JPH06148474A - Heat resistant coated glass fiber - Google Patents

Abstract

PURPOSE:To provide the optical fiber having high heat resistance and sufficient practicable protective strength by incorporating carbon particles or carbon fibers into a coating layer. CONSTITUTION:A thin layer consisting of only the polycarbodiimide resin without contg. carbon or carbon fibers is provided as an inside layer 11 in direct contact with glass and a polycarbodiimide resin dispersed with the carbon or carbon fibers is formed slightly thickly on the outer periphery 12 thereof. Then, the amorphous carbon consisting of the polycarbodiimide resin as a precursor is formed as the base of the coating and, therefore, the glass fiber has the excellent heat resistance and is usable even at a temp. as high as 400 to 800 deg.C. The shrinkage of the polycarbodiimide at the time of calcination is lessened by dispersing the carbon particles or carbon fibers into the polycarbodiimide and, therefore, the distortion acting on the fiber is lessened and the film having a relatively thick film is eventually formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass fiber for optical transmission having a cover on its outer circumference, and more particularly to a glass fiber for optical transmission which has excellent heat resistance and can be used at high temperatures.

[0002]

2. Description of the Related Art A glass fiber is easily broken by an external damage when it is made of glass alone. Therefore, the outer circumference of the glass fiber is coated with a thermosetting resin, an ultraviolet curing resin or a thermoplastic resin to form a protected glass fiber. However, it is used for optical transmission lines. In recent years, the use of optical fibers has expanded, and it is hoped that optical fibers will be used in special environments such as oilfield excavation equipment, electric power-optical composite cables, artificial satellite cables, etc. that are exposed to high thermal energy or radiant energy. There is a need for an optical fiber that can be used in such an environment. Further, glass fibers such as capillary columns used for gas chromatography other than those for optical transmission are strongly required to have a heat resistant coating. Polyimide is used as such a heat-resistant coating material.

[0003]

[Problems to be Solved by the Invention] Polyimide is superior in heat resistance to other resins, but decomposes at 400 ° C. or higher. Ladder-shaped polyorganosiloxane has also been studied as a heat-resistant coating material (JP-A-53-8).
No. 8099), the side chains are decomposed near 400 ° C., and at a temperature higher than that, sufficient properties cannot be obtained as a coating film. On the other hand, a method of using amorphous carbon as a coating means has also been studied, and a hydrocarbon chemical is decomposed by a chemical vapor deposition method (CVD method) and carbon is deposited to coat the glass fiber surface. The film thickness is as thin as 0.1 μm or less. Therefore, sufficient protection strength cannot be obtained as it is. (In particular, the immunity is weak.) In the case of the amorphous carbon coating by the CVD method, it is necessary to further wear a resin such as a UV-curable urethane acrylate in order to obtain a practical protective strength. As a result, the heat resistance of the entire fiber cannot be improved.

[0004]

Means for Solving the Problems As a means for solving the above-mentioned problems, the inventors of the present invention can use a glass fiber having a polycarbodiimide resin as a precursor as a coating to obtain a glass fiber having a temperature of 400 ° C. to 800 ° C. Paying attention to the fact that it can be used at high temperatures such as, by including carbon particles or carbon fibers in this coating layer,
It has been found that an optical fiber having a desired heat resistance and a sufficient practical protection strength can be obtained.

Polycarbodiimide can be dissolved in a solvent and adjusted to an appropriate viscosity, and as shown in FIG. 1, it can be applied to the surface of a glass fiber immediately after drawing using a device similar to a conventional device. it can. When this fiber is passed through a baking oven to remove the solvent, a polycarbodiimide-coated fiber is obtained. Furthermore, when this fiber is fired at about 1000 ° C. in an inert gas, polycarbodiimide becomes amorphous carbon, and a coated optical fiber having excellent heat resistance can be obtained.

