FI20235289A1 - Self-heating and/or -cooling thermal layer and a product containing such a layer - Google Patents

Abstract

The present invention relates to thermal products. Specifically, the invention provides an exothermic multi-layered film or laminate, which can be used in a variety of applications and products.

Description

Self-heating and/or -cooling thermal layer and a product containing such a layer

FIELD OF THE INVENTION

The present invention relates to thermal products. Specifically, the invention provides an exothermic/endothermic film or layer, which can be used in a variety of applications and products.

BACKGROUND OF THE INVENTION

There are situations where living objects or materials such as liquids and gases must be heated or cooled without external energy supply. Thermal protective covers for instance can be a matter of life and death under extreme hypothermic conditions. These products provide a protective cover for the user or they are used as survival items for health-care and military use, respectively.

Today, commercially available thermal protective blankets consist of metalized plastic foil. For example, in the patent publication US 6,007,245 A infrared- reflecting materials are utilized including an insulative polymer and a metalized coating. The thermal insulating materials prevent radiative heat loss thereby helping to maintain the body temperature. There are also self-heating thermal products on the market. These include small warmers for hands and shoulders, medical blankets for post-operation use, survival kit covers, infant warming cocoons etc. The warming effect stems from an exothermic chemical reaction taking place within the product. The thermally active material is typically iron powder that oxidizes and liberates heat. e? One example of cooling products are cold bags which can be used to prevent

S sport injuries. On the other hand, because of global warming in some parts of & world people are suffering from hot climate and cooling blankets can save lives

O in the future. Commercially available cooling products are based on dissolution = 30 of salt which is an endothermic process. a & In present-day products, the thermally active (exothermic or endothermic)

O material is contained in individual small pockets and activated when the air-

O tight packing is opened or when water bag is broken and salt starts to dissolve.

In some cases, also crystallization of salt hydrates from supersaturated solution can be used to store and release thermal energy. The point is that distribution of heat or cooling is not uniform across the whole product. In the case of exothermic products this can lead to dead spaces and localized hotspots which can result in skin damage. Finally, the solutions on the market are for single-use only, and cannot be interrupted or temporary suspended and then restarted later. Thus, in the market there is clearly need for thermal products that can be re-used and which have homogeneous distribution of the thermally active material in the product thus providing uniform heating and/or cooling effect.

The patent publication US 8,425,578 discloses an invention where the thermally active ingredients are contained in a layer separate to the moisture holding layer. This differs from the invention disclosed in this application where all of the thermally active materials form a single continuous layer.

The invention disclosed in the patent publication US 20060073324A1 discloses an invention, where the main focus is on an expanded polymer layer which contains the thermally active material. This invention does not form a continuous layer but comprises of a loaded polymer. This differs from the invention presented in this application where the emphasis is on the exothermic materials being continuous and the medium role is to enable this but it does not define the invention. In the case of US20060073324A1, the medium defines the invention.

US 20170231813 describes a face mask made of self-heating multilayer film, where uniformity of heating is improved using a gridding in the thermally active layer. This improves distribution of the thermally active materials but it is not & continuous in the sense of the present invention.

N

3 BRIEF DESCRIPTION OF THE INVENTION = 30 The present invention relates to an exothermic/endothermic film or layer, which = can be used in a variety of applications and products . The present invention

D also relates to thermal products comprising the exothermic/endothermic film

N or layer and at least a protective layer. The exothermic/endothermic film or

N layer, i.e., the active layer, comprises thermally active material and a medium

N 35 on which the thermally active material is evenly and continuously dispersed.

A coupling agent/a dispersant /a compatibilizer may be added to facilitate the even and continuous dispersion of the thermally active material on the medium. The thermal layer and the product of the present invention can be an exothermic layer or product or an endothermic layer or product.

The objects of the invention are achieved by the products characterized by what is stated in the independent claims. The preferred embodiments of the invention are disclosed in the dependent claims.Other objects, details and advantages of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an example of the self-heating structure with two layers (A) and an example of the self-cooling structure with three layers (B); 1. water layer, 2. thermally active layer and 3. protective layer.

Figure 2 shows the self-heating/cooling layer without a coupling agent (a) and with a coupling agent (b). The coupling agent adjust the surface energy between dissimilar materials.

Figure 3 shows the electrostatic interaction between matrix and thermally active material with a coupling agent.

Figure 4 shows the schematic cross-section of the self-heating layer.

