CA2251839C - A heat pack - Google Patents

Abstract

A heat pack capable of being heated to at least 55 °C is provided and comprises a flexible impervious outer container capable of being sealed to retain a liquid such as water therein and of maintaining its sealed integrity when heated to at least the aforesaid temperature.
A porous, non-rigid filling material, which can absorb at least its own weight of the liquid, is located in the container. Advantageously, the pack contains a weight of liquid in the range 250 g to 1250 g, which liquid comprises water or compounds comprising one or more hydroxyl groups, or a mixture of water and such hydroxyl group compounds. In order to prevent microbial growth within the liquid-filled, sealed container, a predetermined quantity of a preservative at an appropriate concentration is also added to the fill. The filling material is preferably either fibrous or spongy in nature and advantageously may comprise a textile material or paper which is either recycled or would otherwise be treated as scrap or waste. Preferably also, air is removed from the outer container prior to it being sealed. The pack is also capable of use as a negative heat pack, i.e. a cool pack.

Description

A HEAT PACK
The present invention relates to a heat pack and in particular but not exclusively to a heat pack for therapeutic use. The pack could, however, be used for the application of heat in any suitable situation to both live and inanimate subjects. The pack is also capable of use as a negative heat pack, ie a cool pack, to abstract heat from live and inanimate subjects to which it is applied.
A conventional heat pack used for therapeutic use is a hot water bottle. Whilst modern hot water bottles, which are made of rubber, are flexible they have the major disadvantage that they must be filled with hot water, which is usually at a temperature at or nearing boiling point.
This is dangerous, particularly for children, the elderly, and persons with impaired movement or vision.
To overcome the aforementioned disadvantage, gel packs have been developed which can be heated, typically in a microwave oven, and used therapeutically. However, these tend to be expensive and hazardous in the case of a leak.
In LJS-4765338 is disclosed a heating or cooling pack for the entire scalp. The pack has been particularly developed for use as a cooling pack by patients undergoing chemotherapy treatment and has not been designed primarily as a heat pack, unlike the present invention.
In US-54475332 is described a water pillow or "ice bag" which comprises a closed bag made of a cloth or nonwoven fabric that has a high water permeability and that contains a water absorptive high polymer material, i.e. a gelling material. This pack has again been designed for use primarily as a cool pack.
A'~!E~1DED SHEEN' Other conventional heat packs comprise electric blankets and pads, and devices using exothermic chemical and physical reactions. These types of apparatus tend to to be expensive to produce and/or to operate. In addition, those dependent on exothermic reactions can be unreliable and may not be sufficiently flexible in their heat-producing state to be able to mould themselves to a part of the body to be treated.
Variations on all these products have also been produced for use on inanimate objects but usually exhibit the same disadvantages as aforesaid.
The object of the present invention is to provide a heat pack which overcomes or substantially mitigates the aforementioned disadvantages and which is inexpensive and safe to use.
According to the present invention there is provided a heat pack for being heated to at least 55°C and comprising a flexible, impervious outer container which is adapted to be sealed to retain a liquid therein and of maintaining its sealed integrity when heated to at least 55°C and which contains a porous, non-rigid filling material and a predetermined quantity of a preservative at a concentration that inhibits microbial growth within the liquid-filled container when sealed, and characterised in that the filling material comprises at least one of a woven textile material, a nonwoven fabric, a sponge-like material, and paper, which filling material absorbs at least its own weight of said liquid.
For convenience and safety, the liquid used in the heat pack may be water. It will be appreciated, however, that the heat pack if not already supplied to the end-user in a water-filled, sealed condition, can be filled with A~~NDED SHEE.~

cold water and sealed before being heated. The liquid within the container is absorbed by the porous filling material, which in addition to imparting a degree of rigidity to the heat pack is advantageous from a safety point of view after the heat pack has been heated should the outer container be ruptured.
The container may comprise a resealable bag or a sealed bag with a valve permitting it to be emptied, filled or topped up with liquid as desired.
It will be appreciated that when the pack is heated any air trapped inside the pack will expand. In extreme circumstances this can exacerbate expansion of the pack causing rupture. Hence, preferably, air is removed from the outer container prior to it being sealed. Advantageously, therefore, the valve permits air to be removed from the container after it has been filled with the liquid.
Alternatively, the container may be permanently sealedafter the addition of water or other liquid and the removal of air therefrom, a.nd may be supplied to the end user ready for use in this condition.
More specifically, therefore, according to the present invention there is provided a heat pack for being heated to at least 55°C and comprising a flexible, waterproof outer container which has been sealed after having had air removed therefrom to maintain its sealed integrity when heated to at least 55°C and which contains a porous, non-rigid filling material, a liquid and a predetermined quantity of a preservative at a concentration that inhibits microbial growth within the sealed container, and characterised in that the filling material comprises at least one of a woven textile material, a nonwoven fabric, a sponge-like material, and paper in combination with at ASdIEldCED -S~~FF'(' 3a least the filling material's own weight of liquid which is absorbed by said filling material.
The air can be removed from the outer container by any suitable means such as pressing, suction, or vacuum sealing. Preferably, however, the outer container is vacuum sealed.
It has been found that in order to ensure that there is no excessive expansion of the pack during its heating to temperatures suitable for its appJ.ication to parts of the human or animal body, the outer container is preferably exhausted of air down to a pressure equal to 100 millibars or less.
Removal of air from the outer container also imparts A~~AE":D~D BEET

