JPH0643326A - Plastic optical fiber - Google Patents

Abstract

PURPOSE:To provide the plastic optical fiber which is excellent in all of heat resistance, light transmissivity and mechanical characteristics. CONSTITUTION:The fiber of the plastic optical fiber having the fiber, sheath and resin coating is a copolymer consisting of (A) 5 to 50mol.% N-isopropyl maleimide unit, (B) >=35mol.% methyl methacrylate unit, (C) 0 to 50mol.% styrene unit and (D) 0 to 10mol.% other monomer units copolymerizable therewith (where at least either of (C) and (D) is not 0mol.%), the sheath thereof is a fluorine-contained polymer and the resin coating thereof is a polypropylene polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber having a core, a sheath and a resin coating, and more particularly to a plastic optical fiber having excellent heat resistance and translucency.

[0002]

2. Description of the Related Art Conventionally, optical fibers are made of quartz glass,
Manufactured using 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 and inexpensive.

As the polymer constituting the core of this plastic optical fiber, polymethylmethacrylate is predominant because it is excellent in transparency and has no practical problems in weather resistance and mechanical properties.

An optical fiber having a core of polymethylmethacrylate has a 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 plastic optical fibers having higher heat resistance for automobiles or ships.

Improvement of heat resistance of plastic optical fiber,
That is, as one of the methods for improving the use temperature, there is a method for increasing the glass transition temperature of the core component, and the following method is known, for example.

(1) Polycarbonate (Japanese Unexamined Patent Publication No. 57-46204), polyarylate, polyamide or the like is used as a core component, which is a condensation polymer having a high transparency and a high glass transition temperature.

(2) Maleic anhydride (Japanese Unexamined Patent Publication No. 59-200201), styrene derivative (Japanese Unexamined Patent Publication No. 58-34404), methacrylic acid having bulky ester (same as above), etc. are converted into methyl methacrylate. The copolymerized 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 the core component has good heat resistance, it does not have sufficient translucency and heat resistance. this is,
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, it is difficult to increase the heat resistance of the optical fiber using the copolymer (2) 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. However, there arises a problem that the group decomposes and is cheap 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. .

Further, 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. ing. 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.

[0014]

Therefore, the present invention is a plastic system which has excellent light-transmitting performance and mechanical properties comparable to those of poly (methyl methacrylate) and can exhibit excellent thermal stability for a long period of time. Its main purpose is to provide optical fibers.

[0015]

In order to achieve the above object, the present invention provides a plastic optical fiber having a core, a sheath, and a resin coating, wherein the polymer constituting the core is
5 to 50 mol% of N-isopropylmaleimide unit (A), 34 mol% or more of methyl methacrylate unit (B), 0 to 50 mol% of styrene unit (C), and other monomer unit (D) copolymerizable therewith. ) 0 to 10 mol% (however, at least one of (C) and (D) is not 0 mol%), and the polymer constituting the sheath is a fluorine-containing polymer, and The plastic-based optical fiber is characterized in that the polymer constituting the resin coating is a polypropylene-based polymer.

That is, as a result of various studies on the types of N-substituted maleimide monomers to be copolymerized, a copolymer having a specific composition comprising N-isopropylmaleimide units and methyl methacrylate units etc. was used as the core component of a heat-resistant plastic optical fiber. The inventors have found that an optimal heat-resistant optical fiber can be obtained by using a specific polymer as the polymer for the sheath component and the resin coating, and the present invention has been completed.

The N-substituted maleimide unit is generally effective for improving heat resistance, but among them, the N-isopropylmaleimide monomer has a melting point of about 23 ° C. and is easily purified to a high degree by distillation purification. The homopolymer obtained from this monomer has a high glass transition temperature of about 230 ° C., extremely high colorless transparency, and further has good thermal stability and mechanical properties. Therefore, when N-isopropylmaleimide unit is copolymerized with methyl methacrylate, it is possible to satisfy not only the heat resistance but also the translucency, mechanical properties and flexibility required as the core component of the optical fiber.

On the other hand, when a maleimide unit N-substituted with an aromatic group is copolymerized (see, for example, JP-A-61-7).
No. 7806), the maleimide monomer is yellow or pale yellow crystals, and the resulting copolymer is also colored yellow, so that an excellent light-transmitting optical fiber cannot be obtained.

Most of the maleimide monomers N-substituted with an aliphatic group are colorless and transparent, and there is no formation of a coloring matter due to a side reaction and no large characteristic absorption in the visible region, but an aliphatic group other than isopropyl is used. The maleimide substituted with is advantageous and disadvantageous as a monomer for optical fibers.

For example, maleimide substituted with a normal hydrocarbon group such as ethyl, n-propyl and n-butyl does not have a very high glass transition temperature and the heat resistance of the obtained optical fiber is insufficient.

Further, the maleimide substituted with methyl or cyclohexyl has a high glass transition temperature, but since it is a solid at room temperature and cannot be easily purified to a high degree by distillation, the optical transparency of the obtained optical fiber and the thermal stability of the polymer are improved. Not enough points.

Maleimides substituted with t-butyl are not suitable because the thermal stability of the polymer is poor and the substituents are eliminated as isobutene by heating to cause yellowing.

Furthermore, isobutyl, sec-butyl, 2,
In the case of maleimide substituted with 2-dimethylpropyl,
It is inferior to the case of isopropylmaleimide in the glass transition temperature and the flexibility of the obtained optical fiber.

As described above, the N-isopropylmaleimide monomer is most suitable for heat-resistant optical fibers, but its homopolymer is rigid and brittle, so that it is copolymerized with methyl methacrylate or the like from the viewpoint of mechanical properties of the obtained optical fiber. is necessary. The copolymer composition has a working temperature of 115 to 15
From the viewpoint of satisfying well-balanced heat resistance at 0 ° C. and mechanical properties, it is necessary to set N-isopropylmaleimide to 5 to 50 mol%.

Further, it is necessary that the content of methyl methacrylate be 34 mol% or more. Further, it is necessary to include at least one other copolymerizable monomer unit. The copolymerization amount is 50 mol% or less for styrene units, and 10 mol% or less for other monomer units. Examples of other monomer units include ethyl acrylate.

Further, additives such as heat stabilizers and antioxidants may be blended as long as the amount is a very small amount that does not significantly reduce the light transmission performance.

In general, 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 continuous continuous polymerization method with stable mass balance, a comonomer having a remarkably low copolymerizability is used. Unless otherwise specified, a copolymer having a uniform composition can be obtained even if the charged monomer composition and the produced copolymer composition are different. 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 composition of the residual monomer and the composition of the produced copolymer are changed depending on the polymerization rate, and a copolymer having a composition distribution as a whole tends to be formed, resulting in density fluctuation, microphase separation and the like. It becomes a factor of light scattering due to the light-transmissive property and the translucent performance is likely to be deteriorated. However, even in the batch-type polymerization method, when copolymerizing a comonomer having a close copolymerizability with N-isopropylmaleimide, or when the charged composition thereof is close to the azeotropic composition, a uniform copolymer having a small composition distribution can be obtained, which is a problem. Can be used without.

The copolymer composed of N-isopropylmaleimide and methyl methacrylate 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 not particularly limited either,
The range of 70 to 150 ° C is preferable. That is, at a high temperature of more than 150 ° C., the by-products that cause the thermal deterioration of the polymer are vigorously produced, and the stereotactic structure of the polymer is increased in the heterotactic structure 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, and it is difficult to control the reaction.

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 modifier is not particularly limited, but those having adverse effects such as side reaction and coloration during polymerization and those having a chain transfer constant with respect to the monomer extremely smaller than 1.0 are not preferable. From this point, it is preferable to use an appropriate amount of mercaptans and the like. However, in the batch type polymerization method, it is preferable to use one having a chain transfer constant of about 1.0 to the monomer in order to reduce the molecular weight distribution and suppress the light scattering factor due to the density fluctuation.

Generally, as a method for polymerizing methyl methacrylate for plastic optical fibers, a bulk polymerization method without a solvent and 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. Specific examples of this solvent include hydrocarbon compounds such as toluene and xylene, ester compounds such as butyl acetate, ether compounds such as dioxane, etc., but they are inactive in the polymerization reaction and dissolve the monomer and polymer. It is not limited to these as long as it is a solvent.

The polymer solution thus obtained by copolymerization is supplied to the demonomerizing 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.

It is necessary to use a fluorine-containing polymer for the sheath component resin used at this time in order to obtain an optical fiber having excellent light-transmitting performance. As this fluorine-containing polymer, for example, a polymer having a high glass transition temperature and a high degree of colorless transparency such as α-fluoroacrylic acid tetrafluoropropyl / methyl methacrylate copolymer (85/15 molar ratio) is used. .

The composite melt-spun optical fiber is drawn by a usual method and then coated with a resin to form an optical fiber cord. As the resin for this coating, a polypropylene-containing resin having a high melting point and a high heat aging resistance is used. It is necessary to use.

[0036]

The present invention will be described in more detail with reference to the following examples.

The light-transmitting performance in the examples was evaluated by the following method.

The light of the tungsten lamp is split by a diffraction grating, condensed by a lens, and then incident from one end of an optical fiber (sample fiber) of 10-30 m whose both ends are polished,
The light emitted from the other end was detected by the photodiode as optical power (Ps). Next, with the entrance end fixed, the optical fiber was cut 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 optical fiber was heated with a hot air dryer at 125 ° C.
The light loss after heating for 000 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 175.2 g (35 mol%) Styrene 260.4 g (50 mol%) Azo-t-butane 0.36 g Toluene 35% by weight based on the total solution. After adjusting each of the mixtures with each other by distillation,
The mixture was placed in a polymerization tank while being filtered with a 5 μφ Teflon filter. Therefore, the solution was polymerized under nitrogen pressure at 130 ° C for 16 hours, and then gradually heated to 180 ° C for 16 hours.
It was kept for a time to complete the polymerization and to completely decompose the polymerization initiator. After further raising the temperature and maintaining it at 230 ° C. for 1 hour, it was gradually supplied to the demonomerizing 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, as a sheath component, α-fluoroacrylic acid tetrafluoropropyl / methyl methacrylate copolymer (85/15 molar ratio) was melted at 180 ° C. and then supplied to the die part.

Thus, the spinning temperature is 240 ° C. and the take-up speed is 5
The optical fiber obtained at m / min has a core diameter of 980μ.
The optical fiber was concentric and had a thickness of m and a sheath material thickness of 10 μm. Next, the film was stretched 1.8 times at 200 ° C. and then coated with polypropylene resin to be coded.

In the polymer which had been subjected to the demonomerization step, the residual monomer amount was 0.28 wt% as measured by GC, and the glass transition temperature was 132 ° C. as measured by DSC.

The light transmission loss value at 25 ° C. of the coded optical fiber was 218 dB / km at 660 nm. Further, the light transmission loss value after heat treatment at 125 ° C. for 1000 hours was 226 dB / km at 660 nm, which was almost unchanged, and the heat resistance durability was good. Furthermore, the good winding diameter was 1 mm and the 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 5] Optical fibers were obtained in the same manner as in Example 1 except that the monomer compositions were changed as shown in Table 1. The physical properties of the obtained optical fiber are as shown in Table 1, and were inferior to Example 1 in light transmission performance, heat resistance durability and flexibility.

[Example 2 and Comparative Example 6] An optical fiber was prepared in the same manner as in Example 1 except that the monomer composition was changed as shown in Table 1 and the polymerization method was the following continuous solution polymerization. Obtained.

A mixture of the monomer and the solvent was added to 0.
5kg / hr while filtering with 1μφ Teflon filter
Was fed to the polymerization tank at a rate of. 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 with a metering pump at a rate of 5 kg / hr. This solution was fed to an extruder with a vent, and unreacted monomers and solvent were removed under the conditions of 190 to 235 ° C. and 250 to 5 torr.

The reaction rates of the polymers in the polymerized layer were 89 wt% and 90 wt%, respectively, and the analytical compositions of the obtained copolymers were 21.3: 34.1: molar ratios, respectively.
It was 44.6 and 21.5: 34.0: 44.5.

The physical properties of the obtained optical fiber are as shown in Table 1. Example 2 using N-isopropylmaleimide is different from other N-substituted maleimides in light transmission performance, heat resistance durability and flexibility. It was superior to Comparative Example 6 used.

[0052]

[Table 1] [Examples 3 to 5 and Comparative Examples 7 to 9] Examples except that the copolymerization ratio of N-isopropylmaleimide was changed to 0 to 60 mol% as shown in Table 2 and bulk polymerization was performed without using toluene. An optical fiber was obtained in the same manner as in 1. However,
The monomer compositions of Examples 4 and 5 and Comparative Examples 7 and 9 have n
-Butyl mercaptan 0.10 mol% was further added.

As shown in Table 2, excellent heat-resistant optical fibers were obtained when the copolymerization ratio of N-isopropylmaleimide was within the range of 5 to 50 mol%.

[0054]

[Table 2]

[0055]

The plastic optical fiber of the present invention is
It has excellent light-transmitting performance and mechanical properties comparable to optical fibers with polymethylmethacrylate as the 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 in a field where heat resistance is required, such as an automobile engine room, which cannot be used with the conventional plastic optical fiber. It is of high value.

Claims (1)

[Claims] 1. In a plastic optical fiber having a core, a sheath, and a resin coating, the polymer constituting the core contains 5 to 50 mol% of N-isopropylmaleimide unit (A) and 34 mol of methyl methacrylate unit (B). %that's all,
Styrene unit (C) 0 to 50 mol% and other monomer unit (D) 0 to 10 mol% copolymerizable therewith (provided that at least one of (C) and (D) is not 0 mol%). A plastic optical fiber, characterized in that the polymer constituting the sheath is a fluorine-containing polymer, and the polymer constituting the resin coating is a polypropylene polymer.