JP2014222267A - Method of manufacturing plastic clad optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a plastic clad optical fiber in which an optical fiber having small transmission loss enough for practical use is obtained at low cost while having sufficient curability of a plastic clad layer.SOLUTION: There is provided a method of manufacturing a plastic clad optical fiber 18 which has a core of silica glass containing germanium and a clad of resin, the method of manufacturing the plastic clad optical fiber including the processes of: coating the silica glass fiber 14 of the core with an ultraviolet-curing resin composition for clad formation by a coating device 16; and curing the ultraviolet-curing resin composition by ultraviolet light through an ultraviolet-light irradiation device 17 after the coating with the ultraviolet-curing resin composition. Respective conditions are so set that a UVdose value expressed by UVdose=Σ(leakage light from the ultraviolet-light irradiation device) [mW/cm]÷insertion linear velocity [m/min] falls in the range between 8 and 18.

Description

  The present invention relates to a method for producing a plastic clad optical fiber.

  In Patent Document 1, etc., a glass fiber coated with an ultraviolet curable resin composition is inserted into an ultraviolet irradiation device (hereinafter also referred to as “UV furnace”), and the ultraviolet curable resin composition is cured by ultraviolet rays. The production of plastic clad optical fibers is described.

JP 2004-67421 A

In order to irradiate with sufficient ultraviolet rays to cure the ultraviolet curable resin composition for plastic clad layer formation, it is considered to increase the ultraviolet irradiation intensity of the ultraviolet irradiation device or to arrange a plurality of ultraviolet irradiation devices in series. It is done.
However, if a plurality of ultraviolet irradiation devices are arranged, the manufacturing equipment investment cost and the maintenance cost increase. In order to reduce the equipment cost and the maintenance cost, it is necessary to provide a compact manufacturing facility with a reduced number of ultraviolet irradiation devices. On the other hand, if the number of UV irradiation devices is reduced and the UV irradiation intensity is simply increased, the resin cures, but the short wavelength side in the wavelength band used for signal transmission of optical fibers, which is considered to be due to high intensity UV irradiation It was confirmed that the transmission loss increased. From the above, in the production of plastic clad optical fiber, no conditions have been found so far at a low cost that satisfies both sufficient curability of the plastic clad layer and transmission loss sufficient for practical use of the produced optical fiber. It was.

  The present invention has been made in view of the above problems in the production of a conventional plastic clad optical fiber. It is a low-cost, sufficient cured state of the plastic clad layer, and a transmission loss at a level sufficient for practical use. An object is to provide a method for manufacturing a fiber.

  As a result of intensive studies to achieve the above object, the present inventors have found that the relationship between the parameters relating to the ultraviolet irradiation intensity in the ultraviolet irradiation apparatus and the insertion speed to the ultraviolet irradiation apparatus is important, and the present invention has been completed. It came to do.

That is, the invention of the present application is
(1) A method for producing a plastic clad optical fiber having a core made of silica glass containing germanium and a clad made of resin,
Applying an ultraviolet curable resin composition for clad formation to the core;
Inserting the core coated with the ultraviolet curable resin composition through an ultraviolet irradiation device, and curing the ultraviolet curable resin composition with ultraviolet rays, and
This is a method for producing a plastic clad optical fiber in which each condition is set so that the UV dose value represented by the following formula is 8-18.
UV dose = Σ (leakage light from ultraviolet irradiation device) [mW / cm ² ] ÷ insertion speed [m / min]

  According to the present invention, it is possible to manufacture a plastic clad optical fiber having a sufficient level of transmission loss and a practically sufficient transmission loss at a low cost.

It is the schematic which shows an example of the manufacturing method of the plastic clad optical fiber which is one form of this invention. It is the schematic which shows another example of the manufacturing method of the plastic clad optical fiber which is one form of this invention. 5 is a graph showing a relationship between transmission loss, gel fraction of the clad, and UV dose in the method for producing a plastic clad optical fiber according to one embodiment of the present invention. It is a schematic cross section which shows one Embodiment of the plastic clad optical fiber manufactured by one form of this invention.

