JP7567698B2 - Optical fiber manufacturing method - Google Patents

Description

This disclosure relates to a method for manufacturing optical fibers.

Optical fibers in which the outer circumference of a glass fiber is covered with a resin coating layer are known (for example, Patent Document 1).

JP 2012-6797 A

The purpose of this disclosure is to prevent optical fiber breakage.

According to one aspect of the present disclosure,
forming a glass fiber;
forming a resin coating layer so as to cover an outer periphery of the glass fiber;
curing the resin coating layer using a predetermined curing device;
a step of conveying the optical fiber having the cured resin coating layer by a plurality of guide rollers and a capstan;
winding the optical fiber on a bobbin;
having
In the step of forming the resin coating layer,
forming a first resin coating layer and a second resin coating layer in this order from a central axis side to an outer periphery side of the glass fiber as the resin coating layer;
During the process from forming the resin coating layer to winding the optical fiber,
There is provided a method for manufacturing an optical fiber, in which the density of particles having a size equal to or greater than ¼ the thickness of the second resin coating layer in an atmosphere is set to 1060 particles/m3 or ^less .

This disclosure makes it possible to prevent optical fiber breakage.

FIG. 1 is a schematic cross-sectional view illustrating an optical fiber according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram illustrating an optical fiber manufacturing apparatus according to an embodiment of the present disclosure. FIG. 3 is a graph showing the frequency of wire breakage versus the thickness of the second resin coating layer. FIG. 4 is a graph showing the frequency of disconnections versus the target particle density.

[Description of the embodiments of the present disclosure]
<Findings gained by the inventors>
First, the findings of the inventors will be described.

In recent years, there has been a demand for optical fibers with a smaller outer diameter in order to package multiple optical fibers at high density in optical cables. Specifically, the outer diameter of some optical fibers in recent years is 200 μm or less.

In the manufacturing process for optical fibers with such small diameters, the optical fiber is more susceptible to breakage than optical fibers with conventional outer diameters. If the optical fiber breaks during the manufacturing process, the manufacturing efficiency of the optical fiber decreases. For this reason, there was a demand for innovative manufacturing methods.

In order to address the above issues, we focused on particles present in the atmosphere during the manufacturing process and carried out our research.

When particles present in the atmosphere during the manufacturing process adhere to the optical fiber, the particles become interposed between the optical fiber and a guide roller or capstan that transports the optical fiber. At this time, the optical fiber is transported with a certain tension, so the particles that have adhered to the optical fiber are pressed locally against the resin coating layer. This can result in localized stress being applied to the glass fiber. In such cases, damage such as cracks can occur in the glass fiber. As a result, the optical fiber may break due to the damage to the glass fiber.

As a result of thorough research into these particles, the inventors discovered that the relationship between certain particles in the atmosphere and the thickness of the second resin coating layer affects the frequency of breakage of the optical fiber.

This disclosure is based on the above findings made by the present inventors.

[Details of the embodiment of the present disclosure]
Next, an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

<One embodiment of the present disclosure>
(1) Optical Fiber An optical fiber 10 according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing the optical fiber according to the embodiment.

In the following, the "axial direction" of the glass fiber 100 refers to the direction along the central axis of the glass fiber 100, which can be rephrased as the longitudinal direction of the glass fiber 100. The "radial direction" of the glass fiber 100 refers to the direction perpendicular to the axial direction of the glass fiber 100, which can be rephrased as the transverse direction of the glass fiber 100 in some cases. The "circumferential direction" of the glass fiber 100 refers to the direction along the outer periphery of the glass fiber 100 (the circumferential direction in FIG. 1). The same terms as those for the glass fiber 100 can be used for the optical fiber 10.

As shown in FIG. 1, the optical fiber 10 of this embodiment is configured as a linear body in which the outer circumference of the glass fiber 100 is covered with a resin coating layer 200. That is, the optical fiber 10 has, for example, the glass fiber 100 and the resin coating layer 200 in this order from the central axis side of the glass fiber 100 to the outer circumference side.

The term "optical fiber 10" used here includes the optical fiber strand before it is colored and the optical fiber core after it is colored. In the following, for example, the optical fiber 10 will be described as an optical fiber strand.

