JPH0252408B2 - - Google Patents

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to a method of manufacturing a laminated ceramic baritas with an improved means for forming internal electrodes. (Prior Art) Generally, the surge resistance of a ceramic varistor is approximately proportional to the effective area (area of opposing electrodes) when the ceramic varistors have the same composition. Therefore, various types of laminated ceramic varistors have been proposed to provide a large surge resistance without increasing the size of the varistor body. The initial technology for laminated ceramic varistors was disclosed in Japanese Patent Application Laid-open No. 18849/1984.
A pair of electrodes are formed on both the front and back surfaces of a plate-shaped sintered body that has been sintered in advance, and varistor elements, which are continuous with the electrodes and have a lead-out part formed on a part of the side surface, are stacked so as to be connected in parallel, and between the contact electrodes. are connected via adhesive, and since the electrode parts other than the electrode lead-out part are exposed to the outside, they are coated with an exterior resin to protect them. However, the structure described above requires a lot of effort in the lamination work, and it is difficult to protect it from the external environment, as well as the thickness of the sintered body itself.
Since it is difficult to reduce the thickness to 0.3 mm or less, there is a limit to the varistor voltage, which naturally limits its applications. For this reason, there is a method disclosed in Japanese Patent Laid-Open No. 106894/1983 to eliminate these drawbacks. This technology prints internal electrodes on green sheets formed using the doctor blade method, stacks them up, presses them, and sinters them, so that the parts other than the parts where the internal electrodes are taken out to the outside are surrounded by a sintered body. This is effective in that it can eliminate the above drawbacks. However, in the case of a varistor whose main component is zinc oxide, 1) Since it is necessary to sinter at a temperature of 1100℃ or higher, the internal electrode material must be mainly composed of gold, platinum, and palladium, which makes the electrode material expensive and increases the cost. . 2) Sintering temperature
Because the temperature is above 110℃, varistors containing bismuth oxide and praseodymium oxide react with the internal electrodes, which are mainly made of palladium, and corrode the electrodes, resulting in the problem of not being able to secure the electrode thickness or area. . 3) Therefore, the composition of a varistor with this structure should not contain any bismuth oxide or praseodymium oxide.
It needs to be in an extremely small amount of less than mol%, but this would result in extremely inferior characteristics such as nonlinearity, surge resistance, load life, and environmental resistance compared to varistors currently in practical use, and the level required by the market. It is difficult to obtain the characteristics of 4) The element body and internal electrodes are 110
Since simultaneous firing is performed at a high temperature of ℃ or higher, it is necessary to control the amount of diffusion of the constituent elements of the internal electrodes into the varistor sintered body, making compositional design difficult. 5) The coefficient of linear expansion of the internal electrode metal is one order of magnitude larger than that of the varistor sintered body, so if it is exposed to high temperatures during use, there is a risk of stress concentrating on the internal electrode margin due to expansion of the electrode metal and causing cracks. There were many problems that needed to be solved. Under the above circumstances, the technique disclosed in Japanese Patent Application Laid-open No. 1501/1983 has been disclosed for the purpose of eliminating the drawback 1) above, that is, the cost increase factor due to the use of expensive noble metals as internal electrode materials. The technology disclosed in this publication involves stacking and pressurizing ceramic varistor green bodies on which a paste-like substance made of a material that is burnt out by firing or dissolved by solvent is printed, followed by heat treatment or solvent treatment. This is a method of manufacturing a laminated ceramic varistor, in which the paste material is removed and then sintered, and the voids formed in layers are filled with conductive paint to form electrodes. However, such technology requires the use of conductive paint for the external electrodes that lead out the electrodes from the internal electrodes, which have high electrical resistance and generate heat when a surge current flows, causing the conductive paint to peel off from the ceramic. Due to the high resistance value of the conductive paint, the limiting voltage characteristics are very poor. Because conductive paint is used for the internal electrodes, when used at high temperatures for a long period of time, the organic substances contained in the paint will carbonize, making it impossible to maintain contact with the thin layer of varistor material, causing electrical discharge on the contact surface, and the carbonized organic substances deteriorating. However, the varistor material was partially reduced, the leakage current increased, the varistor material self-heated, and eventually thermal runaway occurred, resulting in destruction, and it lacked reliability. (Problems to be solved by the invention) As described above, in the conventionally disclosed technology,
It had various drawbacks and could not be put to practical use. The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for manufacturing a laminated ceramic varistor that not only facilitates workability and contributes to cost reduction, but also exhibits excellent characteristics. [Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a laminated ceramic varistor of the present invention provides a method for manufacturing a laminated ceramic varistor that includes fired particles having the same composition as the varistor composition, carbon particles, a thermoplastic resin, and a volatile component on the surface. Means for obtaining a formed sheet laminate by printing and drying a slit precursor paste, forming a plurality of slit precursor films, and laminating a plurality of molded sheets in such a way that one end of the slit precursor film alternately protrudes toward the opposite side, and bonding them under heat. , means for cutting the sheet molded body into predetermined dimensions to obtain unfired chips in which the ends of the slit precursor film are alternately led out from the opposing surface; and sintering the unfired chips at a gradually elevated temperature to form the slit precursor. A means for obtaining a sintered chip in which volatile components of a film are removed and a slit having a plurality of columnar ceramic particles is formed in this part, and a porous external electrode having continuous pores on the slit outlet surface of the sintered chip. The method is characterized in that it comprises means for forming internal electrodes by preheating the molten metal, then immersing it in the molten metal, depressurizing it, and pressurizing it, and then pressing the molten metal into the slit and slowly cooling it. (Function) According to the above configuration, since there is no internal electrode during the sintering process, there is no mutual reaction between the varistor composition and the internal electrode material, and any composition can be easily laminated, making it a composition that can be applied to laminated ceramic varistors. is expanded. In addition, the columnar ceramic particles formed within the slits cause the laminated layers of the molded sheets to fit together, thereby preventing cracks in the internal electrode margins due to thermal stress.
Furthermore, since the internal electrodes are not baked, the range of use of internal electrode materials is greatly expanded without being limited to expensive noble metals such as gold, platinum, and palladium. (Example) An example of the present invention will be described in detail below.
First, calcined powder with a composition consisting of various metal oxides is ground in a ball mill using water as a solvent, mixed, and dried. Ethyl cellulose and toluene are added to the dry powder and stirred and mixed to form a uniform mixture. obtain. Thereafter, air is removed from this mixture, and a ceramic green sheet is formed using a doctor blade method, followed by drying to obtain a formed sheet. Next, as shown in FIG. 2, fired particles, carbon particles, which are made of the same composition as that of the molded sheet 1, have been sintered in advance, and have a predetermined size (5 to 100μ) are placed on the surface of the molded sheet 1, as shown in FIG. A plurality of slit precursor films 2 are formed by printing and drying a slit precursor paste composed of an acrylic thermoplastic resin and a volatile solvent such as toluene or acetone. As shown in FIG. 3, using a molded sheet 1 on which a plurality of slit precursor films 2 are formed, a plurality of slit precursor films 2 are laminated in such a way that one end of the slit precursor films 2 alternately protrude toward the opposite side, and then heat-pressed and molded. A sheet laminate 3 is obtained. In this case, a molded sheet is used on which the slit precursor film is not formed on the uppermost surface. Next, the formed sheet laminate 3 is cut along the dotted line, and as shown in FIGS.
As shown in the figure, green chips 4 are obtained in which the ends of the slit precursor films 2 are alternately led out to opposing surfaces. Next, the unfired chips 4 are heated to 300 to 650°C at a heating rate of 1 to 20°C for 1 hour, and held at 300 to 650°C for 2 to 15 hours to form the carbon particles constituting the slit precursor film 2. and volatile solvents are decomposed and removed, and then 50 ~
The temperature was raised to 1000-1400°C at a heating rate of 200°C for 1 hour, and sintered at 1000-1400°C for 3.5-4.5 hours to bond the slit precursor film 2 to the laminated sheet 1 as shown in Figure 6. A sintered chip 7 is obtained in which a slit 6 having a plurality of ceramic columnar particles 5 formed therein is formed. As shown in FIG.
For example, a porous silver paste having continuous pores is coated on both end faces from which the slit 6 leads out, and after drying, the porous external electrode 8 is formed by baking at 500 to 650°C. It is made of at least one metal or an alloy containing at least one of Pb and Sn as a main component and at least one of Ag, Al, Cu, and Zn, and the melting point is lower than the melting point of the lowest metal oxide constituting the molded sheet 1. The container containing the molten metal is immersed in molten metal, the pressure of the container containing the molten metal is reduced, and then pressure is applied to force the molten metal into the slit 6 through the porous external electrode 8, and the molten metal is then slowly cooled to form the slit. The porous external electrode 8 and the connected internal electrode 9 are formed in the internal electrode 6 . According to the method for manufacturing the laminated ceramic varistor configured as described above, the internal electrodes 9 are not exposed to the sintering temperature accompanied by high temperatures, so the factor of mutual reaction between the varistor composition and the internal electrode material is eliminated. There is no restriction on the usable varistor composition range, and a laminated ceramic varistor that can satisfy the desired characteristics without deterioration of characteristics can be obtained no matter what composition is used. Further, the slit precursor film 2 includes ceramic particles having the same composition as the varistor composition, and in the sintering process, the ceramic particles become ceramic columnar particles 5, and the laminated layers of the molded sheet 1 are bonded through the ceramic columnar particles 5. Therefore, even if there is heat stress applied during subsequent processes or during use as a finished product, there is no risk of cracks occurring in the margin portion of the internal electrode 9, and in combination with the above-mentioned effects, the conventional example Reliability is significantly improved compared to that of Furthermore, the internal electrodes 9 are formed by press-fitting through the pores of the porous external electrodes 8 into the slits 6 previously formed between the laminated layers of the molded sheets 1 constituting the sintered chip 7, and are heated to high temperatures. Since it is not exposed to the accompanying sintering temperature, it has the advantage of being able to use inexpensive metals without being limited to expensive noble metals such as gold, platinum, and palladium, which can contribute to cost reduction. Next, an example of comparison between an example obtained by the present invention and a reference example obtained by the prior art will be described. Example 1 Composition - Both the present invention and the reference example have zinc oxide as the main component, Bi, Pr, La, Sb, Cr, Mg, Co, Mn, Ni
respectively Bi ₂ O ₃ , Pr ₆ O ₁₁ , La ₂ O ₃ , Sb ₂ O ₃ , Cr ₂ O ₃ ,
It was calculated as MgO, CoO, MnO, and NiO, and consisted of four composition ratios shown in the table below.

[Table] However, the glasses in Table 1 above are SiO ₂ , 2.O, B ₂ O ₃ 9.
It consists of O, ZnO 16.5, and PbO 72.5 ^wt %, and the values are weight % relative to zinc oxide. Green sheet composition - Mix each of the barista raw materials shown in Table 1 above and water using a resin pot and partially stabilized zirconia balls for 6 hours, and after drying
After calcining at ℃ for 2 hours, the calcined raw material and water were crushed again for 16 hours using a resin pot and partially stabilized zirconia balls, and 100 parts by weight of the dried crushed raw material was mixed with trichloroethylene, ethyl alcohol, polyvinyl butyral, and polyethylene. Four types of ceramic green sheets were obtained by adding 20 parts by weight of glycol and mixing the slurry for 24 hours using a resin pot and a resin ball, then deaerating it and using the doctor blade method. Present invention A Molded sheet...The above configuration. Slit precursor paste... *10 parts by weight of fired particles each having a varistor composition of 26 to 37 μm. *40 parts by weight of carbon particles smaller than the fired particle diameter. *Polymethyl methacrylate resin, toluene, 50 parts by weight of octyl phthalate. Molded sheet laminate pressurizing conditions...85℃100g/ ^cm2 ,
1 minute. Slit forming conditions: heating rate of 15°C for 1 hour
After raising the temperature to 600℃, hold at 600℃ for 4 hours - Allow to cool. Sintering conditions: 1150℃ at a heating rate of 100℃ for 1 hour
After raising the temperature to 1150℃, hold it for 4 hours and let it cool. Internal electrode material and forming conditions...Pb70%, Sn30
% The alloy is melted in a container held at 280°C, which is higher than the melting point of the alloy. After depressurizing the container, 15 atm was applied. Reference example B: Japanese Patent Application Laid-Open No. 1983-1983 described in the section (prior art) above
106894, using a molded sheet having the configuration shown in Table 1 above, printing Pd paste on the molded sheet, forming internal electrodes, laminating, cutting, and sintering at 1150°C. Apply Ag paste to both ends and bake at 600℃ to form external electrodes. In addition,
The laminated ceramic baritas has a thickness of 200 μm per layer in both Examples and Reference Examples, a portion facing the internal electrodes of 3 mm x 5 mm, an external dimension of 5 mm x 7 mm, and the number of laminated layers is 10. The results of examining various properties of Invention A and Reference Example B are shown in Table 2.

