JP2948933B2 - Composition for thermistor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition for an NTC thermistor for detecting temperature, and more particularly to a thermistor for realizing a highly reliable thermistor having a small change in resistance with time. To a composition for use. 2. Description of the Related Art A conventional NTC thermistor for temperature detection is:
A composition composed of a metal oxide selected such that the total molar ratio of two or three transition metal elements such as manganese, nickel, cobalt and the like becomes 100%, manganese, nickel, copper, iron, chromium Or a composition comprising an oxide such as (for example, see Japanese Patent Publication No. 58-26803),
For example, a composition comprising an oxide containing three kinds of metals, manganese, nickel and aluminum, is used (for example, Japanese Patent Publication No. 63-35085). However, although these compositions have versatility in characteristics, they cannot provide a material having a high specific resistance and a high B constant, or have a rate of change in the resistance value which changes with time. Had the disadvantage of being large. [0004] In particular, as the operating temperature range is expanded, high specific resistance and high B constant characteristics are provided, and the resistance value changes with time.
That is, a highly reliable thermistor composition having a small resistance value change rate has been required, and the conventional composition cannot satisfy them. [0005] In particular, with respect to the rate of change in resistance, which is a change with time in resistance, the rate of change in resistance of a conventional composition comprising an oxide of manganese, nickel, copper, iron, chromium, etc. is 1%.
The change with time in a constant temperature of 50 ° C. is practical,
At a high temperature of ℃, the change with time is large. Further, compositions comprising oxides of manganese, nickel and aluminum can be used for high temperatures, however, they are not practical in the low temperature range of -50.degree. C. and 3000 hours at high temperatures. The aging characteristics over a long period of time were not satisfactory. Accordingly, an object of the present invention is to have a stable characteristic with a small rate of change in resistance in a wide operating temperature range,
An object of the present invention is to provide a thermistor composition having high specific resistance and high B constant characteristics. Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies and found that manganese: 10 to 9
Three kinds of metal elements containing 0 mol%, nickel: 0.01 to 80 mol%, and aluminum: 0.01 to 50 mol% are mixed to form a metal oxide having a total mixing molar ratio of 100%, and chromium oxide: 0.01 to It has been found that a composition to which 30.0% by weight of iron oxide: 0.01 to 60.0% by weight is added can obtain a highly reliable thermistor having high specific resistance and high B constant characteristics and a small rate of change in resistance value. Was. By using the thermistor composition of the present invention, the thermistor operating temperature range (-50 to +500)
Thermistor characteristics required in ° C.), i.e., the value of 4000~6000K was obtained as a value and B constant of about 10 ³ ~10 ⁷ Ω · cm as a specific resistance value. Furthermore, the composition for a thermistor of the present invention can be fired by a ceramic, and has a very small variation in the substrate resistance of 3% or less, and a variation of the resistance of the formed thermistor at 300.degree. The rate of change in resistance after the passage of time is very small. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the composition of the main metal element will be described. In general, the specific resistance and the B constant of a manganese, nickel and aluminum thermistor can be controlled over a wide range by changing the ratio of each element. However, the composition range that can be used is limited in consideration of the characteristic value of the thermistor in the operating temperature range of the thermistor (for example, −50 ° C. to + 500 ° C.) and the compatibility with the used circuit. That is, the specific resistance in the thermistor operating temperature range is 10 ³ to 10 ⁷ Ω · cm, and the B constant is 4000 to 1000.
It is required that 6000 K be obtained, that ceramic firing be possible, that the base resistance variation is small and that the coefficient of variation be 3% or less, that the resistance value of the thermistor change over time be small, and that it be highly reliable. Table 1 shows the composition of manganese, nickel, and aluminum and the electrical characteristics of the thermistor made of the composition, the specific resistance at 25 ° C., the B constant, and the coefficient of variation. Coefficient of variation = (standard deviation value / mean value) × 100 (%) Next, an embodiment of the present invention will be described. As starting materials, high-purity manganese tetroxide, nickel oxide, aluminum oxide, chromium oxide, and iron oxide are each weighed so that the composition after firing becomes the composition shown in Table 2. [Table 2] The weighed starting materials are wet-mixed in a ball mill for 20 hours. 1 parts of wet mixed starting material
After being dried at 00 to 200 ° C., it is temporarily calcined at 900 to 1100 ° C. for 2 hours, and this calcined material is turned into fine powder by a pulverizer. An appropriate binder such as pure water or PVA (polyvinyl alcohol) is added to the fine powder and mixed and granulated to prepare granules. The granules are 55 mm in diameter and 2 in thickness.
