GB2291321A - Flexible electrically heatable bottle - Google Patents

Abstract

A bottle containing an immersion heater which may substitute for a hot water bottle or act as a seat warmer is filled with glycerol or a liquid glycol. An internal frame is provided for supporting the heating coil to prevent contact with the bottle sides. <IMAGE>

Description

FLEXIBLE ELECTRICALLY HEATABLE BOTTLE The present invention relates to improvements in and relating to flexible electrically heatable bottles.

Flexible containers which can be filled with hot water are well known in the form of hot water bottles, warming pads and similar articles. In order to overcome the inconvenience and possible hazards of filling such a flexible bottle with boiling water every time it is required to be used, there have been proposed flexible bottles having an electric heating element disposed in a liquid inside the bottle. However, such bottles have their own problems. The electric element can melt the walls of the bottle if the latter contact the element.

There is also the possible danger of an electric short circuit or an explosion if vapour is created in the bottle.

Such bottles are usually filled with water which has a high heat capacity and a relatively high boiling point, but it is conductive and if it does boil, there can be an explosion.

GB 2 110 060A describes an electric bed warmer which attempts to overcome some of these problems. A generally loop shaped electric heating element is provided and there are flexible spacer elements which extend across the width of the bottle to reduce contact between the heating element and the walls of the bottle. The bottle may be filled with water, but alternatives such as oil or silica beads are suggested.

It has been found that the bottle of GB 2 110 060 does not fully overcome the problems noted above. Silica beads do not have a sufficiently high heat conductivity to remove heat from the element. There is a danger that oil will dissolve or permeate through the bottle walls.

A thermostat needs to be provided to control the temperature, and it is difficult to place the thermostat in the bottle of GB 2 110 060A in a satisfactory position where it is protected from being squashed but 1S not too close to the element.

All flexible bottles having an electric element have to be able to resist considerable pressure (for example, the weight of a person weighing 22 stones).

The present invention aims to overcome the problems of prior art electrically heatable flexible bottles.

The inventors have discovered that a suitable filling for an electrically heatable bottle is glycerol.

The inventors have further discovered that rapid heating can be provided if an electric heating element is provided, mounted within a frame which keeps the heating element out of contact with the walls of the bottle.

Accordingly, there is provided a flexible electrically heatable bottle comprising a flexible body filled with glycerol or a liquid glycol and an electric heating element inside the bottle.

The invention also provides a flexible electrically heatable bottle comprising a flexible body filled with a liquid, and a frame contained within the body, the frame having a plurality of frame parts, an electric heating element being provided received along substantially the whole of its length in spaces defined between the frame parts, so that the frame parts substantially prevent the electric heating element from contacting the body of the bottle.

The heating element may be wound round the frame to define a coil.

The danger of boiling is decreased if there are no "hot spots" where heat extraction from the heating element is inhibited. Accordingly, it is preferred that there are no sharp angles in the heating element. Further, the frame may be designed so that the heating element is supported by the frame at points which represent a very small fraction of the area of the heating element. The frame may have a very open structure to prevent creation of hot spots.

The heating element may be flexible, so that if the bottle is subjected to a load, the heating element can deform and return to its original shape when the load is removed. The heating element may comprise any suitable type, for example wires wound around a fibreglass core and coated with electrical insulation.

If the heating element is in the form of a coil it may have a return wire from the one end cf the coil passing down the middle of the coil. In this position, it may be kept out of contact with the heating element by the frame.

Thermal fuses may be provided in the heating element, which will melt If the temperature in the bottle becomes too high, to protect the bottle. The fuses may be designed so that in each case the fusible part is subtantially at the temperature of the liquid in the bottle. In this case the heating element will run at a higher temperature than the fuses, for example 150-160 C. The fuses may be set to melt at any suitable temperature below the maximum temperature which the body will stand. For example, the fuses may be set to about 130-1400C. The fuses will also melt if there is no liquid in the bottle, due to heat conducted from the element.

The frame parts may comprise a plurality of projections for receiving the heating element between them or strips ith holes for the heating element to pass through.

Preferably, the frame parts are ribs between which the heating element passes.

