JPH07111186A - Rod-shaped heating element - Google Patents

Abstract

PURPOSE:To reduce the unevenness of a heat generation temperature by providing a heat generating body comprising an electrode at a center part of a rod of conductive resin having a desired volume resistivity, and winding a heat generation body of the same structure and having a smaller outer diameter around it to be an outer circumferential electrode. CONSTITUTION:A heat generating body comprises conductive resin having a volume resistivity of 4800OMEGAcm obtained by melting and kneading maleic acid- denatured polypropylene by 83% and acetylene black by 13% in an extruder or the like. The heat generating body 2 as a base body of application is formed as a rod of a diameter of 6mm, for example, around a center electrode 1 comprising copper twisted wire of 1mm<2>, for example, in the extruder or the like. Separately from this, the heat generating body 2 as an electrode body is formed as a rod of a diameter of 1.5mm, for example, in a similar method. The electrode body heat generating body 2 is wound around the base body heat generating body 2 at a pitch of 1cm, for example, like a coil form the outer circumferential electrode. Both heat generating bodies are heated to their softening point or higher preliminarily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low temperature rod-shaped heating element having excellent flexibility, which is used for road and roof snow melting, tanks, pipes, soil freezing prevention and heating, and heating in buildings.

[0002]

2. Description of the Related Art As a rod-shaped heating element, there is a rod-shaped heating element having a circular cross section, which is disclosed in JP-A-57-187887. However, since the product has a structure in which electrodes are attached to both ends of the heating element, there is a drawback that if the length is increased, the resistance value increases and the amount of heat generation decreases unless the cross-sectional area is increased. Therefore, since the length of the heating element is limited, when laying a large area, the number of heating elements used increases and the number of connection points increases.

A heating element having a structure in which electrode wires are arranged parallel to the longitudinal direction and compensating for the above-mentioned drawbacks is disclosed in Japanese Patent Laid-Open No. 58-2142.
Although there is a feeder linear heating element disclosed in Japanese Patent Publication No. 95, etc., it has a drawback that it can be bent only in a certain direction due to its sectional shape. A heating element having a structure in which a metal wire is installed in a coil shape on the central portion and the outer peripheral portion of a rod-shaped conductive layer having a circular cross section is also conceivable. Since the sectional shape is circular, it can be bent in any direction, but the outer peripheral portion If the metal wire to be installed in is a metal stranded wire having a circular cross section, the contact area with the peripheral portion of the conductive layer is small, so that the contact resistance is large and stable conduction cannot be obtained.

In order to increase the contact area between the metal stranded wire and the conductive layer, the conductive layer is considerably softened, and the stranded wire is buried in the conductive layer while the tension when winding the stranded wire is increased, so that the contact area is increased. It is possible to increase the number, but in this case the deformation of the conductive layer is remarkable and the distance between the electrode wires in the central part and the peripheral part varies, making it difficult to manufacture a heating element with uniform heating characteristics at any part. Is.

[0005]

The present invention has the above-mentioned drawbacks,
That is, the present invention provides a rod-shaped heating element that can obtain a stable amount of heat generation in any part without being restricted by the length of the heating element or the bending direction.

[0006]

The present invention is a rod-shaped heating element characterized in that a conductive layer having a constant cross-sectional shape is provided with electrode wires at the central portion and the outer peripheral portion and is covered with an insulating resin. . The composition used for the conductive layer is a thermoplastic resin, such as polyethylene, polypropylene, polyamide, polyester, polystyrene and its elastomers and acid modified products, and as the conductive material, for example, carbon black, graphite, carbon fiber, metal powder or metal fiber. Is melted and kneaded by a kneader such as a kneader, a Banbury mixer or a twin-screw extruder, and has a volume resistance value of 10 ⁰ to 10 ⁵ having electrical conductivity.

Next, the above composition is melted by an extruder, and a metal wire is continuously inserted at the center of the cross section by a crosshead die to obtain a rod-shaped conductor having a constant cross section. One of the obtained conductors is used as an adherend and the other is used as an electrode body, and is wound in a coiled state in a molten state. The conductor used for the electrode body is manufactured in advance, and when the adherend is manufactured, that is, immediately after inserting the metal wire into the conductive composition with the crosshead die, the conductor to be the adherend is wound by the winding machine. Wind in a coil. At this time, the conductor used for the electrode body needs to be preheated to a softening point or higher with hot air or the like.

