Optical fiber manufacturing method

Abstract

To improve of curing efficiency of a curable resin composition even when an irradiation output is set low in manufacturing an optical fiber.SOLUTION: A method for manufacturing an optical fiber includes: a step of applying a curable resin composition containing a photoinitiator so as to cover a circumference of a glass fiber including a core and a clad; and a step of irradiating the curable resin composition with ultraviolet light and curing the curable resin composition to form a coating layer. In the step of forming a coating layer, two or more non-irradiation periods are provided, three or more times of irradiation of the ultraviolet light are intermittently conducted, and a total duration of non-irradiation periods is 0.010 sec. or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing an optical fiber and a manufacturing apparatus therefor.

Background Art

[0002] A glass fiber is obtained by drawing a preform mainly composed of silica glass and is composed of a core and a cladding. A coating layer made of resin is provided on the outer periphery of the glass fiber to protect the glass fiber, and an optical fiber is produced. The coating layer is formed, for example, by laminating a primary layer and a secondary layer. As a material for forming the coating layer, a curable resin composition containing a photoinitiator is used. The coating layer is formed by irradiating the curable resin composition with ultraviolet rays to cure it (see, for example, Patent Document 1).

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the production of optical fibers, cost reduction is required. As a method for this reduction, for example, it is conceivable to reduce the irradiation output of ultraviolet rays to reduce power consumption.

[0005] However, when the irradiation output is reduced, the curability of the curable resin composition becomes insufficient, and in the coating layer, the properties required to protect the glass fiber may not be satisfied in some cases.

[0006] An object of the present disclosure is to provide a technique for improving the curing efficiency of a curable resin composition even when the irradiation output is set low in the production of optical fibers.

Means for Solving the Problems

[0007] According to one aspect of this disclosure, A process of running glass fibers including the core and cladding, The aforementioned driving A step of applying a curable resin composition containing a photopolymerization initiator to cover the outer circumference of a glass fiber, Multiple ultraviolet irradiation units arranged along the direction of travel of the glass fiber, The process includes a step of curing the curable resin composition by irradiating it with ultraviolet light to form a coating layer, In the process of forming the aforementioned coating layer, The spacing between adjacent ultraviolet irradiation sections is set according to the travel speed of the glass fiber so that the glass fiber is not irradiated with ultraviolet light while traveling between adjacent ultraviolet irradiation sections, and four or more non-irradiation periods are provided during the curing of the curable resin composition, the total duration of the non-irradiation periods is 0.026 seconds or more, and the ultraviolet irradiation is performed intermittently in five or more separate sessions. A method for manufacturing optical fibers is provided.

[0008] According to other aspects of this disclosure, A step of applying a curable resin composition containing a photopolymerization initiator to the outer periphery of a glass fiber including a core and cladding, The process includes a step of curing the curable resin composition by irradiating it with ultraviolet light to form a coating layer, In the process of forming the coating layer, one non-irradiation period is provided, and the ultraviolet irradiation is performed intermittently in two separate periods, with the duration of the non-irradiation period being 0.080 seconds or longer. A method for manufacturing optical fibers is provided.

[0009] According to other aspects of this disclosure, An apparatus for manufacturing optical fibers, wherein a coating layer is applied to the outer periphery of a glass fiber including a core and cladding, A coating section is provided on the outer circumference of the moving glass fiber, to which a curable resin composition containing a photopolymerization initiator is applied. Arranged along the direction of travel of the glass fiber, The system comprises a plurality of ultraviolet irradiation units for irradiating the curable resin composition, which is applied to cover the outer circumference of the glass fiber, with ultraviolet light to cure the curable resin composition and form a coating layer, The spacing between adjacent ultraviolet irradiation units is set according to the travel speed of the glass fiber so that the glass fiber is not irradiated with ultraviolet light while traveling between adjacent ultraviolet irradiation units. The plurality of ultraviolet irradiation sections undergo a non-irradiation period during which ultraviolet light is not irradiated until the curable resin composition is cured. 4 times The above applies, The total duration of the aforementioned non-irradiation period is 0.026 seconds or more. The irradiation of the ultraviolet light 5 times is configured to be intermittently performed in the above-mentioned divided manner, and a manufacturing apparatus for an optical fiber is provided. [Advantages of the Invention]

[0010] According to the present disclosure, even when the irradiation output is set low in the production of an optical fiber, the curing efficiency of the curable resin composition can be improved. [Brief Description of the Drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an optical fiber according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic view of a manufacturing apparatus for an optical fiber according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a diagram for explaining the correlation between the content of a photoinitiator and the Young's modulus of a primary layer. [Modes for Carrying Out the Invention]

[0012] [Description of Embodiments of the Present Disclosure] [Findings Obtained by the Inventors] First, an outline of the findings obtained by the inventors will be described.

