JPS6028195A - Heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heater or safety element having a positive temperature coefficient of resistance (hereinafter abbreviated as PTC).

Structures of Conventional Examples and Problems There have been known resistor compositions having PTC characteristics in which conductive fine powder such as carbon black is dispersed in a crystalline polymer such as tepolyethylene. That PTC
The mechanism that produces this property is that when the crystalline polymer transitions to an amorphous state near its crystalline melting point, the coefficient of expansion rapidly increases, and the chains of dispersed carbon black are broken, resulting in an increase in resistance. considered to be a thing.

Therefore, the temperature range in which remarkable PTC characteristics fG is determined by the crystal melting point of the crystalline polymer, +11:'t
The size of the I silicon coefficient depends on the degree of crystallinity and can be determined by sizing. The PTC properties of this composition change due to heat cycles, etc.
Although there is a slight hysteresis phenomenon, it is comparatively stable and reproducible, and its value as a substitute for PTC heaters has been recognized. A conventional example of PTC heating using such a PTC composition is shown in FIG. In FIG. 1, 1d is a PTC composition made of a mixture of polyethylene and carbon black, and 2 and 2' are a pair of silver paste baked electrodes provided on the surface of the PTC composition. Since this structure has a large cross-sectional area and a small thickness, it is possible to obtain a sufficiently low resistance value even if the weight-111 composition ratio of carbon silicon is reduced, and the heat dissipation resistance against heat generation of the PTC composition is small. The feature is that heat can be easily dissipated. Therefore, low resistance and high output PT
It has an ideal shape and structure for the purpose of constructing a C heater. However, many polymers with a high degree of crystallinity, such as polyethylene, have almost no polar groups and have poor adhesive strength, causing problems in electrical or mechanical bonding with electrodes. For example, even when using a silver paste burnt electrode using an epoxy resin as a binder, which has particularly good adhesive properties, the lack of strength of the coating film itself results in an impractical electrode configuration. Ta. Desirable electricity W1. Paulownia paper is made of low-resistance, high-strength metal foil such as copper foil or nickel foil, but it is difficult to obtain adhesive strength that can overcome silver paste by using epoxy resin, and in any case, The current situation was that it had no choice but to be used for limited purposes.

Purpose of the Invention The present invention provides a means for obtaining a PTC composition that exhibits good adhesion and resistance temperature characteristics to metal foils such as copper foil and nickel foil that have excellent physical properties as electrode materials. The purpose is to provide high output PTC heating with a wide value adjustment range.

Structure of the invention -1 is a crystalline polymer containing a pair of parallel plate electrodes provided close to each other and a functional group with good adhesion to metal provided between the pair of parallel plate electrodes. (
! 1: This is a heater having a PTC characteristic consisting of a conductive fine powder and a resistor composition mainly composed of H11.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to FIGS. 2 and 3. 3 and 3' are electrolytic copper foil electrodes with a plate thickness of 35 μm, and 4 is a PTC resistor made of a kneaded sheet of a crystalline polymer in which a carboxyl group is introduced at the end of a low-density polyethylene molecule and an oil furnace carbon blank. body composition. l) /l/ Hogyyl group-introduced low-density polyethylene is a product in which carboxyl groups are introduced mainly into the wood ends of each molecule, and the copolymers are different, and the crystallinity, crystal melting point, etc. of low-density polyethylene are different. It has almost no effect on the physical properties and provides strong adhesion to Kinzaka 1, which is unique to carboxyl groups.

As a first example, the amount of carbon black added to the PTC resistor composition 4 is 60% by weight, and the average particle diameter of the carbon black that can be observed with an electron microscope is 5ooA.
So, I also observed it using an electron microscope! J1- is used, the shape of which is approximately spherical. The sheet thickness of the PTC resistor silk composition 4 is approximately 3001 tm, and the resistance value at 20°C is 2 per square centimeter, as shown by curve A in Figure 3.
It has an extremely low resistance of 0 mΩ and an i! of over 80"C.
The resistance value begins to increase rapidly in the Ili degree region, reaching approximately 2Ω at 110°C, which is the crystal melting point, and reaching approximately 5Ω.
4. The resistance temperature of PTC is extremely superior by several orders of magnitude. Y gender 1
I'm 11.