[Table] In Table 2 above, α (nonlinear coefficient) is the value at V ₁₀ A−V ₁ mA, and LC is the value when a DC voltage of V ₁ mA1/2 is applied. As is clear from Table 2, the present invention is significantly superior to the reference example in terms of nonlinear characteristics, LC characteristics, and voltage-current characteristics. This is due to a diffusion reaction that changes the original composition of the varistor, and corrosion of the internal electrode material. The sample numbers in Table 2 correspond to the sample numbers in Table 1 showing the composition, and the numerical values are the average values of 50 samples for each sample. Example 2 The present invention A using sample No. 1 shown in Table 2 of the above (Example 1) and the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 1501-1980 described in the section of the above-mentioned (Prior Art) Figures 8 and 8 show the results of comparing the rate of change of V ₁ mA in reference example B obtained and the limiting voltage characteristic V ₁₀ A/V ₁ mA value when the DC maximum allowable circuit voltage was applied for 500 hours in an 85°C atmosphere. The results are as shown in Table 3. The composition of Reference Example B was the same as that of Invention A, and the burned-out material was polyvinyl alcohol paste, and the electrodes were made of conductive paint.

[Table] As is clear from Figure 8 and Table 3, Reference Example B
The limiting voltage characteristics were extremely poor and the reliability was also poor, demonstrating the superiority of the present invention A. In the above example, the varistor composition was explained using zinc oxide as the main component.
Needless to say, it can be applied to materials mainly composed of SrTiO ₃ or other metal oxides such as perovskite type. Further, as shown in FIG. 7, if the slit 6 of the sintered chip 7 is impregnated with a solution such as silver nitrate, a coating film 10 is formed in the slit 6 when the porous external electrode 8 is baked. This is effective because the wettability between the molded sheet 2 and the internal electrode 9 formed by the molten metal press-fitted through the external electrode 8 is improved. [Effects of the Invention] As described above, according to the present invention, it is possible to obtain a method for manufacturing a laminated ceramic varistor of high practical value, which is easy to manufacture and exhibits excellent varistor characteristics regardless of the varistor composition.

[Brief explanation of drawings]

1 to 6 are for explaining a method of manufacturing a laminated ceramic varistor according to an embodiment of the present invention. FIG. 2 is a perspective view showing a molded sheet on which a slit precursor film has been formed, FIG. 3 is a sectional view showing a molded sheet laminate formed by laminating a plurality of molded sheets, and FIGS. 4 and 5.
The figure shows an unfired chip obtained by cutting the formed sheet laminate shown in Fig. 3. Fig. 4 is a perspective view, Fig. 5 is a cross-sectional view taken along the line E-A in Fig. 4, and Fig. 6 shows a slit. FIG. 7 is a cross-sectional view showing the formed sintered chip, and FIG. 7 is a partially cutaway view showing the multilayer ceramic varistor after internal electrodes are formed, for explaining a method for manufacturing a multilayer ceramic varistor according to another embodiment of the present invention. The enlarged sectional view, FIG. 8, is a time-V ₁ mA rate of change characteristic curve. 1... Molded sheet, 2... Slit precursor film, 3
... Molded sheet laminate, 4 ... Unfired chips, 5
...Ceramic columnar particles, 6...Slits, 7...
... Sintered compact chip, 8 ... Porous external electrode, 9 ...
Internal electrode, 10... coating film.

Claims (1)

[Scope of Claims] 1. A means for drying a molded ceramic green sheet containing a metal oxide as a main component to obtain a molded sheet, and adding fired particles and carbon particles having the same composition as that constituting the sheet on the molded sheet. means for printing and drying a slit precursor paste made of a thermoplastic resin and a volatile solvent to form a plurality of slit precursor films, and laminating the plurality of molded sheets so that one end of the slit precursor films alternately protrudes to the opposite side. −
a means for obtaining a formed sheet laminate by heat-pressing; a means for cutting the formed sheet laminate to obtain unfired chips in which the ends of the slit precursor film are alternately led out to opposing surfaces; and a means for gradually raising the unfired chips. A means for obtaining a sintered chip in which carbon particles and volatile components constituting the slit precursor film are removed by high temperature and high humidity sintering, and slits having a plurality of ceramic columnar particles are formed in the slit precursor film; The method comprises means for forming a porous external electrode having continuous pores on the slit exit surface of the solid chip, and means for press-fitting molten metal into the slit through the porous external electrode to form an internal electrode. A method of manufacturing a laminated ceramic varistor characterized by the following. 2 The molten metal contains at least one of Pb and Sn, or at least one of Pb and Sn as a main component, and Ag,
2. The method for producing a laminated ceramic baritas according to claim 1, characterized in that the multilayer ceramic baritas contains at least one of Al, Cu, and Zn. 3. A method for manufacturing a laminated ceramic varistor according to claim 1 or 2, characterized in that the slit is impregnated with a metal solution and a coating film is formed on the inner wall of the slit during baking of the porous external electrode.