JPH03233902A - Manufacture of ptc element - Google Patents

Abstract

PURPOSE:To bond an electrode to an element main body without changing an electrical characteristic by a method wherein the Joule heat by a pulse current is generated at a heater chip via a temperature-control heating power supply, the face coming into contact with the electrode is melted to be in a thin-film shape and the heat of the element main body is dissipated while a pressurized state of the electrode is kept. CONSTITUTION:Since an electric resistance of conductors 6, 7 is extremely small, heat generated by a pulse current of a temperaturecontrol heating power supply 5 is concentrated at a heater chip 1, and the thermal electromotive force of a thermocouple 8 attached to the heater chip 1 is detected by using the temperaturecontrol heating power supply 5. Consequently, the temperaturecontrol heating power supply 5 can control an electric current in such a way that the temperature of the heater chip 1 is kept at a prescribed value. When an electrode 4 is thermocompressionbonded to an element main body 2, an excess thermal hysteresis is not exerted on the element main body 2 because the element main body 2 is not melted wholly but only the face coming into contact with the electrode 4 is melted to be in a thin-film shape by an instantaneous heating operation. Thereby, fundamental characteristics such as an electrical characteristic, a shape and the like of the element main body 2 are not changed even when the electrode 4 is bonded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention is directed to PTC (Positive Temperature
The present invention relates to a method for manufacturing a PTC element, in which the PTC element is formed by bonding electrodes to an element body made of a molded product made of a composition having the following characteristics.

(Prior art) A composition having PTC characteristics in which conductive particles such as carbon black or porous black are dispersed in a crystalline polymer such as polyethylene or polypropylene is made into a molded body, and an electrode is bonded to this molded body to form a crystal. It is already known that a PTC element can be formed in which a steep increase in resistance value occurs near the melting point of a polymer. Then, to a molded body with PTC characteristics,
The following methods are known as methods for joining electrodes by thermocompression bonding.

a. As described in U.S. Pat. No. 4,426,633, a composition having PTC characteristics is extruded into a thin plate-like molded body, and electrodes made of metal foil are placed on both sides of this thin plate-like molded body for several minutes. Electrical device b made of PTC conductive polymer obtained by thermocompression bonding while determining electrical properties by controlling temperature, pressure, and time, and then cutting the molded body together with electrodes into a desired shape, JP-A As described in Japanese Patent No. 62-106602, a composition having PTC characteristics is molded, and electrodes made of metal foil are applied to the upper and lower surfaces of this molded body, and the melting point of the polymer constituting the composition is first adjusted. Pressure and heat are repeated three times for two minutes each at the following temperature, and then pressure and heat are applied three times for two minutes each at a temperature higher than the melting point of the polymer to bond electrodes to both sides of the molded body. Manufacturing method of positive temperature coefficient thermistor C0
As described in JP-A-60-196901, a composition made of a crystalline polymer and carbon black is molded into a plate shape, and electrodes with one side roughened are hot pressed on both sides of the molded body. This method involves bonding at 150° C. for 30 minutes to bond electrodes to both sides of the molded product, and then cutting it into a predetermined size to obtain an organic positive temperature coefficient thermistor.

(Problems to be Solved by the Invention) However, in all of the above conventional methods, when thermocompression bonding the electrodes, heating is performed for minutes to completely melt both the p'rcFft and the shape. For this reason, an extra thermal history is given to the PTC molded body, resulting in a change in its electrical characteristics. Therefore, in order to obtain a PTC element with a desired resistance value, it is necessary to control the temperature, pressure, and time during thermocompression bonding, as well as the pressure applied during cooling, as described in U.S. Pat. No. 4,426,633 of A. Become.

Further, in order to save time, it is necessary to attach electrodes over a wide area, so the electrodes are thermocompression bonded to the molded body and then cut into a predetermined shape. Therefore, the resistance value also changes when the molded body is deformed, such as when the electrode bites into the molded body during cutting. Another problem is that the shape of the resulting device is limited to a sandwich structure in which electrodes are formed on both sides of a plate-shaped molded body.

