JPS62235906A - Production of optical fiber - Google Patents

Abstract

PURPOSE:To obtain a fiber having uniform quality and good optical performance by using a molded polymer from which the volatile component is removed under shearing stress at the temp. higher by >=30 deg.C than the secondary glass transition temp. of a sleeve component polymer for the sleeve component. CONSTITUTION:There is no particular limitation to the compsn. of the sleeve component polymer and the compsn. having the refractive index lower by >=0.01 than the refractive index of a core component is preferred and a fluoropolymer is desirable. The removal of the volatile component is executed by increasing the polymer temp. to the temp. higher by >=30 deg.C than the secondary glass transition temp., and kneading the polymer under the shearing stress until the major axis length of the polymer particles is made <5 times the minor axis length. The extrusion is then stably executed and the impurity component and volatile matter are quickly and efficiently removed. The disturbance at the core/sleeve boundary is suppressed, the coloring by heating is prevented. The resultant optical fiber has the stable performance.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing optical fibers.

[Conventional technology]

The manufacturing method of optical fiber is disclosed in Japanese Patent Publication No. 43-8978 and Japanese Patent Publication No. 5
It is generally known from publications such as No. 3-53339 and Japanese Unexamined Patent Publication No. 59-7906.

[Problem that the invention seeks to solve]

However, in the inventions disclosed in these publications, it is thought that no consideration was given to the particle size or residual volatile content of the molded polymer used as the sheath component, and the supply of the sheath component to the spinning bath was inadequate. In addition, if volatile components are present in the sheath component molding polymer, the sheath component molding polymer may be heated and colored during the optical fiber manufacturing process, or it may cause structural irregularities in the resulting optical fiber. This is a major cause of increased fiber optical transmission loss.

[Means for solving problems]

The present invention aims to eliminate the above-mentioned drawbacks and thereby provide a method for producing optical fibers that are homogeneous and have good optical performance.

In the present invention, when manufacturing an optical fiber by integrally extruding a sheath component made of a thermoplastic polymer around a core component, the sheath component is used as a sheath component with a temperature of 30% higher than the second glass transition temperature of the sheath component polymer.
The present invention relates to a method for producing an optical fiber, characterized in that it uses a sheath component molded polymer whose volatile content has been removed under shear stress at a temperature higher than .degree. C. or higher.

Examples of polymers that can be used as the core component in carrying out the present invention include conventionally used methyl methacrylate polymers, polyglutarimide polymers, styrene polymers, and polycarbonate polymers. For example, the present invention is disclosed in Japanese Unexamined Patent Publication No. 59-790.
It is also fully applicable to the production of optical fibers using glass or silica as a core component as disclosed in Japanese Patent No. 6.

There is no particular limitation on the chemical composition of the sheath component polymer used in the present invention, but it is preferable that it has a refractive index lower than the refractive index of the core component by 0.01 or more,
For example, it is desirable to use a fluorine-based polymer as described in the above-mentioned patent publication.

The step of removing volatile matter from the sheath component polymer is carried out at a temperature of the polymer 30° C. or more higher than its second glass transition temperature (hereinafter referred to as Tf) and under shear stress. If the sheath component polymer is not treated to remove volatile matter at a temperature of 30°C or higher than 'rt, the viscosity of the molten sheath component polymer will be high, so there will be little crosstalk effect due to shearing, and the devolatilization efficiency will be poor.
Almost no volatile matter can be removed. Furthermore, the result is that the power load when shearing the polymer becomes very large.

In addition, the length of the major axis of the sheath component molded polymer is 5 times the length of the minor axis.
If it exceeds twice that, the extrusion of the sheath component molding polymer in the optical fiber manufacturing process will not be carried out smoothly, sheath breakage on the optical fiber and sheath discharge unevenness will occur, making it difficult to manufacture the optical fiber.

In order to remove the volatile content of the sheath component molding polymer and make the particle size uniform, the sheath component polymer was melted using heat and shear using a screw type devolatilizing extruder to remove the volatile content, and then melted and discharged from the tip of the extruder. It is preferable to use a method in which the thread polymer is cut into equal lengths.

