JP2025086185A - Optical fiber ribbon and method for manufacturing the same - Google Patents

Abstract

To improve fiber cord separability of an optical fiber ribbon.SOLUTION: An optical fiber ribbon includes: an optical fiber bare wire; a plurality of optical fiber colored core wires including a primary layer which coats the optical fiber bare wire and is formed of a first ultraviolet curable resin, a secondary layer which coats the primary layer and is formed of a second ultraviolet curable resin, and a colored layer which coats the secondary layer and is formed of a third ultraviolet curable resin; and a ribbon layer which coats the plurality of optical fiber colored core wires and is formed of a fourth ultraviolet curable resin, wherein a conversion ratio of a part contacting the colored layer in the ribbon layer is 83.7% or more, and breaking elongation of the ribbon layer is 9.4% or more.SELECTED DRAWING: Figure 2

Description

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

Technology has been devised to improve the single-core separation of optical fiber ribbons. The technology described in Patent Document 1 improves the single-core separation of optical fiber ribbons by setting a high surface conversion rate of the colored layer of the colored optical fiber core. Note that the single-core separation of optical fiber ribbons refers to the ease of removing the colored optical fiber cores from the optical fiber ribbon.

International Publication No. 2016/017060

However, depending on the manufacturing conditions of the colored optical fiber core, it may not be easy to set a high surface conversion rate of the colored layer, which may make it difficult to improve the single-core separation of the optical fiber ribbon.

The purpose of the present invention is to improve the single-core separation properties of optical fiber ribbons.

According to one aspect of the present invention, there is provided an optical fiber ribbon comprising a plurality of colored optical fiber core wires including a bare optical fiber, a primary layer formed of a first ultraviolet-curable resin covering the bare optical fiber, 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 a ribbon layer formed of a fourth ultraviolet-curable resin covering the plurality of colored optical fiber core wires, the conversion rate of the portion of the ribbon layer that contacts the colored layer being 83.7% or more, and the breaking elongation of the ribbon layer being 9.4% or more.

According to another aspect of the present invention, there is provided an optical fiber ribbon comprising a plurality of colored optical fiber core wires including a bare optical fiber, a primary layer formed of a first ultraviolet-curable resin covering the bare optical fiber, and a secondary layer formed of a second ultraviolet-curable resin covering the primary layer, and a ribbon layer formed of a fourth ultraviolet-curable resin covering the plurality of colored optical fiber core wires, the secondary layer being a colored layer, the conversion rate of the portion of the ribbon layer in contact with the colored layer being 83.7% or more, and the breaking elongation of the ribbon layer being 9.4% or more.

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 first ultraviolet-curing resin to form a primary layer around the bare optical fiber and irradiating the first ultraviolet-curing resin with ultraviolet light from a first light source to form a primary layer, applying a second ultraviolet-curing resin to form a secondary layer around the primary layer and irradiating the second ultraviolet-curing resin with ultraviolet light from a second light source to form a secondary layer, applying a third ultraviolet-curing resin to form a colored layer around the secondary layer and irradiating the third ultraviolet-curing resin with ultraviolet light from a third light source to form a colored layer, and applying a fourth ultraviolet-curing resin to form a ribbon layer around the colored layer and irradiating the fourth ultraviolet-curing resin with ultraviolet light from a fourth light source to form a ribbon layer, wherein the conversion rate of the portion of the ribbon layer in contact with the colored layer is 83.7% or more, and the breaking elongation of the ribbon layer is 9.4% or more.

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 first ultraviolet-curing resin to form a primary layer around the bare optical fiber and irradiating the first ultraviolet-curing resin with ultraviolet light from a first light source to form a primary layer, applying a second ultraviolet-curing resin to form a secondary layer around the primary layer and irradiating the second ultraviolet-curing resin with ultraviolet light from a second light source to form a colored secondary layer, and applying a fourth ultraviolet-curing resin to form a ribbon layer around the secondary layer and irradiating the fourth ultraviolet-curing resin with ultraviolet light from a fourth light source to form a ribbon layer, wherein the conversion rate of the portion of the ribbon layer that contacts the secondary layer is 83.7% or more, and the breaking elongation of the ribbon layer is 9.4% or more.

The present invention can improve the separation of individual fibers in optical fiber ribbons.

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 ribbon according to one embodiment. 1 is a schematic diagram showing a portion of a manufacturing apparatus used in a method for manufacturing an optical fiber ribbon according to an embodiment of the present invention. 1 is a schematic diagram showing a portion of a manufacturing apparatus used in a method for manufacturing an optical fiber ribbon according to an embodiment of the present invention. 1 is a schematic diagram showing a portion of a manufacturing apparatus used in a method for manufacturing an optical fiber ribbon according to an embodiment of the present invention. 2 is a flowchart of a method for manufacturing an optical fiber ribbon according to one embodiment.

Embodiments of the present invention will be described in detail below 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 1 is a cross-sectional view of a colored optical fiber core wire according to this embodiment. The colored optical fiber core wire 6 comprises an optical fiber strand 1 and a colored layer 5 that covers the outer circumference of the optical fiber strand 1. The optical fiber strand 1 also comprises a bare optical fiber 2, a primary layer 3 that covers the outer circumference of the bare optical fiber 2, and a secondary layer 4 that covers the outer circumference of the primary layer 3. The bare optical fiber 2 is covered with three coating layers: the primary layer 3, the secondary layer 4, and the colored layer 5.

