Non-linear resistance element, and method for manufacturing the same

The present invention relates to a non-linear resistance element used in an overvoltage protection device such as a lightning arrester, a surge absorbing element, a voltage stabilizing element, etc., and whose resistance value changes depending on an applied voltage containing zinc oxide as a main component, and a method for manufacturing the same.

A non-linear resistance element generally called a varistor has a characteristic that its resistance value changes depending on an applied voltage, that is, it has a high resistance value when a normal voltage is applied and exhibits an insulating characteristic, and an abnormally high voltage is generated. It has a non-linear voltage-current characteristic that shows a low resistance value when applied. Among the nonlinear resistance elements having such characteristics, the nonlinear resistance element containing zinc oxide as a main component has excellent non-linear voltage-current characteristics.

This nonlinear resistance element is manufactured by, for example, the following method. That is, a large amount of zinc oxide, which is the main component, and a small amount of basic additives such as bismuth oxide, antimony oxide, cobalt oxide, and manganese oxide that exhibit non-linear voltage-current characteristics are wet-mixed and wet-mixed. The slurry obtained in the above step is granulated by spray drying, the granulated powder is formed into a columnar shape, and then the molded body is fired to produce a ceramic sintered body. Then, a side surface high resistance layer for preventing flashing is formed on the side surface of the ceramic sintered body by applying and baking a glass material, and heat treatment is performed as necessary, and further, the upper and lower end surfaces of the ceramic sintered body are subjected to heat treatment. Electrodes are formed by spraying aluminum or the like (see, for example, Patent Document 1).

<p><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2003-59705</text></patcit></p>

<p> By the way, in the conventional nonlinear resistance element, the varistor voltage can be controlled by changing the thickness of the ceramic sintered body, and the energy withstand capacity can be controlled by changing the volume of the ceramic sintered body. For example, in order to obtain a nonlinear resistance element having a low varistor voltage while maintaining a high energy withstand capacity, it can be realized by reducing the plate thickness of the sintered body and increasing the area of the sintered body.</p><p> However, since the conventional non-linear resistance element is composed of an integrally fired ceramics sintered body, when the area of the ceramics sintered body is increased, the sintered body is deformed due to thermal deformation during firing or the like. There was a problem that it was easy to do. Further, since the ceramic sintered body is fragile to an external force, the ceramic sintered body having an increased area may be damaged by an external force generated during transportation or mounting, which is problematic in terms of durability and reliability. was there.</p><p> Further, in the conventional production of a non-linear resistance element, a columnar molded body which is a base of a ceramic sintered body is fired, but when the molded body is manufactured, friction between granulated powders and formation are performed. Due to friction between the granules and the mold, it was difficult to ensure the uniformity of the molding density in the molded product.</p><p> Further, in addition to the non-uniformity of the molding density due to the mold molding, when the molded body is fired, a temperature difference occurs between the inside and the surface portion of the molded body, so that the composition or microstructure in the sintered body It becomes difficult to further ensure uniform uniformity. In particular, when the element shape is very large, for example, a disk having a diameter of 10 cm or more, or a square plate having a size comparable to this, it is difficult to manufacture with a conventional non-linear resistance element, and the composition of the sintered body. There is a problem that the non-uniformity of the target and the microstructure is remarkably increased and the electrical characteristics are extremely lowered.</p><p> Therefore, the present invention has been proposed in view of such problems, and an object of the present invention is to increase the area of the ceramic sintered body while increasing the overall structural properties of the varistor layer. An object of the present invention is to provide a non-linear resistance element capable of improving quality and, by extension, homogenizing electrical characteristics such as non-linear resistance characteristics, and a method for manufacturing the same.</p>

