JPH01167264A - Optical fiber coating method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for coating optical fibers, and provides good mechanical properties and transmission by applying and curing a plurality of ultraviolet curable resin liquids at once. This makes it possible to manufacture optical fiber cores with loss characteristics.

[Prior Art] In general communication optical fibers, the Young's modulus is 0°1 to 0.
Two or more coating layers are formed, consisting of an inner layer with a low Young's modulus of 5 kg/mm2 and an outer layer with a high Young's modulus of 30 to 150 kg/mm2. It is designed to protect the

Conventionally, for example, an apparatus as shown in FIG. 6 has been used to form two coating layers on the surface of an optical fiber.

In FIG. 6, reference numeral 1 indicates an optical fiber preform. This optical fiber preform I is held by a preform delivery device 2 . The optical fiber preform (2) is heated and melted in a heating furnace 3 installed at the lower part of the parent phase delivery device 2 and spun into an optical fiber 4.

While this optical fiber 4 is being wound up by a winding machine 12 to which a winding machine 11 is connected, a coating layer is formed on its surface by each device described below. After the diameter of the optical fiber 4 is measured by the optical fiber diameter measuring device 5, the optical fiber 4 is
A coater 6 applies an ultraviolet curable resin liquid suitable for the diameter, and an ultraviolet ray irradiation device 7 irradiates ultraviolet rays to harden the applied ultraviolet curable resin liquid to form an inner layer.

Next, the second coater 8 reapplies the ultraviolet curable resin liquid onto the previously formed inner layer, and then the ultraviolet ray irradiation device 9 cures the outer layer.

The diameter of the optical fiber 4 on which the two outer and outer coating layers have been formed in this manner is measured by the optical fiber diameter measuring device IO, and then wound by the winder 12 to form an optical fiber core.

[Problems to be Solved by the Invention] However, in the optical fiber coating method shown in FIG. 6, the second and third coating layers are formed after forming the innermost layer, so multilayer coating is required. In some cases, the applied ultraviolet curable resin liquid is exposed to the air without being cured, increasing the chances of it collecting a large number of impurities floating in the air or reacting with oxygen. When such an ultraviolet curable resin liquid is hardened to 3-, crosslinking defects are generated in the cured resin, which causes a decrease in the strength of the optical fiber and an increase in transmission loss.

Therefore, as a method for coating an optical fiber, a method has been proposed in which a plurality of ultraviolet curable resin liquids are applied all at once and cured as described below. In this method, on the surface of the optical fiber,
First, a first ultraviolet curable resin liquid that forms the innermost layer is applied, and while the applied first ultraviolet curable resin liquid remains uncured, second and third ultraviolet curable resin liquids are continuously applied thereon. After applying the mold resin liquid, by irradiating the mold resin liquid with ultraviolet rays and curing them, the chances of the applied ultraviolet curable resin liquid being exposed to the air in an uncured state can be reduced.

However, the problem with curing multiple UV-curable resin liquids coated together is that most of the irradiated ultraviolet rays are absorbed by the outermost layer of the UV-curable resin liquid. Since the curing reaction proceeds from then on, the amount of ultraviolet irradiation to the innermost layer is insufficient and the innermost layer remains uncured.

This reduces the adhesion between the top layer and the surface of the optical fiber, resulting in disadvantages such as a decrease in the mechanical properties of the optical fiber and an increase in transmission loss.

This invention was made in order to solve the problem mentioned in "2", and it is possible to coat an optical fiber by applying multiple layers of ultraviolet curable resin liquid to the optical fiber at once and curing them sequentially starting from the innermost layer. The purpose is to provide a method.

[Means for Solving the Problems] The present invention provides a method in which a plurality of ultraviolet curable resin liquids are applied on the surface of an optical fiber at once, and then ultraviolet rays are irradiated to form a plurality of coating layers. By adding photopolymerization initiators with different absorption wavelength ranges to the resin liquid and sequentially irradiating them with ultraviolet rays with wavelengths that match the absorption wavelength ranges of these photopolymerization initiators, the resin liquid is cured sequentially starting from the innermost layer of the ultraviolet curable resin liquid. The solution is to form multiple coating layers on noni.

