THE FORM OF SOLID MATS [DESCRIPTION]

[0001] The present invention relates to a PTC heating device for va¬ porisers of fragrances or insecticides in the form of solid mats.

[0002] In the field of electric fragrance or insecticide vaporisers for domestic use, the use of so-called PTCs (Positive Temperature Coefficient devices) is by now largely widespread, which PTCs have in fact a number of advantages, in terms of thermo-electric per¬ formance, over the electric resistors previously used.

[0003] However, since the cost of these devices is higher than that of an electric resistor of equal power, field research is now par¬ ticularly addressing the issue of cost reduction of vaporisers, both in terms of costs of material, and especially of assembly costs. Attempts have therefore been made first of all to reduce the widespread use of labour traditionally employed for the assem¬ bling of these devices, re-designing vaporisers and the corre¬ sponding components so as to allow at least part of the assembling to be carried out automatically. On the other hand, an attempt has also been made to reduce the number of components, decreasing ac¬ cordingly the number of operations required for the assembly and consequently the cost of the product.

[0004] Research has further addressed the standardisation of vaporis¬ ers and in particular of inner components thereof which are capa¬ ble of keeping their structure unchanged also in vaporisers with a varying outer appearance. Over time the field industry has in fact had to face two opposite problems: on the one hand the above- mentioned need to curb manufacturing costs which pushed towards full product standardisation; on the other hand, market require¬ ments demanding vaporisers with a frequently-changing appearance to suit the public's constantly evolving taste.

[0005] These opposite requirements were hence satisfyingly met moving from an "individual" design approach, wherein the entire vaporiser used to be designed in view of a specific support onto which the individual inner components used to be mounted directly, to a "modular" design approach, wherein the different technical inner components - and particularly the vaporiser heating device among these - are designed independently from the specific vaporiser and highly standardised, so as to make production thereof easily auto¬ matable and fully independent from that of the outer support wherein they are subsequently introduced during a final assembly operation. It is also to be appreciated that this final assembly operation is itself easily automatable, despite the non-

standardisation of the different types of outer supports, since in this case the mounting process includes relatively large-sized components which may therefore be more easily oriented and han¬ dled, with no need of particularly sophisticated automatic ma¬ chines.

[0006] An example of the known prior art for the "individual" design is illustrated for example in DE-A-91 04 709, wherein all the com¬ ponents are in fact assembled directly on the outer support.

[0007] The present invention addresses instead the field of "modular" vaporiser design and is specifically directed at the production of the essential inner component of said vaporisers, that is, of a PTC electric heating device which is self-supporting and self- contained, complete with a PTC element and with the relative elec¬ tric connectors and protections and further equipped with a heat¬ ing surface whereon a mat imbued with a fragrance or insecticide can be placed directly in contact, once said device has been in¬ troduced in a suitable outer support.

[0008] Heating devices falling into the category defined above are al¬ ready known in the art. Such devices initially consisted of a con¬ tainer entirely made of ceramics wherein the PTC element and the relative metallic contacts were housed. Such containers were later virtually abandoned, substantially due to the difficulty of manu¬ facturing moulded ceramics pieces with a sufficiently small and constant thickness so as to guarantee good heat flow and tempera¬ ture evenness in the mat imbued with a vaporisable substance.

[0009] Containers have later been suggested wherein the container con¬ sists of a ceramics or plastic body, while the part of the con¬ tainer in contact with the mat imbued with the vaporisable sub¬ stance consists of a metal sheet, such as those described for ex¬ ample in GB-A-2 181 629 and WO 97/45008. In this type of heating devices, improved evenness of heat distribution is obtained, thanks to the presence of the metal sheet, but there are still problems as far as electric protections and locking of the differ¬ ent device components are concerned.

[0010] With a view to electric safety, the presence of the outer metal sheet is currently not an appreciated solution, due to the fact that it represents a potential danger for electric shock to the user - especially to children, who may accidentally introduce metal objects in the vaporiser housing intended to house the mat - should the film of insulating material lying between the electric contact and the outer metal sheet have defects in the material or

in the assembly thereof.

[0011] Further, concerning the mutual locking of the various compo¬ nents of a heating device, all the different solutions provided by the known art require the production of specially designed pieces, and hence higher manufacturing costs. In the case of the British patent, in fact, the metal sheet has side walls apt to determine a housing seat for the ceramic support and also a series of flaps departing from said walls to be clinched underneath the ceramic body and thereby performing locking thereof. In the PCT publica¬ tion the specially designed piece is instead the plastic support, which in fact has a plurality of elastically flexible teeth, with which the metal sheet engages, which in this case is flat.

[0012] It is hence an object of the present invention to provide a de¬ vice of the general type illustrated above which eliminates the drawbacks mentioned above, by offering a high level of electric safety and a simplified locking system of the various components thereof.

