JPH0782130B2 - Method for manufacturing plastic optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is a method for producing a high-quality plastic optical fiber which is excellent in mechanical strength, particularly in bending resistance, translucency, and dimensional stability, and has a small wire diameter variation. Regarding

[Prior Art] The development of optical fibers at the core of technological innovation in the communication technology field is remarkable based on glass-based optical fibers. In the short-distance transmission field where cost and processability are important, organic fibers are used. The utilization of optical fibers is drawing attention.

Organic optical fibers, that is, plastic optical fibers, are inferior to glass-based optical fibers in translucency, but are cheap and easy to handle, and are therefore widely used for short-distance transmission.

However, this plastic optical fiber is usually produced by applying a melt-spinning method which is a general synthetic fiber production method, but unlike ordinary synthetic fibers, the polymer used has no crystallinity. Because of the characteristics of the optical fiber, the purity of the polymer used is extremely high, and it is necessary to completely prevent the inclusion of foreign substances and impurities in the fiber manufacturing process. There is a technical difficulty in industrial practice that extremely severe manufacturing processes and conditions must be adopted, such as no irregularities in the interfacial interface.

Among such technical difficulties, in order to improve the mechanical properties of the plastic optical fiber, particularly the bending resistance and flexibility, the melt-spun unstretched fiber is heat-stretched and polymerized in the fiber axial direction. It is necessary to orient the chains. However, in this heating and drawing step, as will be described later, interface irregularity or interfacial peeling between the core component and the sheath component forming the plastic optical fiber may occur, or yarn unevenness may occur due to uneven heating. Therefore, it is extremely important to solve the problems of reducing the light transmission loss of the obtained plastic optical fiber and reducing the fluctuation of the wire diameter.

[Problems to be Solved by the Invention] In such a drawing step, in a conventional heating method such as a heating roll or a heating plate, the sheath component is likely to be damaged or come off due to rubbing in the drawing process. As a result, the light-transmitting property and the mechanical strength are lowered. Therefore, a non-contact heating drawing, for example, a means for drawing while indirectly heating the fiber in a heating atmosphere such as heated air or nitrogen is used instead of the contact heating drawing. Has been adopted.

However, in the case of this non-contact heating drawing, uniform heating of the fiber is apt to be difficult, and when deformed by drawing in a non-uniform state, an interface irregularity occurs, the translucency of the plastic optical fiber is lowered, and the drawing is also unsuccessful. There was a problem that the wire diameter became stable and the wire diameter fluctuation could not be sufficiently reduced.

An object of the present invention is to provide a method capable of obtaining a high-quality plastic optical fiber which is excellent in mechanical strength, particularly in bending resistance, light transmission and dimensional stability and has a small wire diameter variation.

[Means for Solving the Problems] In order to achieve this object, in the present invention, when a plastic optical fiber is heated and drawn in a non-contact manner, the heated air flow is countercurrent to the traveling direction of the optical fiber. The method comprises introducing into a heating drawing zone, and a method for producing a plastic optical fiber which is drawn under the condition represented by the following formula.

Where A: cross-sectional area of stretched fiber (mm ² ) V ₁ : feeding roller speed of plastic optical fiber to the heating stretching zone (m / sec), V ₂ : drawing roller speed of plastic optical fiber from the heating stretching zone (m / s) Sec), L: length of heat-stretching zone (m) In the non-contact heat-stretching of the present invention, the roller speed supplied to the zone for heat-stretching the unstretched plastic optical fiber is V ₁ (m / sec), the stretched plastic When the roller speed for drawing out the optical fiber from the heating / drawing zone is V ₂ (m / sec), the arithmetic average (V ₁ + V ₂ ) / 2 can be used as the average speed of the fiber in the heating / drawing zone. . Therefore, the average transit time T (second) of the fiber when traveling in the heating and drawing zone of length L (m) is T = 2L /
It is represented by (V ₁ + V ₂ ). When the preferable range of the average transit time of the fiber running through the heating / drawing zone was studied for plastic optical fibers having various wire diameters, it was found that when the cross-sectional area of the drawn plastic optical fiber was A (mm ² ), As shown in the figure, In the range of the oblique line, the inventors have found that a high-quality plastic optical fiber having a good light-transmitting property and a good bending resistance and a small wire diameter variation can be obtained, and thus the present invention has been accomplished.

