Title:
NONFLAMMABLE COMPOSITION RESISTOR
United States Patent 3745507
Abstract:
A nonflammable composition resistor comprising a resistor body consisting essentially of finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg°C to (Tg+200)°C, wherein Tg°C is a glass transition temperature of said resin. This nonflammable composition resistor is free from arcing, burning, charring and mechanical damage and exhibits an irreversible extreme increase of electrical resistance under serious overload conditions.
US Patent References:
Plastic resistance elements and methods for making same
Kohler - November 1967 - 3351882
PROCESS FOR MAKING CONDUCTIVE POLYMERS AND RESULTING COMPOSITIONS
Meyer - January 1970 - 3673121
Plastic resistance elements and methods for making same
Kohler - November 1967 - 3351882
PROCESS FOR MAKING CONDUCTIVE POLYMERS AND RESULTING COMPOSITIONS
Meyer - January 1970 - 3673121
Inventors:
Ishida, Tomio (Hirakata-shi, JA)
Sato, Kunio (Neyagawa-shi, JA)
Sugihara, Kanji (Hushata-shi, JA)
Yoshida, Shigeru (Osaka-fu, JA)
Sato, Kunio (Neyagawa-shi, JA)
Sugihara, Kanji (Hushata-shi, JA)
Yoshida, Shigeru (Osaka-fu, JA)
Application Number:
05/281937
Publication Date:
07/10/1973
Filing Date:
08/18/1972
View Patent Images:
Export Citation:
Assignee:
Matsushita Electric Industrial Co., Ltd. (Osaka, JA)
Primary Class:
Other Classes:
219/544, 338/262, 252/511
International Classes:
H01C7/00; H01C7/00
Field of Search:
338/25,226,262 252/511
Primary Examiner:
Goldberg E. A.
Claims:
What we claim is
1. A nonflammable composition resistor comprising a resistor body consisting essentially of finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg °C to (Tg+200)° C, wherein Tg°C is a glass transition temperature of said resin.
2. A nonflammable composition resistor as claimed in claim 1, which further comprises an outer sleeve including finely divided silica powder dispersed in a further resin, said outer sleeve enveloping said resistor body.
3. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of an organic substance selected from the group consisting of carbocyclic compounds and heterocyclic compounds.
4. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of an organic substance selected from the group consisting of anthracene, anthraquinone, 1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchlorpentacyclodecane and copper phthalocyanine.
5. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of anthraquinone.
6. A nonflammable composition resistor as claimed in claim 1, wherein the amount of said additive powder included in said resistor body is from 3 to 70 percent by weight.
7. A nonflammable composition resistor as claimed in claim 1, wherein said resin is thermosetting.
8. A nonflammable composition resistor as claimed in claim 2, wherein said further resin is thermosetting.
9. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of a member selected from the group consisting of phenol resin, urea resin, melamine resin, epoxy resin and mixtures thereof.
10. A nonflammable composition resistor as claimed in claim 2, wherein said further resin consists essentially of a member selected from the group consisting of phenol resin, urea resin, melamine resin, epoxy resin and mixtures thereof.
11. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of phenol resin.
12. A nonflammable composition resistor as claimed in claim 2, wherein said further resin consists essentially of phenol resin.
13. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder consists essentially of at least one member selected from the group consisting of carbon black, graphite, metal and metal alloys.
14. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder consists essentially of carbon black.
15. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder has an average particle size of 0.08 to 150 microns.
16. A nonflammable composition resistor as claimed in claim 1, which further comprises two solder coated electrode leads attached to the respective ends of said resistor body.
17. A nonflammable composition resistor as claimed in claim 16, wherein said two electrode leads have a thermal conductivity of 0.1 to 0.4 cal./cm.sec.°C.
18. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of a phenol resin, said additive powder consists essentially of anthraquinone, and said conducting powder consists essentially of carbon black having an average particle size of 0.08 to 0.24 micron.
1. A nonflammable composition resistor comprising a resistor body consisting essentially of finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg °C to (Tg+200)° C, wherein Tg°C is a glass transition temperature of said resin.
2. A nonflammable composition resistor as claimed in claim 1, which further comprises an outer sleeve including finely divided silica powder dispersed in a further resin, said outer sleeve enveloping said resistor body.
3. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of an organic substance selected from the group consisting of carbocyclic compounds and heterocyclic compounds.
4. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of an organic substance selected from the group consisting of anthracene, anthraquinone, 1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchlorpentacyclodecane and copper phthalocyanine.
5. A nonflammable composition resistor as claimed in claim 1, wherein said additive powder consists essentially of anthraquinone.
6. A nonflammable composition resistor as claimed in claim 1, wherein the amount of said additive powder included in said resistor body is from 3 to 70 percent by weight.
7. A nonflammable composition resistor as claimed in claim 1, wherein said resin is thermosetting.
8. A nonflammable composition resistor as claimed in claim 2, wherein said further resin is thermosetting.
9. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of a member selected from the group consisting of phenol resin, urea resin, melamine resin, epoxy resin and mixtures thereof.
10. A nonflammable composition resistor as claimed in claim 2, wherein said further resin consists essentially of a member selected from the group consisting of phenol resin, urea resin, melamine resin, epoxy resin and mixtures thereof.
11. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of phenol resin.
12. A nonflammable composition resistor as claimed in claim 2, wherein said further resin consists essentially of phenol resin.
13. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder consists essentially of at least one member selected from the group consisting of carbon black, graphite, metal and metal alloys.
14. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder consists essentially of carbon black.
15. A nonflammable composition resistor as claimed in claim 1, wherein said conducting powder has an average particle size of 0.08 to 150 microns.
16. A nonflammable composition resistor as claimed in claim 1, which further comprises two solder coated electrode leads attached to the respective ends of said resistor body.
17. A nonflammable composition resistor as claimed in claim 16, wherein said two electrode leads have a thermal conductivity of 0.1 to 0.4 cal./cm.sec.°C.
18. A nonflammable composition resistor as claimed in claim 1, wherein said resin consists essentially of a phenol resin, said additive powder consists essentially of anthraquinone, and said conducting powder consists essentially of carbon black having an average particle size of 0.08 to 0.24 micron.
Description:
BACKGROUND OF THE INVENTION
This invention relates to a nonflammable composition resistor.
