JPH0690333B2 - Optical transmission fiber and image scope using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a silica glass based optical transmission fiber. The optical transmission fiber of the present invention is a single fiber having a structure composed of one core, a clad layer formed thereon, and a support layer formed thereon, if necessary, or a large number of the single fibers. It may be any of multiple fibers having a structure in which books are fused together. The single fiber of the present invention is suitable for optical communication or illumination, while the multiple fiber is suitable for image transmission. The present invention also relates to an image scope suitable for medical use, industrial use, etc., which uses the multiple fiber as an image transmitter.

2. Description of the Related Art Regardless of whether a silica glass optical transmission fiber is a single fiber or a multiple fiber, a fiber having a diameter as small as possible is required as long as a desired optical transmission characteristic is satisfied. For example, in the case of an optical fiber cable for optical communication consisting of a single fiber, the smaller the outer diameter of each single fiber, the smaller the finished outer diameter of the optical fiber cable, and the larger the number of optical fiber cables within a certain cable installation allowable space. Can be installed. In the case of an imagescope that uses multiple fibers as an image transmitter,
Images that allow direct observation of areas that are normally difficult to observe, such as high-temperature blast furnaces, nuclear reactors in a radiation environment, the narrow interiors of various equipment, or the interiors of human bodies and animals. There is a demand for an image scope that is clear and has a diameter as small as possible.

A silica glass optical transmission fiber is generally manufactured by drawing a base material thereof, and a fiber reinforcing layer is applied onto the fiber immediately after drawing. Conventionally, this fiber reinforcing layer has been formed of an organic resin such as a thermoplastic organic resin or a thermosetting organic resin, but it is necessary to form a fiber reinforcing layer of uniform thickness without uneven thickness using such an organic resin. Was difficult. For this reason, the thickness of the conventional organic resin fiber reinforcing layer is naturally limited due to the above manufacturing restrictions. Therefore, in the quartz glass optical transmission fiber, there is a limit to the thinning of the organic resin fiber reinforcing layer, and thus it has not been possible to sufficiently reduce the diameter.

Means for Solving the Problems The present invention aims to solve the above-mentioned conventional problems, and a novel silica glass-based optical transmission fiber capable of achieving a sufficient diameter reduction and image transmission of the optical transmission fiber. It is intended to provide the image scope used as the body.

That is, the present invention provides (1) a fiber-reinforced layer on a silica glass-based optical transmission fiber, and at least a part of the total length of the fiber-reinforced layer is a polyimide resin layer heat-cured in a C stage state. An optical transmission fiber, which is formed of a char compound obtained by heat thinning treatment to a temperature of 350 to 600 ° C. to 95% to 50% of its initial thickness, and ( 2) On the multiple fiber having an outer diameter of 100 to 5000 μm formed by drawing a bundle of 500 to 5000 silica glass optical fiber preforms, the char compound as set forth in claim 1 and having a thickness of about 2 to 2 (EN) An image scope having an optical transmission fiber having a fiber reinforcing layer of 50 µm as an image transmission body.

Action The present inventors have previously proposed a fiber reinforcing layer made of a char compound obtained by subjecting various organic resin layers to a heating and thinning treatment for various organic resins. 350 ~ 6 of heat-cured polyimide resin layer in the stage state
The char layer obtained by heat thinning treatment to a temperature of 00 ° C to 95% to 50% of its initial thickness has excellent mechanical strength despite being a thin layer. As excellent. Further, the char layer is blackish brown to black and can also function as a light-shielding layer, and has excellent surface smoothness, so that it can be easily inserted into a thin catheter tube.

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings.

1 and 2 are sectional views of an optical transmission fiber made of a single fiber as an embodiment of the present invention.

FIG. 3 is a sectional view of an optical transmission fiber composed of multiple fibers as an embodiment of the present invention, and FIG. 4 is a partially enlarged sectional view thereof.

FIG. 5 is a sectional view of an optical transmission fiber made of another multiple fiber as an embodiment of the present invention, and FIG. 6 is a partially enlarged sectional view thereof.

FIG. 7 is a diagram showing an example of the refractive index distribution of the core of a single fiber which is a constituent material of the multiple fibers shown in FIGS. 3 and 5.

FIG. 8 is a sectional view of an example of an image scope as an embodiment of the present invention in which multiple fibers are used as an image transmitter.

