JP2001158644A - Resin coater for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin coater for optical fiber designed to uniformly coat an optical fiber in high linear velocity with a resin to a thickness so as to be about 400 μm in the outer diameter of the final optical fiber. SOLUTION: This resin coater has such a scheme that the underside of a nipple 2 and the top face of a die 3 with a tapered hole are mutually disposed at an interval and a resin is fed under pressure from the periphery of the gap; the resin is drawn at the tapered part of the die and applied onto an optical fiber passing through the tapered part; the diameter F of the hole of the nipple is smaller than the diameter H at the entrance of the hole of the die, the space B of the gap between the nipple and die is H/4 or greater but not greater than 4H, and the taper angle α of the tapered part of the die is 2 to 8 deg.; and the length D of the straight portion of the exit part of the die is smaller than the diameter G of the exit hole of the die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for applying a resin to an optical fiber, and more particularly to an apparatus for applying a resin to an optical fiber uniformly at a high linear velocity.

[0002]

2. Description of the Related Art As communication optical fibers, those using silica glass are widely used. Since the optical fiber made of quartz glass becomes very weak when scratched, it is usually manufactured by a method of coating with a resin immediately after drawing and before touching a hard object such as a roller. By covering with this resin coating, the practical strength of the optical fiber is maintained.

[0003] The transmission loss of an optical fiber is liable to increase even by a slight bending caused by an external force.
The bending of the optical fiber is called micro-bending or macro-bending depending on the size, but the resin coating layer covering the optical fiber reduces the external force and makes it difficult for the optical fiber to bend. Doubles as well.

[0004] When coating an optical fiber with a resin at a high linear velocity (for example, 500 m / min or more), bubbles are mixed into the applied resin or the resin is not uniformly attached to the outer periphery, so-called uneven thickness occurs. And the outer diameter fluctuates in the longitudinal direction. In an optical fiber core coated with resin unevenly, if a force is applied to the optical fiber from outside the coating layer even if the force is uniform, or if the coating layer expands or contracts due to a temperature change, the optical fiber Micro-bending or macro-bending occurs, causing transmission loss to increase.

[0005] The resin coating device for optical fibers described in Japanese Patent Publication No. Hei 7-91092 addresses such a problem of non-uniform coating.

FIG. 8 is a cross-sectional view of a main part for explaining the optical fiber resin coating apparatus described in the above publication.
In the figure, 1 is an optical fiber, 2 is a nipple, 2a is a nipple hole, 2b is a nipple lower surface, 3 is a die, 3a is a tapered portion of the die, 3b is a die outlet hole, 3c is a die upper surface, 4 is a resin upper surface, and 5 is a resin. Is a holder and 6 is a meniscus. The nipple lower surface 2b and the die upper surface 3c are both formed as surfaces perpendicular to the central axis through which the optical fiber 1 passes.

The optical fiber 1 enters through the nipple hole 2a of the nipple 2, gets wet with the resin 4 by the meniscus 6, and finishes the resin 4 to a predetermined outer diameter at the exit hole 3b of the die 3, so that the optical fiber 1 4 is applied. Resin 4
Through the gap between the nipple lower surface 2b having the nipple hole 2a at the center and the die upper surface 15 having the tapered inlet hole at the center, the nipple is supplied to the inside of the taper portion 3a of the die 3. A resin supply port (not shown) is connected to this gap. A meniscus 6 is formed in a portion of the resin 4 where the optical fiber 1 first gets wet with the resin 4. The resin 4 sufficiently adheres to the optical fiber 1 in the tapered portion 3a of the die 3, and is further applied by passing through the exit hole 3b of the die.

The conditions for uniformly applying a resin at a high linear velocity by using the nipple 2 and the die 3 are as follows.
The diameter of “a” is smaller than the diameter of the entrance hole of the die 3, and the gap between the lower surface 2 b of the nipple through which the resin flows and the upper surface of the die 3 c is １ ／ to 4 times the diameter of the entrance hole of the die 3. The taper angle of the tapered portion 3a of the die 3 is 2 to 8 degrees. The exit portion of the hole 14 of the die 3 has a constant diameter over the length of the exit hole or more, and its axial cross section forms a parallel straight portion as shown in FIG. The length of the tapered portion 13 of the die 3 is
5 times or more of the diameter of the outlet hole 3b.

