JP2006091413A - Method for manufacturing distributed refractive index type plastic optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform annealing treatment of a preform without deforming preform. <P>SOLUTION: In a method for manufacturing distributed refractive index plastic optical fiber preform, after a pipe shaped clad is formed, preform is manufactured by forming cores whose refractive indexes are higher than that of the clad in the hollow section of the clad. The preform is subjected to the annealing treatment by being heated to temperatures equal to or higher than the glass transition temperature of a core with temperature controllers 47 in the state that the preform is contained in polymerization containers 38 and by being held to be roughly horizontal while making columnar shafts of the polymerization containers 38 to be roughly horizontal and by being revolved around these shafts as a center of rotation with a revolving device 41. The number of revolution of the preform at the time of the annealing treatment is made to be equal to or higher than 10 rpm and to be equal to or lower than 5,000 rpm. The non-circle rate of the round shape of the cross section of the hollow section of the plastic optical fiber preform after the annealing treatment is made to be equal to or smaller than 2%. When such a heat treatment is applied to the preform, the deformation by self-weight is suppressed and the preform having no deformation can be manufactured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a graded index plastic optical fiber preform.

  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 parts 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. POF can reduce the cost of the connector part as described above, and can reduce the risk of piercing accidents to the human body due to the nature of plastic, and it is easy to work and install 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.

The POF includes a core portion serving as a core portion and a clad portion as an outer shell of the core portion, and the core portion has a higher refractive index than the clad portion. Recently, as an optical fiber having a high transmission capacity, a refractive index distribution type POF (for example, GI type POF) having a core portion whose refractive index gradually decreases from the center toward the outside has attracted attention. As a method for producing this graded index POF, a method is generally known in which an optical fiber preform (hereinafter referred to as a preform) is prepared, and then the preform is melt-drawn to form POF (for example, Patent Documents 1 to 3).
JP-A-61-130904 Japanese Patent No. 3332922 Japanese Patent Laid-Open No. 10-253838

  In general, the clad portion and the core portion of the preform, which is a base material of POF, are formed using a monomer as a polymer as a raw material. For example, first, a cylindrical clad pipe is formed from the first monomer. Thereafter, a second monomer is injected into the hollow portion of the clad and polymerized to form a core having a refractive index higher than that of the clad to produce a preform. Hereinafter, the first monomer and the second monomer are collectively referred to as raw material monomers. However, in the completed preform, when a part of the raw material monomer remains without being polymerized, or when molecules with a low degree of polymerization remain, or in the preform The density may not be uniform. Hereinafter, the raw material monomer remaining without polymerization is referred to as a residual monomer. When the amount of residual monomer is large, problems such as foaming occur when the preform is melt-stretched, and when molecules with a low degree of polymerization are present, heat resistance, rigidity, strength, etc. Leading to a decline. In addition, when the density is not uniform, there is a problem that transmission characteristics are deteriorated due to light scattering as compared with a uniform one. Therefore, it is common to heat-treat (hereinafter referred to as annealing treatment) the preform produced for the purpose of reducing residual monomers, improving and homogenizing the degree of polymerization, and making the density uniform.

  In a general annealing method, the preform is heated to a temperature equal to or higher than the glass transition temperature (hereinafter referred to as Tg) of the clad or core, and then cooled at a predetermined cooling rate. However, when the annealing process is performed, if the temperature is raised to Tg or more in a state where the preform is left still, deformation occurs due to the weight of the preform. This deformation means that, for example, the thickness of the cylindrical core portion of the preform becomes non-uniform, the circular cross section of the hollow portion becomes an ellipse instead of a perfect circle, or the preform is bent. Means. When this deformation is large, there arises a problem that a POF having a desired shape cannot be obtained. Therefore, the establishment of a method for annealing treatment of a gradient index plastic optical fiber preform that is prevented from being deformed has been a problem.

  The present invention has been made in view of the above problems, and provides a method of manufacturing a gradient index plastic optical fiber preform that is annealed while suppressing deformation of the gradient index plastic optical fiber preform. It is aimed.

  The method for producing a gradient index plastic optical fiber preform according to the present invention comprises a first polymerizable compound and a first refractive index adjusting agent having a higher refractive index than a polymer obtained by polymerization of the first polymerizable compound. The second member having a refractive index higher than that of the first member is generated on the inner surface of the first member by a polymerization reaction that is injected into the cylindrical first member and polymerizes the first polymerizable compound. Forming a gradient index plastic optical fiber preform, and heating the gradient index plastic optical fiber preform at a temperature equal to or higher than the glass transition temperature of the second member while rotating the gradient index plastic optical fiber preform in the circumferential direction of the first member. And an annealing step to perform.

  The refractive index distribution type plastic optical fiber preform is annealed so that the non-circularity of the circular cross section of the hollow portion is 2% or less, and the refractive index distribution type plastic optical fiber is held substantially horizontally. The annealing treatment is performed by rotating, and the number of revolutions of the gradient index plastic optical fiber during the annealing treatment is 10 rpm or more and 5000 rpm or less.

  According to the present invention, a gradient index plastic optical fiber preform having a second member having a higher refractive index than that of the first member in a hollow portion of the first tubular member is used. It is possible to suppress the refractive index distribution type plastic optical fiber preform from being deformed by heating at a temperature equal to or higher than the glass transition temperature of the second member while rotating as the rotation center. Further, the rotation speed is controlled so that the non-circularity of the circular cross section of the hollow portion of the plastic optical fiber preform is 2% or less, and the rotation is performed while the circular tube axis is substantially horizontal. When a POF is manufactured using the produced gradient index plastic optical fiber preform, a POF with a small non-circularity can be obtained.

  Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 is a manufacturing process diagram of a plastic optical cable. The details of each step will be described later, and only the flow of each step will be described here. First, in the clad production process 11, a tubular clad 12 as a first member is produced. The clad 12 is an outer shell portion of a preform to be manufactured later.

  After producing the clad 12, a first injection process 13 and an outer core polymerization process 14 are performed. The first injection step 13 is a step of injecting the outer core monomer as a polymerizable compound into the clad, and the outer core polymerization step 14 is a cylinder in which the outer core monomer is polymerized and the center is a cavity. This is a step of forming a shaped outer core. In the present embodiment, a double-structured core is formed. In this description, a portion (outside) formed in contact with the inner surface of the clad 12 is an outer core, and a portion (inside) formed in the outer core is an inner core.

  In the first injection step 13, the outer core monomer is injected into the cladding 12 in order to form the outer core. Next, in the outer core polymerization step 14, the injected outer core monomer is polymerized to form a cylindrical outer core having a hollow center. However, in the case where an interfacial gel polymerization reaction, which is a kind of bulk polymerization, occurs such that the polymer swells or dissolves and a predetermined reaction proceeds when the polymerizable compound contacts or penetrates into the polymer, As the reaction proceeds, the previously formed polymer dissolves. Therefore, for example, the outer core formed here may be integrated with the inner core due to the inner core generation reaction described later, and the outer core may not be recognized.

  After the outer core is formed inside the clad 12, the second injection step 15 and the inner core polymerization step 16 are performed to produce the preform 17. The second injection step 15 is a step of putting the inner core monomer, which is a polymerizable compound for forming the inner core, into the outer core. The inner core polymerization step 16 is a step of polymerizing the inner core monomer. Forming the inner core. In the present embodiment, the polymerizable compound that forms the outer core and the inner core will be described as the outer core monomer and the inner core monomer, but the polymerizable compound that can be used in the present invention is Both are not limited to monomers, but may contain dimers, trimers, or polymerizable compounds used to form various polymers as described below. Not.

  The preform 17 is stored under predetermined storage conditions until it is subjected to stretching after being produced. In this embodiment, the core is stored while being dried so that the moisture content of the core becomes a predetermined value. About this storage process, the code | symbol 19 is attached | subjected in FIG. 1 as a dehumidification storage process.

