JP2615670B2 - Heat resistant plastic optical fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plastic optical fiber having a core-sheath structure excellent in heat resistance and light transmission performance.

[Prior Art] Conventionally, optical fibers have been manufactured using quartz glass or plastic. Quartz-based optical fibers have excellent light transmission performance and have been put to practical use for long-distance communication and the like, but are not only poor in workability and flexibility but also expensive. In contrast, plastic optical fibers are
Although light transmission performance is inferior, it has advantages such as good flexibility, lightness, good workability, and low cost, and is being used for short distances.

As a core component of the plastic optical fiber, polymethyl methacrylate is generally used. This polymethyl methacrylate has excellent properties such as weather resistance and mechanical properties, such as light transmission performance, among plastics, but is insufficient in heat resistance. Therefore, the use of optical fibers containing this as a core component is limited to about 80 ° C. in applications exposed to high temperatures, and there is a strong demand for improved heat resistance.

The following methods are known for improving the heat resistance of the plastic optical fiber.

(1) Use a condensation polymer having high transparency and high glass transition temperature such as polycarbonate (Japanese Patent Application Laid-Open No.
46204).

(2) Methacrylic acid having a bulky ester such as bornyl methacrylate or adamantyl methacrylate is copolymerized with methyl methacrylate (JP-A-59-22020).

(3) After methyl methacrylate is polymerized to form a polymer, an amine or the like is reacted to cause intramolecular crosslinking.

However, the optical fiber using (1) as a core component has good heat resistance, but is not sufficient in light transmission performance and heat resistance durability. This is because it is difficult to remove by-products generated during the polymerization reaction, or it is colored by by-products or decomposition products of the polymer.

In addition, optical fibers using (2) as a core component often do not have sufficient heat resistance due to insufficient improvement of the glass transition temperature. In addition, when an attempt is made to increase the glass transition temperature by increasing the copolymer composition ratio of the component,
Sufficient mechanical properties cannot be obtained, and bulky ester groups are easily decomposed, and there is a problem in heat resistance and durability.

Further, the optical fiber using (3) as a core component has many by-products, so that a fiber which is colored and has good light transmitting performance cannot be obtained.

In order to further improve such heat resistance, attempts have been made to incorporate hindered phenol into a polymethyl methacrylate polymer (Japanese Patent Application Laid-Open No. 60-222804).
These also do not impair the light transmission performance of the optical fiber,
It did not provide heat resistance satisfying practical performance.

For these reasons, plastic heat-resistant optical fibers have not been put to practical use.

[Problems to be Solved by the Invention] An object of the present invention is to provide a plastic optical fiber having excellent light transmission performance and mechanical properties and excellent heat resistance.

[Means for Solving the Problems] As a result of various studies for the above-described purpose, the present invention has been reached.

That is, the present invention relates to a plastic optical fiber having a core-sheath structure, wherein the core component is a polymer containing an aliphatic N-substituted maleimide monomer unit,
-It relates to a plastic optical fiber excellent in heat resistance characterized by containing an alkoxyphenol.

The present invention is not particularly limited as long as it is a polymer containing an aliphatic N-substituted maleimide monomer unit, but has a low possibility of side reaction and has no characteristic absorption in the visible region.
Those having a hydrocarbon substituent are preferred. Further, a polymer having excellent mechanical properties and thermal stability, and having a high glass transition temperature and a hydrocarbon having an N-substituent of 1 to 6 carbon atoms, such as methyl, ethyl, isopropyl, isobutyl,
Substitutes such as sec-butyl, t-butyl, 2,2-dimethylpropyl, cyclohexyl and the like can be mentioned. Most preferably, it is an N-substituent such as isopropyl, isobutyl, sec-butyl, t-butyl, 2,2-dimethylpropyl, etc., which can be easily purified to increase the purity of the monomer.

In the case of an aromatic substituent of N-substituted maleimide (JP-A-61-77806), since the monomer itself is a yellow or pale yellow crystal, the polymer containing the monomer unit also turns yellow and becomes transparent. Fibers with excellent optical performance cannot be obtained.

The second component copolymerized with the N-substituted maleimide is most preferably methyl methacrylate in consideration of the light transmission performance, mechanical properties, and productivity of the obtained fiber, but any monomer having good copolymerizability may be used. However, it is not limited to this. Further, several types of third components other than the second component, such as methyl acrylate, ethyl acrylate, and styrene, may be contained.

The copolymer composition preferably has 5 to 70% of aliphatic N-substituted maleimide monomer units, and more preferably 10 to 50% of N-substituted maleimide monomer units. If the amount of the N-substituted maleimide monomer unit is less than 5%, sufficient heat resistance cannot be imparted, and if it exceeds 70%, the mechanical properties of the fiber will be significantly reduced.

Thus, by using a polymer containing an aliphatic N-substituted maleimide monomer unit as the core component, a fiber with improved heat resistance was obtained. However, when used in a high temperature environment for a long time, there is a problem that the fiber is colored and the light transmission performance is reduced. Then, in order to solve this problem, various studies were conducted on this polymer, and the present invention was reached.

