JP7637577B2 - Optical fiber manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing optical fibers.

An optical fiber is known in which the outer surface of an optical fiber strand having a cladding surrounding the outer surface of a core is covered with a colored layer made of a colored resin containing a pigment and an ultraviolet curable resin. In an optical fiber ribbon core wire, the colored layers of each optical fiber may be different colors to distinguish between the optical fibers. For this reason, the above optical fiber may be used in an optical fiber ribbon core wire. The following Patent Document 1 discloses a method for manufacturing an optical fiber having such a colored layer.

In the following Patent Document 1, a colored resin containing a pigment and an ultraviolet-curing resin is applied to the outer surface of the optical fiber strand, and the applied colored resin is irradiated with ultraviolet light to harden the colored resin, thereby forming a colored layer that covers the outer surface of the optical fiber strand. In addition, the following Patent Document 1 discloses that light from an ultraviolet LED (Light Emitting Diode) can be used as the ultraviolet light irradiated to the colored resin.

JP 2021-31366 A

The color of the colored layer can be changed by changing the type and amount of pigment contained in the colored resin that will become the colored layer. In this case, if the irradiation conditions of the light from the ultraviolet LED are the same, differences in the color of the colored resin may cause differences in the curing properties of the colored resin, and the colored layer may not be cured to the desired degree. A portion of the light from the ultraviolet LED is absorbed and reflected by the pigment contained in the colored resin, but the amount of light absorbed and reflected by the pigment tends to differ depending on the type and concentration of the pigment. For this reason, it is thought that the amount of light absorbed by the photopolymerization initiator contained in the ultraviolet curing resin in the colored resin differs depending on the color of the colored resin, resulting in differences in the curing properties of the colored resin.

The present invention aims to provide a method for manufacturing optical fiber that can reduce the difference in the degree of hardening of the colored layer caused by differences in the color of the colored resin.

To achieve the above object, the present invention provides a method for manufacturing an optical fiber having an optical fiber strand having a core and a cladding surrounding the outer peripheral surface of the core, and a colored layer made of a colored resin containing a pigment and an ultraviolet curable resin and covering the outer peripheral surface of the optical fiber strand, the method comprising a coating process for coating the outer peripheral surface of the optical fiber strand with the colored resin, and irradiating the coated colored resin with light from an ultraviolet LED to harden the colored resin and form the colored layer, the coating process being characterized in that a predetermined amount of light determined based on the absorbance of the light by the hardened colored resin is irradiated onto the colored resin.

In this optical fiber manufacturing method, as described above, the predetermined amount of irradiation of the light from the ultraviolet LED irradiated onto the colored resin is determined in advance based on the absorbance of the light from the ultraviolet LED of the cured colored resin. The absorbance is a dimensionless quantity that indicates the extent to which the intensity of the light is weakened when the light passes through an object, and the absorbance includes the effects of the absorption and reflection of the light in the object. Therefore, the absorbance of the light from the ultraviolet LED of this colored resin is high when the amount of light absorbed and reflected by the pigment is large, and low when the amount is small. In addition, this absorbance is the absorbance of the cured colored resin. Therefore, compared with the absorbance of the colored resin in an uncured state, the influence of the light absorbed by the photopolymerization initiator contained in the ultraviolet curable resin in the colored resin on the absorbance is small, and the difference in the amount of light absorbed and reflected by the pigment can be appropriately grasped. Therefore, when the amount of light absorbed and reflected by the pigment is large, the amount of irradiation of the light from the ultraviolet LED onto the colored resin can be increased so that the colored resin is sufficiently cured. In addition, when the amount of light absorbed and reflected by the pigment is small, the amount of irradiation of the light from the ultraviolet LED onto the colored resin can be reduced within the range in which the colored resin is sufficiently cured. Therefore, this method of manufacturing optical fiber can reduce the difference in the degree of hardening of the colored layer due to differences in the color of the colored resin, compared to when the amount of light irradiated from the UV LED does not change in response to changes in the type and concentration of the pigment.

The predetermined amount of irradiation may be determined based on the correlation between the absorbance of the colored resin at the peak wavelength of the light, the absorbance of the colored resin of another color at the peak wavelength of the light, and the amount of irradiation of the light that will result in the desired degree of hardening of the colored layer made of the colored resin of the other color.

The inventors have found that the correlation between the absorbance and the amount of irradiation is roughly proportional. Therefore, even for a colored resin for which the amount of irradiation of light that will result in the desired degree of cure has not been determined in advance, the amount of irradiation of light that will result in the desired degree of cure can be found by determining the absorbance of the colored resin at the peak wavelength of light from the ultraviolet LED. Therefore, it is easier to achieve a desired degree of cure for the colored layer compared to determining the amount of irradiation of light that will result in the desired degree of cure through experiments, etc.

Alternatively, the predetermined dose may be determined based on the correlation between the overlap integral between the spectrum of the light and the absorption spectrum of the colored resin, and the overlap integral between the spectrum of the light and the absorption spectrum of the colored resin of another color, and the dose of light at which the colored layer made of the colored resin of the other color reaches the desired degree of hardening.