The bare optical fiber 2 is formed of, for example, silica glass and transmits light. The primary layer 3 is a soft layer and has a function of buffering external forces applied to the bare optical fiber 2. The Young's modulus of the primary layer 3 may preferably be 0.1 MPa or more and 2.0 MPa or less. The secondary layer 4 is a hard layer and has a function of protecting the bare optical fiber 2 and the primary layer 3 from external forces. The Young's modulus of the secondary layer 4 may preferably be 500 MPa or more and 2000 MPa or less. The colored layer 5 is colored to identify the colored optical fiber core 6. The colored layer 5 may be the secondary layer 4 colored with a coloring agent. The coloring agent may be a mixture containing a pigment or a lubricant.

The diameter of the optical fiber 1 may be 190 μm or more and 260 μm or less. 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. Here, the diameter of the optical fiber 1 may be determined by the sum of the diameter of the bare optical fiber 2, the length twice the thickness of the primary layer 3, and the length twice 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 may be selected so that the diameter of the optical fiber 1 is 190 μm or more and 260 μm or less.

When an external force is applied to the bare optical fiber 2, a slight deformation of the bare optical fiber 2 causes a transmission loss of light (microbend loss). By setting the Young's modulus of the primary layer 3 low, the function of buffering the external force of the primary layer 3 is improved, and the microbend loss of the colored optical fiber core 6 is suppressed. The microbend loss of the optical fiber strand 1 and the colored optical fiber core 6 according to this embodiment can be 0.4 dB/km or less.

The Young's modulus of the primary layer 3 of the optical fiber is ISM (In Situ Modulus), and the Young's modulus of the primary layer 3 can be 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 is formed is read with a microscope. Then, the load F is set to 10, 20, 30, 50, and 70 gf (i.e., 98, 196, 294, 490, and 686 mN in sequence), and the rate (slope) of the change in the load F with respect to the displacement δ is calculated. The calculated slope and the following formula (1) are used to calculate the primary elastic modulus. The calculated primary elastic modulus is the so-called ISM, and hereinafter the primary elastic modulus is appropriately referred to as P-ISM. When drawing the optical fiber, the drawing speed and the illuminance of the ultraviolet light are controlled to adjust the P-ISM.
P-ISM=(3F/δ)*(1/2πl)*ln(DP/DG)...(1)

The unit of P-ISM is [MPa]. On the right side of formula (1), F/δ is the rate (slope) of change in load (F) [gf] relative to displacement (δ) [μm], 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 formula (1) 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.

Furthermore, the Young's modulus of the secondary layer 4 of the optical fiber is ISM (In Situ Modulus), and the Young's modulus of the secondary layer 4 can be measured by the following method.

First, the optical fiber is immersed in liquid nitrogen, and the coating layer is stripped off with a stripper to create a hollow cylindrical sample with only the coating layer by pulling out the bare optical fiber 2 from the optical fiber. The end of the sample is fixed to an aluminum plate using adhesive. The aluminum plate is chucked using a Tensilon universal tensile tester in an atmosphere with a temperature of 23°C and a relative humidity of 50%. Next, the sample is stretched with a width of 6 mm, a gauge spacing of 25 mm, and a tensile speed of 1 mm/min, and the force at 2.5% stretch is measured to calculate the elastic modulus S-ISM (2.5% secant elastic modulus) of the secondary layer 4. The coating layer sample includes the primary layer 3 and the secondary layer 4. Since the S-ISM is sufficiently larger than the P-ISM, the effect of the P-ISM on the measured Young's modulus can be ignored and the measured Young's modulus can be considered as the S-IPM.

There are various methods for measuring microbend loss, and the microbend loss can be measured by the following method. First, the transmission loss of the optical fiber wound on a bobbin wrapped with sandpaper is measured, and the transmission loss at this time is defined as the transmission loss of the optical fiber in state A. Next, the transmission loss of the optical fiber wound on a bobbin not wrapped with sandpaper is measured, and the transmission loss at this time is defined as the transmission loss of the optical fiber in state B. The difference between the transmission loss of the optical fiber in state A and the transmission loss of the optical fiber in state B is defined as the microbend loss of the optical fiber. Here, the transmission loss of the optical fiber in state B does not include the transmission loss due to external forces, and is considered to be the transmission loss inherent to the optical fiber. The grit size of the sandpaper is #1000, and the length of the optical fiber is 400 m or more. The optical fibers in states A and B are wound around the bobbin so as not to overlap each other. In other words, the optical fibers in states A and B are wound around the bobbin in a single layer.

This measurement method is similar to the fixed diameter drum method defined in JIS C6823:2010. This measurement method is also called the sandpaper method. This measurement method measures the transmission loss at a wavelength of 1550 nm, so the microbend loss in this embodiment is also a value at a wavelength of 1550 nm.

Furthermore, the effective core area (Aeff) can be used as an index of the susceptibility of an optical fiber to microbend loss. The effective core area (Aeff) is expressed by the following formula (2). The effective core area (Aeff) is described in, for example, C-3-76 and C-3-77 of the 1999 Electronics Society Conference Proceedings of the Institute of Electronics, Information and Communication Engineers.
Aeff=(πk/4)*(MFD) ² ...(2)
Here, the effective core area Aeff 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 Aeff 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 Aeff 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 Aeff of the bare optical fiber 2 is large, the light in the bare optical fiber 2 is likely to leak due to an external force applied to the bare optical fiber 2. For this reason, when the effective core area Aeff of the bare optical fiber 2 is large, the microbend loss of the colored optical fiber 6 is likely to occur.

