GB2393732A - Heat generating formulation/device - Google Patents

Abstract

A heat generating article comprises a coherent/solid mass of iron powder 12, surrounded by gas permeable inner wrapping 13, and positioned between overlapping sheets 21, 22. Sheet 21 is adjacent to a patient when in use, and may have insulating later 23. Sheet 22 is formed with apertures 24, sealed by removable cover 25. On removal of sheet 25, oxygen contacts the heat-generating iron, thus initiating an exothermic reaction. The formulation may also comprise sodium chloride solution, and absorbent material, activated carbon, and a binder. The iron powder may be formed into a strip or tablet by compression. The heat-generating device may be incorporated into a blanket. It may be disposable and sterile.

Description

/ Heat-Generating Articles The present invention relates to heat-

generating articles and, In particular, to articles wherein the heatgenerating agent or formulation is to the form of a coherent mass.

s Such articles are capable of generating heat without the need for an external source of heat or power.

Heat-generating articles which do not require external heat or power supplies are known and they often use exothermc reactions as the heat source. Probably the 0 most commonly used exothermic reaction in this context is the following: 4Fe + 30z 2Fe2O3 The (heat) energy generated by this reaction (AH) is -1652 kJ/mol. This means that 15 the reaction is capable of generating a considerable amount of heat, if properly controlled and catalysed.

This simple chemical reaction has been used as a source of heat in a number of situations since the 1920's, for example in hand or foot warmers, where a local 20 source of heat is used to combat the discomfort of cold hands or feet.

The European patent application number EP 0 526 637A1 (Kiribai Chemical Industry Co. Ltd.) discloses an example of the type of heat-generating article which is known. The exothermlc reaction used is that summarised above and the heat 2s generating formulation comprises iron in powder form along with various catalysts and other additives. The formulation is held in a gas-permeable, inner bag which is in turn kept in a gas- impermeable, outer bag until heat is to be generated. The exothermic reaction requires the presence of oxygen. Thus, until the heat generatng formulation is exposed to oxygen, the reaction will not take place and no 30 heat will be generated. The article is made to generate heat by opening the outer bag and exposing the Iron powder formulation m the inner bag to oxygen. Once the iron powder formulation is exposed to oxygen, the exothermic reaction begins and heat is generated.

- 2 Whllst formulations of the type disclosed in EP O 526 637A1 have been used for decades, the heat-generatng formulations comprising the iron powder and additives have not previously been formed into a coherent mass.

It has now been surprsmgly found that using a formulation formed mto a coherent mass does not hamper the generation of heat. It was previously thought that the use of loose powder was essential in order to ensure that the reaction rate Is high enough to generate heat. The loose powder provides a large exposed surface area 10 with which the oxygen may come into contact and over which the exothermic reaction can take place. Forming a coherent mass from the iron powder was expected to substantially reduce the exposed surface area of the iron, thereby significantly slowing the reaction so as to render it useless for use in heat-generating articles, where a high temperature must be quickly reached and then maintained.

It has also been surprisingly found that the use of the formulation in a coherent mass results in more uniform distribution of heat. Furthermore, the amount of heat generated by the formulation can be more accurately controlled; it is possible to set tighter tolerances than are possible when using a loose powder formulation.

The formulation In a coherent mass also exhibits greater heat stability, with increased heat retention and attendant increased efficiency, compared to equivalent loose powder formulations.

25 Finally, the use of the heat-generating formulation m a coherent mass also overcomes problems associated with the known use of loose powder formulations, namely lumping or uneven distribution of material, which tend to result in uneven temperature distribution.

30 The formation of a coherent mass has the further advantage that it allows the heat-

generatng formulation to be made into a number of convenient forms, including laminates, strips, pads and tablets. These forms can be easily and cleanly incorporated into articles.

- 3 Accordlug to the first aspect of the Invention, a heat-generating formulation is provided which IS formed into a coherent mass. The formulation comprises iron, in the form of a powder.

In one of the preferred embodiments, the formulation further comprises a salt solution (NaC1 in water), which acts as a catalyst of the reaction. Preferably, the formulation also comprises an absorbent material, which controls the release of the salt solution. A wide variety of suitable absorbent materials are known. Amongst 0 the most effective materials are absorbent gelling materials, such as superabsorbents. The absorbent gelling material can be natural, synthetic or modified natural polymers and materials. The absorbent gelling materials can be inorganic materials, such as liquid gels, or organic compounds, such as cross-linked polymers, or alginates, reticular carboxymethylcelluloses, grafted starches, natural 5 modified polysacchardes or synthetic derivatives of acrylamides, acrylonitriles or polyacrylates. Silica gel and water-absorbing resins are examples of preferred absorbent materials.

