JP2006119587A - Plastic optical member and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance optical characteristics such as transmission characteristic by suppressing air bubbles in a plastic optical member. <P>SOLUTION: A columnar preform 11 is longitudinally extended by an extension process 27 to manufacture a plastic optical fiber 21. Before the extension process 27, the preform is heated under reduced pressure by a reduced pressure heating process 26. As a result, a substance that tends to evaporate in the extension process 27 can be preliminarily removed from the preform, enabling air bubbles to be suppressed in the plastic optical fiber. Accordingly, transmission characteristic of the plastic optical fiber can be enhanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plastic optical member and a method for manufacturing the same.

  In optical applications such as optical transmission bodies, plastic materials and quartz materials are generally used. Comparing the two, the plastic material is superior to the quartz material in molding processability, weight reduction of the member, cost reduction, flexibility, impact resistance, and the like. For example, a plastic optical fiber (POF) is not suitable for long-distance optical transmission because of its large optical transmission loss compared to a silica-based optical fiber. It is possible to increase the diameter so that the core portion of the fiber is several hundred μm or more.

  By increasing the diameter, it is not necessary to increase the connection accuracy between various peripheral components used for branching and connection of optical fibers and optical fibers of equipment. As a result, POF has the advantage that it is possible to improve the ease of connection with peripheral parts and devices and the ease of processing a terminal, and the need for highly accurate alignment is eliminated. The POF can reduce the cost of the connector part as described above, and can reduce the risk of a piercing accident to the human body due to the nature of the plastic, and it is highly workable and layable due to its high flexibility. There are also advantages such as excellent vibration resistance and low price. Therefore, the POF is not only attracting attention for home and in-vehicle use, but also as an extremely short distance and large capacity cable in an internal wiring of a high-speed data processing device, a DVI (Digital Video Interface) link, or the like.

  Some plastic optical fibers have a refractive index that increases continuously or stepwise toward the center in the radial direction of the circular cross section, and these are generally referred to as gradient index plastic optical fibers. As a method of manufacturing such a gradient index plastic optical fiber, a plastic optical fiber base material, a so-called preform, is produced by an interfacial gel polymerization method, and then the preform is heated and stretched in the longitudinal direction to produce a plastic optical fiber. There is a method of using a fiber (Patent Documents 1 to 3).

  When a preform is heated and stretched to form a plastic optical fiber, air bubbles are often generated and fine voids are formed in the core portion which is a light guide portion of the plastic optical fiber. A plastic optical fiber having a fine gap has a problem because transmission loss increases. Further, even if a fine gap is not visually confirmed, a gap of the order of μm may be formed, and even at this level of gap, transmission loss is greatly impaired.

The causes of foaming during the heat stretching of the preform have so far been moisture in the preform, dissolved gas in the core portion of the preform, voids in the preform, and the like. In order to reduce the moisture in the preform, a method for producing a plastic optical member that reduces the moisture content of the monomer that is the raw material of the preform has been proposed (see, for example, Patent Document 4). In order to reduce the dissolved gas, it has been proposed to degas the monomer that is a raw material of the core part under reduced pressure and to polymerize and generate the core part under pressure control (see, for example, Patent Document 5). In addition, in order to suppress voids in the preform, in the rotational polymerization in the preform production process, a solation process is provided to increase the monomer addition rate (see, for example, Patent Document 6), or a hollow tube A method of polymerizing a preform by injecting a polymerizable compound into the hollow part of the hollow tube after sealing one end of the hollow tube (see, for example, Patent Document 7), the preform after the core is polymerized and formed A method of cooling at a predetermined cooling rate (see, for example, Patent Document 8) has been proposed.
JP-A-61-130904 Japanese Patent No. 3332922 Japanese Patent Laid-Open No. 10-253838 JP 2003-149463 A JP 2003-329859 A JP 2003-195065 A JP 2003-232940 A JP 2003-329858 A

  However, in the method of Patent Document 4, there is a problem that it is impossible to prevent an increase in the amount of moisture due to moisture absorption during the monomer polymerization reaction step or after the optical member is created. In the method of Patent Document 5, the boiling point is the boiling point of the monomer. There is a problem in that volatile substances that are equal to or higher than are not sufficiently removed by the vacuum degassing treatment of the raw material. Further, the method of Patent Document 6 has a problem that the content of volatile substances other than unreacted monomers, such as moisture, cannot be reduced, and the method of Patent Document 7 suppresses the mixing of bubbles in the polymerization process. Although there is an effect, there is a problem that there is no effect of reducing the volatile substance dissolved in the monomer or dissolved, and the method of Patent Document 8 prevents the generation and growth of voids due to volume shrinkage in polymerization. Although effective, there is a problem in that there is no effect of reducing the volatile substances themselves that cause foaming during the heat stretching of the preform. Thus, in the conventional method, foaming during the heat stretching of the preform could not be sufficiently suppressed. This is because foaming is caused by the components of the core portion of the preform in addition to the above-mentioned causes. That is, bubbles are generated when a material that vaporizes during heating and stretching is used as a component of the core.

  There are monomers that did not polymerize during preform preparation, so-called residual monomers, which are vaporized during heat drawing. There is moisture that has been included. Such a vaporized substance is not sufficiently removed even if the preform is annealed at various temperatures as described above or at a temperature equal to or higher than the glass transition point (Tg) of the polymer in the core portion.

  In addition, various transparent polymers represented by acrylic polymers are used in the core portion of the preform from the viewpoint of optical transmission characteristics. Many of these polymers have a saturated water absorption rate at room temperature of about 0. It is 1 wt% or more and 3.0 wt% or less. For this reason, even when the preform has a very low moisture content in the core at the time of manufacture, the moisture content in the core becomes higher depending on the storage environment as the storage period until heating and stretching becomes longer. There is a problem that the frequency of local foaming at times increases. This problem is common to each preform that is heat-processed into a plastic optical member other than the plastic optical fiber.

  Therefore, an object of the present invention is to provide a method for producing a plastic optical member that suppresses the generation of bubbles when the preform is heated and stretched in order to improve the optical characteristics, for example, transmission characteristics, of the plastic optical member.

  In order to solve the above-mentioned problems, in the present invention, in a method for producing a plastic optical member, which is obtained by heating and stretching a rod-shaped preform in the longitudinal direction, the preform is heated in advance before the heating and stretching. It is structured to be processed.

  The heat treatment is preferably performed under reduced pressure. A polymerizable compound is placed in the hollow portion of the tubular first member and the polymerizable compound is polymerized to form a second member having a refractive index equal to or lower than the refractive index of the first member in the hollow portion. Preferably, the preform has a member and a second member, and the heat treatment is preferably performed so that the moisture content of the second member is 0.001 wt% or more and 0.5 wt% or less. The polymer produced by the polymerization is particularly effective when the saturated water content at 25 ° C. is 1.0 wt% or more and 3.0 wt% or less, and the polymer is more preferably an acrylic polymer. The polymerization is preferably bulk polymerization. The preform is preferably columnar or cylindrical. The second member includes a substance having a refractive index difference of 0.001 or more from the polymer generated by the polymerization, and the substance is distributed with a concentration gradient along a predetermined direction in the second member. It is preferable. The plastic optical member is preferably a plastic optical fiber.

  Furthermore, this invention is comprised including the plastic optical member manufactured by said each manufacturing method.

  According to the present invention, since the generation of bubbles when the preform is heated and stretched can be suppressed, it is possible to produce a plastic optical member having excellent optical characteristics, particularly transmission characteristics.

  Although embodiments of the present invention will be described, the present invention is not limited to the following embodiments. In the present invention, after producing a rod-shaped preform, the preform is stretched in the longitudinal direction to produce a plastic optical member. A plastic optical fiber can be produced by increasing the draw ratio, and a gradient index (GRIN) lens can be produced by making the draw ratio relatively low. In addition, a draw ratio means the length after extending | stretching with respect to the length before extending | stretching in a longitudinal direction. In the following description, a case where a plastic optical fiber is manufactured from a preform is taken as an example. First, the preform structure and its refractive index will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view of a preform, and FIG. 2 is a view showing a refractive index in the radial direction of the cross section of the preform. In FIG. 2, the horizontal axis indicates the cross-sectional radial direction of the preform, and the vertical axis indicates the refractive index. The refractive index means that the upper direction has a high value. A preform 11 shown in FIG. 1 includes a core 12 that transmits an optical signal and an outer cladding portion 16 that is an outer shell portion. The outer cladding portion 16 includes an inner cladding portion 15 that is in contact with the outer periphery of the core 12 and an inner cladding portion 15. It has an outer clad part 16 outside the clad part 15. Therefore, the outer diameter of the inner cladding portion 15 is equal to the inner diameter of the outer cladding portion 16, and the diameter of the core portion 12 is equal to the inner diameter of the inner cladding portion 15.

  The outer clad portion 16 has a tube shape in which the outer diameter and the inner diameter are constant in the longitudinal direction and the thickness is uniform. In this embodiment, the material of the outer clad part 16 is polyvinylidene fluoride (hereinafter referred to as PVDF), and is obtained by melt extrusion molding. However, the material of the outer clad part 16 may be PMMA as described later, or may be another substance described in detail later. The inner clad portion 15 has a tube shape in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is substantially uniform, like the outer clad portion 16. The material of the inner clad part 15 is PMMA. The outer clad part 16 and the inner clad part 15 may be integrally formed at the same time by melt extrusion, or other production methods, for example, the outer clad part 16 is obtained by melt extrusion molding, in which polymerization of MMA or the like is performed. The inner clad portion 15 made of PMMA or the like may be formed sequentially by injecting the active compound to cause a polymerization reaction while rotating.

  In FIG. 2, the range indicated by the symbol (A) on the horizontal axis is the refractive index of the outer cladding portion 16 in FIG. 1, and the range indicated by the symbol (B) is the refractive index of the inner cladding portion 15 in FIG. Yes, the range indicated by the symbol (C) is the refractive index of the core 12 in FIG.