The absorption spectrum, which shows the relationship between wavelength and absorbance for that wavelength, includes the effects of light absorption and reflection in the target object, as well as absorbance. The inventors have found that the correlation between the overlap integral and the dose is roughly proportional. Therefore, even for a colored resin for which the dose of light that will result in the desired degree of cure has not been determined in advance, the dose of light that will result in the desired degree of cure can be found by determining the overlap integral between the spectrum of light from an ultraviolet LED and the absorption spectrum of the colored resin. Therefore, this method of manufacturing optical fiber makes it easier to achieve the desired degree of cure of the colored layer, compared to determining the dose of light that will result in the desired degree of cure through experiments, etc.

In the coating process, the intensity of the light may be adjusted so that the predetermined amount of light is irradiated onto the colored resin.

In this case, it is possible to prevent the time required for production from changing depending on the color of the colored layer.

The irradiation time of the light onto the colored resin may be adjusted so that the predetermined amount of light is irradiated onto the colored resin.

The ultraviolet LEDs may be multiple, and the peak wavelengths of light from at least two of the ultraviolet LEDs may be different from each other. In the coating process, the amount of light irradiated onto the colored resin from a specific ultraviolet LED among the multiple ultraviolet LEDs, the peak wavelength of which is closest to the wavelength at which the amount of light absorbed by the photopolymerization initiator of the ultraviolet curing resin is maximized, may be adjusted to irradiate the colored resin with the predetermined amount of light.

In general, the amount of light absorbed by a photopolymerization initiator tends to be smaller the farther the wavelength of light from the wavelength at which the absorption is greatest. Therefore, according to this optical fiber manufacturing method, it is easier to achieve the desired degree of cure of the colored layer compared to adjusting the amount of light irradiated onto the colored resin from ultraviolet LEDs other than the specific ultraviolet LED described above among multiple ultraviolet LEDs.

In this case, in the covering process, the amount of light irradiated onto the colored resin from at least one of the ultraviolet LEDs other than the specific ultraviolet LED may be kept constant without adjustment. Alternatively, in the covering process, the amount of light irradiated onto the colored resin from at least one of the ultraviolet LEDs other than the specific ultraviolet LED may be further adjusted, and the predetermined amount of light may be irradiated onto the colored resin.

As described above, the present invention provides a method for manufacturing an optical fiber that can reduce the difference in the degree of hardening of the colored layer caused by differences in the color of the colored resin.

1 is a diagram illustrating a cross section perpendicular to the longitudinal direction of an optical fiber according to an embodiment of the present invention. 2 is a flow chart showing steps of a method for manufacturing an optical fiber according to an embodiment of the present invention. FIG. 1 shows examples of measured absorption spectra for several resin samples made of different pigmented resins. 4A to 4C are diagrams illustrating a coating process according to an embodiment of the present invention. FIG. 13 is a diagram for explaining a simulated evaluation method in an experimental example. FIG. 11 is another diagram for explaining the simulated evaluation method in the experimental example.

Below, embodiments for carrying out the method for manufacturing an optical fiber according to the present invention are illustrated with the accompanying drawings. The embodiments illustrated below are intended to facilitate understanding of the present invention, and are not intended to limit the interpretation of the present invention. The present invention can be modified or improved from the following embodiments without departing from the spirit of the present invention. In addition, in this specification, the dimensions of each component may be exaggerated in order to facilitate understanding.

Figure 1 is a schematic diagram showing a cross section perpendicular to the longitudinal direction of an optical fiber according to an embodiment of the present invention. As shown in Figure 1, the optical fiber 1 of this embodiment mainly comprises an optical fiber strand 1N and a colored layer 15 that covers the outer surface of the optical fiber strand 1N. The optical fiber strand 1N of this embodiment is composed of a core 10, a cladding 11 that surrounds the outer surface of the core 10, and a protective resin layer 12 that covers the outer surface of the cladding 11. The diameter of the optical fiber strand 1N is not particularly limited, but is, for example, 240 μm.

The refractive index of the core 10 is made higher than that of the cladding 11. In this embodiment, the core 10 is made of silica glass doped with a dopant such as germanium (Ge) that increases the refractive index, and the cladding 11 is made of silica glass without any additives. The core 10 may be made of silica glass without any additives, and the cladding 11 may be made of silica glass doped with a dopant such as fluorine (F) that decreases the refractive index. The core 10 may be made of silica glass doped with a dopant that increases the refractive index, and the cladding 11 may be made of silica glass doped with a dopant that decreases the refractive index. There are no particular limitations on the dopant that increases the refractive index and the dopant that decreases the refractive index.

Examples of the resin that constitutes the protective resin layer 12 include thermosetting resin and ultraviolet curing resin. The protective resin layer 12 may have a single-layer structure consisting of one resin layer that covers the clad 11, or may have a multi-layer structure consisting of multiple resin layers.

