JP2003294974A - Method of coating optical fiber fusion spliced portion again, and optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of coating an optical fiber fusion spliced portion again, in which the optical fiber fusion spliced portion is coated again to have an outside diameter approximating that of the coating of an optical fiber without bringing about cracks in a mold/coating boundary neither peeling of an overlap part. <P>SOLUTION: The method comprises a coating step for forming a mold coating on a bare fiber portion of the fusion spliced portion of the optical fiber by using a resin compound having characteristics of ≥70% tensile elongation and ≥20 MPa tensile strength. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recoating an optical fiber fusion splicing portion and an optical fiber, and more particularly to recoating an exposed portion of the optical fiber by fusion splicing.

[0002]

2. Description of the Related Art In long-distance optical transmission lines, such as submarine cables, where it is impossible to install a closure or a terminal box,
In some cases, it is necessary to form an optical fiber cable of several tens of kilometers. When manufacturing such a long optical fiber cable, connect the optical fiber that is less than the cable length with low loss and high strength, and form the shape and outer diameter of this connection part to the same extent as the optical fiber coating part. There is a need.

Conventionally, after fusion-splicing of the optical fiber from which the coating has been removed at the end face, re-coating of the exposed optical fiber is performed by coating the re-coated portion with an ultraviolet curable resin and irradiating with ultraviolet rays to re-coat. The approach has been to cure the part and form a mold coating (recoat).

However, in such a method of re-coating a fusion spliced portion of an optical fiber, in order to perform mold coating so as to have a diameter substantially equal to the outer diameter of the coating of the optical fiber, the coating and the resin overlap each other. At the (overlap) portion, the resin thickness to be molded becomes thin. Therefore, cracks may occur at the mold / coating interface, which is the interface between the mold coating and the optical fiber coating, due to the shrinkage of the injected resin when it is cured.

Therefore, for example, a recoating method as disclosed in Patent Document 1 has been proposed. In this re-coating method, as shown in FIGS. 6 (a) and 6 (b), the coating 101a at the ends of the optical fibers 100a and 100b to be connected is partially removed to reduce the outer diameter of the coating 101, Diameter part 102
Is formed. Then, the coating 101 at the tip of the small-diameter portion 102 is removed, the optical fibers 100a and 100b are fusion-spliced, and then the fusion-splicing portion 103 and its vicinity 10
4 is molded with a molding resin 105 so as to have a diameter substantially equal to that of the coating 101 of the optical fibers 100a and 100b.

[0006]

[Patent Document 1] JP-A-5-264848

[0007]

However, according to the re-coating method shown in FIGS. 6 (a) and 6 (b), the outer diameter of the mold resin 105 portion is set to the optical fibers 100a, 1
Although the outer diameter of the coating 101 of 00b can be matched, the following problems remain.

First, there is a structural problem that the thickness of the resin to be molded is still small at the overlapping portion 106 where the molding resin 105 and the coating 101 of the optical fibers 100a and 100b overlap.

In addition to this, the mold shrinkage rate of the mold resin 105 used for the mold coating is large, and the tensile breaking strength of the mold resin 105 itself is low and the tensile breaking elongation is small.
Mold resin 10 caused by shrinkage when 5 is cured
5 cannot be sufficiently prevented from cracking at the interface 107 between the coating 5 and the coating 101. In particular, there remains a problem that cracks are likely to occur when screening (tensioning) rewinding is performed.

At the overlap portion 106, in addition to the problem that the thickness of the mold resin 105 is thin, the adhesive force between the mold resin 105 and the coating 101 forming the outermost layer of the optical fibers 100a and 100b is low. When the wiping process using ethanol or the like (ethanol wiping) is performed to remove extra resin such as burrs after the molding resin 105 is cured, the overlapping portion 10
6 may come off.