  The preform 17 whose core has a predetermined water content is heated and melted in the stretching step 22 and stretched to become POF 25. In the stretching step 22, the cylindrical preform 17 is heated by a predetermined means and stretched in the longitudinal direction. In addition, since the preform 17 has a function as an optical transmission body even in this state, its use is not limited to being used as the POF 25. The preform 17 is subjected to an annealing process 18 that is annealed under a predetermined condition, followed by a dehumidification storage process 19 that is dried and stored by a predetermined drying means, and then subjected to a stretching process 22 to produce a POF 25. However, the order in which the annealing process 18 and the dehumidifying storage process 19 are performed is not particularly limited, and the annealing process 18 may be performed before stretching after the preform 17 is manufactured and the dehumidifying storing process 19 is performed. The POF 25 becomes a plastic optical cable 27 through a coating process 26 in which the outer periphery is coated with a coating material. The coating process 26 is usually a process in which primary coating is performed and then secondary coating is performed. The POF 25 that has passed through the coating process 26 is a plastic optical fiber core or a plastic optical fiber cord (both , Plastic Optical Code). Details regarding the covering step 26 will be described later. In the present embodiment, the number of the fiber cores remains one, and the one further coated as necessary is referred to as a single fiber cable, and a plurality of fiber cores are combined together with a tension member and the like. The one covered with the covering material is called a multi-fiber cable. Further, the plastic optical cable 27 (Plastic Optical Cable) is a general term for including both the single fiber cable and the multi-fiber cable.

  Next, the preform 17, the POF 25, and the manufacturing method thereof in this embodiment will be described. FIG. 2 is a cross-sectional view of an example of the preform 17 manufactured according to the present invention, and FIG. 3 is a diagram showing the refractive index in the radial direction of the circular cross-section of the preform 17. The preform 17 shown in FIG. 2 includes a clad 12 that is an outer shell portion and a core 31 that is an inner shell portion. The core 31 includes an outer core 32 that is in contact with the inner surface of the clad 12 and an inner portion of the outer core 32. Of the inner core 33. The inner side (central part) of the inner core 33 is a hollow part 34. The clad 12 has an outer diameter and an inner diameter that are constant in the longitudinal direction and has a uniform thickness. Also, the refractive index is low among polymers. In the present embodiment, polyvinylidene fluoride (hereinafter referred to as PVDF) is molded by melt extrusion molding. However, the clad 12 may be, for example, PMMA obtained by rotational polymerization, or may be a material as described later, and is not particularly limited.

  As with the clad 12, the outer core 32 has a tube shape in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is uniform. The material of the outer core 32 is selected in consideration of the relationship with at least one of the clad and the inner core. The outer core monomer exemplified in this embodiment is methyl methacrylate (MMA) or all-deuterated methyl methacrylate (MMA-d8), and the outer core 32 formed by these is PMMA or all-deuterated polymethyl. Methacrylate (PMMA-d8). A hollow portion 34 is formed in the central portion of the preform 17 shown in FIG. 2. The diameter of the circular section of the hollow portion 34 and the ratio of this diameter to the outer diameter of the preform are shown in FIG. It is not limited to the mode shown in (1), but varies depending on the manufacturing conditions.

  In FIG. 3, the horizontal axis indicates the cross-sectional radial direction of the preform 17, and the vertical axis indicates the refractive index. Further, the refractive index means a high value in the upward direction of the vertical axis. The range indicated by the symbol (A) on the horizontal axis is the refractive index of the cladding 12 in FIG. 2, the range indicated by the symbol (B) is the refractive index of the outer core 32 in FIG. 2, and the symbol (C) The range indicated by is the refractive index of the inner core 33 in FIG. However, since the range indicated by the symbol (D) is a range corresponding to the cavity 34 in FIG. 2, it is shown as having no value.

  As shown in FIG. 3, the refractive index of the inner core 33 continuously increases from the boundary with the outer core 32 toward the cavity 34. The clad 12 has a lower refractive index than the outer core 32, and the outer core 32 has a lower refractive index than the inner core 33. In the example illustrated as the present embodiment, the refractive index of the inner core 33 of the manufactured preform 17 is continuously refractive index from the outside of the circular cross section toward the cavity 34 as shown in FIG. The rotational gel polymerization method to be described later is applied as a method for forming the inner core 33. 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. The inner core monomer exemplified as this embodiment is MMA or fully deuterated methyl methacrylate (MMA-d8), and the outer core 32 and the inner core 33 after polymerization are mainly composed of PMMA or fully deuterated. Polymethyl methacrylate (PMMA-d8) is obtained. Therefore, although the boundary between the two is shown in FIG. 2 for convenience of explanation, in the obtained preform 17, for example, when an interfacial gel polymerization reaction or the like occurs, it is not clear or as described above. In some cases, the interface disappears.

The refractive index distribution coefficient of the preform 17 and the POF 25 is known as the value of g in the following formula (I). In the following formula (I), R is the outer diameter of the preform 17 or POF 25, r is the distance from the center of the cross-sectional circle to the measurement position, 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 diameter direction, and Δ is a value represented by (n1-n2) / n1.
(I): n (r) = n1 {1- (r / R) g × Δ} 1/2
= N1 (1-Δ)

  The refractive index distribution coefficient of the preform 17 and the POF 25 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, and ideally Is 2.0.

  Next, the POF 25 will be described. 4 is a cross-sectional view of the POF 25 obtained by heating and stretching the preform 17, and FIG. 5 is a schematic diagram showing the refractive index in the cross-sectional radial direction of the POF. As shown in FIG. 4, the POF 25 includes a clad 112 and a core 131 so as to be in contact with the inner side of the clad 112, and the core 131 includes an outer core 132 and an inner core 133. . Further, since the POF 25 is produced by heating and melting the preform 17 and stretching in the longitudinal direction, the central cavity is eliminated.

  The vertical and horizontal axes in FIG. 5 are the same as those in FIG. In FIG. 5, the range indicated by the symbol (E) on the horizontal axis is the refractive index of the cladding 112 in FIG. 4, and the range indicated by the symbol (F) is the refractive index of the outer core 132 in FIG. , (G) indicates the refractive index of the inner core 133 in FIG. As described above, the refractive index in the cross-sectional radial direction of the POF 25 is the lowest in the clad 112 and is higher in the order of the outer core 132 and the inner core 133 in the same manner as the preform 17, and the refractive index of the inner core 133 is , It becomes higher continuously toward the center of POF25. Further, the refractive index distribution coefficient of the POF 25 obtained in this way shows almost the same value as that of the preform 17. The refractive index distribution of the POF 25 is as described above.

  Next, the manufacturing method of the preform 17 will be described in detail with reference to FIGS. FIG. 6 is a cross-sectional view of the polymerization container in a state in which the clad is accommodated, FIG. 7 is a schematic perspective view of the rotating device, and FIG. However, in this invention, it is not limited to the apparatus and container shown in FIGS. 6-8, Moreover, this embodiment is an illustration as one aspect | mode of this invention. In the present embodiment, the clad 12 (see FIG. 2) is made by melt extrusion since PVDF is the main component as described above. Melt extrusion is performed by a commercially available melt extrusion molding machine, and any known method can be used as the method of melt extrusion, and there is no particular limitation.

  One end of the clad 12 is closed with a plug 37 made of a predetermined material. The plug 37 is made of a material that does not dissolve in the polymerizable compound forming the core 31 and does not contain a compound that elutes a plasticizer or the like. Examples of such a material include polytetrafluoroethylene (PTFE). After closing one end of the clad 12 with the plug 37, the outer core-forming monomer is injected into the clad 12, and after the other end of the clad is also plugged with the plug 37, the outer core 32 ( 2). However, when forming the outer core, the clad 12 is placed in a polymerization container 38 as shown in FIG. The superposition | polymerization container 38 has the container main body 38a and the lid | cover 38b, and is made from stainless steel in this embodiment. As shown in FIG. 6, the polymerization vessel 38 preferably has an inner diameter slightly larger than the outer diameter of the clad 12, and is configured so that the clad 12 rotates in conjunction with the rotation of the polymerization vessel as described later. Has been. In addition, as described above, it is preferable to provide a support member for supporting the clad 12 on the inner surface of the polymerization vessel 38 so that the clad 12 can respond to the rotation of the polymerization vessel 38.

  As shown in FIG. 7, the rotation device 41 includes a plurality of support rotation members 43 in the device main body 42, and includes a drive unit 46 that rotates the support rotation member 43 outside the device main body 42. In addition, it has a temperature controller 47 that detects the temperature inside the apparatus main body 42 and controls the internal temperature according to the detection result.

  The support rotation member 43 has a cylindrical shape, and the longitudinal directions thereof are generally parallel to each other and substantially horizontal so that at least one polymerization vessel 38 can be supported by two peripheral surfaces. One end of each support rotation member 43 is rotatably attached to the side surface of the apparatus main body 42 and is driven to rotate by the drive unit 46 under independent conditions. The drive unit 46 includes a motor, a decompressor, a controller (not shown), and the like, and the drive of the drive unit 46 is controlled by the controller. Then, at the time of a predetermined polymerization reaction, as shown in FIG. 8, the polymerization container 38 is placed on the valley formed by the peripheral surfaces of the adjacent support rotation members 43, and rotates according to the rotation of the support rotation members 43. To do. In this embodiment, the rotation of the polymerization vessel 38 is a surface drive type, but the rotation method of the polymerization vessel 38 is not particularly limited.