The frame may be of any suitable shape, but it is preferred that it is relatively long (for example not much shorter than the length of the bottle in which it will be placed) and of a flattened eliptical section, as the overall shape of the bottle is preferably generally flat. Preferably, the frame is wide so that the heating element may be spread over a wide area so that a high heating rate may be obtained with a low heating element temperature.

The frame may be constructed of resilient material which deforms when a load is applied, so that considerable loads can be taken without damage to the heating element or the frame. It may be constructed of a thermoplastic or thermoset material, such as Nylon 66, and it may be coated for example with silicone rubber.

For ease of moulding, the frame may be composed of a number of parts which snap-fit together. For example, it may be composed of front and back parts which meet along the widest central plane of the frame and snap fit together. The frame may then be mounted in the bottle so that any load applied to the bottle is most likely to be applied normal to the plane in which the parts of the frame contact, so that they are pushed together by the load rather than caused to split apart.

In detail, the frame preferably has a flattened curved cross section, U-shaped ribs being provide around the smaller radius curve of the cross section to effectively prevent the heating element touching the internal wall of the bottle body. A large proportion of the space between the side-by-side U-shaped ribs may be open, there being preferably only three narrow interconnecting pieces in order to provide support for the heating element. A relatively large space may be provided between open ends of one U-shaped rib and the U-shaped rib on the other side of the flattened shape.

The frame may provide a mounting for a thermostat so that the thermostat is kept out of contact with the heating element. Preferably, where the wires are in the form of a coil, the thermostat is located within the coil, preferably near the centre line of the coil.

The body of the bottle may be made of any suitable resilient material, preferably an elastic material such as synthetic or natural rubber.

It is preferred that the body is made of a mixture comprising about 60% by weight natural rubber and about 40% by weight EPDM (ethylene propylene terpolymer).

This composition has high tensile strength and good hot-tear strength.

EPDM rubber is unaffected by heat to 110-C and little effected to 130'C. By combining it with natural rubber, a composition with good tensile strength and hot-tear strength can be obtained. Good heat resistance may be obtained if the mixing ratio of EPDM to natural rubber is in the region of 40: 60.

The body may have a wide neck which is sealed with a plug. A wide neck allows a wide frame having a large heating element to be inserted into the bottle during manufacture.

The bottle may be filled with a liquid glycol or, more preferably, glycerine. Glycerine (also known as glycerol) is non toxic, non corrosive, relatively cheap, has a high boiling point; it is compatible with the rubber (it does not dissolve it), is not readily oxidised or decompose, does not attack the wires, has a high flash point and has a reasonably high heat capacity. It does not tend to permeate the rubber walls of the bottle, as it has a substantially polar molecule.

Glycols which may be used include dipropyleneglycol, diethyleneglycol and triethyleneglycol. These have similar properties to glycerol, but are not compatible with natural rubber. A synthetic rubber body would have to be used with these fillings.

The electrically heatable flexible bottle of the invention may be used as a bed-heater, a foot-warmer, a chair-warmer or a thermal pack for arthritis and other complaints.

The present invention will be further described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view of an electrically heatable bottle according to the invention; Figure 2 shows a schematic longitudinal cross-section of the electrically heatable bottle along line II-II of Figure 1; and Figure 3 is an isometric drawing, at a larger scale, showing the frame, with the heating element omitted for clarity.

The electrically heatable flexible bottle according to the invention shown in Figure 1 is in the form of a hot water bottle for use as a bed-warmer, seat-warmer etc.

The flexible electrically heatable bottle 1 comprises a body 2 of elastomeric material which is highly flexible. The body 2 defines a closed flexible vessei sealed at one end by a seal 3 formed in a neck 4. A three-pin plug is formed in the seal 3 for connection to an electricity supply for heating the bottle up.

Figure 2 shows a longitudinal cross-section along the line II-II of Figure 1. The body 2, seal 3 in neck e and the plug 5 are shown. The space 6 within the body 2 iS completely filled with a liquid which, in the preferred embodiment, is glycerol.

The body 2 is constructed of a mixture of 60% by weight natural rubber and 40% by weight EPDM synthetic rubber.

Ribs of the frame are visible in Figure 2, exemplified at 7. As further explained in Figure 3, the frame defines a generally flattened spiral path for a flexible heating element, coils 8 of which are visible in Figure The end 9 of the frame can bear against the end 10 of the bottle 2 to locate the frame within the bottle.

