JPS5984204A - Manufacture of low-loss plastic optical fiber - Google Patents

Abstract

PURPOSE:To manufacture the titled optical fiber superior in heat resistance and light transmission performance by coating a core material composed essentially of a specified deuterium-substd. methyl methacrylate polymer or copolymer with a polymer contg. fluorine. CONSTITUTION:A core material made of a deuterium-substd. methyl methacrylate polymer or copolymer is obtained by adding 0.0002-0.1mol% radical polymn. initiator and 0.01-10mol% chain transfer agent to deuterium-substd. methyl methacrylate or a mixture of it and other copolymerizable monomer, filtering them through a porous film gastightly isolated from the outside and having <=10mum pore diameter for the purpose of purification, introducing them into a continuous bulk polymn. vessel to polymerize them at 90-180 deg.C so as to give 30-80wt% polymer content based on the reaction mixture, heating them to 150-300 deg.C in 10-100kg/cm<2>.G to remove volatile matters, and finally melt spinning the obtained polymer or copolymer. This core material is coated with a sheath material made of a polymer contg. >=20wt% F.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for making low loss plastic optical fibers. More specifically, the present invention has a polymer core mainly composed of deuterated methyl methacrylate, and contains at least 20% of fluorine.
The present invention relates to a method for manufacturing an optical fiber having a core-sheath structure in which the sheath is made of a fluorine-containing polymer containing a weight ratio of fluorine-containing polymer.

Optical fibers have recently attracted attention as new materials with information transmission functions.In addition to conventional glass-based optical fibers,
Plastic-based materials have also been put into practical use.

Although glass optical fibers have extremely good optical transmission properties, they are difficult to connect, are heavy, and
Moreover, it has drawbacks such as poor flexibility and high cost. On the other hand, Planuchik optical fibers have advantages such as superior flexibility, large diameter, and high numerical aperture, which improves the coupling efficiency with the light source and facilitates connection between fibers, but they suffer from transmission loss. The disadvantage is that it is large. Currently, plastic optical fibers with a polymethyl methacrylate core or polystyrene core are not available, but even those using polymethyl methacrylate have a transmission loss of at most 200 dB/km, making it difficult for optical communication. There was a demand for lower transmission loss for use in commercial applications.

On the other hand, as a low-loss glass optical fiber, JP-A-54
A method using a deuterated acrylate polymer as a core as shown in Japanese Patent No. 65556 has been proposed. However, the manufacturing method shown in the above-mentioned publication is a method in which a preform is made in advance over a long period of time, and then a core fiber is formed using the ram extrusion method. This method has low productivity and is not suitable for industrial manufacturing. I can't.

The inventors of the present invention conducted intensive studies to produce a low-loss plastic optical fiber that could be used for optical communications, and as a result, they purified the monomer containing deuterated methyl methacrylate to eliminate trace impurities. Continuous bulk polymerization is carried out by continuously supplying polymethyl methacrylate to the reaction tank, and special polymerization conditions are used to reduce the generation of thermal decomposition products of polymethyl methacrylate to create a core-shaped aggregate, which is then heated and melted. The method of manufacturing optical fibers by spinning, that is, monomer purification using a fine filter, and manufacturing the core component polymer by a continuous bulk polymerization method (r) reduces the amount of impurities in the core component polymer. The inventors have discovered that it is possible to obtain optical fibers with good heat resistance properties and to produce optical fibers with excellent light transmission performance, and have thus arrived at the present invention.

That is, the present invention provides a core-sheath structure in which the core is deuterated polymethyl methacrylate or a copolymer mainly composed of deuterated methyl methacrylate, and the sheath is a fluorine-containing polymer containing at least 20 M of fluorine. When producing optical fibers having a core component material, a monomer mixture containing a radical polymerization initiator and a chain transfer agent is supplied between a pump and a continuous bulk polymerization reaction tank, which are sealed from the outside. Purification is carried out using a porous membrane, and the reaction mixture is continuously supplied to a continuous bulk 1 reaction tank, and the reaction mixture in the reaction tank is stirred and mixed substantially uniformly at a temperature of 90°C or higher and lower than 180°C. A low-loss method characterized in that the reaction mixture is polymerized until the polymer content is 30 to 80% by weight, and then it is continuously fed to a spinning machine through a continuous volatile matter separation step and melt-spun. This is a method for manufacturing plastic optical fibers.

