JP2841119B2 - Plastic optical fiber and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a plastic optical fiber capable of transmitting light over a long distance of 500 m or more and also having flame retardant properties.
More particularly, the present invention relates to a plastic optical fiber having a handling characteristic that does not cause separation of a core-sheath interface even when it is bent.

[Conventional technology]

As an optical fiber that has been conventionally developed, an inorganic glass-based optical fiber that can perform excellent light transmission over a wide wavelength range is known, but this optical fiber has poor workability and weak bending stress. As an optical fiber having better processability, an optical fiber based on plastic has been developed and put into practical use.

This plastic optical fiber is a polymethyl methacrylate (hereinafter referred to as PM) having a large refractive index and good light transmittance.
MA), a core material made of a polymer such as polycarbonate (hereinafter referred to as PC), and a sheath material (clad) made of a polymer such as a fluorine-containing polymer having a smaller refractive index than that of the polymer. There is a core clad type optical fiber (optical fiber element wire) as a basic structural unit, and a bulk fiber in which a functional protective layer is provided on the optical fiber element, and an optical fiber code in which the optical fiber element is covered with a jacket material. , And an aggregate fiber that is an aggregate of bulk fibers,
Further, an optical fiber cable in which a tension member or the like is provided in a bulk optical fiber is known.

[Problems to be solved by the invention]

However, these conventionally developed all-plastic optical fibers have a structure in which the polymer constituting the core contains C-
It has a large number of H bonds, light absorption due to expansion and contraction and vibration of the C—H bond is present in the low wavelength region, and its fifth to eighth harmonics are also present in the near infrared and visible regions, that is, in the wavelength region of 400 nm or more. However, optical transmission loss in this wavelength region has been a major cause. For example, a transmission loss due to light absorption based on C—H bonds of an optical fiber having polymethyl methacrylate as a core is 65%.
About 100 dB / Km at 0 nm wavelength, about 100 dB / Km at 780 nm wavelength
400dB / Km. H in polymethyl methacrylate
The light transmission loss of the optical fiber to the d _8-PMMA was replaced with atomic deuterium and core are in 780nm wavelength and 50 dB / Km, the optical fiber is d _8-PMMA high water absorption of this type Because of this, the core absorbs water over time, and the optical transmission loss increases with time.

LEDs that emit light in the near-infrared region and are capable of high-speed data transmission with high output are manufactured at low cost and in large quantities, but all plastic optical fibers that have been developed conventionally use these near-infrared light emitting devices. Since a possible LED cannot be used as a light source for optical communication, it is difficult to transmit light over 100 m with a single optical fiber, and the development of a LAN using a plastic optical fiber has been delayed. Therefore, in recent years, the development of plastic optical fibers capable of transmitting light in the near-infrared region has been studied. For example, EP340557 (JP-A-1-314206) and EP340555 (JP-A-2-12206) have been studied.
Japanese Patent Application Laid-Open No. H11-163,867 discloses an invention of an optical fiber having a fluoroalkyl ester polymer of α-fluoroacrylic acid as a core and a sheath of vinylidene fluoride-tetrafluoroethylene copolymer. Although this optical fiber can transmit light having a wavelength in the near-infrared region, the difference in the refractive index between the polymer for forming the core and the polymer for forming the sheath cannot be increased. It becomes an optical fiber, which is not sufficient as an optical fiber capable of transmitting a large amount of data. In addition, this type of low aperture angle optical fiber cannot prevent light from leaking from the side surface of the optical fiber due to bending, and is still insufficient as an optical fiber for data transmission. Furthermore, since the vinylidene fluoride-tetrafluoroethylene polymer is not a complete amorphous polymer, it has slight light absorption and light diffuse reflection characteristics, and the all-plastic optical fiber sheathed with the polymer has the light transmission characteristics. Is not always enough.