degree of rigidity to the pack which will thereby retain its shape during and after heating. This can be advantageous if the pack is to be made in a specific shape, for example for use with a particular area of the body or in the form of a toy for a child.
Heating of the pack is preferably accomplished using a microwave oven although other conventional heating methods could be used and would be required if the container were to be made of a metallized material. Such an alternative heating method could comprise immersion of the pack in hot water for a time sufficient to heat the pack through.
Preferably, therefore, the pack is capable of being immersed in water which is at or near boiling point.
Another cause of potentially deleterious expansion of the pack arises if any water contained therein is vaporized during heating of the pack. Although in most embodiments of the invention and in most applications it will not be desirable to heat the pack to temperatures around or in excess of 100°C, if the pack is heated in a microwave oven the heating is not uniform so that whilst, for example, the mean temperature may be only 75°C there may be hot spots with temperatures in excess of 100°C. The universal gas equation states that one gram mole of a substance changing from liquid phase to gas phase will occupy 22.4 litres of volume at normal temperature and pressure. Hence, 18 g of water, i.e. 18 ml of water, would occupy 22.4 litres when boiled and changed into water vapour. Hence, it will be appreciated that the vaporization of even a small percentage of the contents of a pack containing 500 g of water could give rise to a damaging expansion of the product.
In view of the foregoing, it is advantageous in same embodiments of the invention for at least a proportion of the water, and in some cases all of the water, to be replaced by a substance capable of being heated by a microwave oven but with a boiling point significantly higher than water. Suitable substances for this purpose 5 preferably comprise compounds comprising one or more hydroxyl _aroups. For example, such substances may comprise one or more of glycerol, sorbitol or other polyhydric alcohols; ethylene glycol, propylene glycol or other glycols; glucose or other sugars; or any of a wide range of hydroxyl group containing compounds.
It is expected that in cases where a proportion of the water in the pack is replaced by hydroxl group containing compounds that at least one part hydroxyl group compound will be used to four parts water. In one preferred embodiment the pack comprises at least three parts hydroxyl group compound to two parts water.
It will be appreciated that the quantity of liquid Within the pack will determine how quickly it can be heated for any given heating method. However, too little liquid within the pack will cause it to heat too rapidly, which can be dangerous, particularly if the pack is heated by a microwave oven. However, too much liquid is disadvantageous as the heating time is inconveniently protracted.
Preferably, therefore, the quantity of liquid the pack contains is carefully predetermined. Advantageously, the pack contains a weight of liquid in the range 250 g to 1250 g., Optimally, however, from the point of view of user safety, convenience, heat content and weight, the pack contains a weight of liquid in the range 500 g to 1000 g.
Preferably, the container comprises a bag made from a substantially plastics material. Such a plastics material may comprise one of a polymer film, polymer laminate, co-extrusion, metallized plastics film, metallized plastics laminate, and an impervious heat-sealable polymeric nonwoven.
Whilst the heat pack of the invention can be made inexpensively so that it could be disposed of after a single use, it is preferably made from materials which permit it to be heated and cooled, and therefore, used many times.
Preferably, therefore, the plastics material comprises at least one of polypropylene, polyethylene, a polyamide, polyvinyl chloride, an aramid polymer, a polyester. It may also comprise a combination of these plastics materials with at least one of a textile material, such as a textile scrim, a knitted or nonwoven fabric, a metal foil, and a metallized film, as a laminate.
Such materials are also conducive to the production of a container in the form of a bag which could be manufactured by heat sealing or high frequency welding the edges of sheets of such materials together. Alternatively, sheets extruded as a lay-flat tube can also be cut and sealed to form a bag. A resealable container could be produced similarly but with an opening to which a conventional water-tight closure means is attached.
The porous textile or paper filling material is preferably either fibrous or spongy in nature.
Conveniently, such material may comprise scrap, waste or recycled textile or paper materials such as off-cuts and edge trim from other processes. In this way, the invention provides a convenient and beneficial means of using material which would otherwise comprise a troublesome and potentially environmentally damaging waste product.
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The filling material may be used in the form of strips, swatches, rolls, and shreds, or may be specifically shaped, formed or cut.
Preferably, the filling material can absorb at least four times its own weight of liquid. In most cases it is expected that the filling material will be able to absorb between five and eight times its own weight of liquid and that it will be this quantity of liquid which will be used in the heat pack.
Additional filling materials may also be used in certain embodiments of the invention to produce a heat pack with certain properties, for example one with a greater or lesser rigidity or one which will hold its shape after being moulded following heating. Such additional filling materials may comprise any of expanded plastics materials, glass fibres, glass wool, ceramic fibres, and non-absorbent fabrics.
The fill for the container may also be modified by the addition of material containing superabsorbent polymers or other chemical absorbents either in combination with solid filling material, for example in a laminate form therewith, or by the direct addition of such chemicals. It may also be beneficial in some embodiments to add a viscosity modifier, for example a gum, modified cellulose, bentonite, hectorite, polyvinyl alcohol, or similar material to any of these.
Colourings, fragrances, pearlising agents or other effect chemicals may also be added to the fill as required.
- It is necessary to include in the heat pack a preservative to inhibit microbial activity such as fungal and bacterial growth which would detrimentally affect the pack once it had been first filled with water. Such growth would reduce the shelf life of a pack to the extent of rendering it uncommercialand, once present, may present a health hazard to the user.
Preferably, the preservative used in the heat pack comprises at least one of sorbic acid, citric acid, propionic acid, chlorhexidine, chlorbutol, bronopol, phenoxyethanoi, phenyl ethyl alcohol, an ester of para hydroxybenzoic acid, 2.4 dichlorobenzyl alcohol, polyhexanide, a phenolic compound, and a quaternary ammonium compound.
Such preservatives are known for their particular suitability for use in consumer products such as foodstuffs and cosmetics because they are safe to use and are stable enabling the resulting product to exhibit a long-term integrity. However, any suitable preservative could be used.
It will be appreciated that the concentration of preservative required and the nature of the preservative will depend on its own nature, the nature of the filling material and the container, and on the desired life of the heat pack itself.
Whilst fabrics and textile materials which have been pre-treated with biocidal compositions could be used as filling materials for the pack, the use of such filling materials would increase the cost of the heat pack and the invention is not, therefore, limited to their use.
Six examples of heat packs according to the present invention will now be described.

