JP2016122766A - Nonlinear resistive material, and method for manufacturing nonlinear resistance part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonlinear resistive material which enables the control of zinc oxide crystal grains.SOLUTION: A nonlinear resistive material comprises: zinc oxide powder of 5-80 vol.% to its whole composition with the balance consisting of a polymer material including a thermoplastic resin and wax, and inevitable impurities. It is preferable that grains of the zinc oxide powder included in the nonlinear resistive material are spaced apart from one another to avoid their touching each other by the polymer material. Further, the thermoplastic resin accounts for 20-70 vol.% of the polymer material included in the nonlinear resistive material. It is preferable that the balance include wax.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-linear resistance material used for, for example, a surge absorbing element, a voltage stabilizing element, and the like, and a method for manufacturing a non-linear resistance component.

  A non-linear resistance material that exhibits a non-linear current-voltage characteristic that exhibits a high resistance value and exhibits insulation characteristics when a normal voltage is applied, and exhibits a low resistance value when an abnormal high voltage is applied. Widely used in surge absorbers and voltage stabilizers for surge absorption. Among such non-linear resistance materials, the non-linear resistance material mainly composed of zinc oxide is excellent in the characteristic that its resistance value changes depending on the applied voltage, that is, the varistor characteristic.

  This non-linear resistance material is manufactured by the following method, for example. Zinc oxide powder, which is the main component, and a small amount of powdery basic additives such as bismuth oxide, antimony oxide, cobalt oxide, and manganese oxide are wet mixed, and the slurry obtained by the wet mixing is granulated by spray drying. Then, the granulated powder is filled into a pressing mold and molded, and then the molded body is fired to produce a ceramic sintered body (see, for example, Patent Documents 1 and 2).

JP 2003-59705 A Japanese Patent Application Laid-Open No. 2014-123764

  In the non-linear resistance material, it is necessary to uniformly and uniformly disperse the zinc oxide crystal grains in order to suppress variations in varistor characteristics. However, the conventional non-linear resistance material has a density variation at the time of granulation, a variation in filling of the pressing mold, and a density variation at the time of molding, so that it is difficult to obtain crystal grains of uniform size. In addition, since the conventional non-linear resistance material is fired, the crystal grains of zinc oxide grow by firing, and it is very difficult to control the crystal grains of zinc oxide at the time of firing. As a result, the varistor characteristics are difficult to design.

  Further, when adjusting the varistor characteristics of the non-linear resistance material, it is common to change the thickness of the sintered body, but there are restrictions on the thickness and shape due to difficulty in processing.

  Under such circumstances, the present invention provides a non-linear resistance material in which the crystal grains of zinc oxide can be controlled, and a method for manufacturing a non-linear resistance component having excellent formability using the material. The purpose is to do.

  The non-linear resistance material of the present invention contains zinc oxide powder in an amount of 5 to 80% by volume based on the total composition of the non-linear resistance material, and the balance is composed of a polymer material consisting of a thermoplastic resin and wax and inevitable impurities, It is characterized in that zinc oxide powder is dispersed in the polymer material. Here, the polymeric material is used to bind and disperse the zinc oxide powder. For this reason, since the shape of the non-linear resistance component using the non-linear resistance material of the present invention is maintained by the polymer material, there is no need for firing that causes coarsening of crystal grains as in the prior art, and oxidation is not necessary. It is possible to configure the non-linear resistance component as a uniform and finely dispersed zinc. The zinc oxide powder is preferably separated by a polymer material so that adjacent powders do not come into contact with each other.

  In the method for producing a nonlinear resistance component of the present invention, the zinc oxide powder is added by 5 to 80% by volume of a polymer material composed of a thermoplastic resin and a wax with respect to the entire composition of the nonlinear resistance material, and is heated and kneaded. A raw material adjustment step for adjusting the raw material, a filling step for filling the raw material in a predetermined amount of the mold cavity, and a pressure forming step for pressing the raw material in the die with a punch to form a predetermined shape, An extraction step of extracting a molded body obtained after the pressure forming step.

