GB2383539A

GB2383539A - Cooling Article Involving Evaporation of Water from a Polymer Absorbent

Info

Publication number: GB2383539A
Application number: GB0130919A
Authority: GB
Inventors: Patrick Caceres; Franck Caceres
Original assignee: Cryomed France
Current assignee: Cryomed France
Priority date: 2001-12-27
Filing date: 2001-12-27
Publication date: 2003-07-02
Anticipated expiration: 2021-12-27
Also published as: FR2834203B1; GB2383539B; GB0130919D0; FR2834203A1

Abstract

A cooling article for use on the body, providing a "dry cold" sensation, comprising a polymer absorbent enclosed within a bag delimited by a collapsible envelope, having non-watertight walls, wherein said polymer absorbent is in the form of particles, each of which is composed of a core of less cross-linked polymer sequences relative to the shell of the particle. The envelope is composed of a non-woven fabric comprising longer threads or fibres of natural or semi-synthetic nature and shorter polyester or polypropylene fibres.

Description

COOLING ARTICLE INVOLVING EVAPORATION OF WATER FROM A POLYMER ABSORBENT The present invention relates to such cooling devices as are useful for relieving pain from a sore or painful part of an individual's body. Pain relief is here considered as. including reduction to some extent as well as complete alleviation of pain, for at least some amount of time. Among the main means to relieve pain, cryogenics has been used for a long time, and its beneficial effects on health and comfort are well-known. The Invention stands in that field and its main object is to provide such an article that will exhibit a high and long-lasting cooling capability when applied externally on said sore part. More specifically the invention relates to such cooling articles the operation of which involves evaporation of water. It is further desirable that the article according to the invention produce a dry cold and that It be non toxic and easy to use.

It is desirable to enhance the properties of the existing cooling articles, In order on the one hand to achieve a high and long-lasting cooling effect, and on the other hand to provide a great comfort for the user during the application of the article on the sore part. An article with a regularly homogeneous cooling effect and a great comfort in use prooves especially useful in therapeutic applications, for removing extra heat from a member or part of the body to be treated.

However, the invention is not restricted to that field of application of the articles It provides and it extends as well to a great number of other applications where it is desired to bring or maintain an object to a temperature lower than that of the ambiance where it stands.

Thence, an object of the Invention is to provide an article showing cooling properties that are highly improved compared to the prior art. The article of the invention is made of particles of a highly absorbent polymer enclosed within a bag delimited by an

advantageously collapsible envelope having non-watertight walls It differs from those previously known by the fact that water, by evaporating from the article after it has been immersed in water, will provide a long-lasting cooling effect with slow heat uptake.

A further object of the invention is to ensure that although steam can easily escape out of a bag delimited by the envelope through a wall of the bag constituting an outer face of the envelope, an opposed inner face of the envelope supplies a so-called dry cold when applied onto a part to be cooled. As a consequence the wearer will never have the Impression that the surface of the bag has become wet and heat transfer at the contact with the skin will not be disturbed.

Still another object of the invention is to ensure that the heat transfer due to the temperature difference at the interface between the article and the part to cool Is homogeneous all over that part and that it remains unimpaired along time.

In connection with that purpose, the invention provides a cooling article involving evaporation of absorbed water from an absorbent polymer wherein said polymer is enclosed in a bag delimited by an envelope comprising a heat-conductive inner wall for contact with a part to be cooled and an opposite outer wall permeable to moisture escaping from the polymer medium during desorption.

A further object of the invention is to provide a dry cold the dryness of which lasts over time, whatever the external conditions may be. The envelope containing the absorbent polymer remains dry after water absorption by the polymer, and retains its dryness even if submitted to wetting conditions such as sweat, moisture...

Other objects and advantages of the invention will appear from the description below of preferred embodiments of the article according to the invention. They include the fact that In preferred embodiments all matters and materials in the article should be nontoxic for medical external uses and should satisfy to all security requirements in that field.

