the embodiment shown in fig1 includes a case or housing 1 forming an external envelope of a dispenser according to the invention . housing 1 can have any appropriate form and can , in general , have a form similar to a cylinder with a longitudinal axis x - x &# 39 ; and preferably of circular cross section . the cross section of housing 1 can be unvarying along its length , or can , as shown in fig1 be constructed in its lower portion to include a frusto - conic section 2 with a diameter which decreases toward the dispensing end , followed by a cylindrical lower end section 3 having a diameter smaller than that of the main portion of housing 1 . housing 1 is preferably constituted by a unitary body having an outer wall 4 . outer wall 4 preferably has a constant thickness along its length and can be made , for example , of any sufficiently rigid plastic material . housing 1 is associated with a holding or gripping means 5 constituted in its simplest version by the upper part of housing 1 . obviously , as an alternative , housing 1 can be provided with a handle designed to be gripped comfortably by the user and thus constituting the holding means . the dispenser according to the invention further includes a reservoir 8 for storage of the thermoplastic product before its application . preferably , reservoir 8 is disposed within the space enclosed by case 1 and preferably has the same longitudinal axis x - x &# 39 ; as case 1 . reservoir 8 is limited toward the exterior by an envelope 9 preferably having an average thickness of the order of 1 . 5 - 2 mm . at least one part , or only a fraction , of envelope 9 is composed of an electrically conductive plastic material forming an electrical resistance element . such a material can be , for example , an elastomer provided with a carbon filler . according to an advantageous embodiment of the invention , the wall of reservoir 8 , or substantially the entirety of envelope 9 , is made of electrically conductive plastic material . alternatively , only one or several parts of envelope 9 , for example a portion adjacent section 2 and / or section 3 , can be made of electrically conductive plastic material . in effect , passage of electric current through the electrically conductive plastic material generates a heat flux which assures melting of the thermoplastic product . thus , electrically conductive plastic material can be provided at any geometric location or locations of the part or fraction of envelope 9 made of an electrically conductive plastic material to permit , by generation and delivery of heat , melting of the entire mass , or a significant portion of the mass , of thermoplastic material to be applied . in the same manner , by way of a further modification , only a fraction of envelope 9 , defining for example a sector or concave area , whose geometric location is suitably selected , and for example in the lower part of the dispenser , could be made of electrically conductive plastic material . the portion of envelope 9 which is not made of electrically conductive plastic material is made of a material which is a good conductor of heat . envelope 9 , or the portion of envelope 9 made of electrically conductive plastic material , is connected to a pair of electrodes 10 , one of which is visible in fig1 preferably constituted by two strips , bands , meshes or screens of metal disposed on envelope 9 at diametrically opposed locations with respect to axis x - x &# 39 ;. strips , etc , 10 are secured by any appropriate means to the internal or external surface of envelope 9 , or for example are molded into reservoir 9 . as shown particularly in fig1 , reservoir 8 may have a transverse cross section in a form similar to a quadrilateral , and electrodes 10 may preferably extend across the entirety of two opposed lateral faces of reservoir 8 and may be extended by respective connection prongs or feet 10a ( fig1 and 11 ) beyond the end of case 1 which is remote from the outlet end of reservoir 8 . electrodes 10 can also be formed by electrolytic deposition or printing , such as silkscreen printing , of a conductive ink . advantageously , electrodes 10 are disposed on the exterior surface of the walls of envelope 9 , but can also be embedded in envelope 9 , or can extend on the inner surface of envelope 9 where they will be in contact with the wax . envelope 9 , or the fraction of envelope 9 made of electrically conductive plastic material thus constitutes the heating means of the dispenser according to the invention , serving to assure continuous melting of the thermoplastic product stored in reservoir 8 . thus , envelope 9 performs the dual function of resistive heating element and product reservoir . envelope 9 or the fraction of envelope 9 can be made of any plastic material possessing suitable resistive properties , such materials including , inter alia , silicone elastomers , polypropylene containing a carbon filler , polymers rendered conductive by a carbon filler , or even intrinsically conductive polymers , such as pvc having a polyaniline filler , for example . according to the invention , case 1 surrounds reservoir 8 and is thermally isolated from reservoir 8 , or more precisely from envelope 9 , by thermal insulation means 11 . the thermal insulation means can be constituted , as shown in fig1 by establishing a simple dead air space 12 between case 1 and envelope 9 , space 12 having an appropriate thickness . advantageously , as shown in fig3 thermal isolation means 11 can be created by providing a plurality of longitudinal ribs 13 which extend in the direction of the thickness of case 1 and project from the internal face thereof . longitudinal ribs 13 thus bear against the external periphery of reservoir 8 and are spaced apart to delimit a series of longitudinal dead air spaces 14 . it should be evident that , according to modified embodiments , ribs 13 could be formed in , and extend outwardly from , envelope 9 . a dispenser of thermoplastic products according to the invention further includes a product applicator , such as an applicator 18 shown in fig1 and 2 . applicator 18 is located at an outlet opening 20 provided , as shown in fig1 at the lower end of reservoir 8 . applicator 18 is advantageously constituted by a roller 21 supported , as shown most clearly in fig2 by two shafts or pins 22 fixed to