JPS6053903A - Plastic light guide - Google Patents

Abstract

PURPOSE:To obtain an optical fiber free from thermal contraction in uses at high temps. and good in flexibility and light transmittance, etc. by using a copolymer of isobutyl methacrylate and n-butyl methacrylate in a specified mixing ratio for a core material. CONSTITUTION:A copolymer of isobutyl methacryate and n-butyl methacrylate in (4:1)-(2:3) is used for the core material of an optical fiber. This copolymer is spun by extruding it through a die and it is not subjected to special stretching operation. Since this optical fiber is not subjected to stretching operation in manufacture, it is superior in bendability and flexibility, and it does not shrink on being used at high temps. Since the core material is prepared in a gastight system, it is prevented from invasion of optical foreign matters. Since it has no danger of transition and diffusion, it is not necessary to thicken the clad of the core. As a result, it is used for short-distance transmission, a medical fiber scope, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a plastic light guide path used as a plastic fiber or a light guide path for illumination light in a medical 7-eye scope.

Optical fibers are used for optical communications, optical information processing, optical measurement, etc. It is also used in medical fiberscopes.

There are various types of optical fibers, such as quartz glass, multi-component glass, and plastic fiber.

Although plastic fibers have large losses and are unsuitable for long-distance optical transmission, they have the advantage of being low in manufacturing cost and easy to handle.

Plastic fibers have higher elasticity as a material and are more resistant to bending than glass fibers, so they can form light guide paths with a wide cross-sectional area. Thick ones with a diameter of 1 mm are also used.

Since plastic fibers are inexpensive and can have a large light guide cross-sectional area, they are often bundled together with image fibers and used as light guides for illumination light in medical fiberscopes.

Conventionally, plastic fibers have been mainly made of PMMA (polymethyl methacrylate). Polystyrene fibers are also available, but they have a high loss and are not widely used.

(b) Conventional techniques There are only a limited number of plastic materials that are highly transparent to light.

Currently, the commercially available product is polymethyl methacrylate.
) (PMPiIA) as a core and a cladding made of a polyhynylidene fluoride polymer (PVdF), and one yarn having a polystyrene (PST) core and a polymethyl methacrylate cladding.

Since the former method is more important because the loss of light is smaller, the former method will be explained in more detail (prior art).

The plastic optical fiber has Q as shown in the cross section in Figure 1.
Here, core 1, which is a transparent material with a high refractive index, and core 1
A cladding 2 with a lower refractive index is thinly coated on the outside of the cladding 2. Further, as shown in FIG. 2, the illumination light guide path of the medical fiberscope also consists of a core 11 and a cladding 2. The space within the internal cladding is for passage of image fibers and liquids.

The dimensions of the core and cladding are appropriately determined depending on the purpose, but the core diameter is often 0.25 to 1°QOmmφ. The thickness of the cladding is often about 10 to 20 μm (0.01 to 0.02 mm).

The following three types of methacrylate plastic fibers are known.

(A) Polymethyl methacrylate is used as the core material and fluororesin is used as the cladding material.

This fiber is already widely commercially available. It has the advantages of good light transmittance and low absorption loss.

However, this fiber has the disadvantage that it undergoes significant thermal shrinkage at temperatures above 80°C.

For example, at a temperature of 120°C, it shrinks to about 50% of its length in a very short time (several seconds).

The reason for this is that PMMA optical fibers have poor flexibility, and in order to obtain appropriate flexibility, the optical fibers are stretched in the manufacturing process G. When the optical fiber is heated, the portion that was forcibly stretched contracts to return to its original state.

The core material is polymethyl methacrylate mixed with 5% to 30% plasticizer, and the cladding material is fluororesin.

Since this optical fiber contains a plasticizer, it becomes flexible and has enhanced flexibility. Therefore, there is no need for any particular stretching in the manufacturing process. Therefore, heat shrinkability is small.

