JP2005321720A - Manufacturing method and apparatus of clad pipe for optical member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method and apparatus of a clad pipe for optical member which has excellent uniformity of thickness in the peripheral direction and suppresses the deterioration of transmission loss of an optical fiber obtained by using the clad pipe for optical member. <P>SOLUTION: Fused PVDF is extruded from an extrusion dice 43 as a fused pipe 44. A plurality of heaters are attached to an adjustment part 51 of the extrusion dice 43. The fused pipe 44 is sent to a cooling vacuum unit 46 through a sizing dice 45. The outer peripheral surface of the fused pipe 44 is leveled, cooled and solidified by the cooling vacuum unit 46. A cooled pipe 48 is sent out via a vacuum seal 47. The thickness of the cooled pipe 48 is measured by a thickness/outer diameter measuring instrument 49. The measured value is transmitted to a controller 50. The optimum temperature of each heater is calculated such that the thickness of the cooled pipe 48 is made uniform by an arithmetic section 90 of the controller 50. A control section 91 controls the temperature of each heater in accordance with the calculated value. Fine adjustment of pipe thickness by means of the heater is always performed during the manufacture of the clad pipe. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for manufacturing a clad pipe for an optical member.

  In recent years, with the development of the communication industry, the demand for optical fibers has increased, transmission loss is low, and low cost is required. The plastic optical member has advantages such as easy manufacture and processing and low cost compared to the quartz optical member having the same structure. In particular, the plastic optical fiber has a disadvantage that the transmission loss is slightly larger than that of the silica-based optical fiber because the material is made entirely of plastic. However, it has the advantages of having good flexibility, light weight, good workability, and easy manufacturing of an optical fiber having a large diameter compared to a quartz optical fiber. Further, it has an advantage that it can be manufactured at low cost. Therefore, various studies have been made on optical transmission bodies for short distances where the magnitude of transmission loss is not a problem (see, for example, Patent Document 1).

  A plastic optical fiber (hereinafter also referred to as POF) includes a plastic core (hereinafter referred to as a core or core portion) and an outer shell (hereinafter referred to as a cladding or cladding portion) made of plastic having a lower refractive index than the core portion. It is composed of As one method for producing POF, a method is known in which a pipe-shaped clad portion (hereinafter referred to as a clad pipe) is formed by a melt extrusion method, and a core portion is formed in the clad pipe. In particular, a refractive index distribution type (graded index type; hereinafter referred to as GI type) POF having a core part having a distribution of refractive index from the center toward the outside increases the band of the optical signal to be transmitted. Therefore, it has recently been attracting attention as an optical fiber having a high transmission capacity. As one of the methods for producing such GI-type POF, there has been proposed a method of producing a preform (base material) using an interfacial gel polymerization method and then stretching the preform (for example, , See Patent Document 2).

  In the clad pipe, the uniformity of the pipe thickness (wall thickness) in the circumferential direction is important. If the thickness of the pipe in the circumferential direction is not constant, the diameter of the POF may not be constant in the stretching process of stretching the preform to obtain POF. In such a case, the optical performance of the obtained POF is reduced, and the fluctuation of the diameter is greatly unstable, resulting in a decrease in the yield.

  FIG. 7 shows a cross-sectional view of an extrusion die 100 used in the conventional melt extrusion method. The clearance between the inner lip 101 and the outer lip 102 becomes the resin flow path 103 of molten resin. Further, the inner lip 101 and the outer lip 102 are inserted into the cylinder 104. Adjustment screws 105, 106, 107, and 108 are attached to the cylinder 104. The resin flow path 103 is decentered by adjusting the clearance by moving the outer lip 102 with the adjusting screws 105 to 108. In this way, a lip adjustment operation is performed to adjust the resin flow rate in the circumferential direction to make the pipe thickness as uniform as possible.

  Furthermore, it has a sensor that measures the thickness distribution in the circumferential direction, a device that calculates the mold correction value, an adjustment mechanism that moves the mold, and a system that automatically adjusts the thickness using a displacement sensor that measures the amount of movement. A method is known (for example, refer to Patent Document 3). There is also known a method in which a cooled inert gas is sprayed and solidified on a parison (cylindrical material) injected or extruded from an extrusion die (see, for example, Patent Document 4). Alternatively, a method is known in which a supporter having a swingable supporter ring is attached to an extrusion mold and the inner diameter of the synthetic resin is defined by the supporter ring (see, for example, Patent Document 5). Further, there is also known a method in which a rotatable cylinder having a protrusion on the inner surface is installed downstream of the extruder and the resin flowing inside is homogenized by rotating the cylinder (see, for example, Patent Document 6). ).

JP-A-61-130904 Japanese Patent No. 3332922 Japanese Patent Laid-Open No. 5-116201 JP-A-6-170923 JP-A-6-304991 JP 2000-141451 A

  However, as shown in FIG. 7, the adjustment of the resin flow path 103 with the adjustment screws 105 to 108 is suitable for coarse adjustment because the adjustable portion is limited and mechanical adjustment is performed. However, there are drawbacks such as that fine adjustment is very difficult. Therefore, it has been difficult to form a pipe with extremely high thickness uniformity. In addition, many plastic pipes manufactured by the methods described in Patent Documents 3 to 6 are used for water distribution pipes, and as a technique for improving the uniformity of wall thickness, accuracy required for molding of clad pipes is not necessarily required. Cannot be achieved.

  An object of this invention is to provide the manufacturing method and apparatus of the clad pipe for optical members excellent in the thickness uniformity of the circumferential direction. Another object of the present invention is to suppress the deterioration of transmission loss of an optical fiber obtained using the clad pipe for an optical member.

  In order to form a clad pipe for an optical member that is stable and excellent in thickness uniformity regardless of the diameter and thickness of the pipe, the present inventor, in addition to rough adjustment of the lip clearance with an adjustment bolt, By arranging a plurality of heaters in the circumferential direction on the outer peripheral surface of the extrusion die, adjusting the viscosity of the resin flowing inside the extrusion die by finely adjusting the temperature of each heater individually, and adjusting the flow rate in the circumferential direction It has been found that the thickness uniformity of the pipe in the circumferential direction can be improved.

