JP2005350310A - Method of manufacturing optical fiber strand - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber strand by which the optical fiber strand having desired curing degree in a plurality of parts each different in depth is efficiently manufactured. <P>SOLUTION: The manufacturing method is for the optical fiber strand 24 having an outermost layer 3 comprising an ultraviolet-setting resin and formed on the outer periphery of the optical fiber strand 24. The plurality of curing degrees in the parts each different in depth from the surface of the outermost layer 3 are measured and the curing condition of the outermost layer is controlled so that each of the plurality of curing degrees has a prescribed value. The plurality of curing degrees in the parts each different in depth are measured by irradiating the outermost layer 3 with infrared light through a transparent substrate 23 to measure the absorption spectrum of the infrared light reflected in the vicinity of the surface of the outermost layer 3 and repeating the measurement of the absorption spectrum in every one of the plurality of transparent substrates 23 each comprising different material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing an optical fiber.

  In general, an optical fiber is one in which two resin layers called a primary layer and a secondary layer are formed on the outer periphery of a glass fiber. As a material for the resin layer of the optical fiber, an ultraviolet curable resin (hereinafter sometimes referred to as UV resin) is often used, and a liquid UV resin composition is provided on the outer periphery of the glass fiber after the drawing process. The glass fiber coated with the UV resin composition is irradiated with ultraviolet rays to cure the UV resin.

  As a method for evaluating the curing characteristics of the UV resin, for example, a total reflection absorption measurement method (hereinafter referred to as ATR (Attenuated Total Reflection) method) using FT-IR (Fourier Transform Infrared Spectrophotometer). Can be done. An example of an apparatus for evaluating resin curing characteristics by the ATR method is shown in FIG. 6 (see Patent Document 1).

  In the apparatus shown in FIG. 6, two inspection lights in the infrared region are emitted from the light source 101 under the same conditions, one inspection light is guided to the measurement sample chamber 102, and the other inspection light is guided to the reference sample chamber 103. It is burned. In the measurement sample chamber 102, a sample 110 is arranged in which a UV resin 112, which is an object to be measured, is formed in a thin film on a substrate 111 made of a material that reflects infrared rays. The light intensity of the inspection light transmitted through 112 and reflected by the substrate 111 is measured by the first photodetector 104.

The reference sample chamber 103 is set under the same conditions as in the measurement sample chamber 102 except that the thin film of the UV resin 112 is not formed on the substrate 111, and the substrate 111 in the reference sample chamber 103 is set. The second light detector 105 measures the light intensity of the inspection light reflected by.
The computer system 106 controls the light source 101 and processes data of the light intensity measured by the first and second photodetectors 104 and 105 by a predetermined calculation processing method set in advance. Thereby, an infrared absorption spectrum by the UV resin 112 can be obtained.
JP 2000-55806 A

  By the way, when manufacturing an optical fiber, oxygen may enter into the manufacturing apparatus, whereby the outermost layer (secondary layer) of the optical fiber may be insufficiently cured. For example, when the oxygen concentration in the UV curing furnace of the optical fiber is increased, the degree of curing of the outermost ultraviolet curable resin is decreased. If the outermost layer of the optical fiber is not sufficiently hardened, there is a quality problem that the optical fibers are fused when wound on a bobbin or the like, or the surface of the optical fiber is white. It is expected that such a problem will occur or the transmission characteristics of the optical fiber will deteriorate. On the other hand, even if the outermost layer of the optical fiber is hardened too much, if a separate colored layer is provided on the outermost layer, the colored layer is easily peeled off or the transmission characteristics of the optical fiber are deteriorated. is expected.

  In order to solve this problem, prior to the production of the optical fiber, the curing property of the UV resin used for the outermost layer was measured using the curing property evaluation method for the UV resin described in Patent Document 1 above, and the measured UV resin was measured. It is also possible to adjust the manufacturing conditions of the optical fiber by predicting the degree of curing of the outermost layer of the actual optical fiber based on the curing characteristics of the optical fiber. However, even if the degree of cure of the resin layer of the optical fiber strand is predicted in advance, the degree of cure of the surface of the actually produced optical fiber strand may be different from the predicted value. It is difficult to set the manufacturing conditions of the wire accurately.

