Optical Fiber Ribbon and Method for Manufacturing the Same

Abstract

To reduce the difference in microbend loss and strength between a plurality of optical fiber colored cores differing in the color of a colored layer.SOLUTION: Provided is an optical fiber ribbon comprising: a plurality of optical fiber colored cores, each of which includes an optical fiber bare wire, a primary layer formed from a first ultraviolet curable resin that covers the optical fiber bare wire, a secondary layer formed from a second ultraviolet curable resin that covers the primary layer, and a colored layer formed from a third ultraviolet curable resin that covers the secondary layer; and an adhesive layer formed from a fourth ultraviolet curable resin that covers the plurality of optical fiber colored cores, for connecting the plurality of optical fiber colored cores. The Young's modulus of the primary layer is lower than the Young's modulus of the first ultraviolet curable resin, and the difference in the Young's modulus of the primary layer between the optical fiber colored cores, of the plurality of optical fiber colored cores, differing in the color of the colored layer is 0.1 MPa or less.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an optical fiber ribbon and a method for manufacturing the optical fiber ribbon.

Background Art

[0002] There is known a technique for manufacturing an optical fiber colored core wire by forming a primary layer covering an optical fiber bare wire, a secondary layer covering the primary layer, and a colored layer covering the secondary layer with an ultraviolet curable resin so as to have a desired Young's modulus (Patent Documents 1 and 2). When the Young's modulus of the primary layer is set low, an external force applied to the optical fiber bare wire can be buffered, and optical transmission loss (hereinafter referred to as "microbend loss") due to minute deformation of the optical fiber bare wire can be suppressed. Conversely, when the Young's modulus of the secondary layer is set high, the optical fiber bare wire and the primary layer can be protected from external forces. Further, an optical fiber ribbon is manufactured by covering a plurality of optical fiber colored core wires with an ultraviolet curable resin and irradiating ultraviolet rays (UV) to connect the plurality of optical fiber colored core wires to each other. Even if the Young's modulus of the primary layer is low in the optical fiber colored core wire before the manufacturing process of the optical fiber ribbon, the Young's modulus of the primary layer increases when irradiated with UV in the manufacturing process of the optical fiber ribbon, which becomes a cause of microbend loss. On the other hand, a method for manufacturing an optical fiber ribbon in which the primary layer has a Young's modulus close to the saturated Young's modulus (Patent Document 3) and a method of preventing an unintended increase in Young's modulus due to UV exposure in a subsequent process by adding an ultraviolet absorber to the primary layer have been proposed (Patent Document 4).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent optical fiber manufacturing, due to the LED conversion of UV light sources and the increase in drawing speed, etc., optical fiber preforms with insufficient curing of the primary layer are often used. To sufficiently cure the primary layer, for example, significant restrictions are imposed on manufacturing conditions such as increasing the number of UV light sources. Therefore, it is important how to effectively utilize optical fiber preforms with insufficient curing of the primary layer.

[0005] However, when UV irradiation is performed in a subsequent process on an optical fiber element wire with insufficient curing of the primary layer, the Young's modulus of the primary layer increases. Also, depending on the combination of the ultraviolet curable resin used for the coloring layer and the wavelength of the ultraviolet rays irradiated by the UV light source, the absorbance of the coloring layer for the UV light source differs for each color of the coloring layer. Therefore, a difference can occur in the UV irradiation amount that passes through the coloring layer and reaches the inner primary layer in the coloring process, which is one of the subsequent processes. For example, when curing the coloring layer using a UV-LED that irradiates ultraviolet rays with a wavelength of 365 nm, if the absorbance of the ultraviolet curable resin used for the coloring layer for ultraviolet rays with a wavelength of 365 nm varies greatly depending on the color, a difference can occur in the amount of UV light absorbed in the coloring layer. That is, due to the difference in the color of the coloring layer, there is a possibility that the degree of increase in the Young's modulus of the primary layer will differ. As a result, when manufacturing an optical fiber ribbon using a plurality of optical fiber colored core wires with different colors of the coloring layer, optical fiber colored core wires with significantly different Young's moduli of the primary layer can be mixed in the same optical fiber ribbon. Generally, as the Young's modulus of the primary layer increases, microbend loss deteriorates. Therefore, it is conceivable that the microbend loss will change for each optical fiber colored core wire that constitutes the same optical fiber ribbon. And when a difference occurs in the microbend loss between the optical fiber colored core wires contained in the same optical fiber ribbon, it becomes difficult to describe the ribbon specifications and manage the ribbon during use. Furthermore, if the Young's moduli of the primary layers of the optical fiber colored core wires contained in the same optical fiber ribbon are different, a difference can also occur in the strength of each optical fiber colored core wire.

[0006] On the other hand, in the manufacturing method described in Patent Document 3, since it is necessary to cure at a Young's modulus close to the saturated Young's modulus, for example, it is not assumed that the curing of the primary layer becomes insufficient due to the LED conversion of the UV light source or the increase in the drawing speed. Therefore, when the absorbance of the coloring layer for the UV light source differs depending on the color used for the coloring layer, a difference can occur in the Young's modulus of the primary layer due to the UV irradiation during the coloring process. Also, in the manufacturing method described in Patent Document 4, since it is necessary to minimize the spectral overlap of the photoinitiator and the ultraviolet absorber, there are significant restrictions on the options for selecting the resin composition of the optical fiber colored core wire.

[0007] Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to provide an optical fiber ribbon and a method for manufacturing the optical fiber ribbon that reduce the difference in microbend loss and strength between a plurality of optical fiber colored cores having different colors of the colored layer.

Means for Solving the Problems

[0008] According to one aspect of the present invention, there is provided an optical fiber ribbon including: a plurality of optical fiber colored cores each having an optical fiber bare wire, a primary layer formed of a first ultraviolet curable resin covering the optical fiber bare wire, a secondary layer formed of a second ultraviolet curable resin covering the primary layer, and a colored layer formed of a third ultraviolet curable resin covering the secondary layer; and an adhesive layer formed of a fourth ultraviolet curable resin covering the plurality of optical fiber colored cores and connecting the plurality of optical fiber colored cores. The Young's modulus of the primary layer is lower than the maximum Young's modulus of the first ultraviolet curable resin, and the difference in the Young's modulus of the primary layer between the optical fiber colored cores having different colors of the colored layer among the plurality of optical fiber colored cores is 0.1 MPa or less.