In the embodiment shown in FIG. 1, the silica glass based single fiber S comprises a core 11 and a clad layer 12, and a fiber reinforcing layer 14 on the core 11. In the silica glass based single fiber S shown in FIG. 2, a support layer 13 is further provided on the cladding layer 12, and a fiber reinforcing layer is provided thereon.
Have 14.

In the embodiment shown in FIGS. 3 and 4, the silica glass-based multiple fiber M is composed of a bundle of a large number of single fibers 2 fused together and a skin layer 24 formed thereon. And has a fiber reinforcing layer 25 thereon. In addition, each single fiber 2 is a core
21 and a clad layer 22.

In the embodiment shown in FIGS. 5 and 6, the glass-based multiple fiber M has a structure including a bundle of a large number of single fibers 2 fused together and a skin layer 24 formed thereon. And a fiber reinforcement layer 25 thereon. Each single fiber 2 has a core 21,
It is composed of a clad layer 22 and a support layer 23.

The image scope of the embodiment shown in FIG. 8 includes a multiple fiber (for example, the one shown in FIGS. 3 and 5) 3 used as an image transmitter, an objective lens 31 attached to the tip of the multiple fiber 3, Removable eyepiece 3 attached to the rear end of multiple fiber 3
2. An eyepiece 33 installed in the eyepiece 32 and a light guide 4 for illumination. At least a certain length of the tip portion of the light guide 4 is provided with the multiple fiber 3 to protect the entire length of the multiple fiber 3.
It is housed inside, and the remaining rear part is branched and housed in the protection tube 6. When the image scope is required to have heat resistance rather than flexibility, metal such as stainless steel, titanium, and copper is used as the protective tube 5 and the protective tube 6, and flexibility for medical use is particularly required. In this case, a flexible organic polymer such as nylon, polyethylene, polypropylene or polyvinyl chloride is used. When used as a medical image scope,
In addition to the light guide 4, a water supply / air supply pipe, forceps, a balloon, a tip swinging device, a laser fiber, an electric coagulator, or other device is provided in the protective tube 5 together with the multiple fiber 3 as required.

The fiber reinforcing layer 14 in FIGS. 1 and 2 or the fiber reinforcing layer 25 in FIGS. 3 and 5 is a polyimide resin layer heat-cured in a C stage state at least in part under the conditions described below. It is formed of a charcoal of blackish brown or black, preferably black, which is formed by heat thinning treatment. Such a portion is usually a portion of the optical transmission fiber that requires a particularly small diameter, such as a tip portion or a portion to be inserted into the lumen of a catheter in the case of a multiple fiber used for an imagescope. In the invention, of course, the fiber reinforcing layer 14 and the fiber reinforcing layer 25 may be made of char compound over their entire length.

In the present invention, a polyimide resin is used for forming the char layer.

As the polyimide resin, a wide range of resins having an imide group in the main chain are used. Particularly, the repeating unit represented by the following formula (1) is at least 30 mol%, preferably 60
Those containing mol% are preferable.

The repeating unit represented by the formula (1) is the same as the repeating unit in the polyimide obtained by reacting a diamine or diisocyanate with a tetracarboxylic acid or a derivative thereof and heating the obtained polyamic acid, The groups R1 and R2 in (1) are organic groups having 4 to 50 carbon atoms, especially 6 to 20 tetravalent aliphatic, alicyclic, aromatic or heterocyclic structures.

Examples of diamines include metaphenylenediamine, paraphenylenediamine, 2,2-bis (4-aminophenyl) propane, 4,4'-diaminodiphenylmethane, 4,
4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 2,6-diaminopyridine, bis (4-aminophenyl) diethylsilane, bis (4-aminophenyl) diphenylsilane,
Benzidine, 3,3'-dichlorobenzidine, 3,3'-dimethoxybenzidine, bis (4-aminophenyl) ethyl phosphine oxide, 4,4'-diaminobenzophenone, bis (4-aminophenyl) phenylphosphine oxide, bis ( 4-aminophenyl) -N-butyramine,
Bis (4-aminophenyl) -N-methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, N- (3-aminophenyl) -4-aminobenzamide, 4 -Aminophenyl-3-aminobenzoate, 2,4-bis (β-amino-t-butyl) toluene, bis (p-β-amino-t-butylphenyl) ether, p-bis (2-methyl-4-) Aminopentyl) benzene, p-bis (1,1-dimethyl-5-aminopentyl) benzene, m-xylylenediamine, p-xylylenediamine, bis (4-aminophenyl)
-N-phenylamine, and a mixture of two or more thereof.