  It is desirable that the number of heaters arranged on the outer peripheral surface of the extrusion die is as large as possible. However, if the number increases, the output of each heater is lowered and a desired output cannot be obtained. The number of heaters is preferably 4 or more and 24 or less because problems such as complicated wiring and deterioration in workability occur. However, in order to obtain an optimum output value, 8 or more and 16 or less are more desirable.

  The method for producing a clad pipe for optical members of the present invention is a method for producing a clad pipe for optical members by extruding a molten polymer from an extrusion die, and a plurality of clearance adjusting means are provided along the outer peripheral surface of the extrusion die. The plurality of clearances are individually adjusted, and the circumferential thickness of the clad pipe is adjusted.

  The method for producing a clad pipe for optical members of the present invention is a method for producing a clad pipe for optical members by extruding a molten polymer from an extrusion die, and a plurality of heaters are provided along the outer peripheral surface of the extrusion die. Measuring the thickness of the clad pipe, calculating each optimum temperature of the plurality of heaters from the measured thickness value, individually adjusting the temperature of the plurality of heaters based on the calculated value, Adjust the wall thickness in the circumferential direction of the pipe. Preferably, a plurality of clearance adjusting means are provided along the outer peripheral surface of the extrusion die, and the adjustment of the plurality of clearances and the temperature adjustment of the plurality of heaters are performed simultaneously. The clearance adjusting means may adjust the clearance of the heater.

  The clad pipe is preferably a plastic optical fiber clad pipe. The present invention also includes an optical member clad pipe manufactured by the method for manufacturing an optical member clad pipe. The present invention also includes an optical member preform in which a core having a refractive index higher than the refractive index of the clad pipe is formed in the clad pipe for optical member produced by the method for producing a clad pipe for optical member. . In the present invention, a clad pipe for an optical member is produced by the method for producing a clad pipe for an optical member, and a core having a refractive index higher than that of the clad pipe is formed in the clad pipe for an optical member. A plastic optical fiber obtained by producing a preform for an optical member and stretching the preform for an optical member is also included.

  An optical member clad pipe manufacturing apparatus of the present invention is an optical member clad pipe manufacturing apparatus including an extrusion die for extruding a molten polymer into a pipe shape, and a plurality of clearances provided along the outer peripheral surface of the extrusion die. An adjustment unit and a control unit that individually controls the plurality of clearance adjustment units are provided to adjust the circumferential thickness of the clad pipe.

  An optical member clad pipe manufacturing apparatus according to the present invention is an optical member clad pipe manufacturing apparatus including an extrusion die for extruding a molten polymer into a pipe shape, and a plurality of heaters provided along the outer peripheral surface of the extrusion die. A measuring device for measuring the thickness of the extruded clad pipe, a calculation unit for calculating each optimum temperature of the plurality of heaters from the measured thickness value, and the plurality of heaters based on the calculated value And a controller for individually controlling the temperature, and adjusting the circumferential thickness of the clad pipe. It is preferable to have a plurality of clearance adjusting means provided along the outer peripheral surface of the extrusion die, and a second control unit that controls the clearances of the plurality of clearance adjusting means.

  The heater is preferably a band heater, an aluminum cast heater, or a cartridge heater. The number of the plurality of heaters is preferably 4 or more and 24 or less.

  According to the method for producing a clad pipe for optical members of the present invention, in the method for producing a clad pipe for optical members by extruding a molten polymer from an extrusion die, a plurality of clearance adjusting means are provided along the outer peripheral surface of the extrusion die. Since the adjustment of the plurality of clearances is performed individually and the thickness of the clad pipe in the circumferential direction is adjusted, the viscosity and flow rate of the molten resin inside the extrusion die are adjusted to provide excellent thickness uniformity in the circumferential direction. In addition, a clad pipe for an optical member can be produced. Therefore, a plastic optical fiber having a small transmission loss can be stably produced without causing the optical fiber diameter to fluctuate and destabilize when the preform produced using this is drawn.

  According to the method for producing a clad pipe for optical members of the present invention, in the method for producing a clad pipe for optical members by extruding a molten polymer from an extrusion die, a plurality of heaters are provided along the outer peripheral surface of the extrusion die, Measure the wall thickness of the extruded clad pipe, calculate the optimum temperature of each of the plurality of heaters from the measured value of the wall thickness, and individually adjust the temperature of the plurality of heaters based on the calculated value, Since the thickness of the clad pipe in the circumferential direction is adjusted, it is possible to continuously manufacture the clad pipe for optical members having excellent thickness uniformity in the circumferential direction.

  In the past, putting the pipe thickness in the circumferential direction within the standard may be the rate-determining factor for manufacturing, but according to the method for producing a clad pipe for optical members of the present invention, the speed of adjusting the thickness in the circumferential direction is improved. Therefore, loss due to uneven thickness in the circumferential direction at the start of production can be reduced, and the yield can be improved.

  FIG. 1 shows a method of manufacturing a plastic optical fiber manufactured using a clad pipe according to the present invention. In the clad pipe production step 11, the clad pipe 12 is produced by melt extrusion of the raw material polymer. A method for manufacturing the clad pipe 12 will be described later in detail. Next, a liquid for forming an outer core containing a polymerizable composition (hereinafter referred to as an outer core liquid) is prepared, and the outer core polymerization step 13 is performed using the liquid, and the outer core is attached to the hollow portion of the clad pipe 12. Form. Further, a liquid for forming an inner core (hereinafter referred to as an inner core liquid) is prepared, an inner core polymerization step 14 is performed to form an inner core, and a preform 15 is obtained. The preform 15 is heated, melted and stretched in a stretching step 16 to obtain a plastic optical fiber (POF) 17. The POF 17 can be used as an optical fiber as it is. However, it is preferable to form a protective layer in order to facilitate handling and to prevent damage to the outer surface of the POF 17. The protective layer is formed by the coating step 18, and a plastic optical fiber core wire (hereinafter referred to as an optical fiber core wire) 19 in which a coating material is formed as a protective layer on the outer peripheral surface of the POF 17 can be obtained. Furthermore, it can also be used as an optical fiber cable in which a plurality of optical fiber cores are bundled.

  FIG. 2A shows one form of the cross section of the preform 15. The inner core 30 is preferably of a graded index type (hereinafter referred to as GI type) in which the refractive index continuously decreases from the central part to the outer peripheral part so as to obtain high transmission characteristics (hereinafter referred to as GI type). b)). When the inner core 30 is formed, the outer core 31 is formed of a material capable of interfacial gel polymerization. Hereinafter, the raw material and manufacturing method of the clad pipe according to the present invention will be described. Then, a method for producing a preform using the clad pipe and producing a POF and an optical fiber core from the preform will be described.