[0013] The curing of the curable resin composition proceeds by the reaction of radicals (initiating radicals) generated from a photoinitiator by irradiation with ultraviolet light with resin molecules, and the reaction of the radicalized resin molecules (polymer radicals) with each other to extend the molecular chain of the resin. Until now, since this radical reaction has been continuously performed, it has been common to continuously irradiate ultraviolet light.

[0014] However, when continuously irradiating with ultraviolet rays, the above-mentioned curing reaction may not proceed efficiently. In continuous irradiation, the starting radicals generated from the photoinitiator recombine with newly generated starting radicals, or the generated polymer radicals recombine with newly generated starting radicals, resulting in the reaction between polymer radicals not proceeding and the curing reaction stopping.

[0015] From this, the inventors have found that instead of continuously irradiating with ultraviolet rays, intermittent irradiation such as irradiating with ultraviolet rays and then temporarily stopping the irradiation and irradiating again is preferable.

[0016] This disclosure is based on the above findings discovered by the inventors.

[0017] [[ID=1往]]In the following description, starting radicals and polymer radicals are simply referred to as radicals.

[0018] <Embodiments of the Present Disclosure> Next, embodiments of the present disclosure will be listed and described.

[0019] [1] The method for manufacturing an optical fiber according to one aspect of the present disclosure includes a step of applying a curable resin composition containing a photoinitiator so as to coat the outer periphery of a glass fiber including a core and a cladding, a step of forming a coating layer by irradiating the curable resin composition with ultraviolet rays to cure the curable resin composition, and has in the step of forming the coating layer, non-irradiation periods are provided two or more times, the irradiation with ultraviolet rays is performed intermittently in three or more portions, and the total time of the non-irradiation periods is 0.010 seconds or more. According to this configuration, by increasing the number of non-irradiation periods and increasing the number of times of irradiating ultraviolet rays in portions, the curable resin composition can be efficiently cured.

[0020] [2] The method for manufacturing an optical fiber according to one aspect of the present disclosure includes A step of applying a curable resin composition containing a photopolymerization initiator to the outer periphery of a glass fiber including a core and cladding, The process includes a step of curing the curable resin composition by irradiating it with ultraviolet light to form a coating layer, In the process of forming the coating layer, one non-irradiation period is provided, and the ultraviolet irradiation is performed intermittently in two separate periods, with the duration of the non-irradiation period being 0.080 seconds or longer. With this configuration, even if there is only one non-irradiation period, the curable resin composition can be efficiently cured by setting the non-irradiation period to a predetermined duration.

[0021] [3] In the method for manufacturing optical fibers described in [1] or [2] above, In the step of applying the curable resin composition, a second curable resin composition containing a photopolymerization initiator is applied in a laminated manner on top of a first curable resin composition containing a photopolymerization initiator. In the step of forming the coating layer, the coating layer is formed as a two-layer structure in which a secondary layer is laminated on a primary layer. The first curable resin composition contains 0.5% by mass or more and 3.5% by mass or less of the photopolymerization initiator. With this configuration, the curable resin composition can be sufficiently cured in the primary layer with a photopolymerization initiator content within the range described above.

[0022] [4] In the method for manufacturing optical fibers described in [3] above, The Young's modulus of the primary layer at 23°C is 0.40 MPa or higher. This configuration makes it possible to suppress the generation of voids in the primary layer.

[0023] [5] Optical fiber manufacturing apparatus according to other aspects of the present disclosure An apparatus for manufacturing optical fibers, wherein a coating layer is applied to the outer periphery of a glass fiber including a core and cladding, A coating section is provided on the outer circumference of the moving glass fiber, to which a curable resin composition containing a photopolymerization initiator is applied. The system comprises a plurality of ultraviolet irradiation units for irradiating the curable resin composition, which is applied to cover the outer circumference of the glass fiber, with ultraviolet light to cure the curable resin composition and form a coating layer, The plurality of ultraviolet irradiation units are configured to have at least two non-irradiation periods during which ultraviolet light is not irradiated, and to perform ultraviolet light irradiation intermittently in three or more separate periods until the curable resin composition is cured. This configuration allows the curable resin composition to be sufficiently cured.