  In the present embodiment, as shown in FIG. 8, the lids 38 b at both ends of the polymerization vessel 38 are provided with magnets 38 c, respectively, and between the adjacent two supporting rotating members 43, Also, a magnet 45 is provided. This prevents the polymerization vessel 38 from floating from the support rotation member 43 during rotation. As a method for preventing the polymerization container 38 from floating from the support rotation member 43, in addition to or in place of the above method using a magnet, a rotation means similar to the support rotation member 43 is provided at the top of the set polymerization container 38. In some cases, the polymerization vessel 38 may be prevented from floating by being provided so as to be in contact with the substrate and being similarly rotated. In addition to this method, for example, there is a method in which a pressing means or the like is provided above the polymerization vessel 38 and a predetermined load is applied to the polymerization vessel 38. However, the present invention does not depend on the floating prevention method. There is no particular limitation on the floating prevention method.

  Next, the outer core will be described. Various raw materials for the outer core, including the outer core monomer, will be described in detail later. The outer core exists between the clad and the inner core, and is also involved in the polymerization reaction of the inner core monomer. However, the outer core may be unnecessary depending on the formation conditions of the inner core, or may be lost as an integral part of the inner core in the process of generating the inner core as described above. A raw material such as a monomer to be used is used after sufficiently removing a polymerization inhibitor, moisture, impurities and the like by filtration or distillation. Furthermore, after preparing a mixture by mixing a monomer and a polymerization initiator, it is preferable to remove dissolved gas and volatile components contained in the mixture by ultrasonic treatment.

  As described above, after closing the end of the clad with a plug, the outer core is injected with the monomer for forming the outer core into the clad, and after the other end of the clad is also plugged with the plug, by rotation polymerization An outer core is formed. Before and after this injection step, the clad and the injected material may be subjected to a reduced pressure treatment by a known decompression device, if necessary. Thereafter, when the polymerization vessel is loaded while the polymerization is caused to proceed while rotating (horizontal rotation) with the polymerization vessel filled with the clad having a substantially horizontal direction in the longitudinal direction, an outer core is formed. Thus, the outer core is produced by rotational polymerization in which the circular tube axis of the cladding is used as the center of rotation, but prior to rotational polymerization, pre-polymerization may be performed with the cladding standing. In the prepolymerization, the clad circular tube axis may be rotated about the rotation center by a predetermined rotation mechanism as required. In such rotation polymerization, the outer core is easily formed on the entire inner surface of the cladding because the rotation is performed while keeping the longitudinal direction of the cladding generally horizontal. In the present invention, at the time of polymerization of the outer core, it is most preferable to make the longitudinal direction of the cladding horizontal to form the outer core on the entire inner surface of the cladding, 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 raw material for the outer core will be described. As the raw material for the outer core in the present invention, an outer core monomer and a predetermined polymerization initiator (reaction initiator) are used. In addition, as a monomer for outer cores, a radically polymerizable compound and an anion polymerizable compound can be used, and a polymerization initiator can be replaced with a predetermined catalyst. Moreover, you may add a chain transfer agent (molecular weight regulator) in the raw material of an outer core.

  As the outer core monomer, in the present embodiment, a form using methyl methacrylate (MMA) or all-deuterated methyl methacrylate (MMA-d8) is exemplified, but these are obtained by radical polymerization and anionic polymerization. It is a compound that can react. However, in the present invention, radically polymerizable compounds and anionic polymerizable compounds other than these can be used as the outer core monomer. Preferable examples include inner core monomers, which will be described later in detail.

  The polymerization initiator or catalyst for forming the outer core preferably has an addition rate of 0.001 mol% to 5 mol% with respect to the outer core monomer, and is 0.005 mol% to 0.1 mol%. More preferably. When the addition rate of the polymerization initiator or catalyst is more than 5 mol%, the injected outer core raw material boils or bubbles are generated, and the generated bubbles are difficult to escape. . On the other hand, when it is less than 0.001 mol%, a problem that a sufficient reaction initiation effect cannot be obtained is caused.

  As this embodiment, although the form which uses dimethyl 2,2'- azobis (2-methylpropionate) (V-601) as a polymerization initiator is illustrated, this invention is limited to this. The polymerization initiator or the catalyst can be appropriately determined depending on the type of the outer core monomer to be used. Particularly preferred polymerization initiators are those classified as medium-low temperature polymerization initiators among those commercially available as polymerization initiators. The medium / low temperature polymerization initiator is generally a polymerization initiator having a 10-hour half-life temperature of 40 ° C. or higher and 90 ° C. or lower. By using such a polymerization initiator, for example, the reaction at which the optimum reaction temperature when using a high temperature polymerization initiator is 100 ° C. or higher and 130 ° C. or lower is generally performed at 50 ° C. or higher and 90 ° C. or lower. In addition, since the conversion rate in a predetermined time can be suitably controlled to obtain a predetermined polymerization reaction rate, the outer core formation time can be shortened as compared with the conventional method. In addition, since the reaction temperature can be lowered and the reaction time can be shortened, the cladding can be prevented from being deteriorated. Specific examples of the polymerization initiator or catalyst will be described later together with the polymerization initiator or catalyst in the inner core polymerization step.

  The chain transfer agent is preferably used in an amount of 0.05 mol% to 0.8 mol% with respect to the outer core monomer, and is 0.05 mol% to 0.4 mol%. It is more preferable.

  The chain transfer agent is not particularly limited, and is determined according to the type of outer core monomer used. Specific examples will be described later together with the chain transfer agent in the inner core polymerization step.

  The production method of the clad and the outer core in the present invention is not limited to the above-described embodiment, and can be produced by appropriately using a known method depending on the material to be used. For example, the clad and the outer core can be molded by simultaneous integral extrusion. Further, as another method, a glass-made tubular member having a predetermined inner diameter is used instead of the clad, and after the outer core monomer is injected into the hollow portion and polymerized, the glass-shaped tubular member is made. May be removed and a separately formed tubular clad may be attached to the outer core, or the outer peripheral surface of the outer core may be formed by a predetermined method.

  As described above, after the clad on which the outer core is formed is taken out from the rotating device 35, in this embodiment, an annealing treatment for a predetermined time is performed by a heating means such as a thermostat set to a predetermined temperature.

  Next, after the inner core raw material including the inner core monomer is injected into the outer core, it is polymerized under predetermined conditions to form the inner core. In the polymerization, the rotation device 41 (see FIG. 7) used in the outer core polymerization process is used, and the polymerization vessel 38 is rotated so that the longitudinal direction of the clad is rotated substantially horizontally as in the outer core polymerization. To implement. Before and after the injection of the inner core monomer, the clad or the injection material on which the outer core is formed may be subjected to a reduced pressure treatment by a known decompression device, if necessary.

  Thereafter, the inlet is plugged and closed, and the longitudinal direction of the clad formed with the outer core is set in the rotating device 41 so as to be in a horizontal state, and rotated so that the center of the circular cross section of the clad becomes the rotation axis. Then, the reaction is started and polymerization proceeds to form an inner core.

  When the inner core monomer starts polymerization, the inner wall of the outer core is swollen by the inner core monomer, and a swelling layer is formed in the initial stage of polymerization. Since the swelling layer is in a gel state, the polymerization rate is accelerated (referred to as gel effect). From such a phenomenon, in the present invention, a reaction of polymerizing the polymerizable compound by forming a swelling layer by the reaction between the tubular member and the injected polymerizable compound while rotating the previously prepared tubular member. Is referred to as a rotational gel polymerization method. In the polymerization reaction, the longitudinal direction of the tubular member is preferably horizontal as in this embodiment. The polymerization starts from the inner surface of the outer core and proceeds toward the center of the clad 12 having a circular cross section. At this time, since a compound having a smaller molecular volume enters into the inside of the swelling layer preferentially, a dopant having a larger molecular volume is pushed out from the swelling layer toward the center as compared with other compounds that coexist with the progress of polymerization. . As a result, the concentration of the dopant having a high refractive index is increased in the central portion of the formed inner core, and the refractive index is gradually increased toward the center in the radial direction of the circular cross section as shown in FIG. A preform 17 can be obtained.