  As shown in FIG. 2, the core 12 has a refractive index that continuously increases from the boundary with the inner cladding portion 15 toward the center. The outer cladding portion 16 has a refractive index lower than that of the inner cladding portion 15, and the refractive index of the inner cladding portion 15 is equal to or lower than the refractive index of the core 12. Then, an interfacial gel polymerization method, which will be described later, is used to generate the core 12 so that the refractive index of the core 16 continuously increases from the outside to the center of the circular cross section as shown in FIG. preferable. In the radial direction of the circular cross section, the difference between the maximum value and the minimum value of the refractive index is preferably 0.001 or more and 0.3 or less. With such a structure, the preform 11 exhibits a function as an optical transmission body as it is without being drawn into a plastic optical fiber. In FIG. 1, the boundary between the inner clad portion 15 and the core 12 is shown for convenience of explanation. However, the clarity of the boundary differs depending on manufacturing conditions and the like, and may not necessarily be confirmed.

  In addition, the inner cladding portion 15 of the present embodiment has a substantially constant refractive index as shown in FIG. 2, but the refractive index may increase as it approaches the core 16. The closer to the core 16, the larger it may be in steps, or it may increase continuously.

The refractive index distribution coefficient of the preform 11 and the plastic optical fiber 21 is known as the value of g in the following formula (1). In the following formula (1), R is the outer diameter of the preform 11 or the plastic optical fiber 21, r is the distance from the center of the cross-sectional circle to the measurement position, and n1 is the maximum value of the refractive index in the cross-sectional radial direction. N2 is the minimum value of the refractive index in the cross-sectional radial direction, and Δ is a value represented by (n1-n2) / n1.
(1): n (r) = n1 {1- (r / R) ^g × Δ} ^1/2 (when r ≦ R)
= N1 (1-Δ) (when r> R)

  The refractive index distribution coefficient of the preform 11 and the plastic optical fiber 21 exemplified in the present embodiment is preferably 0.5 or more and 4.0 or less, more preferably 1.5 or more and 3.0 or less. Ideally 2.0.

  Further, the present invention can be applied even if the core 12 and the inner cladding 15 have a structure other than the above structure. As another structure of the core 12 and the inner clad part 15, for example, there is no boundary between the inner clad part 15 and the core 12, and the refractive index from the inner periphery of the outer clad part 16 toward the center of the core 12. May be a structure in which the core height increases continuously or stepwise, or a structure in which the core 12 is a multilayer. Moreover, although the outer clad part 16 is made into the single layer structure, this invention is not limited to this, For example, you may be made into the multilayer structure of 2 layers or more as needed. Depending on the manufacturing conditions, the core 12 may be formed in a cylindrical shape as shown in FIG. 1 or may be formed in a tube shape having a hollow portion. In the preform 11 according to the present embodiment and the plastic optical fiber obtained from the preform 11, light incident from the end surface is reflected at the interface between the outer clad and the inner clad and passes through both the inner clad. Sometimes it passes only through the core. Since the preform and the plastic optical fiber have basically the same structure and refractive index distribution, illustration and description of the structure and the refractive index of the plastic optical fiber are omitted.

  Next, a method for producing the preform 11 and a method for producing a plastic optical cable will be described. FIG. 3 is a manufacturing process diagram of a plastic optical fiber and a plastic optical cable using the plastic optical fiber. The details of each process of the manufacturing method will be described later, and only the process flow will be described here. The plastic optical fiber 21 is obtained by stretching a preform 11 prepared in advance in the longitudinal direction. Therefore, the plastic optical fiber 21 has a smaller diameter than the preform 11, but its basic structure is almost the same as the preform 11. That is, the plastic optical fiber 21 has a clad and a core, and the clad is composed of an outer outer clad portion and an inner inner clad portion. The core and clad of the preform 11 become the core and clad of the plastic optical fiber, respectively. Even when the preform core is formed in a tubular shape having a hollow portion, the hollow portion disappears by stretching, and a plastic optical fiber having no hollow portion is produced.

  First, in the outer outer cladding part manufacturing step 22, a pipe 23 that is an outer cladding part of the preform 11 is manufactured. Since the outer clad portion is the outer shell portion of the preform 11 as described above, the obtained outer clad portion pipe 23 is a circular pipe. In the inner cladding portion forming step 24, the inner cladding portion is formed on the inner surface of the outer cladding portion pipe 23 so that the center of the cross section of the preform 11 is hollow. In some cases, the outer clad part and the inner clad part are integrally molded by, for example, melt extrusion. Next, a process of generating a core in the hollow portion of the inner clad part is referred to as a core forming process 25, and the preform 11 is obtained through the core forming process 25. Then, the obtained preform 11 is heated under reduced pressure in the reduced pressure heating step 26, thereby removing the material that is vaporized in the subsequent stretching step 27. Thereafter, the preform 11 is stretched in the longitudinal direction by a stretching step 27 to become a plastic optical fiber 21. The plastic optical fiber 21 becomes a plastic optical cable 29 through a coating process 28 in which the outer periphery is coated with a coating material.

  Below, the manufacturing method of the plastic optical fiber 21 is demonstrated in detail. The pipe 23 for the outer clad part can be obtained by molding a predetermined polymer into a tubular shape by melt extrusion, or can be produced by simultaneously performing a polymerization reaction and molding of a polymerizable compound by a rotational polymerization method or the like. it can. Here, a case will be described in which PVDF is used as a polymer for forming the outer cladding portion (hereinafter referred to as an outer cladding portion cladding forming polymer), and the outer cladding portion is manufactured by melt extrusion. Various commercially available kneading extrusion molding machines can be used for melt extrusion, and there are mainly two types of kneading extrusion molding machines, an inner sizing die system and an outer die vacuum suction system, both of which can be used. it can.

  First, an outline of a molding method by the outer die vacuum suction method will be described. FIG. 4 is a schematic view of a melt molding facility 30 using an outer die vacuum suction system, and FIG. 5 is a cross-sectional view schematically illustrating an example of a molding die. As shown in FIG. 4, the melt molding equipment 30 includes a melt extrusion device 31, an extrusion die 32, a molding die 33, a cooling device 34, and a take-up device 35 for taking up the pipe 23. The melt extrusion apparatus 31 is provided with a pellet charging hopper (hereinafter simply referred to as a hopper) 36 for supplying a raw material polymer therein, and has a melt extrusion part 31a for melting the raw material polymer. . A vacuum pump 37 is attached to the molding die 33. Further, as shown in FIG. 5, the molding die 33 includes a molding tube 40. The molding tube 40 is provided with a number of suction holes 40a for decompressing the polymer as the outer clad pipe 23, and molding is performed. A decompression chamber 43 is provided outside the tube 40.

  Further, the cooling device 34 is provided with a number of nozzles 45, cooling water 46 is discharged from the nozzles 45, and a receiving tray 47 for collecting the cooling water 46 is provided below. Further, the take-up device 35 is provided with a drive roller 48 and a pressure roller 49. A motor 48 a is attached to the drive roller 48, and the take-up speed of the outer clad pipe 23 can be adjusted.

  The raw material polymer 41 introduced from the hopper 36 is melted by the melt extrusion part 31 a, extruded by the extrusion die 32, and sent to the forming die 33. The extrusion speed S (unit: m / min) at this time preferably satisfies 0.1 ≦ S ≦ 10, more preferably 0.3 ≦ S ≦ 5.0, and most preferably 0.4 ≦ S ≦ 1.0. However, the present invention does not depend on the extrusion speed S.

  By passing the raw material polymer 41 through the forming tube 40, the raw material polymer 41 is formed into a cylindrical shape, and the outer clad pipe 23 is obtained. In the molded tube 40, the decompression chamber 43 is depressurized by the vacuum pump 37 so that the outer wall surface of the pipe 23 comes into close contact with the molded surface (inner wall surface) of the molded tube 40, so that the wall thickness t1 of the pipe 23 is constant. To be molded. The pressure (absolute pressure) in the decompression chamber 43 is preferably in the range of 20 kPa to 50 kPa, but is not limited to this range. A throat (outer diameter determining member) 44 for defining the outer diameter of the pipe 23 is preferably attached to the inlet of the forming die 33.

  The pipe 23 formed by the forming die 33 is sent to the cooling device 34. Then, the cooling water 46 is discharged from the nozzle 45 toward the pipe 23. Thereby, the pipe 23 is cooled and solidified. The cooling water 46 is collected by the receiver 47 and discharged from the discharge port 47a. The pipe 23 is drawn out from the cooling device 44 by the take-up device 45. In addition, a minute displacement of the pipe 23 can be corrected by a pressure roller 49 disposed opposite to the driving roller 48 with the pipe 23 interposed therebetween. By adjusting the take-up speed of the driving roller 48 and the extrusion speed of the melt extrusion device 31 or by finely adjusting the moving position of the pipe 23 by the pressure roller 49, the shape of the pipe 23, particularly the wall thickness is made uniform. It becomes possible to. If necessary, the drive roller 48 and the pressure roller 49 can be formed in a belt shape.

  The pipe 23 may be composed of multiple layers in order to impart various functions such as improvement of mechanical strength and flame retardancy, and after producing a hollow tube having an arithmetic average roughness of the inner wall in a specific range. The outer wall surface can be covered with a fluororesin or the like.

  The outer diameter D1 (unit: mm) of the obtained pipe 23, that is, the outer diameter of the obtained preform is preferably in the range of 20 ≦ D1 ≦ 50, more preferably 2 ≦ from the viewpoint of optical properties and productivity. It is the range of D1 ≦ 32. Furthermore, the thickness t1 (unit: mm) of the pipe 23 can be reduced as long as the shape can be maintained, but is preferably in the range of 0.5 ≦ t1 ≦ 3. However, in the present invention, these ranges are not limited to those described above.

  Next, a method for producing a clad by the inner sizing die method will be described. FIG. 6 is a cross-sectional view schematically showing a part of an inner sizing die type extruder, and FIG. 7 is a perspective view of a guide 57 provided in the extruder shown in FIG. In FIG. 6, the raw material polymer and the outer clad pipe are denoted by the same reference numerals as in FIGS. 4 and 5. An inner sizing die type extruder 51 includes an extruder body 52 and a die 54, and an inner rod 55 is provided inside the die 54. The inner rod 55 forms a flow path 54 a of the clad raw material polymer 41 inside the die 54, and a guide 57 for guiding the raw material polymer 41 to the flow path 54 a is provided between the extruder main body 52 and the die 54. Is provided. As shown in FIG. 7, the guide 57 has a guide path 57a for guiding the polymer to the flow path 54b. The guide path 57a forms a guide path 57a with a shaft portion 57b connected to the inner rod 55. At the same time, it is formed by a main body portion 57c for restricting the flow of the polymer and a support portion 57d for supporting the shaft portion 57b on the main body portion 57c. PVDF, which is the raw material polymer 41 in this embodiment, is extruded from the extruder main body 52 to the die 54 by a vented single screw extruder (not shown). The raw material polymer 41 passes through a flow path 54 a between the die 54 and the inner rod 55 and is extruded from the outlet 54 b of the die to form the cylindrical pipe 23. The extrusion speed is not particularly limited, but it is preferably in the range of 1 cm / min to 200 cm / min from the viewpoint of productivity while keeping the shape uniform.