That is, In, the fiber heating is insufficient, the viscosity of the fiber undergoing deformation is high, or the deformation rate per unit length of the fiber is increased, so the deformation stress becomes large, resulting in high tension drawing. However, a large strain is likely to occur and uneven stretching is likely to occur. Especially in general melt spinning, since a gear pump is used as a measuring means during the melt transportation, the wire diameter fluctuation and the discharge at the time of discharging from the spinneret hole based on the rotation fluctuation and the clearance fluctuation of each blade of the gear The unstretched plastic optical fiber has a change in the wire diameter due to melt fracture at the hole introduction portion, melt fracture due to stick-slip on the inner wall of the discharge hole, and the like. Therefore, when subjected to the high-strength stretching action as described above, stress is first concentrated on the small diameter portion of the unstretched plastic optical fiber. Then, the stress propagates to the large diameter portion, so that the drawn plastic optical fiber amplifies the fluctuation of the wire diameter, and the fluctuation of the wire diameter of the unstretched plastic optical fiber is caused even though the average diameter is thinned by the drawing. It reaches several times or more, and even 10 times or more in extreme cases. The target of wire diameter fluctuation is ± 2% or less with respect to the center wire diameter. Alternatively, generally, different polymers are used for the core component polymer and the sheath component polymer that compose the plastic optical fiber. In particular, since the sheath component polymer is required to have a low refractive index, a fluorine-containing polymer is often used, Then, if it is not uniformly heated or if it is deformed by stretching with insufficient heating, irregularities in the interface occur and the translucency of the plastic optical fiber deteriorates. Also Then, only a plastic optical fiber having a large shrinkage and poor dimensional stability can be obtained.

on the other hand, However, since heating is excessive and the degree of orientation of the molecular chains due to stretching is low, only fibers with weak mechanical strength such as bending resistance can be obtained, which is a problem from the viewpoint of stretching operation.

Next, FIG. 1 shows a typical example of the non-contact heating drawing of the present invention.

The present invention will be further described with reference to FIG. At the exit of the zone for heating and stretching the unstretched plastic optical fiber (hereinafter referred to as the heating and stretching zone (6)), the heated air stream (13) is applied from around the optical fiber, and the flow of the heated air stream with respect to the traveling direction of the optical fiber is directed. A heated air stream is introduced into the heating and drawing zone from the introduction section (9) so that it becomes a flow. By introducing such a heating fluid into the heating drawing zone and countercurrent contact between the optical fiber and the heating fluid, the thinning completion point due to the drawing of the optical fiber is fixed near the heating air flow outlet at the outlet part of the heating drawing zone, and heating is performed. It is possible to shorten the stretching zone.

Here, the thinning completion point by stretching does not necessarily mean a necking portion such as seen in polyester fibers. This point will be described with reference to FIG. That is, the second
In the figure, it is a side view showing the completion point of thinning of the plastic optical fiber, but as shown in the figure, the unstretched plastic optical fiber of the set fiber diameter (D ₁ ) is the point (P ₁ ).
From the point where the fiber diameter (D ₂ ) was reduced to 103% of the target fiber diameter (D ₃ ) of the stretched plastic optical fiber, the point (P ₂ ) at which the fiber was thinned was set as the completion point. . 100
% Is not taken into account because the error due to the wire diameter variation is taken into consideration.