  The material constituting the clad is made of a material having a refractive index lower than that of the core portion. As long as the refractive index is low, the material used for the core part described later can also be used preferably. However, the fluororesin has a low refractive index, excellent transparency, flexibility, and mechanical strength. Is also excellent as a cladding for optical members. Further, since the fluororesin is generally hardly soluble in an organic solvent, the molding is mainly performed by melt molding at a high temperature. Examples of fluororesins include polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether. Examples thereof include a polymer (PFA), an ethylene-tetrafluoroethylene copolymer (ETFE), a polychlorotrifluoroethylene (PCTFE), a tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE), and the like.

  Among the fluororesins, polyvinylidene fluoride (PVDF) is preferably used, and a copolymer thereof is also preferably used. For example, a vinylidene fluoride-tetrafluoroethylene copolymer (preferably containing 50% by weight or more of vinylidene fluoride, more preferably containing 70% by weight or more and 90% by weight or less), vinylidene fluoride-hexafluoro Propylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-trifluoroethylene copolymer, and a ternary or more copolymer of vinylidene fluoride. The raw material for the clad pipe according to the present invention is not limited to the fluororesin.

  FIG. 3 shows an embodiment of a production line 40 used in the method for producing the clad pipe 12 according to the present invention. In addition, the manufacturing method which uses PVDF as a cladding pipe raw material is illustrated. A hopper 42 for charging PVDF, which is a raw material polymer, is attached to the extruder 41. The extrusion part 41a of the extruder 41 is heated to a range of 180 ° C. to 230 ° C. to melt the charged PVDF. The molten PVDF is extruded into a pipe shape from the extrusion die 43 using a screw (not shown) provided in the extrusion portion 41a. Hereinafter, this pipe is referred to as a melting pipe 44. The form of the extrusion die 43 will be described in detail later.

  The melting pipe 44 is passed through a sizing die 45 that molds its outer shape. The sizing die 45 is provided in the cooling vacuum device 46. The cooling vacuum device 46 includes a water supply device for supplying and discharging cooling water, a drainage device, and a vacuum device for reducing the pressure to a desired pressure. A vacuum seal 47 is provided at the pipe outlet of the cooling vacuum device 46, and the pressure in the cooling vacuum device 46 is adjusted to be within a desired pressure range. The outer peripheral surface of the melting pipe 44 is smoothed by the inner surface that is the molding surface of the sizing die 45. Moreover, it cools with cooling water and solidifies. The degree of vacuum and the temperature of the cooling water are not particularly limited, but are preferably 1 Pa to 35 Pa in absolute pressure and the temperature is 170 ° C. to 190 ° C. The pipe thickness (outer diameter) of the cooled pipe (hereinafter referred to as a cooling pipe) 48 sent out from the cooling vacuum device 46 is measured by a wall thickness / outer diameter measuring device 49. The measured value is transmitted to the controller 50, and the temperature of each heater attached to the adjusting unit 51 of the extrusion die 43 is adjusted.

  FIG. 4 shows a cross-sectional view of the extrusion die 43 taken along line IV-IV. Moreover, the principal part enlarged view of the manufacturing line 40 is shown in FIG. In the extrusion die 43, an inner lip 70 and an outer lip 71 are inserted into the cylinder 72. Adjustment screws 73, 74, 75, 76, 77, 78, 79, 80 for adjusting the clearance between the inner lip 70 and the outer lip 71 are attached to the adjusting portion 51 of the extrusion die 43. The clearance is adjusted by adjusting the degree of pushing and pulling of the adjusting screws 73-80. The clearance becomes a resin flow path 81 of molten resin. Adjustment of the resin flow path 81 is preferably performed using 1 to 8 adjustment screws, and most preferably 8 screws. The clearance adjustment with this adjustment screw is hereinafter referred to as coarse adjustment.

  Eight heaters 82, 83, 84, 85, 86, 87, 88, and 89 are attached to the adjustment unit 51 along the outer peripheral surface of the cylinder 72. A plurality of heaters 82 to 89 are attached, and the temperature of each is individually adjusted to change the flow rate of PVDF flowing in the resin flow path 81. As a result, the thickness of the pipe 53 can be finely adjusted. Hereinafter, this adjustment method is referred to as fine adjustment. The number of heaters is appropriately selected depending on the level at which the pipe thickness distribution is uniform, the outer diameter of the extrusion die 43, and the heater capacity. A larger number of attachments is preferable because fine adjustment of the temperature can be easily performed, but it also causes a high cost such as complicated wiring. Therefore, the number is preferably 4 or more and 24 or less, and more preferably 8 or more and 16 or less. The heaters 82 to 89 are not particularly limited, but it is preferable to use a band heater, an aluminum cast heater, a cartridge heater, or the like. In addition, the position where the adjustment unit 51 is attached to the extrusion die 43 is preferably on the downstream side from which the molten resin is extruded because the thickness of the pipe can be controlled more strictly. As shown in FIG. 5, the downstream end 51a of the control unit 51 may be attached so as to be at the same position as the downstream end 43a of the extrusion die. You may attach the front-end | tip 51a to the upstream from the extrusion die downstream front-end | tip 43a.

  A method for adjusting the temperature of the heaters 82 to 89 will be described. The thickness of the cooling pipe 48 is measured by a thickness / outer diameter measuring device 49 along the circumferential direction. Based on the measured value, the temperature of the heater corresponding to the thick portion is lowered. Further, the temperature of the heater corresponding to the portion where the wall thickness is thin is increased. Thereby, the flow rate of the molten PVDF in the resin flow path 81 is adjusted, and the pipe 53 having a constant thickness can be obtained.

  More preferably, the temperature control of the heaters 82 to 89 is automated. The measurement value of the wall thickness / outer diameter measuring device 49 is transmitted to the controller 50. The calculation unit 90 of the controller 50 calculates the temperature adjustment amounts of the heaters 82 to 89 based on the measured values. The calculated value is transmitted to the control unit 91. In the control part 91, the temperature adjustment signal of each heater 82-89 is transmitted according to a calculated value, and the temperature of each heater 82-89 is controlled. In this way, by measuring the thickness distribution of the cooling pipe 48 and performing fine adjustment by the heaters 82 to 89, the pipe 53 having a uniform thickness distribution can be continuously manufactured.