<p> The nonlinear resistance element of the present invention is a nonlinear resistance element composed of a varistor layer formed in a sheet shape and a conductive electrode layer bonded to each of the front surface and the back surface parallel to each other of the varistor layer. The varistor layer is composed of a plurality of varistor pieces made of ceramic sintered bodies arranged apart from each other so that the front surface and the back surface of the varistor layer correspond to the front surface and the back surface of the varistor layer, respectively. It is made of an elastic synthetic resin and is formed of a joint made of an insulating synthetic resin that joins adjacent varistor pieces together, and the joint is thicker than the thickness at the joint interface with the varistor pieces. It is characterized by having a small portion.</p><p> According to the nonlinear resistance element of the present invention, a plurality of varistor pieces having a constant thickness are placed on the same plane (so that the front surface and the back surface of the varistor pieces coincide with each other on the front surface and the back surface of the varistor layer). They are joined by an insulating joint in a state where they are arranged apart from each other. Therefore, the area of the sheet-shaped varistor layer can be easily increased.</p><p> Further, the molded body piece that is the base of each varistor piece can be miniaturized to the extent that the firing conditions including the firing temperature are the same on the inside and outside of the molded body piece at the time of firing. Therefore, in each varistor piece of the ceramic sintered body obtained as a result of the firing, the structural properties such as the crystal grain size can be homogenized on the inside and the outside.</p><p> As a result, compared to the case where the varistor layer is integrally fired as in the conventional case, the area of the varistor layer is increased, while the overall structural properties of the varistor layer are homogenized, and thus the non-linear resistance. It is easy to homogenize electrical characteristics such as characteristics.</p><p> The joint is made of an elastic synthetic resin. According to this, since the joint portion is elastically deformed, even if an external force is applied to the varistor layer, the entire varistor layer is more likely to bend as compared with the varistor layer made of an integral ceramic sintered body. This improves the resistance of the varistor layer to external forces. The joint portion has a portion having a thickness smaller than the thickness at the joint interface with the varistor small piece. According to this, the joint portion is made of an elastically deformable synthetic resin and has a portion having a thickness smaller than the joint interface with the varistor small piece. Therefore, the flexibility of the varistor layer is increased as compared with the case where the connecting portion of the varistor layer has a constant thickness.</p><p> In the present invention, it is preferable that a plurality of the varistor layer and the electrode layer are alternately laminated in the perpendicular direction of each of the front surface and the back surface of the varistor layer. According to this, the varistor voltage of the entire element can be easily adjusted only by changing the number of layers.</p><p> In the present invention, it is preferable that the electrode layer is provided with metal fittings for electrical connection with others. As a result, the nonlinear resistance element is easily connected to the circuit board or the like.</p><p> In the present invention, it is preferable to coat both end faces of the varistor layer and the electrode layer with a coating resin material. As a result, the outer peripheral end face of the varistor layer is protected.</p><p> The method for manufacturing a single-layer non-linear resistance element according to the first aspect of the present invention includes a step of firing a plurality of molded body pieces that are the basis of ceramics to form a plurality of the varistor pieces, each of which has the same thickness. By kneading and extruding the plurality of the varistor pieces and the insulating resin, the plurality of varistors are formed so that the front surface and the back surface of the varistor pieces match the front surface and the back surface of the varistor layer, respectively. The step of forming the sheet-shaped varistor layer in which the small pieces are arranged so as to be separated from each other and the adjacent varistor pieces are bonded to each other via the insulating resin, and the front surface and the back surface of the varistor layer, respectively. It is characterized by including a step of forming the conductive electrode layer to be bonded to the electrode layer.</p><p> The method for manufacturing a single-layer non-linear resistance element according to the second aspect of the present invention includes a step of firing a compact piece which is a base of a plurality of ceramics to form the plurality of varistor pieces having the same thickness. , The plurality of varistor pieces are arranged in the same plane with the plurality of varistor pieces separated from each other in the mold, and then an insulating synthetic resin is injected into the gaps between the plurality of varistor pieces to form a sheet-like varistor layer. It is characterized by including a step of forming the conductive electrode layer bonded to each of the front surface and the back surface of the varistor layer.</p><p> The method for manufacturing a laminated non-linear resistance element according to the first aspect of the present invention includes a step of firing a plurality of molded body pieces that are the basis of ceramics to form a plurality of the varistor pieces having the same thickness. By kneading and extruding the plurality of the varistor pieces and the insulating resin, the plurality of varistor pieces are formed so that the front surface and the back surface of the varistor pieces match each of the front surface and the back surface of the varistor layer. A step of forming the sheet-shaped varistor layer in which the varistor pieces are arranged so as to be separated from each other and the adjacent varistor pieces are bonded to each other via the insulating resin, and the varistor layer and the conductive electrode layer. A step of alternately laminating a plurality of the varistor layers in the perpendicular direction of the front surface and the back surface of the varistor layer to form a laminate, and the electrode layer bonded to each of the front surface and the back surface of the laminate. It is characterized by being manufactured by a forming process.</p><p> The method for manufacturing a laminated non-linear resistance element according to the second aspect of the present invention includes a step of firing a plurality of molded body pieces that are the basis of ceramics to form the plurality of varistor pieces having the same thickness. The plurality of varistor pieces are arranged in the same plane with the plurality of varistor pieces separated from each other in the mold, and then the insulating synthetic resin is injected into the gaps between the plurality of varistor pieces to form the sheet-shaped varistor layer. A step of alternately laminating a plurality of the varistor layer and the conductive electrode layer in the perpendicular direction of each of the front surface and the back surface of the varistor layer to form a laminate, and a surface of the laminate. It is characterized by including a step of forming the electrode layer to be bonded to each of the back surface and the back surface.</p>