On the other hand, by increasing the effective core cross-sectional area of the bare optical fiber 2, the light intensity per unit area in the cross section of the bare optical fiber 2 can be reduced. This makes it possible to suppress the nonlinear optical effect of the bare optical fiber 2.

The colored optical fiber core 6 according to this embodiment has a primary layer 3 that can effectively suppress microbend loss. In other words, even if the effective core cross-sectional area of the bare optical fiber 2 is large, the microbend loss of the colored optical fiber core 6 can be effectively suppressed.

The effective core area Aeff of the bare optical fiber 2 is preferably 80 μm ² or more, for example, 130 μm ² or more and 150 μm ² or less. This makes it possible to obtain the colored optical fiber 6 that can suppress the nonlinear optical effect of the bare optical fiber 2.

The primary layer 3, secondary layer 4, and colored layer 5 are formed by curing ultraviolet-curable resin by irradiating it with ultraviolet light. The ultraviolet-curable resin is described in detail below.

An ultraviolet-curable resin is a resin that polymerizes and hardens when irradiated with ultraviolet light. There are no particular limitations on the ultraviolet-curable resin as long as it can be polymerized when irradiated with ultraviolet light. An 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.

The polymerizable unsaturated group in the UV-curable resin may be, for example, a group having an unsaturated double bond, such as a vinyl group, an allyl group, an acryloyl group, or a methacryloyl group, or a group having an unsaturated triple bond, such as a propargyl group. Among these, the acryloyl group and the methacryloyl group 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 either or both of acrylate and methacrylate. The UV-curable resin contains any photopolymerization initiator (photoinitiator) that has sensitivity in the UV region.

A polyether-based urethane (meth)acrylate is a compound that has 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 that has 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.

The UV-curable resin of the primary layer 3 (first UV-curable resin) and the UV-curable resin of the secondary layer 4 (second UV-curable resin) may contain, in addition to the oligomer and photoinitiator, a diluting monomer, a photosensitizer, a UV absorber, an antioxidant, a chain transfer agent, a silane coupling agent, a lubricant such as silicone, and various additives. The diluting monomer may be a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate. Here, the diluting monomer means a monomer for diluting the UV-curable resin.

The UV-curable resin of the colored layer 5 (third UV-curable resin) may contain various additives such as photoinitiators, photosensitizers, UV absorbers, antioxidants, chain transfer agents, silicones, and titanium oxides in addition to oligomers and monomers. The color of the UV-curable resin of the colored layer 5 may be black, gray, blue, light blue, green, yellow, orange, brown, pink, red, or white.

By incorporating a photoinitiator or photosensitizer that absorbs the ultraviolet light emitted by a UV-LED (light-emitting diode) into the ultraviolet-curable resin, the curing of the ultraviolet-curable resin by the ultraviolet light emitted by the UV-LED can be promoted. Since the ultraviolet light emitted by the UV-LED has a single wavelength, a non-initiator or photosensitizer that absorbs the wavelength of the ultraviolet light emitted by the UV-LED can be used. For example, when using a UV-LED that emits ultraviolet light with a wavelength of 300 nm or more, the photoinitiator can be, for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide or bis-(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and the photosensitizer can be, for example, 2,4-diethyl-9H-thioxen-9-one or 2-isopropylthioxanthone.

Figure 2 is a cross-sectional view of the optical fiber ribbon 8 according to this embodiment. The optical fiber ribbon 8 has a plurality of colored optical fiber cores 6 and a ribbon layer 7. The plurality of colored optical fiber cores 6 are arranged side by side. The ribbon layer 7 covers and connects the plurality of colored optical fiber cores 6. The thickness of the optical fiber ribbon 8 can be 210 μm or more and 400 μm or less. The thickness of the ribbon layer 7 is set so that the thickness of the optical fiber ribbon is 210 μm or more and 400 μm or less.

The ribbon layer 7 is composed of an ultraviolet-curable resin. The ultraviolet-curable resin (fourth ultraviolet-curable resin) of the ribbon layer 7 may be composed in the same manner as the ultraviolet-curable resin of the primary layer 3 and the ultraviolet-curable resin of the secondary layer 4. The Young's modulus of the ribbon layer 7 may preferably be 1.0 MPa or more and 2000 MPa or less. By changing the components constituting the ultraviolet-curable resin of the ribbon layer 7, the conversion rate, Young's modulus, breaking elongation, etc. of the ribbon layer 7 can be changed.

The optical fiber ribbon 8 is not limited to the configuration shown in FIG. 2. The optical fiber ribbon 8 may be an intermittent type optical fiber ribbon. When the optical fiber ribbon 8 is an intermittent type optical fiber ribbon, the optical fiber ribbon 8 forms adhesive portions (ribbon layers 7) intermittently in the longitudinal direction of the optical fiber colored core wires 6 in the region where two adjacent optical fiber colored core wires 6 contact each other.