According to a main feature of the invention, the absorbing/desorbing medium is made of polymer particles showing a shell-core structure, i. e. that are individually composed of a core with relatively flexible or elastic sequences and a shell of relatively more rigid polymer sequences. The difference in rigidity, or stiffness, can be achieved at best by additional cross-linking of the polymer in an outer layer of each particle compared to an inner layer forming the core. In such cases, the absorbed water is mainly retained in the flexible core of each particle. The outer shell shows the structure of a tridimensional reticulate net, or web, that does not preclude inflation of the particle when absorbing water up to the swollen state, but facilitates flowability and sliding of the particles on one another with little friction, so it avoids that the swollen particles form a solid hard gel mass. During desorption it does not hinder the passage of evaporated water from the core, and nevertheless does not permit liquid water to circulate easily through it and thereby diffuse from the core of a particle to a next one.

Avoiding close wet contact between the soaked cores, it introduces thereby some delay on the diffusion of water from each particle to the next ones.

Thus, a cooling article according to the invention comprises a polymer absorbent enclosed within a bag delimited by a collapsible envelope having non-watertight walls, and said polymer absorbent is under the form of particles each of which comprises a core of less cross-linked polymer sequences more active in retaining absorbed water and a shell of more cross-linked polymer sequences apt to retard diffusion of moisture from a particle to another during desorption of absorbed water.

The envelope according to the Invention is advantageously flexible and collapsible. As a result, the thickness of the article, very low when the polymer particles are in the dry state, increases when the particles swell. Then, during water desorption, the size of the particles decreases, water escapes from the article and owing to its flexibility, the envelope collapses, meaning that its inner and outer walls come close together. In consequence there Is little, or no, air entry in the envelope. This is of a particular importance, because

some air present in the envelope would disturb heat transfers between the sore part of the body and the water absorbed in the particles, and thus would decrease the efficiency of the long-lasting cooling effect of the article.

Furthermore, the shape of the inner wall of the flexible envelope according to the invention is easily adapted to that of the part of the body to which the article is applied, which provides a better pain relief on the entire painful surface.

In the preferred embodiments the walls of the envelope are made of textile.

A method for relieving pain from a sore part of an individual's body with a cooling article according to the invention comprises wetting said polymer particles with water through said envelope during a sufficient time to swell them into a gel mass filling up said bag, and applying said article on said sore part of the body, thereby maintaining an inner wall in close contact thereon while allowing water vapour desorbed from said particles to escape through an outer wall of said envelope.

Furthermore, the amount of polymer particles enclosed in the bag is in excess compared to that which would just be required to fill up the bag when in the full swollen state. Due to such an excess in connection with the specific structure of the particles, it has been observed that during absorption of water there occurs some expansion of the mass, with light particles not yet completely swollen with water that have a tendency to be expelled from the center, where completely swollen particles concentrate into a gel.

Thence at the end of the absorption process there remains, close to the walls of the bag, a layer of particles that would still be able to absorb some water. Those particles are useful to absorb any trace of water, moisture or sweat penetrating Into the bag through the envelope, which maintains the latter dry. There is thereby provided a better feeling of comfort for the user, and a better heat transfer across the inner wall of the envelope is achieved. Moreover this layer of not fully swollen particles constitutes an additional barrier to

water outlet, which increases the thermal inertia of the article according to the invention.

According to a further important feature of the invention, the fabric for the envelope is composed so as to be resistant to the pressure of the swollen gel mass, during and after water absorption. Preferably, it is also composed so as not to be water-absorbent, so that it does not let water diffuse easily through it out of the gel mass. Fibers showing hydrophobic or water-repellent behaviour can advantageously be used. However, for most applications, and especially for the application as a refreshing bandage in medical uses, it has proven specially suitable to use a partly hydrophilous and partly hydrophobic fabric. In preferred specific embodiments of the invention, a convenient fabric comprises natural or semisynthetic fibers such as cellulosic fibers.

According to a further advantage of the invention, the shellcore structure increases the mechanical resistance of the individual particle. Rather, one can suppose here that the rigid sequences in the outer highly cross-linked layer explain why the cooling articles of the invention can support a high number of absorption/desorption cycles. The same cooling unit can thence be reused many times with the same efficiency, while each time recovering its properties towards absorption and desorption (especially high thermal inertia and long-lasting cooling effect) after it has been stored in the dry state where the polymer powder is dehydrated.