<figref num="1">It is sectional drawing which shows the whole structure of the single layer type nonlinear resistance element in 1st Embodiment of this invention.</figref><figref num="2">It is a flowchart which shows the manufacturing process of the single-layer type nonlinear resistance element of FIG.</figref><figref num="3">It is sectional drawing which shows the whole structure of the laminated type nonlinear resistance element in 2nd Embodiment of this invention.</figref><figref num="4">It is a flowchart which shows the manufacturing process of the laminated type nonlinear resistance element of FIG.</figref><figref num="5">It is sectional drawing which shows the whole structure of the nonlinear resistance element in the 3rd Embodiment of this invention.</figref><figref num="6">It is sectional drawing which shows the junction of the nonlinear resistance element in 4th Embodiment of this invention.</figref><figref num="7">It is explanatory drawing which shows the state in which the nonlinear resistance element of FIG. 6 is spirally wound.</figref>

The first embodiment of the nonlinear resistance element according to the present invention will be described in detail below with reference to FIGS. 1 and 2.

As shown in FIG. 1, the single-layer non-linear resistance element 10 in the first embodiment is made of a ceramic sintered body containing zinc oxide (ZnO) as a main component, and has a plurality of varistor small pieces 11 having a constant thickness. A varistor layer 13 formed into a sheet by individually adhering at an insulating joint 12 in a state of being juxtaposed on the same plane, and an electrode layer made of a conductive material and adhered on the main surface of the varistor layer 13. It is composed of 14. The side surface of the varistor layer 13 is protected by the coating resin material 16 over the entire circumference.

The non-linear resistance element 10 containing zinc oxide as a main component has a constant thickness having parallel planes without stacking the varistor small pieces 11 in the direction orthogonal to the alignment direction (the perpendicular directions of the front surface and the back surface of the varistor layer 13). The varistor small pieces 11 are aligned in the vertical and horizontal directions on the same plane, the joint portion 12 is interposed only between the varistor small pieces 11, and the joint portion 12 does not exist on the front surface and the back surface of the varistor small piece 11, with respect to the electrode layer 14. Has a directly joined structure.

As shown in FIG. 2, the non-linear resistance element 10 is a step of dividing a sheet material containing zinc oxide as a main component into a predetermined size and firing the fragments to form a varistor small piece 11 having a constant thickness. (STEP 11), its varistor pieces 11, and the insulating resin are kneaded and extruded, so that a plurality of varistor pieces 11 are juxtaposed on the same plane and passed through a joint portion 12 made of an insulating resin. It consists of a step of adhering to form a sheet-shaped varistor layer 13 (STEP 12) and a step of adhering and forming an electrode layer 14 made of a conductive material on each of the main surfaces of the varistor layer 13 (STEP 13). It can be manufactured through each process.

Next, a second embodiment of the nonlinear resistance element according to the present invention will be described in detail below with reference to FIGS. 3 and 4.