[Glass fiber]
The glass fiber 100 is configured, for example, as an optical transmission body that transmits light introduced into the optical fiber 10 along the axial direction of the optical fiber 10. The glass fiber 100 is also called, for example, a "bare optical fiber." The glass fiber 100 has, for example, silica (SiO ₂ ) glass as a base material (main component) and has a core 120 and a cladding 140.

[Resin coating layer]
The resin coating layer 200 is provided, for example, so as to cover the outer periphery of the glass fiber 100 and is configured to protect the glass fiber 100 .

In this embodiment, the resin coating layer 200 has, for example, a first resin coating layer (primary resin coating layer) 220 and a second resin coating layer (secondary resin coating layer) 240.

The first resin coating layer 220 is provided, for example, to cover the outer periphery of the clad 140 of the glass fiber 100 and is in contact with the outer periphery of the clad 140. The second resin coating layer 240 is provided, for example, to cover the outer periphery of the first resin coating layer 220 and is in contact with the outer periphery of the first resin coating layer 220.

The first resin coating layer 220 and the second resin coating layer 240 are formed, for example, as a cured product obtained by curing an ultraviolet-curable resin composition by irradiating it with ultraviolet light. Examples of the base resin in the ultraviolet-curable resin composition include urethane acrylate.

In this embodiment, the Young's modulus of the second resin coating layer 240 is preferably, for example, 900 MPa or more. If the Young's modulus of the second resin coating layer 240 is less than 900 MPa, when particles present in the atmosphere adhere to the optical fiber 10 during the manufacturing process, the particles are likely to be locally pushed into the second resin coating layer 240 by contact with the guide roller 552 of the conveying unit 550 described later. For this reason, excessive stress may be applied to the glass fiber 10. As a result, there is a risk that the optical fiber 10 may be easily broken. In contrast, in this embodiment, by making the Young's modulus of the second resin coating layer 240 900 MPa or more, that is, by hardening the second resin coating layer 240, even if particles present in the atmosphere adhere to the optical fiber 10 during the manufacturing process, it is possible to suppress the particles from being locally pushed into the second resin coating layer 240. This makes it possible to suppress the application of excessive stress to the glass fiber 10. As a result, it is possible to stably suppress breakage of the optical fiber 10.

The upper limit of the Young's modulus of the second resin coating layer 240 is not particularly limited. For example, it is preferably 1,400 MPa or less.

It is preferable that the Young's modulus of the first resin coating layer 220 is, for example, 0.15 MPa or more and 1.2 MPa or less.

In this embodiment, the optical fiber 10 is configured to have, for example, a small diameter. Specifically, the outer diameter of the above-mentioned resin coating layer 200 (i.e., the outer diameter of the second resin coating layer 240) is, for example, 190 μm or less. This allows multiple optical fibers 10 to be densely packed into an optical cable.

It is preferable that the outer diameter of the resin coating layer 200 is, for example, 160 μm or more.

In view of the relationship between the outer diameter of the first resin coating layer 220 and the outer diameter of the second resin coating layer 240 described above, it is preferable that the thickness of the second resin coating layer 240 is, for example, 10 μm or more and 25 μm or less.

(2) Optical Fiber Manufacturing Apparatus Next, an optical fiber manufacturing apparatus 50 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing the configuration of the optical fiber manufacturing apparatus according to this embodiment.

As shown in FIG. 2, the optical fiber manufacturing apparatus 50 of this embodiment includes, for example, a drawing furnace 510, a fiber position measuring unit 522, a cooling device 523, an outer diameter measuring unit 524, a resin coating device 530, a curing device 540, a conveying unit 550, a bobbin 560, a control unit 590, a clean booth 620, and an air conditioning system 640. The equipment components other than the control unit 590, the clean booth 620, and the air conditioning system 640 are provided in this order.

Hereinafter, for each device component of the optical fiber manufacturing apparatus 50, the side closer to the gripping mechanism 512 will be referred to as "upstream" and the side closer to the bobbin 560 will be referred to as "downstream."

The drawing furnace 510 is configured to form the glass fiber 100.