  In the present embodiment, the formation of the swelling layer has also been confirmed at the interface between the clad and the outer core and its periphery. Therefore, when manufacturing the preform 17 having, for example, a PVDF clad and an MMA core, the manufacturing method of the above-described embodiment in which the outer core and the inner core are formed in stages may be omitted. Alternatively, a method may be used in which a core monomer mixed with a refractive index adjusting agent is injected and then polymerized while horizontally rotating to form a core at a time.

  In the present embodiment, since the preform is produced while the outer core and the inner core form a swollen layer, there is no clear boundary between the outer core and the inner core. Therefore, in FIG. 2, the boundary between the clad and the core is shown for convenience of explanation. However, in actuality, the affinity between the materials of the outer core and the inner core, the presence or absence of the formation of a swelling layer, and the like Depending on the manufacturing conditions, the clarity of the boundary between the outer core and the inner core in the obtained preform differs. Further, in the rotating gel polymerization method of the present invention, the outer core may be thinner than before the inner core is formed, in addition to the case where the outer core disappears as described above due to the formation of the gel layer.

  Alternatively, the inner core monomer may be rotated or horizontally rotated while the inner core monomer is not polymerized in the hollow portion of the outer core. In this case, since the inner wall of the outer core swells and dissolves in the inner core monomer, the fine irregularities present on the inner surface of the outer core are actively scraped, improving the smoothness of the inner surface. A better inner core region can be formed.

  As described above, in the present invention, by performing the rotating gel polymerization method, the conventional production method, for example, injection and polymerization of a composition such as a polymerizable compound is repeatedly performed, and the polymer is sequentially formed into a cylindrical shape from the outside. The generation of bubbles at the interface between the outer core and the inner core and the inside of the inner core, which has been generated in the method of generating the gas, can be suppressed. Further, in the present invention, in order to carry out polymerization of the outer core and the inner core while rotating with the longitudinal direction of the clad being horizontal, the influence of the volume shrinkage in the polymerization production of each monomer is suppressed, and the entire inner surface of the clad is controlled. As a result, the entire cladding can be used as a POF preform. Further, the rotating gel polymerization method has an advantage that the reaction operation is easy because no pressurization is required. In the present invention, during the polymerization of the inner core, it is most preferable that the longitudinal direction of the clad is horizontal in order to form the inner core on the entire inner surface of the outer core. The allowable angle is preferably within 5 ° with respect to the horizontal.

  In the present embodiment, the outer core and the inner core monomer are reacted together with the polymerization reaction of the inner core monomer, and these reactions are regarded as bulk polymerization reactions. In the embodiment described above, the reaction between the clad and the outer core and the polymerization of the outer core are also regarded as a bulk polymerization reaction. Thereby, generation | occurrence | production of a bubble is suppressed in a core.

  In the above rotating gel polymerization method, the reaction temperature is preferably not higher than the boiling point of the polymerizable compound used. When MMA or MMA-d8 is used as the polymerizable compound as in this embodiment, the reaction temperature is preferably 30 ° C. or higher and 100 ° C. or lower, more preferably 40 ° C. or higher and 90 ° C. or lower. preferable. The reaction time is preferably 0.5 hours or more and 30 hours or less, and more preferably 1.5 hours or more and 25 hours or less.

  The rotation speed of the support rotation member 43 by the motor 46 is preferably 500 rpm or more and 4000 rpm or less, and more preferably 1500 rpm or more and 3500 rpm or less.

  The raw material for the inner core will be described. In the present invention, an inner core monomer, a predetermined polymerization initiator (reaction initiator), and a refractive index adjusting agent (dopant) are used as raw materials for the inner core. As the inner core monomer, a radical polymerizable compound and an anion polymerizable compound can be used. The polymerization initiator can be replaced with a predetermined catalyst. In addition, a chain transfer agent (molecular weight adjusting agent) can be added to the raw material for the inner core as necessary.

  As the inner core monomer, methyl methacrylate (MMA) or fully deuterated methyl methacrylate (MMA-d8) is used in the embodiment exemplified above, and these are compounds that react by radical polymerization and anionic polymerization. is there. However, in the present invention, radically polymerizable compounds and anionic polymerizable compounds other than these can be used as the inner core monomer. Specific examples will be described later together with the outer core monomer.

  The polymerization initiator or catalyst for producing the inner core preferably has an addition rate of 0.001 mol% or more and 5 mol% or less, more preferably 0.010 mol% or more and 0.0. 1 mol% or less. When the addition rate of the polymerization initiator or the catalyst is more than 5 mol%, problems such as boiling and bubbles are generated and it is difficult to remove dissolved gas. Moreover, when the addition rate of a polymerization initiator or a catalyst is less than 0.001 mol%, problems such as an increase in reaction temperature and a longer reaction time occur.

  In this embodiment, dimethyl 2,2′-azobis (2-methylpropionate) (V-601) is used as the polymerization initiator, but the present invention is not limited to this and is used. A polymerization initiator or a catalyst can be appropriately determined according to the type of the outer core monomer. As a particularly preferable polymerization initiator, among those commercially available as a polymerization initiator, the polymerization initiator for medium and low temperatures described in the outer core polymerization method is used. By using the polymerization initiator, for example, the optimum reaction temperature when using a high-temperature polymerization initiator can be generally reduced, and the reaction rate and the conversion rate are controlled so as to satisfy the preferred reaction progress range. Therefore, the inner core generation time can be reduced as compared with the conventional method. Moreover, since it is not necessary to extend the reaction time even if the reaction temperature is lowered, it is possible to prevent the cladding from being deteriorated. A preferable polymerization initiator or catalyst will be described later together with the polymerization initiator or catalyst in the outer core polymerization step.

  For the purpose of shortening the reaction time, it is preferable to use a radical polymerization initiator or the like. It is particularly preferable to use a radical polymerization initiator having a 10-hour half-life temperature of 70 ° C. or lower.

  The chain transfer agent is preferably added in an amount of 0.05 mol% to 0.80 mol%, more preferably 0.15 mol% to 0.4 mol%, relative to the inner core monomer. It is as follows. The chain transfer agent is not particularly limited, and is determined according to the type of the inner core monomer to be used. Specific examples will be described later together with the chain transfer agent in the outer core polymerization step.

  The addition rate of the dopant is preferably 0.01% by weight to 25% by weight and more preferably 1% by weight to 20% by weight with respect to the inner core monomer.

  In the embodiment exemplified above, diphenyl sulfide, which is a low molecular compound that has a high refractive index and a large molecular volume and does not participate in polymerization, was used as a dopant. The refractive index in the radial direction of the core is changed by adding the diphenyl sulfide. It is not always necessary to use a dopant, and the refractive index in the radial direction of the cross section of the core 31 (see FIG. 2) can also be changed by a method such as using two or more types of inner core monomers. As such a method, for example, the first and second compounds that are copolymerizable are used, and the second compound has a higher refractive index than the first compound. A method of polymerizing by utilizing the difference between the reactivity of the first compound and the reactivity between the first and second compounds is exemplified. Specific examples of the dopant will be described later together with the polymerization initiator and the chain transfer agent.

  By the above method, a preform is produced in which the core 31 (see FIG. 2) and the clad 12 are made of plastic, and the core is a cylindrical optical transmission body having a double structure of an outer core and an inner core. can do.

  In the present embodiment, after the polymerization reaction is performed under the above conditions, an annealing process is further performed under predetermined conditions. When the preform 17 is annealed, residual monomers in the preform can be reduced. The annealing treatment is a treatment method in which the preform is heated to a temperature higher than the glass transition temperature (hereinafter referred to as Tg) of the monomer that forms the preform core (see FIG. 2). The temperature during annealing (hereinafter referred to as annealing temperature) varies depending on the monomer. Therefore, the temperature is appropriately set according to the monomer used. However, the annealing temperature is preferably as low as possible in order to suppress migration of the dopant. That is, it is preferably less than the melting point (flow start temperature) of the core above the Tg of the preform core, and more preferably (Tg + 5) or more and (melting point−5) or less of the core of the preform. is there. However, when a preform is prepared by mixing two or more types of monomers or when a dopant is mixed, the Tg of the polymer varies depending on the mixing ratio and blending amount, or the degree of polymerization. Therefore, when two or more types of monomers are mixed, the value having the highest Tg value in the core is set as the Tg of the polymer. For example, when the core is PMMA, the annealing temperature is preferably 110 ° C. or higher and 155 ° C. or lower, and more preferably 115 ° C. or higher and 150 ° C. or lower. The annealing treatment time is 24 hours in this embodiment, but it is preferable to perform the annealing treatment in the range of 10 hours to 48 hours.