This condition will be described with reference to FIG. FIG. 9 is a cross-sectional view of the nipple 2 and the die 3, where A is the length of the die 3, B
Is the gap distance between the lower surface of the nipple and the upper surface of the die, C is the length of the tapered portion, D is the linear portion (appears as a parallel line in the cross-sectional view), F is the diameter of the nipple hole, and G is the exit hole of the die. The diameter of the
H indicates the diameter of the entrance hole of the die, and α indicates the taper angle. The relationship between the above-described values is F <HH / 4 ≦ B ≦ 4H2 ゜ ≦ α ≦ 8 ゜, and D ≧ GC ≧ 5G may be satisfied.

The optical fiber resin coating apparatus described in the above-mentioned publications described with reference to FIGS. 8 and 9 coats an optical fiber having an outer diameter of 125 μm with a resin coating having an outer diameter of about 250 μm (coating thickness of 62.5 μm). Thus, a conventional optical fiber core is manufactured.

[0011] Recently, the outer diameter 12
Compared to a conventional optical fiber core wire in which a 5 μm optical fiber is coated with a resin having an outer diameter of about 250 μm, an outer diameter of 125 μm is applied to an outer diameter of 400 μmφ (coating thickness of 137.5 μm).
The demand for optical fiber cores having the coating structure of m) is increasing, and improvement in productivity has been desired. Then, when an attempt was made to increase the drawing speed, a problem that the application of the resin was not stable occurred. In other words, when the outer diameter of the coating is 400 μm, if the drawing speed of the optical fiber is increased (the coating speed is the same as the drawing speed because the coating is performed while drawing), the resin coating becomes unstable and the resin coating speed becomes high. The problem that it cannot be changed has arisen.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above-mentioned circumstances. An optical fiber having an outer diameter of about 125 μm is coated with a thick resin coating, for example, an outer diameter of 400 μm.
It is an object of the present invention to provide a resin coating device for optical fibers that can uniformly coat a resin at a high linear velocity when coating the resin to a thickness of about m or more.

[0013]

The invention as defined in claim 1 includes a die having a nipple and a tapered hole whose diameter decreases toward an outlet, wherein the die has a hole between the nipple hole and the die hole. In a resin coating device for an optical fiber, the resin is applied from the circumferential direction under pressure, the resin is squeezed by a tapered portion of the die, and the resin is applied to an optical fiber passing therethrough. The surface of the nipple having a hole in the center perpendicular to the central axis through which the fiber passes, and the surface of the entrance of the die having a hole in the center perpendicular to the central axis are arranged so as to have a gap. A resin supply port is connected to the gap so as to be supplied to the tapered portion, the diameter of the nipple hole is smaller than the diameter of the entrance hole of the die, and the gap between the nipple and the die is one of the diameter of the entrance hole of the die.
以上 and 4 times or less, the taper angle of the tapered portion of the die is 2２〜8 °, and the length of the straight portion of the exit portion of the die is shorter than the diameter of the exit hole of the die. Is what you do.

According to a second aspect of the present invention, there is provided a die having a nipple and a tapered hole having a diameter decreasing toward an outlet, wherein a resin is provided between the nipple hole and the die hole in a circumferential direction. The resin is applied under pressure, the resin is squeezed by the tapered portion of the die, and the resin is applied to the optical fiber passing therethrough.In the resin coating device for an optical fiber, the nipple and the die are positioned at a central axis through which the optical fiber passes. The surface of the nipple, which is vertical and has a hole at the center, and the surface of the entrance of the die, which has a hole at the center and is perpendicular to the central axis, are arranged with a gap, and the resin is supplied to the tapered portion of the die through the gap. The resin supply port is connected to the gap so that the diameter of the nipple hole is smaller than the diameter of the die entrance hole, and the gap between the nipple and the die is at least 1/4 and four times the diameter of the die entrance hole. The following is the die No straight portion to the mouth portion, the tapered portion of the die have been formed by the taper of two or more stages,
The taper angle of each step becomes smaller toward the outlet side, and the taper angle at the entrance side is 2 to 8 °.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resin coating apparatus for optical fibers described in the above publication was examined. 240 μm outer diameter
When the coating was carried out, a wire having a structure of C = 4 mm, D = 1 mm and α = 3 °, in which the coating property was stable up to a high linear velocity, was drawn. Coating outer diameter 40
Since it is 0 μm, G = 0.4 mm. Note that C, D, α, and G are values with reference to FIG.