Figure 5 shows a photograph of the cross-section of the self-heating layer. & Figure 6 shows the surface temperatures in °C of the self-heating layer of the present invention after 20 min. ? 2 30 Figure 7 shows the surface temperatures in °C of a commercial thermal

E blanket after 20 min.

O

N DETAILED DESCRIPTION OF THE INVENTION

S The present invention concerns an exothermic i.e., a self-heating thermal film

S 35 or layer and/or an endothermic i.e., a self-cooling thermal film or layer. The present invention also relates to thermal products comprising the exothermic/endothermic film or layer and a protective layer.

The exothermic/endothermic film or layer of the present invention comprises thermally active material and a medium on which the thermally active material is evenly and continuously dispersed. In one embodiment, the exothermic/endothermic film or layer of the present invention comprises thermally active material and a medium on which the thermally active material is evenly and continuously dispersed through addition of a coupling agent/a dispersant /a compatibilizer.

In addition to the thermally active material and the medium on which the thermally active material is evenly and continuously dispersed, the active layer may optionally comprise also other reaction ingredients, such as a catalyst.

In one embodiment, iron is used as the thermally active material in an exothermic reaction. In this embodiment, other reaction ingredients may include but are not limited to water, activated carbon, vermiculite or similar mineral and sodium chloride salt. Sodium chloride acts as a catalyst where the chloride ions accelerates rusting to form a more porous form of rust (B-

FeOOH). The activated carbon facilitates heat distribution and also through its gas adsorption properties brings oxygen more efficiently to the iron particles.

The vermiculite is an inert light-weight mineral that will maintain the optimal moisture level for rusting to occur.

In an embodiment when there is a difference in surface energies between the medium and thermally active material a coupling agent may be used to prevent agglomeration of the thermally active ingredient. The coupling agent adjust the surface energy between dissimilar materials. The coupling agent may also & improve heat transfer properties.

N

3 Figure 2 shows the difference with and without a coupling agent. The coupling 2 30 agent helps the thermally active agent to evenly and continuously disperse on

I the medium since agglomeration is prevented fostering a homogeneous > dispersion. This happens because for many mediums (polymers, nonwovens, x blown polymer etc) the surface energy is below 35 mN/m making the surfaces 2 hydrophobic. The surface energy of thermal active material is hydrophilic

R 35 having surface energy above 45 mN/m. The coupling agent has both hydrophobic and hydrophilic properties and resides at the interface between the medium and the thermally active material (see Figure 2b). Thus, in one embodiment when there is a difference in surface energies between the medium and thermally active material a coupling agent is used to prevent agglomeration of the thermally active ingredient. Especially in an embodiment, where the surface energy of the medium is below 45 mN/m, it is 5 beneficial to use a coupling agent to prevent agglomeration and increase heat transfer properties.

In the present disclosure the terms “dispersant” and “compatibilizer” are used as synonyms to the term “coupling agent”.

In one embodiment the thermal properties are further improved when there is interaction between the thermally active material and the medium. The interaction can be covalent bonding, hydrogen bonding or interaction between the metal and polymer. Electrostatic interaction is based on the electrical double layer at the interface between metal and polymer. Sufficiently close contact between two material with different band structures allows some electron transfer treating the interfacial region of a joint as a parallel plate capacitor. Electrostatic forces across the double layer contribute to the total adhesive bond strength. This interaction between the polymer and metal is increased in the presence of a coupling agent as shown in Figure 3.

The coupling agent can include but is not limited to silanes, maleic anhydride, titanate, aluminate, borate, bimetallic, phosphate.

Oxidation of metallic iron (iron rusting) is an example of an exothermic reaction (see reaction 1). Besides iron and oxygen, the reaction requires water and it is & supplied using activated carbon and/or vermiculite as carrier. Moreover, NaCl is used as catalyst. = 30 4Fe + 302 + H0 — 2Fe20O3 - H20 AH = -1648 kJ/mol (1)

E The reaction starts when oxygen is allowed to contact with iron (when an air- o tight packing is opened, for example) and it will last until all the ingredients are

N used up or until the oxygen is prevented from interacting with iron. Once the

N 35 ingredients are consumed they need to be replaced, because the reaction is

N not reversible. The reaction can be started and stopped several times if the entrance of oxygen can be controlled.

