JP2001350052A - Plastic optical fiber and optical fiber cable using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber, which is improved in mechanical characteristics, more preferably repetitive refraction durability. SOLUTION: A core 12 of the plastic optical fiber, formed by coating the core 12 with a sleeve 14 and providing the circumference of the sheath 14 with a protective layer 16, consists of polymethyl methacrylate over the entire part. An outer peripheral part 122 of the core of 50 μm in thickness (R1-R0) has a segment, where its refractive index is higher by 0.001 or larger than the minimum refractive index within a center region 12a of the core of 100 μm in a radius Ra.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of optical transmission, and more particularly to a plastic optical fiber and an optical fiber cable which are excellent in repeated bending durability among mechanical characteristics.

[0002]

2. Description of the Related Art A plastic optical fiber and an optical fiber cable using the same are used for signal transmission between a sensor in a robot and a signal processing circuit and a data link in a moving body. It is used for short-distance optical communication applications such as. In these applications, the optical fiber is frequently subjected to a bending action based on a mechanical operation of a robot or an inertial force or an external vibration force generated when the moving body moves. Therefore, a plastic optical fiber used in such an environment is required to have not only excellent optical characteristics but also excellent mechanical characteristics, particularly durability against repeated bending.

Generally, in order to improve the mechanical properties of a plastic optical fiber, drawing is performed at an appropriate temperature at an appropriate stretching ratio. However, the stretching process may cause a decrease in optical properties or an increase in heat shrinkage of the plastic optical fiber.Therefore, it is necessary to consider the suppression of these occurrences. Not good. That is, generally speaking, when the draw ratio is increased, the mechanical properties are improved, but the heat shrinkage is increased, and when used at a high temperature, the position with respect to the connector attached to the cable end is increased. The shift causes a problem that the coupling loss in the coupling with the light source or the coupling with the light receiver is likely to increase.

A general step index type plastic optical fiber uses a core material and a sheath material, or, if a further protective layer is used on the outer periphery of the sheath to repeatedly improve bending durability, the material of the protective layer is used. In addition, an undrawn yarn is produced by melt-spinning using a compound spinning nozzle, and only the core material is melt-spun, and a sheath material and a protective layer material are coated around the core material to form a sheath and a protective layer. An undrawn yarn is produced and then manufactured through a drawing process. In spinning at this time, conventionally, it was thought that distortion was applied inside and outside the spinning nozzle to cause deterioration of optical characteristics. Has been spun.

[0005] The conventional plastic optical fiber and the optical fiber cable using the same manufactured as described above can be used in the above-mentioned applications, but they are required to further improve the mechanical properties, particularly the durability against repeated bending. Is required.

[0006]

According to the present invention, there is provided a plastic optical fiber having a core / sheath structure in which a sheath is covered by a sheath, which solves the above technical problems.
A plastic optical fiber, wherein the core is made of a polymer having the same composition throughout, and the core has a portion having a refractive index higher by 0.001 or more than a central region of the core at an outer peripheral portion thereof. You.

In one embodiment of the present invention, the outer peripheral portion has a portion having a refractive index higher than that of the central region by 0.002 or more. In one embodiment of the present invention, the thickness of the outer peripheral portion is 50 μm, and the radius of the central region is a smaller value of the inner diameter of the outer peripheral portion and 100 μm. In one embodiment of the present invention, a protective layer is provided around the sheath. In one aspect of the invention, the core polymer is polymethyl methacrylate.

According to the present invention, there is provided a plastic optical fiber cable characterized in that a coating layer is formed around a plastic optical fiber as described above to solve the above technical problems. Is provided. In one aspect of the present invention, a connector is attached to at least one end so as to expose an end face of the plastic optical fiber.

In general, in the destruction of a material, the starting point of the destruction is a defect point in the material where stress concentration is likely to occur due to external stimulus. In the case of optical fibers, a manufacturing method that does not create defect points such as foreign matter and voids in order to minimize light scattering is adopted, so the destruction start point is near the surface that is easily damaged by external stimuli. Often. Therefore, in order to reduce fatigue fracture due to bending or vibration of the plastic optical fiber, it is important to increase the mechanical strength especially near the surface. The present inventors have conducted intensive studies with the aim of suppressing the thermal shrinkage and increasing the mechanical strength of the plastic optical fiber, and as a result, the present invention as described above has been achieved.

In the plastic optical fiber of the present invention, the molecular orientation of the core outer peripheral portion having a higher refractive index is larger than that of the core central region, so that the mechanical strength near the outer surface is improved. It is supposed to be. That is, as the molecular orientation advances, the density increases. From the Clausius-Mossotti relation, it is known that, in a substance having the same molecular polarizability, that is, a substance having the same molecular structure, the refractive index of the substance increases as the density of the substance increases. It is considered that this increases the refractive index of the core outer peripheral portion.

As a result of various studies, the present inventor has found that a plastic optical fiber spun under certain spinning conditions has a high refractive index in a radially outward direction in a core made of a material having the same composition. It was discovered that the structure was formed. In other words, it is considered that the molecular orientation is increased in the radially outward direction, so that the density of the portion is also increased. The present inventors have proposed a plastic having such a structure and excellent mechanical properties. A method for manufacturing optical fibers has been found.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing an embodiment of a plastic optical fiber (hereinafter, may be abbreviated as “POF”) according to the present invention, and FIG. 2 is an optical fiber according to the present invention using the same. It is a schematic sectional view showing one embodiment of a cable.

FIG. 1 shows a cross section perpendicular to the longitudinal direction of the POF, which has a core / sheath structure, ie, a core 12 is covered by a sheath 14 disposed around it. Have been. The sheath 14 has a protective layer 16 disposed therearound.
Coated with

C indicates the center (center axis) of the POF. The core 12 has a radius (distance from the POF center C) of R1.
And a region including the POF center C up to a radius R0 around the center, in which the refractive index does not substantially change (for example, the difference between the maximum value and the minimum value of the refractive index is 0.001 or less). And an outer peripheral portion 122 located around the central portion 121 and in contact with the sheath 14. The distance from the POF center C to the outer surface of the sheath 14 is R2, and the distance from the POF center C to the outer surface of the protective layer 16 is R3.

R0 is, for example, 100-1400 μm, R1 is, for example, 120-1500 μm, R2 is, for example, 125-2000 μm, and R3 is, for example, 13-13 μm.
0 to 3000 μm. In order to sufficiently improve the mechanical properties of the POF of the present invention, the thickness (R
1−R0) is preferably 20 μm or more, and can be set to, for example, 50 μm.

The core 12 has a central portion 121 and an outer peripheral portion 122.
Is composed of one kind of polymer (including a copolymer or the like) having the same composition and having the same molecular unit composed of the same monomer unit. As the polymer of the core 12, polymethyl methacrylate, a copolymer of methyl methacrylate and another monomer, a copolymer of polystyrene and styrene, a polycarbonate, an amorphous polyolefin, and the like, which are usually used in an optical fiber, are used. Among them, polymethyl methacrylate and a copolymer of methyl methacrylate and another monomer are preferable from the viewpoint of light transmission characteristics. Further, polymethyl methacrylate is more preferred.

As the material of the sheath 14, a known material can be used as long as it has a lower refractive index than the material of the core 12. For example, when polymethyl methacrylate is used as the polymer of the core 12, a copolymer of an alkyl fluorinated methacrylate and a methyl methacrylate, a short-chain fluorinated alkyl methacrylate, a long-chain fluorinated alkyl methacrylate and a methyl Copolymers with methacrylate, vinylidene fluoride-based polymers, blends of vinylidene fluoride-based polymers with polymethyl methacrylate-based polymers, and the like can be used.

The protective layer 16 is formed using a resin having excellent flexibility in order to further improve the bending resistance.
As a material of such a protective layer 16, for example, a vinylidene fluoride-based polymer and a vinylidene fluoride-based copolymer are particularly preferable. However, this protective layer 16 may be omitted.

FIG. 2 shows a cross section orthogonal to the longitudinal direction of the plastic optical fiber cable (POF cable) formed by disposing the covering layer 22 around the POF 20 as described above. That is, the POF 20 of the present invention is used in the form of a cable having a coating layer 22 formed on the outer periphery in order to improve durability and environmental resistance.

The material of the coating layer 22 includes various thermoplastic resins, thermosetting resins, photocurable resins, shape memory resins,
Resin containing metal fine powder or the like can be used. Preferred resins for the thermoplastic resin include vinyl chloride resin, low-density polyethylene, linear low-density polyethylene, chlorinated polyethylene, ethylene-vinyl acetate copolymer, and a blend of polyvinyl chloride and ethylene-vinyl acetate copolymer. Products, polyurethane resins and the like. Among them, ethylene-
A resin having a small elastic modulus such as a vinyl acetate copolymer or a blend of polyvinyl chloride and an ethylene-vinyl acetate copolymer is more preferably used. It is also possible to add a plasticizer to various resins. In the case of a vinyl chloride resin, for example, dioctyl phthalate, trioctyl trimellitate, tricresyl phosphate and the like are used as the plasticizer. However, since the plasticizer may migrate to the POF 20 and degrade its optical performance and mechanical properties, it is preferable to select a plasticizer that does not cause such adverse effects. Also,
As thermosetting resins, phenolic resins, urea resins,
Melamine resin, unsaturated polyester resin, epoxy resin, polyurethane resin and the like are used. As the photocurable resin, for example, a combination of polymethyl methacrylate and a photopolymerization initiator is used. As the shape memory resin, an acrylic resin, trans isoprene, polyurethane, polynorbornene, styrene / butadiene copolymer, or the like is used.

In the present embodiment, the core outer peripheral portion 122 has a refractive index of 0.1 in comparison with the refractive index of the core central region 12a.
001 or higher. Here, the central region 12a
Indicates a region having a radius Ra including the POF center C. The center region radius Ra can be set, for example, as follows.
That is, Ra is equal to R0 when the radius R0 of the central portion 122 is 100 μm or less, and is set to 100 μm when the radius R0 of the central portion 122 exceeds 100 μm (the difference between the inner diameter R0 of the outer peripheral portion 122 and 100 μm). The smaller of these values). And the refractive index of the core material center region 12a is
Minimum refractive index (usually POF) in the core material center region 12a
(Refractive index at the center C).

Here, examples of the method of measuring the refractive index distribution in the cross section of the POF core and the method of evaluating the repeated bending durability of the POF and the POF cable are shown below.

<Method of Measuring Refractive Index Distribution> (1) The sheath 14 of the POF (and the protective layer 16 if the protective layer 16 is provided) is peeled off to obtain a measurement sample having only the core 12; Because it depends on the amount of water in the polymer, (1)
(3) Literature "Y. Kokubun and K. Iga:" Precise measurement
of the refractive index profile of optical fibers
by a nondestructive interference method ", Trans.IE
The refractive index distribution in the radial direction is measured using the lateral differential interferometry introduced in CE Japan Section E, E60, 12, p. 702 (1977).

<Mechanical Properties: Method for Evaluating Repeated Bending Durability> FIG. 3 is a schematic explanatory diagram of a method for evaluating repeated bending durability.

Between two rolls (2) having a radius of 15 mm and spaced in parallel with each other with a gap of 2.3 mm, a diameter of
Hang through 2.2mm POF cable (1) and roll
(2) At the lower side, attach a 0.5 kg weight (3) to the POF cable (1). PO above roll (2)
A holding bracket (6) is attached to the F cable (1), and the holding bracket (6) is a roll (2) shown in FIG.
It is attached to a rotating arm (not shown) that rotates 180 degrees about an axis O parallel to the axis. Here, the axis O is the line of intersection of the plane contacting the upper part of the two rolls (2) and the plane of symmetry of the arrangement of the two rolls (2). That is, the pivot arm is
From the vertical position to the first horizontal position, which is tilted 90 degrees to one side from the vertical position (the POF cable state at this time is indicated by a solid line in FIG. 3), and then to the vertical position. Then, it turns to the second horizontal posture position (at this time, the state of the POF cable is indicated by a dashed line in FIG. 3) which is tilted 90 degrees to the opposite side, and again. The operation of rotating to return to the vertical posture position is repeated. This reciprocating operation is counted as one bending operation, and the bending operation is repeated at a speed of 30 times per minute.

Using an LED having a wavelength of 660 nm as the light source (4),
An optical power meter is used as the photodetector (5), and the detection value of the light emitted from the light source (4) and reaching the photodetector (5) via the POF cable (1) is the initial value (before the repetitive bending operation starts). The value of the number of times of repetitive bending until the value falls by 1 dB from the value) is defined as the number of times of bending until the POF breaks, and the bending durability is evaluated. The bending durability was evaluated by five P
The average value of OF is used.

FIGS. 4 to 6 show specific examples of the refractive index distribution in the radial direction of the POF core measured as described above. The “distance from the center” on the horizontal axis in these figures is the POF center C
Is normalized by setting the radius R1 of the core to 1.0. In addition, “the amount of change in the refractive index” on the vertical axis in these figures is represented by a refractive index difference with respect to the refractive index of the POF center C as a reference (0.000).

FIG. 4 is a refractive index distribution chart of a POF core in which the refractive index is substantially constant over the entire core, and is shown for reference. POF constructed using this POF
The number of bends until breakage in the repeated bending durability test of the cable varies depending on the fiber diameter, the draw ratio, the composition and the thickness of the sheath material, and is generally about 10,000 to 100,000.

FIG. 5 shows a refractive index distribution of a POF core having an outer peripheral portion having a portion having a refractive index larger than that of a central region by about 0.001 obtained by the present invention. The number of breaks in a repeated bending endurance test of a POF having such a refractive index distribution is improved by about 30% as compared with a refractive index distribution having almost uniform refractive index distribution shown in FIG.

FIG. 6 shows an outer peripheral portion having a portion obtained by the present invention and having a refractive index larger than that of the central region by about 0.001 or more. In particular, the refractive index becomes larger by about 0.002 than that of the central region. 3 shows a refractive index distribution of a POF core having a portion having a circle. The number of breaks in a repeated bending durability test of a POF having such a refractive index distribution is as follows:
It is about twice as large as that of the almost uniform refractive index distribution shown in FIG.

As can be seen from FIGS. 5 and 6, the refractive index distribution of the core monotonically increases from the center of the POF toward the outside in the radial direction. The difference in refractive index between the central region and the outer peripheral portion of the core is preferably as large as possible, but is usually 0.005 or less.

In order to produce the plastic optical fiber of the present invention, for example, a composite spinning method is used. In this case, the resin flowing in the spinning nozzle during spinning acts on the outer peripheral polymer near the nozzle wall surface and the polymer in the inner layer. The spinning is carried out under conditions in which the shear stress difference is increased by increasing the average nozzle discharge speed, or by lowering the spinning temperature and increasing the resin viscosity. From such a viewpoint, the average nozzle discharge speed is preferably 20 mm / sec or more, more preferably 40 mm / sec or more. The spinning temperature is preferably set to 230 ° C. or lower, more preferably 200 ° C. or lower.
Further, the melt index (MI) of the polymer used as the material of the core is preferably 10 or less.
In addition, MI is based on JIS K7210, orifice diameter 4mmφ, orifice length 8mm, test temperature 230 ° C,
It is measured as a test load of 5 kg and a sampling time of 10 minutes. In order to facilitate production, the average nozzle discharge speed is preferably 100 mm / sec or less, and the MI of the core polymer is preferably 0.1 or less.

Further, in order not to increase the irregularity of the core-sheath interface at the time of spinning, the inner surface of the nozzle is optically polished so that minute turbulence is not generated in the nozzle at the time of spinning, and the viscosity of the outer peripheral polymer, particularly the sheath material is reduced. By taking measures such as appropriately lowering the optical fiber, it is possible to manufacture an optical fiber having no deterioration in transmission loss.

[0035]

The present invention will be described below with reference to examples and comparative examples.

[Examples 1 to 7] Polymethyl methacrylate (PMMA) having an MI of 5 was used as a core material, and a copolymer of vinylidene fluoride and tetrafluoroethylene having a lower refractive index than the core material was used as a sheath material. These resins were continuously melted and devolatilized using an extruder, and the melted and devolatilized resins were quantitatively supplied to a two-layer composite spinning nozzle by a gear type metering pump.
The spinning was carried out under the spinning conditions as shown in the following, and the unstretched POF having a concentric two-layer structure was obtained by continuously discharging from a spinning nozzle, cooling and solidifying while taking off at a predetermined spinning take-up speed. Subsequently, the unstretched POF is introduced into a 4 m-long hot-air stretching furnace in which hot air at 140 ° C. is circulated at a wind speed of 10 m / sec, and is taken up at twice the introduction speed, thereby performing twice the heating stretching. The treatment was applied continuously. As shown in Examples Nos. 1 to 7 in Table 1, the core material had a difference in refractive index, the number of times of repeated bending until POF breakage, and transmission loss.
The diameter of a 10 μm thick vinylidene fluoride copolymer sheath coated around a 0 μm PMMA core
POF of 00 [μm] and PMMA having a diameter of 730 [μm], which was subjected to double heating drawing by changing the relationship between the discharge amount ratio between the core material and the sheath material and the relationship between the total discharge amount and the spinning take-up speed, were used. Around the core,
A POF having a diameter of 750 [μm] having a structure covered with a sheath of a vinylidene fluoride copolymer having a thickness of 10 [μm] was obtained.

A coating layer was formed by continuously coating the obtained POF with a molten polyethylene using a cable-forming apparatus, and a POF cable having a diameter of 2.2 mm was obtained.

The number of repetitions of bending of the POF cable obtained by converting the obtained POF into a cable until the POF breaks is 100,000.
The number of repetitions was 450,000 times, and the repetition bending durability was excellent, and the transmission loss was as good as 126 to 132 [dB / km].

[0039]

[Table 1] The average nozzle discharge speed in the table is a value obtained by dividing the amount of resin discharged from the nozzle in one second (unit: mm ³ ) by the area of the nozzle outlet (unit: mm ² ).

The difference in the refractive index in the table indicates the difference between the refractive index in the central region of the core and the refractive index in the outer peripheral portion. Here, the refractive index of the central region is the minimum refractive index observed in a range of 100 [μm] from the center of the core, and the refractive index of the outer peripheral portion is 50 [μm] from the outer peripheral surface of the core. It is the maximum refractive index observed in the depth range.

Comparative Examples 1 and 2 Resin was continuously discharged from a spinning nozzle in the same manner as in Example 1 except that spinning was performed under ordinary POF spinning conditions as shown in Table 2. The unstretched POF having a concentric two-layer structure was obtained by cooling and solidifying while taking off at a speed. Subsequently, the unstretched POF is introduced into a 4 m-long hot-air stretching furnace in which hot air at 140 ° C. is circulated at a wind speed of 10 m / sec, and is taken up at twice the introduction speed, thereby performing twice the heating stretching. The treatment was applied continuously. As shown in Comparative Examples Nos. 1 and 2 in Table 2, the thickness around the PMMA core having a diameter of 980 [μm] having a refractive index difference in the core material, the number of times of repeated bending until the POF breaks, and the transmission loss. POF with a diameter of 1000 [μm] of a structure coated with a sheath of vinylidene fluoride copolymer having a thickness of 10 [μm], and the relationship between the discharge amount ratio between the core material and the sheath material and the spinning take-off speed was changed. A POF with a diameter of 750 [μm] having a structure in which a sheath of vinylidene fluoride copolymer having a thickness of 10 [μm] is coated around a core of PMMA having a diameter of 730 [μm], which has been subjected to double heating and stretching. Was.

Then, a cable was formed in the same manner as in Examples 3 to 5, and a POF cable having a diameter of 2.2 mm was obtained.

The number of times of bending of the POF cable obtained by converting the obtained POF into a cable until the POF breakage was 78000.
Times, 145,000 times, POF with the same cross-sectional dimensions of the embodiment
It was lower than that.

[0044]

[Table 2]

[0045]

As described above, the plastic optical fiber of the present invention has a refractive index higher than that of the core center region by 0.001 or more at the outer periphery of the core made of the polymer having the same composition. The bending durability can be repeatedly improved without impairing the characteristics.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing one embodiment of a plastic optical fiber according to the present invention.

FIG. 2 is a schematic sectional view showing an embodiment of the optical fiber cable according to the present invention.

FIG. 3 is a schematic explanatory view of a method for evaluating repeated bending durability.

FIG. 4 is a refractive index distribution diagram of an optical fiber core.

FIG. 5 is a refractive index distribution diagram of an optical fiber core.

FIG. 6 is a refractive index distribution diagram of an optical fiber core.

[Explanation of symbols]

 (1) Plastic optical fiber cable (2) Roll (3) Weight (4) Light source (LED) (5) Photodetector (optical power meter) (6) Holding bracket 12 core 12a core center area 121 core center 122 core Outer part 14 Sheath 16 Protective layer 20 Plastic optical fiber 22 Coating layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshinori Sumi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory F-term (reference) 2H050 AA15 AB42X AB43X AB44Y AB45X AB47Y AB50X AB50Y AC27 AC28 AC76 BB05S BB07S BB08Q BB09S BB10S BB14S BB17S BB32S BB33S BB35S

Claims (7)

[Claims] 1. A plastic optical fiber having a core / sheath structure in which a core is covered with a sheath, wherein the core is made of a polymer having the same composition throughout, and the core is provided at an outer peripheral portion thereof with respect to a central region of the core. A plastic optical fiber having a portion having a refractive index higher than 0.001. 2. The outer peripheral portion is 0.005 from the central region.
The plastic optical fiber according to claim 1, wherein the plastic optical fiber has a portion having a refractive index of 2 or more. 3. The method according to claim 1, wherein the thickness of the outer peripheral portion is 50 μm, and the radius of the central region is a smaller value of the inner diameter of the outer peripheral portion and 100 μm.
3. The plastic optical fiber according to any one of claims 1 to 2. 4. The plastic optical fiber according to claim 1, wherein a protective layer is provided around the sheath. 5. The plastic optical fiber according to claim 1, wherein the core polymer is polymethyl methacrylate. 6. A plastic optical fiber cable, wherein a coating layer is formed around the plastic optical fiber according to claim 1. 7. The plastic optical fiber cable according to claim 6, wherein a connector is attached to at least one end so as to expose an end face of the plastic optical fiber.