[0009] According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber ribbon, comprising the steps of: drawing an optical fiber bare wire from an optical fiber preform; applying a first ultraviolet-curable resin around the optical fiber bare wire to form a primary layer; applying a second ultraviolet-curable resin around the primary layer, and irradiating the second ultraviolet-curable resin with ultraviolet light to form a secondary layer, thereby manufacturing an optical fiber element wire; applying a third ultraviolet-curable resin around the optical fiber element wire, and irradiating the third ultraviolet-curable resin with the ultraviolet light to form a colored layer, thereby manufacturing an optical fiber colored core wire; applying a fourth ultraviolet-curable resin around a plurality of the optical fiber colored core wires, and irradiating the fourth ultraviolet-curable resin with the ultraviolet light to form an adhesive layer, thereby manufacturing an optical fiber ribbon in which a plurality of the optical fiber colored core wires are connected. The Young's modulus of the primary layer is lower than the maximum Young's modulus of the first ultraviolet-curable resin, and the difference in the Young's modulus of the primary layer between the optical fiber colored core wires having different colors of the colored layer among the plurality of optical fiber colored core wires is 0.1 MPa or less.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an optical fiber ribbon and a method for manufacturing the optical fiber ribbon that reduce the difference in microbend loss and strength between a plurality of optical fiber colored core wires having different colors of the colored layer.

Brief Description of the Drawings

[0011]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. Elements having the same functions throughout the drawings are denoted by the same reference numerals, and redundant descriptions may be omitted or simplified.

[0013] FIG. 1A is a cross-sectional view of an optical fiber colored core wire 1 according to the present embodiment. The optical fiber colored core wire 1 includes an optical fiber bare wire 2, a primary layer 3 coated on the outer periphery of the optical fiber bare wire 2, a secondary layer 4 coated on the outer periphery of the primary layer 3, and a colored layer 5 coated on the outer periphery of the secondary layer 4. The optical fiber bare wire 2 is coated with three coating layers, namely the primary layer 3, the secondary layer 4, and the colored layer 5. FIG. 1B is a cross-sectional view of an optical fiber strand 6 according to the present embodiment. The optical fiber strand 6 is a fiber in a state before the colored layer 5 is formed.

[0014] The optical fiber bare wire 2 is formed of, for example, silica glass or the like and transmits light. The primary layer 3, the secondary layer 4, and the colored layer 5 are each formed by curing an ultraviolet curable resin by irradiation with ultraviolet rays. The ultraviolet curable resin is not particularly limited as long as it can be polymerized by irradiation with ultraviolet rays. The ultraviolet curable resin is, for example, a resin that can be polymerized by photoradical polymerization or the like.

[0015] The ultraviolet-curable resin is an ultraviolet-curable resin having a polymerizable unsaturated group such as an ethylenically unsaturated group that polymerizes and cures with ultraviolet rays, such as urethane (meth)acrylate, epoxy (meth)acrylate, and polyester (meth)acrylate, for example, urethane (meth)acrylate such as polyether-based urethane (meth)acrylate and polyester-based urethane (meth)acrylate, and preferably has at least two polymerizable unsaturated groups.

[0016] Examples of the polymerizable unsaturated group in the ultraviolet-curable resin include groups having an unsaturated double bond such as a vinyl group, an allyl group, an acryloyl group, and a methacryloyl group, and groups having an unsaturated triple bond such as a propargyl group. Among these, an acryloyl group and a methacryloyl group are preferable in terms of polymerizability.

[0017] Also, the ultraviolet-curable resin can be a monomer, oligomer, or polymer that starts polymerization and cures upon irradiation with ultraviolet rays, but is preferably an oligomer. An oligomer is a polymer having a degree of polymerization of 2 to 100. Also, in this specification, “(meth)acrylate” means one or both of acrylate and methacrylate. The ultraviolet-curable resin contains an arbitrary photoinitiator (hereinafter referred to as “photoinitiator”) having sensitivity in the ultraviolet region.

[0018] Polyether-based urethane (meth)acrylate is a compound having a polyether segment, (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyether backbone, an organic polyisocyanate compound, and hydroxyalkyl (meth)acrylate. Also, polyester-based urethane (meth)acrylate is a compound having a polyester segment, (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyester backbone, an organic polyisocyanate compound, and hydroxyalkyl (meth)acrylate.

[0019] Furthermore, in addition to the oligomer and the photoinitiator, the ultraviolet curable resin may contain, for example, a diluent monomer, a photosensitizer, a chain transfer agent, and various additives. As the diluent monomer, a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate is used. Here, the diluent monomer means a monomer for diluting the ultraviolet curable resin.

[0020] The primary layer 3 is a soft layer and has a function of buffering an external force applied to the optical fiber bare wire 2. When the optical fiber element wire 6 is formed, there may still be room for curing in the primary layer 3, but when it is in a cured state until the room disappears, the Young's modulus of the primary layer 3 becomes maximum. In the present embodiment, the maximum Young's modulus that the primary layer 3 of the optical fiber element wire 6 can exhibit is defined as the "maximum Young's modulus".

[0021] The irradiation of ultraviolet rays is performed at an appropriate illuminance and irradiation amount as needed, for example, using a mercury lamp, a UV-LED, or the like. Further, the maximum Young's modulus varies depending on the optical fiber manufacturing conditions (for example, linear velocity, UV irradiation intensity, UV light source type, resin coating temperature, etc.) and cannot be uniquely determined by the ultraviolet curable resin used. Also, in the optical fiber element wire 6, the optical fiber colored core wire 1, and the optical fiber ribbon 100 in the present embodiment, the Young's modulus of the primary layer 3 is lower than the maximum Young's modulus of the ultraviolet curable resin forming the primary layer 3.

[0022] The secondary layer 4 is a hard layer preferably having a Young's modulus of 500 MPa or more, and has a function of protecting the optical fiber bare wire 2 and the primary layer 3 from an external force.

[0023] The coloring layer 5 is the outermost layer of the optical fiber colored core wire 1 and has a function of protecting the optical fiber bare wire 2, the primary layer 3, and the secondary layer 4 from an external force. The coloring layer 5 is colored with a colorant mixed with a pigment, a lubricant, etc. to identify the optical fiber colored core wire 1. Examples of the color types include white, black, gray, purple, blue, light blue, green, brown, yellow, orange, pink, red, etc.

