WO2003105530A1

WO2003105530A1 - Method for producing thermoresistors on a support, and thermoresistors obtained thereby

Info

Publication number: WO2003105530A1
Application number: PCT/EP2003/005743
Authority: WO
Inventors: Giacomo Manenti
Original assignee: Suntech S.R.L
Priority date: 2002-06-05
Filing date: 2003-06-02
Publication date: 2003-12-18
Also published as: EP1516515A1; AU2003238187A1; WO2003105530A8; ITMI20021216A1

Abstract

Method for producing thermoresistors and, in particular low voltage thermoresistors: said method comprising, in the following or any suitable order: deposition on a support (17, 1) of a first layer of insulating material (10, 3); deposition of a first electrode (11, 2) ; deposition of a second electrode(11, 5); deposition of a layer of ink with PTC characteristics (15, 7).

Description

METHOD FOR PRODUCING THERMORESISTORS ON A SUPPORT , AND HERMORESISTORS OBTAINED THEREBY

The present invention concerns a method for producing thermoresistors, and in particular low voltage thermoresistors on a non conventional support: such a method comprises at least the steps of producing a layer of insulating material (preferably made of silicone material) on the non conventional support and to print the low voltage thermoresistors on said layer of insulating material, preferably by means of a serigraphy process. The present invention concerns the low voltage thermoresistors produced by means of the aforesaid method. Background art

In addition to traditional electric resistors, present on the world market since several decades, since some years the so-called "low voltage thermoresistors" are increasingly spreading.

Traditional resistors work with direct or alternate current, consist of a plurality of conductors traditionally made of tungsten or another equivalent material, and are fed from the electric supply network at a network voltage or anyway at a relatively high voltage (160-230 V). On the contrary low voltage thermoresistors work at a low voltage (4,5-24 V), more often with direct current, for example from a battery, and are preferably made with serigraphy processes with the same processes and materials used to produce printed circuits. The spreading of low voltage thermoresistors developed "vertically" on the market and involved substantially huge production amounts concentrated in quite a few industry sectors.

In fact, at present low voltage thermoresistors are (substantially) used in the automotive fittings sector and particularly in manufacturing rear-view mirrors, where they are set on the back part of the mirrors to have an efficient demisting and/or defrosting effect.

In industry sectors others than automotive fittings, low voltage thermoresistors have a limited use in manufacturing bathroom mirrors (to obtain a demisting effect) and, in the footwear sector, to produce a quite restricted range of warmed slippers and ski boots.

Long theoretical studies and experimental verifications enabled the Applicant to define a new method for producing thermoresistors on non conventional supports (among which, for instance, aluminium and/or other metallic material, plastic material, glass, fabric, leather and so on) and however different supports than the ones used till now.

This new method allowed to identify new possibilities of exploiting low tension thermoresistors and new sectors in which they can be profitably used, breaking the market "vertical isation" which still exist nowadays.

In particular, such new sectors are (or can be):

-fabric/wear: to warm jackets, wind jackets, ski trousers, work dresses for people who work outdoors and with low ambient temperature (cold stores etc.);

-sport equipment: for warming camping tents, sleeping bags, visors for crash helmets (with demisting effect) etc.;

-food: for warming dishes, glasses, bottles, plastic or aluminium boxes (disposable or reusable dishes and glasses);more generally, supports with or without prepacked drinks and foods (precooked foods or drinks to rewarm).

Summary of the invention The present invention concerns a method for producing thermoresistors: said method comprising: deposition on a support of a first layer of insulating material; deposition of a first electrode; deposition of a second electrode; deposition of a layer of ink with PTC characteristics; optionally, deposition of a second layer of insulating material.

Said first and second electrode not being in direct reciprocal contact.

With the term layer it is intended both a continuos layer and a layer with discontinuities, for example a layer having holes, a series of strips, a net-shaped layer.

With the wording deposition of an electrode it is meant deposition of a layer of conductive material, for instance a metal layer or a conductive ink, in general a conductive ink different from the ink with PTC characteristics and preferably with lower resistivity. The electrodes are generally layer with holes or discontinuities for example nets or patterns similar to those of integrated circuits. The electrodes may comprise connecting means for connecting them to an electrical source (a battery, a solar cell, power supply, or any other source).

The ink with PTC characteristics is an ink having PTC (positive temperature coefficient) behaviour i.e. an ink increasing its electrical resistance with the temperature at least within a given range of temperatures. It is preferred that for the ink used two temperatures may be found , whose difference is lower than 50°C the ratio between the resistivity at the higher of said two temperatures and the resistivity at the lower temperature is at least 2, preferably at least 2.5, preferably at least 3, a suitable value being about 3.5.

