JPH0259051B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a plastic optical fiber with improved light transmission efficiency by using an improved core component methyl methacrylate polymer.

Compared to inorganic glass fibers, especially silica glass fibers, plastic optical fibers have excellent flexibility even when made to a large diameter, are lightweight, and can easily be obtained with a high numerical aperture, resulting in less connection loss with the light source. Since it can be industrially mass-produced, it is extremely inexpensive, and has been applied to short-distance transmission systems. However, plastic optical fibers have the disadvantage of being inferior in light transmission efficiency compared to silica glass fibers, and various technical efforts have been made to improve this.

One factor that reduces optical transmission efficiency is that dust gets mixed into the core component methyl methacrylate polymer, increasing scattering loss. Various purification methods for removing dust have been attempted.

However, especially from an industrial perspective, the inventors of the present invention believe that thorough removal of dust inside the polymerization machine, where polymers are to be formed, will contribute to improving optical transmission efficiency, and have conducted extensive studies. The present invention was achieved by discovering the fact that light transmission efficiency is dramatically improved by using a core component methyl methacrylate polymer as shown in the present invention.

That is, the gist of the present invention is that in the production of plastic optical fiber using a methyl methacrylate polymer as a core component,
Highly purified methyl methacrylate monomer is passed through a filter and circulated inside the polymerization machine in a completely closed system to reduce the amount of dust in the monomer after passing through the polymerization machine, and then bulk polymerized to form the core component. This is a method for producing plastic optical fiber, which is characterized in that a methyl methacrylate polymer is obtained.

This will be explained in detail below.

According to the findings of the present inventors, no matter how highly purified methyl methacrylate monomer is used, when it is polymerized in a polymerization machine, dust attached to the polymerization machine walls, piping, valves, etc. An unexpectedly large amount of dust was mixed into the final polymer at the monomer stage, reducing the light transmission efficiency of the plastic optical fiber.

As a method for cleaning the interior of the polymerization machine, there is a method of cleaning with an organic solvent, but in that case, an operation for removing the residual organic solvent is required, but this is not necessary in the present invention.

By the way, when methyl methacrylate monomer is used as a cleaning solvent, discarding or repurifying the monomer every time washing is repeated is not a preferable method since it adds complicated operations from an industrial standpoint.

Therefore, by installing piping that allows monomer to circulate inside the polymerization machine as shown in Figure 1, inserting a filter in the middle, and circulating the monomer while passing through it, it is possible to effectively circulate the monomer inside the polymerization machine with a small amount of monomer. This enables thorough cleaning, prevents dust from entering the polymer, and
This ultimately contributes to improving optical transmission efficiency.

The methyl methacrylate monomer used in the present invention is purified by removing impurities using a distillation device with a high rectification effect.
Alternatively, a highly pure monomer free of dust, transition metals, and coloring impurities is used after being subjected to appropriate pretreatment and further distilled.

The filter used in the present invention is preferably a solvent-resistant membrane filter with a pore size of 0.2μ or less,
More preferably, a Teflon filter with a pore diameter of 0.1 μm or less is used. If it is necessary to further remove minute dust, it is also possible to use a filter with a pore diameter of 0.01 μm or less.

Although any type of polymerization machine may be used in the present invention, it is preferable to have a structure without dead space so that dust and the like can be easily removed.

Any type of pump may be used to circulate the methyl methacrylate monomer, but in order to prevent the monomer from polymerizing inside the pump, a buffer tank should be provided in the middle of the circulation system. It is preferable to circulate by pressurizing with an inert gas such as nitrogen gas or argon gas.

Further, in order to prevent thermal polymerization of the methyl methacrylate monomer, the circulation system is preferably kept at 5° C. or lower with cold water.

Circulating cleaning of the polymerization system using monomers according to the present invention can be carried out to reduce the amount of dust in the monomers to less than one particle per 1 ^mm3 , for example, by observing with a laser beam inside a pressure-resistant glass tube installed in the middle of the circulation system. You need to repeat it until you get it. According to the findings of the present inventors, it usually takes 30 cycles or more to reach this level, and this result also indicates that a large amount of dust remains inside the polymerization machine, and it is difficult to remove it. It is clear that this is most necessary in order to obtain a pure polymer. In order to further remove this,
It is clear that if the monomer used during cleaning were simply discarded, a large amount of monomer would be required.
From an industrial standpoint, the method of the present invention, in which the material is recycled while being passed through a filter, is an extremely excellent method.

By charging a predetermined amount of monomer, initiator, and chain transfer agent into the polymerization machine that has been cleaned in this way, and using the methyl methacrylate polymer obtained by bulk polymerization as a core component, the light transmission efficiency is improved. A plastic optical fiber with improved properties is obtained.

The core component methyl methacrylate polymer used in the present invention may be a copolymer with 10% by weight or less of other copolymerizable monomers such as methyl acrylate, ethyl acrylate, and butyl acrylate.

