JP2507355B2 - Plastic fiber optic fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic optical fiber having a core-sheath structure, and more particularly to a plastic optical fiber having both excellent heat resistance and translucency. Is.

[Prior Art] Optical fibers have conventionally been manufactured using quartz glass, multi-component glass, or plastic. Quartz optical fibers have been put to practical use for long-distance communication because of their excellent light-transmitting performance. On the other hand, plastic optical fibers are used for short-distance signal transmission and light guides because they are easy to handle because they have good flexibility, light weight, and good workability and are inexpensive.

As the polymer constituting the core of the plastic optical fiber, polymethylmethacrylate is mainly used because of its excellent transparency and weatherability / mechanical properties without any practical problems.

The optical fiber whose core is polymethylmethacrylate,
Due to the heat resistance level of polymethylmethacrylate, the upper limit temperature of use is limited to about 85 ° C. However, in recent years, there has been an increasing demand for a plastic optical fiber having higher heat resistance for use in automobiles or ships.

As one of the methods for improving the heat resistance of plastic optical fibers, that is, for improving the operating temperature, there is a method for increasing the glass transition temperature of the core component. For example, the following method is known.

(1) Polycarbonate (JP-A-57-46204),
A condensation type polymer having high transparency and a high glass transition temperature such as polyarylate and polyamide is used as a core component.

(2) Copolymerizing maleic anhydride (JP-A-59-200201), a styrene derivative (JP-A-58-34404), methacrylic acid having a bulky ester (the same as above), and the like into methyl methacrylate. The above copolymer is used as the core component.

(3) A polymer obtained by polymerizing methyl methacrylate to form a polymer and then intramolecularly cross-linking it with an amine or the like is used as a core component (JP-A-60-185905).

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

Further, in the optical fiber using the copolymer of (2), it is difficult to increase the heat resistance to a sufficient level because the glass transition temperature is not sufficiently improved. In addition, when the copolymerization composition ratio of the components is increased, or when the monomer is provided with a functional group having an extremely large bulkiness to improve the glass transition temperature, sufficient mechanical properties may not be obtained. ,
There arises a problem that the group is easily decomposed and has poor thermal stability. In addition, since most of them are solid at room temperature, the purity is low and impurities are mixed in, resulting in insufficient light-transmitting performance. Also, there are many residual monomers in the polymer, which tends to cause coloration and lower glass transition temperature. .

Furthermore, since the polymer (3) contains a large amount of by-products and is colored, it is difficult to obtain an optical fiber having a good light-transmitting property.

Further, as a second method for improving the heat resistance of an optical fiber, a method in which a protective layer is further provided around the sheath material so as to have a structure of three or more layers is proposed in JP-A-58-18608. However, even with such a structure, the heat shrinkage of polymethylmethacrylate cannot be avoided, and it is difficult to increase the heat resistance to a sufficient level.

For the above reasons, the plastic heat-resistant optical fiber has not yet been put to practical use.

[Problems to be Solved by the Invention] Therefore, the present invention is a plastic system having excellent light-transmitting performance and mechanical properties comparable to those of polymethylmethacrylate and capable of exhibiting excellent heat resistance for a long period of time. Its main purpose is to provide optical fibers.

[Means for Solving Problems] In order to achieve the above object, the present invention provides a plastic optical fiber having a core-sheath structure in which the polymer constituting the core contains 5 to 50 N-isopropylmaleimide units.
It comprises a plastic optical fiber which is a copolymer containing mol% and substantially consisting of N-isopropylmaleimide unit and methylmethacrylate unit.

In the present invention, N- which is copolymerized in the polymer of the core component
Isopropylmaleimide has less possibility of side reaction,
It has no characteristic absorption in the visible region. Further, the polymer has a good balance of mechanical properties, glass transition temperature improving property, thermal stability and the like. Furthermore, since it is a liquid at room temperature, it is easy to distill and it is easy to increase the purity of the monomer.

On the other hand, since the maleimide monomer N-substituted with an aromatic group is a yellow or pale yellow crystal, a polymer obtained by (co) polymerizing the maleimide unit is
It is not suitable as the core component of an optical fiber because it is colored yellow and has a problem in light transmission performance.

A homopolymer obtained from N-isopropylmaleimide has a high glass transition temperature of about 200 ° C., sufficiently high heat resistance and high colorless transparency, but has a problem of insufficient mechanical properties and the like. Therefore, for use as the core component of an optical fiber, it is necessary to copolymerize with methyl methacrylate. The copolymer composition at that time is
Considering the balance of heat resistance and durability that can maintain operating temperature of 115-150 ℃, and further having good mechanical properties, N-isopropylmaleimide has 5-50%.
It is necessary that the content be mol%.

Generally, when two or more kinds of monomers are copolymerized, the composition of the charged monomer and the composition of the produced copolymer are different, but in a stable continuous polymerization method such as mass balance, unless a comonomer having a significantly low copolymerizability is used, Even if the charged monomer composition and the produced copolymer composition are different, a copolymer having a uniform composition can be obtained. Therefore, in order to obtain a polymer having a high light-transmitting property, the continuous polymerization method is preferable from the viewpoint of achieving high cleanliness.

