JP2010134038A - Recoating method of optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recoating method for preventing the occurrence of uneven thickness while preventing mixture of bubbles into a resin coat, for uniforming the thickness of the resin coat and for suppressing the occurrence of peeling of the resin coat even when a high-temperature/high-humidity test is performed. <P>SOLUTION: In the recoating method of an optical fiber having structure obtained by applying a coating material to the outer periphery of a bare fiber, a photo curing resin or heat curing resin with a viscosity range of 1 to 6 Pa s is applied to a bare fiber part of an optical fiber obtained after removing the coating material and fusion-connecting both bare fibers and the applied resin is photo-cured or thermally cured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical fiber recoating method in which a bare fiber portion after fusion splicing is coated with a resin to form a resin protective material for the bare fiber.

In general, it is known to provide a protective layer of a resin in order to protect the optical fiber from external stress at the connection position of the optical fiber after the fusion splicing. As a typical protective layer, a protective layer using a heat-shrinkable tube is known. In addition to the protective layer using the heat-shrinkable tube, a technique (recoating method) is also known in which a necessary portion of a bare fiber (uncoated optical fiber) is coated and recoated with resin.
The optical fiber recoating method is roughly classified into two methods, a die method and a molding method. In general, a recoating material for an optical fiber uses an ultraviolet curable resin (UV curable resin) or a thermosetting resin.

The above-mentioned dice method is to set the connection part of the bare fiber after the fusion splicing to the recoating die, and move the die to which the UV curable resin liquid is supplied to the part that becomes the bare fiber. This is a method of applying a UV curable resin liquid and curing the applied UV curable resin liquid by irradiating the portion with ultraviolet rays with an ultraviolet lamp. Further, when a thermosetting resin is used in the die method, the thermosetting resin is cured by warm air or a heater.
The molding method is performed using glass or the like which is a material that transmits ultraviolet rays. The optical fiber after fusion splicing is sandwiched between two glass plates that have been processed so that the optical fiber can be recoated, and a UV curable resin liquid is poured into a portion that is a bare fiber while being sandwiched, This is a method of curing the applied UV curable resin liquid by irradiating the portion with ultraviolet rays using an ultraviolet lamp. Further, when a thermosetting resin is used in the molding method, the thermosetting resin is cured by warm air or a heater.

Conventionally, as an example of a recoating apparatus used in this type of recoating method, an upper mold, a lower mold, and a light source are provided, and a light transmitting material is used for the mold on the light source side of each of the upper and lower molds. A semi-cylindrical mold groove is provided, a cylindrical space is formed by the mold groove by contacting the opposite surface, and a photo-curing resin injection port is provided so as to communicate with the mold groove, and the resin is placed in the space. There is known an apparatus for recoating the strip portion of an optical fiber by injecting and curing. (See Patent Document 1)
In this type of recoating apparatus, a resin retaining part for retaining the resin liquid for recoating is connected to the injection port, the resin retaining part is heated with a heater, and the resin liquid is removed from the injection port in a cylindrical shape with air bubbles removed. A recoating apparatus configured to be injected into a space and coated with a resin is disclosed.

According to the technique described in Patent Document 1, if the viscosity of the resin liquid injected through the injection port is defined in the range of 0.5 Pa · s to 1.2 Pa · s, bubbles are generated. It is described that since it is not necessary to heat each time a resin having a high viscosity is injected, the efficiency of the optical fiber recoating process and the reduction of heat consumption can be achieved.
JP 2006-178101 A

In the technique described in Patent Document 1, the viscosity of the resin liquid is defined in the range of 0.5 Pa · s to 1.2 Pa · s, and the resin liquid is heated in the resin reservoir to eliminate bubbles. Thus, it is thought that the mixing of bubbles can be avoided, but the reliability of the recoated portion of the optical fiber is not determined only by the presence or absence of mixing of bubbles.
For example, in general, the coating material of an optical fiber contracts or expands due to a temperature change, and it is known that the stress generated by the contraction or expansion affects the optical fiber and causes a characteristic defect such as microbend loss. ing. In addition, when the coating of the optical fiber is biased, nonuniform stress in the radial direction is applied to the optical fiber from the coating, so that it is clear that the characteristics and reliability are lowered. Therefore, it is preferable that the coating material of the optical fiber has a uniform thickness in the radial direction. In the present invention, when the coating material is not uniform in the radial direction of the optical fiber, this is referred to as uneven thickness.