In this way, by shearing and kneading the sheath component polymer in the screw extruder, it is possible to equalize the non-uniformity of performance among the molded polymer particles due to uneven polymerization of the polymer. Further, impurities and volatile matter can be efficiently devolatilized and removed from the sheath component molded polymer in a short time, and colored impurities can be removed.

Further, by setting the length of the long axis of the sheath component molded polymer particles to less than 5 times the length of the short axis, extrusion of the sheath component molded polymer in the optical fiber manufacturing process can be carried out stably.

That is, by melting and devolatilizing the sheath component polymer and extruding it, the polymer is homogenized, and by-products from monomer synthesis, polymerization aids, unpolymerized monomers, dimers, and trimers contained in the sheath component polymer are homogenized. It is possible to remove volatile impurities such as oligomers such as polymers or complex modified products thereof, and suppress the restriction of the flow of the molten polymer during composite melt spinning or the disturbance of the core-sheath interface due to volatile substances. In addition to this, it is also possible to prevent the polymer from being colored by heating, and as a result, the optical fiber obtained has stable and very good optical performance.

Furthermore, as the melt extruder to be used, a twin-screw extruder with better kneading effect is preferable than a single-screw extruder.

When carrying out the present invention, it is also possible to install the step of removing volatile matter under shear stress in the sheath material extruder of the optical fiber shaping spinning machine, in which case the preforming of the sheath polymer is carried out by If the particle size is the same, it becomes unnecessary. It is also preferable in that the thermal history of the sheath polymer is reduced.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 90 parts of 2,2,3,3,3-pentafluoropropyl methacrylate, 8 parts of methyl methacrylate, 2 parts of methacrylic acid
1 part, 0.05 part of azobisisobutyronitrile as a polymerization initiator, and 0.1 part of n-dodecylmercaptan were mixed and dissolved, and the mixture was charged into a 2J bulk polymerization autoclave, which was repeatedly deaerated and replaced with nitrogen, and then sealed. When polymerized by immersing in hot water at 50°C for 10 hours, the internal pressure becomes 10 kg/cm'' gauge pressure, and after further heating and polymerizing at 70°C for 5 hours, the peak due to polymerization heat is completed, and the polymerization is completed and a transparent polymer is formed. The polymerization conversion rate was 99%.

The refractive index of the obtained polymer was 1,422, and 'r7 was 95°C.
Met. This polymer is crushed in a crusher, and a twin-screw devolatilizing extruder (20 mm φ x 2.2 vents) is used.
HJI), extruded into yarn at an extrusion resin temperature of 230°C,
After quenching, the strands with a diameter of 2.5 fi were made into pellets with a length of 3 u using a pelletizer, and used as a polymer base for sheath molding.

100 parts of methyl methacrylate was produced by continuous bulk polymerization using a volatile separation device consisting of a reaction tank equipped with a spiral ribbon stirrer and a twin-screw one-vent extruder.
A monomer mixture consisting of 0.40 parts of t-butyl mercaptan and 0.0017 parts of di-t-butyl peroxide was reacted at a polymerization temperature of 155°C and an average residence time of 4.0 hours.
Next, the temperature of the vent extruder was adjusted to 240°C in the vent part, 230°C in the extrusion part, and a vacuum level of 4 mm HP in the vent part, and after separating the volatile part, the temperature was increased to 230°C through the gear pump part maintained at 230°C.
was supplied to the core-sheath composite spinning head. For the cladding component, the above polymer was fed to a composite spinning head through an extruder with a diameter of 15 mm.
Extrusion at 0°C, 10 m/min, draw ratio: 1.8 times,
After stretching at a stretching temperature of 140°C, the winding diameter is 5.
A composite filament with a core diameter of 480μ and a core diameter of 480μ was obtained.

Microscopic observation revealed that the core-clad interface of this composite filament was perfectly round and no foreign matter was observed. There was also no thickness unevenness in the cladding.

The optical transmission loss of the optical fiber thus obtained was measured by the method disclosed in Japanese Unexamined Patent Publication No. 50-7602.

The measurement wavelength is 650 nm. The results are shown in Table-1.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that the sheath polymer produced by the same method as in Example 1 was crushed using a crusher, and the sheath polymer was separated and removed in accordance with the JIS Z-8801 standard into 7 mesh passes and 32 mesh passes. An optical fiber was obtained. The results are shown in Table-1.

