JP7640440B2 - Optical fiber ribbon and method for manufacturing the same - Google Patents

Description

The present invention relates to an optical fiber ribbon and a method for manufacturing an optical fiber ribbon.

A technology is known for manufacturing colored optical fiber by forming a primary layer covering a bare optical fiber, a secondary layer covering the primary layer, and a colored layer covering the secondary layer from ultraviolet-curable resin so as to have the desired Young's modulus (Patent Documents 1 and 2).
When the Young's modulus of the primary layer is set low, it is possible to buffer the external force applied to the bare optical fiber and suppress the optical transmission loss (microbend loss) caused by minute deformation of the bare optical fiber, whereas when the Young's modulus of the secondary layer is set high, it is possible to protect the bare optical fiber and the primary layer from the external force.
In addition, the optical fiber ribbon is manufactured by covering a plurality of colored optical fiber cores with an ultraviolet-curable resin and connecting the plurality of colored optical fiber cores to each other by irradiating ultraviolet light. Even if the Young's modulus of the primary layer is low in the optical fibers before the manufacturing process of the optical fiber ribbon, the Young's modulus of the primary layer increases when irradiated with UV light in the manufacturing process of the optical fiber ribbon, which causes microbend loss.
In response to this, 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 has been proposed (Patent Document 3), and a method for preventing an unintended increase in Young's modulus due to UV exposure in later processes by adding an ultraviolet absorber to the primary layer has been proposed (Patent Document 4).

JP 2005-162522 A Special Publication No. 2002-524581 International Publication No. 2018/062364 Special table 2019-505648 publication

However, the manufacturing method described in Patent Document 3 requires curing at a Young's modulus close to the saturated Young's modulus, which places restrictions on the manufacturing conditions for the colored optical fiber core. Similarly, the manufacturing method described in Patent Document 4 requires minimizing the spectral overlap of the photoinitiator and the UV absorber, which places significant restrictions on the options for the resin composition of the colored optical fiber core.

The present invention has been made in consideration of the above-mentioned problems, and aims to provide an optical fiber ribbon and a method for manufacturing the optical fiber ribbon that can suppress an increase in the Young's modulus of the primary layer due to additional ultraviolet light irradiation in the ribboning process, without imposing significant restrictions on the manufacturing conditions of the colored optical fiber core or the resin composition that forms the primary layer.

According to one aspect of the present invention, there is provided an optical fiber ribbon comprising: a bare optical fiber; a plurality of colored optical fiber core wires, each of which has a bare optical fiber; a primary layer formed from a primary layer material covering the bare optical fiber; and a secondary layer formed from a secondary layer material covering the primary layer; and an adhesive layer formed from an adhesive layer material covering the plurality of colored optical fiber core wires and connecting the plurality of colored optical fiber core wires, wherein the Young's modulus of the primary layer is lower than the maximum Young's modulus after hardening of the primary layer material, the adhesive layer material has at least one maximum point in a first wavelength range of 350 nm or more and 392 nm or less, where the absorption amount of ultraviolet light is maximized, and a photoinitiator added to the primary layer material has absorption over at least a second wavelength range of 340 nm or more and 410 nm or less .

According to another aspect of the present invention, there is provided a method for manufacturing an optical fiber ribbon, comprising the steps of: drawing a bare optical fiber from an optical fiber preform; applying a primary layer material around the bare optical fiber to form a primary layer; manufacturing a colored optical fiber by applying a secondary layer material around the primary layer and irradiating the secondary layer material with ultraviolet light to form a secondary layer; and applying an adhesive layer material around a plurality of the colored optical fiber core wires and irradiating the adhesive layer material with ultraviolet light to form an adhesive layer that connects the plurality of the colored optical fiber core wires, wherein the Young's modulus of the primary layer is lower than the maximum Young's modulus of the primary layer material after curing, the adhesive layer material has at least one maximum point in a first wavelength range of 350 nm or more and 392 nm or less where the absorption amount of the ultraviolet light is maximized, and a photoinitiator added to the primary layer material has absorption over at least a second wavelength range of 340 nm or more and 410 nm or less .

The present invention provides an optical fiber ribbon and a method for manufacturing the optical fiber ribbon that can suppress an increase in the Young's modulus of the primary layer due to additional ultraviolet light irradiation in the ribboning process, without imposing significant restrictions on the manufacturing conditions of the colored optical fiber core or the resin composition that forms the primary layer.

1 is a cross-sectional view of a colored optical fiber core according to an embodiment of the present invention. 1 is a cross-sectional view of an optical fiber according to an embodiment. 1 is a schematic diagram showing a part of a manufacturing apparatus used in a method for manufacturing a colored optical fiber according to an embodiment of the present invention. 4 is a schematic diagram showing another part of the manufacturing apparatus used in the method for manufacturing a colored optical fiber according to the first embodiment. FIG. 1 is a cross-sectional view of an optical fiber ribbon according to one embodiment. 1 is a schematic diagram of a ribbon forming apparatus used in a method for manufacturing an optical fiber ribbon according to one embodiment. 2 is a flowchart of a method for manufacturing a colored optical fiber and an optical fiber ribbon according to an embodiment. FIG. 11 is a diagram showing changes in ultraviolet absorption wavelength depending on the type and amount of additive in the optical fibers according to the examples and the comparative examples.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Elements having common functions throughout the drawings will be given the same reference numerals, and duplicate descriptions may be omitted or simplified.