The amount of superabsorbent particles placed In the envelope is in excess compared to that required to occupy the whole volume when they are in the full swollen state. The operation of the article of the Invention Involves that the polymer particles medium thus in excess in the bag is swollen with absorbed water by immersion in water, preferably at a cool temperature (for instance at approximately 10 OC). When the absorption is blocked, mainly due to the restricted volume in the envelope, but possibly also because of the immersion being performed in cool water or in addition by optionally taking the article out of the cool water bath before that stage, the swollen gel remains able to absorb more water.

Due to their shell-core structure, the particles are distributed while swelling in the entire bag volume, and the less swollen ones, which retain the higher water absorption capacity, are expelled to the periphery of the bag. The amount of particles introduced in the envelope is thus calculated so that the particles close to, the envelope retain a high absorption rate, at least over 70 %, thence they are still able to absorb water, moisture, sweat... As a consequence, in connection with Its inherent water-repellent properties, the envelope remains dry during all the time of application of the article on the user's sore part. On the contrary, too high an excess of particles would lead to such a decrease of the volume in the envelope available for absorption of water, that it would result In loss of part of the cooling capacity of the article. The excess amount of absorbent particles is thence be calculated so as to achieve the best residual absorption rate of the partly unswollen particles after immersion in water, without interfering significantly with the strong and long-lasting cooling effect of the article.

In preferred embodiments the weight excess of particles is between 5 and 10 percent of the theoretical weight required to just fill the bag completely. It is for instance equal to 8 percent of that amount. After immersion in water is completed, the initial absorption rate is then approximately 80 %, and more generally from 70 to 90 %, at least for the polymer particles nearer to the bag surface, the particles next to the envelope being less swollen than those in depth.

If immersion In water of the article is long enough, the swelling of the particles is blocked due to the lack of space inside the bag. The material for the envelope must thence support the pressure exerted by the incompletely swollen gel. This is achieved with the fabric according to the invention, which, as described above, is resistant to that pressure. In a preferred embodiment, this is even still the case after several cycles of absorption/desorption of the polymer absorbent particles.

According to other features of the invention, the fabric for the inner face of the envelope, the one that comes in contact with

the body, is selected for showing good heat conductivity properties. The outer face must essentially be permeable to vapour. In a preferred embodiment, the envelope is made of a single fabric, which is permeable to water and water-repellent, heat-conductive and resistant to the pressure exerted by the swollen gel.

The properties of the fabric according to the invention are generally presented by woven fabrics such as cotton or cottonviscose woven textile fabrics. However, making the envelope from non-woven fabrics would have the advantage that their manufacturing cost is lower than that of woven ones. The non-woven fabrics available show several major drawbacks, such as imperviousness, low resistance to the pressure exerted by the swollen gel, tendency to split, heat Insulating properties. Thence, a suitable non-woven fabric has been developed that is non-watertight and does not split, that shows high pressure resistance and thermal conductivity and can stand many absorption/desorption cycles.

The fabric used to make the bag's envelope in the preferred embodiments of the invention is a non-woven fabric made of longer threads or fibers of natural or semi-synthetic nature, preferably of a cellulosic material and more specially threads or fibers of viscose, and shorter polyester fibers, preferably polyethylene fibers and more specially polypropylene fibers. The respective proportions expressed as weight percentages are from 10 to 30 percent for the former and 90 to 70 percent for the latter in the total weight of the composition.

According to further features of the invention, the cooling articles can be manufactured so as to show a great variety of shapes adapted to be applied onto different parts of the human body to be treated. However each bag for containing a dose of the polymer medium is preferably of elongated shape with a section having a diameter from 1 to 5 centimeters, preferably less than 3 centimeters, and the whole article may comprise two or more bags, such as can be separated by sewing together two opposite walls of a single envelope.

