JPS6236047A - Production of optical fiber core - Google Patents

Abstract

PURPOSE:To obtain the titled optical fiber core consisting of a molten liq. crystalline high molecular substance exhibiting a stabilized characteristic by evacuating the space between an optical fiber strand and a molten thermoplastic resin and simultaneously compressing from the outer side of the thermoplastic resin. CONSTITUTION:In the production of an optical fiber core by forming the secondary coated layer 4 of a molten liq. crystalline high molecular substance (hereinafter referred to as LCP) on the outer periphery of an optical fiber strand 3, the space between the optical fiber strand 3 and the molten LCP is evacuated 5 and simultaneously the optical fiber strand 3 and the secondary coated layer 4 of LCP are firmly attached by compression 8 from the outside of LCP. By this method, since the attached point 9 between the optical fiber strand 3 and the secondary coated layer 4 of LCP is controlled by both evacuation and compression, the movement of the attached point 9 causing the variations of the diameter of the optical fiber core and the inclusion of air bubbles can be easily controlled and an optical fiber core exhibiting a stabilized characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing an optical fiber coated with a thermoplastic resin having a low coefficient of linear expansion and a high modulus of elasticity.

[Conventional technology]

Hikari 7 Eyepa is a fragile material with a diameter of 150 μm or less, so it is easy to get scratches on its surface during its manufacturing or cable production process, which becomes a source of stress concentration, and easily deteriorates when external stress is applied. It has the disadvantage of breaking.

Therefore, in order to protect the initial surface of the optical fiber and maintain its initial strength, immediately after spinning the optical fiber,
Coating the fiber surface with plastic has been practiced.

This plastic coating generally consists of a primary coating layer and a secondary coating layer. The primary coating layer is made of a material with a low Young's modulus, and is intended to maintain the initial strength of the optical fiber and to prevent an increase in fiber microbending loss due to non-uniformity of the secondary coating. On the other hand, the secondary coating layer is made of a thermoplastic resin such as polyamide or polyethylene, and is intended to facilitate handling during fabrication and cable production, and to resist lateral pressure and prevent increases in macro and micro bending loss of the fiber. However, the coefficient of linear expansion of the conventional secondary coating material is 1
This value is on the order of 0-4°C-1, which is much larger than the coefficient of linear expansion of the fiber itself, which is on the order of 10-7°C''1.

As a result, the fiber was bent due to expansion and contraction of the secondary coating layer due to temperature changes, resulting in an increase in microbending loss. In order to solve the above-mentioned drawbacks, it is necessary that the secondary coating layer itself has a coefficient of linear expansion as low as that of the optical fiber.

The present inventors have already proposed an aromatic polyester that exhibits melt liquid crystallinity as a secondary coating material that has a low coefficient of linear expansion of 10''''6℃-1 or less and can be coated at high speed using the current extrusion coating method. We investigated the use of this material to coat optical fibers by extrusion.

As a result, as described in Japanese Patent Application No. 59-104675, the secondary coating layer exhibits a low coefficient of linear expansion on the order of 10-6°C, and the optical The fiber core showed extremely stable transmission loss temperature characteristics over a wide temperature range of -60°C to 80°C.

The above molten liquid crystalline polymer* (hereinafter abbreviated as LOP) is
The original fiber core that broke down (hereinafter abbreviated as LOP core)
In this case, the secondary coated line is generally the same as the conventional nylon secondary coated line. However, in LOP coating, the molecular chains are oriented in the longitudinal direction of the optical fiber in the coating process, thereby lowering the coefficient of linear expansion of the LCP coating layer, resulting in higher precision compared to nylon coating. Control of coating conditions is required. The orientation of LOP molecular chains, the shear stress between the die and nipple in the extruder head, and the L(
This is caused by the withdrawal of 3F. It is determined by the molecular orientation during drawdown, the drawdown ratio (λ), which is the ratio of the size of the die nipple to the cross-sectional size of the final secondary coating layer, and the speed of drawdown. Conventionally, in order to achieve stable withdrawal conditions, a vacuum is drawn between the optical fiber and the molten secondary coating resin to bring them into close contact and complete the withdrawal in a relatively short time. I've been trying to do that. However, it has been found that when the drawing speed of the optical fiber is changed, the shape at the drawing part changes and the molecular orientation state of the LOP also changes. This will be explained based on FIG.

FIG. 2 is a schematic cross-sectional view of the grip part of the extruder head in a conventional optical fiber secondary coating line. In FIG. 4 is the LOP secondary coating layer, 5 is the direction of evacuation, 6 is the contact point between the optical fiber strand and the LOP secondary coating layer during low-speed pulling, and 6' is the optical fiber strand and the LCP secondary coating during high-speed pulling. In other words, as shown in FIG. 2, the location where the optical fiber and the LOP come into close contact with each other changes depending on the drawing speed of the optical fiber core at the drawing-off section. If the place where the two come into close contact changes or fluctuates in this way,
The variation in the outer diameter of the optical fiber becomes large. Also, light 7
It also causes air bubbles to be trapped between the IPA wire and the secondary coating layer 1. In order to solve the above disadvantages, the pulling speed of the optical fiber core wire is increased and the vacuum is strengthened, and the optical fiber wire and the LCP2 Next, we made sure that the area where the coating resin adhered did not move.

[Problem that the invention seeks to solve]

However, it has become clear that simply increasing the degree of vacuum does not provide sufficient control, and as a result, the LCP secondary coating characteristics change. The present invention was made to solve the above-mentioned problems in the LCP secondary coating process, and its purpose is to provide a Lap core wire that exhibits stable characteristics.

[Means for solving problems]

To summarize the present invention, the present invention relates to a method for manufacturing an optical fiber coated wire. This invention is characterized in that the optical fiber strand and the thermoplastic resin are brought into close contact by drawing a vacuum between the strand and the thermoplastic resin in a molten state and at the same time applying pressure from the outside of the thermoplastic resin. The main feature of the invention is that when manufacturing an LCP core wire, a vacuum is drawn between the optical fiber and the LOP secondary coating resin at the drawing part, and at the same time, pressure is applied from the outside of the LCP secondary coating resin. . Therefore, the difference from the conventional technology is that a pressure difference of 1 atm or more can be used due to the effects of both evacuation and pressurization, and thereby the contact point between the optical fiber and the LcP secondary coating resin can be easily controlled. It is.

FIG. 1 is a schematic cross-sectional view showing the configuration of the present invention. 1st
The figure shows the extruder head, especially the die lip, where numerals 1 to 5 have the same meanings as in Fig. 2, 7 is an attachment for pressurization, 8 is the direction of pressurization, and 9 is an optical fiber. This is the contact point between the wire and the LOP secondary coating layer. In FIG. 1, the optical fiber and LC! The adhesion point 9 of the P secondary coating layer is 1tjll by both the vacuum 5 and the air pressure 8.
IfKl is done. In particular, it is possible to apply a high pressure using a gas cylinder or a compressor as a pressurizing force, and the contact point 9 can be controlled much more easily than by only evacuation 5.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples.

Examples 1 and 2, Comparative Examples 1 and 2 Table 1 shows examples of the present invention in comparison with conventional methods.

A1 Even in the conventional method, when the take-up speed of the optical fiber core is low, it is possible to sufficiently control the point of contact between the optical fiber strand and the LOP secondary coating layer. However, as the take-up speed increases, it becomes impossible to control the vacuum using only the vacuum 5. As a result, the contact point 6 moves and the diameter of the optical fiber varies. On the other hand, in the embodiment of the present invention, even when the take-up speed is high, the contact point 9 does not move by controlling both the evacuation and the pressing force. As a result, there was no variation in the diameter of the optical fiber, and no air bubbles were trapped.

〔Effect of the invention〕

As explained above, according to the present invention, the point of contact between the optical fiber strand and the LOP secondary coating layer is set between the optical fiber strand and the LOP
Vacuuming between the P secondary coating layers and LC! Since the control is performed using both the pressure applied from the outside of the P secondary coating layer, there is an advantage in that it is possible to easily suppress movement of the adhesion point that causes fluctuations in the diameter of the optical fiber and entrapment of air bubbles.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the die lip portion of the extruder head in the optical fiber secondary coating line of the present invention, and FIG. 2 is a cross-sectional schematic diagram of the die lip portion of the extruder head in the conventional optical fiber secondary coating line. . 1... Die of extruder head, 2... Near 7'k,
3... Optical fiber strand, 4... LOP secondary coating layer,
5...Direction of evacuation, 6...Point of contact between the optical fiber strand and the LOP secondary coating layer during low-speed drawing, 6'.
... Point of contact between the secondary coating layer and the optical fiber at high-speed take-up at 9 o'clock, 7... Attachment for pressurization, 8...
- Direction of pressurization, 9... point of contact between the optical fiber strand and the I, OP secondary coating layer in the present invention.

Claims (1)

[Claims] 1. When producing a coated optical fiber by forming a thermoplastic resin layer around the outer periphery of an optical fiber, a vacuum is drawn between the optical fiber and the molten thermoplastic resin, and at the same time, the thermoplastic resin is By applying pressure from the outside of the resin,
1. A method for producing an optical fiber core, the method comprising achieving close contact between an optical fiber strand and a thermoplastic resin.