A conventional composition resistor comprises a resistor body having finely divided conducting powder and silica powder dispersed in a resin. Such resistor, however, has a disadvantage as explained below. When a current larger than the rated value (e.g., at a wattage of 1.5 times the ratted wattage) flows through the resistor, the resistor is rapidly heated by well known Joule-heating. Because of the heat, the resistance of the resistor decreases. Because of this decrease of resistance, the current flowing through the resistor increases, and so the resistor is more heated by Joule-heating. Due to this vicious circle, the resistor finally gets short-circuited, arc occurs, or the resistor burns or gets charred or softened. Accordingly, it has been a great problem to provide a composition resistor which is free from above mentioned disadvantage even if the resistor is operated under a serious overload such as a wattage of 50 times the rated wattage at a temperature of 70°C for 7 hours.
SUMMARY OF THE INVENTION
An object of the invention is to provide a nonflammable composition resistor which is free from arcing, burning, charring or mechanical damage and exhibits an irreversible extreme increase of the electrical resistance, when operated under a overload condition such as a wattage of from 5 to 50 times rated wattage.
Another object of the invention is to provide a nonflammable composition resistor which has extremely high stability with respect to the electrical resistance and other electrical properties such as humidity, load life and current noise characteristics, particularly when operated in a normal conditions for which the resistors are designed.
These objects are provided by a nonflammable composition resistor comprising a resistor body consisting essentially of finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg°C to (Tg+200)°C wherein Tg°C is a glass forming temperature of said resin.
Details of the invention will be apparent upon consideration of the following descriptions taken with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a nonflammable composition resistor according to the present invention, including partially exaggeratedly enlarged sectional views.
FIG. 2 is a graph illustrating the relation between the heating temperature and the change of weight of additive powders.
FIG. 3 is a graph illustrating the relation between the heating temperature and the electrical resistance as a function of the weight ratio of anthraquinone powder.
FIG. 4 is a graph illustrating the relation between the weight ratio of anthraquinone powder and maximum electrical resistance.
FIG. 5 is a graph illustrating the relation between the time exposed to humidity and the electrical resistance change.
FIG. 6 is a graph illustrating the relation between the heating temperature and electrical resistance.
FIG. 7 is a graph illustrating the relating between the heating temperature and electrical resistance.
FIG. 8 is a graph illustrating the relation between an average particle size of a conducting powder and electrical resistance.
FIG. 9 is a graph illustrating the relation between the heating temperature and the electrical resistance, as a function of an average particle size of conducting powder.
FIG. 10 is a graph illustrating the relation between the thermal conductivity of electrode leads and rising rate of electrical resistance.
FIG. 11 is a graph illustrating the relation between the loading time in load life and the resistance change.
FIG. 12 is a graph illustrating the relation between the heating temperature and the change of weight of anthraquinone powder to determine the transforming temperature of anthraquinone.
FIG. 13 is a graph illustrating the relation between the temperature and the coefficient of linear thermal expansion of phenol resin to determine the glass transition temperature of phenol resin.
Before proceeding with a detailed description of the invention, the construction of a nonflammable composition resistor contemplated by this invention will be explained with reference to FIG. 1. Reference numeral 1 designates a resistor body having finely divided conducting powder 4, silica powder 5 and additive powder 6 in resin 7. The resistor body 1 can have any suitable shape, but FIG. 1 shows the case when the resistor body has substantially the shape of cylinder. A pair of solder coated electrodes 3 are embedded in the ends of the nonflammable composition resistor. Reference numeral 2 designates an outer sleeve which includes finely divided silica powder 8 dispersed in a further resin 9 and which can be used to envelop said resistor body 1. The feature of the invention is in that said additive powder 6 has a transforming temperature in the range from Tg°C to (Tg+200)°C wherein Tg°C is a glass transition temperature of said resin 7. Broadly speaking, the word "transforming temperature" of the additive powder as used in the present application means a temperature below which an increase of temperature causes a small decrease of the weight of the additive powder, but above which an increase of temperature causes a great decrease of the weight of the additive powder. The decrease of the weight of the additive powder is caused by vaporization, decomposition or sublimation of the additive powder. Further, the word "glass transition temperature" of the resin as used in the present application means a temperature above which the resin gets to a glassy state. However, precise definition of "transforming temperature" and "glass transition temperature" will be described later.
A nonflammable composition resistor according to the present invention is in an extremely high stability with respect to the electrical resistance and other electrical properties such as humidity, load life and current noise characteristics, particularly when operated in a normal conditions for which the resistors are designed. Furthermore, if the composition resistor is placed under an overlaod of e.g., 5 to 50 times rated wattage at a temperature of 70°C, there occurs initially a substantial increase in current flowing through the resistor, and due to the I 2 R factor, the resistor of the present invention is heated to a temperature over the transforming temperature of the additive powder. This causes the resistance of the resistor body to increase about 5 to 100 times the initial electrical resistance thereof irreversibly. The phrase "to increase irreversibly" means that the increased electrical resistance does not decrease even after the resistor body is cooled to the initial temperature such as room temperature.
The mechanism of the irreversible increase in the electrical resistance of the resistor body of the present invention can be presumed as follows. When an overload is applied to the resistor body, the resistor body is heated over a critical temperature so that the additive powder dispersed in the resistor body emits gas therefrom. The electrical conduction of the resistor body attributes to a chain of conduction paths of the conducting powder surrounded by resin, and the heat of the resistor body is mainly due to the contacts between the particles of the conducting powder. In other words, such phenomena as described above occur within a kind of sealed structure. Accordingly, the vapor pressure of the above mentioned gas from the additive powder becomes very high. If the resistor body has then a temperature of the glass transition temperature or higher of the resin which acts as a binder in the resistor body, the resin greatly loses its elasticity so that the particles of the conducting powder are greatly separated from each other by the high pressure gas from the additive powder. This mentioned mechanism is presumably the reason for the irreversible and remarkable increase in the electrical resistance of the resistor body.
Thus, before-mentioned vicious circle between the increase of Joule heat and the decrease of electrical resistance as occuring in a conventional composition resistor does not occur in the composition resistor of the present invention. The resistor body stays in a stable and safe equilibrium state after the resistance has been increased. Accordingly, the composition resistor of the present invention may act as a fuse. Thus, the present resistor is free from arcing, burning, charring or mechanical damage.
In making nonflammable composition resistors according to the present invention, a mixture of finely divided conducting powder such as carbon black or graphite powder, silica powder and any suitable additive powder in available resin is well mixed at a temperature of 50°C to 100°C by any suitable and available hot rolling method until it acquires the proper plasticity. The conducting powder can be not only carbon black or graphite powder, but also metal or metal alloys, or mixtures thereof. The additive powder can be any suitable organic substance selected from the group consisting of carbocyclic compounds and heterocyclic compounds. In the Examples which will be described later, anthracene, anthraquinone, 1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchlorpentacyclodecane and copper phthalocyanine are exemplified.
The suitable resin can be a thermosetting binder, such as phenol resin, urea resin, melamine resin epoxy resin and mixtures thereof.