The Invention is thereafter described in more detailed examples considering the production of cooling articles providing a

dry cold, intended for use to relieve pain from a sore part of the body by desorption of particles of superabsorbent polymer enclosed in a textile bag.

The particles of superabsorbent polymer are chosen to be notaxic, In a preferred embodiment, the particles used are made of crosslinked sodium polyacrylate. A maximum level of stability of the polymer is thereby obtained without any toxicological effects.

The polymer particles also have good water absorption/ desorption properties. In accordance with the invention, the polymer particles have a shell-core structure, meaning that they possess a flexible part, the core, inside a stiff part, the shell. This is achieved by crosslinking the polymer more on the surface than in the core The polymer particles are separate and not bound together, at least when they are in the dry state, so that they are free to move in the whole volume of the bag where they are enclosed. Despite its stiffness, the shell part is dilatable, which allows the particles to absorb water and swell into a gel mass. As an example, the volume of the particles can thereby increase up to 60 times their initial volume. The polymer particles thereby obtained show improved absorption/desorption properties compared with homogeneously crosslinked polymers. This is supposed to be at least in part because they are less deformable In the swollen state than in the case of a homogeneous crosslinking.

After having swollen into a gel, the polymer particles according to the invention present very low liquid water desorption properties. Because of their shell-core structure, their external stiffness constitutes a barrier to water oulet. However, if sufficient heat is absorbed by the gel, water can evaporate and is desorbed in the vapour state. After complete desorption, the polymer particles resume their initial dry powder state.

The properties of the particles of superabsorbent polymers according to the invention, and more particularly their porosity and their modulus of elasticity, are not affected by deformation under load, nor by reiterated water absorption/desorption cycles. A gel with intact properties can be regenerated by water absorption after

the particles have resumed their initial state, or at any time during the water desorption step. In a preferred embodiment, the setting of the gel can be reproduced 8 to 10 times. As regards the gel formed, this will remain homogeneous.

The polymer particles used are produced according to European Patent application EP 0, 789. 048, by surface crosslinking a polyacrylic polymer obtained by inverse suspension polymerization of a monomer followed by agglomeration of the individual particles.

The precursor monomer can be acrylic acid or methacrylic acid. or preferably a salt thereof, more specifically the sodium salt, but other hydrophilous monomers can also be used.

The amount of particles used, which varies depending on the dimensions of the article, is poured, using a metering device, into a textile bag which may be closed for example by stitching, sewing, or melt bonding.

The amount of particles incorporated into the bag is in excess compared to the amount just necessary to fill up the bag completely. Thence after swelling with water, the particles occupy the entire bag volume, but not all of them are completely swollen, the less swollen ones tying close to the walls of the bag. Those particles will be useful, firstly to absorb the water retained by the envelope after withdrawal of the article from the water bath, and subsequently to absorb the water, sweat and moisture to which the envelope is likely to be submitted during use of the article, and which may originate from the inside of the bag, if liquid water is desorbed from the fully swollen gel under too strong a pressure exerted on the article, or from the external environment, for example if the user sweats, or the atmosphere is humid. As a result a dry cold will be created and maintained all throughout the water desorption phase.

The bag is delimited by a flexible textile envelope providing a tubular space one to three centimeters wide. In a preferred embodiment, the envelope is made of a single fabric, which is permeable to water and water-repellent. As an example, a non- woven fabric made of viscose and polyester fibers is used.

As used for relieving pain according to the invention, the article shows great initial and long-lasting cooling properties. The different steps of the cooling process will now be explained, together with their supposed mechanisms.

The particles of superabsorbent polymer are wetted by immersion of the article into cold water. Each polymer particle, upon contact with water, absorbs water, starting from its core, so that it swells and forms with the others a gel mass which occupies the entire bag volume. The article is then preferably cooled down in a freezer for better effect. Due to the structure of the polymer particles, it retains a suitable flexibility.

When applying the article on the sore part of the body for which it has been intended, the inner face of the envelope comes in close contact with the body. The high difference in temperature between the article and the body and the heat conductibility of the envelope create a thermal shock, with quick heat transfer from the hot body to the cold article, and the user gets a strong immediate feeling of coolness.