Further, an optical fiber 100a to be connected,
Sandpaper is used to reduce the diameter of the coating 101a at the tip of the 100b. However, since the thickness of the coating 101 is only about 60 μm, it requires extremely high skill and time to reduce the diameter. ineffective. Further, there is a possibility that the glass is sometimes damaged and the fiber strength is lowered.

The present invention has been made in view of the above-mentioned problems and has an outer diameter close to the outer diameter of the coating of the optical fiber without causing cracks at the mold / coating interface and peeling of the overlapping portion. It is an object of the present invention to provide a method for recoating an optical fiber fusion splicing part that can perform recoating.

Further, the vicinity of the fusion spliced portion of the optical fiber is also close to the outer diameter of the coating of the optical fiber, and a light having a highly reliable re-coating portion without cracks at the mold / coating interface and peeling off of the overlapping portion is provided. The purpose is to provide a fiber.

[0014]

In order to achieve the above object, the method for recoating an optical fiber fusion spliced part according to the present invention uses a resin composition having a curing shrinkage of less than 6.0% to mold the resin composition. It is characterized in that a coating is formed. Here, the bare fiber includes glass fiber or carbon fiber coated with carbon.

According to this construction, since the curing shrinkage of the mold resin itself is low, there is little shrinkage when the mold resin cures, and it is possible to prevent cracks occurring at the mold / coating interface and peeling of overlapping portions. it can. As a result, it is not necessary to reduce the diameter of the coating on the tip of the optical fiber as in the conventional case, so that it is possible to improve the working efficiency without lowering the strength.

Desirably, a mold coating is applied on the bare fiber portion of the fusion spliced portion of the optical fiber with a resin composition having a tensile elongation at break of 70% or more and a tensile strength of 20 MPa or more after curing. It is characterized by including a coating step of forming.

According to this structure, since the tensile elongation at break of the mold resin is large and the tensile break strength is also high, it is possible to resist the contracting force when the mold resin is cured,
It is possible to prevent the occurrence of cracks at the mold / coating interface. As a result, it is not necessary to reduce the diameter of the coating on the tip of the optical fiber as in the conventional case, so that it is possible to improve the working efficiency without lowering the strength.

In order to prevent the occurrence of cracks at the mold / coating interface, this resin composition has a tensile breaking elongation of 82% or more and a tensile breaking strength of 23 MPa.
The above is more preferable.

Desirably, the resin composition has an adhesion force of 200 N / N with the resin constituting the outermost layer coating of the optical fiber.
It is characterized in that the mold coating is formed using a resin composition having a characteristic of m or more.

According to this structure, since the adhesion between the mold resin and the outermost layer coating of the optical fiber is strong, it is possible to prevent the mold resin from contracting and prevent the overlapping portion from peeling off. As a result, it is not necessary to reduce the diameter of the coating on the tip of the optical fiber as in the conventional case, and thus the working efficiency can be improved without causing a decrease in strength.

On the other hand, when the adhesion is less than 200 N / m, there is a problem that the overlapping portion is peeled off and the strength is reduced.

In order to prevent the peeling of the overlapping portion, it is more preferable that the adhesion is 400 N / m or more. Further, it is more desirable that it is 450 N / m or more.

In order to prevent cracks occurring at the mold / coating interface and peeling of the overlapping portion, it is preferable that the cure shrinkage of the mold resin is 5.5% or less.

Here, the mold coating may be formed so as to completely cover the bare fiber portion, but it is preferably formed so as to overlap the coating on the tip of each optical fiber from above the bare fiber portion. The mold resin itself can resist the shrinking force when it cures and can prevent peeling of the overlapping part, so it does not damage the coating of the optical fiber tip part, By forming an overlapping portion between the fiber coating and the mold resin, reliable protection can be achieved.

Further, even when the molding resin is formed so as to cover only the bare fiber portion and come into contact with the coating of the optical fiber only on a surface perpendicular to the optical axis of the optical fiber, the tensile breaking elongation of the mold resin is large and the tensile breaking elongation is large. Since the strength is high and the shrinkage force when the mold resin is cured is small, it is possible to realize reliable recoating without generation of cracks or peeling.

