JPH065328B2 - Plastic optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic optical fiber having an improved light transmission efficiency using a methyl methacrylate-based weight as an improved core component.

Compared to inorganic glass, especially silica glass fiber, plastic optical fiber has a large diameter and excellent flexibility, and it is easy to obtain a lightweight and high numerical aperture, so there is little loss of connection with the light source, and it is industrially available. Since it can be mass-produced, it is extremely inexpensive and has been applied to short-distance transmission systems. However, the plastic optical fiber has a serious drawback in that it is inferior in light transmission efficiency as compared with the silica glass fiber, and various technical efforts have been made to improve it.

Factors that reduce the light transmission efficiency are increased scattering loss due to the inclusion of dust and scale during the polymerization process, promotion of thermal deterioration in the spinning process due to the formation of coloring substances such as oligomers and coloring-causing substances, and absorption. Increasing losses are being considered.

In order to eliminate or reduce these factors, various improvement methods have been conventionally proposed, for example, Japanese Patent Publication No. 53-42261.
JP-A-58-118603, JP-A-58-88701, and JP-A-58-
A complete homogeneous stirring and mixing type continuous bulk polymerization method using one polymerization reaction tank is disclosed in JP-A-88702 and JP-A-58-171405.

However, this method is used as a general method for producing a methyl methacrylate-based polymer as a molding material.
The amount ratio of the polymerization initiator to the molecular weight modifier, the polymerization rate, the polymerization temperature conditions and the like in the method described in JP-A-65 are merely cited. Therefore, the above-mentioned manufacturing method, which has a primary purpose of mass-producing resins for general molding materials and productivity, is a high-quality methyl methacrylate-based resin whose primary purpose is to obtain a high level of optical transmission efficiency. The manufacturing method of coalescence is significantly different in its technical idea and required quality level. The inventors of the present invention have studied that, in the case of the continuous uniform polymerization method of the complete uniform stirring and mixing type using one polymerization tank as described above, the mixing of dust, coloring substances such as scale and oligomer, and coloring-causing substance It is very easy to produce, and it is clear that, in order to obtain a methyl methacrylate polymer used for plastic optical fibers having a high level of light transmission efficiency, satisfactory results cannot be obtained from the required quality level. Became.

That is, the technical idea of a continuous bulk polymerization system of a complete homogeneous stirring and mixing type using one polymerization tank is, as described in JP-B-52-32665, that "homogeneous mixing is performed over the entire reaction zone". That is, at the time when the polymerization reaction reaches a steady state, a mixture of a monomer, a polymerization initiator and a molecular weight modifier, which is added thereafter, is instantly uniformly stirred and mixed in the entire polymerization reaction tank, The concentrations of the monomer, the polymerization initiator, the molecular weight modifier, and the produced polymer are constant, and it is a necessary condition that the polymer-containing solution having a constant concentration is discharged. .

In order to achieve the above-mentioned necessary conditions, according to the studies by the present inventors, it is necessary to maintain the viscosity of the polymer concentration at 10 poises or less. As also described, the polymerization temperature is 150 ° C.
It is necessary to raise the temperature before and after, or to add a large amount of solvent to reduce the viscosity of the polymerization system.

However, at such a high polymerization temperature, generation of scale,
It is inevitable that adhesion, contamination, coloring substances such as oligomers, and coloring-causing substances are generated. Also, when a large amount of solvent is used, the amount of trace impurities mixed in the solvent increases accordingly, and with the use of a large amount of polymerization initiator due to a decrease in the polymerization temperature, the polymerization initiator residue becomes a polymer. There are disadvantages such as an increase in the number of end groups, resulting in an increase in the functional group responsible for colorability, and the formation of a colorable substance and a colorability-causing substance due to the different reaction between the solvent and the polymerization initiator or the molecular weight modifier.