  When the annealing process is performed, a rotating device 41 shown in FIG. 7 is used. The annealing treatment in the present invention is characterized in that the preform 17 is rotated while being inserted in the polymerization vessel 38, whereby the deformation due to the weight of the preform 17 can be suppressed. The method for operating the rotation by the rotating device 41 is the same as that in the outer core polymerization step 14, and thus the description thereof is omitted. Thus, when annealing is performed while rotating the preform, there is an effect that heat uniformly penetrates into the preform, so that it is possible to effectively equalize the uneven polymerization.

Moreover, it is preferable to set conditions so that the non-circularity of the circular cross-section of the hollow portion of the preform 17 after annealing while rotating is 2% or less. More preferably, it is 1.5% or less, and particularly preferably 1.3% or less. The non-circularity of the circular cross section of the hollow portion indicates the degree of deformation of the preform 17, and when the long side of the preform hollow layer cross section is x1 and the short side is x2, the following formula (II) The value represented. When the POF 25 is manufactured using the preform 17 having a non-circularity greater than 2%, there is often a problem that the non-circularity of the cross-sectional shape of the POF becomes high. Therefore, the smaller the non-circularity, the better.
(II): Non-circularity [%] of circular cross section of hollow portion = (Diameter difference / Maximum diameter) × 100
= [(X1-x2) / x1] × 100
In order to control the non-circularity of the circular cross section of the hollow portion as described above, the rotation speed when rotating the preform 17 is preferably 10 rpm or more and 5000 rpm or less, more preferably 50 rpm or more and 3000 rpm or less, Especially preferably, it is 100 rpm or more and 1000 rpm or less.

  After the annealing process, the preform 17 is cooled at a predetermined cooling rate, but the cooling rate is not particularly limited. The annealed preform 17 is subjected to a drawing step 22 and can be made into a plastic optical fiber when drawn by a predetermined means. In addition, although the produced preform has a hollow part in the center part with a circular cross section, the hollow part is eliminated by stretching in the stretching process, and a POF showing excellent transmission loss is formed. Is done.

  As a preform stretching method, for example, various stretching methods described in JP-A-07-234322 can be applied, whereby a POF having a desired diameter, for example, 200 μm or more and 1000 μm or less can be obtained. .

  As an example of the stretching method, FIG. 9 shows a schematic diagram of a POF manufacturing facility 50 for stretching a preform to form POF, and the stretching method of the preform 17 in this embodiment will be described.

The POF manufacturing facility 50 includes a heating device 51 for heating and melting the preform 17, a wire tension measuring device 52 for measuring the tension when the molten preform 17 is stretched, and this wire. A dancer roller 53 for adjusting the tension for controlling the tension in stretching based on the detection result of the tensile force measuring device 42, and a draw roller pair 56 for controlling the stretching speed; The outer diameter measuring device 57 for measuring the outer diameter of the POF 25, the winding device 60 for winding the POF, and the tension (hereinafter referred to as winding tension) applied to the POF 25 in winding. A winding tension measuring device 61 for measuring.

  Further, on the upstream side of the heating device 51, a holding member 65 for holding the preform 17, a shift device for controlling the holding or releasing of the preform 17 by the holding member 65 and the displacement of the holding member 65. 67, and a motor 68 for driving the shift device 67 are provided. However, in the present embodiment, the holding method using the holding member 65 has been shown as a method for holding the preform 17. However, the preform 17 may be suspended from the upstream side to the downstream side, and the preform 17 may be held. There is no particular limitation as long as it can be performed. The holding member 65 is preferably a hollow member having high rigidity and low non-circularity, and the inner diameter thereof is preferably substantially equal to the outer diameter of the first member.

  The heating device 51 is provided with a cylindrical heating furnace 70, and the heating furnace 70 can change the temperature along the extending direction of the preform 17. The drawing roller pair 56 is configured such that the driving roller 71 and the pressure roller 72 are opposed to each other so as to sandwich the POF 25 therebetween. A motor 73 is connected to the drive roller 71, and the rotation speed of the drive roller 71 is adjusted by adjusting the rotation speed of the motor 73. Furthermore, the dancer roller 53 is provided with a shift mechanism (not shown) for displacement, and tension in stretching is controlled by this displacement. About the tension | tensile_strength by extending | stretching, it can also adjust with the speed which the preform 17 descend | falls, the rotational speed of the drive roller 71, and the heating temperature in the heating furnace 70. FIG.

  The preform 17 is stretched with the upper portion held by the holding member 65. A holding member 65 that holds the upper portion of the preform 17 is connected to a first shift mechanism 67 that is connected to a motor 68. The stretching speed of the holding member 65 is controlled by the motor 68 and the first shift mechanism 67, and the preform 17 is guided into the heating furnace 70 by the downward displacement of the holding member 65 according to the stretching speed. Stretched. At this time, the preform 17 continues to descend at a speed corresponding to the stretching speed. The first shift mechanism 67 is provided with alignment means (not shown), and the center position of the circular cross section of the preform 17 can be precisely adjusted by the alignment means during stretching. . Thereby, the linearity of the POF 25 and the roundness of the cross section can be maintained well.

  In order to prevent the preform 17 from being deteriorated by heating and melting, a supply device (not shown) for supplying an inert gas is preferably attached for the purpose of making the inside of the heating device 51 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 17 is melted little by little from the front end inside the heating furnace 70 and stretched to become POF 25. Although the temperature at the time of a heating can be suitably determined according to the material etc. of the preform 17, generally 180 to 250 degreeC is preferable. The drawing conditions such as the drawing temperature can be appropriately determined in consideration of the diameter of the preform 17, the desired diameter of the POF 25, the material of the preform 17, and the like. In particular, in the GI POF, 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 17 concentrically when the preform 17 is viewed in cross section.

  Further, in the heating furnace 70, it is preferable that a temperature distribution is provided along the longitudinal direction of the preform 17. This means that the time during which the preform 17 is melted can be shortened as much as possible, and the melting range in the longitudinal direction can be shortened as much as possible. If the melting range in the longitudinal direction is long, the time during which the preform 17 is melted becomes long, fluidization of the constituent molecules of the preform 17 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. 3 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 POF 25 is measured for tension (hereinafter referred to as “wire tension”) when stretched by the line tension measuring device 52. Then, the outer diameter is measured by the outer diameter measuring device 57. The drawing speed is set to a desired value (for example, 2 m / min to 50 m / min) by the drawing roller pair 56, and this control is performed by adjusting the rotation speed of the driving roller 71 by the motor 73. . Then, the lowering speed of the holding member 65, the heating temperature in the heating furnace 70, the drawing speed by the drawing roller pair 56, and the like are controlled so that the outer diameter of the POF 25 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 POF 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 POF 25 is wound around a dancer roller 53 for adjusting the tension and conveyed. A drive device (not shown) is attached to the dancer roller 53, and the position of the dancer roller 53 is changed by this drive device. The POF 25 is conveyed to the winding tension measuring device 61 by the roller 62, and the tension (winding tension) is measured. The POF 25 is wound up in a roll shape by a winding device 60 that is rotated by a rotation control means (not shown). The adjustment of the winding tension is performed based on the measured value of the winding tension measured by the winding tension measuring device 61. The winding tension is also controlled by the rotation speed of the winding device 60. When the outer diameter D1 of the preform 17 and the outer diameter of the POF 25 are within the above ranges, the winding tension is preferably 0.098N or more and 1.96N or less, more preferably 0.29N or more and 0. The range is not more than .98N.

  Regarding the POF 25 obtained by the present invention, the bending and lateral pressure characteristics as the POF can be improved by defining the elongation at break and hardness as described in JP-A-7-244220. Further, the transmission performance can be further improved by providing a low refractive index layer on the outer periphery of the clad and making it function as a reflective layer as in JP-A-8-54521 for the POF obtained by the present invention. . By appropriately controlling the various stretching conditions as described above, the orientation of the polymer constituting the POF can be controlled, and the mechanical properties such as the bending performance of the POF and the heat shrinkage can be controlled.