Furthermore, since the area of the bonding surface between the electrode and the molded body is large, there is a problem that air tends to remain on the bonding surface. Another problem is that the two-stage heating and pressing means complicates the process.

Alternatively, if you just want to press the metal foil onto the PTC molded body in a short time, you can also use a compression molding machine or the like to press a large metal hot plate into contact with the PTC molded body to warm it up to the desired temperature for a few seconds, then release it. However, in this case no pressure is applied during cooling. Therefore, there is a problem in that the bonding between the molded body and the metal foil is unstable, and sufficient bonding force and ohmic contact cannot be obtained.

In view of the above-mentioned problems, the present invention has been developed by suppressing the melting of the element body made of a molded PTC composite composition only at the bonding interface with the electrode when joining the electrodes by thermocompression bonding, so that the electrodes can be attached to the PTC element body in the process. To provide a method for manufacturing a PTC element, in which the influence of electrical characteristics and other factors on the PTC element can be reduced as much as possible, the shape of the element body and the mounting position of the electrodes can be arbitrarily selected, and mass production is also possible.

C Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a PTC element according to claim 1 of the present invention provides a method for manufacturing a PTC element by forming a composition having PTC characteristics consisting of conductive particles and a crystalline polymer into a desired shape. Next, an electrode made of metal foil is brought into contact with this element body, and then this electrode is pressed against the element body with a heater chip. Joule heat is generated by a pulse current in the heater chip via a temperature-controlled heating power source to melt the electrode contact surface of the element body into a thin film, and then the element body is caused to radiate heat while maintaining the pressurized state of the electrode. , which allows electrodes to be bonded to the element body without changing the electrical characteristics.

The method for manufacturing a PTC element according to claim 2 of the present invention is the method according to claim 1, wherein the heating time is 10 seconds or less.

In the method for manufacturing a PTC element according to claim 3 of the present invention, in claim 1 or 2, the pressurization during heat dissipation is performed at the melting point Tm of the lowest melting point polymer among the crystalline polymers blended into the element main body. ℃] until Tm [℃] -50[℃].

The method for manufacturing a PTC element according to claim 4 of the present invention is the method according to any one of claims 1 to 3, in which a thermo-controlled welder is used as the temperature-controlled heating power source.

(Function) In the method for manufacturing a PTC element of the present invention, when an electrode is bonded to a chip-like element body made of a composition having PTC characteristics by pressure heating, only the electrode contacting surface is melted into a thin film. Because it is crimped, no extra heat history is applied to the entire molded product.

Therefore, the electrical characteristics of the element body are hardly changed when the electrodes are bonded. Heating required for electrode bonding,
The heat dissipation time is extremely short, only a few seconds, the time required for thermocompression bonding is short, and the time required to attach electrodes to each chip-shaped element body does not affect production costs.

Furthermore, since there is no need to cut the electrodes after bonding, stress such as residual stress or the digging of the electrodes into the element body due to cutting does not occur.

In addition, since the electrode is heat-pressed to the chip-like element body, the electrode contact surface has a small area, and the air remaining on the electrode contact surface is removed by the flow of molten polymer that is melted into a thin film between the electrode and the electrode contact surface of the element body. easily eliminated.

The temperature at which the pressure is maintained during heat dissipation after thermocompression bonding of the electrodes is kept at least 50°C lower than the melting point of the polymer.
Complete resolidification of the polymer occurs to ensure electrode bonding.

The thermo-control welder, which functions as a temperature-controlled heating power source, generates Joule heat by passing pulsed current and instantaneously supplies heat to the electrode bonding surface, and also controls the current by detecting the temperature of the heater chip and terminal voltage. be.

(Example) An example of an apparatus used in an example of the present invention will be explained with reference to FIGS. 1 to 3.

