JPH06186442A - Distributed refractive index type plastic optical transmission body - Google Patents

Abstract

PURPOSE:To obtain a distributed refractive index type optical transmission body superior in translucent performance, mechanical characteristics and heat resistance. CONSTITUTION:A colorless transparent nonpolymeric compound being compatible with a polymer constituting the optical transmission body and also having a higher refractive index than it of the polymer, is dispersed in a concentration distribution continuously decreasing from a central part of the optical transmission body to the peripheral part, and the plastic optical transmission body has a distributed refractive index continuously decreasing from the central part to the peripheral part. A colorless transparent polymer incorporating an aliphatic N-substituted maleimide monomer unit as a copolymer component, is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical transmission medium having a refractive index distribution continuously decreasing from the center to the outer periphery, which is preferably used for an optical transmission medium such as an optical fiber or a rod lens. is there.

[0002]

2. Description of the Related Art Conventionally, an optical transmission body is made of quartz glass and / or
Or manufactured from plastic. Quartz-based optical transmitters have excellent light-transmitting performance, but they are not only poor in workability and flexibility, but also expensive, and when used as fibers, their diameter is very small, so connection is high. Precision is required, and sophisticated technology and high-priced equipment are required.

On the other hand, the plastic type optical transmission body is inferior to the quartz type in light transmission performance, but has advantages such as light weight, good workability, good flexibility and low cost.

Among these plastic type optical transmission bodies, a method for producing an optical transmission body having a refractive index distribution continuously decreasing from a central portion to an outer peripheral portion, which is used for a rod lens, a broadband optical fiber, etc., has already been proposed. Several have been proposed.

For example, a monomer having a refractive index different from that of the polymer is brought into contact with the surface or hollow inner surface of the polymer mainly forming the optical transmission medium and diffused inside the polymer to give a concentration distribution. Method to polymerize later (Japanese Patent Publication No. 52-5857, Japanese Patent Publication No. 56-3)
7521, etc.), a method of imparting a refractive index distribution by photopolymerizing two or more kinds of monomers having different refractive indexes and monomer reactivity ratios in a transparent container (Japanese Patent Publication No. 54-30301).
Japanese Patent Laid-Open No. 61-130904), spinning a polymer containing a monomer having a high volatility and a refractive index different from that of the polymer, and volatilizing the monomer from the surface to give a concentration distribution. Polymerization method (Japanese Patent Laid-Open No. 62-209402, etc.), a polymer container in which two or more kinds of monomers having different monomer reactivity ratios but substantially different refractive indices are dissolved in the monomers. There is a method of polymerizing after filling the inside (JP-A-4-97302 and JP-A-4-97303).

However, all of these methods produce polymers having greatly different refractive indices (for example, 0.04 or more),
And reacting two or more kinds of monomers having slightly different monomer reactivity ratios, or giving a polymer having a refractive index greatly different from that of the polymer formed previously in the polymer molded body. Since the homopolymerization reaction of the monomer is carried out, it is unavoidable that a microscopic phase-separated structure having a different refractive index is formed in the polymerized polymer. Therefore, there is a drawback in that the light transmission performance is adversely affected.

Therefore, in the polymer forming the optical transmission medium,
A non-polymerizable compound that has a different refractive index from this polymer (for example, a low molecular weight substance that is blended in a polymer as a plasticizer) is dispersed with a uniform concentration gradient to obtain a continuous refractive index in a certain direction. A method for providing distribution has been proposed (Abstracts of the Society of Polymer Science, 1992, Vol.41, No.3, 798, 79)
9).

[0008]

However, although this method is excellent in light-transmitting performance, since the non-polymerizable compound is added and dispersed in the polymer, the glass transition temperature of the polymer is lowered, and the heat resistance is lowered. There was a problem that sex deteriorates. This further lowers the heat resistance of the plastic optical transmission body, which has a limited application range as compared with the silica type optical transmission body because the heat resistance thereof is lower than that of the silica type transmission body.

In the case of application for communication, etc., it is necessary that the heat resistance is 85 ° C. or higher in terms of reliability. However, polymethylmethacrylate generally used for plastic optical transmitters is used. A dispersion-containing non-polymerizable compound was used to produce a gradient index plastic optical transmission medium.
It is difficult to maintain heat resistance above 85 ° C. not to mention,
It is difficult to apply to applications that require higher heat resistance.

It is also conceivable to use polycarbonate for production, but an optical transmission body using this is excellent in heat resistance, but there is a problem in light transmission performance and heat durability. This is because it is difficult to remove the by-product generated during the polymerization reaction, or the by-product or the decomposed product of the polymer causes coloring.

As described above, according to the conventional method, it was difficult to produce a plastic optical transmission body having a good light-transmitting property and a continuous refractive index distribution while maintaining a heat resistance level of 85 ° C. or higher.

Therefore, the present invention solves the above-mentioned drawbacks of the prior art, and has not only the light-transmitting performance and mechanical characteristics comparable to those of the polymethylmethacrylate-based step index type optical transmission body, but also 85 ° C. or more. The main object of the present invention is to provide a plastic optical transmission body that also has the above heat resistance and has a refractive index distribution that continuously decreases from the central portion to the outer peripheral portion.

[0013]

In order to achieve this object, the present invention provides a colorless transparent non-polymerizable polymer which is compatible with a polymer constituting an optical transmission medium and has a higher refractive index than the polymer. The compound is a plastic optical transmission medium having a refractive index distribution that is dispersed in a concentration distribution that continuously decreases from the central portion to the outer peripheral portion of the optical transmission member, and that continuously decreases from the central portion to the outer peripheral portion, The above-mentioned polymer is a colorless and transparent polymer containing an aliphatic N-substituted maleimide monomer unit as a copolymerization component, which is a gradient index plastic optical transmission medium.

In the present invention, a high-refractive-index compound that does not polymerize the refractive index distribution that continuously decreases from the central portion to the outer peripheral portion of the optical transmission medium with the monomer forming the polymer of the optical transmission medium, It is formed by dispersing the polymer in a concentration distribution that continuously decreases from the central portion to the outer peripheral portion.

The high refractive index compound has a higher refractive index than the base polymer constituting the optical transmission medium, for example, 0.02 or more higher refractive index, and is compatible with the polymer and has a high refractive index. It is necessary that it can be uniformly dispersed therein, that it is colorless and transparent, and that it is non-polymerizable and does not form a polymer or a copolymer with the monomers of the base polymer. Further, it is preferable that the boiling point is as high as 200 ° C. or higher and that the molecular weight is larger than that of the monomer forming the polymer. By using such a non-polymerizable high-refractive-index compound, it is possible to prevent the deterioration of the light-transmitting performance without forming a microscopic phase-separated structure having a different refractive index in the polymer in which the polymerization is completed. .

As the high refractive index compound, for example, benzyl n-butyl phthalate, dimethyl phthalate, diallyl phthalate, dioctyl phthalate, dipropylene glycol dibenzoate, diethylene glycol dibenzoate, triphenyl phosphate and the like are used. You can

On the other hand, if a monomer that gives a polymer having a refractive index larger than that of the base polymer forming the optical transmission medium is used as the compound for forming the refractive index distribution, the refractive index is obtained by the copolymerization. It is unsuitable because a microscopic phase separation structure different from each other is formed and the light transmission performance is deteriorated.

Further, it is necessary to use a colorless and transparent polymer containing an aliphatic N-substituted maleimide monomer unit as a copolymerization component for the base polymer constituting the optical transmission medium.

The aliphatic N-substituted maleimide monomer units have less possibility of side reactions, have no greater characteristic absorption in the visible region than polymethylmethacrylate, and, in addition, have mechanical properties, glass transition temperatures, From the balance of thermal stability and the like, it is suitable as a copolymerization component for improving the heat resistance of the optical transmission body.

Examples of the aliphatic N-substituted maleimide monomer include methyl, ethyl, isopropyl, isobutyl, sec-butyl, t-butyl, 2,2-dimethylpropyl, cyclohexyl and the like having 1 to 6 carbon atoms. The maleimide monomer N-substituted with the aliphatic hydrocarbon group of is mentioned. Of these, isopropyl, isobutyl, sec-butyl, t-butyl, 2,2-butyl, which are liquids at room temperature, are easy to distill to increase the purity of the monomer, and have high colorless transparency and high thermal stability. Substitutes such as dimethylpropyl are preferable, and among them, isopropyl substitutes, which are most excellent in colorless transparency, are particularly preferable.

On the other hand, the N-substituted maleimide substituted with an aromatic group is not suitable because it is colored yellow or light yellow, which adversely affects the light transmission performance of the optical transmission medium.

However, the homopolymer of the aliphatic N-substituted maleimide monomer has a high colorless transparency and a glass transition temperature of about 200 ° C., which is sufficiently high in heat resistance and durability, but has poor mechanical properties. Since it is sufficient, it is not suitable for an optical transmission body.

