JPH053101A - Electric device - Google Patents

Abstract

PURPOSE: To provide an electric device, with which the trouble of device caused by the intermittent application of voltage is decreased, although such a trouble frequently occurs with the increase in voltage to be applied to the electric device having a PTC conductive polymer element. CONSTITUTION: For an electric device having a radiation bridge PTC polymer element 1 (a) and two electrodes 2 connectable to a power source for allowing a current flow to the PTC element (b), when SEM scanning is applied to the device, maximum voltage difference between two points separated for 10 microns is not higher than 4.0 volts.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electrical devices.

[0002]

BACKGROUND OF THE INVENTION Conducting polymer compositions which exhibit PTC behavior and electrical devices comprising such compositions are known and are described, for example, in U.S. Pat. Nos. 2,952,761 and 2,978,665. No. 3,243,753, No.3,3
51,882, 3,571,777, 3,757,
086, 3,793,716, 3,823,217
No. 3, No. 3,858,144, No. 3,861,029, No. 4,017,715, No. 4,072,848, No. 4,0.
No. 85,286, No. 4,117,312, No. 4,117,
No. 376, No. 4,177,446, No. 4,188,276
No.4,237,441,4,242,573,4,246,468,4,250,400,4,2
55,698, 4,272,471, 4,276,
No. 466, No. 4,314,230; Journal of.
Applied Polymer Science (J. Applied Po)
lymer Science) 19, 813-815 (1975),
Klason and Kubat; Polymer Engineering and Science (Polymer)
Engineering and Science) 18, 649-653
(1978), Narkis et al .; West German Patent Application Publication Nos. 2634999, 2746602 and 27.
No. 55076, No. 2755077, No. 2821799
No. 3030799; European Published Patent No. 002
No. 8142, No. 0030479, No. 0038713
No., 0038714, 0038715, 00
38718; European Patent Application No. 8130176.
7.0, 81301768.8, 8130220
1.9; and US Patent Application No. 176,300, No. 1
84,647, 254,352, 272,854
No. 300,709.

It is known to crosslink PTC conductive polymers by radiation and in practice the doses used are relatively low, eg 10-20 Mrad. However, higher doses have been used for some purposes. That is, West German Patent Application Publication No. 2634999 states that 20 to 45 Mrad is preferable, and British Patent No. 1,071,302 describes a copolymer of ethylene and a vinyl ester or acrylate monomer and 50 to 400% by weight. Irradiated compositions consisting of fillers such as carbon black are described, wherein the irradiation dose is about 2-100 Mrad, preferably about 2-2.
0 Mrad, such a composition is used as a tape to increase the insulation of the cable. Further, U.S. Pat. No. 3,351,882 discloses that a planar electrode is embedded in a PTC conductive polymer element and then a conductive polymer is added in an amount of 50-1.
A method of making an electrical device comprising irradiating and cross-linking at a dose of 00 Mrad is disclosed, but this method does not mean that the polymer between the electrodes is cross-linked at such a dose.

[0004]

The higher the voltage applied to an electrical device comprising a PTC conductive polymer, the more likely it is that the device will fail due to the intermittent application of voltage. This has been a serious problem when used in circuit protection devices, for example, where the voltage drop across the device in the "tripped" state (ie, high resistance state) is greater than about 200 volts. [The voltage mentioned here is a DC value or an RMS value of an AC power supply. ]

[0005]

We have found that such failures are reduced by irradiating the conductive polymer with a very high degree of crosslinking. The gist of the present invention is an electrical device comprising (a) a radiation cross-linked PTC conductive polymer element and (b) two electrodes that can be connected to a power source to pass an electric current through the PTC element, the apparatus comprising: When subjected to SEM scanning, an electric device is characterized in that the maximum voltage difference between two points separated by 10 microns is 4.0 V or less.

Experiments have shown that the higher the irradiation dose, the greater the number of trips (blocks) the device can withstand without failure (ie the number of times it has been converted to the block state). Therefore, the radiation dose is preferably at least 60 Mrad, in particular at least 80 Mrad, but higher radiation doses, eg at least 120 Mrad, or at least 160 Mrad if satisfactory PTC properties are retained and the improved properties are worth the irradiation cost. The dose may be

In addition, a method has been found to determine if a device can withstand a significant number of trips at 200 volts. The method involves using a scanning electron microscope (SEM) to measure the maximum rate at which voltage changes occur in the PTC element when the device is in the blocking state. This maximum rate is the so-called "hot zone" of the PTC element.
It occurs in the (hot zone). When the maximum rate gets smaller,
The number of trips the device can withstand increases.