  The polymer material added to the non-linear resistance material of the present invention can be easily removed from the mold so that a uniform fluidity of the powder in the mold is obtained and a part of the polymer material is softened or melted during extraction. It is comprised with a thermoplastic resin and wax so that it may release.

  The polymer material preferably has a thermoplastic resin ratio of 20 to 70% by volume, with the balance being wax.

  Moreover, it is preferable that the zinc oxide powder contained in the nonlinear resistance material of the present invention is a powder of 50 μm or less.

  The pressure molding step in the method for producing a nonlinear resistance component of the present invention is preferably performed at a temperature equal to or higher than the softening point of the thermoplastic resin contained in the raw material.

  Moreover, it is preferable to perform the extraction process in the manufacturing method of the nonlinear resistance component of this invention at the temperature below the softening point of the said thermoplastic resin contained in the said raw material.

  Since the non-linear resistance material of the present invention does not carry out the firing step, the crystal grains of the zinc oxide powder to be used become the crystal grains of zinc oxide in the product as they are, so that the crystal grains can be easily controlled.

  Further, modeling is facilitated even in a complicated shape due to the plasticity of the polymer material. Furthermore, the formability is improved by utilizing the normal stamping molding, and the cost can be reduced by eliminating the firing process.

It is a cross-sectional photograph (COMP image (reflection electron composition image)) of the nonlinear resistance material which is one Embodiment of this invention.

  The non-linear resistance material according to the present invention is a composite material in which zinc oxide powder is dispersed in a polymer material. In the present invention, the zinc oxide powder is dispersed in the polymer material, whereby each zinc oxide powder is separated and held, and the shape of the nonlinear resistance material is held. Zinc oxide powder is contained in an amount of 5 to 80% by volume based on the total composition of the nonlinear resistance material. If the content of the zinc oxide powder is 5% by volume or more, the varistor characteristics of the nonlinear resistance material can be obtained, and if it is 80% by volume or less, the molded body can be formed without causing cracks.

  In the remaining polymer material, in consideration of moldability, two raw materials having different softening points are used, and specifically, a thermoplastic resin and a wax are used. The polymer material needs to maintain a solid state at room temperature because of the shape retention of the nonlinear resistance material.

  The thermoplastic resin is used to impart plasticity to the nonlinear resistance material, and polystyrene, polyethylene, polypropylene, polyacetal, polyethylene vinyl acetate, and the like can be used. In particular, the wax prevents contact between the zinc oxide powder and the die (die and punch) to achieve an even flow of the zinc oxide powder during pressure molding, and also prevents wear between the molded body and the die during extraction. A paraffin wax, a urethane wax, a carnauba wax, or the like can be used because it is added to reduce and facilitate the extraction. It is preferable that such a thermoplastic resin and wax are configured in a volume ratio of 20:80 to 70:30.

  The zinc oxide powder used as a raw material is suitable to have a particle size of 50 μm or less. When the particle size is 50 μm or less, the zinc oxide powder is easily dispersed even when the shape of the nonlinear resistance component is a thin plate shape.

  By adding the above polymer material to the above zinc oxide powder and kneading with heating, a non-linear resistance material having fine crystal grains and excellent formability can be obtained. When the individual zinc oxide powders are heated and kneaded so that they are covered with the polymer material, the non-linear resistance material obtained after the pressure molding process is made of the polymer material so that adjacent zinc oxide powders do not contact each other. Since it can comprise as a state which is separated and the magnitude | size of zinc oxide can be made uniform and equal, it is preferable.

  In producing a non-linear resistance component, a desired shape may be imparted by a method such as stamping, injection molding or punching using the above non-linear resistance material.

