JPH0660965B2 - Method for manufacturing heat-resistant plastic optical fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a heat-resistant plastic optical fiber. More specifically, the present invention relates to a method for producing a heat-resistant plastic optical fiber that can be used in an automobile, an outdoor duct exposed to direct sunlight, and a high temperature factory where the thermal environment is bad.

2. Description of the Related Art In recent years, optical communication technology using an optical fiber as an information transmission path has rapidly advanced and is already in the stage of practical application.

There are two types of optical fibers, a quartz optical fiber for long-distance communication and a plastic optical fiber for short-distance communication. The latter plastic optical fiber uses a highly transparent thermoplastic resin such as polyethylene or polymethylmethacrylate as a material, and has a concentric shape in which the core has a higher refractive index than the sheath, The light incident from one end is transmitted to the other end while being totally reflected at the interface between the core and the sheath.

Among such plastic optical fibers, those having heat resistance include polycarbonate, a copolymer of methyl methacrylate and maleic anhydride or styrene, a copolymer of methyl methacrylate and α-methylstyrene. , Those having a core material such as a copolymer of methyl methacrylate and isobornyl methacrylate or bornyl methacrylate have been proposed.

However, a plastic optical fiber having a polycarbonate as a core material has excellent heat resistance, but is inferior in light guiding performance and is not suitable for long-distance transmission.

On the other hand, a plastic optical fiber using a methyl methacrylate-based copolymer as a core material has a problem in mechanical strength.

As described above, a practical plastic optical fiber having excellent heat resistance and good light guiding performance and mechanical strength has not been found so far.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a plastic optical fiber which is excellent in heat resistance, light guiding performance and mechanical strength.

Means for Solving the Problems The present inventors have previously described a methyl methacrylate unit, a formula, derived from a copolymer obtained from methyl methacrylate, methacrylic acid and styrene. It was found that the copolymer composed of a 6-membered cyclic anhydride unit, a methacrylic acid unit and a styrene unit represented by the formula (3) has excellent transparency, heat resistance and mechanical strength.
This polymer is obtained by subjecting a polymer obtained by copolymerizing methyl methacrylate, methacrylic acid and styrene to heat treatment under reduced pressure in a devolatilization device to obtain a chain of methacrylic acid units in the polymer or methacrylic acid unit. It can be obtained by dehydration cyclization or demethanol cyclization of a part or all of the chain of a methyl acid unit and a methacrylic acid unit.

Then, the present inventors paid attention to the excellent transparency, heat resistance and mechanical strength of this polymer, and previously proposed a plastic optical fiber having this as a core material (Japanese Patent Laid-Open No. 60-115902). Issue). After that, further research was conducted to sufficiently improve the transparency of this polymer by sufficiently purifying the polymerization raw material and improving the treatment from devolatilization of the reaction solution to molding into a fiber. Based on this finding, the present invention has been completed based on this finding.

That is, the present invention relates to a monomer component consisting of methyl methacrylate, methacrylic acid and styrene from which a polymerization inhibitor, dissolved oxygen and contaminants have been removed in advance, and a chain transfer agent from which dissolved oxygen and contaminants have been removed in advance. , The polymerization initiator and optionally a solvent are continuously supplied to the polymerization zone to carry out the polymerization reaction, and then the obtained reaction mixture is brought to a high temperature and a reduced pressure, and an unreacted monomer is used as necessary. The solvent, water and methanol produced by the reaction are removed, and spinning is carried out as quickly as possible to obtain the formula (A). 1 to 35% by weight of a 6-membered cyclic anhydride unit represented by, (B) methacrylic acid unit of 15% by weight or less, (C) styrene unit 1 to
Forming a polymeric core consisting of 60% by weight and (D) 39-90% by weight of methyl methacrylate units, and then coating this surrounding with a sheath material having a lower refractive index than this core. A method for producing a characteristic heat-resistant plastic optical fiber is provided.

In the present invention, it is necessary to remove insoluble fine particles such as dust and dissolved oxygen in all raw materials used for the polymerization reaction in advance, and the monomer further removes the polymerization inhibitor contained therein in advance. It is necessary to.