An operable composition of the mixture is 5 to 50 weight (percent) of conducting powder, 0 to 70 weight percent of silica powder, 5 to 70 weight percent of additive powder and the balance of resin.
An operable average particle size of said finely divided silica powder ranges from about 0.3 to 20 microns.
An operable average particle size of said finely divided carbon black or graphite powder ranges from about 0.08 to 150 microns to obtain nonflammable carbon composition resistors. The average particle size referred to herein is determined by a well known electron microscope method, for example, described in a literature of J. Soc. Chem. Ind. 62, 374 (1943); Nature, 17, 350 (1953).
After being cooled to room temperature, the mixture is crushed and ground into granules as a starting material for the resistor body. A mixture of finely divided silica powder in available resin is well mixed at a temperature of 50°C to 100°C by any suitable and available hot rolling method until it acquires the proper plasticity. An operable composition of the mixture is 75 to 89 weight percent of silica powder, and the balance of resin.
After being cooled to room temperature, the mixture is crushed and ground into granules to form the starting material for the outer sleeve.
A unitary body having the resistor body enveloped by the outer sleeve is formed by any suitable and available method, for example, by an extrusion method or a pressing method. In an extrusion method, the aforesaid two mixtures in granule form are preheated and are simultaneously supplied to a nozzle for extrusion. The extruded body is in a long cylindrical form and is cut into many short cylinders having the desired length. In a pressing method, the resistor body and the outer sleeve are seperately formed by pressing and then are combined together to form a short cylinder by any suitable method. The short cylinder is provided, at both ends, with two solder coated electrode leads having a thermal conductivity of 0.1 to 0.4 cal/cm, sec. °C, by any suitable method.
For example, the short cylinder is inserted in a molding die, heated to a temperature of 150°C to 200°C, and then is pressed by two punches having two solder coated electrode leads inserted therein. A pressing pressure of 400 to 1,000 Kg per sq. cm. is applied for a time period of 30 to 180 seconds to embed the two electrode leads in the short cylinder. The suitable electrode leads can be made of copper-cromium alloy, copper clad iron, brass, iron or bronze. If necessary, the finished resistor is further heated at a temperature of 130°C to 170°C for 5 to 48 hours to obtain more stable electrical properties.
It has been discovered according to the present invention that when said additive powder for said resistor body has a transforming temperature in the range from Tg° C to (Tg+200)°C, wherein Tg is the glass transition temperature of the resin the resistor body, the resultant resistor is free from arcing, burning, charring or mechanical damage and exhibits an irreversible and extreme increase in its electrical resistance. Said additive powder, for example, anthraquinone powder is in a high purity of 99.7 to 99.9 weight percent of pure anthraquinone and the balance of moisture content.
The transforming temperature of the additive powder such as anthraquinone powder is measured by using the thermogravimetric analyzing apparatus (RIKAGAKU Denki Co. Ltd: No. 8001) in advance of adding the conducting powder to the resistor body.
About 20 milligram of anthraquinone powder is weighed accurately in a 0.5 ml of platinum crucible, and is heated to a range of between 20°C to 400°C at a heating rate of 5°C/min., until anthraquinone powder is allowed to transform (i.e., vaporize, decompose or subline) completely. The change of weight of anthraquinone powder increases according to the increase in the heating temperature. An abrupt increase in the change of weight is observed with anthraquinone powder heated at temperature of 230°C. The temperature 230°C is determined as follows. FIG. 12 shows a graph illustrating the relation between the heating temperature and the change of weight of the anthraquinone powder. Referring to FIG. 12, the curve consists of a first segment which is substantially straight (heating temperature: 180°-200°C), curve (heating temperature: 200°-238°C), and a second segment which is substantially straight (heating temperature: 238-243°C). The dotted lines (i) and (ii) are prologations of the first and the second segments, respectively. The temperature at the crossing point P of the two dotted lines is the above mentioned temperature 230°C. This temperature 230°C is defined as the transforming temperature of anthraquinone powder. The transforming temperatures of other additive powders are defined in the same manner. FIG. 2 is an exemplary graph for illustrating the relation between the heating temperature and the change of weight of various additive powders, and Table 1 lists the transforming temperatures of these additive powders.
TABLE 1
Additive powder Transforming temperature (°C) A Anthraquinone 230 B Anthracene 165 C 1-nitro- 182 anthraquinone D Terephthalic acid 300 E p-terphenyl 225 F Phenolphthalein 300 G Carbazole 170 H Perchloro- 240 pentacyclodecone I Copper phthalocyanine 370
As a general rule, a glass transition temperature Tg° C is dependent on kinds of resin and kinds and quantity of hardener. A glass transition temperature of said resin obtained for the nonflammable composition resistors is obtained from the coefficient of linear thermal expansion test. FIG. 13 shows the manner of determining the glass transition temperature of phenol resin. When a phenol resin having a length l at room temperature is heated gradually, the length of the phenol resin increases to l+ Δl according to the increase of the temperature of phenol resin. The coefficient of linear thermal expansion is defined as Δl/l × 10 3 . FIG. 13 shows the relation between the coefficient of linear thermal expansion and the temperature of the phenol resin. The glass transition temperature of the phenol resin is determined as a crossing point of two substantially straight segments of the obtained curve, in the same manner as in determining the above mentioned transforming temperature. The dotted lines of FIG. 13 are therefore prolongations of the two segments. The glass transition temperature of phenol resin thus obtained is within the range of 140°C to 150°C. This range attributes to errors in measuring. The glass transition temperatures of other resins are defined in the same manner.
Glass transition temperatures of various resins are listed in Table 2.
TABLE 2
kinds of resins manufacturer glass transition temperature (TG°C) Phenol resin Matsushita Denko 140° - 150°C Co., Urea resin Matsushita Denko 130° - 140°C Co., melanine resin Matsushita Denko 135° - 145°C Co., epoxy resin Epikote 828* Shell 180° - 190°C Co., (Hardener DDS) * trade name
EXAMPLE 1.