Figure 1A is a cross-sectional view of a colored optical fiber core wire 1 according to this embodiment. The colored optical fiber core wire 1 comprises a bare optical fiber 2, a primary layer 3 coated on the outer periphery of the bare optical fiber 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 bare optical fiber 2 is coated with three coating layers, the primary layer 3, the secondary layer 4, and the colored layer 5. Figure 1B is a cross-sectional view of an optical fiber strand 6 according to this embodiment. The optical fiber strand 6 is a fiber before the colored layer 5 is formed.

The bare optical fiber 2 is made of, for example, quartz glass, and transmits light. The primary layer 3, secondary layer 4, and colored layer 5 are each formed by curing an ultraviolet-curable resin by irradiating it with ultraviolet light. There are no particular limitations on the ultraviolet-curable resin, so long as it can be polymerized by irradiating it with ultraviolet light. The ultraviolet-curable resin can be polymerized, for example, by photoradical polymerization.

The ultraviolet-curable resin is, for example, an ultraviolet-curable resin having a polymerizable unsaturated group such as an ethylenically unsaturated group that polymerizes and hardens when exposed to ultraviolet light, such as urethane (meth)acrylates, such as polyether-based urethane (meth)acrylates and polyester-based urethane (meth)acrylates, epoxy (meth)acrylates, and polyester (meth)acrylates, and preferably has at least two polymerizable unsaturated groups.

Examples of polymerizable unsaturated groups in ultraviolet-curable resins include groups having an unsaturated double bond, such as vinyl groups, allyl groups, acryloyl groups, and methacryloyl groups, and groups having an unsaturated triple bond, such as propargyl groups. Among these, acryloyl groups and methacryloyl groups are preferred in terms of polymerizability.

The UV-curable resin may be a monomer, oligomer, or polymer that initiates polymerization and hardens when irradiated with UV light, but is preferably an oligomer. An oligomer is a polymer with a degree of polymerization of 2 to 100. In this specification, "(meth)acrylate" means one or both of acrylate and methacrylate. The UV-curable resin contains any photopolymerization initiator (hereinafter referred to as "photoinitiator") that has sensitivity in the UV region.

A polyether-based urethane (meth)acrylate is a compound having a polyether segment, a (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyether skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate. A polyester-based urethane (meth)acrylate is a compound having a polyester segment, a (meth)acrylate, and a urethane bond, such as a reaction product of a polyol having a polyester skeleton with an organic polyisocyanate compound and a hydroxyalkyl (meth)acrylate.

Furthermore, the UV-curable resin may contain, in addition to the oligomer and photoinitiator, 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 UV-curable resin.

The primary layer 3 is a soft layer and has the function of cushioning the external force applied to the bare optical fiber 2. When the optical fiber strand 6 is formed, there may still be room for hardening in the primary layer 3, but when it has hardened to the point where there is no room for hardening, the Young's modulus of the primary layer 3 is at its maximum. In this embodiment, the maximum Young's modulus that the primary layer 3 of the optical fiber strand 6 can exhibit is defined as the "maximum Young's modulus."

Ultraviolet rays are irradiated at an appropriate illuminance and dose using, for example, a mercury lamp or UV-LED. The maximum Young's modulus varies with the optical fiber manufacturing conditions (e.g., line speed, UV irradiation intensity, type of UV light source, resin application temperature, etc.) and cannot be determined uniquely by the ultraviolet-curable resin used. In the bare fiber, colored optical fiber core, and optical fiber ribbon of this embodiment, the Young's modulus of the primary layer 3 is lower than the maximum Young's modulus. The Young's modulus of the primary layer 3 is less than 90% of the maximum Young's modulus at the stage when the manufacture of the optical fiber ribbon is completed by carrying out the ribbonization process described below.

The secondary layer 4 is preferably a hard layer having a Young's modulus of 500 MPa or more, and has the function of protecting the bare optical fiber 2 and the primary layer 3 from external forces. The colored layer 5 is colored to identify the colored optical fiber core 1. The colored secondary layer 4 may be the outermost layer of the colored optical fiber core 1. When the secondary layer 4 is colored, the secondary layer 4 is colored by adding a colorant containing a pigment, a lubricant, etc. to the secondary layer 4. The content of the colorant in the colored secondary layer 4 can be appropriately determined depending on the content of the pigment contained in the colorant and the type of other components such as ultraviolet-curable resin.

The diameter of the optical fiber strand 6 may preferably be 260 μm or less, for example, about 250 μm. The diameter of the bare optical fiber 2 may be 80 μm or more and 150 μm or less, and preferably 124 μm or more and 126 μm or less. The thickness of the primary layer 3 may be 5 μm or more and 60 μm or less. The thickness of the secondary layer 4 may be 5 μm or more and 60 μm or less. The thickness of the colored layer 5 may be several μm.