Example 1 Outer Container 50 micron polypropylene sheets cut to size and rotary heat sealed to form a bag Fill Thermally banded viscose and cotton nonwoven fabric, wetted with 500 g water containing a preservative of 0.2%
methyl para hydroxybenzoate and 0.04%
propyl para hydroxybenzoate.
Example 2 Outer Container A resealable laminate pouch Fill A cotton fibre, cotton towelling wetted with water containing a preservative of 500 ppm benzalkonium chloride and 500 ppm polyhexanide.
Example 3 Outer Container A nylon and polythene co-extrusion pouch capable of retaining 500 ml of liquid Fill 100 g of viscose nonwoven fabric wetted with 200 ml of water and 300 ml of glycerol containing a preservative of 500 ppm benzalkonium chloride and 500 ppm polyhexanide.
' Example 4 Outer Container A nylon and polythene laminate pouch capable of retaining 630 ml of liquid Fill 120 g of viscose nonwoven fabric wetted with 630 ml of water containing a 5 preservative of 500 ppm benzalkonium chloride and 500 ppm polyhexanide.
Example 5 10 Outer Container A high frequency welded polyvinyl chloride bag.
Fill A wet laid viscose and wood pulp cellulose nonwoven fabric and airlaid paper mix wetted with water containing a preservative of 0.5% chlorbutol and 0.5% phenyl ethyl alcohol.
Example 6 Outer Container A high frequency welded polyvinyl chloride bag.
Fill A wet laid viscose and wood pulp cellulose nonwoven fabric wetted with glycerol containing a preservative of 0.5% chlorbutol and 0.5% phenyl ethyl alcohol.
Thus the invention provides a heat pack which is capable of being heated to a temperature of at least 55°C;
which is able to withstand conventional readily available heating methods, such as the use of microwaves; and which is relatively inexpensive and safe to use.
The internal structure of the pack may also be modified as desired by the addition of physical or chemical agents to alter its bulk or rheological properties. In addition, the external appearance, tactile properties, heat transferance, and function of the pack may be modified by the use of fixed or loose coverings.
As previously mentioned, it will be appreciated that in most embodiments detailed above the pack is also capable of use as a negative heat pack, ie. a cool pack, which can be used to abstract heat from live and inanimate subjects to which it is applied. In this case the pack would be cooled, conveniently by being placed in a refrigerator or freezer for a predetermined period, before use in the same manner as the heat pack described heretofore. References herein, in both the description and the claims to the term "heat pack" are therefore to be understood in this light.

