JPS6242402A - Current limiting element - 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 Lumi flow limiting element having a positive temperature coefficient of resistance (so-called "PTC characteristic").

(Prior Art) Conventionally, current fuses that utilize the fusing action caused by overcurrent have been frequently used to protect electric circuits, but these fuses have the disadvantage that they cannot be used again.

In addition, in recent years, magnetic PT whose main component is barium titanate has been developed.
Although C thermistors have become commercially available, these magnetic thermistors have a high initial resistance value (usually, the resistance value at 20° C. is higher than 10,000 Ω-me).

Furthermore, since it cannot be made small, it is not suitable for protecting electronic circuits that are intended to be miniaturized.

On the other hand, JP-A-56-161464 discloses a composition in which a thermoplastic resin is blended with metal particles such as nickel, tungsten, molybdenum, and carbon black. The thermistor obtained from this composition has a large resistance increase in the practical temperature range, and when used as a current limiting element in electric circuits and electronic circuits, the resistance and resistance value easily fluctuate due to ambient temperature and self-heating, so one circuit There was a problem with the design.

(The problem that the invention attempts to solve) Electricity/Electronics #! The current limiting element for I protection is connected in series with the protected circuit, and under normal conditions, a current (I) corresponding to the resistance of the protected circuit also flows through the element (resistance value R
), Joule heat of IH is generated.

The temperature of the element is maintained at a constant temperature as environmental conditions such as ambient temperature, heat dissipation conditions, and this Joule heat are balanced.

On the other hand, since the element has a positive resistance-temperature characteristic, the specific resistance value at equilibrium temperature increases compared to the initial resistance value, but the resistance value at equilibrium temperature increases compared to the initial resistance value. If the initial resistance value becomes too large, the current value to the protected circuit decreases, often resulting in a current-limiting state under normal conditions4.On the other hand, if the initial resistance value is lowered, the above disadvantages disappear, but There is a range in which the current value of the protected circuit (ie, the current of the element) is not limited. However, when an abnormal current flows due to a short circuit, etc., the current limiting element uses Joule heat.
Since the amount of heat generated depends on the magnitude of the resistance value, a composition having resistance-temperature characteristics suitable for the circuit to be protected was required. However, on the other hand, the actual resistance value of the circuit to be protected and the voltage acting on the current limiting element vary, and the appearance of a current limiting element that can adapt to such various conditions has been eagerly awaited.

(Problems and Means for Solving the Problems) In view of the above-mentioned current situation, the inventors of the present invention have conducted intensive studies and found that when mixing a specific amount of conductive particles into a thermoplastic resin, the conductive particles have a surface area within a specific range. By using carbon black and graphite having an average particle diameter below a specific value, and by setting the proportion of graphite in the total amount of conductive particles within a specific range, the initial resistance value is low and the resistance value rapidly increases at a specified temperature. The present invention has been completed.

That is, in the present invention, 40 to 100 parts of conductive particles are blended to 0 parts of thermal DJ plastic resin11), and the conductive particles have a surface area of 20 to 100rr//, carbon black of F and an average A conductive resin composition is formed of graphite having a particle diameter toALm or less, and the graphite has an abundance ratio of 0.1 to 0.6 in the total amount of conductive particles, and the molded product is formed into a predetermined shape. This invention relates to a current limiting element having two or more electrodes separated from each other on its surface.

The current limiting element according to the present invention can be produced by uniformly kneading a predetermined amount of thermoplastic resin, carbon black, and graphite using a mixing roll, forming the mixture into a predetermined shape such as a sheet, film, or plate. Two or more pieces isolated from each other on the surface of the molded product! It can be obtained by a method of providing poles, etc.

This current limiting element has a low initial resistance value, that is, a specific resistance value (R2O) at 20°C of 1 to 10,000 Ω, and a low R (TP-2o)/R2G of 1 to 10.
TP/R20 is at least 1000.

Note that TP is the temperature CC) at which the current limiting element exhibits the maximum resistance value, that is, the peak resistance value (RTP), and R(TP -20
) indicates the specific resistance value at a temperature 20° C. lower than the temperature TP (° C.).

Ideally, the resistance-temperature characteristic of a current limiting element having PTC characteristics as in the present invention is such that there is no change in resistance at temperatures below TP, and the resistance rises steeply at TP. It is normal for resistance to start increasing at lower temperatures. In determining the quality of the PTC current limiting element, T is better than TP.

Resistance value at low temperature (TP4'o) and RzoO ratio, ie.

In resistance temperature characteristics, it is most commonly used to indicate the resistance increase slope in the temperature range from 20°C to (TP-To) and the ratio of the resistance value at R20 and TPO temperature (FTP), that is, the resistance change multiple. It is a means. If To is below 10°C, the resistance and rise will realistically start steeply, making it inconvenient to use as a basis for pass/fail judgment.
At temperatures above 0°C, T
o was set to 20°C.

Therefore, R(TP -20)/R20 is from 20°C to (T
RTP/R2
0 indicates the ratio of the resistance value at 20° C. and the resistance value at TP, that is, the multiple of change in resistance.

If the value of R(TP -20)/R2G is less than 1, the resistance value will be smaller than R20 due to temperature rise, and it will show a negative temperature coefficient of resistance, and when a voltage is applied to the PTC element. As the temperature rises, the resistance value decreases and the current increases, which is a very inconvenient result. Furthermore, if it exceeds 10,
Temperature changes in the element during practical use will cause significant changes in resistance, making it extremely difficult to design electrical circuits using the element.

In some cases, a retention device may be required to keep the element temperature constant.