As shown in FIG. 3, the laminated non-linear resistance element 20 in the second embodiment is made of a ceramic sintered body containing zinc oxide (ZnO) as a main component, and a plurality of varistor small pieces 21 having a constant thickness are identical. The varistor layer 23, which is formed into a sheet by individually adhering at the insulating joint 22 in a state of being juxtaposed on a flat surface, and the electrode layer 25 made of a conductive material are alternately laminated, and the upper and lower parts of the laminated body 27 are laminated. It is provided with a structure in which an electrode layer 24 is adhered to each of the main surfaces of the varistor layer 23 located in. The side surface of the laminated body 27 is protected by the coating resin material 26 over the entire circumference.

In each varistor layer 23 of the non-linear resistance element 20 containing zinc oxide as a main component, the varistor pieces 21 having a parallel plane and having a constant thickness are vertically and horizontally formed on the same plane without stacking the varistor pieces 21 in the direction orthogonal to the alignment direction. A structure that is aligned in the direction, the joint portion 22 is interposed only between the varistor small pieces 21, the joint portion 22 is not present on the front surface and the back surface of the varistor small piece 21, and is directly bonded to the electrode layers 24 and 25. Equipped with.

Further, the electrode layer 25 in the laminated body 27 has a function of merely performing an electrical connection between the varistor layers 23, plays a role of dissipating heat generated inside the device, and locally generates heat inside the device. In that the non-linear resistance element 20 can suppress the above-mentioned, the non-linear resistance element 20 exhibits performance superior to the conventional element in energy capacity and power charge life.

As shown in FIG. 4, the non-linear resistance element 20 is a step of dividing a sheet material containing zinc oxide as a main component into a predetermined size and firing the fragments to form a varistor small piece 21 having a constant thickness. (STEP 21), its varistor pieces 21, and the insulating resin are kneaded and extruded, so that a plurality of varistor pieces 21 are juxtaposed on the same plane and passed through a joint portion 22 made of the insulating resin. A step of adhering to form a sheet-shaped varistor layer 23 (STEP 22) and a step of alternately laminating the varistor layer 23 and an electrode layer 25 made of a conductive material to form a laminate 27 (STEP 23). It is possible to manufacture the laminate through each process including a step of adhering and forming an electrode layer 24 on each of the main surfaces of the varistor layer 23 located above and below the laminated body 27 (STEP 24).

The single-layer type nonlinear resistance element 10 and the laminated type nonlinear resistance element 20 described above are specifically manufactured in the following manner.

First, in ZnO, which is the main component, Bi₂O₃: 0.5mol%, Sb₂O₃: 1.0mol%, Co₂O₃: 0.5mol%, MnO₂: 0.5mol%, Cr₂O₃: 0.5mol%, Al (NO₃) 9H₂O: 0.01 mol% is added, a solvent and a dispersant are added and mixed, and then a binder is added to produce a slurry, and a sheet material having a thickness of 60 μm is produced by the doctor blade method. After dividing this sheet material into 0.6 mm square pieces, the pieces are fired at 1100 ° C. for 2 hours to form 0.5 mm square varistor pieces 11, 21 at a thickness of 50 μm. In addition, the varistor pieces 11 and 21 are heat-treated as needed.

By kneading the varistor pieces 11 and 21 thus obtained and the insulating resin in a fluid state and extruding, the varistor pieces 11 and 21 having a thickness of 50 μm are stacked in a direction orthogonal to the alignment direction. In a state where a plurality of varistor pieces 11 and 21 are separated from each other and juxtaposed on the same plane, they are adhered to each other via joint portions 12 and 22 made of an insulating resin to form a sheet. In the sheet-shaped molded product obtained by the tape molding method of the doctor blade method or the extrusion molding method in this way, the insulating resin adhering to the surface thereof is removed by the sandblasting method using resin beads as an abrasive. The varistor layers 13 and 23 are manufactured by.

In the above, it is explained that the varistor layers 13, 23 are manufactured by the doctor blade method or the extrusion molding method, but the manufacturing method of the varistor layers 13, 23 is not limited to this. For example, a method (injection molding or insert) in which a plurality of varistor pieces 11, 21 are arranged on the same plane with each other separated from each other in a mold, and an insulating resin is injected into a gap between the arranged varistor pieces 11, 21. Varistor layers 13, 23 may be manufactured by molding).