The diameter of the optical fiber strand 6 can be determined by the sum of the diameter of the bare optical fiber 2, twice the length of the thickness of the primary layer 3, and twice the length of the thickness of the secondary layer 4. Therefore, the diameter of the bare optical fiber 2, the thickness of the primary layer 3, and the thickness of the secondary layer 4 can each be selected so that the diameter of the optical fiber strand 6 is about 250 μm.

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

The optical fiber preform BM is made of, for example, quartz-based glass, and is manufactured by a known method such as the VAD method, the OVD method, or the MCVD method. The heating device 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 arranged around the optical fiber preform BM, and is drawn to extract the bare optical fiber 2.

A primary layer coating device 30 is provided below the heating device 20. The primary layer coating device 30 has a resin applicator 31 and an ultraviolet ray irradiation device 32. The resin applicator 31 holds an ultraviolet ray curable resin (hereinafter referred to as "primary layer material"), which is a coating material for forming the primary layer 3. The primary layer material is applied by the resin applicator 31 to the bare optical fiber 2 drawn out from the optical fiber preform BM.

An ultraviolet irradiation device 32 is provided below the resin application device 31. The ultraviolet irradiation device 32 is equipped with any ultraviolet light source such as a metal halide lamp, a mercury lamp, or a UV-LED. The primary layer material is applied to the bare optical fiber 2 by the resin application device 31, and the bare optical fiber 2 enters the ultraviolet irradiation device 32, where the primary layer material is irradiated with ultraviolet light. As a result, the primary layer material is hardened and the primary layer 3 is formed.

A secondary layer coating device 40 is provided below the primary layer coating device 30. The secondary layer coating device 40 has a resin coating device 41 and an ultraviolet ray irradiation device 42. The resin coating device 41 holds an ultraviolet ray curing resin (hereinafter referred to as "secondary layer material"), which is a coating material for forming the secondary layer 4. The secondary layer material is applied to the primary layer 3 by the resin coating device 41.

An ultraviolet irradiation device 42 is provided below the resin application device 41. The ultraviolet irradiation device 42 may be configured similarly to the ultraviolet irradiation device 32. The bare optical fiber 2 coated with the secondary layer material enters the ultraviolet irradiation device 42, and the secondary layer material is irradiated with ultraviolet light. As a result, the secondary layer material is hardened and the secondary layer 4 is formed. The primary layer 3 and the secondary layer 4 are coated on the bare optical fiber 2, forming the optical fiber strand 6.

The resin applicator 31 may be configured to hold the primary layer material and the secondary layer material separately. In this case, the resin applicator 31 applies the primary layer material to the bare optical fiber 2, and then applies the secondary layer material on top of the primary layer material.

The ultraviolet irradiation device 32 irradiates the primary layer material and secondary layer material applied to the bare optical fiber 2 with ultraviolet light. This forms the primary layer 3 and secondary layer 4. In this case, the manufacturing device 10 does not necessarily need to have the secondary layer coating device 40.

A guide roller 45 and a first winding device 50 are provided below the secondary layer coating device 40. The manufactured optical fiber strand 6 is guided by the guide roller 45 and wound up on the first winding device 50.

Figure 2B is a schematic diagram showing other parts of the manufacturing apparatus 10 used in the manufacturing method of the colored optical fiber core wire 1 according to this embodiment. In Figure 2B, the manufacturing apparatus 10 has a bare wire holding device 55, a guide roller 56, a colored layer coating device 60, a guide roller 65, and a second winding device 70. The manufacturing apparatus 10 manufactures the colored optical fiber core wire 1 from the optical fiber bare wire 6 manufactured by the multiple devices shown in Figure 2A.

The wire holding device 55 holds the manufactured optical fiber wire 6 in a wound state. In FIG. 2B, the wire holding device 55 is a separate device from the first winding device 50, but the first winding device 50 may also serve as the wire holding device 55.

A colored layer coating device 60 is provided below the wire holding device 55. The optical fiber strand 6 pulled out from the wire holding device 55 is guided by a guide roller 56 provided between the wire holding device 55 and the colored layer coating device 60, and is transported into the colored layer coating device 60.

The colored layer coating device 60 has a resin coating device 61 and an ultraviolet ray irradiation device 62. The resin coating device 61 holds an ultraviolet ray curing resin (hereinafter referred to as "colored layer material"), which is a coating material for forming the colored layer 5.

A coloring layer material is applied to the optical fiber strand 6 by a resin applicator 61. An ultraviolet ray irradiation device 62 is provided below the resin applicator 61. The ultraviolet ray irradiation device 62 can be configured in the same manner as the ultraviolet ray irradiation devices 32 and 42.

The optical fiber strand 6 with the color layer material applied to the outer periphery of the secondary layer 4 enters the ultraviolet irradiation device 62, where ultraviolet light is irradiated onto the color layer material and the optical fiber strand 6. This hardens the color layer material, forming the color layer 5.

The primary layer 3, secondary layer 4, and colored layer 5 are applied to the bare optical fiber 2 to form the colored optical fiber core 1. After manufacture, the colored optical fiber core 1 is guided by a guide roller 65 provided below the colored layer application device 60, and wound up on the second winding device 70.

