JPH0279806A - Heat resistant coated optical fiber - Google Patents

Abstract

PURPOSE:To obtain good flexibility and high heat resistance by providing a coated and backed layer of a soln. mixture composed of an arom. polyimide soln. and a polysiloxane resin soln. on the outer periphery of a bare optical fiber and providing a secondary covering consisting of the polysiloxane resin of a specific thickness thereon. CONSTITUTION:A primary coating 2 formed by application and baking of the soln. mixture contg. 20 to 80wt.% arom. polyimide and 80 to 20wt.% polysiloxane resin is provided on the outer periphery of the bare optical fiber 1 consisting of a core and clad and the secondary covering 3 of 10 to 50mum thickness consisting of the polysiloxane resin is provided thereon. The polysiloxane resin is obtd. by heating a boron compd. and silane compd. to cause polycondensation and has the noncarbon basic skeleton expressed by formula I. The use of the fiber is possible in this way even if the fiber is exposed to a high temp. of 1,000 deg.C. In addition, the coated optical fiber having good flexibility is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to an optical fiber core having extremely high heat resistance and good flexibility.

(Prior Art) Recently, as a heat-resistant optical fiber core, a bare optical fiber or a bare optical fiber having a primary coating coated with a polyimide resin has been used.

However, polyimide resin is only 400 to 45
It only has a heat resistance of about 0°C and decomposes at temperatures higher than this, so the optical fiber core can be used as a cable for combustion monitoring systems in melting furnaces and boilers, or for emergency systems such as fires. I couldn't do it.

Furthermore, recently, a polyborosiloxane resin having heat resistance of 1000° C. or more has been developed, and an optical fiber core coated with this resin is also being considered.

(Problem to be Solved by the Invention) However, in an optical fiber core in which such a polyborosiloxane resin coating is provided directly on the bare optical fiber, there is a problem that the transmission loss of light increases rapidly. there were.

Furthermore, it has been considered to form a coating by applying and baking a resin solution containing a mixture of polyimide resin and polyborosiloxane resin, but the heat resistance of such optical fiber cores depends on the polyimide resin coating. The value was intermediate between that of the wood and that of the polyborosiloxane front coating, and it could not be said that it had sufficient heat resistance.

The present invention was made to solve these problems, and an object of the present invention is to provide an optical fiber core that can be used even when exposed to high temperatures of 1000°C and has good flexibility. .

[Structure of the Invention] (Means for Solving the Problems) The heat-resistant optical fiber core wire of the present invention includes 20 to 80% by weight of an aromatic polyimide resin and polyborosiloxane on the outer periphery of a bare optical fiber consisting of a core and a cladding. Resin 80~
A primary coating is formed by coating and baking a mixed solution containing 20% by weight, and a secondary coating of 10 to 50 μm thick made of polyborosiloxane resin is provided thereon.

The aromatic polyimide resin solution used in the present invention includes:
For example, as described in Japanese Patent Publication No. 4B-17145, 3.3', 4,4'-benzophenone tetracarboxylic dianhydride and an aromatic diamine with a special structure are heated and polymerized in a phenolic solvent such as cresol. Pyromellitic dianhydride and 4,4'-diaminodiphenyl ether are combined with N-methyl-2-pyrrolidone (N
MP) and those obtained by reacting at low temperatures in special polar solvents such as dimethylacetamide (solutions of polyamic acid resins, which are precursors of polyimide resins).

The polyborosiloxane resin used in the present invention is a resin having the non-carbon basic skeleton shown below, which is obtained by heating and condensing a boric acid compound and a silane compound (more preferably a silanol compound).

10, B -0-8l- / 10 And the polyborosiloxane resin solution is obtained by dissolving such polyborosiloxane resin in a phenolic solvent such as cresol or a polar solvent that can be baked such as NMP. Commercially available products include Show Excel (trade name, Showa Cable and Wire Co., Ltd.).

In the present invention, when forming the primary coating, it is recommended that a polyborosiloxane resin be added and dissolved in the aromatic polyimide resin solution (or its precursor polyamic acid) to form a face-shaped resin solution. Mixed 8
This is preferable because it is easy.

Note that the solvent used at this time is preferably a solvent common to the aromatic polyimide resin solution and the polyborosiloxane resin solution, or a solvent of the same type.

In the present invention, the mixing ratio of the aromatic polyimide resin solution and the polyborosiloxane resin or its solution can be appropriately selected depending on the properties required for the coating, but the solid content of the aromatic polyimide resin is 20 to 20%. 80% by weight,
It is necessary to mix the polyborosiloxane resin in a proportion of 80 to 20% by weight.