[0024] [6] In the optical fiber manufacturing apparatus described in [5] above, The plurality of ultraviolet irradiation units are arranged at predetermined distances along the direction of travel of the glass fiber, The spacing between adjacent ultraviolet irradiation sections and the travel speed of the glass fiber are adjusted so that the curable resin composition is intermittently irradiated with ultraviolet light. This configuration allows for the appropriate adjustment of the number of periods without UV irradiation and their total duration.

[0025] [7] In the optical fiber manufacturing apparatus described in [5] above, At least one of the plurality of ultraviolet irradiation units is an ultraviolet light-emitting diode, configured to intermittently irradiate ultraviolet light by pulse-modulated lighting. This configuration eliminates the need for spacing between UV irradiation units, enabling space savings in the manufacturing equipment.

[0026] [Details of the embodiments of this disclosure] Next, an embodiment of the present disclosure will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims as shown in the claims.

[0027] <One Embodiment of the Present Disclosure> (Outline configuration of optical fiber) First, the optical fiber to be fabricated in this embodiment will be described using Figure 1. Figure 1 is a cross-sectional view showing the schematic configuration of an optical fiber according to one embodiment of this disclosure.

[0028] As shown in Figure 1, the optical fiber 1 comprises a glass fiber 13 having a core 11 and a cladding 12, and a coating layer 14 provided to cover the outer circumference of the glass fiber 13, with a secondary layer 14b laminated on top of a primary layer 14a.

[0029] (Equipment for manufacturing optical fibers) Next, a manufacturing apparatus for optical fibers will be described using Figure 2. Figure 2 is a schematic diagram of a manufacturing apparatus for optical fibers according to one embodiment of this disclosure.

[0030] As shown in Figure 2, the optical fiber manufacturing apparatus 100 is configured to include at least a heating furnace 110, a coating unit 120, an ultraviolet irradiation unit 130, a guide roller 140, and a drum 150.

[0031] The ultraviolet irradiation unit 130 is positioned downstream of the coating unit 120 in the direction of travel of the glass fiber 13, and irradiates the composition that covers the surface of the glass fiber 13 with ultraviolet light. The composition hardens due to the irradiation of ultraviolet light, forming a coating layer 14, and an optical fiber 1 is obtained. In this embodiment, a plurality of ultraviolet irradiation units 130 are arranged at predetermined distances along the direction of travel. As will be described later, the spacing between adjacent ultraviolet irradiation units 130 is adjusted, for example, according to the travel speed of the glass fiber 13. As the ultraviolet irradiation unit 130, for example, an ultraviolet lamp or an ultraviolet light-emitting diode (UVLED) can be used. From the viewpoint of reducing power consumption, a UVLED is preferred. Note that Figure 2 shows the case where the number of ultraviolet irradiation units 130 is 4, but the number is not particularly limited as long as it is 2 or more.

[0032] Furthermore, the heating furnace 110, coating section 120, guide roller 140, and drum 150 may be configured in a conventionally known manner.

[0033] (Manufacturing method for optical fibers) Next, a method for manufacturing the optical fiber 1 using the manufacturing apparatus 100 described above will be explained.

[0034] First, the optical fiber base material 20 is placed in the heating furnace 110, heated and melted, and drawn to form a glass fiber 13. The glass fiber 13 formed by drawing consists of a core 11 and a cladding 12 that covers the core 11.

[0035] Next, the drawn glass fiber 13 is cooled as needed and then introduced into a coating section 120 having a dual die structure. The coating section 120 contains a first curable resin composition (first composition) for forming the primary layer 14a and a second curable resin composition (second composition) for forming the secondary layer 14b. By passing the glass fiber 13 through this coating section 120, the first composition and the second composition are simultaneously applied to the outer circumference of the glass fiber 13 in that order.

[0036] The first and second compositions are liquid compositions comprising at least a resin component and a photopolymerization initiator. The types of resin components and photopolymerization initiators in the first and second compositions may be appropriately selected according to the Young's modulus required for the primary layer 14a and the secondary layer 14b, respectively.

[0037] Conventional resin components can be used, such as urethane (meth)acrylate oligomers or monomers.

