JPH02220389A - Tetrafluoroethylene resin insulation coated heating wire heater - Google Patents

Abstract

PURPOSE:To make the permeability of fluid small and improve the electric insulation durability by coating with an ethylene tetrafluoride resin tube modified to have a specified specific gravity and including sphaerites in part of the inner organization in which mutual linkage is formed between molecules by motion of the molecules. CONSTITUTION:The titled device is composed of a heat wire coated with an ethylene tetrafluoride resin (PTFE) tube modified to have a specific gravity of 2.16-2.20 and composed of an organization including sphaerites radially oriented at least in part of it in which mutual linkage is formed between molecules by motion of the molecules. The permeability of fluid can thus be small and a high electric insulation durability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an improvement in a t1-tetrafluoroethylene resin tube insulated RIJ heating wire heater used for heating a liquid by being directly immersed in the liquid. It is something.

[Conventional technology] Conventionally, in heating wire heaters that are used by being directly immersed in liquids for heating and keeping chemicals, semiconductor processing liquids, cleaning liquids, etc. Fluororesin tubes are used, which have excellent properties such as durability, heat resistance, and electrical insulation.

The above-mentioned fluororesin tube is a polytetrafluoroethylene resin (hereinafter referred to as PTF) manufactured by continuous paste extrusion and firing.
E) tube, or perfluoroalkoxy resin having perfluoroalkoxy in the side chain (hereinafter referred to as PF
A) Tubes are often used.

Then, cover the heating wire with the above insulation coating tube,
The heater is formed by processing it into a coil shape or into other shapes.

[Problems to be Solved by the Invention] However, the above-described PTFE tube for insulating the heating wire of the heater has a drawback in terms of electrical insulation durability during immersion in liquid.

That is, P manufactured by continuous paste extrusion firing
TFE tubes generally have relatively high liquid permeability because the firing time is short, and since the fluid is in a high temperature state, the permeability becomes even higher and may corrode the metal heating wire. Furthermore, the insulating resistance may decrease due to fluid penetration into the PTFE tube.

In addition, PTF manufactured by continuous paste extrusion firing
E-tubes are also unstable in terms of dimensional stability and tend to shorten in length when the tube is heated. Because of this property, when a metal heating wire is coated with a PTFE tube and processed into a coil shape to be used as a heater, or when heat treated before use, the PTFE tube will shrink; Because it is processed, it cannot shrink freely and often breaks. Also, even if the tube cannot be cut, there is always residual distortion in the tube, so
Liquid permeability is high.

On the other hand, P-FA tube is manufactured by continuous paste extrusion firing P
Although TFE tubes have a specific gravity of about 2.15, they are not satisfactory in terms of fluid permeability, and in terms of dimensional stability, continuous paste extrusion fired PTFE
Similar to tube.

[Means for solving the problems] The present invention is particularly directed to the PTF in the above-mentioned electric wire heater.
This was done to improve the fluid permeability of the E-tube, and the PTFE tube has a specific gravity of 2.1.
A PTFE tube adjusted to 6 to 2.20, composed of a structure containing spherulites consisting of radially oriented cameras in at least a part of the structure, and in which mutual termination of molecules is formed by the movement of molecules. The above-mentioned problems are solved by covering the heating wire with the heating wire.

A PTFE tube having the above structure is easily obtained by a process of re-firing a conventional continuous paste extrusion-fired PTFE tube above its melting point and adjusting the cooling rate.

[Effect] Through the above-mentioned re-firing treatment, spherulites grow, the molecules become radially spherical, orientation (anisotropy) is removed, and with the formation of spherulites, one molecule moves, and the molecules mutually In a PTPE tube with a tangled configuration, fusion between the raw material powders is promoted and the structure is more firmly fixed, so that fluid permeability is reduced.

In addition, in the refired PTFE tube, residual strain inside the tube is also removed and the one-dimensional stability is improved.

[Embodiments of the Invention] A heated wire wave rMPTFE tube having the above structure is obtained by re-firing a conventional continuous paste extrusion fired tube.

The heat treatment temperature for re-firing the conventional continuous paste extrusion fired tube is preferably in the range from the melting point of PTFE to 400° C., and the re-baking time is arbitrarily adjusted depending on the heat treatment temperature.

In the above heat treatment, the re-firing temperature and the subsequent cooling method are factors that increase the specific gravity of the PTFE tube. That is, at the same heat treatment temperature, the faster the cooling rate, the lower the specific gravity, and at the same cooling rate, the higher the firing temperature, the higher the specific gravity.

According to experiments, if the spherulites are cooled by air or water after heat treatment for re-firing, the size of the spherulites becomes smaller, but butterflies are formed in the tube, and the cooling rate differs in some parts, resulting in color change. It has been recognized that unevenness tends to occur and quality stability decreases.

However, if the tube is cooled as it is in the re-fired furnace (1! air furnace), the above defects will not occur and a product with stable quality will be obtained. In particular, it has been confirmed that cooling in a furnace facilitates crystallization because the cooling rate and specific gravity can be adjusted appropriately.

The specific gravity of the PTFE tube can be adjusted independently of the formation of spherulites, and the specific gravity can also be controlled by the firing temperature and cooling rate, regardless of whether spherulites are formed.

On the other hand, to generate spherulites in the structure of the PTFE tube,
Temperature and time are required as energy to move the polymers and arrange them in a spherical shape.

