematic sectional views of covering devices according to the invention; Fig. 2 shows a schematic representation of an embodiment of an arrangement according to the invention; Fig. 3a - 3d show schematic representations of covering devices according to the invention; Fig. 4 shows a schematic representation of an embodiment of an arrangement according to the invention; Fig. 5a - 5b show two further schematic representations of an embodiment of an arrangement according to the invention in the wound and rolled-up state; Fig. 6 shows a further embodiment of a covering device according to the invention.

[0048] Fig. 1a shows a schematic sectional view of a first embodiment of a covering device 1. A covering device 1 is shown in the unrolled and flat state. The carrier layer 2 is joined, in particular glued, to the insulation layer 3. The main extension plane 7 runs along the underside of the carrier layer 2 and spans a plane in space, which, in the selected view, represents a line and also the lower edge of the carrier layer 2. The course of this illustrated line of the main extension plane 7 indicates the longitudinal direction of the covering device 1.

[0049] The insulation layer 3 is divided into insulation layer segments 8. In the illustrated embodiment, the depth of the transverse slots 4 essentially corresponds to the thickness of the insulation layer 3. In this embodiment, the insulation layer segments 8 are formed by individual insulation elements. Transverse slots 4 are provided between the insulation layer segments 8.

[0050] The width of the illustrated transverse slots 4 is zero, so that the two transverse slot surfaces 9 of a transverse slot 4 abut one another. In other embodiments not shown, this width may also be greater than zero.

[0051] The thickness of the carrier layer 2 is in this schematic representation significantly smaller than the thickness of the insulation layer 3. Carrier layer thickness and insulation layer thickness are in the embodiment according to Fig. 1a Not shown to scale. In particular, the carrier layer 2 is designed as a foil, and the insulation layer 3 is formed from individual insulation layer segments 8 made of closed-cell plastic. The material of the covering device 1 is weather-resistant and inert in an oxygen-containing environment.

[0052] The insulation elements were bonded to the carrier layer 2 in a prestressed manner or at low temperature, resulting in a positive compressive stress in the insulation elements at an ambient temperature of 25°C in the flat state, and thus a positive surface pressure on the transverse slot surfaces 9 of the transverse slots 4. As the ambient temperature drops, the compressive stress may decrease, but a small positive surface pressure remains at least down to a lower ambient temperature limit of 0°C. This ensures that the transverse slots do not open significantly as the temperature decreases down to 0°C.

[0053] Fig. 1b shows a schematic sectional view of a second embodiment of a possible covering device 1. In contrast to the embodiment of Fig. 1a The depth of the transverse slots 4 is less than the thickness of the insulation layer 3. The insulation layer 3 is one-piece and divided into insulation layer segments 8 by transverse slots 4. The insulation layer 3 is bonded to the carrier layer 2.

[0054] Fig. 1c shows a schematic sectional view of a third embodiment of a covering device 1. The entire covering device 1 comprising carrier layer 2 and insulation layer 3 is in one piece. The transverse slots 4 and insulation layer segments 8 are according to the embodiment of Fig. 1b formed.

[0055] Fig. 2 shows a schematic representation of an embodiment of an arrangement according to the invention of a covering device 1 on a winding device 5. The winding device 5 has a jacket surface 6 which is in contact with the carrier layer 2.

[0056] In the illustrated embodiment, the winding device 5 is a cylindrical body that is set in rotation to wind up the covering device 1. When a covering device 1 is arranged on the winding device 5, the insulation layer segments 8 are spread apart and the transverse slots 4 form wedge-shaped openings.

[0057] Fig. 3a shows a schematic representation of the covering device 1 according to the invention from Fig. 1a in a swimming pool containing water. The carrier layer 2 rests directly on the water surface of the swimming pool, with the water surface bordered by a pool edge 11. The water surface runs approximately parallel to the main extension plane 7 of the cover device 1.

[0058] Furthermore, the cover device 1 has an edge region 10, on which only the carrier layer 2 is provided. The edge region 10 seals the water surface against the pool edge 11. Upon contact of the edge region 10 with the pool edge 11, the edge region 10 bulges upwards and forms a sealing lip, which reduces heat dissipation at the edge regions 10 of the cover device 1.