[0024] Figure 2A is a schematic diagram showing a part of the manufacturing apparatus 10 used in the method for manufacturing the optical fiber colored core wire 1 according to the present embodiment. In Figure 2A, the manufacturing apparatus 10 includes a heating apparatus 20, a primary layer coating apparatus 30, a secondary layer coating apparatus 40, a guide roller 45, and a first winding apparatus 50.

[0025] The optical fiber preform BM is made of, for example, quartz-based glass and is manufactured by well-known methods such as the VAD method, the OVD method, and the MCVD method. The heating apparatus 20 has a heater 21. The heater 21 can be any heat source such as a tape heater, a ribbon heater, a rubber heater, an oven heater, a ceramic heater, or a halogen heater. The end of the optical fiber preform BM is heated and melted by the heater 21 disposed around the optical fiber preform BM, and is drawn to pull out the optical fiber bare wire 2.

[0026] Below the heating apparatus 20, a primary layer coating apparatus 30 is provided. The primary layer coating apparatus 30 includes a resin coating apparatus 31 and an ultraviolet irradiation apparatus 32. The resin coating apparatus 31 holds an ultraviolet curable resin (hereinafter referred to as "first ultraviolet curable resin"), which is a coating material for forming the primary layer 3. The first ultraviolet curable resin is applied to the optical fiber bare wire 2 drawn from the optical fiber preform BM by the resin coating apparatus 31.

[0027] Below the resin coating apparatus 31, an ultraviolet irradiation apparatus 32 is provided. The ultraviolet irradiation apparatus 32 includes any ultraviolet light source such as a metal halide lamp, a mercury lamp, or a UV-LED. The first ultraviolet curable resin is applied to the optical fiber bare wire 2 by the resin coating apparatus 31, and the optical fiber bare wire 2 enters the ultraviolet irradiation apparatus 32, where the first ultraviolet curable resin is irradiated with ultraviolet light. As a result, the first ultraviolet curable resin is cured to form the primary layer 3.

[0028] Below the primary layer coating device 30, a secondary layer coating device 40 is provided. The secondary layer coating device 40 includes a resin coating device 41 and an ultraviolet irradiation device 42. The resin coating device 41 holds an ultraviolet curable resin (hereinafter referred to as "second ultraviolet curable resin"), which is a coating material for forming the secondary layer 4. The second ultraviolet curable resin is applied to the primary layer 3 by the resin coating device 41.

[0029] Below the resin coating device 41, an ultraviolet irradiation device 42 is provided. The ultraviolet irradiation device 42 can be configured in the same manner as the ultraviolet irradiation device 32. The optical fiber bare wire 2 coated with the second ultraviolet curable resin on the primary layer 3 enters the ultraviolet irradiation device 42, and the second ultraviolet curable resin is irradiated with ultraviolet rays. As a result, the second ultraviolet curable resin is cured, and the secondary layer 4 is formed. By coating the primary layer 3 and the secondary layer 4 on the optical fiber bare wire 2, the optical fiber element 6 is formed.

[0030] Note that the resin coating device 31 may be configured to hold the first ultraviolet curable resin and the second ultraviolet curable resin separately. In this case, the resin coating device 31 applies the first ultraviolet curable resin to the optical fiber bare wire 2, and then applies the second ultraviolet curable resin on the first ultraviolet curable resin.

[0031] The ultraviolet irradiation device 32 irradiates ultraviolet rays onto the first ultraviolet curable resin and the second ultraviolet curable resin applied to the optical fiber bare wire 2. Thereby, the primary layer 3 and the secondary layer 4 are formed. In this case, the manufacturing apparatus 10 does not necessarily need to have the secondary layer coating device 40.

[0032] Below the secondary layer coating device 40, a guide roller 45 and a first winding device 50 are provided. The manufactured optical fiber element 6 is guided by the guide roller 45 and wound by the first winding device 50.

[0033] FIG. 2B is a schematic diagram showing another part of the manufacturing apparatus 10 used in the method for manufacturing the optical fiber colored core wire 1 according to the present embodiment. In FIG. 2B, the manufacturing apparatus 10 includes a strand holding device 55, a guide roller 56, a colored layer coating device 60, a guide roller 65, and a second take-up device 70. The manufacturing apparatus 10 manufactures the optical fiber colored core wire 1 from the optical fiber strands 6 manufactured by the plurality of apparatuses shown in FIG. 2A.

[0034] The strand holding device 55 holds the manufactured optical fiber strands 6 in a wound state. In FIG. 2B, the strand holding device 55 is shown as a device separate from the first take-up device 50, but the first take-up device 50 may also serve as the strand holding device 55.

[0035] Below the strand holding device 55, a colored layer coating device 60 is provided. The optical fiber strands 6 drawn out from the strand holding device 55 are guided by a guide roller 56 provided between the strand holding device 55 and the colored layer coating device 60 and conveyed into the colored layer coating device 60.

[0036] The colored layer coating device 60 includes a resin coating device 61 and an ultraviolet irradiation device 62. The resin coating device 61 holds an ultraviolet curable resin (hereinafter referred to as the "third ultraviolet curable resin"), which is a coating material for forming the colored layer 5.

[0037] The third ultraviolet curable resin is applied to the optical fiber strands 6 by the resin coating device 61. Below the resin coating device 61, an ultraviolet irradiation device 62 is provided. The ultraviolet irradiation device 62 can be configured in the same manner as the ultraviolet irradiation devices 32 and 42.

[0038] The optical fiber strands 6 with the third ultraviolet curable resin applied to the outer periphery of the secondary layer 4 enter the ultraviolet irradiation device 62, and the third ultraviolet curable resin and the optical fiber strands 6 are irradiated with ultraviolet light. As a result, the third ultraviolet curable resin is cured, and the colored layer 5 is formed.

[0039] The primary layer 3, the secondary layer 4, and the coloring layer 5 are coated on the bare optical fiber 2, thereby forming the optical fiber colored core wire 1. After manufacturing, the optical fiber colored core wire 1 is guided by a guide roller 65 provided below a coloring layer coating device 60 and wound around a second winding device 70.

[0040] FIG. 3 is a cross-sectional view of an optical fiber ribbon 100 according to this embodiment. The optical fiber ribbon 100 is configured by bundling n (n is a natural number of 2 or more) optical fiber colored core wires 1-1 to 1-n in a band shape via an adhesive layer 101.