Comparative Example 2 A sheath polymer produced in the same manner as in Example 1 was crushed using a crusher, extruded into yarn under the same conditions, and after quenching,
A strand with a diameter of 2.5 m was pelletized into a length of 15 m using a pelletizer. Sheath pellet of Example 1) (3m
An optical fiber was obtained in the same manner as in Example 1, except that a sheath polymer blended with m) containing 8% of the above pellets (15 Dragon) was used. The results are shown in Table 1. 1-ner Example 2 The sheath polymer produced in the same manner as in Example 1 was crushed using a crusher, and then pelletized into a length of 10 m using a pelletizer in the same manner as in Comparative Example 2. The scabbard of Example 1) (
An optical fiber was obtained in the same manner as in Example 1, except for using a blended sheath polymer containing 8% of the above pellets (10 parts m) in 3 mm). The results are shown in Table-1.

, Comparative Example 3 The sheath polymer produced in the same manner as in Example 1 was crushed using a crusher, and then a twin-screw non-pent extruder (15 mm φ×
2), except for melt extrusion at an extrusion resin temperature of 230°C,
An optical fiber was obtained in the same manner as in Example 1. The results are shown in Table-1.

Example 3 90 parts of 2,2.2-trifluoroethyl α-fluoroacrylate, 10 parts of methyl α-fluoroacrylate, 0.05 part of polymerization initiator azobisisobutyronitrile, n-
After mixing and dissolving 0.5 part of dodecyl mercaptan, 2E
It was placed in an autoclave for bulk polymerization, followed by repeated deaeration and nitrogen replacement, and then sealed. Polymerization was carried out by immersing it in hot water at 50°C for 10 hours, and then heating and polymerizing at 70°C for 5 hours. The peak due to the exotherm of polymerization was completed, and the polymerization was completed to obtain a transparent polymer. The polymerization conversion rate was 97%. The obtained polymer had a refractive index of 1.3920 and a T/ of 107°C. This polymer is crushed in a crusher and then crushed in a twin-screw devolatilizing extruder (
20 mm φ x 2.2 vent method, vacuum level 1 pen) 40
11HJ1. 2nd pen) 511 HP) was extruded into yarn at an extrusion resin temperature of 260°C, and after quenching, the strand with a diameter of 2.5 mm was pelletized into a length of 3 mm with a pelletizer to obtain a sheath polymer. Optical fibers were obtained in the same manner as in Example 1, and the results are shown in Table 2.

Comparative Example 4 The same procedure as in Example 2 was carried out, except that a sheath polymer produced by the same method as in Example 3 was crushed using a crusher, and 7 mesh passes and 32 mesh parts were separated and removed according to the JIS Z-8801 standard. An optical fiber was obtained.

The results are shown in Table-2.

Comparative Example 5 A sheath polymer produced in the same manner as in Example 3 was crushed with a crusher and extruded into yarn under the same conditions. After quenching, the strand with a diameter of 2.5 mm was made into a strand with a length of 15 mm using a pelletizer.
Pelleted into silk.

The above bezel) (15
An optical fiber was obtained in the same manner as in Example 2, except that a blended sheath polymer containing 6% of mm) was used. Display the results -
Shown in 2.

Comparative Example 6 The sheath polymer produced in the same manner as in Example 3 was crushed using a crusher, and a twin-screw non-vent extruder (15 mm φ x 2) was used.
An optical fiber was obtained in the same manner as in Example 3, except that it was melt-extruded at an extrusion resin temperature of 230°C. The results are shown in Table-2.

Claims (1)

[Claims] 1. When producing an optical fiber by extruding and integrating a sheath component made of a thermoplastic polymer around a core component, the second glass transition temperature of the sheath component polymer is used as a sheath component. A method for producing an optical fiber, characterized by using a sheath component molded polymer whose volatile content is removed under shear stress at a temperature 30° C. or higher. 2. As a sheath component molded polymer, volatile matter is removed under shear stress at a temperature 30°C or more higher than the primary glass transition temperature of the sheath component polymer, and then the length of the long axis of the molded polymer is 2. The method for producing an optical fiber according to claim 1, wherein molded polymer particles are used which are molded so that the length of the short axis is 5 times or less than the length of the minor axis.