JPH0610683B2 - Plastic fiber optic fiber - Google Patents

Description

The present invention relates to a deuterated and fluorinated polymer or copolymer core, and a synthetic polymer sheath having a refractive index lower than that of the core. However, the present invention relates to a plastic optical fiber which has a low loss in the visible region to the near infrared region and has a small fluctuation in the light guide loss due to the moisture absorption of the core component polymer.

Conventional technology Conventionally, a core is formed of a synthetic polymer excellent in transparency represented by polystyrene or polymethylmethacrylate, and a concentric core whose synthetic polymer having a refractive index lower than that of the core component is a sheath component. A plastic optical fiber is well known in which a composite fiber is constituted by a sheath structure, and light incident on one end of the fiber is totally internally reflected along the length direction of the fiber to be transmitted.

Things to consider when forming this type of optical fiber are:
As the light is transmitted through the inside of the fiber, it is necessary to minimize the factors that enhance the extinction of the light due to absorption or scattering of the light.

An optical fiber using a synthetic polymer has the advantages of being lighter in weight and more flexible than an optical fiber made of a conventionally known inorganic glass, but compared with a glass optical fiber. There is a drawback that the transmission loss of light transmitted inside is large.

According to the knowledge of the present inventors, it has been found that the optical transmission loss of an optical fiber using a synthetic polymer is due to a harmonic of infrared vibration absorption between carbon and hydrogen constituting the synthetic polymer.

FIG. 1 shows the optical transmission characteristics of a plastic optical fiber manufactured by a conventionally known method with polymethyl methacrylate as a core and a fluororesin copolymer as a sheath. In the characteristics shown in FIG. 1, the 7th overtone of carbon-hydrogen infrared absorption appears at the wavelength of 544 nm, the 6th overtone appears at 622 nm, and the 5th overtone appears at 740 nm. Here, the absorption intensity decreases by about one digit each time the order of the overtone increases by one. However, because of the absorption of these absorptions, the optical transmission loss in the so-called loss window is large, and the wavelength of 65% is the minimum attenuation value.
Values of 250 dB / km at 0 nm, 220 dB / km at 570 nm, and 295 dB / km at 530 nm have been achieved. Therefore, it is theoretically possible to manufacture a low-loss plastic optical fiber by reducing or eliminating the carbon-hydrogen vibration absorption by some method.

Therefore, a possible solution is to replace hydrogen with deuterium to eliminate vibration absorption of carbon-hydrogen bond (C-H). Along with this, vibration absorption between carbon-deuterium bond (C-D) appears, but according to the findings of the present inventors,
Infrared vibration absorption between C and D is located on the far longer wavelength side than that between C and H. For example, the fifth overtone of infrared vibration absorption occurring in the visible to near infrared region is 740 nm in C and H. On the other hand, it is 990 nm for CD, and the sixth harmonic is 905 nm for CD with 622 nm for C-H.
It is located on the high wavelength side of about 280 nm. Furthermore, it has been clarified that the intensity of the C-D vibration absorption is smaller than that of the C-H vibration absorption even with the overtone of the same order.

From such a fact, it is possible to produce a plastic optical fiber having a window with extremely low loss, particularly in the visible to near infrared region, by replacing hydrogen in the synthetic polymer with deuterium. Can be expected.

As an example of substituting deuterium for hydrogen in a synthetic polymer, a plastic optical fiber having a resin obtained by substituting methyl methacrylate for deuterium and polymerizing the same has already been proposed (for example, US Pat. 4,138,194 or corresponding JP-A-54-65556). In this example, perdeuterated methyl methacrylate is bulk polymerized in the presence of a chain transfer agent and a polymerization initiator to obtain a core-forming polymer,
Wavelength of 690nm
It has achieved optical transmission loss values of 147 dB / km at 158 nm and 158 dB / km at 790 nm. These loss values are 220 at 570 nm, even with the best loss values of conventional conventional methylmethacrylate polymers.
Considering that it is above dB / km, we realized low loss,
Moreover, it has been shown that the wavelength range that can be transmitted can be expanded from the visible region to the near infrared region, and it can be said that the usefulness of the deuterium-substituted methyl methacrylate polymer has been demonstrated.