In another preferred embodiment, the formulation includes carbon, preferably 20 activated carbon, which serves as a catalyst for the exothermlc reaction. The carbon also aids in the dispersion of the heat generated by the reaction.

In a further preferred embodiment, the formulation may also comprise a binder which assists in the formation of the coherent mass and which ensures that the 25 product remains intact.

Materials commonly used as bmders include starch, gelatin and sugars such as glucose, sucrose, dextrose, lactose and molasses. Natural and synthetic gums including acaia, sodium alginate, carboxymethylcellulose, methylcellulose and 30 polyvinylpyrrolidone. The binders may be used as a solution and/or in a dry form.

Therefore, polymer latexes, also known as emulsion polymers, which are colloidal dispersion of submicroscopic polymer particles in a continuous medium (the best known example is the natural latex produced by the rubber tree Herea brasiliensis

- 4 which is still an Important source of one of the world's most widely used polymers) and man-made latexes, comprising dispersions of polymer (e. g. acrylic, styrene acrylic, PVdC, styrene butadiene and acetate) particles In water may also be used.

5 In one embodiment of the invention, the formulation comprises 10-90% iron powder, 5-60% water, 0-70% salt, 2-25% carbon, 1-50% absorbent material, 0-20% silica gel, and 0-50% binder.

According to a second aspect of the present invention, methods for forming the lo coherent mass heat-generating formulations according to the first aspect of the invention are provided.

A coherent mass may be formed using a variety of known methods, one of which is by compression. Where the formulation IS compressed, it preferably includes a 5 binder, as mentioned above. This will assist in forming the coherent mass and then in maintaining a coherent mass following compression, especially when the coherent mass is packaged and transported, and later during use.

The coherent mass is preferably formed by compression between one or more pairs 20 of rollers. The formulation can be fed between the rollers with confining sheets to produce a relatively thin, sheet-like laminate product. Alternatively, the formulation may be compressed without confining sheets, to produce strips or tablets. In one embodiment, the compressed formulation includes cellulose fibres. These fibres give the coherent mass added structural integrity and help to prevent crumbling of 25 the mass during packaging, transport and use.

Where the formulation is compressed between confining sheets, the sheets are preferably non-woven material or material of a fibrous nature, and can be either man-made or natural. The sheets are preferably highly permeable to oxygen. In 30 another embodiment of the invention, the degree of oxygen permeability of the confining sheets is selected to provide a further level of control of the rate at which the exothermic reaction occurs and, therefore control of the heat generated and the temperatures the heat-generating article reaches.

- 5 One preferred material for use as the confining sheets is cellulose tissue, and more preferably non-woven cellulose tissue. The sheets are preferably between 10 and 100 gsm, with an open pore structure. This affords structural integrity, whilst s allowing high oxygen penetration. Where greater structural stability is required, thicker confiinmg sheets may be used, although the thicker sheets will tend to have reduced oxygen permeability. Clearly, various other materials may be used which have the appropriate properties for putting the present invention into practice.

Examples of alternative materials Include plastic polymer films, woven or non - 10 woven textiles and paper.

In an embodiment of the invention, a heat-generating article is formed by compression, whereby the heat-generating formulation Is compressed between two confiinmg sheets, but the formulation is only compressed in specific areas, so that 15 areas of coherent mass and areas of loose powder are formed. The loose powder is then removed and the areas of coherent mass are cut out and optionally sealed to form packet-lke articles. This method is useful for large-scale manufacture of compressed heat-generating articles.

20 An alternative method of formmg a coherent mass from the heatgenerating formulation is to spray a thick slurry formed from the formulation onto a fabric base. In this method, it is necessary to carefully dry the sprayed product to lower the high water content.

25 In a yet further method, the formulation is formed into a coherent mass using a method based upon a process traditionally used to produce paper. The formulation is provided as a powder and is mixed with cellulose fibres and laid using air pressure variations on to a fibrous substrate. A latex binder solution IS then added and suction applied to force the solution right through the substrate. This is then 30 compressed through rollers and dried using hot rollers In order to lower the water content to an acceptable level for the present invention. Care must be taken when using tints method that the Iron powder does not cause an explosion.