Here, P is the distance (cm) from the heated air flow outlet at the outlet of the heated drawing zone to the thinning completion point by drawing, and the conditions are set so that the formula | P | ≦ 10 (cm) Preferably. As an example of the method of measuring the thinning completion point by stretching here, the plastic optical fiber being stretched is cut while being simultaneously gripped and cut immediately before the inlet of the heating stretching zone and immediately before the stretching roll to give tensile or shrinkage. There is a method of quickly removing from the heated drawing zone without marking and marking at 1 to 5 cm intervals, and checking the fiber diameter change, that is, the thinning profile with a micrometer, etc., by such a method, the drawing point based on the above-mentioned definition Can be asked. The positive / negative of the value of P can be defined as follows.

That is, when the position of the heated airflow outlet at the outlet of the stretching zone is P = 0 and the thinning completion point by stretching is in the direction of the stretching zone, the value of P is a minus (-) value, and the thinning by stretching is P if the completion point is outward from the draw zone exit
The value of can be expressed as a plus (+) value, and the P value is −10 ≦
When it is within the range of P ≦ + 10, it is possible to obtain a high-quality plastic optical fiber which has a small fluctuation of the fiber diameter and is excellent in mechanical properties such as bending resistance with little light transmission loss due to interface irregularity and the like. Of.

When the P value is smaller than -10 cm, that is, when the thinning completion point by stretching is on the inner side of the stretching zone, it is not preferable from the viewpoint of improving the bending resistance of the optical fiber. Also, the P value is +10 cm
If it is larger than that, that is, if the thinning completion point due to stretching is in a region far away from the outlet of the stretching zone, it is not preferable from the viewpoint of suppressing fluctuations in fiber diameter and improving quality.

In such non-contact heating drawing, it is desirable to fix the thinning completion point due to the drawing of the optical fiber near the exit of the drawing zone by blowing a heating fluid into the exit of the drawing zone,
On the other hand, the heated fluid that has been blown into the drawing
For example, the flow of the heating fluid flowing through the drawing zone is stabilized by positively discharging it using an ejector or the like. By applying such heating fluid introduction and discharge means, the heat transfer film on the surface of the optical fiber traveling in the drawing zone can be constantly updated, and the thinning completion point can be fixed, which enables uniform drawing. Further, since the thermal efficiency is high, the heating / drawing zone can be shortened.
In addition, it is generally desirable to circulate and use the exhaust heating fluid from the viewpoint of increasing the thermal efficiency and reusing the thermal energy.

Further, when the glass transition point of the core component polymer constituting the plastic optical fiber is Tg, the non-contact heating drawing temperature is θ (° C.), and the non-contact drawing is performed at a temperature within the range of Tg−10 ≦ θ ≦ Tg + 80. Preferably. Where θ
Tg-10 or more means that under stretching tension, DSC, etc.
It is generally known that the glass transition point is lower than that when statically measured by increasing the temperature by minutes, and even in the actual non-contact heat drawing, the change in wire diameter is not so large and the light-transmitting property is high. Can be adopted because it hardly deteriorates. If it is less than that, the drawing tension is increased, the variation of the wire diameter is increased, and the transparency is deteriorated.

On the other hand, when the temperature exceeds Tg + 80 (° C), the deformation stress is low and the molecular chain orientation becomes insufficient, resulting in poor mechanical properties such as bending resistance.

Next, in order to impart dimensional stability and uniformity to the stretched optical fiber, it is preferable to provide a heat treatment zone (6 ') separate from the heat stretching zone (6) as shown in FIG. In this heat treatment zone (6 '), it is preferable to perform the non-contact fixed length heat treatment at a temperature selected from the non-contact heating and drawing temperature range.

That is, the non-contact constant length heat treatment can reduce the shrinkage ratio of the obtained stretched optical fiber to a considerable extent and improve the dimensional stability. Also in the heat treatment for imparting this dimensional stability, as in the non-contact heating / drawing means, the optical fiber is passed through the heating zone in which the heating fluid circulates and heat-treated under a fixed length to obtain the maximum operating temperature of the target optical fiber. After the heat treatment for 24 hours under dry heat, the heat treatment is performed so that the shrinkage ratio of the optical fiber is 2% or less, preferably 1% or less.

