JPH0152724B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention has a core containing a deuterated methyl methacrylate polymer and a sheath containing a polymer having a lower refractive index than the core. This invention relates to a method of manufacturing lossy plastic optical fiber.

Conventionally, concentric core-sheaths have been made with a core made of a highly transparent organic polymer compound such as polystyrene or polymethyl methacrylate, and a sheath made of an organic polymer compound with a lower refractive index than the core component. Plastic optical fibers are well known in which the structure constitutes a composite optical fiber, and the light incident on one end of the optical fiber is transmitted by total internal reflection along the length of the optical fiber. What should be considered when creating this type of optical fiber is to minimize the factors that increase the attenuation of light due to absorption or scattering when light is transmitted inside the optical fiber. It is. Optical fibers made from organic polymer compounds are lighter, more flexible, and easier to increase numerical aperture than conventionally known optical fibers made from inorganic glass. Although it has advantages, it has the disadvantage that the light transmitted inside it is attenuated to a greater degree than glass optical fibers.
The present invention is directed to reducing the degree of light attenuation of a plastic optical fiber using an organic polymer compound.

According to the findings of the present inventors, the cause of optical transmission loss in optical fibers using organic polymer compounds is due to harmonics of infrared vibration absorption between carbon and hydrogen that constitute the organic polymer compound. There was found. Figure 1 shows the optical transmission characteristics in the visible light range of a plastic optical fiber manufactured by a conventionally known method with a core made of polymethyl methacrylate and a sheath made of a fluororesin copolymer. Horizontal axis)
It is a graph shown in relation to transmission loss (dB/Km) (vertical axis). As is clear from Figure 1, the 7th overtone of carbon-hydrogen infrared vibrational absorption is at a wavelength of 544 nm.
The 6th overtone appears at 622nm, and the 5th overtone appears at 740nm.
Here, the absorption intensity decreases by about one order of magnitude each time the order of overtone increases by one. However, due to the base of these absorptions, the optical transmission loss in the so-called loss window increases, and the minimum value of attenuation is determined by the wavelength.
350dB/Km at 650nm, 330dB/Km at 570nm, 530n
A value of 400 dB/Km has been obtained. Therefore, by somehow reducing or eliminating vibrational absorption between carbon and hydrogen, it becomes possible to produce a plastic optical fiber with low loss.

A possible method for this purpose is to replace hydrogen with deuterium to eliminate vibrational absorption of carbon-hydrogen (C-H). Along with this, vibrational absorption between carbon and deuterium (CD) appears, but according to the findings of the present inventors, infrared vibrational absorption between CD
For example, the fifth harmonic of infrared vibration absorption that occurs in the visible to near-infrared light range is 740 nm for C-H, while it is significantly shifted to the longer wavelength side compared to the case between C-H. It is 990nm, and the 6th overtone is
In C-H it is 622nm, while in C-D it is 622nm.
The wavelength is shifted to a higher wavelength by about 250 to 280 nm, such as 905 nm. Furthermore, it has become clear that even for overtones of the same order, the intensity of C-D vibration absorption is smaller than the intensity of C-H vibration absorption.

In this manner, by deuterating hydrogen in an organic polymer compound, it is possible to produce a plastic optical fiber having a window with extremely low loss, particularly in the visible light region to near-infrared light region.

An example of replacing hydrogen in an organic polymer compound with deuterium is deuteration of methyl methacrylate.
A plastic optical fiber having a core made of polymerized resin has already been proposed (see Japanese Unexamined Patent Publication No. 1983-65556). In this method, monomers are polymerized in a closed system, but dust and impurities mixed in when adding the polymerization initiator and chain transfer agent are removed in the subsequent process using a filter with a pore size of about 0.2 to 1 μm. However, a large amount of particulate matter still remains. Further, even when a molded product for ram extrusion is polymerized in a closed system and then taken out and transferred to a spinning device, contamination with dust and the like is unavoidable. Furthermore, methyl methacrylate polymer is relatively highly hygroscopic, with a water absorption rate of 0.3 to 0.4% after 24 hours even at room temperature (see Modern Plastic Encyclopedia, 1968).
This also applies to deuterated polymers. Here, oxygen-hydrogen (O-H) based on moisture absorption
Vibration absorption between bonds is also a problem in optical fibers made of inorganic glass, and in organic polymer compounds, harmonics of O-H vibration absorption often appear in the loss window, and the presence of a small amount of water The optical transmission characteristics also deteriorate. From these facts, the attenuation of the plastic optical fiber obtained using this method is 147 dB/Km at a wavelength of 690 nm and 158 dB/Km at a wavelength of 790 nm.
Km has only been obtained.