Examples of diisocyanates include ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,12-dodecane diisocyanate, cyclobutene-1,3-diisocyanate, cyclohexane-1,3- and 1,4. -Diisocyanates, 1,3- and 1,4-phenylene diisocyanates, 2,4- and 2,6-
Tolylene diisocyanate, and mixtures of two or more thereof.

The tetracarboxylic acid or its derivative, pyromellitic acid anhydride, 2,3,6,7-naphthalene-tetracarboxylic acid anhydride, 1,2,5,6-naphthalene-tetracarboxylic acid anhydride, 3,4 , 9,10-perylene-tetracarboxylic dianhydride,
Naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene = 1,4,5,8-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetra Carboxylic acid dianhydride,
2,7-Dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3-6,7-Tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, phenanthrene -1,8,9,10-
Tetracarboxylic dianhydride, pyridine-2,3,5,6-tetracarboxylic dianhydride, benzene-1,2,3,4-tetracarboxylic dianhydride, thiophene-2,3,4,5 -Tetracarboxylic dianhydride, and a mixture of two or more thereof.

Examples of the polyimide resin include polyimides having a content of the repeating unit represented by the formula (1) of 100 mol%, for example, U.S. Pat.No. 2,710,853, U.S. Pat.No. 2,712,543, U.S. Pat. Second 90
0,369 and the like, polyamideimides such as those shown in US Pat. No. 2,421,024 and US Pat. No. 3,182,073, polyesterimides such as those shown in US Pat. No. 4,329,397 and the like.

In the present invention, the fiber reinforcing layer made of char is formed by the process described below. That is, the first
On the single fiber S shown in the drawings, FIG. 2 and the like or the multiple fiber M shown in FIGS. 3 and 5 and the like, the above-mentioned polyimide resin layer is formed by an appropriate method immediately after the drawing of those fibers, for example, the resin or its resin. A varnish containing a precursor (used for manufacturing an insulated magnet wire) is formed by die coating, spraying, extrusion, or the like, and heated to cure the polyimide resin layer. By this heat curing treatment, for example, by the secondary curing treatment shown in Comparative Example 1 below, the resin is brought into the C stage state. The heat-cured polyimide resin layer is then subjected to a heat thinning treatment to the extent that it becomes 95% to 50% of its initial thickness (hereinafter, this value is called the thinning rate) at a temperature of 350 to 600 ° C. The char-ized layer can be formed by this treatment. In the case of heat treatment at a high temperature, heating may be performed in the air, an oxygen atmosphere, or a non-oxygen atmosphere such as nitrogen, hydrogen, argon, carbon dioxide, or ammonia gas, or a low oxygen atmosphere.

If the heating temperature is lower than 350 ° C or the thinning rate is less than 95%, a blackish brown to black layer with good mechanical strength and a smooth surface cannot be obtained, while the heating temperature is higher than 600 ° C or thin. If the layering ratio is excessively higher than 50%, the mechanical strength of the char compound layer obtained by the char reaction progressing excessively decreases. Therefore, the heat thinning treatment is preferably carried out under the condition that the thinning rate is 92 to 60% at a temperature of 380 to 500 ° C. The heating time for achieving this thinning rate varies depending on the processing temperature, but at 350 ° C, for example, 30 seconds to 10 minutes, 400
It is 10 to 60 seconds at ℃ and 0.5 to 20 seconds at 500 ℃. By the heat thinning treatment, a blackish brown or black char-forming substance is generated, and the char-forming substance is a ladder polymer forming reaction, a condensation reaction, an aggregating reaction, which occurs from the polyimide resin by the heat thinning treatment. It is believed that it may be a mixture of various condensation residues of an organic resin produced through various reactions such as a residue formation reaction.

The thickness of the polyimide resin layer before heat-thinning treatment is about 10 to 200 μm, preferably about 20 to 100 μm.

In the present invention, as the single fiber S and the multiple fiber M, those cores, cladding layers, or support layers that are formed as necessary, are silica glass-based ones that withstand the above-mentioned char-forming treatment, for example, pure quartz. A material made of glass or doped quartz glass is used. Of the single fiber S and the multiple fiber M, the multiple fiber M is generally required to have a particularly small diameter, particularly when it is used as an image transmitter of a medical imagescope such as an angioscope. Above all,
Particularly preferred as the multiple fiber M in the present invention is that the core 21 of each single fiber is made of doped silica glass having a refractive index distribution as shown in FIG. 7, and more preferably the multiple fiber M is as follows. It has the indicated thickness and refractive index.