In the case of the single-layer type non-linear resistance element 10, a conductive paste containing silver particles and a thermoplastic resin is applied and dried on each of the main surfaces of the varistor layer 13 obtained as described above to form the electrode layer 14. The varistor layer 13 is cut into, for example, 10 mm square, and then the coating resin material 16 is adhered to the entire circumference including the cut surface, whereby the single-layer type nonlinear resistance element 10 is finally completed. To do. On the other hand, in the case of the laminated non-linear resistance element 20, the above-mentioned conductive paste is applied and dried on the main surface of the varistor layer 23 obtained as described above to form the electrode layer 25, and the plurality of varistor layers are formed. 23 are laminated and integrated by heat crimping, electrode layers 24 are formed on each of the main surfaces of the varistor layer 23 located above and below the laminated body 27, cut into 10 mm squares, and then coated resin is applied to the cut surface. By adhering the material 26, the laminated non-linear resistance element 20 is finally completed.

When manufacturing the nonlinear resistance elements 10 and 20, if it is possible to cut the varistor layer 13 or the laminated body 27 so that the varistor pieces 11 and 21 are not exposed on the cut surface, the cut surface is insulating. Since the joint portions 12 and 22 are present, it is not necessary to adhere the coating resin materials 16 and 26 described above.

Both the single-layer type nonlinear resistance element 10 and the laminated type nonlinear resistance element 20 exhibit excellent non-linearity equal to or higher than that of the conventional nonlinear resistance element. Further, as with the conventional nonlinear resistance element, the leakage current tends to decrease with time, and there is no practical problem.

As described above, the varistor layer 13, which is formed into a sheet by adhering a plurality of varistor pieces 11, 21 having a constant thickness in a state of being juxtaposed on the same plane via the joining portions 12, 22 made of an insulating resin. In No. 23, a sheet material containing zinc oxide as a main component is divided into a predetermined size, and the fragments are fired to knead the varistor pieces 11 and 21 having a certain thickness and an insulating resin for extrusion molding. It was produced by. From this, it is easy to secure the compositional uniformity, it is possible to obtain the varistor small pieces 11 and 21 having no large pores, and it is easy to secure the microstructural uniformity.

In other words, since the varistor pieces 11 and 21, which are the constituent units of the element, are manufactured by firing the fragment pieces separated from the sheet material containing zinc oxide as the main component, the firing efficiency is high and the density unevenness is also high. Since the shape is small and the shape at the time of firing is small, the temperature difference between the inside and the surface can be reduced, the residual stress in the fragment is suppressed, the shape accuracy is improved, uniform heating is easy, and the grain boundary after heat treatment is easy. The uniformity of the crystal structure of the layer can be ensured. In this way, the compositional or microstructural uniformity of the varistor pieces 11 and 21 can be ensured, so that it becomes easy to improve the basic performance including non-linearity, energy tolerance and charge life. As a result, it is possible to provide nonlinear resistance elements 10 and 20 that can greatly contribute to the expansion of design freedom, energy saving, and resource saving.

In the first and second embodiments, it is explained that the varistor pieces 11,21 are formed by firing the fragment pieces obtained by dividing the sheet-shaped molded body into small pieces. The method for forming the molded piece is not limited to this. For example, a method may be used in which a mold having an appropriate shape is filled with granulated powder, which is a base for small pieces of the molded product, and molded.

The non-linear resistance elements 10 and 20 have non-linearity and energy resistance by selecting the mixing ratio of the varistor small pieces 11 and 21 of the varistor layers 13 and 23 and the insulating resin and the manufacturing conditions of the varistor small pieces 11 and 21. In addition to the basic performance consisting of the chargeable life, it is also possible to control the electrical characteristics such as the capacitance value and its frequency characteristics, the heat dissipation characteristics and the mechanical strength, and the degree of design freedom is expanded. Here, in the laminated non-linear resistance element 20, each varistor layer 23 is laminated by combining different material compositions of the varistor small pieces 21, a mixing ratio of the varistor small pieces 21 and the insulating resin, and manufacturing conditions of the varistor small pieces 21. By doing so, the degree of freedom in design described above is expanded.

