JP2004133005A - Optical fiber cable and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber cable formed in such a manner that the cable can be easily bent with a small force up to a prescribed bending diameter but that a greater force is needed to bend the cable more than the above diameter and the cable is made hardly bendable and to provide a method for manufacturing the same. <P>SOLUTION: Shells 13 of the optical fiber cable formed by protecting a coated optical fiber 11 by the shells 13 are formed of internal layer coatings 13a consisting of a soft thermoplastic resin and external layer coatings 13b consisting of a thermoplastic resin harder than the internal layer coatings and the internal layer coatings 13b have a plurality of annular grooves 14 exposed with the internal layer coating in a circumferential direction. In bending the optical fiber cable, edges of the external layer coatings 13b on both sides contiguous to each other across the annular grooves 14 therebetween come into contact with each other, thereby preventing the cable from being bent to the prescribed bending diameter or less. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber cable in which an outer sheath as a protective coating is provided on the outer periphery of a single-core optical fiber cable, and a method for manufacturing the same.
[0002]
[Prior art]
A single-core optical fiber cable is used as an optical wiring, a drop cable, or an indoor cable in a vehicle or an apparatus. This optical fiber cable is formed by forming a sheath made of a thermoplastic resin directly or with a tensile fiber interposed on the outer periphery of a single optical fiber core. Since the transmission loss increases due to the bending of the optical fiber, it is necessary to prevent the optical fiber from being bent excessively.
[0003]
2. Description of the Related Art Conventionally, as an optical fiber cable for preventing an increase in transmission loss due to bending, there is known an optical fiber cable having a configuration in which an outer skin is provided with annular irregularities (for example, see Patent Document 1). FIG. 10 is a diagram showing an optical fiber cable provided with an anti-bending coating disclosed in Patent Document 1. In the drawing, 1 indicates an optical fiber, 2 indicates a sheath, and 3 indicates an anti-bending coating.
[0004]
The optical fiber 1 shown in FIG. 10 is an optical fiber (usually referred to as a plastic fiber) in which a core formed of an acrylic resin or a polycarbonate resin is surrounded by a similar resin having a slightly lower refractive index than the core. ) Is formed. The outer periphery of the optical fiber 1 is covered with a sheath 2 made of a stretchable polyethylene resin or vinyl chloride resin, and the outside thereof is covered with an anti-bending coating 3 made of a resin equivalent to the sheath 2. The anti-bending coating 3 has a shape with irregularities formed by inserting a number of annular slits along the circumference of the surface. In the optical fiber cable having this configuration, the adjacent convex portions of the bending prevention coating 3 come into contact with each other when the optical fiber cable is bent, and can be prevented from being bent at a certain angle or more.
[0005]
[Patent Document 1]
JP 11-223752 A
[0006]
[Problems to be solved by the invention]
However, since the above-described bending prevention coating 3 has a structure in which unevenness is provided in a coating portion formed of the same resin such as an elastic polyethylene resin or a vinyl chloride resin, it is bent before and after adjacent convex portions come into contact with each other. The difference in force required is small. Therefore, when the optical fiber cable is bent, there is a risk that the optical fiber cable may be bent to a predetermined bending diameter or more due to inertia or the like. In addition, when adjacent convex portions come into contact with each other, the coating is deformed, and a sufficient bending prevention effect cannot be obtained.
[0007]
The present invention has been made in view of the above-described circumstances, and can be easily bent with a small force up to a predetermined bending diameter, but requires a large force to bend more, and is sufficiently difficult to bend. An object of the present invention is to provide an optical fiber cable exhibiting an excellent bending prevention effect and a method for manufacturing the same.
[0008]
[Means for Solving the Problems]
An optical fiber cable according to the present invention is an optical fiber cable in which an optical fiber core wire is protected by an outer sheath, wherein the outer sheath includes an inner coating made of a soft thermoplastic resin and an outer coating made of an outer thermoplastic resin harder than the inner coating. The outer layer coating has a plurality of annular grooves in which the inner layer coating is exposed in the circumferential direction, and when bending the optical fiber cable, the edges of the outer layer coating on both sides adjacent to each other across the annular groove are in contact with each other, It is characterized in that it is formed so as to be prevented from being bent beyond a predetermined bending radius.