- 6 Both of the latter methods involve the addition of large amounts of water to the formulation. It will therefore be necessary to control the methods carefully, to ensure that the exothermic reaction is not prematurely initiated.

s According to a third aspect of the present invention, articles are provided which incorporate the coherent mass heat-generating formulations according to the first aspect of the invention.

In order for the coherent mass heat-generating formulations to be useful in heat 0 generating articles, it must be possible to control the start of the exothermic reaction. This is done by controlling the exposure of the formulation to oxygen.

To do this, the coherent mass of heat-generating formulation IS preferably packaged in a gas-permeable inner wrapping. This wrapping may be made from gas 5 permeable material or it can simply have holes in it. This inner wrapping is surrounded by a gas-mpermeable outer wrapping which prevents oxygen coming into contact with the heat-generating formulation until the heat-generating article is to be used. Upon use, the outer wrapping is opened or removed, in order to allow oxygen to come into contact with the heat-generating formulation and the 20 exothermic reaction is started.

In an alternative embodiment, the coherent mass of heat-generating formulation may be packaged in a single gas-impermeable inner wrapping. When the exothermic reaction IS to be started, the wrapping is rendered gas-permeable in one of a number 25 of possible ways. For example, the gas-impermeable wrapping could comprise a section which is gas-permeable, but which is covered to render it gas-impermeable until the exothermic reaction IS to be started. To start the reaction, the cover over this section is removed, thereby allowing oxygen mto the wrapping.

30 Once the heat-generating formulation is activated by allowing oxygen to come into contact with it, 80-90% of the full temperature can be reached within 2-3 minutes.

The temperature then quickly plateaus and can be maintained for a number of hours.

- 7 The heat-generating formulation of the present invention may be incorporated into any number of articles to provide a heat source. Such articles Include hand and foot warmers, of the type which are already commercially available.

However, one type of heat-generating article which has not previously been made but which would have many useful applications IS a blanket. Heat-generating blankets, i.e. blankets without an external source of heat or power would be useful in a number of circumstances. In particular, medical applications are envisaged.

The heat-generating blankets comprise one or more flat, thin slabs of heat generating formulation In a coherent mass. The slabs preferably do not cover the entire area of the blanket. Rather, they are positioned between two sheets arranged to spread the heat generated by the heat- generating formulation over the whole area 5 of the blanket.

Insulation is preferably provided to prevent the formation of a localised area of intense heat where the heat-generating formulation is positioned. This insulation also assists in the dispersion of the heat over the whole area of the blanket.

The size of the slab of heat-generating formulation will depend upon the size of the blanket, the temperature to be generated and the length of time over which the temperature is to be maintained. However, a blanket capable of covering an adult human can be heated by one or more flat slabs having a total size of approximately 25 1200 cm2, for example, one slab of 40x30cm or two slabs of 20x30cm.

Preferably, the blanket will maintain a temperature of 36.5 C + 1 C for 4 hours + 1 hour. 30 The sheets are preferably made from a lightweight material. The material is preferably reflective, to help spread the heat generated locally by the heat-genera/lug coherent mass. In a preferred embodiment, the sheets are made from polymer

- 8 films, typically polyolefins, which may incorporate, for example, a foil or foam laminate as Insulation.

A heat-generating blanket according to the present invention is illustrated, by way s of example only, in the accompanying drawing.

Figure 1 shows a schematic, cross-sectional view of a heat-generating blanket.

The heat-generating formulation Is in the form of a coherent mass, shaped as a flat slab 12. The heat-generatng formulation is surrounded by an inner wrapping 13 which is gas permeable. The wrapped heat-generating formulation is positioned between two overlying sheets 21, 22 which help to spread the heat generated by the heat-generating formulation over their entire area. One of the sheets 21 will be adjacent to the patient or user when in use. This sheet includes an insulated area 23 15 adjacent to the heat-generating formulation. The other sheet 22 includes apertures 24 which are sealed by a removable cover sheet 25 before the blanket is to be heated. When the blanket is to be used, the cover sheet is removed and this reveals the apertures through which oxygen is able to enter the space between the sheets.

This oxygen can then come into contact with the heat-generating formulation within 20 the inner wrapping, thereby imtlatmg the exothermc reaction.