[0041] Also, in this embodiment, it is assumed that the colors of the coloring layers 5 of the plurality of optical fiber colored core wires 1-1 to 1-n are not all the same. That is, two or more types of optical fiber colored core wires 1 having coloring layers 5 of different colors are included in the same optical fiber ribbon 100.

[0042] Also, it is preferable that there is no difference in the ultraviolet absorbance depending on the color of the coloring layer 5. For example, when the optical fiber colored core wire 1-1 has a white coloring layer 5 and the optical fiber colored core wire 1-n has a black coloring layer 5, the ultraviolet absorbance may be different between these two optical fiber colored core wires 1. As one solution in this case, a method of adding an additive for adjusting the ultraviolet absorbance with respect to ultraviolet rays of a predetermined wavelength to the third ultraviolet curable resin forming the coloring layer 5 according to the color of the coloring layer 5 to be formed is conceivable. By appropriately adjusting the type and addition amount of the additive for each color of the coloring layer 5, the difference in absorbance between the plurality of optical fiber colored core wires 1-1 to 1-n can be reduced.

[0043] It is preferable that at least a part of the wavelength range (first wavelength range) in which the additive added to the third ultraviolet curable resin absorbs ultraviolet rays overlaps with the wavelength range (second wavelength range) in which the photoinitiator added to the first ultraviolet curable resin absorbs ultraviolet rays.

[0044] The adhesive layer 101 is formed by irradiating a coating material containing an ultraviolet curable resin with ultraviolet light to cure it. In this specification, the adhesive layer 101 is also referred to as a ribbon layer. The ultraviolet curable resin forming the adhesive layer 101 is composed of the same resin as the ultraviolet curable resin forming the primary layer 3, the secondary layer 4, and the colored layer 5. The optical fiber colored core wire 1 can be bundled densely by taking the form of an optical fiber ribbon 100. Note that the optical fiber ribbon 100 is not limited to the configuration shown in FIG. 3. Further, the optical fiber ribbon 100 may take the form of an optical fiber ribbon cable housed by a sheath.

[0045] FIG. 4 is a schematic diagram of a ribbonizing apparatus 80 used in the manufacturing method of the optical fiber ribbon 100 according to the present embodiment. The ribbonizing apparatus 80 includes a resin coating apparatus 81 and an ultraviolet irradiation apparatus 82. The resin coating apparatus 81 holds an ultraviolet curable resin (hereinafter referred to as "fourth ultraviolet curable resin") which is the coating material of the adhesive layer 101.

[0046] A plurality of prepared optical fiber colored core wires 1 of different colors enter the ribbonizing apparatus 80, and the fourth ultraviolet curable resin is applied by the resin coating apparatus 81. The optical fiber colored core wire 1 coated with the fourth ultraviolet curable resin is bundled together with other plurality of optical fiber colored core wires 1 coated with the fourth ultraviolet curable resin. Ultraviolet light is irradiated onto the bundled plurality of optical fiber colored core wires 1 by the ultraviolet irradiation apparatus 82 provided in the ribbonizing apparatus 80. As a result, the fourth ultraviolet curable resin is cured to become the adhesive layer 101. A plurality of optical fiber colored core wires 1 arranged in parallel via the adhesive layer 101 are connected. In this way, the optical fiber ribbon 100 is formed from the plurality of optical fiber colored core wires 1.

[0047] Note that the ribbonizing apparatus 80 may be, for example, the ribbonizing apparatus described in JP-A-2012-118358. Thereby, the adhesive layer 101 is intermittently formed at a predetermined interval in the longitudinal direction of adjacent optical fiber colored core wires 1, and an intermittently adhered type optical fiber ribbon 100 is formed.

[0048] FIG. 5 is a flowchart of a method for manufacturing the optical fiber colored core wire 1 and the optical fiber ribbon 100 according to the present embodiment. First, the user installs the optical fiber base material BM in the manufacturing apparatus 10 (step S101).

[0049] Next, the heater 21 provided in the heating device 20 heats the optical fiber base material BM and starts drawing the optical fiber bare wire 2 (step S102).

[0050] The primary layer coating device 30 applies a first ultraviolet curable resin around the drawn optical fiber bare wire 2, irradiates the first ultraviolet curable resin with ultraviolet rays, and forms the primary layer 3 (step S103).

[0051] Next, the secondary layer coating device 40 applies a second ultraviolet curable resin around the primary layer 3, irradiates the second ultraviolet curable resin with ultraviolet rays, and forms the secondary layer 4 (step S104). Thereby, the optical fiber element wire 6 is obtained. The manufactured optical fiber element wire 6 is wound around the first winding device 50.

[0052] Subsequently, when the coloring layer coating device 60 pulls out the optical fiber element wire 6 from the element wire holding device 55 or the first winding device 50, it applies a third ultraviolet curable resin around the secondary layer 4 of the optical fiber element wire 6, irradiates the third ultraviolet curable resin with ultraviolet rays, and forms the coloring layer 5 (step S105). By coating the coloring layer 5 around the optical fiber element wire 6, the optical fiber colored core wire 1 is obtained. The manufactured optical fiber colored core wire 1 is wound around the second winding device 70.

[0053] In the present embodiment, a plurality of optical fiber colored core wires 1 having different colors of the coloring layer 5 are manufactured. For this reason, it is assumed that the process of step S105 is performed by changing the manufacturing conditions such as the composition of the third ultraviolet curable resin for each color.

[0054] Also, it is not always necessary to irradiate ultraviolet rays in the step of forming the primary layer 3 (step S103). In this case, the primary layer 3 can be cured in the step of forming the secondary layer 4 (step S104).

[0055] After the coloring layer 5 is formed in step S105, the ribbonizing device 80 applies a fourth ultraviolet curable resin so as to cover the plurality of fiber optic colored cores 1 prepared in different colors, and irradiates the fourth ultraviolet curable resin with ultraviolet rays to connect the plurality of fiber optic colored cores 1 to each other (step S106). Thereby, the fiber optic ribbon 100 is manufactured.

[0056] According to the present embodiment, when coloring the optical fiber element wire 6 having an insufficiently cured primary layer, the difference in absorbance with respect to the wavelength of the UV light source for each color of the coloring layer 5 is reduced. Specifically, among the plurality of fiber optic colored cores 1 included in the same fiber optic ribbon 100, the difference in Young's modulus of the primary layer 3 between the fiber optic colored cores 1 having different colors of the coloring layer 5 is adjusted to be 0.1 MPa or less. As a result, even when the same fiber optic ribbon 100 includes a plurality of fiber optic colored cores 1 having different colors of the coloring layer 5, the microbend loss difference and the intensity difference between the plurality of fiber optic colored cores 1 can be reduced.