Monomers used in the present invention, particularly methacrylic acid and styrene, usually include a phenol-based, amine-based, imine-based polymerization inhibitor, and these polymerization inhibitors include, for example, rectification, recrystallization, It can be removed by a treatment such as adsorption. In addition, the dissolved oxygen contained in the raw material causes coloring when undergoing a heat history in the devolatilization step and the spinning step,
In order to remove this dissolved oxygen, it is preferable to carry out countercurrent diffusion using an inert gas such as high-purity nitrogen, or to carry out vacuum degassing. 1/10 or less of the equilibrium oxygen concentration of, preferably
It is desirable to be 1/20 or less. Further, in order to remove dusts and other contaminants, it is preferable to distill the distillable monomers and the solvents individually or in a mixture. In this case, it is desirable to remove the dissolved oxygen after distilling the easily polymerizable monomer in the presence of oxygen.

In addition, a chain transfer agent or a polymerization initiator alone or together with a solvent can remove fine particles of 100 Å or less, preferably 30 Å or less, and from ultrafiltration membranes resistant to these chemicals, for example, polyacrylonitrile hollow fiber. The resulting fine particles may be filtered using an ultrafiltration membrane consisting of the above, or, if distillable, the fine particles may be removed by a distillation treatment. By using a highly purified raw material by such treatment, the transparency of the obtained polymer is significantly improved.

In the present invention, using the raw material treated as described above, after continuously copolymerizing in the absence of solvent or in the presence of a solvent, this reaction solution is continuously supplied to a devolatilization apparatus under reduced pressure. Heat treatment is performed to remove the unreacted monomer or the unreacted monomer and the solvent, as well as the water and methanol generated by the cyclization reaction to remove the methacrylic acid unit in the polymer as completely as possible. Converts to a membered ring acid anhydride unit. If the treatment for converting to such a 6-membered cyclic anhydride unit is not performed,
Even under normal thermoforming conditions, a part of the methacrylic acid unit of the polymer is cyclized, and water or methanol generated at that time causes foaming of the molded product.

In the present invention, the conditions for cyclizing most of the methacrylic acid units are 230 to 280 under a reduced pressure of 100 torr or less.
It is preferable to retain at a temperature of ° C for about 10 to 60 minutes.

As the devolatilizer, a flush tank that can be operated under high temperature and reduced pressure, a devolatilizing extruder, or a combination thereof can be used.

In the present invention, in order to reduce the heat history as much as possible, to have a desired transparency, and to obtain a fiber molded body without foaming, in order to obtain a fiber molded body from the final vent port of the devolatilization device to the die outlet for molding to the fiber It is necessary to keep the time as short as possible and suppress the six-membered cyclization reaction that occurs during this time as much as possible.The cyclization treatment time is also suppressed to the minimum level at which the polymer does not foam during fiber molding. It is desirable to do. In the zone from the final vent port of the devolatilizer to the die outlet for molding into the fiber, there are the metering zone of the extruder, the gear pump, and the composite spinning die, and the average zoning time of the polymer is usually about 2 minutes, In the present invention, the retention time is preferably 60 seconds or less, more preferably 30 seconds or less.

In the present invention, the composition of the polymer used as the core material of the optical fiber is such that the 6-membered cyclic anhydride unit represented by the formula (1) is 1 to 35% by weight, the methacrylic acid unit is 15% by weight or less, and the styrene unit. It should be in the range of 1 to 60% by weight and methyl methacrylate units in the range of 39 to 90% by weight. The 6-membered cyclic anhydride unit plays a role of improving the thermal stability and heat resistance of the polymer, and if the content is less than 1% by weight, the effect cannot be exhibited, while the content of 35% by weight If it exceeds, fluidity of the polymer deteriorates, which is not preferable.
The 6-membered cyclic anhydride unit is 1800 cm by an infrared spectrophotometer.
^It can be quantified by measuring the absorption at ^-1 and 1760 cm ^-1 .

The methacrylic acid unit content of the second component must be 15% by weight or less. When this content exceeds 15% by weight, foaming is inevitable no matter how short the residence time from the final vent port of the devolatilizing extruder to the outlet of the spinning die is shortened.

The content of the styrene unit of the third component is in the range of 1 to 60% by weight. If this content is less than 1% by weight, the amount of methacrylic acid units that can be converted into six-membered cyclic anhydride units increases, and foaming tends to occur during spinning. By sequentially increasing the styrene units, the number of methacrylic acid units bonded to the styrene units increases, the thermal stability increases, and the refractive index increases, so that the selection of the sheath material becomes easy. However, if the amount exceeds 60% by weight, weather resistance and mechanical strength will be unfavorable.

