JPS6121937A - Cladding method of optical fiber - Google Patents

Abstract

PURPOSE:To permit execution of high speed wire drawing in a caldding process for precoating a plastic material drawn to glass fiber from a wire drawing furnace, by using powder of thermoplastic elastomer as the afore-mentioned plastic. CONSTITUTION:Glass fiber for light transmission immediately after drawing from a wire drawing furnace is passed through an electrostatic coating device contg., for example, strene/butadiene block polymer crushed to ca.100mu particle size at low temp. to precoat the drawn glass fiber. The temp. of the glass fiber is ca.300 deg.C, the outside diameter of the clad product is ca.300mu, the wire drawing speed is ca.250m/min. In this case, the styrene/butadiene block polymer as the cladding material is melted in the electrostatic coating device, which forms sufficiently uniform film on the glass fiber at the stage wherein the glass fiber is extruded from the coating device. Further, nylong 12 powder is coated to form a specified outside diameter on the outside of the clad fiber by the similar method.

Description

[Detailed description of the invention] [Background and purpose of the invention] The present invention relates to a method of coating an optical fiber.

The glass fibers used in optical fibers for optical transmission are made of pure quartz or doped quartz and multi-component glasses, but these are inherently brittle and cannot be machined even if they have minute defects on their surfaces. The strength of the material decreases significantly, making it impossible to put it into practical use.

For this reason, a method is adopted in which silicone resin, epoxy resin, polyurethane resin, ultraviolet curable resin, etc. are applied and baked on the surface of the glass fiber.

Both are stored in liquid form in a paint bath equipped with a die. The glass fiber spun from the drawing furnace enters the coating bath, passes through a die, and is coated. The coated fiber is cured by passing through an electric furnace or an ultraviolet curing device before contacting other solid materials. It is said that this method can draw wire at a high speed of about 1000 m/an by using a pressure die.

However, in this method, the bare glass fiber passes through the die, so the glass fiber may come into contact with the die and reduce its strength. Further, these resins require an electric furnace or an ultraviolet curing device to cure them. As the speed increases, the energy required for curing increases, so the electric furnace must be made longer and the number of lamps must be increased. Make sure to wet the glass fiber well.

In order not to reduce the strength of the glass fiber, it is necessary to air-cool the glass fiber to below 150°C, and the drawing speed is 60°C.
In the case of 0 m/m, the air cooling length reaches as much as 6 m.

Therefore, in order to obtain highly economical optical fibers, it is advantageous to develop a pre-coat coating method that prevents the bare glass fiber from coming into contact with the hard die during high-speed drawing, shortens the air cooling length as much as possible, and eliminates the need for a curing process. If this could be done, the factors that inhibit rapid line drawing would be removed, so the development of such a coating method was desired.

The present invention has been made in view of the above points.

The object of the present invention is to provide a method for coating an optical fiber that enables high-speed drawing.

[Summary of the invention]

That is, the present invention is an optical fiber coating method in which plastic is precoated on a glass fiber for light transmission immediately after spinning in a drawing furnace, characterized in that thermoplastic elastomer powder is used as the plastic. The glass fiber is then precoated with a thermoplastic elastomer.

〔Example〕

The present invention will be explained below based on the studied examples. In this example, thermoplastic elastomer powder was used as the plastic. In this way, the glass fiber is precoated with a thermoplastic elastomer.
It is possible to obtain an optical fiber coating method that enables high-speed drawing.

That is, Examples 1 to 6 were studied, which will be explained next. In Example 1, a quartz multimode fiber (core diameter 50μ, cladding diameter 125μ) was spun from a drawing furnace.
A styrene-butadiene block polymer (Shore A hardness = 50) made by crushing μ) into a size of about 100μ at low temperature.
The styrene-butadiene block polymer was glycocoated by passing it through an electrostatic coating machine in which the styrene-butadiene block polymer was coated. The temperature of the quartz multimode fiber, that is, the glass fiber, was approximately 600°C, the outer diameter of the coating was 600μ, and the drawing speed was 250 m.
/nun. In this case, the styrene-butadiene block polymer coating material was bath-melted in a coating machine or electrostatic coating device, and a sufficiently homogeneous coating had been formed on the glass fibers upon exiting the coating machine. Next, nylon 12 powder was coated on the outside of the coated fiber precoated with this styrene-butadiene block polymer using a similar method so that the outer diameter was 500 μm.

The transmission loss of the optical fiber coated in this way was comparable to that of a conventional silicone/nylon coated optical fiber, and the tensile strength also showed good results with an average of 6 kg.

In Example 2, everything was the same as in Example 1 except that a polyether type polyurethane elastomer (Shore A hardness = 65) was used in place of the above-mentioned styrene-butadiene prosol polymer. In this case as well, the transmission loss of the optical fiber was comparable to that of the conventional silicone/nylon coated fiber, and the tensile strength was also good at an average of 6 kg.

In Example 6, the styrene-butadiene block polymer used in Example 1 was powder coated to have an outer diameter of 400 μm and then wound around a bobbin. Next, in a separate step, nylon 12 was extrusion coated to have an outer diameter of 900 μm. The transmission loss of the optical fiber coated in this manner was comparable to that of a conventional silicone/nylon coated optical fiber, and the tensile strength was as good as 6 kg on average.

In this way, the bare glass fiber is pre-coated with thermoplastic elastomer even if it does not come into contact with a solid object such as a die, so there is no decrease in strength, and there is no need to lower the glass fiber temperature, so the air cooling length can be shortened. There is no need for a curing process.

Therefore, high-speed drawing is possible, and in the case of long-distance drawing, an optical fiber with high reliability can be obtained.

The thermoplastic elastomer used for this precoat is desirably one with a small Young's modulus in order to prevent micropend loss, and it is important to use one with little variation in Young's modulus or hardness within the practical temperature range. Preferred examples include polyurethane elastomers (e.g., polyether-based Eo111ar manufactured by Uniroyal, etc.; polyester-based Eo111ar manufactured by Eyer;
pan, etc.), styrene-butadiene block polymer (Kr manufactured by Shell Ch.
a t O? + etc., Krato hydrogenated with butadiene
styrene-isopropylene block polymers such as
Hytre1, etc.) manufactured by the company, etc.) fall under this category. The items listed here are just a guideline, and anything that falls within this range can be used. Further, if necessary, these materials may contain stabilizers, adhesion promoters, softeners, etc.

In order to pre-coat the powder, it is desirable to use a powder coating machine such as electrostatic coating or fluidized dipping.

The advantage of this precoat is that it can be coated while the glass fiber temperature is at a high temperature of 200 to 600°C.
Compared to conventional methods, the distance from the drawing furnace to the coating can be shortened, and it is preferable that the temperature be maintained at a temperature necessary to melt the adhered powder. If the coating does not melt sufficiently, it may be passed through an electric furnace. Furthermore, since no dice are used, there is no contact with dice or the like during coating, and therefore some impurities may be included that do not adversely affect the transmission characteristics.

The glass fiber precoated in this way may be used by winding it up as it is, or may be coated with hard glass for reinforcement. Possible coating methods in this case include extrusion and powder coating.

〔Effect of the invention〕

As described above, according to the present invention, a glass fiber is precoated with a thermoplastic elastomer, thereby making it possible to draw at a high speed, thereby providing an optical fiber coating method that enables high-speed drawing.

Claims (2)

[Claims] (1) An optical fiber coating method in which plastic is precoated on a glass fiber for optical transmission immediately after spinning from a drawing furnace, characterized in that thermoplastic elastomer powder is used as the plastic. Method of coating optical fiber. (2) The thermoplastic elastomer powder is formed from one of polyurethane elastomer, styrene-butadiene block polymer, polybutadiene-styrene graft copolymer, polyester elastomer, and ethylene copolymer. The method for coating an optical fiber according to item 1.