Figure 3 is a cross-sectional view of an optical fiber ribbon 100 according to this embodiment. The optical fiber ribbon 100 is formed by bundling a plurality of colored optical fiber cores 1 into a band shape via an adhesive layer 101.

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 colored optical fiber core wires 1 can be bundled at a high density by taking the form of an optical fiber ribbon 100. The optical fiber ribbon 100 is not limited to the configuration shown in FIG. 3. The optical fiber ribbon 100 may also take the form of an optical fiber ribbon cable in which the optical fiber ribbon 100 is housed in a sheath.

In this embodiment, an additive is added to the ultraviolet-curable resin that forms the adhesive layer 101. At least a portion of the wavelength range in which the adhesive layer 101 absorbs ultraviolet light overlaps with the wavelength range in which the photoinitiator added to the primary layer material absorbs ultraviolet light. Details of the type and amount of additive will be described later.

Figure 4 is a schematic diagram of a ribbon forming device 80 used in the manufacturing method of the optical fiber ribbon 100 according to this embodiment. The ribbon forming device 80 has a resin application device 81 and an ultraviolet irradiation device 82. The resin application device 81 holds an ultraviolet curing resin (hereinafter referred to as "adhesive layer material") which is the coating material for the adhesive layer 101.

The multiple colored optical fiber cores 1 prepared enter the ribbon forming device 80, where the adhesive layer material is applied by the resin application device 81. The colored optical fiber cores 1 to which the adhesive layer material has been applied are bundled together with multiple other colored optical fiber cores 1 to which the adhesive layer material has been applied. The bundled multiple colored optical fiber cores 1 are irradiated with ultraviolet light by the ultraviolet irradiation device 82 provided in the ribbon forming device 80. As a result, the adhesive layer material is hardened to become an adhesive layer 101. The multiple colored optical fiber cores 1 arranged in parallel are connected via the adhesive layer 101. In this way, an optical fiber ribbon 100 is formed from multiple thin-diameter colored optical fiber cores 1.

The ribbon forming device 80 may be, for example, the ribbon forming device described in JP 2012-118358 A. As a result, the adhesive layer 101 is intermittently formed at a predetermined interval in the longitudinal direction of adjacent colored optical fiber cores 1, and an intermittently bonded optical fiber ribbon 100 is formed.

Figure 5 is a flowchart of the manufacturing method of the colored optical fiber core 1 and the optical fiber ribbon 100 according to this embodiment. First, the user places the optical fiber preform BM in the manufacturing device 10 (step S101).

Next, the heater 21 installed in the heating device 20 heats the optical fiber preform BM, and drawing of the bare optical fiber 2 begins (step S102).

The primary layer coating device 30 applies a primary layer material around the drawn bare optical fiber 2 and irradiates the primary layer material with ultraviolet light to form a primary layer 3 (step S103).

Next, the secondary layer coating device 40 applies a secondary layer material around the primary layer 3 and irradiates the secondary layer material with ultraviolet light to form the secondary layer 4 (step S104). This results in the optical fiber strand 6. The manufactured optical fiber strand 6 is wound up by the first winding device 50.

Then, the colored layer coating device 60 pulls out the optical fiber strand 6 from the strand holding device 55 or the first winding device 50, applies a colored layer material around the secondary layer 4 of the optical fiber strand 6, and irradiates the colored layer material with ultraviolet light to form a colored layer 5 (step S105). By coating the optical fiber strand 6 with the colored layer 5, the colored optical fiber core wire 1 is obtained. After manufacture, the colored optical fiber core wire 1 is wound up by the second winding device 70.

It is not necessary to irradiate ultraviolet light in the process of forming the primary layer 3 (step S103). In this case, the primary layer 3 can be hardened in the process of forming the secondary layer 4 (step S104).

After the colored layer 5 is formed in step S105, the ribboning device 80 applies an adhesive layer material to cover the multiple colored optical fiber cores 1 prepared, and irradiates the adhesive layer material with ultraviolet light to connect the multiple colored optical fiber cores 1 to each other (step S106). In this way, the optical fiber ribbon 100 is manufactured.

In the process of manufacturing the optical fiber ribbon 100 from the colored optical fiber core 1, the colored optical fiber core 1 is irradiated with ultraviolet light. In this embodiment, the type and amount of additive are adjusted so that at least a portion of the wavelength range in which the adhesive layer 101 absorbs ultraviolet light overlaps with the wavelength range in which the photoinitiator added to the primary layer material that constitutes the primary layer 3 absorbs ultraviolet light.

As a result, even if the colored optical fiber core 1 is additionally irradiated with ultraviolet light in the process of manufacturing the optical fiber ribbon 100, the ultraviolet light is absorbed by the adhesive layer 101 because at least a portion of the wavelength range (first wavelength range) in which the adhesive layer material absorbs ultraviolet light overlaps with the ultraviolet light absorption wavelength range (second wavelength range) of the photoinitiator added to the primary layer 3. This suppresses further curing of the primary layer 3 by ultraviolet light, making it possible to suppress an increase in the Young's modulus of the primary layer 3. As a result, microbend loss can be suppressed.