The Young's modulus of the ribbon layer 7 can be measured by the following method. An unused single-edged blade is used to scrape off the ribbon layer 7 from the optical fiber ribbon 8. The scraped off ribbon layer 7 is then conditioned at constant temperature and humidity (temperature 23°C, relative humidity 50%) to obtain a sample piece of the ribbon layer 7 with a length of 25 mm. Under constant temperature and humidity conditions (temperature 23°C, relative humidity 50%), the sample piece of the ribbon layer 7 is pulled at a pulling speed of 1 mm/min, and the Young's modulus at 2.5% strain is calculated. The cross-sectional area of the sample piece of the ribbon layer 7 is measured by observation under a microscope.

Next, a manufacturing apparatus used in the manufacturing method of the optical fiber ribbon according to this embodiment will be described. FIG. 3 is a schematic diagram showing a part of a manufacturing apparatus 10 used in the manufacturing method of the optical fiber ribbon according to this embodiment. The manufacturing apparatus 10 has a heating device 20, a primary layer coating device 30, a secondary layer coating device 40, a guide roller 60, and a winding device 70. The manufacturing apparatus 10 shown in FIG. 3 manufactures an optical fiber strand 1 from an optical fiber preform BM.

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 (first light source). The resin applicator 31 holds the ultraviolet ray curing resin of the primary layer 3. The ultraviolet ray curing resin of the primary layer 3 contains the above-mentioned mercapto group-containing compound as an additive. The ultraviolet ray curing resin of the primary layer 3 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 resin application device 31 applies an ultraviolet-curable resin of the primary layer 3 to the bare optical fiber 2, and the bare optical fiber 2 enters the ultraviolet irradiation device 32, where the ultraviolet-curable resin of the primary layer 3 is irradiated with ultraviolet light. As a result, the ultraviolet-curable resin of the primary layer 3 is cured, 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 (second light source). The resin coating device 41 holds the ultraviolet ray curing resin of the secondary layer 4. The ultraviolet ray curing resin of the secondary layer 4 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 in the same manner as the ultraviolet irradiation device 32. The bare optical fiber 2, in which the ultraviolet-curable resin of the secondary layer 4 is coated around the primary layer 3, enters the ultraviolet irradiation device 42, and ultraviolet light is irradiated onto the ultraviolet-curable resin of the secondary layer 4. As a result, the ultraviolet-curable resin of the secondary layer 4 is cured, and the secondary layer 4 is formed. The bare optical fiber 2 is coated with the primary layer 3 and the secondary layer 4, forming the optical fiber strand 1.

The resin application device 31 may be configured to hold the UV-curable resin of the primary layer 3 and the UV-curable resin of the secondary layer 4 separately. In this case, the resin application device 31 applies the UV-curable resin of the primary layer 3 to the bare optical fiber 2, and then applies the UV-curable resin of the secondary layer 4 around the UV-curable resin of the primary layer 3. Furthermore, in this case, the UV irradiation device 32 irradiates the UV-curable resin of the primary layer 3 and the UV-curable resin of the secondary layer 4 applied to the bare optical fiber 2 with UV light. This forms the primary layer 3 and the 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 60 and a winding device 70 are provided below the secondary layer coating device 40. The manufactured optical fiber strand 1 is guided by the guide roller 60 and wound up on the winding device 70.

Figure 4 is a schematic diagram showing a portion of a manufacturing apparatus 10 used in the manufacturing method of an optical fiber ribbon according to this embodiment. The manufacturing apparatus 10 has a colored layer coating device 50, guide rollers 61, 62, and winding devices 70, 71. In Figure 4, the manufacturing apparatus 10 is an apparatus for manufacturing a colored optical fiber core 6 from an optical fiber strand 1.

The optical fiber strand 1 wound by the winding device 70 is guided by the guide roller 61 and transported to the colored layer coating device 50.

The colored layer coating device 50 has a resin applicator 51 and an ultraviolet ray irradiation device 52 (third light source). The resin applicator 51 holds the ultraviolet ray curing resin of the colored layer 5. The ultraviolet ray curing resin of the colored layer 5 is applied to the optical fiber strand 1 by the resin applicator 51.

An ultraviolet irradiation device 52 is provided below the resin application device 51. The ultraviolet irradiation device 52 can be configured in the same manner as the ultraviolet irradiation devices 32 and 42. The optical fiber strand 1 coated with the ultraviolet-curable resin of the colored layer 5 enters the ultraviolet irradiation device 52, and the ultraviolet-curable resin of the colored layer 5 is irradiated with ultraviolet light. As a result, the ultraviolet-curable resin of the colored layer 5 is cured, and the colored layer 5 is formed. The optical fiber strand 1 is coated with the colored layer 5, and the colored optical fiber core 6 is formed.

A guide roller 62 and a winding device 71 are provided below the colored layer coating device 50. After manufacture, the colored optical fiber core 6 is guided by the guide roller 62 and wound up on the winding device 71.

Figure 5 is a schematic diagram showing a portion of a manufacturing apparatus 10 used in the manufacturing method of an optical fiber ribbon according to this embodiment. The manufacturing apparatus 10 has a plurality of supply bobbins 81, guide rollers 82, a resin application device 83, an ultraviolet irradiation device 84, a guide roller 85, and a bobbin 86. In Figure 5, the manufacturing apparatus 10 is an apparatus for manufacturing an optical fiber ribbon 8 from a colored optical fiber core 6.

Multiple supply bobbins 81 are arranged in a line. The supply bobbins 81 are wound with colored optical fiber cores 6. The colored optical fiber cores 6 wound on the supply bobbins 81 are guided by guide rollers 82 and transported to a resin application device 83.

