JP2582618B2 - Manufacturing method of glass based optical fiber - Google Patents

Description

The present invention relates to a glass-based optical fiber such as silica glass having a coating layer made of polyimide, particularly a primary coating layer, such as a communication optical fiber and an image scope multiple fiber. The present invention relates to a novel manufacturing method suitable for manufacturing a silica glass-based multiple fiber for an image scope, such as an illumination light guide.

2. Description of the Related Art Glass-based optical fibers are required to have good flexibility.
Usually, at least after drawing, a primary coat layer of an organic polymer is applied and put to practical use. It is known that polyimide is excellent in heat resistance and radiation resistance among organic polymers, so to obtain an optical fiber with excellent characteristics, it is necessary to apply a polyimide primary coat layer on the fiber. Is an issue.

Problems to be solved By the way, polyimide varnish is particularly easy to foam when heated and cured, and forms a thick film with excellent flexibility and mechanical properties by smoothing the surface, especially a thick film with a thickness of 200 μm or more. There are difficult problems to solve. For this reason, high-quality optical fibers having a polyimide primary layer have not yet been produced on a commercial basis, and such high-quality thick polyimide films can be easily formed on glass-based optical fibers. There is a strong demand for the development of technologies for forming such materials.

Means for Solving the Problems The present invention, as means for solving the above problems, comprises applying a polyimide varnish onto a glass-based optical fiber and curing it to a C-stage state twice or more. When repeatedly forming a polyimide coat layer, the initial outer diameter of the glass-based optical fiber is Di, and the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the (n-1) th step is D _n-1 , When the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the n-th step is D _n , and the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the final step is Dm, D _n / D _n-1 ≤1.3
While satisfying the conditions of the above, the curing treatment to the C stage state in each step is performed at a temperature of 200 to 450 ° C., and Dm / Di ≧ 1.05
A method of manufacturing a glass-based optical fiber, characterized by forming a thick polyimide coat layer satisfying the following conditions.

According to the study of the present inventors, generally, in order to obtain a practically flexible polyimide-coated glass-based optical fiber, the total thickness of the polyimide-coated layer is determined by reducing the initial outer diameter of the glass-based optical fiber. When the outer diameter of the glass-based optical fiber having the Di and the polyimide coat layer formed in the final step is Dm, it is necessary that the thickness be 1.05 or more based on the Dm / Di. Formation of such a thick polyimide coat layer,
This can be achieved by satisfying the following conditions (1) to (3).

That is, (1) a step of applying a polyimide varnish and performing a curing treatment in a C-stage state is repeated twice or more to perform multi-layer coating; (2) a glass system having a polyimide coat layer formed in the (n-1) th step When the outer diameter of the optical fiber is D _n−1 , and the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the n-th step is D _n , D _n / D _n−1 ≦
Reduce the thickness of the polyimide coat layer formed in each step so as to satisfy the conditions of 1.3, and (3) perform the curing treatment to the C stage state in each step.
Performing at a temperature of ~ 450 ° C, especially when using a multiple fiber with an outer diameter (Di) of 200 µm or more obtained by drawing a bundle of many silica glass-based optical fibers as the initial glass-based optical fiber In other words, the condition of performing the curing treatment to the C stage state in each step at a low temperature of 200 to 360 ° C. is satisfied.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, at least the outer diameter (Di) obtained by drawing a bundle of various glass-based optical fibers such as a silica-glass-based optical fiber, particularly a large number of silica-glass-based optical fibers, is at least as large as possible. 20
A silica glass-based multiple fiber of 0 μm or the like is a target of the polyimide varnish coating, and the silica glass-based optical fiber for producing a multiple fiber includes a core and a cladding layer, and a support layer provided on the cladding layer as necessary. In each case, those made of quartz glass such as pure quartz glass and doped quartz glass are used. In particular, an optical fiber having a pure silica glass clad layer doped with B and / or F on a pure silica glass core or a quartz glass having a drawing temperature of at least 1800 ° C. on the optical fiber clad layer. An optical fiber having a support layer is preferred.
In the present invention, among various silica glass-based multiple fibers, those having an outer diameter of 200 to 5000 μm, particularly 250 to 30
Those having a size of 00 μm are preferred.

As a polyimide varnish, those obtained by dissolving or dispersing various polyimide precursors in an organic medium such as N-methylpyrrolidone at a concentration of about 10 to 50% by weight, for example, those used for producing a polyimide insulated magnet wire Is used.

Next, the method of the present invention will be described in the order of steps. As an example of a glass-based optical fiber, the case of a silica glass-based multiple fiber will be described. A polyimide varnish is applied on a multiple fiber obtained by drawing a bundle of optical fibers at a high temperature of about 2200 ° C., and heat-cured. . Heat curing is
The polyimide varnish coating layer may be heated at a high temperature to bring it to the C stage state at once, but preferably, it is first cured to bring the coating layer to the B stage state, and then secondarily cured to bring it to the C stage state. . This varnish application and heat curing (preferably primary curing and then secondary curing) are taken as one step, and two or more steps are repeated to form a polyimide layer having a desired thickness. In each step, if a large amount of polyimide varnish is applied, or if the secondary curing is performed at a high temperature, the polyimide layer foams, and cracks and undulations occur on the surface. In the present invention, therefore, the thickness of the polyimide coating layer which is formed in the n-th step is 1.3 or less based on D _n / D _n-1 mentioned above, preferably applied as thin 1.25 or less, 20 secondary curing
It is carried out at a temperature of 0 to 360 ° C, preferably 250 to 340 ° C. The heat curing of the polyimide varnish layer may be performed in at least two steps of primary curing and secondary curing, in which case the primary curing in each step should be performed in a temperature range well-known for that, particularly 100 to 180 ° C. Is preferred.

Examples Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 A synthetic silica glass skin pipe was filled with 1400 silica glass optical fibers comprising a pure silica glass core, a cladding layer of pure silica glass doped with B and F, and a support layer of synthetic silica glass. Outside at 2200 ℃
A 470 μm multiple fiber was obtained. Immediately after drawing, a polyimide varnish (trade name: Pyralin, manufactured by DuPont, solvent: N-methylpyrrolidone,
Solid content: 25% by weight), and primary cured at 170 ° C.
Next, a second curing is performed at 200 ° C. for 6 hours to a thickness of 28 μm.
Was formed, and the first step was completed. Repeat the same process as the first process three times to get the total thickness
A 148 μm polyimide layer was formed. In addition, 2nd ~
The thickness of the polyimide formed in each step of the final step was 27 μm, 43 μm, and 50 μm, respectively.

Example 2 A different production from Example 1 was performed only in that the secondary curing in each step was performed at 350 ° C. for 2 hours.
An 8 μm polyimide layer was formed.

Example 3 A manufacturing process different from that of Example 1 was performed only in that the type of the optical fiber, the number of steps, and the thickness of the polyimide formed in each step were changed as described below, and a polyimide layer having a total thickness of 148 μm was formed. .

(Glass-based optical fiber: for optical communication with an outer diameter of 470 μm, number of steps: 5 times, thickness of polyimide formed in each step: 13
μm, 27 μm, 30 μm, 35 μm, and 43 μm).

Example 4 Production was performed differently from Example 1 except that the secondary curing in each step was performed under the conditions of 270 ° C. and heating for 3 hours.
A μm polyimide layer was formed.

Comparative Example 1 A polyimide layer having a total thickness of 148 μm was formed by performing a manufacturing process different from that of Example 1 except that the number of steps and the thickness of the polyimide formed in each step were changed as described below.

(Glass-based optical fiber: silica glass-based multi-fiber having an outer diameter of 470 μm, number of steps: twice, thickness of polyimide formed in each step: 85 μm, and 63 μm) Comparative Example 2 The secondary curing in each step was 550. The production was different from that of Example 1 except that the heating was performed under the conditions of heating at 150 ° C. for 15 seconds.
A μm polyimide layer was formed.