Further, it is desirable that the conductor used for the electrode body has a smaller outer diameter than the conductor used as the adherend in order to facilitate the winding work, and it is preferable that the conductor has an outer diameter of 1 / 4 or less is desirable. Further, the winding interval of the electrode body is preferably 20 mm or less in order to obtain uniform heat generation.
The coating layer of the insulating resin can be installed by continuously coating the melted insulating resin on the heating element with an extruder using a crosshead die when the above process is completed. The heating element provided with the coating layer is a cooling method for a molded article generally used in extrusion molding, for example, a water tank or an air-cooled tube,
Solidify the above product by a method of passing through a cooling die,
Cut it to an appropriate length to make a rod-shaped heating element.

[0009]

EXAMPLES The present invention will be described below with reference to examples. In the examples,% means% by weight. Example 1 83% of maleic acid-modified polypropylene with MFR = 1 g / 10 min and 17% of acetylene black were mixed with L / D = 3.
2. Melted and kneaded with a twin-screw extruder having a cylinder inner diameter of 30 mm to obtain a conductive resin composition for a conductive layer in the form of pellets having a volume resistance value of 4800 Ω · cm. The obtained resin composition was melted at 230 ° C. in a single-screw extruder having L / D = 32 and a cylinder inner diameter = 40 mm, and a copper stranded wire having a cross-sectional area of 1 mm ² was passed through a crosshead die while centering it By inserting, an electric conductor for an electrode body having a circular cross section with an outer diameter of 1.5 mm was obtained.

Next, a conductor for an adherend having an outer diameter of 6 mm and a circular cross section is molded from the above composition by the same method as described above, and immediately after the conductor is ejected from the die, it is heated in advance with hot air. The conductor for electrode body preheated to 0 ° C. was wound into a coil at a 1 cm pitch by a winding machine. The heating element after winding is passed through a crosshead die to form a coating layer, and a linear low density polyethylene of MFR = 2 g / 10 min is connected to the crosshead die L / D = 28, cylinder inner diameter = A heating element passing through the die was coated in a molten state at 200 ° C. with a 40 mm single screw extruder.

Further, after discharging the die, a water tank having a length of 2 m is moved to 1 m.
After passing at a speed of / min to cool and solidify, it was cut into a rod-shaped heating element with a length of 2 m. The electric resistance value between the metal wires of the central portion and the peripheral portion of the obtained heating element was measured and found to be 98Ω at 0 ° C, and the calorific value obtained by connecting to a 100V AC power source was 102W. Further, a 100V AC power supply was energized for 30 minutes at 0 ° C with the middle part of the heating element along a cylinder having an outer diameter of 100 mm, but no variation in the heating temperature was observed between the parts of the heating element.

[0012]

According to the present invention, it can be used in any length,
It has become possible to obtain a rod-shaped heating element that can be bent in any direction and that does not cause variations in the heating temperature between regions.

[Brief description of drawings]

FIG. 1 shows a schematic perspective view of a rod-shaped heating element of the present invention.

[Explanation of symbols]

 1: Central metal wire 2: Conductive layer 3: Peripheral metal wire 4: Covering layer

Claims (2)

[Claims] 1. A rod-shaped conductor in which a metal wire is provided as one electrode in the center of a conductive layer having a constant cross-sectional shape, and a conductor in which a metal wire is similarly provided in the center of the conductive layer is used as the other electrode. A rod-shaped heating element having a structure in which the outer surface of the conductor is integrated in a coiled state in a softened state, and the outer surface is covered with an insulating resin. 2. The conductive resin composition used for the conductive layer comprises a thermoplastic resin and a conductive material having a volume resistance value of 10 ⁰ Ω · cm or less, and a volume resistance value of 10 ⁰ to 10 ⁵ Ω · cm.
The rod-shaped heating element according to claim 1, wherein