JPH05243006A - Manufacture of ptc thermistor - Google Patents

Abstract

PURPOSE:To prevent the increase of density of a molded form, to make shape retention and lubricity at the time or extrusion coexist and to give allowance for the conditions of baking by adding a dispersant to a binder. CONSTITUTION:A binder is added to barium titanate used as a main raw material, and kneaded sufficiently until barium titanate is changed into fine particles, thus obtaining a mixture. The binder used at that time is composed of methyl cellulose and glycerin, and a dispersant is added previously to the binder. The mixture is formed in the shape of a specified thermistor, and a molded form is baked. The formation of an electrode, packaging, selection, etc., are conducted, thus completing a product. Accordingly, the loadings of methyl cellulose may be increased for improving shape retention at the time of extrusion molding, but a cooling rate at the time of baking is accelerated for lowering the specific resistance value of the molded form after baking because there is a tendency that the density of the molded form is inversely augmented more than required and the specific resistance value is elevated abnormally, thus acquiring an effect equal to a substance, in which a large quantity of water is added to a body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a PTC thermistor.

[0002]

2. Description of the Related Art As is well known, a PTC thermistor is a positive temperature coefficient thermistor having a positive temperature characteristic in which its resistance value increases as the temperature rises, and is generally manufactured as follows.
First, a binder is added to barium titanate used as a main material, and the barium titanate is sufficiently kneaded until it becomes fine particles to obtain a mixture. Next, the mixture is formed into a predetermined thermistor shape, and the formed body is fired. After that, electrode formation, packaging, selection, etc. are further performed to complete the product.

By the way, generally, a pressing method is frequently used for molding, but the pressing method is suitable for a relatively large-sized molded product such as a disk mold and extruded for a small-sized molded product such as a surface mounting mold. The law is suitable. In the case of manufacturing using extrusion molding, the binder is usually prepared from methyl cellulose, glycerin, and water. Methyl cellulose is specifically, for example, using Metroze manufactured by Shin-Etsu Chemical Co., Ltd. and blending it with barium titanate 100 as a main raw material at a ratio of Metroose 2 to 4, glycerin 4, and water 9 to 16. Then, the optimum extrusion conditions are selected.

[0004]

However, as can be seen from FIG. 2, the extrusion method not only has a great relation between the amount of binder added and the shape retention / lubricity (softness), but also of the PTC thermistor. Since the resistance temperature characteristic is also greatly involved, the setting of the extrusion condition becomes very complicated and strict, and the optimum firing condition of the molded body also largely changes depending on the extrusion condition.

For example, in order to improve the shape-retaining property at the time of extrusion, it is sufficient to increase the addition amount of metroze (namely, methylcellulose), but on the contrary, the density of the molded body is increased more than necessary, that is, the softness becomes small. After that, the specific resistance value of the molded body tends to increase abnormally after firing. Therefore, in order to lower the specific resistance value, it is necessary to increase the cooling rate during firing. In this case, water can be added to improve the lubricity during extrusion (increasing the softness) and suppress the increase in the density of the compact, but a slight fluctuation in the amount of water can significantly change the properties of the clay. In addition to water, water greatly changes depending on temperature, humidity, and kneading conditions, so it is quite difficult to adjust both shape retention and lubricity during extrusion to optimal conditions. On the other hand, if the amount of methyl cellulose added is reduced,
Although the lubricity increases to some extent, problems such as sheet breakage tend to occur.

Therefore, an object of the present invention is to prevent the increase in the density of the molded body, to make the shape retention and the lubricity at the time of extrusion compatible, and to give a margin to the firing conditions.
It is to provide a manufacturing method of a C thermistor.

[0007]

In order to achieve the above object, the method for producing a PTC thermistor of the present invention is characterized in that a dispersant is added to a binder in the conventional production method. This has the same effect as adding a lot of water to the clay. Further, even if a large amount of methyl cellulose, which is a component of the binder, is intentionally added in order to further prevent breakage of the sheet, extrusion molding can be performed while maintaining appropriate lubricity. Moreover, since the density of the molded body does not rise abnormally, it is not necessary to take measures such as rapid cooling of the firing furnace when providing a predetermined resistance temperature characteristic.