The initiator used in the present invention has desired physical properties,
Any one may be selected depending on the polymerization temperature and speed; examples include azobisisobutyronitrile,
Examples include azobisisovaleronitrile, tertiary azobutane, benzoyl peroxide, t-butyl peroxide, and the like. The amount used may be within a range that allows appropriate polymerization control.

Any chain transfer agent used in the present invention may be selected as long as it does not have an adverse effect such as coloring on the final polymer. Examples include n-butyl mercaptan, t-butyl mercaptan, and n-dodecyl mercaptan. Examples include mercaptan, t-dodecyl mercaptan, and the like. The amount used is preferably such that the weight average molecular weight of the final polymer is in the range of 80,000 to 150,000.

As for the method of charging the initiator and chain transfer agent used in the present invention, since the amount used is small, it is possible to dissolve them in a small amount of monomer and charge them to the polymerization machine under environmental conditions where dust and the like are not mixed. In order to avoid unexpected contamination with dust, etc., use a distillable initiator.
-Azobutane, t-butyl peroxide, distillable chain transfer agent n-butyl mercaptan, t-
Butyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, etc. can be prepared by distillation, and after dissolving the initiator and chain transfer agent in a small amount of monomer, they are passed through a filter and charged into the polymerization machine. It is also possible.

The thus obtained methyl methacrylate polymer is used as a core component for spinning. A fluororesin whose refractive index is adjusted to 1.38 to 1.41 is used as the sheath component resin. Further, as the spinning method, any method such as a coating method or a melt spinning method may be selected, and the melt spinning method is preferable from an industrial viewpoint.

The plastic optical fiber obtained as described above has dramatically improved optical transmission efficiency and can be applied to short-distance transmission systems.

The present invention will be explained below with reference to Examples.

The optical transmission efficiency was automatically measured between 400 and 700 nm using an optical fiber loss spectrometer manufactured by Operax Co., Ltd., and was expressed in (dB/Km).

Example As shown in Fig. 1, a cylindrical stainless steel polymerization machine 1 with an internal volume of 1000 c.c. has valves at the top and bottom.
A filter holder loaded with a 0.01μ membrane filter and monomer percirculation system piping with two 10 buffer tanks are connected in a removable manner. Highly purified MMA in buffer tank 2
Add the monomer and add 10Kg/ of high purity nitrogen gas from the top.
The mixture is pressurized to cm ² and passed through a filter 4 from the lower part of the polymerization tube while being washed, and then put into a buffer tank 3. Next, after switching the valve, the same operation is performed on the buffer tank 3, and the monomer is put into the buffer tank 2. By repeating this operation, the polymerization machine is cleaned.

In order to measure the degree of cleaning during cleaning, the amount of monomer dust passing through the pressure-resistant glass tube 5 provided midway through the piping was measured using a laser beam.

When the above cleaning operation was carried out approximately 32 times while maintaining the circulation system at 5° C. or lower, the amount of dust particles per 1 mm ³ of monomer was reduced to 1 or less.

800 c.c. of high-purity methyl methacrylate, 0.8 g of t-azobutane, and 1 g of n-butyl mercaptan are charged and adjusted by distillation into a 1000 c.c. monomer adjustment tank 6. Pressurize from the top and charge it into the polymerization machine. After closing the upper and lower valves, remove the piping, heat the polymerization machine at 130℃ for 76 hours, and then heat it to 180℃.
Polymerization was completed by heating for 16 hours.

60Kg/cm ² from the top while heating the polymerization machine to 200℃
The resin was discharged from the lower part of the pressurized high-purity nitrogen gas, and a fluororesin with a refractive index of 1.40 was used as a sheath resin and composite melt-spun to form a fiber. The optical transmission efficiency of this material was 80 dB/Km at a wavelength of 570 nm.

[Brief explanation of the drawing]

FIG. 1 is an explanatory flow sheet of a polymerization machine equipped with a washing device for producing a methyl methacrylate polymer used as a core material in plastic optical fibers according to the present invention. 1... Polymerization machine, 2, 3... Buffer tank, 4
... Filter, 5 ... Pressure-resistant glass tube, 6 ... Monomer adjustment tank.

Claims (1)

[Claims] 1. In the production of plastic optical fiber using methyl methacrylate polymer as a core component, highly purified methyl methacrylate monomer is circulated in a polymerization machine in a completely closed system while passing through a filter. A method for producing a plastic optical fiber, which comprises reducing the amount of dust in the monomer after passing through a polymerization machine, and then performing bulk polymerization to obtain a methyl methacrylate polymer as a core component. 2. The method for producing a plastic optical fiber according to claim 1, wherein a solvent-resistant membrane filter with a pore size of 0.2 μm or less is used as the filter. 3. The method for producing a plastic optical fiber according to claim 1, wherein a Teflon filter with a pore diameter of 0.1 μm or less is used as the filter. 4. A method for producing a plastic optical fiber according to claim 1, wherein a filter having a pore diameter of 0.01 μm or less is used as the filter.