JP2005326501A - Method for manufacturing plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a plastic optical fiber by coating an optical fiber with a resin, without giving thermal damages to the optical fiber. <P>SOLUTION: The optical fiber (POF) 12 is conveyed to a coating apparatus 23. Polyethylene of 120°C is coated on the POF 12 so that the thickness is 225μm. The first protective layer-formed coated optical fiber 26a is conveyed to a water tank 27. Therein, the first protective layer-formed coated optical fiber 26a is cooled with cooling water of 15°C, and the polyethylene is hardened. The first protective layer-formed coated optical fiber 26a is conveyed to a second coating apparatus 29. Polyethylene of 120°C is coated on the first protective layer-formed coated optical fiber 26a so that the thickness is 225μm. The coated optical fiber 26 is conveyed to a water tank 32. Therein, the coated optical fiber 26 is cooled with cooling water of 15°C, and the polyethylene is hardened. As a result, the coated optical fiber 26 whose protective layer has a thickness of 450μm can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a plastic optical fiber core.

  A plastic optical fiber (hereinafter referred to as POF) whose core and clad are both plastic is made of plastic, and therefore has a disadvantage that its transmission loss is slightly larger than that of a silica-based optical fiber. It has the advantages of flexibility, light weight and good workability. In addition, it has an advantage that it can be easily manufactured as an optical fiber having a large diameter and can be manufactured at a lower cost than a quartz optical fiber. Therefore, for example, between electronic devices that transmit and receive optical communications, as a short-distance optical transmission path in which transmission loss is not a problem, it is frequently used because it is easier to use and cheaper than silica-based optical fibers. This is important in next-generation communication network concepts such as LAN and ISDN (for example, see Patent Document 1).

  POF is generally a core made of an organic compound having a polymer as a matrix (hereinafter referred to as a core or core), and an organic compound having a refractive index different from that of the core (generally having a low refractive index). It is comprised from the outer shell (it is also called a sheath. It is hereafter called a clad part or a clad). Incident light incident on the core part is transmitted while repeating total reflection at the interface between the core part and the clad part. Such a POF is called a step index (SI) type.

  2. Description of the Related Art In recent years, a refractive index distribution type (graded index type, hereinafter referred to as GI type) POF having a core portion having a distribution of refractive index from the center toward the outside (radial direction) is an optical signal to be transmitted. Therefore, it is attracting attention as an optical fiber having a high transmission capacity (see, for example, Patent Documents 2 to 5).

  The GI-type POF is made into a fiber by producing a GI-type plastic optical fiber base material (hereinafter referred to as a preform) and then heating and melting and drawing (stretching). As a result, various POFs having different outer diameters can be produced. When the POF drawn in this way has a high tensile stress, there is a risk of deterioration in transmission loss or breakage. Moreover, it becomes easy to tangle and becomes difficult to handle, and handling properties may deteriorate. Therefore, these problems are solved by coating POF with a polymer such as a thermoplastic resin. In the following description, the resin coated with POF is referred to as a protective layer. As a method of forming a protective layer, a method of coating polyethylene having a melting point of 120 ° C. to 170 ° C. is known (see, for example, Patent Document 6). Furthermore, a method is also known in which a primary polyvinyl chloride layer having a high extrusion temperature of 160 ° C. or higher is coated on a primary polyvinyl chloride layer having a low extrusion temperature of 120 ° C. or lower (see, for example, Patent Document 7). ).

JP-A-61-130904 Japanese Patent No. 3332922 International Publication No. 93/08488 Pamphlet International Publication No. 94/04949 Pamphlet JP-A-8-5848 JP 59-9603 JP-A-6-167642

  By the way, the GI-type POF contains a refractive index adjusting agent in the refractive index at the center of the core portion. Thereby, the glass transition temperature of the polymer forming the center of the core portion is lowered. Therefore, when a plastic optical fiber core (hereinafter referred to as an optical fiber core) is manufactured by coating with polyethylene having a melting point of 120 ° C. to 170 ° C., the core portion may be transformed. The protective layer also has the purpose of improving the bending resistance of the POF to prevent water absorption in the external environment, for example, high humidity, and to improve the degree of freedom of wiring of the optical fiber core wire. However, in the conventional method, since the focus is on protecting from the external environment, no particular consideration is given to the thickness of the protective layer of the target optical fiber core, and the wiring of the optical fiber core is not considered. Improves freedom.

