Optical fiber manufacturing method

Abstract

To provide a method for manufacturing an optical fiber which can further enhance a power saving effect while suppressing an increase in microbend loss.SOLUTION: There is provided a method for manufacturing an optical fiber which comprises: a step of applying a first resin composition; a step of curing the first resin composition by ultraviolet irradiation to form a primary resin layer; a step of applying a second resin composition; and a step of curing the second resin composition by ultraviolet irradiation to form a secondary resin layer, wherein in the step of forming a primary resin layer and the step of forming a secondary resin layer, an ultraviolet LED is used as a light source, respectively and in the step of forming a primary resin layer, when the number of light sources is defined as N, the rated power of the nth light source is defined as n[kW], the power setting ratio of the nth light source is defined φn and the irradiation time of the nth light source is defined as tn[s], the effective power consumption indicated by the expression (1) is 0.056 kWs or more and 0.230 kWs or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to methods for manufacturing optical fibers. [Background technology]

[0002] Patent Document 1 describes a method for manufacturing an optical fiber. This method includes a step of applying a UV-curable resin to a bare optical fiber and then irradiating the optical fiber with UV light using a semiconductor light-emitting element. The semiconductor light-emitting element is an UV LED. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-65949 Summary of the Invention [Problem to be solved by the invention]

[0004] Due to growing environmental awareness worldwide, there has been a rapid shift from the conventional mercury-containing lamps to UV-LEDs as the light source for curing UV-curable resins, which are used as coating materials for optical fibers. UV-LEDs are mercury-free and also offer energy-saving benefits, making them considered effective in reducing environmental impact. However, to maximize their effectiveness, it is necessary to understand the chemical reaction kinetics of the curing reaction of UV-curable resins. Such research has been conducted on UV-curable resin liquids and films. However, no research has been conducted using actual optical fibers.

[0005] In particular, if the UV irradiation is insufficient in the process of forming the primary resin layer, the primary resin layer may harden again in a subsequent process, which may increase the Young's modulus of the primary resin layer and increase the microbend loss of the optical fiber.

[0006] An object of the present disclosure is to provide a method for manufacturing an optical fiber that can further enhance the power saving effect while suppressing an increase in microbend loss. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a method for manufacturing an optical fiber includes a glass fiber, a primary resin layer coating the glass fiber, and a secondary resin layer coating the primary resin layer, the method including the steps of applying an ultraviolet-curable first resin composition to form the primary resin layer, curing the first resin composition by ultraviolet light to form the primary resin layer, and applying an ultraviolet-curable second resin composition to form the secondary resin layer, and curing the second resin composition by ultraviolet light to form the secondary resin layer. The primary resin layer and secondary resin layer forming steps each use an ultraviolet LED as a light source. In the primary resin layer forming step, the effective power consumption, expressed by Equation (1), is 0.056 kWs or more and 0.230 kWs or less, where N is the number of light sources, Bn [kW] is the rated power of the nth light source, φn is the power setting percentage of the nth light source, and tn [s] is the irradiation time of the nth light source. Here, n is a natural number up to N. φn = 1 when the power setting percentage of the nth light source is 100%. The effective power consumption is proportional to the amount of UV radiation applied to the optical fiber.

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[0008] According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber that can further enhance the power saving effect while suppressing an increase in microbend loss. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber according to the first embodiment. [Figure 2] FIG. 2 is a graph in which the rate of change in Young's modulus of the primary resin layer before and after the formation of the colored resin layer is plotted against the effective power consumption in the first forming step. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Description of the embodiments of the present disclosure] First, the details of the embodiments of the present disclosure will be described below. A method for manufacturing an optical fiber according to one aspect of the present disclosure is a method for manufacturing an optical fiber including a glass fiber, a primary resin layer coating the outer periphery of the glass fiber, and a secondary resin layer coating the outer periphery of the primary resin layer, the method including the steps of applying an ultraviolet-curable first resin composition to be the primary resin layer, curing the first resin composition by irradiating ultraviolet light to form the primary resin layer, and applying an ultraviolet-curable second resin composition to be the secondary resin layer, and curing the second resin composition by irradiating ultraviolet light to form the secondary resin layer, wherein the steps of forming the primary resin layer and forming the secondary resin layer each use an ultraviolet LED as a light source, and the step of forming the primary resin layer has an effective power consumption of 0.056 kWs or more and 0.230 kWs or less, where N is the number of light sources, Bn [kW] is the rated power of the n-th light source, φn is the power setting ratio of the n-th light source, and tn [s] is the irradiation time of the n-th light source.