Claims (21)

CLAIMS:

1. A heat pack for being heated to at least 55°C and comprising a flexible, impervious outer container which is adapted to be sealed to retain a liquid therein and to maintain its sealed integrity when heated to at least 55°C and which contains a porous, non-rigid filling material and a predetermined quantity of a preservative at a concentration that inhibits microbial growth within the liquid-filled container when sealed, and characterised in that the filling material is selected from the group consisting of a woven textile material, a nonwoven fabric, a sponge-like material, paper, and combinations thereof, which filling material absorbs at least its own weight of said liquid.

2. A heat pack as claimed in Claim 1, wherein the container comprises a resealable bag.

3. A heat pack as claimed in Claim 1, wherein the container comprises a sealed bag with a valve permitting it to be emptied and filled with liquid as desired.

4. A heat pack as claimed in Claim 3, wherein the valve permits air to be removed from the container after it has been filled with the liquid.

5. A heat pack for being heated to at least 55°C and comprising a flexible, waterproof outer container which has been sealed after having had air removed therefrom to maintain its sealed integrity when heated to at least 55°C and which contains a porous, non-rigid filling material, a liquid and a predetermined quantity of a preservative at a concentration that inhibits microbial growth within the sealed container, and characterised in that the filling material is selected from the group consisting of a woven textile material, a nonwoven fabric, a sponge-like material, paper and combinations thereof, in combination with at least the filling material's own weight of liquid which is absorbed by said filling material.

6. A heat pack as claimed in Claim 5, characterised in that the outer container has been vacuum sealed.

7. A heat pack as claimed in Claim 5 or 6, characterised in that the outer container has been exhausted of air dawn to a pressure equal to 100 millibars or less.

8. A heat pack as claimed in any one of Claims 1 to 7, characterized in that the liquid is selected from the group consisting of water and compounds comprising one hydroxyl group and combinations thereof.

9. A heat pack as claimed in any one of Claims 1 to 8, characterised in that the liquid comprises a mixture of water and compounds comprising one hydroxyl group in the proportion of at least 1 part hydroxyl group compound to 4 parts water upwards towards total replacement of the water.

10. A heat pack as claimed in any one of Claims 1 to 9, characterized in that the liquid selected from the group consisting of water, polyhydric alcohols, glycols, sugars and combinations thereof.

11. A heat pack as claimed in any one of Claims 1 to 10, which is adapted to be heated by microwaves.

12. A heat pack as claimed in any one of Claims 1 to 10, which is adapted to be heated by immersion in water at a temperature at or close to boiling point.

13. A heat pack as claimed in any one of Claims 1 to 12, characterised in that the pack contains a weight of liquid in the range 250 g to 1250 g.

14. A heat pack as claimed in any one of Claims 1 to 13, characterised in that the pack contains a weight of liquid in the range 500 g to 1000 g.

15. A heat pack as claimed in any one of Claims 1 to 14, characterised in that the container comprises a bag made from a plastics material.

16. A heat pack as claimed in Claim 15, characterised in that the plastics material is selected from the group consisting of a polymer film, polymer laminate, co-extrusion, metallized plastics film, metallized plastics laminate and an impervious heat-sealable non-woven polymer.

17. A heat pack as claimed in Claim 15 or Claim 16, characterised in that the plastics material is selected from the group consisting of polyethylene, polypropylene, a polyamide, polyvinyl chloride, an aramid polymer, a polyester and combinations thereof.

18. A heat pack as claimed in Claim 15 or Claim 16, characterised in that the plastics material is selected from the group consisting of polyethylene, polypropylene, a polyamide, polyvinyl chloride, an aramid polymer, and a polyester in combination with one of the group consisting of a textile material, metal foil, and a metallized film as a laminate.

19. A heat pack as claimed in any one of Claims 1 to 18, characterised in that the filling material absorbs at least four times its own weight of liquid.

20. A heat pack as claimed in any one of Claims 1 to 19, characterised in that the preservative is selected from the group consisting of sorbic acid, citric acid, propionic acid, chlorhexidine, chlorbutol, bronopol, phenoxyethanol, phenyl ethyl alcohol, an ester of para hydroxybenzoic acid, 2.4 dichlorobenzyl alcohol, polyhexanide, a phenolic compound, a quaternary ammonium compound and combinations thereof.

21. A heat pack as claimed in any one of Claims 1 to 20, characterised in that the viscosity of the liquid has been modified by adding a substance selected from the group consisting of a gum, modified cellulose, bentonite, hectorite, polyvinyl alcohol and combinations thereof.