When at least a portion of the first wavelength range in the adhesive layer 101 overlaps with the second wavelength range in the primary layer 3, as in this embodiment, the change in Young's modulus of the primary layer 3 before and after the manufacture of the optical fiber ribbon 100 is smaller than when the adhesive layer 101 is formed using an adhesive layer material whose absorption wavelength range does not overlap with the second wavelength range.

In addition, since it is only necessary to adjust the type and amount of additives added to the adhesive layer material that constitutes the adhesive layer 101, which is the outermost layer of the optical fiber ribbon 100, there are no significant restrictions on the composition of the ultraviolet-curable resin that constitutes the optical fiber colored core 1.

The additive having the property of absorbing ultraviolet light in the first wavelength range is preferably added to the adhesive layer material at a concentration of 0.05 wt % or more. When the optical fiber ribbon 100 is manufactured by adding the additive to the adhesive layer material at this ratio, the Young's modulus of the primary layer 3 is lower than when the optical fiber ribbon 100 is manufactured without adding the additive to the adhesive layer material, and is, for example, less than 90%. This makes it possible to suppress an increase in the Young's modulus of the primary layer 3 even when ultraviolet light is irradiated in a later process as described above.

In addition, if too much additive is added, the hardening of the adhesive layer material may be inhibited. For this reason, it is preferable to add the additive in an amount of 10.0 wt% or less to the adhesive layer material. It is even more preferable to add the additive in an amount of 5.0 wt% or less to the adhesive layer material.

The following describes the results of an experiment conducted to simulate the ribboning process for the optical fiber colored core 1 according to an embodiment of the present invention.

Here, when additional UV irradiation was performed on the colored optical fiber core 1, in order to simulate the ribboning process of the optical fiber, the ultraviolet-curable resin constituting the adhesive layer (ribbon layer) 101 was applied to a thickness of 30 μm±3 μm on the quartz glass that does not have absorption properties for the UV light used, and the colored optical fiber core 1 was covered. When an additive was added, the additive was added to the ultraviolet-curable resin constituting the adhesive layer 101. The ultraviolet-curable resin constituting the adhesive layer 101 is composed of oligomers, monomers, etc., and may also contain additives such as photoinitiators, photosensitizers, ultraviolet absorbers, and antioxidants.

Table 1 shows the Young's modulus (MPa), maximum Young's modulus (MPa), type of additive, additive amount (wt%), Young's modulus after additional UV irradiation (MPa), Young's modulus after additional UV irradiation/maximum Young's modulus (%), evaluation of suppression of increase in Young's modulus in the primary layer 3 (evaluation 1), and evaluation of suppression of microbend loss (evaluation 2) in the primary layer 3 in Examples 1 to 7 and Comparative Example 1. The outer diameter of the secondary layer 4 of the optical fiber colored core 1 in Examples 1 to 7 and Comparative Example 1 is 250 μm.

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

First, a commercially available stripper is used to strip off the primary layer 3 and the secondary layer 4 from the middle of the sample optical fiber by a length of several mm, and then one end of the optical fiber on which the coating layer is formed is fixed on a slide glass with an adhesive, and a load F is applied to the other end of the optical fiber on which the coating layer is 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 under a microscope. Then, a graph of the displacement δ against the load F is created by setting the load F to 10, 20, 30, 50, and 70 gf (i.e., 98, 196, 294, 490, and 686 mN, respectively). Then, the primary elastic modulus is calculated using the slope obtained from the graph and the following formula (1). The calculated primary elastic modulus corresponds to the so-called ISM, and is hereinafter referred to as P-ISM as appropriate. When drawing the colored optical fiber 1, the drawing speed and the illuminance of the ultraviolet light were controlled to adjust the P-ISM.
P-ISM=(3F/δ)*(1/2πl)*ln(DP/DG)...(Formula 1)

Here, the unit of P-ISM is [MPa]. F/δ is the slope of the graph of displacement (δ) [μm] against load (F) [gf], l is the sample length (e.g., 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 of the optical fiber. Therefore, when calculating P-ISM using the above formula from the F, δ, and l used, a predetermined unit conversion is required. The outer diameter of the primary layer 3 and the outer diameter of the cladding can be measured by observing the cross section of the optical fiber cut with a fiber cutter under a microscope.

In Table 1, "Young's modulus after additional UV irradiation" refers to the Young's modulus of the primary layer 3 when the manufactured optical fiber colored core 1 is re-irradiated with UV at 1500 mW/cm ² and 50 mJ/cm ² using a UV-LED of 365 nm ± 20 nm, as defined as P-ISM.

"Evaluation 1" in Table 1 indicates whether the P-ISM of the optical fiber colored core 1 after additional UV irradiation is lower than the maximum Young's modulus. If the P-ISM is lower than the maximum Young's modulus, the evaluation is judged as pass (OK). Conversely, if the P-ISM is not lower than the maximum Young's modulus, the evaluation is judged as fail (NG). If the evaluation result is pass (OK), it indicates that the additive added to the ultraviolet-curable resin that constitutes the adhesive layer 101 has been able to suppress the increase in Young's modulus in the primary layer 3 when the colored core is exposed to UV light.