However, when only the polycarbodiimide resin is applied and baked, it is very difficult to form a thick film of 5 μm or more. If the thin film is 5 μm or less, the above-mentioned CVD
Similar to the case of amorphous carbon coating by the method, the practical protective strength is insufficient. (In particular, the resistance to immunity is weak.) If a thick film is formed only from polycarbodiimide resin, there will be a problem that firing will take a long time, and the shrinkage of the coating due to firing will be large and the fiber will be distorted, resulting in transmission loss. Will become bigger. In addition, the coating layer may peel off during the firing step.

The inventors of the present invention have further studied, and a thick film can be formed by applying and baking carbon particles or carbon fibers dispersed in a polycarbodiimide resin-containing solution to form a thick film. It has been found that a coated fiber having excellent heat resistance and practical protection strength can be obtained. However, it was found that the strength of the glass fiber was slightly lowered. Therefore, further studies were carried out, and a thin layer of carbon or a polycarbodiimide resin containing no carbon fiber was provided as an inner layer in direct contact with the glass, and a polycarbodiimide resin layer in which carbon or carbon fiber was dispersed was slightly thickened on the outer periphery thereof. It has been found that when formed, the coated fiber can be obtained without lowering the strength of the glass fiber, having excellent heat resistance, and having practical protective strength.

The polycarbodiimide of the present invention is synthesized by a decarboxylation condensation reaction of diisocyanate in the presence of a catalyst. This polycarbodiimide is obtained in the form of powder or varnish. By dissolving this in a solvent, it is possible to adjust the viscosity suitable for coating using a die or the like in the drawing step.

It is necessary that the solvent has good compatibility with polycarbodiimide and has a suitable boiling point.
It is necessary to remove the solvent at the time of curing, and in that respect, the lower boiling point is preferable. However, if the boiling point is too low, the solvent volatilizes and the viscosity becomes high during coating in the drawing step, or the solvent volatilizes rapidly during curing and bubbles are generated in the coating layer. I have a problem. Therefore, 100-2
Those having a boiling point of 50 ° C. are preferred. Solvents satisfying these boiling points include alcohols, aromatics,
Various types such as ester type are conceivable, but considering the compatibility with polycarbodiimide, tetrachloroethylene,
A halogenated hydrocarbon solvent such as trichlorethylene is particularly preferable.

The carbon to be dispersed in the polycarbodiimide resin may be in the form of particles or fibers, but the fibrous form is dispersed in the longitudinal direction of the fiber by dispersing the carbon in the longitudinal direction. Very high strength fibers can be obtained.

[0011]

The glass fiber of the present invention has a coating base of amorphous carbon containing a polycarbodiimide resin as a precursor, and therefore has excellent heat resistance and a temperature of 400 ° C to 80 ° C.
It can also be used at high temperatures such as 0 ° C. Further, by dispersing the carbon particles or carbon fibers in the polycarbodiimide, it is possible to reduce the shrinkage of the polycarbodiimide during firing, it is possible to reduce the strain on the fiber, resulting in a relatively thick film formation can do. Further, a thin film layer consisting only of polycarbodiimide resin is provided in the inner layer, and further, a carbon fiber, or a polycarbodiimide resin layer in which carbon particles are dispersed is provided in the outer layer thereof, and these are fired to form an amorphous carbon, thereby forming a glass. A coating film can be formed without damaging the fiber, a coating film having a sufficient thickness to obtain a practical protective strength and a glass fiber having a high strength can be obtained.

Polycarbodiimide has the formula (-R-N = C = N
-) It takes the structure of n and is obtained in the form of powder or varnish. This can be adjusted to a suitable clay by dissolving it in a solvent. The solvent used is not particularly limited, but halogen solvents such as trichloroethylene and tetrachloroethylene are preferable from the viewpoint of compatibility. This solution is applied to a glass fiber immediately after drawing with a die or the like, and the solvent is passed through a baking oven to form a polycarbodiimide coating film. This polycarbodiimide is
By heat treatment, self-crosslinking proceeds and heat resistance is imparted. Phenol resins, polyacrylonitrile, and the like, which are usually used as precursors of carbon fibers, are hard and brittle when heat-treated, and do not have sufficient flexibility, and are not suitable as a coating material for glass fibers.

On the other hand, when polycarbodiimide is used as the precursor, the flexibility is maintained and the flexibility is sufficient. The firing temperature is 200 ° C. to 1500 ° C. in an inert gas. The higher the baking temperature is, the harder the film is, and the higher the tensile strength and the heat resistance are. However, if it is baked too much, the elongation is small and sufficient flexibility cannot be obtained.

The amorphous carbon-based coating thus obtained exhibits good heat resistance,
It has the following advantages. Since it is difficult for water to pass through, it is possible to prevent the strength of the glass fiber from decreasing due to water, and it is possible to obtain a glass fiber having excellent fatigue characteristics. Excellent gas barrier property. Since it is difficult for hydrogen to pass through, it is possible to prevent an increase in optical transmission loss due to hydrogen when used as a fiber for optical transmission. Has excellent chemical resistance. It can also be used in environments where acidic, alkaline solutions, oils, etc. are present.

[0015]

EXAMPLE A resin varnish (referred to as resin varnish A) was prepared by adding 3-methyl-1-phenylphosphoren-1-oxide as a catalyst in tetrachloroethylene at 120 ° C. with a composition of 200 g of tolylene diisocyanate and 5 g of phenyl isocyanate. I got). 60 carbon fibers with an average length of about 5 μm were added to resin varnish A.
A resin varnish (referred to as resin varnish B) dispersed in a wt% ratio was prepared. In addition, the resin varnish A has a diameter of 1 μm.
A resin varnish (referred to as resin varnish C) in which φ carbon particles were dispersed at a ratio of 40 wt% was prepared.

(Example 1) Core diameter of wire drawing diameter: 10 μm
After coating the resin varnish B on a single mode optical transmission glass fiber having a diameter of φ and a cladding diameter of 125 μmφ, a polycarbodiimide coating film containing carbon fiber was formed by passing through an infrared furnace to give a coating diameter of 170 μmφ. The coated fiber was fired in argon gas at 1000 ° C. for 24 hours to convert the coating into amorphous carbon, and a coated optical fiber 1 km long as shown in FIG. 3 was obtained. The thus-produced glass fiber for optical transmission had a transmission loss of 0.35 dB / Km at a wavelength of 1.3 μm and a tensile strength of 4 to 6 Kg, which was good while slightly lowering the tensile strength. This optical fiber 6
It was left in a constant temperature bath at 00 ° C for 30 days.
Almost no change was observed in the transmission loss at m, and the tensile strength was maintained at 4 to 6 kg. In addition, no change in appearance was observed.

(Example 2) Core diameter of wire drawing diameter: 10 μm
After coating the resin varnish A on a single mode optical transmission glass fiber having a diameter of φ and a cladding diameter of 125 μmφ, a coating film of polycarbodiimide was formed through an infrared furnace to give a coating diameter of 135 μmφ. Further, the resin varnish B was applied to the outer periphery thereof, and passed through an infrared furnace to form a coating film of carbon fiber-containing polycarbodiimide, and the coating diameter was set to 250 μmφ. This coated fiber was heated in argon gas at 1000 ° C for 2
Baking for 4 hours to make the coating amorphous carbon,
A coated optical fiber of 1 km length as shown in the figure was obtained. The wavelength of the glass fiber for optical transmission manufactured in this way is 1.
The transmission loss at 3 μm was 0.35 dB / Km, and the tensile strength was good at 14 to 15 Kg. This coated optical fiber was left in a constant temperature bath at 600 ° C. for 30 days, but the increase in transmission loss at a wavelength of 1.3 μm was 0.01 dB /
It was Km or less. In addition, no change in appearance was observed.

(Example 3) Core diameter of wire drawing diameter: 10 μm
The resin varnish A was applied to the outer circumference of a single mode optical transmission glass fiber having a diameter of φ and a cladding diameter of 125 μmφ, and a coating film of polycarbodiimide was formed through an infrared furnace to give a coating diameter of 135 μmφ. Furthermore, a resin varnish C is applied to the outer periphery of the resin varnish, and the coating film of polycarbodiimide containing carbon particles is formed through an infrared furnace to obtain a coating diameter of 170 μmφ.
And This coated fiber in argon gas at 1000 ° C
Baking for 24 hours to make the coating amorphous carbon,
A coated optical fiber having a length of 1 km as shown in FIG. 2 was obtained.

The transmission loss of the glass fiber for optical transmission manufactured as described above at a wavelength of 1.3 μm is 0.35 d.
B / Km and tensile strength were good at 7 to 8 kg. This coated optical fiber was left in a constant temperature bath at 600 ° C. for 30 days, but the increase in transmission loss at a wavelength of 1.3 μm was
It was 0.01 dB / Km or less. Tensile strength is 7-8K
I kept g. In addition, no change in appearance was observed.

[0020]

[Comparative Example 3] A resin varnish A was applied several times to the outer circumference of a single mode optical transmission glass fiber having a drawn diameter core diameter of 10 μmφ and a cladding diameter of 125 μmφ, and heating was repeated to form a polycarbodiimide coating film. The coating diameter was 170 μmφ. This coated fiber was fired in argon gas at 1000 ° C. for 24 hours to make the coating amorphous carbon, and an attempt was made to produce a coated optical fiber as shown in FIG. However, the amorphous carbon layer peeled off from the glass fiber during the firing step.

[0021]

As shown in the examples, the coated optical fiber of the present invention has excellent heat resistance because it uses amorphous carbon having polycarbodiimide as a precursor in the coating layer, and has excellent heat resistance. It can also be used at high temperatures. Also, carbon fibers or carbon particles are dispersed in polycarbodiimide, and this is fired to form amorphous carbon, so that a thick film can be formed without straining the glass fiber,
It does not come off from the glass fiber during the firing step. As a result, a heat-resistant coated optical fiber having a practical protection strength and excellent characteristics was obtained, unlike thin-film amorphous carbon.

[Brief description of drawings]

FIG. 1 shows an apparatus for manufacturing a coated optical fiber of the present invention.

FIG. 2 shows a cross-sectional view of a coated optical fiber.

FIG. 3 is the same as FIG.

[Explanation of symbols]

1: Preform base material 2: Drawing furnace 3: Wire diameter measuring device 4: Coating device 5: Baking furnace 6: Winding machine 7: Control system 8: Glass fiber 9: Core 10: Clad 11: Inner layer (polycarbodiimide) A thin-film amorphous carbon layer formed by baking the above) 12: Outer layer (amorphous carbon formed by baking a carbon fiber or carbon particles dispersed in polycarbodiimide) 13: Single coating layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Saito 1-18-1, Nishiarai-cho, Adachi-ku, Tokyo Nisshinbo Ltd. Tokyo Research Center (72) Inventor Takashi Hironaka 1-18, Nishiarai-cho, Adachi-ku, Tokyo No. 1 Inside Tokyo Research Center, Nisshinbo Industries Inc.

Claims (2)

[Claims] 1. A coated glass fiber having a coating layer made of amorphous carbon formed by firing a polycarbodiimide resin containing a carbodiimide group in the molecule on the outer periphery, wherein carbon particles are present in the layer to be covered. Or a heat-resistant coated glass fiber containing carbon fiber. 2. A thin film consisting only of amorphous carbon formed by firing a polycarbodiimide resin as an inner layer on the outer periphery of a glass fiber, and firing a polycarbodiimide resin containing carbon particles or carbon fibers on the outer periphery thereof. A heat-resistant coated glass fiber, characterized in that an amorphous carbon layer containing carbon particles or a carbon fiber thus formed is provided.