Example

[0057] Hereinafter, the experimental results when an experiment simulating the coloring process for the above-described optical fiber element wire 6 will be described.

[0058] When additional UV irradiation is performed on the optical fiber element wire 6, in order to simulate the coloring process of the optical fiber, a third ultraviolet curable resin that forms the coloring layer 5 is applied with a film thickness of 6 μm ± 2 μm on quartz glass that has no absorption characteristics with respect to the UV light used, covering the optical fiber element wire 6. When adding additives, it was carried out on the third ultraviolet curable resin that forms the coloring layer 5. The third ultraviolet curable resin that forms the coloring layer 5 is composed of an oligomer, a monomer, etc., and may additionally contain additives such as a photoinitiator, a photosensitizer, an ultraviolet absorber, an antioxidant, and a pigment.

[0059] Table 1 shows the Young's modulus (MPa), maximum Young's modulus (MPa), Young's modulus increase amount of the primary layer 3 of the used fiber, the color of the ultraviolet curable resin that forms the coloring layer 5, the presence or absence and types of additives, the absorbance with respect to ultraviolet light with a wavelength of 365 nm, the Young's modulus (MPa) after additional UV irradiation, the Young's modulus increase amount, and the difference from the Young's modulus when the color of the coloring layer 5 is white in Examples 1 to 8 and Comparative Examples 1 to 3.

Table 1

[0060] The "maximum Young's modulus" in Table 1 is the maximum Young's modulus that the primary layer 3 of the optical fiber element wire 6 can exhibit. Also, the "Young's modulus" in Table 1 is the ISM (In Situ Modulus) of the primary layer 3 of the optical fiber colored core wire 1. ISM is defined as being measured by the following method.

[0061] First, using a commercially available stripper, the primary layer 3 and the secondary layer 4 in the middle part of the optical fiber serving as a sample are stripped off for a length of several millimeters. Then, one end of the optical fiber with the coating layer formed is fixed on a slide glass with an adhesive, and a load F is applied to the other end of the optical fiber with the coating layer formed. In this state, the displacement δ of the primary layer 3 at the boundary between the part where the coating layer is stripped off and the part where the coating layer is formed is read with a microscope. Then, by setting the load F to 10, 20, 30, 50, and 70 gf (i.e., 98, 196, 294, 490, and 686 mN in sequence), a graph of the displacement δ against the load F is created. Then, the primary elastic modulus is calculated using the slope obtained from the graph and the following formula (1). Since the calculated primary elastic modulus corresponds to the so-called ISM, it will be described as P-ISM as appropriate below. When drawing the optical fiber colored core 1, the drawing speed and the illuminance of ultraviolet light were controlled to adjust the P-ISM. P-ISM = (3F / δ) * (1 / 2πl) * ln(DP / DG) ···(1)

[0062] Here, the unit of P-ISM is [MPa]. Also, F / δ is the slope shown by the graph of the displacement (δ) [μm] against the load (F) [gf], l is the sample length (for example, 10 mm), and DP / DG is the ratio of the outer diameter (DP) [μm] of the primary layer 3 to the outer diameter (DG) [μm] of the cladding part of the optical fiber. Therefore, when calculating P-ISM using the above formula from the used F, δ, and l, it is necessary to perform a predetermined unit conversion. The outer diameter of the primary layer 3 and the outer diameter of the cladding part can be measured by observing the cross-section of the optical fiber cut by a fiber cutter with a microscope.

[0063] Various methods for measuring microbend loss can be considered. In this specification, for a relatively large bobbin wound with #1000 sandpaper, with a tension of 100 gf, the transmission loss of the optical fiber to be measured in state A where an optical fiber with a length of 400 m or more is wound in a single layer without overlapping each other, and the transmission loss of the optical fiber in state B where the same bobbin as in state A is wound with the same tension and the same length without sandpaper, are defined as the value of microbend loss. Here, the transmission loss of the optical fiber in state B does not include microbend loss and is considered to be the transmission loss inherent to the optical fiber itself.

[0064] Note that this measurement method is similar to the fixed-diameter drum method specified in JIS C6823:2010. Also, this measurement method is also called the sandpaper method. Also, in this measurement method, since the transmission loss is measured at a wavelength of 1550 nm, the following microbend loss is also the value at a wavelength of 1550 nm.

[0065] Note that the effective core area (effective core area) Aeff can be cited as an index representing the ease of occurrence of microbend loss in an optical fiber. The effective core area is expressed by the following formula (2). Aeff = (πk / 4)*(MFD) 2 ···(2) Here, the effective core area Aeff is the value at a wavelength of 1550 nm, MFD is the mode field diameter (μm), and k is a constant. The effective core area Aeff represents the area of the cross-section perpendicular to the axis of the optical fiber bare wire 2 through which light having a predetermined intensity passes. Generally, the larger the effective core area Aeff of the optical fiber bare wire 2, the weaker the optical confinement in the cross-section of the optical fiber bare wire 2. That is, when the effective core area Aeff of the optical fiber bare wire 2 is large, the light in the optical fiber bare wire 2 is likely to leak due to an external force applied to the optical fiber bare wire 2. For this reason, when the effective core area Aeff of the optical fiber bare wire 2 increases, the microbend loss of the optical fiber colored core wire 1 is likely to occur.

[0066] In each of the examples and comparative examples, as the optical fiber, an optical fiber having an effective core cross-sectional area Aeff of 80 μm 2 or more is used. In the optical fiber, the effective core cross-sectional area Aeff serves as an index of the microbend sensitivity, indicating that the larger the effective core cross-sectional area Aeff, the higher the microbend sensitivity. Generally, when the effective core cross-sectional area Aeff exceeds 100 μm 2 , it is said that the microbend sensitivity is high. Therefore, when the effective core cross-sectional area Aeff is 130 μm 2 or more and 150 μm 2 or less, the optical fiber has a high microbend sensitivity without problems.