The resin applicator 83 holds the UV-curable resin of the ribbon layer 7. The UV-curable resin of the ribbon layer 7 is applied to the multiple optical fiber colored cores 6 by the resin applicator 83.

An ultraviolet ray irradiation device 84 (fourth light source) is provided below the resin application device 83. The ultraviolet ray irradiation device 84 may be configured similarly to the ultraviolet ray irradiation devices 32, 42, and 52. The multiple colored optical fiber core wires 6 coated with the ultraviolet curable resin of the ribbon layer 7 enter the ultraviolet ray irradiation device 84, and the ultraviolet curable resin of the ribbon layer 7 is irradiated with ultraviolet rays. As a result, the ultraviolet curable resin of the ribbon layer 7 is cured, and the ribbon layer 7 is formed. The multiple colored optical fiber core wires 6 are covered and connected by the ribbon layer 7, thereby forming the optical fiber ribbon 8.

Figure 6 is a flowchart of the method for manufacturing the optical fiber ribbon 8 according to this embodiment. First, the optical fiber preform BM is placed 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 UV-curable resin of the primary layer 3 around the drawn bare optical fiber 2, and irradiates the UV-curable resin of the primary layer 3 with UV light to form the primary layer 3 (step S103).

Next, the secondary layer coating device 40 applies an ultraviolet-curable resin of the secondary layer 4 around the primary layer 3, and irradiates the ultraviolet-curable resin of the secondary layer 4 with ultraviolet light to form the secondary layer 4 (step S104). This results in the optical fiber 1 being obtained. The optical fiber 1 after manufacture is wound up by the winding device 70.

Next, the colored layer coating device 50 applies an ultraviolet-curable resin for the colored layer 5 around the optical fiber strand 1, and irradiates the ultraviolet-curable resin for the colored layer 5 with ultraviolet light to form the colored layer 5 (step S105). This results in the colored optical fiber core wire 6. After production, the colored optical fiber core wire 6 is wound up by the winding device 71.

Next, the manufacturing device 10 applies the UV-curable resin of the ribbon layer 7 to the multiple colored optical fiber cores 6, and irradiates the UV-curable resin of the ribbon layer 7 with UV light to form the ribbon layer 7 (step S106). This results in the optical fiber ribbon 8.

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).

This embodiment improves the ability to separate individual fibers of the optical fiber ribbon 8. The effects of this embodiment will be described in detail below in comparison with the prior art.

In an optical fiber strand 1 or colored optical fiber core 6, a technology is known in which the primary layer 3 covering the bare optical fiber 2, the secondary layer 4 covering the primary layer 3, and the colored layer 5 covering the secondary layer 4 are each formed from an ultraviolet-curable resin. In addition, a technology is known in which an optical fiber ribbon 8 is formed by covering a plurality of colored optical fiber cores 6 with a ribbon layer 7.

Normally, when the optical fiber ribbon 8 is installed, the colored optical fiber core 6 is removed from the optical fiber ribbon 8. For this reason, it is preferable that the colored optical fiber core 6 can be easily removed from the optical fiber ribbon 8, i.e., the optical fiber ribbon 8 has good single-core separation properties. One possible way to improve the single-core separation properties of the optical fiber ribbon 8 is to set the surface conversion rate of the colored layer 5 of the colored optical fiber core 6 to a high value.

However, in the process of forming the colored layer 5, the temperature of the optical fiber strand 1 to which the ultraviolet-curable resin of the colored layer 5 is applied is lowered from the temperature at the time of manufacture to room temperature. On the other hand, in the process of forming the primary layer 3, the bare optical fiber 2 drawn out by melting the optical fiber preform BM is at a higher temperature than room temperature. Also, in the process of forming the secondary layer 4, the primary layer 3 covers the high-temperature bare optical fiber 2 and is heated by the curing heat of the ultraviolet-curable resin of the primary layer 3, so that it is at a higher temperature than room temperature. Therefore, the curing temperature and surface conversion rate of the colored layer 5 are lower than those of the primary layer 3 and secondary layer 4.

Depending on the manufacturing conditions of the optical fiber colored core 6, the surface conversion rate of the colored layer 5 may not be sufficiently high. For example, the ultraviolet light from a mercury lamp contains infrared light, while the ultraviolet light from a UV-LED does not contain infrared light. For this reason, when the light source for ultraviolet irradiation is a UV-LED, the curing temperature and surface conversion rate of the colored layer 5 are low. Furthermore, when a UV-LED that irradiates ultraviolet light with a wavelength of 300 nm or more is used, the wavelength in the short wavelength region that is important for the surface conversion rate of the colored layer 5 is reduced compared to the ultraviolet light from a mercury lamp. Therefore, when the light source for ultraviolet irradiation in the process of forming the colored layer 5 is a UV-LED, the surface conversion rate of the colored layer 5 is low.

Technologies for increasing the surface conversion rate of the colored layer 5 are described in WO 2016/017060, JP 2021-178741, JP 2018-177630, WO 2015/199199, WO 2016/072064, JP 2015-212222, and WO 2016/028668. However, even with these techniques, it is not possible to sufficiently increase the surface conversion rate of the colored layer 5, making it difficult to obtain an optical fiber ribbon 8 with good single-core separation properties.