The content of the methyl methacrylate unit of the fourth component is 39 to 9
It is in the range of 0% by weight. This unit plays a role of maintaining weather resistance and mechanical strength, and the content thereof is determined by the balance with the contents of other components.

The content ratio of each of these units can be appropriately selected according to desired performance such as heat resistance, light guiding performance, mechanical strength, refractive index, and weather resistance of the obtained plastic optical fiber. Further, regarding the proportion of the monomer for obtaining the polymer having the above composition, the sum of the methacrylic acid unit and the six-membered cyclic anhydride unit of the desired polymer is regarded as the methacrylic acid unit, and the methyl methacrylate unit is considered. Assuming a ternary copolymer composed of methacrylic acid unit and styrene unit, and then trying to operate according to a conventional method by using a known copolymerization reactivity ratio of methyl methacrylate, styrene and methacrylic acid. In the polymerization rate, the ratio of each monomer that gives the above-described assumed polymer composition can be obtained by calculation, and the vicinity of this monomer composition can be varied and determined by trial and error.

The reactor used for obtaining the polymer used as the core material of the optical fiber in the present invention is preferably a complete mixing reactor or a combination of a complete mixing reactor and a plug flow reactor. As the polymerization method, a continuous solution polymerization method using a solvent or a continuous bulk polymerization method without a solvent can be used, but from the viewpoint that the polymerization reaction proceeds stably,
The continuous solution polymerization method is preferred. As the polymerization initiator, known radical polymerization initiators such as azobis-tert-
Azoalkanes such as octane and azobis-tert-butane, azonitrile compounds, peroxides and the like can be used. Among them, azoalkanes are preferable from the viewpoint of coloring the polymer obtained.

Further, in order to make the fluidity of the polymer at the time of spin molding appropriate, monovalent mercaptans such as butyl mercaptan, octyl mercaptan, and dodecyl mercaptan, and divalent to tetravalent mercaptans are used as a chain transfer agent. Is preferred. The addition amount of these mercaptans is appropriately selected according to the desired polymer composition and molecular weight. Regarding the degree of polymerization of the polymer, the melt flow index (ASTM
It is desired that the flow rate g) per 10 minutes under -D 1238, 230 ° C and a load of 3.8 kg is in the range of 0.3 to 3.0, preferably 0.5 to 1.5. If this value is too small, a smooth fiber cannot be obtained, and if it is too high, the mechanical strength becomes insufficient.

In the present invention, as the sheath material that coats the polymer of the core material, a polymer having a refractive index lower than that of the polymer and excellent in transparency is used. As such a polymer, for example, a polymer mainly containing a methyl methacrylate unit, a polymer mainly containing a methyl methacrylate unit and a fluoroalkyl methacrylate unit, a methyl methacrylate unit and a styrene unit, and a maleic anhydride unit are mainly contained. A polymer having a methyl methacrylate unit and a methacrylic acid unit, a styrene unit as a main component, a polymer in which a part or all of the methacrylic acid unit of this polymer has been converted to a six-membered acid anhydride, and this polymer. A polymer obtained by modifying a part or all of the six-membered ring acid anhydride unit into a six-membered ring imide unit, a polymer mainly composed of a methyl methacrylate unit and a methacrylic acid unit, and a part of the methacrylic acid unit of this polymer. Or a polymer obtained by converting all or six-membered ring acid anhydride into a polymer or a polymer obtained by modifying a part or all of the six-membered ring anhydride unit of this polymer into a six-membered ring imide unit. A polymer consisting of a fluoroalkyl methacrylate unit, a methyl methacrylate unit and a methacrylic acid unit, a polymer obtained by converting a part or all of the methacrylic acid unit of this polymer into a six-membered cyclic anhydride, a fluoroalkyl methacrylate and a bornyl methacrylate or an isomeric unit. Copolymers with bornyl methacrylate, especially 1
Examples thereof include a copolymer of 7FMA and isobornyl methacrylate, a copolymer of methyl methacrylate, fluoroalkyl methacrylate and o-methylphenylmaleimide. Among these, a particularly preferable polymer is 1% or more, preferably 3% with respect to the refractive index of the polymer used as the core material.
It has the above-mentioned difference in refractive index, has a high softening temperature, and is excellent in transparency.