Thus, in the present invention, when an electrical device is subjected to SEM scanning (defined below), the maximum voltage difference between two points 10 microns apart is provided if each of the electrodes has a substantially planar shape. Generally, it is 4.0 V or less, preferably 3.0 V or less, more preferably 2.0 V or less, and particularly 1.0 V or less. That is, when the electric device is subjected to SEM scanning and the voltage difference between two points 10 microns apart is smaller than the maximum voltage difference value described above,
The electrical device does not fail during many trips and the invention provides such an electrical device.
Therefore, the electric device having the excellent performance of the present invention is SE
Differentiated from other electrical devices by M scanning.

As used herein, "SEM scanning" means the following procedure. The device is PSE element SE
It is tested to see if it is suitable for scanning at M and has exposed clean surfaces present between the electrodes. Without such a surface, one would create such a surface with minimal equipment changes. If the device (or part of it if the device is too large, eg a long heater)
It is mounted in a scanning electron microscope so that the electron beam can traverse from one electrode to the other and strike the clean exposed surface at an angle. A 200 volt DC power supply is used to gradually increase the current flowing through the device until the device is tripped and the total potential drops across the device. The electron beam is then traversed over the surface by the voltage contrast method known in the art to obtain a picture in which the trace is a measure of the brightness (ie potential) of the inter-electrode surface. Such photographs are often known as line scans. Figure 1 shows a schematic representation of a typical micrograph.
Shown in. It is understood that the trace has many small peaks and valleys, which are believed to be primarily or solely due to surface imperfections. The "best line" (dashed line in FIG. 1) is drawn in the trace to average out small variations. 10 from this "best line"
The maximum voltage difference between two points separated by a micron is determined.

As used herein, when referring to an electrode "having a substantially planar shape", the shape and position within the device is such that the electrode enters (or exits) the electrode through a surface that is substantially flat for substantially the entire current flow. It means the electrode that is exposed.

While particularly useful in circuit protection devices, the present invention has application in heaters, particularly laminated heaters. In the first type of device, each of the electrodes is cylindrical. Such a device is shown in FIG. Here, a wire electrode 2 is embedded in a PTC conductive polymer element 1 having a hole 11 extending through the central part.

In a second type of device, usually a circuit protection device, the (A) PTC element is in the form of a strip having substantially planar and parallel ends, the length of the strip being greater than the maximum cross-sectional dimension of the strip. , (B) each of the electrodes is (1) in contact with one end of the PTC element and has a substantially flat end having a cross section substantially the same as that end; and (2)
It is a cap shape having side walls that contact the sides of the PTC element.

A cross-sectional view of such a device is shown in FIG. In the device of this figure, the cap-shaped electrode 2 has a hole 1 through the central portion
1 is in contact with both ends of the cylindrical PTC conductive polymer element 1 having

In a third type of device, typically a heater,
(A) PTC elements are layered, and (B) electrodes are positioned relative to each other such that the interelectrode current is along one of the element's larger dimensions.

In the fourth type of device, each of the electrodes has a substantially planar shape. Although a mesh-shaped flat electrode can be used, a metal foil electrode is preferable. If a metal foil electrode is attached to the PTC element before it is illuminated,
There is a risk of collecting the gas generated during irradiation. Therefore, it is preferable to attach the metal foil electrode after the irradiation crosslinking step. Therefore, the preferred method is: (1) irradiating the layered PTC conductive polymer element in the absence of the electrode, and (2) contacting the crosslinked PTC element obtained in step (1) with a metal foil electrode under heat and pressure conditions. And (3) cooling the PTC element and the metal foil electrode while applying pressure.

PTC conductive polymers suitable for use in the present invention are described in the patents and applications mentioned above. The specific resistance of the polymer at 23 ° C. is preferably 1250 Ω.cm or less, for example 750 Ω.cm or less, and particularly 500 Ω.cm or less, and 50 Ω.cm or less for a circuit protection device.
The following values are preferable. The polymer component must be capable of being crosslinked by irradiation and not significantly degraded. The polymer component is preferably free of thermosetting polymers and often consists essentially of one or more crystalline polymers. Suitable polymers include polyolefins (eg polyethylene) and copolymers of at least one olefin with at least one olefinically unsaturated monomer containing a polar group. The conductive filler is preferably carbon black. The composition may include a non-conductive filler such as alumina trihydrate. The composition may, but preferably does not, include a radiation crosslinking aid. The presence of co-crosslinking agents substantially reduces the irradiation dose required to achieve a certain degree of cross-linking, but its residue adversely affects the electrical properties.

Molding of the conductive polymer is generally carried out by a melt molding method such as melt extrusion or die molding.

Next, the present invention will be specifically described with reference to examples.