[Means for solving the problem]

The present inventors have studied to find an all plastic optical fiber that can solve the above problems, and as a result, have completed the present invention. The gist of the present invention is that α, β represented by the following formula (1): A polymer having a refractive index of n ₁ having a fluorine-containing alkyl ester of an unsaturated monocarboxylic acid as a main component, and having perfluoro (2,2-dimethyl-1,3-dioxole) and at least one other monomer; the copolymerizable ethylenically unsaturated monomer, and a copolymer of a and polymers having a lower refractive index n ₂ than the polymer constituting the core and the sheath, n ₁ -
A core-sheath type optical fiber satisfying the condition of n ₂ ≧ 0.01,
An all plastic optical fiber having a protective layer on its outer periphery.

Wherein X is H, CH ₃ , D, F, Cl or CF ₃ , Y is H or D, R
f represents a linear or branched fluoroalkyl group The polymer constituting the core of an all plastic optical fiber that has been conventionally developed has a large number of C--H bonds in its molecule, so that its transmission loss is large. It cannot be used for long-distance transmission of 1 km or more. On the other hand, the core polymer used in the present invention is composed of molecules having a large amount of fluorine containing a small number of C—H bonds and a large number of C—F bonds. The light absorption loss caused by the above can be greatly reduced. Also, by increasing the fluorine content in the core polymer, the water absorption was extremely small, and therefore, the light absorption by the water absorption of the optical fiber having the polymer as the core could be reduced. When the fluorine content in the core polymer molecule increases, the refractive index of the polymer decreases, and it becomes difficult to select a sheath material.However, the present inventors have proposed a transparent sheath material having a low refractive index as a transparent sheath material. It has been found that copolymers of fluoro (2,2-dimethyl-1,3-dioxole) and at least one other ethylenically unsaturated monomer can be used.

The core polymer used in carrying out the present invention has the following general formula (1) (Where X, Y, and Rf are the same as above), or a copolymer with another comonomer.

Specific examples of the monomer represented by the formula (1) include acrylates in which Rf is a fluoroalkyl group or a perfluoroalkyl group, α-fluoroacrylates, α-chloroacrylates, or methacrylates. As the Rf group,-(CH ₂ ) _m (CF ₂ ) _n Z (m is an integer of 0 to 2,
Is an integer of 1 to 12, Z represents H or F), a linear fluoroalkyl group represented by —CH ₂ C (CF ₃ ) ₂ A (where A is H, D,
F, although aliphatic or an alicyclic alkyl group or an aromatic group) or _{-C (CF 3) 2 A (} A can be given the same) and the like, but is not limited to these monomers .

The core polymer may contain at least 30 mol% or more, preferably 75 mol% or more of the monomer unit represented by the general formula (1). Since the polymer having a monomer unit content of less than 30 mol% has an increased amount of C—H bonds and a high water absorption, an optical fiber having the polymer as a core has good optical transmission characteristics. It is difficult to make a good optical fiber. Other monomers copolymerizable with the monomer of the general formula (1) include methacrylates whose ester groups are methyl ester, ethyl ester, butyl ester, t-butyl ester, cyclohexyl ester, phenyl ester, isobornyl ester, and the like. Or acrylates, maleimide, phenyl amide amide, acrylic acid, methacrylic acid, itaconic acid, styrene, α-methylstyrene, p-
Chlorstyrene, acrylonitrile, vinyl acetate and the like can be mentioned.

The core polymer used in practicing the present invention is intended to improve the light transmission characteristics of an optical fiber having the polymer as a core, so that foreign substances contained therein can be easily passed, and In order to improve the flexibility, it is preferable that the glass transition temperature is 150 ° C. or less, particularly, 140 ° C. to 0 ° C. An optical fiber having a polymer with good over-characteristics of such foreign matter as a core is an optical fiber having an extremely low loss, and is excellent in flexibility and handling properties, and is used for optical communication such as LAN, FA, etc. It can be used as an optical fiber.