The core component polymer constituting the optical fiber of the present invention is not particularly limited, those having various excellent light transmittance, for example, a homopolymer or copolymer containing methyl methacrylate as a main component, Examples thereof include polycarbonate, bornyl homopolymers or copolymers, homopolymers or copolymers containing styrene or maleimide as a main component, and similarly, as the polymer constituting the sheath component, fluorine-containing methacrylate is used. Examples thereof include a system polymer, a copolymer of vinylidene fluoride and tetrafluoroethylene, and a fluorine-containing olefin copolymer.

Further, as an example of the combination of these core and sheath polymer components, it is natural that they have a difference in refractive index, but from the viewpoint of performing composite spinning, the melting points of both polymer components should be as close as possible. desirable.

An example of the non-contact heating stretching-heat treatment method of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of an optical fiber drawing-heat treatment method used in the present invention. In the figure, 1 is a plastic optical fiber, 2 is a spinneret, 3 is a cooling chimney, 4 is a take-up roller for an unstretched plastic optical fiber, and also serves as a supply roller to a stretching zone. This roller speed is V ₁ (m / sec). 5 is a static eliminator, 6 is a stretching zone equipped with a block heater, 6 '
Is a heat treatment zone, 7, 7'is a fan for circulating heated fluid, 8,
8'is a heater for heating the fluid, 9 and 9'is a heating fluid introducing part, 10 is a drawing roller, that is, a roller for drawing the drawn plastic optical fiber from the drawing zone, and this speed is V ₂ (m / sec). is there. Reference numeral 11 represents a winding portion, and 13 represents a heated air stream.

In this way, when the air is circulated countercurrently in the hollow portion of the heating zone, that is, in the yarn passage, the temperature in the yarn passage becomes uniform and the heat transfer film on the surface of the optical fiber can be constantly renewed as described above. Therefore, the heat transfer is good, which makes it possible to shorten the heater length. The temperature cannot be uniformed only by heating the block heater, and the above effect cannot be expected.

In FIG. 1, the unstretched plastic optical fiber 1 discharged from the composite spinneret 2 and cooled is slowly charged with a speed V ₁
(M / sec) to the drawing zone 6, facing the running direction of the optical fiber 1 and blowing a heated air stream from 9, and the backward velocity V
₂ (m / sec) is drawn by a pulling force of a drawing roll to a predetermined ratio, followed by slowing down the electric charge, then performing non-contact fixed length heat treatment with the same device, and sufficiently cooling and winding.

FIG. 2 is a diagram showing a thinning completion point by stretching and is as described above.

FIG. 3 shows a thinning profile due to the stretching deformation of the optical fiber when the manufacturing method of the present invention is adopted. The cross-sectional area A (mm ² ) of the fiber and the length L (m) of the stretching heating zone are shown. And roller speed conditions, that is When the thinning completion point by stretching is considered in the range of −10 ≦ P ≦ 10 as described above, a more uniform optical fiber can be obtained. In that case, like the central BC, the profile of the optical fiber in the cooling area is not disturbed,
The change in wire diameter is small, and the desired transparency and bending resistance can be imparted. Note that A is due to excessive heating, and the mechanical properties are inferior. On the other hand, in the case of D, heating is insufficient and the wire diameter varies greatly.

Fig. 4 shows the average transit time in the drawing zone, with the horizontal axis representing the cross-sectional area A (mm ² ) of the optical fiber. In the drawing, the vertical axis represents the region of the stretching condition that satisfies the object of the present invention.

Hereinafter, the present invention will be described more specifically based on Examples.

[Examples] In the examples, the translucency was confirmed by using a tungsten-halogen lamp as a light source and determining wavelength characteristics using a diffraction grating spectroscope. Usually wavelength 65
Using the value at 0 nm, the target is 30 for a 250 micron wire diameter.
It is preferably 0 dB / km or less, and 180 bB / km or less at 500 microns or more.