"Rating 2" in Table 1 indicates whether the microbend loss in the optical fiber colored core 1 after additional UV irradiation meets a specified standard (0.1 dB/km or less). If the microbend loss meets the standard, the rating is judged as pass (OK), and if the microbend loss does not meet the standard, the rating is judged as fail (NG).

There are various methods for measuring microbend loss. In this specification, the microbend loss value is defined as the difference between the transmission loss of the optical fiber to be measured in state A, where an optical fiber of 400 m or more in length is wound in a single layer with no overlapping, with a tension of 100 gf, around a large bobbin wrapped with #1000 grit sandpaper, and the transmission loss of the optical fiber in state B, where the optical fiber is wound around the same bobbin as in state A, with the same tension and length as in state A, but without sandpaper. Here, the transmission loss of the optical fiber in state B does not include microbend loss, and is considered to be a transmission loss inherent to the optical fiber itself.

This measurement method is similar to the fixed diameter drum method specified in JIS C6823:2010. This measurement method is also called the sandpaper method. In this measurement method, the transmission loss is measured at a wavelength of 1550 nm, so the microbend loss values below are also values at a wavelength of 1550 nm.

The effective core area can be used as an index of the susceptibility of an optical fiber to microbend loss. The effective core area is expressed by the following formula (2).
(effective core cross-sectional area)=(πk/4)*(MFD) ² (Equation 2)
Here, the effective core area is a value at a wavelength of 1550 nm, MFD is a mode field diameter (μm), and k is a constant. The effective core area represents the area of a portion of a cross section perpendicular to the axis of the bare optical fiber 2 through which light having a predetermined intensity passes. In general, the larger the effective core area of the bare optical fiber 2, the weaker the optical confinement in the cross section of the bare optical fiber 2. That is, when the effective core area of the bare optical fiber 2 is large, the light in the bare optical fiber 2 is likely to leak out due to an external force applied to the bare optical fiber 2. For this reason, when the effective core area of the bare optical fiber 2 is large, microbending loss is likely to occur in the colored optical fiber 1.

In this embodiment, an optical fiber having an effective core area (effective core area) Aeff of 80 ^μm2 or more is used as the optical fiber. In an optical fiber, the effective core area is an index of microbending sensitivity, and the larger the effective core area, the higher the microbending sensitivity. In general, it is said that an effective core area exceeding 100 ^μm2 has high microbending sensitivity. Therefore, an effective core area of 130 ^μm2 or more and 150 ^μm2 or less results in an optical fiber with high microbending sensitivity without any problems.

For the colored optical fiber core 1 used in Examples 1 to 7 and Comparative Example 1, first, a primary layer material was applied around the drawn bare optical fiber 2, and then the primary layer material was irradiated with ultraviolet light to form a primary layer 3.

Next, the secondary layer material was applied around the primary layer 3, and the secondary layer material was irradiated with ultraviolet light to form the secondary layer 4. It is also possible to color the secondary layer 4 itself. When drawing the optical fiber 6 or the colored optical fiber core 1, the drawing speed and illuminance were controlled to adjust the P-ISM. 2,4,6-trimethylbenzoyl-diphenylphosphine oxide was used as the photoinitiator for the primary layer 3 of the colored optical fiber core 1. When this photoinitiator is used in a reaction by UV irradiation, the absorbance in the vicinity of 340 to 410 nm decreases.

By comparing the absorbance before and after UV irradiation to confirm the change in absorbance, the absorption wavelength of the photoinitiator contained in the primary layer 3 can be detected. Of course, it is easy to determine whether the absorption wavelength is derived from the photoinitiator without using this method. For example, it is possible to determine the absorption wavelength of the photoinitiator added to the primary layer 3 by comparing it with the absorption wavelength of photoinitiators available on the market.

The diameter of the bare optical fiber 2 was 125 μm. The thickness of the primary layer 3 was 30 μm. The thickness of the secondary layer 4 was 30 μm. The thickness of the colored layer 5 was 3 μm. The colored optical fiber core wire 1 was 251 μm. And, the colored optical fiber core wire 1 was 251 μm.

In Examples 1 to 7 and Comparative Example 1, the optical fiber colored core 1 was manufactured under the same conditions, and the Young's modulus of the primary layer 3 was 0.14 MPa and the maximum Young's modulus was 0.60 MPa.

Additive A is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. Additive B is 2,4-diethyl-9H-thioxanthen-9-one. Additive C is 2,2',4,4'-tetrahydroxybenzophenone. All of the additives have at least a partial absorption region in the same absorption region as the photoinitiator 2,4,6-trimethylbenzoyl-diphenylphosphine oxide of the primary layer 3.