However, the plasticizer-mixed fiber has a thicker cladding than a fiber using PMMA as the core material. This is to prevent the plasticizer from diffusing and migrating when used in a high temperature environment. For example, the cladding thickness is about 100 μm to 500 μm.

It is the core region of the optical fiber that effectively functions as a light guide. As the cladding becomes thicker, the cross-sectional area occupied by the core decreases, resulting in poor transmission efficiency when transmitting illumination light.

For the same outer diameter, it is better to have a larger core diameter and a thinner cladding thickness.

(C) The core material uses polyisobutyl methacrylate, and the cladding material uses fluororesin.

This fiber is made of polymethyl methacrylate (PMMA
) is not used. The loss is almost the same as PMMA. There is also little heat shrinkage.

However, this fiber has the drawback of being brittle and easily broken. It has poor flexibility and high rigidity.

A tensile test shows that the elongation at break is about 5%.

Plastic fiber is strong against bending and tension,
However, this fiber lacks such advantages.

The reason for this is that the butyl group of inbutyl methacrylate is
This is because it is not chain-like but branched (iso-).

(1) Plastic light guide of the present invention The plastic light guide of the present invention is composed of a core material and a cladding, and the core material is a copolymer of inbutyl methacrylate and n-butyl methacrylate, and the blending ratio is 4/1.
~2/3.

What is new is that n-butyl methacrylate is used as the core material.

A conventional cladding material can be used as the cladding material.

For example, (1) copolymer of polyvinylidene fluoride and tetrafluoroethylene (2) fluorine-containing methacrylate polymer (3) copolymer of fluorine-containing methacrylate polymer and methyl methacrylate (4) silicone resin (5) ethylene vinyl acetate The cladding layer can be formed from a material such as a copolymer.

2) Manufacturing method of plastic light guide First, manufacturing of the core material will be explained.

In the plastic light guide of the present invention, an isobutyl methacrylate monomer (abbreviated as iso BMA) and an n-butyl methacrylate monomer (abbreviated as nBMA) are completely mixed and then polymerized to form a copolymer, which is used as a core material.

The blending ratio of iso BMA and n BMA is 4:1 to 2.
Between 23 and 23 is good.

Conventionally, n-BMA has not been used as a light guide material, but the present invention is characterized in that it is used as a core material as a copolymer with iso-BMA.

As a polymerization initiator, N-N-azobisisobutyronitrile, azotart-butane (azo compound), and butyl peroxide (peroxide) can be used.

As a chain transfer agent, n-butyl mercaptan, ter
Use t-butyl mercaptan.

Such copolymer material is extruded through a die into yarn. It is better to change the spinning temperature depending on the blending ratio of isoBMA and nBMA.

When isoBMA:nBMA=4:1, it is preferable to set the spinning temperature to 160°C.

When isoBMA:nBMA=3:2,
The temperature shall be 150°C.

If isoBMA:nBMA=2:3,
The spinning temperature is 140°C.

The outer surface of the core material is coated with a thin layer of cladding material.

As mentioned above, the cladding material is a copolymer of polyvinylidene fluoride and polytetrafluoroethylene, a fluorine-containing methacrylate polymer, a copolymer of fluorine-containing methacrylate and methyl methacrylate, silicone resin,
Ethylene vinyl acetate copolymer or the like can be used. In any case, the thickness of the cladding layer is between 10 μm and 2 μm.
0 μm is sufficient.

Effects (1) The plastic light guide of the present invention does not shrink due to heat even when used at high temperatures (80'C or higher).

This is because this plastic light guide is not stretched during manufacturing. Even without stretching, the fiber itself has excellent bendability and flexibility, so there is no need to stretch it.

Therefore, it can be used in a relatively high temperature environment.

(2) Excellent flexibility.

Polyisobutyl methacrylate (pisoBMA) itself has a lower elastic modulus than PMMA and polystyrene, and
It is not brittle because it is copolymerized with BMA.

(PMMA has a high elastic modulus and has poor flexibility, so it must be stretched.) Since n-BMA has chain butyl groups, it is possible to make a polymer that is more flexible than iso-BMA.