Foreign matter having a diameter of 0.5 μm or more contained in the core-forming polymer significantly lowers the optical transmission characteristics of an optical fiber having the polymer as a core, and is used as an optical fiber for transmitting light of 1 km or more. Is not good. The content of foreign substances in the polymer is preferably 10,000 or less per gram of polymer. In order to produce a polymer having a low foreign substance content, it is preferable to purify a polymerization catalyst, a monomer, a molecular weight controlling material, a polymerization medium, and the like to be used by a distillation method, an excess method using a membrane filter, a sublimation purification method, or the like. The polymerization is preferably performed in a closed system in a dust-free state. Furthermore, when spinning the polymer, it is also an excellent method to pass through a sintered body filter in advance.

The amount of foreign substances contained in the polymer is
A 1% by weight solution is prepared as a sample, and 1 g of this sample is weighed with a liquid fine particle counter (HIAC / ROYCO Liguid Fine Particle Co., Ltd.).
unter: manufactured by HIAC / ROYCO Co., Ltd.) to determine the number of fine particles contained therein.

Refractive index of core polymer used in carrying out the present invention
Na is relatively low at 1.33 to 1.46. Therefore, the refractive index Nb of the sheath-forming polymer used in carrying out the present invention is
1.29 to 1.35, and Na-Nb ≧ 0.01 preferably
The polymer must satisfy the condition of 0.03 or more.

The sheath polymer which can be preferably used in practicing the present invention is perfluoro (2,2-dimethyl-1,3-dioxole).
And other copolymerizable ethylenically unsaturated monomers. The perfluoro (2,2-dimethyl-1,3-dioxol) used in carrying out the present invention can be synthesized, for example, by the method described in U.S. Pat. No. 3,865,845. The copolymer can be produced, for example, by the method described in US Pat. No. 3,978,030.

Examples of the ethylenically unsaturated monomers copolymerizable with perfluoro (2,2-dimethyloxol) include, for example, ethylene, propylene, isobutylene, butene-1, methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, CF ₂ = CF ₂ , CHF = C
F ₂ , CH ₂ = CF ₂ , CH ₂ = CHF, CCl = CF ₂ , CHCl = CF ₂ , CCl ₂
= CF ₂ , CClF = CCIF, CHF = CCl ₂ , CH ₂ = CClF, CCl ₂ = CCl
F and other fluoropropylene compounds such as CF ₃ CF = CF ₂ , C
F ₃ CF = CHF, a monomer having a functional group such as perfluoro (alkyl vinyl ether), methyl-3-
{1- [difluoro [(trifluoroethenyl) oxy] methyl] -1,2,2,2-tetrafluoroethoxy}-
2,2,3,3-tetrafluoropropanoate, 2- {1-
(Difluoro [(trifluoroethenyl) oxy] methyl) -1,2,2,2-tetrafluoroethoxy} -1,1,2,2-
Tetrafluoroethanesulfonyl fluorite and the like can be mentioned as specific examples.

The sheath polymer needs to be an amorphous polymer having a refractive index of 1.29 to 1.35 and having high transparency. In order to obtain a sheath-forming polymer having such properties, the polymerization ratio of perfluoro [2,2-dimethyl-1,3-dioxol] is 20 to 100 mol%, preferably 25 to 99.7 mol%. It is good to be in the range of.

To improve the thermal fluidity of the sheath-forming polymer while maintaining its toughness, a polymer of perfluoro [2,2-dimethyl-1,3-dioxole] having a number average molecular weight of 15,000 or more is used. It is preferable to add a plasticizer having a plasticizing effect and a plasticizer having a number average molecular weight of 10,000 or less, that is, a perfluoroalkyl ether in a proportion of 1 to 50% by weight, preferably 5 to 30% by weight based on the polymer. This plasticizer has a very low leaching phenomenon, and is preferable in the practice of the present invention. Specific examples thereof include perfluoroalkyl ethers such as CF ₂ CF ₃ , tetrahydrofuran, and perfluoroalkyl oxols.