[Description of Embodiment of Present Invention]
One aspect of the present invention is (1) a method for producing a plastic clad optical fiber (hereinafter, also simply referred to as “optical fiber”) having a core made of silica glass containing germanium and a clad made of resin. Applying an ultraviolet curable resin composition for clad formation (hereinafter also simply referred to as “resin composition”) to the core, and inserting the core coated with the resin composition into an ultraviolet irradiation device, And curing the resin composition, and each condition is set so that the UV dose value represented by the following formula is 8-18.
UV dose = Σ (leakage light from ultraviolet irradiation device) [mW / cm ² ] ÷ insertion speed [m / min]

The transmission loss (hereinafter also simply referred to as “transmission loss”) of an optical signal having a wavelength of 850 nm, which is required for an optical fiber to be manufactured according to an embodiment of the present invention, is 10 dB / km or less. This is an example of a fiber loss budget on a typical interconnect cable.
Further, the gel fraction of the clad required for the optical fiber to be manufactured by the method according to one embodiment of the present invention is 95% or more. When the gel fraction is less than 95%, there is a problem that the residual resin component is transferred to the external material and the quality is changed.

The present inventors diligently studied to optimize the transmission loss of the optical fiber to be manufactured and the gel fraction of the clad as described above. The result is shown in the graph of FIG.
In the graph of FIG. 3, the horizontal axis represents the value of UV dose expressed by the above formula, the left vertical axis represents the transmission loss value of the manufactured optical fiber, and the right vertical axis represents the gel content of the clad of the manufactured optical fiber. The rate figures are shown respectively. In the graph of FIG. 3, the transmission loss is indicated by a solid line curve, and the gel fraction of the cladding is indicated by a broken line curve.
From the graph of FIG. 3, it can be seen that the UV dose needs to be 18 or less in order to reduce the transmission loss of the manufactured optical fiber to 10 dB / km or less. Further, it can be seen that the UV dose needs to be 8 or more in order to make the gel fraction of the clad of the manufactured optical fiber 95% or more.

Thus, it was found that it is appropriate that the UV dose represented by the above formula is in the range of 8-18.
When the UV dose is in the range of 8 to 18, the transmission loss of the manufactured optical fiber is 10 dB / km or less, and the gel fraction of the clad of the optical fiber is 95% or more.

  From the above, by setting the relationship between the leakage light from the ultraviolet irradiation device and the insertion line speed within a specific value range, sufficient curability of the plastic clad layer can be obtained at low cost and transmission loss is practical. A level optical fiber can be manufactured.

In addition, when the ultraviolet irradiation intensity at the time of plastic clad layer formation is enlarged, although the detail of the cause which the transmission loss of an optical fiber rises is unknown, it is thought that the glass fiber which is a core is a main factor. In particular, the increase in transmission loss with an optical signal having a wavelength of 1000 nm or more is large, and from the measurement of transmission loss on the short wavelength side, the possibility of oxygen deficiency defects in germanium-doped glass is considered.
Therefore, in the method for producing an optical fiber of the present invention, it is preferably used for a core made of silica glass containing germanium, which has been a main factor in increasing transmission loss, and has a remarkable effect.

(2) It is preferable that the resin composition further contains fluorine. The resin cladding of the manufactured optical fiber contains fluorine, and as a result, the refractive index difference between the core and the cladding of the optical fiber can be increased.
(3) The insertion line speed is preferably 30 to 100 m / min. By setting it as 30 m / min or more, the time for obtaining a fixed production amount can be shortened and manufacturing cost can be reduced. By setting the speed to 100 m / min or less, the cost of adding an ultraviolet irradiation device becomes unnecessary.
(4) Moreover, it is further preferable that the insertion line speed is 40 to 60 m / min. This condition is a condition that enables uniform and stable production in the longitudinal direction when taking into account fluctuations in the drawing speed during drawing.

[Details of the embodiment of the present invention]
(Outline of manufacturing method)
Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic view showing an example of a method for manufacturing an optical fiber according to one embodiment of the present invention.
In the drawing furnace 12 provided with the heater 13, the fed glass fiber preform 11 is heated and melted by the heater 13 and drawn. The drawn glass fiber 14 passes through the cooling cylinder 15 and reaches the resin composition coating device 16 where the resin composition is applied and primary coating is performed. The cooling cylinder 15 is provided at its lower end with an introduction pipe for introducing a cooling gas for cooling the glass fiber 14 in a high temperature state immediately after drawing. The glass fiber coated with the resin composition is irradiated with ultraviolet rays by the ultraviolet irradiation lamp 21 in the ultraviolet irradiation device 17, and the resin composition is cured and integrated into an optical fiber 18. The optical fiber 18 is wound up by a winding device 19.
The ultraviolet irradiation device 17 is a resin composition curing device that cures the resin composition coated on the glass fiber 14, and condenses the ultraviolet rays on the glass fiber 14 in addition to the ultraviolet irradiation lamp 21 inside the main body. Mirror (not shown).

And in the manufacturing method of the optical fiber which is one form of this invention, each condition is set so that the UV dose value represented by a following formula may be 8-18.
UV dose = Σ (leakage light from ultraviolet irradiation device) [mW / cm ² ] ÷ insertion line speed [m / min]

Here, the “leakage light from the ultraviolet irradiation device” in the above expression means the ultraviolet intensity measured in the ultraviolet irradiation device 17 near the insertion entrance of the glass fiber 14 or the insertion exit of the optical fiber 18. It is.
In the example of the manufacturing method shown in FIG. 1, an ultraviolet intensity detector 31 such as a light meter is provided near the insertion outlet of the ultraviolet irradiation device 17.

Further, “Σ (leakage light from the ultraviolet irradiation device)” means the sum of the “leakage light” of all the ultraviolet irradiation devices. In the example of the manufacturing method shown in FIG. 1, the number of the ultraviolet irradiation devices 17 is one. However, as another embodiment, a plurality of the ultraviolet irradiation devices 17 can be provided side by side. For example, FIG. 2 shows an example in which two ultraviolet irradiation devices 17 are provided side by side. In the example of the manufacturing method shown in FIG. 2, an ultraviolet intensity detecting unit 31 such as a light meter is provided in the vicinity of each insertion outlet of the two ultraviolet irradiation devices 17. The sum of the “leakage light” of each of the two ultraviolet irradiation devices 17 is “Σ (leakage light from the ultraviolet irradiation device)”.
Note that the number of the ultraviolet irradiation devices 17 to be installed is preferably smaller from the viewpoint of equipment cost. Specifically, the number of installation is one or two. When the UV intensity is insufficient with one, it is preferable to set the number of installations to two.
Even when the intensity of ultraviolet irradiation to the optical fiber in the ultraviolet irradiation apparatus cannot be measured due to the shape of the apparatus, etc., the leakage light from the apparatus increases as the ultraviolet irradiation intensity in the apparatus increases. It is assumed that.

  In the optical fiber manufacturing method according to one embodiment of the present invention, the manufacturing linear velocity is the same as the “insertion linear velocity” in the above formula for obtaining “UV dose”. The production linear speed (insertion linear speed) is not particularly limited as long as it is a speed range in which the “UV dose” value obtained by the above formula can be in the range of 8 to 18, but may be in the range of 30 to 100 m / min. preferable. If the linear velocity is 30 m / min or more, the production cost can be suppressed because the production efficiency is sufficient, which is preferable. If the linear velocity is 100 m / min or less, the number of UV furnaces used can be suppressed to two or less, and as a result, the equipment cost and the maintenance cost can be reduced, which is preferable. Further, the linear velocity is more preferably 40 to 60 m / min. It is more preferable that the linear velocity is 40 to 60 m / min, since it becomes a condition that enables uniform and stable production in the longitudinal direction when considering the linear velocity fluctuation during drawing.

  Moreover, as shown in FIG.1 and FIG.2, the detection information obtained by the ultraviolet intensity detection part 31 is transmitted to the control part 32, and the winding speed is controlled by the winding device 19 based on the detection information. The manufacturing linear velocity may be controlled to make the above “UV dose” appropriate.

  The core used in the optical fiber manufacturing method according to one embodiment of the present invention is silica glass containing germanium.

(Clad layer forming resin composition)
The resin composition for forming a resin clad used in the method for producing an optical fiber according to one aspect of the present invention is not particularly limited as long as it is cured by ultraviolet irradiation. Specifically, from (A) a fluorine atom-containing urethane (meth) acrylate compound, a (meth) acrylate compound having a fluorinated polyether in the structure, and a (meth) acrylated fluorine atom-containing vinyl polymer Containing at least one selected compound (hereinafter also referred to as a fluorine-based ultraviolet curable resin) and (B) 0.2 to 1% by mass of an alkoxysilane represented by the following general formula (1); What can make content 20-60 mass% is mentioned.

General formula (1) Z—R—Si (X) ₃

(In the formula, Z represents a (meth) acryl group, mercapto group or epoxy group, X represents —OCH ₃ or —OC ₂ H ₅ , and R represents C _n H _2n (n = 1, 2, 3, 4, 5).)

  The fluorine atom-containing urethane (meth) acrylate compound can be obtained, for example, by reacting a fluorine atom-containing (meth) acrylate compound with a diisocyanate compound. The fluorine atom-containing (meth) acrylate compound having a polyether in the molecular structure is obtained by, for example, reacting a fluorine atom-containing (meth) alcohol compound with a fluorine atom-containing (meth) acrylate compound or acrylic acid. be able to.

  In addition to the above compounds, the resin composition is usually used as a material for forming an optical fiber cladding, such as a polymerizable unsaturated monomer such as N-vinylcaprolactam, the following photopolymerization initiator, or various additives. Can be used.

  Furthermore, as the components other than the alkoxysilane in the resin composition, those having a refractive index of 1.401 to 1.450 when the resin composition in which the components other than the alkoxysilane are mixed are cured are used. Preferred (“component other than alkoxysilane” as used herein means a polymerizable compound, a photopolymerization initiator, a fluorine-based ultraviolet curable resin, or the like that is substantially involved in the formation of the clad (simply dissolved, etc.) It does not include volatile solvents that are only added)). It has been confirmed that a resin composition having a refractive index in this range achieves both excellent fiber strength and transmission characteristics (specifically, 1.401, 1.413, 1.430, 1.450). If the refractive index exceeds 1.450, the difference in refractive index from the core is small, which is not suitable for propagating an optical signal. Further, when the compatibility of the fluorine-based ultraviolet curable resin or the like, which is a main material constituting the alkoxysilane and the clad, is lowered, the resin constituting the clad becomes cloudy, which causes a reduction in transmission characteristics. In this resin composition, the refractive index of the resin composition in which components other than alkoxysilane are mixed is in the above numerical range, so that the phase of the fluorine-based ultraviolet resin, etc., which is the main material constituting the cladding, and the above alkoxysilane. The solubility is guaranteed.

  In the resin composition, 0.2 to 1% by mass of the alkoxysilane represented by the general formula (1) is contained in the resin composition. In the resin composition forming the clad, by containing the alkoxysilane represented by the general formula (1) in the above numerical range, the amount of decrease in the dynamic contact angle in the initial 1 second before the resin composition is cured is increased. it can. That is, since the resin composition and the core are compatible with each other in a short time, the adhesion between the formed clad and the core can be remarkably improved.

  Any known photopolymerization initiator may be used as the photopolymerization initiator in the resin composition, but it is required to have good storage stability after blending. Specific examples of such a photopolymerization initiator include 2-hydroxy-2-methyl-1-phenylpropan-1-one.

  The clad formed by curing the resin composition preferably has a fluorine content of 20 to 60% by mass.

In addition, the examination conditions at the time of obtaining the result shown in the graph of FIG. 3 are as follows.
UV furnace: Two I600M / VPS6 manufactured by Fusion were installed.
Core: A graded index (GI) co-appli foam made of silica to which germanium having a maximum refractive index difference of 1.1% was added was drawn to an outer diameter of 80 μm.
Clad: A resin composition having the following composition was used to form a thickness of 22.5 μm.

[Clad layer forming resin composition]
Fluorine atom-containing urethane (meth) acrylate compound 30% by mass
3-Acryloxypropylmethyltrimethoxysilane 0.36% by mass
Photopolymerization initiator LucirinTPO (BASF) 2% by mass
Acrylic acid 3.6% by mass
Multifunctional acrylic monomer (pentaerythritol tetramethacrylate)
40% by mass
Fluorine monomer (Biscoat 17F; 2-perfluorooctylethyl (meth) acrylate, manufactured by Osaka Organic Chemical Industry Co., Ltd.) 25% by mass

  The UV furnace, core, and clad used were as described above, and several types of plastic clad optical fibers were prepared by changing the UV dose by changing the irradiation ultraviolet intensity and linear velocity of the UV furnace. The transmission loss and the gel fraction of the clad were measured for several plastic clad optical fibers obtained. The relationship between UV dose, transmission loss, and gel fraction is shown in the graph of FIG.

(Optical fiber manufactured in an embodiment of the present invention)
One embodiment of an optical fiber manufactured in an embodiment of the present invention is shown in FIG. The optical fiber 18 has a clad 3 on the outer periphery of a core 2 made of, for example, quartz glass in which germania is added to pure silica or the like.
For example, the outer diameter of the core 2 can be 50 to 100 μm, and the thickness of the cladding 3 can be 12 to 38 μm (the outer diameter of the cladding 3 is 125 μm). In particular, when used for a home optical composite USB cable or an HDMI (registered trademark) cable, the outer diameter of the core 2 is set to 50 to 90 μm and the thickness of the cladding 3 is set to 17 in order to reduce the minimum allowable bending radius. It is preferable to make the diameter relatively small as ˜38 μm (the outer diameter of the clad 3 is 125 μm). The minimum allowable bending radius will be described in detail later.

Here, the n value can be used as a parameter for grasping the possibility of breakage when the optical fiber 18 is distorted by bending stress or the like. n value shows that it becomes hard to get tired with respect to distortion, so that it is large. For example, if the adhesion force at the interface with the core 2 is weak and the clad 3 is peeled off to form a hole, the n value becomes small, so that the possibility of breakage increases.
The n value required in the optical fiber 18 manufactured in the embodiment of the present invention varies depending on the application, but can be 23 to 36, for example.

The minimum allowable bending radius refers to the minimum bending radius that can be used. For example, the outer diameter of the core 2 that has been conventionally used for general purposes is 200 μm, and the outer diameter of the cladding 3 is 250 μm (the thickness of the cladding layer). Is 25 μm), the minimum allowable bending radius of the plastic clad optical fiber 1 is about 9 mm.
On the other hand, in the case of a home optical composite USB cable, etc., it may be used in a folded form. Therefore, it is required to be usable even when the cable is folded 180 degrees. It can be 2.5 mm or less. At this time, if the plastic 07-00758600 optical fiber 18 is thin (core 2 outer diameter: 50 to 100 μm, cladding 3 thickness: 12 to 38 μm (clad 3 outer diameter: 110 to 130 μm)), it is relatively easy. It is more preferable because the bending radius can be reduced.

In the case of such a small-diameter optical fiber 18, the n value can also be obtained by a 180-degree bending test in order to approach an actual usage pattern.
In the thin optical fiber 18 having a small minimum allowable bending radius, a larger n value may be required in this way, so that the adhesion force at the interface between the core 2 and the clad 3 is 1.5 g / mm˜ It is preferable to set it as 4.0 g / mm.

2 Core 3 Clad 11 Glass fiber preform 12 Drawing furnace 13 Carbon heater 14 Glass fiber 15 Cooling cylinder 16 Resin composition coating device 17 Ultraviolet irradiation device 18 Optical fiber 19 Winding device 21 Ultraviolet irradiation lamp 31 Ultraviolet intensity detector 32 Control Part

Claims (4)

A method for producing a plastic clad optical fiber having a core made of silica glass containing germanium and a clad made of resin,
Applying an ultraviolet curable resin composition for clad formation to the core;
Inserting the core coated with the ultraviolet curable resin composition through an ultraviolet irradiation device, and curing the ultraviolet curable resin composition with ultraviolet rays,
A method for producing a plastic clad optical fiber, wherein each condition is set so that a UV dose value represented by the following formula is 8-18.
UV dose = Σ (leakage light from the ultraviolet irradiation device) [mW / cm ² ] ÷ insertion speed [m / min]   The method for producing a plastic clad optical fiber according to claim 1, wherein fluorine is contained in the ultraviolet curable resin composition.   The method for producing a plastic-clad optical fiber according to claim 1 or 2, wherein the insertion line speed is 30 to 100 m / min.   The method for producing a plastic-clad optical fiber according to claim 3, wherein the insertion line speed is 40 to 60 m / min.

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