  Moreover, as the curing characteristics of the UV resin of the outermost layer, even if the degree of curing at a specific depth from the surface is the same as the predicted value, it may not match the predicted value at other depths. In other words, even if the degree of cure at a specific depth matches the predicted value and there is no problem, the situation described above may occur due to insufficient curing or excessive curing at different depths. is there.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical fiber manufacturing method capable of efficiently manufacturing an optical fiber having a desired degree of curing.

  An optical fiber manufacturing method according to the present invention is an optical fiber manufacturing method in which an outermost layer made of an ultraviolet curable resin is formed on the outer periphery of an optical fiber, and a plurality of depths from the surface of the outermost layer are different. The degree of curing is measured, and the conditions for curing the outermost layer are adjusted so that the plurality of degrees of curing each have a predetermined value.

  The method for manufacturing an optical fiber according to the present invention uses a method of irradiating the outermost layer with infrared rays through a transparent substrate and measuring an absorption spectrum of infrared rays reflected near the surface of the outermost layer. It is preferable to measure the plurality of curing degrees by repeating the spectrum measurement for each of the plurality of transparent substrates made of different materials.

  In the method for manufacturing an optical fiber according to the present invention, it is preferable to use a substrate made of ZnSe and a substrate made of Ge as the plurality of transparent substrates.

  According to the method for manufacturing an optical fiber according to the present invention, a plurality of degrees of curing at different depths from the surface of the outermost layer of the optical fiber are measured, and the plurality of degrees of curing each have a predetermined value. By adjusting the curing conditions of the outermost layer, it is possible to accurately carry out the optimization of the manufacturing conditions in the production of the optical fiber, and each of the optical fiber elements having a desired degree of curing at different depths. A wire can be manufactured efficiently.

Hereinafter, an embodiment of a method for manufacturing an optical fiber according to the present invention will be described in detail with reference to the drawings.
First, a cross-sectional view of the optical fiber 24 manufactured by the manufacturing method according to the present embodiment is shown in FIG. As shown in FIG. 1C, the optical fiber 24 has a glass fiber 1 at the center, and a primary layer 2 is provided on the outer periphery of the glass fiber 1. (Outermost layer) 3 is provided. The primary layer 2 and the secondary layer 3 are formed by applying an ultraviolet curable resin composition to the outer periphery of the glass fiber 1 and curing it by irradiating with ultraviolet rays. Here, as the ultraviolet curable resin used for the primary layer 2 and the secondary layer 3, urethane acrylate ultraviolet curable resin, silicon acrylate resin, epoxy acrylate resin, polyester acrylate resin, or the like can be used.

  Next, a method for manufacturing the optical fiber 24 according to this embodiment will be described with reference to FIG. A manufacturing apparatus 30 shown in FIG. 3 is an apparatus that can manufacture the optical fiber 24 including the primary layer 2 and the secondary layer 3 shown in FIG. The manufacturing apparatus 30 includes a drawing furnace 32, and a cooling device 33, a coating device 34 a, a curing device 35 a, a coating device 34 b, a curing device 35 b, and a winder 36 are mainly provided downstream of the drawing furnace 32. It is provided as a configuration.

  In order to manufacture an optical fiber using the manufacturing apparatus 30 shown in FIG. 3, an optical fiber preform 31 is heated and melted by a drawing furnace 32, and a capstan (not shown) is formed from the lower end of the heated optical fiber preform 31. The optical fiber 37 is formed by reducing the diameter to a predetermined outer diameter while being pulled by a method such as Then, after cooling the optical fiber 37 with the cooling device 33, the coating device 34a applies the ultraviolet curable resin composition to the optical fiber 37, and the curing device 35a irradiates the ultraviolet light to cure the ultraviolet curable resin. A primary layer is formed at 37. Further, the ultraviolet curable resin composition is applied to the optical fiber 38 on which the primary layer 2 (FIG. 1) is formed by the coating device 34b, and the ultraviolet curable resin is cured by irradiating the ultraviolet light by the curing device 35b. 1) is formed. Finally, the optical fiber 24 coated with the two layers of ultraviolet curable resin is wound up by a winder 36.

