JPS61106442A - Preparation of optical fiber - Google Patents

Abstract

PURPOSE:To cover an optical fiber with plural numbers of a resin layer with good efficiency and good reliability by transporting a layer of the resin under pressure to a die capable of coating plural numbers of the resin layer at the same time with gaseous pressure, and feeding on one hand another resin for another layer with a fixed displacement pump. CONSTITUTION:An ultraviolet ray-cured resin 32 for the first layer having a low viscosity contained in a vessel 27 compressed by gaseous pressure is fed to a feeding port 17 of the material for a coating die 14 by the gaseous pressure, and the resin is flowed toward the direction to an outlet of the die 14 through a clearance 18 between a flow straightening cylinder, and coated on the external periphery of the optical fiber 4. An ultraviolet ray-cured resin 23 for the second layer is fed to the feeding port 19 of the material for the die 14 by a fixed displacement pump 24, and flowed toward the direction to the outlet of the die 14 through the clearance 20 between the flow straightening cylinder, and coated on the external layer of the first layer resin. Then, the optical fiber coated with resin is introduced into an ultraviolet ray curing fur nace, and plural numbers of a resin layer are cured at the same time by passing therethrough. Thus, a target resin-coated optical fiber is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to an improvement in an optical fiber drawing machine, and in particular to an improvement in a method of primary coating an optical fiber with an ultraviolet curing resin immediately after drawing. .

It is well known that optical fibers have low strength when they are drawn, so it is necessary to carefully bake a resin onto the surface of the fibers immediately after drawing them to strengthen them. This coating generally includes a first reinforcing layer to protect the glass surface of the optical fiber and improve tensile strength, and a second cushioning layer to reduce microbend loss. Naturally, different materials are used for the coating resins of the first and second layers. Resin has been used as the coating resin for baking by heating, but it requires time for curing and has drawbacks such as the need for a longer heating furnace if the drawing speed is increased, so recently, ultraviolet curing resin has been used.

A conventional optical fiber manufacturing method uses a manufacturing apparatus as shown in FIG. That is, a preform (2) is held in a chuck (1) of a preform feeding device and sent to a drawing furnace (3) located vertically. An optical fiber (4) is pulled out from the tip of the heated preform (2), coated with the first layer of resin by a coating die (5), and cured in a curing furnace (ultraviolet irradiation furnace) (6). Then, a second layer of resin is coated with a coating die (7), and the second layer of resin is cured with ultraviolet rays in a curing furnace (8). Next is the collection machine (9)
The film is taken up by a winder αB through a dancer roller 00 that controls the winding speed. When the second layer, which is a cushion layer, is required to be thicker, coating may be repeated twice using yet another set of coating dies and curing oven. In any case, two different materials
Several sets of coating dies and curing furnaces are arranged in series to separate the coating into layers. However, this method has the disadvantage that the length of the optical fiber from the drawing furnace to the drawing machine becomes long because the coating dies and the curing furnace are arranged in two or three stages.

In response to this, an improved method has been proposed that utilizes the characteristics of ultraviolet curing resin. Ultraviolet curing resins have the characteristic that the curing speed is only related to the energy of the ultraviolet rays received and the irradiation time, and the thickness of the coating resin has a small contribution. In other words, the power and time applied will remain the same regardless of whether the thickness of the coating is large or small. Therefore, the 10th layer of resin coating is brought to a semi-cured state in a curing oven, the second layer of resin coating is applied, and the first and second layers are completely cured in a second resin coating curing oven. It's a method. This method has the advantage that by increasing the power of the second-stage hardening furnace, the length of the first-stage hardening furnace can be shortened, and the apparatus can be made smaller. However, even with this method, it is necessary to arrange a coating die and a curing furnace in series for the first and second layers, and the height of the wire drawing machine is large (resulting in increased equipment costs). The drawbacks of the conventional method remain unresolved, such as the high cost and the need to run wires in two stages during the initial preparation work, which takes time and reduces the operating rate.

As a further improved method, a method using a coating die that coats two resin layers simultaneously has been proposed.

That is, as shown in Fig. 2, one coating die (5
) is supplied with different types of resin from two resin supply devices @, Q3, and simultaneously coats with two layers of resin. According to this method, due to the characteristics of the ultraviolet-effect resin, the resin can be electrified using only one set of a coating die and a curing furnace, so that the drawbacks of the conventional method are overcome. Coating two layers of resin at the same time with a die is widely used in extrusion molding of thermoplastics. It is known to supply a fixed amount.

It is clear that it would be extremely effective if this device could also be used in an optical fiber drawing device. However, the viscosity of the resin liquid for reinforcing optical fibers is 1/100 to 1/1000 times lower than that of general thermoplastics, so it cannot be pumped using conventional pumps.

This is because if the viscosity is low, the discharge amount of the resin will be unstable due to leakage inside the pump, and due to the incompressibility of the resin, if the discharge amount of the metering pump changes, the pressure of the resin will change. When extruding at 50 to several 100 atmospheres, such as when extruding thermoplastic plastics, the rate of pressure change is small, but in the case of coating resin for optical fibers, which has a low viscosity, it is used at 10 atmospheres or less, so the rate of pressure change becomes large. This is because this appears as a variation in the outer diameter of the coating. Therefore, it is better to use the resin supply device shown in Fig. 8, α3, which uses a gas compression system that uses compressible fluid (gas) as a medium to control the pressure inside the resin tank to maintain a constant resin supply. This fact is well known.

In simultaneous coating of two layers of resin using an optical fiber die, one coat of resin passes through the point of the die.
The first layer of resin is applied, and the second layer of resin joins and coats the outside, and is squeezed with a die and molded. This molding outer diameter d is determined by the pressure generated by the combination of the resin delivery pressure and the pressure increase due to the traction flow of the optical fiber. Since the pressure caused by the traction flow is approximately proportional to the linear velocity i, the outer diameter can be kept constant even if there is some variation in the linear velocity; in other words, the pressure increase due to traction serves a metering function.

However, since the ratio of the thicknesses of the first layer and the second layer is determined by the resin supply pressure, if there is an element of pressure fluctuation between the resin supply section and the formation section, this ratio will fluctuate. This pressure changes depending on the temperature (viscosity) of the material, etc., and the resulting change in pressure in one layer causes a change in the thickness of the other layer, so it is difficult to keep the ratio of the thicknesses of both layers constant. This is extremely difficult, meaning that this system is physically unstable. This point is a drawback of this improved method.

21 Structure of the Invention This invention enables extrusion without pressure fluctuations by feeding the resin of one layer using a metering pump and feeding the resin of the other layer using gas pressure as a medium when simultaneously coating two layers on an optical fiber. At the same time, the ratio of the coating thicknesses of the two layers is kept constant to eliminate the drawbacks of the conventional method.

The present invention will be explained below using the drawings.

FIG. 1 shows a cross section of the coating device of the present invention. First, the structure of the coating die will be described. A nipple α9 is inserted into the upper part of a die nipple holder (hereinafter referred to as hole holder) α0, and a forming die α4 is inserted into the lower part. The holder 00 is provided with a first layer resin material supply port α and a second layer material supply port α9. A rectifying cylindrical gap αυ for the first layer of resin is formed between the holder αG and the nipple α9, and a rectifying cylindrical gap for the second layer resin is formed between the holder α0 and the die α4.

The optical fiber (4) passes through the center of the nipple α9, passes through the die α4, and is drawn out.

According to this coating die, the resin for the first layer is supplied from the supply port αη, is rectified by the rectifying cylindrical gap (to) so that it flows uniformly around the outer circumference of the nipple α9, and is then passed through the die α4.
flows in the direction of the exit. On the other hand, the material for the second layer is the supply port α9.
The flow is then rectified by the rectifying cylindrical gap so that it flows uniformly around the outer periphery of the die α4, passes through the passage υ, flows uniformly around the outer periphery of the first layer, and flows to the outlet of the die α. The optical fiber (4) coming out from the tip of the nipple αS first comes into contact with the first layer of resin, and then the second layer of resin joins and coats the outer periphery of the first layer of resin, and is molded by the die α4.

The first layer of resin (A) is placed in a resin container (C) inside a gas pressurized container (5), and is connected to the gas pressurized container (F) by a pipe (7) via a gas pressure regulator. Gas is allowed to be introduced. (for the first layer of resin) is the resin container (
The water is supplied from c) to the supply port αη of the holder αQ through a pipe 01). The second layer of resin is placed in a resin container (sha), and is pumped through a pipe (c) by a metering pump (goods) to a pipe (to).
The material passes through and is supplied to the second layer material supply port α9 of the holder 00. The pressure inside the gas pressurized container is controlled by a gas pressure regulator. This pressure may be constant, but it may also be finely adjusted to control the coating outer diameter d, or the pressure may be automatically controlled by automatically measuring the value of the coating outer diameter (not shown).

When this coating die device is used, the first layer of coating resin is extruded by gas pressure, passes through the vibro 1), and is uniformly distributed in the axial direction on the outer circumference of the nipple αe by the rectifying cylindrical gap from the resin material supply port α force. flows.

Next, the coating resin for the second layer is supplied in a fixed amount by a metering pump (c), enters the resin material supply port α9 from the pipe (to), and is made to flow uniformly in the axial direction around the die and inner circumference by the rectifying cylindrical gap wire. The flow is rectified, passes through the passage Qυ, and merges with the first layer material. The merged material is applied around the optical fiber coming out from the center of the die, forming a two-layer structure in which the outer periphery of the first layer is coated with the second layer, and is formed with the die α4 and part of the taper of the nipple (2) to form the final outer diameter d. becomes. The resin-coated optical fiber is then cured in an ultraviolet curing oven to form a reinforced optical fiber.

What is important here is that the resin material for the first layer is supplied by gas pressure, and the resin material for the second layer is supplied by a metering pump. In other words, as explained above, the molding pressure by the die is the sum of the pressure for supplying the resin material and the pressure increase due to the pulling flow by the optical fiber. Since it is determined by the pressure inside the pressurized container, the effect is equivalent to extruding only one layer.Moreover, since the second layer of resin is extruded by a metering pump, the molding thickness of the second layer is determined by the influence of the first layer. never fluctuates. In the end, the molding pressure of the second layer is the same as that of the first layer, and it is as if -,
The two layers behave as if they were the same layer, and in the die and nipple forming section, the material pressure and the pressure increase caused by the optical fiber pulling the two layers simultaneously rise to the forming pressure and form the outer diameter d. .

In the above explanation, the case where the first layer is extruded by gas pressure and the second layer resin is extruded by a metering pump is explained, but it goes without saying that the same effect can be obtained even if this is reversed. Furthermore, it is clear from the principle of the present invention that even in simultaneous coating of three or more layers, the same effect can be obtained by extruding one layer with gas and extruding the other two layers using a metering pump. In these cases, the reliability of the metering pump increases as the viscosity of the resin increases, so it is desirable to push out the resin with a low internal viscosity in the plurality of layers using gas pressure.

Effects of the Invention As explained in detail above, the method of the present invention uses a die that simultaneously coats multiple layers when coating an optical fiber with two or more layers of resin, and one of the resin layers is pumped by gas pressure. It is characterized by feeding the coating die and other resin to the die using a metering pump, which allows multiple resin layers to be molded as if they were integrated, so the molding pressure remains constant. Since a uniform outer diameter can be obtained and less metering pumps are used, the reliability of maintaining a constant thickness ratio of multiple layers is improved. If an ultraviolet curing resin is used, which has the characteristic that the thickness of the resin layer does not contribute to the curing time and does not require a long curing oven even if the thickness increases, as shown in Figure 3,
Multiple layers of resin coating can be applied to optical fibers using only one set of coating dies and a short UV irradiation curing furnace, which reduces the overall height of the optical fiber drawing machine, thereby reducing equipment costs and reducing the threading work. It is very effective compared to conventional methods, such as improving the operating rate of machines by improving performance.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of a resin supply device and a coating die used in an embodiment of the present invention. FIG. 2 is a front view of the apparatus used in the conventional manufacturing method, and FIG. 3 is a front view showing the entire system of the optical fiber manufacturing apparatus used in the conventional improved method and the method of the present invention. (1)...Chuck, (2)...Preform, (
Death... wire drawing furnace, ゛(4)... optical fiber,
+51, +7+...Coated dice, +6+
, +81...Curing furnace, (9)...Bow 1 take-up machine, α■...Dancer roller, 0℃...Rewinder, (
2), α3... Resin supply device, α... Molding die,
051...Nipple, αG...Die nipple holder, αη, 09...Material supply port, αNe, (A)・
・・Rectifying cylinder gap, ■G・Passage, °H・・
・Cone gap, (c), (c)...resin container, ■・
・・Quantitative supply pump, (c), CO, (7), GD・
...pipe, (a)...gas pressurized container, kan...
Gas pressure regulator, ■...resin.

Claims (1)

[Claims] 1. An optical fiber manufacturing method using a coating die capable of simultaneously coating multiple layers of resin material by directly coating the outer periphery of a drawn optical fiber and curing the fiber, using an ultraviolet curable resin. One layer of the resin material among the multiple layers is pumped into the coating die by gas pressure, the remaining layer material is supplied by a metering pump to simultaneously coat the outer periphery of the optical fiber, and then passed through an ultraviolet curing oven to coat the multiple layers. A manufacturing method of an optical fiber according to claim 1, characterized in that the resin having the lowest viscosity among the resins used in the plurality of layers is pumped by gas pressure. Production method