JPS64336B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field The present invention relates to a method for reinforcing a glass fiber for optical transmission (hereinafter abbreviated as optical fiber) with plastic coating, which has excellent optical transmission characteristics and sufficient strength. The object is to provide a coated fiber that is weather resistant.

(b) Background technology Optical fibers have a diameter of 200 μm or less in order to maintain flexibility, and are extremely fragile materials. Therefore, it is mechanically difficult to use optical fibers as they are as transmission lines. From a strength standpoint, it's almost impossible. It is also known that the strength of glass decreases over time due to the influence of moisture, etc., which is an inherent property of glass.

For this reason, a method has been proposed for producing a glass fiber having initial strength and strength for long-term use by applying a protective coating of plastic or metal to the surface of the glass fiber.

For example, by coating a glass fiber with a resin composition such as polyamide, polyester, epoxy resin, silicone resin, or polyurethane, which has a polar group in its molecule and has excellent adhesion to glass, such a structure can be created. The breaking load and elongation rate of coated fibers are significantly improved compared to uncoated fibers, especially when a resin composition such as epoxy resin, silicone resin, or polyurethane is thinly coated and baked.
Furthermore, the coated fibers obtained by melt-extrusion coating a thermoplastic resin on top of the coated fibers have sufficient resistance to external forces applied when a plurality of coated fibers are assembled into a cable or when laid in a conduit, etc. With the strength you get.

However, when coated fibers with such a structure are subjected to thermal stress due to temperature changes or stress due to bending, so-called microbending occurs, in which the glass fibers are bent at very small intervals, which increases transmission loss. are doing. For this reason, methods have been proposed in which a resin with a low Young's modulus such as foamed plastic, oil, silicone resin, or ethylene-vinyl acetate copolymer is interposed between the glass fiber and the plastic coating layer to absorb the applied stress. There is.

Among these methods, in the method of forming a stress-absorbing layer of thermosetting silicone resin, after spinning the glass fiber and before contacting other solid materials (in tandem with spinning), epoxy resin, fluororesin, urethane resin, etc. A resin composition such as a resin is applied and baked, and then a silicone resin with a low Young's modulus is applied and baked, either in tandem with the above process or once wound onto a bobbin, etc., or a glass fiber is spun. After that, a silicone resin with a low Young's modulus is directly coated and baked, and the thus obtained optical fiber having a stress-absorbing layer of silicone resin is coated with a thermoplastic resin such as polyamide, polyethylene, polycarbonate, or fluorine resin by melt extrusion. was taken.
However, the above method had the following drawbacks.

A stress absorbing layer made of a silicone resin with a low Young's modulus is mechanically damaged by a roller or the like during extrusion coating with a thermoplastic resin, resulting in a decrease in strength or an increase in transmission loss.

The silicone resin stress absorbing layer already receives a large stress due to residual strain in the thermoplastic resin during extrusion coating, and is no longer able to absorb thermal stress due to temperature changes or stress due to bending or the like.

In an attempt to improve these drawbacks, when coating thermosetting silicone resin on glass fiber or glass fiber that has been primarily coated with epoxy resin, urethane resin, etc., the silicone resin is coated with a die or a coating bath. JP-A No. 54-13352 discloses a method in which the silicone resin is coated with a thermoplastic resin such as polyamide or polyethylene before being applied and cured, and the thermoplastic resin is molded by cooling or the like, and then the silicone resin is thermoset. It is disclosed in the publication No. This method will be explained using the flow sheet shown in FIG. After the optical fiber glass base material 1 is drawn in a drawing furnace 2, epoxy resin, urethane resin, etc. are applied in a primary coating coating device 3, and thermally cured in a curing furnace 4, followed by a stress-absorbing layer resin coating device. A silicone resin is applied in step 5, and then a thermoplastic resin is applied in a crosshead 6 of an extruder for secondary coating, followed by cooling in a secondary coating cooling tank 7 to form a secondary coating layer. Thereafter, the stress-absorbing layer is thermally cured in a stress-absorbing layer curing furnace 8, and then wound onto a winding machine 11 via a winding dancer roller 10 by a capstan 9.

