JPS5816163B2 - Manufacturing method of plastic optical fiber - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method of manufacturing a plastic optical fiber.

A plastic optical fiber is composed of a polymer as a core portion and a polymer with a lower refractive index as a cladding portion.

Conventionally, in the production of plastic optical fibers, transparent polymers such as polystyrene (hereinafter abbreviated as PS) or polymethyl methacrylate (hereinafter abbreviated as PMMA) have been used as the core material, and transparent polymers such as polystyrene (hereinafter abbreviated as PMMA) have been used as the cladding material. A polymer with a low refractive index, for example, PMMA or the like is used when the core material is PS, and a fluorine-containing polymer is used when the core material is PMMA.

Fiberization is achieved by double extrusion molding (hereinafter referred to as double extrusion method) of the clad material so as to form a core fiber coating layer at the same time as the formation of the core fiber of the core material, or by cutting the preformed core fiber. This is done by coating using a coating method.

By the way, the transmission loss of currently available plastic optical fibers is about 1 dB/m, or 10771, even if the best wavelength band is selected, and the strength is reduced by one order of magnitude. Even things are 0
．． It is about 5 dB/m.

In order to find out the cause of this, the present inventors conducted a multifaceted study on the series of steps from the production of the core material and cladding material to the production of fibers using the conventional method, and found the following results.

That is, in the production of conventional plastic optical fibers, the core material and cladding material were generally synthesized by a suspension polymerization method, and then supplied to a fiber manufacturing apparatus.

Suspension polymerization is generally recognized as an industrial polymer synthesis method that yields highly pure polymers.
Since a large amount of water is used, foreign substances contained therein are likely to be mixed into the polymer, and there is also a possibility that foreign substances may be mixed in during the dehydration process.

Furthermore, the polymer obtained by suspension polymerization requires a step of turning it into a fiber as a core material, that is, pelletizing it for melt-proofing, and in terms of equipment, the polymer manufacturing equipment and the fiber manufacturing equipment are separate. Because of this, the fibers are placed in an environment where foreign matter may be mixed in during the pelletizing process and the process of supplying the fibers to the fiber manufacturing equipment, and where they may be oxidized by air.

It is thought that if such obstacles are removed, at least part of the above causes will be resolved.

The present invention has been made based on the above knowledge, and its purpose is to provide a method for manufacturing a plastic optical fiber with improved transmission loss.

To summarize the present invention, the method for producing a plastic optical fiber of the present invention involves subjecting at least a core-forming monomer to thermal bulk polymerization, and then continuously forming a core fiber and a cladding from the obtained polymer. In this specification, thermal bulk polymerization refers to a polymerization method in which bulk polymerization is controlled only by heat without using a polymerization initiator, a molecular weight regulator, etc.

The bulk polymerization method is a method in which distillation of monomers, polymerization, and removal of low molecules such as unreacted monomers are continuously carried out under closed conditions, sometimes in a nitrogen stream, and therefore, it is carried out in the absence of water and oxygen. Therefore, the problems caused by the contamination of foreign substances and the oxidation of the polymer caused by suspension polymerization can be solved.

Since the transmission loss is mainly caused by the polymer in the core part, it is sufficient to apply bulk polymerization to the polymerization of the monomer for forming the core, and it is not necessarily necessary to apply bulk polymerization to the polymerization of the monomer for forming the cladding. This was recognized.

Furthermore, when PS is used as a core material, continuous bulk polymerization of PS can be carried out at a high polymerization temperature without the need for a polymerization initiator or molecular weight regulator, as is clear from the technology that has already been implemented industrially. It is possible to produce a polymer of any molecular weight by simply adjusting the amount, and an extremely pure polymer can be obtained.

In this case, in order to prevent oxygen from entering the polymerization system as much as possible,
It is desirable to place the entire polymerization system under a nitrogen atmosphere.

The bulk-polymerized core material polymer is then melt-spun to form the core of the optical fiber, and according to the invention, this procedure is also carried out in the absence of oxygen.

It is generally believed that polymers, especially PS, are easily colored by heating, but according to experiments conducted by the present inventors, no coloring was observed even when the polymer was kept at a considerably high temperature, for example, 250° C., for more than one week.

Therefore, it is clear that deterioration of the core polymer can be avoided by melt spinning in the absence of oxygen and by stretching the plastic optical fiber so that the molecular chains are aligned in the axial direction of the fiber in order to provide sufficient strength.

For this purpose, in the present invention, the bulk polymerization is followed by the formation of the core fiber and the formation of the cladding in the absence of oxygen.

The cladding material is required to be a polymer with a lower refractive index than the core material, but as long as it is not extremely contaminated it may be used in the form of ordinary pellets or powder as it does not affect the properties of the optical fiber.

The cladding is formed by double extrusion or coating of the cladding material at the same time as the core fiber is formed, so that the core fiber is formed without being exposed to the atmosphere during the fiberizing operation including the drawing process.
The contamination and oxidation of foreign matter are carried out without being suppressed, and the contamination and oxidation of foreign matter are suppressed.

In the double extrusion method, an appropriate drawing ratio can be obtained by appropriately selecting the ratio between the feeding speed of the core material and the cladding material to the extruder and the winding speed.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto in any way.

Example Figure 1 is a block diagram of the apparatus used in this example, in which 1 is a monomer reservoir, 2 is a distiller, 3 is a monomer supply rate control valve, and 4 is a distillation residue discharge valve. , 5 is a cooler, 6 is a cooling water inlet, 7 is a cooling water outlet, 8 is a vacuum pump, 9 is a purified monomer reservoir, 10 is a polymerization vessel, 11 is a screw conveyor, 12 is a motor, 13 is a polymer storage Tank, 14 is a spinning hole having a large number of pores, 15 is a vacuum pump, 16 is a core material extrusion screw, 17 is a motor, 18 is a cladding material extrusion screw, 19 is a motor, 20 is a cladding material supply hopper, 21 2 is a double extrusion nozzle, 22 is an optical fiber, and 23 is a winding roll.

Using this apparatus, a plastic optical fiber consisting of PS as the core material and PMMA as the cladding material was manufactured.

The apparatus is initially maintained under a nitrogen atmosphere, and styrene is stored in a monomer reservoir 1, supplied to a distiller 2 at a constant rate by a monomer supply rate control valve 3, and distilled under reduced pressure in a conventional manner to a cooler 5.
It was condensed and sent to purified monomer reservoir 9.

Next, purified styrene was heated in a polymerization vessel 1 maintained at a temperature of 110°C.
0°C, prepolymerized with a residence time of 8 hours, and further heated to 170°C.
The polymerization was completed within 3 hours of feeding and residence time in the screw conveyor 11 maintained at
P, C method)) was passed through a spinning hole 14 and sent to a polymer storage tank 13 evacuated by a vacuum pump 15 to remove unpolymerized styrene and low molecular weight substances.

Screw 16 for pushing out PS of polymer storage tank 13
At the same time, PMMA pellets, which are the cladding material, are supplied from the hopper 20 to the cladding material extrusion screw 18, and the core material and cladding are extruded by the double extrusion nozzle 21 maintained at 220°C, with the core fiber covered with the cladding. The material was extruded to form an optical fiber 22, and at the same time, it was stretched at a pulling speed of 5 m/min and wound onto a winding roll 23.

The obtained optical fiber had a core diameter of 1 m and a cladding thickness of 200 μm.

The transmission loss characteristics of this optical fiber are shown in FIG.

It can be seen from FIG. 2 that there is a low loss window of 14 QdB/IaIL at 670 nm.

As is clear from the above description, according to the present invention, it is possible to manufacture an optical fiber with a loss that is several times lower than that of conventional plastic optical fibers, and in particular, it is possible to manufacture optical fibers with a loss of a fraction of that of conventional plastic optical fibers.
Since the 6 70 nm valley where the loss of L is obtained can be obtained using an inexpensive red LED (based on a light emitting diode) as a light source, an economical short-distance optical transmission system can be constructed.

Furthermore, plastic optical fibers have the advantage that they can be made larger in diameter than inorganic optical fibers, making it easier to combine them with light sources and to connect fibers together.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a manufacturing apparatus used in carrying out the present invention, and FIG. 2 is a graph showing the loss results of a plastic optical fiber obtained in an embodiment of the present invention. 1... Monomer reservoir, 2... Distiller, 3
. . . Monomer supply rate control valve, 4 . . . Distillation residual discharge valve, 50. . ...Cooler, 6...Cooling water inlet, 7...
...Cooling water outlet, 8...Vacuum pump, 9...
... Purification monomer reservoir, 10 ... Polymerization vessel, 11
... Screw conveyor, 12 ... Motor, 13 ... Polymer storage tank, 14 ...
...Spinning hole, 15...Vacuum pump, 16...
... Screw for extrusion, 17 ... Motor, 18 ... Screw for extrusion of cladding material, 1
9...Motor, 20...Hopper, 21
...Double extrusion nozzle, 22 ... Optical fiber, 23 ... Winding roll.

Claims (1)

[Claims] 1. Subjecting at least a core-forming monomer to thermal bulk polymerization, and then forming a core fiber from the obtained polymer and forming a cladding continuously in the absence of oxygen. A method for manufacturing a plastic optical fiber characterized by: 2. The method for manufacturing a plastic optical fiber according to claim 1, wherein the cladding is formed by a double extrusion method together with the formation of the core fiber.