JPS6228103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention is a method of reinforcing an optical fiber having a protective layer of plastic by applying a long reinforcing fiber and a thermosetting resin impregnated therein.
This invention relates to a method for manufacturing optical fiber cores.

(b) Background technology As shown in Fig. 1, a conventional optical fiber core wire includes an optical fiber 1, a primary coating, 2 (silicon resin), a buffer layer, 3 (silicon resin), and a secondary coating layer thereon. 4 is coated with a thermoplastic resin such as nylon. Although fibers with this structure have the advantage of being relatively easy to manufacture, the temperature dependence of the secondary coating plastic, including the coefficient of linear expansion, is more than two orders of magnitude greater than that of the glass material, resulting in poor transmission characteristics. It also has the drawbacks of high temperature dependence and weak resistance to bending and lateral pressure. For this reason, it is impossible to use this core wire alone, and reinforcing materials such as tension members are required in order to use it as a cable or cord.

In order to eliminate these drawbacks of conventional optical fiber core wires, it is extremely important to use a thermosetting resin reinforced with aromatic polyamide fibers, carbon fibers, etc., so-called FRP (fiber reinforced plastic), as a secondary coating. known to be effective.
The present invention relates to an improved method for successfully manufacturing such FRP coated optical fiber.

In order to manufacture an FRP core wire coated with FRP as a secondary coating layer, a pultrusion method, which is one of the continuous FRP molding methods, is usually adopted. This pultrusion method will be explained using the example shown in FIG.

After reinforcing fibers 11 such as carbon fibers are impregnated with a thermosetting resin such as epoxy or unsaturated polyester resin in a resin impregnation tank 5,
The optical fiber 12 coated up to the buffer layer is supplied and positioned at the center of the reinforcing fiber 11 while passing through the batten 6. Then, while finishing it to a predetermined diameter with a molding die 7, the resin is heated in a heating hardening furnace 8 to harden the resin, and then pulled out from the heating hardening furnace with a drawing device 9 and wound onto a bobbin with a winding device 10, thereby producing the resin.

The problem with this manufacturing method is that the resin impregnated into the reinforcing fibers in the impregnation tank adheres and accumulates in the heat curing furnace, especially near the mold entrance, and is finally hardened by the heat of the curing furnace. This obstructs the running of the reinforcing fibers and ultimately leads to the suspension of production. This problem becomes more important as the production speed increases and as the content of resin in the reinforcing fibers increases.

(C) Disclosure of the Invention The present invention solves the above problems and enables the stable and efficient production of FRP-coated optical fiber core wires over a long period of time. By providing a mold that has been cooled to a temperature below the curing temperature of the resin, the resin adhering to the mold is prevented from curing and excess resin is squeezed out.

The resin in the impregnation bath must be sufficiently impregnated in order to maintain good mutual adhesion of the reinforcing fibers, and for this purpose, the resin is impregnated in an amount greater than the required amount. This excess resin can be squeezed out to some extent with a molding die, but if done too much, the necessary resin may be squeezed out of the reinforcing fibers, and it is difficult to squeeze out only the excess resin with precision. It is inevitable that resin will adhere to the inlet of the mold in the curing furnace. In order to prevent the adhered resin from curing, it is effective to cool a mold provided at the inlet of the curing furnace and directly connected to the curing furnace to a temperature below the curing temperature of the resin.

An example of the method of the present invention will be explained with reference to FIG.

FIG. 3 is a detailed view of the heat curing furnace, in which the primary coated optical fiber strand 12 and the reinforcing fiber 11 run inside the mold 14 in the curing furnace. The mold is a heater 13
The resin in the reinforcing fibers is cured by this heat, and an optical fiber coated with an FRP layer is obtained. In the case of the example shown in FIG. 3, the mold projects out of the heater, the cooling part 17 is provided on the outer periphery of the projecting part, and cooling water is introduced from the cooling water inlet 15 and discharged from the cooling water outlet 16. .
The mold inlet is cooled by this cooling water, and the resin adhering to the mold inlet is prevented from hardening. Therefore, this adhesion causes excess resin to be squeezed out of the fibers. It is preferable to cool the resin to 30°C or less to prevent hardening of the resin. As a result, conventionally,
It is possible to prevent line stoppages caused by resin adhesion and curing, allowing for long production times.

(iv) Best Mode for Carrying Out the Invention An optical fiber wire with a diameter of 0.4 mm that is primarily coated with a silicone layer is impregnated with an unsaturated polyester resin in the glass fiber and cured to produce a light beam with a diameter of 0.1 mm. An attempt was made to manufacture fiber cores. The length of the mold is 200mm, and the heating temperature is 120℃.

In the conventional method, which did not cool the mold, the resin adhering to the mold entrance hardened and production could only take about five hours. On the other hand, when the mold was cooled 50 mm from the entrance where the optical fiber was introduced to 25°C, no problem of hardening of the adhered resin occurred.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the structure of a general optical fiber core, Figure 2 is a flow sheet showing an outline of the pultrusion method for FRP core, and Figure 3 explains the method of the present invention. FIG.

Claims (1)

[Claims] 1. An optical fiber having a protective layer of plastic and a reinforcing fiber impregnated with a thermosetting resin are introduced into a mold in a heating curing furnace, and the resin is heated and hardened to produce an optical fiber coated with the reinforcing fiber. In this process, a mold is provided at the entrance of the heating curing furnace and is directly connected to the curing furnace and cooled to a temperature below the curing temperature of the resin, so that excess resin is squeezed out by the mold. A method for manufacturing a reinforced plastic coated optical fiber core.