JP2000292626A - Manufacture of plastic optical fiber and manufacturing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high quality plastic optical fiber capable of elongating while further homogenizing characteristics, excellent in various characteristics such as transmission characteristics, mechanical characteristics and thermal contraction characteristics and excellent in homogeniety of characteristics by continuously performing multistage heating elongating processes not less than two stages, desirably, not less than three stages on the plastic optical fiber after spinning while successively reducing elongating power to the optical fiber offer spinning. SOLUTION: This manufacturing method and manufacturing device has a first heating elongating means 9, a second heating elongating means 10 and a third heating elongating means 11. Nip rollers 2, 4 are respectively arranged in a front stage and a rear stage of the first heating elongating means 9, and a first stage elongating unit is composed of these. The nip roller 4 also serves as a fiber supply means to the second heating elongating means 10, and a second stage elongating unit is composed of the second heating elongating means 10 and nip rollers 4, 6. Similarly, a third stage elongating unit is composed of the third heating elongating means 11 and nip rollers 6, 8. Elongating power of respective heating elongating processes is successively reduced as the processes proceed to a rear stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a plastic optical fiber which can improve and homogenize various properties by performing uniform heating and stretching when producing a plastic optical fiber. .

[0002]

2. Description of the Related Art A plastic optical fiber has advantages such as a large diameter, low cost, and ease of end face processing and handling compared with a quartz type optical fiber. Used in fields such as wiring. Most of the plastic optical fibers that have been put into practical use are optical fibers with a core-sheath structure using polymethyl methacrylate as the core material. Are concentrically arranged, melt-spun and shaped into a fiber, and then stretched under heating for the purpose of improving mechanical properties.

Various proposals have been made in the manufacturing process of such a plastic optical fiber so far. Regarding the drawing step, there are many drawbacks from the viewpoints of reducing fiber diameter unevenness, improving mechanical properties, and homogenizing various properties. The proposal has been made. For example, JP-A-63-289707 discloses a stretching method by infrared heating, and JP-A-63-303.
No. 304 discloses a method for fixing a stretching region in a furnace and optimizing a residence time in the furnace. Japanese Patent Application Laid-Open No. 2-68503 discloses a method in which cooling air is introduced at a furnace outlet.
No. 128 discloses a method of promoting heat exchange with a fiber by changing a streamline of a heating gas in a heating furnace.

[0004]

However, even with the above proposals, the obtained fiber characteristics and the homogeneity thereof are not sufficient and dissatisfaction remains. An object of the present invention is to provide a high-quality plastic optical fiber which is excellent in transmission characteristics, mechanical characteristics and homogeneity thereof, and has small fluctuation in fiber diameter.

[0005]

Means for Solving the Problems The present inventors have conducted various studies on the method of drawing plastic optical fibers and their characteristics. As a result, a fiber having excellent characteristics and uniformity can be obtained by performing a multistage drawing operation. The inventors have found that they can be obtained, and have reached the present invention. That is, in the method for producing a plastic optical fiber according to the present invention, when the plastic optical fiber is subjected to the heat drawing treatment, the draw ratio is 1.1.
It is characterized in that the heating and stretching step of twice or more is performed in two stages, and the stretching ratio in the heating and stretching step is gradually reduced as it goes to the subsequent stage. Alternatively, when the plastic optical fiber is subjected to the heat drawing, the heat drawing step is divided into n steps (n ≧ 3), and the draw ratio in each heat drawing step is gradually reduced as going to the subsequent step. It is a feature.

In the manufacturing method of the present invention, the total stretching ratio (X) after the completion of the heating stretching process in all the stages, based on the value before heating stretching, and the stretching ratio (X) in the first heating stretching process.
1) and the draw ratio (X
n), and the draw ratio is set such that the following relationship is satisfied: 1+ (X-1) / n ≦ X1 ≦ 1 + (X−1) / 2 and 1.1 ≦ Xn ≦ 1 + (X−1) / n Is preferably set. The core material of the plastic optical fiber is preferably formed of a polymer containing 50 mol% or more of a structural unit composed of methyl methacrylate.

The apparatus for manufacturing a plastic optical fiber according to the present invention comprises n (n ≧ 2) drawing units each provided with a means for heating and drawing the plastic optical fiber and a means for controlling the draw ratio in the heating and drawing means. The stretching ratio in each of the stretching units is sequentially set to be smaller as going to a later stage.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The plastic optical fiber according to the present invention (hereinafter, referred to as
The optical fiber or the fiber may be simply an optical fiber in which a portion contributing to light transmission is made of plastic, and may be an SI type having a core-sheath structure, a GI type having a refractive index distribution, a step-like type. May have any refractive index profile in its cross section. Further, a multi-core formed by assembling islands having such a refractive index profile, or a plurality of islands consisting only of a core and having no refractive index distribution, separated from each other by a common sea material. It may be an optical fiber.

The material constituting the plastic optical fiber is not particularly limited, and a known material can be used. However, it is preferable to use a material which can be formed into a fiber by melt spinning. When manufacturing an SI type optical fiber, in order to obtain a fiber having excellent transmission characteristics, it is preferable to use a polymer containing methyl methacrylate as a core material in an amount of 50 mol% or more, and in particular, a polymer containing methyl methacrylate in an amount of 95 mol% or more. Using polymer as core material,
It is preferable to use a vinylidene fluoride / tetrafluoroethylene copolymer or a fluorinated (meth) acrylate / methyl methacrylate copolymer as the sheath material. In addition, a vinylidene fluoride / tetrafluoroethylene copolymer, a fluorinated (meth) acrylate / methacrylic acid is provided on the outer periphery of a plastic optical fiber having an SI type, a GI type, or a step-like refractive index distribution, or a multi-core optical fiber. A protective layer made of a plastic material such as a methyl copolymer, a blend polymer of polyvinylidene fluoride and polymethyl methacrylate, polymethyl methacrylate, or polycarbonate may be formed.

FIG. 1 is a schematic diagram showing an example of a multi-stage heating and stretching apparatus preferably used in the present invention.
In the figure, reference numeral 1 denotes a plastic optical fiber obtained by spinning. In the present invention, it is preferable to use an optical fiber manufactured by spinning, but it is not necessarily limited to this. The apparatus in this example is a three-stage heating and stretching apparatus including a first heating and stretching means 9, a second heating and stretching means 10, and a third heating and stretching means 11. Further, nip rolls 2 and 4 are provided at a stage before and after the first heating and stretching means 9, respectively, and these constitute a first stage stretching unit. Further, the nip roll 4 at the subsequent stage of the first heating and stretching means 9 also serves as a fiber supply means to the second heating and stretching means 10, and the second stretching unit comprises the second heating and stretching means 10 and the preceding stage. And nip rolls 4 and 6 arranged at the subsequent stage, respectively. Similarly, the third-stage stretching unit is composed of the third heating stretching means 11 and nip rolls 6 and 8 arranged before and after the third heating stretching means 11, respectively. By introducing the plastic optical fiber after spinning into the heating and stretching apparatus thus configured, the plastic optical fiber is continuously subjected to the three-stage heating and stretching process.

Although the heating and stretching apparatus of this embodiment is provided with a three-stage stretching unit, any number of stretching units can be provided in the present invention as long as it has two or more stages. In the present invention, if the number of the stretching units is three or more, the effect of reducing the yarn spots and the effect of improving the mechanical properties of the fiber described later are further improved. As the number of stages increases, a fiber having better characteristics can be obtained.However, since the manufacturing apparatus is complicated and the effect of improving characteristics with the increase in the number of stages is reduced, in actual practice, the number of stages in the heating and drawing process is increased by heating. It is preferable to set the draw ratio, which is calculated from the fiber length before drawing and the fiber length after completion of the heating and drawing steps of all stages, that is, about twice (2X) or less the total drawing ratio (X). For example, when performing stretching at a total stretching ratio of 2 times, three or four steps, at most about five steps,
When the stretching is performed at a total stretching ratio of 3 times, it is preferable to set the number of steps to 3 to 6 steps, at most about 7 steps.

In the present invention, the heat stretching means 9, 10, 1
1 may be any heating and stretching furnace capable of heating and stretching the plastic optical fiber 1, and its shape and heating method are not particularly limited. For example, it is possible to appropriately select from various heating and drawing furnaces that have been proposed as heating furnaces for plastic optical fibers and various plastic fibrous materials. In particular, a heating and stretching furnace using a non-contact heating method using an inert heating medium for a plastic optical fiber is preferable because it does not cause physical damage to the optical fiber due to scratches, rubbing, and the like. Specific examples of preferred heating media include heated air, heated nitrogen, and pressurized steam. The method of introducing the heating medium into the furnace is not particularly limited, and may be any of a countercurrent flow, a cocurrent flow, and a crossflow method with respect to the traveling direction of the fiber, and a suitable introduction method is selected in consideration of the apparatus configuration. do it. In the example of FIG. 1, a cross-flow heating stretching furnace provided with hot air generating / circulating devices 3, 5, 7 is used as the heating stretching means 9, 10, 11, respectively.

On both sides of each of the heating and stretching means 9, 10, and 11, there are provided a mechanism for supplying a plastic optical fiber to the heating and stretching means 9, 10, and 11 at a constant speed, and a mechanism for withdrawing the plastic optical fiber from the heating and stretching means 9, 10, and 11. Each is provided. As such a supply and take-off mechanism, for example, a drive roll such as a nip roll, a godet roll, and a Nelson roll can be suitably used. In the example of FIG. 1, nip rolls 2, 4, 6, and 8 are used. And
By controlling these driving rolls (nip rolls 2, 4, 6, 8), the fiber 1 to each of the heating and stretching means 9, 10, 11 is controlled.
By determining the feed rate and take-off rate of
The stretching magnification of the plastic optical fiber 1 in each stretching unit is determined. For example, assuming that the fiber supply speed in the k-th drawing unit is (Vkin) and the take-up speed is (Vkout), Vkout> Vkin, and the drawing magnification (Xk) in the k-th drawing unit
Is expressed as Xk = Vkout / Vkin. Also, the take-up speed in the k-th stretching unit and the next (k +
1) Since the supply speeds in the drawing units in the first stage are equal, the final drawing ratio (X) after performing the n-stage heating stretching on the optical fiber before the heating stretching is X = Vnout / V1.
(Vnout is the take-up speed in the last stage, and V1in is the supply speed in the first stage).

In the present invention, when performing heat stretching in multiple stages, it is important to set the stretching ratio in each stretching unit so as to gradually decrease in the subsequent stages. By performing the multi-stage stretching while sequentially reducing the stretching ratio, the variation in the higher-order structure of the polymer chains caused by the unevenness in the fiber diameter caused in the heating and stretching process in the previous stage and the unevenness in the temperature in the heating furnace is reduced to the next stage. In the heating and stretching process, the fiber can be stretched while being homogenized, and a plastic optical fiber having both excellent properties and homogeneity can be obtained. In general stretching of plastics, the higher the stretching ratio or deformation ratio, the greater the variation in the higher-order structure of the polymer. For this reason, if an attempt is made to stretch at a later stage at a magnification higher than that of the former stage, not only the variation in the structure in the former stage is reduced but also a larger variation in the structure will be given. Further, by making the stretching ratio smaller than that in the former stage, it becomes possible to perform the relaxation treatment under tension simultaneously with the stretching. In the case of an amorphous polymer such as polymethyl methacrylate used as a core material of a plastic optical fiber, under non-tension, that is, under relaxation, or when heated and relaxed at a constant length,
Even the orientation of the molecular chains that had been applied is relaxed, and the mechanical properties of the fiber are reduced.However, by heating under tension and relaxing, the polymer maintains its molecular chain orientation, It is possible to reduce the variation in chain structure. In order to sufficiently reduce the variation in the structure of the polymer chain while sufficiently maintaining the orientation of the molecular chain, the stretching ratio in each stretching unit is preferably 1.07 times or more,
More preferably, it is 1.1 times or more. When the number of steps in the heat stretching step is two, the stretching ratio in each stretching unit is 1.1 times or more.

Further, in the present invention, between the stretching ratio (X1) and the total stretching ratio (X) in the first heating stretching step, 1+ (X−1) / n ≦ X1 ≦ 1 + (X−1) / 2 is preferable. X1> 1+ (X−
In 1) / 2, since the stretching ratio in the first stage is large, the relaxation in the second and subsequent stages becomes insufficient, and the effect of improving the characteristics of the fiber may be reduced. Also, 1+ (X-1) / n>
In the case of X1, the number of stages is increased, and the device may be complicated. Further, it is preferable that there is a relation of 1.1 ≦ Xn ≦ 1 + (X−1) / n between the stretching ratio (Xn) and the total stretching ratio (X) in the final stage. Xn> 1+ (X−
In 1) / n, variation in polymer structure remains to reduce the homogeneity of the fiber characteristics, and when 1.1> Xn, the preservation of the orientation of the molecular chains provided by stretching may be reduced.

For example, when a plastic optical fiber after spinning is subjected to a heat drawing process at a total draw ratio of 2 using an apparatus having a three-stage drawing unit shown in FIG. As a typical stretching ratio value, the stretching ratio in the first-stage stretching unit is X1 = 1.4, and the stretching ratio in the second-stage stretching unit is X2 = 1.25,3.
X3 = 1.14 in the stretching unit of the stage
Can be set. In the case of a total stretching ratio of 3 times and a stretching unit of 5 stages, for example, X1 = 1.43, X2 =
1.27, X3 = 1.22, X4 = 1.18, X5 =
1.15 can be set. In order to realize such a drawing ratio of the fiber in each stage, the speed ratio of the fiber supply and take-off devices provided on both sides of the drawing furnace may be controlled. Further, the setting of the stretching temperature in each stage is not particularly limited, and may be the same temperature in all stages,
The temperature of each stage may be different. From the viewpoint of suppression of increase in yarn spots due to stretching and preservation of molecular orientation, it is preferable to set the temperature so that the temperature gradually decreases in the later stage.

[0017]

EXAMPLES Hereinafter, the effects of the present invention will be clarified by showing specific examples. (Example 1) Polymethyl methacrylate as a core material, trifluoroethyl methacrylate / perfluorooctylethyl methacrylate / methyl methacrylate terpolymer (copolymer composition 50/30/20% by weight) as a sheath material, Using a vinylidene fluoride / tetrafluoroethylene copolymer (copolymer composition 80/20 mol%) as a protective material, these resins were supplied to a concentric composite nozzle,
It was melt spun at 25 ° C. into a three-layer core / sheath / protection fiber. Subsequently, the spun fiber was supplied to a heating and stretching apparatus provided with a three-stage stretching unit shown in FIG. 1 and subjected to a heating and stretching treatment at a total stretching ratio of 2 times. The stretching conditions (heating conditions and stretching ratios) in the stretching units in each stage are shown in Table 1 below.
Was set as shown in FIG. In the drawing unit of the final stage, it was wound at a speed of 30 m / min to produce a plastic optical fiber having a three-layer structure consisting of a core, a sheath, and protection. The fiber diameter of the obtained plastic optical fiber was measured using a laser outer diameter measuring machine. As a result, the average fiber diameter was 1002 μm,
The transmission loss at a wavelength of 650 nm (25 m-5 m cutback method, incident NA = 0.1) was 135 dB / km. The length of this fiber is 1
Sampling 30 points every 00m, 90
Measurement of axial thermal shrinkage of fiber at 50 ° C dry heat for 50 hours,
Fracture strength was measured using a tensile tester to evaluate fiber properties and its homogeneity. Table 2 shows the results. In this table, the heat shrinkage and the breaking strength show the average and the dispersion of the measured values at the above 30 points. Next, the plastic optical fiber was coated with polyethylene to produce a plastic optical fiber cable having a cable diameter of 2.2 mm. This optical fiber cable is sandwiched between two cylindrical objects having a radius of 15 mm at two end faces, a 500 g weight is attached to one end of the optical fiber cable, and the other end is placed along both sides of the cylindrical object, on both cylindrical object sides. A repetitive bending / rupture test was performed in which the optical fiber cable was bent by 90 degrees for a total of 180 degrees, and the number of bending times until the optical fiber cable was broken was measured. The results are shown in Table 2.

(Examples 2, 3, and 4 and Comparative Examples 1 and 2)
In Example 1, a plastic optical fiber was produced in the same manner as in Example 1 except that the configuration of the plastic optical fiber and the heating and stretching conditions were changed as shown in Table 1 below. The properties and homogeneity of the obtained fiber were evaluated in the same manner as in Example 1. The results are shown in Table 2 below.

[0019]

[Table 1]

[0020]

[Table 2]

From the results shown in Tables 1 and 2, Comparative Example 1 in which the number of heating stretching steps is as small as two and the final stage stretching ratio is small, and when performing three-stage heating stretching, the stretching ratio in each stage. In Comparative Example 2 in which was gradually increased, the fiber diameter of the obtained plastic optical fiber varied greatly, and the transmission characteristics, mechanical characteristics and its homogeneity were inferior to those of Examples 1 to 4. In particular, in Comparative Example 2, the fluctuation of the fiber diameter and the fluctuation of the breaking strength were large, and the repeated bending characteristics were inferior.

[0022]

As described above, according to the method for manufacturing a plastic optical fiber of the present invention, a multi-stage of two or more stages, preferably three or more stages, is sequentially reduced with respect to the drawn plastic optical fiber. By performing the heating and stretching step continuously, the fiber diameter unevenness generated in the preceding heating and stretching step and the variation of the higher-order structure of the polymer chains are alleviated in the next heating and stretching step, and while being homogenized. Since it can be stretched, a high-quality plastic optical fiber having excellent properties such as transmission properties, mechanical properties, and heat shrinkage properties and excellent in homogeneity of properties can be obtained.