EXAMPLES In the examples, the ingredients and amounts shown in the table below were used.

[Table 1] Note: 1) Statex G: Colombian
Sold by Chemicals Chemicals, density 1.8g / cc, surface area (S) 35m ² / g, average particle size (D)
60 millimicrons. 2) Marlex 6003: High density polyethylene with a melt index of 0.3, sold by Phillips Petroleum. 3) Hydral 705: Aluminum Co. of Americ
Alumina trihydrate sold by a). 4) The antioxidant used is 4,4 with an average degree of polymerization of 3-4.
-Thiobis (3-methyl-6-5-butylphenol)
(Described in US Pat. No. 3,986,981).

After drying the polymer at 70 ° C. and carbon black at 150 ° C. in a vacuum oven for 16 hours, the ingredients for the masterbatch were dry blended and then mixed for 12 minutes in a Banbury mixer rotating in a high speed gear. .
The mixture was removed, cooled and granulated. Masterbatch 2439.2 g with filler (Hydral 705) 948.
Dry blend 3 g, then mix the dry blend in a Banbury mixer rotating in a high speed gear for 7 minutes,
The final mixture was prepared. The mixture was discharged, cooled, granulated and then dried at 70 ° C., 1 torr for 6 hours.

Using a crosshead die, the final granulated mixture was stripped into strips 1 cm wide and 0.25 cm thick.
The wire was melt extruded around a wire. 2 out of the wire
The book is preheated 20 AWG (diameter 0.095 cm) 19
/ 32 stranded nickel-coated copper wire, the centers of which are 0.76 cm apart, and the third wire is 24 AWG
(Diameter 0.064 cm) single wire nickel coated copper wire,
It was placed in the center between the other two. A 1 cm long section was cut from the extruded product, the polymer composition was removed from each section about half the length, and the central 24 AWG wire was removed to form a hole through the polymer element. The product is placed in nitrogen at 150 ° C. for 30 minutes, then in air, 11
Heat treatment was performed at 0 ° C. for 60 minutes, and then irradiation was performed.
The samples were irradiated with a dose of 20 Mrad, 80 Mrad or 160 Mrad. When these samples were subjected to SEM scanning, the maximum voltage difference between two points 10 microns apart was about 5.2, about 4.0 and about 2.0, respectively. Some of these samples were then sealed in metal cans. A polypropylene enclosure was provided between the conductive element and the can.

About the obtained circuit protection device, 240
AC power supply, switch, fixed resistor and the device
When tested in an essentially composed circuit, how many test supports
A test was conducted to determine if it could withstand the icicles. The device is
A resistance of 20 to 30 ohms at 23 ° C and a fixed resistance of 33 ohms
I had a switch resistance,
When turned on, the initial current in the circuit was 4-5A. Each trial
The test cycle closes the switch and trips the device.
Stop), open the switch after about 10 seconds, and proceed to the next test cycle.
It consisted of cooling the device for 1 minute. Two
The resistance of the device at 3 ° C was measured initially and after 5 cycles each.
It was measured later. The table below shows the resistance increased to 1.5 times the initial value.
Shows the number of cycles required to run.   Device irradiation dose      Number of cycles required to increase resistance by 1.5 times     20Mrad 40-45 cycles     80Mrad 80-85 cycles   160Mrad 90-95 cycles

[Brief description of drawings]

FIG. 1 is a diagrammatic representation of a typical micrograph.

FIG. 2 is a perspective view of an electric device having a cylindrical electrode.

FIG. 3 is a cross-sectional view of an electric device having a cap-shaped electrode.

[Explanation of symbols] 1 ... PTC conductive polymer element 2 ... Electrode 11 ... hole

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Merry Sandra Matsubatsushiyu             United States 94536 California             Lemont, Stonewood Drive             No. 37415 (72) Inventor Frank Antony Dolzyac             United States 94566 California, Pu             Leisington, Canon Court 3181 (72) Inventor James Michael Taylor             United States 94040 California, Ma             Unten Bieux, Esquiyura Avue             New 149 Sea number

Claims (4)

[Claims] 1. An electrical device comprising: (a) a radiation cross-linked PTC conductive polymer element and (b) two electrodes that can be connected to a power source to pass an electric current through the PTC element,
An electrical device characterized in that when subjected to SEM scanning, the maximum voltage difference between two points 10 microns apart is less than 4.0 volts. 2. The device of claim 1, wherein the maximum voltage difference is less than 3 volts. 3. The device of claim 1, wherein the maximum voltage difference is less than 2.0 volts. 4. The device according to claim 1, wherein each of the electrodes has a cylindrical shape, and the maximum voltage difference is 4.0 V or less.