Examples 1 to 13 and Comparative Examples 1 to 10 After sufficiently purifying commercially available methyl methacrylate, it was sent to a polymerization tank, and an initiator and a chain transfer agent were added to carry out continuous bulk radical polymerization, to a demonomer step. A polymethylmethacrylate having a weight average molecular weight of 84,000 and a residual monomer content of 0.11% by weight was prepared and fed to the core side of the melt-composite spinning section. The Tg measured by the DSC method by raising the temperature by 10 ° C / minute is 118 ° C.
Met.

On the other hand, a commercially available vinylidene fluoride-tetrafluoroethylene copolymer (80/20 molar ratio) was supplied to the sheath side of the composite spinning section, and composite spinning was performed at a spinning temperature of 240 ° C. and a cooling wind speed of 0.4 m / sec. At this time, the discharge amounts on the core side and the sheath side were adjusted for each wire diameter, and the thickness of the sheath portion was set to 5 microns for a wire diameter of 250 microns, and 10 microns for a wire diameter of 1000 microns and 2000 microns. The unstretched plastic optical fiber thus obtained is continuously introduced into the non-contact heating stretching-non-contact fixed length heat treatment apparatus shown in FIG. 1, and stretched and fixed length heat treatment under the conditions shown in Table 1. I did.

The optical fiber in the drawing zone is grasped at the entrance and the exit of the drawing zone, and at the same time, cut at both ends, and is quickly removed from the drawing zone without giving substantial tension or shrinkage, and the change in fiber diameter in the drawing zone is measured with a micrometer. Then, the thinning completion point by stretching was determined based on the above definition.

In addition, the fluctuation range of the wire diameter was obtained with a laser outer diameter measuring device manufactured by Anritsu, and the light transmission loss was measured by the method described above. Further, opposite round rods having a diameter of 10 mm were installed at intervals of 30 mm, and the optical fibers were bent in an S-shape under tension while being alternately and continuously bent to measure the bending resistance. The shrinkage rate was calculated from the rate of change in length before and after treatment in a dry heat oven at 80 ° C for 24 hours without restraint. The results are summarized in Table 2.

The properties of the plastic optical fiber stretched within the range measured by the present invention were all satisfactory, and a high-quality fiber excellent in bending resistance could be obtained.

[Advantages of the Invention] The plastic optical fiber manufactured according to the present invention has a small variation in wire diameter, excellent mechanical properties, particularly, excellent bending resistance, is uniform and high in quality in the longitudinal direction, and has transparency and dimensional stability. Is also good.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an optical fiber drawing-heat treatment method used in the present invention. FIG. 2 is a side view showing the completion point of thinning of the plastic optical fiber. FIG. 3 is an explanatory view showing a thinning profile by stretching an optical fiber when the manufacturing method of the present invention is adopted. Fig. 4 shows the average transit time in the drawing zone with the horizontal axis representing the cross-sectional area A (mm ² ) of the optical fiber FIG. 4 is a relational diagram illustrating a region of a stretching condition that satisfies the object of the present invention when is plotted on the vertical axis. 1: Plastic optical fiber 2: Spinneret 3: Cooling chimney 4: Unstretched plastic optical fiber take-up roller and supply roller to stretching zone 5: Static eliminator 6: Heating stretching zone equipped with block heater 6 ': Equipped with block heater Heat treatment zone 7, 7 ': Fan for circulating heated fluid 8, 8': Heater for fluid heating 9, 9 ': Heated fluid introduction part 10: Stretching roller 11: Heat treatment roller 12: Winding part 13: Heating air flow

Claims (1)

[Claims] 1. When a plastic optical fiber is heated and drawn in a non-contact manner, a heating air stream is introduced into the heating and drawing zone so as to be a countercurrent to the running direction of the optical fiber, and the condition shown by the following formula: A method for producing a plastic optical fiber, which comprises stretching under However, A: target cross-sectional area of drawn fiber (mm ² ) V ₁ : feeding roller speed of plastic optical fiber to heating drawing zone (m / sec), V ₂ : drawing roller speed of plastic optical fiber from heating drawing zone (m / Sec), L: length of heating stretching zone (m)