[Function] When multiple UV-curable resin liquids are applied to the surface of an optical fiber at once and then cured by UV irradiation, the UV-curable resin liquids forming each coating layer are exposed to light with different absorption wavelength regions. Since a polymerization initiator is added, the UV rays will be absorbed and the curing reaction will proceed only when the photopolymerization initiator is irradiated with UV rays of a wavelength compatible with the photopolymerization initiator. If ultraviolet rays matching the absorption wavelength range of the photopolymerization initiator are first irradiated, the curing reaction can be started from the innermost layer without the irradiated ultraviolet rays being absorbed by the outermost layer. After the curing reaction of the innermost layer is completed, the ultraviolet curable resin liquid is cured sequentially from the inner coating layer, so that there is no uncured coating layer of the ultraviolet curable resin liquid.

The present invention will be described in detail below.

FIG. 1 shows an example of an apparatus suitably used for carrying out the optical fiber coating method of the present invention.

This device forms two coating layers, an inner and outer layer, on the surface of an optical fiber.The difference from the device shown in FIG. a batch coater 13 for applying the coating, and an ultraviolet irradiation device 14 corresponding to the number of applied ultraviolet curable resin liquids.
15 are arranged in such a way that the ultraviolet curable resin liquid applied to the optical fiber 4 is cured preferentially from the innermost layer and then sequentially towards the outer layer.

For example, when applying two ultraviolet curable resin liquids, this multi-layer coater 13 consists of two dies, an inner and an outer die, and the spun optical fiber 4 is first transferred to the first die for coating the inner layer. After the UV curable resin liquid for the inner layer is applied, the two ultraviolet rays are guided into the second die for coating the outer layer, which immediately applies the UV curable resin liquid for the outer layer. The curable resin liquid is applied all at once. In this multi-batch coater 13, by arranging dies corresponding to the number of coating layers formed on the optical fiber 4, it is possible to apply an arbitrary number of ultraviolet curable resin liquids of one or more at once.

An inner layer ultraviolet irradiation device 14 and an outer layer ultraviolet irradiation device 15 are arranged below the multi-layer coater I3, and are suitable for curing the ultraviolet curable resin liquid applied to the surface of the optical fiber. It emits wavelengths of ultraviolet light. That is, the inner layer ultraviolet irradiation device 14
Then, ultraviolet rays matching the absorption wavelength range of the photopolymerization initiator added to the ultraviolet curable resin liquid forming the inner layer are irradiated, and the ultraviolet ray irradiation device 15 for outer layer is used to irradiate the ultraviolet rays added to the ultraviolet curable resin liquid forming the outer layer. UV rays matching the absorption wavelength range of the photopolymerization initiator are irradiated.

As the photopolymerization initiator added to the ultraviolet curable resin liquid forming each coating layer in the optical fiber coating method of the present invention, for example, those shown in Table 1 can be used.

Below, in the margin Table 1 ■ Isopropyl benzoin ether ■ Benzyl dimethyl kecool ■ Hydroxymethyl propiophenone ■ Benzophenone ■ Michler's ketone ■ Chlordioxanthone ■ Nomethyl oxanthone As shown in Table 1, each photopolymerization Since the absorbance of the initiator varies greatly depending on the wavelength, the wavelength of the ultraviolet rays to be irradiated may be changed in accordance with the photopolymerization initiator added to each coating layer.