  The length of the extrusion die 43 in the molten resin feeding direction is L1 (mm). The length of the heaters 82 to 89 attached to the adjustment unit 51 is L2 (mm). These lengths L1 and L2 are not particularly limited, but when 200 mm ≦ L1 (mm) ≦ 300 mm, the length is preferably in the range of 40 mm ≦ L2 (mm) ≦ 60 mm. Alternatively, it is preferably in the range of 0.1 ≦ (L2 / L1) ≦ 0.4, more preferably 0.2 ≦ (L2 / L1) ≦ 0.3, and most preferably 0.2 ≦ (L2 / L1) ≦ 0.25. If (L2 / L1) is less than 0.1, the temperature of the molten resin may not be sufficiently adjusted. If (L2 / L1) exceeds 0.4, rough adjustment of the adjusting screws 73 to 80 may be difficult.

  A desired tension is applied to the cooling pipe 48 by the take-up machine 52 to obtain a pipe 53 with improved toughness. The take-up machine 52 is provided with a pair or a plurality of pairs of driving rollers 56 and 57 and nip rollers 58 and 59 to which motors 54 and 55 are connected. By conveying the cooling pipe 48 with a pair of rollers, tension can be applied to the cooling pipe 48. Then, the obtained pipe 53 is cut into a desired length and used as the clad pipe 12.

  The raw material of the core part for making the plastic optical fiber is particularly limited as long as the polymer is light-transmitting to the transmitted light and has a refractive index higher than that of the cladding part. Although it is not a thing, it is preferable to use the material with little transmission loss of the optical signal transmitted.

  Particularly preferably used are organic materials which are generally known as raw materials having high light transmittance, such as (meth) acrylic acid esters (fluorine-free (meth) acrylic acid esters (a), Fluorine (meth) acrylic acid ester (b)), styrene compound (c), vinyl esters (d), polycarbonates and the like can be exemplified, and these homopolymers or two or more of these monomers And a mixture of homopolymers and / or copolymers. Among these, those containing (meth) acrylic acid esters as a composition can be more preferably used.

Specific examples of the polymerizable monomer listed above include (a) fluorine-free methacrylic acid ester and fluorine-free acrylic acid ester: methyl methacrylate (MMA), ethyl methacrylate, isopropyl methacrylate, methacrylic acid-tert - butyl, include phenyl benzyl methacrylate (BzMA), methacrylate, cyclohexyl methacrylate, diphenylmethyl, tricyclo [5 · 2 · 1 · 0 ^2,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate and And methyl acrylate, ethyl acrylate, tert-butyl acrylate, phenyl acrylate, and the like. In addition, (b) fluorine-containing acrylic acid ester and fluorine-containing methacrylate ester include 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3 , 3-Pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2, 3,3,4,4-hexafluorobutyl methacrylate and the like. Furthermore, (c) styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, and the like. Furthermore, (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate and the like. Of course, it is not limited to these. The type and composition ratio of the constituent monomers are selected so that the refractive index of the polymer of the core portion made of a monomer alone or a copolymer is equal to or higher than that of the cladding portion. A particularly preferred polymer is polymethyl methacrylate (PMMA), which is a transparent resin.

  Furthermore, when the optical member is used for near-infrared applications, an absorption loss due to the C—H bond constituting the polymer of the core portion occurs, so that a deuterated polymer as described in Japanese Patent No. 3332922 and the like is used. Hydrogen atoms (H) of C—H bonds such as methyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl-2-fluoroacrylate (HFIP 2-FA), etc. By using a polymer substituted with a hydrogen atom (D), fluorine (F), or the like, the wavelength region causing this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. In addition, in order not to impair the transparency after polymerization of the raw material monomer, it is desirable to sufficiently reduce impurities and foreign substances that become scattering sources before polymerization.

  In the case of producing a polymer by polymerizing monomers, polymerization may be carried out with a polymerization initiator. In this case, as an initiator for initiating the polymerization reaction of the monomer, for example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert- Examples thereof include peroxide compounds such as butyl peroxide (PBD), tert-butyl peroxyisopropyl carbonate (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). Of course, the polymerization initiator is not limited to these, and two or more kinds may be used in combination.

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

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

  In the case of a GI cloth type plastic optical fiber in which the core part which is the center part of the plastic optical fiber has a refractive index distribution from the center of the core part toward the outer peripheral direction, the mode delay is eliminated and the transmission performance is improved. Broadband optical communication can be performed, and it can be preferably used for high-performance communication applications. As a method for imparting a refractive index distribution, a combination of polymers having a plurality of refractive indexes or a copolymer obtained by combining them is used for the polymer forming the core, or the refractive index distribution is applied to the polymer matrix. It is necessary to add a dopant which is an additive for imparting.

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

  Using the above-mentioned properties as a dopant that can stably coexist with the polymer and is stable under the polymerization conditions (polymerization conditions such as heating and pressurization) of the above-described raw material polymerizable monomer. Can do. In the present embodiment, the core portion-forming polymerizable composition contains a dopant, and in the step of forming the core portion, the progress of polymerization is controlled by the interfacial gel polymerization method, and the concentration of the dopant is given a gradient. A method of forming a refractive index distribution structure based on the dopant concentration distribution in the part is illustrated. In this way, the core portion having the refractive index distribution is referred to as a “refractive index distribution type core portion”. By forming the gradient index core portion, the obtained optical member becomes a gradient index plastic optical transmission body having a wide transmission band. In addition, a method of diffusing a dopant after forming a preform is also known. In addition, the dopant may be a polymerizable compound, and when a polymerizable dopant is used, a copolymer containing this as a copolymerization component has a property that the refractive index changes compared to a polymer not containing the copolymer. Use what has. For example, MMA-BzMA copolymer etc. are mentioned.