If the proportion of aromatic polyimide resin is less than 20% by weight and the proportion of polyborosiloxane resin exceeds 80% by weight, it is undesirable because the transmission loss of the coated optical fiber will increase by coating and baking. .

On the other hand, if the proportion of the polyborosiloxane resin is less than 20% by weight and the proportion of the aromatic polyimide resin exceeds 80% by weight, the effect of the polyborosiloxane resin will no longer be recognized.

In the present invention, in order to form the secondary coating made of polyborosiloxane resin, it is desirable to adopt the method of applying and baking the polyborosiloxane resin solution described above. The thickness of this polyborosiloxane resin coating is 10 to 50 μm.
Mouth. The reason why the thickness of the polyborosiloxane resin coating is limited to this range is that if the thickness is less than 1081, the effect of providing the polyborosiloxane resin coating will be reduced and the heat resistance will be insufficient. On the other hand, if the thickness of the polyborosiloxane resin coating exceeds 50 μm, the flexibility becomes so low that it becomes impractical.

To produce the heat-resistant optical fiber core of the present invention, on the outer periphery of a bare optical fiber obtained by spinning by a conventional method,
A coating solution prepared by mixing a polyborosiloxane resin or its solution with an aromatic polyimide resin solution is applied and baked to form a primary coating, and then a polyborosiloxane resin solution is applied and baked to a thickness of 10 to 50 μm. A method of forming a secondary coating is adopted. Although it is preferable that all of these steps are carried out continuously, it is also possible to perform winding and the second coating in a separate step - after the formation of the next coating.

The heat-resistant optical fiber core of the present invention thus obtained is:
A cable unit can also be constructed by twisting a plurality of them around a steel wire or the like and further providing a polyborosiloxane resin coating on the outer periphery thereof.

(Example) Examples of the present invention will be described below.

Examples 1 to 5 As shown in the drawings, a pile ML (solvent NMP) was placed around the outer periphery of a GI type quartz optical fiber bare wire 1 made by the VAD method with a relative refractive index difference of 1%, a core diameter of 50 μl, and a cladding diameter of 125 μl.
and Showexcel (solvent NMP) were mixed in the proportions of aromatic polyimide resin and polyborosiloxane resin as shown in the following table. A primary coating 2 having a thickness shown in the table was formed by baking at a temperature. Next, Showexcel was applied onto this primary coating 2 by a method such as flow coating or dip coating, and baked at 400° C. for about 30 minutes to form a secondary wave 823 having the thickness shown in the table.

For comparison, a mixed paint with the composition shown in the comparative example in the table below was applied and baked on the same bare optical fiber as in the example, and after forming a primary coating with the thickness shown in the table, Shawexcel was applied on top of it. Coating and baking formed a secondary coating. (Comparative example 1
For samples 6 and 6, the application and baking of Showexcel for forming the secondary coating was not performed. ).

The flexibility of the optical fiber cores of Examples and Comparative Examples thus obtained was measured by the following method.

That is, the sample core wire was wound around the outer periphery of a cylinder having a radius 10 times the outer diameter R of the sample, and the flexibility was judged based on whether cracks or cuts occurred in the coating.

In addition, the transmission loss of light with a wavelength of 1.3μ■ at room temperature and the
The increase in transmission loss after heating at a temperature of 0° C. for 24 hours was measured.

The results of these measurements are shown in separate tables.

(The following is a blank space) [Effects of the Invention] As is clear from the above description, the heat-resistant optical fiber core wire of the present invention is obtained by coating and baking a mixed solution of an aromatic polyimide resin solution and a polyborosiloxane resin solution around the outer circumference of a bare optical fiber. layer, and a secondary coating made of polyborosiloxane resin that has a heat resistance of 1000°C or more is provided on top of the layer, so it has good flexibility and extremely high heat resistance, and has a heat resistance of 1000°C or more. There is almost no increase in transmission loss even when exposed to high temperatures.

[Brief explanation of the drawing]

The drawing is a cross-sectional view showing an embodiment of the heat-resistant optical fiber core of the present invention. 1...GI type quartz optical fiber bare wire 2...-Secondary coating 3...Secondary coating Patent attorney Sa Suyama - (1 other person)

Claims (1)

[Claims] (1) A primary coating is applied to the outer periphery of a bare optical fiber consisting of a core and a cladding by applying and baking a mixed solution containing 20 to 80% by weight of an aromatic polyimide resin and 80 to 20% by weight of a polyborosiloxane resin. 1. A heat-resistant optical fiber core, comprising: a secondary coating made of a polyborosiloxane resin having a thickness of 10 to 50 μm.