Further, when continuous bulk polymerization is continued for a long time by the above-mentioned method, as is clear from the theory of average residence distribution, theoretically, a polymer produced on average, a coloring substance such as an oligomer, and a coloring-causing substance , It may be possible to discharge the scale, etc. within the average residence time, but it is realistic and technically impossible to achieve perfect homogeneous stirring and mixing. Then it is self-evident. According to it, these reaction mixtures are partially retained for a long time, during which these reaction products generate a coloring substance, a coloring-causing substance and scale by a more complicated side reaction, and they are generated in the polymerization reactor. It adheres to and accumulates on walls, pipes, valves, and the like, and is mixed into the polymer solution that is gradually discharged, and the amount thereof increases as the polymerization duration time increases. In the case of methyl methacrylate polymer used as a general molding material, it is not necessary to consider the mixing of a small amount of scales, coloring substances, coloring-causing substances, etc. as described above, but high level optical transmission. When the methyl methacrylate polymer obtained by the above method is used for the plastic optical fiber that should achieve efficiency, the coloring substance and the coloring causative substance accelerate the thermal deterioration during the spinning process and increase the absorption loss in the visible region. In addition, it is clear that the inclusion of scale increases scattering loss and fatally lowers the optical transmission efficiency, and even a small amount is not a permissible amount at all. In order to improve such defects, two or more polymerization vessels as described in JP-A-48-86990, JP-A-49-37993 and US Pat. No. 3,252,950 are used. It is easily presumed by those skilled in the art that it is preferable to adopt a continuous bulk polymerization method using a polymerization process having a plug flow type polymerization vessel having excellent self-cleaning property with less retention particularly in a high polymerization rate region. It

Therefore, the above-described continuous uniform polymerization method of a complete homogeneous stirring and mixing type in one polymerization tank is used for the plastic optical fiber having a high level of high transmission efficiency, and a high-quality methyl methacrylate-based polymer is required. It is considered to be inappropriate from the technical point of view to be adopted as a manufacturing method of.

Further, in JP-A-58-88701, JP-A-58-88702, and JP-A-58-118603, there are described in JP-B-52-32665 and JP-B-53-42261. Formula for limiting the amount of the polymerization initiator compounded: 10 ≧ A ^1/2 · B ^{−1 / 2} × 10 ³ (1) 3 ≧ A · B × 10 ⁵ (2) 2.9 ≧ A ⁻¹ (B + 10.3) × 10 ^-6 (3) A = number of moles of radical polymer initiator in 100 g of monomer feed B = half-life (time) of radical polymerization initiator at polymerization temperature, of formulas (2) and (3) The description is excluded. In Japanese Patent Publication No. 52-32665 and Japanese Patent Publication No. 53-42261, when the value of the formula (1) (2) A · B × 10 ⁵ is larger than 3, undesired adhesion of the polymer to the device is caused. (Scale) occurs.

2) When the right side of the equation (3) becomes larger than 2.9, side reactions, especially the production of oligomers, tend to increase. It means that in the range deviating from the formulas (2) and (3), the generation of scales, adhesion, coloring substances such as oligomers, and generation of coloring-causing substances are significantly increased. . Therefore, in the above-mentioned JP-A-58-88701, JP-A-58-88702 and JP-A-58-118603, the high quality used for plastic optical fibers having a high level of optical transmission efficiency is described. The most important technical constitutional requirements for obtaining the required methyl methacrylate polymer have been excluded, and it is claimed that the desired performance can be obtained only by limiting the range of the above formula (1). Are technically and logically contradictory.

The present inventors have conducted extensive studies to improve the fatal defects of the conventional techniques as described above, without the inclusion of scale, coloring substances such as oligomers, less generation of coloring-causing substances, Moreover, the present invention has been achieved by developing a plastic optical fiber in which thermal deterioration in the spinning process is reduced and the light transmission efficiency is dramatically improved.

That is, the present invention is a plastic optical fiber comprising a methyl methacrylate polymer as a core component and a fluorine-containing weight as a sheath component, in which a monomer mainly containing a methyl methacrylate ester, a polymerization initiator and a molecular weight modifier are used. Polymerization of the resulting monomer mixture in one polymerization tank, the polymer content in the obtained polymer solution is 40-60%
(Wt%, the same applies below), the polymer solution was discharged while adding the non-polymerizable organic solvent so as to maintain the above-mentioned polymer content, and the residual monomer and the non-polymerizable organic solvent were added. The present invention relates to a plastic optical fiber characterized by using a methyl methacrylate-based polymer obtained by removing as a core component resin.

The first step of obtaining the plastic optical fiber of the present invention is to charge all of the predetermined amounts of the monomer, the polymerization initiator and the molecular weight regulator into one polymerization tank at once, and
Polymerization is performed at a predetermined polymerization temperature until it reaches 40 to 60%. If the polymerization rate is less than 40%, it will be difficult to remove the residual monomer, and if it exceeds 60%, the viscosity of the polymerization system will increase and stirring will become difficult. It is preferable to maintain the rate, more preferably 45-55%,
Particularly preferably, it is 48 to 50%.