The mixing ratio of the varistor small pieces 11,21 and the insulating resin is controlled according to the element characteristics. For example, when manufacturing a small and highly durable element, the mixing ratio of the varistor small pieces 11,21 is used. If flexibility of the element is required, the compounding ratio of the varistor small pieces 11 and 21 may be decreased. In addition, as the manufacturing conditions for the varistor pieces 11,21, it is basically important to manufacture the varistor pieces 11,21 having a uniform composition and fine structure, and it is necessary to suppress density unevenness during molding and to heat during firing. Bi₂O₃In order to facilitate uniform scattering, a small and thin molded body (for example, in the case of a square, for example, 10 mm square × 2 mm thickness or less, or in the case of a circle, for example, 10 mm diameter × 2 mm thickness or less) is made into granules having a composition similar to that of a varistor. It is desirable to use a manufacturing method in which the molded product is fired while burying it in the mold or rotating the molded product to equalize the heat. Furthermore, in order to improve the performance of the device, in order to improve the compositional uniformity of the varistor pieces 11,21, a mixture of ZnO with an additive added was calcined at 800 ° C to 1000 ° C. After that, it goes without saying that it is desirable to add a binder to the crushed product to prepare a slurry and then mold it into a sheet.

To expand the degree of freedom in this design, it is possible to realize performance that could not be realized by conventional devices, that is, characteristics with low varistor voltage and excellent energy withstand capacity. Since the varistor voltage is determined by the number of grain boundaries, the thickness of the nonlinear resistance element must be reduced in order to reduce the varistor voltage. On the other hand, in order to increase the energy withstand, the volume of the nonlinear resistance element must be increased. Therefore, in order to obtain the characteristics of low varistor voltage and excellent energy withstand, it is necessary to use a large-area and thin nonlinear resistance element. Here, in the conventional non-linear resistance element, since the molded body is deformed when the molded body is sintered and shrunk during firing, when trying to make the shape thin in a large area, the deformation during shrinking becomes remarkable, and it cracks or becomes large after firing. There is a problem that mechanical strain is generated and the yield in the firing process is extremely lowered.

On the other hand, the nonlinear resistance element 10 has a structure in which the varistor layer 13 in which the varistor small pieces 11 are bonded at the insulating joint portion 12 is formed, so that the layer can be easily thinned and the area can be increased, and a large current can be supported. It is possible to design a product with excellent shape accuracy.

Since the laminated non-linear resistance element 20 is formed by laminating the varistor layer 23 whose varistor voltage is fixed, the varistor voltage of the entire element can be determined only by adjusting the number of the varistor layers 23.

The material composition of the varistor pieces 11,21 is zinc oxide, which is the main component, and Bi.₂O₃Bi₂O₃Not limited to system nonlinear resistance elements 10 and 20, Pr₆O₁₁System, BaTiO₃System, SrTiO₃System, TiO₂System, SnO₂System and Fe₃O₄The nonlinear resistance elements 10 and 20 of the system may be used. Further, in the above embodiment, it is explained that the varistor pieces 11 and 21 are made of a sintered body containing zinc oxide as a main component, but for example, non-linear electrical resistance of strontium titanate, silicon carbide, tin oxide and the like. Any ceramic having characteristics may be used.

The planar shape of the varistor pieces 11 and 21 is not limited to a square, and may be another square such as a rectangle or a polygon, an ellipse, or a circle such as a perfect circle. However, it is necessary that the varistor pieces 11 and 21 have a shape suitable for being aligned on the same plane without being stacked by a tape forming method such as a doctor blade method or an extrusion forming method. Since the alignment density of the square shape is higher than that of the circular shape, it is effective when manufacturing small-sized and high-tolerance nonlinear resistance elements 10 and 20.

In addition, the ratio of the square to the thickness to the shorter vertical or horizontal dimension (aspect ratio), and in the case of a perfect circle, the ratio of the diameter to the thickness (aspect ratio) should be large, and the aspect ratio is at least 2. The above is necessary, preferably 5 or more. When producing the varistor pieces 11 and 21, the thin sheet material can be divided into arbitrary sizes. Therefore, the sheet material may be divided so as to have the optimum aspect ratio as described above.