[0038] Examples of urethane (meth)acrylate oligomers include those obtained by reacting polyols, polyisocyanates, and hydroxyl group-containing (meth)acrylates. Examples of polyols include polytetramethylene glycol, polypropylene glycol, and bisphenol A-ethylene oxide addition diols. Examples of polyisocyanates include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, isophorone diisocyanate, and dicyclohexylmethane 4,4'-diisocyanate. Examples of hydroxyl group-containing (meth)acrylates include 2-hydroxyethyl acrylate, 2-hydroxybutyl acrylate, 1,6-hexanediol monoacrylate, pentaerythritol triacrylate, and 2-hydroxypropyl acrylate.

[0039] Conventionally known monomers can be used, including monofunctional monomers having one polymerizable group and polyfunctional monomers having two or more polymerizable groups. Monomers may be used individually or in combination of two or more.

[0040] As a photopolymerization initiator, one can be appropriately selected and used from known radical photopolymerization initiators. Examples include 1-hydroxycyclohexylphenyl ketone (Irgacure 184, BASF), 2,2-dimethoxy-2-phenylacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2,4,4-trimethylpentylphosphine oxide, 2,4,4-trimethylbenzoyldiphenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one (Irgacure 907, BASF), 2,4,6-trimethylbenzoyldiphenylphosphine oxide (Irgacure TPO, BASF), and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (Irgacure 819, BASF). As a photopolymerization initiator, one of these may be used alone, or two or more may be used in combination.

[0041] The content of the photopolymerization initiator is not particularly limited, but in this embodiment, since radical recombination can be suppressed, a sufficient Young's modulus can be obtained in the coating layer 14 even when the content is low. For example, in the first and second compositions for forming the primary layer 14a or the secondary layer 14b, the content of the photopolymerization initiator is preferably 0.5% by mass or more and 3.5% by mass or less. As will be described in detail later, in the primary layer 14a, from the viewpoint of achieving a Young's modulus of 0.40 MPa or more at 23°C, it is more preferable that the content of the photopolymerization initiator be 0.5% by mass or more and 1.5% by mass. Furthermore, a desired high degree of curing can be obtained even with a low content of the photopolymerization initiator. In addition, by reducing the content of the photopolymerization initiator, manufacturing costs can be reduced.

[0042] The first and second compositions may optionally contain other additives besides those described above. Examples of other additives include silane coupling agents, photoacid generators, leveling agents, defoaming agents, and antioxidants.

[0043] The coating thickness of the first composition and the second composition, respectively, may be appropriately changed according to the required thickness of the primary layer 14a and secondary layer 14b in the optical fiber 1.

[0044] Next, the glass fiber 13, on which the composition has been coated, is moved through the coating section 120 and introduced into a plurality of ultraviolet irradiation sections 130. In this embodiment, as the glass fiber 13 passes through a plurality of ultraviolet irradiation sections 130 arranged at predetermined distances along its direction of travel, ultraviolet light is irradiated onto the composition coated on the surface of the glass fiber 13, and the composition is cured. This yields an optical fiber 1.

[0045] In this embodiment, when irradiating with ultraviolet light, one or more non-irradiation periods are provided to suppress the recombination of radicals generated by ultraviolet light, and ultraviolet irradiation is performed intermittently in two or more separate periods. Specifically, while the glass fiber 13 passes through multiple ultraviolet irradiation units 130, irradiation is performed in the ultraviolet irradiation units 130, while non-irradiation is performed between adjacent ultraviolet irradiation units 130, so that ultraviolet irradiation and non-irradiation are repeated alternately, and ultraviolet light is not continuously irradiated onto the composition. In Figure 2, three non-irradiation periods are provided between irradiation in the four ultraviolet irradiation units 130.

[0046] In this way, when curing a curable resin composition, by providing a period of non-irradiation with ultraviolet light and intermittently irradiating it with ultraviolet light, the recombination of generated radicals with newly generated radicals can be suppressed, and the curing reaction in the curable resin composition can be efficiently advanced. Therefore, even when the ultraviolet irradiation output (for example, the power consumption to light up the light source) is reduced, a high degree of curing can be achieved in the coating layer 14 by repeatedly alternating between irradiation and non-irradiation with ultraviolet light.

[0047] The non-irradiation period refers to the time between irradiation by one UV irradiation unit and irradiation by an adjacent UV irradiation unit. If there are two or more non-irradiation periods, these are added together. The non-irradiation period can be adjusted by appropriately changing the spacing between adjacent UV irradiation units 130 and the travel speed of the glass fiber 13. For example, the non-irradiation period can be adjusted by widening the spacing between the UV irradiation units 130 according to the travel speed, or by lowering the travel speed according to the spacing between the UV irradiation units 130.