The polymerization temperature is preferably in the range of 80 to 130 ° C, more preferably 90 to 120 ° C, and particularly preferably 100 to 110 ° C depending on the desired polymerization rate. If the polymerization temperature is lower than 80 ° C, the viscosity of the polymerization system increases and stirring becomes difficult. If the temperature exceeds 130 ° C, coloring substances such as oligomers and coloring-causing substances increase, which is not preferable.

The polymerization rate is preferably 10% / Hr or less, more preferably 5% / Hr or less, and particularly preferably 2 when the desired polymerization rate within the range of 40 to 60% is reached.
% / Hr or less.

When the polymerization rate exceeds 10% / Hr, it becomes difficult to control the polymerization at a desired ultimate polymerization rate, which is not preferable.

The methyl methacrylate-based polymer used as the core component in the present invention may be a copolymer of a monomer copolymerizable with methyl methacrylate in addition to the methyl methacrylate homopolymer, and such copolymerizable Examples of the monomer include methyl acrylate, ethyl acrylate, butyl acrylate and the like, and their compounding ratio is about 10% in the copolymer.

As the polymerization initiator used in the present invention, any conventionally used one can be appropriately selected and used according to the desired ultimate polymerization rate, the polymerization temperature and the polymerization rate. Examples thereof include bisisobutyronitrile, azobiscyclohexanecarbonitrile, benzoyl peroxide, t-butyl peroxide, and the like. The amount of these used may be within a range where proper polymerization control can be performed.

As the molecular weight regulator used in the present invention, any conventionally used one can be appropriately selected and used as long as it does not adversely affect the finally obtained polymer such as coloration. For example, n-butyl mercaptan, t-butyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, etc. can be mentioned, and the amount thereof used is such that the weight average molecular weight of the final polymer is 8 to 15
It is preferable to use it in the range of 100,000.

The methyl methacrylate monomer used in the present invention is one in which impurities are removed by a distiller having a high rectification effect, or is subjected to an appropriate pretreatment and then further distilled to obtain a high concentration free from dust, transition metal, and coloring impurities. Use a pure monomer.

When the polymerization initiator and the molecular weight modifier used in the present invention are charged, they are generally dissolved in a small amount of a monomer under an environmental condition where dust and the like are not mixed because they are minute amounts and charged into a polymerization vessel. It is possible. To avoid unexpected contamination with dust, use the distillation method when using distillable t-butyl peroxide, n-octylazobutane, n-butyl mercaptan, t-butyl mercaptan, etc. It is possible. Further, it is also possible to dissolve the polymerization initiator and the molecular weight modifier in a small amount of the monomer, and then pass the solution through a filter to charge it in the polymerization vessel.

In order to remove dust from the polymer, the above method is sufficient as a method for purifying the monomer, polymerization initiator and molecular weight modifier used. Especially from an industrial point of view,
Above all, it is important to thoroughly remove the dust in the polymerization vessel where the polymer is formed, and as a method therefor, Japanese Patent Application No. 58-42761 and Japanese Patent Application No.
It is necessary to remove the dust in the polymerization vessel as much as possible before the polymerization by employing the method described in each specification of 58-42762.

The second step of obtaining the plastic optical fiber of the present invention is to prepare a non-polymerizable polymer so as to maintain the desired polymer content when the polymer content in the polymer solution reaches the desired polymerization rate. Ejecting the polymer solution while adding an organic solvent. That is, depending on the polymerization rate at the time when the desired polymer content is reached, if the polymer solution is discharged while additionally mixing the non-polymerizable organic solvent containing no polymerization initiator, the polymerization in the polymerization vessel will start. The agent concentration is diluted with additional mixing of the non-polymerizable organic solvent to gradually decrease the polymerization rate, reduce the amount of the monomer mixture, and maintain the polymer content in the polymer solution at a desired constant amount. It becomes possible to do.

Also, keep the initial charge of the monomer mixture small,
After reaching the desired polymer content, a non-polymerizable organic solvent is added in the same manner as above, and the polymerization rate is preferably 2% / Hr or less, more preferably 1% / Hr or less, particularly preferably substantially polymerizing. It is also possible to drain the polymer solution when the velocity reaches zero.

The non-polymerizable organic solvent used in the present invention means an organic solvent having no radically polymerizable unsaturated functional group in the molecule, for example, hexane, toluene, xylene, cyclohexane, Hydrocarbon solvents such as petroleum ether, alcohol solvents such as methanol, ethanol, isopropanol, butanol, dioxane, tetrahydrofuran, diethyl ether, ether solvents such as dibutyl ether, acetone, methyl ethyl ketone, pentanone, ketone solvents such as cyclohexanone, Examples thereof include ester solvents such as methyl acetate, ethyl acetate, butyl acetate, isopentyl acetate, methyl isolactate, and ethyl isolactate.

Like the monomer, the organic solvent used is distilled with a distiller having a high rectification effect to remove dust, transition metals and coloring impurities.

In the present invention, since the organic solvent to be used is used after reaching a desired polymerization rate, a decrease in polymerization rate or a decrease in molecular weight does not occur until the desired polymerization rate is reached, and therefore a coloring substance such as an oligomer is used. It is possible to obtain high quality methyl methacrylate polymer used for high level plastic optical fiber without generation of coloring cause substance and viscosity decrease due to addition of solvent, so there is no scale generation or adhesion. Becomes

The third step of obtaining the plastic optical fiber of the present invention is to remove the residual monomer from the polymer solution to be discharged using a devolatilization device installed directly below the polymerization vessel to obtain a methyl methacrylate-based polymer. This is led to a composite melt spinning device continuously installed in a devolatilization device, and a fluorine-containing polymer is used as a sheath component to obtain a plastic optical fiber having a core-sheath structure.

The devolatilizer used in the present invention is a device shown in JP-B-35-8557, JP-B-38-120 and JP-B-44-20097, or a generally known devolatilizer such as a commercially available multistage belt extruder. It is possible to use a single device or a combination of multiple devices, and easily obtain a high-quality methyl methacrylate-based polymer that should be used for a plastic optical fiber having a high level of light transmission efficiency with a monomer content of 0.1% or less. To be The obtained polymer is introduced into a plurality of melt-spinning devices continuously installed in the devolatilization device to obtain a plastic optical fiber having a core-pod structure using a fluorine-containing polymer as a sheath component resin.

The fluorine-containing polymer used in the present invention has a lower refractive index than the core component methyl methacrylate-based polymer, and any desired numerical aperture and spinnability are selected as long as it is relatively transparent. do it.

Examples of such fluorine-containing polymers include homopolymers or copolymers of tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, etc. (In the formula, n = 1 to 2, m = 1 to 10, X = H or F), a homopolymer of a fluorinated ester of methacrylic acid or a methacrylic acid ester such as methyl methacrylate. Examples thereof include acrylic acid esters such as methyl acrylate, copolymers with acrylic acid, methacrylic acid and the like.

From the viewpoint of light transmission efficiency, the fluorine-containing polymer is preferably a homopolymer or a copolymer of the above-mentioned fluorinated ester of methacrylic acid, and a fluorinated ester of methacrylic acid and a monomer mainly composed of methyl methacrylate. More preferably a copolymer, 1H, 1H, 5H-copolymer of octafluoropentyl methacrylate and methyl methacrylate, 1H, 1H, 2H, 2
Particularly preferred are copolymers of H-heptadecafluorodecyl methacrylate with methyl methacrylate and copolymers of 2,2,3,3,3-pentafluoropropyl methacrylate with methyl methacrylate.

Since the amount of methyl methacrylate polymer used for plastic optical fibers is extremely small compared to the amount produced when it is used for general molding materials, use a polymerization vessel with a capacity that has the polymerization ability according to the spinning ability. If selected, a sufficient amount of fibers can be obtained by one polymerization.

If it is desired to spin a large number of fibers continuously, install two or more polymerization vessels to carry out the above-mentioned polymerization-discharge-
The above objects can be easily achieved by polymerizing by alternately using the two or more polymerization vessels so that the washing cycle is adapted to the spinning ability.

The high-quality methyl methacrylate-based polymer of the present invention obtained as described above is produced without long-term retention at high temperature as compared with the conventional complete homogeneous stirring and mixing type continuous bulk polymerization method. The production of coloring substances such as oligomers and coloring-causing substances is extremely small, and there is no scale adhesion or mixing, and therefore thermal deterioration in the spinning process is reduced.

Therefore, the plastic optical fiber of the present invention has a reduced absorption loss in the visible light region and no scale inclusion, and therefore has a reduced scattering loss and a high level of optical transmission efficiency, and is applicable to short-distance transmission systems. Allows you to dramatically expand the range.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the examples. For the light transmission efficiency, a halogen lamp is used as the light source, and the incident light intensity I _O and the output light intensity I of the plastic optical fiber per length L are calculated by the following equation: transmission loss (dB / km) =-10log (I / I It was evaluated by the transmission loss calculated by substituting it into _o ) / L.

Example 1 1 part of a monomer mixture 800 consisting of 100 parts of methyl methacrylate (parts by weight, the same applies hereinafter), 0.003 parts of azobiscyclohexanecarbonitrile and 0.15 parts of n-butyl mercaptan.
A 000-volume glass-lined polymerization vessel was charged all at once, and polymerization was carried out at 100 ° C. 13 hours after the start of the reaction, the polymer content reached 50% and the polymerization rate reached 2% / Hr.
Toluene was added at 15 kg / hr. The amount of added toluene decreased as the polymerization rate decreased.

On the other hand, the polymer solution was discharged from the polymerizer at 40 kg / Hr, supplied to a multistage belt extruder to remove residual monomers and residual solvent, and then introduced to a composite melt spinning device, which was used as a sheath resin for 2,2 , 3,3,3-Pentafluoropropyl methacrylate
Using a copolymer composed of 80% and methyl methacrylate 20%, composite melt spinning was carried out with a 16-hole nozzle at a spinning speed of 20 m / min to obtain a plastic optical fiber of the present invention.

When spinning was continuously performed for about 20 hours, about 400 km of 1 mmφ fiber was obtained. The transmission loss of the obtained fiber was 18ldB / km at 650nm.

Example 2 Polymerization was carried out under the same polymerization prescription conditions as in Example 1 except that only an additional solvent was changed as shown in Table 1, and the same pod resin and spinning conditions as in Example 1 were adopted to produce the plastic optical material of the present invention. I got a fiber. The transmission loss value is shown in Table 1.

Example 3 Polymerization was carried out in the same manner as in Example 1, and a composite melt was prepared by using a copolymer composed of 80% 1H, 1H, 2H, 2H-heptadecafluorodecyl methacrylate and 20% methyl methacrylate as a sheath resin. The plastic optical fiber of the present invention was obtained by spinning. The transmission loss of the obtained fiber was 176 dB / km at 650 nm.

Example 4 Three glass-lined polymerizers incorporating a line for switching the supply of the polymer solution to the multistage belt extruder were installed.

Methyl methacrylate 100 parts, azobiscyclohexanecarbonitrile 0.005 parts and n-butyl mercaptan 0.15
The monomer mixture 400 consisting of 1 part and 100 parts was charged all at once into the first polymerization vessel, and polymerization was carried out at 100 ° C. After 10 hours, the polymer content reached 50% and the polymerization rate reached 4% / Hr.
At 14 kg / Hr, the polymer solution was discharged at 40 kg / Hr and supplied to a multi-stage belt extruder to remove residual monomers and organic solvents, and then introduced to a composite melt spinning device and spun with a 16-hole nozzle. The plastic optical fiber of the present invention was obtained by spinning at a speed of 20 m / min.

10 hours after the start of polymerization in the first polymerization vessel (ie,
(When the polymerization rate in the polymerization vessel reaches 50% and spinning is started)
Into the second polymerization vessel, a monomer mixture containing the same monomer as described above, a polymerization initiator and a molecular weight modifier was charged and polymerization was initiated. Polymerization in the second polymerization reactor also reached a polymer content of 50% in about 10 hours, so the feed line was switched to feed the polymer solution to the multistage belt extruder, and spinning was continued. At that time, similar polymerization was started in the third polymerization vessel, the first polymerization vessel was washed, and the washing was completed within 10 hours.

In this way, using three polymerization vessels, the polymer solution was continuously supplied to the multistage belt extruder while repeating the operations of polymerization → washing → polymerization in each polymerization vessel, and spinning was continuously performed for about 100 hours. We carried out about 2000 km of 1 mmφ plastic optical fiber.

The used fluorinated resin is 80% 1H, 1H, 5H-octafluoropentyl methacrylate and 20% methyl methacrylate.
It was a copolymer of. The transmission loss of the obtained fiber is
It was 180 dB / km at 650 nm.

Claims (1)

[Claims] 1. A plastic optical fiber comprising a methyl methacrylate polymer as a core component and a fluorine-containing polymer as a sheath component, comprising a monomer mainly containing methyl methacrylate, a polymerization initiator and a molecular weight modifier. The resulting monomer mixture is polymerized in one polymerization tank, and the polymer content in the obtained polymer solution is 40 to 60% by weight.
At the time of reaching, the polymer solution was discharged while adding the non-polymerizable organic solvent so as to maintain the polymer content, and the residual monomer and the non-polymerizable organic solvent were removed to obtain methacrylic acid. A plastic optical fiber characterized by using a methyl acid polymer as a core component resin.