However, the methyl methacrylate polymer is relatively hygroscopic, and has a moisture absorption rate of 0.3 to 0.4% even at room temperature for about 24 hours [Modern Plastic Encyclopedia] (see 1968), The same applies to deuterated polymers in this respect.

Vibration absorption between oxygen-hydrogen bonds (O-H) due to moisture absorption is a problem even in an optical fiber made of inorganic glass, but in an organic polymer compound, a harmonic window of O-H vibration absorption occurs in a loss window. The influence of waves often appears, and the presence of a small amount of water also deteriorates the optical transmission characteristics especially in the near infrared region. For this reason, even if a low loss plastic optical fiber is manufactured by deuteration, there is a problem that the light guiding property fluctuates with a change in humidity under the operating environment conditions (Po.
lym. See Preprints Japan, Vo132, No.4, P810, 1983).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above in detail, the conventional plastic optical fiber has a large vibration absorption in the material, for example, between C—H bonds, and therefore is important as a transmission characteristic of the optical fiber. The requirements for broadband and low loss properties were not sufficiently satisfied.

On the other hand, the above characteristics can be improved by substituting deuterium for hydrogen in plastics. However, deuterated plastics known so far have a high hygroscopic property, so that loss due to hygroscopicity from the use environment is caused. It is known that the effect of vibration absorption of O-H appears in the window of the above, and even if a small amount of water is present, the optical transmission characteristics in the near infrared region are deteriorated even though the band is widened. .

The present invention has been made in view of the current situation of such a conventional plastic optical fiber, and an object thereof is to have a core-pod structure having extremely excellent optical transmission characteristics in the visible region to the near infrared region. Another object of the present invention is to provide a low-loss plastic optical fiber that is less affected by OH vibration absorption accompanying moisture absorption.

Means for Solving the Problems As a result of various studies and studies for achieving the above object, the present inventor has found that a polymer of a specific deuterated and fluorinated monomer or a copolymer of the monomer and a vinyl monomer. It was found that it is extremely effective to use the coalescence as a core material,
The present invention has been completed.

That is, the plastic optical fiber of the present invention has a structural formula: The polymer obtained by radically bulk polymerizing trifluoromethyl pentadeuteromethacrylate represented by is used as a core component, and the fluorinated polymer or copolymer having a refractive index of 1.405 or less is used as a sheath component. To do.

According to another aspect, the plastic optical fiber of the present invention comprises 90 to 99.5 mol% of trifluoromethyl pentadeuteromethacrylate and 0.5% of vinyl monomer for copolymerization.
The core component is a copolymer obtained by radical copolymerization with 10 to 10 mol%, and the core component with respect to the sum of the number of carbon-hydrogen bonds, the number of carbon-deuterium bonds and the number of carbon-fluorine bonds in the core component. The ratio of the number of carbon-hydrogen bonds in the inside is less than 10%, and the sheath is formed of a fluoropolymer or copolymer having a refractive index of 1.405 or less.

Action Trifluoromethylpentadeuteromethacrylate as a monomer, which is a raw material for the core of the optical fiber in the present invention, is obtained by the reaction of perdeuteroacetone and HCN to obtain deuterated acetone cyanohydrin, which is treated with sulfuric acid After treatment to produce deuterium methacrylic acid imide sulphate, and further by reaction with water to synthesize deuterated methacrylic acid,
It can be obtained by reacting deuterated methacryloyl chloride obtained by treatment with phosphoric acid with trifluoromethanol, but those obtained by adopting other synthetic methods can also be used.