Next, the features of the present invention will be explained in detail. One feature of the present invention is as follows. That is, when producing polymethyl methacrylate, which is a core component material, by continuous bulk polymerization, a mixture of raw material monomers, a radical polymerization initiator, and a chain transfer agent mixture is added between a supply pump and a continuous bulk polymerization reaction tank. The point is that the process is over-purified using a porous membrane that is installed in a sealed manner from the outside.

Here, the porous membrane has micropores communicating between the inner and outer surfaces of the wall, and is made of flat (5) membranes or hollow fiber membranes of polycarbonate, polysulfone, polyamide, polytetrafluoroethylene, polyolefin, etc. with a pore diameter of 10
μm or less, preferably 1 μm or less, even better! 0
．． Porous membranes having a diameter of 1 μm or less are particularly preferred, and porous membranes made of polytetrafluoroethylene or polyion fins are particularly preferred.

Since the porous membrane is installed after the supply pump and immediately before the reaction tank, it is possible to eliminate dust contained in the monomer, initiator, and chain transfer agent in the monomer mixture as well as from the supply line. It is possible to completely prevent minute dust, that is, a large number of minute dust generated from inside the piping, inside the valve, inside the storage tank, inside the adjustment tank, inside the supply pipe, etc., from entering the reaction tank.

Raw material monomers are generally purified by distillation before use, but they come into contact with air during transportation and preparation, and thus contain impurities such as dust. Furthermore, radical polymerization initiators are generally difficult to purify by distillation and have low purity. The same is true for chain transfer agents; even if these substances are purified by distillation separately, they tend to come into contact with air during measurement, so distilling them has little industrial advantage (6). Furthermore, if a mixture of raw material monomers, a radical polymerization initiator, and a chain transfer agent is directly distilled, the polymerization initiator will decompose and scale will form in the distillation column, making it impossible to purify the mixture by distillation.

However, by filtering and purifying the raw material monomer, radical polymerization initiator, and chain transfer agent mixture by passing it through a fine filter with small openings, it is possible to remove minute impurities.Furthermore, the filtration is performed in a closed system, resulting in continuous lumps. Since it can be supplied to the polymerization tank, there is no possibility of contamination with impurities during the preparation process.

The present inventors used a polytetrafluoroethylene filter with an opening of 0.1 μm (Fluorobor FPOIO, manufactured by Sumitomo Electric Industries, Ltd.) to purify impurities in the monomer by filtration, and found that the results were similar to those obtained by distillation. It was found to exhibit similar light scattering properties and to be purified very well.

Furthermore, according to the results of intensive study by the inventors,
In order to improve the performance of optical fibers, it is necessary not only to prevent impurities such as dust from being contained in the core component material of optical fibers, but also to reduce the thermal history of the core component polymer during all processes. .

In optical fibers having a core-sheath structure, light is actually transmitted through the core polymer.

At this time, the interfacial state with the sheath component polymer and the transparency of the sheath component polymer itself are important issues in order to prevent light leakage due to light scattering at the core-sheath interface. Furthermore, it is extremely important to improve the light transmittance of the core component material.

From this point of view, we investigated the manufacturing method of deuterated polymethyl methacrylate, which is the core component material, and found that when performing continuous bulk polymerization, we used a raw material monomer mixture purified by a fine filter to achieve heat resistance under special polymerization conditions. If deuterated polymethyl methacrylate with excellent properties is produced and this polymer is used as a core component material under conditions with reduced thermal history, the light transmittance will be higher than that of conventional continuous bulk polymerization or suspension polymerization. It has become clear that optical fibers far superior to deuterated polymethyl methacrylate produced by the above method can be obtained.