  Examples of the organic material having high light transmittance used as the material of the clad and core constituting the preform 17 and the POF 25 include (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), Examples include those obtained by polymerizing fluorinated (meth) acrylic acid ester (b)), styrene compounds (c), vinyl esters (d), bisphenol A, which is a raw material for polycarbonates, as a polymerizable compound. The As the clad forming polymer, polyvinylidene fluoride (PVDF) can also be preferably used. Examples of homopolymers obtained by polymerizing each of these as raw materials, copolymers obtained by combining two or more of these, and mixtures obtained by various combinations of the homopolymers and the copolymers are given as examples. Can be mentioned. In the case of using the mixture, the boiling point Tb of the mixture is set to the lowest temperature among the boiling points of the plurality of raw material compounds constituting the mixture, and when the boiling point is lowered by forming an azeotropic mixture, Is defined as the temperature of Moreover, in the case of the copolymer and blend polymer obtained by using the said mixture as a raw material, the glass transition point of each copolymer or blend polymer is defined as boiling point Tg. Among these, those containing a (meth) acrylic acid ester or a fluorine-containing polymer as a component are more preferable for constituting an optical transmission body.

  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, cyclohexyl methacrylate. , Diphenylmethyl methacrylate, tricyclo [5.2,1.02,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, and the like, methyl acrylate, ethyl acrylate, acrylic acid-tert. -Butyl, phenyl acrylate and the like are exemplified.

  Examples of the (b) fluorine-containing acrylic 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, 2,2,3 , 3,4,4-hexafluorobutyl methacrylate and the like.

  Examples of the (c) styrene compound include styrene, α-methylstyrene, chlorostyrene, and bromostyrene. Furthermore, examples of the (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, and vinyl chloroacetate. However, it is not limited to these. In addition, when the refractive index of a polymer composed of a polymerizable compound alone or a copolymer is molded into an optical transmission body, the type and composition ratio are determined so as to have a predetermined refractive index distribution in the molded body. It is preferable to do.

  Moreover, as a preferable polymer which forms the clad 12, it is preferable that it is a polymer which shows a refractive index lower than a core, and it does not specifically limit. For example, a copolymer of methyl methacrylate (MMA) and a fluorinated (meth) acrylate such as trifluoroethyl methacrylate (FMA) or hexafluoroisopropyl methacrylate can be used. Examples of copolymers of MMA and alicyclic (meth) acrylates such as (meth) acrylate having a branch such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, tricyclodecanyl methacrylate, etc. Is done. Furthermore, polycarbonate (PC), norbornene resin (for example, ZEONEX (registered trademark: manufactured by ZEON CORPORATION)), functional norbornene resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin ( For example, it is possible to use polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc., as well as copolymers of fluororesins (for example, PVDF copolymers), tetrafluoroethylene perfluoro (alkyl vinyl ether) (PFA) random copolymer, chlorotrifluoroethylene (CTFE) copolymer, etc. can also be used, and the hydrogen atom (H) of these polymers is replaced with deuterium atom (D) to reduce transmission loss. Reduction can also be achieved.

  When the optical member is used for near-infrared light, a transmission loss (absorption loss) occurs due to the C—H bond constituting the core through which light passes. For the purpose of avoiding this phenomenon, a polymer in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or fluorine as described in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708 Can be used. When the polymer is used, the wavelength range that causes the transmission loss can be increased, so that the loss of transmission signal light can be reduced. Examples of the polymer include deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP2-FA), and the like. In addition, in order that the compound used as the raw material of the polymer does not impair the transparency after polymerization, it is desirable that impurities and foreign substances serving as a scattering source are sufficiently removed before polymerization.

  Polymerization initiators that generate radicals include benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), and tert-butylperoxyisopropyl carbonate. Examples thereof include peroxide compounds such as (PBI) and 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) are exemplified. The polymerization initiator is not limited to these. Moreover, one type may be used independently and two or more types may be used together, and it does not specifically limit.

  It is preferable to adjust the degree of polymerization in order to keep various physical property values such as mechanical properties and thermophysical properties as a polymer uniform throughout. A chain transfer agent may be used as a means for adjusting the degree of polymerization. About the said chain transfer agent, according to the kind of polymerizable monomer used together, a kind and addition amount can be selected suitably. For the chain transfer constant of the chain transfer agent for each monomer, reference can be made to, for example, Polymer Handbook 3rd edition (edited by J. BRANDRUP and EH IMMERGUT, published by JOHN WILEY & SON). In addition, the chain transfer constant can be obtained by an 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 (eg, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan), thiophenols (thiophenol, m-bromo). Thiophenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used, and in particular, an alkyl mercaptan of n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan is preferably used. preferable. 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. In addition, the said chain transfer agent is not limited to these, Furthermore, 1 type may be used independently and 2 or more types may be used together.

  Since the GI-type POF is excellent in transmission performance and can perform broadband optical communication as compared with other types of POF, it can be preferably used for high-performance communication applications. Examples of a method for imparting a refractive index distribution include a method of incorporating a plurality of polymer units into a core polymer, a method of using a copolymer further combining these polymers, and a method of adding a dopant. In the present embodiment, the GI POF is shown, but the present invention is also effective for all POFs other than the GI POF.

The dopant is a compound having a refractive index different from that of the polymerizable compound as described above. The difference in refractive index between the dopant and the polymerizable compound is preferably 0.005 or more. The polymer containing the dopant has a property that the refractive index is higher than that of the polymer to which the dopant is not added. In the dopant, as described in Japanese Patent No. 3332922 and JP-A-5-173026, the difference from the solubility parameter in comparison with the polymer formed by monomer synthesis is 7 (cal / cm ³ ) ^{1/2 or} less, and the difference in refractive index is 0.001 or more. In addition, the polymer containing the dopant has a property of changing the refractive index as compared with the additive-free polymer, can stably coexist with the polymer, and is a polymerization that is the aforementioned raw material. The compound is not particularly limited as long as it is stable under the polymerization conditions (polymerization conditions such as heating and pressurization) of the functional monomer, and any compound can be used as the dopant.

  In the present embodiment, the dopant is contained in the inner core monomer or the core monomer, and in the polymerization step, the progress direction of the polymerization is controlled by the interfacial gel polymerization method, and the concentration of the refractive index adjusting agent is inclined. And a method of forming a refractive index distribution structure based on the concentration distribution of the refractive index adjusting agent on the core was used. However, other than that, a method of diffusing a refractive index adjusting agent after forming a preform is also known and can be preferably used (hereinafter, a core having a refractive index distribution is referred to as a “refractive index distribution type core”). The optical member obtained by forming the gradient index core is 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), biphenyl (DP), and diphenylmethane. (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO) and the like are exemplified, and among them, BEN, DPS, TPP, DPSO are preferably used. The dopant may be a polymerizable compound such as tribromophenyl methacrylate. In that case, when forming the polymer matrix, it is more difficult to control various properties (particularly optical properties) by copolymerizing the polymerizable monomer and the polymerizable dopant. However, it may be advantageous in terms of heat resistance. Further, the refractive index of the plastic optical fiber can be changed to a desired value by adjusting the concentration and distribution of the dopant in the core portion.

  Other additives can be added to the core, the cladding, or a part thereof as long as the optical transmission performance is not deteriorated. For example, a stabilizer can be added to the core or a part thereof for the purpose of improving weather resistance and durability. Further, for the purpose of improving optical transmission performance, a stimulated emission functional compound for optical signal amplification can be added. By adding these compounds, it is possible to amplify the attenuated signal light with the pumping light, thereby improving the transmission distance, so that it may be used as a fiber amplifier in a part of the optical transmission link. In addition, the additive can be contained in the core, the clad, or a part thereof by polymerizing after being added to the various polymerizable compounds as the raw material.

  As described in Japanese Patent No. 3332922, as a method for producing a GI POF preform, a resin hollow tube serving as a cladding is produced, and a resin composition for forming a core is injected 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. In this case, the polymerization conditions such as the polymerization temperature and the polymerization time vary depending on the monomers and polymerization initiators used, but preferably the polymerization temperature is 60 ° C. or higher and is not higher than the glass transition point of the polymer to be produced. In general, the temperature is preferably 60 ° C. or higher and 150 ° C. or lower. The polymerization time is preferably 5 hours or more and 72 hours or less, and more preferably 5 hours or more and 48 hours or less. Furthermore, it is preferable to perform the polymerization reaction 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 having no variation in density can be formed. In addition, a method for forming a core in which polymerizable compositions having different refractive indexes after polymerization are sequentially added is also known, and this method can also be used in the present invention. Regarding the resin composition, as described above, a resin composition having a single refractive index to which a refractive index adjusting agent is added, a resin having a different refractive index, or a copolymer is used.

  POF has improved product value by bending, improving weather resistance, suppressing performance degradation due to moisture absorption, improving tensile strength, imparting stepping resistance, imparting flame resistance, protecting against chemical damage, preventing noise from external light, and coloring. For the purpose of improvement or the like, the surface is usually coated with one or more protective layers.