[0009]
Further, the method for manufacturing an optical fiber cable according to the present invention is a method for manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core wire with an outer cover, wherein the outer layer of the optical fiber core wire is coated with an inner layer made of a soft thermoplastic resin. Is formed, an outer layer coating made of a thermoplastic resin harder than the inner layer coating is formed, and thereafter, the outer layer coating is spirally formed by using one of a rotating jig having projections, a groove processing roller, a forming roller, and a rotating die. It is characterized by forming an annular groove.
[0010]
Further, another method for manufacturing an optical fiber cable according to the present invention is a method for manufacturing an optical fiber cable for protecting an outer surface of an optical fiber core with an outer sheath, wherein the outer periphery of the optical fiber core is made of a soft thermoplastic resin. After the inner layer coating is formed, a thermoplastic resin tape harder than the inner layer coating is wound sideways so as to form a predetermined groove and bonded and integrated.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The outline of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram illustrating the present invention, and FIG. 2 is a diagram illustrating the operation of the present invention. In the figure, reference numeral 10 denotes an optical fiber cable, 11 denotes an optical fiber core, 12 denotes a tensile fiber, 13 denotes an outer cover, 13a denotes an inner layer coating, 13b denotes an outer layer coating, 14 denotes an annular groove, and 15 denotes a contact portion.
[0012]
The optical fiber cable 10 of the present invention is configured by, for example, providing an outer sheath 13 directly or on the outer periphery of an optical fiber core 11 with a tensile fiber 12 interposed therebetween. As will be described later in detail, the outer cover 13 is formed of an inner coating 13a made of a relatively soft thermoplastic resin and an outer coating 13b made of a thermoplastic resin harder than the inner coating. The outer layer coating 13b is provided with a plurality of annular grooves 14 that extend in the longitudinal direction and reach the inner layer coating 13a in the circumferential direction.
[0013]
When the optical fiber cable 10 is bent as shown in FIG. 1, the annular groove 14 is closed inside the curve, and the annular groove 14 is opened outside the curve. As the bending progresses and the bending radius decreases, the edge portions of the outer layer coating 13b adjacent to each other across the annular groove 14 inside the curve come into contact with each other, and thereafter, starting from the contact portion 15 generated by the contact of the edge portion. The bending proceeds. In the case of further bending with the contact portion 15 as a starting point, it is necessary to extend the optical fiber core 11 located at the center of the cable, but the elongation is suppressed by the tensile strength of the optical fiber core 11. When the tensile strength fiber 12 is present, the tensile strength is further increased, so that the elongation of the optical fiber core 11 is further suppressed, and the optical fiber core 11 is hardly bent.
[0014]
If the user tries to forcibly bend after the contact at the edge of the outer coating 13b, a compressive strain is applied to the contact portion 15 of the outer coating 13b. However, since the outer layer coating 13b itself is formed of a relatively hard thermoplastic resin, the outer layer coating 13b is hardly deformed by compression and hardly bent.
[0015]
FIG. 2 is a diagram for explaining the above operation, and shows the relationship between the bending diameter of the optical fiber cable 10 and the force required for bending. In the figure, the area A has a relatively large bending diameter and the edge of the outer coating 13b is in a non-contact state, and the area B has a small bending diameter and the edge of the outer coating 13b is in contact. Since the inner coating 13a is exposed at the bottom of the annular groove 14 and is made of a relatively soft resin material having a small elastic modulus, in the region A, the inner coating 13a and the optical fiber core 11 or the tensile fiber 12 are formed. Can be bent with a relatively small force within the range of bending stiffness including. In the region B, since a tensile force is applied to the optical fiber core wire 11 or the tensile strength fiber 12, the force required for bending sharply increases.
[0016]
Also in the technology disclosed in the conventional patent document 1, as shown in FIG. 10, the anti-bending coating has a number of annular slits along the circumference of the surface, and has a shape with irregularities. Therefore, the region A and the region B exist, and in the region B, the force required for bending is slightly increased. However, the concave portion (corresponding to the annular groove of the present invention) is formed only up to the middle of the stretchable anti-bending coating made of a single resin. For this reason, even if contact between the convex portions occurs, the difference in the force required for bending before and after contact occurs is small, and the state change from the region A to the region B is not significant, and the bending into the region B is not performed. Bend to the diameter.