In Example 1, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 10 wt% additive A. After that, the colored optical fiber core 1 was irradiated with additional UV light. The Young's modulus of the primary layer 3 after the colored optical fiber core 1 was irradiated with additional UV light was 0.47 MPa, and the ratio of the Young's modulus after additional UV irradiation to the maximum Young's modulus was 78.3%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 2, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 0.1 wt% additive B. After that, the colored optical fiber core 1 was irradiated with additional UV light. After the colored optical fiber core 1 was irradiated with additional UV light, the Young's modulus of the primary layer 3 was 0.54 MPa, and the ratio was 89.3%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 3, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 1 wt% additive B. After that, the colored optical fiber core 1 was irradiated with additional UV light. After the colored optical fiber core 1 was irradiated with additional UV light, the Young's modulus of the primary layer 3 was 0.15 MPa, and the ratio was 25.0%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 4, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 0.05 wt% additive C. After that, the colored optical fiber core 1 was irradiated with additional UV light. After the colored optical fiber core 1 was irradiated with additional UV light, the Young's modulus of the primary layer 3 was 0.34 MPa, and the ratio was 56.7%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 5, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 0.1 wt% additive C. The colored optical fiber core 1 was then subjected to additional UV irradiation. The Young's modulus of the primary layer 3 after the additional UV irradiation of the colored optical fiber core 1 was 0.21, and the ratio was 35.0%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 6, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 1 wt% additive C. After that, the colored optical fiber core 1 was additionally irradiated with UV light. After the colored optical fiber core 1 was additionally irradiated with UV light, the Young's modulus of the primary layer 3 was 0.14 MPa, and the ratio was 23.3%. Therefore, Evaluation 1 was passed (OK). In addition, the microbend loss was below the specified reference value (0.1 dB/km), and Evaluation 2 was passed (OK).

In Example 7, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing 0.01 wt% additive C. The colored optical fiber core 1 was then subjected to additional UV irradiation. The Young's modulus of the primary layer 3 after the additional UV irradiation of the colored optical fiber core 1 was 0.55 MPa, and the ratio was 91.7%. Therefore, Evaluation 1 was passed (OK). However, the microbend loss was equal to or greater than the reference value (0.1 dB/km), and Evaluation 2 was failed (NG).

In Comparative Example 1, the colored optical fiber core 1 was covered with an ultraviolet-curable resin containing no additives. After that, the colored optical fiber core 1 was additionally irradiated with UV light. After the colored optical fiber core 1 was additionally irradiated with UV light, the Young's modulus of the primary layer 3 was 0.60 MPa, and the ratio was 100.0%. For this reason, Evaluation 1 was a failure (NG). In addition, the microbend loss was equal to or greater than the reference value (0.1 dB/km), and therefore Evaluation 2 was a failure (NG).

Figure 6 shows the change in ultraviolet absorption wavelength depending on the type and amount of additive in the optical fibers of the examples and comparative examples. In Figure 6, the horizontal axis shows wavelength (nm) and the vertical axis shows absorbance.

The photoinitiator used in the primary layer 3 in this embodiment and comparative example has the property of absorbing ultraviolet rays with wavelengths of 340 to 410 nm. On the other hand, as shown in FIG. 6, the additive A used in embodiment 1 has the property of absorbing ultraviolet rays with wavelengths of 340 to 410 nm. In addition, in the range of absorption wavelengths of additive A, the maximum point at which the amount of ultraviolet light absorbed is maximized is 380 nm ± 5 nm. In addition, additive B used in embodiments 2 and 3 has the property of absorbing ultraviolet rays with wavelengths of 340 to 410 nm (maximum point is 387 nm ± 5 nm), and additive C used in embodiments 4 to 6 has the property of absorbing ultraviolet rays with wavelengths of 310 to 400 nm (maximum point is 355 nm ± 5 nm). Therefore, there is an effect that the adhesive layer 101 blocks ultraviolet rays absorbed by the photoinitiator used in the primary layer 3. As a result, it is possible to suppress the increase in Young's modulus of the primary layer 3 due to ultraviolet light irradiation.

In this way, by adding an additive that at least partially overlaps with the absorption wavelength of the photoinitiator used in the primary layer 3 to the ultraviolet-curable resin that forms the adhesive layer 101, it is possible to suppress the increase in the Young's modulus of the primary layer 3 due to ultraviolet irradiation.

More preferably, the absorption maximum point of the additive added to the UV-curable resin forming the adhesive layer 101 is included within the absorption wavelength range of the photoinitiator used in the primary layer 3. As a result, when the additional UV is irradiated, most of the UV light in the wavelength range that can cause the photoinitiator to start a photopolymerization reaction is absorbed by the additive in the adhesive layer 101, so that UV curing of the primary layer 3 is more efficiently suppressed.

In addition, in the present embodiment and comparative example, the Young's modulus after additional UV irradiation was defined as the P-ISM when the colored optical fiber core 1 was re-irradiated with ultraviolet light under conditions of 1500 mW/ ^cm2 and 50 mJ/ ^cm2 using a UV-LED with an irradiation wavelength of 365 nm±20 nm, but the UV light source is not limited to a UV-LED with a wavelength of 365 nm±20 nm. For example, the same effect can be obtained when an additive having an absorption region within the range of UV-LEDs with different wavelengths, such as a UV-LED with a wavelength of 385 nm±20 nm or a UV-LED with a wavelength of 395 nm±20 nm, or a metal halide lamp or mercury lamp that emits UV light other than UV-LEDs is used.