Anthraquinone powder is used as an additive powder. The anthraquinone powder in a purity of 99.9 weight percent is obtained by grinding crystalline anthraquinone in a dry ball mill. The obtained anthraquinone powder pass through a-100 Mesh screen. Graphite powder is used as a conducting powder. The used graphite powder is in an average particle size of 50 microns. The used finely divided silica powder is in an average particle size of 10 microns. A mixture of 0 to 85 weight percent of anthrachinone powder, 5 weight percent of graphite powder, 10 weight percent of phenol resin and the balance of silica powder is prepared as shown in Table 3 and is mixed well at 70°C by a hot rolling machine. The mixture is cooled and crushed into granules having a particle size of 5 to 30 mesh. Another granules of mixture of 80 weight percent of silica powder and 20 weight percent of phenol resin is prepared in a way similar to that described above. ------------------------------------------------------------ --------------- TABLE 3
phenol graphite Anthraquinone silica powder resin powder powder ____________________________________________________________ ______________ weight (%) weight (%) weight (%) weight (%) a 10 5 0 85 b 10 5 2 83 c 10 5 5 80 d 10 5 20 65 e 10 5 50 35 f 10 5 70 15 g 10 5 85 0 ____________________________________________________________ ______________
TABLE 4
Anthraquinone Applied wattage current noise 3 powder 1/2 W 2W 5W 10W 15W (μV/V) a 0 weight (%) 1 NB 2 BB B B 0.25 b 2 NB B B B B 0.25 c 5 NB NB NB NB NB 0.25 d 20 NB NB NB NB NB 0.30 e 50 NB NB NB NB NB 0.30 f 70 NB NB NB NB NB 0.30 g 85 NB NB NB NB NB 0.30 1 NB: When resistors are tested as described above, arc, burning or charring does not occur. 2 B: When resistors are tested as described above, arc, burning or charring occurs. 3 Measured utilizing Quan-Tech Labs Resistor Noise Test Set Model 315.
Both kinds of granules are charged into a conventional extrusion press to form plural short cylinders each having a resistor body enveloped by an outer sleeve. The nozzle part of the extrusion machine is heated to 90°C. Each of the short cylinders is provided at each ends with solder coated electrode leads by a well known punching method operated at 180°C for 3 minutes at a pressure of 500 kg/cm 2 . The short cylinders each having two solder coated electrode leads embedded in the ends thereof are heated at a 150°C for 8 hours to form stable resistors. The resultant resistors (Type 1/2 watt) have nominal resistance value of 1.0 kΩ at a room temperature.
These resistors are examined with respect to resistance temperature characteristics test, overload life test, humidity test and current noise level test. Resistance-temperature characteristics test is carried out in a manner similar to that described in MIL-STD-202 at ambient temperatures of 25°C, 65°C, 105°C, 150°C, 180°C, 210°C, 230°C, 260°C, 300°C, 350°C and 400°C. That is, the resistors are kept under each of the ambient temperatures to bring the resistors to each of the ambient temperatures. The resistors are kept of the temperature for 2 minutes, and then the resistances thereof are measured.
Overload test is carried out in a manner similar to that described in MIL-STD-202. In accordance with MIL-STD-202, on overload in excess of 1.0 to 50 times the rated wattage is applied at a temperature of 70°C for 7 hours. Adequate precaution is taken to maintain constant voltage on resistors under test. After test, the resistors are examined whether they are free from arcing, burning, charing or mechanical damage.
The humidity and current noise characteristics tests are carried out in a manner similar to that described in MIL-STD-202.
FIG. 3 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance value as a function of weight ratio of anthraquinone powder FIG. 4(I) is a thus obtained graph illustrating a relation between the weight (percent) of anthraquinone powder and the maximum electrical resistance.
Table 4 shows these testing results in which a (no anthraquinone powder) corresponds to a conventional composition resistor.
FIG. 5 is thus obtained graph illustrating a relation between the time exposed to humidity and the electrical resistance change of the resistors.
As apparent from FIG. 3, FIG. 4 and Table 4. a better result can be obtained by 3 to 70 weight percent of anthrachinone powder as an additive powder. Furthermore, it is apparent from FIG. 5 that the composition resistor of the present invention is about the same as a conventional composition resistor with respect to the characteristics of the electrical resistance change vs. time for the resistor to be exposed to humidity.
EXAMPLE 2.
Four kinds of resistors are prepared in a manner similar to that of Example 1. Finely divided carbazole powder and copper phthalocyanine powder are used as additive powders. These powders are dispersed in resins. The resins are phenol resin and epoxy resin. The composition of each mixtures are substantially the same as those of Example 1, except some conditions for making composition resistors as shown in Table 5.
TABLE 5. ##SPC1##
These resistors are subjected to the tests similar to those of Example 1. FIG. 6 is a thus obtained graph illustrating relation between the heating temperature and electrical resistance. Table 6 shows the tasting results. As apparent from these results, it is possible to determine the temperature at which the resistance value suddenly increases by suitably selecting both the glass transition temperature of used resin and the transforming temperature of used additive powder.
TABLE 6
Kinds of Applied Wattage resistors 0.5watt 2 5 10 15 25 Type 1 NB NB NB NB NB B Type 2 NB B B B B B Type 3 NB B B B B B Type 4 NB NB NB NB NB B
the best result can be obtained by using the additive powders having transforming temperature in the range from Tg°C to (Tg+200)°C, wherein Tg°C is a glass transition temperature of the resin in the resistor body.
EXAMPLE 3
Mixtures of 0 to 85 weight percent of additive powder, 5 weight percent of conducting powder, 10 weight percent of resin and the balance of silica powder are prepared in a manner similar to that of Example 1. The used finely divided additive powders are anthracene,1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchloropentacyclodecane and copper phthalocyanine, as listed in Table 7. The used conducting powder is carbon black, and the used resin is phenol resin.
Composition resistors are prepared from these mixtures in a manner similar to that of Example 1. These resistors are subjected to the tests similar to those of Example 1.
FIG. 4 (II) is a thus obtained graph illustrating a relation between the weight ratio of additive powder and maximum electrical resistance.
FIG. 7 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance. Table 7 shows the overload testing results. ##SPC2##
As apparent from FIG. 4(II), FIG. 7 and Table 7, best results can be obtained by using the additive powders having a transforming temperature in the range from Tg°C to (Tg+200)°C, wherein Tg°C is a glass transition temperature of used resin, and by using 3 to 70 percent by weight of said additive powder.
EXAMPLE 4
Mixtures of 20 weight percent of additive powder, 5 to 20 weight percent of conducting powder, 15 weight percent of resin and the balance of silica powder are prepared. The used additive powder is anthraquinone, and the used resin is phenol resin. The used conducting powders are carbon black and graphite powder having various average particle sizes as shown in Table 8. 14 kinds of resistors are prepared in a manner similar to that of Example 1 as shown in Table 8. The resultant resistors (type 1/2 watt) have nominal electrical resistance of 10 Ω at room temperature. The composition resistors thus made are subjected to the tests similar to those of Example 1.
FIG. 8 is a thus obtained graph illustrating a relation between an average particle size of conductive powders and the electrical resistance.