[0048] The duration of the non-irradiation period is not particularly limited as long as it suppresses the recombination of radicals generated by irradiation with radicals newly generated by irradiation in the adjacent UV irradiation section 130. For example, if two or more non-irradiation periods are provided and UV irradiation is performed in three or more separate sessions before the composition hardens, it is preferable to set the total duration of the non-irradiation period to 0.010 seconds or more, and more preferably to 0.026 seconds or more. There is no particular upper limit, but from the viewpoint of manufacturing efficiency, it is preferable to set it to, for example, 3 seconds or less. Also, for example, if one non-irradiation period is provided and UV irradiation is performed in two separate sessions before the composition hardens, it is preferable to set the duration of the non-irradiation period to 0.080 seconds or more. There is no particular upper limit, but from the viewpoint of manufacturing efficiency, it is preferable to set it to, for example, 3 seconds or less. By setting the non-irradiation period within the above range, the curable resin composition can be sufficiently hardened even when the UV irradiation output is reduced. Furthermore, by increasing the number of non-irradiation periods, reaction inhibition due to radical recombination can be suppressed more reliably, and the curable resin composition can be sufficiently hardened.

[0049] The total irradiation time from the multiple UV irradiation units 130 is not particularly limited as long as the primary layer 14a and the secondary layer 14b are cured to a high degree of hardness. For example, the total irradiation time is preferably 0.015 seconds or more and 0.12 seconds or less. Furthermore, from the viewpoint of suppressing radical recombination while maintaining high manufacturing efficiency, the ratio of the total irradiation time to the total non-irradiation period is preferably 1:8 to 8:1.

[0050] Finally, the optical fiber 1, which has passed through the ultraviolet irradiation section 130, is wound onto the drum 150 via the guide roller 140.

[0051] In the resulting optical fiber 1, the primary layer 14a and secondary layer 14b are formed with a high degree of hardening by intermittent irradiation of ultraviolet light, and therefore have a high Young's modulus. Specifically, it is preferable that the Young's modulus of the primary layer 14a is 0.40 MPa or higher, and the Young's modulus of the secondary layer 14b is 850 MPa or higher. By setting the Young's modulus of the primary layer 14a within the above range, voids in the primary layer 14a can be suppressed even when the optical fiber 1 is subjected to a heat cycle. As a result, transmission loss due to the heat cycle can be suppressed in the optical fiber 1, and high transmission characteristics can be maintained. A void refers to an air gap formed when the primary layer 14a peels off from the glass fiber 13 due to a heat cycle.

[0052] <Other embodiments of this disclosure> Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above, and various modifications are possible without departing from its essence.

[0053] In the embodiments described above, a case was explained in which the spacing of the ultraviolet irradiation units 130 and the travel speed of the glass fiber 13 are adjusted to provide a period of non-irradiation of ultraviolet light, but the present invention is not limited thereto. For example, at least one of the plurality of ultraviolet irradiation units 130 may be a UV LED, and intermittent irradiation may be performed by pulse modulation lighting. With pulse modulation lighting, a non-irradiation interval is not required for the ultraviolet irradiation units 130, resulting in a smaller equipment space.

[0054] Furthermore, in the embodiments described above, the coating layer 14 was configured as a two-layer structure consisting of a primary layer 14a and a secondary layer 14b, but the present invention is not limited thereto, and the coating layer 14 may be composed of a single layer. [Examples]

[0055] Next, embodiments relating to this disclosure will be described. These embodiments are examples of this disclosure and the disclosure is not limited to these embodiments.

[0056] In this embodiment, optical fibers having a two-layer structure of a primary layer and a secondary layer as shown in Figure 1 were manufactured by changing the number of non-irradiation periods and their total duration.

[0057] <Creating optical fibers> First, a first curable resin composition for forming the primary layer and a second curable resin composition for forming the secondary layer were prepared, each mainly composed of urethane methacrylate and containing 1.0% by mass of a photopolymerization initiator.

[0058] Next, the optical fiber preform was heated and melted in a heating furnace, and then drawn to form a glass fiber with a diameter of 125 μm.

[0059] The glass fiber was moved and introduced into a coating section having a dual-die structure, and the first curable resin composition and the second curable resin composition were applied to the surface of the glass fiber in that order.