In this embodiment, by increasing the conversion rate of the portion of the ribbon layer 7 that contacts the colored layer 5, the adhesion between the colored layer 5 and the ribbon layer 7 is reduced. In addition, by increasing the breaking elongation of the ribbon layer 7, when the colored optical fiber core 6 is removed from the optical fiber ribbon 8, the ribbon layer 7 is less likely to remain on the surface of the colored optical fiber core 6, and the ribbon layer 7 can be easily removed. . This improves the single-core separation of the optical fiber ribbon. In this embodiment, the conversion rate of the ribbon layer 7 of the portion of the ribbon layer 7 that contacts the colored layer 5 is 83.7% or more, and the breaking elongation of the ribbon layer 7 is 9.7% or more. Therefore, according to this embodiment, the single-core separation of the optical fiber ribbon 8 can be improved.

In addition, compared to mercury lamps, UV-LEDs have the advantages of a longer lifespan and lower maintenance costs. This allows for a significant reduction in the manufacturing costs of the optical fiber ribbon 8. According to this embodiment, even when the ultraviolet light source in the process of forming the colored layer 5 is a UV-LED, the single-core separation properties of the optical fiber ribbon 8 can be improved.

Furthermore, the deterioration of the surface conversion rate of the colored layer 5 is not limited to cases where the ultraviolet light source is a UV-LED. For example, the surface conversion rate of the colored layer 5 may deteriorate when the manufacturing speed of the colored optical fiber core 6 is high, when the illuminance or dose of ultraviolet light is low, or when the oxygen concentration in the process of forming the colored layer 5 is high. According to the present invention, even in such cases, it is possible to improve the single-core separation property of the optical fiber ribbon 8.

In this embodiment, the optical fiber ribbon 8 may have a bind layer that covers the ribbon layer 7. In this case, the adhesion between the ribbon layer 7 and the bind layer can be improved by lowering the surface conversion rate of the ribbon layer 7. Even in such a case, the single-core separation property of the optical fiber ribbon 8 can be improved by setting the conversion rate of the portion of the ribbon layer 7 that contacts the colored layer 5 to 83.7% or more and the breaking elongation of the ribbon layer 7 to 9.7% or more.

The following describes the measurement results of the optical fiber ribbon 8 according to an embodiment of the present invention.

Table 1 shows the conversion rate (%) of the portion of the ribbon layer that contacts the colored layer, the breaking elongation (%) of the ribbon layer, the breaking elongation (%) of the sheet-like cured product, and the evaluation of the single-core separation property of the optical fiber ribbon.

In the examples and comparative examples, the ultraviolet curing resin of the ribbon layer is any one of resins A to I. The ultraviolet curing resin of the coloring layer was cured by irradiation with ultraviolet light having a wavelength of 395 nm using a UV-LED as a light source. In the examples and comparative examples, the surface conversion rate of the coloring layer was 85% or more and 92% or less. In the examples and comparative examples, the surface conversion rate of the coloring layer was measured by a microscopic ATR (ATR: Attenuated Total Reflection) method of Fourier transform infrared spectroscopy (FT-IR: Fourier Transform Infrared). The surface conversion rate of the coloring layer was determined from the decrease in the height of the peak near 1407 cm ^-1 before and after the ultraviolet curing of the ultraviolet curing resin of the coloring layer, based on the peak area near 1500 cm ^-1 . In the examples and comparative examples, the ultraviolet-curable resin of the ribbon layer was cured by ultraviolet irradiation using a mercury lamp or a UV-LED, or both a mercury lamp and a UV-LED as a light source.

In the examples and comparative examples, the ribbon layer was obtained from the optical fiber ribbon by scraping off the ribbon layer with an unused single blade. Also, a sheet-shaped cured product was obtained by the following method. Using a spin coater, a film of the ultraviolet-curable resin of the ribbon layer was formed on a glass plate with a thickness of 40 μm to 60 μm. The film of the ultraviolet-curable resin of the ribbon layer was irradiated with ultraviolet light from a mercury lamp as a light source. The ultraviolet-curable resin of the ribbon layer was sufficiently cured by the ultraviolet light to obtain a sheet-shaped cured product. The mercury lamp was set to an illuminance of 1000 mW/cm ² and an irradiation amount of 1000 mJ/cm ^2. The illuminance was measured using UV-351 manufactured by Oak Manufacturing Co., Ltd. Note that, "sufficiently curing the resin" refers to curing the resin to a Young's modulus of 90% or more of the maximum Young's modulus that the resin can exhibit.

In the examples and comparative examples, the conversion rate of the ribbon layer was measured by the microscopic ATR method of Fourier transform infrared spectroscopy. The conversion rate of the ribbon layer was determined from the decrease in the height of the peak near 810 cm-1 before and after the UV curing of the UV-curable resin of the ribbon layer, based on the peak area near 1500 ^{cm -1} .

In the examples and comparative examples, the breaking elongation of the ribbon layer and the sheet-shaped cured product was measured by the following method. The ribbon layer and the sheet-shaped cured product were conditioned at constant temperature and humidity (temperature 23°C, relative humidity 50%) to obtain sample pieces with a length of 25 mm. In a constant temperature and humidity atmosphere (temperature 23°C, relative humidity 50%), the sample pieces were elongated at a tensile speed of 50 mm/min, and the breaking elongation was measured from the elongation rate at break. The breaking elongation was measured four or more times for each example and comparative example, and the highest measured value was used as the breaking elongation listed in Table 1. The cross-sectional area of the sample pieces was measured using a microscope.