1 is a heater chip attached to a hand press (not shown). Reference numeral 2 denotes an element body formed by molding a composition having PTC characteristics consisting of conductive particles and a crystalline polymer into a chip shape, and is supported on a substrate 3. Reference numeral 4 denotes an electrode made of metal foil, which is superimposed on the element body 2 and is pressed onto the element body 2 by hand pressing the heater chip 1.

5 is a temperature controlled heating power source (thermochondrol unilder, TCW), TCW-1 manufactured by Nippon Avionics Co., Ltd.
15 is used and is connected to the heater chip 1 by a conductor 6.7. Since the electrical resistance of the conductor 6゜7 is extremely small, the heat generated by the pulse current of the temperature-controlled heating power source 5 is concentrated in the heater chip 1, and a thermocouple 8 is attached to the heater chip 1. The electromotive force is detected by the temperature-controlled heating power source 5. And with this,
The temperature-controlled heating power source 5 controls the current so as to maintain the temperature of the heater chip 1 at a predetermined value.

As shown in FIGS. 2 and 3, the heater chip has a structure in which a 2 mm thick molybdenum plate is bent into a U-shape with an upward opening, and the lower surface is an electrode crimping surface 9 for crimping the electrode 4. It has a structure that has the structural strength to withstand the pressure applied at times, and has a structure that increases the efficiency of heat dissipation. .

The area of the electrode compression surface 9 of this heater chip 1 is II,
l2 = 22 heights x 22 heights, height z3 = 20 heights.

0 It is necessary to reduce the heat capacity of the heater chip 1 in order to enable heating and cooling in a short time, and for this reason, it is desirable to reduce the volume, but the area of the electrode compression surface 9 is smaller than that of the electrode 4. It must be equal to or larger than the area.

Temperature-controlled heating power source 5 as a heating power source for heater chip 1
The heater chip 1 is instantaneously heated by the Joule heat generated by passing a pulse current through the heater chip 1, and the temperature of the heater chip 1 is detected by a thermocouple 8 welded to the heater chip 1.
This is a power source that can adjust the current to maintain the heater chip 1 at a predetermined temperature. Further, the heating time at a predetermined temperature can also be controlled by feeding back the thermoelectromotive force of the thermocouple 8.

As a means for shortening the heat dissipation time of the heater chip 1, there is a method of blowing compressed air.

To this end, a structure with high heat dissipation efficiency is used, for example, as shown in FIGS. 2 and 3, the metal plate is bent into an upward U-shape to widen the heat dissipation area.

Next, the manufacturing process of the present invention using the above apparatus will be explained.

1) A composition having PTC characteristics consisting of conductive particles such as carbon black and a crystalline polymer is molded by a molding method such as compression molding, injection molding, or calendar molding to obtain a chip-like element body 2.

During this molding, the basic properties such as volume resistivity and shape of the PTC element obtained as a product are determined.

Since this element body 2 does not have an electrode 4 attached to it, it can be formed into any shape by a processing machine such as a milling machine, if necessary.

2. The electrode 4 is brought into contact with the element body 2, and the unheated electrode crimping surface 9 of the heater chip 1 is pressed against the electrode 4 by operating a hand press to apply a predetermined pressure.

3. The element body 2 is heated by passing a pulse current through the heater chip 1 connected to the power source 5, and the electrode 4 is in contact with the element body 2.
The contact surface of the electrode is melted into a thin film. At the same time, the thermoelectromotive force of the thermocouple 8 attached to the heater chip 1 is detected to prevent the heater chip 1 from overheating.

Assuming that the heating temperature of the heater chip t for compression bonding is 1250°C, the time required to raise the temperature to 150°C is 3 seconds.

4. Heat radiation is performed by turning off the current for heating the heater chip 1 and blowing compressed air onto the heater chip 1. The melted polymer in the element body 2 is re-solidified by the heat radiation, and the electrode 4 is completely joined to the element body 2.