At first, the cooling effect and thermal shock may priority be due to the cold temperature of the whole frozen article. But then the heat extracted from the body and slowly transfered accross the article comes to the water trapped in the polymer particles which absorbs it without a temperature increase by changing from the liquid state to the vapour state. The polymer particles architecture provides a barrier to the circulation of water, and their outer shell layer opposes resistance to heat transfer, since the water trapped in the core of each particle must substantially be in the vapour phase before it can escape from it. This results in high thermal inertia and low heat losses.

While water evaporates, the production of steam can slowly progress through the article thickness and reach the external face of the envelope which is permeable to vapour, so that it escapes from the article. Evaporation thence provides an insulating effect due to the absorption of heat. A strong and long-lasting cooling effect is

obtained owing to the great quantity of water contained by the polymer particles.

Thus, as long as some water remains in the particles, and up to several days, the article retains its effect of coolness. If not applied to the body, the evaporation process is slow. In order to recover Its cooling effect, the article has to be applied on the body. A few days after wetting and cooling, the initial thermal shock does not take place anymore, but owing to the difference of temperature between the body and the article, some heat is transfered and water evaporates, leading to the recovery of the cooling effect.

During all that time, the envelope remains dry, because the fabric is not absorbent for water, and because the particles in excess, which are not completely swollen, absorb the surrounding moisture and the sweat that may be produced by the suffering individual. As a consequence, the article does not wet or drip, and it ensures cooling through a dry contact with the skin of the wearer, leading to great comfort for him, and to an improved heat conductivity of the envelope.

When all the water has evaporated out of the article, the particles resume their initial state and they gather to an end of the tubular bag as a dry powder. Owing to their good resistance to deformation under load, their initial properties are retained. All that is then required is to immerse the article in water again in order to recover the retention and coolness effect. The swollen article can optionally be kept in a freezer until next use.

As an example of use concerning a specific embodiment of the invention, after the article has been immersed in water at 10"C, for a setting time of the gel of approximately 90 seconds, it shows a heat uptake of between 0. 30"C/min. and O. 9"C/min., and more specifically between 0. 3500/min, and 0. 7OC/min., with an average value of not more than approximately 0. 4 oC/min..

The superabsorbent polymer particles for use according to the invention are advantageously in the form of round balls. This makes it possible to trap water not only in the particles but also

between these particles, the amount of water trapped between the particles, known as"mterstitial water", being greater in the case of ball-shaped particles than crystal-shaped particles. For the same cross-linking average rate, this leads to a higher absorptivity and therefore, as a result of the larger quantity of water stored, to greater thermal inertia. The ball shape also allows avoiding lacerations or injuries through the textile article, unlike other polymer particles the shape of which is not round and smooth but angular, with sharp edges or in the form of crystals.

Besides, the article of the invention ensures pain relief most efficiently from the largest surface of the sore part. For that purpose, the invention provides for different forms of the article and takes benefit of the properties of the particles of absorbent polymer used such as defined above, especially their ability to flow.

On the one hand, the polymer particles, owing to their round shape and to their shell of rigid polymer sequences, present a high mobility. Consequently, while they are swelling, they are easily distributed homogeneously and move to occupy the entire bag volume, all along its length.

On the other hand, the form of the article according to the invention, which may comprise one or more bags, is designed so as to follow the shape of the part of the body on which It is intended to be applied. The article possesses a part that allows a close contact of the bag (s) containing the polymer particles with the body, such as an elastic band. The polymer particles are enclosed into one or several bags delimited by the envelope. The number and the form of the bags are adapted according to the part of the body that must be treated. They are chosen so as get the best between flexibility and contact surface. A high number of bags enhances flexibility, whereas it decreases the contact surface. In most cases, the bags are advantageously of an elongated tubular form and are assembled along their length.

As a further advantage of the invention it can be noticed that the particles in their initial dry powder state are of low hindrance. The increase in volume takes place on contact with

water, when the particles swell into a gel mass. After swelling, the gel formed remains homogeneous and provides the coolness effect for several days. There does not occur any denaturation or variation in the product when it is warmed to temperatures not exceeding 1 opoc..