Further, assuming that the total stretching ratio after the completion of the heating stretching process in all the stages is X, based on the value before heating stretching, the stretching ratio (X1) in the first heating stretching process is 1+ (X-1) / n. ≦ X1 ≦ 1 + (X−1) / 2 is preferably set, whereby a sufficient relaxation effect can be obtained in the second and subsequent heating and stretching steps while avoiding complication of the apparatus, and various characteristics can be obtained. And a plastic optical fiber excellent in uniformity of characteristics can be efficiently obtained. Further, the stretching ratio (Xn) in the final heating and stretching step is preferably set so as to satisfy 1 ≦ Xn ≦ 1 + (X−1) / n, whereby the orientation of the molecular chains formed by stretching is set. While maintaining the above, the variation in the structure of the polymer chain is preferably alleviated, and various characteristics are good.
In addition, a plastic optical fiber having excellent property uniformity can be suitably obtained.

In the present invention, it is preferable to use, as the plastic optical fiber, a fiber whose core material is formed of a polymer containing 50 mol% or more of a structural unit composed of methyl methacrylate. Can be

According to the apparatus for manufacturing a plastic optical fiber of the present invention, n drawing units (n ≧ n) provided with a heating and stretching means for heating and stretching the plastic optical fiber and a means for controlling a stretching ratio in the heating and stretching means. 2) Since there are arranged n-stage heating and stretching devices, and the stretching ratio in each of the stretching units is set to be gradually smaller as going to the later stage, the fiber diameter unevenness generated in the preceding heating and stretching step and the high Variations in the higher-order structure of the molecular chains are reduced in the subsequent heating and stretching step, and the film is stretched while being homogenized. Therefore, a high-quality plastic optical fiber having excellent characteristics such as transmission characteristics, mechanical characteristics, and heat shrinkage characteristics and excellent in uniformity of characteristics can be obtained. Also, by connecting the drawing units and providing them in multiple stages, the plastic optical fiber in a high temperature state is supplied to the second and subsequent heating and stretching means, so that the heating in the heating and stretching means can be efficiently performed and energy saving can be achieved. It is preferable in terms of cost reduction. In addition, by connecting the preceding heating and stretching means and the next heating and stretching means in a connected manner, one driving device functions as both a fiber pulling device from the preceding heating and stretching means and a fiber feeding device to the next heating and stretching means. It is possible to reduce the size and space of the device, reduce the number of components, and reduce the cost.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a heating and stretching apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Plastic optical fiber 2, 4, 6, 8 ... Nip roll (Stretching magnification control means) 10, 11 ... Heat stretching means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshinori Sumi 20-1 Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Shoji Okamoto 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory F-term (reference) 2H050 AA13 AB43X AB43Y AB44Y AB48Y AB50Y AC03 AC05

Claims (5)

[Claims] When a plastic optical fiber is subjected to a heat drawing process, a heat drawing process having a draw ratio of 1.1 times or more is performed in two stages, and the drawing ratio in the heat drawing process is shifted to a subsequent stage. A method for manufacturing a plastic optical fiber, characterized in that the optical fiber is sequentially reduced in size. 2. The method of heating and stretching a plastic optical fiber in n stages (n ≧ 3), and gradually reducing the stretching ratio in each heating and stretching process to the subsequent stages. A method for producing a plastic optical fiber. 3. The total stretching ratio (X) after the completion of the heating and stretching step in all the stages based on the value before the heating and stretching, the stretching ratio (X1) in the first stage of the heating and stretching process, and the ratio in the final stage of the heating and stretching process. The relationship of 1+ (X-1) / n≤X1≤1 + (X-1) / 2 and 1.1≤Xn≤1 + (X-1) / n with the draw ratio (Xn). The method for producing a plastic optical fiber according to claim 1, wherein: 4. The plastic optical fiber according to claim 1, wherein the core material is formed of a polymer containing 50 mol% or more of a structural unit composed of methyl methacrylate.
A method for manufacturing a plastic optical fiber according to any one of claims 1 to 3. 5. A heating and stretching apparatus provided with n (n ≧ 2) stretching units including a heating and stretching means for heating and stretching a plastic optical fiber and a means for controlling a stretching ratio in the heating and stretching means, An apparatus for producing a plastic optical fiber, wherein a stretching magnification in each of the stretching units is set to be gradually smaller as going to a later stage.