The electric heating element 8 is connected by flexible electrical leads 11 to the plug so that the liquid inside the body 2 can be heated by the electric heating element when a source of electricity is plugged in at 5. The return lead from the far end of the heating element returns to the plug 5 along a central space defined within the ribs of the frame. A thermostat 20 is also provided within the central space defined between the ribs 7. Thermal fuses 14 are included in the coil of the heating element at the extremities of the coil. These thermal fuses are designed so that the fusible part is at substantially the same temperature as the surrounding liquid.Therefore this part will melt and cut the supply of current to the heating element if the temperature of the liquid exceeds a given value, in order to prevent damage to the element or the body 2 of the bottle, or to prevent the formation of vapour which could cause an explosion.

The frame 15 is shown in more detail in Figure . In Figure 3, the coils of the heating element have been omitted for clarity, but the return wire 13 is shown.

The frame has a generally flattened eliptical shape.

U-shaped ribs are formed defining the smaller radius curve of the elipse. The ribs 7 are so arranged so as to effectively partially define a flattened helical path. Between the ribs 7, troughs (exemplified at 16) are defined. The heating element is wound around the frame 15 so that it lies inside these troughs 16. The height h of the troughs is greater than the diameter of the wires forming the coils 8 of the heating element so that the heating element is retained substantially out of contact with the wall 2 of the bottle.

The ribs 7 are constructed with cut-outs 17 and are supported on a very open framework defined by longitudinal elements 18 and a small number of transverse elements 19. In this way, a large proportion of the space between side-by-side U-shaped ribs 7 is open so that circulation around the coils 8 of the heating element is good. In particular, a large open space is defined between the open ends of one U-shaped rib 7 and the U-shaped rib 7 on the other side.

The frame defiles a space extending along the middle in which the return wire 13 (which is thick and does not generate heat) is located. The thermostat 13 is also received inside the frame where it is kept away from direct contact with the coils 8 of the heating element so that it does not cut out before the temperature of the liquid has reached the required level.

The frame 15 is constructed of Nylon (66).

The glycerol can be indented into the body 2 as follows. First, the interior 6 of the body 2 is evacuated using a vacuum pump. Secondly, the body 2 is sealed with seal 3. Glycerol is then introduced into the bottle through the body 2 using a hypodermic needle and means such as a high pressure hydraulic ram for pressurising the glycerol. The hole created by the hypodermic needle is then sealed with a plastic pin under compression.

It is noted that the neck 4 is wider than the neck normally provided for hot water bottles.

In the present case, rubber compounds of a suitably high heat resistance do not extend as much as natural rubber for a given load and a wide neck is necessary in order to accommodate the large frame 15.

The invention has been described above by way of example only and modifications can be made within the spirit of the invention.

Claims (9)

1. A flexible electrically heatable bottle comprising a flexible body filled with glycerol or a liquid glycol and an electric heating element inside the bottle.

2. A flexible electrically heatable bottle comprising a flexible body filled with a liquid, and a frame contained within the body, the frame having a plurality of frame parts, an electric heating element being provided received along substantially the whole of its length in spaces defined between the frame parts, so that the frame parts substantially prevent the electric heating element from contacting the body of the bottle.

3. The flexible electrically heatable bottle of claim 2, wherein the heating element is wound round the frame to define a coil.

4. The flexible electrically heatable bottle of claim 2 or 3 wherein the heating element is flexible.

5. The flexible electrically heatable bottle of any of claims 2 to 4, wherein the frame parts comprise a plurality of projections for receiving the heating element between them or strips with holes for the heating element to pass through.

6. The flexible electrically heatable bottle of any of claims 2 to 5, wherein the frame is constructed of resilient material.

7. The flexible electrically heatable bottle of any of claims 2 to 6, wherein the frame provides a mounting for a thermostat so that the thermostat is kept out of contact with the heating element.

8. The flexible, electrically heatable bottle of claim 1, being filled with dipropyleneglycol, diethyleneglycol or triethyleneglycol or a mixture thereof.

9. The flexible, electrically heatable bottle of claim 1 or 8, further having features of any of claims 2 to 7.