The plastic optical fiber of the present invention has a feature that a protective layer is provided on the outer layer of the core-sheath structure. The core and the sheath have some difficulty in the adhesion, and the interface between the two does not peel at a degree of bending, but when a mechanical impact or ironing is applied, the sheath peels off and the light transmission property is impaired. This is a major disadvantage of plastic optical fibers, which greatly impairs good workability, which is a major feature of plastic optical fibers.

The optical fiber of the present invention was able to greatly improve the flexibility of the optical fiber by providing a protective layer on the outer layer of the sheath. The polymer for forming a protective layer used in carrying out the present invention is preferably a polymer having a breaking elongation of 10% or more.
For example, acrylonitrile-butadiene-styrene copolymer (elongation at break: 40%), styrene-butadiene copolymer (100%), ethylene-vinyl alcohol copolymer (200%), ethylene-vinyl chloride copolymer (170)
%), Ethylene-vinyl acetate copolymer (800
%), Ionomer (370%), polymethylpentene (10%), polyethylene (600%), polypropylene (60%), ethylene-α-olefin copolymer (50%)
0%), polycarbonate (100%), polyamide (100%)
100%), polyoxymethylene (60%), polyethylene terephthalate (350%), polybutylene terephthalate (350%), polyurethane (500%), impact-resistant polystyrene (60%), polyvinylidene chloride (150%), polyacrylate (50%), polyethersulfone (60%), polyphenylene oxide (60%), polysulfone (60%), various thermoplastic elastomers (500-700) %), Polyvinylidene fluoride or its copolymer (200-400%), long-chain fluoroalkyl methacrylate polymer (20%), fluoroalkyl acrylate polymer (300%), α-fluoroalkyl acrylate polymer (20%), polychlorotrifluoroethane or a copolymer thereof (100-200%)
%), An alkyl acrylate polymer (700% of the same), a long-chain alkyl methacrylate (50% of the same), a crosslinked epoxy acrylate, a urethane acrylate, and the like, but are not particularly limited thereto. The thickness of the protective layer is preferably from 1 μm to 100 μm. An optical fiber with a protective layer thickness of less than 1 μm is not flexible enough, and when bent, the sheath is liable to peel off. The core occupation ratio of the optical fiber is reduced, and the amount of light incident on the optical fiber is limited, so that the characteristics of the optical fiber for optical communication are impaired. Further, in order to erase the noise due to light (Kuratsudo mode) propagating in Kuratsudo, the refractive index n ₃ is n ₃ -n ₂ ≧ 0 between the refractive index N ₂ of the sheath material polymeric protective material polymers.
It is better to satisfy the condition of 05.

As a method for producing the plastic optical fiber of the present invention, a method of forming the optical fiber of the present invention comprising a core-sheath-protective layer by a concentric three-layer composite melt spinning method, and firstly, a concentric two-layer composite melt spinning method A core-sheath structure is formed, and a method of coating the outer layer with a solvent coating or a protective layer with light or thermosetting protective material or melt-spinning the core fiber is used.・ A method of coating one layer at a time with a coating or light and thermosetting resin, or a method of forming a core-sheath structure by concentric two-layer composite melt spinning and further melting and coating a protective layer on the outer periphery. A method of forming the core and the sheath with a concentric three-layer composite melt spinning in order to secure the productivity, reduce the variation in the diameter of the obtained optical fiber, and ensure the uniformity of the variation in transmission loss. Particularly preferred.

〔The invention's effect〕

According to the present invention, it is a plastic optical fiber capable of transmitting light of 1 km or more, and an optical fiber with extremely good handling properties is obtained, and LA which is considered impossible in the past
The present invention exhibits a great feature that the optical fiber such as N and FA can be constructed.

 Hereinafter, the present invention will be described in more detail with reference to examples.

〔Example〕

Example 1 All the monomers used were sufficiently purified according to a conventional method and used immediately after distillation.