In this way, PTC's resistor, which has a low resistance value at room temperature and has excellent resistance-temperature stability, can be used as a small heater with excellent heat-up properties and is used in low-voltage power sources such as batteries.
Alternatively, it can be used as a safety element in series with a load in case of excessive current flow or temperature. When creating resistors with the same composition and the same composition using low-density polyethylene that does not introduce carboxyl groups, it is possible to create resistors that are visually the same, but the resistance at 20°C Resistance value: 30-60InΩ
The resistance value fluctuates greatly, indicating that there is contact resistance between the resistor composition and the resistor composition. Too bad, the peel strength is low, the contact state is unstable even with external force and thermal cycle, and it is difficult to put it into practical use.
The only countermeasures are to find a solution, use the electrodes with the electrodes crimped, or reduce the carbon blank blending ratio to 50% or less to improve the adhesion to some extent, and these are all major constraints. , low resistance and high reliability PTC
It was not possible to flj the heater.

The best functional group to be introduced into the crystalline polymer is the d-carboxyl group, but the most common method of introduction is simple polymerization with acrylic acid, etc., which has a carboxyl group.・Acrylic acid copolymers, etc. are easily available.However, although the method of introducing functional groups that can create copolymers certainly improves adhesion to metals, it has problems with crystallinity, crystal melting point, etc. The physical property values of the PTC properties also tend to decrease.
Resistance I16: begins to increase on the lower Write side, and the rate of change in resistance value also tends to decrease. therefore,
This is inconvenient when it is desired to utilize the physical properties of low-density polyethylene, high-density polyethylene, etc. to provide only adhesive properties. For such a target, since a functional group is added as a comonomer and polymerized, it is certain that a carboxyl group such as an acid anhydride is added to a polymer such as polyethylene which has already been polymerized. Using a phase separation agent that can react with polyolefins, we selectively react mainly at the terminal ends of each molecule of polyethylene, and then remove unreacted substances. Although it is physically almost polyethylene, it has a carboxyl group. By its effective presence, a crystalline polymer with excellent adhesion to metals can be obtained. Polyolefins with functional groups based on a similar concept include Mitsui Petrochemical Industries'(Kikki's Atmer series); , can exhibit extremely excellent adhesion to metals such as copper foil.Functional groups other than carboxyl groups include hydroxyl groups, amide groups, epoxy groups, and composite groups thereof. You can apply the same idea as in the case.

Next, the effects of the particle size, shape, and composition ratio of carbon black, as well as more favorable ranges, will be described. As shown in FIG. 4, the carbon black to be dispersed in the PTC resistor composition preferably has an average particle size and shape that can be observed with an electron microscope of 400 A or more, and is approximately spherical.
PTC characteristics with phase separation with an average particle size of about 100 to 300A, or a large surface area and a spherical shape (formerly known as I-minute), are not only difficult to be affected by, but also particles with a temperature higher than the crystal melting point. The resistance-temperature characteristics tend to be negative in the n11 degree range, and when a high voltage is applied or used in a high temperature atmosphere, a so-called runaway phenomenon may occur where the power increases as the humidity increases. Indeed, even if spherical carbon black has an average particle size of 4ooA or more, as its weight ratio in the PTC resistor composition is reduced, the temperature coefficient of resistance of PTC will increase, but it will exceed the crystal melting point. The temperature coefficient of resistance becomes a negative characteristic, and if left at that temperature for a long time, the resistance value decreases over time.These phenomena occur when the carbon blank has a small average particle size or when it is Spherical carbon black has a large surface area and has a large filling effect on the crystalline resin, which inhibits the expansion of the resin as the temperature increases, making it impossible to obtain a large rate of change in the resistance temperature characteristic of P'TC.
However, since the cohesive force is strong, redispersion occurs in the direction of creating a chain of carbon blanks in the dispersed form in an amorphous state above the crystal melting point, resulting in negative resistance temperature characteristics and a decrease in resistance value. It seems that this will occur.