The uneven thickness is the ratio of the thickness of the thickest portion of the coating material of the optical fiber to the thinnest portion of the coating. For example, assuming a structure in which the optical fiber 100 is covered with a resin coating layer 101 when the cross-sectional structure of the optical fiber is viewed as shown in FIG. 3, the thickness of the thick portion of the coating layer 101 is denoted as A, When the thickness of the thin portion of the layer 101 is expressed as B, the uneven thickness is expressed by A / B. An optical fiber usually has a core and a clad, and has various cross-sectional structures depending on its function and purpose. In FIG. 3, only a contour is shown as a substantially circular cross section, and the covering layer 101 is also the most. Only the outline is shown as a simple circular approximate cross section.
However, in the technique described in the above-mentioned Patent Document 1, there is no description regarding uneven thickness, and no recoating method considering microbendros caused by uneven thickness and countermeasures are taken into consideration.
Various environmental tests are known as methods for checking the reliability of the optical fiber 100. In the environmental test, an accelerated deterioration test is known in which a sample is allowed to stand under high temperature and high humidity conditions of, for example, 85 ° C. and a relative humidity of 85% to promote thermal deterioration and hydrolysis deterioration. This accelerated deterioration test is an effective method for grasping the reliability of the recoating part. For example, the peeling of the recoating part (the state where the optical fiber and the resin coating material after the recoating are not in close contact) is investigated. Is possible. In general, when the resin coating material is peeled off after recoating, the protection of the optical fiber is insufficient, and the bare fiber of the optical fiber is partially exposed, and there is a concern that the optical fiber may be disconnected. Therefore, it is clear that the resin coating material at the recoating part does not peel off in the high temperature and high humidity test in terms of the reliability of the optical fiber. However, the above-mentioned Patent Document 1 does not disclose any test result at high temperature and high humidity or any countermeasures against peeling.

The present invention has been made in view of the above circumstances, while preventing foam from being mixed into the resin coating, there is no uneven thickness, the thickness of the resin coating is uniform, and a high temperature and high humidity test is performed. An object of the present invention is to provide a recoating method in which peeling of a resin coating material hardly occurs.
That is, the present invention has arrived at the present invention by finding good ranges for the above-mentioned uneven thickness state, thickness uniformity of the resin coating material, and the three characteristics of the high temperature and high humidity resistance test.

The present invention is a method of recoating an optical fiber having a structure in which a coating material is provided on the outer periphery of the bare fiber, and the coating material is removed and the bare fiber portion of the optical fiber after fusion bonding of the bare fibers is 1 A photo-curing resin liquid or a thermosetting resin liquid having a viscosity range of ˜6 Pa · s is applied and photo-cured or thermo-cured.
In the present invention, when a resin liquid is applied to the bare fiber portion, the bare fiber portion is passed through a die having a die hole and a liquid reservoir, and the bare fiber portion is pulled out through the die hole, thereby The resin liquid stored in the liquid reservoir is applied to the periphery of the bare fiber portion, and then the applied resin liquid is cured and recoated as a resin coating material.

  According to the present invention, when performing recoating of an optical fiber, by using a resin liquid having a viscosity in the range of 1 to 6 Pa · s, there is no entrainment of bubbles and excellent adhesion in a state where uneven thickness is suppressed. A covering material can be formed.