The colored layer 15 is made of a colored resin containing a pigment and an ultraviolet curing resin. The color of the colored layer 15 is not particularly limited. The thickness of the colored layer 15 is not particularly limited, but is, for example, 3 μm to 10 μm. Examples of the pigment include natural mineral pigments, synthetic inorganic pigments, and organic pigments. Examples of the ultraviolet curing resin include radical polymerization type ultraviolet curing resins and cationic polymerization type ultraviolet curing resins. Examples of the radical polymerization type ultraviolet curing resin include resins containing an acrylic compound such as urethane acrylate, epoxy acrylate, and polyester acrylate and a photopolymerization initiator, and examples of the photopolymerization initiator in this case include benzophenone-based and alkylphenone-based photopolymerization initiators. Examples of the cationic polymerization type ultraviolet curing resin include resins containing a cyclic ether compound such as epoxy and oxetane and a photopolymerization initiator, and examples of the photopolymerization initiator in this case include sulfonium salt-based and iodonium salt-based photopolymerization initiators.

Next, we will explain the method for manufacturing optical fiber 1.

Figure 2 is a flow chart showing the steps of the method for manufacturing the optical fiber 1 according to this embodiment. As shown in Figure 2, the method for manufacturing the optical fiber 1 according to this embodiment includes a measurement step P1, a determination step P2, an optical fiber strand manufacturing step P3, and a coating step P4.

(Measurement process P1)
This step is a step of measuring the absorbance of light emitted from the ultraviolet LED in the cured colored resin, and the ultraviolet LED is used to cure the colored resin in the coating step P4 described later. As a preparation step for this step, first, a resin sample of a predetermined thickness made of cured colored resin is prepared. In this embodiment, the uncured colored resin is applied to one side of an acrylic plate to a predetermined thickness. This colored resin is irradiated with ultraviolet light to cure the colored resin, and the cured colored resin is peeled off from the acrylic plate to prepare a plate-shaped resin sample of a predetermined thickness. The amount of ultraviolet light irradiated to the colored resin is set to an amount that causes the photopolymerization initiator contained in the ultraviolet curable resin of the colored resin to sufficiently react and cure the colored resin sufficiently. The ultraviolet light irradiated to the colored resin may be light from an ultraviolet LED or light from an ultraviolet lamp. The predetermined thickness is approximately the same as the thickness of the colored layer 15, but may be different from the thickness of the colored layer 15. The method of preparing the sample resin is not particularly limited. The resin sample may also be formed on one surface of a light-transmitting plate-like member, and examples of the plate-like member include a glass plate and an acrylic plate.

Next, the absorbance of the light from the UV LED in the cured colored resin is measured in the prepared resin sample. In this embodiment, the absorption spectrum of the resin sample is measured using a spectrophotometer to determine the absorbance at the peak wavelength of the light from the UV LED. Note that, as described above, when the resin sample is formed on one side of a light-transmitting plate-like member, the absorption spectrum of the member consisting of the resin sample and the light-transmitting plate-like member is measured as the absorption spectrum of the resin sample.

Figure 3 shows examples of absorption spectra measured for several resin samples made of colored resins with different types of pigments. In Figure 3, the spectrum of light from an ultraviolet LED is shown along with the absorption spectra of seven resin samples SA1 to SA7. In Figure 3, the horizontal axis is the wavelength (nm), the vertical axis on the right is the relative radiant intensity of light from the ultraviolet LED, and the vertical axis on the left is the absorbance (Abs) of the resin sample. As shown in Figure 3, the absorption spectrum differs depending on the type of pigment in the colored resin. The colors of the resin samples SA1 to SA7 are blue, yellow, red, purple, white, pink, and light blue, and the colored resins that make up the resin samples SA1 to SA7 contain pigments of these colors. In addition, the ultraviolet curing resins in the colored resins that make up these resin samples SA1 to SA7 are the same, and the thicknesses of these resin samples SA1 to SA7 are also the same. Furthermore, the absorbance of the blue resin sample SA1 at the peak wavelength of light from the ultraviolet LED is 0.93 Abs, the absorbance of the yellow resin sample SA2 is 1.54 Abs, the absorbance of the red resin sample SA3 is 1.23 Abs, the absorbance of the purple resin sample SA4 is 2.58 Abs, the absorbance of the white resin sample SA5 is 2.52 Abs, the absorbance of the pink resin sample SA6 is 2.19 Abs, and the absorbance of the light blue resin sample SA7 is 1.40 Abs.

(Decision process P2)
This step is a step of determining a predetermined dose of light from the ultraviolet LED to be irradiated to the uncured colored resin applied to the outer peripheral surface of the optical fiber 1N in the coating step P4 described later, based on the absorbance of the light from the ultraviolet LED of the colored resin measured in the measurement step P1. The absorbance is a dimensionless quantity indicating the degree to which the intensity of the light is weakened when the light passes through an object, and includes the influence of the absorption and reflection of the light in the object. Therefore, the absorbance of the colored resin is high when the amount of light absorbed and reflected by the pigment is large, and low when the amount is small. Therefore, the predetermined dose is determined to be large so that the colored resin is sufficiently cured when the amount of light absorbed and reflected by the pigment is large, that is, when the absorbance of the colored resin is high. Moreover, the predetermined dose is determined to be small within the range in which the colored resin is sufficiently cured when the amount of light absorbed and reflected by the pigment is small, that is, when the absorbance of the colored resin is low.

