JPS61130909A - Structure of optical fiber core - Google Patents

Abstract

PURPOSE:To improve the effect of protection and reinforcement by forming a foamed buffer layer and a dense layer of the structure which is not foamed into one resin coating layer thereby providing high mechanical strength. CONSTITUTION:An optical fiber core A is constituted of an optical fiber strand (a) consisting of a core a1 and a clad a2 and a foamed resin layer (b) provided around the strand in contact therewith. The layer (b) consists of a dense part b1 which is not foamed and a foamed part b2. The dense part b1 which is not foamed in provided on the outside circumferential surface of the strand (a) in contact therewith. The part b4d1 prevents the intrustion of water from the outside by the dense structure thereof and shares the stress against bending, twisting and tension thus contributing to the improvement in the mechanical strength. The part b2 provides a cushion effect by the foamed structure thereof. The optical fiber is protected and reinforced by the above-mentioned effects by which the ease of handling is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a coated optical fiber. More specifically, the present invention relates to the structure of an optical fiber core made of glass fiber with excellent mechanical strength and high buffering properties.

[Prior Art] In order to improve the microbending characteristics of optical fibers, a loose wire is applied to the outer periphery of an optical fiber made of glass fiber. I11 is provided. In such a conventional example, as shown in the third factor, the core (
An optical fiber (a
) is provided with a dense resin layer (aS) on the outer periphery of the non-foamed resin! ! A resin foam layer (a4) is separately provided on the outer periphery of (aS).

[Problems to be solved by the invention] Conventional all! The optical fiber equipped with II has a two-layer structure consisting of an inner resin layer and an outer resin foam layer, and has an interface, so it does not have high mechanical strength.
There is a problem in that equipment is required for the formation of each layer.

- In view of the above-mentioned circumstances, an object of the present invention is to provide an optical fiber core having a structure with high mechanical strength and excellent cushioning properties.

[Means for Solving the Problems] The optical fiber core wire having the structure of the present invention has a structure in which a resin foam layer is provided around the optical fiber strand, and the resin foam layer is not foamed. It has a structure in which the dense portion is in contact with the outer peripheral surface of the optical fiber strand.

[Function] The optical fiber core wire having the structure of the present invention prevents water from entering from the outside by the dense non-foamed portion of the resin foam layer, and also shares stress against bending, twisting, tension, etc. The foamed part provides a cushioning effect,
Protection and reinforcement are provided.

Further, since the non-foamed portion and the foamed portion are integrally formed in a single resin layer and there is no interface between them, high mechanical strength can be obtained.

[Example] Next, an example of the structure of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a coated optical fiber according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the manufacturing process of the coated optical fiber shown in FIG. 1, and FIG. FIG. 3 is a cross-sectional view of the core wire.

In Fig. 1, (A) is an optical fiber, and the core (
An optical fiber (a
) and a foamed resin layer (b) provided in contact with the periphery of the optical fiber (a).

The resin foam layer (b) has a dense non-foamed portion (b).
+ ) and a foamed part (bl), and the non-foamed dense part (b+) is the optical fiber strand (a).
is provided in contact with the outer peripheral surface of the

Due to its dense structure, the non-foamed portion (bl) prevents water from entering from the outside, and also shares stress against bending, twisting, tension, etc., and is useful for increasing mechanical strength.

The foamed portion (bl) has a cushioning effect due to its foam structure. These functions protect and reinforce the optical fiber, making it easier to handle.

In order to increase the stress sharing function of the resin foam layer (b), the thickness (tl) of the non-foamed portion (bl) may be increased, and in order to enhance the relaxation function, the foamed portion (bl) may be increased. It is preferable to increase the thickness (tl) of the portion (bl).

The thickness ratio (1+2℃2) is the optical fiber core (A)
It may be selected as appropriate depending on the intended use and usage environment, but 1:5 to 1:IGO is usually preferred.

The method for forming the resin foam II (b) is to apply a thermoplastic resin solution dissolved in a solvent with a relatively low boiling point, preferably a boiling point of 150°C or less, to the optical fiber, and then heat it to vaporize and remove the i-medium. A method for forming a resin layer AML by applying or extruding a melt of a composition of a pyrolytic blowing agent and a thermoplastic resin onto an optical fiber and then heating it to a temperature higher than the decomposition temperature of the blowing agent. A method such as forming a resin foam layer is adopted.

In either method, the most important thing is to keep the temperature of the optical fiber at a temperature lower than the decomposition temperature of the solvent or blowing agent during application of the foamable thermoplastic resin solution or melt. . By heating the optical fiber to such a temperature, no foaming occurs during coating, and a dense foamable resin coating layer can be formed. When this foamable resin liquid 111l is then externally heated to a temperature higher than the boiling point of the solvent or higher than the thermal decomposition temperature of the foaming agent, foaming occurs sequentially from the outside of the foamable resin coating layer.

When the external heating time is appropriately adjusted, foaming can be stopped at a desired thickness and depth, and an optical fiber core having the structure of the present invention can be obtained.

By the way, when forming an optical fiber by spinning from a preform made of quartz glass, the preform is
The optical fiber must be heated to 00 to 1500°C, and the temperature of the optical fiber when forming the resin coating layer of a conventional resin-coated optical fiber core is only cooled to about 200 to 400°C at most.

However, in order to obtain the optical fiber core wire having the structure of the present invention, the foamable resin foams at such conventional temperatures, so the optical fiber wire is actively heated in a cooling section to reduce the boiling point of the solvent or the foaming temperature. The temperature must be below the decomposition temperature of the agent.

Examples of thermoplastic resins that use solvents include vinyl chloride resin (solvent: tetrahydrofuran, methyl ethyl ketone, etc.), polyethylene (solvent: xylene, toluene, etc.), nylidene fluoride (solvent: acetone, etc.), polystyrene (solvent: toluene, etc.) ), copolymerized nylon (RG medium: ethyl alcohol, etc.), acrylic resin (solvent: acetone, ethyl acetate, methyl acetate, methyl ethyl ketone, etc.), polycarbonate (solvent: methylene chloride, dioxane, chlorobenzene, etc.).

Examples of thermoplastic resins that use a blowing agent include polyethylene, polypropylene, vinyl chloride resin containing azodicarbonamide as a blowing agent, and 4-carbon resin as a blowing agent.
．． Examples include low density polyethylene containing 4'-oxy-bis-benzenesulfonyl hydrazide.

Also, suitable plasticizers, stabilizers, antioxidants, and surfactants can be incorporated into any type of thermoplastic resin.

Next, the method for manufacturing the optical fiber core of the present invention will be explained with reference to FIG. In Fig. 2, (1) is a preform of an optical fiber material made of quartz glass. 21 is a heater, (3) is a cooler, and (4) is a coating! ! ! (6) is a die for applying the resin forming the coating layer, and (5) is a heater for forming the foamed portion in the coating layer.

The lower end of the preform (1) is approximately 12
The optical fiber element 1(a) is spun at a constant take-off speed.

The spun optical fiber strand (a) is actively cooled by a cooler (3). At least the optical fiber element 111(a) is cooled by the cooler (3) to a temperature below the boiling point of the solvent or the decomposition temperature of the blowing agent, and the optical fiber element (a) passes through the die (4) and is then cooled to a temperature below the boiling point of the solvent or the decomposition temperature of the blowing agent. A fat solution or resin melt is deposited on the surface to form a dense resin layer of a suitably desired thickness.

Thereafter, the optical fiber (a) coated with the resin layer is heated by a heater (5) to a temperature above the boiling point of the l medium or above the decomposition temperature of the blowing agent. The temperature rise due to heating by the heater (5) progresses from the outer circumferential surface of the resin layer toward the inner circumference.
By appropriately controlling the heating time, heating temperature, etc. in Example 1, it is possible to obtain an optical fiber having the structure of the present invention in which only the outer peripheral side of the resin layer is foamed.

[Effects of the Invention] The optical fiber core wire having the structure of the present invention has a foamed m-plane layer and a dense layer of non-foamed structure within one resin coating layer. It has a higher mechanical strength than the conventional example having a coating layer, and also has a sufficient buffering effect, so it is highly effective in protecting and reinforcing the optical fiber.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the optical fiber core wire of the present invention,
FIG. 2 is an explanatory diagram of the manufacturing process of the optical fiber coated wire shown in FIG. 1, and FIG. 3 is a sectional view of the conventional coated optical fiber wire. (Main symbols in the drawing) (a): Optical fiber (b): Resin foam layer (b+): Non-foamed portion of resin foam layer
(bz) : Foamed part of the resin foam layer b2=foamed part';'t'2 Figure

Claims (1)

[Claims] 1 A structure in which a resin foam layer is provided around an optical fiber strand, and the resin foam layer has a dense, non-foamed portion in a portion that is in contact with the outer peripheral surface of the optical fiber strand. The structure of optical fiber.