Hereinafter, embodiments of the present invention will be described in detail.
In the present invention, in a structure of an optical fiber in which a bare fiber having a structure having a core and a clad is covered with a resin coating material, a part of the coating material at the end of the optical fiber to be connected is removed to remove the bare fiber. When the bare fiber ends are fusion spliced together and the bare part of the surrounding bare fiber is recoated with resin, the viscosity of the photocurable liquid resin or thermosetting resin liquid The resin solution of 1 to 6 Pa · s is applied to the exposed portion, and the applied resin solution is light-cured or heat-cured and covered with a coating material for recoating.
When the resin liquid is within the range of viscosity 1 to 6 Pa · s, bubbles are not mixed into the applied resin liquid, and uneven thickness of the resin coating formed around the bare fiber is suppressed. And peeling of the resin coating material can be suppressed. Furthermore, the viscosity of the resin liquid is more preferably in the range of 1.5 to 6 Pa · s.

  When the viscosity of the resin liquid becomes higher than the above range, when the resin liquid is applied to the fused portion of the bare fiber and the periphery thereof, air is blown when the resin liquid hits the end surface of the covering material already covering the bare fiber. The risk of entrainment as bubbles increases. On the contrary, when the viscosity of the resin liquid is lower than the above range, the resin liquid easily flows vertically downward due to the influence of gravity when the resin liquid is poured around the bare fiber. Since the thickness of the coating material on the lower side of the bare fiber tends to be large, and this tends to cause uneven thickness, a lower limit of the viscosity of the resin liquid is set to suppress this uneven thickness. . Also, if the viscosity of the resin liquid is too low, a thin portion of the coating material occurs due to uneven thickness, so when the coating material shrinks after recoating, the glass portion such as the cladding portion of the optical fiber outer periphery and the coating material Therefore, the lower limit of the viscosity of the resin liquid was defined.

Next, an example of a dice apparatus used for the dice method when recoating using a resin liquid having the above viscosity range will be described.
FIG. 1 shows an example of a dice apparatus used in the dice method. A dice apparatus A of this example has a dice body 2 having a funnel-shaped liquid reservoir 1 on the upper side. A die hole 3 penetrating the bottom side of the die body 2 from the lower part of the liquid reservoir 1 is formed.
In order to recoat the optical fiber by carrying out the dicing method using the dice apparatus A, first, the optical fiber 6 having the coating removal portion 5 from which the coating material 4 is partially removed is clamped by the clamps 7 and 7 installed up and down. Hold in the vertical direction (vertical direction). As an example of this coating removal part 5, the structure which removed the coating | coated material of the edge parts of the optical fiber which should be connected, and fused the bare fibers can be illustrated. In addition, the bare fiber used in this embodiment is a main body portion of an optical fiber having at least a core portion and a clad portion, and is usually made of a glass member. There are various types of optical fibers according to their functions and performance, and various types of optical fibers including structural elements other than the core and the clad are also provided. Of course, the present invention can be applied to the present invention.

Next, in this state, the recoating dice apparatus A is set in the coating removal portion 5, and the resin curing means 8 for setting, for example, irradiation with UV light or heating is set below the recoating die apparatus A. Thereafter, an operation of pulling up the dice apparatus A is performed while supplying a molten resin liquid (for example, UV resin liquid) 9 to the liquid reservoir 1 of the dice apparatus A.
Here, if the inner diameter of the die hole 3 is set to be equal to or slightly larger than the outer diameter of the covering material 4, the recoat coating layer 10 having an outer diameter substantially equal to the outer diameter of the covering material 4 is sequentially applied from below. Can be formed. At this time, the resin curing means 8 is also raised in accordance with the rise of the dice apparatus A, and the recoat coating layer 10 is sequentially cured from below by the irradiation of the UV light to obtain the recoat coating material 11. Thereby, the recoat coating | covering material 11 of the shape which covers this part and the upper and lower coating | coated parts 4 and 4 can be formed in the coating removal part 5. FIG.