An optical fiber in which the above-mentioned re-coating, that is, a molding resin is formed on the fusion splicing part of the optical fiber,
There are no cracks at the mold / coating interface, and no peeling of overlapping parts.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

In the present invention, as shown in FIG. 1, the tensile breaking elongation in the cured state is 70% or more and the tensile elongation at break is not less than 70% on the bare fiber portions 12a and 12b in the fusion splicing portion 11 of the optical fibers 10a and 10b. It is characterized in that the mold coating 13 is formed by using a resin composition having a property of breaking strength of 20 MPa or more.

For example, as shown in this recoating step in FIGS. 2 to 4, the molding die 1 (EP1197311A1) is applied to the bare fiber portions 12a and 12b of the optical fiber fusion splicing portion 11.
(See the official gazette). This molding die is composed of a pair of upper and lower molding dies 14A and 14B. Then, here, after supplying the urethane acrylate-based ultraviolet curable resin (mold resin 17) as the resin composition having the above-mentioned characteristics from the resin injection gate 15 of the upper and lower molds 14A and 14B to the cavity region 16, The mold region 17 is cured by irradiating the cavity region 16 with ultraviolet rays 18 as curing energy. After that, remove the upper and lower molds 14A and 14B and press the burrs 1
If there is 9, the flash 19 may be wiped off with alcohol (eg ethanol).

That is, first, FIGS. 2A and 2B.
As shown in FIG. 2, for example, an upper mold die 14A and a lower mold die 14B made of quartz glass that transmits ultraviolet rays 18 are formed.
The bare fiber portion 12 fusion-bonded is arranged at the center of the cavity region 16 formed between the mold cavity 17 and the mold resin 17, which is a urethane acrylate-based UV-curable resin, and the cylindrical cavity region 16 is formed. Fill inside.

In this state, ultraviolet light 1 is applied to the cavity region 16.
8 is irradiated to cure the mold resin 17. At this time, a flash 19 is often formed between the upper mold die 14A and the lower mold die 14B.

Then, as shown in the radial cross-sectional view of FIG. 3, an upper mold die 14A and a lower mold die 14B.
And wipe off the burr 19 using a non-woven fabric impregnated with alcohol.

In this way, a flash-free recoating is obtained, as shown in the radial cross section in FIG. This recoat length L
Is about 8 to 38 mm, although it depends on the coating removal tool for removing the coating before the spliced connection (see FIG. 1).

Next, mold resins having various characteristics were prepared, and remolding was performed using these mold resins 17, and the strength and shrinkage ratio of the mold coating 13 were measured.

First, as the optical fibers 10a and 10b,
The bare fiber portion 12 of the single-mode optical fiber 10 having an outer diameter of 125 μm is coated with two layers 20 of urethane acrylate-based UV-curing resin to have an outer diameter of 245 μm.
The optical fibers 10a and 10b are used.

The coating 20 on the ends of the optical fibers 10a and 10b is removed by a remover or hot sulfuric acid, and the end face of the bare fiber 12 is cut with a fiber cutter.
The glass surface is ultrasonically cleaned with acetone. In addition,
Here, H ₂ SO ₄ may be used instead of acetone. Two sets of such optical fibers 10a and 10b were prepared and the end faces were brought into contact with each other for fusion splicing.

Optical fiber 10 including this fusion spliced portion 11
a and 10b are replaced by the above-mentioned upper and lower mold dies 14A, 14
After being set to B, 6 kinds of molding resin 17 composed of a urethane acrylate oligomer as a base, a diluting monomer, and a photoinitiator added and made of an ultraviolet curable resin are injected into the cavity region 16 and irradiated with ultraviolet rays 18 to mold. Resin 17 was cured.