The present invention was made in view of the current situation, and its purpose is to have a core-sheath structure with extremely excellent light transmission characteristics in the visible light region to the near-infrared light region, and to reduce the O- It is an object of the present invention to provide a method for manufacturing a low-loss plastic optical fiber that is free from the effects of H-vibration absorption.

To summarize the present invention, the method for producing a low-loss plastic optical fiber of the present invention includes a core containing an organic polymer compound mainly composed of a deuterated methyl methacrylate polymer, and a core containing an organic polymer compound containing a deuterated methyl methacrylate polymer as a main component. In manufacturing a plastic optical fiber consisting of a sheath containing an organic polymer compound whose main component is a polymer with a low refractive index, it is necessary to obtain good activity at a temperature higher than the glass transition temperature of the organic polymer compound forming the core. Using the radical polymerization initiator shown below, monomers corresponding to the organic polymer compound forming the core are subjected to bulk polymerization in a closed system at a temperature higher than the glass transition temperature of the organic polymer compound forming the core. After melt-spinning the organic polymer compound and the organic polymer compound forming the sheath through a spinneret, the optical fiber is immediately coated with an organic polymer compound having excellent moisture resistance.

Examples of organic polymer compounds with excellent moisture resistance as coating materials in the present invention include polyethylene, polyvinyl chloride, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, polypropylene, hydrochloric acid rubber, and ethylene-vinyl acetate copolymer. Union,
Examples include polytrifluorochloroethylene, polytetrafluoroethylene, and polyester.

In the present invention, when immediately coating an optical fiber spun into a core-sheath structure, which will be described in detail later, a coating material with high moisture resistance (low moisture permeability and moisture absorption) is first applied, and then the coating is applied. It is effective to further reduce the effect of absorption loss due to O-H groups due to moisture absorption of the optical fiber.
Such coating materials include polyurethane, polybutadiene, polybutene, flexible epoxy resins and alkyd resins, fluorocarbon rubber, tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-acrylic copolymers, and ethylene-acrylic copolymers.
Vinyl acetate copolymers and the like can be applied.

Although silicone resin is used for the primary coat and buffer coat of silica glass optical fibers, it has low hygroscopicity but high moisture permeability, so it cannot be said to be suitable as a coating material in the present invention.

Here, in the present invention, immediately coating the optical fiber with an organic polymer compound having excellent moisture resistance means that the coating is performed before the optical fiber having a core-sheath structure is wound onto a bobbin.

Alternatively, it means that after producing an optical fiber having a core-sheath structure, the optical fiber is temporarily stored in a low humidity tank such as a dryer, and then the optical fiber is taken out and coated immediately.

Such coating methods include (1) a method in which an optical fiber that has been spun into a core-sheath structure using an extruder or the like is immediately coated by passing it through another extruder, and (2) an optical fiber that has been spun into a core-sheath structure is coated. (3) Using three extruders, the core component, sheath component, and coating component are introduced into each extruder, and the core component, sheath component, and coating component are melted and spun. A method of spinning into a triple structure from a spinneret or (4) a method of spinning into a core-sheath structure and winding the optical fiber onto a bobbin is placed in a dryer containing a sufficient amount of silica gel, and then the optical fiber is taken out. , a method of immediately passing the coating through an extruder, etc. can be applied.