[0017]
On the other hand, in the case of the present invention, the annular groove 14 is formed so as to completely penetrate the outer layer coating 13b and reach the inner layer coating 13a. For this reason, the difference in the force required for bending between the area A and the area B is large, and it is possible to easily detect the point in time when the state of the area B is reached when the bending diameter is reduced. As a result, it can be reliably prevented from being bent to a predetermined bending diameter or less.
[0018]
3 to 5 are diagrams for explaining an embodiment of the present invention. FIG. 3A is a diagram showing an example in which the outer skin is directly adhered to the optical fiber core, FIG. 3B is a diagram showing an example having a gap between the optical fiber core and the outer sheath, and FIG. FIG. 4B is a diagram illustrating an example in which an outer skin is formed with a tensile strength fiber interposed therebetween, and FIG. 4B is a diagram illustrating an example in which a tensile strength fiber is mixed into an inner layer coating of the outer skin. FIG. 5 is a diagram showing an example in which the outer skin is covered with a protective layer. The reference numerals in the figure are the same as those used in FIG.
[0019]
The optical fiber core 11 is formed by coating a glass fiber having a core portion and a clad portion with one or two layers of an ultraviolet curable resin. When the optical fiber core 11 is not colored, it may be referred to as an optical fiber strand. In the present invention, the optical fiber core 11 is used in a sense including the optical fiber strand. I do. For example, as the optical fiber core 11, a glass fiber having a nominal outer diameter of 0.125 mm coated with an ultraviolet curable resin having an outer diameter of about 0.24 mm to 0.26 mm is used.
[0020]
The optical fiber cable 10 has an outer sheath 13 formed on the outer periphery of the optical fiber core 11 for protection, and is used as the optical fiber cable 10 as an optical wiring in a vehicle or an apparatus, or as a drop cable or an indoor cable. The outer skin 12 is formed in at least a two-layer structure of an inner coating 13a and an outer coating 13b. A relatively soft thermoplastic resin (for example, polyvinyl chloride) is used for the inner coating 13a, and an inner coating 13a is used for the outer coating 13b. A harder thermoplastic resin (for example, polyvinyl chloride) is used. Although not particularly limited to the present invention, the inner layer coating 13a is preferably made of a thermoplastic resin having an elastic modulus of 50 MPa to 1000 MPa, and the outer layer coating 13b is preferably made of a thermoplastic resin having an elastic modulus of 2500 MPa to 10000 MPa.
[0021]
FIG. 3A shows an example in which the inner layer coating 13a is formed so as to be in close contact with the outer periphery of the optical fiber core 11, and an example in which the annular groove 14 is formed in a spiral shape and continuously formed in the longitudinal direction of the optical fiber cable 10. Is shown. By forming the annular groove 14 in a spiral shape, the formation of the annular groove 14 is relatively easy as described later, enabling high-speed production and improving the productivity. Further, when the hard outer layer coating 13b is peeled off along the spiral groove, the soft inner layer coating 13a is also peeled off together with the outer layer coating 13b, and the optical fiber core 11 inside can be easily taken out.
[0022]
Further, as shown in FIG. 3B, even when the gap P exists between the optical fiber core 11 and the inner layer coating 13a, the bending of the optical fiber core 11 can be restricted. In particular, since the optical fiber core 11 can move freely loosely with respect to the outer cover 13, the influence of the tensile force due to bending is small, and the increase in loss due to bending can be further reduced.
[0023]
As shown in FIG. 4A, an optical fiber cable having a shape in which a tensile fiber 14 is interposed between the optical fiber core wire 11 and the inner layer coating 13a is also effective in regulating bending. For the tensile strength fiber 14, for example, 6000 denier aramid fiber is used. By interposing the tensile strength fiber 14, the breaking strength of the optical fiber core wire 11 can be increased. FIG. 4A shows an example in which the spiral annular groove 14 is formed by a plurality of lines. By forming the annular groove 14 with a plurality of grooves, the forming process of the groove can be sped up. Also, as shown in FIG. 4B, the same applies to an optical fiber cable in which a tensile strength fiber is embedded in an inner layer coating 13a.
[0024]
FIG. 5 shows an optical fiber cable in which the outer periphery of the outer cover 13 is covered with a protective layer 13c. The protective layer 13c is formed of a resin coating that is softer and more elastic than the outer layer coating 13b. The protective layer 13c covers the annular groove 14 of the outer cover 13 and has a cushioning function for cushioning impact, and also prevents foreign substances from entering the annular groove 14. In addition, the appearance of the cable can be improved, and the appearance can be reduced even when the wiring is exposed indoors. Since the protective layer 13c is formed of a soft and stretchable coating, as shown in FIG. 5 (B), it easily expands on the outer diameter side of the bend and becomes slack on the inner diameter side, as shown in FIG. It does not impair the bending characteristics described in 2.
[0025]
6A and 6B are diagrams illustrating examples of the shape of the annular groove, FIG. 6A is a diagram illustrating a spiral annular groove, and FIG. 6B is a diagram illustrating a ring-shaped annular groove. FIG. 6B shows that, other than forming the annular groove 14 in a spiral shape as shown in FIG. By forming the annular groove 14 into a ring-shape, since the annular groove 14 is not continuous in the longitudinal direction, the optical fiber cable 10 is easily bent until the edge portions of the outer layer coatings 13b adjacent to each other across the annular groove 14 are in contact with each other. be able to. The ring-shaped annular groove 14 can be formed, for example, by providing a split mold on a production line and operating it intermittently.
[0026]
As shown in FIGS. 6A and 6B, the annular grooves 14 are formed at a predetermined pitch P in the circumferential direction of the outer cover 13, and are formed such that the inner layer coating 13 a is exposed at the bottom of the annular grooves 14. Is preferred. As shown in FIG. 6A, the cross-sectional shape of the annular groove 14 can be formed in various shapes such as a square groove, a V-shaped groove, a trapezoidal groove, and a U-shaped groove.
[0027]
The depth t of the annular groove 14 is desirably formed so that the bottom of the groove slightly penetrates into the inner layer coating 13a in order to surely expose the inner layer coating 13a from the annular groove 14. Thereby, when bending the optical fiber cable 10, the influence of the hard outer layer coating 13b can be reduced, and the force required for bending in the region A described in FIG. 2 can be reduced. Furthermore, in order to make the difference in the force required for bending between the region A and the region B twice or more, the depth t of the annular groove 14 is formed to be 8% or more and 30% or less of the outer diameter D2 of the outer layer coating 13b. Is preferred.
[0028]
In order to prevent the inner coating 13a from being damaged when the optical fiber cable 10 is bent, the elongation at break of the inner coating 13a is preferably 100% or more. Further, it is desirable that the optical fiber cable 10 be bent smoothly until it reaches a predetermined bending diameter. Therefore, when the pitch of the annular groove 14 is P and the outer diameter D2 of the outer layer coating, it is preferable that “0.2 ≦ P / D2 ≦ 2”. Note that the lower limit is defined from a manufacturing problem.
[0029]
Further, when the optical fiber cable 10 is bent, the edge portion of the outer layer coating 13b comes into contact with the optical fiber cable 10 to be easily crushed. In order to prevent the crushing at the edge portion, the outer layer coating 13a preferably has a Rockwell hardness of Shore D70 or more according to the standard test method (ASTM-D0785).
[0030]
As a specific example, a shape obtained by coating the optical fiber core wire 11 on a glass fiber having an outer diameter of 0.125 mm with an ultraviolet curable resin having an outer diameter of 0.255 mm in the shape shown in FIG. 6B was used. The tensile strength fibers 12 were not used, and the inner coating 13a was formed of polyvinyl chloride having an elastic modulus of 98 MPa at 23 ° C. and an outer coating diameter D1 of 2.0 mm. The outer coating 13b was formed of polyvinyl chloride having an elastic modulus at 23 ° C. of 2940 MPa, and the outer diameter D2 of the outer coating 13b was 3.0 mm. Further, the depth t of the annular groove 14 was 0.5 mm, the width W1 of the annular groove 14 was 0.2 mm, and the width W2 of the ridge of the outer layer coating 13b was 3.0 mm. As a result, when the bending radius was less than 15 mm, it became difficult to bend sharply. When the width W2 of the ridge of the outer layer coating was doubled to 6.0 mm, it became difficult to bend sharply if the bending radius was less than 30 mm.
[0031]
When the outer sheath 13 is formed with the optical fiber core 11 or the tensile strength fiber interposed, the thermoplastic resin of the outer sheath 13 is applied on the optical fiber core 11 and contracts in the longitudinal direction when cured. Due to this contraction, the optical fiber core 11 is subjected to a compressive strain in the axial direction. When the optical fiber 11 is subjected to compressive strain in the axial direction, transmission loss increases. Therefore, in the present invention, when the product of the elastic modulus (E) and the radial sectional area (S) is the ES product, the ES product of the optical fiber core 11 or the optical fiber 11 and the tensile fiber 12 It is desirable to set the outer diameter D1 and the elastic modulus of the inner coating 13a so that the ES product obtained by adding the above is larger than the ES product of the inner coating 13a.
[0032]
FIG. 7 shows the relationship between the transmission loss and the ratio of the ES product of the inner-layer coating 13a to the glass fiber of the optical fiber core 11 in the configuration shown in FIG. 6B. The glass fiber is a quartz fiber having an outer diameter of 0.125 mm. The inner layer coating 13a is formed with an inner diameter of 0.255 mm and an outer diameter of 2.00 mm. ) 49 MPa, (2) 147 MPa, (3) 490 MPa, and (4) 784 MPa.
[0033]
As a result, in the case of (1) to (3) in which the ratio of the ES product is 1.5 or less, the increase in the transmission loss at the wavelength of 1.55 μm is suppressed to the allowable range of 0.05 dB / km or less. Was completed. However, in the example in which the ratio of the ES product in (4) exceeds 2.0, the ratio greatly increased to 0.3 dB / km. Therefore, in order to reduce the transmission loss to 0.05 dB / km or less, the ES product of the optical fiber core 11 in which the ES product of the core coating is added to the glass fiber needs to be larger than the ES product of the inner coating 13a. .
[0034]
As shown in FIG. 6A, when the annular groove 14 is formed in a spiral shape, it is necessary to consider the compressive strain on the optical fiber core 11 due to the outer layer coating 13b. In order to reduce the compression strain, it is preferable to add a filler such as glass fiber, talc, or whisker to the outer layer coating 13b. This reduces the coefficient of linear expansion of the hard outer layer coating, and reduces the compressive strain applied to the optical fiber at low temperatures. However, if a filler is added to the soft inner layer coating 13a, it becomes hard. Therefore, considering the compressive strain to the optical fiber, the ES product of the hard outer layer coating 13b is larger than the ES product of the soft inner layer coating 13a. Is preferred. Further, when the use environment temperature is reduced from 23 ° C. to −30 ° C., it is preferable that the contraction rate of the optical fiber cable is 0.5% or less.
[0035]
The optical fiber cable of the present invention can be formed from a normal single mode optical fiber to other various optical fibers. However, there is a demand for an optical fiber cable which does not cause harmful loss of 1.0 dB or more at the bending point even when the optical fiber cable is bent with a small bending radius.
[0036]
As an optical fiber core wire meeting such a requirement, for example, a mode field diameter defined by Petermann-I at a wavelength of 1.55 μm is 8 μm or less, and a wavelength at a wavelength of 1.3 μm and a wavelength of 1.55 μm. An optical fiber core having an absolute value of dispersion of 12 ps / nm / km or less, a cable cutoff wavelength of 1.26 μm or less, and a mode field diameter of 6 μm or more as defined by Peterman-I at a wavelength of 1.3 μm. Was recently developed. An optical fiber cable using this optical fiber core wire does not cause a loss increase of 1.0 dB or more even when bent at a bending radius of about 15 mm, so that the wiring operation can be performed with ease and ease.
[0037]
In addition to the requirement that the optical fiber cable not cause an increase in loss due to bending, it is also desirable that the optical fiber cable not be broken by pulling. It is desirable that the optical fiber cable has a tensile strength of 50 N or more. For this reason, it is preferable to use one that has cleared the proof level in the tensile strength test of the optical fiber core of 1.2% or more (1.2% elongation is applied to the optical fiber core for 1 second) or more.
[0038]
8 and 9 are views for explaining a method of manufacturing an optical fiber cable according to the present invention. 8A is a schematic view of forming an outer skin, FIG. 8B is a view showing an example of forming an annular groove using a cylindrical rotating jig, and FIG. FIG. 8D shows an example of forming an annular groove using a forming roller, and FIG. 8E shows an example of forming an annular groove using a rotating die. FIG. FIG. 9 is a diagram showing an example in which the outer layer coating is formed by winding a tape. In the figure, 10 is an optical fiber cable after groove processing, 10a is an optical fiber cable immediately after coating, 11 is an optical fiber core, 16 is a supply reel, 17 is a crosshead, 18 is a resin tank, and 19 is an annular groove processing part. , 20 is a capstan, 21 is a take-up reel, 22 is a rotary jig, 23 is a groove processing roller, 23 'is a pressing roller, 24 is a forming roller, 25 is a rotating die, 26 is a resin tape, 27 is a gap, 28 Indicates a heater.
[0039]
In FIG. 8A, the optical fiber core 11 is fed out from a supply reel 16, and an inner layer coating and an outer layer coating are formed by a crosshead 17. A relatively soft thermoplastic resin for the inner layer coating and a thermoplastic resin harder than the inner layer coating for the outer layer coating are supplied to the crosshead 17 from the resin tank 18. Although FIG. 8A shows an example in which the inner layer coating and the outer layer coating are formed by one crosshead 17, the inner layer coating and the outer layer coating may be formed by different crossheads.
[0040]
After forming the inner layer coating and the outer layer coating with the crosshead 17, an annular groove is formed by the annular groove processing portion 19 on the optical fiber cable 10a immediately after the coating, in which the annular groove is not formed. The optical fiber cable 10 after the formation of the annular groove is taken up by the capstan 20 and taken up by the take-up reel 21.
[0041]
FIG. 8B shows a first embodiment of the annular groove processing portion 19 in the manufacturing apparatus of FIG. 8A, using a cylindrical rotary jig 22 having a projection 22a on the inside. The rotating jig 22 is rotatably disposed on the cable immediately after the outer layer coating resin is applied, and forms a spiral annular groove in the outer layer coating resin. The annular groove is formed by pressing the outer-layer coating resin in which the protrusion 22a is in a semi-cured state from the outer periphery, or by forming the protrusion 22a to remove a part of the resin.
[0042]
FIG. 8C shows a second embodiment of the annular groove processing section 19 in the manufacturing apparatus of FIG. 8A, and uses a groove processing roller 23 having an annular projection 23a on the outer periphery. In addition, a pair of holding rollers 23 ′ are arranged adjacent to the groove processing roller 23, follow the rotation of the groove processing roller 23, and press the optical fiber cable 10 a during groove processing from the opposite side. The groove processing roller 23 and the pressing roller 23 'are arranged with their rotation axes inclined with respect to the cable manufacturing line. Each of the rollers rotates in the direction of arrow S, and rotates around the outer periphery of the cable in the direction of arrow T.
[0043]
In the above configuration, the groove processing roller 23 can wrap around the outer periphery of the optical fiber cable 10a immediately after the outer layer coating resin is applied, and form a spiral annular groove in the outer layer coating resin by the annular protrusion 23a. . The annular groove is formed such that the outer layer coating resin in which the annular protrusion 23a is in a semi-cured state is pressed from the outer periphery.
[0044]
FIG. 8D shows a third embodiment of the annular groove processing portion 19 in the manufacturing apparatus of FIG. 8A, using a pair of forming rollers 24 having an annular projection 24a on the outer periphery. The pair of forming rollers 24 are each formed of a concave surface 24b having a semicircular arc equal to the outer diameter of the optical fiber cable 10, and the concave surface is provided with an annular projection 24a inclined with respect to the roller axial direction. Further, it is preferable that the pair of forming rollers 24 be provided with tooth portions 24d and the like that mesh with each other at the roller ends so that the rotations of the forming rollers 24 are synchronized with each other.
[0045]
In the above-described configuration, the optical fiber cable 10a immediately after the outer layer coating resin is applied passes through the circular gap 24c formed between the two forming rollers 24, and the two forming rollers 24 rotate in opposite directions. By doing so, an annular groove can be formed by the annular projection 24a. By providing the annular projection 24a on each of the two forming rollers 24 by a half circumference and aligning the ends of the projections with each other, a spiral annular groove can be continuously formed in the optical fiber cable 10a. In addition, by providing the annular protrusion 24 a so as to make one round on each of the two forming rollers 24, an SZ-shaped groove can be continuously formed from both side surfaces of the optical fiber cable 10.
[0046]
FIG. 8 (E) shows a fourth embodiment of the manufacturing apparatus of FIG. 8 (A), in which a helical annular groove is formed by using a rotary die 25 having a projection 25a at an outlet end of a crosshead 17 forming an outer skin. Is formed. In this case, the crosshead for forming the inner layer coating and the crosshead for forming the outer layer coating may be separately arranged, and a rotary die may be used for the crosshead on which the outer layer coating is formed. By using the rotary die 25, it is not necessary to use the annular groove processing portion as shown in FIGS. 8B to 8D, and therefore, it is possible to increase the manufacturing speed and improve the productivity. .
[0047]
Further, in any of the examples of FIGS. 8B to 8E, the provision of the plurality of protrusions 22a, 23a, 24a, 25a for forming the annular groove can further increase the groove forming speed. Productivity can be improved.
[0048]
FIG. 9 is an example showing another manufacturing method different from FIG. 8, in which a tape is wound around an optical fiber to form an outer layer coating. In this manufacturing method, after the optical fiber core 11 is fed from the supply reel 16, only the inner layer coating is formed by the crosshead 17. A relatively soft thermoplastic resin for covering the inner layer is supplied to the crosshead 17 from a resin tank 18. After the inner layer coating is formed, a resin tape 26 formed of a thermoplastic resin harder than the inner layer coating is spirally wound around the inner layer coating with a gap 27 therebetween to form an outer layer coating.
[0049]
The inner layer coating is in a heated state immediately after formation, and is heated by the heater 28 when the resin tape 26 is wound, so that the resin tape 26 and the inner layer coating can be bonded and integrated by welding. The resin tape 26 may be bonded and integrated on the inner layer coating using a solvent or an adhesive. After the resin tape 26 for covering the outer layer is wound and formed into the optical fiber cable 10, it is taken up by the capstan 19 and wound up by the take-up reel 20. In the optical fiber cable formed by this method, the gap 27 becomes an annular groove, a part of the inner layer coating can be completely exposed, and the manufacture is easy.
[0050]
【The invention's effect】
As is apparent from the above description, according to the present invention, the difference in the force required for bending before and after the edge portions of the outer layer coating adjacent to each other with the annular groove interposed therebetween can be doubled or more. it can. For this reason, it is possible to bend easily with a small force up to a predetermined bending diameter, but to bend more, a large force is required and it is difficult to bend, and a sufficient bending prevention effect can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating the present invention.
FIG. 2 is a diagram illustrating the operation of the present invention.
FIG. 3 is a diagram illustrating an example of an embodiment of the present invention.
FIG. 4 is a diagram illustrating another example of the embodiment of the present invention.
FIG. 5 is a diagram illustrating another example of the embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of the shape of an annular groove according to the present invention.
FIG. 7 is a diagram illustrating a relationship between an ES product and a transmission loss.
FIG. 8 is a diagram illustrating a method for manufacturing an optical fiber cable according to the present invention.
FIG. 9 is a diagram illustrating a method of manufacturing another optical fiber cable according to the present invention.
FIG. 10 is a diagram illustrating a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Optical fiber cable, 11 ... Optical fiber core wire, 12 ... Tensile fiber, 13 ... Outer skin, 13a ... Inner layer coating, 13b ... Outer layer coating, 13c ... Protective layer, 14 ... Annular groove, 15 ... Contact part, 16 ... Supply Reel, 17 ... Cross head, 18 ... Resin tank, 19 ... Circular groove processing part, 20 ... Capstan, 21 ... Take-up reel, 22 ... Rotating jig, 23 is groove processing roller, 23 '... Pressing roller, 24 ... Forming roller, 25: rotating die, 26: resin tape, 27: gap, 28: heater.

Claims (16)

An optical fiber cable in which an optical fiber core wire is protected by an outer sheath, wherein the outer sheath is formed by an inner layer coating made of a soft thermoplastic resin and an outer layer coating made of an outer thermoplastic resin harder than the inner layer coating. The coating has a plurality of annular grooves in which the inner layer coating is exposed in the circumferential direction, and when bending the optical fiber cable, edges of the outer layer coating on both sides adjacent to each other across the annular groove come into contact with each other, and a predetermined An optical fiber cable formed so as to be prevented from being bent beyond a bending radius. The optical fiber cable according to claim 1, wherein a gap is provided between the optical fiber core wire and the inner layer coating. The optical fiber cable according to claim 1, further comprising a tensile fiber between the optical fiber core wire and the inner layer coating. The optical fiber cable according to claim 1 or 2, wherein a tensile strength fiber is contained in the inner layer coating. The optical fiber cable according to any one of claims 1 to 4, wherein an outer surface of the outer layer coating is covered with a protective layer that is softer and more elastic than the outer layer coating. The optical fiber cable according to any one of claims 1 to 5, wherein the annular groove is formed in a spiral shape that is continuous in a longitudinal direction. The optical fiber cable according to any one of claims 1 to 5, wherein the annular groove is formed in a ring shape that is not continuous in a longitudinal direction. The optical fiber core has a mode field diameter of 8 μm or less as defined by Peterman-I at a wavelength of 1.55 μm, and an absolute value of chromatic dispersion at both a wavelength of 1.3 μm and a wavelength of 1.55 μm is 12 ps / nm / km or less. And a cable cut-off wavelength of 1.26 μm or less, and a mode field diameter defined by Peterman-I at a wavelength of 1.3 μm of 6 μm or more, according to any one of claims 1 to 7, An optical fiber cable as described. The optical fiber cable according to claim 8, wherein the optical fiber cable has a proof level of 1.2% or more in a tensile strength test. A method for manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core with an outer cover, comprising: forming an inner layer coating made of a soft thermoplastic resin on the outer periphery of the optical fiber core; A method of manufacturing an optical fiber cable, comprising: forming an outer layer coating made of a plastic resin; and thereafter, forming a spiral annular groove in the outer layer coating by a rotating jig having a projection on the inside. A method for manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core with an outer cover, comprising: forming an inner layer coating made of a soft thermoplastic resin on the outer periphery of the optical fiber core; Forming an outer layer coating made of a plastic resin, thereafter arranging a groove processing roller having projections on its surface at an angle to the fiber axis direction, and rotating the groove processing roller around the fiber axis to form the outer layer coating. A method of manufacturing an optical fiber cable, comprising forming a spiral annular groove in a coating. A method for manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core with an outer cover, comprising: forming an inner layer coating made of a soft thermoplastic resin on the outer periphery of the optical fiber core; An outer layer coating made of a plastic resin is formed, and thereafter, a pair of forming rollers having a convex ridge that is inclined with respect to the fiber axis direction is provided on a roller surface having a concave surface so as to conform to the outer surface of the outer layer coating. Forming a spiral or SZ-shaped annular groove in the outer layer coating. 13. The method according to claim 12, wherein the pair of forming rollers are synchronously rotated by teeth that mesh with each other. A method of manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core with an outer cover, comprising: forming an inner layer coating made of a soft thermoplastic resin on the outer periphery of the optical fiber core; Forming an outer layer coating made of a thermoplastic resin harder than the inner layer coating, and forming a helical annular groove in the outer layer coating by the projections of the rotary die. Method. The method for manufacturing an optical fiber cable according to any one of claims 10 to 14, wherein a plurality of the protrusions are provided to form an annular groove. A method for manufacturing an optical fiber cable for protecting the outer surface of an optical fiber core with an outer cover, comprising: forming an inner layer coating made of a soft thermoplastic resin on the outer periphery of the optical fiber core; A method for manufacturing an optical fiber cable, wherein a plastic resin tape is wound horizontally and bonded and integrated so that a predetermined groove is formed.

Images