When coating is performed under these conditions, a linear velocity of 100
m / min, the coating diameter sharply increased, and the linear velocity was 150 m / min.
In the vicinity of the minute, radial vibration with a fluctuation width of 100 μm was generated, and the linear velocity could not be increased.

This radial vibration phenomenon is considered to be a kind of melt fracture phenomenon. In the tapered portion in the die, the resin is pulled by the running optical fiber, so that the resin internal pressure increases as the cross-sectional area of the resin flow path becomes gradually smaller in the tapered shape. In order to apply a thicker coating than the conventional coating structure, the diameter of the die exit became large, and it was not possible to withstand the increased pressure in the tapered part, and the continuity of resin flow in the straight part of the die would be lost. Conceivable. More specifically, when in an ideal flow state, the resin flow velocity at the die inner wall surface = 0 from the flow continuity, but in the above state, the resin flow velocity at the die inner wall surface ≠ 0, that is, It is considered that slippage has occurred.

When slippage occurs, the amount of resin protruding from the exit hole of the die increases (the coating diameter increases), and at this time, the internal resin pressure at the tapered portion decreases. When the internal resin pressure decreases to a certain threshold, the flow returns to the ideal flow, and the coating diameter becomes thin. Since the resin protrusion amount decreases, the internal pressure of the resin starts to increase again at the tapered portion. 100 μm by repeating this phenomenon
It was considered that vibrations with a coating diameter of up to a maximum occurred.

In order to cope with this, a die in which the length of the straight portion at the exit of the die was increased so as to withstand the rise in the internal resin pressure at the tapered portion was evaluated. I couldn't see it. On the other hand, if the length of the straight portion is longer than this, it is inappropriate to maintain the processing accuracy of the die and the cost of manufacturing the die.

Thus, as described in the above-mentioned publication, with respect to the linear portion of the exit portion of the die, the conventional technology in which the length of the linear portion is equal to or larger than the diameter of the exit hole of the die is 400 μm.
When m coating is performed, it is difficult to achieve high linear velocity and uniform coating.

Japanese Patent Application Laid-Open No. 11-60288 discloses a similar die structure, but does not consider the length of the straight portion at the exit of the die. In view of this, it has been considered that the rise in the resin internal pressure is reduced so that the resin does not slip on the inner wall of the die.
In C = 4 mm α = 3 ゜, the length D of the straight portion at the outlet is 2 mm, 1 mm,
The dies were evaluated for four types of structures, 0.4 mm and 0.1 mm. Note that G = 0.4 mm. As a result, as shown in FIG. 6, it was confirmed that as the length of the linear portion was shortened, the critical linear velocity at which the application was stabilized increased.

FIG. 7 shows a configuration in which a straight portion at the exit of the die is eliminated and a taper portion of 3 mm or less is provided in a section of 1 mm and 2 mm from the exit of the die, and 2 mm from the exit of the die.
In the following sections, it was confirmed that the addition of a taper also increased the coating stability. C = 4 mm α = 3 ° The length of the tapered portion, ie, 2
mm is less than 5 mm because G is 0.4 mm.
G or less.

FIG. 5 is a schematic configuration diagram of an example of an entire apparatus for drawing an optical fiber and applying a resin. In the figure, 1 is an optical fiber, 7 is an optical fiber preform, 8 is a drawing furnace, 9,
9 'is a resin curing device, 10 is a winding device, and 11 and 11' are resin coating devices. The optical fiber 1 fiberized from the base material 7 in the drawing furnace 8 is subjected to primary coating with, for example, an ultraviolet curable resin in a resin coating device 11 and a resin curing device 9, and is further coated with a resin coating device 11 ′ and a resin. In the curing device 9 ′, for example, a secondary coating with an ultraviolet-curable resin is performed, and the film is wound up by the winding device 10.

In the conventional coating structure, the outer diameter of the primary coating is 180 to 210 μm, and the outer diameter of the secondary coating is 23 μm.
0 to 250 μm, but in the embodiment of the present invention,
In the case of a 400 μm coating structure, a desired outer diameter is selected within the range of 200 to 330 μm for the primary coating, and a desired outer diameter is selected within the range of 370 to 400 μm for the secondary coating. . However, it is not necessarily limited to coating in two steps,
In one step, a desired value within the range of 370 to 400 μm may be selected and coated.

FIG. 1 is a sectional view of an essential part for explaining a first embodiment of a resin coating device for optical fibers according to the present invention. In the figure, the same parts as those in FIG. Although the dimensional relationship will be described with reference to FIG. 2, the diameter of the nipple hole 2a is smaller than the diameter of the entrance hole of the die 3, and the resin flows with respect to the optical fiber resin coating device described with reference to FIGS. The gap between the nipple lower surface 2b and the die upper surface 3c is 1/4 of the diameter of the entrance hole of the die 3.
Not less than 4 times and the taper portion 3 of the die 3
The point that the taper angle of a is 2 to 8 ° is the same, but the diameter of the exit hole of the die 3 is increased corresponding to the coating thickness of the resin, The difference is that the length of the straight portion is smaller than the diameter of the exit hole of the die 3, so that an optical fiber core wire having a large coating thickness can be manufactured at a high linear velocity while stabilizing the coating. Can be.

FIG. 2 is a sectional view of the nipple 2 and the die 3 for explaining the dimensional relationship, and the reference numerals of the respective parts are the same as those of FIG. The relationship between the values described in the first embodiment is as follows: F <HH / 4 ≦ B ≦ 4H2 ゜ ≦ α ≦ 8 ゜ D <G, and B is more preferably H / 4 ≦ B ≦ 2H More preferably, H / 2 ≦ B ≦ 2H. H / 2 ≦ B is a condition from a more realistic processing accuracy. Further, the taper angle α can more preferably satisfy 2 ° ≦ α ≦ 5 °, and still more preferably satisfy 2 ° ≦ α ≦ 4 °.

FIG. 3 is a sectional view similar to FIG. 2 for explaining a second embodiment of the resin coating device for optical fibers of the present invention. In this embodiment, the edge portion 12 at the entrance of the die 3 is removed by a slope or a curved surface. This is effective in smoothing the flow of the resin.
However, if the portion chamfered on the slope or the curved surface is extremely large, the applicability deteriorates.

FIG. 4 is a sectional view similar to FIG. 2 illustrating a third embodiment of the resin coating device for optical fibers of the present invention. In this embodiment, a tapered portion is provided at the exit of the die 3. D 'is the length of the tapered portion. As described with reference to FIG. 7, the length of the portion of the outlet portion of 2 mm or less, that is, the length of 5 times or less the diameter of the outlet hole of 0.4 mm was defined as the tapered hole. That is, D ′ ≦ 5G.

The taper angle β is smaller than α, but the closer to α, the better.

In this embodiment, as described in the second embodiment, the edge 12 at the entrance of the die 3 can be formed to have a slope or a curved surface. Further, the number of tapered portions may be more than two. At that time, the taper angle of each stage is reduced as it goes to the outlet side.

According to the optical fiber resin coating apparatus of the present invention, since the hole diameter of the nipple 2 is small and the gap between the nipple 2 and the die 3 through which the resin flows is an appropriate interval, the meniscus 6 does not become large and bubbles Can be avoided.

That is, it is preferable that the cross-sectional area of the flow path along the direction in which the resin flows is monotonously reduced so as not to generate a vortex. In the present invention, in the vicinity of the entrance of the die, through the gap between the nipple and the die, the flow of resin toward the center of the die, along the running direction of the optical fiber, at a point that the direction is changed at a substantially right angle, The flow path cross-sectional area was set to satisfy π (H ² −d ² ) / 4 ≦ πHB. That is, H / 4 ≦ B.

Therefore, at the turning point of the flow of the resin, the cross-sectional area of the flow path monotonously decreases, and no vortex is generated. Also, because the distance between the nipple and the die is not too wide,
The resin flowing through the gap does not flow backward to generate a vortex. The vortex is easily generated when the flow velocity of the resin is high (that is, the linear velocity is high) and is large.

It is known that, in the tapered portion, a so-called self-centering force acts on an optical fiber running at the center so as to always maintain the center of the optical fiber. Experiments have shown that this force is the largest at an angle of about 2 to 4 degrees and becomes very small when it exceeds about 8 degrees.
Angles smaller than 2 ° are extremely difficult and impractical to machine.

As described above, according to the present invention, since the self-centering force is large and the flow of the resin around the optical fiber is smooth without generation of eddies, the optical fiber always passes through the center of the die and is uneven in thickness. Does not occur.

It is preferable that the length of the tapered portion is large in terms of the self-centering force, and that the length of the tapered portion is also required to regulate the flow of the resin at the entrance of the die. A diameter of about 5 times or more works particularly effectively in preventing uneven thickness. However, even if the length is too long and the self-centering force is increased more than necessary, the uniformity of coating is not improved. In addition, if the length is increased, the processing of the die becomes difficult and the cost increases. Therefore, the practical length of the tapered portion is about 10 mm at most.