  The die 54 is preferably provided with a heating means (not shown) for heating the raw polymer 41. For example, one or more heating means are arranged along the flow path 54a so as to cover the die body 52. Examples of the heating means include those using steam, heat transfer oil, electric heaters, and the like. The In this embodiment, a temperature sensor 56 is attached in the vicinity of the die outlet 54b, and the temperature sensor 56 measures the temperature of the die outlet 54b and adjusts the temperature of the pipe 23 based on the measurement result. Yes.

  The heating temperature by the heating means is appropriately set according to the type of the raw material polymer 41. A preferable range of this temperature is equal to or higher than the glass transition point of the raw material polymer 41, whereby the shape of the pipe 23 can be kept uniform. In addition, it is preferable that the temperature of the pipe 23 at the outlet 54b of the die 54 is 40 ° C. or more in terms of suppressing a shape change due to a rapid temperature change. In order to control the temperature of the pipe 23, for example, a cooling means may be attached to the die 54 or may be cooled by natural cooling. When the cooling means is used and the heating means is provided, it is preferable to provide the cooling means downstream of the heating means. Examples of the cooling means include water, antifreeze liquid, oil and other liquids, and those utilizing electronic cooling.

  Next, a preform manufacturing method will be described in detail with reference to FIGS. FIG. 8 is a cross-sectional view of a polymerization vessel in which pipes are loaded, FIG. 9 is a schematic perspective view of a rotary polymerization apparatus, and FIG. 10 is an explanatory view of a polymerization reaction by the polymerization apparatus. However, the present invention does not depend on the polymerization apparatus and the polymerization vessel shown in FIGS. 8 to 10, and this embodiment is an example as one aspect of the present invention.

  The pipe 23 is cut to a length of 600 to 1500 mm. One end of the pipe 23 is closed with a plug 61 made of a predetermined material. The stopper 61 is made of a material that does not dissolve in the polymerizable compound that forms the inner cladding and the core, and does not include a compound that elutes a plasticizer or the like. Examples of such a material include polytetrafluoroethylene (PTFE). After plugging the end portion with the stopper 61, the inner cladding portion forming monomer 15A is injected into the pipe 23, and the other end portion is closed with the stopper 61, and then the inner cladding portion is formed by rotational polymerization (see FIG. 1). ) Is generated. At the time of producing the inner clad, the pipe 23 is placed in a polymerization vessel 62 as shown in FIG. The superposition | polymerization container 62 has the container main body 62a and the lid | cover 62b, and is made from SUS in this embodiment. As shown in FIG. 8, the inner diameter of the polymerization vessel 62 is slightly larger than the outer diameter of the pipe 23, and the pipe 23 can rotate in synchronization with the rotation of the polymerization vessel 62 as described later. Has been. A support member or the like for supporting the pipe 23 may be provided on the inner surface of the polymerization vessel 62 so that the pipe 23 can respond to the rotation of the polymerization vessel 62 as described above.

  As shown in FIG. 9, the rotation polymerization apparatus 71 detects a plurality of rotating members 73 in the apparatus main body 72, a motor 76 outside the apparatus main body 72, and the temperature in the apparatus main body 72. Accordingly, a temperature controller 77 for controlling the internal temperature is provided.

  The rotating member 73 has a cylindrical shape, and the longitudinal directions thereof are substantially parallel to each other and substantially horizontal so that at least one polymerization vessel 62 can be supported by two peripheral surfaces. One end of each rotating member 73 is rotatably attached to the side surface of the apparatus main body 72 and is driven to rotate by a motor 76 under independent conditions. The motor 76 is provided with a controller (not shown), and the drive of the motor 76 is controlled by this controller. At the time of a predetermined polymerization reaction, as shown in FIG. 9, the polymerization container 62 is placed on the valley formed by the peripheral surfaces of the adjacent rotating members 73 and rotates according to the rotation of the rotating member 73. In FIG. 10, the rotating shaft of the rotating member 73 is indicated by reference numeral 73a. Thus, in this embodiment illustrated here, rotation of the superposition | polymerization container 62 is made into the surface drive type, However, About this rotation system, it is not limited.

  As a method for preventing the polymerization vessel 62 from floating from the rotating member 73, a rotation means similar to the rotation member 73 is further provided so as to be in contact with the upper portion of the set polymerization vessel 62 and rotated in the same manner. The polymerization container 62 may be prevented from floating. In addition to this method, for example, there is a method of applying a predetermined load to the polymerization vessel 62 by providing a pressing means or the like on the polymerization vessel 62, but the present invention does not depend on the floating prevention method.

  Then, the production | generation method of an inner clad part is demonstrated. Various raw materials for the inner clad part including the monomer for the inner clad part will be described in detail later. The inner clad part exists between the outer clad and the core part, and is also involved in the polymerization reaction of the core monomer. However, the inner clad portion may be unnecessary depending on the core generation conditions, or may be lost as an integral part of the core in the core generation process as described above. Raw materials such as monomers to be used are used after sufficiently removing a polymerization inhibitor, moisture, impurities and the like by filtration or distillation. Furthermore, after mixing a monomer and a polymerization initiator, it is preferable to remove dissolved gas and volatile components from the mixture by ultrasonic treatment. After the injection, the inlet of the pipe 23 is closed with a plug made of a predetermined material. Before and after this injection step, the outer clad portion 16 and the injected material may be subjected to a reduced pressure treatment by a known decompression device as necessary.

  Thereafter, when the polymerization vessel 62 loaded with the pipe 23 is rotated with its longitudinal direction set in a substantially horizontal state, that is, when polymerization is caused to proceed while rotating horizontally, an inner clad portion is generated and the pipe 23 becomes an outer clad portion. As described above, the inner clad portion is generated by rotational polymerization in which polymerization is performed with the circular axis of the pipe 23 as the rotation center. In addition, you may pre-polymerize in the state which stood the pipe 23 before rotation superposition | polymerization. In this preliminary polymerization, the pipe shaft of the pipe 23 may be rotated about the rotation center by a predetermined rotation mechanism as required. In such rotational polymerization, when the pipe 23 is rotated while the longitudinal direction of the pipe 23 is kept almost horizontal, an inner clad portion is easily formed on the entire inner surface of the pipe 23. In the polymerization of the inner clad part, it is most preferable to make the longitudinal direction of the pipe 23 horizontal in order to form the inner clad part on the entire inner surface of the pipe 23, but it is preferable if it is substantially horizontal. It is particularly preferable that the allowable angle of the rotation axis is approximately within 5 ° with respect to the horizontal.

  The polymerization temperature of the inner clad monomer is preferably 60 to 90 ° C., and the rotation speed in horizontal rotation is preferably 500 to 3000 rpm. When the inner diameter of the outer cladding portion is D2 (mm), the thickness of the inner cladding portion is preferably 0.05 × D2 (mm) or more and 0.3 × D2 (mm) or less.

  The raw material of the inner clad part will be described. In the present invention, an inner clad monomer and a predetermined polymerization initiator (reaction initiator) are used as raw materials for the inner clad. Moreover, you may add a chain transfer agent (molecular weight regulator) in the raw material of an inner clad part.

  As an inner clad monomer, methyl methacrylate (MMA) or deuterated methyl methacrylate (MMA-d8) is used in the embodiment exemplified here. These are compounds that can react by radical polymerization and anionic polymerization. As the monomer for the inner clad part, a radical polymerizable compound and an anion polymerizable compound can be preferably used, and are not limited to MMA or MMA-d8. However, other polymerizable compounds can be used as the inner clad monomer, and preferable examples are described later in detail together with the core monomer.

  In the present invention, the method for producing the clad is not limited to the above embodiment, and the clad can be produced by using a known method as appropriate depending on the material to be used. As an example, the outer clad part and the inner clad part can be formed into a tubular shape by simultaneous integral extrusion. Another method is to use a tubular member made of glass or the like having a predetermined inner diameter instead of the pipe for the outer clad portion, and inject and polymerize the monomer for the inner clad portion into the hollow portion. Remove the tubular member and attach a separately prepared tubular outer cladding pipe to the outer peripheral surface of the resulting tubular inner cladding member, or generate an outer cladding part on the outer peripheral surface of the inner cladding member by a predetermined method You may let them.

  The clad member is taken out from the rotary polymerization apparatus 71 as described above. After taking out, it is preferable to heat-process for a predetermined time with heating means, such as a thermostat set to predetermined temperature, as needed.

  Next, the core monomer is injected into the hollow portion of the inner clad portion. When MMA is used as the core monomer, it is preferable that a polymerization initiator, a chain transfer agent, and an appropriate refractive index adjusting agent (dopant) are injected together with the core monomer. For example, these are mixed in advance with the core monomer before injection, and the mixed solution is filtered by a predetermined filtering means and then injected into the inner clad portion. Thus, it is preferable to provide a filtration step before injection and use the filtrate for injection. The filter medium in this filtration step is preferably, for example, one having a collected particle diameter of about 0.2 μm. Each addition amount of a polymerization initiator, a chain transfer agent, and a dopant will be described later. In addition, the refractive index in the radial direction of the cross section of the core 12 (see FIG. 1) can also be changed by using, for example, two or more kinds of core monomers without using a dopant. In this embodiment, a low molecular weight compound having a high refractive index and a large molecular volume and not involved in polymerization is used as a dopant, and the refractive index in the radial direction of the core is changed by adding this dopant. In addition, before and after the core monomer injection, the clad member and the injected material may be subjected to a reduced pressure treatment by a known decompression device, if necessary.