The deuterated methyl methacrylate used in the present invention is preferably a monomer in which all hydrogens in methyl methacrylate have been replaced with deuterium, but methyl methacrylate partially substituted with deuterium is also a polymer. It can be used as long as it has a hydrogen content of 40 μm or less per unit.

The production of deuterated polymethyl methacrylate used in the present invention begins with a continuous bulk polymerization process at 90°C or higher and lower than 180°C, followed by removal of residual unreacted monomers designed to reduce thermal history. Part 2 of the main continuous separation process of volatiles
It is done in the process.

One reactor is used in the continuous bulk polymerization process, and 0.1
A methyl methacrylate monomer mixture containing a radical polymerization initiator of 0.0002 mol or more and a mercaptan of 0.01 mol or more and less than 10 mol is continuously supplied to the reaction tank. The reaction mixture was heated to 90°C or higher,
The reaction mixture is mixed and stirred substantially uniformly at a temperature below 180°C (9), and the polymer content (wt%) φ of the reaction mixture is 30%.
Continuous polymerization is carried out by continuously taking out the polymer while maintaining a substantially constant value of less than 80%. Subsequently, a polymer is produced by continuously separating and removing volatile substances mainly consisting of unreacted monomers from the reaction mixture containing the thus produced polymer.

Examples of the radical polymerization initiator used in the preparation of the polymer include di-tert-butyl peroxide,
dicumyl peroxide, methyl ethyl ketone peroxide, tart
-butyl perbenzoate, tart-butyl peracetate, di-tart-amyl peroxide, methyl isobutyl ketone peroxide, lauroyl peroxide, cyclohexanone peroxide, 2,5-dimethyl-2,5-ditart-butylperoxyhexane, tert -butyl peroctano (10) eight, t@rt-butyl barine butyrate, tar
Organic peroxides such as t-butylperoxyinglovyl carbonate and diisoglobil peroxydicarbonate, and dimethyl 2゜2'-azobisinbutyrate, 1,1'-azobiscyclohexanecarbonitrile, 2- Phenyl-2,4-dimethyl-4methoxyvaleronite IJA/, 2-carbamoylazoisobutyronitrile, 2,2'-azobis2,4-dimethylvaleronitrile, 2,2'-azobisinbutyronitrile, etc. The following azo compounds are mentioned.

The amount of such a radical polymerization initiator that can be appropriately decomposed must be selected depending on the predetermined polymerization temperature. As claimed in Japanese Patent Publication No. 53-42261, the product of the square root of the number of moles of the initiator used and the reciprocal of the square root of the half-life of the radical initiator at the polymerization temperature preferably satisfies the following formula (1).

1o≧A'(, B-"; x 10"", (1
) However, A = number of moles of radical polymerization initiator in monomer feed 1001 B = half-life (hours) of radical polymerization initiator at polymerization temperature In other words, the right side of equation (1) indicates the amount of radicals generated. , which takes a fairly large value in normal suspension polymerization, but when it comes to manufacturing optical fibers using continuous bulk polymerization,
Since the polymer ends due to generated radicals reduce heat resistance, it is necessary to reduce the generated radicals iLY as much as possible, advance polymerization by chain transfer reaction, strengthen the heat resistance of the polymer ends, and prevent the generation of thermal decomposition products. No. Therefore, the reaction temperature may be set in accordance with the decomposition temperature of the radical polymerization initiator, and the amount of the radical polymerization initiator may be determined to match equation (1).