[0013] Such object is achieved according to the present invention by an electric heating device for vaporisers of fragrances or insec¬ ticides having the features defined in the main claim herewith en¬ closed.

[0014] Further features and details of the heating device of the in¬ vention will in any case be more evident from the following de¬ tailed description of a preferred embodiment thereof, shown in the accompanying drawings, wherein:

[0015] fig. 1 is an exploded view of a heating device according to the invention, seen from the electric contacts side;

[0016] fig. 2 is an exploded view of the heating device of fig. 1, seen from the side of the resting plane of the mat imbued with ac¬ tive substance; and

[0017] fig. 3 is a drawing showing, in the various views specified be¬ low, the assembled device of the invention:

A - a front elevation view;

B - a side elevation view;

C - a bottom plan view;

D - a top plan view;

E - a cross-section view according to line L-L of fig. 3D;

F - a cross-section view according to line K-K of fig. 3D.

[0018] The heating device according to the invention has an extremely simple and highly functional structure. As is clearly visible from figs. 1 and 2, it consists of a rectangular plastic support 1, in-

tended to house within it a first electric contact 2, a PTC heat¬ ing element 3, a second electric contact 4, integrally equipped with a fuse 5, a metal sheet 6, and finally a cover 7 of support 1, itself made of plastic.

[0019] During device assembly, first electric contact 2 is introduced in a suitable recess of support 1, the flat circular part of con¬ tact 2 arranging itself in a housing formed in said recess and marked out by three teeth 9. The elongated portion of contact 2 is instead introduced in an eyelet 8 provided on the floor of support 1 and projects therefrom for connection with an electric plug, in a manner well-known per se. The seat for housing the flat portion of contact 2, formed by the three teeth 9, is also intended to house PTC 3 which is in fact placed on top of such contact 2 whereon a pair of elastically deformable flaps are further pro¬ vided for improved electric contact and in a manner known per se.

[0020] After this first assembly step, the second electric contact 4 is secured to metal sheet 6 by introducing one end thereof below U-bolt 6a provided on said sheet, which U-bolt is then clinched to perform mechanical fixing and electric connection between contact 4 and sheet 6. Thereby sheet 6 hence simultaneously acts both as an electric contact for the PCT and as a diffuser of the heat gen¬ erated by the same, which functions were instead performed by two different elements in known devices. Sheet 6 is then steadily po¬ sitioned in support 1, thanks to its four bent-down corners 6b which are housed in respective seats formed in support 1, whereas the elongated portion of contact 4, in a fully similar way to the corresponding portion of contact 2, enters a cylindrical slit 10 of support 1 projecting therefrom at the opposite side. Once that has been accomplished, the fuse 5 connected with contact 4 is com¬ pletely encircled by a cylindrical safety wall, formed integrally with support 1 in correspondence of slit 10, such wall thereby preventing the outer shell of the vaporiser from being punctured by the fragments of fuse 5, in the event of the same blowing due to a short-circuit.

[0021] Assembly of the heating device is completed by cover 7 which entirely covers metal sheet 6 and, with its side walls, also fully covers the side walls of support 1, whereon it is welded by ultra¬ sonic thermo-welding, thereby accomplishing quick device locking, which is nevertheless extremely stable and may not be further opened. The flat outer surface of cover 7 is hence suitable to be used as a resting surface for mats imbued with fragrances or in-

secticides, thanks to the heat being distributed therein in a par¬ ticularly even and regular manner, due to underlying metal sheet 6 and also to the small and utterly constant thickness of cover 7.

[0022] The device thus assembled is ready for insertion in a corre¬ sponding vaporiser, after a keeper (not shown) has been fitted to the free end of contacts 2 and 4, provided with plugs of the de¬ sired type for insertion in an electric socket. Once the keeper has been clamped on the free ends of contacts 2 and 4, it is in¬ troduced in a suitable seat of the vaporiser and pulled in posi¬ tion against the action of snap-fitting elastic teeth which deter¬ mine permanent fixing thereof. However, during this operation it may sometimes happen that the tensile stress imparted to the plugs is unduly transferred also onto electric contacts 2 and 4; hence in order to avoid any possible damage to such contacts, or to the connections thereof, the elongated portion of each of contacts 2 and 4 has a typical U-shaped loop, which is clearly visible in the drawings and which is capable of imparting to the contacts a suf¬ ficient degree of longitudinal elasticity to absorb any stress which may discharge thereon during assembly operations.

[0023] From the preceding description it should be clear how the pres¬ ent invention has fully achieved the desired objects by providing a heating device with a very simple and linear construction which can hence be easily manufactured in an automated way. Said device has a high degree of electric safety, thanks to the fact that it has no outside metallic surfaces, that a fuse-based short-circuit protection system is further provided, as well as a further pro¬ tection from the ejection of any splinters ih case of blowing of said fuse, and finally that the locking system adopted, in addi¬ tion to being very simple, is also effective against any voluntary or accidental re-opening attempt of the device.