In the heat treatment of a PTFE tube, lamellar crystals (plate-like) are first produced, and then they move to produce a higher-order structure (spherulites). Particularly in the case of PTFE, spherulites are generated after the polymer is thermally degraded to some extent. This generation of spherulites removes the anisotropy of the continuously extruded and fired PTFE tube structure, and the molecules oriented in the same direction move during heat treatment and become entangled, resulting in fusion between the raw material powders. Adhesion is promoted, the tissue becomes more tightly bound, and fluid permeability is reduced.

The size of the generated spherulites is preferably between 1 μm and 25 μm in diameter. If the diameter is less than 1 μm, anisotropy remains in the PTFE tube structure, and the fusion between the raw material powders is insufficient.
Fluid permeability cannot be improved sufficiently, on the other hand, when the diameter of one spherulite exceeds 25 μm.

1) The bending fatigue resistance of the TFE tube is reduced, and air bubbles are generated within the tube material due to coiling, etc.
The appearance tends to become cloudy, fluid permeability increases, and insulation resistance durability decreases.

[Embodiments of the invention] Example (1) A conventional continuous paste extrusion fired PTFE tube (outer diameter 1.8+NW, inner diameter 1.2 m, length 15 m) was
Baked in an electric furnace at 0°C for 7 hours, then heated at 50°C/11r for 10 hours.
After cooling to 0° C., the tube was taken out of the furnace and the ratio 11 was measured. The specific gravity was 2.20 when measured in a room. Also,
11 observations of the internal structure of the tube with a polarized Ilt microscope (1r1
As a result, it was confirmed that spherulites were formed as shown in the microscopic copy of FIG. 1.

Also, nu nu re-Jilt formation needs:
, diameter 0,9 m Q) - covered with black 11 wire,
A heater (Fig. 2) with a heating element total length of 13 m90 an and a capacity Bt of 1.5 W was created. The power density of the heater is 3.83W
/- This heater was connected to a 200V power source, and a test was conducted in which concentrated sulfuric acid and acid were heated to 150°C for 5000 hours.

As a result, the insulation resistance of the heater was changed before and after the test (100M
Ω or more) did not change.

In addition, when determining g+lI of the insulation resistance 115, put a stainless steel strip in the heated liquid at the diameter where the heater is turned off, use it as one electrode, and use the other electrode as the heater conductor to measure the insulation resistance. It was measured.

As the 819 meter, a battery-powered insulation resistance meter (Type-2403) manufactured by Yokogawa Hokutatsu F41 Machine Co., Ltd. was used.

Example (2) A conventional continuous paste extrusion fired PTFE tube (outer diameter 2.0 m, inner diameter 1.4 m, length 25 m) was fired in an electric furnace at 360°C for 7 hours, the electric furnace power was turned off, and the inside of the furnace was The tube was naturally cooled to produce a PTFE tube with a specific gravity of 2.162. Spherulite formation was also confirmed in the tube structure by the same method as in Example (1).

This tube was covered with a nichrome wire having a diameter of 1.0 m to produce a heater with a length of 9 m 53 Qll. The power density of the heater was 6.7 W/cd9, and this heater was
The same test as in Example (1) was conducted by connecting to a 00V power supply. As a result, there was no decrease in insulation resistance, and a resistance value of 100 MΩ or more was observed.

Comparative Example Conventional continuous paste extrusion fired PTFE tube (outer diameter 2.0-1 inner diameter 1.4 mm, length 25 m) was
A heater was produced in the same manner as in Example (2) by coating an on nichrome wire.

The specific gravity of the PTFE tube is 2.154, which is 1.
No formation of spherulites is observed in the tissue.

As a result of performing the same test as in Example (2) on the above heater, it was observed that the insulation resistance decreased by 50 MΩ in 1500 hours.

[Effects of the Invention] As described above, according to the present invention, a conventional continuous paste extrusion fired PTFE tube is heat treated at a temperature higher than the melting point of the tube to adjust the specific gravity to 2.16 to 2.20. In addition, the heating wire is covered with a PTFE tube whose structure is partially or mostly composed of spherulites.
A PTFE tube insulation-coated heating wire heater having low fluid permeability and excellent electrical insulation durability can be obtained.

That is, conventional continuous paste extrusion firing PTI”E
The insulation-coated tube, which is re-fired at a temperature above its melting point, has a higher fluid flow rate than conventional continuous paste extruded and fired PTFE tubes by eliminating residual strain, eliminating molecular orientation, and improving the fusion properties between raw material powders. Penetration is approximately 1/10
Therefore, the performance of electric wire heaters used by being immersed in liquid can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a reproduction of a microscopic photograph of a PTFE tube covering a heater of the present invention, and FIG. 2 is a perspective view of the heater. Patent Applicant: NICHIAS Co., Ltd. Agent: Patent Attorney Nagai 1) Takesanbe Part 1, Figure 2

Claims (1)

[Claims] In a heater constructed by insulating and covering a heating wire with a tetrafluoroethylene resin tube, the tetrafluoroethylene resin tube has a specific gravity adjusted to 2.16 to 2.20, and has spherulites in at least a part of its internal structure. 1. A tetrafluoroethylene resin tube insulation-coated heating wire heater, characterized in that the molecules are entangled with each other due to the movement of the molecules, and the orientation is removed.