JPH0815585A - Heat resistant optical fiber - Google Patents

Abstract

PURPOSE:To produce a heat resistant optical fiber which is improved a heat resistant characteristic by preventing an air in the atmosphere from contacting with a resin covering layer and suppressing oxidative deterioration reaction in an optical fiber covered with resin. CONSTITUTION:The resin covering layer 2 is provided at an outer periphery part of a quartz glass optical fiber 1 and a carbon layer 3 is provided at the outer periphery part of the resin covering layer 2. A permeation of oxygen molecule is prevented since the carbon layer 3 is very dense. As a result. the oxidative deterioration reaction of the resin covering layer 2 is prevented and a heat resistant temp. as the optical fiber 1 is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant optical fiber, and more particularly to a heat-resistant optical fiber having improved heat resistance characteristics by suppressing oxidative deterioration reaction.

[0002]

2. Description of the Related Art Recently, optical fibers are widely used not only for communication but also as sensors. In particular, in monitoring and control systems for blast furnaces, thermal power plants, etc., there is an increasing demand for using optical fibers in a high temperature environment. By the way, a general optical fiber is composed of quartz glass and a coating material such as UV resin or silicone resin provided around the quartz glass.

Quartz glass itself is stable even at 1000 ° C. or higher without being oxidized or decomposed, but the coating material deteriorates at a much lower temperature than this. Therefore, the heat resistance of the optical fiber ultimately depends on the heat resistance of the coating material. 1
In order to meet the demand for use in a high temperature environment exceeding 00 ° C, various materials and structures are currently proposed and implemented as coating materials for heat resistant optical fibers. The typical ones will be described below.

(1) Metal coated optical fiber A metal such as aluminum, nickel or gold is used as a coating material.
Deterioration of the coated metal is not observed up to about 500 ° C., but there are some drawbacks due to the large difference in expansion coefficient between quartz and metal. For example, the heat cycle causes slippage between the coating and the quartz glass, resulting in a decrease in strength and an increase in transmission loss. When a tensile load is applied in a proof test, etc., the metal part plastically deforms and does not return to its original shape even if it is unloaded, whereas the glass part elastically deforms and returns to its original shape, so strain remains after the test and the fiber bends and It causes a decrease in strength.

(2) Polyimide resin-coated optical fiber Polyimide resin is superior in heat resistance and chemical resistance to ordinary UV resins and silicone resins, and the temperature that can be used for a long time is about 300 ° C., which is the highest as an organic material. Is. Recently, the glass transition temperature is 400 ° C or higher, and the thermal decomposition temperature is 550.
Polyimide resins above ℃ have also been developed. Unlike metal-coated optical fibers, the increase in transmission loss due to heat cycles is small, and no strain remains after the proof test. The present invention improves the heat resistance of a heat resistant optical fiber coated with a resin, and particularly improves the heat resistance of a heat resistant optical fiber coated with a polyimide resin.

[0006]

It is generally known that the oxidative deterioration reaction of a polyimide resin starts at a temperature considerably lower than the thermal decomposition temperature. Therefore, when actually used for a long time, the heat resistant temperature of the optical fiber is below the oxidation deterioration temperature. In fact, a polyimide resin having a thermal decomposition temperature of about 550 ° C. has a heat resistant temperature of about 350 ° C. at which it can be used for a long time. Therefore, if the oxidative deterioration reaction can be suppressed, the heat resistant temperature can be improved without changing the material of the coating material. Based on this idea, a method has been proposed in which a resin-coated optical fiber is inserted into a metal tube or the like and filled with an inert gas to remove oxygen in the surroundings.

However, although this method also improves the deterioration temperature of the coating material, distortion is generated due to the difference in the thermal expansion coefficient between the metal tube and the optical fiber, the transmission loss is increased by hydrogen generated from the metal tube, and the ordinary resin-coated light is used. There are still problems such as thicker fiber. The present invention solves the above problems and, in an optical fiber coated with a resin, a heat-resistant optical fiber having improved heat resistance characteristics by preventing oxygen in the atmosphere from contacting the resin coating layer and suppressing an oxidative deterioration reaction. The purpose is to provide.

[0008]

The present invention has the following means in order to solve the above problems. A heat-resistant optical fiber according to claim 1 of the present invention is characterized in that a resin coating layer is provided on an outer peripheral portion of the optical fiber, and a carbon layer is provided on an outer peripheral portion of the resin coating layer. The heat-resistant optical fiber according to claim 2 of the present invention is characterized in that the resin coating layer is made of a polyimide resin.

[0009]

In the heat-resistant optical fiber according to the first aspect of the present invention, the resin coating layer is provided on the outer peripheral portion of the optical fiber, and the carbon layer is provided on the outer peripheral portion of the resin coating layer. Since this carbon layer is very dense, it can prevent the permeation of oxygen molecules. Therefore, the oxidative deterioration reaction of the resin coating layer is hindered, and the heat resistant temperature of the optical fiber is improved.

In the heat-resistant optical fiber according to claim 2 of the present invention, the resin coating layer is made of polyimide resin. Polyimide resin is superior in heat resistance and chemical resistance to ordinary UV resins and silicone resins, and the temperature that can be used for a long time is about 300 ° C., which is the highest temperature for organic materials. Recently, a polyimide resin having a glass transition point of 400 ° C. or higher and a thermal decomposition temperature of 550 ° C. or higher has been developed. Therefore, the present invention in which the resin coating layer is a polyimide resin can sufficiently withstand long-term use at 500 ° C or lower.