Accordingly, in addition to the aliphatic N-substituted maleimide monomer unit, the polymerization component forming this polymer is
It is necessary to use the polymerization component normally used for an optical transmission body.

Examples of the polymerization component include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, cyclohexyl methacrylate, and aliphatic substituted cyclohexyl methacrylate. Among these, methyl methacrylate is preferable because the obtained light transmission body has excellent colorless transparency and a high glass transition temperature.

The copolymer composition at this time is the above-mentioned aliphatic N-
It is preferable that the substituted maleimide be contained in an amount of 5 to 70 mol%, and more preferably 10 to 50 mol%.

When homopolymerized, the aliphatic N-substituted maleimide can give a polymer having a refractive index close to that of an ordinary light transmitting polymer such as polymethylmethacrylate and excellent in colorless transparency. Moreover, since the difference in the monomer reactivity ratio between the aliphatic N-substituted maleimide and the methyl methacrylate is not large, the aliphatic N-substituted maleimide is used in combination with a monomer for an optical transmitter such as methyl methacrylate. Even if polymerized, composition distribution hardly occurs and excellent light-transmitting performance can be exhibited.

By copolymerizing the aliphatic N-substituted maleimide in this manner, the heat resistance of the resulting copolymer can be improved and the glass transition temperature of 130 ° C. or higher can be achieved. A glass transition temperature of 90 ° C. or higher can be obtained even when a high refractive index compound having a high property is dispersedly contained.

The optical transmission article of the present invention can be produced by either a batch production method or a continuous production method. The batch production method is a polymerizable solution (a single amount is a solution of a polymer hollow tube prepared in advance, in which the polymer of the hollow tube is dissolved and the non-polymerizable high refractive index compound is dispersed. Body component, a polymerization initiator, a monomer mixture containing a molecular weight modifier) is filled, the polymerization is advanced from the outside while promoting the diffusion of the non-polymerizable high-refractive-index compound, and a rod-shaped preform is obtained. It is a method of heating and stretching so as to obtain a desired diameter.

In this case, the polymer hollow tube may be formed of the same monomer mixture as that filled in the hollow portion except that it does not contain a non-polymerizable high refractive index compound. They may be formed from different monomer mixtures as long as they have the same main component monomer. Furthermore, it may be composed of a polymer obtained by copolymerizing an aliphatic N-substituted maleimide monomer unit.

As the polymerization initiator, an azo compound such as azobisisobutyronitrile, a normal radical polymerization initiator such as a peroxide such as benzoyl peroxide, and n-butyl mercaptan can be used as the molecular weight regulator. Ordinary radical chain transfer agents such as mercaptans are used.

In the continuous production method, the monomer mixture is polymerized in another polymerization device or in a polymerization device continuously connected to the outer portion of the spinneret having double concentric discharge holes. The polymerization rate is 50 with the polymerization initiator and the molecular weight modifier left.
Polymerization rate of 50 to 90% without leaving a polymerization monomer mixture or a polymerization initiator and a molecular weight modifier
After the polymerization is stopped by (1), a polymer monomer mixture to which a polymerization initiator and a molecular weight modifier are further added is introduced. On the other hand, in the inner part of the same die, a mixed liquid of a monomer mixed liquid containing a high refractive index non-polymerizable compound as it is not polymerized, or the monomer mixed liquid is polymerized to some extent to cause polymerization initiator and molecular weight. Polymer monomer mixture containing a regulator and having a polymerization rate of 50% or less (this polymer monomer mixture may be one in which the polymerization was interrupted while leaving the polymerization initiator and the molecular weight regulator). Then
In addition, a polymerization initiator or a molecular weight modifier may be added after the polymerization is interrupted). And, the viscosity of the outer polymer monomer mixture is 10,000 to 150,
In the state of 000 poise, extruded from the die at the same time as the inner (polymer) monomer mixture to form a core-sheath composite rod-shaped article,
While further accelerating the diffusion of the high refractive index non-polymerizable compound in the inner mixture to the outer peripheral portion, or by further promoting the thermal polymerization or photopolymerization into a complete polymer, further, to obtain a desired diameter It is a method of heating and stretching.

The optical transmission body according to the present invention is represented by an optical fiber obtained by stretching as described above, but may be a rod lens without being stretched.

[0033]

EXAMPLES The present invention will be further described below with reference to examples.

The light transmission performance of the optical fibers in the examples was evaluated by the following method.

The light of the tungsten lamp is demultiplexed by a diffraction grating, condensed by a lens, and then both ends are polished to 10 to 30 m.
The light incident from one end of the optical fiber (fiber length: Ls m) and emitted from the other end was detected by the photodiode as optical power (Ps dBm). Next, a reference fiber (fiber length: Lr m) cut at a distance of about 2 m from the incident end with the incident end being fixed was measured by the so-called cutback method (Pr dBm) in which the same measurement was repeated. Then, the light transmission loss value of the optical fiber was calculated according to the following equation.

Light transmission loss value (dB / km) = (Ps-Pr) /
(Ls−Lr) · 1000 where Ls and Lr are the fiber lengths (m) of the sample optical fiber and the reference fiber, respectively.
Further, Ps and Pr are optical power values (dBm) of the sample optical fiber and the reference fiber, respectively.

The heat resistance durability of the optical fiber was evaluated by the following method.

The optical fiber used for the measurement was heated by a hot air dryer for a predetermined time, and the light transmission loss before and after the heating was measured according to the above method, and the values were compared.

Example 1 30 parts by weight of N-isopropylmaleimide, 70 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile, and 0.010 parts by weight of n-butylmercaptan were respectively distilled. The mixture was later prepared, filtered through a Teflon filter having a pore size of 0.05 μm, and then placed in a glass tube held horizontally.
After sealing both ends, rotate at 50 ° C for 1
After polymerizing for 6 hours, gradually raise the temperature to finally reach 90 ° C.
The polymerization was completed by keeping the temperature for 10 hours to obtain a polymer hollow tube.

Next, inside the hollow tube, 24 parts by weight of N-isopropylmaleimide, 56 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile,
After filling a mixture of 0.010 parts by weight of n-butyl mercaptan and 20 parts by weight of benzyl n-butyl phthalate, the mixture was allowed to stand at room temperature for 4 hours, polymerized at 50 ° C. for 16 hours, and gradually heated. Finally, the mixture was kept at 90 ° C. for 10 hours for polymerization to obtain a colorless and transparent rod having a diameter of 20 mm. The outer glass tube was broken and removed.

The rod thus obtained was cut and pulverized, and only the central portion of the rod was taken out and the glass transition temperature was measured by DSC.

This rod is heated by a cylindrical heater 230
It was melt-stretched at ℃ to obtain an optical fiber with a diameter of 1 mm.

When the refractive index distribution of the obtained optical fiber was measured by an interferco interference microscope, the refractive index continuously decreased from the center to the outer periphery. The central part had a refractive index of 1.519, and the outer peripheral part had a refractive index of 1.506. The light transmission loss value at 25 ° C of this optical fiber is
It was 154 dB / km at 650 nm. Also, 10 at 85 ° C
The light loss value after heat treatment for 00 hours is 15 at 650 nm.
It was 8 dB / km, which was good with almost no change even after heat treatment.
Furthermore, the flexibility was good because the winding diameter could be up to 1 mm.

As described above, the obtained gradient index optical fiber exhibits excellent light-transmitting performance and mechanical characteristics, and further,
It was also excellent in heat resistance.

Example 2 A mixture of 30 parts by weight of N-cyclohexylmaleimide, 70 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile and 0.010 parts by weight of n-butylmercaptan was distilled respectively. After that, it was filtered with a Teflon filter having a hole of 0.05 μm and then put into a glass tube held horizontally. After sealing both ends, polymerization was carried out in the same manner as in Example 1 to obtain a polymer hollow tube. Then, 24 parts by weight of N-cyclohexylmaleimide, 56 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile, and 0.010 of n-butylmercaptan were placed inside the hollow tube.
After charging a mixture of 20 parts by weight of benzyl n-butyl phthalate and 20 parts by weight of benzyl phthalate, the mixture was polymerized in the same manner as in Example 1 to obtain a colorless and transparent rod having a diameter of 20 mm. The glass tube was broken and removed.

The glass transition temperature at the center of the obtained rod was 104 ° C. An optical fiber having a diameter of 1 mm was obtained from this rod in the same manner as in Example 1.

In the refractive index distribution of the obtained optical fiber, the refractive index continuously decreased from the center to the outer circumference. The refractive index of the central portion is 1.522, and the refractive index of the outer peripheral portion is 1.22.
It was 509. The light transmission loss value at 25 ° C. of this optical fiber was 187 dB / km at 650 nm. The light loss value after heat treatment at 85 ° C for 1000 hours is 1 at 650 nm.
It was good with almost no change of 90 dB / km. Furthermore, the flexibility was good because the winding diameter could be up to 1 mm.

Thus, as in Example 1, a gradient index optical fiber having excellent light-transmitting performance, mechanical characteristics and heat resistance could be obtained.

[Example 3] Methyl methacrylate was distilled, and azobisisobutyronitrile and n-butyl mercaptan were mixed to prepare a monomer mixture.
The mixture was filtered with a Teflon filter having a pore size of μm and then placed in a glass tube held horizontally. Then, after sealing both ends, the polymer was thermally polymerized according to a conventional method while rotating to obtain a polymer hollow tube. Inside the polymerization tube, 24 parts by weight of N-isopropylmaleimide, 56 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile, n
After filling a mixture of 0.010 parts by weight of -butyl mercaptan and 20 parts by weight of benzyl n-butyl phthalate, the mixture was polymerized in the same manner as in Example 1 to obtain a colorless and transparent rod having a diameter of 20 mm. The glass transition temperature of the obtained rod central part obtained by breaking and removing the glass tube was 98 ° C. An optical fiber having a diameter of 1 mm was obtained from this rod in the same manner as in Example 1.

In the refractive index distribution of the obtained optical fiber, the refractive index continuously decreased from the center to the outer periphery. The central portion has a refractive index of 1.517, and the outer peripheral portion has a refractive index of 1.
It was 494. The light transmission loss value at 25 ° C. of this optical fiber was 153 dB / km at 650 nm. The light loss value after heat treatment at 85 ° C for 1000 hours is 1 at 650 nm.
It was good with almost no change of 60 dB / km. Further, the flexibility was good because the winding diameter could be up to 1 mm.

As described above, similar to Examples 1 and 2, it was possible to obtain a gradient index optical fiber having excellent light-transmitting performance, mechanical characteristics and heat resistance.

Comparative Example 1 Methyl methacrylate was distilled, and azobisisobutyronitrile and n-butyl mercaptan were mixed to prepare a monomer mixture.
The mixture was filtered through a Teflon filter having a hole of μm and then put into a glass tube held horizontally. Then, after sealing both ends, the polymer was thermally polymerized according to a conventional method while rotating to obtain a polymer hollow tube. A mixture of 80 parts by weight of methyl methacrylate, 0.015 parts by weight of azobisisobutyronitrile, 0.010 parts by weight of n-butyl mercaptan, and 20 parts by weight of benzyl n-butyl phthalate was placed inside the hollow tube. After filling, was polymerized in the same manner as in Example 1 to obtain a colorless and transparent rod having a diameter of 20 mm. The glass tube was broken and removed. The glass transition temperature of the obtained central part of the rod was as low as 78 ° C. An optical fiber having a diameter of 1 mm was obtained from this rod in the same manner as in Example 1.

In the refractive index distribution of the obtained optical fiber, the refractive index continuously decreased from the center to the outer periphery. The refractive index of the central portion is 1.510, and the refractive index of the outer peripheral portion is 1.10.
It was 494. The optical transmission loss value at 25 ° C of this optical fiber is 126 dB / km at 650 nm and is 1 at 85 ° C.
The light loss value after heat treatment for 000 hours is 2 at 650 nm.
It was significantly deteriorated to 10 dB / km. Furthermore, the shape of the refractive index distribution was also changed.

[0054]

Industrial Applicability According to the present invention, there is provided a plastic optical transmission body having a refractive index distribution which continuously decreases from the central portion to the outer peripheral portion.
In addition to maintaining excellent light-transmitting performance and mechanical properties, it also has excellent heat resistance and durability, and has practical reliability that can be used for a long period of time at a practical heat resistant temperature of 85 ° C.

Claims (2)

[Claims] 1. A colorless and transparent non-polymerizable compound which is compatible with a polymer constituting an optical transmission medium and has a higher refractive index than the polymer is continuous from the central portion to the outer peripheral portion of the optical transmission member. A plastic optical transmission medium having a refractive index distribution that is dispersed in a concentration distribution that is gradually reduced and that continuously decreases from a central portion to an outer peripheral portion, wherein the polymer comprises an aliphatic N-substituted maleimide monomer unit. A gradient index plastic optical transmission material, which is a colorless and transparent polymer containing as a copolymerization component. 2. The gradient index plastic optical transmission article according to claim 1, wherein the glass transition temperature of the polymer in the central portion of the optical transmission article is 90 ° C. or higher.