In this embodiment, the predetermined irradiation amount is determined based on the absorbance of the colored resin measured in the measurement process P1, and the correlation between the absorbance of a colored resin of a color different from the color of the colored resin and the irradiation amount of light from the ultraviolet LED at which the colored layer 15 made of the colored resin of the other color has a desired degree of hardening. Note that this absorbance is the absorbance at the peak wavelength of the light from the ultraviolet LED. The inventor has found that when the thickness of the colored layer and the ultraviolet curing resin do not change, the correlation between this absorbance and the irradiation amount is approximately proportional. In this embodiment, this correlation is obtained in advance by experiment. Specifically, two or more pairs of the absorbance of a colored resin of a color different from the color of the colored layer 15 of the optical fiber 1 to be manufactured and the irradiation amount of light from the ultraviolet LED at which the colored layer 15 made of the colored resin of the other color has a desired degree of hardening are obtained in advance by experiment. Based on the obtained two or more pairs of absorbance and irradiation amount, a proportional relationship between the absorbance and the irradiation amount is obtained. The method of obtaining the proportional relationship is not particularly limited, and for example, the proportional relationship may be obtained using the least squares method.

(Optical fiber manufacturing process P3)
This process is a process for manufacturing an optical fiber 1N. In this embodiment, as a preparation step for this process, first, a roughly cylindrical optical fiber preform is prepared, which is composed of a rod-shaped core glass body that becomes the core 10 and a clad glass body that surrounds the outer peripheral surface of the rod-shaped core glass body and becomes the clad 11. This optical fiber preform is heated in a spinning furnace and drawn to obtain a glass wire composed of the core 10 and the clad 11 that surrounds the outer peripheral surface of the core 10. Next, a resin that becomes the protective resin layer 12 is applied to the outer peripheral surface of this glass wire and the resin is cured to form the protective resin layer 12 that covers the outer peripheral surface of the clad 11, thereby obtaining the optical fiber 1N shown in FIG. The optical fiber 1N obtained in this manner is wound on a bobbin.

(Coating process P4)
This process is a process in which a colored resin is applied to the outer surface of the optical fiber strand 1N manufactured in the optical fiber strand manufacturing process P3, and the applied colored resin is irradiated with light from an ultraviolet LED to harden the colored resin and form a colored layer 15.

Figure 4 is a diagram that shows the outline of this process according to this embodiment. As shown in Figure 4, in this embodiment, this process is performed using a coating device 100. This coating device 100 mainly comprises a delivery section 30, an application section 40, a curing section 50, and a winding section 60.

First, the bobbin 31 around which the optical fiber 1N manufactured in the optical fiber manufacturing process P3 is wound is attached to the delivery section 30, and the delivery section 30 delivers the optical fiber 1N from the bobbin 31. The direction of the delivered optical fiber 1N is changed by the turn pulley 35 so that the optical fiber 1N passes through the coating section 40 located below the turn pulley 35. The coating section 40 stores uncured colored resin that will become the colored layer 15, and the optical fiber 1N passes through the coating section 40, causing the colored resin to be applied to the outer circumferential surface of the optical fiber 1N. The curing section 50 located below the coating section 40 irradiates the applied colored resin with light from an ultraviolet LED to cure the colored resin and form the colored layer 15.

The curing section 50 of this embodiment has four curing units 51 arranged in a vertical direction. The optical fiber strand 1N coated with the colored resin passes through these curing units 51 in order. Each curing unit 51 has a housing 52 and an ultraviolet LED 55 arranged in the internal space of the housing 52, and is configured to be able to adjust the intensity of the light emitted from the ultraviolet LED 55. The inner surface of the housing 52 is a reflective surface that reflects the light from the ultraviolet LED 55. Such a curing unit 51 irradiates the colored resin of the optical fiber strand 1N passing through with light from the ultraviolet LED 55. These four curing units 51 have the same configuration, and the peak wavelength at which the intensity of the light from the ultraviolet LED 55 is maximum is approximately 385 nm, and the spectrum of the light is shown in FIG. 3. In this embodiment, the intensity of the light from the ultraviolet LED 55 of all the curing units 51 is adjusted in the same way so that the amount of light irradiated from the ultraviolet LED 55 of the curing section 50 irradiated to the colored resin is the predetermined amount of irradiation determined in the determination step P2. Therefore, the light intensity from all UV LEDs 55 after adjustment is the same.

The configuration of the curing section 50 is not particularly limited. The number of curing units 51 that the curing section 50 has is not particularly limited, and the curing section 50 may be composed of one curing unit 51. The number of ultraviolet LEDs 55 that each curing unit 51 has is not particularly limited.