Carbon blanks that are spherical and have a large average particle size have only one point of contact with each other, and even the slightest movement causes non-contact, compared to carbon black that is non-spherical and has a complex number of contact points. Naturally, it is easier to obtain a change in resistance value, and the cohesive force is also small, and even in the temperature range above the crystal melting point (if the resistance value continues to increase, which clearly reflects the expansion tendency of M fat). In addition, regarding the effect of carbon black's carbon black ratio, the smaller the ratio, the smaller the filling effect on the resin, which tends to inhibit expansion, and the rate of change in the resistance-temperature characteristics of PTC increases. On the other hand, in an amorphous state in a temperature range above the crystal melting point, the filling effect is insufficient and distortion occurs due to internal stress, and the movement of carbon black causes orientation and redispersion phenomena compared to the initial uniformly dispersed state. As shown in Figure 5, the composition ratio at which there is a tendency for a ladder to occur and the resistance value to decrease is a PTC resistor composition of spherical carbon blank and low-density polyethylene with an average particle diameter of 500A. In this case, the heavy composition ratio of carbon black is 4.
It is thought that it becomes noticeable in the range below 0%, and reaches its maximum at the minimum composition ratio of 10% where conductivity can be confirmed.

The above-mentioned negative resistance-temperature characteristics and decrease in resistance at temperatures above the crystal melting point may not pose much of a problem depending on the application. However, it cannot be said that it is sufficiently safe in cases where abnormal voltage application is expected, in applications where it is used at high temperatures for long periods of time, or in cases where it is used as a final safety mechanism. In the PTC heater of this example, the electrodes of different polarities are close to each other and the area is large, so the voltage gradient applied to the PTC resistor composition is quite steep, and there are defects in a very small portion. However, the structure is such that that part can generate abnormal heat. From this point of view, the PTC characteristics must have a sufficient margin, and it is necessary to carefully examine the usage conditions before applying those exhibiting a negative characteristic region or a resistance value reduction phenomenon.

Next, a method for manufacturing a relatively high resistance PTC heater will be described as a second example. In order to make a high resistance PTC heater, the blending ratio of carbon black should be 50.
% by weight or less, and in this case, the resistance temperature characteristic and the resistance value decrease phenomenon occur in the temperature range above the crystal melting point.

In order to prevent this, it is preferable to add a high resistance or electrically insulating filler that can provide a filling effect corresponding to a weight composition ratio of 40 to 70% of carbon black. The weight composition ratio of carbon black is at least 70%, and if it exceeds this limit, it will not only become brittle when subjected to old bending, but also
The rate of change in PTC decreases and kneading becomes impossible. The filling effect cannot be determined by the mechanical properties, PTC properties, and kneading properties, and the optimum composition ratio varies depending on the material and particle size of the filler. By adding a filler, the negative resistance-temperature characteristics at temperatures above the crystal melting point are hardly observed, but this effect is due to the fact that carbon black is also considered to be a filler that has a kind of filling effect. It is thought that a filling effect reaching the microscopic portions of the resin can be obtained, and the same effect can be obtained even with fillers other than carbon black, although there are some differences.

In the PTC heehy of the first embodiment shown in FIG.
In PTC resistor composition 4, the addition of carbon black, which accounts for the total amount of resin and carbon black, was reduced to 35% by weight, and the particle size of 1 μm was added to the total amount.
As a result of adding alumina powder at a ratio of 40% by weight, the resistance value at 20°C per square centimeter was 120Ω, 110'C, as shown in curve B of Figure 3.
Excellent resistance-temperature characteristics were obtained with a resistance value of 800 Ω, about four orders of magnitude less, and compared to curve C when no alumina powder was added, there was a tendency for negative characteristics and a decrease in resistance value at temperatures above 110°C. The phenomenon was hardly observed. This PTC
The resistance-temperature characteristics are slightly smaller than the first example in which only carbon black was added at 60% by weight, or the temperature coefficient '#, t/i is slightly smaller, or it seems to have shifted in parallel to the high resistance side by about 4 orders of magnitude. In addition, by adjusting the composition ratio of the carbon blank and filler, it is possible to create a PTC heater with arbitrary resistance-temperature characteristics. The filler can be used in any shape, such as granular, fibrous, or leaf-like, as well as organic or inorganic types, but it will not be effective if it is a high-resistance or electrically insulating material. An effective ablation agent1 is a material with a wide particle size distribution or a mixture of materials with two or more types of particle size.The temperature coefficient of negative characteristics in the temperature range above the crystal melting point In order to prevent this, it is desirable to use particles with a small particle size that have excellent filling effects in the microscopic range, but they also have a strong tendency to inhibit P and TC properties, so in addition to this, they also have excellent filling effects in the macroscopic range. The most desirable method is to use paulownia size, which has a large particle size that does not impair the PTC properties, in order to obtain the mutual benefit of both.