In the present invention, in producing a low-loss plastic optical fiber, in a closed system, a fraction of deuterated methyl methacrylate monomer distilled under reduced pressure is added to a polymerization initiator obtained by the same distillation. A deuterated methyl methacrylate polymer, to which fractions of an agent and a chain transfer agent are added and subsequently polymerized, can be used as a core component of an optical fiber,
Further, after polymerizing the monomer in a closed system, a core fiber is obtained by melt-spinning the organic polymer compound (hereinafter referred to as core polymer) that forms the obtained core while maintaining the closed state. This is desirable. This not only prevents dust and impurities from entering the core polymer, but also suppresses the formation of minute voids, resulting in significantly reduced scattering loss in the resulting optical fiber, which is superior to conventional fibers. In comparison, the loss is extremely low.

The core component of the optical fiber in the present invention uses a radical polymerization initiator that exhibits good activity at a temperature higher than the glass transition temperature of the deuterated methyl methacrylate polymer as a polymerization initiator. The deuterated methyl methacrylate monomer can be bulk polymerized to form a polymer.

In order to prevent particulate matter such as dust from being mixed into the core polymer as described above, it is not sufficient to simply distill the monomer. That is, if only a filter with a pore diameter of about 0.1 μm is used when adding a polymerization initiator or chain transfer agent to the monomer purified by distillation, a large amount of fine dust will still enter and cause light scattering. Therefore, in the present invention, the polymerization initiator and chain transfer agent are distilled under reduced pressure conditions in a closed system apparatus, and only the distilled fraction is added so as to be mixed with the distilled fraction of the monomer. is desirable. This makes it possible to significantly suppress the incorporation of minute particles and further reduce loss due to light scattering.

As a result, particles such as dust in the monomer to which the polymerization initiator and chain transfer agent have been added, for example,
When irradiated with 632.8 nm He-Ne laser light and observed, the number of observed light spots is 1/100 of that of conventional methods, specifically 0.02 to 20 or less per 10 cm optical path length (0.02 to 20 light spots observed per 10 cm optical path length). ), i.e., 1 cm ³
The concentration of dust can be 1 to 1,000 particles per cubic meter (in most cases less than ¹ particle), in other words, the concentration of dust can be approximately 1 particle or less per 1 mm ³ , and it is easy to reduce the concentration to 1 particle or less per 1 cm 3 .

In the present invention, when melt-spinning the core polymer, the polymer obtained by polymerizing at a temperature higher than the glass transition temperature of the deuterated methyl methacrylate polymer is lowered to a temperature lower than the glass transition temperature. By supplying the fibers to the melt spinning apparatus without causing any internal strain or the generation of minute voids during spinning due to changes in the volume of the polymer, it is possible to obtain an optical fiber with low scattering loss.

In the present invention, the optical fiber spun into a core-sheath structure is immediately coated with an organic polymer compound with excellent moisture resistance, so it cannot be wound onto a bobbin like a conventional plastic optical fiber. Moisture absorption caused by being left alone is significantly suppressed. Therefore, the absorption loss due to O-H groups due to moisture absorption is extremely small, and it is possible to fully utilize the effect of reducing scattering loss by suppressing the incorporation of dust and impurities and the generation of microvoids.

As a result, in the near-infrared light region where the influence of O-H absorption loss is large, it is possible to obtain a plastic optical fiber with significantly lower loss than the conventional plastic optical fiber with a core made of deuterated methyl methacrylate polymer. becomes possible. In addition, since there is almost no absorption loss due to C-H vibration absorption in the visible light range, the light guide loss value of only the intrinsic scattering loss in a plastic optical fiber with a methyl methacrylate polymer core by the conventional method can be reduced. This makes it possible to obtain a plastic optical fiber with extremely low loss compared to the conventional one.

In the present invention, the polymer used as the core component has a residual hydrogen content of at least
Best results are obtained when formed with deuterated methyl methacrylate polymer containing no more than 1.0 g, preferably at least 0.5 g.