Further, if the size of the varistor pieces 11,21 is too small, it becomes difficult to manufacture the varistor pieces 11,21. On the contrary, if it is too large, the compositional or microstructural inhomogeneity of the varistor pieces 11 and 21 will occur, and the number of varistor pieces 11 and 21 in the non-linear resistance elements 10 and 20 will decrease, and the non-linear resistance elements 10 and 20 as a whole. Not only does the uniformity become insufficient, but it also becomes difficult to knead with the insulating resin, so it is desirable to set the range as follows.

In either case of the single-layer type nonlinear resistance element 10 or the laminated type nonlinear resistance element 20, the varistor pieces 11 and 21 suitable for aligning the varistor pieces 11 and 21 on the same plane without being stacked by the tape forming method described above are used. As for the size of 21, 21, in the case of square varistor pieces 11,21, if the shortest side dimension is 50 μm or more and the longest side dimension is 1 mm or less, preferably the shortest side dimension is 100 μm or more and the longest side dimension is 500 μm or less. Often, in the case of circular varistor pieces 11,21, the diameter may be 50 μm to 1 mm, preferably 100 to 500 μm.

Considering the above-mentioned aspect ratio, the thickness of the varistor pieces 11, 21 is about 25 to 500 μm, preferably about 50 to 200 μm. As the size of the varistor pieces 11 and 21 becomes smaller, the basic performance is improved, the characteristic variation is also reduced, and the manufacturing stability is improved. Therefore, the optimum value is selected within the above range.

By a method other than the tape forming method described above, it is also possible to arrange a plurality of varistor pieces 11, 21 on the same plane and form them into a sheet without stacking the varistor pieces 11, 21. For example, when the varistor pieces 11 and 21 are aligned using a mounting machine for small electronic components and then the insulating resin is poured into the sheet to form a sheet, the varistor pieces 11 and 21 can be handled by the mounting machine. The size may be sufficient, and in the case of the square varistor pieces 11,21, the shortest side dimension may be 0.2 mm or more and the longest side size may be 0.4 mm or more, and in the case of the circular varistor small pieces 11,21, the diameter is 0.4. It may be mm or more.

In this case, the size of the shape is restricted in order to maintain the compositional and microstructural uniformity of the varistor pieces 11,21. In the case of a square, the longest side dimension is 10 mm or less, and in the case of a circle, the diameter is 10 mm or less. preferable. Further, the varistor pieces 11 and 21 do not necessarily have to be limited to the tape molding method described above, and if the element has a small shape, it is possible to suppress variations in the density distribution during molding and the temperature distribution during firing. The method may be used.

Further, in the sheet-shaped molded product obtained by the tape molding method, the method for removing the insulating resin adhering to the surface thereof is not limited to the sandblasting method, and for example, an insulating resin is used by using an appropriate solution. A method of dissolving and removing is also effective. Furthermore, when positioning and aligning the varistor pieces 11, 21 using a mounting machine for small electronic components, a resist is used as an insulating adhesive, and the resist on the varistor pieces 11, 21 is subjected to a photoetching method. A method of removing it is also possible.

As the insulating resin for adhering the above-mentioned small varistor pieces 11 and 21, it is possible to improve the thermal properties and the electrical performance by using a resin material having excellent flame retardancy, heat resistance and thermal conductivity. it can. It is effective not only to select the resin material itself, but also to add various additives for improving flame retardancy, heat resistance and thermal conductivity. For example, the addition of oxides such as alumina, aluminum nitride, and boron nitride, non-oxides, and particles whose surface is insulated from thermally conductive particles (whether metal or non-metal compounds), and in some cases conductive particles. A small amount may be added as long as the insulating property is not deteriorated. In addition, when removing the insulating resin adhering to the surface of the sheet-shaped molded product by the sandblasting method in the element manufacturing process, the efficiency of the treatment by the sandblasting method can be improved by selecting the resin material of the insulating resin and various additives. Can be raised.