The deuteration ratio of the vinyl position and the α-methyl group in the polymer serving as the core of the optical fiber in the present invention needs to be 90% or more, and the fluorination ratio of the ester position methyl position in the polymer is also 90%. % Or more is required. That is, when the deuteration rate at the vinyl position and the α-methyl position and the fluorination rate at the ester position methyl position in trifluoromethyl pentadeuteromethacrylate are less than 90%,
The effect of vibration absorption due to C—H bond in the polymer becomes large, and there is a possibility that the effect of reducing O—H vibration absorption, which will be described later, which is brought about by the suppression of moisture absorption of the optical fiber based on the introduction of fluorine, may not be remarkable. .

The core polymer used in the present invention can also be formed from a copolymer of trifluoromethylpentadeuteromethacrylate monomer containing 0.5 to 10 mol% of vinyl monomer for copolymer. In this case, the number of carbon-hydrogen bonds in the core component copolymer, the number of carbon-deuterium bonds, and the number of carbon-
It is preferable that the ratio of the number of carbon-hydrogen bonds in the core component copolymer to the total of the number of fluorine bonds is less than 10% in order to obtain excellent light transmission characteristics. By using the core polymer as a copolymer in this manner, flexibility and mechanical strength are increased as compared with a homopolymer of trifluoromethyl pentadeuteromethacrylate. Here, when the above-mentioned copolymer having a carbon-hydrogen bond ratio of 10% or more is used, the influence of C—H vibration absorption in the copolymer is large, and the optical fiber based on the introduction of fluorine is used. O-H caused by suppression of moisture absorption
The effect of reducing vibration absorption may not be remarkable, which is not desirable.

As the vinyl monomer for copolymerization, methyl acrylate,
Ethyl acrylate, n-propyl acrylate, n-
Butyl acrylate, iso-butyl acrylate, tert
-Acrylic acid esters such as butyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, iso-propyl methacrylate,
Methacrylic acid esters such as n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, lauryl methacrylate, nonyl methacrylate, benzyl methacrylate, styrene, α-
Examples thereof include styrene derivatives such as methylstyrene, fluorostyrene, chlorostyrene and bumorostyrene, and deuterated or fluorinated compounds thereof.

In obtaining the polymer of the core component in the present invention, it is not preferable to use a method such as suspension polymerization, emulsion polymerization or solution polymerization. The reason is that, in suspension polymerization or emulsion polymerization, although a high-purity polymer can be obtained as an industrial method, a large amount of water is used, and therefore foreign matter in water may be mixed in the polymer. When these foreign substances are mixed, the incident light is scattered, which is an obstacle to obtaining an optical fiber with low loss. In addition, since solvent is used also in solution polymerization, impurities or foreign matter in the solvent may be mixed, and a process such as foreign matter separation is required. Therefore, in the present invention, a polymer is formed by bulk polymerization of the core component monomer.

In producing the plastic optical fiber of the present invention, in a closed system, a polymerization initiator and a chain transfer agent are added by distillation to trifluoromethylpentadeuteromethacrylate monomer distilled under reduced pressure conditions, and then the reduced pressure state is maintained. It is preferable to use a trifluoromethylpentadeuteromethacrylate polymer obtained by polymerization while maintaining the above as the core component in order to obtain a plastic optical fiber with low loss. Further, it is desirable to obtain a core fiber by polymerizing the trifluoromethyl pentadeuteromethacrylate monomer in such a closed system and then melt-spinning the obtained core polymer while maintaining the closed state. As a result, not only dust and impurities are not mixed into the core polymer, but also generation of minute voids is suppressed. Further, since no dust is mixed in at the time of spinning the polymer, it becomes possible to obtain a plastic optical fiber in which scattering loss is significantly reduced.

From the above points, it is desirable that the polymerization initiator used in the present invention can be easily distilled under reduced pressure. Examples of such a polymerization initiator include azo-tert-butane and azo-n.
-Butane, azo-iso-propane, azo-n-propane, azo-cyclohexane, and other alkylazo compounds, or di-tert-butylperoxide, dicumylper
Examples thereof include organic peroxides such as oxide and cumene hydroxyperoxide. Among such radical polymerization initiators, an alkylazo compound can be particularly preferably used because the tail of absorption such as electronic transition absorption in the ultraviolet region of the polymerization initiator hardly affects the visible region.