In this way, the colored layer 15 is formed and the outer peripheral surface of the optical fiber strand 1N is coated with the colored layer 15, and the optical fiber strand 1N becomes the optical fiber 1. A turn pulley 65 is disposed below the hardening section 50, and the optical fiber 1 is changed in direction by the turn pulley 65 and wound up on a bobbin 61 by the winding section 60. In this embodiment, the speed of the optical fiber strand 1N passing through the hardening section 50 can be adjusted by adjusting the feed speed of the optical fiber strand 1N by the feed section 30 and the winding speed of the optical fiber 1 by the winding section 60.

As described above, the optical fiber manufacturing method of this embodiment includes a coating process P4. In the coating process P4, the colored resin is irradiated with a predetermined amount of light from the ultraviolet LED 55, which is determined in advance based on the absorbance of the light from the ultraviolet LED 55 of the cured colored resin. As described above, since the absorbance includes the influence of the absorption and reflection of light in the object, the absorbance of the light from the ultraviolet LED 55 in the colored resin is high when the amount of light absorbed and reflected by the pigment is large, and low when the amount is small. In addition, this absorbance is the absorbance of the cured colored resin. Therefore, compared with the absorbance of the colored resin in an uncured state, the influence of the light absorbed by the photopolymerization initiator contained in the ultraviolet curable resin in the colored resin on this absorbance is small, and the difference in the amount of light absorbed and reflected by the pigment can be appropriately grasped. Therefore, when the amount of light from the ultraviolet LED 55 absorbed and reflected by the pigment is large, the amount of light irradiated from the ultraviolet LED 55 to the colored resin can be increased so that the colored resin is sufficiently cured. Furthermore, when the amount of light from the UV LED 55 absorbed and reflected by the pigment is small, the amount of light irradiated onto the colored resin from the UV LED 55 can be reduced to the extent that the colored resin is sufficiently cured. Therefore, according to the optical fiber manufacturing method of this embodiment, the difference in the degree of curing of the colored layer due to differences in the color of the colored resin can be reduced compared to when the amount of light irradiated from the UV LED 55 does not change depending on the type and concentration of the pigment.

In addition, in the manufacturing method of the optical fiber of this embodiment, the predetermined irradiation amount is determined based on the correlation between the absorbance at the peak wavelength of the light from the ultraviolet LED 55 in the colored resin, and the absorbance at the peak wavelength of the light from the ultraviolet LED 55 in the colored resin of another color, and the irradiation amount of the light from the ultraviolet LED 55 that will result in the desired degree of cure of the colored layer 15 made of the colored resin of the other color. The inventor has found that the correlation between the absorbance and the irradiation amount is approximately proportional. Therefore, even if the irradiation amount of the light from the ultraviolet LED that will result in the desired degree of cure has not been determined in advance for a colored resin, the irradiation amount that will result in the desired degree of cure can be found by determining the absorbance at the peak wavelength of the light from the ultraviolet LED 55 in the colored resin. Therefore, it is easier to make the colored layer 15 reach the desired degree of cure than when the irradiation amount of the light from the ultraviolet LED 55 that will result in the desired degree of cure is determined by experiment, etc.

In addition, in the coating process P4 of this embodiment, the intensity of the light from the ultraviolet LEDs 55 is adjusted to irradiate the colored resin with a predetermined amount of light. This makes it possible to prevent the time required for manufacturing from changing depending on the color of the colored layer 15.

Although the present invention has been described above using the above embodiment as an example, the present invention is not limited to this.

For example, in the above embodiment, the predetermined irradiation amount is determined based on the absorbance of the light from the ultraviolet LED 55 at the peak wavelength in the colored resin and the correlation between the absorbance and the irradiation amount. However, the predetermined irradiation amount may be determined based on the absorbance of the light from the ultraviolet LED 55 in the cured colored resin. For example, the predetermined irradiation amount may be determined based on the overlap integral between the spectrum of the light from the ultraviolet LED 55 and the absorption spectrum of the colored resin, and the overlap integral between the spectrum of the light from the ultraviolet LED 55 and the absorption spectrum of the colored resin of another color, and the correlation between the irradiation amount of light from the ultraviolet LED 55 at which the colored layer 15 made of the colored resin of another color has the desired degree of hardening. The inventor has found that when the thickness of the colored layer and the ultraviolet curing resin do not change, the correlation between this overlap integral and the irradiation amount is approximately proportional. Therefore, even if the irradiation amount of light from the ultraviolet LED that will result in the desired degree of hardening is not previously determined for a colored resin, the irradiation amount that will result in the desired degree of hardening can be found by determining the overlap integral between the spectrum of the light from the ultraviolet LED 55 and the absorption spectrum of this colored resin. Therefore, by determining the predetermined irradiation amount in this manner, it is easier to achieve the desired degree of cure of the colored layer 15 compared to a case where the irradiation amount of light from the ultraviolet LED 55 that results in the desired degree of cure is determined by experiment, etc. The correlation between the overlap integral and the irradiation amount is determined in advance by experiment. Specifically, two or more pairs of the irradiation amount of light from the ultraviolet LED and the overlap integral of the spectrum of the light from the ultraviolet LED and the colored resin of a color different from the color of the colored layer 15 of the optical fiber 1 to be manufactured are obtained in advance by experiment. Based on the obtained two or more pairs of overlap integrals and irradiation amounts, a proportional relationship between the overlap integral and the irradiation amount is obtained. The method of obtaining the proportional relationship is not particularly limited, and the proportional relationship may be obtained, for example, using the least squares method.

