This invention relates to portable heating devices suitable for personal , therapeutic or play use, for use as storage heaters or for other uses.

Devices for applying warmth to the human or animal body by the use of a preheated heat storage medium enclosed within a suitable cover are known. Such devices are required to operate within a relatively narrow temperature range which gives perceived warmth without causing discomfort or injury either in normal use or on rupture or breakage or the device. Such devices are preferably adapted to enable close surface contact with a body-part to be achieved, are economical to manufacture and do not require frequent part replacement. Examples of such devices are hand warmers, bed warmers, body pads for therapeutic or comfort use and soft toys.

Toys which are adapted to give a warming effect and which are heated by electrical means are described in German Patent Specification No 2 403 865, PCT Patent Application No GB/00361 and United States Patents No 4 204 110 and 4 954 676. The toys are heated either by electrically preheating a relatively massive heat storage block containing an electrical heating element, for example

by mains electricity, or by the use of a rechargeable battery acting on an electrical circuit within the toy. Such arrangements are relatively complex and expensive to manufacture to a safety standard appropriate to personal use and the toys which contain a heating block may be heavy and dangerous if thrown.

Toys using the basic hot water bottle concept concept have also been described in some of the above-identified patent specifications. In these toys the heat storage medium may be a non-toxic liquid or a salt mixed with such a liquid. It is generally accepted from a safety viewpoint that a device which is to be used by a child should not contain liquid hotter than about 50°C. If the closure is intentionally or unintentionally opened or if the liquid container is ruptured the hot liquid can easily be spilt onto the skin or clothes of a child using the toy causing discomfort or injury. These liquid-based toys require a relatively low use temperature and therefore have a relatively short use-time. Also, being a simple liquid or liquid/solid mixture, the quantity of energy stored and released by the heat storage medium over a safe temperature range is limited.

There is available a hot water bottle variant which contains a water-based gel which maintains its structure when heated. This device may be heated in a microwave oven under strictly controlled conditions which result in an initial temperature of about 50°C. This material is very flowable and if overheated could cause a scald if ruptured. There is also available a hot-pack containing a solution of a salt which develops heat when the salt is triggered to crystallise. The crystallisation takes place in very fluid medium which could again give rise to problems if the container is ruptured.

The invention provides a heating device suitable for portable use comprising a microwave-preheatable heat

storage medium comprising an organic polymeric material which is in the viscous flowable state or the viscoelastic or elastomeric state at use temperatures.

The polymeric material used according to the invention is preferably a synthetic organic polymer or a mixture of organic polymers selected as to molecular weight or degree of crosslinking to give the required viscosity characteristic. This characteristic is that the polymer, if flowable, is sufficiently viscous at the use temperature to flow only relatively slowly under the application of pressure which could be exerted, for example, by the weight of a child. A suitable degree of flowability or viscosity may, for example, be found in screw-applicator packed structural or sealant mastics for household use. When used in relation to the human or animal body the use temperature will be a temperature sufficiently high to give a sensation of warmth to the body but insufficiently high to cause undue discomfort and may be at least 20°C, preferably at least 40°C, and up to 65°C or even 70°C. When the use of the heating device does not involve direct bodily contact, as when it is used as a storage heater, for example, the range of use temperature may extend higher, for example up to 100°C or more.

The polymers may be homo- or co- polymers and may be selected from polyalkylene oxides, for example polyethylene oxide and from polyalkylene glycols, for example polyethylene glycol, polypropylene glycol or polyethylene/polypropylene glycols, having molecular weights greater than 10-^, and possibly up to 10^ or even 10^ or above. The polymers may alternatively be selected from organopolysiloxanes, non-crystallising polyolefins for example polyisobutylene, polyester resins for example polyethyleneadipate, epoxy resins, amide resins and imide resins having similar molecular weights. Those skilled in the art will have no difficulty in identifying suitable polymers from within these families or from other families

on the basis of their physical characteristics and, if applicable, of the implied criteria applicable to a personal use item such as non-toxicity, chemical stability at the temperatures involved and the like.

According to an one embodiment of the invention a polymer which would normally be a relatively flowable liquid and may have a molecular weight of 10^ or less, for example from 10^ to 10^, may be crosslinked to produce a viscous flowable, elastomeric or viscoelastic material, preferably having a molecular weight in the range greater than 10-3 to 10 or higher which is therefore intrinsically more safe in the present application. Alternatively, relatively viscous material may be solidified by crosslinking into a viscoelastic material. The crosslinking may be achieved using polyurethane chemistry, for example by reacting a polyol having a functionality greater than 2, in the presence of the polymer, with a di- or polyisocyanate. The isocyanate may be, for example, hexane diisocyanate, toluene diisocyanate or methane diisocyanate. Alternatively free radical initiated crosslinking may be achieved, where the polymer contains unsaturation, in the presence of another unsaturated compound such as isobutylene. If the polymer is an epoxy- terminated polymer it may be crosslinked by reaction with di- or polyols or di- or polyamines. Other methods for crosslinking the polymers will be apparent to those skilled in the art.

In the case of polyethylene glycols and other hydroxyl group-bearing polymers the material may be transformed into a viscoelastic or elastomeric material or a relatively more viscous flowable material by the inclusion in the material of a small amount of a ultivalent metal salt which is able to dissolve in the material. Preferably, such salts are selected from the alkaline earth metal, preferably magnesium, salts and/or contain anions which are characterised as being very weak bases. Examples of such

bases include Mg(N03) , Mg(ClC>4)2. Mg(BF ₄ ) ₂ and Mg(SCN)2 which are effective in this transformation. Preferably the number of moles of the salt represents approximately not more than three times, particularly preferably less than twice, and at least 1/8, particularly preferably at least 1/5 and ideally about 1/2, the number of moles of polymer. The polymers to be transformed by this method and the final materials may have similar molecular weights to those indicated for crosslinkable and crosslinked polymers.

Certain organic polymers, for example polyethylene glycol, crystallise over a temperature range coinciding at least in part with, or above, the envisaged range of use, for example from 20°C to 100°C, with the release of heat. This mechanism acts to enhance the useful effect of the polymers or to increase their temperature and/or duration of use and it is preferred that the polymers used according to the present invention are selected accordingly. It is a further and separate feature of the invention that organic polymers which crystallise at such temperatures, or at from 40°C to 75°C be used as heat exchange media in heating devices as described herein regardless of their viscosity or viscoelasticity at such temperatures.

Preferably any liquid or liquified materials in the heat storage medium used in the devices according to the invention consist essentially of suitable organic polymers. It is advantageous if the heat storage medium contains no substantial quantity of any liquid as a solvent,diluent or dispersant. The presence of a low boiling liquid, such as water, may cause severe problems due to vaporisation unless heating is closely contlolled particularly where a microwave oven is used and the devices according to the invention are safer to heat in such an oven than those based on heat exchange media comprising aqueous gels. The presence of higher boiling liquids is also deleterious since this would render the device less safe in use. Small quantities of liquids, for example less than 20%,

preferably less than 10% and particularly preferably less than 5%, for example from 0.01% to 1%, by weight of the total heat exchange medium, may be tolerated.

The heat storage medium may contain solid additives to such an extent as will not remove the viscous or viscoelastic character of the material at the temperature of use. Preferably the solid additive is an inorganic polymer filler. The filler may be present in up to 60%, preferably in up to 50%, and in at least 1% and preferably at least 5%, of the weight of the heat storage medium. The filler is preferably in finely divided form. The filler may be a mineral, such as woolastonite, barytes, mica or other suitable mineral or may be an oxide, such as silica or alumina or other suitable oxide. Alternatively the filler may be a suitable organic material. Fillers make a useful contribution to heat storage capacity.

The heat storage medium used according to this invention may be enclosed in a flexible sac. This sac is made of material which is impermeable to the polymer and to liquid spillages onto the outside of the sac by the user. Suitably the sac may be made of a natural or synthetic rubber, of polyvinyl chloride or of other suitable material. It is found that a sac consisting of or mainly comprising natural rubber has excellent flexibility and stretch properties in use, is relatively resistant to splitting or rupture in use and is particularly suitable for microwave heating. It is possible that, in the course of microwave heating, localised and temporary areas of relatively higher temperatures may develop in the heat exchange medium. The rubber, or other polymer, is preferably selected to be able to withstand such relatively high temperatures over a large number of heating/cooling cycles without undue deterioration through ageing. The rubber is preferably vulcanised by a low-sulphur "high efficiency" system. Preferably the vulcanisation mixture contains an effective quantity of antioxidant selected to

maximise ageing resistance. Suitable antioxidants are bisphenol antioxidants, octylated diphenylamine antioxidants or ZMBI antioxidants. Examples of suitable antioxidant products are those known by the Trade Names Antioxidant 2246 from Cyanamid or Wingstay L from Goodyear, each in about 1.5 to 2.5 parts, preferably about 2 parts, by weight per 100 parts of rubber, Octamine from Uniroyal in about 0.25 to 0.75 parts by weight per 100 parts of rubber or Vulkanox ZMB2 from Bayer in about 0.5 to 1.5 parts, preferably about 1 part by weight, per 100 parts of rubber. The fillers used in the rubber formulation are preferably of high purity. Pro-oxidants are preferably avoided and, particularly, the levels of Cu, Mn or Fe in the rubber formulation are preferably below lOppm by weight.

The polymer may be poured into the sac in a powdered or granular form and sealed in by, for example, heat or ultrasonic welding. The size and shape of the sac may be selected to correspond to the conformation of the heating device for which it is intended. In the case of a toy, for example, the sac may be of complex shape to correspond to the shape of the toy so as to distribute heat either throughout the entire toy or only in a selected portion thereof. The sac may be enclosed within the body of the toy or within a cover appropriate to the intended heating device by means of a suitable fastener for example a zip fastener or a Velcro fastener. (The word "Velcro" is a Trade Name.). The cover may be insulated either over its whole area or over a specific portion to achieve a localisation of the heating effect, if desired,and/or to lengthen the use time of the device. Alternatively the heat storage medium may be enclosed in a rigid container, which may be desirable when intended for use as a personal or domestic storage heater. Such a heater may be elactrically heated in the conventional manner.

It is an advantage of the viscous or viscoelastic nature of the heat storage medium and/or of the absence of liquid, or at least the limitation of its quantity, that there is (a) a reduced tendency to rupture the sac or other container due to localised vaporisation when heated which makes the sac more suited to heating in a microwave oven which can readily cause vaporisation in a water-based gel, although it may be heated by other means such as by an oven or by immersion in hot liquid, and (b) if the sac or other container is ruptured in use the heat storage medium either has no tendency to flow out into contact with the user or a greatly reduced tendency to do so. These advantages facilitate the heating of the medium to a temperature somewhat above the temperature of comfortable personal use to allow for heat losses due to the presence of a cover or other enclosure. Thus a heating range up to about 75°C may be envisaged or up to lOOoC or above in the case of a storage heater. The polymer used should remain suitably viscous or viscoelastic at such temperatures. It is pointed out for the minimisation of hazard that it is the responsibility of the purchaser of a heating device according to this invention to ensure that it is used in a safe manner bearing in mind that contact of a person with a medium having a temperature up to 75°C may cause some degree of discomfort or injury. A further advantage of this invention is that the polymers used may have a higher heat capacity than water or an aqueous gel and the release of energy by crystalisation can augment this. The polymeric heat storage medium is reheatable a great number of times unless mistreated.

The invention has been described with reference mainly to personal use. The heating devices of the invention may also be used in the veterinary, animal husbandry or aviculture fields, for example to warm sick or newborn animals or birds.

The invention will now be illustrated by reference to the following non-limiting examples of specific embodiments thereof.

Example 1.

A sac is cut from two sheets of 0.25mm thick polyvinyl chloride and formed by ultrasonic welding around the edges leaving a small opening. A quantity of powdered polyethylene oxide having a molecular weight of 5 x 10^ is poured through the gap which is then sealed hermetically. The sac is adapted to fit within a cavity created in the torso region of a teddy bear toy and to be retained there releasably by means of a zip fastener. The torso of the bear is relatively less insulated at the front to give preferential heat release in that area. The sac containing the powder is placed in a domestic microwave oven and heated at the highest heating level for five minutes to attain a temperature of about 60°C. Placed within the cavity in the bear heat is released over the following two hours.

Example 2.

This is the same as Example 1 except that the sac is filled with a molded elastomeric product of the crosslinking of polyethylene glycol having a molecular weight of 12000 with 1% by weight of polyethyleneglycol triol using a stoichiometric quantity of toluene diisocyanate. This crosslinked polymer starts to crystallise on cooling through 65°C to release extra heat in the range 65°C to 40°C.

Example 3.

750g of polyethylene glycol having an average molecular weight of 8000 is mixed with 5% by weight of alumina and 5% by weight of talc as fillers. The mixture is melted and is then poured into a preformed vulcanised rubber bottle having a volume just sufficient to accomodate the batch and the bottle is sealed. Heating in a 600 watt

microwave oven for 5 minutes renders the contents of the bottle substantially into the viscous flowable or viscoelastic state. The bottle maintains a steady comfortable temperature of around 54°C for many hours.

Heat exchange devices comprising modifications of the above formulation are as follows:

(a) the omission of the alumina/talc fillers

(b) the addition of a small amount, approximately 0.6% by weight of the rubber, of anhydrous magnesium nitrate as a thickening agent for the polyethylene glycol

(c) the combination of modifications (a) and (b) above. The modified devices also give a satisfactory performance.

Example 4.

The unmodified formulation of Example 3 is encased in an enclosure formed by stitching and bonding a rubberised fabric which has pockets formed by the stitching in a quilted pattern. This device is useful as a body warmer and retains a degree of flexibility even when cold. It may be heated in a warming cabinet at approximately 75°C prior to use or it may be microwaved.