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

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

  The pipe 53 obtained by the above method is used as the clad pipe 12 by using the core material described above. A core portion as a buffer layer may be provided when the material of the cladding and the core is not compatible, or when the refractive index distribution region is desired to have an arbitrary size in design. Hereinafter, the core portion that is the buffer layer is referred to as an outer core. Moreover, the core part formed in an outer core is called an inner core. The outer core polymerization step 13 for forming the outer core 31 in the hollow of the clad pipe 12 will be described. The outer core liquid is prepared by adding a desired additive (for example, a polymerization initiator, a chain transfer agent, a dopant, etc.) containing a polymerizable monomer as a main component. The outer core 31 is formed on the inner surface of the clad pipe 12 by a rotational polymerization method so as to form a hollow cylinder for forming an inner core. In the rotation polymerization method, the outer core liquid is put into the hollow portion of the clad pipe 12. The clad pipe 12 is preferably preliminarily polymerized with shaking in warm water to increase the viscosity of the outer core liquid. Thereafter, the clad pipe 12 is held in a horizontal direction (a state in which the height direction of the clad pipe is horizontal), and rotational polymerization is performed while heating.

  Next, the inner core polymerization step 14 for forming the inner core 30 will be described. The inner core liquid is prepared by adding a polymerization initiator, a chain transfer agent, a dopant and the like to MMA which is a polymerizable monomer. Then, using this inner core liquid, gel polymerization described in Japanese Patent No. 3332922, gel polymerization proceeds as a result of the monomer impregnated into the polymer on the inner wall of the hollow tube and swelled / dissolved to eliminate the volume. The preform 15 can be obtained by forming a GI type (graded index type) inner core 30 by applying a method of forming a refractive index distribution by an effect (referred to as an interfacial gel polymerization method). 2). The form of the preform 15 is not particularly limited, but after forming the outer core 31 having a thickness t2 of 5.5 mm to 7 mm using a thickness t1 of the clad pipe 12 of 0.5 mm to 2 mm, the diameter It is preferable to form the inner core 30 having D of 12.2 mm to 13.7 mm. By using the preform 15 of this form, a POF 17 having excellent optical characteristics and mechanical strength can be obtained when a stretching process 16 described later is performed.

  FIG. 6 is a schematic view showing the form of the stretching step 16. The preform 15 is put in the heater 95 and melted. The heater 95 is composed of four sections 95a, 95b, 95c, and 95d that can be independently temperature controlled. POF 17 is obtained by stretching (drawing) the preform 15 at a desired speed.

  The method for producing the GI preform used in the present invention is not limited to the interfacial gel polymerization method as described above. As described above, as the resin composition, those in which a dopant is added to a resin composition having a single refractive index, those in which resins having different refractive indexes are mixed, copolymers, and the like are used. In addition to the GI type, plastic optical fibers having various refractive index profiles such as a step index type having a constant refractive index and a multi-step index type having a stepped refractive index are known. Can be applied to any of these plastic optical fiber manufacturing methods.

  In the present invention, the method for producing the core portion is not limited to the above method. For example, it can be formed by a rotational polymerization method in which interfacial gel polymerization is performed while rotating the inner core 30 of the preform 15 shown in FIG. In this case, after injecting the inner core liquid into the hollow of the clad pipe 12 in which the outer core 31 is formed, one end thereof is sealed and the horizontal state in the rotary polymerization apparatus (the height direction of the clad pipe is horizontal). Polymerization is carried out while rotating. At this time, the inner core liquid may be supplied all at once or sequentially or continuously. Manufacture of multi-step optical fiber with stepwise refractive index distribution in addition to GI type with continuous refractive index distribution by adjusting the supply amount, composition and polymerization degree of the polymerizable composition for inner core It can also be applied to. In the present invention, this polymerization method is referred to as a core part rotation polymerization method (core part rotation gel polymerization method).

  In the core part rotational polymerization method, the surface area of the core liquid can be increased as compared with the interfacial gel polymerization method during the polymerization, so that bubbles generated from the core liquid can be easily degassed. For this reason, it is possible to suppress the inclusion of bubbles in the obtained preform. Further, when the core part is formed by the core part rotational polymerization method, a preform having a hollow center part may be obtained. When the preform is used for a plastic optical member, particularly an optical fiber, there is no particular problem because the hollow is closed while being melt-drawn. Further, when the preform is used for another optical member, for example, a plastic lens, it is possible to obtain a preform in which the hollow of the central portion is closed by performing melt drawing so as to close the hollow portion of the preform. It is possible to produce a plastic lens or the like from this preform.

  By stretching the preform 15, a POF 17 having a desired diameter, for example, 100 μm or more and 1000 μm or less can be obtained. There is no restriction | limiting in particular regarding the manufacturing method performed at the extending | stretching process 16, A known method can be applied equally. In addition, the residual monomer and water | moisture content in a preform can be reduced by drying the preform 15 under reduced pressure before performing the extending | stretching process 16. FIG. Thereby, the generation | occurrence | production of the extending | stretching bubble which arises by the residual monomer and water | moisture content at the time of melt-heating extending | stretching volatilizing and foaming can be suppressed.

  In the stretching step 16, the preform 15 is heated and melted and stretched. The heating temperature can be appropriately determined according to the material of the preform 15 and the like. In general, it is preferably performed in an atmosphere at 180 ° C to 250 ° C. The stretching conditions (stretching temperature and the like) can be appropriately determined in consideration of the diameter of the preform 15, the diameter of the POF 17, the material used, and the like. For example, as described in JP-A-7-234322, the drawing tension is set to 0.1 N or more in order to orient the molten polymer, or described in JP-A-7-234324. Thus, in order not to leave distortion after melt drawing, it is preferable to be 1N or less. Further, as described in JP-A-8-106015, a method of providing preheating at the time of stretching can be used. Regarding the POF 17 obtained by the above method, the bending elongation and lateral pressure characteristics of the optical fiber cable described later can be improved by defining the breaking elongation and hardness as described in JP-A-7-244220.

  POF17 has improved product value by improving bending and weather resistance, suppressing performance degradation due to moisture absorption, improving tensile strength, imparting stepping resistance, imparting flame resistance, protecting from 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.

(Coating structure)
By covering the POF 17 and / or the optical fiber core wire 19, a plastic optical fiber cable (hereinafter referred to as an optical fiber cable) can be manufactured. In this case, as a form of the coating, there are a contact type coating in which the interface between the coating material and the POF is in contact with the entire circumference and a loose type coating having a gap between the coating material and the POF. In loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction.

  However, in the case of the loose type coating, since the coating material and the POF are not in close contact with each other, most of the damage such as stress and heat applied to the optical fiber cable can be alleviated by the coating layer. Therefore, damage to the POF can be reduced, and it can be preferably used depending on the purpose of use. As for the propagation of moisture, filling the voids with a gel-like semi-solid or powder having fluidity can prevent moisture from being transmitted from the end face. It is possible to form a coating with higher performance by having a function different from the prevention of moisture propagation such as improvement of mechanical function. In order to produce a loose-type coating, the gap layer can be formed by adjusting the position of the extrusion nipple of the cross die head and adjusting the degree of vacuum with a decompression device. The thickness of the void layer can be adjusted by adjusting the nipple thickness and the degree of vacuum.

  Specific examples of the protective layer forming material (coating material) used for these coatings include the following materials. As a general covering material, a thermoplastic resin material is exemplified. Examples of these materials are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), polyester, nylon Etc.

  Various elastomers can be used in addition to the thermoplastic resin. Since these have high elasticity, they are also effective in terms of imparting mechanical properties such as bending. Examples of these elastomers include various rubbers such as isoprene rubber, butadiene rubber, and diene special rubber. Further, liquid rubbers such as polydiene-based and polyolefin-based materials that exhibit fluidity at room temperature but are cured by heating to lose their fluidity can also be used. Furthermore, thermoplastic elastomer (TPE), which is a group of substances that exhibit rubber elasticity at room temperature and are plasticized at high temperatures and can be easily molded, can be used.

  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 be used.

  The listed materials are not limited to the above materials as long as they can be molded under conditions that do not affect the refractive index distribution structure of POF, and are combined between the materials or as a copolymer or mixed polymer other than the above. Can also be used. In addition, additives such as flame retardants, antioxidants, radical scavengers, lubricants, and various fillers composed of inorganic compounds and / or organic compounds can be added for the purpose of improving performance.

  The POF according to the present invention may further include the above-mentioned protective layer as a primary coating layer and further provide a secondary (or multilayer) coating layer on the outer periphery as necessary. When the primary coating has a sufficient thickness, thermal damage is reduced due to the presence of the primary coating, so the limit of the curing temperature of the material of the secondary coating layer is the case where the primary coating layer is coated. Compared to, it can be loosened. As described above, a flame retardant, an ultraviolet absorber, an antioxidant, a radical scavenger, a light raising agent, a lubricant and the like may be introduced into the secondary coating layer.

  Some flame retardants include halogen-containing resins such as bromine, additives, and phosphorus-containing ones. However, metal hydroxides such as aluminum hydroxide and magnesium hydroxide can be preferably used as a flame retardant from the viewpoint of safety such as reduction of toxic gas during combustion. The metal hydroxide has water as crystal water inside, and the adhering water in the manufacturing process cannot be completely removed. Therefore, if the metal hydroxide is not a low hygroscopic POF or a lower coating layer, the metal hydroxide It is desirable that the flame retardant coating with an object is provided with a moisture resistant coating on the outer layer of the primary coating layer and further provided as a coating layer on the outer layer.

  As a flame retardancy standard, UL (Underwriters Laboratory) has decided on several test methods. CMX (combustion test is generally called VW-1 test), CM Grades such as (vertical tray combustion test), CMR (riser test), and CMP (plenum test) are set. In the case of coating with POF, the core material is formed of a combustible material, and therefore, it is preferably a cord or cable having a VW-1 standard in order to prevent the spread of fire in the event of a fire.

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

  Also, the shape of the plastic optical cable depends on the type of use, such as a collective type in which the POF 17 or the plastic optical fiber core wire 19 is concentrically arranged, a tape type that is arranged in a line, and a press-wrap or wrap sheath. The usage form is selected according to the application such as a summary.

  Moreover, it is preferable that the optical transmission body using the POF 17 and the optical fiber core wire 19 manufactured by using the clad pipe 12 according to the present invention is securely fixed at the end using a connection optical connector. . As the connector, it is possible to use various commercially available connectors such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type that are generally known.

  An optical fiber as an optical member manufactured using the clad pipe 12 of the present invention, and a system for transmitting an optical signal using an optical fiber cable include various light emitting elements, light receiving elements, optical switches, optical isolators, optical An optical signal processing device including optical components such as an integrated circuit and an optical transceiver module is used. Moreover, you may combine with another optical fiber etc. as needed. Any known technique can be applied as a technique related to them. For example, the basic and actual of plastic optical fiber (published by NTS Corporation), Nikkei Electronics 2001.1.2.3, pages 110 to 127, “Printed Wiring You can refer to "This time, optical components are mounted on the board." Combined with various technologies described in the above documents, internal wiring in computers and various digital devices, internal wiring in vehicles and ships, optical terminals and digital devices, optical links between digital devices, general households and housing complexes・ Suitable for optical transmission systems suitable for short distances such as high-speed, large-capacity data communications and control applications that are not affected by electromagnetic waves, including optical LANs in factories, offices, hospitals, schools, etc. Can be used.

  Furthermore, 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 described in “interconnection by optical sheet bus technology”, and JP-A-10-123350, JP-A-2002-90571, JP-A-2001-290055, etc. Optical bus; described in JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968, JP-A-2001-318263, JP-A-2001-31840, etc. Optical star couplers described in JP 2000-241655 A, etc .; JP 2002-62457, JP 2002-101044, JP 20 Optical signal transmission device and optical data bus system described in each publication such as JP-A-305395; Optical signal processing apparatus described in JP-A-2002-23011; Optical signal cross-connect described in JP-A-2001-86537 System; optical transmission system described in JP-A-2002-26815; multi-function system described in JP-A-2001-339554, JP-A-2001-339555, etc .; and various optical waveguides, optical splitters, By combining with an optical coupler, optical multiplexer, optical demultiplexer, etc., a more advanced optical transmission system using multiplexed transmission / reception can be constructed. In addition to the above light transmission applications, it can also be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  Hereinafter, the present invention will be described more specifically with reference to Example 1. The types of materials, their proportions, operations, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below. The description will be made in detail in Experiment 1 according to the present invention, and in Experiments 2 and 3, description of the same conditions will be omitted. Further, in the experiments 4 and 5 which are comparative examples, the description of the same conditions as in the experiment 1 is omitted. In addition, the average value, maximum value, minimum value, and uneven thickness value (difference between the maximum value and minimum value), deviation, relative standard deviation (RSD), and fiber diameter fluctuation value during stretching Are summarized in Table 1 later.

  In Experiment 1, PVDF (polyvinylidene fluoride; KF polymer # 850 manufactured by Kureha Chemical Industry Co., Ltd.) was extruded into a pipe shape at an extrusion temperature of 180 ° C. with a single screw extruder 41 (plastic engineering laboratory, screw diameter φ50 mm) 41. Extruded from 43. The length L1 of the extrusion die 43 was 250 mm, and the heater used was a band heater with a length L2 of 52 mm. For adjusting the wall thickness of the pipe, eight adjustment screws 73 to 80 attached to the extrusion die 43 were used to roughly adjust the clearance to be the resin flow path 81 within a range of 2 mm ± 0.2 mm. Further, the fine adjustment was performed by adjusting the temperature of the heaters 82 to 89 from the wall thickness distribution value measured by the wall thickness / outer diameter measuring device 49. Then, a sizing die 45 having an inner diameter of about 50 mm was used to form a pipe 53 having an outer diameter of 50 mm and an inner diameter of 46 mm at a take-off speed of 0.5 m / min. While the pipe 53 was being molded, the maximum heating temperature of the heaters 82 to 89 was 205 ° C, and the minimum heating temperature was 195 ° C. The formed pipe 53 was cut in a cross section in the longitudinal direction, and the pipe wall thickness distribution in the cross section was measured at 8 points using a digital micrometer on both spherical surfaces. As a result of the measurement, the average thickness value was 2.013 mm, the maximum thickness value was 2.088 mm, the minimum thickness value was 2.008 mm, and the uneven thickness value (maximum thickness value−minimum thickness value) was 0.080 mm. . The deviation was 0.0241 mm. From the above results, the relative standard deviation ((RSD) = deviation / average wall thickness × 100 (%)) was 1.20%. This pipe was cut into 905 mm to obtain a clad pipe 12.

  The clad pipe 12 was inserted into a sufficiently rigid polymerization vessel having an inner diameter of 20 mm and a length of 1000 mm. The clad pipe 12 was washed with pure water and dried at 90 ° C. Then, one end was sealed with a Teflon (registered trademark) stopper.

  Next, the outer core polymerization step 13 was performed. In an Erlenmeyer flask, 205.0 g of methyl methacrylate (MMA, manufactured by Wako Pure Chemical Industries, Ltd.), 0.0512 g of 2,2′-azobis (dimethyl isoacetate), 1-dodecanethiol (lauryl mercaptan) An outer core solution was prepared by adding 0.766 g. The outer core liquid was put into the clad pipe 12. The tip of the clad pipe 12 was sealed using a silicon stopper and a sealing tape. The clad pipe 12 containing the outer core solution was placed in a 60 ° C. hot water bath and shaken for 2 hours for prepolymerization. Thereafter, the pre-polymerized clad pipe 12 is heated for 2 hours (rotational polymerization) while rotating at 500 rpm while maintaining a temperature of 60 ° C. in a horizontal state (a state in which the height direction of the clad pipe is horizontal). Went. Thereafter, rotational polymerization was performed at a rotational speed of 3000 rpm at 60 ° C. for 16 hours, and further at 3000 rpm at 90 ° C. for 4 hours. A cylindrical tube having an outer core 31 made of PMMA inside the clad pipe 12 was obtained. The outer core 31 had a thickness t2 of 3.8 mm.

  Next, the inner core polymerization process 14 was performed. In an Erlenmeyer flask, 82.0 g of MMA (manufactured by Wako Pure Chemical Industries, Ltd.), 0.070 g of 2,2′-azobis (dimethyl isoacetate), 0.306 g of 1-dodecanethiol, diphenyl sulfide An inner core solution was prepared from 6.0 g of Wako Pure Chemical Industries, Ltd. The clad pipe 12 on which the outer core 31 was formed was kept at 80 ° C. for 20 minutes, and then the inner core liquid was injected into the hollow portion. One end of the clad pipe 12 was covered with a seal tape, and then the clad pipe 12 was placed vertically in the autoclave (the bottom part was down and the part covered with the seal tape was up), and then the autoclave lid was set. The air in the autoclave was replaced with argon gas, and an atmosphere in which a pressure of 0.05 MPa was applied. Polymerization was performed by an interfacial gel polymerization method at 100 ° C. for 48 hours. Thereafter, heat polymerization and heat treatment were further carried out at 120 ° C. for 24 hours to obtain a preform 15. Thereafter, the preform 15 was taken out of the autoclave.

  A stretching step 16 was performed by stretching the preform 15 to form POF 17. The preform 15 was disposed in a heater 95 having four temperature zones in the vertical direction (see FIG. 6). The temperature zones 95a to 95d were adjusted to 250 ° C, 175 ° C, 150 ° C, and 135 ° C in order from the top. POF17 obtained by stretching the preform 15 was placed in a 20 ° C. water bath and cooled and solidified. The stretching speed was 9 m / min, and the film was taken up by a take-up roller. In the take-up roller, a tension of about 0.3 N was applied to the POF 17. When the fluctuation of the outer diameter of the POF 17 during stretching was measured with an outer diameter measuring device 96, it was 10 μm to 15 μm. And POF17 with an outer diameter (average value) of 316 μm and 1500 m was obtained. The transmission loss value of the POF 17 was measured by a known method (for example, see JP-A-55-7653), and it was 145 dB / km at a wavelength of 650 nm.

  In Experiment 2, fine adjustment during manufacturing of the pipe was performed by automatic control using the controller 50. The thickness distribution of the cooling pipe 48 was measured by the wall thickness / outer diameter measuring device 49, and the result was transmitted to the controller 50. In the controller 50, the temperature of the heaters 82 to 89 is adjusted so that the thickness distribution of the cooling pipe 48 is 2 mm ± 0.04 mm. Otherwise, the experiment was performed under the same conditions as in Experiment 1.

  In Experiment 3, a pipe having an outer diameter of 20 mm and an inner diameter of 19 mm was molded at a take-up speed of 1.0 m / min using a sizing die having an inner diameter of about 20 mm. Otherwise, the experiment was performed under the same conditions as in Experiment 1.

  In Experiment 4, which is a comparative example, the temperature of the heaters 82 to 89 was maintained at 200 ° C. after coarse adjustment with the eight adjustment screws 73 to 80. Otherwise, the experiment was performed under the same conditions as in Experiment 1.

  In Experiment 5, which is a comparative example, a pipe having an outer diameter of 20 mm and an inner diameter of 19 mm was formed at a take-up speed of 1.0 m / min using a sizing die having an inner diameter of about 20 mm. The adjustment of the extrusion die was only rough adjustment with eight adjusting screws 73 to 80, and the temperature of the heaters 82 to 89 was kept at 200 ° C. Otherwise, the experiment was performed under the same conditions as in Experiment 1.

  From the comparison between Experiment 1 and Experiment 4, by adjusting the heating temperature of the heaters 82 to 89 installed on the outer peripheral surface of the extrusion die 43, the viscosity of the molten resin is adjusted, and the flow rate is adjusted. It could be about half from 0.153 mm to 0.080 mm. Furthermore, in Experiment 2 in which fine adjustment was automated, the uneven thickness value could be reduced to 0.067 mm. The relative standard deviation (RSD) was 2.75% in Experiment 4 but was 1.20% in Experiment 1 according to the present invention, indicating that a clad pipe with a more uniform thickness can be obtained. Furthermore, in Experiment 2 in which fine adjustment was automated, a clad pipe with an extremely uniform wall thickness of 1.01% could be obtained.

  Further, as is clear from comparison between Experiment 3 and Experiment 5 in which the target thickness is 0.5 mm, even when the pipe thickness is different, the uneven thickness value can be similarly reduced, and the circumference of the clad pipe can be reduced. The thickness uniformity in the direction could be improved. For example, in Experiment 5, the relative standard deviation (RSD) was 4.78%, but in Experiment 3 according to the present invention, the relative standard deviation (RSD) was as small as 3.03%, and a clad pipe with a uniform thickness could be obtained. I understood that I could do it.

  The method and apparatus for producing a clad pipe according to the present invention are not limited to a pipe for an optical member, and can be applied to a field where a pipe having a uniform thickness is preferably used.

It is a flowchart for demonstrating the manufacturing method of a plastic optical fiber. It is a figure for demonstrating sectional drawing and refractive index distribution of the preform manufactured using the clad pipe which concerns on this invention. It is the schematic of the manufacturing line for manufacturing the clad pipe which concerns on this invention. It is sectional drawing of the IV-IV line of FIG. It is a principal part enlarged view of FIG. It is the schematic for demonstrating the process of extending | stretching a preform. It is sectional drawing of the conventional extrusion die.

Explanation of symbols

12 Clad Pipe 40 Production Line 43 Extrusion Die 46 Cooling Vacuum Device 48 Cooling Pipe 49 Wall Thickness / Outer Diameter Measuring Instrument 50 Controller 70 Inner Lip 71 Outer Lip 81 Resin Channel 82, 83, 84, 85, 86, 87, 88, 89 Heater 90 Calculation unit 91 Control unit

Claims (12)

In a method for producing a clad pipe for an optical member by extruding a molten polymer from an extrusion die,
A plurality of clearance adjusting means are provided along the outer peripheral surface of the extrusion die,
Individually adjusting the plurality of clearances,
A method of manufacturing a clad pipe for an optical member, comprising adjusting a thickness in a circumferential direction of the clad pipe. In a method for producing a clad pipe for an optical member by extruding a molten polymer from an extrusion die,
A plurality of heaters are provided along the outer peripheral surface of the extrusion die,
Measure the wall thickness of the extruded clad pipe,
Calculate each optimum temperature of the plurality of heaters from the measured thickness value,
Based on the calculated value, individually adjust the temperature of the plurality of heaters,
A method of manufacturing a clad pipe for an optical member, comprising adjusting a thickness in a circumferential direction of the clad pipe. A plurality of clearance adjusting means are provided along the outer peripheral surface of the extrusion die,
The method for manufacturing a clad pipe for an optical member according to claim 2, wherein the adjustment of the plurality of clearances and the temperature adjustment of the plurality of heaters are performed simultaneously.   4. The method for producing a clad pipe for an optical member according to claim 1, wherein the clad pipe is a clad pipe for plastic optical fiber.   An optical member clad pipe manufactured by the method for manufacturing an optical member clad pipe according to any one of claims 1 to 4.   A core having a refractive index higher than that of the clad pipe is formed in the clad pipe for optical member produced by the method for producing a clad pipe for optical member according to any one of claims 1 to 4. An optical member preform. A clad pipe for an optical member is produced by the method for producing a clad pipe for an optical member according to any one of claims 1 to 4,
Forming a core having a refractive index higher than the refractive index of the clad pipe in the clad pipe for the optical member to produce a preform for the optical member,
A plastic optical fiber obtained by stretching the optical member preform. In the manufacturing apparatus of the clad pipe for optical members provided with an extrusion die for extruding the molten polymer into a pipe shape,
A plurality of clearance adjusting means provided along the outer peripheral surface of the extrusion die;
A control unit for individually controlling the plurality of clearance adjustment means,
An apparatus for manufacturing a clad pipe for an optical member, wherein the thickness in the circumferential direction of the clad pipe is adjusted. In the manufacturing apparatus of the clad pipe for optical members provided with an extrusion die for extruding the molten polymer into a pipe shape,
A plurality of heaters provided along the outer peripheral surface of the extrusion die;
A measuring instrument for measuring the thickness of the extruded clad pipe;
A calculation unit for calculating each optimum temperature of the plurality of heaters from the measured value of the wall thickness;
A controller that individually controls the temperature of each of the plurality of heaters based on the calculated value;
An apparatus for manufacturing a clad pipe for an optical member, wherein the thickness in the circumferential direction of the clad pipe is adjusted. A plurality of clearance adjusting means provided along the outer peripheral surface of the extrusion die;
A second control unit for controlling the clearances of the plurality of clearance adjusting means;
The apparatus for manufacturing a clad pipe for optical members according to claim 9, wherein:   The apparatus for manufacturing a clad pipe for an optical member according to claim 9 or 10, wherein the heater is any one of a band heater, an aluminum casting heater, and a cartridge heater.   The apparatus for manufacturing a clad pipe for an optical member according to any one of claims 9 to 11, wherein the plurality of heaters is 4 or more and 24 or less.

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