JPH0711604B2 - Optical fiber sheath material polymer - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to polymers for use as sheath materials for optical fibers.

As optical fibers, it is known that both the core and the sheath are made of plastic, the core is made of glass, the sheath is made of plastic, and the core and the sheath are made of glass. Since it is flexible and easy to use, it is important for information communication and display for short and medium distances. The polymer for a sheath material of the present invention can be suitably used for such an optical fiber whose core is made of a plastic, particularly a methyl methacrylate polymer.

2. Description of the Related Art The physical properties required for polymers for optical fiber sheath materials include low refractive index, good transparency and heat resistance, high adhesiveness with core polymers, and high mechanical strength. is there.

Until now, for example, the general formula has been used to meet such requirements. (In the formula, X'is H, F or Cl, m'is an integer of 1 to 6,
n'is an integer of 2 to 10) or a fluoroalkyl methacrylate polymer or copolymer (Japanese Patent Publication No. 43-8978) and trifluoromethyl methacrylate polymer (Japanese Patent Publication No. 49-107790). ) Etc. have been proposed.

However, even if these polymers are excellent in transparency and heat resistance, they have insufficient mechanical strength.

On the other hand, a vinylidene fluoride-based material is known as a sheath material having excellent mechanical strength, but this material has a problem in refractive index.

As described above, the refractive index, the heat resistance and the mechanical strength of the polymer that has been used for the sheath material have a contradictory relationship with each other. It was usually made to have excellent physical properties, but satisfactory results have not yet been obtained.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention According to the present invention, a copolymer of long-chain fluoroalkyl methacrylate and methyl methacrylate has excellent mechanical strength and heat resistance unlike the above-mentioned ordinary trifluoroalkyl methacrylate. However, because it has turbidity, it was considered unsuitable when a high level of light guiding property is required, while making use of this excellent mechanical strength and heat resistance, improving transparency, The purpose of the present invention is to provide a polymer in which the properties generally required as a sheath material are enhanced.

Means for Solving the Problems The inventors of the present invention have found that a copolymer of a long-chain fluoroalkyl methacrylate and methyl methacrylate may be significantly clouded depending on polymerization conditions, which is a long-chain fluoroalkyl having a large molecular chain. It is thought that methacrylate is because it causes diffusion obstacle in the latter stage of the polymerization reaction, as a result of various studies on alleviating this diffusion obstacle and suppressing the occurrence of cloudiness, in addition to long-chain fluoroalkyl methacrylate and methyl methacrylate, Further, it was found that the object can be achieved by introducing a short-chain fluoroalkyl methacrylate having a relatively small molecular weight as the third component, and the present invention has been completed based on this finding.

That is, the present invention is based on the formula (a) Long-chain fluoroalkyl methacrylate represented by 30-60
Wt% and (b) general formula (Wherein X is H or F, n is an integer of 1 to 4) 20 to 50% by weight of at least one monomer selected from the short-chain fluoroalkyl methacrylates
(C) A polymer for a sheath material for a plastic optical fiber having a methyl methacrylate-based polymer as a core material, which is substantially composed of a copolymer with 20 to 50% by weight of methyl methacrylate.

The long-chain fluoroalkyl methacrylate component in the copolymer of the present invention must be used within the range of 30 to 60% by weight. If it is less than 30% by weight, sufficient mechanical strength cannot be obtained, and if it exceeds 60% by weight, the refractive index becomes small, but the softening temperature becomes too low, resulting in insufficient heat resistance.

On the other hand, the short-chain fluoroalkyl methacrylate component is preferably trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, or the like. These may be used alone or in combination of two or more. It is used in the range of 20 to 50% by weight, preferably 30 to 40% by weight. If this amount exceeds 50% by weight, the mechanical strength derived from the long-chain fluoroalkyl methacrylate will be lost, and if it is less than 20% by weight, the cloudiness development cannot be sufficiently improved.

Next, methyl methacrylate is a component for forming a copolymer having excellent mechanical strength and heat resistance together with a long-chain fluoroalkyl methacrylate, and is used within a range of 20 to 50% by weight.

In the copolymer used in the present invention, in addition to the above three components (a) to (c), methacrylic acid may be added, if desired, within a range not exceeding 5 parts by weight per 100 parts by weight of the copolymer composition. An acid, o-methylphenyl maleimide, maleimide, maleic anhydride, styrene, methyl acrylate, acrylic acid, a methacrylic acid six-membered cyclized product, or the like can be introduced.

This copolymer is preferably produced, for example, by continuous bulk polymerization and continuous solution polymerization performed in one stage using a complete mixing reaction tank, but it may be produced by batch type bulk polymerization. In this case, the polymerization temperature is preferably 75 ° C. or higher when the polymerization rate is 90% or higher.

The polymer for the sheath material of the present invention is a methyl methacrylate-based polymer, for example, polymethyl methacrylate, in combination with a core material such as a copolymer having methyl methacrylate as a main component, and 200 to 260 ° C. using a composite spinning machine. An optical fiber can be obtained by molding at the temperature of.

EFFECT OF THE INVENTION The sheath material polymer of the present invention has a higher softening temperature and a higher mechanical strength than conventional fluoroalkylmethacrylate sheath materials used for optical fibers having a methyl methacrylate polymer as a core material. It has a low refractive index and excellent transparency. Therefore, when an optical fiber is manufactured using this, the light guiding performance and reliability can be significantly improved.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples. The total light transmittance in the examples is measured according to JIS-Z8722, and the Vicat softening temperature is measured according to ASTM D 1525-65 TI.

Example 1 A monomer mixture consisting of 40% by weight of long-chain fluoroalkylmethacrylate, 39.6% by weight of trifluoroethylmethacrylate, 30% by weight of methyl methacrylate, 0.4% by weight of methacrylic acid, 950 ppm of octyl mercaptan tert-butylperoxy-2. After mixing 2000 ppm of ethylhexanoate and degassing under reduced pressure, bulk polymerization was performed. Polymerization reaction is 80 ℃
After 15 hours at 110 ° C., further 3 hours at 110 ° C. The residual monomers of this polymer were 0.2% for long-chain fluoroalkyl methacrylate and 0.14% for methyl methacrylate. This polymer was crushed and dried at 130 ° C., and then prepared as a sheath material. A press plate having a thickness of 3 mm was formed from the pellets at 240 ° C. to prepare a sample for evaluation, and the light transmittance was 93.8% and the Vicat softening temperature was 82 ° C. Refractive index ▲ n ²⁰ _D ▼ 1.423.
A plastic optical fiber having this polymer as a sheath and a core of polymethylmethacrylate was spun. The light guide performance of this fiber was 77 dB / Km at 570 nm and 145 dB / Km at 650 nm. 180 fibers with a diameter of 0.5 mm
The folding endurance was examined by bending and stretching, and it showed 16 times of endurance.

Example 2 The same catalyst as in Example 1 was added to a monomer mixture consisting of 45% by weight of long-chain fluoroalkyl methacrylate, 20% by weight of tetrafluoropropyl methacrylate and 35% by weight of methyl methacrylate to carry out a polymerization reaction to obtain a polymer. . The light transmittance of a 3 mm plate formed by pressing this polymer is 93.7
%, The Vicat softening temperature was 81 ° C., and the refractive index was ▲ n ²⁰ _D ▼ 1.426. Then, a plastic optical fiber having this polymer as a sheath and a core of polymethylmethacrylate was spun. The light guide performance of this fiber is 80 dB / K at 570 nm.
It was 148 dB / Km at m and 650 nm. Further, when a fiber having a diameter of 0.5 mm was bent 180 degrees and the folding endurance was examined, the endurance was shown 15 times. The adhesion of the core-sheath was also good.

Example 3 The same catalyst as in Example 1 was added to a monomer mixture consisting of 30% by weight of long-chain fluoroalkyl methacrylate, 10% by weight of tetrafluoropropyl methacrylate, 30% by weight of pentafluoromethyl methacrylate and 30% by weight of methyl methacrylate. Polymerization was performed to obtain a polymer. A 3 mm plate press-molded from this polymer had a light transmittance of 93.7%, a Vicat softening temperature of 80 ° C., and a refractive index ▲ n ²⁰ _D ▼ 1.422.
Then, a plastic optical fiber having this polymer as a sheath and a core of polymethylmethacrylate was spun. The light guide performance of this fiber is 146 dB / Km, 570 nm at 650 nm.
At 78 dB / Km. Further, when a fiber having a diameter of 0.5 mm was bent 180 degrees and the folding endurance was examined, the endurance was 10 times. The adhesion of the core-sheath was also good.

Comparative Example 1 60% by weight of long-chain fluoroalkyl methacrylate and 40% by weight of methyl methacrylate were polymerized in the same manner as in Example 1 to obtain a polymer. This polymer was crushed and press-molded at 230 ° C. to obtain a 3 mm plate. This press plate was slightly cloudy in places, and the light transmittance was 93.0%. Using this polymer as a sheath material, a plastic optical fiber having a core of polymethylmethacrylate was manufactured. The light guide performance of this optical fiber is 159 dB / Km at 650 nm and 112 d at 570 nm.
It was B / Km.

Comparative Example 2 80% by weight of tetrafluoropropyl methacrylate and 20% by weight of methyl methacrylate were copolymerized in the same manner as in Example 1 to obtain a polymer. The plate obtained by crushing this polymer and press-molding at 230 ° C. had a light transmittance of 93.5% and a Vicat softening temperature of 81 ° C. The refractive index ▲ n ²⁰ _D ▼ was 1.437. Next, a plastic optical fiber having this polymer as a sheath material and polymethylmethacrylate as a core was manufactured. The light guide performance of this optical fiber is 146 dB at 650 nm.
/ Km and 79 dB / Km at 570 nm. When a fiber having a diameter of 0.5 mm was bent 180 degrees and its folding endurance was examined, the endurance was only 5 times.

Claims (1)

[Claims] 1. A formula Long-chain fluoroalkyl methacrylate represented by 30-60
Wt% and (b) general formula (Wherein X is H or F, n is an integer of 1 to 4) 20 to 50% by weight of at least one monomer selected from the short-chain fluoroalkyl methacrylates
(C) A polymer for a sheathing material for a plastic optical fiber having a methyl methacrylate-based polymer as a core material, which is substantially composed of a copolymer with 20 to 50% by weight of methyl methacrylate.