JPH02236504A - Extruding method for plastic tube - Google Patents

Abstract

PURPOSE:To improve a transmission loss and a heat resistance of a plastic optical fiber by using inert gas or air in which at least impurities whose grain size is <=0.5mum are purified to <=10,000 pieces/ft<3> as gas filled in a plastic tube. CONSTITUTION:At the time of bringing a plastic tube to extrusion molding, inert gas or air in which at least impurities whose grain size is <=0.5mum are purified to <=10,000 pieces/ft<3> is used as gas filled in the tube. If a fluoro - tube is extruded by filling the gas in which impurities whose grain size is <=0.5mum are not cleaned to <=10,000 pieces/ft<3>, smoothness of the inside surface of the fluoro - tube is spoiled, and a transmission loss of a fiber becomes extremely high, but by cleaning the impurities to <=10,000 pieces/ft<3>, the transmission loss can be reduced to 1.0 - 2.0dB/m. In such a way, the plastic tube is extruded in a state that the inside surface is smooth, and the roundness is held, and the transmission loss and the heat resistance of the plastic optical fiber using this tube are improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for extruding plastic tubes.

[Prior Art 1] When making an optical fiber using an acrylic thermosetting resin as a core, a fluororesin is mainly used as a plastic tube serving as a cladding material. Further, the acrylic thermosetting resin is flammable before thermosetting, and it is extremely difficult to directly inject it into a molten fluorine tube. Therefore, an acrylic thermosetting resin is injected under pressure into a fluorine tube that has been cooled and solidified, and after injection, the resin is heated from the outside of the tube to 100 to 120° C. to perform a thermosetting treatment. Furthermore, the inside of the cooled fluorine tube before resin is injected is generally cleaned with alcohol or acetone. On the other hand, when extruding a fluorine tube, the fluororesin is heated and melted at 300 to 380°C and extruded into a tube shape from an extrusion die. At this time, in order to balance the external pressure of the melting tube,
Requires more internal pressure. As a result, the tube is cooled while maintaining its circular shape, and a fluorine tube with good dimensional accuracy can be obtained.

[Problems to be Solved by the Invention] When manufacturing a thermosetting resin optical fiber using a fluorine tube as a cladding material using the above-described conventional technique, it is necessary to clean the inner surface of the tube.

However, it is extremely difficult to clean the inner surface of a tube that has been extruded and cooled. - Generally, there is a method of cleaning the inner surface with a solvent such as the one described above, but a process is required to remove impurities contained in the cleaning agent such as the solvent. In addition, it is necessary to keep containers clean during cleaning and the work environment clean. However, it is still extremely difficult to control the degree of cleaning in the longitudinal direction of the inner surface of the tube. Furthermore, impurities in the uncleaned gas sealed in the tube to balance the internal and external pressures adhere to the inner surface of the molten tube and cannot be removed by cleaning agents such as solvents. When a fluorine tube containing these impurities is used as a cladding material, the transmission loss of the optical fiber becomes large. Furthermore, the heat resistance properties of the optical fiber are also significantly reduced.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an extrusion method that allows a plastic optical fiber to have fewer attenuation layers and improved heat resistance.

[Means for solving the problem] The above purpose is to extrude a plastic tube so that the gas enclosed in the tube has a particle size of at least 0.
．． By using inert gas or air that has been purified to contain impurities of 5 μm or less and 10,000 m/f13 or less,
achieved.

Incidentally, the particle size here refers to the diameter of the particles.

[Function] By the above two means, the plastic tube is extruded with a smooth inner surface and maintains its roundness, and the transmission loss and heat resistance of the plastic optical fiber using this tube are improved. It becomes like this.

The gas sealed in the tube contains at least 10,000 II/ft3 of impurities with a particle size of 0.5 μm or less.
The reason for using the cleaned gas below is based on Figure 2, which shows the transmission loss on the vertical axis and the degree of cleanliness on the horizontal axis, which shows the change in the transmission loss of an optical fiber depending on the degree of cleanliness. it is obvious. In other words, if a fluorine tube is extruded with a gas that has not been cleaned to a level of 10,000 particles/ft3 or less of impurities with a particle diameter of 0.5 μm or less, the smoothness of the inner surface of the fluorine tube will be impaired and the transmission of optical fibers will be impaired. The loss will be extremely high, but if the impurities with a particle size of 0.5 μm or less are contained at 10,000 particles/t t? If you do the following,
This is because transmission loss can be reduced to 1.0 to 2.0 dB/m.