  A plastic optical cable (hereinafter referred to as an optical cable) is manufactured by coating an optical fiber core (optical fiber cord). However, a POF bundled and coated as it is may be referred to as an optical cable. Therefore, as a form of coating, there are a contact-type garment coated in a state where the interface between the coating material and the POF is in contact with the entire circumference, and a loose type coating having a gap at the interface between the coating material and the POF. . In loose type coating, for example, when the coating layer is peeled off at the connection with the connector, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction. In general, it is preferably a close-contact type coating.

  However, in the case of loose type coating, since the coating material and the POF are not in close contact with each other, most of the stress applied to the optical cable and damage such as heat can be alleviated by the coating layer. For this reason, damage to the POF can be reduced, so that it can be preferably used depending on the application. As for the propagation of moisture, moisture propagation from the end face can be prevented by filling the gap with a gel-like semi-solid or powder having fluidity. Moreover, a coating with higher performance can be formed by imparting functions different from the prevention of moisture propagation, such as heat resistance and improvement of mechanical functions, to these semi-solids and granular materials. In order to produce a loose-type coating, the gap layer can be formed by adjusting the position of the extrusion nipple of the crosshead die and further adjusting the pressure reducing device. The thickness of the gap layer can be adjusted by pressurizing / depressurizing the nipple thickness and the gap layer.

  As a covering material used for covering, there is a thermoplastic resin material. Examples of the thermoplastic resin material include polyethylene (PE) polypropylene (PP), vinyl chloride (PVC), ethylene vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polyester, nylon, and the like. Illustrated. In addition to the thermoplastic resin material, various elastomers can be used. Since the elastomer has high elasticity, it is also effective from the viewpoint of imparting mechanical properties such as bending. Examples of the elastomer include various rubbers such as isoprene-based rubber, butadiene-based rubber, and diene-based special rubber, and fluidity at room temperature, but the fluidity disappears when heated, such as polydiene-based and polyolefin-based Examples include liquid rubber or various thermoplastic elastomers (TPE) which are a group of substances that exhibit rubber elasticity at room temperature but are plasticized at high temperatures and can be easily molded. Moreover, what hardens the liquid which mixed the polymer precursor, the reactive agent, etc. can also be used. For example, 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.

  The above-described coating material is not particularly limited as long as it can be molded at a glass transition temperature Tg or lower of the polymer used for POF, and is a copolymer or mixed polymer between materials or other than the above. Can also be used in combination. In addition, for the purpose of improving performance, additives such as flame retardants, antioxidants, radical scavengers, lubricants, and various fillers made of inorganic compounds or organic compounds can be used.

  In the POF according to the present invention, if necessary, the protective layer may be a primary coating layer, and a secondary (or multilayer) coating layer may be further provided on the outer periphery. When the primary coating layer has a sufficient thickness, thermal damage can be reduced by the presence of the primary coating layer, so the limitation on the curing temperature in the material of the secondary coating layer is Compared with the case where the primary coating layer is coated, it can be relaxed. As described in the coating material, additives such as a flame retardant, an ultraviolet absorber, an antioxidant, a radical scavenger, and a lubricant may be introduced into the secondary coating layer.

  Examples of the flame retardant include halogen-containing resins such as bromine, additives, and phosphorus-containing materials. From the viewpoint of safety such as reduction of toxic gases during combustion, aluminum hydroxide and magnesium hydroxide A metal hydroxide such as can also be preferably used. The metal hydroxide has moisture as crystallization water inside, and the adhering water in the production process cannot be completely removed, so that the metal hydroxide is not a low hygroscopic wire or a lower coating layer. In the flame retardant coating with the metal hydroxide, it is desirable to provide a moisture-resistant coating on the outer layer of the primary coating layer, and further provide a coating layer on the outer layer. As flame retardancy standards, UL (Underwriters Laboratory) has determined several test methods, and CMX (combustion test is generally referred to as VW-1 test) from the order of low flame retardancy, Grades such as CM (vertical tray combustion test), CMR (riser test), and CMP (plenum test) are set. In the case of a coating on a plastic optical fiber, since the plastic optical fiber as a core material is made of a flammable material, it is intended to prevent the spread of fire in the event of a fire. A cable is preferred.

  Moreover, in order to give a several function to a coating layer, you may laminate | stack the coating | cover which has various functions further. In addition to the above-mentioned flame retardant, for example, it can have a moisture absorbing tape or moisture absorbing gel as a barrier layer for suppressing moisture absorption or a moisture absorbing material for removing moisture, between the inside of the coating layer or between the coating layers, A cushioning material such as a flexible material layer or a foamed layer for the purpose of stress relaxation at the time of flexibility, or a reinforcing layer for the purpose of improving rigidity can be selected and provided depending on the application. In the case of using a material in which a thermoplastic resin contains a wire material such as a fiber having a high elastic modulus (tensile strength fiber) or a highly rigid metal wire as a structural material other than resin, a cable made of the material is used. It is preferable to use it because the mechanical strength can be reinforced. Examples of the tensile strength fibers include aramid fibers, polyester fibers, and polyamide fibers. Examples of the metal wires include stainless steel wires, zinc alloy wires, and copper wires. Both the tensile strength fiber and the metal wire are not limited to the materials described above. It is also possible to incorporate a mechanism intended to improve the workability at the time of the exterior of the metal tube for the purpose of protection, an aerial support line or wiring.

  Depending on the application, the shape of the plastic optical cable can be POF or plastic optical fiber cores assembled in a concentric circle, tape-types arranged in a row, or press-wound or wrap sheath. You can select a summary.

  In the optical device using the POF obtained by the present invention, it is preferable to securely fix the connecting portion by using an optical connector for connection at the end portion. As the optical connector for connection, commercially available products such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type can be used. Further, the POF obtained by the present invention is combined with an optical signal processing device including optical components such as various light emitting elements, light receiving elements, optical switches, optical isolators, optical integrated circuits, and optical transceiver modules. You may combine with another optical fiber etc. as needed. Any known technique can be applied as the technique related to the combination. For example, refer to the basics and actuality of plastic optical fiber (issued by NTS), Nikkei Electronics 2001.1.2.3, pages 110-127 “Optical components are mounted on printed circuit boards. Can do. By combining POF with various technologies described in the above documents, internal wiring in computers and various digital devices, internal wiring of vehicles and ships, optical terminals and digital devices, optical links between digital devices, Light suitable for short distances such as high-speed, large-capacity data communication and control applications that are not affected by electromagnetic waves, including indoor and regional optical LANs in general homes, apartment houses, factories, offices, hospitals, schools, etc. It can be preferably used in a transmission system.

  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; , Japanese Patent Application Laid-Open No. 2002-90571, Japanese Patent Application Laid-Open No. 2001-290055, etc .; Japanese Patent Application Laid-Open No. 2001-74971, Japanese Patent Application Laid-Open No. 2000-329962, Japanese Patent Application Laid-Open No. 2001-74966, Japanese Patent Application Laid-Open No. 2001-2001 -74968, JP-A-2001-318263, JP-A-2001-31840, etc .; optical branch couplers described in JP-A-2000-241655; optical star couplers described in JP-A-2000-241655; No., JP-A No. 2002-101044, JP-A No. 2001-305395, etc. Optical signal transmission device and optical data bus system; optical signal processing device described in JP-A No. 2002-23011; optical signal cross-connect system described in JP-A No. 2001-86537 etc .; described in JP-A No. 2002-26815 Optical transmission systems; multi-function systems described in JP 2001-339554 A, JP 2001-339555 A, etc .; various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers By combining with an optical device, a more advanced optical transmission system using multiplexed transmission / reception can be constructed. In addition to these optical transmission applications, it can be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

  A PVDF hollow tube having an inner diameter of 18.7 mm and a length of 90 cm produced by melt extrusion molding was used as a clad 12, and a raw material for an outer core was injected into this hollow portion. The raw material for the outer core is a fully deuterated methyl methacrylate (MMA-d8) as a radically polymerizable compound with water removed to 400 ppm or less by distillation (Tg as a fully deuterated polymethyl methacrylate (PMMA-d8)); 204.1 g of 80 ° C. to 115 ° C.) and dimethyl 2,2′-azobis (2-methylpropionate) (trade name; V-601, manufactured by Wako Pure Chemical Industries, Ltd.) (70 A half-life time at 5 ° C .; 5 hours) and n-lauryl mercaptan as a chain transfer agent. The mixture was injected after adjusting to a predetermined temperature. The addition rates of dimethyl 2,2′-azobis (2-methylpropionate) and n-lauryl mercaptan with respect to MMA-d8 were 0.012 mol% and 0.2 mol%, respectively. The clad 12 into which the raw material for the outer core is injected is accommodated in a polymerization vessel 38, the polymerization vessel 38 is set on a rotating device 41 so that the longitudinal direction is horizontal, and the atmosphere at 60 ° C. is rotated at 500 rpm. Heat polymerization was performed for 2 hours under the following conditions, followed by rotation at 3000 rpm for 16 hours in an atmosphere at 60 ° C. and further for 4 hours in an atmosphere at 90 ° C. while rotating at 3000 rpm. At this time, an ungrounded thermocouple was provided in the vicinity of the rotating polymerization vessel 38, 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. Then, a layer made of PMMA was formed on the inner surface of the clad 12, and this layer was used as the outer core 32.

