JPH0729672A - Cord heater - Google Patents

Abstract

PURPOSE:To provide a cord heater which is excellent in heat resistance, oil resistance, and electric characteristic, and causes no void in a product even when heated and cross-linked at ordinary pressure without using a bent type extruder at low cost. CONSTITUTION:A cord heater has an insulating layer 4 or outer layer formed by heating and cross-linking, at ordinary temperature, a composite mainly consisting of a mixture obtained by mixing a methacrylate or acrylate which is a crosslinking assistant and an organic peroxide which is a crosslinking agent with an ethylene tetrafluoride-propylene copolymer, and adding silicon rubber thereto in an amount lower than 200 parts by weight to 100 parts by weight of the ethylene tetrafluoride-propylene copolymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cord-shaped heater excellent in heat resistance, oil resistance and electric characteristics.

[0002]

2. Description of the Related Art Conventionally, a cord-shaped heater has a heating core formed by spirally winding a metal resistance wire around a glass fiber string or a polyester fiber string, on which a vinyl chloride resin, silicone rubber, fluorine is used as an insulating layer. It is covered with resin or the like.

[0003]

However, the vinyl chloride resin is inferior in heat resistance, and regarding the silicone rubber and the fluororesin which are excellent in heat resistance, the former is inferior in oil resistance and solvent resistance, and the latter is inferior in flexibility. There is a drawback that.

On the other hand, in the field of electric wires, although the price is higher than vinyl chloride resin or silicone rubber, it has excellent heat resistance, oil resistance and electrical characteristics.
Insulated electric wires having an insulating layer or an outer layer made of a composition containing a propylene-based copolymer as a main component have begun to be used for automobiles, machine tools, generators, motor lead wires, and the like. An insulated wire having an insulating layer or an outer layer of the composition containing the tetrafluoroethylene-propylene-based copolymer as a main component contains an allyl compound as a crosslinking aid and an organic peroxide as a crosslinking agent in the composition. , After extrusion coating the composition onto a conductor,
After pressure heating and cross-linking with pressurized steam or pressurized liquid so that voids do not occur in the product, or using a vent type extruder, after vacuum suction of a small amount of water, gas, etc. contained in the composition, A method is employed in which a conductor is extrusion-coated and then heat-crosslinked at normal pressure.

Therefore, it is conceivable to use the composition containing the tetrafluoroethylene-propylene copolymer as a main component as an insulating layer or an outer layer of the cord-shaped heater. However, since the cord-shaped heater is also manufactured by the same method as the insulated wire as described above, in the case of pressure heating and crosslinking, a boiler for generating pressurized steam or a device for pressurizing a liquid is required. On the other hand, when using a vent-type extruder that can be heat-crosslinked under normal pressure, it takes a considerable amount of time to set up unlike an extruder that is normally used, and always pay attention not to lower the vacuum degree of the vacuum pump. In addition, the vent type extruder is a large device with a special structure that requires multiple cylinders or large cylinders equivalent to it and a vacuum pump, so it is not only expensive but also requires a large installation space. In addition, a large amount of compound remains in the cylinder, resulting in higher process cost than an extruder that is normally used, which is economically disadvantageous.

The present invention has been made on the basis of the above points, and an object thereof is to have excellent heat resistance, oil resistance, and electrical characteristics, and to heat-crosslink under normal pressure without using a vent type extruder. Even so, it is to provide a cord-shaped heater that does not generate voids in the product at low cost.

[0007]

In order to achieve the above object, the cord-shaped heater according to the present invention comprises a tetrafluoroethylene-propylene copolymer, a methacrylic acid ester or an acrylic acid ester as a cross-linking agent, and a cross-linking agent. A composition containing a mixture of an organic peroxide as an agent and 200 parts by weight or less of silicone rubber with respect to 100 parts by weight of a tetrafluoroethylene-propylene copolymer is used as a main component. It is characterized by having an insulating layer or an outer layer formed by pressure heating and crosslinking.

In the tetrafluoroethylene-propylene copolymer, it is usual to use an allyl compound as a cross-linking aid and an organic peroxide as a cross-linking agent, and to carry out cross-linking in combination with each other. In the above, a methacrylic acid ester or an acrylic acid ester is used as a cross-linking aid, and is cross-linked with an organic peroxide which is a cross-linking agent. Do not use methacrylic acid ester or acrylic acid ester together with organic peroxide when using a cross-linking auxiliary agent such as allyl compound, oxime compound, sulfur, maleimide compound, etc. instead of methacrylic acid ester or acrylic acid ester as a crosslinking auxiliary agent. When it is used alone, or when it is used alone as a cross-linking agent, it takes a long time for cross-linking, and at atmospheric pressure, numerous voids are generated in the product.

Examples of the methacrylic acid ester or acrylic acid ester used as a crosslinking aid include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, ethylene dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, cyclohexyl methacrylate, dialkyl. Examples thereof include aminoalkyl methacrylate, aluminum methacrylate, aluminum acrylate, zinc methacrylate and zinc acrylate. These may be used alone or in combination of two or more. As the organic peroxide used as the cross-linking agent, various commonly used peroxide compounds can be used. In addition to the above-mentioned cross-linking agent and cross-linking aid, additives such as a filler, a reinforcing agent, a lubricant and a pigment can be used if necessary.

In the present invention, a silicone rubber is further added to a mixture obtained by adding a methacrylic acid ester or an acrylic acid ester which is a crosslinking aid and an organic peroxide which is a crosslinking agent to a tetrafluoroethylene-propylene copolymer. Added. This silicone rubber is extremely important for suppressing the viscosity of the resulting composition. When silicone rubber is not added, the viscosity of the composition becomes high and scorch is generated due to self-heating in the cylinder of the extruder, resulting in a poor appearance of the product. The addition amount is preferably 200 parts by weight or less with respect to 100 parts by weight of the tetrafluoroethylene-propylene-based copolymer, and when it exceeds 200 parts by weight, the oil resistance and the solvent resistance are significantly deteriorated. Examples of the silicone rubber include dimethyl silicone rubber, methyl vinyl silicone rubber, methylphenyl vinyl silicone rubber and the like. These usually contain a filler and the like in an amount of about 30 to 100 parts by weight based on 100 parts by weight of the silicone rubber. But,
It is commercially available as a silicone rubber compound.
It is possible to use a silicone oil having excellent heat resistance as a softening agent in place of the silicone rubber, but this is not preferable because the physical properties such as tensile strength are significantly lowered.

The method for manufacturing the cord-shaped heater according to the present invention is the same as the atmospheric pressure heating crosslinking method, which is low in the process cost of the silicone rubber cord-shaped heater. That is, the composition according to the present invention is extrusion-coated on a heating core with a predetermined wall thickness, and then heat-crosslinked under atmospheric pressure for about 30 seconds to 5 minutes in a heating furnace maintained at about 200 to 300 ° C. . At this time, the temperature of the cylinder and head of the extruder is preferably 50 ° C. or lower in consideration of the fact that the composition according to the present invention is crosslinked at about 80 ° C.

[0012]

According to the present invention, the tetrafluoroethylene-propylene-based copolymer is mixed with a methacrylic acid ester or an acrylic acid ester which is a cross-linking aid and an organic peroxide which is a cross-linking agent so that the vent Voids do not occur in the product even if it is heated and crosslinked at atmospheric pressure without using a die extruder. Furthermore, by adding a predetermined amount of silicone rubber, it is possible to achieve low viscosity and cost reduction of the composition at the same time. It is possible to provide an inexpensive cord-shaped heater.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the drawings. FIG. 1 is a partially cutaway perspective view of a cord-shaped heater. In this example, the materials shown in Table 1 were kneaded with a 12-inch open roll, and the obtained composition was mixed with a 40 mmφ rubber extruder into a glass fiber string 1 having an outer diameter of about 1.0 mm and an outer diameter of 0. A heating core 3 formed by spirally winding a metal resistance wire 2 of 18 mm is extrusion-coated to a thickness of 0.8 mm to form an insulating layer 4, and immediately thereafter at normal pressure in a heating furnace maintained at 200 ° C. It was heated for 5 minutes to crosslink the insulating layer 4 to form a cord-shaped heater. At this time, the temperature of the cylinder and head of the extruder was 50 ° C. In the composition of Table 1, the siliceous filler was used as a filler and sodium stearate was used as a lubricant.

Here, the cord-shaped heaters of the present embodiment and Comparative Examples 1 to 4 were cut into predetermined lengths, which were used as test products. The presence or absence of voids, tensile strength and elongation, heat resistance, and resistance A comparative test was conducted for solvent properties. As a test method, first, with respect to the presence or absence of a void, the test product was cut at several places and its cross section was visually confirmed. The tensile strength and elongation were measured according to JIS C 3004. Heat resistance was measured by heating the test product in a constant temperature bath maintained at 220 ° C for 96 hours, then taking it out, cooling it to room temperature, and then measuring it according to JIS C.
According to 3004, the residual tensile strength and the residual elongation were determined. Regarding the solvent resistance, the test product was immersed in the fuel oil C specified in JIS K 6301 at room temperature for 72 hours, then taken out, and the outer diameter was immediately measured to obtain the outer diameter change rate. The test results are shown in Table 2.

[0015]

[Table 1]

[0016]

[Table 2]

According to the test results, in Examples 1 to 4 in which the methacrylic acid ester or acrylic acid ester as the crosslinking aid and the organic peroxide as the crosslinking agent are used in combination, the process cost is low. Although voids are not generated in the test product even after performing normal pressure heating crosslinking, Comparative Examples 1 to 3 using other crosslinking aids instead of methacrylic acid ester or acrylic acid ester, It can be seen that numerous voids are generated in the test product. Although methacrylic acid ester is used as a crosslinking aid,
In Comparative Example 4 in which the amount of silicone rubber added is outside the range of the present invention, it is found that the oil resistance, which is a characteristic of the tetrafluoroethylene-propylene-based copolymer, is lost.

The present invention is not limited to the above embodiment, but may be used as an outer layer of a cord-shaped heater which already has an insulating layer.

[0019]

As described in detail above, the cord-shaped heater according to the present invention is excellent in heat resistance, oil resistance and electric characteristics. In addition, this cord-shaped heater can be manufactured by atmospheric pressure heat-crosslinking without using a vent type extruder, and is mixed with silicone rubber which is cheaper than tetrafluoroethylene-propylene-based copolymer. Therefore, it is extremely economical.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a cord-shaped heater.

[Explanation of symbols]

 1 Glass fiber string 2 Metal resistance wire 3 Heating core 4 Insulating layer

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area // (C08L 27/18 83:04) (C08L 83/04 27:18)

Claims (1)

[Claims] 1. A tetrafluoroethylene-propylene copolymer is mixed with a methacrylic acid ester or an acrylic acid ester which is a cross-linking agent and an organic peroxide which is a cross-linking agent, and a silicone rubber is added thereto. It has an insulating layer or an outer layer formed by crosslinking a composition containing 200 parts by weight or less of a mixture containing 100 parts by weight of a fluorinated ethylene-propylene copolymer as a main component and heating the mixture at atmospheric pressure. A cord-shaped heater that does.