roller 21 and rotatably mounted in recesses which are formed in case 1 and which constitute bearings . alternatively , roller 21 can be supported directly by envelope 9 within outlet opening 20 . roller 21 is dimensioned relative to the dimensions of opening 20 in order to cause a thin film of thermoplastic product , which according to exemplary embodiments of the invention is depilatory wax , to be formed on the surface or roller 21 and to then be applied to the user &# 39 ; s skin . preferably , roller 21 is mounted to be freely rotatable . however , roller 21 can also be mounted to be rotated by any conventional drive means . fig4 and 5 illustrate an alternative embodiment of the invention in which roller 21 is mounted in a manner to be capable of being displaced , under the force of gravity , substantially in the direction of longitudinal axis x - x &# 39 ;. for this purpose , shafts 22 are supported in slots 25 which are formed in case 1 or in envelope 9 and which constitute slide paths . slots 25 have a generally oblong form with an axis of symmetry substantially parallel to longitudinal axis x - x &# 39 ;. the dimensional relations between opening 20 and roller 21 , and particularly the diameter of roller 21 , are such that when roller 21 bears against a surface p , this typically being the user &# 39 ; s skin , roller 21 comes to occupy the abutment position shown in fig4 . in this position , roller 21 , under the effect of a reaction force imposed by the user &# 39 ; s skin on roller 21 , moves to an abutment position in which shafts 22 are pressed against the upper extremity 26 of slots 25 . roller 21 then occupies an upper , or retracted , position . in this position , a larger gap exists between the periphery or roller 22 and an edge 27 of opening 20 . melted or softened thermoplastic product , such as wax , can then flow out of the dispenser . fig5 shows roller 21 in a lower , or extended , position , which is achieved when roller 21 is not pressing against the user &# 39 ; s skin , and is thus free to move , under the influence of the force of gravity , to a position in which shafts 22 come to bear against the lower extremities 28 of slots 25 . in this position , the dimensional relations between roller 21 and opening 20 are such that roller 21 can substantially completely block opening 20 . fig6 is a detail view showing one embodiment of roller 21 which is provided on its surface with circular protrusions , or lands , which effectively increase the thickness of roller 21 . these lands 30 have for their effect to thicken the film , or layer , of wax , roller 21 even being able to advantageously have a reduced diameter at its axial ends in order to assure the presence of a bead of wax along each edge of the band which is dispensed via opening 20 . these beads , which have a thickness greater than that of the part of the band of wax between the edges , help to facilitate subsequent lifting of the wax strip as a unit during hair removal . roller 21 can also be provided with ridges , or striations , ( not shown ) in the longitudinal direction of its axis of rotation y - y &# 39 ; shown in fig6 to promote rotation of roller 21 on the user &# 39 ; s skin and to assure thickening of the band of wax . roller 21 can be made of any material capable of developing a relatively weak adherence with wax , or with any other thermoplastic material that is to be dispensed , which adherence is in any case weaker than the adherence of the wax , or other thermoplastic material , to the skin , or other surface to which the material is to be applied . roller 21 could be made of , for example , polypropylene or silicone . a dispenser according to the invention can be provided with a switch 60 ( fig1 ) capable of applying either one of two voltages between electrodes 10 . one of these voltages can have a relatively high value and can be used when the contents of reservoir 8 are at room temperature and are to be heated to the desired operating temperature . the second voltage , which has a lower value than the first voltage , is applied to maintain the thermoplastic material at an average desired application temperature after it has been first heated to that temperature . this arrangement permits the initial delivery of a high level of thermal energy to initially permit a rapid melting of the thermoplastic material contained in reservoir 8 , after which a lower level of thermal energy is delivered to maintain the mass at the desired temperature . alternatively , a similar effect can be achieved if the electrically conductive plastic material of envelope 9 is a material having a high positive thermal coefficient of resistance . case 1 is closed at its upper end , remote from opening 20 , by a closing plug 31 affixed by any appropriate means . fig1 - 12 illustrate another embodiment of the invention which differs from those previously described by the fact that roller 21 is removably installed . in this embodiment , roller 21 is mounted on a cap 40 which is constructed to be slipped over the associated end of case 1 and locked in position , for example by latching or clipping onto walls of case 1 . cap 40 has an opening 41 arranged to be in line with outlet opening 20 and two tongues 42 which are folded over to bear against end faces of envelope 9 , at the end of envelope 9 associated with outlet passage 29 . tongues 42 have extremities provided with support elements , for example disks , intended to be inserted into openings or recesses 43 provided along the axis of rotation of roller 21 . cap 40 thus serves as a mean for supporting roller 21 , while permitting roller 21 to be removed from cap 40 for purposes of replacement or cleaning , when cap 40 is withdrawn from case 1 . the mounting of roller 21 in a removable cap 40 facilitates cleaning of roller 21 and allows reservoir 8 to easily be refilled via outlet passage 20 . as a result , the embodiment of fig1 - 12 need not be provided with a removable plug or closing element , such as the element 31 of the embodiment of fig1 - 3 . according to another alternative of the invention , and as shown in fig1 - 12 , the walls of reservoir 8 may present , at the level of outlet passage 20 , an external collar 44 having outwardly inclined edges . in these edges there are formed at least two , and preferably a total of four , slits 45 , which extend through the thickness of the outwardly inclined edges . slits 45 are preferably arranged at the corners of outlet opening 20 at the level of the junctions between the different sides of envelope 9 . slits 45 permit , during flow of wax in a softened or liquid state , the formation of beads , or thickened edges of the band of wax being deposited . as noted above , the resulting band of wax becomes easier to remove from the user &# 39 ; s skin . the provision of four slits 45 enables the device of fig1 - 11 to be moved in either one of two directions while applying wax , i . e . to apply wax while roller 21 is rotating in either sense about its axis of rotation , without disturbing the airwax system necessary for a satisfactory application of the wax film or layer . as shown in fig1 , switch 60 may be connectable to a power source and may include a three position switch element connected to a voltage dividing resistor . the switch element may be moved between two voltage applying positions manually or under control of a temperature responsive unit in thermal communication with reservoir 8 . the functioning of a dispenser of thermoplastic products according to the invention will now be described . the user , after having filled reservoir 8 with the thermoplastic product to be dispensed , for example depilatory wax , initially provided in the form of a relatively solid block of wax , operates switch 60 to apply a voltage between electrodes 10 , this preferably being the higher of the two voltages described above if the dispenser has a dual voltage switch . the mass of wax then absorbs heat generated by envelope 11 and the mass of wax , particularly that in the portion of reservoir 8 adjacent roller 21 , is progressively softened or liquified , to such an extent that roller 21 , which when cold can become stuck to the walls of case 1 or envelope 9 , becomes detached therefrom . this detachment then permits the passage of a thin film or layer of wax through opening 20 . the user who previously took hold of the dispenser can then begin applying the wax by rolling roller 21 along the skin . the fact of using a heating envelope 9 permits the heating temperature to be distributed in a uniform manner in the entire mass of wax , which assures a rapid temperature increase , followed by an optimal regulation of the wax application temperature . the possibility of making use of a wax dispenser provided with a mobile applicator roller permits the user to be freed of any concern about uncontrolled flow of the wax into the environment , since roller 21 automatically blocks orifice 20 when the dispenser , and specifically roller 21 , is not in contact with the user &# 39 ; s skin . another variation according to the invention is shown in fig7 - 9 , differing from those already described in that they include an opening 20 in the form of a slit and by the provision of an applicator means in the form of a deformable tip 35 . thus , in the arrangements shown in fig7 - 9 , there is no roller . deformable tip 35 has a lower face 36 which contacts the skin surface during application of a wax film . in lower face 36 there is provided a slit 20 &# 39 ; preferably having a rectangular outline . when the user presses tip 35 against skin p , the application force permits tip 35 to be deformed in a manner to enlarge the opening provided by slit 20 &# 39 ;, as shown in fig8 . melted or softened wax can then flow via the opening defined by slit 20 &# 39 ; and is spread by the forward part of the lower application surface 36 . advantageously , the rear part of application face 36 , forming a heel 37 , extends in a plane which is substantially offset toward the bottom with respect to a plane which forms an extension of the forward part of application face 36 . this relationship has for its effect to facilitate flow of a film of wax during displacement of the dispenser in the direction of arrow a of fig8 . fig9 shows a variation of the embodiment of fig7 and 8 in which orifice 20 &# 39 ; in the form of a slit is disposed in the vicinity of the forward part of application face 36 . in further accordance with the invention , thermal regulation of the dispenser can be promoted by giving envelope 9 a variable thickness , and in particular a greater thickness in the vicinity of outlet opening , and for example at the level of section 2 and / or section 3 . increasing the thickness of envelope 9 at the level of outlet orifice 20 can be effected in a continuous or discontinuous manner , i . e . it can be regular or nonregular , or gradual or abrupt . to this end , there can be provided a series of internal ribs , or ridges ( not shown in the drawings ) in the thickness dimension of envelope 9 in order to increase at intervals the electric power dissipated and the conduction between opposed electrodes 10 . according to a further embodiment of the invention , it is possible to mount roller 21 on a rigid support if the material of case 1 cannot , because of its flexibility , properly support said roller . this application relates to subject matter disclosed in french application number 9212378 , filed on oct . 9 , 1992 , the disclosure of which is incorporated herein by reference . while the description above refers to particular embodiments of the present invention , it will be understood that many modifications may be made without departing from the spirit thereof . the accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention . the presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive , the scope of the invention being indicated by the appended claims , rather than the foregoing description , and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .
a dispenser for dispensing a thermoplastic product in a fluid state , the dispenser including : a case having a manual holding part ; a reservoir composed of a wall forming an enclosure for holding a supply of the product ; a product applicator disposed in proximity to a reservoir opening for receiving product in a fluid state from the reservoir , wherein at least a portion of the reservoir wall is made of an electrically conductive plastic constituting a heat source , and the dispenser further has electrodes connected to the electrically conductive plastic of the reservoir portion for delivering heating current to the heat source .