The invention relates to a patch comprising a matrix made of a material having self-adhesive properties to being applied to the skin. The patch includes a permeable structure completely embedded in said matrix close to its surface so as to modify the overall adhesive power thereof.

The present invention relates to a patch for temporary application to the
 skin to exert a cosmetic and/or pharmaceutical treatment action thereon.
 BACKGROUND OF THE INVENTION
 Patches are known that comprise a backing sheet coated on one face in a
 layer forming a reservoir known as a "matrix", containing one or more
 active substances that are to be diffused into the skin and/or that are to
 act thereon.
 The matrix can be made of a material having adhesive properties, whether
 intrinsic or otherwise, in which case the patch has an adhesive coating on
 its surface.
 In which case, it is necessary to ensure that the coating does not impede
 the action of the active substance(s) contained in the matrix.
 The invention relates more particularly to a patch in which the matrix is
 made of a material presenting intrinsic adhesive properties.
 Selecting this material raises difficulties, and in particular:
 it must be capable of containing the active substance(s) for acting on the
 skin;
 its adhesion to the skin must not be too strong, particularly if it is to
 be applied in repeated manner, since otherwise the region of the body on
 which the patch is applied will be come irritated, and removing the patch
 will become painful;
 its adhesion must not be too weak either, since otherwise it will not be
 able to adhere to the skin if it is moist or if it becomes moist, e.g.
 because of sweating;
 it must be sufficiently flexible to allow the patch to fit over the shape
 of the region of the body on which it is applied;
 it must remain on the backing sheet when the patch is removed; and
 finally, it must make it possible to extract the impurities that are to be
 found on the surface of the skin, in particular sebum or sweat.
 In spite of these difficulties, several materials have been proposed for
 making the matrix, however they are not necessarily suitable for all of
 the active substances that it might be desirable to incorporate therein.
 French patent 2 738 744 or European patent 0 309 309 teach in particular
 the use of hydrophobic or hyposoluble materials for constituting the
 matrix.
 The hydrosoluble material described in European patent 0 309 309 is
 relatively impractical in use since it does not present the required
 adhesive properties prior to application to the skin and it requires the
 skin to be previously moistened.
 European patent application EP-A-0 412 869 describes a composite film
 having a silicone polymer matrix adjacent to an occlusive matrix. On its
 side remote from the occlusive layer, the matrix has a
 reinforcement--constituting screen and a removable protective membrane.
 The screen reduces the adhesive area of the protective membrane on the
 matrix.
 In such a composite film, the screen locally prevents the matrix from
 coming into contact with the skin. When the film is withdrawn, the screen
 runs the risk of leaving a mark on the skin with the mark being all the
 more pronounced with increasing adhesion of the material constituting the
 matrix. For a silicone polymer matrix, whose adhesive power (TAC) is
 relatively low (about 100 g/cm.sup.2), this drawback is nevertheless not
 too troublesome. Finally, the screen prevents a mechanical cleansing
 action being exerted on the entire area of the skin that is covered by the
 film.
 OBJECTS AND SUMMARY OF THE INVENTION
 The present invention seeks to facilitate selecting the material
 constituting the matrix, but without thereby complicating use of the
 patch.
 This is achieved by the invention by a novel patch comprising a matrix made
 of a material having self-adhesive properties prior to application to the
 skin, the patch including a permeable structure completely embedded in
 said matrix close to its surface so as to modify its overall adhesive
 power.
 Preferably, the permeable structure is hydrophobic.
 Also preferably, said permeable structure is constituted by a perforated
 film, or a solid-fiber cloth that may be woven or non-woven.
 When using a hollow fiber cloth, the porosity of the fibers is preferably
 selected so that they are filled substantially completely by the matrix.
 Thus, the permeable structure is not suitable for absorbing moisture
 present on the skin or the active agent that may be present in the matrix.
 There is thus no risk of these agents accumulating in the permeable
 structure, which could delay diffusion thereof into the skin.
 Preferably, the permeable structure used is selected so as to present
 little ability for elongation in the long direction of the patch, so as to
 make the patch easier to unstick.
 Because of the invention, it is possible to control the adhesive properties
 of the patch on the skin by acting on the nature of the permeable
 structure used and on the thickness of the matrix situated between the
 permeable structure and the surface that is to be applied against the
 skin.
