JPH0225483B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fibers with excellent light transmission properties.

Fibers that transmit light have been known for a long time, and optical transmission fibers made of glass, especially quartz, have already been put into practical use. However, although optical transmission fibers made of glass or quartz have excellent optical transmission properties, they have drawbacks such as poor flexibility, heavy weight, and very high cost. Against this background, although the optical transmission properties are inferior to that of glass-based optical transmission fibers,
Recently, attempts have been made to use plastic optical transmission fibers, which are easy to handle and inexpensive, for short-distance communications.

Compared to glass-based optical transmission fibers, plastic optical transmission fibers can easily be made larger in diameter and have a higher numerical aperture, so they have higher coupling efficiency with light sources or between fibers, and are easy to connect. However, it has the characteristics of being lightweight and highly flexible, being able to be industrially mass-produced, and being extremely inexpensive. Therefore, it is expected to be applied to indoor wiring around computers, etc.

However, even with plastic fibers that use a methyl methacrylate polymer for the core component and a fluorine-containing polymer for the sheath component, which is currently said to have the best optical transmission properties, the fiber Although it depends on the diameter and wavelength, the optical transmission performance is at most 300 dB/Km, and it is necessary to further improve the optical transmission performance in order to use it for short-distance communication.

In order to improve optical transmission performance, so far,
Attempts have been made to thoroughly remove dust, transition metals, colored substances, etc. from the core component to improve its purity.
Another major factor that reduces the optical transmission performance of optical transmission fibers is considered to be air bubbles present in the core component material and poor adhesion at the interface between the core component material and the sheath component material.

Among these factors, the present inventors believe that air bubbles present in the core component material are the most significant factor in deteriorating optical transmission performance, and have diligently investigated a manufacturing method that does not generate air bubbles in the core component material. As a result, it was discovered that a plastic optical transmission fiber with significantly improved optical transmission performance could be obtained, and the present invention was achieved.

That is, the gist of the present invention is to provide an optical transmission fiber having a core-sheath structure consisting of a methyl methacrylate-based polymer as a core component material and a fluorine-containing polymer containing at least 30% by weight of fluorine as a sheath component material. A method for producing a light transmitting fiber is characterized in that during the production, the melt-extruded fiber is passed through a continuous area immediately below a spinning nozzle and cooled under pressure.

The present invention will be explained in more detail below.

The methyl methacrylate-based polymer, which is the core component material used in the present invention, may be a methyl methacrylate homopolymer, and may be a methacrylic acid containing 20% by weight or less of a copolymer component such as methyl acrylate or ethyl acrylate. It may also be a methyl copolymer.
In order to improve the optical transmission performance of methyl methacrylate polymers, it is necessary to purify and polymerize the monomer so that impurities such as dust, transition metals, and colored substances are contained as little as possible. From this point of view, bulk polymerization is preferred.

After forming a core material using such a methyl methacrylate polymer by a melt spinning method, it is coated with a polymer having a lower refractive index than the methyl methacrylate polymer as a sheath material material. Alternatively, the optical transmission fiber is produced by composite melt spinning of the core material and the sheath material using a composite spinning nozzle.

The sheath material used in the present invention should be a fluorine-containing polymer containing at least 30% by weight of fluorine. As a fluorine-containing polymer,
Examples include copolymers of vinylidene fluoride and tetrafluoroethylene, homopolymers of fluorinated esters of methacrylic acid represented by the following formula, and copolymers of these with methyl methacrylate, butyl acrylate, etc. Ru.

(In the formula, n = 1 to 2, m = 1 to 10, and X = H or F) The methyl methacrylate polymer used for the core material is often obtained by bulk polymerization. As it is, it usually contains several weight percent or more of residual monomer. In order to reduce the amount of residual monomer as much as possible, the residual monomer is usually contained in an amount of 0.5 to 2% by weight, even if the polymer is subjected to stationary bulk polymerization. When such a methyl methacrylate-based polymer containing, for example, 0.5% by weight of residual monomer is melt-spun using a conventional method, a large number of bubbles are generated in the fiber, which significantly reduces optical transmission performance.

Generally, in order to prevent the generation of such bubbles during fiber formation, a method is widely used in which residual monomer is removed in advance using a demonomer device such as a vented extruder or a thin film evaporator. By such a method, it is possible to reduce the amount of residual monomer to 0.1% by weight or less. However, if you try to reduce the amount of residual monomer to 0.1% by weight or less using a vented extruder or thin film evaporator, it is inevitable that foreign substances such as metal powder and sealing material powder will get mixed in from the equipment itself, and excessive thermal history will occur. It is also unavoidable that the resin will deteriorate due to exposure to heat.

This demonomerization method removes residual monomers.
It is possible to reduce the content to 0.1% by weight or less, or even 0.05% by weight or less, in which case generation of air bubbles is hardly observed during fiber formation. On the other hand, however, in the demonomerization step, the optical transmission performance of the fibers is significantly reduced because the contamination of foreign substances such as metal powder and sealing material powder and the deterioration of the resin are unavoidable.

As a result of intensive study by the present inventors on a method that does not involve the demonomer process that would degrade optical transmission performance and also does not generate bubbles during fiber formation,
In the process of cooling the molten extruded fiber by passing it through a continuous area directly below the spinning nozzle, if the fiber is cooled under pressure, no air bubbles will be generated, making it possible to produce an optical transmission fiber with extremely excellent optical transmission performance. I discovered that.

In addition, the methyl methacrylate-based polymer used in the present invention preferably has a residual monomer content of 3% by weight or less, and may be treated by a method of reducing the residual monomer amount to 3% by weight or less by flushing etc. after bulk polymerization, or by static polymerization. A method of reducing the amount of residual monomer to 3% by weight or less is adopted.

The degree of pressurization in the present invention depends on the spinning temperature, fiber diameter, cold air temperature, and spinning speed, but is preferably 2 kg/cm ² or more, preferably 3 kg/cm ² or more. As the upper limit pressure, it is meaningful to set it slightly above the vapor pressure at the spinning temperature of methyl methacrylate (approximately 2 kg/cm ² above), and raising it higher than that only increases the cost of the equipment and is not very meaningful.

Although the present invention can be embodied in various forms, representative examples thereof will be explained with reference to the drawings. However, these are illustrative of the principles of the invention, and the invention is not limited to these examples.

In FIG. 1, 1 is a composite melt spinning nozzle; 2 is a composite melt spinning nozzle;
is a melt-extruded fiber, which is wound up by a winding machine 3. 4 is a pressurized cooling box, 5 is a cold air inlet, and 6 is a pressurization adjustment valve. Still another example is shown in FIG. 1 is a melt-spinning nozzle, and 2 is a fiber made of a melt-extruded core material. 7 is a bath containing a sheath material used to coat the core material with the sheath material. The fiber whose core material is coated with the sheath material is wound up by a winding machine 3. 4
5 is a pressurized cooling box, 5 is a cold air inlet, 6 is a pressure adjustment valve, and 8 is a cold air outlet.

The optical transmission fiber obtained as described above has extremely excellent optical transmission properties, and can dramatically expand the range of application to short-distance transmission systems.

The present invention will be explained below with reference to Examples.

The optical transmission performance is determined by the incident light intensity I ₀ of the optical transmission fiber per length L using a halogen lamp as the light source,
Evaluation was made by transmission loss calculated from the output light intensity I using the following formula.

Transmission loss (dB/Km) = -10log (I/I ₀ )/L Example 1 Methyl methacrylate polymer that was carefully subjected to static bulk polymerization to avoid containing impurities such as dust, transition metals, and colored substances as much as possible. An optical transmission fiber was produced using the apparatus shown in FIG. 1 when composite melt spinning was performed using vinylidene fluoride/tetrafluoroethylene copolymer (molar ratio 7:3) as a core material and a sheath material, respectively. The remaining monomer of methyl methacrylate polymer is
0.8% by weight, spinning nozzle temperature 220℃, pressure 10
It was Kg/ ^cm2 .

No bubbles were observed in this fiber, and the transmission loss was 70 dB/Km at a wavelength of 570 mμ.

For comparison, when no pressure was applied during cooling (atmospheric pressure), bubbles were observed in the fibers, and the transmission loss was over 1000 dB/Km.

Example 2 Using the same core material as in Example 1,
First, the core material is melt-spun, and as the sheath material, 10% by weight of methyl methacrylate and 90% by weight of the following formula: When coating a core material with a copolymer of a fluorinated ester of methacrylic acid represented by the following formula, an optical transmission fiber was manufactured using the apparatus shown in FIG. The spinning nozzle temperature is 220℃, the pod material bath temperature is 120℃, and the pressure is 10℃.
It was Kg/ ^cm2 .

No bubbles were observed in this fiber, and the transmission loss was 65 dB/Km at a wavelength of 570 mμ.

For comparison, when no pressure was applied during cooling (atmospheric pressure), air bubbles were observed in the fibers, and the transmission loss was
It was over 1000dB/Km.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are both explanatory diagrams of an example of an apparatus for carrying out the present invention. 1... Spinning nozzle, 2... Fiber, 2'... Fiber (core material), 3... Winder, 4... Pressure cooling box, 5... Cold air inlet, 6... Pressure adjustment valve,
7...Sheath wood bath, 8...Cold air outlet.

Claims (1)

[Claims] 1 Methyl methacrylate-based polymer as the core component material, and at least 30% of fluorine as the sheath component material.
When producing a light transmitting fiber having a core-sheath structure made of a fluorine-containing polymer containing % by weight, the melt-extruded fiber is cooled by passing it through a continuous area directly below the spinning nozzle, under pressure. A method for producing an optical transmission fiber characterized by cooling it to