Next, a method of coating an optical fiber according to the present invention using the above-mentioned apparatus will be explained. First, an optical fiber preform 1 is prepared using an optical fiber preform I manufacturing apparatus (not shown). This optical fiber preform l is installed in the preform delivery device 2, and the heating furnace 3
The optical fiber 4 is obtained by heating and melt spinning. Next, after measuring the diameter with the optical fiber diameter measuring device 5, the two ultraviolet curable resin liquids are applied at once using a multi-layer coater 13 so as to apply an amount of ultraviolet curable resin liquid suitable for the diameter. Apply. Next, this optical fiber 4 is led to the inner layer ultraviolet irradiation device I4, and is irradiated with ultraviolet rays of a wavelength that matches the absorption wavelength range of the photopolymerization initiator added to the ultraviolet curable resin liquid that forms the inner coating layer. Then, the curing of the ultraviolet curable resin liquid in the inner layer is completed. Next, the resin is led to the outer layer ultraviolet irradiation device I5, and the ultraviolet curable resin liquid forming the outer coating layer is cured. The diameter of the optical fiber 4 on which a plurality of coating layers have been formed in this way is measured again in the optical fiber diameter measuring device 10, and then passed through the take-up machine 11 and wound up by the wind-up machine 12 to form an optical fiber core. It is used as a line.

[Example] Figure 1? By using the optical fiber coating apparatus shown above and the optical fiber coating method of the present invention, the fiber diameter is 125 μm.
Two coating layers made of two kinds of ultraviolet curable resins were formed on a single moat fiber of m as follows.

Michler's ketone was added as a photopolymerization initiator to a resin composition consisting of an oligomer in which a monoethylenically unsaturated polymerization group was bonded to the end of a polyalkylene polyester and a monoethylenically unsaturated monomer as an ultraviolet curable resin liquid forming the inner layer. A resin composition containing noacrylate ester of diglycidyl ether and polyurethane 7 as the main components and isopropyl benzoin ether as a photopolymerization initiator was prepared as an ultraviolet curable resin liquid to form the outer layer. multiple layers −
After filling the bulk coater and applying it all at once to the optical fiber, the inner layer ultraviolet irradiation device uses a UV light beam with an emission center wavelength of 390 nm, which matches the absorption wavelength region of 360 nm of Michler's ketone, as shown in Figure 3. Ultraviolet luminescent lamp with emission spectrum (Fusion, D bulb)
In order to match the absorption wavelength region of isopropyl benzoin ether at 260 nm, the ultraviolet irradiation device for the outer layer uses an ultraviolet light emitting lamp with an emission center wavelength of 260 nm and an emission spectrum as shown in Figure 2. (F
US ion, I-1 valve) at a linear speed of 120
It was passed through at a speed of m/min and irradiated with ultraviolet light to form two coating layers.

In this way, in the first irradiation with ultraviolet light with a wavelength of 390 nm, the absorption wavelength of the photopolymerization initiator in the outer layer is 250 nm.
Since isopropyl benzoin ether with a wavelength of 260 nm was used, ultraviolet rays with a wavelength of around 360 nm ("j") were not absorbed but were transmitted and absorbed by the ultraviolet curable resin liquid to which Michler's ketone was added in the inner layer, and the curing reaction proceeded, causing the inner layer to reached a predetermined degree of curing, and an optical fiber with an outer diameter of 200 μm was obtained. After this, the curing of the outer layer was completed by a second UV irradiation, and the optical fiber surface had a predetermined Young's modulus of approximately 0 and 2.
An optical fiber having an outer diameter of 250 μm and having two inner and outer covering layers was obtained.

The loss temperature characteristic of this optical fiber at 140°C shows that the loss increase is +〇,O]dB/km, and the Weibull distribution of the tensile breaking strength is also good as shown by the solid line in Figure 5. Ta. The tensile strength test was conducted under the following conditions: 100 samples, a strain rate of 10% for 7 minutes, and a sample length of 10 m.

(Comparative Example 1) Monoethylenically unsaturated polymerized fJ was bonded to the end of polyalkylene polyester as an ultraviolet curable resin liquid forming an inner layer to a single mode fiber with a fiber diameter of 125 μm similar to that in Example 1. A resin composition consisting of an oligomer and a monoethylenically unsaturated monomer is prepared, and a resin composition mainly composed of diacrylate ester of diglycidyl ether and polyurethane is prepared as an ultraviolet curable resin liquid forming the outer layer. Michler's ketone is added to each as a polymerization initiator to form multiple layers.
The above optical fiber was coated all at once using a batch coater. After this,
An ultraviolet luminescent lamp (Fusion Inc.,
D bulb) was used to irradiate ultraviolet rays by passing through the ultraviolet irradiation device for inner and outer layers at a linear speed of 120 m/min.