A mixture obtained by adding 0.15% by weight of n-octyl mercaptan and 30 ppm of di-tert-butyl peroxide to 100 parts of a monomer mixture composed of 70 mol% of trifluoroethyl methacrylate and 30 mol% of methyl methacrylate was added to a tetramer having a thickness of 0.02 μm. The mixture was filtered through a fluoroethylene membrane filter and polymerized at 150 ° C. under N ₂ pressure for 5 hours to obtain a syrup having a polymerization rate of 47%. The syrup was continuously supplied to a devolatilizing extruder, and the residual monomer content was 0.5%. 210 ° C for the following polymer
The core was supplied to the core supply section of the spinning machine heated in the above. The obtained polymer has a glass transition temperature of 96 ° C (measured by DSC) and a refractive index.
It was 1.424. On the other hand, perfluoro (2,2-dimethyl-
1,3-dioxole) / tetrafluoroethylene = 50/50
The mol% of the copolymer was melted by a melt extruder and supplied to the sheath material supply section of the spinning machine. The obtained polymer had a glass transition point of 110 ° C. and a refractive index of 1.308.

Further, a copolymer composed of 80 mol% of vinylidene fluoride and 20 mol% of tetrafluoroethylene was melted by a melt extruder and supplied to the protective material supply section of the spinning machine. The obtained polymer had a refractive index of 1.403. An optical fiber having a core diameter of 980 μm, a sheath thickness of 5 μm, a protective thickness of 5 μm, and an outer diameter of 1 mmφ was obtained with a core-sheath-protection structure using a three-layer composite spinning nozzle in a spinner.
The transmission loss of the obtained optical fiber is 97 dB / K at 650 nm.
m, 3650 dB / Km at 770 nm and 813 dB / Km at 950 nm, which were very small. After the obtained optical fiber was allowed to stand for 24 hours under the moist heat condition of 50 ° C. and 95% RH, the transmission loss of the optical fiber was 386 dB / Km at 770 nm, showing little increase in the transmission loss. In addition, when the obtained optical fiber was wrapped around a 10 mmφ rod, there was no appearance deterioration such as peeling of the sheath,
It had excellent mechanical strength.

Comparative Example 1 An optical fiber having a core diameter of 990 μm and a sheath thickness of 5 μm was obtained by a core-sheath type two-layer composite spinning method using the same polymer for forming the core and the sheath as in Example 1. The transmission loss of the obtained optical fiber was very small at 95 dB / Km at 650 nm, 378 dB / Km at 770 nm, and 820 dB / Km at 950 nm.However, when the fiber was wound on a rod of 100 mmφ, the sheath was peeled off. It was something that was irrelevant to sex.

Example 2 All the monomers used were sufficiently purified according to a conventional method and used immediately after distillation.

A film of a monomer mixture obtained by adding 0.3 parts by weight of n-octyl mercaptan and 18 ppm of di-tert-butyl peroxide to 100 parts by weight of α-fluoro 1,1,1,3,3,3-hexafluoroisopropyl acrylate Filtered with a 0.02μ tetrafluoroethylene membrane filter, 150 ° C N
₂ Polymerization under pressure for 3 hours to obtain a syrup having a polymerization rate of 54%. This syrup is continuously supplied to a devolatilizing extruder to obtain a polymer having a residual monomer content of 0.5% or less.
Was supplied to the core material supply section of the spinning machine which was heated at a time. The obtained polymer had a glass transition temperature of 103 ° C. and a refractive index of 1.356.
On the other hand, a perfluoro (2,2-dimethyl-1,3-dioxole) / tetrafluoroethylene = 50/50 mol% copolymer (n _D 1.308) was melted by a melt extruder, and the sheath material of the spinning machine was supplied. Parts.

Further, bisphenol A-type polycarbonate (viscosity average molecular weight: 19,000) was melted by a melt extruder and supplied to the protective material supply section of the spinning machine. An optical fiber having a core diameter of 970 μm, a sheath thickness of 5 μm, a protection thickness of 10 μm, and an outer diameter of 1 mmφ was obtained with a core-sheath-protection structure using a three-layer composite spinning nozzle in a spinner. The transmission loss of the obtained fiber is 76d at 650nm.
At B / Km and 770 nm, it was 94 dB / Km and 950 nm and 183 dB / Km, which were very small. In addition, the obtained optical fiber is 10 mm
When wrapped around a φ rod, there was no appearance deterioration such as peeling of the sheath, and the mechanical strength was excellent.