Conventionally, it has been considered that the flow of the resin is further stabilized if a portion having a constant diameter is provided at the exit of the die. However, it has been found that when the outer diameter of the coating of the optical fiber is large, it is not good that the length of the portion having a constant diameter is too long because the coating diameter is vibrated. In the die of the present invention, it is effective if the length of the fixed diameter portion of the outlet portion is equal to or less than the diameter of the outlet hole of the die, and at a high linear velocity, application is stable and uneven thickness occurs. It becomes difficult. Similar results can be obtained by forming a second tapered portion at the exit of the die to form a taper having two or more steps.

[0038]

As is apparent from the above description, according to the present invention, a resin coating device for an optical fiber for manufacturing an optical fiber core can uniformly apply a resin to an optical fiber at a high linear velocity. This is particularly effective when the applied thickness of the resin is large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part for describing a first embodiment of a resin coating device for an optical fiber of the present invention.

FIG. 2 is a sectional view for explaining a dimensional relationship between a nipple and a die in FIG. 1;

FIG. 3 is a cross-sectional view of a nipple and a die for describing a second embodiment of the resin coating device for optical fibers of the present invention.

FIG. 4 is a sectional view of a nipple and a die for explaining a third embodiment of the optical fiber resin coating device of the present invention.

FIG. 5 is a schematic configuration diagram of an example of an entire apparatus for drawing an optical fiber and applying a resin.

FIG. 6 is an explanatory diagram of an experimental result.

FIG. 7 is an explanatory diagram of an experimental result.

FIG. 8 is a sectional view of a main part for describing a conventional optical fiber resin coating device.

FIG. 9 is a cross-sectional view of the nipple and the die of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Nipple, 2a ... Nipple hole, 2
b: Nipple lower surface, 3: Die, 3a: Tapered portion of die, 3b: Die outlet hole, 3c: Die upper surface, 4: Resin,
5 holder, 6 meniscus, 7 optical fiber preform,
8 drawing furnace, 9 and 9 'resin curing device, 10 winding device, 11 and 11' resin coating device.

Continued on the front page F term (reference) 2H050 BA12 BA13 BA23 BB33Q BB33S 4D075 AB12 AB14 AB32 AB36 CA47 DA01 DB13 DC24 4F040 AA27 AB04 AC01 BA43 BA49 CC02 CC15 4G060 AA01 AD22 AD58 AD59

Claims (2)

[Claims] 1. A die having a nipple and a tapered hole having a diameter decreasing toward an outlet, wherein a resin is supplied between the nipple hole and the die hole under pressure from a circumferential direction. In an optical fiber resin coating apparatus in which the resin is narrowed by a tapered portion and the resin is applied to an optical fiber passing therethrough, the nipple and the die have a hole at the center perpendicular to the central axis through which the optical fiber passes. The surface of the nipple and the surface of the entrance of the die having a hole in the center perpendicular to the central axis,
A resin supply port is connected to the gap so that the resin is supplied to the tapered portion of the die through the gap. The diameter of the hole of the nipple is smaller than the diameter of the entrance hole of the die. The distance between the gaps is 1/4 or more and 4 times or less the diameter of the entrance hole of the die, the taper angle of the tapered portion of the die is 2 to 8 °, and the length of the linear portion of the exit portion of the die is A resin coating device for an optical fiber, wherein the diameter is shorter than the diameter of the exit hole of the die. 2. A die having a nipple and a tapered hole having a diameter reduced toward an outlet, wherein a resin is supplied between the nipple hole and the die hole under pressure from a circumferential direction. In an optical fiber resin coating apparatus in which the resin is narrowed by a tapered portion and the resin is applied to an optical fiber passing therethrough, the nipple and the die have a hole at the center perpendicular to the central axis through which the optical fiber passes. The surface of the nipple and the surface of the entrance of the die having a hole in the center perpendicular to the central axis,
A resin supply port is connected to the gap so that the resin is supplied to the tapered portion of the die through the gap. The diameter of the hole of the nipple is smaller than the diameter of the entrance hole of the die. Is not less than 1/4 and not more than 4 times the diameter of the entrance hole of the die, there is no linear portion at the exit of the die, and the taper portion of the die is formed by two or more steps of taper. A taper angle of each step decreases toward an outlet side, and a taper angle at an entrance side is 2 to 8 °.