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(11) | EP 0 129 997 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
Process for the production of PTC thermistors Verfahren zum Herstellen von PTC-Thermistoren Procédé de fabrication de thermistors PTC |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0002] As is well-known in the art, a thermistor aimed at sensing temperature alone includes a thermistor element sealed in glass or resin so as to keep it from being affected by other factors such as humidity or gas. Referring especially to NTC thermistors, there are available glass-sealed type thermistors which are inexpensive, easy to mass-produce and have stabilized properties, in addition to resin-sealed type disc-form thermistors.
[0003] Turning to PTC thermistors, however, use is made of resin-sealed disc-form PTC thermistors or PTC thermistors in which metals are mechanically pressed onto electrodes.
[0004] This may be attributable to the properties of PTC thermistors which are significantly affected by the temperature and atmosphere at and in which the thermistor elements are sealed in glass.
[0005] Conventional-NTC thermistors are prepared by glass sealing in vacuum or an atmosphere such as N2 or Ar gas so as to prevent Dumet wires or heaters from being oxidized. In consequence of the studies made by the present inventors, it has been revealed that the application of such glass sealing in a reducing atmosphere to PCT thermistors causes the properties thereof to deteriorate to a considerable extent. It has also been found that, under such conditions, the glass sealing temperature reaches as high at 650°C, at which temperature the properties of PTC thermistors deteriorate significantly.
[0006] U.S. Patent 3,377,561 discloses a process for the production of PTC thermistors comprising the step of sealing a positive temperature coefficient semiconductor ceramic material in glass in the presence of air.
[0007] In view of the foregoing, a main object of the present invention is to provide inexpensive glass-sealed type PTC thermistors which show a great change in resistance, especially a markedly increased change in resistance at switching temperatures, and which have stabilized properties.
[0008] According to the present invention, there is provided a process for the production of PTC thermistors by sealing a positive temperature coefficient semiconductor ceramic material in low-melting glass having a softening point of no higher than 560°C in the presence of air, oxygen or an air/oxygen mixture containing higher than 0% to lower than 100% volume of air.
[0009] The invention will be more particularly described with reference to the accompanying drawings, in which:-
Figure 1 is a schematic view showing one embodiment of the steps of a process according to the present invention; and '
. Figures 2 to 4 inclusive are views showing the temperature-specific resistance characteristics of the products prepared under different conditions.
[0010] As the semiconductor ceramic material having a positive temperature coefficient used in the present invention, there are mentioned those obtained by adding to barium titanate base compositions any one of trivalent antimony, trivalent bismuth, pentavalent tantalum, pentavalent niobium or a rare earth metal. The glass used has a softening point of 450°C-560°C inclusive, and includes those glasses based on B203-PbO-ZnO, B203-PbO-SiO2, B203-PbO-TiO2, B203-Pb0-Si02-AI203-ZnO, B203-Pb0-V205, S!02-PbO-K20, Si02-PbO-Na2O and SiO2-PbO-K20-Na2O, Preference is given to a Si02-PbO-K20 base glass, since this glass shows desirous thermal expansion and wettability with respect to lead wires (Dumet wires, viz., Fe-Ni alloy wires plated with Cu).
[0011] When a glass having a softening point of below 450°C is used, certain limitations are imposed upon the temperature at which the resulting glass-sealed type PTC thermistors are employed.
[0012] Referring now to Figure 1, a semiconductor barium titanate ceramic material 1 is first sliced to any suitable thickness having regard to the length of a glass tube 4 in which the finished thermistor element is to be sealed. Silver electrodes 2 and 2 are applied to both sides of the thus obtained element, and deposited thereto for 20 minutes at 600°C. Figure 1(a) shows a section of the electrode-provided element.
[0013] As shown in Figure 1 (b), the element is then cut to any length corresponding to the diameter of the glass tube 4.
[0014] The element is placed in the tube 4 of a glass having a softening point of no higher than 560°C, into both ends of which Dumet wires 3 and 3 are inserted. Finally, the glass tube 4 is sealed by means of a carbon heater jig. The sealing temperature is determined depending upon the softening point of the glass used, and is generally higher than the softening point of the glass used by 50°C or more.
[0015] In the prior art NTC glass sealed thermistors, a glass having a softening point exceeding 560°C is used and sealing is carried out at a temperature exceeding 610°C. If sealing of a PTC thermistor is carried out under such conditions, there is a marked drop in the properties of the resulting PTC thermistor. According to the present invention, however, it is possible to obtain stable PTC thermistors whose properties drop only slightly by sealing the thermistor elements in a low-melting glass having a softening point of no higher than 560°C.
[0016] Figure 2 shows the results of an experiment run wherein PTC thermistor elements having a Curie point of 120°C were sealed in glasses in the art.
[0017] Although the resulting properties having slightly dropped from the initial ones (prior to sealing), yet the PTC thermistor element sealed in a glass having a softening point of 536°C or 560°C has been found to show excellent properties. It has also been found that similar results are obtained with PTC thermistor elements having different Curie points. The results of Figure 2 are also numerically given in Table 1.
[0018] Figure 3 is a characteristic diagram of a PTC thermistor sealed in glass in various atmospheres. The PTC thermistor used had a Curie point of 120°C, and sealing was carried out at 610°C.
[0019] It is clear from the diagram that sealing in air or oxygen gas yields a better PTC thermistor as compared with one treated in vacuo or in an inert or reducing gas atmosphere. The results of Figure 3 are numerically given in Table 2.
[0020] It is to be understood that similar results are obtained in air/oxygen mixture and/or with a PTC thermistor element having a different Curie point.
[0021] Figure 4 is a graphical view showing the relation between the specific resistance and the temperature of PTC thermistors obtained by sealing a PTC thermistor element having a Curie point of 120°C in glass in air and/or oxygen gas. The results of Figure 4 are numerically given in Table 3.
[0022] From these results, it is found that by a process according to the present invention PTC thermistors are obtained which show a large change in resistance, which is comparable to the properties prior to sealing.
[0023] It is to be understood that similar results are obtained in an air/oxygen mixture and/or with PTC thermistor elements having a different Curie point.
1. A process for the production of PTC thermistors comprising the step of sealing
a positive temperature coefficient semiconductor ceramic material (1) in a low-melting
glass (4) having a softening point of no higher than 560°C in the presence of air,
oxygen or an air/oxygen mixture containing higher than 0% to lower than 100% volume
of air.
2. A process according to Claim 1, characterised in that the glass (4) has a softening
point of from 450°C to 560°C inclusive.
3. A process according to Claim 1 or 2, characterised in that the glass (4) is in
the form of a tube sealed at both ends.
4. A process according to Claim 3, characterised in that lead wires (3) are inserted
into opposite ends of the glass tube (4) prior to the sealing thereof.
5. A process according to Claim 3 or 4, characterised in that electrodes (2) are applied
to opposite sides of the semiconductor material (1) prior to its insertion in the
glass tube (4).
6. A process according to any one of the preceding claims, characterised in that the
glass used is based on B2O3-PbO-ZnO, B203-PbO-SiO2, B203-PbO-TiO2, B2O3-PbO-SiO2-Al2O3-ZnO, B2O3-PbO-V2O5, SiO2-PbO-K20, Si02-PbO-Na20 or SiO2-PbO-K2O-Na2O.
7. A process according to any one of the preceding claims, characterised in that the
semiconductor material (1) is a barium titanate ceramic material.
8. A process according to Claim 7, characterised in that the barium titanate ceramic
material has added thereto any one of trivalent antimony, trivalent bismuth, pentavalent
tantalum, pentavalent niobium or a rare earth metal.
1. Verfahren zur Herstellung von PTC-Thermistoren mit einem Schritt, bei dem ein einen
positiven Temperaturkoeffizienten aufweisendes halbleitendes Keramikmaterial (1) in
einem teifschmelzenden Glas (4), das einen Erweichungspunkt besitzt, der nicht größer
als 560°C ist, in der Anwesenheit von Luft, Sauerstoff oder eines Luft/Sauerstoff-Gemisches
abgedichtet wird, das mehr als 0 Vol.-% bis weniger als 100 Vol.-% Luft enthält.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Glas (4) einen Erweichungspunkt
von 450°C bis 560°C inclusive aufweist.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Glas (4) die
Form eines an beiden Enden abgeschlossenen Rohres aufweist.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß Anschlußdrähte (3) in entgegengesetzte
Enden des Glasrohres (4) vor der Abdichtung derselben eingeführt werden.
5. Verfahren nach Anspruch 3 oder 4, dadurch gekennzeichnet, daß Elektroden (2) an
entgegengesetzten Seiten des halbleitenden Materials (1) angebracht werden, bevor
dieses in das Glasrohr (4) eingeführt wird.
6. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, daß das
verwendete Glas auf B203-PbO-ZnO, B203-PbO-Si02, B203-PbO-Ti021 B2O3-PbO-SiO2-Al2O3-ZnO, B203-PbO-V205, SiO2-PbO-K2O, Si02-PbO-Na20 oder Si02-PbO-K20-Na20 basiert.
7. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, daß das
Halbleitermaterial (1) ein Bariumtitanat-Keramikmaterial ist.
8. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß zu dem Bariumtitanat-Keramikmaterial
irgendein Element der Elemente dreiwertiges Antimon, dreiwertiges Wismuth, fünfwertiges
Tantal, fünfwertiges Niob oder ein Element aus der Gruppe der Seltenen Erdemetalle
hinzugefügt ist.
1. Procédé pour la production de thermistors CTP comportant un stade de scellement
d'un matériau céramique semiconducteur à coefficient thermique positif (1) dans un
verre à bas point de fusion (4) ayant un point de ramolissement inférieure à 560°C
en présence d'air, d'oxygène ou d'un mélange d'air et d'oxygène contenant plus de
0% à moins de 100% en volume d'air.
2. Procédé selon la revendication 1, caractérisé en ce que le verre (4) a un point
de ramollissement compris entre 450°C et 560°C inclusivement.
3. Procédé selon la revendication 1 ou la revendication 2, caractérisé en ce que le
verre (4) se présente sous la forme d'un tube scellé à ses deux extrémités.
4. Procédé selon la revendication 3, caractérisé en ce que des fils conducteurs (3)
sont introduits dans les extrémités opposées du tube de verre (4) avant le scellement
de celui-ci.
5. Procédé selon la revendication 3 ou la revendication 4, caractérisé en ce que des
électrodes (2) sont appliquées sur les côtés opposés du matériau semi-conducteur (1)
avant son introduction dans le tube de verre (4).
6. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce
que le verre utilisé est à base de B203-PbO-ZnO, B203-PbO-S!02, B203-PbO-TiO2, B2O3-PbO-SiO2-Al2O3-ZnO, B203-PbO-V205, Si02-PbO-K20, SiO2-PbO-Na2O ou Si02-PbO-K20-Na20.
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce
que le matériau semi-conducteur (1) est un matériau céramique à base de titanate de
baryum.
8. Procédé selon la revendication 7, caractérisé en ce qu'on ajoute au matériau céramique
à base de titanate de baryum l'un quelconque des corps suivants: antimoine trivalent,
bismuth trivalent, tantale pentavalent, niobium pentavalent, ou un métal de terres
rares.