It is also desirable that the chain transfer agent can be easily distilled under reduced pressure. Suitable chain transfer agents are mercaptans such as n-butyl and n-butyl.
First mercaptan such as propyl, sec-butyl, second mercaptan such as isopropyl, tert-butyl, tert
-Tertiary mercaptans such as hexyl or aromatic mercaptans such as phenylmercaptan.

In the present invention, when melt-spinning the core polymer, the core polymer polymerized at a glass transition temperature or higher of the trifluoromethyl pentadeuteromethacrylate polymer is melt-spun without lowering the temperature below the glass transition temperature. By supplying the optical fiber to the device, an optical fiber having a small scattering loss can be obtained without generating internal strain and generating minute voids due to the volume change of the polymer during spinning.

The sheath component used in the present invention is a synthetic polymer having a refractive index of 1.405 or less. The synthetic polymer has, for example, a general formula: In the formula, R _f represents a fluoroalkyl group having 10 or less carbon atoms, a homopolymer of fluoroalkyl methacrylate represented by, or a copolymer of two different fluoroalkyl methacrylates, fluoroalkyl methacrylate and another vinyl Monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-
Butyl methacrylate, tert-butyl methacrylate,
Examples thereof include benzyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, tert-butyl acrylate, and copolymers thereof with fluorides. Further, with these homopolymers and copolymers, other polymers and copolymers such as vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene terpolymer, etc. And a mixture with. In particular, two kinds of fluoroalkyl methacrylate copolymers having different fluoroalkyl groups are suitable. In this case, a plastic optical fiber having particularly excellent light transmittance is formed by using a copolymer in which fluoroalkyl methacrylate having excellent adhesiveness is combined with fluoroalkyl methacrylate having relatively high heat distortion temperature. It is possible.

By using a composition in which a fluoroalkyl methacrylate-methyl methacrylate copolymer is melt-mixed with vinylidene fluoride-tetrafluoroethylene copolymer as a mixture, it is possible to obtain a plastic optical fiber having excellent light transmittance. Is.

Here, when a homopolymer of a fluoroalkyl methacrylate monomer is used as a sheath component, the proportion of total fluorine in the molecular weight of the monomer is preferably 40% or more. When the proportion of total fluorine is less than 40%, it becomes difficult to obtain a sufficient relative refractive index difference from the core component.

When the refractive index of these sheath component polymers or copolymers, or polymer mixtures exceeds 1.405, the numerical aperture of the obtained plastic optical fiber becomes smaller as it becomes less than 0.25. Since the values do not differ, the advantages of high numerical aperture of the plastic optical fiber and high coupling efficiency with the light source cannot be obtained.

FIG. 2 is a sectional view showing the structure of the plastic optical fiber 1 of the present invention, which is composed of a core 2 and a sheath 3 in the central portion.

As described in detail above, in the plastic optical fiber of the present invention, the methyl group of the ester part is perfluorinated and other hydrogen (vinyl position and α-methyl position) is present.
Is a polymer obtained by radical bulk polymerization from a deuterium-substituted monomer, or a copolymer of a similar monomer and a vinyl monomer, the carbon-hydrogen bond content of which is less than or equal to a predetermined value. Was used as the core material, and the fluorinated polymer or copolymer having a refractive index of 1.405 or less was used as the sheath material.

Such a material makes it possible to solve the problems due to the hygroscopicity found in conventionally known synthetic polymers, that is, those obtained by substituting deuterium for hydrogen in the polymer. That is, it is possible to obtain a plastic optical fiber that is effective over a wide band from the visible region to the near-infrared region and that exhibits good optical transparency even when near-infrared light is used as a light source.

Examples Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. A tungsten-halogen lamp was used as a light source for measuring the optical transmission characteristics of the optical fiber, and a transmission attenuation factor was obtained using a diffraction grating spectroscope. In addition, the optical fiber was allowed to stand under high temperature and high humidity conditions, and the increase in loss value due to moisture absorption of the optical fiber was determined by measuring the transmission attenuation factor.