In the present invention, the above polymer is used as the sheath material, and the core polymer is coated with the composite spinning die at a temperature usually in the range of 220 to 270 ° C. At the same time, the sheath material may be further coated with polyamide such as 6-nylon, 6,6-nylon or 11-nylon, high density polyethylene, polyvinylidene fluoride or polycarbonate.

For such a multi-layer coating method, it is preferable to use the method previously proposed by the present inventors (JP-A-52-80847).

The plastic optical fiber obtained by the method of the present invention has excellent heat resistance and can be used even in the temperature range of 90 to 130 ° C. which cannot be used in the conventional plastic optical fiber. It can be used in outdoor ducts exposed to direct sunlight and in high temperature factories with poor thermal environment.

EXAMPLES Next, the present invention will be described in more detail with reference to Examples.
The invention is in no way limited by these examples.

Example 1 Methyl methacrylate to which no polymerization inhibitor was added, methacrylic acid containing no polymerization inhibitor purified by recrystallization, and styrene to which 1 ppm of tert-butylcatechol was added as a polymerization inhibitor were used as monomers. Each of the monomers was rectified in the presence of an oxygen partial pressure to remove a slight amount of the polymerization inhibitor and a coloring matter, and then deoxygenated with high-purity nitrogen gas. The concentration of dissolved oxygen was set to 1/20 or less based on the deviation of the guideline for measuring the oxygen concentration in an equilibrium state under the atmospheric pressure of 20 ° C. with an oxygen concentration measuring instrument for organic solvents.
80 parts by weight of methyl methacrylate, 8 parts by weight of styrene, and 12 parts by weight of methacrylic acid thus purified were charged into a complete mixing reactor. On the other hand, 0.145 parts by weight of octyl mercaptan and 0.006 parts by weight of azobis-tert-octane were dissolved in 20 parts by weight of ethylbenzene which was highly treated with alumina, and an ultrafiltration membrane HC-1 made of polyacrylonitrile hollow fiber manufactured by Asahi Kasei was used. After filtration, the product was degassed by high-purity nitrogen gas, then deoxidized, and then charged into a polymerization vessel. Polymerization was carried out at 140 ° C for 2.5 hours, and the polymer content was 40
A weight% reaction solution was obtained. This reaction solution is vacuumed at 40 torr
r, the temperature was set to 255 ° C, and the solution was introduced into a flash tank and allowed to stay for 15 minutes before being supplied to the devolatilizing extruder.
It was devolatilized at 250 ° C. and a vacuum degree of 5 torr, and then spinning was performed so that the residence time from the vent port to the exit of the composite spinning die was 30 seconds.

The core polymer thus obtained has a six-membered cyclic anhydride unit of 17% by weight, a methacrylic acid unit of 5% by weight, a styrene unit of 10% by weight, a methylmethacrylate unit of 68% by weight, and a refractive index of 1.514. It was The melt flow index of this polymer was 0.9 g / 10 minutes. On the other hand, heptadecafluorodecanyl methacrylate 30 as a sheath material
Wt% and tetrafluoropropylmethacrylate 5 wt%
And methyl methacrylate 64.6% by weight and methacrylic acid 0.4% by weight, and using a copolymer with a refractive index of 1.45 and a bigat softening temperature of 99 ° C, a plastic optical fiber with a core diameter of 0.98 mm and a sheath outer diameter of 1.0 mm. Obtained.

The light guide loss of this plastic optical fiber is 4 at 660 nm.
It was 50 dB / km. Furthermore, it was left in a dry heat oven at 120 ° C for 1 hour to reach 470 dB / km, but 100 hours later the performance stabilized at 475 dB / km. When this fiber was bent 90 degrees with a finger and the number of times it was cut was measured, it was 10 times or more, and it had sufficient strength.