Regarding the method of adjusting the resistance value, it is possible to change the thickness of the PTC Hee Hee resistor composition, but if it is too thick,
For example, when π7n is exceeded, the thermal resistance inside the resistor increases, and a considerable temperature gradient is required to match the heat flux passing through the resistor.

Even if the temperature distribution in the voltage application direction inside the resistor is 1°C, the temperature coefficient of resistance is 0.21. 'PT over C
In the C resistor, the resistance value distribution is 20%, and there is a heat generation density distribution with a difference of 20- in proportion to the resistance value. If the temperature distribution exceeds 5°C, a heat generation density distribution of 1.2 to the fifth power, that is, 2.5 times, will occur, and the resistor at the highest temperature will reach the heat generation part that exceeds the limit, and the carbon Black redispersion will occur and irreversible resistance changes will occur. The thermal conductivity of general crystalline polymers is in the range of 0.1 to 0.4, 7/ml + °C, so it is stable at 80 °C at room temperature 20 °C, and 600K
In a PTC resistor that generates and dissipates heat as much as J7, the temperature difference per 1 vnη thickness should be 1.5 to 6°C. Furthermore, considering high temperature PTC resistors and large loads, it is 1000 to 10000 W/l.
ri! In that case, the temperature difference per 1 mm thickness would be 2.5 to 100°C.

If 10,000 K+i/nf is generated, it is thought that the temperature is near room temperature with a small PTC temperature coefficient, or the load is sufficiently cold, and the heat generation density distribution according to the temperature coefficient is not very large. However, even so, a temperature difference of more than 100°C is considered to be close to the limit for an organic heater. -For example, when drawing a submerged heater that heats a liquid at 20°C using a PTC heater whose resistance value increases rapidly in the IBM temperature range of 100°C or higher, the temperature of the heater Even if the surface temperature is 2°C, the inside temperature is 120°C.
, and the distribution of resistance values between them is non′j
：【It will become a big thing.】 In this case, the part that essentially functions as a heat generating part has high resistance, high voltage gradient,
It is considered to be a very thin section with high power density. The other parts are 141 heat transfer paths, and rather serve only as heat insulators. From the above point of view, 1mm or more
A PTC resistor with a thickness of two is considered to be completely meaningless. In addition, as a means of alleviating the imitation point mentioned below, there is a method of adding a filler with high thermal conductivity.For example, high purity alumina powder with a thermal conductivity of 30 h/m h'C, By adding silicon carbide powder of 90 W/m hoC, the thermal conductivity of the resistor was increased to 0.5-1 J/m.
Since it is technically easy to set the temperature to m11°C, in a heater with a thickness of 1 mm and an output of 10,000 kl/nfh, it is possible to achieve a temperature distribution of 1 to 20°C. This filler can be used in combination with the aforementioned filler for improving the negative resistance-temperature characteristics in the high temperature range, or it can be added independently. Fillers that improve thermal conductivity are relatively advantageous if they have a large particle size, and in extreme cases, they may straddle a pair of electrodes. To summarize the results described below, the thermal resistance value of the PTC resistor in the thickness direction is 0.01 h° per square meter.
It can be specified as c/W or less.

Next, the heat resistance stability of this PTC resistor will be described.