  As a preferable method for producing a non-linear resistance component using the above non-linear resistance material, there is a die molding. That is, a stamping device comprising a stamping die that molds the outer peripheral shape of a nonlinear resistance component, a lower punch that molds the lower surface of the nonlinear resistance component, and an upper punch that molds the upper surface of the nonlinear resistance component The shape of the non-linear resistance component is formed by filling the above-mentioned non-linear resistance material as a raw material into the cavity formed by the die hole of the stamping die and the lower punch, and press-molding this raw material with the upper and lower punches Then, the non-linear resistance component can be extracted from the die hole of the stamping die.

  Even when the above-described pressure forming process is performed in a cold manner, the wax component contained in the raw material (nonlinear resistance material) flows to easily form the shape of the desired non-linear resistance component. Can do. However, if the raw material (nonlinear resistance material) is in a fluid state in the pressure molding process, the gap in the mold can be filled and high pressure molding can be performed. It is preferable to heat to a temperature above the softening point of the thermoplastic resin contained. Moreover, it is more preferable to heat to a temperature equal to or higher than the melting point of the thermoplastic resin that maximizes the fluidity of the raw material. This heating may be performed after a raw material is filled in the mold by installing a heater in the mold, or the material may be preheated and supplied. After the material is softened, it is shaped by pressing with a punch from above and below.

  In addition, when press-molding by heating a raw material beforehand, it is desirable to extract after cooling to the temperature below the softening point of the thermoplastic resin contained in a polymeric material. By doing in this way, a molded object hardens | cures, and even if it is thin, the shape of a molded object is hold | maintained at the time of extraction and after extraction, and handling becomes easy. In this case, it is more preferable that the temperature be equal to or higher than the softening point and not higher than the melting point of the wax contained in the polymer material because the extraction pressure becomes the smallest.

  As described above, in order to obtain a state in which the material is heated to a temperature equal to or higher than the softening point of the thermoplastic resin during pressurization and is cooled to a temperature equal to or lower than the softening point of the thermoplastic resin during extraction, If a heating means such as a heater and a cooling means such as a refrigerant conducting pipe are provided at the same time, the temperature of the raw material can be easily controlled. In this case, a heating means can be provided in the raw material supply apparatus. In the case of these apparatus configurations, a pressure molding step is performed by supplying a raw material heated above the softening point of the thermoplastic resin to a mold heated above the softening point of the thermoplastic resin by a heating means provided in the mold in advance. More preferably, after that, the raw material and the die are cooled to a temperature not higher than the softening point of the thermoplastic resin contained in the raw material by the cooling means provided in the die and then the extraction step is performed.

  Another preferred method for manufacturing a non-linear resistance component using the above non-linear resistance material is injection molding. That is, an injection mold comprising a fixed mold having a mold hole that forms a part of the outer shape of the nonlinear resistance component and a movable mold having a mold hole that forms the remainder of the outer shape of the nonlinear resistance component. And after the fixed mold and the movable mold are clamped, the non-linear resistance material that is heated and flowed above the softening point of the thermoplastic resin contained in the non-linear resistance material is used as the fixed mold. Injecting from the raw material introduction path communicating with the cavity formed from the mold hole of the mold and the mold hole of the movable mold, the cavity is filled with the non-linear resistance material in a fluid state, and the non-linear resistance component After giving the shape, the fixed die and the movable die are cooled to a temperature below the softening point of the thermoplastic resin contained in the non-linear resistance material to solidify the non-linear resistance material. Drive the mold, open the mold, solidify the straight Taking out a sexual resistance component from the fixed mold. At this time, since the non-linear resistance component is formed integrally with the non-linear resistance material solidified in the raw material introduction path called the runner, the non-linear resistance component is taken out together with the runner from the fixed mold, and then the runner Can be separated to obtain a non-linear resistance component. Here, the introduction path for guiding the nonlinear resistance material in a fluid state to the cavity may be provided in the fixed mold, the movable mold, or both.

  Further, in the injection mold apparatus as described above, if a raw material introduction path shielding means for shielding the communication path on the cavity side of the raw material introduction path is provided, the non-linear resistance material in a fluid state is injected into the cavity. After that, by blocking the communication path on the cavity side of the raw material introduction path by the raw material introduction path shielding means, it becomes possible to separate the non-linear resistance component and the runner in advance, and the runner separation after taking out from the fixed mold This is preferable because no work is required.

  The zinc oxide powder having a particle size shown in Table 1 was prepared. Also prepared as a polymer material is a mixture of thermoplastic resin polyacetal (softening point 110 ° C., melting point 170 ° C.) and paraffin wax (softening point 40 ° C., melting point 60 ° C.) in a volume ratio of 4: 6. did. These were blended and kneaded in the proportions shown in Table 1 to prepare a nonlinear resistance material. This raw material was supplied to a pressing mold heated to the temperature shown in Table 1 and formed into a shape having a diameter of 10 mm × length of 0.5 mm. After cooling to the temperature shown in Table 1, extraction was performed. Table 1 shows the results of these moldability.

  Samples with sample numbers 01 to 08 in the table are examples in which the addition amount of the polymer material was confirmed. From these samples, in the sample of sample number 01 in which the amount of the polymer material added was less than 20% by volume, the amount of the polymer material serving as the binder was small, and the shape could not be maintained due to the formation of molding cracks. On the other hand, in the sample (sample numbers 02 to 08) in which the addition amount of the polymer material was 20% by volume or more, a sample having a good appearance could be produced. From the above, it was confirmed that a molded article sample having a good appearance was obtained when the addition amount of the polymer material was 20 to 95% by volume. In addition, in the appearance evaluation of Table 1, “◎” indicates the case where the dimensions are as designed and has a smooth surface, and for other defective samples, “× (unusable)” or “○ (conditionally Can be used).

  Sample Nos. 05 and 09, 10, and 11 in Table 1 are examples in which the influence of the powder particle size was examined. From these samples, it can be seen that samples of sample numbers 05, 09, and 10 having a particle size of 50 μm or less have obtained molded body samples having a good appearance. On the other hand, the sample of Sample No. 11 having a particle size exceeding 100 μm has irregularities on the surface, indicating that it is difficult to use depending on the shape. It was confirmed that the powder to be used is preferably 50 μm or less.

  Sample Nos. 05, 12 and 13 in Table 1 are examples in which the influence of the heating temperature (molding temperature) during molding was examined. In the samples Nos. 05 and 13 in which the heating temperature at the time of molding was equal to or higher than the softening point temperature of the thermoplastic resin, a molded body having a good appearance and a high molded body density was obtained. On the other hand, in the molding of the sample No. 12 where the heating temperature at the time of molding is less than the softening point temperature of the thermoplastic resin, the fluidity of the raw material is lowered and the gap in the mold is not completely filled. As a result, the molded body density was low. From this, the heating temperature at the time of molding is not particularly limited, but it is confirmed that it is preferable to set the heating temperature at the time of molding to a temperature equal to or higher than the softening point temperature of the thermoplastic resin used for the binder because the molded body density can be increased. It was.

  Sample Nos. 05, 14 and 15 in Table 1 are examples in which the influence of the cooling temperature (extraction temperature) at the time of extraction was examined. Sample No. 05, which has a mold cooling temperature at the time of extraction (that is, this temperature substantially coincides with the temperature of the molded body at the time of extraction) above the softening point temperature of wax and below the melting point of wax, has good wax lubricity. And was able to perform good extraction with a low extraction pressure. On the other hand, in the sample No. 14 in which the cooling temperature at the time of extraction was less than the softening point temperature of the wax contained in the binder, a sample having a good appearance could be produced, but the extraction pressure increased because the lubricating effect of the wax decreased. It was observed. Further, in the sample of Sample No. 15 in which the cooling temperature at the time of extraction greatly exceeded the melting point of the wax, a sample having a good appearance could be produced, but the oil film of the wax that exerts a lubricating action at the time of extraction was partially interrupted and the extraction pressure was Increased. From this, it was confirmed that it is preferable to set the cooling temperature at the time of extraction to a temperature not lower than the softening point temperature and not higher than the melting point of the wax used, because the extraction pressure can be reduced and the extraction process can be performed efficiently.

  Sample Nos. 05, 16 and 17 in Table 1 are examples in which the influence of the thermoplastic resin was examined. Sample No. 16 is the result of changing the polyacetal to polypropylene (softening point 110 ° C., melting point 170 ° C.) and molding and extracting at the temperatures shown in Table 1. Similarly, sample number 17 is the result of molding and drawing at the temperatures shown in Table 1 after changing the polyacetal to polyethylene (softening point 80 ° C., melting point 130 ° C.). In the samples of Sample Nos. 16 and 17, a molded body having a good appearance was obtained. From this, it was confirmed that molding was possible using a thermoplastic resin having a softening point.

  FIG. 1 is a COMP image (reflected electron composition image) obtained by observing a cross section of the sample No. 05 with a scanning electron microscope. It was confirmed that the non-linear resistance material of the present invention is a material in which zinc oxide powder is uniformly dispersed in a polymer material.

  A composite material in which zinc oxide powder is dispersed in the polymer material of the present invention is suitable as a nonlinear resistance material. For example, it is suitable as a material for a lightning protection element.

  10 ... zinc oxide powder, 11 ... polymer material.

Claims (10)

  A non-linearity characterized in that the zinc oxide powder is 5 to 80% by volume, the balance is made of a polymer material made of thermoplastic resin and wax, and inevitable impurities, and the zinc oxide powder is dispersed in the polymer material. Resistance material.   The nonlinear resistance material according to claim 1, wherein the zinc oxide powders are separated from each other by the polymer material.   3. The nonlinear resistance material according to claim 1, wherein the thermoplastic resin in the polymer material is 20 to 70% by volume, and the balance is a wax. 4.   The non-linear resistance material according to claim 1, wherein the zinc oxide powder is a powder of 50 μm or less. A raw material adjustment step of adjusting the raw material by heating and kneading a raw material consisting of a polymer material consisting of 5 to 80% by volume of zinc oxide powder, the balance being a thermoplastic resin and wax, and inevitable impurities,
A filling step of filling a predetermined amount of the raw material into the mold cavity of the mold;
A pressure forming step of pressing the raw material in the mold with a punch to form a predetermined shape;
A non-linear resistance component manufacturing method comprising: an extraction step of extracting a molded body obtained after the pressure forming step.   The method for producing a non-linear resistance component according to claim 5, wherein the thermoplastic resin in the polymer material is 20 to 70% by volume and the balance is wax.   The method for manufacturing a non-linear resistance component according to claim 6 or 7, wherein the zinc oxide powder is a powder of 50 µm or less.   The method for producing a nonlinear resistance component according to claim 5, wherein the pressure molding step is performed at a temperature equal to or higher than a softening point of the thermoplastic resin included in the raw material.   The method of manufacturing a nonlinear resistance component according to claim 8, wherein the extracting step is performed at a temperature equal to or lower than a softening point of the thermoplastic resin included in the raw material. A raw material adjustment step of adjusting the raw material by heating and kneading a raw material consisting of a polymer material consisting of 5 to 80% by volume of zinc oxide powder, the balance being a thermoplastic resin and wax, and inevitable impurities,
A fixed mold having a mold hole forming a part of the outer shape of the non-linear resistance component and a movable mold having a mold hole forming the remainder of the non-linear resistance component are clamped, and the fixed mold A non-linear resistance that is heated and flowed above the softening point of the thermoplastic resin contained in the non-linear resistance material from the raw material introduction path into the cavity formed by the mold hole of the mold and the mold hole of the movable mold A raw material injection step of injecting material and filling the cavity with a non-linear resistance material in a fluid state;
A cooling step of solidifying the non-linear resistance material by cooling the non-linear resistance material filled in the cavity to a temperature below the softening point of the thermoplastic resin contained in the non-linear resistance material;
A method of manufacturing a non-linear resistance component, comprising: opening the mold by driving the movable mold, and taking out the solidified non-linear resistance component from the fixed mold.