Example 1 0.01 mol / tert-butylperoxide as an initiator and 0.01 mol / mol as a chain transfer agent were added to a trifluoromethylpentadeuteromethacrylate monomer in a closed-type polymerization apparatus substantially free of oxygen. N-butyl mercaptan was added and mixed well, and then bulk polymerization was carried out at 120 ° C for 12 hours, and then gradually heated to increase the polymerization rate, and finally at 160 ° C for 6 hours. Upon completion, a core component polymer was obtained. The refractive index of this polymer was 1.427. On the other hand, as a sheath component, 1H, 1H, 5H-octafluoropentyl methacrylate polymer was used and melt spinning was performed with a core polymer using a composite spinneret, and the core diameter was 0.6 m.
An optical fiber having a thickness of m and a sheath component of 0.05 mm was obtained. The optical transmission characteristics of this optical fiber are shown in Table 1. Wavelength 680nm, 790n
m and 870nm low loss windows, 50dB / km, 60dB / km,
The attenuation was 100 dB / km, and an optical fiber having a loss value of 100 dB / km or less was obtained over the visible to near infrared region. The optical fiber having this trifluoromethyl pentadeuteromethacrylate core was left standing for 2 days and night under the temperature and humidity conditions of 60 ° C. and 90% RH, and then taken out to measure the optical transmission characteristics immediately. As shown in Table 1, the increase in loss after moisture absorption was extremely small at a wavelength of 680 nm.

Example 2 In Example 1, a mixture of 97 mol% of trifluoromethyl pentadeuteromethacrylate and 3 mol% of methyl acrylate was used as a monomer, and 1H-hexafluoroisopropyl methacrylate polymer was used as a sheath component. Composite spinning was performed in the same manner as in Example 1 except that the fiber was used, and an optical fiber having a core diameter of 0.5 mm and a sheath component film thickness of 0.05 mm was obtained. The optical transmission characteristics of this optical fiber and the increase in loss after moisture absorption are as shown in Tables 1 and 2, and it was a plastic optical fiber having excellent characteristics.

Example 3 A monomer in Example 1 in which the trifluoromethyl group of the trifluoromethyl pentadeuteromethacrylate monomer has a fluorination ratio of 95% and the deuteration ratios of vinyl and α-methyl positions are 90%. Using the body, as a pod ingredient, 1H, 1
A copolymer of 80 mol% of H, 5H-octafluoropentyl methacrylate and 20 mol% of methyl methacrylate,
Vinylidene fluoride 70 mol% and tetrafluoroethylene 30
In addition to using a composition obtained by melt-mixing 50% by weight of a copolymer with mol%, composite spinning was performed in the same manner as in Example 1, and the diameter of the core was 0.6 mm and the film of the sheath component was used. An optical fiber with a thickness of 0.05 mm was obtained. The optical transmission characteristics and the increase in loss after moisture absorption are as shown in Tables 1 and 2, and it was a plastic optical fiber having excellent transparency.

Comparative Example 1 In Example 1, perjuteromethyl metaflate was used as a monomer, and 0.01 mol / azo-tert- was used as an initiator.
Using butane and 0.025 mol / -butyl mercaptan as a chain transfer agent, bulk polymerization was carried out at 135 ° C for 12 hours, then the temperature was gradually raised to finally complete the polymerization at 180 ° C for 8 hours to complete the core component. The polymer is obtained, and as a sheath component, 1H, 1H,
5H-octafluoropentyl methacrylate 80 mol%,
1H, 1H, 3H-Tetrafluoropropyl methacrylate 20
Composite spinning was performed in the same manner as in Example 1 except that the mol% copolymer was used, and the diameter of the core was 0.6 mm and the thickness of the sheath component was 0.1.
An optical fiber of mm was obtained. The optical transmission characteristics of the optical fiber having the deuterated methyl methacrylate polymer as the core are excellent as shown in Table 1, but after absorbing moisture, as shown in Table 2, as shown in Table 2, Due to the influence, there was an extremely large increase in loss, and it was found that it is difficult to use especially in the near infrared region.