Also, it is better to have % Rrp/R20 as large as possible, but when a current of 1000 mm is applied in practical use, the temperature may rise due to self-heating and exceed the allowable temperature of the element, and the element itself has a resistance. This is because the use of 6D and small resistance change multipliers that utilize temperature changes is limited.

The reason why R20 is set to 1 to 10,000 Ω-us is related to practical design, and is limited by problems related to the shape of the element. That is, when the resistance is 1 Ω-α, the distance between the electrodes becomes long, and when it exceeds 10000 Ω-α, the electrodes become large.

Next, an example of the current limiting element according to the present invention will be explained with reference to the drawings. Figures 1 to 4 show examples of current limiting elements, and in Figure 1, a sheet-like molded material 11 (flow limiting element body) made of a conductive resin composition is shown so as to cover the entire surface and back surface of the current limiting element. A metal foil electrode 2.3, such as a copper foil, is provided by means of heat fusion, adhesion with a conductive adhesive, or the like.

Figures 2 and 3 show other examples.

FIG. 2 shows band-shaped electrodes 2 along both sides of the surface of the molded product 10.
．． 3, and in FIG. 3, strip-shaped electrodes 2.3 are provided on the front and back surfaces of the molded product 1, respectively.

FIG. 4 shows yet another example, in which band-shaped electrodes 2.3 are provided along both sides of the front surface of the molded product 1, and an electrode 4 is provided on the back surface to cover the entire surface thereof.

In the present invention, various thermoplastic resins can be used without particular limitation, but polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, and the like are practically preferred. This thermoplastic resin can be crosslinked by electron beam irradiation or the like.

This thermoplastic resin contains carbon black and graphite as conductive particles in a total amount of 40 to 100 parts by weight based on 100 parts by weight of the resin. If the amount of conductive particles blended is too small, the initial resistance value will be high, and if the blended amount is too large, when the resin composition is molded into a predetermined shape such as a sheet, the mechanical strength of the molded product will be reduced. .

Both are unfavorable.

In the present invention, both carbon black and graphite are used in combination as conductive particles as described above, and the abundance ratio of graphite in the total amount of conductive particles is 0.1 to 0.6. . The abundance ratio of graphite is 0
．． If it is less than 1, R20 and R(TP-2
0)/R20 is large and the abundance ratio exceeds 0.6, R
Both are unfavorable since TP/R20 becomes small.

In addition, the abundance ratio of graphite is calculated by the following formula.

Further, the carbon black used in the present invention has a surface area of 20 to 100 rrl/i (measured value by J3ET method), and the average particle diameter of graphite is 10 μm or less. If the surface area of carbon black is as small as 20 d/ji, the valleys of the carbon black become bulky, which not only makes it difficult to mix uniformly with the resin and graphite, but also makes it difficult to mold this mixture. If it exceeds 1oOyr//g, RT))/R20 becomes small, so neither is preferable.Also, if the average particle size of graphite is 10μ
If it is larger than a duck, R(TP-xo)/R20 becomes small, which is not preferable.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that "parts" in the examples are "parts by weight."

Example: Surface area: 45 rl for 100 parts of high-density polyethylene pellets (manufactured by Mitsui Petrochemicals, trade name: H2-5300E)
/j9 carbon black 40 parts 2 and average particle size 4μ
Mix 30 parts of graphite (111f) for 30 minutes using a mixing roll at a temperature of 165° C. (to melt the polyethylene and mix the three components uniformly).

Next, this mixture was heated to 165°C using an electric heating press.
, heat and pressurize for 30 minutes at a pressure of 5 kP/c14.

Thereafter, the pressure was maintained at 5 kfi'/cA and cooled to room temperature.
A sheet-like molded product is obtained.

After crosslinking the polyethylene by irradiating this sheet-like material with an electron beam of 10 Mrad, a thickness of 0.5 mm was formed on both the front and back surfaces;
Copper foils of 20 CrIL are arranged vertically and horizontally, and the temperature is 1.
A current limiting element (sample number 1) having the same structure as that shown in Fig. 1 was obtained by heat-sealing at 65°C and a pressure of 5 kl//cA and then cooling.
I got it.

Furthermore, carbon black and graphite formulation 1,
Current limiting elements of Sample Nos. 2 to 7 were obtained by carrying out the same operations as for Sample No. 1 except that the surface area of carbon black and the average particle diameter of graphite were set as shown in Table 1.

R20% R(TP-2
0), RTP and TP measurement data, R (TP-20)/R20,RTP calculated based on these data
/ The value of R20 is shown in Table 1. In addition, R2(l s
Measurements were made using R (TP-20) and RTP digital multimeters.

For comparison, the currents of sample numbers 8 to 16 were obtained by performing the same operations as sample number 1 except for setting the average particle diameter of carbon black, the surface area of graphite, and the combination of both fk as shown in Table 1. The data of the limiting elements are shown at the same time.

(Effects of the Invention) As can be seen from the above embodiments, the present invention has an initial resistance value (R
20) is not a low value, but R(TP-20)/R
z.

is small and RTp/R20 is large, with remarkable PT
It has characteristics showing C characteristics.

[Brief explanation of the drawing]

1 to 4 are side views showing examples of the current limiting element according to the present invention.

Claims (1)

[Claims] 40-10 parts by weight of conductive particles per 100 parts by weight of thermoplastic resin
0 parts by weight is blended, and the conductive particles have a surface area of 2
0 to 100 m^2/g of carbon black and graphite with an average particle diameter of 10 μm or less, and the graphite has an abundance ratio of 0.1 to 0.6 in the total amount of conductive particles.
1. A current limiting element, characterized in that a conductive resin composition is molded into a predetermined shape, and two or more electrodes isolated from each other are provided on the surface of the molded product.