[0011]

The present invention will be described below in detail with reference to examples.

Example 1 An optical fiber having the cross section shown in FIG. 1 was obtained by coating the optical fiber with a polyimide resin and a carbon coating on the outer surface as follows. In the figure, 1 is a silica glass optical fiber, 2 is a resin coating layer made of polyimide resin, and 3 is a carbon layer. The silica glass optical fiber 1 is a 1.3 μm band single mode optical fiber having a diameter of 125 μm spun from a silica glass optical fiber base material by a drawing furnace at a temperature of about 2000 ° C.

The polyimide resin of the resin coating layer 2 is a thermoplastic or thermosetting polymer having an imide bond in the molecule. Aromatic polyimide has excellent heat resistance and is suitable as a protective layer for the optical fiber of the present invention. Typical ones are the reaction of trimellitic anhydride with 4,4-diaminodiphenyl ether, benzophenonetetracarboxylic dianhydride with tetraaminobiphenyl, and benzophenonetetracarboxylic dianhydride with 4,4-oxydianiline. It is a polycondensation product of the obtained polyamic acid.

To form the resin coating layer 2 of polyimide resin on the outer circumference of the silica glass optical fiber 1, the liquid composition comprising the above polyamic acid oligomer solution is applied to the outer circumference of the silica glass optical fiber 1 using a wire rod coating die. Coated,
The coating is cured by passing through a heating oven to evaporate the solvent. At this time, the polyamic acid is polycondensed to form a polyimide resin. The thickness of the resin coating layer 2 of polyimide resin is preferably about 10 μm to about 30 μm.

The silica glass optical fiber 1 having the resin coating layer 2 obtained as described above is set in a container filled with a hydrocarbon gas and irradiated with a carbon dioxide laser while moving in the longitudinal direction. The carbon layer 3 is formed on the surface of 2. The heat resistance of the heat resistant optical fiber manufactured by the above method was investigated. As shown in Table 1, a heat-resistant optical fiber A of the present invention, a polyimide-coated optical fiber B of a conventional structure, and a polyimide-coated optical fiber B of the conventional type, which is sent through a SUS tube and filled with nitrogen, are prepared, and each of them is electrically charged. The coating was observed by heating in a furnace under the conditions shown in Table 2.

The observation results are shown in Table 3. From Table 3, the heat-resistant optical fiber A (sample A) provided with the carbon layer 3 is superior in heat resistance at high temperature as compared with the case of the polyimide resin coating (sample B), and no deterioration is observed at 350 ° C. × 120 hours.
The surface was slightly roughened at 00 ° C for 120 hours. This result shows that it has heat resistance characteristics equivalent to those of the heat-resistant optical fiber with inserted SUS tube (Sample C) that has been conventionally used, and it was found that the oxygen blocking by the carbon layer 3 is effective.

That is, since the carbon layer deposited on the polyimide resin layer is extremely dense, it is possible to prevent the permeation of oxygen molecules. Therefore, the oxidation deterioration reaction of the polyimide is hindered, and the heat resistant temperature of the optical fiber is improved. Further, thermal change of the microscopic structure of the carbon layer at high temperature includes graphitization, but since it starts at around 1500 ° C, there is no problem in the currently used operating temperature range of 500 ° C or lower. It is known that the oxidation reaction is hardly seen at 550 ° C. or lower, and it can be said that the carbon layer also has satisfactory heat resistance in this respect.

(Embodiment 2) In Embodiment 1, the polyimide resin is used as the resin coating layer, but the resin coating layer is not limited to the polyimide resin, and a resin that can be used as the resin coating layer of the optical fiber, for example, a silicone resin. As in the case of Example 1, the urethane acrylate resin also improved the heat resistance due to the effect of blocking oxygen.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

As described above, the claims 1 to 3 of the present invention are as follows.
In No. 2 heat-resistant optical fiber, a resin coating layer is provided on the outer peripheral portion of the optical fiber, and a carbon layer is provided on the outer peripheral portion of the resin coating layer. Since this carbon layer is very dense, it can prevent the permeation of oxygen molecules. Therefore, the oxidative deterioration reaction of the resin coating layer is hindered, and the heat resistant temperature of the optical fiber is improved.

In the heat-resistant optical fiber according to claim 2 of the present invention, since the resin coating layer is made of polyimide resin,
The heat resistant temperature at which continuous use is possible for a long time approaches the thermal decomposition temperature of polyimide, and the heat resistance can be significantly improved as compared with the conventional heat resistant optical fiber.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a heat resistant optical fiber of the present invention.

[Explanation of symbols]

 1 Quartz glass optical fiber 2 Resin coating layer 3 Carbon layer

Claims (2)

[Claims] 1. A heat-resistant optical fiber, wherein a resin coating layer is provided on an outer peripheral portion of the optical fiber, and a carbon layer is provided on an outer peripheral portion of the resin coating layer. 2. The heat resistant optical fiber according to claim 1, wherein the resin coating layer is made of a polyimide resin.