FIG. 9 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance as a function of an average particle size of conductive powder. ##SPC3##
Table 8 shows the overload testing results. As apparent from FIG. 8, FIG. 9 and Table 8, better results can be obtained by using conducting powder of an average particle size of 0.080 to 150 microns, and the best results are obtained by using phenol resin as the resin, anthraquinone as the additive powder and carbon black having an average particle size of 0.080 to 0.24 micron as the conducting powder.
EXAMPLE 5
Eight kinds of composition resistors are prepared in a manner similar to test of Example 1. Solder coated electrode leads are used which have various thermal conductivities of 0.06 to 0.93 (cal/cm.sec.°C at 20°C). The kinds of electrode leads used are copper, aluminum, copper-chromium alloy, copper clad iron, brass, iron and bronze, as shown in Table 9.
TABLE 9
thermal kinds of electrode conductivity composition leads (at 20°C) a Copper 0.93 cal/ cm.sec..degree .C b Aluminum 0.53 c Copper-chromium Cr: 0.4 0.9wt(%) 0.40 alloy d Copper clad iron 0.35 e Brass Cu: 67%, Zn: 33% 0.26 f Iron 0.17 g Bronze (1) Cu: 90%, Sn: 10% 0.10 h Bronze (2) Cu: 75%, Sn: 25% 0.06
The composition of each resistor body are exactly the same as those of Example 1 (Table 3 (d) ). The resultant resistors (Type 1/2 watt) have nominal electrical resistance of 1.0 kΩ at a room temperature. These resistors are examined with resistance-temperature characteristics test and overload test similar to those of Example 1.
FIG. 10 is a thus obtained graph illustrating the relation between the thermal conductivity of solder coated electrode leads and the electrical resistance change. Table 10 shows the testing results.
TABLE 10
Thermal conductivity Applied Wattage at 20°C 5watt 10 15 20 25 a 0.93 cal/cm.sec.°C NB NB NB B B b 0.53 NB NB NB B B. c 0.40 NB NB NB NB NB d 0.35 NB NB NB NB NB e 0.26 NB NB NB NB NB f 0.17 NB NB NB NB NB g 0.10 NB NB NB NB NB h 0.06 NB NB NB NB NB
the load life test is carried out in a manner similar to that described in MIL-STD-202.
FIG. 11 is a thus obtained graph illustrating the relation between the loading time in load life and the electrical resistance change.
As apparent from these results, the electrical resistance change increases with a decrease in the thermal conductivity. An abrupt increase in the electrical resistance change is observed with solder coated electrode leads having a thermal conductivity of 0.4 cal/cm.sec.°C or less. However, if the thermal conductivity is less than 0.1, the resistor (FIG. 11 h) shows a resistance change of move than 10 percent maximum after applying the rated voltage for intervals of 1.5 hours followed by a rest interval of 0.5 hours at 70°C for continuous 1,000 hours. Furthermore, it is known that the thermal conductivity hardly changes with the change of temperature at measurement. Therefore, best results can be obtained by using the two solder coated electrode leads having thermal conductivity of 0.1 to 0.4 cal/cm.sec.°C.
This invention relates to a nonflammable composition resistor.
A conventional composition resistor comprises a resistor body having finely divided conducting powder and silica powder dispersed in a resin. Such resistor, however, has a disadvantage as explained below. When a current larger than the rated value (e.g., at a wattage of 1.5 times the ratted wattage) flows through the resistor, the resistor is rapidly heated by well known Joule-heating. Because of the heat, the resistance of the resistor decreases. Because of this decrease of resistance, the current flowing through the resistor increases, and so the resistor is more heated by Joule-heating. Due to this vicious circle, the resistor finally gets short-circuited, arc occurs, or the resistor burns or gets charred or softened. Accordingly, it has been a great problem to provide a composition resistor which is free from above mentioned disadvantage even if the resistor is operated under a serious overload such as a wattage of 50 times the rated wattage at a temperature of 70°C for 7 hours.
SUMMARY OF THE INVENTION
An object of the invention is to provide a nonflammable composition resistor which is free from arcing, burning, charring or mechanical damage and exhibits an irreversible extreme increase of the electrical resistance, when operated under a overload condition such as a wattage of from 5 to 50 times rated wattage.
Another object of the invention is to provide a nonflammable composition resistor which has extremely high stability with respect to the electrical resistance and other electrical properties such as humidity, load life and current noise characteristics, particularly when operated in a normal conditions for which the resistors are designed.
These objects are provided by a nonflammable composition resistor comprising a resistor body consisting essentially of finely divided conducting powder, silica powder and an additive powder dispersed in resin, said additive powder having a transforming temperature in the range from Tg°C to (Tg+200)°C wherein Tg°C is a glass forming temperature of said resin.
Details of the invention will be apparent upon consideration of the following descriptions taken with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a nonflammable composition resistor according to the present invention, including partially exaggeratedly enlarged sectional views.
FIG. 2 is a graph illustrating the relation between the heating temperature and the change of weight of additive powders.
FIG. 3 is a graph illustrating the relation between the heating temperature and the electrical resistance as a function of the weight ratio of anthraquinone powder.
FIG. 4 is a graph illustrating the relation between the weight ratio of anthraquinone powder and maximum electrical resistance.
FIG. 5 is a graph illustrating the relation between the time exposed to humidity and the electrical resistance change.
FIG. 6 is a graph illustrating the relation between the heating temperature and electrical resistance.
FIG. 7 is a graph illustrating the relating between the heating temperature and electrical resistance.
FIG. 8 is a graph illustrating the relation between an average particle size of a conducting powder and electrical resistance.
FIG. 9 is a graph illustrating the relation between the heating temperature and the electrical resistance, as a function of an average particle size of conducting powder.
FIG. 10 is a graph illustrating the relation between the thermal conductivity of electrode leads and rising rate of electrical resistance.
FIG. 11 is a graph illustrating the relation between the loading time in load life and the resistance change.
FIG. 12 is a graph illustrating the relation between the heating temperature and the change of weight of anthraquinone powder to determine the transforming temperature of anthraquinone.
FIG. 13 is a graph illustrating the relation between the temperature and the coefficient of linear thermal expansion of phenol resin to determine the glass transition temperature of phenol resin.
Before proceeding with a detailed description of the invention, the construction of a nonflammable composition resistor contemplated by this invention will be explained with reference to FIG. 1. Reference numeral 1 designates a resistor body having finely divided conducting powder 4, silica powder 5 and additive powder 6 in resin 7. The resistor body 1 can have any suitable shape, but FIG. 1 shows the case when the resistor body has substantially the shape of cylinder. A pair of solder coated electrodes 3 are embedded in the ends of the nonflammable composition resistor. Reference numeral 2 designates an outer sleeve which includes finely divided silica powder 8 dispersed in a further resin 9 and which can be used to envelop said resistor body 1. The feature of the invention is in that said additive powder 6 has a transforming temperature in the range from Tg°C to (Tg+200)°C wherein Tg°C is a glass transition temperature of said resin 7. Broadly speaking, the word "transforming temperature" of the additive powder as used in the present application means a temperature below which an increase of temperature causes a small decrease of the weight of the additive powder, but above which an increase of temperature causes a great decrease of the weight of the additive powder. The decrease of the weight of the additive powder is caused by vaporization, decomposition or sublimation of the additive powder. Further, the word "glass transition temperature" of the resin as used in the present application means a temperature above which the resin gets to a glassy state. However, precise definition of "transforming temperature" and "glass transition temperature" will be described later.
A nonflammable composition resistor according to the present invention is in an extremely high stability with respect to the electrical resistance and other electrical properties such as humidity, load life and current noise characteristics, particularly when operated in a normal conditions for which the resistors are designed. Furthermore, if the composition resistor is placed under an overlaod of e.g., 5 to 50 times rated wattage at a temperature of 70°C, there occurs initially a substantial increase in current flowing through the resistor, and due to the I 2 R factor, the resistor of the present invention is heated to a temperature over the transforming temperature of the additive powder. This causes the resistance of the resistor body to increase about 5 to 100 times the initial electrical resistance thereof irreversibly. The phrase "to increase irreversibly" means that the increased electrical resistance does not decrease even after the resistor body is cooled to the initial temperature such as room temperature.
The mechanism of the irreversible increase in the electrical resistance of the resistor body of the present invention can be presumed as follows. When an overload is applied to the resistor body, the resistor body is heated over a critical temperature so that the additive powder dispersed in the resistor body emits gas therefrom. The electrical conduction of the resistor body attributes to a chain of conduction paths of the conducting powder surrounded by resin, and the heat of the resistor body is mainly due to the contacts between the particles of the conducting powder. In other words, such phenomena as described above occur within a kind of sealed structure. Accordingly, the vapor pressure of the above mentioned gas from the additive powder becomes very high. If the resistor body has then a temperature of the glass transition temperature or higher of the resin which acts as a binder in the resistor body, the resin greatly loses its elasticity so that the particles of the conducting powder are greatly separated from each other by the high pressure gas from the additive powder. This mentioned mechanism is presumably the reason for the irreversible and remarkable increase in the electrical resistance of the resistor body.
Thus, before-mentioned vicious circle between the increase of Joule heat and the decrease of electrical resistance as occuring in a conventional composition resistor does not occur in the composition resistor of the present invention. The resistor body stays in a stable and safe equilibrium state after the resistance has been increased. Accordingly, the composition resistor of the present invention may act as a fuse. Thus, the present resistor is free from arcing, burning, charring or mechanical damage.
In making nonflammable composition resistors according to the present invention, a mixture of finely divided conducting powder such as carbon black or graphite powder, silica powder and any suitable additive powder in available resin is well mixed at a temperature of 50°C to 100°C by any suitable and available hot rolling method until it acquires the proper plasticity. The conducting powder can be not only carbon black or graphite powder, but also metal or metal alloys, or mixtures thereof. The additive powder can be any suitable organic substance selected from the group consisting of carbocyclic compounds and heterocyclic compounds. In the Examples which will be described later, anthracene, anthraquinone, 1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchlorpentacyclodecane and copper phthalocyanine are exemplified.
The suitable resin can be a thermosetting binder, such as phenol resin, urea resin, melamine resin epoxy resin and mixtures thereof.
An operable composition of the mixture is 5 to 50 weight (percent) of conducting powder, 0 to 70 weight percent of silica powder, 5 to 70 weight percent of additive powder and the balance of resin.
An operable average particle size of said finely divided silica powder ranges from about 0.3 to 20 microns.
An operable average particle size of said finely divided carbon black or graphite powder ranges from about 0.08 to 150 microns to obtain nonflammable carbon composition resistors. The average particle size referred to herein is determined by a well known electron microscope method, for example, described in a literature of J. Soc. Chem. Ind. 62, 374 (1943); Nature, 17, 350 (1953).
After being cooled to room temperature, the mixture is crushed and ground into granules as a starting material for the resistor body. A mixture of finely divided silica powder in available resin is well mixed at a temperature of 50°C to 100°C by any suitable and available hot rolling method until it acquires the proper plasticity. An operable composition of the mixture is 75 to 89 weight percent of silica powder, and the balance of resin.
After being cooled to room temperature, the mixture is crushed and ground into granules to form the starting material for the outer sleeve.
A unitary body having the resistor body enveloped by the outer sleeve is formed by any suitable and available method, for example, by an extrusion method or a pressing method. In an extrusion method, the aforesaid two mixtures in granule form are preheated and are simultaneously supplied to a nozzle for extrusion. The extruded body is in a long cylindrical form and is cut into many short cylinders having the desired length. In a pressing method, the resistor body and the outer sleeve are seperately formed by pressing and then are combined together to form a short cylinder by any suitable method. The short cylinder is provided, at both ends, with two solder coated electrode leads having a thermal conductivity of 0.1 to 0.4 cal/cm, sec. °C, by any suitable method.
For example, the short cylinder is inserted in a molding die, heated to a temperature of 150°C to 200°C, and then is pressed by two punches having two solder coated electrode leads inserted therein. A pressing pressure of 400 to 1,000 Kg per sq. cm. is applied for a time period of 30 to 180 seconds to embed the two electrode leads in the short cylinder. The suitable electrode leads can be made of copper-cromium alloy, copper clad iron, brass, iron or bronze. If necessary, the finished resistor is further heated at a temperature of 130°C to 170°C for 5 to 48 hours to obtain more stable electrical properties.
It has been discovered according to the present invention that when said additive powder for said resistor body has a transforming temperature in the range from Tg° C to (Tg+200)°C, wherein Tg is the glass transition temperature of the resin the resistor body, the resultant resistor is free from arcing, burning, charring or mechanical damage and exhibits an irreversible and extreme increase in its electrical resistance. Said additive powder, for example, anthraquinone powder is in a high purity of 99.7 to 99.9 weight percent of pure anthraquinone and the balance of moisture content.
The transforming temperature of the additive powder such as anthraquinone powder is measured by using the thermogravimetric analyzing apparatus (RIKAGAKU Denki Co. Ltd: No. 8001) in advance of adding the conducting powder to the resistor body.