  Here, the structure inside the curing device 35b will be described with reference to FIGS. 4A shows a longitudinal sectional view of the curing device 35b, and FIG. 4B shows a transverse sectional view of the curing device 35b. As shown in FIGS. 4A and 4B, a quartz tube 42 through which an optical fiber passes is provided inside the curing device 35b, and ultraviolet rays are irradiated in parallel with the longitudinal direction of the quartz tube 42. A cylindrical ultraviolet bulb 44 is arranged. A reflection mirror 43 (FIG. 4B) is disposed around the quartz tube 42 and the ultraviolet bulb 44 so as to surround them. The reflection mirror 43 has an elliptical cross section, and the quartz tube 42 and the ultraviolet bulb 44 are arranged so as to be positioned at the focal point of the reflection mirror 43. The ultraviolet rays emitted from the ultraviolet bulb 44 are reflected by the reflection mirror 43 and are efficiently emitted to the quartz tube 42.

An inlet cover 45 and an outlet cover 46 are respectively provided at the upper end opening and the lower end opening of the quartz tube 42, and the optical fiber 38 enters the quartz tube 42 from the inlet 45 a of the inlet cover 45, and enters the inside of the quartz tube 42. After passing, it goes out of the curing device 35 from the outlet 46a of the outlet cover 46. Airtight packings 48 and 49 are respectively provided between the inlet cover 45 and the outlet cover 46 and the quartz tube 42, and the airtightness inside the quartz tube 42 is maintained by the airtight packings 48 and 49.
Further, a gas introduction port 47 is provided on the side surface of the inlet cover 45, and purge gas is blown immediately above the upper end opening of the quartz tube 42 so as to fill the purge gas inside the quartz tube 42. The inflow amount of the purge gas introduced into the quartz tube 42 is detected by the flow meter 50, and the inflow amount of the purge gas is adjusted by the flow rate controller 51. As the purge gas, for example, nitrogen gas can be used.

  In the manufacturing method according to the present embodiment, several optical fiber strands manufactured in this way are cut out, and a plurality of degrees of curing at different depths are measured in the outermost layer 3 of the optical fiber strand 24. The ATR method is preferably used as a method for measuring the degree of cure of the outermost layer 3. That is, it is preferable to measure the degree of cure of the outermost layer by irradiating the outermost layer with infrared rays through a transparent substrate and measuring the infrared absorbance reflected on the surface of the outermost layer.

  Hereinafter, as an example, a method for measuring the degree of cure of the outermost layer using the ATR method will be described with reference to FIGS. FIG. 1A is a schematic configuration diagram showing an example of an infrared spectroscopic analyzer 20 based on the ATR method. As shown in FIG. 1A, the infrared spectroscopic analyzer 20 includes a light source 21 and a measurement sample chamber 22. The light source 21 is a device that emits inspection light 28 in the infrared region, and is arranged such that the inspection light 28 emitted from the light source 21 is emitted toward the measurement sample chamber 22.

A sample 26 is arranged inside the measurement sample chamber 22, and the sample 26 includes a transparent substrate 23 and an optical fiber 24. In addition, the infrared spectroscopic analyzer 20 includes a detector 27 that detects infrared rays by detecting infrared rays so that the detector 27 can detect the reflected light 29 reflected in the measurement sample chamber 22. Has been placed. Further, a data analysis unit 25 is connected to the detector 27.
As shown in FIG. 1B, the sample 26 is formed by arranging a plurality of optical fiber strands 24 cut to a predetermined length on the lower surface of the transparent substrate 23. The plurality of optical fiber strands 24 are arranged in parallel so that the optical fiber strands 24 are in close contact with each other.