The PTC resistor shown below is highly stable in itself;
If a polyolefin-based material is used for the resin, the polyolefin may undergo significant oxidative deterioration due to ions of heavy metals R used in the electrode.

Particular attention must be paid to this point since the PTC heehy copper foil electrode of the present invention is constructed in close proximity. In addition, in order to prevent the deterioration process due to 9J breakage of the main chain of polyolefin and crosslinking that occurs as a secondary reaction, we will also investigate whether the best effect can be obtained by using a phenol-based hepthioether-based stabilizer in combination. The presence of thioether also causes a phenomenon in which electrodes such as copper foil deteriorate. In order to prevent this phenomenon, it is effective to add a heavy metal ion deactivator that can combine with heavy metal ions to form metal lead compounds, and this will ensure long-term reliability. ) is necessary. If the blending ratio of these stabilizers is sufficient to counteract the inhibitory effect of the carbon blank, it is necessary to add 1 to 10% of the resin (7 ether-based Yoshithiocotel-based stabilizers). %, and the heavy metal 1-like ion deactivator is effective when added to I) in an amount of 0.5 to 2%, which is higher than usual.

Effects of the Invention As described above, the heater of the present invention provides the following effects.

(1) Good adhesion to metal can be obtained even with a low-resistance PTC composition containing conductive fine powder in multiple orders of magnitude, so by providing a resistor between parallel plate electrodes, A reliable heater with low resistance can be made.

(2) It has a large PTC resistance change rate and small internal thermal resistance, and has a wide adjustment range of resistance value, and has a wide range of applications as a heater and a safety element.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional heater, Figure 2 (r) is a perspective view of a heater that is an embodiment of the present invention, and Figure 3 is a diagram showing the relationship between the resistance value and temperature of the heater of the embodiment. Figure 4 shows P of a composition of low density polyethylene and various carbon blacks.
FIG. 5 is a diagram showing the relationship between the composition ratio of low density polyethylene and carbon black having an average particle size of 500A and the PTC characteristics. 3. Copper foil electrode, 4. PTC resistor composition. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure?

Claims (1)

[Scope of Claims] (1) A pair of parallel plate-like electrodes provided close to each other, and a crystal containing a functional group with good adhesion to metal provided between the pair of parallel plate-like electrodes. 1. A heater having a positive temperature coefficient of resistance, comprising a resistor composition whose main components are a conductive polymer and a conductive fine powder. (2) It consists of a functional group-introduced crystalline polymer in which functional groups with good adhesion to metals are placed mainly at the ends of the molecules of the base crystalline polymer, and the crystallinity before and after the introduction of functional groups The heater according to claim 1, in which the physical property value of the crystal melting point changes very little. (3) A heater according to claim 2 (I) in which the functional group introduced is a carboxyl group. 4) The heater according to claim 1 or claim 2, comprising a carbon blank in which the conductive fine powder has an average particle diameter of 400 A or more and a shape of 1 square sphere. (5) The heater according to claim 1 or 2, wherein the proportion of carbon black in the resistor composition is 10 to 70% by weight. (6) The resistor composition contains an electrically insulating or high-resistance filler as a subcomponent, and the tensile strength of the resistor composition is
The heater according to claim 2, whose mechanical strength in bending and shearing is within the mechanical strength of a resistor composition with a carbon black composition ratio of 40 to 70% when no filler is included. . (7) The resistor composition contains as an accessory component a filler having electrical insulation or high resistance and a thermal conductivity of 20 &7/inh°C or higher. heater. (8) The thermal resistance between a pair of electrodes is 0 per square meter,
01 b'C//6' or less
Item 2 is the heater described in Item 2. (9) Create a metal complex compound for heavy metal ions as part of the stabilizer in the resistor composition. ) The heater according to claim 1 or 2, further comprising a deactivating agent. (10) The crystalline polymer of the resistor composition is a polyolefin resin, and contains a phenol-based or thioether-based stabilizer and a deactivating agent capable of forming a metal complex compound with respect to heavy metal ions, and the electrode is The heater according to claim 1 or 2, which is made of a metal containing copper.