Example 2 After purifying a raw material in the same manner as in Example 1, polymerization was performed. The polymerization mixture was directly supplied to a devolatilizing extruder equipped with a two-stage vent without being supplied to a flush tank, and the first stage was operated at 240 ° C., 20 torr and the second stage was operated at 250 ° C., 5 torr. The residence time from the second vent to the composite spinning die exit was 20 seconds. The obtained core polymer was composed of 6% by weight of 6-membered acid anhydride unit and 12% by weight of methacrylic acid unit.
Styrene unit 10% by weight, methyl methacrylate unit 75
% By weight, and there was no foaming. The melt flow index of this polymer was 0.9 g / min.
The light guide loss of the plastic optical fiber obtained by the composite spinning in the same manner as in Example 1 was 310 dB / km at 660 nm. The light guide loss after leaving this fiber at 120 ° C for 100 hours was 330 dB / km, which was extremely high performance.

The bending test was possible 10 times or more.

Comparative Example 1 In Example 2, except that a device having a residence time of 2 minutes from the devolatilizing extruder vent port to the composite spinning die outlet was used.
A fiber was prepared in the same manner as in Example 2. This fiber foamed and was unusable.

Example 3 Using the monomer purified in the same manner as in Example 1, 37.2 parts by weight of methyl methacrylate, 34.3 parts by weight of styrene, and methacrylic acid were used.
8.5 parts by weight were charged, 0.04 parts by weight of octyl mercaptan and 0.0060 parts by weight of perhexa3M were dissolved in 20 parts by weight of ethylbenzene and treated in the same manner as in Example 1, then charged, and polymerization was carried out at 125 ° C. for a residence time of 3 hours. Then, spinning was performed using the same devolatilizing extruder and composite spinning die as in Example 2.

The composition of the core polymer was such that the 6-membered cyclic anhydride unit was 3% by weight, the methacrylic acid unit was 11% by weight, the styrene unit was 43% by weight, and the methyl methacrylate unit was 43% by weight. The melt flow index of this polymer is 1.0
It was g / 10 minutes.

The light guide loss of the plastic optical fiber thus obtained was 450 dB / km at 660 nm. Furthermore, this fiber was left at 115 ° C for 100 hours, but the light guide loss was 460d.
It only deteriorated to B / km.

Example 4 Using the monomer purified in the same manner as in Example 1, 32 parts by weight of methyl methacrylate, 6 parts by weight of styrene, 2 parts of methacrylic acid were used.
2 parts by weight were charged, 0.20 parts by weight of octyl mercaptan and 0.0060 parts by weight of perhexa3M were dissolved in 40 parts by weight of ethyl cellosolve, treated in the same manner as in Example 1, charged and polymerized at 125 ° C. for 3 hours.

Then, the reaction solution was introduced into a flash tank at 255 ° C. and 40 torr, and after being retained for 20 minutes, it was subjected to composite spinning through a devolatilizing extruder in the same manner as in Example 1 to obtain a plastic optical fiber. The composition of this core polymer was 30% by weight of a 6-membered acid anhydride unit, 9% by weight of a methacrylic acid unit, 10% by weight of a styrene unit and 51% by weight of a methylmethacrylate unit. The melt flow index of this polymer was 0.8 g / 10 minutes. The light guide loss of the plastic optical fiber thus obtained is 1200d at 660nm.
It was B / km. The light guide loss was 1220 dB / km when the fiber was left at 130 ° C for 100 hours. Further, the bending test of this fiber was 10 times or more, and it had sufficient mechanical strength.

Claims (1)

[Claims] 1. A chain transfer agent in which a monomer component consisting of methyl methacrylate, methacrylic acid and styrene from which a polymerization inhibitor, dissolved oxygen and foreign matters have been removed beforehand is removed from dissolved oxygen and foreign matters. , The polymerization initiator and optionally a solvent are continuously supplied to the polymerization zone to carry out the polymerization reaction, and then the obtained reaction mixture is brought to a high temperature and a reduced pressure, and an unreacted monomer is used as necessary. The solvent, water and methanol produced by the reaction are removed, and spinning is carried out as quickly as possible to obtain the formula (A). 1 to 35% by weight of a 6-membered cyclic anhydride unit represented by, (B) methacrylic acid unit of 15% by weight or less, (C) styrene unit 1 to
Forming a polymeric core consisting of 60% by weight and (D) 39-90% by weight of methyl methacrylate units, and then coating this surrounding with a sheath material having a lower refractive index than this core. A method for producing a heat-resistant plastic optical fiber, which is a feature.