Note: Descriptions are shown in the official language in which they were submitted.
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REUSABLE HEAT PACK
Field of the invention
The present invention relates to a reusable heat pack. The present invention
also relates to a trigger device for a heat pack. The invention also relates
to a
supercooled supersaturated recrystalizable solution for use in heat pack and
to a
process for the preparation thereof.
Background of the invention
Use of heating or cooling for many applications has been done by a variety of
1o techniques depending on the specific need. For example, persons suffering
from
muscular pains normally use rubber bags filled with hot boiling water to
alleviate the
pain. ln case of any head injury normally the doctor's prescription is to
apply ice as a
first aid. In case of high fever the common house remedy, has been to apply a
cloth
soaked in cold water on the forehead to bring down the temperature. Many a
time on a
recreational trip people tend to take packed food or even carry cooking
apparatus and
the raw, materials for cooking food. The other need of heat energy is in the
remote
areas where availability of the fuels may not be possible or may be very
expensive.
Therefore to get over all these difficult situations it is necessary to
clevise ways and
means to generate heat in an economical way and preferably without the use of
conventional fuels. To address this very need, development of device called
the heat
pack has occurred over the past 15 years. The main principle underlying the
heat pack
is to use heat generated due to a start of a chemical reaction between two or
more
chemicals 'or due to triggering of initiation of crystallization of a
supercooled
chemical solution. In the context of the present invention it is the second
aspect which
is disclosed
Several; warming materials are available in the market such as hot water bag,
portable electrical bag warmer or battery operated warmer. However, in case of
hot
water bag, hotwater is to be poured in the bag which can only be obtained
either by
using fuel or electrical energy. Further the heat of the water bag does not
last lorxg
3o enough for giving any observable effect. In case of electrical bag warmer a
permanent
supply of electricity is needed. This limits the use of this heating device to
only such
places where there is electricity available i:e only indoors. Irt case of
battery operated
warmer the battery needs to be charged regularly and needs replacement as and
when
. . . . . . .,]
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it gets exhausted. In all these cases another drawback is that the use is very
liainited
and safety precautions need to be taken in case of electrical heat packs.
A non-conventional heat pack has been disclosed in a US Patent 4,532,110
(1985). In this disclosure heat energy is generated by a trigger action on a
supercooled .
saturated solution of sodium acetate. The triggering is accomplished by a
specially
designed device. The entire assembly of trigger and the supercooled solution
is kept in
a plastic container made of PVC, polyurethane or the like. The drawback in the
invention is that the trigger used to initiate the crystallization of the
super cooled
sodium acetate solution has to have a protective layer of gold or silver to
prevent any
lo corrosion due to contact with the chemical. This is not desirable since the
material
usedfor the trigger is already an expensive CuBe alloy. Further the PVC
material for
the heat pack manufacturing has a very limited shelf life due to inevitable
leaching of
the chloride ion due to the presence of sodium salt solution.. This drawback
is present
in the other disclosed inventions as well as disclosed in US Patents
4,572,158;
5,058,563 and 5,205,278. A further drawback in the disclosed inventions,
except in
5,058,563, isthat the supercooled solution tends to flow to one side giving
rise to
uneven heating effects thereby rendering the heat pack difficult to use by
needing to
adjust the contour of the pack for a particular application before initiation
of
crystallisation and resultant heat generation.
In [7S Patent 5,058,563 use has been made of an additive to induce gelation
during crystallisation. This gelation helps in maintaining the desired density
of the
solution and hence uniformity of heat over the entire useful area. The
gelation
material used in the said disclosure is a water soluble hydroethyl cellulose
polymer.
This material though giving the advantage of gelling the solution suffers from
the
disadvantage of being unstable, thereby rendering the heat pack in capable of
reuse.
US Patent 5,843,145 discloses a reusable heat pack wherein a mixture of thi-ee
constituents forming a,gel, is sealed in a plastic bag. This reusable heat
pack needs an
external heating or cooling means to give a useful application of the device.
Ln case of
heating application, the heat pack is put in a microwave oven or any other
heating
means to energise the pack. It is claimed that the temperature of the heat
pack is
maintained for a sufficient length oftime thereby claiming its use as a heat
pack. In
view of the fact; that the pack needs an external heating means, the invention
proves to
be disadvantageous in its claimed use as-a heat pack. This is mainly due to
the fact
that in the invention discloses that the preeonditioning of -the pack is to be
done for a
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time period typically two hours. This renders the pack as
disclosed not advantageous in an emergency practical
situation and also in remote areas, where heating means such
as microwave oven may not be available.
JP 58180575 discloses a cooling pack with a
mixture provided therein containing inter alia, aniline
chloride. However, in this disclosure, the mixture acts as
an endothermic material wherein the material when dissolved
in water absorbs heat and produces a cooling effect.
The present invention circumvents the drawbacks of
the inventions of the prior art.
Summary of the invention
The present invention provides a reusable heat
pack which obviates or at least mitigates the drawbacks
mentioned above. The invention provides a heat pack with a
shelf life of at least six months. The present invention
provides a heat pack which can be recycled at least a
hundred times. The present invention provides a heat pack
with heat retention for at least two hours. The present
invention provides a heat pack capable of being used for
therapeutic application.
Accordingly the present invention provides a
reusable heat pack, which comprises a soft sealed plastic
bag containing a mixture of supercooled supersaturated
recrystalizable solution of inorganic substance, alcohol,
chemical compound additives, and means to trigger
recrystallization of supercooled supersaturated
recrystalizable solution of inorganic substance.
In an embodiment of the invention the plastic bag
is made of polypropylene or polyvinyl chloride.
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In another embodiment of the invention, the
inorganic substance is selected from sodium acetate and
calcium nitrate.
In still another embodiment of the present
invention the supercooled supersaturated recrystalizable
solution of inorganic substance is made in good quality
water.
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In a further embodiment of the invention, the good quality water is bacteria
free municipal supply or distilled water.
In a further embodiment of the present invention the alcohol is selected from
ethylene glycol and glycerol.
In yet another ern.bodiment of the present invention the chemical additive
comprises an organic amine.
In a further embodiinent of the invention, the organic amine comprises
aniline.
In another embodiment of the invention, the supercooled supersaturated
recrystalizable solution comprises a mixture of hydrated salt of sodium
acetate 50 -
70 wt%, ethylene glycol I - 10 wt%; aniline 10 - 20 wt% and water 10 - 29 wt%.
In another embodiment of the - present invention the means for triggering
recrystallization comprises a mechanical device selected from the group
consisting of
crocodile clip and a safety pin.
In a further embodiment of the present invention the material of the means ~or
trigger comprises a noncorrosive material.
In a fiarther embodiment of the invention, the non-corrosive material for the
trigger means comprises stainless steel.
In a further embodiment of the invention the heat pack has a shelf life of at
least six months.
In sti11another embodiment of the invention the heat pack is capable of being
recycled for at.least 100 cycles.
In another embodiment of thepresent invention the heat pack retains heat for
at least two hours.
In still another embodiment of the present invention the heat pack is used for
therapeutic applications, body warming in high altitudes.
The invention also relates to a process for the preparation of a reusable heat
pack said process comprising preparinga hydrated solution of an inorganic
substance
in water, adding an alcohol to this solution and mixing thoroughly, adding
aniline and
thoroughly mixing the resultant mixture, enclosing the mixture in a soft
sealed plastic
bag and adding; a trigger means thereto.
The present invention also relates to a mixture for use in reusable heat
packs;
said mixture comprising a solution of an inorganic substance in water, alcohol
and
aniline.
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In one embodiment of the invention, the mixture comprises a mixture of
hydrated salt of sodium acetate 50 - 70 wt%, ethylene glycol 1- 10 wt%,
anilirm. 10
- 20 wt% and water 10 - 29 wt%a.
The invention also relates to sprocess for the preparation of a mixture for
use in
reusable heat packs, said process comprising preparing a hydrated solution of
an
inorganic substance in water, adding an alcohol to this solution and mixing
thoroughly, adding aniline and thoroughly mixing the resultant mixture.
The mixture of the invention for use in a reusable heat pack is a synergistic
admixture with properties over and above the aggregation of properties of the
individual constituents and is not a simple admixture.
Detailed descriptionof the invention
First a hydrated solution of preferably sodium acetate of a preferred purity
of
was prepared in ordinary water by mixing 500-7-00 gms. in 0.1 to 0.3 liters of
water.
The solution was prepared by thoroughly mixing sodium acetate in water. To
this was
added a polyhydric alcohol and preferably ethylene glycol. This mixture was
thoroughly mixed and to this was then added another additive and preferably
aniline
and the resultant nzixture was thoroughly mixed. The addition of polyhydric
alcohol is
to provide smoothness to the recrystallised supercooled saturated solution of
sodium
acetate. This is achieved by controlled increase in viscosity of the resulting
mixture
after recrystallisation due to triggering action by a mechanical device. The
use of
aniline in the mixture of the heat pack increases the shelf life of the heat
pack and also
to give the unique property of recyclability of the heat pack. After the
mixture has
been prepared the same is poured into a plastic bag of preferred dimension of
100mm2
and made of thin sheet of polyvinyl chloride (PVC). The use of aniline as an
additive
gives the desired property of preventing the leaching of the plastic material
and
thereby enhancing the shelf life. Astainless steel crocodile clip is inserted
in the heat
pack and then finally sealed from the open end. The heat pack is now ready
having
typical contents, but not limited to, of hydrated salt of sodiuni acetate
50wt%,
ethylene glycollwt%, aniline 20wt%o and water 29 wt%. The recrystallisation
activity,
was initiated by softly p'ressing the crocodile clip and instantaneously
releasing the
same. The re crystallization took place and instantaneously heat was generated
over
the entire heat pack. This heat pack could be easily contoured over a body
part and the
part warmed thereby. The temperature of the pack was 45 C above ambient and;
maintained for about two to three hours depending on the size of the heat
pack.
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In a typical therapeutic application, after energizing the pack the same is
wrapped in a towel and applied on the patient. The cooling of the pack to
ambient
took place in about four hours time. The pack was reactivated by putting the
same in
hot water resulting in melting of the crystallized content of the pack and
then taking it
out from hot water and cooled to ambient temperature. This way the heat pack
was
ready for use again.
The principle underlying the invention is that the formation of the hydrated
salt results in an endothermic reaction absorbing heat of crystallization.
When the
crystallization is effected by the triggering action the heat of
crystallization is released
to the container thereby heating the exterior surface of the container,. This
renders the
device useful for any application. The temperature attainable with the heat
pack can
be fixed by the amount of the supercooled supersaturated solution of the
hydrated salt.
Accordingly the shelf life of the device will also be adjusted by
correspondingly
increasing the quantity of the aniline or any of the other additives like
hydroxides or
carbonates.
The novelty of the present invention lies in the heat pack being reusable and
having a long shelf life and being, capable of recyclable.
This no,velty of the heat pack is due to the inveritive step of adding
hydroxides,
carbonates or amines to the recrystallizable mixture.
In the embodiment of the -examples the heat pack is manufactured by first
dissolving hydrated salt of sodium acetate in water. Ethylene glycol was added
to this.
This was mixed thoroughly and to this aniline was added. Again the mixture was
thoroughly mixed and ihen poured in a plastic bag of PVC. The trig),er used is
a
stainless steel erocodile clip and is put inside the bag and then the whole
assembly
was sealed.
The following exatnples are given by way of illustration only and slaould not
be construed to limit the scope of the invention.
Example 1:
Heat pack contained hydrated salt of sodium acetate 50 wt%o, ethylene glycol
1wt%, aniline 20 wt lo and water 29 wt o. Triggering action was done by
pressing the
clip three times. The crystallization resulted in instantaneous temperature
rise to 75 C.
The cooling of the pack to reach to ambient temperature took place in about
four
hours time.
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Example 2=
Heat pack contained hydrated salt of sodium acetate 60 wt%, ethylene glycol
4wt%, aniline 15 wt% and water 21 wt% n. The triggering action was done by
pressing
the clip three times.. The crystallization resulted in instantaneous
temperature rise to
65 C. The cooling of the pack to reach to ambient temperature took place in
about
four hours time.
Example 3:
Heat pack contained hydrated salt of sodium acetate 70 wtolo, ethylene glycol
6wtolo, aniline 10 wt% and water 14 wt%o. The triggering, action was done by
pressing
io the clip three times. The crystallization resulted in instantaneous
temperature rise to
75 C. The cooling of the pack.. to. reac.h to am:hie:nt. temperature took
place in about
four hours time.
Example 4;
Heat pack contained hydrated salt of sodium acetate 70 wt%, ethylene glycol
lOwt%, aniline 10 wt% and water 10 wt%, The triggering action was done by
pressing the clip three times. The crystallization resulted in instantaneous
temperature
rise to 70 C. The cooling of the. pack to reach ta ambient temperature took
place in
about four hours time.
Table 1 shows the consolidated results of the examples.
Table -1
Item Wei.ght percent, of materials
Sodium acetate 50 60 70 70
Ethylene Glycol 1 4 6 10
Aniline 20 15 10 10
Water 29 21 14 10
Temp of Heat pack C 75 65 75 70
The main advantages of the present invention are:
1. It is easy to manufacture from commonly available chemicals and of moderate
purity.
2. The heat pack can be stored for at least six months
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3. The pack' can be easily put on any contour due to its being flexible even
after re
crystallization.
10
20
30
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