[0060] Next, glass fibers coated with the curable resin composition were introduced and passed through multiple ultraviolet (UV) irradiators (UVLEDs) arranged along their direction of travel, thereby irradiating the curable resin composition with ultraviolet light. During this irradiation, for samples 1 to 10, the number of non-irradiation periods and their total duration were changed by appropriately adjusting the glass fiber travel speed, the number of UVLEDs installed, and the spacing between adjacent UVLEDs, as shown in Table 1 below. The curable resin composition was then cured by ultraviolet irradiation, and optical fibers for samples 1 to 10 were fabricated. In the optical fibers, the thickness of the primary layer was 20 μm, the thickness of the secondary layer was 12.5 μm, and the thickness of the coating layer composed of these was 32.5 μm. The output (energy amount) of the ultraviolet light irradiated by each UVLED was set to 90%. In addition, non-irradiation periods were provided for each sample so that the total ultraviolet irradiation time was the same at 0.03 seconds.

[0061] [Table 1]

[0062] <Rating> The Young's modulus of the primary and secondary layers, as well as the resistance to heat cycling (heat cycle characteristics) of the obtained optical fibers, were evaluated. The evaluation methods are described below.

[0063] (Young's modulus) The Young's moduli of the primary and secondary layers were measured as follows:

[0064] The primary layer was measured using a pullout modulus test at 23°C. Specifically, first, an incision was made in the coating layer of the optical fiber using a razor or similar tool, the coating layer (primary and secondary layers) was fixed, and the glass fiber was pulled out. Next, the amount of elastic deformation of the primary layer before the glass fiber was pulled out and the force applied to the glass fiber were used to determine the stress on the primary layer and the Young's modulus of the primary layer at 23°C.

[0065] For the secondary layer, the optical fiber was immersed in a mixed solvent of acetone and ethanol, and only the coating layer was extracted in a cylindrical shape. Subsequently, the solvent was removed by vacuum drying, and then a tensile test (tensile speed of 1 mm / min) was performed in a constant temperature chamber at 23°C. The Young's modulus of the coating layer was then determined using the secant equation with 2.5% strain. The Young's modulus obtained in this way can be considered as essentially the Young's modulus of the secondary layer.

[0066] (Heat cycle characteristics) The fabricated optical fibers were subjected to 50 heat cycles between -40°C and 23°C (held for 1 hour at each temperature, with a transition time of 60 minutes). The transmission characteristics of a 1550nm wavelength signal light were measured under both 23°C and -40°C conditions, and the transmission loss at 23°C and -40°C was determined. Fibers with a transmission loss difference of less than 0 dB / km (lower transmission loss at -40°C) were evaluated as A, those between 0 dB / km and 0.01 dB / km were evaluated as B, and those above 0.01 dB / km were evaluated as C. In this example, an evaluation of B or higher indicated low transmission loss and excellent heat cycle resistance.

[0067] <Evaluation Results> The results of each evaluation are shown in Table 1.

[0068] As shown in Table 1, in samples 1 to 6, intermittent UV irradiation was performed with non-irradiation periods to suppress radical recombination. This allowed for efficient curing of the curable resin composition, and it was confirmed that the Young's modulus of the primary layer could be increased to 0.40 MPa or higher, and the Young's modulus of the secondary layer to 850 MPa or higher. Furthermore, due to the high Young's modulus obtained, transmission loss was low in the heat cycle test, and high heat cycle resistance was confirmed.

[0069] In contrast, in Sample 7, the curable resin composition was continuously irradiated with ultraviolet light without a non-irradiation period. As a result, the Young's modulus of the primary and secondary layers was lower than that of Samples 1-6, and the heat cycle resistance was also lower. This is presumed to be because radical recombination occurred during irradiation, preventing the curing reaction from proceeding efficiently.

[0070] Furthermore, in samples 8-10, although a non-irradiation period was provided, a sufficient time was not ensured to suppress radical recombination. As a result, similar to sample 7, the Young's modulus was low and the heat cycle resistance was also low.