Further, for the electrode layers 14, 24, 25, a room temperature curable conductive adhesive containing silver as conductive particles or a thermosetting conductive adhesive other than that can be used. Further, as the conductive particles, copper, gold, carbon or the like can be used in addition to silver. As a method for forming the electrode layers 14, 24, 25, there are a chemical electrode forming method such as plating, a physical electrode forming method such as thin film deposition and sputtering, or a method of applying nano-sized silver particles and baking them. .. From the viewpoint of preventing burnout accidents of the nonlinear resistance elements 10 and 20, it is possible to use a resin having a fuse function as the adhesive constituting the electrode layers 14 and 24 because the resistance increases rapidly as the temperature rises. Is. In addition to providing the electrode layers 14 and 24 with a fuse function in this way, a layer composed of sintered small pieces of a positive characteristic thermistor (PTC thermistor) is applied to one or both surfaces of the nonlinear resistance elements 10 and 20. , 24 may be used for bonding.

Here, the laminated non-linear resistance element 20 has a structure in which the electrode layer 25 is interposed in the laminated body 27, and the electrode layer 25 exerts an action of dissipating heat generated inside the element and is inside the element. It is also possible to form the electrode layer 25 with a conductive resin containing an additive for improving heat resistance in that local heat generation can be suppressed. It is easy to design the thickness of the electrode layer 25 so as to improve the heat dissipation of the entire element, or to change the thickness of the electrode layer 25 for each layer and optimize it so as to suppress local heat generation.

By adopting a resin contained in the nonlinear resistance elements 10 and 20, for example, a resin having a property of discoloring by heating as an insulating resin, the presence or absence of surge voltage application and the degree of element deterioration can be visually confirmed. It can be used, and its practical value is great in determining the timing of element replacement. In this case, if the electrode layers 14 and 24 on both sides of the device are transparent electrodes such as ITO (indium tin oxide) formed by a physical electrode forming method for vapor deposition, sputtering, etc., the visual confirmation thereof becomes even easier.

Next, the third and fourth embodiments of the nonlinear resistance element according to the present invention will be described in detail below with reference to FIGS. 5 to 7.

The same components as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. The nonlinear resistance element 10 in the third and fourth embodiments differs only in the configuration of the joint portion 12 for adhering the varistor small pieces 11 in the first embodiment.

The joint portion 12 in the third embodiment is made of an insulating resin having excellent flexibility that can flex elastically in addition to flame retardancy, heat resistance, and thermal conductivity. For example, it is desirable that it is made of a synthetic resin such as a urethane-based elastomer or an olefin-based elastomer.

As a result, as shown by the arrows in FIG. 5, even if an external force is applied to the varistor layer 13, the varistor layer 13 can be bent by the elastic force of the joint portion 12, so that the external force is received by the entire varistor layer 13. Can be done. As a result, the resistance of the varistor layer 13 to external force is improved.

Further, the joint portion 12 in the fourth embodiment is made of an insulating resin having excellent flexibility as in the third embodiment, and further, as shown in FIG. 6, from the joint interface with the varistor small piece 11. A recess 121 is formed inside. The recess 121 is formed by scraping the joint portion 12 by a sandblast method or the like. When the varistor layers 13 and 23 are formed by injection molding or insert molding, a mold configured so that a recess 121 is formed in the joint portion 12 may be used.

The recess 121 is thinner than the joint interface between the varistor piece 11 and the joint 12. Therefore, the elastic force of the joint portion 12 is also increased by the joint portion 12 of the third embodiment, and the entire varistor layer 13 can be curved.

As a result, it is possible to change the form of the varistor layer 13 to fit the narrow space that could not be mounted with the conventional integrally fired ceramics sintered body. It becomes. For example, as shown in FIG. 7, a method of stacking the varistor layer 13 and the insulating sheet 3 and spirally winding them up to form a capacitor can be considered. As a result, the varistor layer 13 can be easily handled at the time of mounting, and the convenience is improved.

The shape of the recess 121 may be any shape that increases the elastic force of the joint portion 12. For example, as shown in FIG. 6 (a), it may be a square shape, or as shown in FIG. 6 (b), it may be an R shape. Further, as shown in FIG. 6C, recesses 121 may be formed on both the front and back surfaces of the joint portion 12.

Further, in the third and fourth embodiments, the single-layer type nonlinear resistance element is described, but the effect of the present invention can be obtained even with the laminated type nonlinear resistance element.

10,20 .. Non-linear resistance element, 11,21 .. Varistor piece, 12,22 .. Junction, 13,23 .. Varistor layer, 14,24,25 .. Electrode layer.