JP2002236238A - Coated optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated optical fiber having excellent water-resistance in which the generation of water bubbles in the inside of a primary coating layer and blisters on a glass fiber/the primary coating layer boundary face are suppressed and the increase of an optical loss is avoided. SOLUTION: In the coated optical fiber in which at least the primary coating layer 3 and a secondary coating layer 4 are coated from the inside on the outer peripheral surface of a bare wire 2 consisting of a glass fiber, the primary coating layer material and the secondary coating layer material are composed of material in which the diameter of a water bubble contained in the primary coating layer material becomes 50 μm or less after a sandwich shaped laminating sheet sample which is formed by holding both surfaces of the primary coating layer material of a sheet shape of 200 μm or less thickness with the secondary coating layer material of a sheet shape of 200 μm or less thickness is dipped in warm water of 60 deg.C for seven days.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber core having excellent water resistance and mainly used for an optical cable.

[0002]

2. Description of the Related Art In recent years, the demand for large-capacity data transmission has increased,
In addition, the FTTH (Fiber to the h
The demand for ome) is rapidly increasing, and the laying of optical cable networks is increasingly urgent. As these optical cables, there are used optical fiber cables having a structure in which a plurality of tape-shaped optical fiber cores obtained by unifying a plurality of optical fiber cores into a tape shape are housed in a slot in a stacked state. FIG. 1 is a sectional view showing the structure of a normal optical fiber core 1 used for such an optical fiber cable. The optical fiber core 1 has a primary coating layer 3 made of an ultraviolet curable resin on the outer peripheral surface of the bare glass fiber 2.
, A secondary coating layer 4 made of an ultraviolet curable resin is formed on the outer periphery thereof, and a colored layer 5 made of a colored ultraviolet curable resin is further formed on the outer peripheral surface thereof. FIG. 2 is a cross-sectional view of a tape-shaped optical fiber core 7 in which a plurality of optical fiber cores 1 shown in FIG. 1 are arranged and integrated into a tape by a collective coating layer (tape layer) 6 made of an ultraviolet curable resin. is there.

[0003] Such optical cables have been mainly used in so-called trunk systems connecting telephone offices, but the use of FTTH means that optical fiber cables are laid from the telephone office to the terminal private house. . Therefore, opportunities to be exposed to various environments that were not considered in the conventional trunk system are greatly increased. Naturally, the sheath of the above optical cable is damaged and water enters the cable,
It is fully conceivable that the optical fiber will be left submerged for a long time. It has been reported that conventional optical fibers increase the optical loss due to water immersion. When the optical fiber core is flooded for a long period of time, the flooding reduces, for example, the adhesion at the interface between the glass fiber and the primary coating layer and causes partial peeling, and water accumulates to generate blisters. When blisters are generated at the interface between the glass fiber and the primary coating layer, a lateral pressure is applied to the glass to increase light loss due to microbending (hereinafter, sometimes referred to as microbending loss). In addition, not only at the glass fiber / primary coating layer interface, but also at the secondary coating layer / coloring layer interface and the coloring layer / tape layer interface, partial separation occurs due to the intrusion of water, and blisters are generated. Increases have been reported to occur.

To solve these problems, for example, Japanese Patent Application Laid-Open No. 9-5
In Japanese Patent No. 587, a blister generated when an optical fiber core wire is immersed in water is defined by an initial adhesion force between an interface between a glass layer and a primary coating layer by a fiber pulling force.
It can be suppressed. In addition, Japanese Patent Application Laid-Open
In Japanese Patent No. 5588, the water absorption of the primary coating layer is set to 1.5.
It is stated that blister generation at the glass fiber / primary coating layer interface can be suppressed by setting the content to not more than wt%. In Japanese Patent Application Laid-Open No. H11-31723, blisters are similarly generated at the interface between the secondary coating layer and the coloring layer due to the intrusion of water, and light loss occurs. It is stated that by defining the range of the adhesive force at the interface of the secondary coating layer, the generation of blisters at the interface between the colored layer and the secondary coating layer can be suppressed. Japanese Patent Application Laid-Open No. 7-3113
No. 24 discloses that the increase in light loss at the time of water infiltration of the tape core wire is due to partial peeling of the tape layer, and the interface adhesion between the colored layer and the tape layer is adjusted to a specific range, and A technique is described in which light loss is reduced by causing peeling quickly across the entire interface between the colored layer and the tape layer. That is, the optical fiber core wire and the tape core wire are partially peeled off at the interface of the glass fiber / primary coating layer, secondary coating layer / colored layer, and colored layer / tape layer when they are submerged. It was said that the accumulation of water and the formation of blisters increased microbend loss. Therefore, improvements have been made so far by increasing the water absorption properties of the material and the interfacial adhesion.

[0005] However, the occurrence of light loss in the tape core is not only caused by the occurrence of blisters at the interface of the glass fiber / primary coating layer and the like, but also when the tape core is immersed in warm water.
As a result of studies by the inventors, it has been found that water bubbles are generated inside the primary coating layer and cause light loss. The phenomenon that water bubbles are generated in the primary coating layer may be caused by increasing the initial interface adhesion force as disclosed in JP-A-9-5587, or by increasing the water absorption of the primary coating layer as disclosed in JP-A-9-5588. It has become clear that it is not possible to suppress simply by lowering. Further, as a result of intensive studies by the inventors, it has been found that the adhesion at the glass fiber / primary coating layer interface is greatly reduced by immersion in warm water, no matter how high the initial adhesion is. In addition, it has been clarified that the tendency also differs depending on the kind of oligomer used for the primary coating material, the kind of adhesive monomer which greatly affects the glass fiber / primary coating layer interface adhesion, and the like. Therefore, only by increasing the adhesion before immersion in warm water, the glass fiber / 1
Blisters generated at the interface of the next coating layer cannot be suppressed. Furthermore, even if the interface adhesion between the secondary coating layer and the colored layer is increased as described in JP-A-11-31723, blisters between the glass fiber / primary coating layer and water bubbles inside the primary coating layer are generated. Cannot be suppressed. Similarly, JP-A-7-311
As described in JP-A-324, even if the adhesion at the colored layer / tape layer interface is controlled, generation of blisters between the glass fiber / primary coating layer and water bubbles inside the primary coating layer cannot be suppressed.

[0006]

Therefore, the present invention suppresses the occurrence of water bubbles inside the primary coating layer and blisters at the interface between the glass fiber and the primary coating layer even when water is immersed for a long time, thereby reducing the increase in light loss. It is an object of the present invention to provide an optical fiber core having excellent water resistance.

[0007]

Means for Solving the Problems The present inventor has conducted intensive studies in view of the above-mentioned problems. Water is diffused into the resin layer and aggregates into fine defects inside the resin layer to grow into water bubbles, or the interfacial peeling of the glass fiber / primary coating layer is reduced due to the penetration of the water, resulting in interface separation. This led to the present invention based on this finding. That is, the present invention provides (1) a primary coating layer material and a secondary coating layer in an optical fiber core wire in which at least a primary coating layer and a secondary coating layer are coated on the outer peripheral surface of a bare glass fiber from inside. A sandwich-like laminated sheet sample formed by sandwiching both surfaces of a sheet-like primary coating layer material having a thickness of 200 μm or less between the sheet-like secondary coating layer materials having a thickness of 200 μm or less was prepared at 60 ° C. An optical fiber core comprising a material in which the diameter of water bubbles contained in the primary coating layer material is 50 μm or less after being immersed in warm water for 7 days; (2) an outer peripheral surface of a bare glass fiber; In an optical fiber core coated with at least a primary coating layer and a secondary coating layer from the inside, a primary coating material is obtained by coating a sample in which the primary coating material is coated on a glass plate with hot water at 60 ° C. To 2
After immersion for a day, the sample was taken out of the warm water to remove the water on the surface of the sample, and left for 1 hour in an environment of a temperature of 23 ° C. ± 2 ° C. and a relative humidity of 50% ± 5%. The optical fiber core according to (1), wherein the optical fiber is a material having a peeling force of 2 N / m or more when peeling at an angle of 90 degrees. (3) (1) to (2)
(4) The colored optical fiber according to any one of (4) and (3), wherein a colored coating layer is provided on the outer peripheral surface of the optical fiber. Are arranged in parallel, and are collectively coated and integrated to form a tape-shaped optical fiber core, and (5) at least one inner surface of an outer peripheral surface of the bare glass fiber.
A tape-shaped optical fiber in which a plurality of colored optical fiber cores in which a colored coating layer is provided on the outer peripheral surface of an optical fiber core coated with a secondary coating layer and a secondary coating layer are arranged in parallel and collectively coated. After immersing the core wire in hot water of 60 ° C. for 30 days, 1
An object of the present invention is to provide a tape-shaped optical fiber core, wherein the diameter of a water bubble contained in the inside of the next coating layer is 25 μm or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The form of an optical fiber cable to which the present invention can be applied is not particularly limited, and examples thereof include those shown in FIG. In the embodiment shown in FIG. 1, the diameter of the bare glass fiber 2 is not limited, but is made of, for example, a silica glass fiber or a multi-component glass fiber having an outer diameter of 125 μm. The material of the primary and secondary coating layers may be any resin. For example, there are UV curable resin and thermosetting resin, but UV curable resin which can be cured in a short time with a small device and has no solvent evaporation. (U
V) Resins are preferred. As a prepolymer, a molecular weight of 10
Particularly preferred are those obtained by adding a polyfunctional acrylate monomer to urethane acrylate, epoxy acrylate, polyester acrylate, or the like of about 00 to 10,000.
These resin coating layers are coated at the time of drawing a bare glass fiber, and the thickness of each of the primary coating layer 3 and the secondary coating layer 4 is not particularly limited. 60 μm, more preferably 20 to 50
The layer thickness is about μm. As described above, the colored layer 5 of a predetermined thickness (preferably about 5 to 20 μm thick) made of an ultraviolet curable resin or the like is formed on the outer periphery when the optical fiber is drawn.
To form a colored optical fiber. Furthermore, a tape-shaped optical fiber core wire as shown in FIG. 2 in which the core wire is cut into a plurality of wires and a collective coating layer is provided on the outer periphery in a state of being arranged in parallel can be produced.

The primary coating layer and the secondary coating layer used in the present invention must satisfy the following test results. In the optical fiber core coated with the primary coating layer and the secondary coating layer of the present invention, the primary coating layer material and the secondary coating layer material are each a sheet-like primary coating material having a thickness of 200 μm or less. A sandwich-like laminated sheet sample formed by sandwiching both surfaces of the above-mentioned sheet-like secondary coating layer material having a thickness of 200 μm or less is immersed in warm water at 60 ° C. for 7 days, and then generated in the primary coating layer material. It is necessary to use a coating layer material having a water bubble diameter of 50 μm or less. In this test, the thickness of the secondary coating material can be variously set to a thickness of 200 μm or less as described above, so that the diameter of the water bubbles generated in the primary coating material at this thickness is reduced. 50
What is necessary is just to set it as below μm. The thickness of the secondary coating layer material of 200 μm or less is a film thickness at the time of a test for generation of water bubbles, and does not specify the thickness of the secondary coating layer of the optical fiber.

Incidentally, water bubbles inside the primary coating layer and blisters at the glass fiber / coating interface are considered to be the object of the present invention and are considered to be a factor of light loss. It is considered that water diffuses into the resin layer and agglomerates into fine defects inside the resin layer to grow into water bubbles, or the permeation of water lowers the adhesive strength at the glass fiber / primary coating layer interface, causing interface separation and blistering. Can be The present inventors conducted an experiment in which optical fiber cores and sheets using various coating layer materials were prepared and immersed in hot water at 60 ° C. based on the above estimation. As a result, the present inventors have found a new evaluation method for reproducing the above two phenomena considered to be the causes of light loss on a resin sheet. This will be described in more detail below. First, regarding the generation of water bubbles inside the primary coating layer, for example, even if the primary coating layer sheet made of the same material as the primary coating layer was immersed in warm water, no generation of water bubbles was observed. However, as a result of repeating the hot water immersion test on the sheets having various structures, a primary sheet and a secondary sheet made of the same material were immersed in hot water when the laminated sheet prepared so that the primary coating layer material was sandwiched between the secondary coating layer materials. It has been found that water bubbles similar to those generated when the optical fiber coated with the coating layer is immersed in warm water are generated in the primary coating layer.

[0011] This is because water aggregates into fine defects existing in the primary coating layer, and eluted components in the resin enter therein, and the concentration becomes high.
It is presumed that the secondary coating layer acts as a semipermeable membrane of water, greatly accelerating the aggregation of water and growing into water bubbles. Also, regarding the occurrence of blisters between the glass fiber and the primary coating layer, a correlation between the glass fiber and the adhesive strength between the primary coating layers was naturally considered. However, according to experiments performed by the inventors, the initial glass adhesive strength was high. In some cases, blisters were generated by immersion in optical fiber hot water. Therefore, as a result of further study, a single-layer sheet formed of a primary coating layer material on a glass substrate of the same kind as glass fiber was immersed in warm water for 2 days, taken out and wiped off the moisture on the sheet surface at 23 ± 2 ° C., relative humidity It was found that by defining the 90 ° peel force measured after being left for 1 hour in an environment of 50 ± 5% (glass adhesion force) as described above, the occurrence of blisters during immersion of the optical fiber can be further suppressed. Note that the measurement conditions of the glass adhesion force are for defining the adhesion force, and are not limited to those measured by the optical fiber ribbon of the present invention under these measurement conditions.

[0012]

Next, the present invention will be described in more detail with reference to examples. First, the test method will be described below. In order to evaluate the water resistance of the primary coating material, a single-layer sheet 10 in which a primary coating material 8 is coated on a glass substrate 9 as shown in FIG. Further, as shown in FIG. 4, a laminated sheet 13 in which an inner layer 11 made of a primary coating material is sandwiched between outer layers 12 made of a secondary coating material to form a sandwich is prepared. These sheets are prepared so that the thickness of each layer is 200 μm or less in order to test as close as possible to the coating layer constituting the optical fiber core.

In order to evaluate the glass adhesion, the single-layer sheet 10 shown in FIG. 3 is cut into a tape having a width of 1 cm on a glass substrate, and the primary coating layer and the glass are peeled off at 90 ° in a tensile tester. The force required for this is measured, and this is taken as the initial glass adhesion. Further, the same single-layer sheet 10 is immersed in warm water at 60 ° C. for 2 days, and immediately after being taken out, the occurrence of water bubbles in the primary coating layer and the occurrence of blisters at the interface between the glass and the primary coating layer are observed with a microscope. Further, the single-layer sheet 10 was taken out from the hot water, the moisture on the sheet surface was wiped off, and the sheet was left in a room at 23 ± 2 ° C. and 50 ± 5% relative humidity for 1 hour. The glass adhesion was determined. In the case of the laminated sheet 13 of FIG. 4, it was immersed in warm water at 60 ° C. for 7 days, and immediately after being taken out, the occurrence of water bubbles in the primary coating layer was observed with a microscope. Next, four optical fiber core wires of FIG. 1 composed of the materials shown in Table 2 below are arranged in parallel, and in this state, a batch resin coating layer 6 (s = 0.3 mm t) made of an ultraviolet curable resin is provided on the outer periphery. = 1.1 mm) and a tape-shaped optical fiber core wire 7 as shown in FIG. 2 was prepared. The tape-shaped optical fiber was immersed in hot water at 60 ° C. for 30 days, and after removal, the increase in light loss was measured with light having a wavelength of 1.55 μm. The occurrence of water bubbles in the primary coating layer and the occurrence of blisters at the glass fiber / primary coating layer interface were observed with a microscope.
The immersion test of the tape-shaped optical fiber (four cores) is based on the actual use condition, and the result corresponds to the test result of a single optical fiber. Further, the water absorption of the primary coating layer sheet was measured in accordance with JIS K-7209.

As the UV resin for the primary coating layer and the secondary coating layer, coating resins a to g and x to z are prepared by adjusting the types and amounts of the urethane acrylate UV-curable oligomer and the polyfunctional acrylate monomer. Then, the combinations described below were compared for water resistance.

[0015]

[Table 1]

EXAMPLE 1 A single-layer sheet 10 (FIG. 3), a laminated sheet 13 (FIG. 4) and an optical fiber core 1 (FIG. 1) using a material as a primary coating layer and an x material as a secondary coating layer. It was created. Single layer sheet
A sample was prepared by coating a material having a thickness of 200 μm on a quartz glass substrate having a thickness of 1 mm and forming a 100 mm × 100 mm sheet piece. The laminated sheet has a thickness of 200
The outer surface of the material a sheet of μm was sandwiched between x materials having a thickness of 200 μm to form a sandwich, thereby obtaining a laminated sheet sample of 30 mm × 30 mm. The optical fiber core wire is prepared by applying a primary coating layer made of a material and a secondary coating layer made of x material on the outer peripheral surface of a bare glass fiber of silica glass having an outer diameter of 125 μm, and then UV-curable coloring. The agent was applied. Next, this optical fiber core wire was cut into four pieces to form a tape-shaped optical fiber core wire (tape width: 1.1 mm, tape thickness: 0.3 mm) having the configuration shown in FIG. In order to evaluate the water resistance of the single-layer sheet, the laminated sheet, and the tape-shaped optical fiber, each sample was processed by the above-described method, and observed and measured.
Table 2 shows the results.

Example 2 A single-layer sheet, a laminated sheet, and the like were used in the same manner as in Example 1 except that the material b was used as the primary coating layer and the material y was used as the secondary coating layer.
Optical fiber cores and tape-shaped optical fiber cores were prepared and similarly used as samples. The same test as in Example 1 was performed to evaluate the water resistance of the single-layer sheet, the laminated sheet, and the tape-shaped optical fiber core (four cores). Table 2 shows the results. Example 3 A single-layer sheet, a laminated sheet, and the like were used in exactly the same manner as in Example 1 except that the material c was used as the primary coating layer and the material z was used as the secondary coating layer.
Optical fiber cores and tape-shaped optical fiber cores were prepared and similarly used as samples. The same test as in Example 1 was performed to evaluate the water resistance of the single-layer sheet, the laminated sheet, and the tape-shaped optical fiber core (four cores). Table 2 shows the results.

Comparative Examples 1 to 3 Single-layer sheets were prepared in exactly the same manner as in Example 1 except that the material d was used as the primary coating layer, and the materials x, y and z were used as the secondary coating layers. , A laminated sheet, an optical fiber ribbon, and a tape-shaped optical fiber ribbon were prepared, and similarly used as samples. The same test as in Example 1 was performed to evaluate the water resistance of each of the single-layer sheet, the laminated sheet, and the optical fiber ribbon (four cores). Table 2 shows the results. Comparative Example 4 to Comparative Example 6 Materials e, f, and g were used as primary coating layers, respectively.
A single-layer sheet, a laminated sheet, an optical fiber core, and a tape-shaped optical fiber were prepared in exactly the same manner as in Example 1 except that the x material was used as the next coating layer. The same test as in Example 1 was performed to evaluate the water resistance of each of the single-layer sheet, the laminated sheet, and the optical fiber ribbon (four cores). Table 2 shows the results.

[0019]

[Table 2]

As can be seen from the results in Table 2, no water bubbles were generated when the single-layer sheet was immersed in warm water. Blisters at the glass fiber / primary coating layer interface occurred when both d and f were used as the primary coating material in both the single-layer sheet and the tape-shaped optical fiber core. Comparing the glass adhesion of the primary coating material, the initial adhesion for both d and f materials in which blisters are generated is as follows:
Although it is as large as 19 N / m or more, the adhesion after one hour of taking out hot water is as small as 1 N / m or less. Therefore, in order to prevent blisters from being generated at the glass fiber / primary coating layer interface after immersion in hot water, it is preferable to use a primary coating material having a glass adhesion of 2 N / m or more after one hour of taking out hot water. It has been found. A comparison between the laminated sheet and the tape-shaped optical fiber core for the water bubbles inside the primary coating layer shows that the tape-shaped optical fiber core wire using the coating material having a smaller water bubble diameter generated in the laminated sheet has a water bubble diameter inside the primary coating layer. Tended to be small, and no water bubbles were generated in the tape-shaped optical fiber core wire for the a and c materials having a water bubble diameter of 10 μm or less in the laminated sheet. Also, the increase in light loss tends to be suppressed as the water bubble diameter in the tape-shaped optical fiber core is smaller, and a tape using a, b, or c material in which the water bubble diameter in the tape-shaped optical fiber core is 25 μm or less. The maximum optical loss increase is 0.0
There was almost no light loss change of 2 dB / km.
It is considered that the smaller the water bubble diameter in the tape-shaped optical fiber core, the smaller the microbend generated by the water bubbles. Accordingly, in order to suppress an increase in light loss due to water bubbles inside the primary coating layer, a sandwich-like laminated sheet as shown in FIG.
It has been found that it is necessary to use a material that does not generate water bubbles exceeding 50 μm in diameter inside the next coating layer. It was also found that the optical loss hardly increased unless water bubbles exceeding 25 μm in diameter were generated inside the primary coating layer after immersing the tape-shaped optical fiber core in hot water at 60 ° C. for 30 days.

Further, when comparing the increase in light loss and the water absorption of the primary coating layer, the increase in light loss after immersion in warm water is 0.38 dB / km or more even in an optical fiber using a material having a low water absorption such as d material. It became clear that the increase in light loss due to water infiltration cannot be suppressed only by selecting a material having a small water absorption as the primary coating layer. In the present invention, the test condition is 1
It is limited to a laminated sheet in which the secondary coating layer material is sandwiched between the secondary coating layer materials, but it is important whether or not water bubbles are generated in the primary coating layer, and has a Young's modulus similar to that of the secondary coating layer material. Needless to say, the same effect can be obtained with a material.

[0022]

According to the present invention, as described above, the optical fiber core in which the outer peripheral surface of the bare glass fiber is coated with the primary coating layer and the outer peripheral surface of the primary coating layer is coated with the secondary coating layer. In the wire, the primary coating material is sandwiched between the secondary coating materials, and immersed in hot water at 60 ° C. for 7 days as a sandwich laminated sheet. Since the coating material is coated when the glass fiber bare wire is drawn, an optical fiber core excellent in water resistance can be obtained. By limiting the primary coating material and the secondary coating material of the optical fiber core as described above, the water resistance of the optical fiber core is greatly improved.
Water bubbles are not generated even if immersed for a few days, or even if they are generated, the number is extremely small and small, and blisters are not generated.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical fiber.

FIG. 2 is a cross-sectional view of an optical fiber ribbon.

FIG. 3 is a sectional view of a single-layer sheet.

FIG. 4 is a sectional view of a laminated sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber core wire 2 Glass fiber bare wire 3 Primary coating layer 4 Secondary coating layer 5 Colored layer 6 Batch coating layer 7 Tape-shaped optical fiber core wire 8 Primary coating material 9 Glass substrate 10 Single layer sheet 11 Inner layer 12 Outer layer 13 Laminated sheet

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H001 BB15 DD23 DD35 KK02 KK17 KK22 PP01 2H050 AB02Z AC71 BC03 BD02 BD05

Claims (5)

[Claims] 1. An optical fiber core comprising an outer peripheral surface of a bare glass fiber coated with at least a primary coating layer and a secondary coating layer from the inside, wherein the primary coating layer material and the secondary coating layer material are: The sheet 1 having a thickness of 200 μm or less.
A sandwich-like laminated sheet sample formed by sandwiching both surfaces of the secondary coating layer material between the sheet-like secondary coating layer materials having a thickness of 200 μm or less is immersed in hot water at 60 ° C. for 7 days. The diameter of water bubbles contained in the material is 50
An optical fiber core comprising a material having a thickness of not more than μm. 2. An optical fiber core comprising an outer peripheral surface of a bare glass fiber covered with at least a primary coating layer and a secondary coating layer from the inside, wherein the primary coating material is the primary coating material. Is coated on a glass plate, immersed in warm water of 60 ° C. for 2 days, taken out of the warm water to remove moisture on the surface of the sample, and the temperature is 23 ° C. ± 2 ° C. and the relative humidity is 50% ± 5%.
The material having a peeling force of 2 N / m or more when the primary coating layer material is peeled off from the glass plate at an angle of 90 degrees after being left for 1 hour in the above environment. Item 2. An optical fiber core according to Item 1. 3. A colored optical fiber, wherein a colored coating layer is provided on the outer peripheral surface of the optical fiber according to any one of claims 1 and 2. 4. A tape-shaped optical fiber core, wherein a plurality of the colored optical fiber cores according to claim 3 are arranged in parallel, coated collectively and integrated. 5. A colored optical fiber core in which a colored coating layer is provided on an outer peripheral surface of an optical fiber core obtained by coating at least a primary coating layer and a secondary coating layer on the outer peripheral surface of a bare glass fiber from the inside. A plurality of wires are arranged in parallel, and the diameter of water bubbles contained in the primary coating layer is 25 μm or less after the tape-shaped optical fiber core coated in a lump is immersed in warm water at 60 ° C. for 30 days. And a tape-shaped optical fiber core.