JP2519699B2 - Optical fiber bundle manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an optical fiber bundle capable of directly transmitting an image.

(Prior Art) Image guides used in medical or industrial endoscopes are generally used in narrow places or in bent places, so the optical fiber bundle forming the image guides has a small outer diameter and is High flexibility is required. Therefore, it is generally manufactured by bundling optical fibers having an extremely small diameter with an outer diameter of 10 μm to 100 μm.

(Problems to be Solved by the Invention) In the method of manufacturing an optical fiber bundle such as a ride guide or an image guide according to the related art, since optical fibers having a very small diameter are bundled, black spots may occur due to breakage during the process. In addition, it is difficult to make a regular arrangement for producing an image guide and to obtain a long one.

A method has also been proposed in which a bundle of a plastic optical fiber bundle and a plastic sheath containing the bundle is heated integrally and stretched to obtain an optical fiber bundle (Japanese Utility Model Publication No. 50-108452). However, according to this method, there is a drawback that bubbles are generated between the optical fibers. Further, there is a defect that the obtained image lacks in sharpness and brightness.

As a method of arranging the optical fibers in regular pitches, a method of using a spacer plate to fix the optical fibers on the plate and then laminating them to produce an optical fiber bundle has been proposed (for example, Japanese Patent Laid-Open No. 58-58). 181002). Although the method is excellent in that it gives a clear image, it has a drawback in that the complexity of the work is unavoidable.

On the other hand, an image guide made of glass fiber has a small difference in the refractive index between the core and the cladding, and therefore image bleeding easily occurs.
Therefore, the core diameter cannot be reduced and the cladding layer needs to be thickened, so that the number of pixels cannot be increased. Therefore, the resolution is limited. Problems such as these have been pointed out.

An object of the present invention is to provide an industrially advantageous manufacturing method of an optical fiber bundle which has few defective products due to breakage and the like in the manufacturing process, is less likely to cause image bleeding, and gives a clear image.

(Means for Solving the Problems) The inventors of the present invention have made various studies in view of the above-mentioned object, and under the specific condition setting, the optical fibers are convergently arranged in a thick state, and the fibers which are convergently arranged. It was confirmed that an optical fiber bundle having a fine core with extremely high uniformity can be obtained by stretching the bundle in the state of the fiber bundle, and the present invention was accomplished.

That is, the present invention is to form a rod by filling a plurality of strands of a plastic optical fiber consisting of a core and a cladding in a plastic pipe in the same longitudinal direction as each other to form a rod, which is then subjected to the heat deformation temperature of each material. When producing an optical fiber bundle having a plurality of small core diameters by drawing under heating and solidifying by cooling, (a) as the core and the cladding material, the viscosity of the cladding material is higher than the viscosity of the core material at the stretching temperature. (B) The relationship between the outer diameter Do (mm) of the wire, the core diameter do (mm) of the wire, and the core diameter dm (mm) of the drawn wire is given by )
It is a method for producing an optical fiber bundle, which satisfies the following condition.

Here, the above equation causes the deformation of the cladding at the same time as stretching, and when the voids between the optical fiber strands are filled with the cladding material, the core gap in each of the closest packed optical fiber strands is It is set so as to satisfy the condition of keeping 1 μm or more.

When the condition (a) is satisfied, the cladding is deformed simultaneously with the stretching, and the voids between the optical fiber strands can be filled with the cladding material. In particular, the larger the difference between the viscosity of the cladding material and the viscosity of the core material, the easier the shape of the core in the obtained optical fiber bundle can be kept in a perfect circle, which is preferable.

Generally, a viscosity ratio of the core to the cladding of 1.5 or more, particularly 2 or more is preferable. Although there is no upper limit to the viscosity ratio, it is usually 25 or less, preferably 20 or less so that stretching is easy. A particularly preferred viscosity ratio is in the range of 5-15. As for the absolute values of the viscosities of the core material and the cladding material, materials within the range that can be stretched are used. It is important to maintain mechanical strength that both core and cladding materials have high viscosity. On the other hand, if the viscosity is too high, stretching becomes difficult. The viscosity of the preferred cladding material is, in terms of zero shear viscosity, 500 poise or more and 50,000 poise or less, particularly 5,000 to 30,000 poise.

By satisfying the above condition (b), an optical fiber bundle giving a clear image with less bleeding can be obtained. Condition (b)
In, the left side (Do-do) expresses the thickness of the cladding material of the optical fiber strand. The smaller this value is as long as the above equation is satisfied, the smaller the volume of the cladding material in the obtained optical fiber bundle is, resulting in an optical fiber bundle having a large image transmission area. Therefore, although there is no upper limit to the value in the present invention, in general, the value is practically expressed by the following formula (I
It is set within the range that satisfies I).

Outside the range of the formula (I), the thickness of the grate forming the gap between the cores becomes smaller than 1 μm, and image bleeding occurs, and as a result, a clear image cannot be obtained.

In the present invention, the distance between the cores after stretching (corresponding to the cladding thickness) satisfying the above conditions is used, but the most preferable image guide is that the cladding thickness is 5 to 5 times the core diameter. 50%, especially 10-30%
It is in the range of.

According to the present invention, since the wires are arranged in a thick state, the wires can be arranged regularly, accurately, and efficiently. Since the regular array is uniformly stretched in the state of being filled in one plastic pipe and made into fine fibers, the obtained fiber bundle has the feature of maintaining the regular array as it is.
Further, according to the present invention, by using the plastic optical fiber, the refractive index difference between the core and the cladding can be increased. Therefore, the amount of incident light can be increased, and light leakage is less likely to occur. Therefore, since the cladding layer can be thinned, the occupied area of the core can be increased when the diameter of the strand is the same. As a result, the amount of light guide can be increased, and a bright optical fiber bundle can be obtained. Further, according to the present invention, since fine fibers can be formed, the number of pixels can be increased.
Therefore, the resolution can be increased. Also, a long product can be easily obtained.

As the strand of the plastic optical fiber used in the present invention, the optical fiber composed of the core and the cladding or its preform can be used as it is.

As the thermoplastic resin used for the core component, known transparent resins represented by polystyrene and polymethylmethacrylate can be used. Regarding the cladding component, a known transparent resin having a refractive index lower than that of the core component used by, for example, 0.01 or more can be used. Specifically, polymethyl methacrylate, poly (vinylidene fluoride), poly (vinylidene fluoride) -tetrafluoroethylene copolymer, poly (2,2,2) trifluoroethyl methacrylate, etc. can be used. In order to reduce the image bleeding, it is preferable to use a transparent resin having a refractive index of 0.05 or more lower than that of the core component for the cladding component. The simplest method for satisfying the condition (a) is to select a combination of the types of resins used for the core component and the cladding component, and it is easy to select those resins having different molecular weights.

For example, an optical fiber having polystyrene as a core and polymethylmethacrylate as a cladding will be described below as an example. The molecular weights of polystyrene and polymethylmethacrylate used for ordinary optical fibers are about 100,000, respectively, and at zero shear viscosity 220 ° C, polystyrene is 30,000 poise and polymethylmethacrylate is 150,000 poise, respectively. . Therefore, if the optical fiber is stretched under this condition, the core portion is significantly deformed, and as a result, only an optical fiber bundle having a large loss can be obtained. On the other hand, polystyrene having a molecular weight of about 300,000 and polymethyl methacrylate having a molecular weight of about 80,000 have a viscosity at 260 ° C. of polystyrene of 90,000 poise and polymethyl methacrylate of 10,000 poise, respectively. Therefore, this combination satisfies the condition (a) of the present invention.

Further, the thermoplastic plastic pipe used in the present invention is not particularly limited, and known thermoplastic resins such as polystyrene, polymethylmethacrylate, polycarbonate, polyvinyl chloride and the like can be used. It is preferable to select a resin whose viscosity is higher than that of the cladding component and lower than that of the core component at the stretching temperature because the shape retention of the entire optical fiber bundle during the stretching step is good.

On the other hand, when a material of the same quality as the cladding component is selected, the image distortion in the outermost layer of the optical fiber bundle or in the vicinity thereof is extremely small.

In the present invention, a method of filling rods by filling a plurality of wires in the plastic pipe in the same longitudinal direction as each other and filling the rods is as follows. After arranging the strands on a plane so that the strands do not overlap with each other, the strands are fused or attached to each other to produce a sheet made of strands. Then, the sheets can be laminated to form a pipe shape as shown in FIGS. 1 to 4, and the sheets can be packed in a plastic pipe.

After forming a rod by filling a pipe with a sheet temporarily adhered using a water-soluble organic polymer as an adhesive, the rod is removed by dissolving and removing the temporarily adhered water-soluble organic polymer with water or steam. The stretching method is particularly preferable because foreign matters other than the core component and the cladding component are not mixed in the optical fiber bundle. Examples of the water-soluble organic polymer include polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, starch and the like.

The method of making an optical fiber bundle is that the rods made by filling plastic pipes with 10 or more strands having the same major axis direction are heated in a cylindrical heating furnace and stretched without contact. It is obtained by

Specifically, one end of the rod is thermally sealed, and the pressure is kept constant in a non-contact manner from the side where the rod is sealed while depressurizing it in a heating furnace heated above the thermal deformation temperature of each material constituting the rod. The wire is inserted at a speed and drawn while controlling the drawing speed so that the wire diameter after drawing becomes a predetermined wire diameter. An optical fiber bundle can be obtained by winding after cooling.
Before the rod is stretched, the moisture content of each material
Drying may be performed to 0.1% or less, preferably 0.01% or less.

Further, in the above-mentioned stretching step, the rods may be arranged vertically or horizontally, but it is preferable to arrange them in the vertical direction.

The optical fiber bundle obtained by the present invention may be further bundled into a plurality of fibers and filled in a plastic pipe to be stretched in the same manner as described above. This method is advantageous for producing an optical fiber bundle having a larger number of filled fibers.