A molded body formed by pressure molding with a molding machine into a disk shape of about 0 mm is finally fired at a temperature of 1200 to 1500 ° C. The fired ingot sintered body is sliced and cut into a wafer. The wafer is lapped and polished to a thickness of, for example, 0.25 mm. After the electrodes are formed on the wafer with a noble metal paste such as Au, Ag, Pd-Ag or the like, the wafer is cut with a dicing saw to obtain chips of, for example, □ 0.40 mm. This thermistor chip is housed in a glass tube, sandwiched with slag leads from both sides, and sealed with a glass sealing machine to obtain a glass-sealed NTC thermistor. The electrical characteristics of each thermistor element thus obtained are measured. That is, it is a B constant between these temperatures calculated from the specific resistance (ρ25) at 25 ° C. and the resistance values at 25 ° C. and 85 ° C. Further, in order to examine the change with time of the thermistor element, the rate of change in resistance value after holding at high temperature storage condition: 300 ° C. for 3000 hours is also measured. Table 2 shows the results. Samples in Table 2
No. is the same as that of Table 1, and the same number is the same composition. The sample Nos. Marked with x are in the composition range other than the examples of the present invention, and are shown for comparison with the present invention. In Table 2, iron oxide Fe ₂ O ₃ ,
The purity of chromium oxide Cr ₂ O ₃ is 4N. Resistance change rate = (Rt−Ro) / Ro × 100 (%) where, Rt: resistance value after t time Ro: initial resistance value As is clear from Table 2, the thermistor element of the present invention has a specific resistance. Value is 10 ³ to 10 ⁷ Ω · cm, B constant is 4
A high specific resistance of 000 to 6000K and a high B constant can be obtained, and the change with time of the thermistor resistance value is as small as 4% or less. Next, the reasons for limiting the composition of the present invention will be described. The manganese content is less than 10 mol% and the nickel content is less than 0.1%.
When the content is less than 01 mol% and the content of aluminum is less than 0.01 mol%, the change over time in the resistance value becomes large. If the manganese content exceeds 90 mol%, the required thermistor characteristics are not satisfied, the base resistance variation increases, and the variation coefficient exceeds 3%. When the content of nickel exceeds 80 mol%, the required thermistor characteristics are not satisfied, the variation in the base resistance increases, and the coefficient of variation exceeds 3%. When the content of aluminum exceeds 50 mol%, the required thermistor characteristics are not satisfied, the variation in the base resistance increases, and the coefficient of variation exceeds 3%. If the addition amount of iron oxide is less than 0.01% by weight, the rate of change of the resistance value is remarkably deteriorated (for example, see Sample Nos. 3, 7, 8, 9, and 10 in Table 2). When the amount of iron oxide exceeds 60.0% by weight,
Characteristics of the formed element, that is, specific resistance at 25 ° C., B
The constant and the rate of change of the resistance value are not different from those of the composition within the range of the present invention, but the sinterability of the substrate is deteriorated, the variation of the substrate resistance is increased, and the coefficient of variation is increased. (For example, sample No. 3-6 in Table 2)
7-6, 8-6, 9-6, and 10-6). If the addition amount of chromium oxide is less than 0.01% by weight, the change of the resistance value of the thermistor with time deteriorates, and the rate of change of the resistance value increases (for example, sample Nos. 3, 7, and
8, 9, 10). If the amount of chromium oxide exceeds 30.0% by weight, the characteristics of the formed device, that is, the specific resistance at 25 ° C., the B constant, and the rate of change of the resistance value are not different from those of the composition within the range of the present invention. However, the sinterability of the substrate deteriorates, the variation in the substrate resistance increases, and the coefficient of variation increases, so that the yield of the manufactured device deteriorates (for example, sample No.
-6, 7-6, 8-6, 9-6, and 10-6). The composition for a thermistor according to the present invention provides a thermistor having a high specific resistance and a high B constant at a temperature of -50 ° C. to + 500 ° C.
In a wide operating temperature range. Further, the change of the resistance value of the thermistor with time is small, and even after 3000 hours at 300 ° C., the change rate of the resistance value is less than 4%. Therefore, a highly reliable thermistor can be realized. In particular, not only can it be used for home electric appliances and NTC thermistors for temperature detection used in the field of automobiles, but also widely used in various fields. Can be provided.

Claims (1)

(57) [Claims] Three kinds of metal elements including manganese: 10 to 90 mol%, nickel: 0.01 to 80 mol%, and aluminum: 0.01 to 50 mol% are mixed, and the total mixing molar ratio is 100. %. A composition for a thermistor, characterized in that chromium oxide: 0.01 to 30.0% by weight and iron oxide: 0.01 to 60.0% by weight, respectively, are added to the metal oxide.