That is, when various stabilizers were added to a polymer having a core component containing an aliphatic N-substituted maleimide monomer unit, the heat resistance was further improved surprisingly only when p-alkoxyphenol was contained. The resulting plastic optical fiber was obtained. When a stabilizer other than p-alkoxyphenol, for example, a hindered phenol, an amine, a sulfur compound, a phosphorus compound, etc. is added, not only does the heat resistance not improve, but on the contrary, it becomes yellower and translucent than the system without the addition. Performance deteriorated. That is, in the present invention, it is important that a polymer containing an aliphatic N-substituted maleimide monomer unit contains p-alkoxyphenol.
However, it is possible to use other stabilizers at the same time as the p-alkoxyphenol in very small amounts without deteriorating the thermal stability.

The type of the p-alkoxyphenol is not particularly limited as long as it does not deteriorate the light transmission performance. However, in consideration of the stability, productivity, and the like of the compound itself, the substituent has 1 to 8 carbon atoms. Hydrocarbons are good, and examples thereof include substituents such as methyl, ethyl, propyl, butyl, hexyl, and octyl.

The method of compounding these compounds into the core polymer is not particularly limited.
It can be contained in the core polymer via a demonomer-spinning step, or can be blended in the demonomer step or the spinning step.

The compounding amount of the compound is 30 to 5,000 ppmA, more preferably 50 to 3,000 ppmA. If it is less than 30 ppm, the effect of improving the heat resistance cannot be exhibited, and if it exceeds 5,000 ppm, the heat resistance decreases and the light transmission performance also deteriorates.

Generally, as a polymerization method of a core polymer used for a plastic optical fiber, a bulk polymerization method and a continuous polymerization method having a polymerization rate of 40 to 70% have been proposed. Although this method can be employed in the present invention, a solution polymerization method is also possible. Specific examples of the solvent that can be used for the solution polymerization include hydrocarbon compounds such as toluene and xylene, fatty acid ester compounds such as butyl acetate, and ether compounds such as dioxane.

Either a continuous polymerization method or a batch polymerization method can be employed, but the continuous polymerization method is more preferable not only for achieving a high degree of cleanness but also for obtaining a polymer having a uniform copolymer composition and molecular weight.

The polymerization temperature is preferably in the range of 60 to 160 ° C, and the viscosity of the polymerization mixture for obtaining a uniform polymer by stirring is 10 to 5 ° C.
A range of 00 poise is preferred.

The type of the polymerization initiator at this time is not particularly limited as long as it does not adversely affect the side reaction or coloring during the polymerization, and the type and amount of the polymerization initiator are determined according to the polymerization temperature, the polymerization rate, and the polymerization time. You can choose. Examples thereof include azo compounds such as azo-t-butane and azo-t-octane, and organic peroxides such as benzoyl peroxide, di-t-butyl peroxide and di-t-butyl perbenzoate.

Although the type of the molecular weight regulator is not particularly specified, those having adverse effects such as side reactions and coloration during polymerization and those having a chain transfer constant extremely smaller than 1.0 are not preferred. From this point, it is preferable to use mercaptans such as n-propyl, n-butyl, n-hexyl, n-dodecyl, isobutyl, isopentyl, t-butyl, and t-hexyl in an appropriate amount. By appropriately designing the amount, the molecular weight can be adjusted without using a molecular weight regulator.

The polymer solution thus obtained by the polymerization reaction is supplied to a demonomerization step to remove volatiles such as unreacted monomers. However, since the glass transition temperature decreases in proportion to the amount of the volatiles, the polymer solution in the polymer is removed. It is preferable to reduce the content of volatile matter as much as possible, and specifically, it is better to make it 0.5% by weight or less.

The core polymer from which volatile substances have been removed is simultaneously melt-extruded from a composite spinneret together with a sheath polymer having a lower refractive index than the core polymer, whereby a plastic optical fiber having a concentric structure can be produced.

The sheath component that can be used at this time is not particularly limited as long as it has at least a 2% lower flexion factor than the core polymer shown in the present invention and is excellent in transparency. Polymers or copolymers such as fluoroalkyl and α-fluoroalkyl acrylate, and polyfluoroolefins can be preferably used.

Further, it is possible to use the optical fiber by covering the optical fiber with a coating material for the purpose of improving environmental resistance. Preferred coating materials include polyolefins such as polyethylene, polypropylene and polyvinyl chloride, or crosslinked polyolefins, polyamides such as nylon 12, and polyester elastomers which are copolymers of polybutylene terephthalate and polytetramethylene glycol. And the like.

Hereinafter, the present invention will be described more specifically with reference to examples.

The evaluation of the light transmission performance in the examples was performed as follows.

The light from the tungsten lamp is split by a diffraction grating, collected by a lens, then incident from one end of a 10-30m optical fiber whose both ends are polished, and the light emitted from the other end is detected as optical power by a photodiode. . Next, the optical fiber was cut at a distance of about 2 m from the incident end while the incident end was fixed, and the measurement was repeated using the so-called cutback method. The transmission loss of the optical fiber was calculated according to the following equation.

Loss value (dB / km) = (Pr-Ps) / (Ls-Lr) 1000 L: Fiber length (m) P: Optical power value (dBm) s: Sample fiber r: Reference fiber The property was evaluated by the following method.

After the optical fiber subjected to the measurement was heated by a hot air drier for a predetermined time, the transmission loss at the initial stage and after the heating was measured and compared according to the above method.

[Examples] Example 1 N-isopropylmaleimide 200.0 parts by weight Methyl methacrylate 466.7 parts by weight n-butylmercaptan 0.82 parts by weight Azo-t-butane 1.0 part by weight p-Methoxyphenol 0.67 parts by weight (1,000 ppm) The mixture was charged into the polymerization tank while being filtered through a 0.05 μφ (filtration diameter) filter made of tetrafluoroethylene. Then, polymerization was carried out at 130 ° C for 16 hours under nitrogen pressure, and then gradually heated and finally kept at 180 ° C for 16 hours.

After the temperature was further increased and maintained at 230 ° C. for 1 hour, the mixture was gradually supplied to a demonomerization step under nitrogen pressure to remove volatiles and obtain a polymer. Next, this container was installed in a composite spinning machine having a core-sheath double-layer spinneret.

On the other hand, a sheath material of tetrafluoropropyl α-fluoroacrylate / trifluoroethyl α-fluoroacrylate (85/15 weight ratio) was melted at 210 ° C., and then supplied to a die.

The fiber obtained at a spinning temperature of 230 ° C and a take-up speed of 5 m / min was stretched 2.0 times at 160 ° C and the core material diameter was 980.
A concentric optical fiber having a thickness of 10 μm and a sheath portion thickness of 10 μm was obtained. Next, it was coded by coating with polypropylene.

The polymer that has undergone the demonomerization step has a residual monomer amount of
The result of GC measurement was 0.16% by weight, and the glass transition temperature was DSC.
As a result of the measurement, it was 137 ° C.

The transmission loss value of the coded optical fiber at 25 ℃ was 220 dB / km at 660 nm, and the transmission loss value after heat treatment at 125 ℃ for 2000 h was almost unchanged at 224 dB / km.
In addition, the minimum diameter that can be wound was up to 1 mm, and the flexibility was good, and a plastic optical fiber with excellent heat resistance was obtained while maintaining the light transmission performance and mechanical properties comparable to polymethyl methacrylate.

Comparative Example 1 An optical fiber was obtained in the same manner as in Example 1 except that p-alkoxyphenol was not added.

Example 2.3, Comparative Example 2.3 An optical fiber was obtained in the same manner as in Example 1, except that the type and amount of p-alkoxyphenol were changed as shown in Table 1.

 The physical property evaluation is shown in Table 1 below.

Comparative Example 4.5 As an additive, instead of p-alkoxyphenol, a stabilizer represented by the following chemical formula “IRGANOX101” was used, respectively.
An optical fiber was obtained in the same manner as in Example 1, except that "IRGANOX1222" was used. "IRGANOX" is a registered trademark of Ciba Geigy.

Example 4 An optical fiber was prepared in the same manner as in Example 1 except that the monomer composition and the additives were changed as shown in Table 1 and solution polymerization was carried out by charging toluene to 70% by weight of the total mixed solution. Obtained.

Example 5 N-isopropylmaleimide 24.5 wt% Methyl methacrylate 45.5 wt% Toluene 30.0 wt% Azo-t-octane 0.095 wt% p-methoxyphenol 0.07 wt% (1,000 ppm) 0.1 μφ (filtration diameter) And fed to the polymerization tank at a rate of 5 kg / hr while filtering through a tetrafluoroethylene filter. The polymerization temperature was 135 ° C., the average residence time in the polymerization tank was 4 hours, and the reacted polymer solution was continuously discharged at a rate of 5 kg / hr by a metering pump. This solution was fed to a vented extruder to remove unreacted monomers and solvent at 190-250 ° C and 250-2 torr, and then introduced as a core component into a composite spinning machine.

Thereafter, an optical fiber was obtained in the same manner as in Example 1.

The reaction rate of the polymer discharged from the polymerization tank was 88% by weight as a result of GC measurement, and the composition of the copolymer was 33% by weight of N-isopropylmaleimide as a result of elemental analysis.

[Effects of the Invention] The plastic optical fiber of the present invention is far superior in heat resistance and durability, while maintaining comparable light transmission performance and mechanical properties, as compared with a conventional fiber having polymethyl methacrylate as a core component. It was.

Claims (1)

(57) [Claims] 1. A plastic optical fiber having a core-sheath structure, wherein the core component comprises a polymer containing an aliphatic N-substituted maleimide monomer unit, and the core component contains 30-5,000 ppm of p-alkoxyphenol. A heat-resistant plastic optical fiber, characterized in that: