JPH0128487B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a method for manufacturing a voltage nonlinear resistor that maintains a high nonlinear coefficient α and high reliability and can obtain any desired rise voltage without changing the varistor composition, sintered body thickness, or sintering conditions. Regarding. In recent years, with the rapid development of semiconductor elements and circuits such as ICs, transistors, and thyristors, and their applications, the use of semiconductor elements and circuits in measurement control equipment, communication equipment, and power equipment has become widespread, and the miniaturization of these equipment has increased. , high performance is progressing rapidly. However, the voltage resistance, surge resistance, and noise resistance of these devices and their components are not necessarily sufficient. Therefore, protecting these devices and components from abnormal surges and noise and stabilizing circuit voltages have become extremely important issues. To achieve this goal, a zinc oxide varistor has been developed as an excellent varistor. The voltage-current characteristics of a varistor are generally expressed by the following relationship: I=(V/C). Here, V is the voltage applied to the varistor and I is the current flowing through the varistor. Further, C is a constant corresponding to the voltage when a given current is passed. Here, instead of expressing the varistor characteristics by C and α, it will be expressed by the rising voltage V1mA at 1 mA and α. α is a nonlinear coefficient, and α=1 is an ordinary resistor that follows Ohm's law, and it can be said that the larger α is, the better the nonlinearity is. The zinc oxide varistor has V1mA
A variety of values are manufactured. If the rising voltage at a sintered body thickness of 1 mm is V1mA/mm, approximately V1mA/mm=22V, 40V, 100V,
Four types of 200V varistors are manufactured. In these zinc oxide varistors having V1mA/mm, V1mA/mm is determined by the size of zinc oxide crystal grains within the sintered body. In order to obtain a low V1mA/mm, this crystal grain must be grown large, and
In order to obtain a high V1mA/mm, it is necessary to suppress the growth of crystal grains. Therefore, on the premise of the above contents, it is possible to have a high non-linear coefficient α and high reliability, and to achieve the desired V1mA/mm.
Conventionally, the following methods have been considered as means for obtaining a zinc oxide-based varistor with In other words, the types of varistor compositions and their ratios should be changed, the sintering conditions should be changed, the thickness of the compact forming the sintered body should be changed, or these elements should be combined. It is. However, if these measures are implemented;
The manufacturing conditions are complicated, and this method cannot be said to be suitable as an industrial manufacturing method, resulting in many practical problems. The present invention was completed after various studies in order to solve the above-mentioned problems.The present invention has been completed by carrying out various studies to solve the above-mentioned problems. By suppressing the movement of grain boundaries and suppressing the growth of zinc oxide crystal grains by the presence of foreign particles made of boride, a high nonlinear coefficient α and high reliability are maintained, and any rising voltage V1mA/mm is maintained. It is an object of the present invention to provide a method for manufacturing a voltage nonlinear resistor that allows a varistor to be obtained. Hereinafter, the present invention will be explained in detail. That is, zinc oxide as the main component constituting the varistor composition and MgO, Bi ₂ O ₃ as additives,
Sb ₂ O ₃ , CoO, MnO, Cr ₂ O ₃ , Fe ₂ O ₃ , Al ₂ O ₃ ,
SiO ₂ , TiO ₂ , SnO ₂ , CuO, BaO, CaO, NiO,
PbO, B ₂ O ₃ , MoO ₃ , Li ₂ O, V ₂ O ₅ , ZrO ₂ ,
A predetermined amount of other metal oxides such as In ₂ O ₃ , _{WO 3} , Ta 2 O ₅ , SrO, Ga ₂ O ₃ , GeO ₂ is weighed out, and mixed and ground in a ball mill for several hours to form a slurry. Thereafter, this slurry contains ZrB, which does not react with the varistor composition during the sintering process and remains as foreign particles at the zinc oxide grain boundaries in the sintered body.
Impurities consisting of borides such as WB, TiB ₂ , MoB, TaB, NbB, or VB ₂ are mixed in and dispersed in a predetermined amount without being crushed. Next, after drying this mixture, for example, polyvinyl alcohol is added and granulated, after which it is formed into a predetermined shape and sintered at a high temperature of 1000 to 1450°C, so that the zinc oxide crystal grain boundaries in the sintered body are granulated. It is made in such a way that foreign particles made of boride are present. In this case, the impurity consisting of boride mixed in to make foreign particles exist in the zinc oxide crystal grain boundaries is not mixed and pulverized with the varistor composition at the same time, for example, because it is weighed at the same time as the varistor composition characteristic raw material, If these raw materials are mixed and ground into a slurry at any time, impurities will be ground into fine particles during the grinding process, and will react with the varistor composition during the sintering process (altering the varistor composition due to the same effect as additives). This is because the particles cannot exist as foreign particles at the zinc oxide grain boundaries of the sintered body, making it impossible to achieve the object of the present invention. Further, in this case, the particle size of the impurity made of the boride is not controlled by any special means and is in a general raw material state. Next, explanation will be given based on specific experimental results. First, V1mA/mm=22V, 40V, 100V, 200V
Table 1 shows the results of examining the manufacturing conditions of the embodiment according to the present invention and the conventional reference example in which no impurities are mixed when obtaining each varistor. In Examples (A), (B), and (C) shown in Table 1, the composition of the varistor composition and the sintering temperature were kept constant, and the amount of impurities made of boride was appropriately selected. The relationship between the voltage (V1 mA/mm) and the number of foreign particles in 1 cm ³ of the sintered body existing at the zinc oxide grain boundaries of the sintered body is clarified. The molded bodies (before sintering) used as samples were disk-shaped in both Examples and Reference Examples with a diameter of 15 mm and a thickness of 1 mm. Note that foreign particles present in the zinc oxide grain boundaries of the sintered body were confirmed using an electron microscope. Furthermore, the number of foreign particles present at the zinc oxide crystal grain boundaries was calculated using the following formula for calculating the weight (W) of impurities mixed into the slurry. W=N×ρ ₂ ×4/3π(D/-/2) ³ ×10 ^-12 ×W _G
K/ρ ₁ The above equation was obtained by substituting the equation into the equation obtained by the following procedure. That is, when the number of foreign particles in 1 cm ³ of the sintered body is N and the specific gravity of impurities is ρ ₂ , the weight per 1 cm ³ of the sintered body is N×ρ ₂ ×4/3π (D/-/2) ³ ×10 ^-12 ...Formula is the average particle amount of impurities The required weight of the varistor composition to constitute 1 ^cm3 of sintered body is W _G ×K=W _S ...Formula W _G is the weight of the varistor composition K is the sintered The weight loss series W _S is the weight of the sintered body. Here, the volume of the sintered body (V _S ) is calculated by dividing the formula by the specific gravity of the sintered body (ρ ₁ ). W _S /ρ ₁ =V _S W _S =V _S・ρ ₁ ...Formula Substitute into the equation W _G ×K=V _S・ρ ₁ V _S =W _G K／ρ ₁ ...Formula Now, in the equation The required impurity weight (W) is determined by multiplying by the volume of the sintered body. W=N×ρ ₂ ×4/3π(D/-/2) ³ ×10 ^-12 ×V _S
……formula

[Table] As is clear from Table 1, any rising voltage
In order to obtain a V1 mA/mm varistor, in the conventional example, when the thickness of the molded body was kept constant, the varistor composition and sintering temperature had to be changed each time, making the process complicated and making it difficult to use as an industrial manufacturing method. On the other hand, in Examples (A), (B), and (C), foreign particles made of boride are allowed to exist in the zinc oxide grain boundaries of the sintered body without changing the varistor composition or sintering temperature. By simply changing the number of
It can be seen that an extremely simple method of simply mixing a predetermined boride impurity corresponding to the desired V1mA/mm into the slurry of the varistor composition is sufficient. The above will become clearer from the experimental results described below. That is, as a result of investigating the change in the average grain size of zinc oxide crystal particles and the change in V1mA/mm when the number of foreign particles existing in the zinc oxide crystal grain boundaries of the sintered body was changed, the results shown in Figs. 1 and 2 It was as shown in the figure. As is clear from Figures 1 and 2, the growth of zinc oxide crystal grains can be suppressed depending on the abundance of foreign particles present at the zinc oxide grain boundaries of the sintered body, and therefore V1mA/mm can be set arbitrarily. It can be seen that it can be controlled. Next, V1mA/mm of the reference example and Example (A) in Table 1
The nonlinear coefficient α and current waveform corresponding to are 8 × 20 μs.
V1m when applying 1000A impact current 10 times
The results of comparing the rate of change in rising voltage corresponding to A/mm were as shown in FIGS. 3 and 4. According to this, in Example (A), the desired number of foreign particles is made to exist at the zinc oxide grain boundaries of the sintered body without changing the varistor composition and sintering temperature.
It can be seen that a varistor with the same characteristics as the reference example can be obtained by simply changing the amount of impurity made of boride. In addition, if the number of foreign particles existing in the zinc oxide grain boundaries of the sintered body is less than 10 ⁵ /cm ³ , it is difficult to maintain V1mA/mm = 22V by keeping the varistor composition and sintering conditions constant. Furthermore, it has been experimentally confirmed that if the number exceeds 2×10 ⁷ pieces/cm ³ , the sinterability of the sintered body is poor, which is contrary to the spirit of the present invention. As described in detail above, according to the present invention, foreign particles made of desired boride are added to the zinc oxide grain boundaries without changing complicated manufacturing conditions such as the varistor composition, sintering temperature, or compact thickness. A voltage that maintains a high nonlinear coefficient α and high reliability by suppressing the movement of grain boundaries and suppressing the growth of zinc oxide crystal grains, and provides a varistor with an arbitrary rise voltage of V1mA/mm. A method for manufacturing a non-linear resistor can be obtained.

[Brief explanation of drawings]

Figure 1 is a curve diagram showing the average particle size of zinc oxide crystal particles versus the amount of foreign particles present, Figure 2 is a curve diagram showing the change in V1mA/mm versus the amount of foreign particles present, and Figure 3 is a curve diagram showing V1mA/mm. FIG. 4 is a curve diagram showing a comparison of the rate of change in the rising voltage with respect to V1 mA/mm when an impact current is applied.

Claims (1)

[Scope of Claims] 1. A means for preparing a slurry by mixing and pulverizing a varistor composition comprising zinc oxide as a main component and adding several other metal oxides, and adding the varistor composition to this slurry in a sintering process. means for mixing and dispersing an impurity consisting of a boride that does not react with the zinc oxide grain boundary of the sintered body and exists as foreign particles until the end;
A method for producing a voltage nonlinear resistor, comprising means for forming and sintering this mixture to obtain a sintered body. 2 Borides include ZrB, WB, TiB ₂ , MoB, TaB,
The method for manufacturing a voltage nonlinear resistor according to claim 1, wherein the voltage nonlinear resistor is made of NbB or _VB2 . 3. The voltage according to claim 1 or 2, characterized in that the amount of impurities mixed in is such that the number of foreign particles in 1 cm ³ of the sintered body is 10 ⁵ to 2 × 10 ⁷ . A method of manufacturing a nonlinear resistor.