Then, the optical fibers 10a, 10b are taken out from the molding dies 14A, 14B, unnecessary portions (including uncured portions) such as the flash 19 are wiped with ethanol, and the mold coating 13 is observed under a microscope. At the same time, the occurrence of cracks at the interface 21 between the mold coating 13 and the coating 20 of the optical fiber 10 and the coating 20
Then, the occurrence of peeling of the overlapping portion 13a of the mold coating 13 was examined.

Furthermore, screening rewinding was performed by applying a constant tension, and the mold coating 13 was observed again under a microscope.

The results of the above observations are shown in Table 1. As the mold resin 17, six types of resins A to F, whose characteristics were changed by adjusting the urethane group concentration of the oligomer, the molecular weight and the compounding amount, and the type and the compounding amount of the monomer, were adopted.

[0041]

[Table 1]

The tensile breaking elongation and tensile breaking strength were measured by measuring the tensile breaking elongation and the tensile breaking strength of a test piece having the same composition as each mold resin 17 in accordance with JISK7127. The distance between marked lines at this time is 25 m
m, temperature 23 ° C, humidity 50% RH, tensile speed 5
It was measured at 0 mm / min.

The test piece at this time was obtained as follows. First, a liquid composition having the same composition as each mold resin 17 is applied onto glass using an applicator. Then, by using a metal halide lamp and irradiating with ultraviolet rays of 1.0 J / cm ^{2 in} an air atmosphere, a cured film having a thickness of about 200 μm is produced. The No. 2 test piece was obtained from the cured film thus formed.

The adhesion (sticking force) with the outermost coating 20 of the optical fiber was measured as follows. As shown in FIG. 5, first, the liquid composition of the resin for coating the outermost layer of the optical fiber is applied on the glass plate 22 using an applicator, and 0.5 J / cm ² of ultraviolet light is applied in a nitrogen atmosphere using a metal halide lamp. Irradiate, and the thickness is about 130μ
A cured film 23A of m is prepared.

Further, the liquid composition for the mold resin 17 is applied on the above-mentioned cured film 23A using an applicator,
0.1J under air atmosphere using metal halide lamp
/ Cm ² of ultraviolet rays is irradiated to form a cured film 23B having a thickness of about 130 μm.

After forming a strip-shaped cut 24 having a constant length and a width of 1 cm in the cured film 23B, one end of the slit 24 is peeled off and the fixed length is bent at 90 degrees to form a bent portion 25. Then, the tip of the bent portion 25 was pulled to peel the whole, and the pulling force F at the time of peeling was divided by the width to obtain the adhesive force. The measurement was performed in an environment of a temperature of 23 ° C. and a humidity of 50% RH.

Further, the curing shrinkage ratio is set as follows: curing shrinkage ratio = {(ds-di) / ds} × 100 (%) where di is the specific gravity of the liquid resin before curing and ds is the specific gravity of the resin after curing. can get.

Here, the crack generation rate of the mold / coating interface 21 or the peeling rate of the overlapping portion 13a after wiping with ethanol was calculated for 15 samples. Furthermore, the crack occurrence rate of the mold / coating interface 21 or the peeling rate of the overlapping portion 13a after the screening rewinding is the same as the cracking rate of the mold / coating interface 21 after wiping with ethanol, and the peeling of the overlapping portion 13a. Calculated for the sample that did not exist.

As shown in Table 1, mold resins A and B
In the case of using, the crack at the mold / coating interface does not occur after the curing of the molding resin due to the decrease in the curing shrinkage ratio, and the tensile breaking strength and the tensile breaking elongation are high, so that the crack may occur after the screening rewinding. lost. Further, since the adhesiveness to the outermost layer coating 20 is high, the overlapping portion 13a is not peeled off, and it can be seen that proper re-coating is performed.