Comparative Example 2 Composite spinning was performed in the same manner as in Example 1 except that a mixture of 80 mol% trifluoromethylpentadeuteromethacrylate and 20 mol% methyl acrylate was used as the monomer in Example 1. An optical fiber having a core diameter of 0.5 mm and a sheath component film thickness of 0.05 mm was obtained. The optical transmission characteristics of this optical fiber and the loss increase after moisture absorption are shown in Table 1 and Table 2, respectively. It is clear that as the light attenuation increases, the moisture absorption suppressing effect also decreases.

Comparative Example 3 In Example 1, a monomer having a deuteration rate of 80% at the vinyl and α-methyl positions of the trifluoromethyl pentadeuteromethacrylate monomer was used, and 1H-hexafluoroisopropyl was used as the sheath component. Composite spinning was performed in the same manner as in Example 1 except that the methacrylate polymer was used to obtain an optical fiber having a core diameter of 0.5 mm and a sheath component film thickness of 0.05 mm. The optical transmission characteristics of this optical fiber and the loss increase after moisture absorption are as shown in Table 1 and Table 2, respectively, and although the characteristic fluctuation after moisture absorption was small, the light transmittance was not good.

Effects of the Invention As described above, the plastic optical fiber according to the present invention has extremely excellent optical transmission characteristics in the visible region to the near-infrared region as compared with the conventional plastic optical fiber, and is exposed to high temperature and high humidity conditions. However, since the increase in loss is extremely small, there is an advantage that even if a light source in the near infrared region is used as an optical signal transmission medium for a distance of several hundred meters, it can be stably used. In addition, since the light transmittance at wavelengths around 680 nm, which is the red light region, is also extremely stable, inexpensive visible light emitting diodes such as GaAlAs (LE
There is an advantage that an optical signal transmission system excellent in economic efficiency can be constructed by using D).

[Brief description of drawings]

FIG. 1 is a graph showing measurement results of light transmission characteristics in the visible region of a low-loss plastic optical fiber manufactured by a conventional method, and FIG. 2 is a sectional view of the plastic optical fiber of the present invention. (Main reference numbers) 1 ... optical fiber, 2 ... core, 3 ... sheath

Claims (4)

[Claims] 1. In a plastic optical fiber having a core and a sheath made of a synthetic polymer, the deuteration ratio at the vinyl position and the α-methyl position is 90% or more, and the fluorination ratio at the ester position methyl position is at least 90%. The core is formed by deuterated methyl fluorinated methacrylate polymer obtained by radical bulk polymerization of methyl methacrylate monomer which is 90% or more, and by the fluorine-containing polymer or copolymer whose refractive index is 1.405 or less. A plastic optical fiber, characterized by forming the sheath. 2. The pod has the general formula: In the formula, R _f represents a fluoroalkyl group having 10 or less carbon atoms, and among the monomers represented by, the main component is a monomer in which the proportion of total fluorine in the molecular weight of the monomer is 40% or more. The plastic optical fiber according to claim 1, which is a polymer. 3. A plastic optical fiber having a core and a sheath made of a synthetic polymer, having a structural formula: 90 to 99.5 mol% of the monomer represented by the following, and the core is formed by a copolymer of 0.5 to 10 mol% of a vinyl monomer for copolymerization, and the number of carbon-hydrogen bonds in the core component copolymer The ratio of the number of carbon-hydrogen bonds in the core component copolymer with respect to the sum of the number of carbon-deuterium bonds and the number of carbon-fluorine bonds is less than 10%, and the sheath has a refractive index of 1.405 or less. A plastic optical fiber formed of a fluoropolymer or a copolymer. 4. The pod is a polymer whose main component is a fluoroalkyl methacrylate monomer having 10 or less carbon atoms, in which the proportion of total fluorine in the molecular weight of the monomer is 40% or more. Claim 3 characterized in that
The plastic optical fiber according to the item.