  Polyvinyl chloride is mixed with a plasticizer for the purpose of improving elasticity. When polyvinyl chloride is used as the protective layer forming resin, there is a problem that the optical properties of the POF deteriorate due to the plasticizer moving into the POF component. Such a problem is particularly caused when the GI POF having a diameter of 500 μm or less is coated with a resin having a melting point of 120 ° C. or more with a thickness exceeding 500 μm, and the transmission loss of the optical fiber core is greatly deteriorated. It becomes.

  An object of the present invention is to provide a method of manufacturing a plastic optical fiber core in which a resin is coated on the plastic optical fiber without deteriorating the transmission loss of the plastic optical fiber.

  The method for producing a plastic optical fiber core according to the present invention is a method for producing a plastic optical fiber core by coating at least two layers of a molten resin on a plastic optical fiber having a core and a clad and having a diameter of 500 μm or less. The temperature of the molten resin is 130 ° C. or less, the plastic optical fiber is coated with the first molten resin so that the coating thickness is in the range of 100 μm or more and 350 μm or less, and the temperature of the second molten resin is 120 ° C. or more. The second molten resin is coated on the first molten resin so that the temperature is 140 ° C. or lower and the coating thickness is in the range of 100 μm to 350 μm. It is preferable that the refractive index of the core continuously decreases from the center toward the radial direction in the cross section.

  It is preferable that the coating using the first molten resin and the coating using the second molten resin are continuously performed. It is preferable that the time until the second molten resin comes into contact with the first molten resin after the plastic optical fiber is coated with the first molten resin is preferably 2 seconds or more. The clad is preferably made of a resin having a low refractive index. In the present invention, the fact that the clad has a low refractive index means that the maximum refractive index of the core is greater than the refractive index of the clad by 0.001 or more. It is preferable that the first and second molten resins are polyolefin resins.

  According to the method for manufacturing a plastic optical fiber core of the present invention, in the method for manufacturing a plastic optical fiber core wire, a plastic optical fiber having a core and a cladding having a diameter of 500 μm or less is coated with at least two layers of molten resin. The temperature of the first molten resin is 130 ° C. or less, the plastic optical fiber is coated with the first molten resin so that the coating thickness is in the range of 100 μm to 350 μm, and the temperature of the second molten resin is 120 Since the second molten resin is coated on the first molten resin so that the coating thickness is in the range of 100 μm or more and 350 μm or less, the protection is achieved without deteriorating the transmission loss of the plastic optical fiber. A layer can be formed.

  When the core is a so-called GI type whose refractive index continuously decreases from the center toward the radial direction in the cross section, the effect of the present invention that does not deteriorate the transmission loss of the plastic optical fiber is more manifested. Can be made. Moreover, since polyolefin resin is used for the first and second molten resins, it is possible to further suppress the deterioration of the transmission loss of the plastic optical fiber due to the precipitation of the plasticizer.

  A method for manufacturing a plastic optical fiber core according to the present invention will be described with reference to a method for manufacturing a GI optical fiber core as an example. However, the present invention is applicable to other types of plastic optical fibers such as a step index (SI) type multimode plastic optical fiber core, an SI type single mode plastic optical fiber core, and a single mode (SM) type plastic optical fiber core. It is possible to apply to the manufacturing method of a core wire. The description will be made in the order of the raw material for core and clad production, the material for forming the protective layer, the preform production method, the POF production method, and the optical fiber core wire production method.

  The raw material of the core part is not particularly limited as long as the optical transmission function is not impaired. Particularly used raw material monomers include methyl methacrylate (MMA), deuterated methyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl-2-fluoroacrylate and the like. A polymer is polymerized from each of these monomers and used as a core part. Moreover, you may form a core part from a copolymer (copolymer) using 2 or more types of these monomers. Examples of the polymer used include a homopolymer of methyl methacrylate (polymethyl methacrylate: PMMA). In addition, monofunctional (meth) acrylates, fluorinated alkyl (meth) acrylates, polyfunctional (meth) acrylates, transparent copolymers of acrylic acid and methacrylic acid monomers and methyl methacrylate are listed. It is done. In the present invention, it is preferable to form the core portion with polymethyl methacrylate (PMMA) obtained by polymerizing MMA, which is easily bulk polymerized.

  In a specific wavelength region, the monomer is polymerized using a monomer in which a hydrogen atom of MMA is substituted with a deuterium atom (D) or a halogen atom for the purpose of reducing light transmission loss due to C—H bond. It is preferable to use a polymer. As the halogen atom, a fluorine atom (F) is preferably used. Examples of such a polymer include deuterated polymethyl methacrylate (PMMA-d8). Thereby, the wavelength which a transmission loss produces can be lengthened, and the loss of transmission light can be reduced.

  When the polymer is polymerized from the monomer, a polymerization initiator is used. The polymerization initiator can be appropriately selected according to the monomer used and the polymer to be polymerized. For example, benzoyl peroxide (BPO), t-butyl peroxy-2-ethyl hexanate (PBO), di-t-butyl peroxide (PBD), t-butyl peroxyisopropyl carbonate (PBI), n-butyl- Examples include, but are not limited to, 4,4-bis (t-butylperoxy) valerate (PHV). Two or more kinds of polymerization initiators may be used in combination.

  For the purpose of controlling the molecular weight and molecular weight distribution of the polymer, it is preferable to use a chain transfer agent (also referred to as a polymerization regulator). 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, alkyl mercaptans such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan are preferably used. Of course, the chain transfer agent is not limited to these. Two or more chain transfer agents may be used in combination.

  When producing a GI-type preform, a refractive index adjusting agent (hereinafter referred to as a dopant) is added to the core portion. The dopant has the property that the polymer containing it has a higher refractive index than the additive-free polymer. A material that has this property and can stably coexist with a polymer and is stable under polymerization conditions (such as heating and pressurization) is used. For example, benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), benzyl-n-butyl phthalate (BBP), diphenyl phthalate (DPP), biphenyl (DP), diphenylmethane (DPM) , Tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO) and the like, and BEN, DPS, TPP, and DPSO are particularly preferable.

  The light transmitted through the core part is totally reflected at the interface between the clad part and the core part. Therefore, a compound whose refractive index is lower than that of the core is used for the cladding. Further, those having good adhesion to the core part, excellent toughness and excellent heat resistance are preferably used. Examples thereof include acrylic resins that are polymerized from methyl methacrylate, deuterated methyl methacrylate, trifluoroethyl methacrylate, hexafluoroisopropyl-2-fluoroacrylate, and the like. Moreover, a perfluoroalkyl methacrylate type | system | group polymer, a methacrylic acid ester copolymer, etc. are mentioned.

  The polymerization initiator and chain transfer agent used to form the core part can also be used when polymerizing the polymer in the clad part from the monomer.

  Moreover, a fluorine resin can also be used for the clad. For example, polyvinylidene fluoride (PVDF: melting point 160 ° C. to 180 ° C.), polyvinyl fluoride (PVF: melting point 206 ° C.), polytetrafluoroethylene (PTFE: melting point 330 ° C.), tetrafluoroethylene-hexafluoropropylene copolymer ( FEP: melting point 250 ° C. to 280 ° C.), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA: melting point 300 ° C. to 310 ° C.), ethylene-tetrafluoroethylene copolymer (ETFE: melting point 260 ° C. to 270 ° C.) , Polychlorotrifluoroethylene (PCTFE: melting point 210 ° C.), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPE: melting point 290 ° C. to 300 ° C.) and the like.

  Furthermore, a vinylidene fluoride polymer can also be used. This also includes a copolymer, such as 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-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-trifluoroethylene copolymer, and a ternary or more copolymer of vinylidene fluoride. .

  Additives may be added to the cladding part within a range that does not deteriorate the optical transmission performance. The additive can be easily contained in the polymer by polymerizing the polymer from the monomer after being added to the raw material monomer. Examples of the additive include a stabilizer that improves weather resistance and durability, and a stimulated emission functional compound for optical signal amplification that improves optical transmission performance. By adding the stimulated emission functional compound, the attenuated signal light can be amplified by the excitation light. This improves the transmission distance, so that it can be used as a fiber amplifier in a part of the optical transmission link. In addition, these additives can also be contained in a core part by adding to a monomer at the time of formation of a core part.

  The resin for forming the protective layer is preferably a polyolefin-based resin because it has good chemical resistance and flexibility, but is not limited thereto. Examples of the polyolefin-based resin include ethylene, propylene, and α-olefin polymers. Examples of the α-olefin include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-peptene, 1-octene and the like. Examples of these polymers include polyethylene, a copolymer of ethylene and propylene, a copolymer of ethylene and α-olefin, polypropylene, a copolymer of propylene and α-olefin, polybutene, and polyisoprene. Further, the polyolefin diameter resin may be blended in an appropriate combination in consideration of the physical properties to be obtained.

  The molecular weight and molecular weight distribution of the polyolefin resin are not particularly limited. However, the weight average molecular weight is usually 5000 to 5000000, preferably 20000 to 300000, and the molecular weight distribution (weight average molecular weight Mw / number average molecular weight Mn) is 2 to 80, preferably 3 to 40.

  The polyolefin resin preferably has a melting point of less than 120 ° C. and an MFR of 10 or more and 95 or less. When the melting point exceeds 120 ° C., it is necessary to increase the temperature at the time of coating molding, which may cause thermal damage to the POF. Further, when the MFR is less than 10, there is a problem that the load on the extruder increases unless the coating resin temperature is raised. When the MFR is 95 or more, the POF cannot be coated with a uniform thickness, which causes a problem that the heat amount of the core cross section tends to be uneven. Therefore, the polyolefin resin used in the present invention preferably has a melting point of less than 120 ° C. and an MFR of 10 to 95, more preferably a melting point of less than 120 ° C. and an MFR of 15 to 80. By using a polyolefin-based resin having such properties, even if the resin temperature is 140 ° C. or less, the resin is fluid and can be coated.

  In the SI type POF, when PMMA is used for the core part, it is preferable to use a fluororesin for the clad part. This is because the difference in refractive index between the PMMA at the core and the fluororesin at the cladding is within a preferable range for an optical fiber, and the strength of the fluororesin is high. The production method of SI-type POF is preferably carried out by melt spinning. In the melt spinning method, PMMA serving as a core portion and fluororesin serving as a cladding portion are discharged from the composite spinning nozzle for each hole. Thereafter, a fluororesin is coated around the PMMA with a nozzle and combined to obtain a preform. Thereafter, a POF can be obtained by performing a drawing while transporting using a number of take-up rollers.

  A method for manufacturing the GI POF will be described. First, a hollow cylindrical tube made of PMMA is prepared. In addition, this hollow cylindrical tube becomes a clad part. The hollow cylindrical tube may be manufactured by a known rotational polymerization method, or a commercially available pipe may be used. The hollow cylindrical tube is preferably bottomed because it is used as a polymerization vessel. Then, MMA and a dopant (for example, benzyl methacrylate) are put into the hollow cylindrical tube, and an interfacial gel polymerization method is performed. A core portion mainly composed of a polymer (PMMA) is formed in the hollow cylindrical tube, and a preform can be obtained.

  As shown in FIG. 1, the preform 10 is placed in a heating furnace 11. When heated in the heating furnace 11, a part of the preform 10 is melted. In addition, although melting temperature is not specifically limited, It is preferable that it is the range of 160 to 270 degreeC. The melted portion is drawn (stretched) from the leading end 10a as a starting point to form a POF 12, and after passing through a wire diameter monitor 13, is wound around a core material 14 of a winding device (not shown), and a plastic optical fiber roll (hereinafter referred to as POF roll). 15) is obtained. When drawing, the outer diameter of the POF 12 is monitored by the wire diameter monitor 13, and the position of the preform 10 in the heating furnace 11, the heating of the heating furnace 11, and the winding speed of the winding device are appropriately adjusted.

The POF roll 15 is attached to the feeder 21 of the coating line 20 shown in FIG. The POF 12 is sent out to the coating line 20 using the sending machine 21. The POF 12 is conveyed to the coating device 23 while the tension is adjusted by the tension controller 22. The tension during coating is preferably as small as possible so as not to deform the POF 12. For example, it is preferably 700 N / cm ² or less, and more preferably 500 N / cm ² or less. The coating device 23 includes a mold 24 and a resin supply device 25 is attached. The resin supplied from the resin supply device 25 is extruded by coating the POF 12 from the mold 24 by an extruder (not shown) of the coating device 23. As a result, a first protective layer is formed on the POF 12. In the following description, this is referred to as a first protective layer-formed optical fiber core 26a. The first protective layer forming optical fiber core 26a is conveyed to the water tank 27 in order to cure the resin. In addition, it is preferable because the thickness of the first protective layer formed from the coating resin can be made uniform by passing the sizing die 28 before being conveyed to the water tank 27.

  When the temperature of the resin when forming the first protective layer exceeds 130 ° C., the temperature of the POF 12 rises due to the heat conduction of the coated resin, and may exceed the softening point. As a result, the GI structure is likely to be disturbed, and interface irregularities and microbending due to plastic deformation are likely to occur. Therefore, in the present invention, the resin temperature when forming the first protective layer is set to 130 ° C. or lower. On the other hand, when the thickness of the first protective layer exceeds 350 μm, even if the resin temperature is 130 ° C. or lower, the cooling of the central portion of the coating resin is poor and the POF temperature rises, causing problems such as GI-type structural disorder. Moreover, the coating of less than 100 μm causes a problem in construction because the adhesion with POF is lowered. Therefore, the thickness of the first protective layer is preferably 100 μm or more and 350 μm or less.

  The first protective layer-forming optical fiber core wire 26 a is sent to the second coating device 29. The coating device 29 also includes a mold 30 and a resin supply device 31 is attached thereto. The coating device 29 further coats the resin on the first protective layer to form a second protective layer, thereby obtaining the optical fiber core 26. Thereafter, the optical fiber core wire 26 is conveyed to the water tank 32 to cure the resin. Moreover, it is preferable that the coating of the resin for forming the second protective layer is performed after 2 seconds or more have elapsed after coating the resin of the first protective layer. Particularly preferably, cooling is performed after the first protective layer forming resin is coated. This is because the POF temperature before coating the second protective layer, especially the temperature of the core, is kept low, so that the temperature rise of the POF, especially the core, is suppressed during the formation of the second protective layer, and the disturbance of the GI structure is suppressed. It is to do. If the resin for forming the second protective layer is coated in less than 2 seconds, the heat accumulation of the resin of the first protective layer and the heat of the resin of the second protective layer are added to increase the POF temperature, resulting in defects such as GI-type structural disorder May occur.

  When the second protective layer is formed, if the resin temperature is less than 120 ° C., there is a problem that the resin viscosity increases and the load on the extruder increases. In addition, there is a problem that the coating thickness varies due to the discharge of the unmelted resin. In addition, when the resin temperature exceeds 140 ° C., the POF temperature, particularly the temperature of the core part may exceed the pour point, which may cause problems such as disturbance of the GI structure. Therefore, the resin temperature for forming the second protective layer is preferably in the range of 120 ° C. or higher and 140 ° C. or lower.

  When the thickness of the second protective layer exceeds 350 μm, even if the resin temperature is 140 ° C. or lower, the cooling of the central portion of the coating resin is poor, and the temperature of the POF, particularly the core portion, rises, resulting in problems with the GI type structure. May occur. In addition, a coating of less than 100 μm may be difficult to extrude stably due to a low flow rate, and may cause diameter blurring. Therefore, the thickness of the second protective layer is preferably in the range of 100 μm to 350 μm.

  The optical fiber core 26 passes through the water tank 32 and the resin is cured to form the second protective layer. And it is conveyed over the some take-up rollers 35 and 36 of the take-up machine 34, and is conveyed. The tension when the optical fiber 26 is wound around the core member 38 by the winding tension controller 37 is adjusted. A winder 39 is connected to the core member 38. The optical fiber core 26 is wound around the core member 38, and the optical fiber core roll 40 is obtained.

  When the cooling water temperature of the water tanks 27 and 32 is higher than 15 ° C., the cooling capacity is deteriorated, and the POF temperature, particularly the temperature of the core part is hardly lowered, and is easily damaged by heat. On the other hand, if it is less than 5 ° C., an apparatus having a very large refrigerant cooling capacity is required. Moreover, since the coating resin is rapidly cooled, there is a possibility that molding defects such as cracks may occur. Therefore, the cooling water temperature is preferably in the range of 5 ° C to 15 ° C.