[0067] The absorbance in each of the examples and comparative examples was determined as follows. A third ultraviolet curable resin constituting the colored layer was applied on quartz glass with a film thickness of 6 μm ± 2 μm, and the absorbance of the produced quartz glass with the coating film was measured using a spectrophotometer (PerkinElmer, Lambda 900). However, the absorbance of the third ultraviolet curable resin forming the colored layer 5 was determined by subtracting the absorbance of only the quartz glass measured in advance from the absorbance of the quartz glass with the coating film. The absorbance A in each of the examples and comparative examples is represented by the following formula (3). A = -log(I / I0) = -log(T / 100) = εcl ···(3) Here, T is the transmittance, I is the transmitted light intensity, I0 is the incident light intensity, A is the absorbance, ε is the molar absorption coefficient, c is the concentration of the absorbing substance, and l is the distance of the medium through which the light passes.

[0068] The "Young's modulus after additional UV irradiation" in Table 1 is defined as P-ISM when the optical fiber strand 6 is re-irradiated with UV using a UV-LED that irradiates ultraviolet light with a wavelength of 365 nm ± 20 nm at an illuminance of 1500 mW / cm 2 and an irradiation dose of 500 mJ / cm 2 .

[0069] In the optical fiber strand 6 used in each of the examples and comparative examples, first, a first ultraviolet curable resin was applied around the drawn optical fiber bare wire 2, and the first ultraviolet curable resin was irradiated with ultraviolet light to form the primary layer 3.

[0070] Next, a second ultraviolet-curable resin was applied around the primary layer 3, and the secondary layer 4 was formed by irradiating the second ultraviolet-curable resin with ultraviolet light. Note that it is not always necessary to irradiate ultraviolet light in the step of forming the primary layer 3. In this case, the primary layer 3 can be cured by the irradiation of ultraviolet light in the step of forming the secondary layer 4.

[0071] When drawing the optical fiber element wire 6, the wire speed and illuminance were controlled in order to adjust the Young's modulus of the P-ISM or the secondary layer 4. 2,4,6-Trimethylbenzoyl-diphenylphosphine oxide was used as the photoinitiator of the primary layer 3 of the optical fiber colored core wire 1. When this photoinitiator is used in the reaction by UV irradiation, the absorbance in the vicinity of 340 to 410 nm decreases.

[0072] By comparing the absorbance before and after UV irradiation and confirming the change in absorbance, the absorption wavelength of the photoinitiator contained in the primary layer 3 can be detected. Of course, even without this method, it is easy to determine whether it is the absorption wavelength derived from the photoinitiator. For example, as an example, it is also possible to determine the absorption wavelength of the photoinitiator added to the primary layer 3 by comparing it with the absorption wavelength of the photoinitiator distributed on the market.

[0073] The diameter of the optical fiber bare wire 2 is 80 μm or more and 150 μm or less, and preferably can be 124 μm or more and 126 μm or less. The thickness of the primary layer 3 can be 5 μm or more and 60 μm or less. The thickness of the secondary layer 4 can be 5 μm or more and 60 μm or less. Also, the thickness of the colored layer 5 can be about several μm.

[0074] In each of the examples and comparative examples, the used optical fibers were adjusted to have various Young's moduli and maximum Young's moduli by controlling the manufacturing conditions (linear velocity and illuminance) and by selecting the first ultraviolet curable resin that forms the primary layer 3. Further, the Young's modulus of the secondary layer 4 is 800 to 1000 MPa.

[0075] In Examples 1, 4, and 7, 1.0 wt% of 2,2’,4,4’-tetrahydroxybenzophenone was added as additive A. In Examples 2, 5, and 8, 10.0 wt% of TiO2 (Ishibashi Sangyo Co., Ltd. / CR-60-2) was added as additive B. By adding these additives to the ultraviolet curable resin that forms the colored layer, the absorbance with respect to ultraviolet rays in a predetermined wavelength range increases.

[0076] In Example 1, an optical fiber strand 6 having a Young's modulus of 0.15 MPa and a maximum Young's modulus of 1.15 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet rays with a wavelength of 365 nm (Example 1a), the Young's modulus after additional UV irradiation was 0.82 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet curable resin that forms a black colored layer 5 with an absorbance of 0.66 with respect to ultraviolet rays with a wavelength of 365 nm by adding additive A (Example 1b), the Young's modulus after additional UV irradiation was 0.81 MPa, and the difference from the white color was 0.01 MPa.

[0077] In Example 2, an optical fiber strand 6 with a Young's modulus of 0.15 MPa and a maximum Young's modulus of 1.15 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 2a), the Young's modulus after additional UV irradiation was 0.82 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a black colored layer 5 with an additive B added to have an absorbance of 0.55 with respect to ultraviolet light having a wavelength of 365 nm (Example 2b), the Young's modulus after additional UV irradiation was 0.89 MPa, and the difference from the white color was 0.07 MPa.

[0078] In Example 3, an optical fiber strand with a Young's modulus of 0.37 MPa and a maximum Young's modulus of 0.40 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 3a), the Young's modulus after additional UV irradiation was 0.38 MPa. On the other hand, when the optical fiber strand was covered with an ultraviolet-curable resin that forms a black colored layer having an absorbance of 0.25 with respect to ultraviolet light having a wavelength of 365 nm (Example 3b), the Young's modulus after additional UV irradiation was 0.39 MPa, and the difference from the white color was 0.01 MPa.

[0079] In Example 4, an optical fiber strand with a Young's modulus of 0.39 MPa and a maximum Young's modulus of 0.73 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 4a), the Young's modulus after additional UV irradiation was 0.58 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a black colored layer 5 with an additive A added to have an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 4b), the Young's modulus after additional UV irradiation was 0.62 MPa, and the difference from the white color was 0.04 MPa.

[0080] In Example 5, an optical fiber strand with a Young's modulus of 0.39 MPa and a maximum Young's modulus of 0.73 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 5a), the Young's modulus after additional UV irradiation was 0.58 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a black colored layer 5 with an additive B added to have an absorbance of 0.55 with respect to ultraviolet light having a wavelength of 365 nm (Example 5b), the Young's modulus after additional UV irradiation was 0.63 MPa, and the difference from white was 0.05 MPa.

[0081] In Example 6, an optical fiber strand with a Young's modulus of 0.43 MPa and a maximum Young's modulus of 0.56 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 6a), the Young's modulus after additional UV irradiation was 0.51 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a black colored layer 5 having an absorbance of 0.25 with respect to ultraviolet light having a wavelength of 365 nm (Example 6b), the Young's modulus after additional UV irradiation was 0.55 MPa, and the difference from white was 0.04 MPa.