  In the present embodiment, the polymerization of the core monomer is performed by a rotational gel polymerization method. In this method, the tubular clad 13 is injected with a mixture of a core monomer and a polymerization initiator, a chain transfer agent, a dopant, and the like, and then the end is closed with a stopper 61 and put into the polymerization vessel 62 again. Then, similarly to the method of forming the inner clad portion, a polymerization reaction in horizontal rotation occurs and proceeds. When the core monomer starts to polymerize, the inner wall of the inner clad portion swells with the core monomer, and a swelling layer is formed at the initial stage of polymerization. This swelling layer is in a gel state, and therefore the polymerization rate is accelerated (referred to as gel effect). That is, the reaction here is bulk polymerization. Then, the polymerization starts from the inner surface of the inner cladding portion and proceeds toward the center of the cross section. At this time, since the compound having a smaller molecular volume enters the inside of the swelling layer preferentially, as the polymerization proceeds, a dopant having a larger molecular volume is pushed out from the swelling layer toward the center as compared with other coexisting compounds. It is. As a result, the concentration of the dopant having a high refractive index is increased in the central portion of the formed core portion with a circular cross section, and the refractive index gradually increases toward the center in the radial direction of the circular cross section, as shown in FIG. An elevated preform can be obtained.

  In the present embodiment, the inner clad part and the core are both made of PMMA, and the preform is created while forming the swelling layer as described above. It does not have a critical boundary. In other words, the clarity of the boundary between the inner clad part and the core in the obtained preform was different depending on the production conditions such as the mutual affinity of the material of the inner clad part and the core or the presence or absence of the swollen layer formation. It will be a thing. And it is preferable that the outer diameter of a core is 0.73 * D2 (mm) or more and 0.97 * D2 (mm) or less.

  The polymerization of the core monomer is preferably performed under heating. The temperature is determined according to the type of the core monomer and the type of polymerization initiator used, and is mainly determined in consideration of the polymerization rate and the modification temperature. For example, when a typical methacrylate low molecular weight compound is used as the main component of the core monomer, the temperature is preferably 50 ° C to 150 ° C, more preferably 80 ° C to 140 ° C. The temperature is particularly preferably 60 to 120 ° C. By setting it as such a temperature range, there exists an effect that a core with little optical loss can be formed. The polymerization time is preferably 4 hours to 72 hours, but this is also determined according to the type of the core monomer. And it is preferable that the rotational speed in horizontal rotation is 500-3000 rpm. By setting it as such a rotational speed, there exists an effect that sufficient centrifugal force which can form a core of a uniform diameter is obtained.

  Further, after carrying out the heat polymerization under pressure as described above, the polymerization is further carried out by performing a heat treatment under a predetermined condition, and this polymerization is completed. In the present specification, each polymerizable compound that forms the inner clad part and the core part is referred to as an inner clad monomer and a core monomer. It may be a body or a trimer. The present invention does not depend on the preform manufacturing method.

  The preform is heated under reduced pressure so that no bubbles are generated when the preform is formed. Thereby, since the substance vaporized by the heating at the time of extending | stretching is removed, bubble generation | occurrence | production in the core at an extending process is suppressed. This reduced pressure heat treatment has a greater effect in a preform in which an inner clad, a core, or the like is formed by polymerization than in a preform manufactured by coextrusion molding. In co-extrusion molding, the polymer is once heated and melted to make a predetermined shape. However, in the production of a preform by polymerization, the content of unpolymerized substances and oligomers is higher than that of the preform by co-extrusion. It is thought from. The vacuum drying can be performed with a known vacuum heating apparatus such as a vacuum constant temperature apparatus. However, it is more preferable that the substance to be vaporized can be discharged out of the vacuum drying apparatus.

  The temperature during reduced pressure heating is preferably 20 ° C. or higher and 120 ° C. or lower, more preferably 40 ° C. or higher and 110 ° C. or lower, and further preferably 50 ° C. or higher and 100 ° C. or lower. However, this temperature is preferably changed as appropriate depending on the material constituting the preform, and is not limited to the above temperature range. As a method for setting the temperature, it is preferable to consider the glass transition point of the material, the thermal deformation temperature, the detected melting point, and the like. If the temperature is too high, problems such as deformation of the preform and disturbance of the refractive index distribution due to movement of the dopant in the preform may occur.

  The pressure during reduced pressure heating is preferably as low as possible. For example, in a preform mainly containing PMMA and PVDF, it is preferably 50 Pa or less, more preferably 10 Pa or less, and even more preferably 5 Pa or less. By reducing the pressure, the vaporized substance can be effectively removed even if the temperature is set lower than when the pressure is not reduced. Even when the pressure is higher than 50 Pa, there is not much effect of removing the vaporized substance and lowering the set temperature.

  The time of the reduced pressure heat treatment is preferably 5 hours or more and 48 hours or less, more preferably 8 hours or more and 40 hours or less, and further preferably 10 hours or more and 30 hours or less. In addition, the removal effect of the vaporized substance is hardly improved after about 48 hours.

  By the way, the produced preform may be stored in a predetermined storage place until it is subjected to melt drawing. The storage environment of the preform is preferably controlled so that the moisture content of the core during stretching is 0.001 wt% or more and 1.0 wt% or less. When the clad has a multilayer structure and the inner clad portion contains a hygroscopic material, the moisture content of the inner clad is also considered in consideration of the movement of moisture in the preform and fluctuations in the outer diameter due to foaming. It is more preferable to be in the above range. When the preform immediately after being produced has the moisture content described above, the preform may be stored in an environment where the moisture content can be maintained. However, when it is difficult to secure a storage place that can maintain the moisture content, it is preferable to perform the reduced-pressure heating treatment within the above moisture content range immediately before being subjected to stretching. By setting the moisture content of the core at the time of stretching within the above range, foaming is suppressed. When the water content during stretching is greater than 1.5 wt%, foaming frequently occurs and stretching cannot be performed, or bubbles are often generated in the obtained plastic optical fiber. The moisture content is preferably as low as possible, but is preferably 0.001 wt% in consideration of both treatment time and moisture content reduction.

  The moisture content is preferably controlled by a drying means that can control at least one of pressure, temperature, and relative humidity. Examples of the drying means include a desiccator having a vacuum processing function. However, the drying means can suppress an increase in the moisture content in the preform core as much as possible, or the moisture content is within the above range. Others may be used as long as they can be dried. Examples of other drying means include a temperature controller having a decompression processing function.

  In the case where a desiccator is used as the drying means, a method of standing and storing the preform in an internal atmosphere of 23 ° C. and 20% RH or less is exemplified. Note that it is particularly preferable to maintain the moisture content of the entire preform as well as the core and inner cladding at a low moisture content.

  The moisture content in the core when stretched is more preferably 0.001 wt% or more and 0.5 wt% or less, still more preferably 0.001 wt% or more and 0.2 wt% or less, and particularly preferably 0.001 wt% or less. It is 005 wt% or more and 0.1 wt% or less. The moisture content in the present invention is a value determined by the Karl Fischer method, and this Karl Fischer method is particularly preferable among the moisture content measurement methods for materials in consideration of both simplicity of measurement and accuracy of measurement values. This is the preferred method. However, the method for measuring the moisture content in the present invention is not limited to this, and even when measured by other methods, the correlation between the measured value and the measurement by the Karl Fischer method is determined in advance. As a result, it is effective even when the corresponding value in the Karl Fischer method falls within the above range.

The Karl Fischer method is a kind of destructive inspection method. As shown in the following formula (I), a Karl Fischer reagent (for example, iodine, sulfur dioxide, base, alcohol, etc.) that reacts selectively and quantitatively with water. This is a method of measuring the amount of water using a solvent). However, the method for determining the water content in the preform is not particularly limited as long as it is a method capable of determining the water content contained in the polymer.
(I): I ₂ + SO ₂ + 3Base + ROH + H ₂ O =>
2Base · HI + Base · HSO ₄ R

  The Karl Fischer method includes a coulometric titration method and a volumetric titration method, and many moisture meters using these titration methods are commercially available. In the present embodiment, a device in which a moisture vaporizer (ADP-351, Kyoto Electronics Co., Ltd.) is connected to a Karl Fischer moisture meter (model; MKC-210, Kyoto Electronics Industry Co., Ltd.) using a coulometric titration method. Thus, the amount of water in the preform was determined using Karl Fischer reagent as Coulomat A and Coulomat C, but the titration method and apparatus are not particularly limited. The principle of a simple titration method for the coulometric titration method and the volumetric titration method will be described below.

[Karl Fischer method (coulometric titration)]
(1) A predetermined amount x (g) is taken using a sample obtained by pulverizing the preform in a sealed state, and the inside of the container containing the collected sample is purged with nitrogen (N ₂ ) to be replaced with N ₂ To do.
(2) The sample of (1) is added to an electrolytic solution mainly composed of a solvent such as iodide ion, sulfur dioxide, base and alcohol. At this time, iodine is generated by electrolytic oxidation such as the following formula (II) occurring in the liquid.
(II): 2I + 2e ⁻ → I ₂
At this time, since the generated iodine is generated in proportion to the amount of electricity based on Faraday's law, the amount of water in the sample is obtained from the amount of coulomb required for electrooxidation. However, 1 mg of water = 10.71 coulombs.

[Karl Fischer method (volumetric titration method)]
(1) was taken a predetermined amount x (g) a material obtained by grinding in sealing the preform as a sample, collected and placed and the inside of the container samples by N ₂ purge, substituted with N _2.
(2) In a predetermined container A (for example, a titration flask), an amount of dehydrated solvent corresponding to the sample amount x (g) in the above (1) is put, and the Karl Fischer reagent is further stored in the container A. Is added to make the dehydrated solvent anhydrous, and then the sample of (1) is added.
(3) Titration is performed using the Karl Fischer reagent whose titer (mgH ₂ O / ml) has been determined in advance by a predetermined means, and the amount of water in the sample is determined from the titration amount (ml).

  By the way, although acrylic polymer is excellent in processability and transmission characteristics as compared with other well-known core materials (for example, polystyrene, polycarbonate, poly-4-methylpentene-1, etc.), it is saturated at 25 ° C. Moisture content is relatively high. For example, the saturated water content of the former is about 0.01% to 0.4%, and the saturated water content of the latter is about 0.01% to 0.4%. The present invention is particularly effective when the material of the preform core and the inner clad portion is the above material.

  Next, the preform is drawn into a plastic optical fiber. FIG. 11 is a schematic view of a drawing facility for drawing a preform into a plastic optical fiber. However, the present invention does not depend on a stretching method and stretching equipment, and a known stretching method and stretching equipment can be used.