  In order to obtain an infrared absorption spectrum of the outermost layer (secondary layer) of the optical fiber using the infrared spectroscopic analyzer 20, first, the inspection light 28 is incident from the light source 21 into the measurement sample chamber 22. At this time, the incident angle is adjusted so that total reflection occurs at the boundary surface between the transparent substrate 23 of the sample 26 and the outermost layer of the optical fiber 24. The inspection light 28 enters the outermost layer of the optical fiber 24 slightly by a predetermined depth and then totally reflects (hereinafter, the depth at which the inspection light 28 enters the outermost layer is referred to as “penetration depth”). ) The totally reflected reflected light 29 is detected by the detector 27, and the infrared absorbance of the reflected light 29 is measured by the detector 27. Infrared absorbance data is transmitted from the detector 27 to the data analysis unit 25, and the data analysis unit 25 obtains an infrared absorption spectrum on the outermost layer surface of the optical fiber 24 by Fourier transform.

Further, a plurality of crystal substrates are used as the transparent substrate 23 for the same optical fiber 24 and the above operation is repeated to obtain an infrared absorption spectrum for each of the plurality of crystal substrates.
As the plurality of crystal substrates, a substrate having a large refractive index is preferably used, and a substrate made of ZnSe (zinc selenide) and a substrate made of Ge (germanium) are more preferably used. The substrate made of ZnSe has a penetration depth of 5 μm, and can measure the degree of cure on the relatively outermost layer. The substrate made of Ge has a penetration depth of 0.3 to 1.8 μm, and the degree of cure of the extreme surface layer can be measured.

  In this way, the degree of cure of the outermost layer of the optical fiber can be measured, and by using a plurality of crystal substrates, the degree of cure of portions having different penetration depths from the outermost layer surface can be measured. Therefore, the degree of cure from the outermost layer surface to a desired depth can be measured. Therefore, the curing characteristics of the outermost layer surface of the optical fiber can be measured in detail.

From the infrared absorption spectrum of the outermost layer of the optical fiber measured by the infrared spectroscopic analyzer 20, the curing characteristics of the outermost layer can be further quantitatively evaluated. A method for quantitatively evaluating the curing characteristics of the outermost layer will be described with reference to FIGS. 2 (A) and 2 (B). 2A and 2B are diagrams schematically showing an infrared absorption spectrum obtained by the infrared spectroscopic analyzer 20 (FIG. 1), in which the horizontal axis indicates the wave number and the vertical axis indicates the infrared absorbance. Yes.
In general, when comparing infrared absorption spectra before and after curing an ultraviolet curable resin, as shown in FIG. 2A, a peak (Pc) where the peak intensity does not change before and after curing and a peak where the peak intensity changes due to curing ( Pd) appears. The change in the peak intensity due to curing at the peak (Pd) is considered to occur because the molecular structure is changed by a curing reaction such as a polymerization reaction or a crosslinking reaction (for example, a decrease in double bonds between carbons in the resin). In the method for measuring the degree of cure according to the present embodiment, the ratio of the peak intensity (pd) in Pd to the peak intensity (pc) in Pc using Pc as a reference peak using the change in the infrared absorption spectrum due to the change in the molecular structure. That is, by determining the peak intensity ratio (pd / pc), the degree of cure of the outermost layer of the optical fiber can be quantitatively measured.

For example, when a urethane acrylate ultraviolet curable resin is used as the ultraviolet curable resin for forming the outermost layer, the infrared absorption spectrum obtained by the infrared spectroscopic analyzer 20 is involved in the degree of cure at a wave number of about 775 cm ^−1. Peak (Pc) appears. In addition, a peak (Pd) due to an acrylic double bond appears in the vicinity of a wave number of 810 cm ⁻¹ , which is related to the degree of curing. From the intensity (pc) of the peak not related to curing near 775 cm ⁻¹ and the intensity (pd) of the peak due to the acrylic double bond near 810 cm ⁻¹ , the ratio of peak intensity at both wave numbers (pd / pc) is obtained. Can be calculated.
Further, in the case of this urethane acrylate ultraviolet curable resin, acrylic double bonds are reduced by a curing reaction by ultraviolet irradiation, and accordingly, the intensity of the peak due to the acrylic double bonds in the vicinity of 810 cm ⁻¹ is reduced. Therefore, the intensity of the peak due to the acrylic double bonds in the vicinity of the 810 cm ^-1 (pd), the ratio of the intensities of the peaks that do not participate in the curing reaction around ^{775cm -1 (pc) (pd /} pc) , the curing of the resin As the value proceeds, the value decreases.