[0059] Fig. 3b shows a schematic representation of the covering device 1 according to the invention from Fig. 1a in a swimming pool containing water. In the illustrated embodiment, the insulation layer 3 lies directly on the water surface, with the water surface being bordered by a pool edge 11.

[0060] Furthermore, the cover device 1 has an edge region 10 where no insulation layer 3 is provided. The edge region 10 seals the water surface against the pool edge 11. Upon contact of the edge region 10 with the pool edge 11, the edge region 10 bulges downward and forms a sealing lip, which reduces heat dissipation at the edge regions 10 of the cover device 1.

[0061] Fig. 3c shows a schematic representation of the covering device 1 according to the invention from Fig. 1a in a swimming pool. Here, the water surface between the edge area 10 and the pool edge 11 is sealed with a sealing tape 13.

[0062] In the embodiment shown, the sealing strip 13 is designed as a rubber hose with a slit. The hose is placed over the edge region 10 of the carrier layer 2. In other embodiments, the sealing strip 13 does not have a slit but is connected to the edge region 10 on its outer side.

[0063] Fig. 3d shows a schematic representation of the covering device 1 according to the invention from Fig. 1a in a swimming pool. Here, the water surface between the edge area 10 and the pool edge 11 is sealed with a row of sealing lips 15 of a sealing body 14. The sealing body 14 is made of rubber and is connected to the edge area 10 or the sealing lip.

[0064] Fig. 4 shows a further schematic representation of an embodiment of an arrangement according to the invention of a covering device 1 on a winding device 5. The carrier layer 2 and insulation layer 3 are in the arrangement shown according to Fig. 1a The winding device 5 has a lateral surface 6 which is in contact with the underside of the carrier layer 2.

[0065] The winding device 5 is a cylindrical body that winds up the cover device 1 upon rotation about the rotation axis D. When a cover device 1 is arranged on the winding device 5, the insulation layer segments 8 gape apart and the transverse slots 4 form wedges. The cover device 1 winds itself spirally around the winding device 5 until the entire length of the cover device 1 wraps around the winding device 5. This achieves the most space-saving configuration possible.

[0066] In an embodiment not shown, the winding device 5 is designed as a hollow cylinder or as a non-cylindrical body, for example as a cuboid or hollow cuboid.

[0067] Fig. 5a shows a further schematic representation of an embodiment of an arrangement according to the invention of a covering device 1 on a winding device 5 in the rolled-up state.

[0068] The winding device 5 is barrel-shaped. The transverse slots 4 of the covering device 1 are not visible and run essentially at right angles to the longitudinal slots 12 shown. The transverse slots 4 and longitudinal slots 12 form a rectangular grid. The longitudinal slots 12 extend through the entire insulation layer 3. Due to the barrel-shaped design of the winding device 5, the covering device 1 centers itself during winding on the winding device 5, which rotates about the rotational axis D.

[0069] Fig. 5b shows a schematic plan view of an embodiment of an inventive arrangement of a covering device 1 on a winding device 5 in a flat state. Transverse slots 4 and longitudinal slots 12 intersect each other and form a substantially rectangular grid.

[0070] Fig. 6 shows a further embodiment of a covering device according to the invention. In this embodiment, an elastic film 16 or an elastic net is provided that covers the transverse slots 4 and is connected to the insulation layer segments 8 via fastening means 17. The fastening means 17 are, for example, nails or pins and are preferably arranged centrally on the surface of the insulation layer segments 8 in order to achieve maximum stretching of the film 16 over the transverse slots 4. The film 16 covers the transverse slots 4 in the illustrated rolled-up state in order to protect them from dirt and mechanical damage. The film 16 is weather-resistant and can therefore also be used on the side facing away from the water surface.This embodiment allows for easier rolling up and unrolling on both support sides, so that either the insulation layer 3 or the carrier layer 2 can rest on the water surface. Bezugszeichen

[0071] 1Cover device 2Support layer 3Insulation layer 4Transverse slot 5Winding device 6Shell surface 7Main extension plane 8Insulation layer segments 9Transverse slot surfaces 10Edge area 11Pool edge 12Longitudinal slot 13Sealing tape 14Sealing body 15Sealing lip row 16Foil 17Fasteners

Claims

1. A covering device (1) for liquid containers, in particular for swimming pools, comprising a carrier layer (2) and an insulating layer (3), wherein the covering device (1) is flexible and can be brought from a rolled-up state into a flat state for covering the liquid container, and wherein the carrier layer (2) and the insulating layer (3) extend along a main extension plane (7) of the covering device (1) in the flat state, characterized in that the insulating layer (3) has a plurality of transverse slits (4) which, in the flat state, extend substantially parallel to one another and orthogonally to the main plane of extension (7), such that the insulating layer (3) is divided by the transverse slits (4) into a plurality of insulating layer segments (8), preferably of substantially equal size.