Several tests have been carried out with an article according to the invention conformed as a headband, obtained by incorporating particles of a superabsorbent sodium polyacrylate medium wherein the individual polymer particles had been subjected to an additional surface selective crosslinking, into a stitched nonwoven textile envelope. The particles were as obtained by the process of European Patent Application EP 0,789, 048 and conformed to the following properties :-their saline water absorptivity equals at least 50 g/g ;-a bed of the gel of 1. 5 g of the polymer under a load of 5 kPa has a saline water absorption of at least 20 g/g.

The initial size of the polymer particles used, measured when dry in the dehydrated state, i. e. before immersion in water, is between 30 and 1500 lim, and preferably between 100 and 800 m.

Preferably, less than 1% of the particles are smaller than 1 00 lm.

The envelope Is made of a non-woven fabric comprising 85 % polypropylene and 15 % viscose rayon under a thickness of 0. 6 millimeters and a surface weight of 48 g/m2. That fabric is stable at the hydrophobic/hydrophilous equilibrium point and it can stand more than twenty wettings without loosing its properties. Its strength in resisting to breaking is more than 50 N in the manufacturing or fibers length direction and still higher than 12 N in the cross direction, both whether the fabric is dry or wet. Its absorption capacity is above 600 percent.

The envelope is composed of two different parts with two identical longitudinal tubular front bags receiving the polymer particles, which are intended to be applied on the forehead, and an elastic band, sewn to the front bags, that, when the headband is worn around the head, is situated at the back of the head and maintains said front bags in close contact with the forehead. The

length of the bags is from 25 to 30 cm (28.5 cm in the example), so that they cover the forehead in its entire length. Their thickness or diameter when fully swollen is about 1. 5 to 2 cm.

The dose of superabsorbent particles that are placed in the envelope is in excess compared to that required for full occupation of the bag volume when the particles are in the full swollen state In preferred examples, the weight excess of the particles is between 5 and 10 percent of the theoretical weight required to just fill the bag completely. It is for instance equal to 8 percent of that amount.

Thence, after immersion in water and swelling of the particles to a complete filling of the bag volume, the particles next to the walls of the envelope remain still able to absorb more water, including ambiant moisture when at room temperature. In the examples described here, their initial absorption rate is between 70 to SO %, and for instance approximately 80 %.

The following experiment was carried out : The headband is immersed in water for one or two minutes, to allow the particles to swell into a gel mass, which occupies homogeneously the entire volume of both bags. The headband is then optionally stored in a freezer for 30 minutes.

When applying it on the head, the feeling of coolness is immediate, due to the thermal shock between the cold envelope and the forehead. The contact is furthermore very tight and homogeneous on the entire forehead, due to the elastic band and to the flexibility of the front part of the headband, confered to it by the form of its two round elongated bags.

The cooling effect remains for a long period. Indeed, three days after wetting, upon applying the headband on the forehead, the feeling of coolness is still immediate. The volume of the front part has started decreasing and the envelope is dry. After four days, the envelope has lost part of its tension, but the bags are still wellshaped. After five days, the thickness of the front part has reduced to almost the same as that of the elastic part. The particules are though still uniformely dispatched in the bags.

In this experiment, where the headband was always kept in room condition of temperature and humidity and was only worn from times to times, it was not before five or six days after wetting and cooling that, when applying the article on the forehead, the user would no longer feel it as ice immediately. However, even then, after

.... - - - having worn it for a few minutes, the impression of coolness would be recovered, which could not be explained but as being due to the evaporation of water from the polymer particles. At that stage, the particles has not yet come back to hard granules. They are still individually in the gel form, but they are separate, not completely swollen, and they concentrate into a small volume at an end of the bags.

All along this experiment, despite the amblant moisture, the headband has remained dry.

In order to further illustrate the high thermal properties of headbands constituted with articles according to the invention compared to the prior art, the following temperature uptake experiment was carried out.

The headband according to the invention is designed here by NM. A similar headband, i. e. containing the same excess of particles of the same polymer absorbent, but included in an envelope constituted of a woven textile fabric, is designed as SM.

The woven fabric is made of polyester-cotton, not treated with dye fixers so as not to retain water. As a reference, a headband containing a gel of absorbent polymer particles wherein there is no substantial difference in the cross-linking rate between core and shell as described by the prior art, is called BG.

All three samples are wetted then cooled down to 0"C. The NM sample reaches 0"C three hours before the BG sample. The temperature uptake of the samples is then monitored during 120 min.. The results are shown in the following table, indicating the heat uptake values in"C :

Time (min. ) NM ( C) SM ( C) BG ('C) 0 0 0 0 3 1.4 0 4 10 2.8 0 8 20 4.2 0.5 11. 5 30 6.48 3.5 15 40 9.28 4.5 16 50 11 8.5 18 60 13.4 11.5 19 120 20. 5 18 23.5

As shown by these results, the headband according to the invention NM shows a lower temperature uptake than the headband of the prior art BG. The uptake difference is particularly high during the first 30 min. of the experiment. The temperature uptake of the NM sample is only of about 6. 5"C during this period, whereas the BG sample already increases its temperature of 15"C, which is more than twice as much.

Indeed the heat uptake In the BG sample increases following an exponential curve starting with a steep slope, whereas the uptake progresses very slowly in the case of the NM and SM samples. Compared to the SM sample, the NM sample shows the advantage that the heat uptake follows a linear curve over the time of the experiment.

The above examples clearly illustrate the advantageous features of the articles according to the invention, which in particular provide a regularly homogeneous cooling effect which lasts along time, together with presenting a great comfort in use.

Such cooling articles are especially useful for use in pain relief.

Similar articles may be produced for other uses in medecine, such as : - as an anti-inflammatory agent in the treatment of inflammatory disorders, especially abdominal or dental postoperative disorders, and in the treatment of pain in general ;

- in pediatrics, for treating hyperthermia in infants ; - for traumatic postoperative treatments and for general traumatology ; - for example, in the form of cooling stockings or socks in the treatment of venous deficiencies and blood-circulation pathologies ; - for treating rheumatic pathologies, for example abarticular rheumatic pathologies of tendinous origin, or for traumatic postoperative treatments and for general traumatology ; - for the manufacture of a medical compress, which optionally may contain one or more therapeutic agents.

Another beneficial application of articles according to the invention is that of heat protection for people working at high temperatures, especially in the metal-conversion industry, in the steelmaking industry, or for firemen.

Claims

CLAIMS 1. A cooling article, especially for application in pain relief by water desorption from a water-swollen gel, comprising a polymer absorbent enclosed within a bag delimited by a collapsible envelope having non-watertight walls, wherein said polymer absorbent is under the form of particles each of which comprises a core of less cross-linked polymer sequences more active in retaining absorbed water and a shell of more cross- linked polymer sequences apt to retard diffusion of water from a particle to another during desorption of absorbed water.
2. An article according to claim 1. wherein the amount of said polymer particles enclosed in said bag is in excess compared to that which would just be required to fill up the bag when they are in the full swollen state.
3. An article according to claim 2, wherein said excess is from 5 to 10 percent by weight of the theoretical weight required to just fill the bag completely.
4. An article according to any of claims 1 to 3, wherein said envelope is made of a non-woven fabric comprising longer threads or fibers of natural or semi-synthetic nature and shorter polyester fibers.
5. An article according to claim 4, wherein said longer threads or fibers are made of a cellulosic material.
6. An article according to claim 4, wherein said longer threads or fibers are fibers of viscose.

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7. An article according to any of claims 4 to 6, wherein said shorter fibers are polypropylene fibers.
8. An article according to any of claims 4 to 7, wherein - - the- respective proportions between said longer threads or fibers and said shorter polyester fibers, expressed as weight percentages, are from 10 to 30 percent for the former and from 90 to 70 percent for the latter of the total weight of the composition.
9. An article according to any of claims 1 to 8, wherein said polymer has a sodium polyacrylate base.