[0011] In this optical fiber, the effective power consumption in the process of forming the primary resin layer is 0.056 kWs or more, allowing the primary resin layer to be sufficiently cured. This prevents the primary resin layer from being cured again in a later process, which would increase the Young's modulus of the primary resin layer. This prevents an increase in microbend loss in the optical fiber. Furthermore, the effective power consumption is 0.230 kWs or less, thereby enhancing the power saving effect.

[0012] The method for manufacturing the optical fiber may further include the steps of applying an ultraviolet-curable third resin composition (a colored resin containing a pigment, a dye, etc.) to the outer periphery of the secondary resin layer, and curing the third resin composition by irradiating it with ultraviolet light to form a colored resin layer. In this case, since the primary resin layer is sufficiently cured, even if further ultraviolet light is irradiated in the step of forming the colored resin layer, the primary resin layer is not cured again, and an increase in the Young's modulus of the primary resin layer is suppressed. Therefore, microbend loss of the optical fiber is suppressed.

[0013] The step of forming the primary resin layer may be performed together with the step of forming the secondary resin layer after the step of applying the second resin composition. In this case, the first resin composition and the second resin composition can be cured by irradiating them with ultraviolet light from the same light source, thereby forming the primary resin layer and the secondary resin layer.

[0014] The step of forming the primary resin layer may be performed before the step of applying the second resin composition, in which case residual strain (stress) in the primary resin layer is reduced, making it less likely that voids will occur in the primary resin layer when the optical fiber passes through the capstan.

[0015] [Details of the embodiments of the present disclosure] Specific examples of the method for manufacturing an optical fiber according to this embodiment will be described below with reference to the drawings as necessary. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In the following description, the same elements in the drawings will be given the same reference numerals, and duplicated explanations will be omitted.

[0016] (optical fiber) FIG. 1 is a diagram showing a cross section perpendicular to the axial direction of an optical fiber according to an embodiment. The optical fiber 1 complies with at least one of the ITU-T G.652 standard, the ITU-T G.654 standard, and the ITU-T G.657 standard. Complying with the ITU-T G.652 standard means complying with at least one of G.652.A, G.652.B, G.652.C, and G.652.D. Complying with the ITU-T G.654 standard means complying with at least one of G.654.A, G.654.B, G.654.C, G.654.D, and G.654.E. Complying with the ITU-T G.657 standard means complying with at least one of G.657.A and G.657.B. The optical fiber 1 includes a glass fiber 10 and a coating resin layer 20 provided on the outer periphery of the glass fiber 10.

[0017] The glass fiber 10 includes a core 12 and a clad 14. The clad 14 surrounds the core 12. The core 12 and the clad 14 mainly contain glass such as silica glass. For example, the core 11 can be made of germanium-doped silica glass or pure silica glass. The clad 14 can be made of pure silica glass or fluorine-doped silica glass. Here, pure silica glass refers to silica glass that is substantially free of impurities.

[0018] The diameter of the core 12 is 6.0 μm or more and 12.0 μm or less. The outer diameter of the cladding 14 is 125 μm±0.5 μm, that is, 124.5 μm or more and 125.5 μm or less. The outer diameter of the cladding 14 matches the diameter of the glass fiber 10.

[0019] The coating resin layer 20 includes a primary resin layer 22, a secondary resin layer 24, and a colored resin layer 26. The primary resin layer 22 is in contact with the outer peripheral surface of the clad 14 and coats the entire clad 14. The secondary resin layer 24 is in contact with the outer peripheral surface of the primary resin layer 22 and coats the entire primary resin layer 22. The colored resin layer 26 is in contact with the outer peripheral surface of the secondary resin layer 24 and coats the entire secondary resin layer 24. The colored resin layer 26 constitutes the outermost layer of the coating resin layer 20.

[0020] The primary resin layer 22 and the secondary resin layer 24 are made of a cured product of an ultraviolet-curable resin composition. This resin composition contains a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator. Here, (meth)acrylate refers to an acrylate or its corresponding methacrylate. The monomer may be a monofunctional monomer having one polymerizable group or a polyfunctional monomer having two or more polymerizable groups. Two or more types of monomers may be mixed. The photopolymerization initiator may be appropriately selected from known radical photopolymerization initiators. The resin composition may further contain a silane coupling agent, a photoacid generator, a leveling agent, an antifoaming agent, an antioxidant, etc. The primary resin layer 22 and the secondary resin layer 24 do not contain pigments or dyes and are substantially transparent.

[0021] The colored resin layer 26 is made of a cured product of an ultraviolet-curable resin composition containing a colored ink (pigment, dye). This resin composition contains, for example, a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator. The monomer may be a monofunctional monomer having one polymerizable group or a polyfunctional monomer having two or more polymerizable groups. Two or more types of monomers may be mixed together. The photopolymerization initiator may be appropriately selected from known radical photopolymerization initiators. The resin composition may further contain a silane coupling agent, a photoacid generator, a leveling agent, an antifoaming agent, an antioxidant, etc. The optical fiber 1, having the colored resin layer 26, is a so-called colored optical fiber.

[0022] The thickness of the primary resin layer 22 is, for example, 7.5 μm or more and 36.5 μm or less. The thickness of the secondary resin layer 24 is, for example, 10 μm or more and 40 μm or less. The thickness of the colored resin layer 16 is, for example, 3 μm or more and 10 μm or less.

[0023] The Young's modulus of the primary resin layer 22 is 0.05 MPa or more and 0.60 MPa or less at 23° C. The Young's modulus of the secondary resin layer 24 is 800 MPa or more and 2800 MPa or less at 23° C. The Young's modulus of the colored resin layer 26 is 1000 MPa or more and 1500 MPa or less at 23° C.

[0024] (Optical fiber manufacturing method) The method for manufacturing the optical fiber 1 according to this embodiment includes a drawing step, a first coating step, a first forming step, a second coating step, a second forming step, a third coating step, and a third forming step. The optical fiber 1 is manufactured through each of these steps. Each step will be described below.

[0025] The drawing process is a process of drawing a glass fiber 10 from an optical fiber preform. For example, an optical fiber preform containing synthetic quartz as a main component can be used. The optical fiber preform is heated, melted, and drawn by an optical fiber drawing machine.

[0026] The first application step is a step of applying an ultraviolet-curable resin composition (first resin composition) that will become a primary resin layer. The first resin composition is applied to the outer peripheral surface of the glass fiber 10. For example, a die is used as an application device for applying the first resin composition.

[0027] The first forming step is a step of curing the first resin composition by irradiating it with ultraviolet light to form the primary resin layer 22. In the first forming step, ultraviolet LEDs are used as light sources to irradiate the first resin composition with ultraviolet light. For example, multiple light sources are arranged radially around the glass fiber 10. The first forming step is performed at least after the first applying step. The ultraviolet light irradiation conditions will be described later.

[0028] The second coating step is a step of coating an ultraviolet-curable resin composition (second resin composition) that will become the secondary resin layer. The second coating step is performed at least after the first coating step. The first coating step may be performed before the first forming step or after the first forming step. When the first coating step is performed before the first forming step, the second resin composition is coated on the outer peripheral surface of the first resin composition (wet-on-wet method). When the second coating step is performed after the first forming step, the second resin composition is coated on the outer peripheral surface of the primary resin layer 22 (wet-on-dry method). For example, a die is used as a coating device for coating the second resin composition.