The breaking elongation of the ribbon layer of an optical fiber ribbon can vary depending on the manufacturing conditions of the optical fiber ribbon. The breaking elongation of the sheet-shaped cured material can be an indicator of the maximum breaking elongation possible for the UV-curable resin of the ribbon layer. Therefore, in general, the breaking elongation of the sheet-shaped cured material is greater than the breaking elongation of the ribbon layer.

"Rating 1" in Table 1 indicates whether the single-core separation property of the optical fiber ribbon is good or not. The single-core separation property of the optical fiber ribbon was evaluated by the following method. First, a crack was made in the tape layer at the end of the optical fiber ribbon without using a special tool. Next, the ribbon layer was removed to separate the colored optical fiber core from the optical fiber ribbon. If the separated colored optical fiber core does not peel off the colored layer or break the colored optical fiber core, and the cuticle of the ribbon layer does not adhere to the surface of the colored layer, then the rating of 1 is judged to be good (OK). If the separated colored optical fiber core peels off or breaks the colored layer, or the cuticle of the ribbon layer adheres to the surface of the colored layer, then the rating of 1 is judged to be poor (NG).

In Example 1, the UV-curable resin of the ribbon layer was Resin A. The conversion rate of the ribbon layer was 83.7%. The breaking elongation of the ribbon layer was 41.0%. The breaking elongation of the sheet-shaped cured product was 60.5%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 2, the UV-curable resin of the ribbon layer was resin B. The conversion rate of the ribbon layer was 87.4%. The breaking elongation of the ribbon layer was 18.2%. The breaking elongation of the sheet-shaped cured product was 64.7%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 3, the UV-curable resin of the ribbon layer was resin C. The conversion rate of the ribbon layer was 84.5%. The breaking elongation of the ribbon layer was 20.5%. The breaking elongation of the sheet-shaped cured product was 65.0%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 4, the UV-curable resin of the ribbon layer was Resin D. The conversion rate of the ribbon layer was 91.0%. The breaking elongation of the ribbon layer was 54.0%. The breaking elongation of the sheet-shaped cured product was 54.3%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 5, the UV-curable resin of the ribbon layer was Resin E. The conversion rate of the ribbon layer was 94.1%. The breaking elongation of the ribbon layer was 15.8%. The breaking elongation of the sheet-shaped cured product was 38.7%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 6, the UV-curable resin of the ribbon layer was Resin F. The conversion rate of the ribbon layer was 95.0%. The breaking elongation of the ribbon layer was 9.4%. The breaking elongation of the sheet-shaped cured product was 23.6%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. In addition, the skin of the ribbon layer did not adhere to the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Example 7, the UV-curable resin of the ribbon layer was resin G. The conversion rate of the ribbon layer was 90.2%. The breaking elongation of the ribbon layer was 13.3%. The breaking elongation of the sheet-shaped cured product was 33.8%. When the colored optical fiber core was separated from the optical fiber ribbon, there was no peeling of the colored layer and no breakage of the colored optical fiber core. Furthermore, no cuticle of the ribbon layer remained on the surface of the colored layer. Therefore, the evaluation 1 was good (OK).

In Comparative Example 1, the UV-curable resin of the ribbon layer was Resin H. The conversion rate of the ribbon layer was 81.8%. The breaking elongation of the ribbon layer was 41.1%. The breaking elongation of the sheet-shaped cured product was 60.5%. When the colored optical fiber core was separated from the optical fiber ribbon, the colored layer peeled off, or the skin of the ribbon layer adhered to the surface of the colored layer. Therefore, the evaluation 1 was poor (NG).

In Comparative Example 2, the UV-curable resin of the ribbon layer was Resin I. The conversion rate of the ribbon layer was 94.3%. The breaking elongation of the ribbon layer was 5.4%. The breaking elongation of the sheet-shaped cured product was 8.4%. When the colored optical fiber core was separated from the optical fiber ribbon, the colored layer peeled off, or the skin of the ribbon layer adhered to the surface of the colored layer. Therefore, the evaluation 1 was poor (NG).

In the examples and comparative examples, the number of cores in the optical fiber ribbon is 4. However, measurement results similar to those in Table 1 can be obtained even when the number of cores in the optical fiber ribbon is, for example, 2, 8, 12, or 24.

When the colored layer of the colored core wire used in the examples and comparative examples was formed using a mercury lamp instead of a UV-LED as the light source, the surface conversion rate of the colored layer was 92% or more and 96% or less. The surface conversion rate of the colored layer can vary depending on the manufacturing conditions of the optical fiber colored core wire, the composition of the ultraviolet-curable resin of the colored layer, and the color of the colored layer. In the examples and comparative examples, the colored layer is blue or brown. In general, a colored layer formed by ultraviolet irradiation from a mercury lamp has a higher surface conversion rate than a colored layer formed by ultraviolet irradiation from a UV-LED. For each of Examples 1 to 7 and Comparative Examples 1 to 2, the single-core separation property of the optical fiber ribbon when the colored layer was formed by ultraviolet irradiation from a mercury lamp was evaluated. In Examples 1 to 7 and Comparative Example 1, Evaluation 1 was good (OK), and in Comparative Example 2, Evaluation 1 was poor (NG).

Note that even if the wavelength of the UV-LED in the examples and comparative examples is not 395 nm, the same measurement results as in Table 1 are obtained. For example, even if the wavelength of the UV-LED is 275 nm, 365 nm, or 385 nm, the same measurement results as in Table 1 are obtained.

It is preferable that the ribbon layer has a conversion rate of 83.7% or more in the portion in contact with the colored layer, and the ribbon layer has a breaking elongation of 9.4% or more. This makes it possible to provide an optical fiber ribbon with good single-core separation properties.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, an example in which a part of the configuration of one of the embodiments is added to another embodiment, or an example in which a 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.

1 Optical fiber 2 Bare optical fiber 3 Primary layer 4 Secondary layer 5 Colored layer 6 Colored optical fiber core 7 Ribbon layer 8 Optical fiber ribbon

Claims (21)

a plurality of colored optical fiber core wires including a bare optical fiber, a primary layer formed of a first ultraviolet-curable resin covering the bare optical fiber, 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;
a ribbon layer formed of a fourth ultraviolet curing resin covering the plurality of colored optical fiber cores;
The conversion rate of the portion of the ribbon layer in contact with the colored layer is 83.7% or more,
An optical fiber ribbon, wherein the ribbon layer has a breaking elongation of 9.4% or more. a plurality of colored optical fiber core wires including a bare optical fiber, a primary layer formed of a first ultraviolet-curable resin covering the bare optical fiber, and a secondary layer formed of a second ultraviolet-curable resin covering the primary layer;
a ribbon layer formed of a fourth ultraviolet curing resin covering the plurality of colored optical fiber cores;
the secondary layer is a colored layer that is colored,
The conversion rate of the portion of the ribbon layer in contact with the colored layer is 83.7% or more,
An optical fiber ribbon, wherein the ribbon layer has a breaking elongation of 9.4% or more. The optical fiber ribbon according to claim 1 or 2, characterized in that the surface conversion rate of the colored layer is 96.0% or less. The optical fiber ribbon according to claim 1 or 2, characterized in that the surface conversion rate of the colored layer is 92.0% or less. The optical fiber ribbon according to claim 1 or 2, characterized in that the conversion rate of the portion of the ribbon layer that contacts the colored layer is 95.0% or less. The optical fiber ribbon according to claim 1 or 2, characterized in that the breaking elongation of the ribbon layer is 65.0% or less. The optical fiber ribbon according to claim 1, characterized in that the third ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. The optical fiber ribbon according to claim 1 or 2, characterized in that the fourth ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. The optical fiber ribbon according to claim 2, characterized in that the second ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. A step of drawing a bare optical fiber from an optical fiber preform;
a step of applying a first ultraviolet curing resin for forming a primary layer around the bare optical fiber and irradiating the first ultraviolet curing resin with ultraviolet light from a first light source to form a primary layer;
applying a second ultraviolet-curable resin to form a secondary layer around the primary layer, and irradiating the second ultraviolet-curable resin with ultraviolet light from a second light source to form a secondary layer;
a step of applying a third ultraviolet curing resin to form a colored layer around the secondary layer, and irradiating the third ultraviolet curing resin with ultraviolet light from a third light source to form a colored layer;
applying a fourth ultraviolet-curing resin to form a ribbon layer around the colored layer, and irradiating the fourth ultraviolet-curing resin with ultraviolet light from a fourth light source to form a ribbon layer;
The conversion rate of the portion of the ribbon layer in contact with the colored layer is 83.7% or more,
A method for manufacturing an optical fiber ribbon, wherein the ribbon layer has a breaking elongation of 9.4% or more. The method for manufacturing an optical fiber ribbon according to claim 10, characterized in that at least one of the first light source, the second light source, the third light source, and the fourth light source is a light-emitting diode. The method for manufacturing an optical fiber ribbon according to claim 10, characterized in that the third ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. The method for manufacturing an optical fiber ribbon according to claim 10, characterized in that the third light source includes a light emitting diode. The method for manufacturing an optical fiber ribbon according to claim 10, characterized in that the fourth light source includes a light emitting diode. The method for manufacturing an optical fiber ribbon according to claim 10, characterized in that the fourth ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. A step of drawing a bare optical fiber from an optical fiber preform;
a step of applying a first ultraviolet curing resin for forming a primary layer around the bare optical fiber and irradiating the first ultraviolet curing resin with ultraviolet light from a first light source to form a primary layer;
applying a second ultraviolet-curable resin to form a secondary layer around the primary layer, and irradiating the second ultraviolet-curable resin with ultraviolet light from a second light source to form a colored secondary layer;
and applying a fourth ultraviolet-curing resin to form a ribbon layer around the secondary layer, and irradiating the fourth ultraviolet-curing resin with ultraviolet light from a fourth light source to form a ribbon layer.
The conversion rate of the portion of the ribbon layer in contact with the secondary layer is 83.7% or more;
A method for manufacturing an optical fiber ribbon, wherein the ribbon layer has a breaking elongation of 9.4% or more. The method for manufacturing an optical fiber ribbon according to claim 16, characterized in that at least one of the first light source, the second light source and the fourth light source is a light-emitting diode. The method for manufacturing an optical fiber ribbon according to claim 16, characterized in that the second ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode. The method for manufacturing an optical fiber ribbon according to claim 16, characterized in that the second light source includes a light emitting diode. The method for manufacturing an optical fiber ribbon according to claim 16, characterized in that the fourth light source includes a light emitting diode. The method for manufacturing an optical fiber ribbon according to claim 16, characterized in that the fourth ultraviolet-curable resin is cured by ultraviolet light emitted by a light-emitting diode.