(3) Good permeability.

When a plasticizer is mixed with PMMA, the core material is produced in a closed system. Therefore, there is no need to worry about contamination with optical foreign matter. The optical loss is less than 1 d, 87 m.

(4) The cladding thickness may be about the same as that of PMMA fiber.

Unlike fine materials that are made flexible by plasticizers, there is no need to worry about plasticizer migration or diffusion at high temperatures.
The cladding may have a wall thickness of 10 μm to 20 μm, which is the same as that of the A fiber. Fine glue with plasticizer 100 μm ~ 50
A cladding with a wall thickness of approximately 0 μm is required.

(Strength) Example Three types of plastic optical fibers were manufactured by changing the blending ratio of iso BMA and n BMA. These are referred to as Examples 1.2.3, respectively. The blending ratio is 4:1.3; 2, respectively.
．． The ratio is 2:3.

Table 1 shows Example 1.2.3 (7) iso BMA
It is a table showing the formulation of and n BMA.

Table 1: Blend ratio of Examples Polymerization conditions were 80°C for 14 hours, heated to 100°C.
The temperature was raised to 130°C for 1.5 hours, and the reaction was continued at 130°C for 24 hours. 0.01 mol % of N-N-azobisisobutyronitrile is added as a polymerization initiator.

Three plastic fibers were used as comparative examples. A
, B, and C.

A: Commercially available PMMA core fiber B: DEP content 30% PMI value A fiber C:
p-iso BMA core material fibers These plastic fibers A, B, and C have been proposed.

Thermal shrinkage, elastic modulus, elongation, loss, and cladding thickness were measured for the fibers of Example 1.2.3, Comparative Example A, and BSC. Table 2 shows the measurement results.

Table 2 Measurement results of example and comparative example fibers Here, the heat shrinkage rate refers to the 120°
It is the heat shrinkage rate when left at C for 60 minutes.

Elastic modulus was measured by Inslon tensile test.

"Stretch" refers to the rate at which the fiber stretches when it breaks during the Inslon tensile test.

The "loss" of light is measured by using a 5 m long fiber as a sample.
Pass the e-Ne L/-the light (688nnI) into the fiber to measure the intensity of the incident light. The output light intensity was measured and calculated using the following formula.

Here, L is the loss and L is the length of the fiber.

The heat shrinkage of Examples 1, 2, and 3 was 4%, and that of Comparative Example A (
PMMA core fiber).

The elastic modulus of Examples 1, 2, and 3 was low, indicating that they were sufficiently flexible.

A short elongation at break means that it is brittle. In both Examples 1, 2, and 3, the elongation at break was sufficiently long;
It is as strange as Comparative Examples A and B.

It can be seen that as the proportion of nBMA increases, the elongation at break becomes longer, making the material softer and stronger.

Regarding the loss, both Examples 1 and 2.3 are 1.0 dB/
m, which cannot be said to be better than Comparative Examples A and C that have already been proposed. It can be seen that 7I/<B containing a plasticizer has a large loss.

The clad wall thickness was 0.01 to 0.0 in both Examples 1, 2, and 3.
02'l#l, which is similar to Comparative Example A1C.

Thus, although the examples of the present invention cannot be said to be superior to the known comparative examples in all properties, they can be said to be superior overall.

G) Applications The present invention can be used in (1) optical fibers for short-distance transmission, (2) small-diameter optical fiber light guides for medical use, and the like.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating the core and cladding structure of a plastic optical fiber. FIG. 2 is a sectional view of the illumination light guide path of the medical fiberscope. 1 ・・・ ・・・ ・・・ Core 2 ・・・・・・・・・ Clad Inventor Nori Matsumiya Bunshi Yoshinobu Ha Patent Applicant Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] A plastic comprising a core material and a cladding covering the core material, the core material being a copolymer of inbutyl mechacrylate and n-butyl methacrylate in a blending ratio of 4:1 to 2:3. light guide path.