It is important to note that in an embodiment where iron is used as the thermally active material, the active layer must be packed under oxygen-free conditions before use. Another option of adjusting the iron oxidation reaction is to add a certain amount of water, to maintain optimal moisture level, in the uniform active layer in normal air conditions. In an embodiment, where iron oxidation is the chemical reaction, the outer surface(s) of the active layer should be permeable or semi-permeable to oxygen. The oxidation reaction can be stopped by preventing oxygen to get into the active layer.

The heating performance when iron is used depends greatly on the oxygen circulation. Therefore the pore size in the outer surface(s) and the number of pores play an important role. Moreover, the active layer must be porous in order for the oxygen to reach the iron.

In an embodiment of the invention, the exothermic thermally active material is composed of fine iron particles with a large surface area to prolong the life of the thermal product.

In an embodiment of the invention, the initiation of iron oxidation can be delayed or accelerated using a porous outer or inner surface that controls the air flow to the reactive material.

In an embodiment of the invention, the thermally active material is supersaturated salt solution that releases heat during crystallization. In this embodiment, crystallization of salt hydrates from supersaturated solution is used to store and release thermal energy. When sodium acetate is used, the & thermally active material is the supersaturated aqueous solution and it

N crystallizes according to eguation (2). 3

NaC2H3Ox(aa) <> NaC2H302 - 3H20(s) — AH = -19.7 kJ/mol (2)

E Activating the reaction reguires exposing the sodium acetate solution to a 2 metal. The metal surface acts as a nucleation site for immediate crystallization 0 and release of heat. In some cases, the reaction can be initiated by squeezing

O 35 the product resulting in spontaneous crystallization.

The reverse reaction represents the melting process. In this case heat needs to be added and the easiest way to heat up the crystals is either in boiling water or in the microwave oven. Either method will return the solid into a supersaturated solution again.

In an embodiment of the invention, the endothermic thermally active material is a salt that consumes energy when dissolving in water. Heat-consuming (endothermic) processes include dissolution of NaCl, KCI, NH4CI, NH4NOs,

K2S04, KNO3, and/or CO(NH2)2 in water. The process is the same as the reverse reaction in (2) and for urea dissolution, AH = 15.4 kJ/mol.

In an embodiment, where urea or other salt is used as an endothermic active material, water should be packed in a separate layer, which can be easily brought into contact with the active layer. In an embodiment, the outer surface of the active layer may be water-proof consisting of any material that prevents the permeation or leaking of water or moisture. Endothermic reaction energy can be adjusted by controlling the amount of water next to the active layer.

The medium of the active layer can be, but is not limited to, any sheet-like porous material, on which the thermally active material and other reaction ingredients can be evenly and continuously dispersed. The medium can be in the form of woven or non-woven fibers prepared by conventional methods or by electro-spinning but is not limited to these methods. The medium can also be a cross-linked porous polymer gel. The thermally active material and the reaction ingredients are included on/in the medium either during spinning or they are added afterwards using suitable methods. The active layer should be & easy to remove for replacement in case where iron is used or for reheating and

N crystallization via boiling in the case where e.g. sodium acetate is the thermally 3 active material. 2 30

I In one embodiment of the invention, the thermal layer can be reused several > times.

S x In one embodiment, the thermal reaction in the active layer of the present invention can be initiated anywhere without needing external connection.

The present invention also relates to a thermal product comprising the exothermic/endothermic film or layer and at least a protective layer.

The product of the present invention is formed of the thermally active layer and at least a protective layer. The active layer comprises the thermally active material, other reaction ingredients including catalyst, and the medium.

In one embodiment, the protective layer is close to the skin when used as a blanket and close to the product when used as a cover. It should allow heat transfer from the active layer and feel comfortable when in skin contact.

In an embodiment, where iron oxidation is the chemical reaction, the protective layer must be permeable or semi-permeable to oxygen. The oxidation reaction can be stopped by preventing oxygen to get into the active layer.

The heating performance when iron is used depends greatly on the oxygen circulation. Therefore the pore size in the protective layer and/or the number of pores therein play an important role.

In an embodiment, where there are several layers between the protective layer and the active layer then the air (oxygen) permeation restriction of these materials needs to be considered (Iron oxidation reaction). One way to handle this is to make sure the reactive iron oxidation ingredients are close to an external surface of the active layer.

In one embodiment, the outer surface of thermal product is thermally insulating.

S

N In one embodiment of the invention, the thermal product is an endothermic 3 product. In one embodiment, the endothermic product comprises a water layer. 2 30

I In one embodiment of the invention, the thermal product can be reused several > times.

S x In the products of the present invention, the thermal reaction can be initiated anywhere without needing external connection. The thermal products can reach much more even heating/warming/cooling effect than other materials. Different exothermic and/or endothermic reactions can be used depending on if the product should be disposable or reusable. The self-heating and/or cooling thermal protect products can quickly restore the body temperature quicker than any other products.

The thermal product of the present invention can be a blanket, a protective cover for temperature sensitive cargo, a material to be made into thermal clothing or a general-purpose heat source or sink but it is not limited to these products only.

The following examples are given to further illustrate the invention without, however, restricting the invention thereto.

EXAMPLES

Example 1. The homogeneous self-heating layer was prepared using non- woven polyester cloth as medium. Iron powder containing also activated carbon, vermiculite, food flour, NaCl and water was used as thermally active material and it was obtained from commercial hand heaters. The fluffy cloth was first ironed to render the outer surface impermeable for the solid particles.

The thermally active material was poured between two pre-treated cloths and they were thermally seamed to produce a continuous non-woven fabric that contains the thermally active material evenly distributed. Loading of the thermally active material was 500 g/m?.

Schematic and actual cross-sections of the self-heating layer are shown in

Figures 4 and 5.

Temperature distribution of a 50x50 cm self-heating layer was measured after & 20 min and the results are shown in Figure 6. The indicated temperatures do

N not represent real situation, where the reaction rate is controlled by semi-

S permeable oxygen barrier. However, the results clearly show the even heating 2 30 effect that contrasts the patch-like heating in existing self-heating products.

E Furthermore, temperature difference in the different measuring points is less o than 10°C. 2 & A self-cooling layer can be prepared correspondingly using an endothermic

N 35 reaction mixture as thermally active material.

Reference example 1. Temperature distribution of a commercial thermal blanket was studied by opening a vacuum-packed blanket and by measuring temperature after 20 min. The results are shown in Figure 7. In the commercial thermal blanket, the thermally active material consists of iron powder, activated carbon, vermiculite, food flour, NaCl and water and it is packed in separate. As can be clearly seen from the results, temperature distribution in the surface of the blanket is not uniform and the difference between the maximum and minimum temperatures was 25-30°C. The results shown here proof that the thermal layer comprising of a thermally active material evenly and continuously dispersed in a medium gives more even surface temperature distribution than in the case of thermal blanket, in which the thermally active material is packed in separate pockets.

O

N

O

N

O

<Q

O

I

=

O eo]

N

LO

O

N oo

Al

Claims (16)

Claims

1. A thermal layer comprising of a thermally active material and a medium on which the thermally active material is evenly and continuously dispersed and optionally a coupling agent.

2. The thermal layer of claim 1, wherein the medium is in the form of woven or non-woven fibers.

3. The thermal layer of claim 1, wherein the medium is a cross-linked polymer gel.

4. The thermal layer of any of claims 1-3, wherein the layer further comprises a catalyst.

5. The thermal layer of any of claims 1-4, wherein the layer is an exothermic layer.

6. The thermal layer of claim 5, wherein the thermally active material is iron.

7. The thermal layer of claim 6, wherein the layer is permeable or semi- permeable to oxygen.

8. The thermal layer of claim 5, wherein the thermally active material is a supersaturated aqueous salt solution.

9. The thermal layer of any one of claims 1-4, wherein the layer is an endothermic layer.

10. The thermal layer of claim 9, wherein the thermally active material is urea or sodium acetate.

11. The thermal layer of claim 9, wherein the endothermic reaction is based on dissolution of NaCl, KCI, NH4CI, NH4NO3, K2S04, KNO3, and/or CO(NH2)2 in water. &

12. The thermal layer of any of claims 1-11, wherein the outer surface is N water-proof preventing the permeation/leaking of water or moisture. 3

13. Athermal product comprising the thermal layer of any of claims 1-12 2 30 and a protective layer. I

14. The thermal product of claim 13, wherein the protective layer is > permeable or semi-permeable to oxygen. x

15. The thermal product of claim 13 or 14, wherein the product is an 2 endothermic product comprising an additional water-containing layer. R 35

16. The thermal product of any one of claims 13-15, wherein the outer surface of the product is thermally insulating.