  FIG. 3 shows a cross-sectional view of the plastic optical fiber core wire 26 according to the present invention. The diameter D (μm) of the POF 12 is not particularly limited, but is preferably 500 μm or less. The diameter of the core 12a is not particularly limited, but is preferably in the range of 200 μm to 500 μm. The thickness of the clad 12b is not particularly limited, but is preferably in the range of 10 μm to 100 μm. The thickness L1 (μm) of the first protective layer 41 is preferably in the range of 100 μm to 350 μm. The thickness L2 (μm) of the second protective layer 42 is preferably in the range of 100 μm to 350 μm. Thereby, the thickness of the protective layer formed on the POF 12 can be appropriately selected and formed within a range of 200 μm or more and 700 μm or less.

  One resin supply device 61 may be used as in the covering line 60 shown in FIG. The resin is supplied from the resin supply device 61 to the two coating devices 23, 29, and the first or second is used by the molds 24, 30 by an extruder (not shown) provided in each coating device 23, 29. Each protective layer can be formed by extruding a resin for forming the protective layer.

  It is also possible to reverse the transport direction of the POF 12 or the like using a reversing machine 71 as in the coating line 70 shown in FIG. By using the reversing machine 71, the total length of the place where the covering line 70 is installed may be short, and the degree of freedom of the place where the covering line 70 is installed is improved. In addition, about the same location as the coating line 20 in the coating lines 60 and 70, the same code | symbol is attached | subjected and description is abbreviate | omitted. Also, as shown in FIGS. 2, 4 and 5, the resin coating for forming two or more protective layers can be performed in a continuous process to improve the adhesion between the layers. Therefore, it is more preferable.

  Further, in the present invention, the series of steps for drawing POD 12 by drawing from preform 10 and performing coating is not limited to the form of winding once as POF roll 15. For example, after the preform 10 is manufactured, the POF 12 is produced by drawing and drawing using the heating furnace 11, the POF 12 is transported to the coating line, and the protective layer is formed by coating the resin using the coating apparatus. good.

FIG. 6A shows a graph explaining the relationship between the radial direction and the refractive index of the GI POF, and FIG. 6B shows the SI POF. In the GI POF, the difference between the maximum refractive index nco _max of the core 12a and the refractive index ncl of the clad 12b is preferably 0.001 or more. Further, in the SI type POF, the difference between the refractive index nco of the core 80 and the refractive index ncl of the clad 81 is preferably 0.001 or more. The upper limit of each refractive index difference is not particularly limited, and can be arbitrarily set from transmission performance and manufacturing suitability.

  Hereinafter, the present invention will be described more specifically with reference to examples. The types of materials, ratios thereof, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. The description will be made in detail in Experiment 1 according to the present invention, and for Experiments 2 to 4, which are comparative examples, descriptions of the same conditions as in Experiment 1 are omitted. The experimental conditions and results of each experiment are summarized in Table 1 later.

  In Experiment 1, a clad portion made of PMMA was manufactured by a known rotational polymerization method to obtain a hollow cylindrical tube. Next, the core part was produced with MMA (methyl methacrylate) as the main raw material by the interfacial gel polymerization method. Using diphenyl sulfide (DPS) as a dopant, 7.0 mass% was added to MMA. Thereafter, interfacial gel polymerization was carried out at 100 ° C. for 48 hours. A preform 10 having a diameter of 20 mm and a length of 1000 mm was obtained. The refractive index of the preform 10 was such that the center of the core portion had a maximum refractive index of 1.501 and the cladding portion had 1.492. The preform 10 was heated at 240 ° C. and drawn (stretched). And POF12 whose outer diameter D is 300 micrometers was obtained. The transmission loss of this POF 12 at a wavelength of 650 nm was 150 dB / km.

