JPH0547454A - Ptc heating unit - Google Patents

Abstract

PURPOSE:To provide a PTC heating unit having the capability of showing stable PTC characteristics even at a high temperature (e.g. 200 deg.C or higher). CONSTITUTION:Two or more electrodes 2 and 2 are so buried as to be near each other and bridged in a conductive composite 1 comprising a mixture of a conductivity imparting addition material and crystalline monomer containing at least one ethylenic double bond with crystalline polymer. In this constitution, stable PTC characteristics with a less change in resistance value can be provided, even in use at a high temperature such as 200 deg.C, due to the existence of the monomer containing the ethylenic double bond.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to high temperatures (for example, 200 ° C.).
The above also relates to a PTC heating element exhibiting stable PTC characteristics.

[0002]

2. Description of the Related Art Conventionally, PTC (Positive)
As an excellent composition having a Temperature Coefficient characteristic, a composition in which a conductivity-imparting material such as carbon black is mixed with an ethylene-tetrafluoroethylene copolymer (ETFE) which is a crystalline polymer has been proposed. That is, when a heat-generating body such as a self-temperature control heater or other heat-generating device is manufactured using this composition, excellent thermal, chemical and mechanical properties can be obtained even in the vicinity of its melting point and higher temperatures. It is because it shows. Therefore, the PTC heating element using ETFE as a base resin is used by being attached to a pipe cleaning device used at a temperature of 200 ° C. or higher, for example.

[0003]

However, the inventors of the present invention have made a detailed observation of the use state of the PTC heating element using ETFE as the base resin at the above high temperature.
It has been found that when the PTC heating element is energized at a high temperature, the resistance value of the heating element gradually decreases and the output increases conversely.

Therefore, the present inventors have conducted various studies on ETFE and polymers related thereto, and found that at least one ethylenic double bond was contained in these compositions before crosslinking. It has been found that when the monomers are mixed and then cross-linked, a stable PTC characteristic can be obtained without lowering the resistance even when energized at a high temperature of 200 ° C. or higher.

[0005]

Means for Solving the Problems and Actions Thereof The present invention has been made based on the above facts, and the characteristic point of the present invention is that the conductivity-imparting material and at least one ethylene are contained in the crystalline polymer. It is a PTC heating element in which two or more electrodes are embedded in close proximity to each other in a conductive composition obtained by mixing a monomer containing a ionic double bond and crosslinked.

The following are examples of the monomer containing at least one ethylenic double bond in the present invention. Allyl esters of polycarboxylic acids and other acid components such as cyanuric acid, such as triallyl cyanurate and isocyanurate, maleates and itaconates and tetraallyl pyromellitate.
Bis and trimaleimides such as N.N'-ethylene- and N.N'-m-phenylene-bis-maleimide. Acrylic acid or methacrylic acid esters of polyhydric alcohols, such as dipentaerythritol hexamethacrylate, ethylene glycol dimethacrylate, 1
-3-butylene glycol dimethacrylate and penta-erythritol tetramethacrylate etc. Vinyl esters of polybasic acids such as trivinyl cyanurate and citrate. Allyl or vinyl ethers of polyhydric alcohols such as tetra-allyl and tetra-vinyl ether of pentaerythritol. Bisacrylamide, such as N.N'-methylene- and N.
N'-p-phenylene-bis-acrylamide and the like. Also, monomers containing a single ethylene bond such as vinyl stearate, dibutyl maleate and styrene can be used as well.

The mixing of such monomers effectively prevents the resistance of the PTC heating element from decreasing at high temperatures. The addition amount of this monomer and the reduction of resistance depend on the specific monomer component, but generally, the addition amount of the monomer is preferably 1 to 10% by weight of the composition. Especially 3-5
Weight percent is optimal. Further, a particularly preferable monomer is triallyl cyanurate.

Thus at least one ethylenic 2
An example of a PTC heating element in which a monomer containing a heavy bond and a conductivity-imparting material are mixed in a crystalline polymer and crosslinked,
As shown in FIG. This PTC heating element is a belt-shaped heater, and in the figure, 1 is the above-mentioned conductive composition, 2 and 2 are a pair of electrodes embedded in the composition 1, and 3 is the composition 1 coated on the composition. It is an insulating layer. In manufacturing this heater, the composition 1 is extrusion-molded on the electrodes 2 and 2, and thereafter, the insulating layer 3 is covered by coextrusion or the like.
When the composition 1 is extruded, the composition temperature and the conductor temperature may be the same or close to each other. The method for crosslinking the composition 1 is not particularly limited, but a high energy electron beam irradiation method and a gamma ray irradiation method are preferable. The irradiation dose at this time is generally in the range of 1 to 10 Mrad. For example, in the case of a composition in which the base resin is ETFE, about 3 Mrad is preferable.

[0009]

EXAMPLES The formulations shown in Table 1 were kneaded with a Banbury mixer to produce pellets of a conductive composition, and the pellets were extruded onto the electrode as shown in FIG. The target PTC heating element (Examples 1 to 5, Comparative Example 6) was obtained by irradiating with an electron beam and crosslinking. A resistance value measurement test was performed on each of the PTC heating elements (Examples 1 to 5 and Comparative Example 1). This resistance value measurement test is carried out in a 200 ° C. oven at 200 V of a PTC heating element.
The voltage was applied, and then the resistance value at room temperature (20 ° C.) was measured at intervals of about 50 hours. The results are as shown in FIG. 2, in which characteristic lines 1 to 5 correspond to Examples 1 to 5 and characteristic line 6 corresponds to Comparative Example 1.

[0010]

[Table 1]

As is clear from Table 1 and FIG.
In the heating element of Comparative Example 1, the resistance value decreases in a short time, whereas in the heating elements of Examples 1 to 5 according to the present invention,
It can be seen that the resistance value is stabilized at high temperature depending on the relationship between the addition amount of triallyl cyanurate and the irradiation amount of the electron beam or the like. Especially, in the case of Example 5, it is understood that excellent characteristics are obtained.

[0012]

As is apparent from the above description, the PTC heating element according to the present invention is a conductive polymer obtained by mixing a conductivity-imparting material and a monomer containing at least one ethylenic double bond in a crystalline polymer. Since two or more electrodes are embedded in a conductive composition in close proximity to each other and cross-linked, the monomer containing the ethylenic double bond acts even when used at a high temperature such as 200 ° C. A stable PTC characteristic can be obtained with little change in resistance value.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a PTC heating element according to the present invention.

FIG. 2 is a graph showing the relationship between the rate of change in resistance and time in a voltage application test.

[Explanation of symbols]

 1 conductive composition, 2 electrodes, 3 insulating layer,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05B 3/56 8715-3K

Claims (2)

[Claims] 1. A conductive composition in which a conductivity-imparting material and a monomer containing at least one ethylenic double bond are mixed in a crystalline polymer, and two or more electrodes are embedded in close proximity to each other, A PTC heating element characterized by being crosslinked. 2. The monomer containing at least one ethylenic double bond is an allyl ester of polycarboxylic acid or cyanuric acid, bismaleimide or trimaleimide, acrylic acid or methacrylic acid ester of polyhydric alcohol, polybasic acid. 2. The PT according to claim 1, which is a vinyl ester of the above, an allyl or vinyl ether of a polyhydric alcohol, or bisacrylamide.
C heating element.