2. The covering device (1) according to claim 1, characterized in that transverse slit surfaces (9) are formed by the transverse slits (4), wherein the transverse slit surfaces (9) of neighbouring insulating layer segments (8) are substantially parallel to one another in the flat state and are preferably in direct contact with one another, and are not parallel to one another and are preferably spaced apart in the rolled-up state, and / or in that the transverse slits (4) have a depth which is less than or equal to the thickness of the insulating layer (3).

3. The covering device (1) according to one of claims 1 to 2, characterized in that the carrier layer (2) and the insulating layer (3) are formed integrally from a common material.

4. The covering device (1) according to one of claims 1 to 2, characterized in that the carrier layer (2) and the insulating layer (3) are formed from different materials, which are preferably bonded to one another over their entire surface, wherein the insulating layer segments (8) are preferably formed as separate insulation elements arranged on the carrier layer (2).

5. The covering device (1) according to one of claims 1 to 4, characterized in that the insulating layer segments (8) are prestressed together in the flat state by surface pressure of the transverse slits (4) in the main extension plane (7), in particular with at least 2 N / cm2, preferably with at least 5 N / cm2, and in particular in that the insulating layer segments (8) are prestressed in the flat state at a temperature above 20°C and are not prestressed at a temperature below 10°C.

6. The covering device (1) according to one of claims 1 to 5, characterized in that the covering device (1) has at least one peripheral region (10) at which no insulating layer (3) is provided, or in that two peripheral regions (10) are provided which extend along two opposite sides of the covering device (1), wherein the peripheral regions (10) optionally extend substantially orthogonally to the transverse slits (4).

7. The covering device (1) according to one of claims 1 to 6, characterized in that at least one peripheral region (10) has a sealing strip (13) designed as a hose or cord, in particular made of rubber, or a sealing body (14) provided with a row of sealing lips (15), in particular made of rubber.

8. The covering device (1) according to one of claims 1 to 7, characterized in that the carrier layer (2) is formed from a flexible polymer comprising a UV stabiliser and / or is UV-stabilised and / or in that the insulating layer (3) comprises or consists of a closed-pore plastic material, for example a polyethylene foam or a chloroprene rubber.

9. The covering device (1) according to one of claims 1 to 8, characterized in that the insulating layer (3) has longitudinal slits (12) which preferably extend substantially orthogonally to the transverse slits (4) and divide the insulating layer segments (8) into further segments.

10. The covering device (1) according to one of claims 1 to 9, characterized in that the insulating layer (3) has an elastic film (16) covering the transverse slits (4), which optionally is connected to the insulating layer segments (8) via fastening elements (17).

11. An arrangement, comprising a covering device (1) according to one of claims 1 to 10 and a winding device (5), wherein the winding device (5) comprises a circumferential surface (6) for the covering device (1) to rest against, wherein the carrier layer (2) rests against the circumferential surface (6) of the winding device (5) in the wound-up state of the covering device (1).

12. The arrangement according to claim 11, characterized in that the winding device (5) is designed as a substantially rotationally symmetrical, in particular cylindrical, body.

13. The arrangement according to claim 11, characterized in that the winding device (5) is designed as a substantially barrel-shaped body.

14. The arrangement according to one of claims 11 to 13, characterized in that the covering device (1) is arranged on the winding device (5) in such a way that the insulating layer (3) rests against the surface of the medium contained in the liquid container when the covering device (1) is unrolled.

15. The arrangement according to one of claims 11 to 13, characterized in that the covering device (1) is arranged on the winding device (5) in such a way that the carrier layer (2) rests against the surface of the medium contained in the liquid container when the covering device (1) is unrolled.