WO1997002054A1

WO1997002054A1 - Heater with ptc heating elements for evaporators of solid or liquid insecticides or deodorants

Info

Publication number: WO1997002054A1
Application number: PCT/EP1996/002964
Authority: WO
Inventors: Franco Zobele
Original assignee: Zobele Industrie Chimiche S.P.A.
Priority date: 1995-07-06
Filing date: 1996-07-05
Publication date: 1997-01-23
Also published as: ITMI950475U1; IT237007Y1; ITMI950475V0

Abstract

The present invention relates to a heating device for insecticide or deodorant evaporators of the dual purpose type (for solid and liquid formulations), consisting of a support body made of heat-resistant material and designed to house in a seat at least one PTC heating element elastically retained between two metal plates, at least one of which has elastic means. Said seat is closed by a cover made of material which is heat-conducting but electrically insulating.

Description

HEATER WITH PTC HEATING ELEMENT FOR EVAPORATORS OF SOLID OR LIQUID INSECTICIDES OR DEODORANTS

* o * o * o * o *

For some time now, for the controlled supply and dispensing of odour-emitting substances such as deodorants and insecticides, it has been known to use devices designed to disperse these substances in the environment by means of heating thereof. In fact, the active substance is normally available either in solid form, being absorbed in suitable small- sized pressed cardboard supports, commonly known as "mats", or in Iiquid form, inside closed bottles from which a wick emerges and draws up the

Iiquid by means of capillarity. In both cases, heating causes evaporation - more or less rapid - of the active substance which is thus dispersed in the surrounding environment.

Historically speaking, vaporizable insecticides consisting of a Iiquid formulation appeared after mats, in response to the demand for a product which lasted longer. In fact, while mats are generally used up in about one night, Iiquid formulations last a lot longer, for example 30 to 60 nights.

The technical development of these formulations has obviously been accompanied by the development of the associated heating devices, commonly and simply referred to as "heaters". Whereas, initially, these heaters were specifically designed for the type of formulation used, i.e. iiquid or solid, nowadays the tendancy is to design universal heaters, i.e. which are able to accommodate both types of formulation existing on the market, and therefore referred to as "dual purpose". Within the context of this type of heater, the technology has adopted, with different degrees of success, two different solutions for the heating elements:

- electric coil resistances; and

- positive temperature coefficient elements (abbreviated as "PTC elements").

The PTC elements consist of tablets of pressed, granular, conducting material with special electrical properties; in fact, in PTC elements the resistivity decreases with an increase in the temperature, unlike that which normally happens with metal resistances. This electrical characteristic is such that the heat generated in the PTC elements owing to the Joule effect does not exceed a predetermined level and hence makes them particularly suitable for simple applications - i.e. with no other temperature control systems - where the heat generated must remain as constant as possible over time. Despite the fact that the costs of PTC elements are higher than those of metal coil resistances, they are preferable because they offer more interesting features, such as automatic temperature regulation and the possibility for easy design in widely varying forms. For this reason, the use of PTC elements has recently become of considerable importance.

PTC elements, as already stated, are obtained by pressing a suitable granular material, possessing the well-defined electrical characteristics mentioned above, into the form of tablets of uniform thickness; the electrical connection is normally established by connecting the terminals of an electrical circuit to the two opposite faces of the tablet. In order to join the terminals to the faces of the tablet, the current technology proposes basically two types of solution: a first solution, whereby the terminals of the circuit are welded directly onto the surfaces of the PTC element which have been metallized beforehand, and a second solution, on the other hand, whereby the terminals are welded to two metal plates which are normally kept elastically pressed against the opposite surfaces of the PTC element. Within the field of application of the solution consisting of metal plates, it is of considerable importance to provide a connection between the actual plates and the PTC tablet which is simple and economical, but stable over time. In fact, a problem which arises with a certain frequency during the practical application of this type of PTC element to the heating devices considered within the scope of the present invention is that of ensuring perfect adhesion of the metal plates to the tablet, when positioning the PTC elements in the body of the heater, and preventing undesirable relative displacement of the plates and PTC elements during handling and use of the heater.

Different types of said plates have been proposed hitherto, but none of them have proved to be entirely satisfactory, in particular when the heating element and plates are fixed in the correct assembly position, embedding them in bonding cement, since any infiltration of the cement between the plates and the tablet may result in zones causing an interruption in the electrical connection and hence incorrect functioning of the PTC element.

The search for a perfect structural design of the electric connections has been accompanied by innovations and improvements as regards the form and structure of the support body of the heaters. The problem is in fact that of uniformly heating the mat or, respectively, the wick along which the Iiquid solution rises, without causing any local overheating which could result in irregular consumption of the mat or premature carbonization of the active substance with which the wick is impregnated, preventing or reducing the capacity of the latter for further absorption. This problem has been resolved with various solutions which can nevertheless be substantially classified into two types: heaters with heating elements positioned in the ceramic body of the heater in a suitable arrangement and subsequently fixed with cements or adhesives, and heaters with heating elements which are inserted with a certain amount of play into seats formed around the wick. The present invention falls into the latter category of design of heating devices and its main objects are therefore that of providing, on the one hand, a heater in which the PTC heating element together with the metal contact plates, once inserted into their seats, are free from any problems of electrical conductivity for the whole of the working life of the heater itself and, on the other hand, ensuring the arrangement thereof such that the wick or mat impregnated with the active substance to be vaporized is heated in a uniform and constant manner.

It is already known from the Italian Utility Model Application

MI95U000267, in the name of the same Applicant, to use metal contact plates which, owing to their special cup shape, tend to exert an elastic force between the walls of the seats into which they are introduced. In this way, when arranged between the surfaces of the PTC tablet and the walls of the containment cavity, they fix in their seat the PTC element / plates assembly and ensure a good electrical contact. In the Application

MI95U000267 a description is given of a heating device in which the PTC element, together with its elastic contact plates, is introduced into a cavity inside the support element which is accessed via an opening formed on the side surface adjacent to the surface on which the insecticide mat rests.

In the present invention, however, introduction of the various components into the support body is performed "from the bottom", i.e. the surface opposite the surface on which the mat rests is in the form of a cover and is removed, in order to mount the heating element and the plates, and is then replaced in the working position, achieving a notable reduction in the assembly times and better control as regards positioning of the PTC elements and the associated contact plates. In fact, the heating device for insecticide or deodorant evaporators, according to the present invention, is of the type comprising: a support body made of heat-resistant material having a seat for a heating element, a cover for closing said seat, a flat surface opposite said cover for positioning a mat consisting of a solid formulation, and at least one hole or a saddle-shaped seat designed to house a wick for a iiquid formulation, and at least one PTC heating element, housed in said seat, the opposite faces of which have pressed against them metal conducting plates connected to the terminals of an electric supply circuit, wherein one of said plates has elastic means designed to ensure perfect adhesion between said plate and said PTC element inside the said seat closed by the associated cover.

The invention will in any case now be described in greater detail, with reference to a preferred embodiment thereof, illustrated in the accompanying drawings, in which: Figure 1 is a plan view of the heating device according to the present invention;

Figure 2 is a cross-sectional view along the line k-k of Figure 1 ; Figure 3 is an exploded view of the components of Figure 2; Figures 4A and 4B show, respectively, a plan view and a side elevation view of the contact plates with elastic means;

Figures 5A and 5B show, respectively, a plan view and a side elevation view of the flat contact plate;

Figure 6 is a plan view of the device according to the present invention with which an electric signalling circuit is associated; Figure 7 is a plan view of a variant of the device according to the present invention comprising two PTC heating elements.

As can be seen from Figures 1 and 2, a support body 1 of the heating device, which has a generally prismatic shape and is made of heat- resistant material, has a seat 2, open at the bottom, which has a complex shape and a variable depth designed to receive with precision an upper metal plate 4, at least one PTC heating element 3, a Iower metal plate 5, and a cover 6, respectively indicated in the same order in which they are mounted inside the seat 2 (Figure 3). The support 1 has formed in it also a hole 8, or alternately an open saddle-shaped seat, designed to receive a wick which emerges from a bottle containing the Iiquid insecticide or deodorant solution.

As is known, in order to supply the desired amount of heat to the mat or wick impregnated with the vaporizable substances, an electric circuit is formed such that the current is made to flow across the PTC tablet 3, producing heat owing to the Joule effect. In this specific case the electric current flows between the plate 4 and the plate 5 passing through the PTC tablet.

So that this electrical connection is sufficiently reliable and in order to avoid any faulty contacts, in the present invention one of the two plates, preferably the Iower plate 5 (Figures 2 and 3), is provided with a plurality of elastic means 7 which impart to the plate itself an elastic force intended to keep it in electrical contact with the surface of the PTC tablet

3 and, at the same time, press the tablet 3 against the other plate, in this case the upper plate 4, thus ensuring perfect transmission of the heat to the support body 1 and to the surface 1 a on which the mat rests. In so doing, it is possible to ensure not only perfect adhesion of all conducting elements, but also stability of the PTC element / plates assembly, which remains compressed inside the seat 2 once it is closed with the cover 6.

The plates 4 and 5 have a circular shape (see Figures 4A, 4B, and 5A, 5B), with a surface corresponding to that of the PTC tablet 3, from which there projects an elongated terminal, respectively 4a and 5a, provided with a deformable ring, respectively 4b and 5b, which is mechanically riveted onto the respective end of an electric cable. The elastic means 7 are preferably formed by notching in the plate itself a plurality of peripheral tongues 7a and a central tongue 7b. The tongues 7a and 7b are bent slightly, causing them to emerge from the plane along which the plate extends, so as to be able to make use of their elasticity once the PTC element/ plates assembly has been closed inside its seat by means of the cover 6. Preferably, the tongues 7a, which have small dimensions (about 2 mm), are formed on the perimeter of the plate 5, at an equal distance from one another, and act on the upper surface 6b of the cover 6, while the tongue 7b, which has larger dimensions, is formed in a central position and acts on the surface of the tablet 3. When the PTC tablet 3 is inserted between the plate 4 and the plate

5 inside the seat 2 and the cover 6 then mounted, the tongues 7a and 7b are elastically deformed and exert a pressure on the PTC tablet 3, ensuring both locking of the assembly and perfect and constant electrical contact between the surfaces of the PTC element 3 and those of the plates 4 and

5. As regards the support body 1 it may be made of solid ceramic material, although a plastic heat-resistant material (for example a plastic material based on phenylene polysulphide - PPS) may also be suitable for this purpose. In this latter case the support body 1 is advantageously shaped with a non-solid form, for example comprising thin walls or ribs for containing the PTC element 3, so that heating can also be performed by means of convection in addition to conduction, thus offsetting the negative effect of the low heat conductivity coefficient of the plastic material.

The flat cover 6 is made with a material which is good conductor of heat, but an electrical current insulator (so as to avoid unintentional short- circuits between the two plates), such as ceramic or a plastic material.

This cover has dimensions such that it can be force-fitted into the seat 2, remaining flush with the upper surface of the support body 1 .

As seen above, therefore, the combination consisting of the PTC element 3 and the plates 4 and 5 enable the desired results to be achieved. In fact, owing to the elastic action of the plate 5, it is not necessary to fix the PTC tablet 3 in the seat 2 using adhesives or cements. These products may in fact cause immediate problems of electrical conductivity - infiltrating between the plates and the PTC element - and moreover, since they poorly withstand the numerous heating/cooling cycles to which they are exposed, lead to malfunctioning of the heater after only a relatively short lifespan of the latter. The elimination of these products makes it possible to avoid these drawbacks, thus achieving a first object of the present invention.

Furthermore, the seat 2, designed for assembly of the device by means of "bottom loading", simplifies and speeds up the assembly and verification operations. Furthermore, the "central" arrangement of the seat 2 ensures that the distribution of heat in the various parts of heater is particularly uniform and that there are no overheated zones, thus achieving the second object of the invention. During operation, the PTC element 3 heats up owing to the effect of the current which, passing from one metal plate to the other, crosses the element, thus transmitting heat by means of conduction to the support body 1 . Heating of the support body 1 similarly induces heating of the mat placed above the support surface 1 a or of the wick inserted into the hole 8, causing evaporation of the active substance with which the mat or wick are impregnated and hence dispersion thereof in the surrounding enivoronment.

According to an alternative configuration of the heating device, illustrated in Figure 6, the ends of a small electric circuit can be connected in parallel to the terminals of the plates 4 and 5, thus making it possible to incorporate a lamp for signalling the working condition.

Furthermore, according to a variant of the present invention, two PTC heating elements may be used (Figure 7). In this case the conducting plates 4 and 5 have the form of an eye-glass, so that they cover both the circular surfaces of the two PTC tablets 3' arranged alongside one another, and, similarly to what happens with a single PTC tablet, the elastic tongues are present both along the perimeter of the plates and at the centre of each of them, so as to ensure optimum distribution of the pressures.

It is understood that protection of the invention described above is not limited to the particular configuration illustrated, but is extended to all other constructional variants which are technically equivalent.

Claims

Claims 1 . Heating device for insecticide or deodorant evaporators, of the type comprising: a support body made of heat-resistant material having a seat for a heating element, a cover for closing said seat, a flat surface opposite said cover for positioning a mat consisting of a solid formulation, and at least one hole or a saddle-shaped seat designed to house a wick for a Iiquid formulation, and at least one PTC heating element, housed in said seat, the opposite faces of which have pressed against them metal conducting plates connected to the terminals of an electric supply circuit, characterized in that one of said plates has elastic means designed to ensure perfect adhesion between said plate and said PTC element inside the said seat closed by the associated cover.

2. Device as claimed in claim 1 , wherein the plate provided with elastic means is the one positioned between said PTC element and said cover.

3. Device as claimed in claim 1 or 2, wherein said elastic means are in the form of tongues notched in the plate itself and bent so as to emerge from the plane in which the plate extends.

4. Device as claimed in claim 3, wherein said tongues are, in part, evenly distributed along the perimetral extension of the associated plate and, in part, formed at the centre of said plate.

5. Device as claimed in any one of the preceding claims, wherein elongated terminals provided with a deformable ring designed to be riveted mechanically onto the ends of electric cables project from said metal plates.

6. Device as claimed in any one of the preceding claims, wherein said flat cover is force-fitted onto said support body.

7. Device as claimed in any one of the preceding claims, wherein said flat cover is made of a heat-conducting and electrically insulating material.

8. Device as claimed in any one of the preceding claims, wherein two PTC heating elements are present.

9. Device as claimed in any one of the preceding claims, comprising moreover a lamp for signalling the working condition, electrically connected in parallel to said plates.

10. Device as claimed in any one of the preceding claims, wherein said support body and the associated cover are made of solid ceramic material.

1 1 . Device as claimed in any one of the preceding claims, wherein said support body and the associated cover are made of a foamed plastic material which is preferably based on phenylene polysulphide (PPS).