As the first protective layer forming resin, a polyethylene resin having a melting point of 100 ° C. and MFR70 was used. The first protective layer was formed by coating so that the first protective layer thickness L1 was 225 μm at a linear velocity of 16 m / min and a resin temperature of 120 ° C. After coating, the polyethylene was cured by cooling in a water bath 27 containing cooling water at 15 ° C. for 40 seconds. Three seconds after the polyethylene was cured, coating was performed so that the second protective layer thickness L2 was 225 μm at a resin temperature of 120 ° C. After coating, the polyethylene was cured by cooling in a water bath 32 containing cooling water at 15 ° C. for 40 seconds. Note that the tension at the time of coating was 700 N / cm ² . The outer diameter of the optical fiber core 26 was 1200 μm. When the transmission loss of the optical fiber 26 at a wavelength of 650 nm was measured, it was 180 dB / km.

  Experiment 2, which is a comparative example, was performed under the same conditions as Experiment 1, except that the thickness L1 of the first protective layer was 450 μm and the resin temperature was 110 ° C. The outer diameter of the optical fiber core 26 was 1650 μm. The transmission loss of the optical fiber core 26 was measured and found to be 800 dB / km.

  Experiment 3 as a comparative example was performed under the same conditions as Experiment 1 except that the temperature of the second protective layer forming resin was 160 ° C. The transmission loss of the optical fiber core 26 was measured and found to be 850 dB / km.

  In Experiment 4 as a comparative example, polyvinyl chloride containing 60% by mass of a phthalate ester as a plasticizer was used as a coating resin. The other conditions were the same as in Experiment 1. The transmission loss of the optical fiber was measured and found to be 800 dB / km.

  From Experiment 2 in Table 1, it can be seen that POF suffers thermal damage when the thickness of the protective layer exceeds 350 μm. As a result, the GI structure is disturbed, microbending occurs due to interface irregularities and plastic deformation, and transmission loss deteriorates. Further, from Experiment 3, it is considered that when the resin temperature is higher than 140 ° C., the same thermal damage is given to the POF. Furthermore, when Polyvinyl chloride containing 60% by mass of additive is used as a protective layer-forming resin from Experiment 4, POF is deteriorated due to precipitation of the plasticizer.

It is a figure for demonstrating the manufacturing method of the plastic optical fiber core wire which concerns on this invention. It is the schematic of the coating line used for the manufacturing method of the plastic optical fiber core wire which concerns on this invention. It is sectional drawing of the plastic optical fiber core wire which concerns on this invention. It is the schematic of the coating line of other embodiment used for the manufacturing method of the plastic optical fiber core wire which concerns on this invention. It is the schematic of the coating line of other embodiment used for the manufacturing method of the plastic optical fiber core wire which concerns on this invention. It is a graph for demonstrating the refractive index distribution of a plastic optical fiber.

Explanation of symbols

12 POF
20 coating line 23, 30 coating device 26 optical fiber core wire 29 coating device 41 first protective layer 42 second protective layer D POF diameter L1 first protective layer thickness L2 second protective layer thickness

Claims (6)

In a method of manufacturing a plastic optical fiber core by coating a plastic optical fiber having a core and a clad with a diameter of 500 μm or less with at least two layers of molten resin,
The temperature of the first molten resin is 130 ° C. or less, and the plastic optical fiber is coated with the first molten resin so that the coating thickness is in the range of 100 μm to 350 μm,
A plastic characterized in that the temperature of the second molten resin is 120 ° C. or higher and 140 ° C. or lower, and the second molten resin is coated on the first molten resin so that the coating thickness is in the range of 100 μm or more and 350 μm or less. Manufacturing method of optical fiber core wire.   2. The method of manufacturing a plastic optical fiber core wire according to claim 1, wherein the core has a refractive index that continuously decreases from the center toward the radial direction in a cross section.   3. The method of manufacturing a plastic optical fiber core wire according to claim 1, wherein the coating using the first molten resin and the coating using the second molten resin are continuously performed. After coating the first molten resin on the plastic optical fiber,
The method for producing a plastic optical fiber core wire according to any one of claims 1 to 3, wherein a time until the second molten resin comes into contact with the first molten resin is 2 seconds or more.   5. The method of manufacturing a plastic optical fiber core wire according to claim 1, wherein the clad is made of a resin having a low refractive index.   6. The method of manufacturing a plastic optical fiber core wire according to claim 1, wherein the first and second molten resins are polyolefin resins.

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