In the above embodiment, the coating process P4 is described as an example in which a colored resin is applied to the outer peripheral surface of the optical fiber strand 1N sent out from the bobbin 31, and the applied colored resin is irradiated with light from the ultraviolet LED 55 to harden the colored resin to form the colored layer 15. However, the coating process P4 may be performed during the optical fiber strand manufacturing process P3. In this case, for example, the coating unit 40 of the coating device 100 is disposed below the hardening unit that hardens the resin that becomes the protective resin layer 12 applied to the outer peripheral surface of the glass wire, and the hardening unit 50 is disposed below the coating unit 40. In this case, there may be no hardening unit that hardens the resin that becomes the protective resin layer 12, and the hardening unit 50 may harden both the resin that becomes the protective resin layer 12 applied to the outer peripheral surface of the glass wire and the colored resin applied to the outer peripheral surface of the resin.

In the above embodiment, the optical fiber 1N having the protective resin layer 12 has been described as an example. However, the optical fiber 1N only needs to have the core 10 and the cladding 11 surrounding the outer peripheral surface of the core 10. For example, the optical fiber 1N does not need to have the protective resin layer 12. In this case, the colored layer 15 covers the outer peripheral surface of the cladding 11, and the colored layer 15 also serves as the protective resin layer 12.

In the above embodiment, the coating process P4 is described as an example in which a colored layer 15 is formed on the optical fiber 1N manufactured in the optical fiber manufacturing process P3. However, in the coating process P4, the colored layer 15 may be formed on the optical fiber 1N that has been prepared by purchase or the like.

In the above embodiment, the intensity of light from all the ultraviolet LEDs 55 provided in the curing unit 50 is adjusted in the same way, and the coating process P4 is described as an example in which the colored resin is irradiated with the light from the ultraviolet LEDs 55 at a predetermined irradiation amount determined in the determination process P2. However, it is sufficient that the irradiation amount of light from the ultraviolet LEDs 55 is the predetermined irradiation amount determined in the determination process P2. The number of curing units 51 that adjust the intensity of light from the ultraviolet LEDs 55 is not particularly limited, and for example, the irradiation amount of light from the ultraviolet LEDs 55 of at least one curing unit 51 may be constant regardless of the colored resin. In addition, the irradiation time of the light from the ultraviolet LEDs 55 to the colored resin may be adjusted so that the irradiation amount becomes the predetermined irradiation amount. In this case, for example, the speed of the optical fiber strand 1N passing through the curing unit 50 is adjusted by the sending unit 30 and the winding unit 60. In addition, the intensity of light from the ultraviolet LEDs 55 and the speed of the optical fiber strand 1N passing through the curing unit 50 may be adjusted so that the irradiation amount of light from the ultraviolet LEDs 55 becomes the predetermined irradiation amount. With this configuration, the number of ultraviolet LEDs can be reduced compared to adjusting the number of ultraviolet LEDs that irradiate the colored resin, and the size of the coating device 100 can be prevented from increasing. Note that, by adjusting the intensity of the light from the ultraviolet LEDs 55 as in the above embodiment, when a predetermined amount of light from the ultraviolet LEDs 55 is irradiated onto the colored resin, the time required for manufacturing can be prevented from changing depending on the color of the colored layer.

In the above embodiment, the curing unit 50 is provided with a plurality of ultraviolet LEDs 55, and the peak wavelength of the light from each ultraviolet LED is the same. However, the peak wavelengths of at least two ultraviolet LEDs 55 may be different from each other. In this case, in the coating process P4, the amount of light irradiated onto the colored resin from a specific ultraviolet LED 55, among the multiple ultraviolet LEDs 55, whose peak wavelength is closest to the wavelength at which the amount of light absorbed by the photopolymerization initiator of the ultraviolet curing resin is maximized, may be adjusted, and a predetermined amount of light may be irradiated onto the colored resin by the curing unit 50. In general, the amount of light absorbed by the photopolymerization initiator tends to be smaller the farther the wavelength of light from the wavelength at which the amount of absorption is maximized. For this reason, by doing this, it is easier to make the colored layer have a desired degree of hardening compared to the case where the amount of light irradiated onto the colored resin from the ultraviolet LEDs 55 other than the specific ultraviolet LED 55 among the multiple ultraviolet LEDs 55 is adjusted. In this case, in the coating process P4, the amount of light irradiated onto the colored resin from at least one ultraviolet LED 55 other than the specific ultraviolet LED 55 may be kept constant without adjustment. Alternatively, the amount of light irradiated onto the colored resin from at least one ultraviolet LED 55 other than the specific ultraviolet LED 55 may be further adjusted, and a predetermined amount of light may be irradiated onto the colored resin by the curing unit 50. In this case, when the predetermined amount of irradiation is determined based on the correlation between the overlap integral and the amount of light irradiation as described above, it may be easier to adjust the temperature of the colored resin during light irradiation compared to when the amount of irradiation of all ultraviolet LEDs 55 other than the specific ultraviolet LED 55 is constant. Therefore, for example, it may be easier to reduce temperature differences due to differences in the colors of the colored resin.