Example 5 A polyimide varnish of Example 1 with the exception of using Toray's trade name Treenice # 3000 (solid content: 23%) as a polyimide varnish.
And a polyimide layer having a total thickness of 148 μm was formed.

The outer diameter characteristics in Examples 1 to 5 and Comparative Examples 1 and 2 are shown in the following table.

In the table, T ₁ , T ₂ , T ₃ ... Indicate the thickness of the polyimide coating layer (PI) formed in each step, and Di is the initial outer diameter of the glass-based optical fiber, D ₁ , D ₂ , D ₃ ... Mean the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in each step, and Dm means the outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the final step.

Each of the polyimide-coated multiple fibers obtained in Examples 1 to 5 had a smooth surface of the polyimide-coated layer, and could be wound around a mandrel having a diameter of 5 cm. On the other hand, in each of the polyimide-coated multiple fibers obtained in Comparative Examples 1 and 2, foaming occurred in the polyimide coat layer, and it was impossible to wind even a mandrel having a diameter of 10 cm.

Example 6 A synthetic silica glass skin pipe was filled with 30,200 silica glass optical fibers comprising a pure silica glass core, a cladding layer of pure silica glass doped with B and F, and a support layer of synthetic silica glass. Then, it was drawn at 2200 ° C. to obtain a multiple fiber having an outer diameter of 2100 μm. Immediately after the drawing, a polyimide varnish (trade name: Pyralin manufactured by DuPont, solvent: N-methylpyrrolidone, solid content concentration: 25% by weight) was applied twice on the multiple fiber, and the solution was heated at 170 ° C. for 1 hour.
Next curing was performed, followed by secondary curing at 330 ° C. for 1 hour to form a C-stage film having a thickness of 50 μm, thereby completing the first process. The same process as the first process was repeated twice in total to form a polyimide layer having a total thickness of 175 μm. In addition,
The thickness of the polyimide formed in each of the second and final steps was 50 μm and 75 μm, respectively.

In each of the polyimide-coated multiple fibers thus obtained, the surface of the polyimide-coated layer was smooth and could be wound around a mandrel having a diameter of 30 cm.

Effect of the Invention According to the method of the present invention, even on a glass-based optical fiber having various outer diameters, particularly a thick silica glass-based multiple fiber having an outer diameter of 200 μm or more, a thick polyimide layer, which has been conventionally difficult, is coated. It became possible. Therefore, according to the present invention, a heat-resistant optical fiber, in particular, a silica glass-based multiple fiber excellent in heat resistance and radiation resistance and also excellent in flexibility can be manufactured on a commercial basis.

Claims (2)

(57) [Claims] 1. A step of applying a polyimide varnish on a glass-based optical fiber and curing it to a C-stage state.
In forming the polyimide coat layer by repeating the above process at least twice, the initial outer diameter of the glass optical fiber is Di, and the outer diameter of the glass optical fiber having the polyimide coat layer formed in the (n-1) th step is D _n-1. The outer diameter of the glass-based optical fiber having the polyimide coat layer formed in the n-th step
D _n, and when the Dm outer diameter of the glass optical fiber having a polyimide coating layer formed in the final step, D _n / D
While satisfying the condition of _n-1 ≦ 1.3, the curing treatment to the C stage state in each step is performed at a temperature of 200 to 450 ° C., and Dm / D
A method for producing a glass-based optical fiber, comprising forming a thick polyimide coat layer satisfying a condition of i ≧ 1.05. 2. An outer diameter (Di) obtained by drawing a bundle of a large number of silica glass optical fibers as an initial glass optical fiber.
The manufacturing method according to claim 1, wherein the curing treatment to the C stage state in each step is performed at a temperature of 200 to 360 ° C using a multiple fiber of 200 µm or more.