About 20 milligram of anthraquinone powder is weighed accurately in a 0.5 ml of platinum crucible, and is heated to a range of between 20°C to 400°C at a heating rate of 5°C/min., until anthraquinone powder is allowed to transform (i.e., vaporize, decompose or subline) completely. The change of weight of anthraquinone powder increases according to the increase in the heating temperature. An abrupt increase in the change of weight is observed with anthraquinone powder heated at temperature of 230°C. The temperature 230°C is determined as follows. FIG. 12 shows a graph illustrating the relation between the heating temperature and the change of weight of the anthraquinone powder. Referring to FIG. 12, the curve consists of a first segment which is substantially straight (heating temperature: 180°-200°C), curve (heating temperature: 200°-238°C), and a second segment which is substantially straight (heating temperature: 238-243°C). The dotted lines (i) and (ii) are prologations of the first and the second segments, respectively. The temperature at the crossing point P of the two dotted lines is the above mentioned temperature 230°C. This temperature 230°C is defined as the transforming temperature of anthraquinone powder. The transforming temperatures of other additive powders are defined in the same manner. FIG. 2 is an exemplary graph for illustrating the relation between the heating temperature and the change of weight of various additive powders, and Table 1 lists the transforming temperatures of these additive powders.
TABLE 1
Additive powder Transforming temperature (°C) A Anthraquinone 230 B Anthracene 165 C 1-nitro- 182 anthraquinone D Terephthalic acid 300 E p-terphenyl 225 F Phenolphthalein 300 G Carbazole 170 H Perchloro- 240 pentacyclodecone I Copper phthalocyanine 370
As a general rule, a glass transition temperature Tg° C is dependent on kinds of resin and kinds and quantity of hardener. A glass transition temperature of said resin obtained for the nonflammable composition resistors is obtained from the coefficient of linear thermal expansion test. FIG. 13 shows the manner of determining the glass transition temperature of phenol resin. When a phenol resin having a length l at room temperature is heated gradually, the length of the phenol resin increases to l+ Δl according to the increase of the temperature of phenol resin. The coefficient of linear thermal expansion is defined as Δl/l × 10 3 . FIG. 13 shows the relation between the coefficient of linear thermal expansion and the temperature of the phenol resin. The glass transition temperature of the phenol resin is determined as a crossing point of two substantially straight segments of the obtained curve, in the same manner as in determining the above mentioned transforming temperature. The dotted lines of FIG. 13 are therefore prolongations of the two segments. The glass transition temperature of phenol resin thus obtained is within the range of 140°C to 150°C. This range attributes to errors in measuring. The glass transition temperatures of other resins are defined in the same manner.
Glass transition temperatures of various resins are listed in Table 2.
TABLE 2
kinds of resins manufacturer glass transition temperature (TG°C) Phenol resin Matsushita Denko 140° - 150°C Co., Urea resin Matsushita Denko 130° - 140°C Co., melanine resin Matsushita Denko 135° - 145°C Co., epoxy resin Epikote 828* Shell 180° - 190°C Co., (Hardener DDS) * trade name
EXAMPLE 1.
Anthraquinone powder is used as an additive powder. The anthraquinone powder in a purity of 99.9 weight percent is obtained by grinding crystalline anthraquinone in a dry ball mill. The obtained anthraquinone powder pass through a-100 Mesh screen. Graphite powder is used as a conducting powder. The used graphite powder is in an average particle size of 50 microns. The used finely divided silica powder is in an average particle size of 10 microns. A mixture of 0 to 85 weight percent of anthrachinone powder, 5 weight percent of graphite powder, 10 weight percent of phenol resin and the balance of silica powder is prepared as shown in Table 3 and is mixed well at 70°C by a hot rolling machine. The mixture is cooled and crushed into granules having a particle size of 5 to 30 mesh. Another granules of mixture of 80 weight percent of silica powder and 20 weight percent of phenol resin is prepared in a way similar to that described above. ------------------------------------------------------------ --------------- TABLE 3
phenol graphite Anthraquinone silica powder resin powder powder ____________________________________________________________ ______________ weight (%) weight (%) weight (%) weight (%) a 10 5 0 85 b 10 5 2 83 c 10 5 5 80 d 10 5 20 65 e 10 5 50 35 f 10 5 70 15 g 10 5 85 0 ____________________________________________________________ ______________
TABLE 4
Anthraquinone Applied wattage current noise 3 powder 1/2 W 2W 5W 10W 15W (μV/V) a 0 weight (%) 1 NB 2 BB B B 0.25 b 2 NB B B B B 0.25 c 5 NB NB NB NB NB 0.25 d 20 NB NB NB NB NB 0.30 e 50 NB NB NB NB NB 0.30 f 70 NB NB NB NB NB 0.30 g 85 NB NB NB NB NB 0.30 1 NB: When resistors are tested as described above, arc, burning or charring does not occur. 2 B: When resistors are tested as described above, arc, burning or charring occurs. 3 Measured utilizing Quan-Tech Labs Resistor Noise Test Set Model 315.
Both kinds of granules are charged into a conventional extrusion press to form plural short cylinders each having a resistor body enveloped by an outer sleeve. The nozzle part of the extrusion machine is heated to 90°C. Each of the short cylinders is provided at each ends with solder coated electrode leads by a well known punching method operated at 180°C for 3 minutes at a pressure of 500 kg/cm 2 . The short cylinders each having two solder coated electrode leads embedded in the ends thereof are heated at a 150°C for 8 hours to form stable resistors. The resultant resistors (Type 1/2 watt) have nominal resistance value of 1.0 kΩ at a room temperature.
These resistors are examined with respect to resistance temperature characteristics test, overload life test, humidity test and current noise level test. Resistance-temperature characteristics test is carried out in a manner similar to that described in MIL-STD-202 at ambient temperatures of 25°C, 65°C, 105°C, 150°C, 180°C, 210°C, 230°C, 260°C, 300°C, 350°C and 400°C. That is, the resistors are kept under each of the ambient temperatures to bring the resistors to each of the ambient temperatures. The resistors are kept of the temperature for 2 minutes, and then the resistances thereof are measured.
Overload test is carried out in a manner similar to that described in MIL-STD-202. In accordance with MIL-STD-202, on overload in excess of 1.0 to 50 times the rated wattage is applied at a temperature of 70°C for 7 hours. Adequate precaution is taken to maintain constant voltage on resistors under test. After test, the resistors are examined whether they are free from arcing, burning, charing or mechanical damage.
The humidity and current noise characteristics tests are carried out in a manner similar to that described in MIL-STD-202.
FIG. 3 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance value as a function of weight ratio of anthraquinone powder FIG. 4(I) is a thus obtained graph illustrating a relation between the weight (percent) of anthraquinone powder and the maximum electrical resistance.
Table 4 shows these testing results in which a (no anthraquinone powder) corresponds to a conventional composition resistor.
FIG. 5 is thus obtained graph illustrating a relation between the time exposed to humidity and the electrical resistance change of the resistors.
As apparent from FIG. 3, FIG. 4 and Table 4. a better result can be obtained by 3 to 70 weight percent of anthrachinone powder as an additive powder. Furthermore, it is apparent from FIG. 5 that the composition resistor of the present invention is about the same as a conventional composition resistor with respect to the characteristics of the electrical resistance change vs. time for the resistor to be exposed to humidity.
EXAMPLE 2.
Four kinds of resistors are prepared in a manner similar to that of Example 1. Finely divided carbazole powder and copper phthalocyanine powder are used as additive powders. These powders are dispersed in resins. The resins are phenol resin and epoxy resin. The composition of each mixtures are substantially the same as those of Example 1, except some conditions for making composition resistors as shown in Table 5.
TABLE 5. ##SPC1##
These resistors are subjected to the tests similar to those of Example 1. FIG. 6 is a thus obtained graph illustrating relation between the heating temperature and electrical resistance. Table 6 shows the tasting results. As apparent from these results, it is possible to determine the temperature at which the resistance value suddenly increases by suitably selecting both the glass transition temperature of used resin and the transforming temperature of used additive powder.
TABLE 6
Kinds of Applied Wattage resistors 0.5watt 2 5 10 15 25 Type 1 NB NB NB NB NB B Type 2 NB B B B B B Type 3 NB B B B B B Type 4 NB NB NB NB NB B
the best result can be obtained by using the additive powders having transforming temperature in the range from Tg°C to (Tg+200)°C, wherein Tg°C is a glass transition temperature of the resin in the resistor body.
EXAMPLE 3
Mixtures of 0 to 85 weight percent of additive powder, 5 weight percent of conducting powder, 10 weight percent of resin and the balance of silica powder are prepared in a manner similar to that of Example 1. The used finely divided additive powders are anthracene,1-nitroanthraquinone, terephthalic acid, p-terphenyl, phenolphthalein, carbazole, perchloropentacyclodecane and copper phthalocyanine, as listed in Table 7. The used conducting powder is carbon black, and the used resin is phenol resin.
Composition resistors are prepared from these mixtures in a manner similar to that of Example 1. These resistors are subjected to the tests similar to those of Example 1.
FIG. 4 (II) is a thus obtained graph illustrating a relation between the weight ratio of additive powder and maximum electrical resistance.
FIG. 7 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance. Table 7 shows the overload testing results. ##SPC2##
As apparent from FIG. 4(II), FIG. 7 and Table 7, best results can be obtained by using the additive powders having a transforming temperature in the range from Tg°C to (Tg+200)°C, wherein Tg°C is a glass transition temperature of used resin, and by using 3 to 70 percent by weight of said additive powder.
EXAMPLE 4
Mixtures of 20 weight percent of additive powder, 5 to 20 weight percent of conducting powder, 15 weight percent of resin and the balance of silica powder are prepared. The used additive powder is anthraquinone, and the used resin is phenol resin. The used conducting powders are carbon black and graphite powder having various average particle sizes as shown in Table 8. 14 kinds of resistors are prepared in a manner similar to that of Example 1 as shown in Table 8. The resultant resistors (type 1/2 watt) have nominal electrical resistance of 10 Ω at room temperature. The composition resistors thus made are subjected to the tests similar to those of Example 1.
FIG. 8 is a thus obtained graph illustrating a relation between an average particle size of conductive powders and the electrical resistance.
FIG. 9 is a thus obtained graph illustrating a relation between the heating temperature and the electrical resistance as a function of an average particle size of conductive powder. ##SPC3##
Table 8 shows the overload testing results. As apparent from FIG. 8, FIG. 9 and Table 8, better results can be obtained by using conducting powder of an average particle size of 0.080 to 150 microns, and the best results are obtained by using phenol resin as the resin, anthraquinone as the additive powder and carbon black having an average particle size of 0.080 to 0.24 micron as the conducting powder.
EXAMPLE 5
Eight kinds of composition resistors are prepared in a manner similar to test of Example 1. Solder coated electrode leads are used which have various thermal conductivities of 0.06 to 0.93 (cal/cm.sec.°C at 20°C). The kinds of electrode leads used are copper, aluminum, copper-chromium alloy, copper clad iron, brass, iron and bronze, as shown in Table 9.
TABLE 9
thermal kinds of electrode conductivity composition leads (at 20°C) a Copper 0.93 cal/ cm.sec..degree .C b Aluminum 0.53 c Copper-chromium Cr: 0.4 0.9wt(%) 0.40 alloy d Copper clad iron 0.35 e Brass Cu: 67%, Zn: 33% 0.26 f Iron 0.17 g Bronze (1) Cu: 90%, Sn: 10% 0.10 h Bronze (2) Cu: 75%, Sn: 25% 0.06
The composition of each resistor body are exactly the same as those of Example 1 (Table 3 (d) ). The resultant resistors (Type 1/2 watt) have nominal electrical resistance of 1.0 kΩ at a room temperature. These resistors are examined with resistance-temperature characteristics test and overload test similar to those of Example 1.
FIG. 10 is a thus obtained graph illustrating the relation between the thermal conductivity of solder coated electrode leads and the electrical resistance change. Table 10 shows the testing results.
TABLE 10
Thermal conductivity Applied Wattage at 20°C 5watt 10 15 20 25 a 0.93 cal/cm.sec.°C NB NB NB B B b 0.53 NB NB NB B B. c 0.40 NB NB NB NB NB d 0.35 NB NB NB NB NB e 0.26 NB NB NB NB NB f 0.17 NB NB NB NB NB g 0.10 NB NB NB NB NB h 0.06 NB NB NB NB NB
the load life test is carried out in a manner similar to that described in MIL-STD-202.
FIG. 11 is a thus obtained graph illustrating the relation between the loading time in load life and the electrical resistance change.
As apparent from these results, the electrical resistance change increases with a decrease in the thermal conductivity. An abrupt increase in the electrical resistance change is observed with solder coated electrode leads having a thermal conductivity of 0.4 cal/cm.sec.°C or less. However, if the thermal conductivity is less than 0.1, the resistor (FIG. 11 h) shows a resistance change of move than 10 percent maximum after applying the rated voltage for intervals of 1.5 hours followed by a rest interval of 0.5 hours at 70°C for continuous 1,000 hours. Furthermore, it is known that the thermal conductivity hardly changes with the change of temperature at measurement. Therefore, best results can be obtained by using the two solder coated electrode leads having thermal conductivity of 0.1 to 0.4 cal/cm.sec.°C.