Next, when mold resin C was used, the cure shrinkage was 5.7%, the tensile strength at break was 82%, the tensile elongation at break was 24 MPa, and the adhesion to the outermost layer coating 20 was 280 N / m. there were. At this time, when the ethanol was wiped after the mold resin was cured, cracks were generated at the mold / coating interface 21, and the generation rate was 3/15. In addition, the mold /
A crack was generated on the coating interface 21, and the occurrence rate was 2/10. Furthermore, at this time, peeling of the overlap portion 13a after wiping with ethanol occurred, the peeling occurrence rate after ethanol wiping was 2/15, and the peeling occurrence rate after screening rewinding was 2/10.

Next, when mold resin D was used, the cure shrinkage was 5.6%, the tensile breaking strength was 94%, the tensile breaking elongation was 19 MPa, and the adhesion to the outermost layer coating 20 was 280 N / m. there were. At this time, cracks occurred in the mold / coating interface 21 after the mold resin was cured after wiping with ethanol. The incidence was 3/15. Furthermore, since the tensile rupture strength is low, cracks are generated at the mold / coating interface 21 in all the samples after screening rewinding, and it can be said that the recoating is inappropriate. Further, at this time, peeling occurred in the overlapping portion 13a after wiping with ethanol, and the occurrence rate was 2/15.

Next, when mold resin E was used, the curing shrinkage was 5.2%, the tensile breaking strength was 23 MPa, and
The tensile elongation at break was 67% and the adhesion to the outermost layer coating 20 was 250 N / m. Cracks at the mold / coating interface 21 did not occur after the curing of the mold resin due to the decrease in the curing shrinkage ratio, but cracks occurred at the mold / coating interface 21 for all the samples after screening rewinding due to the small tensile elongation at break, and It can be said that it is a proper recoating. Further, at this time, peeling of the overlap portion 13a occurred after wiping with ethanol, the peeling occurrence rate after ethanol wiping was 3/15, and the peeling occurrence rate after screening rewinding was 3/12.

Next, when the mold resin F was used, since the curing shrinkage rate was as large as 6.1%, cracks occurred at the mold / coating interface 21 after the mold resin was cured (after wiping with ethanol) in all the samples, Moreover, since the adhesion to the outermost layer coating 20 was as low as 150 N / m, peeling of the overlapping portion 13a occurred in all the samples. This can be said to be an incorrect recoating.

As described above, as in the case where the molding resins D to F are used, if the cracks are generated at the mold / coating interface 21 or the overlapping portions 13a are peeled off, the corresponding portions are scraped off and the molding is performed again. A correction work of applying and hardening the resin 17 is required, and the work efficiency is significantly reduced. Therefore, it can be said that the recoating is inappropriate.

From the above measurement results, the curing shrinkage ratio was 6.1.
%, Cracking occurred at the interface after blowing with ethanol in all cases. It can be seen that when the curing shrinkage is 6.1%, it is too large and unsuitable. When the curing shrinkage ratio is 5.7% or less,
The rate of cracking at the interface is significantly reduced after wiping with ethanol. It can be seen that the tensile breaking elongation is too small at 67% and the tensile breaking strength is too low at 19 MPa. Further, it can be seen that the adhesion is too low at 150 N / m.

From these results, the tensile elongation at break is 70%.
As described above, the tensile breaking strength is 20 MPa or more and the adhesion is 200.
If the mold resin 17 has a characteristic of N / m or more,
It can be seen that proper recoating can be done. Also,
According to the inspection results of Examples 3, 4 and 5, those having a tensile elongation at break of 82% and a tensile strength of 23 MPa or more have a remarkable crack occurrence rate at the interface through the screening and a peeling occurrence rate at the overlap portion. Few.

As described above, if the mold coating 17 is the mold resin 17 having a tensile breaking elongation of 90% or more and a tensile strength of 25 Mpa and an adhesive force of 400 N / m or more, extremely proper recoating can be performed. I know that I can do it.