[0071] Furthermore, when comparing samples 1, 2, and 8, it was confirmed that when there are two or more non-irradiation periods, it is preferable to have a total non-irradiation time of 0.010 seconds or more, and more preferable to have a total non-irradiation time of 0.020 seconds or more, from the viewpoint of efficiently advancing the curing reaction. On the other hand, when comparing samples 6 and 10, it was confirmed that even when there is only one non-irradiation period, the curing reaction can be efficiently advanced and a high Young's modulus can be obtained by making the non-irradiation time 0.080 seconds or more. It is presumed that the reason why the non-irradiation time can be shortened when there are two or more non-irradiation periods compared to when there is only one is that increasing the number of non-irradiation periods increases the number of times radical recombination is suppressed, thereby making the curing reaction more efficient.

[0072] Furthermore, when comparing samples 2-4, it was confirmed that even with the same total non-irradiation time, increasing the number of non-irradiation periods allowed for a more efficient curing reaction.

[0073] Furthermore, samples 1-6 confirmed that even with a low photopolymerization initiator content of 1% by mass in the primary layer, it was possible to achieve a Young's modulus of 0.4 MPa or higher in the primary layer.

[0074] Here, the correlation between the photoinitiator content and the Young's modulus of the primary layer will be explained using Figure 3. Figure 3 is a diagram illustrating the correlation between the photoinitiator content and the Young's modulus of the primary layer. In Figure 3, the solid line, dashed line, and broken line show the change in the Young's modulus of the primary layer when the photoinitiator content in the primary layer is changed under the following irradiation conditions in Sample 1. The solid line shows the correlation when the number of non-irradiation periods is 2, the total non-irradiation period time is 0.01 seconds, and the total irradiation time is 0.03 seconds. The dashed line shows the correlation when the number of non-irradiation periods is 1, the non-irradiation period time is 0.08 seconds, and the irradiation time is 0.03 seconds. The broken line shows the correlation when continuous irradiation is performed with an irradiation time of 0.03 seconds without any non-irradiation period.

[0075] As shown in Figure 3, in the case of continuous irradiation, for example, in order to achieve a Young's modulus of 0.4 MPa or higher in the primary layer, the photoinitiator content must be 4.0% by mass or higher. In contrast, in the case of intermittent irradiation with a non-irradiation period, it was confirmed that a Young's modulus of 0.4 MPa or higher can be achieved even with a photoinitiator content of 0.5% by mass or higher and 3.5% by mass or lower. Furthermore, it was confirmed that a Young's modulus of 0.45 MPa or higher can be achieved when the content is 1.5% by mass or higher and 3.5% by mass or higher. From this, it was confirmed that by providing a non-irradiation period, radical recombination is suppressed and the curing reaction can be advanced efficiently, so that a sufficient Young's modulus can be obtained even with a low photoinitiator content.

[0076] As described above, in the manufacturing of optical fibers, by providing a non-irradiation period during which the curable resin composition is not irradiated with ultraviolet light, and intermittently irradiating it with ultraviolet light, radical recombination can be suppressed, and even when the ultraviolet output is set low, the desired high degree of curing can be achieved in the coating layer. [Explanation of Symbols]

[0077] 1 Optical fiber 11 cores 12 clad 13. Glass fiber 14 Covering layer 14a Primary layer 14b Secondary layer 20 Optical fiber base material 100 Manufacturing equipment 110 Heating Furnace 120 Coating area 130 UV irradiation area 140 Guide Rollers 150 drums

Claims

1. A process of running glass fibers including the core and cladding, A step of applying a curable resin composition containing a photopolymerization initiator so as to cover the outer circumference of the moving glass fiber, The process includes a step of forming a coating layer by irradiating the curable resin composition with ultraviolet light using a plurality of ultraviolet irradiation units arranged along the direction of travel of the glass fiber, thereby curing the curable resin composition. In the step of applying the curable resin composition, a second curable resin composition containing a photopolymerization initiator is applied in a laminated manner on top of a first curable resin composition containing 0.5% by mass or more and 3.5% by mass or less of a photopolymerization initiator. In the process of forming the aforementioned coating layer, The spacing between adjacent ultraviolet irradiation sections is set according to the travel speed of the glass fiber so that the glass fiber is not irradiated with ultraviolet light while traveling between adjacent ultraviolet irradiation sections, and four or more non-irradiation periods are provided during the curing of the curable resin composition, the total duration of the non-irradiation periods being 0.026 seconds or more, and the ultraviolet irradiation is performed intermittently in five or more separate sessions, and the coating layer is formed as a two-layer structure in which a secondary layer is laminated on a primary layer. A method for manufacturing optical fibers.

2. The Young's modulus of the primary layer at 23°C is 0.40 MPa or higher. A method for manufacturing an optical fiber according to claim 1.

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