 This way of acting on the adhesive properties of the patch make it possible
 to use a material for making the matrix where, in the absence of said
 permeable structure, the material would otherwise adhere too strongly to
 the skin to be suitable for making the looked-for patch.
 Thus, by means of the invention, any novel material having intrinsic
 adhesive properties and that is of interest because of its physical and
 chemical compatibility with the active substance(s) to be incorporated
 therewith can be used without any fear of excessively strong adhesion to
 the skin.
 In addition, the permeable structure used makes it possible for the active
 substance(s) contained in the matrix to diffuse and/or act towards and/or
 onto the surface of the skin.
 Because the permeable structure used for modifying the adhesive power of
 the matrix is completely embedded in the material constituting the matrix,
 it is possible to exert mechanical cleansing action over the entire area
 of the skin covered by the patch, if so desired, since the entire area of
 the patch that is to come into contact with the skin is adhesive. The risk
 of leaving a mark on the skin having a pattern corresponding to that of
 the permeable structure used is also reduced. Finally, when active
 substances are contained in the matrix, they can exert their action over
 the entire area of the skin which is in contact with the patch, whereas in
 European patent application EP-A-0 412 869, the screen applied directly on
 the skin hinders diffusion of the active agents into the skin, to some
 extent.

MORE DETAILED DESCRIPTION
 FIG. 1 shows a patch 1 constituting a first embodiment of the invention,
 comprising a backing sheet 2 coated on one face in a matrix 3 made of a
 material having self-adhesive properties.
 The backing sheet 2 may have been subjected to corona treatment in order to
 improve the adhesion of the matrix.
 A perforated structure constituted in this case by a polyamide net 4 is
 embedded in the matrix 3 close to its surface 5 that is to come into
 contact with the skin.
 The perforated structure used is advantageously hydrophobic and has no
 particular ability at absorbing moisture and/or the active substances that
 may be contained in the matrix 3. Thus, it is not liable to swell with
 water or with active substances while the patch is in use, since that
 could reduce adhesion of the patch and/or delay diffusion of said
 substances into the skin.
 It will be observed that the presence of the net 4 close to the surface of
 the patch that is to come into contact with the skin has no effect on the
 adhesion of the matrix to the backing sheet.
 In the example described, the total thickness e.sub.max of the matrix 3 is
 constant, e.g. lying in the range 0.1 mm to 3 mm.
 The net 4 is situated at a distance e.sub.min from the surface 5, and its
 strands co-operate therewith to define zones of reduced thickness, and
 thus of reduced adhesion for the material constituting the matrix 3.
 Preferably, the ratio e.sub.min /e.sub.max is less than or equal to 1/10.
 For given thickness of the matrix 3, the presence of the net 4 within the
 matrix 3 gives rise to local variations in the adhesion of the patch 1 on
 the skin, and to overall adhesion of the patch 1 that is less than that
 which it would have been if the net 4 were omitted.
 It is possible to act on the ratio e.sub.min /e.sub.max to adapt the
 adhesion of the patch 1 as a function of the sensitivity of the zone on
 which it is to be applied, and where appropriate to the active
 substance(s) incorporated within the matrix 3.
 The backing sheet 2 is made of a flexible material, e.g. polyester,
 polyethylene, or polypropylene, or any other appropriate material,
 optionally an occlusive material.
 It can be advantageous to metallize the backing sheet 2 so as to reflect
 thermal radiation from the body back towards the surface of the skin, and
 to enable the matrix 3 to be raised quickly to the temperature of the
 user, which can have the consequence of increasing the adhesion of the
 patch and/or of enhancing diffusion and/or the action of the active
 substance(s) optionally contained therein.
 The thickness of the metallized backing sheet can lie, for example, in the
 range 20 .mu.m to 120 .mu.m.
 In a variant, the backing sheet can be constituted by a metal foil.
 The patch may also have a layer suitable for picking up thermal radiation
 from outside radiation.
 It may also be advantageous to color the matrix 3 and/or the net 4 and/or
 the backing sheet 2 using a dark color so that after the user has removed
 the patch 1, the user can, by contrast, observe the quantity and/or the
 nature of the impurities removed. The user can then determine whether
 further application is required and also, where appropriate, whether the
 frequency and/or the nature of the treatment need to be modified. For
 example, it is possible to incorporate in the matrix violet pigments as
 sold by RDF Chimie under the reference DC violet 2K7014.