Examples 3 to 5 The core-forming polymer, the sheath-forming polymer, and the protection-forming polymer are listed in Table 1, respectively. The core diameter is 960 μm, the sheath thickness is 10 μm, and the protection is the same as in Example 1. Thickness 10μm, outer diameter 1,0
An optical fiber of 00 μm was obtained. Table 1 shows the transmission loss and mechanical strength of the obtained optical fiber.

Example 6 Using an α-fluoro-1,1,1,3,3,3-hexafluoroisopropyl acrylate polymer as a polymer for forming a core, and using -fluoro (2,2-dimethyl-1,3-dioxole)
/ Polymer 90 / tetrafluoroethylene = 60/40 mol%
Weight percent (Perfluoroalkyl ether with a number average molecular weight of 8,250: Krytox 143AD (trade name, manufactured by DuPont)) A resin composition having a refractive index of 1.303 and containing 10% by weight was used as a polymer for forming a sheath, and further vinylidene fluoride / tetrafluoroethylene = 80. / 20mol% copolymer as a polymer for protection formation, core-sheath-protection three-layer composite spinning, core diameter 960μ
m, a sheath thickness of 10 μm, a protective thickness of 10 μm, and an outer diameter of 1,000 μm were obtained. The transmission loss of this optical fiber was 70 dB / Km at 650 nm, and even when wound around a 5 mmφ rod, there was no appearance deterioration such as peeling of the sheath at all, and it showed extremely excellent mechanical properties.

Comparative Example 2 Using the same core and sheath-forming polymer as in Example 6,
Core diameter 980μm, sheath thickness 10μm, outer diameter 1,000μ by layer composite spinning
m optical fibers were obtained. The transmission loss of this fiber is 65
It was as good as 70 dB / Km at 0 nm, but when it was wound around a 5 mmφ rod, the sheath was peeled off and the sheath was flexible.

Continuation of the front page (72) Inventor Hiroaki Onishi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside the Central Research Laboratory Mitsubishi Rayon Co., Ltd. (56) References JP-A-1-302303 (JP, A) JP-A-61- 240206 (JP, A)

Claims (5)

(57) [Claims] _{1. A} polymer having a refractive index of n1 obtained by polymerizing a monomer represented by the general formula [I] as a main monomer, and a perfluoro (2,2-dimethyl-1,3-di- mer) as a core. Dioxol) as a main monomer and a refractive index n ₂ polymer obtained by polymerization as a sheath, n ₁ −n ₂ ≧ 0.
A plastic optical fiber comprising a three-layer optical fiber having a protective layer on the outer periphery of the optical fiber satisfying the condition 01. Wherein X is H, CH ₃ , D, F, Cl or CF ₃ , Y is H or D, R
f represents a linear or branched fluoroalkyl group 2. The sheath-forming polymer according to claim 1, wherein the perfluoro- (2,2
-Dimethyl-1,3-dioxole) and 50 to 99% by weight of a polymer having a main monomer and perfluoroalkyl ether 1 to 1
2. The plastic optical fiber according to claim 1, wherein the optical fiber is formed of a mixture with 50% by weight. 3. The plastic optical fiber according to claim 1, wherein the protective layer has a thickness of 1 to 100 μm. 4. The method according to claim 1, wherein the refractive index n _{2 of the} polymer for forming the sheath and the refractive index n _{3 of the} polymer for forming the protective material satisfy a condition of n ₃ −n ₂ ≧ 0.03. 4. The plastic optical fiber according to item 2 or 3. 5. The plastic light according to claim 1, wherein the core layer, the sheath layer and the protective layer are integrally formed by three-layer composite melt spinning. Fiber manufacturing method.