3 to 6, D _f is the diameter of the single fiber 2, D _c is the diameter of the core 21 (note that the core 21 has an average radius r ₁ ), and T ₁ is the thickness of the cladding layer 22. , T ₂ indicates the thickness of the support layer 23, T _s indicates the thickness of the skin layer 24, D _m indicates the diameter of the multiple fiber M, and T _p indicates the thickness of the fiber reinforcing layer 25.

The multiple fiber M is usually made of a fiber preform having a circular cross section having the same cross sectional structure as the single fiber 2.
² to 10 ⁷ , especially 10 ³ to 10 ⁶ are aligned in a skin pipe made of natural quartz glass or synthetic quartz glass, preferably synthetic quartz glass (material for forming the skin layer 24 in FIGS. 3 and 5). It can be manufactured by filling in, and then drawing the skin pipe together. Due to the fusion of the optical fibers during the drawing, the respective fiber preforms are
As shown in the figure, the cross section is transformed into a hexagonal shape or a hexagonal shape is deformed slightly or considerably. Unless otherwise specified below, the respective values of D _f , D _c , T ₁ and T ₂ are representative of the values of the parallel portions of the hexagonal cross section as shown in the drawing, but the hexagonal shape is considerably deformed. For things,
The value of the parallel portion as shown is shown for a hexagon having the same cross-sectional area as that of the shape. The refractive index distribution of the core 21 will be described in FIG. 7 assuming that the core has a circular cross section with an average radius r _1. However, when the core has a hexagonal or other cross sectional shape other than a circle, The explanation for circles of the same area as those cross sections shall apply.

Each single fiber 2 has a core in the cross section of the fiber.
It is preferred that the space factor of 21 is at least 20%. If the core space factor is less than 20%, the light transmission amount of the core 21 is insufficient and it is difficult to transmit a bright image. Note that if the core space factor is too large, the cladding layer 22 becomes too thin unless the flexibility of the multiple fibers M is sacrificed, and a bleeding phenomenon occurs in the transmitted image, making it difficult to obtain a clear image. Therefore, the core space factor is preferably 60% or less, and particularly preferably 25 to 50%.

In FIG. 4, the values of D _f and T ₁ are 3 to 16 μm, respectively.
m, about 0.5 to 5 μm, and in FIG. 6, D _f , T
_The values of ₁ and T ₂ are 3 to 16 μm, 0.3 to 4 μm, and 0.01, respectively.
It is about 2 μm.

FIG. 7 is a preferable refractive index distribution curve in the core 21 of each single fiber 2 constituting the multiple fiber M. In the curve, the refractive index n ₀ of the center r ₀ of the core 21 (usually has the maximum refractive index) and the refractive index n _{1 of the} outermost core r ₁ of the core 21.
The difference (Δn) from (which usually has the minimum refractive index), that is, (n ₀ −n ₁ ) is 0.015 to 0.080, preferably 0.02 to 0.050.
Is.

In the refractive index distribution shown in the curve, the decrease of the refractive index is gentle in the section from the center r _{0 of} the core to the average radius r ₂ , that is, 0.65r ₁ , and the average radius r ₂ to the average radius of the core
The refractive index sharply decreases in the section up to r _1, that is, the outermost portion of the core. In other words, the change in the refractive index is small in the section r ₀ to r ₂ . Moreover the refractive index n ₂ is n ₁ at the position of radius r ₂ +0.50 (Δn) (e.g. [Delta] n is 0.025
In this case, n ₁ + 0.65 × 0.025 = n ₁ +0.0125) or more. Therefore, the core 21 has a refractive index distribution of one kind of GI type, but has a smaller decrease in the refractive index in the section r ₂ than the central portion r ₀ and has a refractive index of a certain value or more. Not only that section but also an area slightly outside thereof has sufficient brightness for practical use.

For the reasons described above, a sudden change of the refractive index in the outer portion of the core 21, preferably as a change in refractive index in the central portion of the core is slow, therefore, the refractive index n ₂ in r _2, the following formula ( It is more preferable to satisfy 1).

n ₂ ≧ n ₁ +0.65 (n ₀ −n ₁ ) (1) Further, the curve shows that not only the refractive index n _{2 of} r ₂ (= 0.65r ₁ ) has the above value, but also r Refractive index n of ₃ (= 0.5r ₁ )
It is preferable that the refractive index n ₄ of ₃ and / or r ₄ (= 0.33r ₁ ) has a value represented by the following formulas (2) to (5).