Further, the reason why the gas to be sealed is an inert gas or air is to avoid reaction with the fluorine tube which becomes the cladding material and the acrylic resin which becomes the core material.

[Example] The present invention will be described above based on the illustrated example. FIG. 1 shows an embodiment of the invention. In this example, when extrusion molding the fluorine tube 1 which is a cladding material for a plastic optical fiber, the gas sealed in the fluorine tube 1 is cleaned to at least contain 10,000 particles/ft3 or less of impurities with a particle diameter of 0.5 μm or less. The pressure of the gas sealed in the molten fluorine tube 1 from the extrusion crosshead 2 is increased to 150 ml using a fluorinated inert gas or air.
Controlled under sAQiX. By doing this, the fluorine tube 1 has a smooth inner surface and is extruded while maintaining its roundness, which improves the transmission loss and heat resistance of the plastic optical fiber using this fluorine tube 1. It is possible to obtain an extrusion method that improves heat resistance with less attenuation of the plastic optical fiber and improves heat resistance with nJ performance.

That is, the pressure is adjusted from a tank 3 of inert gas or air by a pressure reducing valve 4 while observing a pressure gauge 5, and in order to further increase the cleanliness, the inert gas or air is fed into a nibble into the extrusion crosshead 2 through a filter 6. Enclose air. Fluorine tube 1 extruded through the outside of the nibble
Since cleaned inert gas or air passes through the inside of the fluorine tube 1, there is no adhesion of dust or the like to the fluorine tube 1, and the fluorine tube 1 with a smooth inner surface is extruded. Moreover, since the gas is sent under a pressure of 150 s+Aq or less, the extrusion is maintained while maintaining its roundness.

Furthermore, since an inert gas or air is used, the gas does not react with the fluorine tube 1 or the acrylic resin serving as the core material, so that it does not adversely affect the plastic optical fiber.

In this way, according to this example, the inner surface of the fluorine tube is cleaned and the roundness is extremely high, so that when it is made into a plastic optical fiber, the transmission loss is 1.0 to 2,0 dB/m.
Furthermore, the heat resistance was increased by approximately 50°C.

In addition, because it is extruded while enclosing gas at a constant pressure,
This made it possible to extrude fluorine tubes with extremely small outside diameter fluctuations.

Since the fluorine tube extruded according to the above embodiment has a clean inner surface, it can also be used for medical purposes. For example, even if blood passes through a fluorine tube, it will not react because it is an inert gas or air.

Further, in the above embodiment, a method for extruding a fluorine tube was described, but the present invention is not limited to this, and is applicable to all plastic tubes used as cladding materials for plastic optical fibers.

[Effects of the Invention] As described above, the present invention uses an inert gas or air that has been purified to contain at least 10,000 impurities with a particle size of 0.5 μm or less/ft3 as the gas sealed in the plastic tube. Since the fluorine tube has a smooth inner surface and is extruded while maintaining its roundness, the transmission loss and heat resistance of the plastic optical fiber using this tube can be improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a mechanism for sealing clean gas into the fluorine tube during extrusion of the fluorine tube according to an embodiment of the extrusion method of the present invention, and Fig. 2 shows the degree of cleanliness of the gas sealed in the fluorine tube. FIG. 3 is a characteristic diagram of changes in transmission loss of an optical fiber. 1: Fluorine tube, 2: Extrusion crosshead. 1st item

Claims (1)

[Claims] 1. In an extrusion method in which a plastic tube is extruded with a gas sealed therein, the gas sealed in the tube contains at least 10,000 impurities with a particle size of 0.5 μm or less/ft^3 An extrusion method characterized by using purified inert gas or air. 2. The method for extruding a plastic tube according to claim 1, characterized in that the sealing pressure of the gas is controlled to 150 mmAq or less.