On the other hand, in the case of the batch-type polymerization method, the residual monomer composition and the composition of the produced copolymer are changed depending on the polymerization rate, and it is easy to form a copolymer having a composition distribution as a whole, and light scattering due to density fluctuations, microphase separation, etc. It becomes a factor and easily deteriorates the light transmission performance. However, since methyl methacrylate does not differ greatly in reactivity from N-isopropylmaleimide, it is possible to obtain an optical fiber having a good light-transmitting performance even in batch polymerization, not to the extent of continuous polymerization.

Therefore, it is most preferable to copolymerize with methyl methacrylate in order to maintain the transparency and weather resistance of the polymer. Therefore, the copolymer consisting essentially of N-isopropylmaleimide and methyl methacrylate is the most suitable. However, other copolymer components may be contained as long as they are impurities. Further, additives such as heat stabilizers and antioxidants may be blended as long as the amount is an extremely small amount that does not significantly reduce the light transmission performance.

The copolymer used as the core component in the present invention can be produced by radical polymerization of the above monomers. The type of the polymerization initiator at this time is not particularly limited as long as it does not adversely affect side reactions or coloring during the polymerization, and the type and the amount thereof may be changed depending on the polymerization temperature, the polymerization rate, and the polymerization time. You just have to choose.

The polymerization temperature is also not particularly limited, but is 70 to 150 ° C.
Is preferred. That is, at a temperature higher than 150 ° C., the by-products that cause the thermal deterioration of the polymer are violently generated, and the stereotactic structure of the polymer is increased in stereoregularity to lower the glass transition temperature. On the other hand, if the temperature is lower than 70 ° C, the viscosity is too high and the gel effect is severe, making it difficult to control the reaction. If a low polymerization rate is used to prevent this, the productivity will decrease.

In order to obtain a viscosity suitable for spinning, it is preferable to add a molecular weight modifier during polymerization. The type of the molecular weight regulator is not particularly limited, but those having adverse effects such as side reactions and coloring during polymerization, and chain transfer constants for monomers are
Those extremely smaller than 1.0 are not preferable. From this point, it is preferable to use an appropriate amount of mercaptans and the like.

Generally, as a polymerization method of methyl methacrylate for plastic optical fibers, a bulk polymerization method without a solvent is used.
Moreover, a continuous polymerization method having a polymerization rate of 40 to 70% is adopted. This method may also be adopted in the present invention. Alternatively, a solution polymerization method may be used. When the polymer is obtained by copolymerization as in the present invention, it is more productive to discard the mixture recovered by the solution polymerization method having a higher polymerization rate than to fractionate and reuse the recovered monomer mixture. Is effective for reducing the glass transition temperature and reducing the high boiling point residual monomer that causes thermal coloring. Therefore, the obtained copolymer has a lower residual monomer ratio by solution polymerization,
Along with this, translucency and heat resistance are slightly improved.

Specific examples of this solvent include hydrocarbon compounds such as toluene and xylene, ester compounds such as butyl acetate, ether compounds such as dioxane, and the like, which are inert in the polymerization reaction and in which the monomer and the polymer dissolve. However, it is not limited to these.

The polymer solution obtained by the copolymerization in this manner is supplied to the monomer removal step to remove volatile substances such as unreacted monomers. Then, it is supplied to the spinning machine in a molten state, and merges with the polymer of the sheath component to form a plastic optical fiber having a core-sheath structure. The sheath component resin used at this time is not particularly limited as long as it has a lower refractive index than the core component resin shown in the present invention and excellent transparency, and for example, a fluoropolymer is used. it can.

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

The evaluation of the light transmission performance in the examples was performed by the following method.

The light from the tungsten lamp is split by a diffraction grating, condensed by a lens, and then incident on one end of an optical fiber (sample fiber) of 10 to 30 m whose both ends are polished, and the light emitted from the other end is converted by a photodiode. Detected as power (Ps). Next, while keeping the entrance end fixed, cutting was performed at about 2 m from the entrance end, and the measurement of the optical power (Pr) was repeated in the same manner. This cut-back method was used for measurement, and the light transmission loss of the optical fiber was calculated according to the following formula.

Light transmission loss (dB / km) = (Ps-Pr) / (Ls-Lr) 1000 where L: optical fiber length (m), P: optical power value (dBm), s: sample fiber, r: reference Fiber.

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

The light transmission loss after heating the optical fiber in a hot air dryer at 125 ° C. for 1000 hours was measured according to the above method. Then, the heat resistance durability was evaluated by comparing with the value of the light transmission loss before heating and from the increased value of the light transmission loss due to heating.

Example 1 N-isopropylmaleimide 104.4 g (15 mol%) methyl methacrylate 425.5 g n-butyl mercaptan 0.81 g Azo-t-butane 0.36 g After adjusting each mixture by distillation, 0.05 μm
It was charged in a polymerization tank while being filtered with a φ polytetrafluoroethylene filter. So under nitrogen pressurization at 130 ℃ 1
After polymerization for 6 hours, the mixture was gradually heated and finally kept at 180 ° C. for 16 hours to complete the polymerization and decompose the polymerization initiator completely. After further heating and holding at 230 ° C for 1 hour,
It was gradually supplied to the demonomerization step under nitrogen pressure to remove unreacted monomers and the like to obtain a polymer.

Next, the obtained polymer was supplied as a core component of a composite spinning machine having a core-sheath two-layer structure spinneret.

On the other hand, for the sheath component, α-fluoroacrylic acid tetrafluoropropyl / methyl methacrylate copolymer (85/1
(5 mol ratio) was melted at 180 ° C. and then supplied to the die part.

The optical fiber thus obtained at a spinning temperature of 240 ° C. and a take-up speed of 5 m / min has a core material diameter of 980 μm and a sheath material thickness of 10 μm.
It was a concentric optical fiber of m. Then at 200 ° C
After stretching 1.8 times, it was coated with polypropylene resin and coded.

The polymer that has undergone the demonomerization process has a
The result of GC measurement is 0.28% by weight, and the glass transition temperature is DSC.
The measurement result was 129 ° C.

The transmission loss value of the coded optical fiber at 25 ° C. was 213 dB / km at 660 nm. In addition, the light transmission loss value after heat treatment at 125 ° C. for 1000 hours was 220 dB / km at 660 nm, which was almost unchanged, and the heat resistance durability was good. Furthermore,
Good wrapping diameter was up to 1 mm and flexibility was good. Thus, a plastic optical fiber having excellent light-transmitting performance and mechanical properties comparable to those of polymethylmethacrylate and excellent heat resistance was obtained.

Comparative Examples 1 to 2 Example 1 except that the N-substituted maleimide was changed to N-normal propyl maleimide or Nt-butyl maleimide.
An optical fiber was obtained in the same manner as in. The physical properties of the obtained optical fiber are as shown in Table 1, and in the case of using N-normal propylmaleimide, the heat resistance and durability are shown in Example 1.
It was much worse, and in the case of using Nt-butylmaleimide, the light transmission performance, heat resistance durability and flexibility were inferior to those of Example 1.

Comparative Examples 3 to 5 The same as Example 1 except that the type of the N-substituted maleimide was changed as shown in Table 1, and the solution polymerization was performed by charging toluene to 65 wt% in the total mixed solution. I got an optical fiber. The physical properties of the obtained optical fiber are as shown in Table 1. Since the solution polymerization was carried out, the amount of the residual monomer was reduced as compared with the case of the bulk polymerization of Example 1 and Comparative Examples 1 and 2, and the heat resistance durability should be improved as a result. 1 was different from that of Example 1, and was inferior to Example 1 using N-isopropylmaleimide in light transmission performance, heat resistance durability and flexibility.

Example 2 and Comparative Example 6 Example 1 was repeated except that the copolymerization ratio of N-isopropylmaleimide was changed to 30 mol% as shown in Table 1 or N-isopropylmaleimide was not copolymerized.
An optical fiber was obtained in the same manner as in. However, the spinning temperature of Comparative Example 6 was 230 ° C.

As shown in Table 1, by copolymerizing N-isopropylmaleimide with methyl methacrylate, an optical fiber having excellent heat resistance was obtained.

Example 3 N-isopropylmaleimide 20 mol% Methyl methacrylate 80 mol% Azo-t-octane 0.15 mol% n-Butyl mercaptan 0.10 mol% Butyl acetate A mixture containing 35% by weight, based on the total solution, of polytetrahydrofuran of 0.1 μφ was used. While filtering with a filter made of fluoroethylene, it was supplied to the polymerization tank at a rate of 5 kg / hr. The polymerization temperature was 130 ° C., the liquid level was controlled so that the average residence time in the polymerization tank was 4 hours, and the reacted polymer solution was discharged at a rate of 5 kg / hr by a metering pump. This solution was fed to a vented extruder, 190-235
The unreacted monomer and the solvent were removed under the conditions of 250 ° C. and 250 torr and introduced into the composite spinning machine as a core component.

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

The reaction rate of the polymer in the polymerization tank was about 85 as a result of GC measurement.
% By weight, and the composition of the copolymer is N-
It contained 18 mol% of isopropylmaleimide.

The obtained optical fiber was excellent in light transmission performance, heat resistance durability and flexibility.

[Effect of the Invention] The plastic optical fiber of the present invention has excellent light-transmitting performance and mechanical properties comparable to those of an optical fiber containing polymethylmethacrylate as a core component, and also has excellent heat resistance and durability.

Therefore, the plastic optical fiber of the present invention can be used for a long period of time even in the field where heat resistance is required, such as an automobile engine room, which cannot be used with the conventional plastic optical fiber, and has industrial significance and value. It is expensive.

Claims (1)

(57) [Claims] 1. In a plastic optical fiber having a core-sheath structure, the polymer constituting the core contains 5 to 50 mol% of N-isopropylmaleimide units, and substantially N-isopropylmaleimide units and methyl methacrylate. A plastic optical fiber, which is a copolymer composed of only units.