However, it has been found that this method also has the following problems.

The thermoplastic resin that serves as the secondary coating material is usually coated onto the optical fiber by extrusion processing by heating and melting. It is very difficult to apply the above-mentioned secondary coating without curing. That is, in FIG. 1, a part of the thermosetting resin applied to the optical fiber by the stress-absorbing layer resin coating device 5 begins to harden in the crosshead 6 of the extruder at the part through which the optical fiber passes, and becomes thermosetting. The amount of resin applied becomes non-uniform, making it impossible to obtain a long coated optical fiber.

If the curing temperature of the curing furnace 8 for curing the internal thermosetting resin composition is increased after the secondary coating is applied, the temperature cannot be increased because the secondary coating will be melted. Therefore, it takes a long time to cure, so the line speed does not increase and productivity is poor.
Furthermore, the elongation of the coating material due to heating cannot be reduced to zero.

(C) Disclosure of the Invention The present invention has been made for the purpose of solving the problems of the prior art as described above, and is characterized by using an ultraviolet curable resin that does not heat cure as a stress absorbing layer. By using an ultraviolet curable resin, the stress-absorbing layer does not harden due to high temperatures during the coating process of the secondary coating material, making it easier to apply the secondary coating while the stress-absorbing layer is uncured. be.

That is, the present invention provides a method for reinforcing a light transmission glass fiber in which a reaction curable resin is interposed as a stress absorbing layer between the light transmission glass fiber and a thermoplastic resin coating layer, in which an ultraviolet curable resin is used as the reaction curable resin. A method for reinforcing a glass fiber for optical transmission, comprising simultaneously extrusion coating the ultraviolet curable resin and a thermoplastic resin, cooling and molding the thermoplastic resin, and then curing the ultraviolet curable resin; The present invention relates to the reinforcing method described above, wherein the ultraviolet curable resin of the stress absorbing layer is a silicone resin, a butadiene resin, or a urethane resin.

In fact, as shown in Fig. 1, the application section 5 and the crosshead 6
Apart from separating the thermosetting resin, when trying to press-fit the thermosetting resin into the crosshead, it is necessary to use a special structure of the extruder crosshead to insulate the part where the thermosetting resin flows when applying the secondary coating. It was necessary to prevent heat from the extruder from being transmitted. However, complete insulation cannot be achieved at the point where the secondary coating material is melt-extruded and contacts the thermosetting resin. If the curing temperature of the resin is lowered to slow down the curing speed in order to prevent curing due to heat, the disadvantage arises that it takes more time to heat cure the resin after coating.

On the other hand, if an ultraviolet curable resin is used as in the present invention, it is possible to apply an ultraviolet curable resin to the part where the optical fiber passes inside the crosshead, as shown in Figure 3 below, without devising the heat insulation structure as described above. It is only necessary to make it press-fittable, and since the stress-absorbing layer does not undergo thermosetting, there is no limit to the extrusion length.
Because it is cured by ultraviolet rays, the secondary coating material can be cured without melting, elongating, or deforming.

The method of the present invention will be further explained with reference to FIG. 2 and FIG. 3, which is an enlarged view of the crosshead portion of FIG. As in the case of FIG. 1, after drawing the optical fiber glass base material, the optical fiber A that has been subjected to the primary coding B is sent from the supply device 12 to the extruder crosshead 14 for the secondary coating D. An ultraviolet curing resin C is supplied from a resin supply device 13. The enlarged view of this part is shown in the 3rd page.
As shown in the figure. In FIG. 3, 15 is an extrusion die, 16 is a nipple, and 17 is a nipple holder. The optical fiber A having the primary coating layer B coated with the ultraviolet curable resin C on the outer periphery and the secondary coating material D on the outer periphery in this way enters the cooling trough 18 where the secondary coating material layer D is cooled, shaped, and then Curing the ultraviolet curable resin layer C with an ultraviolet curing device 19,
A capstan 20 is used, a dancer 21 is used, and a winder 22 winds up the film.

In this way, an optical fiber A as shown in FIG. 4 is obtained which has a primary coating B, a stress absorbing layer C made of an ultraviolet curable resin, and a secondary coating layer D sequentially provided on its outer periphery.

The primary coating layer used in the method of the present invention may be made of a conventional epoxy resin or urethane resin, and its thickness is generally 100 μm or less. Examples of ultraviolet curable resins include silicone resins, butadiene resins, and urethane resins, and the stress absorbing layer made of these resins generally has a thickness of 100 μm to 500 μm. Polyamide, polyethylene, etc. are used as the thermosetting resin, and the thickness is 50 μm to 400 μm.
m is common.

As described above, in the method of the present invention, the effects of heat can be ignored, so the following effects can be achieved.

1. The structure of the extruder crosshead during secondary coating can be simplified.

2. Covering can be applied to any length and can be made longer.

3. Post-curing is simple and can be completed in a short time because the secondary coating material does not undergo heat deformation during the post-curing process.

4. By providing the post-curing ultraviolet oven in the cooling water, there is no reheating process for the secondary coating material, so the elongation strain of the secondary coating material can be reduced to zero.

(d) Best Mode for Carrying Out the Invention Example 1 Optical fiber with an outer diameter of 250 μm (glass diameter
125 μm), an ultraviolet curable silicone resin was press-fitted using an extruder crosshead, and nylon was extruded and coated on top. With inner diameter of nylon coating
After finishing it to 400 μm and 900 μm in outer diameter, it was cured online through an ultraviolet lamp with an output of 80 W/cm. The silicone resin could be completely cured at an extrusion line speed of 100 m/min. There was no particular restriction on the extrusion length, and a single-length optical fiber core of 5 km or more was obtained.

Comparative Example 1 Similarly, an optical fiber coated with a primary coating having an outer diameter of 250 μm was coated with thermosetting silicone resin, fed into the crosshead of an extruder so as not to touch nipples, dies, etc., and coated with nylon by extrusion.

As a result, stable production was possible for about 500 m, and because the nylon extrusion was withdrawn largely to avoid contact with the resin, air bubbles were likely to form at the interface between the silicone resin and nylon. The reason why the single length was shortened to 500 m was because the applied silicone resin came into contact with the inside of the nipple due to the slight vibration of the fiber and hardened. In addition, the manufactured optical fiber core wire was thermally cured off-line, which required 30 minutes at 120°C.

Comparative Example 2 An optical fiber core wire having the same cross-sectional structure as the above two examples was produced by modifying the extruder crosshead and water-cooling and insulating the part where the thermosetting silicone resin was press-fitted. The stable production length was approximately 1000 m, but the outside diameter fluctuated due to resin clogging at the tip of the nipple. Curing of the resin took 2 hours offline at 120°C.

Example 2 Optical fiber with an outer diameter of 250 μm (glass diameter 125 μm) with a primary coating of epoxy resin
On (m), an ultraviolet curable silicone resin was press-fitted using the crosshead of an extruder, and nylon was extrusion coated thereon. The structure was the same as in Example 1, and there were no problems in manufacturability.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing the flow of the optical fiber reinforcing method as a prior art of the present invention, and FIG. 2 is a flow sheet showing the flow of the method of the present invention.
FIG. 3 is an enlarged cross-sectional view of the crosshead portion of the extruder for secondary coating shown in FIG. 2, and FIG. 4 is a cross-sectional view showing the structure of the optical fiber obtained by the method of the present invention.

Claims (1)

[Scope of Claims] 1. A method for reinforcing a glass fiber for optical transmission, in which a reactive hardening resin is interposed as a stress absorbing layer between the glass fiber for optical transmission and a thermoplastic resin coating layer, wherein ultraviolet rays are used as the reactive hardening resin. Reinforcement of glass fiber for optical transmission, characterized by using a curable resin, simultaneously extruding the ultraviolet curable resin and a thermoplastic resin, cooling and molding the thermoplastic resin, and then curing the ultraviolet curable resin. Method. 2. The method for reinforcing a glass fiber for optical transmission according to claim 1, wherein the ultraviolet curable resin of the stress absorbing layer is a silicone resin, a butadiene resin, or a urethane resin.