To this invention? Mercaptans used include n-propyl, n-butyl, isobutyl, n-pentyl, impentyl, neopentyl, n-hexyl, isohexyl, n-heptyl, n-octyl, n-decyl, n-dodecyl, n- Primary mercaptans such as tetradecyl, n-hexadecyl, n-octadecyl, or Improvil, 5ec-butyl, 5ea-pentyl, Hatake ec-hexyl, 1l13e-heptyl, 5ea-octyl, gl
Secondary mercaptans such as ee-nonyl, 5ee-decyl, or tert-butyl, tart-hexyl,
tart-heptyl, tert-octyl, tert
Tertiary mercaptans such as -nonyl and tert-dodecyl, or aromatic mercaptans such as phenylmercaptan, 4-tert-butyl to O-thiocresol, and 4-tart-butylthiophenol, or glycol dimercaptoacetate, trimethylolpropanol, etc. Examples include polyfunctional mercaptans such as trithioglycolate, trimethylolpropane trismercaptoprobionate, and pentaerythritol tetrathioglycolate. Of these mercapta/, tert-
Butyl and n-octylmercabutane are particularly preferred. Mel (13) The amount of captan used is 0.01 molti or more based on the monomer,
Less than 10 molti is preferable. The amount of mercaptan used is 0.
If it is less than 0.01 molar, the polymerization degree will increase and it will be subjected to high thermal history after the continuous degassing step. If it is added in excess of 10 moles, the degree of polymerization will decrease and the fiber strength will decrease, which is not preferable. The polymerization degree of the polymer is 100 to 2000, preferably 800 to 150.
The amount of mercaptan is determined so that it falls within the range of 0.

The polymerization reaction is carried out by substantially uniformly mixing and stirring the reaction mixture at a temperature of 90°C or higher and lower than 180°C. When the temperature of the reaction mixture is 90° C. or lower, the viscosity of the reactant becomes high, making it difficult to control the reaction. Furthermore, if the temperature of the reaction mixture is 180° C. or higher, side reactants will be produced, which will adversely affect the performance of the optical fiber. Therefore, the polymerization temperature is 90°C or higher, 1
The temperature is less than 80°C, preferably 140°C or more and 170°C or less.

In the reaction tank, the polymerization temperature is controlled by conventional heating using a salmon rack (14). At this time, adhesion of the 1 compound can be prevented by cooling the upper part of the reaction tank.

The polymer content φ of the reaction mixture must be controlled within the range of 30'M weight percent or more and less than 80 weight percent. In the range of 80% by weight or more, the viscosity of the polymer mixture increases and it becomes difficult to control the polymer content. On the other hand, if it is less than 30% by weight, the cost of separating volatiles mainly composed of unreacted monomers will increase and the industrial benefits will be reduced.

In the volatile matter separation process, which consists mainly of unreacted monomers, a continuously fed reaction mixture having a predetermined polymerization rate is heated to 150 to 300°C under pressure to continuously remove most of the volatile matter. Separate and remove. The equipment used for volatile matter separation is generally vent extrusion type, but in order to improve the performance of optical fibers, it is important to prevent the generation of thermal decomposition products of the polymer, and for that purpose, volatile matter separation is necessary. The process needs to be carried out at the lowest possible temperature and in the shortest possible time. Specifically, a reaction mixture having a predetermined polymerization rate is
Volatiles separation is carried out by pressurizing to 0 kt/cm''G, raising the temperature to 150-300°C, preferably 180-220°C, and blowing into a vented extruder.

The volatile components (mainly deuterated methyl methacrylate) separated and removed by the vent extruder are separately purified or decomposed and reused as monomer raw materials.

In addition, in addition to producing completely deuterated methyl methacrylate, the above-mentioned method for polymerizing deuterated methyl methacrylate also involves the production of 40 m2 or less of hydrogen, preferably 30 m2 or less, per 11 core-type coalescing bodies.
■It can also be applied to the production of products containing the following: In other words, not only perdeuterated methyl methacrylate, but also polymers of methyl methacrylate in which at least 4 of the 8 hydrogens in methyl methacrylate are deuterated, or combinations with these deuterated methyl methacrylates. It can be applied to the production of copolymers, etc. with a polymerizable second or third component.

The copolymerization component is selected from, for example, alkyl acrylates or alkyl methacrylates (excluding methyl methacrylate) having an alkyl group having 1 to 18 carbon atoms, such as methyl, ethyl, n-7' lobil, n -7
Examples include alkyl acrylates or alkyl methacrylates having alkyl groups such as ethyl, 2-ethylhexyl, dodecyl, and stearyl.

Furthermore, esters of acrylic acid or methacrylic acid containing a benzene nucleus, such as benzyl methacrylate, can also be used as a copolymerization component. As these copolymerization components, those obtained by deuterating some or all of the hydrogen atoms of the above-mentioned esters can also be used.

The deuterated methyl methacrylate or copolymer component used in the present invention is described, for example, in Journal of Polymer Science J, Vol. 162, No. 174, P, 95-98 (1).
962), or one obtained by directly reacting methyl methacrylate and 1 water in the presence of a catalyst (17), etc. can be used as appropriate.

Before transferring the polymer to the spinning process, it is possible to take it out in the form of pellets, heat it again, melt it, and spin it.
There are many opportunities for foreign substances such as dust to get mixed in during the process, and there are also many chances for thermal decomposition products of the polymer to be generated by repeating heating and melting. Therefore, in order to produce a low-loss optical fiber, it is necessary to perform the devolatilizing extrusion of the core-type assembly and the spinning process continuously. In addition, although the core mold combination has sufficient heat resistance to be used as a regular molding material resin,
From the point of view of optical fiber performance, long-term heating can cause discoloration, and heating operations must be reduced as much as possible. Additionally, if the polymer is left in the air in the form of a pellet, small particles floating in the air may adhere to the resin, and small particles may also adhere to the resin during the process of drying the pellet in a vacuum dryer. I do things. Such dust greatly reduces the performance of optical fibers. Therefore, in the production of optical fibers (conventional shaping and spinning of resins and fibers)
] 8) Compared to yarn technology, it requires advanced dust-proof equipment, deaeration equipment, etc. to suppress the contamination of foreign substances such as dust.

However, industrially, it is necessary to install equipment that can satisfy these requirements and perform process control, which means that a sophisticated management system is required from the standpoint of productivity and equipment protection. This method, which directly connects spinning equipment to continuous bulk polymerization that can sufficiently remove dust without installing dust-proof equipment and reduce thermal history, is suitable for industrial optical fiber manufacturing. It is advantageous for

In the present invention, as the sheath component polymer of the optical fiber having a core-sheath structure, a fluorine-containing polymer containing at least 2ON of heptads and having a refractive index of 1.43 or less is used. Specific examples of such fluorine-containing polymers include the general formula (11% formula %) or the general formula (Ill to CF).

(Y is H or CF, ) fluorine-containing acrylic ester or methacrylic ester polymer or vinylidene fluoride,
Tetrafluoroethylene, hexafluoropropylene/,
Examples include copolymers obtained by copolymerizing one or more selected from methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid, methacrylic acid, and the like.

Among these sheath components, those represented by the general formula (1)62
, 2.2-) Lifluoroethyl methacrylate or 2.2.3.3.3-pentafluoropropyl methacrylate and methyl methacrylate, ethyl methacrylate, methyl acrylate or ethyl acrylate, and acrylic acid or methacrylic acid The three-component copolymer is most preferred from the viewpoint of adhesion to the core component and transmission properties.

These carrier component polymers can be produced by conventionally known methods. In the case of the sheath component polymer, in the case of the core component polymer, the influence of the manufacturing method on optical transmission cannot be eliminated, so if the sheath component polymer is manufactured in particular to avoid contamination with foreign matter such as dust. good.

The production of the optical transmission fiber having a core-sheath structure according to the present invention can be broadly classified into the following two methods.

The first method is to attach a spinning machine with a core-sheath spinneret to the final outlet of the polymer in the continuous polymerization process, and use the polymer in the core component and the pre-produced fluorine in the sheath component. Containing Weight (21) This is a method of extruding the combined melt and continuously spinning the composite.