The time required to lower the temperature of the heater chip 1 from 150°C to 80°C is about 3 seconds.

The melting point of the crystalline polymer constituting the element body 2 is 132°C.
If this is the case, the temperature necessary for crimping the electrode 4 will naturally be higher than this melting point.

The temperature at which pressure is maintained during cooling is set at least 50°C below the melting point.The reason for this is that if the temperature is just below the melting point, the polymer will not completely re-solidify, resulting in poor bonding. So that there may be enough. The surfaces on which the pair of electrodes 4 are attached to the element body 2 do not have to be parallel to each other. For example, depending on the shape of the element body 2, the pair of electrodes 4.4 can be joined either in a direction perpendicular to each other or in three directions inclined at 60'. Also, if necessary, 3
It is also possible to join more than one electrode 4 at any position.

Furthermore, the electrode 4 to be bonded can also have an arbitrary shape.

Example 1 Table 1 A composition having the PTC characteristics shown in Table 1 was heated and kneaded, and then pulverized to a diameter of 2 mm or less and compression molded. For molding, put the above-mentioned crushed product into a mold and weigh 465kg1/
While applying pressure using a car press mold, the temperature was raised from room temperature to 200°C in 5 minutes, kept at 200°C for 3 minutes, and then
9 to 50℃ while applying a pressure of 116kg1/car.
After cooling for a few minutes, the mold was removed from the mold 4 to form a 14X7 mold as shown in Figure 4. 5
An element main body 2 of XA' 6 =I3 mm x 13 mm x 3.5 mm was obtained.

Electrodes 4 made of rough electrolytic nickel foil (manufactured by Fukuda Metal Foil & Powder Industries Ltd.) with a thickness of 25 μm and an area equal to the area of the electrode crimping surface 9 of the heater chip 1 are placed on both the upper and lower surfaces of the element body 2 by the following method. Joined.

First step: The electrode 4 is brought into close contact with the surface of the element body, and pressure is applied from above with the pressure bonding surface 9 of the heater chip 1. The pressing force was 4 Qkgl/ci.

2nd stage: Heater chip 1 to desired temperature (150°C)
Increase the temperature for 3 seconds and keep at that temperature for 3 seconds. During this process, the pressurization at the 11th stage continues to be maintained.

Third step: Heat is radiated by blowing compressed air onto the heater chip 1 to a temperature of 80° C. or lower while maintaining the pressurization. Heat dissipation is completed in approximately 3 seconds. 5. Keep the pressure applied for about 10 seconds.

In this three-step process, the electrode 4 is firmly bonded to the surface of the element body 2. The time required is about 20 seconds.

Next, the element body 2 is turned over and the same operation is repeated to bond the electrode 4 to the back side of the element body 2 as well.

As described above, the resistance value of the PTC element having the electrodes 4.4 bonded to the front and back surfaces of the element body 2 was measured and the volume resistivity was calculated.

In addition, as a comparative example, a PTC element was prepared using the same method, and electrodes were formed by applying silver paste (manufactured by Tokuriki Kagaku Kenkyujoku; trade name: Silvest) on both the upper and lower surfaces of the element body without changing the volume resistivity. The resistance value was measured and the volume resistivity was calculated.

The results are shown in Table 2.

(See next page) 6 As shown in Table 2, the volume resistivity of the PTC element obtained by the method of Example 1 is different from that of Comparative Example 1, which shows no change in volume resistivity due to the formation of electrodes. It can be seen that the electrodes can be attached without changing the volume resistivity. Although a small amount of PTC composition flakes appear around the electrode during close contact, the decrease in thickness is less than 2% in all cases, indicating that the electrode can be attached without changing the shape of the molded article.

7 Example 2 The conductive particles and crystalline polymer having the composition shown in Table 3 were heated and kneaded and then ground to a diameter of 2 mm or less, which was compression molded in the same manner as in Example 1 to obtain an element body 2. . The shape of this element body 2 is also similar to that of the first embodiment.