_{n 3 ≧ n 1 +0.55 (n} 0 -n 1) ... (2) _{Preferably, n 3 ≧ n 1 +0.67 (} n 0 -n 1) ... (3) n 4 ≧ n 1 +0.60 ( n ₀ −n ₁ ) (4) Preferably n ₄ ≧ n ₁ +0.70 (n ₀ −n ₁ ) (5) The above-mentioned refractive index distribution of the core serves to increase the refractive index of the silica glass. This can be achieved by using a dopant such as germanium or phosphorus and adjusting the amount of the dopant according to the above refractive index distribution by the VAD method, the CVD method or the like.

In the present invention, the core 21 of each single fiber 2 is
Although it may have only one clad layer 22 as in the embodiment of FIG. 4, it may have two layers having different refractive indexes as shown in FIG. Third,
It may have a fourth layer.

In the embodiment shown in FIG. 4, the refractive index difference between the outermost refractive index n ₁ of the core 21 and the cladding layer 22 may be the same, preferably at least 0.008. In the embodiment shown in FIG. 6, the cladding layer 22 preferably has a refractive index of at least 0.004 lower than the support layer 23 as well as the minimum refractive index value n _{1 at} the outermost portion of the core 71.

The clad layer 22 of FIG. 4 and the clad layer 22 of FIG.
It is preferable that each of them is made of quartz glass doped with fluorine and / or boron or a dopant containing at least one of them as a main component. On the other hand, the support layer 23 in FIG. 6 may be made of quartz glass doped with a dopant, but the drawing temperature is at least 1800 ° C., for example, pure quartz glass, and particularly purity 99.99% by weight or more. It is preferably composed of a high-purity material.

At least a radius from the center of the cross section of the multiple fiber M
If the single fibers 2 existing in the area within 80% are fused to each other in a honeycomb structure as regular as possible (a part in which the honeycomb structure is collapsed or dark spots in the area within 80% of the radius) Defect portion may be present, and the honeycomb structure may be not only a set of geometric hexagons but also a set of slightly deformed hexagons), but generally a clear transmission image can be obtained. Such a multiple fiber M includes a relatively small number of single fibers of about 500 to 5000 and has a small outer diameter (D _m ) of 0.5 mm or less and is suitable for medical use, particularly for angioscopy. There is.

In FIGS. 3 and 5, the thickness of the skin layer 24 is preferably at least about 3 μm, and particularly preferably 5 to 20 μm. When the image scope of the present invention is used for medical purposes, particularly for angioscopy, the thickness of the fiber reinforcing layer 25 made of char is preferably 2 to 30 μm, particularly 5 to 20 μm.

The multiple fibers of the present invention are industrial and medical imagescopes, particularly coronary arteries, fallopian tubes, ureters, endoscopes for various tubes in the body such as bile ducts, gastroscopes, hysteroscopes, cystoscopes, dental mirrors,
It is useful as an image transmitter of a medical image scope such as a fetal mirror, an otoscope, an ophthalmoscope, a encephaloscope, and an arthroscope.

Furthermore, when the image scope of the present invention is used as the above-mentioned various tube endoscopes, particularly as a coronary endoscope, the following (1) to
Those satisfying the condition (2) are preferable.

(1) The number of single fibers 2 in the multiple fiber M is 500 to 5,000, and the outer diameter thereof is about 0.15 to 0.6 mm including the fiber reinforcing layer. (2) In the image scope of FIG. The outer diameter of the protective tube 5 should be 3 mm or less, especially 2.5 mm or less, and the tip 5 to 15 cm of the protective tube 5 should have an outer diameter of 1.8 mm or less.

When the image scope of the present invention is used as an endoscope for digestive organs such as the esophagus, stomach, and intestines, it is preferable to satisfy the following conditions (3) to (4).

(3) The number of single fibers 2 in the multiple fiber M is 5,000 to 30,000, and the outer diameter thereof is about 0.4 to 1.0 mm including the fiber reinforcing layer. (4) In the image scope of FIG. The outer diameter of the protective tube 5 should be about 3 to 10 mm, especially about 4 to 7 mm.

The image scope of the present invention is a hysteroscope, cystoscope, fetal speculum,
In particular, when used as an endoscope for precision observation as an endoscope for arthroscope or other organs, which replaces the conventionally used lens scope, it is preferable to satisfy the following conditions (5) to (6).

(5) The number of single fibers in the multiple fiber M is 30,000 to 100,000, and the outer diameter thereof is about 0.7 to 2.0 mm including the fiber reinforcing layer. (6) In the image scope of FIG. The outer diameter of the protective tube 5 should be about 2 to 10 mm, especially about 3 to 7 mm.

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

Comparative Example 1 3,070 single fiber preforms were densely filled in a pure silica glass tube, and the pure silica glass tube was drawn together at 2100 ° C. to obtain a multiple fiber having an outer diameter of 240 μm. The multiple fiber is made of pure silica glass doped with germanium, and the refractive index n2, n3, n4 at each position of r2, r3, r4 is 1.470, 1.473, respectively.
1.478, n0-n1 is 0.028, the refractive index profile is as shown in FIG. 7, and the Dc is 2.732 μm. The core is made of pure silica glass doped with boron and fluorine, and has a refractive index and a thickness. Clad layers with T1 of 1.442 and 0.892 μm,
3,070 single fibers made of pure silica glass and having support layers having a refractive index and a thickness T2 of 1.453 and 0.117 μm are fused at the support layer, and further made of pure silica glass at the outermost portion, and The structure has a skin layer having a thickness Ts of 10 μm.

On the multiple fibers immediately after drawing, polyimide varnish (trade name Pyralin manufactured by DuPont, solvent: N-methylpyrrolidone, solid content concentration: 25% by weight) is applied, 170
Primary curing was carried out at 0 ° C., and then secondary curing was carried out at 200 ° C. for 6 hours to form a C-stage film having a thickness of 30 μm. A black paint is further applied on the cured resin layer to give a thickness of 10 μm.
The light-shielding layer was formed. The finished outer diameter of the fiber thus obtained is 320 μm.

Example 1 The fiber before the application of the black light-shielding layer obtained in Comparative Example 1, that is, the multiple fiber having the cured polyimide resin layer, was heat-treated in the atmosphere for 20 seconds using an electric furnace having a furnace temperature of 450 ° C. As a result, the cured resin layer is changed to a black char layer having a surface gloss of 14 μm and thus having an outer diameter of 268.
A fiber with a black layer of μm was obtained. The fiber reinforcement layer made of the black char compound of Example 1 is equivalent to that of the fiber reinforcement layer of Comparative Example 1 in light-shielding performance, while being comparative in various points such as mechanical strength, heat resistance, and surface slipperiness. The performance was higher than that of the fiber reinforcement layer of No. 1. If the fiber reinforcing layer has good surface slipperiness, it is easy to insert the catheter into the narrow lumen, which is extremely advantageous for mass production of the medical image scope.
Furthermore, although the number of pixels of each fiber of Example 1 and Comparative Example 1 is the same as 3,070, the finished outer diameter of Comparative Example 1 is 320 μm, whereas that of Example 1 is only 268 μm. . This means that the fiber of Example 1 allows insertion into a more narrow lumen of the catheter.

Example 2 The fiber before the application of the black light-shielding layer obtained in Comparative Example 1, that is, the multiple fiber having the cured resin layer was heat-treated in the atmosphere for 50 seconds using an electric furnace having a furnace temperature of 380 ° C. As a result, the cured resin layer was changed into a black char layer having a surface gloss of 17 μm and excellent in surface gloss, thus obtaining a fiber having a black layer having an outer diameter of 274 μm.

Example 3 Example 1 was repeated, except that Toray Nice # 3000 (solid content concentration: 23%) manufactured by Toray Industries, Inc. was used as the polyimide varnish.
In the same manner as described above, a fiber having an outer diameter of 270 μm having a black char layer having a thickness of 15 μm (thickness of the cured resin layer before char treatment: 30 μm) having excellent surface gloss was obtained.

Example 4 As a polyamide-imide varnish, a product name manufactured by Nitto Denko Corporation
A thickness of 12 was obtained in the same manner as in Example 1 except that DAI-500 was used.
Outer diameter 266 having a black char layer with excellent surface gloss of μm (thickness of cured resin layer before char treatment: 30 μm)
A μm fiber was obtained.

Example 5 A surface gloss having a thickness of 12 μm (thickness of a cured resin layer before char treatment: 32 μm) was carried out in the same manner as in Example 1 except that as the polyesterimide varnish, a trade name Isomid 38M manufactured by Schenectady, USA was used. A fiber having an outer diameter of 264 μm having an excellent black char layer was obtained.

Example 6 The thickness was 13 μm (the thickness of the cured resin layer before the char treatment: 3) in the same manner as in Example 1 except that Terebec 800 manufactured by Dainichiseika Co., Ltd. was used as the polyesteramide imide varnish.
A fiber having an outer diameter of 266 μm having a black char compound having an excellent surface gloss of 1 μm) was obtained.

Example 7 The same structure as the multiple fiber used in Example 1, but immediately after the multiple fiber having 1500 pixels and an outer diameter of the skin layer of 200 μm was drawn and obtained. A polyimide resin varnish used in 1 was used to form a cured resin layer having a thickness of 30 μm in the same manner as in the example, and then heated in an electric furnace filled with air at 450 ° C. for 15 seconds to give a surface gloss of 15 μm. A char-charging layer of black having excellent properties and mechanical strength was obtained.

Effect The fiber reinforcing layer made of a char compound of a polyimide resin layer heat-cured in the C stage state can be easily formed by heat-thinning the resin layer previously applied on the optical transmission fiber. In addition, the resin layer can be made significantly thinner than the resin layer before the char treatment. Therefore, it is possible to reduce the diameter of the optical transmission fiber of the present invention by constructing the fiber reinforcing layer at least at the necessary portions with the above-mentioned char compound. The char layer also has excellent surface smoothness and mechanical strength.

Furthermore, in order to use an optical transmission fiber whose fiber reinforcement layer is made of only organic resin as an image transmission body of an image scope, it is necessary to provide a black light-shielding layer on the outermost part, so it is necessary to apply a separate black paint on it. However, there is a problem that this coating further increases the outer diameter of the fiber. On the other hand, since the char layer itself is black, it is not necessary to separately apply a black paint, and there is no problem of increasing the outer diameter. Therefore, the optical transmission fiber of the present invention has a good surface-sliding property of the fiber reinforcing layer and can be thinned, so that it can be inserted into a narrow lumen of a catheter, and in terms of mass production of medical image scopes. It will be extremely advantageous.

[Brief description of drawings]

1 and 2 are sectional views of an optical transmission fiber made of a single fiber as an embodiment of the present invention. FIG. 3 is a sectional view of an optical transmission fiber composed of multiple fibers as an embodiment of the present invention, and FIG. 4 is a partially enlarged sectional view thereof. FIG. 5 is a sectional view of an optical transmission fiber made of another multiple fiber as an embodiment of the present invention, and FIG. 6 is a partially enlarged sectional view thereof. FIG. 7 is a view showing the refractive index distribution of the core 21 of the single fiber 2 which is a constituent material of the multiple fibers shown in FIGS. 3 and 5. FIG. 8 is a sectional view of an example of an image scope as an embodiment of the present invention in which multiple fibers are used as an image transmitter. In FIGS. 1 and 2, S is a glass-based single fiber, 11 is a core, 12 is a clad layer, 13 is a support layer, and 14 is a fiber reinforcing layer. In FIGS. 3 to 6, M is a glass-based multiple fiber, 2 is a single fiber which is a component of the multiple fiber M, 21 is a core of the single fiber 2, 22 is the same clad layer, 23 is the same support layer, 24 Is a skin layer, and 25 is a fiber reinforcing layer. In FIG. 8, 3 is a multiple fiber used as an image transmitter, 31 is an objective lens, 32 is a removable eyepiece, 33 is an eyepiece lens, 4 is a light guide for illumination, and 5 and 6 are protective tubes. Is.

Claims (2)

[Claims] 1. A fiber-reinforced layer is provided on a silica glass-based optical transmission fiber, and at least a part of the total length of the fiber-reinforced layer is a polyimide resin layer heat-cured in a C stage state in a range of 350 to 600. 95% of its initial thickness at a temperature of ℃ ~
An optical transmission fiber, which is formed of a char compound obtained by heating and thinning to a degree of 50%. 2. A plurality of silica glass-based optical fiber preforms each having a diameter of 100 to 5000 .mu.m formed by drawing a bundle of silica glass optical fiber preforms, and formed of the char compound according to claim 1 and having a thickness. An image scope having an optical transmission fiber having a fiber reinforcing layer of about 2 to 50 μm as an image transmission body.