  As described above, when the recoating method according to the die method using the die apparatus A is performed, a resin liquid having a viscosity of 1 to 6 Pa · s, more preferably, a viscosity of 1.5 to 6 Pa · s. By using the resin liquid, it is possible to form the covering material 11 having excellent adhesiveness in a state where uneven thickness is suppressed without entraining bubbles.

Examples of the present invention will be described below, but it is obvious that the present invention is not limited to the following examples.
“Test Example 1”
A single mode optical fiber (fiber diameter; φ = 125 μm) and a plurality of ultraviolet curable resins (urethane acrylate ultraviolet curable resins) manufactured by JSR Corporation are prepared. A recoat test was performed when different ultraviolet curable resin solutions were used properly. FSM-45 type fusion splicer manufactured by Fujikura Co., Ltd. was used for the fusion splicing of the single mode optical fiber. The inner diameter of the die hole was 0.3 mm, the recoat length was 25 mm, and the coating diameter of the recoat part was 0.29 mm. It was.
The ultraviolet curable resin liquid used in this recoating test is a resin liquid having a viscosity of 0.5 Pa · s, a resin liquid having a viscosity of 1 Pa · s, a resin liquid having a viscosity of 1.5 Pa · s, a resin liquid having a viscosity of 2 Pa · s, and a viscosity. A resin liquid having a viscosity of 3 Pa · s, a resin liquid having a viscosity of 6 Pa · s, a resin liquid having a viscosity of 8 Pa · s, and a resin liquid having a viscosity of 10 Pa · s. The number of test samples was 10 for each recoat test.
The recoat portion of each sample obtained by the recoat test was observed with a microscope, and the presence or absence of bubbles in the recoated coating material was measured.
"Test Example 2"
The recoat portion of each sample obtained by the recoat test was observed with a microscope, the uneven thickness of the recoated coating material was investigated, and the average value was calculated. As described above, the thickness deviation is calculated by observing the structure of the optical fiber 100 covered with the resin coating layer 101 by looking at the cross-sectional structure of the optical fiber as shown in FIG. When the thickness of the thickest portion is expressed as A and the thickness of the thinnest portion of the coating layer 101 is expressed as B, the thickness deviation is expressed as A / B.
“Test Example 3”
Each sample obtained by the recoating test was stored in an environmental test apparatus having a temperature of 85 ° C. and a relative humidity of 85% for one week, and then taken out from the environmental test apparatus and observed with a microscope to count the presence or absence of peeling of the coating material. .

“Test Example 4”
In order to evaluate the adhesion between the bare fiber (glass portion) of the single-mode optical fiber subjected to the test and the coating material, the method of measuring the force when the bare fiber is pulled out of the coating material is called the drawing method. The adhesion was evaluated using the evaluation method described above. In this drawing method, as shown in FIG. 2 (A), a fixing jig 31 called a piece having a V-shaped groove 30 formed at the center of the surface is used, and an optical fiber 35 having a recoated coating material 33 is shown in FIG. As shown in FIG. 5B, the V-shaped groove 30 is bonded and fixed, and a notch with a depth that reaches the bare fiber 36 is formed around a portion of the covering material 33 around the covering material 33. This is a method of measuring the force required for extraction when the optical fiber 35 located outside the groove 30 is extracted along the V-shaped groove 30.
For the measurement of this test, a fixing jig having a length of 5 mm in the V-shaped groove direction was used, and the pulling force was measured by setting the pulling speed to 3 mm / min. In this drawing test, if the drawing force is 2 N / mm or more, it can be evaluated that the covering material is sufficiently adhered to the bare fiber.
The test results of Test Examples 1 to 4 described above are also shown in Table 1 below.

As shown in Table 1, in the result of Test Example 1, when the viscosity of the resin solution used in the recoating method is increased, bubbles are mixed. The reason is that when the resin solution is applied to the coating removal portion with a die apparatus, the end of the coating removal portion This is because when the resin liquid collides with the end face of the covering material located at the position, the resin liquid does not sufficiently flow into the gap between the die hole and the bare fiber, and bubbles are involved.
In the results of Test Example 2 shown in Table 1, the reason why the uneven thickness deteriorates when the viscosity of the resin liquid is low is that the resin liquid layer (recoat portion) appropriately formed by passing the resin liquid through the die hole is gravity. This is because the film flows downward in the vertical direction due to the influence of the above, and the coating layer thickness is deformed.
Furthermore, in Test Example 2, the reason why the uneven thickness deteriorates when the viscosity of the resin liquid is high is that the formation of the coating liquid layer (recoating part) tends to be disturbed when the resin liquid exits the die hole. This is because is incomplete.

In the results of Test Example 3 shown in Table 1, the reason why the coating material is peeled off when the viscosity of the resin solution is low is that the coating of the recoat portion tends to be thin when the viscosity of the resin solution is low, and the coating is performed when the coating material is thin. This is because it is easily affected by the curing shrinkage of the material, and when the recoat portion shrinks, the adhesiveness with the bare fiber (glass portion) is lowered and peeling occurs.
In Test Example 3, the reason why peeling occurs when the viscosity of the resin solution is high is that when the temperature change is repeated, non-uniform stress is generated from the coating material of the recoated portion due to the influence of the entrained foam, and the bare fiber (glass This is because the adhesion to the part) decreases and peeling occurs.
In Test Example 4, the pulling force was 2 N / mm similar under all conditions, and the coating material was firmly adhered to the bare fiber. Note that the pull-out force was highly material-dependent, and no difference in evaluation results appeared.

  From the results shown in Table 1, as the viscosity of the resin liquid used for the recoating is within the range of 1 to 6 Pa · s, no mixing of bubbles is observed in the coating material of the recoated part, and the uneven thickness of the coating material It has been found that the coating material hardly peels off even in an environment with a relative humidity of 85% or more, and that it is possible to form a coating material with excellent pull-out test results.

FIG. 1 is a schematic cross-sectional view showing an example of a dice apparatus used when carrying out the recoating method according to the present invention. FIG. 2 is an explanatory diagram showing an example of a method for testing the pulling force of the coating material after recoating. FIG. 3 is a block diagram for explaining the thickness of the coating material coated on the bare fiber.

Explanation of symbols

  DESCRIPTION OF SYMBOLS A ... Die apparatus, B ... Mold apparatus, 1 ... Resin reservoir part, 2 ... Dies, 3 ... Die hole, 4, 17 ... Cover material, 5, 15 ... Bare fiber, 6, 16 ... Optical fiber, 8 ... Resin hardening Means: 9 ... Resin liquid, 11 ... Coating material, 12 Upper mold, 13 ... Lower mold, 20 ... Fitting groove, 21 ... Mold groove, 22 ... Injection hole, 23 ... Injection path.

Claims (2)

  A method of recoating an optical fiber having a structure in which a coating material is provided on the outer periphery of a bare fiber, wherein the coating material is removed and a bare fiber portion of the optical fiber after fusion-bonding the bare fibers is 1 to 6 Pa · s. An optical fiber recoating method comprising applying a photo-curing resin liquid or a thermosetting resin liquid having a viscosity range of 1 to a resin coating material by photo-curing or thermo-curing.   When the resin liquid is applied to the bare fiber portion, the bare fiber portion is passed through a die having a die hole and a liquid reservoir portion, and the bare fiber portion is pulled out through the die hole to thereby form the liquid reservoir portion. 2. The optical fiber according to claim 1, wherein the stored resin liquid is applied to the periphery of the bare fiber portion, and then the applied resin liquid is cured and recoated as a resin coating material. Recoat method.

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