 The material used for making the matrix 3 advantageously includes one or
 more acrylic or vinyl polymers, polyurethane, EPDM, or an elastomer whose
 adhesion (measured parallel to the surfaces in contact) preferably lies in
 the range 300 g/cm.sup.2 to 800 g/cm.sup.2.
 For example, an acrylic adhesive is used in a solvent base (ethyl acetate
 hexane ethanol) that is self-curing, sensitive to pressure, having initial
 adhesion of about 100 g/cm.sup.2, and adhesive power (TAC) after it has
 been in place for a sufficient length of time of about 300 g/cm.sup.2. One
 such adhesive is sold by MAPEI under the name AGXL.
 The use of a metallized backing sheet makes it possible to reduce the time
 required for the adhesive to reach adhesive power close to its maximum
 adhesive power, by concentrating heat on the skin/matrix interface.
 Because of the presence of the net 4, the adhesive power of the material
 used for making the matrix 3 can be reduced to 50% or even less, e.g. from
 600 g/cm.sup.2 without a net to 200 g/cm.sup.2 or even 150 g/cm.sup.2 in
 the presence of the net.
 Advantageously, the matrix 3 has one or more active substances that have an
 effect on the skin, e.g. such as, anti-oxidants, free radical scavengers,
 moisturizers, depigmenting agents, liporegulators, anti-acne agents,
 anti-dandruff agents, anti-aging agents, softeners, anti-wrinkle agents,
 keratolytic agents, anti-inflammatory agents, fresheners, healing agents,
 vascular protectors, antibacterial agents, antifungal agents,
 antiperspirants, deodorants, skin conditioners, anesthetics,
 immunomodulators and nourishing agents, moisture absorbers (cotton,
 polyacrylate), and sebum absorbers (Orgasol).
 Preferably, the patch 1 is covered, prior to use, with a removable
 protective membrane overlying its surface that is to come into contact
 with the skin.
 This protective membrane preferably has two portions 9a and 9b that overlap
 in the middle region of the patch so as to enable the user to remove them
 without the fingers touching the matrix 3, and thus without causing it to
 lose its adhesive power.
 The patch of the invention can be manufactured by coating the net 4 with
 the material that is to constitute the matrix 3 while soaked in one or
 more solvents, thereafter bringing the assembly into contact with a
 temporary backing that withstands temperature, and then pressing the
 entire assembly in an oven for evaporating the above-specified solvent(s).
 On leaving the oven, the temporary backing is separated from the matrix 3
 which has been secured to the net 4, and the matrix and the net are
 applied together to the face 7 of the backing sheet 2, the assembly then
 being calendared.
 It should be understood that the invention is not limited solely to using a
 net 4 as described for making the perforated structure. It is also
 possible to use any other permeable structure, perforated film, or woven
 or non-woven cloth, for example.
 FIG. 2 shows a patch constituting a second embodiment of the invention.
 This patch differs from that described with reference to FIG. 1 in that the
 permeable structure used is not a net but a non-woven cloth 8 of
 polyethylene fibers through which, where appropriate, one or more
 substances contained in the matrix can diffuse.
 The non-woven cloth 8 is positioned within the matrix 3 so as to modify the
 overall adhesive power thereof and thus obtain the desired adhesion.
 The overall adhesive power of the patch can also be modified, where
 appropriate, by having relief present in the surface of the matrix.
 Such relief can be implemented by using an embossed protective membrane
 which leaves the desired relief on the matrix after it has been removed.
 The patch 1 is preferably presented to the user in a pre-cutout state, so
 as to fit the shape of the region of the body that is to be treated, with
 its size lying, for example, in the range 1 cm.sup.2 to 30 cm.sup.2.
 The patch is preferably packaged in a protective sachet made up of two
 sheets of a watertight composite of paper and plastics material film, e.g.
 made of polypropylene, where the paper is coated in an adhesive that
 operates cold, with the sheets being stuck together around the patch by
 putting adhesive-coated faces into contact.
 Such packaging serves to protect the patch from air and to improve its
 conditions of conservation.
 The length of time the patch is applied to the skin can lie in the range 30
 seconds to 5 minutes, for example, and preferably lies in the range 1
 minute to 5 minutes.