[0029] The second forming step is a step of curing the second resin composition by irradiating it with ultraviolet light to form the secondary resin layer 24. In the second forming step, ultraviolet light is irradiated onto the second resin composition using ultraviolet LEDs as a light source. For example, multiple light sources are arranged radially around the glass fiber 10. In the wet-on-wet method, the first forming step is performed together with the second forming step after the second coating step. In this case, the first forming step and the second forming step are essentially performed as a single step. Both the first resin composition and the second resin composition are irradiated with ultraviolet light from the same light source to cure them, thereby forming the primary resin layer 22 and the secondary resin layer 24. In the wet-on-dry method, the first forming step and the second forming step are performed separately. The first forming step is performed before the second coating step. The second forming step is performed after the second coating step.

[0030] The third application step is a step of applying an ultraviolet-curable resin composition (third resin composition) that will become the colored resin layer 26. The third resin composition is applied to the outer peripheral surface of the secondary resin layer 24 using a die. The third application step is performed after the second formation step.

[0031] The third forming step is a step of curing the third resin composition by irradiating it with ultraviolet light to form the colored resin layer 26. In the third forming step, an ultraviolet lamp is used as a light source to irradiate the third resin composition with ultraviolet light. For example, multiple light sources are arranged radially around the glass fiber 10. The third forming step is performed after the third applying step.

[0032] As described above, an optical fiber 1 including the glass fiber 10 and the coating resin layer 20 is manufactured and wound around a bobbin. The fiber before being coated with the colored resin layer 26 is also called a "strand" and the fiber after being coated with the colored resin layer 26 is also called a "core wire." The strand includes the glass fiber 10, the primary resin layer 22, and the secondary resin layer 24. The core wire is the optical fiber 1. In the method for manufacturing the optical fiber 1, the strand may be temporarily wound around a bobbin after the second forming step is performed. In this case, the strand is unwound from the bobbin, and the third coating step and third forming step are performed, and the core wire is wound around another bobbin.

[0033] (Analysis of curing reaction) The curing reaction of UV-curable resin can be described mainly by the following three elementary steps. (a) Initiation reaction: PI + ultraviolet light (hν) → 2R · (b) Growth reaction: R· + M → RM· (c) Termination reaction: R + R → RR PI represents a photopolymerization initiator, R· represents a radical molecule, and M represents a monomer or oligomer. Here, we created an analytical model focusing on the initiation reaction (a) and examined the reaction efficiency and power saving effects. When ordinary UV-curable resins are cured, the number of UV photons is in great excess relative to the number of photopolymerization initiator molecules. Therefore, we assumed that the initiation reaction (a) is a pseudo-first-order reaction.

[0034] Consider the case where N light sources are used to cure ultraviolet curable resin. When the rated power of the nth light source is Bn [kW], the power setting ratio (illuminance) of the nth light source is φn, and the irradiation time of the nth light source is tn [s], the effective power consumption is expressed by formula (1). Here, n is a natural number up to N.

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[0035] The ratio of the post-curing concentration (unreacted concentration of photopolymerization initiator) to the initial concentration of the photopolymerization initiator is represented as C. Assuming that the reaction rate constant of the initiation reaction (a) is constant (= k) for each light source, equation (2) is obtained.

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[0036] By plotting lnC against the effective power consumption and approximating it with a straight line passing through the origin, the reaction rate constant k can be calculated from the slope of the approximated line. Furthermore, from equation (2), the power consumption required to reduce the photopolymerization initiator to a concentration ratio of C = 1 / e (~0.37) can be expressed as 1 / k. This value was used as an index of the power saving effect.