Alternatively, the core may contain at least 90 mole percent deuterated methyl methacrylate and other synthetic vinyl monomers, such as acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, propyl acrylate, and butyl acrylate, or methyl acrylate. It can also be formed from copolymers with methacrylic acid alkyl esters such as methacrylate, ethyl methacrylate, propyl methacrylate and butyl methacrylate. The copolymer should contain at least 1.0 g or less, preferably at least 0.8 g, of hydrogen per 100 g. In this case, at least 90 mol% of the core copolymer, preferably 95 mol%
In order to obtain excellent optical transmission characteristics, it is desirable that the material be made of deuterated methyl methacrylate.
The advantage of using a copolymer is that it has greater flexibility and mechanical strength than a deuterated methyl methacrylate homopolymer. If a copolymer component other than deuterated methyl methacrylate is contained in an amount of 10 mol % or more, vibrational absorption based on carbon-hydrogen bonds increases, which becomes an obstacle to obtaining a low-loss plastic optical fiber.

Furthermore, the core may be an alkyl ester of deuterated acrylic or methacrylic acid, such as deuterated acrylic ester or deuterated ethyl methacrylate, such as deuterated methyl acrylate, ethyl acrylate propyl acrylate and butyl acrylate. It can also be formed from a copolymer of deuterated methacrylic acid ester monomers such as propyl methacrylate, butyl methacrylate and benzyl methacrylate, and deuterated methyl methacrylate.
This copolymer contains at least 1.0 hydrogen per 100g.
It should contain no more than 0.5 g, preferably at least 0.5 g. Thereby, excellent optical transmission characteristics can be obtained extremely easily.

In any of the above cases, 100 g of deuterated methyl methacrylate polymer or copolymer
If it contains more than 1g of hydrogen, the remaining C-H bonds will reduce the loss due to absorption caused by the 5th and 4th harmonics of infrared vibration absorption, especially in the near-infrared region. becomes smaller.

The copolymer component also needs to be easy to distill, similar to deuterated methyl methacrylate, and to be able to be added to the deuterated methyl methacrylate monomer by distillation. As a result, the content of impurities and dust can be significantly reduced, and therefore a plastic optical fiber having a copolymer core with low light scattering can be obtained.

Here, deuterated methyl methacrylate is described by Nagai et al., Journal of Polymer Science (J.Poly.Sci.), 62 , S95.
-98 (1962). Briefly, deuterated acetone is reacted with hydrocyanic acid to produce deuterated acetone cyanohydrin, which is treated with sulfuric acid to form a sulfate salt, and then reacted with deuterated methanol to form deuterated acetone cyanohydrin. Hydrogenated methyl methacrylate can be obtained.

In the present invention, when polymerizing the core component,
It is undesirable to use methods such as suspension polymerization, emulsion polymerization and solution polymerization. The reason for this is that although suspension polymerization and emulsion polymerization can produce highly pure polymers as industrial methods, they use a large amount of water, so there is a risk that foreign substances in the water may mix into the polymer. Moreover, moisture adheres to or dissolves in the obtained polymer, which becomes an obstacle in obtaining a low-loss plastic optical fiber. Also, in solution polymerization,
Since a solvent is used, there is a risk of contamination with impurities or foreign substances in the solvent, and a process for separating foreign substances is required. Therefore, in the present invention, a polymer is formed by bulk polymerizing the core component.

As mentioned above, the polymerization system of the present invention contains a small amount of a polymerization initiator and a chain transfer agent (a small amount of the total monomer content).
(approximately 0.001 to 0.5 mol%). For the reasons mentioned above, it is desirable that these can be easily distilled under reduced pressure. Such polymerization initiators include organic peroxides such as di-tertiary butyl peroxide, dicumyl peroxide, and cumene hydroxy peroxide, or azo-tertiary butane, azo-n-butane, azo-iso Mention may be made of alkylazo compounds such as -propane, azo-n-propane and azo-cyclohexane. Among these, alkylazo compounds can be particularly preferably used because the absorption path of the polymerization initiator, such as electronic transition absorption in the ultraviolet light region, has little effect on the visible light region. In addition, mercaptans are suitable as chain transfer agents, such as n-
Primary mercaptans such as butyl mercaptan and n-propyl mercaptan, secondary mercaptans such as secondary butyl mercaptan and isopropyl mercaptan, tertiary mercaptans or phenyl mercaptans such as tertiary butyl mercaptan and tertiary hexyl mercaptan. Aromatic mercaptans such as

The sheath component used in the present invention has a refractive index of at least 0.5%, preferably at least 2%, and most preferably at least 5% greater than the refractive index of the core component.
% an organic polymer compound with a low refractive index.
In particular, excellent light transmission properties can be obtained by using a substantially amorphous polymer. As such a sheath component, for example, two types of fluoroalkyl methacrylate copolymers having different fluoroalkyl groups are particularly suitable. In this case, by using a copolymer that combines fluoroalkyl methacrylate, which has particularly excellent adhesiveness, and fluoroalkyl methacrylate, which has a relatively high heat distortion temperature, a plastic optical fiber having particularly excellent light transmittance can be produced. It is possible to form

In order to obtain such a fluoroalkyl methacrylate copolymer, necessary amounts of two different types of fluoroalkyl methacrylates are mixed, a polymerization initiator and a chain transfer agent are added, deaeration is performed under reduced pressure, and polymerization is carried out in the absence of oxygen. conduct. Here, the molecular weight of the copolymer is preferably in the range of 20,000 to 100,000 as a weight average molecular weight.

It is also possible to obtain a plastic optical fiber with excellent light transmittance by using a composition obtained by melt-mixing a vinylidene fluoride-tetrafluoroethylene copolymer and a fluoroalkyl methacrylate polymer as the sheath component. .

In addition, copolymers of fluoroalkyl methacrylate and fluoroalkyl acrylate, copolymers of fluororesins such as tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, and trifluorochloroethylene can be used as the sheath component. .

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples. Note that tungsten was used as a light source for the optical transmission characteristics of the optical fiber shown in the examples.
The wavelength characteristics were determined using a halogen lamp and a diffraction grating spectrometer.

Example 1 Deuterated acetone cyanohydrin obtained by reacting deuterated acetone with hydrocyanic acid was once made into a sulfate salt, and then deuterated methyl methacrylate was synthesized by reaction with deuterated methanol. (distillation method). Next, using this monomer and other components, polymerization and spinning were carried out using the apparatus shown in Figs. 2 and 3 to produce a plastic optical fiber having the cross section shown in Fig. 4. That is, FIG. 2 is a schematic diagram showing a specific example of the core component polymerization process in the plastic optical fiber manufacturing apparatus used in the method of the present invention, and FIG. 3 is a schematic diagram showing a specific example of the spinning process. FIG. 4 is a schematic cross-sectional view of a plastic optical fiber produced by the method of the present invention, in which 1 is a monomer reservoir, 2 is a monomer distillation vessel,
3 is a monomer supply valve, 4 is a cooler, 5 is a kettle, 6
is a stirrer, 7 is a mixing container, 8 is a mixture supply valve,
9 is a drain pot, 10 is a polymerization initiator pot, 11
12 is a polymerization initiator supply valve, 12 is a polymerization initiator distillation pot,
13 is a chain transfer agent reservoir, 14 is a chain transfer agent supply valve, 15 is a chain transfer agent distillation vessel, 16 is a monomer mixture supply pipe, 17 is a pressure regulating valve, 18 is a polymerization container, 1
9 is a pressure increase/depressurization port, 20 is a polymer supply valve, 21 is a pressure reduction port, 22 is a polymer storage tank, 23 is a polymer supply valve, 24 is a discharge port, 25 is a supply port, 26 is a heat retaining part, and 27 is a 28 is a screw extruder for the core, 28 is a hopper for the pod, 29 is an extruder for the pod, 30 is a double spinneret, 31 is an optical fiber, 32 is a core, 33
The sheath portion and 34 represent the covering portion.

After purification, the deuterated methyl methacrylate monomer is transferred from the monomer reservoir 1 to the monomer distillation vessel 2 by opening the monomer supply valve 3, and in the same manner as the azo-tertiary monomer as a polymerization initiator. Butane was placed in a polymerization initiator distillation vessel 12, and n-butyl mercaptan as a chain transfer agent was placed in a chain transfer agent distillation vessel 15. After the entire apparatus was sealed, the system was evacuated to 150-200 mmHg. Subsequently, the monomer distillation vessel 2 was heated and the deuterated methyl methacrylate was transferred to the mixing vessel 7. In this case, if the monomer has been distilled in advance to form a middle distillate, add a predetermined amount of the fraction from the initial distillate to the mixing container 7, or if the monomer has not been distilled in advance, Drain the distillate 9
After discarding it by the operation, a predetermined amount of the middle distillate is added to the mixing container 7. Subsequently, the polymerization initiator distillation vessel 12 and the chain transfer agent distillation vessel 15 were heated, and predetermined amounts of the polymerization initiator and chain transfer agent were transferred to the mixing container 7. After stirring the mixing container 7 thoroughly, add
When the amount of remaining dust was detected by irradiating He-Ne laser light, only 0.02 or less light spots were observed per 10 cm of optical path length, which revealed that the amount of dust was less than 1 per 1 ^cm3 . did.

This mixture was transferred to a polymerization container 18 and heated to 130°C for 16
After carrying out bulk polymerization for a period of time, the temperature was gradually raised to increase the polymerization rate, and the polymerization was finally completed at 180°C to obtain a deuterated methyl methacrylate polymer that would become the core. While maintaining the fluidity of this polymer, the polymer is extruded with dry nitrogen from the pressurization/decompression port 19,
The liquid was introduced into the heat retaining section 26 through the supply port 25 shown in FIG. 3, which was connected to the discharge port 24 while maintaining a closed state. At the time of introduction, the pressure in the heat retaining section 26 was reduced, and the necessary amount of the above polymer was introduced.

The introduced polymer is supplied to the screw extruder 27, and at the same time, 1H, 1H, 5H octafluoropentyl methacrylate and 1H, 1H, 3H tetrafluoroprupyl methacrylate are added as organic polymer compound polymers that will become the sheath part. A copolymer with a ratio of 70 mol % to 30 mol % is used, and the copolymer that will become the pod part is fed to the extruder 29 for the sheath part, and the polymer that will become the core part is heated to 200°C by the double spinneret 30. 180℃
It was extruded and spun. The obtained optical fiber 31 is immediately passed through another extruder (not shown) and coated with molten polyethylene, so that the core part 32 has a diameter of 0.65 mm and the sheath part 33 has a film thickness of 0.65 mm as shown in FIG. but
A plastic optical fiber having a thickness of 0.10 mm and a coating portion 34 of 0.30 mm was obtained.

FIG. 5 is a graph showing the optical transmission characteristics of the plastic optical fiber thus obtained in the visible to near-infrared light range in terms of the relationship between wavelength and transmission loss. As is clear from Figure 5, 50dB/Km over a wide visible light range from wavelength 520nm to 720nm.
Extremely low loss values such as the following can be obtained, and in particular,
30dB/Km or less from 575nm to 705nm,
Furthermore, the loss value is 20 dB/Km or less in the wavelength range of 652 to 662 nm, which is comparable to the light guiding properties of multi-component glass optical fiber in the visible light range. On the other hand, in the near-infrared light range from 760nm to 790nm,
The light guide loss value is less than 50dB/Km, especially less than 30dB/Km around 775nm, and also less than 30dB/Km at around 855nm.
A loss value of 70dB/Km or less was obtained. These values are 147 dB/Km at 690 nm and 158 dB/Km at 790 nm, which are the top data of conventional loss values for plastic optical fibers made of deuterated methyl methacrylate polymer as the core (both of which are based on the above-mentioned Japanese Patent Application Laid-Open No. 1989-1993). 65556), and the plastic optical fiber produced by the method of the present invention has extremely low loss. Thus, it can be seen that by using the method of manufacturing plastic optical fiber according to the method of the present invention, absorption loss due to moisture absorption is small, and dust and microvoids, etc., which cause scattering loss, are significantly reduced. .