In the method of re-coating the fusion spliced portion of the optical fiber according to the present invention, the outer diameter of the coating 20 of the optical fiber 10 is close to that of the mold / coating interface 21 without cracks and peeling of the overlapping portion 13a. Recoating can be done at the outer diameter.

The method of re-coating the fusion spliced portion of the optical fiber according to the present invention is not limited to the above-described embodiment, but can be appropriately modified and improved.

That is, in the above-mentioned embodiment, the urethane acrylate resin is used as the ultraviolet curable resin, but it goes without saying that another ultraviolet curable resin may be used.

Further, the present invention is not limited to the ultraviolet curable resin, but can be applied to a thermosetting resin which is cured by heat energy.

[0062]

As described above, according to the method of recoating an optical fiber fusion splicing portion according to the present invention, an optical fiber can be produced without causing cracks at the mold / coating interface and peeling of overlapping portions. Recoating can be performed with an outer diameter close to the outer diameter of the coating.

Further, according to the optical fiber of the present invention, neither cracking nor peeling of the overlapping portion occurs at the mold / coating interface even at the recoating portion,
It is possible to realize a highly reliable long-distance optical fiber.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a re-covered portion performed by a method of re-coating an optical fiber fusion splicing part according to the present invention.

2 (a) and 2 (b) are cross-sectional views showing one step of a method for recoating an optical fiber fusion splicing part according to the present invention.

FIG. 3 is a cross-sectional view of the re-coated portion before removing the flash.

FIG. 4 is a cross-sectional view of the recoated portion after removing the flash.

FIG. 5 is a perspective view showing an adhesion measuring method.

6 (a) and 6 (b) are cross-sectional views of a re-coated portion by a conventional method of re-coating an optical fiber fusion splicing portion.

[Explanation of symbols]

10 optical fibers 11 Fusion splicing part 12 Bare fiber part 13 Mold coating 14A, 14B Mold die 16 cavity area 17 Mold resin (resin composition) 18 UV rays (curing energy) 20 coating

Claims (9)

[Claims] 1. A coating step of forming a mold coating on a bare fiber portion of an optical fiber fusion splicing portion using a resin composition having a characteristic that a curing shrinkage rate is less than 6.0%. Recoating method for optical fiber fusion splicing part. 2. The resin composition has a tensile elongation at break of 70%.
The method for recoating an optical fiber fusion splicing part according to claim 1, wherein the method has the above-mentioned characteristics and a tensile breaking strength of 20 MPa or more. 3. The optical fiber according to claim 1, wherein the resin composition has a characteristic that an adhesive force with a resin forming the outermost layer coating of the optical fiber is 200 N / m or more. Recoating method for fusion spliced part. 4. The resin composition has a cure shrinkage of 5.7%.
The method for recoating an optical fiber fusion splicing part according to any one of claims 1 to 3, characterized in that the method has the following property. 5. The resin composition has a tensile elongation at break of 82%.
The method of recoating an optical fiber fusion spliced part according to any one of claims 1 to 3, wherein the tensile breaking strength is 23 MPa or more. 6. The resin composition according to any one of claims 1 to 5, wherein the resin composition has a characteristic that an adhesive force with a resin forming an outermost layer coating of an optical fiber is 400 N / m or more. Recoating method for optical fiber fusion splicing part. 7. An optical fiber having an optical fiber fusion splicing portion, and a resin composition which is disposed on the bare fiber portion of the optical fiber fusion splicing portion and has a characteristic that the curing shrinkage rate is less than 6.0%. An optical fiber comprising a mold coating made of a material. 8. The resin composition has a tensile elongation at break of 70%.
The optical fiber according to claim 7, which has the characteristics described above and a tensile breaking strength of 20 MPa or more. 9. The optical fiber according to claim 7, wherein the resin composition has a characteristic that an adhesive force with a resin forming the outermost layer coating of the optical fiber is 200 N / m or more. .