The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to these.

The optical fiber 1N shown in FIG. 1 was manufactured by the optical fiber manufacturing process P3 shown in FIG. 2. The diameter of the optical fiber 1N was 239 μm, the protective resin layer 12 was made of urethane acrylate, and the thickness of the protective resin layer 12 was 57 μm. In addition, blue, yellow, red, purple, white, pink, and light blue colored resins were prepared. These colored resins were the same as the colored resins used to form the resin samples SA1 to SA7 whose absorption spectra were shown in FIG. 3, and the ultraviolet curing resin in the colored resins contained epoxy acrylate and a benzophenone-based photopolymerization initiator. Using the coating device 100 shown in FIG. 4, the prepared blue colored resin was applied to the optical fiber 1N, and the colored resin was cured to form a blue colored layer 15, as in the above embodiment, and multiple optical fibers 1 shown in FIG. 1 were manufactured. When manufacturing each optical fiber 1, the intensity of the light from the ultraviolet LED 55 was changed by changing the light output of the ultraviolet LED 55 from 50% to 100% without changing the irradiation time of the light from the ultraviolet LED 55. Also, similar to the case of the blue colored resin, the prepared purple colored resin was applied to the optical fiber strand 1N, and the colored resin was cured to form a purple colored layer 15, and multiple optical fibers 1 shown in FIG. 1 were manufactured. When manufacturing each optical fiber 1, the light output of the ultraviolet LED 55 was changed from 50% to 100% to change the intensity of the light from the ultraviolet LED 55.

The curability of the colored layer 15 was evaluated for each of the optical fibers 1 having the blue colored layer 15 and the optical fibers 1 having the purple colored layer 15 by the simulation evaluation described below. As shown in Figures 5 and 6, the uncured ultraviolet curing resin 71 was applied to the upper surface of each of eight flat-plate-shaped bases 70 made of acrylic to a thickness of 80 μm. Ten samples 75 obtained by cutting the optical fiber 1 were placed on the ultraviolet curing resin 71 of each base 70. Note that Figure 5 is a diagram for explaining the method of the simulation evaluation in the experimental example, and is a diagram of one base 70 on which the sample 75 is placed, viewed from above. Also, Figure 6 is another diagram for explaining the method of the simulation evaluation in the experimental example, and is a diagram of one base 70 on which the sample 75 is placed, viewed from one end side of the sample 75 along the longitudinal direction of the sample 75. In Figures 5 and 6, only one sample 75 is given a symbol. The length of the sample 75 was approximately 10 cm, and ¼ or more of the outer circumference of the colored layer 15 was in contact with the ultraviolet curing resin 71, and one end of the sample 75 protruded from the edge of the base 70. Next, the ultraviolet curing resin 71 of each base 70 was irradiated with light from an ultraviolet lamp to cure the ultraviolet curing resin 71, and the ultraviolet curing resin 71 and the colored layer 15 were bonded together. The amount of light irradiated from the ultraviolet lamp was an amount that allowed the photopolymerization initiator contained in the ultraviolet curing resin 71 to react sufficiently. Next, one end of the sample 75 was pulled toward the top of the base 70 to move the sample 75. The speed at which the sample 75 left the base 70 during the movement was 2 cm/sec or less. Next, the state of the sample 75 after the movement was observed, and the failure rate was calculated when the colored layer 15 was not peeled off from the optical fiber 1N and the failure rate was calculated when the colored layer 15 was not peeled off. The curability of the colored layer 15 was set to a desired degree of curing so that the failure rate was approximately 10% to 20%. Sample 75 having a blue colored layer 15 with the desired degree of cure was manufactured when the light output of the UV LED 55 was set to 60%. Sample 75 having a purple colored layer 15 with the desired degree of cure was manufactured when the light output of the UV LED 55 was set to 80%. The number of bases 70 and samples 75 required to obtain the defect rate is not particularly limited, and may be changed as appropriate depending on the desired accuracy.

As described above, the absorbance of the blue resin sample SA1 at the peak wavelength of the light from the ultraviolet LED 55 is 0.93 Abs, and the absorbance of the purple resin sample SA4 is 2.58 Abs. It was known from other experiments that the defect rate and the light output of the ultraviolet LED 55 are roughly proportional to each other. For this reason, it was predicted that the absorbance and the light output of the ultraviolet LED 55 at which the colored layer 15 is cured to the desired degree of hardening would be proportional to each other, and the correlation was determined as a proportional relationship from these absorbances and the results of this simulation evaluation. As described above, the absorbance of the yellow resin sample SA2 is 1.54 Abs, the absorbance of the red resin sample SA3 is 1.23 Abs, the absorbance of the white resin sample SA5 is 2.52 Abs, the absorbance of the pink resin sample SA6 is 2.19 Abs, and the absorbance of the light blue resin sample SA7 is 1.40 Abs. Based on these absorbances and the correlation obtained, the light emission output of the ultraviolet LED 55 was calculated for each of the yellow, red, white, pink, and light blue colored resins. Next, as in the case of the blue colored resin, the colored resin was applied to the optical fiber 1N for each of the yellow, red, white, pink, and light blue colored resins, and the colored resin was cured to form the colored layer 15, thereby manufacturing the optical fiber 1 shown in FIG. 1. At this time, the light emission output of the ultraviolet LED 55 was the calculated light emission output, and the above-mentioned simulation evaluation was performed for each of the obtained optical fibers 1. The results are shown in Table 1.

As shown in Table 1, it was found that the defect rate was generally 10% to 20% even for the yellow, red, white, pink, and light blue colored resins. Since the irradiation time of light from the ultraviolet LED 55 was the same, the light output of the ultraviolet LED 55 was proportional to the amount of light irradiated from the ultraviolet LED 55. Therefore, it was found that there was a roughly proportional relationship between the absorbance at the peak wavelength of light from the ultraviolet LED in the resin samples SA1 to SA7 as the cured colored resin and the amount of light irradiated from the ultraviolet LED 55 at which the colored layer 15 reached the desired degree of curing.

The present invention provides a method for manufacturing optical fiber that can reduce the difference in the degree of hardening of the colored layer due to differences in the color of the colored resin, and can be used in various fields related to optical fibers.

1... Optical fiber 1N... Optical fiber strand 15... Colored layer 40... Coating section 50... Curing section 51... Curing unit 55... Ultraviolet LED
P1: Measuring step P2: Determining step P3: Optical fiber manufacturing step P4: Coating step 100: Coating device

Claims (8)

A method for manufacturing an optical fiber having an optical fiber wire including a core and a cladding surrounding an outer peripheral surface of the core, and a colored layer made of a colored resin including a pigment and an ultraviolet curable resin and covering an outer peripheral surface of the optical fiber wire, comprising:
a coating step of coating the colored resin on an outer peripheral surface of the optical fiber strand, and irradiating the coated colored resin with light from an ultraviolet LED to harden the colored resin to form the colored layer;
A method for manufacturing an optical fiber, characterized in that in the coating step, the colored resin is irradiated with a predetermined amount of light that is determined in advance based on the absorbance of the light by the hardened colored resin. The method for manufacturing an optical fiber according to claim 1, characterized in that the specified irradiation amount is determined based on a correlation between the absorbance of the colored resin at the peak wavelength of the light, and the absorbance of the colored resin of another color at the peak wavelength of the light, and the irradiation amount of the light that results in a desired degree of hardening of the colored layer made of the colored resin of the other color. The method for manufacturing an optical fiber as described in claim 2, characterized in that the specified irradiation amount is determined based on a correlation between an overlap integral between the spectrum of the light and the absorption spectrum of the colored resin, and an overlap integral between the spectrum of the light and the absorption spectrum of the colored resin of another color, and the irradiation amount of the light at which the colored layer made of the colored resin of the other color achieves a desired degree of hardening. 4. The method for manufacturing an optical fiber according to claim 1, wherein in the coating step, the intensity of the light is adjusted, and the predetermined amount of the light is irradiated onto the colored resin. 5. The method for manufacturing an optical fiber according to claim 1, wherein in the coating step, a time for irradiating the colored resin with the light is adjusted, and the colored resin is irradiated with the predetermined amount of light. The ultraviolet LED is a plurality of LEDs,
The peak wavelengths of the light from at least two of the ultraviolet LEDs are different from each other;
6. The optical fiber manufacturing method according to claim 1, wherein in the coating process, the amount of irradiation of light from a specific ultraviolet LED among the multiple ultraviolet LEDs, the specific ultraviolet LED having a peak wavelength closest to the wavelength at which the amount of light absorbed by the photopolymerization initiator of the ultraviolet curing resin is maximized, is adjusted, and the specific amount of irradiation of light is irradiated onto the colored resin. The method for manufacturing an optical fiber according to claim 6, characterized in that, in the coating process, the amount of irradiation of the colored resin with light from at least one ultraviolet LED other than the specific ultraviolet LED is kept constant without adjustment. The method for manufacturing an optical fiber according to claim 6, characterized in that in the coating process, the amount of irradiation of light from at least one of the ultraviolet LEDs other than the specific ultraviolet LED onto the colored resin is further adjusted, and the predetermined amount of the light is irradiated onto the colored resin.

Images