Example 2 In Example 1, 75% by weight of a copolymer of 85% by mole of vinylidene fluoride and 15% by mole of tetrafluoroethylene was used as the organic polymer compound for the sheath part.
25% by weight of 1H, 1H, 3H, and tetrafluoropropyl methacrylate polymers were added to the mixture, mixed and melted to form a uniform transparent composition, which was then fed to the extruder 29 for the sheath section, and then passed through the double spinneret 30. The core polymer and the sheath polymer were extruded at 200°C. The obtained optical fiber 31 was immediately passed through another extruder (not shown) and coated with molten polyethylene to obtain a plastic optical fiber. This plastic optical fiber has a wavelength of 655nm to 685nm.
This is an extremely low loss value for a plastic optical fiber of 16 dB/Km over a distance of 30 dB/Km.
The following wavelengths also cover a wide wavelength range from 570nm to 710nm. In addition, extremely low loss values were obtained in the near-infrared light region, such as 23 dB/Km from 770 nm to 776 nm and 50 dB/Km around 850 nm.

Note that residual hydrogen in the deuterated methyl methacrylate polymer used in Examples 1 and 2 was
This residual hydrogen was measured by nuclear magnetic resonance method at 0.50 g per 100 g of polymer.

Example 3 95 mol% deuterated methyl methacrylate and 5 mol% methyl acrylate as core monomers
Polymerization was carried out in the same manner as in Example 1, except that a mixture of 1H, 1H,
5H octafluoropentyl methacrylate,
A copolymer with a ratio of 80 mol % to 20 mol % of 1H, 1H, 3H, and tetrafluoropropyl methacrylate is supplied to the extruder 29 for the sheath part, and the core part is formed by a double spinneret 30. The diameter of 32 is 0.55
mm, the thickness of the sheath part 33 is 0.10 mm
I got it. This optical fiber was coated using a coating machine shown in FIG. That is, FIG. 6 is a schematic diagram showing a specific example of an optical fiber coating machine used in the method of the present invention, where 35 is a coating machine, 36 is a heater, and 37 is an orifice. The optical fiber is immediately placed in a coating machine 35, guided through an orifice 37 into a melt of ethylene-vinyl acetate copolymer heated and melted by a heater 36, continuously coated with a coating component, and then cooled. A plastic optical fiber with a coating 34 having a thickness of 0.30 mm was obtained. FIG. 7 is a graph showing the optical transmission characteristics of the plastic optical fiber thus obtained in the visible to near-infrared light range in terms of the relationship between wavelength and transmission loss. As is clear from FIG. 7, the lowest loss window was at 650 nm, and the loss value here was 30 dB/Km or less. Also, 576nm
There are also low-loss windows at 770nm and 848nm in the near-infrared light range, with windows of 35dB/Km, 50dB/Km and 848nm, respectively.
It can be seen that a loss value of less than 90 dB/Km was obtained, indicating that a plastic optical fiber with a copolymer core having significantly lower loss than conventional ones has been obtained.

In addition, 95 mol% of deuterated methyl methacrylate and 5 mol% of methyl acrylate used here
When the residual hydrogen in the copolymer was measured using nuclear magnetic resonance at 90MHz, it was found that the residual hydrogen in the copolymer was
It was 0.95g per 100g.

Example 4 In Example 1, the optical fiber 31 having a core-sheath structure was extruded using the double spinneret 30 and wound around a bobbin, and then it was placed in a dryer containing a sufficient amount of silica gel. I placed it. After 16 hours, the bobbin was removed, and the optical fiber was immediately passed through an extruder and coated with molten polyethylene to obtain a plastic optical fiber. This optical fiber has a wavelength of less than 30dB/Km from 575nm to 705nm.
It has an extremely low loss of 20 dB/Km or less at 652 to 662 nm. Also, over 760-790nm
It was a plastic optical fiber with extremely low loss even in the near-infrared region, with a loss of less than 50 dB/Km and less than 70 dB/Km even at around 855 nm.

As explained above, the plastic optical fiber produced by the method of the present invention can be used over a wider range of visible light to near-infrared light than conventional optical fiber made from non-deuterated methyl methacrylate monomer. It has excellent optical transmission characteristics, and compared to conventional optical fibers made from deuterated methyl methacrylate monomers, it is less susceptible to light absorption due to moisture due to the optical fiber's moisture absorption and light absorption due to the presence of dust. It has no effect of scattering and has extremely low loss. In particular, the loss value of 20 dB/Km or less at a wavelength around 660 nm is close to the loss limit value for a plastic optical fiber, and can be said to be an extremely low loss plastic optical fiber. As described above, the plastic optical fiber according to the present invention has extremely low loss, so it can be used as an optical signal transmission medium over distances of about 1 km, and has the advantages of being lighter and more flexible than inorganic glass optical fiber. It has the advantage of being able to be used to the fullest.

Furthermore, since the plastic optical fiber produced by the method of the present invention has an extremely low loss window at 660 nm as described above, it can constitute an economically efficient optical signal transmission system using an inexpensive GaAlAs red light emitting diode for display purposes as a light source. It has the advantage of being able to In addition, the plastic optical fiber produced by the method of the present invention has a wavelength of less than 30 dB/Km at around 775 nm and a wavelength of around 855 nm.
With a loss value of 70 dB/Km or less, near-infrared laser diodes and light emitting diodes for optical communications can be used as light sources, and it is easy to combine with optical transmission systems using inorganic glass optical fibers. It has the advantage of being

[Brief explanation of drawings]

Figure 1 is a graph showing the optical transmission characteristics of plastic optical fibers manufactured by the conventional method in the visible light range in relation to wavelength and transmission loss, and Figure 2 is a graph of the plastic optical fibers used in the method of the present invention. FIG. 3 is a schematic diagram showing a specific example of the core component polymerization process in the manufacturing apparatus, FIG. 3 is a schematic diagram showing a specific example of the spinning process, and FIG. FIG. 5 is a graph showing the optical transmission characteristics of the plastic optical fiber produced by the method of the present invention (Example 1) in the visible to near-infrared light range in relation to wavelength and transmission loss. , FIG. 6 is a schematic diagram showing a specific example of an optical fiber coating machine used in the method of the present invention (Example 3), and FIG. 7 is a schematic diagram showing a plastic light coater manufactured by the method of the present invention (Example 3). 1 is a graph showing the optical transmission characteristics of a fiber in the visible to near-infrared light region in relation to wavelength and transmission loss. 1... Monomer reservoir, 2... Monomer distillation pot, 4...
...Cooler, 7...Mixing container, 8...Mixture supply valve, 9...Drain pot, 10...Polymerization initiator reservoir, 12...Polymerization initiator distillation pot, 13...Chain transfer agent reservoir, 15... Chain transfer agent distillation pot, 16...
Monomer mixture supply pipe, 17... pressure reduction valve, 18
... Polymerization container, 19 ... Pressure/decompression port, 21 ... Pressure reduction port, 22 ... Polymer storage tank, 26 ... Heat retention section, 27 ... Screw extruder for core section, 29 ...
Extruder for pod section, 30...Double spinneret, 31...
...Optical fiber, 32...Core part, 33...Sheath part,
34...Coating section, 35...Coating machine, 36...Heater, 37...Orifice.

Claims (1)

[Scope of Claims] 1. A core containing an organic polymer compound whose main component is a deuterated methyl methacrylate polymer, and an organic polymer whose main component is a polymer having a refractive index lower than that of the core, surrounding the core. In producing a plastic optical fiber consisting of a sheath containing a molecular compound, the core is formed using a radical polymerization initiator that exhibits good activity at a temperature higher than the glass transition temperature of the organic polymer compound forming the core. The corresponding monomer of the organic polymer compound is subjected to bulk polymerization in a closed system at a temperature higher than the glass transition temperature of the organic polymer compound forming the core, and the resulting organic polymer compound and the organic polymer forming the sheath are A method for producing a low-loss plastic optical fiber, which comprises melt-spinning a polymer compound through a spinneret and then immediately coating the optical fiber with an organic polymer compound having excellent moisture resistance. 2. The method for producing a low-loss plastic optical fiber according to claim 1, wherein the organic polymer compound forming the core is fed to a melt spinning device without lowering it below its glass transition temperature. 3. Distilling the corresponding monomers, polymerization initiator, and chain transfer agent of the organic polymer compound forming the core under reduced pressure in a closed system apparatus, and subsequently mixing these fractions while maintaining the closed system. A method for producing a low-loss plastic optical fiber according to claim 1 or 2, which comprises performing post-bulk polymerization.