Table 3 (Note) Porous black is carbon black made porous by vapor phase etching.

Electrodes 4.4 made of the roughened electrolytic nickel foil used in Example 1 were bonded to both upper and lower surfaces of this element body 2 in the same manner as in Example 1 to obtain a PTC element.

The obtained PTC element was thermally aged at 100° C. for 2 hours, and then irradiated with gamma rays to cause crosslinking. There are two levels of irradiation dose: 10 Mrad and 60 Mrad. This product was subjected to a beer test and its peel strength was measured. As Comparative Example 2, when performing compression molding under the same conditions as Example 2, the element body 2 was sandwiched with Ni.
Comparative Example 2 was obtained by arranging electrodes made of foil on the upper and lower surfaces, and attaching the electrodes at the same time as molding. Comparative Example 2 was subjected to similar heat aging and gamma ray irradiation, and then subjected to a beer test. The results are shown in Table 4.

(See next page) As is clear from Table 4, the adhesion strength of the electrode 4 according to Example 2 is larger than that of Comparative Example 2 when irradiated with the same amount of γ-rays. Comparative Example 2 shows completely melted PT.
Since the bonding is performed while applying pressure to the C composition, the bonding strength is similar to that of the conventional thermocompression bonding method.0 The reason why Example 2 shows a high bonding strength is that in Comparative Example 2, it took a long time to cool down, so the polymer During resolidification, the degree of crystallinity increases, and the shrinkage of the PTC composition biting into the rough surface of the metal foil of the electrode progresses, making it impossible to maintain firm biting into the rough surface of the metal foil of electrode 4. On the other hand, in Example 2, the cooling rate was very high, so the electrode 4
It is thought that the degree of crystallinity of the polymer biting into the rough surface of the metal foil was lowered and shrinkage was small, so that biting into the rough surface was maintained and the bonding strength increased.

Example 3 A sample manufactured in the same manner as in Example 2 and a sample according to Comparative Example 2 were both irradiated with γ-rays of 60 Mrad and were designated as Example 3 and Comparative Example 3. Then, voltage was repeatedly applied to both Example 3 and Comparative Example 3. Application conditions are 30V 5 times, 100V 4 times
150V was applied twice, 200V was applied twice, and 250V was applied four times for 2 minutes each, and an interval of 20 minutes or more was left before the next application. Note that both samples had the same initial resistance value and thickness. As the application was repeated, an increase in resistance value was observed in both Example 3 and Comparative Example 3. The degree of increase was almost the same in both cases. After the above-mentioned application ends, the resistance value change rate is 65% for both.
When the temperature increased, the application test was discontinued, and a beer test was conducted for Example 3 and Comparative Example 3, respectively. Example 3
is 0.62kgj/cn on one side and 0.73kg on the other side.
+/(1). On the other hand, in Comparative Example 3, one side was 0.52 kgf/an and the other side was 0.57 kgf/an.
It was n. As a result, even after repeated PTC operations are performed on the PTC element in the electrode attachment according to Example 3, the electrode 4 is firmly attached to the element body 2 than in the case of the thermocompression bonding method of Comparative Example 3. Recognize.

Example 4 The same PTC composition as in Example 2 was compression molded, and then the corners were cut off with a grinder and processed into the shape shown in FIG.
An element body 2 having a size of 5wn, IIo=51rrm, and Az=11mm was obtained. Embodiment 2 Electrodes 4.4 having the same area as the A and B planes were closely bonded to the A and B planes, which were orthogonal to each other, by the same method as in Example 1. The conditions for electrode 4.4 and bonding are the same as in Example 1. A beer test was conducted on both sides. In addition, as Comparative Example 4, a pair of electrodes were formed in close contact with parallel surfaces at the same time as the element body was molded, and a beer test was conducted on this.