  The stretching equipment 120 includes a heating device 121 for heating the preform 11, a wire tension measuring device 122 for measuring the tension when stretching the heated preform, and the wire tension measuring device 122. The dancer roller 123 for adjusting the tension for controlling the tension in the stretching based on the detection result of the above, the drawing roller pair 126 for controlling the stretching speed, and the outer diameter of the plastic optical fiber 21 produced by the stretching. An outer diameter measuring device 127 for measuring, a winding device 130 for winding the plastic optical fiber 21, and a tension applied to the plastic optical fiber 21 in the winding (hereinafter referred to as winding tension). A winding tension measuring device 131 for measuring.

  Further, on the upstream side of the heating device 121, a holding member 135 for displacing the preform 11 while holding the preform 11, holding and releasing the preform 11 by the holding member 135, and displacement of the holding member 135 are provided. A shift device 137 for controlling is provided.

  The heating device 121 is provided with a cylindrical heating furnace 140, and the heating furnace 140 can change the temperature along the conveying direction of the preform 11. The drawing roller pair 126 is configured such that the driving roller 141 and the pressure roller 142 are opposed to each other so as to sandwich the plastic optical fiber 21 therebetween. A motor 143 is connected to the drive roller 141, and the rotation speed of the drive roller 141 is adjusted by adjusting the rotation speed of the motor 143. Furthermore, the dancer roller 123 is provided with a shift mechanism (not shown) for displacement, and tension in stretching is controlled by this displacement. Further, the tension due to stretching can be adjusted by the speed at which the preform 11 descends, the rotational speed of the drive roller 141, and the heating temperature in the heating furnace 140.

  The preform 11 is stretched with the upper portion held by the holding member 135. The holding member 135 that holds the upper portion of the preform 11 is displaced downward according to the stretching speed. The fact that most of the preform 11 has been stretched and reached a predetermined position is detected by the shift mechanism 137, and the shift mechanism 137 releases the holding by the holding member 135.

  The preform 11 is stretched while being guided by the inside of the heating furnace 140 while being held by the holding member 135, and continues to descend at a speed corresponding to the stretching speed. The first shift mechanism 137 is provided with an alignment means (not shown), and the center position of the circular cross section of the preform 11 can be precisely adjusted by the alignment means during stretching. it can. Thereby, the linearity and the roundness of the cross section of the plastic optical fiber 21 can be maintained well.

  In order to prevent the preform 11 from being deteriorated by heating and melting, it is preferable to attach a supply device (not shown) for supplying an inert gas in order to make the inside of the heating device 121 an inert atmosphere. The inert gas is not particularly limited, and examples thereof include nitrogen gas, helium gas, neon gas, and argon gas. Nitrogen gas is preferably used from the viewpoint of cost, and helium gas is preferably used from the viewpoint of heat conduction efficiency. A mixed gas in which a plurality of types of gases such as a mixed gas of helium gas and argon gas are mixed can also be used.

  The preform 11 is melted little by little from the tip in the heating furnace 140 and drawn to become the plastic optical fiber 21. Although the temperature at the time of a heating can be suitably determined according to the material etc. of the preform 11, generally 180 to 250 degreeC is preferable. The stretching conditions such as the stretching temperature can be appropriately determined in consideration of the diameter of the preform 11, the desired diameter of the plastic optical fiber 21, the material of the preform 11, and the like. In particular, in the GI type plastic optical fiber, since the refractive index changes from the center of the circular cross section toward the circumference, it is necessary to perform heating and stretching uniformly so as not to destroy this refractive index change. Therefore, it is preferable to use a cylindrical heating furnace or the like that can uniformly heat the preform 11 concentrically when the preform 11 is viewed in cross section.

  Further, in the heating furnace 140, it is preferable that a temperature distribution is provided along the longitudinal direction of the preform 11. That is, this means that the time during which the preform 11 is melted can be shortened as much as possible, and the melting range in the longitudinal direction can be shortened as much as possible. When the melting range in the longitudinal direction is long, the time during which the preform 11 is melted becomes long, fluidization of the constituent molecules of the preform 11 occurs, and the refractive index change in the radial direction of the circular section may be disturbed. Therefore, by shortening the melting range in the longitudinal direction, the shape of the refractive index distribution curve in the radial direction as shown in FIG. 2 is hardly distorted and the yield can be increased. Therefore, in the heating furnace, it is preferable that the temperature condition can be set so that the upstream side of the melting region becomes the preheating region and the downstream side becomes the cooling region so that the length in the longitudinal direction of the preform as the melting region becomes as short as possible. The cooling in this cooling region may be slow cooling by natural cooling. Furthermore, as a heat source used for the melting region, for example, a laser or the like that can supply high output energy to a narrow range can be used.

  The plastic optical fiber 21 is measured for a tension (hereinafter referred to as a “wire tensile force”) when the plastic optical fiber 21 is stretched by the wire tensile force measuring device 122. Then, the outer diameter is measured by the outer diameter measuring device 127. The drawing speed is set to a desired value, for example, 2 m / min to 50 m / min by the drawing roller pair 126, and this control is performed by adjusting the rotation speed of the driving roller 141 by the motor 143. Then, the lowering speed of the holding member 135, the heating temperature in the heating furnace 140, the drawing speed by the drawing roller pair 126, and the like are controlled so that the outer diameter of the plastic optical fiber 21 becomes a predetermined value.

  As described in JP-A-7-234322, the drawing tension is preferably 0.098 N or more in order to orient the molten polymer. Further, as described in JP-A-7-234324, it is preferably 0.98 N or less in order not to leave molecular orientation distortion after melt drawing. However, since the optimum value of the drawing tension varies depending on the diameter of the target plastic optical fiber and the type of the material, it is necessary to adjust it appropriately. Further, in the present invention, as described in JP-A-8-106015, preheating can be performed before melting.

  The plastic optical fiber 21 is wound around a dancer roller 123 that adjusts the tension and conveyed. A drive device (not shown) is attached to the dancer roller 123, and the position of the dancer roller 123 is changed by this drive device. The plastic optical fiber 21 is conveyed to the winding tension measuring device 131 by the roller 132, and the tension (winding tension) is measured. The plastic optical fiber 21 is wound in a roll shape on a winding device 130 that is rotated by a rotation control means (not shown). The winding tension is adjusted based on the measured value of the winding tension measured by the winding tension measuring device 131. The winding tension is also controlled by the rotational speed of the winding device 130.

  The plastic optical fiber obtained by the present invention can improve the bending and lateral pressure characteristics as a plastic optical fiber by defining the breaking elongation and hardness as described in JP-A-7-244220. it can. Further, the transmission performance can be further improved by providing a low refractive index layer on the outer periphery of the clad as described in JP-A-8-54521 for the plastic optical fiber obtained by the present invention and functioning it as a reflective layer. it can. By appropriately controlling the various stretching conditions as described above, the orientation of the polymer constituting the plastic optical fiber can be controlled, and the mechanical properties such as the bending performance of the plastic optical fiber and the heat shrinkage can be controlled. .

  In the present invention, the clad and core materials constituting the preform are not particularly limited as long as the optical transmission function is not impaired. Particularly preferably, the organic material has high light transmittance. However, when the incident light is totally reflected at the interface between the outer cladding part and the core, the material of the outer cladding part is a polymer having a refractive index lower than that of the inner cladding part. Further, the material of the inner clad part and the core is preferably an amorphous polymer so as not to cause light scattering. More preferably, the heat and moisture resistance is also excellent. Furthermore, since it is preferable to prevent moisture from entering the core as much as possible, the material of the clad, particularly the outer clad portion, may have a low water absorption rate. For example, the outer clad part is preferably composed mainly of a polymer having a saturated water absorption rate of less than 1.8%. More preferably, the outer clad is formed of a polymer having a saturated water absorption of less than 1.5%, more preferably a saturated water absorption of less than 1.0%. Here, the saturated water absorption is a value based on ASTM D570, and specifically, a value obtained by measuring the water absorption when a sample is immersed in water at 23 ° C. for one week.

  Examples of materials for the core and inner clad part include (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)), styrenic compounds ( c), vinyl esters (d), bisphenol A, which is a raw material for polycarbonates, and the like can be polymerized using the polymerizable compound. As the clad forming polymer, polyvinylidene fluoride (PVDF) is also preferable. Examples include homopolymers obtained by polymerizing each of these as raw materials, copolymers obtained by combining two or more of these, and mixtures of various combinations of the above homopolymers and copolymers. it can. In the case of using a mixture, the boiling point Tb is defined as the lowest temperature among the boiling points of a plurality of raw material compounds constituting the mixture, or the temperature after the boiling point is lowered when the boiling point is lowered by forming an azeotropic mixture. . In the case of a copolymer and a blend polymer obtained using a mixture as a raw material, the glass transition point of each copolymer or blend polymer is defined as Tg. And among these, what contains (meth) acrylic acid esters or a fluorine-containing polymer as a component is more preferable when comprising an optical transmission body. Next, the above example will be described in more detail.

  Examples of (a) fluorine-free methacrylic acid ester and fluorine-free acrylic acid ester include methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, and methacrylic acid. Examples include cyclohexyl, diphenylmethyl methacrylate, tricyclo [5 · 2 · 1 · 02,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid- Examples thereof include tert-butyl and phenyl acrylate.

  In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, Examples include 3,3,4,4-hexafluorobutyl methacrylate.

  Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, the present invention is not limited to these, and the refractive index of a polymer composed of a polymerizable compound alone or a copolymer may have a predetermined refractive index distribution in the molded body when molded into an optical transmission body. In addition, it is preferable to determine the type and composition ratio.

  Moreover, as a preferable polymer which forms an outer clad part, the following can be illustrated other than said various compounds of a core and an inner clad part. For example, a copolymer of methyl methacrylate (MMA) and a fluorinated (meth) acrylate such as trifluoroethyl methacrylate (FMA) or hexafluoroisopropyl methacrylate can be given. In addition, a copolymer of MMA and an alicyclic (meth) acrylate such as (meth) acrylate having a branch such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, tricyclodecanyl methacrylate, etc. is there. Furthermore, polycarbonate (PC), norbornene-based resin (for example, ZEONEX (registered trademark: manufactured by Nippon Zeon Co., Ltd.)), functional norbornene-based resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin (for example, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.) can also be used. In addition, a fluororesin copolymer (for example, PVDF copolymer), tetrafluoroethylene perfluoro (alkyl vinyl ether (PFA) random copolymer, chlorotrifluoroethylene (CTFE) copolymer, or the like may be used. it can.