[0082] In Example 7, an optical fiber strand with a Young's modulus of 0.54 MPa and a maximum Young's modulus of 0.76 MPa was used. When the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 7a), the Young's modulus after additional UV irradiation was 0.63 MPa. On the other hand, when the optical fiber strand 6 was covered with a third ultraviolet-curable resin that forms a black colored layer 5 with an additive A added to have an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 7b), the Young's modulus after additional UV irradiation was 0.63 MPa, and the difference from white was 0.00 MPa.

[0083] In Example 8, an optical fiber strand with a Young's modulus of 0.54 MPa and a maximum Young's modulus of 0.76 MPa was used. When the optical fiber strand was coated with a third ultraviolet-curable resin that forms a white colored layer having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Example 8a), the Young's modulus after additional UV irradiation was 0.63 MPa. On the other hand, when the optical fiber strand 6 was coated with a third ultraviolet-curable resin that forms a black colored layer 5 with an additive B added to have an absorbance of 0.55 with respect to ultraviolet light having a wavelength of 365 nm (Example 8b), the Young's modulus after additional UV irradiation was 0.67 MPa, and the difference from white was 0.04 MPa.

[0084] In Comparative Example 1, an optical fiber strand 6 with a Young's modulus of 0.15 MPa and a maximum Young's modulus of 1.15 MPa was used. When the optical fiber strand 6 was coated with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Comparative Example 1a), the Young's modulus after additional UV irradiation was 0.82 MPa. On the other hand, when the optical fiber strand was coated with a third ultraviolet-curable resin that forms a black colored layer 5 having an absorbance of 0.25 with respect to ultraviolet light having a wavelength of 365 nm (Comparative Example 1b), the Young's modulus after additional UV irradiation was 1.04 MPa. The difference between white and black was 0.22 MPa, which was 0.1 MPa or more.

[0085] In Comparative Example 2, an optical fiber strand 6 with a Young's modulus of 0.39 MPa and a maximum Young's modulus of 0.73 MPa was used. When the optical fiber strand 6 was coated with a third ultraviolet-curable resin that forms a white colored layer 5 having an absorbance of 0.66 with respect to ultraviolet light having a wavelength of 365 nm (Comparative Example 2a), the Young's modulus after additional UV irradiation was 0.58 MPa. On the other hand, when the optical fiber strand 6 was coated with a third ultraviolet-curable resin that forms a black colored layer 5 having an absorbance of 0.25 with respect to ultraviolet light having a wavelength of 365 nm (Comparative Example 2b), the Young's modulus after additional UV irradiation was 0.71 MPa. The difference between white and black was 0.13 MPa, which was 0.1 MPa or more.

[0086] In Comparative Example 3, the optical fiber strand 6 with a Young's modulus of 0.54 MPa and a maximum Young's modulus of 0.76 MPa was used. When the optical fiber strand 6 was covered with the third ultraviolet curable resin that forms the white colored layer 5 with an absorbance of 0.66 for ultraviolet rays with a wavelength of 365 nm (Comparative Example 3a), the Young's modulus after additional UV irradiation was 0.63 MPa. On the other hand, when the optical fiber strand was covered with the third ultraviolet curable resin that forms the black colored layer 5 with an absorbance of 0.25 for ultraviolet rays with a wavelength of 365 nm (Comparative Example 3b), the Young's modulus after additional UV irradiation was 0.74 MPa. The difference between white and black was 0.11 MPa, which was 0.1 MPa or more.

[0087] In the above-described Examples and Comparative Examples, the cases where the color of the colored layer is white and black were taken up. However, the present invention can be similarly applied to any combination of colors having a difference in absorbance in the UV region to be used. Examples of the types of colors include white, black, gray, purple, blue, light blue, green, brown, yellow, orange, pink, red, and the like.

[0088] Also, in each of the Examples and Comparative Examples, the Young's modulus after additional UV irradiation was defined as P-ISM when the optical fiber strand 6 was re-irradiated with ultraviolet rays under the conditions of 1500 mW / cm 2 , 500 mJ / cm 2 by a UV-LED with an irradiation wavelength of 365 nm ± 20 nm. However, the UV light source is not limited to a UV-LED with a wavelength of 365 nm ± 20 nm. For example, for UV-LEDs with different wavelengths such as a UV-LED with a wavelength of 385 nm ± 20 nm and a UV-LED with a wavelength of 395 nm ± 20 nm, and also for those that emit UV light such as metal halide lamps and mercury lamps other than UV-LEDs, the same effect can be obtained when an additive having an absorption region in that range is used. Also, regarding the illuminance and irradiation dose, the same effect can be obtained even when irradiated under other conditions.

[0089] In addition, the additives used in Examples 1, 2, 4, 5, and 7 are only examples, and are not limited to ultraviolet absorbers and pigments. Any additives such as photoinitiators and photosensitizers having absorption wavelengths in the ultraviolet wavelength range of the UV light source used may be used. In addition to Additives A and B, for example, compounds such as bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-isopropylthioxanthone, 2,2-Dihydroxy-4,4-dimethoxybenzophenone, 2,4,6-Tris[4-(hexyloxy)-2-hydroxy-3-methylphenyl]-1,3,5-triazine, and 2-(2-Hydroxy-5-methylphenyl)benzotriazole can also be additives.

[0090] It is also clear that the types of effective additives vary depending on the absorption wavelength of the photoinitiator used in the primary layer 3. Therefore, it is important to add additives having an absorption wavelength range that partially overlaps with the absorption wavelength range of the photoinitiator used.

[0091] The Young's modulus of the primary layer 3 shown in each of the examples and comparative examples is only an example and is not limited thereto. For example, the Young's modulus of the primary layer 3 can be in the range of 0.1 to 2.0 MPa. The Young's modulus of the secondary layer can be in the range of 500 to 2000 MPa, for example.

[0092] In addition, 19 types of optical fiber colored cores 1 with different Young's moduli of the primary layer 3 were randomly selected, where the Young's modulus of the secondary layer 4 was about 1000 MPa, and the Young's modulus difference and microbend loss difference of each primary layer 3 were calculated.

[0093] FIG. 6 is a graph showing the relationship between the Young's modulus difference of the primary layer 3 of the optical fiber colored core wire 1 according to the embodiment and the ratio at which the microbend loss difference becomes 0.05 dB / km or more. As shown in FIG. 6, when the ratio at which the microbend loss difference becomes 0.05 dB / km or more was calculated for each 0.05 MPa range of the Young's modulus difference, it was confirmed that the ratio at which the microbend loss difference becomes 0.05 dB / km or more rapidly increases at the boundary of the Young's modulus difference of 0.1 MPa. Thus, it was found that it is desirable that the difference in Young's modulus of the primary layer 3 for each optical fiber colored core wire 1 used in the same optical fiber ribbon 100 be 0.1 MPa or less. This also agreed with the results of the above-described Examples 1 to 8.

[0094] The present invention is not limited to the above-described embodiments and can be variously modified. For example, an example in which a part of the configuration of one embodiment is added to another embodiment or an example in which a part of the configuration of another embodiment is replaced is also an embodiment of the present invention. Also, regarding parts not particularly described or illustrated in the embodiments, well-known techniques and publicly known techniques in the relevant technical field can be appropriately applied.

[0095] 1 Optical fiber colored core wire 2 Optical fiber bare wire 3 Primary layer 4 Secondary layer 5 Coloring layer 6 Optical fiber element wire 100 Optical fiber ribbon 101 Adhesive layer

Claims

1. A plurality of optical fiber colored core wires each having an optical fiber bare wire, a primary layer formed of a first ultraviolet curable resin covering the optical fiber bare wire, a secondary layer formed of a second ultraviolet curable resin covering the primary layer, and a colored layer formed of a third ultraviolet curable resin covering the secondary layer, An adhesive layer formed of a fourth ultraviolet curable resin covering the plurality of optical fiber colored core wires and connecting the plurality of optical fiber colored core wires, An optical fiber ribbon comprising: The Young's modulus of the primary layer is lower than the maximum Young's modulus of the first ultraviolet curable resin, Among the plurality of optical fiber colored core wires, the difference in the Young's modulus of the primary layer between the optical fiber colored core wires having different colors of the colored layer is 0.1 MPa or less, The photoinitiator added to the first ultraviolet curable resin has absorption in the wavelength range of 340 nm or more and 410 nm or less, An optical fiber ribbon characterized by the above.

2. When the photoinitiator reacts, the absorbance decreases in the wavelength range of 340 nm or more and 410 nm or less, The optical fiber ribbon according to claim 1, characterized by the above.

3. The Young's modulus of the primary layer is 0.15 MPa or more and 0.89 MPa or less, The optical fiber ribbon according to claim 1 or 2, characterized by the above.

4. At least one of the type and addition amount of an additive that changes the absorbance of the third ultraviolet curable resin is adjusted so that the difference in absorbance of the third ultraviolet curable resin becomes small according to the color of the colored layer in the wavelength range absorbed by the photoinitiator added to the first ultraviolet curable resin, The optical fiber ribbon according to any one of claims 1 to 3, characterized by the above.

5. The difference in absorbance with respect to ultraviolet rays between the third ultraviolet curable resins forming the colored layers having different colors is 0.41 or less at a wavelength of 365 nm, The optical fiber ribbon according to any one of claims 1 to 4, characterized by the above.

6. The difference in absorbance with respect to ultraviolet rays between the third ultraviolet curable resins forming the colored layers having different colors is 0.11 or less at a wavelength of 365 nm. The optical fiber ribbon according to claim 5.

7. A step of drawing an optical fiber bare wire from an optical fiber base material, A step of applying a first ultraviolet-curable resin around the optical fiber bare wire to form a primary layer; A step of manufacturing an optical fiber element wire by applying a second ultraviolet-curable resin around the primary layer and irradiating the second ultraviolet-curable resin with ultraviolet light to form a secondary layer; A step of manufacturing an optical fiber colored core wire by applying a third ultraviolet-curable resin around the optical fiber element wire and irradiating the third ultraviolet-curable resin with the ultraviolet light to form a colored layer; A step of manufacturing an optical fiber ribbon in which a plurality of the optical fiber colored core wires are connected by applying a fourth ultraviolet-curable resin around the plurality of the optical fiber colored core wires and irradiating the fourth ultraviolet-curable resin with the ultraviolet light to form an adhesive layer; comprising; The Young's modulus of the primary layer is lower than the maximum Young's modulus of the first ultraviolet-curable resin; Among the plurality of optical fiber colored core wires, the difference in the Young's modulus of the primary layer between the optical fiber colored core wires having different colors of the colored layer is 0.1 MPa or less; The photoinitiator added to the first ultraviolet-curable resin has absorption in the wavelength range of 340 nm or more and 410 nm or less; A method for manufacturing an optical fiber ribbon, characterized in that.

8. When the photoinitiator reacts, the absorbance decreases in the wavelength range of 340 nm or more and 410 nm or less; The method for manufacturing an optical fiber ribbon according to claim 7, characterized in that.

9. The difference between the Young's modulus of the primary layer and the maximum Young's modulus in the optical fiber element wire is greater than 0.13 MPa; The method for manufacturing an optical fiber ribbon according to claim 7 or 8, characterized in that.

10. The Young's modulus of the primary layer is 0.15 MPa or more and 0.89 MPa or less; The method for manufacturing an optical fiber ribbon according to any one of claims 7 to 9, characterized in that.

11. At least one of the type and the addition amount of an additive for changing the absorbance of the third ultraviolet-curable resin is adjusted so that the difference in the absorbance of the third ultraviolet-curable resin becomes small according to the color of the colored layer in the wavelength range absorbed by the photoinitiator added to the first ultraviolet-curable resin; The method for manufacturing an optical fiber ribbon according to any one of claims 7 to 10, characterized in that.

12. The difference in absorbance with respect to ultraviolet light between the third ultraviolet-curable resins that respectively form the colored layers with different colors is 0.41 or less at a wavelength of 365 nm. The method for manufacturing an optical fiber ribbon according to any one of claims 7 to 11, characterized by the above. **Claim 13** The method for manufacturing an optical fiber ribbon according to claim 12, wherein the difference in absorbance with respect to ultraviolet light between the third ultraviolet-curable resins that respectively form the colored layers with different colors is 0.11 or less at the wavelength of 365 nm. **Claim 14** In the step of manufacturing the optical fiber element wire, irradiate the first ultraviolet-curable resin and the second ultraviolet-curable resin with the ultraviolet light. The method for manufacturing an optical fiber ribbon according to any one of claims 7 to 13, characterized by the above.

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