The same effect can be obtained even if the illuminance and dose are irradiated under other conditions. For example, if additional UV irradiation is performed with a dose of 50 mJ/cm2 or ^more , the amount of UV radiation received by the primary layer 3 is further increased.

In addition, the additives used in Examples 1 to 7 are merely examples, and are not limited to photoinitiators, photosensitizers, and UV absorbers. Any additive may be used as long as it has an absorption wavelength that overlaps even partially with the absorption wavelength range of the photoinitiator used in the primary layer 3. In addition to additives A, B, and C, for example, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (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, Compounds such as 5-triazine (2,4,6-Tris[4-(hexyloxy)-2-hydroxy-3-methylphenyl]-1,3,5-triazine) and 2-(2-hydroxy-5-methylphenyl)benzotriazole can also be used as additives.

It is also clear that the type of additive that is effective varies depending on the absorption wavelength of the photoinitiator used in the primary layer 3. Therefore, by adding an additive that has an absorption wavelength range that is at least partially the same as the absorption wavelength range of the photoinitiator used, it is possible to suppress the increase in Young's modulus even when exposed to UV light after production of the colored optical fiber core 1.

The Young's modulus of the primary layer 3 shown in Examples 1 to 7 and Comparative Example 1 is merely an example and is not limited to this. For example, the Young's modulus of the primary layer 3 can be in the range of 0.1 to 2.0 MPa.

As described above, according to this embodiment, it is possible to suppress the increase in primary Young's modulus due to UV exposure in the ribboning process without imposing significant restrictions on the resin composition of the optical fiber colored core wire 1.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, an example in which part of the configuration of one of the embodiments is added to another embodiment, or an example in which part of the configuration of another embodiment is replaced with another embodiment, is also an embodiment of the present invention. Furthermore, with regard to parts not specifically explained or illustrated in the embodiments, well-known or publicly known techniques in the relevant technical field can be applied as appropriate.

Reference Signs List 1 Colored optical fiber core 2 Bare optical fiber 3 Primary layer 4 Secondary layer 5 Colored layer 6 Optical fiber core 100 Optical fiber ribbon 101 Adhesive layer

Claims (10)

a plurality of colored optical fiber core wires, each of which has a bare optical fiber, a primary layer formed of a primary layer material covering the bare optical fiber, and a secondary layer formed of a secondary layer material covering the primary layer;
an adhesive layer formed of an adhesive layer material covering the plurality of colored optical fiber cores and connecting the plurality of colored optical fiber cores;
Equipped with
the Young's modulus of the primary layer is less than the maximum Young's modulus of the primary layer material after curing;
the adhesive layer material has at least one maximum point at which the amount of ultraviolet light absorbed is maximized in a first wavelength range of 350 nm or more and 392 nm or less;
The photoinitiator added to the primary layer material has absorption over at least a second wavelength range of 340 nm to 410 nm.
1. An optical fiber ribbon comprising: The additive that absorbs the ultraviolet light in the second wavelength range is added to the adhesive layer material at 0.05 wt % or more.
2. The optical fiber ribbon according to claim 1. In the first wavelength range, at least the maximum point at which the absorption amount of the ultraviolet light is maximized is included in the second wavelength range.
3. The optical fiber ribbon according to claim 1 or 2. The Young's modulus is less than 90% of the maximum Young's modulus.
4. The optical fiber ribbon according to claim 1, wherein the optical fiber ribbon is a ferroelectric. The additive is added in an amount of 10.0 wt % or less to the adhesive layer material.
3. The optical fiber ribbon according to claim 2. The adhesive layer is formed intermittently at a predetermined interval in the longitudinal direction of the adjacent colored optical fiber.
6. The optical fiber ribbon according to claim 1, wherein the optical fiber ribbon is a ferroelectric. A step of drawing a bare optical fiber from an optical fiber preform;
applying a primary layer material around the bare optical fiber to form a primary layer;
a step of applying a secondary layer material around the primary layer and irradiating the secondary layer material with ultraviolet light to form a secondary layer, thereby producing a colored optical fiber;
applying an adhesive layer material around the plurality of colored optical fiber cores and irradiating the adhesive layer material with the ultraviolet light to form an adhesive layer connecting the plurality of colored optical fiber cores;
Equipped with
the Young's modulus of the primary layer is less than the maximum Young's modulus of the primary layer material after curing;
the adhesive layer material has at least one maximum point at which the absorption amount of the ultraviolet light is maximized in a first wavelength range of 350 nm or more and 392 nm or less;
The photoinitiator added to the primary layer material has absorption over at least a second wavelength range of 340 nm to 410 nm.
A method for manufacturing an optical fiber ribbon comprising the steps of: An additive that absorbs the ultraviolet light in at least a part of the second wavelength range is added to the adhesive layer material at 0.05 wt % or more.
8. The method for producing an optical fiber ribbon according to claim 7. In the step of forming the primary layer, the primary layer material is irradiated with the ultraviolet light.
9. The method for producing an optical fiber ribbon according to claim 7 or 8. In the step of forming the secondary layer, the primary layer material and the secondary layer material are irradiated with the ultraviolet light.
9. The method for producing an optical fiber ribbon according to claim 7 or 8.

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