  When the polymer constituting the preform contains a hydrogen atom (H), it is preferable that the hydrogen atom is replaced with a deuterium atom (D). Transmission loss at wavelengths in the infrared region can be reduced.

  Furthermore, for use in near-infrared light, absorption loss due to C—H bonds constituting the polymer occurs, so that it is described in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708. In addition, by using a polymer in which the hydrogen atom of C—H bond is substituted with deuterium atom or fluorine, the wavelength region causing this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. Can do. Examples of such polymers include deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP 2-FA), and the like. it can. In addition, in order not to impair the transparency after polymerization of the compound as a raw material, it is desirable that impurities and foreign substances serving as scattering sources are sufficiently removed before polymerization.

  In addition, the polymer forming the preform preferably has a weight average molecular weight of 10,000 to 1,000,000, more preferably 30,000 to 500,000 from the viewpoint that the preform can be suitably stretched. Furthermore, suitability for stretching is also related to molecular weight distribution (MWD: weight average molecular weight / number average molecular weight). If the MWD is too large, stretchability may be deteriorated when extremely high molecular weight components are mixed, and stretching may become impossible. Therefore, a preferable MWD range is 4 or less, and a more preferable range is 3 or less.

  In the case of polymerizing the polymer, a polymerization initiator may be used. As the polymerization initiator, for example, there are various types that generate radicals. For example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), tert-butylperoxyisopropyl carbonate (PBI) ) And peroxide compounds such as n-butyl-4,4-bis (tert-butylperoxy) valerate (PHV). 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylbutane), 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2 '-Azobis (2-methylhexane), 2,2'-azobis (2,4-dimethylpentane), 2,2'-azobis (2,3,3-trimethylbutane), 2,2'-azobis (2 , 4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3'-azobis 3-ethylpentane), dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-tert-butyl-2,2 ′ -Azo compounds such as azobis (2-methylpropionate). In addition, a polymerization initiator is not limited to these, Moreover, you may use 2 or more types together.

  In order to keep various physical property values such as mechanical properties and thermophysical properties uniform when used as a polymer, it is preferable to adjust the degree of polymerization. A chain transfer agent can be used to adjust the degree of polymerization. About a chain transfer agent, according to the kind of polymerizable monomer used together, a kind and addition amount can be selected suitably. The chain transfer constant of the chain transfer agent for each monomer can be referred to, for example, Polymer Handbook 3rd edition (edited by J. BRANDRUP and EH IMMERGUT, published by JOHN WILEY & SON). The chain transfer constant can also be obtained by experiment with reference to Takayuki Otsu and Masaaki Kinoshita "Experimental Method for Polymer Synthesis", Kagaku Dojin, published in 1972.

  Examples of the chain transfer agent include alkyl mercaptans (for example, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan, etc.), thiophenols (thiophenol, m-bromothio). Phenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used. In particular, it is preferable to use an alkyl mercaptan such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan. A chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom can also be used. Of course, the chain transfer agent is not limited to these, and two or more of these chain transfer agents may be used in combination.

The dopant is a compound having a refractive index different from that of the polymerizable compound as described above. The refractive index difference is preferably 0.005 or more. The dopant has the property that the polymer containing it has a higher refractive index than the additive-free polymer. These have a difference in solubility parameter of 7 (cal / cm ³ ) in comparison with a polymer produced by monomer synthesis as described in Japanese Patent No. 3332922 and JP-A-5-173026. ^{In addition to being} within ^1/2 , the difference in refractive index is 0.001 or more, and the polymer containing this has the property of changing the refractive index as compared with the additive-free polymer. Any of those which can coexist and are stable under the polymerization conditions (polymerization conditions such as heating and pressurization) of the polymerizable monomer which is the above-mentioned raw material can be used.

  The dopant may be a polymerizable compound. When a dopant of a polymerizable compound is used, it is preferable to use a copolymer that has a property of increasing the refractive index compared to a polymer that does not include the copolymer as a copolymer component. It has the above properties, can stably coexist with the polymer, and is stable under various polymerization conditions (polymerization conditions such as heating and pressurization) of the polymerizable compound that is the core monomer or inner clad raw material described above. Some can be used as a dopant. In the present embodiment, the core monomer contains a dopant, and in the step of forming the core, the progress of polymerization is controlled by the interfacial gel polymerization method, the concentration of the refractive index adjusting agent is inclined, and the refractive index of the core is increased. The method of forming a refractive index distribution structure based on the concentration distribution of the adjusting agent is exemplified, but other than that, a method of diffusing the refractive index adjusting agent after forming a preform is also known (hereinafter referred to as refractive index distribution). The core portion having a "refractive index distribution type core portion"). By forming the gradient index core portion, the obtained optical member becomes a gradient index plastic optical member having a wide transmission band.

  Examples of the dopant include benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), benzyl-n-butyl phthalate (BBP), diphenyl phthalate (DPP), and diphenyl (DP). , Diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO) and the like, among which BEN, DPS, TPP and DPSO are preferable. The dopant may be a polymerizable compound such as tribromophenyl methacrylate. In that case, when forming the matrix, the polymerizable monomer and the polymerizable dopant are copolymerized, so that various properties (especially optical properties). ) Is more difficult to control, but may be advantageous in terms of heat resistance. By adjusting the concentration and distribution of the dopant in the core, the refractive index of the plastic optical fiber can be changed to a desired value.

  About each addition amount of the polymerization initiator mentioned above, a chain transfer agent, and a refractive index regulator, a preferable range can be suitably determined according to the kind etc. of the monomer for cores to be used. In this embodiment, the polymerization initiator is added so that it may become 0.005-0.050 mass% with respect to the monomer for cores, and this addition rate is 0.010-0.020 mass%. More preferably. The chain transfer agent is added to the core monomer so as to be 0.10 to 0.40% by mass, and the addition rate may be 0.15 to 0.30% by mass. More preferred. And like this embodiment, it is preferable that the addition rate in the case of adding a dopant shall be 1 mass% or more and 50 mass% or less with respect to the monomer for cores.

  In addition, other additives can be added to the core, the clad, or a part of them in a range that does not deteriorate the optical transmission performance. For example, a stabilizer can be added to at least a part of the core for the purpose of improving weather resistance, durability and the like. Further, for the purpose of improving optical transmission performance, a stimulated emission functional compound for optical signal amplification can be added. By adding the compound, the attenuated signal light can be amplified by the pumping light, and the transmission distance is improved. For example, it can be used as a fiber amplifier in a part of the optical transmission link. These additives can also be contained in the core, the clad, or a part of them by adding to the various polymerizable compounds as the raw material and then polymerizing.

  As described in Japanese Patent No. 3332922, a method for manufacturing a preform for a GI type plastic optical fiber is to create a hollow resin tube, and inject a resin composition that forms a core into the tube. An example is a method of forming a core by polymerizing a polymer by an interfacial gel polymerization method, which is a kind of bulk polymerization method. The polymerization conditions in this case, that is, the polymerization temperature and the ordering time vary depending on the monomers and polymerization initiator used, but there are generally preferred conditions from the viewpoint of productivity and ease of handling. With respect to the conditions, for example, the polymerization temperature is preferably 60 ° C. or higher and preferably not higher than the glass transition point of the polymer to be produced, and preferably 60 ° C. or higher and 150 ° C. or lower. For example, the polymerization time is preferably 0.5 to 72 hours, more preferably 1.5 to 48 hours. The polymerization reaction is preferably performed in an inert gas atmosphere, and pressurization or decompression may be performed as necessary. In addition, by applying the polymerization conditions described in International Publication No. 03/19252 pamphlet, a core portion free from density fluctuation can be formed. In addition, a method for forming a core part is also known in which polymerizable compositions having different refractive indexes after polymerization are sequentially added. In addition, the manufacturing method of the preform of the GI type optical fiber used in the present invention is not limited to the interfacial gel polymerization method as described above. As described above, as the resin composition, a resin composition having a single refractive index to which a refractive index adjusting agent is added, a resin having a different refractive index, a copolymer, or the like is used. In addition to the GI type, plastic optical fibers having various refractive index profiles such as a single mode type and a step index type are known, and the present invention is a plastic optical fiber manufactured by these manufacturing methods. It can also be applied to.

  In the case of plastic optical fiber, bending, improved weather resistance, reduced performance degradation due to moisture absorption, improved tensile strength, imparted stepping resistance, imparted flame resistance, protected from chemical damage, prevented noise from external rays, colored For the purpose of improving the commercial value due to the above, or the like, the surface is usually coated with one or more protective layers.

  Specific examples of the protective layer forming material include the following materials. Since these have high elasticity, they are also effective in terms of imparting mechanical properties such as bending. First, rubber which is one form of polymer can be used. Specifically, isoprene rubber (for example, natural rubber, isoprene rubber, etc.), butadiene rubber (for example, styrene-butadiene copolymer rubber, butadiene rubber, etc.), diene special rubber (for example, nitrile rubber, chloroprene rubber, etc.) ), Olefin rubber (for example, ethylene-propylene rubber, acrylic rubber, butyl rubber, halogenated butyl rubber, etc.), ether rubber, polysulfide rubber, urethane rubber and the like.

  Further, as the protective layer forming material, it is possible to use a liquid rubber that exhibits fluidity at room temperature and is cured by heating to lose its fluidity. Specifically, polydiene-based (for example, basic structure is polyisoprene, polybutadiene, butadiene-acrylonitrile copolymer, polychloroprene, etc.), polyolefin-based (for example, basic structure is polyolefin, polyisobutylene, etc.), polyether-based (for example, , Basic structure is poly (oxypropylene), etc., polysulfide type (eg, basic structure is poly (oxyalkylene disulfide), etc.), polysiloxane type (eg, basic structure is poly (dimethylsiloxane), etc.) Can do.

  A thermoplastic elastomer (TPE) can also be used as the protective layer forming material. Thermoplastic elastomers are a group of substances that exhibit rubber elasticity at room temperature and are plasticized at high temperatures and are easy to mold. Specific examples include styrene TPE, olefin TPE, vinyl chloride TPE, urethane TPE, ester TPE, amide TPE, and the like. The listed polymers are not particularly limited to the above materials as long as they can be molded at a glass transition temperature Tg or lower of the strand polymer, and copolymers or mixed polymers other than the above materials or other than the above are used. You can also

  Moreover, what hardens the liquid which mixed the polymer precursor, the reactive agent, etc. can be used as a protective layer forming material. Examples thereof include a one-component thermosetting urethane composition produced from an NCO block prepolymer and a fine powder coating amine described in JP-A-10-158353. Further, a one-component thermosetting urethane composition comprising an NCO group-containing urethane prepolymer described in International Publication No. 95/26374 pamphlet and a solid amine of 20 μm or less can also be used. In addition, additives such as flame retardants, antioxidants, radical scavengers, lubricants, and various fillers composed of inorganic compounds and / or organic compounds can be added for the purpose of improving performance.

  In the present invention, a predetermined optical transmission body may be used in which the protective layer is a primary coating layer and a secondary (or multilayer) coating layer is further provided on the outer periphery as necessary. When the primary coating has a sufficient thickness, thermal damage is reduced due to the presence of the primary coating, so the limit of the curing temperature of the material of the secondary coating layer is the case where the primary coating layer is coated. Compared to, it can be loosened. As described above, a flame retardant, an ultraviolet absorber, an antioxidant, a radical scavenger, a light raising agent, a lubricant and the like may be introduced into the secondary coating layer. Some flame retardants include halogen-containing resins such as bromine, additives and phosphorus, but metal hydroxides can be preferably used as flame retardants from the viewpoint of safety such as reduction of toxic gases. . Since the metal hydroxide has water as crystal water inside, and the adhering water in the manufacturing process cannot be completely removed, the flame retardant coating by the metal hydroxide is the outer layer of the primary coating layer. It is desirable to provide a moisture-resistant coating on the outer layer and further provide a coating layer on the outer layer.

  Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to the above-mentioned flame retardancy, it is possible to have a barrier layer for suppressing moisture absorption or a moisture absorbing material for removing moisture, such as a moisture absorbing tape or moisture absorbing gel, in the coating layer or between the coating layers, and flexible. A cushioning material such as a flexible material layer or a foamed layer for stress relaxation at times, a reinforcing layer for improving rigidity, and the like can be selected and provided depending on the application. In addition to the resin, if the thermoplastic resin contains a fiber having a high elastic modulus (so-called tensile fiber) and / or a highly rigid metal wire, the mechanical strength of the resulting cable can be reinforced. It is preferable because it is possible. Examples of the tensile strength fiber include aramid fiber, polyester fiber, and polyamide fiber. Examples of the metal wire include stainless steel wire, zinc alloy wire, copper wire and the like. None of these are limited to those described above. In addition, a metal tube exterior for protection, an aerial support line, and a mechanism for improving workability during wiring can be incorporated.

  Moreover, the plastic optical fiber manufactured by the present invention is suitable for a plastic optical cable, and the shape of the cable is a collective cable in which plastic optical fibers are concentrically arranged according to the use form, or a tape shape in which these are arranged side by side. The shape can be selected according to the application, such as an assembly cable in which they are gathered together with a presser roll or a wrap sheath.

  Moreover, when using the optical device using the plastic optical fiber according to the present invention, it is preferable to securely fix the connection portion in the optical device by using a connection optical connector. As the connector, it is possible to use various commercially available connectors such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type that are generally known.

  In the plastic optical fiber according to the present invention, various light emitting elements can be used. However, the light emission angle is narrow and the integration rate is increased. Since the wavelength can be changed, a surface emitting semiconductor laser (VCSEL) is used as a light source as described in JP-A-7-307525, JP-A-10-242558, and JP-A-2003-152284. It is more preferable. In addition, in the present invention, communication can be performed by combining various light receiving elements, optical switches, optical isolators, optical integrated circuits, optical signal processing apparatuses including optical components such as optical transceiver modules, and the like. Any known technique can be applied as a technique related to them. For example, the basic and actual of plastic optical fiber (published by NTS Corporation), Nikkei Electronics 2001.1.2.3, pp. 110-127 “Printed Wiring You can refer to "This time, optical components are mounted on the board." Combined with various technologies described in the above documents, internal wiring in computers and various digital devices, internal wiring in vehicles and ships, optical terminals and digital devices, optical links between digital devices, general households and housing complexes・ Suitable for optical transmission systems suitable for short distances such as high-speed, large-capacity data communication and control applications that are not affected by electromagnetic waves, including optical LANs in factories, offices, hospitals, schools, etc. Can be used.

  Further, IEICE TRANS. ELECTRON. , VOL. E84-C, No. 3, MARCH 2001, p. 339-344 “High-Uniformity Star Coupler Using Diffused Light Transmission”, Journal of Japan Institute of Electronics Packaging, Vol. 3, No. 6,2000, pages 476 to 480, which are described in “Interconnection by Optical Sheet Bus Technology”, and the arrangement of light emitting elements on the waveguide surface described in Japanese Patent Application Laid-Open No. 2003-152284; , JP-A-2002-90571, JP-A-2001-290055, and the like; JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968 , JP 2001-318263, JP 2001-31840, etc .; optical branch couplers described in JP 2000-241655 A; optical star couplers described in JP 2000-241655, etc .; Optical signal transmission devices described in Japanese Patent Laid-Open Nos. 2002-101044 and 2001-305395 An optical data bus system; an optical signal processing apparatus described in JP-A No. 2002-23011; an optical signal cross-connect system described in JP-A No. 2001-86537; an optical transmission system described in JP-A No. 2002-26815; Multi-function systems described in JP 2001-339554 A, JP 2001-339555 A, etc .; and various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers, etc. Therefore, it is possible to construct a more advanced optical transmission method using multiplexed transmission / reception. In addition to the above light transmission applications, it can also be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  The present invention is also applicable to the case where, for example, a step index (SI) type or single mode (SM) type plastic optical fiber is manufactured as other than the GI type plastic optical fiber of the above embodiment. is there.

  The pipe 23 as an outer clad part was produced by melt extrusion molding. The pipe 23 is a PVDF pipe having an inner diameter of 18.7 mm and a length of 90 cm. The raw material for the inner clad part was injected into the hollow part of the pipe 23. The raw material for the inner clad part was 204.1 g of deuterated methyl methacrylate (MMA-d8) as a radical polymerizable compound from which water was removed to 100 ppm or less by distillation (polydeuterated methyl methacrylate (PMMA-)). d8) Tg; 80 ° C. to 115 ° C.), dimethyl 2,2′-azobis (2-methylpropionate) as a polymerization initiator (trade name; V-601, manufactured by Wako Pure Chemical Industries, Ltd.) (70 And a mixture of n-lauryl mercaptan as a chain transfer agent and the mixture was injected after adjusting to a predetermined temperature. The addition ratio of dimethyl 2,2'-azobis (2-methylpropionate) and n-lauryl mercaptan to MMA was 0.012 mol% and 0.2 mol%, respectively. The outer clad injected with the raw material for the outer core is put in the container main body 62a, and is set in the apparatus main body 72 of the rotation polymerization apparatus 71 so that the longitudinal direction is horizontal, and the atmosphere at 70 ° C. is rotated at 3000 rpm. The polymerization was carried out under heat for 22 hours. At this time, an ungrounded thermocouple was provided in the vicinity of the rotating polymerization vessel 62, specifically at a distance of 1 to 2 cm, and the temperature measured by this thermocouple was regarded as the temperature due to the polymerization reaction. And the temperature peak (henceforth an exothermic peak) in the exotherm of the polymerization reaction measured by this method was calculated | required. In Example 1, an exothermic peak of 60.8 ° C. was observed when about 15 hours passed from the start of polymerization. Thus, a layer made of PMMA-d8 was formed on the inner surface of the pipe 23, and this layer was used as the inner clad portion 13.

    The core raw material was injected into the hollow portion of the inner cladding portion 13 under normal temperature and normal pressure. The raw materials for the core are 81.7 g of MMA-d8 with moisture removed to 100 ppm or less, dimethyl 2,2′-azobis (2-methylpropionate) (V-601) as a polymerization initiator, chain A mixture of n-lauryl mercaptan as a transfer agent and diphenyl sulfide (DPS) as a dopant was used. Note that DPS is a non-polymerizable compound. Addition ratios of dimethyl-2,2′-azobis (2-methylpropionate), n-lauryl mercaptan and DPS to MMA were 0.04 mol%, 0.2 mol% and 7 wt%, respectively. Next, the clad 13 was set again in the apparatus main body 72 of the rotation polymerization apparatus 71 so that the longitudinal direction was horizontal, and was heated and polymerized in an atmosphere of 70 ° C. for 5 hours while rotating at a rotation speed of 3000 rpm. . Thereafter, the atmosphere was heated to 90 ° C. for 5 hours, and further heated at 120 ° C. for 24 hours while rotating at a rotation speed of 500 rpm, thereby forming an inner core. Furthermore, it was naturally cooled while rotating to obtain a preform 11 as a base material for GI-POF.

    The produced preform 11 was allowed to stand for one week using a desiccator as a drying means having an atmosphere of 23 ° C./5% or less inside. Thereafter, the preform 11 was stretched to obtain a plastic optical fiber 21. The moisture content of the preform 11 when stretched was 0.023 wt% according to the Karl Fischer method.

  The storage conditions for the produced preform 11 are the same as those in Example 1 except that the storage conditions are 23 ° C./25% RH and 1 week. The moisture content of the preform 11 at the time of stretching was 0.185 wt%.

  The storage conditions for the produced preform 11 are the same as those in Example 1 except that the storage conditions are 23 ° C./60% RH and 1 week. The moisture content of the preform 11 at the time of stretching was 0.482 wt%.

  The preform 11 produced under the same conditions as in Example 1 was dried under reduced pressure for 15 hours in an atmosphere of 50 ° C. and 1 kPa or less using a vacuum dryer (form; DP63, manufactured by Yamato Scientific Co., Ltd.). Further, the plastic preform 21 was produced by stretching the standing preform 11. The moisture content of the preform 11 during stretching was 0.018 wt% as a result of determination by the Karl Fischer method.

  The produced preform 11 was dried under reduced pressure for 40 hours in an atmosphere of 90 ° C. and 1 kPa or less using a vacuum dryer (form; DP63, manufactured by Yamato Scientific Co., Ltd.). The moisture content of the preform 11 at the time of stretching was 0.007 wt% as a result of obtaining by the Karl Fischer method.

  The storage conditions of the preform 11 produced under the same production conditions as in Example 1 were set to 25 ° C./55% RH in a desiccator for 1 week. Thereafter, the preform 11 was stretched to produce a plastic optical fiber 21. The moisture content of the preform 11 at the time of stretching was 0.822 wt%.

〔Evaluation methods〕
About Examples 1-6, the presence or absence of the local foaming produced when producing the plastic optical fiber 21 with a length of 1000 m and the size thereof were visually observed and evaluated. At this time, the case where local foaming could be confirmed was indicated as x, the case where local foaming could not be confirmed was indicated as ◯, and the case where slight foaming was confirmed was indicated as Δ. About the magnitude | size, the plastic optical fiber 21 after extending | stretching was observed over the full length with the magnifier 20 times in the longitudinal direction, and the number of the foaming parts which are 1 m or more in length was investigated. Further, when the plastic optical fiber 21 is produced, the fluctuation of the outer diameter of the plastic optical fiber 21 is measured with a laser dimension measuring device (model: LS-3000, manufactured by Keyence Corporation), and the value is taken as the value of the fluctuation of the wire diameter. did.

  Table 1 shows implementation conditions and evaluation results in Examples 1 to 6.

  As is apparent from Table 1, the moisture content before stretching (hereinafter referred to as moisture content) of the preform 11 stored in a desiccator for a predetermined period or dried under reduced pressure with a vacuum dryer, and the presence and size of local foaming during stretching. In comparison, in Example 1 in which the moisture content was 0.023 wt%, local foaming could not be confirmed (◯), and the POF wire diameter variation was as small as ± 5 μm. It was. On the other hand, in Example 6 whose water content is 0.822 wt%, local foaming was confirmed (×). In addition, local foaming of 1 m or more per 100 m of POF confirmed at that time was as many as six. In addition, the POF wire diameter variation was as large as ± 50 μm. In Example 4 in which drying was performed under reduced pressure and the water content was 0.018 wt% and Example 5 in which the moisture content was 0.007 wt%, local foaming was not visually observed during stretching (◯), and 1 m in POF The above local foaming was not confirmed. The wire diameter fluctuation at that time was also as very small as ± 3 μm.

  By comparing the results of Examples 1 to 6, it is possible to grasp the influence of the moisture content before stretching on the degree of local foaming generated during stretching. As is clear from Table 1, local foaming could not be confirmed when the water content was 0.482 wt% or less (◯) or slightly (Δ). On the other hand, in Example 6, local foaming was confirmed (x). When comparing each water content with the occurrence of local foaming, it was found that the lower the water content, the more local foaming can be suppressed and the size can be reduced. In particular, regarding the water content, it was also confirmed that a difference in the generation of local foaming occurred at 0.5 wt% as a boundary. From the above, the moisture content before stretching has an effect on the state of the formation of local foaming, and when the moisture content is 0.5 wt% or less, it is particularly effective in suppressing the production of local foaming. I found out. Further, since the preform 11 having a lower moisture content before stretching was able to suppress the occurrence of local foaming, it is also important to maintain a low moisture content during the period after the preform 11 is stretched until it is stretched. I found out.

[Experiment 1]
A pipe 23 for the outer clad portion 16 made of PVDF was produced by melt extrusion molding. The pipe 23 has an outer diameter of 20 mm, an inner diameter of 19 mm, and a length of 905 mm. The pipe 23 was loaded into a polymerization vessel 62 having sufficient rigidity. The pipe 23 was washed with pure water and dried at 90 ° C., and thereafter, one end of the pipe 23 was closed with a plug 61 using a predetermined material (KF850 pellets, manufactured by Kureha Chemical Co., Ltd.). Thereafter, a pretreatment for forming the inner clad portion 15 was performed. This pretreatment is a cleaning treatment and an evacuation treatment of the inner surface of the pipe 23 with ethanol. This decompression treatment condition is 12 hours in an oven at 80 ° C. under a reduced pressure of −0.08 MPa (vs. atmospheric pressure).

  Next, the inner clad part 15 was formed. A liquid mixture was prepared by mixing a polymerization initiator and a chain transfer agent with all the deuterated methyl methacrylate (MMA-d8) as the inner clad monomer at the following concentrations. Dimethyl-2,2′-azobis (2-methylpropionate) (V-601) as a polymerization initiator is 0.012 mol%, and n-lauryl mercaptan as a chain transfer agent is 0.2 mol%. It is. About 200 g of this mixed solution was injected into the pipe 23.

  After the air at the tip of the pipe 23 was replaced with argon, the other end of the pipe 23 was closed with a silicon plug 61 and sealed with a sealing tape. The pipe 23 containing the inner clad liquid is placed in the polymerization vessel 62, set in the rotation polymerization apparatus 71, rotated in a horizontal state to polymerize the inner clad liquid, and the inner clad portion 15 is formed on the inner surface of the pipe 23. Formed. This rotational polymerization is a two-stage condition. The first condition is a polymerization temperature of 60 ° C. for 18 hours, and the next condition is a polymerization temperature of 90 ° C. for 4 hours. The rotation speed is 500 to 3000 rpm for all.

  Next, the core 12 was formed. A liquid mixture was prepared by mixing all the deuterated methyl methacrylate (MMA-d8) as a core monomer with a polymerization initiator, a chain transfer agent and a dopant in the following concentrations. Dimethyl-2,2′-azobis (2-methylpropionate) (V-601) as a polymerization initiator is 0.04 mol%, and n-lauryl mercaptan as a chain transfer agent is 0.2 mol%. And dimethyl sulfide (DPS) as a dopant is 7% by weight. About 100 g of this mixed solution was injected into the hollow portion of the clad 13 as a core solution.

  The clad 13 containing the core liquid was placed in a polymerization vessel 62, set in a rotation polymerization apparatus 71, rotated in a horizontal state to polymerize the core liquid, and the core 12 was formed on the inner surface of the clad 13. This rotational polymerization is a three-stage condition. The first condition is a polymerization temperature of 70 ° C. for 5 hours, the next condition is a polymerization temperature of 90 ° C. for 5 hours, and the next condition is a polymerization temperature of 120 ° C. 24 hours. The rotation speed is 500 to 2000 rpm for all.

  The obtained preform 21 was put into a commercially available reduced pressure and constant temperature drying apparatus and depressurized, and heated under reduced pressure at a pressure of 50 Pa or less and a temperature of 90 ° C. for 15 hours. The preform 21 after heating under reduced pressure was subjected to thermogravimetric analysis up to 200 ° C., and the weight loss ratio was 0.106%.

  After storing the preform 21 under the same storage conditions as in Example 1, the preform 21 was stretched using a stretching equipment 120 as shown in FIG.

  The heating furnace 140 for stretching is an electric furnace and includes four regions in order to change the temperature along the traveling direction of the preform 11. The set temperature in each region was 240 ° C., 220 ° C., 170 ° C., and 140 ° C. from the upstream side. When the tip of the melted preform 11 became thinner, the stretching conditions were adjusted so that the outer diameter was stabilized, and continuous stretching was performed. The obtained POF 21 has an outer diameter of 316 μm.

  With the in-line bubble detector that continuously captures images of the plastic optical fiber 21 with a camera installed in the drawing machine, the obtained plastic optical fiber 21 is measured and evaluated for the presence and size of voids, and the transmission loss is optically measured. Measurement was performed at a wavelength of 650 nm. As a result, no gap was confirmed in the plastic optical fiber 21, and the transmission loss was 65 dB / km.

[Comparative Experiment 1]
The test was performed under the same conditions as in Experiment 1 of Example 7, except that the preform 21 was not heat-treated under reduced pressure. And when the thermogravimetric analysis to 200 degreeC was implemented about the preform used for extending | stretching, the weight loss rate was 0.2%.

  In the plastic optical fiber obtained in this comparative experiment 1, many long and narrow gaps having a length of about 20 mm and a width of about 50 μm were confirmed, and the transmission loss was 100 dB / km.

  It can be seen from Example 7 that the present invention can suppress the generation of bubbles due to heat stretching and can provide a plastic optical fiber having no voids. This also shows that the transmission loss of the plastic optical fiber can be reduced.

It is sectional drawing of the preform as embodiment of this invention. It is a figure which shows the refractive index in the radial direction of a preform. It is a manufacturing-process figure of a plastic optical cable. It is the schematic of the melt molding equipment of an outer die decompression suction system used in order to create a pipe used as an outer clad part. It is sectional drawing which shows the outline of an example of a shaping | molding die. It is sectional drawing which shows the one part outline of the extrusion molding machine of an inner sizing die system. It is a perspective view of the guide with which an inner sizing die is equipped. It is sectional drawing which shows the outline of the superposition | polymerization container for rotation polymerization. It is a perspective view which shows the outline of a rotation polymerization apparatus. It is explanatory drawing of the rotation method in a rotation superposition | polymerization apparatus. It is the schematic of an extending | stretching installation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Preform 12 Core 13 Clad 15 Inner clad part 16 Outer clad part 21 Plastic optical fiber 26 Pressure reduction heating process

Claims (11)

In the method for producing a plastic optical member, which is obtained by heating and stretching a rod-shaped preform in the longitudinal direction,
A method for producing a plastic optical member, wherein the preform is subjected to a heat treatment in advance before the heating and stretching.   The method for producing a plastic optical member according to claim 1, wherein the heat treatment is performed under reduced pressure.   By forming a polymerizable compound in the hollow part of the tubular first member and polymerizing the polymerizable compound, a second member having a refractive index equal to or lower than the refractive index of the first member is formed in the hollow part. The method of manufacturing a plastic optical member according to claim 1, wherein the preform includes the first member and the second member.   The method for producing a plastic optical member according to claim 3, wherein the heat treatment is performed so that the moisture content of the second member is 0.001 wt% or more and 0.5 wt% or less.   5. The method for producing a plastic optical member according to claim 3, wherein the polymer produced by the polymerization has a saturated water content at 25 ° C. of 1.0 wt% or more and 3.0 wt% or less.   6. The method for producing a plastic optical member according to claim 4, wherein the polymer is an acrylic polymer.   The method for producing a plastic optical member according to claim 3, wherein the polymerization is bulk polymerization.   The method for producing a plastic optical member according to claim 1, wherein the preform has a columnar shape or a cylindrical shape. The second member includes a substance having a refractive index difference of 0.001 or more with respect to the polymer generated by the polymerization,
9. The method of manufacturing a plastic optical member according to claim 3, wherein the substance is distributed with a concentration gradient along a predetermined direction in the second member.   10. The method for producing a plastic optical member according to claim 1, wherein the plastic optical member is a plastic optical fiber. A plastic optical member manufactured by the manufacturing method according to claim 1.

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