According to a preferred embodiment , below said lower temperature the slope of resistivity versus temperature is lower than between said two temperatures. The resistivity at said lower temperature is preferably comprised between 1.5 and 4 KΩ square at 15μm (i.e. the resistance between two opposite sides of a square shaped layer having a 15μm thickness), preferred values being 3-3.5 KΩ/square at 15μm. Preferably the lower of said temperatures is between 10 and 40°C, more preferably between 15 and 30 °C. For example the two temperatures may advantageously be 25 and 70 °C. A preferred ink with PTC characteristics is PTC 100 (Coates Electrographics - division of Sun Chemical Inc.) or mixtures thereof, for example with other conductive inks (such as XZ 351- Coates Electrographics - division of Sun Chemical Inc.). The deposition of the layers of insulating materials and of the electrodes may follow the order given above or a different order.

According to an embodiment of the present invention the deposition of the first and second electrode is performed simultaneously, and the two electrodes will lie on the same plane. The ink with PTC characteristics is then deposed on the electrodes connecting them (the ink with PTC characteristics may be deposed before, and then the electrodes, if found desirable). The first layer of insulating material is preferably deposed directly on the support. According to another embodiment the deposition of the first electrode precedes the deposition of the first layer of insulating material; the deposition of the second electrode the deposition of said first layer of insulating material. According to this embodiment at least one electrode is a layer having holes, e.g. is net shaped and the first layer of insulating material has also holes in correspondence with portions of one of the electrodes and in correspondence of the holes of the other electrode.

The layer of ink with PTC characteristics is deposed so as to connect the holes of the layer of insulating material (and then one of the electrodes) with the other electrode; it may be deposed before or after the first electrode (if it has holes in correspondence to the holes of the first insulating layer), after the insulating layer, or preferably after the second electrode (if the first electrode has portions in correspondence to the holes of the layer); in the latter two cases the first electrode may be a continuous layer.

The support may be of a rigid material, such as aluminium or other metallic material, a plastic material (for instance thermoplastic material), glass. According to a preferred embodiment of the invention the support is of a flexible material, such as leather, fabric (woven or non-woven), plastic flexible materials (such as plastic sheets or films) or other equivalent material.

If the support is an insulating material with suitable features (e.g. thermoplastic resins and sheets of thermoplastic materials), at least the first electrode may be deposed directly on it.

The present invention concerns moreover the thermoresistors produced according to the aforesaid method.

The term ink can mean an ink or a paste, in general a material that can be deposed by known printing techniques (such as serigraphy, transfer, ink jet printing, pad printing...).

The second layer of insulating material can advantageously be deposed at last and be a continuous layer.

List of Figures The invention will be better described by means of reference to non limiting embodiments shown in the enclosed Figures, wherein: -Figure 1 shows schematically a section view of a thermoresistor produced according to the invention on a support 17;

-Figure 2 shows schematically a top view of layers 10 to 16 of the thermoresistor of Figure 1 , set side by side each to the other. -Figure 3 shows schematically a section view of a thermoresistor produced according to another embodiment of the invention.

-Figure 4 shows schematically a top view of the thermoresistor of figure 3.

Detailed description of the invention

Figure 1 shows schematically a section view of a thermoresistor produced according to the aforesaid method on a support 17: in the figure the first layer 10 of insulating material, set between the support 17 and the first and second electrode, printed on the insulating layer 10 (preferably) by means, for example of a serigraphy process, per se known, can be seen.

In the described embodiment, the thermoresistor can be produced according a known layout: a layer 15 made of ink with PTC characteristics, as described above is deposed on the electrodes 11.

In the described embodiment, the thermoresistor a second layer of insulating material 16, made of the same or a different insulating material than that used to make layer 10, protects the thermoresistors from the outside environment. Therefore, the method according to the present invention can further comprise the step of deposing layer 16 made of insulating material on the thermoresistor, which is a preferred embodiment.

Printing the thermoresistors on supports consisting of materials (such as, for instance, aluminium or other metallic material; plastic material; fabric, leather or other equivalent material; etc.) different from the ones normally used to print such a thermoresistors is a feature of the method according to the present invention. It is particular, it is preferred that the material composing said first layer of conductive material is a printable ink or paste that may be deposed by known printing techniques (ink jet printing, serigraphy, transfer, pad printing); by using a suitable material for said first layer of insulating material, it is possible to create, preferably by printing techniques, thermoresistors directly on fabric, which is a preferred embodiment of the invention. The Applicant verified experimentally that the aforesaid problems find an adequate solution by means of interposing the first layer of insulating material between the electrodes and the support, in particular by printing said first layer. According to a preferred embodiment, all the electrodes and layers are deposed by printing techniques, preferably serigraphy techniques but, without departing from the scope of the present invention, advantageously other printing processes per se known can be used, such as for example pad-printing, "transfer" etc. The Applicant verified experimentally that, taking into account the material of which the support is made and the product characteristics (camping equipment, working dresses, sport equipment etc.) on which the thermoresistors must be set or on which must be inserted, the optimum ways to print thermoresistors according to the present invention can be obtained by combining together the characteristics (material, thickness, etc.) of the insulating layer, the conductive inks and/or pastes and the printing processes to be used for printing the thermoresistors. The thermoresistors, in particular are especially suited for flexible materials.

A further advantage of the present invention is the use of inks with PTC characteristics as set forth above. This permits to produce thermoresistors without the need of thermostats or control equipment. The control of the temperature to be reached being due to the increased resistivity of the material, which reduces the current automatically as the temperature increase.

Figure 2 shows schematically a top view of layers 10-16 of the thermoresistor of Figure 1, set one beside the others; from said Figure it can be noted that, according to this embodiment: -the insulating layer 10 and the protection layer 16 may consist of two continuous stripes of insulating material;

-the electrodes, 11 may comprise a plurality of elements 12 connected to each other and to the supply terminals 13 by means of two conductive strips 14; without departing from the scope of the present invention, a skilled technician can modify in a way per se known the layout of the electrodes 11 shown in Figure 2 to match specific needs;

-layer 15 of ink with PTC characteristic may consist of a plurality of pads 18, separated form each other and each of which has dimensions comparable to the ones of a heating element 12, upon which it is laid when the thermoresistor is assembled.

Any other layout may be designed by the skilled in the art, according to specific needs. According to a possible embodiment, the thickness of the first layer of insulating material 10 may be comprised between 0.01 and 0.2 mm); the thickness of electrodes 11 may be comprised between 0.015 and 0.4 mm, the thickness of the layer of ink with PTC characteristic 15 may be comprised between 0.015 and 0.2 mm) and the thickness of the second layer of insulating material 16 may be comprised between 0.015 and 0.4 mm.

According to the embodiment shown in figures 3 and 4, the first electrode 2 is deposed on the support 1. If the support 1 is an insulating material, for example a thermoplastic material, preferably a polyester film, the electrode 2 is directly deposed on the support, otherwise an insulating layer may be deposed between them. The first layer of insulating material 3 is then deposed on the first electrode having holes 4 in correspondence of portions of the first electrode. The second electrode 5, which, according to a possible embodiment is net shaped, is deposed on layer 3 with holes 6 in correspondence to the holes 4 of the layer 3, so that the electrodes 2 and 5 are not in contact with each other. Then a layer of ink with PTC characteristics 7 (in black in figure 4) is deposed; it may be a continuous layer or a layer with holes (e.g. a net shaped layer) and is positioned so as to connect the two electrodes through hole 4.

A second layer of insulating material may then be deposited to protect the device from the outside environment. According to a preferred embodiment the electrodes and the layer of ink with PTC characteristics may have the same shape, in particular a net shape. The layer of ink with PTC characteristics may substantially overlap the first electrode, while the second electrode does not overlap, as shown in figure 4 (where the first electrode is covered by the layer of ink with PTC characteristic), and intersects the layer of ink with PTC characteristics. The first electrode may also be a continuos layer deposed on the support. It may be obtained by printing techniques or also by metallisation techniques, i.e. a technique by which a layer of metal (for example aluminium, copper, silver) is deposed on a plastic material, for example a polyester, from gas phase under low pressure. The metallisation technique is well known in the art, and allows the creation of very thin metal layers. Commonly polyester films are metallised. A premetallised film can thus be used as support and first electrode layer, the step of deposing a first electrode having already been performed, without departing from the scope of the present invention. As already stated, the order of deposition of layers and electrodes may change; in particular it is preferred that the first and second electrode are separated by a layer of insulating material. An important advantage of the process according to this embodiment, is that it is possible to produce a thermoresistor that can be cut in almost any shape, without prejudice for its functioning, while a thermoresistor with the two electrodes lying on the same plane cannot in general be cut; thus, it is possible, for example, to create a thermoresistor on sheets of plastic material and then cut the sheet in any size and shape desired. The thickness of the different layers may be chosen according to the needs and may be the same indicated above for another embodiment. Further embodiments are possible; for example, a the layer of ink with PTC characteristics may be interrupted in correspondence of the holes 4. A second layer of insulating materials may be applied over the device having bubble shaped portions in correspondence of the holes 4, said portions being lifted from the underlying layers. Said portions have an inner surface coated with conductive material, and, when pushed come into contact with both the layer of PTC ink and the first electrode, thus closing the circuit. As stated above the material for the first layer of insulating material is preferably a printable ink , particularly if it has to be applied directly on the support. The material can be a polymer that polymerises or reticulates or sets after having been deposed. That may happen by heating, for example by hot air flow, by UV irradiation, or in any known way, depending on the material employed. The kind of material is chosen according to the nature of the material on which it is deposed. For example, if it must be deposed on a conductive support (for example aluminium) it must have strong dielectric properties (for example XB1200, UV10 UV40-317 (Coates Electrographics - division of Sun Chemical Inc.). If it must be deposed on a fabric support and must have flexibility properties an example is PVC based resin XZ 93S (Coates Electrographics - division of Sun Chemical Inc.). For glass an example is UV10 (Coates Electrographics - division of Sun Chemical Inc.), an acrilic type resin polymerised by UV. For certain applications also silicon base materials are suitable.

With regard to the material for the electrodes, it may also be printable, and this is a preferred embodiment; for example are suitable carbon based pastes (hot air polymerisable) such as XZ 302 and 26-8203 (Coates Electrographics - division of Sun Chemical Inc.), silver based pastes (hot air polymerisable) such as XZ250 XZ251, XZ253 (Coates Electrographics - division of Sun Chemical Inc.), Parelec Parmond Silver, silver based pastes (UV polymerisable) such as UV800 (Coates Electrographics - division of Sun Chemical Inc.). Also the ink with PTC characteristics is preferably a printable ink. The insulating material, the electrodes and the ink with PTC characteristic may also be deposed by transfer technique.

According to the present invention, low voltage thermoresistors (for example thermoresistors working with a voltage of 4.5-24 V) are produced, but, if found desirable also medium voltage thermoresistors (for example thermoresistors working with a voltage of 110-240 V) may also be produced. The present invention relates also to a thermoresistor produced by the method described above.

Without departing from the scope of the present invention, a skilled technician can bring to the method for producing thermoresistors on non conventional supports previously described all modifications and improvements suggested by normal practice and natural evolution of technology.

Claims

1. Method for producing thermoresistors: said method comprising: deposition on a support (17, 1 ) of a first layer of insulating material; deposition of a first electrode (11 , 2) ; deposition of a second electrode(11 , 5); deposition of a layer of ink with PTC characteristics (15, 7).

2. Method according to claim 1 , further comprising the deposition of a second layer of insulating material (16).

3. Method according to any preceding claims wherein an ink with PTC characteristics is employed such that two temperatures may be found, whose difference is lower than 50°C, the ratio between the resistivity of said ink with PTC characteristics, at the higher of said two temperatures and its resistivity at the lower temperature being at least 2.

4. Method according to claim 3, wherein said ratio is at least 2.5.

5. Method according to claim 4, wherein said ratio is at least 3.

6. Method according to any of claims 3-5 the resistivity of said ink with PTC characteristics at said lower temperature is preferably comprised between 1.5 and 4 KΩ/square at 15μm .

7. Method according to any of claims 3-5 wherein said lower temperature is between 15 and 30 °C.

8. Method according to any of the preceding claims, wherein said first layer of insulating material is made of a printable ink.

9. Method according to claim 8 wherein said first layer of insulating material is deposed by a printing technique.

10. Method according to any of the preceding claims, wherein said first layer of insulating material is deposed directly on the support.

11. Method according to claim 10 wherein deposition of said first and second electrode occurs simultaneously.

12. Method according to claim 10 or 11 wherein said support is glass, leather, aluminium or fabric.

13. Method according to any of claims 10-12 wherein said first layer of insulating material is deposed by printing or transfer techniques.

14. Method according to any of claims 10-13 wherein said first and second electrode are deposed by printing or transfer techniques.

15. Method according to any of claims 10-14 wherein said support is a flexible material.

16. Method according to any of claims 1-9 wherein said first electrode is deposed before said first layer of insulating material and said layer of insulating material has holes.

17. Method according to claim 16 wherein said first electrode is deposed directly on said support.

18. Method according to any of claims 16-17 wherein said second electrode has holes.

19. Method according to claim 18 wherein said second electrode is net shaped.

20. Method according to any of claims 18-19 wherein said layer of ink with PTC characteristic is deposed to connect said first and second electrode through said holes.

21. Method according to any of claims 16-20 wherein said support is a plastic material.

22. Method according to claim 21 wherein said support is a sheet of thermoplastic material.

23. Method according to claim 22 wherein said thermoplastic material is a polyester.

24. Method according to claim 22 or 23 wherein said first electrode is deposed by a metallisation technique.

25. Thermoresistor obtainable by a method according to any of the preceding claims.