Here, the easiest method is to store the sheath component polymer in advance as pellets and then remelt it as necessary, but in some cases, the sheath component polymer may be continuously polymerized in the same way as the core component polymer. A method can be adopted in which this is continuously transferred to the spinning process.

In the second method, a spinning machine with a conventional spinneret is attached to the final outlet of the polymer in the continuous polymerization step, and the core component polymer is first spun alone, cooled, and stretched in some cases. A light transmitting fiber is produced by continuously coating the fibrous core material with a concentrated solution of the sheath component polymer and then removing the solvent of the sheath component polymer.

The melt spinning temperature varies somewhat depending on the properties of the core and sheath polymers, but is usually 180 to 280°C, preferably 200 to 265°C.

When employing such a composite spinning method using a core-sheath spinneret (22), it is important to bring the melt viscosities of the core component polymer and sheath component polymer as close as possible in order to produce uniform fibers. . As a method of changing the melt viscosity of a polymer, generally a method of changing the molecular weight of a single polymer or a method of forming a copolymer is used.

The composite spun optical fiber is drawn at an appropriate temperature of 100 to 160° C. with the main purpose of imparting toughness against curling.

In order to provide sufficient mechanical performance without deteriorating optical performance, the elongation ratio is preferably 1.3 times or more, preferably 1.
A stretching process of 5 to 2.5 times is applied.

When coating a core polymer with a sheath polymer solution, it is generally preferred to use the sheath polymer solution as a concentrated solution. The fibrous core component polymer that has passed through the concentrated liquid of the sheath component polymer stored in the upper part of the die is continuously taken out through the die, where the core component polymer is mixed with the sheath component polymer at a constant thickness. coated.

Thereafter, the adhering solvent is removed by an appropriate method (for example, heating to a constant temperature) to produce an optical transmission fiber having a core-sheath structure.

When preparing a concentrated solution of the sheath component polymer, a solvent that dissolves the sheath component polymer but does not dissolve the core component polymer, and a low boiling point solvent is particularly preferable, but a solvent that dissolves the core component polymer is particularly preferable. Even if a solvent is used, if a concentrated solution of the sheath component polymer is used, modification of the core component by the solvent can be almost eliminated.

The solvent for dissolving the sheath component polymer that can be used in the present invention varies somewhat depending on the sheath component polymer used, but in general, it is 1, 1.2-) IJ full: r o -1,
2,2-) halogenated hydrocarbons such as dichloroethane,
Ketones such as acetone, methyl ethyl ketone, methyl butyl ketone, amide solvents such as dimethyl formamide and dimethyl acetamide, acetate esters such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, or fluorine-containing acid, lylic acid, or methacrylic acid. The ester monomer itself can be mentioned.

The concentration of the polymer in the solution of the sheath component polymer using such a solvent is usually 10 to 60% by weight, and the preferable content is 20 to 50%.
Weight%.

The present invention will be explained in more detail with reference to Examples below. Note that all parts in the examples indicate parts by weight.

Example 1 A core component polymer was produced using an apparatus system in which a storage tank, a continuous supply pump, a reaction tank equipped with a paddle spiral stirrer, a reactant take-out pump, and a volatile matter separator were connected in series. The internal volume of the reaction tank was 1 (1), and a single screw vent extruder was used as the volatile matter separator.

The raw material monomer mixture was filtered in advance through a 0.1 μm polytetrafluoroethylene filter (Fluorobor FPOIO
, manufactured by Sumitomo Electric Industries, Ltd.) to remove impurities.

The composition of the raw material monomer mixture consists of 100 parts of bar deuterated methacrylate (25), 0.37 parts of tert-butyl mercaptan, and 0.0017 parts of di-tert-7' methyl peroxide. Increase the internal pressure to 7! ,/CIIL 30 sheets of 0.1 μm polytetrafluoroethylene filters (Fluorobor FPOIO, manufactured by Sumitomo Electric Industries, Ltd.) were piled up using a feed pump in a reaction tank kept at 2 gauge pressure and a temperature of 145° C. while performing f-filtration. and polymerization was carried out with thorough stirring.

The average residence time in the reaction tank was 3 hours, and the average polymerization rate was 4ON. The reaction mixture was heated from 155°C to 170°C between the reactor and the volatile separator.

The temperature of the vent extruder, which also serves as a volatile separator, is at vent section 2.
20℃, extrusion section 230℃, vent section vacuum level 5Tsuru H? And so.

The polymer produced from the vented extruder is guided to a spinning head directly connected to this, and the low refractive index polymer is transferred from another extruder placed in parallel, where it is spun into a composite fiber to create a uniform spinning head. A composite fiber with a core-sheath composition (26) was prepared.

As the sheath polymer, a 2,2,2-)+1 fluoroethyl methacrylate polymer was used. The refractive index of this polymer was 1.41. The spinning head temperature was 235° C., and the core-sheath polymer blending ratio was 90:10 by weight.

The optical fiber thus obtained has an optical transmission property of 660 nm.
It showed extremely excellent performance at a light wavelength of 30 dB/km.

The degree of polymerization of the core component polymer obtained in this example was 900, and the amount of residual monomer in the core component polymer was 0.
It was less than 1% by weight.

Example 2 Instead of subjecting the polymer produced from the vented extruder to composite spinning in Example 1, a one-filament extrusion accessory was attached to the spinning head, and the polymer continuously supplied from the vented extruder was , was continuously coated through a low refractive index polymer solution placed in a coating pot. As a low refractive index polymer solution, coating treatment was performed using a 30% methyl acetate solution of 2,2.2-) trifluoroethyl methacrylate polymer, and the coating thickness was adjusted to 2% of the fiber diameter. After coating, it was heated in an air heating oven at 140°C to remove methyl acetate as a coating bath medium. The optical fiber thus obtained had an extremely excellent optical transmission property of 35 dB/km at a wavelength of 660 nm.

Example 3 In Example 1, d5 deuterated methyl methacrylate d, (n-methyl ester of deuterated methacrylic acid) was used instead of deuterated methyl methacrylate as the core component monomer, and Example 1 Polymerization was carried out in the same manner. The polymerization temperature was adjusted to 150°C Vr:, the average residence time of the reaction mixture in the reaction tank was 3.5 hours, and the average polymerization rate (・
It was a steamed rice cake weighing 45 pounds.

The reaction mixture is led to a vented extruder, and the bottom part is heated at 200°C.
The extrusion section was set at 220° C., and the vacuum level at the bed/bottom section was set at 5 H/. The polymer discharged from the vent extruder was made into a core-sheath composite fiber in the same manner as in Example 1. However, here, as a low refractive index polymer, 2.2.3.3゜3-pentafluoropropyl methacrylate, methyl methacrylate, methacrylic acid 90:
A copolymer having a weight ratio of 8:2 was used, and the spinning head temperature was 230°C.

The optical fiber thus obtained had an optical transmission property of 60 dB/km at a light wavelength of 650 nm.

(29)

Claims (1)

[Claims] 1. The core is deuterated polymethyl methacrylate or a copolymer mainly composed of deuterated methyl methacrylate,
When producing an optical fiber having a core-sheath structure using a fluorine-containing polymer containing at least 20% by weight of fluorine as a sheath, the production of the core component material is carried out using a monomer mixture containing a radical polymerization initiator and a chain transfer agent. The reaction mixture in the reaction tank is over-purified using a porous membrane installed between the supply pump and the continuous bulk polymerization reaction tank so as to be sealed from the outside, and then continuously supplied to the continuous bulk polymerization reaction tank. 90℃ or higher, 180℃
The reaction mixture is stirred and mixed substantially uniformly at a temperature below 100 mL, polymerized so that the polymer content of the reaction mixture is 30 to 80% by weight, and then continuously fed to a spinning machine through a continuous volatile matter separation process. A method for producing low-loss plastic optical fibers, which is characterized by melt spinning.