The inside of the furnace tube 514 is heated and the softened glass is stretched to form a thin glass fiber 100.

The fiber position measurement unit 522 is configured to measure the horizontal position of the glass fiber 100.

The cooling device 523 is configured to cool the glass fiber 100 formed in the drawing furnace 510.

The outer diameter measuring unit 524 is configured to measure the outer diameter of the glass fiber 100 before it is resin-coated.

The resin coating device 530 is configured to form a resin coating layer 200 so as to cover the outer periphery of the glass fiber 100. The resin coating layer 200 has a die that applies an ultraviolet-curable resin composition to the outer periphery of the glass fiber 100 while inserting the glass fiber 100.

In this embodiment, the resin coating device 530 has two dies that form the first resin coating layer 220 and the second resin coating layer 240 in this order from the central axis side to the outer periphery side of the glass fiber 100.

The curing device 540 is configured to irradiate the resin coating layer 200 with ultraviolet light to cure the resin coating layer 200.

The conveying section 550 is configured to convey the optical fiber 10 with the resin coating layer 200 cured. Specifically, the conveying section 550 has, for example, a plurality of guide rollers 552, 556 and a capstan 554. The direct below roller 552a, which is one of the plurality of guide rollers 552, is located, for example, directly below the curing device 540. The capstan 554 is, for example, provided downstream of the direct below roller 552a and configured to convey (pull) the optical fiber 10 with a predetermined tension while gripping the optical fiber 10 between the belt and the roller. The screening rollers 552c, 552d and 552e of the plurality of guide rollers 552 are provided downstream of the capstan 554 and configured to apply a screening tension to the optical fiber 10 together with the capstan 554. The guide roller 556 is provided downstream of the screening roller 552e and configured to adjust the tension of the optical fiber 10 by moving up and down in response to fluctuations in the tension of the optical fiber 10.

The bobbin 560 is provided, for example, downstream of the guide roller 556 and is configured to wind up the optical fiber 10.

The control unit 590 is, for example, connected to each part of the optical fiber manufacturing apparatus 50 and configured to control them. The control unit 590 is, for example, configured as a computer.

Here, in this embodiment, the environment from the resin coating device 530 to the bobbin 560 is maintained to meet the target particle density requirements in the atmosphere described below.

Specifically, the optical fiber manufacturing apparatus 50 has, for example, a clean booth 620 and an air conditioning system 640.

The clean booth 620 is provided, for example, to surround the area from the resin coating device 530 to the bobbin 560. The clean booth 620 has, for example, a resin plate or a resin film that separates the area from the resin coating device 530 to the bobbin 560 from the other areas.

The air conditioning system 640 is configured, for example, to suck air from within the clean booth 620, remove particles through a filter, and supply the purified air to the clean booth 620. Examples of the filters in the air conditioning system 640 include a HEPA filter (High Efficiency Particulate Air Filter) and a ULPA filter (Ultra Low Penetration Air Filter). The air conditioning system 640 is also configured, for example, to maintain the pressure within the clean booth 620 at a higher pressure than the pressure in the area outside the clean booth 620.

Furthermore, in this embodiment, at least one of the multiple guide rollers 552, the capstan 554, and the bobbin 560 is configured to be able to eliminate static electricity so as to satisfy the requirements for the amount of static electricity of the optical fiber 10 after winding, which will be described later.

Specifically, each of the guide rollers 552, the capstan 554, and the bobbin 560 is provided with, for example, an ionizer 580 (590a to 580h). The ionizer 580 is configured to, for example, blow ionized air onto an object to neutralize the object.

(3) Method for Manufacturing Optical Fiber Next, a method for manufacturing the optical fiber 10 according to this embodiment will be described with reference to Fig. 2. In the following, steps are abbreviated as "S".

The manufacturing method of the optical fiber 10 of this embodiment includes, for example, a glass fiber forming process (drawing process) S100, a cooling process S200, a resin coating layer forming process S300, a hardening process S400, a conveying process S500, and a winding process S600. These processes are performed continuously in this order in the optical fiber manufacturing apparatus 50. Each component of the optical fiber manufacturing apparatus 50 is controlled by the control unit 590.

[S100: Wire drawing process]
First, the glass base material G is introduced into the furnace core tube 514 of the drawing furnace 510, and the glass base material G in the furnace core tube 514 is heated by the heating element 516. After the glass base material G is heated, the softened glass is drawn from the lower end of the glass base material G to form a glass fiber 100 having a small diameter.

[S200: Cooling process]
Next, the glass fiber 100 formed in the drawing furnace 510 is introduced into a cooling device 523 and air-cooled.

At this time, the amount of glass base material fed in is controlled so that the outer diameter of the glass fiber 100 before resin coating measured by the outer diameter measuring unit 524 remains constant.

[S300: Resin coating layer forming step]
Next, a resin coating layer 200 is formed by a resin coating device 530 so as to cover the outer periphery of the glass fiber 100 .

At this time, in this embodiment, the resin coating layer 200 is formed by continuously forming a first resin coating layer 220 and a second resin coating layer 240 in this order from the central axis side to the outer periphery side of the glass fiber 100.

In this embodiment, the outer diameter of the resin coating layer 200 is set to, for example, 190 μm or less.

[S400: Curing process]
Next, the resin coating layer 200 is irradiated with ultraviolet light by the curing device 540 to cure the resin coating layer 200. By setting the Young's modulus of the cured second resin coating layer 240 to 900 MPa or more, the resin coating layer 200 can be made less susceptible to damage by particles.

[S500: Transport process]
Next, the optical fiber 10 with the cured resin coating layer 200 is transported by the transport unit 550. Specifically, in the transport unit 550, the optical fiber 10 is transported with a predetermined tension through the direct below roller 552a, the guide roller 552b, the capstan 554, the screening rollers 552c, 552d, and 552e, and the guide roller 556.

[S600: Winding process]
Next, the optical fiber 10 is wound around the bobbin 560 .

In this embodiment, from the resin coating layer forming step S300 to the winding step S600, for example, the density of particles having a size (particle diameter) of ¼ or more times the thickness of the second resin coating layer 240 in the atmosphere is set to 1060 particles/m3 ^or less. The density of the particles is also called the "target particle density." If CF (cubic feet) is used as a unit, the above-mentioned target particle density corresponds to 30 particles/CF or less.

In this embodiment, by setting the target particle density to 1060 particles/m3 ^or less, the probability that particles with a large size ratio to the thickness of the second resin coating layer 240 will adhere to the optical fiber 10 can be reduced.

The lower limit of the target particle density is not particularly limited, as the lower the better.

The above-mentioned target particle density is adjusted, for example, by the type of filter in the air conditioning system 640, the number of filters in the air conditioning system 640, the intake speed of the air conditioning system 640, the supply speed of clean air in the air conditioning system 640, the pressure inside the clean booth 620, etc.

In addition, in this embodiment, in the processes from the transporting step S500 to the winding step S600, at least one of the multiple guide rollers 552, the capstan 554, and the bobbin 560 is de-electrified so that the absolute value of the static electricity of the entire optical fiber 10 after winding onto the bobbin 560 is 6 kV or less. By de-electrifying each part so as to satisfy the above-mentioned requirements for the amount of static electricity, it is possible to suppress adhesion of particles to the optical fiber 10 due to charging of the optical fiber 10.

Note that the "static charge of the entire optical fiber 10 after winding on the bobbin 560" referred to here can be rephrased as the static charge of the entire optical fiber 10 in a state where it is wound on the bobbin 560. The reason for specifying the static charge of the entire optical fiber 10 after winding is that it is not possible to measure the static charge of the optical fiber 10 during the transport process of the optical fiber 10. As described above, satisfying the static charge of the entire optical fiber 10 after winding is equivalent to suppressing the accumulation of static charge in the optical fiber 10 during the transport process of the optical fiber 10.

The lower limit of the amount of static electricity in the optical fiber 10 after winding is not particularly limited, as the lower the better.

As a specific method of discharging electricity, for example, ionized air having a polarity opposite to that to which the optical fiber 10 is charged is blown by each ionizer 580 onto at least one of the guide rollers 552, the capstan 554, and the bobbin 560. It is preferable that the ionized air is blown onto the object at a location where the optical fiber 10 comes into contact. This method can offset the static electricity of the optical fiber 10. As a result, the optical fiber 10 can be stably discharged.

In addition, in this embodiment, it is preferable to use an ionizer 580 to neutralize at least one of the multiple guide rollers 552 and the capstan 554 located upstream of the bobbin 560. Because the optical fiber 10 is transported upstream of the bobbin 560, the optical fiber 10 tends to approach particles in the atmosphere. Therefore, by actively neutralizing the optical fiber 10 upstream of the bobbin 560 as described above, adhesion of particles to the optical fiber 10 can be stably suppressed even during periods when the optical fiber 10 may approach particles in the atmosphere.

In addition, in this embodiment, it is even more preferable to, for example, neutralize the capstan 554 using the ionizer 580c. In the capstan 554, the optical fiber 10 rubs between the belt and the roller, so the optical fiber 10 is likely to become charged. Therefore, by actively neutralizing the capstan 554 as described above, it is possible to stably suppress the charging of the optical fiber 10. As a result, it is possible to stably suppress the adhesion of particles to the optical fiber 10.

In this embodiment, it is most preferable to neutralize all of the guide rollers 552, the capstan 554, and the bobbin 560 using the ionizers 580. This reliably prevents the optical fiber 10 from becoming electrically charged during transport, and reliably prevents particles from adhering to the optical fiber 10.

This is how the optical fiber 10 of this embodiment is manufactured.

(4) Effects of the Present Embodiment According to the present embodiment, one or more of the following effects can be obtained.

(a) In the process from the resin coating layer forming step S300 to the winding step S600 in this embodiment, the density of particles having a size equal to or greater than ¼ of the thickness of the second resin coating layer 240 in the atmosphere is set to 1060 particles/m3 ^or less.

If the target particle density exceeds 1060 particles/ ^m3 , there is a high probability that particles having a large size ratio relative to the thickness of the second resin coating layer 240 will adhere to the optical fiber 10. If such large particles adhere to the optical fiber 10, the particles are likely to be locally pushed into the second resin coating layer 240 by contact with the guide roller 552 of the conveying unit 550, etc. This may cause excessive stress to be applied to the glass fiber 100. As a result, the optical fiber 10 may be prone to breakage.

In contrast, in the present embodiment, by setting the target particle density to 1060 particles/m3 ^or less, it is possible to reduce the probability that particles having a large ratio of size to the thickness of the second resin coating layer 240 will adhere to the optical fiber 10. By suppressing particle adhesion, it is possible to suppress localized pushing of particles into the second resin coating layer 240. This makes it possible to suppress the application of excessive stress to the glass fiber 100. As a result, it is possible to stably suppress breakage of the optical fiber 10.

By reducing the frequency of breakage of the glass fiber 100 in this way, it is possible to prevent a decrease in the manufacturing efficiency of the optical fiber 10.

(b) In the resin coating layer forming process S300 of this embodiment, the Young's modulus of the second resin coating layer 240 is set to 900 MPa or more. In other words, by hardening the second resin coating layer 240, even if particles present in the atmosphere during the manufacturing process adhere to the optical fiber 10, it is possible to suppress the particles from being locally pushed into the second resin coating layer 240. This makes it possible to suppress the application of excessive stress to the glass fiber 100. As a result, breakage of the optical fiber 10 can be stably suppressed.

(c) In the steps from the transport step S500 to the winding step S600 of this embodiment, at least one of the multiple guide rollers 552, the capstan 554, and the bobbin 560 is de-electrified so that the absolute value of the static electricity of the entire optical fiber 10 after winding onto the bobbin 560 is 6 kV or less.

Here, during the transport of the optical fiber 10 by the multiple guide rollers 552 and the capstan 554, and during the winding of the optical fiber 10 by the bobbin 560 (collectively referred to as the transport process of the optical fiber 10), the optical fiber 10 comes into contact with various parts. For this reason, the optical fiber 10 is easily charged.

The absolute value of the static electricity of the entire optical fiber 10 after winding being less than 6 kV corresponds to the accumulation of static electricity in the optical fiber 10 during the transport process of the optical fiber 10 described above. As described above, if the optical fiber 10 is charged during the transport process of the optical fiber 10, particles are more likely to adhere to the optical fiber 10 due to static electricity during the transport process of the optical fiber 10. If particles adhere to the optical fiber 10, excessive stress may be applied to the glass fiber 100 due to the particles being pushed into the resin coating layer 200 as described above. As a result, the optical fiber 10 may become more susceptible to breakage.

In contrast, reducing the amount of static electricity in the entire optical fiber 10 after winding, as in this embodiment, is equivalent to suppressing the accumulation of static electricity in the optical fiber 10 during the transport process of the optical fiber 10. By suppressing the accumulation of static electricity in the optical fiber 10, it is possible to suppress adhesion of particles to the optical fiber 10 caused by charging the optical fiber 10. This makes it possible to suppress the application of excessive stress to the glass fiber 10 caused by particles being pushed into the resin coating layer 200. As a result, breakage of the optical fiber 10 can be stably suppressed.

(d) In this embodiment, the outer diameter of the resin coating layer 200 of the optical fiber 10 is 190 μm or less. When manufacturing such a small-diameter optical fiber 10, the optical fiber 10 is likely to break due to the adhesion of particles having a size equal to or greater than 1/4 the thickness of the second resin coating layer 240, as in the examples described below. Therefore, the above-described manufacturing method is particularly effective for manufacturing an optical fiber 10 in which the outer diameter of the resin coating layer 200 is 190 μm or less.

<Other embodiments of the present disclosure>
Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit and scope of the present disclosure.

In the above embodiment, the optical fiber 10 is illustrated and described as an optical fiber strand before being colored, but as described above, the optical fiber 10 may be an optical fiber core wire after being colored. In other words, the optical fiber 10 may have a colored layer that covers the outer periphery of the resin coating layer 200.

In the above embodiment, the resin coating layer 200 is described as being composed of two layers, but this is not limited to this case. The resin coating layer 200 may be composed of only one layer, or may be composed of three or more layers.

In the above embodiment, the case where all of (i), (ii), and (iii) below are implemented has been described, but the present invention is not limited to this case.
(i) During the process from the resin coating layer forming step S300 to the winding step S600, the density of particles having a size equal to or greater than ¼ of the thickness of the second resin coating layer 240 in the atmosphere is set to 1060 particles/ ^m3 or less.
(ii) The Young's modulus of the second resin coating layer 240 is set to 900 MPa or more.
(iii) In the processes from the transporting step S500 to the winding step S600, at least one of the multiple guide rollers 552, the capstan 554, and the bobbin 560 is de-electrified so that the absolute value of the static electricity of the entire optical fiber 10 after winding onto the bobbin 560 is 6 kV or less.
By implementing at least (i), the above-mentioned effect can be obtained to a certain extent. However, the above-mentioned effect can be obtained more stably by implementing at least one of (ii) and (iii) in addition to the above-mentioned (i).

In the above embodiment, the clean booth 620 is used to separate the area from the resin coating device 530 to the bobbin 560 from the other areas, and the air conditioning system 640 is used to reduce the target particle density in the clean booth 620, but this is not limited to the above. The air conditioning system may be used to reduce the target particle density throughout the entire clean room in which the optical fiber manufacturing device 50 is installed.

In the above embodiment, the density of particles having a size of 1/4 or more times the thickness of the second resin coating layer 240 in the atmosphere is set to 1060 pieces/m3 ^or less during the resin coating layer forming step S300 to the winding step S600, but this is not limited to this case. Instead of adjusting the target particle density, the thickness of the second resin coating layer 240 may be adjusted. That is, the thickness of the second resin coating layer 240 may be set to, for example, 4 times or more the size of the particle that exists most frequently in the atmosphere (for example, more than 30 pieces/CF). However, since the thickness of the second resin coating layer 240 is determined by the specifications of the optical fiber 10, it is preferable to adjust the target particle density as described above.

Next, examples of the present disclosure will be described. These examples are merely examples of the present disclosure, and the present disclosure is not limited to these examples.

(1) Preparation of Optical Fiber Each sample optical fiber was prepared under the following conditions.

When preparing each sample, the target particle density in the atmosphere was adjusted by changing the opening and closing state of the clean booth.

[Common conditions]
Outer diameter of glass fiber: 125 μm
Outer diameter of optical fiber (outer diameter of second resin coating layer): 180 μm
Number of resin coating layers: 2 Manufacturing equipment: Configuration shown in Figure 2

[Experiment 1]
Thickness of the second resin coating layer: 5 to 30 μm (the outer diameter of the second resin coating layer is fixed at 180 μm)
Particle size: 3.75 μm or 5 μm
Particle density: 30 particles/CF
Young's modulus of second resin coating layer: 900 MPa
Neutralization by ionizer in the transfer section and bobbin: None

[Experiment 2]
Thickness of second resin coating layer: 20 μm
Target particle density: 0 to 50 particles/CF
Young's modulus of second resin coating layer: 900 MPa
Neutralization by ionizer in the transfer section and bobbin: None

[Experiment 3]
Thickness of second resin coating layer: 20 μm
Target particle density: 30 particles/CF
Young's modulus of second resin coating layer: 800 to 2000 MPa
Neutralization by ionizer in conveyor and bobbin: Yes Amount of static electricity on optical fiber after winding (absolute value): 6 kV

[Experiment 4]
Thickness of second resin coating layer: 20 μm
Target particle density: 30 particles/CF
Young's modulus of second resin coating layer: 900 MPa
Static electricity elimination by ionizer in the transport section and bobbin: Yes or no Amount of static electricity (absolute value) on optical fiber after winding: 0.3 to 30 kV
(Sample B4-2 was not subjected to static elimination.)

(2) Evaluation [Target particle density]
The particle density in the clean booth surrounding the area from the resin coating device to the bobbin was measured using a particle counter (Met One Model 237B) that can detect the size and number of particles contained when 1CF of air is sucked in.

[Static electricity amount]
The absolute value of the static electricity quantity of the optical fiber after it was wound around the bobbin was measured by a static electricity quantity meter.

[Disconnection frequency measurement]
In the manufacturing process of the optical fiber of each sample described above, the number of breaks in the optical fiber was measured. For each sample, the number of breaks per 1000 km was calculated as the "break frequency (times/Mm)". As a result, a break frequency of less than 5 times/Mm was evaluated as "good", and a break frequency of 5 times/Mm or more was evaluated as "poor".

(3) Results [Experiment 1]
The results of Experiment 1 regarding the dependency of the thickness of the second resin coating layer will be described with reference to FIG.

As shown in Figure 3, in the manufacture of optical fiber in an atmosphere in which particles of a certain size are present, the frequency of breakage of the optical fiber gradually increased as the thickness of the second resin coating layer became thinner from a certain threshold value. In addition, a comparison of particles of different sizes revealed that the threshold thickness of the second resin coating layer at which the frequency of breakage of the optical fiber becomes 5 times/mm or more is about four times the particle size, and is proportional to the particle size.

[Experiment 2]
The results of Experiment 2 regarding the dependency of the target particle density are illustrated with reference to FIG.

As shown in Figure 4, as the density of particles (target particle density) having a size equal to or greater than 1/4 the thickness of the second resin coating layer in the atmosphere increases from a predetermined threshold, the frequency of breakage of the optical fiber gradually increases. It was found that the threshold of the target particle density at which the frequency of breakage of the optical fiber becomes 5 times/mm or more is 30 particles/CF.

The results of Experiments 1 and 2 confirmed that the frequency of breakage of optical fiber can be reduced by keeping the density of particles having a size of 1/4 or more times the thickness of the second resin coating layer in the atmosphere to 30 particles/CF or less during the resin coating layer formation process and the winding process.

[Experiment 3]
The results of Experiment 3 regarding the dependency of the Young's modulus of the second resin coating layer will be described with reference to Table 1 below.

In sample B3-1, in which the Young's modulus of the second resin coating layer was less than 900 MPa, the frequency of breakage of the optical fiber was 5 times/mm or more.

In sample B3-1, when particles adhered to the optical fiber, the particles were easily pushed into the second resin coating layer. As a result, it is believed that the optical fiber in sample B3-1 was more susceptible to breakage.

In contrast, in samples A3-1 to A3-4, in which the Young's modulus of the second resin coating layer was 900 MPa or more, the frequency of breakage of the optical fiber was less than 5 times/Mm. Also, in samples A3-1 to A3-4, there was a tendency for the frequency of breakage of the optical fiber to decrease as the Young's modulus of the second resin coating layer increased.

In samples A3-1 to A3-4, the Young's modulus of the second resin coating layer was set to 900 MPa or more, so that even if particles adhered to the optical fiber, it was possible to prevent the particles from being pushed locally into the second resin coating layer. As a result, it was confirmed that samples A3-1 to A3-4 were able to stably prevent breakage of the optical fiber 10.

[Experiment 4]
The results of Experiment 4 regarding the dependence of the amount of static electricity will be explained with reference to Table 2 below.

In samples B4-1 and B4-2, in which the absolute value of the static electricity in the optical fiber after winding was more than 6 kV, the frequency of optical fiber breakage was 5 times/Mm or more. In addition, in samples B4-1 and B4-2, there was a tendency for the frequency of optical fiber breakage to increase as the absolute value of the static electricity in the optical fiber after winding increased.

In samples B4-1 and B4-2, static electricity accumulated in the optical fiber during the optical fiber transport process. This made it easier for particles to adhere to the optical fiber. As a result, it is believed that the optical fiber 10 in samples B4-1 and B4-2 was more susceptible to breakage.

In contrast, in samples A4-1 to A4-3, in which the absolute value of the static electricity in the optical fiber after winding was 6 kV or less, the frequency of optical fiber breakage was less than 5 times/Mm. In addition, in samples A4-1 to A4-3, there was a tendency for the frequency of optical fiber breakage to decrease as the absolute value of the static electricity in the optical fiber after winding became lower.

In samples A4-1 to A4-3, it was possible to suppress the accumulation of static electricity in the optical fiber during the optical fiber transport process. This made it possible to suppress the adhesion of particles to the optical fiber. As a result, it was confirmed that samples A4-1 to A4-3 were able to stably suppress breakage of the optical fiber.

10 Optical fiber 50 Optical fiber manufacturing apparatus 100 Glass fiber 120 Core 140 Cladding 200 Resin coating layer 220 First resin coating layer 240 Second resin coating layer 430 Hardening device 510 Drawing furnace 512 Holding mechanism 514 Furnace tube 516 Heating element 518 Gas supply unit 522 Fiber position measurement unit 523 Cooling device 524 Outer diameter measurement unit 530 Resin coating device 540 Hardening device 550 Conveyor unit 552 Guide roller 552a Directly below roller 552b Guide roller 552c, 552d, 552e Screening roller 554 Capstan 555 Vibration suppression unit 556 Guide roller 560 Bobbin 580, 580a to 580h Ionizer 590 Control unit 620 Clean booth 640 Air conditioning system

Claims (3)

forming a glass fiber;
forming a resin coating layer so as to cover an outer periphery of the glass fiber;
curing the resin coating layer using a predetermined curing device;
a step of conveying the optical fiber having the cured resin coating layer by a plurality of guide rollers and a capstan;
winding the optical fiber on a bobbin;
having
In the step of forming the resin coating layer,
forming a first resin coating layer and a second resin coating layer in this order from a central axis side to an outer periphery side of the glass fiber as the resin coating layer;
During the process from forming the resin coating layer to winding the optical fiber,
A method for manufacturing an optical fiber, in which the density of particles having a size equal to or greater than 1/4 the thickness of the second resin coating layer in an atmosphere is set to 1060 particles/m3 ^or less. In the step of forming the resin coating layer,
2. The method for producing an optical fiber according to claim 1, wherein the second resin coating layer has a Young's modulus of 900 MPa or more. In the steps from the step of transporting the optical fiber to the step of winding the optical fiber,
3. The method for manufacturing an optical fiber according to claim 1, wherein at least one of the guide rollers, the capstan, and the bobbin is neutralized so that the absolute value of the amount of static electricity in the entire optical fiber after winding onto the bobbin is 6 kV or less.