  The raw material for the inner core was injected into the hollow part of the outer core 32 under normal temperature and normal pressure. The raw material for the inner core is 81.7 g of MMA-d8 with moisture removed to 400 ppm or less, dimethyl 2,2′-azobis (2-methylpropionate) (V-601) as a polymerization initiator, chain A mixture obtained by mixing n-lauryl mercaptan as a transfer agent and diphenyl sulfide (DPS) as a dopant was used. Note that DPS is a non-polymerizable compound. The addition ratios of 2,4-dimethylvaleronitrile, n-lauryl mercaptan and DPS to MMA were 0.04 mol%, 0.2 mol% and 7 wt%, respectively. Next, the clad 12 is set in the rotating device 41 so that the longitudinal direction is horizontal, and rotated at 70 ° C. for 5 hours while rotating at a rotation speed of 2000 rpm, and then rotated at a rotation speed of 500 rpm. Polymerization was carried out under an atmosphere of 90 ° C. for 5 hours to obtain a preform 17 as a base material for GI POF.

  While the preform 17 was inserted into the polymerization vessel, the rotating device 41 was annealed at 120 ° C. and a rotation speed of 500 rpm for 24 hours. After the annealed preform 17 was stored in a desiccator, it was further melt-stretched in a stretching step 22 to produce POF25.

  A preform 17 manufactured using the same manufacturing conditions (including method) and materials as in Example 1 was annealed and stored, and further stretched in a stretching step 22 to manufacture POF25. However, while the annealing conditions for the preform 17 were the same as those in Example 1, the rotating apparatus 41 was annealed in a state where the preform 17 was placed on the polymerization vessel 38 and supported without being rotated.

  After producing the preform 17 using the same production conditions (including method) and materials as in Example 1, the preform 17 was stored without annealing, and the preform 17 was stretched by the stretching step 22 to produce POF25. .

  After producing the preform 17 using the same production conditions (including method) and materials as in Example 1, the preform 17 is left standing in a state where the preform 17 is stood in a constant temperature bath while maintaining the same heating temperature and heating time as in Example 1. Then, annealing was performed without rotating. Further, the preform 17 was stretched by the stretching step 22 to produce POF25.

  A preform 17 manufactured using the same manufacturing conditions (including method) and materials as in Example 1 was annealed and stored, and further stretched in a stretching step 22 to manufacture POF25. However, the annealing condition for the preform 17 was set to 150 ° C. for 24 hours, and the rotating apparatus 41 was annealed in a state where the preform 17 was placed on the polymerization vessel 38 and supported without being rotated.

〔Evaluation methods〕
In each Example, the deformation in the core layer of the preform 17 after the annealing treatment was obtained, and the influence of the annealing treatment on the preform 17 was evaluated. As deformation in the core layer, uneven thickness and non-circularity of the circular cross section of the hollow portion were determined. The uneven thickness is the ratio of the difference between the maximum and minimum measured thicknesses in the same plane (the ratio of unevenness of the surface shape). In this embodiment, the uneven thickness ratio in the preform 17 is visually determined. The case where the uneven thickness was not confirmed by visual observation was evaluated as ◯, and the case where the uneven thickness was confirmed by visual inspection was evaluated as x. In the non-circularity, the long side x1 and the short side x2 of the cross-sectional diameter of the hollow portion in the preform 17 before and after the annealing treatment are measured, and the non-circularity before the annealing treatment is calculated as P1, annealing according to the above formula (II). The non-circularity after the treatment was determined as P2, respectively.

  The evaluation results and execution conditions in each example are shown in Table 1.

  In Example 1, it was not possible to confirm the uneven thickness of the core layer (◯). Moreover, P1 was 0.36% and P2 was 0.37%, the difference between the two was small, and the non-circularity did not deteriorate. In Example 2, the uneven thickness of the core layer was confirmed (x). Moreover, P1 was 0.78% and P2 was 2.14%, and the non-circularity rate deteriorated. In Example 3, it was not possible to confirm the uneven thickness of the core layer and changes in the non-circularity. However, since annealing was not performed, there was a problem of foaming during melt stretching. In Example 4, an uneven thickness of the core layer was confirmed (x), and a large non-circularity value was obtained. Also in Example 5, the uneven thickness of the core layer was confirmed (x), and a large non-circularity value was obtained.

  When annealing was performed while rotating the preform 17 as in Example 1, it was not possible to confirm uneven thickness and deterioration of non-circularity despite the annealing. On the other hand, as in Example 2, when annealing was performed without rotating, uneven thickness and deterioration of non-circularity occurred. Further, as in Example 3, the POF 25 produced without annealing treatment had problems such as being unable to be stretched due to foaming during melt stretching. In Example 4, the annealing was performed without supporting the polymerization vessel 38 in the direction of the cylinder axis and without rotating around the axis of the circular tube. In this case, both uneven thickness and non-circularity were inappropriate. A good value was obtained. In Example 5, the annealing temperature was raised to 150 ° C., and the annealing process was performed without rotating. At this time, the non-yen rate worsened further. Therefore, in order to obtain a POF with a small unevenness and a small non-circularity, the cylindrical axis of the polymerization vessel 38 is made substantially horizontal, and the preform is rotated while being supported with this axis as the center of rotation, and annealing treatment is performed. However, it turned out to be very effective.

It is the schematic which shows the manufacturing process of the plastic optical fiber in this invention. It is sectional drawing of the preform in this invention. It is a figure which shows the refractive index in the cross-sectional radial direction of the preform of FIG. It is sectional drawing of POF. It is a figure which shows the refractive index in the cross-sectional radial direction of POF of FIG. It is sectional drawing of a superposition | polymerization container. It is the schematic of a rotation apparatus. It is explanatory drawing about the rotation method of a superposition | polymerization container. It is the schematic regarding the extending | stretching method of POF.

Explanation of symbols

16 Inner Core Polymerization Step 31 Preform Core 38 Polymerization Container 41 Rotating Device 43 Support Rotating Member 131 POF Core 132 POF Outer Core 133 POF Inner Core

Claims (7)

A refractive index distribution type in which a polymerizable compound is injected into a hollow first member to form a second member serving as a light guide in the first member by a polymerization reaction in which the polymerizable compound is polymerized. In the manufacturing method of plastic optical fiber preform,
A refractive index profile comprising: an annealing process in which the plastic optical fiber preform is heated at a temperature equal to or higher than the glass transition temperature of the second member while rotating in the circumferential direction of the first member. Method for manufacturing a plastic optical fiber preform.   2. The method of manufacturing a gradient index plastic optical fiber preform according to claim 1, wherein the annealing treatment is performed so that a noncircularity of a hollow portion of the plastic optical fiber preform is 2% or less.   3. The method of manufacturing a graded index plastic optical fiber preform according to claim 1, wherein the annealing is performed by rotating the plastic optical fiber preform while being held substantially horizontally.   4. The method of manufacturing a plastic optical fiber preform according to claim 3, wherein the plastic optical fiber preform is inserted into a hollow holding member during the annealing process.   5. The method of manufacturing a graded index plastic optical fiber preform according to claim 3, wherein the number of rotations during the annealing treatment is 10 rpm or more and 5000 rpm or less.   The second member includes at least one substance having a refractive index difference of 0.001 or more in comparison with the polymer constituting the second member, and the substance has a concentration gradient along a specific direction. 6. The method of manufacturing a graded index plastic optical fiber preform according to claim 1, wherein the refractive index distribution type plastic optical fiber preform is distributed. A gradient index plastic optical fiber obtained by stretching a gradient index plastic optical fiber preform obtained by the manufacturing method according to claim 6.

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