In this optical fiber, since the same photopolymerization initiator was added to the inner and outer layers, most of the energy of the irradiated ultraviolet rays was consumed in the curing reaction of the outer layer, resulting in insufficient curing of the inner layer. Ta. For this reason, the adhesion between the optical fiber and the inner layer was low, and the tensile breaking strength test was conducted under the same conditions as in Example I, but as shown by the dotted line in Figure 5, sufficient strength could not be obtained, and the optical fiber was wound. (-It broke at the J part.

Also, the loss temperature characteristic at ~40°C is approximately 1dB/km.
This made it unsuitable for use as an optical fiber for communications.

(Comparative Example 2) A single mode fiber with a fiber diameter of 125 μm similar to that in Example 1 was prepared using an oligomer and a monoethylene unsaturated polymer spool bonded to the end of a polyalkylene polyester as an ultraviolet curable resin liquid forming an inner layer. A resin composition consisting of an ethylenically unsaturated monomer to which Michler's ketone is added as a photopolymerization initiator is used as an ultraviolet curable resin liquid that forms the outer layer, and a resin whose main components are noacrylate ester of ngrinonol ether and polyurethane. A composition with Michler's ketone added thereto as a photopolymerization initiator was prepared, and these were coated at a line speed of 70 using a conventionally used coating device as shown in Fig. 6.
The fibers were spun at a speed of m/min to form two inner and outer covering layers. As a result, the obtained optical fiber had loss temperature characteristics equivalent to those of Example 1 and a tensile breaking strength as shown by the dashed line in FIG.

"Effects of the Invention" - As explained above, the optical fiber coating method of the present invention involves coating the optical fiber surface with a plurality of ultraviolet curable resin liquids at once, and then irradiating the optical fiber with ultraviolet rays to form a plurality of coating layers. In the formation phase method, photopolymerization initiators with different absorption wavelength ranges are added to each ultraviolet curing B (g resin liquid), and by sequentially irradiating ultraviolet rays with wavelengths that match the absorption wavelength ranges of these photopolymerization initiators, the maximum Since multiple coating layers are formed by sequentially curing the inner layer of UV-curable resin, there is less chance that the uncured UV-curable resin will react with oxygen or impurities in the air, making it easier for machines to It is possible to manufacture a coated optical fiber suitable for communication that has high characteristics and low transmission loss.

Furthermore, since curing starts from the innermost layer, the curing of the multiple ultraviolet curable resins applied to the optical fiber progresses rapidly, allowing the drawing speed of the optical fiber to be increased and improving the productivity of the optical fiber. In addition, it is no longer necessary to prepare as many UV-curable resin coating devices as there are coating layers to be formed on the optical fiber, which is the case in the past. 2. It is economically effective.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a manufacturing apparatus suitably used to carry out the optical fiber coating method of the present invention;
2 to 4 each show an example of the emission spectrum of the ultraviolet rays used in the manufacturing apparatus shown in FIG. 1. FIG. 5 is a graph showing the tensile strength at break of an optical fiber having two coating layers obtained by the optical fiber coating method of the present invention and the conventional coating method. FIG. 6 is a schematic diagram showing an example of a manufacturing apparatus conventionally used for coating optical fibers. 13 Multiple layer-blanket coater, 14... Inner layer ultraviolet irradiation device, 15 Outer layer ultraviolet irradiation device.

Claims (1)

[Claims] In a method in which a plurality of ultraviolet curable resin liquids are applied on the surface of an optical fiber at once and then irradiated with ultraviolet rays to form a plurality of coating layers, each ultraviolet curable resin liquid has a different absorption wavelength range. By adding a photopolymerization initiator and sequentially irradiating it with ultraviolet rays with wavelengths that match the absorption wavelength range of these photopolymerization initiators, the innermost layer of the ultraviolet curable resin liquid is cured sequentially to form multiple coating layers. A method for coating an optical fiber, characterized in that: