JPS63112443A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To prevent occurrence of a slipping phenomenon and homogeneously and stably coat an optical fiber at a high speed, by coating a coated or uncoated optical fiber drawn from an optical fiber preform with a liquid ultraviolet curing type resin under specific conditions and curing the resin. CONSTITUTION:An optical fiber drawn from an optical fiber preform or a coated optical fiber is coated with a liquid ultraviolet curing type resin, e.g. urethane acrylate, through a coating die under conditions of 500-3,000cP viscosity under low shearing speed at the coating temperature and 60-100 deg.C temperature and then passed through an ultraviolet ray irradiation device to cure the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an optical fiber, and more particularly to a method for uniformly coating an optical fiber with a protective coating resin at high speed.

[Conventional technology]

FIG. 2 is a diagram illustrating a conventional optical fiber coating process. 3 is an optical fiber, 4 is a liquid resin, 5 is a coating die,
6 is a curing device for curing the applied liquid resin, 7 is a coated optical fiber, and 8 is a winder. Whether the optical fiber 3 is a bare fiber with no coating immediately after being drawn or is already coated, the coating is performed in the same process.

Optical fibers are usually coated with multiple layers from the viewpoint of mechanical strength and transmission characteristics. Covering materials are classified based on their curing method, and generally thermosetting resins and ultraviolet curable resins are mainly used, but in recent years the latter type of ultraviolet curable resin has become mainstream. The reason for this is that the use of a photocuring reaction makes it possible to increase the drawing speed of optical fibers, and the use of a smaller UV curing furnace for curing equipment, such as a curing furnace, compared to a conventional thermal curing furnace. Therefore, in addition to the simplification of equipment, the cost of the ultraviolet curable resin material itself has been reduced in terms of raw material composition, making it economically effective.

Conventionally, in the coating process for optical fibers using ultraviolet curable resin, it was generally done at room temperature! '-C', viscosity measured at low shear rate of about 1 sec-' is 1000 to 1000
A signal with a speed of about 0 cps is used. In the coating method using a coating die 5 as shown in FIG.
Empirically, the viscosity of is generally between 500 and 30
00 cps, and if the viscosity was too high at room temperature, the temperature was slightly raised to adjust the viscosity of the liquid resin 4 to within the above range. The coating temperature at this time was usually a maximum of about 50°C.

[Problem that the invention seeks to solve]

With the rapid increase in demand for optical fibers, low-cost production is required, and high productivity, that is, high-speed coating, is important in the coating process. However, in conventional coating methods, the upper limit of the drawing speed at which liquid resin can be stably and uniformly applied is low. Although the cause is not clear, the following reasons are considered. That is, within the coating die, there is a flow rate distribution of resin as shown, for example, in FIGS. 3a and 3b, and the shear rate is generally not constant. On the other hand, as shown in FIG. 4, the viscosity of the resin decreases as the shear rate increases, so a so-called "slip" phenomenon occurs in which the resin cannot keep up in the portions of the die where the shear rate is high.

This "slip" occurs because the viscosity of the resin suddenly decreases when the shear rate exceeds a certain limit, and therefore, there is a problem in that stable and uniform coating becomes difficult at high drawing speeds.

[Means for solving problems]

In order to solve the conventional problems, the present invention coats an optical fiber drawn from an optical fiber base material or a coated optical fiber with a liquid ultraviolet curable resin using a coating die, and then coats it with an ultraviolet ray irradiation device. In an optical fiber manufacturing method in which a liquid ultraviolet curable resin is cured by passing through a Shear rate viscosity is 500 cps to 3000
It is characterized by being cps.

[For production]

The viscosity of the present invention at low shear rate at coating temperature is 500c.
By using a liquid UV-curable resin with a ps to 3000 cps and applying it at a temperature range of 60°C to 100°C, there is no sudden drop in resin viscosity even during high-speed drawing, and the phenomenon of "slip" is eliminated. The fact that resin coating can be performed uniformly and stably at high speed with little occurrence of this will be explained below.

The viscosity characteristics of the resin, that is, the dependence on temperature and shear rate, are
It varies depending on the composition of the resin, such as the type and molecular weight distribution of prepolymers and monomers, additives, etc.

Therefore, we synthesized resins with various compositions and measured the shear rate dependence of their viscosity. As a result, as shown in Figure 5,
Three resins A and B with similar resin compositions such that the viscosity at low shear rates is the same.

When the temperatures for C are set as TI, Tz, and Tl (however, Tl <Tz'< Tl),
The following trends were found. That is, resins A, B, and C with similar compositions, which have high viscosity at the same temperature, are treated at different temperatures TI, T2, and Tl, respectively, but TI<T2<Tl
Among the resins whose viscosity was measured by lowering the viscosity at high temperatures, resin C was more difficult to decrease than resin B, and resin B was more difficult to decrease than resin B in the high shear rate region (1 direction was observed. This tendency was Epoxy acrylate type, urethane acrylate type,
This was common to all silicone acrylate and silicone types.

Furthermore, at the same temperature, even for different types of resins, the shear rate (
Hereinafter referred to as critical shear rate. ) are almost the same.

In general, UV-curable resins have the above-mentioned viscosity.
Therefore, when a high viscosity resin is applied to an optical fiber at high temperature, the critical shear rate is high, and the high shear rate region of the resin flow in the die, for example, in many cases, Fig. 3a "Slip" is less likely to occur on the fiber surface in Figure 3 or on the die wall surface in Figure 3, and stable and uniform coating is possible even at high drawing speeds.

In addition, the upper limit of the coating temperature range is approximately 10
It is 0°C. The basis for the lower limit of 60°C will be explained in Examples below.

- At IQ, the optical fiber is coated with one or more layers while being drawn. In this case, the temperature of the fiber to be coated, that is, the bare glass fiber for the -th layer and the coated fiber for the second and subsequent layers, changes depending on the drawing speed. This temperature change is due to the high temperature melting of the glass in bare glass fibers, and the change in cooling time for coated fibers after reaching a high temperature due to curing heat, etc. From the viewpoint of uniform and stable coating, it is desirable to reduce the temperature difference between the fiber to be coated and the resin to be coated, and to have a small temperature distribution (referred to as viscosity distribution) of the resin in the die. For this reason, it is preferable to control the fiber temperature before applying the resin to match the temperature of the resin. Specific examples will be described below.

〔Example〕

Examples will be described in which several types of optical fibers of this type were produced as prototypes using the optical fiber manufacturing method steps shown in FIG. 1, and were comparatively evaluated. In FIG. 1, the same reference numerals as in FIG. 2 indicate the same parts. 1 is an optical fiber preform, and 2 is a drawing furnace.

Example 1: While drawing a glass fiber with an outer diameter of 125 μmφ, it was coated with nine types of resin shown in Table 1 at a drawing speed of 100 m/min to 600 m/min, finished to an outer diameter of 200 μmφ, and uniformity of coating was observed. and stability was investigated and evaluated.

Table 1 From the results shown in Table 1, sample No. 2.3, 5°6.9
It was possible to apply a uniform and stable coating.

From this, it is recognized that uniform and stable coating can be performed using a resin having high viscosity at low temperature and at a temperature of the resin to be coated in the range of 60°C to 100°C.

Example 2: A glass fiber with an outer diameter of 125 μmφ was coated with urethane acrylate.A urethane acrylate coated optical fiber with an outer diameter of 200 μmφ was coated with the six types of resins shown in Table 2 at a drawing speed of 500 m/min, and the outer diameter was It was finished to a diameter of 300 μmφ, and the uniformity and stability of the coating was examined and evaluated.

Table 2 From the results shown in Table 2, sample No. 2. 3. 6
was able to achieve uniform and stable application. This result also confirms that uniform and stable coating can be performed using a low-temperature, high-viscosity resin at a temperature of 60°C to 100°C.

The present invention is not particularly limited to the coating structure of the optical fiber in the above embodiments, but can be applied to a wide range of ordinary ultraviolet curable resin-coated optical fibers.

〔Effect of the invention〕

As described above, according to the optical fiber manufacturing method of the present invention, even during high-speed drawing, there is no sudden drop in the viscosity of the resin during the application/coating process of the ultraviolet curable resin, so the "slip" phenomenon does not occur. This makes it possible to uniformly and stably coat the ultraviolet curable resin with high-speed wire drawing, which is highly effective.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the process of manufacturing an optical fiber according to the present invention, Fig. 2 is an explanatory diagram of the coating process of a conventional optical fiber, Figs. Figure 4 shows the shear rate dependence of typical resin viscosity, Figure 5 shows the shear rate dependence of similar composition resin viscosity, and Figure 6 shows the shear rate dependence of resin viscosity of similar compositions.
The figure shows the shear rate dependence of the viscosity of different resins. ■...Optical fiber base material, 2...Drawing furnace, 3...Optical fiber, 4...Liquid resin, 5...Coating die, 6
Curing device, 7 Coated optical fiber, 8 Winding machine Patent applicant Sumitomo Electric Industries Co., Ltd. Agent Patent attorney Hisashi Tamamushi 5 Part shear rate (sec') Shear of typical resin viscosity Rate-dependent bacteria Figure 4 Shear rate Figure 6

Claims (2)

[Claims] (1) After coating an optical fiber drawn from an optical fiber base material or a coated optical fiber with a liquid ultraviolet curable resin using a coating die, the liquid is passed through an ultraviolet irradiation device. In the method for manufacturing an optical fiber in which an ultraviolet curable resin is cured, the liquid ultraviolet curable resin applied to the optical fiber has a coating temperature in the range of 60°C to 100°C, and a viscosity of a low shear rate at the coating temperature. is 500cps to 3
A method for manufacturing an optical fiber, characterized in that the optical fiber has a speed of 0.000 cps. (2) The method for manufacturing an optical fiber according to claim 1, wherein the liquid ultraviolet curable resin is coated on the optical fiber while drawing the optical fiber preform.