The results are shown in Table 5.

Table 5 As shown in Table 5, it can be seen that according to Example 4, the electrodes can be closely attached to the element body 2 with sufficient strength even if they are not facing each other.

〔Effect of the invention〕

According to the present invention, when an electrode is thermocompression bonded to a chip-shaped element body made of a composition having PTC characteristics consisting of conductive particles and a crystalline polymer, the electrode can be bonded instantaneously without melting the entire element body. Since only the contact surface of the electrode is melted into a thin film by heating, there is no excess heat history on the element body, and basic characteristics such as the electrical characteristics and shape of the element body can be changed by bonding the electrodes. There is no. Therefore, in the past, the resistance value of the element body changed due to pressure, temperature, time, etc. when attaching electrodes because the entire element body was melted, so temperature, pressure, time, etc. were controlled when thermocompression bonding of electrodes was performed. do not have.

In addition, since the entire element body is not melted when attaching electrodes,
Even if the element body has a complicated shape, an element body of any shape can be obtained with almost no change in shape. Moreover, a small thermal history also prevents thermal deterioration of the polymer component.

Furthermore, since the electrodes can be bonded in an extremely short time, there is no wasted time attaching electrodes to each chip-shaped element body (and mass production is possible.Moreover, only one element body By attaching the electrodes to four electrodes at a time, the electrodes can be attached to any position on the element body, regardless of the shape of the element body.

In addition, in the past, for mass production, electrodes were attached to a large element body and then cut into chips, which caused stress such as the electrodes digging into the element body and residual stress due to cutting. This problem can also be avoided because it is not cut into chips afterwards.

Furthermore, since the area of the joint surface between the chip-like element body and the electrode is small, the air remaining on this joint surface is easily removed to the outside by the flow of the molten polymer in the form of a thin film, so that the step of removing air can be omitted.

Further, during heat dissipation, by applying pressure until the melting point of the polymer constituting the element body becomes 50° C. or more lower, the polymer is completely resolidified and the electrodes are bonded securely.

Furthermore, by using a thermo-controlled welder as a temperature-controlled heating power source, it is possible to apply a pulse current to the heater chip to generate Joule heat and instantaneously supply heat to the electrode bonding surface. It can detect voltage and control current.

[Brief explanation of drawings]

The first engineering drawing is an explanatory diagram of the apparatus used in the method of manufacturing a PTC element of the present invention, FIG. 2 is a front view of the same heater chip, and FIG.
FIG. 4 is a perspective view of the previous element body with electrodes, and FIG. 5 is a perspective view of the element body showing the same embodiment. 1. Heater chip, 2. Element body, 3. Substrate, 4
... Electrode, 5... Power supply. Procedural amendment (voluntary) February 6, 1991

Claims (4)

[Claims] (1) A composition having PTC characteristics consisting of conductive particles and a crystalline polymer is formed into a chip shape having a desired shape and electrical properties to obtain a chip-like element body, and then a metal foil is attached to this element body. Next, this electrode is pressed against the element body using a heater chip, and Joule heat is generated by a pulse current in this heater chip via a temperature-controlled heating power source, so that the electrode contact surface of the element body is brought into contact with the electrode. A method for manufacturing a PTC element, which comprises melting it into a thin film, then radiating heat from the element body while maintaining the pressurized state of the electrode, and joining the electrode to the element body without changing the electrical characteristics. (2) The method for manufacturing a PTC element according to claim 1, wherein the heating time is 10 seconds or less. (3) Pressure during heat dissipation is maintained until the melting point Tm [°C] of the polymer with the lowest melting point among the crystalline polymers blended in the element body reaches -50 [°C]. The method for manufacturing a PTC element according to claim 1 or 2, characterized in that: (4) Claims 1 to 3, characterized in that a thermo-controlled welder is used as the temperature-controlled heating power source.
A method for manufacturing a PTC element according to any one of the above.