Examples of the dispersant added to the binder in the production method of the present invention include ceramizole manufactured by NOF CORPORATION, rapizole, marialim, and polystar. The amount of these dispersants added varies somewhat depending on the components of the binder and the compounding ratio of each component. For example, the binder is composed of methyl cellulose and glycerin, and the compounding ratio is 2 to 100% barium titanate to methyl cellulose.
4, in the case of glycerin 4, 10 to 10 of the amount of glycerin added
20%.

[0009]

EXAMPLES A method of manufacturing a PTC thermistor of the present invention will be described below based on examples. However, in order to further clarify the effect of the present invention, a conventional example is also described. Here, PT
As barium titanate, the main raw material for C thermistors,
By using RT05D manufactured by Fuji Titanium, a binder composed of the components in the following mixing ratios was prepared with respect to 100 parts of barium titanate.

Examples Conventional example Methylcellulose 3% 3% (Shin-Etsu Chemical Co., Ltd. 60SH-4000) Glycerin 3.5% 4% Dispersant 0.5%-(Nippon Yushi Ceramizole) Water 20% 20 % In the examples and conventional examples, the binder containing the above components is added to barium titanate and kneaded until the particles are sufficiently small, and the obtained mixture is extruded into a predetermined shape. In the examples, there is appropriate lubricity (softness), it is not necessary to adjust the choke bar adjusting screw of the extruder at the time of extrusion, and the shape retention is also good. However, in the conventional example, the lubricity is poor (the hardness is small and the hardness is low), the extrusion pressure is very large, and it is necessary to constantly adjust the choke bar adjusting screw during extrusion.

The firing conditions performed after molding are as follows. In the examples, first, the maximum temperature was 1340 ° C.
After firing for 1 minute, 10 ° C from 1340 ° C to 1200 ° C
After cooling at 0 ° C./h and holding at 1200 ° C. for 1 hour, further cooling from 1200 ° C. to 1000 ° C. at 100 ° C./h. This is almost the same as the firing condition of RT05D manufactured by Fuji Titanium. The resistance-temperature characteristic of the example obtained by this firing is shown by a line in the graph of FIG.

In the conventional example, in order to obtain almost the same resistance temperature characteristic as that of the example (see the line -- in the graph of FIG. 1), after firing at the maximum temperature of 1340 ° C. for 30 minutes, the temperature was changed from 1340 ° C. to 1000 ° C. It must be quenched at 200 ° C / h. For this reason, the firing conditions are more stringent than in the examples. For reference, the resistance-temperature characteristic in the case of firing under the firing conditions similar to those of the above-mentioned examples in the conventional example is also shown in FIG.
─Indicated by a line.

After the firing, the PTC thermistor is finished by performing electrode formation, packaging, selection and the like as in the conventional case.

[0014]

As described above, in the method for producing a PTC thermistor of the present invention, since a dispersant is added to the binder, it is possible to prevent an increase in the density of the molded product during extrusion molding, and to contradict the shape retention. Compatibility with lubricity and extrusion conditions can be easily optimized. Moreover, since it is not necessary to perform treatment such as quenching during firing in order to bring out a predetermined resistance temperature characteristic, productivity is unlikely to be influenced by the structure of the firing furnace, and a margin for firing conditions is created.

[Brief description of drawings]

FIG. 1 is a PTC obtained by the present invention and a conventional manufacturing method.
It is a graph which shows the resistance temperature characteristic of a thermistor.

FIG. 2 is a graph for explaining extrusion conditions when the binder component amounts are changed.

Claims (2)

[Claims] 1. A method for producing a PTC thermistor in which a binder is added to a raw material of a PTC thermistor, the mixture is kneaded, the mixture obtained is extruded into a predetermined shape, and then the molded body is fired. A dispersant is added to the binder. P characterized by
Manufacturing method of TC thermistor. 2. The PTC according to claim 1, wherein the binder comprises methyl cellulose and glycerin.
Manufacturing method of thermistor.