[0037] (Ultraviolet irradiation conditions) The ultraviolet irradiation conditions for the first forming step in the manufacturing method according to the embodiment are set. That is, in the above formula (2), k=20, and the range of effective power consumption is set so that the ratio C of the post-curing concentration of the photopolymerization initiator to the initial concentration is 0.010 or more and 0.326 or less. By setting the ratio C to 0.326 or less, the primary resin layer 22 can be sufficiently cured in the first forming step. This prevents the primary resin layer 22 from being cured again by ultraviolet irradiation in the third forming step. The change rate of the Young's modulus of the primary resin layer 22 at 23°C before and after the third forming step is 50% or less. In this way, the increase in the Young's modulus of the primary resin layer 22 due to the third forming step is suppressed, and therefore the increase in microbend loss of the optical fiber 1 is suppressed. By setting the ratio C to 0.010 or more, excessive ultraviolet irradiation is suppressed, further enhancing the power saving effect. The rate of change in Young's modulus of the primary resin layer 22 at 23°C is expressed as (E2-E1) / E1 [%], where E1 is the Young's modulus of the primary resin layer 22 at 23°C before the third formation process and E2 is the Young's modulus of the primary resin layer 22 at 23°C after the third formation process.

[0038] (Experimental example) Using an optical fiber drawing machine, an optical fiber preform primarily composed of synthetic quartz was heated and melted and drawn to an outer diameter of 125 μm. The outer circumference of the resulting glass fiber was coated with a first resin composition and a second resin composition, in that order, using an applicator, followed by curing with an ultraviolet LED. The resulting fiber was wound around a bobbin. The fiber was then unwound from the bobbin, and a third resin composition was applied around the fiber using an applicator, followed by curing with an ultraviolet lamp. The resulting core (optical fiber) was wound around another bobbin. The number N of light sources and the power setting ratio φ were varied while maintaining a constant linear velocity during the formation of the fiber, to produce optical fibers according to Experimental Examples 1 to 9. 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Omnirad TPO, manufactured by IGM Resins) (hereinafter referred to as TPO) was used as the photopolymerization initiator for the first and second resin compositions. A photopolymerization initiator different from TPO was used as the photopolymerization initiator for the third resin composition.

[0039] Using the optical fibers of Experimental Examples 1 to 9, the relationship between the effective power consumption in the first forming step and the rate of change in Young's modulus of the primary resin layer before and after the formation of the colored resin layer was investigated. The Young's modulus of the primary resin layer was measured at 23°C using the bare wire before the colored resin layer was formed and the core wire after the colored resin layer was formed, respectively, using the pullout modulus (POM) method. Two points on the bare wire or core wire were fixed with two chuck devices, and the coating resin layer portion between the two chuck devices was removed. Here, the coating resin layer portion refers to the primary resin layer and secondary resin layer in the case of a bare wire, and the primary resin layer, secondary resin layer, and colored resin layer in the case of a core wire. Next, one chuck device was fixed, and the other chuck device was slowly moved in the opposite direction from the fixed chuck device. When the length of the portion of the wire or core wire clamped by the moving chuck device is L, the amount of movement of the chuck is Z, the outer diameter of the primary resin layer is Dp, the outer diameter of the glass fiber is Df, the Poisson's ratio of the primary resin layer is n, and the load when the chuck device is moved is W, the Young's modulus of the primary resin layer was calculated using the following formula. Young's modulus [MPa] = ((1 + n)W / πLZ) × ln(Dp / Df)

[0040] Table 1 shows the relationship between the effective power consumption in the first forming step and the rate of change in Young's modulus of the primary resin layer before and after the formation of the colored resin layer. [Table 1]

[0041] Figure 2 is a graph plotting the rate of change in Young's modulus of the primary resin layer before and after the formation of the colored resin layer versus the effective power consumption in the first formation process. As shown in Table 1 and Figure 2, by setting the effective power consumption to 0.056 kWs or more, the rate of change in Young's modulus can be suppressed to 50% or less of the rate before the formation of the colored resin layer. When the effective power consumption exceeds 0.230 kWs, the decrease in the rate of change in Young's modulus becomes smaller. Therefore, by setting the effective power consumption to 0.230 kWs or less, the power saving effect can be enhanced. By setting the effective power consumption to 0.208 kWs or less, the power saving effect can be further enhanced.