In the stretching step of the present invention, the pressure inside the rod may be reduced. By performing this operation, it becomes easy to fill the voids with the cladding material, and at the same time, it is possible to prevent oxidation during the stretching process and prevent an increase in loss.

The optical fiber bundle obtained by the method of the present invention is exactly the same as a normal optical fiber bundle, cut into a desired length, both end surfaces are polished, and an image is obtained by attaching an objective lens and an eyepiece lens. Can be used as a guide.

(Examples) The present invention will be described in more detail with reference to the following examples. The zero shear viscometry has a diameter of 1.00 mm and a length of 10.0.
Using a 0 mm capillary, the measurement was carried out by a capillary graph manufactured by Toyo Seiki Seisakusho.

Example 1 Polymethylmethacrylate (molecular weight: 80,000) having a thickness of 4 mm was attached to the outer layer of a polystyrene round bar (molecular weight: 300,000) having an outer diameter of 44 mm and a length of 300 mm to obtain an outer diameter of 52 mm and a length of 300 mm. A preform was prepared. The preform was dried under reduced pressure at 60 ° C. for 5 days, then the tip was melted in a cylindrical heating furnace heated to 260 ° C., stretched at a speed of 5 m / min, and reheated to remove internal strain. An optical fiber wire having an outer diameter of 0.5 mm and a cladding thickness of about 38 μm was prepared. The strand of this optical fiber
After wrapping one layer in a line on a 1-m cylindrical drum, a polyvinyl alcohol aqueous solution was applied, and heated nitrogen gas was blown to dry the adjacent filaments to bond them together.
After that, the filament was cut at right angles to the fiber axis direction to prepare a sheet in which the filament was aligned. On the other hand, a pipe with an outer diameter of 50 mm, an inner diameter of 48 mm, and a length of 300 mm was made from the same material as the cladding material. As shown in FIG. 4, the sheet was sprinkled in a spiral shape and filled in a pipe to prepare a rod. The number of strands is about
It will be 8800. Warm water was poured into this rod to dissolve out polyvinyl alcohol and then air-dried. Then, this rod was further dried at 70 ° C. for 5 days under reduced pressure to reduce the water content to 0.01% by weight or less, and then one end was thermally sealed. As shown in Fig. 5, in order to keep the inside of the rod in a vacuum, the upper end of the rod is fused and integrated into a sealing system holding a vacuum system connecting pipe and heated on a cylinder heated to 260 ° C from the end sealed under reduced pressure. It was inserted into the furnace in a non-contact manner, and while being melted at its tip, it was drawn at a speed of about 5 m / min and wound up with a wire diameter of 1 mm after drawing. Under these conditions, the core had a viscosity of 90,000 poise and the cladding had a viscosity of 10,000 poise. When the obtained optical fiber bundle was sampled, the end face was polished and observed with a microscope, a core having a small non-circularity could be observed. Also, the cladding was fused and integrated.

When the optical fiber bundle was cut into 1 m, the other end was coated with black tape, both ends were polished, and both ends were equipped with an objective lens and an eyepiece to see the object, a clear image could be seen.

Comparative Example An optical fiber strand was prepared in exactly the same manner as in Example except that polystyrene having a molecular weight of 100,000 and polymethylmethacrylate having a molecular weight of 100,000 were used and the drawing temperature was set to 200 ° C.
Next, an optical fiber bundle was obtained in exactly the same manner as in the example except that polymethylmethacrylate having a molecular weight of 100,000 was used as the pipe and the drawing temperature was set to 220 ° C.

When the object was viewed as an image guide as in the example, the optical fiber bundle was lacking in sharpness and image brightness as compared with the image guide of the example. Examination with an optical microscope revealed that the polystyrene core lacked in circularity, which probably affected the performance as an image guide.

(Effect of the invention) The method of the present invention makes it bright and less bleeding,
High resolution, no image distortion, few black spots,
It is possible to easily obtain a large amount of optical fiber bundles capable of producing an image guide having an arbitrary length.

[Brief description of drawings]

1 to 4 are explanatory views for forming a pipe-shaped shape from a sheet-shaped optical fiber bundle, and FIG. 5 shows a method for stretching the optical fiber bundle in the present invention. FIG. In the figure, 1 is an optical fiber strand, 2 is a pipe, 3 is a rod, 6
Is a heating furnace, and 7 is a take-up roll.

Claims (1)

(57) [Claims] 1. A rod is formed by filling a plurality of strands of a plastic optical fiber consisting of a core and a clad in a plastic pipe so that their longitudinal axes are the same, and then the rod is formed. When producing an optical fiber bundle having a plurality of small core diameters by stretching while being heated as above and solidifying by cooling, (a) as the core and the clad material, the viscosity of the clad material is higher than that of the core material at the stretching temperature. Select one that is low and has a viscosity ratio of 1.5 to 25. (b) The outer diameter D _o (mm) of the wire, the core diameter d _o (mm) of the wire, and the drawn wire. A method for producing an optical fiber bundle, characterized in that the relationship with the core diameter d _m (mm) of the wire satisfies the following equation.