The heat-generating blankets can be used, for example, in mountain rescues or the like, where people have been exposed to the elements and are suffering from hypothermia or at risk thereof. The blankets are completely portable and so would 25 have the added advantage that they could be used immediately, without the need to first get the person to a power supply.

Another important area where such blankets may be used is before, during and after surgery. It has long been recognsed that it is very important to maintain a patient's 30 body temperature at the normal temperature of 37 C (97 F). It has been found that there is a significant risk that the body temperature of patients undergoing surgery will drop below this. This is due to a number of factors, including cool operating theatres, open body cavities, intravenous fluids and anaesthesia, which impairs body

temperature regulation. A drop in body temperature below 37 C stresses the cardiovascular system and can provoke irregular heartbeats and heart attacks.

Furthermore, it has been found that a drop In body temperature during surgery not only results in patient discomfort, but also appears to extend the time the patient 5 need to spend in intensive care after the operation.

At present, heated blankets such as Bair Huggers blankets are used in operating theatres. These are rather like air mattresses which are placed over the patient during surgery and through which warm air is forced. The benefits of this so-called 10 forced-air warming therapy are well documented. However, the blankets are bulky and they cannot be used when certain types of operation are being carried out, such as hip or knee operations. Infection is a particular problem associated with these types of operations.

15 The heat-generating blankets, incorporating using the coherent mass heat-generating formulations discussed above, have a number of advantages over the Bair Huggers blankets. Firstly, the heat-generating blankets are not as bulky as the Bair Hugger(I) blankets.

20 They also allow the surgeons better access to the patient. Additionally, the heat-

generating blankets may be easily shaped to accommodate surgery of any type and ensuring that as much of the patient's body is covered and warmed as possible.

Secondly, the coherent nature of the heat source and its packaging means that there 25 is no risk of infection from the blankets. Indeed, these simple articles can easily be stertlised. Even if the blanket were to be damaged during use, they would not pose any danger and their use could even be continued. This would clearly not be the case if the heatgeneratng formulation were In a loose powder form rather than a coherent mass.

The high degree of control afforded by the heat-generating formulation in a coherent mass means that heat-generating articles such as blankets can be produced

- 10 which reach a specified temperature for a predetermined length of time. Thus, blankets can be tailored to different situations or even different types of operations.

Thus, to summarise, the use of a heat-generating formulation in the form of a s coherent mass presents a number of advantages over the known loose powder formulations. Furthermore, forming a coherent mass will allow the heat-generating formulations to be used in articles for which they previously could not seriously be con side red.

Claims (1)

1. Claims

   1. A heat-generating formulation comprlsmg iron powder, wherein the formulation is formed into a coherent mass.

   s 2. A formulation as claimed In claim 1, wherem the formulation further comprises a salt solution.

   3. A formulation as claimed in claim 2, wherein the formulation further 10 comprises an absorbent material.

   4. A formulation as claimed m any one of the preceding claims, wherein the formulation further comprises carbon.

   15 5. A formulation as claimed in any one of the preceding claims, wherein the formulation further comprises a binder.

   6. A method for forming the heat-generating formulation as claimed in any one of the preceding claims, wherein the formulation IS formed into a coherent mass by 20 compression.

   7. A method as claimed m claim 6, wherein the formulation is compressed between one or more pairs of rollers.

   25 8. A method as claimed m claim 7, wherein the formulation is compressed between two confining sheets to form a laminate product.

   9. A method as claimed in claim 7, wherein the formulation is compressed into strips or tablets.

   10. A heat-generating article comprising a heat-generating formulation as claimed in any one of claims 1-5.

   - 12 11. An article as claimed in claim 10, wherein the article is a blanket.

   12. An article as claimed m claim 11, wherein the heat-generatng formulation is in the form of a flat, laminate product.

   s 13. An article as claimed in either of claims 11 and 12, wherein the blanket comprises the heat-generatng formulation positioned between two sheets.

   14. An article as claimed in claim 13, wherein the formulation extends over only 10 a portion of the area of the blanket.

   15. An article as claimed in any one of claims 11-14, wherein an insulated area is provided adjacent to the heat-generating formulation.

   15 16. An article as claimed in any one of claims 10-15, wherein the article is disposable. 17. An article as claimed in any one of claims 1016, wherein the article is sterile.