[0042] A screening test was conducted on the optical fibers (bare wires) of Experimental Examples 1 to 9, in which the fibers were rewound while being pulled with a tension of 1.5 kg. Thereafter, the transmission loss of the optical fibers for light with a wavelength of 1.3 μm was measured at room temperature. Next, the transmission loss of the optical fibers for light with a wavelength of 1.3 μm was measured at -60°C, and the increase in transmission loss was calculated. The increase in transmission loss is expressed as α2 - α1, where α1 is the transmission loss measured at room temperature and α2 is the transmission loss measured at -60°C. In all of the optical fibers of Experimental Examples 1 to 9, the increase in transmission loss was 0.010 dB / km or less.

[0043] The optical fibers of Experimental Examples 3 and 8 were analyzed to examine the residual rate of the photopolymerization initiator remaining in the two layers, the primary resin layer and the secondary resin layer. Specifically, the TPO concentration in the two layers, the primary resin layer and the secondary resin layer, was measured using a bare fiber. The TPO concentration was measured as follows: First, the remaining molecules contained in the coating resin layer to be measured were dissolved in an organic solvent such as acetone or methyl ethyl ketone (MEK). Next, the phosphorus concentration contained in the TPO was quantitatively measured as the TPO concentration using ICP (inductively coupled plasma) optical emission spectroscopy.

[0044] It has been found that there is a positive correlation between the amount of photopolymerization initiator remaining in the entire wire (i.e., the percentage of photopolymerization initiator remaining in both the primary and secondary resin layers) and the rate of increase in Young's modulus of the primary resin layer before and after the formation of the colored resin layer. Therefore, the amount of photopolymerization initiator remaining in the entire wire can be used as an indicator of the rate of increase in Young's modulus of the primary resin layer before and after the formation of the colored resin layer.

[0045] The remaining rate of the photopolymerization initiator remaining in the two layers of the primary resin layer and the secondary resin layer before the formation of the colored resin layer was 66% in Experimental Example 3 and 1% in Experimental Example 8.

[0046] Although the embodiments have been described above, the present disclosure is not necessarily limited to the above-described embodiments and modifications, and various modifications are possible without departing from the spirit of the present disclosure. [Explanation of symbols]

[0047] 1...Optical fiber 10...Glass fiber 12...Core 14...Clad 20...Coating resin layer 22...Primary resin layer 24...Secondary resin layer 26...Colored resin layer

Claims

1. A method for manufacturing an optical fiber comprising: a glass fiber; a primary resin layer covering an outer periphery of the glass fiber; and a secondary resin layer covering an outer periphery of the primary resin layer, a step of applying an ultraviolet-curable first resin composition that will become the primary resin layer; curing the first resin composition by irradiation with ultraviolet light to form the primary resin layer; a step of applying an ultraviolet-curable second resin composition that will become the secondary resin layer; and curing the second resin composition by irradiating it with ultraviolet light to form the secondary resin layer, In the step of forming the primary resin layer and the step of forming the secondary resin layer, an ultraviolet LED is used as a light source instead of a mercury-containing lamp, In the step of forming the primary resin layer, when the number of the light sources is N, the rated power of the n-th light source is Bn [kW], the power setting ratio of the n-th light source is φn, and the irradiation time of the n-th light source is tn [s], the effective power consumption expressed by formula (1) is 0.056 kWs or more and 0.230 kWs or less. [Equation 1] Optical fiber manufacturing method.

2. applying an ultraviolet-curable third resin composition to the outer periphery of the secondary resin layer; and curing the third resin composition by ultraviolet irradiation to form a colored resin layer. The method for manufacturing the optical fiber according to claim 1 .

3. the step of forming the primary resin layer is carried out together with the step of forming the secondary resin layer after the step of applying the second resin composition; 3. The method for manufacturing an optical fiber according to claim 1.

4. the step of forming the primary resin layer is performed before the step of applying the second resin composition; 3. The method for manufacturing an optical fiber according to claim 1.

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