  When the degree of curing is measured quantitatively as described above, the peak area ratio may be obtained by obtaining a peak area from an infrared absorption spectrum instead of the peak intensity ratio (pd / pc). That is, as shown in FIG. 2B, the peak area (Ac) of the peak (Pc) where the intensity does not change before and after curing and the peak area (Ad) of the peak (Pd) where the intensity changes due to curing are obtained. Similarly, by using Pc as a reference peak, the ratio of the peak intensity (Ad) in Pd to the peak area (Ac) in Pc, that is, the peak area ratio (Ad / Ac) is also quantitatively determined. Can be evaluated.

Different infrared absorption spectra can be obtained according to the penetration depth of the transparent substrate, and the peak intensity ratio or peak area ratio can be calculated from the different absorption spectra respectively, so that the different depths from the outermost layer surface can be cured quantitatively The degree can be measured.
As described above, the degree of cure of the outermost layer can be quantitatively determined from the infrared absorption spectrum of the outermost layer of the optical fiber. In the manufacturing method according to the present embodiment, the manufacturing conditions are adjusted according to the data of the degree of cure of the outermost layer.

  More specifically, when it is determined that overcuring or curing is insufficient from the degree of curing of the outermost layer, the manufacturing conditions in the manufacturing apparatus 30 shown in FIG. 3 are adjusted. As a specific means for adjusting the manufacturing conditions, in particular, since the oxygen concentration in the quartz tube 42 in the curing device 35b greatly affects the degree of curing of the optical fiber, the amount of purge gas inflow in the curing device 35b is adjusted. Thus, the oxygen concentration in the quartz tube 42 can be adjusted.

For example, when it is determined that the outermost layer surface is insufficiently cured as a result of the measurement by the method for measuring the degree of curing of the optical fiber, the amount of purge gas flowing into the quartz tube 42 of the curing device 35b is increased. Thus, the oxygen concentration can be reduced, and the degree of cure of the outermost layer surface can be increased. On the other hand, if it is determined that the outermost layer surface is overcured, the amount of purge gas flowing into the quartz tube 42 of the curing device 35b can be decreased to increase the oxygen concentration, and the degree of curing of the outermost layer surface can be decreased. Thus, by adjusting the oxygen concentration in the quartz tube 42 of the curing device 35b on the surface of the outermost layer, the process for optimizing the manufacturing conditions can be performed accurately.
In addition, as means for adjusting the manufacturing conditions for setting the degree of curing of the outermost layer of the optical fiber to a desired range, members in the curing device 35b such as airtight packings 48 and 49, an ultraviolet bulb, a reflection mirror plate, etc. It is possible to use means such as exchanging the light, changing the ultraviolet irradiation time by the ultraviolet bulb 44, and adjusting the power volume of the ultraviolet intensity.

  As described above, according to the manufacturing method of the present invention, measuring a plurality of curing degrees with different depths of the outermost layer, and adjusting the curing conditions of the outermost layer so that the plurality of curing degrees each have a predetermined value. Therefore, even if the degree of cure differs for each depth, the measurement results for each degree of cure can be fed back when actually manufacturing the optical fiber, so the process for optimizing the production conditions can be accurately performed. Therefore, it is possible to efficiently manufacture an optical fiber having a desired degree of curing at a plurality of different depths.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the scope of the present invention is not limited to the following examples.
1. Manufacture of an optical fiber strand An optical fiber strand was manufactured using the optical fiber manufacturing apparatus shown in FIG. As the UV curable resin for the secondary layer, a hard urethane acrylate UV curable resin having a Young's modulus of about 70 kg / mm ² was used.
At the time of manufacturing the optical fiber, the amount of nitrogen gas introduced into the curing device 35b is adjusted by using nitrogen gas as the purge gas in the curing device 35b, and the oxygen concentration in the quartz tube 42 is set to 0.01 to 5%. Enabled to adjust by range. The winding speed (linear speed) was 500 to 1000 m / min.

2. Measurement of degree of cure of optical fiber strand For the optical fiber strand manufactured as described above, a ZnSe transparent substrate and a Ge transparent substrate are used in the infrared spectroscopic analyzer 20 shown in FIG. 1, and the peak area ratio (Ac / Ad) is measured. ) Was measured. The result is shown in FIG. In the graph shown in FIG. 5, the peak area ratio (Ad / Ac) measured using a ZnSe transparent substrate is plotted on the horizontal axis, and the peak area ratio (Ad / Ac) measured using a Ge transparent substrate is plotted on the vertical axis. It is a result.

From the graph shown in FIG. 5, areas A to I were determined as shown in Table 1. In Table 1, the peak area ratio (Ad / Ac) measured with a ZnSe substrate is A _ZnSe, and the peak area ratio (Ad / Ac) measured with a Ge substrate is A _Ge .

3. Adjustment of manufacturing conditions of optical fiber strand Using this result, the degree of cure of the outermost layer of the regularly manufactured optical fiber strand was measured to inspect which area among the above A to I. And when it entered into the area of B-E and I, the subsequent manufacturing conditions were changed as follows.
When entering the area B: Lower the light intensity adjustment volume of the UV furnace to lower the light intensity.
When entering the area C: Lower the light intensity adjustment volume of the UV furnace to lower the light intensity. In addition, the N ₂ gas purge amount introduced into the UV furnace is increased to lower the O ₂ concentration from 1% to 0.1% or less.
When entering the area of D: Decrease the light intensity adjustment volume of the UV furnace to lower the light intensity. In addition, the N ₂ gas purge amount introduced into the UV furnace is increased to lower the O ₂ concentration from 2% to 0.1% or less.
When entering the area E: The N ₂ gas purge amount introduced into the UV furnace is increased, and the O ₂ concentration is decreased from 1-2% to 0.1% or less.
When entering the area I: Increase the light intensity adjustment volume of the UV furnace to increase the light intensity.
In addition, when entering the F, G, and H areas, the resin design is changed.
By manufacturing the optical fiber while performing the above operation, it was possible to efficiently manufacture a good optical fiber having a curing degree in the above range.

It is a schematic block diagram which shows an example of the infrared spectroscopy analyzer used suitably for the manufacturing method of this invention. (A) And (B) is the figure which showed typically the infrared absorption spectrum obtained by the infrared spectroscopy analyzer shown in FIG. It is a schematic block diagram which shows an example of the manufacturing apparatus used suitably for the manufacturing method of the optical fiber which concerns on this invention. It is a schematic block diagram which shows the hardening apparatus 35b shown in FIG. It is a figure which shows the relationship between the peak area ratio (Ad / Ac) measured using the ZnSe substrate, and the peak area ratio (Ad / Ac) measured using the Ge substrate. It is the schematic block diagram which showed the apparatus which evaluates the resin hardening characteristic by the conventional ATR method.

Explanation of symbols

3 Secondary layer (outermost layer)
23 Transparent substrate 24 Optical fiber

Claims (3)

A method of manufacturing an optical fiber in which an outermost layer made of an ultraviolet curable resin is formed on an outer periphery of an optical fiber, wherein a plurality of degrees of curing at different depths from the surface of the outermost layer are measured, and the plurality of degrees of curing are A method of manufacturing an optical fiber, wherein the conditions for curing the outermost layer are adjusted so that each has a predetermined value. Using the method of irradiating the outermost layer with infrared rays through a transparent substrate and measuring the absorption spectrum of infrared rays reflected near the surface of the outermost layer, the absorption spectrum is measured for each of a plurality of transparent substrates of different materials. The method of manufacturing an optical fiber according to claim 1, wherein the plurality of curing degrees are measured by repeating. The method for manufacturing an optical fiber according to claim 2, wherein a substrate made of ZnSe and a substrate made of Ge are used as the plurality of transparent substrates.

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